Enhanced cytocompatibility and antibacterial property of zinc phosphate coating on biodegradable zinc materials

Facile fabrication of biodegradable endothelium-mimicking coatings on bioabsorbable zinc-alloy stents by one-step electrophoretic deposition

The zinc-alloy stent is one of the best potential candidates for bioabsorbable metal stents because of its appropriate corrosion rate aligned to the duration of the healing process of the surrounding vessel tissues. However, excessive release of zinc ions, causing cytotoxicity of endothelial cells, and insufficient surface bio-functions of Zn-alloy stents lead to considerable challenge in their application. Herein, one-step electrophoretic deposition was employed to apply a hybrid coating of polycarbonate, tannic acid, and copper ions with tailored functions on Zn-alloy stents to enhance their corrosion resistance and provide an endothelium-mimicking surface. Specifically, the synthesized amino-functionalized aliphatic polycarbonates endowed the hybrid coating with specific surface-erosion properties, resulting in superior corrosion resistance and long-term stability in degradation tests both in vitro and in vivo. The immobilized copper ions enabled the catalytic generation of nitric oxide and promoted the adhesion and proliferation of endothelial cells on zinc alloy. The added tannic acid firmly chelated the copper ions and formed durable phenolic-copper-amine crosslinked networks by electrostatic interaction, resulting in long-term stability of the hybrid coating during the 21 day dynamic immersion test. Tannic acid exerted a synergistic antibacterial effect with copper ions as well as a reduction in the inflammatory response to the zinc substrate. In addition, the hybrid coating improved the in vitro hemocompatibility of zinc alloys. By adjusting the amount of chelated copper in the coating system, the biological function of the corresponding coatings can be controlled, providing a facile surface treatment strategy to promote the progress of zinc-alloy stents in clinical applications.

Corrosion Behavior and Biocompatibility of Na2EDTA-Induced Nacre Coatings on AZ91D Alloys Prepared via Hydrothermal Treatment

An effective method for controlling the corrosion rate of Mg-based implants must be urgently developed to meet the requirements of clinical applications. As a naturally occurring osteoid material, nacre offers a strategy to endow biomedical Mg alloys with excellent biocompatibility, and corrosion resistance. In this study, pearl powder and NaH2PO4 were used as precursors to deposit coatings on AZ91D alloy substrates hydrothermally based on Na2EDTA-assisted induction. Na2EDTA-induced nacre coatings were fabricated at various pH values, and its chemical composition and microstructure were analyzed via energy-dispersive X-ray, scanning electron microscopy, and X-ray diffraction spectroscopy. The corrosion-resistant performance and cytocompatibility of the samples were evaluated via electrochemical measurements and in vitro cell experiments. Results showed that the samples hydrothermally treated under faint acid conditions present excellent corrosion resistance, whereas the samples treated under slight alkaline conditions demonstrate improved biocompatibility due to high Ca and P content and large Ca/P atomic ratio. This study provides substantial evidence of the potential value of nacre coatings in expanding the biological applications of implanted biomaterials.

"Dual-functional" strontium titanate nanotubes designed based on fusion peptides simultaneously enhancing anti-infection and osseointegration

Currently, there is an increasing clinical demand for implants that effectively resist bacterial infections while promoting osseointegration. In this study, the fusion peptide technology was used to linearly fuse the antimicrobial peptide (AMP, HHC36) and the bone-promoting peptide (RGD), so that the titanium (Ti)-based implant modified by the polypeptide had the dual function of "antibacterial-promoting bone". Firstly, self-organized vertically-oriented strontium-doped titanium dioxide nanotubes (STN) were manufactured by anodizing and hydrothermal synthesis methods. Secondly, the fusion peptide (HHC36-RGD) was loaded into the tubular structure by a simple vacuum-assisted physical adsorption method. Finally, STN loaded with HHC36-RGD (H-R-STN) was obtained. The characterization results demonstrated that the surface of the H-R-STN had a roughness and hydrophilicity that promoted cell adhesion. Additionally, electrochemical tests showed that H-R-STN coating can reduce the corrosion rate of pure Ti. The fusion peptide and Sr²⁺ in H-R-STN were released in the initial fast and subsequent slow kinetic model. Expected, H-R-STN can kill more than 99% of clinically common pathogenic bacteria (Staphylococcus aureus and Escherichia coli), and significantly inhibit the formation of bacterial biofilms. Simultaneously, under the synergistic effect of RGD in the fusion peptide and strontium in STN, H-R-STN markedly promoted the adhesion and proliferation of mouse osteoblasts, and significantly promoted osteogenic markers (alkaline phosphatase, runt-related transcription, collagen, mineralization) expression. In summary, the bifunctional titanium-based implant constructed by H-R-STN in this article can effectively prevent bacterial infections and promote early osseointegration. The main advantage of the titanium surface treatment method of the study was that its simplicity, low cost, especially its versatility made it a promising anti-infective bone repair material.

Peculiarities of the formation, structural and morphological properties of zinc whitlockite (Ca18Zn2(HPO4)2(PO4)12) synthesized via a phase transformation process under hydrothermal conditions

In the present work, the formation of zinc whitlockite via a dissolution–precipitation process was investigated in detail. The influence of medium pH, reaction time, temperature and concentration of precursors on the formation of the material was studied.

A review on current research status of the surface modification of Zn-based biodegradable metals

Recently, zinc and its alloys have been proposed as promising candidates for biodegradable metals (BMs), owning to their preferable corrosion behavior and acceptable biocompatibility in cardiovascular, bone and gastrointestinal environments, together with Mg-based and Fe-based BMs. However, there is the desire for surface treatment for Zn-based BMs to better control their biodegradation behavior. Firstly, the implantation of some Zn-based BMs in cardiovascular environment exhibited intimal activation with mild inflammation. Secondly, for orthopedic applications, the biodegradation rates of Zn-based BMs are relatively slow, resulting in a long-term retention after fulfilling their mission. Meanwhile, excessive Zn2+ release during degradation will cause in vitro cytotoxicity and in vivo delayed osseointegration. In this review, we firstly summarized the current surface modification methods of Zn-based alloys for the industrial applications. Then we comprehensively summarized the recent progress of biomedical bulk Zn-based BMs as well as the corresponding surface modification strategies. Last but not least, the future perspectives towards the design of surface bio-functionalized coatings on Zn-based BMs for orthopedic and cardiovascular applications were also briefly proposed.

Improved mechanical, degradation, and biological performances of Zn–Fe alloys as bioresorbable implants

Zinc (Zn) is a promising bioresorbable implant material with more moderate degradation rate compared to magnesium (Mg) and iron (Fe). However, the low mechanical strength and localized degradation behavior of pure Zn limit its clinical applications. Alloying is one of the most effective ways to overcome these limitations. After screening the alloying element candidates regarding their potentials for improvement on the degradation and biocompatibility, we proposed Fe as the alloying element for Zn, and investigated the in vitro and in vivo performances of these alloys in both subcutaneous and femoral tissues. Results showed that the uniformly distributed secondary phase in Zn–Fe alloys significantly improved the mechanical property and facilitated uniform degradation, which thus enhanced their biocompatibility, especially the Zn-0.4Fe alloy. Moreover, these Zn–Fe alloys showed outstanding antibacterial property. Taken together, Zn–Fe alloys could be promising candidates as bioresorbable medical implants for various cardiovascular, wound closure, and orthopedic applications.

