In vivo degradation of magnesium plate/screw osteosynthesis implant systems: Soft and hard tissue response in a calvarial model in miniature pigs

Titanium versus plasma electrolytic oxidation surface-modified magnesium miniplates in a forehead secondary fracture healing model in sheep

Magnesium as a biodegradable material offers promising results in recent studies of different maxillo-facial fracture models. To overcome adverse effects caused by the fast corrosion of pure magnesium in fluid surroundings, various alloys, and surface modifications are tested in animal models. In specified cases, magnesium screws already appeared for clinical use in maxillofacial surgery. The present study aims to compare the bone healing outcome in a non-load-bearing fracture scenario of the forehead in sheep when fixed with standard-sized WE43 magnesium fixation plates and screws with plasma electrolytic oxidation (PEO) surface modification in contrast to titanium osteosynthesis. Surgery was performed on 24 merino mix sheep. The plates and screws were explanted en-bloc with the surrounding tissue after four and twelve weeks. The outcome of bone healing was investigated with micro-computed tomography, histological, immunohistological, and fluorescence analysis. There was no significant difference between groups concerning the bone volume, bone volume/ total volume, and newly formed bone in volumetric and histological analysis at both times of investigation. The fluorescence analysis revealed a significantly lower signal in the magnesium group after one week, although there was no difference in the number of osteoclasts per mm2. The magnesium group had significantly fewer vessels per mm2 in the healing tissue. In conclusion, the non-inferiority of WE43-based magnesium implants with PEO surface modification was verified concerning fracture healing under non-load-bearing conditions in a defect model. STATEMENT OF SIGNIFICANCE: Titanium implants, the current gold standard of fracture fixation, can lead to adverse effects linked to the implant material and often require surgical removal. Therefore, degradable metals like the magnesium alloy WE43 with plasma electrolytic oxidation (PEO) surface modification gained interest. Yet, miniplates of this alloy with PEO surface modification have not been examined in a fracture defect model of the facial skeleton in a large animal model. This study shows, for the first time, the non-inferiority of magnesium miniplates compared to titanium miniplates. In radiological and histological analysis, bone healing was undisturbed. Magnesium miniplates can reduce the number of interventions for implant removal, thus reducing the risk for the patient and minimizing the costs.

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.

Challenges and Pitfalls of Research Designs Involving Magnesium-Based Biomaterials: An Overview

Magnesium-based biomaterials hold remarkable promise for various clinical applications, offering advantages such as reduced stress-shielding and enhanced bone strengthening and vascular remodeling compared to traditional materials. However, ensuring the quality of preclinical research is crucial for the development of these implants. To achieve implant success, an understanding of the cellular responses post-implantation, proper model selection, and good study design are crucial. There are several challenges to reaching a safe and effective translation of laboratory findings into clinical practice. The utilization of Mg-based biomedical devices eliminates the need for biomaterial removal surgery post-healing and mitigates adverse effects associated with permanent biomaterial implantation. However, the high corrosion rate of Mg-based implants poses challenges such as unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. The biocompatibility and degradability of materials based on magnesium have been studied by many researchers in vitro; however, evaluations addressing the impact of the material in vivo still need to be improved. Several animal models, including rats, rabbits, dogs, and pigs, have been explored to assess the potential of magnesium-based materials. Moreover, strategies such as alloying and coating have been identified to enhance the degradation rate of magnesium-based materials in vivo to transform these challenges into opportunities. This review aims to explore the utilization of Mg implants across various biomedical applications within cellular (in vitro) and animal (in vivo) models.

Research progress and perspective of metallic implant biomaterials for craniomaxillofacial surgeries

Craniomaxillofacial bone serves a variety of functions. However, the increasing number of cases of craniomaxillofacial bone injury and the use of selective rare implants make the treatment difficult, and the cure rate is low. If such a bone injury is not properly treated, it can lead to a slew of complications that can seriously disrupt a patient's daily life. For example, premature closure of cranial sutures or skull fractures can lead to increased intracranial pressure, which can lead to headaches, vomiting, and even brain hernia. At present, implant placement is one of the most common approaches to repair craniomaxillofacial bone injury or abnormal closure, especially with biomedical metallic implants. This review analyzes the research progress in the design and development of degradable and non-degradable metallic implants in craniomaxillofacial surgery. The mechanical properties, corrosion behaviours, as well as in vitro and in vivo performances of these materials are summarized. The challenges and future research directions of metallic biomaterials used in craniomaxillofacial surgery are also identified.

Near-Infrared Spectroscopy for the In Vivo Monitoring of Biodegradable Implants in Rats

Magnesium (Mg) alloys possess unique properties that make them ideal for use as biodegradable implants in clinical applications. However, reports on the in vivo assessment of these alloys are insufficient. Thus, monitoring the degradation of Mg and its alloys in vivo is challenging due to the dynamic process of implant degradation and tissue regeneration. Most current works focus on structural remodeling, but functional assessment is crucial in providing information about physiological changes in tissues, which can be used as an early indicator of healing. Here, we report continuous wave near-infrared spectroscopy (CW NIRS), a non-invasive technique that is potentially helpful in assessing the implant-tissue dynamic interface in a rodent model. The purpose of this study was to investigate the effects on hemoglobin changes and tissue oxygen saturation (StO₂) after the implantation of Mg-alloy (WE43) and titanium (Ti) implants in rats' femurs using a multiwavelength optical probe. Additionally, the effect of changes in the skin on these parameters was evaluated. Lastly, combining NIRS with photoacoustic (PA) imaging provides a more reliable assessment of tissue parameters, which is further correlated with principal component analysis.

Degradation behavior and osseointegration of Mg-Zn-Ca screws in different bone regions of growing sheep: a pilot study

Magnesium (Mg)-based implants are highly attractive for the orthopedic field and may replace titanium (Ti) as support for fracture healing. To determine the implant-bone interaction in different bony regions, we implanted Mg-based alloy ZX00 (Mg < 0.5 Zn < 0.5 Ca, in wt%) and Ti-screws into the distal epiphysis and distal metaphysis of sheep tibiae. The implant degradation and osseointegration were assessed in vivo and ex vivo after 4, 6 and 12 weeks, using a combination of clinical computed tomography, medium-resolution micro computed tomography (µCT) and high-resolution synchrotron radiation µCT (SRµCT). Implant volume loss, gas formation and bone growth were evaluated for both implantation sites and each bone region independently. Additionally, histological analysis of bone growth was performed on embedded hard-tissue samples. We demonstrate that in all cases, the degradation rate of ZX00-implants ranges between 0.23 and 0.75 mm/year. The highest degradation rates were found in the epiphysis. Bone-to-implant contact varied between the time points and bone types for both materials. Mostly, bone-volume-to-total-volume was higher around Ti-implants. However, we found an increased cortical thickness around the ZX00-screws when compared with the Ti-screws. Our results showed the suitability of ZX00-screws for implantation into the distal meta- and epiphysis.

