Carrier For Bone Morphogenetic Protein-2 Research Articles

Nanoclay gels attenuate BMP2-associated inflammation and promote chondrogenesis to enhance BMP2-spinal fusion

Bone morphogenetic protein 2 (BMP2) is clinically applied for treating intractable fractures and promoting spinal fusion because of its osteogenic potency. However, adverse effects following the release of supraphysiological doses of BMP2 from collagen carriers are widely reported. Nanoclay gel (NC) is attracting attention as a biomaterial, given the potential for localized efficacy of administered agents. However, the efficacy and mechanism of action of NC/BMP2 remain unclear. This study explored the efficacy of NC as a BMP2 carrier in bone regeneration and the enhancement mechanism. Subfascial implantation of NC containing BMP2 elicited superior bone formation compared with collagen sponge (CS). Cartilage was uniformly formed inside the NC, whereas CS formed cartilage only on the perimeter. Additionally, CS induced a dose-dependent inflammatory response around the implantation site, whereas NC induced a minor response, and inflammatory cells were observed inside the NC. In a rat spinal fusion model, NC promoted high-quality bony fusion compared to CS. In vitro, NC enhanced chondrogenic and osteogenic differentiation of hBMSCs and ATDC5 cells while inhibiting osteoclastogenesis. Overall, NC/BMP2 facilitates spatially controlled, high-quality endochondral bone formation without BMP2-induced inflammation and promotes high-density new bone, functioning as a next-generation BMP2 carrier.

Noggin-Loaded PLA/PCL Patch Inhibits BMP-Initiated Reactive Astrogliosis

Myelomeningocele (MMC) is a congenital birth defect of the spine and spinal cord, commonly treated clinically through prenatal or postnatal surgery by repairing the unclosed spinal canal. Having previously developed a PLA/PCL polymer smart patch for this condition, we aim to further expand the potential therapeutic options by providing additional cellular and biochemical support in addition to its mechanical properties. Bone morphogenetic proteins (BMPs) are a large class of secreted factors that serve as modulators of development in multiple organ systems, including the CNS. We hypothesize that our smart patch mitigates the astrogenesis induced, at least partly, by increased BMP activity during MMC. To test this hypothesis, neural stem or precursor cells were isolated from rat fetuses and cultured in the presence of Noggin, an endogenous antagonist of BMP action, with recombinant BMPs. We found that the developed PLA/PCL patch not only serves as a biocompatible material for developing neural stem cells but was also able to act as a carrier for BMP–Notch pathway inhibitor Noggin, effectively minimizing the effect of BMP2 or BMP4 on NPCs cultured with the Noggin-loaded patch.

RhBMP-2-loaded hydroxyapatite/beta-tricalcium phosphate microsphere/hydrogel composite promotes bone regeneration in a novel rat femoral nonunion model.

Nonunion following fracture treatment remains a significant clinical challenge, adversely affecting the patient's quality of life and imposing a substantial economic burden. The emergence of bone morphogenetic protein 2 (BMP-2) for bone regeneration represents a promising avenue, albeit limited by side effects such as inflammatory reactions primarily due to suboptimal drug delivery systems. This study focuses on NOVOSIS putty (NP), a novel biomaterial designed for the sustained release of BMP-2, aiming to mitigate these limitations and enhance bone healing. This research aimed to evaluate the effectiveness of NP, a hydroxyapatite granules/β-tricalcium phosphate hydrogel composite (HA/β-TCP/hydrogel), as a BMP-2 carrier for promoting bone regeneration in a new rat nonunion model of long bone. Using Sprague Dawley rats, a 2-mm silicone disk was interposed at the femoral fracture site, and intramedullary fixation with K-wire was performed to create a nonunion with a 2-mm bone defect. After 3weeks, internal fixation with a plate, removal of the silicon disk, and refreshing the nonunion site were performed by implanting three different materials into the nonunion sites: allogenic iliac bone (IB), collagen sponge (CS) containing 10μg of BMP-2, or NP containing 10μg of BMP-2. Bone healing was evaluated weekly using micro-computed tomography (CT); ex vivo micro-Ct and histological evaluation were conducted at 6weeks. At 6weeks, NP demonstrated a significantly higher bone union rate (76.5%) compared with the CS group (35.3%, p = 0.037), and the IB group (6.3%, p < 0.0001). Bone mineral density (BMD) and bone volume/tissue volume (BV/TV) were also significantly higher in the NP group compared with the CS group (BMD, p < 0.0001; BV/TV, p = 0.031). Histological analysis showed the fracture gap in the NP group was filled with more trabecular bone and less fibrous tissue compared with the CS group. The study confirms NP is a highly effective BMP-2 carrier, significantly improving bone union rates and new bone formation in nonunion fractures. The sustained release of BMP-2 from the hydrogel component reduced inflammatory responses and enhanced bone regeneration. NP can be a promising alternative to collagen-based BMP-2 delivery systems.

