Synergistic effects of surface chemistry and topologic structure from modified microarc oxidation coatings on Ti implants for improving osseointegration

Engineered Chimeric Peptides with IGF-1 and Titanium-Binding Functions to Enhance Osteogenic Differentiation In Vitro under T2DM Condition

Due to the complexity of the biomolecules and titanium (Ti) combination, it is a challenge to modify the implant surface with biological cytokines. The study proposed a new method for immobilizing cytokines on implant surface to solve the problem of low osseointegration under type 2 diabetes mellitus (T2DM) condition. This new modified protein that connected Ti-binding artificial aptamer minTBP-1 with Insulin-like growth factor I (IGF-I), had a special strong affinity with Ti and a therapeutic effect on diabetic bone loss. According to the copies of minTBP-1, three proteins were prepared, namely minTBP-1-IGF-1, 2minTBP-1-IGF-1 and 3minTBP-1-IGF-1. Compared with the other modified proteins, 3minTBP-1-IGF-1 adsorbed most on the Ti surface. Additionally, this biointerface demonstrated the most uniform state and the strongest hydrophilicity. In vitro results showed that the 3minTBP-1-IGF-1 significantly increased the adhesion, proliferation, and mineralization activity of osteoblasts under T2DM conditions when compared with the control group and the other modified IGF-1s groups. Real-time PCR assay results confirmed that 3minTBP-1-IGF-1 could effectively promote the expression of osteogenic genes, that is, ALP, BMP-2, OCN, OPG, and Runx2. All these data indicated that the 3minTBP-1-IGF-1 had the most efficacious effect in promoting osteoblasts osteogenesis in diabetic conditions, and may be a promising option for further clinical use.

Electrochemical, Tribological and Biocompatible Performance of Electron Beam Modified and Coated Ti6Al4V Alloy

Vacuum cathodic arc TiN coatings with overlaying TiO₂ film were deposited on polished and surface roughened by electron beam modification (EBM) Ti6Al4V alloy. The substrate microtopography consisted of long grooves formed by the liner scan of the electron beam with appropriate frequencies (500 (AR500) and 850 (AR850) Hz). EBM transformed the α + β Ti6Al4V mixed structure into a single α'-martensite phase. Тhe gradient TiN/TiO₂ films deposited on mechanically polished (AR) and EBM (AR500 and AR850) alloys share the same surface chemistry and composition (almost stoichiometric TiN, anatase and rutile in different ratios) but exhibit different topographies (S_a equal to approximately 0.62, 1.73, and 1.08 μm, respectively) over areas of 50 × 50 μm. Although the nanohardness of the coatings on AR500 and AR850 alloy (approximately 10.45 and 9.02 GPa, respectively) was lower than that measured on the film deposited on AR alloy (about 13.05 GPa), the hybrid surface treatment offered improvement in critical adhesive loads, coefficient of friction, and wear-resistance of the surface. In phosphate buffer saline, all coated samples showed low corrosion potentials and passivation current densities, confirming their good corrosion protection. The coated EBM samples cultured with human osteoblast-like MG63 cells demonstrated increased cell attachment, viability, and bone mineralization activity especially for the AR500-coated alloy, compared to uncoated polished alloy. The results underline the synergetic effect between the sub-micron structure and composition of TiN/TiO₂ coating and microarchitecture obtained by EBM.

Multifunctional Scaffolds and Synergistic Strategies in Tissue Engineering and Regenerative Medicine

The increasing demand for organ replacements in a growing world with an aging population as well as the loss of tissues and organs due to congenital defects, trauma and diseases has resulted in rapidly evolving new approaches for tissue engineering and regenerative medicine (TERM). The extracellular matrix (ECM) is a crucial component in tissues and organs that surrounds and acts as a physical environment for cells. Thus, ECM has become a model guide for the design and fabrication of scaffolds and biomaterials in TERM. However, the fabrication of a tissue/organ replacement or its regeneration is a very complex process and often requires the combination of several strategies such as the development of scaffolds with multiple functionalities and the simultaneous delivery of growth factors, biochemical signals, cells, genes, immunomodulatory agents, and external stimuli. Although the development of multifunctional scaffolds and biomaterials is one of the most studied approaches for TERM, all these strategies can be combined among them to develop novel synergistic approaches for tissue regeneration. In this review we discuss recent advances in which multifunctional scaffolds alone or combined with other strategies have been employed for TERM purposes.

The Synergy of Topographical Micropatterning and Ta|TaCu Bilayered Thin Film on Titanium Implants Enables Dual-Functions of Enhanced Osteogenesis and Anti-Infection

Poor osteogenesis and implant-associated infection are the two leading causes of failure for dental and orthopedic implants. Surface design with enhanced osteogenesis often fails in antibacterial activity, or vice versa. Herein, a surface design strategy, which overcomes this trade-off via the synergistic effects of topographical micropatterning and a bilayered nanostructured metallic thin film is presented. A specific microgrooved pattern is fabricated on the titanium surface, followed by sequential deposition of a nanostructured copper (Cu)-containing tantalum (Ta) (TaCu) layer and a pure Ta cap layer. The microgrooved patterns coupled with the nanorough Ta cap layer shows strong contact guidance to preosteoblasts and significantly enhances the osteogenic differentiation in vitro, while the controlled local sustained release of Cu ions is responsible for high antibacterial activity. Importantly, rat calvarial defect models in vivo further confirm that the synergy of microgrooved patterns and the Ta|TaCu bilayered thin film on titanium surface could effectively promote bone regeneration. The present effective and versatile surface design strategy provides significant insight into intelligent surface engineering that can control biological response at the site of healing in dental and orthopedic implants.

