Advances in Natural Polymeric Nanoparticles for the Drug Delivery

*Vikas Pandey, Tanweer Haider, Poornima Agrawal, Sakshi Soni and Vandana Soni*

## **Abstract**

Natural and biodegradable polymers have been the key area for utilizing their advantages which make them a possible option for development of various drug delivery systems. The complexity of diseases and the intrinsic drug toxicity and side effects has led to an interest for development and optimization of drug delivery systems. The advancements in nanotechnology have favored the development of novel formulations which can modulate the biopharmaceutical properties of bioactives and thus improves the pharmacological and therapeutic action. The shape, size, and charge nanoscale delivery system, such as nanoparticles (NPs) are required to be investigated and changed in order to promote and optimize the formulations. The various natural polymeric NPs (PNPs) have been found to be key tool to enhance bioavailability or specific delivery to certain site of action. In this chapter, the uses of various polymeric materials for the development of NPs as drug delivery systems for various ailments have been described. The entrapment of bioactive compounds in PNPs systems is a hopeful move toward improvement of efficacy of drug toward the treatments of various diseases.

**Keywords:** polymeric material, drug delivery, nanoparticles, targeting

#### **1. Introduction**

The research for natural polymeric material for the advancement in the drug delivery has been a prime focused for the researchers in the last two decades. The concept of natural polymeric material is one of the frontier research areas and is being focused for the enhancing the bioavailability along with the specific/targeted drug delivery and therapeutic index for the treatment of some life threatening diseases, like cancer [1]. Polymeric drug delivery system has been used to enable the delivery of drug molecule into the body for the therapeutic action. Various polymers biodegradable and non-biodegradable origin has been widely identified and used which are accompanying various advantageous features with them. For different novel drug delivery systems development, biodegradable and bio-reducible polymers are used which make a possible choice helping delivery of bioactives.

Nanotechnology is the branch which deals in the system, structures and devices in the range of nanometer. Nanotechnology has been a keen interest area in today's novel growing world associated with the significant development in controlled delivery of genes and drugs. NPs in the field of nanotechnology found to be very advantageous proving their efficiency for drug delivery, biodegradable nature, better bioavailability, versatility, less toxicity and high encapsulation efficiency. NPs carriers play a competent role for the controlled delivery of drug molecules for cancer therapy and site specific delivery of bioactive molecules as target site [2, 3].

The present chapter has complied the various natural polymeric material extensively used in the delivery of drugs and genes acting as the backbone for the development and delivery of bioactive agents in various cases.

## **2. Natural polymers for drug delivery**

Natural polymers for the development of drug delivery and delivery of bioactive molecules have been extensively investigated producing better encapsulation of drugs, thus have attracted tremendous attention. These natural polymers do have the inherent advantages, such as biocompatibility, specific interactions with some biomolecules, controlled enzyme degradation, and easy surface modification furnish them with greater versatility in drug delivery. Different types of natural polymers and derivatives have been chemically and physically modified which are focusing the efficiently therapy through the use of various bioactive for smart stimuli-triggered or targeted delivery [4].

#### **2.1 Animal-based biopolymers**

#### *2.1.1 Gelatin*

Gelatin being a fibrous protein is identified as a natural, biocompatible, biodegradable, non-antigenic, low cost and multipurpose biopolymer and due to its unique mechanical and technological properties since timely memorial is commonly used in pharmaceutical (drug and vaccine delivery) cosmetic, food, and medical applications [5]. Gelatin is obtained from its parent molecule collagen in various thermo-reversible forms and the major commercial sources of gelatin are porcine or bovine skin, bones, aquatic and poultry sources [6]. But it has been observed that gelatin obtained from mammalian source is preferred over that produced from aquatic animal sources due to its strong gel strength, ideal gelling and melting temperatures, acceptable viscosity, and lack of fishy odor or allergens [7]. When gelatin is considered structurally it has triplets of the amino acids' alanine, proline, and glycine in repeating sequences that give gelatin its triple helical shape and both cationic and anionic groups chemically. It is this chemical composition of gelatin which is responsible for its stability and is exploited for chemical modification and covalent drug attachment in preparation of drug delivery systems [8]. These wide ranges of opportunities for chemical alterations and drug attachment of drug via covalent bond can be carried out either within the particle matrix or on the particle surface. In the former scenario, the gelatin macromolecules must undergo chemical alterations prior to the formation of NPs, whereas in the latter scenario, the particle surface is utilized [9].

Depending on its so easy to handle and play with availability of structure, it has been adapted for non viral gene delivery in various forms like alendronate gelatin,

#### *Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

PEGylated gelatin, cationic gelatin, thiolated gelatin, and EGFR gelatin NPs [10]. In context with these [11] designed MMP-2-triggered gelatin NPs loaded with doxorubicin (DOX) and 5-Aminolevulinic acid (5-ALA) providing combined chemotherapeutic and photodynamic therapy for breast cancer. The system employed the naturally occurring MMP-2 enzyme in tumor tissue, which via its high expression level was employed for gelatin degradation and targeted drug release was achieved [11]. Kirar et al. [12] found that a singlet oxygen was produced by biodegradable gelatin NPs damaging the microbial cell membrane, leading to cell death. The therapy regimen was adorned by Rose Bengal (RB) conjugated and entrapped in gelatin nanoparticlebased biodegradable nanophototheranostic. According to the study, gelatin NPs can be used in place of substances like potassium iodide, calcium chloride, ethylenediaminetetraacetic acid (EDTA), and polymyxin nonapeptide to allow drugs to penetrate cell membranes and exert antibacterial action [12].

#### *2.1.2 Albumin*

Albumin has been identified as most common protein in blood. Due to its function in the maintenance of intravascular colloid osmotic pressure, neutralization of toxins, high availability, non-immunogenic, strong binding capabilities for both hydrophobic and hydrophilic medicines, a lengthy half-life, the ability to target specific regions of inflammation, and almost little toxicity they have been readily accepted since the early twentieth century and welcomed for transport of therapeutic agents [13]. There are three forms of their existence and mainly utility is seen as bovine serum albumin, Human serum albumin, and Ovalbumin, [14]. The versatility of albumin-based NPs lies in their specificity been explored not only for deliverance of drugs but at the same time for navigating the possibilities of various drug delivery routes [15], multifunctional bioimaging [16], delivery of albumin functionalized aptamers [17–20] allowing its use as modified versions enhancing their interactions with enzymes like myeloperoxidases at inflamed site [21] achieving site specific drug delivery. In addition to these they are also utilized for conjugation with antibodies increasing their half life in circulation and was reported by [22] that engineered human albumin maintained FcRn-binding characteristics after conjugation and drop in glycemia was observed as a function of receptor targeting when given orally to human FcRn-expressing mice that had been given diabetes-inducing drugs, with a reduction up to 40% occurrence 1 h after delivery [22]. Albumin has also been explored for conjugation with nanobodies which are derived from different region of immunoglobulin's heavy chain single domain antibody [23]. Henaki et al. reported that a genetic fusion between the irrelevant nanobody R2 and the HER2-targeted nanobody 11A4 to increase binding with albumin-binding domain (ABD) leading to extended serum half-life noticeably, and uniform tumor formation [24].

#### *2.1.3 Hyaluronic acid (HA) and its derivatives*

HA is a natural polysaccharide discovered in 1934 from bovine eyes found in abundance as extracellular matrix's primary component, crucial to the human body's physiological processes. It is chemically composed of 1,3 and 1,4 glycosidic connections that frequently connect N-acetylglucosamine and glucuronic acid [25]. Since its discovery and further derivatization according to advances in drug delivery target potentials, improvisation of stability and shelf life is achieved. With these advancements, utility of HA and its derivatives in surgery, medication development, treatment of arthritis, targeting, formation of nanoparticulate/gel/microsphere/ gene vectors based drug delivery systems has also enhanced over the past few years [26]. Bai et al. reported the construction of supramolecular self-assemblies of β-cyclodextrin and HA which were further drug–drug conjugates self-assembled into NPs for achieving active targeting. This multifunctional delivery system demonstrated co-drug delivery and release patterns that were responsive to pH and esterase, achieving improved synergistic therapeutic efficacy, and active targeting capability [27]. Hyaluronic acid mediated treatment possibility was checked by Lu et al., were by linking an o-phenylenediamine group, levofloxacin was conjugated with hyaluronic acid to create a CD44 mediated cellular targeting via NO-sensitive nano-micelles which provided with their ability to fight against bacteria leading to reduction in the inflammatory levels [28]. Duan et al., worked on coping up with thrombosis considered as one of the major complications of cancer by incorporating anticoagulant heparin (Hep) as an adjuvant to the therapy with carbon dots as drug delivery system loaded with doxorubicin hydrochloride. He found that this dual drug and adjuvant therapy enhanced the blood compatibility of the system and in vitro MTT and scratch tests showed that this drug delivery method could specifically suppress cancer cell growth and migration [29]. Hyaluronate mediated targeting of cancerous cell was also seen in breast cancer where Batool et al., create a papain grafted S-protected HA-lithocholic acid co-block (PAP-HA-ss-LCA) polymeric excipient that functions as an amphiphilic muco penetrating stabilizer for breast cancer epithelial cells. These cells are overexpressed with CD44 receptors. By creating a tamoxifen (TMX) loaded self-nanoemulsifying drug delivery system, the mucopermeating, stabilizing, and targeting capabilities of the PAP-HA-ss-LCA polymeric excipient were studied [30].

#### *2.1.4 Silk fibroin*

Polymer-based delivery systems that are effective must be biocompatible, biodegradable, low toxic, have the right mechanical properties, call for ambient production conditions, and offer sustained release. Due to its distinct structural characteristics of self-assembling capacity, high strength, processing flexibility, biodegradability, and biocompatibility, silk a natural polymeric biomaterial meet these needs [31]. A fibrous fundamental protein called Silk Fibroin (SF) and a stick-like coating made of sericin make up silk as it is well known. Commercially silk has been obtained from silk cocoons from silkworms of *Bombyx mori* mainly. Although Eight subspecies of Bombycoidea family, have been exploited but only the Bombycidae (mulberry) and Saturniidae (non-mulberry) are significant commercially [32]. According to descriptions of SF, it is a naturally occurring amphiphilic block co-polymer made up of hydro-phobic (highly conserved, arranged) and hydrophilic (less conserved, more complicated, less organized) blocks that combine to give SF its flexibility and strength. From a morphological perspective, SF consists of recurring chains made up of small side chain amino acids, such as glycine and alanine, and hydrophilic blocks having H-bonding and hydrophobic interactions, which are the basis of SF's tensile strength. Together with the less organized hydrophilic blocks, these effective hydrophobic blocks produce the flexibility [33, 34].

