Dual Function of Magnesium in Bone Biomineralization

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

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

Supplemental Magnesium Gluconate Enhances Scaffold-Mediated New Bone Formation and Natural Bone Healing by Angiogenic- and Wnt Signal-Associated Osteogenic Activation

Local implantation or supplementation of magnesium gluconate (MgG) is being investigated as an effective approach to bone repair. Although studies have highlighted the possible mechanisms in Mg ion-stimulated new bone formation, the role of MgG in healing bone defects and the signaling mechanisms are not yet completely understood. In this study, we explored how supplemental MgG has bone-specific beneficial effects by delivering MgG locally and orally in animal models. We fabricated MgG-incorporated (CMC-M) and -free chitosan (CMC) scaffolds with good microstructures and biocompatible properties. Implantation with CMC-M enhanced bone healing in rat model of mandible defects, compared with CMC, by activating Wnt signals and Wnt-related osteogenic and angiogenic molecules. Oral supplementation with MgG also stimulated bone healing in mouse model of femoral defects along with the increases in Wnt3a and angiogenic and osteogenic factors. Supplemental MgG did not alter nature bone accrual and bone marrow (BM) microenvironment in adult mouse model, but enhanced the functioning of BM stromal cells (BMSCs). Furthermore, MgG directly stimulated the induction of Wnt signaling-, angiogenesis-, and osteogenesis-related molecules in cultures of BMSCs, as well as triggered the migration of endothelial cells. These results suggest that supplemental MgG improves bone repair in a way that is synergistically enhanced by Wnt signal-associated angiogenic and osteogenic molecules. Overall, this study indicates that supplemental MgG might ameliorate oxidative damage in the BM, improve the functionality of BM stem cells, and maintain BM-microenvironmental homeostasis.

Exploring Biomineralization Processes Using In Situ Liquid Transmission Electron Microscopy: A Review

Liquid transmission electron microscopy (TEM) is a newly established technique broadly used to study reactions in situ. Since its emergence, complex and multifaceted biomineralization processes have been revealed with real-time resolution, where classical and non-classical mineralization pathways have been dynamically observed primarily for Ca and Fe-based mineral systems in situ. For years, classical crystallization pathways have dominated theories on biomineralization progression despite observations of non-traditional routes involving precursor phases using traditional- and cryo-TEM. The new dynamic lens provided by liquid TEM is a key correlate to techniques limited to time-stamped, static observations - helping shift paradigms in biomineralization toward non-classical theories with dynamic mechanistic visualization. Liquid TEM provides new insights into fundamental biomineralization processes and essential physiological and pathological processes for a wide range of organisms. This review critically reviews a summary of recent in situ liquid TEM research related to the biomineralization field. Key liquid TEM preparation and imaging parameters are provided as a foundation for researchers while technical challenges are discussed. In future, the expansion of liquid TEM research in the biomineralization field will lead to transformative discoveries, providing complementary dynamic insights into biological systems.

A bilayer hydrogel mimicking the periosteum-bone structure for innervated bone regeneration

In bone tissue, nerves are primarily located in the periosteum and play an indispensable role in bone defect repair. However, most bone tissue engineering approaches ignored the reconstruction of the nerve network. Herein, we aimed to develop a bilayer hydrogel simulating periosteum-bone structure to induce innervated bone regeneration. The bottom "bone" layer consisted of gelatin methacryloyl (GelMA), poly(ethylene glycol) diacrylate (PEGDA), and nano-hydroxyapatite (nHA), whereas the upper "periosteum" layer consisted of GelMA, sodium alginate (SA) and MgCl2. The mechanical properties of the upper and bottom hydrogels were designed to be suitable for neurogenesis and osteogenesis, respectively. Besides, Mg2+ from the "periosteum" layer released at the early stage (within 7 d), which aligned with the optimal time window for nerve regeneration and osteogenic related neuropeptide release. Simultaneously, the prevention of long-term Mg2+ release (after 7 d) could avoid osteogenic inhibition caused by prolonged Mg2+ exposure. Additionally, the incorporation of nHA in the bottom "bone" layer supported the long-term osteogenesis due to its osteoconductivity and slow degradation. In vitro biological experiments revealed that the bilayer hydrogel (GS@Mg/GP@nHA) promoted neurite growth and calcitonin gene-related peptide (CGRP) expression in rat dorsal root ganglion (DRG) neurons, as well as the osteogenesis of rat bone-derived mesenchymal stem cells (BMSCs). Moreover, the in vivo experiments demonstrated that the GS@Mg/GP@nHA hydrogel efficiently promoted nerve network reconstruction and bone regeneration of rat calvarial bone defects. Altogether, the bilayer hydrogel GS@Mg/GP@nHA could promote innervated bone regeneration, providing new insights for biomaterial design for bone tissue engineering.

Biodegradable magnesium and zinc composite microspheres with synergistic osteogenic effect for enhanced bone regeneration

Biodegradable polymer microspheres in bone tissue engineering have become appealing as their non-invasive advantages in irregular damage bone repair. However, current microspheres used in BTE still lack sufficient osteogenic capacity to induce effective bone regeneration. In this study, we developed osteogenic composite microspheres concurrently loaded with magnesium oxide (MgO) and zinc oxide (ZnO), both of which are osteogenic active substances, using a facile and scalable emulsification method. The osteogenic composite microspheres exhibited a sequential yet complementary release profile characterized by a rapid release of Mg2+ and a gradual release of Zn2+ in a physiological environment, thereby maintaining the concentration of bioactive ions at a sustained high level. As a result, the combination of Mg2+ and Zn2+ in the composite microspheres led to a synergistic enhancement in biomimetic mineralization and the upregulation in the expression of osteogenic-related genes and proteins at the cellular level. Through a critical-sized calvarial rate defect model, the osteogenic composite microspheres were demonstrated to have strong osteogenic ability to promote new bone formation via ultrasonic imaging, histological and immunohistochemical evaluations. In sum, these osteogenic composite microspheres as microcarriers of Mg2+ and Zn2+ have great potential in the delivery of therapeutic ions for treating bone defects.

Advanced Hybrid Strategies of GelMA Composite Hydrogels in Bone Defect Repair

To date, severe bone defects remain a significant challenge to the quality of life. All clinically used bone grafts have their limitations. Bone tissue engineering offers the promise of novel bone graft substitutes. Various biomaterial scaffolds are fabricated by mimicking the natural bone structure, mechanical properties, and biological properties. Among them, gelatin methacryloyl (GelMA), as a modified natural biomaterial, possesses a controllable chemical network, high cellular stability and viability, good biocompatibility and degradability, and holds the prospect of a wide range of applications. However, because they are hindered by their mechanical properties, degradation rate, and lack of osteogenic activity, GelMA hydrogels need to be combined with other materials to improve the properties of the composites and endow them with the ability for osteogenesis, vascularization, and neurogenesis. In this paper, we systematically review and summarize the research progress of GelMA composite hydrogel scaffolds in the field of bone defect repair, and discuss ways to improve the properties, which will provide ideas for the design and application of bionic bone substitutes.

Development and evaluation of an injectable ChitHCl-MgSO4-DDA hydrogel for bone regeneration: In vitro and in vivo studies on cell migration and osteogenesis enhancement

Nonunion and delayed union of the bone are situations in orthopedic surgery that can occur even if the bone alignment is correct and there is sufficient mechanical stability. Surgeons usually apply artificial bone grafts in bone fracture gaps or in bone defect sites for osteogenesis to improve bone healing; however, these bone graft materials have no osteoinductive or osteogenic properties, and fit the morphology of the fracture gap with difficulty. In this study, we developed an injectable chitosan-based hydrogel with MgSO4 and dextran oxidative, with the purpose to improve bone healing through introducing an engineered chitosan-based hydrogel. The developed hydrogel can gelate and fit with any morphology or shape, has good biocompatibility, can enhance the cell-migration capacity, and can improve extracellular calcium deposition. Moreover, the amount of new bone formed by injecting the hydrogel in the bone tunnel was assessed by an in vivo test. We believe this injectable chitosan-based hydrogel has great potential for application in the orthopedic field to improve fracture gap healing.

