Dual growth factor delivery from biofunctionalized allografts: Sequential VEGF and BMP-2 release to stimulate allograft remodeling

Strategies of functionalized GelMA-based bioinks for bone regeneration: Recent advances and future perspectives

Gelatin methacryloyl (GelMA) hydrogels is a widely used bioink because of its good biological properties and tunable physicochemical properties, which has been widely used in a variety of tissue engineering and tissue regeneration. However, pure GelMA is limited by the weak mechanical strength and the lack of continuous osteogenic induction environment, which is difficult to meet the needs of bone repair. Moreover, GelMA hydrogels are unable to respond to complex stimuli and therefore are unable to adapt to physiological and pathological microenvironments. This review focused on the functionalization strategies of GelMA hydrogel based bioinks for bone regeneration. The synthesis process of GelMA hydrogel was described in details, and various functional methods to meet the requirements of bone regeneration, including mechanical strength, porosity, vascularization, osteogenic differentiation, and immunoregulation for patient specific repair, etc. In addition, the response strategies of smart GelMA-based bioinks to external physical stimulation and internal pathological microenvironment stimulation, as well as the functionalization strategies of GelMA hydrogel to achieve both disease treatment and bone regeneration in the presence of various common diseases (such as inflammation, infection, tumor) are also briefly reviewed. Finally, we emphasized the current challenges and possible exploration directions of GelMA-based bioinks for bone regeneration.

Enzyme-Mediated Nerve Growth Factor Release from Nanofibers Using Gelatin Microspheres

Spinal cord injury is a complex environment, with many conflicting growth factors present at different times throughout the injury timeline. Delivery of multiple growth factors has received mixed results, highlighting a need to consider the timing of delivery for possibly antagonistic growth factors. Cell-mediated degradation of delivery vehicles for delayed release of growth factors offers an attractive way to exploit the highly active immune response in the spinal cord injury environment. In this study, growth factor-loaded gelatin microspheres (GMS) combined with methacrylated hyaluronic acid (MeHA) were electrospun to create GMS fibers (GMSF) for delayed release of growth factors (GFs). GMS were successfully combined with MeHA while electrospinning, with an average fiber diameter of 365 ± 10 nm and 44% ± 8% fiber alignment. GMSF with nerve growth factor (NGF) was tested on dissociated chick dorsal root ganglia cells. We further tested the effect of M1 macrophage-conditioned media (M1CM) to simulate macrophage invasion after spinal cord injury for cell-mediated degradation. We hypothesized that neurons grown on GMSF with loaded NGF would exhibit longer neurites in M1CM, showing a release of functional NGF, as compared with controls. GMSF in M1CM was significantly different from MeHA in serum-free media (SFM) and M0-conditioned media (M0CM), as well as GMSF in M0CM (p < 0.05). Moreover, GMSF + NGF in all media conditions were significantly different from MeHA in SFM and M0CM (p < 0.05). The goal of this study was to develop a biomaterial system where drug delivery is triggered by immune response, allowing for more control and longer exposure to encapsulated drugs. The spinal cord injury microenvironment is known to have a robust immune response, making this immune-medicated drug release system particularly significant for directed repair.

Reducing retraction in engineered tissues through design of sequential growth factor treatment

Heart valve disease is associated with high morbidity and mortality worldwide, resulting in hundreds of thousands of heart valve replacements each year. Tissue engineered heart valves (TEHVs) have the potential to overcome the major limitations of traditional replacement valves; however, leaflet retraction has led to the failure of TEHVs in preclinical studies. Sequentially varying growth factors over time has been utilized to promote maturation of engineered tissues and may be effective in reducing tissue retraction, yet it is difficult to predict the effects of such treatments due to complex interactions between the cells and the extracellular matrix (ECM), biochemical environment, and mechanical stimuli. We hypothesize that sequential treatments of fibroblast growth factor 2 (FGF-2) and transforming growth factor beta 1 (TGF-β1) can be used to minimize cell-generated tissue retraction by decreasing active cell contractile forces exerted on the ECM and by inducing the cells to increase the ECM stiffness. Using a custom culturing and monitoring system for 3D tissue constructs, we designed and tested various TGF-β1 and FGF-2 based growth factor treatments, and successfully reduced tissue retraction by 85% and increased the ECM elastic modulus by 260% compared to non-growth factor treated controls, without significantly increasing the contractile force. We also developed and verified a mathematical model to predict the effects of various temporal variations in growth factor treatments and analyzed relationships between tissue properties, the contractile forces, and retraction. These findings improve our understanding of growth factor-induced cell-ECM biomechanical interactions, which can inform the design of next generation TEHVs with reduced retraction. The mathematical models could also potentially be applied toward fast screening and optimizing growth factors for use in the treatment of diseases including fibrosis.

3D-Printing for Critical Sized Bone Defects: Current Concepts and Future Directions

The management and definitive treatment of segmental bone defects in the setting of acute trauma, fracture non-union, revision joint arthroplasty, and tumor surgery are challenging clinical problems with no consistently satisfactory solution. Orthopaedic surgeons are developing novel strategies to treat these problems, including three-dimensional (3D) printing combined with growth factors and/or cells. This article reviews the current strategies for management of segmental bone loss in orthopaedic surgery, including graft selection, bone graft substitutes, and operative techniques. Furthermore, we highlight 3D printing as a technology that may serve a major role in the management of segmental defects. The optimization of a 3D-printed scaffold design through printing technique, material selection, and scaffold geometry, as well as biologic additives to enhance bone regeneration and incorporation could change the treatment paradigm for these difficult bone repair problems.