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Zn-0.4Fe alloy significantly improved the mechanical strength and ductility.

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Zn-0.4Fe alloy showed a uniform degradation behavior.

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Subcutaneous and femoral implantations to compare in vivo performances.

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Zn-0.4Fe alloy showed superior hemocompatibility and in vivo osteointegration.

Limitation of Water-Soluble Tetrazolium Salt for the Cytocompatibility Evaluation of Zinc-Based Metals

Zinc (Zn) and its alloys have been regarded as promising biodegradable metals. The standardized cytotoxicity evaluation is a mandatory step to screen the biocompatibility of novel Zn and its alloys. Nevertheless, the suitability of the tetrazolium-based assay in the direct contact test for some metallic biomaterials (i.e., magnesium and manganese) is questionable. In this study, our results demonstrate an obvious inconsistency between qualitative observation via fluorescence staining and quantitative assessment using water-soluble tetrazolium salt (CCK-8). Subsequent experiments revealed that Zn and pre-treated Zn can directly convert tetrazolium salts to formazan, falsifying the cytotoxicity results. Therefore, we conclude that the CCK-8 assay is not suitable for evaluating the cytotoxicity of biodegradable Zn-based metals in the direct contact test.

Electrodeposited dopamine/strontium-doped hydroxyapatite composite coating on pure zinc for anti-corrosion, antimicrobial and osteogenesis

Zinc-based biometal is expected to become a new generation of biodegradable implants. Due to its antibacterial and biocompatibility in vivo, zinc metals is recently considered to be the most promising biodegradable metal, However, cytotoxicity is the thorny problem that currently restrict its application, due to the excessive Zn ions released during degradation. In order to solve these problems, dopamine modified strontium-doped hydroxyapatite coating (SrHA/PDA) was fabricated on alkali-treated pure zinc to improve its corrosion rate and cytocompatibility by electrodeposition for the first time. The obtained coating showed a dense structure and high crystallinity, which was attributed to the attraction of Ca²⁺ ions by polydopamine. The results showed that the SrHA/PDA coating delayedthe degradation rate of zinc metal, which reduced the release of Zn²⁺, thereby reducing its cytotoxicity. Additionally, electrochemical tests showed that SrHA/PDA coating can reduce the corrosion rate of pure zinc. In vitro cell viability showed that even at high Zn²⁺ concentrations (3.11 mg/L), preosteoblasts (MC3T3-E1) cells proliferated at a high rate on SrHA/PDA, thus confirming that Sr²⁺ counteracted the cytotoxic effects of Zn²⁺ and promoted cell differentiation. Moreover, the SrHA/PDA coating still maintained excellent antibacterial effects against pathogenic bacterial strains (Escherichia coli and Staphylococcus aureus). Mild pH changes had no significant effect on the viability of cells and bacterias. Collectively, the present study elucidated that by coating SrHA/PDA/Zn(OH)₂ on Zn, a controllable corrosion rate, original antibacterial properties and better cell compatibility can be achieved. This provided a new strategy for the surface modification of biodegradable Zn.

Additively manufactured biodegradable porous magnesium implants for elimination of implant-related infections: An in vitro and in vivo study

Magnesium (Mg) alloys that have both antibacterial and osteogenic properties are suitable candidates for orthopedic implants. However, the fabrication of ideal Mg implants suitable for bone repair remains challenging because it requires implants with interconnected pore structures and personalized geometric shapes. In this study, we fabricated a porous 3D-printed Mg-Nd-Zn-Zr (denoted as JDBM) implant with suitable mechanical properties using selective laser melting technology. The 3D-printed JDBM implant exhibited cytocompatibility in MC3T3-E1 and RAW267.4 cells and excellent osteoinductivity in vitro. Furthermore, the implant demonstrated excellent antibacterial ratios of 90.0% and 92.1% for methicillin-resistant S. aureus (MRSA) and Escherichia coli, respectively. The 3D-printed JDBM implant prevented MRSA-induced implant-related infection in a rabbit model and showed good in vivo biocompatibility based on the results of histological evaluation, blood tests, and Mg²⁺ deposition detection. In addition, enhanced inflammatory response and TNF-α secretion were observed at the bone-implant interface of the 3D-printed JDBM implants during the early implantation stage. The high Mg²⁺ environment produced by the degradation of 3D-printed JDBM implants could promote M1 phenotype of macrophages (Tnf, iNOS, Ccl3, Ccl4, Ccl5, Cxcl10, and Cxcl2), and enhance the phagocytic ability of macrophages. The enhanced immunoregulatory effect generated by relatively fast Mg²⁺ release and implant degradation during the early implantation stage is a potential antibacterial mechanism of Mg-based implant. Our findings indicate that 3D-printed porous JDBM implants, having both antibacterial property and osteoinductivity, hold potential for future orthopedic applications.

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Porous JDBM implants promising mechanical properties was fabricated by selective laser melting.

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3D-printed JDBM implant exhibited excellent antibacterial property, osteoinductivity, and biocompatibility.

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Temporally enhanced immunoregulatory effect in early stage was a potential antibacterial mechanism of Mg-based implant.

Dissolution-Precipitation Synthesis and Characterization of Zinc Whitlockite with Variable Metal Content

In the present work, a series of zinc whitlockite (CaxZny(HPO4)2(PO4)12) powders was synthesized by a low-temperature dissolution-precipitation process for the first time. The phase conversion from calcium hydroxyapatite to zinc whitlockite occurred in an acidic medium in the presence of Zn2+ ions. Variable chemical composition of the synthesis products was achieved by changing Ca-to-Zn molar ratio in the reaction mixture. Investigation of the phase evolution as a function of time demonstrated that phase-pure zinc whitlockite powders can be synthesized in just 3 h. It is also demonstrated that single-phase products can be obtained when the Ca-to-Zn ratio in the reaction medium is in the range from 9 to 30. With higher or lower ratios, neighboring crystal phases such as scholzite or calcium hydroxyapatite were obtained. The morphology of the synthesized powders was found to be dependent on the chemical composition, transforming from hexagonal to rhombohedral plates with the increase of Zn content. Thermal stability studies revealed that the synthesized compounds were thermally unstable and decomposed upon heat treatment.

The microstructure, mechanical properties, corrosion performance and biocompatibility of hydroxyapatite reinforced ZK61 magnesium-matrix biological composite

Magnesium (Mg)-based composites, as biomaterials, have attracted widespread attention due to their adjustable mechanical properties like elastic modulus, ductility, ultimate tensile strength, and corrosion resistance. In this study, hydroxyapatite (HA) reinforced ZK61 Mg-matrix composites were prepared by powder metallurgy and hot extrusion methods. The influence of the content of HA (10 wt%, 20 wt%, and 30 wt%) on the microstructure, density, mechanical properties, corrosion property and biocompatibility were investigated. The results showed that the density and yield strength of the composites match those of natural bone. Moreover, the composite with 10 % HA (ZK61-10HA) exhibited the best corrosion resistance, as determined by the electrochemical measurement and immersion test in simulated body fluid (SBF) at 37 °C. In addition, the ZK61-10HA composite significantly enhanced the cell viability (≥78 %) compared with ZK61 alloy in vitro testing. It is demonstrated that the mechanical properties, corrosion resistance and biocompatibility of Mg alloy can be effectively controlled by adjusting the content of HA, which suggested that the ZK61-HA composites were promising candidates for degradable implant materials.

