Validation of a Femoral Critical Size Defect Model for Orthotopic Evaluation of Bone Healing: A Biomechanical, Veterinary and Trauma Surgical Perspective

TiNbSn alloy plates with low Young's modulus modulates interfragmentary movement and promote osteosynthesis in rat femur

Orthopedic implants such as arthroplasty prostheses, fracture plates, and intramedullary nails often use materials like Ti6Al4V alloy and commercially pure titanium (CP-Ti), which have Young's modulus significantly higher than that of human cortical bone, potentially causing stress shielding and inhibiting effective fracture healing. TiNbSn alloy, a β-type titanium alloy with a lower Young's modulus (40-49 GPa), has shown promise in reducing stress shielding and enhancing bone healing by promoting effective load sharing with bone. This study used 5-hole plates made from TiNbSn alloy and CP-Ti to investigate their effects on bone healing in a rat femoral fracture model. Micro-CT analysis and mechanical testing were performed six weeks postoperatively to assess bone healing. Additionally, Finite element method (FEM) analysis was employed to evaluate stress shielding and interfragmentary movement (IFM) at the fracture site. Micro-CT analysis revealed significantly higher bone volume and mineral density in the TiNbSn group than in the CP-Ti group. Mechanical testing showed increased maximum load and stiffness in the TiNbSn group (77.2 ± 10.0 N for the TiNbSn alloy plate group versus 53.3 ± 8.5 N for the CP-Ti group (p = 0.002)). FEM analysis indicated that TiNbSn plates reduced stress shielding and allowed for greater displacement and strain, promoting IFM conducive to bone healing. The findings suggest that TiNbSn alloy plates are more effective than CP-Ti plates in promoting bone healing by reducing stress shielding and enhancing IFM. The lower Young's modulus of TiNbSn allows better load distribution, facilitating bone regeneration and strengthening at the fracture site.

Advances in Animal Models for Studying Bone Fracture Healing

Fracture is a common traumatic injury that is mostly caused by traffic accidents, falls, and falls from height. Fracture healing is a long-term and complex process, and the mode of repair and rate of healing are influenced by a variety of factors. The prevention, treatment, and rehabilitation of fractures are issues that urgently need to be addressed. The preparation of the right animal model can accurately simulate the occurrence of fractures, identify and observe normal and abnormal healing processes, study disease mechanisms, and optimize and develop specific treatment methods. We summarize the current status of fracture healing research, the characteristics of different animal models and the modeling methods for different fracture types, analyze their advantages and disadvantages, and provide a reference basis for basic experimental fracture modeling.

The effect of soft tissue defect on callus formation in Kunming mice different tibial injury models.. [DOI: 10.21203/rs.3.rs-2006802/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Objective: To investigated the highly replicable bone injury model and the effect of soft tissue defect on bone repair. Methods: Fifty 6-week-old female kunming mice were randomly divided into 5 groups, and the 4 groups of them underwent fracture or bone defect surgery on the right tibia with or without tibialis anterior muscle defect respectively. The right injured tibias and heart blood were collected on day 10 after operation for Micro-CT, histological and ELISA analysis respectively. The fifth group was control group，and the cardiac blood was collected at the same time for ELISA.RESULTS: Micro-CT and histological examination indicated that our modelling approach could successfully provide different animal models of open bone injury. Micro-CT showed a significant increase in the ratio of bone volume to tissue volume (BV/TV, %) after soft tissue defect in different bone injury models compared to the soft tissue preserved group. Histomorphometric analysis demonstrated a significant increase in the amount of total bone callus, cartilage callus and fibrous tissue after soft tissue defects, while the amount of hard callus was significantly reduced. Immunohistochemical analysis showed higher levels of CYR61 and VEGFR2 after soft tissue defect. ELISA results revealed no significant difference in IL-1β levels between the soft tissue preserved and soft tissue defect groups. HE staining also confirmed no significant difference in the degree of inflammatory cell infiltration after soft tissue defect.Conclusion: The above models were simple，highly reproducible, and provided reliable animal models for studying the bone healing. We inferred that mechanical stability played an important role in the process of bone healing, and the soft tissue around the injury site mainly provided fixation and protection.

The Induced Membrane Technique—The Filling Matters: Evaluation of Different Forms of Membrane Filling with and without Bone Marrow Mononuclear Cells (BMC) in Large Femoral Bone Defects in Rats

The Masquelet technique is used to treat large bone defects; it is a two-stage procedure based on an induced membrane. To improve the induced membrane process, demineralized bone matrix in granular (GDBM) and fibrous form (f-DBM) was tested with and without bone marrow mononuclear cells (BMC) as filling of the membrane against the gold standard filling with syngeneic cancellous bone (SCB). A total of 65 male Sprague–Dawley rats obtained a 5 mm femoral defect. These defects were treated with the induced membrane technique and filled with SCB, GDBM, or f-DBM, with or without BMC. After a healing period of eight weeks, the femurs were harvested and submitted for histological, radiological, and biomechanical analyses. The fracture load in the defect zone was lower compared to SCB in all groups. However, histological analysis showed comparable new bone formation, bone mineral density, and cartilage proportions and vascularization. The results suggest that f-DBM in combination with BMC and the induced membrane technique cannot reproduce the very good results of this material in large, non-membrane coated bone defects, nevertheless it supports the maturation of new bone tissue locally. It can be concluded that BMC should be applied in lower doses and inflammatory cells should be removed from the cell preparation before implantation.

The Masquelet Technique: Can Disposable Polypropylene Syringes be an Alternative to Standard PMMA Spacers? A Rat Bone Defect Model

BACKGROUND

Usually, the two-stage Masquelet induced-membrane technique for extremity reconstruction begins with a polymethylmethacrylate (PMMA) cement spacer-driven membrane, followed by an autologous cancellous bone graft implanted into the membrane cavity to promote healing of large bone defects. In exceptional cases, spacers made of polypropylene disposable syringes were successfully used instead of the usual PMMA spacers because of a PMMA cement shortage caused by a lack of resources. However, this approach lacks clinical evidence and requires experimental validation before being recommended as an alternative to the conventional technique.

QUESTIONS/PURPOSES

To (1) develop and (2) validate a critical-sized femoral defect model in rats for two stages of the Masquelet technique and to (3) compare the biological and bone healing properties of polypropylene-induced membranes and PMMA-induced membranes in this model.

METHODS

Fifty male Sprague Dawley rats aged 8 weeks old received a 6-mm femur defect, which was stabilized with an external fixator that was converted into an internal device. In the development phase, the defect was filled with PMMA in 16 rats to determine the most favorable timing for bone grafting. Two rats were excluded since they died of anesthetic complications. The other 14 were successively euthanized after 2 weeks (n = 3), 4 weeks (n = 4), 6 weeks (n = 4), and 8 weeks (n = 3) for induced membrane analyses. In the validation phase, 12 rats underwent both stages of the procedure using a PMMA spacer and were randomly assigned to two groups, whether the induced membrane was preserved or removed before grafting. To address our final objective, we implanted either polypropylene or PMMA spacers into the defect (Masquelet technique Stage 1; n = 11 rats per group) for the period established by the development phase. In each group, 6 of 11 rats were euthanized to compare the biological properties of polypropylene-induced membranes and PMMA-induced membranes using histological qualitative analysis, semiquantitative assessment of the bone morphogenic protein-2 content by immunostaining, and qualitative assessment of the mesenchymal stromal cell (MSC; CD31-, CD45-, CD90+, and CD73+ phenotypes) content by flow cytometry. Quantitative measurements from serum bone turnover markers were also performed. The five remaining rats of each group were used for Masquelet technique Stage 2, in which rat bone allografts were implanted in the induced membrane cavity after the polypropylene or PMMA spacers were removed. These rats recovered for 10 weeks before being euthanized for microCT quantitative measurements and bone histology qualitative assessment to evaluate and compare the extent of bone regeneration between groups.

