Chitosan Coacervation

Other experiments on the chitinolytic activity of immobilized cells and culture medium of carrot cells (Table V) indicate that chitosan, in concentrations available to plant cells during the preparation of kappa-carrageenan-chitosan coacervate capsules, is detrimental to chitinase activity in plant cells and culture medium. This is also of interest in light of the data presented on the elicitor effect of chitosan on chitinase production at minute chitosan concentrations (see Table IX). 

Current research has reported various surface charged chitosan coacervates and its wide applications in biomedical research. Tavares et al. reported various chitosan coacervated nanoparticles and their applications. Similarly various other reports have been explored with its simplistic fabrication methods and its applications in biomedical research especially in drag delivery [150],... 

Tavares IS, Caroni ALPF, Dantas Neto AA, Pereira MR, Fonseca JLC. Surface charging and dimensions of chitosan coacervated nanoparticles. Colloids Surf B Biointerfaces. 2012 90(l) 254-8. 

This method used the physicochemical properties of polymers like chitosan, which is insoluble in alkaline pH medium and therefore precipitates/coa-cervates when it comes in contact with alkaline solution. Particles are produced by blowing chitosan solution into an alkali solution like NaOH using a compressed air nozzle to form coacervate droplets (Agnihotri et al. 2004). 

Plant cell cultures represent a potentially rich source of secondary metabolites of commercial importance and have been shown to produce them in higher concentrations than the related intact plants. However, plant cell cultures often produce metabolites in lower concentrations than desired and commonly store them intracellularly. These limitations can be overcome by product yield enhancement procedures, including immobilization of cultured cells, and permeabilization, or ideally using a combined immobilization/ permeabilization process with retained plant cell viability. Complex coacervate capsules consisting of chitosan and alginate or carrageenan proved to be effective biomaterials for entrapment, controlled permeabilization of cells and to allow control of capsule membrane diffusivity. 

Figure 1. Simplified protocol of chitosan/alginate or alginate/ chitosan complex coacervate capsule formation (adapted from 10,20,22). ...

Table III. Effect of buffer treatment and esterification of alginate on the mechanical stability of chitosan/alginate coacervate capsules3...

Beaumont and Knorr (ID) described the detrimental effect of chitosan on cell viability of Apium graveolens. Later it was found that at chitosan concentrations <250 yg/mL (Beaumont, M. and Knorr, D., Univ. of Delaware, unpublished data), plant cell viability was retained. Development of complex coacervate capsules consisting of alginate chitosan (22) and kappa-carrageenan-chitosan (10) allowed the concurrent release of secondary metabolites while still maintaining reasonable cell viability. Chitosan comprised the outer layer of the gel capsule and chitosan diffusivity could be controlled via capsule membrane permeability. 

Data in Table IV show the permeabilizing effect of chitosan expressed in release of total proteins when chitosan was used as the immobilizing agent in complex coacervate capsules, but suggest low cell viability as measured by respiration. However, Beaumont and Knorr (10) reported that fresh weight of cells recovered at the end of a culture period in the growth medium is a better indicator of actual cell viability than respiration data. 

Several researchers [163-165] have studied simple coacervation of chitosan in the production of chitosan beads. In general, chitosan is dissolved in aqueous acetic acid or formic acid. Using a compressed air nozzle, this solution is blown... 

The advantage of complex coacervates is that high payloads can be obtained. Chitosan/alginate coacervates have been reported to encapsulate up to 87% shark liver oil, which is rich in omega-3 fatty acids (Peniche et al. 2004). Microspheres of carboxymethyl chitosan/alginate hardened with calcium chloride have been used for encapsulation of up to 80% bovine serum albumin (Zhang et al. 2004). 

Remunanlopex, C. Bodmeier, R. Effect of formulation and process variables on the formation of chitosan-gelatin coacervates. Int. J. Pharm. 1996, 135 (1-2), 63-72. 

Bayomi MA, al-Suwayeh SA, el-Helw AM, Mesnad AF. Preparation of casein-chitosan microspheres containing diltiazem hydrochloride by an aqueous coacervation technique. Pharma Acta Helv 1998 73 187-192. 

Figure 11.17 Ternary phase diagram of complex coacervation between pRE-luciferase plasmid and chitosan at 55°C in 50 mmol dm No2S04. Sodium sulfate solution was regarded as one component, since the concentration change in the experiment range was minimal. The region to the right of line the ABC depicts the conditions under which phase separation occurs. The concentration ranges in the small grid area yield distinct particles.

There have been excellent reviews published in recent years as related to gelatin replacement for microencapsulation. Table 12.2 lists some of the examples of non-gelatin based complex coacervation systems. Proteins derived from plants, such as pea protein, - wheat protein," ° soy protein, whey protein from dairy products, " chitosan from marine crustaceans, and collagen have been used to replace gelatin in complex coacervation. 

Baruch, L. and M. Machluf, Alginate-chitosan complex coacervation for cell encapsulation Effect on mechanical properties and on long-term viability. Biopolymers, 82(6) (2006) 570-579. 

Ritthidej, G.C. Tiyaboonchai, W. Formulation and drug entrapment of microcapsules prepared from chitosan-carboxymethylcellulose complex coacervation. Thai. J. Pharm. Sci. 1997, 21 (1), 137-144. 

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