Scaffold-Free Bone Marrow-Derived Mesenchymal Stem Cell Sheets Enhance Bone Formation in a Weight-Bearing Rat Critical Bone Defect Model

Researchers have been exploring alternative methods for bone tissue engineering, as current management of critical bone defects may be a significant challenge for both patient and surgeon with conventional surgical treatments associated with several potential complications and drawbacks. Recent studies have shown mesenchymal stem cell sheets may enhance bone regeneration in different animal models. We investigated the efficacy of implanted scaffold-free bone marrow-derived mesenchymal stem cell (BMSC) sheets on bone regeneration of a critical bone defect in a weight-bearing rat model. BMSCs were isolated from the femora of male Sprague-Dawley rats 5-6 weeks of age and cell sheets were produced on temperature-responsive culture dishes. Nine male Sprague-Dawley rats 6-8 weeks of age were utilized. A bilateral femoral critical bone defect was created with a bridge plate serving as internal fixation. One side was randomly selected and BMSC sheets were implanted into the bone defect (BMSC group), with the contralateral side receiving no treatment (control). Rats were anesthetized and radiographs were performed at 2-week intervals. At the 8-week time point, rats were euthanized, femurs harvested, and microcomputed tomography and histological analysis was performed. We found a statistically significant increase in new bone formation and bone volume fraction compared with the control. Histomorphometry analysis revealed a larger percent of newly formed bone and a higher total histological score. Our results suggest that scaffold-free BMSC sheets may be used in the management of large weight-bearing bone defects to complement a different surgical technique or as a standalone approach followed by internal fixation. However, further research is still needed.

Engineering 3D-Printed Strontium-Titanium Scaffold-Integrated Highly Bioactive Serum Exosomes for Critical Bone Defects by Osteogenesis and Angiogenesis

Currently, healing of large bone defects faces significant challenges such as a bulk of bone regeneration and revascularization on the bone defect region. Here, a "cell-free scaffold engineering" strategy that integrates strontium (Sr) and highly bioactive serum exosomes (sEXOs) inside a three-dimensional (3D)-printed titanium (Ti) scaffold (Sc) is first developed. The constructed SrTi Sc can serve as a sophisticated biomaterial platform for maintaining bone morphological characteristics of the radius during the period of critical bone defect (CBD) repair and further accelerating bone formation and fibroblastic suppression via the controlled release of Sr from the superficial layer of the scaffold. Moreover, compared with sEXO from healthy donors, the sEXO extracted from the serum of the femoral fracture rabbit model at the stage of fracture healing, named BF EXO, is robustly capable of facilitating osteogenesis and angiogenesis. In addition, the underlying therapeutic mechanism is elucidated, whereby altering miRNAs shuttled by BF EXO enables osteogenesis and angiogenesis. Further, the in vivo study revealed that the SrTi Sc + BF EXO composite dramatically accelerated bone repair via osteoconduction, osteoinduction, and revascularization in radial CBD of rabbits. This study broadens the source and biomedical potential of specifically functionalized exosomes and provides a comprehensive clinically feasible strategy for therapeutics on large bone defects.

One Stage Masquelets Technique: Evaluation of Different Forms of Membrane Filling with and without Bone Marrow Mononuclear Cells (BMC) in Large Femoral Bone Defects in Rats

The classic two-stage masquelet technique is an effective procedure for the treatment of large bone defects. Our group recently showed that one surgery could be saved by using a decellularized dermis membrane (DCD, Epiflex, DIZG). In addition, studies with bone substitute materials for defect filling show that it also appears possible to dispense with the removal of syngeneic cancellous bone (SCB), which is fraught with complications. The focus of this work was to clarify whether the SCB can be replaced by the granular demineralized bone matrix (g-DBM) or fibrous demineralized bone matrix (f-DBM) demineralized bone matrix and whether the colonization of the DCD and/or the DBM defect filling with bone marrow mononuclear cells (BMC) can lead to improved bone healing. In 100 Sprague Dawley rats, a critical femoral bone defect 5 mm in length was stabilized with a plate and then encased in DCD. Subsequently, the defect was filled with SCB (control), g-DBM, or f-DBM, with or without BMC. After 8 weeks, the femurs were harvested and subjected to histological, radiological, and biomechanical analysis. The analyses showed the incipient bony bridging of the defect zone in both groups for g-DBM and f-DBM. Stability and bone formation were not affected compared to the control group. The addition of BMCs showed no further improvement in bone healing. In conclusion, DBM offers a new perspective on defect filling; however, the addition of BMC did not lead to better results.

