Enhanced Biological Performance of Fractal Geometry Design on Titanium for Dental Implant Application: An In Vitro Study

Abstract

This study evaluates the biological performance of titanium surfaces featuring fractal geometry designs—Koch snowflake (KS) and Sierpinski pentagon (SP)—fabricated by selective laser melting (SLM). Fractal titanium specimens with increasing hierarchical iterations were digitally designed and manufactured. Surface characteristics were comprehensively analyzed. Rat bone marrow mesenchymal stem cells (rBMMSCs) were cultured on fractal and smooth titanium surfaces (control) to assess cytotoxicity, adhesion, proliferation, and osteogenic differentiation via CCK-8, live/dead staining, fluorescence imaging, DNA quantification, alkaline phosphatase activity, Alizarin Red staining, and gene expression analysis (BMP2, RUNX2, OCN, COL-1). Mechanistic pathways involving Piezo1 and ATF4 were investigated using qRT-PCR and Western blot. Fractal surfaces exhibited significantly increased hierarchical roughness and superior hydrophilicity compared to controls. All specimens demonstrated excellent cytocompatibility. Fractal designs significantly enhanced cell adhesion, proliferation, and osteogenic activity from Day 7 onward, with higher hierarchical iterations showing superior performance. ALP activity, mineralization, and osteogenic marker expression were significantly upregulated on fractal surfaces. Importantly, multiple regression analysis revealed that fractal dimension independently contributed to cell proliferation (β = 0.38, p = 0.04) beyond the effect of roughness alone, and higher-order fractal iterations enhanced ALP activity and mineralization by 60–80% compared to smooth controls. Mechanistically, fractal geometries activated Piezo1 mechanosensitive channels and upregulated ATF4 expression. In general, fractal microarchitectures exhibit hierarchical features that enhance surface bioactivity through combined physical and biochemical cues, activating mechanotransduction pathways to promote osteoblast differentiation. Furthermore, fractal-designed titanium implants fabricated via SLM represent a promising strategy for improving osseointegration and long-term stability in dental applications.