Experimental Study of Vascularized Tissue-Engineered Bone Grafts

The Combination of Platelet Rich Plasma Gel, Human Umbilical Mesenchymal Stem Cells and Nanohydroxyapatite/polyamide 66 Promotes Angiogenesis and Bone Regeneration in Large Bone Defect

BACKGROUND

In the present study, a novel tissue engineering bone graft including platelet rich plasma gel (PRP gel), human umbilical mesenchymal stem cells (HUMSCs) and nanohydroxyapatite/polyamide 66 (nHA-PA66) was constructed. We explored whether the composite scaffolds could enhance the angiogenesis and bone repair capacity in rat femoral large bone defect (LBD). This study aimed to provide evidence for the clinical application of the composite scaffold in LBD treatment.

METHODS

PRP was prepared, the platelets and growth factors were measured. HUMSCs were isolated and identified. the osteogenic capacity of PRP in vitro was measured. Then HUMSCs-PRP-gel/nHA-PA66 composite scaffolds were synthesized and observed. The proliferation and osteogenesis differentiation of HUMSCs on the composite scaffold was measured. The angiogenic capacity of PRP in vitro was measured by capillary-like tube formation assay. Finally, the angiogenesis and bone repair capacity of the composite scaffolds was measured in rat LBD.

RESULTS

PRP contained high level of platelets and growth factors after activation, and promoted osteogenic and angiogenic differentiation in vitro. The HUMSCs-PRP-gel/nHA-PA66 composite scaffold was porosity and promoted the proliferation and osteogenesis differentiation of HUMSCs. At 12th weeks, more micro-vessels and new bone were formed around the composite scaffolds compared with other groups, the defect was almost repaired.

CONCLUSION

Our study for the first time identified that the combination of PRP gel, HUMSCs and nHA-PA66 scaffold could significantly promote angiogenesis and bone regeneration in rat LBD, which may have implications for its further application in clinical LBD treatment.

Motivating role of type H vessels in bone regeneration

Coupling between angiogenesis and osteogenesis has an important role in both normal bone injury repair and successful application of tissue‐engineered bone for bone defect repair. Type H blood vessels are specialized microvascular components that are closely related to the speed of bone healing. Interactions between type H endothelial cells and osteoblasts, and high expression of CD31 and EMCN render the environment surrounding these blood vessels rich in factors conducive to osteogenesis and promote the coupling of angiogenesis and osteogenesis. Type H vessels are mainly distributed in the metaphysis of bone and densely surrounded by Runx2⁺ and Osterix⁺ osteoprogenitors. Several other factors, including hypoxia‐inducible factor‐1α, Notch, platelet‐derived growth factor type BB, and slit guidance ligand 3 are involved in the coupling of type H vessel formation and osteogenesis. In this review, we summarize the identification and distribution of type H vessels and describe the mechanism for type H vessel‐mediated modulation of osteogenesis. Type H vessels provide new insights for detection of the molecular and cellular mechanisms that underlie the crosstalk between angiogenesis and osteogenesis. As a result, more feasible therapeutic approaches for treatment of bone defects by targeting type H vessels may be applied in the future.

A unidirectional porous beta-tricalcium phosphate promotes angiogenesis in a vascularized pedicle rat model

BACKGROUND

Various types of artificial bone have been developed as alternatives to autologous bone grafts. In designing artificial bone, a porous structure is essential for the infiltration of blood and cells, which promotes angiogenesis within the bone matrix and ultimately ossification. However, it remains unclear what kind of pore system best promotes ossification. Here, we investigated angiogenesis in three different types of porous β-tricalcium phosphate (β-TCP) in a vascularized pedicle rat model.

METHODS

Three types of porous β-TCP-β-TCP60 (60% porosity), β-TCP75 (75% porosity), and unidirectional porous β-tricalcium phosphate (UDPTCP; 57% porosity)-were examined. A cylindrical piece of artificial bone was implanted beneath the superficial inferior epigastric (SIE) vessels in the groin of rats and angiogenesis was allowed to occur. Two weeks after surgery, India ink or lectin was systemically injected to detect newly formed blood vessels originating from the SIE vessels. Immunohistochemistry for von Willebrand factor, α-smooth muscle actin, or type IV collagen was performed to clarify the structural features of the newly formed capillaries within the vascularized UDPTCP.

