**1. Introduction**

Encapsulation, a process involving entrapment of an active ingredient or diagnostic tool within a carrier (capsule, shell, coating material or a matrix) is an old technology that has gained traction over the years with advances in polymer science and encapsulation technologies. The applications of encapsulation span pharmaceuticals, biotechnology, agrochemical, environmental, food and cosmetic spaces with immense benefits found in the pharmaceutical and biotechnology spaces. Encapsulation is used for immobilization of volatile compounds, enzymes, and microorganisms; protection and stabilization from environmental factors; safe handling of hazardous but useful materials; controlled release; taste, odor and color masking; site-specific delivery and solidifying of liquid droplets. Encapsulation improves on the challenges of conventional dosage forms in enhancing stability, taste, bioavailability and biodistribution. Some drugs such as insulin are not given orally because of degradation in the GIT before absorption. Encapsulation may be an approach to change route of administration from intravenous to oral.

The parameters for encapsulation of active ingredients depend on the physicochemical properties of the active ingredient such as solubility, thermal and redox stability; however, the release of the active is then modulated by mechanical process, pH variations, enzymatic actions or other external stimuli [1]. The encapsulation methods classified as chemical, physicochemical and physicomechanical methods are used to encapsulate an active ingredient with the specific method chosen based on application and desired outcomes. The choice of materials to be used for encapsulation to accommodate the physicochemical behavior of the active in order to produce the desire encapsulation efficiency, shell or capsule size, surface morphology and functionalities of the capsule and the behavior of encapsulated active ingredient are fundamental preformulation studies before a new encapsulated product is developed. The bioavailability of existing poorly soluble drugs and those in the development pipeline can be significantly enhanced by encapsulation with the right encapsulating material(s).

Natural polymers are choice materials for encapsulation. Natural polymers are macromolecules of large molecular weights obtained from nature and are preferred due to their flexibility to modification, biocompatibility, biodegradability, renewability, and low toxicity [2]. Being of natural origins such as plants, animals and microorganisms, they are able to interact with tissues and cells displaying some properties the body identifies with and as a result do not treat them as foreign bodies [3]. Natural polymers such as proteins, polysaccharides and lipids have been employed as encapsulation materials for encapsulating hydrophilic or hydrophobic active ingredients which may be in liquid, solid and gaseous states for transport and delivery to the sites they are needed. The chapter reviews fabrication techniques, lipids, and their applications in micro- and nanoencapsulation elucidating their functionalities which enable them to be utilized for encapsulation of therapeutics and diagnostics producing delivery systems with the desired outcomes. Polysaccharides and proteins are covered in part (II) of this chapter.

#### **2. Encapsulation**

Encapsulation is the process of enclosing, entrapping, coating, or surrounding a liquid, solid or gas active compound within a material to achieve a more controlled/ sustained release, protect the active compound/active pharmaceutical ingredient from degradation before reaching the site of absorption or before reaching the site of action as well as reducing the associated adverse effects that go along with some non-encapsulated compounds like NSAIDS [4, 5]. Research on encapsulation utilizing natural polymers and their derivatives (semi-synthetic polymers) has evolved

**5**

*Natural Polymers in Micro- and Nanoencapsulation for Therapeutic and Diagnostic…*

over time with the particle size as the main difference. Encapsulation on the micro scale is referred to as microencapsulation while when encapsulation is done on the

Microencapsulation refers to the formulation process of encapsulating a bioactive compound in a particle size that is 1–1000 μm in diameter for the purpose of controlled and sustained delivery as well as protection of the encapsulated bioactive compound from the surrounding environment [7, 8]. Microencapsulation technology came into existence with the focus of achieving controlled and extended release profiles. Due to the size of micro carriers, encapsulation of macromolecules with large molecular weight such as proteins for controlled release can be encapsulated. Bochenek *et al.,* [9] utilized chemically modified alginate microsphere formulations to encapsulate allogeneic pancreatic islet cells for transient islet-graft function that have reached clinical trial stage for management insulin deficiency in diabetic populations. This was due to the fact that the immune-modulating alginate copolymer employed had controlled release profile that caused encapsulated islet cells to remain viable after transplantation into the general intraperitoneal (IP) space of human subjects, while also exhibiting lowered foreign-body reaction (FBR) compared to previous formulations. Chitosan-alginate microcapsules encapsulating biologically active compounds from aqueous extracts of *Garcinia kola* (GK) and *Hunteria umbellata* (HU) seeds, have also been shown to have selective release patterns depending on the pH of the medium [10]. Slower release of the GK and HU microcapsules of the active compounds was observed at pH 1.2, but increased controlled extended release profiles were observed to occur at pH 6.8 unlike conventional tablets that did not show controlled extended release profiles [10].

Nanoencapsulation can be defined as the entrapment, enclosure, or coating of a bioactive compound within a carrier that is on the nanoscale dimension [5]. Nanoscale dimension is seen as particle sizes 1–100 nm [6]. However more recent definitions have given room for 1–300 nm and others 1–1000 nm [11]. The advancement of encapsulation from the micro scale to the nano scale was driven by the need for more site selective targeting purposes such as the use of chemotherapeutics in cancer. The main draw back in cancer chemotherapeutics has been that severe adverse effects occur due to toxicity caused by the non-selective action on both cancer cells and healthy cells at therapeutic doses. Hence, the inception of nanomedicines that could achieve active targeting was born. Nanoencapsulation in drug delivery has the merit of having a higher encapsulation efficiency, due to enhanced

Silk fibroin nanoparticles encapsulating curcumin were found to demonstrate selective cytotoxicity for cancer therapy in neuroblastoma cells and hepatocarcinoma cells while not adversely affecting the healthy cells [13]. Diagnostics are also gaining from the merits of encapsulation. This was demonstrated in the simultaneous co-encapsulation of MRI contrast agent Gd-DTPA and fluorescent label ATTO488 in multimodal PEG – crosslinked hyaluronic acid nanoparticles (PEG-cHANPs) to formulate a probe for diagnostic purposes [14]. The PEG-cHANPs were observed to improve MR signals while concurrently magnifying the relaxation time, T1 5 times due to the presence of the ATTO 488 in the human glioma U87 MG cell line. Tammaro *et al.,* [14] implied that this could lead to the decrease in the administered dose of the probe, thereby resulting in a better resolution and higher quality images.

drug solubility of bioactive molecules in the core [12].

*DOI: http://dx.doi.org/10.5772/intechopen.94856*

**2.1 Microencapsulation**

**2.2 Nanoencapsulation**

nanoscale it is referred to as nanoencapsulation [6].

over time with the particle size as the main difference. Encapsulation on the micro scale is referred to as microencapsulation while when encapsulation is done on the nanoscale it is referred to as nanoencapsulation [6].
