Bioeffects of micron-size magnesium particles on inflammatory cells and bone turnover in vivo and in vitro

Investigating the Potential of Magnesium Microparticles on Cartilage and Bone Regeneration Utilizing an In Vitro Osteoarthritis Model

Osteoarthritis (OA) is a significant condition that profoundly impacts synovial joints, including cartilage and subchondral bone plate. Biomaterials that can impede OA progression are a promising alternative or supplement to anti-inflammatory and surgical interventions. Magnesium (Mg) alloys known for bone regeneration potential were assessed in the form of Mg microparticles regarding their impact on tissue regeneration and prevention of OA progression. In vitro assays based on mesenchymal stem cells (SCP-1) were applied to evaluate the Mg microparticle's compatibility and function. Biocompatibility documented through live-dead staining and lactate dehydrogenase assay revealed a 90% cell viability at a concentration below 10 mM after 3 days of exposure. An in vitro OA model based on the supplementation of the cytokines IL-1β, and TNF-α was established and disclosed the effect of Mg degradation products in differentiating SCP-1 cells. Sustained differentiation was confirmed through extracellular matrix staining and increased gene marker expression. The Mg supplementation reduced the release of inflammatory cytokines (IL-6 and IL-8) while promoting the expression of proteins such as collagen X, collagen I, and osteopontin in a time-dependent manner. The in vitro study suggests that Mg microparticles hold a therapeutic potential for OA treatment with their ability to support bone and cartilage repair mechanisms even under inflammatory conditions.

Inflammatory response toward a Mg-based metallic biomaterial implanted in a rat femur fracture model

The immune system plays an important role in fracture healing, by modulating the pro-inflammatory and anti-inflammatory responses occurring instantly upon injury. An imbalance in these responses can lead to adverse outcomes, such as non-union of fractures. Implants are used to support and stabilize complex fractures. Biodegradable metallic implants offer the potential to avoid a second surgery for implant removal, unlike non-degradable implants. However, considering our dynamic immune system it is important to conduct in-depth studies on the immune response to these implants in living systems. In this study, we investigated the immune response to Mg and Mg-10Gd in vivo in a rat femur fracture model with external fixation. In vivo imaging using liposomal formulations was used to monitor the fluorescence-related inflammation over time. We combine ex vivo methods with our in vivo study to evaluate and understand the systemic and local effects of the implants on the immune response. We observed no significant local or systemic effects in the Mg-10Gd implanted group compared to the SHAM and Mg implanted groups over time. Our findings suggest that Mg-10Gd is a more compatible implant material than Mg, with no adverse effects observed in the early phase of fracture healing during our 4-week study. STATEMENT OF SIGNIFICANCE: Degradable metallic implants in form of Mg and Mg-10Gd intramedullary pins were assessed in a rat femur fracture model, alongside a non-implanted SHAM group with special respect to the potential to induce an inflammatory response. This pre-clinical study combines innovative non-invasive in vivo imaging techniques associated with multimodal, ex vivo cellular and molecular analytics. The study contributes to the development and evaluation of degradable biometals and their clinical application potential. The study results indicate that Mg-10Gd did not exhibit any significant harmful effects compared to the SHAM and Mg groups.

Effect of unsoluble corrosion products of WE43 alloys in vitro on macrophages

Magnesium alloys have been used to manufacture biodegradable implants, bone graft substitutes, and cardiovascular stents. WE43 was the most widely used magnesium alloy. The degradation process begins when the magnesium alloy stent is implanted in the body and comes into contact with body fluid. The degradation products include hydrogen, Mg2+ , local alkaline environment, and unsoluble products. A large number of studies focused on Mg2+ and pH in vitro, and in vivo of magnesium alloys, but few studies on unsoluble corrosion products (UCPs). In this study, UCPs of WE43 alloy were prepared by immersion in vitro, and their effects on macrophages were investigated. The results showed that the unsoluble corrosion products were Mg24Y5, Mg12YNd, and MgCO3 ·3H2 O, which were dose-dependent on the apoptosis and necrosis of macrophages. After phagocytosis of UCPs, macrophages mainly metabolize in lysosome, and autophagy also participates in the metabolism of UCPs. It also decreases mitochondrial membrane potential and increases lysosomes, endoplasmic reticulum stress, and P2X7 receptor activation. These will increase reactive oxygen species (ROS) in cells, activating NLRP3 inflammatory corpuscles, activating the downstream pro-IL18 and pro-IL1β, and converting it to IL-18, and IL-1β. However, its pro-inflammatory effect is far lower than that of the classical Lipopolysaccharide (LPS) pro-inflammatory pathway. This work has increased our understanding of magnesium alloy metabolism and provides new ideas for the clinical application of magnesium alloys.