RESULTS

The vascularity of the UDPTCP was superior to that of β-TCP60 and β-TCP75. The UDPTCP pore structure was completely filled with capillaries at 3 weeks after implantation. Immunohistochemistry showed that the walls of the capillaries contained endothelial cells, pericytes, and basement membrane originating from the SIE vessels, and that the cells proliferated and the basement membrane formed simultaneously as the newly formed capillaries extended through the unidirectional pore structure of the UDPTCP.

CONCLUSIONS

UDPTCP had greater angiogenic potential than β-TCP60 and β-TCP75 in a vascularized pedicle rat model. Vascularized UDPTCP grafts may be an alternative to vascularized autologous bone grafts.

Engineering tissue-specific blood vessels

Vascular diversity among organs has recently become widely recognized. Several studies using mouse and human fetal tissues revealed distinct characteristics of organ-specific vasculature in molecular and functional levels. Thorough understanding of vascular heterogeneities in human adult tissues is significant for developing novel strategies for targeted drug delivery and tissue regeneration. Recent advancements in microfabrication techniques, biomaterials, and differentiation protocols allowed for incorporation of microvasculature into engineered organs. Such vascularized organ models represent physiologically relevant platforms that may offer innovative tools for dissecting the effects of the organ microenvironment on vascular development and expand our present knowledge on organ-specific human vasculature. In this article, we provide an overview of the current structural and molecular evidence on microvascular diversity, bioengineering methods used to recapitulate the microenvironmental cues, and recent vascularized three-dimensional organ models from the perspective of tissue-specific vasculature.

Current advances for bone regeneration based on tissue engineering strategies

Bone tissue engineering (BTE) is a rapidly developing strategy for repairing critical-sized bone defects to address the unmet need for bone augmentation and skeletal repair. Effective therapies for bone regeneration primarily require the coordinated combination of innovative scaffolds, seed cells, and biological factors. However, current techniques in bone tissue engineering have not yet reached valid translation into clinical applications because of several limitations, such as weaker osteogenic differentiation, inadequate vascularization of scaffolds, and inefficient growth factor delivery. Therefore, further standardized protocols and innovative measures are required to overcome these shortcomings and facilitate the clinical application of these techniques to enhance bone regeneration. Given the deficiency of comprehensive studies in the development in BTE, our review systematically introduces the new types of biomimetic and bifunctional scaffolds. We describe the cell sources, biology of seed cells, growth factors, vascular development, and the interactions of relevant molecules. Furthermore, we discuss the challenges and perspectives that may propel the direction of future clinical delivery in bone regeneration.

Autologous platelet-rich plasma induces bone formation of tissue-engineered bone with bone marrow mesenchymal stem cells on beta-tricalcium phosphate ceramics

Background

The purpose of the study is to investigate whether autologous platelet-rich plasma (PRP) can serve as bone-inducing factors to provide osteoinduction and improve bone regeneration for tissue-engineered bones fabricated with bone marrow mesenchymal stem cells (MSCs) and beta-tricalcium phosphate (β-TCP) ceramics. The current study will give more insight into the contradictory osteogenic capacity of PRP.

Methods

The concentration of platelets, platelet-derived growth factor-AB (PDGF-AB), and transforming growth factor-β1 (TGF-β1) were measured in PRP and whole blood. Tissue-engineered bones using MSCs on β-TCP scaffolds in combination with autologous PRP were fabricated (PRP group). Controls were established without the use of autologous PRP (non-PRP group). In vitro, the proliferation and osteogenic differentiation of MSCs on fabricated constructs from six rabbits were evaluated with MTT assay, alkaline phosphatase (ALP) activity, and osteocalcin (OC) content measurement after 1, 7, and 14 days of culture. For in vivo study, the segmental defects of radial diaphyses of 12 rabbits from each group were repaired by fabricated constructs. Bone-forming capacity of the implanted constructs was determined by radiographic and histological analysis at 4 and 8 weeks postoperatively.

