High-purity magnesium interference screws promote fibrocartilaginous entheses regeneration in the anterior cruciate ligament reconstruction rabbit model via accumulation of BMP-2 and VEGF

Tissue-Engineered Decellularized Allografts for Anterior Cruciate Ligament Reconstruction

Anterior cruciate ligament (ACL) reconstruction with allografts is limited by high immunogenicity, poor cellularization, and delayed tendon-bone healing. Decellularized tendons (DAs) have been used as bioscaffolds to reconstruct ligaments with variable success. In the study, four kinds of decellularized allogeneic hamstring tendons were prepared and their microstructure and cytocompatibility were examined in vitro. The results showed that decellularized allografts neutralized by 5% calcium bicarbonate had typical reticular and porous microstructures with optical cytocompatibility. Tissue-engineering decellularized allografts (TEDAs) were prepared with the selected decellularized allografts and tendon stem/progenitor cells and used for ACL reconstruction in a rabbit model. Histological staining showed that the TEDAs promoted cellular infiltration and new vessel formation significantly and improved tendon-bone healing moderately compared to decellularized allografts. Better macroscopic scores and biomechanical results were observed in TEDA groups, but there were no significant differences between DA and TEDA groups at months 1, 2, and 3 postoperatively. Immunohistochemical data showed that the tissue-engineering decellularized allografts enhanced the expression of collagen I at each timepoint and collagen III at months 1 and 2. ELISA analysis showed that the tissue-engineering decellularized allografts reduced the secretion of IgE and IL-1β within 1 month and promoted the secretion of IL-2, IL-4, IL-10, and IL-17 after 1 month. The results showed that tissue-engineering decellularized allografts strengthened intra-articular graft remodeling significantly and provided moderate improvements in tendon-bone healing by creating more suitable immune responses than decellularized allografts. The study revealed that tissue-engineering decellularized allografts as a promising option for ACL reconstruction could achieve more favorable outcomes.

Targeting Local Osteogenic and Ancillary Cells by Mechanobiologically Optimized Magnesium Scaffolds for Orbital Bone Reconstruction in Canines

Large-sized orbital bone defects have serious consequences that destroy orbital integrity and result in maxillofacial deformities and vision loss. The treatment of orbital bone defects is currently palliative and not reparative, suggesting an urgent demand for biomaterials that regenerate orbital bones. In this study, via alloying, extrusion and surface modification, we developed mechanobiologically optimized magnesium (Mg) scaffolds (Ca-P-coated Mg-Zn-Gd scaffolds, referred to as Ca-P-Mg) for the orthotopic reconstruction of large-sized orbital bone defects. At 6 months after transplanting the scaffolds to a clinically relevant canine large animal model, large-sized defects were successfully bridged by an abundance of new bone with normal mechanical properties that corresponded to gradual degradation of the implants. The osteogenic and ancillary cells, including vascular endothelial cells and trigeminal neurons, played important roles in this process. The scaffolds robustly enhanced bone marrow mesenchymal stem cell (BMSC) osteogenic differentiation. In addition, the increased angiogenesis including increased ratio of the specific endothelial subtype CD31^hi endomucin^hi (CD31^hiEmcn^hi) endothelial cells can facilitate osteogenesis. Furthermore, the scaffolds trigger trigeminal neurons via transient receptor potential vanilloid subtype 1 (Trpv1) to produce the neuropeptide calcitonin gene-related peptide (CGRP), which promotes angiogenesis and osteogenesis. Overall, our investigations revealed the efficacy of Ca-P-Mg scaffolds in healing orbital bone defects and warrant further exploration of these scaffolds for clinical applications.

High-purity magnesium pin enhances bone consolidation in distraction osteogenesis model through activation of the VHL/HIF-1α/VEGF signaling

Distraction osteogenesis has widespread clinical use in the treatment of large bone defects. Nonetheless, the prolonged consolidation period carries the risk of complications. Magnesium-based materials have been shown to promote bone regeneration in fracture healing both in vitro and in vivo. Here, we investigated whether high-purity magnesium could enhance bone formation in distraction osteogenesis. High-purity magnesium pins were placed into the medullary cavity in the rat distraction osteogenesis model. Results showed that the bone volume/total tissue volume, bone mineral density, and mechanical properties of new callus were significantly higher in the high-purity magnesium group compared to stainless steel and control group (p < 0.01). Histological analyses confirmed improved bone consolidation and vascularization in high-purity magnesium group. Further, polymerase chain reaction-array investigation, Western blot, and immunohistochemical results found that vascular endothelial growth factor and hypoxia inducible factor-1α were highly expressed in the high-purity magnesium group, while Von Hippel–Lindau protein was the opposite (p < 0.01). In conclusion, high-purity magnesium implants have the potential to enhance angiogenesis and bone consolidation in the distraction osteogenesis application, and this process might be via the regulation of Von Hippel–Lindau/hypoxia inducible factor-1α/vascular endothelial growth factor signaling.

Microstructure controls the corrosion behavior of a lean biodegradable Mg-2Zn alloy

Microstructural design was a long-term sustainable development method to improve the biodegradability and mechanical properties of low alloyed biomedical Mg alloys. In this study, the microstructural features (including grain size, deformation twin, deformed grains, sub-grains, and recrystallized grains) of the MZ2 ((Mg-2Zn (wt%)) alloy were controlled by different single-passed rolling reductions at high temperature. Besides the effect of grain size, we found that deformation twins and deformed grains influenced corrosion performance. Grain refinement with uniform distribution, meanwhile reducing the content of deformation twins, deformed grains, and sub-grains, was a practical method to improve both corrosion resistance and mechanical properties of MZ2 alloy. This finding proposed a better understanding of the development of lean biomedical Mg alloys with superior mechanical properties and favorable corrosion resistance. STATEMENT OF SIGNIFICANCE: Current research and development of biomedical Mg focused on alloying methods. The lean biodegradable Mg, which reduced the materials' compositional complexity, was the benefit of development for long-term sustainability. Here, our work revealed the relationship between microstructural features and corrosion resistance of a lean Mg-2Zn alloy during the different single-passed rolling processes. We found that recrystallized fine grains with partially ultra-fine grains could improve both strength and corrosion resistance. This study could give a new understanding of the development of lean biodegradable Mg alloys by using microstructural design to improve the overall performance of biomedical applications.

Preparation and evaluation of osteogenic nano-MgO/PMMA bone cement for bone healing in a rat critical size calvarial defect

The clinical outcomes of polymethylmethacrylate (PMMA) bone cement used to fill gaps or marrow cavities of bones and bone defects are limited due to poor handling properties, mismatched mechanical properties with natural bone and lack of osteogenesis for bone healing. In this study, a series of PMMA bone cements containing active nano-MgO particles (nano-MgO/PMMA) were prepared. The handling and mechanical properties were systemically evaluated according to an International Standardization Organization standard (ISO 5833:2002). The biocompatibility and osteogenic activity of nano-MgO/PMMA were also analysed in vitro. The osteogenic effects of nano-MgO/PMMA were assessed in a rat calvarial critical bone defect model. The addition of less than 15 wt% nano-MgO to PMMA improved the handling properties of PMMA. Compared with PMMA, the compression modulus and strength of 20MP (20 wt% nano-MgO to PMMA) decreased to 0.725 ± 0.023 GPa and 25.38 ± 2.82 MPa, respectively. In vitro studies with MC3T3-E1 showed that nano-MgO/PMMA had better biocompatibility than the PMMA group after 7 days of culture. The nano-MgO/PMMA groups showed more calcium nodules and higher osteogenic gene expression levels than PMMA after 12 days of osteogenic induction of the rat BMSCs. The in vivo studies analysed by micro-CT and histomorphology results proved that nano-MgO/PMMA could significantly enhance new bone formation. The mean new bone mineral density in the nano-MgO/PMMA group was 50% greater than that in the PMMA group. In addition, biomechanical tests showed that nano-MgO/PMMA was superior to PMMA in bone-bonding strength after 12 weeks implantation. Therefore, the nano-MgO/PMMA bone cement has good potential in joint fixation and bone defect filling applications.

