Titanium dioxide nanotubes enhance bone bonding in vivo

Advances in implants and bone graft types for lumbar spinal fusion surgery

The increasing prevalence of spinal disorders worldwide necessitates advanced treatments, particularly interbody fusion for severe cases that are unresponsive to non-surgical interventions. This procedure, especially 360° lumbar interbody fusion, employs an interbody cage, pedicle screw-and-rod instrumentation, and autologous bone graft (ABG) to enhance spinal stability and promote fusion. Despite significant advancements, a persistent 10% incidence of non-union continues to result in compromised patient outcomes and escalated healthcare costs. Innovations in lumbar stabilisation seek to mimic the properties of natural bone, with evolving implant materials like titanium (Ti) and polyetheretherketone (PEEK) and their composites offering new prospects. Additionally, biomimetic cages featuring precisely engineered porosities and interconnectivity have gained traction, as they enhance osteogenic differentiation, support osteogenesis, and alleviate stress-shielding. However, the limitations of ABG, such as harvesting morbidities and limited fusion capacity, have spurred the exploration of sophisticated solutions involving advanced bone graft substitutes. Currently, demineralised bone matrix and ceramics are in clinical use, forming the basis for future investigations into novel bone graft substitutes. Bioglass, a promising newcomer, is under investigation despite its observed rapid absorption and the potential for foreign body reactions in preclinical studies. Its clinical applicability remains under scrutiny, with ongoing research addressing challenges related to burst release and appropriate dosing. Conversely, the well-documented favourable osteogenic potential of growth factors remains encouraging, with current efforts focused on modulating their release dynamics to minimise complications. In this evidence-based narrative review, we provide a comprehensive overview of the evolving landscape of non-degradable spinal implants and bone graft substitutes, emphasising their applications in lumbar spinal fusion surgery. We highlight the necessity for continued research to improve clinical outcomes and enhance patient well-being.

An Overview of Hydrothermally Synthesized Titanate Nanotubes: The Factors Affecting Preparation and Their Promising Pharmaceutical Applications

Recently, titanate nanotubes (TNTs) have been receiving more attention and becoming an attractive candidate for use in several disciplines. With their promising results and outstanding performance, they bring added value to any field using them, such as green chemistry, engineering, and medicine. Their good biocompatibility, high resistance, and special physicochemical properties also provide a wide spectrum of advantages that could be of crucial importance for investment in different platforms, especially medical and pharmaceutical ones. Hydrothermal treatment is one of the most popular methods for TNT preparation because it is a simple, cost-effective, and environmentally friendly water-based procedure. It is also considered as a strong candidate for large-scale production intended for biomedical application because of its high yield and the special properties of the resulting nanotubes, especially their small diameters, which are more appropriate for drug delivery and long circulation. TNTs' properties highly differ according to the preparation conditions, which would later affect their subsequent application field. The aim of this review is to discuss the factors that could possibly affect their synthesis and determine the transformations that could happen according to the variation of factors. To fulfil this aim, relevant scientific databases (Web of Science, Scopus, PubMed, etc.) were searched using the keywords titanate nanotubes, hydrothermal treatment, synthesis, temperature, time, alkaline medium, post treatment, acid washing, calcination, pharmaceutical applications, drug delivery, etc. The articles discussing TNTs preparation by hydrothermal synthesis were selected, and papers discussing other preparation methods were excluded; then, the results were evaluated based on a careful reading of the selected articles. This investigation and comprehensive review of different parameters could be the answer to several problems concerning establishing a producible method of TNTs production, and it might also help to optimize their characteristics and then extend their application limits to further domains that are not yet totally revealed, especially the pharmaceutical industry and drug delivery.

Polydopamine-Modified Titanium Dioxide Nanotube Arrays Doped with Calcium as a Sustained Drug Delivery System

Titanium nanotube (TNT) arrays manufactured via electrochemical anodization have been widely used as local drug carriers due to their excellent biocompatibility and customizable nanotubular structures. However, the uncontrollable and abrupt drug release at the early stage decreases the drug release duration, leading to excessive drug concentration at the implantation site. In this study, a continuous drug delivery system based on TNTs was created. Initially, a basic ultrasound-assisted approach was utilized to deposit a polydopamine (PDA) coating onto TNTs to obtain PDA-modified TNTs. Next, TNTs-PDA were submerged in a calcium chloride solution to include Ca2+ through Ca2+ coordination between the PDA layer's catechol groups. Sodium alendronate (NaAL) was used as a model drug and loaded onto TNTs-PDA-Ca2+ by immersing them in an NaAL solution. In the final step, NaAL was covalently attached to TNTs-PDA-Ca2+ through coordination bonds with Ca2+. The samples underwent characterization through the use of various techniques, including field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction patterning, X-ray photoelectron spectroscopy, and inductively coupled plasma emission spectrometry. The results indicated that the bioactivity of TNTs improved, and there was an enhancement in drug loading capacity and release performance due to modification with PDA and Ca2+. Furthermore, acidic conditions can cause significant drug release due to the cleavage of coordination bonds between the drug and Ca2+ ions. Thus, the aforementioned drug delivery system represents a potentially promising approach for achieving sustained and controllable drug release.

Nanoscale implant anchorage aided by cement line deposition into titanium dioxide nanotubes

The success of titanium dental implants relies on osseointegration, the load-bearing connection between bone tissue and the device that, in contact osteogenesis, comprises the deposition of bony cement line matrix onto the implant surface. Titanium dioxide nanotubes (NTs) are considered a promising surface for improved osseointegration, yet the mechanisms of cement line integration with such features remains elusive. Herein, we illustrate cement line deposition into NTs on the surface of titanium implants with two underlaying microstructures: a machined surface or a blasted/acid etched surface placed in the tibiae of Wistar rats. After retrieval, scanning electron microscopy of tissue reflected from the implant surface indicated minimal incursion of the cement line matrix into the NTs. To investigate this further, focused ion beam was utilized to prepare cross-sectional samples that could be characterized using scanning transmission electron microscopy. The cement line matrix covered NTs regardless of underlying microstructure, which was further confirmed by elemental analysis. In some instances, cement line infiltration into the NTs was noted, which reveals a mechanism of nanoscale anchorage. This study is the first to demonstrate cement line deposition into titanium NTs, suggesting nano-anchorage as a mechanism for the success of the NT modified surfaces in vivo.

Disturbing cytoskeleton by engineered nanomaterials for enhanced cancer therapeutics

Cytoskeleton plays a significant role in the shape change, migration, movement, adhesion, cytokinesis, and phagocytosis of tumor cells. In clinical practice, some anti-cancer drugs achieve cytoskeletal therapeutic effects by acting on different cytoskeletal protein components. However, in the absence of cell-specific targeting, unnecessary cytoskeletal recombination in organisms would be disastrous, which would also bring about severe side effects during anticancer process. Nanomedicine have been proven to be superior to some small molecule drugs in cancer treatment due to better stability and targeting, and lower side effects. Therefore, this review summarized the recent developments of various nanomaterials disturbing cytoskeleton for enhanced cancer therapeutics, including carbon, noble metals, metal oxides, black phosphorus, calcium, silicon, polymers, peptides, and metal-organic frameworks, etc. A comprehensive analysis of the characteristics of cytoskeleton therapy as well as the future prospects and challenges towards clinical application were also discussed. We aim to drive on this emerging topic through refreshing perspectives based on our own work and what we have also learnt from others. This review will help researchers quickly understand relevant cytoskeletal therapeutic information to further advance the development of cancer nanomedicine.

Nanoscale Morphologies on the Surface of 3D-Printed Titanium Implants for Improved Osseointegration: A Systematic Review of the Literature

Three-dimensional (3D) printing is serving as the most promising approach to fabricate personalized titanium (Ti) implants for the precise treatment of complex bone defects. However, the bio-inert nature of Ti material limits its capability for rapid osseointegration and thus influences the implant lifetime in vivo. Despite the macroscale porosity for promoting osseointegration, 3D-printed Ti implant surface morphologies at the nanoscale have gained considerable attention for their potential to improve specific outcomes. To evaluate the influence of nanoscale surface morphologies on osseointegration outcomes of 3D-printed Ti implants and discuss the available strategies, we systematically searched evidence according to the PRISMA on PubMed, Embase, Web of Science, and Cochrane (until June 2022). The inclusion criteria were in vivo (animal) studies reporting the osseointegration outcomes of nanoscale morphologies on the surface of 3D-printed Ti implants. The risk of bias (RoB) was assessed using the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE's) tool. The quality of the studies was evaluated using the Animal Research: Reporting of In Vivo Experiments (ARRIVE) guidelines. (PROSPERO: CRD42022334222). Out of 119 retrieved articles, 9 studies met the inclusion criteria. The evidence suggests that irregular nano-texture, nanodots and nanotubes with a diameter of 40-105nm on the surface of porous/solid 3D-printed Ti implants result in better osseointegration and vertical bone ingrowth compared to the untreated/polished ones by significantly promoting cell adhesion, matrix mineralization, and osteogenic differentiation through increasing integrin expression. The RoB was low in 41.1% of items, unclear in 53.3%, and high in 5.6%. The quality of the studies achieved a mean score of 17.67. Our study demonstrates that nanostructures with specific controlled properties on the surface of 3D-printed Ti implants improve their osseointegration. However, given the small number of studies, the variability in experimental designs, and lack of reporting across studies, the results should be interpreted with caution.

