Current status on clinical applications of magnesium-based orthopaedic implants: A review from clinical translational perspective

Application of biodegradable implants in pediatric orthopedics: shifting from absorbable polymers to biodegradable metals

Over the past two decades, advances in pediatric orthopedics and closed reduction combined with percutaneous internal fixation techniques have led to significant growth in pediatric orthopedics surgery. Implants such as Kirschner-wires, cannulated screws and elastic stabilization intramedullary nails are commonly used in these procedures. However, traditional implants made of metal or inert materials are not absorbable, leading to complications that affect treatment outcomes. To address this issue, absorbable materials with excellent mechanical properties, good biocompatibility, and controlled degradation rates have been developed and applied in clinical practice. These materials include absorbable polymers and biodegradable metals. This article provides a comprehensive summary of these resorbable materials from a clinician's perspective. In addition, an in-depth discussion of the feasibility of their clinical applications and related research in pediatric orthopedics is included. We found that the applications of absorbable implants in pediatric orthopedics are shifting from absorbable polymers to biodegradable metals and emphasize that the functional characteristics of resorbable materials must be coordinated and complementary to the treatment in pediatric orthopedics.

Effect of diffusion in the model tissue on biocorrosion of Mg alloys

Current in vitro test fails in predicting the in vivo corrosion behaviour of Mg and its alloys. The diffusion of ions and gases through the tissue remains the critical factor influencing the discrepancy between the in vitro and in vivo corrosion rates. To overcome this, the in vitro model tissue with different diffusion rate was developed by the addition of appropriate concentrations of a thickener to the cell culture medium. The corrosion behaviour of WE43 and AZ31 alloys were analysed by immersion studies up to 28 days, electrochemical impedance spectroscopy, and potentiodynamic polarization studies. Both the immersion and electrochemical tests demonstrated the decrease in the corrosion rate of Mg alloys by the addition of thickener. The corrosion rate of WE43 decreased with increase in the thickener concentration whereas those of AZ31 was not obviously influenced by the thickener concentration. This low susceptibility of AZ31 against the change in diffusion rate might be attributed to its slower charge transfer process, as confirmed by the smaller Icorr and larger Rct values. Immersion in the model tissue reduced Ca and P concentrations in the insoluble salt layer on WE43. The lower susceptibility of AZ31 in the model tissue suggests the stability of AZ31 corrosion behaviour in the different tissue with different diffusion rate, which even derives from the difference in the individual patient's pathological condition. The developed model tissue provides an important information on the biocorrosion behaviour of various Mg alloys in consideration of biodegradable implant application.

A biodegradable magnesium alloy promotes subperiosteal osteogenesis via interleukin-10-dependent macrophage immunomodulation

In situ bone regeneration and vertical bone augmentation have been huge problems in clinical practice, always imposing a significant economic burden and causing patient suffering. Herein, MgZnYNd magnesium alloy rod implantation in mouse femur resulted in substantial subperiosteal new bone formation, with osteoimmunomodulation playing a pivotal role. Abundant macrophages were attracted to the subperiosteal new bone region and proved to be the most important regulation cells for bone regeneration. Periosteum stripping, macrophage depletion, and interleukin-10 (IL-10) blockade effectively diminished the MgZnYNd alloy-induced subperiosteal osteogenesis. Mechanistically, the degradation products of MgZnYNd alloy promoted M2 macrophage polarization and the secretion of anti-inflammatory cytokine IL-10, which enhanced periosteum-derived stem cells (PDSCs) osteogenesis through the JAK1-STAT3 pathway. An anti-IL-10 neutralizing antibody or STAT3 inhibitor significantly inhibited M2 macrophage-mediated osteogenic differentiation of PDSCs. Transcriptomics and proteomics revealed that periostin is the core regulator of PDSCs osteogenic differentiation. Furthermore, a novel clinical translation application of Mg-induced subperiosteal osteogenesis was developed, demonstrating its ability to preserve the height and width of the alveolar crest in rats and rabbits following tooth extraction. Collectively, these findings unveil a previously undefined role for Mg alloy-induced subperiosteal osteogenesis via macrophage-mediated osteoimmunomodulation, suggesting the therapeutic potential of magnesium alloy in bone regeneration and bone augmentation.

Bioabsorbable Magnesium-Based Materials Potential and Safety in Bone Surgery: A Systematic Review

The goal of this study was to evaluate the clinical outcomes, safety, and clinical applications of bioabsorbable magnesium-based materials for fixation in bone surgeries. The review was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. An initial search was performed on electronic databases, followed by manual and reference searches. The articles selected were evaluated for patient characteristics, biocompatibility, the need for revision surgery, bone union rates, and the incidence of gas formation associated with implant degradation. Out of the 631 initially identified articles, 8 studies including a total of 386 patients were included in the final qualitative analysis. The magnesium (Mg) group carried a lower rate of revision surgery (1/275) when compared to the titanium (Ti) group (18/111). A high rate of bone union was found in the Mg group and a low infection rate (3/275) was found in the Mg group. The serum level of Mg and calcium (Ca) were not found to be affected. Mg implants are applied in various orthopedic surgeries but they are not applied in in oral or maxillofacial surgeries. Mg implants appear to be a safe alternative for bone fixation and are resorbable. Future research into the application of Mg implants in bone fixation in different anatomical sites is essential to fully harness their potential benefits for patients.

Impact of pH and chloride content on the biodegradation of magnesium alloys for medical implants: An in vitro and phase-field study

The individual contributions of pH and chloride concentration to the corrosion kinetics of bioabsorbable magnesium (Mg) alloys remain unresolved despite their significant roles as driving factors in Mg corrosion. This study demonstrates and quantifies hitherto unknown separate effects of pH and chloride content on the corrosion of Mg alloys pertinent to biomedical implant applications. The experimental setup designed for this purpose enables the quantification of the dependence of corrosion on pH and chloride concentration. The in vitro tests conclusively demonstrate that variations in chloride concentration, relevant to biomedical applications, have a negligible effect on corrosion kinetics. The findings identify pH as a critical factor in the corrosion of bioabsorbable Mg alloys. A variationally consistent phase-field model is developed for assessing the degradation of Mg alloys in biological fluids. The model accurately predicts the corrosion performance of Mg alloys observed during the experiments, including their dependence on pH and chloride concentration. The capability of the framework to account for mechano-chemical effects during corrosion is demonstrated in practical orthopedic applications considering bioabsorbable Mg alloy implants for bone fracture fixation and porous scaffolds for bone tissue engineering. The strategy has the potential to assess the in vitro and in vivo service life of bioabsorbable Mg-based biomedical devices.

Controlled biodegradation of AZ31 alloy by chitosan/Fe-doped bioactive glass composite coating deposited via electrophoretic deposition for orthopaedic implants

The fast degradation rate of implants of AZ 31 alloy in the physiological body fluid is a critical problem for orthopaedic applications. The surface modification of AZ 31 can regulate fast degradation by depositing a biocompatible composite coating. Herein, chitosan/ iron-doped bioactive glass (Fe-doped BG) particles were deposited on AZ 31 via electrophoretic deposition (EPD) at optimized parameters (electric field 15 V/cm with 5 min as deposition time). Scanning electron microscopy (SEM) images revealed that the composite coating exhibited uniform morphology with a thickness of 32.5 ± 2.5 μm, while energy dispersive spectroscopy (EDS) and X-ray fluorescence (XRF) confirmed the presence of Fe, Ca, and Si in the composite coating. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of the functional groups of the composite coating. The composite coating exhibited the average roughness (Ra) of 1.32 ± 0.03 μm with a moderate hydrophilic nature (contact angle 68 ± 2.5°) which would be favorable for a cellular response. The composite coating exhibited 3 N adhesion strength evaluated by scratch test. The turbidity test revealed the antibacterial nature of the composite coating. The alkaline phosphate (ALP) activity was also assessed to confirm the bioactive nature of the composite coating. Electrochemical impedance spectroscopy (EIS) showed improved barrier properties by increased charge transfer resistance. The composite coating controlled the degradation rate of AZ 31 (best results compared to the literature) for orthopaedic applications.

Application and optimization of bioengineering strategies in facilitating tendon-bone healing

Tendon-bone insertion trauma is prevalent in both rotator cuff and anterior cruciate ligament injuries, which are frequently encountered conditions in the field of sports medicine. The main treatment for such injuries is reconstructive surgery. The primary determinant impacting this process is the graft's capacity to integrate with the bone tunnel. In recent years, researchers have attempted to use a variety of methods to facilitate tendon-bone healing after reconstructive surgery. Such as the implantation of biological materials, cytokines and the local application of permanently differentiated cells from various sources. However, there are limitations to the efficacy of one therapy alone in facilitating tendon-bone healing. Therefore, researchers are trying to combine strategies to overcome this conundrum. At present, most studies are based on biomaterial combined with other therapeutic strategies for tissue repair and regeneration. Biomaterials mainly include the application of bioengineering scaffolds, hydrogels and bioabsorbable interference screws. By conducting a thorough review of relevant literature, this study provides a comprehensive overview of the present research progress in enhancing tendon-bone healing using biomaterials. Additionally, it explores the potential benefits of combining biomaterials with other approaches to promote tendon-bone healing. The ultimate goal is to offer insights for future basic research endeavors and establish a solid groundwork for advancing clinical applications in the near future.