Zn-0.8Mg-0.2Sr (wt.%) Absorbable Screws-An In-Vivo Biocompatibility and Degradation Pilot Study on a Rabbit Model

In this pilot study, we investigated the biocompatibility and degradation rate of an extruded Zn-0.8Mg-0.2Sr (wt.%) alloy on a rabbit model. An alloy screw was implanted into one of the tibiae of New Zealand White rabbits. After 120 days, the animals were euthanized. Evaluation included clinical assessment, microCT, histological examination of implants, analyses of the adjacent bone, and assessment of zinc, magnesium, and strontium in vital organs (liver, kidneys, brain). The bone sections with the implanted screw were examined via scanning electron microscopy and energy dispersive spectroscopy (SEM-EDS). This method showed that the implant was covered by a thin layer of phosphate-based solid corrosion products with a thickness ranging between 4 and 5 µm. Only negligible changes of the implant volume and area were observed. The degradation was not connected with gas evolution. The screws were fibrointegrated, partially osseointegrated histologically. We observed no inflammatory reaction or bone resorption. Periosteal apposition and formation of new bone with a regular structure were frequently observed near the implant surface. The histological evaluation of the liver, kidneys, and brain showed no toxic changes. The levels of Zn, Mg, and Sr after 120 days in the liver, kidneys, and brain did not exceed the reference values for these elements. The alloy was safe, biocompatible, and well-tolerated.

Application of nanoparticles in bone tissue engineering; a review on the molecular mechanisms driving osteogenesis

The introduction of nanoparticles into bone tissue engineering strategies is beneficial to govern cell fate into osteogenesis and the regeneration of large bone defects. The present study explored the role of nanoparticles to advance osteogenesis with a focus on the cellular and molecular pathways involved. Pubmed, Pubmed Central, Embase, Scopus, and Science Direct databases were explored for those published articles relevant to the involvement of nanoparticles in osteogenic cellular pathways. As multifunctional compounds, nanoparticles contribute to scaffold-free and scaffold-based tissue engineering strategies to progress osteogenesis and bone regeneration. They regulate inflammatory responses and osteo/angio/osteoclastic signaling pathways to generate an osteogenic niche. Besides, nanoparticles interact with biomolecules, enhance their half-life and bioavailability. Nanoparticles are promising candidates to promote osteogenesis. However, the interaction of nanoparticles with the biological milieu is somewhat complicated, and more considerations are recommended on the employment of nanoparticles in clinical applications because of NP-induced toxicities.

Inorganic Agents for Enhanced Angiogenesis of Orthopedic Biomaterials

Aseptic loosening of a permanent prosthesis remains one of the most common reasons for bone implant failure. To improve the fixation between implant and bone tissue as well as enhance blood vessel formation, bioactive agents are incorporated into the surface of the biomaterial. This study reviews and compares five bioactive elements (copper, magnesium, silicon, strontium, and zinc) with respect to their effect on the angiogenic behavior of endothelial cells (ECs) when incorporated on the surface of biomaterials. Moreover, it provides an overview of the state-of-the-art methodologies used for the in vitro assessment of the angiogenic properties of these elements. Two databases are searched using keywords containing ECs and copper, magnesium, silicon, strontium, and zinc. After applying the defined inclusion and exclusion criteria, 59 articles are retained for the final assessment. An overview of the angiogenic properties of five bioactive elements and the methods used for assessment of their in vitro angiogenic potential is presented. The findings show that silicon and strontium can effectively enhance osseointegration through the simultaneous promotion of both angiogenesis and osteogenesis. Therefore, their integration onto the surface of biomaterials can ultimately decrease the incidence of implant failure due to aseptic loosening.

Calcium phosphate coatings enhance biocompatibility and degradation resistance of magnesium alloy: Correlating in vitro and in vivo studies

Magnesium (Mg) and its alloys are promising biodegradable materials for orthopedic applications. However, one of the major problems is their rapid degradation rate with quick evolution of hydrogen gas. To overcome this problem, calcium phosphate (CaP) coatings have been used to improve the degradation resistance and the biocompatibility of Mg materials. This study focuses on the comparison and correlation of the in vitro and in vivo degradation and biocompatibility behaviors of these materials. A CaP coating consisting of dicalcium phosphate dihydrate (DCPD) was deposited on an AZ60 Mg alloy by the chemical conversion method. Then, the in vitro degradation testing including electrochemical and immersion tests, and in vivo implantation of the CaP coated Mg alloy were conducted to compare the degradation behaviors. Next, the in vitro cell behavior and in vivo bone tissue response were also compared on both uncoated and CaP-coated Mg samples. Data showed that the CaP coating provided the Mg alloy with significantly better biodegradation behavior and biocompatibility. The in vitro and in vivo biocompatibility tests exhibited good consistency while not the case for biodegradation. Results showed that the in vitro electrochemical test could be a quick screening tool for the biodegradation rate, while the in vitro immersion degradation rate was often 2-4 folds faster than the in vivo degradation rate.

Research status of biodegradable metals designed for oral and maxillofacial applications: A review

The oral and maxillofacial regions have complex anatomical structures and different tissue types, which have vital health and aesthetic functions. Biodegradable metals (BMs) is a promising bioactive materials to treat oral and maxillofacial diseases. This review summarizes the research status and future research directions of BMs for oral and maxillofacial applications. Mg-based BMs and Zn-based BMs for bone fracture fixation systems, and guided bone regeneration (GBR) membranes, are discussed in detail. Zn-based BMs with a moderate degradation rate and superior mechanical properties for GBR membranes show great potential for clinical translation. Fe-based BMs have a relatively low degradation rate and insoluble degradation products, which greatly limit their application and clinical translation. Furthermore, we proposed potential future research directions for BMs in the oral and maxillofacial regions, including 3D printed BM bone scaffolds, surface modification for BMs GBR membranes, and BMs containing hydrogels for cartilage regeneration, soft tissue regeneration, and nerve regeneration. Taken together, the progress made in the development of BMs in oral and maxillofacial regions has laid a foundation for further clinical translation.

Induced Biological Response in Contact with Ag-and Cu-Doped Carbon Coatings for Potential Orthopedic Applications

Silver and copper as additives of various biomaterials have been reported as the potential solutions for biomedicine applications, mostly because of inducing bactericidal effects. The application of those admixtures in diamond-like carbon (DLC) coatings may be desirable for orthopedic implants. In the present manuscript, the biological effect of coatings with up to about 7 at.% and 14 at.% of, respectively, Cu and Ag is compared. The morphology, chemical structure, and composition of films deposited on AISI 316LVM and Ti6Al7Nb is characterized. The live/dead analysis conducted with Escherichia coli shows a higher bactericidal potential of silver than copper. Although the Cu-doped coatings can positively affect the proliferation of Saos-2 and EA.hy926 cell lines, the results of XTT test are on the verge of 70% of viability. Biological effect of silver on EA.hy926 cell lines is negative but that admixture ensures high proliferation of osteoblasts in contact with coatings deposited on titanium alloy (over 20% better than for substrate material). In that case, the viability is reaching about 85% for Ag-doped coatings on AISI 316LVM and 75% on Ti6Al7Nb. The results indicate that for the sake of bactericidal coatings that may promote osteointegration, the candidates are DLC with silver content no higher than 10 at.%.

