Surface Modification Techniques of Titanium and its Alloys to Functionally Optimize Their Biomedical Properties: Thematic Review

The Effect of Antibacterial-Osteogenic Surface Modification on the Osseointegration of Titanium Implants: A Static and Dynamic Strategy

Titanium (Ti) and its alloys are widely used biomaterials in bone repair. Although these biomaterials possess stable properties and good biocompatibility, the high elastic modulus and low surface activity of Ti implants have often been associated with infection, inflammation, and poor osteogenesis. Therefore, there is an urgent need to modify the surface of Ti implants, where changes in surface morphology or coatings loading can confer specific functions to help them adapt to the osseointegration formation phase and resist bacterial infection. This can further ensure a healthy microenvironment for bone regeneration as well as the promotion of immunomodulation, angiogenesis, and osteogenesis. Therefore, in this review, we evaluated various functional Ti implants after surface modification, both in terms of static modifications and dynamic response strategies, mainly focusing on the synergistic effects of antimicrobial activities and functionalized osteogenic. Finally, the current challenges and future perspectives are summarized to provide innovative and effective solutions for osseointegration and bone defect repair.

A Multifunctional Metal-Phenolic Nanocoating on Bone Implants for Enhanced Osseointegration via Early Immunomodulation

Surface modification is an important approach to improve osseointegration of the endosseous implants, however it is still desirable to develop a facile yet efficient coating strategy. Herein, a metal-phenolic network (MPN) is proposed as a multifunctional nanocoating on titanium (Ti) implants for enhanced osseointegration through early immunomodulation. With tannic acid (TA) and Sr2+ self-assembled on Ti substrates, the MPN coatings provided a bioactive interface, which can facilitate the initial adhesion and recruitment of bone marrow mesenchymal stem cells (BMSCs) and polarize macrophage toward M2 phenotype. Furthermore, the TA-Sr coatings accelerated the osteogenic differentiation of BMSCs. In vivo evaluations further confirmed the enhanced osseointegration of TA-Sr modified implants via generating a favorable osteoimmune microenvironment. In general, these results suggest that TA-Sr MPN nanocoating is a promising strategy for achieving better and faster osseointegration of bone implants, which can be easily utilized in future clinical applications.

A comprehensive review on the biomedical frontiers of nanowire applications

This comprehensive review examines the immense capacity of nanowires, nanostructures characterized by unbounded dimensions, to profoundly transform the field of biomedicine. Nanowires, which are created by combining several materials using techniques such as electrospinning and vapor deposition, possess distinct mechanical, optical, and electrical properties. As a result, they are well-suited for use in nanoscale electronic devices, drug delivery systems, chemical sensors, and other applications. The utilization of techniques such as the vapor-liquid-solid (VLS) approach and template-assisted approaches enables the achievement of precision in synthesis. This precision allows for the customization of characteristics, which in turn enables the capability of intracellular sensing and accurate drug administration. Nanowires exhibit potential in biomedical imaging, neural interfacing, and tissue engineering, despite obstacles related to biocompatibility and scalable manufacturing. They possess multifunctional capabilities that have the potential to greatly influence the intersection of nanotechnology and healthcare. Surmounting present obstacles has the potential to unleash the complete capabilities of nanowires, leading to significant improvements in diagnostics, biosensing, regenerative medicine, and next-generation point-of-care medicines.

Surface (bio)-functionalization of metallic materials: How to cope with real interfaces?

Metallic materials are an important class of biomaterials used in various medical devices, owing to a suitable combination of their mechanical properties. The (bio)-functionalization of their surfaces is frequently performed for biocompatibility requirements, as it offers a powerful way to control their interaction with biological systems. This is particularly important when physicochemical processes and biological events, mainly involving proteins and cells, are initiated at the host-material interface. This review addresses the state of "real interfaces" in the context of (bio)-functionalization of metallic materials, and the necessity to cope with it to avoid frequent improper evaluation of the procedure used. This issue is, indeed, well-recognized but often neglected and emerges from three main issues: (i) ubiquity of surface contamination with organic compounds, (ii) reactivity of metallic surfaces in biological medium, and (iii) discrepancy in (bio)-functionalization procedures between expectations and reality. These disturb the assessment of the strategies adopted for surface modifications and limit the possibilities to provide guidelines for their improvements. For this purpose, X-ray photoelectrons spectroscopy (XPS) comes to the rescue. Based on significant progresses made in methodological developments, and through a large amount of data compiled to generate statistically meaningful information, and to insure selectivity, precision and accuracy, the state of "real interfaces" is explored in depth, while looking after the two main constituents: (i) the bio-organic adlayer, in which the discrimination between the compounds of interest (anchoring molecules, coupling agents, proteins, etc) and organic contaminants can be made, and (ii) the metallic surface, which undergoes dynamic processes due to their reactivity. Moreover, through one of the widespread (bio)-functionalization strategy, given as a case study, a particular attention is devoted to describe the state of the interface at different stages (composition, depth distribution of contaminants and (bio)compounds of interest) and the mode of protein retention. It is highlighted, in particular, that the occurrence or improvement of bioactivity does not demonstrate that the chemical schemes worked in reality. These aspects are particularly essential to make progress on the way to choose the suitable (bio)-functionalization strategy and to provide guidelines to improve its efficiency.

Effectiveness of strontium/silver-based titanium surface coatings in improving antibacterial and osteogenic implant characteristics: a systematic review of in-vitro studies

Introduction: Due to the high incidence of implant failures, dual functionalization of titanium surfaces with antibacterial and osteogenic agents, like silver (Ag) and strontium (Sr), has gained significant attention in recent years. However, so far, the combined antibacterial and osteoinductive effectiveness of Ag/Sr-based titanium surface coatings has only been analyzed in individual studies. Methods: This systematic review aims to evaluate the existing scientific literature regarding the PICOS question "Does dual incorporation of strontium/silver enhances the osteogenic and anti-bacterial characteristics of Ti surfaces in vitro?". As a result of a web-based search adhering to the PRISMA Guidelines using three electronic databases (PubMed, Scopus, and Web of Science) until March 31, 2023, a total of 69 publications were identified as potentially relevant and 17 of which were considered appropriate for inclusion into this review. Results and Discussion: In all included publications, the use of Sr/Ag combination showed enhanced osteogenic and antibacterial effects, either alone or in combination with other agents. Moreover, the combination of Sr and Ag shows potential to synergistically enhance these effects. Nevertheless, further studies need to validate these findings under clinically more relevant conditions and evaluate the mechanism of antimicrobial and osteogenic activity of Sr/Ag combination.

3Y-TZP/Ta Biocermet as a Dental Material: An Analysis of the In Vitro Adherence of Streptococcus Oralis Biofilm and an In Vivo Pilot Study in Dogs

The surface adhesion of bacterial cells and the in vivo biocompatibility of a new ceramic-metal composite made of zirconium dioxide and tantalum were evaluated. Within the framework of an in vitro study using the crystal violet staining and colony counting methods, a relatively similar adhesion of Streptococcus oralis to the 3Y-TZP/Ta biocermet (roughness Ra = 0.12 ± 0.04 µm) and Ti-Al6-V4 titanium alloy (Ra = 0.04 ± 0.01 µm) was found. In addition, in an in vivo preliminary study focused on the histological analysis of a series of rods implanted in the jaws of beagle dogs for a six-month period, the absence of any fibrous tissue or inflammatory reaction at the interface between the implanted 3Y-TZP/Ta biocermets and the new bone was found. Thus, it can be concluded that the developed ceramic-metal biocomposite may be a promising new material for use in dentistry.

