Mechanical properties and degradation studies of poly(mannitol sebacate)/cellulose nanocrystals nanocomposites

Polyesters based on polyols and sebacic acid, known as poly(polyol sebacate) s (PPS) are good candidates to develop degradable materials, due to their combination of flexibility and degradability, which are both useful properties in the context of soft-tissue engineering (Z. Sun, C. Chen, M. Sun, C. Ai, X. Lu, Y. Zheng, B. Yang and D. Dong, Biomaterials, 2009, 30, 5209, C. Sundback, J. Shyu, Y. Wang, W. Faquin, R. Langer, J. Vacanti and T. Hadlock, Biomaterials, 2005, 26, 5454, D. Motlagh, J. Yang, K. Lui, A. Webb and G. Ameer, Biomaterials, 2006, 27, 4315, A. Mahdavi, L. Ferreira, C. Sundback, J. W. Nichol, E. P. Chan, D. J. D. Carter, C. J. Bettinger, S. Patanavanich, L. Chignozha, E. Ben-Joseph, A. Galakatos, H. Pryor, I. Pomerantseva, P. T. Masiakos, W. Faquin, A. Zumbuehl, S. Hong, J. Borenstein, J. Vacanti, R. Langer and J. M. Karp, Proc. Natl. Acad. Sci. U. S. A., 2008, 105, 2307). However, PPS generally display poor mechanical properties, in particular a low modulus, that limit the true potential of these materials in the biomedical field. Here, we introduce an approach to obtain nanocomposites based on poly(mannitol sebacate) (PMS) matrices reinforced with cellulose nanocrystals (CNCs) in order to improve the application range of these materials. Different strategies were used based on varying the feed ratios between mannitol : sebacic acid (1 : 1 and 1 : 2), crosslinking conditions and CNCs content, resulting in different degrees of crosslinking and, therefore, mechanical and degradation behavior. All of the developed nanocomposites displayed the expected mass loss during the degradation studies in simulated body fluid (SBF) similar to the neat matrix, however, doubling the sebacic acid feed ratio or extending the curing temperature and time, resulted in higher mechanical properties, structural integrity, and shape stability during a degradation time lessening mass loss rate. Changing mannitol : sebacic acid reaction ratios from 1 : 1 to 1 : 2 and for low crosslinking degree neat samples, the Young's modulus increases four-fold, while mass loss after 150 days of incubation is reduced by half. The Young's modulus range obtained with this process covers the range of human elastic soft tissues to tough tissues (0.7-200 MPa).