Ultraviolet treatment overcomes time-related degrading bioactivity of titanium

Enhanced intracellular signaling pathway in osteoblasts on ultraviolet lighttreated hydrophilic titanium

Ultraviolet (UV) light treatment of titanium immediately prior to use, or photofunctionalization, reactivates the time-dependent degradation of bioactivity of titanium (biological aging of titanium) and increases its osseointegration capacity beyond the inherent maximal level. Although the initial osteoblast attachment is reportedly enhanced on UV-treated titanium surfaces, the detailed mechanism behind the increase in osseointegration is unknown. This study examined the potential modulation of intracellular signaling pathway in osteoblasts on UV-treated titanium surfaces. Rat bone marrow-derived osteoblasts were cultured on 4-week-old, new, and UV-treated titanium surfaces. The new and UV-treated surfaces were superhydrophilic, whereas the 4-week-old surface was hydrophobic. Although the rate of protein adsorption was similarly increased on the new and UV-treated surfaces compared with the 4-week-old surface, the number of attached cells and their spreading behavior were further enhanced on the UV-treated surface. This additional enhancement was associated with the remarkably upregulated expression of paxillin and phospho-paxillin and exclusive upregulation of Rho GTPase family genes. This study provides with the first molecular evidence of the enhanced initial behavior of osteoblasts on UV-treated titanium surfaces. The enhancement was accentuated and distinct from the new titanium surface with similar hydrophilicity, suggesting that surface properties other than the level of hydrophilicity are responsible.

Titanium implants coated with UV-irradiated vitamin D precursor and vitamin E: in vivo performance and coating stability

OBJECTIVES

This study aimed at evaluating the biological response of titanium implants coated with UV-irradiated 7-dehydrocholesterol (7-DHC) and vitamin E (VitE) in vivo and analyzing the effects of aging on their stability and bioactivity in vitro.

MATERIAL AND METHODS

Titanium surfaces were coated with 7-DHC and VitE, UV-irradiated and incubated for 48 h at 23°C to allow cholecalciferol synthesis. The in vivo biological response was tested using a rabbit tibia model after 8 weeks of healing by analyzing the wound fluid and the mRNA levels of several markers at the bone-implant interface (N = 8). The stability of the coating after storage up to 12 weeks was determined using HPLC analysis, and the bioactivity of the stored modified implants was studied by an in vitro study with MC3T3-E1 cells (N = 6).

RESULTS

A significant increase in gene expression levels of osteocalcin was found in the bone tissue attached to implants coated with the low dose of 7-DHC and VitE, together with a higher ALP activity in the wound fluid. Implants treated with the high dose of 7-DHC and VitE showed increased tissue necrosis and inflammation. Regarding the aging effects, coated implants were stable and bioactive up to 12 weeks when stored at 4°C and avoiding oxygen, light and moisture.

CONCLUSION

This study demonstrates that Ti implants coated with UV-irradiated 7-DHC and VitE promote in vivo gene expression of bone formation markers and ALP activity, while they keep their osteopromotive potential in vitro and composition when stored up to 12 weeks at 4°C.

Long-Term Progressive Degradation of the Biological Capability of Titanium

Titanium undergoes time-dependent degradation in biological capability, or “biological aging”. It is unknown whether the biological aging of titanium occurs beyond four weeks and whether age-related changes are definitely associated with surface hydrophilicity. We therefore measured multiple biological parameters of bone marrow-derived osteoblasts cultured on newly prepared, one-month-old, three-month-old, and six-month-old acid-etched titanium surfaces, as well as the hydrophilicity of these surfaces. New surfaces were superhydrophilic with a contact angle of ddH₂O of 0°, whereas old surfaces were all hydrophobic with the contact angle of around 90°. Cell attachment, cell spread, cell density, and alkaline phosphatase activity were highest on new surfaces and decreased in a time-dependent manner. These decreases persisted and remained significant for most of the biological parameters up to six-months. While the number of attached cells was negatively correlated with hydrophilicity, the other measured parameters were not. The biological capability of titanium continues to degrade up to six months of aging, but these effects are not directly associated with time-dependent reductions in hydrophilicity. A full understanding of the biological aging will help guide regulatory improvements in implant device manufacturing and develop countermeasures against this phenomenon in order to improve clinical outcomes.

