In vitro study on cytocompatibility and osteogenesis ability of Ti-Cu alloy

Titanium alloys with varying surface micro-area potential differences have antibacterial abilities and a favorable cellular response

OBJECTIVES

Surface micro-area potential difference (MAPD) can achieve bacteriostatic performance independent of metal ion dissolution. To study the influence of MAPD on antibacterial properties and the cellular response, Ti-Ag alloys with different surface potentials were designed and prepared by changing the preparation and heat treatment processes.

MATERIALS AND METHODS

Ti-Ag alloys (T4, T6, and S) were prepared by vacuum arc smelting, water quenching, and sintering. Cp-Ti was set as a control group in this work. The microstructures and surface potential distributions of the Ti-Ag alloys were analyzed by SEM and energy dispersive spectrometry. Plate counting and live/dead staining methods were used to evaluate the antibacterial properties of the alloys, and the mitochondrial function, ATP levels, and apoptosis were assessed in MC3T3-E1 cells to analyze the cellular response.

RESULTS

Due to the formation of the Ti-Ag intermetallic phase in the Ti-Ag alloys, Ti-Ag (T4) without the Ti-Ag phase had the lowest MAPD, Ti-Ag (T6) with a fine Ti2Ag phase had a moderate MAPD, and Ti-Ag (S) with a Ti-Ag intermetallic phase had the highest MAPD. The primary results demonstrated that the Ti-Ag samples with different MAPDs exhibited different bacteriostatic effects, ROS expression levels, and apoptosis-related protein expression levels in cells. The alloy with a high MAPD exhibited a strong antibacterial effect. A moderate MAPD stimulated cellular antioxidant regulation (GSH/GSSG) and downregulated the expression of intracellular ROS. MAPD could also promote the transformation of the inactive mitochondria to biologically active mitochondria by increasing the ΔΨm and reducing apoptosis.

CONCLUSION

The results here indicated that moderate MAPD not only had bacteriostatic effects but also promoted mitochondrial function and inhibited cell apoptosis, which provides a new strategy to improve the surface bioactivity of titanium alloys and a new idea for titanium alloy design.

CLINICAL RELEVANCE

There are some limitations of the mechanism of MAPD. However, researchers will become increasingly aware of the advantages and disadvantages of MAPD and MAPD might provide an affordable solution of peri-implantitis.

Corrosion Behavior and Bio-Functions of the Ultrafine-Grained Ti6Al4V-5Cu Alloy with a Dual-Phase Honeycomb Shell Structure in Simulated Body Fluid

Titanium alloys are widely used in biomedical applications. However, cases of implant failure due to fatigue fracture and bacterial infection are common. In addition, implants are susceptible to metal ions (Al, V) released by long-term exposure to human body fluids, which causes neuropathy, mental disorders, and other diseases. Thus, development of novel materials to achieve long-term safety of implants is currently a research hotspot. Recently, our research group has developed an ultrafine-grained Ti6Al4V-5Cu alloy with a unique "dual-phase honeycomb shell" (DPHS) structure, which possesses high fatigue strength and stability. This study further affirmed its higher corrosion behavior, antibacterial properties, and cytocompatibility compared to the coarse-grained Ti6Al4V and Ti6Al4V-5Cu alloys. The ultrafine-grained structure of Ti6Al4V-5Cu having DPHS increased the proportion of phases (Cu-rich phases, β-phase, and Ti₂Cu intermetallic phase) with a lower surface potential. It was observed that the developed microstructure was conducive to a stable configuration of the oxide (passive) layer on the alloy surface. In addition, the low-phase interfacial energies of the ultrafine-grained structure with DPHS even facilitated the improvement of the denseness of the protective passive film and eventually enhanced the corrosion behavior. Besides, the fine-Cu-rich phases and the micro-galvanic couples formed between them and the matrix significantly increased the contact frequency of bacteria, thus increasing the contact sterilization efficiency of the ultrafine-grained Ti6Al4V-5Cu alloy. These results showed that the new ultrafine-grained Ti6Al4V-5Cu alloy has excellent corrosion resistance and biological functions for clinical application.

