BMP-2 and bFGF in an irradiated bone model

Aligned electrospun fibers of different diameters for improving cell migration capacity

Electrospun fibers have gained significant attention as scaffolds in skin tissue engineering due to their biomimetic properties, which resemble the fibrous extracellular matrix. The morphological characteristics of electrospun fibers play a crucial role in determining cell behavior. However, the effects of electrospun fibers' arrangement and diameters on human skin fibroblasts (HSFs) remain elusive. Here, we revealed the impact of electrospun fiber diameters (700 nm, 2000 nm, and 3000 nm) on HSFs' proliferation, migration, and functional expression. The results demonstrated that all fibers exhibited good cytocompatibility. HSFs cultured on nanofibers (700 nm diameter) displayed a more dispersed and elongated morphology. Conversely, fibers with a diameter of 3000 nm exhibited a reduced specific surface area and lower adsorption of adhesion proteins, resulting in enhanced cell migration speed and effective migration rate. Meanwhile, the expression levels of migration-related genes and proteins were upregulated at 48 h for the 3000 nm fibers. This study demonstrated the unique role of fiber diameters in controlling the physiological functions of cells, especially decision-making and navigating migration in complex microenvironments of aligned electrospun fibers, and highlights the utility of these bioactive substitutes in skin tissue engineering applications.

The Use of Hydrogel-Based Materials for Radioprotection

Major causes of the radiation-induced disease include nuclear accidents, war-related nuclear explosions, and clinical radiotherapy. While certain radioprotective drug or bioactive compounds have been utilized to protect against radiation-induced damage in preclinical and clinical settings, these strategies are hampered by poor efficacy and limited utilization. Hydrogel-based materials are effective carriers capable of enhancing the bioavailability of compounds loaded therein. As they exhibit tunable performance and excellent biocompatibility, hydrogels represent promising tools for the design of novel radioprotective therapeutic strategies. This review provides an overview of common approaches to radioprotective hydrogel preparation, followed by a discussion of the pathogenesis of radiation-induced disease and the current states of research focused on using hydrogels to protect against these diseases. These findings ultimately provide a foundation for discussions of the challenges and future prospects associated with the use of radioprotective hydrogels.

Applications of Hydrogels in Drug Delivery for Oral and Maxillofacial Diseases

Oral and maxillofacial diseases have an important impact on local function, facial appearance, and general health. As a multifunctional platform, hydrogels are widely used in the biomedical field due to their excellent physicochemical properties. In recent years, a large number of studies have been conducted to adapt hydrogels to the complex oral and maxillofacial environment by modulating their pore size, swelling, degradability, stimulus-response properties, etc. Meanwhile, many studies have attempted to use hydrogels as drug delivery carriers to load drugs, cytokines, and stem cells for antibacterial, anticancer, and tissue regeneration applications in oral and maxillofacial regions. This paper reviews the application and research progress of hydrogel-based drug delivery systems in the treatment of oral and maxillofacial diseases such as caries, endodontic diseases, periodontal diseases, maxillofacial bone diseases, mucosal diseases, oral cancer, etc. The characteristics and applications of hydrogels and drug-delivery systems employed for the treatment of different diseases are discussed in order to provide a reference for further research on hydrogel drug-delivery systems in the future.

The Functions and Mechanisms of Basic Fibroblast Growth Factor in Tendon Repair

Tendon injury is a disorder of the musculoskeletal system caused by overuse or trauma, which is characterized by pain and limitations in joint function. Since tendon healing is slowly and various treatments are generally ineffective, it remains a clinically challenging problem. Recent evidences suggest that basic fibroblast growth factor (bFGF) not only plays an important role in tendon healing, but also shows a positive effect in laboratory experimentations. The purpose of this review is to summarize the effects of bFGF in the tendon healing. Firstly, during the inflammatory phase, bFGF stimulates the proliferation and differentiation of vascular endothelial cells to foster neovascularization. Furthermore, bFGF enhances the production of pro-inflammatory factors during the early phase of tendon healing, thereby accelerating the inflammatory response. Secondly, the cell proliferation phase is accompanied by the synthesis of a large number of extracellular matrix components. bFGF speeds up tendon healing by stimulating fibroblasts to secrete type III collagen. Lastly, the remodeling phase is characterized by the transition from type III collagen to type I collagen, which can be promoted by bFGF. However, excessive injection of bFGF can cause tendon adhesions as well as scar tissue formation. In future studies, we need to explore further applications of bFGF in the tendon healing process.

Alveolar ridge preservation with fibroblast growth factor-2 modified acellular dermal matrix membrane and a bovine-derived xenograft: An experimental in vivo study

OBJECTIVE

To investigate the effect of a bone substitute material combined with fibroblast growth factor-2 (FGF-2) loaded barrier membrane on the preservation of alveolar ridge after tooth extraction.

MATERIAL AND METHODS

Four dogs were included. Six extraction sockets of each animal received the 3 treatments and were randomly divided into three groups. Group A: negative control; Group B: bovine xenografts + membrane; and Group C: bovine xenografts + FGF-2-loaded membrane. CBCT and histological analysis were performed to evaluate changes in the width and height of alveolar ridges and extraction socket bone healing 8 weeks post-extraction.

RESULTS

CBCT showed that the alveolar bone in Group A was significantly thinner than that in Group B and Group C at 1 and 3 mm apically from the alveolar crest. The alveolar width at 1 mm in Group C (60.99 ± 15.36%) was significantly thicker than that in Group B (39.75 ± 30.18%). Histomorphmetrical measurements showed that the buccal alveolar width at 1 mm was significantly thicker in Groups B and C than in Group A. Additionally, buccal bone height and lingual bone width at 1 mm in Group C (87.06 ± 10.34%, 89.09 ± 10.56%) were significantly greater than in Group A (53.48 ± 23.94%, 82.72 ± 12.59%).

CONCLUSION

The present findings indicate that application of bovine bone combined with barrier membrane with or without FGF-2 over tooth sockets can effectively reduce ridge absorption, especially in terms of ridge width and FGF-2 modified membrane seems to improve the outcomes obtained with membrane alone.