Development of gelatin-methacryloyl composite carriers for bone morphogenetic Protein-2 delivery: A potential strategy for spinal fusion.

To reduce the risk of nonunion after spinal fusion surgery, the in situ transplantation of bone marrow mesenchymal stem cells (BMSCs) induced toward osteogenic differentiation by bone morphogenetic protein-2 (BMP2) has been proven effective. However, the current biological agents used for transplantation have limitations, such as a short half-life and low bioavailability. To address this, our study utilized a safe and effective gelatin-methacryloyl (GelMA) as a carrier for BMP2. In vitro, experiments were conducted to observe the ability of this composite vehicle to induce osteogenic differentiation of BMSCs. The results showed that the GelMA hydrogel, with its critical properties and controlled release performance of BMP2, exhibited a slow release of BMP2 over 30 days. Moreover, the GelMA hydrogel not only enhanced the proliferation activity of BMSCs but also significantly promoted their osteogenic differentiation ability, surpassing the BMP2 effects. To investigate the potential of the GelMA-BMP2 composite vehicle, a rabbit model was employed to explore its ability to induce in situ intervertebral fusion by BMSCs. Transplantation experiments in rabbits demonstrated the effective induction of intervertebral bone fusion by the GelMA-BMP2-BMSC composite vehicle. In conclusion, the GelMA-BMP2-BMSC composite vehicle shows promising prospects in preclinical translational therapy for spinal intervertebral fusion. It addresses the limitations of current biological agents and offers a controlled release of BMP2, enhancing the proliferation and osteogenic differentiation of BMSCs.

Calcium Phosphate Silicate Microspheres with Soybean Lecithin as a Sustained-Release Bone Morphogenetic Protein-Delivery System for Bone Tissue Regeneration.

Bone morphogenetic protein (BMP) is a growth factor that effectively promotes osteogenesis. Microsphere-based drug-delivery systems can facilitate an increase in the local concentration of BMP, thus promoting bone formation. In this study, calcium phosphate silicate (CPS) microspheres were used as drug-loading systems for BMP. Three groups─CPS, CPS + BMP, and CPS + BMP + soy lecithin (SL)─were set up, where SL was used to prolong the osteogenic effect of the microsphere system. Bone marrow mesenchymal stem cells and femoral defects in rats were used to compare the osteogenic ability of the three groups. The results indicated that CPS microspheres were good carriers of BMP, facilitating a smoother release into the cells and tissues. SL loading improved the loading rate of BMP, which promoted the osteogenic effect of the microspheres with BMP. We propose CPS microspheres as potential drug-delivery systems that can be effectively used in the treatment of bone defects.

Hybrid Implants Based on Calcium-Magnesium Silicate Ceramics Diopside as a Carrier of Recombinant BMP-2 and Demineralized Bone Matrix as a Scaffold: Dynamics of Reparative Osteogenesis in a Mouse Craniotomy Model.