Surface engineering of biomaterials in orthopedic and dental implants: Strategies to improve osteointegration, bacteriostatic and bactericidal activities

BACKGROUND

The success of biomedical implants in orthopedic and dental applications is usually limited due to insufficient bone-implant integration, and implant-related infections. Biointerfaces are critical in regulating their interactions and the desirable performance of biomaterials in biological environment. Surface engineering has been widely studied to realize better control of the interface interaction to further enhance the desired behavior of biomaterials.

PURPOSE AND SCOPE

This review aims to investigate surface coating strategies in hard tissue applications to address insufficient osteointegration and implant-related infection problems.

SUMMARY

We first focused on surface coatings to enhance the osteointegration and biocompatibility of implants by emphasizing calcium phosphate-related, nanoscale TiO₂ -related, bioactive tantalum-based and biomolecules incorporated coatings. Different coating strategies such as plasma spraying, biomimetic deposition, electrochemical anodization and LENS are discussed. We then discussed techniques to construct anti-adhesive and bactericidal surface while emphasizing multifunctional surface coating techniques that combine potential osteointegration and antibacterial activities. The effects of nanotopography via TiO₂ coatings on antibacterial performance are interesting and included. A smart bacteria-responsive titanium dioxide nanotubes coating is also attractive and elaborated.

CONCLUSION

Developing multifunctional surface coatings combining osteogenesis and antimicrobial activity is the current trend. Surface engineering methods are usually combined to obtain hierarchical multiscale surface structures with better biofunctionalization outcomes.

The synergistic promotion of osseointegration by nanostructure design and silicon substitution of hydroxyapatite coatings in a diabetic model

Accumulating evidence indicates much higher failure rates for biomedical titanium implants in diabetic patients. This phenomenon is attributed to impaired osteoblastic function, suppressed angiogenesis capacity, and abnormal osteoclast activation in diabetic patients. Our previous study demonstrated that titanium implants coated with highly crystalline nanostructured hydroxyapatite (nHA) promoted the osteogenic differentiation of bone marrow stromal cells (BMSCs) and bone-implant osseointegration under healthy conditions. Furthermore, recent studies showed that silicon-substituted biomaterials exhibited excellent osteogenesis and angiogenesis performance while repressing osteoclastogenesis. Hence, we proposed that a combination of nanostructural modification and Si substitution might produce synergetic effects to mitigate the impaired osseointegration of bone implants under diabetes mellitus (DM) conditions. To confirm this hypothesis, titanium implants coated with highly crystalline Si-substituted nHA (Si-nHA) were successfully fabricated via atmospheric plasma spraying combined with hydrothermal treatment. An in vitro study demonstrated that compared to the original HA coating, the nHA coating improved osteogenic and angiogenic differentiation and altered the OPG/RANKL ratio of DM-BMSCs. In addition, the Si-nHA coating further enhanced cell proliferation, improved osteogenic and angiogenic differentiation, and repressed osteoclastogenesis in DM-BMSCs. An in vivo study confirmed that the titanium implants coated with nHA or Si-nHA effectively promoted bone formation and bone-implant osseointegration in a diabetic rabbit model, with the Si-nHA coating exhibiting the best stimulatory effect. Collectively, the results suggest that the nanostructured topography and Si substitution act synergistically to ameliorate the poor bone regeneration and osseointegration associated with DM. Thus, the results provide a promising coating method for dental and orthopedic applications under diabetic conditions.

Rapid structural regulation, apatite-inducing mechanism and in vivo investigation of microwave-assisted hydrothermally treated titania coating

Owing to the poor bioactivity of microarc oxidation (MAO) coating and the rapid activation ability of the microwave hydrothermal (MH) technique, MH treatment was applied to optimize the in vivo interface status between MAO-treated titanium and bone. In this study, consequently, new outermost layers were prepared using hydroxyapatite (HA) nanorods, HA submicron pillars or sodium titanate nanosheets. The results revealed that the NaOH concentration significantly influenced the surface structure and phase constitution of the MAO samples. Moreover, on enhancing the NaOH concentration, the number of HA phases was decreased. Further, the influence of the NaOH concentration on the interfacial bonding strength was insignificant for concentrations ≤0.5 mol L⁻¹. Transmission electron microscopy (TEM) analysis showed that the induction of apatite was accompanied by the dissolution of the HA crystals and there was excellent crystallographic matching with the HA crystals. The in vitro and in vivo analyses revealed that the MH-treated MAO sample with the HA nanorods possessed superior apatite-formation ability and osseointegration, including a small amount of soft tissue and optimal bone–implant interfacial bonding force, thus signifying strong potential for the optimization of the bone–implant interfacial status.

In this work, the micro/nano scale structures of HA nanorods integrated on a titanium were prepared using MAO and MH treatment. The in vivo results indicate that HA crystals play a crucial role in the improvement of the osseointegration.

