The challenge of establishing preclinical models for segmental bone defect research

Guided Bone Regeneration with a Nitric-Oxide Releasing Polymer Inducing Angiogenesis and Osteogenesis in Critical-Sized Bone Defects

Synthetic scaffolds, as bone grafts, provide a favorable environment for the repair and growth of new bone tissue at defect sites. However, the lack of angio- and osteo-induction limits the usefulness of artificial scaffolds for bone regeneration. Nitric oxide (NO) performs essential roles in healing processes, such as regulating inflammation and addressing incomplete revascularization. In this study, we developed a polymer capable of controlled NO release to promote the osteogenic capacity in artificial scaffolds. The biological efficiency of the NO compound was assessed by its effect on pre-osteoblasts and macrophages in vitro and the extent of vascularization and bone formation in the calvaria defect model in vivo. The compound did not inhibit cell adhesion or proliferation. NO treatment significantly increased both alkaline phosphatase activity and mineralization in pre-osteoblasts. Macrophages treated with NO secreted high levels of anti-inflammatory factors and adopted the pro-regenerative M2 phenotype. In the critical-sized defect model, the collagen scaffold containing the NO compound enhanced neovascularization and bone formation. The developed NO-releasing system promoted osteogenesis and regeneration of damaged bone tissue. As the multiple functions of NO involve macrophage modulation and angiogenesis, such release systems may be valuable for guiding bone regeneration in critical-sized defects. This article is protected by copyright. All rights reserved.

Design and Analysis of Biomedical Scaffolds Using TPMS-Based Porous Structures Inspired from Additive Manufacturing

Gyroid (G) and primitive (P) porous structures have multiple application areas, ranging from thermal to mechanical, and fall in the complex triply periodic minimal surface (TPMS) category. Such intricate bioinspired constructs are gaining attention because they meet both biological and mechanical requirements for osseous reconstruction. The study aimed to develop G and P structures with varying porosity levels from 40% to 80% by modulating the strut thickness to proportionally resemble the stiffness of host tissue. The performance characteristics were evaluated using Ti6Al4V and important relationships between feature dimension, strut thickness, porosity, and stiffness were established. Numerical results showed that the studied porous structures could decrease stiffness from 107 GPa (stiffness of Ti6Al4V) to the range between 4.21 GPa to 29.63 GPa of varying porosities, which matches the human bone stiffness range. Furthermore, using this foundation, a subject-specific scaffold (made of P unit cells with an 80% porosity) was developed to reconstruct segmental bone defect (SBD) of the human femur, demonstrating a significant decrease in the stress shielding effect. Stress transfer on the bone surrounded by a P scaffold was compared with a solid implant which showed a net increase of stress transfer of 76% with the use of P scaffold. In the conclusion, future concerns and recommendations are suggested.

Union, complication, reintervention and failure rates of surgical techniques for large diaphyseal defects: a systematic review and meta-analysis

To understand the potential and limitations of the different available surgical techniques used to treat large, long-bone diaphyseal defects by focusing on union, complication, re-intervention, and failure rates, summarizing the pros and cons of each technique. A literature search was performed on PubMed, Web of Science, and Cochrane databases up to March 16th, 2022; Inclusion criteria were clinical studies written in English, of any level of evidence, with more than five patients, describing the treatment of diaphyseal bone defects. The primary outcome was the analysis of results in terms of primary union, complication, reintervention, and failure rate of the four major groups of techniques: bone allograft and autograft, bone transport, vascularized and non-vascularized fibular graft, and endoprosthesis. The statistical analysis was carried out according to Neyeloff et al., and the Mantel–Haenszel method was used to provide pooled rates across the studies. The influence of the various techniques on union rates, complication rates, and reintervention rates was assessed by a z test on the pooled rates with their corresponding 95% CIs. Assessment of risk of bias and quality of evidence was based on Downs and Black’s “Checklist for Measuring Quality” and Rob 2.0 tool. Certainty of yielded evidence was evaluated with the GRADE system. Seventy-four articles were included on 1781 patients treated for the reconstruction of diaphyseal bone defects, 1496 cases in the inferior limb, and 285 in the upper limb, with trauma being the main cause of bone defect. The meta-analysis identified different outcomes in terms of results and risks. Primary union, complications, and reinterventions were 75%, 26% and 23% for bone allografts and autografts, 91%, 62% and 19% for the bone transport group, and 78%, 38% and 23% for fibular grafts; mean time to union was between 7.8 and 8.9 months in all these groups. Results varied according to the different aetiologies, endoprosthesis was the best solution for tumour, although with a 22% failure rate, while trauma presented a more composite outcome, with fibular grafts providing a faster time to union (6.9 months), while cancellous and cortical-cancellous grafts caused less complications, reinterventions, and failures. The literature about this topic has overall limited quality. However, important conclusions can be made: Many options are available to treat critical-size defects of the diaphysis, but no one appears to be an optimal solution in terms of a safe, satisfactory, and long-lasting outcome. Regardless of the bone defect cause, bone transport techniques showed a better primary union rate, but bone allograft and autograft had fewer complication, reintervention, and failure rates than the other techniques. The specific lesion aetiology represents a critical aspect influencing potential and limitations and therefore the choice of the most suitable technique to address the challenging large diaphyseal defects.

Evaluating bone biopsy quality by technique in an animal model

Rationale and Objectives

Powered bone biopsy technique is popular due to its ease of use. However, there is conflicting evidence regarding the diagnostic quality of the samples. The purpose of this study is to evaluate the diagnostic adequacy of different bone biopsy devices and techniques as it relates to the frequency of sample artifacts.

Materials and Methods

Bone biopsy was performed on same-day processed lamb femora using the following techniques: manual, pulsed powered and full powered. Ten samples were collected using each method by a single musculoskeletal-trained radiologist and were reviewed by 3 blinded pathologists. Samples were compared across multiple categories: length, bone dust, thermal/crush artifact, cellular morphology, fragmentation, and diagnostic acceptability. Bayesian Multilevel Nonlinear Regression models were performed assessing the association between the techniques across the categories.

Results

Statistical analysis revealed that the manual technique outperformed any powered technique across all categories: decreased thermal/crush artifact (P = 0.014), decreased bone dust (p<0.001), better cellular morphology (P = 0.005), less fragmentation (P < 0.0001) and better diagnostic acceptability (P < 0.0001).

Conclusion

Manually obtained bone biopsy samples generally produce a more diagnostic sample as compared to powered techniques in an animal model. Given these results, manual bone biopsy methods should be encouraged after consideration for lesion composition, difficulty of access and the patient's overall condition.

Bone Defects in Tibia Managed by the Bifocal vs. Trifocal Bone Transport Technique: A Retrospective Comparative Study

Background

The purpose of this study is to evaluate the clinical effectiveness and determine the differences, if any, between the trifocal bone transport (TFT) technique and the bifocal bone transport (BFT) technique in the reconstruction of long segmental tibial bone defects caused by infection using a monolateral rail external fixator.

Methods

A total of 53 consecutive patients with long segmental tibial bone defects caused by infection and treated by monolateral rail external fixator in our department were retrospectively collected and analyzed from the period January 2013 to April 2019, including 39 males and 14 females with an average age of 38.8 ± 12.4 years (range 19–65 years). Out of these, 32 patients were treated by the BFT technique, and the remaining 21 patients were managed by the TFT technique. The demographic data, operation duration (OD), docking time (DT), external fixation time (EFT), and external fixation index (EFI) were documented and analyzed. Difficulties that occur during the treatment were classified according to Paley. The clinical outcomes were evaluated by following the Association for the Study and Application of the Method of Ilizarov (ASAMI) criteria at the last clinical visit.

Results

All patients achieved an infection-free union finally, and there was no significant difference between the two groups in terms of demographic data and both ASAMI bone and functional scores (p > 0.05). The mean defect size and OD in TFT (9.4 ± 1.5 cm, 161.9 ± 8.9 min) were larger than that in BFT (7.8 ± 1.8 cm, 122.5 ± 11.2 min) (p < 0.05). The mean DT, EFT, and EFI in TFT (65.9 ± 10.8 days, 328.0 ± 57.2 days, 34.8 ± 2.1 days/cm) were all less than those in BFT (96.8 ± 22.6 days, 474.5 ± 103.2 days, 60.8 ± 1.9 days/cm) (p < 0.05). Difficulties and complications were more prevalent in the BFT group than in the TFT group (p < 0.05).

