Hybrid composite cellulose nanocrystal, hydroxyapatite, and chitosan material with controlled hydrophilic/hydrophobic properties as a remineralizable dental material

It is expected that cellulose nanocrystals (CNCs) will be utilized for biomedical applications, especially hard tissue engineering, because of their low toxicity to the human body and exceptional physicochemical properties. In our group, CNC@HAp, composed of hydroxyapatite (HAp), a component of enamel, and CNC, with high mechanical strength and biocompatibility, was developed as a biocompatible dental restorative material. However, due to the high hydrophilicity of CNC@HAp, it cannot be used in the oral cavity and has limited the restorative function of HAp, called remineralization. In this work, we developed CNC@HAp/chitosan (CNC@HAp/CS) materials as novel dental biomaterials by mixing the organic‒inorganic CNC@HAp particles with a CS matrix. We confirmed that CNC@HAp and CS were successfully composited using FT-IR, XRD, and SEM–EDX. The hydrophobicity of the prepared samples was drastically improved and consequently protected the sample from deterioration in water. This was supported by the contact angle measurements of CNC@HAp (32.7°) and CNC@HAp/CS (72.1°). SEM–EDX analysis of the sample before and after the immersion of CNC@HAp/CS in artificial saliva confirmed that the HAp layer had formed by remineralization after immersion. Furthermore, the TGA measurements implied that the amount of HAp increased with increasing immersion time in artificial saliva. Therefore, it was confirmed that CNC@HAp/CS promoted remineralization. Based on these results, CNC@HAp/CS can be applied as a dental material with self-healing properties due to its ability to mediate remineralization. Graphical abstract