In this work, a new polyurethane (PU) chain extender was developed to incorporate a Glycine-Leucine (Gly-Leu) dipeptide, the cleavage site of several matrix metalloproteinases. PUs were synthesized with either the Gly-Leu-based chain extender (Gly-Leu PU) or a phenylalanine-based chain extender (Phe PU). Both PUs had high molecular weight averages (Mw > 125,000 g/mol) and were phase segregated, semi-crystalline polymers (Tm ~ 42°C) with a low soft segment glass transition temperature (Tg < -50°C). Uniaxial tensile testing of PU films revealed that the polymers could withstand high ultimate tensile strengths (~ 8-13 MPa) and were flexible with breaking strains of ~ 870-910% but the two PUs exhibited a significant difference in mechanical properties. The Phe and Gly-Leu PUs were electrospun into porous scaffolds for degradation and cell-based studies. Fibrous Phe and Gly-Leu PU scaffolds were formed with randomly organized fibers and an average fiber diameter of approximately 3.6 µm. In addition, the Phe PU was electrospun into scaffolds of varying architecture to investigate how fiber alignment affects the orientation response of cardiac cells. To achieve this, the Phe PU was electrospun into aligned and unaligned scaffolds and the physical, thermal, and mechanical properties of the scaffolds were investigated. The degradation of the Phe and Gly-Leu PU scaffolds was investigated in the presence of active MMP-1, active MMP-9, and a buffer solution over 28 days to test MMP-mediated and passive hydrolysis of the PUs. Mass loss and structural assessment suggested that neither PU experienced significant hydrolysis to observe degradation over the course of the experiment. In cell-based studies, Phe and Gly-Leu PU scaffolds successfully supported a high density of viable and adherent mouse embryonic fibroblasts (MEFs) out to at least 28 days. Culturing murine embryonic stem cell-derived cardiomyocytes (mESCDCs) alone and with MEFs on aligned and unaligned Phe PU scaffolds revealed both architectures supported adherent and functionally contractile cells. Importantly, fiber alignment and coculture with MEFs improved the organization and differentiation of mESCDCs suggesting these two parameters are important for developing engineered myocardial constructs using mESCDCs and PU scaffolds.

In this work, a new polyurethane (PU) chain extender was developed to incorporate a Glycine-Leucine (Gly-Leu) dipeptide, the cleavage site of several matrix metalloproteinases. PUs were synthesized with either the Gly-Leu-based chain extender (Gly-Leu PU) or a phenylalanine-based chain extender (Phe PU). Both PUs had high molecular weight averages (Mw > 125,000 g/mol) and were phase segregated, semi-crystalline polymers (Tm ~ 42°C) with a low soft segment glass transition temperature (Tg < -50°C). Uniaxial tensile testing of PU films revealed that the polymers could withstand high ultimate tensile strengths (~ 8-13 MPa) and were flexible with breaking strains of ~ 870-910% but the two PUs exhibited a significant difference in mechanical properties. The Phe and Gly-Leu PUs were electrospun into porous scaffolds for degradation and cell-based studies. Fibrous Phe and Gly-Leu PU scaffolds were formed with randomly organized fibers and an average fiber diameter of approximately 3.6 µm. In addition, the Phe PU was electrospun into scaffolds of varying architecture to investigate how fiber alignment affects the orientation response of cardiac cells. To achieve this, the Phe PU was electrospun into aligned and unaligned scaffolds and the physical, thermal, and mechanical properties of the scaffolds were investigated. The degradation of the Phe and Gly-Leu PU scaffolds was investigated in the presence of active MMP-1, active MMP-9, and a buffer solution over 28 days to test MMP-mediated and passive hydrolysis of the PUs. Mass loss and structural assessment suggested that neither PU experienced significant hydrolysis to observe degradation over the course of the experiment. In cell-based studies, Phe and Gly-Leu PU scaffolds successfully supported a high density of viable and adherent mouse embryonic fibroblasts (MEFs) out to at least 28 days. Culturing murine embryonic stem cell-derived cardiomyocytes (mESCDCs) alone and with MEFs on aligned and unaligned Phe PU scaffolds revealed both architectures supported adherent and functionally contractile cells. Importantly, fiber alignment and coculture with MEFs improved the organization and differentiation of mESCDCs suggesting these two parameters are important for developing engineered myocardial constructs using mESCDCs and PU scaffolds.