*4.3.2 Nanoprecipitation*

*Nano- and Microencapsulation - Techniques and Applications*

surfactant. The monomer solution is then added to it dropwise.

to bring about polymerization [67].

decreased with increasing oil concentration.

**4.3 Physicochemical techniques**

*4.3.1 Solvent evaporation*

for cancer therapy.

The crosslinkers, ethyleneglycoldimethacrylate, was added to the formed emulsion

Emulsion polymerization: In this procedure, the core material is dissolved in a

Suspension polymerization: In this approach, the monomers used are insoluble in the continuous phase hence, they are dispersed as liquid droplets, in the aqueous phase, in the presence of a stabilizer using high pressure homogenization. The polymer is obtained as dispersed solid in the continuous phase. Racoti and coworkers [70] recently used suspension polymerization for the microencapsulation of ginger oil in polymethyl methacrylate shell using triethyleneglycol dimethachrylate as a monomer and Azobisisobutyronitrile (AIBN) as initiator. Their study showed that particle size increased with initiator concentration while encapsulation efficiency

The physicochemical techniques discussed here are classified as chemical methods by some authors. However, they are classified as physicochemical techniques here because each technique involves one or two physical steps. Such techniques are

The first step is the dispersion of the core material in the coating solution to form an oil-in-water emulsion. The mixture is then homogenized in the presence of stabilizers such as polyvinyl alcohol (PVA), tween 80 and span 80 to obtain appropriately sized microcapsules. The last step is to evaporate the solvent off either at ambient or elevated temperatures depending on the solvent. For double emulsion solvent evaporation, the formed oil-in-water emulsion is emulsified again, homogenized before solvent evaporation [71]. The type of emulsion chosen will be dependent on the lipophilicity or hydrophilicity of the core material. Double emulsions of the w/o/w type are usually used for highly hydrophilic materials in order to improve their encapsulation efficiency and limit their diffusion out of the capsule into the continuous phase of oil-in-water emulsions [71]. Another approach that has been used for hydrophilic payloads is the suspension in organic phase template [72]. Solvent evaporation is the common method for preparing nanoparticles. Hoa and coworkers [73] prepared PVA stabilized ketoprofen loaded Eudragit E100-Eudragit RS nanoparticles using the solvent evaporation method. They studied effect of process and formulation parameters on the properties of the nanoparticles. They confirmed that the size and morphology of the particles depended on polymer and surfactant concentration, power and duration of applied energy, and volume ratio of water to oil phases. More recently, Jiang and colleagues [74] developed nanoparticles of Ginkoglide using solvent evaporation method. Likewise, Urbaniak and Musial [72], using solvent evaporation technique, prepared submicron sized capsules from lamivudine conjugated poly-ɛ-caprolactone polymer and studied the influencing parameters such as concentration and type, homogenization time and

solvent evaporation, coacervation, layer by layer deposition and liposomes.

Dispersion polycondensation: In the category, all the components including the monomer, the dispersant and the initiator are present in a solvent in which the polymer to be formed is insoluble. Here, swelling of the polymer occur leading to growth of microcapsules which is sustained by continued addition of monomer and oligomer [68]. Jiang and colleagues [69] used this method to prepare a core shell for site specific delivery of a small molecule, doxorubicin and a protein drug, TRAIL,

**20**

This technique also known as solvent displacement technique was patented by Fessi in 1989 [75] for making nanospheres and nanocapsules. It has close resemblance to solvent evaporation technique. Here, the solvent phase containing the film forming polymer, and the drug to be encapsulated is a water miscible solvent such as acetone or methanol, and the non-solvent phase which is a water immiscible solvent such as chloroform or dichloromethane, also called the oil phase, are mixed under stirring. Thereafter, the solvent is removed to yield nanoparticles suspension or nanocapsules if a mineral oil was added. Centrifuging and freeze drying will yield the powder. Chitosan, starch, and gelatin are among the commonly used natural polymer film formers. Many studies have tried to analyze the difference in nanoparticles generated by solvent evaporation and solvent displacement. Hernández-Giottonini and colleagues [76] evaluated the effect of process parameters and formulation parameters on polylactic-co-glycolic acid (PLGA) nanoparticles prepared by both techniques. While particle size was dominantly affected by PLGA and PVA concentrations for the nanoprecipitation method, solvent fraction had the most effect of the particle size for the solvent evaporation technique. However, the influence of agitation speed in both techniques was the same- a decrease in average particle diameter [76].

