Regional gene therapy with 3D printed scaffolds to heal critical sized bone defects in a rat model

In vivo effects of cell seeding technique in an ex vivo regional gene therapy model for bone regeneration

When delivering cells on a scaffold to treat a bone defect, the cell seeding technique determines the number and distribution of cells within a scaffold, however the optimal technique has not been established. This study investigated if human adipose-derived stem cells (ASCs) transduced with a lentiviral vector to overexpress bone morphogenetic protein 2 (BMP-2) and loaded on a scaffold using dynamic orbital shaker could reduce the total cell dose required to heal a critical sized bone defect when compared with static seeding. Human ASCs were loaded onto a collagen/biphasic ceramic scaffold using static loading and dynamic orbital shaker techniques, compared with our labs standard loading technique, and implanted into femoral defects of nude rats. Both a low dose and standard dose of transduced cells were evaluated. Outcomes investigated included BMP-2 production, radiographic healing, micro-computerized tomography, histologic assessment, and biomechanical torsional testing. BMP-2 production was higher in the orbital shaker cohort compared with the static seeding cohort. No statistically significant differences were noted in radiographic, histomorphometric, and biomechanical outcomes between the low-dose static and dynamic seeding groups, however the standard-dose static seeding cohort had superior biomechanical properties. The standard-dose 5 million cell dose standard loading cohort had superior maximum torque and torsional stiffness on biomechanical testing. The use of orbital shaker technique was labor intensive and did not provide equivalent biomechanical results with the use of fewer cells.

3D printed polycaprolactone/gelatin/ordered mesoporous calcium magnesium silicate nanocomposite scaffold for bone tissue regeneration

Tissue engineering scaffolds are three-dimensional structures that provide an appropriate environment for cellular attachment, proliferation, and differentiation. Depending on their specific purpose, these scaffolds must possess distinct features, including appropriate mechanical properties, porosity, desired degradation rate, and cell compatibility. This investigation aimed to fabricate a new nanocomposite scaffold using a 3D printing technique composed of poly(ε-caprolactone) (PCL)/Gelatin (GEL)/ordered mesoporous calcium-magnesium silicate (om-CMS) particles. Different weight ratios of om-CMS were added and optimized, and a series of scaffolds were constructed for comparison purposes, including PCL 50%/Gel 50%, PCL 50%/Gel 45%/om-CMS%5, and PCL 50%/Gel 40%/om-CMS%10. The optimized weight ratio of om-CMS was 10% without leaving behind negative effects on the filaments' structure. The scaffolds' physical and chemical properties were assessed using various techniques, and their degradation rate, bioactivity potential, cell viability, attachment, and ALP activity were evaluated in vitro. The results demonstrated that the PCL 50%/Gel 40%/om-CMS10% scaffold had promising potential for further studies in bone tissue regeneration.

β-catenin mRNA encapsulated in SM-102 lipid nanoparticles enhances bone formation in a murine tibia fracture repair model

Fractures continue to be a global economic burden as there are currently no osteoanabolic drugs approved to accelerate fracture healing. In this study, we aimed to develop an osteoanabolic therapy which activates the Wnt/β-catenin pathway, a molecular driver of endochondral ossification. We hypothesize that using an mRNA-based therapeutic encoding β-catenin could promote cartilage to bone transformation formation by activating the canonical Wnt signaling pathway in chondrocytes. To optimize a delivery platform built on recent advancements in liposomal technologies, two FDA-approved ionizable phospholipids, DLin-MC3-DMA (MC3) and SM-102, were used to fabricate unique ionizable lipid nanoparticle (LNP) formulations and then tested for transfection efficacy both in vitro and in a murine tibia fracture model. Using firefly luciferase mRNA as a reporter gene to track and quantify transfection, SM-102 LNPs showed enhanced transfection efficacy in vitro and prolonged transfection, minimal fracture interference and no localized inflammatory response in vivo over MC3 LNPs. The generated β-cateninGOF mRNA encapsulated in SM-102 LNPs (SM-102-β-cateninGOF mRNA) showed bioactivity in vitro through upregulation of downstream canonical Wnt genes, axin2 and runx2. When testing SM-102-β-cateninGOF mRNA therapeutic in a murine tibia fracture model, histomorphometric analysis showed increased bone and decreased cartilage composition with the 45 μg concentration at 2 weeks post-fracture. μCT testing confirmed that SM-102-β-cateninGOF mRNA promoted bone formation in vivo, revealing significantly more bone volume over total volume in the 45 μg group. Thus, we generated a novel mRNA-based therapeutic encoding a β-catenin mRNA and optimized an SM-102-based LNP to maximize transfection efficacy with a localized delivery.