Structural Design of Biodegradable Mg Gastrointestinal Anastomosis Staples for Corrosion and Mechanical Strength Analysis

Magnesium (Mg) and its alloys, as next-generation materials for anastomosis staples, offer promising advantages such as biodegradability, biocompatibility, and reduced risk of long-term complications compared to traditional titanium materials. However, the performance of biodegradable staples is highly dependent on their structure. In this study, a biodegradable high-purity (HP) Mg staple with an optimized structure intended for small intestine anastomosis was developed and evaluated in vitro. The designed staple, with a diameter of 0.3 mm, featured an interior angle of 100° and a height of 3.8 mm. This design exhibited a maximum effective stress of approximately 170 MPa and an effective strain of 1.63. The staple could maintain structural integrity without fracture after 7 days of in vitro corrosion testing and exhibited a relatively high burst pressure of approximately 54.70 ± 2.51 mmHg. These findings indicate that the newly designed HP Mg staple combines superior corrosion resistance and anastomosis strength, confirming its potential for clinical application.

Artificial Bone Materials for Infected Bone Defects: Advances in Antimicrobial Functions

Infected bone defects, caused by bacterial contamination following disease or injury, result in the partial loss or destruction of bone tissue. Traditional bone transplantation and other clinical approaches often fail to address the therapeutic complexities of these conditions effectively. In recent years, advanced biomaterials have attracted significant attention for their potential to enhance treatment outcomes. This review explores the pathogenic mechanisms underlying infected bone defects, including biofilm formation and bacterial internalization into bone cells, which allow bacteria to evade the host immune system. To control bacterial infection and facilitate bone repair, we focus on antibacterial materials for bone regeneration. A detailed introduction is given on intrinsically antibacterial materials (e.g., metal alloys, oxide materials, carbon-based materials, hydroxyapatite, chitosan, and Sericin). The antibacterial functionality of bone repair materials can be enhanced through strategies such as the incorporation of antimicrobial ions, surface modification, and the combined use of multiple materials to treat infected bone defects. Key innovations discussed include biomaterials that release therapeutic agents, functional contact biomaterials, and bioresponsive materials, which collectively enhance antibacterial efficacy. Research on the clinical translation of antimicrobial bone materials has also facilitated their practical application in infection prevention and bone healing. In conclusion, advancements in biomaterials provide promising pathways for developing more biocompatible, effective, and personalized therapies to reconstruct infected bone defects.

Versatile application of magnesium-related bone implants in the treatment of bone defects

Magnesium-related bone implants have garnered significant attention in the treatment of bone defects. The applications of magnesium in promoting bone repair mainly include degradable magnesium-based scaffolds owing to its special physical properties and composite materials modified by magnesium ions because of its biological activity. Although numerous studies have confirmed the unique application advantages and efficacy of magnesium in promoting bone repair, some obvious shortcomings persist, including the rapid degradation of magnesium-based scaffolds. In this review, the deficiencies of magnesium and its alloys in the construction of orthopedic implants and their key influencing factors were summarized; furthermore, some advanced improvement schemes were summarized and analyzed. Additionally, the application strategies of magnesium-modified bone implants are summarized and discussed. Lastly, this review incorporates the latest research and discoveries on magnesium in orthopedic science, comprehensively exploring the mechanism of magnesium's role in the complex microenvironment of bone defects from multiple dimensions. This paper provides a comprehensive summary and analysis of cutting-edge concepts in the design and development of magnesium-based bone implants, considering various perspectives such as the physical properties and biological functions of magnesium.

Degradation products of magnesium implant synergistically enhance bone regeneration: Unraveling the roles of hydrogen gas and alkaline environment

Biodegradable magnesium (Mg) implant generally provides temporary fracture fixation and facilitates bone regeneration. However, the exact effects of generated Mg ions (Mg2+), hydrogen gas (H2), and hydroxide ions (OH-) by Mg degradation on enhancing fracture healing are not fully understood. Here we investigate the in vivo degradation of Mg intramedullary nail (Mg-IMN), revealing the generation of these degradation products around the fracture site during early stages. Bulk-RNA seq indicates that H2 and alkaline pH increase periosteal cell proliferation, while Mg2+ may mainly enhance extracellular matrix formation and cell adhesion in the femur ex vivo. In vivo studies further reveal that H2, Mg2+ and alkaline pH individually generate comparable effects to the enhanced bone regeneration in the Mg-IMN group. Mechanistically, the degradation products elevate sensory calcitonin gene-related peptide (CGRP) and simultaneously suppress adrenergic factors in newly formed bone. H2 and Mg2+, instead of alkaline pH, increase CGRP synthesis and inhibit adrenergic receptors. Our findings, for the first time, elucidate that Mg2+, H2, and alkaline pH environment generated by Mg-IMN act distinctly and synergistically mediated by the skeletal interoceptive regulation to accelerate bone regeneration. These findings may advance the understanding on biological functions of Mg-IMN in fracture repair and even other bone disorders.

In Vivo Degradation Behavior of AZ91 Magnesium Alloy: Comprehensive Microstructural and Crystallographic Characterization by TEM and NBED

Magnesium alloys have attracted significant attention in recent years as biodegradable metals. However, their degradation mechanisms in vivo remain insufficiently understood. The present work investigates the degradation mechanism of AZ91 magnesium alloy in a critical-size rat defect model over an 8-week period in vivo, employing advanced characterization techniques such as transmission electron microscopy (TEM) and nanobeam electron diffraction (NBED). The degradation layer is observed to consist of three distinct sub-layers: a dense and compact poor crystallinity layer (PCL) layer primarily composed of calcium phosphate, a loose and porous amorphous layer (AL) of magnesium/calcium phosphate, and a hybrid layer (HL)layer containing degradation channels and composed of magnesium/calcium phosphate, layered double hydroxide (LDH), and magnesium hydroxide. The corrosion resistance of AZ91 is enhanced by the presence of the compact PCL layer, the uniform distribution of the Mg17Al12 phase, and the formation of impervious LDH at the corrosion interface. The degradation is primarily driven by micro-galvanic corrosion, which is influenced by the interaction between the Mg matrix and the Mg17Al12 phase. These findings provide critical insights into the stable degradation mechanism of Mg-Al alloys in vivo, advancing the development of biodegradable magnesium-based implants.

Development of a Zeolitic Imidazolate Framework Based Superhydrophobic Surface with Abrasion Resistance, Corrosion Protection, and Anti-icing

Herein, a superhydrophobic surface was designed and fabricated based on the "lotus effect" construction mechanism. The zeolitic imidazolate framework (ZIF-90) micro-nanoparticles were initially synthesized via a one-pot method, combined with long-chain stearic acid (STA), and subsequently embedded in polyvinyl butyral (PVB) to form a superhydrophobic surface at room temperature. The superhydrophobic surface demonstrated mechanical stability and retained its superhydrophobicity with a water contact angle (CA) greater than 150°, even at a wear distance of 400 cm. The composite coating formed by applying this superhydrophobic surface to magnesium (Mg) alloy exhibited a high corrosion potential (Ecorr = -0.86 V) and a low corrosion current density (icorr = 3.66 × 10-12 A·cm-2) compared to the uncoated Mg substrate (Ecorr = -1.53 V, icorr = 1.14 × 10-4 A·cm-2), indicating that the coating effectively enhances the corrosion resistance of the substrate. Notably, the superhydrophobic composite coating demonstrated corrosion resistance durability with a high charge transfer resistance (Rct = 5.12 × 109 Ω·cm2) after 5 days of immersion in 3.5 wt % NaCl aqueous solution. In addition, the as-prepared superhydrophobic surface also displayed excellent performance in self-cleaning and anti-icing. We believe that this work can facilitate the application of ZIFs on superhydrophobic surfaces and provide a new approach for metal corrosion protection.