Construction and osteogenic effects of 3D-printed porous titanium alloy loaded with VEGF/BMP-2 shell-core microspheres in a sustained-release system

The repair and reconstruction of bone defects remain a challenge in orthopedics. The present study offers a solution to this problem by developing a vascular endothelial growth factor (VEGF)/bone morphogenetic protein 2 (BMP-2) shell-core microspheres loaded on 3D-printed porous titanium alloy via gelatin coating to prepare a titanium-alloy microsphere scaffold release system. The composite scaffold was characterized via scanning electron microscope (SEM) and energy disperse spectroscopy (EDS), and the effect of the composite scaffold on the adhesion, proliferation, and differentiation of osteoblasts were determined in vitro. Furthermore, a rabbit femoral defect model was established to verify the effect of the composite scaffold on osteogenesis and bone formation in vivo. The results demonstrated that the composite scaffold could release VEGF and BMP-2 sequentially. Meanwhile, the composite scaffold significantly promoted osteoblast adhesion, proliferation, and differentiation (p < 0.05) compared to pure titanium alloy scaffolds in vitro. Furthermore, the composite scaffold can exhibit significant osteogenic differentiation (p < 0.05) than gelatin-coated titanium alloy scaffolds. The in vivo X-rays demonstrated that the implanted scaffolds were in a good position, without inflammation and infection. Micro-CT and quantitative results of new bone growth illustrated that the amount of new bone in the composite scaffold is significantly higher than that of the gelatin-coated and pure titanium alloy scaffolds (p < 0.05). Similarly, the fluorescence labeling and V-G staining of hard tissue sections indicated that the bone integration capacity of the composite scaffold was significantly higher than the other two groups (p < 0.05). This research suggests that VEGF/BMP-2 shell-core microspheres loaded on 3D-printed titanium alloy porous scaffold through gelatin hydrogel coating achieved the sequential release of VEGF and BMP-2. Most importantly, the in vitro and in vivo study findings have proven that the system could effectively promote osteogenic differentiation and osseointegration.

Effect of bone-shaped nanotube-hydrogel drug delivery system for enhanced osseointegration

Anodic titanium dioxide nanotubes (TNT) have a range of beneficial theranostic properties. However, a lack of effective osseointegration is a problem frequently associated with the titanium dental implant surface. Here, we investigated whether bone-shaped nanotube titanium implants could enhance osseointegration via promoting initial release of vascular endothelial growth factor 165 (VEGF165) and dual release of recombinant human bone morphogenetic protein-2 (rhBMP-2). Thus, we generated cylindrical-shaped nanotubes (TNT1) and bone-shaped nanotubes (TNT2) through voltage-varying and time-varying electrochemical anodization methods, respectively. Additionally, we prepared rhBMP-2-loaded cylindrical-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F1) and rhBMP-2-loaded bone-shaped nanotubes/VEGF165-loaded hydrogel (TNT-F2) drug delivery systems. We evaluated the characteristics and release kinetics of the drug delivery systems, and then analyzed the cytocompatibility and osteogenic differentiation of these specimens with mesenchymal stem cells (MSCs) in vitro. Finally, we utilized a rat femur defect model to test the bone formation capacity of nanotube-hydrogel drug delivery system in vivo. Among these different nanotubes structures, the bone-shaped one was the optimum structure for growth factor release.

Nano-Hydroxyapatite as a Delivery System for Promoting Bone Regeneration In Vivo: A Systematic Review

Nano-hydroxyapatite (nHA) has been widely used as an orthopedic biomaterial and vehicle for drug delivery owing to its chemical and structural similarity to bone minerals. Several studies have demonstrated that nHA based biomaterials have a potential effect for bone regeneration with very minimal to no toxicity or inflammatory response. This systematic review aims to provide an appraisal of the effectiveness of nHA as a delivery system for bone regeneration and whether the conjugation of proteins, antibiotics, or other bioactive molecules to the nHA further enhances osteogenesis in vivo. Out of 282 articles obtained from the literature search, only 14 articles met the inclusion criteria for this review. These studies showed that nHA was able to induce bone regeneration in various animal models with large or critical-sized bone defects, open fracture, or methicillin-resistant Staphylococcus aureus (MRSA)-induced osteomyelitis. The conjugations of drugs or bioactive molecules such as bone-morphogenetic protein-2 (BMP-2), vancomycin, calcitriol, dexamethasone, and cisplatin were able to enhance the osteogenic property of nHA. Thus, nHA is a promising delivery system for a variety of compounds in promoting bone regeneration in vivo.

Development of novel gene carrier using modified nano hydroxyapatite derived from equine bone for osteogenic differentiation of dental pulp stem cells

Hydroxyapatite (HA) is a representative substance that induces bone regeneration. Our research team extracted nanohydroxyapatite (EH) from natural resources, especially equine bones, and developed it as a molecular biological tool. Polyethylenimine (PEI) was used to coat the EH to develop a gene carrier. To verify that PEI is well coated in the EH, we first observed the morphology and dispersity of PEI-coated EH (pEH) by electron microscopy. The pEH particles were well distributed, while only the EH particles were not distributed and aggregated. Then, the existence of nitrogen elements of PEI on the surface of the pEH was confirmed by EDS, calcium concentration measurement and fourier transform infrared spectroscopy (FT-IR). Additionally, the pEH was confirmed to have a more positive charge than the 25 kD PEI by comparing the zeta potentials. As a result of pGL3 transfection, pEH was better able to transport genes to cells than 25 kD PEI. After verification as a gene carrier for pEH, we induced osteogenic differentiation of DPSCs by loading the BMP-2 gene in pEH (BMP-2/pEH) and delivering it to the cells. As a result, it was confirmed that osteogenic differentiation was promoted by showing that the expression of osteopontin (OPN), osteocalcin (OCN), and runt-related transcription factor 2 (RUNX2) was significantly increased in the group treated with BMP-2/pEH. In conclusion, we have not only developed a novel nonviral gene carrier that is better performing and less toxic than 25 kD PEI by modifying natural HA (the agricultural byproduct) but also proved that bone differentiation can be effectively promoted by delivering BMP-2 with pEH to stem cells.