SiONx Coating Regulates Mesenchymal Stem Cell Antioxidant Capacity via Nuclear Erythroid Factor 2 Activity under Toxic Oxidative Stress Conditions

Healing in compromised and complicated bone defects is often prolonged and delayed due to the lack of bioactivity of the fixation device, secondary infections, and associated oxidative stress. Here, we propose amorphous silicon oxynitride (SiONx) as a coating for the fixation devices to improve both bioactivity and bacteriostatic activity and reduce oxidative stress. We aimed to study the effect of increasing the N/O ratio in the SiONx to fine-tune the cellular activity and the antioxidant effect via the NRF2 pathway under oxidative stress conditions. The in vitro studies involved using human mesenchymal stem cells (MSCs) to examine the effect of SiONx coatings on osteogenesis with and without toxic oxidative stress. Additionally, bacterial growth on SiONx surfaces was studied using methicillin-resistant Staphylococcus aureus (MRSA) colonies. NRF2 siRNA transfection was performed on the hMSCs (NRF2-KD) to study the antioxidant response to silicon ions. The SiONx implant surfaces showed a >4-fold decrease in bacterial growth vs. bare titanium as a control. Increasing the N/O ratio in the SiONx implants increased the alkaline phosphatase activity >1.5 times, and the other osteogenic markers (osteocalcin, RUNX2, and Osterix) were increased >2-fold under normal conditions. Increasing the N/O ratio in SiONx enhanced the protective effects and improved cell viability against toxic oxidative stress conditions. There was a significant increase in osteocalcin activity compared to the uncoated group, along with increased antioxidant activity under oxidative stress conditions. In NRF2-KD cells, there was a stunted effect on the upregulation of antioxidant markers by silicon ions, indicating a role for NRF2. In conclusion, the SiONx coatings studied here displayed bacteriostatic properties. These materials promoted osteogenic markers under toxic oxidative stress conditions while also enhancing antioxidant NRF2 activity. These results indicate the potential of SiONx coatings to induce in vivo bone regeneration in a challenging oxidative stress environment.

Nanoscale Topography of Anodic TiO2 Nanostructures Is Crucial for Cell-Surface Interactions

Anodic titanium dioxide (TiO2) nanostructures, i.e., obtained by electrochemical anodization, have excellent control over the nanoscale morphology and have been extensively investigated in biomedical applications owing to their sub-100 nm nanoscale topography range and beneficial effects on biocompatibility and cell interactions. Herein, we obtain TiO2 nanopores (NPs) and nanotubes (NTs) with similar morphologies, namely, 15 nm diameter and 500 nm length, and investigate their characteristics and impact on stem cell adhesion. We show that the transition of TiO2 NPs to NTs occurs via a pore/wall splitting mechanism and the removal of the fluoride-rich layer. Furthermore, in contrast to the case of NPs, we observe increased cell adhesion and proliferation on nanotubes. The enhanced mesenchymal stem cell adhesion/proliferation seems to be related to a 3-fold increase in activated integrin clustering, as confirmed by immunogold labeling with β1 integrin antibody on the nanostructured layers. Moreover, computations of the electric field and surface charge density show increased values at the inner and outer sharp edges of the top surfaces of the NTs, which in turn can influence cell adhesion by increasing the bridging interactions mediated by proteins and molecules in the environment. Collectively, our results indicate that the nanoscale surface architecture of the lateral spacing topography can greatly influence stem cell adhesion on substrates for biomedical applications.

Surface-modified titanium and titanium-based alloys for improved osteogenesis: A critical review

As implantable materials, titanium, and its alloys have garnered enormous interest from researchers for dental and orthopedic procedures. Despite their success in wide clinical applications, titanium, and its alloys fail to stimulate osteogenesis, resulting in poor bonding strength with surrounding bone tissue. Optimizing the surface topology and altered compositions of titanium and titanium-based alloys substantially promotes peri-implant bone regeneration. This review summarizes the utilization and importance of various osteogenesis components loaded onto titanium and its alloys. Further, different surface-modification methods and the release efficacy of loaded substances are emphasized. Finally, we summarize the article with prospects. We believe that further investigation studies must focus on identifying novel loading components, exploring various innovative, optimized surface-modification methods, and developing a sustained-release system on implant surfaces to improve peri-implant bone formation.

Micro-arc oxidation (MAO) and its potential for improving the performance of titanium implants in biomedical applications

Titanium (Ti) and its alloys have good biocompatibility, mechanical properties and corrosion resistance, making them attractive for biomedical applications. However, their biological inertness and lack of antimicrobial properties may compromise the success of implants. In this review, the potential of micro-arc oxidation (MAO) technology to create bioactive coatings on Ti implants is discussed. The review covers the following aspects: 1) different factors, such as electrolyte, voltage and current, affect the properties of MAO coatings; 2) MAO coatings affect biocompatibility, including cytocompatibility, hemocompatibility, angiogenic activity, corrosion resistance, osteogenic activity and osseointegration; 3) antibacterial properties can be achieved by adding copper (Cu), silver (Ag), zinc (Zn) and other elements to achieve antimicrobial properties; and 4) MAO can be combined with other physical and chemical techniques to enhance the performance of MAO coatings. It is concluded that MAO coatings offer new opportunities for improving the use of Ti and its alloys in biomedical applications, and some suggestions for future research are provided.

Synergistic effect of chlorhexidine and azoles on candida biofilm on titanium surface

BACKGROUND

Candida infections of orthopedic implants are one of the most detrimental orthopedic implant-related complications with unsuccessful treatment and a poor prognosis. Most orthopedic Candida infections form biofilms and have resistance to the commonly used antifungal agents. This study aimed to develop a novel combination of normally prescribed drugs against Candida biofilm on orthopedic implants.

METHODS

We cultured 26 clinical isolates of Candida strains to form biofilm without titanium sheets or on titanium sheets, which are the most commonly used materials for permanent or orthopedic implants. The checkerboard method was used to evaluate the synergistic effects of chlorhexidine (CHL) and azoles on these Candida biofilms. For the evaluation of synergistic effects, we constructed the cell viability assay by fluorescence staining and CFU reduction hot map of Candida.

RESULTS

Twenty-six clinical isolates of Candida strains formed biofilm in 96-well plates without titanium sheets, and we selected 9 of them to form biofilm on titanium sheets in 24-well plates. In Candida biofilm formed in 96-wells, the synergistic rates of CHL with fluconazole, itraconazole, and voriconazole were 61% (16/26), 65% (17/26), and 23% (6/26), respectively. When compared to the blank control group, CHL monotherapy significantly inhibited biofilm formation on titanium sheets (P < 0.05). We demonstrated 100% synergistic rates of the CHL and fluconazole combination against Candida biofilm formation on titanium sheets, and the minimum inhibitory concentration of CHL and FLU decreased four- to eight-fold.

CONCLUSIONS

We concluded that CHL combined with azoles inhibited the Candida biofilm formation 96-wells or on titanium sheets and has the potential to control the infections of orthopedic implants.

Titanium Boston keratoprosthesis with corneal cell adhesive and bactericidal dual coating

The Boston keratoprosthesis (BKPro) is a medical device used to restore vision in complicated cases of corneal blindness. This device is composed by a front plate of polymethylmethacrylate (PMMA) and a backplate usually made of titanium (Ti). Ti is an excellent biomaterial with numerous applications, although there are not many studies that address its interaction with ocular cells. In this regard, despite the good retention rates of the BKPro, two main complications compromise patients' vision and the viability of the prosthesis: imperfect adhesion of the corneal tissue to the upside of the backplate and infections. Thus, in this work, two topographies (smooth and rough) were generated on Ti samples and tested with or without functionalization with a dual peptide platform. This molecule consists of a branched structure that links two peptide moieties to address the main complications associated with BKPro: the well-known RGD peptide in its cyclic version (cRGD) as cell pro-adherent motif and the first 11 residues of lactoferrin (LF1-11) as antibacterial motif. Samples were physicochemically characterized, and their biological response was evaluated in vitro with human corneal keratocytes (HCKs) and against the gram-negative bacterial strain Pseudomonas aeruginosa. The physicochemical characterization allowed to verify the functionalization in a qualitative and quantitative manner. A higher amount of peptide was anchored to the rough surfaces. The studies performed using HCKs showed increased long-term proliferation on the functionalized samples. Gene expression was affected by topography and peptide functionalization. Roughness promoted α-smooth muscle actin (α-SMA) overexpression, and the coating notably increased the expression of extracellular matrix components (ECM). Such changes may favour the development of unwanted fibrosis, and thus, corneal haze. In contrast, the combination of the coating with a rough topography decreased the expression of α-SMA and ECM components, which would be desirable for the long-term success of the prosthesis. Regarding the antibacterial activity, the functionalized smooth and rough surfaces promoted the death of bacteria, as well as a perturbation in their wall definition and cellular morphology. Bacterial killing values were 58 % for smooth functionalised and 68 % for rough functionalised samples. In summary, this study suggests that the use of the dual peptide platform with cRGD and LF1-11 could be a good strategy to improve the in vitro and in vivo performance of the rough topography used in the commercial BKPro.

