The Role of Surface Topography in Bacterial Adhesion to Amorphous TiO₂-Coated PMMA

Background/Objectives: Polymethyl methacrylate (PMMA) is widely used in medical and dental applications because of its favorable mechanical properties and ease of processing. However, its clinical performance is limited by low surface hardness, hydrophobicity, and susceptibility to microbial colonization and biofilm formation. This study aimed to investigate the effects of amorphous titanium dioxide (TiO₂) nanolayers deposited by atomic layer deposition (ALD) on the surface morphology and antibacterial properties of PMMA-based materials. Methods: Amorphous TiO₂ coatings were deposited on bone cement PMMA and dental PMMA substrates using ALD with TiCl₄ and H₂O precursors at 80 °C. The low deposition temperature enabled the conformal of thermally sensitive polymer substrates. Surface characterization was performed using atomic force microscopy (AFM) and scanning electron microscopy (SEM) to evaluate coating morphology and nanoscale topography. Antibacterial activity was assessed against S. aureus and P. aeruginosa through planktonic growth and biofilm formation assays, with additional evaluation of ultraviolet (UV) activation and surface polishing. Results: AFM analysis revealed that amorphous TiO₂ coating on standardly laboratory practice-polished PMMA increased the arithmetical mean roughness (Ra) from 1.82 nm to 14.60 nm, and maximum height (Rmax) from 36.20 nm to 298.00 nm. Polishing before coating significantly increased surface roughness and height variation, resulting in complex micro- and nanotopography. Microbiological analyses demonstrated variable antibacterial effects depending on bacterial species and surface characteristics. Comparison of planktonic growth, biofilm formation and OD590 ratio showed that amorphous TiO2 coating on polished PMMA reduced biofilm formation and planktonic growth in P. aeruginosa with a decreased OD ratio, while S. aureus biofilm formation was reduced. S. aureus had a consistently higher OD590 than P. aeruginosa. UV treatment alone did not produce consistent antibacterial enhancement. Conclusions: The study findings suggest that the surface topography had a greater role than UV treatment in determining bacterial adhesion. Surface roughness was strongly associated with S. aureus adhesion., whereas P. aeruginosa showed minimal response to the tested surface modifications. These findings suggest that TiO₂ coating after standard polishing alone may not provide consistent antibacterial activity under the tested conditions and point to the importance of nanoscale surface design in developing antimicrobial polymer biomaterials.