Plasma of Argon Affects the Earliest Biological Response of Different Implant Surfaces: An In Vitro Comparative Study

The aim of this in vitro study was to evaluate the early cell response and protein adsorption elicited by the argon plasma treatment of different commercially available titanium surfaces via a chair-side device. Sterile disks made of grade 4 titanium (n= 450, 4-mm diameter) with 3 surface topographies (machined, plasma sprayed, and zirconia blasted and acid etched) were allocated to receive 4 testing treatments (2% and 10% protein adsorption and cell adhesion with MC3T3-E1 and MG-63). Furthermore, the specimens were divided to undergo 1) argon plasma treatment (10 W, 1 bar for 12 min) in a plasma reactor, 2) ultraviolet (UV) light treatment for 2 h (positive control group), or 3) no treatment (control group). Pretreatment surface analyses based on a scanning electron microscope and profilometer images were also performed. Profilometric analysis demonstrated that the evaluated specimens perfectly suit the standard parameters. The use of argon plasma was capable of affecting the quantity of proteins adsorbed on the different surfaces, notwithstanding their roughness or topographic features at a low fetal bovine serum concentration (2%). UV light treatment for 2 h attained similar results. Moreover, both the plasma of argon and the UV light demonstrated a significant increase in the number of osteoblasts adherent at 10 min in all tested surfaces. Within its limitations, this in vitro study highlights the potential biological benefits of treating implant surfaces with plasma of argon or UV, irrespective of the roughness of the titanium surface. However, in vivo experiments are needed to confirm these preliminary data and settle the rationale of a treatment that might be clinically relevant in case of bone-reparative deficiencies.

Engineering bone-implant integration with photofunctionalized titanium microfibers

There are significant challenges in regenerating large volumes of bone tissue, and titanium implant therapy is extremely difficult or contraindicated when there is no supporting bone. Surface conditioning of titanium implants with UV light immediately prior to use, or photofunctionalization, improves the speed and degree of bone-implant integration. Here, we hypothesized that photofunctionalized titanium microfibers are capable of promoting bone ingrowth into the microfiber scaffold to improve bone-implant integration in bone defects. Titanium implants (1 mm in diameter, 2 mm in length) enfolded with 0.7 mm-thick titanium microfibers were placed into 2.4-mm diameter osteotomy in rat femurs. Titanium microfibers and implants were photofunctionalized by treatment with UV light for 12 min using a photo device immediately prior to surgery. Photofunctionalized microfibers and implants were hydrophilic, while as-made microfiber-enfolded implants were hydrophobic. Implant anchorage strength was 2.5 times and 2.2 times greater for photofunctionalized microfiber-enfolded implants than as-made ones at weeks 2 and 4 of healing, respectively. Robust bone formation was only seen at the implant surface of photofunctionalized microfiber-enfolded implants. Bone formation as measured by the Ca/Ti ratio was 5 to over 20 times greater for photofunctionalized than as-made microfiber scaffolds. The Ca/P ratio was 1.55-1.65 in the tissue produced in photofunctionalized microfibers and 1.1-1.3 in tissue in as-made microfibers. In vitro, the number of attached osteoblasts and their alkaline phosphatase activity, both near zero on as-received microfibers, were significantly increased on photofunctionalized microfibers. In conclusion, bone ingrowth occurred in photofunctionalized titanium microfiber scaffolds, enabling successful bone-implant integration when the microfiber-enfolded implants were placed in a site without primary bone support. The combined use of titanium microfibers and photofunctionalization may provide a novel and effective strategy to regenerate and integrate bone in a wider range of applications.

Ultraviolet photofunctionalization increases removal torque values and horizontal stability of orthodontic miniscrews

INTRODUCTION

The objective of this study was to examine the effects of ultraviolet-mediated photofunctionalization of miniscrews and the in-vivo potential of bone-miniscrew integration.

METHODS

Self-drilling orthodontic miniscrews made from a titanium alloy were placed in rat femurs. Photofunctionalization was performed by treating the miniscrews with ultraviolet light for 12 minutes with a photo device immediately before implantation. Maximum insertion torque (week 0), removal torque (weeks 0 and 3), and resistance to lateral tipping force (week 3) were examined.

