Novel anodization technique using a block copolymer template for nanopatterning of titanium implant surfaces

Optimizing alkaline hydrothermal treatment for biomimetic smart metallic orthopedic and dental implants

Orthopedic and dental implant failure continues to be a significant concern due to localized bacterial infections. Previous studies have attempted to improve implant surfaces by modifying their texture and roughness or coating them with antibiotics to enhance antibacterial properties for implant longevity. However, these approaches have demonstrated limited effectiveness. In this study, we attempted to engineer the titanium (Ti) alloy surface biomimetically at the nanometer scale, inspired by the cicada wing nanostructure using alkaline hydrothermal treatment (AHT) to simultaneously confer antibacterial properties and support the adhesion and proliferation of mammalian cells. The two modified Ti surfaces were developed using a 4 h and 8 h AHT process in 1 N NaOH at 230 °C, followed by a 2-hour post-calcination at 600 °C. We found that the control plates showed a relatively smooth surface, while the treatment groups (4 h & 8 h AHT) displayed nanoflower structures containing randomly distributed nano-spikes. The results demonstrated a statistically significant decrease in the contact angle of the treatment groups, which increased wettability characteristics. The 8 h AHT group exhibited the highest wettability and significant increase in roughness 0.72 ± 0.08 µm (P < 0.05), leading to more osteoblast cell attachment, reduced cytotoxicity effects, and enhanced relative survivability. The alkaline phosphatase activity measured in all different groups indicated that the 8 h AHT group exhibited the highest activity, suggesting that the surface roughness and wettability of the treatment groups may have facilitated cell adhesion and attachment and subsequently increased secretion of extracellular matrix. Overall, the findings indicate that biomimetic nanotextured surfaces created by the AHT process have the potential to be translated as implant coatings to enhance bone regeneration and implant integration.

Application of femtosecond laser microfabrication in the preparation of advanced bioactive titanium surfaces

The surface activation of titanium plays a key role in the biological properties of titanium implants as bone repair materials. Improving the ability to induce apatite precipitation on the surface was a well-accepted titanium bioactivation route. In this study, advanced femtosecond laser microfabrication was applied to modify titanium surfaces, and the effect of femtosecond laser etching on apatite precipitation was investigated and compared with popular titanium modification methods. Meanwhile, the mechanism of apatite formation after femtosecond laser modification was interpreted from the point of materials science. The surface physical-chemical characterization results showed that femtosecond laser etching can improve the surface hydrophilicity and increase the surface energy. Compared with traditional abrasive paper and acid-alkali treatment, this method increased the contents of active sites including titanium oxide and titanium-hydroxyl on titanium surfaces. TiO2 on the surface was transformed to TiO after femtosecond laser treatment. The samples etched with 0.3 W and 0.5 W femtosecond lasers had a better ability to induce apatite deposition than those treated with traditional mechanical treatment and popular acid-alkali modification, which would lead to better bioactivity and osteointegration. Considering the technical advantages of femtosecond lasers in microfabrication, it provides a more efficient and controllable scheme for the bioactivation of titanium. This research would improve the application potential of femtosecond laser treatment, such as micropattern preparation and surface activation, in the field of biomaterials.

Nanopatterned Titanium Implants Accelerate Bone Formation In Vivo

Accelerated de novo formation of bone is a highly desirable aim of implants targeting musculoskeletal injuries. To date, this has primarily been addressed by biologic factors. However, there is an unmet need for robust, highly reproducible yet economic alternative strategies that strongly induce an osteogenic cell response. Here, we present a surface engineering method of translating bioactive nanopatterns from polymeric in vitro studies to clinically relevant material for orthopedics: three-dimensional, large area metal. We use a titanium-based sol-gel whereby metal implants can be engineered to induce osteoinduction both in vitro and in vivo. We show that controlled disordered nanotopographies presented as pillars with 15-25 nm height and 100 nm diameter on titanium dioxide effectively induce osteogenesis when seeded with STRO-1-enriched human skeletal stem cells in vivo subcutaneous implantation in mice. After 28 days, samples were retrieved, which showed a 20-fold increase in osteogenic gene induction of nanopatterned substrates, indicating that the sol-gel nanopatterning method offers a promising route for translation to future clinical orthopedic implants.

