Influence of microstructure and chemical composition of sputter deposited TiO2 thin films on in vitro bioactivity

The effects of plasma electrolytically oxidized layers containing Sr and Ca on the osteogenic behavior of selective laser melted Ti6Al4V porous implants

Surface biofunctionalization is frequently applied to enhance the functionality and longevity of orthopedic implants. Here, we investigated the osteogenic effects of additively manufactured porous Ti6Al4V implants whose surfaces were biofunctionalized using plasma electrolytic oxidation (PEO) in Ca/P-based electrolytes with or without strontium. Various levels of Sr and Ca were incorporated in the oxide layers by using different current densities and oxidation times. Increasing the current density and oxidation time resulted in thicker titanium oxide layers and enhanced the release of Ca²⁺ and Sr²⁺. Biofunctionalization with strontium resulted in enhanced pore density, a thinner TiO₂ layer, four-fold reduced release of Ca²⁺, and mainly anatase phases as compared to implants biofunctionalized in electrolytes containing solely Ca/P species under otherwise similar conditions. Different current densities and oxidation times significantly increased the osteogenic differentiation of MC3T3-E1 cells on implants biofunctionalized with strontium, when the PEO treatment was performed with a current density of 20 A/dm² for 5 and 10 min as well as for a current density of 40 A/dm² for 5 min. Therefore, addition of Sr in the PEO electrolyte and control of the PEO processing parameters represent a promising way to optimize the surface morphology and osteogenic activity of future porous AM implants.

Sputtered crystalline TiO2 film drives improved surface properties of titanium-based biomedical implants

Different crystalline phases in sputtered TiO₂ films were tailored to determine their surface and electrochemical properties, protein adsorption and apatite layer formation on titanium-based implant material. Deposition conditions of two TiO₂ crystalline phases (anatase and rutile) were established and then grown on commercially pure titanium (cpTi) by magnetron sputtering to obtain the following groups: A-TiO₂ (anatase), M-TiO₂ (anatase and rutile mixture), R-TiO₂ (rutile). Non-treated commercially pure titanium (cpTi) was used as a control. Surfaces characterization included: chemical composition, topography, crystalline phase and surface free energy (SFE). Electrochemical tests were conducted using simulated body fluid (SBF). Albumin adsorption was measured by bicinchoninic acid method. Hydroxyapatite (HA) precipitation was evaluated after 28 days of immersion in SBF. MC3T3-E1 cell adhesion, morphology and spreading onto the experimental surfaces were evaluated by scanning electron microscopy. Sputtering treatment modified cpTi topography by increasing its surface roughness. CpTi and M-TiO₂ groups presented the greatest SFE. In general, TiO₂ films displayed improved electrochemical behavior compared to cpTi, with M-TiO₂ featuring the highest polarization resistance. Rutile phase exhibited a greater influence on decreasing the current density and corrosion rate, while the presence of a bi-phasic polycrystalline condition displayed a more stable passive behavior. M-TiO₂ featured increased albumin adsorption. HA morphology was dependent on the crystalline phase, being more evident in the bi-phasic group. Furthermore, M-TiO₂ displayed normal cell adhesion and morphology. The combination of anatase and rutile structures to generate TiO₂ films is a promising strategy to improve biomedical implants properties including greater corrosion protection, higher protein adsorption, bioactivity and non-cytotoxicity effect.

Drug loading and release of Tobramycin from hydroxyapatite coated fixation pins

This paper evaluates the loading and release properties of Tobramycin incorporated by adsorptive loading from a solution into plasma sprayed and biomimetically coated Hydroxyapatite (HA) fixation pins. The aim of this study is to contribute towards designing a functional implant surface offering local release of the antibiotic agent to prevent post-surgical infections. Cathodic arc deposition is used to coat stainless steel fixation pins with a bioactive, anatase phase dominated, TiO₂ coating onto which a HA layer is grown biomimetically. The loading and release properties are evaluated by studying the subsequent release of Tobramycin using high performance liquid chromatography and correlated to the differences in HA coating microstructure and the physical conditions under loading. The results from these studies show that a dual loading strategy consisting of a solution temperature of 90 °C and a pressure of 6 bar during a loading time of 5 min release a sufficient amount of Tobramycin to guarantee the inhibition of Staphylococcus aureus up to 2 days for plasma sprayed HA coatings and for 8 days for biomimetic coatings. The present study emphasizes the advantages of the nanoporous structure of biomimetically deposited HA over the more dense structure of plasma sprayed HA coatings in terms of antibiotic incorporation and subsequent sustained release and provides a valuable outline for the design of implant surfaces aiming for a fast-loading and controlled, local drug administration.

