Nanoplex-Mediated Codelivery of Fibroblast Growth Factor and Bone Morphogenetic Protein Genes Promotes Osteogenesis in Human Adipocyte-Derived Mesenchymal Stem Cells

Clinical challenges in bone tissue engineering - A narrative review

Bone tissue engineering (BTE) has emerged as a promising approach to address large bone defects caused by trauma, infections, congenital malformations, and tumors. This review focuses on scaffold design, cell sources, growth factors, and vascularization strategies, highlighting their roles in developing effective treatments. We explore the complexities of balancing mechanical properties, porosity, and biocompatibility in scaffold materials, alongside optimizing mesenchymal stem cell delivery methods. The critical role of growth factors in bone regeneration and the need for controlled release systems are discussed. Vascularization remains a significant hurdle, with strategies such as angiogenic factors, co-culture systems, and bioprinting under investigation. Mechanical challenges, tissue responses, and inflammation management are examined, alongside gene therapy's potential for enhancing osteogenesis and angiogenesis via both viral and non-viral delivery methods. The review emphasizes the impact of patient-specific factors on bone healing outcomes and the importance of personalized approaches. Future directions are described, emphasizing the necessity of interdisciplinary cooperation to advance the field of BTE and convert laboratory results into clinically feasible solutions.

A Proof-of-Concept Preparation of Lipid-Plasmid DNA Particles Using Novel Extrusion-Based 3D-Printing Technology, SMART

Gene therapy is a promising approach with delivery of mRNA, small interference RNA, and plasmid DNA to elicit a therapeutic action in vitro using cationic or ionizable lipid nanoparticles. In the present study, a novel extrusion-based Sprayed Multi Adsorbed-droplet Reposing Technology (SMART) developed in-house was employed for the preparation, characterization, and transfection abilities of the green fluorescence protein (GFP) plasmid DNA in cancer cells in vitro. The results showed 100% encapsulation of pDNA (GFP) in LNPs of around 150 nm (N/P 5) indicating that the processes developed using SMART technology are consistent and can be utilized for commercial applications.

Strategies for in situ tissue engineering of vascularized bone regeneration (Review)

Numerous physiological processes occur following bone fracture, including inflammatory cell recruitment, vascularization, and callus formation and remodeling. In particular circumstances, such as critical bone defects or osteonecrosis, the regenerative microenvironment is compromised, rendering endogenous stem/progenitor cells incapable of fully manifesting their reparative potential. Consequently, external interventions, such as grafting or augmentation, are frequently necessary. In situ bone tissue engineering (iBTE) employs cell-free scaffolds that possess microenvironmental cues, which, upon implantation, redirect the behavior of endogenous stem/progenitor cells towards a pro-regenerative inflammatory response and reestablish angiogenesis-osteogenesis coupling. This process ultimately results in vascularized bone regeneration (VBR). In this context, a comprehensive review of the current techniques and modalities in VBR-targeted iBTE technology is provided.

Fibroblasts as Turned Agents in Cancer Progression

Differentiated epithelial cells reside in the homeostatic microenvironment of the native organ stroma. The stroma supports their normal function, their G0 differentiated state, and their expansion/contraction through the various stages of the life cycle and physiologic functions of the host. When malignant transformation begins, the microenvironment tries to suppress and eliminate the transformed cells, while cancer cells, in turn, try to resist these suppressive efforts. The tumor microenvironment encompasses a large variety of cell types recruited by the tumor to perform different functions, among which fibroblasts are the most abundant. The dynamics of the mutual relationship change as the sides undertake an epic battle for control of the other. In the process, the cancer "wounds" the microenvironment through a variety of mechanisms and attracts distant mesenchymal stem cells to change their function from one attempting to suppress the cancer, to one that supports its growth, survival, and metastasis. Analogous reciprocal interactions occur as well between disseminated cancer cells and the metastatic microenvironment, where the microenvironment attempts to eliminate cancer cells or suppress their proliferation. However, the altered microenvironmental cells acquire novel characteristics that support malignant progression. Investigations have attempted to use these traits as targets of novel therapeutic approaches.

Gene Therapy for Regenerative Medicine

The development of biological methods over the past decade has stimulated great interest in the possibility to regenerate human tissues. Advances in stem cell research, gene therapy, and tissue engineering have accelerated the technology in tissue and organ regeneration. However, despite significant progress in this area, there are still several technical issues that must be addressed, especially in the clinical use of gene therapy. The aims of gene therapy include utilising cells to produce a suitable protein, silencing over-producing proteins, and genetically modifying and repairing cell functions that may affect disease conditions. While most current gene therapy clinical trials are based on cell- and viral-mediated approaches, non-viral gene transfection agents are emerging as potentially safe and effective in the treatment of a wide variety of genetic and acquired diseases. Gene therapy based on viral vectors may induce pathogenicity and immunogenicity. Therefore, significant efforts are being invested in non-viral vectors to enhance their efficiency to a level comparable to the viral vector. Non-viral technologies consist of plasmid-based expression systems containing a gene encoding, a therapeutic protein, and synthetic gene delivery systems. One possible approach to enhance non-viral vector ability or to be an alternative to viral vectors would be to use tissue engineering technology for regenerative medicine therapy. This review provides a critical view of gene therapy with a major focus on the development of regenerative medicine technologies to control the in vivo location and function of administered genes.