Biodegradable Magnesium-Based Implants in Orthopedics-A General Review and Perspectives

Biodegradable Mg-based metals may be promising orthopedic implants for treating challenging bone diseases, attributed to their desirable mechanical and osteopromotive properties. This Review summarizes the current status and future research trends for Mg-based orthopedic implants. First, the properties between Mg-based implants and traditional orthopedic implants are compared on the following aspects: in vitro and in vivo degradation mechanisms of Mg-based implants, peri-implant bone responses, the fate of the degradation products, and the cellular and molecular mechanisms underlying the beneficial effects of Mg ions on osteogenesis. Then, the preclinical studies conducted at the low weight bearing sites of animals are introduced. The innovative strategies (for example, via designing Mg-containing hybrid systems) are discussed to address the limitations of Mg-based metals prior to their clinical applications at weight-bearing sites. Finally, the available clinical studies are summarized and the challenges and perspectives of Mg-based orthopedic implants are discussed. Taken together, the progress made on the development of Mg-based implants in basic, translational, and clinical research has laid down a foundation for developing a new era in the treatment of challenging and prevalent bone diseases.

High-purity weight-bearing magnesium screw: Translational application in the healing of femoral neck fracture

Magnesium (Mg)-based metals can be used as next-generation fracture internal fixation devices due to their specific properties. We used vascularized bone grafting fixed by degradable pure Mg screws and obtained satisfactory results in the treatment of osteonecrosis of the femoral head. However, the mechanical properties of these screws make them weaker than those made of traditional metals. In particular, one of the main challenges of using screws made of Mg-based metals is their application in fixation at important weight-bearing sites in the human body. Femoral neck fracture is a common clinical injury. In this injury, the large bearing stress at the junction requires a fixation device with extremely high mechanical strength. Surgery and appropriate internal fixation can accelerate the healing of femoral neck fractures. Traditional internal fixation devices have some disadvantages after surgery, including stress shielding effects and the need for secondary surgery to remove screws. On the basis of previous work, we developed high-strength pure Mg screws for femoral neck fractures. In this study, we describe the first use of high-purity Mg to prepare large-size weight-bearing screws for the fixation of femoral neck fractures in goats. We then performed a 48 weeks follow-up study using in vivo transformation experiments. The results show that these biodegradable high-purity Mg weight-bearing screws had sufficient mechanical strength and a degradation rate compatible with bone repair. Furthermore, good bone formation was achieved during the degradation process and reconstruction of the bone tissue and blood supply of the femoral head and femoral neck. This study provides a basis for future research on the clinical transformation of biodegradable high-purity Mg weight-bearing screws.

Evaluation of a bioengineered ACL matrix's osteointegration with BMP-2 supplementation

A poly (l-lactic) acid bioengineered anterior cruciate ligament (ACL) matrix has previously demonstrated the ability to support tissue regeneration in a rabbit ACL reconstruction model. The matrix was designed for optimal bone and ligament regeneration by developing a matrix with differential pore sizes in its bone and ligament compartments. Building upon past success, we designed a new bioengineered ACL matrix that is easier to install and can be used with endobutton fixation during ACL reconstruction. To achieve this, a new braiding procedure was developed to allow the matrix to be folded in half, making two-limbs, while maintaining its bone and ligament compartments. The osteointegration of the matrix with and without bone morphogenetic protein 2 (BMP-2) supplementation was evaluated in a rabbit ACL reconstruction model. Two doses of BMP-2 were evaluated, 1 and 10 μg, and delivered by saline injection into the bone tunnel at the end of surgery. A fibrous matrix-to-bone interface with occasional Sharpey’s fibers was the primary mode of osteointegration observed. The matrix was also found to support a fibrocartilage matrix-to-bone interface. In some cases, the presence of chondrocyte-like cells was observed at the aperture of the bone tunnel and the center of the matrix within the bone tunnel. Treatment with BMP-2 was associated with a trend towards smaller bone tunnel cross-sectional areas, and 1 μg of BMP-2 was found to significantly enhance osteoid seam width in comparison with no BMP-2 or 10 μg of BMP-2 treatment. Regenerated tissue was well organized within the bioengineered ACL matrix and aligned with the poly (l-lactic) acid fibers. Disorganized tissue was found between the two-limbs of the bioengineered ACL matrix and hypothesized to be due to a lack of structural scaffolding. This study suggests that the bioengineered ACL matrix can undergo similar modes of osteointegration as current autografts and allografts, and that BMP-2 treatment may enhance osteoblastic activity within the bone tunnels.

Local intragranular misorientation accelerates corrosion in biodegradable Mg

Mg-based implants are used in biomedical applications predominantly because of their degradable property. In this paper, the effect of local misorientations (intragranular misorientation) on the corrosion behavior of high-purity Mg (HPM) was systematically investigated according to microstructure characterization and corrosion measurements. The results showed that local misorientation introduced into grains by deformation could result in corrosion around the grain boundary (GB), which ultimately reduces the corrosion resistance of HPM. After removing the local misorientation by annealing, the corrosion around GB could be eliminated. This work is expected to inspire better control over the degradation behaviors of biomedical Mg through microstructure design to be used for various biomedical applications. STATEMENT OF SIGNIFICANCE: 1. Fine grains, fine grains with large local misorientation, and coarse grains could be obtained, respectively, in high-purity Mg by sequential hot rolling, compression deformation, and annealing treatments. 2. Large local misorientation introduced into grains could lead to corrosion around the grain boundary and ultimately reduce corrosion resistance. 3. In the absence of local misorientation, refining grain size could improve the corrosion resistance of Mg.

Magnesium-enriched microenvironment promotes odontogenic differentiation in human dental pulp stem cells by activating ERK/BMP2/Smads signaling

Background

Magnesium (Mg²⁺)-enriched microenvironment promotes odontogenic differentiation in human dental pulp stem cells (DPSCs), but the regulatory mechanisms remain undefined. The aim of this work was to assess magnesium’s function in the above process and to explore the associated signaling pathway.

Methods

DPSCs underwent culture in odontogenic medium with the addition of 0, 1, 5, or 10 mM MgCl₂. Intracellular Mg²⁺ levels in DPSCs were evaluated flow cytometrically using Mag-Fluo-4-AM. Mg²⁺-entry was inhibited by TRPM7 inhibitor 2-aminoethoxydiphenyl borate (2-APB). RNA-Sequencing was carried out for assessing transcriptome alterations in DPSCs during odontogenic differentiation associated with high extracellular Mg²⁺. KEGG pathway analysis was performed to determine pathways related to the retrieved differentially expressed genes (DEGs). Immunoblot was performed for assessing magnesium’s role and exploring ERK/BMP2/Smads signaling.

Results

Mg²⁺-enriched microenvironment promoted odontogenic differentiation in DPSCs via intracellular Mg²⁺ increase. Consistently, the positive effect of high extracellular Mg²⁺ on odontogenic differentiation in DPSCs was blocked by 2-APB, which reduced Mg²⁺ entry. RNA-sequencing identified 734 DEGs related to odontogenic differentiation in DPSCs in the presence of high extracellular Mg²⁺. These DEGs participated in many cascades such as MAPK and TGF-β pathways. Consistently, ERK and BMP2/Smads pathways were activated in DPSCs treated with high extracellular Mg²⁺. In agreement, ERK signaling inhibition by U0126 blunted the effect of high extracellular Mg²⁺ on mineralization and odontogenic differentiation in DPSCs. Interestingly, BMP2, BMPR1, and phosphorylated Smad1/5/9 were significantly decreased by U0126, indicating that BMP2/Smads acted as downstream of ERK.

Conclusions

Mg²⁺-enriched microenvironment promotes odontogenic differentiation in DPSCs by activating ERK/BMP2/Smads signaling via intracellular Mg²⁺ increase. This study revealed that Mg²⁺-enriched microenvironment could be used as a new strategy for dental pulp regeneration.

Translational status of biomedical Mg devices in China

Magnesium (Mg) and its alloys as temporary medical implants with biodegradable and properly mechanical properties have been investigated for a long time. There are already three kinds of biodegradable Mg implants which are approved by Conformite Europeene (CE) or Korea Food and Drug Administration (KFDA), but not China Food and Drug Administration (CFDA, now it is National Medical Products Administration, NMPA). As we know, Chinese researchers, surgeons, and entrepreneurs have tried a lot to research and develop biodegradable Mg implants which might become other new approved implants for clinical applications. So in this review, we present the representative Mg implants of three categories, orthopedic implants, surgical implants, and intervention implants and provide an overview of current achievement in China from academic publications and Chinese patents. We would like to provide a systematic way to translate Mg and its alloy implants from experiment designs to clinical products.