Effect of Hydrothermal Coatings of Magnesium AZ31 Alloy on Osteogenic Differentiation of hMSCs: From Gene to Protein Analysis

An Mg-based alloy device manufactured via a superplastic forming process (Mg-AZ31+SPF) and coated using a hydrothermal method (Mg AZ31+SPF+HT) was investigated as a method to increase mechanical and osteointegration capability. The cell viability and osteointegrative properties of alloy-derived Mg AZ31+SPF and Mg AZ31+SPF+HT extracts were investigated regarding their effect on human mesenchymal stem cells (hMSCs) (maintained in basal (BM) and osteogenic medium (OM)) after 7 and 14 days of treatment. The viability was analyzed through metabolic activity and double-strand DNA quantification, while the osteoinductive effects were evaluated through qRT-PCR, osteoimage, and BioPlex investigations. Finally, a preliminary liquid mass spectrometry analysis was conducted on the secretome of hMSCs. Biocompatibility analysis revealed no toxic effect on cells' viability or proliferation during the experimental period. A modulation effect was observed on the osteoblast pre-commitment genes of hMSCs treated with Mg-AZ31+SPF+HT in OM, which was supported by mineralization nodule analysis. A preliminary mass spectrometry investigation highlighted the modulation of protein clusters involved in extracellular exosomes, Hippo, and the lipid metabolism process. In conclusion, our results revealed that the Mg AZ31+SPF+HT extracts can modulate the canonical and non-canonical osteogenic process in vitro, suggesting their possible application in bone tissue engineering.

Overview of porous magnesium-based scaffolds: development, properties and biomedical applications

Magnesium (Mg) and its alloys are revolutionizing the field of interventional surgeries in the medical industry. Their high biocompatibility, biodegradability, and a similar elastic modulus to natural bone make porous Mg-based structures potential candidates for orthopedic implants and tissue engineering scaffolding. However, fabricating and machining porous Mg-based structures is challenging due to their complexity and difficulties in achieving uniform or gradient porosity. This review aims to thoroughly explore various fabrication procedures used to create metallic scaffolds, with a specific focus on those made from Mg-based alloys. Both traditional manufacturing techniques, including the directional solidification of metal-gas eutectic technique, pattern casting, methods using space holders, and modern fabrication methods, which are based on additive manufacturing, are covered in this review article. Furthermore, the paper highlights the most important findings of recent studies on Mg-based scaffolds in terms of their microstructure specifications, mechanical properties, degradation and corrosion behavior, antibacterial activity, and biocompatibility (both in vivo and in vitro). While extensive research has been conducted to optimize manufacturing parameters and qualities of Mg-based scaffolds for use in biomedical applications, specifically for bone tissue engineering applications, further investigation is needed to fabricate these scaffolds with specific properties, such as high resistance to corrosion, good antibacterial properties, osteoconductivity, osteoinductivity, and the ability to elicit a favorable response from osteoblast-like cell lines. The review concludes with recommendations for future research in the field of medical applications.

Internal fixation with biodegradable high purity magnesium screws in the treatment of ankle fracture

Background

Metal plates and screws are widely used as internal fixations in the treatment of ankle fracture. However, there are many disadvantages such as "stress shielding" effect and the need for secondary surgical removal, which potentially affected the blood supply around the fracture site. In recent years, many studies confirmed that the biodegradable high purity magnesium (Mg) screws exhibited sufficient mechanical strength with adequate degradation rate for effective bone healing, avoiding the need for implant removal operations.

Method

We conducted a prospective study on patients with ankle fractures treated at Affiliated Zhongshan Hospital of Dalian University between January 2020 and January 2021. Twenty-four patients (twelve patients for each group) with ankle fractures were treated with high purity Mg screws or conventional titanium alloy plates and screws. Hematological examinations were performed in the early postoperative period, X-ray examinations were performed in the long-term postoperative follow-up. Postoperative complications, including infection, failure of internal fixation and malunion, were recorded during the follow-up. The visual analogue scale (VAS) was used to evaluate postoperative pain perceived by the patients, and the American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot scoring system was used to evaluate their postoperative ankle function.

Results

All patients achieved good fracture alignment, and imaging examination showed that the biodegradable high purity Mg screws degraded gradually without breakage or displacement. None of the patients experienced infection, failure of internal fixation, malunion or other complications in both groups.

Conclusion

The results showed that biodegradable high purity Mg screws could be effectively used in the clinical treatment of ankle fractures, ensuring safety and satisfactory postoperative functional recovery.The translational potential of this article: The biodegradable high purity Mg screws could provide sufficient mechanical strength and fixation stability for ankle fracture. Our study extended the clinical application of the biodegradable high purity Mg screws for fracture.

Implantable Dental Barrier Membranes as Regenerative Medicine in Dentistry: A Comprehensive Review

BACKGROUND

Periodontitis and bone loss in the maxillofacial and dental areas pose considerable challenges for both functional and aesthetic outcomes. To date, implantable dental barrier membranes, designed to prevent epithelial migration into defects and create a favorable environment for targeted cells, have garnered significant interest from researchers. Consequently, a variety of materials and fabrication methods have been explored in extensive research on regenerative dental barrier membranes.

METHODS

This review focuses on dental barrier membranes, summarizing the various biomaterials used in membrane manufacturing, fabrication methods, and state-of-the-art applications for dental tissue regeneration. Based on a discussion of the pros and cons of current membrane strategies, future research directions for improved membrane designs are proposed.

RESULTS AND CONCLUSION

To endow dental membranes with various biological properties that accommodate different clinical situations, numerous biomaterials and manufacturing methods have been proposed. These approaches provide theoretical support and hold promise for advancements in dental tissue regeneration.

Investigating the Effect of Thickener Concentrations on the Corrosion Behavior of Pure Mg

Magnesium (Mg) and its alloys are promising biodegradable implant materials due to their biocompatibility and ease of corrosion in physiological environment. In the tissue, diffusion of ions and gas released by Mg corrosion reaction will be interfered by extracellular matrix and cells, which may retard the corrosion reaction. Therefore, in the present study, we developed the in vitro model tissue with different diffusion rates to understand the effect of diffusion on the Mg corrosion. A thickener called gellan gum was added to the cell culture medium at appropriate concentrations to simulate tissues with different diffusion rates. The immersion study up to 28 days and the electrochemical studies were performed to evaluate the Mg corrosion behavior. The pure Mg specimens without thickener showed the highest corrosion rate in both immersion and electrochemical tests. The highest amount of insoluble salt layer with the lowest Mg and highest O concentrations were deposited on the specimen surface without thickener. The microfocus X-ray computed tomography (μCT) analysis confirmed these findings, showing the lowest remaining volume for specimens without thickener. There is an impediment of ion diffusion in the model tissue with increased thickener concentrations, thereby decreasing the corrosion rate. The corrosion rate for 0.2-0.3 wt. % thickener matched in the range of reported in vivo results. Hence, this model proves to be an effective tool for investigating biodegradation and understanding the mechanisms and controlling factors of this phenomenon.

A cross-linked coating loaded with antimicrobial peptides for corrosion control, early antibacterial, and sequential osteogenic promotion on a magnesium alloy as orthopedic implants

Magnesium (Mg)-based alloys have been recognized as desirable biodegradable materials for orthopedic implants. However, their clinical application has been limited by rapid degradation rates, insufficient antibacterial and osteogenic-promotion properties. Herein, a MgF2 priming layer was first constructed on AZ31 surface. Then, dopamine and polyphenols (EGCG) were cross-linked onto this AZ31-F surface to promote osteogenesis and further enhance corrosion protection, followed by chemical grafting of antimicrobial peptides (AMPs) via Michael-addition and Schiff-base reaction to confer antibacterial properties. In vitro electrochemical corrosion tests showed that icorr of AZ31-FE/AMPs (4.36×10-7 A/cm2) is two orders of magnitude lower than that of AZ31 (4.17×10-5 A/cm2). In vitro immersion degradation showed that AZ31-FE/AMPs exhibited the lowest hydrogen release (2.38 mL) after 400 h immersion with the lowest hydrogen evolution rate among them. Further, AZ31-FE/AMPs displayed inhibitory effects against S. aureus and E. coil in the initial stage and even after 7 days immersion in PBS (antibacterial rate > 85 %). AZ31-FE/AMPs promoted ALP secretion and calcium nodule formation in MC3T3-E1 cells. Transcriptome sequencing results indicated that osteogenic promotion mechanism of AZ31-FE/AMPs in MC3T3-E1 may involve the PI3K-Akt signalling pathway. Further, AZ31-FE/AMPs enhanced new bone formation when implanted in a rat femoral bone defect model. This coating strategy addresses initial antibacterial and later osteogenesis needs based on the corrosion control, which is crucial for the surface design of Mg-based implants. STATEMENT OF SIGNIFICANCE: It is critical for magnesium-based orthopedic implants to achieve sequential functions in the bone repair process while controlling an appropriate degradation rate. A MgF2 priming layer/phenolic-amine grafted AMPs (antimicrobial peptides) duplex coating was constructed on AZ31 surface in this study. The MgF2 layer provided a basic corrosion protection to magnesium substrate, and dopamine and polyphenols (EGCG) were then cross-linked to the MgF2 pretreated AZ31 to promote osteogenesis and enhance corrosion resistance, followed by chemical grafting of AMPs to confer antibacterial property. This strategy effectively meets the initial need for infection resistance and later osteogenic promotion on the basis of controlling the substrate corrosion rate, thus holding significant implications for the surface design of magnesium-based implants.