RESULTS

The removal torque at 3 weeks of healing was higher for the photofunctionalized screws than for the untreated screws. The regenerated bone tissue was more intact and contiguous around the photofunctionalized miniscrews than around the untreated ones. The miniscrew-bone complex seemed to produce interface failure, not cohesive fracture, in both groups. The displacement of untreated screws under a lateral tipping force was greater than that of photofunctionalized miniscrews.

CONCLUSIONS

These results suggest that photofunctionalization increases the bioactivity of titanium-alloy miniscrews and improves the anchoring capability of orthodontic miniscrews, even without modification of the surface topography.

Photofunctionalization enhances bone-implant contact, dynamics of interfacial osteogenesis, marginal bone seal, and removal torque value of implants: a dog jawbone study

OBJECTIVE

Ultraviolet (UV) light treatment of titanium, ie, photofunctionalization, has been extensively reported to enhance the osteoconductivity of titanium in animal and in vitro studies. This is the first study to examine whether photofunctionalization is effective on commercial dental implants in vivo.

MATERIALS AND METHODS

Dental implants with a microroughened surface were placed into dog jawbones. Photofunctionalization was performed by treating implants with UV light for 15 minutes using a photo device immediately before placement. Four weeks after placement, bone-implant integration was evaluated using a removable torque test and static and dynamic histology.

RESULTS

Implant surfaces were converted from hydrophobic to super-hydrophilic after photofunctionalization. Removable torque for photofunctionalized implants was significantly higher by 50% than that for untreated implants. Bone-implant contact (BIC) was significantly higher for photofunctionalized implants in all zones examined: marginal, cortical, and bone marrow zones. An intensive mineralized layer was exclusively present in marginal bone at photofunctionalized interface. Dynamic histology identified early-onset, long-lasting robust bone deposition at photofunctionalized interface.

CONCLUSIONS

Photofunctionalization enhanced the morphology, quality, and behavior of periimplant osteogenesis, including the increased BIC, expedited robust interfacial bone deposition, and improved marginal bone seal and support.

Biological Effect of Ultraviolet Photocatalysis on Nanoscale Titanium with a Focus on Physicochemical Mechanism

Physicochemical properties, regulated by various surface modifications, influence the biological performance of materials. The interaction between surface charge and biomolecules is key to understanding the mechanism of surface-tissue integration. The objective of this study was to evaluate the biological response to a nanoscale titanium surface after ultraviolet (UVC, λ = 250 ± 20 nm) irradiation and to analyze the effects via a physicochemical mechanism. The surface characteristics were evaluated by field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, surface profilometry, and contact angle assay. In addition, we applied the zeta-potential, a direct method to measure the electrostatic charge on UV-treated and UV-untreated titanium nanotube surfaces. The effect of the Ti surface after UV treatment on the biological process was determined by analyzing bovine serum albumin (BSA) adsorption and osteoblast-like MG-63 early adhesion, morphology, cytoskeletal arrangement, proliferation, and focal adhesion. Compared to an anodized titanium nanotube coating, UV irradiation altered the contact angles on the control surface from 51.5° to 6.2° without changing the surface topography or roughness. Furthermore, titanium nanotubes after UV treatment showed a significant reduction in the content of acidic hydroxyl groups and held less negative charge than the anodized coating. With regard to the biological response, along with an enhanced capability to adsorb BSA, osteoblasts exhibited higher colonization and viability on the UV-treated material. The results suggest that UV treatment enhances the biocompatibility by reducing the electrostatic repulsion between biomaterials and biomolecules.

Implant stability change and osseointegration speed of immediately loaded photofunctionalized implants

OBJECTIVES

This study evaluated the degree and rate of implant stability development for photofunctionalized dental implants in humans.

MATERIALS AND METHODS

Thirty-three implants (7 patients) placed in the maxilla and immediate loaded were evaluated. Photofunctionalization was performed by treating implants with ultraviolet for 15 minutes immediately before placement. Implant stability was assessed by measuring the implant stability quotient (ISQ) weekly starting from implant placement up to 3 months. Osseointegration speed index (OSI), defined as ISQ increase per month, was also evaluated.

