Microarc oxidation coating covered Ti implants with micro-scale gouges formed by a multi-step treatment for improving osseointegration

Multifunctional Coatings of Titanium Implants Toward Promoting Osseointegration and Preventing Infection: Recent Developments

Titanium and its alloys are dominant material for orthopedic/dental implants due to their stable chemical properties and good biocompatibility. However, aseptic loosening and peri-implant infection remain problems that may lead to implant removal eventually. The ideal orthopedic implant should possess both osteogenic and antibacterial properties and do proper assistance to in situ inflammatory cells for anti-microbe and tissue repair. Recent advances in surface modification have provided various strategies to procure the harmonious relationship between implant and its microenvironment. In this review, we provide an overview of the latest strategies to endow titanium implants with bio-function and anti-infection properties. We state the methods they use to preparing these efficient surfaces and offer further insight into the interaction between these devices and the local biological environment. Finally, we discuss the unmet needs and current challenges in the development of ideal materials for bone implantation.

Osteoblast Response to Copper-Doped Microporous Coatings on Titanium for Improved Bone Integration

Due to their excellent mechanical properties and good biocompatibility, titanium alloys have become a popular research topic in the field of medical metal implants. However, the surface of the titanium alloy does not exhibit biological activity, which may cause poor integration between the interface of the titanium implant and the interface of the bone tissue and subsequently may cause the implant to fall off. Therefore, surface biological inertness is one of the problems that titanium alloys must overcome to become an ideal orthopedic implant material. Surface modification can improve the biological properties of titanium, thereby enhancing its osseointegration effect. Copper is an essential trace element for the human body, can promote bone formation and plays an important role in maintaining the physiological structure and function of bone and bone growth and development. In this study, a microporous copper-titanium dioxide coating was prepared on the surface of titanium by microarc oxidation. Based on the evaluation of its surface characteristics, the adhesion, proliferation and differentiation of MC3T3-E1 cells were observed. A titanium rod was implanted into the rabbit femoral condyle, and the integration of the coating and bone tissue was evaluated. Our research results show that the microporous copper-titanium dioxide coating has a nearly three-dimensional porous structure, and copper is incorporated into the coating without changing the structure of the coating. In vitro experiments found that the coating can promote the adhesion, proliferation and differentiation of MC3T3-E1 cells. In vivo experiments further confirmed that the titanium copper-titanium dioxide microporous coating can promote the osseointegration of titanium implants. In conclusion, copper-titanium dioxide microporous coatings can be prepared by microarc oxidation, which can improve the biological activity and biocompatibility of titanium, promote new bone formation and demonstrate good osteoinductive properties. Therefore, the use of this coating in orthopedics has potential clinical application.

Multifunctional natural polymer-based metallic implant surface modifications

High energy traumas could cause critical damage to bone, which will require permanent implants to recover while functionally integrating with the host bone. Critical sized bone defects necessitate the use of bioactive metallic implants. Because of bioinertness, various methods involving surface modifications such as surface treatments, the development of novel alloys, bioceramic/bioglass coatings, and biofunctional molecule grafting have been utilized to effectively integrate metallic implants with a living bone. However, the applications of these methods demonstrated a need for an interphase layer improving bone-making to overcome two major risk factors: aseptic loosening and peri-implantitis. To accomplish a biologically functional bridge with the host to prevent loosening, regenerative cues, osteoimmunomodulatory modifications, and electrochemically resistant layers against corrosion appeared as imperative reinforcements. In addition, interphases carrying antibacterial cargo were proven to be successful against peri-implantitis. In the literature, metallic implant coatings employing natural polymers as the main matrix were presented as bioactive interphases, enabling rapid, robust, and functional osseointegration with the host bone. However, a comprehensive review of natural polymer coatings, bridging and grafting on metallic implants, and their activities has not been reported. In this review, state-of-the-art studies on multifunctional natural polymer-based implant coatings effectively utilized as a bone tissue engineering (BTE) modality are depicted. Protein-based, polysaccharide-based coatings and their combinations to achieve better osseointegration via the formation of an extracellular matrix-like (ECM-like) interphase with gap filling and corrosion resistance abilities are discussed in detail. The hypotheses and results of these studies are examined and criticized, and the potential future prospects of multifunctional coatings are also proposed as final remarks.

