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

Mechanisms of bone regeneration repair and potential and efficacy of small molecule drugs

Bone regeneration and repair is a complex physiological process of bone formation. To date, existing research has greatly enhanced our understanding of bone regeneration and repair, achieving significant success in treating bone injuries. However, extensive bone defects, bone nonunion, and metabolic bone diseases remain incompletely solved challenges in modern medicine. With the emergence of High-Throughput Screening (HTS) technology, previous studies have identified numerous small molecule compounds with potential for inducing bone formation and enhancing bone metabolism. However, the effects of these small molecules on bone regeneration and repair through related signaling pathways have not been systematically elaborated. Therefore, in this literature review, we focus on summarizing the classical signaling pathways affecting bone regeneration and repair, as well as the research progress and applications of related small molecule drugs.

Bioactive hydrogel formulations for regeneration of pathological bone defects

Bone defects caused by osteoporosis, infection, diabetes, post-tumor resection, and nonunion often cause severe pain and markedly increase morbidity and mortality, which remain a significant challenge for orthopedic surgeons. The precise local treatments for these pathological complications are essential to avoid poor or failed bone repair. Hydrogel formulations serve as injectable innovative platforms that overcome microenvironmental obstacles and as delivery systems for controlled release of various bioactive substances to bone defects in a targeted manner. Additionally, hydrogel formulations can be tailored for specific mechanical strengths and degradation profiles by adjusting their physical and chemical properties, which are crucial for prolonged drug retention and effective bone repair. This review summarizes recent advances in bioactive hydrogel formulations as three-dimensional scaffolds that support cell proliferation and differentiation. It also highlights their role as smart drug-delivery systems with capable of continuously releasing antibacterial agents, anti-inflammatory drugs, chemotherapeutic agents, and osteogenesis-related factors to enhance bone regeneration in pathological areas. Furthermore, the limitations of hydrogel formulations in pathological bone repair are discussed, and future development directions are proposed, which is expected to pave the way for the repair of pathological bone defects.

Gene-activation of surface-modified 3D printed calcium phosphate scaffolds

Large volume bone defects that do not spontaneously heal despite surgical stabilization ("critical-sized" defects) remain a challenge to treat clinically. Recent research investigating bone regenerative implants made from 3D printed materials have shown promise as a potential alternative to current treatment methods, such as autografting, allografting, and multi-step surgical interventions. Recent work has shown that implanting 3D printed calcium phosphate cement (CPC) scaffolds loaded with bone morphogenetic protein-2 (BMP-2) can provide a one-step surgical intervention that has similar bone healing outcomes to a popular two-step intervention: the Masquelet technique. The aim of this study was to investigate whether a 3D printed CPC scaffold loaded with a lyophilized polyplex gene-delivery formulation could serve as an alternative to loading BMP-2 protein onto such scaffolds. We 3D printed CPC scaffolds, hardened them with multiple methods, and explored the impact of these hardening methods on surface texture, mechanical strength, osteogenic differentiation, and ion flux. We then gene-activated these materials with cationic polyplexes containing plasmid DNA encoding reporter genes to investigate transfection from the gene-activated scaffolds. We found that incubating CPC scaffolds in aqueous solutions after initial hardening in a humid environment could enhance scaffold mechanical strength (compressive strength of 21.28 MPa vs. 6.54 MPa) and osteogenic differentiation. We also found that when we increased the total surface area of the CPC material exposed to polyplex solutions, there was a reduction in transfection via adsorption of polyplexes to the CPC surface. This study shows that 3D printed, gene-activated CPC scaffolds are a promising avenue for future exploration in the field of bone regeneration, though the level of gene expression induced by the scaffolds must be improved.

The assessment of marrow adiposity in type 1 diabetic rabbits through magnetic resonance spectroscopy is linked to bone resorption

Background

Enhanced marrow adiposity is frequently linked with a decline in bone density. The underlying mechanisms responsible for bone loss in diabetes are not well understood. In this investigation, we employed an alloxan-induced diabetes rabbit model to unravel the association between marrow fat content and bone resorption, utilizing magnetic resonance spectroscopy.

Methods

Forty 4-month-old male New Zealand rabbits were randomly allocated into two groups: a control group and an alloxan-induced diabetic group, each consisting of 20 rabbits. Biochemical analyses covered plasma glucose, enzyme levels, lipid profiles, blood urea nitrogen, creatinine levels, and markers of bone turnover. Quantification of bone marrow adipose tissue utilized both MR spectroscopy and histological examinations. Dual-energy X-ray absorptiometry and microcomputed tomography were employed to determine bone density and trabecular bone microarchitectures. The expression levels of marrow adipocyte markers (peroxisome proliferator-activated receptor-gamma2, CCAAT/enhancer-binding protein-α, and fatty acid binding protein 4) and markers of bone resorption [tartrate-resistant acid phosphatase (TRACP) and cathepsin K] were assessed using RT-PCR.