Growth Factors, Carrier Materials, and Bone Repair

This chapter provides an overview of the growth factors active in bone regeneration and healing. Both normal and impaired bone healing are discussed, with a focus on the spatiotemporal activity of the various growth factors known to be involved in the healing response. The review highlights the activities of most important growth factors impacting bone regeneration, with a particular emphasis on those being pursued for clinical translation or which have already been marketed as components of bone regenerative materials. Current approaches the use of bone grafts in clinical settings of bone repair (including bone grafts) are summarized, and carrier systems (scaffolds) for bone tissue engineering via localized growth factor delivery are reviewed. The chapter concludes with a consideration of how bone repair might be improved in the future.

Development of a standardized mucositis and osteoradionecrosis animal model using external radiation

Objectives

Although the side effects of radiation therapy vary from mucositis to osteomyelitis depending on the dose of radiation therapy, to date, an experimental animal model has not yet been proposed. The aim of this study was to develop an animal model for assessing complications of irradiated bone, especially to quantify the dose of radiation needed to develop a rat model.

Materials and Methods

Sixteen Sprague-Dawley rats aged seven weeks with a mean weight of 267.59 g were used. Atraumatic extraction of a right mandibular first molar was performed. At one week after the extraction, the rats were randomized into four groups and received a single dose of external radiation administered to the right lower jaw at a level of 14, 16, 18, or 20 Gy, respectively. Clinical alopecia with body weight changes were compared and bony volumetric analysis with micro-computed tomography (CT), histologic analysis with H&E were performed.

Results

The progression of the skin alopecia was different depending on the irradiation dose. Micro-CT parameters including bone volume, bone volume/tissue volume, bone mineral density, and trabecular spaces, showed no significant differences. The progression of osteoradionecrosis (ORN) along with that of inflammation, fibrosis, and bone resorption, was found with increased osteoclast or fibrosis in the radiated group. As the radiation dose increases, osteoclast numbers begin to decrease and osteoclast tends to increase. Osteoclasts respond more sensitively to the radiation dose, and osteoblasts are degraded at doses above 18 Gy.

Conclusion

A standardized animal model clinically comparable to ORN of the jaw is a valuable tool that can be used to examine the pathophysiology of the disease and trial any potential treatment modalities. We present a methodology for the use of an experimental rat model that incorporates a guideline regarding radiation dose.

Bone microarchitecture and turnover in the irradiated human mandible

OBJECTIVES

The aim of this study was to assess the microarchitecture and turnover in irradiated cancellous mandibular bone and the relation with radiation dose, to elucidate the effects of radiotherapy on the mandible.

PATIENTS AND METHODS

Mandibular cancellous bone biopsies were taken from irradiated patients and controls. Micro-CT scanning was performed to analyze microstructural bone parameters. Bone turnover was assessed by histomorphometry. Local radiation dose at the biopsy site (Dmax) was estimated from radiotherapy plans.

RESULTS

Twenty-seven irradiated patients and 35 controls were included. Osteoid volume (Osteoid Volume/Bone Volume, OV/BV) [0.066/0.168 (median/interquartile range (IQR), OV/BV; %), P < 0.001], osteoid surface (Osteoid Surface/Bone Surface, OS/BS) [0.772/2.17 (median/IQR, OS/BS; %), P < 0.001] and osteoclasts number (Osteoclasts per millimetre bone surface, Ocl/mmBS; mm²) [0.026/0.123 (median/IQR, Ocl/mmBS; mm²), P < 0.001] were decreased; trabecular number (Tb.N) was lower [1.63/0.63 (median/IQR, Tb.N; 1/mm^-1), P = 0.012] and trabecular separation (Tb.Sp) [0.626/0.24 (median/IQR, Tb.Sp; μm), P = 0.038] was higher in irradiated mandibular bone. With higher Dmax, trabecular number increases (Spearman's correlation R = 0.470, P = 0.018) and trabecular separation decreases (Spearman's correlation R = -0.526, P = 0.007). Bone mineral density (BMD, milligrams hydroxyappetite per cubic centimetre, mgHA/cm³) [1016/99 (median/IQR, BMD; mgHA/cm³), P = 0.03] and trabecular separation [0.739/0.21 (median/IQR, Tb.Sp; μm), P = 0.005] are higher whereas connectivity density (Conn Dens) [3.94/6.71 (median/IQR, Conn Dens), P = 0.047] and trabecular number [1.48/0.44 (median/IQR, Tb.N; 1/mm^-1), P = 0.002] are lower in Dmax ≤50 Gy compared to controls.

CONCLUSIONS

Radiotherapy dramatically impairs bone turnover in the mandible. Deterioration in microarchitecture only affects bone irradiated with a Dmax of <50 Gy. The 50 Gy value seems to be a critical threshold to where the effects of the radiation is more detrimental.

Systematic scoping review of mandibular bone tissue engineering

Tissue engineering is a promising alternative that may facilitate bony regeneration in small defects in compromised host tissue as well as large mandibular defects. This scoping systematic review was therefore designed to assess in vivo research on its use in the reconstruction of mandibular defects in animal models. A total of 4524 articles were initially retrieved using the search algorithm. After screening of the titles and abstracts, 269 full texts were retrieved, and a total of 72 studies included. Just two of the included studies employed osteonecrosis as the model of mandibular injury. All the rest involved the creation of a critical defect. Calcium phosphates, especially tricalcium phosphate and hydroxyapatite, were the scaffolds most widely used. All the studies that used a scaffold reported increased formation of bone when compared with negative controls. When combined with scaffolds, mesenchymal stem cells (MSC) increased the formation of new bone and improved healing. Various growth factors have been studied for their potential use in the regeneration of the maxillofacial complex. Bone morphogenic proteins (BMP) were the most popular, and all subtypes promoted significant formation of bone compared with controls. Whilst the studies published to date suggest a promising future, our review has shown that several shortfalls must be addressed before the findings can be translated into clinical practice. A greater understanding of the underlying cellular and molecular mechanisms is required to identify the optimal combination of components that are needed for predictable and feasible reconstruction or regeneration of mandibular bone. In particular, a greater understanding of the biological aspects of the regenerative triad is needed before we can to work towards widespread translation into clinical practice.

