A Biomimetic Zinc Alloy Scaffold Coated with Brushite for Enhanced Cranial Bone Regeneration

Imidazole functionalized photo-crosslinked aliphatic polycarbonate drug-eluting coatings on zinc alloys for osteogenesis, angiogenesis, and bacteriostasis in bone regeneration

Zinc (Zn) alloys have demonstrated significant potential in healing critical-sized bone defects. However, the clinical application of Zn alloys implants is still hindered by challenges including excessive release of zinc ions (Zn2+), particularly in the early stage of implantation, and absence of bio-functions related to complex bone repair processes. Herein, a biodegradable aliphatic polycarbonate drug-eluting coating was fabricated on zinc-lithium (Zn-Li) alloys to inhibit Zn2+ release and enhance the osteogenesis, angiogenesis, and bacteriostasis of Zn alloys. Specifically, the photo-curable aliphatic polycarbonates were co-assembled with simvastatin and deposited onto Zn alloys to produce a drug-loaded coating, which was crosslinked by subsequent UV light irradiation. During the 60 days long-term immersion test, the coating showed distinguished stable drug release and Zn2+ release inhibition properties. Benefiting from the regulated release of Zn2+ and simvastatin, the coating facilitated the adhesion, proliferation, and differentiation of MC3T3-E1 cells, as well as the migration and tube formation of EA.hy926 cells. Astonishingly, the coating also showed remarkable antibacterial properties against both S. aureus and E. coli. The in vivo rabbit critical-size femur bone defects model demonstrated that the drug-eluting coating could efficiently promote new bone formation and the expression of platelet endothelial cell adhesion molecule-1 (CD31) and osteocalcin (OCN). The enhancement of osteogenesis, angiogenesis, and bacteriostasis is achieved by precisely controlling of the released Zn2+ at an appropriate level, as well as the stable release profile of simvastatin. This tailored aliphatic polycarbonate drug-eluting coating provides significant potential for clinical applications of Zn alloys implants.

Feasibility Insights of the Green-Assisted Calcium-Phosphate Coating on Biodegradable Zinc Alloys for Biomedical Application: In Vitro and In Vivo Studies

In the field of bone tissue engineering, recently developed Zn alloy scaffolds are considered potential candidates for biodegradable implants for bone regeneration and defect reconstruction. However, the clinical success of these alloys is limited due to their insufficient surface bioactivities. Further, the higher concentration of Zn2+ produced during degradation promotes antibacterial activity, but deteriorates osteogenic properties. This study fabricated an Azadirachta indica (neem)-assisted brushite-hydroxyapatite (HAp) coating on the recently developed Zn-2Cu-0.5Mg alloy to tackle the above dilemma. The microstructure, degradation behavior, antibacterial activity, and hemocompatibility, along with in vitro and in vivo cytocompatibility of the coated alloys, are systematically investigated. Microstructural analysis reveals flower-like morphology with uniformly grown flakes for neem-assisted deposition. The neem-assisted deposition significantly improves the adhesion strength from 12.7 to 18.8 MPa, enhancing the mechanical integrity. The potentiodynamic polarization study shows that the neem-assisted deposition decreases the degradation rate, with the lowest degradation rate of 0.027 mm/yr for the ZHN2 sample. In addition, the biomineralization process shows the apatite formation on the deposited coating after 21 days of immersion. In vitro cytotoxicity assay exhibits the maximum cell viability of 117% for neem-assisted coated alloy in 30% extract after 5d and the improved cytocompatibility which is due to the controlled release of Zn2+ ions. Meanwhile, neem-assisted coated alloy increases the ZOI by 32 and 24% for Gram-positive and Gram-negative bacteria, respectively. Acceptable hemolysis (<5%) and anticoagulation parameters demonstrate a promising hemocompatibility of the coated alloy. In vivo implantation illustrates a slight inflammatory response and vascularization after 2 weeks of subcutaneous implantation, and neo-bone formation in the defect areas of the rat femur. Micro-CT and histology studies demonstrate better osseointegration with satisfactory biosafety response for the neem-assisted coated alloy as compared to that without neem-assisted deposition. Hence, this neem-assisted brushite-Hap coating strategy elucidates a new perspective on the surface modification of biodegradable implants for the treatment of bone defects.

