BMP2 expressing genetically engineered mesenchymal stem cells on composite fibrous scaffolds for enhanced bone regeneration in segmental defects

Immobilization and Release of Platelet-Rich Plasma from Modified Nanofibers Studied by Advanced X-ray Photoelectron Spectroscopy Analyses

Platelet-rich Plasma (PRP) is an ensemble of growth factors, extracellular matrix components, and proteoglycans that are naturally balanced in the human body. In this study, the immobilization and release of PRP component nanofiber surfaces modified by plasma treatment in a gas discharge have been investigated for the first time. The plasma-treated polycaprolactone (PCL) nanofibers were utilized as substrates for the immobilization of PRP, and the amount of PRP immobilized was assessed by fitting a specific X-ray Photoelectron Spectroscopy (XPS) curve to the elemental composition changes. The release of PRP was then revealed by measuring the XPS after soaking nanofibers containing immobilized PRP in buffers of varying pHs (4.8; 7.4; 8.1). Our investigations have proven that the immobilized PRP would continue to cover approximately fifty percent of the surface after eight days.

Recent advances in gene therapy for bone tissue engineering

Autografting, a major treatment for bone fractures, has potential risks related to the required surgery and disease transmission. Bone morphogenetic proteins (BMPs) are the most common osteogenic factors used for bone-healing applications. However, BMP delivery can have shortcomings such as a short half-life and the high cost of manufacturing the recombinant proteins. Gene delivery methods have demonstrated promising alternative strategies for producing BMPs or other osteogenic factors using engineered cells. These approaches can also enable temporal overexpression and local production of the therapeutic genes in the target tissues. This review addresses recent progress on engineered viral, non-viral, and RNA-mediated gene delivery systems that are being used for bone repair and regeneration. Advances in clustered regularly interspaced short palindromic repeats/Cas9 genome engineering for bone tissue regeneration also is discussed.

Improved repair of rabbit calvarial defects with hydroxyapatite/chitosan/polycaprolactone composite scaffold-engrafted EPCs and BMSCs

Endothelial progenitor cells (EPCs) expressing vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) and bone marrow mesenchymal stem cells (BMSCs) expressing endogenous bone morphogenetic protein-2 (BMP-2) play the important role in new bone formation. This study investigated the effects of a porous hydroxyapatite (HA)/chitosan (CS)/polycaprolactone (PCL) composite scaffold-engrafted EPCs and BMSCs on the expression of BMP-2, VEGF, and PDGF in the calvarial defect rabbit model in vivo. It showed that a three-dimensional composite scaffold was successfully constructed by physical interaction with a pore size of 250 μm. The HA/CS/PCL scaffold degraded slowly within 10 weeks and showed non-cytotoxicity. By X-ray, micro-CT examination, and H&E staining, compared with the HA/CS/PCL group, HA/CS/PCL + EPCs, HA/CS/PCL + BMSCs, and HA/CS/PCL + EPCs + BMSCs groups performed a more obvious repair effect, and the dual factor group presented particularly significant improvement on the percentages of bone volume at week 4 and week 8, with evident bone growth. Osteogenesis marker (BMP-2) and vascularization marker (VEGF and PDGF) expression in the dual factor group were much better than those of the HA/CS/PCL control group and single factor groups. Collectively, the HA/CS/PCL composite scaffold-engrafting EPCs and BMSCs is effective to repair calvarial defects by regulating endogenous expression of BMP-2, VEGF, and PDGF. Thus, this study provides important implications for the potential clinical application of biomaterial composite scaffold-engrafted engineering cells.

Reconstruction of critical-size segmental defects in rat femurs using carbonate apatite honeycomb scaffolds

Critical-size segmental defects are formidable challenges in orthopedic surgery. Various scaffolds have been developed to facilitate bone reconstruction within such defects. Many previously studied scaffolds achieved effective outcomes with a combination of high cost, high-risk growth factors or stem cells. Herein, we developed honeycomb scaffolds (HCSs) comprising carbonate apatite (CO3 Ap) containing 8% carbonate, identical to human bone composition. The CO3 Ap HCSs were white-columned blocks harboring regularly arranged macropore channels of a size and wall thickness of 156 ± 5 μm and 102 ± 10 μm, respectively. The compressive strengths of the HCSs parallel and perpendicular to the macropore channel direction were 51.0 ± 11.8 and 15.6 ± 2.2 MPa, respectively. The HCSs were grafted into critical-sized segmental defects in rat femurs. The HCSs bore high-load stresses without any observed breakage. Two-weeks post-implantation, calluses formed around the HCSs and immature bone formed in the HCS interior. The calluses and immature bone matured until 8 weeks via endochondral ossification. At 12 weeks post-implantation, large parts of the HCSs were gradually replaced by newly formed bone. The bone reconstruction efficacy of the CO3 Ap HCSs alone was comparable to that of protein and cell scaffolds, while achieving a lower cost and increased safety.