Calcium-magnesium silicate ceramics, diopside, is a promising material for use in bone plastics, but until now the possibility of its use as a carrier of recombinant bone morphogenetic protein-2 (BMP-2) has not been studied, as well as the features of reparative osteogenesis mediated by the materials based on diopside with BMP-2. Powder of calcium-magnesium silicate ceramics was obtained by solid-state synthesis using biowaste - rice husks and egg shells - as source components. Main phase of the obtained ceramics was diopside. The obtained particles were irregularly shaped with an average size of about 2.3 μm and ~20% porosity; average pore size was about 24 nm, which allowed the material to be classified as mesoporous. Diopside powder adsorbs more than 150 μg of recombinant BMP-2 per milligram, which exceeds binding capacity of hydroxyapatite, a calcium-phosphate ceramic often used in hybrid implants, by more than 3 times. In vitro release kinetics of BMP-2 was characterized by a burst release in the first 2 days and a sustained release of approximately 0.4 to 0.5% of the loaded protein over the following 7 days. In vivo experiments were performed with a mouse model of cranial defects of critical size with implantation of a suspension of diopside powder with/without BMP-2 in hyaluronic acid incorporated into the disks of demineralized bone matrix with 73-90% volume porosity and macropore size from 50 to 650 μm. Dynamics of neoosteogenesis and bone tissue remodeling was investigated histologically at the time points of 12, 21, 48, and 63 days. Diopside particles were evenly spread in the matrix and caused minimal foreign body reaction. In the presence of BMP-2 by the day 63 significant foci of newly formed bone tissue were formed in the implant pores with bone marrow areas, moreover, large areas of demineralized bone matrix in the implant center and maternal bone at the edges were involved in the remodeling. Diopside could be considered as a promising material for introduction into hybrid implants as an effective carrier of BMP-2.

A 3D-printed bioactive polycaprolactone scaffold assembled with core/shell microspheres as a sustained BMP2-releasing system for bone repair

Integration of biological factors and hierarchical rigid scaffolds is of great interest in bone tissue engineering for fabrication of biomimetic constructs with high physical and biological performance for enhanced bone repair. Core/shell microspheres (CSMs) delivering bone morphogenetic protein-2 (BMP-2) and a strategy to integrate CSMs with 3D-printed scaffolds were developed herein to form a hybrid 3D system for bone repair. The scaffold was printed with polycaprolactone (PCL) and then coated with polydopamine. Shells of CSMs were electrosprayed with alginate. Cores were heparin-coated polylactic acid (PLA) microparticles fabricated via simple emulsion and heparin coating strategy. Assembly of microspheres and scaffolds was realized via a self-locking method with the assistance of controlled expansion of CSMs. The hybrid system was evaluated in the rat critical-sized bone defect model. CSMs released BMP-2 in a tunable manner and boosted osteogenic performance in vitro. CSMs were then successfully integrated inside the scaffolds. The assembled system effectively promoted osteogenesis in vitro and in vivo. These observations show the importance of how BMP-2 is delivered, and the core/shell microspheres represent effective BMP-2 carriers that could be integrated into scaffolds, together forming a hybrid system as a promising candidate for enhanced bone regeneration.

Bioactive chitosan biguanidine-based injectable hydrogels as a novel BMP-2 and VEGF carrier for osteogenesis of dental pulp stem cells

Nowadays, vascularization and mineralization of bone defects is the main bottleneck in the bone regeneration field that is needed to be overcome and developed. Here, we prepared novel in-situ formed injectable hydrogels based on chitosan biguanidine and carboxymethylcellulose loaded with vascular endothelial growth factor (VEGF) and recombinant Bone morphogenetic protein 2 (BMP-2) and studied its influence on osteoblastic differentiation of dental pulp stem cells (DPSCs). The sequential release behavior of the VEGF and BMP-2 from hydrogels adjusted with the pattern of normal human bone growth. MTT assay exhibited that these hydrogels were non-toxic and significantly increased DPSCs proliferation. The Real-time PCR and Western blot analysis on CG11/BMP2-VEGF showed significantly higher gene and protein expression of ALP, COL1α1, and OCN. These results were confirmed by mineralization assay by Alizarin Red staining and Alkaline phosphatase enzyme activity. Based on these evaluations, these hydrogel holds potential as an injectable bone tissue engineering platform.

Acceleration of bone formation using insitu-formed hyaluronan-hydrogel containing bone morphogenetic protein-2 in a mouse critical size bone defect model.

