Preparation and ectopic osteogenesis in vivo of scaffold based on mineralized recombinant human-like collagen loaded with synthetic BMP-2-derived peptide

The Impact of Nano-Hydroxyapatite Scaffold Enrichment on Bone Regeneration In Vivo-A Systematic Review

OBJECTIVES

In order to ensure improved and accelerated bone regeneration, nano-hydroxyapatite scaffolds are often enriched with different bioactive components to further accelerate and improve bone healing. In this review, we critically examined whether the enrichment of nHAp/polymer scaffolds with growth factors, hormones, polypeptides, microRNAs and exosomes improved new bone formation in vivo.

MATERIALS AND METHODS

Out of 2989 articles obtained from the literature search, 106 papers were read in full, and only 12 articles met the inclusion criteria for this review.

RESULTS

Several bioactive components were reported to stimulate accelerated bone regeneration in a variety of bone defect models, showing better results than bone grafting with nHAp scaffolds alone.

CONCLUSIONS

The results indicated that composite materials based on nHAp are excellent candidates as bone substitutes, while nHAp scaffold enrichment further accelerates bone regeneration. The standardization of animal models should be provided in order to clearly define the most significant parameters of in vivo studies. Only in this way can the adequate comparison of findings from different in vivo studies be possible, further advancing our knowledge on bone regeneration and enabling its translation to clinical settings.

Functionalization of biomimetic mineralized collagen for bone tissue engineering

Mineralized collagen (MC) is the basic unit of bone structure and function and is the main component of the extracellular matrix (ECM) in bone tissue. In the biomimetic method, MC with different nanostructures of neo-bone have been constructed. Among these, extra-fibrous MC has been approved by regulatory agencies and applied in clinical practice to play an active role in bone defect repair. However, in the complex microenvironment of bone defects, such as in blood supply disorders and infections, MC is unable to effectively perform its pro-osteogenic activities and needs to be functionalized to include osteogenesis and the enhancement of angiogenesis, anti-infection, and immunomodulation. This article aimed to discuss the preparation and biological performance of MC with different nanostructures in detail, and summarize its functionalization strategy. Then we describe the recent advances in the osteo-inductive properties and multifunctional coordination of MC. Finally, the latest research progress of functionalized biomimetic MC, along with the development challenges and future trends, are discussed. This paper provides a theoretical basis and advanced design philosophy for bone tissue engineering in different bone microenvironments.

Osteogenic Peptides and Attachment Methods Determine Tissue Regeneration in Modified Bone Graft Substitutes

The inclusion of biofunctional molecules with synthetic bone graft substitutes has the potential to enhance tissue regeneration during treatment of traumatic bone injuries. The clinical use of growth factors has though been associated with complications, some serious. The use of smaller, active peptides has the potential to overcome these problems and provide a cost-effective, safe route for the manufacture of enhanced bone graft substitutes. This review considers the design of peptide-enhanced bone graft substitutes, and how peptide selection and attachment method determine clinical efficacy. It was determined that covalent attachment may reduce the known risks associated with growth factor-loaded bone graft substitutes, providing a predictable tissue response and greater clinical efficacy. Peptide choice was found to be critical, but even within recognised families of biologically active peptides, the configurations that appeared to most closely mimic the biological molecules involved in natural bone healing processes were most potent. It was concluded that rational, evidence-based design of peptide-enhanced bone graft substitutes offers a pathway to clinical maturity in this highly promising field.

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

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

Functional Protein-Based Bioinspired Nanomaterials: From Coupled Proteins, Synthetic Approaches, Nanostructures to Applications

Protein-based bioinspired nanomaterials (PBNs) combines the advantage of the size, shape, and surface chemistry of nanomaterials, the morphology and functions of natural materials, and the physical and chemical properties of various proteins. Recently, there are many exciting developments on biomimetic nanomaterials using proteins for different applications including, tissue engineering, drug delivery, diagnosis and therapy, smart materials and structures, and water collection and separation. Protein-based biomaterials with high biocompatibility and biodegradability could be modified to obtain the healing effects of natural organisms after injury by mimicking the extracellular matrix. For cancer and other diseases that are difficult to cure now, new therapeutic methods involving different kinds of biomaterials are studied. The nanomaterials with surface modification, which can achieve high drug loading, can be used as drug carriers to enhance target and trigger deliveries. For environment protection and the sustainability of the world, protein-based nanomaterials are also applied for water treatment. A wide range of contaminants from natural water source, such as organic dyes, oil substances, and multiple heavy ions, could be absorbed by protein-based nanomaterials. This review summarizes the formation and application of functional PBNs, and the details of their nanostructures, the proteins involved, and the synthetic approaches are addressed.

