In vivo corrosion behaviour of magnesium alloy in association with surrounding tissue response in rats

Effect of hematoma on early degradation behavior of magnesium after implantation

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

Multifunctional Prosthesis Surface: Modification of Titanium with Cinnamaldehyde-Loaded Hierarchical Titanium Dioxide Nanotubes

Orthopedic prostheses are the ultimate therapeutic solution for various end-stage orthopedic conditions. However, aseptic loosening and pyogenic infections remain as primary complications associated with these devices. In this study, a hierarchical titanium dioxide (TiO2) nanotube drug delivery system loaded with cinnamaldehyde for the surface modification of titanium implants, is constructed. These specially designed dual-layer TiO2 nanotubes enhance material reactivity and provide an extensive drug-loading platform within a short time. The introduction of cinnamaldehyde enhances the bone integration performance of the scaffold (simultaneously promoting bone formation and inhibiting bone resorption), anti-inflammatory capacity, and antibacterial properties. In vitro experiments have demonstrated that this system promoted osteogenesis by upregulating both Wnt/β-catenin and MAPK signaling pathways. Furthermore, it inhibits osteoclast formation, suppresses macrophage-mediated inflammatory responses, and impedes the proliferation of Staphylococcus aureus and Escherichia coli. In vivo experiments shows that this material enhances bone integration in a rat model of femoral defects. In addition, it effectively enhances the antibacterial and anti-inflammatory properties in a subcutaneous implant in a rat model. This study provides a straightforward and highly effective surface modification strategy for orthopedic Ti implants.

In vitroanalysis of insoluble salt formation mechanism associated with Mg corrosion-variations depending on the diffusion environment in model tissue

Magnesium (Mg) alloys have attracted attention as biodegradable metals, but the details of their corrosion behavior under biological environment have not been elucidated. Previous studies have suggested that diffusion through blood flow may influence Mg corrosion. Therefore, to understand the degradation behaviors of Mg, we analyzed insoluble salt precipitation associated with Mg corrosion in model tissue with different diffusion rates. A pure Mg specimen was immersed into a model tissue prepared with cell culture medium supplemented by a thickener at a different concentration (0.2%-0.5%) to form the gel. Micro-focus x-ray computed tomography of the gel was performed to observe gas cavity formation around the specimen. The insoluble salt layer formed on the specimen surface were analyzed by scanning electron microscopy with energy-dispersive x-ray spectroscopy, and Raman spectroscopy. As results, gas cavity formation was observed for all specimens. At day 7, the gas cavity volume was the highest at 0.5% thickener gel followed by 0.3% thickener gel. The insoluble salts were classified into three types based on their morphology; plate-like, granular-like, and crater-like salts. The crater-like salts were observed to cover 16.8 ± 3.9% of the specimen surface immersed in the 0.5% thickener gel, at the specimen area contacted to the gas cavity. The crater-like salts were composed by Mg hydroxide and carbonate from the deepest to the top layer. In plate-like or granular-like salts, Mg carbonate was formed in the deepest layer, but phosphates and carbonates, mainly containing calcium not Mg, were formed on the surface layer. In conclusion, the increase in the thickener concentration increased the gas cavity volume contacting to the specimen surface, resulting in the increase in precipitation of Mg hydroxide and carbonate, composing crater-like salts. Mg hydroxide and carbonate precipitation suggests the local increase in OH-concentration, which may be attributed to the decrease in diffusion rate.

