Hybrid engineered dental composites by multiscale reinforcements with chitosan-integrated halloysite nanotubes and S-glass fibers

Novel combinations of mechanical and biological properties are required when developing new polymer-based restorative dental composites. This study reports a promising strategy to develop preventive and restorative dental materials by synthesizing multifunctional dental composites reinforced with chitosan integrated halloysite nanotubes (CHI-HNTs). An enhanced dispersion capability of CHI-HNTs in the urethane-dimethacrylate/triethyleneglycol-dimethacrylate based dental composite is obtained by a sonication-supported chitosan integrating process, resulting in increased mechanical properties such as flexural strength, modulus, and breaking energy of the composites (2 wt% CHI-HNTs, 45 wt% glass particle, 5 wt% glass fiber) up to 8.1%, 17.2%, and 9.8% compared to control composites without CHI-HNT. Microscopic fractography of the fracture surface reveals that highly dispersed CHI-HNTs contribute to the increased mechanical strength of the composites. This is achieved via a dispersion-strengthening mechanism such as nanotube pinning and bridging/pull-out reinforcements. The highly dispersed CHI-HNTs in the composites also have antibacterial capability against Streptococcus mutans. With 2 wt% of CHI-HNTs in the composites, the viability of S. mutans biofilm decreases by approximately 39%. The positively charged amine groups (-NH₃⁺) of chitosan are involved in improving the dispersion effect of HNTs and antibacterial activity of the CHI-HNTs reinforced dental composites. These findings open the route for developing advanced dental composites and engineered biomaterials with well-controlled HNTs dispersion.