Conclusion

Both the trifocal and BFT techniques achieve satisfactory clinical outcomes in the reconstruction of long segmental tibial bone defects caused by infection using a monolateral rail external fixator. The TFT technique can significantly decrease the DT, EFT, EFI, difficulties, and complications compared with the BFT technique.

Characterisation of Selected Materials in Medical Applications

Tissue engineering is an interdisciplinary field of science that has developed very intensively in recent years. The first part of this review describes materials with medical and dental applications from the following groups: metals, polymers, ceramics, and composites. Both positive and negative sides of their application are presented from the point of view of medical application and mechanical properties. A variety of techniques for the manufacture of biomedical components are presented in this review. The main focus of this work is on additive manufacturing and 3D printing, as these modern techniques have been evaluated to be the best methods for the manufacture of medical and dental devices. The second part presents devices for skull bone reconstruction. The materials from which they are made and the possibilities offered by 3D printing in this field are also described. The last part concerns dental transitional implants (scaffolds) for guided bone regeneration, focusing on polylactide-hydroxyapatite nanocomposite due to its unique properties. This section summarises the current knowledge of scaffolds, focusing on the material, mechanical and biological requirements, the effects of these devices on the human body, and their great potential for applications.

Effects of Channels and Micropores in Honeycomb Scaffolds on the Reconstruction of Segmental Bone Defects

The reconstruction of critical-sized segmental bone defects is a key challenge in orthopedics because of its intractability despite technological advancements. To overcome this challenge, scaffolds that promote rapid bone ingrowth and subsequent bone replacement are necessary. In this study, we fabricated three types of carbonate apatite honeycomb (HC) scaffolds with uniaxial channels bridging the stumps of a host bone. These HC scaffolds possessed different channel and micropore volumes. The HC scaffolds were implanted into the defects of rabbit ulnar shafts to evaluate the effects of channels and micropores on bone reconstruction. Four weeks postoperatively, the HC scaffolds with a larger channel volume promoted bone ingrowth compared to that with a larger micropore volume. In contrast, 12 weeks postoperatively, the HC scaffolds with a larger volume of the micropores rather than the channels promoted the scaffold resorption by osteoclasts and bone formation. Thus, the channels affected bone ingrowth in the early stage, and micropores affected scaffold resorption and bone formation in the middle stage. Furthermore, 12 weeks postoperatively, the HC scaffolds with large volumes of both channels and micropores formed a significantly larger amount of new bone than that attained using HC scaffolds with either large volume of channels or micropores, thereby bridging the host bone stumps. The findings of this study provide guidance for designing the pore structure of scaffolds.

PCL-PEG copolymer based injectable thermosensitive hydrogels

A number of stimuli-responsive-based hydrogels has been widely explored in biomedical applications in the last few decades because of their excellent biodegradability and biocompatibility. The development of synthetic chemistry and materials science leads to the emergence of in situ stimuli-responsive hydrogels. In this regard, several synthetic and natural polymers have been synthesized and utilized to prepare temperature-sensitive in situ forming hydrogels. This could be best used via injections as temperature stimulus could trigger in situ hydrogels gelation and swelling behaviors. There are many smart polymers available for the formulation of the in situ based thermoresponsive injectable hydrogel. Among these, poly (ε-caprolactone) (PCL) polymer has been recognized and approved by the FDA for numerous biomedical applications. More specifically, the PCL is coupled with polyethylene glycol (PEG) to obtain amphiphilic thermosensitive "smart" copolymers (PCL-PEG), to form rapid and reversible physical gelation behavior. However, the chemical structure of the copolymer is a critical aspect in determining water solubility, thermo-gelation behavior, drug release rate, degradation rate, and the possibility to deliver a diverse range of drugs. In this review, we have highlighted the typical PCL-PEG-based thermosensitive injectable hydrogels progress in the last decade for tissue engineering and localized drug delivery applications to treat various diseases. Additionally, the impact of molecular weight of PCL-PEG upon gelling behavior has also been critically highlighted for optimum hydrogels properties for potential pharmaceutical and biomedical applications.

Differential effects of anti-RANKL monoclonal antibody and zoledronic acid on necrotic bone in a murine model of Staphylococcus aureus-induced osteomyelitis

Osteomyelitis is characterized by progressive inflammatory bone destruction accompanied by severe pain and disability. However, with the exception of antibiotic therapies, there is no established therapy to protect the bone from infectious osteolysis. The anti-receptor activator of nuclear factor-kB ligand (RANKL) monoclonal antibody (anti-RANKL Ab) is a potential drug based on its proven effectiveness in preventing joint bone erosion in rheumatoid arthritis; however, the efficacy and adverse effects of anti-RANKL Ab in osteomyelitis remain to be investigated. In this study, we investigated the effects of anti-mouse RANKL Ab on acute osteomyelitis and compared them with those of zoledronic acid (ZA) using a murine model. Mice were inoculated with bioluminescent Staphylococcus aureus (Xen 29) on their left femur and then treated with ZA, anti-RANKL Ab, or phosphate-buffered saline as control. A 21-day longitudinal observational study using microcomputed tomography showed that both anti-RANKL Ab and ZA had an osteoprotective effect against infectious osteolysis. However, it was also demonstrated through bioluminescence imaging that ZA delayed the spontaneous reduction of bacterial load and through histology that it increased the amount of necrotic bone, while anti-RANKL Ab did not. Findings from histopathological and in vitro studies suggest that an intense inflammatory response around the necrotic bone could induce osteoclasts in a RANKL-independent manner, leading to the removal of necrotic bone, even after administration of the anti-RANKL Ab therapy. Collectively, anti-RANKL Ab may exert an osteoprotective effect without hampering the removal of the necrotic bone, which serves as a nidus for infection in osteomyelitis.

3D-printed porous Ti6Al4V scaffolds for long bone repair in animal models: a systematic review

BACKGROUND

Titanium and its alloys have been widely employed for bone tissue repair and implant manufacturing. The rapid development of three-dimensional (3D) printing technology has allowed fabrication of porous titanium scaffolds with controllable microstructures, which is considered to be an effective method for promoting rapid bone formation and decreasing bone absorption. The purpose of this systematic review was to evaluate the osteogenic potential of 3D-printed porous Ti6Al4V (Ti64) scaffold for repairing long bone defects in animal models and to investigate the influential factors that might affect its osteogenic capacity.

METHODS

Electronic literature search was conducted in the following databases: PubMed, Web of Science, and Embase up to September 2021. The SYRCLE's tool and the modified CAMARADES list were used to assess the risk of bias and methodological quality, respectively. Due to heterogeneity of the selected studies in relation to protocol and outcomes evaluated, a meta-analysis could not be performed.

RESULTS

The initial search revealed 5858 studies. Only 46 animal studies were found to be eligible based on the inclusion criteria. Rabbit was the most commonly utilized animal model. A pore size of around 500-600 µm and porosity of 60-70% were found to be the most ideal parameters for designing the Ti64 scaffold, where both dodecahedron and diamond pores optimally promoted osteogenesis. Histological analysis of the scaffold in a rabbit model revealed that the maximum bone area fraction reached 59.3 ± 8.1% at weeks 8-10. Based on micro-CT assessment, the maximum bone volume fraction was found to be 34.0 ± 6.0% at weeks 12.

CONCLUSIONS

Ti64 scaffold might act as a promising medium for providing sufficient mechanical support and a stable environment for new bone formation in long bone defects. Trail registration The study protocol was registered in the PROSPERO database under the number CRD42020194100.