Porous tantalum oxide with osteoconductive elements and antibacterial core-shell nanoparticles: A new generation of materials for dental implants

Implant surfaces with cytocompatible and antibacterial properties are extremely desirable for the prevention of implant's infection and the promotion of osseointegration. In this work, both micro-arc oxidation (MAO) and DC magnetron sputtering techniques were combined in order to endow tantalum-based surfaces with osteoblastic cytocompatibility and antibacterial activity. Porous Ta₂O₅ layers containing calcium (Ca) and phosphorous (P) were produced by MAO (TaCaP) to mimic the bone tissue morphology and chemical composition (Ca/P ratio close to 1.67). Furthermore, zinc (Zn) nanoparticles were deposited onto the previous surfaces by DC magnetron sputtering without or with an additional thin carbon layer deposited over the nanoparticles (respectively, TaCaP-Zn and TaCaP-ZnC) to control the Zn ions (Zn²⁺) release. Before osteoblastic cell seeding, the surfaces were leached for three time-points in PBS. All modified samples were cytocompatible. TaCaP-Zn slightly impaired cell adhesion but this was improved in the samples leached for longer immersion times. The initial cell adhesion was clearly improved by the deposition of the carbon layer on the Zn nanoparticles, which also translated to a higher proliferation rate. Both Zn-containing surfaces presented antibacterial activity against S. aureus. The two surfaces were active against planktonic bacteria, and TaCaP-Zn also inhibited sessile bacteria. Attributing to the excellent in vitro performance of the nanostructured Ta surface, with osteoconductive elements by MAO followed by antimicrobial nanoparticles incorporation by magnetron sputtering, this work is clearly a progress on the strategy to develop a new generation of dental implants.

Acceleration of Bone Formation and Adhesion Ability on Dental Implant Surface via Plasma Electrolytic Oxidation in a Solution Containing Bone Ions

The present study examined the in vitro and in vivo bone formation and adhesion ability on the surface of a titanium dental implant made by plasma electrolytic oxidation (PEO) in electrolytes containing bioactive ions. To achieve this goal, screw-shaped fabricated Ti-6Al-4V alloy implants were processed via PEO using an electrolyte solution containing calcium (Ca), phosphorous (P), magnesium (Mg), zinc (Zn), strontium (Sr), silicon (Si), and manganese (Mn) species. The screw implants doped with bioactive elements via PEO were placed in rabbit tibia, and the results were compared to the sand-blasted Ti-6Al-4V alloy implants. At eight-week post-surgery, there was no significant difference in the values of removal torque between sand-blasted and PEO-treated implants. However, it was observed that the PEO treatment of dental implants led to the formation of more periphery bone as compared to the case of sand-blasted implants. Accordingly, the PEO-treated implants have the potential to be used as promising materials for dental applications.

Micro/nanostructured calcium phytate coating on titanium fabricated by chemical conversion deposition for biomedical application

A bioactive micro/nanostructured calcium phytate coating was successfully prepared on titanium surfaces by chemical conversion deposition, mainly through hydrothermal treatment of a mixed solution of phytic acid and saturated calcium hydroxide solution. Ultraviolet radiation was carried out to improve the adhesion of the coating to the titanium substrate. Pure titanium with a sandblasted/acid-etched surface was used as the control group. The topography and chemical composition of the modified surfaces were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDX), and static water contact angle measurement. A pull-off test was performed to measure the coating-to-substrate adhesion strength. Bovine serum albumin was used as a model to study the protein adsorption effect. Cells were cultured on titanium surfaces for 7 days in osteogenic differentiation medium, then the osteoblast compatibility in vitro were explored by alkaline phosphatase and alizarin red staining. After 1, 2, 4 and 8 wks of immediate implantation of titanium implants into the mandibles of New Zealand white rabbits, biological effects in vivo were researched by microcomputed tomography analysis and histological evaluation. The results indicated that the roughness and hydrophilicity of the modified surfaces with micro/nanostructure remarkably increased compared to those of the control group. The pull-off test showed the average adhesion strength at the coating-substrate interface to be higher than 13.56 ± 1.71 MPa. In addition, approximately 4.41 mg/L calcium ion was released from the calcium phytate micro/nano coatings to the local environment after 48 h of immersion. More importantly, the micro/nanostructure titanium substrates significantly promoted cellular differentiation in vitro and in vivo. After 8 wks, the bone implant contact ratio (BIC, %) of the modified implants was higher than that of the control group, at 94.09 ± 0.55% and 86.18 ± 1.99% (p < 0.05). Overall, this study provided new insights into the factors promoting early osseointegration of titanium alloys, which had great potential not only for dental implants but also for various other biomaterial applications.

Nano-needle strontium-substituted apatite coating enhances osteoporotic osseointegration through promoting osteogenesis and inhibiting osteoclastogenesis

Implant loosening remains a major clinical challenge for osteoporotic patients. This is because osteoclastic bone resorption rate is higher than osteoblastic bone formation rate in the case of osteoporosis, which results in poor bone repair. Strontium (Sr) has been widely accepted as an anti-osteoporosis element. In this study, we fabricated a series of apatite and Sr-substituted apatite coatings via electrochemical deposition under different acidic conditions. The results showed that Ca and Sr exhibited different mineralization behaviors. The main mineralization products for Ca were CaHPO₄·2H₂O and Ca₃(PO₄)₂ with the structure changed from porous to spherical as the pH values increased. The main mineralization products for Sr were SrHPO₄ and Sr₅(PO₄)₃OH with the structure changed from flake to needle as the pH values increased. The in vitro experiment demonstrated that coatings fabricated at high pH condition with the presence of Sr were favorable to MSCs adhesion, spreading, proliferation, and osteogenic differentiation. In addition, Sr-substituted apatite coatings could evidently inhibit osteoclast differentiation and fusion. Moreover, the in vivo study indicated that nano-needle like Sr-substituted apatite coating could suppress osteoclastic activity, improve new bone formation, and enhance bone-implant integration. This study provided a new theoretical guidance for implant coating design and the fabricated Sr-substituted coating might have potential applications for osteoporotic patients.

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Ca²⁺ and Sr²⁺ showed different mineralization behaviors in acidic environments.

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Apatites fabricated at high pH conditions were beneficial to MSCs growth.

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Sr-substituted apatite exhibited superior anti-osteoclast activity ability.

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Sr-substituted apatite facilitated osteogenesis, bone growth, and osseointegration.

