Functional restoration of critically sized segmental defects with bone morphogenetic protein-2 and heparin treatment

Novel Strategies for Spatiotemporal and Controlled BMP-2 Delivery in Bone Tissue Engineering

Bone morphogenetic protein-2 (BMP-2) has been commercially approved by the Food and Drug Administration for use in bone defects and diseases. BMP-2 promotes osteogenic differentiation of mesenchymal stem cells. In bone tissue engineering, BMP-2 incorporated into scaffolds can be used for stimulating bone regeneration in organoid construction, drug testing platforms, and bone transplants. However, the high dosage and uncontrollable release rate of BMP-2 challenge its clinical application, mainly due to the short circulation half-life of BMP-2, microbial contamination in bone extracellular matrix hydrogel, and the delivery method. Moreover, in clinical translation, the requirement of high doses of BMP-2 for efficacy poses challenges in cost and safety. Based on these, novel strategies should ensure that BMP-2 is delivered precisely to the desired location within the body, regulating the timing of BMP-2 release to coincide with the bone healing process, as well as release BMP-2 in a controlled manner to optimize its therapeutic effect and minimize side effects. This review highlights improvements in bone tissue engineering applying spatiotemporal and controlled BMP-2 delivery, including molecular engineering, biomaterial modification, and synergistic therapy, aiming to provide references for future research and clinical trials.

The Auxiliary Role of Heparin in Bone Regeneration and its Application in Bone Substitute Materials

Bone regeneration in large segmental defects depends on the action of osteoblasts and the ingrowth of new blood vessels. Therefore, it is important to promote the release of osteogenic/angiogenic growth factors. Since the discovery of heparin, its anticoagulant, anti-inflammatory, and anticancer functions have been extensively studied for over a century. Although the application of heparin is widely used in the orthopedic field, its auxiliary effect on bone regeneration is yet to be unveiled. Specifically, approximately one-third of the transforming growth factor (TGF) superfamily is bound to heparin and heparan sulfate, among which TGF-β1, TGF-β2, and bone morphogenetic protein (BMP) are the most common growth factors used. In addition, heparin can also improve the delivery and retention of BMP-2 in vivo promoting the healing of large bone defects at hyper physiological doses. In blood vessel formation, heparin still plays an integral part of fracture healing by cooperating with the platelet-derived growth factor (PDGF). Importantly, since heparin binds to growth factors and release components in nanomaterials, it can significantly facilitate the controlled release and retention of growth factors [such as fibroblast growth factor (FGF), BMP, and PDGF] in vivo. Consequently, the knowledge of scaffolds or delivery systems composed of heparin and different biomaterials (including organic, inorganic, metal, and natural polymers) is vital for material-guided bone regeneration research. This study systematically reviews the structural properties and auxiliary functions of heparin, with an emphasis on bone regeneration and its application in biomaterials under physiological conditions.

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.

Biomaterials for bone regeneration: an orthopedic and dentistry overview

Because bone-associated diseases are increasing, a variety of tissue engineering approaches with bone regeneration purposes have been proposed over the last years. Bone tissue provides a number of important physiological and structural functions in the human body, being essential for hematopoietic maintenance and for providing support and protection of vital organs. Therefore, efforts to develop the ideal scaffold which is able to guide the bone regeneration processes is a relevant target for tissue engineering researchers. Several techniques have been used for scaffolding approaches, such as diverse types of biomaterials. On the other hand, metallic biomaterials are widely used as support devices in dentistry and orthopedics, constituting an important complement for the scaffolds. Hence, the aim of this review is to provide an overview of the degradable biomaterials and metal biomaterials proposed for bone regeneration in the orthopedic and dentistry fields in the last years.

Advances in Extracellular Matrix-Mimetic Hydrogels to Guide Stem Cell Fate

In the fields of regenerative medicine and tissue engineering, stem cells offer vast potential for treating or replacing diseased and damaged tissue. Much progress has been made in understanding stem cell biology, yielding protocols for directing stem cell differentiation toward the cell type of interest for a specific application. One particularly interesting and powerful signaling cue is the extracellular matrix (ECM) surrounding stem cells, a network of biopolymers that, along with cells, makes up what we define as a tissue. The composition, structure, biochemical features, and mechanical properties of the ECM are varied in different tissues and developmental stages, and serve to instruct stem cells toward a specific lineage. By understanding and recapitulating some of these ECM signaling cues through engineered ECM-mimicking hydrogels, stem cell fate can be directed in vitro. In this review, we will summarize recent advances in material systems to guide stem cell fate, highlighting innovative methods to capture ECM functionalities and how these material systems can be used to provide basic insight into stem cell biology or make progress toward therapeutic objectives.