The Cell Adhesion and Proliferation Enhancement Impact of Low-Temperature Atmospheric Pressure Plasma-Polymerized Heptylamine on the Surface of Ti6Al4V Alloy

To chemically functionalize the Ti6Al4V alloy surface, a custom-made low-temperature atmospheric pressure plasma reactor device was used to polymerize heptylamine on it. The effect of different deposition times, an important process parameter, was also investigated. For each deposition time group, the surface morphology was observed via scanning electron microscopy (SEM). The surface chemical content was analyzed via X-ray photoelectron spectroscopy, and surface hydrophilicity was measured via water contact angle. The adhesion of bone marrow stromal cells (BMSCs) on the modified Ti6Al4V alloy surfaces was also observed via SEM. A quantitative evaluation of cell proliferation was performed via the Cell Counting Kit-8 assay. The results revealed that amino groups were introduced on the Ti6Al4V alloy surface via plasma-polymerized heptylamine (PPHA). The percentages of NH2/C for various deposition times (0 s, 30 s, 45 s, 60 s, 90 s, and 120 s) were 3.39%, 5.14%, 6.71%, 6.72%, 7.31%, and 7.65%. A 30 s, 45 s, and 60 s deposition time could significantly increase surface hydrophilicity with a mean water contact angle of 62.1 ± 1.6°, 65.7 ± 1.1°, and 88.2 ± 1.4°, respectively. Meanwhile, a 60 s, 90 s, and 120 s deposition time promoted BMSCs cell adhesion and proliferation. However, this promotion effect differed non-significantly among the three groups. In conclusion, the introduction of amino groups on the Ti6Al4V alloy surface exhibited surface modification and enhancement of cell adhesion and proliferation, which was partially associated with deposition time.

In Vitro and In Vivo Bone Regeneration Assessment of Titanium-Doped Waste Eggshell-Derived Hydroxyapatite in the Animal Model

In this work, a titanium-doped hydroxyapatite (HAp) scaffold was produced from two different sources (natural eggshell and laboratory-grade reagents) to compare the efficacy of natural and synthetic resources of HAp materials on new bone regeneration. This comparative study also reports the effect of Ti doping on the physical, mechanical, and in vitro as well as in vivo biological properties of the HAp scaffold. Pellets were prepared in the conventional powder metallurgy route, compacted, and sintered at 900 °C, showing sufficient porosity for bony ingrowth. The physical-mechanical characterizations were performed by density, porosity evaluation, XRD, FTIR, SEM analysis, and hardness measurement. In vitro interactions were evaluated by bactericidal assay, hemolysis, MTT assay, and interaction with simulated body fluid. All categories of pellets showed absolute nonhemolytic and nontoxic character. Furthermore, significant apatite formation was observed on the Ti-doped HAp samples in the simulated body fluid immersion study. The developed porous pellets were implanted to assess the bone defect healing in the femoral condyle of healthy rabbits. A 2 month study after implantation showed no marked inflammatory reaction for any samples. Radiological analysis, histological analysis, SEM analysis, and oxytetracycline labeling studies depicted better invasion of mature osseous tissue in the pores of doped eggshell-derived HAp scaffolds as compared to the undoped HAp, and laboratory-made samples. Quantification using oxytetracycline labeling depicted 59.31 ± 1.89% new bone formation for Ti-doped eggshell HAp as compared to Ti-doped pure HAp (54.41 ± 1.93) and other undoped samples. Histological studies showed the presence of abundant osteoblastic and osteoclastic cells in Ti-doped eggshell HAp in contrast to other samples. Radiological and SEM data also showed similar results. The results indicated that Ti-doped biosourced HAp samples have good biocompatibility, new bone-forming ability, and could be used as a bone grafting material in orthopedic surgery.

Palladium(II) Metal Complex Fabricated Titanium Implant Mitigates Dual-Species Biofilms in Artificial Synovial Fluid

Metallodrugs have a potent application in various medical fields. In the current study, we used a novel Palladium(II) thiazolinyl picolinamide complex that was directly fabricated over the titanium implant to examine its potency in inhibiting dual-species biofilms and exopolysaccharides. Additionally, inhibition of mono- and dual-species biofilms by coated titanium plates in an in vitro joint microcosm was performed. The study was carried out for 7 days by cultivating mono- and dual-species biofilms on titanium plates placed in both growth media and artificial synovial fluid (ASF). By qPCR analysis, the interaction of co-cultured biofilms in ASF and the alteration in gene expression of co-cultured biofilms were studied. Remarkable alleviation of biofilm accumulation and EPS secretion was observed on the coated titanium plates. The effective impairment of biofilms and EPS matrix of biofilms on Pd(II)-E-coated titanium plates were visualized by Scanning Electron Microscopy. Moreover, coated titanium plates improved the adhesion of osteoblast cells, which is crucial for a bone biomaterial. The potential bioactivity of coated plates was also confirmed at the molecular level using qPCR analysis. The stability of coated plates in ASF for 7 days was examined with FESEM-EDAX analysis. Collectively, the present study provided an excellent anti-infective effect on Pd(II)-E-coated titanium plates without affecting their biocompatibility with bone cells.

In Vitro Evaluation of Ag- and Sr-Doped Hydroxyapatite Coatings for Medical Applications

Osseointegration plays the most important role in the success of an implant. One of the applications of hydroxyapatite (HAp) is as a coating for metallic implants due to its bioactive nature, which improves osteoconduction. The purpose of this research was to assess the in vitro behavior of HAp undoped and doped with Ag and/or Sr obtained by galvanostatic pulsed electrochemical deposition. The coatings were investigated in terms of chemical bonds, contact angle and surface free energy, electrochemical behavior, in vitro biomineralization in acellular media (SBF and PBS), and biocompatibility with preosteoblasts cells (MC3T3-E1 cell line). The obtained results highlighted the beneficial impact of Ag and/or Sr on the HAp. The FTIR spectra confirmed the presence of hydroxyapatite within all coatings, while in terms of wettability, the contact angle and surface free energy investigations showed that all surfaces were hydrophilic. The in vitro behavior of MC3T3-E1 indicated that the presence of Sr in the HAp coatings as a unique doping agent or in combination with Ag elicited improved cytocompatibility in terms of cell proliferation and osteogenic differentiation. Therefore, the composite HAp-based coatings showed promising potential for bone regeneration applications.

Preparation and properties of composite manganese/fluorine coatings on metallic titanium

Titanium is widely used in implants because of its good mechanical properties and biocompatibility. However, titanium has no biological activity and is prone to causing implant failure after implantation. In this study, we prepared a manganese- and fluorine-doped titanium dioxide coating on a titanium surface by microarc oxidation technology. The surface characteristics of the coating were evaluated by field emission scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and atomic force microscopy and profiler, and the corrosion resistance and wear resistance of the coating were also evaluated. The bioactivity of the coating on bone marrow mesenchymal stem cells was evaluated by in vitro cell experiments, and the antibacterial properties of the coating were evaluated by in vitro bacterial experiments. The results confirmed that the manganese- and fluorine-doped titanium dioxide coating was successfully prepared on the titanium surface, and manganese and fluorine were successfully introduced into the coating. The doping of manganese and fluorine did not change the surface morphology of the coating, and the coating had good corrosion resistance and wear resistance. The results of the in vitro cell experiment showed that the titanium dioxide coating with manganese and fluoride could promote the proliferation, differentiation and mineralization of bone marrow mesenchymal stem cells. The results of the bacterial experiment in vitro showed that the coating material could inhibit the propagation of Staphylococcus aureus and had a good antibacterial effect. Conclusion: it is feasible to prepare a manganese- and fluorine-doped titanium dioxide coating on titanium surfaces by microarc oxidation. The coating not only has good surface characteristics but also has good bone-promoting and antibacterial properties and has potential for clinical application.