Surgically-induced deformation in biodegradable orthopaedic implant devices

The biocompatibility and mechanical performance of biodegradable metals (e.g. magnesium, iron, and zinc-based alloys) in orthopaedic-targeted applications are contingent on limiting the rate of corrosion in vivo throughout the bone healing. Concurrently, the surgical procedure for the implantation of internal bone fixation devices may impart plastic deformation to the device, potentially altering the corrosion rate of the device. However, the potential effect of the surgical implantation procedure on the mechanochemical performance of metallic degradable orthopaedic devices in vivo remains largely unresolved. The objective of the present study is to develop a robust technique that permits the quantification of the strain introduced due to surgical implantation of degradable orthopaedic devices. Specifically, a novel combined experimental-modelling approach based on 3D laser scanning in situ and the finite element method is utilised to quantify the plastic strain introduced to a bone fixation plate following surgical implantation in a cadaveric porcine model where the plate is based on a ternary magnesium-zinc-calcium alloy (ZX10). The magnitude of plastic strains determined by the above approach for the Mg craniofacial miniplate confirms that the surgical procedure itself has the potential to enhance the corrosion rate of the Mg alloy in an accelerated and potentially localised manner. STATEMENT OF SIGNIFICANCE: Biodegradable metallic orthopaedic implant devices have emerged as a potential alternative to permanent implants, although successful adoption is contingent on achieving an acceptable degradation profile. Plastic strain that is introduced to the device during surgical implantation may influence the resulting degradation behaviour of the implant. In the present work, 3D laser scanning is combined with computer simulation to estimate the level and distribution of surgically-induced plastic strain in a magnesium alloy (ZX10). Subsequently, clinically-relevant pre-strain is shown to influence the rate of corrosion of ZX10 in vitro, indicating the value of such an approach in the design of biodegradable metallic devices under multiaxial loading.

Surgical Classification for Preclinical Rat Femoral Bone Defect Model: Standardization Based on Systematic Review, Anatomical Analysis and Virtual Surgery

Though surgical techniques profoundly influence in vivo experiments, significant heterogeneity exists in current surgeries for inducing rat femoral bone defects. Such variations reduce the reproducibility and comparability of preclinical studies, and are detrimental to clinical translation. The purposes of this study were: (1) to conduct a systematic review of rat femoral defect models, summarizing and analyzing the surgical techniques; (2) to analyze surgical design and potential pitfalls via 3D anatomy and virtual surgeries for fostering future precision research; and (3) to establish a surgical classification system, for improving the reproducibility and comparability among studies, avoiding unnecessary repetitive experiments. The online database PubMed was searched to identify studies from January 2000 to June 2022 using keywords, including rat, femur, bone defect. Eligible publications were included for a review of surgical methods. Anatomical analysis and virtual surgeries were conducted based on micro-CT reconstruction of the rat femur for further investigation and establishment of a classification system. A total of 545 publications were included, revealing marked heterogeneity in surgical methods. Four major surgical designs were reported for inducing defects from the proximal to distal femur: bone tunnel, cortical window, segmental defect, and wedge-shaped defect. Anatomical analysis revealed potential pitfalls hindering efficient clinical translation. A classification system was established according to the anatomical region, surgical design, and fixation devices. This systematic review in combination with 3D analysis and virtual surgery provides a general overview of current surgical approaches to inducing femoral defects in rats, and establishes a surgical classification facilitating preclinical research of quality and translational value.

Development of a Model System for Gas Cavity Formation Behavior of Magnesium Alloy Implantation