ROS-responsive magnesium-containing microspheres for antioxidative treatment of intervertebral disc degeneration

Intervertebral disc degeneration (IVDD) is a degenerative disease characterized by lower-back pain, causing disability globally. Antioxidant therapy is currently considered one of the most promising strategies for IVDD treatment, given the crucial role of reactive oxygen species (ROS) in IVDD pathogenesis. Herein, a ROS-responsive magnesium-containing microsphere (Mg@PLPE MS) was constructed for the antioxidative treatment of IVDD. The Mg@PLPE MS has a core-shell structure comprising poly(lactic-co-glycolic acid) (PLGA) and ROS-responsive polymer poly(PBT-co-EGDM) as the shell and a magnesium microparticle as the core. The poly(PBT-co-EGDM) can be destroyed by H₂O₂ through the H₂O₂-triggered hydrophobic-to-hydrophilic transition, subsequently promoting an Mg-water reaction to produce H₂. Thus, Mg@PLPE MS provides a valuable platform for H₂O₂ elimination and controlled H₂ release. The generated H₂ scavenge for ROS by reacting with noxious •OH. Notably, the Mg@PLPE MS exerted significant antioxidative and anti-inflammatory effects in a disc degeneration rat model and alleviated extracellular matrix degradation and disc cells apoptosis, thereby underlining its efficacy in IVDD treatment. The Mg@PLPE MS also exhibited robust biocompatibility and negligible toxicity, presenting the promise for the antioxidative treatment of IVDD in vivo. STATEMENT OF SIGNIFICANCE: Antioxidant therapy is currently considered one of the most promising strategies for intervertebral disc degeneration (IVDD) treatment, given the crucial role of reactive oxygen species (ROS) in IVDD pathogenesis. Here, ROS-responsive magnesium-containing microspheres (Mg@PLPE MSs) were constructed to alleviate IVDD through controlled release of hydrogen gas. The Mg@PLPE MSs can effectively scavenge overproduced ROS by simultaneously reacting with H₂O₂ and •OH, thus creating a suitable microenvironment for inhibition of ECM degradation. As a result, Mg@PLPE MSs treated IVDD rats exhibit minimal nucleus pulposus decrease, less extracellular matrix degradation, minimal radial fissure of fibrous rings, and higher disc height index. Therefore, the as-prepared Mg@PLPE MSs may shed a new light on clinical treatment of IVDD.

Tissue responses after implantation of biodegradable Mg alloys evaluated by multimodality 3D micro-bioimaging in vivo

The local response of tissue triggered by implantation of degradable magnesium-based implant materials was investigated in vivo in a murine model. Pins (5.0 mm length by 0.5 mm diameter) made of Mg, Mg-10Gd, and Ti were implanted in the leg muscle tissue of C57Bl/6N mice (n = 6). Implantation was generally well tolerated as documented by only a mild short term increase in a multidimensional scoring index. Lack of difference between the groups indicated that the response was systemic and surgery related rather than material dependent. Longitudinal in vivo monitoring utilizing micro-computed tomography over 42 days demonstrated the highest and most heterogeneous degradation for Mg-10Gd. Elemental imaging of the explants by micro X-ray fluorescence spectrometry showed a dense calcium-phosphate-containing degradation layer. In order to monitor resulting surgery induced and/or implant material associated local cell stress, sphingomyelin based liposomes containing indocyanine green were administered. An initial increase in fluorescent signals (3-7 days after implantation) indicating cell stress at the site of the implantation was measured by in vivo fluorescent molecular tomography. The signal decreased until the 42nd day for all materials. These findings demonstrate that Mg based implants are well tolerated causing only mild and short term adverse reactions.

