Acceleration of bone union after structural bone grafts with a collagen-binding basic fibroblast growth factor anchored-collagen sheet for critical-size bone defects

Preparation of Collagen/Hydroxyapatite Composites Using the Alternate Immersion Method and Evaluation of the Cranial Bone-Forming Capability of Composites Complexed with Acidic Gelatin and b-FGF

Bone-substitute materials are essential in dental implantology. We prepared collagen (Col)/hydroxyapatite (Hap)/acidic gelatin (AG)/basic fibroblast growth factor (b-FGF) constructs with enhanced bone-forming capability. The Col/Hap apatite composites were prepared by immersing Col sponges alternately in calcium and phosphate ion solutions five times, for 20 and 60 min, respectively. Then, the sponges were heated to 56 °C for 48 h. Scanning electron microscopy/energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analyses showed that the Col/Hap composites contained poorly crystalline Hap precipitates on the Col matrix. Col/Hap composite granules were infiltrated by AG, freeze-dried, and immersed in b-FGF solution. The wet quaternary constructs were implanted in rat cranial bone defects for 8 weeks, followed by soft X-ray measurements and histological analysis. Animal studies have shown that the constructs moderately increase bone formation in cranial bone defects. We found that an alternate immersion time of 20 min led to the greatest bone formation (p < 0.05). Constructs placed inside defects slightly extend the preexisting bone from the defect edges and lead to the formation of small island-like bones inside the defect, followed by disappearance of the constructs. The combined use of Col, Hap, AG, and b-FGF might bring about novel bone-forming biomaterials.

Acceleration of Bone Healing by In Situ-Forming Dextran-Tyramine Conjugates Containing Basic Fibroblast Growth Factor in Mice

An enzymatic crosslinking strategy using hydrogen peroxide (H₂O₂) and horseradish peroxidase (HRP) has been receiving increasing attention for use with in situ-formed hydrogels (IFHs). Several studies have reported the application of IFHs in cell delivery and tissue engineering. IFHs may also be ideal carrier materials for bone repair, although their potential as a carrier for basic fibroblast growth factor (bFGF) has yet to be evaluated. Here, we examined the effect of an IFH made of dextran (Dex)-tyramine (TA) conjugates (IFH-Dex-TA) containing bFGF in promoting bone formation in a fracture model in mice. Immediately following a fracture procedure, animals either received no treatment (control) or an injection of IFH-Dex-TA/phosphate-buffered saline (IFH-Dex-TA/PBS) or IFH-Dex-TA containing 1 μg bFGF (IFH-Dex-TA/bFGF) into the fracture site (n=10, each treatment). Fracture sites injected with IFH-Dex-TA/bFGF showed significantly greater bone volume, mineral content, and bone union than sites receiving no treatment or treated with IFH-Dex-TA/PBS alone (each n=10). This Dex-TA gel may be an effective drug delivery system for optimizing bFGF therapy.

Polyglycolic acid-collagen tube combined with collagen-binding basic fibroblast growth factor accelerates gait recovery in a rat sciatic nerve critical-size defect model

Several nerve conduits have been investigated for their potential as alternative sources of autografts for bridging neural gaps. However, autologous nerve transplants remain the most effective for nerve repair. We examined clinically approved nerve conduits containing collagen and polyglycolic acid (PGA-c) combined with collagen-binding basic fibroblast growth factor (bFGF) containing a polycystic kidney disease (PKD) domain and collagen binding domain (CBD) (bFGF-PKD-CBD) in a rat 15-mm sciatic nerve critical-size defect model. The treatment groups were: PGA-c immersed in phosphate-buffered saline (PBS) (PGA-c/PBS group), bFGF (PGA-c/bFGF group), or bFGF-PKD-CBD (PGA-c/bFGF-PKD-CBD group), and no treatment (Defect group). Gait and histological analyses were performed. Four weeks after treatment, the recovery rate of the paw print area was significantly greater in the PGA-c/bFGFPKD-CBD group than the PGA-c/PBS and PGA-c/bFGF groups. Mean intensity of paw prints was significantly greater in the PGA-c/bFGF-PKD-CBD group than the PGA-c/PBS and Defect groups. Swing time was significantly greater in the PGA-c/PBS, PGA-c/bFGF, and PGA-c/bFGF-PKD-CBD groups than the Defect group. At 8 weeks, all three parameters were significantly greater in the PGA-c/PBS, PGA-c/bFGF, and PGA-c/bFGF-PKD-CBD groups than the Defect group. Regenerated myelinated fibers were observed in 7/8 (87.5%) rats in the PGA-c/bFGF-PKD-CBD group after 8 weeks, and in 1/8 (12.5%) and 3/8 (37.5%) rats in the PGA-c/PBS and PGA-c/bFGF groups, respectively. PGA-c/bFGF-PKD-CBD composites may be promising biomaterials for promoting functional recovery of long-distance peripheral nerve defects in clinical practice.