Applications of Biodegradable Magnesium-Based Materials in Reconstructive Oral and Maxillofacial Surgery: A Review

Reconstruction of defects in the maxillofacial region following traumatic injuries, craniofacial deformities, defects from tumor removal, or infections in the maxillofacial area represents a major challenge for surgeons. Various materials have been studied for the reconstruction of defects in the maxillofacial area. Biodegradable metals have been widely researched due to their excellent biological properties. Magnesium (Mg) and Mg-based materials have been extensively studied for tissue regeneration procedures due to biodegradability, mechanical characteristics, osteogenic capacity, biocompatibility, and antibacterial properties. The aim of this review was to analyze and discuss the applications of Mg and Mg-based materials in reconstructive oral and maxillofacial surgery in the fields of guided bone regeneration, dental implantology, fixation of facial bone fractures and soft tissue regeneration.

Comparative Osteogenesis and Degradation Behavior of Magnesium Implant in Epiphysis and Diaphysis of the Long Bone in the Rat Model

Magnesium (Mg), as a biodegradable material, is a promising candidate for orthopedic surgery. Long-bone fractures usually occur in cancellous-bone-rich epiphysis at each end or the cortical-rich diaphysis in the center, with different bone healing processes. Little is known about the differences in results between the two regions when applying Mg implants. Therefore, this study aimed to compare the biodegradation and osteogenesis of Mg implants in a rat model's epiphysis and diaphysis of the long bone. Twelve male Sprague Dawley rats underwent Mg rod implantation in the distal femoral epiphyses and tibial diaphyses. Every three weeks for up to twelve weeks, degradation behavior, gas evolution, and new bone formation were measured by micro CT. Histomorphology was analyzed by Hematoxylin and Eosin, Villanueva bone staining, and TRAP staining for osteoclastogenesis evaluations. Micro-CT analysis showed statistically significant higher new bone formation in the epiphysis group than in the diaphysis group, which correlated with a lower gas volume. Histological analysis showed higher osseointegration of Mg implants in the epiphyseal region than in the diaphyseal region. The magnesium implant's osteoclastogenesis-inhibiting properties were shown in the surrounding areas in both the cortical bone of the diaphysis and the cancellous bone of the epiphysis. Our findings show the differences in the magnesium implant's osteogenesis and biodegradation in the epiphysis and the diaphysis. These dissimilarities indicate a better response of the epiphyseal region to the Mg implants, a promising biomaterial for orthopedic surgery applications.

In vivo performance of a rare earth free Mg–Zn–Ca alloy manufactured using twin roll casting for potential applications in the cranial and maxillofacial fixation devices

A magnesium alloy containing essential, non-toxic, biodegradable elements such as Ca and Zn has been fabricated using a novel twin-roll casting process (TRC). Microstructure, mechanical properties, in vivo corrosion and biocompatibility have been assessed and compared to the properties of the rare earth (RE) element containing WE43 alloy. TRC Mg-0.5 wt% Zn- 0.5 wt% Ca exhibited fine grains with an average grain size ranging from 70 to 150 μm. Mechanical properties of a TRC Mg-0.5Zn-0.5Ca alloy showed an ultimate tensile strength of 220 MPa and ductility of 9.3%. The TRC Mg-0.5Zn-0.5Ca alloy showed a degradation rate of 0.51 ± 0.07 mm/y similar to that of the WE43 alloy (0.47 ± 0.09 mm/y) in the rat model after 1 week of implantation. By week 4 the biodegradation rates of both alloys studied were lowered and stabilized with fewer gas pockets around the implant. The histological analysis shows that both WE43 and TRC Mg-0.5Zn-0.5Ca alloy triggered comparable tissue healing responses at respective times of implantation. The presence of more organized scarring tissue around the TRC Mg-0.5Zn-0.5Ca alloys suggests that the biodegradation of the RE-free alloy may be more conducive to the tissue proliferation and remodelling process.

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Mg-0.5Zn-0.5Ca alloy plates were fabricated by a twin-roll casting (TRC) process.

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TRC alloy showed an ultimate strength and elongation of 221 ± 2 MPa and 9 ± 2%.

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Gas development during in vivo degradation was analysed using μ-CT techniques.

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Histological analysis revealed a good biocompatibility and promoted healing.

[Cement augmentation and bone graft substitutes-Materials and biomechanics]

BACKGROUND

Materials with different characteristics are used for cement augmentation and as bone graft substitutes.

OBJECTIVE

Cement augmentation and bone graft substitutes are the subject of current research. The evaluation of new knowledge allows its specific application.

MATERIAL AND METHODS

Selective literature search and outline of experimental research results on cement augmentation and bone graft substitutes.

RESULTS

Augmentation and bone graft substitutes are essential components of current trauma surgical procedures. Despite intensive research all materials have specific disadvantages. Cement augmentation of implants enhances not only the anchorage but also influences the failure mode.

CONCLUSION

Cement augmentation has large potential especially in osteoporotic bone. In load-bearing regions acrylic-based cements remain the standard of choice. Ceramic cements are preferred in non-load-bearing areas. Their combination with resorbable metals offers still largely unexplored potential. Virtual biomechanics can help improve the targeted application of cement augmentation.