Modulating macrophage activities to promote endogenous bone regeneration: Biological mechanisms and engineering approaches

A coordinated interaction between osteogenesis and osteoimmune microenvironment is essential for successful bone healing. In particular, macrophages play a central regulatory role in all stages of bone repair. Depending on the signals they sense, these highly plastic cells can mediate the host immune response against the exterior signals of molecular stimuli and implanted scaffolds, to exert regenerative potency to a varying extent. In this article, we first encapsulate the immunomodulatory functions of macrophages during bone regeneration into three aspects, as sweeper, mediator and instructor. We introduce the phagocytic role of macrophages in different bone healing periods ('sweeper') and overview a variety of paracrine cytokines released by macrophages either mediating cell mobilisation, vascularisation and matrix remodelling ('mediator'), or directly driving the osteogenic differentiation of bone progenitors and bone repair ('instructor'). Then, we systematically classify and discuss the emerging engineering strategies to recruit, activate and modulate the phenotype transition of macrophages, to exploit the power of endogenous macrophages to enhance the performance of engineered bone tissue.

The bioeffects of degradable products derived from a biodegradable Mg-based alloy in macrophages via heterophagy

Biodegradable magnesium alloys are promising candidates for use in biomedical applications. However, degradable particles (DPs) derived from Mg-based alloys have been observed in tissue in proximity to sites of implantation, which might result in unexpected effects. Although previous in vitro studies have found that macrophages can take up DPs, little is known about the potential phagocytic pathway and the mechanism that processes DPs in cells. Additionally, it is necessary to estimate the potential bioeffects of DPs on macrophages. Thus, in this study, DPs were generated from a Mg-2.1Nd-0.2Zn-0.5Zr alloy (JDBM) by an electrochemical method, and then macrophages were incubated with the DPs to reveal the potential impact. The results showed that the cell viability of macrophages decreased in a concentration-dependent manner in the presence of DPs due to effects of an apoptotic pathway. However, the DPs were phagocytosed into the cytoplasm of macrophages and further degraded in phagolysosomes, which comprised lysosomes and phagosomes, by heterophagy instead of autophagy. Furthermore, several pro-inflammatory cytokines in macrophages were upregulated by DPs through the induction of reactive oxygen species (ROS) production. To the best of our knowledge, this is the first study to show that DPs derived from a Mg-based alloy are consistently degraded in phagolysosomes after phagocytosis by macrophages via heterophagy, which results in an inflammatory response owing to ROS overproduction. Thus, our research has increased the knowledge of the metabolism of biodegradable Mg metal, which will contribute to an understanding of the health effects of biodegradable magnesium metal implants used for tissue repair. STATEMENT OF SIGNIFICANCE: Biomedical degradable Mg-based alloys have great promise in applied medicine. Although previous studies have found that macrophages can uptake degradable particles (DPs) in vitro and observed in the sites of implantation in vivoin vivo, few studies have been carried out on the potential bioeffects relationship between DPs and macrophages. In this study, we analyzed the bioeffects of DPs derived from a Mg-based alloy on the macrophages. We illustrated that the DPs were size-dependently engulfed by macrophages via heterophagy and further degraded in the phagolysosome rather than autophagosome. Furthermore, DPs were able to induce a slight inflammatory response in macrophages by inducing ROS production. Thus, our research enhances the knowledge of the interaction between DPs of Mg-based alloy and cells, and offers a new perspective regarding the use of biodegradable alloys.

Magnesium inference screw supports early graft incorporation with inhibition of graft degradation in anterior cruciate ligament reconstruction

Patients after anterior cruciate ligament (ACL) reconstruction surgery commonly encounters graft failure in the initial phase of rehabilitation. The inhibition of graft degradation is crucial for the successful reconstruction of the ACL. Here, we used biodegradable high-purity magnesium (HP Mg) screws in the rabbit model of ACL reconstruction with titanium (Ti) screws as a control and analyzed the graft degradation and screw corrosion using direct pull-out tests, microCT scanning, and histological and immunohistochemical staining. The most noteworthy finding was that tendon graft fixed by HP Mg screws exhibited biomechanical properties substantially superior to that by Ti screws and the relative area of collagen fiber at the tendon-bone interface was much larger in the Mg group, when severe graft degradation was identified in the histological analysis at 3 weeks. Semi-quantitative immunohistochemical results further elucidated that the MMP-13 expression significantly decreased surrounding HP Mg screws with relatively higher Collagen II expression. And HP Mg screws exhibited uniform corrosion behavior without displacement or loosening in the femoral tunnel. Therefore, our results demonstrated that Mg screw inhibited graft degradation and improved biomechanical properties of tendon graft during the early phase of graft healing and highlighted its potential in ACL reconstruction.