Modulating the biological response in vitro through hydrofluoric acid surface etching of ceria-stabilized zirconia/alumina/strontium hexa-aluminate composites

Ceria-stabilized Zirconia/Alumina/Strontium hexa-Aluminate composites are promising candidates as metal-free dental implants. Isostatic pressed and sintered Ce₁₁ZA₈Sr₈ composites were prepared as regular disks starting from powders with composition 84 vol% ceria-stabilized zirconia (at 11 mol% ceria), 8 vol% α-Al₂O₃ and 8 vol% SrAl₁₂O₁₉ and they were either exposed to increasing etching treatment time (1 h, 2 h, 3 h) with hydrofluoric acid, or kept as a control, to determine the biological response elicited in human mesenchymal stem/stromal cells (ASCs), oral epithelial cells (SGs), and oral primary fibroblasts (PFs) cultured in vitro. FESEM microscopy and surface roughness assessment evidenced qualitatively and quantitatively an increasing roughness according to the etching time. Surface free energy was increased on roughened surfaces. The three cell types responded differently in terms of immediate adhesion (20 min), cell morphology (24 h), and proliferation up to 3 days. ASCs grew slowly, while SGs proliferated increasingly on all the surfaces, and PFs grew significantly more on the non-etched surface than on the etched surfaces (second and third day). ASCs were osteodifferentiated up to 4 weeks, studying gene expression and osteocalcin release. The interface characteristics of Ce₁₁ZA₈Sr₈ composites could be exploited to modulate cell response in vitro, with promising results for future in vivo application.