Cao et al., utilized FDA-approved SF, to utilize the advantages of the features as carrier polymer, demonstrating a single-step electrospraying procedure without an emulsion process uses the blends SF and polyvinyl alcohol (PVA) with drug. A distinct core-shell structure was obtained with doxorubicin encapsulated in the core. *Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

By changing the PVA/SF ratio, the controlled drug release profiles were possible to achieve. The SF coating reduced the drug's first burst release, but a lot of drug molecules were still retained by the carrier polymers and portrayed a pH dependent drug release [35]. Chouhan et al., critically presented the use of SF in wound healing premises and showed the efficacy of silk based matrices for healing efficiency [36]. To overcome the problem of intravenous administration Gangrade et al., utilized two silk proteins and created a nano hybrid silk hydrogel-based delivery of anticancer medications locally, precisely, and instantly. The β-sheet structure helped to form the hydrogel network and payload efficiency was enhanced using the carbon nano tubes [37]. Air spun nanofibers for drug delivery [38], temperature-responsive poly (N-isopropylacrylamide) (PNIPAM) hydrogel and SF scaffold microcarriers for controlled and sustained drug release [39], silk based embolic material a potential next-generation multifunctional embolic agent including nivolumab labeled with albumin was delivered to treat vascular disorders, including malignancies, as well as achieve embolization [40]. Its utilization has been explored nevertheless in all possible directions for drug delivery.

#### **2.2 Plant-based biopolymers**

#### *2.2.1 Cellulose*

Cellulose is a high-molecular-weight natural homopolysaccharide, materialized as multifunctional drug delivery polymer because of their inbuilt porosity, which can aid in the liquid uptake. Water and cellulose can interact significantly, causing cellulose to swell easily in water. This swelling property is correlated with the cellulosic polymer network's capillarity. It is common knowledge that a medicine with a speedy swelling effect will also dissolve quickly and thus enhances the dissolution process [41]. Structurally cellulose connected to acetal molecule between the C-4 of hydroxyl group and C-1 of the carbon by covalent bond. One primary and two secondary hydroxyl groups can be found in anhydro glucose molecules. Because of the extremely strong inter- and intramolecular hydrogen bonds created by this hydroxyl group, cellulose is insoluble in aqueous or organic solvents. Cellobiose units are composed of two glucose moieties joined by a 1–4 bond having high molecular weight. D-hydroxyl glucose's is a good candidate for modification and the formation of various derivatives. Various derivatives of cellulose have been in use for various purposes depending on their physical properties like ethyl cellulose, methyl cellulose, carboy methyl cellulose, carboxy ethyl cellulose, hydroxy propyl methyl cellulose (HPMC), hydroxy ethyl cellulose, etc. [42]. Because of their properties they are used in ocular, rectal, vaginal, antitumor deliveries.

Recently, Long et al., recreated the efficacy of cellulose nanocrystals (CNCs) by utilizing the numerous hydroxyl active functional groups on the surface of CNCs allowing for easy chemical modification to improve targeting via manifesting weakly acidic tumor environment with a hydrazone bond along with anti-cancer drug. Owing to its properties Sheng et al., came up with CaCO3 microspheres with methotrexate and aspirin co-entrapped in hydrogels, achieving significant pH dependent drug release on sites [43]. Pooresmaeil et al. [44], made use of Green chemistry to prepare layered double hydroxides LDHs known for their high ion exchangeability to deliver controlled and sustained drug release at acidic medium of stomach through loading of this LDH Zn/Al 5-Fluro uracil in CMC on site.

#### *2.2.2 Starch*

Starch, a readily available material, is most abundant and affordable biopolymer after cellulose and chitin that has been employed in a variety of biomedical applications, drug delivery systems, and tissue engineering platforms. Starch is a composition of two, amylose and amylopectin, which combine to generate these granules in chloroplast of plant cells. Amylose, a straight or slightly branched polysaccharide, is made up of glucose units connected by 1–4 glycosidic linkages while amylopectin is a branching biopolymer with extra -1-6 glycosidic linkages [45]. Shehabeldine et al. synthesized eco-friendly ciprofloxacin hydrochloride (CIP) loaded green-based nanocomposite to improve its activity and regulate the antibiotic's release and bioavailability. Microbiological glycoside hydrolases assist in the enzymatic hydrolysis of starch. Using an environmentally friendly process, hydrolyzed starch/chitosan loaded with CIP (HS/Ch-NC) was created. And optimal release of CIP was achieved [46]. A water soluble polysaccharide called as Pullulan is composed of maltotriose units and is produce by the fungus *Aureobasidium pullulans*, was reviewed by Grigoras for producing drug delivery systems enhancing therapeutic efficacy of hydrophobic drugs, increasing their water solubility [47]. Promoting the use of natural constituents for treatment purpose Nallasamy et al., designed a polyherbal nano-formulation incorporating Triphala churna in starch NPs exhibiting high loading efficiency, sustained release and its antibacterial, antibiofilm, and neuroprotective properties were equally retained [48].

#### *2.2.3 Soy protein*

After getting approved by UDFDA in 1999 as protective for coronary heart diseases its incorporation and utilization for various health treatments as adjuvants drastically increased. A globular protein extracted from soy beans, soy protein is relatively stable and has a long shelf life. Soy proteins when considered chemically have albumins and globulins as their primary components, which can be further segregated on the basis of sedimentation coefficients into 2S, 7S, 11S and even 15S fractions where 7S (SC), 11S (SG), or 15S fractions often correlate to the globulins, while the albumins in soy proteins are reported in the 2S form [49]. Mainly extracted from soy beans, they exist as soy flour, soy protein concentrate, and soy protein isolate available in quantities ranging from 50–90% after removal of carbohydrates, fats, oils, moisture and other components [50]. Its most commonly existing form is 11S (SG) consisting of 6 subunits. A disulfide bond connects the basic polypeptide (B) with the acidic polypeptide (A) that makes up each subunit. These subunits with functional groups like -NH2, -OH, and -SH in soy protein make it easy to modify the protein chemically or physically or mix it with other biopolymers, which is equally reflected in the changes that the protein undergoes on heating, pH and other environmental exposures which are exploited for preparation of pH responsive gels, nano-formulations [51]. Being a good source of plant-based protein, it adds on formulations benefit in a way of being less immunogenic, more stable. They have a strong propensity to aggregate and gel, act as good emulsifiers, and are frequently employed as functional additives in food compositions. Its physical propensity has been identified with other plant-based ingredients like cellulose and pine needle extract for development of packaging material as well. Xu et al., by breaking the hydrogen bonds that existed between the N—H groups of soy proteins and water molecules added cellulose nanocrystals CNCs which reduced the moisture content, elongation at break

#### *Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

of the film samples and increased the tensile strength as a result of the filling action of CNCs. Addition of pine extract not only added to antioxidant properties to the film but at the same time decreased its water permeability enhancing its water vapor barrier capacity [52]. Cheng et al. further advanced the drug release pattern and accumulation in cancer lines by grafting soya protein with D-α-Tocopheryl polyethylene glycol succinate which acted as an adjuvant to the Cisplatin delivery system by itself being a good stabilizer, wetting agent and solubilizer and provided acid responsive delivery [53]. Soy protein has been incorporated as 2D surfactant to enhance the electrical conduction of nanocomposites [54], as an excellent promoter of enzymatic hydrolysis extracted from inexpensive defatted soy powder (DSP) in liquid hot water pretreated lignocellulosic substrates making the process inexpensive and biocompatible [25, 55], as a 4D printing food material along with carrageenan, and vanilla as flavor enhancer [56].

#### *2.2.4 Zein*

First identified in nineteenth century, zein is a plant based prolamins extracted majorly from corn existing as α, β, γ, and δ zein. α zein ia considered the most common and abundant among existing varieties. It is a hydrophobic protein that dissolves better in aqueous acetone, aqueous ethanol, and various organic solvents other than in plain water. Being a hydrophobic protein, it is found to be suitable for drug delivery system designing due to its certain important features, like biocompatible, and biodegradable nature [57]. Its utility has been reported in multi-domains of pharmaceutical industry like food coating, packaging, tissue engineering as well. Various zein based delivery systems such as nanocarriers, microspheres, tablets, capsules electro-spun fibers, etc. for delivery of drugs in spatiotemporal manner has been used widely [58]. Manifesting its natural non immunogenic existence Ruberedo et al., reported preparation of PEG-coated zein NPs made by a simple and repeatable process without the use of reactive chemicals suitable for increasing the oral bioavailability of bioactives and other physiologically active substances with limited permeability [59]. The poor stability and re-dispersibility of zein NPs was mitigated by preparation of loading of anti-inflammatory drug imidazole into zeolitic imidazole framework-8 frame and further coating this with succinylated zein, these modifications were able to provide pH responsive oral delivery which was tested due to the stable under neutral conditions and rapidly degradation phenomenon in an acid environment due to protonation of zeolitic imidazole framework-8.

## **2.3 Biopolymers from marine organisms**

## *2.3.1 Alginate*

Alginates are polysaccharide polymers made up of sequence of two (1Ñ4)- linked α-L-guluronate (G) and β-D- (M) derived from brown seaweed (Phaeophyceae). They are biocompatible, show low toxicity and possess carboxyl groups which shows charge at pH values more than 3–4, making them soluble in alkaline and neutral environments. This pH dependent solubility portrayed by alginates and it's salts is promotive for some medications, for whom additional safeguards are required for preferential absorption in the lower gastrointestinal tract and thus are used to design various modified release dosage forms [60]. Santinon et al., reported delivery of Valsartan through sericin and alginate matrix, where addition of alginate during

particle formation stage due to the gelation capacity on contacting with multivalent cations, such as Ca2+, which helped in evaluating the efficacy of cross-linking agents like proanthocyanin, PVA, PEG, citric acid in formulations drug loading and drug release [61]. Properties of alginate to form pH sensitive gels was further extrapolated by Esfahlan et al., reported gelatin (Gel) and alginate (Alg) based a magnetic natural hydrogel, where after partly oxidizing alginate (OAlg), the Alg-Gel chemical hydrogel was created via a "Shift-Base" condensation process and then Fe3O4 magnetic NPs (MNPs) were entrapped into this gel via in situ chemical co-precipitation method. This resulted an efficient and "smart" drug delivery system for cancer chemotherapy as it out-performed free doxorubicin in terms of pH-dependent and delayed drug release profile, magnetic property for diagnosis by MRI approach, and isolation at targeted region [62]. They are utilized handsomely in pharmaceutical industry as thickening, gel-forming, and stabilizing properties whose action changes with concentration, environment/medium of dissolution involved [63].

#### *2.3.2 Carrageenan*

Carageenans discovered first in Ireland, are marine sourced linear polysachharides of red algae's that are sulphated [64]. Since 1973, the Food and Drug Administration (FDA) has deemed carageenans to be "Generally Recognized As Safe" (GRAS) (FDA SCOGS) (Select Committee on GRAS Substances). The European Food Safety Authority has certified carrageenan (E-407) and semi-refined carrageenan (E-407a) as food additives [65]. After receive of such approvals their inclusion in foods, pharmaceutical drug delivery systems increased. With time its efficiency has been seen in tissue engineering and regenerative medicines as well. Khan et al., designed porous polymeric nanocomposites and made use of sulphonic groups in carrageenan's structure which due to the self-assembly of their helical structures exhibit several biological properties along with acrylic-acid/graphene/hydroxyapatite. These nanocomposite scaffolds were able to enhance bone regeneration efficiently [66]. Vijaykumar et al., prepared zinc oxide NPs enveloped in kappa-carrageenan for antiinflammatory effects on Methicillin resistant *Staphylococcus aureus* (MRSA) culture, where this MRSA causes human skin and nosocomial infections. The formulation acted as super bug for MRSA growth at a minimal concentration, reducing bacterial cell surface hydrophobicity with no evidence of hemolytic or morphological changes in human RBC [67]. It has been reported that sulphated algae polysaccharides showed anti-viral activity for which carrageenan and fucoidan where considered the norms for viral crisis of which kappa carrageenan with higher sulphated content proved to be really effective [68].

