Enhanced healing of rabbit segmental radius defects with surface-coated calcium phosphate cement/bone morphogenetic protein-2 scaffolds

Spatial rhBMP2 delivery from hydroxyapatite scaffolds sustains bone regeneration in rabbit radius

Regenerating large bone defects requires a multi-faceted approach combining optimal scaffold designs with appropriate growth factor delivery. Supraphysiological doses of recombinant human bone morphogenetic protein 2(rhBMP2); typically used for the regeneration of large bone defects clinically in conjunction with an acellular collagen sponge (ACS), have resulted in many complications. In the current study, we develop a hydroxyapatite/collagen I (HA/Col) scaffold to improve the mechanical properties of the HA scaffolds while maintaining open connected porosity. Varying rhBMP2 dosages were then delivered from a collagenous periosteal membrane and paired with HA or HA/Col scaffolds to treat critical sized (15mm) diaphyseal radial defect in New Zealand white rabbits. The groups examined were ACS+76µg rhBMP2 (clinically used INFUSE dosage), HA+76µg rhBMP2, HA+15µg rhBMP2, HA/Col+15µg rhBMP2 and HA/Col+15µg rhBMP2+bone marrow derived stromal cells (bMSCs). After 8 weeks of implantation, all regenerated bones were evaluated using micro computed tomography, histology, histomorphometry and torsional testing. It was observed that the bone volume regenerated in the HA/Col + 15 µg rhBMP2 group was significantly higher than that in the groups with 76µg rhBMP2. The same scaffold and growth factor combination resulted in the highest bone mineral density of the regenerated bone, and the most bone apposition on the scaffold surface. Both the HA and HA/Col scaffolds paired with 15 µg rhBMP2 had sustained ingrowth of the mineralization front after 2 weeks compared to the groups with 76µg rhBMP2 which had far greater mineralization in the first 2 weeks after implantation. Complete bridging of the defect site and no significant differences in torsional strength, stiffness or angle at failure was observed across all groups. No benefit of additional bMSC seeding was observed on any of the quantified metrics, while bone-implant apposition was reduced in the cell seeded group. This study demonstrated that the controlled spatial delivery of rhBMP2 at the periosteum at significantly lower doses can be used as a strategy to improve bone regeneration around space maintaining scaffolds.

A Review on the Enhancement of Calcium Phosphate Cement with Biological Materials in Bone Defect Healing

Calcium phosphate cement (CPC) is a promising material used in the treatment of bone defects due to its profitable features of self-setting capability, osteoconductivity, injectability, mouldability, and biocompatibility. However, the major limitations of CPC, such as the brittleness, lack of osteogenic property, and poor washout resistance, remain to be resolved. Thus, significant research effort has been committed to modify and reinforce CPC. The mixture of CPC with various biological materials, defined as the materials produced by living organisms, have been fabricated by researchers and their characteristics have been investigated in vitro and in vivo. This present review aimed to provide a comprehensive overview enabling the readers to compare the physical, mechanical, and biological properties of CPC upon the incorporation of different biological materials. By mixing the bone-related transcription factors, proteins, and/or polysaccharides with CPC, researchers have demonstrated that these combinations not only resolved the lack of mechanical strength and osteogenic effects of CPC but also further improve its own functional properties. However, exceptions were seen in CPC incorporated with certain proteins (such as elastin-like polypeptide and calcitonin gene-related peptide) as well as blood components. In conclusion, the addition of biological materials potentially improves CPC features, which vary depending on the types of materials embedded into it. The significant enhancement of CPC seen in vitro and in vivo requires further verification in human trials for its clinical application.