Antibacterial Titanium Implants Biofunctionalized by Plasma Electrolytic Oxidation with Silver, Zinc, and Copper: A Systematic Review

Patients receiving orthopedic implants are at risk of implant-associated infections (IAI). A growing number of antibiotic-resistant bacteria threaten to hamper the treatment of IAI. The focus has, therefore, shifted towards the development of implants with intrinsic antibacterial activity to prevent the occurrence of infection. The use of Ag, Cu, and Zn has gained momentum as these elements display strong antibacterial behavior and target a wide spectrum of bacteria. In order to incorporate these elements into the surface of titanium-based bone implants, plasma electrolytic oxidation (PEO) has been widely investigated as a single-step process that can biofunctionalize these (highly porous) implant surfaces. Here, we present a systematic review of the studies published between 2009 until 2020 on the biomaterial properties, antibacterial behavior, and biocompatibility of titanium implants biofunctionalized by PEO using Ag, Cu, and Zn. We observed that 100% of surfaces bearing Ag (Ag-surfaces), 93% of surfaces bearing Cu (Cu-surfaces), 73% of surfaces bearing Zn (Zn-surfaces), and 100% of surfaces combining Ag, Cu, and Zn resulted in a significant (i.e., >50%) reduction of bacterial load, while 13% of Ag-surfaces, 10% of Cu-surfaces, and none of Zn or combined Ag, Cu, and Zn surfaces reported cytotoxicity against osteoblasts, stem cells, and immune cells. A majority of the studies investigated the antibacterial activity against S. aureus. Important areas for future research include the biofunctionalization of additively manufactured porous implants and surfaces combining Ag, Cu, and Zn. Furthermore, the antibacterial activity of such implants should be determined in assays focused on prevention, rather than the treatment of IAIs. These implants should be tested using appropriate in vivo bone infection models capable of assessing whether titanium implants biofunctionalized by PEO with Ag, Cu, and Zn can contribute to protect patients against IAI.

Regulating size of silver nanoparticles on calcium carbonate via ultrasonic spray for effective antibacterial efficacy and sustained release

Calcium carbonate is used as bone-filling material due to its good biocompatibility, bioactivity, and bioabsorbability, but the prevalence of infectious complications associated with calcium carbonate has created a persisting challenge in the treatment of bone defect. Therefore, this greatly necessitate the need to endow calcium carbonate with antibacterial properties. In this study, calcium carbonate powders loaded with silver nanoparticles (Ag-CaCO₃) were prepared in attempt to serve as a novel antibacterial inorganic filler material. This objective was achieved using ultrasonic spray-pyrolysis (USSP) route to produce Ag-CaCO₃ with 1, 5 and 10 mol% silver. The size of silver nanoparticles on CaCO₃ microspheres could be regulated by adjusting silver concentration to facilitate effective release of Ag⁺ ions. This was demonstrated in Ag-CaCO₃ (1), where the lowest silver content at 1 mol% achieved the highest Ag⁺ ions release over 28 days. This in turn gave rise to effective antibacterial efficiency against Staphylococcus aureus and Escherichia coli. Furthermore, CaCO₃ (1) could also support osteoblast-like cells (MG-63) at a cell viability of 80%. Overall, this work extends the capabilities in employing USSP to produce inorganic filler materials with sustained antibacterial properties, bringing one step closer to the development of antibacterial products.

The Influence of Nanometals, Dispersed in the Electrophoretic Nanohydroxyapatite Coatings on the Ti13Zr13Nb Alloy, on Their Morphology and Mechanical Properties

In this work, nanohydroxyapatite coatings with nanosilver and nanocopper have been fabricated and studied. The presented results concern coatings with a chemical composition that has never been proposed before. The present research aims to characterize the effects of nanosilver and nanocopper, dispersed in nanohydroxyapatite coatings and deposited on a new, non-toxic Ti13Zr13Nb alloy, on the physical and mechanical properties of coatings. The coatings were obtained by a one-stage electrophoretic process. The surface topography, and the chemical and phase compositions of coatings were examined with scanning electron microscopy, atomic force microscopy, X-ray diffractometry, glow discharge optical emission spectroscopy, and energy-dispersive X-ray spectroscopy. The mechanical properties of coatings were determined by nanoindentation tests, while coatings adhesion was determined by nanoscratch tests. The results demonstrate that copper addition increases the hardness and adhesion. The presence of nanosilver has no significant influence on the adhesion of coatings.

The Chemical and Biological Properties of Nanohydroxyapatite Coatings with Antibacterial Nanometals, Obtained in the Electrophoretic Process on the Ti13Zr13Nb Alloy

The risk of an early inflammation after implantation surgery of titanium implants has caused the development of different antimicrobial measures. The present research is aimed at characterizing the effects of nanosilver and nanocopper dispersed in the nanohydroxyapatite coatings, deposited on the Ti13Zr13Nb alloy, and on the chemical and biological properties of the coatings. The one-stage deposition process was performed by the electrophoretic method at different contents of nanomaterials in suspension. The surface topography of the coatings was examined with scanning electron microscopy. The wettability was expressed as the water contact angle. The corrosion behavior was characterized by the potentiodynamic technique. The release rate of copper and silver into the simulated body fluid was investigated by atomic absorption spectrometry. The antibacterial efficiency was evaluated as the survivability and adhesion of the bacteria and the growth of the biofilm. The cytotoxicity was assessed for osteoblasts. The results demonstrate that silver and copper increase the corrosion resistance and hydrophilicity. Both elements together effectively kill bacteria and inhibit biofilm growth but appear to be toxic for osteoblasts. The obtained results show that the nanohydroxyapatite coatings doped with nanosilver and nanocopper in a one-stage electrophoretic process can be valuable for antibacterial coatings.

Designing Better Cardiovascular Stent Materials - A Learning Curve

Cardiovascular stents are life-saving devices and one of the top 10 medical breakthroughs of the 21st century. Decades of research and clinical trials have taught us about the effects of material (metal or polymer), design (geometry, strut thickness, and the number of connectors), and drug-elution on vasculature mechanics, hemocompatibility, biocompatibility, and patient health. Recently developed novel bioresorbable stents are intended to overcome common issues of chronic inflammation, in-stent restenosis, and stent thrombosis associated with permanent stents, but there is still much to learn. Increased knowledge and advanced methods in material processing have led to new stent formulations aimed at improving the performance of their predecessors but often comes with potential tradeoffs. This review aims to discuss the advantages and disadvantages of stent material interactions with the host within five areas of contrasting characteristics, such as 1) metal or polymer, 2) bioresorbable or permanent, 3) drug elution or no drug elution, 4) bare or surface-modified, and 5) self-expanding or balloon-expanding perspectives, as they relate to pre-clinical and clinical outcomes and concludes with directions for future studies.

