Matrix influence of collagen: fibrin interpenetrating hydrogels on microvascular networks and osteogenesis

Blended interpenetrating collagen: fibrin (col: fib) blend hydrogels of differing blend ratios (100:0, 25:75, 50:50, 75:25, and 0:100 col.:fib respectively) were synthesized for the purposes of supporting angiogenesis and osteogenesis. Gels were seeded with microvascular fragments (MVFs) to evaluate how the col.: fib matrix alone supported angiogenesis. Gels were also seeded with mesenchymal stem cells (MSCs) in conjunction with the MVFs to determine how stromal support in addition to the matrix supported both angiogenesis and osteogenesis, with stromal conditioning from osteogenic differentiation media. Gel blends with higher amounts of fibrin content supported angiogenesis of MVF seeded samples better with increased levels of vessel network formation and sprouting. When stromal cell support was added, this trend remained, with evidence that stromal cells aided in faster and more robust vessel formation. Gene expression levels indicate that the 50C50F blend balances osteogenic and angiogenic support. Altogether, we found that matrix composition dictates vessel infiltration and spreading and that with the addition of stromal cells, both angio- and osteogenesis were accelerated. The results of this study demonstrate that a blend ratio of 50:50 col.:fib balances angiogenesis and osteogenesis within a co-culture of MSCs and MVFs.