Bone Morphogenetic Proteins, Carriers, and Animal Models in the Development of Novel Bone Regenerative Therapies

Bone morphogenetic proteins (BMPs) possess a unique ability to induce new bone formation. Numerous preclinical studies have been conducted to develop novel, BMP-based osteoinductive devices for the management of segmental bone defects and posterolateral spinal fusion (PLF). In these studies, BMPs were combined with a broad range of carriers (natural and synthetic polymers, inorganic materials, and their combinations) and tested in various models in mice, rats, rabbits, dogs, sheep, and non-human primates. In this review, we summarized bone regeneration strategies and animal models used for the initial, intermediate, and advanced evaluation of promising therapeutical solutions for new bone formation and repair. Moreover, in this review, we discuss basic aspects to be considered when planning animal experiments, including anatomical characteristics of the species used, appropriate BMP dosing, duration of the observation period, and sample size.

BMSC seeding in different scaffold incorporation with hyperbaric oxygen treats seawater-immersed bony defect

Introduction

The experiment was undertaken to estimate the effect of BMSC seeding in different scaffold incorporation with HBO on the repair of a seawater-immersed bone defect. And future compared n-HA/PLGA with β-TCP/PLGA as a scaffold in treatment effect of the seawater-immersed bone defect.

Methods

Sixty New Zealand White rabbits with standard seawater defect in radius were randomly divided into group A (implant with nothing), group B (implanted with autogenous bone), group C (implanted with n-HA/PLGA/BMSCs), and group D (implanted with β-TCP/PLGA/BMSCs). After the implant, each rabbit receives HBO treatment at 2.4 ATA 100% oxygen for 120 min/day for 2 weeks. Radiograph, histological, and biomechanical examinations were used to analyze osteogenesis.

Result

X-ray analysis shows that n-HA/PLGA/BMSCs and β-TCP/PLGA/BMSCs could accelerate the new bone formation, and the new bone formation in group C was larger than that in group D or group A and close to group B (P < 0.05). After 12 weeks, in group A, the defect without scaffold shows a loose connect tissue filled in the areas. The medullary canal in group B was recanalized. Defects in groups C and D show a larger number of woven bone formation. The new woven bone formation in defect areas in group C was larger than that in group D. The mechanical examination revealed ultimate strength at 12 weeks was group D > group C > group B > group A (P < 0.05).

Conclusion

Scaffolds of n-HA/PLGA and β-TCP/PLGA incorporation with HBO and BMSCs were effective to treat seawater-immersed bone defect, and n-HA/PLGA was more excellent than β-TCP/PLGA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02368-8.

Building Osteogenic Microenvironments With Strontium-Substituted Calcium Phosphate Ceramics

Bioceramics have experienced great development over the past 50 years. Modern bioceramics are designed to integrate bioactive ions within ceramic granules to trigger living tissue regeneration. Preclinical and clinical studies have shown that strontium is a safe and effective divalent metal ion for preventing osteoporosis, which has led to its incorporation in calcium phosphate-based ceramics. The local release of strontium ions during degradation results in moderate concentrations that trigger osteogenesis with few systemic side effects. Moreover, strontium has been proven to generate a favorable immune environment and promote early angiogenesis at the implantation site. Herein, the important aspects of strontium-enriched calcium phosphate bioceramics (Sr-CaPs), and how Sr-CaPs affect the osteogenic microenvironment, are described.

Improved BMP2-CPC-stimulated osteogenesis in vitro and in vivo via modulation of macrophage polarization

This study aimed to explore the in vitro and in vivo roles of macrophages in the osteogenesis stimulated by BMP2-CPC. In vitro, the alteration of macrophage polarization and cytokine secretion induced by BMP2-CPC or CPC was investigated. The influence of conditioned medium derived from BMP2-CPC- or CPC-stimulated macrophages on the migration and osteogenic differentiation of MSCs were evaluated. The in vivo relationship between macrophage polarization and osteogenesis was examined in a rabbit calvarial defect model. The in vitro results indicated that BMP2-CPC and CPC induced different patterns of macrophage polarization and subsequently resulted in distinct patterns of cytokine expression and secretion. Conditioned medium derived from BMP2-CPC- or CPC-stimulated macrophages both exhibited apparent osteogenic effect on MSCs. Notably, BMP2-CPC induced more M2-phenotype polarization and higher expression of anti-inflammatory cytokines and growth factors than did CPC, which led to the better osteogenic effect of conditioned medium derived from BMP2-CPC-stimulated macrophages. The rabbit calvarial defect model further confirmed that BMP2-CPC facilitated more bone regeneration than CPC did by enhancing M2-phenotype polarization in local macrophages and then alleviating inflammatory reaction. In conclusion, this study revealed that the favorable immunoregulatory property of BMP2-CPC contributed to the strong osteogenic capability of BMP2-CPC by modulating macrophage polarization.