A Systematic Review and Network Meta-Analysis of Biomedical Mg Alloy and Surface Coatings in Orthopedic Application

Magnesium alloys have great application prospects as ideal bone implant materials. However, their poor corrosion resistance limits their clinical orthopedic application. Surface modification promotes the corrosion resistance of magnesium. Conversion coatings, such as calcium phosphate (Ca-P) coating, microarc oxidation (MAO) treatment, and fluoride (FLU) treatment, have been extensively investigated in in vivo studies. This systematic review and network meta-analysis compared the influence of different conversion coatings on bone repair, material properties, and systemic host response in orthopedic applications. Using the PICOS model, the inclusion criteria for biodegradable magnesium and its alloys were determined for in vivo studies. Four databases were used. The standard and weight mean differences with 95% confidence intervals were used to analyze new bone formation and degradation rate. Network structure and forest plots were created, and ranking probabilities were estimated. The risk of bias and quality of evidence were assessed using SYRCLE, CERQual, and GRADE tools. In the qualitative analysis, 43 studies were selected, and the evaluation of each outcome indicator was not entirely consistent from article to article. In the quantitative analysis, 21 articles were subjected to network meta-analysis, with 16 articles on implant degradation and 8 articles for new bone formation. Additionally, SUCRA indicated that Ca-P coating exhibited the highest corrosion resistance, followed by FLU treatment. MAO demonstrated the best capability for new bone formation, followed by Ca-P coating. Ca-P coating exhibited the highest overall performance. To conclude, coated Mg can promote better new bone formation than bare Mg and has considerable biocompatibility. Ca-P-coated Mg and MAO-coated Mg have the greatest potential to significantly promote corrosion resistance and bone regeneration, respectively. The findings of this study will provide a theoretical basis for the investigation of composite coatings and guidance for the orthopedic application of Mg bone implants.

Bone Union Quality after Fracture Fixation of Mandibular Head with Compression Magnesium Screws

For some years now, fixation devices created with resorbable magnesium alloys for the mandibular head have been clinically available and are beginning to be used. It is thus valuable to evaluate the quality of unions in these cases. The aim of this study was radiological comparison of magnesium versus titanium open reduction and rigid fixations in the mandible condylar head. Thirty-one patients were treated for fractures of the mandibular head with magnesium WE43 alloy headless compression screws (diameter 2.3 mm) and, as a reference group, 29 patients were included with similar construction titanium screws (diameter 1.8 mm). The 12-month results of the treatment were evaluated by the texture analysis of CT. Near similar treatment results were found with magnesium screws in traditional titanium fixation. Magnesium screws result in a higher density of the bone structure in the mandibular head. Conclusions: The quantitative evaluation of bone union after surgical treatment of mandibular head fracture with magnesium compression headless screws indicates that stable consolidation was achieved. Undoubtedly, the resorption process of the screws was found to be incomplete after 12 months, evidenced by a marked densification of the bone structure at the fracture site.

In Silico Biomechanical Evaluation of WE43 Magnesium Plates for Mandibular Fracture Fixation

Titanium fixation devices are the gold standard for the treatment of mandibular fractures; however, they present serious limitations, such as non-degradability and generation of imaging artifacts. As an alternative, biodegradable magnesium alloys have lately drawn attention due to their biodegradability and biocompatibility. In addition, magnesium alloys offer a relatively high modulus of elasticity in comparison to biodegradable polymers, being a potential option to substitute titanium in highly loaded anatomical areas, such as the mandible. This study aimed to evaluate the biomechanical competence of magnesium alloy WE43 plates for mandibular fracture fixation in comparison to the clinical standard or even softer polymer solutions. A 3D finite element model of the human mandible was developed, and four different fracture scenarios were simulated, together with physiological post-operative loading and boundary conditions. In a systematic comparison, the material properties of titanium alloy Ti-6Al-4V, magnesium alloy WE43, and polylactic acid (PLA) were assigned to the fixation devices, and two different plate thicknesses were tested. No failure was predicted in the fixation devices for any of the tested materials. Moreover, the magnesium and titanium fixation devices induced a similar amount of strain within the healing regions. On the other hand, the PLA devices led to higher mechanical strains within the healing region. Plate thickness only slightly influenced the primary fixation stability. Therefore, magnesium alloy WE43 fixation devices seem to provide a suitable biomechanical environment to support mandibular fracture healing in the early stages of bone healing. Magnesium WE43 showed a biomechanical performance similar to clinically used titanium devices with the added advantages of biodegradability and radiopacity, and at the same time it showed a remarkably higher primary stability compared to PLA fixation devices, which appear to be too unstable, especially in the posterior and more loaded mandibular fracture cases.

Corrosion Resistance and Cytocompatibility of Magnesium-Calcium Alloys Modified with Zinc- or Gallium-Doped Calcium Phosphate Coatings

In orthopedic surgery, metals are preferred to support or treat damaged bones due to their high mechanical strength. However, the necessity for a second surgery for implant removal after healing creates problems. Therefore, biodegradable metals, especially magnesium (Mg), gained importance, although their extreme susceptibility to galvanic corrosion limits their applications. The focus of this study was to control the corrosion of Mg and enhance its biocompatibility. For this purpose, surfaces of magnesium-calcium (MgCa1) alloys were modified with calcium phosphate (CaP) or CaP doped with zinc (Zn) or gallium (Ga) via microarc oxidation. The effects of surface modifications on physical, chemical, and mechanical properties and corrosion resistance of the alloys were studied using surface profilometry, goniometry, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), nanoindentation, and electrochemical impedance spectroscopy (EIS). The coating thickness was about 5-8 μm, with grain sizes of 43.1 nm for CaP coating and 28.2 and 58.1 nm for Zn- and Ga-doped coatings, respectively. According to EIS measurements, the capacitive response (Y_c) decreased from 11.29 to 8.72 and 0.15 Ω^-1 cm^-2 sⁿ upon doping with Zn and Ga, respectively. The E_corr value, which was -1933 mV for CaP-coated samples, was found significantly electropositive at -275 mV for Ga-doped ones. All samples were cytocompatible according to indirect tests. In vitro culture with Saos-2 cells led to changes in the surface compositions of the alloys. The numbers of cells attached to the Zn-doped (2.6 × 10⁴ cells/cm²) and Ga-doped (6.3 × 10⁴ cells/cm²) coatings were higher than that on the surface of the undoped coating (1.0 × 10³ cells/cm²). Decreased corrosivity and enhanced cell affinity of the modified MgCa alloys (CaP coated and Zn and Ga doped, with Ga-doped ones having the greatest positive effect) make them novel and promising candidates as biodegradable metallic implant materials for the treatment of bone damages and other orthopedic applications.

Dynamic in vivo monitoring of fracture healing process in response to magnesium implant with multimodal imaging: Pilot longitudinal study in a rat external fixation model

Rodent models are commonly used in pre-clinical research of magnesium (Mg) -based and other types of biomaterials for fracture treatment. Most studies selected unstable fixation methods, and there is a...