Biofabrication of Gingival Fibroblast Cell-Laden Collagen/Strontium-Doped Calcium Silicate 3D-Printed Bi-Layered Scaffold for Osteoporotic Periodontal Regeneration

Periodontal disease is a chronic disease that can lead to lose teeth and even tooth loss if left untreated. Osteoporosis and periodontal disease share similar characteristics and associated factors. Current regenerative techniques for periodontal diseases are ineffective in restoring complete function and structural integrity of periodontium due to unwanted migration of cells. In this study, we applied the concept of guided tissue regeneration (GTR) and 3D fabricated gingival fibroblast cell-laden collagen/strontium-doped calcium silicate (SrCS) bi-layer scaffold for periodontal regeneration. The results revealed that the bioactive SrCS had a hydroxyapatite formation on its surface after 14 days of immersion and that SrCS could release Sr and Si ions even after 6 months of immersion. In addition, in vitro results showed that the bi-layer scaffold enhanced secretion of FGF-2, BMP-2, and VEGF from human gingival fibroblasts and increased secretion of osteogenic-related proteins ALP, BSP, and OC from WJMSCs. In vivo studies using animal osteoporotic models showed that the 3D-printed cell-laden collagen/SrCS bi-layer scaffold was able to enhance osteoporotic bone regeneration, as seen from the increased Tb.Th and BV/TV ratio and the histological stains. In conclusion, it can be seen that the bi-layer scaffolds enhanced osteogenesis and further showed that guided periodontal regeneration could be achieved using collagen/SrCS scaffolds, thus making it a potential candidate for future clinical applications.

Incorporation of Calcium Sulfate Dihydrate into a Mesoporous Calcium Silicate/Poly-ε-Caprolactone Scaffold to Regulate the Release of Bone Morphogenetic Protein-2 and Accelerate Bone Regeneration

Tissue engineering and scaffolds play an important role in tissue regeneration by supporting cell adhesion, proliferation, and differentiation. The design of a scaffold is critical in determining its feasibility, and it is critical to note that each tissue is unique in terms of its morphology and composition. However, calcium-silicate-based scaffolds are undegradable, which severely limits their application in bone regeneration. In this study, we developed a biodegradable mesoporous calcium silicate (MS)/calcium sulfate (CS)/poly-ε-caprolactone (PCL) composite and fabricated a composite scaffold with 3D printing technologies. In addition, we were able to load bone morphogenetic protein-2 (BMP-2) into MS powder via a one-step immersion procedure. The results demonstrated that the MS/CS scaffold gradually degraded within 3 months. More importantly, the scaffold exhibited a gradual release of BMP-2 throughout the test period. The adhesion and proliferation of human dental pulp stem cells on the MS/CS/BMP-2 (MS/CS/B) scaffold were significantly greater than that on the MS/CS scaffold. It was also found that cells cultured on the MS/CS/B scaffold had significantly higher levels of alkaline phosphatase activity and angiogenic-related protein expression. The MS/CS/B scaffold promoted the growth of new blood vessels and bone regeneration within 4 weeks of implantation in rabbits with induced critical-sized femoral defects. Therefore, it is hypothesized that the 3D-printed MS/CS/B scaffold can act both as a conventional BMP-2 delivery system and as an ideal osteoinductive biomaterial for bone regeneration.

Fabrication of ultrahigh-molecular-weight polyethylene porous implant for bone application

Porous implants play a crucial role in allowing ingrowth of host connective tissue and thereby help in keeping the implant in its place. With the aim of mimicking the microstructure of natural extracellular matrix, ultrahigh-molecular-weight polyethylene (UHMWPE) porous samples with a desirable pore size distribution were developed by combining thermally induced phase separation and salt leaching techniques. The porous UHMWPE samples consisted of a nanofibrous UHMWPE matrix with a fibre diameter smaller than 500 nm, highly interconnected, with a controllable pore diameter from nanoscale to 300 µm. Moreover, a porous UHMWPE sample was also developed as a continuous and homogeneous coating onto the UHMWPE dense sample. The dense/porous UHMWPE sample supported human foetal osteoblast 1.19 cell line proliferation and differentiation, indicating the potential of porous UHMWPE with a desirable pore size distribution for bone application. An osseointegration model in the sheep revealed substantial bone formation within the pore layer at 12 weeks via SEM evaluation. Ingrown bone was more closely opposed to the pore wall when compared to the dense UHMWPE control. These results indicate that dense/porous UHMWPE could provide improved osseointegration while maintaining the structural integrity necessary for load-bearing orthopaedic application.