## *2.3.3 Chitosan*

Chitosan is a linear naturally occurring amino polysaccharide, Rouget made the initial discovery and discussion of it in 1859 revealing its generation from chitin. After celluloe, chitosan is considered to be the second most prevalent amino polysaccharide after cellulose. Significant research has been conducted on pharmaceutical and biomedical and applications, such as drug delivery, tissue engineering, wound-healing dressing, etc. because of its nontoxic, biocompatible, antibacterial, and biodegradable qualities. It is structurally made up of repeated glycosidic units made of *N*-acetyl-dglucosamine and d-glucosamine units, each of which has two hydroxyl groups and one amino group. The amino group which carve out for the cationic versatility of

#### *Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

chitosan to provide rate and time specific drug release, bio-adhesion, in situ gelation, antibacterial, permeation enhancement, etc. [69]. Chitosan can be classified according to its inherent features, such as purity, molar mass, viscosity, acetylation level, quality, and physical shape. Chitosan's performance, synthesis, characterization, and applications are all influenced by its degree of acetylation characteristics as well as its molar mass [70]. Baghaei et al., prepared a polyelectrolyte complex of trimethyl chitosan, hyaluronate/dextran/alginate NPs using D optimal design and checked their efficacy for gene delivery and for further translational work in industries. He found that chitosan and hyaluronate showed desired size, entrapment efficiency and in-vitro killing [71]. Ziminska et al., in line of promoting the patient compliance, a thermo responsive gel was designed for minimal invasive delivery utilizing free radical polymerization to create a stable, hydrogel network at body temperature, with low molecular weight chitosan of 75–85% deacetylation and *N*-isopropylacrylamide with unique physical characteristics were used. The fact that NCTC-929 cells could be transfected by the released RALA/pEGFP-N1 indicates that the hydrogel had no effect on the stability of the supplied nucleic acid [72].

#### *2.3.4 Fucoidan*

Enormous marine supply of ingredients showing biocompatibility, nonimmunogenicity, and bioavailability has increased their demand in numerous fields, including biology, food science, pharmacology and cosmetics, empowering the value of this resource. Three major categories of marine biomaterials are as follows: lipids, polysaccharides, and proteins [73]. Out of these three biomaterials, marine polysaccharides are most stable, with fundamental or covalent structure which shows the arrangement of monomeric units throughout the chain which are used to categorize them. By restricting the orientations of the monomers, these repeating units are joined by covalent chemical bonds. This property limits the forms that a polysaccharide chain may take on, known as "secondary structures". Depending on these fundamental sequences marine polysaccharides possess inherent qualities that are extremely important in the field of medication delivery. Biomaterials utilizing enzymatic and chemical processes, developing stimuli-responsive delivery vehicles, modified as gels, and produce interpenetrated polymeric networks [74]. These may further get conjugated, and complexes with bioactive molecules or proteins [75]. Fucoidan is one such marine sulfated polysaccharide obtained from brown algae and invertebrates from marine origin. A top-notch candidate for pharmaceutical uses is fucoidan. Because of its many biological features, including antiviral, anticoagulant, antiangiogenic, anticancer, antioxidant, antiproliferative, anti-inflammatory, and immunomodulating activities, fucoidan has recently received attention [76]. For instance, fucoidan's anticancer action is mostly associated with its lower molecular weight [77]. Shanmugapriya et al., designed fucoidan-based nanomaterials for the precise medicine administration to the cancer cells in the gastrointestinal tract loaded with nanohydroxyapatite/collagen. The formulation showed effective results with potent administration of drug at target site [78].

## **3. Natural PNPs for cancer nanomedicine**

As cancer is becoming the main cause of mortality in wealthy nations. In fact, according to specialists, there will be a 70% increase in the occurrence of this disease during the next 20 years [79, 80]. Surgery, chemotherapy, and radiation make up the standard treatment regimen for treating cancer. The most general form of cancer treatment is chemotherapy, but it has a high level of toxicity since it affects both healthy and malignant cells [81]. An option that is more focused is known as "nanomedicine," which is the use of materials at the nanometric scale in medicine. Its primary goal in oncology is to deliver the medication solely to cancer cells in order to increase its efficacy and lessen its toxicity. Additionally, early cancer detection technologies and combination medicines that improve treatment effectiveness and prognosis are both possible applications of nanomedicine [80]. Many PNPs have been employed up to this point to transport anticancer medications like paclitaxel, doxorubicin, or camptothecin in various cancers. By experimenting with new drug delivery methods, mixing active ingredients to enhance their effects, or combining with other therapies like gene therapy, the usage of PNPs can lead to advancements in cancer treatment. As an alternative to intravenous delivery, Ahmad et al. [82] suggested improving the oral bioavailability of doxorubicin by surface-modified biodegradable PNPs. They investigated the pharmacokinetics of doxorubicin and drug-loaded PEGylated PLGA NPs in Wistar rats. Results indicated that when compared to oral medications, NPs had superior activity and higher bioavailability. Soma et al. [83] investigated the synergistic impact of doxorubicin and cyclosporin A nanoparticulate formulations in comparison to NPs alone is successful in slowing the growth rate of P388/ADR cells, according to the results. The FDA has authorized albumin-bound (nab)-paclitaxel NPs (Abraxane®) for the treatment of cancer in 2012. Since then, a wide range of cancers, including pancreatic cancer, metastatic breast cancer, and lung carcinoma have been treated with it. These NPs were created to help with paclitaxel's pharmacokinetics and pharmacodynamics as well as to prevent the toxicities of the polyoxyethylated castor oil solvent (Cremophor), which was previously employed since paclitaxel had a difficult time dissolving in water. Additionally, these NPs plus gentamicin together had a somewhat higher survival probability for advanced and metastatic pancreatic cancer. A new paclitaxel liposome-albumin composite that was recently developed at the nanoscale had a remarkable encapsulation effectiveness of 99.8% [84].

Brain Targeted PNPs were also investigated by researchers and to be found affective drug delivery. Crpanl et al. [85] investigated camptothecin-loaded cyclodextrin NPs for brain cancer. The effectiveness of these NPs demonstrated an increase in the survival time and was studies in a rat glioma model for brain cancers. Pandey et al., reported the improved delivery of anticancerous agent doxorubicin via surface modified silk fibroin NPs through Tween-80 coating. The hydrophobic nature of these NPs assists make then susceptible for macrophageal and reticulo-endothelial system (RES) uptake which was overcome by surface coating of NPs with Tween-80 which is a hydrophilic stabilizers, thus making them long circulating and helping to cross blood brain barrier (BBB) by low density lipoprotein (LDL) [34].

Breast cancer, most common kind of cancer in women, is accounting for a staggering 30% of all instances that have been officially diagnosed. In order to better understand the effects of pH-sensitive PEG-PLGA-PGlu (polyglutamic acid) NPs implanted with doxorubicin and curcumin on breast tumor cells and drug-resistant cancer stem cells, Yuan et al. used mouse models [86]. Hu et al. looked at the usage of photodynamic therapy and nanoparticulate systems together in the treatment of breast cancer. They created oxygen-producing theranostic poly(caprolactone-colactide)-b-PEG-b-poly(caprolactone-co-lactide) NPs of doxorubicin, chlorin e6, and

#### *Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

colloidal MnO2 to create oxygen in tumor environment, relieve tumor hypoxia, and enhance photodynamic therapy. The NPs also improves the action of doxorubicin [87]. Breast cancer has also been studied in relation to MDR.

As the third cause of death brought on by oncologic diseases, liver cancer is the most common malignancies with high mortality rate. The majorities of anti-cancer medications have considerable liver toxicity and can result in serious adverse effects. With the aim of to increase the efficiency of anticancer medications and to lessen the emergence of adverse effects, PNPs are used as potential carriers. Zhu et al. reported a novel galactosamine-conjugated polydopamine-modified copolymer (Gal-pD-TPGS-PLA) NPs to create a nanosystem [88]. Gal-pD-TPGS-PLA NPs was used to target HepG2 cells by ASGP receptor-mediated recognition, and dramatically decrease cell growth, according to an in vitro cellular uptake and cytotoxicity study. Furthermore, docetaxel-loaded Gal-pD-TPGS-PLA NPs decreased tumor growth more as compared to docetaxel-loaded TPGS-PLA NPs, pD-TPGS-PLA NPs, or saline, in vivo. An overview of the nanoparticulate systems used as drug delivery system for cancer therapy are summarized in **Table 1**.


#### **Table 1.**

*Polymeric NPs bearing anticancer drug for cancer treatment.*

## **4. Methods of preparations for PNPs**

Methods of preparations for PNPs are classified as general methods and modern methods which are discussed in details as follow.

## **4.1 General methods**

Recently, various biodegradable polymers and their co-polymers have been used to create NPs, being the most frequently used to create PNPs and encapsulate bioactive. Micelles, platelets, dendrimers, fibers, spheroids colloids, core-shells, and polymer matrixes with embedded NPs are just a few examples of multi-functionalized polymeric nanocarrier systems (**Figure 1**).

Depending on the specific application, PNPs must have their characteristics tuned. The method of preparation is crucial in achieving the desired qualities. Consequently, it is very beneficial to have preparation methods on hand in order to create PNPs with the appropriate characteristics for a certain application. Various methods are employed, including polymerization, premade polymers, ionic gelation, etc. These can be completed using the many techniques listed below.


#### **Figure 1.** *General methods of preparation of PNPs.*

*Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

Methods for preparation of NPs from polymerization of monomers


## *4.1.1 Solvent evaporation*

The first technique created to make PNPs was solvent evaporation. This method involves development of polymer solutions in volatile solvents and creating emulsions. Ethyl acetate, which has a superior toxicity profile, has replaced dichloromethane and chloroform premade polymer [92], which were once frequently utilized. As the solvent evaporates and allowed to pass into the continuous phase of the emulsion, the emulsion is transformed into a suspension of NPs. The manufacture of single-emulsions, such as oil-in-water (o/w) or double-emulsions, such as w/o/w, are the two major techniques utilized in the conventional procedures for creating emulsions. These techniques involve ultrasonication or high-speed homogenization, followed by the solvent evaporation either by continuous magnetic stirring at ambient temperature or under decreased pressure. NPs can be recovered by ultracentrifugation and rinsed with distilled water to get rid of additives (**Figure 2**). The product is lyophilized at the end [92, 93].

## *4.1.2 Nanoprecipitation*

Solvent displacement technique is another name for nanoprecipitation. A polymer from organic solution gets precipitated, and the organic solvent diffuses across the

#### **Figure 2.**

*Solvent-evaporation technique for NPs formation.*

#### **Figure 3.**

*Nanoprecipitation technique (surfactant is optional) for NPs formation.*

aqueous medium whether a surfactant is present or not [94, 95]. The nanospheres precipitation occurs for the polymer, typically PLA, which get dissolved in a water-miscible solvent (medium polarity). This phase is added to an aqueous solution with agitation and contains a stabilizer as a surfactant. Instantaneous production of a colloidal suspension results from polymer deposition on the water-organic solvent interface brought on by the solvent's rapid diffusion [96]. Phase separation is carried out using a fully miscible solvent that is also a non-solvent of the polymer to help the production of colloidal polymer particles during the first step of the operation [97]. Although acetone and dichloromethane (ICH, class 2) are employed to dissolve and enhance drug entrapment, the dichloromethane increases mean particle size [98], and it is therefore hazardous. Due to the solvent's miscibility with the aqueous phase, this approach can only be used to encapsulate lipophilic pharmaceuticals and is ineffective for water-soluble medications. Numerous polymeric polymers, including PLGA, PLA, PCL, and poly (methyl vinyl ether-comaleic anhydride) (PVM/MA), have been subjected to this technique [99, 100]. Entrapment efficiencies of up to 98% showed that this method was well suited for the inclusion of cyclosporin A [101]. The antifungal medications Bifonazole and Clotrimazole were loaded into nanoparticulate systems using the solvent displacement approach (**Figure 3**) [102].