Results

Diabetic rabbits exhibited significant increases in marrow fat fraction (MFF) over time (MFF increased by 13.2% at 1.5 months and 24.9% at 3 months relative to baseline conditions, respectively). These changes were accompanied by the deterioration of trabecular microarchitectures. Marrow adipogenesis was evident through a 31.0% increase in adipocyte size, a 60.0% rise in adipocyte number, a 103.3% increase in the percentage of adipocyte area, and elevated mRNA expressions of marrow adipocyte markers. Osteoclast markers (TRACP and cathepsin K RNA and serum TRACP5b levels) were elevated in diabetic rabbits. MFF exhibited a robust correlation with trabecular bone microarchitectures. A significant positive correlation was identified between ΔMFF and serum ΔTRACP5b levels. Moreover, MFF at 3 months showed a strong positive correlation with serum TRACP5b levels (r = 0.763), as well as with the mRNA expression of osteoclast markers, including TRACP (r = 0.784) and cathepsin K (r = 0.659), all with p <0.001.

Conclusions

Rabbits with type 1 diabetes experience an expansion of marrow adiposity, and this enhanced marrow adiposity is associated with increased osteoclast activity.

Biomimetic Mineralized Collagen Scaffolds for Bone Tissue Engineering: Strategies on Elaborate Fabrication for Bioactivity Improvement

Biomimetic mineralized collagen (BMC) scaffolds represent an innovative class of bone-repair biomaterials inspired by the natural biomineralization process in bone tissue. Owing to their favorable biocompatibility and mechanical properties, BMC scaffolds have garnered significant attention in bone tissue engineering. However, most studies have overlooked the importance of bioactivity, resulting in collagen scaffolds with suboptimal osteogenic potential. In this review, the composition of the mineralized extracellular matrix (ECM) in bone tissue is discussed to provide guidance for biomimetic collagen mineralization. Subsequently, according to the detailed fabrication procedure of BMC scaffolds, the substances that can regulate both the fabrication process and biological activities is summarized. Furthermore, a potential strategy for developing BMC scaffolds with superior mechanical properties and biological activities for bone tissue engineering is proposed.

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.

Recent progress in bone-repair strategies in diabetic conditions

Bone regeneration following trauma, tumor resection, infection, or congenital disease is challenging. Diabetes mellitus (DM) is a metabolic disease characterized by hyperglycemia. It can result in complications affecting multiple systems including the musculoskeletal system. The increased number of diabetes-related fractures poses a great challenge to clinical specialties, particularly orthopedics and dentistry. Various pathological factors underlying DM may directly impair the process of bone regeneration, leading to delayed or even non-union of fractures. This review summarizes the mechanisms by which DM hampers bone regeneration, including immune abnormalities, inflammation, reactive oxygen species (ROS) accumulation, vascular system damage, insulin/insulin-like growth factor (IGF) deficiency, hyperglycemia, and the production of advanced glycation end products (AGEs). Based on published data, it also summarizes bone repair strategies in diabetic conditions, which include immune regulation, inhibition of inflammation, reduction of oxidative stress, promotion of angiogenesis, restoration of stem cell mobilization, and promotion of osteogenic differentiation, in addition to the challenges and future prospects of such approaches.

Novel scaffold platforms for simultaneous induction osteogenesis and angiogenesis in bone tissue engineering: a cutting-edge approach

Despite the recent advances in the development of bone graft substitutes, treatment of critical size bone defects continues to be a significant challenge, especially in the elderly population. A current approach to overcome this challenge involves the creation of bone-mimicking scaffolds that can simultaneously promote osteogenesis and angiogenesis. In this context, incorporating multiple bioactive agents like growth factors, genes, and small molecules into these scaffolds has emerged as a promising strategy. To incorporate such agents, researchers have developed scaffolds incorporating nanoparticles, including nanoparticulate carriers, inorganic nanoparticles, and exosomes. Current paper provides a summary of the latest advancements in using various bioactive agents, drugs, and cells to synergistically promote osteogenesis and angiogenesis in bone-mimetic scaffolds. It also discusses scaffold design properties aimed at maximizing the synergistic effects of osteogenesis and angiogenesis, various innovative fabrication strategies, and ongoing clinical studies.

Enhanced Bone Formation by Rapidly Formed Bony Wall over the Bone Defect Using Dual Growth Factors

BACKGROUND

In guided bone regeneration (GBR), there are various problems that occur in the bone defect after the wound healing period. This study aimed to investigate the enhancement of the osteogenic ability of the dual scaffold complex and identify the appropriate concentration of growth factors (GF) for new bone formation based on the novel GBR concept that is applying rapid bone forming GFs to the membrane outside of the bone defect.