Ectopic osteogenesis effect of antigen-extracted xenogeneic cancellous bone graft with chitosan/rhBMP-2/bFGF sequential sustained-release nanocapsules

To explore the ectopic osteogenesis effect of sequential sustained release application of recombinant human bone morphogenic protein-2 (rhBMP-2) and basic fibroblast growth factor (bFGF). Antigen-extracted xenogeneic cancellous bone coupled with growth factor-loaded chitosan nanocapsules were implanted in rats in intramuscular site in accordance with the following experimental pattern: group A: simultaneous burst release of rhBMP-2 and bFGF; group B: simultaneous sustained release of rhBMP-2 and bFGF; group C: preferential burst release of rhBMP-2, then sustained release of bFGF; group D: preferential burst release of bFGF, then sustained release of rhBMP-2; group E: sustained release of rhBMP-2 alone; group F: sustained release of bFGF alone, blank control group G: antigen-extracted xenogeneic cancellous bone graft only; negative control group H: not filled with anything. Specimens were obtained after executing the animals at 2 and 4 weeks for general observation and weighing, calcium content detection, micro-CT scanning and bone parameter measurement analysis, H&E staining, ALP staining and CD34 staining. The materials weight of A-2, B-2, C-2, A-4, B-4, C-4, D-4 and E-4 were significantly higher than that of preoperative materials ( P < 0.05). The concentration of calcium of group B-4 was the highest (414.7 ± 12.03 mg/dl). Micro-CT scanning and bone parameter measurement analysis showed that the values of bone mineral density and trabecular thickness of group A, B, D, E at 4 weeks were both higher than the ones at 2 weeks ( P < 0.05), and both the bone mineral density (367.52 ± 11.64 mg/cc) and the trabecular thickness (126.17 ± 11.36 μm) of group B-4 were the highest. H&E staining showed that a large region of calcified cartilage and haemopoietic tissues were newly formed, especially in group B-4. ALP staining and CD34 staining showed the most positive expression region in group B-4. Therefore, we conclude that simultaneous sustained release of rhBMP-2 and bFGF is the ideal way to release drug, and has better inducement of antigen-extracted xenogeneic cancellous bone graft.

Bone intramedullary reaming grafts the fracture site with CD146+ skeletal progenitors and downmodulates the inflammatory environment

INTRODUCTION

Femoral shaft fractures generally occur in young adults following a high-energy trauma and are prone to delayed union/non-union. Novel therapies to stimulate bone regeneration will have to mimic some of the aspects of the biology of fracture healing; however, which are these aspects is unclear. Locked intramedullary nailing is the current treatment of choice for the stabilisation of femur shaft fractures, and it is associated with accelerated healing and increased union rates. These benefits were partially attributed to the reaming procedure, which, regardless of significantly destroying the haematoma, stimulates the healing response. To better understand how reaming influences healing, we evaluated the viability of the nucleated cell fraction and the frequency of CD146⁺ skeletal progenitors, which contain multipotent cells, in the post-reaming haematoma. We also screened the concentrations of inflammatory mediators and growth factors in the fracture site after reaming compared with those in the original haematoma.

METHODS

Pre- and post-reaming haematomas were percutaneously aspirated from the fracture site of 15 patients with closed femoral shaft fractures. Cellular viability and the percentage of CD146+ progenitors were analysed by flow cytometry. The concentrations of cytokines and growth factors were determined by ELISA.

RESULTS

AnnexinV/Pi analysis showed that the viability of the total nucleated cell fraction was decreased in the post-reaming haematoma. However, the procedure increased the percentage of CD146+ skeletal progenitors in the fracture site. Analysis of cytokines and growth factors in supernatants showed a decreased concentration of the inflammatory mediators IL-6, CCL-4, and MCP-1, along with an increase of anti-inflammatory IL-10, and the growth factors bFGF and PDGF-AB.

