Encapsulating Wall Materials for Micro-/Nanocapsules

*Shaluah Vijeth, Geetha B. Heggannavar, Mahadevappa Y. Kariduraganavar*

## **Abstract**

Wall materials play a vital role in the development of micro-/nanocapsules to protect the bioactive compounds against external factors. The encapsulation process and the type of polymers exert a direct impact on the development of bioactive micro-/nanocapsules, which greatly reflect in encapsulation efficiency, solubility, stability, surface permeability, and release profile of desired bioactive compounds. Among the polymers, biodegradable polymeric materials have been the focus for various applications in food, pharmaceutical, and cosmetic industries. Thus, this chapter focuses on different encapsulation techniques and the importance of biodegradable polymers employed as wall materials for developing stable and safe micro-/nanocapsules. Among the natural polymers, protein- and polysaccharide-based polymers are widely used. Similarly, the most commonly used synthetic polymers are polycaprolactone, poly(lactic-co-glycolic acid), and polyethylene glycol. Synthetic polymers have been classified based on their exogenous and endogenous responsive natures. At the end, we have also discussed on the applications of biodegradable polymers employed in the development of micro-/ nanocapsules. To compile this chapter and to provide adequate information to the readers, we have explored various sources, such as reviews, research articles, books, and book chapters including Google sites.

**Keywords:** biodegradable polymers, microcapsules, nanocapsules, responsive polymers

### **1. Introduction**

Encapsulation is a process in which tiny particles or droplets are surrounded by a coating to form capsules. Microcapsules and nanocapsules are small spheres with a uniform wall around it. The material inside the capsule is referred as the core, internal phase, or fill, whereas the wall is called as the shell, coating, or membrane. The core material may be liquid or solid, active constituents, stabilizers, diluents, excipients, and release-rate retardants or accelerators.

Encapsulation can be done for multiple reasons. The primary purpose of encapsulation is either for sustained or prolonged drug release. For orally delivered drugs, this method has been widely used for masking taste and odor to improve patient compliance, reduce toxicity, and gastrointestinal irritation. This method can be used to convert liquid drugs to a free flowing powder form, prevent vaporization of volatile drugs, alter the site of absorption, and to prevent incompatibility among the drugs. The drugs which are sensitive to oxygen, moisture, light, or pH changes can

be stabilized by encapsulation. Depending on the applications, the wall material of the capsules is designed to serve the desired specific purpose.

Thus, the wall material is the most vital component in any capsule. The selection of appropriate wall material decides the physical and chemical properties of the resultant micro-/nanocapsules. The wall material should have the properties like being inert toward core active ingredients, stabilize the core material, film-forming, pliable and tasteless, non-hygroscopic, moderate viscosity, economical and soluble in an aqueous media or solvent, or melting, the coating may be flexible, brittle, hard, and thin, controlled release at the specific site under specific conditions.

Understanding the importance of polymers as wall materials, we have attempted to give a review of wall materials used in micro- and nanocapsules for the sustained/controlled delivery of drugs. A detailed account on encapsulation techniques is given. The biodegradable materials employed as wall materials are discussed adequately. The advantages of biodegradable materials including their limitations are covered in the chapter. The release profiles were discussed based on both exogenous and endogenous responsiveness of the wall materials. At the end of the chapter, future prospects and challenges of the wall materials are highlighted.

#### **2. Encapsulation techniques**

Microencapsulation of active compounds can be achieved by physical and chemical methods. Though these techniques are neither purely physical nor purely chemical, they are classified as physical and chemical methods based on the predominant or primary principle involved. In **Table 1**, we have listed commonly used physical and chemical methods used for encapsulation.


**Table 1.** *Encapsulation techniques.*

### **3. Polymers as wall materials**

#### **3.1 Natural polymers**

Natural polymers are broadly classified into protein-based polymers and polysaccharide-based polymers. Albumin and gelatin are the examples of proteinbased polymers. Polysaccharide-based polymers are agarose, alginate, hyaluronic acid, dextran, chitosan, etc. These natural polymers are highly biodegradable and biocompatible in nature.

**5**

*Encapsulating Wall Materials for Micro-/Nanocapsules DOI: http://dx.doi.org/10.5772/intechopen.82014*

therapeutic cargo from nanocapsules inside the endosomes.

ent approved by the US FDA for pharmaceutical applications.

compounds, susceptibility to enzymatic hydrolysis, and nontoxicity.

*3.1.2 Polysaccharide-based polymers*

Albumin is a biodegradable and water soluble protein and thus plays an important role in the circulating system. It is involved in osmotic pressure regulation, binding, and transport of nutrients to the cells that can be obtained from a variety of sources including egg white, bovine serum, and human serum. It is stable in the pH range of 4–9 and can be heated at 60°C up to 10 h without any deleterious effects [1]. It undergoes degradation by protease enzymes, which helps the microcapsules to release the drugs in the small intestine. It also facilitates the release of

Gelatin is biodegradable, inexpensive, easily sterilized, non-pyrogenic, nontoxic, non-immunogenic, and easy to be crosslinked or modified chemically. Gelatin has many ionizable groups, such as carboxyl, amino, phenol, guanidine, and imidazole, which are potential sites for conjugation or chemical modifications. Chemical crosslinking agents like glutaraldehyde improves the integrity and performance of the gelatin and provides gelatin with greater stability, shape, and increased circulation time *in vivo* [2]. The degree of crosslinking determines the release of drugs from the gelatin capsules. Thus, gelatin is regarded as a safe excipi-

Chitosan, the second most abundant polysaccharide in nature, is a promising biopolymer widely used in biomedical and pharmaceutical fields like wound dressing, tissue engineering and drug delivery. It is produced from chitin which is the structural element found in the exoskeleton of crustaceans like shrimps, lobsters, and crabs. Chitosan has been reported to exhibit many therapeutic properties, such as activation of immune response, cholesterol lowering activity, anti-hypertensive activity, inhibition of growth of microorganism, pain alleviation, and promotion of hemostasis and epidermal cell growth [3]. This is all due to the favorable pharmaceutical properties of chitosan, such as biocompatibility, low production cost, ability to bind some organic

Chitosan is considered as the most important polysaccharide-based polymer owing to its cationic character based on its primary amino groups, which are responsible for its versatile properties, such as mucoadhesion (improves pulmonary drug delivery), controlled drug release, transfection, in situ gelation, and efflux pump inhibitory properties and permeation enhancement [4]. The major drawback is its poor solubility at physiological pH due to partial protonation of the amino groups in the presence of proteolytic enzymes and thereby causing presystemic metabolism of drugs in intestinal and gastric fluids. To overcome these inherent drawbacks, various derivatives of chitosan, such as carboxylated, different conjugates, thiolated and acylated chitosan have been used in drug-delivery systems [3]. Chitosan is produced by the deacetylation of chitin. The degree of deacetylation is related to chitosan's crystallinity and degradation rates. Chitosan's solubility can

*3.1.1 Protein-based polymers*

*3.1.1.1 Albumin*

*3.1.1.2 Gelatin*

*3.1.2.1 Chitosan*

#### *3.1.1 Protein-based polymers*
