A lithium-doped surface inspires immunomodulatory functions for enhanced osteointegration through PI3K/AKT signaling axis regulation

Mineralised collagen regulated the secretion of adrenomedullin by macrophages to activate the PI3K/AKT signalling pathway to promote bone defect repair

Biomaterials can affect the osteogenic process by regulating the function of macrophages and transforming the bone immune microenvironment. Mineralised collagen (MC) is an artificial bone that is highly consistent to the microstructure of the native osseous matrix. The studies have confirmed that MC can achieve effective regeneration of bone defects, but the potential mechanism of MC regulating osteogenesis is still unclear. This study confirmed that MC regulate the high expression of adrenomedullin (ADM) in macrophages and promote the osteogenic differentiation, proliferation and migration of BMSCs. Moreover, ADM activated the PI3K/Akt pathway, while the inhibition of PI3K/Akt hindered the proliferation, migration and osteogenic differentiation of BMSCs promoted by ADM. Additionally, the rat mandibular defect model confirmed that ADM promote the repair of mandibular defects, and the inhibition of PI3K/Akt pathway hinders the osteogenic effect of ADM. Our study suggests that MC regulates ADM secretion by macrophages, creates an ideal bone immune microenvironment, activates the PI3K/AKT signalling pathway, and promotes osteogenesis.

Utilization of a highly adaptable murine air pouch model for minimally invasive testing of the inflammatory potential of biomaterials

Introduction: The biocompatibility of an implanted material strongly determines the subsequent host immune response. After insertion into the body, each medical device causes tissue reactions. How intense and long-lasting these are is defined by the material properties. The so-called foreign body reaction is a reaction leading to the inflammation and wound healing process after implantation. The constantly expanding field of implant technology and the growing areas of application make optimization and adaptation of the materials used inevitable. Methods: In this study, modified liquid silicone rubber (LSR) and two of the most commonly used thermoplastic polyurethanes (TPU) were compared in terms of induced inflammatory response in the body. We evaluated the production of inflammatory cytokines, infiltration of inflammatory cells and encapsulation of foreign bodies in a subcutaneous air-pouch model in mice. In this model, the material is applied in a minimally invasive procedure via a cannula and in one piece, which allows material testing without destroying or crushing the material and thus studying an intact implant surface. The study design includes short-term (6 h) and long-term (10 days) analysis of the host response to the implanted materials. Air-pouch-infiltrating cells were determined by flow cytometry after 6 h and 10 days. Inflammation, fibrosis and angiogenesis markers were analyzed in the capsular tissue by qPCR after 10 days. Results: The foreign body reaction was investigated by macroscopic evaluation and scanning electron microscopy (SEM). Increased leukocyte infiltration was observed in the air-pouch after 6 h, but it markedly diminished after 10 days. After 10 days, capsule formations were observed around the materials without visible inflammatory cells. Discussion: For biocompatibility testing materials are often implanted in muscle tissue. These test methods are not sufficiently conclusive, especially for materials that are intended to come into contact with blood. Our study primarily shows that the presented model is a highly adaptable and minimally invasive test system to test the inflammatory potential of and foreign body reaction to candidate materials and offers more precise analysis options by means of flow cytometry.

Immune regulation enhances osteogenesis and angiogenesis using an injectable thiolated hyaluronic acid hydrogel with lithium-doped nano-hydroxyapatite (Li-nHA) delivery for osteonecrosis

Osteonecrosis is a devastating orthopedic disease in clinic that generally occurs in the femoral head associating with corticosteroid use up to 49 % in patients. In particular, glucocorticoids induced osteonecrosis of the femoral head is closely related to the local immune response that characterized by abnormal macrophage activation and inflammatory cell infiltration at the necrotic site, forming a pro-inflammatory microenvironment dominated by M1 macrophages, and thus leads to failure of bone repair and regeneration. Here, we report a bone regeneration strategy that constructs an immune regulatory biomaterial platform using an injectable thiolated hyaluronic acid hydrogel with lithium-doped nano-hydroxyapatite (Li-nHA@Gel) delivery for osteonecrosis treatment. Li-nHA@Gel achieved a sustain and longterm release of Li ions, which might enhance M2 macrophage polarization through the activation of the JAK1/STAT6/STAT3 signaling pathway, and the following induced pro-repair immune microenvironment mediated the enhancement of the osteogenic and angiogenic differentiation. Moreover, both in vitro and in vivo studies indicated that Li-nHA@Gel enhanced M2 macrophage polarization, osteogenesis, and angiogenesis, and thus promoted the bone and blood vessel formation. Taken together, this novel bone immunomodulatory biomaterial platform that promotes bone regeneration by enhancing M2 macrophage polarization, osteogenesis, and angiogenesis could be a promising strategy for osteonecrosis treatment.

