Ectopic bone formation induced by biodegradable hydrogels incorporating bone morphogenetic protein

Bioactive gelatin-sheets as novel biopapers to support prevascularization organized by laser-assisted bioprinting for bone tissue engineering

Despite significant advances in the management of patients with oral cancer, maxillofacial reconstruction after ablative surgery remains a clinical challenge. In bone tissue engineering, biofabrication strategies have been proposed as promising alternatives to solve issues associated with current therapies and to produce bone substitutes that mimic both the structure and function of native bone. Among them, laser-assisted bioprinting (LAB) has emerged as a relevant biofabrication method to print living cells and biomaterials with micrometric resolution onto a receiving substrate, also called 'biopaper'. Recent studies have demonstrated the benefits of prevascularization using LAB to promote vascularization and bone regeneration, but mechanical and biological optimization of the biopaper are needed. The aim of this study was to apply gelatin-sheet fabrication process to the development of a novel biopaper able to support prevascularization organized by LAB for bone tissue engineering applications. Gelatin-based sheets incorporating bioactive glasses (BGs) were produced using various freezing methods and crosslinking (CL) parameters. The different formulations were characterized in terms of microstructural, physical, mechanical, and biological properties in monoculture and coculture. Based on multi-criteria analysis, a rank scoring method was used to identify the most relevant formulations. The selected biopaper underwent additional characterization regarding its ability to support mineralization and vasculogenesis, its bioactivity potential andin vivodegradability. The biopaper 'Gel5wt% BG1wt%-slow freezing-CL160 °C 24 h' was selected as the best candidate, due to its suitable properties including high porosity (91.69 ± 1.55%), swelling ratio (91.61 ± 0.60%), Young modulus (3.97 × 104± 0.97 × 104Pa) but also its great cytocompatibility, osteogenesis and bioactivity properties. The preorganization of human umbilical vein endothelial cell using LAB onto this new biopaper led to the formation of microvascular networks. This biopaper was also shown to be compatible with 3D-molding and 3D-stacking strategies. This work allowed the development of a novel biopaper adapted to LAB with great potential for vascularized bone biofabrication.

Standard in vitro evaluations of engineered bone substitutes are not sufficient to predict in vivo preclinical model outcomes

Understanding the optimal conditions required for bone healing can have a substantial impact to target the problem of non-unions and large bone defects. The combination of bioactive factors, regenerative progenitor cells and biomaterials to form a tissue engineered (TE) complex is a promising solution but translation to the clinic has been slow. We hypothesized the typical material testing algorithm used is insufficient and leads to materials being mischaracterized as promising. In the first part of this study, human bone marrow - derived mesenchymal stromal cells (hBM-MSCs) were embedded in three commonly used biomaterials (hyaluronic acid methacrylate, gelatin methacrylate and fibrin) and combined with relevant bioactive osteogenesis factors (dexamethasone microparticles and polyphosphate nanoparticles) to form a TE construct that underwent in vitro osteogenic differentiation for 28 days. Gene expression of relevant transcription factors and osteogenic markers, and von Kossa staining were performed. In the second and third part of this study, the same combination of TE constructs were implanted subcutaneously (cell containing) in T cell-deficient athymic Crl:NIH-Foxn1^rnu rats for 8 weeks or cell free in an immunocompetent New Zealand white rabbit calvarial model for 6 weeks, respectively. Osteogenic performance was investigated via MicroCT imaging and histology staining. The in vitro study showed enhanced upregulation of relevant genes and significant mineral deposition within the three biomaterials, generally considered as a positive result. Subcutaneous implantation indicates none to minor ectopic bone formation. No enhanced calvarial bone healing was detected in implanted biomaterials compared to the empty defect. The reasons for the poor correlation of in vitro and in vivo outcomes are unclear and needs further investigation. This study highlights the discrepancy between in vitro and in vivo outcomes, demonstrating that in vitro data should be interpreted with extreme caution. In vitro models with higher complexity are necessary to increase value for translational studies. STATEMENT OF SIGNIFICANCE: Preclinical testing of newly developed biomaterials is a crucial element of the development cycle. Despite this, there is still significant discrepancy between in vitro and in vivo test results. Within this study we investigate multiple combinations of materials and osteogenic stimulants and demonstrate a poor correlation between the in vitro and in vivo data. We propose rationale for why this may be the case and suggest a modified testing algorithm.

Self-Prepared Hyaluronic Acid/Alkaline Gelatin Composite with Nano-Hydroxyapatite and Bone Morphogenetic Protein for Cranial Bone Formation

New bone-forming substitute materials are highly useful in dental implantology. The purpose of this study was to prepare cross-linked hyaluronic acid (cHLA)/cross-linked alkaline gelatin (cAG)/nano-hydroxyapatite (nHAp)/bone morphogenic protein (BMP) constructs; and evaluate their bone-forming capabilities in rat cranial bone defects. The cHLA and cAG liquids processed with an epoxy cross-linker were blended with a 3:1 volume ratio, followed by freeze-drying. The dry composites were further infiltrated with water containing nHAp only (BMP (−)) or with water containing nHAp and BMP (BMP (+)). Prepared wet constructs (BMP (−) and BMP (+)) were implanted in rat cranial bone defects, while defects only were also made, and animals were fed for 8 weeks, followed by subsequent soft X-ray measurements and histological observations. The X-ray results showed that BMP (+) constructs disappeared, though caused inward extension of peripherical bone from defect edges with an increase in length of approximately 24%, larger than those of BMP (−) constructs and defect only with approximately 17% and 8% increments, respectively (p < 0.05). Histological observations of BMP (+) construct samples clearly indicated active bone extension consisting of an array of island-like bones. It was concluded that cHLA/cAG/nHAp/BMP could be used as novel bone-substitute materials.

The efficacy of rhBMP-2 loaded hydrogel composite on bone formation around dental implants in mandible bone defects of minipigs

Background

In dental or orthopedic surgery, bone substitutes are inserted with implants to promote osteogenesis and enhance osseointegration. The purpose of this research was to evaluate the efficacy of rhBMP-2 (recombinant human bone morphogenetic protein-2) loaded hydrogel composite for bone formation around dental implant in minipig mandible bone defect models.

Methods

We made bone defects with a diameter of 4 mm in minipig mandibles and inserted implants of the same size, to mimic the cases of inserting the screws in the bone defect or poor-quality bone. The rhBMP-2 (300 μg) loaded hydrogel composite (0.5 cc) inserted in the bone defect with the implant in the rhBMP-2 group. After 4 weeks, the mandibles were harvested to evaluate the new bone mass around implants using plain radiographs, micro-CT, and histology.

Results

The micro-CT analysis result showed that the quantity of new bone generation around the implant in the rhBMP-2 group was greater than that in the other groups. Comparing the ratios of bone to implant area in three groups by histology, the amount of newly formed bone in the rhBMP-2 group was the most.

Conclusion

The rhBMP-2 loaded hydrogel composite promotes osteogenesis around dental implant in minipig mandible bone defect, and enhance osseointegration between the dental implant and host bone.