TiO2nanotubes induce early mitochondrial fission in BMMSCs and promote osseointegration

Nanotopography can promote osseointegration, but how bone marrow mesenchymal stem cells (BMMSCs) respond to this physical stimulus is unclear. Here, we found that early exposure of BMMSCs to nanotopography (6 h) caused mitochondrial fission rather than fusion, which was necessary for osseointegration. We analyzed the changes in mitochondrial morphology and function of BMMSCs located on the surfaces of NT100 (100 nm nanotubes) and ST (smooth) by super-resolution microscopy and other techniques. Then, we found that both ST and NT100 caused a significant increase in mitochondrial fission early on, but NT100 caused mitochondrial fission much earlier than those on ST. In addition, the mitochondrial functional statuses were good at the 6 h time point, this is at odds with the conventional wisdom that fusion is good. This fission phenomenon adequately protected mitochondrial membrane potential (MMP) and respiration and reduced reactive oxygen species. Interestingly, the MMP and oxygen consumption rate of BMMSCs were reduced when mitochondrial fission was inhibited by Mdivi-1(Inhibition of dynamin-related protein 1 fission) in the early stage. In addition, the effect on osseointegration was significantly worse, and this effect did not improve with time. Taken together, the findings indicate that early mitochondrial fission plays an important role in nanotopography-mediated promotion of osseointegration, which is of great significance to the surface structure design of biomaterials.

Altering the Surface Properties of Metal Alloys Utilizing Facile and Ecological Methods

The development of a superhydrophobic and, even, water-repellent metal alloy surface is reported utilizing a simple, fast, and economical way that requires minimum demands on the necessary equipment and/or methods used. The procedure involves an initial irradiation of the metallic specimen using a femtosecond laser, which results in a randomly roughened surface, that is subsequently followed by placing the item in an environment under moderate vacuum (pressure 10^-2 mbar) and/or under low-temperature heating (at temperatures below 120 °C). The effects of both temperature and low pressure on the surface properties (water contact angle and contact angle hysteresis) are investigated and surfaces with similar superhydrophobicity are obtained in both cases; however, a significant difference concerning their water-repellent ability is obtained. The surfaces that remained under vacuum were water-repellent, exhibiting very high values of contact angle with a very low contact angle hysteresis, whereas the surfaces, which underwent thermal processing, exhibited superhydrophobicity with high water adhesion, where water droplets did not roll off even after a significant inclination of the surface. The kinetics of the development of superhydrophobic behavior was investigated as well. The findings were understood when the surface roughness characteristics were considered together with the chemical composition of the surface.

Molecular Response to Nanopatterned Implants in the Human Jaw Bone

Implant surface modification by nanopatterning is an interesting route for enhancing osseointegration in humans. Herein, the molecular response to an intentional, controlled nanotopography pattern superimposed on screw-shaped titanium implants is investigated in human bone. When clinical implants are installed, additional two mini-implants, one with a machined surface (M) and one with a machined surface superimposed with a hemispherical nanopattern (MN), are installed in the posterior maxilla. In the second-stage surgery, after 6-8 weeks, the mini-implants are retrieved by unscrewing, and the implant-adherent cells are subjected to gene expression analysis using quantitative polymerase chain reaction (qPCR). Compared to those adherent to the machined (M) implants, the cells adherent to the nanopatterned (MN) implants demonstrate significant upregulation (1.8- to 2-fold) of bone-related genes (RUNX2, ALP, and OC). No significant differences are observed in the expression of the analyzed inflammatory and remodeling genes. Correlation analysis reveals that older patient age is associated with increased expression of proinflammatory cytokines (TNF-α and MCP-1) on the machined implants and decreased expression of pro-osteogenic factor (BMP-2) on the nanopatterned implants. Controlled nanotopography, in the form of hemispherical 60 nm protrusions, promotes gene expressions related to early osteogenic differentiation and osteoblastic activity in implant-adherent cells in the human jaw bone.

Effect of micro/nanoscaled Ti phosphate/Ti oxide hybrid coating on the osseointegration of Ti implants

OBJECTIVES

This study was performed to fabricate a bionic coating with titanium (Ti) phosphate to promote the osseointegration of Ti substrate implants.

METHODS

Phosphorylated micro/nanocoating was prepared on the surface of pure titanium (i.e., TiP-Ti) by hydrothermal process under special pressure, and the untreated smooth pure titanium (cp-Ti) was selected as the control. To evaluate the characteristics of the coating surface, scanning electron microscopy, X-ray diffraction, atomic force microscopy, and contact-angle measurement were performed. In addition, the effects of TiP-Ti on the proliferation, adhesion, and differentiation of rat bone marrow mesenchymal stem cells (BMSCs) were investigated by using in vitro cytology. Finally, TiP-Ti implants were implanted into the rat tibia, and the effect of TiP-Ti on the osseointegration in the host was evaluated after 12 weeks.

RESULTS

The TiP-Ti surface presented a bionic structure with coexisting nanoscale 3D spatial structure and microscale pores. In vitro experiments showed that the BMSCs had enhanced adhesion, proliferation, and osteogenic differentiation on the TiP-Ti surface. Furthermore, in vivo, TiP-Ti showed considerably stronger osseointegration compared with pure titanium, and the ultimate shear strength and maximum pushing force were significantly improved.

CONCLUSIONS

A bionic structure with TiP-Ti micro/nanoscale coating was successfully fabricated, indicating a promising method for modifying the surface of implants.

Porous Nanomaterials Targeting Autophagy in Bone Regeneration

Porous nanomaterials (PNMs) are nanosized materials with specially designed porous structures that have been widely used in the bone tissue engineering field due to the fact of their excellent physical and chemical properties such as high porosity, high specific surface area, and ideal biodegradability. Currently, PNMs are mainly used in the following four aspects: (1) as an excellent cargo to deliver bone regenerative growth factors/drugs; (2) as a fluorescent material to trace cell differentiation and bone formation; (3) as a raw material to synthesize or modify tissue engineering scaffolds; (4) as a bio-active substance to regulate cell behavior. Recent advances in the interaction between nanomaterials and cells have revealed that autophagy, a cellular survival mechanism that regulates intracellular activity by degrading/recycling intracellular metabolites, providing energy/nutrients, clearing protein aggregates, destroying organelles, and destroying intracellular pathogens, is associated with the phagocytosis and clearance of nanomaterials as well as material-induced cell differentiation and stress. Autophagy regulates bone remodeling balance via directly participating in the differentiation of osteoclasts and osteoblasts. Moreover, autophagy can regulate bone regeneration by modulating immune cell response, thereby modulating the osteogenic microenvironment. Therefore, autophagy may serve as an effective target for nanomaterials to facilitate the bone regeneration process. Increasingly, studies have shown that PNMs can modulate autophagy to regulate bone regeneration in recent years. This paper summarizes the current advances on the main application of PNMs in bone regeneration, the critical role of autophagy in bone regeneration, and the mechanism of PNMs regulating bone regeneration by targeting autophagy.

Nanomaterials as a Successor of Antibiotics in Antibiotic-Resistant, Biofilm Infected Wounds?

Chronic wounds are a growing problem for both society and patients. They generate huge costs for treatment and reduce the quality of life of patients. The greatest challenge when treating a chronic wound is prolonged infection, which is commonly caused by biofilm. Biofilm makes bacteria resistant to individuals’ immune systems and conventional treatment. As a result, new treatment options, including nanomaterials, are being tested and implemented. Nanomaterials are particles with at least one dimension between 1 and 100 nM. Lipids, liposomes, cellulose, silica and metal can be carriers of nanomaterials. This review’s aim is to describe in detail the mode of action of those molecules that have been proven to have antimicrobial effects on biofilm and therefore help to eradicate bacteria from chronic wounds. Nanoparticles seem to be a promising treatment option for infection management, which is essential for the final stage of wound healing, which is complete wound closure.