Crevice corrosion - A newly observed mechanism of degradation in biomedical magnesium

Crevice-induced corrosion is not desirable to occur in metallic magnesium (Mg) during many industrial applications. However, orthopedic implants made of Mg alloys have been demonstrated to degrade faster between the joining surface of bone plates and screws after implantation, suggesting the crevice corrosion may occur in the physiological environment. In this paper, a resin device is designed to parallel high purity magnesium (HP-Mg) plates with closely spaced slits. After a standard corrosion test in the phosphate-buffered saline (PBS) solution, the paralleled HP-Mg samples embedded in the custom-made resin device corrode faster than those without the resin device. The corrosion morphology of Mg with the resin device exhibits features of crevice corrosion with many deep holes and river-like texture. Moreover, implantation of the bone plate and screws in vivo demonstrates similar corrosion morphology as that of the in vitro test, suggesting the occurrence of crevice-enhanced corrosion in the bone-bone plate interface, as well as the contact area between the bone plate and the screws. STATEMENT OF SIGNIFICANCE: Understanding the corrosion behavior of Mg and Mg alloys after implantation is one of the main challenges for developing desirable biodegradable Mg alloys or effective methods to adjust the corrosion rate of Mg-based implants. In this paper, we attempted to understand the corrosion behaviors of HP-Mg at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues after implantation. We designed an in vitro setup to mimic the crevice environment of the in vivo joining surface and found that the crevices existing on the HP-Mg would significantly accelerate the corrosion rate and change the corrosion morphology of HP-Mg plates. The in vivo implantation also showed similar corrosion morphology caused by crevice corrosion, which appeared at the joining surface between HP-Mg plates or HP-Mg screws and bone tissues. Then, we proposed a new corrosion mechanism of Mg-based alloys inside the crevice. The findings of this study can help us broaden our cognition on the corrosion behavior of Mg and Mg alloy-based orthopedic implants.

Three-dimensional printing of metals for biomedical applications

Three-dimensional (3D) printing technology has received great attention in the past decades in both academia and industry because of its advantages such as customized fabrication, low manufacturing cost, unprecedented capability for complex geometry, and short fabrication period. 3D printing of metals with controllable structures represents a state-of-the-art technology that enables the development of metallic implants for biomedical applications. This review discusses currently existing 3D printing techniques and their applications in developing metallic medical implants and devices. Perspective about the current challenges and future directions for development of this technology is also presented.

Antibacterial properties and biocompatibility in vivo and vitro of composite coating of pure magnesium ultrasonic micro-arc oxidation phytic acid copper loaded

Bone infection and implant secondary removal remains a clinical challenge. We used ultrasonic micro-arc oxidation (UMAO) and conversion of phytic acid copper plating to prepare a pure magnesium polyhydric biofilm; we evaluated the surface microstructures, phase, element composition, and wettability of the film in vitro. The antibacterial activity of films with different Cu contents was confirmed by coating method, imaging examination, and microbiological cultures in vitro. The biocompatibility of biofilms was confirmed by cell proliferation, vitality, and morphology assays in vitro and histological evaluation in vivo. MC3T3-E1 cells were co-cultured with different films to assess cell viability on the films. The results showed that the mass fraction of Cu increased with increasing time of copper plating, and the surface of the Cu group was more dense and uniform. Additionally, copper coating significantly inhibited the growth of E. coli and Staphylococcus aurous. We also found that the adhesion, proliferation, and differentiation of the cells on the surface of copper plating were enhanced. Copper implantation of animals in vivo showed fine ability to promote bone growth. Antibacterial activity and biocompatibility of pure magnesium UMAO-phytic acid-Cu3min implant film are excellent, so the film has potential application value in the treatment of bone implantation.

Local Administration of Magnesium Promotes Meniscal Healing Through Homing of Endogenous Stem Cells: A Proof-of-Concept Study

BACKGROUND

Although many strategies have been developed to modify the biological and biomechanical environment of the meniscal suture repair to improve the chances of healing, the failure rates remain high. Thus, new methods to promote meniscal regeneration and repair are needed.

HYPOTHESIS

Administration of magnesium (via a repair using magnesium stitches) might enhance recruitment and adherence of endogenous stem cells to the site of the lesion, thereby promoting in situ meniscal regeneration and chondroprotective functions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Synovial fluid-derived mesenchymal stem cells (SMSCs) were identified and isolated from the knees of rabbits with a meniscal injury of 4 weeks' duration. An in vitro analysis of adherence and chemotaxis of SMSCs was performed. For the in vivo assay, rabbits (n = 120) with meniscal lesions were divided into 3 groups: repair with high-purity magnesium stitches (Mg group), repair with absorbable sutures (Control group), and no repair (Blank group). Healing of the regenerated tissue and degeneration of the articular cartilage were evaluated by gross and histological analysis at postoperative weeks 1, 3, 6, and 12. The mechanical properties of the repaired meniscus were also analyzed (tensile testing).

RESULTS

In vitro, magnesium promoted the adhesion and migration of SMSCs, which were identified and increased in the knee joints with meniscal lesions. Moreover, fibrochondrogenesis of SMSCs was stimulated by magnesium. Compared with the other groups, the Mg group had enhanced tissue regeneration, lower cartilage degeneration, and retained mechanical strength at 12 weeks after meniscal repair.

CONCLUSION/CLINICAL RELEVANCE

Magnesium could be used for in situ meniscal repair due to the potential capacity of magnesium to recruit endogenous stem cells and promote synthesis of fibrocartilaginous matrix.

Effect of Low-Intensity Pulsed Ultrasound After Autologous Adipose-Derived Stromal Cell Transplantation for Bone-Tendon Healing in a Rabbit Model

BACKGROUND

Low-intensity pulsed ultrasound (LIPUS), as a safe biophysiotherapy, can enhance bone-tendon (B-T) healing in vivo and induce osteogenic or chondrogenic differentiation of mesenchymal stromal cells in vitro. This study aimed to determine whether LIPUS can improve the efficacy of transplanted mesenchymal stromal cells on B-T healing.

HYPOTHESIS

LIPUS can induce lineage-specific differentiation of transplanted adipose-derived stromal cells (ASCs) at the B-T healing site, thus resulting in superior healing quality when compared with LIPUS or ASCs alone.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 112 mature rabbits with partial patellectomy in the hindlimb were randomly assigned into mock sonication without ASCs (control), ultrasonication without ASCs (LIPUS), mock sonication with ASCs (ASCs), and ultrasonication with ASCs (LIPUS + ASCs). The treatment time of the mock sonication or ultrasonication was 20 minutes per day. Autologous ASCs were transplanted to the healing site by fibrin glue during the operation, and LIPUS was delivered daily starting at postoperative day 3 until euthanasia. The patella-patellar tendon junctions were postoperatively harvested at 8 and 16 weeks for radiological, histological, and mechanical evaluations. Additionally, 9 animals were used for ASC tracking with mCherry protein.

RESULTS

Radiologically, there was more new bone formation and remodeling in the LIPUS + ASCs group as compared with the other groups. Synchrotron radiation micro-computed tomography showed that the LIPUS + ASCs group significantly increased bone volume fraction, trabecular thickness, and trabecular number at the healing site as compared with the other groups at postoperative 8 weeks ( P < .05 for all). Histologically, immunohistochemical staining confirmed that the transplanted mCherry-ASCs can differentiate into osteoblasts and fibrochondrocytic-like cells. Meanwhile, as compared with the other groups, the LIPUS + ASCs group showed more formation and maturity of the fibrocartilage layer and new bone at postoperative weeks 8 and 16 ( P < .05 for all). Biomechanically, the LIPUS + ASCs group showed significantly higher failure load and stiffness versus the other groups at postoperative weeks 8 and 16 ( P < .05 for all).

CONCLUSION

Autologous ASC transplantation stimulated with LIPUS can result in superior B-T healing quality when compared with LIPUS or ASCs alone.

CLINICAL RELEVANCE

This study demonstrates the effectiveness of using ASC transplantation stimulated with LIPUS for B-T healing and provides a foundation for future clinical studies.