Improved in vivo osseointegration and degradation behavior of PEO surface-modified WE43 magnesium plates and screws after 6 and 12 months

Magnesium is a highly promising candidate with respect to its future use as a material for resorbable implants. When magnesium degrades, hydrogen gas is released. High doses of gas emergence are reported to impair osseointegration and may therefore lead to fixation failure. The successful delay and reduction of the degradation rate by applying plasma electrolytic oxidation (PEO) as a post processing surface modification method for magnesium alloy has recently been demonstrated. The aim of this study was thus to compare the degradation behavior of a WE43-based plate system with and without respective PEO surface modification and to further investigate osseointegration, as well as the resulting effects on the surrounding bony tissue of both variants in a miniature pig model. WE43 magnesium screws and plates without (WE43) and with PEO surface modification (WE43-PEO) were implanted in long bones of Göttingen Miniature Pigs. At six and twelve months after surgery, micro-CT and histomorphometric analysis was performed. Residual screw volume (SV/TV; WE43: 28.8 ± 21.1%; WE43-PEO: 62.9 ± 31.0%; p = 0.027) and bone implant contact area (BIC; WE43: 18.1 ± 21.7%; WE43-PEO: 51.6 ± 27.7%; p = 0.015) were increased after six months among the PEO-modified implants. Also, surrounding bone density within the cortical bone was not affected by surface modification (BVTV; WE43: 76.7 ± 13.1%; WE43-PEO: 73.1 ± 16.2%; p = 0.732). Intramedullar (BV/TV; WE43: 33.2 ± 16.7%; WE43-PEO 18.4 ± 9.0%; p = 0.047) and subperiosteal (bone area; WE43: 2.6 ± 3.4 mm²; WE43-PEO: 6,9 ± 5.2 mm²; p = 0.049) new bone formation was found for both, surface-modified and non-surface-modified groups. After twelve months, no significant differences of SV/TV and BV/TV were found between the two groups. PEO surface modification of WE43 plate systems improved osseointegration and significantly reduced the degradation rate within the first six months in vivo. Osteoconductive and osteogenic stimulation by WE43 magnesium implants led to overall increased bone growth, when prior PEO surface modification was conducted.

A review of the physiological impact of rare earth elements and their uses in biomedical Mg alloys

Magnesium (Mg) is well-tolerated by the body, displaying exceedingly low toxicity, rapid excretion, and numerous bioactive effects, including improved bone formation and protection against oxidative stresses; further, Mg alloys can be degraded in vivo to allow complete removal of an implant without surgical intervention, avoiding revision surgery and thrombosis concerns seen with permanent implants. Rare earth elements (REEs) have been of particular interest in alloying Mg alloys for nearly a century due to their unique chemical and physical properties but have attracted increasing attention in recent decades. The REEs contribute greatly to the mechanical and biological properties of metal alloys, and so are common in Mg alloys in a wide variety of applications; in particular, they represent the dominant alloying additions in current, clinically applied Mg alloys. Notably, the use of these elements may assist in the development of advanced Mg alloys for use as biodegradable orthopedic implants and cardiovascular stents. To this end, current research progress in this area, highlighting the physiological impact of REEs in Mg alloys, is reviewed. Clinical work and preclinical data of REE-containing Mg alloys are analyzed. The biological roles of REEs in cellular responses in vivo require further research in the development of biofunctional Mg alloy medical devices. STATEMENT OF SIGNIFICANCE: The presented work is a review into the biological impact and current application of rare-earth elements (REEs) in biodegradable Mg-based biomaterials. Despite their efficacy in improving corrosion, mechanical, and manufacturability properties of Mg alloys, the physiological effects of REEs remain poorly understood. Therefore, the present work was undertaken to both provide guidance in the development of new biomedical alloys, and highlight areas of existing concerns and unclear knowledge. Key findings of this review include a summary of current clinical and preclinical work, and the identification of Sc as the most promising REE with regards to physiological impact. Y, Ce, Pr, Gd, Dy, Yb, Sm, and Eu should be considered carefully before their use as alloying elements, with other REEs intermediate or insufficiently studied.

A Visual Hydrogen Sensor Prototype for Monitoring Magnesium Implant Biodegradation

Alternative metals such as magnesium (Mg) and its alloys have been recently developed for clinical applications such as temporary implants for bone and tissue repair due to their desirable mechanical properties and ability to biodegrade harmlessly in vivo by releasing Mg²⁺, OH^-, and H₂ as biodegradation products. The current methods for monitoring in vivo Mg-alloy biodegradation are either invasive and/or costly, complex, or require large equipment and specially trained personnel, thus making real-time and point-of-care monitoring of Mg-alloy implants problematic. Therefore, innovative methods are critically needed. The objective of this research was to develop a novel, thin, and wearable visual H₂ sensor prototype for noninvasive monitoring of in vivo Mg-implant biodegradation in medical research and clinical settings with a fast response time. In this work, we successfully demonstrate such a prototype composed of resazurin and catalytic bimetallic gold-palladium nanoparticles (Au-Pd NPs) incorporated into a thin agarose/alginate hydrogel matrix that rapidly changes color from blue to pink upon exposure to various levels of H₂ at a constant flow rate. The irreversible redox reactions occurring in the sensor involve H₂, in the presence of Au-Pd NPs, converting resazurin to resorufin. To quantify the sensor color changes, ImageJ software was used to analyze photographs of the sensor taken with a smartphone during H₂ exposure. The sensor concentration range was from pure H₂ down to limits of detection of 6 and 8 μM H₂ (defined via two methods). This range is adequate for the intended application of noninvasively monitoring in vivo Mg-alloy implant biodegradation in animals for medical research and patients in clinical settings.

Biodegradable magnesium-based biomaterials: An overview of challenges and opportunities

As promising biodegradable materials with nontoxic degradation products, magnesium (Mg) and its alloys have received more and more attention in the biomedical field very recently. Having excellent biocompatibility and unique mechanical properties, magnesium-based alloys currently cover a broad range of applications in the biomedical field. The use of Mg-based biomedical devices eliminates the need for biomaterial removal surgery after the healing process and reduces adverse effects induced by the implantation of permanent biomaterials. However, the high corrosion rate of Mg-based implants leads to unexpected degradation, structural failure, hydrogen evolution, alkalization, and cytotoxicity. To overcome these limitations, alloying Mg with suitable alloying elements and surface treatment come highly recommended. In this area, open questions remain on the behavior of Mg-based biomaterials in the human body and the effects of different factors that have resulted in these challenges. In addition to that, many techniques are yet to be verified to turn these challenges into opportunities. Accordingly, this article aims to review major challenges and opportunities for Mg-based biomaterials to minimize the challenges for the development of novel biomaterials made of Mg and its alloys.

