Microspheres and microcapsules for protein delivery: strategies of drug activity retention

With the recent progress in biotechnology and genetic engineering, a variety of proteins have formed a very important class of therapeutic agents. However, most proteins have short half-lives in vivo requiring multiple treatments to provide efficacy. In order to overcome this limitation, sustained release systems as hydrophilic microspheres and hydrophobic microcapsules have received extensive attention in recent years. As therapeutic proteins delivery systems, it is necessary to maintain protein bioactivity during microspheres or microcapsules formation as much as possible. This paper reviews different influencing factors that are closely involved in protein denaturation during the preparation of hydrophilic polymer microspheres and hydrophobic polymer microcapsules. The various strategies usually employed for overcoming these obstacles are described in detail. Both processing and formulation parameters can be modified for improving protein stability. The maximum or full protein stability retention within the microspheres or microcapsules might be achieved by individual or combined optimized strategies. In addition, the common techniques for proteins stability determination are also briefly reviewed.