## *4.3.3 Coacervation*

This technique involves the phase separation of one or more hydrocolloids from its initial solution brought about by changes such as pH, ionic strength, temperature, solvent type or polarity and the subsequent deposition of the separated coacervate on the core droplets in the solution [77]. The lower particle diameter obtainable from simple coacervation is 20 μm while that for complex coacervation is 1 μm; and 500 μm capsules are also possible from both [33]. Generally, the first step in any coacervation process is the dispersion of the oil phase in the solution of the hydrocolloid (formation of oil-in-water emulsion). The next step involves the precipitation of the hydrocolloid by temperature, polarity, pH, or ionic strength change (polyelectrolyte complex formation). This is usually achieved by addition of a salt such as sodium sulphate, or desolvation with water miscible non-solvent, in simple coacervation [78]. Induction of polymer-polymer gelling by addition of a second oppositely charged hydrocolloid happens only in complex coacervation. The resulting complex is stabilized by crosslinking (usually glutaraldehyde, transglutaminase, calcium ions or tripolyphosphate) and the harvested microcapsules washed and dried. Complex coacervation is advantageous due to the high loading of payload up to 99%. From the relatively simple and early use of pork skin gelatin and gum arabic, many other variations have emerged including patented deviations. Majority of the polymers used are natural polysaccharides such as starches, maltodextrins, and gum arabic; and proteins such as albumin, gelatin, and casein; and lipids such as diglycerides [77].

Brito de Souza and coworkers [79] used complex coacervation as a tool to protect the phenolic compounds and mask the astringent taste of spray dried hydrophilic proanthocyanidins-rich cinnamon using a combination of various polysaccharides and gelatin as the coacervate wall material. They also evaluated the stability of the microcapsules under various storage conditions. Their study showed that

gelatin/k-carrageenan and gelatin/cashew tree gum were exceptional in maintaining the stability of the microcapsules as wall material. Complex coacervation using these combinations enabled the efficient use of proanthocyanidins-rich cinnamon extract in ice cream formulation while keeping the taste masked [79]. Lemos and colleagues [80] evaluated the effect of homogenizing speed and the hydrodynamics int. coacervation medium on the carotenoid rich Buriti oil microcapsules formulated using gelatin-alginate wall material. They found that as the Reynold number increased beyond 70,000, the particle size reduced to 200 μm. With about 80% encapsulation efficiency, the hydrodynamic conditions affected the particle size of the complex coacervates [80].

#### *4.3.4 Layer by layer (LbL) deposition*

This encapsulation technique is a straightforward versatile technique that involves the serial alternate deposition of oppositely charged polyelectrolytes films on a colloidal particle used commonly as a sacrificial template that is later eliminated or calcined. The technique permits the assembly of different compounds that interact through primary electrostatic interactions, though other bonds such as dipole–dipole moment, hydrogen bonds, host-guest interaction, acid–base interaction, and Van der Waals forces are possible. In the preparation of LbL capsules, layers have been deposited by dipping, spraying, and spin coating with the polyelectrolyte [81]. It is important to wash with distilled water after each layer deposition to minimize cross contamination by polyelectrolytes. Parameters that require monitoring include number of deposition cycles, ionic strength, pH, polyelectrolyte concentration to tune the thickness, roughness and porosity of the product [82]. Both nanocapsules and microcapsules can be prepared by this technique. The availability of wide permeability coefficient spectrum permits tuning to achieve specific application targets which could be biosensing, drug delivery, bioreactor, or biogenic application. With careful selection of the layering material, and assembly conditions final properties of the capsule can be determined. A major drawback is the lengthy fabrication process though this has drastically been reduced by the spraying approach [81]. Piccinino and colleagues [83] prepared micro- and nanocapsules of mixed polyphenols, tannic acid and sulfonate lignin using Manganese carbonate (MnCO3) and organosolv lignin nanoparticles as a template and polydiallyldimethylammonium chloride and chitosan as supporting layers. The prepared nano and microcapsules displayed good antioxidant activity and photo-shielding and electrochemical responsiveness that was higher than that possible from the individual homopolymers. Rochín-Wong and coworkers [84] recently developed a LbL assembly of two natural polymers, κ-carrageenan and chitosan on diflunisal nanoemulsion droplets with the aim of studying the release properties. They reported the formation of stable 300 nmsized particles that demonstrated controlled released of diflunisal in proportion to the number of adsorbed layers. Paşcalău and colleagues [85] recently developed Sorafenib nanocapsules using the LbL deposition. They initially co-precipitated bovine serum, BSA, with the sacrificial calcium carbonate (CaCO3) porous templates to form the BSA gel core microtemplate. The microtemplate was then coated Ca2+ crosslinked hyaluronic acid hydrogel and subsequently alternated with chitosan in a multilayer assembly. Subsequently, the sacrificial template was removed through a semipermeable membrane and the BSA thermo-gelled. The sorafenib was then loaded into the microcapsule by diffusion to yield a delivery system that was thermo-responsive.