Development and In Vitro Biodegradation of Biomimetic Zwitterionic Phosphorylcholine Chitosan Coating on Zn1Mg Alloy

Zinc (Zn) alloys are promising alternatives to magnesium (Mg)- and iron (Fe)-based alloys because of their moderate corrosion rate and superior biocompatibility. To reduce the mass release of Zn²⁺ and improve the biocompatibility of Zn implants, the biomimetic zwitterionic polymer layer (phosphorylcholine chitosan-PCCs) was immobilized on the plasma-treated Zn1Mg surface. It is the chemical bonds between the -NH₂ groups of the PCCs chain and O-C═O (C═O) groups on the plasma-treated Zn1Mg (Zn1Mg-PP) that contributes to the strong bonding strength between the film and the substrate, by which the PCCs (approx. 200 nm thick) layer can bear a 5.93 N normal load. The electrochemical impedance spectroscopy (EIS) results showed that the PCCs layer remarkably increased the resistance against corrosion attack, protecting substrates from over-quick degradation, and the protective effect of the layer with a thickness of 200 nm lasts for about 24 h. The corrosion products of Zn1Mg-PP-PCC in NaCl solution were determined as Zn₅(OH)₈Cl₂·H₂O and Zn₃(PO₄)₂. Besides, the bulk Zn1Mg can trigger more aggressive macrophage activity, while the surface of Zn1Mg-PP and Zn1Mg-PP-PCC and their corrosion products (Zn₃(PO₄)₂) tend to promote the differentiation of macrophages into the M2 phenotype, which is beneficial for implant applications.

Development of biodegradable Zn-1Mg-0.1RE (RE = Er, Dy, and Ho) alloys for biomedical applications

Zinc (Zn) and its alloys are receiving great attention as promising biodegradable materials due to their suitable corrosion resistance, good biocompatibility, and highly desirable biofunctionality. Nevertheless, the low mechanical strength of pure Zn impedes its practical clinical application and there have been calls for further research into the Zn alloys and thermomechanical processes to enhance their mechanical properties and biocompatibility. Here, we report on the alloying efficacy of rare earth elements (REEs) including erbium (Er), dysprosium (Dy), and holmium (Ho) on the microstructure, mechanical properties, corrosion and wear behavior, and in vitro biological properties of Zn-1Mg-0.1RE alloys. Microstructural characterization revealed that the addition of 0.1 wt.% REEs had a significant refining effect on the grain size of the α-Zn matrix and the second phases of the alloys. Alloying of the REEs and hot-rolling effectively improved the mechanical properties due to both precipitation strengthening of the second phases of ErZn₅, DyZn₅, and Ho₂Zn₁₇ and grain-refinement strengthening. The highest ultimate tensile strength of 259.4 MPa and yield strength of 234.8 MPa with elongation of 16.8% were achieved in the hot-rolled Zn-1Mg-0.1Ho. Alloying of REEs also improved the wear and corrosion resistance, and slowed down the degradation rate in Hanks' solution. Zn-1Mg-0.1Er showed the highest cytocompatibility of MC3T3-E1 cells cultured directly on the alloy surface and of MG-63 cells cultured in the alloy extract. Zn-1Mg-0.1Dy showed the best anticoagulant property among all the alloys. Overall, these Zn-1Mg-0.1RE (Er, Dy, and Ho) alloys can be considered promising biodegradable metallic materials for orthopedic applications.

Sol-Gel Derived Hydroxyapatite Coatings for Titanium Implants: A Review

With the growing demands for bone implant therapy, titanium (Ti) and its alloys are considered as appropriate choices for the load-bearing bone implant substitutes. However, the interaction of bare Ti-based implants with the tissues is critical to the success of the implants for long-term stability. Thus, surface modifications of Ti implants with biocompatible hydroxyapatite (HAp) coatings before implantation is important and gained interest. Sol-gel is a potential technique for deposition the biocompatible HAp and has many advantages over other methods. Therefore, this review strives to provide widespread overview on the recent development of sol-gel HAp deposition on Ti. This study shows that sol-gel technique was able to produce uniform and homogenous HAp coatings and identified the role of surface pretreatment of Ti substrate, optimizing the sol-gel parameters, substitution, and reinforcement of HAp on improving the coating properties. Critical factors that influence on the characteristics of the deposited sol-gel HAp films as corrosion resistance, adhesion to substrate, bioactivity, morphological, and structural properties are discussed. The review also highlights the critical issues, the most significant challenges, and the areas requiring further research.

Appropriately adapted properties of hot-extruded Zn-0.5Cu-xFe alloys aimed for biodegradable guided bone regeneration membrane application

Appropriately adapted comprehensive mechanical properties, degradation behavior and biocompatibility are prerequisites for the application of Zn-based biodegradable implants. In this study, hot-extruded Zn-0.5Cu-xFe (x = 0.1, 0.2 and 0.4 wt%) alloys were fabricated as candidates for biodegradable materials for guided bone regeneration (GBR) membranes. The hot-extrusion process and Cu alloying were expected mostly to enhance the mechanical properties, and the Fe alloying was added mainly for regulating the degradation. The microstructure, mechanical properties and in vitro degradation behavior were systematically investigated. The ZnCuFe alloys were composed of a Zn matrix and FeZn₁₃ phase. With increasing Fe content, a higher FeZn₁₃ phase precipitation with larger particles was observed. Since elongation declined significantly until fracture with increasing Fe content up to 0.4 wt%, the ZnCuFe (0.2 wt%) alloy achieved a good balance between mechanical strength and ductility, with an ultimate tensile strength of 202.3 MPa and elongation at fracture of 41.2%. Moreover, the addition of Fe successfully accelerated the degradation of ZnCuFe alloys. The ZnCuFe (0.2 wt%) alloy showed relatively uniform corrosion in the long-term degradation test. Furthermore, extracts of the ZnCuFe (0.2 wt%) alloy showed no apparent cytotoxic effects against L929 fibroblasts, Saos-2 osteoblasts or TAg periosteal cells. The ZnCuFe (0.2 wt%) alloy exhibited the potential to inhibit bacterial adhesion of Streptococcus gordonii and mixed oral bacteria. Our study provides evidence that the ZnCuFe (0.2 wt%) alloy can represent a promising material for the application as a suitable GBR membrane.

Assessment of human ovarian follicular fluid derived mesenchymal stem cells in chitosan/PCL/Zn scaffold for bone tissue regeneration

Bone tissue engineering compasses the use of mesenchymal stem cells (MSCs) along with engineered biomaterial construct to augment bone regeneration. Till now, MSCs were isolated from various sources and used in cellular constructs. For the first time, in this study, MSCs were isolated from human Ovarian Follicular Fluid (OFF) and characterized by CD 44⁺ and CD 105⁺ markers via confocal microscopy and flow cytometry. Additionally, MSCs stemness, proliferation and colony-forming unit ability, multi-lineage differentiation potential were also studied. To test its suitability for bone tissue engineering applications, we grew the MSCs with the conditioned medium obtained from biocomposite scaffold by fusing a natural polymer, Chitosan (CS) and a synthetic polymer, Polycaprolactone (PCL) and the scaffold were coated with Zinc divalent ions to impart osteogenic properties. The physico-chemical characterization of scaffold, such as FTIR, XRD, and SEM studies was carried out. The biological characterization showed that the scaffolds were compatible with MSCs and promoted osteoblast differentiation which was confirmed at both cellular and molecular levels. The cellular construct increased calcium deposition, analyzed by alizarin red staining and ALP activity at cellular level. At the molecular level, the osteoblast markers expression such as Runx2 and type 1 collagen mRNAs, and osteonectin (ON) and osteocalcin (OC) secretory proteins were increased in the presence of scaffold. Overall, the current study recommends that MSCs can be easily obtained from human waste OFF, and grown in standard in vitro conditions. Successful growth of such MSCs with CS/PCL/Zn scaffold opens new avenues in utilizing the cell source for bone tissue engineering.