An enzymatic crosslinking strategy using hydrogen peroxide and horseradish peroxidase is receiving increasing attention for application with in situ-formed hydrogels (IFHGs). IFHGs may also be ideal carrier materials for bone repair, although their ability to carry bone morphogenetic protein-2 (BMP2) has yet to be examined. We examined the effectiveness of an IFHG made of hyaluronan (IFHG-HA) containing BMP2 for promoting bone formation in a mouse critical size bone defect model. C57/BL6J mice received a 2-mm femoral critical-sized bone defect before being randomly assigned to one of the following treatment groups (n =6): control (no treatment), IFHG-HA only, PBS with BMP2, and IFHG-HA with BMP2. X-ray radiographs were utilized to track new bone formation, and micro-computed tomography and histological examination were performed on new bone formed at the bone defect site two weeks after surgery. Mice treated with PBS with BMP2 and IFHG-HA with BMP2 had greater bone volume (BV) and bone mineral content (BMC) than those receiving control, and successfully achieved consolidation. Mice treated with IFHG-HA with BMP2 had significantly higher BV and BMC than those treated with PBS with BMP2. IFHG-HA may be an effective carrier for BMP2 to enable delivery for bone defect repair.

Bioactivity of a Novel Polycaprolactone-Hydroxyapatite Scaffold Used as a Carrier of Low Dose BMP-2: An In Vitro Study.

Scaffolds of polycaprolactone-30% hydroxyapatite (PCL-30% HA) were fabricated using melt stretching and multilayer deposition (MSMD), and the in vitro response of osteoblasts to the scaffolds was assessed. In group A, the scaffolds were immersed in 10 µg/mL bone morphogenetic protein-2 (BMP-2) solution prior to being seeded with osteoblasts, and they were cultured in the medium without BMP-2. In group B, the cell-scaffold constructs without BMP-2 were cultured in medium containing 10 µg/mL BMP-2. The results showed greater cell proliferation in group A. The upregulation of runt-related transcription factor 2 and osteocalcin genes correlated with the release of BMP-2 from the scaffolds. The PCL-30% HA MSMD scaffolds appear to be suitable for use as osteoconductive frameworks and BMP-2 carriers.

A novel nano-hydroxyapatite/synthetic polymer/bone morphogenetic protein-2 composite for efficient bone regeneration

BACKGROUNDEfficient bone regeneration using recombinant human bone morphogenetic protein-2 (BMP-2) is needed to reduce side effects caused by high-dose BMP-2 use. The composite material of polylactic acid–polyethene glycol (PLA-PEG) for sustained release and an osteogenic nano-hydroxyapatite (nHAp) can contribute to efficient bone regeneration by BMP-2. STUDY DESIGNAn experimental in vitro and in vivo study. PURPOSEThe objective of this study is to investigate the effectiveness of a novel composite material of PLA-PEG and nHAp as a carrier for BMP-2. METHODSThe release kinetics of BMP-2 from the composites was investigated by ELISA. Thirty-six male Sprague–Dawley rats underwent posterolateral spinal fusion on L4–L5 with three different doses of BMP-2 (0 µg [control], 3 µg [low dose], and 10 µg [high dose]). Weekly µCT results and histology and a manual palpation test at 8 weeks postoperatively were used for assessment of the spinal fusion. RESULTSELISA demonstrated the sustained release of BMP-2 until day 21. µCT and manual palpation test demonstrated a solid fusion in 91.6% (11/12) of specimens in both the low- and high-dose groups. N mice in the control group attained bony fusion (0%, 0/9). nHAp was resorbed between 2 and 4 weeks postoperatively, and regenerated fusion mass at 8 weeks postoperatively consisted of only newly formed bone. CONCLUSIONSThe nHAp/PLA-PEG composite enabled efficient bone regeneration with low-dose BMP-2. The sustained release of BMP-2 by PLA-PEG and the osteogenic and biodegradable scaffold of nHAp might contribute to efficient bone regeneration. CLINICAL SIGNIFICANCEThis novel composite material has potential in clinical applications (spinal fusion, large bone defect and non-union) by enabling efficient bone formation by BMP-2.

&lt;i&gt;In vitro&lt;/i&gt; evaluation of bone grafting materials on macrophage polarization, osteogenic differentiation, and the potential as bone morphogenetic protein-2 carriers

&lt;i&gt;In vitro&lt;/i&gt; evaluation of bone grafting materials on macrophage polarization, osteogenic differentiation, and the potential as bone morphogenetic protein-2 carriers

Nanostructured Carbonated Hydroxyapatite Associated to rhBMP-2 Improves Bone Repair in Rat Calvaria.