METHODS

Four bone defects with a diameter of 8 mm were formed in the calvaria of New Zealand white rabbits each to perform GBR. Collagen membrane and biphasic calcium phosphate (BCP) were applied to the bone defects with the four different concetration of BMP-2 or FGF-2. After 2, 4, and 8 weeks of healing, histological, histomorphometric, and immunohistochemical analyses were conducted.

RESULTS

In the histological analysis, continuous forms of new bones were observed in the upper part of bone defect in the experimental groups, whereas no continuous forms were observed in the control group. In the histomorphometry, The group to which BMP-2 0.5 mg/ml and FGF-2 1.0 mg/ml was applied showed statistically significantly higher new bone formation. Also, the new bone formation according to the healing period was statistically significantly higher at 8 weeks than at 2, 4 weeks.

CONCLUSION

The novel GBR method in which BMP-2, newly proposed in this study, is applied to the membrane is effective for bone regeneration. In addition, the dual scaffold complex is quantitatively and qualitatively advantageous for bone regeneration and bone maintenance over time.

Metabolic regulation by biomaterials in osteoblast

The repair of bone defects resulting from high-energy trauma, infection, or pathological fracture remains a challenge in the field of medicine. The development of biomaterials involved in the metabolic regulation provides a promising solution to this problem and has emerged as a prominent research area in regenerative engineering. While recent research on cell metabolism has advanced our knowledge of metabolic regulation in bone regeneration, the extent to which materials affect intracellular metabolic remains unclear. This review provides a detailed discussion of the mechanisms of bone regeneration, an overview of metabolic regulation in bone regeneration in osteoblasts and biomaterials involved in the metabolic regulation for bone regeneration. Furthermore, it introduces how materials, such as promoting favorable physicochemical characteristics (e.g., bioactivity, appropriate porosity, and superior mechanical properties), incorporating external stimuli (e.g., photothermal, electrical, and magnetic stimulation), and delivering metabolic regulators (e.g., metal ions, bioactive molecules like drugs and peptides, and regulatory metabolites such as alpha ketoglutarate), can affect cell metabolism and lead to changes of cell state. Considering the growing interests in cell metabolic regulation, advanced materials have the potential to help a larger population in overcoming bone defects.

Osteogenesis Enhancement with 3D Printed Gene-Activated Sodium Alginate Scaffolds

Natural and synthetic hydrogel scaffolds containing bioactive components are increasingly used in solving various tissue engineering problems. The encapsulation of DNA-encoding osteogenic growth factors with transfecting agents (e.g., polyplexes) into such scaffold structures is one of the promising approaches to delivering the corresponding genes to the area of the bone defect to be replaced, providing the prolonged expression of the required proteins. Herein, a comparative assessment of both in vitro and in vivo osteogenic properties of 3D printed sodium alginate (SA) hydrogel scaffolds impregnated with model EGFP and therapeutic BMP-2 plasmids was demonstrated for the first time. The expression levels of mesenchymal stem cell (MSC) osteogenic differentiation markers Runx2, Alpl, and Bglap were evaluated by real-time PCR. Osteogenesis in vivo was studied on a model of a critical-sized cranial defect in Wistar rats using micro-CT and histomorphology. The incorporation of polyplexes comprising pEGFP and pBMP-2 plasmids into the SA solution followed by 3D cryoprinting does not affect their transfecting ability compared to the initial compounds. Histomorphometry and micro-CT analysis 8 weeks after scaffold implantation manifested a significant (up to 46%) increase in new bone volume formation for the SA/pBMP-2 scaffolds compared to the SA/pEGFP ones.

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.

Application of Lyophilized Gene-Delivery Formulations to Dental Implant Surfaces: Non-Cariogenic Lyoprotectant Preserves Transfection Activity of Polyplexes Long-Term

Titanium is the metal of choice for dental implants because of its biocompatibility and ability to merge with human bone tissue. Despite the great success rate of dental implants, early and late complications occur. Coating titanium dental implant surfaces with polyethyleneimine (PEI)-plasmid DNA (pDNA) polyplexes improve osseointegration by generating therapeutic protein expression at the implantation site. Lyophilization is an approach for stabilizing polyplexes and extending their shelf life; however, most lyoprotectants are sugars that can aid bacterial growth in the peri-implant environment. In our research, we coated titanium surfaces with polyplex solutions containing varying amounts of lyoprotectants. We used two common lyoprotectants (sucrose and polyvinylpyrrolidone K30) and showed for the first time that sucralose (a sucrose derivative used as an artificial sweetener) might act as a lyoprotectant for polyplex solutions. Human embryonic kidney (HEK) 293T cells were used to quantify the transfection efficiency and cytotoxicity of the polyplex/lyoprotectant formulations coating titanium surfaces. Polyplexes that were lyophilized in the presence of a lyoprotectant displayed both preserved particle size and high transfection efficiencies. Polyplexes lyophilized in 2% sucralose have maintained transfection efficacy for three years. These findings suggest that modifying dental implants with lyophilized polyplexes might improve their success rate in the clinic.