3D Printing of a Porous Zn-1Mg-0.1Sr Alloy Scaffold: A Study on Mechanical Properties, Degradability, and Biosafety

In recent years, the use of zinc (Zn) alloys as degradable metal materials has attracted considerable attention in the field of biomedical bone implant materials. This study investigates the fabrication of porous scaffolds using a Zn-1Mg-0.1Sr alloy through a three-dimensional (3D) printing technique, selective laser melting (SLM). The results showed that the porous Zn-1Mg-0.1Sr alloy scaffold featured a microporous structure and exhibited a compressive strength (CS) of 33.71 ± 2.51 MPa, a yield strength (YS) of 27.88 ± 1.58 MPa, and an elastic modulus (E) of 2.3 ± 0.8 GPa. During the immersion experiments, the immersion solution showed a concentration of 2.14 ± 0.82 mg/L for Zn2+ and 0.34 ± 0.14 mg/L for Sr2+, with an average pH of 7.61 ± 0.09. The porous Zn-1Mg-0.1Sr alloy demonstrated a weight loss of 12.82 ± 0.55% and a corrosion degradation rate of 0.36 ± 0.01 mm/year in 14 days. The Cell Counting Kit-8 (CCK-8) assay was used to check the viability of the cells. The results showed that the 10% and 20% extracts significantly increased the activity of osteoblast precursor cells (MC3T3-E1), with a cytotoxicity grade of 0, which indicates safety and non-toxicity. In summary, the porous Zn-1Mg-0.1Sr alloy scaffold exhibits outstanding mechanical properties, an appropriate degradation rate, and favorable biosafety, making it an ideal candidate for degradable metal bone implants.

Zinc based biodegradable metals for bone repair and regeneration: Bioactivity and molecular mechanisms

Bone fractures and critical-size bone defects are significant public health issues, and clinical treatment outcomes are closely related to the intrinsic properties of the utilized implant materials. Zinc (Zn)-based biodegradable metals (BMs) have emerged as promising bioactive materials because of their exceptional biocompatibility, appropriate mechanical properties, and controllable biodegradation. This review summarizes the state of the art in terms of Zn-based metals for bone repair and regeneration, focusing on bridging the gap between biological mechanism and required bioactivity. The molecular mechanism underlying the release of Zn ions from Zn-based BMs in the improvement of bone repair and regeneration is elucidated. By integrating clinical considerations and the specific bioactivity required for implant materials, this review summarizes the current research status of Zn-based internal fixation materials for promoting fracture healing, Zn-based scaffolds for regenerating critical-size bone defects, and Zn-based barrier membranes for reconstituting alveolar bone defects. Considering the significant progress made in the research on Zn-based BMs for potential clinical applications, the challenges and promising research directions are proposed and discussed.

Mechanical and Computational Fluid Dynamic Models for Magnesium-Based Implants

Today, mechanical properties and fluid flow dynamic analysis are considered to be two of the most important steps in implant design for bone tissue engineering. The mechanical behavior is characterized by Young's modulus, which must have a value close to that of the human bone, while from the fluid dynamics point of view, the implant permeability and wall shear stress are two parameters directly linked to cell growth, adhesion, and proliferation. In this study, we proposed two simple geometries with a three-dimensional pore network dedicated to a manufacturing route based on a titanium wire waving procedure used as an intermediary step for Mg-based implant fabrication. Implant deformation under different static loads, von Mises stresses, and safety factors were investigated using finite element analysis. The implant permeability was computed based on Darcy's law following computational fluid dynamic simulations and, based on the pressure drop, was numerically estimated. It was concluded that both models exhibited a permeability close to the human trabecular bone and reduced wall shear stresses within the biological range. As a general finding, the proposed geometries could be useful in orthopedics for bone defect treatment based on numerical analyses because they mimic the trabecular bone properties.

Fabrication of a Nanoscale Magnesium/Copper Metal-Organic Framework on Zn-Based Guided Bone Generation Membranes for Enhancing Osteogenesis, Angiogenesis, and Bacteriostasis Properties

Recently, zinc (Zn) and its alloys have demonstrated great potential as guided bone regeneration (GBR) membranes to treat the problems of insufficient alveolar bone volume and long-term osseointegration instability during dental implantology. However, bone regeneration is a complex process consisting of osteogenesis, angiogenesis, and antibacterial function. For now, the in vivo osteogenic performance and antibacterial activity of pure Zn are inadequate, and thus fabricating a platform to endow Zn membranes with multifunctions may be essential to address these issues. In this study, various bimetallic magnesium/copper metal-organic framework (Mg/Cu-MOF) coatings were fabricated and immobilized on pure Zn. The results indicated that the degradation rate and water stability of Mg/Cu-MOF coatings could be regulated by controlling the feeding ratio of Cu2+. As the coating and Zn substrate degraded, an alkaline microenvironment enriched with Zn2+, Mg2+, and Cu2+ was generated. It significantly improved calcium phosphate deposition, differentiation of osteoblasts, and vascularization of endothelial cells in the extracts. Among them, Mg/Cu1 showed the best comprehensive performance. The superior antibacterial activity of Mg/Cu1 was demonstrated in vitro and in vivo, which indicated significantly enhanced bacteriostatic activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli as compared to that of the bare sample. Bimetallic Mg/Cu-MOF coating could properly coordinate the multifunction on a Zn membrane and could be a promising platform for promoting its bone regeneration, which could pave the way for Zn-based materials to be used as barrier membranes in oral clinical trials.

