Carboxymethylation of ulvan and chitosan and their use as polymeric components of bone cements

Ulvan, extracted from the green algae Ulva lactuca, and chitosan, extracted from Loligo forbesis squid-pen, were carboxymethylated, yielding polysaccharides with an average degree of substitution of similar to 98% (carboxymethyl ulvan, CMU) and similar to 87% (carboxymethyl chitosan, N,O-CMC). The carboxymethylation was confirmed by Fourier transform infrared spectroscopy and quantified by conductimetric titration and H-1 nuclear magnetic resonance. The average molecular weight increased with the carboxymethylation (chitosan, M-n 145 -> 296 kDa and M-w, 227 -> 416 kDa; ulvan, M-n, 139 -> 261 kDa and M-w 368 -> 640 kDa), indicating successful chemical modifications. Mixtures of the modified polysaccharides were tested in the formulation of polyacrylic acid-free glass-ionomer bone cements. Mechanical and in vitro bioactivity tests indicate that the inclusion of CMU in the cement formulation, i.e. 0.50:0.50 N,O-CMC:CMU, enhances its mechanical performance (compressive strength 52.4 +/- 8.0 MPa and modulus 23 +/- 0.3 GPa), generates non-cytotoxic cements and induces the diffusion of Ca and/or P-based moieties from the surface to the bulk of the cements. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.