Strategies of immobilizing BMP-2 with 3D-printed scaffolds to improve osteogenesis

The management and definitive treatment of critical-size bone defects in severe trauma, tumor resection and congenital malformation are troublesome for orthopedic surgeons and patients worldwide without recognized good treatment strategies. Researchers and clinicians are working to develop new strategies to treat these problems. This review aims to summarize the techniques used by additive manufacturing scaffolds loaded with BMP-2 to promote osteogenesis and to analyze the current status and trends in relevant clinical translation. Optimize composite scaffold design to enhance bone regeneration through printing technology, material selection, structure design and loading methods of BMP-2 to advance the clinical therapeutic bone repair field.

Bioglass/collagen scaffolds combined with bone marrow stromal cells on bone healing in an experimental model in cranial defects in rats

This study aimed to develop bone regenerative therapeutic strategies, based on the addition of bone marrow stromal cells (BMSC) on bioglass/collagen (BG/COL) scaffolds. For this purpose, an in vivo study was conducted using tissue response of the BG/COL scaffolds combined with BMSC in a critical-size defects. Wistar rats were submitted to the surgical procedure to perform the cranial critical size bone defects and distributed in four groups (20 animals per group): Control Group (CG) (rats submitted to the cranial bone defect surgery without treatment), Bioglass Group (BG) (rats treated with BG), BG/COL Group (rats treated with BG/COL) and Bioglass/Collagen and BMSC Group (BG/COL/BMSC) (rats treated with BG/COL scaffolds enriched with BMSCs). Animals were euthanized 15 and 30 days after surgery. Scanning electron microscopy, histopathological and immunohistochemistry analysis were used. SEM analysis demonstrated that porous scaffolds were obtained, and Col fibers were successfully impregnated to BG matrices. The implantation of the BMSC on BG/COL based scaffolds was effective in stimulating newly bone formation and produced an increased immunoexpression of markers related to the bone repair. These results highlight the potential of BG/COL scaffolds and BMSCs to be used as a therapeutic approach for bone regeneration.

Engineering Multifunctional Hydrogel With Osteogenic Capacity for Critical-Size Segmental Bone Defect Repair

Treating critical-size segmental bone defects is an arduous challenge in clinical work. Preparation of bone graft substitutes with notable osteoinductive properties is a feasible strategy for critical-size bone defects. Herein, a biocompatible hydrogel was designed by dynamic supramolecular assembly of polyvinyl alcohol (PVA), sodium tetraborate (Na2B4O7), and tetraethyl orthosilicate (TEOS). The characteristics of the supramolecular hydrogel were evaluated by rheological analysis, swelling ratio, degradation experiments, and scanning electron microscopy (SEM). In in vitro experiments, this TEOS-hydrogel had self-healing property, low swelling rate, degradability, good biocompatibility, and induced osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) by upregulating the expression of Runx-2, Col-1, OCN, and osteopontin (OPN). In segmental bone defect rabbit models, the TEOS-containing hydrogel accelerated bone regeneration, thus restoring the continuity of bone and recanalization of the medullary cavity. The abovementioned results demonstrated that this TEOS-hydrogel has the potential to realize bone healing in critical-size segmental bone defects.

