UV Light-Generated Superhydrophilicity of a Titanium Surface Enhances the Transfer, Diffusion and Adsorption of Osteogenic Factors from a Collagen Sponge

Beyond microroughness: novel approaches to navigate osteoblast activity on implant surfaces

Considering the biological activity of osteoblasts is crucial when devising new approaches to enhance the osseointegration of implant surfaces, as their behavior profoundly influences clinical outcomes. An established inverse correlation exists between osteoblast proliferation and their functional differentiation, which constrains the rapid generation of a significant amount of bone. Examining the surface morphology of implants reveals that roughened titanium surfaces facilitate rapid but thin bone formation, whereas smooth, machined surfaces promote greater volumes of bone formation albeit at a slower pace. Consequently, osteoblasts differentiate faster on roughened surfaces but at the expense of proliferation speed. Moreover, the attachment and initial spreading behavior of osteoblasts are notably compromised on microrough surfaces. This review delves into our current understanding and recent advances in nanonodular texturing, meso-scale texturing, and UV photofunctionalization as potential strategies to address the "biological dilemma" of osteoblast kinetics, aiming to improve the quality and quantity of osseointegration. We discuss how these topographical and physicochemical strategies effectively mitigate and even overcome the dichotomy of osteoblast behavior and the biological challenges posed by microrough surfaces. Indeed, surfaces modified with these strategies exhibit enhanced recruitment, attachment, spread, and proliferation of osteoblasts compared to smooth surfaces, while maintaining or amplifying the inherent advantage of cell differentiation. These technology platforms suggest promising avenues for the development of future implants.

Optimizing implant osseointegration, soft tissue responses, and bacterial inhibition: A comprehensive narrative review on the multifaceted approach of the UV photofunctionalization of titanium

Titanium implants have revolutionized restorative and reconstructive therapy, yet achieving optimal osseointegration and ensuring long-term implant success remain persistent challenges. In this review, we explore a cutting-edge approach to enhancing implant properties: ultraviolet (UV) photofunctionalization. By harnessing UV energy, photofunctionalization rejuvenates aging implants, leveraging and often surpassing the intrinsic potential of titanium materials. The primary aim of this narrative review is to offer an updated perspective on the advancements made in the field, providing a comprehensive overview of recent findings and exploring the relationship between UV-induced physicochemical alterations and cellular responses. There is now compelling evidence of significant transformations in titanium surface chemistry induced by photofunctionalization, transitioning from hydrocarbon-rich to carbon pellicle-free surfaces, generating superhydrophilic surfaces, and modulating the electrostatic properties. These changes are closely associated with improved cellular attachment, spreading, proliferation, differentiation, and, ultimately, osseointegration. Additionally, we discuss clinical studies demonstrating the efficacy of UV photofunctionalization in accelerating and enhancing the osseointegration of dental implants. Furthermore, we delve into recent advancements, including the development of one-minute vacuum UV (VUV) photofunctionalization, which addresses the limitations of conventional UV methods as well as the newly discovered functions of photofunctionalization in modulating soft tissue and bacterial interfaces. By elucidating the intricate relationship between surface science and biology, this body of research lays the groundwork for innovative strategies aimed at enhancing the clinical performance of titanium implants, marking a new era in implantology.

Optimization of blood and protein flow around superhydrophilic implant surfaces by promoting contact hemodynamics

PURPOSE

We examined blood and protein dynamics potentially influenced by implant threads and hydrophilic/hydrophobic states of implant surfaces.

METHODS

A computational fluid dynamics model was created for a screw-shaped implant with a water contact angle of 70° (hydrophobic surface) and 0° (superhydrophilic surface). Movements and density of blood and fibrinogen as a representative wound healing protein were visualized and quantified during constant blood inflow.