A comparative study on the effects of biodegradable high-purity magnesium screw and polymer screw for fixation in epiphyseal trabecular bone

With mechanical strength close to cortical bone, biodegradable and osteopromotive properties, magnesium (Mg)-based implants are promising biomaterials for orthopedic applications. However, during the degradation of such implants, there are still concerns on the potential adverse effects such as formation of cavities, osteolytic phenomena and chronic inflammation. Therefore, to transform Mg-based implants into clinical practice, the present study evaluated the local effects of high-purity Mg screws (HP-Mg, 99.99 wt%) by comparing with clinically approved polylactic acid (PLA) screws in epiphyseal trabecular bone of rabbits. After implantation of screws at the rabbit distal femur, bone microstructural, histomorphometric and biomechanical properties were measured at various time points (weeks 4, 8 and 16) using micro-CT, histology and histomorphometry, micro-indentation and scanning electron microscope. HP-Mg screws promoted peri-implant bone ingrowth with higher bone mass (BV/TV at week 4: 0.189 ± 0.022 in PLA group versus 0.313 ± 0.053 in Mg group), higher biomechanical properties (hardness at week 4: 35.045 ± 1.000 HV in PLA group versus 51.975 ± 2.565 HV in Mg group), more mature osteocyte LCN architecture, accelerated bone remodeling process and alleviated immunoreactive score (IRS of Ram11 at week 4: 5.8 ± 0.712 in PLA group versus 3.75 ± 0.866 in Mg group) as compared to PLA screws. Furthermore, we conducted finite element analysis to validate the superiority of HP-Mg screws as orthopedic implants by demonstrating reduced stress concentration and uniform stress distribution around the bone tunnel, which led to lower risks of trabecular microfractures. In conclusion, HP-Mg screws demonstrated greater osteogenic bioactivity and limited inflammatory response compared to PLA screws in the epiphyseal trabecular bone of rabbits. Our findings have paved a promising way for the clinical application of Mg-based implants.

Bone and vascular effects of magnesium supplements in CKD patients (the MagicalBone Pilot Study)

BACKGROUND AND OBJECTIVE

The progression of chronic kidney disease (CKD) involves the development of alterations in mineral metabolism that are closely related to cardiovascular outcomes and bone disease. Hypomagnesemia is associated with more rapid progression of CKD and other comorbidities. Our objective was to analyze in CKD patients stages 3-4 the impact of the administration of magnesium (Mg) carbonate on bone mineral density (BMD) and hemodynamic changes associated with by vascular calcification (VC).

MATERIAL AND METHODS

Patients with CKD stages 3-4 were randomized into controls (n=12) or intervention (n=7) group receiving 360mg of Mg carbonate daily during a 15-month period. Parameters related to mineral metabolism, BMD, VC, and pulse wave velocity (PWV) were evaluated.

RESULTS

Supplementation with Mg produced an increase in the urinary excretion of Mg while serum Mg levels remained stable and no episodes of hypermagnesemia were reported. In addition, no significant changes were found in the degree of VC assessed by Adragao index, however, both serum and urine Mg were significantly associated with a decrease in PWV, suggesting an increase in vascular compliance. Likewise, BMD did not change following treatment, but serum Mg significantly correlated with the levels of N-terminal propeptide of collagen alpha-1(I) chain (PINP), a marker of bone synthesis.

CONCLUSIONS

In sum, these results suggest a possible beneficial effect of Mg on vascular compliance with no detrimental effects on bone status. In addition, our results highlight the need to consider monitorization of urinary Mg status in CKD patients.

Environmental and Genetic Determinants of Ankylosing Spondylitis

Exposure to heavy metals and lifestyle factors like smoking contribute to the production of free oxygen radicals. This fact, combined with a lowered total antioxidant status, can induce even more damage in the development of ankylosing spondylitis (AS). Despite the fact that some researchers are looking for more genetic factors underlying AS, most studies focus on polymorphisms within the genes encoding the human leukocyte antigen (HLA) system. The biggest challenge is finding the effective treatment of the disease. Genetic factors and the influence of oxidative stress, mineral metabolism disorders, microbiota, and tobacco smoking seem to be of great importance for the development of AS. The data contained in this review constitute valuable information and encourage the initiation and development of research in this area, showing connections between inflammatory disorders leading to the pathogenesis of AS and selected environmental and genetic factors.

Nano-laponite encapsulated coaxial fiber scaffold promotes endochondral osteogenesis

Osteoinductive supplements without side effects stand out from the growth factors and drugs widely used in bone tissue engineering. Lithium magnesium sodium silicate hydrate (laponite) nanoflake is a promising bioactive component for bone regeneration, attributed to its inherent biosafety and effective osteoinductivity. Up to now, the in vivo osteogenic potential and mechanisms of laponite-encapsulated fibrous membranes remain largely unexplored. This study presents a unique method for homogeneously integrating high concentrations of laponite RDS into a polycaprolactone (PCL) matrix by dispersing laponite RDS sol into the polymer solution. Subsequently, a core-shell fibrous membrane (10RP-PG), embedding laponite-loaded PCL in its core, was crafted using coaxial electrospinning. The PCL core's slow degradation and the shell's gradient degradation enabled the sustained release of bioactive ions (Si and Mg) from laponite. In vivo studies on a critical-sized calvarial bone defect model demonstrated that the 10RP-PG membrane markedly enhanced bone formation and remodeling by accelerating the process of endochondral ossification. Further transcriptome analysis suggested that osteogenesis in the 10RP-PG membrane is driven by Mg and Si from endocytosed laponite, activating pathways related to ossification and endochondral ossification, including Hippo, Wnt and Notch. The fabricated nanocomposite fibrous membranes hold great promise in the fields of critical-sized bone defect repair.

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.

Citrate Improves Biomimetic Mineralization Induced by Polyelectrolyte-Cation Complexes Using PAsp-Ca&Mg Complexes

Magnesium ions are highly enriched in early stage of biological mineralization of hard tissues. Paradoxically, hydroxyapatite (HAp) crystallization is inhibited significantly by high concentration of magnesium ions. The mechanism to regulate magnesium-doped biomimetic mineralization of collagen fibrils has never been fully elucidated. Herein, it is revealed that citrate can bioinspire the magnesium-stabilized mineral precursors to generate magnesium-doped biomimetic mineralization as follows: Citrate can enhance the electronegativity of collagen fibrils by its absorption to fibrils via hydrogen bonds. Afterward, electronegative collagen fibrils can attract highly concentrated electropositive polyaspartic acid-Ca&Mg (PAsp-Ca&Mg) complexes followed by phosphate solution via strong electrostatic attraction. Meanwhile, citrate adsorbed in/on fibrils can eliminate mineralization inhibitory effects of magnesium ions by breaking hydration layer surrounding magnesium ions and thus reduce dehydration energy barrier for rapid fulfillment of biomimetic mineralization. The remineralized demineralized dentin with magnesium-doped HAp possesses antibacterial ability, and the mineralization mediums possess excellent biocompatibility via cytotoxicity and oral mucosa irritation tests. This strategy shall shed light on cationic ions-doped biomimetic mineralization with antibacterial ability via modifying collagen fibrils and eliminating mineralization inhibitory effects of some cationic ions, as well as can excite attention to the neglected multiple regulations of small biomolecules, such as citrate, during biomineralization process.