Effects of pentoxifylline and tocopherol on an osteoradionecrosis animal model

PURPOSE

Osteoradionecrosis (ORN) is known to be a refractory disease in the oral and maxillofacial field. The purpose of this study was to examine the effects of pentoxifylline (PTX) and tocopherol (TP) on an ORN animal model focused on bone healing.

MATERIALS AND METHODS

A total of 48 Sprague-Dawley rats were used: 40 received a single irradiation dose of 35 Gy on the left mandible, and eight were used as the nonirradiated control group. The rats received PTX (T1, C1), TP (T2, C2), a combination of PTX and TP (T3, C3), or normal saline (T4, C4). Three weeks after irradiation, the mandibular posterior teeth were extracted. The rats were sacrificed 4 weeks after extraction.

RESULTS

In the T3 group, bone volume/tissue volume was 19.62 ± 16.03 (%), bone mineral density was as 0.31 ± 0.16 (g/cm³) in the micro-CT analysis, which were higher than that of other groups (p = 0.025, p = 0.012, respectively). In the histological analysis, bone regeneration was the most prominent in the T3 group. The ratio of empty lacunae was the highest in the T4 group, 68.77 ± 15.47 (%, p = 0.004). Immunohistochemistry showed that the expression of TNF-α was relatively lower in the T3 than in the T4 or T2 groups. The RT-qPCR showed the expression level of PECAM, VEGF-A, and osteocalcin was more than twofold as high as in the T3 group compared to the other groups.

CONCLUSION

The combination of PTX and TP appears to promote angiogenesis and osteogenesis in a rat ORN model. Therefore, PTX and TP might be useful in the treatment and prevention of ORN.

Development of an experimental model for radiation-induced inhibition of cranial bone regeneration

Background

Radiation therapy is widely employed in the treatment of head and neck cancer. Adverse effects of therapeutic irradiation include delayed bone healing after dental extraction or impaired bone regeneration at the irradiated bony defect. Development of a reliable experimental model may be beneficial to study tissue regeneration in the irradiated field. The current study aimed to develop a relevant animal model of post-radiation cranial bone defect.

Methods

A lead shielding block was designed for selective external irradiation of the mouse calvaria. Critical-size calvarial defect was created 2 weeks after the irradiation. The defect was filled with a collagen scaffold, with or without incorporation of bone morphogenetic protein 2 (BMP-2) (1 μg/ml). The non-irradiated mice treated with or without BMP-2-included scaffold served as control. Four weeks after the surgery, the specimens were harvested and the degree of bone formation was evaluated by histological and radiographical examinations.

Results

BMP-2-treated scaffold yielded significant bone regeneration in the mice calvarial defects. However, a single fraction of external irradiation was observed to eliminate the bone regeneration capacity of the BMP-2-incorporated scaffold without influencing the survival of the animals.

Conclusion

The current study established an efficient model for post-radiation cranial bone regeneration and can be applied for evaluating the robust bone formation system using various chemokines or agents in unfavorable, demanding radiation-related bone defect models.

Newly Formed Bone Induced by Recombinant Human Bone Morphogenetic Protein-2: A Histological Observation

PURPOSE

To observe, histologically, bone induced by recombinant human bone morphogenetic protein-2 (rhBMP-2) in onlay grafted and sinus lifted alveolaris.

MATERIAL AND METHODS

Eighteen patients were treated with rhBMP-2 at concentration 1.5 mg/mL with an absorbable collagen sponge (ACS). The treated bone was harvested with small trephine bur at 5 or 7 months after surgery for the micro Computer Scanning (CT) and light microscopic observation.

RESULTS

Micro CT showed clearly 3-dimensional trabecular bone structure. New bone formation and bone marrow structure were observed in the observed area. Osteoblastic cells existed along the new bone, and osteopontin was localized in the bone matrix weakly. In the connective tissue around the new bone, many CD34-positive blood vessel cells were present. Some tartrate-resistant acid phosphatase (TRAP)-positive osteoclastic cells were observed around bone at this stage.

CONCLUSION

The application of rhBMP-2 with ACS induced a new bone accompanied by blood vessels in atrophied alveolaris. This suggests that rhBMP-2 is capable of osteoinductivity in human jaw.

Outcome of nonunion fractures in dogs treated with fixation, compression resistant matrix, and recombinant human bone morphogenetic protein-2

Objectives: To report the use of compression resistant matrix (CRM) infused with recombinant human bone morphogenetic protein (rhBMP-2) prospectively in the healing of non union long-bone fractures in dogs.

Methods: A longitudinal cohort of dogs that were presented with nonunion fractures were classified and treated with CRM soaked with rhBMP-2 and fracture fixation. They were followed with serial radiographs and evaluated for healing times and complications according to the time frame and definitions previously established for orthopaedic clinical cases.

Results: Eleven nonunion fractures in nine dogs were included. Median healing time was 10 weeks (range: 7–20 weeks). Major perioperative complications due to bandage morbidity were encountered in two of 11 limbs and resolved. All other complications were minor. They occurred perioperatively in eight of 11 limbs. Minor follow-up complications included short-term in one of two limbs, mid-term in one of three, and long-term in four of five limbs. Nine limbs returned to full function and two limbs returned to acceptable function at the last follow-up.

Clinical significance: Nonunion fractures given a poor prognosis via standard-of-care treatment were successfully repaired using CRM with rhBMP-2 accompanying fixation. These dogs, previously at high risk of failure, returned to full or acceptable function.