Endowing polyetheretherketone with anti-inflammatory ability and improved osteogenic ability

Both osteogenesis and anti-inflammatory bioactive materials play a vital role in the regeneration of skeletal defects. Bone inflammation is hard to cure and can lead to malformation or amputation. The purpose of this study is to use anti-inflammatory drugs to endow polyetheretherketone (PEEK) with the dual ability to achieve anti-inflammatory effects while maintaining favorable biocompatibility. In this experiment, the porous PEEK was immersed in an aspirin (ASP) solution after sulfonation, and the obtained porous PEEK had significantly improved the anti-inflammatory abilities. Additionally, grafting the bone forming peptide (BFP) onto the porous PEEK can distinctly enchance the osteogenesis capability. The effects of the BFP polypeptide on the proliferation of MC3T3-E1 cells and ALP activity, and the effects of aspirin on inflammation were systematically investigated. The modified material showed favorable biocompatibility and osteogenic ability. The results suggest that the combination of the BFP polypeptide with aspirin may lead to a synergetic effect on the stimulation of osteogenesis and on the reduction of inflammation.

A Novel Cytocompatibility Strengthening Strategy of Ultrafine-Grained Pure Titanium

Ultrafine-grained pure (UFG) titanium processed by equal channel angular pressing possesses mechanical properties comparable to those of Ti-6Al-4V and features more favorable friction resistance, biocompatibility, and corrosion resistance than does commercially pure (CP) titanium. Nevertheless, UFG titanium is still a bio-inert material with a lack of bone-inducing ability. Here, TiO₂-hydroxyapatite (TiO₂-HA) coatings were fabricated on CP titanium and UFG titanium through combining micro-arc oxidation and hydrothermal treatment together to improve their cytocompatibility. The results indicate that, compared with conventional coatings that use CP titanium as the substrate, such coatings formed on the UFG titanium possess additional hydrophilicity and in vitro cytocompatibility. The fantastic hierarchical structure of the UFG TiO₂-HA coating (UG-MH coating), including microscale and nanoscale pores and short column-shaped and sheet-shaped HA grains with varying geometric shapes, excellent hydrophilicity, and high polar force, enhances the mutual effects between the osteoblasts and titanium implant since it provides an adequate microenvironment for the ingrowth of osteoblasts, inducing osteoblast adhesion, proliferation, and differentiation. The UG-MH coating has a synergistic effect due to its fantastic hydrophilic hierarchical structure and high polar force on the up-regulated expression of cytoskeletal actin proteins as well as osteocalcin, protein kinase C (PKC), nuclear factor of activated T-cells (NFAT), and Wnt5, enabling osteoblasts to differentiate via the Wnt calcium-dependent signaling pathway. This study highlights the idea that the modified UFG titanium will be more suitable than CP titanium in dental and orthopedic applications.

Rapid Fabrication, Microstructure, and in Vitro and in Vivo Investigations of a High-Performance Multilayer Coating with External, Flexible, and Silicon-Doped Hydroxyapatite Nanorods on Titanium

A high-performance multilayer coating with external, flexible, and silicon-doped hydroxyapatite (Si-HA) nanorods was designed using bionics. Plasma electrolytic oxidation (PEO) and the microwave hydrothermal (MH) method were used to rapidly deposit this multilayer coating on a titanium (Ti) substrate, applied for 5 and 10 min, respectively. The bioactive multilayer coating was composed of four layers, and the outermost layer was an external growth layer that consisted of many Si-HA nanorods with a single-crystal structure. The Si-HA nanorods exhibited good flexibility, likely because of their complete single-crystal structures, smooth surfaces, and suitable diameters and lengths. This multilayer coating with a high surface energy was superhydrophilic and exhibited good in vitro bioactivities, such as good apatite formation ability, good cell spreading, and high osteogenic gene expression levels. After implantation in the tibia of rabbits for 16 weeks, almost no soft tissues were formed at the MH treated PEO implant-bone interface. A direct bone contact interface was formed by a bridging effect of the flexible Si-HA nanorods, which further produced a high implant-bone interface bonding strength. The current results demonstrated that the bioactive multilayer layers with the flexible Si-HA nanorods displayed a very good osseointegration ability, showing promising applications in the biomedical field.

Bioinspired surface modification of orthopedic implants for bone tissue engineering

Biomedical implants have been widely used in various orthopedic treatments, including total hip arthroplasty, joint arthrodesis, fracture fixation, non-union, dental repair, etc. The modern research and development of orthopedic implants have gradually shifted from traditional mechanical support to a bioactive graft in order to endow them with better osteoinduction and osteoconduction. Inspired by structural and mechanical properties of natural bone, this review provides a panorama of current biological surface modifications for facilitating the interaction between medical implants and bone tissue and gives a future outlook for fabricating the next-generation multifunctional and smart implants by systematically biomimicking the physiological processes involved in formation and functioning of bones.

In Vitro Corrosion and in Vivo Response to Zinc Implants with Electropolished and Anodized Surfaces

Zinc (Zn)-based biodegradable metals have been widely investigated for cardiovascular stent and orthopedic applications. However, the effect of Zn surface features on adverse biological responses has not been well established. Here, we hypothesized that a metallic zinc implant's surface oxide film character may critically influence early neointimal growth and development. Electropolishing of surfaces has become the industry standard for metallic stents, while anodization of surfaces, although not practiced on stents at present, could increase the thickness of the stable oxide film and delay early-stage implant degradation. In this study, pure zinc samples were electropolished (EP) and anodized (AD) to engineer oxide films with distinctive physical and degradation characteristics, as determined by potentiodynamic polarization, electrochemical impedance spectroscopy, and static immersion tests. The samples were then implanted within the aortic lumen of adult Sprague-Dawley rats to determine the influence of surface engineering on biocompatibility responses to Zn implants. It was found that in vitro corrosion produced a porous corrosion layer for the EP samples and a densified layer on the AD samples. The AD material was more resistant to corrosion, while localized corrosion and pitting was seen on the EP surface. Interestingly, the increased variability from localized corrosion due to the surface film character translated directly to the in vivo performance, where 100% of the AD implants but only 44% of the EP implants met the biocompatibility benchmarks. Overall, the results suggest that oxide films on degradable zinc critically affect early neointimal progression and overall success of degradable Zn materials.