Research to Clinics: Clinical Translation Considerations for Anodized Nano-Engineered Titanium Implants

Titania nanotubes (TNTs) fabricated on titanium orthopedic and dental implants have shown significant potential in "proof of concept" in vitro, ex vivo, and short-term in vivo studies. However, most studies do not focus on a clear direction for future research towards clinical translation, and there exists a knowledge gap in identifying key research challenges that must be addressed to progress to the clinical setting. This review focuses on such challenges with respect to anodized titanium implants modified with TNTs, including optimized fabrication on clinically utilized microrough surfaces, clinically relevant bioactivity assessments, and controlled/tailored local release of therapeutics. Further, long-term in vivo investigations in compromised animal models under loading conditions are needed. We also discuss and detail challenges and progress related to the mechanical stability of TNT-based implants, corrosion resistance/electrochemical stability, optimized cleaning/sterilization, packaging/aging, and nanotoxicity concerns. This extensive, clinical translation focused review of TNTs modified Ti implants aims to foster improved understanding of key research gaps and advances, informing future research in this domain.

Gentamicin-Releasing Titania Nanotube Surfaces Inhibit Bacteria and Support Adipose-Derived Stem Cell Growth in Cocultures

Infection is the second leading cause of failure of orthopedic implants following incomplete osseointegration. Materials that increase the antimicrobial properties of surfaces while maintaining the ability for bone cells to attach and proliferate could reduce the failure rates of orthopedic implants. In this study, titania nanotubes (Nts) were modified with chitosan/heparin polyelectrolyte multilayers (PEMs) for gentamicin delivery. The antimicrobial activity of the surfaces was tested by coculturing bacteria with mammalian cells. Over 60% of gentamicin remained on the surface after an initial burst release on the first day. Antimicrobial activity of these surfaces was determined by exposure to Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Escherichia coli (E. coli) for up to 24 h. Gentamicin surfaces had less live E. coli and S. aureus by 6 h and less E. coli by 24 h compared to Nt surfaces. S. aureus and human adipose-derived stem cells (hADSCs) were cocultured on surfaces for up to 7 days to characterize the so-called "race to the surface" between bacteria and mammalian cells, which is hypothesized to ultimately determine the outcome of orthopedic implants. By day 7, there was no significant difference in bacteria between surfaces with gentamicin adsorbed on the surface and surfaces with gentamicin in solution. However, gentamicin delivered in solution is toxic to hADSCs. Alternatively, gentamicin presented from PEMs enhances the antimicrobial properties of the surfaces without inhibiting hADSC attachment and cell growth. Delivering gentamicin from the surfaces is therefore superior to delivering gentamicin in solution and represents a strategy that could improve the antimicrobial activity of orthopedic implants and reduce risk of failure due to infection, without reducing mammalian cell attachment.

Local and Systemic In Vivo Responses to Osseointegrative Titanium Nanotube Surfaces

Orthopedic implants requiring osseointegration are often surface modified; however, implants may shed these coatings and generate wear debris leading to complications. Titanium nanotubes (TiNT), a new surface treatment, may promote osseointegration. In this study, in vitro (rat marrow-derived bone marrow cell attachment and morphology) and in vivo (rat model of intramedullary fixation) experiments characterized local and systemic responses of two TiNT surface morphologies, aligned and trabecular, via animal and remote organ weight, metal ion, hematologic, and nondecalcified histologic analyses. In vitro experiments showed total adherent cells on trabecular and aligned TiNT surfaces were greater than control at 30 min and 4 h, and cells were smaller in diameter and more eccentric. Control animals gained more weight, on average; however, no animals met the institutional trigger for weight loss. No hematologic parameters (complete blood count with differential) were significantly different for TiNT groups vs. control. Inductively coupled plasma mass spectrometry (ICP-MS) showed greater aluminum levels in the lungs of the trabecular TiNT group than in those of the controls. Histologic analysis demonstrated no inflammatory infiltrate, cytotoxic, or necrotic conditions in proximity of K-wires. There were significantly fewer eosinophils/basophils and neutrophils in the distal region of trabecular TiNT-implanted femora; and, in the midshaft of aligned TiNT-implanted femora, there were significantly fewer foreign body giant/multinucleated cells and neutrophils, indicating a decreased immune response in aligned TiNT-implanted femora compared to controls.

Drug release from polymer-coated TiO2 nanotubes on additively manufactured Ti-6Al-4V bone implants: a feasibility study

Insufficient osseointegration, inflammatory response and bacterial infection are responsible for the majority of bone implant failures. Drug-releasing implants subjected to adequate surface modification can concurrently address these challenges to improve the success of implant surgeries. This work investigates the use of Ti-6Al-4V (Ti64) with a dual-scale surface topography as a platform for local drug delivery. Dual-scale topography was obtained combining the inherent microscale roughness of the Ti64 samples manufactured by selective laser melting (SLM) with the nanoscale roughness of TiO2 nanotubes (TNTs) obtained by subsequent electrochemical anodization at 60 V for 30 min. TNTs were loaded with a solution of penicillin-streptomycin, a common antibiotic, and drug release was tested in vitro. Three biocompatible and biodegradable polymers, i.e. chitosan, poly(ε-caprolactone) and poly(3-hydroxybutyrate), were deposited by spin coating, while preserving the microscale topography of the substrate underneath. The presence of polymer coatings overall modified the drug release pattern, as revealed by fitting of the experimental data with a power-law model. A slight extension in the overall duration of drug release (about 17% for a single layer and 33% for two layers of PCL and PHB) and reduced burst release was observed for all polymer-coated samples compared to uncoated, especially when two layers of coatings were applied.

Electrochemical Deposition of Nanostructured Hydroxyapatite Coating on Titanium with Enhanced Early Stage Osteogenic Activity and Osseointegration

Purpose

The aim of research is to fabricate nanostructured hydroxyapatite (HA) coatings on the titanium via electrochemical deposition (ED). Additionally, the biological properties of the ED-produced HA (EDHA) coatings with a plate-like nanostructure were evaluated in vitro and in vivo by undertaking comparisons with those prepared by acid/alkali (AA) treatment and by plasma spray-produced HA (PSHA) nanotopography-free coatings.

Materials and Methods

Nanoplate-like HA coatings were prepared through ED, and nanotopography-free PSHA coatings were fabricated. The surface morphology, phase composition, roughness, and wettability of these samples were investigated. Furthermore, the growth, proliferation, and osteogenic differentiation of MC3T3-E1 cells cultured on each sample were evaluated via in vitro experiments. Histological assessment and push-out tests for the bone–implant interface were performed to explore the effect of the EDHA coatings on the interfacial osseointegration in vivo.

Results

XRD analysis showed that the strongest intensity for the EDHA coatings was at the (002) plane rather than at the regular (211) plane. Relatively higher surface roughness and greater wettability were observed for the EDHA coatings. Cellular experiments revealed that the plate-like nanostructured EDHA coatings not only possessed an ability, similar to that of PSHA coatings, to promote the adhesion and proliferation of MC3T3-E1 cells but also demonstrated significantly enhanced early or intermediate markers of osteogenic differentiation. Significant osseointegration enhancement in the early stage of implantation period and great bonding strength were observed at the interface of bone and EDHA samples. In comparison, relatively weak osseointegration and bonding strength of the bone–implant interface were observed for the AA treatment.

Conclusion

The biological performance of the plate-like nanostructured EDHA coating, which was comparable with that of the PSHA, improves early-stage osteogenic differentiation and osseointegration abilities and has great potential for enhancing the initial stability and long-term survival of uncemented or 3D porous titanium implants.

Crystallized TiO2 Nanosurfaces in Biomedical Applications

Crystallization alters the characteristics of TiO2 nanosurfaces, which consequently influences their bio-performance. In various biomedical applications, the anatase or rutile crystal phase is preferred over amorphous TiO2. The most common crystallization technique is annealing in a conventional furnace. Methods such as hydrothermal or room temperature crystallization, as well as plasma electrolytic oxidation (PEO) and other plasma-induced crystallization techniques, present more feasible and rapid alternatives for crystal phase initiation or transition between anatase and rutile phases. With oxygen plasma treatment, it is possible to achieve an anatase or rutile crystal phase in a few seconds, depending on the plasma conditions. This review article aims to address different crystallization techniques on nanostructured TiO2 surfaces and the influence of crystal phase on biological response. The emphasis is given to electrochemically anodized nanotube arrays and their interaction with the biological environment. A short overview of the most commonly employed medical devices made of titanium and its alloys is presented and discussed.

Titanium Dioxide Nanotube Arrays for Cardiovascular Stent Applications

Efficient stent implantation among others depends on avoiding the aggregation of platelets in the blood vessels and appropriate proliferation of endothelial cells and controlled proliferation of smooth muscle cells, which reduces the development of pathology, such as neointimal hyperplasia, thrombosis, and restenosis. The current article provides an elegant solution for prevention of platelet and smooth muscle cell adhesion and activation on stent surfaces while obtaining surface conditions to support the growth of human coronary artery endothelial cells. This was achieved by surface nanostructuring and chemical activation of the surface. Specific nanotopographies of titanium were obtained by electrochemical anodization, while appropriate chemical properties were attained by treatment of titanium oxide nanotubes by highly reactive oxygen plasma. Surface properties were studied by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. Wettability was evaluated by measuring the water contact angle. The influence of nanostructured morphology and plasma modification on in vitro biological response with human coronary artery endothelia and smooth muscle cells as well as whole blood was studied. Our results show that a combination of nanostructuring and plasma modification of the surfaces is an effective way to achieve desired biological responses necessary for implantable materials such as stents.