Repair of segmental rabbit radial defects with Cu/Zn co-doped calcium phosphate scaffolds incorporating GDF-5 carrier

Repair of segmental bone defects is a challenge in orthopaedics. A bone substitute is a potential solution for this challenge, and angiogenesis and osteogenesis are critical to the performance of scaffold materials. For enhancing angiogenesis and osteogenesis activities of implanted scaffolds, Cu/Zn co-doped calcium phosphate scaffolds carrying GDF-5-release microspheres were prepared and implanted into surgically created critical-sized rabbit radial defects. Radiological examination, histological analysis and biomechanical tests were used to evaluate the bone healing-union. Results showed that, with increasing Cu/Zn concentrations, new bone area, new blood vessel density, and bending failure load all increased significantly. Furthermore, Cu/Zn co-doped scaffolds incorporating GDF-5-release microspheres exhibited further increased angiogenesis and osteogenesis (vs. Cu/Zn co-doped alone), as well as a superior bending failure load. These show that, simultaneous incorporation of trace essential ions and GDF-5 combines pro-angiogenic and pro-osteogenic actions of these bioactive substances, potentially offering an effective approach to assist the healing of critical-sized bone defects.

Collagen and bone morphogenetic protein-2 functionalized hydroxyapatite scaffolds induce osteogenic differentiation in human adipose-derived stem cells

Surface modification is one important way to fabricate successful biocompatible materials in bone tissue engineering. Hydroxyapatite (HAp) materials have received considerable attention as suitable bioceramics for manufacturing osseous implants because of their similarity to bone mineral in terms of chemical composition. In this study, the surface of porous HAp scaffold was modified by collagen treatment and bone morphogenetic protein-2 (BMP-2) conjugation. The surface modification did not affect the HAp scaffold's bulk properties. No significant difference in compressive strength was found among different scaffolds, with HAp, collagen modified HAp, and collagen-BMP-2-functionalized HAp having compressive strengths of 45.8 ± 3.12, 51.2 ± 4.09, and 50.7 ± 3.98 MPa, respectively. In vitro studies were performed to compare adhesion and osteogenic differentiation between human adipose-derived stem cells (hADSCs) with modified surfaces and those unmodified HAp surfaces. Collagen or BMP-2 alone was insufficient and that both collagen and BMP-2 are necessary to get the desired results. The findings suggest the possibility of using three-dimensional HAp scaffold treated with gold-standard collagen coating and highly researched BMP-2 growth factor as a platform to deliver hADSCs. Results of this study could be used to develop treatment strategy for regenerating completely transected models using more synergistic approaches.

Improving osteogenesis of calcium phosphate bone cement by incorporating with lysine: An in vitro study

Calcium phosphate bone cement (CPC) has attracted extensive interests from surgeons and material scientists. However, its actual application is still limited because of its poor osteogenesis. In this work, lysine, one of the essential components of proteins, was incorporated into the CPC to improve its osteogenesis ability. Effects of lysine on the phase, morphology, physicochemical properties, protein adsorption, lysine release and cytocompatibility of CPC were investigated. Results showed that lysine had no significant influence on the phase and morphology of the hydrated cements, but evidently raised the compressive strength, apparent porosity and setting time of the cements in a content-dependent manner of lysine. In contrast to the control, the lysine-incorporated CPCs had notably enhanced in vitro osteogenesis capability. It was supposed to be synergistically attributed to the improvements of fibronectin (FN) anchoring and bone mesenchymal stem cells (BMSCs) adhesion on the hydrated cements as well as the sustained release of bioactive amino acid molecules. Hence, lysine was expected to be applied as a novel bioactive admixture in the development of CPC with the improved osteogenesis ability and physicochemical properties for numerous orthopedic applications.