Construction of Magnesium Phosphate Chemical Conversion Coatings with Different Microstructures on Titanium to Enhance Osteogenesis and Angiogenesis

Titanium (Ti) and its alloys are widely used as hard tissue substitutes in dentistry and orthopedics, but their low bioactivity leads to undesirable osseointegration defects in the early osteogenic phase. Surface modification is an important approach to overcome these problems. In the present study, novel magnesium phosphate (MgP) coatings with controllable structures were fabricated on the surface of Ti using the phosphate chemical conversion (PCC) method. The effects of the microstructure on the physicochemical and biological properties of the coatings on Ti were researched. The results indicated that accelerators in PCC solution were important factors affecting the microstructure and properties of the MgP coatings. In addition, the coated Ti exhibited excellent hydrophilicity, high bonding strength, and good corrosion resistance. Moreover, the biological results showed that the MgP coatings could improve the spread, proliferation, and osteogenic differentiation of mouse osteoblast cells (MC3T3-E1) and vascular differentiation of human umbilical vein endothelial cells (HUVECs), indicating that the coated Ti samples had a great effect on promoting osteogenesis and angiogenesis. Overall, this study provided a new research idea for the surface modification of conventional Ti to enhance osteogenesis and angiogenesis in different bone types for potential biomedical applications.

Nanosized Silk-Magnesium Complexes for Promotion of Angiogenic and Osteogenic Activities

Injectable hydrogels with osteogenic and angiogenetic properties are of interest in bone tissue engineering. Since the bioactivity of ions is concentration-dependent, nanosized silk-magnesium (Mg) complexes were previously developed and assembled into hydrogels with angiogenic capabilities but failed to control both osteogenic and angiogenetic activities effectively. Here, nanosized silk particles with different sizes were obtained by using ultrasonic treatment to control silk-Mg coordination and particle formation, resulting in silk-Mg hydrogels with different types of bioactivity. Fourier transform infrared and X-ray diffraction results revealed that different coordination intensities were present in the different complexes as a basis for the differences in activities. Slow Mg ion release was controlled by these nanosized silk-Mg complexes through degradation. With the same amount of Mg ions, the different silk-Mg complexes exhibited different angiogenic and osteogenic capacities. Complexes with both angiogenic and osteogenic capacities were developed by optimizing the sizes of the silk particles, resulting in faster and improved quality of bone formed in vivo than complexes with the same composition of silk and Mg but only angiogenic or osteogenic capacities. The biological selectivity of silk-Mg complexes should facilitate applications in tissue regeneration.

How surface-to-volume ratio affects degradation of magnesium: in vitro and in vivo studies

Despite the many studies carried out over the past decade to determine the biodegradation performance of magnesium and its alloys, few studies focused on the effect of altered surface area to volume ratio on in vitro and in vivo degradation rate and osteogenesis. Here, high purity magnesium cylindrical rods with gradient of surface area to volume ratio were processed by excavating different numbers of grooves on the side surface. The immersion test in SBF solution and the rat femoral condylar bone defect model were used to evaluate the degradation of magnesium rods in vitro and in vivo, respectively. We demonstrated that, the increased number of grooves on the HP magnesium surface represented a decrease in the percentage of residual volume over time, not necessarily an increase in absolute degradation volume or a regular change in corrosion rate. Furthermore, there were strong linear correlations between the relative degradation volume and the initial surface-to-volume ratio of HP magnesium rods both in vitro and in vivo. The difference in the slope of this relationship in vitro and in vivo might help to determine the possible range of in vivo degradation rates via in vitro data. In addition, the corrosion rate is more suitable for evaluating bone formation surrounding the different HP magnesium rods. Our findings in this work may facilitate adjusting the in vivo degradation and osteogenesis of different kinds of orthopedic implants made of the same magnesium-based material, and thus, accelerate the clinical popularization and application.

A Dual Reversible Cross-Linked Hydrogel with Enhanced Mechanical Property and Capable of Proangiogenic and Osteogenic Activities for Bone Defect Repair

The clinical treatment of bone defects presents ongoing challenges. One promising approach is bone tissue engineering (BTE), wherein hydrogels have garnered significant attention. However, the application of hydrogels in BTE is severely limited due to their poor mechanical properties, as well as their inferior proangiogenic and osteogenic activities. To address these limitations, our develop a dual cross-linked alendronate (ALN)-Ca2+ /Mg2+ -doped sulfated hyaluronic acid (SHA@CM) hydrogel, using a one-step mixing injection molding method known as "three-in-one" approach. This approach enabled the simultaneous formation of Schiff-Base crosslinking and electric attraction-based crosslinking within the hydrogel. The Schiff-Base crosslinking contributed to the majority of the hydrogel's mechanical strength, while the electric attraction-based crosslinking served as a release reservoir for Ca2+ /Mg2+ and ALN, promoting enhanced osteogenic activities and providing additional mechanical reinforcement to the hydrogel. These experimental data demonstrates several favorable properties of the SHA@CM hydrogel, including satisfactory injectability, rapid gelation, self-healing capacity, and excellent cytocompatibility. Moreover, the presence of sulfated groups and Mg2+ within the SHA@CM hydrogel exhibited pro-angiogenic effects, while the controlled release of nanoparticles formed by Ca2+ /Mg2+ and ALN further enhanced the osteogenesis of the hydrogel. Overall, these results indicate that the SHA@CM hydrogel holds significant potential for the clinical translation of BTE.

Ion incorporation into bone grafting materials

The use of biomaterials in regenerative medicine has expanded to treat various disorders caused by trauma or disease in orthopedics and dentistry. However, the treatment of large and complex bone defects presents a challenge, leading to a pressing need for optimized biomaterials for bone repair. Recent advances in chemical sciences have enabled the incorporation of therapeutic ions into bone grafts to enhance their performance. These ions, such as strontium (for bone regeneration/osteoporosis), copper (for angiogenesis), boron (for bone growth), iron (for chemotaxis), cobalt (for B12 synthesis), lithium (for osteogenesis/cementogenesis), silver (for antibacterial resistance), and magnesium (for bone and cartilage regeneration), among others (e.g., zinc, sodium, and silica), have been studied extensively. This review aims to provide a comprehensive overview of current knowledge and recent developments in ion incorporation into biomaterials for bone and periodontal tissue repair. It also discusses recently developed biomaterials from a basic design and clinical application perspective. Additionally, the review highlights the importance of precise ion introduction into biomaterials to address existing limitations and challenges in combination therapies. Future prospects and opportunities for the development and optimization of biomaterials for bone tissue engineering are emphasized.

Cobalt-doped layered hydroxide coating on titanium implants promotes vascularization and osteogenesis for accelerated fracture healing

Angiogenesis at the fracture site plays crucial roles in the endogenous osteogenesis process and is a prerequisite for the efficient repair of implant fixed bone defects. To improve the peri-implant vascularization of titanium implant for accelerating defect healing, we developed a Co-doped Mg-Al layered hydroxide coating on the surface of titanium using hydrothermal reaction and then modified the surface with gallic acid (Ti-LDH/GA). Gallic acid coating enabled the sustained release of Co2+ and Mg2+ to the defect site over a month. Ti-LDH/GA treatment profoundly stimulated the angiogenic potential of endothelial cells by upregulating the vascularization regulators such as vascular endothelial growth factor VEGF) and hypoxia-inducible factor-1α (HIF-1α), leading to enhanced osteogenic capability of mesenchymal stem cells (MSCs). These pro-bone healing benefits were attributed to the synergistic effects of Co ions and Mg ions in promoting angiogenesis and new bone formation. These insights collectively suggested the potent pro-osteogenic effect of Ti-LDH/GA through leveraging peri-implant vascularization, offering a new approach for developing biofunctional titanium implants.