Titanium implant surface properties enhance osseointegration in ovariectomy induced osteoporotic rats without pharmacologic intervention

OBJECTIVES

This study determined whether implant surfaces that promote osseointegration in normal rats can promote osseointegration in osteoporotic rats without pharmacologic intervention.

MATERIALS AND METHODS

Virgin female 8-month-old CD Sprague Dawley rats (N = 25) were ovariectomized. At 6 weeks, microstructured/non-nanostructured/hydrophobic, microstructured/nanostructured/hydrophobic, or microstructured/nanostructured/hydrophilic Ti implants (Ø2.5 × 3.5 mm; Institut Straumann AG, Basel, Switzerland) were placed in the distal metaphysis of each femur. At 28 days, bone quality and implant osseointegration were assessed using microCT, histomorphometrics, and removal torque values (RTVs). Calvarial osteoblasts were isolated and cultured for 7 days on Ø15 mm Ti disks processed to exhibit similar surface characteristics as the implants used for the in vivo studies. The phenotype was assessed by measuring the production of osteocalcin, osteoprotegerin, osteopontin, BMP2, VEGF, and RANKL.

RESULTS

Microstructured/nanostructured/hydrophilic implants promoted increased bone-to-implant contact and RTVs in vivo and increased osteoblastic marker production in vitro compared to microstructured/non-nanostructured/hydrophobic and microstructured/nanostructured/hydrophobic implants, suggesting that osseointegration occurs in osteoporotic animals, and implant surface properties improve its rate.

CONCLUSIONS

Although all modified implants were able to osseointegrate in rats with OVX-induced osteoporosis without pharmacologic intervention, the degree of osseointegration was greater around microstructured/nanostructured/hydrophilic implant surfaces. These results suggest that when appropriate microstructure is present, hydrophilicity has a greater influence on Ti implant osseointegration compared to nanostructures. Moreover, modified implant surfaces can exert their control over the altered bone turnover observed in osteoporotic patients to stimulate functional osseointegration. These results provide critical insight for developing implants with improved osseointegration in patients with metabolic disorders of bone remodeling.

Zn-Incorporated TiO2 Nanotube Surface Improves Osteogenesis Ability Through Influencing Immunomodulatory Function of Macrophages

PURPOSE

Zinc (Zn), an essential trace element in the body, has stable chemical properties, excellent osteogenic ability and moderate immunomodulatory property. In the present study, a Zn-incorporated TiO2 nanotube (TNT) was fabricated on titanium (Ti) implant material. We aimed to evaluate the influence of nano-scale topography and Zn on behaviors of murine RAW 264.7 macrophages. Moreover, the effects of Zn-incorporated TNT surface-regulated macrophages on the behaviors and osteogenic differentiation of murine MC3T3-E1 osteoblasts were also investigated.

METHODS

TNT coatings were firstly fabricated on a pure Ti surface using anodic oxidation, and then nano-scale Zn particles were incorporated onto TNTs by the hydrothermal method. Surface topography, chemical composition, roughness, hydrophilicity, Zn release pattern and protein adsorption ability of the Zn-incorporated TiO2 nanotube surface were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), surface profiler, contact angle test, Zn release test and protein adsorption test. The cell behaviors and both pro-inflammatory (M1) and pro-regenerative (M2) marker gene and protein levels in macrophages cultured on Zn-incorporated TNTs surfaces with different TNT diameters were detected. The supernatants of macrophages were extracted and preserved as conditioned medium (CM). Furthermore, the behaviors and osteogenic properties of osteoblasts cultured in CM on various surfaces were evaluated.

RESULTS

The release profile of Zn on Zn-incorporated TNT surfaces revealed a controlled release pattern. Macrophages cultured on Zn-incorporated TNT surfaces displayed enhanced gene and protein expression of M2 markers, and M1 markers were moderately inhibited, compared with the LPS group (the inflammation model). When cultured in CM, osteoblasts cultured on Zn-incorporated TNTs showed strengthened cell proliferation, adhesion, osteogenesis-related gene expression, alkaline phosphatase activity and extracellular mineralization, compared with their TNT counterparts and the Ti group.

CONCLUSION

This study suggests that the application of Zn-incorporated TNT surfaces may establish an osteogenic microenvironment and accelerate bone formation. It provided a promising strategy of Ti surface modification for a better applicable prospect.

UV Treatment Improves the Biocompatibility and Antibacterial Properties of Crystallized Nanostructured Titanium Surface

This study describes the production of a new material composed of pure titanium (Ti) metal with a crystallized nanostructure and investigated whether heat treatment and ultraviolet (UV) irradiation improved its biocompatibility and antibacterial properties. We compared the performance of UV-irradiated and non-irradiated Ti nanosheets (TNS) formed by dark alkaline treatment and heating at 600 °C with that of untreated pure Ti nanostructure (positive control). In vitro and in vivo experiments to assess biocompatibility and effects on cell behavior were performed using human umbilical vein endothelial cells and rat bone marrow cells. The material surface was characterized by X-ray photoelectron spectroscopy (XPS). The antibacterial properties of the irradiated material were evaluated using Staphylococcus aureus, a common pathogenic bacterium. The UV-irradiated TNS exhibited high angiogenic capacity and promoted cell adherence and differentiation relative to the control. Further, surface analysis via XPS revealed a lower C peak for the UV-treated material, indicating a reduced amount of dirt on the material surface. Moreover, UV irradiation decreased the viability of S. aureus on the material surface by stimulating reactive oxygen species production. The biocompatibility and antibacterial properties of the TNS were improved by UV irradiation. Thus, TNS may serve as a useful material for fabrication of dental implants.

Osseointegration effects of local release of strontium ranelate from implant surfaces in rats

BACKGROUND

Numerous studies have reported the beneficial effects of strontium on bone growth, particularly by stimulating osteoblast proliferation and differentiation. Thus, strontium release around implants has been suggested as one possible strategy to enhance implant osseointegration.

AIM

This study aimed to evaluate whether the local release of strontium ranelate (Sr-ranelate) from implants coated with mesoporous titania could improve bone formation around implants in an animal model.

MATERIALS AND METHODS

Mesoporous titania (MT) thin coatings were formed utilizing the evaporation induced self-assembly (EISA) method using Pluronic (P123) with or without the addition of poly propylene glycol (PPG) to create materials with two different pore sizes. The MT was deposited on disks and mini-screws, both made of cp Ti grade IV. Scanning electron microscopy (SEM) was performed to characterize the MT using a Leo Ultra55 FEG instrument (Zeiss, Oberkochen, Germany). The MT was loaded with Sr-ranelate using soaking and the drug uptake and release kinetics to and from the surfaces were evaluated using quartz crystal microbalance with dissipation monitoring (QCM-D) utilizing a Q-sense E4 instrument. For the in vivo experiment, 24 adult rats were analyzed at two time points of implant healing (2 and 6 weeks). Titanium implants shaped as mini screws were coated with MT films and divided into two groups; supplied with Sr-ranelate (test group) and without Sr-ranelate (control group). Four implants (both test and control) were inserted in the tibia of each rat. The in vivo study was evaluated using histomorphometric analyses of the implant/bone interphase using optical microscopy.

RESULTS

SEM images showed the successful formation of evenly distributed MT films covering the entire surface with pore sizes of 6 and 7.2 nm, respectively. The QCM-D analysis revealed an absorption of 3300 ng/cm² of Sr-ranelate on the 7.2 nm MT, which was about 3 times more than the observed amount on the 6 nm MT (1200 ng/cm²). Both groups showed sustained release of Sr-ranelate from MT coated disks. The histomorphometric analysis revealed no significant differences in bone implant contact (BIC) and bone area (BA) between the implants with Sr-ranelate and implants in the control groups after 2 and 6 weeks of healing (BIC with a p-value of 0.43 after 2 weeks and 0.172 after 6 weeks; BA with a p-value of 0.503 after 2 weeks, and 0.088 after 6 weeks). The mean BIC and BA values within the same group showed significant increase among all groups between 2 and 6 weeks.

CONCLUSION

This study could not confirm any positive effects of Sr-ranelate on implant osseointegration.

