Influence of Charge and Heat on the Mechanical Properties of Scaffolds from Ionic Complexation of Chitosan and Carboxymethyl Cellulose

Funding Information: The authors acknowledge the financial support for this study received from the Slovenian Research Agency (G. no.: P2-0118 and J4-1764) and the Austrian Research Promotion Agency (FFG no. 846065). They also acknowledge Dr. Silvo Hribernik, Dr. Matej Bračič, Dr. Irena Ban, and Sabina Markuš (University of Maribor, Slovenia) for their support regarding the potentiometric charge titration, scanning electron microscopy, and thermogravimetic analysis, as well as Prof. Dr. Cornelia Kasper (University of Natural Resources and Life Sciences, Austria) for her support regarding the biocompatibility testing. Dr. Brigitte Bitschnau from Graz University of Technology, Austria, is also acknowledged for her support regarding XRD measurements. Publisher Copyright: © 2021 The Authors. Published by American Chemical Society. As one of the most abundant, multifunctional biological polymers, polysaccharides are considered promising materials to prepare tissue engineering scaffolds. When properly designed, wetted porous scaffolds can have biomechanics similar to living tissue and provide suitable fluid transport, both of which are key features for in vitro and in vivo tissue growth. They can further mimic the components and function of glycosaminoglycans found in the extracellular matrix of tissues. In this study, we investigate scaffolds formed by charge complexation between anionic carboxymethyl cellulose and cationic protonated chitosan under well-controlled conditions. Freeze-drying and dehydrothermal heat treatment were then used to obtain porous materials with exceptional, unprecendent mechanical properties and dimensional long-term stability in cell growth media. We investigated how complexation conditions, charge ratio, and heat treatment significantly influence the resulting fluid uptake and biomechanics. Surprisingly, materials with high compressive strength, high elastic modulus, and significant shape recovery are obtained under certain conditions. We address this mostly to a balanced charge ratio and the formation of covalent amide bonds between the polymers without the use of additional cross-linkers. The scaffolds promoted clustered cell adhesion and showed no cytotoxic effects as assessed by cell viability assay and live/dead staining with human adipose tissue-derived mesenchymal stem cells. We suggest that similar scaffolds or biomaterials comprising other polysaccharides have a large potential for cartilage tissue engineering and that elucidating the reason for the observed peculiar biomechanics can stimulate further research.