#### *4.3.5 Supercritical fluids (SCF)*

This technique involves the use of SCFs which are substances that exist above their critical temperature and pressure (at this point they exist in single phase and exhibit properties of both gases and liquids) and therefore can diffuse through solids

**23**

**Figure 9.**

*Schematic representation of the RESS process [86].*

**Figure 8.**

*Phase diagram of SCCO2 (not to scale) [86].*

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

caused desolvation and deposition of polymer material shell on the core.

like a gas would and dissolve solids and liquids like a liquid. They exhibit densities close to that of a liquid but with viscosities and diffusion coefficients like that of a gas as shown in **Figure 8**. Supercritical carbon dioxide is the commonly used SCF for encapsulation because it is cheap, easily available, inert, non-toxic, uninflammable, with low critical temperature of 31.06°C. The technique may involve supercritical CO2 (SCCO2) as a solvent, antisolvent, co-solvent, or nebulizer. The process generally involves dissolution of both the core material and wall material in the SCF. Then, the solution is released through a small nozzle and the rapid reduction in pressure

Approaches using SCCO2 as a solvent involves rapid expansion of a supercritical solution (RESS) as shown in **Figure 9**. In this process, components are dissolved in SCCO2 and the solution is then released into a collector through tiny nozzles at atmospheric pressure. The rapid decrease in pressure brings about the desolvation of SCCO2

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

#### *Natural Polymers in Micro- and Nanoencapsulation for Therapeutic and Diagnostic… DOI: http://dx.doi.org/10.5772/intechopen.94856*

like a gas would and dissolve solids and liquids like a liquid. They exhibit densities close to that of a liquid but with viscosities and diffusion coefficients like that of a gas as shown in **Figure 8**. Supercritical carbon dioxide is the commonly used SCF for encapsulation because it is cheap, easily available, inert, non-toxic, uninflammable, with low critical temperature of 31.06°C. The technique may involve supercritical CO2 (SCCO2) as a solvent, antisolvent, co-solvent, or nebulizer. The process generally involves dissolution of both the core material and wall material in the SCF. Then, the solution is released through a small nozzle and the rapid reduction in pressure caused desolvation and deposition of polymer material shell on the core.

Approaches using SCCO2 as a solvent involves rapid expansion of a supercritical solution (RESS) as shown in **Figure 9**. In this process, components are dissolved in SCCO2 and the solution is then released into a collector through tiny nozzles at atmospheric pressure. The rapid decrease in pressure brings about the desolvation of SCCO2

**Figure 8.** *Phase diagram of SCCO2 (not to scale) [86].*

**Figure 9.**

*Schematic representation of the RESS process [86].*

*Nano- and Microencapsulation - Techniques and Applications*

*4.3.4 Layer by layer (LbL) deposition*

gelatin/k-carrageenan and gelatin/cashew tree gum were exceptional in maintaining the stability of the microcapsules as wall material. Complex coacervation using these combinations enabled the efficient use of proanthocyanidins-rich cinnamon extract in ice cream formulation while keeping the taste masked [79]. Lemos and colleagues [80] evaluated the effect of homogenizing speed and the hydrodynamics int. coacervation medium on the carotenoid rich Buriti oil microcapsules formulated using gelatin-alginate wall material. They found that as the Reynold number increased beyond 70,000, the particle size reduced to 200 μm. With about 80% encapsulation efficiency, the hydrodynamic conditions affected the particle size of the complex coacervates [80].

