The influence of yttrium and manganese additions on the degradation and biocompatibility of magnesium-zinc-based alloys:In vitro and in vivo studies

The repair and regeneration of bone defects are highly challenging orthopedic problems.Recently,Mg-based implants have gained popularity due to their unique biodegradation and elastic modulus similar to that of human bone.The aim of our study is to develop a magnesium alloy with a controllable degradation that can closely match bone tissue to help injuries heal in vivo and avoid cytotoxicity caused by a sudden increase in ion concentration.In this study,we prepared and modified Mg-3Zn,Mg-3Zn-1Y,and Mg-2Zn-1Mn by hot extrusion,and used Mg-2.5Y-2.5Nd was as a control.We then investigated the effect of additions of Y and Mn on alloys'properties.Our results show that Mn and Y can improve not only compression strength but also corrosion resistance.The alloy Mg-2Zn-1Mn demonstrated good cytocompatibility in vitro,and for this reason we selected it for implantation in vivo.The degraded Mg-2Zn-1Mn implanted a bone defect area did not cause obvious rejection and inflammatory reaction,and the degradation products left no signs of damage to the heart,liver,kidney,or brain.Furthermore,we find that Mg-2Zn-1Mn can promote an osteoinductive response in vivo and the formation of bone regeneration.

Guided bone regeneration in long-bone defect with a bilayer mineralized collagen membrane

Bone regeneration for large,critical-sized bone defects remains a clinical challenge nowadays.Guided bone regeneration(GBR)is a promising technique for the repair of multiple bone defects,which is widely used in oral and maxillofacial bone defects but is still unsatisfied in the treatment of long bone defects.Here,we successfully fabricated a bilayer mineralized collagen/collagen(MC/Col)-GBR membrane with excellent osteoinductive and barrier function by coating the MC particles prepared via in situ biomimetic mineralization process on one side of a sheet-like pure collagen layer.The aim of the present study was to investigate the physicochemical properties and biological functions of the MC/Col film,and to further evaluate its bone regeneration efficiency in large bone defect repair.Fouriertransform infrared spectra and X-ray diffraction patterns confirmed the presence of both hydroxyapatite and collagen phase in the MC/Col film,as well as the chemical interaction between them.stereo microscope,scanning electron microscopy and atomic force microscope showed the uniform distribution of MC particles in the MC/Col film,resulting in a rougher surface compared to the pure Col film.The quantitative analysis of surface contact angle,light transmittance and tensile strength demonstrated that the MC/Col film have better hydrophilicity,mechanical properties,light-barrier properties,respectively.In vitro macrophage co-culture experiments showed that the MC/Col film can effectively inhibit macrophage proliferation and fusion,reducing fibrous capsule formation.In vivo bone repair assessment of a rabbit critical segmental radial defect proved that the MC/Col film performed better than other groups in promoting bone repair and regeneration due to their unique dual osteoinductive/barrier function.These findings provided evidence that MC/Col film has a great clinical potential for effective bone defect repair.

The Clinical Application of Human Bone Matrix Gelatin

This paper reports the results of 24 cases of bone defect resulting from bone tumor or tumor condition excision, and of posterior spinal fusion, treated by human bone matrix gelatin. The success rate of bone defect repair and spinal fusion is 91. 67 %. The results suggest that human bone matrix gelatin has. excellent osteoinductive effect and is ideal substitute for bone autografts.

Remote control of the recruitment and capture of endogenous stem cells by ultrasound for in situ repair of bone defects