RESULTS

Induced membrane analyses together with serum bone turnover measurements indicated that a 4-week interval time between stages was the most favorable. Removal of the induced membrane before grafting led to almost constant early implant failures with poor bone formation. Four-week-old rats with polypropylene-triggered induced membranes displayed similar histologic organization as rats with PMMA-driven induced membranes, without any difference in the cell density of the extracellular matrix (4933 ± 916 cells per mm2 for polypropylene versus 4923 ± 1284 cells per mm2 for PMMA; p = 0.98). Induced membrane-derived MSCs were found in both groups with no difference (4 of 5 with polypropylene versus 3 of 3 with PMMA; p > 0.99). Induced membrane bone morphogenic protein-2 immunolabeling and serum bone turnover marker levels were comparable between the polypropylene and PMMA groups. MicroCT analysis found that bone regeneration in the polypropylene group seemed comparable with that in the PMMA group (29 ± 26 mm3 for polypropylene versus 24 ± 18 mm3 for PMMA; p > 0.99). Finally, qualitative histological assessment revealed a satisfactory endochondral ossification maturation in both groups.

CONCLUSION

Using a critical-sized femoral defect model in rats, we demonstrated that polypropylene spacers could induce membrane encapsulation with histologic characteristics and bone regenerative capacities that seem like those of PMMA spacers.

CLINICAL RELEVANCE

In a same bone site, polymers with close physical properties seem to lead to similar foreign body reactions and induce encapsulating membranes with comparable bone healing properties. Polypropylene spacers made from disposable syringes could be a valuable alternative to PMMA. These results support the possibility of a cementless Masquelet technique in cases of PMMA shortage caused by a lack of resources.

A Composite Lactide-Mineral 3D-Printed Scaffold for Bone Repair and Regeneration

Orthopedic tumor resection, trauma, or degenerative disease surgeries can result in large bone defects and often require bone grafting. However, standard autologous bone grafting has been associated with donor site morbidity and/or limited quantity. As an alternate, allografts with or without metallic or polyether-etherketone have been used as grafting substitutes. However, these may have drawbacks as well, including stress shielding, pseudarthrosis, disease-transmission, and infection. There is therefore a need for alternative bone substitutes, such as the use of mechanically compliant three-dimensional (3D)-printed scaffolds. Several off-the-shelf materials are available for low-cost fused deposition 3D printing such as polylactic acid (PLA) and polycaprolactone (PCL). We have previously described the feasibility of 3D-printed PLA scaffolds to support cell activity and extracellular matrix deposition. In this study, we investigate two medical-grade filaments consistent with specifications found in American Society for Testing and Materials (ASTM) standard for semi-crystalline polylactide polymers for surgical implants, a pure polymer (100M) and a copolymeric material (7415) for their cytocompatibility and suitability in bone tissue engineering. Moreover, we assessed the impact on osteo-inductive properties with the addition of beta-tricalcium phosphate (β-TCP) minerals and assessed their mechanical properties. 100M and 7415 scaffolds with the additive β-TCP demonstrated superior mesenchymal stem cells (MSCs) differentiation detected via increased alkaline phosphatase activity (6-fold and 1.5-fold, respectively) and mineralized matrix deposition (14-fold and 5-fold, respectively) in vitro. Furthermore, we evaluated in vivo compatibility, biosafety and bone repair potential in a rat femur window defect model. 100M+β -TCP implants displayed a positive biosafety profile and showed significantly enhanced new bone formation compared to 100M implants evidenced by μCT (39 versus 25% bone volume/tissue volume ratio) and histological analysis 6 weeks post-implantation. These scaffolds are encouraging composite biomaterials for repairing bone applications with a great potential for clinical translation. Further analyses are required with appropriate evaluation in a larger critical-sized defect animal model with long-term follow-up.

Fibrous Demineralized Bone Matrix (DBM) Improves Bone Marrow Mononuclear Cell (BMC)-Supported Bone Healing in Large Femoral Bone Defects in Rats

Regeneration of large bone defects is a major objective in trauma surgery. Bone marrow mononuclear cell (BMC)-supported bone healing was shown to be efficient after immobilization on a scaffold. We hypothesized that fibrous demineralized bone matrix (DBM) in various forms with BMCs is superior to granular DBM. A total of 65 male SD rats were assigned to five treatment groups: syngenic cancellous bone (SCB), fibrous demineralized bone matrix (f-DBM), fibrous demineralized bone matrix densely packed (f-DBM 120%), DBM granules (GDBM) and DBM granules 5% calcium phosphate (GDBM5%Ca2+). BMCs from donor rats were combined with different scaffolds and placed into 5 mm femoral bone defects. After 8 weeks, bone mineral density (BMD), biomechanical stability and histology were assessed. Similar biomechanical properties of f-DBM and SCB defects were observed. Similar bone and cartilage formation was found in all groups, but a significantly bigger residual defect size was found in GDBM. High bone healing scores were found in f-DBM (25) and SCB (25). The application of DBM in fiber form combined with the application of BMCs shows promising results comparable to the gold standard, syngenic cancellous bone. Denser packing of fibers or higher amount of calcium phosphate has no positive effect.

Bone defect reconstruction with a novel biomaterial containing calcium phosphate and aluminum oxide reinforcement

Background

Reconstruction of metaphyseal fractures represents a clinical challenge for orthopedic surgeons. Especially in osteoporotic bone, these fractures are frequently accompanied by osseous substance defects. In order to ensure rapid mobilization of patients, high stability requirements must be met by osteosynthesis. Various bone graft materials have been introduced in the past, such as autologous bone or exogenous bone substitute materials. These are used as bone void fillers or as augmentation techniques to ensure safe fixation of osteosynthesis. New calcium phosphate-based bone void-filling materials could be a promising alternative to autologous bone or to the currently and widely used polymethylmethacrylate (PMMA)-based cement. The aim of this study was to evaluate a novel paste-like bone void filler in vivo and in vitro with regard to biocompatibility and osteoconductivity.

Methods

In addition to in vitro testing of cell compatibility using pre-osteoblasts (MC3T3-E1), 35 Wistar rats were treated in vivo with implantation of various material mixtures based on calcium phosphate and aluminum oxide reinforcement in a metaphyseal drill hole defect. After 4 weeks, an examination by micro-computed tomography (μCT) and histology was performed.