This encapsulation technique is a straightforward versatile technique that involves the serial alternate deposition of oppositely charged polyelectrolytes films on a colloidal particle used commonly as a sacrificial template that is later eliminated or calcined. The technique permits the assembly of different compounds that interact through primary electrostatic interactions, though other bonds such as dipole–dipole moment, hydrogen bonds, host-guest interaction, acid–base interaction, and Van der Waals forces are possible. In the preparation of LbL capsules, layers have been deposited by dipping, spraying, and spin coating with the polyelectrolyte [81]. It is important to wash with distilled water after each layer deposition to minimize cross contamination by polyelectrolytes. Parameters that require monitoring include number of deposition cycles, ionic strength, pH, polyelectrolyte concentration to tune the thickness, roughness and porosity of the product [82]. Both nanocapsules and microcapsules can be prepared by this technique. The availability of wide permeability coefficient spectrum permits tuning to achieve specific application targets which could be biosensing, drug delivery, bioreactor, or biogenic application. With careful selection of the layering material, and assembly conditions final properties of the capsule can be determined. A major drawback is the lengthy fabrication process though this has drastically been reduced by the spraying approach [81]. Piccinino and colleagues [83] prepared micro- and nanocapsules of mixed polyphenols, tannic acid and sulfonate lignin using Manganese carbonate (MnCO3) and organosolv lignin nanoparticles as a template and polydiallyldimethylammonium chloride and chitosan as supporting layers. The prepared nano and microcapsules displayed good antioxidant activity and photo-shielding and electrochemical responsiveness that was higher than that possible from the individual homopolymers. Rochín-Wong and coworkers [84] recently developed a LbL assembly of two natural polymers, κ-carrageenan and chitosan on diflunisal nanoemulsion droplets with the aim of studying the release properties. They reported the formation of stable 300 nmsized particles that demonstrated controlled released of diflunisal in proportion to the number of adsorbed layers. Paşcalău and colleagues [85] recently developed Sorafenib nanocapsules using the LbL deposition. They initially co-precipitated bovine serum, BSA, with the sacrificial calcium carbonate (CaCO3) porous templates to form the BSA gel core microtemplate. The microtemplate was then coated Ca2+ crosslinked hyaluronic acid hydrogel and subsequently alternated with chitosan in a multilayer assembly. Subsequently, the sacrificial template was removed through a semipermeable membrane and the BSA thermo-gelled. The sorafenib was then loaded into the microcapsule

by diffusion to yield a delivery system that was thermo-responsive.

This technique involves the use of SCFs which are substances that exist above their critical temperature and pressure (at this point they exist in single phase and exhibit properties of both gases and liquids) and therefore can diffuse through solids

**22**

*4.3.5 Supercritical fluids (SCF)*

and the solution components deposited as submicron particles. The major setback is that many polymer materials, fats, and encapsulants are poorly soluble in SCCO2.

Another approach is the antisolvent gas, GAS approach (**Figure 10**). In this approach, the components of microcapsules are dissolved in a suitable (primary) organic solvent and then introduced into SCCO2 which reduces the solubility of the components in the organic solvent. SCCO2 does this by rapidly permeating through the solution due to its high diffusion coefficient effecting a mass transfer process that is evidenced by increase in volume, decrease in viscosity and density. Decrease in density significantly reduces the solubility of the components in the solvent, producing a supersaturated solution from which the components precipitate as micro and nano particles. The solutes used in this process must have minimal solubility in SCCO2. The GAS technique is advantageous for the encapsulation of polar compounds and compounds not soluble in SCCO2 using organic solvents may leave worrisome traces in the capsules.