In vitro and in vivo studies on biodegradable Zn porous scaffolds with a drug-loaded coating for the treatment of infected bone defect

Additively manufactured biodegradable zinc (Zn) scaffolds have great potential to repair infected bone defects due to their osteogenic and antibacterial properties. However, the enhancement of antibacterial properties depends on a high concentration of dissolved Zn2+, which in return deteriorates osteogenic activity. In this study, a vancomycin (Van)-loaded polydopamine (PDA) coating was prepared on pure Zn porous scaffolds to solve the above dilemma. Compared with pure Zn scaffolds according to comprehensive in vitro tests, the PDA coating resulted in a slow degradation and inhibited the excessive release of Zn2+ at the early stage, thus improving cytocompatibility and osteogenic activity. Meanwhile, the addition of Van drug substantially suppressed the attachment and proliferation of S. aureus and E. coli bacterial. Furthermore, in vivo implantation confirmed the simultaneously improved osteogenic and antibacterial functions by using the pure Zn scaffolds with Van-loaded PDA coating. Therefore, it is promising to employ biodegradable Zn porous scaffolds with the proposed drug-loaded coating for the treatment of infected bone defects.

Performance of 3D printed porous polyetheretherketone composite scaffolds combined with nano-hydroxyapatite/carbon fiber in bone tissue engineering: a biological evaluation

Polyetheretherketone (PEEK) has been one of the most promising materials in bone tissue engineering in recent years, with characteristics such as biosafety, corrosion resistance, and wear resistance. However, the weak bioactivity of PEEK leads to its poor integration with bone tissues, restricting its application in biomedical fields. This research effectively fabricated composite porous scaffolds using a combination of PEEK, nano-hydroxyapatite (nHA), and carbon fiber (CF) by the process of fused deposition molding (FDM). The experimental study aimed to assess the impact of varying concentrations of nHA and CF on the biological performance of scaffolds. The incorporation of 10% CF has been shown to enhance the overall mechanical characteristics of composite PEEK scaffolds, including increased tensile strength and improved mechanical strength. Additionally, the addition of 20% nHA resulted in a significant increase in the surface roughness of the scaffolds. The high hydrophilicity of the PEEK composite scaffolds facilitated the in vitro inoculation of MC3T3-E1 cells. The findings of the study demonstrated that the inclusion of 20% nHA and 10% CF in the scaffolds resulted in improved cell attachment and proliferation compared to other scaffolds. This suggests that the incorporation of 20% nHA and 10% CF positively influenced the properties of the scaffolds, potentially facilitating bone regeneration. In vitro biocompatibility experiments showed that PEEK composite scaffolds have good biosafety. The investigation on osteoblast differentiation revealed that the intensity of calcium nodule staining intensified, along with an increase in the expression of osteoblast transcription factors and alkaline phosphatase activities. These findings suggest that scaffolds containing 20% nHA and 10% CF have favorable properties for bone induction. Hence, the integration of porous PEEK composite scaffolds with nHA and CF presents a promising avenue for the restoration of bone defects using materials in the field of bone tissue engineering.

Zinc-based biomaterials for bone repair and regeneration: mechanism and applications

Zinc (Zn) is one of the most important trace elements in the human body and plays a key role in various physiological processes, especially in bone metabolism. Zn-containing materials have been reported to enhance bone repair through promoting cell proliferation, osteogenic activity, angiogenesis, and inhibiting osteoclast differentiation. Therefore, Zn-based biomaterials are potential substitutes for traditional bone grafts. In this review, the specific mechanisms of bone formation promotion by Zn-based biomaterials were discussed, and recent developments in their application in bone tissue engineering were summarized. Moreover, the challenges and perspectives of Zn-based biomaterials were concluded, revealing their attractive potential and development directions in the future.

Bioactive Scaffolds as a Promising Alternative for Enhancing Critical-Size Bone Defect Regeneration in the Craniomaxillofacial Region

Reconstruction of critical-size bone defects (CSDs) in the craniomaxillofacial (CMF) region remains challenging. Scaffold-based bone-engineered constructs have been proposed as an alternative to the classical treatments made with autografts and allografts. Scaffolds, a key component of engineered constructs, have been traditionally viewed as biologically passive temporary replacements of deficient bone lacking intrinsic cues to promote osteogenesis. Nowadays, scaffolds are functionalized, giving rise to bioactive scaffolds promoting bone regeneration more effectively than conventional counterparts. This review focuses on the three approaches most used to bioactivate scaffolds: (1) conferring microarchitectural designs or surface nanotopography; (2) loading bioactive molecules; and (3) seeding stem cells on scaffolds, providing relevant examples of in vivo (preclinical and clinical) studies where these methods are employed to enhance CSDs healing in the CMF region. From these, adding bioactive molecules (specifically bone morphogenetic proteins or BMPs) to scaffolds has been the most explored to bioactivate scaffolds. Nevertheless, the downsides of grafting BMP-loaded scaffolds in patients have limited its successful translation into clinics. Despite these drawbacks, scaffolds containing safer, cheaper, and more effective bioactive molecules, combined with stem cells and topographical cues, remain a promising alternative for clinical use to treat CSDs in the CMF complex replacing autografts and allografts.