Results

The in vitro analysis showed good biocompatibility with a high cell survival of osteoblasts. In the in vivo experiments, a significantly higher bone ingrowth compared to the empty defect was shown by μCT and histological analysis. Here, the group receiving material reinforced with aluminum oxide (Al₂O₃) showed a bone volume/tissue volume (BV/TV) of 89.19% compared to a BV/TV of 83.14% for the empty defect (p = 0.0013). In the group treated with a polysaccharide matrix, no increase in BV/TV was observed given a mean ratio of 80.14%. Scoring of histological sections did not reveal a significant difference between CaP and CaP that was substituted with Al₂O₃.

Conclusion

The results of this study show an encouraging first step towards the development of new pasty, bone void-filling materials. We demonstrated that a new paste-like bone-filling material, based on calcium phosphate granulates and aluminum oxide to provide strength, exhibits good biocompatibility and osteoconductivity. Further biomechanical test in an osteoporotic animal model will have to be performed, to prove feasibility in metaphyseal defects.

First Human Leucocyte Antigen (HLA) Response and Safety Evaluation of Fibrous Demineralized Bone Matrix in a Critical Size Femoral Defect Model of the Sprague-Dawley Rat

Treatment of large bone defects is one of the great challenges in contemporary orthopedic and traumatic surgery. Grafts are necessary to support bone healing. A well-established allograft is demineralized bone matrix (DBM) prepared from donated human bone tissue. In this study, a fibrous demineralized bone matrix (f-DBM) with a high surface-to-volume ratio has been analyzed for toxicity and immunogenicity. f-DBM was transplanted to a 5-mm, plate-stabilized, femoral critical-size-bone-defect in Sprague-Dawley (SD)-rats. Healthy animals were used as controls. After two months histology, hematological analyses, immunogenicity as well as serum biochemistry were performed. Evaluation of free radical release and hematological and biochemical analyses showed no significant differences between the control group and recipients of f-DBM. Histologically, there was no evidence of damage to liver and kidney and good bone healing was observed in the f-DBM group. Reactivity against human HLA class I and class II antigens was detected with mostly low fluorescence values both in the serum of untreated and treated animals, reflecting rather a background reaction. Taken together, these results provide evidence for no systemic toxicity and the first proof of no basic immunogenic reaction to bone allograft and no sensitization of the recipient.

The Masquelet technique: Current concepts, animal models, and perspectives

Bone reconstruction within a critical-sized defect remains a real challenge in orthopedic surgery. The Masquelet technique is an innovative, two-step therapeutic approach for bone reconstruction in which the placement of a poly (methylmethacrylate) spacer into the bone defect induces the neo-formation of a tissue called "induced membrane." This surgical technique has many advantages and is often preferred to a vascularized bone flap or Ilizarov's technique. Although the Masquelet technique has achieved high clinical success rates since its development by Alain-Charles Masquelet in the early 2000s, very little is known about how the process works, and few animal models of membrane induction have been developed. Our successful use of this technique in the clinic and our interest in the mechanisms of tissue regeneration (notably bone regeneration) prompted us to develop a surgical model of the Masquelet technique in rats. Here, we provide a comprehensive review of the literature on animal models of membrane induction, encompassing the defect site, the surgical procedure, and the histologic and osteogenic properties of the induced membrane. We also discuss the advantages and disadvantages of those models to facilitate efforts in characterizing the complex biological mechanisms that underlie membrane induction.

Osteogenic in vitro training of bone marrow mesenquimal cells for application in segmentary bone resections

OBJECTIVE

To achieve bone continuity in an experimental model of segmental resection of femur bone by applying a treatment with committed to osteogenic bone linage mesenchymal stem cells.

MATERIAL AND METHOD

Bone marrow mesenchymal stem cells, obtained from syngeneic Wistar murine, were committed into osteogenic lineage and embedded within a hydroxipatite block. They were implanted in an experimentally created diaphyseal femur resection model. The diaphysis was synthetized with a 1.5mm thick plate. In order to calculate binomial distributions, we stablished one experimental and 3 control groups of 8 elements each: Group I, filling the gap with allograft; group ii, filling with a hydroxyapatite block without cells; group iii, filling with the hydroxyapatite block embedded with committed cells, and group iv, with the hydroxyapatite embedded with osteoinduced cells in a 3 dimensions TRAP culture. Descriptive analysis was performed by frequency distribution and Fisher statistic test. Level of statistical significance was considered at P<.05.

RESULTS

Group I presented good bone consolidation and no plate breakage. Group II showed fibrous but non-bone tissue, with rupture of all plates. Group III showed bone tissue in all cases, but the plates broke in all of them, while in group iv bone consolidation was achieve without any plate rupture.

CONCLUSION

Cell therapy with mesenchymal stem cells, trained in a 3 dimensions cell culture, produces bone tissue and ensures the permanence of the mechanical stabilization performed in a segmental resection model.

LIMITATIONS

A study with a larger sample size is necessary before planning the human inference.

Determination of the effective dose of bone marrow mononuclear cell therapy for bone healing in vivo

Introduction

Cell-based therapy by bone marrow mononuclear cells (BMC) in a large-sized bone defect has already shown improved vascularization and new bone formation. First clinical trials are already being conducted. BMC were isolated from bone marrow aspirate and given back to patients in combination with a scaffold within some hours. However, the optimal concentration of BMC has not yet been determined for bone healing. With this study, we want to determine the optimal dosage of the BMC in the bone defect to support bone healing.

Material and methods

Scaffolds with increasing BMC concentrations were inserted into a 5 mm femoral defect, cell concentrations of 2 × 10⁶ BMC/mL, 1 × 10⁷ BMC/mL and 2 × 10⁷ BMC/mL were used. Based on the initial cell number used to colonize the scaffolds, the groups are designated 1 × 10⁶, 5 × 10⁶ and 1 × 10⁷ group. Bone healing was assessed biomechanically, radiologically (µCT), and histologically after 8 weeks healing time.

Results

Improved bone healing parameters were noted in the 1 × 10⁶ and 5 × 10⁶ BMC groups. A significantly higher BMD was observed in the 1 × 10⁶ BMC group compared to the other groups. Histologically, a significantly increased bone growth in the defect area was observed in group 5 × 10⁶ BMC. This finding could be supported radiologically.

Conclusion

It was shown that the effective dose of BMC for bone defect healing ranges from 2 × 10⁶ BMC/mL to 1 × 10⁷ BMC/mL. This concentration range seems to be the therapeutic window for BMC-supported therapy of large bone defects. However, further studies are necessary to clarify the exact BMC-dose dependent mechanisms of bone defect healing and to determine the therapeutically effective range more precisely.

Effect of ultrasound on bone fracture healing: A computational mechanobioregulatory model

Bone healing process is a complicated phenomenon regulated by biochemical and mechanical signals. Experimental studies have shown that ultrasound (US) accelerates bone ossification and has a multiple influence on cell differentiation and angiogenesis. In a recent work of the authors, a bioregulatory model for providing bone-healing predictions was addressed, taking into account for the first time the salutary effect of US on the involved angiogenesis. In the present work, a mechanobioregulatory model of bone solidification under the US presence incorporating also the mechanical environment on the regeneration process, which is known to affect cellular processes, is presented. An iterative procedure is adopted, where the finite element method is employed to compute the mechanical stimuli at the linear elastic phases of the poroelastic callus region and a coupled system of partial differential equations to simulate the enhancement by the US cell angiogenesis process and thus the oxygen concentration in the fractured area. Numerical simulations with and without the presence of US that illustrate the influence of progenitor cells' origin in the healing pattern and the healing rate and simultaneously demonstrate the salutary effect of US on bone repair are presented and discussed.