Recent Advances in Copper-Doped Titanium Implants

Titanium (Ti) and its alloys have been extensively used as implant materials in clinical practice due to their high corrosion resistance, light weight and excellent biocompatibility. However, the insufficient intrinsic osteogenic capacity of Ti and its alloys impedes bone repair and regeneration, and implant-related infection or inflammation remains the leading cause of implant failure. Bacterial infections or inflammatory diseases constitute severe threats to human health. The physicochemical properties of the material are critical to the success of clinical procedures, and the doping of Cu into Ti implants has been confirmed to be capable of enhancing the bone repair/regeneration, angiogenesis and antibacterial capability. This review outlines the recent advances in the design and preparation of Cu-doped Ti and Ti alloy implants, with a special focus on various methods, including plasma immersion implantation, magnetron sputtering, galvanic deposition, microarc oxidation and sol-gel synthesis. More importantly, the antibacterial and mechanical properties as well as the corrosion resistance and biocompatibility of Cu-doped Ti implants from different methods are systematically reviewed, and their prospects and limitations are also discussed.

Promoting osteointegration effect of Cu alloyed titanium (TiCu) in ovariectomized rats

Osteoporosis is a common skeletal disease making patients be prone to the osteoporotic fracture. However, the clinical implants made of titanium and its alloys with a poor osseointegration need a long time for healing and easily to loosening. Thus, a new class of Cu-alloyed titanium (TiCu) alloys with excellent mechanical properties and bio-functionalization has been developed. In this study, the osteoporosis modeled rats were used to study the osteointegration effect and underlying mechanism of TiCu. The results showed that after implantation for 4 weeks, TiCu alloy could promote the reconstruction of vascular network around the implant by up-regulating vascular endothelial growth factor expression. After 8 weeks, it could further promote the proliferation and differentiation of osteoblasts, mineralization and deposition of collagens, and then significantly increasing bone mineral density around the implant. In conclusion, TiCu alloy would enhance the fixation stability, accelerate the osteointegration, and thus reduce the risk of aseptic loosening during the long-term implantation in the osteoporosis environment. This study was the first to report the role and mechanism of a Cu-alloyed metal in promoting osteointegration in osteoporosis environment, which provides a new attractive support for the improvement of future clinical applications of Cu-alloyed antibacterial titanium alloys.

Inhibition efficiency of 304-Cu stainless steel against oral bacterial biofilm

PURPOSE

This study aims to evaluate the antibacterial properties of 304 Cu-bearing stainless steel (SS) with different Cu contents (0, 2.5, 4.5 wt.%) against oral biofilms of Streptococcus mutans (S. mutans), Streptococcus sanguinis (S. sanguinis), and their mixture.

METHODS

Bacterial biofilms on the surface of 304-Cu SS were characterized by plate counting, 4', 6-diamidino-2-phenylindole (DAPI) staining with aid of sanning electron microscopy (SEM) and 2, 3-bis (2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide inner salt (XTT). In addition, the inhibition zone method was also employed to evaluate the antibacterial properties of 304-Cu SS. Cell Counting Kit-8 (CCK-8) and flow cytometry were used to assess the cytotoxicity and apoptosis rate of 304-Cu SS, respectively.

RESULTS

304-4.5Cu SS could effectively inhibit the attachment, formation, activity, and metabolism of bacterial biofilm, possessing the best antibacterial properties exceeding 99.9% of antibacterial rate against S. mutans, S. sanguinis, and their mixture. The diameters of inhibition zones to S. mutans and S. sanguinis on the surface of 304-4.5Cu SS were 21.7 and 14.7 mm, respectively. The results of cell experiments in vitro showed that both 304-2.5Cu SS and 304-4.5Cu SS had no evident cytotoxicity with an identical grade 1. The apoptosis rate exhibited a gradually increased tendency with increase of the Cu content in 304 SS.

CONCLUSIONS

304-4.5Cu SS without cytotoxic effect on NIH3T3 cells has obvious antibacterial activity against S. mutans, S. sanguinis and their mixture.