RESULTS

The average ISQ for photofunctionalized implants at week 6 was 78.0, which was considerably higher than the average ISQ of 66.1, reported in literature for various as-received implants after a longer healing time of 2 to 6 months. No stability dip was observed for photofunctionalized implants regardless of the initial ISQ values. The OSI for photofunctionalized implants was 6.3 and 3.1 when their initial ISQ was 65 to 70 and 71 to 75, respectively, whereas the OSI values for as-received implants calculated from literature ranged from -3.0 to 1.17 with an average of -0.10.

CONCLUSIONS

Photofunctionalization accelerated and enhanced osseointegration of dental implants, providing novel and practical avenues for further advancement in implant therapy.

Osteogenic cell sheets reinforced with photofunctionalized micro-thin titanium

Cell sheet technology has been used to deliver cells in single-sheet form with an intact extracellular matrix for soft tissue repair and regeneration. Here, we hypothesized that titanium-reinforced cell sheets could be constructed for bone tissue engineering and regeneration. Fifty-µm-thick titanium plates containing apertures were prepared and roughened by acid etching, some of which were photofunctionalized with 12 min of UV light treatment. Cell sheets were prepared by culturing rat calvarial periosteum-derived cells on temperature-responsive culture dishes and attached to titanium plates. Titanium-reinforced osteogenic cell sheet construction was conditional on various technical and material factors: cell sheets needed to be double-sided and sandwich the titanium plate, and the titanium plates needed to be micro thin and contain apertures to allow close apposition of the two cell sheets. Critically, titanium plates needed to be UV-photofunctionalized to ensure adherence and retention of cell sheets. Single-sided cell sheets or double-sided cell sheets on as-made titanium contracted and deformed within 4 days of incubation. Titanium-reinforced cell sheets on photofunctionalized titanium were structurally stable at least up to 14 days, developed the expected osteogenic phenotypes (ALP production and mineralization), and maintained structural integrity without functional degradation. Successful construction of titanium-reinforced osteogenic cell sheets was associated with increased cell attachment, retention, and expression of vinculin, an adhesion protein by photofunctionalization. This study identified the technical and material requirements for constructing titanium-reinforced osteogenic cell sheets. Future in vivo studies are warranted to test these titanium-reinforced cell sheets as stably transplantable, mechanically durable, and shape controllable osteogenic devices.

Latham J, G. Dunlop D, Oreffo RO. Bone and metal: an orthopaedic perspective on osseointegration of metals

The area of implant osseointegration is of major importance, given the predicted significant rise in the number of orthopaedic procedures and an increasingly ageing population. Osseointegration is a complex process involving a number of distinct mechanisms affected by the implant bulk properties and surface characteristics. Our understanding and ability to modify these mechanisms through alterations in implant design is continuously expanding. The following review considers the main aspects of material and surface alterations in metal implants, and the extent of their subsequent influence on osseointegration. Clinically, osseointegration results in asymptomatic stable durable fixation of orthopaedic implants. The complexity of achieving this outcome through incorporation and balance of contributory factors is highlighted through a clinical case report.

Photofunctionalization increases the bioactivity and osteoconductivity of the titanium alloy Ti6Al4V

This study examined the effect of photofunctionalization on bioactivity and osteoconductivity of titanium alloy Ti6Al4V. We also tested a hypothesis that the effect of photofunctionalization is as substantial as the one of surface roughening. Two different surface morphology, a roughened surface (sandblasted and acid-etched surface) and relatively smooth surface (machined surface), was tested. Ti6Al4V samples were photofunctionalized with UV light for 15 min using a photo device. Photofunctionalization converted Ti6Al4V surfaces from hydrophobic to superhydrophilic. The attachment, spread, proliferation, and the expression of functional phenotype of bone marrow-derived osteoblasts were promoted on photofunctionalized Ti6Al4V surfaces. The strength of bone-implant integration examined using a biomechanical push-in test in a rat femur model was at least 100% greater for photofunctionalized implants than for untreated implants. These effects were seen on both surface types. The strength of bone-implant integration for photofunctionalized machined implants was greater than that for untreated roughened implants, indicating that the impact of photofunctionalization may be greater than that of surface roughening. Newly prepared Ti alloy was hydrophilic, whereas the hydrophilic status degraded with time and was converted to hydrophobic in 4 weeks. This finding uncovered biological aging of Ti alloy and allowed us to consider photofunctionalization as a countermeasure for aging. These results suggest that photofunctionalization accelerates and enhances bone-implant integration of Ti6Al4V regardless of smooth and roughened surface features, supporting photofunctionalization as an effective and viable measure for improving efficacy of a wide range of Ti6Al4V-based materials used in dental and orthopedic medicine.