Results

PRP produced significantly higher concentration of platelets, PDGF-AB, and TGF-β1 than whole blood. In vitro study, MTT assay demonstrated that the MSCs in the presence of autologous PRP exhibited excellent proliferation at each time point. The results of osteogenic capacity detection showed significantly higher levels of synthesis of ALP and OC by the MSCs in combination with autologous PRP after 7 and 14 days of culture. In vivo study, radiographic observation showed that the PRP group produced significantly higher score than the non-PRP group at each time point. For histological evaluation, significantly higher volume of regenerated bone was found in the PRP group when compared with the non-PRP group at each time point.

Conclusions

Our study findings support the osteogenic capacity of autologous PRP. The results indicate that the use of autologous PRP is a simple and effective way to provide osteoinduction and improve bone regeneration for tissue-engineered bone reconstruction.

Biomimetic Approaches for Bone Tissue Engineering

Although autologous bone grafts are considered a gold standard for the treatment of bone defects, they are limited by donor site morbidities and geometric requirements. We propose that tissue engineering technology can overcome such limitations by recreating fully viable and biological bone grafts. Specifically, we will discuss the use of bone scaffolds and autologous cells with bioreactor culture systems as a tissue engineering paradigm to grow bone in vitro. We will also discuss emergent vascularization strategies to promote graft survival in vivo, as well as the role of inflammation during bone repair. Finally, we will highlight some recent advances and discuss new solutions to bone repair inspired by endochondral ossification.

Promotion of Osteogenesis and Angiogenesis in Vascularized Tissue-Engineered Bone Using Osteogenic Matrix Cell Sheets

BACKGROUND

The regeneration of large, poorly vascularized bone defects remains a significant challenge. Although vascularized bone grafts promote osteogenesis, the required tissue harvesting causes problematic donor-site morbidity. Artificial bone substitutes are promising alternatives for regenerative medicine applications, but the incorporation of suitable cells and/or growth factors is necessary for their successful clinical application. The inclusion of vascular bundles can further enhance the bone-forming capability of bone substitutes by promoting tissue neovascularization. Little is known about how neovascularization occurs and how new bone extends within vascularized tissue-engineered bone, because no previous studies have used tissue-engineered bone to treat large, poorly vascularized defects.

METHODS

In this study, the authors developed a novel vascularized tissue-engineered bone scaffold composed of osteogenic matrix cell sheets wrapped around vascular bundles within β-tricalcium phosphate ceramics.

RESULTS

Four weeks after subcutaneous transplantation in rats, making use of the femoral vascular bundle, vascularized tissue-engineered bone demonstrated more angiogenesis and higher osteogenic potential than the controls. After vascularized tissue-engineered bone implantation, abundant vascularization and new bone formation were observed radially from the vascular bundle, with increased mRNA expression of alkaline phosphatase, bone morphogenetic protein-2, osteocalcin, and vascular endothelial growth factor-A.

CONCLUSION

This novel method for preparing vascularized tissue-engineered bone scaffolds may promote the regeneration of large bone defects, particularly where vascularization has been compromised.

The study on vascularisation and osteogenesis of BMP/VEGF co-modified tissue engineering bone in vivo

To evaluate the osteogenic capacity of tissue engineering bone in vivo and compare the vascularization and osteogenesis between co- and single-modified tissue engineered bone.

Role of angiogenesis in bone repair

Bone vasculature plays a vital role in bone development, remodeling and homeostasis. New blood vessel formation is crucial during both primary bone development as well as fracture repair in adults. Both bone repair and bone remodeling involve the activation and complex interaction between angiogenic and osteogenic pathways. Interestingly studies have demonstrated that angiogenesis precedes the onset of osteogenesis. Indeed reduced or inadequate blood flow has been linked to impaired fracture healing and old age related low bone mass disorders such as osteoporosis. Similarly the slow penetration of host blood vessels in large engineered bone tissue grafts has been cited as one of the major hurdle still impeding current bone construction engineering strategies. This article reviews the current knowledge elaborating the importance of vascularization during bone healing and remodeling, and the current therapeutic strategies being adapted to promote and improve angiogenesis.