DMP1 and IFITM5 Regulate Osteogenic Differentiation of MC3T3-E1 on PEO-Treated Ti-6Al-4V-Ca2+/Pi surface

Despite numerous studies on various surface modifications on titanium and its alloys, it remains unclear what kind of titanium-based surface modifications are capable of controlling cell activity. This study aimed to understand the mechanism at the cellular and molecular levels and investigate the in vitro response of osteoblastic MC3T3-E1 cultured on the Ti-6Al-4V surface modified by plasma electrolytic oxidation (PEO) treatment. A Ti-6Al-4V surface was prepared by PEO at 180, 280, and 380 V for 3 or 10 min in an electrolyte containing Ca²⁺/P_i ions. Our results showed that PEO-treated Ti-6Al-4V-Ca²⁺/P_i surfaces enhanced the cell attachment and differentiation of MC3T3-E1 compared to the untreated Ti-6Al-4V control but did not affect cytotoxicity as shown by cell proliferation and cell death. Interestingly, on the Ti-6Al-4V-Ca²⁺/P_i surface treated by PEO at 280 V for 3 or 10 min, MC3T3-E1 showed a higher initial adhesion and mineralization. In addition, the alkaline phosphatase (ALP) activity significantly increased in MC3T3-E1 on the PEO-treated Ti-6Al-4V-Ca²⁺/P_i (280 V for 3 or 10 min). In RNA-seq analysis, the expression of dentin matrix protein 1 (DMP1), sortilin 1 (Sort1), signal-induced proliferation-associated 1 like 2 (SIPA1L2), and interferon-induced transmembrane protein 5 (IFITM5) was induced during the osteogenic differentiation of MC3T3-E1 on the PEO-treated Ti-6Al-4V-Ca²⁺/P_i. DMP1 and IFITM5 silencing decreased the expression of bone differentiation-related mRNAs and proteins and ALP activity in MC3T3-E1. These results suggest that the PEO-treated Ti-6Al-4V-Ca²⁺/P_i surface induces osteoblast differentiation by regulating the expression of DMP1 and IFITM5. Therefore, surface microstructure modification through PEO coatings with Ca²⁺/P_i ions could be used as a valuable method to improve biocompatibility properties of titanium alloys.

A Review on Nano Ti-Based Oxides for Dark and Photocatalysis: From Photoinduced Processes to Bioimplant Applications

Catalysis on TiO₂ nanomaterials in the presence of H₂O and oxygen plays a crucial role in the advancement of many different fields, such as clean energy technologies, catalysis, disinfection, and bioimplants. Photocatalysis on TiO₂ nanomaterials is well-established and has advanced in the last decades in terms of the understanding of its underlying principles and improvement of its efficiency. Meanwhile, the increasing complexity of modern scientific challenges in disinfection and bioimplants requires a profound mechanistic understanding of both residual and dark catalysis. Here, an overview of the progress made in TiO₂ catalysis is given both in the presence and absence of light. It begins with the mechanisms involving reactive oxygen species (ROS) in TiO₂ photocatalysis. This is followed by improvements in their photocatalytic efficiency due to their nanomorphology and states by enhancing charge separation and increasing light harvesting. A subsection on black TiO₂ nanomaterials and their interesting properties and physics is also included. Progress in residual catalysis and dark catalysis on TiO₂ are then presented. Safety, microbicidal effect, and studies on Ti-oxides for bioimplants are also presented. Finally, conclusions and future perspectives in light of disinfection and bioimplant application are given.

Vapor-Induced Pore-Forming Atmospheric-Plasma-Sprayed Zinc-, Strontium-, and Magnesium-Doped Hydroxyapatite Coatings on Titanium Implants Enhance New Bone Formation-An In Vivo and In Vitro Investigation

OBJECTIVES

Titanium implants are regarded as a promising treatment modality for replacing missing teeth. Osteointegration and antibacterial properties are both desirable characteristics for titanium dental implants. The aim of this study was to create zinc (Zn)-, strontium (Sr)-, and magnesium (Mg)-multidoped hydroxyapatite (HAp) porous coatings, including HAp, Zn-doped HAp, and Zn-Sr-Mg-doped HAp, on titanium discs and implants using the vapor-induced pore-forming atmospheric plasma spraying (VIPF-APS) technique.

METHODS

The mRNA and protein levels of osteogenesis-associated genes such as collagen type I alpha 1 chain (COL1A1), decorin (DCN), osteoprotegerin (TNFRSF11B), and osteopontin (SPP1) were examined in human embryonic palatal mesenchymal cells. The antibacterial effects against periodontal bacteria, including Porphyromonas gingivalis and Prevotella nigrescens, were investigated. In addition, a rat animal model was used to evaluate new bone formation via histologic examination and micro-computed tomography (CT).

RESULTS

The ZnSrMg-HAp group was the most effective at inducing mRNA and protein expression of TNFRSF11B and SPP1 after 7 days of incubation, and TNFRSF11B and DCN after 11 days of incubation. In addition, both the ZnSrMg-HAp and Zn-HAp groups were effective against P. gingivalis and P. nigrescens. Furthermore, according to both in vitro studies and histologic findings, the ZnSrMg-HAp group exhibited the most prominent osteogenesis and concentrated bone growth along implant threads.

SIGNIFICANCE

A porous ZnSrMg-HAp coating using VIPF-APS could serve as a novel technique for coating titanium implant surfaces and preventing further bacterial infection.

Noninfectious tissue interactions at periprosthetic interfaces

The success of hip arthroplasty is based on modern materials in addition to the continuous development of surgical techniques and clinical experience gained over six decades. The biocompatible implant materials used in hip arthroplasty can be textured or coated with biomimetic surfaces to ensure durable component ingrowth and moderate host response. Material integrity plays a critical role in the durability of the stable interface between implant components and periprosthetic tissues. Inflammation at the interfaces due to the release of degradation products from the implant materials is one of the causes of hip arthroplasty failure. This review summarizes the implant materials currently used in hip arthroplasty, their preclinical testing and the postoperative neogenesis of periprosthetic tissues, and the interactions of periprosthetic bone and the implant materials at the periprosthetic interfaces.

Biocompatibility of Subperiosteal Dental Implants: Effects of Differently Treated Titanium Surfaces on the Expression of ECM-Related Genes in Gingival Fibroblasts

INTRODUCTION

Titanium alloys currently are the most used material for the manufacture of dental endosseous implants. However, in partially or totally edentulous patients, varying degrees of maxillary bone resorption usually occur, making the application of these devices difficult or even impossible. In these cases, a suitable alternative is offered by subperiosteal implants, whose use is undergoing a revival of interest following the introduction of novel, computer-assisted manufacturing techniques. Several procedures have been developed for the modification of titanium surfaces so to improve their biocompatibility and integration with bone. Information is, however, still incomplete as far as the most convenient surface modifications to apply with subperiosteal implants, in which an integration with soft mucosal tissues is just as important.

OBJECTIVES

The present study aimed at evaluating whether different treatments of titanium surfaces can produce different effects on the viability, attachment, and differentiation of gingival fibroblasts, i.e., the cell type mainly involved in osteointegration as well as the healing of soft tissues injured by surgical procedures, in order to verify whether any of the treatments are preferable under these respects.

METHODOLOGY

The human immortalized gingival fibroblast (CRL-4061 line) were cultured in the presence of titanium specimens previously treated with five different procedures for surface modification: (i) raw machined (Ti-1); (ii) electropolished (Ti-2); (iii) sand-blasted acid-etched (Ti-3); (iv) Al Ti Color™ proprietary procedure (Ti-4); and (v) anodized (Ti-5). At different times of incubation, viability and proliferation of cells, was determined along with the changes in the expression patterns of ECM-related genes involved in fibroblast attachment and differentiation: vinculin, fibronectin, collagen type I-alpha 1 chain, focal adhesion kinase, integrin β-1, and N-cadherin. Three different experiments were carried out for each experimental point. The release from fibroblasts of endothelin-1 was also analyzed as a marker of inflammatory response. The proliferation and migration of fibroblasts were evaluated by scratch tests.