Effect of Biomaterial Electrical Charge on Bone Morphogenetic Protein-2-Induced In Vivo Bone Formation

IMPACT STATEMENT

Biomaterials can play a dual role in bone regeneration: they enable local sustained delivery of growth factors, such as bone morphogenetic protein-2 (BMP-2), while they provide structural support as scaffold. By better imitating the properties of native bone tissue, scaffolds may be both osteoconductive and osteoinductive. The latter can be achieved by modifying the electrical charge of the surface. The present work uses tunable oligo[(polyethylene glycol) fumarate] hydrogel and demonstrates that negative charge enhances BMP-2-induced bone formation compared with neutral or positive charge. Altogether, this indicates that tissue-specific surface charge modifications of biomaterials hold great promise in the field of tissue regeneration.

The Osteoinductive Effect of Controlled Bone Morphogenic Protein 2 Release Is Location Dependent

IMPACT STATEMENT

The main challenge in bone morphogenic protein 2 (BMP-2)-based application lies in finding strategies to prolong its biologic activity as it has a short biological half-life. The present study uses a phosphate-modified oligo[(polyethylene glycol) fumarate] hydrogel that can be tuned to achieve differential release profiles of biologically active BMP-2 release. We demonstrate that this platform outperforms Infuse^®, currently used in the clinic and that the osteoinductive effect of BMP-2 is location dependent. Altogether, this study stresses the importance of evaluating efficacy of bone tissue engineering strategies at an orthotopic location rather than subcutaneously. Even more so, it emphasizes the role of biomaterials as a scaffold to achieve proper bone tissue engineering.

Bone morphogenetic protein-2 release profile modulates bone formation in phosphorylated hydrogel

The optimal release profile of locally delivered bone morphogenetic protein-2 (BMP-2) for safe and effective clinical application is unknown. In this work, the effect of differential BMP-2 release on bone formation was investigated using a novel biomaterial oligo[(polyethylene glycol) fumarate] bis[2-(methacryloyloxy) ethyl] phosphate hydrogel (OPF-BP) containing poly(lactic-co-glycolic acid) microspheres. Three composite implants with the same biomaterial chemistry and structure but different BMP-loading methods were created: BMP-2 encapsulated in microspheres (OPF-BP-Msp), BMP-2 encapsulated in microspheres and adsorbed on the phosphorylated hydrogel (OPF-BP-Cmb), and BMP-2 adsorbed on the phosphorylated hydrogel (OPF-BP-Ads). These composites were compared with the clinically used BMP-2 carrier, Infuse® absorbable collagen sponge (ACS). Differential release profiles of bioactive BMP-2 were achieved by these composites. In a rat subcutaneous implantation model, OPF-BP-Ads and ACS generated a large BMP-2 burst release (>75%), whereas a more sustained release was seen for OPF-BP-Msp and OPF-BP-Cmb (~25% and 50% burst, respectively). OPF-BP-Ads generated significantly more bone than did all other composites, and the bone formation was 12-fold higher than that of the clinically used ACS. Overall, this study clearly shows that BMP-2 burst release generates more subcutaneous bone than do sustained release in OPF-BP-microsphere composites. Furthermore, composites should not only function as a delivery vehicle but also provide a proper framework to achieve appropriate bone formation.

One-Step Fabrication of Bone Morphogenetic Protein-2 Gene-Activated Porous Poly-L-Lactide Scaffold for Bone Induction

Bone morphogenetic protein 2 (BMP2) is an efficacious inducer for the osteogenesis of mesenchymal stem cells (MSCs). Conventional applications of BMP2 have involved either the direct incorporation of BMP2 protein or ex vivo BMP2 gene transfer into stem cells prior to their transplantation. These approaches are able to promote bone formation to some extent; however, they are hampered by either the lack of stability and sustainability of BMP2 protein or the time-consuming and cost-prohibitive in vitro cell culture procedure. To overcome these limitations, we have developed a gene-activated poly-L-lactide acid (PLLA) scaffold with the encapsulation of recombinant adeno-associated viral (AAV) vector encoding a full-length cDNA of human BMP2 using an ice-based microparticle porogenization method that was recently developed. Results showed continuous release of AAV particles from the micropores of scaffolds for up to 1 week, subsequently transducing embedded human MSCs and producing functional BMP2. MSCs within scaffolds underwent efficacious osteogenesis, on the basis of osteoinductive gene expression and osteogenic differentiation, which resulted in robust new bone formation in vivo at 4 weeks. These findings show the potential of the technology toward developing clinical applications of a rapid, cost-effective, and potentially point-of-care approach for the repair of bone defects.

Soluble VEGFR1 reverses BMP2 inhibition of intramembranous ossification during healing of cortical bone defects

BMP2 is widely used for promotion of bone repair and regeneration. However, bone formation induced by BMP2 is quite variable. Bone forming progenitor cells in different locations appear to respond to BMP2 in different ways, and repair outcomes can vary as a consequence of modulating effects by other factors. In this study, we have examined the effects of VEGF on BMP2-induced repair of a cortical bone defect, a 1 mm diameter drill hole, in the proximal tibia of mice. Treatment of the defect with either a bolus of PBS or soluble VEGFR1 (sVEGFR1), a decoy receptor for VEGF, had the same effects on bone formation via intramembranous ossification in the defect and cartilage formation and injured periosteum, during the healing process. In contrast, treatment with BMP2 inhibited intramembranous bone formation in the defect while it promoted cartilage and endochondral bone formation in the injured periosteum compared with mice treated with PBS or sVEGFR1. The inhibitory effect of BMP2 on bone formation was unlikely due to increased osteoclast activity and decreased invasion of blood vessels in the defect. Most importantly, co-delivery of BMP2 and sVEGFR1 reversed the inhibition of intramembranous bone formation by BMP2. Furthermore, the decreased accumulation of collagen and production of bone matrix proteins in the defect of groups with BMP2 treatment could also be prevented by co-delivery of BMP2 and sVEGFR1. Our data indicate that introducing a VEGF-binding protein, such as sVEGFR1, to reduce levels of extracellular VEGF, may enhance the effects of BMP2 on intramembranous bone formation. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1461-1469, 2017.

Hydrogels That Allow and Facilitate Bone Repair, Remodeling, and Regeneration

Bone defects can originate from a variety of causes, including trauma, cancer, congenital deformity, and surgical reconstruction. Success of the current "gold standard" treatment (i.e., autologous bone grafts) is greatly influenced by insufficient or inappropriate bone stock. There is thus a critical need for the development of new, engineered materials for bone repair. This review describes the use of natural and synthetic hydrogels as scaffolds for bone tissue engineering. We discuss many of the advantages that hydrogels offer as bone repair materials, including their potential for osteoconductivity, biodegradability, controlled growth factor release, and cell encapsulation. We also discuss the use of hydrogels in composite devices with metals, ceramics, or polymers. These composites are useful because of the low mechanical moduli of hydrogels. Finally, the potential for thermosetting and photo-cross-linked hydrogels as three-dimensionally (3D) printed, patient-specific devices is highlighted. Three-dimensional printing enables controlled spatial distribution of scaffold materials, cells, and growth factors. Hydrogels, especially natural hydrogels present in bone matrix, have great potential to augment existing bone tissue engineering devices for the treatment of critical size bone defects.