Advancements in incorporating metal ions onto the surface of biomedical titanium and its alloys via micro-arc oxidation: a research review

The incorporation of biologically active metallic elements into nano/micron-scale coatings through micro-arc oxidation (MAO) shows significant potential in enhancing the biological characteristics and functionality of titanium-based materials. By introducing diverse metal ions onto titanium implant surfaces, not only can their antibacterial, anti-inflammatory and corrosion resistance properties be heightened, but it also promotes vascular growth and facilitates the formation of new bone tissue. This review provides a thorough examination of recent advancements in this field, covering the characteristics of commonly used metal ions and their associated preparation parameters. It also highlights the diverse applications of specific metal ions in enhancing osteogenesis, angiogenesis, antibacterial efficacy, anti-inflammatory and corrosion resistance properties of titanium implants. Furthermore, the review discusses challenges faced and future prospects in this promising area of research. In conclusion, the synergistic approach of micro-arc oxidation and metal ion doping demonstrates substantial promise in advancing the effectiveness of biomedical titanium and its alloys, promising improved outcomes in medical implant applications.

Macrophages in the process of osseointegration around the implant and their regulatory strategies

PURPOSE/AIM OF THE STUDY

To summarize and discuss macrophage properties and their roles and mechanisms in the process of osseointegration in a comprehensive manner, and to provide theoretical support and research direction for future implant surface modification efforts.

MATERIALS AND METHODS

Based on relevant high-quality articles, this article reviews the role of macrophages in various stages of osseointegration and methods of implant modification.

RESULTS AND CONCLUSIONS

Macrophages not only promote osseointegration through immunomodulation, but also secrete a variety of cytokines, which play a key role in the angiogenic and osteogenic phases of osseointegration. There is no "good" or "bad" difference between the M1 and M2 phenotypes of macrophages, but their timely presence and sequential switching play a crucial role in implant osseointegration. In the implant surface modification strategy, the induction of sequential activation of the M1 and M2 phenotypes of macrophages is a brighter prospect for implant surface modification than inducing the polarization of macrophages to the M1 or M2 phenotypes individually, which is a promising pathway to enhance the effect of osseointegration and increase the success rate of implant surgery.

Metal ions: the unfading stars of bone regeneration-from bone metabolism regulation to biomaterial applications

In recent years, bone regeneration has emerged as a remarkable field that offers promising guidance for treating bone-related diseases, such as bone defects, bone infections, and osteosarcoma. Among various bone regeneration approaches, the metal ion-based strategy has surfaced as a prospective candidate approach owing to the extensive regulatory role of metal ions in bone metabolism and the diversity of corresponding delivery strategies. Various metal ions can promote bone regeneration through three primary strategies: balancing the effects of osteoblasts and osteoclasts, regulating the immune microenvironment, and promoting bone angiogenesis. In the meantime, the complex molecular mechanisms behind these strategies are being consistently explored. Moreover, the accelerated development of biomaterials broadens the prospect of metal ions applied to bone regeneration. This review highlights the potential of metal ions for bone regeneration and their underlying mechanisms. We propose that future investigations focus on refining the clinical utilization of metal ions using both mechanistic inquiry and materials engineering to bolster the clinical effectiveness of metal ion-based approaches for bone regeneration.

Molecular Mechanism Underlying the Action of a Celastrol-Loaded Layered Double Hydroxide-Coated Magnesium Alloy in Osteosarcoma Inhibition and Bone Regeneration