* Calvarial Bone Regeneration Is Enhanced by Sequential Delivery of FGF-2 and BMP-2 from Layer-by-Layer Coatings with a Biomimetic Calcium Phosphate Barrier Layer

A drug delivery coating for synthetic bone grafts has been developed to provide sequential delivery of multiple osteoinductive factors to better mimic aspects of the natural regenerative process. The coating is composed of a biomimetic calcium phosphate (bCaP) layer that is applied to a synthetic bone graft and then covered with a poly-l-Lysine/poly-l-Glutamic acid polyelectrolyte multilayer (PEM) film. Bone morphogenetic protein-2 (BMP-2) was applied before the coating process directly on the synthetic bone graft and then, bCaP-PEM was deposited followed by adsorption of fibroblast growth factor-2 (FGF-2) into the PEM layer. Cells access the FGF-2 immediately, while the bCaP-PEM temporally delays the cell access to BMP-2. In vitro studies with cells derived from mouse calvarial bones demonstrated that Sca-1 and CD-166 positive osteoblast progenitor cells proliferated in response to media dosing with FGF-2. Coated scaffolds with BMP-2 and FGF-2 were implanted in mouse calvarial bone defects and harvested at 1 and 3 weeks. After 1 week in vivo, proliferation of cells, including Sca-1+ progenitors, was observed with low dose FGF-2 and BMP-2 compared to BMP-2 alone, indicating that in vivo delivery of FGF-2 activated a similar population of cells as shown by in vitro testing. At 3 weeks, FGF-2 and BMP-2 delivery increased bone formation more than BMP-2 alone, particularly in the center of the defect, confirming that the proliferation of the Sca-1 positive osteoprogenitors by FGF-2 was associated with increased bone healing. Areas of bone mineralization were positive for double fluorochrome labeling of calcium and alkaline phosphatase staining of osteoblasts, along with increased TRAP+ osteoclasts, demonstrating active bone formation distinct from the bone-like collagen/hydroxyapatite scaffold. In conclusion, the addition of a bCaP layer to PEM delayed access to BMP-2 and allowed the FGF-2 stimulated progenitors to populate the scaffold before differentiating in response to BMP-2, leading to improved bone defect healing.

The role of myofibroblasts in the development of osteoradionecrosis in a newly established rabbit model

This study aimed to establish a proper animal model of osteoradionecrosis of jaws (ORNJ) and to observe preliminarily the characteristics of myofibroblasts, the key effector cell of fibrosis, in ORNJ. Rabbit mandibles were irradiated at three different doses based on a human equivalent radiation schedule, and examined by gross manifestation, single-photon emission computed tomography (SPECT), micro-computed tomography, sequential fluorochrome labeling, and histology. Immunohistochemistry staining of α-SMA was applied to detect the existence of myofibroblasts. The exposed necrotic bone, which is the main indication of ORNJ, started to be observed at all rabbits at 9 Gy. With the radiation dose increasing, the microarchitecture of the irradiated mandibles was more destroyed, the metabolism and mineralization of the irradiated mandibles diminished, the osteocytes number decreased, and more mature bones were substituted by fibrosis in the irradiated mandibles. In addition, as the radiation dose increased, the myofibroblast number increased and collected around the separated sequestrum, which indicated that myofibroblasts might relate to the pathogenesis of ORNJ. In summary, a clinically translational ORNJ model was successfully established in our study, and the role of myofibroblasts in the pathogenesis of ORNJ is described for the first time.

Development of mandibular osteoradionecrosis in rats: Importance of dental extraction

OBJECTIVES

To develop an animal model of mandibular osteoradionecrosis (ORN) using a high-energy radiation source (as used in human therapeutics) and to assess the role of tooth extraction on ORN development.

MATERIALS AND METHODS (STUDY DESIGN)

Ten animals were irradiated with a single 35- or 50-Gy dose. Three weeks later, the second left mandibular molar was extracted from three animals in each group. Nine weeks after irradiation, the animals were euthanized, with an injection of contrast agent in the bloodstream to highlight vascularization. Mandibles were harvested and studied using micro-CT, histology, tartrate-resistant acid phosphatase activity and scanning electron microscopy.

RESULTS

This study demonstrates that a single 50-Gy dose associated with molar extraction is necessary for ORN development. In these conditions, absence of healing of the mucosa and bone, dental effects, fibrosis, an increase in osteoclast activity and a decrease in vascularization were observed. We also determined that molar extraction increases the impact of the cellular effects of radiation.

CONCLUSION

The mandibular ORN animal model was validated after 50-Gy irradiation and molar extraction. The results of this study therefore support an animal ORN model and tissue engineering strategies will now be developed to regenerate bone for patients with head and neck cancer.

A rat model of radiation injury in the mandibular area

BACKGROUND

Radiation technology focuses on delivering the radiation as precisely as possible to the tumor, nonetheless both acute and long-term damage to surrounding normal tissue may develop. Injuries to the surrounding normal tissue after radiotherapy of head and neck cancer are difficult to manage. An animal model is needed to elucidate good treatment modalities. The aim of this study was to establish a rat model where a certain radiation dose gives reproducible tissue reactions in the mandibular area corresponding to injuries obtained in humans.

METHOD

The left mandible of male Sprague Dawley rats was irradiated by external radiotherapy (single fraction 15 Gy, total dose 75 Gy) every second week five times. Endpoint was six weeks after last radiation treatment, and the test group was compared to non-irradiated controls. Morphological alterations of the soft tissues, bone and tooth formation, as well as alterations of salivation, vascularity and collagen content were assessed. An unpaired, non-parametric Mann-Whitney test was used to compare the statistical differences between the groups.

RESULTS

Analysis of the soft tissues and mandible within the radiation field revealed severe unilateral alopecia and dermatitis of the skin, extensive inflammation of the submandibular gland with loss of serous secretory cells, hyperkeratinization and dense connective fiber bundles of the gingival tissue, and disturbed tooth development with necrosis of the pulp. Production of saliva and the vascularity of the soft tissues were significantly reduced. Furthermore, the collagen fibril diameter was larger and the collagen network denser compared to non-irradiated control rats.

CONCLUSION

We have established an animal model of radiation injury demonstrating physiological and histological changes corresponding to human radiation injuries, which can be used for future therapeutic evaluations.