RESULTS

Blood plasma did not occupy 40-50% of the implant interface or the inside of threads around hydrophobic implants, whereas such blood voids were nearly completely eliminated around superhydrophilic implants. Whole blood field vectors were disorganized and random within hydrophobic threads but formed vortex nodes surrounded by stable blood streams along the superhydrophilic implant surface. The averaged vector within threads was away from the implant surface for the hydrophobic implant and towards the implant surface for the superhydrophilic implant. Rapid and massive whole blood influx into the thread zone was only seen for the superhydrophilic implant, whereas a line of conflicting vectors formed at the entrance of the thread area of the hydrophobic implant to prevent blood influx. The fibrinogen density was up to 20-times greater at the superhydrophilic implant interface than the hydrophobic one. Fibrinogen density was higher at the interface than outside the threads only for the superhydrophilic implant.

CONCLUSIONS

Implant threads and surface hydrophilicity have profound effects on vector and distribution of blood and proteins. Critically, implant threads formed significant biological voids at the interface that were negated by superhydrophilicity-induced contact hemodynamics.

Influence of Surface Contaminants and Hydrocarbon Pellicle on the Results of Wettability Measurements of Titanium

Hydrophilicity/hydrophobicity-or wettability-is a key surface characterization metric for titanium used in dental and orthopedic implants. However, the effects of hydrophilicity/hydrophobicity on biological capability remain uncertain, and the relationships between surface wettability and other surface parameters, such as topography and chemistry, are poorly understood. The objective of this study was to identify determinants of surface wettability of titanium and establish the reliability and validity of the assessment. Wettability was evaluated as the contact angle of ddH2O. The age of titanium specimens significantly affected the contact angle, with acid-etched, microrough titanium surfaces becoming superhydrophilic immediately after surface processing, hydrophobic after 7 days, and hydrorepellent after 90 days. Similar age-related loss of hydrophilicity was also confirmed on sandblasted supra-micron rough surfaces so, regardless of surface topography, titanium surfaces eventually become hydrophobic or hydrorepellent with time. On age-standardized titanium, surface roughness increased the contact angle and hydrophobicity. UV treatment of titanium regenerated the superhydrophilicity regardless of age or surface roughness, with rougher surfaces becoming more superhydrophilic than machined surfaces after UV treatment. Conditioning titanium surfaces by autoclaving increased the hydrophobicity of already-hydrophobic surfaces, whereas conditioning with 70% alcohol and hydrating with water or saline attenuated pre-existing hydrophobicity. Conversely, when titanium surfaces were superhydrophilic like UV-treated ones, autoclaving and alcohol cleaning turned the surfaces hydrorepellent and hydrophobic, respectively. UV treatment recovered hydrophilicity without exception. In conclusion, surface roughness accentuates existing wettability and can either increase or decrease the contact angle. Titanium must be age-standardized when evaluating surface wettability. Surface conditioning techniques significantly but unpredictably affect existing wettability. These implied that titanium wettability is significantly influenced by the hydrocarbon pellicle and other contaminants inevitably accumulated. UV treatment may be an effective strategy to standardize wettability by making all titanium surfaces superhydrophilic, thereby allowing the characterization of individual surface topography and chemistry parameters in future studies.

The Effects of a Biomimetic Hybrid Meso- and Nano-Scale Surface Topography on Blood and Protein Recruitment in a Computational Fluid Dynamics Implant Model

The mechanisms underlying bone-implant integration, or osseointegration, are still incompletely understood, in particular how blood and proteins are recruited to implant surfaces. The objective of this study was to visualize and quantify the flow of blood and the model protein fibrinogen using a computational fluid dynamics (CFD) implant model. Implants with screws were designed with three different surface topographies: (1) amorphous, (2) nano-trabecular, and (3) hybrid meso-spikes and nano-trabeculae. The implant with nano-topography recruited more blood and fibrinogen to the implant interface than the amorphous implant. Implants with hybrid topography further increased recruitment, with particularly efficient recruitment from the thread area to the interface. Blood movement significantly slowed at the implant interface compared with the thread area for all implants. The blood velocity at the interface was 3- and 4-fold lower for the hybrid topography compared with the nano-topography and amorphous surfaces, respectively. Thus, this study for the first time provides insights into how different implant surfaces regulate blood dynamics and the potential advantages of surface texturization in blood and protein recruitment and retention. In particular, co-texturization with a hybrid meso- and nano-topography created the most favorable microenvironment. The established CFD model is simple, low-cost, and expected to be useful for a wide range of studies designing and optimizing implants at the macro and micro levels.