Patient-Specific Bioimplants and Reconstruction Plates for Mandibular Defects: Production Workflow and In Vivo Large Animal Model Study

A major challenge with extensive craniomaxillofacial bone reconstruction is the limited donor-site availability to reconstruct defects predictably and accurately according to the anatomical shape of the patient. Here, patient-specific composite bioimplants, consisting of cross-linked poly(trimethylene carbonate) (PTMC) networks and β-tricalcium phosphate (β-TCP), were tested in vivo in twelve Göttingen minipigs in a large mandibular continuity defect model. The 25 mm defects were supported by patient-specific titanium reconstruction plates and received either osteoconductive composite bioimplants (PTMC+TCP), neat polymer network bioimplants (PTMC), autologous bone segments (positive control) or were left empty (negative control). Post-operatively, defects treated with bioimplants showed evident ossification at 24 weeks. Histopathologic evaluation revealed that neat PTMC bioimplant surfaces were largely covered with fibrous tissue, while in the PTMC+TCP bioimplants, bone attached directly to the implant surface showing good osteoconduction and histological signs of osteoinductivity. However, PTMC+TCP bioimplants were associated with high incidence of necrosis and infection, possibly due to rapid resorption and/or particle size of the used β-TCP. The study highlights the importance of testing bone regeneration implants in a clinically relevant large animal model and at the in situ reconstruction site, since results on small animal models and studies in non-loadbearing areas do not translate directly. This article is protected by copyright. All rights reserved.

The Development of a Magnesium-Releasing and Long-Term Mechanically Stable Calcium Phosphate Bone Cement Possessing Osteogenic and Immunomodulation Effects for Promoting Bone Fracture Regeneration

Bone grafts are commonly used for the treatment of critical sized bone defects. Since the supply of autologous bone is insufficient, allogeneic bone grafts have been used most of the time. However, the poor osteogenic property of allogeneic bone grafts after pretreatment results in delayed union, non-union, or even occasional deformity. Calcium phosphate cement (CPC) is one of the most promising bone filling materials due to its good biocompatibility and similar chemical components as natural bone. However, clinical applications of CPC were hampered by limited osteogenic effects, undesired immune response which results in resorption, and poor mechanical stability in vivo. Magnesium (Mg) has been proven to trigger bone regeneration through modulating cell behaviors of mesenchymal stem cells and macrophages significantly. Unfortunately, the degradation raters of pure Mg and Mg oxide are extremely fast, resulting in early collapse of Mg contained CPC. In this study, we developed a novel magnesium contained calcium phosphate bone cement (Mg-CPC), possessing long-term mechanical stability and osteogenic effects through sustained release of Mg. Furthermore, in vitro studies showed that Mg-CPC had no cytotoxic effects on hBMMSCs and macrophage RAW 264.7, and could enhance the osteogenic differentiation as determined by alkaline phosphate (ALP) activity and calcium nodule staining, as well as suppress the inflammatory as determined by expression of anti-inflammatory cytokine IL-1RA. We also found that Mg-CPC promoted new bone formation and bone maturation in vivo. These results suggest that Mg-CPC should be a good substitute material for bone grafts in clinical use.

Effect of Polymer Molecular Mass and Structure on the Mechanical Properties of Polymer-Glass Hybrids

Organic-inorganic hybrid materials are a promising class of materials for tissue engineering and other biomedical applications. In this systematic study, the effect of the polymer molecular mass (MM) with a linear architecture on hybrid mechanical properties is reported. Well-defined linear poly(methyl methacrylate-co-(3-(trimethoxysilyl)propyl methacrylate)) polymers with a range of MMs of 9 to 90 kDa and one 90 kDa star-shaped polymer were synthesized and then used to form glass-polymer hybrids. It was demonstrated that increasing linear polymer MM decreases the resultant hybrid mechanical strength. Furthermore, a star-polymer hybrid was synthesized as a comparison and demonstrated significantly different mechanical properties relative to its linear-polymer counterpart.

Microenvironment-mediated cancer dormancy: Insights from metastability theory

Dormancy is an evolutionarily conserved protective mechanism widely observed in nature. A pathological example is found during cancer metastasis, where cancer cells disseminate from the primary tumor, home to secondary organs, and enter a growth-arrested state, which could last for decades. Recent studies have pointed toward the microenvironment being heavily involved in inducing, preserving, or ceasing this dormant state, with a strong focus on identifying specific molecular mechanisms and signaling pathways. Increasing evidence now suggests the existence of an interplay between intracellular as well as extracellular biochemical and mechanical cues in guiding such processes. Despite the inherent complexities associated with dormancy, proliferation, and growth of cancer cells and tumor tissues, viewing these phenomena from a physical perspective allows for a more global description, independent from many details of the systems. Building on the analogies between tissues and fluids and thermodynamic phase separation concepts, we classify a number of proposed mechanisms in terms of a thermodynamic metastability of the tumor with respect to growth. This can be governed by interaction with the microenvironment in the form of adherence (wetting) to a substrate or by mechanical confinement of the surrounding extracellular matrix. By drawing parallels with clinical and experimental data, we advance the notion that the local energy minima, or metastable states, emerging in the tissue droplet growth kinetics can be associated with a dormant state. Despite its simplicity, the provided framework captures several aspects associated with cancer dormancy and tumor growth.

Optimal regenerative repair of large segmental bone defect in a goat model with osteoinductive calcium phosphate bioceramic implants

So far, how to achieve the optimal regenerative repair of large load-bearing bone defects using artificial bone grafts is a huge challenge in clinic. In this study, a strategy of combining osteoinductive biphasic calcium phosphate (BCP) bioceramic scaffolds with intramedullary nail fixation for creating stable osteogenic microenvironment was applied to repair large segmental bone defects (3.0 cm in length) in goat femur model. The material characterization results showed that the BCP scaffold had the initial compressive strength of over 2.0 MPa, and total porosity of 84%. The cell culture experiments demonstrated that the scaffold had the excellent ability to promote the proliferation and osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (BMSCs). The in vivo results showed that the intramedullary nail fixation maintained the initial stability and structural integrity of the implants at early stage, promoting the osteogenic process both guided and induced by the BCP scaffolds. At 9 months postoperatively, good integration between the implants and host bone was observed, and a large amount of newborn bones formed, accompanying with the degradation of the material. At 18 months postoperatively, almost the complete new bone substitution in the defect area was achieved. The maximum bending strength of the repaired bone defects reached to the 100% of normal femur at 18 months post-surgery. Our results demonstrated the good potential of osteoinductive BCP bioceramics in the regenerative repair of large load-bearing bone defects. The current study could provide an effective method to treat the clinical large segmental bone defects.

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A novel strategy of achieving regenerative repair for large segmental bone defects with osteoinductive calcium phosphate bioceramics was developed successfully.

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The critical-sized goat femur defects (3.0 cm in length) were completely repaired by osteoinductive calcium phosphate bioceramics without using exogenous active factors or cells.

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The current study could provide an effective method to solve the clinical problem about large load-bearing bone defect repair.

Development and validation of a parametric human mandible model to determine internal stresses for the future design optimization of maxillofacial implants

Large segmental mandible bone defects still represent a challenge for endogenous regeneration. Despite the bone's capacity to heal in many clinical situations, bone defects over a critical size do not heal spontaneously. An emerging treatment of critically sized mandibular defects is the implantation of individually manufactured scaffolds consisting of biodegradable magnesium alloys. Biomedical engineers faced the challenge of developing a scaffold structure that not only provides sufficient stability, but also stimulates and promotes bone growth while considering the degradation of the magnesium alloy. The porosity of the scaffold must also support bone ingrowth and neovascularization. For an optimal design and subsequent structural optimization knowledge of external load cases is essential. However, currently the muscle and joint forces of the mandible cannot be measured directly. The aim of our study was therefore the development of a parametric human mandible model to determine the relevant boundary conditions for the subsequent structural optimization of individual jawbone implants. Using a model-based approach, determining the essential external load of the mandible as a function of the age and sex of a patient individually and the realistic simulation of the mechanical stress for patient-specific loads and anatomies has been realized. The developed model is successfully validated by evaluating the deformations and stresses of the lower jaw of a possible patient and comparing them with the results of dental research. Based on the results of the modelling, in a subsequent optimization process section forces at the interface between the bone tissue and jawbone implant can be determined and used to optimize the design of the jawbone implant.