New approach for the treatment of osteoradionecrosis with pentoxifylline and tocopherol

Osteoradionecrosis (ORN) of the jaw is a significant complication of radiotherapy for oral cavity cancer. In addition to antibiotic medication, treatment options such as hyperbaric oxygen therapy, surgical approaches, and combined therapy with pentoxifylline and tocopherol have been recently introduced. In this review article, we will discuss the definition and classifications of osteoradionecrosis, its etiology and pathophysiology, previous treatment options, oral and maxillofacial complications of radiotherapy, basic information on pentoxifylline and tocopherol, recent reports of pentoxifylline and tocopherol combined therapy, and, finally, ORN-induced animal models and future approaches.

A basic fibroblast growth factor analog for protection and mitigation against acute radiation syndromes

The effects of fibroblast growth factors and their potential as broad-spectrum agents to treat and mitigate radiation injury have been studied extensively over the past two decades. This report shows that a peptide mimetic of basic fibroblast growth factor (FGF-P) protects and mitigates against acute radiation syndromes. FGF-P attenuates both sepsis and bleeding in a radiation-induced bone marrow syndrome model and reduces the severity of gastrointestinal and cutaneous syndromes; it should also mitigate combined injuries. FGF-2 and FGF-P induce little or no deleterious inflammation or vascular leakage, which distinguishes them from most other growth factors, angiogenic factors, and cytokines. Although recombinant FGFs have proven safe in several ongoing clinical trials, they are expensive to synthesize, can only be produced in limited quantity, and have limited shelf life. FGF-P mimics the advantageous features of FGF-2 without these disadvantages. This paper shows that FGF-P not only has the potential to be a potent yet safe broad-spectrum medical countermeasure that mitigates acute radiotoxicity but also holds promise for thermal burns, ischemic wound healing, tissue engineering, and stem-cell regeneration.

Synergistic induction of early stage of bone formation by combination of recombinant human bone morphogenetic protein-2 and epidermal growth factor

This study evaluates whether the combination of the rhBMP-2 and various types of growth factors including EGF, FGF, PDGF and VEGF increases osteoinductivity compared to the single use of rhBMP-2 through in vitro and in vivo study. Cultured human MSCs were treated with rhBMP-2 only or in combination with growth factors. For in vivo evaluation, rhBMP-2 only or with growth factors was implanted into the calvarial defect made on SD rats. Both EGF and PDGF significantly increased both ALP activity and expression level in hMSCs when treated in combination with rhBMP-2 at 3 and 7 days of differentiation and significantly raised the accumulation of the calcium at day 14. Furthermore, micro-CT scanning revealed that the EGF an FGF groups show significantly increased new bone surface ratio compared to the rhBMP-2 only group and, the EGF treatment significantly up regulated percent bone volume and trabecular number at two weeks after the surgery. VEGF treatment also significantly raised trabecular number and FGF treatment significantly increased the trabecular thickness. Histological examination revealed that the EGF combination group showed enhanced bone regeneration than the rhBMP-2 only group two weeks after the implantation. Even though the treatment of rhBMP-2 with PDGF and FGF failed to show enhanced osteogenesis in vitro and in vivo simultaneously, these results suggest that the positive effect of the combination of EGF and rhBMP-2 is expected to induce the bone formation earlier compared to the single use of rhBMP-2 in vitro and in vivo. © 2014 The Authors. Journal of Tissue Engineering and Regenerative Medicine published by John Wiley & Sons Ltd.

A magnetic resonance imaging study on changes in rat mandibular bone marrow and pulp tissue after high-dose irradiation

PURPOSE

This study was designed to evaluate whether magnetic resonance imaging (MRI) is appropriate for detecting early changes in the mandibular bone marrow and pulp tissue of rats after high-dose irradiation.

MATERIALS AND METHODS

The right mandibles of Sprague-Dawley rats were irradiated with 10 Gy (Group 1, n=5) and 20 Gy (Group 2, n=5). Five non-irradiated animals were used as controls. The MR images of rat mandibles were obtained before irradiation and once a week until week 4 after irradiation. From the MR images, the signal intensity (SI) of the mandibular bone marrow and pulp tissue of the incisor was interpreted. The MR images were compared with the histopathologic findings.

RESULTS

The SI of the mandibular bone marrow had decreased on T2-weighted MR images. There was little difference between Groups 1 and 2. The SI of the irradiated groups appeared to be lower than that of the control group. The histopathologic findings showed that the trabecular bone in the irradiated group had increased. The SI of the irradiated pulp tissue had decreased on T2-weighted MR images. However, the SI of the MR images in Group 2 was high in the atrophic pulp of the incisor apex at week 2 after irradiation.

CONCLUSION

These patterns seen on MRI in rat bone marrow and pulp tissue were consistent with histopathologic findings. They may be useful to assess radiogenic sclerotic changes in rat mandibular bone marrow.

Enhanced bone regeneration of cortical segmental bone defects using porous titanium scaffolds incorporated with colloidal gelatin gels for time- and dose-controlled delivery of dual growth factors

Porous titanium scaffolds are a promising class of biomaterials for grafting large bone defects, because titanium provides sufficient mechanical support, whereas its porous structure allows bone ingrowth resulting in good osseointegration. To reinforce porous titanium scaffolds with biological cues that enhance and continue bone regeneration, scaffolds can be incorporated with bioactive gels for time- and dose-controlled delivery of multiple growth factors (GFs). In this study, critical femoral bone defects in rats were grafted with porous titanium scaffolds incorporated with nanostructured colloidal gelatin gels. Gels were loaded with bone morphogenetic protein-2 (BMP-2, 3 μg), fibroblast growth factor-2 (FGF-2, 0.6 μg), BMP-2, and FGF-2 (BMP-2/FGF-2, ratio 5:1) or were left unloaded. GF delivery was controlled by fine tuning the crosslinking density of oppositely charged nanospheres. Grafted femurs were evaluated using in vivo and ex vivo micro-CT, histology, and three-point bending tests. All porous titanium scaffolds containing GF-loaded gels accelerated and enhanced bone regeneration: BMP-2 gels gave an early increase (0-4 weeks), and FGF-2 gels gave a late increase (8-12 weeks). Interestingly, stimulatory effects of 0.6 μg FGF-2 were similar to a fivefold higher dose of BMP-2 (3 μg). BMP-2/FGF-2 gels gave more bone outside the porous titanium scaffolds than gels with only BMP-2 or FGF-2, resulted in bridging of most defects and showed superior bone-implant integrity in three-point bending tests. In conclusion, incorporation of nanostructured colloidal gelatin gels capable of time- and dose-controlled delivery of BMP-2 and FGF-2 in porous titanium scaffolds is a promising strategy to enhance and continue bone regeneration of large bone defects.