CLINICAL SIGNIFICANCE

The Cu-bearing stainless steel provides a new solution to be used as oral orthodontic devices for inhibiting oral microflora imbalance and enamel demineralization.

In Vitro Characterization of In Situ Alloyed Ti6Al4V(ELI)-3 at.% Cu Obtained by Laser Powder Bed Fusion

The intensive cytotoxicity of pure copper is effectively kills bacteria, but it can compromise cellular behavior, so a rational balance must be found for Cu-loaded implants. In the present study, the individual and combined effect of surface composition and roughness on osteoblast cell behavior of in situ alloyed Ti6Al4V(ELI)-3 at.% Cu obtained by laser powder bed fusion was studied. Surface composition was studied using scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction. Surface roughness measurements were carried out using confocal microscopy. In vitro osteoblast performance was evaluated by means of cell morphology observation of cell viability, proliferation, and mineralization. In vitro studies were performed at 1, 7, and 14 days of cell culture, except for cell mineralization at 28 days, on grounded and as-built (rough) samples with and without 3 at.% Cu. The addition of 3 at.% Cu did not show cell cytotoxicity but inhibited cell proliferation. Cell mineralization tends to be higher for samples with 3 at.% Cu content. Surface roughness inhibited cell proliferation too, but showed enhanced cell mineralization capacity and therefore, higher osteoblast performance, especially when as-built samples contained 3 at.% Cu. Cell proliferation was only observed on ground samples without Cu but showed the lowest cell mineralization.

Zinc Oxide and Copper Chitosan Composite Films with Antimicrobial Activity

The role of the oral microbiome and its effect on dental diseases is gaining interest. Therefore, it has been sought to decrease the bacterial load to fight oral cavity diseases. In this study, composite materials based on chitosan, chitosan crosslinked with glutaraldehyde, chitosan with zinc oxide particles, and chitosan with copper nanoparticles were prepared in the form of thin films, to evaluate a new alternative with a more significant impact on the oral cavity bacteria. The chemical structures and physical properties of the films were characterized using by Fourier transform infrared spectroscopy (FTIR,) Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis (EDX), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and contact angle measurements. Subsequently, the antimicrobial activity of each material was evaluated by agar diffusion tests. No differences were found in the hydrophilicity of the films with the incorporation of ZnO or copper particles. Antimicrobial activity was found against S. aureus in the chitosan film crosslinked with glutaraldehyde, but not in the other compositions. In contrast antimicrobial activity against S. typhimurium was found in all films. Based on the data of present investigation, chitosan composite films could be an option for the control of microorganisms with potential applications in various fields, such as medical and food industry.

Anodic TiO2 Nanotubes: Tailoring Osteoinduction via Drug Delivery

TiO₂ nanostructures and more specifically nanotubes have gained significant attention in biomedical applications, due to their controlled nanoscale topography in the sub-100 nm range, high surface area, chemical resistance, and biocompatibility. Here we review the crucial aspects related to morphology and properties of TiO₂ nanotubes obtained by electrochemical anodization of titanium for the biomedical field. Following the discussion of TiO₂ nanotopographical characterization, the advantages of anodic TiO₂ nanotubes will be introduced, such as their high surface area controlled by the morphological parameters (diameter and length), which provides better adsorption/linkage of bioactive molecules. We further discuss the key interactions with bone-related cells including osteoblast and stem cells in in vitro cell culture conditions, thus evaluating the cell response on various nanotubular structures. In addition, the synergistic effects of electrical stimulation on cells for enhancing bone formation combining with the nanoscale environmental cues from nanotopography will be further discussed. The present review also overviews the current state of drug delivery applications using TiO₂ nanotubes for increased osseointegration and discusses the advantages, drawbacks, and prospects of drug delivery applications via these anodic TiO₂ nanotubes.

Copper-based biomaterials for bone and cartilage tissue engineering

Backgroud

Tissue engineering using cells, scaffolds, and bioactive molecules can promote the repair and regeneration of injured tissues. Copper is an essential element for the human body that is involved in many physiological activities and in recent years, copper has been used increasingly in tissue engineering.

