Long-term clinical study and multiscale analysis of in vivo biodegradation mechanism of Mg alloy

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.

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.

An In Silico Model to Examine the Interaction Between Implant Degradation and Fracture Healing Under Mechanical Loading

Biodegradable implants are promising for fracture fixation but they have not been applied to the load-bearing skeletal sites. A critical issue is how implant degradation and fracture healing affect each other under mechanical loading. To address this issue, we first developed a finite element model of a long bone fracture fixed with a Zn alloy-based screw-plate system, where implant degradation and bone healing were simulated based upon the continuum damage mechanics and mechano-regulated tissue differentiation algorithm, respectively. For comparison, non-degradable Ti alloy implant with normal bone healing and non-healing fracture with normal implant degradation were served as two reference controls. In terms of the effect of implant degradation on bone healing, the results indicated that implant degradation resulted in a greater volume of newly formed bone within the callus (16% for the degradable implant vs 12% for the non-degradable implant) and a better biomechanical recovery of the fractured bone (bone stiffness fraction: 107% vs 95%) at week 8. Regarding the effect of bone healing on implant degradation, fracture healing led to a significant decrease in the degradation rate of the implant (implant stiffness fraction at week 4: 8% for non-healing vs 40% for healing) and an increase in the overall period from 4 to 8 weeks for a complete degradation of the implant. These results together suggest that implant degradation and fracture healing significantly affect each other under mechanical loading. The in silico model developed here may provide a valuable platform to consider interactions between material degradation and bone healing when designing biodegradable implants for orthopaedic internal fixation at the load-bearing sites.

Promotion of bone defect repairs using multiscale 3D printed silk porous hydrogel scaffolds

Porosity plays a critical role in influencing the biological properties and performance of materials and devices. This study introduces hydrocolloid inks by incorporating porogens into silk fibroin (silk) protein solutions to generate porous hydrogel scaffolds. These inks exhibit robust printability, enabling the fabrication of complex geometries with hierarchical porosity, ranging from microscale porogen-templated pores (40 to 200 μm, with over 50 % ≥100 μm) to macroscale features determined by the 3D printing process (≥200 μm). Compatibility studies using human bone marrow mesenchymal stem cells (hMSCs) and murine embryonic osteoblast precursor cells (MC3T3-E1) demonstrate cell adhesion, infiltration, and proliferation both on the surface and within these hydrogels. Subcutaneous implantation in rats confirmed biocompatibility and the ability to support endogenous cell migration and proliferation by the hydrogels. In a rat femoral defect model, the microscale biomimetic structures significantly improved bone repair, outperforming control groups, including small pore-sized silk hydrogels (∼21.39 μm) and other 3D-printed constructs with a thickening agent (∼20.78 μm). These innovative multiscale silk 3D biomimetic scaffolds present a promising approach for effective bone defect repair for future clinical applications. STATEMENT OF SIGNIFICANCE: This study presents a transformative approach to bone defect repair through the development of 3D-printed silk hydrogel scaffolds with multiscale porosity. By incorporating dextran gel particles as sacrificial porogens, the silk scaffolds achieve hierarchical pore structures optimized for cell adhesion, proliferation, and migration. In vitro and in vivo results demonstrate that these scaffolds support robust cellular activity and significantly enhance bone regeneration compared to conventional designs, providing a scalable, biocompatible solution. The integration of silk's superior biological properties with advanced 3D printing methodologies underscores its potential to set new benchmarks in bone tissue engineering and regenerative medicine.

Gas Bubbles from Biodegradable Magnesium Implants Convey Mechanical Cues and Promote Immune Cell Stimulation

In ever-increasing numbers, patients are treated with biodegradable magnesium implants. While gas bubbles frequently arise in soft tissue overlying magnesium implants, their biological implications remain uncertain. This study investigates how bubble accumulation and evolution across various biological lengths and time scales influence adjacent tissue and cell behavior in rats. Bubbles accumulate in tissues around magnesium during initial postimplantation days, then fully resorb. Alterations in tissue and cell geometry around bubbles coincide with accumulation of cells, many with macrophage phenotypes, and increased expression of the mechanosensitive ion-channel Piezo1. Using spatially resolved transcriptomics, strong proinflammatory pathway activation is revealed near bubbles with marked expression of the proliferative macrophage marker secreted phosphoprotein 1 (Spp1). Spatial transcriptomics also reveals strong enrichment of cytoskeletal rearrangement genes, demonstrating that cells respond to mechanical cues from bubbles. Notably, both time and bubble-implant distance strongly influence the cellular response. Over time, as bubbles are located farther from the implant, regenerative processes decline, and inflammation predominates. These findings suggest that bubbles from magnesium implant degradation create an intricate local response influencing tissue healing through inflammatory and mechanical pathways. This study underscores the need for magnesium implants with controlled gas release and meticulous monitoring of bubble evolution in patients.

Magnesium as an emerging bioactive material for orthopedic applications: bedside needs lead the way from innovation to clinical translation

With the rapid increase in population aging, the number of surgical operations in orthopedics is expected to increase. The gap between the materials applied in clinical orthopedics and materials in discovery and research is obvious due to regulatory requirements for biosafety and treatment efficacy. For the bedside needs, it is important to overcome hurdles by achieving impactful innovation and clinical translation of orthopedic materials. Magnesium (Mg), as an emerging bioactive material, is one of the vital components of the human body and mainly stored in the musculoskeletal system as either a matrix component or an intracellular element for the homeostasis of various physiological functions. However, the degradation and biomechanical performance limit the applications of Mg. This review aims to explore the current challenges and future directions of Mg for clinical translation and provide an update on biomaterials used in orthopedics, factors driving orthopedic innovation, physiology of magnesium ions (Mg2+) and its potential clinical applications. To achieve orthopedic application, modification of the performance of Mg as implantable metals and function of the degradation products of Mg in vivo are described. For the clinical needs of treating the steroid-associated osteonecrosis (SAON), Mg screws and Mg-based composite porous scaffolds (Mg/PLGA/TCP: magnesium/poly(lactic-co-glycolic acid) (PLGA)/tricalcium phosphate (TCP)) have been developed, but the challenges of Mg-based implants in load-bearing skeletal sites still exist. To utilize the beneficial biological effects of Mg degradation and overcome the weakness in mechanical stability for fracture fixation, the concept of developing Mg/titanium (Ti) hybrid orthopedic implants is reported, where the Ti component provides effective mechanical support while the inclusion of Mg component potentially optimizes the biomechanical properties of Ti component and facilitate bone healing. This review provides a reference frame for the translation of novel materials and promotes the development of innovative orthopedic biomaterials for clinical applications.