#### *4.1.3 Emulsification/solvent diffusion (ESD)*

A modified form of the solvent evaporation technique is used here [103]. To attain the initial thermodynamic equilibrium of liquids phase, the polymer gets dissolved in a slightly water soluble solvent, like propylene carbonate. It is necessary to encourage the diffusion of the dispersed phase's solvent by dilution with an excess of water which results in the formation of precipitate of the polymer and the subsequent NPs formation. Then, depending on the ratio of oil to polymer, the polymer-water solvent phase is emulsified in an aqueous solution with stabilizer, resulting solvent diffusion to exterior phase leading to the formation of nanocapsules or nanospheres (**Figure 4**). Depending on its boiling point, the solvent is finally removed via evaporation or filtering. **Figure 4** shows the process in action. The mesotetra(hydroxyphenyl)porphyrin- and doxorubicin-loaded PLGA (p-THPP) NPs, the plasmid DNA- and coumarin-loaded PLA NPs, the indocyanine- and the cyclosporine (Cy-A)-loaded gelatin- and sodium glycolateloaded NPs were NPs developed by the ESD technique (**Figure 4**) [104].

*Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

#### **Figure 4.**

*Emulsification/ solvent diffusion technique for NPs formation.*

#### *4.1.4 Salting out*

The principle behind salting out is the use of the salting out phenomenon to separate a water miscible solvent from aqueous solution. A variant of the emulsification/solvent diffusion process is the salting out process. The salting-out agent such as electrolytes (calcium chloride, magnesium chloride, etc) or non-electrolytes (sucrose) and a colloidal stabilizer (PVP or hydroxyethyl cellulose) are added to the initially dissolved polymer and drug is dissolved in a solvent, like acetone. This o/w emulsion is thinned out with enough aqueous solution to speed up acetone's diffusion into the liquid phase, which causes the production of nanospheres [93]. Salting out agent selection is crucial since it can have a significant impact on how effectively the medicine is encapsulated (**Figure 5**). To remove both the solvent and salting out agent, cross-flow filtration is used. This method is very effective and simple to scale up. Salting out has the principal benefit of reducing stress on protein encapsulants [105]. When heat-sensitive materials need to be treated, salting out may be helpful because it does not need a rise in temperature [106].

**Figure 5.** *Salting out technique for NPs formation.*

## *4.1.5 Dialysis*

Small, narrow-distributed NPs can be produced using a quick and efficient procedure called dialysis [107–109]. A dialysis tube is filled with a polymer dissolved in an organic solvent and has had the appropriate molecular weight cut off. Another non-solvent miscible with the solvent is used for dialysis. The polymer gradually gets aggregates as a result of decrease in solubility leading to development of homogenous NPs suspensions. The shape and size of NPs are influenced by type of solvent evolve to make the polymer solution. For the manufacture of different natural and synthetic PNPs, Chronopoulou et al. [110] developed a unique osmosis-based technique (**Figure 6**). This method is based on physical barrier (dialysis membrane or semi-permeable membranes) which enable the passive transit of solvents resulting decelerate the mixing process of nonsolvent with polymer. The polymer solution presents in the dialysis membrane.

## *4.1.6 Supercritical fluid technology*

The use of supercritical fluids technology is more environmentally friendly having the power to produce the highly pure PNPs without any traces of organic solvent [111]. With the majority of the limitations of conventional approaches avoided, supercritical fluid technology and dense gas technology are predicted to offer an intriguing and efficient method of particles creation.

For the synthesis of NPs with supercritical fluids, two concepts have been developed:


## *4.1.6.1 Rapid expansion of supercritical solution*

RESS involves dissolving the solute in a supercritical fluid to create a solution, which is then rapidly expanded over an aperture or a capillary nozzle into the surrounding air. The creation of well-dispersed particles is caused by homogeneous nucleation. For homogeneous nucleation, the high degree of super saturation and

**Figure 6.** *Osmosis-based method for polymer NPs formation.*

*Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

**Figure 7.** *RESS method for polymer NPs formation.*

quick pressure reduction in the expansion are the requirements. Both nanometer and micrometer sized particles are able to get produced through expansion jet. Three main components of the RESS experimental equipment are (a) high pressure stainless steel mixing cell, (b) a syringe pump, and (c) a preexpansion unit. At room temperature, a polymer solution in CO2 is created. Syringe pumps are used to pump the solution to the pre-expansion unit where it is isobarically heated to the pre-expansion temperature before it leaves the nozzle. Now, at atmospheric pressure, the supercritical solution is left to expand through the nozzle (**Figure 7**). For RESS, the particle size and shape are significantly influenced by the polymer's concentration and saturation level [112, 113].

## *4.1.6.2 Rapid expansion of supercritical solution into liquid solvent*

Expansion of the supercritical solution into solvent rather than ambient air is a straightforward but important adjustment to the RESS process [106]. Poly (heptadecafluorodecyl acrylate) NPs having size less than 50 nm were created. Although, there is no organic solvents involvement in the RESS process for the formation of PNPs, still the fundamental disadvantage of RESS is that the primary products created using this technique are microscaled rather than nanoscaled. A new supercritical fluid technique called RESOLV has been created to get over this limitation. The liquid solvent in RESOLV inhibits particle development in the expansion jet, allowing the formation of mostly nanosized particles (**Figure 8**) [114].

## *4.1.7 NPs formation by polymerization of a monomer*

Designing appropriate polymer NPs can be done during the polymerization of monomers in order to get the needed characteristics for a specific application. The procedures for creating PNPs by polymerizing monomers are explained below.

## *4.1.7.1 Emulsion polymerization*

The quickest and most scalable process for producing NPs is emulsion polymerization. Depending on whether an organic or an aqueous continuous phase is used, the approach is grouped into two groups. In order to use the continuous organic phase

approach, a monomer must be dispersed into an emulsion, an inverse microemulsion, or a substance in which it is not soluble (nonsolvent). Using this technique, polyacrylamide nanospheres were created [115]. Later, via dispersion of surfactants into solvents including cyclohexane, n-pentane, and toluene as the organic phase, poly(ethylcyanoacrylate) (PECA), poly(methylmethacrylate) (PMMA), and poly(butylcyanoacrylate) (PBCA) NPs were generated. Surfactants or emulsifiers are not required in the dissolving continuous aqueous phase. When a monomer molecule get dispersed in continuous phase, it strikes an initiator molecule (may be ion or a free radical) initiation starts. As an alternative, powerful ultraviolet or visible light, high-energy radiation can convert the monomer molecule to act as an initiating radical. According to an anionic polymerization process, chain development begins when starting monomer ions or radicals strike additional monomer molecules. Before or after the polymerization process has finished, phase separation and the production of solid particles may occur [116].

## *4.1.7.2 Mini-emulsion polymerization*

Water, a monomer combination, a costabilizer, a surfactant, and an initiator make up a typical formulation for miniemulsion polymerization. Differences between mini-emulsion polymerization and emulsion polymerization is the use of a high-shear device and a low molecular mass molecule which act as co-stabilizer (ultrasound, etc.).

## *4.1.7.3 Micro-emulsion polymerization*

A novel and successful method for producing PNPs has gained a lot of attention: micro-emulsion polymerization. The emulsion and micro-emulsion polymerization techniques are involved in the formation of colloidal polymeric particles via using completely different kinetic. Micro-emulsion polymerization technique results in

#### *Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

much lower particle sizes. A thermodynamically stable micro-emulsion with swollen micelles is introduced to the aqueous phase of micro-emulsion polymerization together with water-soluble initiator. The polymerization starts from this spontaneously point which help in production of thermodynamically stable state which depends on large amounts of surfactant complexes having almost zero interfacial tension at the o/w contact. Additionally, due to the application of surfactant in high amount, the particles are totally covered by surfactant. The delicate micro-emulsions are later destabilized by the elastic and osmotic impact of the chains, which generally result in a rise in particle size, the generation of empty micelles, and subsequent nucleation. In the finished product, the bulk of empty micelles coexist with very tiny latexes, with size of about 5–50 nm. Some of the key variables influencing the kinetics and characteristics of PNP in microemulsion polymerization techniques are the type and concentrations of the initiators, surfactant, monomer, and reaction temperature [117].

#### *4.1.7.4 Interfacial polymerization*

It is one of the tried-and-true techniques for creating polymer NPs. The reaction for the process occurs at the interface of the two liquids. It utilizes the polymerization as step by step process of two reactive monomers that are distributed in two phases, respectively. By using interfacial cross-linking processes (polyaddition, polycondensation, radical polymerization) nanometer-sized hollow polymeric particles were formed [118]. By polymerizing monomers at the o/w interface of o/w micro-emulsion, oil-containing nanocapsules were created. It was thought that the interfacial polymerization of the monomer took place at the surface of the oil droplets which was formed during emulsification and organic solvent (miscible with water) functioned as a monomer carrier. Aprotic solvents like acetone and acetonitrile should be used to encourage the development of nanocapsules [119].

#### *4.1.8 Controlled/living radical polymerization*

Future commercial success of controlled/living radical polymerization depends on its application in the industrially significant aqueous dispersion systems, which produces PNPs having control over particle size and size distribution. Atom transfer radical polymerization (ATRP), reversible addition and fragmentation transfer chain polymerization (RAFT), and Nitroxide-mediated polymerization (NMP) are some of the successful in-depth approaches for controlled/living radical polymerization that are now accessible [120]. Hydrophilic polymers may gel or accelerate ionically. Some biodegradable hydrophilic polymers like gelatin, sodium alginate, and chitosan are generally used for the development of PNPs. By using ionic gelation, a technique for producing hydrophilic chitosan NPs was developed. Ionic gelation was used to create chitosan NPs that were loaded with dexamethasone sodium phosphate [121]. Chitosan is a di-block co-polymer of ethylene oxide or propylene oxide (PEO-PPO), and poly anion sodium tripolyphosphate are the two aqueous phases that are mixed together in the procedure. Through the interaction with the negatively charged tripolyphosphate, positively charged amino groups of chitosan forms coacervates of size range in nanometer. In contrast to ionic gelation, which occurs when a substance changes from a liquid to a gel as a consequence of ionic interaction conditions at ambient temperature, coacervates are created via electrostatic contact between two aqueous phases. Ionic gelation method for formation of PNPs is shown in **Figure 9**.

**Figure 9.** *Ionic gelation method for formation of PNPs.*

## **4.2 Modern methods**

The recognition of the multi-functional, environment-responsive, targeted, and controlled drug delivery system has recently made PNPs as one of the most promising and practical technological platforms. In a rapidly developing new technical field called "polymer in smart medication delivery", many therapeutic uses of nanotechnology are anticipated to address patient concerns in the medical field.