Triple growth factor delivery promotes functional bone regeneration following composite musculoskeletal trauma

Successful bone healing in severe trauma depends on early revascularization to restore oxygen, nutrient, growth factor, and progenitor cell supply to the injury. Therapeutic angiogenesis strategies have therefore been investigated to promote revascularization following severe bone injuries; however, results have been inconsistent. This is the first study investigating the effects of dual angiogenic growth factors (VEGF and PDGF) with low-dose bone morphogenetic protein-2 (BMP-2; 2.5 µg) on bone healing in a clinically challenging composite bone-muscle injury model. Our hydrogel-based delivery systems demonstrated a more than 90% protein entrapment efficiency and a controlled simultaneous release of three growth factors over 28 days. Co-stimulation of microvascular fragment constructs with VEGF and PDGF promoted vascular network formation in vitro compared to VEGF or PDGF alone. In an in vivo model of segmental bone and volumetric muscle loss injury, combined VEGF (5 µg) and PDGF (7.5 µg or 15 µg) delivery with a low dose of BMP-2 significantly enhanced regeneration of vascularized bone compared to BMP-2 treatment alone. Notably, the regenerated bone mechanics reached ~60% of intact bone, a value that was previously only achieved by delivery of high-dose BMP-2 (10 µg) in this injury model. Overall, sustained delivery of VEGF, PDFG, and BMP-2 is a promising strategy to promote functional vascularized bone tissue regeneration following severe composite musculoskeletal injury. Although this study is conducted in a clinically relevant composite injury model in rats using a simultaneous release strategy, future studies are necessary to test the regenerative potential of spatiotemporally controlled delivery of triple growth factors on bone healing using large animal models. STATEMENT OF SIGNIFICANCE: Volumetric muscle loss combined with delayed union or non-union bone defect causes deleterious effects on bone regeneration even with the supplementation of bone morphogenetic protein-2 (BMP-2). In this study, the controlled delivery of dual angiogenic growth factors (vascular endothelial growth factor [VEGF] + Platelet-derived growth factor [PDGF]) increases vascular growth in vitro. Co-delivering VEGF+PDGF significantly increase the bone formation efficacy of low-dose BMP-2 and improves the mechanics of regenerated bone in a challenging composite bone-muscle injury model.

Musculoskeletal tissue engineering: Regional gene therapy for bone repair

Bone loss associated with fracture nonunion, revision total joint arthroplasty (TJA), and pseudoarthrosis of the spine presents a challenging clinical scenario for the orthopaedic surgeon. Current treatment options including autograft, allograft, bone graft substitutes, and bone transport techniques are associated with significant morbidity, high costs, and prolonged treatment regimens. Unfortunately, these treatment strategies have proven insufficient to safely and consistently heal bone defects in the stringent biological environments often encountered in clinical cases of bone loss. The application of tissue engineering (TE) to musculoskeletal pathology has uncovered exciting potential treatment strategies for challenging bone loss scenarios in orthopaedic surgery. Regional gene therapy involves the local implantation of nucleic acids or genetically modified cells to direct specific protein expression, and has shown promise as a potential TE technique for the regeneration of bone. Preclinical studies in animal models have demonstrated the ability of regional gene therapy to safely and effectively heal critical sized bone defects which otherwise do not heal. The purpose of the present review is to provide a comprehensive overview of the current status of gene therapy applications for TE in challenging bone loss scenarios, with an emphasis on gene delivery methods and models, scaffold biomaterials, preclinical results, and future directions.

Periosteum Mimetic Coating on Structural Bone Allografts via Electrospray Deposition Enhances Repair and Reconstruction of Segmental Defects

Structural bone allograft transplantation remains one of the common strategies for repair and reconstruction of large bone defects. Due to the loss of periosteum that covers the outer surface of the cortical bone, the healing and incorporation of allografts is extremely slow and limited. To enhance the biological performance of allografts, herein, we report a novel and simple approach for engineering a periosteum mimetic coating on the surface of structural bone allografts via polymer-mediated electrospray deposition. This approach enables the coating on allografts with precisely controlled composition and thickness. In addition, the periosteum mimetic coating can be tailored to achieve desired drug release profiles by making use of an appropriate biodegradable polymer or polymer blend. The efficacy study in a murine segmental femoral bone defect model demonstrates that the allograft coating composed of poly(lactic-co-glycolic acid) and bone morphogenetic protein-2 mimicking peptide significantly improves allograft healing as evidenced by decreased fibrotic tissue formation, increased periosteal bone formation, and enhanced osseointegration. Taken together, this study provides a platform technology for engineering a periosteum mimetic coating which can greatly promote bone allograft healing. This technology could eventually result in an off-the-shelf and multifunctional structural bone allograft for highly effective repair and reconstruction of large segmental bone defects. The technology can also be used to ameliorate the performance of other medical implants by modifying their surfaces.

New Function of RUNX2 in Regulating Osteoclast Differentiation via the AKT/NFATc1/CTSK Axis

Cleidocranial dysplasia is an autosomal dominant skeletal disorder resulting from RUNX2 mutations. The influence of RUNX2 mutations on osteoclastogenesis and bone resorption have not been reported. To investigate the role of RUNX2 in osteoclast, RUNX2 expression in macrophages (RAW 264.7 cells) was detected. Stable RAW 264.7 cell lines expressing wild-type RUNX2 or mutated RUNX2 (c.514delT, p.172 fs) were established, and their functions in osteoclasts were investigated. Wild-type RUNX2 promoted osteoclast differentiation, formation of F-actin ring, and bone resorption, while mutant RUNX2 attenuated the positive differentiation effect. Wild-type RUNX2 increased the expression and activity of mTORC2. Subsequently, mTORC2 specifically promoted phosphorylation of AKT at the serine 473 residue. Activated AKT improved the nuclear translocation of NFATc1 and increased the expression of downstream genes, including CTSK. Inhibition of AKT phosphorylation abrogated the osteoclast formation of wild-type macrophages, whereas constitutively activated AKT rescued the osteoclast formation of mutant macrophages. The present study suggested that RUNX2 promotes osteoclastogenesis and bone resorption through the AKT/NFATc1/CTSK axis. Mutant RUNX2 lost the function of regulating osteoclast differentiation and bone remodeling, resulting in the defective formation of the tooth eruption pathway and impaction of permanent teeth in cleidocranial dysplasia. This study, for the first time, verifies the effect of RUNX2 on osteoclast differentiation and bone resorption and provides new insight for the explanation of cleidocranial dysplasia.