Transcriptomics and differential gene expression in Whitmania pigra (Annelida: Clitellata: Hirudinida: Hirudinidae): Contrasting feeding and fasting modes

The medicinal utility of leeches has been demonstrated through decades of use in modern hospital settings, mainly as relievers of venous congestion following flap or digit replantation surgery. In the present study, we sequence and annotate (through BLAST- and Gene Ontology-based approaches) the salivary transcriptome of the nonblood feeding hirudinid Whitmania pigra and assess the differential gene expression of anticoagulation factors (through both quantitative real-time PCR [qRT-PCR] and in silico-based methods) during feeding and fasting conditions. This was done in order to evince the diversity of putative anticoagulation factors, as well as estimate the levels of upregulation of genes immediately after feeding. In total, we found sequences with demonstrated orthology (via both phylogenetic analyses and BLAST-based approaches) to seven different proteins that have previously been linked to anticoagulatory capabilities-eglin C, bdellin, granulin, guamerin, hyaluronidase, destabilase I, and lipocalin. All of these were recovered from leeches both in the fasting and in the feeding conditions, but all show signs of upregulation in the feeding leeches. Interestingly, our RNA-seq effort, coupled with a hypergeometric test, indicated that the differentially expressed genes were disproportionately involved in three main immunological pathways (endocytosis, peroxisome regulation, and lysosome regulation). The results and implications of the finding of anticoagulants in this nonblood feeding leech and the putative upregulation of anticoagulation factors after feeding are briefly discussed in an evolutionary context.

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.

Bone tissue engineering: Scaffold preparation using chitosan and other biomaterials with different design and fabrication techniques

In the recent years, a paradigm shift is taking place where metallic/synthetic implants and tissue grafts are being replaced by tissue engineering approach. A well designed three-dimensional scaffold is one of the fundamental tools to guide tissue formation in vitro and in vivo. Bone is a highly dynamic and an integrative tissue, and thus enormous efforts have been invested in bone tissue engineering to design a highly porous scaffold which plays a critical role in guiding bone growth and regeneration. Numerous techniques have been developed to fabricate highly interconnected, porous scaffold for bone tissue engineering applications with the help of biomolecules such as chitosan, collagen, gelatin, silk, etc. We aim, in this review, to provide an overview of different types of fabrication techniques for scaffold preparation in bone tissue engineering using biological macromolecules.

Biomaterials for the Delivery of Growth Factors and Other Therapeutic Agents in Tissue Engineering Approaches to Bone Regeneration

Bone fracture followed by delayed or non-union typically requires bone graft intervention. Autologous bone grafts remain the clinical "gold standard". Recently, synthetic bone grafts such as Medtronic's Infuse Bone Graft have opened the possibility to pharmacological and tissue engineering strategies to bone repair following fracture. This clinically-available strategy uses an absorbable collagen sponge as a carrier material for recombinant human bone morphogenetic protein 2 (rhBMP-2) and a similar strategy has been employed by Stryker with BMP-7, also known as osteogenic protein-1 (OP-1). A key advantage to this approach is its "off-the-shelf" nature, but there are clear drawbacks to these products such as edema, inflammation, and ectopic bone growth. While there are clinical challenges associated with a lack of controlled release of rhBMP-2 and OP-1, these are among the first clinical examples to wed understanding of biological principles with biochemical production of proteins and pharmacological principles to promote tissue regeneration (known as regenerative pharmacology). After considering the clinical challenges with such synthetic bone grafts, this review considers the various biomaterial carriers under investigation to promote bone regeneration. This is followed by a survey of the literature where various pharmacological approaches and molecular targets are considered as future strategies to promote more rapid and mature bone regeneration. From the review, it should be clear that pharmacological understanding is a key aspect to developing these strategies.

Loading of BMP-2-related peptide onto three-dimensional nano-hydroxyapatite scaffolds accelerates mineralization in critical-sized cranial bone defects

Extrusion free-forming, as a rapid prototyping technique, is extensively applied in fabricating ceramic material in bone tissue engineering. To improve the osteoinductivity of nano-hydroxyapatite (nHA) scaffold fabricated by extrusion free-forming, in this study, we incorporated a new peptide (P28) and optimized the superficial microstructure after shaping by controlling the sintering temperature. P28, a novel bone morphogenic protein 2 (BMP-2)-related peptide, was designed in this study. Analysis of the structure, physicochemical properties and release kinetics of P28 from nHA sintered at temperatures ranging from 1000 °C to 1400 °C revealed that nHA sintered at 1000 °C had higher porosity, preferable pore size and better capacity to control P28 release than that sintered at other temperatures. Moreover, the nHA scaffold sintered at 1000 °C with P28 showed improved adhesion, proliferation and osteogenic differentiation of MC3T3-E1 cells compared with scaffolds lacking P28 or BMP-2. In vivo, nHA scaffolds sintered at 1000 °C with P28 or BMP-2 induced greater bone regeneration in critical-sized rat cranial defects at 6 and 12 weeks post-implantation compared with scaffolds lacking P28 or BMP-2. Thus, nHA scaffolds sintered at 1000 °C and loaded with P28 may be excellent biomaterials for bone tissue engineering. Copyright © 2016 John Wiley & Sons, Ltd.

