Biodegradable Polyurethanes for Tissue Engineering: Influence of L-Lactide Content on Degradation and Mechanical Properties

Abstract

The influence of L-lactide content (between 15% and 43%) on the degradation of biodegradable polyurethanes (PUs) for tissue engineering was systematically addressed in this study. An ideal tissue scaffold should exhibit a mechanical response and degradability appropriate for the host tissue. To achieve it, polyols containing ε-caprolactone and L-lactide moieties were used, with the random distribution of lactide units disrupting the regularity, and hence the crystallinity, of poly(caprolactone) segments, facilitating their degradation. The biodegradable PUs were synthesised using these copolymers as soft segments and were characterised through various physicochemical techniques, including bioassays and water absorption measurements. It was determined that mechanical behaviour and water absorption depended significantly on molecular weight, L-lactide content in the soft segment, and the crystallinity of the hard segment. Additionally, two types of chain extenders were also evaluated: hydrolysable and non-hydrolysable. PUs based on hydrolysable chain extenders achieved higher molecular weights and exhibited better mechanical performance than their non-hydrolysable counterparts. To assess the cytocompatibility of these materials, an endothelial model was used, involving metabolic activity and DNA content analysis. The results demonstrated good cell adhesion and the absence of toxicity, confirming the viability of cell growth on the surfaces of these biodegradable PUs. The PUs developed in this study exhibited a low initial modulus and adjustable mechanical properties, highlighting their potential application in tissue engineering as biodegradable and biocompatible biomedical materials.

Keywords: L-lactide content; biodegradability; cell adhesion; hydrolysable chain extender; thermoplastic polyurethane.

Scheme 1

Synthetic route for N,N′-ethylene-bis(6-hydroxycaproamide).

Scheme 2

Synthetic route for the preparation of biodegradable poly(ester-urethane)s.

Figure 1

¹H-NMR spectrum of poly(ester-urethane) PU8015-HB-35 in deuterated dimethylsulfoxide (DMSO-d6). The residual peak of the deuterated solvent is indicated by an asterisk (*).

Figure 2

Second heating DSC thermograms of two PU samples synthetized with different chain extender.

Figure 3

Weight variation in weight with time after the immersion in PBS for polyurethanes based on CAPA^®-8015, CAPA^®-8021, CAPA^®-8025, and CAPA^®-8038 polyols and 35% HDI-EDA-2CL as HS.

Figure 4

Weight variation with time after the immersion in PBS of polyurethanes based on CAPA^®-8015, CAPA^®-8038 polyols, HDI, and EDA-2CL or BD as HS.

Figure 5

SEM micrographs of scaffold PU8038-HB-50 (a) ×4000 (b) ×8000 (c) ×15,000.

Figure 6

Up images of endothelial C166-GFP cell cultures after 24 h, 48 h, and 192 h on PU8038-HB-50 at 15× Down. Metabolic activity of cell culture at 192 h over samples (Alamar Blue). Significant differences stand for * (p ≤ 0.05).