Magnetic lanthanum-doped hydroxyapatite/chitosan scaffolds with endogenous stem cell-recruiting and immunomodulatory properties for bone regeneration

Magnetic lanthanum hydroxyapatite/chitosan scaffolds can better repair bone defects through stem cell recruitment and immunomodulation.

Biomimetic Nanosilica-Collagen Scaffolds for In Situ Bone Regeneration: Toward a Cell-Free, One-Step Surgery

Current approaches to fabrication of nSC composites for bone tissue engineering (BTE) have limited capacity to achieve uniform surface functionalization while replicating the complex architecture and bioactivity of native bone, compromising application of these nanocomposites for in situ bone regeneration. A robust biosilicification strategy is reported to impart a uniform and stable osteoinductive surface to porous collagen scaffolds. The resultant nSC composites possess a native-bone-like porous structure and a nanosilica coating. The osteoinductivity of the nSC scaffolds is strongly dependent on the surface roughness and silicon content in the silica coating. Notably, without the use of exogenous cells and growth factors (GFs), the nSC scaffolds induce successful repair of a critical-sized calvarium defect in a rabbit model. It is revealed that topographic and chemical cues presented by nSC scaffolds could synergistically activate multiple signaling pathways related to mesenchymal stem cell recruitment and bone regeneration. Thus, this facile surface biosilicification approach could be valuable by enabling production of BTE scaffolds with large sizes, complex porous structures, and varied osteoinductivity. The nanosilica-functionalized scaffolds can be implanted via a cell/GF-free, one-step surgery for in situ bone regeneration, thus demonstrating high potential for clinical translation in treatment of massive bone defects.

Experimental study of the synergistic effect and network regulation mechanisms of an applied combination of BMP-2, VEGF, and TGF-β1 on osteogenic differentiation

The study aimed to explore the osteogenic effect induced by the combined use of bone morphogenetic protein-2 (BMP-2), vascular endothelial growth factor (VEGF), and transforming growth factor-β1 (TGF-β1), attain the best combination for osteogenic quality and efficiency, and explore the network regulation mechanisms of induced osteogenesis. MC3T3-E1 cells were cultured in vitro, and BMP-2, VEGF, and TGF β1 were added to osteogenic induction mediums in different combinations to conduct experiments. At 7 and 14 days, the alkaline phosphatase (ALP) and Alizarin Red S (ARS) staining of the applied BMP-2 and VEGF combination were deeper and the quantitative analysis were higher than those of the other groups. After optimizing the time-effect relationship of the combined application, with BMP-2, VEGF, and TGF-β1 adding in the early stage and BMP-2 and VEGF adding in the late, the ALP and ARS staining of these groups were deeper and the quantitative analyses were meaningfully higher than the BMP-2 and VEGF combination group at 7 and 14 days. The expression of the RUNX2 gene and the Smad1 signaling pathway in the optimized combination group was also significantly higher. The results demonstrate that the combination of BMP-2, VEGF, and TGF-β1 applied according to the time-effect relationship can significantly promote osteogenic differentiation mainly through the classical BMP-receptor-Smad signal pathway.

Dual functional approaches for osteogenesis coupled angiogenesis in bone tissue engineering

Bone fracture healing is a multistep and overlapping process of inflammation, angiogenesis and osteogenesis. It is initiated by inflammation, causing the release of various cytokines and growth factors. It leads to the recruitment of stem cells and formation of vasculature resulting in the functional bone formation. This combined phenomenon is used by bone tissue engineers from past few years to address the problem of vasculature and osteogenic differentiation during bone regeneration. In this review, we have discussed all major studies reporting the dual functioning approach to promote osteogenesis coupled angiogenesis using various scaffolds. These scaffolds are broadly classified into four types based on the nature of their structural and functional components. The functionality of the scaffold is either due to the structural components or the loaded cargo which conducts or induces the coupled functionality. Dual delivery system for osteoinductive and angioinductive factors ensures the co-delivery of two different types of molecules to induce osteogenesis and angiogenesis. Single delivery scaffold for angioinductive and osteoinductive molecule releases single type of molecules which could induce both angiogenesis and osteogenesis. Osteoconductive scaffold consisted of bone constituents releases angioinductive factors. Osteoconductive and angioconductive scaffold composed of components which provide the native substrate features for osteogenesis and angiogenesis. This review article also discusses the studies highlighting the synergism of physico-chemical stimuli as dual functioning feature to enhance angiogenesis and osteogenesis simultaneously. In addition, this article covers one of the least discussed area of the bone regeneration i.e. 'cartilage formation as a median between angiogenesis and osteogenesis'.