Zero-order controlled release of BMP2-derived peptide P24 from the chitosan scaffold by chemical grafting modification technique for promotion of osteogenesis in vitro and enhancement of bone repair in vivo

Combination of tissue-engineered bone scaffolds with cell-adhesive, osteoconductive, or osteoinductive biomolecules is a critical strategy to improve their properties that significantly influence cellular behaviors, such as adhesion, proliferation, and differentiation, which is beneficial for critical-sized bone defects repairing. However, the traditional surface modification techniques, such as physical adsorption, coating, and plasma treatment, et al, have great limitations for immobilization of bioactive molecules due to undesirable controlled delivery performance or overly complex multistep procedures. In this study, we functionalized the chitosan/hydroxyapatite (CS/HA) biomimetic composite scaffold for controlled delivery of BMP2-derived peptide (P24) by the chemical grafting modification technique: firstly, P24 was conjugated with a thiolated chitosan, chitosan-4-thiobutylamidine (CS-TBA); secondly, the resultant CS-P24 was then combined with HA to prepare CS-P24/HA scaffolds. The effect of CS-P24/HA scaffolds on bone regeneration was evaluated, along with the underlying biological mechanisms responsible in vitro and in vivo. In vitro, the controlled and sustained release of bioactive P24 could last up to 90 days, furthermore, the release profiles of CS-5%P24/HA and CS-10%P24/HA were linear and could be fitted according to zero-order kinetic model (R²=0.9929; R²=0.9757); P24 on the scaffold significantly promoted cell adhesion, proliferation, osteodifferentiation, and mineralization with synergistic effects. Bone marrow stromal cells (BMSCs) revealed spindle-shaped surface morphology, indicating the CS-P24/HA scaffolds supported cell adhesion and possessed a high proliferation rate that varied according to the P24 concentration levels. Furthermore, mRNA levels for OCN, Runx2, and collagen I were significantly up-regulated on CS-P24/HA scaffolds compared with cells grown on CS/HA scaffolds in vitro (p < 0.05). Similarly, the BMSCs exhibited a higher ALP expression and calcium deposition level on CS-P24/HA scaffolds compared with CS/HA scaffolds (p < 0.05). In vivo, osteoinductive studies revealed a significantly higher ectopic osteogenesis level of CS-10%P24/HA scaffolds in rat dorsal muscle pockets compared with that of CS/HA scaffolds. Finally, CS-P24/HA scaffolds showed superior performance in the reconstruction of rat calvarial bone defects. This novel CS-P24/HA scaffold is deemed a strong potential candidate for the repair of bone defects in human bone tissue engineering.

The enhancement of osteogenic capacity in a synthetic BMP-2 derived peptide coated mineralized collagen composite in the treatment of the mandibular defects

The novel synthetic peptide P17-BMP-2 could promote cell attachment and enhance osteogenic capability. A composite, comprising nano-hydroxyapatite, collagen and poly(L-lactide) (nHAC/PLLA), was an efficient scaffold for carrier of P17-BMP-2. Our aim was to investigate whether nHAC/PLLA/P17-BMP-2 accelerates the osteogenesis as a reliable method for mandibular defect healing in this study. The repair capability was assessed by the gross observation, X-ray test and histological observation in four animal experiment groups at 2 week and 4 week after surgery: Group A (control), Group B (nHAC/PLLA treatment), Group C (nHAC/PLLA with 2 mg/g P17-BMP-2 treatment) and Group D (nHAC/PLLA with 10 mg/g P17-BMP-2 treatment). The Lane-Sandhu X-ray scores of the four groups were compared among four groups as well. The results showed that the composites containing the highest content of P17- BMP-2 performed best. Therefore, the nHAC/PLLA with P17-BMP-2 composite can accelerate the osteogenesis for mandibular defect healing and could be an ideal biological material as a bone graft material option for clinical applications.

Repair of rat calvarial defects using Si-doped hydroxyapatite scaffolds loaded with a bone morphogenetic protein-2-related peptide

Tissue engineering promises therapies ideal for treating conventional large bone injuries and defects. In the present study, we developed a novel Si-HA scaffold loaded with a synthetic BMP-2-related peptide, P28, and tested its ability to repair a critical-sized calvarial defect. We created a calvarial defect (5 mm in diameter) in the parietal bone of 32 rats and implanted one of the following biomaterials: No implant (control), Si-HA, P28/Si-HA, or rhBMP-2/Si-HA. As assessed by micro CT imaging and histological evaluations, the P28/Si-HA scaffold promoted bone recovery to a similar degree as the rhBMP-2/Si-HA scaffold. In addition, both P28/Si-HA and rhBMP-2/Si-HA promoted recovery better than Si-HA alone. The novel P28/Si-HA scaffold might represent a promising biomaterial for future bone tissue engineering applications. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1874-1882, 2016.

Polydopamine-assisted BMP-2-derived peptides immobilization on biomimetic copolymer scaffold for enhanced bone induction in vitro and in vivo