Osteosarcoma (OS) is a malignant bone tumor that threatens human health. Surgical removal of the tumor and followed by implantation with a graft is the golden standard for its clinical treatment. However, avoiding recurrence by enhancing the antitumor properties of the implants and improving osteogenesis around the implants remain a challenge. Here, we developed a layered double hydroxide (LDH)-coated magnesium (Mg) alloy and loaded it with celastrol. The celastrol-loaded Mg alloy exhibited enhanced corrosion resistance and sustained release of celastrol. In vitro cell culture suggested that the modified Mg alloy loaded with an appropriate amount of celastrol significantly inhibited the proliferation and migration of bone tumor cells while having little influence on normal cells. A mechanistic study revealed that the celastrol-loaded Mg alloy upregulated reactive oxygen species (ROS) generation in bone tumor cells, resulting in mitochondrial dysfunction due to reduced membrane potential, thereby inducing bone tumor cell apoptosis. Furthermore, it was found that celastrol-induced autophagy in tumor cells inhibited cell apoptosis in the initial 6 h. After ≥12 h of culture, inhibition of the PI3K-Akt-mTOR signaling pathway was noted, resulting in excessive autophagy in tumor cells, finally causing cell apoptosis. The celatsrol-loaded Mg alloy also exhibited effective antitumor properties in a subcutaneous tumor model. In vitro tartrate-resistant acid phosphatase (TRAP) staining and gene expression results revealed that the modified Mg alloy reduced the viability of osteoclasts, inducing a potential pathway for the increased bone regeneration around the modified Mg alloy seen in vivo. Together, the results of our study show that the celatsrol-loaded Mg alloy might be a promising implant for treating OS.

Regulatory of miRNAs in tri-lineage differentiation of C3H10T1/2

MicroRNAs (miRNAs) are non-coding single-stranded RNA molecules encoded by endogenous genes, which play a vital role in cell generation, metabolism, apoptosis and stem cell differentiation. C3H10T1/2, a mesenchymal cell extracted from mouse embryos, is capable of osteogenic differentiation, adipogenic differentiation and chondrogenic differentiation. Extensive studies have shown that not only miRNAs can directly trigger targeted genes to regulate the tri-lineage differentiation of C3H10T1/2, but it also can indirectly regulate the differentiation by triggering different signaling pathways or various downstream molecules. This paper aims to clarify the regulatory roles of different miRNAs on C3H10T1/2 differentiation, and discussing their balance effect among osteogenic differentiation, adipogenic differentiation and chondrogenic differentiation of C3H10T1/2. We also review the biogenesis of miRNAs, Wnt signaling pathways, MAPK signaling pathways and BMP signaling pathways and provide some specific examples of how these signaling pathways act on C3H10T1/2 tri-lineage differentiation. On this basis, we hope that a deeper understanding of the differentiation and regulation mechanism of miRNAs in C3H10T1/2 can provide a promising therapeutic method for the clinical treatment of bone defects, osteoporosis, osteoarthritis and other diseases.

Zinc-doped ferric oxyhydroxide nano-layer enhances the bactericidal activity and osseointegration of a magnesium alloy through augmenting the formation of neutrophil extracellular traps

Implant-associated infections (IAI) and osseointegration disorders are the most common complications in orthopedics. Studies have shown that neutrophils surrounding implants play a vital role in regulating these complications. Although magnesium (Mg) and its alloys are considered promising biodegradable bone implants, their role in neutrophil-mediated antibacteria has not yet been examined. Considering the rapid corrosion of Mg, it is necessary to develop methods to inhibit its corrosion. To solve these issues, a zinc-doped ferric oxyhydroxide nano-layer modified plasma electrolytic oxidation (PEO)-coated Mg alloy (PEO-FeZn) was developed in this study, and its antibacterial, immune anti-infective, and osteogenic ability were systematically evaluated. The results showed that PEO-FeZn nano-layer enhanced the corrosion resistance, biocompatibility, bactericidal activity, and osteoblastic differentiation activity of the Mg alloy. Moreover, PEO-FeZn nano-layer inhibited immune evasion-related gene expression and contributed to the formation of neutrophil extracellular traps (NETs) by activating the extracellular release of DNA fibers and granule proteins, and thereby suppressing bacterial invasion and promoting osseointegration in vivo in Staphylococcus aureus (S. aureus)-infected rat femurs. Overall, the findings of this study could serve as a reference for the fabrication of highly biocompatible and corrosion resistant Mg alloys to address the challenges of IAI and osseointegration disorders. STATEMENT OF SIGNIFICANCE: The widely used metallic biomaterials usually come with the risk of IAI. As the first responder around the biomaterials, neutrophils could form NETs to defense against microorganism and promote tissue remodeling. Therefore, biomaterials addressing antibacterial and neutrophils-modulatory strategies are highly necessary in reducing IAI. To solve these issues, we grew PEO-FeZn nano-layers in situ on Mg alloy using a simple and green technique. The nano-layer not only enhanced the corrosion resistance and biocompatibility of Mg alloy, but also elevated the antibacterial and osteogenesis capability. Moreover, nano-layer contributed to NETs formation, thereby suppressing bacterial invasion and even promoting osseointegration in S.aureus-infected femurs. Accordingly, this functionalized multilayer coating with antibacterial immunity represents a novel therapeutic strategy for IAI and weak osseointegration.