Facial nerve regeneration using basic fibroblast growth factor-impregnated gelatin microspheres in a rat model

Basic fibroblast growth factor (bFGF) plays a crucial role in the regeneration of peripheral nerve defects by affecting nerve cells, Schwann cells and fibroblasts, and by promoting axon outgrowth from the proximal nerve stump. However, the use of exogenous bFGF for in vivo regeneration of the peripheral nerves is limited by its short in vivo half-life. In this study, a drug delivery system for bFGF was developed that uses acidic gelatin hydrogel, which sustainably released bFGF in vivo over several weeks; its ability to promote peripheral nerve regeneration was also examined. In 8-week-old Lewis rats, 7-mm gaps were made in the buccal branch of the left facial nerve. Acidic gelatin hydrogel microspheres (10 µl) with or without bFGF (50 µg) were infused into a 10 mm silicone tube using a micropipette, and the silicone tube was then implanted into the gap. A 1-mm long nerve stump was inserted into each end of the tube. Histological examination at 7 weeks after implantation revealed (1) a significantly increased rate of nerve regeneration, (2) inducement of a number of regenerating nerve axons, and (3) a better degree of maturation of nerve axons in the bFGF microsphere group than that in the bFGF-free microsphere group. Copyright © 2014 John Wiley & Sons, Ltd.

Controlled release of granulocyte colony-stimulating factor enhances osteoconductive and biodegradable properties of Beta-tricalcium phosphate in a rat calvarial defect model

Autologous bone grafts remain the gold standard for the treatment of congenital craniofacial disorders; however, there are potential problems including donor site morbidity and limitations to the amount of bone that can be harvested. Recent studies suggest that granulocyte colony-stimulating factor (G-CSF) promotes fracture healing or osteogenesis. The purpose of the present study was to investigate whether topically applied G-CSF can stimulate the osteoconductive properties of beta-tricalcium phosphate (β-TCP) in a rat calvarial defect model. A total of 27 calvarial defects 5 mm in diameter were randomly divided into nine groups, which were treated with various combinations of a β-TCP disc and G-CSF in solution form or controlled release system using gelatin hydrogel. Histologic and histomorphometric analyses were performed at eight weeks postoperatively. The controlled release of low-dose (1 μg and 5 μg) G-CSF significantly enhanced new bone formation when combined with a β-TCP disc. Moreover, administration of 5 μg G-CSF using a controlled release system significantly promoted the biodegradable properties of β-TCP. In conclusion, the controlled release of 5 μg G-CSF significantly enhanced the osteoconductive and biodegradable properties of β-TCP. The combination of G-CSF slow-release and β-TCP is a novel and promising approach for treating pediatric craniofacial bone defects.

Evaluation of multifunctional polysaccharide hydrogels with varying stiffness for bone tissue engineering

The use of hydrogels for bone regeneration has been limited due to their inherent low modulus to support cell adhesion and proliferation as well as their susceptibility to bacterial infections at the wound site. To overcome these limitations, we evaluated multifunctional polysaccharide hydrogels of varying stiffness to obtain the optimum stiffness at which the gels (1) induce proliferation of human dermal fibroblasts, human umbilical vascular endothelial cells (HUVECs), and murine preosteoblasts (MC3T3-E1), (2) induce osteoblast differentiation and mineralization, and (3) exhibit an antibacterial activity. Rheological studies demonstrated that the stiffness of hydrogels made of a polysaccharide blend of methylcellulose, chitosan, and agarose was increased by crosslinking the chitosan component to different extents with increasing amounts of genipin. The gelation time decreased (from 210 to 60 min) with increasing genipin concentrations. Proliferation of HUVECs decreased by 10.7 times with increasing gel stiffness, in contrast to fibroblasts and osteoblasts, where it increased with gel stiffness by 6.37 and 7.8 times, respectively. At day 14 up to day 24, osteoblast expression of differentiation markers-osteocalcin, osteopontin-and early mineralization marker-alkaline phosphatase, were significantly enhanced in the 0.5% (w/v) crosslinked gel, which also demonstrated enhanced mineralization by day 25. The antibacterial efficacy of the hydrogels decreased with the increasing degree of crosslinking as demonstrated by biofilm formation experiments, but gels crosslinked with 0.5% (w/v) genipin still demonstrated significant bacterial inhibition. Based on these results, gels crosslinked with 0.5% (w/v) genipin, where 33% of available groups on chitosan were crosslinked, exhibited a stiffness of 502±64.5 Pa and demonstrated the optimal characteristics to support bone regeneration.

Bone Regeneration of Rat Calvarial Defect by Magnesium Calcium Phosphate Gelatin Scaffolds with or without Bone Morphogenetic Protein-2

Regeneration of large bone losses has been achieved with limited success due to either donor site complications in autogenous bone graft or lack of an ideal biomaterial in the case of allografts. Magnesium calcium phosphate-gelatin sponges were prepared with different concentrations of MCP; namely 0, 50 and 90 wt%. Eight mm defects were drilled in the calvaria of 48 male Fischer 344 rats. MCP-gelatin scaffolds containing or without bone morphogenetic protein were placed at the defect site. Animals were sacrificed at 3 and 12 weeks, post-operatively, with evaluation of bone regeneration by using micro CT and histological examinations. Results showed that the combination of BMP-2 and gelatin sponges could provide a slow release system that significantly enhanced bone regeneration at both 3 and 12 weeks in comparison with the non BMP-2-containing 90 wt% MCP-gelatin sponges. The combination of 50 wt% MCP-gelatin sponges and BMP-2 showed significant bone formation at 3 weeks in comparison with the non BMP-2 containing gelatin sponges, indicating that the addition of MCP to the gelatin scaffold had a synergistic advantage in combination with BMP-2. This novel scaffold has shown adequate porosity to allow cell growth, amenability for sterilization, biocompatibility and biodegradability with the ability to provide a slow release system for BMP-2 to enhance bone regeneration.

Growth factor delivery: how surface interactions modulate release in vitro and in vivo

Biomaterial scaffolds have been extensively used to deliver growth factors to induce new bone formation. The pharmacokinetics of growth factor delivery has been a critical regulator of their clinical success. This review will focus on the surface interactions that control the non-covalent incorporation of growth factors into scaffolds and the mechanisms that control growth factor release from clinically relevant biomaterials. We will focus on the delivery of recombinant human bone morphogenetic protein-2 from materials currently used in the clinical practice, but also suggest how general mechanisms that control growth factor incorporation and release delineated with this growth factor could extend to other systems. A better understanding of the changing mechanisms that control growth factor release during the different stages of preclinical development could instruct the development of future scaffolds for currently untreatable injuries and diseases.

Biological properties of solid free form designed ceramic scaffolds with BMP-2: in vitro and in vivo evaluation

Porous ceramic scaffolds are widely studied in the tissue engineering field due to their potential in medical applications as bone substitutes or as bone-filling materials. Solid free form (SFF) fabrication methods allow fabrication of ceramic scaffolds with fully controlled pore architecture, which opens new perspectives in bone tissue regeneration materials. However, little experimentation has been performed about real biological properties and possible applications of SFF designed 3D ceramic scaffolds. Thus, here the biological properties of a specific SFF scaffold are evaluated first, both in vitro and in vivo, and later scaffolds are also implanted in pig maxillary defect, which is a model for a possible application in maxillofacial surgery. In vitro results show good biocompatibility of the scaffolds, promoting cell ingrowth. In vivo results indicate that material on its own conducts surrounding tissue and allow cell ingrowth, thanks to the designed pore size. Additional osteoinductive properties were obtained with BMP-2, which was loaded on scaffolds, and optimal bone formation was observed in pig implantation model. Collectively, data show that SFF scaffolds have real application possibilities for bone tissue engineering purposes, with the main advantage of being fully customizable 3D structures.