Effects of strontium-modified calcium phosphate cement combined with bone morphogenetic protein-2 on osteoporotic bone defects healing in rats

The objective of the present study was to incorporate strontium into calcium phosphate cement combined with a lower single-dose local administration of bone morphogenetic protein-2 to enhance its in vivo biodegradation and bone tissue growth. After the creation of a rodent critical-sized femoral metaphyseal bone defect, strontium-modified calcium phosphate cement was prepared by mixing sieved granules of calcium phosphate cement and 5% SrCO3 for medical use, and then strontium-modified calcium phosphate cement with dripped bone morphogenetic protein-2 solution (5 µg) was implanted into the defect of OVX rats until death at eight weeks. The defected area in distal femurs of rats was harvested for evaluation by histology, micro-CT, and biomechanics. The results of our study show that a lower single-dose local administration of bone morphogenetic protein-2 combined local usage of strontium-modified calcium phosphate cement can increase the healing of defects in OVX rats. Furthermore, treatments with single-dose local administration of bone morphogenetic protein-2 and strontium-modified calcium phosphate cement showed a stronger effect on accelerating the local bone formation than calcium phosphate cement and strontium-modified calcium phosphate cement used alone. The results from our study demonstrate that combination of a lower single-dose local administration of bone morphogenetic protein-2 and strontium-modified calcium phosphate cement had an additive effect on local bone formation in osteoporosis rats.

Preclinical models for orthopedic research and bone tissue engineering

In this review, we broadly define and discuss the preclinical rodent models that are used for orthopedics and bone tissue engineering. These range from implantation models typically used for biocompatibility testing and high-throughput drug screening, through to fracture and critical defect models used to model bone healing and severe orthopedic injuries. As well as highlighting the key methods papers describing these techniques, we provide additional commentary based on our substantive practical experience with animal surgery and in vivo experimental design. This review also briefly touches upon the descriptive and functional outcome measures and power calculations that are necessary for an informative study. Obtaining informative and relevant research outcomes can be very dependent on the model used, and we hope this evaluation of common models will serve as a primer for new researchers looking to undertake preclinical bone studies. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:832-840, 2018.

Porous Particle-Reinforced Bioactive Gelatin Scaffold for Large Segmental Bone Defect Repairing

Large segmental bone defect repairing remains a big challenge in clinics, and synthetic bone grafts suitable for this purpose are still highly demanded. In this article, hydrophilic composite scaffolds (bioactive hollow particle (BHP)-gel scaffold) composed of bioactive hollow nanoparticles and cross-linked gelatin have been developed. The bioactive nanoparticles have a porous structure as well as high specific surface area; thus, they interact strongly with gelatin to overcome the swelling problem that a hydrophilic polymer scaffold will usually face. With this combination, these BHP-gel scaffolds showed porous structure and mechanical properties similar to those of the cancellous bone. They also showed excellent bioactivity and cell growth promotion performance in vitro. The best of them, namely, 10BHP-gel scaffold, was evaluated in vivo on a rat femur model, where it was found that the 5 mm segmental bone defect almost healed with new bone tissue formed in 12 weeks and the scaffold itself degraded at the same time. Thus, 10BHP-gel scaffold may become a potential bone graft for large segmental bone defect healing in the future.