Immunolocalization of bone morphogenetic protein 2 during the early healing events after guided bone regeneration

OBJECTIVE

The objective of this study was to evaluate the immunolocalization of bone morphogenetic protein 2 (BMP-2) after autogenous block grafting covered or not with an e-PTFE membrane.

STUDY DESIGN

Forty-eight rats were divided into 2 groups, autogenous block graft (B) and autogenous block graft + e-PTFE membrane (MB), and were evaluated by immunohistochemistry at baseline and 3, 7, 14, 21, and 45 days.

RESULTS

The largest number of positive cells in the recipient bed was observed after 3 days in both groups. At the graft border, the largest number of positive cells was seen after 7 days in group B and after 14 days in group MB. The highest proportion of staining in the graft was observed after 3 days in group B and after 21 days in group MB.

CONCLUSIONS

High proportions of stain were related to intense revascularization and osteogenesis. Except for the interface, BMP-2 staining occurred later in group MB than in group B in all structures analyzed.

Localized delivery of growth factors for angiogenesis and bone formation in tissue engineering

Angiogenesis is a key component of bone formation. Delivery of growth factors for both angiogenesis and osteogenesis is about to gain important potential as a future therapeutic tool. This review focuses on these growth factors that have dual functions in angiogenesis and osteogenesis, and their localized application. A major hurdle in the clinical development of growth factor therapy so far is how to assure safe and efficacious therapeutic use of such factors and avoid unwanted side effects and toxicity. It is now firmly established from the available information that the type, dose, combinations and delivery kinetics of growth factors all play a decisive role for the success of growth factor therapy. All of these parameters have to be adapted and optimized for each animal model or clinical case. In this review we discuss some important parameters associated with growth factor therapy and present an overview of selected preclinical studies, followed by a conceptual description of both established and proposed delivery strategies meeting therapeutic needs.

Combined delivery of BMP-2 and bFGF from nanostructured colloidal gelatin gels and its effect on bone regeneration in vivo

During the process of bone regeneration, a multitude of morphogenetic signaling factors regulate cellular behavior and ultimately tissue response. These factors are presented to cells under strong spatial and temporal control, which stresses the relevance of controlled delivery of multiple growth factors for bone tissue regeneration. This demand for biomimetic delivery has prompted the development of a novel generation of biomaterials that is capable of delivering multiple growth factors in a controlled manner. Therefore, the current study has exploited the strong capacity of colloidal gels solely made of oppositely charged gelatin nanospheres to obtain controlled release of angiogenic and osteogenic growth factors. The release kinetics of dual delivery of osteogenic bone morphogenetic protein-2 (BMP-2) and angiogenic basic fibroblast growth factor (bFGF) were investigated in vitro by radiolabeling the respective growth factors and monitoring their release in vitro. Furthermore, the effect of single or dual delivery of BMP-2 and bFGF on bone regeneration was evaluated in vivo using a rat femoral condyle defect model. The in vitro results confirmed that the delivery kinetics of BMP-2 and/or bFGF are more dependent on the degree of crosslinking than on the type of gelatin. Sequential release characterized by rapid release of angiogenic bFGF and more sustained release of BMP-2 was obtained by loading bFGF onto cationic nanospheres of low crosslinking density and BMP-2 onto anionic nanospheres of high crosslinking density. The in vivo study demonstrated the biocompatibility and biodegradability of bare colloidal gelatin gels, and did not show any adverse effects on the process of bone healing after 4 week of implantation since the volumes of new bone formation were comparable to empty control defects. An obvious stimulatory effect on bone regeneration was observed for the colloidal gels loaded with BMP-2, whereas bFGF-loaded colloidal gelatin gels did not influence the rate of bone regeneration. In contrast, the combined delivery of BMP-2 and bFGF resulted into an inhibitory effect on osteogenesis under the current experimental conditions. Summarizing, the current study proved that nanostructured colloidal gelatin gels are suitable carriers for programmed and sustained release of multiple therapeutic proteins for tissue regeneration.

Bone morphogenetic proteins in craniofacial surgery: current techniques, clinical experiences, and the future of personalized stem cell therapy

Critical-size osseous defects cannot heal without surgical intervention and can pose a significant challenge to craniofacial reconstruction. Autologous bone grafting is the gold standard for repair but is limited by a donor site morbidity and a potentially inadequate supply of autologous bone. Alternatives to autologous bone grafting include the use of alloplastic and allogenic materials, mesenchymal stem cells, and bone morphogenetic proteins. Bone morphogenetic proteins (BMPs) are essential mediators of bone formation involved in the regulation of differentiation of osteoprogenitor cells into osteoblasts. Here we focus on the use of BMPs in experimental models of craniofacial surgery and clinical applications of BMPs in the reconstruction of the cranial vault, palate, and mandible and suggest a model for the use of BMPs in personalized stem cell therapies.

