Cytocompatible and Anti-bacterial Adhesion Nanotextured Titanium Oxide Layer on Titanium Surfaces for Dental and Orthopedic Implants

Abstract

It is widely recognized that surface nanotextures applied on a biomaterial can affect wettability, protein absorption and cellular and/or bacterial adhesion; accordingly, they are nowadays of great interest to promote fast osseointegration and to maintain physiological healing around biomedical implants. In order to be suitable for clinical applications, surface nanotextures must be not only safe and effective, but also, they should be produced through industrial processes scalable to real devices with sustainable processes and costs: this is often a barrier to the market entry. Based on these premises, a chemical surface treatment designed for titanium and its alloys able to produce an oxide layer with a peculiar sponge like nanotexture coupled with high density of hydroxyl group is here presented. The modified Ti-based surfaces previously showed inorganic bioactivity intended as the ability to induce apatite precipitation in simulated body fluid. Physicochemical properties and morphology of the obtained layers have been characterized by means of FESEM, XPS, and Zeta-potential. Biological response to osteoblasts progenitors and bacteria has been tested. The here proposed nanotextured surfaces successfully supported osteoblasts progenitors' adhesion, proliferation and extracellular matrix deposition thus demonstrating good biocompatibility. Moreover, the nanotexture was able to significantly reduce bacteria surface colonization when the orthopedic and the periodontal pathogens Staphylococcus aureus and Aggregatibacter actinomycetemcomitans strains were applied for a short time. Finally, the applicability of the proposed surface treatment to real biomedical devices (a 3D acetabular cup, a dental screw and a micro-sphered laryngeal implant) has been here demonstrated.

Keywords: bacterial adhesion; bone contact; nanotexture; surface modification; titanium.

Figure 1

FESEM images revealed the presence of the nanotextured oxide layer obtained after the chemical treatment on the mirror polished flat Ti6Al4V discs (A,B). Surface roughness obtained by AFM measurements (C–E) confirmed that the surface texture is in the nanoscale (10–100 nm depending on the measurement area due to the complex roughness at the nano- and micro-scale of the surface).

Figure 2

Schematic representation of the multi-scale surface topography.

Figure 3

Macroscopic appearance of the untreated cup (a); FESEM images of the untreated (b–d) and chemically treated (e–h) samples at different magnifications. In the treated specimens the sponge-like nanotexture resulted as homogeneously distributed onto all the cup surface.

Figure 4

Macroscopic appearance (A), and FESEM observations (B–D) of a treated dental screw. Once again, the sponge-like nanotexture introduced by the chemical treatment was evident and homogeneous onto the screw surface.

Figure 5

FESEM observations of treated sintered titanium micro-spheres. The original spherical shape was maintained after the chemical treatment (A,B) that was effective in introducing the nanotextured layer (C,D) as previously observed for cup and screw.

Figure 6

Biofilm adhesion. The surface nanotexture (Ti6Al4V—CT) was able to significantly reduce bacteria metabolism of S. aureus (A, p < 0.05, indicated by^*) and A. actinomycetemcomitans (C, p < 0.05, indicated by^*) in comparison with the smooth controls (Ti6Al4V—MP). This reduction was probably due to the lowering number of adhered bacteria as demonstrated by the reduction of viable colonies count (CFU) of S. aureus (B, p < 0.05, indicated by ^*) and A. actinomycetemcomitans (D, p > 0.05), respectively. Bars represent means and standard deviations. SEM images (E, bar scale = 2 μm, magnification = 10,000x) confirmed that bacteria were successfully detached from specimen's surface and that the detected differences were due to surfaces' properties.

Figure 7

Cytocompatibility evaluation. No differences were noticed in terms of cells viability between the untreated control (Ti6Al4V—MP) and the treated specimens (Ti6Al4V—CT) after 1 (A), 2 (B), and 3 (C) days of direct cultivation; result were comparable and not significant (p > 0.05) as summarized in (D). Moreover, cells were able to deposit matrix onto both surfaces as demonstrated by the evident collagen I (COL 1) accumulation after 3 days (E). Bars represent means and standard deviations.