A coating with biomacromolecules can improve the performance of electrospun 3D scaffolds and 2D matrices that show morphology similar to that of native ECM, but their mechanical and biological properties are often inadequate, particularly in applications in contact with blood. In this work, a gelatin coating was applied to electrospun silk fibroin (ESF) mats and tubes intended for the regeneration of cardiovascular tissues. The crosslinking reaction used is based on a Michael-type addition in water that promotes the formation of covalent bonds between gelatin amino groups and β-carbons of N-N′-methylene bis-acrylamide (MBA). ESF mats and tubes were coated with gelatin MBA crosslinked in situ by loading or dipping the ESF samples with the crosslinking solution by use of static or dynamic homemade systems. SEM analysis on coated samples showed a homogeneous coating with gelatin penetrating the whole thickness of the SF matrix (≈120 µm for mats and ≈212 µm for tubes), with an increase of thickness of about 40% in wet conditions. Water uptake tests indicated for coated samples a faster and higher swelling (1600% after 14 days) than not coated ones (500%), due to the presence of gelatin. Tensile mechanical tests showed higher values of ultimate stress and elastic modulus for silk fibroin samples (b = 2.4, E = 1.82 MPa) compared to gelatin-coated ones (b = 1.2, E = 0.58 MPa), with not significant differences in the ultimate deformation (≈150%). Indirect cytocompatibility tests, performed by culturing L929 cells in the presence of eluates obtained by immersing coated and uncoated samples up to 7 days in culture medium, demonstrated a cell viability higher than the control. For direct contact tests, primary human umbilical vein endothelial cell (HUVEC), obtained by enzymatic digestion, and cell adhesion and growth on the MBA-crosslinked gelatin was analyzed by OM after fixing with formalin and staining with toluidine blue. HUVEC were seeded onto ESF and ESF-coated samples and cultured under standard tissue culture conditions. After 7 days from seeding, cell proliferation was evaluated from the quantitation of total proteins in cell lysates (BCA protein assay) and the obtained results indicated a significantly higher (p < 0.05) cell growth on gelatin-coated ESF samples. Overall, these results point out that the described gelatin coating allows for the production of a structure with adequate mechanical properties for cardio-vascular applications and biological characteristics even better than those of silk fibroin.
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