The Efficacy of Recombinant Platelet-Derived Growth Factor on Beta-Tricalcium Phosphate to Regenerate Femoral Critical Sized Segmental Defects: Longitudinal In Vivo Micro-CT Study in a Rat Model

Background and Objectives: Beta-tricalcium phosphate (beta-TCP) has been used for bone regeneration. The objective of this study was to assess longitudinally, the regeneration of critical sized segmental defects (CSSD) in rat femur using beta-TCP with or without recombinant platelet-derived growth factor (PDGF) through in vivo micro-computed tomography (micro-CT). Materials and Methods: Following ethical approval unilateral femoral CSSD measuring 5 mm was surgically created, under general anesthesia, in 30 male Wistar-Albino rats (aged 12-18 months; weighing 450-500 g). CSSD was stabilized using titanium mini-plate (4 holes, 1.0 mm thick with 8 mm bar). Depending upon biomaterial used for regeneration, the animals were randomly divided into: Control group (N = 10): CSSD covered with resorbable collagen membrane (RCM) only; Beta-TCP group (N = 10): CSSD filled with beta-TCP and covered by RCM; Beta-TCP + PDGF group (N = 10): CSSD filled with beta-TCP soaked in recombinant PDGF and covered by RCM. Longitudinal in vivo micro-CT analysis of the CSSD was done postoperatively at baseline, 2nd, 4th, 6th, and 8th weeks to assess volume and mineral density of newly formed bone (NFB) and beta-TCP. Results: Significant increase in NFB volume (NFBV) and mineral density (NFBMD) were observed from baseline to 8-weeks in all groups. Based on longitudinal in vivo micro-CT at 8-weeks, beta-TCP + PDGF group had significantly higher (p < 0.01) NFBV (38.98 ± 7.36 mm³) and NFBMD (3.72 ± 0.32 g/mm³) than the beta-TCP (NFBV-31.15 ± 6.68 mm³; NFBMD-2.28 ± 0.86g/mm³) and control (NFBV: 5.60 ± 1.06 mm³; NFBMD: 0.27 ± 0.02 g/mm³) groups. Significantly, higher reduction in beta-TCP volume (TCPV) and mineral density (TCPMD) were 1 observed in the beta-TCP + PDGF group when compared to the beta-TCP group. Conclusion: Addition of recombinant PDGF to beta-TCP enhanced bone regeneration within rat femoral CSSD and increased resorption rates of beta-TCP particles.

Scaffolds of bioactive glass-ceramic (Biosilicate®) and bone healing: A biological evaluation in an experimental model of tibial bone defect in rats

This study aimed to investigate the in vivo tissue response of the Biosilicate® scaffolds in a model of tibial bone defect. Sixty male Wistar rats were distributed into bone defect control group (CG) and Biosilicate® scaffold group (BG).  Animals were euthanized 15, 30 and 45 days post-surgery. Stereomicroscopy, scanning electron microscopy, histopathological, immunohistochemistry and biomechanical analysis were used. Scaffolds had a total porosity of 44%, macroporosity of 15% with pore diameter of 230 μm. Higher amount of newly formed bone was observed on days 30 and 45 in BG. Immunohistochemistry analysis showed that the COX-2 expression was significantly higher on days 15 and 30 in BG compared with the CG. RUNX-2 immunoexpression was significantly higher in BG on days 15 and 45. No statistically significant difference was observed in RANKL immunoexpression in all experimental groups. BMP-9 immunoexpression was significantly upregulated in the BG on day 45. Biomechanical analysis showed a decrease in the biomechanical properties of the bone callus on days 30 and 45. The implantation of the Biosilicate® scaffolds was effective in stimulating newly bone formation and produced an increased immunoexpression of markers related to the bone repair.

Pedicled Transplantation of Axially Vascularized Bone Constructs in a Critical Size Femoral Defect

INTRODUCTION

Axial vascularization represents a mandatory requirement for clinically applied larger scale vascularized bone grafts. The aim of this study was to combine the arteriovenous (AV) loop model in the rat with a critically sized femoral bone defect and to successfully transplant axially vascularized bone constructs into the defect.

MATERIALS AND METHODS

In Groups A and C, an AV loop together with a clinically approved hydroxyapatite and beta-tricalcium phosphate (HA/β-TCP) matrix, mesenchymal stem cells, and recombinant human bone morphogenetic protein 2 were implanted into a newly designed porous titanium chamber with an integrated osteosynthesis plate in the thighs of rats, whereas in Groups B and D, the same matrix composition without AV loop and, in Group E, only the HA/β-TCP matrix were implanted. After 6 weeks, the constructs were transplanted into a 10 mm femoral defect created in the same leg, in Groups A and C, under preservation of the AV loop pedicle. Group F served as a control group with an empty chamber. Ten days (Groups A and B) and 12 weeks (Groups C-F) after transplantation, the femora together with the constructs were explanted and investigated using computed tomography (CT), micro-CT, X-ray, histology, and real-time polymerase chain reaction (RT-PCR).

RESULTS

Ten days after transplantation, Group A showed a maintained vascular supply leading to increased vascularization, cell survival in the scaffold center, and bone generation compared to Group B. After 12 weeks, there was no difference detectable among all groups regarding total vessel number, although Group C, using the AV loop, still showed increased vascularization of the construct center compared to Groups D and E. In Group C, there was still enhanced bone generation detectable compared to the other groups and increased bony fusion rate at the proximal femoral stump.

CONCLUSIONS

This study shows the combination of the AV loop model in the rat with a critically sized femoral defect. By maintenance of the vascular supply, the constructs initially showed increased vascularization, leading to increased bone formation and bony fusion in the long term.

Composite biopolymers for bone regeneration enhancement in bony defects

For the past century, various biomaterials have been used in the treatment of bone defects and fractures. Their role as potential substitutes for human bone grafts increases as donors become scarce. Metals, ceramics and polymers are all materials that confer different advantages to bone scaffold development. For instance, biocompatibility is a highly desirable property for which naturally-derived polymers are renowned. While generally applied separately, the use of biomaterials, in particular natural polymers, is likely to change, as biomaterial research moves towards mixing different types of materials in order to maximize their individual strengths. This review focuses on osteoconductive biocomposite scaffolds which are constructed around natural polymers and their performance at the in vitro/in vivo stages and in clinical trials.