Numerical Simulation of Dynamic Degradation and Fatigue Damage of Degradable Zinc Alloy Stents

Current research on the fatigue properties of degradable zinc alloy stents has not yet considered the issue of the fatigue life changing with material properties during the dynamic degradation process. Therefore, in this paper, we established a fatigue damage algorithm to study the fatigue problem affected by the changing of material properties during the dynamic degradation process of the stent under the action of pulsating cyclic loading. Three models: the dynamic degradation model, the dynamic degradation model under pulsating cyclic loading, and the coupled model of fatigue damage and dynamic degradation, were developed to verify the effect of fatigue damage on stent life. The results show that fatigue damage leads to a deeper degree of inhomogeneous degradation of the stent, which affects the service life of the stent. Fatigue damage is a factor that cannot be ignored. Therefore, when studying the mechanical properties and lifetime of degradable stents, incorporating fatigue damage into the study can help more accurately assess the lifetime of the stents.

Corrosion-tailoring, osteogenic, anti-inflammatory, and antibacterial aspirin-loaded organometallic hydrogel composite coating on biodegradable Zn for orthopedic applications

Zn and its alloys are receiving increasing interest for biodegradable orthopedic implant applications owing to their moderate corrosion rate and the potential functionality of Zn2+. However, their non-uniform corrosion behavior and insufficient osteogenic, anti-inflammatory, and antibacterial properties do not meet the comprehensive requirements of orthopedic implants in clinical use. Herein, an aspirin (an acetylsalicylic acid, ASA, 10, 50, 100, and 500 mg/L)-loaded carboxymethyl chitosan (CMC)/gelatin (Gel)-Zn2+ organometallic hydrogel composite coating (CMC/Gel&Zn2+/ASA) was fabricated on a Zn surface via an alternating dip-coating method, aiming to obtain a material with these comprehensive properties improved. The organometallic hydrogel composite coatings, ca. 12-16 μm in thickness, showed compact, homogeneous, and micro-bulge structured surface morphology. The coatings protected well the Zn substrate from pitting/localized corrosion and contained the release of the bioactive components, Zn2+ and ASA, in a sustained and stable manner in long-term in vitro immersions in Hank's solution. The coated Zn showed greater ability to promote proliferation and osteogenic differentiation for MC3T3-E1 osteoblasts, and better anti-inflammatory capacity when compared with uncoated Zn. Additionally, this coating displayed excellent antibacterial activity against both Escherichia coli (>99 % antibacterial rate) and Staphylococcus aureus (>98 % antibacterial rate). Such appealing properties can be attributed to the compositional nature of the coating, namely the sustained release of Zn2+ and ASA, as well as the surface physiochemical properties because of its unique microstructure. This organometallic hydrogel composite coating can be considered a promising option for the surface modification of biodegradable Zn-based orthopedic implants among others.

A drug-loaded composite coating to improve osteogenic and antibacterial properties of Zn-1Mg porous scaffolds as biodegradable bone implants

Zinc (Zn) alloy porous scaffolds produced by additive manufacturing own customizable structures and biodegradable functions, having a great application potential for repairing bone defect. In this work, a hydroxyapatite (HA)/polydopamine (PDA) composite coating was constructed on the surface of Zn-1Mg porous scaffolds fabricated by laser powder bed fusion, and was loaded with a bioactive factor BMP2 and an antibacterial drug vancomycin. The microstructure, degradation behavior, biocompatibility, antibacterial performance and osteogenic activities were systematically investigated. Compared with as-built Zn-1Mg scaffolds, the rapid increase of Zn²⁺, which resulted to the deteriorated cell viability and osteogenic differentiation, was inhibited due to the physical barrier of the composite coating. In vitro cellular and bacterial assay indicated that the loaded BMP2 and vancomycin considerably enhanced the cytocompatibility and antibacterial performance. Significantly improved osteogenic and antibacterial functions were also observed according to in vivo implantation in the lateral femoral condyle of rats. The design, influence and mechanism of the composite coating were discussed accordingly. It was concluded that the additively manufactured Zn-1Mg porous scaffolds together with the composite coating could modulate biodegradable performance and contribute to effective promotion of bone recovery and antibacterial function.