CONCLUSION

These findings support the view that the positive effects of reaming on fracture healing might result from mechanically grafting the fracture site with a population of skeletal progenitors that contain multipotent cells; transitioning the signalling environment to a less inflammatory state, and enhancing the availability of specific osteogenic and angiogenic factors. A better understanding of the requisite stimuli for optimal bone repair, considering the disturbances made by orthopaedic treatments, will be determinant for the development of innovative treatments for bone repair.

Basic Fibroblast Growth Factor-Anchored Multilayered Mesenchymal Cell Sheets Accelerate Periosteal Bone Formation

Cell-based regenerative therapy has the potential to repair bone injuries or large defects that are recalcitrant to conventional treatment methods, including drugs and surgery. Here, we developed a multilayered cell-based bone formation system using cells coated with fibronectin-gelatin (FN-G) nanofilms. The multilayered mesenchymal cells (MLMCs) were formed after two days of culture and were shown to express higher levels of BMP-2 and VEGF compared to monolayer cultures of MCs. The MLMCs were used as a graft material in combination with a fusion protein consisting of basic fibroblast growth factor (bFGF), polycystic kidney disease (PKD) domain, and the collagen-binding domain (CBD) of Clostridium histolyticum collagenase. In femur sites grafted with the MLMCs, significantly higher levels of callus volume and bone mineral content were observed compared to the sham controls. The callus volume and bone mineral content were further increased in femur sites grafted with bFGF-PKD-CBD/MLMCs. Taken together, these results suggest that bFGF-PKD-CBD/MLMCs, which can be simply and rapidly generated in vitro, have the potential to promote bone repair when grafted into large defect sites.

A highly versatile adaptor protein for the tethering of growth factors to gelatin-based biomaterials

In the field of tissue engineering, the tethering of growth factors to tissue scaffolds in an oriented manner can enhance their activity and increase their half-life. We chose to investigate the capture of the basic Fibroblast Growth Factor (bFGF) and the Epidermal Growth Factor (EGF) on a gelatin layer, as a model for the functionalization of collagen-based biomaterials. Our strategy relies on the use of two high affinity interactions, that is, the one between two distinct coil peptides as well as the one occurring between a collagen-binding domain (CBD) and gelatin. We expressed a chimeric protein to be used as an adaptor that comprises one of the coil peptides and a CBD derived from the human fibronectin. We proved that it has the ability to bind simultaneously to a gelatin substrate and to form a heterodimeric coiled-coil domain with recombinant growth factors being tagged with the complementary coil peptide. The tethering of the growth factors was characterized by ELISA and surface plasmon resonance-based biosensing. The bioactivity of the immobilized bFGF and EGF was evaluated by a human umbilical vein endothelial cell proliferation assay and a vascular smooth muscle cell survival assay. We found that the tethering of EGF preserved its mitogenic and anti-apoptotic activity. In the case of bFGF, when captured via our adaptor protein, changes in its natural mode of interaction with gelatin were observed.

STATEMENT OF SIGNIFICANCE

In an effort to functionalize collagen/gelatin-based biomaterials with growth factors, we have designed an adaptor protein corresponding to a collagen-binding domain fused to a coil peptide. In our strategy, this adaptor protein captures growth factors being tagged with the partner coil peptide in a specific, stable and oriented manner. We have found that the tethering of the Epidermal Growth Factor preserved its mitogenic and anti-apoptotic activity. In the case of the basic Fibroblast Growth Factor, the captured growth factor remained bioactive although its tethering via this adaptor protein modified its natural mode of interaction with gelatin. Altogether this strategy is easily adaptable to the simultaneous tethering of various growth factors.

Design and Use of Chimeric Proteins Containing a Collagen-Binding Domain for Wound Healing and Bone Regeneration

Collagen-based biomaterials are widely used in the field of tissue engineering; they can be loaded with biomolecules such as growth factors (GFs) to modulate the biological response of the host and thus improve its potential for regeneration. Recombinant chimeric GFs fused to a collagen-binding domain (CBD) have been reported to improve their bioavailability and the host response, especially when combined with an appropriate collagen-based biomaterial. This review first provides an extensive description of the various CBDs that have been fused to proteins, with a focus on the need for accurate characterization of their interaction with collagen. The second part of the review highlights the benefits of various CBD/GF fusion proteins that have been designed for wound healing and bone regeneration.