Green Chemistry for Biomimetic Materials: Synthesis and Electrospinning of High-Molecular-Weight Polycarbonate-Based Nonisocyanate Polyurethanes

Abstract

Conventional synthesis routes for thermoplastic polyurethanes (TPUs) still require the use of isocyanates and tin-based catalysts, which pose considerable safety and environmental hazards. To reduce both the ecological footprint and human health dangers for nonwoven TPU scaffolds, it is key to establish a green synthesis route, which eliminates the use of these toxic compounds and results in biocompatible TPUs with facile processability. In this study, we developed high-molecular-weight nonisocyanate polyurethanes (NIPUs) through transurethanization of 1,6-hexanedicarbamate with polycarbonate diols (PCDLs). Various molecular weights of PCDL were employed to maximize the molecular weight of NIPUs and consequently facilitate their electrospinnability. The synthesized NIPUs were characterized by nuclear magnetic resonance, Fourier-transform infrared spectroscopy, gel permeation chromatography, and differential scanning calorimetry. The highest achieved molecular weight (M _w) was 58,600 g/mol. The NIPUs were consecutively electrospun into fibrous scaffolds with fiber diameters in the submicron range, as shown by scanning electron microscopy (SEM). To assess the suitability of electrospun NIPU mats as a possible biomimetic load-bearing pericardial substitute in cardiac tissue engineering, their cytotoxicity was investigated in vitro using primary human fibroblasts and a human epithelial cell line. The bare NIPU mats did not need further biofunctionalization to enhance cell adhesion, as it was not outperformed by collagen-functionalized NIPU mats and hence showed that the NIPU mats possess a great potential for use in biomimetic scaffolds.

Scheme 1. Synthesis Route for NIPUs

Figure 1

FTIR spectra of 1,6-HDC, PCDL500, and NIPU-D.

Figure 2

¹H-NMR (a) and ¹³C-NMR (b) spectra of NIPU-D in DMF-d₇.

Figure 3

SEM micrographs of electrospun NIPU-A mats electrospun at 30 wt % (a), 40 wt % (b), and 50 wt % (c) in HFIP.

Figure 4

SEM micrographs and the corresponding intra-sample distribution of the fiber diameters of electrospun NIPU-D mats, which were electrospun at a concentration of 30 wt % (a) and 35 wt % (b) in HFIP with low conductivity (<0.1 μS/cm) and of those which were electrospun at a concentration of 25 wt % (c), 30 wt % (d), and 35 wt % (e) in HFIP with high conductivity (10 μS/cm).

Figure 5

(a) Live/dead staining of hDFs and MeT-5A cells on electrospun NIPU-D mats after 7 days of static cell culture. (b) SEM images of hDFs and MeT-5A cells on electrospun NIPU-D mats after 24 h of static cell culture. NC: glass, non-adh. PC: Parafilm. Representative images from three independent experiments (n = 3).