Comparison ofin-situversusex-situdelivery of polyethylenimine-BMP-2 polyplexes for rat calvarial defect repair via intraoperative bioprinting

Gene therapeutic applications combined with bio- and nano-materials have been used to address current shortcomings in bone tissue engineering due to their feasibility, safety and potential capability for clinical translation. Delivery of non-viral vectors can be altered using gene-activated matrices to improve their efficacy to repair bone defects.Ex-situandin-situdelivery strategies are the most used methods for bone therapy, which have never been directly compared for their potency to repair critical-sized bone defects. In this regard, we first time explore the delivery of polyethylenimine (PEI) complexed plasmid DNA encoding bone morphogenetic protein-2 (PEI-pBMP-2) using the two delivery strategies,ex-situandin-situdelivery. To realize these gene delivery strategies, we employed intraoperative bioprinting (IOB), enabling us to 3D bioprint bone tissue constructs directly into defect sites in a surgical setting. Here, we demonstrated IOB of an osteogenic bioink loaded with PEI-pBMP-2 for thein-situdelivery approach, and PEI-pBMP-2 transfected rat bone marrow mesenchymal stem cells laden bioink for theex-situdelivery approach as alternative delivery strategies. We found thatin-situdelivery of PEI-pBMP-2 significantly improved bone tissue formation compared toex-situdelivery. Despite debates amongst individual advantages and disadvantages ofex-situandin-situdelivery strategies, our results ruled in favor of thein-situdelivery strategy, which could be desirable to use for future clinical applications.

Stromal Co-Cultivation for Modeling Breast Cancer Dormancy in the Bone Marrow

Cancers metastasize to the bone marrow before primary tumors can be detected. Bone marrow micrometastases are resistant to therapy, and while they are able to remain dormant for decades, they recur steadily and result in incurable metastatic disease. The bone marrow microenvironment maintains the dormancy and chemoresistance of micrometastases through interactions with multiple cell types and through structural and soluble factors. Modeling dormancy in vitro can identify the mechanisms of these interactions. Modeling also identifies mechanisms able to disrupt these interactions or define novel interactions that promote the reawakening of dormant cells. The in vitro modeling of the interactions of cancer cells with various bone marrow elements can generate hypotheses on the mechanisms that control dormancy, treatment resistance and reawakening in vivo. These hypotheses can guide in vivo murine experiments that have high probabilities of succeeding in order to verify in vitro findings while minimizing the use of animals in experiments. This review outlines the existing data on predominant stromal cell types and their use in 2D co-cultures with cancer cells.

The International Society of RNA Nanotechnology and Nanomedicine (ISRNN): The Present and Future of the Burgeoning Field

The International Society of RNA Nanotechnology and Nanomedicine (ISRNN) hosts an annual meeting series focused on presenting the latest research achievements involving RNA-based therapeutics and strategies, aiming to expand their current biomedical applications while overcoming the remaining challenges of the burgeoning field of RNA nanotechnology. The most recent online meeting hosted a series of engaging talks and discussions from an international cohort of leading nanotechnologists that focused on RNA modifications and modulation, dynamic RNA structures, overcoming delivery limitations using a variety of innovative platforms and approaches, and addressing the newly explored potential for immunomodulation with programmable nucleic acid nanoparticles. In this Nano Focus, we summarize the main discussion points, conclusions, and future directions identified during this two-day webinar as well as more recent advances to highlight and to accelerate this exciting field.

Collagen-based biocomposites inspired by bone hierarchical structures for advanced bone regeneration: ongoing research and perspectives

Bone is a hard-connective tissue composed of matrix, cells and bioactive factors with a hierarchical structure, where the matrix is mainly composed of type I collagen and hydroxyapatite. Collagen fibers assembled by collagen are the template for mineralization and make an important contribution to bone formation and the bone remodeling process. Therefore, collagen has been widely clinically used for bone/cartilage defect regeneration. However, pure collagen implants, such as collagen scaffolds or sponges, have limitations in the bone/cartilage regeneration process due to their poor mechanical properties and osteoinductivity. Different forms of collagen-based composites prepared by incorporating natural/artificial polymers or bioactive inorganic substances are characterized by their interconnected porous structure and promoting cell adhesion, while they improve the mechanical strength, structural stability and osteogenic activities of the collagen matrix. In this review, various forms of collagen-based biocomposites, such as scaffolds, sponges, microspheres/nanoparticles, films and microfibers/nanofibers prepared by natural/synthetic polymers, bioactive ceramics and carbon-based materials compounded with collagen are reviewed. In addition, the application of collagen-based biocomposites as cytokine, cell or drug (genes, proteins, peptides and chemosynthetic) delivery platforms for proangiogenesis and bone/cartilage tissue regeneration is also discussed. Finally, the potential application, research and development direction of collagen-based biocomposites in future bone/cartilage tissue regeneration are discussed.

The biological applications of DNA nanomaterials: current challenges and future directions

DNA, a genetic material, has been employed in different scientific directions for various biological applications as driven by DNA nanotechnology in the past decades, including tissue regeneration, disease prevention, inflammation inhibition, bioimaging, biosensing, diagnosis, antitumor drug delivery, and therapeutics. With the rapid progress in DNA nanotechnology, multitudinous DNA nanomaterials have been designed with different shape and size based on the classic Watson-Crick base-pairing for molecular self-assembly. Some DNA materials could functionally change cell biological behaviors, such as cell migration, cell proliferation, cell differentiation, autophagy, and anti-inflammatory effects. Some single-stranded DNAs (ssDNAs) or RNAs with secondary structures via self-pairing, named aptamer, possess the ability of targeting, which are selected by systematic evolution of ligands by exponential enrichment (SELEX) and applied for tumor targeted diagnosis and treatment. Some DNA nanomaterials with three-dimensional (3D) nanostructures and stable structures are investigated as drug carrier systems to delivery multiple antitumor medicine or gene therapeutic agents. While the functional DNA nanostructures have promoted the development of the DNA nanotechnology with innovative designs and preparation strategies, and also proved with great potential in the biological and medical use, there is still a long way to go for the eventual application of DNA materials in real life. Here in this review, we conducted a comprehensive survey of the structural development history of various DNA nanomaterials, introduced the principles of different DNA nanomaterials, summarized their biological applications in different fields, and discussed the current challenges and further directions that could help to achieve their applications in the future.