In this study, a polydopamine (pDA)-coated PLGA-[Asp-PEG]n scaffold was developed for sustained delivery of bone morphogenetic protein-2 (BMP-2)-derived peptide (designated as P24), and then used to address the hypothesis that P24 peptides delivered from the scaffolds could enhance bone induction in vitro and in vivo. We found pDA coating as compared with physical adsorption could more efficiently mediate the grafting of peptides onto polymer surfaces, and the release of P24 peptides from PLGA-[Asp-PEG]n-pDA-P24 was sustained for about 21 days, while a burst P24 release was observed in initial 4h and almost all peptides were released within 24h in physisorbed PLGA-[Asp-PEG]n-P24 group. In vitro, significantly greater ALP activity and mRNA expressions of osteo-specific markers of rat-derived mesenchymal stem cells (rMSCs) were observed in the sustained delivery system than those in physisorbed PLGA-[Asp-PEG]n-P24 and unmodified PLGA-[Asp-PEG]n groups. In vivo, ectopic bone formation studies showed that the sustained delivery system could induce bone formation to a much greater extent than physisorbed PLGA-[Asp-PEG]n-P24. Meanwhile, there were no evidences of bone formation in non-P24-loaded PLGA-[Asp-PEG]n. It is concluded that PLGA-[Asp-PEG]n-pDA-P24 biomaterial can delivery bioactive P24 peptides in a sustained manner, which can more efficiently promote osteogenic differentiation of rMSCs in vitro and induce ectopic bone formation in vivo, as compared with PLGA-[Asp-PEG]n-P24 delivering P24 in a burst manner. This pDA-coated PLGA-[Asp-PEG]n-pDA-P24 composite promises to be an excellent biomaterial for inducing bone regeneration. Moreover, pDA-mediated catechol functionalization can be an effective, simple technique for developing sustained delivery systems.

Characterization of a shorter recombinant polypeptide chain of bone morphogenetic protein 2 on osteoblast behaviour

BACKGROUND

Recombinant bone morphogenetic protein two (rhBMP2) has been utilised for a variety of clinical applications in orthopaedic surgery and dental procedures. Despite its widespread use, concerns have been raised regarding its short half-life and transient bioactivity in vivo. Recent investigation aimed at developing rhBMP2 synthesized from a shorter polypeptide chain (108 amino acids) has been undertaken.

METHODS

The osteopromotive properties of BMP2 were investigated on cell behaviour. Five concentrations of rhBMP2_108 including 10, 50, 100, 200 and 500 ng/ml were compared to a commercially available rhBMP2 (100 ng/ml). Each of the working concentrations of rhBMP2_108 were investigated on MC3T3-E1 osteoblasts for their ability to induce osteoblast recruitment, proliferation and differentiation as assessed by alkaline phosphatase (ALP) staining, alizarin red staining, and real-time PCR for genes encoding ALP, osteocalcin (OCN), collagen-1 (COL-1) and Runx2.

RESULTS

The results demonstrate that all concentrations of rhBMP2_108 significantly improved cell recruitment and proliferation of osteoblasts at 5 days post seeding. Furthermore, rhBMP2_108 had the most pronounced effects on osteoblast differentiation. It was found that rhBMP2_108 had over a four fold significant increase in ALP activity at seven and 14 days post-seeding and the concentrations ranging from 50 to 200 ng/ml demonstrated the most pronounced effects. Analysis of real-time PCR for genes encoding ALP, OCN, COL-1 and Runx2 further confirmed dose-dependant increases at 14 days post-seeding. Furthermore, alizarin red staining demonstrated a concentration dependant increase in staining at 14 days.

CONCLUSION

The results from the present study demonstrate that this shorter polypeptide chain of rhBMP2_108 is equally as bioactive as commercially available rhBMP2 for the recruitment of progenitor cells by facilitating their differentiation towards the osteoblast lineage. Future in vivo study are necessary to investigate its bioactivity.

Biphasic nanofibrous constructs with seeded cell layers for osteochondral repair

Biphasic scaffolds have gained increasing attention for the regeneration of osteochondral interfacial tissue because they are expected to effectively define the interfacial structure of tissue that comprises stratified cartilage with a degree of calcification. Here, we propose a biphasic nanofiber construct made of poly(lactide-co-caprolactone) (PLCL) and its mineralized form (mPLCL) populated with cells. Primary rat articular chondrocytes (ACs) and bone marrow-derived mesenchymal stem cells (MSCs) were cultured on the layers of bare PLCL and mPLCL nanofibers, respectively, for 7 days, and the biphasic cell-nanofiber construct was investigated at 4 weeks after implantation into nude mice. Before implantation, the ACs and MSCs grown on each layer of PLCL and mPLCL nanofibers exhibited phenotypes typical of chondrocytes and osteoblasts, respectively, under proper culture conditions, as analyzed by electron microscopy, histological staining, cell growth kinetics, and real-time polymerase chain reaction. The biphasic constructs also showed the development of a possible formation of cartilage and bone tissue in vivo. Results demonstrated that the cell-laden biphasic nanofiber constructs may be useful for the repair of osteochondral interfacial tissue structure.

Osteoinductive nanohydroxyapatite bone substitute prepared via in situ hydrothermal transformation of cuttlefish bone

The capacity to induce a rapid and controlled healing of bone defects is critical for a bone substitute. Previous studies have reported hydrothermal transformation (HT) of aragonite from cuttlebone (CB) to cuttlebone hydroxyapatite (CBHA). However, the biocompatibility and in vivo characteristic of CBHA have not been fully investigated. We fabricated CBHA via the in situ HT of aragonite from CB. This CBHA exhibited a highly porous structure and nanoscaled surface morphology with a significantly higher protein adsorption rate than CB. Marrow mesenchymal stem cells (MSCs) were seeded and cultured on the CBHA and CB to evaluate their influence on cell proliferation and differentiation. According to scanning electronic microscopy observation and MTT assay, the MSCs adhered and proliferated well on both the CBHA and CB. Compared with the cells on the CB, the MSCs on CBHA exhibited enhanced alkaline phosphatase activity and osteocalcin levels after 13 days of culture. In vivo testing revealed that CBHA could induce ectopic bone formation after implantation, while no bone formation being observed in the CB. These findings demonstrated that a nanoscaled and osteoinductive bone substitute could be produced by hydrothermally transforming an aragonite of CB into a hydroxyapatite.