The third approach is particles from gas saturated solution, PGSS, (**Figure 11**) that depends on the high solubility of SCCO2 in materials such as molten fats, lipids and polymers at relatively low pressures, and the cooling effect of depressurization (Joule- Thompson effect). In this procedure, SCCO2 is introduced into a substrate, its suspension or solution in an organic solvent at high pressure. The resulting saturated solution is rapidly expanded through a tiny nozzle using moderate pressure which leads to reduction in temperature and the formation of particles due to the cooling effect. Zhu and colleagues [87] encapsulated menthol in beeswax using the PGSS.

Equipment required for SCF encapsulation include a compressed SCCO2 cylinder, two high pressure liquid pumps for SCCO2 and the other solvents, high pressure chambers, product separation units, liquefying units, recirculating pumps, manometers, in-line filters, thermocouples, and a host of others. Parameters that needs to be optimized for each application include temperature, pressure, and feed emulsion rate. Karim and coworkers [88] used the GAS process to microencapsulate fish oil using a semi synthetic polymer, ethyl cellulose.

#### *4.3.6 Sol: Gel technique*

Translated literally means solution gelling and basically refers to an encapsulation method involving solutions (sol) that transform to a gel in response to alternating

**25**

*4.3.7 Liposomes*

**Figure 11.**

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

physicochemical changes. In this process, the sol precursor is added to water which gels or hardens to capsules enclosing any included cargo. Generally, the steps involved are hydrolysis, condensation, gelling, aging, drying and densification. Organosilanes are the most commonly used encapsulation sols in contemporary times [89]. Their properties including surface functionalities, biocompatibility with many drugs and biomolecules, mild processing conditions of temperature and pH. This technique is commonly used for encapsulation of biomolecules, enzymes, and drugs. The alkoxysilanes precursors such as tetraethyl orthosilicate, triethoxysilane, trimethoxysiliane, methyltrimethoxysilane, tetraethylorthosilicate are insoluble in water so their dispersion in water in the presence of a surfactant and possibly a hydrophobic cargo results in the formation of emulsion droplets that serve as templates from which hydrolysis, condensation and polycondensation occurs at room temperature in the presence of water and an acid to form silanol groups which subsequently condense at basic pH to form organosillane matrixes or cages of different porosity and size rang-

Precursor+Si(OR) 2H O Active SiO 2ROH 4 2 + → ++<sup>2</sup> (1)

One byproduct of that reaction is ethanol which acts as a preservative for enclosed biomolecules. The matrix can be dried to form xerogels and can serves as a container for the enclosed biomolecule since there is no covalent relationship between them. Although rotation and unfolding movements are restricted for proteins, their inclu-

Liposomes are lipid bilayer phospholipid vesicles with diameters ranging from

25 nm to 10 μm. They form spontaneously when disrupted in water. They can

ing from 1 to 40 μm [90]. The general equation is given in Eq. (1).

sions can still be detected in appropriate setting by the target receptors.

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

*Schematic representation of the PGSS approach [86].*

**Figure 10.** *Schematic representation of the GAS process [86].* *Natural Polymers in Micro- and Nanoencapsulation for Therapeutic and Diagnostic… DOI: http://dx.doi.org/10.5772/intechopen.94856*

**Figure 11.** *Schematic representation of the PGSS approach [86].*

physicochemical changes. In this process, the sol precursor is added to water which gels or hardens to capsules enclosing any included cargo. Generally, the steps involved are hydrolysis, condensation, gelling, aging, drying and densification. Organosilanes are the most commonly used encapsulation sols in contemporary times [89]. Their properties including surface functionalities, biocompatibility with many drugs and biomolecules, mild processing conditions of temperature and pH. This technique is commonly used for encapsulation of biomolecules, enzymes, and drugs. The alkoxysilanes precursors such as tetraethyl orthosilicate, triethoxysilane, trimethoxysiliane, methyltrimethoxysilane, tetraethylorthosilicate are insoluble in water so their dispersion in water in the presence of a surfactant and possibly a hydrophobic cargo results in the formation of emulsion droplets that serve as templates from which hydrolysis, condensation and polycondensation occurs at room temperature in the presence of water and an acid to form silanol groups which subsequently condense at basic pH to form organosillane matrixes or cages of different porosity and size ranging from 1 to 40 μm [90]. The general equation is given in Eq. (1).