The biological aging of titanium implants

Despite the substantial contribution of titanium implants in the field of dental and orthopedic reconstructive therapy, there is a crucial unaddressed question of why bone-implant contact does not reach the ideal 100%. This review article introduces the recently reported time-dependent reduction in osteoconductivity and other biological capabilities of titanium since processing. This phenomenon is defined as the biological aging of titanium and provides insight to significantly advance the understanding of osseointegration and to further improve implant surfaces in the future.

Effect of photofunctionalization on fluoride-treated nanofeatured titanium

The objective of this study was to evaluate the effect of ultraviolet light treatment, known as photofunctionalization, on the biological and osseointegration capability of nanofeatured titanium created by a combination of sandblasting and hydrofluoric acid treatment. Titanium samples in disk and cylinder forms were photofunctionalized by treatment with ultraviolet light for 15 min. The nanofeatured surface was converted from hydrophobic to superhydrophilic after photofunctionalization. The strength of osseointegration measured by a biomechanical push-in test in a rat model was stronger for photofunctionalized implants than for untreated implants by 2.2 and 2.3 times, respectively, at the early (week 2) and late (week 4) stages of healing, implying that photofunctionalization did not only accelerate but also increased the degree of osseointegration. Culture studies using bone marrow-derived osteoblasts showed that the attachment, spread, and functional phenotypes of osteogenic cells, such as alkaline phosphatase activity and mineralization, were remarkably increased on photofunctionalized titanium. In conclusion, photofunctionalization substantially increased biological and osseointegration capability of a nanofeatured titanium surface. In light with proven effectiveness on microfeatured surfaces in the literature, photofunctionalization may provide a novel and practical avenue to further improve osseointegration capability of implants in a wide range of surface morphology with micro-to-nano features.

Gamma ray treatment enhances bioactivity and osseointegration capability of titanium

The time-dependent degradation of titanium bioactivity (i.e., the biological aging of titanium) has been reported in previous studies. This phenomenon is caused by the loss of hydrophilicity and the inevitable occurrence of progressive contamination of titanium surfaces by hydrocarbons. In this study, we tested the hypothesis that gamma ray treatment, owing to its high energy to decompose and remove organic contaminants, enhances the bioactivity and osteoconductivity of titanium. Titanium disks were acid-etched and stored for 4 weeks. Rat bone marrow-derived osteoblasts (BMOs) were cultured on titanium disks with or without gamma ray treatment (30 kGy) immediately before experiments. The cell density at day 2 increased by 50% on gamma-treated surfaces, which reflected the 25% higher rate of cell proliferation. Osteoblasts on gamma-treated surfaces showed 30% higher alkaline phosphatase activity at day 5 and 60% higher calcium deposition at day 20. The strength of in vivo bone-implant integration increased by 40% at the early healing stage of week 2 for gamma-treated implants. Gamma ray-treated surfaces regained hydrophilicity and showed a lower percentage of carbon (35%) as opposed to 48% on untreated aged surfaces. The data indicated that gamma ray pretreatment of titanium substantially enhances its bioactivity and osteoconductivity, in association with the significant reduction in surface carbon and the recovery of hydrophilicity. The results suggest that gamma ray treatment could be an effective surface enhancement technology to overcome biological aging of titanium and improve the biological properties of titanium implants.