Structural Evolution of an Optimized Highly Interconnected Hierarchical Porous Mg Scaffold under Dynamic Flow Challenges

The development of Mg and its alloys as bone screws has garnered significant attention due to their exceptional biocompatibility and unique biodegradability. Notably, the controlled release of Mg2+ ions during degradation can positively influence bone fracture healing. The advantages of Mg raise appeal for application in bone tissue engineering. However, porous Mg scaffolds, while offering high surface areas, face challenges in maintaining slow degradation rates and preserving interconnectivity, which are crucial features for tissue ingrowth. To address these issues, this study introduces a highly interconnected hierarchical porous Mg scaffold and investigates its degradation behavior within a bioreactor, simulating body fluid flow rates to mimic the in vivo degradation performance at different implantation sites. The focus lies on elucidating the evolution of the porous structure, particularly the impact of degradation behavior on scaffold interconnectivity. Our findings reveal that the initial high interconnectivity of the scaffold is significantly influenced by the flow rate. The dynamic fluid flow modulates the transport of degradation byproducts and the deposition patterns. At lower flow rates, Mg2+ ions accumulate within pores, leading to the formation of substantial deposits that directly reduce porosity. Specifically, after 42 days, porosities decreased to 68.80 ± 2.31, 58.52 ± 2.53, and 41.25 ± 2.82% at flow rates of 2.0, 1.0, and 0.5 mL/min, respectively. This porosity reduction and pore space occlusion by deposits sequentially hinder the interconnectivity. The magnitude of decreased porosity could be used to evaluate the ability of the microarchitecture to maintain scaffold interconnectivity. Meanwhile, the long-term degradation deposition behavior of the highly interconnected hierarchical porous Mg scaffold potentially revealed the structural integrity loss from the original design to its in vivo degraded structure at different body fluid flow rates. The present work might bring valuable insight into the design of pore strut and interconnectivity characterization methods for the progress of a high-performance tissue engineering scaffold.

Next-Generation Approaches for Biomedical Materials Evaluation: Microfluidics and Organ-on-a-Chip Technologies

Biological evaluation of biomedical materials faces constraints imposed by the limitations of traditional in vitro and animal experiments. Currently, miniaturized and biomimetic microfluidic technologies and organ-on-chip systems have garnered widespread attention in the field of drug development. However, their exploration in the context of biomedical material evaluation and medical device development remains relatively limited. In this review, a summary of existing biological evaluation methods, highlighting their respective advantages and drawbacks is provided. The application of microfluidic technologies in the evaluation of biomedical materials, emphasizing the potential of organ-on-chip systems as highly biomimetic in vitro models in material evaluation is then focused. Finally, the challenges and opportunities associated with utilizing organ-on-chip systems to evaluate biomedical materials in the field of material evaluation are discussed. In conclusion, the integration of advanced microfluidic technologies and organ-on-chip systems presents a potential paradigm shift in the biological assessment of biomedical materials, offering the prospective of more accurate and predictive in vitro models in the development of medical devices.

Prospects of osteosynthesis with fixators based on magnesium alloys, mechanical and physiological properties. The state of the problem at the current stage

OBJECTIVE

Aim: The aim of this work is to analyze the available scientific information regarding to the prospects of metal-osteosynthesis with biodegradable fixators based on magnesium alloys.

PATIENTS AND METHODS

Materials and Methods: A set of general and special methods of scientific knowledge are used in the article. Search and analysis of full-text articles and scientific publications - carried out in databases of systematic reviews of MEDLINE, PubMed, Web of Science, Google Scholar, Scopus.

CONCLUSION

Conclusions: Magnesium-based implants contribute to a tissue regeneration and healing during degradation and do not require removal. This allows you to avoid the second surgical intervention and reduces treatment costs. That is why the development and implementation of biodegradable fixators for osteosynthesis is of great importance.

The Biological Effects of Magnesium-Based Implants on the Skeleton and Their Clinical Implications in Orthopedic Trauma Surgery

Magnesium (Mg)-based implants have evolved as a promising innovation in orthopedic trauma surgery, with the potential to revolutionize the treatment of bone diseases, including osteoporotic fractures and bone defects. Available clinical studies mostly show excellent patient outcomes of resorbable Mg-based implants, without the need for subsequent implant removal. However, the occurrence of radiolucent zones around Mg-based implants seems to be a noticeable drawback for a more widespread clinical use. Mechanistically, both in vivo and in vitro studies demonstrated beneficial effects on the formation of new bone, a unique characteristic of Mg-based implants. In this regard, Mg has been shown to exert pleiotropic functions on osteogenic differentiation and migration of osteoblasts and their precursors. Additionally, collective evidence suggests that Mg-based implants promote angiogenesis in newly formed bone and exert immunomodulatory effects in the bone microenvironment. Likewise, Mg-based implants and their degradation products were shown to inhibit bone resorption by impairing osteoclastogenesis. The purpose of this review is to provide a state-of-the-art summary of the clinical and basic science evidence regarding the performance of currently used Mg-based implants. In addition to the status of in vivo and in vitro research and clinical applications, future challenges and perspectives of Mg-based orthopedic implants are discussed.

Biomaterials for bone tissue engineering: achievements to date and future directions

Advancement in medicine and technology has resulted into prevention of countless deaths and increased life span. However, it is important to note that, the modern lifestyle has altered the food habits, witnessed increased life-style stresses and road accidents leading to several health complications and one of the primary victims is the bone health. More often than ever, healthcare professionals encounter cases of massive bone fracture, bone loss and generation of critical sized bone defects. Surgical interventions, through the use of bone grafting techniques are necessary in such cases. Natural bone grafts (allografts, autografts and xenografts) however, have major drawbacks in terms of delayed rehabilitation, lack of appropriate donors, infection and morbidity that shifted the focus of several investigators to the direction of synthetic bone grafts. By employing biomaterials that are based on bone tissue engineering (BTE), synthetic bone grafts provide a more biologically acceptable approach to establishing the phases of bone healing. In BTE, various materials are utilized to support and enhance bone regeneration. Biodegradable polymers like poly-(lactic acid), poly-(glycolic acid), and poly-(ϵ-caprolactone) are commonly used for their customizable mechanical properties and ability to degrade over time, allowing for natural bone growth. PEG is employed in hydrogels to promote cell adhesion and growth. Ceramics, such as hydroxyapatite and beta-tricalcium phosphate (β-TCP) mimic natural bone mineral and support bone cell attachment, withβ-TCP gradually resorbing as new bone forms. Composite materials, including polymer-ceramic and polymer-glasses, combine the benefits of both polymers and ceramics/glasses to offer enhanced mechanical and biological properties. Natural biomaterials like collagen, gelatin, and chitosan provide a natural matrix for cell attachment and tissue formation, with chitosan also offering antimicrobial properties. Hybrid materials such as decellularized bone matrix retain natural bone structure and biological factors, while functionalized scaffolds incorporate growth factors or bioactive molecules to further stimulate bone healing and integration. The current review article provides the critical insights on several biomaterials that could yield to revolutionary improvements in orthopedic medical fields. The introduction section of this article focuses on the statistical information on the requirements of various bone scaffolds globally and its impact on economy. In the later section, anatomy of the human bone, defects and diseases pertaining to human bone, and limitations of natural bone scaffolds and synthetic bone scaffolds were detailed. Biopolymers, bioceramics, and biometals-based biomaterials were discussed in further depth in the sections that followed. The article then concludes with a summary addressing the current trends and the future prospects of potential bone transplants.

Dynamic-Cross-Linked, Regulated, and Controllable Mineralization Degree and Morphology of Collagen Biomineralization

The cross-linking process of collagen is one of the more important ways to improve the mineralization ability of collagen. However, the regulatory effect of dynamic cross-linking on biomineralization in vitro remains unclear. Dynamic-cross-linked mineralized collagen under different cross-linking processes, according to the process of cross-linking and mineralization of natural bone, was prepared in this study. Mineralization was performed for 12 h at 4, 8, and 12 h of collagen cross-linking. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the characteristics of dynamic-cross-linked mineralization in terms of morphological transformation and distribution. Fourier transform infrared spectroscopy (FTIR) analysis showed the crystallinity characteristics of the hydroxyapatite (HA) crystal formation. Pre-cross-linked dynamic-cross-linked mineralization refers to the process of cross-linking for a period of time and then side cross-linked mineralization. The mineral content, enzyme stability, and mechanical properties of mineralized collagen were improved through a dynamic cross-linking process of pre-cross-linking. The swelling performance was reduced through the dynamic cross-linking process of pre-cross-linking. This study suggests that the dynamic cross-linking process through pre-cross-linking could make it easier for minerals to permeate and deposit between collagen fibers, improve mineralization efficiency, and, thus, enhance the mechanical strength of biomineralization. This study can provide new ideas and a theoretical basis for designing mineralized collagen scaffolds with better bone repair ability.

