Stability of Proteins and Their Delivery from Biodegradable Polymer Microspheres

This chapter discusses the concepts of biochemistry, polymer science, and microencapsulation to examines the complexity of formulating these dosage forms; particular emphasis is placed on the strategies and experimental methods used to handle the problems associated with protein stability. Although it has become a routine objective to analyze release kinetics of proteins, the number of publications that consider the stability of protein being delivered from polymers is very low. The stability of proteins encapsulated in biodegradable polymer microspheres may be separated into at least three complex themes and their interrelations: processing polymers into microspheres, hydration and erosion of the polymer during release incubation, and the intrinsic stability of the protein. A phase separation occurs at the surface of the polymer and second aqueous solution, leading to a polymer-rich phase at the microsphere surface and a more dilute polymer solution in the interior. Mechanistic analysis of the stability of proteins during processing, storage, and delivery from polymers is also virtually nonexistent.