Decomposing Organic Molecules on Titanium with Vacuum Ultraviolet Light for Effective and Rapid Photofunctionalization

Ultraviolet (UV) photofunctionalization counteracts the biological aging of titanium to increase the bioactivity and osseointegration of titanium implants. However, UV photofunctionalization currently requires long treatment times of between 12 min and 48 h, precluding routine clinical use. Here, we tested the ability of a novel, xenon excimer lamp emitting 172 nm vacuum UV (VUV) to decompose organic molecules coated on titanium as a surrogate of photofunctionalization. Methylene blue as a model organic molecule was coated on grade 4 commercially pure titanium and treated with four UV light sources: (i) ultraviolet C (UVC), (ii) high-energy UVC (HUVC), (iii) proprietary UV (PUV), and (iv) VUV. After one minute of treatment, VUV decomposed 57% of methylene blue compared with 2%, 36%, and 42% for UVC, HUVC, and PUV, respectively. UV dose-dependency testing revealed maximal methylene blue decomposition with VUV within one minute. Equivalent decomposition was observed on grade 5 titanium alloy specimens, and placing titanium specimens in quartz ampoules did not compromise efficacy. Methylene blue was decomposed even on polymethyl methacrylate acrylic specimens at 20-25% lower efficiency than on titanium specimens, indicating a relatively small contribution of titanium dioxide-mediated photocatalytic decomposition to the total decomposition. Load-testing revealed that VUV maintained high efficacy of methylene blue decomposition regardless of the coating density, whereas other UV light sources showed low efficacy with thin coatings and plateauing efficacy with thicker coatings. This study provides foundational data on rapid and efficient VUV-mediated organic decomposition on titanium. In synergy with quartz ampoules used as containers, VUV has the potential to overcome current technical challenges hampering the clinical application of UV photofunctionalization.

A Novel Cell Delivery System Exploiting Synergy between Fresh Titanium and Fibronectin

Delivering and retaining cells in areas of interest is an ongoing challenge in tissue engineering. Here we introduce a novel approach to fabricate osteoblast-loaded titanium suitable for cell delivery for bone integration, regeneration, and engineering. We hypothesized that titanium age influences the efficiency of protein adsorption and cell loading onto titanium surfaces. Fresh (newly machined) and 1-month-old (aged) commercial grade 4 titanium disks were prepared. Fresh titanium surfaces were hydrophilic, whereas aged surfaces were hydrophobic. Twice the amount of type 1 collagen and fibronectin adsorbed to fresh titanium surfaces than aged titanium surfaces after a short incubation period of three hours, and 2.5-times more fibronectin than collagen adsorbed regardless of titanium age. Rat bone marrow-derived osteoblasts were incubated on protein-adsorbed titanium surfaces for three hours, and osteoblast loading was most efficient on fresh titanium adsorbed with fibronectin. The number of osteoblasts loaded using this synergy between fresh titanium and fibronectin was nine times greater than that on aged titanium with no protein adsorption. The loaded cells were confirmed to be firmly attached and functional. The number of loaded cells was strongly correlated with the amount of protein adsorbed regardless of the protein type, with fibronectin simply more efficiently adsorbed on titanium surfaces than collagen. The role of surface hydrophilicity of fresh titanium surfaces in increasing protein adsorption or cell loading was unclear. The hydrophilicity of protein-adsorbed titanium increased with the amount of protein but was not the primary determinant of cell loading. In conclusion, the osteoblast loading efficiency was dependent on the age of the titanium and the amount of protein adsorption. In addition, the efficiency of protein adsorption was specific to the protein, with fibronectin being much more efficient than collagen. This is a novel strategy to effectively deliver osteoblasts ex vivo and in vivo using titanium as a vehicle.

