High doses of bone morphogenetic protein 2 induce structurally abnormal bone and inflammation in vivo

Implantable electrical stimulation bioreactor with liquid crystal polymer-based electrodes for enhanced bone regeneration at mandibular large defects in rabbit

The osseous regeneration of large bone defects is still a major clinical challenge in maxillofacial and orthopedic surgery. Previous studies demonstrated that biphasic electrical stimulation (ES) stimulates bone formation; however, polyimide electrode should be removed after regeneration. This study presents an implantable electrical stimulation bioreactor with electrodes based on liquid crystal polymer (LCP), which can be permanently implanted due to excellent biocompatibility to bone tissue. The bioreactor was implanted into a critical-sized bone defect and subjected to ES for one week, where bone regeneration was evaluated four weeks after surgery using micro-CT. The effect of ES via the bioreactor was compared with a sham control group and a positive control group that received recombinant human bone morphogenetic protein (rhBMP)-2 (20 μg). New bone volume per tissue volume (BV/TV) in the ES and rhBMP-2 groups increased to 132% (p < 0.05) and 174% (p < 0.01), respectively, compared to that in the sham control group. In the histological evaluation, there was no inflammation within the bone defects and adjacent to LCP in all the groups. This study showed that the ES bioreactor with LCP electrodes could enhance bone regeneration at large bone defects, where LCP can act as a mechanically resistant outer box without inflammation. Graphical abstract To enhance bone regeneration, a bioreactor comprising collagen sponge and liquid crystal polymer-based electrode was implanted in the bone defect. Within the defect, electrical current pulses having biphasic waveform were applied from the implanted bioreactor.

Local application of alendronate controls bone formation and β-tricalcium phosphate resorption induced by recombinant human bone morphogenetic protein-2

This study examined the ability of local alendronate (ALN) administration to control β-tricalcium phosphate (β-TCP) resorption as well as the induction of bone formation by recombinant human bone morphogenetic protein-2 (rhBMP-2). A 15-mm critical-sized bone defect was created in the diaphysis of rabbit ulnae. Nine female rabbits (4 to 5 months-old) were divided into 3 groups. Group 1 (n = 6 ulnae) animals received implants consisting of β-TCP granules and 25 μg of rhBMP-2 in 6.5% collagen gel. Group 2 (6 ulnae) and Group 3 (6 ulnae) animals received the same implants, but with 10^-6 M and 10^-3 M ALN-treated TCP granules, respectively. Two weeks postsurgery, tartrate-resistant acid phosphatase-positive cell counts, new bone formation, and residual β-TCP were evaluated. This study showed that a high dose of ALN strongly reduced osteoclastic resorption of β-TCP induced by rhBMP-2, resulting in decreased bone formation. In contrast, a low dose of ALN slightly reduced the bone resorptive effect but increased bone formation. These results suggest that osteoclast-mediated resorption plays an important role in bone formation and a coupling-like phenomenon could occur in the β-TCP-implanted area, and that administration of a low dose of ALN may solve clinical bone resorptive problems induced by rhBMP-2.

rhBMP2 alone does not induce macrophage polarization towards an increased inflammatory response

Once thought to have revolutionized therapeutic intervention in surgery, Recombinant Human Bone Morphogenic Protein 2 (rhBMP2) is now in its second decade of sustained controversy over the side effects associated with its use. Side effects associated with clinical use of rhBMP2 (Infuse, Medtronic Inc) include a marked inflammatory response, pain, therapeutic failures, ectopic bone, tissue degradation, and death. What is missing, despite the depth of literature on the subject, is a direct interrogation of rhBMP2, specifically for inflammation. Here we set out to determine if rhBMP2 alters traditional macrophage markers associated with pro-inflammatory responses, and pro-reparative responses to injury. Based on our previous work, we hypothesized there would be no direct effect of the peptide on macrophage polarization. Here we utilized commercially available murine macrophages, RAW 264.7, and treated these cells with rhBMP2 in standard growth media or macrophage polarizing media (M1 and M2) at several doses of the peptide. Our readouts were cell viability, apoptosis, gene expression of M1 and M2 markers, and ELISA for M1 marker iNOS, and M2 marker Arg1. Our data give very little evidence to support an alteration in macrophage phenotype by rhBMP2 alone, or alteration of the phenotype when cultured in enriched M1 or M2 media. These results further suggest that other factors associated with the clinical use of Infuse, likely supraphysiological rhBMP2 doses and off label usage, are more likely the culprit for poor outcomes. This further reinforces the utility of rhBMP2 and other peptides in tissue engineering therapies when conditions are tightly controlled.

Current and Future Concepts for the Treatment of Impaired Fracture Healing

Bone regeneration represents a complex process, of which basic biologic principles have been evolutionarily conserved over a broad range of different species. Bone represents one of few tissues that can heal without forming a fibrous scar and, as such, resembles a unique form of tissue regeneration. Despite a tremendous improvement in surgical techniques in the past decades, impaired bone regeneration including non-unions still affect a significant number of patients with fractures. As impaired bone regeneration is associated with high socio-economic implications, it is an essential clinical need to gain a full understanding of the pathophysiology and identify novel treatment approaches. This review focuses on the clinical implications of impaired bone regeneration, including currently available treatment options. Moreover, recent advances in the understanding of fracture healing are discussed, which have resulted in the identification and development of novel therapeutic approaches for affected patients.

A natural bioactive feed additive alters expression of genes involved in inflammation in whole blood of healthy Angus heifers

A greater demand for food animal production without antibiotics has created the common practice of feeding food animals dietary immunomodulatory feed additives (IFA) throughout their life cycle. However, little is known about the impact of IFA on cytokine and chemokine signaling in non-stressed, non-pathogen-challenged food animals during the early feeding period. We evaluated the expression of 82 genes related to cytokine and chemokine signaling in the whole blood of growing Angus heifers to determine the effect of IFA supplementation on cytokine and chemokine signaling during the first 28 d of feeding. One gene (CCL1) was significantly up-regulated and 14 genes (17%) were significantly down-regulated by IFA feeding during the entire early feeding period including 5 of 21 (24%) evaluated chemokine and IL receptors (CCR1, CCR2, IL1R1, IL10RA, IL10RB). These data when taken together suggest providing an IFA in the diet of growing beef cattle during the early feeding period may suppress the inflammatory response through cytokine–cytokine receptor signaling.

Is NO the Answer? The Nitric Oxide Pathway Can Support Bone Morphogenetic Protein 2 Mediated Signaling

The growth factor bone morphogenetic protein 2 (BMP2) plays an important role in bone development and repair. Despite the positive effects of BMP2 in fracture healing, its use is associated with negative side effects and poor cost effectiveness, partly due to the large amounts of BMP2 applied. Therefore, reduction of BMP2 amounts while maintaining efficacy is of clinical importance. As nitric oxide (NO) signaling plays a role in bone fracture healing and an association with the BMP2 pathway has been indicated, this study aimed to investigate the relationship of BMP2 and NO pathways and whether NO can enhance BMP2-induced signaling and osteogenic abilities in vitro. To achieve this, the stable BMP reporter cell line C2C12BRELuc was used to quantify BMP signaling, and alkaline phosphatase (ALP) activity and gene expression were used to quantify osteogenic potency. C2C12BRELuc cells were treated with recombinant BMP2 in combination with NO donors and substrate (Deta NONOate, SNAP & L-Arginine), NOS inhibitor (LNAME), soluble guanylyl cyclase (sGC) inhibitor (LY83583) and activator (YC-1), BMP type-I receptor inhibitor (LDN-193189), or protein kinase A (PKA) inhibitor (H89). It was found that the NOS enzyme, direct NO application, and sGC enhanced BMP2 signaling and improved BMP2 induced osteogenic activity. The application of a PKA inhibitor demonstrated that BMP2 signaling is enhanced by the NO pathway via PKA, underlining the capability of BMP2 in activating the NO pathway. Collectively, this study proves the ability of the NO pathway to enhance BMP2 signaling.