Recent advances in gene therapy for bone tissue engineering

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

Barrier Membranes for Guided Bone Regeneration (GBR): A Focus on Recent Advances in Collagen Membranes

Guided bone regeneration (GBR) has become a clinically standard modality for the treatment of localized jawbone defects. Barrier membranes play an important role in this process by preventing soft tissue invasion outgoing from the mucosa and creating an underlying space to support bone growth. Different membrane types provide different biological mechanisms due to their different origins, preparation methods and structures. Among them, collagen membranes have attracted great interest due to their excellent biological properties and desired bone regeneration results to non-absorbable membranes even without a second surgery for removal. This work provides a comparative summary of common barrier membranes used in GBR, focusing on recent advances in collagen membranes and their biological mechanisms. In conclusion, the review article highlights the biological and regenerative properties of currently available barrier membranes with a particular focus on bioresorbable collagen-based materials. In addition, the advantages and disadvantages of these biomaterials are highlighted, and possible improvements for future material developments are summarized.

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.

Clinically relevant preclinical animal models for testing novel cranio-maxillofacial bone 3D-printed biomaterials

Bone tissue engineering is a rapidly developing field with potential for the regeneration of craniomaxillofacial (CMF) bones, with 3D printing being a suitable fabrication tool for patient-specific implants. The CMF region includes a variety of different bones with distinct functions. The clinical implementation of tissue engineering concepts is currently poor, likely due to multiple reasons including the complexity of the CMF anatomy and biology, and the limited relevance of the currently used preclinical models. The 'recapitulation of a human disease' is a core requisite of preclinical animal models, but this aspect is often neglected, with a vast majority of studies failing to identify the specific clinical indication they are targeting and/or the rationale for choosing one animal model over another. Currently, there are no suitable guidelines that propose the most appropriate animal model to address a specific CMF pathology and no standards are established to test the efficacy of biomaterials or tissue engineered constructs in the CMF field. This review reports the current clinical scenario of CMF reconstruction, then discusses the numerous limitations of currently used preclinical animal models employed for validating 3D-printed tissue engineered constructs and the need to reduce animal work that does not address a specific clinical question. We will highlight critical research aspects to consider, to pave a clinically driven path for the development of new tissue engineered materials for CMF reconstruction.

Controlled Co-delivery of pPDGF-B and pBMP-2 from intraoperatively bioprinted bone constructs improves the repair of calvarial defects in rats

Intraoperative bioprinting (IOB), which refers to the bioprinting process performed on a live subject in a surgical setting, has made it feasible to directly deliver gene-activated matrices into craniomaxillofacial (CMF) defect sites. In this study, we demonstrated a novel approach to overcome the current limitations of traditionally fabricated non-viral gene delivery systems through direct IOB of bone constructs into defect sites. We used a controlled co-delivery release of growth factors from a gene-activated matrix (an osteogenic bioink loaded with plasmid-DNAs (pDNA)) to promote bone repair. The controlled co-delivery approach was achieved from the combination of platelet-derived growth factor-B encoded plasmid-DNA (pPDGF-B) and chitosan-nanoparticle encapsulating pDNA encoded with bone morphogenetic protein-2 (CS-NPs(pBMP2)), which facilitated a burst release of pPDGF-B in 10 days, and a sustained release of pBMP-2 for 5 weeks in vitro. The controlled co-delivery approach was tested for its potential to repair critical-sized rat calvarial defects. The controlled-released pDNAs from the intraoperatively bioprinted bone constructs resulted in ∼40% bone tissue formation and ∼90% bone coverage area at 6 weeks compared to ∼10% new bone tissue and ∼25% total bone coverage area in empty defects. The delivery of growth factors incorporated within the intraoperatively bioprinted constructs could pose as an effective way to enhance bone regeneration in patients with cranial injuries in the future.