ONO-1301 loaded nanocomposite scaffolds modulate cAMP mediated signaling and induce new bone formation in critical sized bone defect

Recent studies on bone regeneration demonstrate the use of low cost and stable small molecules, which avoid the adverse effect and high cost of growth factors. Herein, we investigate the chemotactic, angiogenic and osteoinductive potential of a prostacyclin analogue, ONO-1301, when delivered through a biomimetic nanocomposite scaffold (nanohydroxyapatite-gelatin matrix reinforced with fibers) for bone tissue regeneration. The small molecule was loaded onto the scaffold in three different concentrations. There was burst release from all the groups of scaffolds within 24 h followed by a sustained release up to 14 days, but the concentration was dependent on loading percentage. ONO-1301 loaded scaffolds augmented the migration, proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs), but increasing the concentration beyond a certain dose did not show any effect. The osteoinduction was mediated through the prostaglandin I₂ receptor and cyclic AMP (cAMP) signaling pathway. They also promoted new bone formation in large sized calvarial defects in rats compared to the scaffold alone, but did not show any impact on angiogenesis. Hence, this study suggests the chemotactic and osteoinductive capability of ONO-1301 for the repair and regeneration of critical sized bone defects.

Is Tissue Engineering Helping Orthopaedic Care in Trauma?

Tissue engineering in orthopaedic trauma is needed. Progress has been made in all areas including regenerating bone, cartilage, soft tissue, and making up for bone defects with scaffolds. Bone regeneration and managing bone defects with scaffolds continue to be successful in the basic science realm with promising results, but currently, these successes are mostly limited to small animal models. Cartilage defects have more clinically available treatment options, but the benefits of "off-the-shelf" allograft options, and scaffolds, have little clinical evidence in the acute fracture setting. Most of the true chondrocyte replacement therapies such as matrix-induced autologous chondrocyte implantation and osteochondral allografts require delayed treatment while cell growth or graft matching occurs. Soft-tissue defects can be managed with tissue engineering for the skin with success, but muscle and nerve defects are still limited to the basic science arena. Although significant gains have been made in all areas for tissue engineering in basic science, and is very promising, this success currently comes with limited translation into clinical availability for the orthopaedic trauma patient.

Dual release of growth factor from nanocomposite fibrous scaffold promotes vascularisation and bone regeneration in rat critical sized calvarial defect

A promising strategy for augmenting bone formation involves the local delivery of multiple osteoinductive and vasculogenic growth factors. However, success depends on sustained growth factor release and its appropriate combination to induce stem cells and osteogenic cells at the bony site. Herein, we have developed a nanocomposite fibrous scaffold loaded with fibroblast growth factor 2 (FGF2), vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP2) and its ability to promote vascularisation and bone regeneration in critical sized calvarial defect was compared to the scaffold with VEGF + BMP2 and FGF2 + BMP2. Simple loading of growth factors on the scaffold could provide a differential release pattern, both in vitro and in vivo (VEGF release for 1 week where as BMP2 and FGF2 release for 3 weeks). Among all the groups, dual growth factor loaded scaffold (VEGF + BMP2 & FGF2 + BMP2) enhanced vascularisation and new bone formation, but there was no difference between FGF2 and VEGF loaded scaffolds although its release pattern was different. FGF2 mainly promoted stem cell migration, whereas VEGF augmented new blood vessel formation at the defect site. This study suggests that biomimetic nanocomposite scaffold is a promising growth factor delivery vehicle to improve bone regeneration in critical sized bone defects.

STATEMENT OF SIGNIFICANCE

Many studies have shown the effect of growth factors like VEGF-BMP2 or FGF2-BMP2 in enhancing bone formation in critical sized defects, but there are no reports that demonstrate the direct comparison of VEGF-BMP2 and FGF2-BMP2. In this study, we have developed a nanocomposite fibrous scaffold that could differentially release growth factors like VEGF, BMP2 and FGF2 (VEGF release for 1 week where as BMP2 and FGF2 release for 3 weeks), which in turn promoted neovascularisation and new bone formation in critical sized defects. There was no difference in vascularisation and bone formation induced by VEGF + BMP2 or FGF2 + BMP2. The growth factor was loaded in a simple manner, which would ensure ease of use for the end-user, especially for the surgeons treating a patient in an operating room.

Mesenchymal Stem Cell Expressing TRAIL as Targeted Therapy against Sensitised Tumour

Tapping into the ability of engineered mesenchymal stem cells (MSCs) to mobilise into the tumour has expanded the scope of cancer treatment. Engineered MSCs expressing tumour necrosis factor (TNF)-related apoptosis inducing ligand (MSC-TRAIL) could serve as a platform for an efficient and targeted form of therapy. However, the presence of cancer stem cells (CSCs) that are resistant to TRAIL and apoptosis may represent a challenge for effective treatment. Nonetheless, with the discovery of small molecular inhibitors that could target CSCs and tumour signalling pathways, a higher efficacy of MSC-TRAIL mediated tumour inhibition can be achieved. This might pave the way for a more effective form of combined therapy, which leads to a better treatment outcome. In this review, we first discuss the tumour-homing capacity of MSCs, its effect in tumour tropism, the different approach behind genetically-engineered MSCs, and the efficacy and safety of each agent delivered by these MSCs. Then, we focus on how sensitisation of CSCs and tumours using small molecular inhibitors can increase the effect of these cells to either TRAIL or MSC-TRAIL mediated inhibition. In the conclusion, we address a few questions and safety concerns regarding the utilization of engineered MSCs for future treatment in patients.