Establishment of a Segmental Femoral Critical-size Defect Model in Mice Stabilized by Plate Osteosynthesis

The use of tissue-engineered bone constructs is an appealing strategy to overcome drawbacks of autografts for the treatment of massive bone defects. As a model organism, the mouse has already been widely used in bone-related research. Large diaphyseal bone defect models in mice, however, are sparse and often use bone fixation which fills the bone marrow cavity and does not provide optimal mechanical stability. The objectives of the current study were to develop a critical-size, segmental, femoral defect in nude mice. A 3.5-mm mid-diaphyseal femoral ostectomy (approximately 25% of the femur length) was performed using a dedicated jig, and was stabilized with an anterior located locking plate and 4 locking screws. The bone defect was subsequently either left empty or filled with a bone substitute (syngenic bone graft or coralline scaffold). Bone healing was monitored noninvasively using radiography and in vivo micro-computed-tomography and was subsequently assessed by ex vivo micro-computed-tomography and undecalcified histology after animal sacrifice, 10 weeks postoperatively. The recovery of all mice was excellent, a full-weight-bearing was observed within one day following the surgical procedure. Furthermore, stable bone fixation and consistent fixation of the implanted materials were achieved in all animals tested throughout the study. When the bone defects were left empty, non-union was consistently obtained. In contrast, when the bone defects were filled with syngenic bone grafts, bone union was always observed. When the bone defects were filled with coralline scaffolds, newly-formed bone was observed in the interface between bone resection edges and the scaffold, as well as within a short distance within the scaffold.

The present model describes a reproducible critical-size femoral defect stabilized by plate osteosynthesis with low morbidity in mice. The new load-bearing segmental bone defect model could be useful for studying the underlying mechanisms in bone regeneration pertinent to orthopaedic applications.

A new, low cost, locking plate for the long-term fixation of a critical size bone defect in the ratfemur: in vivo performance, biomechanical and finite element analysis

BACKGROUND

The optimum fixation device for the critical size bone defect is not established yet.

OBJECTIVE

A reliable, feasible and low-cost fixation device for the long-term maintenance of a critical bone defect.

METHODS

A custom-made plate made of poly-methyl-methacrylate was used for the fixation of a critical defect of rats' femurs. The screws were securely fixing both on the plate and the bone. A three point bending test, aimed to resemble the in vivo loading pattern, a Finite Element Analysis and a 24-week in vivo monitoring of the integrity of the plate fixation were utilized.

RESULTS

The plate has linear and reproducible behavior. It presents no discontinuities in the stress field of the fixation. Its properties are attributed to the material and the locking principle. It fails beyond the level of magnitude of the normal ambulatory loads. In vivo, 100% of the plates maintained the bone defect intact up to 12 weeks and 85% of them at 24 weeks.

CONCLUSION

This novel locking plate shows optimal biomechanical performance and reliability with high long-term in vivo survival rate. It is fully implantable, inexpensive and easily manufactured. It can be qualified for long term critical defect fixation in bone regeneration studies.

The masquelet induced membrane technique with BMP and a synthetic scaffold can heal a rat femoral critical size defect

Long bone defects can be managed by the induced membrane technique together with autologous bone graft. However, graft harvest is associated with donor site morbidity. This study investigates if a tricalcium phosphate hydroxyapatite scaffold can be used alone or in combination with bone active drugs to improve healing. Sprague Dawley rats (n = 40) were randomized into four groups. (A) scaffold, (B) BMP-7, (C) BMP-7 + scaffold, and (D) BMP-7 + scaffold + systemic bisphosphonate at 2 weeks. Locked femoral nailing was followed by 6 mm segment removal and implantation of an epoxy spacer. At 4 weeks, the spacers were removed and the defects grafted. Eleven weeks later, the bones were explanted for evaluation with radiography, manual assessment, micro-CT, histology, and Fourier Transform Infrared spectroscopy (FTIR). Isolated scaffolds (A) did not heal any defects, whereas the other treatments led to healing in 7/10 (B), 10/10 (C), and 9/10 (D) rats. Group D had greater volume of highly mineralized bone (p < 0.01) and higher bone volume fraction (p < 0.01) compared to all other groups. A synthetic scaffold + BMP-7 combined with a bisphosphonate improved the callus properties in a rat femoral critical size defect, compared to both BMP-7 and scaffold alone or the two combined.

Porous bioactive scaffolds: characterization and biological performance in a model of tibial bone defect in rats

The aim of this study was to evaluate the effects of highly porous Biosilicate(®) scaffolds on bone healing in a tibial bone defect model in rats by means of histological evaluation (histopathological and immunohistochemistry analysis) of the bone callus and the systemic inflammatory response (immunoenzymatic assay). Eighty Wistar rats (12 weeks-old, weighing±300 g) were randomly divided into 2 groups (n=10 per experimental group, per time point): control group and Biosilicate® group (BG). Each group was euthanized 3, 7, 14 and 21 days post-surgery. Histological findings revealed a similar inflammatory response in both experimental groups, 3 and 7 days post-surgery. During the experimental periods (3-21 days post-surgery), it was observed that the biomaterial degradation, mainly in the periphery region, provided the development of the newly formed bone into the scaffolds. Immunohistochemistry analysis demonstrated that the Biosilicate® scaffolds stimulated cyclooxygenase-2, vascular endothelial growth factor and runt-related transcription factor 2 expression. Furthermore, in the immunoenzymatic assay, BG presented no difference in the level of tumor necrosis factor alpha in all experimental periods. Still, BG showed a higher level of interleukin 4 after 14 days post-implantation and a lower level of interleukin 10 in 21 days post-surgery. Our results demonstrated that Biosilicate® scaffolds can contribute for bone formation through a suitable architecture and by stimulating the synthesis of markers related to the bone repair.

Effect of low-level laser therapy on bone repair: a randomized controlled experimental study

The aim of this study was to investigate the effect of low-level laser therapy (LLLT) on bone repair in femoral fractures. Sixty adult Wistar rats were randomly assigned into one of two groups: group A (ostectomy + LLLT) or group B (ostectomy + sham laser). An experimental model of complete bone fracture was surgically created by removing a 2-mm fragment from the middle third of the femoral shaft. Data were analyzed on days 8, 13, and 18 after the fracture (subgroups 1, 2, and 3). Samples were assessed for changes in inflammatory infiltration; trabecular bone matrix, periosteal, and new bone formations; and changes in the expression of particular osteogenic-related proteins (osteocalcin, osteopontin, and osteonectin). Microscopic analysis revealed a significant decrease in inflammatory infiltration, intense trabecular bone matrix and periosteal formation, and an increase in newly formed bone after laser irradiation. We also found an increase in the expression of bone matrix proteins with LLLT, with a significant difference measured for osteocalcin in the LLLT group at day 8 (p = 0.007). We show that LLLT plays an important role in augmenting bone tissue formation, which is relevant to fracture healing. LLLT may therefore be indicated as an adjunct therapeutic tool in clinical practice for the treatment or recovery of nonunion injuries.

Preparation of an rhBMP-2 loaded mesoporous bioactive glass/calcium phosphate cement porous composite scaffold for rapid bone tissue regeneration

An rhBMP-2/MBG/CPC scaffold is beneficial for rapid bone tissue regeneration in the early stage.

Non-union site debridement increased the efficacy of rhBMP-2 in a rodent model

In our study we investigated the influence of debridement on bone healing in a rodent critical size defect model with and without rhBMP-2 in fibrin matrix. A total of 58 male Sprague-Dawley rats underwent a first surgical procedure where a femoral osteotomy was performed. In the single step group the defect remained empty and the specimens were collected 4 weeks later. A silicone spacer was implanted to inhibit bone healing within the defect in all the other groups. At 4 weeks the spacer was removed in a second operation with and without debridement of the bone ends and fibrin matrix alone or combined with 10 μg rhBMP-2 were applied. 4 weeks after the primary operation those specimens were collected. All the specimens were evaluated by μCT scans and histological analysis. Debridement of the defect significantly increased bone volume in the animals treated with rhBMP-2. In the control groups without growth factor application the effect of debridement was not significant concerning the union rate and the bone volume. In our experimental setting surgical debridement of the non-union site particularly promoted bone healing in combination with BMP-2 administration in fibrin matrix.