Metal-organic Zn-zoledronic acid and 1-hydroxyethylidene-1,1-diphosphonic acid nanostick-mediated zinc phosphate hybrid coating on biodegradable Zn for osteoporotic fracture healing implants

Zn and its alloys are increasingly under consideration for biodegradable bone fracture fixation implants owing to their attractive biodegradability and mechanical properties. However, their clinical application is a challenge for osteoporotic bone fracture healing, due to their uneven degradation mode, burst release of zinc ions, and insufficient osteo-promotion and osteo-resorption regulating properties. In this study, a type of Zn2+ coordinated zoledronic acid (ZA) and 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) metal-organic hybrid nanostick was synthesized, which was further mixed into zinc phosphate (ZnP) solution to mediate the deposition and growth of ZnP to form a well-integrated micro-patterned metal-organic/inorganic hybrid coating on Zn. The coating protected noticeably the Zn substrate from corrosion, in particular reducing its localized occurrence as well as suppressing its Zn2+ release. Moreover, the modified Zn was osteo-compatible and osteo-promotive and, more important, performed osteogenesis in vitro and in vivo of well-balanced pro-osteoblast and anti-osteoclast responses. Such favorable functionalities are related to the nature of its bioactive components, especially the bio-functional ZA and the Zn ions it contains, as well as its unique micro- and nano-scale structure. This strategy provides not only a new avenue for surface modification of biodegradable metals but also sheds light on advanced biomaterials for osteoporotic fracture and other applications. STATEMENT OF SIGNIFICANCE: Developing appropriate biodegradable metallic materials is of clinical relevance for osteoporosis fracture healing, whereas current strategies are short of good balance between the bone formation and resorption. Here, we designed a micropatterned metal-organic nanostick mediated zinc phosphate hybrid coating modified Zn biodegradable metal to fulfill such a balanced osteogenicity. The in vitro assays verified the coated Zn demonstrated outstanding pro-osteoblasts and anti-osteoclasts properties and the coated intramedullary nail promoted fracture healing well in an osteoporotic femur fracture rat model. Our strategy may offer not only a new avenue for surface modification of biodegradable metals but also shed light on better understanding of new advanced biomaterials for orthopedic application among others.

CaP-coated Zn-Mn-Li alloys regulate osseointegration via influencing macrophage polarization in the osteogenic environment

Immune response is an important factor in determining the fate of bone replacement materials, in which macrophages play an important role. It is a new idea to design biomaterials with immunomodulatory function to reduce inflammation and promote bone integration by regulating macrophages polarization. In this work, the immunomodulatory properties of CaP Zn-Mn-Li alloys and the specific mechanism of action were investigated. We found that the CaP Zn0.8Mn0.1Li alloy promoted the polarization of macrophages toward M2 and reduced inflammation, which could effectively upregulate osteogenesis-related factors and promote new bone formation, indicating the important role of macrophages polarization in biomaterial induction of osteogenesis. In vivo studies further demonstrated that CaP Zn0.8Mn0.1Li alloy could stimulate osteogenesis better than other Zn-Mn-Li alloys implantations by regulating macrophages polarization and reducing inflammation. In addition, transcriptome results showed that CaP Zn0.8Mn0.1Li played an important regulatory role in the life process of macrophages, activating Toll-like receptor signaling pathway, which participated in the activation and attenuation of inflammation, and accelerated bone integration. Thus, by preparing CaP coatings on the surface of Zn-Mn-Li alloys and combining the bioactive ingredient with controlled release, the biomaterial will be imbibed with beneficial immunomodulatory properties that promote bone integration.

Poly (Butylene Succinate)/Silicon Nitride Nanocomposite with Optimized Physicochemical Properties, Biocompatibility, Degradability, and Osteogenesis for Cranial Bone Repair

Congenital disease, tumors, infections, and trauma are the main reasons for cranial bone defects. Herein, poly (butylene succinate) (PB)/silicon nitride (Si₃N₄) nanocomposites (PSC) with Si3N4 content of 15 w% (PSC15) and 30 w% (PSC30) were fabricated for cranial bone repair. Compared with PB, the compressive strength, hydrophilicity, surface roughness, and protein absorption of nanocomposites were increased with the increase in Si₃N₄ content (from 15 w% to 30 w%). Furthermore, the cell adhesion, multiplication, and osteoblastic differentiation on PSC were significantly enhanced with the Si₃N₄ content increasing in vitro. PSC30 exhibited optimized physicochemical properties (compressive strength, surface roughness, hydrophilicity, and protein adsorption) and cytocompatibility. The m-CT and histological results displayed that the new bone formation for SPC30 obviously increased compared with PB, and PSC30 displayed proper degradability (75.3 w% at 12 weeks) and was gradually replaced by new bone tissue in vivo. The addition of Si₃N₄ into PB not only optimized the surface performances of PSC but also improved the degradability of PSC, which led to the release of Si ions and a weak alkaline environment that significantly promoted cell response and tissue regeneration. In short, the enhancements of cellular responses and bone regeneration of PSC30 were attributed to the synergism of the optimized surface performances and slow release of Si ion, and PSC30 were better than PB. Accordingly, PSC30, with good biocompatibility and degradability, displayed a promising and huge potential for cranial bone construction.