3D printed titanium scaffolds with homogeneous diamond-like structures mimicking that of the osteocyte microenvironment and its bone regeneration study

Biofabrication of personalized titanium scaffold mimicking that of the osteocyte microenvironment is challenging due to its complex geometrical cues. The effect of scaffolds geometrical cues and implantation sites on osteogenesis is still not clear. In this study, personalized titanium scaffolds with homogeneous diamond-like structures mimicking that of the osteocyte microenvironment were precisely designed and fabricated by selected laser melting method. The effects of different geometric cues, including porosity, pore sizes and interconnection properties, on cellular behavior were investigated. Biomimetic mechanical properties of porous titanium alloy scaffold were predesigned and simulated by finite element analysis. In vitro experiment revealed that homogeneous diamond-like structures mimicking that of the osteocyte microenvironment triggered osteocyte adhesion and migration behavior. Typical implantation sites, including rabbit femur, beagle femur, and beagle skull, were used to study the implantation sites effects on bone regeneration. In vivo experimental results indicated that different implantation sites showed significant differences. This study helps to understand the scaffolds geometrical microenvironment and implantation sites effects on osteogenesis mechanism. And it is beneficial to the development of bone implants with better bone regeneration ability.

Photofunctionalization as a suitable approach to improve the osseointegration of implants in animal models-A systematic review and meta-analysis

OBJECTIVES

To determine whether photofunctionalization influences dental implant osseointegration.

MATERIAL AND METHODS

Data on osseointegration rates were extracted from 8 databases, based on bone-to-implant contact (BIC) and pushout tests. Internal validity was accessed through the SYRCLE risk of bias tool for animal experimental studies. Meta-analyses were performed for investigation of the influence of photofunctionalization on implant osseointegration, with a random effect and a confidence interval of 95%. The certainty of evidence was accessed through the GRADE approach.

RESULTS

Thirty-four records were identified, and 10 were included in the meta-analysis. Photofunctionalized implants showed higher mean values for BIC in rabbits (MD 6.92 [1.01, 12.82], p = .02), dogs (MD 23.70 [10.23, 37.16], p = .001), rats (MD 20.93 [12.91, 28.95], p < .0001), and in the pooled BIC analyses (MD 14.23 [7.80, 20.66], p < .0001) compared to those in control implants in the overall assay. Conversely, at late healing periods, the pooled BIC meta-analyses showed no statistically significant differences (p > .05) for photofunctionalized and control implants at 12 weeks of follow-up. For pushout analysis, photofunctionalized implants presented greater bone strength integration (MD 19.92 [13.88, 25.96], p < .0001) compared to that of control implants. The heterogeneity between studies ranged from "not important" to "moderate" for rabbits I²  = 24%, dogs I²  = 0%, rats I²  = 0%, and pooled BIC (I²  = 49%), while considerable heterogeneity was observed for pushouts (I²  = 90%).

CONCLUSION

Photofunctionalization improves osseointegration in the initial healing period of implants, as summarized from available data from rabbit, dog, and rat in vivo models.

Sustainable release of vancomycin from micro-arc oxidised 3D-printed porous Ti6Al4V for treating methicillin-resistant Staphylococcus aureus bone infection and enhancing osteogenesis in a rabbit tibia osteomyelitis model