RESULTS

None of the five types of titanium surface tested significantly affected the fibroblasts' viability and proliferation. The release of endothelin-1 was also not significantly affected by any of the specimens. On the other hand, all titanium specimens significantly stimulated the expression of ECM-related genes at varying degrees. The proliferation and migration abilities of fibroblasts were also significantly stimulated by all types of titanium surface, with a higher-to-lower efficiency in the order: Ti-3 > Ti-4 > Ti-5 > Ti-2 > Ti-1, thus identifying sandblasting acid-etching as the most convenient treatment.

CONCLUSIONS

Our observations suggest that the titanium alloys used for manufacturing subperiosteal dental implants do not produce cytotoxic or proinflammatory effects on gingival fibroblasts, and that sandblasting acid-etching may be the surface treatment of choice as to stimulate the differentiation of gingival fibroblasts in the direction of attachment and migration, i.e., the features allegedly associated with a more efficient implant osteointegration, wound healing, and connective tissue seal formation.

Interproximal implant thread exposure after initial bone remodeling as a risk indicator for peri-implantitis

BACKGROUND

Due to the clinical challenges involved in successfully treating peri-implantitis, it is imperative to identify patient- and implant-level risk factors for its prevention. The main goal of this retrospective longitudinal radiographic and clinical study was to investigate whether interproximal radiographic implant thread exposure after physiological bone remodeling may be a risk factor for peri-implantitis. The secondary goal was to evaluate several other potential risk indicators.

METHODS

Of 4325 active dental school patients having implants placed, 165 partially edentulous adults (77 men, 88 women) aged 30-91 with ≥2 years of follow-up upon implant restoration were included. Implants with ≥1 interproximal thread exposed (no bone-to-implant contact) (n = 98, 35%) constituted the test group and those without exposed threads (n = 182, 65%) the control group. Descriptive, binary, and multivariate regression analyses were evaluated for goodness of fit. Wald tests were used to evaluate for significance set at 0.05.

RESULTS

Of the 280 implants (98 test, 182 control), 8 (2.9%) failed over a mean follow-up period of 7.67 (±2.63) years, and 27 implants (19 test, 8 control) developed peri-implantitis, with the exposed group having eight-fold (7.82 times) adjusted greater odds than the non-exposed. The risk increased four-fold (3.77 times) with each thread exposed. No other patient- or implant-related potentially confounding risk factors were identified.

CONCLUSIONS

Exposed interproximal implant threads after physiologic bone remodeling may be an independent risk indicator for incident peri-implantitis. Hence, clinicians should closely monitor patients with implant threads that have no bone-to-implant contact for incident peri-implantitis.

Microstructural response and wear behaviour of Ti-6Al-4V impregnated with Ni/Al2O3 + TiO2 nanostructured coating using an electric arc

Titanium alloys are known for their excellent corrosion resistance; however, low surface hardness results in poor wear resistance, which limits its potential application. This study employs a novel two-step process to embed a hard Ni coating containing a mixture of nanosized particles (Al₂O₃ and TiO₂) into the surface of the Ti-6Al-4V alloy using an electric arc produced during the inert tungsten gas welding process. The surface of the sample was evaluated using Vickers Microhardness, Scanning electron microscopy, Energy dispersive spectroscopy and pin-on-plate wear testing. Microstructural analysis showed that impregnating the titanium surface with Ni/(Al₂O₃ and TiO₂) nanomaterials resulted in the formation of a hard martensitic structure to a depth of approximately 2 mm below the surface. The changes observed are driven by modification of the surface chemistry and the presence of nickel, causing grain size reduction, solid solution strengthening and dispersion strengthening of the treated layer by the nanoparticles. The hardness of the treated layer increased by more than 180% when 40 nm Al₂O₃ and 30 nm TiO₂ particles were embedded into the surface. Similarly, the wear resistance of the treated surface improved by 100%.

Promotion of bone formation and antibacterial properties of titanium coated with porous Si/Ag-doped titanium dioxide

Implant materials are mainly used to repair and replace defects in human hard tissue (bones and teeth). Titanium (Ti) and Ti alloys are widely used as implant materials because of their good mechanical properties and biocompatibilities, but they do not have the ability to induce new bone formation and have no antibacterial properties. Through surface modification, Ti and its alloys have certain osteogenic and antibacterial properties such that Ti implants can meet clinical needs and ensure integration between Ti implants and bone tissue, and this is currently an active research area. In this study, bioactive Si and Ag were introduced onto a Ti surface by plasma oxidation. The surface morphology, structure, elemental composition and valence, surface roughness, hydrophilicity and other physical and chemical properties of the coating were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), a profiler and a contact angle meter (CA). Adhesion and extensions of osteoblasts on the surface of the material were observed by scanning electron microscopy, and mineralization of osteoblasts on the surface of the material were observed by alizarin red staining. The antibacterial properties of the material were tested by culturing Staphylococcus aureus on the surface of the material. The osteogenic properties of Ti implants with porous Si/Ag TiO₂ (TCP-SA) coatings were evaluated with in vivo experiments in rats. The results showed that Si and Ag were successfully introduced onto the Ti surface by plasma oxidation, and doping with Si and Ag did not change the surface morphology of the coating. The osteoblasts showed good adhesion and extension on the surfaces of Si/Ag coated samples, and the porous Si/Ag TiO₂ coating promoted cell proliferation and mineralization. The bacterial experiments showed that the porous TiO₂ coatings containing Si/Ag had certain antibacterial properties. The animal experiments showed that Si/Ag-coated Ti implants promoted integration between the implants and the surrounding bone. It was concluded that the porous Si/Ag TiO₂ coating on the Ti surface had good osteogenic and antibacterial properties and provides an optimal strategy for improving the osteogenic and antibacterial properties of Ti implants.

Design of Cefotaxime Sodium-Loaded Polydopamine Coatings with Controlled Surface Roughness for Titanium Implants

The success rate of dental implants is limited by peri-implant infection and insufficient osseointegration. Therefore, reducing the occurrence of peri-implantitis and promoting osseointegration are in demand. A roughened surface has commonly been applied to improve the osseointegration of implants, but it will accelerate the attachment of bacteria. We have developed novel antibiotic-decorated titanium (Ti) surfaces by the immobilization of dopamine and cefotaxime sodium (CS) simultaneously. Moreover, the surface roughness of the polydopamine (PDA)/CS coating was controlled by the changes in polymerization times as determined by atomic force microscopy. Then, all antibiotic-grafted Ti surfaces could effectively prevent the adhesion and proliferation of both Escherichia coli and Streptococcus mutans in comparison to the pristine control. For the culture and osteogenic differentiation of human umbilical mesenchymal stem cells (hUMSCs) on the substrate surface, PDA/CS coating with polymerization times less than 30 min showed acceptable biocompatibility, but the upregulation of marker genes and proteins was detected when the polymerization time was more than 30 min. Moreover, the best calcium deposition results were found in the 30 min PDA/CS group with or without the addition of osteogenic factors. Therefore, our PDA/CS coating with a polymerization time of 30 min holds great potential to design dental implants with dual bacteriostatic and osteogenic properties.

Effect of microtopography on osseointegration of implantable biomaterials and its modification strategies

Orthopedic implants are widely used for the treatment of bone defects caused by injury, infection, tumor and congenital diseases. However, poor osseointegration and implant failures still occur frequently due to the lack of direct contact between the implant and the bone. In order to improve the biointegration of implants with the host bone, surface modification is of particular interest and requirement in the development of implant materials. Implant surfaces that mimic the inherent surface roughness and hydrophilicity of native bone have been shown to provide osteogenic cells with topographic cues to promote tissue regeneration and new bone formation. A growing number of studies have shown that cell attachment, proliferation and differentiation are sensitive to these implant surface microtopography. This review is to provide a summary of the latest science of surface modified bone implants, focusing on how surface microtopography modulates osteoblast differentiation in vitro and osseointegration in vivo, signaling pathways in the process and types of surface modifications. The aim is to systematically provide comprehensive reference information for better fabrication of orthopedic implants.