A collagen-hydroxyapatite scaffold allows for binding and co-delivery of recombinant bone morphogenetic proteins and bisphosphonates

An emerging paradigm in orthopedics is that a bone-healing outcome is the product of the anabolic (bone-forming) and catabolic (bone-resorbing) outcomes. Recently, surgical and tissue engineering strategies have emerged that combine recombinant human bone morphogenetic proteins (rhBMPs) and bisphosphonates (BPs) in order to maximize anabolism and minimize catabolism. Collagen-based scaffolds that are the current surgical standard can bind rhBMPs, but not BPs. We hypothesized that a biomimetic collagen-hydroxyapatite (CHA) scaffold would bind both agents and produce superior in vivo outcomes. Consistent with this concept, in vitro elution studies utilizing rhBMP-2 ELISA assays and scintillation counting of (14)C-radiolabeled zoledronic acid (ZA) confirmed delayed release of both agents from the CHA scaffold. Next, scaffolds were tested for their capacity to form ectopic bone after surgical implantation into the rat hind limb. Using CHA, a significant 6-fold increase in bone volume was seen in rhBMP-2/ZA groups compared to rhBMP-2 alone, confirming the ability of ZA to enhance rhBMP-2 bone formation. CHA scaffolds were found to be capable of generating mineralized tissue in the absence of rhBMP-2. This study has implications for future clinical treatments of critical bone defects. It demonstrates the relative advantages of co-delivering anabolic and anti-catabolic agents using a multicomponent scaffold system.

The mineralized collagen for the reconstruction of intra-articular calcaneal fractures with trabecular defects

BACKGROUND

In cases of severe subversion of the morphology of calcaneal fractures with trabecular defects, bone graft is often necessary to provide a mechanical buttress. The mineralized collagen (MC) is a novel bone substitute that is developed by biomimetic synthesis strategy that mimics the extracellular matrix (ECM) of natural bone in structure and chemical composition. It can avoid donor site morbidity and complications associated with harvesting autologous bone graft.

OBJECTIVE

In this study, we conducted a retrospective matched-pair analysis to assess the clinical and radiological performances of MC as a bone graft substitute in intra-articular calcaneal fractures with trabecular defects.

METHODS

24 pairs of intra-articular calcaneal fractures with trabecular defects were treated with open reduction, internal fixation, and grafting either with MC or autograft. Patient demographics, medical history, and CT fracture classification were matched. Fractures were monitored 6 weeks, 12 weeks, 6 months, and 1 year postoperatively for healing and postoperative complications and results were analyzed.

RESULTS

All patients had follow-up at a minimum of 12 months after surgery with a mean follow-up time of 17 months. All fractures were healed; there were no significant differences in the meantime to union and clinical between the two groups. The radiographic evaluation confirmed that a significant improvement in the mean Böhler's angle, Gissane's angle and the calcaneus height was observed in all patients in both treatment groups. A total of 29% (7/24) of patients suffered from harvest-site morbidity at 12 months in the autograft group. In contrast, all patients were free from postoperative local complications in the iliac region and no patient developed adverse reactions attributable to MC in the MC group.

CONCLUSION

These results justify and favor the use of MC as a good autograft alternative in displaced intra-articular calcaneal fractures with trabecular defects.

In vitro and in vivo enhancement of osteogenic capacity in a synthetic BMP-2 derived peptide-coated mineralized collagen composite

Enhancement of osteogenic capacity was achieved in a mineralized collagen composite, nano-hydroxyapatite/collagen (nHAC), by loading with synthetic peptides derived from BMP-2 residues 32-48 (P17-BMP-2). Rabbit marrow stromal cells (MSCs) were used in vitro to study cell biocompatibility, attachment and differentiation on the mineralized collagen composite by a cell counting kit, scanning electron microscopy (SEM) and real-time reversed transcriptase-polymerase chain reaction analysis (RT-PCR). Optimal peptide dosage (1.0 µg/mL) was obtained by RT-PCR analysis in vitro. In addition, the relative expression level of OPN and OCN was significantly upregulated on P17-BMP-2/nHAC compared with nHAC. In vitro results of P17-BMP-2 release kinetics demonstrated that nHAC released P17-BMP-2 in a controlled and sustained manner. In the rabbit mandibular box-shaped bone defect model, osteogenic capacity of three groups (nHAC, P17-BMP-2/nHAC, rhBMP-2/nHAC) was evaluated. Compared to the nHAC group, bone repair responses in both P17-BMP-2/nHAC and rhBMP-2/nHAC group implants were significantly improved based on histological analysis. The osteogenic response of the P17-BMP-2/nHAC group was similar to that of the rhBMP-2/nHAC group.