Use of a bioactive scaffold for the repair of bone defects in a novel reproducible vertebral body defect model

Bone defects in vertebral bodies (VB) usually occur after the reduction of fractures or are caused by bone disease. Besides the treatment of original disease, repair of the bone defect can restore the structure of VB and improve stabilization of the spine to protect the spinal cord nerves. To aid studies of the efficacy of bioengineering techniques for repair of VB, we developed a rat model with a critical size bone defect in VB. Air-motivated burrs were used to create two sizes of bone defect (2 x 3 x 1.5 mm; 2 x 3 x 3 mm) in the anterior part of VB in 6-month-old Fischer 344 rats. Quantitative CT analyses and histological assays demonstrated that neither defects self-repaired by 8 weeks post surgery. Moreover, the tendency of bone formation was monitored in the same animal by serial CT image evaluations, allowing us to demonstrate that there was significant bone growth during the 4- to 6-week period after the creation of the bone defect. We then implanted sintered poly(lactic-co-glycolic acid) (PLGA) microsphere scaffolds loaded with Matrigel with or without recombinant human bone morphogenetic protein 2 (rhBMP2; 2.0 microg rhBMP2/10 microL Matrigel/scaffold) into the bone defect (2 x 3 x 3 mm) in the VB. Bone formation was detected by quantitative analyses of serial CT images, which demonstrated bone growth in rats that received the rhBMP2 implant, in both surrounding areas and inside area of the scaffold. In addition to a rapid increase within 2 weeks of the operation, another significant bone formation period was found between 4 and 8 weeks after the implantation. By contrast, the control group that received the implant without rhBMP2 did not show similar bone formation tendencies. The results of CT analyses were confirmed by histological studies. This study suggests that a critical size bone defect of the anterior VB can be developed in a rat model. Characterization of this model demonstrated that 4 to 6 weeks after creation of the defect was a significant bone growth period for VB bone repair in rats. This animal model has further utility for the study of different biomaterials for VB bone repair. Implantation of a bioactive PLGA scaffold carrying rhBMP2 allowed more successful repair of the VB defect. Although further characterization studies are needed, the bioactive PLGA scaffold developed in this study will likely adapt easily to other in vivo osteogenesis applications.

rBMP represses Wnt signaling and influences skeletal progenitor cell fate specification during bone repair

Bone morphogenetic proteins (BMPs) participate in multiple stages of the fetal skeletogenic program from promoting cell condensation to regulating chondrogenesis and bone formation through endochondral ossification. Here, we show that these pleiotropic functions are recapitulated when recombinant BMPs are used to augment skeletal tissue repair. In addition to their well-documented ability to stimulate chondrogenesis in a skeletal injury, we show that recombinant BMPs (rBMPs) simultaneously suppress the differentiation of skeletal progenitor cells in the endosteum and bone marrow cavity to an osteoblast lineage. Both the prochondrogenic and antiosteogenic effects are achieved because rBMP inhibits endogenous beta-catenin-dependent Wnt signaling. In the injured periosteum, this repression of Wnt activity results in sox9 upregulation; consequently, cells in the injured periosteum adopt a chondrogenic fate. In the injured endosteum, rBMP also inhibits Wnt signaling, which results in the runx2 and collagen type I downregulation; consequently, cells in this region fail to differentiate into osteoblasts. In muscle surrounding the skeletal injury site, rBMP treatment induces Smad phosphorylation followed by exuberant cell proliferation, an increase in alkaline phosphatase activity, and chondrogenic differentiation. Thus different populations of adult skeletal progenitor cells interpret the same rBMP stimulus in unique ways, and these responses mirror the pleiotropic effects of BMPs during fetal skeletogenesis. These mechanistic insights may be particularly useful for optimizing the reparative potential of rBMPs while simultaneously minimizing their adverse outcomes.

Regulation of the protein-loading capacity of hydroxyapatite by mercaptosuccinic acid modification

Loading and releasing protein in a controllable way is extremely important for the protein vehicles used in bone tissue engineering. To obtain a suitable carrier material for basic proteins, such as BMP or bFGF, hydroxyapatite particles containing mercaptosuccinic acid (mercaptosuccinic acid (Mer), (Mer-HAp)) were synthesized. Physicochemical evaluation of Mer-HAp suggested that Mer was contained in HAp particles: it either simply adsorbed onto HAp crystals or was trapped among the HAp crystals. A protein adsorption study using basic and acidic model proteins indicated that the synthesized Mer-HAp had selective loading properties of the basic protein. The loaded protein was gradually released from Mer-HAp in phosphate buffered saline. The protein release rate was different in each Mer-HAp synthesized with a different concentration of Mer. In addition, the protein release from Mer-HAp showed a similar profile with the Ca dissolution in different pH solutions, indicating that the Mer-HAp dissolution was concerned with the protein release from Mer-HAp. Thus, Mer-HAp is a useful candidate for the basic protein carrier because it has properties which enable the loading and releasing of protein in a controllable way.

Delivery systems for bone growth factors — the new players in skeletal regeneration

Given the challenge of an increasing elderly population, the ability to repair and regenerate traumatised or lost tissue is a major clinical and socio-economic need. Pivotal in this process will be the ability to deliver appropriate growth factors in the repair cascade in a temporal and tightly regulated sequence using appropriately designed matrices and release technologies within a tissue engineering strategy. This review outlines the current concepts and challenges in growth factor delivery for skeletal regeneration and the potential of novel delivery matrices and biotechnologies to influence the healthcare of an increasing ageing population.

Biocompatibility and safety of a hybrid core-shell nanoparticulate OP-1 delivery system intramuscularly administered in rats

A hybrid, localized and release-controlled delivery system for bone growth factors consisting of a liposomal core incorporated into a shell of alternating layer-by-layer self-assembled natural polyelectrolytes has been formulated. Hydrophilic, monodisperse, spherical and stable cationic nanoparticles (< or =350 nm) with an extended shelf-life resulted. Cytocompatibility was previously assayed with MC3T3-E1.4 mouse preosteoblasts showing no adverse effects on cell viability. In this study, the in vivo biocompatibility of unloaded and loaded nanoparticles with osteogenic protein-1 or OP-1 was investigated. Young male Wistar rats were injected intramuscularly and monitored over a period of 10 weeks for signs of inflammation and/or adverse reactions. Blood samples (600 microL/collection) were withdrawn followed by hematological and biochemical analysis. Body weight changes over the treatment period were noted. Major organs were harvested, weighed and examined histologically for any pathological changes. Finally, the injection site was identified and examined immunohistochemically. Overall, all animals showed no obvious toxic health effects, immune responses and/or change in organ functions. This hybrid core-shell nanoparticulate delivery system localizes the effect of the released bioactive load within the site of injection in muscle with no significant tissue distress. Hence, a safe and promising carrier for therapeutic growth factors and possibly other biomolecules is presented.

