Photofunctionalization of anodized titanium surfaces using UVA or UVC light and its effects against Streptococcus sanguinis

Silver-Doped Titanium Oxide Layers for Improved Photocatalytic Activity and Antibacterial Properties of Titanium Implants

Titanium has a long history of clinical use, but the naturally forming oxide is not ideal for bacterial resistance. Anodization processes can modify the crystallinity, surface topography, and surface chemistry of titanium oxides. Anatase, rutile, and mixed phase oxides are known to exhibit photocatalytic activity (PCA)-driven bacterial resistance under UVA irradiation. Silver additions are reported to enhance PCA and reduce bacterial attachment. This study investigated the effects of silver-doping additions to three established anodization processes. Silver doping showed no significant influence on oxide crystallinity, surface topography, or surface wettability. Oxides from a sulfuric acid anodization process exhibited significantly enhanced PCA after silver doping, but silver-doped oxides produced from phosphoric-acid-containing electrolytes did not. Staphylococcus aureus attachment was also assessed under dark and UVA-irradiated conditions on each oxide. Each oxide exhibited a photocatalytic antimicrobial effect as indicated by significantly decreased bacterial attachment under UVA irradiation compared to dark conditions. However, only the phosphorus-doped mixed anatase and rutile phase oxide exhibited an additional significant reduction in bacteria attachment under UVA irradiation as a result of silver doping. The antimicrobial success of this oxide was attributed to the combination of the mixed phase oxide and higher silver-doping uptake levels.

Bacterial Adhesion Strength on Titanium Surfaces Quantified by Atomic Force Microscopy: A Systematic Review

Few studies have been able to elucidate the correlation of factors determining the strength of interaction between bacterial cells and substrate at the molecular level. The aim was to answer the following question: What biophysical factors should be considered when analyzing the bacterial adhesion strength on titanium surfaces and its alloys for implants quantified by atomic force microscopy? This review followed PRISMA. The search strategy was applied in four databases. The selection process was carried out in two stages. The risk of bias was analyzed. One thousand four hundred sixty-three articles were found. After removing the duplicates, 1126 were screened by title and abstract, of which 57 were selected for full reading and 5 were included; 3 had a low risk of bias and 2 moderated risks of bias. (1) The current literature shows the preference of bacteria to adhere to surfaces of the same hydrophilicity. However, this fact was contradicted by this systematic review, which demonstrated that hydrophobic bacteria developed hydrogen bonds and adhered to hydrophilic surfaces; (2) the application of surface treatments that induce the reduction of areas favorable for bacterial adhesion interfere more in the formation of biofilm than surface roughness; and (3) bacterial colonization should be evaluated in time-dependent studies as they develop adaptation mechanisms, related to time, which are obscure in this review.

Antibacterial and biocompatible polyaniline-doped titanium oxide layers

Titanium anodization has been shown to produce crystalline oxides exhibiting photocatalytic reactions that form reactive oxygen species (ROS) when exposed to UV light. The ROS subsequently attack bacteria cells, and thus reduce bacteria attachment on titanium implant surfaces. Polyaniline (PANI) is a conductive polymer that has shown antibacterial properties when electropolymerized onto titanium. Our research group hypothesized the addition of PANI to crystalline titanium oxide surfaces would increase the available free electrons and thus increase photocatalytic activity (PCA). This research led to the development of a novel single-step anodization approach for PANI doping crystalline titanium oxide layers. The objective of the present study was to determine the proper aniline electrolyte concentration needed to maximize the PCA and reduce bacterial attachment on the formed oxides. Aniline concentrations up to 1 M were added into a 1 M sulfuric acid electrolyte. The formed oxides exhibited increased PANI surface coverage but decreased anatase and rutile crystalline titanium oxide phase formation with increasing aniline electrolyte concentrations. Despite exhibiting the lowest levels of anatase and rutile formation, the 0.75 M and 1 M aniline oxides with the greatest PANI surface coverage also exhibited the highest PCA levels. 1 M aniline oxides showed significantly higher PCA under UVA irradiation compared to oxides formed from aniline concentrations up to 0.5 M (p < 0.001). 0.75 M aniline oxides exhibited significant reductions in Staphylococcus aureus attachment with or without UVA irradiation compared to control oxides without PANI. MTT and live/dead assays confirmed cytocompatibility and nearly 100% cell viability for the PANI doped oxides.