Modified Biodegradation Behavior Induced Beneficial Microenvironments for Bone Regeneration by Low Addition of Gadolinium in Zinc

Zinc (Zn) shows a great potential as a biodegradable material for bone implants after a decade of systematic research and development. However, uncontrollable biodegradation behavior and biphasic dose-response prevent Zn from fulfilling its essential role in facilitating bone regeneration. In this study, the low addition of gadolinium (Gd) modifies the intrinsic microstructure of Zn in terms of grain size distribution, grain boundary misorientation, and texture. Adding Gd refines grain size distribution and creates a stronger basal plane texture in Zn, consequently, changing the current density distribution and reducing the anode dissolution rate during corrosion. As a result, uniform degradation is more predominant in Zn-0.4Gd alloy implant, in comparison to localized degradation in pure Zn implant in bone environments. The modified biodegradation behavior of the Zn-0.4Gd alloy implant induces significantly better new bone formation and osseointegration compared to the pure Zn implant. Therefore, Gd with trace amounts is able to tune the degradation behavior and improve the performance of Zn-based implants in promoting bone regeneration.

Small extracellular vesicles derived from hypoxic mesenchymal stem cells promote vascularized bone regeneration through the miR-210-3p/EFNA3/PI3K pathway

Angiogenesis is closely coupled with osteogenesis and has equal importance. Thus, promoting angiogenesis during the bone repair process is vital for ideal bone regeneration. As important mediators of cell-cell communication and biological homeostasis, mesenchymal stem cell-derived small extracellular vesicles (MSC-sEVs) have been proved to be highly involved in bone and vascular regeneration. Because hypoxia microenvironment promotes the proangiogenic activity of MSCs, in the present study, we investigate the effect and underlying molecular mechanisms of sEVs from hypoxia-preconditioned MSCs (hypo-sEVs) on angiogenesis and develop an effective strategy to promote vascularized bone regeneration. Compared to sEVs from normoxia MSCs (nor-sEVs), hypo-sEVs promoted the proliferation, migration, and angiogenesis of HUVECs and ultimately enhanced bone regeneration and new blood vessel reconstruction in a critical-size calvarial bone defect model. miRNA sequence and the verified results showed that miR-210-3p in hypo-sEVs was increased via HIF-1α under hypoxia. The upregulated miR-210-3p in hypo-sEVs promoted angiogenesis by downregulating EFNA3 expression and enhancing the phosphorylation of the PI3K/AKT pathway. Thus, this study suggests a successful strategy to enhance vascularized bone regeneration by utilizing hypo-sEVs via the miR-210-3p/EFNA3/PI3K/AKT pathway. STATEMENT OF SIGNIFICANCE: Considering the significance of vascularization in ideal bone regeneration, strategies to promote angiogenesis during bone repair are required. Hypoxia microenvironment can promote the proangiogenic potential of mesenchymal stem cells (MSCs). Nonetheless, the therapeutic effect of small extracellular vesicles (sEVs) from hypoxia-preconditioned MSCs on cranio-maxillofacial bone defect remains unknown, and the underlying mechanism is poorly understood. This study shows that hypo-sEVs significantly enhance the proliferation, migration, and angiogenesis of HUVECs as well as promote vascularized bone formation. Moreover, this work indicates that HIF-1α can induce overexpression of miR-210-3p under hypoxia, and miR-210-3p can hinder EFNA3 expression and subsequently activate the PI3K/AKT pathway. The application of hypo-sEVs provides a facile and promising strategy to promote vascularized bone regeneration in a critical-size bone defect model.

Effects of Zinc, Magnesium, and Iron Ions on Bone Tissue Engineering

Large-sized bone defects are a great challenge in clinics and considerably impair the quality of patients' daily life. Tissue engineering strategies using cells, scaffolds, and bioactive molecules to regulate the microenvironment in bone regeneration is a promising approach. Zinc, magnesium, and iron ions are natural elements in bone tissue and participate in many physiological processes of bone metabolism and therefore have great potential for bone tissue engineering and regeneration. In this review, we performed a systematic analysis on the effects of zinc, magnesium, and iron ions in bone tissue engineering. We focus on the role of these ions in properties of scaffolds (mechanical strength, degradation, osteogenesis, antibacterial properties, etc.). We hope that our summary of the current research achievements and our notifications of potential strategies to improve the effects of zinc, magnesium, and iron ions in scaffolds for bone repair and regeneration will find new inspiration and breakthroughs to inspire future research.