Additively manufactured biodegradable porous metals

Partially due to the unavailability of ideal bone substitutes, the treatment of large bony defects remains one of the most important challenges of orthopedic surgery. Additively manufactured (AM) biodegradable porous metals that have emerged since 2018 provide unprecedented opportunities for fulfilling the requirements of an ideal bone implant. First, the multi-scale geometry of these implants can be customized to mimic the human bone in terms of both micro-architecture and mechanical properties. Second, a porous structure with interconnected pores possesses a large surface area, which is favorable for the adhesion and proliferation of cells and, thus, bony ingrowth. Finally, the freeform geometrical design of such biomaterials could be exploited to adjust their biodegradation behavior so as to maintain the structural integrity of the implant during the healing process while ensuring that the implant disappears afterwards, paving the way for full bone regeneration. While the AM biodegradable porous metals that have been studied so far have shown many unique properties as compared to their solid counterparts, the unprecedented degree of flexibility in their geometrical design has not yet been fully exploited to optimize their properties and performance. In order to develop the ideal bone implants, it is important to take advantage of the full potential of AM biodegradable porous metals through detailed and systematic study on their biodegradation behavior, mechanical properties, biocompatibility, and bone regeneration performance. This review paper presents the state of the art in AM biodegradable porous metals and is focused on the effects of material type, processing, geometrical design, and post-AM treatments on the mechanical properties, biodegradation behavior, in vitro biocompatibility, and in vivo bone regeneration performance of AM porous Mg, Fe, and Zn as well as their alloys. We also identify a number of knowledge gaps and the challenges encountered in adopting AM biodegradable porous metals for orthopedic applications and suggest some promising areas for future research.

Interleukin-4 assisted calcium-strontium-zinc-phosphate coating induces controllable macrophage polarization and promotes osseointegration on titanium implant

Titanium (Ti) and its alloys are believed to be promising scaffold materials for dental and orthopedic implantation due to their ideal mechanical properties and biocompatibility. However, the host immune response always causes implant failures in the clinic. Surface modification of the Ti scaffold is an important factor in this process and has been widely studied to regulate the host immune response and to further promote bone regeneration. In this study, a calcium-strontium-zinc-phosphate (CSZP) coating was fabricated on a Ti implant surface by phosphate chemical conversion (PCC) technique, which modified the surface topography and element constituents. Here, we envisioned an accurate immunomodulation strategy via delivery of interleukin (IL)-4 to promote CSZP-mediated bone regeneration. IL-4 (0 and 40 ng/mL) was used to regulate immune response of macrophages. The mechanical properties, biocompatibility, osteogenesis, and anti-inflammatory properties were evaluated. The results showed that the CSZP coating exhibited a significant enhancement in surface roughness and hydrophilicity, but no obvious changes in proliferation or apoptosis of bone marrow mesenchymal stem cells (BMMSCs) and macrophages. In vitro, the mRNA and protein expression of osteogenic related factors in BMMSCs cultured on a CSZP coating, such as ALP and OCN, were significantly higher than those on bare Ti. In vivo, there was no enhanced bone formation but increased macrophage type 1 (M1) polarization on the CSZP coating. IL-4 could induce M2 polarization and promote osteogenesis of BMMSCs on CSZP in vivo and in vitro. In conclusion, the CSZP coating is an effective scaffold for BMMSCs osteogenesis, and IL-4 presents the additional advantage of modulating the immune response for bone regeneration on the CSZP coating in vivo.

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A chemical conversion calcium-strontium-zinc-phosphate (CSZP) coating is prepared on titanium.

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The CSZP coating exhibits micellar lamellar crystal morphology in micro-nano scale.

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The CSZP coating has an optimal topography and element composition for osteogenesis.

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Interleukin-4 assisted CSZP coating can obtain better osteoimmunomodulation properties.

Evaluation of in vitro corrosion behavior of zinc-hydroxyapatite and zinc-hydroxyapatite-iron as biodegradable composites

Zinc (Zn) based biomaterials have been emerged as one of the capable biodegradable materials for biomedical applications because of the ideal degradation properties. In the present work, corrosion kinetics of Zn-hydroxyapatite (HA), and Zn-HA-iron (Fe) materials developed using microwave sintering process were investigated. The effect of the inclusion of HA and Fe in Zn on corrosion properties have been evaluated in the simulated body fluid solution. Further, the wettability test of the developed composites was performed to confirm the hydrophilic nature of the surface of all samples. Zn-3HA was found to have better hydrophilicity as compared to other samples. Increased corrosion rate and pH of Zn-5HA-2Fe samples were attributed to the addition of HA and Fe in the Zn matrix. The corrosion rate and weight loss rate from electrochemical and immersion testing of all samples were found in the order from highest to lowest: Zn-5HA-2Fe > Zn-3HA > Zn-3HA-2Fe > Zn. The highest cell viability nearly 100% was obtained for Zn-3HA samples, whereas other samples also showed sufficient biocompatibility to be utilized for biomedical applications.

A study of degradation behaviour and biocompatibility of Zn-Fe alloy prepared by electrodeposition

Zinc is a biodegradable metal, which exhibits more moderate biodegradability than magnesium and iron, so that it has great application potential in the field of biomedical materials. Alloying of zinc and iron may lead to producing a new type of implant material Zn-Fe alloy, which might be able to meet the requirements for a moderate degradation rate. However, due to the huge difference in the melting point between zinc and iron, the preparation of Zn-Fe alloy is quite challenging and hence rarely reported. In this study, we show that Zn-Fe alloys can be successfully prepared by electrodeposition technology. The microstructures, composition, degradation properties and biocompatibility of the Zn-Fe alloys were systematically studied. The results showed that the content of iron in the alloys ranged from 0 to 8 wt%, depending on the concentration of Fe ions and the current density. In the alloys, the major's phases were η, δ and Г₁, and they were mainly affected by the ion concentration in the electrolyte. In the in vitro immersion tests, the Zn-Fe alloy ZF2-1 showed the highest immersion corrosion rate, while ZF3-1 showed the highest electrochemical corrosion rate. Moreover, we found that the corrosion rates of the alloys were significantly higher than that of the pure Fe. In the in vivo experiments, we confirmed that the Zn-Fe alloy possessed good biocompatibility. These results demonstrate that the electrodeposition technology is a good method to prepare Zn-Fe alloys, and the Zn-Fe alloys prepared by this method are potentially promising materials for biomedical applications.

Micro-/Nanotopography on Bioresorbable Zinc Dictates Cytocompatibility, Bone Cell Differentiation, and Macrophage Polarization

Bioresorbable metals are quickly advancing in the field of regenerative medicine for their promises of tissue restoration without adverse consequences from their lifelong presence. Zn has recently risen to the top of bioresorbable metals with great potential as a medical implant. However, cell adhesion and colonization on the Zn substrate surface remains challenging, which could damper interfacial tissue-implant integration. Inspired by the fact that surface topography can regulate cell function and fate, we hypothesize that topography on bioresorbable Zn can dictate material biocompatibility, cell differentiation, and immunomodulation. To verify this, surface-engineered Zn plates with nano-, submicro-, and microtopographies were systematically investigated. The microscale topography exhibited increased adhesion, pronounced self-renewal, and enhanced osteogenic differentiation of bone cells as well as less macrophage inflammatory polarization, reduced platelet adhesion, and better hemocompatibility. Thus, surface topography could be a viable strategy to enhance bioresorbable Zn's biocompatibility and integration with surrounding tissues while reducing inflammation.