Biomaterials for bone defect repair: Types, mechanisms and effects

Bone defects or bone discontinuities caused by trauma, infection, tumours and other diseases have led to an increasing demand for bone grafts and biomaterials. Autologous bone grafts, bone grafts with vascular tips, anastomosed vascular bone grafts and autologous bone marrow components are all commonly used in clinical practice, while oversized bone defects require the use of bone tissue engineering-related biomaterials to repair bone defects and promote bone regeneration. Currently, inorganic components such as polysaccharides and bioceramics, as well as a variety of bioactive proteins, metal ions and stem cells can be loaded into hydrogels or 3D printed scaffold materials to achieve better therapeutic results. In this review, we provide an overview of the types of materials, applications, potential mechanisms and current developments in the repair of bone defects.

Mineral coated microparticles doped with fluoride and complexed with mRNA prolong transfection in fracture healing

Introduction: Impaired fracture healing, specifically non-union, has been found to occur up to 14% in tibial shaft fractures. The current standard of care to treat non-union often requires additional surgeries which can result in long recovery times. Injectable-based therapies to accelerate fracture healing have the potential to mitigate the need for additional surgeries. Gene therapies have recently undergone significant advancements due to developments in nanotechnology, which improve mRNA stability while reducing immunogenicity. Methods: In this study, we tested the efficacy of mineral coated microparticles (MCM) and fluoride-doped MCM (FMCM) to effectively deliver firefly luciferase (FLuc) mRNA lipoplexes (LPX) to the fracture site. Here, adult mice underwent a tibia fracture and stabilization method and all treatments were locally injected into the fracture. Level of osteogenesis and amount of bone formation were assessed using gene expression and histomorphometry respectively. Localized and systemic inflammation were measured through gene expression, histopathology scoring and measuring C-reactive protein (CRP) in the serum. Lastly, daily IVIS images were taken to track and measure transfection over time. Results: MCM-LPX-FLuc and FMCM-LPX-FLuc were not found to cause any cytotoxic effects when tested in vitro. When measuring the osteogenic potential of each mineral composition, FMCM-LPX-FLuc trended higher in osteogenic markers through qRT-PCR than the other groups tested in a murine fracture and stabilization model. Despite FMCM-LPX-FLuc showing slightly elevated il-1β and il-4 levels in the fracture callus, inflammation scoring of the fracture callus did not result in any differences. Additionally, an acute systemic inflammatory response was not observed in any of the samples tested. The concentration of MCM-LPX-FLuc and FMCM-LPX-FLuc that was used in the murine fracture model did not stimulate bone when analyzed through stereological principles. Transfection efficacy and kinetics of delivery platforms revealed that FMCM-LPX-FLuc prolongs the luciferase signal both in vitro and in vivo. Discussion: These data together reveal that FMCM-LPX-FLuc could serve as a promising mRNA delivery platform for fracture healing applications.