Laser-Guided Corrosion Control: A New Approach to Tailor the Degradation of Mg-Alloys

Despite corrosion being commonly seen as a problem to be avoided, applications such as batteries or biodegradable implants do benefit from corrosion-like phenomena. However, current strategies address corrosion control from a global perspective for a whole component, without considering local adaptations to functionality specifications or inhomogeneous environments. Here, a novel concept is presented: the local control and guidance of corrosion through a laser surface treatment. Immersion tests in saline solution of AZ31 magnesium alloy samples show degradation rates reduced up to 15 times with the treatment, owing to a fast passivation after the induced microstructural modifications. By controlling the treatment conditions, the degradation can be restricted to delimited regions and driven towards specific directions. The applicability of the method for the design of tailored degradation biomedical implants is demonstrated and uses for cathodic protection systems and batteries can also be anticipated.

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

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

In Vivo Evaluation of Bioabsorbable Fe-35Mn-1Ag: First Reports on In Vivo Hydrogen Gas Evolution in Fe-Based Implants

This work investigates the influence of Ag (1 wt%) on the mechanical properties, in vitro and in vivo corrosion, and biocompatibility of Fe-35Mn. The microstructure of Fe-35Mn-1Ag possesses a uniform dispersion of discrete silver particles. Slight improvements in compressive properties are attributed to enhanced density and low porosity volume. Fe-35Mn-1Ag exhibits good in vitro and in vivo corrosion rate of Fe-35Mn due to an increase in microgalvanic corrosion. Gas pockets, which originate from an inflammatory response to the implants, are observed in the rats after 4 weeks implantation but are undetectable after 12 weeks. No chronic toxicity is observed with the Fe-35Mn-1Ag, suggesting acceptable in vivo biocompatibility. The high corrosion rate of the alloy triggers an increased level of nonadverse tissue inflammatory responses 4 weeks after implantation, which subsequently subsides at 12 weeks. The Fe-35Mn-1Ag displays properties that are suitable for orthopedic applications.

WE43 and WE43-T5 Mg alloys screws tested in-vitro cellular adhesion and differentiation assay and in-vivo histomorphologic analysis in an ovine model

WE43 Mg alloy proved to be an ideal candidate for production of resorbable implants in both clinical and trial settings. In previous studies we tested biocompatibility and degradation properties of WE43 (as-cast) and artificially aged (WE43-T5) Mg alloys in a sheep model. Both alloys showed excellent biocompatibility with the as-cast, WE43, form showing increased degradability compared to the artificially aged, WE43-T5. In the present study, our group assessed the biological behavior and degradation pattern of the same alloys when implanted as endosteal implants in a sheep model. Twelve screws (3x15 mm) were evaluated, one screw per each composition was placed bi-cortically in the mandible of each animal with a titanium (2x12 mm) screw serving as an internal positive control. At 6 and 24 weeks histomorphological analysis was performed, at 6 weeks as cast, WE43, yielded a higher degradation rate, increased bone remodeling and osteolysis compared to the WE43-T5 alloy; however, at 24 weeks WE43-T5 showed higher degradation rate and increased bone remodeling than as-cast. In vitro assay of cell growth, adhesion and differentiation was also conducted to investigate possible mechanisms underlying the behavior expressed from the alloys in vivo. In conclusion WE43-T5 indicated bone/implant interaction properties that makes it more suitable for fabrication of endosteal bone screws.

Bioabsorbable Osteofixation Materials for Maxillofacial Bone Surgery: A Review on Polymers and Magnesium-Based Materials

Clinical application of osteofixation materials is essential in performing maxillofacial surgeries requiring rigid fixation of bone such as trauma surgery, orthognathic surgery, and skeletal reconstruction. In addition to the use of titanium plates and screws, clinical applications and attempts using bioabsorbable materials for osteofixation surgery are increasing with demands to avoid secondary surgery for the removal of plates and screws. Synthetic polymeric plates and screws were developed, reaching satisfactory physical properties comparable to those made with titanium. Although these polymeric materials are actively used in clinical practice, there remain some limitations to be improved. Due to questionable physical strength and cumbersome molding procedures, interests in resorbable metal materials for osteofixation emerged. Magnesium (Mg) gained attention again in the last decade as a new metallic alternative, and numerous animal studies to evaluate the possibility of clinical application of Mg-based materials are being conducted. Thanks to these researches and studies, vascular application of Mg-based biomaterials was successful; however, further studies are required for the clinical application of Mg-based biomaterials for osteofixation, especially in the facial skeleton. The review provides an overview of bioabsorbable osteofixation materials in maxillofacial bone surgery from polymer to Mg.

Enhanced osteoinductivity and corrosion resistance of dopamine/gelatin/rhBMP-2-coated β-TCP/Mg-Zn orthopedic implants: An in vitro and in vivo study

Magnesium-based biomaterials are attracting increasingly more attention for orthopedic applications based on their appropriate mechanical properties, biodegradability, and favorable biocompatibility. However, the high corrosion rate of these materials remains to be addressed. In this study, porous β-Ca3(PO4)2/Mg-Zn (β-TCP/Mg-Zn) composites were fabricated via a powder metallurgy method. The β-TCP/Mg-Zn composites with 6% porosity exhibited optimal mechanical properties, and thus, they were selected for surface modification. A novel dopamine/gelatin/recombinant human bone morphogenetic protein-2 (rhBMP-2) coating with demonstrated stability was prepared to further improve the corrosion resistance of the composite and enhance early osteoinductivity. The homogeneously coated β-TCP/Mg-Zn composite showed significantly improved corrosion resistance according to electrochemical and immersion tests. In addition, extracts from the dopamine/gelatin/rhBMP-2-coated β-TCP/Mg-Zn composite not only facilitated cell proliferation but also significantly enhanced the osteogenic differentiation of Sprague-Dawley rat bone marrow-derived mesenchymal stem cells in vitro. Furthermore, in vivo experiments were performed to evaluate the biodegradation, histocompatibility, and osteoinductive potential of the coated composite. No obvious pathological changes in the vital visceral organs were observed after implantation, and radiography and hematoxylin-eosin staining showed strong promotion of new bone formation, matched composite degradation and bone regeneration rates, and complete absorption of the released hydrogen gas. Collectively, these results indicate that the dopamine/gelatin/rhBMP-2-coated β-TCP/Mg-Zn composite offers improved corrosion resistance, favorable biocompatibility, and enhanced osteoinductive potential for use in the fabrication of orthopedic implants.