Micro-scale assessment of the postoperative effect of anterior cruciate ligament reconstruction preclinical study using a 7.1T micro-magnetic resonance imaging

High-field micro-magnetic resonance imaging (MRI) scanning may provide additional information for quantitative analysis of graft bone healing processes, thus serving as a promising supplementary method in graft and bone healing evaluation following anterior cruciate ligament reconstruction (ACLR) surgery during preclinical studies. The present study included 12 New Zealand white rabbits that underwent ACLR with polyethylene terephthalate (PET) ligament. At 4, 8, and 16 weeks following surgery, 4 rabbits were euthanized and knee joint samples were harvested for a 7.1T micro-magnetic resonance imaging (MRI) scan. The graft bone tunnel diameter and signal noise ratio (SNR) at the region of interest (ROI) were measured. Hematoxylin-eosin staining was performed at each time point to verify the graft bone healing process in histology. The bone tunnel diameter at the graft tunnel interface decreased over time in both femoral and tibial parts. Notably, the tunnel size was smaller than the diameter of the drilling Kirschner wire that was used to observe the femoral part and proximal site of the tibial part at 16 weeks following surgery. SNR research demonstrated that both the femoral and tibial part PET ligaments selected in the ROI exhibited a marked increase in SNR from the initial 4-week results. The micro-MRI result was consistent with that of histological analysis. Micro-MRI scanning was applied in an animal model that underwent ACL reconstruction surgery with PET ligament, and it was determined that micro-MRI is promising in quantitatively observing graft bone healing processes directly with a focus on graft tunnel distances and SNRs.

Effect of stress on corrosion of high-purity magnesium in vitro and in vivo

Magnesium-based implants are subjected to complicated stresses during implantation in the human body. The stress effects on corrosion of magnesium (Mg) in vitro were investigated in previous studies, whereas in this study, the corrosion behaviors of high-purity (HP) Mg under stress were comparatively studied in vitro in Hank's solution and in vivo in the subcutaneous environment of rats. Loading devices were designed to apply compressive stress (15.1 ± 0.5 MPa) and tensile stress (13.2 ± 0.2 MPa) on HP Mg specimens both in vitro and in vivo. Corrosion rates of HP Mg were characterized by mass and volume losses. It was shown that the applied compressive stress had no effect on in vitro corrosion behaviors and the applied tensile stress accelerated the in vitro corrosion, thereby causing severe pitting corrosions and stress corrosion cracking (SCC). However, there was no significant change for corrosion behaviors in vivo under neither compressive stress nor tensile stress. Severe pitting corrosion and SCC did not occur in vivo. Histological evaluation revealed that a fibrotic capsule induced by foreign body reaction was formed on the corrosion surfaces of HP Mg in the subcutaneous environment. It was proposed that the fibrotic capsule suppressed the effects of stress in vivo by protecting the corrosion surfaces. These results provided new insights into understanding the stress effects on the corrosion of Mg both in vitro and in vivo. STATEMENT OF SIGNIFICANCE: Mg and its alloys have shown potential as biodegradable metallic materials. During implantation, Mg is subjected to various mechanical environments in the human body. It is necessary to have a clear understanding of different effects of stress on Mg corrosion. However, few studies were performed in vivo. It is important to analyze the effect of quantitative stress on Mg corrosion in vivo. Therefore, in this study, quantitative stresses were applied on Mg both in vitro and in vivo. The effects of stress on in vitro and in vivo corrosions of Mg were investigated and compared.

Intercondylar eminence fracture treated by resorbable magnesium screws osteosynthesis: A case series

INTRODUCTION

Tibial spine avulsion fractures are mostly a paediatric injury which appropriate treatment is currently debated in literature. The choice between conservative and surgical treatment is based on the radiographic classification of Meyers-McKeever. The most diffused surgical techniques involve either internal fixation devices (screws) or bone tunnels fixation with resorbable sutures. Today, a third option is represented by resorbable magnesium screws which could combine the best features of the two classical systems. Objective of this study is to investigate the efficacy of these new devices in the surgical treatment of tibial spine avulsions.

MATERIALS AND METHODS

Since 2014 we have seen seven patients with tibial eminence fracture. Patients underwent clinical and radiological examination (MRI, CT scan) before surgery. Only 3 patients that presented with a grade III or IV lesion were treated surgically with internal fixation with magnesium resorbable screws. In post-operative follow-up, functional recovery was evaluated at 1, 2, 4, 6 and 12 months, clinically and by X-ray. Lysholm and IKDC scores were submitted at 1, 2, 6 and 12 months. MRI was repeated at 6 and 12 months.

RESULTS

All three surgical patients showed progressive clinical and functional improvement during the follow-up period. The first case showed a quicker overall recovery rate, which might be due to the lower grade of the lesion. Radiographs and MRI evaluation showed regular healing of the injury. The devices appeared completely resorbed at the 6 months follow-up and replaced by newly formed bone at the 12 months follow-up.

CONCLUSIONS

The treatment of tibial spine avulsion fractures with arthroscopic reduction and internal fixation (ARIF) technique by magnesium resorbable screws seems to result in an excellent functional recovery without complications related to fixation devices, which were completely resorbed after 6 months and replaced by newly formed bone after 12 months. This new method could be considered as an alternative option to classic techniques by non resorbable fixation devices or bone tunnel fixation. Further studies are needed in order to evaluate the efficacy of these new devices in a wider group of patients.

Evaluation of the internal fixation effect of nano-calcium-deficient hydroxyapatite/poly-amino acid composite screws for intraarticular fractures in rabbits

Objective

To evaluate the internal fixation effect of nano-calcium-deficient hydroxyapatite/poly-amino acid (n-CDHA/PAA) composite screws in the intraarticular fracture model.

Materials and methods

A total of 35 New Zealand White rabbits were used in a bilateral femoral intercondylar fracture model and randomly divided into two groups. n-CDHA/PAA screws were used in the experimental group, and medical metal screws were used in the control group. The fracture condition, range of motion, and the screw push-out strength were assessed, and an arthroscopic examination of knee joint was performed at 4, 8, and 12 weeks after surgery. The biodegradation of the n-CDHA/PAA screws in vivo was tested through weighing, and changes in screw structure were assessed by X-ray diffraction at 12 weeks after surgery.

Results

The general situation of all animals was good and showed no incision infection and dehiscence after surgery. X-ray scanning showed that significant callus growth was present in both groups at 4 weeks after surgery, and there was no significant difference (P>0.05) in the Lane-Sandhu score between the experimental and control groups at all time points after surgery. There were no statistically significant differences (P>0.05) in the range of motion and Oswestry Arthroscopy Score of arthroscopic examination of the knee joints between the two groups. The screw push-out strength of the control group was stronger than that of the experimental group at 4 weeks after surgery (P<0.05), but after that, there was no significant difference between the groups (P>0.05). The degradation tests showed that the n-CDHA/PAA screws degraded gradually after implantation, and the weight loss rate was approximately 16% at 12 weeks after surgery. The X-ray diffraction results showed that the crystal structure of the outer surface of the n-CDHA/PAA screw has changed at 12 weeks after surgery.

Conclusion

The n-CDHA/PAA screw is an effective and safe implant as a potential internal fixation device for an intercondylar fracture of the femur, and its internal fixation effect was similar to that of medical metal screw.

Special Biodegradable Fixation Device for Anterior Cruciate Ligament Reconstruction-Safety and Efficacy in a Beagle Model

This study aimed to evaluate the safety and efficacy of the special WE43 magnesium alloy stretch plates (SPs) used as fixation device for anterior cruciate ligament (ACL) reconstruction in a beagle model. Eleven beagle dogs underwent ACL reconstruction using WE43 SPs to fix the ligament grafts with the femoral ends, whereas titanium interferences were employed in the tibia ends. Load-to-failure tests were conducted to evaluate the mechanical properties. A comprehensive set of histological observations was performed to observe the local tissue response and assess the status of the attachment between the bone tissue and ligament grafts. Microcomputed tomography and scanning electron microscopy in conjunction with energy spectrum analysis were conducted to evaluate the degradation rate in vivo and investigate the morphology of the cross-section of the SPs and the element distribution in vivo. Immersion tests were employed to investigate the corrosion properties in vitro. The special WE43 SPs showed not only good mechanical strength but also a suitable degradation rate in vivo. The results indicated the special WE43 SP could be considered as a novel fixation device for ACL reconstruction.

