Evaluation of the Effect of Nanocoating on Mechanical and Biofilm Formation in Thermoplastic Polyurethane Aligner Sheets.

Objective: The objective of this research is to determine whether the thermoplastic polyurethane (TPU) coated with carboxymethylcellulose chitosan has better mechanical and antibacterial action (anti-Streptococcus mutans) when utilized in intraoral simulations with synthetic saliva.

Materials and methods: The TPU sheets (n = 45) were divided into three groups. Control (n = 15) consists of as-received TPU sheets. Test 1 consists of TPU sheets coated with carboxymethyl cellulose (CMC) chitosan (CHI) (n = 15). Test 2 consists of thermoformed nano-coated TPU (n = 15). For the polyurethane sheets, CHI-CMC sheets, and thermoformed CHI-CMC sheets, scanning electron microscopy (SEM) and three-point flexural tests were conducted and assessed. The materials testing software was used to calculate the elastic modulus and tensile strength. To study the bacterial accumulation, the cut circles of the TPU aligner were placed in centrifuge tubes with 2.5 mL of bacterial suspension at a concentration of 104 or 105 CFU/mL. SEM was done to assess the presence of cell growth in all three groups.

Results: According to SEM analyses of bacterial buildup, the coated TPU had minimal biofilms compared to the bare TPUs numerous biofilms. The effect of aging on coating thickness reveals that the thickness of thermoformed coated TPU films dramatically decreased over time, while the thickness of coated TPU films was maintained. When TPU is coated with CMC/CHI, the elastic modulus and tensile strength were observed to improve.

Conclusion: The development of a super-hydrophilic coating by the CHI CMC coating on TPU sheets improved the coating's biocompatibility while also changing the shape of the multilayer film to prevent bacterial adhesion. The effect on the improvement in the mechanical properties diminished after the material underwent a thermoforming process. It is therefore suggested that the nanofilm be used in therapeutic applications following the thermoforming process.