Enhanced functionalities of biomaterials through metal ion surface modification

The development of new artificial biomaterials for bone defect repair is an ongoing area of clinical research. Metal ions such as zinc, copper, magnesium, calcium, strontium, silver, and cerium play various roles in bone tissue regeneration in the human body and possess a range of biochemical functions. Studies have demonstrated that appropriate concentrations of these metal ions can promote osteogenesis and angiogenesis, inhibit osteoclast activity, and deter bacterial infections. Researchers have incorporated metal ions into biomaterials using various methods to create artificial bone materials with enhanced osteogenic and antibacterial capabilities. In addition to the osteogenic properties of all the aforementioned metal ions, Zn, Sr, and Ce can indirectly promote osteogenesis by inhibiting osteoclast activity. Cu, Mg, and Sr significantly enhance angiogenesis, while the antibacterial properties of Zn, Cu, Ag, and Ce can reduce the likelihood of infection and inflammation caused by implanted materials. This paper reviews the mechanisms through which metal ions promote bone tissue growth and improve the antibacterial activity of biomaterials. It also summarizes common loading methods on the surface of biomaterials with different metals and highlights the potential clinical applications of these new artificial bone materials.

Additively manufactured biodegradable Zn-Mn-based implants with an unprecedented balance of strength and ductility

Additively manufactured (AM) biodegradable zinc alloys hold huge potential as promising candidates for bone defect and fracture repair, thanks to their suitable biodegradation rates and acceptable biocompatibility. However, the mechanical properties of AM zinc alloys developed so far, ductility in particular, fall short of the requirements for bone substitution. Here, we present Zn-1Mn and Zn-1Mn-0.4Mg alloy implants with unique microstructures, fabricated using laser powder bed fusion (LPBF). Notably, the LPBF Zn-Mn-Mg alloy exhibited an extraordinary balance of strength and ductility, with an ultimate tensile strength of 289 MPa, yield strength of 213.5 MPa, and elongation over 20 %, outperforming all previously reported AM zinc alloys. The simultaneously enhanced strength and ductility of the ternary alloy were attributed to the strong grain-refining effect of the Mg2Zn11 second phase and the synthetic strengthening caused by the dispersion of the MnZn13 and Mg2Zn11 second phases inside the grains and at the grain boundaries. In addition, both alloys had similar rates of in vitro biodegradation (∼0.15 mm/year), properly aligned with the bone remodeling process, while also demonstrating favorable biocompatibility and upregulating multiple osteogenic markers. The Zn-Mn-Mg alloy showed even better osteogenic potential than the Zn-Mn alloy, owing to the addition of Mg. The combined attributes of the LPBF Zn-Mn-Mg ternary alloy indicated huge potential for its use as a bone repair material, especially for load-bearing bone fixation. STATEMENT OF SIGNIFICANCE: The mechanical properties of previously developed additively manufactured biodegradable zinc alloys, especially ductility, have not met the requirements for bone repair. Using laser powder bed fusion (LPBF), we fabricated Zn-1Mn and Zn-1Mn-0.4Mg alloy implants with unique microstructures. The LPBF Zn-Mn-Mg alloy demonstrated an exceptional balance of strength and ductility, achieving a tensile strength of 289 MPa, yield strength of 213.5 MPa, and elongation over 20 %, surpassing all reported AM zinc alloys. This study is the first to produce a directly printed biodegradable alloy meeting the mechanical requirements for bone fixation devices without post-processing. Additionally, the alloy exhibited moderate a biodegradation rate and excellent biocompatibility, underscoring its potential for load-bearing bone repair applications.

Evaluation of the efficacy of magnesium alloy fixation screws in a goat femoral condylar fracture model

This study investigated the efficacy and safety of magnesium alloy screws in repairing small bone fractures using goat lateral femoral condyle fracture models. The animals were randomized into an experimental group receiving magnesium alloy screws (CS/Ф 3.2 × 28 mm, Suzhou Zhuoqia Medical Technology) and a control group receiving titanium alloy screws (CS/Ф 3.2 × 28 mm, Samo Medical Technology Co., Ltd). Postoperative evaluations at 3- and 6-month intervals included assessments of fracture repair, animal health, hematological parameters, histology, and screw degradation. Hematological tests revealed no significant intergroup variations. While gas accumulation near the magnesium screws was noted, the fracture healing outcomes were similar between the magnesium and titanium screw groups, with no deleterious health effects attributed to magnesium screw degradation. Gas liberation during magnesium degradation had no detrimental effect on small fracture recovery. Magnesium screw implementation appears to present no general health risks. Consequently, magnesium alloy could be a promising biomaterial for future fixation screw applications in orthopedics.

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.

Multifaceted bone response to immunomodulatory magnesium implants: Osteopromotion at the interface and adipogenesis in the bone marrow

Orthopedic implants made of biodegradable magnesium (Mg) provide an alternative to nondegradable implants for fracture repair. Widely reported to be pro-osteogenic, Mg implants are also believed to be anti-inflammatory and anti-osteoclastic, but this is difficult to reconcile with the early clinical inflammation observed around these implants. Here, by surveying implant healing in a rat bone model, we determined the cellular responses and structural assembly of bone correlated with the surface changes of Mg implants inherent in degradation. We show that, compared to titanium, both high-purity (99.998 %) and clinical-grade, rare earth-alloyed (MgYREZr) Mg implants create an initial, transient proinflammatory environment that facilitates inducible nitric oxide synthase-mediated macrophage polarization, osteoclastogenesis, and neoangiogenesis programs. While this immunomodulation subsequently reinforces reparative osteogenesis at the surface of both Mg implants, the faster degradation of high-purity Mg implants, but not MgYREZr implants, elicits a compositional alteration in the interfacial bone and a previously unknown proadipogenic response with persistent low-grade inflammation in the surrounding bone marrow. Beyond the need for rigorous tailoring of Mg implants, these data highlight the need to closely monitor osseointegration not only at the immediate implant surface but also in the peri-implant bone and adjacent bone marrow.

Micro/Nanobiomimetic Iron-Based Scaffold Induces Vascularized Bone Regeneration To Repair Large Segmental Bone Defect in Load-Bearing Sites

Biodegradable scaffolds, including metals, ceramics, and polymers, show great potential in bone tissue regeneration. However, current biodegradable scaffolds do not simultaneously possess suitable mechanical properties, biodegradability and osteoinductivity, which severely limits their clinical application for large segmental bone defect repair. Herein, we developed a biomimetic and hierarchically micro-nanoporous iron-based scaffold utilizing a synergistic approach combining 3-dimensional printing, surface dealloying treatment and electrochemical deposition. Compared to traditional periodic lattice structures, the biomimetic scaffold with a stochastic lattice structure promised superior stress transfer efficiency. Cell experiments revealed that the biomimetic scaffold notably enhanced osteogenesis and angiogenesis in vitro via EGFR-mediated Ras/Raf/MAPK signaling. Upon implantation in a rat femoral condyle defect model, the scaffold achieved a dynamic equilibrium between in vivo material degradation and bone formation. More importantly, the study conducted in a large animal model with an extended cycle of up to 1 year demonstrated that bionic iron-based scaffolds effectively facilitated the repair and functional reconstruction of large bone defects in load-bearing regions by inducing vascularized bone regeneration. This study not only introduces a potential solution for addressing critical-sized bone defects in load-bearing regions but also provides a viable approach for the design of other biomimetic biomaterials.