Many biomaterials are used for Bone Morphogenetic Proteins (BMPs) delivery in bone tissue engineering. The BMP carrier system’s primary function is to hold these growth factors at the wound’s site for a prolonged time and provide initial support for cells to attach and elaborate the extracellular matrix for bone regeneration. This study aimed to evaluate the nanostructured carbonated hydroxyapatite microspheres (nCHA) as an rhBMP-2 carrier on rats calvaria. A total of fifteen male Wistar rats were randomly divided into three groups (n = 5): clot (control group), rhBMP-2 associated with collagen membrane (COL/rhBMP-2) or associated with the microspheres (nCHA/rhBMP-2). After 45 days, the calvaria defect samples were evaluated through histological, histomorphometric, and SR-µCT analyses to investigate new-formed bone and connective tissue volume densities. The descriptive histological analysis showed that nCHA/rhBMP-2 improved bone formation compared to other groups. These results were confirmed by histomorphometric and SR-µCT analysis that showed substantially defect area filling with a higher percentage of newly formed (36.24 ± 6.68) bone than those with the COL/rhBMP-2 (0.42 ± 0.40) and Clot (3.84 ± 4.57) (p < 0.05). The results showed that nCHA is an effective carrier for rhBMP-2 encouraging bone healing and an efficient alternative to collagen membrane for rhBMP-2 delivery.

Acceleration of bone union by in situ-formed hydrogel containing bone morphogenetic protein-2 in a mouse refractory fracture model

BackgroundAn enzymatic crosslinking strategy using hydrogen peroxide and horseradish peroxidase is receiving increasing attention for application with in situ-formed hydrogels (IFHs). Several studies have reported the application of IFHs in cell delivery and tissue engineering. IFHs may also be ideal carrier materials for bone repair, although their potential as a carrier for bone morphogenetic protein (BMP)-2 has yet to be examined. Here, we examined the effect of an IFH made of hyaluronic acid (IFH-HA) containing BMP-2 in promoting osteogenesis in a mouse refractory fracture model.MethodsImmediately following a fracture procedure, animals either received no treatment (control) or an injection of IFH-HA/PBS or IFH-HA containing 2 μg BMP-2 (IFH-HA/BMP-2) into the fracture site (n = 16, each treatment).ResultsFracture sites injected with IFH-HA/BMP-2 showed significantly greater bone volume, bone mineral content, and bone union compared with sites receiving no treatment or treated with IFH-HA/PBS alone (each n = 10). Gene expression levels of osteogenic markers, Alpl, Bglap, and Osx, were significantly raised in the IFH-HA/BMP-2 group compared to the IFH-HA/PBS and control groups (each n = 6).ConclusionIFH-HA/BMP-2 may contribute to the treatment of refractory fractures.

Osteogenic-differentiated mesenchymal stem cell-secreted extracellular matrix as a bone morphogenetic protein-2 delivery system for ectopic bone formation

While human bone morphogenetic protein-2 (BMP-2) is a promising growth factor for bone regeneration, a major challenge in biomedical applications is finding an optimal carrier for its delivery at the site of injury. Because of their natural affinities for growth factors (including BMP-2) as well as their role in instructing cell function, cultured cell-derived extracellular matrices (ECM) are of special interest. We hereby hypothesized that a “bony matrix” containing mineralized, osteogenic ECM is a potential efficacious carrier of BMP-2 for promoting bone formation and, therefore, compared the efficacy of the decellularized ECM derived from osteogenic-differentiated human mesenchymal stem cells (hMSCs) to the one obtained from ECM from undifferentiated hMSCs. Our results provided evidence that both ECMs can bind BMP-2 and promote bone formation when implanted ectopically in mice. The osteoinductive potential of BMP-2, however, was greater when loaded within an osteogenic MSC-derived ECM; this outcome was correlated with higher sequestration capacity of BMP-2 over time in vivo. Interestingly, although the BMP-2 mainly bound onto the mineral crystals contained within the osteogenic MSC derived-ECM, these mineral components were not involved in the observed higher osteoinductivity, suggesting that the organic components were the critical components for the matrix efficacy as BMP-2 carrier.