Novel Strategies for Spatiotemporal and Controlled BMP-2 Delivery in Bone Tissue Engineering

Bone morphogenetic protein-2 (BMP-2) has been commercially approved by the Food and Drug Administration for use in bone defects and diseases. BMP-2 promotes osteogenic differentiation of mesenchymal stem cells. In bone tissue engineering, BMP-2 incorporated into scaffolds can be used for stimulating bone regeneration in organoid construction, drug testing platforms, and bone transplants. However, the high dosage and uncontrollable release rate of BMP-2 challenge its clinical application, mainly due to the short circulation half-life of BMP-2, microbial contamination in bone extracellular matrix hydrogel, and the delivery method. Moreover, in clinical translation, the requirement of high doses of BMP-2 for efficacy poses challenges in cost and safety. Based on these, novel strategies should ensure that BMP-2 is delivered precisely to the desired location within the body, regulating the timing of BMP-2 release to coincide with the bone healing process, as well as release BMP-2 in a controlled manner to optimize its therapeutic effect and minimize side effects. This review highlights improvements in bone tissue engineering applying spatiotemporal and controlled BMP-2 delivery, including molecular engineering, biomaterial modification, and synergistic therapy, aiming to provide references for future research and clinical trials.

Multiscale morphological analysis of bone microarchitecture around Mg-10Gd implants

The utilization of biodegradable magnesium (Mg)-based implants for restoration of bone function following trauma represents a transformative approach in orthopaedic application. One such alloy, magnesium-10 weight percent gadolinium (Mg-10Gd), has been specifically developed to address the rapid degradation of Mg while enhancing its mechanical properties to promote bone healing. Previous studies have demonstrated that Mg-10Gd exhibits favorable osseointegration; however, it exhibits distinct ultrastructural adaptation in comparison to conventional implants like titanium (Ti). A crucial aspect that remains unexplored is the impact of Mg-10Gd degradation on the bone microarchitecture. To address this, we employed hierarchical three-dimensional imaging using synchrotron radiation in conjunction with image-based finite element modelling. By using the methods outlined, the vascular porosity, lacunar porosity and the lacunar-canaliculi network (LCN) morphology of bone around Mg-10Gd in comparison to Ti in a rat model from 4 weeks to 20 weeks post-implantation was investigated. Our investigation revealed that within our observation period, the degradation of Mg-10Gd implants was associated with significantly lower (p < 0.05) lacunar density in the surrounding bone, compared to Ti. Remarkably, the LCN morphology and the fluid flow analysis did not significantly differ for both implant types. In summary, a more pronounced lower lacunae distribution rather than their morphological changes was detected in the surrounding bone upon the degradation of Mg-10Gd implants. This implies potential disparities in bone remodelling rates when compared to Ti implants. Our findings shed light on the intricate relationship between Mg-10Gd degradation and bone microarchitecture, contributing to a deeper understanding of the implications for successful osseointegration.

Calcium carbonate-actuated ion homeostasis perturbator for oxidative damage-augmented Ca2+/Mg2+ interference therapy

Ion homeostasis distortion through exogenous overload or underload of intracellular ion species has become an arresting therapeutic approach against malignant tumor. Nevertheless, treatment outcomes of such ion interference are always compromised by the intrinsic ion homeostasis maintenance systems in cancer cells. Herein, an ion homeostasis perturbator (CTC) is facilely designed by co-encapsulation of carvacrol (CAR) and meso-tetra-(4-carboxyphenyl)porphine (TCPP) into pH-sensitive nano-CaCO3, aiming to disrupt the self-defense mechanism during the process of ion imbalance. Upon the endocytosis of CTC into tumor cells, lysosomal acidity can render the decomposition of CaCO3, resulting in the instant Ca2+ overload and CO2 generation in cytoplasm. Simultaneously, CaCO3 disintegration triggers the release of CAR and TCPP, which are devoted to TRPM7 inhibition and sonosensitization, respectively. The malfunction of TRPM7 can impede the influx of Mg2+ and allow unrestricted influx of Ca2+ based on the antagonism relationship between Mg2+ and Ca2+, leading to an aggravated Ca2+/Mg2+ dyshomeostasis through ion channel deactivation. In another aspect, US-triggered cavitation can be significantly enhanced by the presence of inert CO2 microbubbles, further amplifying the generation of reactive oxygen species. Such oxidative damage-augmented Ca2+/Mg2+ interference therapy effectively impairs the mitochondrial function of tumor, which may provide useful insights in cancer therapy.

Organic Matrix Derived from Host-Microbe Interplay Contributes to Pathological Renal Biomineralization

Matrix stones are a rare form of kidney stones. They feature a high percentage of hydrogel-like organic matter, and their formation is closely associated with urinary tract infections. Herein, comprehensive materials and biochemical approaches were taken to map the organic-inorganic interface and gather insights into the host-microbe interplay in pathological renal biomineralization. Surgically extracted soft and slimy matrix stones were examined using micro-X-ray computed tomography and various microspectroscopy techniques. Higher-mineral-density laminae were positive for calcium-bound Alizarin red. Lower-mineral-density laminae revealed periodic acid-Schiff-positive organic filamentous networks of varied thickness. These organic filamentous networks, which featured a high polysaccharide content, were enriched with zinc, carbon, and sulfur elements. Neutrophil extracellular traps (NETs) along with immune response-related proteins, including calprotectin, myeloperoxidase, CD63, and CD86, also were identified in the filamentous networks. Expressions of NETs and upregulation of polysaccharide-rich mucin secretion are proposed as a part of the host immune defense to "trap" pathogens. These host-microbe derived organic matrices can facilitate heterogeneous nucleation and precipitation of inorganic particulates, resulting in macroscale aggregates known as "matrix stones". These insights into the plausible aggregation of constituents through host-microbe interplay underscore the unique "double-edged sword" effect of the host immune response to pathogens and the resulting renal biominerals.

Evaluation of Physiochemical and Biological Properties of Biofunctionalized Mg-Based Implants Obtained via Large-Scale PEO Process for Dentistry Applications

An increasing number of tooth replacement procedures ending with implant failure generates a great need for the delivery of novel biomedical solutions with appropriate mechanical characteristics that would mimic natural tissue and undergo biodegradation. This phenomenon constitutes a significant difficulty for scientists, since currently applied biomaterials dedicated for this purpose are based on stainless steel, Ti, and Ti and CoCr alloys. One of the most promising raw materials is magnesium, which has been proven to promote bone regeneration and accelerate the tissue healing process. Nevertheless, its high reactivity with body fluid components is associated with fast and difficult-to-control biocorrosion, which strongly limits the application of Mg implants as medical devices. The achievement of appropriate functionality, both physiochemical and biological, to enable the commercial use of Mg biomaterials is possible only after their superficial modification. Therefore, the obtainment of uniform, reproducible coatings increasing resistance to the aqueous environment of the human body combined with a nanostructured surface that enhances implant-cell behaviors is an extremely important issue. Herein, we present a successful strategy for the modification of Mg implants via the PEO process, resulting in the obtainment of biomaterials with lower corrosion rates and superior biological properties, such as the promotion of extracellular matrix formation and a positive impact on the proliferation of MG-63 cells. The implants were investigated regarding their chemical composition using the FT-IR and XRD methods, which revealed that MgO layer formation, as well as the incorporation of electrolyte components such as fluorine and silica, were responsible for the increased microhardness of the samples. An extensive study of the biomaterials' morphology confirmed that successful surface modification led to a microporous structure suitable for the attachment and proliferation of cells. The three-layer nature of the newly-formed coatings, typical for PEO modification, was confirmed via cross-section analysis. A biocorrosion and biodegradation study proved that applied modification increased their resistance to body fluids. The cell culture study performed herein confirmed that the correct adjustment of modification parameters results in a lack of cytotoxicity of the magnesium implants, cell proliferation enhancement, and improvement in extracellular matrix formation.