Contemporary concepts in treatment planning, reconstruction and rehabilitation of the maxillofacial region: an overview of methods used in practice

Treatment planning, reconstruction and rehabilitation of maxillofacial and dental defects have always been a challenge for a maxillofacial surgeon. Reconstruction of the oral cavity is often a difficult task as it involves the restoration of both the esthetic or cosmetic form as well as the preoperative function. Understanding the oral cavity anatomy as well the functional capacities of its various subunits is required to achieve good results. The recent advances in treatment planning, diagnostic imaging and reconstructive techniques, especially in the field of osseointegration, tissue expanders, perforator flaps, microvascular free tissue transfer and bone engineering, have yielded excellent functional and esthetic outcomes. This article provides a brief overview on various advanced reconstructive and rehabilitation techniques available in contemporary clinical practice.

Mesenchymal stem cells show radioresistance in vivo

Irradiation impacts on the viability and differentiation capacity of tissue-borne mesenchymal stem cells (MSC), which play a pivotal role in bone regeneration. As a consequence of radiotherapy, bones may develop osteoradionecrosis. When irradiating human bone-derived MSC in vitro with increasing doses, the cells’ self-renewal capabilities were greatly reduced. Mitotically stalled cells were still capable of differentiating into osteoblasts and pre-adipocytes. As a large animal model comparable to the clinical situation, pig mandibles were subjected to fractionized radiation of 2 χ 9 Gy within 1 week. This treatment mimics that of a standardized clinical treatment regimen of head and neck cancer patients irradiated 30 χ 2 Gy. In the pig model, fractures which had been irradiated, showed delayed osseous healing. When isolating MSC at different time points post-irradiation, no significant changes regarding proliferation capacity and osteogenic differentiation potential became apparent. Therefore, pig mandibles were irradiated with a single dose of either 9 or 18 Gy in vivo, and MSC were isolated immediately afterwards. No significant differences between the untreated and 9 Gy irradiated bone with respect to proliferation and osteogenic differentiation were unveiled. Yet, cells isolated from 18 Gy irradiated specimens exhibited a reduced osteogenic differentiation capacity, and during the first 2 weeks proliferation rates were greatly diminished. Thereafter, cells recovered and showed normal proliferation behaviour. These findings imply that MSC can effectively cope with irradiation up to high doses in vivo. This finding should thus be implemented in future therapeutic concepts to protect regenerating tissue from radiation consequences.

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.

ICRP publication 118: ICRP statement on tissue reactions and early and late effects of radiation in normal tissues and organs--threshold doses for tissue reactions in a radiation protection context

This report provides a review of early and late effects of radiation in normal tissues and organs with respect to radiation protection. It was instigated following a recommendation in Publication 103 (ICRP, 2007), and it provides updated estimates of 'practical' threshold doses for tissue injury defined at the level of 1% incidence. Estimates are given for morbidity and mortality endpoints in all organ systems following acute, fractionated, or chronic exposure. The organ systems comprise the haematopoietic, immune, reproductive, circulatory, respiratory, musculoskeletal, endocrine, and nervous systems; the digestive and urinary tracts; the skin; and the eye. Particular attention is paid to circulatory disease and cataracts because of recent evidence of higher incidences of injury than expected after lower doses; hence, threshold doses appear to be lower than previously considered. This is largely because of the increasing incidences with increasing times after exposure. In the context of protection, it is the threshold doses for very long follow-up times that are the most relevant for workers and the public; for example, the atomic bomb survivors with 40-50years of follow-up. Radiotherapy data generally apply for shorter follow-up times because of competing causes of death in cancer patients, and hence the risks of radiation-induced circulatory disease at those earlier times are lower. A variety of biological response modifiers have been used to help reduce late reactions in many tissues. These include antioxidants, radical scavengers, inhibitors of apoptosis, anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, growth factors, and cytokines. In many cases, these give dose modification factors of 1.1-1.2, and in a few cases 1.5-2, indicating the potential for increasing threshold doses in known exposure cases. In contrast, there are agents that enhance radiation responses, notably other cytotoxic agents such as antimetabolites, alkylating agents, anti-angiogenic drugs, and antibiotics, as well as genetic and comorbidity factors. Most tissues show a sparing effect of dose fractionation, so that total doses for a given endpoint are higher if the dose is fractionated rather than when given as a single dose. However, for reactions manifesting very late after low total doses, particularly for cataracts and circulatory disease, it appears that the rate of dose delivery does not modify the low incidence. This implies that the injury in these cases and at these low dose levels is caused by single-hit irreparable-type events. For these two tissues, a threshold dose of 0.5Gy is proposed herein for practical purposes, irrespective of the rate of dose delivery, and future studies may elucidate this judgement further.

Enhanced bone regeneration with sequential delivery of basic fibroblast growth factor and sonic hedgehog

BACKGROUND

Bone regeneration approaches that mimic the natural processes of bone repair have generated significant attention. We hypothesized that early delivery of an angiogenic factor combined with sustained exposure to an osteogenic factor would recapitulate the critical aspects of natural bone repair.

MATERIALS AND METHODS

Basic fibroblast growth factor (bFGF) and sonic hedgehog (Shh) were constructed to the recombinant adeno-associated virus, respectively (rAAV2-tet-off-bFGF and rAAV2-Shh). The previous viral vector allowed for regulation of the bFGF expression by the addition of doxycycline, a tetracycline analogue. These two viral vectors were used to cotransduce bone marrow-derived mesenchymal stem cells (BMSCs). Several osteogenic markers such as core-binding factor a-1, alkaline phosphatase and osteocalcin were detected by quantitative real-time reverse transcriptase polymerase chain reaction. Meanwhile, protein expressions of transgenes were measured by western blot. Furthermore, these cotransduced BMSCs were seeded on β-tricalcium phosphate (β-TCP) granules and then were implanted into the calvarium defect in a rat model. A sample of 30 Sprague-Dawley rats was divided into six groups (n=5); an 8-mm critical-sized bone defect was made in calvarium of all subjects. Each group was treated with various transgenic BMSCs and β-TCP composites; and the sixth group is the negative control which was implanted with nothing. At 4 weeks after treatment, the samples were evaluated with histological staining.

