Synthesis and characterization of biodegradable elastomeric polyurethane scaffolds fabricated by the inkjet technique

Biodegradable polyurethanes (PUs) were synthesized from methylene di-p-phenyl-diisocyanate (MDI), polycaprolactone diol (PCL-diol) and N,N-bis (2-hydorxyethyl)-2-aminoethane-sulfonic acid (BES), serving as a hard segment, soft segment and chain extender, respectively. MDI was chosen due to its reactivity and wide application in synthesis of biomedical polyurethanes due to its reactivity; PCL-diol was chosen because of its biodegradability; and BES was chosen because it allowed the introduction sulfonic acid groups onto the polymer chains. We evaluated the polyurethanesʹ degradation rate, mechanical properties, hydrophilicity, antithrombogenecity, and ability to support fibroblast cell attachment and growth by comparing with polymers having a 2,2-(methylimino)diethanol (MIDE) chain extender. Mechanical testing demonstrated that the PU containing BES has tensile strengths of about 17 MPa and elongations up to 400%, about three times the strength and four times the elongation than the MIDE based PUs. The polymers showed decreased in vitro degradation rates, lower glass transition temperature (Tg) and hydrophilicity possibly due to enhanced microphase separation. Preliminary cytocompatibility studies showed that all the PUs are non-toxic, but PU containing BES exhibited much lower cell attachment and proliferation than the MIDE chain extended polymers. An in vitro platelet adhesion assay showed lower platelet attachment on BES containing PU. Additionally, due to the existence of sulfonic acid groups, the BES extended PU became water soluble in basic condition and insoluble in acidic condition, a phenomenon that is reversible at pH value of 8.7, making this a pH sensitive polymer attractive for bioprinting applications. By adding acetic acid into an inkjet cartridge and printing it onto a PU solution with pH above 8.7, precision fabricated scaffolds can be obtained, suggesting that BES based PUs are promising candidates as synthetic inks used for customizable fabrication of tissue engineering scaffolds.