Heparin-mediated delivery of bone morphogenetic protein-2 improves spatial localization of bone regeneration

Supraphysiologic doses of bone morphogenetic protein-2 (BMP-2) are used clinically to promote bone formation in fracture nonunions, large bone defects, and spinal fusion. However, abnormal bone formation (i.e., heterotopic ossification) caused by rapid BMP-2 release from conventional collagen sponge scaffolds is a serious complication. We leveraged the strong affinity interactions between heparin microparticles (HMPs) and BMP-2 to improve protein delivery to bone defects. We first developed a computational model to investigate BMP-2-HMP interactions and demonstrated improved in vivo BMP-2 retention using HMPs. We then evaluated BMP-2-loaded HMPs as a treatment strategy for healing critically sized femoral defects in a rat model that displays heterotopic ossification with clinical BMP-2 doses (0.12 mg/kg body weight). HMPs increased BMP-2 retention in vivo, improving spatial localization of bone formation in large bone defects and reducing heterotopic ossification. Thus, HMPs provide a promising opportunity to improve the safety profile of scaffold-based BMP-2 delivery.

Enhanced in vivo retention of low dose BMP-2 via heparin microparticle delivery does not accelerate bone healing in a critically sized femoral defect

Bone morphogenetic protein-2 (BMP-2) is an osteoinductive growth factor used clinically to induce bone regeneration and fusion. Some complications associated with BMP-2 treatment have been attributed to rapid release of BMP-2 from conventional collagen scaffolds, motivating the development of tunable sustained-release strategies. We incorporated BMP-2-binding heparin microparticles (HMPs) into a hydrogel scaffold to improve spatiotemporal control of BMP-2 delivery to large bone defects. HMPs pre-loaded with BMP-2 were mixed into alginate hydrogels and compared to hydrogels containing BMP-2 alone. BMP-2 release from scaffolds in vitro, BMP-2 retention within injury sites in vivo, and bone regeneration in a critically sized femoral defect were evaluated. Compared to hydrogel delivery alone, BMP-2-loaded HMPs reduced BMP-2 release in vitro and increased early BMP-2 retention in the bone defect. BMP-2-loaded HMPs induced bone formation at both ectopic and orthotopic sites; however, the volume of induced bone was lower for defects treated with BMP-2-loaded HMPs compared to hydrogel delivery. To better understand the effect of HMPs on BMP-2 release kinetics, a computational model was developed to predict BMP-2 release from constructs in vivo. The model suggested that HMPs limited BMP-2 release into surrounding tissues, and that changing the HMP density could modulate BMP-2 release. Taken together, these experimental and computational results suggest the importance of achieving a balance of BMP-2 retention within the bone defect and BMP-2 release into surrounding soft tissues. HMP delivery of BMP-2 may provide a method of tuning BMP-2 release in vivo that can be further investigated to improve current methods of bone regeneration.

STATEMENT OF SIGNIFICANCE

The development of effective biomaterials for sustained protein delivery is a crucial component of tissue engineering strategies. However, in most applications, including bone repair, the optimal balance between protein presentation in the injury site and protein release into the surrounding tissues is unknown. Herein, we introduced heparin microparticles (HMPs) into a tissue engineered construct to increase in vivo retention of bone morphogenetic protein-2 (BMP-2) and enhance healing in femoral defects. Although HMPs induced bone regeneration, no increase in bone volume was observed, leading to further experimental and computational analysis of the effect of HMP-BMP-2 interactions on protein retention and release. Ultimately, this work provides insight into designing tunable protein-material interactions and their implications for controlling BMP-2 delivery.