Supramolecular self-assembling peptides to deliver bone morphogenetic proteins for skeletal regeneration.

Recombinant human bone morphogenetic proteins (BMPs) have shown clinical success in promoting bone healing, but they are also associated with unwanted side effects. The development of improved BMP carriers that can retain BMP at the defect site and maximize its efficacy would decrease the therapeutic BMP dose and thus improve its safety profile. In this review, we discuss the advantages of using self-assembling peptides, a class of synthetic supramolecular biomaterials, to deliver recombinant BMPs. Peptide amphiphiles (PAs) are a broad class of self-assembling peptides, and the use of PAs for BMP delivery and bone regeneration has been explored extensively over the past decade. Like many self-assembling peptide systems, PAs can be designed to form nanofibrous supramolecular biomaterials in which molecules are held together by non-covalent bonds. Chemical and biological functionality can be added to PA nanofibers, through conjugation of chemical moieties or biological epitopes to PA molecules. For example, PA nanofibers have been designed to bind heparan sulfate, a natural polysaccharide that is known to bind BMPs and potentiate their signal. Alternatively, PA nanofibers have been designed to synthetically mimic the structure and function of heparan sulfate, or to directly bind BMP specifically. In small animal models, these bio-inspired PA materials have shown the capacity to promote bone regeneration using BMP at doses 10-100 times lower than established therapeutic doses. These promising results have motivated further evaluation of PAs in large animal models, where their safety and efficacy must be established before clinical translation. We conclude with a discussion on the possiblity of combining PAs with other materials used in orthopaedic surgery to maximize their utility for clinical translation.

Sequential Delivery of BMP2-Derived Peptide P24 by Thiolated Chitosan/Calcium Carbonate Composite Microspheres Scaffolds for Bone Regeneration

The combination of tissue-engineered bone scaffolds with osteogenic induction molecules is an important strategy for critical-sized bone defects repair. We synthesized a novel thiolated chitosan/calcium carbonate composite microsphere (TCS-P24/CA) scaffold as a carrier for bone morphogenetic protein 2- (BMP2-) derived peptide P24 and evaluated the release kinetics of P24. The effect of TCS-P24/CA scaffolds on the proliferation and differentiation of bone marrow mesenchymal stem cells (BMSCs) was evaluated by scanning electron microscope (SEM), CCK-8, ALP assay, alizarin red staining, and PCR. A 5 mm diameter calvarial defect was created, then new bone formation was evaluated by Micro-CT and histological examination at 4 and 8 weeks after operation. We found the sequential release of P24 could last for 29 days. Meanwhile, BMSCs revealed spindle-shaped surface morphology, indicating the TCS-P24/CA scaffolds could support cell adhesion and mRNA levels for ALP, Runx2, and COL1a1 were significantly upregulated on TCS-10%P24/CA scaffold compared with other groups in vitro (p&lt;0.05). Similarly, the BMSCs exhibited a higher ALP activity as well as calcium deposition level on TCS-10%P24/CA scaffolds compared with other groups (p&lt;0.05). Analysis of in vivo bone formation showed that the TCS-10%P24/CA scaffold induced more bone formation than TCS-5%P24/CA, TCS/CA, and control groups. This study demonstrates that the novel TCS-P24/CA scaffolds might contribute to the delivery of BMP2-derived Peptide P24 and is considered to be a potential candidate for repairing bone defects.

Improving the handling properties and long-term stability of polyelectrolyte complex by freeze-drying technique for low-dose bone morphogenetic protein 2 delivery.

A variety of controlled release carriers for bone morphogenetic protein 2 (BMP-2) delivery have been developed and tested in animal models. An alginate-based polyelectrolyte complex (PEC) for controlled release of low-dose BMP-2 has shown promising results in preclinical research. However, the poor handling properties and long-term stability of PEC need to be improved for translational applications. This study aimed to address these limitations of alginate-based PEC by employing a freeze-drying technique. The size and structure of freeze-dried PEC (FD-PEC) were maintained with the addition of a cryoprotectant, trehalose. The release profile of BMP-2 from FD-PEC was similar to that of freshly prepared PEC. In vitro bioactivity analysis of the released BMP-2 showed that the carrier performance of PEC was not compromised by freeze-drying up to three-month storage at room temperature. BMP-2-bound FD-PEC induced comparable bone formation to that using freshly prepared regular PEC in a rat posterolateral spinal fusion model. These results suggest that FD-PEC is capable of delivering low-dose BMP-2 and could be developed as an off-the-shelf product for translational applications. The simplicity of this preservation method provides promise for the translational application of PEC.