Influence of surface modifications on the degradation of standard-sized magnesium plates and healing of mandibular osteotomies in miniature pigs

Biodegradable magnesium alloys are suitable osteosynthesis materials. Despite the alloy composition, surface modifications appear to have an influence on the degradation process and biocompatibility. The aim of this study was to investigate the impact of hydrogenation and fluoridation of the surface in a mandibular osteotomy model. Standard-sized plates and screws were implanted in an osteotomy at the mandibular angle in nine miniature pigs. The plates and screws were harvested together with the adjacent tissues at 8 weeks after surgery and were investigated by micro-computed tomography and histological analysis. The bone healing of the osteotomy was undisturbed, independent of the surface properties. The adjacent bone tissue showed new bone formation at the implant surface; however, formation of some lacunae could be observed. The corrosion was between 9.8% and 11.6% (fluoridated<hydrogenated<non-modified) in histological specimens, while radiologically neither the volume nor the density of the osteosynthesis material was reduced in any treatment group. The soft tissues exhibited full biocompatibility with every surface property. In summary, surface modification by hydrogenation and fluoridation did not significantly influence bone healing, biocompatibility, or corrosion kinetics of the magnesium osteosynthesis at the mandibular angle.

Radiographic and histologic effects of bone morphogenetic protein-2/hydroxyapatite within bioabsorbable magnesium screws in a rabbit model

Background

Hydrogen gas formed by magnesium (Mg) screw corrosion can accumulate around the implant and create bone cysts, long-term osteolysis lesions, and bone healing delay. Thus, several authors currently do not recommend Mg implants for clinical use. In contrast, bone morphogenetic proteins (BMP)-2 have a very strong osteoinductive activity. The purpose of this study was to evaluate the effect of rhBMP-2/hydroxyapatite (HA) inside specially designed Mg cannulated screws in a rabbit femur model for hydrogen gas formation avoidance.

Methods

Fifteen rabbits underwent randomly different cannulated Mg screw implantation in both distal femora; 30 femora were divided into three groups depending on the materials fill in the cannulated Mg screw: control group (Mg screw with no treatment), HA group (Mg screw with HA), and BMP-2/HA group (Mg screw with a composite BMP-2/HA). Plain radiography, micro-CT, and histological analysis were accomplished, and the ability to release BMP-2 of the screws was evaluated by immersion of both the screw with no treatment and screw with a composite BMP-2/HA into the SBF for up to 7 days.

Results

X-ray assessment found the gas shadow around the implant was slightly smaller in the BMP-2/HA group than the HA and control groups at 8 weeks. Micro-CT analysis demonstrated statistically significant higher new bone formation in the BMP-2/HA group than the other groups, respectively, which also correlated with a decreased gas volume. Histological analysis showed higher osteointegration between implants and host femurs in the BMP-2/HA group than the HA and control groups at 12 weeks.

Conclusions

This study indicates that the combination of BMP-2/HA within Mg screws enhances new bone formation and therefore has the potential to decrease the complications of hydrogen gas formation around these implants.

Degradation and interaction with bone of magnesium alloy WE43 implants: A long-term follow-up in vivo rat tibia study

The aim of this in vivo study was to examine the degradation and biocompatibility of the WE43 magnesium alloy containing magnesium yttrium, rare earth elements, and zirconium over a one-year long-term follow-up period. Additionally, we compared anodized WE43 implants with monolithic ones and clarified the effect of the anodization. WE43 cylindrical implants with and without anodization (length, 10 mm; diameter, 0.3 mm) were transplanted into the rat tibia. In both groups, the development of corrosion and the change in implant volume were evaluated by in vivo micro-computed tomography until 12 months, and the bone tissue reaction was observed histologically. In the monolithic WE43 implants, hydrogen gas was evident until 14 days and the volume loss was 36.3% after 12 months. In the anodized WE43 implants, the development of hydrogen gas was inhibited and the volume loss was 27.7% after 12 months. The anodized WE43 implants showed a significantly slower corrosion process in the early phase. Therefore, these implants may require a prolonged period to degrade completely and may even resist complete degradation. At one year post surgery, bone maturation progressed and lamellar bone structure developed around the implant in both groups. In conclusion, the WE43 implants showed good long-term stability and biocompatibility in bone tissue.

Assessment of magnesium-based biomaterials: from bench to clinic

This review presents the operation procedures of commonly used standard methods for assessment of Mg-based biomaterials from bench to clinic.

The current trends of Mg alloys in biomedical applications-A review

Magnesium (Mg) has emerged as an ideal alternative to the permanent implant materials owing to its enhanced properties such as biodegradation, better mechanical strengths than polymeric biodegradable materials and biocompatibility. It has been under investigation as an implant material both in cardiovascular and orthopedic applications. The use of Mg as an implant material reduces the risk of long-term incompatible interaction of implant with tissues and eliminates the second surgical procedure to remove the implant, thus minimizes the complications. The hurdle in the extensive use of Mg implants is its fast degradation rate, which consequently reduces the mechanical strength to support the implant site. Alloy development, surface treatment, and design modification of implants are the routes that can lead to the improved corrosion resistance of Mg implants and extensive research is going on in all three directions. In this review, the recent trends in the alloying and surface treatment of Mg have been discussed in detail. Additionally, the recent progress in the use of computational models to analyze Mg bioimplants has been given special consideration. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1970-1996, 2019.