Photocatalytic inactivation of biofilms on bioactive dental adhesives

Biofilms are the most prevalent mode of microbial life in nature and are 10-1000 times more resistant to antibiotics than planktonic bacteria. Persistent biofilm growth associated at the margin of a dental restoration often leads to secondary caries, which remains a challenge in restorative dentistry. In this work, we present the first in vitro evaluation of on-demand photocatalytic inactivation of biofilm on a novel dental adhesive containing TiO2 nanoparticles. Streptococcus mutans biofilm was cultured on this photocatalytic surface for 16 h before photocatalytic treatment with ultraviolet-A (UV-A) light. UV-A doses ranging from 3 to 43 J/cm(2) were applied to the surface and the resulting viability of biofilms was evaluated with a metabolic activity assay incorporating phenol red that provided a quantitative measure of the reduction in viability due to the photocatalytic treatments. We show that an UV-A irradiation dose of 8.4 J/cm(2) leads to one order of magnitude reduction in the number of biofilm bacteria on the surface of the dental adhesives while as much as 5-6 orders of magnitude reduction in the corresponding number can be achieved with a dose of 43 J/cm(2). This material maintains its functional properties as an adhesive in restorative dentistry while offering the possibility of a novel dental procedure in the treatment or prevention of bacterial infections via on-demand UV-A irradiation. Similar materials could be developed for the treatment of additional indications such as peri-implantits.

Improvement of drug elution in thin mineralized collagen coatings with PLGA-PEG-PLGA micelles

A mineralized collagen (MC) coating on metallic implants has shown great potential as orthopedic material due to high biological responses. However, their drug delivery capacity remains unsatisfactory since a serious burst release may occur and long-term release is hard to be achieved. Aiming to improve the drug-eluting capability, we incorporated drug-loaded PLGA-PEG-PLGA (PPP) micelles into the thin coating. The in vitro release profiles showed that the burst release in the initial 8 h of the modified coating decreased from 81% to 58% compared to MC coating alone; meanwhile, the release duration was prolonged from 3 days to 1 week. Additionally, the release kinetics of vancomycin hydrochloride (VH, the model drug) could be adjusted by changing the size and concentration of PPP micelles. Interestingly, less initial release of VH caused by micelle immobilization did not affect the antibacterial activity in the early stage of implantation according to the antimicrobial test. The cytocompatibility assay demonstrated that the VH-loaded PPP micelles did not have negative effect on the bioactivity of coating which greatly enhanced cell activity compared to bare Ti substrates. Thus, the MC coatings with PPP micelles could be an effective implant route for bone repair.

Photocatalytic and antimicrobial properties of surgical implant coatings of titanium dioxide deposited though cathodic arc evaporation

Nanostructured crystalline titanium dioxide coatings deposited by cathodic arc evaporated on titanium grade five medical implant substrates were demonstrated to exhibit UV-induced photocatalytic activity that can be utilized to provide bactericidal effects against Staphylococcus epidermidis. The photocatalytic activity of the coatings was confirmed via degradation of Rhodamine B under UV illumination. A 90 % reduction of viable bacteria was achieved in a clinically suitable time of only 2 min with a UV dose of 2.4 J delivered at 365 nm. These results are encouraging for the development of antimicrobial surfaces in orthopedics and dentistry in order to prevent or treat post-surgical infections.

PURPOSE OF WORK

To assess the possibility of employing photocatalysis for elimination of S. epidermidis, known to cause medical device related infections, under short enough times to be clinically useful on an implant surface produced with a technique that is suitable for mass production.