$$\text{Precurve} + \text{Si(OR)}\_4 + 2\text{H}\_2\text{O} \rightarrow \text{Active} + \text{SiO}\_2 + 2\text{ROH} \tag{1}$$

One byproduct of that reaction is ethanol which acts as a preservative for enclosed biomolecules. The matrix can be dried to form xerogels and can serves as a container for the enclosed biomolecule since there is no covalent relationship between them. Although rotation and unfolding movements are restricted for proteins, their inclusions can still be detected in appropriate setting by the target receptors.

#### *4.3.7 Liposomes*

Liposomes are lipid bilayer phospholipid vesicles with diameters ranging from 25 nm to 10 μm. They form spontaneously when disrupted in water. They can

*Nano- and Microencapsulation - Techniques and Applications*

using a semi synthetic polymer, ethyl cellulose.

*4.3.6 Sol: Gel technique*

and the solution components deposited as submicron particles. The major setback is that many polymer materials, fats, and encapsulants are poorly soluble in SCCO2. Another approach is the antisolvent gas, GAS approach (**Figure 10**). In this approach, the components of microcapsules are dissolved in a suitable (primary) organic solvent and then introduced into SCCO2 which reduces the solubility of the components in the organic solvent. SCCO2 does this by rapidly permeating through the solution due to its high diffusion coefficient effecting a mass transfer process that is evidenced by increase in volume, decrease in viscosity and density. Decrease in density significantly reduces the solubility of the components in the solvent, producing a supersaturated solution from which the components precipitate as micro and nano particles. The solutes used in this process must have minimal solubility in SCCO2. The GAS technique is advantageous for the encapsulation of polar compounds and compounds not soluble in SCCO2 using organic solvents may leave worrisome traces in the capsules. The third approach is particles from gas saturated solution, PGSS, (**Figure 11**) that depends on the high solubility of SCCO2 in materials such as molten fats, lipids and polymers at relatively low pressures, and the cooling effect of depressurization (Joule- Thompson effect). In this procedure, SCCO2 is introduced into a substrate, its suspension or solution in an organic solvent at high pressure. The resulting saturated solution is rapidly expanded through a tiny nozzle using moderate pressure which leads to reduction in temperature and the formation of particles due to the cooling effect. Zhu and colleagues [87] encapsulated menthol in beeswax using the PGSS. Equipment required for SCF encapsulation include a compressed SCCO2 cylinder, two high pressure liquid pumps for SCCO2 and the other solvents, high pressure chambers, product separation units, liquefying units, recirculating pumps, manometers, in-line filters, thermocouples, and a host of others. Parameters that needs to be optimized for each application include temperature, pressure, and feed emulsion rate. Karim and coworkers [88] used the GAS process to microencapsulate fish oil

Translated literally means solution gelling and basically refers to an encapsulation method involving solutions (sol) that transform to a gel in response to alternating

**24**

**Figure 10.**

*Schematic representation of the GAS process [86].*

encapsulate polar materials in their core while keeping hydrophobic materials in their lipid bilayer. Liposomes are traditionally made by the film hydration method with constituents like lipid, cholesterol, and solvent. Film hydration involves the dissolution of the lipid components in a suitable solvent most commonly ethanol and chloroform. The solvent is removed in a rotary evaporator leaving behind a thin film which is rehydrated to yield large multilamellar vesicles liposomes. The size of the liposomes can be reduced by passing through successively smaller sized polycarbonate filters. Ultrasonication method of preparing liposomes involves an aqueous dispersion of lipids using a strong sonicator probe and usually yields small unilamellar vesicles. Reverse phase evaporation is another method for liposome preparation [91]. In this method, a mixture of lipids and cholesterol dissolved in an appropriate solvent is subjected to the rotary evaporator for solvent removal. The residue is dried with hydrogen and resuspended in an organic solvent usually diethyl ether. An aqueous solution of the drug to be encapsulated is added to the lipid solution and sonicated under nitrogen until a homogenous mixture result. The solvent is then removed to yield large unilamelar vesicles usually used to encapsulate large molecular weight biomolecules. Ether vaporization method involves a mixture of lipids dissolved in an organic solvent such as ether and subsequently injected into a hot aqueous solution resulting in osmotic liposomes [92].