Synthesis and application of nanostructured calcium phosphate ceramics for bone regeneration

In the past two decades, nanotechnology has entered the field of regenerative medicine, resulting in the development of a novel generation of instructive, nanostructured biomaterials that are able to orchestrate cellular behavior by presenting specific morphological and biological cues. Using nanotechnology, materials containing nanosized features (e.g., pores, patterns, textures, grain sizes) can be obtained that exhibit properties that are considerably altered compared with micron-structured materials. Inspired by the hierarchical nanostructure of bone, the application of nanostructured materials for bone regeneration is gaining increasing interest in the field of biomaterials research. Because crystallographic and chemical studies have shown that synthetic hydroxyapatite closely resembles the inorganic phase found in bone and teeth, synthesis and applications of nanostructured calcium phosphate ceramics have been reviewed. Synthesis techniques for the preparation of calcium phosphate nanoparticles include precipitation, sol-gel, and hydrothermal processes, whereas four main biomedical applications of nanostructured calcium phosphate ceramics in bone regeneration have been addressed in more detail, that is, (1) polymer/calcium phosphate nanocomposites, (2) nanostructured monophasic calcium phosphate bone fillers, (3) nanostructured precursor phases for calcium phosphate cements, and (4) nanostructured calcium phosphate coatings.

Strategies for controlled delivery of growth factors and cells for bone regeneration

The controlled delivery of growth factors and cells within biomaterial carriers can enhance and accelerate functional bone formation. The carrier system can be designed with pre-programmed release kinetics to deliver bioactive molecules in a localized, spatiotemporal manner most similar to the natural wound healing process. The carrier can also act as an extracellular matrix-mimicking substrate for promoting osteoprogenitor cellular infiltration and proliferation for integrative tissue repair. This review discusses the role of various regenerative factors involved in bone healing and their appropriate combinations with different delivery systems for augmenting bone regeneration. The general requirements of protein, cell and gene therapy are described, with elaboration on how the selection of materials, configurations and processing affects growth factor and cell delivery and regenerative efficacy in both in vitro and in vivo applications for bone tissue engineering.

Bone induction through controlled release of novel BMP-2-related peptide from PTMC₁₁-F127-PTMC₁₁ hydrogels

Bone morphogenetic protein 2 (BMP-2) is the most powerful osteogenic factor; its effectiveness in enhancing osteoblastic activation has been confirmed both in vitro and in vivo. We developed a novel peptide (designated P24) derived from the 'knuckle' epitope of BMP-2 and found it also had osteogenic bioactivity to some extent. The main objective of this study was to develop a controlled release system based on poly(trimethylene carbonate)-F127-poly(trimethylene carbonate) (PTMC₁₁-F127-PTMC₁₁) hydrogels for the P24 peptide, to promote bone formation. By varying the copolymer concentrations, we demonstrated that P24/PTMC₁₁-F127-PTMC₁₁ hydrogels were an efficient system for the sustained release of P24 over 21-35 days. The P24-loaded hydrogels elevated alkaline phosphatase activity and promoted the expression of osteocalcin mRNA in bone marrow stromal cells (BMSCs) in vitro. Radiographic and histological examination showed that P24-loaded hydrogels could induce more effective ectopic bone formation in vivo than P24-free hydrogels. These results indicate that the PTMC₁₁-F127-PTMC₁₁ hydrogel is a suitable carrier for the controlled release of P24, and is a promising injectable biomaterial for the induction of bone regeneration.

Osteogenesis of mineralized collagen bone graft modified by PLA and calcium sulfate hemihydrate: in vivo study

In this study, the biocompatibility and bone regeneration performance of nano-hydroxyapatite/collagen/poly(L-lactide) (nHAC/PLA) and nano-hydroxyapatite/collagen/calcium sulfate hemihydrate (nHAC/CSH) as bone-filling materials were evaluated and compared in a critical box-shaped defect model in the mandible of the rabbits. In vivo results indicated that there was significant difference in early bone remodeling between two types of bone substitutes. nHAC/PLA has shown excellent biocompatibility, but no adequate handling properties. The addition of CSH to nHAC provided better manipulability compared to nHAC/PLA. Furthermore, nHAC/CSH possesses superior properties in restoring critical-sized bone defects of maxillofacial region at the early stage of remodeling over nHAC/PLA. Our results suggested that nHAC/CSH could be an alternative to the conventionally used bone tissue engineering materials.

Repair of rat cranial bone defects with nHAC/PLLA and BMP-2-related peptide or rhBMP-2

An ideal artificial substitute has good biocompatibility properties and is able to provide for rapid bone formation. Bone morphogenetic protein-2 (BMP-2) is considered as one of the most important growth factors for bone regeneration. In this study, a synthetic BMP-2-related peptide (designated P24) corresponding to residues of the knuckle epitope of BMP-2 was introduced into a bioactive scaffold based on nano-hydroxyapatite/collagen/poly(L-lactic acid) (nHAC/PLLA); its in vitro release kinetics was then measured. A 5 mm diameter cranial bone defect was created in the calvariae of 30 rats and randomly implanted with three groups of biomaterials: Group A (nHAC/PLLA alone); Group B (P24/nHAC/PLLA composite); and Group C (recombinant human BMP-2 (rhBMP-2)/nHAC/PLLA composite). The P24/nHAC/PLLA implants significantly stimulated bone growth similarly to the rhBMP-2/nHAC/PLLA implants based on the radiographic and three-dimensional CT evaluation and histological examination, thereby confirming the enhanced bone healing rate of these compounds compared with the stand-alone nHAC/PLLA scaffold material. The osteoinductive ability of 3 mg P24 was similar to that of 1 µg rhBMP-2. P24/nHAC/PLLA is a promising scaffold biomaterial for bone tissue regeneration.