The use of several contemporary techniques, including microelectromechanical systems [122], microfluidic systems [123], electrodropping system [77], advanced high pressure homogenization, microneedle based system, interfacial emulsion polymerization, etc. are helpful to synthesize a variety of novel biocompatible polymers with well-defined nanometers to a few micrometers structures. The few contemporary methods for creating PNPs are shown in **Figure 10**. Based on the particular application, the physiochemical properties of PNPs must be tuned. To

#### **Figure 10.**

*Schematic diagrams representation of the advanced techniques for preparation of PNPs via sonication based system and csore- shell particulate system.*

#### *Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

create different nano-particulate systems with different polymers, several techniques can be applied. The creation of multifunctional PNPs for single/dual or multiple drug release, including nano hydrogel, environment-responsive micelles, core-shell NPs, colloids, nano-spheres, and core-shell nano-spheres, has already been produced. The mechanism of the formulation approach is crucial in obtaining the required qualities. Therefore, having a synthesis technique available is crucial for approaching multifunctional PNPs with precise physiochemical characteristics for a given application.

Recent studies have focused on developing smart delivery methods for target biomolecules for a variety of therapies. The design of multi-functional PNPs for delivery of bioactives are closely related to the regulation of multiple cellular events. In particular, various peptides, proteins, growth factors, and cytokine therapy for different ailments are helpful in plying an important role in cellular responses [124]. In the sonication techniques, prob. sonication was used to generate the self-assembled NPs, and process involved cavitation, nucleation, and reversible locking concept, giving the formed nanostructure greater flexibility in its nature [125]. Self-assembled and core-shell particulate delivery systems, such as water-soluble polymeric drug compound conjugates, block polymeric micelles [126], long-circulating nano encapsulations, polymeric micelles, and core-shell nano-spheres were developed by using an in situ two-step semi-batch emulsion polymerization technique as a means of accurately and consistently delivering the right dose of drugs. Additionally, pH-responsive controlled release of hydrophobic anticancer drugs and its transport to tumor tissues/ cells with acidic pH have been accomplished by core-shell nanospheres. Recently, an electrodropping system was designed and developed to create uniform, biocompatible core and shell capsules for angiogenesis in dual delivery systems [127], with an emphasis on regenerative medicine. The particle aggregation and drug encapsulation efficiency can be overcome by this electro-dropping technique.

In terms of micro-fluidics, the many applications have been significantly impacted by the cutting-edge science and technology used to manipulate micro/nano-scale volumes in micro-fluidic channels. Most micro-fluidic systems for synthesis, PNPs are still under development and they have the widest possible to develop because they are easily modifiable, highly reproducible, and can be combined with other techniques. Some advancement in micro-fluidics are anticipated to improve the preparation of PNPs and shift to clinical evaluation. Numerous microfluidic devices have recently been developed to allow quick mixing without the need of stimuli like electric force or stirring. The flow-focusing, droplet mixers, and other technologies are often used and enable micro-mixing inside the micro channel [128]. A fast solvent exchange through diffusion occurs as a result of the flow concentrating, which squeezes the solvent stream between two anti-solvent streams.

#### **5. Future perspectives**

The developments of the natural based PNPs have made the treatments to be more efficient and safe, utilizing the enormous variety of NPs design along with various functionalization. PNPs have to be biodegradable in nature and must possess a high capacity of circulation to avoid their removal from the systemic circulation. They developed systems should be nontoxic and non-immunogenic and should be able to produce the required effects as aimed. The role of copolymers could not be avoided in considering the tuning of the NPs system with the body components like blood proteins or mucosa which help in controlling their in vivo fate and the stabilizing of NPs.

Stimuli responding polymers are gaining interest for the coming future and research will be focused while considering their tuning properties for the development of NPs. The development of NPs with numerous potential, such as image contrast enhancement and targeting (as multifunctional NPs) has to be considered to match the various objectives required for the preparation and reaching hope of better scenario.

## **6. Conclusions**

Natural polymers have been now taken into consideration for the development of NPs and are gaining sky-scraping consideration due to the biodegradability, biocompatibility, and flexibility ability of these materials using varieties of natural materials to obtain the required characteristics for a precise function. The continue demand for natural biomaterials has always been their due various advantages associated with these natural materials, like polysaccharides and proteins leading to the development of more stable formulation under industrial processing environment and biological matrix, through techniques such as cross-linking is among the most advanced research area nowadays while using different techniques.

## **Disclosures**

There is no conflict of interest and disclosures associated with the manuscript.

## **Abbreviations**


*Advances in Natural Polymeric Nanoparticles for the Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.107513*

## **Author details**

Vikas Pandey1 \*, Tanweer Haider2 , Poornima Agrawal<sup>2</sup> , Sakshi Soni2 and Vandana Soni<sup>2</sup>

1 Amity Institute of Pharmacy, Amity University Gwalior, Madhya Pradesh, India

2 Department of Pharmaceutical Sciences, Dr. Harisingh Gour University, Sagar, India

\*Address all correspondence to: vikaspandeydops@gmail.com and vpandey@gwa.amity.edu

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 3**

## Recent Strategies for Ocular Drug Delivery: Promises and Challenges

*Amal H. El-Kamel and Asmaa A. Ashour*

#### **Abstract**

Ocular diseases include various anterior and posterior segment diseases. Due to the unique anatomy and physiology of the eye, efficient ocular drug delivery is a great challenge to researchers. The emerging nanoscience is playing an important role in the development of novel strategies for ocular disease management. Various active molecules have been designed to associate with nanocarriers to overcome ocular barriers and interact with certain ocular tissues. In this chapter, highlights will be made on barrier to intraocular delivery, general pathways for ocular absorption, and factors affecting intraocular bioavailability. The recent attempts of nanotechnology for treating anterior and posterior ocular diseases will be explored. This will include nanomicelles, nanoparticles, nanosuspensions, vesicular systems, in situ gel, dendrimers, contact lenses, implants, microneedles, and cell-based delivery systems. In addition, gene-based ocular delivery systems will be discussed. In this chapter, we will also provide a comprehensive overview of drug-device combinations used for ocular diseases such as glaucoma, dry eye disease, infections, and inflammations. Furthermore, drug delivery devices for ocular surgeries are discussed. Finally, challenges and future prospective of ocular delivery systems will be explored.

**Keywords:** nanocarriers, microneedles, gene, cell-based therapy, ocular devices

#### **1. Introduction**

Globally, eye diseases and consequential visual impairment are considered as the nation's absolute threat, compromising physical and mental health. As reported by the World Health Organization, worldwide, the number of people suffering from visual impairment is more than 2.2 billion [1]. Additionally, an analysis by Lancet Glob Health stated that, as population gets older, the number of moderate to severe vision impairment and blindness cases would increase to 600 million and 115 million by 2050, respectively [1].

Anatomically speaking, the human eye consists of two regions: the anterior segment including aqueous humor, cornea, conjunctiva, iris, ciliary body, and lens. Whereas the posterior segment includes vitreous humor, retina, choroid, and optic nerve. In other words, the eye consists of several attached tissue layers. In the anterior segment, the collagenous layer providing the mechanical strength is the cornea that is responsible for focusing the light on the retina. In the posterior segment, the opaque collagenous layer is the fibrous sclera. The middle layer in the anterior segment is called Uvea, which involves the iris and ciliary body. The ciliary body contains smooth muscles that produce the aqueous humor. The latter has many functions such as suppling nutrients to the avascular tissues in the anterior segment, maintaining the intraocular pressure, and drainage of waste from lens and cornea. In the posterior segment, the middle layer comprises enormous network of capillaries called vascular choroid that provides the retina with all the essential nutrients. The innermost layer is the retina, which transports the light signal to the brain [2].

Based on the aforementioned background, the eye comprises unique anatomical and physiological barriers hindering effective intraocular drug delivery that would be discussed in the following section.

## **2. Barriers to intraocular drug delivery**

The eye consists of numerous barriers and defense mechanisms to protect it from the environment. Barriers to intraocular drug delivery are categorized as physiological and anatomical. Physiological barriers involve blinking, tear turn over and nasolachrymal drainage. Whereas anatomical barriers include various static and dynamic barriers that impede drug entry into the eye segment [3].

In the anterior chamber, the static barriers are corneal epithelium, stroma, and blood aqueous barrier (BAB). Whereas dynamic barriers are the conjunctival blood and lymph flow along with tear drainage. BAB consists of tight junctions between the non-pigmented epithelial cells in the ciliary body, junctions of the iridial tissues as well as the blood vessels of the iris. BAB restricts the movement of molecules from blood to aqueous humor through iris ciliary capillaries [3].

In the posterior chamber, static barriers are sclera, bruch's membrane in choroid, and blood retinal barrier (BRB), which involves tight junctions in retinal capillary endothelial cells and retinal pigmented epithelium. While dynamic barriers comprise the drainage of administered drugs by blood and lymphatic vessels [3].

It is worth mentioning that the blood ocular barrier consists of both BAB and BRB. Its function is to maintain optimum intraocular pressure via preserving the fluid composition of the eye [3].

Mucin, covering the corneal and conjunctival surfaces for protection, constitutes an additional ocular barrier for diffusion of large drugs molecules. Moreover, the expression of many efflux pumps (P-glycoprotein, multidrug-resistant protein, and breast cancer resistant protein) on the capillary endothelium represents another barrier limiting drug ocular bioavailability [3].

#### **3. General pathways for ocular absorption**

Absorption of drug into the inner eye occurs through two major pathways, either corneal or non-corneal. The corneal route is considered as the major pathway for ocular drug absorption after topical administration. This route involves the penetration of the administered drug through the corneal epithelium. Afterward, the drug gets to the corneal stroma, endothelium, and aqueous humor. Subsequently, the drug may either be eliminated by the drainage of the aqueous humor through trabecular meshwork into Schlemm's canal, or it may reach the iris-ciliary body blood vessels and then enter the systemic circulation. Additionally, drugs also may distribute to a lesser extent to the lens and vitreous humor from the aqueous humor [4].

On the other hand, the non-corneal route for ocular drug absorption encompasses the passage of drugs across the conjunctiva and sclera. After that, they reach the ciliary body followed by the iris without access to the aqueous humor. Concerning the non-corneal route, it is important to highlight that the conjunctiva contains numerous blood vessels. Accordingly, a large portion of the drug dose is suspected to enter the blood circulation rather than diffusing into the sclera [4].

The next section designates the different factors affecting intraocular drug bioavailability, which makes ocular delivery challenging.

## **4. Factors influencing intraocular drug bioavailability**

Poor ocular bioavailability of the topically administered drugs represents a main concern associated with ophthalmic dosage forms. The presence of numerous physiological and anatomical constraints resulted in absorption of a very small portion of the topically instilled dose. The several factors affecting drug ocular bioavailability will be discussed in detail in the following subsections.

#### **4.1 Precorneal fluid drainage**

It constitutes one of the major reasons for poor ocular drug absorption. A large portion of the topically instilled volume (~80–90%) is drained into the nasolacrimal duct. The nasolacrimal drainage aids in preserving a fixed volume of the precorneal fluid (~7–10 μl). Consequently, it represents a natural protective physiological mechanism that is responsible for loss of any excess fluid.