Electrically polarized TiO2 nanotubes on Ti implants to enhance early-stage osseointegration

Ti is characteristically bioinert and is supplemented with modifications in surface topography and chemistry to find use in biomedical applications. The aim of this study is to understand the effects of surface charge on TiO2 nanotubes (TNT) on Ti implants towards early stage osseointegration. We hypothesize that charge storage on TNT will improve bioactivity and enhance early-stage osseointegration in vivo. Commercially pure Ti surface was altered by growing TNT via anodic oxidation followed by the introduction of surface charge through electrothermal polarization to form bioelectret. Our results indicate a stored charge of 37.15 ± 14 mC/cm2 for TNT surfaces. The polarized TNT (TNT-Ps) samples did not show any charge leakage up to 18 months, and improved wettability with a measured contact angle less than 1°. No cellular toxicity through osteoblast proliferation and differentiation in vitro were shown by the TNT-Ps. Enhanced new bone formation at 5 weeks post-implantation for the TNT-Ps in contrast to TNTs was observed in vivo. Histomorphometric analyses show ∼40% increase in mineralized bone formation around the TNT-P implants than the TNTs at 5 weeks, which is indicative of accelerated bone remodeling cycle. These results show that stored surface charge on TiO2 nanotubes helped to accelerate bone healing due to early-stage osseointegration in vivo. STATEMENT OF SIGNIFICANCE: To improve surface bioactivity of metallic biomaterials, various approaches have been proposed and implemented. Among them, stored surface charge has been explored to enhance biological responses for hydroxyapatite ceramics where charged surfaces show favorable bone tissue ingrowth. However, surface charge effects have not yet been explored as a way to mitigate bio-inertness of titanium. This study intends to understand novel integration of bioactive titania-nanotubes and charge storage as surface modification for titanium implants. Our results show excellent biological response due to surface charge on titania-nanotubes offering possibilities of faster healing particularly for patients with compromised bone health.

Titania nanotube-based protein delivery system to inhibit cranial bone regeneration in Crouzon model of craniosynostosis

BACKGROUND

Craniosynostosis is a developmental disorder characterized by the premature fusion of skull sutures, necessitating repetitive, high-risk neurosurgical interventions throughout infancy. This study used protein-releasing Titania nanotubular implant (TNT/Ti) loaded with glypican 3 (GPC3) in the cranial critical-sized defects (CSDs) in Crouzon murine model (Fgfr2c342y/+ knock-in mutation) to address a key challenge of delaying post-operative bone regeneration in craniosynostosis.

MATERIALS AND METHODS

A 3 mm wide circular CSD was created in two murine models of Crouzon syndrome: (i) surgical control (CSDs without TNT/Ti or any protein, n=6) and (ii) experimental groups with TNT/Ti loaded with GPC3, further subdivided into the presence or absence of chitosan coating (on nanotubes) (n=12 in each group). The bone volume percentage in CSDs was assessed 90 days post-implantation using micro-computed tomography (micro-CT) and histological analysis.

RESULTS

Nano-implants retrieved after 90 days post-operatively depicted well-adhered, hexagonally arranged, and densely packed nanotubes with average diameter of 120±10 nm. The nanotubular architecture was generally well-preserved. Compared with the control bone volume percentage data (without GPC3), GPC3-loaded TNT/Ti without chitosan coating displayed a significantly lower volume percent in cranial CSDs (P<0.001). Histological assessment showed relatively less bone regeneration (healing) in GPC3-loaded CSDs than control CSDs.

CONCLUSION

The finding of inhibition of cranial bone regeneration by GPC3-loaded TNT/Ti in vivo is an important advance in the novel field of minimally-invasive craniosynostosis therapy and holds the prospect of altering the whole paradigm of treatment for affected children. Future animal studies on a larger sample are indicated to refine the dosage and duration of drug delivery across different ages and both sexes with the view to undertake human clinical trials.

Modification of Titanium Implant and Titanium Dioxide for Bone Tissue Engineering

Bone tissue engineering using titanium (Ti) implant and titanium dioxide (TiO₂) with their modification is gaining increasing attention. Ti has been adopted as an implant material in dental and orthopedic fields due to its superior properties. However, it still requires modification in order to achieve robust osteointegration between the Ti implant and surrounding bone. To modify the Ti implant, numerous methods have been introduced to fabricate porous implant surfaces with a variety of coating materials. Among these, plasma spraying of hydroxyapatite (HA) has been the most commonly used with commercial success. Meanwhile, TiO₂ nanotubes have been actively studied as the coating material for implants, and promising results have been reported about improving osteogenic activity around implants recently. Also porous three-dimensional constructs based on TiO₂ have been proposed as scaffolding material with high biocompatibility and osteoconductivity in large bone defects. However, the use of the TiO₂ scaffolds in load-bearing environment is somewhat limited. In order to optimize the TiO₂ scaffolds, studies have tried to combine various materials with TiO₂ scaffolds including drug, mesenchymal stem cells, Al₂O₃-SiO₂ solid and HA. This article will shortly introduce the properties of Ti and Ti-based implants with their modification, and review the progress of bone tissue engineering using the TiO₂ nanotubes and scaffolds.

Surface Immobilization of TiO2 Nanotubes with Bone Morphogenetic Protein-2 Synergistically Enhances Initial Preosteoblast Adhesion and Osseointegration

Although titanium (Ti) alloys have been widely used as implant materials, the bioinertness of pristine Ti impairs their bioactivity and early osseointegration. In the present work, we prepared TiO₂ nanotubes (TNT) layer on the titanium (Ti) surface by anodic oxidation. The anodized surface was functionalized with human bone morphogenetic protein-2 coating to form the hBMP-2/TNT surface. The release behavior of hBMP-2 on the hBMP-2/TNT surface displayed a controlled and sustained pattern, compared to that on the hBMP-2/Ti surface, which showed a rapid release. In vitro cellular activity tests demonstrated that both TNT and hBMP-2/Ti surfaces, particularly the hBMP-2/TNT surface, enhanced adhesion, proliferation, and differentiation of osteoblast cells. Increased cell adhesion, improved cytoskeleton organization, and immunofluorescence staining of vinculin were observed on the modified surfaces. The TNT, hBMP-2/Ti, and hBMP-2/TNT surfaces, especially the hBMP-2/TNT surface, further displayed an upregulated gene expression of adhesion and osteogenic markers vinculin, collagen type 1, osteopontin, and osteocalcin, compared to the pristine Ti surface. In vivo experiments using a rat model demonstrated that the TNT and hBMP-2/Ti surfaces, in particular the hBMP-2/TNT surface, improved osseointegration and showed a superior bone bonding ability compared to Ti. Our study revealed a synergistic role played by TiO₂ nanotubes nanotopography and hBMP-2 in promoting initial osteoblast adhesion, proliferation, differentiation, and osseointegration, thus suggesting a promising method for better modifying the implant surface.

A Novel Methodology for Economical Scale-Up of TiO2 Nanotubes Fabricated on Ti and Ti Alloys

The prospective use of nanotechnology for medical devices is increasing. While the impact of material surface nanopatterning on the biological response is convincing, creating a large surface area with such nanotechnology remains an unmet challenge. In this paper, we describe, for the first time, a reproducible scale-up manufacturing technique for creating controlled nanotubes on the surfaces of Ti and Ti alloys. We describe an average of approximately 7.5-fold increase in cost and time efficiency with regards to the generation of 20, 50, and 100 nm diameter nanotubes using an anodisation technique. These novel materials have great potential in the medical field through their influence on cellular activity, in particular, protein absorption, focal adhesion, and osteoinduction. In this paper, we provide a step-by-step guide to optimise an anodisation system, starting with design rationale, proof of concept, device upscaling, consistency, and reproducibility check, followed by cost and efficiency analysis. We show that the optimised device can produce a high number of anodised specimens with customisable specimen shape at reduced cost and time, without compromising the repeatability and consistency. The device can fabricate highly uniform and vertically oriented TiO2 nanotube layer with desired pore diameters.

Advanced scanning probe lithography using anatase-to-rutile transition to create localized TiO2 nanorods

In this article, we demonstrate the position-controlled hydrothermal growth of rutile TiO₂ nanorods using a new scanning probe lithography method in which a silicon tip, commonly used for atomic force microscopy, was pulled across an anatase TiO₂ film. This process scratches the film causing tiny anatase TiO₂ nanoparticles to form on the surface. According to previous reports, these anatase particles convert into rutile nanocrystals and provide the growth of rutile TiO₂ nanorods in well-defined areas. Due to the small tip radius, the resolution of this method is excellent and the method is quite inexpensive compared to electron-beam lithography and similar methods providing a position-controlled growth of semiconducting TiO₂ nanostructures.