Hybrid fracture fixation systems developed for orthopaedic applications: A general review

Orthopaedic implants are applied daily in our orthopaedic clinics for treatment of musculoskeletal injuries, especially for bone fracture fixation. To realise the multiple functions of orthopaedic implants, hybrid system that contains several different materials or parts have also been designed for application, such as prosthesis for total hip arthroplasty. Fixation of osteoporotic fracture is challenging as the current metal implants made of stainless steel or titanium that are rather rigid and bioinert, which are not favourable for enhancing fracture healing and subsequent remodelling. Magnesium (Mg) and its alloys are reported to possess good biocompatibility, biodegradability and osteopromotive effects during its in vivo degradation and now tested as a new generation of degradable metallic biomaterials. Several recent clinical studies reported the Mg-based screws for bone fixation, although the history of testing Mg as fixation implant was documented more than 100 years ago. Truthfully, Mg has its limitations as fixation implant, especially when applied at load-bearing sites because of rather rapid degradation. Currently developed Mg-based implants have only been designed for application at less or non-loading-bearing skeletal site(s). Therefore, after years research and development, the authors propose an innovative hybrid fixation system with parts composed of Mg and titanium or stainless steel to maximise the biological benefits of Mg; titanium or stainless steel in this hybrid system can provide enough mechanical support for fractures at load-bearing site(s) while Mg promotes the fracture healing through novel mechanisms during its degradation, especially in patients with osteoporosis and other metabolic disorders that are unfavourable conditions for fracture healing. This hybrid fixation strategy is designed to effectively enhance the osteoporotic fracture healing and may potentially also reduce the refracture rate. The translational potential of this article: This article systemically reviewed the combination utility of different metallic implants in orthopaedic applications. It will do great contribution to the further development of internal orthopaedic implants for fracture fixation. Meanwhile, it also introduced a titanium-magnesium hybrid fixation system as an alternative fixation strategy, especially for osteoporotic patients.

An innovative Mg/Ti hybrid fixation system developed for fracture fixation and healing enhancement at load-bearing skeletal site

Magnesium (Mg) is a potential biomaterial suitable for developing biodegradable orthopaedic implants, especially as internal fixators for fracture fixation at non-load bearing skeletal sites. However, Mg alone cannot provide sufficient mechanical support for stable fracture fixation at load bearing sites due to its rapid degradation in the early stage after implantation. In consideration of the strengths and weaknesses of Mg, we developed an innovative magnesium/titanium (Mg/Ti) hybrid fixation system for long bone fracture fixation and investigated the fixation efficacy. The finite element analysis (FEA) results indicated that the Mg/Ti hybrid fixation system provided sufficient mechanical support for fracture fixation at load-bearing skeletal site. As a proof-of-concept, we performed a "Z-shaped" open osteotomy at the mid-shaft of rabbit tibia. For comparison, the animals were divided into two groups: Mg/Ti group (fixated with Mg screws and Ti fixators) and Ti control group (fixated with Ti screws and Ti fixators). The radiographic, four-point bending mechanical test, histological and histomorphometric analysis were postoperatively performed in a temporal manner up to 12 weeks. Both X-ray and micro-CT images of the Mg/Ti group showed a larger callus (14.7% at 3rd week and 24.8% at 6th week, n = 5-7, p < 0.05) in the regions of interest (ROIs) over time, especially at the opposite cortex of the fixation plate. At the 12th week post-operation, the biomechanical test result indicated that the rabbit tibia in the Mg/Ti group healed better and the overall mechanical strength was approximately 3-fold higher (n = 8, p < 0.05) than that at 6th week. Furthermore, the FEA revealed that the Mg/Ti group had a higher mechanical strength (19.5% at week 6 and 31.5% at week 12) at the specified ROI and resulted in an earlier and faster endochondral ossification (68.0% at week 3 and 71.4% at week 6) with a higher expression of osteocalcin (54.0%) and collagen I (34.2%) than the Ti control group (n = 4, p < 0.05). Further evaluation suggested that a higher expression of calcitonin gene-related peptide (CGRP), a known osteogenic neuron peptide, in the fracture callus of the Mg/Ti group might be a major underlying mechanism of enhanced fracture healing attributed to the release of Mg ions during the degradation of Mg screws.

The "Magnesium Sacrifice" Strategy Enables PMMA Bone Cement Partial Biodegradability and Osseointegration Potential

Poly (methyl methacrylate) (PMMA)-based bone cements are the most commonly used injectable orthopedic materials due to their excellent injectability and mechanical properties. However, their poor biocompatibility and excessive stiffness may cause complications such as aseptic implant loosening and stress shielding. In this study, we aimed to develop a new type of partially biodegradable composite bone cement by incorporating magnesium (Mg) microspheres, known as "Mg sacrifices" (MgSs), in the PMMA matrix. Being sensitive to the physiological environment, the MgSs in PMMA could gradually degrade to produce bioactive Mg ions and, meanwhile, result in an interconnected macroporous structure within the cement matrix. The mechanical properties, solidification, and biocompatibility, both in vitro and in vivo, of PMMA⁻Mg bone cement were characterized. Interestingly, the incorporation of Mg microspheres did not markedly affect the mechanical strength of bone cement. However, the maximum temperature upon setting of bone cement decreased. This partially biodegradable composite bone cement showed good biocompatibility in vitro. In the in vivo study, considerable bony ingrowth occurred in the pores upon MgS degradation. Together, the findings from this study indicate that such partially biodegradable PMMA⁻Mg composite may be ideal bone cement for minimally invasive orthopedic surgeries such as vertebroplasty and kyphoplasty.

The effect of femoral bone tunnel configuration on tendon-bone healing in an anterior cruciate ligament reconstruction: An animal study

Objectives

To compare the effect of femoral bone tunnel configuration on tendon-bone healing in an anterior cruciate ligament (ACL) reconstruction animal model.

Methods

Anterior cruciate ligament reconstruction using the plantaris tendon as graft material was performed on both knees of 24 rabbits (48 knees) to mimic ACL reconstruction by two different suspensory fixation devices for graft fixation. For the adjustable fixation device model (Socket group; group S), a 5 mm deep socket was created in the lateral femoral condyle (LFC) of the right knee. For the fixed-loop model (Tunnel group; group T), a femoral tunnel penetrating the LFC was created in the left knee. Animals were sacrificed at four and eight weeks after surgery for histological evaluation and biomechanical testing.

Results

Histologically, both groups showed a mixture of direct and indirect healing patterns at four weeks, whereas only indirect healing patterns were observed in both groups at eight weeks. No significant histological differences were seen between the two groups at four and eight weeks in the roof zone (four weeks, S: mean 4.8 sd 1.7, T: mean 4.5 sd 0.5, p = 0.14; eight weeks, S: mean 5.8 sd 0.8, T: mean 4.8 sd 1.8, p = 0.88, Mann-Whitney U test) or side zone (four weeks, S: mean 5.0 sd 1.2, T: mean 4.8 sd 0.4, p = 0.43; eight weeks, S: mean 5.3 sd 0.8,T: mean 5.5 sd 0.8, p = 0.61, Mann-Whitney U test) . Similarly, no significant difference was seen in the maximum failure load between group S and group T at four (15.6 sd 9.0N and 13.1 sd 5.6N) or eight weeks (12.6 sd 3.6N and 17.1 sd 6.4N, respectively).

Conclusion

Regardless of bone tunnel configuration, tendon-bone healing after ACL reconstruction primarily occurred through indirect healing. No significant histological or mechanical differences were observed between adjustable and fixed-loop femoral cortical suspension methods.

Cite this article: Y. Sato, R. Akagi, Y. Akatsu, Y. Matsuura, S. Takahashi, S. Yamaguchi, T. Enomoto, R. Nakagawa, H. Hoshi, T. Sasaki, S. Kimura, Y. Ogawa, A. Sadamasu, S. Ohtori, T. Sasho. The effect of femoral bone tunnel configuration on tendon-bone healing in an anterior cruciate ligament reconstruction: An animal study. Bone Joint Res 2018;7:327–335. DOI: 10.1302/2046-3758.75.BJR-2017-0238.R2.

In vivo quantification of hydrogen gas concentration in bone marrow surrounding magnesium fracture fixation hardware using an electrochemical hydrogen gas sensor

Magnesium (Mg) medical devices are currently being marketed for orthopedic applications and have a complex degradation process which includes the evolution of hydrogen gas (H₂). The effect of H₂ exposure on relevant cell types has not been studied; and the concentration surrounding degrading Mg devices has not been quantified to enable such mechanistic studies. A simple and effective method to measure the concentration of H₂ in varying microenvironments surrounding Mg implants is the first step to understanding the biological impact of H₂ on these cells. Here, the in vivo measurement of H₂ surrounding fracture fixation devices implanted in vivo is demonstrated. An electrochemical H₂ microsensor detected increased levels of H₂ at three anatomical sites with a response time of about 30 s. The sensor showed the H₂ concentration in the bone marrow at 1 week post-implantation (1460 ± 320 µM) to be much higher than measured in the subcutaneous tissue (550 ± 210 µM) and at the skin surface (120 ± 50 µM). Additionally, the H₂ concentrations measured in the bone marrow exceeded the concentration in a H₂ saturated water solution (∼800 µM). These results suggest that H₂ emanating from Mg implants in bone during degradation pass through the bone marrow and become at least partially trapped because of slow permeation through the bone. This study is the first to identify H₂ concentrations in the bone marrow environment and will enable in vitro experiments to be executed at clinically relevant H₂ concentrations to explore possible biological effects of H₂ exposure.