Magnesium hydroxide-incorporated PLGA composite attenuates inflammation and promotes BMP2-induced bone formation in spinal fusion

Spinal fusion has become a common surgical technique to join two or more vertebrae to stabilize a damaged spine; however, the rate of pseudarthrosis (failure of fusion) is still high. To minimize pseudarthrosis, bone morphogenetic protein-2 (BMP2) has been approved for use in humans. In this study, we developed a poly(lactide-co-glycolide) (PLGA) composite incorporated with magnesium hydroxide (MH) nanoparticles for the delivery of BMP2. This study aimed to evaluate the effects of released BMP2 from BMP2-immobilized PLGA/MH composite scaffold in an in vitro test and an in vivo mice spinal fusion model. The PLGA/MH composite films were fabricated via solvent casting technique. The surface of the PLGA/MH composite scaffold was modified with polydopamine (PDA) to effectively immobilize BMP2 on the PLGA/MH composite scaffold. Analyzes of the scaffold revealed that using PLGA/MH-PDA improved hydrophilicity, degradation performance, neutralization effects, and increased BMP2 loading efficiency. In addition, releasing BMP2 from the PLGA/MH scaffold significantly promoted the proliferation and osteogenic differentiation of MC3T3-E1 cells. Furthermore, the pH neutralization effect significantly increased in MC3T3-E1 cells cultured on the BMP2-immobilized PLGA/MH scaffold. In our animal study, the PLGA/MH scaffold as a BMP2 carrier attenuates inflammatory responses and promotes BMP2-induced bone formation in posterolateral spinal fusion model. These results collectively demonstrate that the BMP2-immobilized PLGA/MH scaffold offers great potential in effectively inducing bone formation in spinal fusion surgery.

Synergistic Effect of NELL-1 and an Ultra-Low Dose of BMP-2 on Spinal Fusion

Bone morphogenetic protein 2 (BMP-2) is widely used in spinal fusion but it can cause adverse effects such as ectopic bone and adipose tissue in vivo. Neural epidermal growth factor like-like molecule-1 (NELL-1) has been shown to suppress BMP-2-induced adverse effects. However, no optimum carriers that control both NELL-1 and BMP-2 releases to elicit long-term bioactivity have been developed. In this study, we employed polyelectrolyte complex (PEC) as a control release carrier for NELL-1 and BMP-2. An ultra-low dose of BMP-2 synergistically functioned with NELL-1 on bone marrow mesenchymal stem cells osteogenic differentiation with greater mineralization in vitro. The osteoinductive ability of NELL-1 and an ultra-low dose of BMP-2 in PEC was investigated in rat posterolateral spinal fusion. Our results showed increased fusion rate, bone architecture, and improved bone stiffness at 8 weeks after surgery in the combination groups compared with NELL-1 or BMP-2 alone. Moreover, the formation of ectopic bone and adipose tissue was negligible in all the PEC groups. In summary, dual delivery of NELL-1 and an ultra-low dose of BMP-2 in the PEC control release carrier has greater fusion efficiency compared with BMP-2 alone and could potentially be a better alternative to the currently used BMP-2 treatments for spinal fusion. Impact Statement In this study, polyelectrolyte complex was used to absorb neural epidermal growth factor like-like molecule-1 (NELL-1) and bone morphogenetic protein 2 (BMP-2) to achieve controlled dual release. The addition of NELL-1 significantly reduced the effective dose of BMP-2 to 2.5% of its conventional dose in absorbable collagen sponge, to produce solid spinal fusion without significant adverse effects. This study was the first to identify the efficacy of combination NELL-1 and BMP-2 in a control release carrier in spinal fusion, which could be potentially used clinically to increase fusion rate and avoid the adverse effects commonly associated with conventional BMP-2.