Biodistribution of lentiviral transduced adipose-derived stem cells for "ex-vivo" regional gene therapy for bone repair

Ex-vivo gene therapy has been shown to be an effective method for treating bone defects in pre-clinical models. As gene therapy is explored as a potential treatment option in humans, an assessment of the safety profile becomes an important next step. The purpose of this study was to evaluate the biodistribution of viral particles at the defect site and various internal organs in a rat femoral defect model after implantation of human ASCs transduced with lentivirus (LV) with two-step transcriptional activation (TSTA) of bone morphogenetic protein-2 (LV-TSTA-BMP-2). Animals were sacrificed at 4-, 14-, 56-, and 84-days post implantation. The defects were treated with either a standard dose (SD) of 5 million cells or a high dose (HD) of 15 million cells to simulate a supratherapeutic dose. Treatment groups included (1) SD LV-TSTA-BMP-2 (2) HD LV-TSTA-BMP-2, (3) SD LV-TSTA-GFP (4) HD LV-TSTA-GFP and (5) SD nontransduced cells. The viral load at the defect site and ten organs was assessed at each timepoint. Histology of all organs, ipsilateral tibia, and femur were evaluated at each timepoint. There were nearly undetectable levels of LV-TSTA-BMP-2 transduced cells at the defect site at 84-days and no pathologic changes in any organ at all timepoints. In conclusion, human ASCs transduced with a lentiviral vector were both safe and effective in treating critical size bone defects in a pre-clinical model. These results suggest that regional gene therapy using lentiviral vector to treat bone defects has the potential to be a safe and effective treatment in humans.

Delivery of Growth Factors to Enhance Bone Repair

The management of critical-sized bone defects caused by nonunion, trauma, infection, malignancy, pseudoarthrosis, and osteolysis poses complex reconstruction challenges for orthopedic surgeons. Current treatment modalities, including autograft, allograft, and distraction osteogenesis, are insufficient for the diverse range of pathology encountered in clinical practice, with significant complications associated with each. Therefore, there is significant interest in the development of delivery vehicles for growth factors to aid in bone repair in these settings. This article reviews innovative strategies for the management of critical-sized bone loss, including novel scaffolds designed for controlled release of rhBMP, bioengineered extracellular vesicles for delivery of intracellular signaling molecules, and advances in regional gene therapy for sustained signaling strategies. Improvement in the delivery of growth factors to areas of significant bone loss has the potential to revolutionize current treatment for this complex clinical challenge.

Customized Additive Manufacturing in Bone Scaffolds-The Gateway to Precise Bone Defect Treatment

In the advancing landscape of technology and novel material development, additive manufacturing (AM) is steadily making strides within the biomedical sector. Moving away from traditional, one-size-fits-all implant solutions, the advent of AM technology allows for patient-specific scaffolds that could improve integration and enhance wound healing. These scaffolds, meticulously designed with a myriad of geometries, mechanical properties, and biological responses, are made possible through the vast selection of materials and fabrication methods at our disposal. Recognizing the importance of precision in the treatment of bone defects, which display variability from macroscopic to microscopic scales in each case, a tailored treatment strategy is required. A patient-specific AM bone scaffold perfectly addresses this necessity. This review elucidates the pivotal role that customized AM bone scaffolds play in bone defect treatment, while offering comprehensive guidelines for their customization. This includes aspects such as bone defect imaging, material selection, topography design, and fabrication methodology. Additionally, we propose a cooperative model involving the patient, clinician, and engineer, thereby underscoring the interdisciplinary approach necessary for the effective design and clinical application of these customized AM bone scaffolds. This collaboration promises to usher in a new era of bioactive medical materials, responsive to individualized needs and capable of pushing boundaries in personalized medicine beyond those set by traditional medical materials.

Exploring microRNAs in craniofacial regenerative medicine

microRNAs (miRs) have been reported over the decades as important regulators in bone development and bone regeneration. They play important roles in maintaining the stem cell signature as well as regulating stem cell fate decisions. Thus, delivering miRs and miR inhibitors to the defect site is a potential treatment towards craniofacial bone defects. However, there are challenges in translation of basic research to clinics, including the efficiency, specificity, and efficacy of miR manipulation methods and the safety of miR delivery systems. In this review, we will compare miR oligonucleotides, mimics and antagomirs as therapeutic reagents to treat disease and regenerate tissues. Newer technology will be discussed as well as the efficiency and efficacy of using these technologies to express or inhibit miRs in treating and repairing oral tissues. Delivery of these molecules using extracellular vesicles and nanoparticles can achieve different results and depending on their composition will elicit specific effects. We will highlight the specificity, toxicity, stability, and effectiveness of several miR systems in regenerative medicine.