Novel insights into nanomaterials for immunomodulatory bone regeneration

Bone defect repair caused by trauma, congenital malformation, tumors, infection or systemic diseases remains the focus of attention in regeneration medicine. Recent advances in osteoimmunology indicate that immune cells and correlative cytokines modulate the delicate balance between osteoblasts and osteoclasts and induce a favorable microenvironment for bone regeneration. With superior attributes that imitate the three-dimensional architecture of natural bone, excellent fabricability, mechanical and biological properties, nanomaterials (NMs) are becoming attractive in the field of bone tissue engineering. Particularly, it could be an effective strategy for immunomodulatory bone regeneration by engineering NMs involved in composition nature, nanoarchitectural morphology, surface chemistry, topography and biological molecules, whose mechanisms potentially refer to regulating the phenotype of high-plastic immune cells and inducing cytokine secretion to accelerate osteogenesis. Despite these prominent achievements, the employment of NMs is poorly translated into clinical trials due to the lack of knowledge about the interaction between NMs and the immune system. For this reason, we sketch out the hierarchical structure of bone and its natural healing process, followed by discussion about the effects of immune cells on bone regeneration. Novel horizons focusing on recent progressions in the architectural and physicochemical performances of NMs and their impacts on the body defence mechanism are also emphasized, hoping to provide novel insights for the fabrication of bone graft materials in tissue engineering.

Tissue Engineered Neurovascularization Strategies for Craniofacial Tissue Regeneration

Craniofacial tissue injuries, diseases, and defects, including those within bone, dental, and periodontal tissues and salivary glands, impact an estimated 1 billion patients globally. Craniofacial tissue dysfunction significantly reduces quality of life, and successful repair of damaged tissues remains a significant challenge. Blood vessels and nerves are colocalized within craniofacial tissues and act synergistically during tissue regeneration. Therefore, the success of craniofacial regenerative approaches is predicated on successful recruitment, regeneration, or integration of both vascularization and innervation. Tissue engineering strategies have been widely used to encourage vascularization and, more recently, to improve innervation through host tissue recruitment or prevascularization/innervation of engineered tissues. However, current scaffold designs and cell or growth factor delivery approaches often fail to synergistically coordinate both vascularization and innervation to orchestrate successful tissue regeneration. Additionally, tissue engineering approaches are typically investigated separately for vascularization and innervation. Since both tissues act in concert to improve craniofacial tissue regeneration outcomes, a revised approach for development of engineered materials is required. This review aims to provide an overview of neurovascularization in craniofacial tissues and strategies to target either process thus far. Finally, key design principles are described for engineering approaches that will support both vascularization and innervation for successful craniofacial tissue regeneration.

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.

Systemically impaired fracture healing in small animal research: A review of fracture repair models

Fracture healing is a complex process requiring mechanical stability, an osteoconductive matrix, and osteoinductive and osteogenic biology. This intricate process is easily disrupted by various patient factors such as chronic disease and lifestyle. As the medical complexity and age of patients with fractures continue to increase, the importance of developing relevant experimental models is becoming paramount in preclinical research. The objective of this review is to describe the most common small animal models of systemically impaired fracture healing used in the orthopedic literature including osteoporosis, diabetes mellitus, smoking, alcohol use, obesity, and ageing. This review will provide orthopedic researchers with a summary of current models of systemically impaired fracture healing used in small animals and present an overview of the methods of induction for each condition.

Application of nanoparticles in bone tissue engineering; a review on the molecular mechanisms driving osteogenesis

The introduction of nanoparticles into bone tissue engineering strategies is beneficial to govern cell fate into osteogenesis and the regeneration of large bone defects. The present study explored the role of nanoparticles to advance osteogenesis with a focus on the cellular and molecular pathways involved. Pubmed, Pubmed Central, Embase, Scopus, and Science Direct databases were explored for those published articles relevant to the involvement of nanoparticles in osteogenic cellular pathways. As multifunctional compounds, nanoparticles contribute to scaffold-free and scaffold-based tissue engineering strategies to progress osteogenesis and bone regeneration. They regulate inflammatory responses and osteo/angio/osteoclastic signaling pathways to generate an osteogenic niche. Besides, nanoparticles interact with biomolecules, enhance their half-life and bioavailability. Nanoparticles are promising candidates to promote osteogenesis. However, the interaction of nanoparticles with the biological milieu is somewhat complicated, and more considerations are recommended on the employment of nanoparticles in clinical applications because of NP-induced toxicities.

Applications of nanotechnology in 3D printed tissue engineering scaffolds

Tissue engineering is an interdisciplinary field that aims to combine life sciences and engineering to create therapies that regenerate functional tissue. Early work in tissue engineering mostly used materials as inert scaffolding structures, but research has shown that constructing scaffolds from biologically active materials can help with regeneration by enabling cell-scaffold interactions or release of factors that aid in regeneration. Three-dimensional (3D) printing is a promising technique for the fabrication of structurally intricate and compositionally complex tissue engineering scaffolds. Such scaffolds can be functionalized with techniques developed by nanotechnology research to further enhance their ability to stimulate regeneration and interact with cells. Nanotechnological components, nanoscale textures, and microscale/nanoscale printing can all be incorporated into the manufacture of 3D printed scaffolds. This review discusses recent advancements in the merging of nanotechnology with 3D printed tissue engineering scaffolds, with a focus on applications of nanoscale components, nanoscale texture, and innovative printing techniques and the effects observed in vitro and in vivo.