The factors affecting the drainage rate include the Instilled volume, viscosity, pH, tonicity, and drug type. Concerning the instilled volume, the larger the volume, the more the drainage. For viscosity, increasing viscosity of an instilled dose results in prolongation of its ocular residence time. Regarding the pH effect, instillation of alkaline or acidic solutions gives rise to excessive lacrimation and hence loss of the administered medication. Therefore, the pH of the ophthalmic formulations must be adjusted to 7–7.7 to mimic the physiological pH of tear fluid (7.4). Regarding tonicity, preparations intended for ocular use should be isotonic with tear fluid. Severe irritation with excessive tear secretion occurs upon instillation of hypertonic solutions. As for drug type, it was reported that certain drugs can affect tear secretion. For instance, epinephrine can induce lacrimation, while tetracaine can suppress it [3].

#### **4.2 Binding of drugs to tear proteins or melanin**

The protein content of the tear fluid is ~0.7% of total body protein. Binding of drugs to tear proteins may bring about a significant decrease in drug concentration reaching the target site [3].

Concerning melanin binding, certain drugs such as ephedrine and timolol were reported to possess a high binding affinity to melanin pigment present in the iris and ciliary body, thereby lowering their ocular bioavailability [3].

#### **4.3 Drug absorption to the systemic circulation**

It may occur either directly from the conjunctival blood capillaries or after drainage of the instilled solution to the nasal cavity. Accordingly, this can result in remarkable drug loss into the systemic circulation, hence lowering its ocular bioavailability [3].

#### **4.4 Corneal barrier**

Cornea is a complex tissue that is made of six different layers. It plays an essential role in decreasing drug ocular bioavailability acting as a physical constraint impeding drug permeability [3].

#### **4.5 Drug metabolism**

Several metabolizing enzymes (cytochrome P450, cyclooxygenases, aldehyde oxidases, and monoamine oxidases) are expressed in various ocular tissues as cornea, lens, iris, ciliary body, and retina. These enzymes have the ability to metabolize the instilled drugs, decreasing their ocular bioavailability [3].

## **5. Nanocarriers for ocular drug delivery**

As illustrated previously, drug delivery to the eye is challenging for formulators owing to its barrier nature. Additionally, the chronic nature of various ocular diseases necessitates frequent administration of drugs. In this context, nanocarriers are elaborated to overcome the limitations of conventional ocular formulations as well as guarantee controlled and targeted drug delivery [5].

Nano delivery systems are colloidal systems with a particle size in the nanometer range (10–1000 nm) and a certain surface charge. They have various biomedical applications depending on their size. Additionally, their surface charge contributes to their retention at the specific site. For example, the negative charge on the surface of both the corneal and conjunctival tissues paves the way for cationic nanoparticles to be interacted to these tissues via electrostatic attraction. Consequently, increasing their residence in the anterior segment of the eye [5].

Based on the aforementioned background, nanocarriers are predicted to overcome the numerous ocular barriers thanks to their unique nano-size and surface characteristics. The different nanocarriers and their targeting ability for ocular drug delivery will be presented in detail in the following subsections.

#### **5.1 Nanomicelles**

Nanomicelles are nanostructures (10–100 nm) formed spontaneously in the aqueous environment by the self-assembly of certain block copolymers having amphoteric properties. They have many advantages for ocular drug delivery such as enhancing the aqueous solubility and stability for the hydrophobic drugs, prolongation of drugs' ocular retention, improving drug corneal permeability, and modification of drug release [1]. The amphoteric nature of the nanomicelles facilitates their penetration through both lipophilic (corneal epithelial and endothelial cells) and hydrophilic matrices. As well, their small size permits their uptake by the corneal cells. Moreover, they were reported to improve drug bioavailability by inhibiting the efflux transporter proteins by the use of the proper surfactants in their backbone structure [1, 6].

Accordingly, nanomicelles have attracted increasing attention as noninvasive ocular drug delivery systems owing to their unique properties.

#### *Recent Strategies for Ocular Drug Delivery: Promises and Challenges DOI: http://dx.doi.org/10.5772/intechopen.106335*

Concerning the targeting potential of the nanomicelles to the anterior segment of the eye, several studies have reported that the administration of the drug in a nanomicellar formulation rather than ointment, suspension, or emulsion formulations resulted in improved corneal, trans-corneal, and conjunctival uptake [7]. The clear Cyclosporine-A nanomicellar formulation prepared by Cholkar et al. [8] for treatment of dry eye disease in rabbits was approved by the United States Food and Drug Administration (FDA) in 2018. Cequa® (cyclosporine-A 0.09%) is a unique nanomicellar formulation, that is a clear solution approved for clinical use. In another study, Safwat et al. [9] prepared poly ethylene glycol-block-poly lactic acid nanomicelles containing triamcinolone acetonide. The selected formulations were dispersed into chitosan hydrogel to evaluate their anti-inflammatory potential in a carrageenan-induced ocular inflammatory rabbit model. The prepared micelles had good in-vitro characteristics (size: 176.80 ± 2.25 nm, drug loading: 15–25%, sustained drug release over a period of 1 week and 10-fold increase in drug aqueous solubility). Furthermore, the elaborated micellar hydrogel formulation resulted in complete disappearance of the corneal inflammatory signs in tested rabbits based on histopathological examination [9].

For targeting posterior segment of the eye, Xu et al. [10] prepared chitosan oligosaccharide-valylvaline-stearic acid nanomicelles to actively target peptide transporter-1 for topical ocular dexamethasone delivery to treat macular edema. Fluorescence microscopical images of frozen sections for various ocular tissues from tested animals indicated that the coumarin-6 labeled nanomicelles reached the posterior segment mainly through conjunctival route. Following topical administration, dexamethasone concentration in the posterior segment reached the therapeutic levels at 0.5 h and 1 h and can still be detected at 1.5 h post administration [10].

#### **5.2 Polymeric nanoparticles**

Polymeric nanoparticles made of biodegradable polymers and having sizes from 10 to 100 nm are widely used in ocular therapy. These nanocarriers consist of various polymers, in which the drug may be just adsorbed on the surface or incorporated into the polymer matrix. Polymeric nanoparticles offer numerous advantages for ocular delivery, which mainly related to their unique properties, as biodegradability, biocompatibility, and muco-adhesiveness. Therefore, pericorneal retention time is prolonged, and hence drug bioavailability is improved. For that purpose, many researchers prepared ocular drug delivery systems coated with mucoadhesive polymers (poloxamers, hyaluronic acid, chitosan, sodium alginate, among others) to increase drug ocular bioavailability [11].

For instance, Radwan et al. [12] prepared bovine serum albumin nanoparticles coated with chitosan by the desolvation method for the topical delivery of tetrandrine for management of glaucoma. The optimized formulation had a size of 237.9 nm and zeta potential of 24 mV and high % EE > 95% with a sustained-release drug profile. Moreover, the prepared nanosystem exhibited a significantly enhanced ex -vivo transcorneal permeation with improved in-vitro antioxidant and antiproliferative action on corneal stromal fibroblasts. In addition, the elaborated formulation succeeded to increase the drug bioavailability in the aqueous humor of treated rabbits by twofold compared with the free drug together with a remarkable reduction in intraocular pressure in a rabbit model for glaucoma.

In order to achieve active targeting to the posterior eye chamber for treatment of diabetic retinopathy, apatinib -loaded bovine serum albumin nanoparticles coated

with hyaluronic acid were developed [13]. Hyaluronic acid was exploited to achieve a dual role as a mucoadhesive polymer with capability to target the CD44 receptors expressed on retinal cells. The elaborated nanoplatform had good colloidal and mucoadhesive properties with no in-vitro cytotoxicity on rabbit corneal epithelial cells. The in-vivo evaluation revealed the ability of the topically instilled nano formulation to alleviate the corneal histopathological manifestations in diabetic retinopathy rat model with improved retinal accumulation as evidenced by confocal microscopy [13].

#### **5.3 Lipid-based nanoparticles**

Solid lipid nanoparticles (SLNs) are nanocarrier systems (10–500 nm) consist of lipids dispersed in an aqueous surfactant system. They are reserved for the delivery of hydrophobic drugs. The main method of their preparation depends on solidification of the produced nanoemulsion. SLNs were reported to have enhanced retinal permeation in addition to prolongation of drug ocular retention [5].

Nanostructured lipid carriers (NLCs) were introduced as next-generation lipid nanocarriers to overcome the limitations of SLNs, such as low drug loading capacity due to its expulsion by crystallization of lipids. NLCs are composed of both solid and liquid lipids and thereby have asymmetric structure, which prevents drug expulsion and brings about comparatively slower drug release [5].

The aqueous dispersion of lipid nanoparticles is mainly applied topically for delivery of the entrapped medication to the anterior segment of the eye. The aim of the use of this nanocarrier is to prolong retention time at surface of the cornea by muco-adhesion as well as enhance corneal permeation.

For this purpose, cationic lipid nanoparticles were prepared by using cationic lipids [14, 15] that can interact with the negatively charged mucus. Additionally, coating lipid nanoparticles with bio-adhesive polymers such as hydroxypropyl methyl cellulose [16], hyaluronic acid [17], and chitosan [18–20] was also employed.

For example, Wang et al. [18] prepared chitosan-coated solid lipid nanoparticles loaded with methazolamide for glaucoma treatment. Their findings proved the enhanced lowering in intraocular pressure effect of the coated formulation compared with either the uncoated one or a commercial methazolamide eye drop.

Furthermore, the lipid nanocarrier could be incorporated in a thermo-sensitive gel aiming to increase corneal contact time [20].

Nanostructured lipid carriers as well have gained popularity in ocular drug delivery [21–25]. They were reported as an efficient drug delivery system for the posterior segment of the eye due to their lipid nature, high drug-loading capacity, and enhanced trans-corneal penetration [5]. For instance, palmitoylethanolamide-loaded nanostructured lipid carrier was prepared for treatment of diabetic retinopathy in rat model [25]. In-vivo evaluation of the developed system confirmed its ability to reach the retina upon topical administration as evidenced by the significant inhibition in the levels of retinal tumor necrosis factor-α compared with the free drug in diabetic rats [25].

#### **5.4 Nanosuspensions**

Nanosuspensions are a nanometric colloidal dispersions of hydrophobic drugs stabilized by polymers or surfactants. The ocular bioavailability of many hydrophobic drugs could be improved using nanosuspension technology via increasing their retention time [26]. Numerous corticosteroids such as prednisolone,

dexamethasone [27], and hydrocortisone [27, 28] were formulated as nanosuspensions for their anti-inflammatory effect in the anterior eye segment. This resulted in elimination of the expected adverse effects associated with administration of large doses of theses corticosteroids such as production of glaucoma, cataract, and the most serious optic nerve degeneration [27]. Moreover, other drugs such as the cyclosporine [29] and antibacterial sparfloxacin [30] demonstrated a sustained drug release profile with better therapeutic efficacy when prepared as in nanosuspension form.

#### **5.5 Vesicular delivery systems**

#### *5.5.1 Liposomes*

They are spherical lipid vesicles composed mainly of phospholipids and cholesterol. A good biocompatibility, sustained release properties together with their ability to encapsulate both hydrophobic and hydrophilic drugs make liposomes ideal candidates for ocular drug delivery to both anterior and posterior segments of the eye [26]. Liposomes as an ocular delivery system were first introduced in 1981 for the delivery of the antiviral idoxuridine for treatment of keratitis [31]. Afterward, they were widely used to deliver various drugs to the eye.