Viral and non-viral gene therapy using 3D (bio)printing

The overall success in launching discovered drugs is tightly restricted to the high rate of late-stage failures, which ultimately inhibits the distribution of medicines in markets. As a result, it is imperative that methods reliably predict the effectiveness and, more critically, the toxicity of medicine early in the drug development process before clinical trials be continuously innovated. We must stay up to date with the fast appearance of new infections and diseases by rapidly developing the requisite vaccinations and medicines. Modern in vitro models of disease may be used as an alternative to traditional disease models, and advanced technology can be used for the creation of pharmaceuticals as well as cells, drugs, and gene delivery systems to expedite the drug discovery procedure. Furthermore, in vitro models that mimic the spatial and chemical characteristics of native tissues, such as a 3D bioprinting system or other technologies, have proven to be more effective for drug screening than traditional 2D models. Viral and non-viral gene delivery vectors are a hopeful tool for combinatorial gene therapy, suggesting a quick way of simultaneously deliver multiple genes. A 3D bioprinting system embraces an excellent potential for gene delivery into the different cells or tissues for different diseases, in tissue engineering and regeneration medicine, in which the precise nucleic acid is located in the 3D printed tissues and scaffolds. Non-viral nanocarriers, in combination with 3D printed scaffolds, are applied to their delivery of genes and controlled release properties. There remains, however, a big obstacle in reaching the full potential of 3D models because of a lack of in vitro manufacturing of live tissues. Bioprinting advancements have made it possible to create biomimetic constructions that may be used in various drug discovery research applications. 3D bioprinting also benefits vaccinations, medicines, and relevant delivery methods because of its flexibility and adaptability. This review discusses the potential of 3D bioprinting technologies for pharmaceutical studies.

Effects of cell seeding technique and cell density on BMP-2 production in transduced human mesenchymal stem cells

Small animal models have demonstrated the efficacy of ex vivo regional gene therapy using scaffolds loaded with BMP-2-expressing mesenchymal stem cells (MSCs). Prior to clinical translation, optimization of seeding techniques of the transduced cells will be important to minimize time and resource expenditure, while maximizing cell delivery and BMP-2 production. No prior studies have investigated cell-seeding techniques in the setting of transduced cells for gene therapy applications. Using BMP-2-expressing transduced adipose-derived MSCs and a porous ceramic scaffold, this study compared previously described static and dynamic seeding techniques with respect to cell seeding efficiency, uniformity of cell distribution, and in vitro BMP-2 production. Static and negative pressure seeding techniques demonstrated the highest seeding efficiency, while orbital shaking was associated with the greatest increases in BMP-2 production per cell. Low density cell suspensions were associated with the highest seeding efficiency and uniformity of cell distribution, and the greatest increases in BMP-2 production from 2 to 7 days after seeding. Our results highlight the potential for development of an optimized cell density and seeding technique that could greatly reduce the number of MSCs needed to produce therapeutic BMP-2 levels in clinical situations. Further studies are needed to investigate in vivo effects of cell seeding techniques on bone healing.

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.

Gene Therapy in Orthopaedics: Progress and Challenges in Pre-Clinical Development and Translation

In orthopaedics, gene-based treatment approaches are being investigated for an array of common -yet medically challenging- pathologic conditions of the skeletal connective tissues and structures (bone, cartilage, ligament, tendon, joints, intervertebral discs etc.). As the skeletal system protects the vital organs and provides weight-bearing structural support, the various tissues are principally composed of dense extracellular matrix (ECM), often with minimal cellularity and vasculature. Due to their functional roles, composition, and distribution throughout the body the skeletal tissues are prone to traumatic injury, and/or structural failure from chronic inflammation and matrix degradation. Due to a mixture of environment and endogenous factors repair processes are often slow and fail to restore the native quality of the ECM and its function. In other cases, large-scale lesions from severe trauma or tumor surgery, exceed the body’s healing and regenerative capacity. Although a wide range of exogenous gene products (proteins and RNAs) have the potential to enhance tissue repair/regeneration and inhibit degenerative disease their clinical use is hindered by the absence of practical methods for safe, effective delivery. Cumulatively, a large body of evidence demonstrates the capacity to transfer coding sequences for biologic agents to cells in the skeletal tissues to achieve prolonged delivery at functional levels to augment local repair or inhibit pathologic processes. With an eye toward clinical translation, we discuss the research progress in the primary injury and disease targets in orthopaedic gene therapy. Technical considerations important to the exploration and pre-clinical development are presented, with an emphasis on vector technologies and delivery strategies whose capacity to generate and sustain functional transgene expression in vivo is well-established.