Stronger and coarser-grained biodegradable zinc alloys

Zinc is emerging as a key material for next-generation biodegradable implants1-5. However, its inherent softness limits its use in load-bearing orthopaedic implants. Although reducing the grain size of zinc can make it stronger, it also destabilizes its mechanical properties and thus makes it less durable at body temperature6. Here we show that extruded Zn alloys of dilute compositions can achieve ultrahigh strength and excellent durability when their micron-scale grain size is increased while maintaining a basal texture. In this inverse Hall-Petch effect, the dominant deformation mode changes from inter-granular grain boundary sliding and dynamic recrystallization at the original grain size to intra-granular pyramidal slip and unusual twinning at the increased grain size. The role of the anomalous twins, termed 'accommodation twins' in this work, is to accommodate the altered grain shape in the plane lying perpendicular to the external loading direction, in contrast to the well-known 'mechanical twins' whose role is to deliver plasticity along the external loading direction7,8. The strength level achieved in these dilute zinc alloys is nearly double those of biodegradable implants made of magnesium alloys-making them the strongest and most stable biodegradable alloys available, to our knowledge, for fabricating bone fixation 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.

Ultrasound-Triggered Mg2+ Blasting Release Hydrogel Microspheres for Promoting Bone Reconstruction

Mg2+ (Magnesium ion) can affect bone tissue metabolism by regulating related signaling pathways in bone metabolism. However, how to realize precise controlled release of Mg2+ in bone regeneration treatment still presents a challenge. Herein, for the first time, the GelMA-BP (Gelatin Methacryloyl-Bisphosphonate) and the composite nano-bubble system are fused to construct the Mg2+ blasting controlled-release hydrogel microspheres, the stability of the nano-bubbles in the microspheres is enhanced through metal coordination complexation, and the burst of the nano-bubbles is controlled by using ultrasonic cavitation to achieve the precise controlled release of Mg2+, ultimately effectively promoting bone reconstruction. First, GelMA-BP composite is prepared by Schiff base reaction. Second, the nanobubble BP (Bisphosphonate) system is constructed, and Mg2+ is combined with the ligand coordination to prepare the composite nanobubble system. Thirdly, through Mg2+ co-coordination, the ultrasound-triggered Mg2+ blasting controlled release microspheres were prepared to achieve bone repair. Overall, this innovative strategy effectively solves the problem of accurate controlled release of Mg2+, and finally effectively activates in situ bone tissue regeneration.

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.

Cytocompatibility, cell-material interaction, and osteogenic differentiation of MC3T3-E1 pre-osteoblasts in contact with engineered Mg/PLA composites

Bioabsorbable Mg wire-reinforced poly-lactic acid (PLA) matrix composites are potential candidate for load-bearing orthopedic implants offering tailorable mechanical and degradation properties by stacking sequence, volume fraction and surface modification of Mg wires. In this study, we investigated the cytocompatibility, cell-material interaction, and bone differentiation behavior of MC3T3-E1 pre-osteoblast cells for medical-grade PLA, Mg/PLA, and PEO-Mg/PLA (having PEO surface modification on Mg wires) composites. MTT and live/dead assay showed excellent biocompatibility of both composites while cell-material interaction analysis revealed that cells were able to adhere and proliferate on the surface of composites. Cells on the longitudinal surface of composites showed a high and uniform cell density while those on transversal surfaces initially avoided Mg regions but later migrated back after the formation of the passivation layer. Bone differentiation tests showed that cells in extracts of PLA and composites were able to initiate the differentiation process as osteogenesis-related gene expressions, alkaline phosphatase protein quantity, and calcium mineralization increased after 7 and 14 days of culture. Interestingly, the bone differentiation response of PEO-Mg/PLA composite was found to be similar to medical-grade PLA, proving its superiority over Mg/PLA composite.

Finite Element and Density Functional Theory Modeling Effectively Predict Pitting Degradation of Hydroxyapatite-Coated Pure Magnesium

The emergence of degradable orthopedic implants for fracture fixation may abrogate the need for implant removal surgery and minimize pain associated with permanent implants. Magnesium (Mg) and its alloys are being explored as a biomaterial for degradable implants due to mechanical properties similar to those of bone. Previous in vitro studies have determined the degradation rate of pure Mg to be relatively fast when compared to bone regeneration. Hydroxyapatite (HA), the mineral component of bone, may serve as a surface coating on Mg-based implants to effectively slow and control the degradation rate. The objective of this work was to develop and implement a finite element (FE) model that utilizes a damage evolution law for pitting corrosion to predict the degradation of pure Mg (non-coated) and HA-coated pure Mg (coated) materials simulated in physiological conditions. Finite element analysis (FEA) was performed on a cylindrical Mg specimen (25.4 mm diameter, 8 mm height) through Abaqus/Standard software to incrementally monitor the damage value of each Mg element and subsequently delete fully-degraded elements from the simulation. A Fortran user-material (UMAT) subroutine assigned each element a pitting parameter, controlling the rate of degradation throughout the simulation and providing necessary inputs of elastic material properties and degradation model parameters for pure Mg and HA into Abaqus. The simulations allowed for the visualization of both pure Mg and HA-coated pure Mg degradation over a 120-day period, displaying expected degradation trends such as lower corrosion rates for HA-coated Mg and degradation propagating from the edges inward. Simulation results were calibrated with our prior results from a 30-day experimental degradation study via direct comparison with mass loss over time. Additionally, lower length scale, density functional theory (DFT) simulations were performed to provide physical meaning for the model pitting parameter. The FE simulation was extended to model resin-enclosed pure Mg and HA-coated pure Mg degradation, where only the top surface of the specimen was exposed to the corrosion surface, for investigating changes in Mg surface roughness (height) over time. The impacts of this work include the establishment of a computational model of pure Mg and HA-coated pure Mg degradation calibrated using in vitro degradation data to advance the use of Mg-based biomaterials, and more broadly, to predict degradation rates of next-generation orthopedic implants.

Osteoinduction and Osteoconduction Evaluation of Biodegradable Magnesium Alloy Scaffolds in Repairing Large Segmental Defects in Long Bones of Rabbit Models

Magnesium (Mg) alloy scaffolds demonstrate promising potential for clinical applications in the repair of segmental bone defects. However, the specific mechanisms of osteoconduction and osteoinduction facilitated by these scaffolds themselves during the bone reconstruction process remain inadequately defined. This investigation systematically assesses the properties of MAO-coated Mg base implants both in vitro and in vivo. Furthermore, it elucidates the correlation between scaffold characteristics and bone regeneration in the repair of extensive long-bone defects, measuring up to 20 mm, without the use of additional bone graft materials. Electrochemical measurements and immersion tests conducted in vitro indicate that the MAO coating substantially enhances the corrosion resistance of the underlying Mg alloy. Meanwhile, the application of MAO coatings has been shown to significantly improve cytocompatibility, cellular adhesion, and osteogenic differentiation, as evidenced by the CCK-8 assays, ALP activity measurements, Western blot, and RT-qPCR in vitro. At 24 weeks postimplantation with the MAO-coated Mg alloy scaffold, the large segmental defects were effectively repaired concerning both integrity and continuity. The Micro-CT gradual replacement of old bone with new bone on the implant surface was observed by X-ray and Micro-CT. Meanwhile, the histological results indicated that the MAO-coated Mg alloy scaffold maintained a robust osteogenic response. In summary, the MAO-coated Mg alloy scaffold independently exhibits effective osteoconduction and osteoinduction, playing a significant role in bone repair function without the need for additional bone graft materials.