Impact of Bacterial Infections on Osteogenesis: Evidence From In Vivo Studies

The clinical impact of bacterial infections on bone regeneration has been incompletely quantified and documented. As a result, controversy exists about the optimal treatment strategy to maximize healing of a contaminated defect. Animal models are extremely useful in this respect, as they can elucidate how a bacterial burden influences quantitative healing of various types of defects relative to non-infected controls. Moreover, they may demonstrate how antibacterial treatment and/or bone grafting techniques facilitate the osteogenic response in the harsh environment of a bacterial infection. Finally, it a well-known contradiction that osteomyelitis is characterized by uncontrolled bone remodeling and bone loss, but at the same time, it can be associated with excessive new bone apposition. Animal studies can provide a better understanding of how osteolytic and osteogenic responses are related to each other during infection. This review discusses the in vivo impact of bacterial infection on osteogenesis by addressing the following questions (i) How does osteomyelitis affect the radiographic bone appearance? (ii) What is the influence of bacterial infection on histological bone healing? (iii) How do bacterial infections affect quantitative bone healing? (iv) What is the effect of antibacterial treatment on the healing outcome during infection? (v) What is the efficacy of osteoinductive proteins in infected bones? (vi) What is the balance between the osteoclastic and osteoblastic response during bacterial infections? (vii) What is the mechanism of the observed pro-osteogenic response as observed in osteomyelitis? © 2019 The Authors. Journal of Orthopaedic Research^© published by Wiley Periodicals, Inc. on behalf of Orthopaedic Research Society. J Orthop Res 37:2067-2076, 2019.

Anisotropic Cryostructured Collagen Scaffolds for Efficient Delivery of RhBMP-2 and Enhanced Bone Regeneration

In the treatment of bone non-unions, an alternative to bone autografts is the use of bone morphogenetic proteins (BMPs), e.g., BMP–2, BMP–7, with powerful osteoinductive and osteogenic properties. In clinical settings, these osteogenic factors are applied using absorbable collagen sponges for local controlled delivery. Major side effects of this strategy are derived from the supraphysiological doses of BMPs needed, which may induce ectopic bone formation, chronic inflammation, and excessive bone resorption. In order to increase the efficiency of the delivered BMPs, we designed cryostructured collagen scaffolds functionalized with hydroxyapatite, mimicking the structure of cortical bone (aligned porosity, anisotropic) or trabecular bone (random distributed porosity, isotropic). We hypothesize that an anisotropic structure would enhance the osteoconductive properties of the scaffolds by increasing the regenerative performance of the provided rhBMP–2. In vitro, both scaffolds presented similar mechanical properties, rhBMP–2 retention and delivery capacity, as well as scaffold degradation time. In vivo, anisotropic scaffolds demonstrated better bone regeneration capabilities in a rat femoral critical-size defect model by increasing the defect bridging. In conclusion, anisotropic cryostructured collagen scaffolds improve bone regeneration by increasing the efficiency of rhBMP–2 mediated bone healing.

Biomodulation of an implant for enhanced bone-implant anchorage

Aseptic loosening of implants is the major cause for revision surgery. By modulating the bone-implant interface, early bone-implant anchorage could be improved. Implant surface manipulation by the addition of osteopromotive molecules locally and systemically to promote implant integration has been described with limited success. This study describes a novel approach by making the implant capable of biologically modulating its surroundings. It was hypothesized that the early implant fixation would improve by filling the interior of the implant with a carrier providing spatio-temporal release of bone active drugs with known osteogenic effect. The implant consisted of a threaded polyether ether ketone (PEEK) hollow chamber with holes at the bottom. The implant was filled with a calcium sulphate (CaS)/hydroxyapatite (HA) carrier, delivering two bone active molecules; zoledronic acid (ZA) and bone morphogenic protein-2 (BMP-2). At first, a rat abdominal muscle pouch model indicated a sustained in-vivo release of both ¹²⁵I-rhBMP-2 (57%) and ¹⁴C-ZA (22%) from the CaS/HA carrier over a period of 4-weeks. The biomodulated implant was then inserted in the proximal tibia in rats with the following experimental groups: G1) Empty implant, G2) Implant + CaS/HA, G3) Implant + CaS/HA + ZA and G4) Implant + CaS/HA + ZA + rhBMP-2. Significantly higher bone volume (BV) was seen around the implant in groups G3 (3.3 ± 0.7 mm³) and G4 (3.1 ± 0.7 mm³) compared to the control (1.3 ± 0.4 mm³) using micro-computed tomography and qualitative histology. Group G3, also exhibited significantly higher pull-out force and absorbed energy when compared to the control group G1. These findings indicate that a low dose of ZA alone, released in a controlled manner from within a fenestrated implant is enough to improve implant anchorage without the need of adding rhBMP-2. This simple method of using a fenestrated implant containing a ceramic carrier releasing bone active molecules improved bone anchorage and could clinically reduce prosthetic failure. STATEMENT OF SIGNIFICANCE: Aseptic loosening remains as a major cause for implant revisions and early reaction of surrounding bone to the prosthesis is important for longevity. A novel approach to enhance early bone-implant anchorage is presented. The implant is filled with a carrier providing controlled release of bone active molecules. In an animal model, a calcium sulphate (CaS)/hydroxyapatite (HA) carrier was used to provide a spatio-temporal release of bone morphogenic protein-2 (BMP-2) and zoledronic acid (ZA). Significantly better bone-implant integration was achieved using ZA alone, thereby eliminating the need for adding BMP-2. The developed method of implant biomodulation holds potential to prevent implant loosening and is an alternative to prosthetic coatings or systemic drug treatment. Importantly, all constituents are approved for clinical use.

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.

Growth factor-mediated augmentation of long bones: evaluation of a BMP-7 loaded thermoresponsive hydrogel in a murine femoral intramedullary injection model

Background

Due to our aging population, an increase in proximal femur fractures can be expected, which is associated with impaired activities of daily living and a high risk of mortality. These patients are also at a high risk to suffer a secondary osteoporosis-related fracture on the contralateral hip. In this context, growth factors could open the field for regenerative approaches, as it is known that, i.e., the growth factor BMP-7 (bone morphogenetic protein 7) is a potent stimulator of osteogenesis. Local prophylactic augmentation of the proximal femur with a BMP-7 loaded thermoresponsive hydrogel during index surgery of an osteoporotic fracture could be suitable to reduce the risk of further osteoporosis-associated secondary fractures. The present study therefore aims to test the hypothesis if a BMP-7 augmented hydrogel is an applicable carrier for the augmentation of non-fractured proximal femurs. Furthermore, it needs to be shown that the minimally invasive injection of a hydrogel into the mouse femur is technically feasible.

Methods

In this study, male C57BL/6 mice (n = 36) received a unilateral femoral intramedullary injection of either 100 μl saline, 100 μl 1,4 Butan-Diisocyanat (BDI)-hydrogel, or 100 μl hydrogel loaded with 1 μg of bone morphogenetic protein 7. Mice were sacrificed 4 and 12 weeks later. The femora were submitted to high-resolution X-ray tomography and subsequent histological examination.

Results

Analysis of normalized CtBMD (Cortical bone mineral density) as obtained by X-ray micro-computed tomography analysis revealed significant differences depending on the duration of treatment (4 vs 12 weeks; p < 0.05). Furthermore, within different anatomically defined regions of interest, significant associations between normalized TbN (trabecular number) and BV/TV (percent bone volume) were noted. Histology indicated no signs of inflammation and no signs of necrosis and there were no cartilage damages, no new bone formations, or new cartilage tissues, while BMP-7 was readily detectable in all of the samples.