Osteoclasts and their precursors are present in the induced-membrane during bone reconstruction using the Masquelet technique

In 2000, Masquelet reported a long bone reconstruction technique using an induced membrane formed around a polymethylmethacrylate (PMMA) spacer placed in the defect with appropriate stabilization followed by secondary bone graft after PMMA removal. This reconstruction procedure allows rapid and safe bone reformation for septic, traumatic, neoplastic or congenital bone defects. A rat model of the Masquelet technique was developed to further characterize the biological activities of this induced membrane. Our model allows healing of a critical-sized femoral defect (8 mm) by means of this procedure over a period of 18 weeks. Comparison of induced membranes obtained 3, 4, 5 and 6 weeks after PMMA insertion indicated that this tissue changes over time. Several mineralization spots and bone cells were observed in contact with the PMMA, when assessed by Alizarin Red, Von Kossa, Alkaline phosphatase and Tartrate-resistant acid phosphatase staining of the membranes. CTR (calcitonin receptor)- and RANK (Receptor Activator of Nuclear factor Kappa B)- positive mononuclear cells were detected in the induced membrane, confirming the presence of osteoclasts in this tissue. These cells were observed in a thin, highly cellular layer in the induced membrane in contact with the PMMA. Together, these findings suggest that the membrane is able to promote osteointegration of autologous corticocancellous bone grafts during the Masquelet technique by creating local conditions that may be favourable to graft bone remodelling and osteointegration. Copyright © 2014 John Wiley & Sons, Ltd.

Establishment of a bilateral femoral large segmental bone defect mouse model potentially applicable to basic research in bone tissue engineering

BACKGROUND

To understand the cellular mechanism underlying bone defect healing in the context of tissue engineering, a reliable, reproducible, and standardized load-bearing large segmental bone defect model in small animals is indispensable. The aim of this study was to establish and evaluate a bilateral femoral defect model in mice.

MATERIALS AND METHODS

Donor mouse bone marrow mesenchymal stem cells (mBMSCs) were obtained from six mice (FVB/N) and incorporated into partially demineralized bone matrix scaffolds to construct tissue-engineered bones. In total, 36 GFP(+) mice were used for modeling. Titanium fixation plates with locking steel wires were attached to the femurs for stabilization, and 2-mm-long segmental bone defects were created in the bilateral femoral midshafts. The defects in the left and right femurs were transplanted with tissue-engineered bones and control scaffolds, respectively. The healing process was monitored by x-ray radiography, microcomputed tomography, and histology. The capacity of the transplanted mBMSCs to recruit host CD31(+) cells was investigated by immunofluorescence and real-time polymerase chain reaction.

RESULTS

Postoperatively, no complication was observed, except that two mice died of unknown causes. Stable fixation of femurs and implants with full load bearing was achieved in all animals. The process of bone defect repair was significantly accelerated due to the introduction of mBMSCs. Moreover, the transplanted mBMSCs attracted more host CD31(+) endothelial progenitors into the grafts.

CONCLUSIONS

The present study established a feasible, reproducible, and clinically relevant bilateral femoral large segmental bone defect mouse model. This model is potentially suitable for basic research in the field of bone tissue engineering.

Defining the critical-sized defect in a rat segmental mandibulectomy model

IMPORTANCE

Advances in tissue engineering offer potential alternatives to current mandibular reconstructive techniques; however, before clinical translation of this technology, a relevant animal model must be used to validate possible interventions.

OBJECTIVE

To establish the critical-sized segmental mandibular defect that does not heal spontaneously in the rat mandible.

DESIGN AND SETTING

Prospective study of mandibular defect healing in 29 Sprague-Dawley rats in an animal laboratory.

INTERVENTIONS

The rats underwent creation of 1 of 4 segmental mandibular defects measuring 0, 1, 3, and 5 mm. All mandibular wounds were internally fixated with 1-mm microplates and screws and allowed to heal for 12 weeks, after which the animals were killed humanely.

MAIN OUTCOMES AND MEASURES

Analysis with micro-computed tomography of bony union and formation graded on semiquantitative scales.

RESULTS

Seven animals were included in each experimental group. No 5-mm segmental defects successfully developed bony union, whereas all 0- and 1-mm defects had continuous bony growth across the original defect on micro-computed tomography. Three of the 3-mm defects had bony continuity, and 3 had no healing of the bony wound. Bone union scores were significantly lower for the 5-mm defects compared with the 0-, 1-, and 3-mm defects (P < .01).

CONCLUSIONS AND RELEVANCE

The rat segmental mandible model cannot heal a 5-mm segmental mandibular defect. Successful healing of 0-, 1-, and 3-mm defects confirms adequate stabilization of bony wounds with internal fixation with 1-mm microplates. The rat segmental mandibular critical-sized defect provides a clinically relevant testing ground for translatable mandibular tissue engineering efforts.

Evaluation of injectable constructs for bone repair with a subperiosteal cranial model in the rat

While testing regenerative medicine strategies, the use of animal models that match the research questions and that are related to clinical translation is crucial. During the initial stage of evaluating new strategies for bone repair, the main goal is to state whether the strategies efficiently induce the formation of new bone tissue at an orthotopic site. Here, we present a subperiosteal model in rat calvaria that allow the evaluation of a broad range of approaches including bone augmentation, replacement and regeneration. The model is a fast to perform, minimally invasive, and has clearly defined control groups. The procedure enables to evaluate the outcomes quantitatively using micro-computed tomography and qualitatively by histology and immunohistochemistry. We established this new model, using bone morphogenetic protein-2 as an osteoinductive factor and hyaluronic acid hydrogel as injectable biomaterial. We showed that this subperiosteal cranial model offers a minimally invasive and promising solution for a rapid initial evaluation of injectables for bone repair. We believe that this approach could be a powerful platform for orthopedic research and regenerative medicine.

Controlled release strategies for bone, cartilage, and osteochondral engineering--Part I: recapitulation of native tissue healing and variables for the design of delivery systems

The potential of growth factors to stimulate tissue healing through the enhancement of cell proliferation, migration, and differentiation is undeniable. However, critical parameters on the design of adequate carriers, such as uncontrolled spatiotemporal presence of bioactive factors, inadequate release profiles, and supraphysiological dosages of growth factors, have impaired the translation of these systems onto clinical practice. This review describes the healing cascades for bone, cartilage, and osteochondral interface, highlighting the role of specific growth factors for triggering the reactions leading to tissue regeneration. Critical criteria on the design of carriers for controlled release of bioactive factors are also reported, focusing on the need to provide a spatiotemporal control over the delivery and presentation of these molecules.