Surface engineering of orthopedic implants for better clinical adoption

Musculoskeletal disorders are on the rise, and despite advances in alternative materials, treatment for orthopedic conditions still heavily relies on biometal-based implants and scaffolds due to their strength, durability, and biocompatibility in load-bearing applications. Bare metallic implants have been under scrutiny since their introduction, primarily due to their bioinert nature, which results in poor cell-material interaction. This challenge is further intensified by mechanical mismatches that accelerate failure, tribocorrosion-induced material degradation, and bacterial colonization, all contributing to long-term implant failure and posing a significant burden on patient populations. Recent efforts to improve orthopedic medical devices focus on surface engineering strategies that enhance the interaction between cells and materials, creating a biomimetic microenvironment and extending the service life of these implants. This review compiles various physical, chemical, and biological surface engineering approaches currently under research, providing insights into their potential and the challenges associated with their adoption from bench to bedside. Significant emphasis is placed on exploring the future of bioactive coatings, particularly the development of smart coatings like self-healing and drug-eluting coatings, the immunomodulatory effects of functional coatings and biomimetic surfaces to tackle secondary infections, representing the forefront of biomedical surface engineering. The article provides the reader with an overview of the engineering approaches to surface modification of metallic implants, covering both clinical and research perspectives and discussing limitations and future scope.

Failure analysis and design improvement of retrieved plates from revision surgery

Background

The fracture of bone plate can cause considerable pain for the patient and increase the burden on the public finances. This study aims to explore the failure mechanism of 49 plates retrieved from revision surgery and introduce pure magnesium (Mg) block to improve the biomechanical performance of the plate via decreasing the stiffness and to stimulate the biological response of the plate potentially by the degradation of Mg block.

Methods

The morphological analysis and component analysis of the plates were conducted to determine the fracture reason of the plates combining the clinical data. According to the structural feature, the 49 retrieved plates were divided into: traditional plate (TP), asymmetrical plate (AP), reconstructive plate (RP) and central enhancement plate (CEP), and their structure features are normalized in a commercial plate, respectively. The biomechanical performance of the plates was evaluated using a validated femoral finite element model. A block of pure Mg with a thickness of 1 mm, 1.5 mm and 2 mm was also incorporated into the CEP to be assessed.

Results

The results indicated that the retrieved plates mainly failed due to fatigue fracture induced by delayed union or nonunion (44/49), and using pure titanium plates in weight-bearing areas increased the risk of fracture compared with Ti alloy plates when the delayed union or nonunion occurred. The TP demonstrated the highest compression resistance and bending resistance, while CEP had the highest rotational resistance. As the thickness of the Mg block was increased, the stress on the plate in compression decreased, but the stress in rotation increased. The plate with a 1.5 mm Mg block demonstrated excellent compression resistance, bending resistance and rotational resistance.

Conclusion

Fatigue fracture resulting from the delayed union or nonunion is the primary failure reason of plates in clinic. The incorporation of Mg block into plate improves the biomechanical performance and has the potential to promote bone healing. The plate with a 1.5 mm Mg block may be suitable for use in orthopaedics.

The translational potential of this article

This study assessed the failure mechanism of retrieved bone plates and used this data to develop a novel plate incorporating a 1.5 mm block of pure Mg block at the position corresponding to the fracture line. The novel plate exhibited excellent compression resistance, bending resistance and rotational resistance due to the alleviation of stress concentrations. The Mg block has the potential to degrade over time to promote fracture healing and prevents fatigue fracture of plates.

Safety and efficacy of Mg-Dy membrane with poly-L-lactic acid coating for guided bone regeneration

The aim of this study was to evaluate safety and efficacy of a poly-L-lactic acid (PLLA)-coated magnesium (Mg)-Dysprosium (Dy) membrane in guided bone regeneration (GBR) using a rabbit calvarium model. The microstructure of the Mg-Dy membrane surface and thickness of the PLLA coating were examined. In vitro degradation and cytotoxicity test was conducted. The in vivo study used 24 white male rabbits with two 8 mm-diameter defects created on the calvaria; 12 defects were randomly assigned per group: (1) Negative control, (2) positive control, (3) uncoated Mg, and (4) PLLA-coated Mg group. Specimens were harvested at 4, 8, and 12 weeks postoperatively for radiological, histological, and histomorphometric analyses. The PLLA-coated Mg-Dy membrane showed a low degree of degradation, indicating that the coating exerted a protective effect. In the cytotoxicity test, no deformed or degenerated cells were observed. In the in vivo study, radiographic and histomorphometric analyses indicated favorable new bone formation and maintenance of the graft material for PLLA-coated Mg group. PLLA-coated Mg group, compared to the uncoated counterpart, restored the bony contour more completely, without inducing significant inflammatory response. Our results support the safety and efficacy of PLLA-coated Mg-Dy membranes for GBR both in vitro and in vivo.

Magnesium-Titanium Alloys: A Promising Solution for Biodegradable Biomedical Implants

Magnesium (Mg) has attracted considerable attention as a biodegradable material for medical implants owing to its excellent biocompatibility, mitigating long-term toxicity and stress shielding. Nevertheless, challenges arise from its rapid degradation and low corrosion resistance under physiological conditions. To overcome these challenges, titanium (biocompatibility and corrosion resistance) has been integrated into Mg. The incorporation of titanium significantly improves mechanical and corrosion resistance properties, thereby enhancing performance in biological settings. Mg-Ti alloys are produced through mechanical alloying and spark plasma sintering (SPS). The SPS technique transforms powder mixtures into bulk materials while preserving structural integrity, resulting in enhanced corrosion resistance, particularly Mg80-Ti20 alloy in simulated body fluids. Moreover, Mg-Ti alloy revealed no more toxicity when assessed on pre-osteoblastic cells. Furthermore, the ability of Mg-Ti-based alloy to create composites with polymers such as PLGA (polylactic-co-glycolic acid) widen their biomedical applications by regulating degradation and ensuring pH stability. These alloys promote temporary orthopaedic implants, offering initial load-bearing capacity during the healing process of fractures without requiring a second surgery for removal. To address scalability constraints, further research is necessary to investigate additional consolidation methods beyond SPS. It is essential to evaluate the relationship between corrosion and mechanical loading to confirm their adequacy in physiological environments. This review article highlights the importance of mechanical characterization and corrosion evaluation of Mg-Ti alloys, reinforcing their applicability in fracture fixation and various biomedical implants.

Hydrogen-releasing magnesium hydrogel mitigates post laminectomy epidural fibrosis through inhibition of neutrophil extracellular traps

Epidural fibrosis is a primary contributor to the failure of laminectomy surgeries, leading to the development of failed back surgery syndrome (FBSS). Post-laminectomy, neutrophils infiltrate the surgical site, generating neutrophil extracellular traps (NETs) that contribute to epidural fibrosis. Reactive oxygen species (ROS) play a pivotal role in mediating NETs formation. Molecular hydrogen, recognized for its selective antioxidant properties and biosafety, emerges as a potential therapeutic gas in suppressing epidural fibrosis. In this study, we developed an in-situ hydrogen release hydrogel that inhibits the formation of NETs and mitigates epidural scarring. Biodegradable magnesium (Mg) microspheres served as a hydrogen source, coated with PLGA to regulate hydrogen release. These microspheres (Mg@PLGA) were then incorporated into a PLGA-PEG-PLGA thermosensitive hydrogel (Mg@PLGA@Gel), providing a surgical implant for sustained, long-term hydrogen release. In vitro experiments confirmed the biocompatibility of the system, demonstrating that hydrogen produced by Mg@PLGA effectively neutralizes neutrophil intracellular ROS and inhibits NETs formation. Histological analyses, including H&E staining, MRI, Masson staining, and immunohistochemistry, collectively indicate that Mg@PLGA@Gel is biocompatible and effectively inhibits epidural fibrosis post-laminectomy. Furthermore, Mg@PLGA@Gel inhibits ROS accumulation and NETs formation at the surgical site. These findings suggest that Mg@PLGA@Gel ensures continuous, therapeutic hydrogen concentration, providing relief from epidural fibrosis in a laminectomy mouse model. STATEMENT OF SIGNIFICANCE.

