New concepts in controlled drug delivery

A large number of both natural and synthetic polymers have been studied for powible application in drug delivery. The great advantage of synthetic polymers is their advantageous properties and wide choice availability. Two promising synthetic polymers which have been developed for biomedical applications are polyvinylpyrolidone and polyethylene glycol acrylate based hydrogels. Both of them are biodegradable and forms copolymers with natural macromolecules. On the other hand, natural polymers have the advantage of high biocompatibility and less immunogenicity. Among the natural polymers studied a special mention has to be made to collagen and gelatin. Other natural polymers include chitosan, alginate, starch, pectin, casein and cellulose derivatives. The composites of some the above natural polymers with synthetic polymers give added advantage as carriers for drug delivery by complimenting the properties of each other. Collagen poly-HEMA hydrogels have been prepared in our laboratory as an implant for delivering anticancer drugs such as 5-fluorouracil, mitomycin and bleomycin for solid fibrosarcoma in rat model. The same hydrogels have been used with some modifications for the delivery of model protein bovine serum albumin and vaccines such as tetanus and diphtheria toxoids in mice. Hybrid copolymers of collagen with biodegradable synthetic polymers polyethyleneglycol 6000 and polyvinylpyrolidone were developed for the controlled release of contraceptive steroids. The entrapped testosterone released 40% of steroid in first 10 days and there after the release was very slow. The total amount of drug released by 90 days was about 66%.