Bone cells influence the degradation interface of pure Mg and WE43 materials: Insights from multimodal in vitro analysis

In this study, the interaction of pure Mg and WE43 alloy under the presence of osteoblast (OB) and osteoclast (OC) cells and their influence on the degradation of materials have been deeply analyzed. Since OB and OC interaction has an important role in bone remodeling, we examined the surface morphology and dynamic changes in the chemical composition and thickness of the corrosion layers formed on pure Mg and WE43 alloy by direct monoculture and coculture of pre-differentiated OB and OC cells in vitro. Electrochemical techniques examined the corrosion performance. The corrosion products were characterized using a combination of the focused ion beam (FIB), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). Cell viability and morphology were assessed by fluorescent microscopy and SEM. Our findings demonstrate cell spread and attachment variations, which differ depending on the Mg substrates. It was clearly shown that cell culture groups delayed degradation processes with the lowest corrosion rate observed in the presence of OBOC coculture for the WE43 substrate. Ca-P enrichment was observed in the outer-middle region of the corrosion layer but only after 7 days of OBOC coculture on WE43 and after 14 days on the pure Mg specimens. STATEMENT OF SIGNIFICANCE: Magnesium metallic materials that can degrade over time provide distinct opportunities for orthopedic application. However, there is still a lack, especially in elucidating cell-material interface characterization. This study investigated the influence of osteoblast-osteoclast coculture in direct Mg-material contact. Our findings demonstrated that pre-differentiated osteoblasts and osteoclasts cocultured on Mg substrates influenced the chemistry of the corrosion layers. The cell spread and attachment were Mg substrate-dependent. The findings of coculturing bone cells directly on Mg materials within an in vitro model provide an effective approach for studying the dynamic degradation processes of Mg alloys while also elucidating cell behavior and their potential contribution to the degradation of these alloys.

In situ engineered magnesium alloy implant for preventing postsurgical tumor recurrence

Invasive tumors are difficult to be completely resected in clinical surgery due to the lack of clear resection margins, which greatly increases the risk of postoperative recurrence. However, chemotherapy and radiotherapy as the traditional means of postoperative adjuvant therapy, are limited in postoperative applications, such as multi-drug resistance and low sensitivity, etc. Therefore, an engineered magnesium alloy rod is designed as a postoperative implant to completely remove postoperative residual tumor tissue and inhibit tumor recurrence by gas and mild magnetic hyperthermia therapy (MMHT). As a reactive metal, magnesium alloy responds to the acidic tumor microenvironment by continuously generating hydrogen. The in-situ generation of hydrogen not only protects the surrounding normal tissue, but also enables the magnesium alloy to achieve MMHT under low-intensity alternating magnetic field (AMF). Furthermore, the numerous reactive oxygen species (ROS) produced by heat stress will combine with nitric oxide (NO) generated in situ, to produce more toxic reactive nitrogen species (RNS) storm. In summary, engineered magnesium alloy can completely remove residual tumor tissue and inhibit tumor recurrence by MMHT and RNS storm under low-intensity AMF, and the biodegradability of magnesium alloy makes great potential for clinical application.

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.

Biodegradable magnesium based metal materials inhibit the growth of cervical cancer cells

Traditional chemotherapy drugs for cervical cancer often cause significant toxic side effects and drug resistance problems, highlighting the urgent need for more innovative and effective treatment strategies. Magnesium alloy is known to be degradable and biocompatible. The release of degradation products Mg2+, OH-, and H2 from magnesium alloy can alter the tumor microenvironment, providing potential anti-tumor properties. We explored the innovative use of magnesium alloy biomaterials in the treatment of cervical cancer, investigating how various concentrations of Mg2+ on the proliferation and cell death of cervical cancer cells. The results revealed that varying concentrations of Mg2+ significantly inhibited cervical cancer by arresting the cell cycle in the G0/G1 phase and inducing apoptosis in SiHa cells, effectively reducing tumor cell proliferation. In vivo experiments demonstrated that 20 mM Mg2+ group had the smallest tumor volume, exhibiting a potent inhibitory effect on the biological characteristics of cervical cancer. This enhances the therapeutic potential of this biomaterial as a local anti-tumor therapy and lays a theoretical foundation for the potential application of magnesium in the treatment of cervical cancer.

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.

Biomechanical optimization of the magnesium alloy bionic cannulated screw for stabilizing femoral neck fractures: a finite element analysis

Purposes

The magnesium alloy bionic cannulated screw (MABCS) was designed in a previous study promoting cortical-cancellous biphasic healing of femoral neck fractures. The main purpose was to analyze the bore diameters that satisfy the torsion standards and further analyze the optimal pore and implantation direction for stabilizing femoral neck fractures.

Methods

The MABCS design with bionic holes with a screw diameter of less than 20% met the torsion standard for metal screws. The MABCS was utilized to repair the femoral neck fracture via Abaqus 6.14 software, which simulated the various stages of fracture healing to identify the optimal biomechanical environment for bionic hole size (5%, 10%, 15%, and 20%) and implantation direction (0°, 45°, 90°, and 135°).

Results

The stress distribution of the MABCS fracture fixation model is significantly improved with an implantation orientation of 90°. The MABCS with a bionic hole and a screw diameter of 10% provides optimal stress distribution compared with the bionic cannulated screw with diameters of 5%, 15%, and 20%. In addition, the cannulated screw fixation model with a 10% bionic hole size has optimal bone stress distribution and better internal fixation than the MABCS fixation models with 5%, 15%, and 20% screw diameters.

Conclusion

In summary, the MABCS with 10% screw diameter bionic holes has favorable biomechanical characteristics for stabilizing femoral neck fractures. This study provides a biomechanical foundation for further optimization of the bionic cannulated screw.

Usefulness of multiple bioabsorbable Mg screws/K‑wires for comminuted radial head fractures

PURPOSE

We hypothesized that multiple absorbable screws/K-wires would be effective for native head preservation in comminuted radial head fracture fixation (com-RHFs).

METHODS

Seventeen patients who met the inclusion criteria between 2018 and 2020 were included. Radiologic findings indicating proper union and clinical outcomes such as the range of elbow motion, visual analog scale score, and Mayo Elbow Performance Score were assessed prospectively after surgery and at least three years of follow-up.