STATEMENT OF SIGNIFICANCE

An electrochemical H₂ sensor was used to monitor the degradation of a Mg fracture fixation system in a lapine ulna fracture model. Interestingly, the H₂ concentration in the bone marrow is 82% higher than H₂ saturated water solution. This suggests H₂ generated in situ is trapped in the bone marrow and bone is less permeable than the surrounding tissues. The detectable H₂ at the rabbit skin also demonstrates a H₂ sensor's ability to monitor the degradation process under thin layers of tissue. H₂ sensing shows promise as a tool for monitoring the degradation of Mg alloy in vivo and creating in vitro test beds to more mechanistically evaluate the effects of varying H₂ concentrations on cell types relevant to osteogenesis.

Electrospun Heparin-Loaded Core-Shell Nanofiber Sutures for Achilles Tendon Regeneration In Vivo

Achilles tendon reconstruction surgery is the primary clinical method for repairing acute Achilles tendon ruptures. However, the efficacy of the postoperative healing process and the recovery of physiological function are inadequate. This study examines the healing mechanism of ruptured rat Achilles tendons seamed with heparin-loaded core-shell fiber sutures fabricated via near-field electrospinning. High-heparin-concentration sutures (PPH3.0) perform better than the low-heparin-concentration sutures and commercial sutures (CSs). The PPH3.0 suture recruits fewer inflammatory cells and shows good histocompatibility in peritoneal implantation experiments. Staining of the Achilles tendon rupture repair zone demonstrates that a high heparin concentration in sutures reduces immune-inflammatory responses. Immunohistochemical analysis reveals that the transforming growth factor-β staining scores of the PPH3.0 sutures are not significantly different from those of the corresponding control group but are significantly different from those of the CSs and non-heparin-loaded-suture groups. According to vascular endothelial growth factor (VEGF) analysis, the concentration of VEGF in the group treated with the PPH3.0 suture increases by 37.5% compared with that in its control group. No significant difference in tension strength is observed between the PPH3.0 group and healthy Achilles tendons. These findings illustrate that this novel method effectively treats Achilles tendon rupture and promotes healing and regeneration.

Magnesium enhances the chondrogenic differentiation of mesenchymal stem cells by inhibiting activated macrophage-induced inflammation

Magnesium deficiency increases the generation of pro-inflammatory cytokines, which is consistently accompanied by the sensitization of cells such as neutrophils, macrophages and endothelial cells. We investigated the potential of magnesium to regulate macrophage polarization and macrophage-induced inflammation with or without lipopolysaccharide (LPS) and interferon-γ (IFN-γ) activation and further elucidated whether these effects impact the inhibitory functions of activated macrophage-induced inflammation on cartilage regeneration. The results showed that magnesium inhibited the activation of macrophages, as indicated by a significant reduction in the percentage of CCR7-positive cells, while the percentage of CD206-positive cells decreased to a lesser degree. After activation, both pro-inflammatory and anti-inflammatory cytokines were down-regulated at the mRNA level and certain cytokines (IL-1β, IL-6 and IL-10) were decreased in the cell supernatant with the addition of magnesium. Moreover, magnesium decreased the nuclear translocation and phosphorylation of nuclear factor-κB (NF-κB) to impede its activation. A modified micromass culture system was applied to assess the effects of activated macrophage-conditioned medium with or without magnesium treatment on the chondrogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs). Magnesium enhanced the chondrogenic differentiation of hBMSCs by reversing the adverse effects of activated macrophage-induced inflammation.

Magnesium (Mg) based interference screws developed for promoting tendon graft incorporation in bone tunnel in rabbits

How to enhance tendon graft incorporation into bone tunnels for achieving satisfactory healing outcomes in patients with anterior cruciate ligament reconstruction (ACLR) is one of the most challenging clinical problems in orthopaedic sports medicine. Several studies have recently reported the beneficial effects of Mg implants in bone fracture healing, indicating the use potential of Mg devices in promoting the tendon graft osteointegration. Here, we developed an innovative Mg-based interference screws for fixation of the tendon graft in rabbits underwent ACLR and investigated the biological role of Mg-based implants in the graft healing. The titanium (Ti) interference screw was used as the control. We demonstrated that Mg interference screw significantly accelerated the incorporation of the tendon graft into bone tunnels via multiscale analytical methods including scanning electronic microscopy/energy dispersive spectrometer (SEM/EDS), micro-hardness, micro-Fourier transform infrared spectroscopy (μFTIR), and histology. Our in vivo study showed that Mg implants enhanced the recruitment of bone marrow stromal stem cells (BMSCs) towards peri-implant bone tissue, which may be ascribed to the upregulation of local TGF-β1 and PDGF-BB. Besides, the in vitro study revealed that higher Mg ions was beneficial to the improvement of capability in cell adhesion and osteogenic differentiation of BMSCs. Thus, the enhancement in cell migration, cell adhesion and osteogenic differentiation of BMSCs may contribute to an improved tendon graft osteointegration in the Mg group. Our findings in this work may further facilitate clinical applications of Mg-based interference screws for enhancing tendon graft-bone junction healing in patients indicated for ACLR.

STATEMENT OF SIGNIFICANCE

How to promote tendon-bone junction healing is one of the major challenging issues for satisfactory clinical outcomes in patients after ACL reconstruction. The improvement of bony ingrowth into the tendon graft-bone interface can enhance the tendon graft osteointegration. In this study, we applied Mg based interference screws to fix the tendon graft in rabbits and found the use of Mg screws could accelerate and significantly increase mineralized matrix formation at the tendon-bone interface in animals when compared to those with Ti screws. We elucidated the mechanism behind the favorable effects of Mg screws on the graft healing in both in vitro and in vivo studies from multiscale technologies. The optimized interface structure and function in Mg group may be ascribed to the improved cell migration capability, enhanced cell adhesion strength and promoted osteogenic differentiation ability of BMSCs under the stimuli of Mg ions degraded from implanted Mg screws. Our findings may help us broaden our thinking in the application potential of Mg interference screws in future clinical trials.

[Effect of injectable composites of calcium sulfate and hyaluronate in enhancing osteogenesis]

Objective

To fabricate an injectable composite bone substitute with hyaluronic acid (HA) and calcium sulfate and to evaluate the biocompatibility and effect of the composite on cell proliferation, osteogenic differentiation in vitro and osteogenic capability in vivo.

Methods

Calcium sulfate powder was mixed with HA solution, cross-linked HA solution, and phosphate buffer solution (PBS) in a ratio of 2∶1 ( W/ V) to get composites of CA+HA, CA+HAC, and CA. The standard extracts from above 3 materials were prepared according to ISO10993-5, and were used to culture mouse MC3T3-E1 cells. The composite biocompatibility and cell proliferation in different concentrations of extract were tested with cell counting kit-8 (CCK-8). The cells were cultured with standard medium as a control. The optimal concentration was selected for osteogenic differentiation test, and ELISA Kit was used to determine the alkaline phosphatase (ALP), collagen type I (COL-I), and osteocalcin (OCN). The femoral condylar bone defect was made on New Zealand white rabbits and repaired with CA+HA, CA+HAC, and CA. Micro-CT was done to evaluate new bone formation with bone volume/tissue volume (BV/TV) ratio at 6 and 12 weeks. HE staining was used to observe bone formation.