Methods

The current advances of copper-based biomaterial for bone and cartilage tissue engineering were searched on PubMed and Web of Science.

Results

Various forms of copper-based biomaterials, including pure copper, copper ions, copper nanoparticles, copper oxides, and copper alloy are introduced. The incorporation of copper into base materials provides unique properties, resulting in tuneable porosity, mechanical strength, degradation, and crosslinking of scaffolds. Copper also shows promising biological performance in cell migration, cell adhesion, osteogenesis, chondrogenesis, angiogenesis, and antibacterial activities. In vivo applications of copper for bone and cartilage tissue engineering are discussed.

Conclusion

This review focuses on copper’s physiochemical and biological effects, and its applications in bone and cartilage tissue engineering. The potential limitations and future perspectives are also discussed.

Translational potential of this article

This review introduces the recent advances in copper-based biomaterial for bone and cartilage tissue engineering. This revie could guide researchers to apply copper in biomaterials, improving the generation of bone and cartilages, decrease the possibility of infection and shorten the recovery time so as to decrease medical costs.

Biological applications of copper-containing materials

Copper is an indispensable trace metal element in the human body, which is mainly absorbed in the stomach and small intestine and excreted into the bile. Copper is an important component and catalytic agent of many enzymes and proteins in the body, so it can influence human health through multiple mechanisms. Based on the biological functions and benefits of copper, an increasing number of researchers in the field of biomaterials have focused on developing novel copper-containing biomaterials, which exhibit unique properties in protecting the cardiovascular system, promoting bone fracture healing, and exerting antibacterial effects. Copper can also be used in promoting incisional wounds healing, killing cancer cells, Positron Emission Tomography (PET) imaging, radioimmunological tracing and radiotherapy of cancer. In the present review, the biological functions of copper in the human body are presented, along with an overview of recent progress in our understanding of the biological applications and development of copper-containing materials. Furthermore, this review also provides the prospective on the challenges of those novel biomaterials for future clinical applications.

Nano-Modified Titanium Implant Materials: A Way Toward Improved Antibacterial Properties

Titanium and its alloys have superb biocompatibility, low elastic modulus, and favorable corrosion resistance. These exceptional properties lead to its wide use as a medical implant material. Titanium itself does not have antibacterial properties, so bacteria can gather and adhere to its surface resulting in infection issues. The infection is among the main reasons for implant failure in orthopedic surgeries. Nano-modification, as one of the good options, has the potential to induce different degrees of antibacterial effect on the surface of implant materials. At the same time, the nano-modification procedure and the produced nanostructures should not adversely affect the osteogenic activity, and it should simultaneously lead to favorable antibacterial properties on the surface of the implant. This article scrutinizes and deals with the surface nano-modification of titanium implant materials from three aspects: nanostructures formation procedures, nanomaterials loading, and nano-morphology. In this regard, the research progress on the antibacterial properties of various surface nano-modification of titanium implant materials and the related procedures are introduced, and the new trends will be discussed in order to improve the related materials and methods.

The Fabrication and Function of Strontium-modified Hierarchical Micro/Nano Titanium Implant

Background

Relying on surface topography alone to enhance the osteointegration of implants is still inadequate. An effective way to combine long-term ion release and surface topography to enhance osteogenic property is urgently needed.

Purpose

The objective of this study is to fabricate a long-term strontium ion release implant system and confirm the biological function in vitro and in vivo.

Methods

The biomimic surface was fabricated through alkali-heat treatment and magnetron sputtering. The in vitro biological function assays were determined by MTT, fluorescence staining, alkaline phosphatase activity, extracellular mineralization, and quantitative real-time polymerase chain reaction assays. The in vivo experiments were detected by micro-CT, HE staining and Masson staining.

Results

The biomimic surface structure has been successfully fabricated. The in vitro cell assays determined that AH-Ti/Sr90 possessed the best biological function. The in vivo experiments demonstrated that AH-Ti/Sr90 could promote osteointegration significantly under both in normal and osteoporotic conditions.

Conclusion

We determined that AH-Ti/Sr90 possesses the best osteogenic property, long-term ion release capacity and osteointegration promotion ability. It has potential clinic application prospects.