Gene- and RNAi-activated scaffolds for bone tissue engineering: Current progress and future directions

Large bone defects are usually managed by replacing lost bone with non-biological prostheses or with bone grafts that come from the patient or a donor. Bone tissue engineering, as a field, offers the potential to regenerate bone within these large defects without the need for grafts or prosthetics. Such therapies could provide improved long- and short-term outcomes in patients with critical-sized bone defects. Bone tissue engineering has long relied on the administration of growth factors in protein form to stimulate bone regeneration, though clinical applications have shown that using such proteins as therapeutics can lead to concerning off-target effects due to the large amounts required for prolonged therapeutic action. Gene-based therapies offer an alternative to protein-based therapeutics where the genetic material encoding the desired protein is used and thus loading large doses of protein into the scaffolds is avoided. Gene- and RNAi-activated scaffolds are tissue engineering devices loaded with nucleic acids aimed at promoting local tissue repair. A variety of different approaches to formulating gene- and RNAi-activated scaffolds for bone tissue engineering have been explored, and include the activation of scaffolds with plasmid DNA, viruses, RNA transcripts, or interfering RNAs. This review will discuss recent progress in the field of bone tissue engineering, with specific focus on the different approaches employed by researchers to implement gene-activated scaffolds as a means of facilitating bone tissue repair.

Polydopamine functionalized VEGF gene-activated 3D printed scaffolds for bone regeneration

Bone is a highly vascularized organ and the formation of new blood vessels is essential to regenerate large critical bone defects. In this study, polylactic acid (PLA) scaffolds of 20-80% infill were three-dimensionally (3D) printed using a fused deposition modeling based 3D printer. The PLA scaffolds were coated with polydopamine (PDA) and then were surface-functionalized with polyethyleneimine (PEI) and VEGF-encoding plasmid DNA (pVEGF) nanoplexes (PLA-PDA-PEI-pVEGF). The PLA-PDA-PEI-pVEGF scaffolds with 40% infill demonstrated higher encapsulation efficiency and sustained release of pVEGF than scaffolds with 20, 60 and 80% infill and were therefore used for in vitro and in vivo studies. The PLA-PDA-PEI-pVEGF increased the translation and secretion of VEGF and BMP-2. The PLA-PDA-PEI-pVEGF also yielded a 2- and 4.5-fold change in VEGF and osteocalcin gene expression in vitro, respectively. A tube formation assay using human umbilical vascular endothelial cells (HUVECs) showed a significant increase in tube length when exposed to the PLA-PDA-PEI-pVEGF scaffold, in comparison to PLA and PLA-PDA scaffolds. The PLA-PDA-PEI-pVEGF scaffold in an in vivo rat calvarial critical bone defect model demonstrated 1.6-fold higher new bone formation compared to the PLA-PDA scaffold. H&E and Masson's trichrome staining of bone sections also revealed that the PLA-PDA-PEI-pVEGF scaffold facilitated the formation of more blood vessels in the newly formed bone compared to the PLA and PLA-PDA scaffold groups. Thus, PLA-PDA-PEI-pVEGF might be a potential 3D printed gene activated scaffold for bone regeneration in clinical situations.

Encapsulating Polyethyleneimine-DNA Nanoplexes into PEGylated Biodegradable Microparticles Increases Transgene Expression In Vitro and Reduces Inflammatory Responses In Vivo

Encapsulating genetic material into biocompatible polymeric microparticles is a means to improving gene transfection while simultaneously decreasing the tendency for inflammatory responses; and can be advantageous in terms of delivering material directly to the lungs via aerosolization for applications such as vaccinations. In this study, we investigated the advantages of using polymeric microparticles carrying the luciferase reporter gene in increasing transfection efficiency in the readily transfectable HEK293 cell line and the difficult to transfect RAW264.7 cell line. The results indicated that there was a limit to the ratio of nitrogen in polyethylenimine (PEI) to phosphate in DNA (N/P ratio) beyond which further increases in transgene expression no longer, or only marginally, occurred. Microparticles encapsulating PEI:DNA nanoplexes induced cellular toxicity in a dose-dependent manner. PEGylation increased transgene expression, likely related to enhanced degradation of particles. Furthermore, intra-tracheal instillation in rats allowed us to investigate the inflammatory response in the lung as a function of PEGylation, porosity, and size. Porosity did not influence cell counts in bronchoalveolar lavage fluid in the absence of PEG, but in particles containing PEG, non-porous particles recruited fewer inflammatory cells than their porous counterparts. Finally, both 1 μm and 10 μm porous PLA-PEG particles recruited more neutrophils than 4 μm particles. Thus, we have shown that PEGylation and lack of porosity are advantageous for faster release of genetic cargo from microparticles and a reduced inflammatory response, respectively.

Non-viral delivery of the BMP2 gene for bone regeneration

Gene-activated bone grafts and substitutes are promising tools for the bone defect healing, which are capable to induce prolonged production of growth factors with a therapeutic effect at physiological concentrations. Non-viral methods of delivering plasmid constructs with target genes are the safest for clinical use, but their efficiency is lower in comparison with viral vectors. To solve the problem of plasmid delivery into cells, some systems with a high transfection capacity and ensure sufficient cell viability are being developed. Moreover, there are different approaches to improve the level of expression of target genes and targeted delivery to the bone defect in order to achieve local therapeutic concentrations. This review considers approaches which are aimed to increase the efficiency of bone tissue regeneration methods based on non-viral delivery systems for osteoinduction genes using the example of the bone morphogenetic protein-2 gene.

Nonviral Gene Delivery Embedded in Biomimetically Mineralized Matrices for Bone Tissue Engineering

Research in bone tissue engineering aims to design materials that are effective at generating bone without causing significant side effects. The osteogenic potential of combining matrices and protein growth factors has been well documented, however, improvements are necessary to achieve optimal therapeutic benefits upon clinical translation. In this article, rat calvarial defects were treated with gene-activated matrices (GAMs). The GAMs used were collagen sponges mineralized with a simulated body fluid (SBF) containing a nonviral gene delivery system. Both in vitro and in vivo studies were performed to determine the optimal mode of gene delivery. After 6 weeks, the defects were extracted to assess bone formation and tissue quality through histological and microcomputed tomography analyses. The optimal GAM consisted of a collagen sponge with polyethylenimine plasmid DNA (PEI-pDNA) complexes embedded in a calcium phosphate coating produced by SBF, which increased total bone formation by 39% compared with 19% for control samples. A follow-up in vivo study was performed to optimize the ratio of growth factors included in the GAM. The optimal ratio for supporting bone formation after 6 weeks of implantation was five parts of pBMP-2 to three parts pFGF-2. These studies demonstrated that collagen matrices biomimetically mineralized and activated with plasmids encoding fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) can optimally improve bone regeneration outcomes. Impact statement Bone tissue engineering has explored both nonviral gene delivery and the concept of biomimetic mineralization. In this study, we combined these two concepts to further enhance bone regeneration outcomes. We demonstrated that embedding polyethylenimine (PEI)-based gene delivery within a mineral layer formed from simulated body fluid (SBF) immersion can increase bone formation rates. We also demonstrated that the ratio of growth factors utilized for matrix fabrication can impact the amount of bone formed in the defect site. This research highlights a combined approach using SBF and nonviral gene delivery both in vitro and in vivo and prepares the way for future optimization of synthetic gene activated matrices.