Anticancer and bone-enhanced nano-hydroxyapatite/gelatin/polylactic acid fibrous membrane with dual drug delivery and sequential release for osteosarcoma

Surgical resection of osteosarcoma is always accompanied by residual metastasis of tumor cells and bone tissue defects. In this work, a novel kind of gelatin/polylactic acid (PLA) coaxial fiber membrane with a shell layer containing doxorubicin-loaded hydroxyapatite (DOX@nHAp) nanoparticles and a core layer containing Icariin (ICA) was developed for antitumor and bone enhancement at the defect site. Physical evaluation displayed that the composite membrane provided moderate hydrophilicity, enhanced tensile strength (Dry: 2-3 MPa, wet: 1-2 MPa) and elasticity (70-100 %), as well as increased specific surface area and pore volume (19.39 m²/g and 0.16 cm³/g). In SBF, DOX@nHAp in the fibers promoted biomineralization on the fiber surface. In in vitro evaluation, approximately 80 % of DOX had a short-term release during the first 8 days, followed by long-term release behavior of ICA for up to 40 days. CCK-8 results confirmed that the membrane could actively support MC3T3-E1 cells proliferation and was conductive to high alkaline phosphatase expression, while the viability of MG-63 cells was effectively inhibited to 50 %. Thus, the dual-loaded fibrous membrane with a coaxial structure and nHAp is a promising system for anticancer and defects reconstruction after osteosarcoma surgery.

Magnesium Administration in Chronic Kidney Disease

Awareness of the clinical relevance of magnesium in medicine has increased over the last years, especially for people with chronic kidney disease (CKD), due to magnesium's role in vascular calcification and mineral metabolism. The inverse association between serum magnesium and clinically relevant, adverse outcomes is well-established in people with CKD. Subsequent intervention studies have focused on the effect of magnesium administration, mainly in relation to cardiovascular diseases, mineral bone metabolism, and other metabolic parameters. The most commonly used routes of magnesium administration are orally and by increasing dialysate magnesium. Several oral magnesium formulations are available and the daily dosage of elemental magnesium varies highly between studies, causing considerable heterogeneity. Although data are still limited, several clinical studies demonstrated that magnesium administration could improve parameters of vascular function and calcification and mineral metabolism in people with CKD. Current clinical research has shown that magnesium administration in people with CKD is safe, without concerns for severe hypermagnesemia or negative interference with bone metabolism. It should be noted that there are several ongoing magnesium intervention studies that will contribute to the increasing knowledge on the potential of magnesium administration in people with CKD.

Orchestration of energy metabolism and osteogenesis by Mg2+ facilitates low-dose BMP-2-driven regeneration

The clinical application of bone morphogenetic protein-2 (BMP-2) is limited by several factors, including ineffectiveness at low doses and severe adverse effects at high doses. To address these efficacy and safety limitations, we explored whether orchestration of energy metabolism and osteogenesis by magnesium ion (Mg²⁺) could reduce the dose and thereby improve the safety of BMP-2. Our results demonstrated that rapid metabolic activation triggered by BMP-2 was indispensable for subsequent osteogenesis. Moreover, inadequate metabolic stimulation was shown to be responsible for the ineffectiveness of low-dose BMP-2. Next, we identified that Mg²⁺, as an ''energy propellant", substantially increased cellular bioenergetic levels to support the osteogenesis via the Akt-glycolysis-Mrs2-mitochondrial axis, and consequently enhanced the osteoinductivity of BMP-2. Based on the mechanistic discovery, microgel composite hydrogels were fabricated as low-dose BMP-2/Mg²⁺ codelivery system through microfluidic and 3D printing technologies. An in vivo study further confirmed that rapid and robust bone regeneration was induced by the codelivery system. Collectively, these results suggest that this bioenergetic-driven, cost-effective, low-dose BMP-2-based strategy has substantial potential for bone repair.

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BMP-2 triggered rapid metabolic adaption, characterized by the successive activation of glycolysis and OxPhos.

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Inadequate activation of metabolic state led to the ineffectiveness of low-dose BMP-2.

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Mg²⁺ elevated the bioenergetic levels and enhance the efficacy of BMP-2 via the Akt-glycolysis-Mrs2-mitochondrial axis.

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Composite hydrogels with BMP-2 and "energy propellant" Mg²⁺ were fabricated to orchestrate metabolism and osteogenesis.

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The hydrogels achieved efficient low-dose BMP-2-driven regeneration in vivo.

Tantalum and magnesium nanoparticles enhance the biomimetic properties and osteo-angiogenic effects of PCL membranes

Segmental bone defects, accompanied by periosteum stripping or injury, usually lead to delayed bone union or nonunion, which have challenged orthopedic surgeons. The periosteum, which provides essential blood supply and initial stem cells for bone tissue, plays an important role in the repair of bone defects. The reconstruction of the destroyed periosteum has attracted the attention of researchers exploring more satisfactory therapies to repair bone defects. However, periosteum-like biomaterials have yet to meet the clinical requirements and resolve this challenging problem. In this study, we manufactured a nanofiber periosteum replacement based on poly-ε-caprolactone (PCL), in which tantalum nanoparticles (TaNPs) and nanoscale magnesium oxide (MgO) were introduced to enhance its osteogenic and angiogenic ability. The results of in vitro experiments indicated that the PCL/Ta/MgO periosteum replacement, with excellent cytocompatibility, promoted the proliferation of both bone marrow mesenchymal stem cells (BMSCs) and endothelial progenitor cells (EPCs). Furthermore, the incorporation of TaNPs and nano-MgO synergistically enhanced the osteogenic differentiation of BMSCs and the angiogenic properties of EPCs. Similarly, the results of in vivo experiments from subcutaneous implantation and critical-sized calvarial defect models showed that the PCL/Ta/MgO periosteum replacement combined the osteogenesis and angiogenesis abilities, promoting vascularized bone formation to repair critical-sized calvarial defects. The results of our study suggest that the strategy of stimulating repairing bone defects can be achieved with the periosteum repaired in situ and that the proposed periosteum replacement can act as a bioactive medium to accelerate bone healing.

AMPK/mTOR Pathway Is Involved in Autophagy Induced by Magnesium-Incorporated TiO2 Surface to Promote BMSC Osteogenic Differentiation

Magnesium has been extensively utilized to modify titanium implant surfaces based on its important function in promoting osteogenic differentiation. Autophagy has been proven to play a vital role in bone metabolism. Whether there is an association between autophagy and magnesium in promoting osteogenic differentiation remains unclear. In the present study, we focused on investigating the role of magnesium ions in early osteogenic activity and the underlying mechanism related to autophagy. Different concentrations of magnesium were embedded in micro-structured titanium surface layers using the micro-arc oxidation (MAO) technique. The incorporation of magnesium benefited cell adhesion, spreading, and viability; attenuated intracellular ATP concentrations and p-mTOR levels; and upregulated p-AMPK levels. This indicates the vital role of the ATP-related AMPK/mTOR signaling pathway in the autophagy process associated with osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) induced by magnesium modification on titanium surfaces. The enhanced osteogenic differentiation and improved cellular autophagy activity of BMSCs in their extraction medium further confirmed the function of magnesium ions. The results of the present study advance our understanding of the mechanism by which magnesium regulates BMSC osteogenic differentiation through autophagy regulation. Moreover, endowing implants with the ability to activate autophagy may be a promising strategy for enhancing osseointegration in the translational medicine field in the future.