Multiscale experimental study on the effects of different weight-bearing levels during moderate treadmill exercise on bone quality in growing female rats

Background

Bone tissue displays a hierarchical organization. Mechanical environments influence bone mass and structure. This study aimed to explore the effects of different mechanical stimuli on growing bone properties at macro–micro–nano scales.

Methods

Sixty five-week-old female Wistar rats were treadmill exercised at moderate intensity with the speed of 12 m/min, and then randomly divided into five groups according to weight-bearing level. After 8 weeks of experiment, femurs were harvested to perform multiscale tests.

Results

Bone formation was significantly increased by weight-bearing exercise, whereas bone resorption was not significantly inhibited. Trabecular and cortical bone mineral densities showed no significant increase by weight-bearing exercise. The microstructure of trabecular bone was significantly improved by 12% weight-bearing exercise. However, similar positive effects were not observed with further increase in weight-bearing levels. The nanomechanical properties of trabecular bone were not significantly changed by weight-bearing exercise. The macrostrength of whole femur and the nanomechanical properties of cortical bone significantly decreased in the 19% and 26% weight-bearing exercise groups.

Conclusion

When rats ran on the treadmill at moderate intensity during growth period, additional 12% weight-bearing level could significantly increase bone formation, improve microstructure of trabecular bone, as well as maintain the structure and mechanical properties of cortical bone. Excessive weight-bearing level caused no positive effects on the trabecular bone microstructure and properties of cortical bone at all scales. In addition, increased weight-bearing level exerted no significant influence on trabecular and cortical bone mineral densities.

Fabrication of a Low Adhesive Superhydrophobic Surface on Ti6Al4V Alloys Using TiO₂/Ni Composite Electrodeposition

A superhydrophobic surface with low adhesion and good wear resistance was fabricated on Ti6Al4V substrates via TiO₂/Ni composite electrodeposition, and subsequently modified with a fluoroalkylsilane (FAS) film. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and optical contact angle measurements were used to characterize the surface morphologies, chemical compositions, and surface wettability. The superhydrophobicity of the as-prepared surface results from the fabrication of a hierarchical structure and the assembly of low-surface energy fluorinated components. The as-prepared surface had a water contact angle as high as 162.6° and a sliding angle close to 1.8°. Scratch and abrasion tests showed that the superhydrophobic coating provided a superior wear resistance and stable mechanical abrasion protection. In addition, the influence of processing conditions, such as working voltage, deposited time, pH value, and TiO₂ concentration, was also investigated.

Fabrication of Adhesive Resistance Surface with Low Wettability on Ti6Al4V Alloys by Electro-Brush Plating

Anti-adhesive Ni coatings with low wettability were successfully fabricated on Ti6Al4V substrates via an electro-brush plating method, and subsequently modified with a fluoroalkylsilane (FAS) film. The surface morphology, chemical compositions, and wettability of the as-prepared coatings were measured using scanning electron microscopy (SEM), X-ray diffractometer (XRD), Fourier transform infrared spectrophotometry (FTIR), and contact angle measurements. The results showed that the surface of Ti6Al4V substrate was endowed with flower-like structures. Each flower-like cluster was constituted by a large number of Ni ions. After surface modification of FAS, the as-prepared Ti6Al4V surface had a water contact angle as high as 151.5°, a sliding angle close to 2.1°, and a solid surface energy as low as 0.97 mJ/m². Potentiodynamic polarization tests showed that the Ni coating could provide a stable corrosion protection. In addition, the effects of processing conditions, such as working voltage, relative velocity, electrolyte concentration, and processing time, were investigated. The mechanism of the adhesive resistance was proposed, and the low wettability of Ti6Al4V surfaces was explained by Cassie–Baxter model. As a result, it was necessary to reduce the fraction of the solid–liquid interface in order to achieve anti-adhesive surface.

Strontium/adiponectin co-decoration modulates the osteogenic activity of nano-morphologic polyetheretherketone implant

Polyetheretherketone (PEEK)-based implants have become popular in hard tissue orthopedic and dental field. However, its inherent bio-inertness limited its applications for bone repair/substitution of osteoporosis patients, with poor osteogenesis capability. In order to ameliorate their bioactivity, the 3D porous PEEK substrate was created by sulfonate processing, and the substrate was subsequently incorporated with strontium (Sr) through a hydrothermal reaction in Sr(OH)₂ solutions. The adiponectin (APN) protein membrane was deposited on the substrate via polydopamine-assisted deposition. Surface characterization results disclosed that the nanostructures had been formed on sPEEK-Sr-APN surafces, and APN coatings on the substrates could adjust Sr release rate and further mediate cell-material interactions. in vitro experiments indicated that the cellular effects (proliferation and differentiation) of MC3T3-E1 were significantly increased with Sr/APN coordinated regulation. This study provides bioactive Sr and APN as promising active components for bio-functional bone regeneration/substitution, and optimizes the osteointegration of PEEK implants in clinic.