Effects of osteoinduction on bone regeneration in distraction: results of a pilot study

Rate and frequency of distraction as well as stimulatory effects transmitted by growth factors and local gene therapy have a decisive influence on bone regeneration. In a pilot study we tested the effect of four different morphogenetic and mitotic proteins and a genetically transferred vector system on bone healing in continuous osteodistraction in a large animal experiment on 24 Goettingen mini-pigs. For this purpose bone morphogenetic protein (BMP-2), BMP-7, TGF-beta, IGF-1 and a liposome vector were instilled into the distraction gap. The animals were killed after 1-4 weeks of consolidation. Histological and radiological evaluations showed maximum bone formation after the application of BMP-2/7, whereas the application of TGF-beta, IGF-1 and the liposomal vector had only a limited effect on bone regeneration. The quantitative analysis demonstrated an average amount of bone in the distraction gap of 50% and 61% after instillation of BMP-2 and 7, respectively. The BMP-2 expression, however, was maximal after induction with the non-viral vector. Only after BMP-2/7 application could physical, radiographic and histological evidence of bone union be detected. In bone distraction with a short observation period the application of morphogenetic proteins seems to enhance bone regeneration significantly. Before application in humans further studies are necessary to measure the dose-effect relationship, the mode of application and the efficacy of different inductive proteins. The combination of osteodistraction with osteoinduction, however, could shorten treatment times dramatically.

Ultrasound enhances recombinant human BMP-2 induced ectopic bone formation in a rat model

Two methods to improve bone repair include the use of recombinant human bone morphogenetic protein-2 (rhBMP-2) and low-intensity pulsed ultrasound (LIPUS). The present study was designed to determine if LIPUS enhances the effect of rhBMP-2-induced bone formation in a well characterized ectopic implant model. Absorbable collagen sponges loaded with 0-, 1-, 2.5- or 5-microg doses of rhBMP-2 were implanted subcutaneously in 11-week-old, male Long Evans rats, followed by daily 20-min LIPUS or sham LIPUS treatment beginning 1 d after surgery. Explanted sponges were assessed for bone volume, mineral density and mineral content by microcomputed tomography (microCT). At two weeks, LIPUS had no effect on rhBMP-2-induced bone formation, but at four weeks, LIPUS increased bone volume in the 1-microg rhBMP-2-treated implants 117.7-fold (0.02 +/- 0.04 mm(3)vs. 2.07(S.E.M.) +/- 1.67 mm(3);p = 0.028), and 2.3-fold in the 5-microg dose implants (5.96 +/- 3.68 mm(3)vs. 13.52 +/- 6.81 mm(3);p = 0.077) compared with sham LIPUS. Bone mineral density was not affected by LIPUS treatment. Total mineral content followed the same pattern as bone volume. Histologic staining for mineralized tissue was consistent with the microCT observations. The present study is the first to demonstrate that LIPUS enhances bone formation induced by rhBMP-2.

Gene expression profile on chitosan/rhBMP-2 films: A novel osteoinductive coating for implantable materials

This study focusses on the gene expression profile related to a new rhBMP-2 carrier material, chitosan film. This film could be suitable for use as an osteoinductive coating of commercially available titanium implants. The developed material was characterized, biocompatibility was tested and the cellular response was extensively characterized by transcriptional expression studies. Finally, in vivo studies were carried out to confirm the osteoinductivity of the developed coating. Results show good material properties for cell adhesion and proliferation. Presented data show cellular differentiation to the osteoblastic phenotype due to rhBMP-2, with a 90% common transcriptional response between the control rhBMP-2 treatment and the developed chitosan/rhBMP-2 film. The growing surface also had an influence on the observed cellular response and was quantified as 7% of the total. These results indicate that both the growth factor and the material induce a cell response, but this is mainly driven by the osteoinductor factor. In vivo, new bone formation and early vascularization was observed around chitosan/rhBMP-2 coated titanium pieces implanted in mouse muscle. In contrast, control implants did not induce this reaction. This work, therefore, shows both in vitro and in vivo that chitosan/rhBMP-2 film is a promising osteoinductive coating for titanium implantable materials.

Widespread and early tracheal cartilage regeneration by synchronous slow release of b-FGF and BMP-2

Our previous studies have demonstrated that slow release of basic fibroblast growth factor (b-FGF) or bone morphogenetic protein 2 (BMP-2) induces cartilage regeneration. In the present study, we investigated whether synchronous slow release of b-FGF and BMP-2 would induce more widespread and earlier cartilage regeneration than that induced by each growth factor alone. A 1-cm defect was made in the mid-ventral portion of each of 10 consecutive tracheal rings. In four controls, the defect was left untreated. In the gelatin group (n = 4), empty gelatin sponge was implanted. In the b-FGF + BMP-2 group (n = 5), two gelatin sponges containing 100 microg of b-FGF or BMP-2 solution were implanted. After various periods, we euthanatized the dogs, and examined the implant sites. In the b-FGF + BMP-2 group, regenerated fibrous cartilage connected the host cartilage stumps and completely filled the defect between them at 1, 2, 3, and 12 months. Regenerated cartilage was covered by regenerated perichondrium originating from the host perichondrium, and showed neovascularization in the extracellular matrix. We succeeded in inducing more widespread and earlier cartilage regeneration using synchronous slow release of b-FGF and BMP-2 than that induced by release of each growth factor alone.

Preparation of collagen/gelatin sponge scaffold for sustained release of bFGF

Artificial dermis (AD) has been used to regenerate dermis-like tissues in the treatment of full-thickness skin defects, but it takes 2 or 3 weeks to complete dermal regeneration. Our previous study demonstrated that injection of basic fibroblast growth factor (bFGF)-impregnated gelatin microspheres (MS) into the AD accelerates the regeneration of dermis-like tissue. However, injection of gelatin MS before clinical use is complicated and time consuming. This study investigated a new scaffold, in which collagen and gelatin are integrated, and which is capable of sustained bFGF release. We produced collagen/gelatin sponges with a gelatin concentration of 0wt%, 10wt%, 30wt%, and 50wt%. The mean pore size in each sponge decreased with the gelatin concentration. In an in vitro study, proliferation of fibroblasts in each sponge was not significantly different over 7 days of culture. As for in vivo sustained release of bFGF, a radioisotope study demonstrated that retention of bFGF in gelatin 10wt% and 30wt% sponges was significantly larger than that in gelatin 0wt% sponge. The collagen/gelatin sponges were grafted on full-thickness skin defects created on a rabbit ear, and we evaluated regeneration of dermis-like tissue by measuring the amount of hemoglobin and size of dermis-like tissue on histological sections. Seven days after implantation, the amount of hemoglobin in dermis-like tissue in gelatin 10wt% sponge was significantly larger than those in control and gelatin 50wt% sponge. Twenty-eight days after implantation, the area of dermis-like tissue in gelatin 10wt% sponge was significantly larger than those in the other specimens. We conclude that the collagen sponge integrated with 10wt% gelatin has the most potential for sustained release of bFGF and that the combination of collagen/gelatin 10wt% sponge and bFGF is a promising therapeutic modality for the treatment of full-thickness skin defects.

Tracheal cartilage regeneration and new bone formation by slow release of bone morphogenetic protein (BMP)-2

We investigated the efficiency of bone morphogenetic protein (BMP)-2 released slowly from gelatin sponge for tracheal cartilage regeneration. A 1-cm gap was made in the mid-ventral portion of each of 10 consecutive tracheal cartilages. In the control group (n = 4), the resulting gap was left untreated. In the gelatin group (n = 4), plain gelatin was implanted in the gap. In the BMP-2 group (n = 4), gelatin containing 100 microg BMP-2 was implanted. We euthanatized all dogs in each group at 1, 3, 6, and 12 months after the implantation, respectively, and then examined the implant site macro- and microscopically. In the BMP-2 group, regenerated fibrous cartilage and newly formed bone were observed at 1 and 12 months. Regenerated cartilage was observed at the ends of the host cartilage stumps, with newly formed bone in the middle portion. The gaps were filled with regenerated cartilage and newly formed bone. At 3 and 6 months, regenerated cartilage, but not newly formed bone, was evident. The regenerated cartilage was covered with perichondrium and showed continuity with the host cartilage. We succeeded in inducing cartilage regeneration and new bone formation in canine trachea by slow release of 100 microg BMP-2 from gelatin.