Nanocements produced from mesoporous bioactive glass nanoparticles

Biomedical cements are considered promising injectable materials for bone repair and regeneration. Calcium phosphate composition sized with tens of micrometers is currently one of the major powder forms. Here we report a unique cement form made from mesoporous bioactive glass nanoparticles (BGn). The nanopowder could harden in reaction with aqueous solution at powder-to-liquid ratios as low as 0.4-0.5 (vs. 2.0-3.0 for conventional calcium phosphate cement CPC). The cementation mechanism investigated from TEM, XRD, FT-IR, XPS, and NMR analyses was demonstrated to be the ionic (Si and Ca) dissolution and then reprecipitation to form Si-Ca-(P) based amorphous nano-islands that could network the particles. The nanopowder-derived nanocement exhibited high surface area (78.7 m²/g); approximately 9 times higher than conventional CPC. The immersion of nanocement in simulated body fluid produced apatite nanocrystallites with ultrafine size of 10 nm (vs. 55 nm in CPC). The ultrafine nanocement adsorbed protein molecules (particularly positive charged proteins) at substantial levels; approximately 160 times higher than CPC. The nanocement released Si and Ca ions continuously over the test period of 2 weeks; the Si release was unique in nanocement whereas the Ca release was in a similar range to that observed in CPC. The release of ions significantly stimulated the responses of cells studied (rMSCs and HUVECs). The viability and osteogenesis of rMSCs were significantly enhanced by the nanocement ionic extracts. Furthermore, the in vitro tubular networking of HUVECs was improved by the nanocement ionic extracts. The in vivo neo-blood vessel formation in CAM model was significantly higher by the nanocement implant when compared with the CPC counterpart, implying the Si ion release might play a significant role in pro-angiogenesis. Furthermore, the early bone forming response of the nanocement, based on the implantation in a rat calvarial bone defect, demonstrated a sign of osteoinductivity along with excellent osteocondution and bone matrix formation. Although more studies remain to confirm the potential of nanocement, some of the intriguing physico-chemical properties and the biological responses reported herein support the promise of the new 'nanopowder-based nanocement' for hard tissue repair and regeneration.

Autogenous bone particle/titanium fiber composites for bone regeneration in a rabbit radius critical-size defect model

PURPOSE

To explore the effects of autogenous bone particle/titanium fiber composites on repairing segmental bone defects in rabbits.

MATERIALS AND METHODS

A model of bilateral radial bone defect was established in 36 New Zealand white rabbits which were randomly divided into 3 groups according to filling materials used for bilaterally defect treatment: in group C, 9 animal bone defect areas were prepared into simple bilateral radius bone defect (empty sham) as the control group; 27 rabbits were used in groups ABP and ABP-Ti. In group ABP, left defects were simply implanted with autogenous bone particles; meanwhile, group ABP-Ti animals had right defects implanted with autogenous bone particle/titanium fiber composites. Animals were sacrificed at 4, 8, and 12 weeks, respectively, after operation.

RESULTS

Micro-CT showed that group C could not complete bone regeneration. Bone volume to tissue volume values in group ABP-Ti were better than group ABP. From histology and histomorphometry Groups ABP and ABP-Ti achieved bone repair, the bone formation of group ABP-Ti was better. The mechanical strength of group ABP-Ti was superior to that of other groups.

CONCLUSIONS

These results confirmed the effectiveness of autologous bone particle/titanium fiber composites for promoting bone regeneration and mechanical strength.

* Extracellular Matrices for Bone Regeneration: A Literature Review

The gold standard material for bone regeneration is still autologous bone, a mesenchymal tissue that consists mainly of extracellular matrix (ECM) (90% v/v) and little cellular content (10% v/v). However, the fact that decellularized allogenic bone grafts often present a clinical performance comparable to autologous bone grafts demonstrates the crucial role of ECM in bone regeneration. For long, the mechanism by which bone allografts function was not clear, but recent research has unveiled many unique characteristics of ECM that seem to play a key role in tissue regeneration. This is further confirmed by the fact that synthetic biomaterials with composition and properties resembling bone ECM present excellent bone regeneration properties. In this context, ECM molecules such as glycosaminoglycans (GAGs) and self-assembly peptides (SAPs) can improve the performance of bone regeneration biomaterials. Moreover, decellularized ECM derived either from native tissues such as bone, cartilage, skin, and tooth germs or from cells such as osteoblasts, chondrocytes, and stem cells has shown promising results in bone regeneration applications. Understanding the role of ECM in bone regeneration is crucial for the development of the next generation of biomaterials for bone tissue engineering. In this sense, this review addresses the state-of-the-art on this subject matter.