Effect of cleaning and sterilization on titanium implant surface properties and cellular response

Titanium (Ti) has been widely used as an implant material due to the excellent biocompatibility and corrosion resistance of its oxide surface. Biomaterials must be sterile before implantation, but the effects of sterilization on their surface properties have been less well studied. The effects of cleaning and sterilization on surface characteristics were bio-determined using contaminated and pure Ti substrata first manufactured to present two different surface structures: pretreated titanium (PT, Ra=0.4 μm) (i.e. surfaces that were not modified by sandblasting and/or acid etching); (SLA, Ra=3.4 μm). Previously cultured cells and associated extracellular matrix were removed from all bio-contaminated specimens by cleaning in a sonicator bath with a sequential acetone-isopropanol-ethanol-distilled water protocol. Cleaned specimens were sterilized with autoclave, gamma irradiation, oxygen plasma, or ultraviolet light. X-ray photoelectron spectroscopy (XPS), contact angle measurements, profilometry, and scanning electron microscopy were used to examine surface chemical components, hydrophilicity, roughness, and morphology, respectively. Small organic molecules present on contaminated Ti surfaces were removed with cleaning. XPS analysis confirmed that surface chemistry was altered by both cleaning and sterilization. Cleaning and sterilization affected hydrophobicity and roughness. These modified surface properties affected osteogenic differentiation of human MG63 osteoblast-like cells. Specifically, autoclaved SLA surfaces lost the characteristic increase in osteoblast differentiation seen on starting SLA surfaces, which was correlated with altered surface wettability and roughness. These data indicated that recleaned and resterilized Ti implant surfaces cannot be considered the same as the first surfaces in terms of surface properties and cell responses. Therefore, the reuse of Ti implants after resterilization may not result in the same tissue responses as found with never-before-implanted specimens.

Effects of UV photofunctionalization on the nanotopography enhanced initial bioactivity of titanium

This study addresses the control of the biological capabilities of titanium through specific nanosurface features and its potential modulation by UV photofunctionalization. Rat bone marrow derived osteoblasts were cultured on titanium disks with micropits alone, micropits with 100 nm nodules, micropits with 300 nm nodules, or micropits with 500 nm nodules, with or without UV treatment. After a 24 h incubation protein adsorption, as well as the attachment, retention, and spread of osteoblasts were examined in correlation with the topographical parameters of the titanium substrates. Each of the biological events was governed by a different set of multiple surface topographical factors with a distinctive pattern of regulation. For instance, without UV treatment the protein adsorption and cell attachment capability of titanium substrates increased linearly with increasing average roughness (Ra) and surface area of titanium disks, but increased polynomially with increasing nanonodule diameter. The cell retention capability increased polynomially with increasing nanonodular diameter and Ra, but increased linearly with increasing surface area. Consequently, the micropits with 300 nm nodules created the most favorable environment for this initial osteoblast behavior and response. UV treatment of the nanonodular titanium surfaces resulted in considerable enhancement of all biological events. However, the pattern of UV-mediated enhancement was disproportionate; exponential and overriding effects were observed depending upon the biological event and topographical parameter. As an example of overriding enhancement, the cell retention capability, which fluctuated with changes in various topographical parameters, became invariably high after UV treatment. The present data provide a basis for understanding how to optimize nanostructures to create titanium surfaces with increased biological capabilities and uncover a novel advantage of UV photofunctionalization of titanium substrates that synergistically increases its nanotopography enhanced biological capabilities whereby most of the initial biological events of osteoblasts were overwhelmingly enhanced beyond a simple proportional increase.

Cluster Ion Beam Processing: Review of Current and Prospective Applications

Cluster ion beam processes which employ ions comprised of a few hundred to several thousand atoms are being developed into a new field of ion beam technology. The processes are characterized by low energy surface interaction effects, lateral sputtering phenomena and high-rate chemical reaction effects. This paper reviews the current status of studies of the fundamental cluster ion beam characteristics as they apply to nanoscale processing and present industrial applications. As new prospective applications, techniques are now being developed to employ cluster ions in surface analysis tools such as XPS and SIMS and to modify surfaces of bio-materials. Results related to these new projects will also be reviewed.

