576 Controlled Release of VEGF in the Infarct Region: Epicardial Implantation of a Microsphere-Loaded Patch

Abstract

The delivery of growth factors to the heart following a myocardial infarction can enhance angiogenesis and tissue repair. Intrapericardial administration of growth factors can induce a therapeutic response in the pathological heart; however, a single injection is prone to degradation and generates a global effect. Biomaterial-based delivery systems constructed for epicardial implantation can be designed to localize and prolong growth factor release to elicit a robust regenerative response. Using a water-in-oil single emulsion, we produced non-porous Ca2+-alginate microspheres with an average diameter of ∼2 μm. To construct an implantable cytokine delivery system with prolonged protein release, the microspheres were compacted via centrifugation into a biodegradable porous patch. To evaluate protein release, fluorescein-conjugated bovine serum albumin was loaded into the patch, which was subsequently incubated in PBS. The fluorescent signal of the protein released into the surrounding PBS was measured daily for 11 days. The bulk release of protein occurred over 5 days and closely resembled first-order kinetics. At 1, 3, and 5 days, protein released was 30%, 70%, and 85%, respectively, avoiding an early burst release. To evaluate the biological function of cytokine release from the patch, patches were loaded with vascular endothelial growth factor (VEGF) and incubated in cell growth media. The release media was collected over 3 days and incubated with human umbilical vein endothelial cells. An MTT assay showed a 40% increase (p<0.01) in proliferation compared to cells treated with release media from a patch without VEGF. To determine its effectiveness as a suitable biomaterial release system in vivo, the patch was loaded with VEGF and implanted onto the epicardium of a rat heart following coronary artery ligation and secured in place using a chitosan sheet. Patch degradation was monitored with magnetic resonance imaging. The patch was still present at the site of implantation after 1 month, but only 50% of the patch remained. Histology revealed cell infiltration into the patch, indicating a continuous connection between the patch and underlying heart to facilitate protein diffusion. The epicardial implantation of a VEGF-loaded patch permits growth factor delivery into a cardiac region and provides an opportunity to induce localized angiogenesis. Sustained release of VEGF or other growth factors with biomaterial-based delivery systems, such as this epicardial patch, could be a powerful therapeutic strategy. This new tissue-engineered platform provides an opportunity to improve recovery and tissue regeneration of the ischemic heart.