Repair of Large-Scale Rib Defects Based on Steel-Reinforced Concrete-Designed Biomimetic 3D-Printed Scaffolds with Bone-Mineralized Microenvironments

Tissue engineering technology provides a promising approach for large-scale bone reconstruction in cases of extensive chest wall defects. However, previous studies did not consider meticulous scaffold design specific to large-scale rib regeneration in terms of three-dimensional (3D) shape, proper porous structures, enough mechanical strength, and osteogenic microenvironments. Thus, there is an urgent need to develop an appropriate bone biomimetic scaffold (BBS) to address this problem. In this study, a BBS with controllable 3D morphology, appropriate mechanical properties, good biocompatibility and biodegradability, porous structure suitable for cell loading, and a biomimetic osteogenic inorganic salt (OIS) microenvironment was successfully prepared by integrating computer-aided design, 3D-printing, cast-molding, and freeze-drying technologies. The addition of the OIS in the scaffold substantially promoted ectopic bone regeneration in vivo, which might be attributed to the activation of osteogenic and angiogenic signaling pathways as well as upregulated expression of osteogenic genes. More importantly, dual long rib defects could be successfully repaired and medullary cavity recanalized by the rib-shaped mature cortical bone, which might be mediated by the activation of osteoclast signaling pathways. Thus, this paper presents a reliable BBS and proposes a new strategy for the repair of large-scale bone defects.

Controlled magnesium ion delivery system for in situ bone tissue engineering

Magnesium cation (Mg²⁺) has been an emerging therapeutic agent for inducing vascularized bone regeneration. However, the therapeutic effects of current magnesium (Mg) -containing biomaterials are controversial due to the concentration- and stage-dependent behavior of Mg²⁺. Here, we first provide an overview of biochemical mechanism of Mg²⁺ in various concentrations and suggest that 2-10 mM Mg²⁺in vitro may be optimized. This review systematically summarizes and discusses several types of controlled Mg²⁺ delivery systems based on polymer-Mg composite scaffolds and Mg-containing hydrogels, as well as their design philosophy and several parameters that regulate Mg²⁺ release. Given that the continuous supply of Mg²⁺ may prevent biomineral deposition in the later stage of bone regeneration and maturation, we highlight the controlled delivery of Mg²⁺ based dual- or multi-ions system, especially for the hierarchical therapeutic ion release system, which shows enhanced biomineralization. Finally, the remaining challenges and perspectives of Mg-containing biomaterials for future in situ bone tissue engineering are discussed as well.

Controlled and Sequential Delivery of Stromal Derived Factor-1 α (SDF-1α) and Magnesium Ions from Bifunctional Hydrogel for Bone Regeneration

Bone healing is a complex process that requires the participation of cells and bioactive factors. Stromal derived factor-1 α (SDF-1α) and magnesium ions (Mg²⁺) both are significant bioactive factors for cell recruitment and osteogenesis during bone regeneration. Thus, a bifunctional hydrogel containing a sequential delivery system is fabricated to improve osteogenesis. During sequential delivery of the hydrogel, SDF-1α is predominantly released at the early stage of bone mesenchymal stem cells (BMSCs) recruitment, while Mg²⁺ are constantly delivered at a later stage to improve osteogenic differentiation of recruited cells. In addition, due to the early release of SDF-1α, the hydrogel showed strong BMSCs recruitment and proliferation activity. Mg²⁺ can not only induce up-regulation of osteogenic gene expression in vitro, but also promote bone tissue and angiogenesis in vivo. Taken together, the injection of xanthan gum-polydopamine crosslinked hydrogel co-loading SDF-1α and Mg²⁺ (XPMS hydrogel) provides a novel strategy to repair bone defects.

Assessment of Optimal Conditions for Marine Invertebrate Cell-Mediated Mineralization of Organic Matrices

Cellular strategies and regulation of their crystallization mechanisms are essential to the formation of biominerals, and harnessing these strategies will be important for the future creation of novel non-native biominerals that recapitulate the impressive properties biominerals possess. Harnessing these biosynthetic strategies requires an understanding of the interplay between insoluble organic matrices, mineral precursors, and soluble organic and inorganic additives. Our long-range goal is to use a sea anemone model system (Nematostella vectensis) to examine the role of intrinsically disordered proteins (IDPs) found in native biomineral systems. Here, we study how ambient temperatures (25–37 °C) and seawater solution compositions (varying NaCl and Mg ratios) will affect the infiltration of organic matrices with calcium carbonate mineral precursors generated through a polymer-induced liquid-precursor (PILP) process. Fibrillar collagen matrices were used to assess whether solution conditions were suitable for intrafibrillar mineralization, and SEM with EDS was used to analyze mineral infiltration. Conditions of temperatures 30 °C and above and with low Mg:Ca ratios were determined to be suitable conditions for calcium carbonate infiltration. The information obtained from these observations may be useful for the manipulation and study of cellular secreted IDPs in our quest to create novel biosynthetic materials.

A Composite of Cubic Calcium-Magnesium Sulfate and Bioglass for Bone Repair

Calcium sulfate (CS) bone cement has been shown to have good biocompatibility and can be used as a bone filler for repairing bone defects. However, its clinical application is limited due to its low compressive strength and weak bone repair activity. To this end, in this study, cubic crystalline magnesium-doped calcium sulfate (MgCS) was prepared and mixed with 45S5 bioglass (BG) to form a composite bone cement (MgCS/BG). The results show that cubic crystal calcium sulfate helps to increase the compressive strength of the composite bone cement to more than 60 MPa. More importantly, the obtained magnesium-doped composite bone cement can promote the adhesion and differentiation of mesenchymal stem cells and has good bioactivity. Through a skull defect model, it was found that MgCS/BG can significantly enhance bone defect repair and new bone formation. This new composite MgCS/BG is very promising for future translation into clinical applications.

Hierarchical Therapeutic Ion‐Based Microspheres with Precise Ratio‐Controlled Delivery as Microscaffolds for In Situ Vascularized Bone Regeneration

Therapeutic ions, such as Si and Mg, play vital roles in regulating metabolism and promoting tissue repair, hence providing an efficient strategy in tissue engineering. The regenerative outcome is strongly dependent on the targeted delivery and controlled release of therapeutic ions. Nevertheless, it remains challenging to deliver multiple ions at controlled manners and ratios. Herein, hierarchical therapeutic ion‐based microspheres are fabricated. The coordinated release of Mg and Si ions at pre‐set ratios is achieved, based on which, Mg favors osteogenesis by inducing highly efficient cell recruitment and angiogenesis, and Si promotes massive collagen secretion and biomineralization to accelerate the bone maturation process. These therapeutic ion‐based microspheres (namely PNM2) can steadily release Mg and Si ions at an optimized ratio of 2:1, which shows the most significant synergistic effect on angiogenesis and osteogenesis. Furthermore, in a rat calvarial defects model, the volume and maturity of the vascularized neo‐bone tissue regenerated with PNM2 microspheres are comparable with or even surpassing those defects regenerated with growth factors and/or cell‐laden scaffolds. Overall, this platform provides a controllable strategy for the coordinated delivery of Mg/Si ions, opening a new avenue for developing therapeutic ion‐based microscaffold for tissue engineering.

