Molecular Biocompatibility Assessment of PETG Aligners After Processing by Laser or Milling

Polyethylene terephthalate glycol-modified (PETG) is a transparent, stable copolymer commonly used in biomedical devices such as surgical guides, clear aligners, and anatomical models. Its biocompatibility must be assessed not only for cytotoxicity, but also for subtle molecular and immunological responses, especially when in contact with mucosal or hormone-sensitive tissues. This study evaluated the biological safety of PETG processed via CNC milling and CO₂ laser cutting, two methods that preserve bulk chemistry but may alter surface properties. PETG diskettes were analyzed by FT-IR, ¹H-NMR, and GC-MS to confirm chemical integrity and absence of degradation products. Biocompatibility was tested using MCF-7 epithelial cells and THP-1 monocytes. Cell viability remained above 90% over seven days. Inflammatory (COX-2, TNFα, IL-8, IL-1α, IL-4, IL-10, IFNγ) and hormone-related (ERα, ERβ) gene expression was analyzed by qRT-PCR. Gene profiling revealed only modest, non-significant changes: COX-2 was upregulated 1.8-fold after laser processing, and ERα increased 1.6-fold following milling-both below thresholds considered biologically active. These findings indicate that mechanical surface treatments induce minimal bioactivity, with no meaningful immune or hormonal stimulation. PETG remains functionally inert under the tested conditions, supporting its continued safe use in intraoral and hormone-sensitive biomedical applications.