Astragaloside IV promotes the proliferation and migration of osteoblast-like cells through the hedgehog signaling pathway

The present study aimed to investigate the effects of astragaloside IV on osteoblast-like cell proliferation and migration, in addition to the underlying signaling pathway. In order to observe the effect on proliferation, a Cell Counting Kit-8 assay and flow cytometry were used. To detect cell migration ability, cell scratch and Transwell cell migration assays were performed. The RNA and protein expression levels of hedgehog signaling molecules, including Sonic hedgehog (SHH) and GLI family zinc finger 1 (GLI1), were examined by reverse transcription-quantitative polymerase chain reaction and western blot analyses. To inhibit the hedgehog signaling pathway, cyclopamine was used. Astragaloside IV, at a dosage of 1×10⁻²µg/ml in MG-63 cells and 1×10⁻³µg/ml in U-2OS cells, resulted in the enhanced proliferation and migration of cells, and the gene expression levels of the SHH and GLI1 were significantly increased. The combination of astragaloside IV and cyclopamine reduced MG-63 and U-2OS cell proliferation and migration, and inhibited the gene expression of SHH and GLI1. Astragaloside IV enhanced the proliferation and migration of human osteoblast-like cells through activating the hedgehog signaling pathway. The results of the present study provide a rational for the mechanistic link in astragaloside IV promoting the proliferation and migration of osteoblasts via the hedgehog signaling pathway.

Combinatorial Surface Roughness Effects on Osteoclastogenesis and Osteogenesis

Implant surface properties are a key factor in bone responses to metallic bone implants. In view of the emerging evidence on the important role of osteoclasts in bone regeneration, we here studied how surface roughness affects osteoclastic differentiation and to what extent these osteoclasts have stimulatory effects on osteogenic differentiation of osteoprogenitor cells. For this, we induced osteoclasts derived from RAW264.7 cell line and primary mouse macrophages on titanium surfaces with different roughness ( R_a 0.02-3.63 μm) and analyzed osteoclast behavior in terms of cell number, morphology, differentiation, and further anabolic effect on osteoblastic cells. Surfaces with different roughness induced the formation of osteoclasts with distinct phenotypes, based on total osteoclast numbers, morphology, size, cytoskeletal organization, nuclearity, and osteoclastic features. Furthermore, these different osteoclast phenotypes displayed differential anabolic effects toward the osteogenic differentiation of osteoblastic cells, for which the clastokine CTHRC1 was identified as a causative factor. Morphologically, osteoclast potency to stimulate osteogenic differentiation of osteoblastic cells was found to logarithmically correlate with the nuclei number per osteoclast. Our results demonstrate the existence of a combinatorial effect of surface roughness, osteoclastogenesis, and osteogenic differentiation. These insights open up a new dimension for designing and producing metallic implants by considering the implant roughness to locally regulate osseointegration through coupling osteoclastogenesis with osteogenesis.

Enhanced Osseointegration of Hierarchically Structured Ti Implant with Electrically Bioactive SnO2-TiO2 Bilayered Surface

The poor osseointegration of Ti implant significantly compromise its application in load-bearing bone repair and replacement. Electrically bioactive coating inspirited from heterojunction on Ti implant can benefit osseointegration but cannot avoid the stress shielding effect between bone and implant. To resolve this conflict, hierarchically structured Ti implant with electrically bioactive SnO₂-TiO₂ bilayered surface has been developed to enhance osseointegration. Benefiting from the electric cue offered by the built-in electrical field of SnO₂-TiO₂ heterojunction and the topographic cue provided by the hierarchical surface structure to bone regeneration, the osteoblastic function of basic multicellular units around the implant is significantly improved. Because the individual TiO₂ or SnO₂ coating with uniform surface exhibits no electrical bioactivity, the effects of electric and topographic cues to osseointegration have been decoupled via the analysis of in vivo performance for the placed Ti implant with different surfaces. The developed Ti implant shows significantly improved osseointegration with excellent bone-implant contact, improved mineralization of extracellular matrix, and increased push-out force. These results suggest that the synergistic strategy of combing electrical bioactivity with hierarchical surface structure provides a new platform for developing advanced endosseous implants.

Titanium Surfaces Functionalized with siMIR31HG Promote Osteogenic Differentiation of Bone Marrow Mesenchymal Stem Cells

Titanium (Ti) implants are widely used in the clinic as bone substitutes and dental implants, but further improvements are needed to obtain high osteogenic ability and consequent osseointegration. Knockdown of long noncoding RNA MIR31HG promotes osteogenic differentiation and bone formation. In this study, we fabricated a Ti surface functionalized with siRNA targeting MIR31HG (siMIR31HG) and accelerated osteogenesis of bone marrow mesenchymal stem cells (BMSCs). Chitosan/siRNA complex was loaded onto the thermal alkali-treated Ti surface to fabricate the siMIR31HG-functionalized Ti surface. The surface morphology, siRNA loading and release efficiency, and transfection efficacy were investigated, and the biological effects, such as cell proliferation, cell morphology, and osteogenic activity, were determined. The results showed that the siMIR31HG-functionalized Ti implant generated an ∼50% knockdown of MIR31HG, with no apparent cytotoxicity, which consequently enhanced osteogenic differentiation of BMSCs, as indicated by the increase of ALP production, extracellular matrix mineralization, osteogenic gene expression, and ectopic bone formation in vivo. The siMIR31HG biofunctionalization can be used to obtain better osseointegration of Ti implant in the clinic.