Electrochemical deposition of lithium coating on titanium implant with enhanced early stage osseointegration

Recently, a large number of studies have reported that lithium (Li) displayed a positive effect on osteogenesis. However, only a few studies have investigated the Li-incorporated surfaces through electrochemical deposition. In this study, electrochemical deposition was conducted on a CHI600E electrochemical workstation. The characterization of electrochemical deposition (ECD) and ECD-Li surfaces were detected by field-emission scanning electron microscopy with energy-dispersive spectrometer. rBMSCs were cultured on two surfaces for subsequent adhesion, proliferation and live/dead assay. To evaluate the effects of Li-incorporated implants by electrochemical deposition on osseointegration in vivo, teeth extraction of two premolars and one first molar in bilateral mandible were performed on six male beagle dogs. After 3 months, ZDI and ZDI-Li implants were inserted into the bilateral mandible of each beagle dog. Micro Computed Tomography (Micro-CT) and hard tissue sectioning analysis were carried out to evaluate the osseointegration at 4- and 8-weeks post-implantation. Results showed that ECD-Li surface promoted adhesion and proliferation of BMSCs in the early stage. More importantly, through micro-CT analysis, the values of bone volume/total volume (BV/TV) (0.374 ± 0.015), bone-implant contact (BIC) (0.831 ± 0.025), and Tb.Th (0.412 ± 0.007) in ZDI-Li group was significantly higher than those of ZDI group (0.302 ± 0.009, 0.700 ± 0.023, 0.353 ± 0.001, p < .01) at 4 weeks. Similarly, ZDI-Li group manifested more bone contact with the implant surfaces at 4 weeks based on hard tissue sectioning analysis, whereas no significant difference was detected between two groups at 8 weeks. Therefore, incorporating Li into implant surface through ECD could enhance early osseointegration in vivo.

Construction of Local Drug Delivery System on Titanium-Based Implants to Improve Osseointegration

Titanium and its alloys are the most widely applied orthopedic and dental implant materials due to their high biocompatibility, superior corrosion resistance, and outstanding mechanical properties. However, the lack of superior osseointegration remains the main obstacle to successful implantation. Previous traditional surface modification methods of titanium-based implants cannot fully meet the clinical needs of osseointegration. The construction of local drug delivery systems (e.g., antimicrobial drug delivery systems, anti-bone resorption drug delivery systems, etc.) on titanium-based implants has been proved to be an effective strategy to improve osseointegration. Meanwhile, these drug delivery systems can also be combined with traditional surface modification methods, such as anodic oxidation, acid etching, surface coating technology, etc., to achieve desirable and enhanced osseointegration. In this paper, we review the research progress of different local drug delivery systems using titanium-based implants and provide a theoretical basis for further research on drug delivery systems to promote bone–implant integration in the future.

Neuronal Death Mechanisms and Therapeutic Strategy in Ischemic Stroke

Ischemic stroke caused by intracranial vascular occlusion has become increasingly prevalent with considerable mortality and disability, which gravely burdens the global economy. Current relatively effective clinical treatments are limited to intravenous alteplase and thrombectomy. Even so, patients still benefit little due to the short therapeutic window and the risk of ischemia/reperfusion injury. It is therefore urgent to figure out the neuronal death mechanisms following ischemic stroke in order to develop new neuroprotective strategies. Regarding the pathogenesis, multiple pathological events trigger the activation of cell death pathways. Particular attention should be devoted to excitotoxicity, oxidative stress, and inflammatory responses. Thus, in this article, we first review the principal mechanisms underlying neuronal death mediated by these significant events, such as intrinsic and extrinsic apoptosis, ferroptosis, parthanatos, pyroptosis, necroptosis, and autophagic cell death. Then, we further discuss the possibility of interventions targeting these pathological events and summarize the present pharmacological achievements.