Drug Delivery (Nano)Platforms for Oral and Dental Applications: Tissue Regeneration, Infection Control, and Cancer Management

The oral cavity and oropharynx are complex environments that are susceptible to physical, chemical, and microbiological insults. They are also common sites for pathological and cancerous changes. The effectiveness of conventional locally-administered medications against diseases affecting these oral milieus may be compromised by constant salivary flow. For systemically-administered medications, drug resistance and adverse side-effects are issues that need to be resolved. New strategies for drug delivery have been investigated over the last decade to overcome these obstacles. Synthesis of nanoparticle-containing agents that promote healing represents a quantum leap in ensuring safe, efficient drug delivery to the affected tissues. Micro/nanoencapsulants with unique structures and properties function as more favorable drug-release platforms than conventional treatment approaches. The present review provides an overview of newly-developed nanocarriers and discusses their potential applications and limitations in various fields of dentistry and oral medicine.

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.

Demineralized bone matrix scaffold modified with mRNA derived from osteogenically pre-differentiated MSCs improves bone repair

Gene therapy based on mRNA provides a promising approach for bone regeneration. Quick mRNA translation and controlled protein production could be earned by implantation of mRNA-activated scaffold in bone remodeling region. Furthermore, the expression levels of osteogenic-related mRNA in the cytoplasm of osteogenically pre-differentiated mesenchymal stem cells (MSCs) were high and the expression levels were different at different stages of osteogenically differentiated MSCs. This study intended to investigate the effect of osteoinductive-mRNAs (Oi-mRNAs), derived from osteogenically pre-differentiated MSCs at various stages (Day 1 (Oi1-mRNA), Day 3 (Oi3-mRNA), Day 7 (Oi7-mRNA), Day 14 (Oi14-mRNA) and Day 21 (Oi21-mRNA), respectively), on the osteogenic differentiation of MSCs. Further, the Oi-mRNAs combined with cationic polymer polyethylenimine (PEI) were loaded onto demineralized bone matrix (DBM) scaffold (Oi-mRNA/DBM). The results revealed that the Oi1-mRNA, Oi3-mRNA and Oi21-mRNA had no obvious effect on the osteogenic differentiation of MSCs, while the Oi7-mRNA increased the expression of alkaline phosphatase (ALP) and the Oi14-mRNA significantly promoted the expression of osteocalcin (OC) and osteopontin (OPN), and calcium deposition. In addition, the Oi14-mRNA/DBM scaffold could significantly enhance extracellular matrix (ECM) secretion and new collagen formation of MSCs. After being implanted into rat critical-sized cranium defect model, the Oi14-mRNA/DBM scaffold could promote the infiltration of cells and repair of bone defect in vivo. The DBM scaffold loaded with mRNA encoding osteoinductive protein may provide a powerful tool for bone defect repair.

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.

Emerging local delivery strategies to enhance bone regeneration

In orthopedics and dentistry there is an increasing need for novel biomaterials and clinical strategies to achieve predictable bone regeneration. These novel molecular strategies have the potential to eliminate the limitations of currently available approaches. Specifically, they have the potential to reduce or eliminate the need to harvest autogenous bone, and the overall complexity of the clinical procedures. In this review, emerging tissue engineering strategies that have been, or are currently being, developed based on the current understanding of bone biology, development and wound healing will be discussed. In particular, protein/peptide based approaches, DNA/RNA therapeutics, cell therapy, and the use of exosomes will be briefly covered. The review ends with a summary of the current status of these approaches, their clinical translational potentials and their challenges.

Scaffold-Mediated Gene Delivery for Osteochondral Repair

Osteochondral defects involve both the articular cartilage and the underlying subchondral bone. If left untreated, they may lead to osteoarthritis. Advanced biomaterial-guided delivery of gene vectors has recently emerged as an attractive therapeutic concept for osteochondral repair. The goal of this review is to provide an overview of the variety of biomaterials employed as nonviral or viral gene carriers for osteochondral repair approaches both in vitro and in vivo, including hydrogels, solid scaffolds, and hybrid materials. The data show that a site-specific delivery of therapeutic gene vectors in the context of acellular or cellular strategies allows for a spatial and temporal control of osteochondral neotissue composition in vitro. In vivo, implantation of acellular hydrogels loaded with nonviral or viral vectors has been reported to significantly improve osteochondral repair in translational defect models. These advances support the concept of scaffold-mediated gene delivery for osteochondral repair.