Hybrid fracture fixation systems developed for orthopaedic applications: A general review

Orthopaedic implants are applied daily in our orthopaedic clinics for treatment of musculoskeletal injuries, especially for bone fracture fixation. To realise the multiple functions of orthopaedic implants, hybrid system that contains several different materials or parts have also been designed for application, such as prosthesis for total hip arthroplasty. Fixation of osteoporotic fracture is challenging as the current metal implants made of stainless steel or titanium that are rather rigid and bioinert, which are not favourable for enhancing fracture healing and subsequent remodelling. Magnesium (Mg) and its alloys are reported to possess good biocompatibility, biodegradability and osteopromotive effects during its in vivo degradation and now tested as a new generation of degradable metallic biomaterials. Several recent clinical studies reported the Mg-based screws for bone fixation, although the history of testing Mg as fixation implant was documented more than 100 years ago. Truthfully, Mg has its limitations as fixation implant, especially when applied at load-bearing sites because of rather rapid degradation. Currently developed Mg-based implants have only been designed for application at less or non-loading-bearing skeletal site(s). Therefore, after years research and development, the authors propose an innovative hybrid fixation system with parts composed of Mg and titanium or stainless steel to maximise the biological benefits of Mg; titanium or stainless steel in this hybrid system can provide enough mechanical support for fractures at load-bearing site(s) while Mg promotes the fracture healing through novel mechanisms during its degradation, especially in patients with osteoporosis and other metabolic disorders that are unfavourable conditions for fracture healing. This hybrid fixation strategy is designed to effectively enhance the osteoporotic fracture healing and may potentially also reduce the refracture rate. The translational potential of this article: This article systemically reviewed the combination utility of different metallic implants in orthopaedic applications. It will do great contribution to the further development of internal orthopaedic implants for fracture fixation. Meanwhile, it also introduced a titanium-magnesium hybrid fixation system as an alternative fixation strategy, especially for osteoporotic patients.

In vivo quantification of hydrogen gas concentration in bone marrow surrounding magnesium fracture fixation hardware using an electrochemical hydrogen gas sensor

Magnesium (Mg) medical devices are currently being marketed for orthopedic applications and have a complex degradation process which includes the evolution of hydrogen gas (H₂). The effect of H₂ exposure on relevant cell types has not been studied; and the concentration surrounding degrading Mg devices has not been quantified to enable such mechanistic studies. A simple and effective method to measure the concentration of H₂ in varying microenvironments surrounding Mg implants is the first step to understanding the biological impact of H₂ on these cells. Here, the in vivo measurement of H₂ surrounding fracture fixation devices implanted in vivo is demonstrated. An electrochemical H₂ microsensor detected increased levels of H₂ at three anatomical sites with a response time of about 30 s. The sensor showed the H₂ concentration in the bone marrow at 1 week post-implantation (1460 ± 320 µM) to be much higher than measured in the subcutaneous tissue (550 ± 210 µM) and at the skin surface (120 ± 50 µM). Additionally, the H₂ concentrations measured in the bone marrow exceeded the concentration in a H₂ saturated water solution (∼800 µM). These results suggest that H₂ emanating from Mg implants in bone during degradation pass through the bone marrow and become at least partially trapped because of slow permeation through the bone. This study is the first to identify H₂ concentrations in the bone marrow environment and will enable in vitro experiments to be executed at clinically relevant H₂ concentrations to explore possible biological effects of H₂ exposure.

STATEMENT OF SIGNIFICANCE

An electrochemical H₂ sensor was used to monitor the degradation of a Mg fracture fixation system in a lapine ulna fracture model. Interestingly, the H₂ concentration in the bone marrow is 82% higher than H₂ saturated water solution. This suggests H₂ generated in situ is trapped in the bone marrow and bone is less permeable than the surrounding tissues. The detectable H₂ at the rabbit skin also demonstrates a H₂ sensor's ability to monitor the degradation process under thin layers of tissue. H₂ sensing shows promise as a tool for monitoring the degradation of Mg alloy in vivo and creating in vitro test beds to more mechanistically evaluate the effects of varying H₂ concentrations on cell types relevant to osteogenesis.

Gas formation and biological effects of biodegradable magnesium in a preclinical and clinical observation

Magnesium alloys are biodegradable metals receiving increasing attention, but the clinical applications of these materials are delayed by concerns over the rapid corrosion rate and gas formation. Unlike corrosion, which weakens mechanical properties, the gas formation issue has received little attention. Therefore, we evaluated the gas formation and biological effects for Mg implants through preclinical (immersed in Earle's balanced salt solution and in vivo) and clinical studies. The immersion test examined the gas volume and composition. The in vivo study also examined gas volume and histological analysis. The clinical study examined the gas volume and safety after Mg screw metatarsal fixation. Gas was mainly composed of H₂, CO and CO₂. Maximum volumes of gas formed after 5 days for in vivo and 7 days in clinical study. Within the clinical examination, two superficial wound complications healed with local wound care. Osteolytic lesions in the surrounding metaphysis of the Mg screw insertion developed in all cases and union occurred at 3 months. Mg implants released gas with variable volumes and composition (H₂, CO, and CO₂), with no long-term toxic effects on the surrounding tissue. The implants enabled bone healing, although complications of wound breakdown and osteolytic lesions developed.

Biocompatibility and Efficiency of Biodegradable Magnesium-Based Plates and Screws in the Facial Fracture Model of Beagles

PURPOSE

A biodegradable magnesium alloy system has been developed as a substitute for conventional plates and screws made of titanium or absorbable polymer. However, previous studies were limited to small animal experiments using screws or wires. In the present study, we preliminarily evaluated the biocompatibility and effectiveness of human standard-size biodegradable magnesium-based plates and screws in facial fractures of beagles.

MATERIALS AND METHODS

Fracture lines were created bilaterally in the zygomatic arches of 6 beagles. They were fixed in situ with plates and screws made of magnesium alloy mixed with calcium and zinc (experimental group) or absorbable polymer (control group). Laboratory testing, radiologic imaging, histologic analysis, and mechanical testing were performed 4 weeks postoperatively.

RESULTS

Inflammatory reactions were not significantly increased in any animal. Mechanical testing showed greater ultimate load and structural stiffness in the experimental group. In the histologic analysis, the void area and bone regeneration area were increased in the experimental, and the implant area and soft tissue area were increased in the control group. Radiologically, 3-dimensional micro-computed tomography showed no differences in the bone gap area between the 2 groups. A temporary increase in hydrogen gas around the magnesium implants regressed spontaneously and did not affect bone healing significantly.

CONCLUSIONS

Magnesium-based biodegradable plates and screws showed good biocompatibility and offered considerable stability for fixating facial bone fractures in the early bone-healing process. These results show the possibilities for the future development of magnesium alloy plates and screws for craniomaxillofacial fixation in humans.