Conclusions

In conclusion, the murine femoral intramedullary injection model appears to be feasible and worth to be used in subsequent studies that are directed to examine the therapeutic potential of BMP-7 loaded BDI-hydrogel. Although we were unable to detect any significant osseous effects arising from the mode or duration of treatment in the present trial, the effect of different concentrations and duration of treatment in an osteoporotic model appears of interest for further experiments to reach translation into clinic and open new strategies of growth factor-mediated augmentation.

Electronic supplementary material

The online version of this article (10.1186/s13018-019-1315-6) contains supplementary material, which is available to authorized users.

Treatment of Critical-Sized Calvarial Defects in Rats with Preimplanted Transplants

The local environment and the defect features have made the skull one of the most difficult regions to repair. Finding alternative strategies to repair large cranial defects, thereby avoiding the current limitations of autograft or polymeric and ceramic prostheses constitute an unmet need. In this study, the regeneration of an 8 mm critical-sized calvarial defect treated by autograft or by a monetite scaffold directly placed in the defect or preimplanted (either cranial bone transplant or subcutaneous pocket) and then transplanted within the bone defect is compared. The data reveal that transplantation of preimplanted monetite transplant scaffolds greatly improves the skull vault closure compared to subcutaneously preimplanted or directly placed materials. Autografts, while clearly filling the defect volume with bone appear effective since bone volume inside the defect volume is obviously high, but are not well fused to the skull. The preimplantation site has a large influence on the regeneration of the defect. Transplantation of induced bone inside materials has the potential to reduce the need for autograft harvest without damaging the skeleton. This first demonstration indicates that cranial repair may be possible without recourse to bioactives or cultured cell therapies.

Hierarchically Porous Hydroxyapatite Hybrid Scaffold Incorporated with Reduced Graphene Oxide for Rapid Bone Ingrowth and Repair

Hydroxyapatite (HA), the traditional bone tissue replacement material was widely used in the clinical treatment of bone defects because of its excellent biocompatibility. However, the processing difficulty and poor osteoinductive ability greatly limit the application of HA. Although many strategies have been reported to improve the machinability and osteointegration ability, the performance including mechanical strength, porosity, cell adhesion, etc. of material still can not meet the requirements. In this work, a soft template method was developed and a porous scaffold with hierarchical pore structure, nano surface morphology, suitable porosity and pore size, and good biomechanical strength was successfully prepared. The hierarchical pore structure is beneficial for cell adhesion, fluid transfer, and cell ingrowth. Moreover, the loaded reduced graphene oxide (rGO) can improve the adhesion and promote the proliferation and spontaneous osteogenic differentiation bone marrow mesenchymal stem cells. The scaffold is then crushed, degraded and wrapped by the newly formed bone and the newly formed bone gradually replaces the scaffold. The degradation rate of the scaffold well matches the rate of the new bone formation. The hierarchical porous HA/rGO composite scaffolds can greatly accelerate the bone ingrowth in the scaffold and bone repair in critical bone defects, thus providing a clinical potential candidate for large segment bone tissue engineering.

The regulatory role of sulfated polysaccharides in facilitating rhBMP-2-induced osteogenesis

Sulfated polysaccharides have received much attention in recent years due to their special biological activities, especially the regulation of the biological activity of growth factors such as the representative inductive growth factor recombinant human bone morphogenetic protein-2 (rhBMP-2). However, the regulatory mechanisms from the aspect of the molecular chain structure have rarely been reported. In this article, we selected three kinds of sulfonates containing different backbone structures and functional groups, 2-N,6-O-sulfated chitosan (26 SCS), sulfated dextran (DSS) and poly(sodium-p-styrenesulfonate) (PSS), to explore the interaction between them and rhBMP-2. From in vivo and in vitro osteogenesis-related experiments, 26 SCS showed the best promoting effect on rhBMP-2 induced osteogenic differentiation and the sulfated amino group in 26 SCS could specifically bind to rhBMP-2. These findings indicated that the polysaccharide chain structure was a prerequisite for the synergy effect between 26 SCS and rhBMP-2; the effective combination of -SO₃^- and rhBMP-2 was an important factor in protecting the bioactivity of rhBMP-2. In addition, the presence of the sulfated amino group was the key factor in the specific binding between 26 SCS and rhBMP-2 and provided the possibility of capturing factors in vivo.

Polyelectrolyte Complexes between Polycarboxylates and BMP-2 for Enhancing Osteogenic Differentiation: Effect of Chemical Structure of Polycarboxylates

Bone morphogenetic protein 2 (BMP-2) has received considerable attention because of its osteoinductivity, but its use is limited owing to its instability and adverse effects. To reduce the dose of BMP-2, complexation with heparin is a promising approach, because heparin enhances the osteoinductivity of BMP-2. However, the clinical use of heparin is restricted because of its anticoagulant activity. Herein, to explore alternative polymers that show heparin-like activity, four polycarboxylates, poly(acrylic acid) (PAA), poly(methacrylic acid) (PMAA), poly(aspartic acid) (PAsp), and poly(glutamic acid) (PGlu), were selected and their capability to modulate the osteoinductivity of BMP-2 was evaluated. Dynamic light scattering indicated that these polycarboxylates formed polyelectrolyte complexes with BMP-2. The osteogenic differentiation efficiency of MC3T3-E1 cells treated with the polycarboxylate/BMP-2 complexes was investigated in comparison to that of the heparin/BMP-2 complex. As a result, PGlu/BMP-2 complex showed the highest activity of alkaline phosphatase, which is an early-stage marker of osteogenic differentiation, and rapid mineralization. Based on these observations, PGlu could serve as an alternative to heparin in the regenerative therapy of bone using BMP-2.

Rapid healing of a critical-sized bone defect using a collagen-hydroxyapatite scaffold to facilitate low dose, combinatorial growth factor delivery

The healing of large, critically sized bone defects remains an unmet clinical need in modern orthopaedic medicine. The tissue engineering field is increasingly using biomaterial scaffolds as 3D templates to guide the regenerative process, which can be further augmented via the incorporation of recombinant growth factors. Typically, this necessitates supraphysiological doses of growth factor to facilitate an adequate therapeutic response. Herein, we describe a cell-free, biomaterial implant which is functionalised with a low dose, combinatorial growth factor therapy that is capable of rapidly regenerating vascularised bone tissue within a critical-sized rodent calvarial defect. Specifically, we demonstrate that the dual delivery of the growth factors bone morphogenetic protein-2 (osteogenic) and vascular endothelial growth factor (angiogenic) at a low dose (5 μg/scaffold) on an osteoconductive collagen-hydroxyapatite scaffold is highly effective in healing these critical-sized bone defects. The high affinity between the hydroxyapatite component of this biomimetic scaffold and the growth factors functions to sequester them locally at the defect site. Using this growth factor-loaded scaffold, we show complete bridging of a critical-sized calvarial defect in all specimens at a very early time point of 4 weeks, with a 28-fold increase in new bone volume and seven-fold increase in new bone area compared with a growth factor-free scaffold. Overall, this study demonstrates that a collagen-hydroxyapatite scaffold can be used to locally harness the synergistic relationship between osteogenic and angiogenic growth factors to rapidly regenerate bone tissue without the need for more complex controlled delivery vehicles or high total growth factor doses.