A Multi-Functional Implant Induces Bone Formation in a Diabetic Model

Patients with diabetes mellitus (DM) have defective healing of bone fractures. It was previously shown that nonviral gene delivery of plasmid DNA (pDNA) that independently encodes bone morphogenetic protein-2 (BMP-2) and fibroblast growth factor-2 (FGF-2), acts synergistically to promote bone regeneration in a DM animal model. Additionally, both insulin (INS) and the hormonally active form of vitamin D3, 1α,25-dihydroxyvitamin D3 (1α,25(OH)₂ D₃ ) (VD3) have independently been shown to play key roles in regulating bone fracture healing in DM patients. However, these individual therapies fail to adequately stimulate bone regeneration, illustrating a need for novel treatment of bone fractures in diabetic patients. Here, the ability of local delivery of INS and VD3 along with BMP-2 and FGF-2 genes is investigated to promote bone formation ectopically in Type-2 diabetic rats. A composite consisting of VD3 and INS is developed that contains poly(lactic-co-glycolic acid) microparticles (MPs) embedded in a fibrin gel surrounded by a collagen matrix that is permeated with polyethylenimine (PEI)-(pBMP-2+pFGF-2) nanoplexes. Using a submuscular osteoinduction model, it is demonstrated that local delivery of INS, VD3, and PEI-(pBMP-2+pFGF-2) significantly improves bone generation compared to other treatments, thusimplicating this approach as a method to promote bone regeneration in DM patients with bone fractures.

Application of BMP-2/FGF-2 gene-activated scaffolds for dental pulp capping

OBJECTIVES

To evaluate the effect of non-viral gene therapy on human dental pulp stem cells (DPSCs) in an in vitro and an ex vivo model.

MATERIALS AND METHODS

Nanoplexes comprising polyethyleneimine (PEI) and plasmid DNA (pDNA) encoding for fibroblast growth factor-2 (pFGF-2) and bone morphogenic protein-2 (pBMP-2) were cultured with DPSCs to evaluate cytotoxicity, protein expression, and mineralization activity. Collagen scaffolds loaded with these nanoplexes or mineral trioxide aggregate (MTA) were utilized in an ex vivo tooth culture model to assess pulp response, over a period of 14 days. All nanoplex formulations were characterized for size and zeta potential by measuring dynamic light scattering and electrophoretic mobility, respectively.

RESULTS

DPSCs treated with the nanoplexes showed increased cell proliferation and enhanced expression of BMP-2 and FGF-2 proteins. Collagen scaffolds containing PEI-pBMP-2 and/or pFGF-2 nanoplexes significantly increased cell proliferation, BMP-2 and FGF-2 expression, and mineralization when compared to MTA. Ex vivo histology showed a well-preserved pulp and healthy tissue in both the MTA and scaffold groups. Connective tissue in contact with the scaffold was dense and homogeneous, with some cells present in contact and within the scaffold.

CONCLUSION

Transfection of DPSCs with pBMP-2/pFGF-2 nanoplexes resulted in increased expression of BMP-2 and FGF-2, enhanced proliferation, and mineralization properties compared to MTA. These findings were supported by the ex vivo observations.

CLINICAL RELEVANCE

This biological approach in pulp capping brings new insights into the effective management of engineered pulp tissues, mainly those generated by the transplantation of DPSCs in empty root canals.

Adipose-derived stem cells: An appropriate selection for osteogenic differentiation

Mesenchymal stem cells (MSCs) are a major component of various forms of tissue engineering. MSCs have self-renewal and multidifferential potential. Osteogenic differentiation of MSCs is an area of attention in bone regeneration. One form of MSCs are adipose-derived stem cells (ASCs), which can be simply harvested and differentiated into several cell lineages, such as chondrocytes, adipocytes, or osteoblasts. Due to special properties, ASCs are frequently used in vitro and in vivo bone regeneration. Identifying factors involved in osteogenic differentiation of ASCs is important for better understanding the mechanism of osteogenic differentiation. Different methods are used to stimulate osteogenesis of ASCs in literature, including common osteogenic media, growth factors, hormones, hypoxia, mechanical and chemical stimuli, genetic modification, and nanotechnology. This review article provides an overview describing the isolation procedure, characterization, properties, current methods for osteogenic differentiation of ASCs, and their basic biological mechanism.

Inhibition of BMP9 Induced Bone Formation by Salicylic-acid Polymer Capping

This work focuses on the development of a system to control the formation of bone to complement developments that have enabled potent regeneration of bony tissue. Scaffolds were fabricated with chemically modified RNA encoding for bone morphogenetic protein-9 (cmBMP9) and capped with salicylic acid (SA)-containing polymer (SAPAE). The goal was to determine if SAPAE could inhibit the formation of bone in a pilot animal study since cmBMP9 has been demonstrated to be highly effective in regenerating bone in a rat calvarial defect model. The results indicated that cmBMP9 increased bone formation (30% increase in area covered compared to control) and that SAPAE trended toward reducing the bone formation. These results suggest SAPAE could be useful as a chemical agent in reducing unwanted bone formation in implants loaded with cmBMP9.