Competitive Protein Binding Influences Heparin-Based Modulation of Spatial Growth Factor Delivery for Bone Regeneration

Tissue engineering strategies involving the in vivo delivery of recombinant growth factors are often limited by the inability of biomaterials to spatially control diffusion of the delivered protein within the site of interest. The poor spatiotemporal control provided by porous collagen sponges, which are used for the clinical delivery of bone morphogenetic protein-2 (BMP-2) for bone regeneration, has necessitated the use of supraphysiological protein doses, leading to inflammation and heterotopic ossification. This study describes a novel tissue engineering strategy to spatially control rapid BMP-2 diffusion from collagen sponges in vivo by creating a high-affinity BMP-2 sink around the collagen sponge. We designed an electrospun poly-ɛ-caprolactone nanofiber mesh containing physically entrapped heparin microparticles, which have been previously demonstrated to bind and retain large amounts of BMP-2. Nanofiber meshes containing 0.05 and 0.10 mg of microparticles/cm2 demonstrated increased BMP-2 binding and decreased BMP-2 release in vitro compared with meshes without microparticles. However, when microparticle-containing meshes were used in vivo to limit the diffusion of BMP-2 delivered by using collagen sponges in a rat femoral defect, no differences in heterotopic ossification or biomechanical properties were observed. Further investigation revealed that, although BMP-2 binding to heparin microparticles was rapid, the presence of serum components attenuated microparticle-BMP-2 binding and increased BMP-2 release in vitro. These observations provide a plausible explanation for the results observed in vivo and suggest that competitive protein binding in vivo may hinder the ability of affinity-based biomaterials to modulate growth factor delivery.

Heparin cross-linked collagen sponge scaffolds improve functional regeneration of rat tracheal epithelium

Tracheal epithelial cells maintain airway homeostasis by mediating mucociliary clearance. Following tracheal reconstruction, timely epithelial regeneration is required to prevent respiratory compromise and infectious diseases. To achieve rapid tracheal epithelial regeneration, a heparin cross-linked collagen sponge containing fibroblast growth factor-2 (FGF-2) was prepared as a graft for tracheal reconstruction. The heparin cross-linked sponge exhibited a high FGF-2 retaining capacity, and tracheal epithelial and mesenchymal cells cultured in this sponge containing FGF-2 showed high proliferative capacities. Subsequently, heparin-free collagen sponge scaffolds (C/F scaffold) and collagen sponge scaffolds cross-linked with 10 μg/ml heparin retained FGF-2 (C/H10/F scaffold), and were transplanted into rats with tracheal defects. Invasion of both epithelial and non-epithelial cells was greater in rats treated with the C/H10/F scaffold at 1 week post-transplantation than in rats treated with the C/F scaffold. Moreover, at 2 weeks after transplantation, improved cilia formation was observed in the C/H10/F scaffold group, with higher motility and more potent posterior-anterior flow generation than in the C/F scaffold group. These results suggest that heparin improves functional regeneration of tracheal epithelium. Copyright © 2017 John Wiley & Sons, Ltd.

Heparin-Based Polyelectrolyte Complex Enhances the Therapeutic Efficacy of Bone Morphogenetic Protein-2 for Posterolateral Fusion in a Large Animal Model

STUDY DESIGN

The study was based on porcine posterolateral fusion model.

OBJECTIVE

The study aims to prove that polyelectrolyte complex (PEC) carrier could enhance the efficacy and safety profile of bone morphogenetic protein-2 (BMP-2).

SUMMARY OF BACKGROUND DATA

BMP-2 was introduced to enhance posterolateral fusion; however, extremely high doses of this molecule were often used which contributed to various complications. This was attributed to the poor modulation capacity of the traditional carrier absorbable collagen sponge (ACS). To reduce the efficacious dose of BMP-2 and its associated complications, heparin-based PEC was introduced.

METHODS

L3/L4 and L5/L6 two-level posterolateral spinal fusion was performed on six pigs using two doses of BMP-2 with PEC or ACS: (1) PEC with 800 μg BMP-2 (n = 2); (2) PEC with 400 μg BMP-2 (n = 2); (3) ACS with 800 μg BMP-2 (n = 1); (4) ACS with 400 μg of BMP-2 (n = 1). The construct was loaded into a rigid bioabsorbable cage for implantation. Fusion rate and quality were assessed 2 months after operation.