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Biodegradable Zn-Cu alloys show antibacterial activity against MRSA bone infection by inhibiting pathogen adhesion and biofilm formation

Bone and joint-related infections remain the primary and most critical complications of orthopedic surgery. We have innovatively prepared Zn-Cu alloys to achieve outstanding material and antibacterial properties. In this study, we systematically assessed the material properties and antibacterial activity of these Zn-Cu alloys. Our results showed that the Zn-2Cu alloy had the best mechanical properties, biocompatibility, and osteogenic properties. Findings of microbial cultures, CLSM, SEM, and TEM indicated that Zn-2Cu alloy can inhibit both coagulase-positive and coagulase-negative staphylococci, as well as antibiotic-resistant strains (MRSA and MRSE), by preventing the bacteria adhesion and the biofilm formation. Zn-2Cu alloy could broadly affect the expression of MRSA genes associated with adhesion, autolysis, biofilm formation, virulence, and drug resistance. A rat femur intramedullary nail infection-prevention model was established and the Zn-2Cu alloy-treated group showed significant antibacterial activity against MRSA and reduced the inflammatory toxic side-effects and infection-related bone loss. Collectively, our results indicate the potential utility of Zn-Cu alloy implants with 2 wt% Cu in treating orthopedic infections. Statement of significance: Osteomyelitis is a serious complication of orthopedic surgeries. Wide use of antibiotics contributes to the appearance of multi-drug resistant strains like methicillin-resistant staphylococcus aureus (MRSA). Alternatively, anti-osteomyelitis implants with broad-spectrum antibacterial properties can be favorable. Here, the antibacterial performance of biodegradable Zn-Cu alloys was evaluated with four different bacteria strains including antibiotic-resistant strains (MRSA and MRSE). Zn-Cu alloys exert excellent bacterial killing capability in all strains. In a rat femur infection model, the alloy showed significant antibacterial activity against MRSA and reduced inflammatory toxic side-effects as well as infection-related bone loss. The antibacterial property of Zn-2Cu alloy was associated with inhibition of gene expression related to wall synthesis, adhesion, colonization, biofilm formation, autolysis, and secretion of virulence factors in MRSA.

The Effect of Copper Content on the Mechanical and Tribological Properties of Hypo-, Hyper- and Eutectoid Ti-Cu Alloys

Titanium alloys are widely used in aerospace, chemical, biomedical and other important fields due to outstanding properties. The mechanical behavior of Ti alloys depends on microstructural characteristics and type of alloying elements. The purpose of this study was to investigate the effects of different Cu contents (2.5 wt.%, 7 wt.% and 14 wt.%) on mechanical and frictional properties of titanium alloys. The properties of titanium alloy were characterized by tensile test, electron microscope, X-ray diffraction, differential scanning calorimetry, reciprocating friction and wear test. The results show that the intermediate phase that forms the eutectoid structure with α-Ti was identified as FCC Ti₂Cu, and no primary β phase was formed. With the increase of Cu content, the Ti₂Cu phase precipitation in the alloy increases. Ti₂Cu particles with needle structure increase the dislocation pinning effect on grain boundary and improve the strength and hardness of titanium alloy. Thus, Ti-14Cu shows the lowest elongation, the best friction and wear resistance, which is caused by the existence of Ti₂Cu phases. It has been proved that the mechanical and frictional properties of Ti-Cu alloys can be adjusted by changing the Cu content, so as to better meet its application in the medical field.

Msx2 plays an important role in BMP6-induced osteogenic differentiation of two mesenchymal cell lines: C3H10T1/2 and C2C12