SLM Magnesium Alloy Micro-Arc Oxidation Coating

In this study, we utilized Selective Laser Melting (SLM) technology to fabricate a magnesium alloy, and subsequently subject it to micro-arc oxidation treatment. We analyzed and compared the microstructure, elemental distribution, wetting angle, and corrosion resistance of the SLM magnesium alloy both before and after the micro-arc oxidation process. The findings indicate that the SLM magnesium alloy exhibits surface porosity defects ranging from 2% to 3.2%, which significantly influence the morphology and functionality of the resulting film layer formed during the micro-arc oxidation process. These defects manifest as pores on the surface, leading to an uneven distribution of micropores with varying sizes across the layer. The surface roughness of the 3D-printed magnesium alloy exhibits a high roughness value of 180 nanometers. The phosphorus (P) content is lower within the film layer compared to the surface, suggesting that the Mg3(PO4)2 phase predominantly resides on the surface, whereas the interior is primarily composed of MgO. The micro-arc oxidation process enhances the hydrophilicity and corrosion resistance of the SLM magnesium alloy, thereby potentially endowing it with bioactivity. Additionally, the increased surface roughness post-treatment promotes cell proliferation. However, certain inherent defects present in the SLM magnesium alloy samples negatively impact the improvement of their corrosion resistance.

Metal-organic frameworks in oral drug delivery

Metal-organic frameworks (MOFs) offer innovative solutions to the limitations of traditional oral drug delivery systems through their unique combination of metal ions and organic ligands. This review systematically examines the structural properties and principles of MOFs, setting the stage for their application in drug delivery. It discusses various classes of MOFs, including those based on zirconium, iron, zinc, copper, titanium, aluminum, potassium, and magnesium, assessing their drug-loading capacities, biocompatibility, and controlled release mechanisms. The effectiveness of MOFs is illustrated through case studies that highlight their capabilities in enhancing drug solubility, providing protection against the harsh gastrointestinal environment, and enabling precise drug release. The review addresses potential challenges, particularly the toxicity concerns associated with MOFs, and calls for further research into their biocompatibility and interactions with biological systems. It concludes by emphasizing the potential of MOFs in revolutionizing oral drug delivery, highlighting the critical need for comprehensive research to harness their full potential in clinical applications.

SrHPO4-coated Mg alloy implant attenuates postoperative pain by suppressing osteoclast-induced sensory innervation in osteoporotic fractures

Osteoporotic fractures have become a common public health problem and are usually accompanied by chronic pain. Mg and Mg-based alloys are considered the next-generation orthopedic implants for their excellent osteogenic inductivity, biocompatibility, and biodegradability. However, Mg-based alloy can initiate aberrant activation of osteoclasts and modulate sensory innervation into bone callus resulting in postoperative pain at the sequential stage of osteoporotic fracture healing. Its mechanism is going to be investigated. Strontium hydrogen phosphate (SrHPO4) coating to delay the Mg-based alloy degradation, can reduce the osteoclast formation and inhibit the growth of sensory nerves into bone callus, dorsal root ganglion hyperexcitability, and pain hypersensitivity at the early stage. Liquid chromatography-mass spectrometry (LC-MS) metabolomics analysis of bone marrow-derived macrophages (BMMs) treated with SrHPO4-coated Mg alloy extracts shows the potential effect of increased metabolite levels of AICAR (an activator of the AMPK pathway). We demonstrate a possible modulated secretion of AICAR and osteoclast differentiation from BMMs, which inhibits sensory innervation and postoperative pain through the AMPK/mTORc1/S6K pathway. Importantly, supplementing with AICAR in Mg-activated osteoclasts attenuates postoperative pain. These results suggest that Mg-induced postoperative pain is related to the osteoclastogenesis and sensory innervation at the early stage in the osteoporotic fractures and the SrHPO4 coating on Mg-based alloys can reduce the pain by upregulating AICAR secretion from BMMs or preosteoclasts.

Construction of a Titanium-Magnesium Composite Internal Fixation System for Repairing Bone Defects

The repair and regeneration of maxillofacial bone defects are major clinical challenges. Titanium (Ti)-magnesium (Mg) composites are a new generation of revolutionary internal fixation materials encompassing the mechanical strength and bioactive advantages of Ti and Mg alloys, respectively. This study was aimed to construct a Ti-Mg composite internal plate/screw fixation system to fix and repair bone defects. Further, the effects of different internal fixation systems on bone repair were analyzed through radiological and histological analyses. Notably, Ti6Al4V with rolled Mg foil was used as the experimental group, and a bone defect model of transverse complete amputation of the ulna in rabbits similar to the clinical condition was established. The internal fixation system with the highest osteogenic efficiency was selected based on in vivo results, and the direct and indirect bone repair abilities of the selected materials were evaluated in vitro. Notably, the thin Mg foil-Ti6Al4V internal fixation system exhibited the best fixation effect in the bone defect model and promoted the formation of new bone and early healing of bone defect areas. In vitro, the thin Mg foil-Ti6Al4V composite enhanced the activity of MC3T3-E1 cells; promoted the proliferation, adhesion, extension, and osteogenic differentiation of MC3T3-E1 cells; and regulated new bone formation. Further, it also promoted the polarization of RAW264.7 cells to M2 macrophages, induced the osteogenic immune microenvironment, and indirectly regulated the bone repair process. Therefore, a internal fixation system holds a promising potential for the internal fixation of maxillofacial bone defects. Our findings provide a theoretical and scientific basis for the design and clinical application of Ti-Mg internal fixation systems.

A comparative study on the effects of biodegradable high-purity magnesium screw and polymer screw for fixation in epiphyseal trabecular bone

With mechanical strength close to cortical bone, biodegradable and osteopromotive properties, magnesium (Mg)-based implants are promising biomaterials for orthopedic applications. However, during the degradation of such implants, there are still concerns on the potential adverse effects such as formation of cavities, osteolytic phenomena and chronic inflammation. Therefore, to transform Mg-based implants into clinical practice, the present study evaluated the local effects of high-purity Mg screws (HP-Mg, 99.99 wt%) by comparing with clinically approved polylactic acid (PLA) screws in epiphyseal trabecular bone of rabbits. After implantation of screws at the rabbit distal femur, bone microstructural, histomorphometric and biomechanical properties were measured at various time points (weeks 4, 8 and 16) using micro-CT, histology and histomorphometry, micro-indentation and scanning electron microscope. HP-Mg screws promoted peri-implant bone ingrowth with higher bone mass (BV/TV at week 4: 0.189 ± 0.022 in PLA group versus 0.313 ± 0.053 in Mg group), higher biomechanical properties (hardness at week 4: 35.045 ± 1.000 HV in PLA group versus 51.975 ± 2.565 HV in Mg group), more mature osteocyte LCN architecture, accelerated bone remodeling process and alleviated immunoreactive score (IRS of Ram11 at week 4: 5.8 ± 0.712 in PLA group versus 3.75 ± 0.866 in Mg group) as compared to PLA screws. Furthermore, we conducted finite element analysis to validate the superiority of HP-Mg screws as orthopedic implants by demonstrating reduced stress concentration and uniform stress distribution around the bone tunnel, which led to lower risks of trabecular microfractures. In conclusion, HP-Mg screws demonstrated greater osteogenic bioactivity and limited inflammatory response compared to PLA screws in the epiphyseal trabecular bone of rabbits. Our findings have paved a promising way for the clinical application of Mg-based implants.

Dissolving magnesium hydroxide implants enhance mainly cancellous bone formation whereas degrading RS66 implants lead to prominent periosteal bone formation in rabbits

Bone fractures often require internal fixation using plates or screws. Normally, these devices are made of permanent metals like titanium providing necessary strength and biocompatibility. However, they can also cause long-term complications and may require removal. An interesting alternative are biocompatible degradable devices, which provide sufficient initial strength and then degrade gradually. Among other materials, biodegradable magnesium alloys have been developed for craniofacial and orthopaedic applications. Previously, we tested implants made of magnesium hydroxide and RS66, a strong and ductile ZK60-based alloy, with respect to biocompatibility and degradation behaviour. Here, we compare the effects of dissolving magnesium hydroxide and RS66 cylinders on bone regeneration and bone growth in rabbit condyles using microtomographical and histological analysis. Both magnesium hydroxide and RS66 induced a considerable osteoblastic activity leading to distinct but different spatio-temporal patterns of cancellous and periosteal bone growth. Dissolving RS66 implants induced a prominent periosteal bone formation on the medial surface of the original condyle whereas dissolving magnesium hydroxide implants enhance mainly cancellous bone formation. Especially periosteal bone formation was completed after 6 and 8 weeks, respectively. The observed bone promoting functions are in line with previous reports of magnesium stimulating cancellous and periosteal bone growth and possible underlying signalling mechanisms are discussed. STATEMENT OF SIGNIFICANCE: Biodegradable magnesium based implants are promising candidates for use in orthopedic and traumatic surgery. Although these implants are in the scientific focus for a long time, comparatively little is known about the interactions between degrading magnesium and the biological environment. In this work, we investigated the effects of two degrading cylindrical magnesium implants (MgOH2 and RS66) both on bone regeneration and on bone growth. Both MgOH2 and RS66 induce remarkable osteoblastic activities, however with different spatio-temporal patterns regarding cancellous and periosteal bone growth. We hypothesize that degradation products do not diffuse directionless away, but are transported by the restored blood flow in specific spatial patterns which is also dependent on the used surgical technique.