Clinical applications of magnesium (Mg)-based screws have reported gas cavity formation in the surrounding tissue, which sometimes delays the fixation of the bone fracture. The gas cavity formation is considered to depend on the balance between hydrogen generation by Mg corrosion reacting with water in the body fluid and its diffusion into the surrounding tissue by capillary flow. In order to understand the gas cavity formation behavior by Mg-based material implantation, we developed a new in vitro model system to recreate this cavity formation phenomenon: the hydrogen generation by corrosion and its diffusion into the medium. A model tissue is prepared by gelation of the cell culture medium in a sterile condition. The immersion of Mg alloy samples was performed under 5% CO₂ atmosphere with periodic observation by X-ray computed tomography, which enabled us to observe gas cavity growth up to 28 d. For demonstrating the usefulness of our model system, Mg alloy samples with different corrosion rates were prepared by a biodegradable polymer coating. AZ31 screws were spin-coated by poly-l-lactide (PLLA) and classified into three groups by their coating thickness as 1.0 ± 0.0, 1.6 ± 0.2, and 2.0 ± 0.1 μm (ave. ± s.d.). Upon their immersion into the model tissue, the gas cavity volumes formed were 1.57 ± 0.23, 1.06 ± 0.22, and 0.38 ± 0.09 mm³/mm² for 1.0, 1.6, and 2.0 μm coating samples, having the weight loss of 20.2 ± 2.93, 18.5 ± 2.84, and 11.3 ± 3.54 μg/mm², respectively (ave. ± s.d.). This result clearly indicates the dependence of gas cavity formation on the corrosion rate of the sample. The gas cavity volume was only 3.3∼7.5% of the total hydrogen gas volume estimated based on the weight loss of the samples at 28 d, which is in the range of those calculated from the clinical report (3.2∼9.4% at 4w). This system can be an effective tool to investigate the gas cavity formation behavior and contribute to understand the mechanisms and controlling factors of this phenomenon.

Degradation Behavior and Mechanical Integrity of a Mg-0.7Zn-0.6Ca (wt.%) Alloy: Effect of Grain Sizes and Crystallographic Texture

The microstructural characteristics of biodegradable Mg alloys determine their performance and appropriateness for orthopedic fixation applications. In this work, the effect of the annealing treatment of a Mg-0.7Zn-0.6Ca (ZX11) alloy on the mechanical integrity, corrosive behavior, and biocompatibility-osteoinduction was studied considering two annealing temperatures, 350 and 450 °C. The microstructure showed a recrystallized structure, with a lower number of precipitates, grain size, and stronger basal texture for the ZX11-350 condition than the ZX11-450. The characteristics mentioned above induce a higher long-term degradation rate for the ZX11-450 than the ZX11-350 on days 7th and 15th of immersion. In consequence, the mechanical integrity changes within this period. The increased degradation rate of the ZX11-450 condition reduces 40% the elongation at failure, in contrast with the 16% reduction for the ZX11-350 condition. After that period, the mechanical integrity remained unchanged. No cytotoxic effects were observed for both treatments and significant differentiation of mesenchymal stem cells into the osteoblast phenotype was observed.

In vivo biocompatibility and degradability of a Zn-Mg-Fe alloy osteosynthesis system

Zinc is generally considered to be one of the most promising materials to be used in biodegradable implants, and many zinc alloys have been optimized to improve implant biocompatibility, degradation, and mechanical properties. However, long-term degradation leads to the prolonged presence of degradation products, which risks foreign body reactions. Herein, we investigated the in vivo biocompatibility and degradation of a biodegradable Zn–Mg–Fe alloy osteosynthesis system in the frontal bone, mandible, and femur in beagles for 1 year. Results of the routine blood, biochemical, trace element, and histological analyses of multiple organs, peripheral blood CD4/CD8a levels, and serum interleukin 2 and 4 levels showed good biocompatibility of the Zn–Mg–Fe alloy. Zinc content analysis revealed zinc accumulation in adjacent bone tissue, but not in the liver, kidney, and spleen, which was related to the degradation of the Zn–Mg–Fe alloy. The alloy demonstrated a uniform slowing degradation rate in vivo. No degradation differences in the frontal bone, mandible, and femur were observed. The degradation products included zinc oxide [ZnO], zinc hydroxide [Zn(OH)₂], hydrozincite [Zn₅(OH)₆(CO₃)₂], and hopeite [Zn₃(PO₄)₂·4H₂O]. The good biocompatibility and degradation properties of the Zn–Mg–Fe alloy render it a very attractive osteosynthesis system for clinical applications.

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Zn–Mg–Fe alloy possesses good biocompatibility.

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Zn–Mg–Fe alloy demonstrates a uniform slowing-down degradation rate in vivo.

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No degradation differences are observed in different sites, which supports the design of degradable osteosynthesis systems.