Different effects of implanting sensory nerve or blood vessel on the vascularization, neurotization, and osteogenesis of tissue-engineered bone in vivo

To compare the different effects of implanting sensory nerve tracts or blood vessel on the osteogenesis, vascularization, and neurotization of the tissue-engineered bone in vivo, we constructed the tissue engineered bone and implanted the sensory nerve tracts (group SN), blood vessel (group VB), or nothing (group Blank) to the side channel of the bone graft to repair the femur defect in the rabbit. Better osteogenesis was observed in groups SN and VB than in group Blank, and no significant difference was found between groups SN and VB at 4, 8, and 12 weeks postoperatively. The neuropeptides expression and the number of new blood vessels in the bone tissues were increased at 8 weeks and then decreased at 12 weeks in all groups and were highest in group VB and lowest in group Blank at all three time points. We conclude that implanting either blood vessel or sensory nerve tract into the tissue-engineered bone can significantly enhance both the vascularization and neurotization simultaneously to get a better osteogenesis effect than TEB alone, and the method of implanting blood vessel has a little better effect of vascularization and neurotization but almost the same osteogenesis effect as implanting sensory nerve.

Different angiogenic abilities of self-setting calcium phosphate cement scaffolds consisting of different proportions of fibrin glue

To investigate the different angiogenic abilities of the self-setting calcium phosphate cement (CPC) consisting of different proportions of fibrin glue (FG), the CPC powder and the FG solution were mixed at the powder/liquid (P/L) ratios of 1 : 0.5, 1 : 1, and 1 : 2 (g/mL), respectively, and pure CPC was used as a control. After being implanted into the lumbar dorsal fascia of the rabbit, the angiogenic process was evaluated by histological examination and CD31 immunohistochemistry to detect the new blood vessels. The result of the new blood vessel showed that the P/L ratio of 1 : 1 group indicated the largest quantity of new blood vessel at 4 weeks, 8 weeks, and 12 weeks after implantation, respectively. The histological evaluation also showed the best vascular morphology in the 1 : 1 group at 4 weeks, 8 weeks, and 12 weeks after the operation, respectively. Our study indicated that the CPC-FG composite scaffold at the P/L ratio of 1 : 1  (g/mL) stimulated angiopoiesis better than any other P/L ratios and has significant potential as the bioactive material for the treatment of bone defects.

Microsurgical techniques used to construct the vascularized and neurotized tissue engineered bone

The lack of vascularization in the tissue engineered bone results in poor survival and ossification. Tissue engineered bone can be wrapped in the soft tissue flaps which are rich in blood supply to complete the vascularization in vivo by microsurgical technique, and the surface of the bone graft can be invaded with new vascular network. The intrinsic vascularization can be induced via a blood vessel or an arteriovenous loop located centrally in the bone graft by microsurgical technique. The peripheral nerve especially peptidergic nerve has effect on the bone regeneration. The peptidergic nerve can be used to construct the neurotized tissue engineered bone by implanting the nerve fiber into the center of bone graft. Thus, constructing a highly vascularized and neurotized tissue engineered bone according with the theory of biomimetics has become a useful method for repairing the large bone defect. Many researchers have used the microsurgical techniques to enhance the vascularization and neurotization of tissue engineered bone and to get a better osteogenesis effect. This review aims to summarize the microsurgical techniques mostly used to construct the vascularized and neurotized tissue engineered bone.