Skeletal regeneration for segmental bone loss: Vascularised grafts, analogues and surrogates

Massive segmental bone defects (SBD) are mostly treated by removing the fibula and transplanting it complete with blood supply. While revolutionary 50 years ago, this remains the standard treatment. This review considers different strategies to repair SBD and emerging potential replacements for this highly invasive procedure. Prior to the technical breakthrough of microsurgery, researchers in the 1960s and 1970s had begun to make considerable progress in developing non autologous routes to repairing SBD. While the breaktthrough of vascularised bone transplantation solved the immediate problem of a lack of reliable repair strategies, much of their prior work is still relevant today. We challenge the assumption that mimicry is necessary or likely to be successful and instead point to the utility of quite crude (from a materials technology perspective), approaches. Together there are quite compelling indications that the body can regenerate entire bone segments with few or no exogenous factors. This is important, as there is a limit to how expensive a bone repair can be and still be widely available to all patients since cost restraints within healthcare systems are not likely to diminish in the near future. STATEMENT OF SIGNIFICANCE: This review is significant because it is a multidisciplinary view of several surgeons and scientists as to what is driving improvement in segmental bone defect repair, why many approaches to date have not succeeded and why some quite basic approaches can be as effective as they are. While there are many reviews of the literature of grafting and bone repair the relative lack of substantial improvement and slow rate of progress in clinical translation is often overlooked and we seek to challenge the reader to consider the issue more broadly.

Scaffold-guided bone regeneration in large volume tibial segmental defects

Large volume losses in weight bearing long bones are a major challenge in clinical practice. Despite multiple innovations over the last decades, significant limitations subsist in current clinical treatment options which is driving a strong clinical demand for clinically translatable treatment alternatives, including bone tissue engineering applications. Despite these shortcomings, preclinical large animal models of large volume segmental bone defects to investigate the regenerative capacity of bone tissue engineering strategies under clinically relevant conditions are rarely described in literature. We herein present a newly established preclinical ovine animal model for the treatment of XL volume (19 cm³) segmental tibial defects. In eight aged male Merino sheep (age > 6 years) a mid-diaphyseal tibial segmental defect was created and stabilized with a 5.6 mm Dynamic Compression Plate (DCP). We present short-term (3 months) and long-term (12-15 months) results of a pilot study using medical grade Polycaprolactone-Tricalciumphosphate (mPCL-TCP) scaffolds combined with a dose of 2 mg rhBMP-7 delivered in Platelet-Rich- Plasma (PRP). Furthermore, detailed analyses of the mechanical properties of the scaffolds as well as interfragmentary movement (IFM) and DCP-surface strain in vitro and a comprehensive description of the surgical and post-surgery protocol and post-mortem analysis is given.

Dopamine based adhesive nano-coatings on extracellular matrix (ECM) based grafts for enhanced host-graft interfacing affinity

Interfacing affinity between grafts and host tissues is an urgent issue that needs to be addressed for the clinical translation of tissue engineered extracellular matrix (ECM) based grafts. Dopamine is known as a universal adhesive, the catechol groups on which could form chelating bonds with metal ions. Herein we developed an adhesive nano-coating on ECM based grafts which could crosslink in situ with ferric ions for fixation with surrounding tissues after implantation without affecting the porous structures of the grafts. Therefore, decellularized living hyaline cartilage graft (dLhCG), a model ECM-based graft, with dopamine based natural biological material adhesive coatings was manufactured to address the interfacing affinity issue between ECM-based grafts and cartilage. A macromolecule backbone was needed for the coating material to avoid the formation of a rigid crosslinking system and adverse effects caused by small molecules of dopamine. Chondroitin sulfate (CS), a cartilage derived sulfated GAG, was chosen as the backbone to fabricate dopamine modified CS (CSD) with no impurities introduced to the joint. Dopamine modified serum albumin (BCD) was also chosen for the favorable biocompatibility of albumin. Both dLhCG coated with CSD and dLhCG coated with BCD showed enhanced adhesive strength with cartilage after chelating with ferric ions in situ compared to dLhCG and further potential in improving the interfacing affinity of dLhCG with cartilage.

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.

High-strength, porous additively manufactured implants with optimized mechanical osseointegration

Optimization of porous titanium alloy scaffolds designed for orthopedic implants requires balancing mechanical properties and osseointegrative performance. The tradeoff between scaffold porosity and the stiffness/strength must be optimized towards the goal to improve long term load sharing while simultaneously promoting osseointegration. Osseointegration into porous titanium implants covering a wide range of porosity (0%-90%) and manufactured by laser powder bed fusion (LPBF) was evaluated with an established ovine cortical and cancellous defect model. Direct apposition and remodeling of woven bone was observed at the implant surface, as well as bone formation within the interstices of the pores. A linear relationship was observed between the porosity and benchtop mechanical properties of the scaffolds, while a non-linear relationship was observed between porosity and the ex vivo cortical bone-implant interfacial shear strength. Our study supports the hypothesis of porosity dependent performance tradeoffs, and establishes generalized relationships between porosity and performance for design of topological optimized implants for osseointegration. These results are widely applicable for orthopedic implant design for arthroplasty components, arthrodesis devices such as spinal interbody fusion implants, and patient matched implants for treatment of large bone defects.

Pre-Clinical Models in Implant Dentistry: Past, Present, Future

Biomedical research seeks to generate experimental results for translation to clinical settings. In order to improve the transition from bench to bedside, researchers must draw justifiable conclusions based on data from an appropriate model. Animal testing, as a prerequisite to human clinical exposure, is performed in a range of species, from laboratory mice to larger animals (such as dogs or non-human primates). Minipigs appear to be the animal of choice for studying bone surgery around intraoral dental implants. Dog models, well-known in the field of dental implant research, tend now to be used for studies conducted under compromised oral conditions (biofilm). Regarding small animal models, research studies mostly use rodents, with interest in rabbit models declining. Mouse models remain a reference for genetic studies. On the other hand, over the last decade, scientific advances and government guidelines have led to the replacement, reduction, and refinement of the use of all animal models in dental implant research. In new development strategies, some in vivo experiments are being progressively replaced by in vitro or biomaterial approaches. In this review, we summarize the key information on the animal models currently available for dental implant research and highlight (i) the pros and cons of each type, (ii) new levels of decisional procedures regarding study objectives, and (iii) the outlook for animal research, discussing possible non-animal options.

Biomimetic Polydopamine-Modified Silk Fibroin/Curcumin Nanofibrous Scaffolds for Chemo-photothermal Therapy of Bone Tumor

The simultaneous therapy of tumor recurrence and bone defects resulting from surgical resection of osteosarcoma is still a challenge in the clinic. Combination therapy based on a localized drug-delivery system shows great promise in the treatment of osteosarcoma. Herein, bifunctional polydopamine (PDA)-modified curcumin (CM)-loaded silk fibroin (SF) composite (SF/CM-PDA) nanofibrous scaffolds, which combined photothermal therapy with chemotherapy to synergistically enhance osteosarcoma therapy, were prepared by PDA coating of the SF/CM nanofibrous scaffolds fabricated by supercritical carbon dioxide (SC-CO₂) technology. The PDA coating improved hydrophilicity and mechanical strength of the SF/CM scaffolds. The SF/CM-PDA scaffolds present good photothermal conversion capacity and excellent photostability. The low pH and near-infrared (NIR) irradiation could effectively accelerate release of CM in the SF/CM-PDA scaffolds. The in vitro anticancer results indicated that the biocompatible SF/CM-PDA scaffolds had a long-term, stable, and superior anticancer effect compared to pure CM. Furthermore, the SF/CM-PDA scaffolds significantly increased the growth inhibition of osteosarcoma MG-63 cells under NIR irradiation (808 nm and 1.3 W/cm²). Besides, the SF/CM-PDA scaffolds could enhance osteoblast MC3T3-E1 cell proliferation in vitro when the mass ratio of CM was 0.05-0.5%. This work has therefore demonstrated that the bifunctional SF/CM-PDA scaffolds provide a competitive strategy for local osteosarcoma therapy and bone regeneration.

The Effect of Mesenchymal Stem Cell-Enriched Scaffolds on MMP-8 and TGF-β Levels of Vertebrae Postlaminoplasty in Rabbit Model

INTRODUCTION

Some laminoplasty procedures still have restenosis because of bony-bridging failure of the laminar hinge. The present study aimed to determine the effect of mesenchymal stem cell (MSC)-enriched scaffolds on vertebral regeneration after laminoplasty on the basis of the number of osteoblasts, matrix metalloproteinase-8 (MMP-8), and transforming growth factor-beta (TGF-β) levels.