Comparative evaluation of in vivo osteogenic differentiation of fetal and adult mesenchymal stem cell in rat critical-sized femoral defect model

Mesenchymal stem cells (MSCs) can be obtained from various sources. MSCs from different origins appear to have different preferences for differentiation. In this study, we have compared the in vivo osteogenic potential of adult MSCs from adipose tissue (AT) and bone marrow (BM) with fetal MSCs from umbilical cord (UC) and umbilical cord blood (UCB) by using a rat critical-sized femoral defect model. We have also sought to determine whether pretreatment with an osteogenic medium promotes osteogenesis in MSCs. Study groups were divided as follows: (1) defect only, (2) scaffold only, (3) AT MSCs in scaffolds, (4) BM MSCs in scaffolds, (5) UC MSCs in scaffolds and (6) UCB MSCs in scaffolds. Groups with MSCs were further divided with respect to their pretreatment. At 12 weeks after surgery, in vivo osteogenesis was measured radiographically and by micro-computed tomography (CT). Based on quantitative assessment by micro-CT, no significant difference of the mean bone volume fraction value (BV/TV) was seen between adult MSCs (AT and BM MSCs) and fetal MSCs (UC and UCB MSCs). The mean BV/TVs were significantly higher in non-pretreated BM MSC (14.2±1.4%) and UCB MSC (14.0±1.2%) and pretreated UC MSC (14.8±2.0%) than in those with the scaffold only (11.3±1.3%; P<0.05). In addition, AT (from 10.4±1.2% to 13.1±2.2%) and UC (from 10.3±0.7% to 14.8±2.0%) MSCs from solid tissues showed a significant increase in the mean BV/TV with pretreatment (P<0.05). In contrast, BM MSC (from 14.2±1.4% to 10.9±1.2%) and UCB MSC (from 14.0±1.2% to 11.6±1.0%) from non-solid tissues showed a significant decrease with pretreatment (P<0.05).

External fixation of femoral defects in athymic rats: Applications for human stem cell implantation and bone regeneration

An appropriate animal model is critical for the research of stem/progenitor cell therapy and tissue engineering for bone regeneration in vivo. This study reports the design of an external fixator and its application to critical-sized femoral defects in athymic rats. The external fixator consists of clamps and screws that are readily available from hardware stores as well as Kirschner wires. A total of 35 rats underwent application of the external fixator with creation of a 6-mm bone defect in one femur of each animal. This model had been used in several separate studies, including implantation of collagen gel, umbilical cord blood mesenchymal stem cells, endothelial progenitor cells, or bone morphogenetic protein-2. One rat developed fracture at the proximal pin site and two rats developed deep tissue infection. Pin loosening was found in nine rats, but it only led to the failure of external fixation in two animals. In 8 to 10 weeks, various degrees of bone growth in the femoral defects were observed in different study groups, from full repair of the bone defect with bone morphogenetic protein-2 implantation to fibrous nonunion with collagen gel implantation. The external fixator used in these studies provided sufficient mechanical stability to the bone defects and had a comparable complication rate in athymic rats as in immunocompetent rats. The external fixator does not interfere with the natural environment of a bone defect. This model is particularly valuable for investigation of osteogenesis of human stem/progenitor cells in vivo.

Effect of sonic hedgehog/β-TCP composites on bone healing within the critical-sized rat femoral defect

The creation of entirely synthetically derived bone substitute materials which are as effective as autologous bone grafts is desirable. Osteogenesis involves the concerted action of several proteins within a signaling cascade. Hedgehog proteins act upstream of this cascade, inducing the expression of various bone morphogenetic proteins (BMPs) and promoting physiological bone healing. Therefore, the hypothesis that hedgehog signaling in bone defects improves bone healing more than BMP signaling alone was tested. Recombinant N-terminal sonic hedgehog protein (N-SHh), BMP-2 or a combination of the two was added to β-tricalcium phosphate (β-TCP) and 5-mm femoral midshaft defects in nude rats were filled with these composites. The defects were stabilized with mini-plates. After eight weeks, the animals were sacrificed and the femora were explanted. The radiological evaluation was followed by a three-point bending test and histological examination. BMP-2/β-TCP composites showed a trend of increased stiffness compared with the controls (β-TCP without protein). N-SHh/β-TCP composites had lower stiffness compared with the control group and the N-SHh/BMP-2/β-TCP composites also had lower average stiffness compared with the controls (all not significant). Histomorphometry, however, revealed abundant cartilage and bone core formation in the N-SHh-composite groups. The sum of the new cartilage and bone was highest in the combination group N-SHh/BMP-2 (not significant). The addition of N-SHh to bone substitute materials appears to delay bone healing at the applied concentration and observation time but also showed a trend for higher amounts of ossifying cartilage.

Comparison of tenocytes and mesenchymal stem cells seeded on biodegradable scaffolds in a full-size tendon defect model

In order to investigate cell-based tendon regeneration, a tendon rupture was simulated by utilizing a critical full-size model in female rat achilles tendons. For bridging the defect, polyglycol acid (PGA) and collagen type I scaffolds were used and fixed with a frame suture to ensure postoperatively a functional continuity. Scaffolds were seeded with mesenchymal stem cells (MSC) or tenocytes derived from male animals, while control groups were left without cells. After a healing period of 16 weeks, biomechanical, PCR, histologic, and electron microscopic analyses of the regenerates were performed. Genomic PCR for male-specific gene was used to detect transplanted cells in the regenerates. After 16 weeks, central ossification and tendon-like tissue in the superficial tendon layers were observed in all study groups. Biomechanical test showed that samples loaded with tenocytes had significantly better failure strength/cross-section ratio (P < 0.01) compared to MSC and the control groups whereas maximum failure strength was similar in all groups. Thus, we concluded that the application of tenocytes improves the outcome in this model concerning the grade of ossification and the mechanical properties in comparison to the use of MSC or just scaffold materials.

A novel murine femoral segmental critical-sized defect model stabilized by plate osteosynthesis for bone tissue engineering purposes

Mouse models are invaluable tools for mechanistic and efficacy studies of the healing process of large bone defects resulting in atrophic nonunions, a severe medical problem and a financial health-care-related burden. Models of atrophic nonunions are usually achieved by providing a highly stable biomechanical environment. For this purpose, external fixators have been investigated, but plate osteosynthesis, despite its high clinical relevance, has not yet been considered in mice. We hereby proposed and investigated the use of an internal osteosynthesis for stabilizing large bone defects. To this aim, a 3.5-mm-long segmental bone defect was induced in the mid-shaft of the femur using a Gigli saw and a jig. Bone fixation was performed using a titanium microlocking plate with four locking screws. The bone defect was either left empty or filled with a syngenic bone graft or filled with a coralline scaffold. Healing was monitored using radiographs. The healing process was further assessed using microcomputed tomography and histology 10 weeks after surgery. With the exception of one mouse that died during the surgical procedure, no complications were observed. A stable and reproducible bone fixation as well as a reproducible fixation of the implanted materials with full weight bearing was obtained in all animals tested. Nonunion was consistently observed in the group in which the defects were left empty. Bone union was obtained with the syngenic bone grafts, providing evidence that, although such defects were of critical size, bone healing was possible when the gold-standard material was used to fill the defect. Although new bone formation was greater in the coralline scaffold group than in the left-empty animal group, it remained limited and localized close to the bony edges, a consequence of the critical size of such bone defect. Our study established a reproducible, clinically relevant, femoral, atrophic nonunion, critical-sized defect, low morbidity mouse model. The present study was successful in designing and testing in a small animal model, a novel surgical method for the assessment of bone repair; this model has the potential to facilitate investigations of the molecular and cellular events involved in bone regeneration in load-bearing, segmental-bone defects.