Generation of osteogenic construct using periosteal-derived osteoblasts and polydioxanone/pluronic F127 scaffold with periosteal-derived CD146 positive endothelial-like cells

The purpose of this study was to generate tissue-engineered bone using human periosteal-derived osteoblasts (PO) and polydioxanone/pluronic F127 (PDO/pluronic F127) scaffold with preseeded human periosteal-derived CD146 positive endothelial-like cells (PE). PE were purified from the periosteal cell population by cell sorting. One of the important factors to consider in generating tissue-engineered bone using osteoprecursor and endothelial cells and a specific scaffold is whether the function of osteoprecursor and endothelial cells can be maintained in originally different culture medium conditions. After human PE were preseeded into PDO/pluronic F127 scaffold and cultured in endothelial cell basal medium-2 for 7 days, human PO were seeded into the PDO/pluronic F127 scaffold with PE, and then, this cell-scaffold construct was cultured in endothelial cell basal medium-2 with osteogenic induction factors, including ascorbic acid, dexamethasone, and β-glycerophosphate, for a further 7 days. Then, this 2-week cultured construct was grafted into the mandibular defect of miniature pig. Twelve weeks after implantation, the animal was sacrificed. Clinical examination revealed that newly formed bone was seen more clearly in the defect with human PO and PDO/pluronic F127 scaffold with preseeded human PE. The experimental results suggest that tissue-engineered bone formation using human PO and PDO/pluronic F127 scaffold with preseeded human PE can be used to restore skeletal integrity to various bony defects when used in clinics.

Vascular and micro-environmental influences on MSC-coral hydroxyapatite construct-based bone tissue engineering

Bone tissue engineering (BTE) has been demonstrated an effective approach to generate bone tissue and repair bone defect in ectopic and orthotopic sites. The strategy of using a prevascularized tissue-engineered bone grafts (TEBG) fabricated ectopically to repair bone defects, which is called live bone graft surgery, has not been reported. And the quantitative advantages of vascularization and osteogenic environment in promoting engineered bone formation have not been defined yet. In the current study we generated a tissue engineered bone flap with a vascular pedicle of saphenous arteriovenous in which an organized vascular network was observed after 4 weeks implantation, and followed by a successful repaire of fibular defect in beagle dogs. Besides, after a 9 months long term observation of engineered bone formation in ectopic and orthotopic sites, four CHA (coral hydroxyapatite) scaffold groups were evaluated by CT (computed tomography) analysis. By the comparison of bone formation and scaffold degradation between different groups, the influences of vascularization and micro-environment on tissue engineered bone were quantitatively analyzed. The results showed that in the first 3 months vascularization improved engineered bone formation by 2 times of non-vascular group and bone defect micro-environment improved it by 3 times of ectopic group, and the CHA-scaffold degradation was accelerated as well.

Repair of bone defect with vascularized tissue engineered bone graft seeded with mesenchymal stem cells in rabbits

This study evaluated the results of repair of the radius defect with a vascularized tissue engineered bone graft composed by implanting mesenchymal stem cells (MSCs) and a vascular bundle into the xenogeneic deproteinized cancellous bone (XDCB) scaffold in a rabbit model. Sixty-four rabbits were used in the study. Among them, four rabbits were used as the MSCs donor. Other 57 rabbits were divided into five groups. In group one (n = 9), a 1.5 cm bone defect was created with no repair. In group two (n = 12), the bone defect was repaired by a XDCB graft alone. In group three (n = 12), the defect was repaired by a XDCB graft that included a vascular bundle. In group four (n = 12), the defect was repaired by a XDCB graft seeded with MSCs. In group five (n = 12), the defect was repaired by a XDCB graft including a vascular bundle and MSCs implantation. The rest three rabbits were used as the normal control for the biomechanical test. The results of X-ray and histology at postoperative intervals (4, 8, and 12 weeks) and biomechanical examinations at 12 weeks showed that combining MSCs and a vascular bundle implantation resulted in promoting vascularization and osteogenesis in the XDCB graft, and improving new bone formation and mechanical property in repair of radius defect with this tissue engineered bone graft. These findings suggested that the vascularized tissue engineered bone graft may be a valuable alternative for repair of large bone defect and deserves further investigations.