RESULTS

The mean follow-up period was 4.6 years. Eleven, one, three, and two patients presented with isolated com-RHFs, type 2 (accompanied injury of medial collateral ligament), type 4 ("terrible triad") fractures, and type 5 posterior olecranon fracture-dislocations, respectively. Union was achieved after a mean of nine weeks postoperatively. The head and shaft angles did not differ significantly from the contralateral normal values (p = 0.778 and 0.872, coronal and sagittal, respectively). At the final follow-up, the mean flexion-extension/pronation-supination arcs were 126.47 ± 4.92°/135.59 ± 10.13°, and thus were significantly different from those on the contralateral side (p < 0.001, both), however the arcs were functional ranges for ordinary daily life. Also, functional status was satisfactory in all individuals. The arthritis grade and extent of heterotrophic ossification were satisfactory in all cases, and there were no serious complications requiring revision surgery.

CONCLUSIONS

Absorbable screw/K-wire fixation for com-RHFs is an option before radial head arthroplasty associated with a low complication rate and no need for revision.

Research status and prospects of biodegradable magnesium-based metal guided bone regeneration membranes

Biodegradable magnesium-based metal guided bone regeneration (GBR) membranes possess excellent mechanical properties, biodegradability, and osteopromotive capabilities, making them ideal implants for the treatment of maxillofacial bone defects. This review summarizes the current status and future research trends related to magnesium-based GBR membranes. First, the research history and application fields of magnesium-based metals are introduced, and the advantages of the use of magnesium-based materials for GBR membranes, including their mechanical properties, biocompatibility, osteopromotive performance, and underlying mechanisms are discussed. Finally, this review addresses the current limitations of magnesium-based GBR membranes and their applications and prospects in the field of dentistry. In conclusion, considerable advancements have been in fundamental and translational research on magnesium-based GBR membranes, which lays a crucial foundation for the treatment of maxillofacial bone defects.

Degradation Behavior of Medical MgZZC-1 in Various Simulated Body Fluids

Magnesium-based biodegradable metal bone implants exhibit superior mechanical properties compared to biodegradable polymers for orthopedic and cardiovascular stents. In this study, MgZZC-x (x = 1, 1.2) alloys were screened by in vitro biocompatibility tests in three simulated body fluids under nontoxic conditions. The MgZZC-1 alloys with better biocompatibility were selected to predict the days required for complete degradation. The evolution of degradation products was analyzed, and the mechanism of formation of the product film was inferred. A degradation kinetic model was established to investigate the effect of MEM components on the degradation of the alloys. The results demonstrate that the proteins in MEM can greatly retard the degradation progress by attaching to the surface of MgZZC-1 alloys, which are predicted to degrade completely within 341 days. The carbonate and phosphate buffers were adjusted to pH in MEM solution, delaying the degradation of magnesium alloys. This process in MEM more accurately reflects the actual degradation in the body and is superior to that in Hanks and SBF solutions. This study will promote the application of biodegradable materials in clinical medicine.

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.

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.

Leveraging the Recent Advancements in GelMA Scaffolds for Bone Tissue Engineering: An Assessment of Challenges and Opportunities

The field of bone tissue engineering has seen significant advancements in recent years. Each year, over two million bone transplants are performed globally, and conventional treatments, such as bone grafts and metallic implants, have their limitations. Tissue engineering offers a new level of treatment, allowing for the creation of living tissue within a biomaterial framework. Recent advances in biomaterials have provided innovative approaches to rebuilding bone tissue function after damage. Among them, gelatin methacryloyl (GelMA) hydrogel is emerging as a promising biomaterial for supporting cell proliferation and tissue regeneration, and GelMA has exhibited exceptional physicochemical and biological properties, making it a viable option for clinical translation. Various methods and classes of additives have been used in the application of GelMA for bone regeneration, with the incorporation of nanofillers or other polymers enhancing its resilience and functional performance. Despite promising results, the fabrication of complex structures that mimic the bone architecture and the provision of balanced physical properties for both cell and vasculature growth and proper stiffness for load bearing remain as challenges. In terms of utilizing osteogenic additives, the priority should be on versatile components that promote angiogenesis and osteogenesis while reinforcing the structure for bone tissue engineering applications. This review focuses on recent efforts and advantages of GelMA-based composite biomaterials for bone tissue engineering, covering the literature from the last five years.

A magnesium screw with optimized geometry exhibits improved corrosion resistance and favors bone fracture healing

Stress-induced corrosion impairs the mechanical integrity of magnesium (Mg) and its alloys as potential orthopedic implants. Although there has been extensive work reporting the effects of stress on Mg corrosion in vitro, the geometric design principles of the Mg-based orthopedic devices still remain largely unknown. In this work, a numerical simulation model mimicking fractured bone fixation and surgical animal models were applied to investigate the effects of the geometric design of Mg screws on the stress distribution and the stress-induced degradation behavior. Finite element (FE) analysis was used for calculation of stress concentrations around the Mg screws, with different thread type, thread pitch, and thread width. Afterward, the Mg screws of the pre-optimization and post-optimization groups exhibiting the highest and lowest stress concentrations, respectively, were implanted in the fractured distal femora and back subcutaneous tissue of rabbits. Encouragingly, there was a significant difference between the pre-optimization and the post-optimization groups in the degradation rate of the stressed screw parts located around the fracture line. Interestingly, there was no significant difference between the two groups in the degradation rate of the non-stressed screw parts. Consistently, the Mg screw post-optimization exhibited a significantly lower degradation rate than that pre-optimization in the back subcutaneous implantation model, which generated stress in the whole screw body. The alteration in geometric design did not affect the corrosion rate of the Mg screws in an immersion test without load applied. Importantly, an accelerated new bone formation with less fibrous encapsulation around the screws was observed in the Mg group post-optimization relative to the Mg group pre-optimization and the poly (lactic acid) group. Geometry optimization may be a promising strategy to reduce stress-induced corrosion in Mg-based orthopedic devices. STATEMENT OF SIGNIFICANCE: Stress concentrations influence corrosion characteristics of magnesium (Mg)-based implants. The geometric design parameters, including thread type, thread pitch, and thread width of the Mg screws, were optimized through finite element analysis to reduce stress concentrations in a fractured model. The Mg screws with triangular thread type, 2.25 mm pitch, and 0.3 mm thread width, exhibiting the lowest maximum von Mises stress, showed a significant decrease in the volume loss relative to the Mg screws pre-optimization. Compared with the Mg screw pre-optimization and the poly(lactic acid) screw, the Mg screw post-optimization favored new bone formation while inhibiting fibrous encapsulation. Collectively, optimization in the geometric design is a promising approach to reduce stress-induced corrosion in Mg-based implants.

