Polyetheretherketone and titanium surface treatments to modify roughness and wettability – Improvement of bioactivity and antibacterial properties

Among the materials available for implant production, titanium is the most used while polyetheretherketone (PEEK) is emerging thanks to its stability and to the mechanical properties similar to the ones of the bone tissue. Material surface properties like roughness and wettability play a paramount role in cell adhesion, cell proliferation, osteointegration and implant stability. Moreover, the bacterial adhesion to the biomaterial and the biofilm formation depend on surface smoothness and hydrophobicity. In this work, two different treatments, sandblasting and air plasma, were used to increase respectively roughness and wettability of two materials: titanium and PEEK. Their effects were analyzed with profilometry and contact angle measurements. The biological properties of the material surfaces were also investigated in terms of cell adhesion and proliferation of NIH-3T3 cells, MG63 cells and human Dental Pulp Stem Cells. Moreover, the ability of Staphylococcus aureus to adhere and form a viable biofilm on the samples was evaluated. The biological properties of both treatments and both materials were compared with samples of Synthegra® titanium, which underwent laser ablation to obtain a porous micropatterning, characterized by a smooth surface to discourage bacterial adhesion. All cell types used were able to adhere and proliferate on samples of the tested materials. Cell adhesion was higher on sandblasted PEEK samples for both MG63 and NIH-3T3 cell lines, on the contrary, the highest proliferation rate was observed on sandblasted titanium and was only slightly dependent on wettability; hDPSCs were able to proliferate similarly on sandblasted samples of both tested materials. The highest osteoblast differentiation was observed on laser micropatterned titanium samples, but similar effects, even if limited, were also observed on both sandblasted materials and air plasma treated titanium. The lowest bacterial adhesion and biofilm formation was observed on micropatterned titanium samples whereas, the highest biofilm formation was detected on sandblasted PEEK samples, and in particular on samples not treated with air-plasma, which displayed the highest hydrophobicity. The results of this work showed that all the tested materials were able to sustain osteoblast adhesion and promote cell proliferation; moreover, this work highlights the feasible PEEK treatments which allow to obtain surface properties similar to those of titanium. The results here reported, clearly show that cell behavior depends on a complex combination of surface properties like wettability and roughness and material nature, and while a rough surface is optimal for cell adhesion, a smooth and less hydrophilic surface is the best choice to limit bacterial adhesion and biofilm formation.