Corrosion Behavior in Magnesium-Based Alloys for Biomedical Applications

Magnesium alloys exhibit superior biocompatibility and biodegradability, which makes them an excellent candidate for artificial implants. However, these materials also suffer from lower corrosion resistance, which limits their clinical applicability. The corrosion mechanism of Mg alloys is complicated since the spontaneous occurrence is determined by means of loss of aspects, e.g., the basic feature of materials and various corrosive environments. As such, this study provides a review of the general degradation/precipitation process multifactorial corrosion behavior and proposes a reasonable method for modeling and preventing corrosion in metals. In addition, the composition design, the structural treatment, and the surface processing technique are involved as potential methods to control the degradation rate and improve the biological properties of Mg alloys. This systematic representation of corrosive mechanisms and the comprehensive discussion of various technologies for applications could lead to improved designs for Mg-based biomedical devices in the future.

PCL nanofibrous incorporating unique matrix fusion protein adsorbed mesoporous bioactive glass for bone tissue engineering

Mesoporous bioactive glass (MBG) is a potential biomedical material in bone defect repairment because of its bioactivity, biocompatibility, and osteoinduction properties. Here we report that Mg-doped MBG scaffold with 3:1 Ca/Mg ratio (MBG-Ca/Mg-3) is good for MC3T3-E1 osteoblast differentiation and mineralization. Mimicking bone extracellular matrix structure by electrospinning, we used MBG-Ca/Mg-3 adsorbed with Osteocalcin-Osteopontin-Biglycan (OOB), a new unique matrix fusion protein, to form OOB@MBG-Ca/Mg-3 scaffold, which has multifunctional ability in calvarial bone defect repairment in vivo. Intriguingly, we found that OOB@MBG-Ca/Mg-3 scaffold increases the expression of osteoblastic marker genes, including bone morphogenetic protein (Bmp2), osteopontin (Opn), Osterix, Runx2 through activation of ERK1/2. We concluded that OOB@MBG-Ca/Mg-3 scaffold promotes osteoblast differentiation and mineralization through ERK1/2 pathway and it can also enhance bone formation in vivo, which provides a new biomaterial in bone tissue engineering.

Construction of a magnesium hydroxide/graphene oxide/hydroxyapatite composite coating on Mg–Ca–Zn–Ag alloy to inhibit bacterial infection and promote bone regeneration

The improved corrosion resistance, osteogenic activity, and antibacterial ability are the key factors for promoting the large-scale clinical application of magnesium (Mg)-based implants. In the present study, a novel nanocomposite coating composed of inner magnesium hydroxide, middle graphene oxide, and outer hydroxyapatite (Mg(OH)₂/GO/HA) is constructed on the surface of Mg-0.8Ca–5Zn-1.5Ag by a combined strategy of hydrothermal treatment, electrophoretic deposition, and electrochemical deposition. The results of material characterization and electrochemical corrosion test showed that all the three coatings have high bonding strength, hydrophilicity and corrosion resistance. In vitro studies show that Mg(OH)₂ indeed improves the antibacterial activity of the substrate. The next GO and GO/HA coating procedures both promote the osteogenic differentiation of MC3T3-E1 cells and show no harm to the antibacterial activity of Mg(OH)₂ coating, but the latter exhibits the best promoting effect. In vivo studies demonstrate that the Mg alloy with the composite coating not only ameliorates osteolysis induced by bacterial invasion but also promotes bone regeneration under both normal and infected conditions. The current study provides a promising surface modification strategy for developing multifunctional Mg-based implants with good corrosion resistance, antibacterial ability and osteogenic activity to enlarge their biomedical applications.

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A Mg(OH)₂/GO/HA composite coating with high bonding strength was constructed on the surface of Mg–Ca–Zn–Ag alloy.

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The outer HA layer with excellent osteogenic activity recovered the high corrosion resistance of inner Mg(OH)₂ layer.

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The Mg(OH)₂/GO/HA composite coating promoted new bone regeneration significantly under both normal and infected conditions.

Biodegradable magnesium implant enhances angiogenesis and alleviates medication-related osteonecrosis of the jaw in rats

Background

Medication-related osteonecrosis of the jaw (MRONJ) is a serious complication associated with antiresorptive and antiangiogenic medications, of which impaired angiogenesis is a key pathological alteration. Since Magnesium (Mg)-based implants possess proangiogenic effects, we hypothesized that the biodegradable Mg implant could alleviate the development of MRONJ via enhancing angiogenesis.

Methods

MRONJ model was established and divided into the Veh ​+ ​Ti group (Vehicle-treated rat, with Titanium (Ti) implant), BP ​+ ​Ti group (Bisphosphonate (BP)-treated rat, with Ti implant), BP ​+ ​Mg group (BP-treated rat, with Mg implant), BP ​+ ​Mg ​+ ​SU5416 group (BP-treated rat, with Mg implant and vascular endothelial growth factor (VEGF) receptor-2 inhibitor), BP ​+ ​Mg ​+ ​BIBN group (BP-treated rat, with Mg implant and calcitonin gene-related peptide (CGRP) receptor antagonist), and BP ​+ ​Mg ​+ ​SU5416+BIBN group (BP-treated rat, with Mg implant and VEGF receptor-2 inhibitor and CGRP receptor antagonist). The occurrence of MRONJ, alveolar bone necrosis, new bone formation and vessel formation were assessed by histomorphometry, immunohistochemistry, and micro-CT analysis.

Results

Eight weeks after surgery, the BP ​+ ​Mg group had significantly reduced occurrence of MRONJ-like lesion and histological osteonecrosis, increased bone microstructural parameters, and increased expressions of VEGFA and CGRP, than the BP ​+ ​Ti group. By simultaneously blocking VEGF receptor-2 and CGRP receptor, the vessel volume and new bone formation in the BP ​+ ​Mg group were significantly decreased, meanwhile the occurrence of MRONJ-like lesion and histological bone necrosis were significantly increased.

Conclusion

Biodegradable Mg implant could alleviate the development of MRONJ-like lesion, possibly via upregulating VEGF- and CGRP-mediated angiogenesis. Mg-based implants have the translational potential to be developed as a novel internal fixation device for patients with the risk of MRONJ.

The Translational potential of this article

This work reports a biodegradable Mg implant which ameliorates the development of MRONJ-like lesions possibly due to its angiogenic property. Mg-based implants have the potential to be developed as a novel internal fixation device for patients at the risk of MRONJ.

Mg-HA-C/C Composites Promote Osteogenic Differentiation and Repair Bone Defects Through Inhibiting miR-16

The hydroxyapatite (HA) coating on carbon/carbon (C/C) is reasonable and feasible to obtain bone graft materials with appropriate mechanical and biological properties. However, improvement of the physical and chemical properties of HA-C/C composites to promote bone regeneration and healing remains a challenge. In our present study, the HA coatings on C/C with magnesium (Mg) (Mg-HA-C/C) composites were synthesized that Ca (NO3)2, Mg (NO3)2, and NH4H2PO4 were mixed and coatings were made by electromagnetic induction deposition’s heating. As determined with in vitro experiments, Mg-HA-C/C composites containing 10 and 20% Mg decreased miR-16 levels, increased cell viability, elevated the levels of osteogenesis-related genes, and promoted osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) seeded on their surfaces. In a rat model of skull defects, compared to the control group, at 4 and 12 weeks after the operation, the bone volume fraction (BV/TV) of Mg-HA-C/C composite group was increased by 8.439 ± 2.681% and 23.837 ± 7.845%, as well as the trabecular thickness (Tb.Th) was 56.247 ± 24.238 μm and 114.911 ± 34.015 μm more. These composites also increased the levels of ALP and RUNX2 in skull. The Mg-HA-C/C composite-enhanced bone regeneration and healing were blocked by in situ injection of an miR-16 mimic lentivirus vector. Thus, Mg-HA-C/C composites promote osteogenic differentiation and repair bone defects through inhibiting miR-16.