Controlled in vivo Bone Formation and Vascularization Using Ultrasound-Triggered Release of Recombinant Vascular Endothelial Growth Factor From Poly(D,L-lactic-co-glycolicacid) Microbubbles

Bone defects are challenging to treat in musculoskeletal system due to the lack of vascularization. Biomaterials with internal vascularization ability and osteoinduction bioactivity are promising strategies for orthopedic applications. Vascular endothelial growth factor (VEGF) has been widely used for angiogenesis and osteogenesis. Here, we developed VEGF-loaded PLGA microbubbles (MBs) for improvement of angiogenesis and osteogenesis in bone defect repair in combination with ultrasound-targeted microbubble destruction (UTMD). Release profile showed UTMD promoted the burst release of VEGF from PLGA MBs. We subsequently investigated the combination of ultrasound application with VEGF MBs for in vitro osteogenesis. The results demonstrated that the expression of osteogenesis-related genes and calcium deposits were increased by VEGF MBs in combination of UTMD. Micro-computed tomography (micro-CT) and histological analysis were conducted 4 and 8 weeks post-surgery. In vivo results show that VEGF MBs in combination of UTMD could significantly enhance new bone formation and vascular ingrowth at the defect site in a rat calvarial defect model. In summary, VEGF MBs in combination of UTMD could augment bone regeneration and vascularization at calvarial bone defects and hold huge potential for clinical translation.

A New Method for Partial Breast Reconstruction: 3-Year New Zealand Experience

In New Zealand, oncoplastic surgery is common, but partial breast reconstruction presents challenges for radiation therapy targeting. Tissue rearrangement creates ambiguity when targeting the tumor bed, with resultant overestimation of treatment volumes. Thus, adoption of advanced methods of radiation therapy have been hindered. This pilot study describes use of a novel three-dimensional implant that provides a scaffolding for tissue ingrowth during partial breast reconstruction and delineates the tumor bed more precisely to assist radiation planning and mammographic surveillance. After informed consent, 15 women were implanted with the three-dimensional bioabsorbable implant. The device was sutured to the tumor bed during lumpectomy, and tissue flaps were mobilized and attached to the implant. Visualization of the marker and radiation treatment volumes were recorded and compared. The implant provided volume replacement and helped to maintain breast contour. Cosmetic outcomes were excellent; no device- or radiation-related complications occurred. One patient had a postoperative hematoma that resolved after percutaneous drainage; there were no postoperative infections. Three-year follow-up shows no tumor recurrences and no untoward effects. When compared to conventional radiation targeting, use of the implant showed that a greater than 50 percent reduction in treatment volume was possible in some cases. Three-year mammograms show no significant artifact, normal tissue ingrowth, and minimal fibrosis. This study describes a method of oncoplastic breast reconstruction using an implantable device that marks the site of tumor excision and provides for volume replacement with tissue ingrowth. Patients tolerated it well, and radiation therapy planning, positioning, and treatment were facilitated.

Nasal Dorsal Augmentation with Freeze-Dried Allograft Bone: 10-Year Comprehensive Review

Supplemental Digital Content is available in the text.

Background:

The aim of this study was to evaluate freeze-dried cortical allograft bone for nasal dorsal augmentation. The 42-month report on 18 patients was published in 2009 in Plastic and Reconstructive Surgery with 89 percent success at level II evidence, and this article is the 10-year comprehensive review of 62 patients.

Methods:

All grafts met standards recommended by the American Association of Tissue Banks, the U.S. Food and Drug Administration, and the Centers for Disease Control and Prevention. Objective evaluation of the persistence of graft volume was obtained by cephalometric radiography, cone beam volumetric computed tomography, and computed tomography at up to 10 years. Vascularization and incorporation of new bone elements within the grafts were demonstrated by fluorine-18 sodium fluoride positron emission tomography at up to 10 years. Subjective estimation of graft volume persisting up to 10 years was obtained by patient response to a query conducted by an independent surveyor.

Results:

The authors report objective proof of persistence of volume alone or combined with proof of neovascularization in 16 of 19 allografts. The authors report the patient’s subjective opinion of volume persistence in 37 of 43 grafts. The dorsal augmentation was assessed overall to be successful in 85 percent of 62 patients evaluated between 1 and 10 years, with a mean of 4.7 years.

Conclusions:

Freeze-dried allograft bone is a safe and equal alternative for dorsal augmentation without donor-site morbidity. Further studies are needed to (1) confirm these findings for young patients needing long-term reconstruction, and (2) partially demineralize allograft bone to allow carving with a scalpel.

CLINICAL QUESTION/LEVEL OF EVIDENCE:

Therapeutic, IV.

Intravenous administration of multipotent stromal cells and bone allograft modification to enhance allograft healing

Aim: This study investigated a coordinated strategy of revitalizing bone allograft with circulating multipotent stromal cells (MSCs). Materials & methods: After chemotactic and releasing assessments, stromal cell-derived factor 1 and platelet-derived growth factor BB in copolymers were coated on the bone allograft (Allo_S-P). Allograft coated with copolymers alone (Allo), as controls, or Allo_S-P was implanted into the femur of athymic mice, which received intravenous injections of human MSCs or saline at weeks 1, 2 and 3. Results: At week 8, the total callus volume (both cartilaginous and bony callus) around the allograft was the largest in the Allo_S-P + MSC group (p < 0.05). Conclusion: Coating bone allograft with stromal cell-derived factor 1 and platelet-derived growth factor BB and intravenous injections of MSCs improved allograft incorporation.

Osteogenesis and angiogenesis are simultaneously enhanced in BMP2-/VEGF-transfected adipose stem cells through activation of the YAP/TAZ signaling pathway

While bone has the capability to heal itself, there is a great difficulty in reconstituting large bone defects created by heavy trauma or the resection of malignant tumors.

Combination Use of BMP2 and VEGF165 Promotes Osseointegration and Stability of Titanium Implants in Irradiated Bone

Background

Clinical data demonstrated that failure rate of titanium implant in irradiated bone was 2-3 times higher than that in nonirradiated bone and it is difficult to get the ideal results in irradiated bone.

Purpose

The aim of the study was to investigate the effects of HBO, BMP2, VEGF165, and combined use of BMP2/VEGF165 on osseointegration and stability of titanium implant in irradiated bone.