Effects of calcium concentration on nonviral gene delivery to bone marrow-derived stem cells

BACKGROUND

Calcium ions (Ca²⁺ ) influence natural bone healing, and calcium is frequently used in bone tissue engineering scaffolds and cements. Scaffolds can also incorporate gene delivery systems to further promote osteoblast differentiation. Thus, our goal was to identify if Ca²⁺ concentration affects the transfection of bone marrow stromal cells because these cells play a major role in bone healing and can infiltrate gene-activated scaffolds designed to promote bone growth.

METHODS

Bone marrow-derived mesenchymal stem cells (BMSCs) were cultured in media with Ca²⁺ concentrations ranging from 0 to 20 mM and transfected with polyethyleneimine-plasmid DNA (PEI-pDNA) complexes. Cell viability and transfection efficiency were determined using MTS assays and flow cytometry, respectively. PEI-pDNA complex localization in BMSCs was assessed using fluorescence microscopy. To determine BMSC differentiation, messenger RNA (mRNA) for osteocalcin and CBFA1 was quantified using real time-polymerase chain reaction (PCR). Calcium deposition was qualitatively assessed after three and 14 days using Alizarin Red staining.

RESULT

Our results indicate that Ca²⁺ levels between 8 and 12 mM positively impacted transfection of BMSCs with PEI-pDNA complexes in terms of cell viability and transfection efficiency. A Ca²⁺ concentration of 10 mM also increased the expression of an osteogenic gene, osteocalcin, when the cells were transfected with plasmid DNA encoding bone morphogenetic protein 2 (BMP-2).

CONCLUSION

Ca²⁺ at a 10 mM concentration can significantly reduce toxicity and enhance transfection efficiency when combined with PEI-pDNA complexes, and this combination can be specifically applied to further enhance the differentiation of BMSCs by using the combination of polyethyleneimine-plasmid bone morphogenetic protein 2 (PEI-pBMP-2) and 10 mM Ca²⁺ as compared with PEI-pBMP-2 alone.

MicroRNA-200c Attenuates Periodontitis by Modulating Proinflammatory and Osteoclastogenic Mediators

This study tested whether microRNA (miR)-200c can attenuate the inflammation and alveolar bone resorption in periodontitis by using an in vitro and a rat model. Polyethylenimine (PEI) was used to facilitate the transfection of plasmid DNA encoding miR-200c into primary human gingival fibroblasts (HGFs) and gingival tissues of rats. We first analyzed how proinflammatory and osteoclastogenic mediators in HGFs with overexpression of miR-200c responded to Porphyromonas gingivalis lipopolysaccharide (LPS-PG) challenge in vitro. We observed that overexpression of miR-200c significantly reduced interleukin (IL)-6 and 8 and repressed interferon-related developmental regulator-1 (IFRD1) in HGFs. miR-200c also downregulated p65 and p50. In a rat model of periodontitis induced by an LPS injection at the gingival sulcus of the second maxillary molar (M2), we analyzed how the mediators in rat gingiva and alveolar bone resorption responded to miR-200c treatment by a local injection of PEI-plasmid miR-200 nanoplexes. We observed that the local injection of miR-200c significantly upregulated miR-200c expression in gingiva and reduced IL-6, IL-8, IFRD1, and the ratio of receptor activator of nuclear factor kappa-B ligand/osteoprotegerin. Using micro-computed tomography analysis and histomorphometry, we further confirmed that local treatment with miR-200c effectively protected alveolar bone resorption in the rat model of periodontitis by reducing the distance between the cemento-enamel junction and the alveolar bone crest and the inter-radicular space in the upper maxilla at M2. These findings imply that miR-200c may serve as a unique means to prevent periodontitis and associated bone loss.

Scaffold-Based Delivery of Nucleic Acid Therapeutics for Enhanced Bone and Cartilage Repair

Recent advances in tissue engineering have made progress toward the development of biomaterials capable of the delivery of growth factors, such as bone morphogenetic proteins, in order to promote enhanced tissue repair. However, controlling the release of these growth factors on demand and within the desired localized area is a significant challenge and the associated high costs and side effects of uncontrolled delivery have proven increasingly problematic in clinical orthopedics. Gene therapy may be a valuable tool to avoid the limitations of local delivery of growth factors. Following a series of setbacks in the 1990s, the field of gene therapy is now seeing improvements in safety and efficacy resulting in substantial clinical progress and a resurgence in confidence. Biomaterial scaffold-mediated gene therapy provides a template for cell infiltration and tissue formation while promoting transfection of cells to engineer therapeutic proteins in a sustained but ultimately transient fashion. Additionally, scaffold-mediated delivery of RNA-based therapeutics can silence specific genes associated with orthopedic pathological states. This review will provide an overview of the current state-of-the-art in the field of gene-activated scaffolds and their use within orthopedic tissue engineering applications. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1671-1680, 2019.

Poly-l-lysine-coated PLGA/poly(amino acid)-modified hydroxyapatite porous scaffolds as efficient tissue engineering scaffolds for cell adhesion, proliferation, and differentiation

Ideal bone tissue engineering scaffolds should be biocompatible, biodegradable, and mechanically robust and have the ability to regulate cell function.

Nanoparticle-Based Delivery of CRISPR/Cas9 Genome-Editing Therapeutics

The recent progress in harnessing the efficient and precise method of DNA editing provided by CRISPR/Cas9 is one of the most promising major advances in the field of gene therapy. However, the development of safe and optimally efficient delivery systems for CRISPR/Cas9 elements capable of achieving specific targeting of gene therapy to the location of interest without off-target effects is a primary challenge for clinical therapeutics. Nanoparticles (NPs) provide a promising means to meet such challenges. In this review, we present the most recent advances in developing innovative NP-based delivery systems that efficiently deliver CRISPR/Cas9 constructs and maximize their effectiveness.

Recent Advances and Future of Gene Therapy for Bone Regeneration

PURPOSE OF REVIEW

The purpose of this review is to discuss the recent advances in gene therapy as a treatment for bone regeneration. While most fractures heal spontaneously, patients who present with fracture nonunion suffer from prolonged pain, disability, and often require additional operations to regain musculoskeletal function.

