Creating Ultrastrong and Osteogenic Chitin Nanocomposite Hydrogels via Chitin Whiskers with Different Surface Chemistries

The commonly used chitin whiskers (CHWs) prepared by the acid hydrolysis method are easy to agglomerate in an alkaline matrix, which limits their applications in many aspects. Herein, maleation chitin whiskers (mCHWs) with lots of −COOH groups were designed, which can stably exist and homogeneously disperse in the alkaline chitin matrix due to their relatively strong electronegativities. Subsequently, the CHWs and mCHWs were utilized as reinforcing fillers to enhance the mechanical strength of the chitin hydrogel. As expected, the CHWs played an extremely limited role in reinforcing the chitin hydrogel. Conversely, due to good dispersibility and strong interfacial interaction, the mCHWs exhibited a significantly superior enhancement effect on the chitin hydrogel. Moreover, the tensile strength and modulus of the as-prepared mCHW/chitin composite hydrogels were strongly dependent on the content of mCHWs, and the highest values of 5.8 ± 0.2 and 5.2 ± 0.6 MPa were obtained with 3 wt % mCHW content, which are higher than those of polysaccharide hydrogels reported in the most literature. Importantly, both CHWs and mCHWs can facilitate the adhesion, proliferation, and differentiation of mouse embryo osteoblast precursor (MC3T3-E1) cells. Moreover, the mCHWs also play these promoting effects in a content-dependent manner. Interestingly, CHWs and mCHWs mainly contain −NH₂ and −COOH groups, respectively; as a result, surface protein adsorption and calcium-phosphate mineralization are different. But there are very small differences in cell adhesion, proliferation, and differentiation between the corresponding 3%CHW/chitin and 3%mCHW/chitin composite hydrogels. This work provides a promising strategy to construct a polysaccharide nanocomposite hydrogel with robust mechanical strength and osteogenesis for potential application as an artificial periosteum.