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The degradation products are zinc oxide, zinc hydroxide, hydrozincite, and hopeite.

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Zn–Mg–Fe alloy is a promising candidate for an osteosynthesis system.

In vitro and in vivo evaluation of the safety and efficacy of a novel liquid fiducial marker for image-guided radiotherapy

The true extent of a tumor is difficult to visualize, during radiotherapy, using current modalities. In the present study, the safety and feasibility of a mixture of N-butyl cyanoacrylate and lipiodol (NBCA/Lip) was evaluated in order to investigate the optimal combination for application as a fiducial marker for radiotherapy. Four combinations of NBCA/Lip injection (1:1–0.1, 1:1–0.15, 1:3–0.1 and 1:3–0.15 ml) were injected into the subcutaneous tissue of BALB/c mice. The changes in gross histopathology, body weight, skin score, marker volume, neutrophil and macrophage counts were observed to analyze the effects of the different mixing ratios and injection volumes, in order to identify the best combination. Evaluation according to the International Organization for Standardization criteria was further conducted in order to test the biocompatibility of the mixture, including an acute systematic assay with mice, cytotoxicity with L929 fibroblasts and delayed-type hypersensitivity tests with guinea pigs and an intradermal test with rabbits. The results revealed that at the seventh week, 42 markers (42/48; 87.5%) were still visible using computed tomography (CT) imaging. No serious adverse effects were observed throughout the study period; however, the combination of 1:1–0.1 ml had the lowest body weight and worst skin score. A review of the histopathological reaction to NBCA/Lip revealed a combination of acute inflammation, chronic inflammation, granulation tissue, foreign-body reaction and fibrous capsule formation. The 1:1 NBCA combination ratio resulted in the most intense tissue repair reaction and a slower degradation rate of markers. In general, the combination of 1:3–0.15 ml had a better fusion with local tissue, maintained a stable imaging nodule on CT images for 7 weeks and the final biocompatibility test demonstrated its safety. Overall, the findings of the present study demonstrated NBCA/Lip as a safe and feasible fiducial marker, when using the 1:3–0.15 ml combination.

In vitro and in vivo analysis of the biodegradable behavior of a magnesium alloy for biomedical applications

The present study was designed to investigate the biodegradation behavior of Mg alloy plates in the maxillofacial region. For in vitro analysis, the plates were immersed in saline solution and simulated body fluid. For in vivo, the plates were implanted into the tibia, head, back, abdominal cavity, and femur and assessed at 1, 2, and 4 weeks after implantation. After implantation, the plate volumes and the formed insoluble salt were measured via micro-computed tomography. SEM/EDX analysis of the insoluble salt and histological analysis of the surrounding tissues were performed. The volume loss of plates in the in vitro groups was higher than that in the in vivo groups. The volume loss was fastest in the abdomen, followed by the head, back, tibia, and femur. There were no statistically significant differences in the insoluble salt volume of the all implanted sites. The corrosion of the Mg alloy will be affected to the surrounding tissue responses. The material for the plate should be selected based on the characteristic that Mg alloys are decomposed relatively easily in the maxillofacial region.

In vivo study of self-assembled alkylsilane coated degradable magnesium devices

Magnesium (Mg) and its alloys are candidate materials for resorbable implantable devices, such as orthopedic devices or cardiovascular stents. Mg has a number advantages, including mechanical properties, light weight, its osteogenic effects and the fact that its degradation products are nontoxic and naturally present in the body. However, production of H2 gas during the corrosion reaction can cause formation of gas pockets at the implantation site, posing a barrier to clinical applications of Mg. It is therefore desirable to develop methods to control corrosion rate and gas pocket formation around the implants. Here we evaluate the potential of self-assembled multilayer alkylsilane (AS) coatings to control Mg device corrosion and formation of gas pockets in vivo and to assess effects of the AS coatings on the surrounding tissues in a subcutaneous mouse model over a 6 weeks' period. The coating significantly slowed down corrosion and gas pocket formation as evidenced by smaller gas pockets around the AS coated implants (ANOVA; p = 0.013) and decrease in the weight loss values (t test; p = 0.07). Importantly, the microCT and profilometry analyses demonstrated that the coating inhibited the pitting corrosion. Specifically, the roughness of the coated samples was ∼30% lower than uncoated specimen (p = 0.02). Histological assessment of the tissues under the implant revealed no inflammation or foreign body reaction. Overall, our results demonstrate the feasibility of use of the seld assembled AS coatings for reduction of gas pocket formation around the resorbable Mg devices. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 342-351, 2019.