TiO2 micro-nano-hybrid surface to alleviate biological aging of UV-photofunctionalized titanium

Bioactivity and osteoconductivity of titanium degrade over time after surface processing. This time-dependent degradation is substantial and defined as the biological aging of titanium. UV treatment has shown to reactivate the aged surfaces, a process known as photofunctionalization. This study determined whether there is a difference in the behavior of biological aging for titanium with micro-nano-hybrid topography and titanium with microtopography alone, following functionalization. Titanium disks were acid etched to create micropits on the surface. Micro-nano-hybrid surfaces were created by depositioning 300-nm diameter TiO₂ nodules onto the micropits using a previously established self-assembly protocol. These disks were stored for 8 weeks in the dark to allow sufficient aging, then treated with UV light for 48 hours. Rat bone marrow–derived osteoblasts were cultured on fresh disks (immediately after UV treatment), 3-day-old disks (disks stored for 3 days after UV treatment), and 7-day- old disks. The rates of cell attachment, spread, proliferation, and levels of alkaline phosphatase activity, and calcium deposition were reduced by 30%–50% on micropit surfaces, depending on the age of the titanium. In contrast, 7-day-old hybrid surfaces maintained equivalent levels of bioactivity compared with the fresh surfaces. Both micropit and micro-nano-hybrid surfaces were superhydrophilic immediately after UV treatment. However, after 7 days, the micro-nano- hybrid surfaces became hydrorepellent, while the micropit surfaces remained hydrophilic. The sustained bioactivity levels of the micro-nano-hybrid surfaces were nullified by treating these surfaces with Cl⁻anions. A thin TiO₂ coating on the micropit surface without the formation of nanonodules did not result in the prevention or alleviation of the time-dependent decrease in biological activity. In conclusion, the micro-nano-hybrid titanium surfaces may slow the rate of time-dependent degradation of titanium bioactivity after UV photofunctionalization compared with titanium surfaces with microtopography alone. This antibiological aging effect was largely regulated by its sustained electropositivity uniquely conferred in TiO₂ nanonodules, and was independent of the degree of hydrophilicity. These results demonstrate the potential usefulness of these hybrid surfaces to effectively utilize the benefits of UV photofunctionalization and provide a model to explore the mechanisms underlying antibiological aging properties.

A modified porous titanium sheet prepared by plasma-activated sintering for biomedical applications

This study aimed to develop a contamination-free porous titanium scaffold by a plasma-activated sintering within an originally developed TiN-coated graphite mold. The surface of porous titanium sheet with or without a coated graphite mold was characterized. The cell adhesion property of porous titanium sheet was also evaluated in this study. The peak of TiC was detected on the titanium sheet processed with the graphite mold without a TiN coating. Since the titanium fiber elements were directly in contact with the carbon graphite mold during processing, surface contamination was unavoidable event in this condition. The TiC peak was not detectable on the titanium sheet processed within the TiN-coated carbon graphite mold. This modified plasma-activated sintering with the TiN-coated graphite mold would be useful to fabricate a contamination-free titanium sheet. The number of adherent cells on the modified titanium sheet was greater than that of the bare titanium plate. Stress fiber formation and the extension of the cells were observed on the titanium sheets. This modified titanium sheet is expected to be a new tissue engineering material in orthopedic bone repair.

Electrostatic control of protein adsorption on UV-photofunctionalized titanium

Ultraviolet (UV)-photofunctionalization of titanium to enable the establishment of a nearly complete bone-implant contact was reported recently. However, the underlying mechanism for this is unknown. We hypothesized that UV-treated titanium surfaces acquire distinct electrostatic properties that may play important roles in determining the bioactivity of these surfaces. The objective of this study was to determine the protein adsorption capability of UV-treated titanium surfaces under various electrostatic environments. The amount of albumin adsorbed on UV-treated and untreated titanium disks was evaluated under different pH conditions above and below the isoelectric points of albumin and titanium. The effects of additional treatment with various ionic solutions were also examined. Albumin adsorption on UV-treated surfaces at pH 7.0 was considerably greater (6-fold after 3h of incubation and 2.5-fold after 24h) than that to UV-untreated surfaces. UV-enhanced albumin adsorption was abrogated at pH 3.0 or when these titanium surfaces were treated with anions, while maintaining UV-induced superhydrophilicity. Albumin adsorption on UV-untreated titanium surfaces increased after treating these surfaces with divalent cations but not after treating them with monovalent cations. These results indicated that UV-treated titanium surfaces are electropositively charged as opposed to electronegatively charged UV-untreated titanium surfaces. This distinct UV-induced electrostatic property predominantly regulates the protein adsorption capability of titanium, superseding the effect of hydrophilic status, and converts titanium surfaces from bioinert to bioactive. As a result, direct titanium-protein interactions take place exclusively on UV-treated titanium surfaces without the aid of bridging ions.