Self-assembling antimicrobial peptides on nanotubular titanium surfaces coated with calcium phosphate for local therapy

Bacterial infection is a serious medical problem leading to implant failure. The current antibiotic based therapies rise concerns due to bacterial resistance. The family of antimicrobial peptides (AMP) is one of the promising candidates as local therapy agents due to their broad-spectrum activity. Despite AMPs receive increasing attention to treat infection, their effective delivery to the implantation site has been limited. Here, we developed an engineered dual functional peptide which delivers AMP as a biomolecular therapeutic agent onto calcium phosphate (Ca-P) deposited nanotubular titanium surfaces. Dual functionality of the peptide was achieved by combining a hydroxyapatite binding peptide-1 (HABP1) with an AMP using a flexible linker. HABP functionality of the peptide provided a self-coating property onto the nano-topographies that are designed to improve osteointegration capability, while AMP offered an antimicrobial protection onto the implant surface. We successfully deposited calcium phosphate minerals on nanotubular titanium oxide surface using pulse electrochemical deposition (PECD) and characterized the minerals by XRD, FT-IR, FE-SEM. Antimicrobial activity of the engineered peptide was tested against S. mutans (gram- positive) and E. coli (gram-negative) both in solution and on the Ca-P coated nanotubular titanium surface. In solution activity of AMP and dual functional peptide have the same Minimum Inhibitory Concentration (MIC) (32 mg/mL). The peptide also resulted in the reduction of the number of bacteria both for E.coli and S. mutans compare to control groups on the surface. Antimicrobial features of dual functional peptides are strongly correlated with their structures suggesting tunability in design through linkers regions. The dual-function peptide offers single-step solution for implant surface functionalization that could be applicable to any implant surface having different topographies.

Antibiofilm Peptides and Peptidomimetics with Focus on Surface Immobilization

Bacterial biofilms pose a major threat to public health, as they are associated with at least two thirds of all infections. They are highly resilient and render conventional antibiotics inefficient. As a part of the innate immune system, antimicrobial peptides have drawn attention within the last decades, as some of them are able to eradicate biofilms at sub-minimum inhibitory concentration (MIC) levels. However, peptides possess a number of disadvantages, such as susceptibility to proteolytic degradation, pH and/or salinity-dependent activity and loss of activity due to binding to serum proteins. Hence, proteolytically stable peptidomimetics were designed to overcome these drawbacks. This paper summarizes the current peptide and peptidomimetic strategies for combating bacteria-associated biofilm infections, both in respect to soluble and surface-functionalized solutions.

A unique hybrid-structured surface produced by rapid electrochemical anodization enhances bio-corrosion resistance and bone cell responses of β-type Ti-24Nb-4Zr-8Sn alloy

Ti-24Nb-4Zr-8Sn (Ti2448), a new β-type Ti alloy, consists of nontoxic elements and exhibits a low uniaxial tensile elastic modulus of approximately 45 GPa for biomedical implant applications. Nevertheless, the bio-corrosion resistance and biocompatibility of Ti2448 alloys must be improved for long-term clinical use. In this study, a rapid electrochemical anodization treatment was used on Ti2448 alloys to enhance the bio-corrosion resistance and bone cell responses by altering the surface characteristics. The proposed anodization process produces a unique hybrid oxide layer (thickness 50-120 nm) comprising a mesoporous outer section and a dense inner section. Experiment results show that the dense inner section enhances the bio-corrosion resistance. Moreover, the mesoporous surface topography, which is on a similar scale as various biological species, improves the wettability, protein adsorption, focal adhesion complex formation and bone cell differentiation. Outside-in signals can be triggered through the interaction of integrins with the mesoporous topography to form the focal adhesion complex and to further induce osteogenic differentiation pathway. These results demonstrate that the proposed electrochemical anodization process for Ti2448 alloys with a low uniaxial tensile elastic modulus has the potential for biomedical implant applications.

Pheochromocytoma (PC12) Cell Response on Mechanobactericidal Titanium Surfaces

Titanium is a biocompatible material that is frequently used for making implantable medical devices. Nanoengineering of the surface is the common method for increasing material biocompatibility, and while the nanostructured materials are well-known to represent attractive substrata for eukaryotic cells, very little information has been documented about the interaction between mammalian cells and bactericidal nanostructured surfaces. In this study, we investigated the effect of bactericidal titanium nanostructures on PC12 cell attachment and differentiation—a cell line which has become a widely used in vitro model to study neuronal differentiation. The effects of the nanostructures on the cells were then compared to effects observed when the cells were placed in contact with non-structured titanium. It was found that bactericidal nanostructured surfaces enhanced the attachment of neuron-like cells. In addition, the PC12 cells were able to differentiate on nanostructured surfaces, while the cells on non-structured surfaces were not able to do so. These promising results demonstrate the potential application of bactericidal nanostructured surfaces in biomedical applications such as cochlear and neuronal implants.

A comparative in vivo study of strontium-functionalized and SLActive™ implant surfaces in early bone healing

Purpose

Studies have shown that strontium-doped medical applications benefit bone metabolism leading to improved bone healing and osseointegration. Based on this knowledge, the aim of the study was to evaluate the performance of an implant surface, functionalized by a physical vapor deposition (PVD) coating (Ti-Sr-O), designed to yield predictable release of strontium. The Ti-Sr-O functionalized surface is compared to a routinely used, commercially available surface (SLActive™) with respect to bone-to-implant contact (BIC%) and new bone formation (BF%) in two defined regions of interest (ROI-I and ROI-II, respectively).

Materials and methods:

Ti-Sr-O functionalized, SLActive, and Grade 4 titanium implants were inserted in the femoral condyle of adult male New Zealand White rabbits. The PVD magnetron-sputtered Ti-Sr-O surface coating was characterized using scanning electron microscopy (SEM) for morphology and coating thickness. Strontium release and mechanical stability of the coating, under simulated insertion conditions, were evaluated. Furthermore, histomorphometrical BIC and BF were carried out 2 weeks after insertion.

Results

Histomorphometry revealed increased bone formation of Ti-Sr-O with significant differences compared to SLActive and Grade 4 titanium in both regions of interest, ROI-I and ROI-II, at 0–250 µm and 250–500 µm distance from the implant surfaces. Analogous results of bone-to-implant contact were observed for the two modified surfaces.

Conclusion

The results show that a nanopatterned Ti-Sr-O functionalized titanium surface, with sustained release of strontium, increases peri-implant bone volume and could potentially contribute to enhancement of bone anchorage of osseointegrated implants.

Surface Modification of Ti-35Nb-10Ta-1.5Fe by the Double Acid-Etching Process

Surface topography and composition influence the osteoblastic proliferation and osseointegration rates, which favor the biomechanical stability of bone anchoring and implants. In recent years, beta titanium alloys have been developed, and are composed of biocompatible elements, have low elastic modulus, high corrosion resistance, and mechanical properties to improve the long performance behavior of biomaterials. In the present research, the influence of the acid-etching process was studied in Ti6Al4V ELI and Ti35Nb10Ta1.5Fe. Samples were etched in a two-step acid treatment. Surface roughness parameters were quantified under a confocal microscope, topography was studied by scanning electron microscopy, and surface composition was analyzed with energy dispersive X-ray spectroscopy. The results revealed that the two-step acid treatment changes the topography of the β alloy, increases the surface area, and changes the chemical composition of the surface. Two differentiated regions were identified in the Ti35Nb10Ta1.5Fe alloy after the acid-etching process: The α + β region with higher values of mean roughness due to the lower chemical resistance of this region; and the β region with lower values of roughness parameters.

Dose reduction of bone morphogenetic protein-2 for bone regeneration using a delivery system based on lyophilization with trehalose

Introduction

To induce sufficient new bone formation, high doses of bone morphogenetic protein-2 (BMP-2) are applied in regenerative medicine that often induce serious side effects. Therefore, improved treatment strategies are required. Here, we investigate whether the delivery of BMP-2 lyophilized in the presence of trehalose reduced the dose of BMP-2 required for bone regeneration.

Materials and methods

A new growth factor delivery system was fabricated using BMP-2-loaded TiO₂ nanotubes by lyophilization with trehalose (TiO₂-Lyo-Tre-BMP-2). We measured BMP-2 release characteristics, bioactivity, and stability, and determined the effects on the osteogenic differentiation of bone marrow stromal cells in vitro. Additionally, we evaluated the ability of this formulation to regenerate new bone around implants in rat femur defects by micro-computed tomography (micro-CT), sequential fluorescent labelling, and histological analysis.

Results

Compared with absorbed BMP-2-loaded TiO₂ nanotubes (TiO₂-BMP-2), TiO₂-Lyo-Tre-BMP-2 exhibited sustained release, consistent bioactivity, and higher stability of BMP-2, and resulted in greater osteogenic differentiation of BMSCs. Eight weeks post-operation, TiO₂-Lyo-Tre-BMP-2 nanotubes, with various dosages of BMP-2, regenerated larger amounts of new bone than TiO₂-BMP-2 nanotubes.

Conclusion

Our findings indicate that delivery of BMP-2 lyophilized with trehalose may be a promising method to reduce the dose of BMP-2 and avoid the associated side effects.