Anatomical Brushite-Coated Mg-Nd-Zn-Zr Alloy Cage Promotes Cervical Fusion: One-Year Results in Goats

In this study, an anatomical brushite-coated Mg-Nd-Zn-Zr alloy cage was fabricated for cervical fusion in goats. The purpose of this study was to investigate the cervical fusion effect and degradation characteristics of this cage in goats. The Mg-Nd-Zn-Zr alloy cage was fabricated based on anatomical studies, and brushite coating was prepared. Forty-five goats were divided into three groups, 15 in each group, and subjected to C2/3 anterior cervical decompression and fusion with tricortical bone graft, Mg-Nd-Zn-Zr alloy cage, or brushite-coated Mg-Nd-Zn-Zr alloy cage, respectively. Cervical radiographs and computed tomography (CT) were performed 3, 6, and 12 months postoperatively. Blood was collected for biocompatibility analysis and Mg2+ concentration tests. The cervical spine specimens were obtained at 3, 6, and 12 months postoperatively for biomechanical, micro-CT, scanning electron microscopy coupled with energy dispersive spectroscopy, laser ablation-inductively coupled plasma-time-of-flight mass spectrometry, and histological analysis. The liver and kidney tissues were obtained for hematoxylin and eosin staining 12 months after surgery for biosafety analysis. Imaging and histological analysis showed a gradual improvement in interbody fusion over time; the fusion effect of the brushite-coated Mg-Nd-Zn-Zr alloy cage was comparable to that of the tricortical bone graft, and both were superior to that of the Mg-Nd-Zn-Zr alloy cage. Biomechanical testing showed that the brushite-coated Mg-Nd-Zn-Zr alloy cage achieved better stability than the tricortical bone graft at 12 months postoperatively. Micro-CT showed that the brushite coating significantly decreases the corrosion rate of the Mg-Nd-Zn-Zr alloy cage. In vivo degradation analysis showed higher Ca and P deposition in the degradation products of the brushite-coated Mg-Nd-Zn-Zr alloy cage, and no hyperconcentration of Mg was detected. Biocompatibility analysis showed that both cages were safe for cervical fusion surgery in goats. To conclude, the anatomical brushite-coated Mg-Nd-Zn-Zr alloy cage can promote cervical fusion in goats, and the brushite-coated Mg-Nd-Zn-Zr alloy is a potential material for developing absorbable fusion cages.

Recent progress and treatment strategy of pectin polysaccharide based tissue engineering scaffolds in cancer therapy, wound healing and cartilage regeneration

Natural polymers and its mixtures in the form of films, sponges and hydrogels are playing a major role in tissue engineering and regenerative medicine. Hydrogels have been extensively investigated as standalone materials for drug delivery purposes as they enable effective encapsulation and sustained release of drugs. Biopolymers are widely utilised in the fabrication of hydrogels due to their safety, biocompatibility, low toxicity, and regulated breakdown by human enzymes. Among all the biopolymers, polysaccharide-based polymer is well suited to overcome the limitations of traditional wound dressing materials. Pectin is a polysaccharide which can be extracted from different plant sources and is used in various pharmaceutical and biomedical applications including cartilage regeneration. Pectin itself cannot be employed as scaffolds for tissue engineering since it decomposes quickly. This article discusses recent research and developments on pectin polysaccharide, including its types, origins, applications, and potential demands for use in AI-mediated scaffolds. It also covers the materials-design process, strategy for implementation to material selection and fabrication methods for evaluation. Finally, we discuss unmet requirements and current obstacles in the development of optimal materials for wound healing and bone-tissue regeneration, as well as emerging strategies in the field.

Nanotechnology-based bone regeneration in orthopedics: a review of recent trends

Nanotechnology has revolutionized the field of bone regeneration, offering innovative solutions to address the challenges associated with conventional therapies. This comprehensive review explores the diverse landscape of nanomaterials - including nanoparticles, nanocomposites and nanofibers - tailored for bone tissue engineering. We delve into the intricate design principles, structural mimicry of native bone and the crucial role of biomaterial selection, encompassing bioceramics, polymers, metals and their hybrids. Furthermore, we analyze the interface between cells and nanostructured materials and their pivotal role in engineering and regenerating bone tissue. In the concluding outlook, we highlight emerging frontiers and potential research directions in harnessing nanomaterials for bone regeneration.

Entropically Toughened Robust Biodegradable Polymer Blends and Composites for Bone Tissue Engineering

Biodegradable polymers and composites are promising candidates for biomedical implants in tissue engineering. However, state-of-the-art composite scaffolds suffer from a strength-toughness dilemma due to poor interfacial adhesion and filler dispersion. In this work, we propose a facile and scalable strategy to fabricate strong and tough biocomposite scaffolds through interfacial toughening. The immiscible biopolymer matrix is compatible by the direct incorporation of a third polymer. Densely entangled polymer chains lead to massive crazes and global shear yields under tension. Weak chemical interaction and high-shear melt processing create nanoscale dispersion of nanofillers within the matrix. The resultant ternary blends and composites exhibit an 11-fold increase in toughness without compromising stiffness and strength. At 70% porosity, three-dimensional (3D)-printed composite scaffolds demonstrate high compressive properties comparable to those of cancellous bones. In vitro cell culture on the scaffolds demonstrates not only good cell viability but also effective osteogenic differentiation of human mesenchymal stem cells. Our findings present a widely applicable strategy to develop high-performance biocomposite materials for tissue regeneration.

The development of magnesium-based biomaterials in bone tissue engineering: A review

Bone regeneration is a vital clinical challenge in massive or complicated bone defects. Recently, bone tissue engineering has come to the fore to meet the demand for bone repair with various innovative materials. However, the reported materials usually cannot satisfy the requirements, such as ideal mechanical and osteogenic properties, as well as biocompatibility at the same time. Mg-based biomaterials have considerable potential in bone tissue engineering owing to their excellent mechanical strength and biosafety. Moreover, the biocompatibility and osteogenic activity of Mg-based biomaterials have been the research focuses in recent years. The main limitation faced in the applications of Mg-based biomaterials is rapid degradation, which can produce excessive Mg2+ and hydrogen, affecting the healing of the bone defect. In order to overcome the limitations, researchers have explored several ways to improve the properties of Mg-based biomaterials, including alloying, surface modification with coatings, and synthesizing other composite materials to control the degradation rate upon implantation. This article reviewed the osteogenic mechanism and requirement for appropriate degradation rate and focused on current progress in the biomedical use of Mg-based biomaterials to inspire more clinical applications of Mg in bone regeneration in the future.

Mg-Zn-Ca Alloy (ZX00) Screws Are Resorbed at a Mean of 2.5 Years After Medial Malleolar Fracture Fixation: Follow-up of a First-in-humans Application and Insights From a Sheep Model

BACKGROUND

In the ongoing development of bioresorbable implants, there has been a particular focus on magnesium (Mg)-based alloys. Several Mg alloys have shown promising properties, including a lean, bioresorbable magnesium-zinc-calcium (Mg-Zn-Ca) alloy designated as ZX00. To our knowledge, this is the first clinically tested Mg-based alloy free from rare-earth elements or other elements. Its use in medial malleolar fractures has allowed for bone healing without requiring surgical removal. It is thus of interest to assess the resorption behavior of this novel bioresorbable implant.

QUESTIONS/PURPOSES

(1) What is the behavior of implanted Mg-alloy (ZX00) screws in terms of resorption (implant volume, implant surface, and gas volume) and bone response (histologic evaluation) in a sheep model after 13 months and 25 months? (2) What are the radiographic changes and clinical outcomes, including patient-reported outcome measures, at a mean of 2.5 years after Mg-alloy (ZX00) screw fixation in patients with medial malleolar fractures?