The optimal carrier for BMP-2: a comparison of collagen versus fibrin matrix

INTRODUCTION

The aim of our study was to investigate in vitro and in a new in vivo rat model for impaired bone healing whether a low dose BMP-2 preparation in fibrin would be equivalent or better than the combination of collagen and a high dose of BMP-2 which is currently in clinical use.

MATERIALS AND METHODS

In a 14 day period we compared the in vitro release kinetics of an absorbable collagen sponge (ACS) with 72 μg rhBMP-2 in the BMPC group and fibrin matrix with 10 μg rhBMP-2 in the BMPF group. In our in vivo experiment a critical sized osteotomy was performed in the rat femur, which was filled with a spacer, inhibiting bone formation for a period of 4 weeks. In a second operation this spacer was removed and the test item was applied into the defect. We compared the BMPF and BMPC groups with the ACS alone, FIBRIN alone and the EMPTY (4w/8w) control groups. 4 and 8 weeks after the second operation, specimens were analysed by X-ray and μCT imaging. Mechanically stable femurs were biomechanically evaluated.

RESULTS

Cumulative BMP-2 release was five times higher in the BMPF group than in the BMPC group during the observation period. μCT analysis revealed that both the extent of bone union and the bone volume were significantly higher in the group with a lower dose of BMP-2 in fibrin matrix than in the groups without BMP-2 treatment. However there was no statistically significant difference between the BMPF and BMPC groups.

CONCLUSION

We conclude that fibrin matrix is an excellent carrier for BMP-2 and that it provides equivalent results with a sevenfold lower dose of BMP-2 compared with ACS.

In vivo models of bone repair

This review is aimed at clinicians appraising preclinical trauma studies and researchers investigating compromised bone healing or novel treatments for fractures. It categorises the clinical scenarios of poor healing of fractures and attempts to match them with the appropriate animal models in the literature.

We performed an extensive literature search of animal models of long bone fracture repair/nonunion and grouped the resulting studies according to the clinical scenario they were attempting to reflect; we then scrutinised them for their reliability and accuracy in reproducing that clinical scenario.

Models for normal fracture repair (primary and secondary), delayed union, nonunion (atrophic and hypertrophic), segmental defects and fractures at risk of impaired healing were identified. Their accuracy in reflecting the clinical scenario ranged greatly and the reliability of reproducing the scenario ranged from 100% to 40%.

It is vital to know the limitations and success of each model when considering its application.

Biodegradable composite scaffolds incorporating an intramedullary rod and delivering bone morphogenetic protein-2 for stabilization and bone regeneration in segmental long bone defects

In this study, a two-part bone tissue engineering scaffold was investigated. The scaffold consists of a solid poly(propylene fumarate) (PPF) intramedullary rod for mechanical support surrounded by a porous PPF sleeve for osseointegration and delivery of poly(dl-lactic-co-glycolic acid) (PLGA) microspheres with adsorbed recombinant human bone morphogenetic protein-2 (rhBMP-2). Scaffolds were implanted into critical size rat segmental femoral defects with internal fixation for 12 weeks. Bone formation was assessed throughout the study via radiography, and following euthanasia, via microcomputed tomography and histology. Mechanical stabilization was evaluated further via torsional testing. Experimental implant groups included the PPF rod alone and the rod with a porous PPF sleeve containing PLGA microspheres with 0, 2 or 8 μg of rhBMP-2 adsorbed onto their surface. Results showed that presence of the scaffold increased mechanical stabilization of the defect, as evidenced by the increased torsional stiffness of the femurs by the presence of a rod compared to the empty defect. Although the presence of a rod decreased bone formation, the presence of a sleeve combined with a low or high dose of rhBMP-2 increased the torsional stiffness to 2.06 ± 0.63 and 1.68 ± 0.56 N·mm, respectively, from 0.56 ± 0.24 N·mm for the rod alone. The results indicate that, while scaffolds may provide structural support to regenerating tissues and increase their mechanical properties, the presence of scaffolds within defects may hinder overall bone formation if they interfere with cellular processes.

Vascular and micro-environmental influences on MSC-coral hydroxyapatite construct-based bone tissue engineering

Bone tissue engineering (BTE) has been demonstrated an effective approach to generate bone tissue and repair bone defect in ectopic and orthotopic sites. The strategy of using a prevascularized tissue-engineered bone grafts (TEBG) fabricated ectopically to repair bone defects, which is called live bone graft surgery, has not been reported. And the quantitative advantages of vascularization and osteogenic environment in promoting engineered bone formation have not been defined yet. In the current study we generated a tissue engineered bone flap with a vascular pedicle of saphenous arteriovenous in which an organized vascular network was observed after 4 weeks implantation, and followed by a successful repaire of fibular defect in beagle dogs. Besides, after a 9 months long term observation of engineered bone formation in ectopic and orthotopic sites, four CHA (coral hydroxyapatite) scaffold groups were evaluated by CT (computed tomography) analysis. By the comparison of bone formation and scaffold degradation between different groups, the influences of vascularization and micro-environment on tissue engineered bone were quantitatively analyzed. The results showed that in the first 3 months vascularization improved engineered bone formation by 2 times of non-vascular group and bone defect micro-environment improved it by 3 times of ectopic group, and the CHA-scaffold degradation was accelerated as well.

A model for tissue engineering applications: femoral critical size defect in immunodeficient mice

Animal models for preclinical functionality assays lie midway between in vitro systems such as cell culture and actual clinical trials. We have developed a novel external fixation device for femoral critical size defect (CSD) in the femurs of immunodeficient mice as an experimental model for studying bone regeneration and bone tissue engineering. The external fixation device comprises four pointed rods and dental acrylic paste. A segmental bone defect (2 mm) was created in the midshaft of the mouse femur. The CSD in the femur of the mice were either left untreated or treated with a bone allograft, a cell-scaffold construct, or a scaffold-only construct. The repair and healing processes of the CSD were monitored by digital x-ray radiography, microcomputed tomography, and histology. Repair of the femoral CSD was achieved with the bone allografts, and partial repair of the femoral CSD was achieved with the cell scaffold and the scaffold-only constructs. No repair of the nongrafted femoral CSD was observed. Our results establish the feasibility of this new mouse femoral model for CSD repair of segmental bone using a simple stabilized external fixation device. The model should prove especially useful for in vivo preclinical proof-of-concept studies that involve cell therapy-based technologies for bone tissue engineering applications in humans.

Experimental trauma models: an update

Treatment of polytrauma patients remains a medical as well as socioeconomic challenge. Although diagnostics and therapy improved during the last decades, multiple injuries are still the major cause of fatalities in patients below 45 years of age. Organ dysfunction and organ failure are major complications in patients with major injuries and contribute to mortality during the clinical course. Profound understanding of the systemic pathophysiological response is crucial for innovative therapeutic approaches. Therefore, experimental studies in various animal models are necessary. This review is aimed at providing detailed information of common trauma models in small as well as in large animals.