Translational mechanobiology: Designing synthetic hydrogel matrices for improved in vitro models and cell-based therapies

Synthetic hydrogels have ideal physiochemical properties to serve as reductionist mimics of the extracellular matrix (ECM) for studies on cellular mechanosensing. These studies range from basic observation of correlations between ECM mechanics and cell fate changes to molecular dissection of the underlying mechanisms. Despite intensive work on hydrogels to study mechanobiology, many fundamental questions regarding mechanosensing remain unanswered. In this review, I first discuss historical motivation for studying cellular mechanobiology, and challenges impeding this effort. I next overview recent efforts to engineer hydrogel properties to study cellular mechanosensing. Finally, I focus on in vitro modeling and cell-based therapies as applications of hydrogels that will exploit our ability to create micro-environments with physiologically relevant elasticity and viscoelasticity to control cell biology. These translational applications will not only use our current understanding of mechanobiology but will also bring new tools to study the fundamental problem of how cells sense their mechanical environment. STATEMENT OF SIGNIFICANCE: Hydrogels are an important tool for understanding how our cells can sense their mechanical environment, and to exploit that understanding in regenerative medicine. In the current review, I discuss historical work linking mechanics to cell behavior in vitro, and highlight the role hydrogels played in allowing us to understand how cells monitor mechanical cues. I then highlight potential translational applications of hydrogels with mechanical properties similar to those of the tissues where cells normally reside in our bodies, and discuss how these types of studies can provide clues to help us enhance our understanding of mechanosensing.

Systemic administration of enzyme-responsive growth factor nanocapsules for promoting bone repair

Accelerating the healing of bone fractures by local delivery of growth factors possessing osteoinductive activity has been extensively demonstrated. Unfortunately, for some complex clinical fractures, such as osteoporotic vertebral compression fracture, it is not possible to adopt such a strategy because of access restrictions. Systemic administration of growth factors is considered to be an appropriate alternative method due to its easy operability and precise spatiotemporal compatibility at fracture sites. But this therapy method was hampered by the poor in vivo stability, inefficient distribution at the fracture site and potential side effects of growth factors. To address these challenges, we conceived a systemic delivery platform of growth factors based on nanocapsules, taking advantage of the unique physiological character of bone fracture, i.e., the malformed blood vessels and the over-expression of matrix metalloproteinases (MMPs). In this work, bone morphogenetic protein-2 (BMP-2), 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) and the bisacryloylated VPLGVRTK peptide were respectively used as the model growth factor, monomer, and MMP-cleavable crosslinker. Nanocapsules were formed by in situ free radical polymerization on the surface of BMP-2 with MPC and peptides. The structure and function of BMP-2 were well maintained during the preparation process. BMP-2 nanocapsules (n(BMP-2)) were of uniform small size (∼30 nm) possessing a long circulation time (half-life is ∼48 h) and could be passively targeted to the fracture site through malformed blood vessels after systemic administration. Once accumulated at the fracture site, the shells of nanocapsules could be degraded by MMP and thus BMP-2 was released. Animal experiments proved that n(BMP-2) showed a better ability of bone repair than native BMP-2. In addition, n(BMP-2) showed a much lower inflammatory irritation. The results demonstrated that the systemic administration of growth factor nanocapsules could enhance their in vivo stability and fracture site delivery efficiency, realizing the efficient repair of a bone fracture. This rational delivery system may expand the bone repair types which can be administered with growth factors. Furthermore, the concept of taking advantage of the malformed vascular structure to deliver drugs potentially inspires researchers for the therapy of other diseases, especially sudden disease (such as cerebral hemorrhage).

Multifunctional scaffolds for facile implantation, spontaneous fixation, and accelerated long bone regeneration in rodents

Graft-guided regenerative repair of critical long bone defects achieving facile surgical delivery, stable graft fixation, and timely restoration of biomechanical integrity without excessive biotherapeutics remains challenging. Here, we engineered hydration-induced swelling/stiffening and thermal-responsive shape-memory properties into scalable, three-dimensional–printed amphiphilic degradable polymer-osteoconductive mineral composites as macroporous, non–load-bearing, resorbable synthetic grafts. The distinct physical properties of the grafts enabled straightforward surgical insertion into critical-size rat femoral segmental defects. Grafts rapidly recovered their precompressed shape, stiffening and swelling upon warm saline rinse to result in 100% stable graft fixation. The osteoconductive macroporous grafts guided bone formation throughout the defect as early as 4 weeks after implantation; new bone remodeling correlated with rates of scaffold composition-dependent degradation. A single dose of 400-ng recombinant human bone morphogenetic protein-2/7 heterodimer delivered via the graft accelerated bone regeneration bridging throughout the entire defect by 4 weeks after delivery. Full restoration of torsional integrity and complete scaffold resorption were achieved by 12 to 16 weeks after surgery. This biomaterial platform enables personalized bone regeneration with improved surgical handling, in vivo efficacy and safety.

The Influence of Polymer Blends on Regulating Chondrogenesis

The influence of polymer blend coatings on the differentiation of mouse mesenchymal stem cells was investigated. Polymer blending is a common means of producing new coating materials with variable properties. Stem cell differentiation is known to be influenced by both chemical and mechanical properties of the underlying scaffold. We therefore selected to probe the response of stem cells cultured separately on two very different polymers, and then cultured on a 1:1 blend. The response to mechanical properties was probed by culturing the cells on polybutadiene (PB) films, where the film moduli was varied by adjusting film thickness. Cells adjusted their internal structure such that their moduli scaled with the PB films. These cells expressed chondrocyte markers (osterix (OSX), alkaline phosphatase (ALP), collagen X (COL-X), and aggrecan (ACAN)) without mineralizing. In contrast, cells on partially sulfonated polystyrene (PSS28) deposited large amounts of hydroxyapatite and expressed differentiation markers consistent with chondrocyte hypertrophy (OSX, ALP, COL-X, but not ACAN). Cells on phase-segregated PB and PSS28 films differentiated identically to those on PSS28, underscoring the challenges of using polymer templates for cell patterning in tissue engineering.

[Research progress on controlled release of various growth factors in bone regeneration]

OBJECTIVE

To summarize the research progress of controlled release of angiogenic factors and osteogenic factors in bone tissue engineering.

METHODS

The domestic and abroad literature on the controlled release structure of growth factors during bone regeneration in recent years was extensively reviewed and summarized.

RESULTS

The sustained-release structure includes direct binding, microsphere-three-dimensional scaffold structure, core-shell structure, layer self-assembly, hydrogel, and gene carrier. A sustained-release system composed of different sustained-release structures combined with different growth factors can promote bone regeneration and angiogenesis.

CONCLUSION

Due to its controllability and persistence, the growth factor sustained-release system has become a research hotspot in bone tissue engineering and has broad application prospects.

Intervertebral disc regeneration: From cell therapy to the development of novel bioinspired endogenous repair strategies

Low back pain (LBP), frequently associated with intervertebral disc (IVD) degeneration, is a major public health concern. LBP is currently managed by pharmacological treatments and, if unsuccessful, by invasive surgical procedures, which do not counteract the degenerative process. Considering that IVD cell depletion is critical in the degenerative process, the supplementation of IVD with reparative cells, associated or not with biomaterials, has been contemplated. Recently, the discovery of reparative stem/progenitor cells in the IVD has led to increased interest in the potential of endogenous repair strategies. Recruitment of these cells by specific signals might constitute an alternative strategy to cell transplantation. Here, we review the status of cell-based therapies for treating IVD degeneration and emphasize the current concept of endogenous repair as well as future perspectives. This review also highlights the challenges of the mobilization/differentiation of reparative progenitor cells through the delivery of biologics factors to stimulate IVD regeneration.

Efficacy of Recombinant Human BMP2 and PDGF-BB in Orofacial Bone Regeneration: A Systematic Review and Meta-analysis

With the rapid development of tissue engineering therapies, there is a growing interest in the application of recombinant human growth factors (rhGFs) to regenerate human orofacial bones. However, despite reports of their ability to promote orofacial bone regeneration in animal experiments, their benefits in human clinical treatments remain unclear. Furthermore, the appropriate concentrations or indications of a specific rhGF remain ambiguous. Therefore it is essential to collect data from diverse clinical trials to evaluate their effects more precisely. Here we reviewed randomized clinical trials (RCT) that focused on the utilization of rhGFs in orofacial bone regeneration. Data from included studies were extracted, pooled and then quantitatively analyzed according to a pre-established protocol. Our results indicate that all current concentrations of rhBMP-2 produces insufficient effect on promoting either tooth extraction socket healing, sinus augmentation or reconstruction of alveolar clefts. However, 0.3 mg/ml rhPDGF-BB promotes the healing of tooth extraction sockets, though the effect does not reach a level of statistical significance. Summarily, we recommend concentrations of 0.3 mg/ml rhPDGF-BB only for the healing of tooth extraction sockets.