Bioinspired, biocompatible and peptide-decorated silk fibroin coatings for enhanced osteogenesis of bioinert implant

In this study, we develop an osteopromotive polyetheretherketone (PEEK) implant decorated with silk fibroin and bone forming peptide, in which the surface of bioinert PEEK implant is firstly sulfonated to form a three-dimensional, porous topography and then is functionalized with silk fibroin via spin-coating process and peptide decoration. The bio-test results show that cells on the functional bioinert implants exhibit better cell adhesion, proliferation and spreading, when compared with the uncoated ones. Moreover, the peptide-decorated silk fibroin coatings have ability to hasten the osteogenic differentiation and maturation of osteoblast-like cells. Our findings show the potential of the functional PEEK implants with superior bioactivity and osteoinductive property in orthopedics and dentistry. Besides, the facile, bioinspired, osteopromotive modification strategy can be used in other orthopedic and dental implants, such as titanium, zirconium dioxide.

Effects of titanium surface roughness on the mediation of osteogenesis via modulating the immune response of macrophages

Osteoblastic lineage cells are commonly used to evaluate the in vitro osteogenic ability of bone biomaterials. However, contradictory results obtained from in vivo and in vitro studies are not uncommon. With the increasing understanding of osteoimmunology, the immune response has been recognized as playing an important role in bone regeneration. In this study, we examined the effect of submicron-scaled titanium surface roughness (ranging from approximately 100 to 400 nm) on the response of osteoblasts and macrophages. The results showed that osteoblast differentiation enhanced with increased surface roughness of titanium substrates. The cytoskeleton of macrophages altered with the variation in titanium surface roughness. The production of cytokines (TNF-α, IL-6, IL-4 and IL-10) could be regulated by titanium surface roughness. Moreover, macrophages cultured on titanium surfaces exhibited a tendency to polarize to M1 phenotype with the increase of surface roughness. Material/macrophage conditioned medium tended to promote osteoblast differentiation with the increase of surface roughness. The results indicate that increasing surface roughness in the submicron range is beneficial for osteogenesis via modulating the immune response of macrophages. Modifying biomaterial surfaces based on their immunomodulatory effects is considered as a novel strategy for the improvement of their biological performance.

A multifaceted coating on titanium dictates osteoimmunomodulation and osteo/angio-genesis towards ameliorative osseointegration

A multifaceted coating for hard tissue implants, with favorable osteogenesis, angiogenesis, and osteoimmunomodulation abilities, would be of great value since it could improve osseointegration and alleviate prosthesis loosening. However, to date there are few coatings that fully satisfy these criteria. Herein we describe a microporous TiO₂ coating decorated with hydroxyapatite (HA) nanoparticles that is generated by micro-arc oxidation of pure titanium (Ti) and followed annealing. By altering the annealing temperature, it is possible to simultaneously tune the coating's physical (morphology and wettability) and chemical (composites and crystallinity) properties. A coating produced with micro-arc oxidization (MAO) with an annealing temperature of 650 °C (MAO-650) exhibits numerous favorable physicochemical properties, such as hybrid micro-nano morphology, superhydrophilicity, and highly crystalline HA nanoparticles. In vitro experiments reveal that the MAO-650 coating not only supports proliferation and differentiation of both osteoblasts and endothelial cells, but also inhibits the inflammatory response of macrophages and enables a favorable osteoimmunomodulation to facilitate osteo/angio-genesis. In vivo evaluation mirrors these results, and shows that the MAO-650 coating results in ameliorative osseointegration when compared with the pristine MAO coating. These data highlight the profound effect of surface physicochemical properties on the regulation of osteo/angio-genesis and osteoimmunomodulation in the enhancement of osseointegration.

Lithium doped silica nanospheres/poly(dopamine) composite coating on polyetheretherketone to stimulate cell responses, improve bone formation and osseointegration

Osseointegration is crucial for early fixation as well as long-term success of orthopedic implants. Bioactive composite containing lithium doping silica nanospheres (LSNs) and poly(dopamine) (PDA) were coated on polyetheretherketone (PK) surface (LPPK), and effects of the LSNs/PDA composite (LPC) coating on the biological properties of LPPK were assessed both in vitro and in vivo. Results showed that LPPK with improved bioactivity remarkably promoted apatite mineralization in simulated body fluid (SBF) compared with PDA coated on PK (PPK) and PK. Moreover, the LPPK remarkably stimulated rat bone marrow stromal cells (rBMSCs) responses compared with PPK and PK. Furthermore, the LPPK significantly promoted bone tissues responses in vivo compared with PPK and PK. It could be suggested that the improvements of cells and bone tissues responses were attributed to the surface characteristics of the bioactive LPC coating on LPPK. The LPPK would be a great candidate for orthopedic and dental applications.

Electrically bioactive coating on Ti with bi-layered SnO2–TiO2 hetero-structure for improving osteointegration

SnO₂–TiO₂ surface with the bi-layered structure on Ti provides internal electric stimulation to promote osteointegration of implant.

Cytocompatibility and antibacterial activity of nanostructured H2Ti5O11·H2O outlayered Zn-doped TiO2 coatings on Ti for percutaneous implants

To improve skin-integration and antibacterial activity of percutaneous implants, the coatings comprising an outer layer of H2Ti5O11·H2O (HTO) nanoarrays and an inner layer of microporous Zn-doped TiO2 were fabricated on Ti by micro-arc oxidation (MAO) followed with hydrothermal treatment (HT). During HT process, a large proportion of Zn2+ migrated out from TiO2 layer. TiO2 reacted with OH- and H2O, resulting in the nucleation of HTO. The nuclei grew to nanoplates, nanorods and nanofibres with HT process prolonged. Simultaneously, the orientation of nanoarrays changed from quasi-vertical to parallel to substrate. Compared to Ti, adhesion and proliferation of fibroblasts were enhanced on as-MAOed TiO2 and HTed coatings. The phenotype, differentiation and extracellular collagen secretion were obviously accelerated on vertical nanorods with proper interspace (e.g. 63 nm). HTed coatings showed enhanced antibacterial activity, which should be ascribed to the nano-topography of HTO.