A novel single-step anodization approach for PANI-doping oxide surfaces to improve the photocatalytic activity of titanium implants

Crystalline titanium oxides have shown photocatalytic activity (PCA) and the formation of antibacterial reactive oxygen species (ROS) when stimulated with UV light. Polyaniline (PANI) is a conductive polymer that has shown antibacterial effects. Previously, titanium oxides have been PANI-doped using a multi-step approach. In the present study, we compared PANI-doped specimens produced with a two-step method (ACV), to PANI-doped specimens produced by a novel single-step direct anodization (AAn) method, and a control group of anodized un-doped specimens. The surface morphology, oxide crystallinity, surface elemental composition, surface roughness, surface wettability, oxide adhesion, corrosion resistance, PCA, and ROS generation of each oxide group were evaluated. All groups exhibited mixed anatase and rutile phase oxides. The AAn group revealed less anatase and rutile, but more PANI-surface coverage. The AAn group exhibited significantly increased PCA after 60 minutes of direct UVA illumination compared to the ACV group, despite containing lower amounts of anatase and rutile. The ACV and AAn groups showed significant increases in ROS production after 4 hours UVA illumination while the control group showed similar ROS production. These findings suggested that PANI doping using the novel direct anodization technique significantly improved PCA even for oxides containing less crystallinity. The S. aureus attachment response to each oxide group was also compared under UVA pre-illumination, UVA direct illumination, and no illumination (dark) lighting conditions. Although no significant differences were shown in the bacterial response, both PANI-doped groups exhibited less average bacterial attachment compared to the control group. The response of MC3T3-E1 pre-osteoblast cells to each oxide group was evaluated using MTT and live/dead assays, and no evidence of cytotoxicity was found. Since many, if not most, titanium implant devices are routinely anodized as a part of the manufacturing processes, these study findings are applicable to a wide variety of implant applications.

Clinical Applications of Photofunctionalization on Dental Implant Surfaces: A Narrative Review

Dental implant therapy is a common clinical procedure for the restoration of missing teeth. Many methods have been used to promote osseointegration for successful implant therapy, including photofunctionalization (PhF), which is defined as the modification of titanium surfaces after ultraviolet treatment. It includes the alteration of the physicochemical properties and the enhancement of biological capabilities, which can alter the surface wettability and eliminate hydrocarbons from the implant surface by a biological aging process. PhF can also enhance cellular migration, attachment, and proliferation, thereby promoting osseointegration and coronal soft tissue seal. However, PhF did not overcome the dental implant challenge of oral cancer cases. It is necessary to have more clinical trials focused on complex implant cases and non-dental fields in the future.

Microbial Decontamination and Antibacterial Activity of Nanostructured Titanium Dental Implants: A Narrative Review

Peri-implantitis is the major cause of the failure of dental implants. Since dental implants have become one of the main therapies for teeth loss, the number of patients with peri-implant diseases has been rising. Like the periodontal diseases that affect the supporting tissues of the teeth, peri-implant diseases are also associated with the formation of dental plaque biofilm, and resulting inflammation and destruction of the gingival tissues and bone. Treatments for peri-implantitis are focused on reducing the bacterial load in the pocket around the implant, and in decontaminating surfaces once bacteria have been detached. Recently, nanoengineered titanium dental implants have been introduced to improve osteointegration and provide an osteoconductive surface; however, the increased surface roughness raises issues of biofilm formation and more challenging decontamination of the implant surface. This paper reviews treatment modalities that are carried out to eliminate bacterial biofilms and slow their regrowth in terms of their advantages and disadvantages when used on titanium dental implant surfaces with nanoscale features. Such decontamination methods include physical debridement, chemo-mechanical treatments, laser ablation and photodynamic therapy, and electrochemical processes. There is a consensus that the efficient removal of the biofilm supplemented by chemical debridement and full access to the pocket is essential for treating peri-implantitis in clinical settings. Moreover, there is the potential to create ideal nano-modified titanium implants which exert antimicrobial actions and inhibit biofilm formation. Methods to achieve this include structural and surface changes via chemical and physical processes that alter the surface morphology and confer antibacterial properties. These have shown promise in preclinical investigations.

Overview of Antibacterial Strategies of Dental Implant Materials for the Prevention of Peri-Implantitis

As dental implants have become one of the main treatment options for patients with tooth loss, the number of patients with peri-implant diseases has increased. Similar to periodontal diseases, peri-implant diseases have been associated with dental plaque formation on implants. Unconventional approaches have been reported to remove plaque from infected implants, but none of these methods can completely and permanently solve the problem of bacterial invasion. Fortunately, the constant development of antibacterial implant materials is a promising solution to this situation. In this review, the development and study of different antibacterial strategies for dental implant materials for the prevention of peri-implantitis are summarized. We hope that by highlighting the advantages and limitations of these antimicrobial strategies, we can assist in the continued development of oral implant materials.