Quantitative Imaging of Magnesium Biodegradation by 3D X‐Ray Ptychography and Electron Microscopy

Magnesium‐based alloys are excellent materials for temporary medical implants, but understanding and controlling their corrosion performance is crucial. Most nanoscale corrosion studies focus on the surface, providing only 2D information. In contrast, macro‐ and microscale X‐ray tomography offers representative volume information, which is, however, comparatively low in resolution and rather qualitative. Here a new mesoscale approach overcomes these drawbacks and bridges the scale gap by combining 3D measurements using ptychographic X‐ray computed tomography (PXCT) with electron microscopy. This combination allows to observe the corrosion progress non‐destructively in 3D and provides high‐resolution chemical information on the corrosion products. A medical Mg–Zn–Ca alloy is used and compared the same sample in the pristine and corroded states. With PXCT an isotropic resolution of 85 and 123 nm is achieved for the pristine and corroded states respectively, which enables to distinguish nanoscale Mg2Ca precipitates from the matrix. The corroded state in best approximation to the in situ conditions is imaged and reveals the complexity of corrosion products. The results illustrate that the corrosion‐layer is dense and defect‐free, and the corrosion of the material is grain‐orientation sensitive. The developed workflow can advance research on bioactive materials and corrosion‐sensitive functional materials.

An overview of magnesium-based implants in orthopaedics and a prospect of its application in spine fusion

Due to matching biomechanical properties and significant biological activity, Mg-based implants present great potential in orthopedic applications. In recent years, the biocompatibility and therapeutic effect of magnesium-based implants have been widely investigated in trauma repair. In contrast, the R&D work of Mg-based implants in spinal fusion is still limited. This review firstly introduced the general background for Mg-based implants. Secondly, the mechanical properties and degradation behaviors of Mg and its traditional and novel alloys were reviewed. Then, different surface modification techniques of Mg-based implants were described. Thirdly, this review comprehensively summarized the biological pathways of Mg degradation to promote bone formation in neuro-musculoskeletal circuit, angiogenesis with H-type vessel formation, osteogenesis with osteoblasts activation and chondrocyte ossification as an integrated system. Fourthly, this review followed the translation process of Mg-based implants via updating the preclinical studies in fracture fixation, sports trauma repair and reconstruction, and bone distraction for large bone defect. Furthermore, the pilot clinical studies were involved to demonstrate the reliable clinical safety and satisfactory bioactive effects of Mg-based implants in bone formation. Finally, this review introduced the background of spine fusion surgeryand the challenges of biological matching cage development. At last, this review prospected the translation potential of a hybrid Mg-PEEK spine fusion cage design.

Effect of hematoma on early degradation behavior of magnesium after implantation

The corrosion of magnesium (Mg)-based bioabsorbable implanting devices is influenced by implantation environment which dynamically changes by biological response including wound healing. Understanding the corrosion mechanisms along the healing process is essential for the development of Mg-based devices. In this study, a hematoma model was created in a rat femur to analyze Mg corrosion with hematoma in the early stage of implantation. Pure Mg specimen (99.9%,ϕ1.2 × 6 mm) was implanted in rat femur under either hematoma or non-hematoma conditions. After a designated period of implantation, the specimens were collected and weighed. The insoluble salts formed on the specimen surfaces were analyzed using scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Raman spectroscopy on days 1, 3, and 7. The results indicate that hematomas promote Mg corrosion and change the insoluble salt precipitation. The weight loss of the hematoma group (27.31 ± 5.91 µg mm-2) was significantly larger than that of the non-hematoma group (14.77 ± 3.28 µg mm-2) on day 7. In the non-hematoma group, carbonate and phosphate were detected even on day 1, but the only latter was detected on day 7. In the hematoma group, hydroxide was detected on day 1, followed by the formation of carbonate and phosphate on days 3 and 7. The obtained results suggest the hypoxic and acidic microenvironment in hematomas accelerates the Mg corrosion immediately after implantation, and the subsequent hematoma resorption process leads to the formation of phosphate and carbonate with organic molecules. This study revealed the risk of hematomas as an acceleration factor of the corrosion of Mg-based devices leading to the early implant failure. It is important to consider this risk in the design of Mg-based devices and to optimize surgical procedures controlling hemorrhage at implantation and reducing unexpected bleeding after surgery.

Time-Sequential and Multi-Functional 3D Printed MgO2/PLGA Scaffold Developed as a Novel Biodegradable and Bioactive Bone Substitute for Challenging Postsurgical Osteosarcoma Treatment

Osteosarcoma (OS) is the most commonly occurring primary bone malignant tumor. The clinical postsurgical OS treatment faces big challenges for the staged therapeutic requirements of early anti-tumor, anti-bacterial, and long-lasting osteogenesis. Herein, multi-functional bioactive scaffolds with time-sequential functions of preventing tumor recurrence, inhibiting bacterial infection, and promoting bone defect repair are designed as a novel strategy. Nanocomposite scaffold magnesium peroxide (MgO2)/poly (lactide-co-glycolide) is prepared by low-temperature 3D printing for controllable releasing magnesium ions (Mg2+) and reactive oxygen species in a time-sequential manner. The scaffold with 20 wt% MgO2 (20MP) is verified with desired mechanical properties, as well as exhibits staged release behavior of bioactive elements with hydrogen peroxide (H2O2) release for the first 3 weeks, and long-lasting Mg2+ release for 12 weeks. The released H2O2 initiates chemodynamic therapy to induce apoptosis and ferroptosis in tumor cells, along with activating the anticancer immune microenvironment by M1 polarization of macrophages. The released Mg2+ subsequently enhances bone repair by activating the Wnt3a/GSK-3β/β-catenin signaling pathway to promote osteogenic differentiation of bone marrow mesenchymal stem cells and create osteopromotive immune microenvironment by M2 polarization of macrophages. In conclusion, the multi-functional 20MP scaffold demonstrates time-sequential therapeutic properties as an innovative strategy for OS-associated bone defect treatment.

Advances in biodegradable materials: Degradation mechanisms, mechanical properties, and biocompatibility for orthopedic applications

Mg-based and Zn-based biodegradable materials have the potential to become the next-generation implant materials to treat bone diseases, because of their desired degradation and mechanical properties. This article reviews the status of these implant materials. The required properties of biodegradable materials such as biodegradability, mechanical properties, and biocompatibility for performance evaluation were briefly discussed. The influence of fabrication techniques, microstructure, alloying elements, and post-processing techniques on the properties of Mg and Zn-based materials was addressed. The degradation mechanism by dissolution, oxidation, and interaction with human body cells was discussed. The biocompatibility of Mg and Zn-based biodegradable materials was analyzed. The significance of in vitro and in vivo biocompatibility testing was highlighted, emphasizing the superiority of in vivo results over cell line studies. This article identifies the many Mg and Zn-based biodegradable materials and summarizes the key findings.

Effect of Gentamicin Sulfate and Polymeric Polyethylene Glycol Coating on the Degradation and Cytotoxicity of Iron-Based Biomaterials

The work is focused on the degradation, cytotoxicity, and antibacterial properties, of iron-based biomaterials with a bioactive coating layer. The foam and the compact iron samples were coated with a polyethylene glycol (PEG) polymer layer without and with gentamicin sulfate (PEG + Ge). The corrosion properties of coated and uncoated samples were studied using the degradation testing in Hanks' solution at 37 °C. The electrochemical and static immersion corrosion tests revealed that the PEG-coated samples corroded faster than samples with the bioactive PEG + Ge coating and uncoated samples. The foam samples corroded faster compared with the compact samples. To determine the cytotoxicity, cell viability was monitored in the presence of porous foam and compact iron samples. The antibacterial activity of the samples with PEG and PEG + Ge against Escherichia coli CCM 3954 and Staphylococcus aureus CCM 4223 strains was also tested. Tested PEG + Ge samples showed significant antibacterial activity against both bacterial strains. Therefore, the biodegradable iron-based materials with a bioactive coating could be a suitable successor to the metal materials studied thus far as well as the materials used in the field of medicine.