RECENT FINDINGS

In the last few years, BMP gene delivery by means of electroporation and sonoporation resulted in repair of nonunion bone defects in mice, rats, and minipigs. Ex vivo transfection of porcine mesenchymal stem cells (MSCs) resulted in bone regeneration following implantation in vertebral defects of minipigs. Sustained release of VEGF gene from a collagen-hydroxyapatite scaffold to the mandible of a human patient was shown to be safe and osteoinductive. In conclusion, gene therapy methods for bone regeneration are systematically becoming more efficient and show proof-of-concept in clinically relevant animal models. Yet, on the pathway to clinical use, more investigation is needed to determine the safety aspects of the various techniques in terms of biodistribution, toxicity, and tumorigenicity.

Fabrication of hybrid scaffold based on hydroxyapatite-biodegradable nanofibers incorporated with liposomal formulation of BMP-2 peptide for bone tissue engineering

In the present study, we fabricated an efficient, simple biomimetic scaffold to stimulate osteogenic differentiation of mesenchymal stem cells (MSCs). Electrospun poly L-lactic acid nanofibers were employed to mimic the nanofibrillar structure of bone proteins and coated with hydroxyapatite nanoparticles to simulate bone minerals. Thereafter, we regulated the release pattern of BMP-2 peptide through covalent attachment of an optimized liposomal formulation to the scaffold. The fabricated platform provided a sustained release profile of BMP-2 peptide up to 21 days while supporting cellular attachment and proliferation without cytotoxicity. In-vitro results confirmed the superiority of the scaffold containing liposomes through enhancement of growth and differentiation of MSCs. Ectopic bone formation model exhibited significant localized initiation of bone formation of liposome incorporated scaffold. Consequently, these findings demonstrated that our designed platform with modified release properties of BMP-2 peptide considerably promoted osteogenic differentiation of MSCs making it a unique candidate for bone regeneration therapeutics.

In situ polymerization of poly(γ-benzyl-l-glutamate) on mesoporous hydroxyapatite with high graft amounts for the direct fabrication of biodegradable cell microcarriers and their osteogenic induction

Large-scale cell culture for cell expansion in tissue engineering is currently a major focus of research. One method to achieve better cell amplification is to utilize microcarriers. In this study, different amounts of poly(γ-benzyl-l-glutamate) (PBLG) (from 11 wt% to 50 wt%) were grafted on mesoporous hydroxyapatite (MHA) by the in situ ring opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydride (BLG-NCA), and biodegradable and biocompatible PBLG-g-MHA microcarriers were directly fabricated using the oil-in-water (O/W) solvent-evaporation technique for bone tissue engineering. The amount of grafted PBLG could be controlled by adjusting the feed ratio of MHA and BLG-NCA. The relationships between sphere morphology and graft amount or solution concentration were explored. Furthermore, cytological assays were performed to evaluate the biological properties of the PBLG-g-MHA microcarriers. For a solution concentration of 3% (w/v) and PBLG graft amounts of 33 wt% and 50 wt%, the microspheres could be harvested with optimal spherical shapes. In vitro cell culture revealed that the PBLG-g-MHA microspheres had favorable properties for cell proliferation and significantly enhanced the osteogenic differentiation of MC3T3-E1 cells and bone matrix formation.

Ginsenoside Rg1 and platelet-rich fibrin enhance human breast adipose-derived stem cell function for soft tissue regeneration

Adipose-derived stem cells (ASCs) can be used to repair soft tissue defects, wounds, burns, and scars and to regenerate various damaged tissues. The cell differentiation capacity of ASCs is crucial for engineered adipose tissue regeneration in reconstructive and plastic surgery. We previously reported that ginsenoside Rg1 (G-Rg1 or Rg1) promotes proliferation and differentiation of ASCs in vitro and in vivio. Here we show that both G-Rg1 and platelet-rich fibrin (PRF) improve the proliferation, differentiation, and soft tissue regeneration capacity of human breast adipose-derived stem cells (HBASCs) on collagen type I sponge scaffolds in vitro and in vivo. Three months after transplantation, tissue wet weight, adipocyte number, intracellular lipid, microvessel density, and gene and protein expression of VEGF, HIF-1α, and PPARγ were higher in both G-Rg1- and PRF-treated HBASCs than in control grafts. More extensive new adipose tissue formation was evident after treatment with G-Rg1 or PRF. In summary, G-Rg1 and/or PRF co-administration improves the function of HBASCs for soft tissue regeneration engineering.

Mesenchymal Stem Cells and Calcium Phosphate Bioceramics: Implications in Periodontal Bone Regeneration

In orthopedic medicine, a feasible reconstruction of bone structures remains one of the main challenges both for healthcare and for improvement of patients' quality of life. There is a growing interest in mesenchymal stem cells (MSCs) medical application, due to their multilineage differentiation potential, and tissue engineering integration to improve bone repair and regeneration. In this review we will describe the main characteristics of MSCs, such as osteogenesis, immunomodulation and antibacterial properties, key parameters to consider during bone repair strategies. Moreover, we describe the properties of calcium phosphate (CaP) bioceramics, which demonstrate to be useful tools in combination with MSCs, due to their biocompatibility, osseointegration and osteoconduction for bone repair and regeneration. Also, we overview the main characteristics of dental cavity MSCs, which are promising candidates, in combination with CaP bioceramics, for bone regeneration and tissue engineering. The understanding of MSCs biology and their interaction with CaP bioceramics and other biomaterials is critical for orthopedic surgical bone replacement, reconstruction and regeneration, which is an integrative and dynamic medical, scientific and bioengineering field of research and biotechnology.