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.

High Magnesium Corrosion Rate has an Effect on Osteoclast and Mesenchymal Stem Cell Role During Bone Remodelling

The aim of this study was to gain an understanding on the collective cellular effects of magnesium (Mg) corrosion products on the behaviour of cells responsible for bone formation and remodelling. The response of mesenchymal stem cells (MSCs) and osteoclast cells to both soluble (Mg ions) and insoluble (granule) corrosion products were recapitulated in vitro by controlling the concentration of the corrosion products. Clearance of corrosion granules by MSCs was also inspected by TEM analysis at sub-cellular level. The effect of Mg corrosion products varied depending on the state of differentiation of cells, concentration and length of exposure. The presence of the corrosion products significantly altered the cells' metabolic and proliferative activities, which further affected cell fusion/differentiation. While cells tolerated higher than physiological range of Mg concentration (16 mM), concentrations below 10 mM were beneficial for cell growth. Furthermore, MSCs were shown to contribute to the clearance of intercellular corrosion granules, whilst high concentrations of corrosion products negatively impacted on osteoclast progenitor cell number and mature osteoclast cell function.

Bio-Functional Design, Application and Trends in Metallic Biomaterials

Introduction of metals as biomaterials has been known for a long time. In the early development, sufficient strength and suitable mechanical properties were the main considerations for metal implants. With the development of new generations of biomaterials, the concepts of bioactive and biodegradable materials were proposed. Biological function design is very import for metal implants in biomedical applications. Three crucial design criteria are summarized for developing metal implants: (1) mechanical properties that mimic the host tissues; (2) sufficient bioactivities to form bio-bonding between implants and surrounding tissues; and (3) a degradation rate that matches tissue regeneration and biodegradability. This article reviews the development of metal implants and their applications in biomedical engineering. Development trends and future perspectives of metallic biomaterials are also discussed.

In vivo analysis of covering materials composed of biodegradable polymers enriched with flax fibers

BACKGROUND

The objective of this study was to investigate the in vivo effect of bioactive composites with poly(lactic acid) (PLA) or polycaprolactone (PCL) as the matrix, reinforced with bioplastic flax fibers, on the surrounding muscle tissue.

METHODS

Materials of pure PLA and PCL and their composites with flax fibers from genetically modified plants producing poly-3-hydroxybutyrate (PLA-transgen, PCL-transgen) and unmodified plants (PLA-wt, PCL-wt) were placed subcutaneous on the M. latissimus dorsi for four weeks.

RESULTS

The analysis of histological samples revealed that every tested material was differently encapsulated and the capsule thickness is much more pronounced when using the PCL composites in comparison with the PLA composites. The encapsulation by connective tissue was significantly reduced around PCL-transgen and significantly increased in the cases of PLA-transgen and PLA-wt. In the collected muscle samples, the measured protein expression of CD45, lymphocyte common antigen, was significantly increased after the use of all tested materials, with the exception of pure PCL. In contrast, the protein expression of caveolin-1 remained unchanged after treatment with the most examined materials. Only after insertion of PLA-wt, a significant increase of caveolin-1 protein expression was detected, due to the improved neovascularization.

CONCLUSION

These data support the presumption that the new bioactive composites are biocompatible and they could be applicable in the medical field to support the regenerative processes.