Effects of Channels and Micropores in Honeycomb Scaffolds on the Reconstruction of Segmental Bone Defects

The reconstruction of critical-sized segmental bone defects is a key challenge in orthopedics because of its intractability despite technological advancements. To overcome this challenge, scaffolds that promote rapid bone ingrowth and subsequent bone replacement are necessary. In this study, we fabricated three types of carbonate apatite honeycomb (HC) scaffolds with uniaxial channels bridging the stumps of a host bone. These HC scaffolds possessed different channel and micropore volumes. The HC scaffolds were implanted into the defects of rabbit ulnar shafts to evaluate the effects of channels and micropores on bone reconstruction. Four weeks postoperatively, the HC scaffolds with a larger channel volume promoted bone ingrowth compared to that with a larger micropore volume. In contrast, 12 weeks postoperatively, the HC scaffolds with a larger volume of the micropores rather than the channels promoted the scaffold resorption by osteoclasts and bone formation. Thus, the channels affected bone ingrowth in the early stage, and micropores affected scaffold resorption and bone formation in the middle stage. Furthermore, 12 weeks postoperatively, the HC scaffolds with large volumes of both channels and micropores formed a significantly larger amount of new bone than that attained using HC scaffolds with either large volume of channels or micropores, thereby bridging the host bone stumps. The findings of this study provide guidance for designing the pore structure of scaffolds.

Rat Calvarial Bone Regeneration by 3D-Printed β-Tricalcium Phosphate Incorporating MicroRNA-200c

Advanced fabrication methods for bone grafts designed to match defect sites that combine biodegradable, osteoconductive materials with potent, osteoinductive biologics would significantly impact the clinical treatment of large bone defects. In this study, we engineered synthetic bone grafts using a hybrid approach that combined three-dimensional (3D-)printed biodegradable, osteoconductive β-tricalcium phosphate (β-TCP) with osteoinductive microRNA(miR)-200c. 3D-printed β-TCP scaffolds were fabricated utilizing a suspension-enclosing projection-stereolithography (SEPS) process to produce constructs with reproducible microarchitectures that enhanced the osteoconductive properties of β-TCP. Collagen coating on 3D-printed β-TCP scaffolds slowed the release of plasmid DNA encoding miR-200c compared to noncoated constructs. 3D-printed β-TCP scaffolds coated with miR-200c-incorporated collagen increased the transfection efficiency of miR-200c of both rat and human BMSCs and additionally increased osteogenic differentiation of hBMSCs in vitro. Furthermore, miR-200c-incorporated scaffolds significantly enhanced bone regeneration in critical-sized rat calvarial defects. These results strongly indicate that bone grafts combining SEPS 3D-printed osteoconductive biomaterial-based scaffolds with osteoinductive miR-200c can be used as superior bone substitutes for the clinical treatment of large bone defects.

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.

Regional Gene Therapy with Transduced Human Cells: The Influence of "Cell Dose" on Bone Repair