Biomaterials and biotechnology for periodontal tissue regeneration: Recent advances and perspectives

Periodontal tissues are organized in a complex three-dimensional (3D) architecture, including the alveolar bone, cementum, and a highly aligned periodontal ligament (PDL). Regeneration is difficult due to the complex structure of these tissues. Currently, materials are developing rapidly, among which synthetic polymers and hydrogels have extensive applications. Moreover, techniques have made a spurt of progress. By applying guided tissue regeneration (GTR) to hydrogels and cell sheets and using 3D printing, a scaffold with an elaborate biomimetic structure can be constructed to guide the orientation of fibers. The incorporation of cells and biotic factors improves regeneration. Nevertheless, the current studies lack long-term effect tracking, clinical research, and in-depth mechanistic research. In summary, periodontal tissue engineering still has considerable room for development. The development of materials and techniques and an in-depth study of the mechanism will provide an impetus for periodontal regeneration.

Osteogenic and angiogenic bioactive collagen entrapped calcium/zinc phosphates coating on biodegradable Zn for orthopedic implant applications

Zinc is becoming one of the leading candidate materials for biodegradable orthopedic implants owing to its attractive properties in terms of degradation behavior and mechanical properties. However, the insufficient surface bio-activities postpone its clinical application. In this study, an organic-inorganic collagen entrapped calcium/zinc phosphates coating was constructed on Zn surface to lessen Zn²⁺ releasing rate and to leverage the surface osteogenic and angiogenic properties. Collagen molecules were immobilized onto Zn substrate and subsequently coordinated with calcium and zinc ions to promote the CaZnP inorganic phase growth, ensuing an intertwined collagen-CaZnP hybrid system. Consequently, the hybrid coating was highly coalesced and compact. Such high quality warranted the contained Zn²⁺ releasing in a tolerable rate favorable for cells viability. The collagen-CaZnP coated Zn showed remarkedly stronger osteogenicity as compared to the untreated Zn, ascertained by the MC3T3-E1 osteoblast cell proliferation and differentiation assays, such as alkaline phosphatase expression and calcium nodule formation results. In addition, this hybrid coating supported human umbilical vein endothelial cells (HUVECs) migration and tube formation. The enhanced osteogenic and angiogenic properties could be ascribed to the nature of collagen and calcium/zinc phosphate components, the hybrid micro/nano-structure as well as the ability of controlling the Zn²⁺ release of Zn substrate into a suitable concentration range. Our strategy provides a new avenue to surface modification of biodegradable metals for bone regenerative perspective.

In Vitro Study of Degradation and Cytocompatibility of Ceramics/PLA Composite Coating on Pure Zinc for Orthopedic Application

Zinc and its alloys are considered to be next-generation materials for fabricating absorbable biomedical devices. However, cytotoxicity has been reported to be associated with rapid degradation. To address these issues, a composite coating (PLA/Li-OCP) consisting of CaHPO4 conversion coating (Ca-P) and polylactic acid (PLA) decorated with Li-octacalcium phosphate particles was constructed on pure zinc. The immersion tests showed that the presence of Ca-P coating and PLA/Li-OCP coating on pure zinc could reduce the pH value. Compared with Ca-P coating, the introduction of the PLA/Li-OCP film on the Ca-P-coated samples could enhance the corrosion resistance, and there was one order of magnitude decrease in the corrosion current density. The cytocompatibility assay suggested that the PLA/Li-OCP coating favored the cell viability and upregulated the expression of related osteogenic-genes including RUNX2, OCN, and BMP. Therefore, the presence of the PLA/Li-OCP coating on pure zinc could effectively improve the degradation rate and cytocompatibility of pure zinc.

A review on current research status of the surface modification of Zn-based biodegradable metals

Recently, zinc and its alloys have been proposed as promising candidates for biodegradable metals (BMs), owning to their preferable corrosion behavior and acceptable biocompatibility in cardiovascular, bone and gastrointestinal environments, together with Mg-based and Fe-based BMs. However, there is the desire for surface treatment for Zn-based BMs to better control their biodegradation behavior. Firstly, the implantation of some Zn-based BMs in cardiovascular environment exhibited intimal activation with mild inflammation. Secondly, for orthopedic applications, the biodegradation rates of Zn-based BMs are relatively slow, resulting in a long-term retention after fulfilling their mission. Meanwhile, excessive Zn2+ release during degradation will cause in vitro cytotoxicity and in vivo delayed osseointegration. In this review, we firstly summarized the current surface modification methods of Zn-based alloys for the industrial applications. Then we comprehensively summarized the recent progress of biomedical bulk Zn-based BMs as well as the corresponding surface modification strategies. Last but not least, the future perspectives towards the design of surface bio-functionalized coatings on Zn-based BMs for orthopedic and cardiovascular applications were also briefly proposed.