Effects of titanium nanotubes on the osseointegration, cell differentiation, mineralisation and antibacterial properties of orthopaedic implant surfaces

The development and pre-clinical evaluation of nano-texturised, biomimetic, surfaces of titanium (Ti) implants treated with titanium dioxide (TiO₂) nanotube arrays is reviewed. In vitro and in vivo evaluations show that TiO₂ nanotubes on Ti surfaces positively affect the osseointegration, cell differentiation, mineralisation, and anti-microbial properties. This surface treatment can be superimposed onto existing macro and micro porous Ti implants creating a surface texture that also interacts with cells at the nano level. Histology and mechanical pull-out testing of specimens in rabbits indicate that TiO₂ nanotubes improves bone bonding nine-fold (p = 0.008). The rate of mineralisation associated with TiO₂ nanotube surfaces is about three times that of non-treated Ti surfaces. In addition to improved osseointegration properties, TiO₂ nanotubes reduce the initial adhesion and colonisation of Staphylococcus epidermidis. Collectively, the properties of Ti implant surfaces enhanced with TiO₂ nanotubes show great promise.

Cite this article: Bone Joint J 2018;100-B(1 Supple A):9–16.

Antimicrobial and Osseointegration Properties of Nanostructured Titanium Orthopaedic Implants

The surface design of titanium implants influences not only the local biological reactions but also affects at least the clinical result in orthopaedic application. During the last decades, strong efforts have been made to improve osteointegration and prevent bacterial adhesion to these surfaces. Following the rule of “smaller, faster, cheaper”, nanotechnology has encountered clinical application. It is evident that the hierarchical implant surface micro- and nanotopography orchestrate the biological cascades of early peri-implant endosseous healing or implant loosening. This review of the literature gives a brief overview of nanostructured titanium-base biomaterials designed to improve osteointegration and prevent from bacterial infection.

Synergistic effect of nanotopography and bioactive ions on peri-implant bone response

Both bioactive ion chemistry and nanoscale surface modifications are beneficial for enhanced osseointegration of endosseous implants. In this study, a facile synthesis approach to the incorporation of bioactive Ca²⁺ ions into the interlayers of nanoporous structures (Ca-nano) formed on a Ti6Al4V alloy surface was developed by sequential chemical and heat treatments. Samples with a machined surface and an Na⁺ ion-incorporated nanoporous surface (Na-nano) fabricated by concentrated alkali and heat treatment were used in parallel for comparison. The bone response was investigated by microcomputed tomography assessment, sequential fluorescent labeling analysis, and histological and histomorphometric evaluation after 8 weeks of implantation in rat femurs. No significant differences were found in the nanotopography, surface roughness, or crystalline properties of the Ca-nano and Na-nano surfaces. Bone–implant contact was better in the Ca-nano and Na-nano implants than in the machined implant. The Ca-nano implant was superior to the Na-nano implant in terms of enhancing the volume of new bone formation. The bone formation activity consistently increased for the Ca-nano implant but ceased for the Na-nano implant in the late healing stage. These results suggest that Ca-nano implants have promising potential for application in dentistry and orthopedics.

Nanoscale Surface Modifications of Orthopaedic Implants: State of the Art and Perspectives

Background:

Orthopaedic implants such as the total hip or total knee replacement are examples of surgical interventions with postoperative success rates of over 90% at 10 years. Implant failure is associated with wear particles and pain that requires surgical revision. Improving the implant - bone surface interface is a key area for biomaterial research for future clinical applications. Current implants utilise mechanical, chemical or physical methods for surface modification.

Methods:

A review of all literature concerning the nanoscale surface modification of orthopaedic implant technology was conducted.

Results:

The techniques and fabrication methods of nanoscale surface modifications are discussed in detail, including benefits and potential pitfalls. Future directions for nanoscale surface technology are explored.

Conclusion:

Future understanding of the role of mechanical cues and protein adsorption will enable greater flexibility in surface control. The aim of this review is to investigate and summarise the current concepts and future directions for controlling the implant nanosurface to improve interactions.

Effects of nanoporous anodic titanium oxide on human adipose derived stem cells

The aim of current bone biomaterials research is to design implants that induce controlled, guided, successful, and rapid healing. Titanium implants are widely used in dental, orthopedic, and reconstructive surgery. A series of studies has indicated that cells can respond not only to the chemical properties of the biomaterial, but also, in particular, to the changes in surface topography. Nanoporous materials remain in focus of scientific queries due to their exclusive properties and broad applications. One such material is nanostructured titanium oxide with highly ordered, mutually perpendicular nanopores. Nanoporous anodic titanium dioxide (TiO₂) films were fabricated by a three-step anodization process in propan-1,2,3-triol-based electrolyte containing fluoride ions. Adipose-derived stem cells offer many interesting opportunities for regenerative medicine. The important goal of tissue engineering is to direct stem cell differentiation into a desired cell lineage. The influence of nanoporous TiO₂ with pore diameters of 80 and 108 nm on cell response, growth, viability, and ability to differentiate into osteoblastic lineage of human adipose-derived progenitors was explored. Cells were harvested from the subcutaneous abdominal fat tissue by a simple, minimally invasive, and inexpensive method. Our results indicate that anodic nanostructured TiO₂ is a safe and nontoxic biomaterial. In vitro studies demonstrated that the nanotopography induced and enhanced osteodifferentiation of human adipose-derived stem cells from the abdominal subcutaneous fat tissue.

Gene-Activated Titanium Surfaces Promote In Vitro Osteogenesis

PURPOSE

Commercially pure titanium (CpTi) and its alloys possess favorable mechanical and biologic properties for use as implants in orthopedics and dentistry. However, failures in osseointegration still exist and are common in select individuals with risk factors such as smoking. Therefore, in this study, a proposal was made to enhance the potential for osseointegration of CpTi discs by coating their surfaces with nanoplexes comprising polyethylenimine (PEI) and plasmid DNA (pDNA) encoding bone morphogenetic protein-2 (pBMP-2).

MATERIALS AND METHODS

The nanoplexes were characterized for size and surface charge with a range of N/P ratios (the molar ratio of amine groups of PEI to phosphate groups in pDNA backbone). CpTi discs were surface characterized for morphology and composition before and after nanoplex coating using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD). The cytotoxicity and transfection ability of CpTi discs coated with nanoplexes of varying N/P ratios in human bone marrow-derived mesenchymal stem cells (BMSCs) was measured via MTS assays and flow cytometry, respectively.

RESULTS

The CpTi discs coated with nanoplexes prepared at an N/P ratio of 10 (N/P-10) were considered optimal, resulting in 75% cell viability and 14% transfection efficiency. Enzyme-linked immunosorbent assay results demonstrated a significant enhancement in BMP-2 protein secretion by BMSCs 7 days posttreatment with PEI/pBMP-2 nanoplexes (N/P-10) compared to the controls, and real-time PCR data demonstrated that the BMSCs treated with PEI/pBMP-2 nanoplex-coated CpTi discs resulted in an enhancement of Runx-2, alkaline phosphatase, and osteocalcin gene expressions on day 7 posttreatment. In addition, these BMSCs demonstrated enhanced calcium deposition on day 30 posttreatment as determined by qualitative (alizarin red staining) and quantitative (atomic absorption spectroscopy) assays.

CONCLUSION

It can be concluded that PEI/pBMP-2 nanoplex (N/P-10)-coated CpTi discs have the potential to induce osteogenesis and enhance osseointegration.

TiO2 nanotube platforms for smart drug delivery: a review

Titania nanotube (TNT) arrays are recognized as promising materials for localized drug delivery implants because of their excellent properties and facile preparation process. This review highlights the concept of localized drug delivery systems based on TNTs, considering their outstanding biocompatibility in a series of ex vivo and in vivo studies. Considering the safety of TNT implants in the host body, studies of the biocompatibility present significant importance for the clinical application of TNT implants. Toward smart TNT platforms for sustainable drug delivery, several advanced approaches were presented in this review, including controlled release triggered by temperature, light, radiofrequency magnetism, and ultrasonic stimulation. Moreover, TNT implants used in medical therapy have been demonstrated by various examples including dentistry, orthopedic implants, cardiovascular stents, and so on. Finally, a future perspective of TNTs for clinical applications is provided.

In Vivo Response of Laser Processed Porous Titanium Implants for Load-Bearing Implants

Applications of porous metallic implants to enhance osseointegration of load-bearing implants are increasing. In this work, porous titanium implants, with 25 vol.% porosity, were manufactured using Laser Engineered Net Shaping (LENS™) to measure the influence of porosity towards bone tissue integration in vivo. Surfaces of the LENS™ processed porous Ti implants were further modified with TiO₂ nanotubes to improve cytocompatibility of these implants. We hypothesized that interconnected porosity created via additive manufacturing will enhance bone tissue integration in vivo. To test our hypothesis, in vivo experiments using a distal femur model of male Sprague-Dawley rats were performed for a period of 4 and 10 weeks. In vivo samples were characterized via micro-computed tomography (CT), histological imaging, scanning electron microscopy, and mechanical push-out tests. Our results indicate that porosity played an important role to establish early stage osseointegration forming strong interfacial bonding between the porous implants and the surrounding tissue, with or without surface modification, compared to dense Ti implants used as a control.

