A new concept of bio-multifunctional nanotubular surfaces for dental implants: tribocorrosion resistant, antibacterial and osteogenic

Dental implant market is continuously growing over the past few decades due to the constant increase in life expectancy and higher concerns on oral hygiene and aesthetics. Titanium-based materials are the most widely used in dental implants due to their superior biocompatibility, mechanical properties, and excellent corrosion resistance. However, despite the high overall success rate of dental implants, a significant number of failures still occur.

Implant failures in dentistry may be ascribed essentially to three main causes, namely the lack of an adequate implant-bone integration, microbial infection, and corrosion/tribocorrosion processes. The modification of Ti surface features has been a strategy currently adopted in the attempt to overcome these complications. Ideally, the implant should be able to display concomitantly two contradictory properties: the enhancement of human cell adhesion and the inhibition of the adhesion of undesirable microorganisms. Additionally, the implant surface should be also tailored with the ability to withstand the combined actions of corrosion and wear (tribocorrosion), at which they are exposed to in the human body. Nanotechnology is an emerging area in the field of dentistry, and in particular, nanotubular TiO2 surfaces have been widely recognized as promising candidates to improve the performance of dental implants. However, the construction of effective nanotubular systems based on an integrated approach addressin, simultaneously, the three main causes of failure, is still missing.

This thesis aims the synthesis of multifunctional TiO2 nanotubes (NTs) in Ti surfaces, tailored to exhibit simultaneously tribo-electrochemical resistance, antibacterial activity, and adequate osseointegration ability. To achieve the main aim, TiO2 NTs were synthesized by anodization, and functionalized with bone-constituting elements such as calcium, phosphorous, and zinc, through a novel methodology based on reverse polarization anodization processes. After bio-functionalization, Ti surfaces decorated with TiO2 NTs displayed an outstanding tribo-electrochemical behavior, the capacity to impair bacterial viability, and the ability to improve human cell responses. These multiple functions were ascribed to the morphological, topographical, and physicochemical features of bio-functionalized TiO2 NTs, as well as to their mechanical properties and adhesion strength to Ti.

The outcomes of this work remarkably show that significant improvements have been achieved. By means of a simple approach, key functionalities of conventional TiO2 NTs were improved, which are expected to have a major clinical impact in dental implant therapies.