Application of Hydroxycholesterols for Alveolar Cleft Osteoplasty in a Rodent Model

BACKGROUND

Bone morphogenetic proteins (BMPs) have played a central role in the regenerative therapies for bone reconstruction, including alveolar cleft and craniofacial surgery. However, the high cost and significant adverse effect of BMPs limit their broad application. Hydroxycholesterols, naturally occurring products of cholesterol oxidation, are a promising alternative to BMPs. The authors studied the osteogenic capability of hydroxycholesterols on human mesenchymal stem cells and the impact of hydroxycholesterols on a rodent alveolar cleft model.

METHODS

Human mesenchymal stem cells were treated with control medium or osteogenic medium with or without hydroxycholesterols. Evaluation of cellular osteogenic activity was performed. A critical-size alveolar cleft was created and one of the following treatment options was assigned randomly to each defect: collagen sponge incorporated with hydroxycholesterols, BMP-2, or no treatment. Bone regeneration was assessed by means of radiologic and histologic analyses and local inflammation in the cleft evaluated. Moreover, the role of the hedgehog signaling pathway in hydroxycholesterol-mediated osteogenesis was examined.

RESULTS

All cellular osteogenic activities were significantly increased on human mesenchymal stem cells treated with hydroxycholesterols relative to others. The alveolar cleft treated with collagen sponge with hydroxycholesterols and BMP-2 demonstrated robust bone regeneration. The hydroxycholesterol group revealed histologically complete bridging of the alveolar defect with architecturally mature new bone. The inflammatory responses were less in the hydroxycholesterol group compared with the BMP-2 group. Induction of hydroxycholesterol-mediated in vitro osteogenesis and in vivo bone regeneration were attenuated by hedgehog signaling inhibitor, implicating involvement of the hedgehog signaling pathway.

CONCLUSION

Hydroxycholesterols may represent a viable alternative to BMP-2 in bone tissue engineering for alveolar cleft.

Radiographic and histologic effects of bone morphogenetic protein-2/hydroxyapatite within bioabsorbable magnesium screws in a rabbit model

Background

Hydrogen gas formed by magnesium (Mg) screw corrosion can accumulate around the implant and create bone cysts, long-term osteolysis lesions, and bone healing delay. Thus, several authors currently do not recommend Mg implants for clinical use. In contrast, bone morphogenetic proteins (BMP)-2 have a very strong osteoinductive activity. The purpose of this study was to evaluate the effect of rhBMP-2/hydroxyapatite (HA) inside specially designed Mg cannulated screws in a rabbit femur model for hydrogen gas formation avoidance.

Methods

Fifteen rabbits underwent randomly different cannulated Mg screw implantation in both distal femora; 30 femora were divided into three groups depending on the materials fill in the cannulated Mg screw: control group (Mg screw with no treatment), HA group (Mg screw with HA), and BMP-2/HA group (Mg screw with a composite BMP-2/HA). Plain radiography, micro-CT, and histological analysis were accomplished, and the ability to release BMP-2 of the screws was evaluated by immersion of both the screw with no treatment and screw with a composite BMP-2/HA into the SBF for up to 7 days.

Results

X-ray assessment found the gas shadow around the implant was slightly smaller in the BMP-2/HA group than the HA and control groups at 8 weeks. Micro-CT analysis demonstrated statistically significant higher new bone formation in the BMP-2/HA group than the other groups, respectively, which also correlated with a decreased gas volume. Histological analysis showed higher osteointegration between implants and host femurs in the BMP-2/HA group than the HA and control groups at 12 weeks.

Conclusions

This study indicates that the combination of BMP-2/HA within Mg screws enhances new bone formation and therefore has the potential to decrease the complications of hydrogen gas formation around these implants.

Enhanced osteogenic differentiation of mesenchymal stem cells in ankylosing spondylitis: a study based on a three-dimensional biomimetic environment

The mechanism of pathological osteogenesis in Ankylosing spondylitis (AS) is largely unknown. Our previous studies demonstrated that the imbalance between BMP-2 and Noggin secretion induces abnormal osteogenic differentiation of marrow-derived mesenchymal stem cells (MSCs) from AS patients in a two-dimensional culture environment. In this study, HA/β-TCP scaffolds were further used as a three-dimensional (3D) biomimetic culture system to mimic the bone microenvironment in vivo to determine the abnormal osteogenic differentiation of AS-MSCs. We demonstrated that when cultured in HA/β-TCP scaffolds, AS-MSCs had a stronger osteogenic differentiation capacity than that of MSCs from healthy donors (HD-MSCs) in vitro and in vivo. This dysfunction resulted from BMP2 overexpression in AS-MSCs, which excessively activated the Smad1/5/8 and ERK signalling pathways and finally led to enhanced osteogenic differentiation. Both the signalling pathway inhibitors and siRNAs inhibiting BMP2 expression could rectify the enhanced osteogenic differentiation of AS-MSCs. Furthermore, BMP2 expression in ossifying entheses was significantly higher in AS patients. In summary, our study demonstrated that AS-MSCs possess enhanced osteogenic differentiation in HA/β-TCP scaffolds as a 3D biomimetic microenvironment because of BMP2 overexpression, but not Noggin. These results provide insights into the mechanism of pathological osteogenesis, which can aid in the development of niche-targeting medications for AS.

Strontium enhances BMP-2 mediated bone regeneration in a femoral murine bone defect model

The application of strontium is one option for the clinical treatment of osteoporosis-a disease characterized by reduced bone density and quality-in order to reduce the risk of vertebral and nonvertebral fractures. Unlike other drugs used in osteoporosis therapy, strontium shows a dual effect on bone metabolism by attenuating cellular resorption and simultaneously enhancing new bone tissue formation. Current concerns regarding the systemic application of highly dosed strontium ranelate led to the development of strontium-modified scaffolds based on mineralized collagen (MCM) capable to release biologically active Sr²⁺ ions directly at the fracture site. In this study, we investigated the regenerative potential of these scaffolds. For in vitro investigations, human mesenchymal stromal cells were cultivated on the scaffolds for 21 days (w/ and w/o osteogenic supplements). Biochemical analysis revealed a significant promoting effect on proliferation rate and osteogenic differentiation on strontium-modified scaffolds. In vivo, scaffolds were implanted in a murine segmental bone defect model-partly additionally functionalized with the osteogenic growth factor bone morphogenetic protein 2 (BMP-2). After 6 weeks, bridging calluses were obtained in BMP-2 functionalized scaffolds; the quality of the newly formed bone tissue by means of morphological scores was clearly enhanced in strontium-modified scaffolds. Histological analysis revealed increased numbers of osteoblasts and blood vessels, decreased numbers of osteoclasts, and significantly enhanced mechanical properties. These results indicate that the combined release of Sr²⁺ ions and BMP-2 from the biomimetic scaffolds is a promising strategy to enhance bone regeneration, especially in patients suffering from osteoporosis. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 108B:174-182, 2020.