Results

CA+HA and CA+HAC were better in injectability and stability in PBS than CA. The biocompatibility test showed that absorbance ( A) value of CA group was significantly lower than that of control group ( P<0.05) at 6, 12, and 24 hours after culture, but no significant difference was found in A values between CA+HA group or CA+HAC group and control group ( P>0.05). The proliferation test showed 25% and 50% extract of all 3 materials had significantly higher A value than control group ( P<0.05). For 75% and 100% extract, only CA+HA group had significantly higher A value than control group ( P<0.05). And 50% extract was selected for osteogenic differentiation test. At 14 and 21 days, ALP, COL-I and OCN concentrations of CA+HA group and CA+HAC group were significantly higher than those of CA group and control group ( P<0.05). Micro-CT results showed higher BV/TV in CA+HA group and CA+HAC group than CA group at 6 and 12 weeks ( P<0.05), but no significant difference was found between CA+HA group and CA+HAC group ( P>0.05). HE staining revealed that a little bone tissue was seen in CA+HA group and CA+HAC group, but there was no bone formation in CA group at 6 weeks; more streak bone tissue in CA+HA group and CA+HAC group than CA group at 12 weeks.

Conclusion

Composites prepared with calcium sulfate and HA or with cross-linked HA are stable, injectable, and biocompatible. The materials have excellent effect on proliferation and differentiation of mouse MC3T3-E1 cells. They also show good osteogenic capability in vivo. So it is a potential bone substitutes for bone defective diseases.

Synergistic effects of fibronectin and bone morphogenetic protein on the bioactivity of titanium metal

To improve the biological properties of bioactive titanium metal, recombinant human bone morphogenetic protein 2(rhBMP-2) and fibronectin (Fn) were adsorbed on its surface solely or contiguously to modify the anodic oxidized titanium (AO-Ti), acid-alkali-treated titanium (AA-Ti), and polished titanium (P-Ti). It is found that the different bioactive titanium surface structures had great influence on protein adsorption. The adsorption amounts of BMP adsorbed solely and Fn/BMP adsorbed contiguously were AA-Ti > P-Ti > AO-Ti, and that for Fn adsorbed solely was AA-Ti ≈ P-Ti > AO-Ti. The conformation of proteins was changed remarkably after the adsorption. For BMP, the α-helix decreased on AA-Ti and stabilized on P-Ti and AO-Ti. For Fn, the β-sheet on PT-Ti and AA-Ti increased significantly. For Fn/BMP, the percentage of β-sheet on AA-Ti increased, and that of α-helix on all samples was stable. MSCs showed greater adhesion and spreading on Fn/BMP groups. MTT and Elisa tests showed that the synergistic effects of proteins made the cells proliferate and differentiate faster. It indicated both the surface structure and the synergistic effects of proteins could influence the biological properties of titanium metals. It provides research foundation for improving the biological properties of bioactive titanium metals by simultaneous application of several proteins. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2485-2498, 2017.

An osteogenesis/angiogenesis-stimulation artificial ligament for anterior cruciate ligament reconstruction

To solve the poor healing of polyethylene terephthalate (PET) artificial ligament in bone tunnel, copper-containing bioactive glass (Cu-BG) nanocoatings on PET artificial ligaments were successfully prepared by pulsed laser deposition (PLD). It was hypothesized that Cu-BG coated PET (Cu-BG/PET) grafts could enhance the in vitro osteogenic and angiogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) and in vivo graft-bone healing after anterior cruciate ligament (ACL) reconstruction in a goat model. Scanning electron microscope and EDS mapping analysis revealed that the prepared nanocoatings had uniform element distribution (Cu, Ca, Si and P) and nanostructure. The surface hydrophilicity of PET grafts was significantly improved after depositing Cu-BG nanocoatings. The in vitro study displayed that the Cu-BG/PET grafts supported the attachment and proliferation of rBMSCs, and significantly promoted the expression of HIF-1α gene, which up-regulated the osteogenesis-related genes (S100A10, BMP2, OCN) and angiogenesis-related genes (VEGF) in comparison with PET or BG coated PET (BG/PET) grafts which do not contain Cu element. Meanwhile, Cu-BG/PET grafts promoted the bone regeneration at the graft-host bone interface and decreased graft-bone interface width, thus enhancing the bonding strength as well as angiogenesis (as indicated by CD31 expression) in the goat model as compared with BG/PET and pure PET grafts. The study demonstrates that the Cu-containing biomaterials significantly promote osteogenesis and angiogenesis in the repair of bone defects of large animals and thus offering a promising method for ACL reconstruction by using Cu-containing nanobioglass modified PET grafts.

STATEMENT OF SIGNIFICANCE

It remains a significant challenge to develop an artificial graft with distinct osteogenetic/angiogenetic activity to enhance graft-bone healing for ligament reconstruction. To solve these problems, copper-containing bioactive glass (Cu-BG) nanocoatings on PET artificial ligaments were successfully prepared by pulsed laser deposition (PLD). It was found that the prepared Cu-BG/PET grafts significantly stimulated the proliferation and osteogenic/angiogenic differentiation of bone marrow stromal cells (BMSCs) through activating HIF-1α/S100A10/Ca²⁺ signal pathway. The most important is that the in vivo bone-forming ability of Cu-containing biomaterials was, for the first time, elucidated in a large animal model, revealing the enhanced capacity of osteogenesis and angiogenesis with incorporation of bioactive Cu element. It is suggested that the copper-containing biomaterials significantly promote osteogenesis and angiogenesis in large animal defects and thus offering a promising method for ACL reconstruction by using Cu-containing nanobioglass modification of PET grafts, paving the way to apply Cu-containing biomaterials for tissue engineering and regenerative medicine.

Ag-loaded MgSrFe-layered double hydroxide/chitosan composite scaffold with enhanced osteogenic and antibacterial property for bone engineering tissue

Bone tissue engineering scaffolds for the reconstruction of large bone defects should simultaneously promote osteogenic differentiation and avoid postoperative infection. Herein, we develop, for the first time, Ag-loaded MgSrFe-layered double hydroxide/chitosan (Ag-MgSrFe/CS) composite scaffold. This scaffold exhibits three-dimensional interconnected macroporous structure with a pore size of 100-300 μm. The layered double hydroxide nanoplates in the Ag-MgSrFe/CS show lateral sizes of 200-400 nm and thicknesses of ∼50 nm, and the Ag nanoparticles with particle sizes of ∼20 nm are uniformly dispersed on the scaffold surfaces. Human bone marrow-derived mesenchymal stem cells (hBMSCs) present good adhesion, spreading, and proliferation on the Ag-MgSrFe/CS composite scaffold, suggesting that the Ag and Sr elements in the composite scaffold have no toxicity to hBMSCs. When compared with MgFe/CS composite scaffold, the Ag-MgSrFe/CS composite scaffold has better osteogenic property. The released Sr²⁺ ions from the composite scaffold enhance the alkaline phosphatase activity of hBMSCs, promote the extracellular matrix mineralization, and increase the expression levels of osteogenic-related RUNX2 and BMP-2. Moreover, the Ag-MgSrFe/CS composite scaffold possesses good antibacterial property because the Ag nanoparticles in the composite scaffold effectively prevent biofilm formation against S. aureus. Hence, the Ag-MgSrFe/CS composite scaffold with excellent osteoinductivity and antibacterial property has a great potential for bone tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 863-873, 2018.

In vivo and in vitro assessment of the biocompatibility and degradation of high-purity Mg anastomotic staples

Titanium (Ti) staples are not biodegradable, and anastomotic complications related to Ti staples are reported frequently. In the present study, the biocompatibility and degradation behavior of high-purity magnesium (HP Mg) staples with the small intestine were investigated. HP Mg staples did not affect the relative growth rate, cell cycle and apoptosis of primary rectal mucosal epithelial cells (IEC-6) in vitro. At one, two and three days after immersion in intestinal juice, the weight of the 30 rinsed HP Mg staples reduced by 7.5 ± 1.6, 10.6 ± 2.2 and 13.5 ± 2.1 mg, respectively, and those in the Hanks' solution reduced by 3.9 ± 0.8, 6.1 ± 1.2 and 7.1 ± 2.4 mg. Extracts of HP Mg staples were bio-safe for IEC-6, and the corrosion rate of HP staples was faster in the small intestinal juice than in the Hanks' solution. In the in vivo experiments, the small intestine of the minipigs was anastomosed by HP Mg and Ti staples. HP Mg staples neither affected important bio-chemical parameters nor induced serious inflammation or necrosis in the anastomosis tissues. The residual weight of a HP Mg staples (0.81 ± 0.13 mg) was 89.7% of the original weight (9 ± 0.09 mg) one month after surgery. The in vivo corrosion rate for one HP Mg staple was determined to be∼0.007 ± 0.001 mm·month^-1. The preliminary results of the biocompatibility and degradation of high-purity Mg anastomotic staples are promising, and further studies will be initiated to study in more detail.