METHODS

Laminoplasty procedure using the Hirabayashi technique was conducted at the lumbar level in 32 rabbits that were divided into four and three groups of the control (C) and treatment groups, respectively, with different types of laminoplasty spacer (T1, autograft; T2, scaffold; and T3, scaffold with MSCs). Histopathological studies were conducted to calculate the number of osteoblasts and enzyme-linked immunosorbent assay tests to detect MMP-8 and TGF-β 4 weeks after the surgery.

RESULTS

The results showed a significant decrease in MMP-8 level in the T3 group compared with that in the control group (p < 0.05). A significant difference exists between the average number of newly formed osteoblasts in the control group compared with that in the T3 group (p < 0.05) with a higher mean blood TGF-β level of all experimental groups compared with that of the control group (p = 0.58).

CONCLUSION

The significant decrease in MMP-8 levels, increase in TGF-β levels, and increased number of osteoblasts on MSC-seeded polylactic acid scaffolds could be useful to support the laminoplasty procedure to prevent restenosis because it was biocompatible and promoted the bone healing process.

Influence of a novel scaffold composed of polyurethane, hydroxyapatite, and decellularized bone particles on the healing of fourth metacarpal defects in mares

OBJECTIVE

To determine the effect of a novel scaffold, designed for use in bone regeneration, on healing of splint bone segmental defects in mares.

STUDY DESIGN

In vivo experimental study.

SAMPLE POPULATION

Five adult mares (4-10 years old; mean weight, 437.7 kg ± 29 kg).

METHODS

Bilateral 2-cm full-thickness defects were created in the fourth metacarpal bones (MCIV) of each horse. Each defect was randomly assigned to either a novel scaffold treatment (n = 5) or an untreated control (n = 5). The scaffold was composed of polyurethane, hydroxyapatite, and decellularized bone particles. Bone healing was assessed for a period of 60 days by thermography, ultrasonography, radiography, and computed tomography (CT). Biopsies of each defect were performed 60 days after surgery for histological evaluation.

RESULTS

On the basis of radiographic analysis, scaffold-treated defects had greater filling (67.42% ± 26.7%) compared with untreated defects (35.88% ± 32.7%; P = .006). After 60 days, CT revealed that the density of the defects treated with the scaffolds (807.80 ± 129.6 Hounsfield units [HU]) was greater than density of the untreated defects (464.80 ± 81.3 HU; P = .004). Evaluation of histology slides provided evidence of bone formation within an average of 9.43% ± 3.7% of the cross-sectional area of scaffolds in contrast to unfilled defects in which connective tissue was predominant throughout the biopsy specimens.

CONCLUSION

The novel scaffold was biocompatible and supported bone formation within the MCIV segmental defects.

CLINICAL SIGNIFICANCE

This novel scaffold offers an effective option for filling bone voids in horses when support of bone healing is indicated.

Animal models of vertical bone augmentation (Review)

Vertical bone augmentation is an important challenge in dental implantology. Existing vertical bone augmentation techniques, along with bone grafting materials, have achieved certain clinical progress but continue to have numerous limitations. In order to evaluate the possibility of using biomaterials to develop bone substitutes, medical devices and/or new bone grafting techniques for vertical bone augmentation, it is essential to establish clinically relevant animal models to investigate their biocompatibility, mechanical properties, applicability and safety. The present review discusses recent animal experiments related to vertical bone augmentation. In addition, surgical protocols for establishing relevant preclinical models with various animal species were reviewed. The present study aims to provide guidance for selecting experimental animal models of vertical bone augmentation.

Temporal Changes in Reverse Torque of Locking-Head Screws Used in the Locking Plate in Segmental Tibial Defect in Goat Model

The objective of this study was to evaluate changes in peak reverse torque (PRT) of the locking head screws that occur over time. A locking plate construct, consisting of an 8-hole locking plate and 8 locking screws, was used to stabilize a tibia segmental bone defect in a goat model. PRT was measured after periods of 3, 6, 9, and 12 months of ambulation. PRT for each screw was determined during plate removal. Statistical analysis revealed that after 6 months of loading, locking screws placed in position no. 4 had significantly less PRT as compared with screws placed in position no. 5 (p < 0.05). There were no statistically significant differences in PRT between groups as a factor of time (p > 0.05). Intracortical fractures occurred during the placement of 151 out of 664 screws (22.7%) and were significantly more common in the screw positions closest to the osteotomy (positions 4 and 5, p < 0.05). Periosteal and endosteal bone reactions and locking screw backout occurred significantly more often in the proximal bone segments (p < 0.05). Screw backout significantly, negatively influenced the PRT of the screws placed in positions no. 3, 4, and 5 (p < 0.05). The locking plate-screw constructs provided stable fixation of 2.5-cm segmental tibia defects in a goat animal model for up to 12 months.

Development of a tibial experimental non-union model in rats

BACKGROUND

Many non-union animal models have been developed to explore the problems surrounding fracture healing. However, the existing models are not perfect and cannot satisfy all non-union studies. This study aimed to make a non-union model of the tibia in rats by cauterization of the posterior of 2 mm on both sides of the fracture end after open osteotomy of the tibia and fixing the fractured tibia with a Kirschner wire 0.8 mm in diameter.

METHODS

For this study, 96 female adult Sprague-Dawley (SD) rats were used. The rats underwent surgery to produce a tibial open fracture and were fixed with a 0.8-mm diameter Kirschner wire. In 48 of the rats, the periosteum proximal and distal to the fracture end was cauterized.

RESULTS

At 2, 4, 6, and 8 weeks after surgery, radiological and histological analysis showed typical physiological healing in the control group, and the healing rate was 100% at 6 weeks. But the non-union group was characterized by resorption of the fracture ends with few callus formations and no bridging callus formation, and the healing rate was 0% at 8 weeks.

CONCLUSIONS

This method represents a reproducible model to create atrophic non-unions. This model provides a new option for studying the basic healing mechanisms and evaluating new therapies for bone regeneration and treatment of non-unions.

Systematic Review of the Preclinical Technology Readiness of Orthopedic Gene Therapy and Outlook for Clinical Translation

Bone defects and improper healing of fractures are an increasing public health burden, and there is an unmet clinical need in their successful repair. Gene therapy has been proposed as a possible approach to improve or augment bone healing with the potential to provide true functional regeneration. While large numbers of studies have been performed in vitro or in vivo in small animal models that support the use of gene therapy for bone repair, these systems do not recapitulate several key features of a critical or complex fracture environment. Larger animal models are therefore a key step on the path to clinical translation of the technology. Herein, the current state of orthopedic gene therapy research in preclinical large animal models was investigated based on performed large animal studies. A summary and an outlook regarding current clinical studies in this sector are provided. It was found that the results found in the current research literature were generally positive but highly methodologically inconsistent, rendering a comparison difficult. Additionally, factors vital for translation have not been thoroughly addressed in these model systems, and the risk of bias was high in all reviewed publications. These limitations directly impact clinical translation of gene therapeutic approaches due to lack of comparability, inability to demonstrate non-inferiority or equivalence compared with current clinical standards, and lack of safety data. This review therefore aims to provide a current overview of ongoing preclinical and clinical work, potential bottlenecks in preclinical studies and for translation, and recommendations to overcome these to enable future deployment of this promising technology to the clinical setting.

Functional repair of critically sized femoral defects treated with bioinspired titanium gyroid-sheet scaffolds

Despite the innate ability for bone to remodel and repair, its regeneration has a limit. In these cases of critically sized bone defects (CSBD), the bone deficit must be repaired using reconstructive techniques that support immediate load bearing and encourage bone bridging across the defect. High-strength porous titanium implants offer a solution for treatment of CSBD in which the scaffold can support physiological loads, provide a matrix to guide ingrowth, and carry graft materials and/or biologics. Fabrication of titanium meta-materials via additive manufacturing (AM) has unlocked the potential to modulate mechanical and biological performance to achieve a combination of properties previously unachievable. Meta-material scaffolds with topology based on triply periodic minimal surfaces (TPMS) have gained increasing interest for use in biomedical applications due to their bioinspired nature. Despite enthusiasm for TPMS-based titanium scaffolds due to their high strength to stiffness ratio, high permeability, and curvature similar to trabecular bone, there is little preclinical evidence to support their in vivo response in bone. The present study sought to evaluate the performance of gyroid-sheet titanium scaffolds produced via AM to repair a critically size femoral cortical bone defect in rats. Empty gyroid-sheet scaffolds were shown to repair segmental defects with up to 38% of torsional strength and 54% torsional stiffness of the intact femur (control) at 12-weeks. Gyroid-sheet scaffolds carrying recombinant bone morphogenic protein-2 demonstrated bridging bone growth across the length of the defect, with torsional strength and stiffness superior to that of the intact controls.

