Tertiary Biomaterial Encapsulation Controls the Release of FGF-2 without Impacting Bioactivity

Abstract

Diseases that restrict the flow of blood to muscles in the peripheral limbs or the heart remain prevalent causes of reduced quality of life and death in developed countries. Signaling molecules that play a role in the regenerative responses are currently being exploited as potential therapies to restore blood flow and tissue function. Fibroblast growth factor-2 (FGF-2) is a potent stimulator of neovascularization. It is believed that a controlled release of a delivered cytokine is superior to a bolus administration for achieving the desired regenerative effect. Therefore, we incorporated FGF-2-containing microspheres into a hydrogel and further encased this hydrogel into a collagen capsule for implantation. Cytokine release was controlled and constant over a month-long study period, and FGF-2 released from this tertiary encapsulation system maintained its bioactivity, as measured by its proliferative effects on endothelium. In a subcutaneous mouse model, FGF-2 treatment induced a systemic response that included increased stem cell chemoattractant cytokines, the mobilization of a potent CXCR4 + angiogenic population, and also an increase in the density of small diameter blood vessels. These observations were accompanied by no changes in the systemic levels of inflammatory cytokines. Overall, tertiary encapsulation of FGF-2 retards its release and allows for a more controlled and constant delivery of FGF-2, while maintaining its bioactive effects on endothelial cells and systemic responses in vivo.