Bone morphogenetic protein-2 sustained delivery by hydrogels with microspheres repairs rabbit mandibular defects

Mandible defect is a difficult issue in dental surgery owing to limited therapeutic options. Recombinant human bone morphogenetic protein-2 (rhBMP2) is osteoinductive in bone regeneration. This article prepared chitosan/collagen hydrogels with rhBMP2-incorporated gelatin microsphere (GMs) for a sustained release of rhBMP2 to induce bone regeneration in rabbits. In experiments, mandibular defects of 8 mm in diameter and 3 mm in depth were surgically prepared on the right cheek of 27 rabbits. Either chitosan/collagen hydrogels alone, rhBMP2-incorporated hydrogels, or hydrogels with rhBMP2-incorporated GMs were implanted to the defect sites. The animals were euthanized at 2, 6, 12 weeks following surgery. In results, scanning electronic microscope images revealled spherical GMs. The complex delivery systems, hydrogels with rhBMP2-incorporated GMs, exhibited ideal release profiles in vitro. The complex delivery systems resulted in apparent new bone formation within 12 weeks, as evidenced by computed tomography and histological observations. All these results demonstrated that the chitosan/collagen hydrogels with rhBMP2-incorporated GMs had a better capacity to heal mandible defects than other two hydrogel scaffolds. Chitosan/collagen hydrogels with rhBMP2-incorporated GMs might be potential carriers of rhBMP2 for accelerating the repair of mandibular defects.

Three-Dimensional Porous Gelapin-Simvastatin Scaffolds Promoted Bone Defect Healing in Rabbits

Treatment of large bone defects (LBDs) is technically demanding. Tissue engineering is an option. A bioactive graft may be produced by combining tissue scaffolds and healing promotive factors in order to accelerate bone repair. We investigated the role of Simvastatin (Sim)-embedded porous Gelapin (Gel) scaffold on experimental bone healing. At first, the effectiveness of different concentrations of Gel and Sim powders was investigated in an experimentally induced femoral hole model in rabbits (n = 6) for 30 days. Then bone bioactive grafts were produced by combination of the effective concentrations of Gel, Sim, and Genipin. The bioimplants were subcutaneously tested in a rabbit model (n = 9) to determine their biocompatibility and biodegradability for 10-30 days. Finally, a large radial bone defect model was produced in rabbits (n = 20), and the bioimplants were inserted in the defects. The untreated and autograft-treated bone defects were served as controls. The animals were euthanized after 30 and 60 days of bone injury. The bone samples were evaluated by radiography, three-dimensional CT scan, bone densitometry, histopathology, and nano-indentation. At a concentration of 5 mg/hole, Sim closed the femoral bone holes after 30 days, while in the defect, autograft, and Gel groups, the holes were open. Both the Gel and Gel-Sim scaffolds were biocompatible and biodegradable. Subcutaneously, the Gel-Sim scaffold was replaced with the newly regenerated ectopic bone after 30 days. After implantation of the Gel-Sim scaffold in the radial bone defects, the scaffold was completely replaced with new woven bone after 30 days which was then matured and remodeled into a cortical bone after 60 days. Sixty days after bone injury, the Gel-Sim-treated defects had significantly higher bone volume, matrix mineralization, elastic modulus, and contact hardness when compared to the controls. The Gel-Sim scaffold may be a suitable option in managing LBDs.