Regional gene therapy using a lentiviral vector containing the BMP-2 complementary DNA (cDNA) has been shown to heal critical-sized bone defects in rodent models. An appropriate "cellular dose" needs to be defined for eventual translation into human trials. The purpose of this study was to evaluate bone defect healing potential and quality using three different doses of transduced human bone marrow cells (HBMCs). HBMCs were transduced with a lentiviral vector containing either BMP-2 or green fluorescent protein (GFP). All cells were loaded onto compression-resistant matrices and implanted in the bone defect of athymic rats. Treatment groups included femoral defects that were treated with a low-dose (1 × 10⁶ cells), standard-dose (5 × 10⁶ cells), and high-dose (1.5 × 10⁷ cells) HBMCs transduced with lentiviral vector containing BMP-2 cDNA. The three control groups were bone defects treated with HBMCs that were either nontransduced or transduced with vector containing GFP. All animals were sacrificed at 12 weeks. The bone formed in each defect was evaluated with plain radiographs, microcomputed tomography (microCT), histomorphometric analysis, and biomechanical testing. Bone defects treated with higher doses of BMP-2-producing cells were more likely to have healed (6/14 of the low-dose group; 12/14 of the standard-dose group; 14/14 of the high-dose group; χ²(2) = 15.501, p < 0.001). None of the bone defects in the control groups had healed. Bone defects treated with high dose and standard dose of BMP-2-producing cells consistently outperformed those treated with a low dose in terms of bone formation, as assessed by microCT and histomorphometry, and biomechanical parameters. However, statistical significance was only seen between defects treated with high dose and low dose. Larger doses of BMP-2-producing cells were associated with a higher likelihood of forming heterotopic ossification. Femurs treated with a standard- and high-dose BMP-2-producing cells demonstrated similar healing and biomechanical properties. Increased doses of BMP-2 delivered through higher cell doses have the potential to heal large bone defects. Adapting regional gene therapy for use in humans will require a balance between promoting bone repair and limiting heterotopic ossification. Impact statement Critical bone loss may result from complex traumatic bone injury (i.e., open fracture or blast injury), revision total joint arthroplasty, and spine pseudoarthrosis. This is a challenging clinical problem to treat and regional gene therapy is an innovative means of addressing it. This study provides information regarding the quantity of cells or "cell dose" of transduced cells needed to treat a critical-sized bone defect in a rat model. This information may be extrapolated for use in humans in future trials.

Stem cell-seeded 3D-printed scaffolds combined with self-assembling peptides for bone defect repair

Bone defects caused by infection, tumor, trauma and so on remain difficult to treat clinically. Bone tissue engineering (BTE) has great application prospect in promoting bone defect repair. Polycaprolactone (PCL) is a commonly used material for creating BTE scaffolds. In addition, self-assembling peptides (SAPs) can function as the extracellular matrix and promote osteogenesis and angiogenesis. In the work, a PCL scaffold was constructed by 3D printing, then integrated with bone marrow mesenchymal stem cells (BMSCs) and SAPs. The research aimed to assess the bone repair ability of PCL/BMSC/SAP implants. BMSC proliferation in PCL/SAP scaffolds was assessed via Cell Counting Kit-8. In vitro osteogenesis of BMSCs cultured in PCL/SAP scaffolds was assessed by alkaline phosphatase staining and activity assays. Enzyme linked immunosorbent assays were also performed to detect the levels of osteogenic factors. The effects of BMSC-conditioned medium from 3D culture systems on the migration and angiogenesis of human umbilical vein endothelial cells (HUVECs) were assessed by scratch, transwell, and tube formation assays. After 8 weeks of in vivo transplantation, radiography and histology were used to evaluate bone regeneration, and immunohistochemistry staining was utilized to detect neovascularization. In vitro results demonstrated that PCL/SAP scaffolds promoted BMSC proliferation and osteogenesis compared to PCL scaffolds, and the PCL/BMSC/SAP conditional medium (CM) enhanced HUVEC migration and angiogenesis compared to the PCL/BMSC CM. In vivo results showed that, compared to the blank control, PCL, and PCL/BMSC groups, the PCL/BMSC/SAP group had significantly increased bone and blood vessel formation. Thus, the combination of BMSC-seeded 3D-printed PCL and SAPs can be an effective approach for treating bone defects.

New Designed Decellularized Scaffolds for Scaffold-based Gene Therapy from Elastic Cartilages via Supercritical Carbon Dioxide Fluid and Alkaline/Protease Treatments

BACKGROUND

Scaffold-based gene therapy provides a promising approach for tissue engineering, which is important and popular, that combines medical applications with engineering materials knowledge.