Preliminary Investigation on Degradation Behavior and Cytocompatibility of Ca-P-Sr Coated Pure Zinc

Zinc and its alloys show a good application prospect as a new biodegradable material. However, one of the drawbacks is that Zn and its alloys would induce the release of more Zn ions, which are reported to be cytotoxic to cells. In this study, a Ca-P-Sr bioactive coating was prepared on the surface of pure zinc by the hydrothermal method to address this issue. The morphology, thickness, and composition were characterized, and the effects of the coating on the degradation, cell viability, and ALP staining were investigated. The results demonstrated that the degradation rate of pure zinc was reduced, while the cytocompatibility was significantly improved after pure zinc was treated with Ca-P-Sr coating. It is considered that the Ca-P-Sr bioactive coating prepared by the hydrothermal method has promising application in the clinic.

Bone Scaffolds: An Incorporation of Biomaterials, Cells, and Biofactors

Large injuries to bones are still one of the most challenging musculoskeletal problems. Tissue engineering can combine stem cells, scaffold biomaterials, and biofactors to aid in resolving this complication. Therefore, this review aims to provide information on the recent advances made to utilize the potential of biomaterials for making bone scaffolds and the assisted stem cell therapy and use of biofactors for bone tissue engineering. The requirements and different types of biomaterials used for making scaffolds are reviewed. Furthermore, the importance of stem cells and biofactors (growth factors and extracellular vesicles) in bone regeneration and their use in bone scaffolds and the key findings are discussed. Lastly, some of the main obstacles in bone tissue engineering and future trends are highlighted.

Electrodeposited dopamine/strontium-doped hydroxyapatite composite coating on pure zinc for anti-corrosion, antimicrobial and osteogenesis

Zinc-based biometal is expected to become a new generation of biodegradable implants. Due to its antibacterial and biocompatibility in vivo, zinc metals is recently considered to be the most promising biodegradable metal, However, cytotoxicity is the thorny problem that currently restrict its application, due to the excessive Zn ions released during degradation. In order to solve these problems, dopamine modified strontium-doped hydroxyapatite coating (SrHA/PDA) was fabricated on alkali-treated pure zinc to improve its corrosion rate and cytocompatibility by electrodeposition for the first time. The obtained coating showed a dense structure and high crystallinity, which was attributed to the attraction of Ca²⁺ ions by polydopamine. The results showed that the SrHA/PDA coating delayedthe degradation rate of zinc metal, which reduced the release of Zn²⁺, thereby reducing its cytotoxicity. Additionally, electrochemical tests showed that SrHA/PDA coating can reduce the corrosion rate of pure zinc. In vitro cell viability showed that even at high Zn²⁺ concentrations (3.11 mg/L), preosteoblasts (MC3T3-E1) cells proliferated at a high rate on SrHA/PDA, thus confirming that Sr²⁺ counteracted the cytotoxic effects of Zn²⁺ and promoted cell differentiation. Moreover, the SrHA/PDA coating still maintained excellent antibacterial effects against pathogenic bacterial strains (Escherichia coli and Staphylococcus aureus). Mild pH changes had no significant effect on the viability of cells and bacterias. Collectively, the present study elucidated that by coating SrHA/PDA/Zn(OH)₂ on Zn, a controllable corrosion rate, original antibacterial properties and better cell compatibility can be achieved. This provided a new strategy for the surface modification of biodegradable Zn.

Biomaterial design strategies to address obstacles in craniomaxillofacial bone repair

Biomaterial design to repair craniomaxillofacial defects has largely focused on promoting bone regeneration, while there are many additional factors that influence this process. The bone microenvironment is complex, with various mechanical property differences between cortical and cancellous bone, a unique porous architecture, and multiple cell types that must maintain homeostasis. This complex environment includes a vascular architecture to deliver cells and nutrients, osteoblasts which form new bone, osteoclasts which resorb excess bone, and upon injury, inflammatory cells and bacteria which can lead to failure to repair. To create biomaterials able to regenerate these large missing portions of bone on par with autograft materials, design of these materials must include methods to overcome multiple obstacles to effective, efficient bone regeneration. These obstacles include infection and biofilm formation on the biomaterial surface, fibrous tissue formation resulting from ill-fitting implants or persistent inflammation, non-bone tissue formation such as cartilage from improper biomaterial signals to cells, and voids in bone infill or lengthy implant degradation times. Novel biomaterial designs may provide approaches to effectively induce osteogenesis and new bone formation, include design motifs that facilitate surgical handling, intraoperative modification and promote conformal fitting within complex defect geometries, induce a pro-healing immune response, and prevent bacterial infection. In this review, we discuss the bone injury microenvironment and methods of biomaterial design to overcome these obstacles, which if unaddressed, may result in failure of the implant to regenerate host bone.