History of microsurgery

In the mid-1500s, the techniques of vascular ligature and vascular suture were developed sporadically by several pioneers in this field. However, vascular surgery became realistic experimentally as a result of the work by Carrel and Guthrie in the early 1900s, in which they performed replantations and transplantations of several composite tissues and organs, including amputated limbs, kidneys, and others using experimental animals. In contrast, the development of heparin by Howell and Holt in 1918 accelerated the rate of these types of operations being performed with increasing success in humans. Since the first use of a monocular microscope for ear surgery by Nylen in 1921 and a binocular microscope by Holmgren in 1923, in addition to the timely developments of the Zeiss operating microscope, microsurgical instruments, and suture materials, microsurgery was born in several surgical disciplines in the ensuing 50-year period. The application of microvascular surgery and microneurosurgery in the fields of hand, plastic, and reconstructive surgery resulted in revolutionary advances in clinical replantation and transplantation of composite tissues and more allotransplantations.

The repair of large segmental bone defects in the rabbit with vascularized tissue engineered bone

Management of segmental bone defects is a considerable challenge for orthopedic surgeons. Tissue engineering is a promising method for repairing bone defects, and vascularization is critical to the performance of a tissue engineered bone. We report herein the construction of a vascularized tissue engineered bone with mesenchymal stem cells (MSCs) and MSC-derived endothelial cells (ECs) co-cultured in porous beta-tricalcium phosphate ceramic (beta-TCP) to repair 1.5-cm ulnar defects in the rabbit. Examination by X-ray and single photon emission computed tomography (SPECT), histologic analysis, and biomechanical tests were used to evaluate repair and the vascularization of the implants. The results showed that by co-seeding MSCs and MSC-derived ECs, the resulting vascularization was able to promote osteogenesis and improve mechanical properties. The rabbits treated with vascularized tissue engineered bone exhibited far more extensive osteogenesis and good vascularization. Therefore, we suggest that the vascularized tissue engineered bone constructed by co-culture of MSCs and MSC-derived ECs in porous beta-TCP may be an effective approach to promote repair of segmental bone defects and have potential for repairing large segmental bone defects in a clinical setting.

Tissue engineered bone grafts: biological requirements, tissue culture and clinical relevance

The tremendous need for bone tissue in numerous clinical situations and the limited availability of suitable bone grafts are driving the development of tissue engineering approaches to bone repair. In order to engineer viable bone grafts, one needs to understand the mechanisms of native bone development and fracture healing, as these processes should ideally guide the selection of optimal conditions for tissue culture and implantation. Engineered bone grafts have been shown to have capacity for osteogenesis, osteoconduction, osteoinduction and osteointegration - functional connection between the host bone and the graft. Cells from various anatomical sources in conjunction with scaffolds and osteogenic factors have been shown to form bone tissue in vitro. The use of bioreactor systems to culture cells on scaffolds before implantation further improved the quality of the resulting bone grafts. Animal studies confirmed the capability of engineered grafts to form bone and integrate with the host tissues. However, the vascularization of bone remains one of the hurdles that need to be overcome if clinically sized, fully viable bone grafts are to be engineered and implanted. We discuss here the biological guidelines for tissue engineering of bone, the bioreactor cultivation of human mesenchymal stem cells on three-dimensional scaffolds, and the need for vascularization and functional integration of bone grafts following implantation.

Spatial and temporal patterns of bone formation in ectopically pre-fabricated, autologous cell-based engineered bone flaps in rabbits

Biological substitutes for autologous bone flaps could be generated by combining flap pre-fabrication and bone tissue engineering concepts. Here, we investigated the pattern of neotissue formation within large pre-fabricated engineered bone flaps in rabbits. Bone marrow stromal cells from 12 New Zealand White rabbits were expanded and uniformly seeded in porous hydroxyapatite scaffolds (tapered cylinders, 10-20 mm diameter, 30 mm height) using a perfusion bioreactor. Autologous cell-scaffold constructs were wrapped in a panniculus carnosus flap, covered by a semipermeable membrane and ectopically implanted. Histological analysis, substantiated by magnetic resonance imaging (MRI) and micro-computerized tomography scans, indicated three distinct zones: an outer one, including bone tissue; a middle zone, formed by fibrous connective tissue; and a central zone, essentially necrotic. The depths of connective tissue and of bone ingrowth were consistent at different construct diameters and significantly increased from respectively 3.1+/-0.7 mm and 1.0+/-0.4 mm at 8 weeks to 3.7+/-0.6 mm and 1.4+/-0.6 mm at 12 weeks. Bone formation was found at a maximum depth of 1.8 mm after 12 weeks. Our findings indicate the feasibility of ectopic pre-fabrication of large cell-based engineered bone flaps and prompt for the implementation of strategies to improve construct vascularization, in order to possibly accelerate bone formation towards the core of the grafts.