Osteosynthesis of a cranio-osteoplasty with a biodegradable magnesium plate system in miniature pigs

Biodegradable magnesium alloys are a new class of implant material suitable for bone surgery. The aim of this study was to investigate plates and screws made of magnesium for osteosynthesis in comparison to titanium in a cranial fracture model. Implants were used for internal fixation of a cranio-osteoplasty in nine minipigs. Computed tomography was conducted repeatedly after surgery. The implants and the adjacent tissues were harvested 10, 20 and 30weeks after surgery and investigated by micro-computed tomography and histological analysis. The surgical procedure and the inserted osteosynthesis material were well tolerated by the animals, and the bone healing of the osteoplasty was undisturbed at all times. The adjacent bone showed formation of lacunas in the magnesium group, resulting in a lower bone-to-implant contact ratio than that of titanium (72 vs. 94% at week 30), but this did not lead to clinical side effects. Radiological measurements showed no reduction in osteosynthesis material volume, but indicated signs of degradation: distinct volumes within the magnesium osteosynthesis group had lower density in micro-computed tomography, and these volumes increased up to 9% at week 30. The histological preparations showed areas of translucency and porosity inside the magnesium, but the outer shape of the osteosynthesis material remained unchanged. No fracture or loosening of the osteosynthesis devices appeared. Soft tissue probes confirmed sufficient biocompatibility. Given their biodegradable capacity, biocompatibility, mechanical strength and visibility on radiographs, osteosynthesis plates made of magnesium alloys are suitable for internal fixation procedures.

STATEMENT OF SIGNIFICANCE

To the best of our knowledge this is the first study that used biodegradable magnesium implants for osteosynthesis in a cranial fracture model. The cranio-osteoplasty in miniature pigs allowed in vivo application of plate and screw osteosynthesis of standard-sized implants and the implementation of surgical procedures similar to those conducted on human beings. The osteosynthesis configuration, size, and mechanical properties of the magnesium implants within this study were comparable to those of titanium-based osteosynthesis materials. The results clearly show that bone healing was undisturbed in all cases and that the biocompatibility to hard- and soft tissue was sufficient. Magnesium implants might help to avoid long-term complications and secondary removal procedures due to their biodegradable properties.

Effects of degradable osteosynthesis plates of MgYREZr alloy on cell function of human osteoblasts, fibroblasts and osteosarcoma cells

The aim was to evaluate the biocompatibility of osteosynthesis plates of the MgYREZr/WE43 alloy by using human cells in vitro. Eluates of degradable magnesium osteosynthesis plates as well as halved plates were used for incubation with human osteoblasts, fibroblasts and osteosarcoma cells. The cell viability was evaluated by using FDA/PI-Staining and LDH analysis. Cell proliferation was assessed by MTT, WST-Test and BrdU-ELISA. Scanning electron microscope was used for investigation of the cell adhesion. The number of devitalized cells in all treatment groups did not significantly deviate from the control group. According to MTT results, the number of metabolically active cells was not significantly affected by the addition of the eluates. The number of metabolically active cells was reduced by 24 to 38% compared to the control on incubation in direct contact with the osteosynthesis plates. The proliferation of the cells was inhibited by the addition of the eluates. While the eluate of the half-hour elution has only a very small effect, the 24 h eluate significantly inhibits proliferation by 23-25% compared to the control. The roughened surface of the magnesium osteosynthesis plate after incubation showed adherent cells. However, some areas of the plates were also free of adherent cells. WE43 based magnesium alloys showed favorable biocompatibility considering the viability of the cells evaluated; however, proliferation rates were reduced in a time dependent manner, especially in fibroblast group. This might be a potential clinical benefit of magnesium osteosynthesis plates and their superiority to titanium, thus the fibroblastic ingrowth might negatively influence the bone-plate contact.

Biocompatibility and degradation of LAE442-based magnesium alloys after implantation of up to 3.5years in a rabbit model

Magnesium as basic implant material has long been the center of orthopedic research. Latest progress is achieved with a European certification and clinical use of a magnesium based compression screw. However, long term studies with implantation duration that exceed one year considerably do not exist. The present examinations analyzed the degradation progress from nine months to 3.5year after implantation of cylindrical pins into the medullary cavity of New Zealand White rabbits. Evaluation included clinical assessment, in vivo μ-computed tomography, analysis of the implants by three-point-bending and examination of the adjacent tissue by means of histology and of inner organs by mass- and optical emission spectrometry using inductively coupled plasma. Clinical acceptance was without objections in all animals. Immoderate reaction of the surrounding bone could be found in neither of the applied techniques. While in vivo μ-computed tomography showed a very slow degradation rate up to 72weeks, three-point-bending revealed a percentage loss of F(max) of 41.1% for implants after 9months implantation and 88.47% for the implant after 3.5years implantation. Although the total amounts of RE detected in the inner organs were very low, the organs of rabbits with LAE442 cylinders showed 10-20-fold increased concentrations of the alloying elements lanthanum, cerium, neodymium and praseodymium compared to animals without any implanted material.

STATEMENT OF SIGNIFICANCE

This is the first animal study investigating the degradation process of a magnesium alloy in vivo for up to 3.5years. Currently available data from different other in vivo studies cover only implantation durations up to one year. Therefore, the analysis of these long-time effects in the present study is highly significant and of great interest. Comprehensive outcome achieved by different techniques was assessed. The degradation process was slow and homogenous. Maximum applied force (F(max)) reduced by 41.1% for implants after 9months and by 88.47% for the implant after 3.5years implantation. Total amounts of RE detected in the inner organs were very low; the organs of rabbits with LAE442 cylinders showed 10-20-fold increased concentrations.

Biodegradable magnesium wire promotes regeneration of compressed sciatic nerves

Magnesium (Mg) wire has been shown to be biodegradable and have anti-inflammatory properties. It can induce Schwann cells to secrete nerve growth factor and promote the regeneration of nerve axons after central nervous system injury. We hypothesized that biodegradable Mg wire may enhance compressed peripheral nerve regeneration. A rat acute sciatic nerve compression model was made, and AZ31 Mg wire (3 mm diameter; 8 mm length) bridged at both ends of the nerve. Our results demonstrate that sciatic functional index, nerve growth factor, p75 neurotrophin receptor, and tyrosine receptor kinase A mRNA expression are increased by Mg wire in Mg model. The numbers of cross section nerve fibers and regenerating axons were also increased. Sciatic nerve function was improved and the myelinated axon number was increased in injured sciatic nerve following Mg treatment. Immunofluorescence histopathology showed that there were increased vigorous axonal regeneration and myelin sheath coverage in injured sciatic nerve after Mg treatment. Our findings confirm that biodegradable Mg wire can promote the regeneration of acute compressed sciatic nerves.