Osteogenic Enhancement Between Icariin and Bone Morphogenetic Protein 2: A Potential Osteogenic Compound for Bone Tissue Engineering

Icariin, a typical flavonol glycoside, is the main active component of Herba Epimedii, which was used to cure bone-related diseases in China for centuries. It has been reported that Icariin can be delivered locally by biomaterials and it has an osteogenic potential for bone tissue engineering. Biomimetic calcium phosphate (BioCaP) bone substitute is a novel drug delivery carrier system. Our study aimed to evaluate the osteogenic potential when Icariin was internally incorporated into the BioCaP granules. The BioCaP combined with Icariin and bone morphogenetic protein 2 (BMP-2) was investigated in vitro using an MC3T3-E1 cell line. We also investigated its efficacy to repair 8 mm diameter critical size bone defects in the skull of SD male rats. BioCaP was fabricated according to a well-established biomimetic mineralization process. In vitro, the effects of BioCaP alone or BioCaP with Icariin and/or BMP-2 on cell proliferation and osteogenic differentiation of MC3T3-E1 cells were systematically evaluated. In vivo, BioCaP alone or BioCaP with Icariin and/or BMP-2 were used to study the bone formation in a critical-sized bone defect created in a rat skull. Samples were retrieved for Micro-CT and histological analysis 12 weeks after surgery. The results indicated that BioCaP with or without the incorporation of Icariin had a positive effect on the osteogenic differentiation of MC3T3-E1. BioCaP with Icariin had better osteogenic efficiency, but had no influence on cell proliferation. BioCap + Icariin + BMP-2 showed better osteogenic potential compared with BioCaP with BMP-2 alone. The protein and mRNA expression of alkaline phosphatase and osteocalcin and mineralization were higher as well. In vivo, BioCaP incorporate internally with both Icariin and BMP-2 induced significantly more newly formed bone than the control group and BioCaP with either Icariin or BMP-2 did. Micro-CT analysis revealed that no significant differences were found between the bone mineral density induced by BioCaP with icariin and that induced by BioCaP with BMP-2. Therefore, co-administration of Icariin and BMP-2 was helpful for bone tissue engineering.

Sub-clinical dose of bone morphogenetic protein-2 does not precipitate rampant, sustained inflammatory response in bone wound healing

Large bone injuries, defects, and chronic wounds present a major problem for medicine. Several therapeutic strategies are used clinically to precipitate bone including a combination therapy delivering osteoinductive bone morphogenetic protein 2 (rhBMP-2) via an osteoconductive scaffold (absorbable collagen sponge [ACS], i.e., INFUSE). Adverse side effects reportedly associated with rhBMP2 administration include rampant inflammation and clinical failures. Although acute inflammation is necessary for proper healing in bone, inflammatory cascade dysregulation can result in sustained tissue damage and poor healing. We hypothesized that a subclinical dose of rhBMP2 modeled in the murine calvarial defect would not precipitate alterations to inflammatory markers during acute phases of bone wound healing. We utilized the 5 mm critical size calvarial defect in C57BL6 wild-type mice which were subsequently treated with ACS and a subclinical dose of rhBMP2 shown to be optimal for healing. Three and 7-day postoperative time points were used to assess the role that rhBMP-2 plays in modulating inflammation vs. ACS alone by cytokine array and histological interrogation. Data revealed that rhBMP-2 delivery resulted in substantial modulation of several markers associated with inflammation, most of which decreased to levels similar to control by the 7-day time point. Additionally, while rhBMP-2 administration increased macrophage response, this peptide had a little noticeable effect on traditional markers of macrophage polarization (M1-iNOS, M2-Arg1). These results suggest that rhBMP-2 delivered at a lower dose does not precipitate rampant inflammation. Thus, an assessment of dosing for rhBMP-2 therapies may lead to better healing outcomes and less surgical failure.

Effects of BMP-2 dose and delivery of microvascular fragments on healing of bone defects with concomitant volumetric muscle loss

Traumatic composite bone-muscle injuries, such as open fractures, often require multiple surgical interventions and still typically result in long-term disability. Clinically, a critical indicator of composite injury severity is vascular integrity; vascular damage alone is sufficient to assign an open fracture to the most severe category. Challenging bone injuries are often treated with bone morphogenetic protein 2 (BMP-2), an osteoinductive growth factor, delivered on collagen sponge. Previous studies in a composite defect model found that a minimally bridging dose in the segmental defect model was unable to overcome concomitant muscle damage, but the effect of BMP dose on composite injuries has not yet been studied. Here, we test the hypotheses that BMP-2-mediated functional regeneration of composite extremity injuries is dose dependent and can be further enhanced via co-delivery of adipose-derived microvascular fragments (MVF), which have been previously shown to increase tissue vascular volume. Although MVF did not improve healing outcomes, we observed a significant BMP-2 dose-dependent increase in regenerated bone volume and biomechanical properties. This is the first known report of an increased BMP-2 dose improving bone healing with concomitant muscle damage. While high dose BMP-2 delivery can induce heterotopic ossification (HO) and increased inflammation, the maximum 10 μg dose used in this study did not result in HO and was associated with a lower circulating inflammatory cytokine profile than the low dose (2.5 μg) group. These data support the potential benefits of an increased, though still moderate, BMP-2 dose for treatment of bone defects with concomitant muscle damage. Published 2019. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res.

The BMP-2 mutant L51P: a BMP receptor IA binding-deficient inhibitor of noggin

The antagonist-specific regulation in tissue engineering constitutes important attempts to achieve an improved and rapid bone regeneration by controlling the natural biological response of the natural body growth factors. L51P is molecularly engineered bone morphogentic protein-2 (BMP-2) variant with a substitution of the 51st leucine with a proline residue. L51P is deficient in BMP receptor binding, but maintains its structure and affinity for inhibitory proteins such as noggin, chordin, and gremlin. These modifications convert the BMP-2 variant L51P into a receptor-inactive inhibitor of BMP antagonists. This current approach may prevent the uncontrolled bone overgrowth using high concentration of BMPs and thus regulates the possible growth factor's high-dose side effects. Exploring of L51P biological functions is required to broad our understanding of BMP mutant biological functions and their potential clinical applications. The progress of L51P researches would hopefully lead to the development of multiple applications for using the L51P in bone and fracture healing disorders.

Peroxisome Proliferator-Activated Receptor-γ Knockdown Impairs Bone Morphogenetic Protein-2-Induced Critical-Size Bone Defect Repair

The Food and Drug Administration-approved clinical dose (1.5 mg/mL) of bone morphogenetic protein-2 (BMP2) has been reported to induce significant adverse effects, including cyst-like adipose-infiltrated abnormal bone formation. These undesirable complications occur because of increased adipogenesis, at the expense of osteogenesis, through BMP2-mediated increases in the master regulatory gene for adipogenesis, peroxisome proliferator-activated receptor-γ (PPARγ). Inhibiting PPARγ during osteogenesis has been suggested to drive the differentiation of bone marrow stromal/stem cells toward an osteogenic, rather than an adipogenic, lineage. We demonstrate that knocking down PPARγ while concurrently administering BMP2 can reduce adipogenesis, but we found that it also impairs BMP2-induced osteogenesis and leads to bone nonunion in a mouse femoral segmental defect model. In addition, in vitro studies using the mouse bone marrow stromal cell line M2-10B4 and mouse primary bone marrow stromal cells confirmed that PPARγ knockdown inhibits BMP2-induced adipogenesis; attenuates BMP2-induced cell proliferation, migration, invasion, and osteogenesis; and escalates BMP2-induced cell apoptosis. More important, BMP receptor 2 and 1B expression was also significantly inhibited by the combined BMP2 and PPARγ knockdown treatment. These findings indicate that PPARγ is critical for BMP2-mediated osteogenesis during bone repair. Thus, uncoupling BMP2-mediated osteogenesis and adipogenesis using PPARγ inhibition to combat BMP2's adverse effects may not be feasible.

Immunohistochemical examination in arthrofibrosis of the knee joint

INTRODUCTION

Arthrofibrosis (AF) is the result of increased cell proliferation and synthesis of matrix proteins (collagen I, III, and VI). Especially after invasive knee surgery, e.g., ligament reconstruction or knee replacement, abnormal fibroblast proliferation with pathological periarticular fibrosis can be observed leading to severely limited joint motion. The pathogenesis of AF is currently not fully understood. The present work aims to determine pathogenic factors.