OBJECTIVE

The decellularization techniques were employed to remove the cellular components from porcine elastic cartilages, leaving a native decellularized extracellular matrix(dECM) composition and architecture integrity of largely insoluble collagen, elastin, and tightly bound glycosaminoglycans. For newly designed collagen scaffold samples, elastic cartilages was hydrolyzed by protease with different concentrations. In this way, it could gain state completely and clearly.

METHODS

An extraction process of supercritical carbon dioxide(ScCO2) was used to remove cellular components from porcine elastic cartilage. The dECM scaffolds with collagen must be characterized by Fourier transform infrared spectroscopy(FTIR), thermo-gravimetric analysis (TGA), and scanning electron microscope(SEM).

RESULTS

The study provided a new treatment combined with supercritical carbon dioxide and alkaline/protease to prepare dECM scaffolds with hole-scaffold microstructures and introduce into a potential application on osteochondral tissue engineering using scaffold-based gene therapy. The new process is simple and efficient. The pore-scaffold microstructures were observed in dECM scaffolds derived from porcine elastic cartilages. The Tdmax values of the resulting dECM scaffolds were observed over 330oC.

CONCLUSION

A series of new scaffolds were successfully obtained from porcine tissue by using ScCO2 and alkaline/enzyme treatments such as an aqueous mixing solution of NH4OH and papain. The dECM scaffolds with high thermal stability were obtained. The resulting scaffold with clean pore-scaffold microstructure could be a potential application for scaffold-based gene therapy.

Regional gene therapy for bone healing using a 3D printed scaffold in a rat femoral defect model

At the present time there are no consistently satisfactory treatment options for some challenging bone loss scenarios. We have previously reported on the properties of a novel 3D-printed hydroxyapatite-composite material in a pilot study, which demonstrated osteoconductive properties but was not tested in a rigorous, clinically relevant model. We therefore utilized a rat critical-sized femoral defect model with a scaffold designed to match the dimensions of the bone defect. The scaffolds were implanted in the bone defect after being loaded with cultured rat bone marrow cells (rBMC) transduced with a lentiviral vector carrying the cDNA for BMP-2. This experimental group was compared against 3 negative and positive control groups. The experimental group and positive control group loaded with rhBMP-2 demonstrated statistically equivalent radiographic and histologic healing of the defect site (p > 0.9), and significantly superior to all three negative control groups (p < 0.01). However, the healed defects remained biomechanically inferior to the unoperated, contralateral femurs (p < 0.01). When combined with osteoinductive signals, the scaffolds facilitate new bone formation in the defect. However, the scaffold alone was not sufficient to promote adequate healing, suggesting that it is not substantially osteoinductive as currently structured. The combination of gene therapy with 3D-printed scaffolds is quite promising, but additional work is required to optimize scaffold geometry, cell dosage and delivery.

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.

BMP-2 Gene Delivery-Based Bone Regeneration in Dentistry

Bone morphogenetic protein-2 (BMP-2) is a potent growth factor affecting bone formation. While recombinant human BMP-2 (rhBMP-2) has been commercially available in cases of non-union fracture and spinal fusion in orthopaedics, it has also been applied to improve bone regeneration in challenging cases requiring dental implant treatment. However, complications related to an initially high dosage for maintaining an effective physiological concentration at the defect site have been reported, although an effective and safe rhBMP-2 dosage for bone regeneration has not yet been determined. In contrast to protein delivery, BMP-2 gene transfer into the defect site induces BMP-2 synthesis in vivo and leads to secretion for weeks to months, depending on the vector, at a concentration of nanograms per milliliter. BMP-2 gene delivery is advantageous for bone wound healing process in terms of dosage and duration. However, safety concerns related to viral vectors are one of the hurdles that need to be overcome for gene delivery to be used in clinical practice. Recently, commercially available gene therapy has been introduced in orthopedics, and clinical trials in dentistry have been ongoing. This review examines the application of BMP-2 gene therapy for bone regeneration in the oral and maxillofacial regions and discusses future perspectives of BMP-2 gene therapy in dentistry.