Enhancing Cell Proliferation and Osteogenic Differentiation of MC3T3-E1 Pre-osteoblasts by BMP-2 Delivery in Graphene Oxide-Incorporated PLGA/HA Biodegradable Microcarriers

Lack of bioactivity has seriously restricted the development of biodegradable implants for bone tissue engineering. Therefore, surface modification of the composite is crucial to improve the osteointegration for bone regeneration. Bone morphogenetic protein-2 (BMP-2), a key factor in inducing osteogenesis and promoting bone regeneration, has been widely used in various clinical therapeutic trials. In this study, BMP-2 was successfully immobilized on graphene oxide-incorporated PLGA/HA (GO-PLGA/HA) biodegradable microcarriers. Our study demonstrated that the graphene oxide (GO) facilitated the simple and highly efficient immobilization of peptides on PLGA/HA microcarriers within 120 min. To further test in vitro, MC3T3-E1 cells were cultured on different microcarriers to observe various cellular activities. It was found that GO and HA significantly enhanced cell adhesion and proliferation. More importantly, the immobilization of BMP-2 onto the GO-PLGA/HA microcarriers resulted in significantly greater osteogenic differentiation of cells in vitro, as indicated by the alkaline phosphate activity test, quantitative real-time polymerase chain reaction analysis, immunofluorescence staining and mineralization on the deposited substrates. Findings from this study revealed that the method to use GO-PLGA/HA microcarriers for immobilizing BMP-2 has a great potential for the enhancement of the osseointegration of bone implants.

Synergistic effects of fibroblast growth factor-2 and bone morphogenetic protein-2 on bone induction

The present study investigated the synergistic effect of co-administering fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) on osteoblastic differentiation in C2C12 cells and in rats. C2C12 murine myoblast cells represent a well-accepted in vitro model system to study the ability of BMP-2 to alter cell lineage from the myogenic to the osteogenic phenotype. The osteoblastic differentiation potency was determined by alkaline phosphatase (ALP) and Alizarin red S staining. ALP activity and calcium concentrations were colorimetrically measured. Simultaneous administration of 4 µg/ml recombinant human BMP-2 with 2 ng/ml FGF-2 markedly enhanced ALP activity (an early marker of osteogenesis) of C2C12 cells. This combination also increased extracellular signal-regulated kinase1/2 mitogen activated protein kinase signaling that is involved in the promoting effect of FGF-2 on BMP-2-induced osteoblastic differentiation in C2C12 cells. Calcium deposition (a late marker of osteogenesis) and the expression of CD34 (a marker of new vessels) were promoted optimally by simultaneous local sustained administration of FGF-2 and BMP-2 using collagen and chitosan-coated antigen-extracted porcine cancellous implants in a rat ectopic implantation model. The synergistic effects of a combination of BMP-2 and FGF-2 may have potential for bone regenerative therapeutics.

Nanofat-derived stem cells with platelet-rich fibrin improve facial contour remodeling and skin rejuvenation after autologous structural fat transplantation

Traditional autologous fat transplantation is a common surgical procedure for treating facial soft tissue depression and skin aging. However, the transplanted fat is easily absorbed, reducing the long-term efficacy of the procedure. Here, we examined the efficacy of nanofat-assisted autologous fat structural transplantation. Nanofat-derived stem cells (NFSCs) were isolated, mechanically emulsified, cultured, and characterized. Platelet-rich fibrin (PRF) enhanced proliferation and adipogenic differentiation of NFSCs in vitro. We then compared 62 test group patients with soft tissue depression or signs of aging who underwent combined nanofat, PRF, and autologous fat structural transplantation to control patients (77 cases) who underwent traditional autologous fat transplantation. Facial soft tissue depression symptoms and skin texture were improved to a greater extent after nanofat transplants than after traditional transplants, and the nanofat group had an overall satisfaction rate above 90%. These data suggest that NFSCs function similarly to mesenchymal stem cells and share many of the biological characteristics of traditional fat stem cell cultures. Transplants that combine newly-isolated nanofat, which has a rich stromal vascular fraction (SVF), with PRF and autologous structural fat granules may therefore be a safe, highly-effective, and long-lasting method for remodeling facial contours and rejuvenating the skin.

Regeneration of bone using nanoplex delivery of FGF-2 and BMP-2 genes in diaphyseal long bone radial defects in a diabetic rabbit model

Bone fracture healing impairment related to systemic diseases such as diabetes can be addressed by growth factor augmentation. We previously reported that growth factors such as fibroblast growth factor-2 (FGF-2) and bone morphogenetic protein-2 (BMP-2) work synergistically to encourage osteogenesis in vitro. In this report, we investigated if BMP-2 and FGF-2 together can synergistically promote bone repair in a leporine model of diabetes mellitus, a condition that is known to be detrimental to union. We utilized two kinds of plasmid DNA encoding either BMP-2 or FGF-2 formulated into polyethylenimine (PEI) complexes. The fabricated nanoplexes were assessed for their size, charge, in vitro cytotoxicity, and capacity to transfect human bone marrow stromal cells (BMSCs). Using diaphyseal long bone radial defects in a diabetic rabbit model it was demonstrated that co-delivery of PEI-(pBMP-2+pFGF-2) embedded in collagen scaffolds resulted in a significant improvement in bone regeneration compared to PEI-pBMP-2 embedded in collagen scaffolds alone. This study demonstrated that scaffolds loaded with PEI-(pBMP-2+pFGF-2) could be an effective way of promoting bone regeneration in patients with diabetes.

Gene-Activated Titanium Surfaces Promote In Vitro Osteogenesis

PURPOSE

Commercially pure titanium (CpTi) and its alloys possess favorable mechanical and biologic properties for use as implants in orthopedics and dentistry. However, failures in osseointegration still exist and are common in select individuals with risk factors such as smoking. Therefore, in this study, a proposal was made to enhance the potential for osseointegration of CpTi discs by coating their surfaces with nanoplexes comprising polyethylenimine (PEI) and plasmid DNA (pDNA) encoding bone morphogenetic protein-2 (pBMP-2).

MATERIALS AND METHODS

The nanoplexes were characterized for size and surface charge with a range of N/P ratios (the molar ratio of amine groups of PEI to phosphate groups in pDNA backbone). CpTi discs were surface characterized for morphology and composition before and after nanoplex coating using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD). The cytotoxicity and transfection ability of CpTi discs coated with nanoplexes of varying N/P ratios in human bone marrow-derived mesenchymal stem cells (BMSCs) was measured via MTS assays and flow cytometry, respectively.