Use of bone morphogenetic proteins for augmentation of bone regeneration

A large body of preclinical and clinical data now documents that recombinant BMPs can be used for skeletal regeneration in humans and animals. Recombinant human BMP-2 and BMP-7 have been approved for use in human patients with long-bone fractures and nonunions and in patients undergoing lumbar fusion or various maxillofacial and dental regenerative procedures. These products have also been made available for veterinary use.

Mesenchymal stem cell-mediated gene delivery of bone morphogenetic protein-2 in an articular fracture model

In articular fractures, both bone and cartilage are injured. We tested whether stem cells transduced with bone morphogenetic protein 2 (BMP2) can promote bone and cartilage repair. Distal femoral articular osteotomies in nude rats were treated with stem cells, either wild-type or transduced with an adenoviral (Ad) BMP2. Cells were delivered in alginate (ALG) carrier or by direct injection in saline solution. Gene expression of these cells at the osteotomy site was confirmed by in vivo imaging. At day 14, only the group that received AdBMP2 stem cells by direct injection showed completely healed osteotomies, while other groups remained unhealed (P < 0.0003). In ALG groups, bone healing was impeded by the development of a chondroid mass, most pronounced in the AdBMP2 ALG group (P < 0.002). We were successful in achieving repair of both bone and cartilage in vivousing direct stem cell injection. Our data suggests that BMP2 augmentation might be critically important in achieving this effect.

BMP-2 Dose-Response and Release Studies in Functionally Graded HAp

Hydroxyapatite (HAp) has been used as a biomaterial for hard tissues. Critical characteristics of biomaterials will include surface geometry, hydrophobicity and hydrophilicity, crystallinity, biodegradation rates, and release pharmacokinetics (PK) of incorporated molecules such as BMP-2. Optimizing BMP-2 for clinical application may be dependent on localized sustained release from biomaterials. We forcused on in vivo local BMP-2 PK and bone induction in two ceramics systems, based on different surface structures. The functionally graded apatites (fg-HAp) was designed by the step-wise calcinations and partial dissolution-precipitation methods. We estimated the in vivo release profile of 125I-labeled BMP-2 from fg-HAp and the dose response of bone induction by BMP-2 in the back subcutis histologically. Bulk-HAp (b-HAp) by only the step-wise calcinations was prepared as a control. The amount of BMP-2 remaining in the fg-HAp at 1 day after implantation was 83.8%, while that was 34.6% in the b-HAp. Moreover, ectopic bone formation were found surely in the fg-HAp/BMP-2 (0.5μg) system at 3 weeks, not in the b-HAp/BMP-2 system. By using fg-HAp, it is likely that an extremely low dose of BMP-2 is enough to enhance bone induction if BMP-2 is appropriately delivered to the site of action.

Human BMP-2 gene transfer using transcutaneous in vivo electroporation induced both intramembranous and endochondral ossification

It has been generally accepted that bone morphogenetic protein-2 (BMP-2) can induce osteogenesis in skeletal muscles via endochondral ossification. However, it is not clear how the ossification process occurs after the BMP-2 gene transfer to skeletal muscles in rats using in vivo electroporation. In this study, we evaluated the ossification process by BMP-2 gene transfer using in vivo electroporation. The gastrocnemius muscles of Wistar rats were injected with human BMP-2 gene expression vector (pCAGGS-BMP-2), followed by electroporation under the condition of 100 V, 50 msec per 1 sec, x8. Light and electron microscopic and radiographic analyses were performed at 1, 3, 5, 7, and 10 days after treatment. At 7 days, no sign of cartilage and/or bone formation was detected. However, at 10 days after in vivo electroporation, soft X-ray analysis revealed small lucent areas around the plasmid-injected region. Clusters of both cartilage tissues, leading to endochondral ossification and intramembranous bones of various sizes, were observed between muscle fibers. RT-PCR detected osteocalcin mRNA, showing bone formation at 10 days. Our findings strongly suggest that BMP-2 gene transfer using in vivo electroporation induces not only endochondral ossification but also intramembranous ossification.

Preparation of poly(ethylene glycol)-introduced cationized gelatin as a non-viral gene carrier

The objective of this study was to prepare cationized gelatins grafted with poly(ethylene glycol) (PEG) (PEG-cationized gelatin) and evaluate the in vivo efficiency as a non-viral gene carrier. Cationized gelatin was prepared by chemical introduction of ethylenediamine to the carboxyl groups of gelatin. PEG with one terminal of active ester group was coupled to the amino groups of cationized gelatin to prepare PEG-cationized gelatins. Electrophoretic experiments revealed that the PEG-cationized gelatin with low PEGylation degrees was complexed with a plasmid DNA of luciferase, in remarked contrast to that with high PEGylation degrees. When the plasmid DNA complexed with the cationized gelatin or PEG-cationized gelatin was mixed with deoxyribonuclease I (DNase I) in solution to evaluate the resistance to enzymatic degradation, stronger protection effect of the PEG-cationized gelatin was observed than that of the cationized gelatin. The complex of plasmid DNA and PEG-cationized gelatin had an apparent molecular size of about 300 nm and almost zero surface charge. These findings indicate that the PEG-cationized gelatin-plasmid DNA complex has a nano-order structure where the plasmid DNA is covered with PEG molecules. When the PEG-cationized gelatin-plasmid DNA complex was intramuscularly injected, the level of gene expression was significantly increased compared with the injection of plasmid DNA solution. It is concluded that the PEG-cationized gelatin was a promising non-viral gene carrier to enhance gene expression in vivo.

Preparation and biological characteristics of recombinant human bone morphogenetic protein-2-loaded dextran-co-gelatin hydrogel microspheres, in vitro and in vivo studies

Hydrogels are based on hydrophilic polymers which are cross-linked to prevent dissolution in water. Because hydrogels can contain large amounts of water, they are interesting devices for the delivery of protein drugs. In this contribution, biodegradable dextran-co-gelatin hydrogel microspheres (DG-MPs) are described which are based on physical interactions and are particularly suitable for the controlled delivery of pharmaceutically active proteins. The unique feature of this preparation system is that the hydrogel microsphere formation takes place in an all-aqueous solution, by which the use of organic solvents is avoided. We investigated the preparation and biological activities of recombinant human bone morphogenetic protein-2 (rhBMP2)-loaded dextran-co-gelatin hydrogel microspheres (rhBMP2-DG-MPs), which aimed to keep rhBMP2's biological activity and to achieve a long-term sustained release of rhBMP2. The microspheres' average diameter was about 20-40 microm and rhBMP2 release in vitro could be maintained for >10 days. Cytology studies showed that using rhBMP2-DG-MPs could promote the proliferation and osteoblastic differentiation of periodontal ligament cells better than using rhBMP2 aqueous solution. By a freeze-drying method, rhBMP2-DG-MPs could be adhered in chitosan membranes for guided tissue regeneration use, namely functionalized membranes. To evaluate bone regeneration induced by rhBMP2-DG-MPs, an animal experiment with canine class III furcation defects was adopted and the results indicated that using rhBMP2-DG-MPs incorporating scaffolds and functionalized membranes could gain more periodontal tissue regeneration than using scaffolds and general membranes soaked with concentrated rhBMP2 aqueous solution. Therefore, those studies demonstrate the potential of DG-MPs in the sustained delivery of low dosages of rhBMP2 to periodontal defects.