MATERIALS AND METHODS

A descriptive, histological and immunohistochemical comparative study was performed on tissue samples of 14 consecutive patients undergoing arthrolysis for joint stiffness due to AF. Seven human autopsy specimens served as control. Samples were stained for expression of relevant markers such as CD68, α-smooth muscle actin (ASMA), beta-catenin, BMP-2 and examined for the histological grade of AF (cell-rich versus cell-poor) and compared to a control. Furthermore, a microscopic evaluation of the samples for cell differentiation and number was performed.

RESULTS

Tissue sections of cell-rich fibrosis showed a significantly higher expression of CD68 compared to the control with less than 10% of CD68 positive cells (p = 0.002). In cell-poor fibrosis no statistically significant difference was obvious (p = 0.228). Expression of ASMA in synovia, vessels, cell-rich and cell-poor fibrosis showed median values of 2.00 in the AF group and 1.75 in the control. Both groups differed significantly (p = 0.003). AF tissue showed a significantly difference in expression of β-catenin (p < 0.001) compared to the control. The overall difference between AF and control group in expression of BMP-2 was also statistically significant (p = 0.002).

CONCLUSIONS

Expression of CD68, ASMA, beta-catenin and BMP-2 is significantly increased in AF tissue samples. Based on presented findings, histological evaluation and immunohistochemical assessment of CD68, ASMA, β-catenin and BMP-2 expression may proof useful to diagnose AF and to analyze AF activity.

Bone Marrow Cells Inhibit BMP-2-Induced Osteoblast Activity in the Marrow Environment

Bone morphogenetic protein 2 (BMP-2) is widely known as a potent growth factor that promotes bone formation. However, an increasing number of studies have demonstrated side effects of BMP-2 therapy. A deeper understanding of the effect of BMP-2 on cells other than those involved directly in bone remodeling is of fundamental importance to promote a more effective delivery of BMP-2 to patients. In this study, we aimed to investigate the effect of BMP-2 in the marrow environment. First, BMP-2 adsorbed onto titanium implants was delivered at the tooth extraction socket (marrow-absent site) or in the mandible marrow of beagle dogs. BMP-2 could induce marked bone formation around the implant at the tooth extraction socket. Surprisingly, however, no bone formation was observed in the BMP-2-coated titanium implants inserted in the mandible marrow. In C57BL/6 mice, BMP-2 adsorbed in freeze-dried collagen pellets could induce bone formation in marrow-absent calvarial bone. However, similar to the canine model, BMP-2 could not induce bone formation in the femur marrow. Analysis of osteoblast differentiation using Col1a1(2.3)-GFP transgenic mice revealed a scarce number of osteoblasts in BMP-2-treated femurs, whereas in the control group, osteoblasts were abundant. Ablation of femur marrow recovered the BMP-2 ability to induce bone formation. In vitro experiments analyzing luciferase activity of C2C12 cells with the BMP-responsive element and alkaline phosphatase activity of MC3T3-E1 osteoblasts further revealed that bone marrow cells inhibit the BMP-2 effect on osteoblasts by direct cell-cell contact. Collectively, these results showed that the effect of BMP-2 in inducing bone formation is remarkably repressed by marrow cells via direct cell-cell contact with osteoblasts; this opens new perspectives on the clarification of the side-effects associated with BMP-2 application. © 2018 American Society for Bone and Mineral Research.

Mineralized nanofiber segments coupled with calcium-binding BMP-2 peptides for alveolar bone regeneration

Bone loss around tooth extraction sites can occur, thus making future placement of dental implants difficult. Alveolar bone regeneration can be guided by the application of a nanofibrous bone graft coupled with osteoinductive proteins/peptides, following tooth loss or tooth extraction. In the present study, we demonstrate the potential of mineralized nanofiber segments coupled with calcium-binding bone morphogenetic protein 2 (BMP-2) mimicking peptides for periodontal bone regeneration. Thin electrospun nanofiber membranes of PLGA-collagen-gelatin (2:1:1 wt ratios) were mineralized in 10× modified simulated body fluid (10× mSBF) and cryocut to segments of 20 µm. For predetermined weights of the mineralized nanofiber segments, it was possible to load various amounts of heptaglutamate E7-domain-conjugated BMP-2 peptide. Mineralized short fiber grafts (2 mg), with and without E7-BMP-2 peptides, were implanted into 2 mm × 2 mm (diameter × depth) critical-sized socket defects created in rat maxillae, following extraction of the first molar teeth. A sustained release profile of E7-BMP-2 from the mineralized nanofiber segments was recorded over 4 weeks. X-ray microcomputed tomography (µ-CT) analysis of peptide-loaded nanofiber graft filled defects revealed ∼3 times greater new bone volume and bone mineral density over 4 weeks in comparison to unfilled control defects. Further, histopathology data confirmed the formation of greater new osseous tissue in the BMP2 peptide-loaded, mineralized nanofiber segment group than that of fibrous connective tissue in the unfilled defect group. Altogether, the mineralized nanofiber segments coupled with E7-BMP-2 peptides may be an effective treatment option for alveolar bone loss and defects. STATEMENT OF SIGNIFICANCE: With the high incidence of dental implants/fixtures for missing teeth, the success of the surgical procedures in restorative dentistry is dictated by the quality and quantity of the supporting alveolar bone. To address the problem of alveolar bone loss and defects due to tumor, periodontitis, or even postextraction remodeling, the present study is the first report on the application of mineralized nanofiber fragments coupled with calcium-binding osteoinductive BMP-2 peptides as a synthetic graft material for oral bone regeneration. The ease of fabrication and application of cryocut mineralized nanofiber fragments as maxillofacial bone defect fillers present a promising alternative to the current dental bone graft formulations. Furthermore, the nanofiber segments may also be utilized for several biomedical applications including hemostasis, soft tissue engineering, and wound healing.

An in vitro long-term study of cryopreserved umbilical cord blood-derived platelet-rich plasma containing growth factors-PDGF-BB, TGF-β, and VEGF

PURPOSE

Umbilical cord blood-derived platelet-rich plasma (UCB-PRP) containing growth factors has attracted attention as a biomaterial useful for regenerative medicine. The osteoblastic differentiation of umbilical cord-derived mesenchymal stromal cells (UC-MSCs) can be induced by UCB-PRP.

MATERIALS AND METHODS

Nine samples of UC and UCB were used to conduct an in vitro study that determined the contents of three growth factors (i.e., platelet-derived growth factor, transforming growth factor β-1, and vascular endothelial growth factor) and that examined, by staining with Alizarin red, their ability to induce the osteoblastic differentiation of UC-MSCs at the baseline, 3 months, and 3 years of cryopreservation.

RESULTS

The contents of growth factors in cryopreserved UCB-PRP were markedly elevated compared to those found in UCB at baseline. The samples of UCB that were added with cryopreserved UCB-PRP and those with bone morphogenetic protein-2 were stained granularly with Alizarin red, thus indicating the presence of calcium. The samples of UCB that were not added with UCB-PRP were not stained with Alizarin red. The above-mentioned contents and ability were maintained at 3 years of cryopreservation. Cryopreserved UCB-PRP possibly and advantageously induced the osteoblastic differentiation of UC-MSCs.

CONCLUSION

The potential clinical application of cryopreserved UCB-PRP to regenerative medicine was suggested.