Comprehensive analysis of differentially expressed microRNAs and mRNAs involved in diabetic corneal neuropathy

AIMS

Corneal nerve fibers are derived from the ophthalmic division of the trigeminal ganglion (TG). Here, by sequencing of microRNAs (miRNAs) and messenger RNAs (mRNAs) from diabetic and normal TG tissues, we aimed to uncover potential miRNAs, mRNAs, and the network of their interactions involved in the pathogenesis of diabetic corneal neuropathy.

MAIN METHODS

We performed RNA sequencing to systematically screen out differentially expressed miRNAs and mRNAs in TG tissues from diabetic and normal mice. Functional enrichment analyses were performed to illustrate the biological functions of differentially expressed mRNAs (DEmRNAs). Following this, miRNA-mRNA regulatory networks were built by means of bioinformatics methods to suggest regulatory role for miRNAs in the pathogenesis of diabetic corneal neuropathy. Finally, the credibility of the sequencing-based results was validated using qRT-PCR.

KEY FINDINGS

Sequencing analyses disclosed that 68 miRNAs and 114 mRNAs were differentially expressed in diabetic TG tissues compared with normal TG samples. The functional analyses showed that DEmRNAs participated in diabetes-related biological processes. After applying an optimized approach to predict miRNA-mRNA pairs, a miRNA-mRNA interacting network was inferred. Subsequently, the expression and correlation of miR-350-5p and Mup20, miR-592-5p and Angptl7 as well as miR-351-5p and Elovl6 were preliminarily validated.

SIGNIFICANCE

Our study provides a systematic characterization of miRNA and mRNA expression in the TG during diabetic corneal neuropathy and will contribute to the development of clinical diagnostic and therapeutic strategies for diabetic corneal neuropathy.

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.

Bioactive Factors-imprinted Scaffold Vehicles for Promoting Bone Healing: The Potential Strategies and the Confronted Challenges for Clinical Production

Abstract Wound repair of bone is a complicated multistep process orchestrated by inflammation, angiogenesis, callus formation, and bone remodeling. Many bioactive factors (BFs) including cytokine and growth factors (GFs) have previously been reported to be involved in regulating wound healing of bone and some exogenous BFs such as bone morphogenetic proteins (BMPs) were proven to be helpful for improving bone healing. In this regard, the BFs reported for boosting bone repair were initially categorized according to their regulatory mechanisms. Thereafter, the challenges including short half-life, poor stability, and rapid enzyme degradation and deactivation for these exogenous BFs in bone healing are carefully outlined in this review. For these issues, BFs-imprinted scaffold vehicles have recently been reported to promote the stability of BFs and enhance their half-life in vivo. This review is focused on the incorporation of BFs into the modulated biomaterials with various forms of bone tissue engineering applications: firstly, rigid bone graft substitutes (BGSs) were used to imprint BFs for large scale bone defect repair; secondly, the soft sponge-like scaffold carrying BFs is discussed as filling materials for the cavity of bone defects; thirdly, various injectable vehicles including hydrogel, nanoparticles, and microspheres for the delivery of BFs were also introduced for irregular bone fracture repair. Meanwhile, the challenges for BFs-imprinted scaffold vehicles are also analyzed in this review.

Current Trends in Research on Bone Regeneration: A Bibliometric Analysis

Background

Bone regeneration is a frequent research topic in clinical studies, but macroscopic studies on the clinical application of bone regeneration are rare. We conducted a bibliometric analysis, using international databases, to explore the clinical application and mechanism of bone regeneration, to highlight the relevant research hotspots and prospects. Material and Methods. Scientific reports on bone regeneration published during 2009–2019 were retrieved from PubMed. VOSviewer for cooccurrence keywords and authorship analysis. BICOMB software was used to retrieve high-frequency words and construct a text/coword matrix. The matrix was inputted into gCLUTO software, managed by biclustering analysis, in order to identify hotspots, which could achieve mountain and matrix visualizations. The matrix was also analyzed by using Ucinet 6 software for social network analysis. A strategic diagram was used for further analysis of the research hotspots of bone regeneration by “SCIMAT” software. We searched the Web of Science for relevant articles.

Results

Eighty-nine high-frequency major MeSH terms were obtained from 10237 articles and were divided into 5 clusters. We generated a network visualization map, an overlay visualization mountain map, and a social network diagram. Then, the MeSH terms were subdivided into 7 categories according to each diagram; current research hotspots were identified as scaffold, drug effect, osseointegration in dental implant, guided bone regeneration, factors impacting bone regeneration, treatment of bone and tissue loss, and bone regeneration in dental implants.