Bone marrow stem cells and biological scaffold for bone repair in aging and disease

The loss of bone mass observed in aging enhances the risk of fractures. The process of bone repair in aging is slow and limited due to reduced activity of the osteoblasts. Bone marrow stem cells (MSCs) residing in the bone marrow are the progenitors for osteoblasts. The ability to enhance healing of bone defect in aging by MSCs can contribute in the prevention of the complications resulting from long-term immobilization that are especially fatal in old age. Our aim was to test the ability of MSCs inserted into a biological scaffold to enhance bone defect repair. Osteoprogenitor cells were selected from rat bone marrow stem cells cultured in DMEM medium supplemented with FCS, antibiotics, ascorbic acid, beta-glycerophosphate, and dexamethasone. The selected osteogenic subpopulation was identified by osteocalcin immunohistochemistry as well as Alizarin red S and von Kossa staining which are specific for bone matrix and mineral deposition. Committed osteoprogenitor cells cultured on the hydrogel scaffold were transplanted into the area of a rat tibia segmental bone defect and examined after 6 weeks. Radiology images revealed that 6 weeks post-implantaion, calcified material was present in the site of the defect, indicating new bone formation. It is concluded that committed osteogenic MSCs contained in a biocompatible scaffold can provide a promising surgical tool for enhancement of bone defect healing that will minimize the complications of bone repair in aging and disease.

The therapeutic effects of basic fibroblast growth factor contained in gelatin hydrogel microspheres on experimental osteoarthritis in the rabbit knee

OBJECTIVE

To investigate the therapeutic effects of basic fibroblast growth factor (bFGF) contained in gelatin hydrogel microspheres on osteoarthritis (OA) development in rabbit knee joints.

METHODS

(125)I-labeled bFGF contained in gelatin hydrogel microspheres was administered to the knee joints of normal rabbits to confirm the sustained-release kinetics of bFGF in the knee joint. In addition, the expression of proteoglycan core protein messenger RNA was examined using real-time polymerase chain reaction to confirm the anabolic effects on the cartilage treated with the sustained release of bFGF. The bFGF in gelatin hydrogel microspheres was administered to the knee joint once every 3 weeks (a total of twice) from 4 weeks after anterior cruciate ligament transection (ACLT). Ten weeks after ACLT, gross morphologic and histologic examinations were performed.

RESULTS

Sustained release of bFGF in the knee joint continued for >7 days and induced the anabolic effects on the cartilage. Intraarticular injections of bFGF contained in gelatin hydrogel microspheres suppressed the progression of OA in the ACLT rabbit model.

CONCLUSION

Our findings demonstrated that sustained release of bFGF into the joint had therapeutic effects on OA development in a rabbit model. Our results suggest the potential feasibility of a new conservative treatment for OA.

Bone defect repair in rat tibia by TGF-β1 and IGF-1 released from hydrogel scaffold

Bone repair is one of the major challenges facing reconstructive surgery. Bone regeneration is needed for the repair of large defects and fractures. The ability of TGF-beta1 and IGF-1 incorporated into hydrogel scaffold to induce bone regeneration was evaluated in a rat tibia segmental defect model. External fixation was performed prior to the induction of the segmental bone defect in order to stabilize the defect site. Hydrogel scaffold containing either TGF-beta, IGF-1, TGF-beta + IGF-1, hydrogel containing saline or saline, were inserted in the defect. Calcified material was observed in the defects treated with TGF-beta 2 weeks following the start of treatment. Bone defects treated with TGF-beta, IGF-1 or TGF-beta + IGF-1 revealed significant bone formation after 4 and 6 weeks when compared to the control specimens. X-ray images showed that solid bone was present at the defect site after 6 weeks of treatment with TGF-beta or TGF-beta + IGF-1. A less pronounced bone induction was observed in the control specimens and bones treated with IGF-1. Percent closure ratio of bone defects after 6 weeks were 40, 80, 89, and 97% for saline, hydrogel, IGF-1, TGF-beta and IGF-1 + TGF-beta groups, respectively. It is concluded that hydrogel scaffold can serve as a good osteoconductive matrix for growth factors, and that it provides a site for bone regeneration and enhances bone defect healing and could be used as alternative graft material.

Effect of Culture Substrates and Fibroblast Growth Factor Addition on the Proliferation and Differentiation of Rat Bone Marrow Stromal Cells

This study is an investigation of the proliferation and differentiation of bone marrow stromal cells (BMSCs) on film substrates with different surface properties. Films of noncharged polymers with several water wettabilities; cell culture plates coated with collagen type I or IV, gelatin, or basic fibroblast growth factor (bFGF); and glass were used. BMSCs isolated from rat bone marrow were cultured on the various substrates in medium with dexamethasone [Dex(+)] or without dexamethasone [Dex(-)] to assess cell proliferation and differentiation. The number of proliferated BMSCs depended on the water wettability of substrates, although the cell number was greater in Dex(-) medium than in Dex(+) medium. Protein-coated substrates exhibited a high proliferation rate compared with noncoated substrates. Alkaline phosphatase (ALP) activity increased with increasing cell number, whereas ALP activity per cell correlated well with cell number. When cultured in Dex(+) medium containing bFGF or on culture plates coated with bFGF, BMSC proliferation tended toward enhancement with an increase in the amount of bFGF added in solution form, whereas it did not depend on the amount of bFGF in coated form. On the other hand, ALP activity and calcium content of BMSCs became maximal with bFGF coated at about 1 x 10(3) to 2 x 10(3) ng, in contrast to bFGF in solution form. Irrespective of the amount of bFGF, ALP activity and calcium content levels for bFGF in coated form were higher than for bFGF in solution form. It is concluded that the type of culture substrate and the manner of addition of bFGF affect the proliferation and differentiation of BMSCs.

Local and controlled release of growth factors (combination of IGF-I and TGF-beta I, and BMP-2 alone) from a polylactide coating of titanium implants does not lead to ectopic bone formation in sheep muscle

The osteoinductive potential of growth factors leads not only to a stimulated bone formation in bony tissue but also in extra skeletal tissue. This potential depends on the dosage and potentially on the application method and may limit the clinical use. The aim of the present study was to investigate the potential of IGF-I, TGF-beta1 and BMP-2 released from a newly developed application systems of orthopaedic implants to induce ectopic bone formation in muscles. This bioactive coating showed a stimulating effect on fracture healing in several experimental studies before. Titanium discs were coated on one side with the drug carrier poly(d,l-lactide) (PDLLA), with the carrier plus IGF-I and TGF-beta1 or with the carrier plus BMP-2. The discs were implanted in the Musculus cleidomastoideus of sheep and followed up for 3 months. X-rays were taken after the operation and the day of sacrifice. The muscles plus implant were harvested and prepared for histology. Neither the radiology nor the histology revealed any signs of ectopic ossification in the implant/muscle interface or in a distance to the plate in any group. An influence of the locally applied growth factor, however, was seen in the formation of a soft tissue capsule. Histomorphometric analysis revealed a significantly larger capsule area over the growth factor coated side in comparison to the uncoated side or the pure titanium plate, indicating an effect of the applied growth factors on cells, however, not resulting in osteoinduction in muscle. The result showed that the local and controlled release of growth factors from PDLLA coated implants does not induce ectopic bone formation in sheep muscle and could be used in orthopaedic surgery to increase healing without the risk of ectopic bone formation in the surrounding soft tissue.