Chondroitin Sulfate Glycosaminoglycan Scaffolds for Cell and Recombinant Protein-Based Bone Regeneration

Bone morphogenetic protein 2 (BMP‐2)‐loaded collagen sponges remain the clinical standard for treatment of large bone defects when there is insufficient autograft, despite associated complications. Recent efforts to negate comorbidities have included biomaterials and gene therapy approaches to extend the duration of BMP‐2 release and activity. In this study, we compared the collagen sponge clinical standard to chondroitin sulfate glycosaminoglycan (CS‐GAG) scaffolds as a delivery vehicle for recombinant human BMP‐2 (rhBMP‐2) and rhBMP‐2 expression via human BMP‐2 gene inserted into mesenchymal stem cells (BMP‐2 MSC). We demonstrated extended release of rhBMP‐2 from CS‐GAG scaffolds compared to their collagen sponge counterparts, and further extended release from CS‐GAG gels seeded with BMP‐2 MSC. When used to treat a challenging critically sized femoral defect model in rats, both rhBMP‐2 and BMP‐2 MSC in CS‐GAG induced comparable bone formation to the rhBMP‐2 in collagen sponge, as measured by bone volume, strength, and stiffness. We conclude that CS‐GAG scaffolds are a promising delivery vehicle for controlling the release of rhBMP‐2 and to mediate the repair of critically sized segmental bone defects. stem cells translational medicine2019;8:575–585

Enhanced bone regeneration of the silk fibroin electrospun scaffolds through the modification of the graphene oxide functionalized by BMP-2 peptide

Introduction

Bone tissue engineering has become one of the most effective methods to treat bone defects. Silk fibroin (SF) is a natural protein with no physiological activities, which has features such as good biocompatibility and easy processing and causes minimal inflammatory reactions in the body. Scaffolds prepared by electrospinning SF can be used in bone tissue regeneration and repair. Graphene oxide (GO) is rich in functional groups, has good biocompatibility, and promotes osteogenic differentiation of stem cells, while bone morphogenetic protein-2 (BMP-2) polypeptide has an advantage in promoting osteogenesis induction. In this study, we attempted to graft BMP-2 polypeptide onto GO and then bonded the functionalized GO onto SF electrospun scaffolds through electrostatic interactions. The main purpose of this study was to further improve the biocompatibility of SF electrospun scaffolds, which could promote the osteogenic differentiation of bone marrow mesenchymal stem cells and the repair of bone tissue defects.

Materials and methods

The successful synthesis of GO and functionalized GO was confirmed by transmission electron microscope, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Scanning electron microscopy, atomic force microscopy, mechanical test, and degradation experiment confirmed the preparation of SF electrospun scaffolds and the immobilization of GO on the fibers. In vitro experiment was used to verify the biocompatibility of the composite scaffolds, and in vivo experiment was used to prove the repairing ability of the composite scaffolds for bone defects.

Results

We successfully fabricated the composite scaffolds, which enhanced biocompatibility, not only promoting cell adhesion and proliferation but also greatly enhancing in vitro osteogenic differentiation of bone marrow stromal cells using either an osteogenic or non-osteogenic medium. Furthermore, transplantation of the composite scaffolds significantly promoted in vivo bone formation in critical-sized calvarial bone defects.

Conclusion

These findings suggested that the incorporation of BMP-2 polypeptide-functionalized GO into chitosan-coated SF electrospun scaffolds was a viable strategy for fabricating excellent scaffolds that enhance the regeneration of bone defects.

A case of multiple osseous choristomas arising on the medial side of the lateral pterygoid muscle

Osseous choristoma is a rare entity in the oral and maxillofacial region. The most common site is the tongue, followed by the buccal mucosa. Osseous choristoma of the muscle is unusual and few cases have been described in the literature. No reports have described osseous choristoma arising on the medial side of the lateral pterygoid muscle. Herein, we report the first such case. A 61-year-old woman was referred to our facility for treatment of temporomandibular joint disorder. Computed tomography (CT) revealed two osseous lesions on the medial side of the lateral pterygoid muscle. Preoperatively, a three-dimensional (3D) life-sized model of the skull was fabricated from the CT imaging data. The 3D skull model was used to clarify the 3D positional relationships of the osseous lesions relative to the surrounding anatomical structures. Surgery to remove the osseous lesions was performed under general anesthesia. Unfortunately, only the larger of the two masses was able to be resected because of the risk of nerve and vascular injury. Histological examination revealed that the resected lesion comprised mature lamellar bone with regular osteocytes and no atypia. The diagnosis was multiple osseous choristomas based on the histological and clinical findings.

PDGF Modulates BMP2-Induced Osteogenesis in Periosteal Progenitor Cells

BMPs are used in various clinical applications to promote bone formation. The limited success of the BMPs in clinical settings and supraphysiological doses required for their effects prompted us to evaluate the influence of other signaling molecules, specifically platelet‐derived growth factor (PDGF) on BMP2‐induced osteogenesis. Periosteal cells make a major contribution to fracture healing. We detected broad expression of PDGF receptor beta (PDGFRβ) within the intact periosteum and healing callus during fracture repair. In vitro, periosteum‐derived progenitor cells were highly responsive to PDGF as demonstrated by increased proliferation and decreased apoptosis. However, PDGF blocked BMP2‐induced osteogenesis by inhibiting the canonical BMP2/Smad pathway and downstream target gene expression. This effect is mediated via PDGFRβ and involves ERK1/2 MAPK and PI3K/AKT signaling pathways. Therapeutic targeting of the PDGFRβ pathway in periosteum‐mediated bone repair might have profound implications in the treatment of bone disease in the future. © 2018 The Authors JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Bone Morphogenetic Proteins (BMPs) and Bone Regeneration

Many research methods exist to elucidate the role of BMP-2 during bone regeneration. This chapter briefly reviews important animal models used in these studies and provides details on the rat femur defect model. This animal model is frequently utilized to measure the efficacy of osteogenic factors like BMP-2. Detailed information about delivery methods, dose range, and dose duration used in BMP-2-related studies are provided.

Bioinks and bioprinting technologies to make heterogeneous and biomimetic tissue constructs

The native tissues are complex structures consisting of different cell types, extracellular matrix materials, and biomolecules. Traditional tissue engineering strategies have not been able to fully reproduce biomimetic and heterogeneous tissue constructs because of the lack of appropriate biomaterials and technologies. However, recently developed three-dimensional bioprinting techniques can be leveraged to produce biomimetic and complex tissue structures. To achieve this, multicomponent bioinks composed of multiple biomaterials (natural, synthetic, or hybrid natural-synthetic biomaterials), different types of cells, and soluble factors have been developed. In addition, advanced bioprinting technologies have enabled us to print multimaterial bioinks with spatial and microscale resolution in a rapid and continuous manner, aiming to reproduce the complex architecture of the native tissues. This review highlights important advances in heterogeneous bioinks and bioprinting technologies to fabricate biomimetic tissue constructs. Opportunities and challenges to further accelerate this research area are also described.

Materials Science and Design Principles of Growth Factor Delivery Systems in Tissue Engineering and Regenerative Medicine

Growth factors (GFs) are signaling molecules that direct cell development by providing biochemical cues for stem cell proliferation, migration, and differentiation. GFs play a key role in tissue regeneration, but one major limitation of GF-based therapies is dosage-related adverse effects. Additionally, the clinical applications and efficacy of GFs are significantly affected by the efficiency of delivery systems and other pharmacokinetic factors. Hence, it is crucial to design delivery systems that provide optimal activity, stability, and tunable delivery for GFs. Understanding the physicochemical properties of the GFs and the biomaterials utilized for the development of biomimetic GF delivery systems is critical for GF-based regeneration. Many different delivery systems have been developed to achieve tunable delivery kinetics for single or multiple GFs. The identification of ideal biomaterials with tunable properties for spatiotemporal delivery of GFs is still challenging. This review characterizes the types, properties, and functions of GFs, the materials science of widely used biomaterials, and various GF loading strategies to comprehensively summarize the current delivery systems for tunable spatiotemporal delivery of GFs aimed for tissue regeneration applications. This review concludes by discussing fundamental design principles for GF delivery vehicles based on the interactive physicochemical properties of the proteins and biomaterials.