Mechanical, biological, and characterization of nanoparticle-reinforced polyurethane for clear orthodontic aligners

Abstract

In the present work, the performance of polyurethane is enhanced through reinforcement with fluorapatite nanoparticles to develop a nanocomposite material suitable for advanced orthodontic applications. Fluorapatite nanoparticles with an average size of 53.5 nm are incorporated into the PU matrix at four different weight fractions (0.1, 0.2, 0.3, and 0.4 wt.%). The structural characteristics and interfacial interactions are examined using Fourier Transform Infrared Spectroscopy (FTIR), while the dispersion state of the nanoparticles is evaluated by Scanning Electron Microscopy (SEM). The results demonstrated that low nanoparticle loadings led to a uniform distribution within the polymer matrix, effectively minimizing agglomeration. Mechanical testing showed a marked improvement in hardness, increasing from 72 Shore D for pristine PU to 85 Shore D after nanoparticle reinforcement. Moreover, tensile strength exhibited a steady increase from 45 MPa in neat PU to 93 MPa at the highest nanoparticle concentration. These improvements are associated with enhanced interfacial bonding, reduced polymer chain mobility, and efficient load transfer across the nanocomposite structure. Biological performance assessment revealed an increase in antibacterial activity with increasing nanoparticle content, while all nanocomposite samples maintained acceptable biocompatibility. The findings confirm that fluorapatite-reinforced polyurethane nanocomposites possess improved mechanical strength and biological functionality, making them a promising material for next-generation clear dental aligners.