RESULTS

Manual palpation revealed successful fusion in all groups. Radiological fusion score of PEC groups was, however, higher than that of ACS groups. The newly formed bone in PEC groups appeared to be well integrated into the native bone with no overgrowth into the adjacent structure. On comparison, in ACS groups, large gaps were observed between the newly formed bone and the fusion bed with heterotopic ossification into the psoas muscle. The microarchitecture on the newly formed bone in PEC groups was superior to that in ACS groups, which was demonstrated by higher three-dimensional parameters.

CONCLUSION

The present study demonstrated that BMP-2 delivered by PEC induced successful posterolateral fusion in porcine model. The efficacy of BMP-2 was improved and bony overgrowth was reduced. The microarchitecture of BMP-2-induced bone tissue was also enhanced by PEC.

LEVEL OF EVIDENCE

N/A.

A review on carrier systems for bone morphogenetic protein-2

Bone morphogenetic protein-2 (BMP-2) has unique bone regeneration property. The powerful osteoinductive nature makes it considered as second line of therapy in nonunion bone defect. A large number of carriers and delivery systems made up of different materials have been investigated for controlled and sustained release of BMP-2. The delivery systems are in the form of hydrogel, microsphere, nanoparticles, and fibers. The carriers used for the delivery are made up of metals, ceramics, polymers, and composites. Implantation of these protein-loaded carrier leads to cell adhesion, degradation which eventually releases the drug/protein at site specific. But, problems like ectopic growth, lesser protein delivery, inactivation of the protein are reported in the available carrier systems. Therefore, it is need of an hour to modify the available carrier systems as well as explore other biomaterials with desired properties. In this review, all the reported carrier systems made of metals, ceramics, polymers, composites are evaluated in terms of their processing conditions, loading capacity and release pattern of BMP-2. Along with these biomaterials, the attempts of protein modification by adding some functional group to BMP-2 or extracting functional peptides from the protein to achieve the desired effect, is also evaluated. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 904-925, 2017.

Biomaterial strategies for controlling stem cell fate via morphogen sequestration

This review explores the role of protein sequestration in the stem cell niche and how it has inspired the design of biomaterials that exploit natural protein sequestration to influence stem cell fate.

Calcium homeostasis disorder during and after neonatal extracorporeal membrane oxygenation

BACKGROUND AND AIMS

Extracorporeal membrane oxygenation (ECMO) is used during pediatric resuscitation in case of refractory hypoxemia or septic shock under maximum therapy. Previous studies describe calcium homeostasis dysregulation. The aim of this study was to confirmed of calcium homeostasis dysregulation in neonates under ECMO and supposed news explanation.

SUBJECTS AND METHODS

From November 2012 to July 2013, we performed a prospective single center observational study. Eleven neonatal patients were included. Blood was obtained before and during ECMO (day 7, 14 and 21) for parathyroid hormone (PTH), protein adjusted serum calcium, ionized calcium, magnesium, and calcitriol levels. All surviving patients underwent a consultation up to 6 months after ECMO weaning.

RESULTS

During ECMO PTH was inadequately high with normal serum calcium on day 7 (PTH: 73.54 ± 40 ng/l; calcemia: 2.33 ± 0.21 mmol/l), day 14 (PTH: 57.63 ± 29.57 ng/l; calcemia: 2.44 ± 0.43 mmol/l) and day 21 (PTH: 54.93 ± 8.43 ng/l; calcemia: 2.13 ± 0.09 mmol/l). The absence of correlation between serum calcium and PTH levels seem to confirm the dysregulation of PTH - serum calcium metabolism during ECMO. Six months after ECMO weaning, we noticed hypercalcemia with normal PTH.

CONCLUSIONS

We confirmed the existence of severe disturbances of calcium homeostasis in neonates on ECMO and supposed the possible damage of calcium regulation. We did not succeed in finding clear explanations of these disturbances.

