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Comparative evaluation of physicochemical, mechanical, and biological properties of biodegradable poly(lactic acid)
Mayuri Parappullil Vellayappan1, Sean Johnson2, Taylor Stewart3
1Division of Biomaterials, Department of Restorative Sciences, School of Dentistry, University of Minnesota, Minneapolis, MN, USA; Minnesota Dental Research Center for Biomaterials and Biomechanics, School of Dentistry, University of Minnesota, Minneapolis, MN, USA; Department of Materials Engineering, Indian Institute of Science, Bengaluru, Karnataka, India.
Objectives:
This study aimed to evaluate bio-based, biodegradable polylactic acid (PLA) as a sustainable material for clear aligners by comparing its physicochemical, mechanical, and biological properties with commercial aligner materials (Essix Ace, Essix C+, Zendura FLX, and Zendura).
Methods:
PLA and commercial materials, both neat and aged in artificial saliva for up to 14 days, were examined as sheets. Thermal properties were measured using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Mechanical and optical properties were evaluated using a universal testing machine (UTM) and UV-visible spectrophotometry. Degradation behavior was assessed via weight and average molar mass changes, and surface morphology via scanning electron microscopy (SEM). Cytotoxicity was tested using human gingival fibroblasts with an MTT assay.
Results:
PLA showed a glass transition temperature of 55.4 °C, melting temperature of 152.1°C, and degradation onset temperature of 362.9 °C, comparable to commercial aligner materials. Its tensile strength and yield stress were similar to those of commercial materials, indicating adequate strength. However, PLA exhibited lower elongation at break and higher Young's modulus, reflecting higher brittleness and stiffness. Aging caused negligible water absorption, minimal weight loss, and minor thermal property change. Mechanical properties remained stable upon aging. Aged PLA was transparent when wet but became hazy when dry, which occurs reversibly. Extracts from PLA were non-cytotoxic, maintaining 90% cell viability in average.
Significance:
PLA demonstrated properties comparable to commercial aligner materials, with the exception of increased stiffness and brittleness. Its stability during aging and favorable biocompatibility supports its potential as a sustainable alternative for clear aligner applications.