Elimination of infection and enhancement of osteogenesis by orthopaedic implants are two critical factors in the treatment of complex bone infections. A prolonged and expensive procedure requiring two surgical steps and a 6-8-week period of joint immobilisation is utilised as a primary treatment for revision arthroplasty of an infected prosthesis, greatly affecting long-term patient care for the ageing population. Here, we evaluated the effects of vancomycin-loaded in micro-arc oxidised (MAO) three-dimensional (3D) printed porous Ti6Al4V scaffolds on osteogenesis. This system showed a high loading capacity and sustained vancomycin release kinetics, as demonstrated using high-performance liquid chromatography. In vivo, 0.1 mL of 10⁸ colony forming units (CFU) methicillin-resistant Staphylococcus aureus was injected into the tibias of rabbits to induce severe osteomyelitis. Physical, haematological, radiographic, microbiological, and histopathological analyses were performed to evaluate the effects of treatment. Rabbits with vancomycin-loaded in MAO scaffolds showed the inhibition of bone infection and enhancement of osteogenesis, resulting in better outcomes than in the other groups. Overall, these findings demonstrated the potential of this 3D printed porous Ti6Al4V, with good osteogenesis and sustained vancomycin release properties, for application in the treatment of complex bone infections.

Enhanced Bone Remodeling Effects of Low-Modulus Ti-5Zr-3Sn-5Mo-25Nb Alloy Implanted in the Mandible of Beagle Dogs under Delayed Loading

Titanium (Ti) and its alloys are widely used in the dental and prosthetic implant fields due to their favorable biocompatibility. In this study, porous surface coatings incorporated with nanoscale hydroxyapatite particles on the surface of Ti and Ti-5Zr-3Sn-5Mo-25Nb (TLM) alloy were fabricated by microarc oxidation followed by hydrothermal treatment; the surface roughness and hydrophilicity were obviously enhanced by the surface modification procedure. In vivo, four adult male beagle dogs were selected for an implantation procedure and restored with full metal crowns after healing for 3 months. The bone responses were evaluated via histomorphological observation. Raman spectral analysis and nanoindentation experiments were used to quantitatively and qualitatively estimate the characteristics of the bone formed around the implants. Compared to the Ti group, the TLM titanium alloy group showed a significant increase in the percentage of bone-implant interface contact, bone inside the thread, mineralization, crystallinity, modulus of elasticity, and hardness of the integrated bone after delayed loading in the TLM group. Therefore, the TLM titanium alloy is considered a candidate implant material with desirable biomechanical compatibility, especially under applied stress.

[Study on antibacterial properties of titanium metallic surface due to synergistic action of micro/nano-structure and antimicrobial peptides]

Objective

To investigate the effects of micro/nano-structure and antimicrobial peptides (AMPs) on antibacterial properties for titanium (Ti) metal surface.

Methods

Ti disks were treated via sandblasted large-grit acid-etched (SLA) and alkali-heat treatment (AHT) to build the micor/nano-structure, on which AMPs were spin-coated with a certain amount (10, 30, 50, 70, and 90 μg). Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) were used to observe the surface structure and characterize the surface elements (i.e. contents of C, N, O, and Ti). Ti disks loaded with AMPs of difference amounts were co-cultured with Staphylococcus aureus ( S. aureus) for 24 hours. After that, the formation and dimension of antibacterial circle were measured. Furthermore, the Ti disks treated with different approaches (untreated, SLA treatment, SLA+THA treatment, and loaded with 90 μg AMPs) were co-cultured with S. aureus and Escherichia coli ( E.coli) for 3 hours, bacterial adhesion on the disks were evaluated by using SEM. The antibacterial performances in solution were quantitatively evaluated by immersing the Ti disks in bacterial solutions and measuring the absorbance ( A) values.

Results

It was found that the nanoporous structure could be easily constructed by SLA+AHT approach. After spin-coating AMPs, the nanopores with the diameter less than 200 nm were almost covered. According to the element analysis, with the increase of AMPs, the C content gradually increased; the N content was not detected until AMPs amount reached 70 μg on the disks. The diameter of antibacterial circle clearly depended on the AMPs amount. The Ti disks loaded with 90 μg AMPs had significantly larger antibacterial circles than the other Ti disks ( P<0.05). Based on the SEM observation, the Ti disks loaded with 90 μg AMPs has the least bacterial attachment compared with the other Ti disks ( P<0.05). The A value of bacterial solution immersed with the Ti disks loaded with 90 μg AMPs was much lower than the other Ti disks ( P<0.05).

Conclusion

The approach of micro/nano-structure and AMPs can improve the antibacterial properties of Ti metal surface.

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.