Nanoreinforced Hydrogels for Tissue Engineering: Biomaterials that are Compatible with Load-Bearing and Electroactive Tissues

Given their highly porous nature and excellent water retention, hydrogel-based biomaterials can mimic critical properties of the native cellular environment. However, their potential to emulate the electromechanical milieu of native tissues or conform well with the curved topology of human organs needs to be further explored to address a broad range of physiological demands of the body. In this regard, the incorporation of nanomaterials within hydrogels has shown great promise, as a simple one-step approach, to generate multifunctional scaffolds with previously unattainable biological, mechanical, and electrical properties. Here, recent advances in the fabrication and application of nanocomposite hydrogels in tissue engineering applications are described, with specific attention toward skeletal and electroactive tissues, such as cardiac, nerve, bone, cartilage, and skeletal muscle. Additionally, some potential uses of nanoreinforced hydrogels within the emerging disciplines of cyborganics, bionics, and soft biorobotics are highlighted.

Magnesium-based implants: Beyond fixators

The mystery behind magnesium-induced bone formation is revealed by linking the neuropeptide(s) from sensory nerves with the osteogenic differentiation of stem cells in the periosteum. Zhang and colleagues' study sheds light on the development of magnesium pills or calcitonin gene-related peptide-delivery system for the prevention or treatment of osteoporosis.

The translational potential of this article

For the first time, magnesium is shown to be beneficial for fracture healing at the weight-bearing site. In addition, calcitonin gene-related peptide-delivery system will also be another translational direction, as the promotive role of calcitonin gene-related peptide in fracture healing is supportive. These cost-effective and innovative treatment approaches will definitely bring a reduction not only in the suffering of patients, but also in the economic burden for their families and our society.

Biodegradable Magnesium Screws Accelerate Fibrous Tissue Mineralization at the Tendon-Bone Insertion in Anterior Cruciate Ligament Reconstruction Model of Rabbit

The incorporation of tendon graft into bone tunnel is one of the most challenging clinical issues in anterior cruciate ligament (ACL) reconstruction. As a biodegradable metal, Mg has appropriate mechanical strength and osteoinductive effects, thus may be a promising alternative to commercialized products used for graft fixation. Therefore, it was hypothesized that Mg based interference screws would promote tendon graft-bone junction healing when compared to Ti screws. Herein, we compared the effects of Mg and Ti screws on tendon graft healing in rabbits with ACL reconstruction via histological, HR-pQCT and mechanical analysis. The histological results indicated that Mg screws significantly improved the graft healing quality via promoting mineralization at the tendon graft enthesis. Besides, Mg screws significantly promoted bone formation in the peri-screw region at the early healing stage. Importantly, Mg screws exhibited excellent corrosion resistance and the degradation of Mg screws did not induce bone tunnel widening. In tensile testing, there were no significant differences in the load to failure, stress, stiffness and absorption energy between Mg and Ti groups due to the failure mode at the midsubstance. Our findings demonstrate that Mg screws can promote tendon graft healing after ACL reconstruction, implying a potential alternative to Ti screws for clinical applications.

Current status on clinical applications of magnesium-based orthopaedic implants: A review from clinical translational perspective

As a new generation of medical metallic material, magnesium (Mg) and its alloys with or without surface coating have attracted a great deal of attention due to its biodegradability and potential for avoiding a removal operation after the implant has fulfilled its function for surgical fixation of injured musculoskeletal tissues. Although a few clinical cases on Mg-based orthopaedic implants were reported more than a century ago, it was not until recently that clinical trials using these implants with improved physicochemical properties were carried out in Germany, China and Korea for bone fracture fixation. The promising results so far suggest a bright future for biodegradable Mg-based orthopaedic implants and would warrant large scale phase II/III studies. Given the increasing interest on this emerging biomaterials and intense effort to improve its properties for various clinical applications, this review covers the evolution, current strategies, and future perspectives in the development of Mg-based orthopaedic implants. We also highlight a few clinical cases performed in China that may be unfamiliar to the general orthopaedic community.

Research of a novel biodegradable surgical staple made of high purity magnesium

Surgical staples made of pure titanium and titanium alloys are widely used in gastrointestinal anastomosis. However the Ti staple cannot be absorbed in human body and produce artifacts on computed tomography (CT) and other imaging examination, and cause the risk of incorrect diagnosis. The bioabsorbable staple made from polymers that can degrade in human body environment, is an alternative. In the present study, biodegradable high purity magnesium staples were developed for gastric anastomosis. U-shape staples with two different interior angles, namely original 90° and modified 100°, were designed. Finite element analysis (FEA) showed that the residual stress concentrated on the arc part when the original staple was closed to B-shape, while it concentrated on the feet for the modified staple after closure. The in vitro tests indicated that the arc part of the original staple ruptured firstly after 7 days immersion, whereas the modified one kept intact, demonstrating residual stress greatly affected the corrosion behavior of the HP-Mg staples. The in vivo implantation showed good biocompatibility of the modified Mg staples, without inflammatory reaction 9 weeks post-operation. The Mg staples kept good closure to the Anastomosis, no leaking and bleeding were found, and the staples exhibited no fracture or severe corrosion cracks during the degradation.

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A modified structure with about 100° interior angle of U-shape was selected by using FEA.

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In vitro immersion experiment showed homogeneous corrosion behavior of the modified HP-Mg surgical staple.

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In vivo implantation suggested that the modified HP-Mg surgical staple had enough closure strength and good biocompatibility.

Biomechanical comparison of pure magnesium interference screw and polylactic acid polymer interference screw in anterior cruciate ligament reconstruction-A cadaveric experimental study

Background

Polylactic acid polymer interference screws are commonly used in anterior cruciate ligament (ACL) reconstructions, especially in proximal tibia fixation. However, several concerns have been raised, including the acid products during its degradation in vivo. In recent years, biodegradable magnesium (Mg)-based implants have become attractive because of their favourable mechanical properties, which are more similar to those of natural bone when compared with other degradable materials, such as polymers, apart from their alkaline nature during degradation.

Methods

We developed a pure Mg interference screw for ACL reconstruction. In the present study, 24 fresh cadaver knees were used to compare the mechanical properties of pure Mg interference screws and polylactic acid polymer interference screws for ACL reconstruction via their application on the proximal tibia tested using specific robotics.

Results

Results showed that the pure Mg interference screw group showed similar mechanical stability to the polylactic acid polymer interference screw group, implying comparable postoperative fixation effects.

Conclusion

As there are no commercially available Mg-based interference screws for ACL reconstruction clinically and the in vivo degradation of pure Mg promotes bone formation, our cadaveric study supports its clinical tests for ACL reconstruction.

A Comparative Animal Study of Tendon Grafts Healing After Remnant-Preserving Versus Conventional Anterior Cruciate Ligament Reconstruction

BACKGROUND The aim of this study was to determine if anterior cruciate ligament (ACL) reconstruction by remnant preservation promotes cell proliferation, vascularization, proprioception recovery, and improved biomechanical properties of the tendon grafts. MATERIAL AND METHODS 75 New Zealand rabbits were randomly assigned into the control group (group A), conventional ACL reconstruction group (group B), ACL reconstruction using remnant preservation and graft through remnant sleeve technique group (group C), and ACL reconstruction using remnant preservation and remnant tensioning technique group (group D). The remnant and healing of tendon grafts in groups C and D were observed at 3, 6, and 12 weeks after surgery, and the mRNA expression levels of VEGF, NT-3 and GAP-43 in ACL (group A) or tendon graft samples (groups B, C, and D) were determined by real-time PCR. Tendon graft cell count, microvessel density (MVD), and proprioceptors were determined by H&E staining, CD34, and S-100 immunohistochemical staining. The biomechanical properties of the tendon graft at week 12 in groups B, C, and D were examined by using a tensile strength test. RESULTS Remnant and tendon grafts were not healed at 3, 6, and 12 weeks after the operation in groups C and D. VEGF, NT-3, and GAP-43 mRNA expressions in groups B, C, and D were higher than those in group A (P<0.05), but no significant difference was observed between groups B, C, and D (P>0.05). Furthermore, tendon graft cell count, MVD, proprioception, and biomechanical properties showed no significant differences (P>0.05) among groups B, C, and D at various time points. CONCLUSIONS There was no significant difference in cell proliferation, vascularization, proprioception recovery, or biomechanical properties of the tendon grafts between remnant-preserving and conventional ACL reconstruction methods.

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

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