Porous zinc scaffolds for bone tissue engineering applications: A novel additive manufacturing and casting approach

As a degradable metal, zinc (Zn) has attracted an immense amount of interest as the next generation of bioresorbable implants thanks to its modest corrosion rate and its vital role in bone remodeling, yet very few studies have thoroughly investigated its functionality as a porous implant for bone tissue engineering purposes. Zn bone scaffolds with two different pore sizes of 900 μm and 2 mm were fabricated using additive manufacturing-produced templates combined with casting. The compressive properties, corrosion rates, biocompatibility, and antibacterial performance of the bioscaffolds were examined and compared to a non-porous control. The resulting textured and porous Zn scaffolds exhibit a fully interconnected pore structure with precise control over topology. As pore size and porosity increased, mechanical strength decreased, and corrosion rate accelerated. Cell adhesion and growth on scaffolds were enhanced after an ex vivo pretreatment method. In vitro cellular tests confirmed good biocompatibility of the scaffolds. As porosity increased, potent antibacterial rates were also observed. Taken together, these results demonstrate that Zn porous bone scaffolds are promising for orthopedic applications.

Salt Preform Texturing of Absorbable Zn Substrates for Bone-implant Applications

Surface roughness is an important factor in improving the bone-implant contact area to enhance bone regeneration, yet this aspect has not been applied to absorbable metals. Textured zinc surfaces with varying degrees of surface roughness were produced using a salt-preform method with fine- and coarse-grained salts and compared to a polished control sample. The resulting surfaces were characterized by scanning electron microscopy (SEM), surface roughness, corrosion rates, and in vitro cytotoxicity. The resulting textured surfaces exhibit micron-sized cavities and increased roughness consistent with the initial salt particle size. The corrosion rate was shown to accelerate significantly as compared to the polished control sample, and pre-osteoblasts displayed healthy morphologies on the textures. The results confirm textured zinc surfaces support cell adhesion and can be used to control the corrosion rate. This study represents an important intermediate step that can be applied to porous absorbable metal scaffolds for bone-implant applications.

In vitro and in vivo studies of Zn-Mn biodegradable metals designed for orthopedic applications

In recent years, Zn-based materials provide a new option as biodegradable metals for orthopedic applications. To improve the low strength and brittle nature of pure Zn, small amounts of alloying element Mn (0.1, 0.4 and 0.8 wt.%) were added into Zn to fabricate binary Zn-Mn alloys. An extremely high elongation (83.96 ± 2.36%) was achieved in the resulting Zn-0.8 wt.%Mn alloy. Moreover, Zn-Mn alloys displayed significantly improved cytocompatibility as compared to pure Zn, according to cell proliferation and morphology analyses. More importantly, a significantly improved osteogenic activity was verified after adding Mn regarding ALP activity and osteogenic expression. Furthermore, Zn-0.8 wt.%Mn alloy scaffolds were implanted into the rat femoral condyle for repairing bone defects with pure Ti as control. Enhanced osteogenic activities were confirmed for Zn-0.8Mn alloy in contrast to pure Ti based on Micro-CT and histological results, and favorable in vivo biosafety of Zn-0.8Mn alloy was verified by H&E staining and blood tests. The exceptional mechanical performance and favorable osteogenic capability render Zn-Mn alloy a promising candidate material in the treatment of bone defects or fracture repair. STATEMENT OF SIGNIFICANCE: The element Mn, on the one hand, as an essential trace element in the human body, promotes cell proliferation, adhesion, spreading, and regulates bone metabolism; on the other hand, it could significantly improve the ductility of Zn alloys. Here, we systematically reported the biocompatibility and biofunctionality of binary biodegradable Zn-Mn alloys in the bone environment. The Zn-Mn alloys promoted MC3T3-E1 cell proliferation, adhesion, spreading, and osteogenic differentiation in vitro. Furthermore, a rat femoral condyle defect model was established; porous Zn-Mn alloy scaffolds were manufactured to repair the bone defects. Significant bone regenerations, considerable bone ingrowth, and desirable biosafety were confirmed in vivo. Therefore, biodegradable Zn-Mn with promising osteogenic properties may become new options for orthopedic implant materials.

Biofunctionalization of selective laser melted porous titanium using silver and zinc nanoparticles to prevent infections by antibiotic-resistant bacteria

Antibiotic-resistant bacteria are frequently involved in implant-associated infections (IAIs), making the treatment of these infections even more challenging. Therefore, multifunctional implant surfaces that simultaneously possess antibacterial activity and induce osseointegration are highly desired in order to prevent IAIs. The incorporation of multiple inorganic antibacterial agents onto the implant surface may aid in generating synergistic antibacterial behavior against a wide microbial spectrum while reducing the occurrence of bacterial resistance. In this study, porous titanium implants synthesized by selective laser melting (SLM) were biofunctionalized with plasma electrolytic oxidation (PEO) using electrolytes based on Ca/P species as well as silver and zinc nanoparticles in ratios from 0 to 100% that were tightly embedded into the growing titanium oxide layer. After the surface bio-functionalization process, silver and zinc ions were released from the implant surfaces for at least 28 days resulting in antibacterial leaching activity against methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, the biofunctionalized implants generated reactive oxygen species, thereby contributing to antibacterial contact-killing. While implant surfaces containing up to 75% silver and 25% zinc nanoparticles fully eradicated both adherent and planktonic bacteria in vitro as well as in an ex vivo experiment performed using murine femora, solely zinc-bearing surfaces did not. The minimum inhibitory and bactericidal concentrations determined for different combinations of both types of ions confirmed the presence of a strong synergistic antibacterial behavior, which could be exploited to reduce the amount of required silver ions by two orders of magnitude (i.e., 120 folds). At the same time, the zinc bearing surfaces enhanced the metabolic activity of pre-osteoblasts after 3, 7, and 11 days. Altogether, implant biofunctionalization by PEO with silver and zinc nanoparticles is a fruitful strategy for the synthesis of multifunctional surfaces on orthopedic implants and the prevention of IAIs caused by antibiotic-resistant bacteria. STATEMENT OF SIGNIFICANCE: Implant-associated infections are becoming increasingly challenging to treat due to growing antibiotic resistance against antibiotics. Here, we propose an alternative approach where silver and zinc nanoparticles are simultaneously used for the biofunctionalization of rationally designed additively manufactured porous titanium. This combination of porous design and tailored surface treatment allows us to reduce the amount of required silver nanoparticles by two orders of magnitude, fully eradicate antibiotic-resistant bacteria, and enhance the osteogenic behavior of pre-osteoblasts. We demonstrate that the resulting implants display antibacterial activity in vitro and ex vivo against methicillin-resistant Staphylococcus aureus.