Preparation and characterization of novel lithium magnesium phosphate bioceramic scaffolds facilitating bone generation

Both magnesium and lithium are able to stimulate osteogenic and angiogenic activities. In this study, lithium magnesium phosphate (Li_0.5Mg_2.75(PO₄)₂, Li₁Mg_2.5(PO₄)₂ and Li₂Mg₂(PO₄)₂) biomaterials were synthesized by a solid-state reaction method, and their bioceramic blocks and scaffolds were fabricated by compression molding and 3D printing, respectively. The results indicated that the lithium magnesium phosphates consisted of the Mg₃(PO₄)₂ phase and/or LiMgPO₄ phase. Compared with the lithium-free Mg₃(PO₄)₂ bioceramics, the lithium magnesium phosphate bioceramics showed a lower porosity and consequently a higher compressive strength, and stimulated in vitro cellular proliferation, osteogenic differentiation and proangiogenic activity. In vivo results manifested that the Li₂Mg₂(PO₄)₂ bioceramic scaffolds efficiently promoted bone regeneration of critical-size calvarial defects in rats. Benefiting from the high compressive strength and capacity of stimulating osteogenesis and angiogenesis, the Li₂Mg₂(PO₄)₂ bioceramic scaffolds are considered promising for efficiently repairing the bone defects.

Li-Doped Ti Surface for the Improvement of Osteointegration

Aseptic loosening is the main factor that leads to the failure of orthopedic implants. Enhancing the early osteointegration of a bone implant can lower the risk of aseptic loosening. Here, a Li-doped surface was constructed on a Ti surface via plasma electrolytic oxidation (PEO) to improve osteointegration. The prepared Li-doped PEO coating showed a porous morphology and the sustained release of Li ions. In vitro results of rat bone marrow mesenchymal stem cell (rBMSC) culture studies suggested that the Li-doped Ti surface significantly favored cell adhesion. Moreover, it was found that the Li-doped surface enhanced alkaline phosphatase activity and extracellular matrix mineralization of rBMSCs. In addition, the surface improved the expression of osteogenesis-related genes. Furthermore, a bone implantation model indicated that the Li-doped Ti surface showed improved osteointegration. The incorporation of Li into a Ti surface is a promising method for orthopedic applications.

Regulating Macrophage Polarization in High Glucose Microenvironment Using Lithium-Modified Bioglass-Hydrogel for Diabetic Bone Regeneration

Diabetes mellitus is a chronic metabolic disease with a proinflammatory microenvironment, causing poor vascularization and bone regeneration. Due to the lack of effective therapy and one-sided focus on the direct angiogenic properties of biomaterials and osteogenesis stimulation, the treatment of diabetic bone defect remains challenging and complex. In this study, using gelatin methacryloyl (GelMA) as a template, a lithium (Li) -modified bioglass-hydrogel for diabetic bone regeneration is developed. It exhibits a sustained ion release for better bone regeneration under diabetic microenvironment. The hydrogel is shown to be mechanically adaptable to the complex shape of the defect. In vitro, Li-modified bioglass-hydrogel promoted cell proliferation, direct osteogenesis, and regulated macrophages in high glucose (HG) microenvironment, with the secretion of bone morphogenetic protein-2 and vascular endothelial growth factor to stimulate osteogenesis and neovascularization indirectly. In vivo, composite hydrogels containing GelMA and Li-MBG (GM/M-Li) release Li ions to relieve inflammation, providing an anti-inflammatory microenvironment for osteogenesis and angiogenesis. Applying Li-modified bioglass-hydrogel, significantly enhances bone regeneration in a diabetic rat bone defect. Together, both remarkable in vitro and in vivo outcomes in this study present an opportunity for diabetic bone regeneration on the basis of HG microenvironment.

Strontium-Containing Barium Titanate-Modified Titanium for Enhancement of Osteointegration

One of the major challenges for Ti-based implants is insufficient osteointegration, which might result in the loosening of the implant. In this study, we fabricated strontium (Sr)-containing barium titanate (BST) on the surface of Ti to improve the bioactivity for osteointegration enhancement. The introduction of Sr significantly reduced the crystallization time and improved crystallinity, which was proved by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. Compared with Ti, the BST film showed greater wettability surface and lower elastic modulus and hardness. Furthermore, in synergy with the release of Sr ions, the BST film improved early adhesion and followed osteogenic differentiation of rat bone mesenchymal stem cells. Furthermore, the bone implantation experiment suggested that the BST film could significantly improve the in vivo osteogenesis and osteointegration capabilities of Ti implants. In summary, this study revealed that BST-modified Ti has potential application in bone repair.