Heparin microparticle effects on presentation and bioactivity of bone morphogenetic protein-2

Biomaterials capable of providing localized and sustained presentation of bioactive proteins are critical for effective therapeutic growth factor delivery. However, current biomaterial delivery vehicles commonly suffer from limitations that can result in low retention of growth factors at the site of interest or adversely affect growth factor bioactivity. Heparin, a highly sulfated glycosaminoglycan, is an attractive growth factor delivery vehicle due to its ability to reversibly bind positively charged proteins, provide sustained delivery, and maintain protein bioactivity. This study describes the fabrication and characterization of heparin methacrylamide (HMAm) microparticles for recombinant growth factor delivery. HMAm microparticles were shown to efficiently bind several heparin-binding growth factors (e.g. bone morphogenetic protein-2 (BMP-2), vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (FGF-2)), including a wide range of BMP-2 concentrations that exceeds the maximum binding capacity of other common growth factor delivery vehicles, such as gelatin. BMP-2 bioactivity was assessed on the basis of alkaline phosphatase (ALP) activity induced in skeletal myoblasts (C2C12). Microparticles loaded with BMP-2 stimulated comparable C2C12 ALP activity to soluble BMP-2 treatment, indicating that BMP-2-loaded microparticles retain bioactivity and potently elicit a functional cell response. In summary, our results suggest that heparin microparticles stably retain large amounts of bioactive BMP-2 for prolonged periods of time, and that presentation of BMP-2 via heparin microparticles can elicit cell responses comparable to soluble BMP-2 treatment. Consequently, heparin microparticles present an effective method of delivering and spatially retaining growth factors that could be used in a variety of systems to enable directed induction of cell fates and tissue regeneration.

Biomolecule delivery to engineer the cellular microenvironment for regenerative medicine

To realize the potential of regenerative medicine, controlling the delivery of biomolecules in the cellular microenvironment is important as these factors control cell fate. Controlled delivery for tissue engineering and regenerative medicine often requires bioengineered materials and cells capable of spatiotemporal modulation of biomolecule release and presentation. This review discusses biomolecule delivery from the outside of the cell inwards through the delivery of soluble and insoluble biomolecules as well as from the inside of the cell outwards through gene transfer. Ex vivo and in vivo therapeutic strategies are discussed, as well as combination delivery of biomolecules, scaffolds, and cells. Various applications in regenerative medicine are highlighted including bone tissue engineering and wound healing.

Complexation and sequestration of BMP-2 from an ECM mimetic hyaluronan gel for improved bone formation

Bone morphogenetic protein-2 (BMP-2) is considered a promising adjuvant for the treatment of skeletal non-union and spinal fusion. However, BMP-2 delivery in a conventional collagen scaffold necessitates a high dose to achieve an efficacious outcome. To lower its effective dose, we precomplexed BMP-2 with the glycosaminoglycans (GAGs) dermatan sulfate (DS) or heparin (HP), prior to loading it into a hyaluronic acid (HA) hydrogel. In vitro release studies showed that BMP-2 precomplexed with DS or HP had a prolonged delivery compared to without GAG. BMP-2-DS complexes achieved a slightly faster release in the first 24 h than HP; however, both delivered BMP-2 for an equal duration. Analysis of the kinetic interaction between BMP-2 and DS or HP showed that HP had approximately 10 times higher affinity for BMP-2 than DS, yet it equally stabilized the protein, as determined by alkaline phosphatase activity. Ectopic bone formation assays at subcutaneous sites in rats demonstrated that HA hydrogel-delivered BMP-2 precomplexed with GAG induced twice the volume of bone compared with BMP-2 delivered uncomplexed to GAG.

Over-sulfated chondroitin sulfate derivatives induce osteogenic differentiation of hMSC independent of BMP-2 and TGF-β1 signalling

Natural glycosaminoglycans (GAGs) and chemically modified GAG derivatives are known to support osteogenic differentiation of mesenchymal stromal cells (MSC). This effect has mainly been described to be mediated by increasing the effectiveness of bone anabolic growth factors such as bone morphogenetic proteins (BMPs) due to the binding and presentation of the growth factor or by modulating its signal transduction pathway. In the present study, the influence of chondroitin sulfate (CS) and two chemically over-sulfated CS derivatives on osteogenic differentiation of human mesenchymal stromal cells (hMSC) and on BMP-2 and transforming growth factor β1 (TGF-β1) signalling was investigated. Over-sulfated CS derivatives induced an increase of tissue non-specific alkaline phosphatase (TNAP) activity and calcium deposition, whereas collagen synthesis was slightly decreased. The BMP-2-induced Smad1/5 activation was inhibited in the presence of over-sulfated CS derivatives leading to a loss of BMP-2-induced TNAP activity and calcium deposition. In contrast, the TGF-β1-induced activation of Smad2/3 and collagen synthesis were not affected by the over-sulfated CS derivatives. BMP-2 and TGF-β1 did not activate the extracellular signal-regulated kinase 1/2 or mitogen-activated protein kinase p38 in hMSC. These data suggest that over-sulfated CS derivatives themselves are able to induce osteogenic differentiation, probably independent of BMP-2 and TGF-β1 signalling, and offer therefore an interesting approach for the improvement of bone healing.

