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The inherent flexibility of polyurethane (PU) chemistry allows the incorporation of specific chemical moieties into the backbone structure conferring a unique biological function to these synthetic polymers. We describe here the synthesis and characterization of a PU containing a Gly–Leu linkage, the cleavage site of several matrix metalloproteinases. A Gly–Leu dipeptide was introduced into the chain extender of the polyurethane through the reaction with 1,4-cyclohexane dimethanol. PUs synthesized with the Gly–Leu-based chain extender had a high weight-average molecular weight (Mw > 125 × 103) and were phase segregated, semi-crystalline polymers with a low soft-segment glass-transition temperature (Tg < –50°C). Uniaxial tensile testing of PU films indicated that the polymer could withstand high ultimate tensile strengths (approx. 13 MPa) and were flexible with breaking strains of approx. 900%. The Gly–Leu PU had a significantly higher initial modulus, yield stress and ultimate stress compared to a PU previously developed in our laboratory containing a phenylalanine-based chain extender (Phe PU). The Gly–Leu-based chain extender allowed for better hard segment packing and hydrogen bonding leading to enhanced mechanical properties. Electrospinning was used to form scaffolds with randomly organized fibers and an average fiber diameter of approx. 3.6 μm for both the Gly–Leu and Phe PUs. Mouse embryonic fibroblasts were successfully cultured on the PU scaffolds out to 28 days. Further investigations into cell-mediated polymer degradation will help to identify the suitability of this new biomaterial as scaffolds for soft tissue applications. [ABSTRACT FROM AUTHOR]

Recombinantly-engineered elastin-like polypeptides (ELPs) possess many of the favourable attributes of the native elastin protein, making them an attractive option for designing biomaterials for tissue-engineering applications. The focus of this study was to synthesize and characterise the bulk material properties of two ELP sequences, ELP2 and ELP4, cross-linked with lysine diisocyanate (LDI). The two distinct ELPs consist of repeating hydrophobic and hydrophilic cross-linking domains in a block co-polymer structure, however, differ by the number of respective domains. Depending on the conditions sets for the cross-linking reactions, two different ELP-based materials were synthesized: a gel-like relatively non-porous material and a porous foam-like material, from both ELP sequences. The physical material properties were characterised by scanning electron microscopy, compression testing, differential calorimetry analysis and swelling analysis. The bulk material properties were found to vary depending on the ELP sequence investigated. ELP gels were also found to have a more dense solidified morphology, lower compressive moduli, higher melting temperature and greater swelling capacity than the porous ELP foams. These novel cross-linked bio-elastomeric materials show promising properties for soft tissue replacement, particularly in load-bearing applications. [ABSTRACT FROM AUTHOR]

A polyurethane designed to be biodegradable via hydrolysis and enzyme-mediated chain cleavage, has been investigated for its use as a temporary scaffold in tissue-engineering applications. The phase-segregated nature of the polyurethane imparts elastomeric properties that are attractive for soft tissue engineering. This polyurethane has been electrospun in order to create scaffolds that incorporate several biomimetic features including small fiber diameter, large void volume, and an interconnected porous network. Material properties were evaluated via gel-permeation chromatography, differential scanning calorimetry and Raman spectroscopy before and after processing. Analysis by gel-permeation chromatography showed that the molecular weights were similar, indicating that the bulk of the polymer chains were not degraded during processing. Thermal analysis revealed that the glass transition temperature did not shift and Raman spectra of the bulk polyurethane film compared to the electrospun mat were identical, confirming that the conformation of the polymer was unaffected by the shear and electric field used in the electrospinning process. In addition, field emission scanning electron microscopy revealed that the morphology of the electrospun mats had a broad fiber diameter distribution, and mechanical analysis showed that the mats had an ultimate tensile stress of 1.33 MPa and ultimate tensile strain of 78.6%. The degradation profile was investigated in the presence of chymotrypsin. These results were compared to a previous study of thin films of this polyurethane, and it was found that the increase of surface area aided the surface-mediated erosion of the material. It is believed that an electrospun matrix of this biodegradable polyurethane shows promise for use in soft tissue engineering and regenerative medicine applications. [ABSTRACT FROM AUTHOR]