Stem cell-based tissue engineering has provided a promising platform for repairing of bone defects.However,the use of exogenous bone marrow mesenchymal stem cells(BMSCs)still faces many challenges such as limited sources and potential risks.It is important to develop new approach to effectively recruit endogenous BMSCs and capture them for in situ bone regeneration.Here,we designed an acoustically responsive scaffold(ARS)and embedded it into SDF-1/BMP-2 loaded hydrogel to obtain biomimetic hydrogel scaffold complexes(BSC).The SDF-1/BMP-2 cytokines can be released on demand from the BSC implanted into the defected bone via pulsed ultrasound(p-US)irradiation at optimized acoustic parameters,recruiting the endogenous BMSCs to the bone defected or BSC site.Accompanied by the daily p-US irradiation for 14 days,the alginate hydrogel was degraded,resulting in the exposure of ARS to these recruited host stem cells.Then another set of sinusoidal continuous wave ultrasound(s-US)irradiation was applied to excite the ARS intrinsic resonance,forming highly localized acoustic field around its surface and generating enhanced acoustic trapping force,by which these recruited endogenous stem cells would be captured on the scaffold,greatly promoting them to adhesively grow for in situ bone tissue regeneration.Our study provides a novel and effective strategy for in situ bone defect repairing through acoustically manipulating endogenous BMSCs.

Hippo-YAP/TAZ signaling in osteogenesis and macrophage polarization:Therapeutic implications in bone defect repair

Bone defects caused by diseases or surgery are a common clinical problem.Researchers are devoted to finding biological mechanisms that accelerate bone defect repair,which is a complex and continuous process controlled by many factors.As members of transcriptional costimulatory molecules,Yes-associated protein(YAP)and transcriptional co-activator with PDZ-binding motif(TAZ)play an important regulatory role in osteogenesis,and they affect cell function by regulating the expression of osteogenic genes in osteogenesis-related cells.Macrophages are an important group of cells whose function is regulated by YAP/TAZ.Currently,the relationship between YAP/TAZ and macrophage polarization has attracted increasing attention.In bone tissue,YAP/TAZ can realize diverse osteogenic regulation by mediating macrophage polarization.Macrophages polarize into M1 and M2 phenotypes under different stimuli.M1 macrophages dominate the inflammatory response by releasing a number of inflammatory mediators in the early phase of bone defect repair,while massive aggregation of M2 macrophages is beneficial for inflammation resolution and tissue repair,as they secrete many anti-inflammatory and osteogenesis-related cytokines.The mechanism of YAP/TAZ-mediated macrophage polarization during osteogenesis warrants further study and it is likely to be a promising strategy for bone defect repair.In this article,we review the effect of Hippo-YAP/TAZ signaling and macrophage polarization on bone defect repair,and highlight the regulation of macrophage polarization by YAP/TAZ.

A new osteogenic protein isolated from Dioscorea opposita Thunb accelerates bone defect healing through the mTOR signaling axis

Delayed bone defect repairs lead to severe health and socioeconomic impacts on patients. Hence, there are increasing demands for medical interventions to promote bone defect healing. Recombinant proteins such as BMP-2 have been recognized as one of the powerful osteogenic substances that promote mesenchymal stem cells (MSCs) to osteoblast differentiation and are widely applied clinically for bone defect repairs. However, recent reports show that BMP-2 treatment has been associated with clinical adverse side effects such as ectopic bone formation, osteolysis and stimulation of inflammation. Here, we have identified one new osteogenic protein, named ‘HKUOT-S2’ protein, from Dioscorea opposita Thunb. Using the bone defect model, we have shown that the HKUOT-S2 protein can accelerate bone defect repair by activating the mTOR signaling axis of MSCs-derived osteoblasts and increasing osteoblastic biomineralization. The HKUOT-S2 protein can also modulate the transcriptomic changes of macrophages, stem cells, and osteoblasts, thereby enhancing the crosstalk between the polarized macrophages and MSCs-osteoblast differentiation to facilitate osteogenesis. Furthermore, this protein had no toxic effects in vivo. We have also identified HKUOT-S2 peptide sequence TKSSLPGQTK as a functional osteogenic unit that can promote osteoblast differentiation in vitro. The HKUOT-S2 protein with robust osteogenic activity could be a potential alternative osteoanabolic agent for promoting osteogenesis and bone defect repairs. We believe that the HKUOT-S2 protein may potentially be applied clinically as a new class of osteogenic agent for bone defect healing.