Dental Pulp-Derived Stem Cells Are as Effective as Bone Marrow-Derived Mesenchymal Stromal Cells When Implanted into a Murine Critical Bone Defect

Background While bone marrow-derived mesenchymal stromal cells (BM-MSCs) have been used for many years in bone tissue engineering applications, the procedure still has drawbacks such as painful collection methods and damage to the donor site. Dental pulp-derived stem cells (DPSCs) are readily accessible, occur in high amounts and show a high proliferation and differentiation capability. Therefore, DPSCs may be a promising alternative for BM-MSCs to repair bone defects. Objective The aim of this study was to investigate the bone regenerative potential of DPSCs in comparison to BM-MSCs in vitro and in vivo. Methods In vitro investigations included analysis of cell doubling time as well as proliferation and osteogenic differentiation. For the in vivo study 36 male NMRI nude mice were randomized into 3 groups: 1) control (cell-free mineralized collagen matrix (MCM) scaffold), 2) MCM + DPSCs and 3) MCM + BM-MSCs. Critical size 2 mm bone defects were created at the right femur of each mouse and stabilized by an external fixator. After 6 weeks animals were euthanized and microcomputed tomography scans (µCT) and histological analyses were performed. Results In vitro DPSCs showed a 2-fold lower population doubling time and a 9-fold higher increase in proliferation when seeded onto MCM scaffolds as compared to BM-MSCs, but DPSCs showed a significantly lower osteogenic capability than BM-MSCs. In vivo, the healing of the critical bone defect in NMRI nude mice was comparable among all groups. Conclusions Pre-seeding of MCM scaffolds with DPSCs and BM-MSCs did not enhance bone defect healing. </p>.

A New Design of Porosity Gradient Ti-6Al-4V Encapsulated Hydroxyapatite Dual Materials Composite Scaffold for Bone Defects

The tibia of New Zealand White rabbits was used as a model of critical bone defects to investigate a new design of composite scaffold for bone defects composed of dual materials. The all-in-one design of a titanium alloy (Ti-6Al-4V) scaffold comprised the structure of a bone plate and gradient porosity cage. Hydroxyapatite (HAp), a biodegradable material, was encapsulated in the center of the scaffold. The gradient pore structure was designed with 70%-65%-60%-55%-50% porosity, since the stresses could be distributed more uniformly when the all-in-one scaffold was placed on the bone contact surface. By covering the center of the scaffold with a low strength of HAp to contact the relatively low strength of bone marrow tissues, the excessive stiffness of the Ti-6Al-4V can be effectively reduced and further diminish the incidence of the stress shielding effect. The simulation results show that the optimized composite scaffold for the 3D model of tibia had a maximum stress value of 27.862 MPa and a maximum strain of 0.065%. The scaffold prepared by selective laser melting was annealed and found that the Young’s coefficient increased from 126.44 GPa to 131.46 GPa, the hardness increased from 3.9 GPa to 4.12 GPa, and the strain decreased from 2.27% to 1.13%. The result demonstrates that the removal of residual stress can lead to a more stable structural strength, which can be used as a reference for the design of future clinical tibial defect repair scaffolds.

Regional Gene Therapy with Transduced Human Cells: The Influence of "Cell Dose" on Bone Repair

Regional gene therapy using a lentiviral vector containing the BMP-2 complementary DNA (cDNA) has been shown to heal critical-sized bone defects in rodent models. An appropriate "cellular dose" needs to be defined for eventual translation into human trials. The purpose of this study was to evaluate bone defect healing potential and quality using three different doses of transduced human bone marrow cells (HBMCs). HBMCs were transduced with a lentiviral vector containing either BMP-2 or green fluorescent protein (GFP). All cells were loaded onto compression-resistant matrices and implanted in the bone defect of athymic rats. Treatment groups included femoral defects that were treated with a low-dose (1 × 10⁶ cells), standard-dose (5 × 10⁶ cells), and high-dose (1.5 × 10⁷ cells) HBMCs transduced with lentiviral vector containing BMP-2 cDNA. The three control groups were bone defects treated with HBMCs that were either nontransduced or transduced with vector containing GFP. All animals were sacrificed at 12 weeks. The bone formed in each defect was evaluated with plain radiographs, microcomputed tomography (microCT), histomorphometric analysis, and biomechanical testing. Bone defects treated with higher doses of BMP-2-producing cells were more likely to have healed (6/14 of the low-dose group; 12/14 of the standard-dose group; 14/14 of the high-dose group; χ²(2) = 15.501, p < 0.001). None of the bone defects in the control groups had healed. Bone defects treated with high dose and standard dose of BMP-2-producing cells consistently outperformed those treated with a low dose in terms of bone formation, as assessed by microCT and histomorphometry, and biomechanical parameters. However, statistical significance was only seen between defects treated with high dose and low dose. Larger doses of BMP-2-producing cells were associated with a higher likelihood of forming heterotopic ossification. Femurs treated with a standard- and high-dose BMP-2-producing cells demonstrated similar healing and biomechanical properties. Increased doses of BMP-2 delivered through higher cell doses have the potential to heal large bone defects. Adapting regional gene therapy for use in humans will require a balance between promoting bone repair and limiting heterotopic ossification. Impact statement Critical bone loss may result from complex traumatic bone injury (i.e., open fracture or blast injury), revision total joint arthroplasty, and spine pseudoarthrosis. This is a challenging clinical problem to treat and regional gene therapy is an innovative means of addressing it. This study provides information regarding the quantity of cells or "cell dose" of transduced cells needed to treat a critical-sized bone defect in a rat model. This information may be extrapolated for use in humans in future trials.