METHODS

A sheep model was used to assess 18 Mg-alloy (ZX00) different-length screws (29 mm, 24 mm, and 16 mm) implanted in the tibiae and compared with six titanium-alloy screws. Micro-CT was performed at 13 and 25 months to quantify the implant volume, implant surface, and gas volume at the implant sites, as well as histology at both timepoints. Between July 2018 and October 2019, we treated 20 patients with ZX00 screws for medial malleolar fractures in a first-in-humans study. We considered isolated, bimalleolar, or trimalleolar fractures potentially eligible. Thus, 20 patients were eligible for follow-up. However, 5% (one patient) of patients were excluded from the analysis because of an unplanned surgery for a pre-existing osteochondral lesion of the talus performed 17 months after ZX00 implantation. Additionally, another 5% (one patient) of patients were lost before reaching the minimum study follow-up period. Our required minimum follow-up period was 18 months to ensure sufficient time to observe the outcomes of interest. At this timepoint, 10% (two patients) of patients were either missing or lost to follow-up. The follow-up time was a mean of 2.5 ± 0.6 years and a median of 2.4 years (range 18 to 43 months).

RESULTS

In this sheep model, after 13 months, the 29-mm screws (initial volume: 198 ± 1 mm 3 ) degraded by 41% (116 ± 6 mm 3 , mean difference 82 [95% CI 71 to 92]; p < 0.001), and after 25 months by 65% (69 ± 7 mm 3 , mean difference 130 [95% CI 117 to 142]; p < 0.001). After 13 months, the 24-mm screws (initial volume: 174 ± 0.2 mm 3 ) degraded by 51% (86 ± 21 mm 3 , mean difference 88 [95% CI 52 to 123]; p = 0.004), and after 25 months by 72% (49 ± 25 mm 3 , mean difference 125 [95% CI 83 to 167]; p = 0.003). After 13 months, the 16-mm screws (initial volume: 112 ± 5 mm 3 ) degraded by 57% (49 ± 8 mm 3 , mean difference 63 [95% CI 50 to 76]; p < 0.001), and after 25 months by 61% (45 ± 10 mm 3 , mean difference 67 [95% CI 52 to 82]; p < 0.001). Histologic evaluation qualitatively showed ongoing resorption with new bone formation closely connected to the resorbing screw without an inflammatory reaction. In patients treated with Mg-alloy screws after a mean of 2.5 years, the implants were radiographically not visible in 17 of 18 patients and the bone had homogenous texture in 15 of 18 patients. No clinical or patient-reported complications were observed.

CONCLUSION

In this sheep model, Mg-alloy (ZX00) screws showed a resorption to one-third of the original volume after 25 months, without eliciting adverse immunologic reactions, supporting biocompatibility during this period. Mg-alloy (ZX00) implants were not detectable on radiographs after a mean of 2.5 years, suggesting full resorption, but further studies are needed to assess environmental changes regarding bone quality at the implantation site after implant resorption.

CLINICAL RELEVANCE

The study demonstrated successful healing of medial malleolar fractures using bioresorbable Mg-alloy screws without clinical complications or revision surgery, resulting in pain-free ankle function after 2.5 years. Future prospective studies with larger samples and extended follow-up periods are necessary to comprehensively assess the long-term effectiveness and safety of ZX00 screws, including an exploration of limitations when there is altered bone integrity, such as in those with osteoporosis. Additional use of advanced imaging techniques, such as high-resolution CT, can enhance evaluation accuracy.

Magnesium Alloys in Orthopedics: A Systematic Review on Approaches, Coatings and Strategies to Improve Biocompatibility, Osteogenic Properties and Osteointegration Capabilities

There is increasing interest in using magnesium (Mg) alloy orthopedic devices because of their mechanical properties and bioresorption potential. Concerns related to their rapid degradation have been issued by developing biodegradable micro- and nanostructured coatings to enhance corrosion resistance and limit the release of hydrogen during degradation. This systematic review based on four databases (PubMed®, Embase, Web of Science™ and ScienceDirect®) aims to present state-of-the-art strategies, approaches and materials used to address the critical factors currently impeding the utilization of Mg alloy devices. Forty studies were selected according to PRISMA guidelines and specific PECO criteria. Risk of bias assessment was conducted using OHAT and SYRCLE tools for in vitro and in vivo studies, respectively. Despite limitations associated with identified bias, the review provides a comprehensive analysis of preclinical in vitro and in vivo studies focused on manufacturing and application of Mg alloys in orthopedics. This attests to the continuous evolution of research related to Mg alloy modifications (e.g., AZ91, LAE442 and WE43) and micro- and nanocoatings (e.g., MAO and MgF2), which are developed to improve the degradation rate required for long-term mechanical resistance to loading and excellent osseointegration with bone tissue, thereby promoting functional bone regeneration. Further research is required to deeply verify the safety and efficacy of Mg alloys.

Bone Regeneration Induced by Patient-Adapted Mg Alloy-Based Scaffolds for Bone Defects: Present and Future Perspectives

Treatment of bone defects resulting after tumor surgeries, accidents, or non-unions is an actual problem linked to morbidity and the necessity of a second surgery and often requires a critical healthcare cost. Although the surgical technique has changed in a modern way, the treatment outcome is still influenced by patient age, localization of the bone defect, associated comorbidities, the surgeon approach, and systemic disorders. Three-dimensional magnesium-based scaffolds are considered an important step because they can have precise bone defect geometry, high porosity grade, anatomical pore shape, and mechanical properties close to the human bone. In addition, magnesium has been proven in in vitro and in vivo studies to influence bone regeneration and new blood vessel formation positively. In this review paper, we describe the magnesium alloy's effect on bone regenerative processes, starting with a short description of magnesium's role in the bone healing process, host immune response modulation, and finishing with the primary biological mechanism of magnesium ions in angiogenesis and osteogenesis by presenting a detailed analysis based on a literature review. A strategy that must be followed when a patient-adapted scaffold dedicated to bone tissue engineering is proposed and the main fabrication technologies are combined, in some cases with artificial intelligence for Mg alloy scaffolds, are presented with examples. We emphasized the microstructure, mechanical properties, corrosion behavior, and biocompatibility of each study and made a basis for the researchers who want to start to apply the regenerative potential of magnesium-based scaffolds in clinical practice. Challenges, future directions, and special potential clinical applications such as osteosarcoma and persistent infection treatment are present at the end of our review paper.