Engineering the regenerative microenvironment with biomaterials

Modern synthetic biomaterials are being designed to integrate bioactive ligands within hydrogel scaffolds for cells to respond and assimilate within the matrix. These advanced biomaterials are only beginning to be used to simulate the complex spatio-temporal control of the natural healing microenvironment. With increasing understanding of the role of growth factors and cytokines and their interactions with components of the extracellular matrix, novel biomaterials are being developed that more closely mimic the natural healing environments of tissues, resulting in increased efficacy in applications of tissue repair and regeneration. Herein, the important aspects of the healing microenvironment, and how these features can be incorporated within innovative hydrogel scaffolds, are presented.

Enhanced control of in vivo bone formation with surface functionalized alginate microbeads incorporating heparin and human bone morphogenetic protein-2

In this study, we tested the hypothesis that a surface functionalization delivery platform incorporating heparin onto strontium alginate microbeads surfaces would convert this "naive carriers" into "mini-reservoirs" for localized in vivo delivery of recombinant human bone morphogenetic protein-2 (rhBMP-2) that will induce functional bone regeneration. In vitro evaluation confirmed that (1) heparin incorporation could immobilize and prolong rhBMP-2 release for approximately 3 weeks; (2) a significant decrease (p<0.01) in rhBMP-2 burst release is attainable depending on initial protein load; and (3) rhBMP-2 released from surface functionalized microbeads retained bioactivity and stimulated higher alkaline phosphatase activity in cultured C(2)C(12) cells when compared with daily administration of fresh bolus rhBMP-2. Subsequently, surface functionalized microbeads were used for in vivo delivery of rhBMP-2 at local sites of posterolateral spinal fusion surgery in rats. The microbeads were loaded into the pores of medical-grade polyepsilone caprolactone-tricalcium phosphate scaffolds before implantation. Results revealed robust bone formation and a biomechanically solid fusion after 6 weeks. When compared with a control group consisting of an equivalent amount of rhBMP-2 that was directly adsorbed onto bare-surfaced microbeads with no heparin, a 5.3-fold increase in bone volume fraction and a 2.6-fold increase in bending stiffness (flexion/extension) were observed. When compared with collagen sponge carriers of rhBMP-2, a 1.5-fold and a 1.3-fold increase in bone volume fraction and bending stiffness were observed, respectively. More importantly, 3D micro-computed tomography images enabled the visualization of a well-contained newly formed bone at ipsilateral implant sites with surface functionalized rhBMP-2 delivery. This was absent with collagen sponge carriers where newly formed bone tissue was poorly contained and crossed over the posterior midline to contralateral implants. These findings are important because of complications with current rhBMP-2 delivery method, including excessive, uncontrolled bone formation.

Studies of bone morphogenetic protein-based surgical repair

Over the past several decades, recombinant human bone morphogenetic proteins (rhBMPs) have been the most extensively studied and widely used osteoinductive agents for clinical bone repair. Since rhBMP-2 and rhBMP-7 were cleared by the U.S. Food and Drug Administration for certain clinical uses, millions of patients worldwide have been treated with rhBMPs for various musculoskeletal disorders. Current clinical applications include treatment of long bone fracture non-unions, spinal surgeries, and oral maxillofacial surgeries. Considering the growing number of recent publications related to clincal research of rhBMPs, there exists enormous promise for these proteins to be used in bone regenerative medicine. The authors take this opportunity to review the rhBMP literature paying specific attention to the current applications of rhBMPs in bone repair and spine surgery. The prospective future of rhBMPs delivered in combination with tissue engineered scaffolds is also reviewed.