Preliminary Results of the "Capasquelet" Technique for Managing Femoral Bone Defects-Combining a Masquelet Induced Membrane and Capanna Vascularized Fibula with an Allograft

We describe the preliminary results of a novel two-stage reconstruction technique for extended femoral bone defects using an allograft in accordance with the Capanna technique with an embedded vascularized fibula graft in an induced membrane according to the Masquelet technique. We performed what we refer to as "Capasquelet" surgery in femoral diaphyseal bone loss of at least 10 cm. Four patients were operated on using this technique: two tumors and two traumatic bone defects in a septic context with a minimum follow up of one year. Consolidation on both sides, when achieved, occurred at 5.5 months (4-7), with full weight-bearing at 11 weeks (8-12). The functional scores were satisfactory with an EQ5D of 63.3 (45-75). The time to bone union and early weight-bearing with this combined technique are promising compared to the literature. The osteoinductive role of the induced membrane could play a positive role in the evolution of the graft. Longer follow up and a larger cohort are needed to better assess the implications. Nonetheless, this two-stage technique appears to have ample promise, especially in a septic context or in adjuvant radiotherapy in an oncological context.

Controlled Delivery of Growth Factor by Hierarchical Nanostructured Core-Shell Nanofibers for the Efficient Repair of Critical-Sized Rat Calvarial Defect

Electrospun nanofibers have received much attention as bone tissue-engineered scaffolds for their capacity to mimic the structure of natural extracellular matrix (ECM). Most studies have reproduced nanofibers with smooth surface for tissue engineering. This is quite different from the triple-helical nanotopography of natural collagen nanofibrils. In this study, hierarchical nanostructures were coated on the surface of drug-loaded core-shell nanofibers to mimic natural collagen nanofibrils. The nanoshish-kebab (SK) structure was decorated regularly on the surface of the nanofibers, and the inner-loaded bone morphogenetic protein 2 (BMP2) exhibited a gentle release pattern, similar to a zero-order release pattern in kinetics. The in vitro study also showed that the SK structure could accelerate cell proliferation, attachment, and osteogenic differentiation. Four groups of scaffolds were implanted in vivo to repair critical-sized rat calvarial defects: (1) PCL/PVA (control); (2) SK-PCL/PVA; (3) PCL/PVA-BMP2; and (4) SK-PCL/PVA-BMP2. Much more bone was formed in the SK-PCL/PVA group (24.57 ± 3.81%) than in the control group (1.21 ± 0.23%). The BMP2-loaded core-shell nanofibers with nanopatterned structure (SK-PCL/PVA-BMP2) displayed the best repair efficacy (76.38 ± 4.13%), followed by the PCL/PVA-BMP2 group (39.86 ± 5.74%). It was believed that the hierarchical nanostructured core-shell nanofibers could promote osteogeneration and that the SK structure showed synergistic ability with nanofiber-loaded BMP2 in vivo for bone regeneration. Thus, this BMP2-loaded core-shell nanofiber scaffold with hierarchical nanostructure holds great potential for bone tissue engineering applications.

