chitosan and plga microspheres as drug delivery ... - UniCA Eprints

1. General Introductionremoval and limits their applicability. In the 1970s biodegradable polymers were suggested asappropriate drug delivery materials circumventing the requirement of removal (131). The ideaof polymer microspheres as delivery systems was reported as early as the 1960s (132) anddegradation was incorporated by Mason et al. (133) through the employment of a degradablepolymer.Recent literature shows that suspensions of degradable microspheres can be employed forsustained drug release at desirable doses. Biocompatibility can be achieved by the use ofnatural polymers such as cellulose, chitin, and chitosan or by the employment of semisynteticpolymers made from naturally occurring monomers such as lactic and glycolic acids.Polymers derived from synthetic monomers also show excellent delivery properties.However, their toxicity effects may require evaluation. The factors affecting drug release arecontrollable; they are attributed to properties such as polymer molecular weight, as well asmicrosphere size, distribution, morphology and make-up.For preparation of microspheres using biodegradable polymers, it is important to choose anappropriate encapsulation process which meets the following requirements. First, thechemical stability and biological activity of the incorporated drugs should be maintainedduring the encapsulation process. For example, since most proteins are readily denatured uponcontact with hydrophobic organic solvents or acidic/basic aqueous solutions, the processshould avoid such harshenvironments. Second, the encapsulation efficiency and the yield of the microparticles shouldbe high enough for mass production. Third, the microparticles produced should have thereasonable size range. Fourth, the release profile of the drug should be reproducible withoutthe significant initial burst. Fifth, the process employed should produce free-flowingmicroparticles, thus making it easy to prepare uniform suspension of the microparticles. Thereare a number of techniques available for microencapsulation of drugs such as the emulsionsolventevaporation/extraction method, spray drying, phase separation-coacervation,interfacial deposition, precipitation method, in situ polymerization, etc. Each method has itsown advantages and disadvantages. The choice of a particular technique depends on theattributes of the polymer and the drug, the site of the drug action, and the duration of thetherapy (134, 135, 136).Increasing or controlling the encapsulation efficiency (E%) is desirable, it can prevent the lossof precious medication and it can help to extend the duration and dosage of treatment. Yang etal. (137) have provided a revealing study which correlated the encapsulation efficiency to27