Optimizing In Vitro Osteogenesis in Canine Autologous and Induced Pluripotent Stem Cell-Derived Mesenchymal Stromal Cells with Dexamethasone and BMP-2

A growing body of work suggests that canine mesenchymal stromal cells (cMSCs) require additional agonists such as bone morphogenic protein-2 (BMP-2) for consistent in vitro osteogenic differentiation. BMP-2 is costly and may challenge the translational relevance of the canine model. Dexamethasone enhances osteogenic differentiation of human MSCs (hMSCs) and is widely utilized in osteogenic protocols. The aim of this study was to determine the effect of BMP-2 and dexamethasone on early- and late-stage osteogenesis of autologous and induced pluripotent stem cell (iPS)-derived cMSCs. Two preparations of marrow-derived cMSCs were selected to represent exceptionally or marginally osteogenic autologous cMSCs. iPS-derived cMSCs were generated from canine fibroblasts. All preparations were evaluated using alkaline phosphatase (ALP) activity, Alizarin Red staining of osteogenic monolayers, and quantitative polymerase chain reaction. Data were reported as mean ± standard deviation and compared using one- or two-way analysis of variance and Tukey or Sidak post hoc tests. Significance was established at P < 0.05. In early-stage assays, dexamethasone decreased ALP activity for all cMSCs in the presence of BMP-2. In late-stage assays, inclusion of dexamethasone and BMP-2 at Day 1 of culture produced robust monolayer mineralization for autologous cMSCs. Delivering 100 nM dexamethasone at Day 1 improved mineralization and reduced the BMP-2 concentrations required to achieve mineralization of the marginal cMSCs. For iPS-cMSCs, dexamethasone was inhibitory to both ALP activity and monolayer mineralization. There was increased expression of osteocalcin and osterix with BMP-2 in autologous cMSCs but a more modest expression occurred in iPS cMSCs. While autologous and iPS-derived cMSCs respond similarly in early-stage osteogenic assays, they exhibit unique responses to dexamethasone and BMP-2 in late-stage mineralization assays. This study demonstrates that dexamethasone and BMP-2 can be titrated in a time- and concentration-dependent manner to enhance osteogenesis of autologous cMSC preparations. These results will prove useful for investigators performing translational studies with cMSCs while providing insight into iPS-derived cMSC osteogenesis.

A systematic review of preclinical in vivo testing of 3D printed porous Ti6Al4V for orthopedic applications, part I: Animal models and bone ingrowth outcome measures

For Ti6Al4V orthopedic and spinal implants, osseointegration is often achieved using complex porous geometries created via additive manufacturing (AM). While AM porous titanium (pTi) has shown clinical success, concerns regarding metallic implants have spurred interest in alternative AM biomaterials for osseointegration. Insights regarding the evaluation of these new materials may be supported by better understanding the role of preclinical testing for AM pTi. We therefore asked: (a) What animal models have been most commonly used to evaluate AM porous Ti6Al4V for orthopedic bone ingrowth; (b) What were the primary reported quantitative outcome measures for these models; and (c) What were the bone ingrowth outcomes associated with the most frequently used models? We performed a systematic literature search and identified 58 articles meeting our inclusion criteria. We found that AM pTi was evaluated most often using rabbit and sheep femoral condyle defect (FCD) models. Additional ingrowth models including transcortical and segmental defects, spinal fusions, and calvarial defects were also used with various animals based on the study goals. Quantitative outcome measures determined via histomorphometry including ''bone ingrowth'' (range: 3.92-53.4% for rabbit/sheep FCD) and bone-implant contact (range: 9.9-59.7% for rabbit/sheep FCD) were the most common. Studies also used 3D imaging to report outcomes such as bone volume fraction (BV/TV, range: 4.4-61.1% for rabbit/sheep FCD), and push-out testing for outcomes such as maximum removal force (range: 46.6-3092 N for rabbit/sheep FCD). Though there were many commonalities among the study methods, we also found significant heterogeneity in the outcome terms and definitions. The considerable diversity in testing and reporting may no longer be necessary considering the reported success of AM pTi across all model types and the ample literature supporting the rabbit and sheep as suitable small and large animal models, respectively. Ultimately, more standardized animal models and reporting of bone ingrowth for porous AM materials will be useful for future studies.

Low Dose BMP2-Doped Calcium Phosphate Graft Promotes Bone Defect Healing in a Large Animal Model

Background: Bone grafts are in high demand due to the increase in the cases of bone defects mainly caused by trauma, old age, and disease-related bone damages. Tissue-engineered calcium phosphate (CaP) biomaterials match the major inorganic contents of bone, thereby could be the potential bone graft substitute. However, CaP-bone grafts lack the osteoinductivity that is vital for effective bone regeneration. In this study, we aimed to test the bone defect healing potential of biomimetically fabricated low dose BMP2-doped CaP (BMP2.BioCaP) grafts in a large animal model.

Methods: Low dose BMP2 was doped internally (BMP2-int.BioCaP) or on the surface of CaP (BMP2-sur.BioCaP) grafts during the fabrication process. Our previous study showed the robust bone regenerative potential of BMP2-int.BioCaP and BMP2-sur.BioCaP grafts in the rat ectopic model. In this study, we investigated the bone defect healing potential of BMP2.BioCaP grafts in sheep humerus/femoral defects, as well as compared with that of autologous bone graft and clinically used deproteinized bovine bone (DBB) xenograft.

Results: Different ways of BMP2 doping did not affect the surface morphology and degradation properties of the graft materials. Micro-CT and histology results showed robustly higher bone defect-healing potential of the BMP2.BioCaP grafts compared to clinically used DBB grafts. The bone defect healing potential of BMP2.BioCaP grafts was as effective as that of the autologous bone graft. Although, BMP2-int.BioCaP doped half the amount of BMP2 compared to BMP2-sur.BioCaP, its' bone defect healing potential was even robust. The BMP2.BioCaP grafts showed less immunogenicity compared to BioCaP or DBB grafts. The volume density of blood vessel-like and bone marrow-like structures in both BMP2.BioCaP graft groups were in a similar extent to the autologous group. Meticulous observation of higher magnification histological images showed active bone regeneration and remodeling during bone defect healing in BMP2.BioCaP graft groups.

Conclusion: The robust bone regenerative potential of BMP2.BioCaP grafts in the ectopic model and in-situ bone defects in small and large animals warrant the pre-clinical studies on large animal critical-sized segmental bone defects.

Comparison of the Translational Potential of Human Mesenchymal Progenitor Cells from Different Bone Entities for Autologous 3D Bioprinted Bone Grafts

Reconstruction of segmental bone defects by autologous bone grafting is still the standard of care but presents challenges including anatomical availability and potential donor site morbidity. The process of 3D bioprinting, the application of 3D printing for direct fabrication of living tissue, opens new possibilities for highly personalized tissue implants, making it an appealing alternative to autologous bone grafts. One of the most crucial hurdles for the clinical application of 3D bioprinting is the choice of a suitable cell source, which should be minimally invasive, with high osteogenic potential, with fast, easy expansion. In this study, mesenchymal progenitor cells were isolated from clinically relevant human bone biopsy sites (explant cultures from alveolar bone, iliac crest and fibula; bone marrow aspirates; and periosteal bone shaving from the mastoid) and 3D bioprinted using projection-based stereolithography. Printed constructs were cultivated for 28 days and analyzed regarding their osteogenic potential by assessing viability, mineralization, and gene expression. While viability levels of all cell sources were comparable over the course of the cultivation, cells obtained by periosteal bone shaving showed higher mineralization of the print matrix, with gene expression data suggesting advanced osteogenic differentiation. These results indicate that periosteum-derived cells represent a highly promising cell source for translational bioprinting of bone tissue given their superior osteogenic potential as well as their minimally invasive obtainability.