Long-Term Temporospatial Complementary Relationship between Degradation and Bone Regeneration of Mg-Al Alloy

The utilization of guided tissue regeneration membranes is a significant approach for enhancing bone tissue growth in areas with bone defects. Biodegradable magnesium alloys are increasingly being used as guided tissue regeneration membranes due to their outstanding osteogenic properties. However, the degradation rates of magnesium alloy bone implants documented in the literature tend to be rapid. Moreover, many studies focus only on the initial 3-month period post-implantation, limiting their applicability and impeding clinical adoption. Furthermore, scant attention has been given to the interplay between the degradation of magnesium alloy implants and the adjacent tissues. To address these gaps, this study employs a well-studied magnesium-aluminum (Mg-Al) alloy membrane with a slow degradation rate. This membrane is implanted into rat skull bone defects and monitored over an extended period of up to 48 weeks. Observations are conducted at various intervals (2, 4, 8, 12, 24, and 48 weeks) following the implantation. Assessment of degradation behavior and tissue regeneration response is carried out using histological sections, micro-CT scans, and scanning electron microscopy (SEM). The findings reveal that the magnesium alloy membranes demonstrate remarkable biocompatibility and osteogenic capability over the entire observation duration. Specifically, the Mg-Al alloy membranes sustain their structural integrity for 8 weeks. Notably, their osteogenic ability is further enhanced as a corrosion product layer forms during the later stages of implantation. Additionally, our in vitro experiments employing extracts from the magnesium alloy display a significant osteogenic effect, accompanied by a notable increase in the expression of osteogenic-related genes. Collectively, these results strongly indicate the substantial potential of Mg-Al alloy membranes in the context of guided tissue regeneration.

Magnesium-based alloys with adapted interfaces for bone implants and tissue engineering

Magnesium and its alloys are one of the most used materials for bone implants and tissue engineering. They are characterized by numerous advantages such as biodegradability, high biocompatibility and mechanical properties with values close to the human bone. Unfortunately, the implant surface must be adequately tuned, or Mg-based alloys must be alloyed with other chemical elements due to their increased corrosion effect in physiological media. This article reviews the clinical challenges related to bone repair and regeneration, classifying bone defects and presenting some of the most used and modern therapies for bone injuries, such as Ilizarov or Masquelet techniques or stem cell treatments. The implant interface challenges are related to new bone formation and fracture healing, implant degradation and hydrogen release. A detailed analysis of mechanical properties during implant degradation is extensively described based on different literature studies that included in vitro and in vivo tests correlated with material properties' characterization. Mg-based trauma implants such as plates and screws, intramedullary nails, Herbert screws, spine cages, rings for joint treatment and regenerative scaffolds are presented, taking into consideration their manufacturing technology, the implant geometrical dimensions and shape, the type of in vivo or in vitro studies and fracture localization. Modern technologies that modify or adapt the Mg-based implant interfaces are described by presenting the main surface microstructural modifications, physical deposition and chemical conversion coatings. The last part of the article provides some recommendations from a translational perspective, identifies the challenges associated with Mg-based implants and presents some future opportunities. This review outlines the available literature on trauma and regenerative bone implants and describes the main techniques used to control the alloy corrosion rate and the cellular environment of the implant.

Fabrication and Characterization of Zn Particle Incorporated Fibrous Scaffolds for Potential Application in Tissue Healing and Regeneration

Zinc (Zn) metal and its alloys have received a lot of interest in biomedical applications due to their biodegradability, biocompatibility, antimicrobial activity, and ability to stimulate tissue regeneration. Bulk Zn has been successfully utilized in a variety of implant applications, most notably as bioabsorbable cardiac stents and orthopedic fixation devices, where it provides adequate mechanical properties while also releasing helpful Zn ions (Zn2+) during degradation. Such beneficial ions are dose-dependent and, when released in excess, can induce cellular toxicity. In this study, we hypothesize that embedding Zn metal particles into a polymer nanofibrous scaffold will enable control of the degradation and time release of the Zn2+. We designed and fabricated two polymer scaffolds, polycaprolactone (PCL) and polycaprolactone-chitosan (PCL-CH). Each scaffold had an increasing amount of Zn. Several physicochemical properties such as fiber morphology, crystallinity, mechanical strength, hydrophilicity, degradation and release of Zn2+, thermal properties, chemical compositions, and so forth were characterized and compared with the PCL fibrous scaffold. The biological properties of the scaffolds were evaluated in vitro utilizing direct and indirect cytotoxicity assays and cell viability. All the data show that the addition of Zn changed various physical properties of the PCL and PCL-CH scaffolds except their chemical structure. Further investigation reveals that the PCL-CH scaffolds degrade the Zn particles relatively faster than the PCL because the presence of the hydrophilic CH influences the faster release of Zn2+ in cell culture conditions as compared to the PCL fibrous scaffold. The combined advantages of CH and Zn in the PCL scaffold enriched 3T3 fibroblast cells' survival and proliferation except the ones with the higher concentration of Zn particles. These new composite scaffolds are promising and can be further considered for tissue healing and regeneration applications.

Analysis of Antibacterial Efficacy and Cellular Alignment Regulation on Plasma Nanotextured Chitosan Surfaces

To address implant-related infections, antibacterial solutions specific to biomaterials are required to prevent bacterial proliferation. Traditional antibiotic usage has been found insufficient, motivating researchers to investigate alternative strategies such as surface modification and the application of antifouling or infection-resistant properties. A developing interest lies in designing surfaces that mimic natural antibacterial nanotopographies. In this study, we conducted a quantitative analysis of the outcomes from plasma nanotexturing, with particular emphasis on how the organization of topography influences antibacterial efficacy and the regulation of cell alignment. Plasma nanotexturing was applied to chitosan surfaces, which gradually transformed from nanopores to pillars and eventually into tilted pillars, as the plasma parameters (fluence and angle) increased. We used directed plasma nanosynthesis, a plasma-based technique that primarily induces topographical alterations on the surfaces. The surfaces were systematically characterized, incorporating methods such as scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). A comprehensive comparison of the nanotextures was executed by utilizing a trapezoidal method to calculate aspect ratios and assess texture orientation by examining the gaps in the nanostructures. We evaluated antibacterial properties against E. coli and S. aureus strains and assessed the survival and alignment of human bone marrow mesenchymal stem cells. Our findings reveal a significant reduction in bacterial adhesion (>80%) and growth on nanotextured surfaces, underscoring their potential for clinical applications. Moreover, we measured cell alignment, presenting the results in both a color-coded and numerical format to demonstrate the preferential alignment orientation induced specially by the tilted nanotexture. These insights highlight the profound impacts of plasma nanotexturing, indicating its potential for innovative biomedical applications such as advanced wound healing and tissue engineering.

Advances in Bioresorbable Materials and Electronics

Transient electronic systems represent an emerging class of technology that is defined by an ability to fully or partially dissolve, disintegrate, or otherwise disappear at controlled rates or triggered times through engineered chemical or physical processes after a required period of operation. This review highlights recent advances in materials chemistry that serve as the foundations for a subclass of transient electronics, bioresorbable electronics, that is characterized by an ability to resorb (or, equivalently, to absorb) in a biological environment. The primary use cases are in systems designed to insert into the human body, to provide sensing and/or therapeutic functions for timeframes aligned with natural biological processes. Mechanisms of bioresorption then harmlessly eliminate the devices, and their associated load on and risk to the patient, without the need of secondary removal surgeries. The core content focuses on the chemistry of the enabling electronic materials, spanning organic and inorganic compounds to hybrids and composites, along with their mechanisms of chemical reaction in biological environments. Following discussions highlight the use of these materials in bioresorbable electronic components, sensors, power supplies, and in integrated diagnostic and therapeutic systems formed using specialized methods for fabrication and assembly. A concluding section summarizes opportunities for future research.