Materials and Methods

Sixty rabbits were randomly assigned to 5 groups (control group, HBO group, VEGF165 group, BMP2 group, and BMP2/VEGF165 group) after receiving 15 Gy radiation. Implant surgery was performed on tibias eight weeks later. They were sacrificed at two or eight weeks after operation. Implant stability, calcium, and ALP activity in serum, the ratio of bone volume to total volume, the rate of bone growth, and gene expression were assessed.

Result

There was no mortality and no implants failed during the experiment. Implant stability was significantly compromised in the control group compared to the other four experimental groups, and the BMP2/VEGF165 group had the highest implant stability. HBO, BMP2, and VEGF165 significantly increased BV/TV and the rate of bone growth, while the BMP2/VEGF165 showed the best effect among groups. The expression of RUNX2 in HBO, BMP2, and VEGF165/BMP2 group was higher than that in the VEGF165 and control groups at two weeks. The expression of OCN in HBO, BMP2, VEGF165, and VEGF165/BMP2 groups was higher than that in the control group, and the gene expression of CD31 was higher in HBO, VEGF165, and BMP2/VEGF165 groups than that in control and BMP2 groups.

Conclusion

HBO, BMP2, and VEGF165 could increase bone formation around the implant and improved the implant stability in irradiated bone. The combination use of BMP2 and VEGF165 may be promising in the treatment of implant patients with radiotherapy.

Three-Dimensional Hierarchical Nanofibrous Collagen Scaffold Fabricated Using Fibrillated Collagen and Pluronic F-127 for Regenerating Bone Tissue

It is well known that a nanoscale fibrous structure can provide a unique stage for encouraging reasonable cell activities including attachment and proliferation owing to its similar topological structure to the extracellular matrix. Hence, the structure has been widely applied in tissue regeneration. Type-I collagen has been typically used as a typical tissue regenerative material owing to its biocompatibility and abundance, although it has potential for antigenicity. In particular, collagen has been fabricated in two different forms, porous spongy and nanofibers. However, although the structures provided outstanding cellular activities, they exhibit disadvantages such as low cell migration capabilities in a spongy scaffold owing to the low degree of interconnected macropores and low processability in fabricating three-dimensional (3D) structures in an electrospun collagen scaffold. Hence, the fabrication of 3D nanofibrous collagen structures with interconnected macropores can be extremely challenging. In this work, we developed a 3D collagen scaffold consisting of multilayered nanofibrous struts fabricated using a 3D printing process and pluronic F-127 (PF-127), which is a thermoreversible polymer. After optimizing various processing conditions, we successfully achieved the 3D nanofibrous collagen mesh structure with fully interconnected macropores. A 3D-printed collagen scaffold that was fabricated using a low-temperature printing process was applied as a control. Through various analyses using physical properties (surface morphology, fibronectin absorption, mechanical properties, etc.) and cell activities using preosteoblasts (MC3T3-E1), we are convinced that the newly designed 3D nanofibrous collagen scaffold can be a new promising scaffold for bone tissue engineering.

Immunomodulatory properties of graphene oxide for osteogenesis and angiogenesis

Background

The osteo-immunomodulatory properties of biomaterials play an important role in the outcomes of bone regeneration. Graphene oxide (GO) has been widely applied in many research fields due to its unique properties. However, the immunomodulatory properties of GO as a biomaterial for bone tissue engineering are still unclear.

Materials and methods

In this study, we evaluated the Inflammatory response of RAW264.7 cells influenced by GO. Then the osteogenic differentiation of BMSCs, and angiogenic differentiation of human umbilical vein endothelial cells (HUVECs) by stimulation with GO/RAW 264.7-conditioned culture medium were accessed. We also further investi gated the possible mechanisms underlying the osteo- and angio-immunomodulatory effects of GO.

Results

Our results showed that GO stimulates the secretion of oncostatin M, tumor necrosis factor alpha and other factors through the nuclear factor-κB pathway. GO/RAW264.7-conditioned medium promoted the osteogenic differentiation of BMSCs, stimulated upregulation of the HUVECs of vascular-related receptors, and promoted their tube formation in vitro.

Conclusion

In conclusion, our research shows that GO, as a biomaterial, can induce the formation of a beneficial osteo-immunomodulatory environment and is a promising biomaterial for bone tissue engineering.

Synergistic Effects of Controlled-Released BMP-2 and VEGF from nHAC/PLGAs Scaffold on Osteogenesis

Tissue engineering bones take great advantages in massive bone defect repairing; under the induction of growth factors, seed cells differentiate into osteoblasts, and the scaffold materials gradually degrade and are replaced with neogenetic bones, which simulates the actual pathophysiological process of bone regeneration. However, mechanism research is required and further developed to instruct elements selection and optimization. In the present study, we prepared vascular endothelial growth factor/bone morphogenetic protein-2- nanohydroxyapatite/collagen (VEGF/ BMP-2- nHAC/ PLGAs) scaffolds and inoculated mouse MC3T3-E1 preosteoblasts to detect osteogenic indexes and activation of related signaling pathways. The hypothesis is to create a three-dimensional environment that simulates bone defect repairing, and p38 mitogen-activated kinase (p38) inhibitor was applied and osterix shRNA was transferred into mouse MC3T3-E1 preosteoblasts to further investigate the molecular mechanism of crosstalk between BMP-2 and VEGF. Our results demonstrated the following: (1) BMP-2 and VEGF were sustainably released from PLGAs microspheres. (2) nHAC/PLGAs scaffold occupied a three-dimensional porous structure and has excellent physical properties. (3) MC3T3-E1 cells proliferated and differentiated well in the scaffold. (4) Osteogenic differentiation related factors expression of VEGF/BMP-2 loaded scaffold was obviously higher than that of other groups; p38 inhibitor SB203580 decreased the nucleus/cytoplasm ratio of osterix expression. To conclude, the active artificial bone we prepared could provide a favorable growth space for MC3T3-E1 cells, and osteogenesis and maturation reinforced by simultaneous VEGF and BMP-2 treatment may be mainly through the activation of the p38 MAPK pathway to promote nuclear translocation of osterix protein.