Preclinical studies on pleiotropic functions of erythropoietin on bone healing

Erythropoietin (ЕPО) is a glycoprotein hormone, mainly known for its haemopoietic function. For orthopaedics, its pleiotropic effects – osteogenic and angiogenic potential, are of primary interest. The exact mechanism of EPO action is still unclear. The effects of EPO on bone healing were investigated through experiments with rats, mice, rabbits and pigs. Each of used models for experimental bone defects (calvarial models, long bone segmental defects, posterolateral spinal fusion and corticosteroid-induced femoral head osteonecrosis) has specific advantages and flaws. Obtaining specific and correct results is largely dependent on the used model. The brief evaluation of models could serve for standardisation of preclinical studies on bone regeneration.

3D bioprinting for orthopaedic applications: Current advances, challenges and regulatory considerations

In the era of personalised medicine, novel therapeutic approaches raise increasing hopes to address currently unmet medical needs by developing patient-customised treatments. Three-dimensional (3D) bioprinting is rapidly evolving and has the potential to obtain personalised tissue constructs and overcome some limitations of standard tissue engineering approaches. Bioprinting could support a wide range of biomedical applications, such as drug testing, tissue repair or organ transplantation. There is a growing interest for 3D bioprinting in the orthopaedic field, with remarkable scientific and technical advances. However, the full exploitation of 3D bioprinting in medical applications still requires efforts to anticipate the upcoming challenges in translating bioprinted products from bench to bedside. In this review we summarised current trends, advances and challenges in the application of 3D bioprinting for bone and cartilage tissue engineering. Moreover, we provided a detailed analysis of the applicable regulations through the 3D bioprinting process and an overview of available standards covering bioprinting and additive manufacturing.

Reduction-responsive sulfur dioxide polymer prodrug nanoparticles loaded with irinotecan for combination osteosarcoma therapy

Combination therapy can boost the therapeutic effectiveness of monotherapies by achieving synergy between therapeutic agents. Herein, a reduction-responsive sulfur dioxide (SO₂) polymer prodrug was synthesized as a nanocarrier to load irinotecan (IRN) to be used in combination osteosarcoma therapy. The SO₂ prodrug (denoted as mPEG-PLG (DNs)) was synthesized by coupling a small-molecule SO₂ donor, N-(3-azidopropyl)-2,4-dinitrobenzenesulfonamide (AP-DNs), to the side chains of methoxy poly (ethylene glycol)-block-poly (γ-propargyl-_L-glutamate) block copolymer. The mPEG-PLG (DNs) had the ability to self-assemble into micelles while simultaneously encapsulating IRN in aqueous media. The formed micelles led to enhanced SO₂ and IRN release in reductive conditions. Using nile red as a model drug, the loaded micelles were efficiently internalized by cancer cells, demonstrated by confocal laser scanning microscopy and flow cytometry. The release of SO₂ within nanoparticles (NPs) in tumor cells led to enhanced intracellular reactive oxygen species amounts together with induced oxidative destruction to cancer cells. Furthermore, the IRN-loaded SO₂ polymer prodrug NPs mediated synergistic therapeutic effects against osteosarcoma cells, leading to improved biodistribution and enhanced tumor growth inhibition over control groups in a murine osteosarcoma model. Taken together, this work highlights the potential of SO₂ polymer prodrugs as reduction-responsive nanocarriers to load chemotherapeutics for effective combination osteosarcoma therapy.

Biological and mechanical performance and degradation characteristics of calcium phosphate cements in large animals and humans

Calcium phosphate cements (CPCs) have been used to treat bone defects and support bone regeneration because of their good biocompatibility and osteointegrative behavior. Since their introduction in the 1980s, remarkable clinical success has been achieved with these biomaterials, because they offer the unique feature of being moldable and even injectable into implant sites, where they harden through a low-temperature setting reaction. However, despite decades of research efforts, two major limitations concerning their biological and mechanical performance hamper a broader clinical use. Firstly, achieving a degradation rate that is well adjusted to the dynamics of bone formation remains a challenging issue. While apatite-forming CPCs frequently remain for years at the implant site without major signs of degradation, brushite-forming CPCs are considered to degrade to a greater extent. However, the latter tend to convert into lower soluble phases under physiological conditions, which makes their degradation behavior rather unpredictable. Secondly, CPCs exhibit insufficient mechanical properties for load bearing applications because of their inherent brittleness. This review places an emphasis on these limitations and provides an overview of studies that have investigated the biological and biomechanical performance as well as the degradation characteristics of different CPCs after implantation into trabecular bone. We reviewed studies performed in large animals, because they mimic human bone physiology more closely in terms of bone metabolism and mechanical loading conditions compared with small laboratory animals. We compared the results of these studies with clinical trials that have dealt with the degradation behavior of CPCs after vertebroplasty and kyphoplasty.

A facile one-stage treatment of critical bone defects using a calcium sulfate/hydroxyapatite biomaterial providing spatiotemporal delivery of bone morphogenic protein-2 and zoledronic acid

Bone morphogenic proteins (BMPs) are the only true osteoinductive molecules. Despite being tremendously potent, their clinical use has been limited for reasons including supraphysiological doses, suboptimal delivery systems, and the pro-osteoclast effect of BMPs. Efforts to achieve spatially controlled bone formation using BMPs are being made. We demonstrate that a carrier consisting of a powder of calcium sulfate/hydroxyapatite (CaS/HA) mixed with bone active molecules provides an efficient drug delivery platform for critical femoral defect healing in rats. The bone-active molecules were composed of osteoinductive rhBMP-2 and the bisphosphonate, and zoledronic acid (ZA) was chosen to overcome BMP-2-induced bone resorption. It was demonstrated that delivery of rhBMP-2 was necessary for critical defect healing and restoration of mechanical properties, but codelivery of BMP-2 and ZA led to denser and stronger fracture calluses. Together, the CaS/HA biomaterial with rhBMP-2 and/or ZA can potentially be used as an off-the-shelf alternative to autograft bone.

ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect

The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO₂-10.3CaO-3.3P₂O₅-4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN + MSC, 4ZN + OST or 4ZN + MSC + OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological, and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice.

Mechano-Bactericidal Titanium Surfaces for Bone Tissue Engineering

Despite advances in the development of bone substitutes and strict aseptic procedures, the majority of failures in bone grafting surgery are related to nosocomial infections. Development of biomaterials combining both osteogenic and antibiotic activity is, therefore, a crucial public health issue. Herein, two types of intrinsically bactericidal titanium supports were fabricated by using commercially scalable techniques: plasma etching or hydrothermal treatment, which display two separate mechanisms of mechano-bactericidal action. Hydrothermal etching produces a randomly nanostructured surface with sharp nanosheet protrusions killing bacteria via cutting of the cell membrane, whereas plasma etching of titanium produces a microscale two-tier hierarchical topography that both reduce bacterial attachment and rupture those bacteria that encounter the surface. The adhesion, growth, and proliferation of human adipose-derived stem cells (hASCs) on the two mechano-bactericidal topographies were assessed. Both types of supports allowed the growth and proliferation of the hASCs in the same manner and cells retained their stemness and osteogenic potential. Furthermore, these supports induced osteogenic differentiation of hASCs without the need of differentiation factors, demonstrating their osteoinductive properties. This study proves that these innovative mechano-bactericidal titanium surfaces with both regenerative and bactericidal properties are a promising solution to improve the success rate of reconstructive surgery.

Bone Healing Evaluation Following Different Osteotomic Techniques in Animal Models: A Suitable Method for Clinical Insights

Osteotomy is a common step in oncological, reconstructive, and trauma surgery. Drilling and elevated temperature during osteotomy produce thermal osteonecrosis. Heat and associated mechanical damage during osteotomy can impair bone healing, with consequent failure of fracture fixation or dental implants. Several ex vivo studies on animal bone were recently focused on heating production during osteotomy with conventional drill and piezoelectric devices, particularly in endosseous dental implant sites. The current literature on bone drilling and osteotomic surface analysis is here reviewed and the dynamics of bone healing after osteotomy with traditional and piezoelectric devices are discussed. Moreover, the methodologies involved in the experimental osteotomy and clinical studies are compared, focusing on ex vivo and in vivo findings.

