Analysis of crystallization kinetics and shape memory performance of PEG-PCL/MWCNT based PU nanocomposite for tissue engineering applications

In this work, a series of reactive in-situ polyurethane (PU) nanocomposites based on the triblock copolymer of PCL1000-PEG1000-PCL1000, chemically cross-linked by hydroxyl-functionalized MWCNTs (um-MWCNT) and PCL-grafted MWCNTs (mod-MWCNT), were synthesized. In order to optimize the shape memory performance, crystallization mechanisms of the soft domains were tuned. The nanoparticles, acting as phase controller of the block copolymer, affected the chain’s confinement and crystals’ morphology leading to a wide range of shape fixity (84–100%) and shape recovery (78–97%) ratios. Non-isothermal crystallization studies revealed that using mod- MWCNTs increased the melting temperature (Tm) as an indication of higher thermal stability of the formed crystallites. Moreover, isothermal DSC measurements, fitted to the Avrami equation, were used to measure the changes in the growth rate and morphological features of the formed crystallites. The results indicated an increase in Avrami exponent (n) from 1.43 to 3.11, and crystallization half-time (t0.5) decreased from 6.16 to 2.67 minutes for crystallization temperature (Tc) of –25 °C, attributed to the effect of PCL grafts on PUs’ microstructure. In addition, the results of cell viability, evaluated by HFF cells, proved a proper cytocompatibility. Culturing hMSCs also showed good adhesion and cell spreading, as a function of hydrophilicity. The optimum sample, containing 0.5% PCL-g-MWCNT, showed 97% shape recovery at body temperature (37°C).