Biofunctionalization of 3D Printed Porous Tantalum Using a Vancomycin-Carboxymethyl Chitosan Composite Coating to Improve Osteogenesis and Antibiofilm Properties

3D-printed porous tantalum scaffold has been increasingly used in arthroplasty due to its bone-matching elastic modulus and good osteoinductive ability. However, the lack of antibacterial ability makes it difficult for tantalum to prevent the occurrence and development of periprosthetic joint infection. The difficulty and high cost of curing periprosthetic joint infection (PJI) and revision surgery limit the further clinical application of tantalum. Therefore, we fabricated vancomycin-loaded porous tantalum scaffolds by combining the chemical grafting of (3-aminopropyl)triethoxysilane (APTES) and the electrostatic assembly of carboxymethyl chitosan and vancomycin for the first time. Our in vitro experiments show that the scaffold achieves rapid killing of initially adherent bacteria and effectively prevents biofilm formation. In addition, our modification preserves the original excellent structure and biocompatibility of porous tantalum and promotes the generation of mineralized matrix and osteogenesis-related gene expression by mesenchymal stem cells on the surface of scaffolds. Through a rat subcutaneous infection model, the composite bioscaffold shows efficient bacterial clearance and inflammation control in soft tissue and creates an immune microenvironment suitable for tissue repair at an early stage. Combined with the economic friendliness and practicality of its preparation, this scaffold has great clinical application potential in the treatment of periprosthetic joint infection.

Advances in surface modification of tantalum and porous tantalum for rapid osseointegration: A thematic review

After bone defects reach a certain size, the body can no longer repair them. Tantalum, including its porous form, has attracted increasing attention due to good bioactivity, biocompatibility, and biomechanical properties. After a metal material is implanted into the body as a medical intervention, a series of interactions occurs between the material’s surface and the microenvironment. The interaction between cells and the surface of the implant mainly depends on the surface morphology and chemical composition of the implant’s surface. In this context, appropriate modification of the surface of tantalum can guide the biological behavior of cells, promote the potential of materials, and facilitate bone integration. Substantial progress has been made in tantalum surface modification technologies, especially nano-modification technology. This paper systematically reviews the progress in research on tantalum surface modification for the first time, including physicochemical properties, biological performance, and surface modification technologies of tantalum and porous tantalum.

Titanium or Biodegradable Osteosynthesis in Maxillofacial Surgery? In Vitro and In Vivo Performances

Osteosynthesis systems are used to fixate bone segments in maxillofacial surgery. Titanium osteosynthesis systems are currently the gold standard. However, the disadvantages result in symptomatic removal in up to 40% of cases. Biodegradable osteosynthesis systems, composed of degradable polymers, could reduce the need for removal of osteosynthesis systems while avoiding the aforementioned disadvantages of titanium osteosyntheses. However, disadvantages of biodegradable systems include decreased mechanical properties and possible foreign body reactions. In this review, the literature that focused on the in vitro and in vivo performances of biodegradable and titanium osteosyntheses is discussed. The focus was on factors underlying the favorable clinical outcome of osteosyntheses, including the degradation characteristics of biodegradable osteosyntheses and the host response they elicit. Furthermore, recommendations for clinical usage and future research are given. Based on the available (clinical) evidence, biodegradable copolymeric osteosyntheses are a viable alternative to titanium osteosyntheses when applied to treat maxillofacial trauma, with similar efficacy and significantly lower symptomatic osteosynthesis removal. For orthognathic surgery, biodegradable copolymeric osteosyntheses are a valid alternative to titanium osteosyntheses, but a longer operation time is needed. An osteosynthesis system composed of an amorphous copolymer, preferably using ultrasound welding with well-contoured shapes and sufficient mechanical properties, has the greatest potential as a biocompatible biodegradable copolymeric osteosynthesis system. Future research should focus on surface modifications (e.g., nanogel coatings) and novel biodegradable materials (e.g., magnesium alloys and silk) to address the disadvantages of current osteosynthesis systems.

Mg-, Zn-, and Fe-Based Alloys With Antibacterial Properties as Orthopedic Implant Materials

Implant-associated infection (IAI) is one of the major challenges in orthopedic surgery. The development of implants with inherent antibacterial properties is an effective strategy to resolve this issue. In recent years, biodegradable alloy materials have received considerable attention because of their superior comprehensive performance in the field of orthopedic implants. Studies on biodegradable alloy orthopedic implants with antibacterial properties have gradually increased. This review summarizes the recent advances in biodegradable magnesium- (Mg-), iron- (Fe-), and zinc- (Zn-) based alloys with antibacterial properties as orthopedic implant materials. The antibacterial mechanisms of these alloy materials are also outlined, thus providing more basis and insights on the design and application of biodegradable alloys with antibacterial properties as orthopedic implants.

The potential influence of high uric acid exposure on surface and corrosion susceptibility of pure titanium

This study investigated the corrosion susceptibility of pure titanium under uric acid exposure for 7 days based on surface analysis. The prepared pure titanium specimens, exposed to different concentrations of uric acid, were examined for surface microstructure, surface element composition and surface wettability using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and static contact angle measurement, respectively. The corrosion behaviors of titanium specimens were measured by open-circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The titanium ion release from the prepared specimens, which were immersed in Hank's balanced salt solution (HBSS) containing different amount of uric acid, was measured by inductively coupled plasma atomic emission spectrometry (ICP-AES). More irregular pitting holes were observed on titanium surfaces exposed to a high concentration of uric acid, and XPS analyses revealed that the amount of titanium dioxide (TiO₂) decreased. Titanium surfaces pre-treated with high uric acid became more hydrophobic. Furthermore, the results of OCP and potentiodynamic polarization tests showed increased corrosion susceptibility of titanium samples, while EIS data indicated more active corrosion behavior of titanium materials. The high concentration of uric acid also induced titanium ion release. High concentration of uric acid negatively influenced the surface characteristics and corrosion properties of titanium materials, which destroyed the titanium oxide film barrier. High uric acid exposure increased corrosion susceptibility of pure titanium specimens and accelerated titanium ion release. Graphical abstract.

Inhibition of Inflammatory Response and Promotion of Osteogenic Activity of Zinc-Doped Micro-Arc Titanium Oxide Coatings

An early and sustained immune response can lead to chronic inflammation after the implant is placed in the body. The implantable materials with immunomodulatory effects can reduce the body's immune response and promote the formation of ideal osseointegration between the implants and bone tissue. In this study, zinc-coated titanium micro-arc oxide coating was prepared on titanium surface by micro-arc oxidation. The physical properties, anti-inflammation, and osteogenesis of the material were evaluated. We have physically characterized the surface structure of the coatings by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and atomic force microscopy (AFM) and detected the release of Zn²⁺ from the coating surface by inductively coupled optical plasma emission spectrometry (ICP-OES). The BMSCs were inoculated on the surface of the coating, and the biocompatibility of the coating was evaluated by CCK-8 analysis and living and dead cell staining. The osteogenic effect of the layer on BMSCs was evaluated by alkaline phosphatase (ALP) assays, osteocalcin (OCN) immunofluorescence, and quantitative polymerase chain reaction (q-PCR). The survival status of RAW264.7 on the coating surface and the mRNA expression of the associated proinflammatory markers, tumor necrosis factor-α (TNF-α), cluster of differentiation 86 (CD86), and inducible nitric oxide (INOS) were detected by CCK-8 analysis and q-PCR. In parallel, the cell counting kit-8 (CCK-8) analysis and q-PCR screened and evaluated the effective concentration of Zn²⁺ anti-inflammatory in vitro. The results show that the coating has good physical characterization, and Zn is uniformly bound to the surface of titanium and shows stable release and good biocompatibility to BMSCs, downregulating the expression of inflammation-related genes promoting the bone formation of BMSCs. We have successfully prepared zinc-coated micro-arc titanium oxide coating on the titanium surface, which has good osteogenesis and great anti-inflammatory potential and provides a new way for osseointegration in the implant.

Li-Doped Ti Surface for the Improvement of Osteointegration

Aseptic loosening is the main factor that leads to the failure of orthopedic implants. Enhancing the early osteointegration of a bone implant can lower the risk of aseptic loosening. Here, a Li-doped surface was constructed on a Ti surface via plasma electrolytic oxidation (PEO) to improve osteointegration. The prepared Li-doped PEO coating showed a porous morphology and the sustained release of Li ions. In vitro results of rat bone marrow mesenchymal stem cell (rBMSC) culture studies suggested that the Li-doped Ti surface significantly favored cell adhesion. Moreover, it was found that the Li-doped surface enhanced alkaline phosphatase activity and extracellular matrix mineralization of rBMSCs. In addition, the surface improved the expression of osteogenesis-related genes. Furthermore, a bone implantation model indicated that the Li-doped Ti surface showed improved osteointegration. The incorporation of Li into a Ti surface is a promising method for orthopedic applications.