Research hotspots and trends of bone defects based on Web of Science: a bibliometric analysis

BACKGROUND

Bone defects can be seen everywhere in the clinic, but it is still a challenge for clinicians. Bibliometrics tool CiteSpace is based on the principle of "co-citation analysis theory" to reveal new technologies, hotspots, and trends in the medical field. In this study, CiteSpace was used to perform co-citation analysis on authors, countries (regions) and institutions, journals and cited journals, authors and cited literature, as well as keywords to reveal leaders, cooperative institutions, and research hotspots of bone defects and predict development trends.

METHOD

Data related to bone defect from 1994 to 2019 were retrieved from the Web of Science core collection; then, we use Excel to construct an exponential function to predict the number of annual publications; conduct a descriptive analysis on the top 10 journals with the largest number of publications; and perform co-citation analysis on authors, countries (regions) and institutions, journals and cited journals, authors and cited reference, and keywords using CiteSpace V5.5 and use the Burst Detection Algorithm to perform analysis on the countries (regions) and institutions and keywords, as well as cluster the keywords using log-likelihood ratio.

RESULTS

A total of 5193 studies were retrieved, and the number of annual publications of bone defects showed an exponential function Y = 1×10- 70e0.0829x (R2 = 0.9778). The high-yield author was Choi Seong-Ho at Yonsei University in South Korea. The high-yielding countries were the USA and Germany, and the high-yielding institutions were the Sao Paulo University and China and the Chinese Academy of Sciences which were the emerging research countries and institutions. The research results were mainly published in the fields of dentistry, bone, and metabolism. Among them, the Journal of Dental Research and Journal of Bone and Mineral Research were high-quality journals that report bone defect research, but the most cited journal was the Clinical Orthopaedics and Related Research. Hot keywords were regeneration, repair, in vitro, bone regeneration, reconstruction, and graft. The keywords that were strongly cited in 2010-2019 were transportation, osteogenic differentiation, proliferation, and biomaterials. After 2018, proliferation, osteogenic differentiation, stromal cells, transmission, and mechanical properties have become new vocabulary. The drug delivery, vascularization, osteogenic differentiation and biomaterial properties of bone defects were expected to be further studied.

CONCLUSION

The application of CiteSpace can reveal the leaders, cooperating institutions and research hotspots of bone defects and provide references for new technologies and further research directions.

Advances in translational orthopaedic research with species-specific multipotent mesenchymal stromal cells derived from the umbilical cord

Compliance with current regulations for the development of innovative medicines require the testing of candidate therapies in relevant translational animal models prior to human use. This poses a great challenge when the drug is composed of cells, not only because of the living nature of the active ingredient but also due to its human origin, which can subsequently lead to a xenogeneic response in the animals. Although immunosuppression is a plausible solution, this is not suitable for large animals and may also influence the results of the study by altering mechanisms of action that are, in fact, poorly understood. For this reason, a number of procedures have been developed to isolate homologous species-specific cell types to address preclinical pharmacodynamics, pharmacokinetics and toxicology. In this work, we present and discuss advances in the methodologies for derivation of multipotent Mesenchymal Stromal Cells derived from the umbilical cord, in general, and Wharton's jelly, in particular, from medium to large animals of interest in orthopaedics research, as well as current and potential applications in studies addressing proof of concept and preclinical regulatory aspects.

Real-Time Wireless Platform for In Vivo Monitoring of Bone Regeneration

For the monitoring of bone regeneration processes, the instrumentation of the fixation is an increasingly common technique to indirectly measure the evolution of bone formation instead of ex vivo measurements or traditional in vivo techniques, such as X-ray or visual review. A versatile instrumented external fixator capable of adapting to multiple bone regeneration processes was designed, as well as a wireless acquisition system for the data collection. The design and implementation of the overall architecture of such a system is described in this work, including the hardware, firmware, and mechanical components. The measurements are conditioned and subsequently sent to a PC via wireless communication to be in vivo displayed and analyzed using a developed real-time monitoring application. Moreover, a model for the in vivo estimation of the bone callus stiffness from collected data was defined. This model was validated in vitro using elastic springs, reporting promising results with respect to previous equipment, with average errors and uncertainties below 6.7% and 14.04%. The devices were also validated in vivo performing a bone lengthening treatment on a sheep metatarsus. The resulting system allowed the in vivo mechanical characterization of the bone callus during experimentation, providing a low-cost, simple, and highly reliable solution.

3D Biomimetic Porous Titanium (Ti6Al4V ELI) Scaffolds for Large Bone Critical Defect Reconstruction: An Experimental Study in Sheep

Simple Summary

The authors propose a new reconstructive technique that proved to be suitable to reach this purpose through the use of a custom-made biomimetic porous titanium scaffold. An in vivo study was undertaken where a complete critical defect was experimentally created in the diaphysis of the right tibia of twelve sheep and replaced with a five-centimeter porous scaffold of electron beam melting (EBM)-manufactured titanium alloy or a porous hydroxyapatite scaffold. Our results show that EBM-formed titanium devices, if used to repair critical bone defects in a large animal model, can guarantee immediate body weight-bearing, a rapid functional recovery, and a good osseointegration. The porous hydroxyapatite scaffolds proved to be not suitable in this model of large bone defect due to their known poor mechanical properties.

Abstract

The main goal in the treatment of large bone defects is to guarantee a rapid loading of the affected limb. In this paper, the authors proposed a new reconstructive technique that proved to be suitable to reach this purpose through the use of a custom-made biomimetic porous titanium scaffold. An in vivo study was undertaken where a complete critical defect was experimentally created in the diaphysis of the right tibia of twelve sheep and replaced with a five-centimeter porous scaffold of electron beam melting (EBM)-sintered titanium alloy (EBM group n = 6) or a porous hydroxyapatite scaffold (CONTROL group, n = 6). After surgery, the sheep were allowed to move freely in the barns. The outcome was monitored for up to 12 months by periodical X-ray and clinical examination. All animals in the CONTROL group were euthanized for humane reasons within the first month after surgery due to the onset of plate bending due to mechanical overload. Nine months after surgery, X-ray imaging showed the complete integration of the titanium implant in the tibia diaphysis and remodeling of the periosteal callus, with a well-defined cortical bone. At 12 months, sheep were euthanized, and the tibia were harvested and subjected to histological analysis. This showed bone tissue formations with bone trabeculae bridging titanium trabeculae, evidencing an optimal tissue-metal interaction. Our results show that EBM-sintered titanium devices, if used to repair critical bone defects in a large animal model, can guarantee immediate body weight-bearing, a rapid functional recovery, and a good osseointegration. The porous hydroxyapatite scaffolds proved to be not suitable in this model of large bone defect due to their known poor mechanical properties.

Obesity/Metabolic Syndrome and Diabetes Mellitus on Peri-implantitis

Literature has reported that up to 50% of dental implants may be affected by peri-implantitis, a bacteria-induced chronic inflammatory process, which promotes osteoclast-mediated bone resorption and inhibits bone formation, leading to progressive bone loss around implants. Current evidence points toward an increased risk for the development of peri-implantitis in both obesity/metabolic syndrome (MetS) and diabetes mellitus (DM) conditions relative to the healthy population. Currently, there is no effective treatment for peri-implantitis and the 50% prevalence in MetS and DM, along with its predicted increase in the worldwide population, presents a major concern in implant dentistry as hyperglycemic conditions are associated with bone-healing impairment; this may be through dysfunction of osteocalcin-induced glucose metabolism. The MetS/DM proinflammatory systemic condition and altered immune/microbiome response affect both catabolic and anabolic events of bone-healing that include increased osteoclastogenesis and compromised osteoblast activity, which could be explained by the dysfunction of insulin receptor that led to activation of signals related with osteoblast differentiation. Furthermore, chronic hyperglycemia along with associated micro- and macro-vascular ailments leads to delayed/impaired wound healing due to activation of pathways that are particularly important in initiating events linked to inflammation, oxidative stress, and cell apoptosis; this may be through deactivation of AKT/PKB protein, which possesses a pivotal role in drive survival and eNOS signaling. This review presents an overview of the local and systemic mechanisms synergistically affecting bone-healing impairment in MetS/DM individuals, as well as a rationale for hierarchical animal model selection, in an effort to characterize peri-implantitis disease and treatment.