CHAPTER 9: Parenteral Delivery of Therapeutic Proteins, Peptides and Small Molecules Using Biodegradable Silica

Biodegradable silica, produced by sol–gel processing, has been used to encapsulate active pharmaceutical ingredients (APIs), and to achieve controlled release of APIs. The feasibility of this encapsulation method has been shown for many types of APIs, ranging from small-molecule drugs, peptides, and proteins to viral vectors. Biodegradable silica can be processed into many different morphologies and dosage forms, e.g., implants, microparticles, and hydrogels. Recently, an injectable silica dosage form, a silica–silica composite has been developed. It consists of sol–gel-derived silica microparticles with an encapsulated API embedded into an injectable silica hydrogel. This dosage form combines several beneficial properties, and it is feasible for small, large, and sensitive APIs. The rate of biodegradation, and consequently the release rate of API, can be adjusted from days to months, and even up to years. The basic technology and preparation of the injectable silica–silica composite is discussed briefly. Case examples of in vivo protein and peptide release from the dosage form are also discussed. Typical methods used to characterize the dosage form and the results from these methods are presented in more detail for a specific case in which a pharmaceutical protein was encapsulated into the dosage form and characterized in vitro. To conclude, the injectable silica–silica composite also has other potential applications in the future, and these are briefly discussed.