Adverse Biological Effect of TiO₂ and Hydroxyapatite Nanoparticles Used in Bone Repair and Replacement

The adverse biological effect of nanoparticles is an unavoidable scientific problem because of their small size and high surface activity. In this review, we focus on nano-hydroxyapatite and TiO₂ nanoparticles (NPs) to clarify the potential systemic toxicological effect and cytotoxic response of wear nanoparticles because they are attractive materials for bone implants and are widely investigated to promote the repair and reconstruction of bone. The wear nanoparticles would be prone to binding with proteins to form protein-particle complexes, to interacting with visible components in the blood including erythrocytes, leukocytes, and platelets, and to being phagocytosed by macrophages or fibroblasts to deposit in the local tissue, leading to the formation of fibrous local pseudocapsules. These particles would also be translocated to and disseminated into the main organs such as the lung, liver and spleen via blood circulation. The inflammatory response, oxidative stress, and signaling pathway are elaborated to analyze the potential toxicological mechanism. Inhibition of the oxidative stress response and signaling transduction may be a new therapeutic strategy for wear debris-mediated osteolysis. Developing biomimetic materials with better biocompatibility is our goal for orthopedic implants.

The role of well-defined nanotopography of titanium implants on osseointegration: cellular and molecular events in vivo

Purpose

Mechanisms governing the cellular interactions with well-defined nanotopography are not well described in vivo. This is partly due to the difficulty in isolating a particular effect of nanotopography from other surface properties. This study employed colloidal lithography for nanofabrication on titanium implants in combination with an in vivo sampling procedure and different analytical techniques. The aim was to elucidate the effect of well-defined nanotopography on the molecular, cellular, and structural events of osseointegration.

Materials and methods

Titanium implants were nanopatterned (Nano) with semispherical protrusions using colloidal lithography. Implants, with and without nanotopography, were implanted in rat tibia and retrieved after 3, 6, and 28 days. Retrieved implants were evaluated using quantitative polymerase chain reaction, histology, immunohistochemistry, and energy dispersive X-ray spectroscopy (EDS).

Results

Surface characterization showed that the nanotopography was well defined in terms of shape (semispherical), size (79±6 nm), and distribution (31±2 particles/µm²). EDS showed similar levels of titanium, oxygen, and carbon for test and control implants, confirming similar chemistry. The molecular analysis of the retrieved implants revealed that the expression levels of the inflammatory cytokine, TNF-α, and the osteoclastic marker, CatK, were reduced in cells adherent to the Nano implants. This was consistent with the observation of less CD163-positive macrophages in the tissue surrounding the Nano implant. Furthermore, periostin immunostaining was frequently detected around the Nano implant, indicating higher osteogenic activity. This was supported by the EDS analysis of the retrieved implants showing higher content of calcium and phosphate on the Nano implants.

Conclusion

The results show that Nano implants elicit less periimplant macrophage infiltration and downregulate the early expression of inflammatory (TNF-α) and osteoclastic (CatK) genes. Immunostaining and elemental analyses show higher osteogenic activity at the Nano implant. It is concluded that an implant with the present range of well-defined nanocues attenuates the inflammatory response while enhancing mineralization during osseointegration.

In vivo osseointegration of Ti implants with a strontium-containing nanotubular coating

Novel biomedical titanium (Ti) implants with high osteogenic ability for fast and good osseointegration under normal as well as osteoporotic conditions are urgently needed. Expanding on our previous in vitro results, we hypothesized that nanotubular, strontium-loaded (NT-Sr) structures on Ti implants would have favorable osteogenic effects and evaluated the in vivo osseointegration of these implants in rats. The structures with nanotubes of different diameters were fabricated by electrochemical anodization at 10 and 40 V, and the amounts of Sr loaded were adjusted by using two hydrothermal treatment times of 1 and 3 hours. Qualitative microcomputed tomography in two and three dimensions showed that the NT-Sr formed with an anodization voltage of 10 V and hydrothermal treatment time of 3 hours best supported bone growth in vivo. Histomorphometric examination of osseointegration also showed that more newly formed bone was found at its surface. The bone–implant contact percentage was highest (92.48%±0.76%) at 12 weeks. In conclusion, the NT-Sr formed with an anodization voltage of 10 V and hydrothermal treatment time of 3 hours showed excellent osteogenic properties, making it an attractive option for Ti surface modification with considerable clinical potential.

Silicon-Doped Titanium Dioxide Nanotubes Promoted Bone Formation on Titanium Implants

While titanium (Ti) implants have been extensively used in orthopaedic and dental applications, the intrinsic bioinertness of untreated Ti surface usually results in insufficient osseointegration irrespective of the excellent biocompatibility and mechanical properties of it. In this study, we prepared surface modified Ti substrates in which silicon (Si) was doped into the titanium dioxide (TiO₂) nanotubes on Ti surface using plasma immersion ion implantation (PIII) technology. Compared to TiO₂ nanotubes and Ti alone, Si-doped TiO₂ nanotubes significantly enhanced the expression of genes related to osteogenic differentiation, including Col-I, ALP, Runx2, OCN, and OPN, in mouse pre-osteoblastic MC3T3-E1 cells and deposition of mineral matrix. In vivo, the pull-out mechanical tests after two weeks of implantation in rat femur showed that Si-doped TiO₂ nanotubes improved implant fixation strength by 18% and 54% compared to TiO₂-NT and Ti implants, respectively. Together, findings from this study indicate that Si-doped TiO₂ nanotubes promoted the osteogenic differentiation of osteoblastic cells and improved bone-Ti integration. Therefore, they may have considerable potential for the bioactive surface modification of Ti implants.

Enhanced osteogenic activity and anti-inflammatory properties of Lenti-BMP-2-loaded TiO₂ nanotube layers fabricated by lyophilization following trehalose addition

To enhance biocompatibility and osseointegration between titanium implants and surrounding bone tissue, numerous efforts have been made to modify the surface topography and composition of Ti implants. In this paper, Lenti-BMP-2-loaded TiO2 nanotube coatings were fabricated by lyophilization in the presence of trehalose to functionalize the surface. We characterized TiO2 nanotube layers in terms of the following: surface morphology; Lenti-BMP-2 and trehalose release; their ability to induce osteogenesis, proliferation, and anti-inflammation in vitro; and osseointegration in vivo. The anodized TiO2 nanotube surfaces exhibited an amorphous glassy matrix perpendicular to the Ti surface. Both Lenti-BMP-2 and trehalose showed sustained release over the course of 8 days. Results from real-time quantitative polymerase chain reaction studies demonstrated that lyophilized Lenti-BMP-2/TiO2 nanotubes constructed with trehalose (Lyo-Tre-Lenti-BMP-2) significantly promoted osteogenic differentiation of bone marrow stromal cells but not their proliferation. In addition, Lyo-Tre-Lenti-BMP-2 nanotubes effectively inhibited lipopolysaccharide-induced interleukin-1β and tumor necrosis factor-α production. In vivo, the formulation also promoted osseointegration. This study presents a promising new method for surface-modifying biomedical Ti-based implants to simultaneously enhance their osteogenic potential and anti-inflammatory properties, which can better satisfy clinical needs.

The effects of hierarchical micro/nanosurfaces decorated with TiO2 nanotubes on the bioactivity of titanium implants in vitro and in vivo

In the present work, a hierarchical hybrid micro/nanostructured titanium surface was obtained by sandblasting with large grit and acid etching (SLA), and nanotubes of different diameters (30 nm, 50 nm, and 80 nm) were superimposed by anodization. The effect of each SLA-treated surface decorated with nanotubes (SLA + 30 nm, SLA + 50 nm, and SLA + 80 nm) on osteogenesis was studied in vitro and in vivo. The human MG63 osteosarcoma cell line was used for cytocompatibility evaluation, which showed that cell adhesion and proliferation were dramatically enhanced on SLA + 30 nm. In comparison with cells grown on the other tested surfaces, those grown on SLA + 80 nm showed an enhanced expression of osteogenesis-related genes. Cell spread was also enhanced on SLA + 80 nm. A canine model was used for in vivo evaluation of bone bonding. Histological examination demonstrated that new bone was formed more rapidly on SLA-treated surfaces with nanotubes (especially SLA + 80 nm) than on those without nanotubes. All of these results indicate that SLA + 80 nm is favorable for promoting the activity of osteoblasts and early bone bonding.