Falling Leaves Inspired ZnO Nanorods-Nanoslices Hierarchical Structure for Implant Surface Modification with Two Stage Releasing Features

Inspired from falling leaves, ZnO nanorods-nanoslices hierarchical structure (NHS) was constructed to modify the surfaces of two widely used implant materials: titanium (Ti) and tantalum (Ta), respectively. By which means, two-stage release of antibacterial active substances were realized to address the clinical importance of long-term broad-spectrum antibacterial activity. At early stages (within 48 h), the NHS exhibited a rapid releasing to kill the bacteria around the implant immediately. At a second stage (over 2 weeks), the NHS exhibited a slow releasing to realize long-term inhibition. The excellent antibacterial activity of ZnO NHS was confirmed once again by animal test in vivo. According to the subsequent experiments, the ZnO NHS coating exhibited the great advantage of high efficiency, low toxicity, and long-term durability, which could be a feasible manner to prevent the abuse of antibiotics on implant-related surgery.

Osseodensification for enhancement of spinal surgical hardware fixation

Integration between implant and bone is an essential concept for osseous healing requiring hardware placement. A novel approach to hardware implantation, termed osseodensification, is described here as an effective alternative. 12 sheep averaging 65kg had fixation devices installed in their C2, C3, and C4 vertebral bodies; each device measured 4mm diameter×10mm length. The left-sided vertebral body devices were implanted using regular surgical drilling (R) while the right-sided devices were implanted using osseodensification drilling (OD). The C2 and C4 vertebra provided the t=0 in vivo time point, while the C3 vertebra provided the t=3 and t=6 week time points, in vivo. Structural competence of hardware was measured using biomechanical testing of pullout strength, while the quality and degree of new bone formation and remodeling was assessed via histomorphometry. Pullout strength demonstrated osseodensification drilling to provide superior anchoring when compared to the control group collapsed over time with statistical significance (p<0.01). On Wilcoxon rank signed test, C2 and C4 specimens demonstrated significance when comparing device pullout (p=0.031) for both, and C3 pullout tests at 3 and 6 weeks collapsed over time had significance as well (p=0.027). Percent bone-to-implant contact (%BIC) analysis as a function of drilling technique demonstrated an OD group with significantly higher values relative to the R group (p<0.01). Similarly, percent bone-area-fraction-occupancy (BAFO) analysis presented with significantly higher values for the OD group compared to the R group (p=0.024). As a function of time, between 0 and 3 weeks, a decrease in BAFO was observed, a trend that reversed between 3 and 6 weeks, resulting in a BAFO value roughly equivalent to the t=0 percentage, which was attributed to an initial loss of bone fraction due to remodeling, followed by regaining of bone fraction via production of woven bone. Histomorphological data demonstrated autologous bone chips in the OD group with greater frequency relative to the control, which acted as nucleating surfaces promoting new bone formation around the implants, providing superior stability and greater bone density. This alternative approach to a critical component of hardware implantation encourages assessment of current surgical approaches to hardware implantation.

Surface properties of Ti-6Al-4V alloy part I: Surface roughness and apparent surface free energy

Titanium (Ti) and its alloys are the most often used implants material in dental treatment and orthopedics. Topography and wettability of its surface play important role in film formation, protein adhesion, following osseointegration and even duration of inserted implant. In this paper, we prepared Ti-6Al-4V alloy samples using different smoothing and polishing materials as well the air plasma treatment, on which contact angles of water, formamide and diiodomethane were measured. Then the apparent surface free energy was calculated using four different approaches (CAH, LWAB, O-W and Neumann's Equation of State). From LWAB approach the components of surface free energy were obtained, which shed more light on the wetting properties of samples surface. The surface roughness of the prepared samples was investigated with the help of optical profilometer and AFM. It was interesting whether the surface roughness affects the apparent surface free energy. It was found that both polar interactions the electron donor parameter of the energy and the work of water adhesion increased with decreasing roughness of the surfaces. Moreover, short time plasma treatment (1min) caused decrease in the surface hydrophilic character, while longer time (10min) treatment caused significant increase in the polar interactions and the work of water adhesion. Although Ti-6Al-4V alloy has been investigated many times, to our knowledge, so far no paper has been published in which surface roughness and changes in the surface free energy of the alloy were compared in the quantitative way in such large extent. This novel approach deliver better knowledge about the surface properties of differently smoothed and polished samples which may be helpful to facilitate cell adhesion, proliferation and mineralization. Therefore the results obtained present also potentially practical meaning.

Synergistic effects of elastic modulus and surface topology of Ti-based implants on early osseointegration

Elastic modulus and surface micro-scale topographical structure of Ti alloy implants have a synergistic effect on cell attachment, osteogenic differentiation of rBMSCs in vitro and early osseointegration in vivo.

Tailoring biomaterial surface properties to modulate host-implant interactions: implication in cardiovascular and bone therapy

Host body response to a foreign medical device plays a critical role in defining its fate post implantation. It is thus important to control host-material interactions by designing innovative implant surfaces. In the recent years, biochemical and topographical features have been explored as main target to produce this new type of bioinert or bioresponsive implants. The review discusses specific biofunctional materials and strategies to achieve a precise control over implant surface properties and presents possible solutions to develop next generation of implants, particularly in the fields of bone and cardiovascular therapy.