Surface Activation of Titanium Dental Implants by Using UVC-LED Irradiation

Organic contaminants significantly limit the bioactivity of titanium implants, resulting in the degradation known as the ageing of titanium. To reactivate the surfaces, they can be photofunctionalized, i.e., irradiated with C-range ultraviolet (UVC) light. This descriptive in vitro study compares the effectiveness of novel light-emitting diode (LED) technology to remove contaminant hydrocarbons from three different commercially available titanium dental implants: THD, TiUnite, and SLA. The surface topography and morphology were characterized by scanning electron microscopy (SEM). The chemical compositions were analyzed by X-ray photoelectron spectroscopy (XPS), before and after the lighting treatment, by a pair of closely placed UVC (λ = 278 nm) and LED devices for 24 h. SEM analysis showed morphological differences at the macro- and micro-scopic level. XPS analysis showed a remarkable reduction in the carbon contents after the UVC treatment: from 25.6 to 19.5 C at. % (carbon atomic concentration) in the THD; from 30.2 to 20.2 C at. % in the TiUnite; from 26.1 to 19.2 C at. % in the SLA surface. Simultaneously, the concentration of oxygen and titanium increased. Therefore, LED-based UVC irradiation decontaminated titanium surfaces and improved the chemical features of them, regardless of the kind of surface.

Decontamination of Ti Oxide Surfaces by Using Ultraviolet Light: Hg-Vapor vs. LED-Based Irradiation

C-range Ultraviolet (UVC) mercury (Hg)-vapor lamps have shown the successful decontamination of hydrocarbons and antimicrobial effects from titanium surfaces. This study focused on surface chemistry modifications of titanium dental implants by using two different light sources, Hg-vapor lamps and Light Emitting Diodes (LEDs), so as to compare the effectivity of both photofunctionalization technologies. Two different devices, a small Hg-vapor lamp (λ = 254 nm) and a pair of closely placed LEDs (λ = 278 nm), were used to irradiate the implants for 12 min. X-ray Photoelectron Spectroscopy (XPS) was employed to characterize the chemical composition of the surfaces, analysing the samples before and after the lighting treatment, performing a wide and narrow scan around the energy peaks of carbon, oxygen and titanium. XPS analysis showed a reduction in the concentration of surface hydrocarbons in both UVC technologies from around 26 to 23.4 C at.% (carbon atomic concentration). Besides, simultaneously, an increase in concentration of oxygen and titanium was observed. LED-based UVC photofunctionalization has been suggested to be as effective a method as Hg-vapor lamps to remove the hydrocarbons from the surface of titanium dental implants. Therefore, due to the increase in worldwide mercury limitations, LED-based technology could be a good alternative decontamination source.

Photocatalytic activity and antibacterial efficacy of UVA-treated titanium oxides

Studies have shown ultraviolet-A (UVA) irradiation of crystalline titanium oxides leads to the production of reactive oxygen species (ROS) via a photocatalytic process. The ROS exhibit antimicrobial properties that may be of benefit in preventing bacterial attachment to implant devices. Recent studies have suggested a potential benefit of mixed anatase and rutile oxides and dopants on the photocatalytic properties of titanium oxides. The goal of this work was to compare the photocatalytic activity of different anodized commercially pure titanium grade 4 (CPTi4) surfaces. CPTi4 specimens were anodized in three mixed-acid electrolytes to create crystalline oxide surfaces that were either primarily anatase, primarily rutile, or a combination of anatase and rutile. Additionally, the primarily anatase and combination oxides incorporated some phosphorous from the phosphoric acid component in the electrolyte. The photocatalytic activity of the anodized specimens was measured using both methylene blue (MB) degradation assay and comparing the attachment of S. aureus under irradiation with UVA light of differing intensities (1 mW/cm², 8 mW/cm², and 23 mW/cm²). Primarily rutile oxides exhibited significantly higher levels of MB degradation after exposure to 1 mW/cm² UVA lights. Primarily rutile specimens also had the largest reduction in bacterial attachment followed by the mixed phase specimens and the primarily anatase specimens at 1 mW/cm² UVA lights. Phosphorous-doped, mixed phase oxides exhibited an accelerated MB degradation response during exposure to 8 mW/cm² and 23 mW/cm² UVA lights. All anodized and unanodized CPTi4 groups revealed similar S. aureus attachment at the two higher UVA intensities. Although MB degradation assay and the bacteria attachment assay both confirmed photocatalytic activity of the oxides formed in this study, the results of the MB degradation assay did not accurately predict the oxides performance against S. aureus.

Modifications of Dental Implant Surfaces at the Micro- and Nano-Level for Enhanced Osseointegration

This review paper describes several recent modification methods for biocompatible titanium dental implant surfaces. The micro-roughened surfaces reviewed in the literature are sandblasted, large-grit, acid-etched, and anodically oxidized. These globally-used surfaces have been clinically investigated, showing survival rates higher than 95%. In the past, dental clinicians believed that eukaryotic cells for osteogenesis did not recognize the changes of the nanostructures of dental implant surfaces. However, research findings have recently shown that osteogenic cells respond to chemical and morphological changes at a nanoscale on the surfaces, including titanium dioxide nanotube arrangements, functional peptide coatings, fluoride treatments, calcium–phosphorus applications, and ultraviolet photofunctionalization. Some of the nano-level modifications have not yet been clinically evaluated. However, these modified dental implant surfaces at the nanoscale have shown excellent in vitro and in vivo results, and thus promising potential future clinical use.