Advances in Engineered Three-Dimensional (3D) Body Articulation Unit Models

Indeed, the body articulation units, commonly referred to as body joints, play significant roles in the musculoskeletal system, enabling body flexibility. Nevertheless, these articulation units suffer from several pathological conditions, such as osteoarthritis (OA), rheumatoid arthritis (RA), ankylosing spondylitis, gout, and psoriatic arthritis. There exist several treatment modalities based on the utilization of anti-inflammatory and analgesic drugs, which can reduce or control the pathophysiological symptoms. Despite the success, these treatment modalities suffer from major shortcomings of enormous cost and poor recovery, limiting their applicability and requiring promising strategies. To address these limitations, several engineering strategies have been emerged as promising solutions in fabricating the body articulation as unit models towards local articulation repair for tissue regeneration and high-throughput screening for drug development. In this article, we present challenges related to the selection of biomaterials (natural and synthetic sources), construction of 3D articulation models (scaffold-free, scaffold-based, and organ-on-a-chip), architectural designs (microfluidics, bioprinting, electrospinning, and biomineralization), and the type of culture conditions (growth factors and active peptides). Then, we emphasize the applicability of these articulation units for emerging biomedical applications of drug screening and tissue repair/regeneration. In conclusion, we put forward the challenges and difficulties for the further clinical application of the in vitro 3D articulation unit models in terms of the long-term high activity of the models.

DNA/Magnetic Nanoparticles Composite to Attenuate Glass Surface Nanotopography for Enhanced Mesenchymal Stem Cell Differentiation

Mesenchymal stem cells (MSCs) have extensive pluripotent potential to differentiate into various cell types, and thus they are an important tool for regenerative medicine and biomedical research. In this work, the differentiation of hTERT-transduced adipose-derived MSCs (hMSCs) into chondrocytes, adipocytes and osteoblasts on substrates with nanotopography generated by magnetic iron oxide nanoparticles (MNPs) and DNA was investigated. Citrate-stabilized MNPs were synthesized by the chemical co-precipitation method and sized around 10 nm according to microscopy studies. It was shown that MNPs@DNA coatings induced chondrogenesis and osteogenesis in hTERT-transduced MSCs. The cells had normal morphology and distribution of actin filaments. An increase in the concentration of magnetic nanoparticles resulted in a higher surface roughness and reduced the adhesion of cells to the substrate. A glass substrate modified with magnetic nanoparticles and DNA induced active chondrogenesis of hTERT-transduced MSC in a twice-diluted differentiation-inducing growth medium, suggesting the possible use of nanostructured MNPs@DNA coatings to obtain differentiated cells at a reduced level of growth factors.

Sequence Does Not Matter: The Biomedical Applications of DNA-Based Coatings and Cores

Biomedical applications of DNA are diverse but are usually associated with specific recognition of target nucleotide sequences or proteins and with gene delivery for therapeutic or biotechnological purposes. However, other aspects of DNA functionalities, like its nontoxicity, biodegradability, polyelectrolyte nature, stability, thermo-responsivity and charge transfer ability that are rather independent of its sequence, have recently become highly appreciated in material science and biomedicine. Whereas the latest achievements in structural DNA nanotechnology associated with DNA sequence recognition and Watson–Crick base pairing between complementary nucleotides are regularly reviewed, the recent uses of DNA as a raw material in biomedicine have not been summarized. This review paper describes the main biomedical applications of DNA that do not involve any synthesis or extraction of oligo- or polynucleotides with specified sequences. These sequence-independent applications currently include some types of drug delivery systems, biocompatible coatings, fire retardant and antimicrobial coatings and biosensors. The reinforcement of DNA properties by DNA complexation with nanoparticles is also described as a field of further research.

Biomineralization Induced by Cells of Sporosarcina pasteurii: Mechanisms, Applications and Challenges

Biomineralization has emerged as a novel and eco-friendly technology for artificial mineral formation utilizing the metabolism of organisms. Due to its highly efficient urea degradation ability, Sporosarcina pasteurii(S. pasteurii) is arguably the most widely investigated organism in ureolytic biomineralization studies, with wide potential application in construction and environmental protection. In emerging, large-scale commercial engineering applications, attention was also paid to practical challenges and issues. In this review, we summarize the features of S. pasteurii cells contributing to the biomineralization reaction, aiming to reveal the mechanism of artificial mineral formation catalyzed by bacterial cells. Progress in the application of this technology in construction and environmental protection is discussed separately. Furthermore, the urgent challenges and issues in large-scale application are also discussed, along with potential solutions. We aim to offer new ideas to researchers working on the mechanisms, applications and challenges of biomineralization.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

A Three-in-One Strategy: Injectable Biomimetic Porous Hydrogels for Accelerating Bone Regeneration via Shape-Adaptable Scaffolds, Controllable Magnesium Ion Release, and Enhanced Osteogenic Differentiation

The repair of bone defects with irregular shapes, particularly in a minimally invasive manner, remains a major challenge. For synthetic bone grafts, injectable hydrogels are superior to conventional scaffolds because they can adapt satisfactorily to the defect margins and can be injected into deeper areas of injury via a minimally invasive procedure. Based on the poly(lactide-co-glycolide)(PLGA)/1-methyl-2-pyrrolidinone solution reported in our previous study, we successfully synthesized injectable MgO/MgCO₃@PLGA (PMM) hydrogels, namely, injectable biomimetic porous hydrogels (IBPHs), to accelerate bone regeneration. In addition to exhibiting excellent injectability, PMM hydrogels could transform into porous scaffolds in situ through a liquid-to-solid phase transition and completely fill irregular bone defects via their superb shape adaptability. Moreover, sustainable and steady release of Mg²⁺ was achieved by regulating the weight ratio of the incorporated MgO and MgCO₃ particles. Via controlled release of Mg²⁺, PMM hydrogels significantly promoted proliferation, osteogenic differentiation, migration, and biomineral deposition of immortalized mouse embryonic fibroblasts. More importantly, micro-CT imaging and histological analysis indicated that concomitant with their gradual degradation, PMM hydrogels effectively stimulated in situ bone regeneration in rat calvarial defects with an increase in the bone volume fraction of almost 2-fold compared with that in the control group. These findings suggest that injectable PMM hydrogels can satisfactorily match bone defects and form porous scaffolds in situ and can significantly promote bone regeneration via controllable Mg²⁺ release. The remarkable features of IPBHs may open a new avenue for the exploration of in situ repair systems for irregular bone defects to accelerate bone regeneration and have great potential for clinical translation.

Calcium-Collagen Coupling is Vital for Biomineralization Schedule

Biomineralization is a chemical reaction that occurs in organisms in which collagen initiates and guides the growth and crystallization of matched apatite minerals. However, there is little known about the demand pattern for calcium salts and collagen needed by biomineralization. In this study, natural bone biomineralization is analyzed, and a novel interplay between calcium concentration and collagen production is observed. Any quantitative change in one of the entities causes a corresponding change in the other. Translocation-associated membrane protein 2 (TRAM2) is identified as an intermediate factor whose silencing disrupts this relationship and causes poor mineralization. TRAM2 directly interacts with the sarcoplasmic/endoplasmic reticulum calcium ATPase 2b (SERCA2b) and modulates SERCA2b activity to couple calcium enrichment with collagen biosynthesis. Collectively, these findings indicate that osteoblasts can independently and directly regulate the process of biomineralization via this coupling. This knowledge has significant implications for the developmentally inspired design of biomaterials for bone regenerative applications.