Establishment and effects of allograft and synthetic bone graft substitute treatment of a critical size metaphyseal bone defect model in the sheep femur

Assessment of bone graft material efficacy is difficult in humans, since invasive methods like staged CT scans or biopsies are ethically unjustifiable. Therefore, we developed a novel large animal model for the verification of a potential transformation of synthetic bone graft substitutes into vital bone. The model combines multiple imaging methods with corresponding histology in standardized critical sized cancellous bone defect. Cylindrical bone voids (10 ml) were created in the medial femoral condyles of both hind legs (first surgery at right hind leg, second surgery 3 months later at left hind leg) in three merino‐wool sheep and either (i) left empty, filled with (ii) cancellous allograft bone or (iii) a synthetic, gentamicin eluting bone graft substitute. All samples were analysed with radiographs, MRI, μCT, DEXA and histology after sacrifice at 6 months. Unfilled defects only showed ingrowth of fibrous tissue, whereas good integration of the cancellous graft was seen in the allograft group. The bone graft substitute showed centripetal biodegradation and new trabecular bone formation in the periphery of the void as early as 3 months. μCT gave excellent insight into the structural changes within the defects, particularly progressive allograft incorporation and the bone graft substitute biodegradation process. MRI completed the picture by clearly visualizing soft tissue ingrowth into unfilled bone voids and presence of fluid collections. Histology was essential for verification of trabecular bone and osteoid formation. Conventional radiographs and DEXA could not differentiate details of the ongoing transformation process. This model appears well suited for detailed in vivo and ex vivo evaluation of bone graft substitute behaviour within large bone defects.

Preclinical induced membrane model to evaluate synthetic implants for healing critical bone defects without autograft

Critical bone defects pose a formidable orthopaedic problem in patients with bone loss. We developed a preclinical model based on the induced membrane technique using a synthetic graft to replace autograft for healing critical bone defects. Additionally, we used a novel osteoconductive scaffold coupled with a synthetic membrane to evaluate the potential for single-stage bone regeneration. Three experimental conditions were investigated in critical femoral defects in rats. Group A underwent a two-stage procedure with insertion of a polymethylmethacrylate (PMMA) spacer followed by replacement with a 3D printed polycaprolactone(PCL)/β-tricalcium phosphate (β-TCP) osteoconductive scaffold after 4 weeks. Group B received a single-stage PCL/β-TCP scaffold wrapped in a PCL-based microporous polymer film creating a synthetic membrane. Group C received a single-stage bare PCL/β-TCP scaffold. All groups were examined by serial radiographs for callus formation. After 12 weeks, the femurs were explanted and analyzed with micro-CT and histology. Mean callus scores tended to be higher in Group A. Group A showed statistically significant greater bone formation on micro-CT compared with other groups, although bone volume fraction was similar between groups. Histology results suggested extensive bone ingrowth and new bone formation within the macroporous scaffolds in all groups and cell infiltration into the microporous synthetic membrane. This study supports the use of a critical size femoral defect in rats as a suitable model for investigating modifications to the induced membrane technique without autograft harvest. Future investigations should focus on bioactive synthetic membranes coupled with growth factors for single-stage bone healing. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

Controlling Arteriogenesis and Mast Cells Are Central to Bioengineering Solutions for Critical Bone Defect Repair Using Allografts

Although most fractures heal, critical defects in bone fail due to aberrant differentiation of mesenchymal stem cells towards fibrosis rather than osteogenesis. While conventional bioengineering solutions to this problem have focused on enhancing angiogenesis, which is required for bone formation, recent studies have shown that fibrotic non-unions are associated with arteriogenesis in the center of the defect and accumulation of mast cells around large blood vessels. Recently, recombinant parathyroid hormone (rPTH; teriparatide; Forteo) therapy have shown to have anti-fibrotic effects on non-unions and critical bone defects due to inhibition of arteriogenesis and mast cell numbers within the healing bone. As this new direction holds great promise towards a solution for significant clinical hurdles in craniofacial reconstruction and limb salvage procedures, this work reviews the current state of the field, and provides insights as to how teriparatide therapy could be used as an adjuvant for healing critical defects in bone. Finally, as teriparatide therapy is contraindicated in the setting of cancer, which constitutes a large subset of these patients, we describe early findings of adjuvant therapies that may present future promise by directly inhibiting arteriogenesis and mast cell accumulation at the defect site.