Bioactive Effects of Low-Temperature Argon-Oxygen Plasma on a Titanium Implant Surface

Although titanium is the most commonly used dental implant material, its biological aging directly leads to a lower rate of osseointegration. The aim of this study is to treat aged titanium disc surfaces using low-temperature argon-oxygen plasma (LTAOP) to obtain a more hydrophilic surface in order to enhance biological activities of osteoblasts on dental implant materials. In this study, smooth-machined titanium (SM Ti) and sandblasted and acid-etched titanium (SLA Ti) substrates were used. Aged titanium discs (SM and SLA Ti) were activated by LTAOP and the surface properties were analyzed. Osteoblasts were then seeded onto the aged and LTAOP-treated surfaces. Cell morphology, viability, and features of osteogenesis were examined. We showed that after the LTAOP treatment, the surfaces of both SM and SLA titanium substrates become more hydrophilic with a larger active oxygen species composition, whereas no obvious morphological changes were observed. Osteoblasts were found to be attached and stretched well on the surfaces of LTAOP treatment specimens. Moreover, the proliferation and osteocalcin secretion of osteoblasts on the plasma-activated titanium samples were superior to the untreated counterparts. LTAOP activation can enhance the attachment, proliferation, and mineralization of osteoblasts on the surfaces of the aged titanium substrates. This research provides a new strategy to modify the surface of titanium dental implants for improved biological functions.

Multifunctional Coatings and Nanotopographies: Toward Cell Instructive and Antibacterial Implants

In biomaterials science, it is nowadays well accepted that improving the biointegration of dental and orthopedic implants with surrounding tissues is a major goal. However, implant surfaces that support osteointegration may also favor colonization of bacterial cells. Infection of biomaterials and subsequent biofilm formation can have devastating effects and reduce patient quality of life, representing an emerging concern in healthcare. Conversely, efforts toward inhibiting bacterial colonization may impair biomaterial-tissue integration. Therefore, to improve the long-term success of medical implants, biomaterial surfaces should ideally discourage the attachment of bacteria without affecting eukaryotic cell functions. However, most current strategies seldom investigate a combined goal. This work reviews recent strategies of surface modification to simultaneously address implant biointegration while mitigating bacterial infections. To this end, two emerging solutions are considered, multifunctional chemical coatings and nanotopographical features.

Harnessing Nanotopography to Enhance Osseointegration of Clinical Orthopedic Titanium Implants-An in Vitro and in Vivo Analysis

Despite technological advancements, further innovations in the field of orthopedics and bone regeneration are essential to meet the rising demands of an increasing aging population and associated issues of disease, injury and trauma. Nanotopography provides new opportunities for novel implant surface modifications and promises to deliver further improvements in implant performance. However, the technical complexities of nanotopography fabrication and surface analysis have precluded identification of the optimal surface features to trigger osteogenesis. We herein detail the osteoinductive potential of discrete nanodot and nanowire nanotopographies. We have examined the ability of modified titanium and titanium alloy (Ti64) surfaces to induce bone-specific gene activation and extracellular matrix protein expression in human skeletal stem cells (SSCs) in vitro, and de novo osteogenic response within a murine calvarial model in vivo. This study provides evidence of enhanced osteogenic response to nanowires 300 surface modifications, with important implications for clinical orthopedic application.