RESULTS

The CpTi discs coated with nanoplexes prepared at an N/P ratio of 10 (N/P-10) were considered optimal, resulting in 75% cell viability and 14% transfection efficiency. Enzyme-linked immunosorbent assay results demonstrated a significant enhancement in BMP-2 protein secretion by BMSCs 7 days posttreatment with PEI/pBMP-2 nanoplexes (N/P-10) compared to the controls, and real-time PCR data demonstrated that the BMSCs treated with PEI/pBMP-2 nanoplex-coated CpTi discs resulted in an enhancement of Runx-2, alkaline phosphatase, and osteocalcin gene expressions on day 7 posttreatment. In addition, these BMSCs demonstrated enhanced calcium deposition on day 30 posttreatment as determined by qualitative (alizarin red staining) and quantitative (atomic absorption spectroscopy) assays.

CONCLUSION

It can be concluded that PEI/pBMP-2 nanoplex (N/P-10)-coated CpTi discs have the potential to induce osteogenesis and enhance osseointegration.

Bone Regeneration Using Gene-Activated Matrices

Gene delivery to bone is a potential therapeutic strategy for directed, sustained, and regulated protein expression. Tissue engineering strategies for bone regeneration include delivery of proteins, genes (viral and non-viral-mediated delivery), and/or cells to the bone defect site. In addition, biomimetic scaffolds and scaffolds incorporating bone anabolic agents greatly enhance the bone repair process. Regional gene therapy has the potential of enhancing bone defect healing and bone regeneration by delivering osteogenic genes locally to the osseous lesions, thereby reducing systemic toxicity and the need for using supraphysiological dosages of therapeutic proteins. By implanting gene-activated matrices (GAMs), sustained gene expression and continuous osteogenic protein production in situ can be achieved in a way that stimulates osteogenesis and bone repair within osseous defects. Critical parameters substantially affecting the therapeutic efficacy of gene therapy include the choice of osteogenic transgene(s), selection of non-viral or viral vectors, the wound environment, and the selection of ex vivo and in vivo gene delivery strategies, such as GAMs. It is critical for gene therapy applications that clinically beneficial amounts of proteins are synthesized endogenously within and around the lesion in a sustained manner. It is therefore necessary that reliable and reproducible methods of gene delivery be developed and tested for their efficacy and safety before translating into clinical practice. Practical considerations such as the age, gender, and systemic health of patients and the nature of the disease process also need to be taken into account in order to personalize the treatments and progress towards developing a clinically applicable gene therapy for healing bone defects. This review discusses tissue engineering strategies to regenerate bone with specific focus on non-viral gene delivery systems.

Bone morphogenetic protein 9 (BMP9) induces effective bone formation from reversibly immortalized multipotent adipose-derived (iMAD) mesenchymal stem cells

Regenerative medicine and bone tissue engineering using mesenchymal stem cells (MSCs) hold great promise as an effective approach to bone and skeletal reconstruction. While adipose tissue harbors MSC-like progenitors, or multipotent adipose-derived cells (MADs), it is important to identify and characterize potential biological factors that can effectively induce osteogenic differentiation of MADs. To overcome the time-consuming and technically challenging process of isolating and culturing primary MADs, here we establish and characterize the reversibly immortalized mouse multipotent adipose-derived cells (iMADs). The isolated mouse primary inguinal MAD cells are reversibly immortalized via the retrovirus-mediated expression of SV40 T antigen flanked with FRT sites. The iMADs are shown to express most common MSC markers. FLP-mediated removal of SV40 T antigen effectively reduces the proliferative activity and cell survival of iMADs, indicating the immortalization is reversible. Using the highly osteogenic BMP9, we find that the iMADs are highly responsive to BMP9 stimulation, express multiple lineage regulators, and undergo osteogenic differentiation in vitro upon BMP9 stimulation. Furthermore, we demonstrate that BMP9-stimulated iMADs form robust ectopic bone with a thermoresponsive biodegradable scaffold material. Collectively, our results demonstrate that the reversibly immortalized iMADs exhibit the characteristics of multipotent MSCs and are highly responsive to BMP9-induced osteogenic differentiation. Thus, the iMADs should provide a valuable resource for the study of MAD biology, which would ultimately enable us to develop novel and efficacious strategies for MAD-based bone tissue engineering.

Photo-immobilization of bone morphogenic protein 2 on PLGA/HA nanocomposites to enhance the osteogenesis of adipose-derived stem cells

Poly(lactide-co-glycolide) and nano-hydroxyapatite composites are surface-modified with BMP-2 via photo-reactive gelatin to make the composites exhibit excellent bioactivities for the adhesion, proliferation and osteogenic differentiation of ADSCs.

Chemically modified RNA activated matrices enhance bone regeneration

There exists a dire need for improved therapeutics to achieve predictable bone regeneration. Gene therapy using non-viral vectors that are safe and efficient at transfecting target cells is a promising approach to overcoming the drawbacks of protein delivery of growth factors. Here, we investigated the transfection efficiency, cytotoxicity, osteogenic potential and in vivo bone regenerative capacity of chemically modified ribonucleic acid (cmRNA) (encoding BMP-2) complexed with polyethylenimine (PEI) and made comparisons with PEI complexed with conventional plasmid DNA (encoding BMP-2). The polyplexes were fabricated at an amine (N) to phosphate (P) ratio of 10 and characterized for transfection efficiency using human bone marrow stromal cells (BMSCs). The osteogenic potential of BMSCs treated with these polyplexes was validated by determining the expression of bone-specific genes, osteocalcin and alkaline phosphatase as well as through the detection of bone matrix deposition. Using a calvarial bone defect model in rats, it was shown that PEI-cmRNA (encoding BMP-2)-activated matrices promoted significantly enhanced bone regeneration compared to PEI-plasmid DNA (BMP-2)-activated matrices. Our proof of concept study suggests that scaffolds loaded with non-viral vectors harboring cmRNA encoding osteogenic proteins may be a powerful tool for stimulating bone regeneration with significant potential for clinical translation.