Synergistic effects of dual growth factor delivery from composite hydrogels incorporating 2-N,6-O-sulphated chitosan on bone regeneration

A promising strategy to accelerate bone generation is to deliver a combination of certain growth factors to the integration site via a controlled spatial and temporal delivery mode. Here, a composite hydrogel incorporating poly(lactide-co-glycolide) (PLGA) microspheres was accordingly prepared to load and deliver the osteogenic rhBMP-2 and angiogenic rhVEGF₁₆₅ in the required manner. In addition, 2-N,6-O-sulphated chitosan (26SCS), which is a synergetic factor of growth factors, was incorporated in the composite hydrogel as well. The system showed a similar release behaviour of the two growth factors regardless of 26SCS inclusion. RhBMP-2 loaded in PLGA microspheres showed a sustained release over a period of 2 weeks, whereas rhVEGF₁₆₅ loaded in hydrogel eluted almost completely from the hydrogel over the first 16 days. Both growth factors retained their efficacy, as quantified with relevant in vitro assays. Moreover, an enhanced cell response was achieved upon the delivery of dual growth factors, compared to that obtained with a single factor. Furthermore, in the presence of 26SCS, the system revealed significantly upregulated alkaline phosphatase activity, human umbilical vein endothelial cell proliferation, sprouting, nitric oxide secretion, and angiogenic gene expression. This study highlighted that the composite hydrogel incorporated with 26SCS appears to constitute a promising approach to deliver multiple growth factors. From our findings, we could also conclude that rhBMP-2 can promote angiogenesis and that the mechanism is worthy of further study in subsequent research.

Cell Type Influences Local Delivery of Biomolecules from a Bioinspired Apatite Drug Delivery System

Recently, the benefit of step-wise sequential delivery of fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 from a bioinspired apatite drug delivery system on mouse calvarial bone repair was demonstrated. The thicknesses of the nanostructured poly-l-Lysine/poly-l-Glutamic acid polyelectrolyte multilayer (PEM) and the bone-like apatite barrier layer that make up the delivery system, were varied. The effects of the structural variations of the coating on the kinetics of cell access to a cytotoxic factor delivered by the layered structure were evaluated. FGF-2 was adsorbed into the outer PEM, and cytotoxic antimycin-A (AntiA) was adsorbed to the substrate below the barrier layer to detect the timing of the cell access. While MC3T3-E1 osteoprogenitor cells accessed AntiA after three days, the RAW 264.7 macrophage access occurred within 4 h, unless the PEM layer was removed, in which case the results were reversed. Pits were created in the coating by the RAW 264.7 macrophages and initiated delivery, while the osteoprogenitor cell access to drugs occurred through a solution-mediated coating dissolution, at junctions between the islands of crystals. Macrophage-mediated degradation is therefore a mechanism that controls drug release from coatings containing bioinspired apatite.

A review of biomaterials in bone defect healing, remaining shortcomings and future opportunities for bone tissue engineering: The unsolved challenge

Despite its intrinsic ability to regenerate form and function after injury, bone tissue can be challenged by a multitude of pathological conditions. While innovative approaches have helped to unravel the cascades of bone healing, this knowledge has so far not improved the clinical outcomes of bone defect treatment. Recent findings have allowed us to gain in-depth knowledge about the physiological conditions and biological principles of bone regeneration. Now it is time to transfer the lessons learned from bone healing to the challenging scenarios in defects and employ innovative technologies to enable biomaterial-based strategies for bone defect healing. This review aims to provide an overview on endogenous cascades of bone material formation and how these are transferred to new perspectives in biomaterial-driven approaches in bone regeneration.

Cite this article: T. Winkler, F. A. Sass, G. N. Duda, K. Schmidt-Bleek. A review of biomaterials in bone defect healing, remaining shortcomings and future opportunities for bone tissue engineering: The unsolved challenge. Bone Joint Res 2018;7:232–243. DOI: 10.1302/2046-3758.73.BJR-2017-0270.R1.

Mesoporous silicate nanoparticles/3D nanofibrous scaffold-mediated dual-drug delivery for bone tissue engineering

Controlled delivery systems play a critical role in the success of bone morphogenetic proteins (i.e., BMP2 and BMP7) for challenged bone repair. Instead of single-drug release that is currently and commonly prevalent, dual-drug delivery strategies are highly desired to achieve effective bone regeneration because natural bone repair process is driven by multiple factors. Particularly, angiogenesis is essential for osteogenesis and requires more than just one factor (e.g., Vascular Endothelial Growth Factor, VEGF). Therefore, we developed a novel mesoporous silicate nanoparticles (MSNs) incorporated-3D nanofibrous gelatin (GF) scaffold for dual-delivery of BMP2 and deferoxamine (DFO). DFO is a hypoxia-mimetic drug that can activate hypoxia-inducible factor-1 alpha (HIF-1α), and trigger subsequent angiogenesis. Sustained BMP2 release system was achieved through encapsulation into large-pored MSNs, while the relative short-term release of DFO was engineered through covalent conjugation with chitosan to reduce its cytotoxicity and elongate its half-life. Both MSNs and DFO were incorporated onto a porous 3D GF scaffold to serve as a biomimetic osteogenic microenvironment. Our data indicated that DFO and BMP2 were released from a scaffold at different release rates (10 vs 28 days) yet maintained their angiogenic and osteogenic ability, respectively. Importantly, our data indicated that the released DFO significantly improved BMP2-induced osteogenic differentiation where the dose/duration was important for its effects in both mouse and human stem cell models. Thus, we developed a novel and tunable MSNs/GF 3D scaffold-mediated dual-drug delivery system and studied the potential application of the both FDA-approved DFO and BMP2 for bone tissue engineering.