Major instability issues with liposomes is related to hydrolysis, oxidation, aggregation, and fusion. Appropriate buffer inclusion is necessary to limit oxidation of liposome phospholipids. Freeze drying has also been used to overcome the effect of temperature on liposomes. Such proliposomes are then reconstituted in water just before use. Research by Gomez and coworkers [91] showed that the encapsulation efficiency of any liposome preparation depend on the encapsulated molecule.

#### *4.3.8 Molecular inclusion complexes*

Inclusion complexes are microcapsules made by including a material to be encapsulated into the cavity of cyclodextrin molecule. Cyclodextrins are a family of cyclic oligosaccharides made up of glucopyranosyl linked by α (1,4) bonds. The most common members of the family are α-, β-, and γ- cyclodextrins consisting of 6, 7, and 8 glucopyranose units respectively. The most frequently used is β-cyclodextrin. The unique nature of a cyclodextrin molecule with a hydrophobic cavity enclosed by a hydrophilic container makes them targets for encapsulation of hydrophobic molecules. They serve as host to a great variety of hydrophobic compounds. Materials are enclosed into their cavity through different means.

Physical mixing through a kneading action of a solution of guest molecule with a slurry of cyclodextrin. The kneaded paste is dried and washed with a solvent. This is usually reserved for very poorly soluble materials and unsuitable for large scale production. In co-precipitation method, the guest molecule is dissolved is a suitable organic solvent such as diethyl ether, chloroform. Then, an aqueous solution of the cyclodextrin is added under agitation. The complex formed is precipitated out of solution using temperature reduction. The crystals are collected, washed with organic solvent and dried at 50°C. This method is usually reserved for payloads not too soluble in water [93].

Heating can also be used for inclusion complex formation. For this procedure, the physical mixture of the guest and the host can adsorb water and thereafter is heated in an enclosed vessel at a temperature of 40–145°C. This process yields crystalline complexes but can only be used for payloads stable at such temperature range [93]. Freeze drying is usually reserved for heat labile water-soluble cargoes. The required quantities of both guest and host materials are dissolved in water with stirring and then freeze dried. The obtained crystals are then washed with an organic solvent and dried in vacuum. This method is scalable and gives good yields [93].

**27**

**Figure 12.**

*Classification of polysaccharides based on their origin [100].*

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

Spray drying has also been used to obtain host-guest complexes. The host and guest molecules are dissolved in deionized water under agitation and subsequently dried in a spray dryer. There is need to optimize the operation conditions and this

In 1953, Hermann Staudinger was awarded the Nobel Prize in chemistry for demonstrating the existence of "*Makromoleküle*" macromolecules which led to the birth of the polymer chemistry field [94]. In the past 50 years, various natural, synthetic and semi-synthetic polymers have been investigated for developing diverse nano-, micro-, and macroscale drug delivery system (DDSs) for various therapeutic and diagnostic applications [94–96]. Natural polymers along with their derivatives (semi-synthetic polymers) are the safest micro- and nanocarriers due to their low toxicity, biocompatibility and intrinsic biodegradability by enzymes [97, 98]. This section highlights the main types of natural polysaccharides, proteins and lipids that have been employed as nanocarriers for therapeutic and theranostic applications.

Polysaccharides are the most abundant natural biopolymers derived from diverse bioresources, **Figure 12**. Polysaccharides are different from proteins, nucleic acids,

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

**5. Natural polymers in encapsulation**

**5.1 Polysaccharides**

process may be unsuitable for heat labile materials [93].

*Natural Polymers in Micro- and Nanoencapsulation for Therapeutic and Diagnostic… DOI: http://dx.doi.org/10.5772/intechopen.94856*

Spray drying has also been used to obtain host-guest complexes. The host and guest molecules are dissolved in deionized water under agitation and subsequently dried in a spray dryer. There is need to optimize the operation conditions and this process may be unsuitable for heat labile materials [93].