For anterior eye disorders, Cyclosporine A-liposomes showed a significantly higher AUC 0–24 h in rabbits tears film compared with Restasis® (commercial cyclosporin A emulsion) with lower irritation potential [32]. Additionally, ciprofloxacin loaded liposomes exhibited a three-fold increase in ocular bioavailability in rabbits when compared with Ciprocin® eye drops [33]. Similarly, in-vivo evaluation of cationic liposomes containing ibuprofen versus ibuprofen eye drops revealed improved precorneal retention time and ocular bioavailability [34].

For posterior eye disorders, liposomes were extensively studied for effective drug delivery to the back of the eye. For instance, a novel liposomal formulation succeeded to enhance the bioavailability of flurbiprofen by 11.3 times compared with the free drug in the vitreous humor after intravitreal injection in rabbits [35]. In addition, the use of multivesicular liposomes to deliver the antibody Bevacizumab to the posterior eye chamber after intravitreal injection in rabbits was reported in treatment of choroidal neovascularization [36]. The elaborated system demonstrated an increase in intravitreal retention time as confirmed by in-vivo imaging of rat vitreous cavity, and hence the number of injection times was reduced [36]. Interestingly, the topical application of triamcinolone acetonide loaded chitosan-coated liposomes achieved better therapeutic outcomes in management of retinal edema instead of intravitreal injection of the drug [37, 38].

Despite the huge research conducted in the field of liposomal ocular drug delivery, their industrial production is limited owing to poor long-term stability, limited drug loading capacity, and difficulty during sterilization [6].

#### *5.5.2 Niosomes*

Niosomes were developed to overcome the limitations encountered by liposomes. Similar to liposomes, they are nontoxic vesicles and can encapsulate both hydrophilic and hydrophobic drugs, but they are chemically stable and do not require special techniques for handling. Niosomes are submicron-sized non-ionic surfactant vesicles that have potential applications in ocular drug delivery [39].

There are tremendous research articles reporting the use of niosomes in ocular therapy. Niosomes have been investigated for the ocular delivery of wide range of drugs such as anticholinergic drugs, anti-inflammatory drugs, anti-glaucoma drugs, and antibiotics [40].

To name a few, the antibacterial vancomycin was incorporated in niosomes integrated in pH-sensitive in-situ gel aiming to minimize drug-induced ocular irritation and prolong its effect [41]. The prepared formulation succeeded to eradicate infection with methicillin-resistant *Staphylococcus aureus* infection in rabbits as confirmed by the increase in the antibacterial effect by 180- and 2.5-fold compared with untreated animals and those treated with free drug solution, respectively [41].

For glaucoma management, latanoprost-loaded niosomes in thermo-sensitive Pluronic® F127 gel were developed [42]. The in-vivo evaluation of the prepared gel in rabbits confirmed its biocompatibility besides its longer duration of action (3 days) as compared with the commercial eye drops [42].

#### *5.5.3 Discosomes*

Discosomes are considered as modified niosomal formulations. They differ from niosomes by the addition of solulan C24 (non-ionic surfactant derived from lanolin). Interestingly, their large size (12–16 μm) prevents their drainage into the systemic circulation. Furthermore, their disc shape guarantees better fitting into the conjunctival sac [2]. Discosomes were reported to entrap larger quantity of timolol maleate compared with niosomes, thus increasing ocular bioavailability [43].

#### *5.5.4 Spanlastics*

They are elastic span containing vesicles that are composed of non-ionic surfactants (Span 40/60/80) and edge activators (sodium taurocholate, sodium deoxycholate, and Tween 80). The edge activators are responsible for providing flexibility to these vesicles. In addition, they were reported to be non-irritant and safe for ocular use. Furthermore, they are superior to niosomes in being highly deformable and thus can effectively deliver the entrapped drugs to the posterior eye segment. Therefore, the topical instillation of spanlastics can replace the intravitreal injections and hence increase patient compliance [44].

For instance, ketoconazole-loaded spanlastics demonstrated two times better corneal permeation compared with the niosomal formulation [45]. Fluorescently labeled spanlastics were detected in the virtuous humor of the rabbit's eye after 2 hours from topical instillation confirming their entry to the back of the eye. Similar observations were reported for the use spanlastics to deliver fluconazole, which showed enhanced permeability coefficient compared with either niosomes or Zocon ® eye drops [46].

#### **6. New and advanced ocular drug delivery systems**

#### **6.1 Contact lenses**

They are thin curved plastic lenses of disc shape that are placed on the cornea. Drug-releasing contact lenses are considered as drug reservoirs that permit continuous drug release near the tear fluid [47]. The first and most frequently used polymer for the manufacture of these lenses was poly hydroxy ethyl methacrylate cross-linked

#### *Recent Strategies for Ocular Drug Delivery: Promises and Challenges DOI: http://dx.doi.org/10.5772/intechopen.106335*

with ethylene glycol dimethyl acrylate. Recently, the use of silicone lenses was employed. Substantial research was conducted on the use of lenses as a drug carrier for ocular delivery. For example, they were investigated for many drugs such as ciprofloxacin [48], cyclosporine [49], dexamethasone [50], timolol [51], antifungal drugs [52], among others. Drug-eluting lenses were reported to increase drugs ocular bioavailability via prolongation of their duration of action and increase their corneal penetration [47].

Various methods of loading drugs on the contact lenses were reported. The simplest method is soaking the lenses with the drug solution. However, this method suffers from many limitations such as low drug loading capacity and rapid drug release within few hours failing to provide extended drug release [51]. In this context, Wei et al. [51] studied the effect of encapsulation of the antiglaucoma drug, timolol, into microemulsion before loading on contact lenses by soaking on the drug loading efficiency versus soaking the lenses with free drug solution. The use of microemulsion technology achieved a two-fold improvement in loading efficiency with sustained drug release pattern up to 48–96h. In addition, it provided prolonged reduction in the intraocular pressure for 96 h in rabbit model for glaucoma. Additionally, they reported that the entrapment of timolol in microemulsion before loading on contact lenses did not alter either the swelling or the transmittance of the developed lenses [51]. Similar findings were reported for the ability of liposomes [53] or polymeric nanoparticles [54] to extend and control the release rate of the entrapped drugs from the contact lenses.

It is also worth mentioning that Johnson & Johnson company lunched Acuvue® Theravision™ (etafilcon A drug-eluting contact lens with ketotifen). This product is the world's first and only drug-eluting contact lenses indicated for prevention of ocular itching due to allergic conjunctivitis upon daily application. Additionally, this product is used for vision correction in patients having no red eyes [55].

#### **6.2 Implants**

Implants are a solid form of a drug that is intended to achieve controlled drug release over an extended period of time. The implants can be surgically inserted in the subconjunctival, epidural, or vitreous areas. They provide sustained and localized drug delivery with higher patient compliance compared with the topical drops [47].

Surodex ® (Oculex Pharmaceuticals, Inc., Sunnyvale, CA, USA) is a dexamethasone containing a biodegradable implant (1×5 mm) made of poly (lactic-co-glycolic acid). It is inserted in the anterior segment of the eye for the relief of inflammation after cataract surgeries. The drug is released at a constant rate for 7–10 days [47].

Lux Biosciences produced a silicone-based episcleral implant (LX201) for delivery of cyclosporine-A to the anterior chamber of the eye for 1 year. LX 201 is also being assessed in phase III clinical trials for prevention of corneal graft rejection [47].

Vitrasert® (Bausch & Laumb, Inc.) is the first intravitreal delivery system loaded with ganciclovir for treatment of cytomegalovirus retinitis. It is designed to release the drug over a period of 6–8 month [47].

Retisert® is another intravitreal implant (Bausch & Laumb, Inc.) that can release fluocinolone acetonide up to 3 years into the vitreous humor. It is approved for treatment of posterior uveitis [47].

Fluocinolone acetonide is also included in the Iluvien® intravitreal implant (Alimera Sciences, Inc.). It is indicated for treatment of diabetic macular edema. Iluvien is being assessed in phase II clinical trials for its efficacy in dry and wet age-related macular degeneration as well as macular edema secondary to retinal vein occlusion compared with Lucentis® injection containing ranibizumab [47].

The Ozurdex® intravitreal dexamethasone implant is designed to release the drug for 3–6 months. It is approved for use in diabetic macular edema, posterior uveitis, and retinal vein occlusion [47].

Recently, a lot of sustained-release intraocular implants have been developed for glaucoma treatment. For example, Durysta™ (Allergan plc, Dublin, Ireland) is bimatoprost implant, which was approved by FDA in March 2020 for treatment of open-angle glaucoma and ocular hypertension. It can provide a sustained drug release up to 3–4 months [56]. Another example is the iDose® implant (Glaukos, California, USA) containing travoprost. It is a titanium implant of dimensions 1.8 mm x 0.5 m that is anchored within the trabecular meshwork. It achieves a zero-order drug release over a period of 6 months or longer. It showed promising results in phase II clinical trials versus topical solution of 0.5% timolol. Currently, the recruitment of patients for phase III clinical studies has started [56].

#### **6.3 Microneedles**

Microneedles (MNs) are a revolutionary delivery method that facilitates drug delivery to a variety of eye ailments with potential healthcare applications. MNs now allow localized, effective, less invasive, and targeted drug delivery in the eye. MNs were originally created as a painless, minimally invasive, and effective transdermal medication conveyance technique [57].

Microneedle applications on various ocular targets of the suprachoroid space of the rabbit eye [58, 59], the cornea of the mouse eye [60], and the sclera of a human cadaver eye [61] have been reported.

The use of MN in the eye may also have numerous advantages over invasive intraocular injections using long, typical hypodermic needles. MNs possess long enough dimensions to pass through the ocular obstacles of both the anterior and posterior sectors of the eye, allowing for targeted administration to the sclera, stroma, and suprachoroidal area [62].

MNs, as opposed to hypodermic needles, lower the risk of pain, tissue injury, and infection. Because little research has been done in this field, using MNs in ocular drug delivery is a relatively novel approach.

Applying MNs to biological membranes can establish microdimensional transport channels and improve drug penetration across biological membrane boundaries. They're produced from a variety of materials, such as silicon, stainless steel, glass, and polymers, and available in a variety of shapes, including solid and hollow design [63]. Many techniques such as micro molding, laser drilling, and lithography can be used to fabricate microneedles [63].

Using MNs, it's possible to deposit medicines or drug delivery systems into the sclera or the suprachoroidal region, which is the space between the sclera and the choroid (SCS). Micropuncturing the sclera layer may allow for more drugs or drug carriers to be deposited in the sclera, resulting in enhanced drug permeation into the deeper ocular tissues [64].

To inject particles of sizes 20–100 nm, a minimum pressure of 250 kPa and a minimum microneedle length of 800 μm should be maintained; on the other hand, a minimum pressure of 300 kPa and a needle length of 1000 μm are required for particles sizes between 500 and 1000 nm to penetrate the sclera [65].

Numerous research studies, according to Gupta and Yadava, have lately shown the use of MNs in ocular diseases such as glaucoma, age-related macular degeneration, uveitis, retinal vascular occlusion, retinitis pigmentosa, and others [66].

Patel et al. invented the hollow MN, which was injected into the SCS using a hollow glass microneedle [67]. SCS targeting allows for precise dosing and reduces medication exposure to non-targeted tissues. Patel et al. showed that clearance of molecules and particles injected into the SCS occurred at varying speeds depending on their size in a rabbit cadaver model [58].