Selective cell affinity of biomimetic micro-nano-hybrid structured TiO2 overcomes the biological dilemma of osteoblasts

OBJECTIVE

There is a great demand for dental implant surfaces to accelerate the process of peri-implant bone generation to reduce its healing time and enable early loading. To this end, an inverse correlation between the proliferation and functional maturation (differentiation) in osteoblasts presents a challenge for the rapid generation of greater amounts of bone. For instance, osteoblasts exhibit faster differentiation but slower proliferation on micro-roughened titanium surfaces. Using a unique micro-nano-hierarchical topography of TiO(2) that mimics biomineralized matrices, this study demonstrates that this challenge can be overcome without the use of biological agents.

METHODS

Titanium disks of grade 2 commercially pure titanium were prepared by machining (smooth surface). To create a microtexture with peaks and valleys (micropit surface), titanium disks were acid-etched. To create 200-nm TiO(2) nanonodules within the micropits (nanonodule-in-micropit surface), TiO(2) was sputter-deposited onto the acid-etched surface. Rat bone marrow-derived osteoblasts and NIH3T3 fibroblasts were cultured on machined smooth, micropit, and nanonodule-in-micropit surfaces.

RESULTS

Despite the substantially increased surface roughness, the addition of 200-nm nanonodules to micropits increased osteoblast proliferation while enhancing their functional differentiation. In contrast, this nanonodule-in-micropit surface decreased proliferation and function in fibroblasts.

SIGNIFICANCE

The data suggest the establishment of cell-selectively functionalized nano-in-micro smart titanium surfaces that involve a regulatory effect on osteoblast proliferation, abrogating the inhibitory mechanism on the micropitted surface, while enhancing their functional differentiation. Biomimetic and controllable nature of this nanonodules-in-micropits surface may offer a novel micro-to-nanoscale hierarchical platform to biologically optimize nanofeatures of biomaterials. Particularly, this micro-nano-hybrid surface may be an effective approach to improve current dental implant surfaces for accelerated bone integration.

Enhancement of bone-titanium integration profile with UV-photofunctionalized titanium in a gap healing model

In this study, we tested the potential of UV-photofunctionalized titanium surfaces to overcome compromised bone-titanium integration in a gap healing model. Titanium in rod and disk forms was acid etched and then stored for 4 weeks under dark ambient conditions. Titanium rods with and without UV pretreatment were placed into a rat femur with (contact healing) or without (gap healing) contact with the innate cortical bone. The titanium implants were subjected to a biomechanical push-in test, micro-CT bone morphometry, and surface elemental analysis after 2 weeks of healing. The strength of bone-titanium integration in the gap healing model was one-third of that in the contact healing model. However, UV-treated implants in the gap healing condition produced a strength of bone-titanium integration equivalent to that of untreated implants in the contact healing condition. Bone volume around UV-treated implants was 2- to 3-fold greater than that around the untreated implants in the gap healing model. A bone generation profile drawn along the long axis of the implant exhibited greater contrast between the untreated and UV-treated surfaces in the cortical area than in the bone marrow area. The bone tissue formed on UV-treated implants showed a higher Ca/P ratio than that formed on untreated titanium. The rate of cell proliferation, alkaline phosphatase activity, and calcium deposition in femoral periosteal cells and in bone marrow-derived osteoblasts were greater in cultures on UV-treated titanium disks than in cultures on untreated disks. The UV-enhanced function in periosteal cells was more pronounced when they were co-cultured with bone marrow-derived osteoblasts, indicating a synergistic effect of UV-treated titanium with biological signals from bone marrow-derived osteoblasts. Within the limitation of the model used in this study, UV-photofunctionalized titanium surfaces may overcome the challenging condition of bone-titanium integration without cortical bone support. UV treatment of implants induced marked improvements in the behavior of bone formation and quantity and quality of bone tissue around the implants. These effects may be related to the promoted function of both periosteum- and bone marrow-derived osteogenic cells at the local level around UV-treated titanium surfaces.