Design, clinical applications and post-surgical assessment of bioresorbable 3D-printed craniofacial composite implants

This study details the design, fabrication, clinical trials' evaluation, and analysis after the clinical application of 3D-printed bone reconstruction implants made of nHAp@PLDLLA [nanohydroxyapatite@poly(L-lactide-co-D,L-lactide)] biomaterial. The 3D-printed formulations have been tested as bone reconstruction Cranioimplants in 3 different medical cases, including frontal lobe, mandibular bone, and cleft palate reconstructions. Replacing one of the implants after 6 months provided a unique opportunity to evaluate the post-surgical implant obtained from a human patient. This allowed us to quantify physicochemical changes and develop a spatial map of osseointegration and material degradation kinetics as a function of specific locations. To the best of our knowledge, hydrolytic degradation and variability in the physicochemical and mechanical properties of the biomimetic, 3D-printed implants have not been quantified in the literature after permanent placement in the human body. Such analysis has revealed the constantly changing properties of the implant, which should be considered to optimize the design of patient-specific bone substitutes. Moreover, it has been proven that the obtained composition can produce biomimetic, bioresorbable and bone-forming alloplastic substitutes tailored to each patient, allowing for shorter surgery times and faster patient recovery than currently available methods.

Mg-Cross-Linked Alginate Hydrogel Induces BMSC/Macrophage Crosstalk to Enhance Bone Tissue Regeneration via Dual Promotion of the Ligand-Receptor Pairing of the OSM/miR-370-3p-gp130 Signaling Pathway

Macrophages play a pivotal role in the crosstalk between the immune and skeletal systems, while Mg-based biomaterials demonstrate immunomodulatory capabilities in this procedure. However, the mechanism of how Mg2+ promotes osteogenesis through the interplay of bone marrow-derived mesenchymal stem cells (BMSCs) and macrophages remains undescribed. Here, we demonstrated that a Mg-cross-linked alginate hydrogel exerted a dual enhancement of BMSCs osteogenic differentiation through the ligand-receptor pairing of the OSM/miR-370-3p-gp130 axis. On the one hand, Mg2+, released from the Mg-cross-linked hydrogel, stimulates bone marrow-derived macrophages to produce and secrete more OSM. On the other hand, Mg2+ lowers the miR-370-3p level in BMSCs and in turn, reverses its suppression on gp130. Then, the OSM binds to the gp130 heterodimer receptor and activates intracellular osteogenic programs in BMSCs. Taken together, this study reveals a novel cross-talk pattern between the skeletal and immune systems under Mg2+ stimulation. This study not only brings new insights into the immunomodulatory properties of Mg-based biomaterials for orthopedic applications but also enriches the miRNA regulatory network and provides a promising target to facilitate bone regeneration in large bone defects.

Metal-organic complex coating for enhanced corrosion control and biocompatibility on biodegradable magnesium alloy for orthopaedic implants

Magnesium alloy is currently regarded as the most favourable biodegradable metal; however, obstacles remain to be overcome in terms of managing its corrosion and ensuring its biocompatibility. In this study, a metal-organic complex comprising Ca ions incorporated in tannic acid (TA) was prepared and used to coat magnesium alloy by chemical conversion and dipping processes, followed by modification with stearic acid (SA). This metal-organic complex coating was demonstrated to be homogeneous and compact, and it significantly improved the electrochemical corrosion resistance and long-term degradation behaviour of the coated samples. Consequently, the well-controlled release of Mg and Ca ions, as well as the osteo-compatible TA and SA molecules, promoted the proliferation of osteoblast cells. This metal-organic complex coating offers a promising modifying strategy for magnesium-based orthopaedic implants.

Application and Perspectives: Magnesium Materials in Bone Regeneration

The field of bone regeneration has always been a hot and difficult research area, and there is no perfect strategy at present. As a new type of biodegradable material, magnesium alloys have excellent mechanical properties and bone promoting ability. Compared with other inert metals, magnesium alloys have significant advantages and broad application prospects in the field of bone regeneration. By searching the official Web sites and databases of various funds, this paper summarizes the research status of magnesium composites in the field of bone regeneration and introduces the latest scientific research achievements and clinical transformations of scholars in various countries and regions, such as improving the corrosion resistance of magnesium alloys by adding coatings. Finally, this paper points out the current problems and challenges, aiming to provide ideas and help for the development of new strategies for the treatment of bone defects and fractures.

Chronic kidney disease: a contraindication for using biodegradable magnesium or its alloys as potential orthopedic implants?

Magnesium (Mg) has gained widespread recognition as a potential revolutionary orthopedic biomaterial. However, whether the biodegradation of the Mg-based orthopedic implants would pose a risk to patients with chronic kidney disease (CKD) remains undetermined as the kidney is a key organ regulating mineral homeostasis. A rat CKD model was established by a 5/6 subtotal nephrectomy approach, followed by intramedullary implantation of three types of pins: stainless steel, high pure Mg with high corrosion resistance, and the Mg-Sr-Zn alloy with a fast degradation rate. The long-term biosafety of the biodegradable Mg or its alloys as orthopedic implants were systematically evaluated. During an experimental period of 12 weeks, the implantation did not result in a substantial rise of Mg ion concentration in serum or major organs such as hearts, livers, spleens, lungs, or kidneys. No pathological changes were observed in organs using various histological techniques. No significantly increased iNOS-positive cells or apoptotic cells in these organs were identified. The biodegradable Mg or its alloys as orthopedic implants did not pose an extra health risk to CKD rats at long-term follow-up, suggesting that these biodegradable orthopedic devices might be suitable for most target populations, including patients with CKD.

Mg alloys with antitumor and anticorrosion properties for orthopedic oncology: A review from mechanisms to application strategies

As a primary malignant bone cancer, osteosarcoma (OS) poses a great threat to human health and is still a huge challenge for clinicians. At present, surgical resection is the main treatment strategy for OS. However, surgical intervention will result in a large bone defect, and some tumor cells remaining around the excised bone tissue often lead to the recurrence and metastasis of OS. Biomedical Mg-based materials have been widely employed as orthopedic implants in bone defect reconstruction, and, especially, they can eradicate the residual OS cells due to the antitumor activities of their degradation products. Nevertheless, the fast corrosion rate of Mg alloys has greatly limited their application scope in the biomedical field, and the improvement of the corrosion resistance will impair the antitumor effects, which mainly arise from their rapid corrosion. Hence, it is vital to balance the corrosion resistance and the antitumor activities of Mg alloys. The presented review systematically discussed the potential antitumor mechanisms of three corrosion products of Mg alloys. Moreover, several strategies to simultaneously enhance the anticorrosion properties and antitumor effects of Mg alloys were also proposed.

Multifaceted Materials for Enhanced Osteogenesis and Antimicrobial Properties on Bioplastic Polyetheretherketone Surfaces: A Review

Implant-associated infections and the increasing number of bone implants loosening and falling off after implantation have become urgent global challenges, hence the need for intelligent alternative solutions to combat implant loosening and falling off. The application of polyetheretherketone (PEEK) in biomedical and medical therapy has aroused great interest, especially because its elastic modulus close to bone provides an effective alternative to titanium implants, thereby preventing the possibility of bone implants loosening and falling off due to the mismatch of elastic modulus. In this Review, we provide a comprehensive overview of recent advances in surface modifications to prevent bone binding deficiency and bacterial infection after implantation of bone implants, starting with inorganics for surface modification, followed by organics that can effectively promote bone integration and antimicrobial action. In addition, surface modifications derived from cells and related products of biological activity have been proposed, and there is increasing evidence of clinical potential. Finally, the advantages and future challenges of surface strategies against medical associated poor osseointegration and infection are discussed, with promising prospects for developing novel osseointegration and antimicrobial PEEK materials.

The Characterization of a Biodegradable Mg Alloy after Powder Bed Fusion with Laser Beam/Metal Processing for Custom Shaped Implants

A new Mg-Zn-Zr-Ca alloy in a powder state, intended to be used for custom shaped implants, was obtained via a mechanical alloying method from pure elemental powder. Further, the obtained powder alloy was processed by a PBF-LB/M (powder bed fusion with laser beam/of metal) procedure to obtain additive manufactured samples for small biodegradable implants. A series of microstructural, mechanical and corrosion analyses were performed. The SEM (scanning electron microscopy) analysis of the powder alloy revealed a good dimensional homogeneity, with a uniform colour, no agglutination and almost rounded particles, suitable for the powder bed fusion procedure. Further, the PBF-LB/M samples revealed a robust and unbreakable morphology, with a suitable porosity (that can reproduce that of cortical bone) and without an undesirable balling effect. The tested Young's modulus of the PBF-LB/M samples, which was 42 GPa, is close to that of cortical bone, 30 GPa. The corrosion tests that were performed in PBS (Phosphate-buffered saline) solution, with three different pH values, show that the corrosion parameters have a satisfactory evolution comparative to the commercial ZK 60 alloy.