Novel approaches to bone grafting: porosity, bone morphogenetic proteins, stem cells, and the periosteum

The disadvantages involving the use of a patient's own bone as graft material have led surgeons to search for alternative materials. In this review, several characteristics of a successful bone graft material are discussed. In addition, novel synthetic materials and natural bone graft materials are being considered. Various factors can determine the success of a bone graft substitute. For example, design considerations such as porosity, pore shape, and interconnection play significant roles in determining graft performance. The effective delivery of bone morphogenetic proteins and the ability to restore vascularization also play significant roles in determining the success of a bone graft material. Among current approaches, shorter bone morphogenetic protein sequences, more efficient delivery methods, and periosteal graft supplements have shown significant promise for use in autograft substitutes or autograft extenders.

A novel nanoparticle-enhanced photoacoustic stimulus for bone tissue engineering

In this study, we introduce a novel nanoparticle-enhanced biophysical stimulus based on the photoacoustic (PA) effect. We demonstrate that the PA effect differentiates bone marrow-derived marrow stromal cells (MSCs) grown on poly(lactic-co-glycolic acid) (PLGA) polymer films toward osteoblasts. We further show that the osteodifferentiation of the MSCs due to PA stimulation is significantly enhanced by the presence of single-walled carbon nanotubes (SWCNTs) in the polymer. MSCs, without the osteogenic culture supplements (0.01 M β-glycerophosphate, 50 mg/L ascorbic acid, 10(-8) M dexamethasone), were seeded onto plain glass slides, glass slides coated with PLGA, or glass slides coated with SWCNT-PLGA films and photoacoustically stimulated by a 527 nm Nd:YLF pulse laser, with a 200 ns pulse duration, and 10 Hz pulse frequency for 10 min a day for 15 consecutive days. The study had four control groups; three baseline controls similar to the three experimental groups but without PA stimulation, and one positive control where MSCs were grown on glass slides without PA stimulation but with osteogenic culture supplements. The osteogenic differentiation of all the groups was evaluated using quantitative assays (alkaline phosphatase, calcium, osteopontin) and qualitative staining (alizarin red). After 15 days, the PA stimulated groups showed up to a 350% increase in calcium content when compared with the non-PA stimulated positive control. Further, within the PA stimulated group, the PLGA-SWCNT group had 130% higher calcium values than the PLGA film without SWCNTs. These results were further corroborated by the analysis of osteopontin secretion, alkaline phosphatase expression, and qualitative alizarin red staining of extracellular matrix calcification. The results indicate that PA stimulation holds promise for bone tissue engineering and that the nanomaterials which enhance the PA effect should allow the development of biophysical rather than biochemical strategies to induce osteoinductive properties into tissue engineering scaffolds.

Extracellular matrix-mimetic adhesive biomaterials for bone repair

Limited osseointegration of current orthopedic biomaterials contributes to the failure of implants such as arthroplasties, bone screws, and bone grafts, which present a large socioeconomic cost within the United States. These implant failures underscore the need for biomimetic approaches that modulate host cell-implant material responses to enhance implant osseointegration and bone formation. Bioinspired strategies have included functionalizing implants with extracellular matrix (ECM) proteins or ECM-derived peptides or protein fragments, which engage integrins and direct osteoblast adhesion and differentiation. This review discusses (1) bone ECM composition and key integrins implicated in osteogenic differentiation, (2) the use of implants functionalized with ECM-mimetic peptides/protein fragments, and (3) growth factor-derived peptides to promote the mechanical fixation of implants to bone and to enhance bone healing within large defects.

Vascular endothelial growth factor inhibits bone morphogenetic protein 2 expression in rat mesenchymal stem cells

INTRODUCTION

While several studies report that bone morphogenetic proteins (BMPs) and vascular endothelial growth factor (VEGF) can act synergistically to improve bone tissue engineering, others suggest that VEGF inhibits osteogenesis. The purpose of these experiments was therefore to evaluate the effect of dual transfection of these growth factors and potential mechanisms of interaction on gene expression and osteogenesis in vitro and in vivo.

METHODS

Marrow-derived mesenchymal stem cells (MSCs) were exposed to recombinant VEGF protein or transfected with adenoviruses encoding BMP2, VEGF, or LacZ in a variety of ratios. Alterations in gene and protein expression in vitro as well as bone formation in vivo were assessed.

RESULTS

MSC exposure to AdV-VEGF or recombinant VEGF inhibited BMP2 mRNA expression, protein production, and MSC differentiation. Coculture experiments revealed that BMP2 suppression occurs through both an autocrine and a paracrine mechanism, occurring at the transcriptional level. Compared to controls, cotransfection of VEGF and BMP2 transgenes prevented ectopic bone formation in vivo.

CONCLUSION

VEGF is a potent inhibitor of BMP2 expression in MSCs, and supplementation or overexpression of VEGF inhibits osteogenesis in vitro and ectopic bone formation in vivo. Strategies to utilize MSCs in bone tissue engineering therefore require careful optimization and precise delivery of growth factors for maximal bone formation.