Controllable biodegradation and enhanced osseointegration of ZrO2-nanofilm coated Zn-Li alloy: In vitro and in vivo studies

Zinc and its alloys have emerged as a new research direction of biodegradable metals (BMs) due to the significant physiological functions of Zn²⁺ ions in human body. However, low inhibitory concentration threshold value to cause cytotoxicity by Zn²⁺ ions during in vitro study and delayed osseointegration in vivo are two key flaws for the bulk Zn-based BMs. To combat these issues, we constructed a barrier layer of ZrO₂ nanofilm on the surface of Zn-0.1(wt.%) Li alloy via atomic layer deposition (ALD). A decreased release of Zn²⁺ ions accompanied with accelerated release of Li⁺ ions was observed on account of galvanic coupling between the coating compositions and Zn-0.1Li alloy substrate. Cytocompatibility assay reflected that ZrO₂ nanofilm coated Zn-0.1Li alloy exhibited improved cell adhesion and viability. Histological analysis also demonstrated better in vivo osseointegration for the ZrO₂ nanofilm coated Zn-0.1Li alloy. Hence, the present study elucidated that the ALD of ZrO₂ nanofilm on Zn-based BMs can effectively promote osseointegration and control their biodegradation behavior. STATEMENT OF SIGNIFICANCE: Zn-Li binary alloy was reported recently to be the promising biodegradable metals with ultimate tensile strength over 500 MPa, yet the low inhibitory concentration threshold value to cause cytotoxicity by Zn²⁺ ions is the obstacle needed to be overcome. As a pilot study, a systematic investigation on the ZrO₂ nanofilm coated Zn-Li alloy, prepared by atomic layer deposition (ALD) technique, was conducted in the present study, which involved in the formation process, in vitro and in vivo degradation behavior as well as biocompatibility evaluation. We found a controllable corrosion rate and better in vivo osseointegration can be achieved by ZrO₂ nanofilm coating on Zn-Li alloy, which provides new insight into the surface modification on biodegradable Zn alloys for usage within bone.

Evolution of metallic cardiovascular stent materials: A comparative study among stainless steel, magnesium and zinc

A cardiovascular stent is a small mesh tube that expands a narrowed or blocked coronary artery. Unfortunately, current stents, regardless metallic or polymeric, still largely fall short to the ideal clinical needs due to late restenosis, thrombosis and other clinical complications. Nonetheless, metallic stents are preferred clinically thanks to their superior mechanical property and radiopacity to their polymeric counterparts. The emergence of bioresorbable metals opens a window for better stent materials as they may have the potential to reduce or eliminate late restenosis and thrombosis. In fact, some bioresorbable magnesium (Mg)-based stents have obtained regulatory approval or under trials with mixed clinical outcomes. Some major issues with Mg include the too rapid degradation rate and late restenosis. To mitigate these problems, bioresorbable zinc (Zn)-based stent materials are being developed lately with the more suitable degradation rate and better biocompatibility. The past decades have witnessed the unprecedented evolution of metallic stent materials from first generation represented by stainless steel (SS), to second generation represented by Mg, and to third generation represented by Zn. To further elucidate their pros and cons as metallic stent materials, we systematically evaluated their performances in vitro and in vivo through direct side-by-side comparisons. Our results demonstrated that tailored Zn-based material with proper configurations could be a promising candidate for a better stent material in the future.

R, T. S. N. SN. Cathodic electrodeposition of zinc–zinc phosphate–calcium phosphate composite coatings on pure iron for biodegradable implant applications

Faster degradation of iron based degradable implants in physiological media, particularly during the initial stages of implantation, poses difficulties in directly using them for clinical applications.

Bioactive glass coatings on metallic implants for biomedical applications

Metallic implant materials possess adequate mechanical properties such as strength, elastic modulus, and ductility for long term support and stability in vivo. Traditional metallic biomaterials, including stainless steels, cobalt-chromium alloys, and titanium and its alloys, have been the gold standards for load-bearing implant materials in hard tissue applications in the past decades. Biodegradable metals including iron, magnesium, and zinc have also emerged as novel biodegradable implant materials with different in vivo degradation rates. However, they do not possess good bioactivity and other biological functions. Bioactive glasses have been widely used as coating materials on the metallic implants to improve their integration with the host tissue and overall biological performances. The present review provides a detailed overview of the benefits and issues of metal alloys when used as biomedical implants and how they are improved by bioactive glass-based coatings for biomedical applications.

Biofunctionalization of metallic implants by calcium phosphate coatings

Metallic materials have been extensively applied in clinical practice due to their unique mechanical properties and durability. Recent years have witnessed broad interests and advances on surface functionalization of metallic implants for high-performance biofunctions. Calcium phosphates (CaPs) are the major inorganic component of bone tissues, and thus owning inherent biocompatibility and osseointegration properties. As such, they have been widely used in clinical orthopedics and dentistry. The new emergence of surface functionalization on metallic implants with CaP coatings shows promise for a combination of mechanical properties from metals and various biofunctions from CaPs. This review provides a brief summary of state-of-art of surface biofunctionalization on implantable metals by CaP coatings. We first glance over different types of CaPs with their coating methods and in vitro and in vivo performances, and then give insight into the representative biofunctions, i.e. osteointegration, corrosion resistance and biodegradation control, and antibacterial property, provided by CaP coatings for metallic implant materials.

In vitro evaluation of the ZX11 magnesium alloy as potential bone plate: Degradability and mechanical integrity

Considering the excellent biocompatibility of magnesium (Mg) alloys and their better mechanical properties compared to polymer materials, a wrought MgZnCa alloy with low contents of Zn (0.7 wt%) and Ca (0.6 wt%) (ZX11) was developed by twin roll casting (TRC) technology as potential biodegradable bone plates. The degradability and cell response of the ZX11 alloy were evaluated in vitro, as well as the mechanical integrity according to tensile tests after immersion. The results revealed a slightly higher degradation rate for the rolled ZX11, in comparison to that of the annealed one. It was mainly caused by the deformation twins and residual strain stored in the rolled alloy, which also seemed to promote localized degradation, thereby leading to a relatively fast deterioration in mechanical properties, especially the fracture strain/elongation. In contrast, after the annealing treatment, the alloy showed relatively lower strength, yet a lower degradation rate and quite stable elongation during the initial weeks of immersion were observed. More importantly, the ZX11 alloy, regardless of the annealing treatment, showed good in vitro cytocomopatibility regarding human primary osteoblasts. The assessment indicates the rolled alloy as a good choice for implantation sites where relatively high mechanical strength is needed during the early implantation, while the annealed alloy is a potential candidate for the sites which demand stable mechanical integrity during service. STATEMENT OF SIGNIFICANCE: The development of magnesium alloys as bone implants demands low degradation rate to gain not only a slow hydrogen evolution, but also a stable mechanical integrity during service. The present study develops a micro-alloyed MgZnCa alloy via twin roll casting (TRC) technology. It exhibited limited cytotoxicity, fairly low degradation rate and comparable strength to the reported Mg-1Zn-5Ca alloy which has been used as bone screws in clinical trials, indicating the great potential application as biodegradable bone implants. Furthermore, it showed good mechanical integrity during immersion to support the defect healing. Our results can aid other researchers to evaluate the mechanical integrity of biodegradable materials and to pay more attention to the effect of degradation behaviour on mechanical integrity of materials.

Bioinspired surface modification of orthopedic implants for bone tissue engineering

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