Continuously released Zn^(2+)in 3D-printed PLGA/β-TCP/Zn scaffolds for bone defect repair by improving osteoinductive and anti-inflammatory properties

Long-term nonunion of bone defects has always been a major problem in orthopedic treatment.Artificial bone graft materials such as Poly(lactic-co-glycolic acid)/β-tricalcium phosphate(PLGA/β-TCP)scaffolds are expected to solve this problem due to their suitable degradation rate and good osteoconductivity.However,insufficient mechanical properties,lack of osteoinductivity and infections after implanted limit its large-scale clinical application.Hence,we proposed a novel bone repair bioscaffold by adding zinc submicron particles to PLGA/β-TCP using low temperature rapid prototyping 3D printing technology.We first screened the scaffolds with 1 wt%Zn that had good biocompatibility and could stably release a safe dose of zinc ions within 16 weeks to ensure long-term non-toxicity.As designed,the scaffold had a multi-level porous structure of biomimetic cancellous bone,and the Young’s modulus(63.41±1.89 MPa)and compressive strength(2.887±0.025 MPa)of the scaffold were close to those of cancellous bone.In addition,after a series of in vitro and in vivo experiments,the scaffolds proved to have no adverse effects on the viability of BMSCs and promoted their adhesion and osteogenic differentiation,as well as exhibiting higher osteogenic and anti-inflammatory properties than PLGA/β-TCP scaffold without zinc particles.We also found that this osteogenic and anti-inflammatory effect might be related to Wnt/β-catenin,P38 MAPK and NFkB pathways.This study lay a foundation for the follow-up study of bone regeneration mechanism of Zn-containing biomaterials.We envision that this scaffold may become a new strategy for clinical treatment of bone defects.

Biodegradable metals for bone defect repair:A systematic review and meta-analysis based on animal studies

Biodegradable metals are promising candidates for bone defect repair.With an evidence-based approach,this study investigated and analyzed the performance and degradation properties of biodegradable metals in animal models for bone defect repair to explore their potential clinical translation.Animal studies on bone defect repair with biodegradable metals in comparison with other traditional biomaterials were reviewed.Data was carefully collected after identification of population,intervention,comparison,outcome,and study design(PICOS),and following the inclusion criteria of biodegradable metals in animal studies.30 publications on pure Mg,Mg alloys,pure Zn and Zn alloys were finally included after extraction from a collected database of 2543 publications.A qualitative systematic review and a quantitative meta-analysis were performed.Given the heterogeneity in animal model,anatomical site and critical size defect(CSD),biodegradable metals exhibited mixed effects on bone defect repair and degradation in animal studies in comparison with traditional non-degradable metals,biodegradable polymers,bioceramics,and autogenous bone grafts.The results indicated that there were limitations in the experimental design of the included studies,and quality of the evidence presented by the studies was very low.To enhance clinical translation of biodegradable metals,evidence-based research with data validity is needed.Future studies should adopt standardized experimental protocols in investigating the effects of biodegradable metals on bone defect repair with animal models.

Evaluation on the corrosion resistance, antibacterial property and osteogenic activity of biodegradable Mg-Ca and Mg-Ca-Zn-Ag alloys

The rapid degradation of magnesium(Mg)-based implants in physiological environment limits its clinical applications, and alloying treatment is an effective way to regulate the degradation rate of Mg-based materials. In the present study, three Mg alloys, including Mg-0.8Ca(denoted as ZQ), Mg-0.8Ca-5Zn-1.5Ag(denoted as ZQ71) and Mg-0.8Ca-5Zn-2.5Ag(denoted as ZQ63), were fabricated by alloying with calcium(Ca), zinc(Zn) and silver(Ag). The results obtained from electrochemical corrosion tests and in vitro degradation evaluation demonstrated that the three Mg alloys exhibited distinct corrosion resistance, and ZQ71 exhibited the lowest degradation rate in vitro among them. After addition of Zn and Ag, the antibacterial potential of Mg alloys was also enhanced. The in vitro cell experiments showed that all the three Mg alloys had good biocompatibility. After implantation in a rat femoral defect, ZQ71 showed significantly higher osteogenic activity and bone substitution rate than ZQ63 and ZQ, due to its higher corrosion resistance as well as the stimulatory effects of the released metallic ions. In addition, the average daily degradation rate of each Mg alloy in vivo was significantly higher than that in vitro, as could be due to the implantation site located in the highly vascularized trabecular region. Importantly, the correlations between the in vitro and in vivo degradation parameters of the Mg alloys were systematically analyzed to find out the potential predictors of the in vivo degradation performance of the materials. The current work not only evaluated the clinical potential of the three biodegradable Mg alloys as bone grafts but also provided a feasible approach for predicting the in vivo degradation behavior of biodegradable materials.

