Controlled release of thymosin β4 using collagen-chitosan composite hydrogels promotes epicardial cell migration and angiogenesis

Rapid vascularization at the infarcted site is crucial for cardiac repair following myocardial infarction. Thymosin beta 4 (T beta 4), a 43-amino acid peptide, is both angiogenic and cardioprotective. T beta 4 in soluble form was previously shown to promote cell migration from quiescent adult cardiac explants. Here we developed a collagen-chitosan hydrogel for the encapsulation of T beta 4, which allowed its controlled release over 28 days to elicit localized and prolonged effects. Contrastingly, T beta 4 was fully released over 3 days when encapsulated in collagen-only hydrogels due to charge repulsion and lack of interconnected pores as shown by SEM. The charge of encapsulated molecules affected their release from collagen-chitosan hydrogels. While the release of neutral polyalanine was size-controlled diffusion, that of negatively-charged T beta 4 and positively-charged polylysine was affected by electrostatic interactions of peptides with collagen/chitosan molecules. Hydrogels with encapsulated T beta 4 significantly increased cell migration and outgrowth of CD31-positive capillaries from mouse and rat epicardial explants in vitro, compared to T beta 4-free and soluble controls. Potential advantage of T beta 4 over commonly-used angiogenic growth factors is that it can induce recruitment and differentiation of both endothelial and smooth muscle cells necessary for vascular stability. Importantly, T beta 4-encapsulated collagen-chitosan hydrogels promoted angiogenesis in vivo upon subcutaneous injection, compared to collagen-only hydrogels. (C) 2011 Elsevier B.V. All rights reserved.