Bone morphogenetic proteins (BMPs), have been shown to enhance the osteogenic differentiation of mesenchymal cells (MCs) and to promote bone formation. BMP6 is known to play an important role in the process of MCs towards osteogenic differentiation by virtue of their osteoinductive and cell type specific proliferative activity. However, the molecular mechanism relate to BMP6 osteoinductive activity is still unclear and continues to warrant further investigation. Msx2 is a member of the homeobox gene family of transcription factors and promotes calcification. Hence, we wondered if it might also play a role in BMP6-induced osteogenesis. In this study, two mouse mesenchymal cell lines were treated with BMP6, adenovirus-Msx2 (Ad-Msx2) or adenovirus-siMsx2 (Ad-siMsx2). Based on the results of mRNA and protein expression, it was indicated that BMP6 could enhance the expression of Msx2 and activate the phosphorylation of Smad 1/5/8, p38 and ERK1/2. Being transfected by Ad-Msx2, the BMP6-induced activation of phosphorylation was significantly promoted. On the contrary, two cell lines transfected by Ad-siMsx2 presented an inhibited expression of three phosphorylated proteins even after being induced by BMP6. The evaluation of ALP, OPN, OC and calcium deposits revealed the osteogenic results those were corresponding to the results of mRNA and protein. Taken together, these findings can be a novel viewpoint for the understanding of the mechanisms of BMP6-induced osteogenesis and provide therapeutic targets of bone defect.

Effect of ultrasonic micro-arc oxidation on the antibacterial properties and cell biocompatibility of Ti-Cu alloy for biomedical application

In order to improve antibacterial properties and cell biocompatibility of Ti-Cu alloy, an ultrasonic micro-arc oxidation (UMAO) has been applied to Ti-Cu alloy. The corrosion resistance, antibacterial activity and cell compatibility of Ti-Cu alloy before and after UMAO were studied in detail by means of electrochemical test, plate count method and CCK-8 test scanning electron microscopy (SEM) technology to evaluate the application possibilities of UMAO as a surface bio-modification method for Ti-Cu alloy. The surface microstructure characterisation showed that a typical porous coating with a pore diameter of 3-8 μm and a thickness of 5-15 μm was formed on the surface of the Ti-Cu alloy, which significantly improved the surface roughness and hydrophilicity. The plate count method demonstrated that UMAO coatings on Ti-Cu alloy showed strong antibacterial activity (≥99%) against Staphylococcus aureus (S. aureus) even after being immersed in a physiological saline for up to 20 days, indicating that UMAO-treated Ti-Cu alloy had very strong long-term antibacterial properties. It is believed that the strong long-term antimicrobial properties of Ti-Cu-UMAO samples were mainly due to the formation of Cu₂O and CuO in UMAO coatings. The results of cell compatibility evaluation showed that UMAO treatment did not bring about cytotoxicity but improved the early adhesion of MC3T3 cell.

Candida albicans aspects of binary titanium alloys for biomedical applications

Titanium and its alloys are widely used in biomedical devices, e.g. implants, due to its biocompatibility and osseointegration ability. In fact, fungal (Candida spp.) infection has been identified as one of the key reasons causing the failure of the device that is inevitable and impactful to the society. Thus, this study evaluated the surface morphology, surface chemical composition and Candida albicans adhesion on specimens of 16 binary Ti-alloys (∼5 wt% of any one of the alloy elements: Ag, Al, Au, Co, Cr, Cu, Fe, In, Mn, Mo, Nb, Pd, Pt, Sn, V and Zr) compared with cp-Ti, targeting to seek for the binary Ti-alloys which has the lowest C. albicans infection. Candida albicans cultures were grown on the specimens for 48 h, and colony forming units (CFUs) and real-time polymerase chain reaction (RT-PCR) were used to evaluate the biofilm formation ability. Scanning electron microscopy and confocal laser scanning microscopy confirmed the formation of C. albicans biofilm on all specimens' surfaces, such that CFU results showed Ti-Mo, Ti-Zr, Ti-Al and Ti-V have less C. albicans formed on the surfaces than cp-Ti. RT-PCR showed Ti-Zr and Ti-Cu have significantly higher C. albicans DNA concentrations than Ti-Al and Ti-V (P < 0.05), whereas Ti-Cu has even showed a statistically higher concentration than Ti-Au, Ti-Co, Ti-In and Ti-Pt (P < 0.05). This study confirmed that Ti-Mo, Ti-Zr, Ti-Al and Ti-V have lower the occurrence of C. albicans which might be clinically advantageous for medical devices, but Ti-Cu should be used in caution.