RESULTS

The expression of osteogenic marker mRNA had an increased tendency after two genes transduction (p<0.05). In addition, dramatically enhanced regeneration of critical-sized calvarial defects was observed in the groups which were implanted with two transgenic BMSCs and β-TCP composites. And in these experimental groups, bone areas and vascular densities were increased significantly (p<0.05) than other groups.

CONCLUSION

Sequential delivery of angiogenic and osteogenic factors likely has a synergistic effect, mimicking the molecular events of natural bone regeneration.

Reconstruction of a mandibular defect with autogenous, autoclaved bone grafts and tissue engineering: An in vivo pilot study

Reconstruction of bone defects with autogenous, autoclaved bone grafts has already been described but does have one major insuperable problem-the loss of the ostoinductive potential of the graft. In this study, we investigated if autogenous, autoclaved grafts in combination with tissue engineered bone can overcome this problem. An en-bloc resection was done in the mandible of eight pigs. The grafts were autoclaved and filled with autogenous, osseogen differentiated bone marrow cells and compared with four animals without bone marrow cells. After 120 days, the specimens were qualitatively and quantitatively evaluated by means of microradiography and light microscopy. Within the experimental group, osseous remodeling was detected in all cases and new bone formation was visible. Quantitative assessment of the osseous bridging of the osteotomy sites was significantly higher in the test group in comparison with the control group (p = 0.03). The histological evaluation by means of an osseous integration of the grafts revealed a statistically significant difference between both groups as well (p = 0.01). The results of this study indicate that the method investigated hereby represents a further possibility in the therapy of bony defects, such as those arising as a result of tumor operations.

Radiation effects on bone healing and reconstruction: interpretation of the literature

OBJECTIVE

Reconstructing irradiated mandibles with biomaterials is still a challenge but little investigated. We collected data that could help us understand studies in the field of regeneration with biomaterials and irradiated bone.

STUDY DESIGN

Systematic review of the literature.

RESULTS

Delay and duration of radiation delivery and total equivalent dose are the most variable parameters in the various studies, resulting in confusion when interpreting the literature. Most reproducible experiments show that radiation reduces osteogenic cell numbers, alters cytokine capacity, and delays and damages bone remodeling. Interindividual variations and how such changes become irreversible lesions are still uncertain. In the case of regeneration using biomaterials, most studies have addressed the question of reconstruction in previously irradiated bone. The results show that osseointegration is often possible, although the failure rate is higher. The sooner the implantation takes place after the end of the radiation, the higher the likelihood of failure. Few studies have focused on primary reconstruction followed by early irradiation, and most of the currently available engineering models would be altered by radiation. Good outcomes have been obtained with bone morphogenetic protein and with total bone marrow transplanation.

CONCLUSION

This review points out the difficulties in achieving reproducible experiments and interpreting literature in this underinvestigated field.

Validation of histologic changes induced by external irradiation in mandibular bone. An experimental animal model

The present experimental study sought to determine the effect of high-dose irradiation on the rat mandible in order to establish an experimental model of radiogenic bone damage. The left mandibles of 20 adult Wistar rats were irradiated (single fraction 1500cGy, total dose 60Gy) by means of a hypofractionated stereotactic radiotherapy (hfSRT) over a period of 6 weeks. Follow-up was 6 weeks (group 1, n=10) and 12 weeks (group 2, n=10). The contralateral mandibles as well as 5 non-irradiated animals served as controls. Primary endpoints were fibrosis, loss of cell count, decreased immunohistochemical labelling for bone morphogenetic protein-2 (BMP-2) and osteocalcin as well as increased expression of transforming growth factor (TGF-beta). Cell loss, progressive fibrosis, and focal necrosis were detected in all irradiated sites. Quantitative measurement revealed 32.0+/-8.7% and 37.3+/-9.5% empty osteocyte lacunae for groups 1 and 2 resp., compared to 16.3+/-4.7% and 18.9+/-4.9% on the contralateral side and 7.9+/-1.7% for unirradiated controls (Mann-Whitney U test; p<.01). BMP-2 and osteocalcin labelling showed a marked decrease in irradiated and contralateral sides while TGF-beta was expressed strongly in irradiated sites only (for all p<.05). External hypofractionated irradiation with a total dose of 60Gy is feasible in rats and yields all histologic changes attributed to osteoradionecrosis (ORN) after a follow-up of 6 weeks. The irradiation protocol is suitable for an assessment of regenerative options in severe radiogenic bone damage. As a split mouth design entails major inaccuracies healthy animals have to be used as controls.

A preliminary report on the effect of dimeric rhGDF-5 and its monomeric form rhGDF-5C465A on bone healing of rat cranial defects

INTRODUCTION

The purpose of the study was to compare the efficacy on rat skull defects of two bone growth factors derived from the GDF-5 family.

MATERIAL AND METHODS

The study was conducted on 17 adult Wistar rats. On each animal, two symmetrical 6-mm wide, full-thickness, skull defects were carried out in the parietal regions. In 15 out of 17 animals, both experimental defects were filled by the implants. In the group I (n=2), both defects were left empty for control. The 15 other rats were divided into 3 groups: In group II (n=5), a collagen sponge was implanted. In group III (n=5), a collagen sponge impregnated with rhGDF-5 (the genuine dimeric form) was implanted. In group IV (n=5), a collagen sponge impregnated with rhGDF-5C465A (a monomeric form of GDF-5) was implanted. All animals were sacrificed at 8 weeks. The harvested specimens were processed for contact radiography and standard histological examination. The quantitative results were assessed with a semi-quantitative histological scoring system.

RESULTS

One animal in the group II was excluded because it died of unknown reasons. In group I, no bone healing was observed in the defects. In group II, no bone healing was observed in 4 out of 10 defects, and partial bone healing was observed in 5 out of 10 defects. In group III, partial bone healing was also observed in 3 out of 8 defects and complete bone healing in 4 out of 8 defects. In group IV, partial bone healing was observed in 8 out of 10 defects and complete bone healing in 2 out of 10 defects.

CONCLUSION

Bone healing was improved in all treated groups. Further studies are necessary to determine the optimal formulation of these composite implants.