Numerical and Experimental Analysis of Titanium Sheet Forming for Medical Instrument Parts

The paper analyses the forming of the surgical instrument handles made of Grade 2 titanium sheets. Sheet metal forming is a technology ensuring high strength and light weight of products. Replacing stainless steels with titanium further reduces instrument weight and additionally provides the required resistance to corrosive environments typical for surgeries. The low instrument weight is important to prevent fatigue of surgeons and allow them to maintain high operational accuracy during long term surgeries. The numerical analysis of the technological process was performed in order to adapt it to forming tool handles using titanium sheets instead of steel sheets. The numerical calculations were experimentally verified. It was found that, in the case of titanium handles, it is necessary to use a blank holder in the first forming operation to eliminate sheet wrinkling in the flange area. The shape and dimensional accuracy of the drawn part after trimming were high enough and the 4th forming operation became unnecessary. Moreover, the process modification included lubrication using rapeseed oil with the addition of boric acid, which effectively prevents the galling of titanium on the working surfaces of the steel tools and ensures a more uniform distribution of plastic strains in the drawn part.

Titanium Nanobowl-Based Nest-Like Nanofiber Structure Prepared at Room Temperature and Pressure Promotes Osseointegration of Beagle Implants

Nest-like nanofiber structures have potential applications in surface modifications of titanium implants. In this study, nest-like nanofiber structures were prepared on a titanium surface at room temperature and pressure by using the nanobowl template-assisted method combined with alkali etching. The characterization and biocompatibility of this material were analyzed by cellular adhesion, death, CCK-8, ALP, and RT-PCR assays in vitro, and osseointegration was evaluated by micro-CT and fluorescent labeling in vivo. The results showed that this nest-like nanofiber structure has a firmer and asperate surface than nanotubes, which leads to better cellular adhesion, proliferation, and differentiation capacity. In a beagle alveolar bone implant model, the nest-like nanofiber structure showed a better osseointegration capacity. In conclusion, this nest-like nanofiber structure has potential applications in dental implantology.

Emerging titanium surface modifications: The war against polymicrobial infections on dental implants

Abstract Dental implants made of titanium (Ti) material is recognized as the leading treatment option for edentulous patients’ rehabilitation, showing a high success rate and clinical longevity. However, dental implant surface acts as a platform for microbial adhesion and accumulation once exposed to the oral cavity. Biofilm formation on implant surfaces has been considered the main etiologic factor to induce inflammatory diseases, known as peri-implant mucositis and peri-implantitis; the latter being recognized as the key reason for late dental implant failure. Different factors, such as biofilm matrix production, source of carbohydrate exposure, and cross-kingdom interactions, have encouraged increased microbial accumulation on dental implants, leading to a microbiological community shift from a healthy to a pathogenic state, increasing inflammation and favoring tissue damage. These factors combined with the spatial organization of biofilms, reduced antimicrobial susceptibility, complex microbiological composition, and the irregular topography of implants hamper biofilm control and microbial killing. In spite of the well-known etiology, there is still no consensus regarding the best clinical protocol to control microbial accumulation on dental implant surfaces and treat peri-implant disease. In this sense, different coatings and Ti surface treatments have been proposed in order to reduce microbial loads and control polymicrobial infections on implantable devices. Therefore, this critical review aims to discuss the current evidence on biofilm accumulation on dental implants and central factors related to the pathogenesis process of implant-related infections. Moreover, the potential surface modifications with anti-biofilm properties for dental implant devices is discussed to shed light on further promising strategies to control peri-implantitis.

Electrochemical Surface Biofunctionalization of Titanium through Growth of TiO2 Nanotubes and Deposition of Zn Doped Hydroxyapatite

The current research aim is to biofunctionalize pure titanium (Ti, grade IV) substrate with titania nanotubes and Zn doped hydroxyapatite-based coatings by applying a duplex electrochemical treatment, and to evaluate the influence of Zn content on the physico-chemical properties of hydroxyapatite (HAp). The obtained nanostructured surfaces were covered with HAp-based coatings doped with Zn in different concentrations by electrochemical deposition in pulsed galvanostatic mode. The obtained surfaces were characterized in terms of morphology, elemental and phasic composition, chemical bonds, roughness, and adhesion. The nanostructured surface consisted of titania nanotubes (NT), aligned, vertically oriented, and hollow, with an inner diameter of ~70 nm. X-ray Diffraction (XRD) analysis showed that the nanostructured surface consists of an anatase phase and some rutile peaks as a secondary phase. The morphology of all coatings consisted of ribbon like-crystals, and by increasing the Zn content the coating became denser due to the decrement of the crystals’ dimensions. The elemental and phase compositions evidenced that HAp was successfully doped with Zn through the pulsed galvanostatic method on the Ti nanostructured surfaces. Fourier Transform Infrared spectroscopy (FTIR) and XRD analysis confirmed the presence of HAp in all coatings, while the adhesion test showed that the addition of a high quantity leads to some delamination. Based on the obtained results, it can be said that the addition of Zn enhances the properties of HAp, and through proper experimental design, the concentration of Zn can be modulated to achieve coatings with tunable features.

A comprehensive review on metallic implant biomaterials and their subtractive manufacturing

There is a tremendous increase in the demand for converting biomaterials into high-quality industrially manufactured human body parts, also known as medical implants. Drug delivery systems, bone plates, screws, cranial, and dental devices are the popular examples of these implants - the potential alternatives for human life survival. However, the processing techniques of an engineered implant largely determine its preciseness, surface characteristics, and interactive ability with the adjacent tissue(s) in a particular biological environment. Moreover, the high cost-effective manufacturing of an implant under tight tolerances remains a challenge. In this regard, several subtractive or additive manufacturing techniques are employed to manufacture patient-specific implants, depending primarily on the required biocompatibility, bioactivity, surface integrity, and fatigue strength. The present paper reviews numerous non-degradable and degradable metallic implant biomaterials such as stainless steel (SS), titanium (Ti)-based, cobalt (Co)-based, nickel-titanium (NiTi), and magnesium (Mg)-based alloys, followed by their processing via traditional turning, drilling, and milling including the high-speed multi-axis CNC machining, and non-traditional  abrasive water jet machining (AWJM), laser beam machining (LBM), ultrasonic machining (USM), and electric discharge machining (EDM) types of subtractive manufacturing techniques. However, the review further funnels down its primary focus on Mg, NiTi, and Ti-based alloys on the basis of the increasing trend of their implant applications in the last decade due to some of their outstanding properties. In the recent years, the incorporation of cryogenic coolant-assisted traditional subtraction of biomaterials has gained researchers' attention due to its sustainability, environment-friendly nature, performance, and superior biocompatible and functional outcomes fitting for medical applications. However, some of the latest studies reported that the medical implant manufacturing requirements could be more remarkably met using the non-traditional subtractive manufacturing approaches. Altogether, cryogenic  machining among the traditional routes and EDM among the non-traditional means along with their variants, were identified as some of the most effective subtractive manufacturing techniques for achieving the dimensionally accurate and biocompatible metallic medical implants with significantly modified surfaces.

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.

Modifying a 3D-Printed Ti6Al4V Implant with Polydopamine Coating to Improve BMSCs Growth, Osteogenic Differentiation, and In Situ Osseointegration In Vivo

Nowadays, 3D printing technology has been applied in dentistry to fabricate customized implants. However, the biological performance is unsatisfactory. Polydopamine (PDA) has been used to immobilize bioactive agents on implant surfaces to endow them with multiple properties, such as anti-infection and pro-osteogenesis, benefiting rapid osseointegration. Herein, we fabricated a PDA coating on a 3D-printed implant surface (3D-PDA) via the in situ polymerization method. Then the 3D-PDA implants' pro-osteogenesis capacity and the osseointegration performance were evaluated in comparison with the 3D group. The in vitro results revealed that the PDA coating modification increased the hydrophilicity of the implants, promoting the improvement of the adhesion, propagation, and osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) in vitro. Additionally, the 3D-PDA implant improved osteointegration performance in vivo. The present study suggested that PDA coating might be a feasible strategy to optimize 3D-printed implant surfaces, making a preliminary research basis for the subsequent work to immobilize bioactive factors on the 3D-printed implant surface.