"Ruffled border" formation on a CaP-free substrate: A first step towards osteoclast-recruiting bone-grafts materials able to re-establish bone turn-over

Osteoclasts are large multinucleated giant cells that actively resorb bone during the physiological bone turnover (BTO), which is the continuous cycle of bone resorption (by osteoclasts) followed by new bone formation (by osteoblasts). Osteoclasts secrete chemotactic signals to recruit cells for regeneration of vasculature and bone. We hypothesize that a biomaterial that attracts osteoclasts and re-establishes BTO will induce a better healing response than currently used bone graft materials. While the majority of bone regeneration efforts have focused on maximizing bone deposition, the novelty in this approach is the focus on stimulating osteoclastic resorption as the starter for BTO and its concurrent new vascularized bone formation. A biodegradable tyrosine-derived polycarbonate, E1001(1k), was chosen as the polymer base due to its ability to support bone regeneration in vivo. The polymer was functionalized with a RGD peptide or collagen I, or blended with β-tricalcium phosphate. Osteoclast attachment and early stages of active resorption were observed on all substrates. The transparency of E1001(1k) in combination with high resolution confocal imaging enabled visualization of morphological features of osteoclast activation such as the formation of the "actin ring" and the "ruffled border", which previously required destructive forms of imaging such as transmission electron microscopy. The significance of these results is twofold: (1) E1001(1k) is suitable for osteoclast attachment and supports osteoclast maturation, making it a base polymer that can be further modified to optimize stimulation of BTO and (2) the transparency of this polymer makes it a suitable analytical tool for studying osteoclast behavior.

BMP2 and VEGF165 transfection to bone marrow stromal stem cells regulate osteogenic potential in vitro

An exogenous supply of bone morphogenetic protein 2 (BMP2) and vascular endothelial growth factors 165 (VEGF165) will synergize to promote bone regeneration in vivo. The aim of this study was to confirm the role of VEGF165 on the osteogenesis potential of bone mesenchymal stem cells (BMSCs) transduced by adenovirus vector containing BMP2 gene in vitro.Rabbit BMSCs were isolated and transfected with various adenovirus vectors: Ad-BMP2-VEGF165 (BMP2+VEGF165 group), Ad-BMP2 (BMP2 group), Ad-VEGF165 (VEGF165 group), and Ad-green fluorescent protein (GFP group). The multiplicity of infection was detected by GFP expression. Expression of BMP2 and VEGF165 was detected by Western blot and ELISA, and the osteogenic biological activity of BMP2 and VEGF165 by osteogenic assay. Meanwhile, the osteogenic biological activity of BMP2 and VEGF165 was evaluated by detection of Col I (collagen type I), OC (osteocalcin), and ALP (alkaline phosphatase) activity using OC staining, ALP activity assay, and real-time PCR assay.Expression of target genes and proteins reached peak values at 5 days and then gradually declined. The OC staining, ALP activity, and real-time PCR assay of ColI, OC, and ALP were all increased in cells transfected with Ad-BMP2-VEGF165, Ad-BMP2, Ad-VEGF165, and Ad-GFP. However, the osteogenic biological activity in cells transfected with Ad-BMP2 was higher compared to cells transfected with other vectors after transfection at 14 and 21 days. We also found that BMP2 +VEGF165 group showed more osteogenic activity effect than the VEGF165 or control group. Furthermore, osteogenic assays in VEGF165 showed that a slightly lower osteogenic effect when compared to controls at 21 days.VEGF165 might be a potent inhibitor of BMSCs differentiation into osteoblasts. The strategies to use BMP2 and VEGF165 in bone regeneration and the molecular mechanism of their interaction require further investigation.

Strategies to develop endogenous stem cell-recruiting bioactive materials for tissue repair and regeneration

A leading strategy in tissue engineering is the design of biomimetic scaffolds that stimulate the body's repair mechanisms through the recruitment of endogenous stem cells to sites of injury. Approaches that employ the use of chemoattractant gradients to guide tissue regeneration without external cell sources are favored over traditional cell-based therapies that have limited potential for clinical translation. Following this concept, bioactive scaffolds can be engineered to provide a temporally and spatially controlled release of biological cues, with the possibility to mimic the complex signaling patterns of endogenous tissue regeneration. Another effective way to regulate stem cell activity is to leverage the inherent chemotactic properties of extracellular matrix (ECM)-based materials to build versatile cell-instructive platforms. This review introduces the concept of endogenous stem cell recruitment, and provides a comprehensive overview of the strategies available to achieve effective cardiovascular and bone tissue regeneration.

Bone Morphogenetic Protein Coating on Titanium Implant Surface: a Systematic Review

Objectives

The purpose of the study is to systematically review the osseointegration process improvement by bone morphogenetic protein coating on titanium implant surface.

Material and Methods

An electronic literature search was conducted through the MEDLINE (PubMed) and EMBASE databases. The search was restricted for articles published during the last 10 years from October 2006 to September 2016 and articles were limited to English language.

Results

A total of 41 articles were reviewed, and 8 of the most relevant articles that are suitable to the criteria were selected. Articles were analysed regarding concentration of bone morphogenetic protein (BMP), delivery systems, adverse reactions and the influence of the BMP on the bone and peri-implant surface in vivo. Finally, the present data included 340 implants and 236 models.

Conclusions

It’s clearly shown from most of the examined studies that bone morphogenetic protein increases bone regeneration. Further studies should be done in order to induce and sustain bone formation activity. Osteogenic agent should be gradually liberated and not rapidly released with priority to three-dimension reservoir (incorporated) titanium implant surface in order to avoid following severe side effects: inflammation, bleeding, haematoma, oedema, erythema, and graft failure.