A comparative study of autogenous, allograft and artificial bone substitutes on bone regeneration and immunotoxicity in rat femur defect model

Repair and reconstruction of large bone defect were often difficult,and bone substitute materials,including autogenous bone,allogenic bone and artificial bone,were common treatment strategies.The key to elucidate the clinical effect of these bone repair materials was to study their osteogenic capacity and immunotoxicological compatibility.In this paper,the mechanical properties,micro-CT imaging analysis,digital image analysis and histological slice analysis of the three bone grafts were investigated and compared after different time points of implantation in rat femur defect model.Autogenous bone and biphasic calcium phosphate particular artificial bone containing 61.4% HA and 38.6%β-tricalcium phosphate with 61.64%porosity and 0.8617±0.0068 g/cm^(3) den-sity(d≤2 mm)had similar and strong bone repair ability,but autogenous bone implant materials caused greater secondary damage to experimental animals;allogenic bone exhibited poor bone defect repair ability.At the early stage of implantation,the immunological indexes such as Immunoglobulin G,Immunoglobulin M concentration and CD4 cells'population of allogenic bone significantly increased in compared with those of autologous bone and artificial bone.Although the repair process of artificial bone was relatively inefficient than autologous bone graft,the low immunotoxicological indexes and acceptable therapeutic effects endowed it as an excellent alter-native material to solve the problems with insufficient source and secondary trauma of autogenous bone.

Large-sized bone defect repair by combining a decalcified bone matrix framework and bone regeneration units based on photo-crosslinkable osteogenic microgels

Physiological repair of large-sized bone defects is great challenging in clinic due to a lack of ideal grafts suitable for bone regeneration.Decalcified bone matrix(DBM)is considered as an ideal bone regeneration scaffold,but low cell seeding efficiency and a poor osteoinductive microenvironment greatly restrict its application in large-sized bone regeneration.To address these problems,we proposed a novel strategy of bone regeneration units(BRUs)based on microgels produced by photo-crosslinkable and microfluidic techniques,containing both the osteogenic ingredient DBM and vascular endothelial growth factor(VEGF)for accurate biomimic of an osteoinductive microenvironment.The physicochemical properties of microgels could be precisely controlled and the microgels effectively promoted adhesion,proliferation,and osteogenic differentiation of bone marrow mesenchymal stem cells(BMSCs)in vitro.BRUs were successfully constructed by seeding BMSCs onto microgels,which achieved reliable bone regeneration in vivo.Finally,by integrating the advantages of BRUs in bone regeneration and the advantages of DBM scaffolds in 3D morphology and mechanical strength,a BRU-loaded DBM framework successfully regenerated bone tissue with the desired 3D morphology and effectively repaired a large-sized bone defect of rabbit tibia.The current study developed an ideal bone biomimetic microcarrier and provided a novel strategy for bone regeneration and large-sized bone defect repair.

Biodegradable Thermogel as Culture Matrix of Bone Marrow Mesenchymal Stem Cells for Potential Cartilage Tissue Engineering

Poly（lactide-co-glycolide）-poly（ethylene glycol）-poly（lactide-co-glycolide）（PLGA-PEG-PLGA） triblock copolymer was synthesized through the ring-opening polymerization of LA and GA with PEG as macroinitiator and stannous octoate as catalyst. The amphiphilic copolymer self-assembled into micelles in aqueous solutions, and formed hydrogels as the increase of temperature at relatively high concentrations（〉 15 wt%）. The favorable degradability of the hydrogel was confirmed by in vitro and in vivo degradation experiments. The good cellular and tissular compatibilities of the thermogel were demonstrated. The excellent adhesion and proliferation of bone marrow mesenchymal stem cells endowed PLGA-PEGPLGA thermogelling hydrogel with fascinating prospect for cartilage tissue engineering.