Osteoblast response to disordered nanotopography

The ability to influence stem cell differentiation is highly desirable as it would help us improve clinical outcomes for patients in various aspects. Many different techniques to achieve this have previously been investigated. This concise study, however, has focused on the topography on which cells grow. Current uncemented orthopaedic implants can fail if the implant fails to bind to the surrounding bone and, typically, forms a soft tissue interface which reduces direct bone contact. Here, we look at the effect of a previously reported nanotopography that utilises nanodisorder to influence mesenchymal stromal cell (as may be found in the bone marrow) differentiation towards bone and to also exert this effect on mature osteoblasts (as may be found in the bone). As topography is a physical technique, it can be envisaged for use in a range of materials such as polymers and metals used in the manufacture of orthopaedic implants.

Surface bioactivation through the nanostructured layer on titanium modified by facile HPT treatment

Facile fabrication of nanostructured surface is of great importance for the use of titanium (Ti) implants in biomedical field. In this study, a low-cost and easy-to-operate method called HPT (hydrothermal & pressure) here has been developed and used to fabricate the expected nanostructured surface on Ti substrates. The effects of experimental parameters on the morphology of Ti surface were investigated and characterized. The results indicated that by altering the hydrothermal pressure, NaOH concentration and treating time, surface nanostructure like nanopetals or nanoflakes could be formed on the surface of Ti substrates. The orthogonal experiments were conducted to demonstrate the optimized operation conditions. A formation mechanism of the nanostructured titanate layer was proposed, revealing that the nanostructured layer could be formed via a special upward and downward co-growth manner. In vitro cell culture showed that the HPT treated Ti substrates, especially the T-10 sample, could greatly enhance the cell-material interactions, i.e. the cell proliferation and differentiation, focal protein adhesion, and osteogenic factor expression. The HPT method paves a new way to modify the surface of Ti implants with better bioactivity and promising prospect for future biomedical applications.

Non-thermal atmospheric pressure plasma functionalized dental implant for enhancement of bacterial resistance and osseointegration

OBJECTIVE

Even though roughened titanium (Ti) and Ti alloys have been clinically used as dental implant, they encourage bacterial adhesion, leading to failure of the initial stability. Here, the non-thermal atmospheric pressure plasma jet (NTAPPJ) functionalized Ti and Ti alloy were investigated to promote cellular activities but inhibit the initial attachment of the adherent pioneer bacterium, Streptococcus sanguinis, without topographical changes.

METHODS

After the produced radicals from NTAPPJ were characterized, bacterial adhesion to specimens was assessed by PrestoBlue assay and live-dead staining with or without the NTAPPJ functionalizing. After the surface was characterized using optical profilometry, X-ray photoelectron spectroscopy and contact angle analysis, the ions released from the specimens were investigated. In vitro initial cell attachment (4h or 24h) with adhesion images and alkaline phosphatase activity (ALP, 14 days) measurements were performed using rat bone marrow-derived mesenchymal stem cells.

RESULTS

The initial bacterial adhesion to the Ti and Ti alloy was significantly inhibited after NTAPPJ functionalizing (p<0.05) compared to those without NTAPPJ functionalizing. The bacterial adhesion-resistance effect was induced by carbon cleaning, which was dependent on the working gas used on the Ti specimens (nitrogen>ammonia and air, p<0.05). The initial cell adhesion with well-developed vinculin localization and consequent ALP activity at 14days to the NTAPPJ-functionalized specimens were superior to the non-treated specimens.

SIGNIFICANCE

For the promising success of dental implants, NTAPPJ functionalizing is suggested as a novel surface modification technique; this technique can help ensure the success of integration between the dental implants and bone tissues with less concern of inflammation.

Mesenchymal Stem Cell Fate: Applying Biomaterials for Control of Stem Cell Behavior

The materials pipeline for biomaterials and tissue engineering applications is under continuous development. Specifically, there is great interest in the use of designed materials in the stem cell arena as materials can be used to manipulate the cells providing control of behavior. This is important as the ability to "engineer" complexity and subsequent in vitro growth of tissues and organs is a key objective for tissue engineers. This review will describe the nature of the materials strategies, both static and dynamic, and their influence specifically on mesenchymal stem cell fate.