Thakur et al. in 2014 utilized hollow MN devices of heights of 400, 500, and 600 μm made from hypodermic needles. These hollow MNs were used to inject a thermo-responsive poloxamer-based hydrogel containing sodium fluorescein as a model drug into the scleral tissue of a rabbit to form an in-situ implant within the micro-channels, resulting in a sustained release of fluorescein sodium over 24 hours in an in-vitro experiment. This type of implant production, which does not require surgery, would improve patient acceptability and could also deliver sustained medication levels, decreasing the need for frequent application of eye drops [68].

For targeted drug delivery, intrascleral hollow microneedles are being created. These microneedles can transport medications into the posterior portion of the eye via suprachoroidal, subconjunctival, and transcleral pathways. This delivery method can transfer nanoparticles, microparticles, and drugs solutions in a less intrusive way. However, to distribute microparticles, administration must be accompanied with spreading enzymes such as hyaluronidase and collagenase, which aid in the quick hydrolysis of the sclera's collagenous and extracellular matrix structure [69].

Datta et al. developed a fast-dissolving polyvinyl pyrrolidone MN ocular patch to deliver cyclosporin-A (CsA) to the cornea. CsA diffuses slowly into deeper ocular tissues and promote drug retention in the excised porcine cornea and resulted in effective ocular administration [70].

Dissolvable polyvinyl alcohol and polyvinyl pyrrolidone matrix were used to produce a dissolving microneedle ocular patch in the shape of a contact lens. These MNs, which include either amphotericin B loaded liposome or free amphotericin B, were found to be efficient in treating *Candida albicans* infection in both ex-vivo and rabbit models as well as improving corneal membrane epithelial and stromal differentiation [71].

In 2022, Shi et al. created a dissolving microneedle array patch based on poly(D,L-lactide) (PLA) and hyaluronic acid (HA) and containing fluconazole to develop a minimally invasive delivery system for treating fungal keratitis (FK). Interestingly, the rabbit model of FK reveals that the medicated topical MN patch has superior effect compared with the traditional eye drop formulation and is also equivalent to the clinical intrastromal injection technique [72].

For treatment of corneal neovascularization, a flexible double-layer microreservoir polymeric eye patch with a row of biodegradable detachable microneedles demonstrated to be more effective than topical eye drops. These biodegradable microneedles can penetrate through ocular barriers and self-implanted as a drug reservoir matrix for controlled drug release. Furthermore, rapid diclofenac release followed by extended monoclonal antibody release produces a synergistic effect in the treatment of corneal neovascularization [60].

In conclusion, MNs are thought to have the capacity to deliver other substances such as protein pharmaceuticals and DNA across the corneal epithelium with excellent effectiveness, which needs further exploration. MNs may serve as micro-drug reservoirs for targeted, regulated, and efficient ocular medication administration.

MNs are acceptable, harmless, and painless approach, resulting in a cost-effective treatment for a variety of ocular disorders.

#### **6.4 Cell-based ocular therapy**

Cell therapy is used to treat retinal degenerative illnesses by injecting cells into the subretina, usually with a microcatheter. Generally, in this method stem cells were injected into the retinal layers to stimulate cell regeneration. While animal studies imply that this approach is safe and nontoxic, the significant risk of consequences is an important concern [73]. Recently, Gandhi et al. have showed the safety and efficacy of degradable fibrin hydrogels for subretinal implantation to aid in the accurate implantation of retinal pigment epithelium monolayer. These promising hydrogels completely disintegrated after 8 weeks, making them the first fully biodegradable scaffold designed to treat macular degeneration disease [74].

#### **6.5 Gene-based ocular delivery systems**

The practice of transferring genetic material to remove, replace, repair, or introduce a gene to treat disorders is known as gene therapy [75]. Viral vectors, naked DNA, and nonviral vectors such as nanoparticles, microinjection, electroporation, sonoporation, and iontophoresis might all be used to deliver genes. Furthermore, cutting-edge approaches such as Genome Editing System, CRISPR-Cas Delivery, and siRNA treatment have been examined [76].

Retrovirus, adenovirus, and lentivirus are viral vectors that have shown excellent potential for transgene delivery to target cells in the eye because of the high transduction efficacy [75]. Kopone et al. reported that intraocular gene therapy for neovascularization has been found to be safe in clinical trials, with no serious side effects. Clinical trials, however, have not progressed beyond Phase II trials [75].

Although there are benefits to employing viral vectors, there are also numerous constraints. Preexisting immunity to viral vehicles (e.g., adenovirus) is a major concern, since it may result in low transduction rates and reduced expression of the therapeutic gene within cells. Furthermore, the residual viral proteins have the potential to trigger inflammation in their intended target [77].

Naked DNA can be used for gene therapy without a vector; however, its structural instability may limit adequate cell uptake [76]. Stechschulte et al. reported that naked DNA delivery to the cornea was safe, effective, titratable, and has the potential to alter the treatment of a wide variety of corneal and anterior segment diseases [78].

Nonviral vectors including metal [79], polymeric [80], lipid nanoparticle [81], and dendrimers [82] are also employed to deliver therapeutic genes to cells in the anterior and posterior portions of the eye. Nonviral vectors, in contrast to viral vectors, have been demonstrated to be more biologically safe, with reduced immunogenicity and pathogenicity. Nonviral vectors also have the advantage of being inexpensive and easy to produce. However, nonviral vehicles may have a lower transfection yield [83].

Physical methods are also applied to force DNA cellular entry, such as microinjection, electroporation, sonophoresis, and iontophoresis.

To facilitate plasmid gene transfer, electroporation uses high-intensity electric impulses to create pores within the cell membrane. To avoid corneal injury, edema, or inflammation, the ideal electrical field strength for this type of gene transfer is 200 V/cm. When compared with DNA injection alone, gene transfer in the cornea is 1000-fold higher [84].

#### *Recent Strategies for Ocular Drug Delivery: Promises and Challenges DOI: http://dx.doi.org/10.5772/intechopen.106335*

On the other hand, sonoporation uses ultrasound waves to physically create transitory and limited pores inside cell membranes, allowing DNA to be transferred to the nucleus. Sonoporation can improve the amount of therapeutic gene expression by up to 15-fold when compared with naked DNA [85].

Concerning iontophoresis, it is a technique that uses low currents to create transitory and localized pores in the cell membrane, allowing ionized molecules to pass through. Iontophoresis has been shown to boost gene or drug transport across the cell membrane by 2.3 and 2.5 times in the cornea and 4.0 and 3.4 times in the conjunctiva, respectively; however, after the current was removed, the transfer recovered to baseline levels in rabbit cornea and conjunctiva [86].

Small interfering RNAs (siRNAs) are a type of non-coding, double-stranded RNA molecules with about 20–25 base pairs in length that influence mRNA gene expression. Several eye diseases have been treated with siRNAs, including retinal abnormalities, glaucoma, wound healing, and neovascularization [87]. The majority of these research used animal models, while some were evaluated in human disorders and other siRNAs still under clinical trials [88].

CRISPR-Cas9 genome editing is becoming a hot topic in gene therapy [76]. The effectiveness demonstrated in delivering this gene-editing system to the posterior eye [89] via viral and nonviral approaches provides a starting guide for additional research concerning anterior segment diseases.

In conclusion, the future development of efficient gene treatments will rely on a better knowledge of the mutations and mechanisms that cause visual abnormalities, as well as the development of more efficient clinical vectors.

#### **6.6 Drug-device combinations used for ocular diseases**

Several drug devices and combinations have been designed to improve drug delivery to the eye, but only a few have reached the market. They boost medication retention and penetration while allowing for long-term drug release. They also have a lower level of toxicity and better patient compliance. Genes, drugs, and cell-based pharmaceuticals, as well as their combinations with medical devices, all fall within the category of advanced therapeutics medicinal products (ATMPs).

In 2017, Rupenthal reported that devices, namely collagen shield and contact lenses that gradually dissolve into a gel are effective for dry eye management and enhance wound healing after corneal surgery. They're also employed as antibiotic and anti-inflammatory medicine reservoirs before and after surgery [90].

Yellepeddi et al. described a device known as punctal plugs (PPs) that prevents tears from draining via the canaliculi, which connects the eye to the nose. PPs are recommended in some cases of laser in situ keratomileusis and contact lens intolerance due to their capacity to preserve tears. The insertion of PPs has also been shown to increase tear film stability, tear osmolarity, and functional visual sharpness in dry eye patients. Silicone has been used to create PP designs. Another example produced by (Medenium, CA, USA) and commercialized as SmartPLUG™ was designed to improve PP retention in the puncta. SmartPLUG™ comprises a biocompatible hydrophobic thermosensitive copolymer [91].

In another study, PPs loaded with the antibiotic moxifloxacin (Ocular Therapeutix, MA, USA) were produced for prolonged drug administration in the treatment of bacterial conjunctivitis [92].

Eibl-Lindner and coworkers created erufosine-loaded intraocular lenses (IOLs) for prophylaxis against posterior capsule opacification. They stated that the designed IOP

could have a therapeutic potential. They also reported that heparin-coated IOLs could be useful for reducing intraocular inflammation after cataract surgery [93].

Some of the devices mentioned in the literature are studied in clinical trials. For example, a live-cell delivery system that allows ciliary neurotrophic factor to be released from genetically engineered retinal pigment epithelium (RPE) cells. Implants utilizing this technique, designated as "Encapsulated Cell TechnologyR" (ECT) by the production company, have been shown to deliver protein drugs efficiently. ECT is made up of live cells loaded in an implanted matrix that acts as a medical device, allowing proteins generated by the cells to enter the body's fluids.

Finally, we can assert that manufacturing these devices under a pharmaceutical quality assurance system is a crucial step toward a faster production and efficient clinical application. This necessitates the formation of diverse research teams as well as the creation of infrastructure that adheres to GMP standards and meets the regulatory requirements of pharmaceutical quality systems.

## **7. Conclusions**

The development of innovative, noninvasive, safe, and patient-compliant drug delivery techniques is the focus of intense ocular research.

Numerous drug delivery carrier systems utilizing nanotechnology, cell-based systems, microneedles, contact lenses, implants, and different devices are being developed. Ocular gene therapy has recently emerged as a promising method for treating, curing, or preventing diseases by altering the gene expression in the eyes. However, the creation of future effective treatments using gene delivery will depend on a deeper comprehension of the mutations that lead to visual impairments.

Assessment of in-vivo effect utilizing ocular models of cell lines may help to further generate accurate data at the preclinical and clinical phases since many ocular drug delivery studies are only confined to in-vitro performances.

In spite of numerous research articles published in this field, there is still a large gap in the study on ocular therapeutic systems. The absence of valid and reliable ex-vivo models that can accurately simulate the physiology of the ocular tissues is the main essential obstacle to establishing highly optimized ocular drug delivery systems.

Finally, we might anticipate that within the next 10 years, the market would have a significant increase in the development of novel drug delivery technologies due to the pace at which ocular research and efforts are being done.

*Recent Strategies for Ocular Drug Delivery: Promises and Challenges DOI: http://dx.doi.org/10.5772/intechopen.106335*

## **Author details**

Amal H. El-Kamel\* and Asmaa A. Ashour Faculty of Pharmacy, Department of Pharmaceutics, Alexandria University, Alexandria, Egypt

\*Address all correspondence to: amalelkamel@alexu.edu.eg

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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## **Chapter 4**