Resveratrol-loaded titania nanotube coatings promote osteogenesis and inhibit inflammation through reducing the reactive oxygen species production via regulation of NF-κB signaling pathway

Although titanium and its alloys are widely used in bone surgeries, the implantation failures caused by sterile inflammation still occur. The excessive reactive oxygen species (ROS) in the peri-implant region are considered to cause inflammation and impede the osseointegration of titanium implants. In this study, a coating of resveratrol-loaded titania nanotube (TNT-Res) for eliminating ROS was fabricated on titanium surface through electrochemical anodization and following surface adsorption of resveratrol. The resveratrol concentration of released from TNT-Res coating was controlled by modulating the loading amount. The ROS production in macrophage cell lineage RAW 264.7 and bone mesenchymal stem cells (BMSCs) were significantly decreased when cultured on TNT-Res coatings. The pro-inflammatory factors, including tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β), and NO produced by RAW 264.7 cells were reduced when cells were cultured on TNT-Res coatings. These results proved that the TNT-Res coating can effectively eliminate ROS and inhibit inflammation. Moreover, the osteogenic indicators, including alkaline phosphatase (ALP) production, extracellular calcium deposition, and osteogenesis-related gene expression, including collagen І (Col-І), osteocalcin (OCN), osteopontin (OPN), and runt-related transcription factor 2 (Runx2), were significantly promoted for TNT-Res groups, which demonstrated that the TNT-Res coating can enhance the osteogenic differentiation of BMSCs. Additionally, the phosphorylation of nuclear factor κ-B (NF-κB) were down-regulated both in RAW 264.7 cells and BMSCs, which indicated that the TNT-Res coating could inhibit inflammation and promote osteogenesis by inhibiting the activation of NF-κB signaling pathway. The TNT-Res coating could be an effective implant surface for improving osseointegration ability of titanium implants.

A polydopamine-assisted strontium-substituted apatite coating for titanium promotes osteogenesis and angiogenesis via FAK/MAPK and PI3K/AKT signaling pathways

Early osteointegration is essential for biomedical implants. Surface modifications can significantly compensate for an implant's lack of biocompatibility and osteo-differentiation. They can also be designed to promote angiogenesis in order to assist osteogenesis and ultimately facilitate bone regeneration. In this study, a polydopamine-assisted strontium-substituted apatite coating (Ti@PDA + SrHA) was fabricated on a multifunctional titanium implant to induce both angiogenic and osteogenic abilities for rapid osseointegration. Polydopamine and Sr-substituted hydroxyapatite were coated on the implant through biomineralization. The in vitro results showed that Ti@PDA + SrHA improved cell adhesion and increased the proliferation of rat bone marrow-derived mesenchymal stem cells (rBMSCs) and human umbilical vein endothelial cells (HUVECs). Ti@PDA + SrHA upregulated the expression of ALP activity and osteogenic genes in rBMSCs and elevated angiogenic genes in both rBMSCs and HUVECs. Mechanically, the FAK/MAPK signaling pathway was activated in rBMSCs, and the PI3K/AKT signaling pathway was activated in both rBMSCs and HUVECs. Consistent with these findings, Ti@PDA + SrHA accelerated new bone formation and rapid osseointegration in the femoral condyle implantation study with good stability. Overall, we fabricated a multifunctional biocompatible implant with better angiogenic and osteogenic performance compared to the non-coated implant.

Fitting pieces into the puzzle: The impact of titanium-based dental implant surface modifications on bacterial accumulation and polymicrobial infections

Polymicrobial infection is the main cause of dental implant failure. Although numerous studies have reported the ability of titanium (Ti) surface modifications to inhibit microbial adhesion and biofilm accumulation, the majority of solutions for the utilization of Ti antibacterial surfaces have been testedin in vitro and animal models, with only a few developed surfaces progressing into clinical research. Motivated by this huge gap, we critically reviewed the scientific literature on the existing antibacterial Ti surfaces to help understand these surfaces' impact on the "puzzle" of undesirable dental implant-related infections. This manuscript comprises three main sections: (i) a narrative review on topics related to oral biofilm formation, bacterial-implant surface interactions, and on how implant-surface modifications can influence microbial accumulation; (ii) a critical evidence-based review to summarize pre-clinical and clinical studies in an attempt to "fit pieces into the puzzle" to unveil the best way to reduce microbial loads and control polymicrobial infection around dental implants showed by the current in vivo evidence; and (iii) discussion and recommendations for future research testing emerging antibacterial implant surfaces, connecting basic science and the requirements for future clinical translation. The findings of the present review suggest no consensus regarding the best available Ti surface to reduce bacterial colonization on dental implants. Smart release or on-demand activation surface coatings are a "new piece of the puzzle", which may be the most effective alternative for reducing microbial colonization on Ti surfaces, and future studies should focus on these technologies.

The osteogenic effects of porous Tantalum and Titanium alloy scaffolds with different unit cell structure

Porous scaffolds have long been regarded as optimal substitute for bone tissue repairing. In order to explore the influence of unit cell structure and inherent material characteristics on the porous scaffolds in terms of mechanical and biological performance, selective laser melting (SLM) technology was used to fabricate porous tantalum (Ta) and titanium alloy (Ti6Al4V) with diamond (Di) or rhombic dodecahedron (Do) unit cell structure. The mechanical strength of all the porous scaffolds could match that of trabecular bone, while the biological performance of each scaffold was diverse from each other. Moreover, the ILK/ERK1/2/Runx2 signaling pathway had been verified to be involved in the osteogenic differentiation of rat bone mesenchymal stem cells (rBMSCs) cultured on those porous scaffolds. Unit cell structure and material characteristics of the porous Ta and Ti6Al4V scaffolds can synergistically modulate this axis and further impact on the osteogenic effects. Our results hence illustrate that porous Ta scaffold with diamond unit cell structure possesses excellent osteogenic effects and moderate mechanical strength and porous Ti6Al4V scaffold with rhombic dodecahedron unit cell structure has the highest mechanical strength and moderate osteogenic effects. Both porous Ta and Ti6Al4V can be applied in different settings requiring either better biological performance or higher mechanical demand.

Biomimetic Deposition of Hydroxyapatite Layer on Titanium Alloys

Over the last decade, researchers have been concerned with improving metallic biomaterials with proper and suitable properties for the human body. Ti-based alloys are widely used in the medical field for their good mechanical properties, corrosion resistance and biocompatibility. The TiMoZrTa system (TMZT) evidenced adequate mechanical properties, was closer to the human bone, and had a good biocompatibility. In order to highlight the osseointegration of the implants, a layer of hydroxyapatite (HA) was deposited using a biomimetic method, which simulates the natural growth of the bone. The coatings were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD), micro indentation tests and contact angle. The data obtained show that the layer deposited on TiMoZrTa (TMZT) support is hydroxyapatite. Modifying the surface of titanium alloys represents a viable solution for increasing the osseointegration of materials used as implants. The studied coatings demonstrate a positive potential for use as dental and orthopedic implants.

2D materials for bone therapy

Due to their prominent physicochemical properties, 2D materials are broadly applied in biomedicine. Currently, 2D materials have achieved great success in treating many diseases such as cancer and tissue engineering as well as bone therapy. Based on their different characteristics, 2D materials could function in various ways in different bone diseases. Herein, the application of 2D materials in bone tissue engineering, joint lubrication, infection of orthopedic implants, bone tumors, and osteoarthritis are firstly reviewed comprehensively together. Meanwhile, different mechanisms by which 2D materials function in each disease reviewed below are also reviewed in detail, which in turn reveals the versatile functions and application of 2D materials. At last, the outlook on how to further broaden applications of 2D materials in bone therapies based on their excellent properties is also discussed.