Recombinant AAV-mediated VEGF gene therapy induces mandibular condylar growth

Craniofacial anomalies resulting from impaired growth of mandibular condyles require multidisciplinary interventions, which impose a substantial burden on patients and their families. So far, correcting such deformities with an alternative strategy - gene therapy - is still an uncharted territory. Here, we established an effective in vivo gene delivery system with recombinant adeno-associated virus (rAAV)-mediated vascular endothelial growth factor (VEGF) to enhance mandibular condylar growth. With in situ hybridization, RT-PCR, immunostaining and Western blot, transgene expression was clearly detected in the mandibular condyles during the whole experiment periods. At defined time points, specific osteogenetic markers (alkaline phosphatase and osteocalcin) and chondrogenetic markers (collagen type II and collagen type X) were assessed by means of biochemical analysis and their expression significantly changed from day 30. Proliferation index by proliferating cell nuclear antigen staining showed also a significant increase in cell proliferation. Morphological measurement identified that the size of mandibular condyle significantly increased from day 30. Taken together, rAAV-VEGF was successfully established as an efficient delivery system to induce mandibular condylar growth, which provides the basis for future gene therapy to treat patients with craniofacial deformities.

Tissue Transplantation in Plastic Surgery

The functional and aesthetic outcome following application of conventional reconstructive procedures or prosthetic materials is not satisfactory, especially in patients who have severe deformities and disabilities. Since the first successful hand transplantation in France in 1998, composite tissue allograft transplantation has gained a great deal of interest in the field of plastic surgery. It is obvious that composite tissue allograft transplantation will improve patients' life quality, but this might be at the expense of decreasing life expectancy. Currently, the main obstacle for composite tissue allograft transplantation is the use of life-long immunosuppression therapy because of their well-known side effects. In addition, the ethical, social, and psychologic issues are raised when discussing face transplantation. The long-term results of the recently performed partial face transplantations will be critical to judge the future applications of partial or total face transplantation.

Bone Regeneration on a Collagen Sponge Self-Assembled Peptide-Amphiphile Nanofiber Hybrid Scaffold

The objective of this study was to create a novel approach to promote bone induction through sustained release of growth factor from a 3-dimensional (3D) hybrid scaffold. Peptide-amphiphile (PA) was synthesized by standard solid-phase chemistry that ends with the alkylation of the NH2 terminus of the peptide. Collagen sponge was reinforced by incorporation of poly(glycolic acid) (PGA) fiber. A 3D network of nanofibers was formed by mixing basic fibroblast growth factor (bFGF) suspensions with dilute aqueous solutions of PA. A hybrid scaffold was fabricated by combination of self-assembled PA nanofibers and collagen sponge reinforced with incorporation of PGA fibers. The in vitro release profile of bFGF from hybrid scaffold was investigated, and ectopic bone formation induced by the released bFGF was assessed after subcutaneous implantation of hybrid scaffold into the backs of rats. Homogeneous bone formation was histologically observed throughout the hybrid scaffolds, in marked contrast to collagen sponge-incorporated bFGF. The level of alkaline phosphatase activity and osteocalcin content at the implanted sites of hybrid scaffolds were significantly high compared with collagen sponge incorporated with bFGF. The combination of bFGF incorporated in a collagen sponge self-assembled PA nanofiber hybrid scaffold is a promising procedure to improve bone regeneration.