Ultraviolet Treatment of Titanium to Enhance Adhesion and Retention of Oral Mucosa Connective Tissue and Fibroblasts

Peri-implantitis is an unsolved but critical problem with dental implants. It is postulated that creating a seal of gingival soft tissue around the implant neck is key to preventing peri-implantitis. The objective of this study was to determine the effect of UV surface treatment of titanium disks on the adhesion strength and retention time of oral connective tissues as well as on the adherence of mucosal fibroblasts. Titanium disks with a smooth machined surface were prepared and treated with UV light for 15 min. Keratinized mucosal tissue sections (3 × 3 mm) from rat palates were incubated for 24 h on the titanium disks. The adhered tissue sections were then mechanically detached by agitating the culture dishes. The tissue sections remained adherent for significantly longer (15.5 h) on the UV-treated disks than on the untreated control disks (7.5 h). A total of 94% of the tissue sections were adherent for 5 h or longer on the UV-treated disks, whereas only 50% of the sections remained on the control disks for 5 h. The adhesion strength of the tissue sections to the titanium disks, as measured by tensile testing, was six times greater after UV treatment. In the culture studies, mucosal fibroblasts extracted from rat palates were attached to titanium disks by incubating for 24, 48, or 96 h. The number of attached cells was consistently 15–30% greater on the UV-treated disks than on the control disks. The cells were then subjected to mechanical or chemical (trypsinization) detachment. After mechanical detachment, the residual cell rates on the UV-treated surfaces after 24 and 48 h of incubation were 35% and 25% higher, respectively, than those on the control surfaces. The remaining rate after chemical detachment was 74% on the control surface and 88% on the UV-treated surface for the cells cultured for 48 h. These trends were also confirmed in mouse embryonic fibroblasts, with an intense expression of vinculin, a focal adhesion protein, on the UV-treated disks even after detachment. The UV-treated titanium was superhydrophilic, whereas the control titanium was hydrophobic. X-ray photoelectron spectroscopy (XPS) chemical analysis revealed that the amount of carbon at the surface was significantly reduced after UV treatment, while the amount of TiOH molecules was increased. These ex vivo and in vitro results indicate that the UV treatment of titanium increases the adhesion and retention of oral mucosa connective tissue as a result of increased resistance of constituent fibroblasts against exogenous detachment, both mechanically and chemically, as well as UV-induced physicochemical changes of the titanium surface.

Osteoblast Attachment Compromised by High and Low Temperature of Titanium and Its Restoration by UV Photofunctionalization

Titanium implants undergo temperature fluctuations during manufacturing, transport, and storage. However, it is unknown how this affects their bioactivity. Herein, we explored how storage (six months, dark conditions) and temperature fluctuations (5-50 °C) affected the bioactivity of titanium implants. Stored and fresh acid-etched titanium disks were exposed to different temperatures for 30 min under wet or dry conditions, and their hydrophilicity/hydrophobicity and bioactivity (using osteoblasts derived from rat bone marrow) were evaluated. Ultraviolet (UV) treatment was evaluated as a method of restoring the bioactivity. The fresh samples were superhydrophilic after holding at 5 or 25 °C under wet or dry conditions, and hydrophilic after holding at 50 °C. In contrast, all the stored samples were hydrophobic. For both fresh and stored samples, exposure to 5 or 50 °C reduced osteoblast attachment compared to holding at 25 °C under both wet and dry conditions. Regression analysis indicated that holding at 31 °C would maximize cell attachment (p < 0.05). After UV treatment, cell attachment was the same or better than that before temperature fluctuations. Overall, titanium surfaces may have lower bioactivity when the temperature fluctuates by ≥20 °C (particularly toward lower temperatures), independent of the hydrophilicity/hydrophobicity. UV treatment was effective in restoring the temperature-compromised bioactivity.