Analysis of Osteoclastogenesis/Osteoblastogenesis on Nanotopographical Titania Surfaces

A focus of orthopedic research is to improve osteointegration and outcomes of joint replacement. Material surface topography has been shown to alter cell adhesion, proliferation, and growth. The use of nanotopographical features to promote cell adhesion and bone formation is hoped to improve osteointegration and clinical outcomes. Use of block-copolymer self-assembled nanopatterns allows nanopillars to form via templated anodization with control over height and order, which has been shown to be of cellular importance. This project assesses the outcome of a human bone marrow-derived co-culture of adherent osteoprogenitors and osteoclast progenitors on polished titania and titania patterned with 15 nm nanopillars, fabricated by a block-copolymer templated anodization technique. Substrate implantation in rabbit femurs is performed to confirm the in vivo bone/implant integration. Quantitative and qualitative results demonstrate increased osteogenesis on the nanopillar substrate with scanning electron microscopy, histochemical staining, and real-time quantitative reverse-transcription polymerase chain reaction analysis performed. Osteoblast/osteoclast co-culture analysis shows an increase in osteoblastogenesis-related gene expression and reduction in osteoclastogenesis. Supporting this in vitro finding, in vivo implantation of substrates in rabbit femora indicates increased implant/bone contact by ≈20%. These favorable osteogenic characteristics demonstrate the potential of 15 nm titania nanopillars fabricated by the block-copolymer templated anodization technique.

High-Resolution Metal Nanopatterning by Means of Switchable Block Copolymer Templates

In this review, recent developments in the fabrication of hexagonal and parallel ordered arrays of metallic nanodomains on a substrate are described. We focus on the nanopatterning approach by means of switchable block copolymer thin films. This approach is highly advantageous, because it can lead to extremely regular patterns with metal subunits of only a few nanometers in diameter and center-to-center distances of tens of nanometers. Hence, the resulting 1D or 2D periodic arrays of metal nanodots and nanowires on silicon substrates can be fabricated with extremely high unit densities and on very large areas. The templated deposition of presynthesized metal nanoparticles on functional block copolymers is described in detail. Current challenges are discussed and an outlook for further developments is given.

Mineral substituted hydroxyapatite coatings deposited on nanoporous TiO2 modulate the directional growth and activity of osteoblastic cells

The biocompatibility of anodized titanium was improved by electrophoretically deposited mineral substituted HAP.

2D and 3D nanopatterning of titanium for enhancing osteoinduction of stem cells at implant surfaces

The potential for the use of well-defined nanopatterns to control stem cell behaviour on surfaces has been well documented on polymeric substrates. In terms of translation to orthopaedic applications, there is a need to develop nanopatterning techniques for clinically relevant surfaces, such as the load-bearing material titanium (Ti). In this work, a novel nanopatterning method for Ti surfaces is demonstrated, using anodisation in combination with PS-b-P4VP block copolymer templates. The block copolymer templates allows for fabrication of titania nanodot patterns with precisely controlled dimensions and positioning which means that this technique can be used as a lithography-like patterning method of bulk Ti surfaces on both flat 2D and complex shaped 3D surfaces. In vitro studies demonstrate that precise tuning of the height of titania nanodot patterns can modulate the osteogenic differentiation of mesenchymal stem cells. Cells on both the 8 nm and 15 nm patterned surfaces showed a trend towards a greater number of the large, super-mature osteogenic focal adhesions than on the control polished Ti surface, but the osteogenic effect was more pronounced on the 15 nm substrate. Cells on this surface had the longest adhesions of all and produced larger osteocalcin deposits. The results suggest that nanopatterning of Ti using the technique of anodisation through a block copolymer template could provide a novel way to enhance osteoinductivity on Ti surfaces.