Slow release of bone morphogenetic protein 2 from a gelatin sponge to promote regeneration of tracheal cartilage in a canine model

OBJECTIVES

We investigated whether bone morphogenetic protein 2, released slowly from a gelatin sponge, could induce cartilage regeneration in a canine model of tracheomalacia and evaluated the long-term results.

METHODS

A 1 x 5-cm gap was made in the anterior cervical trachea by removing 5-cm long strips of 10 sequential cartilagines. In the control group (n = 5), the gaps were left untreated. In the gelatin sponge group (n = 5), a gelatin sponge soaked in a buffer solution was implanted in each defect. In the bone morphogenetic protein group (n = 5), a gelatin sponge soaked in a buffer solution containing 12 microg bone morphogenetic protein 2 was implanted in each defect.

RESULTS

Tracheomalacia was observed in the control and gelatin sponge groups but not in the bone morphogenetic protein group. No regenerated cartilage was detected in the control or gelatin sponge groups, even 6 months after surgery. In contrast, regenerated cartilage, which had developed from the host perichondrium, was observed around the stumps of the resected cartilagines in the bone morphogenetic protein group. This regenerated cartilage maintained the integrity of the internal lumen for longer than 6 months. A compressive fracture test revealed that the tracheal cartilage in the bone morphogenetic protein group was significantly more stable than that in the gelatin sponge and control groups (P =.0015 and P =.0001, respectively).

CONCLUSIONS

In this canine model of tracheomalacia, cartilage regeneration was induced around the stumps of tracheal cartilagines by bone morphogenetic protein 2 released slowly from a gelatin sponge. This regenerated cartilage was not reabsorbed for longer than 6 months and was strong enough to maintain the integrity of the internal lumen of the trachea.

Carrier dependent cell differentiation of bone morphogenetic protein-2 induced osteogenesis and chondrogenesis during the early implantation stage in rats

To evaluate the osteoinductive effects of recombinant human bone morphogenetic protein (rhBMP)-2 during the early stages of rat ectopic bone formation, we prepared two distinct carriers. Two carriers, insoluble bone matrix (IBM) and fibrous glass membrane (FGM) were combined with rhBMP-2 and implanted into the backs of rats to evaluate the osteoinductive effects of the two rhBMP-2 carrier systems. Insoluble bone matrix particle size was 320 to 620 microm. Fibrous glass membrane was constructed from unwoven glass fibers 1 microm in diameter. Alkaline phosphatase (ALP) activity and type II collagen were detected in IBM/rhBMP-2 at 5 days postimplantation. Calcium (Ca) was also detected in IBM/rhBMP-2 at 7 and 9 days postimplantation. In contrast, ALP and type II collagen were detected in FGM/rhBMP-2 at 7 days. Calcium was undetected, indicating that the bone formation in IBM/rhBMP-2 proceeded faster than in FGM/rhBMP-2 during the early stage of BMP-induced osteogenesis. In addition, mRNA expression level of KDR, a receptor for vascular endothelial growth factor, was also increased in IBM/rhBMP-2. To investigate the in vivo release profile of rhBMP-2, iodine 125 ((125)I)-labeled BMP-2-incorporating IBM and FGM implants were inserted into the back subcutis of mice. More than 60% of the rhBMP-2 was released from the IBM/rhBMP-2 carrier within 1 day after implantation, whereas 50% of the rhBMP-2 was released from the FGM/rhBMP-2 10 days postimplantation. These results indicated that osteo- and chondrogenesis depends highly upon the geometry of the carrier and the in situ retention of rhBMP-2 during the early stage of rhBMP-2 induced bone formation.

A trial on regeneration therapy of rat liver cirrhosis by controlled release of hepatocyte growth factor

This paper is an investigation of therapeutic trial on the liver cirrhosis by the controlled release of hepatocyte growth factor (HGF). Biodegradable microspheres were prepared from gelatin for the controlled release of HGF. Rats with liver cirrhosis were prepared by the intraperitoneal injection of thioacetamide at a dose of 0.2 g/kg every other day for 10 weeks. The rats received single intraperitoneal injection of gelatin microspheres incorporating 2 or 0.4 mg of HGF, 2 or 0.4 mg of free HGF, and HGF-free, empty gelatin microspheres 3 weeks after the last thioacetamide injection. Histological observation of the rat liver revealed that injection of gelatin microspheres incorporating HGF effectively allowed to recovery from the liver fibrosis, inducing liver regeneration. When the histological score, the area of fibrous linkage, and the hydroxyproline content in the liver were evaluated, all values were significantly smaller than those of the free HGF and empty gelatin microspheres injection, irrespective of the HGF dose. It is concluded that the gelatin microspheres incorporating HGF are a promising therapeutic method of inducing successful liver regeneration by fibrosis digestion in rats with cirrhosis.

A novel method to obtain protein release from porous polymer scaffolds: emulsion coating

To obtain the controlled release of proteins from macro-porous polymeric scaffolds, a novel emulsion-coating method has been developed. In this process, a water-in-oil emulsion, from an aqueous protein solution and a polymer solution, is forced through a prefabricated scaffold by applying a vacuum. After solvent evaporation, a polymer film, containing the protein, is then deposited on the porous scaffold surface. This paper reports the effect of processing parameters on the emulsion coating characteristics, scaffold structure, and protein release and stability. Poly(ether-ester) multiblock copolymers were chosen as the polymer matrix for both scaffolds and coating. Macro-porous scaffolds, with a porosity of 77 vol% and pores of approximately 500 microm were prepared by compression moulding/salt leaching. A micro-porous, homogeneous protein-loaded coating could be obtained on the scaffold surface. Due to the coating, the scaffold porosity was decreased, whereas the pore interconnection was increased. A model protein (lysozyme) could effectively be released in a controlled fashion from the scaffolds. Complete lysozyme release could be achieved within 3 days up to more than 2 months by adjusting the coated emulsion parameters. In addition, the coating process did not reduce the enzymatic activity. This new method appears to be promising for tissue engineering applications.

Cartilage regeneration using slow release of bone morphogenetic protein-2 from a gelatin sponge to treat experimental canine tracheomalacia: a preliminary report

We investigated whether saber sheath-type tracheomalacia could be treated by the slow release of bone morphogenetic protein (BMP)-2 from a gelatin sponge. A 1 cm gap was made in the middle portion of each of 10 consecutive tracheal cartilage rings in the canine cervix (control group, n = 3), then a gelatin sponge containing 12 microg of BMP-2 solution was implanted in the gap (12 microg group, n = 3). In another group (120 microg + P group, n = 3), the implanted gelatin sponge contained 120 microg of BMP-2 solution, and the gap was covered with periosteum. All of the control dogs developed saber sheath-type tracheomalacia, whereas tracheomalacia was not observed in the 12 microg and 120 microg + P groups. In the 12 microg group, fibrous cartilage was observed at the ends of the cartilage stumps. In the 120 microg + P group, newly formed bone and cartilage were observed to form a bridge between the cartilage stumps. The regeneration of cartilage or bone induced by the slow release of BMP-2 from a gelatin sponge might be useful for treatment of tracheomalacia.