Bone induction by biomimetic PLGA-(PEG-ASP)n copolymer loaded with a novel synthetic BMP-2-related peptide in vitro and in vivo

BMP-2 is one of the most important growth factors of bone regeneration. Polylactide-co-glycolic acid (PLGA), which is used as a biodegradable scaffold for delivering therapeutic agents, has been intensively investigated. In previous studies, we synthesized a novel BMP-2-related peptide (designated P24) and found that it could enhance the osteoblastic differentiation of bone marrow stromal cells (BMSCs). The objective of this study was to construct a biomimetic composite by incorporating P24 into a modified PLGA-(PEG-ASP)n copolymer to promote bone formation. In vitro, our results demonstrated that PLGA-(PEG-ASP)n scaffolds were shown to be an efficient system for sustained release of P24. Significantly more BMSCs attached to the P24/PLGA-(PEG-ASP)n and PLGA-(PEG-ASP)n membranes than to PLGA, and the cells in the two groups subsequently proliferated more vigorously than those in the PLGA group. The expression of osteogenic markers in P24/PLGA-(PEG-ASP)n group was stronger than that in the PLGA-(PEG-ASP)n and PLGA groups. Radiographic and histological examination, Western blotting and RT-PCR showed that P24/PLGA-(PEG-ASP)n scaffold could induce more effective ectopic bone formation in vivo, as compared with PLGA-(PEG-ASP)n or gelatin sponge alone. It is concluded that the PLGA-(PEG-ASP)n copolymer is a good P24 carrier and can serve as a good scaffold for controlled release of P24. This novel P24/PLGA-(PEG-ASP)n composite promises to be an excellent biomaterial for inducing bone regeneration.

Enhanced bone formation in large segmental radial defects by combining adipose-derived stem cells expressing bone morphogenetic protein 2 with nHA/RHLC/PLA scaffold

In this study, rabbit adipose-derived stem cells (rASCs) were isolated, cultured in vitro, and transfected with recombinant adenovirus vector containing human bone morphogenetic protein 2 (Ad-hBMP2). These cells were combined with a nano-hydroxyapatite/recombinant human-like collagen/poly(lactic acid) scaffold (nHA/RHLC/PLA) to fabricate a new biocomposite (hBMP2/rASCs-nHA/RHLC/PLA, group 1) and cultured in osteogenic medium. Non-transfected rASCs mixed with nHA/RHLC/PLA (rASCs-nHA/RHLC/PLA, group 2) and nHA/RHLC/PLA scaffold alone (group 3) served as controls. Scanning electron microscope (SEM) demonstrated integration of rASCs with the nHA/RHLC/PLA scaffold. Quantitative real-time RT-PCR analyses of collagen I, osteonectin, and osteopontin cDNA expression indicated that the osteogenic potency of rASCs was enhanced by transfection with Ad-hBMP2. After in vitro culture for seven days, three groups were implanted into 15-mm length critical-sized segmental radial defects in rabbits. After 12 weeks, radiographic and histological analyses were performed. In group 1, the medullary cavity was recanalised, bone was rebuilt and moulding was finished, the bone contour had begun to remodel and scaffold was degraded completely. In contrast, bone defects were not repaired in groups 2 or 3. Furthermore, the scaffold degradation rate in group 1 was significantly higher than in groups 2 or 3. In summary, after transduction with Ad-hBMP2, the osteogenesis of rASCs was enhanced; a new biocomposite created with these cells induced repair of a critical bone defect in vivo in a relatively short time.

Murine preosteoblast differentiation induced by a peptide derived from bone morphogenetic proteins-9

Bone morphogenetic proteins (BMPs) increase the differentiation of osteoblasts implicated in bone formation and repair. In a previous study, we demonstrated that a peptide derived from BMP-9 (pBMP-9) at 400 ng/mL inhibited murine preosteoblasts MC3T3-E1 proliferation. Here, we compared the effects of equimolar concentrations of BMP-2 (50 ng/mL), BMP-9 (42.3 ng/mL), and pBMP-9 (4.52 ng/mL) on the differentiation of MC3T3-E1 in a serum-free medium. Like BMP-2, BMP-9 and pBMP-9 activated the Smad pathway. In contrary to BMP-2, the Smad phosphorylation induced by BMP-9 and pBMP-9 is not prevented by noggin, an extracellular antagonist of BMP-2. Further, BMP-9 and pBMP-9 increased, dose dependently, alkaline phosphatase activity, an early marker of osteoblast differentiation, after 1 day. Quantitative real-time polymerase chain reaction analysis demonstrated that BMP-2, BMP-9, and pBMP-9 (4.52 or 400 ng/mL) all activated the transcription of Runx2, Osterix, type I collagen alpha1 chain, and Osteocalcin genes within day 6. Alizarin red S quantification demonstrated that pBMP-9 (400 ng/mL) and pBMP-9 (4.52 ng/mL) allowed a slight deposition of Ca(2+) in the extracellular matrix of cells within 12 and 18 days, respectively. Therefore, pBMP-9 might be a promising replacement for costly BMP in tissue engineering applications that require a well-defined serum-free medium.