Conclusion

BICOMB, VOSviewer, and other bibliometric tools revealed that dental implants, scaffolds, and factors impacting bone regeneration are hot research topics, while scaffolds also hold promise from the perspective of bone tissue regeneration.

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.

In situ bone tissue engineering using gene delivery nanocomplexes

Gene delivery offers promising outcomes for functional recovery or regeneration of lost tissues at cellular and tissue levels. However, more efficient carriers are needed to safely and locally delivery of genetic materials. Herein, we demonstrate microfluidic-assisted synthesis of plasmid DNA (pDNA)-based nanocomplexe (NC) platforms for bone tissue regeneration. pDNA encoding human bone morphogenesis protein-2 (BMP-2) was used as a gene of interest. Formation and fine-tuning of nanocomplexes (NCs) between pDNA and chitosan (CS) as carriers were performed using a micromixer platform. Flow characteristics were adjusted to tune mixing time and consequently size, zeta potential, and compactness of assembled NCs. Subsequently, NCs were immobilized on a nanofibrous Poly(ε-caprolactone) (PCL) scaffold functionalized with metalloprotease-sensitive peptide (MMP-sensitive). This construct can provide an environmental-sensitive and localized gene delivery platform. Osteogenic differentiation of bone marrow-derived mesenchymal stem cells (MSCs) was studied using chemical and biological assays. The presented results converge to indicate a great potential of the developed methodology for in situ bone tissue engineering using immobilized microfluidic-synthesized gene delivery nanocomplexes, which is readily expandable in the field of regenerative nanomedicine. STATEMENT OF SIGNIFICANCE: In this study, we demonstrate microfluidic-assisted synthesis of plasmid DNA (pDNA)-based nanocomplexes (NCs) platforms for bone tissue regeneration. We used pDNA encoding human bone morphogenesis protein-2 (BMP-2) as the gene of interest. Using micromixer platform nanocomplexes (NCs) between pDNA and chitosan (CS) were fabricated and optimized. NCs were immobilized on a nanofibrous polycaprolactone scaffold functionalized with metalloprotease-sensitive peptide. In vitro and in vivo assays confirmed the osteogenic differentiation of mesenchymal stem cells (MSCs). The obtained data indicated great potential of the developed methodology for in situ bone tissue engineering using immobilized microfluidic-synthesized gene delivery nanocomplexes, which is readily expandable in the field of regenerative nanomedicine.

Effects of Targeted Delivery of Metformin and Dental Pulp Stem Cells on Osteogenesis via Demineralized Dentin Matrix under High Glucose Conditions

High glucose condition inhibited osteoblast differentiation could be a main mechanism contributing to the decreased bone repair associated with diabetes. Metformin, a widely prescribed antidiabetic drug, was shown to have osteogenic properties in our previous study. Transplanted mesenchymal stromal cells (MSCs) may differentiate into osteoblasts and promote bone regeneration. Our study aimed to combine the benefits of metformin and MSCs transplantation on osteogenesis in high glucose conditions. We developed demineralized dentin matrix (DDM) as a carrier to target deliver metformin and dental pulp-derived MSCs (DPSCs). We collected clinically discarded teeth, isolated DPSCs from the dental pulp, and prepared the DDM from the dentin. The DDM was observed by scanning electron microscopy and was found to have well-distributed tubes. Then, metformin was loaded into the DDM to form the DDM-Met complex (DDM-Met); DDM-Met released metformin at a favorable concentration. The DPSCs seeded with the DDM-Met in a high glucose medium showed satisfactory attachment and viability together with increased mineralization and upregulated osteogenesis-related genes, including alkaline phosphatase (ALP), osteocalcin (OCN), runt-related transcription factor 2 (Runx2), and osteopontin (OPN). A possible mechanism of the enhanced osteogenic differentiation of DPSCs was explored, and the adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) pathway was found to play a role in the enhancement of osteogenesis. DDM-Met appeared to be a successful metformin and DPSC carrier that allowed for the local delivery of metformin and DPSCs in high glucose conditions. DDM-Met-DPSC construct has promising prospects to promote osteogenesis and enhance the much-needed diabetic bone regeneration.

A proof of concept gene-activated titanium surface for oral implantology applications

Dental implants are very successful medical devices, yet implant failures do occur due to biological and mechanical complications. Peri-implantitis is one such biological complication that is primarily caused by bacteria and their products at the implant soft tissue interface. Bacterial infiltration can be prevented by the formation of a reliable soft tissue seal encircling dental implants. Platelet-derived growth factor-BB (PDGF-BB) has significant chemotactic and proliferative effects on various mesenchymal cell types, including fibroblasts, and therefore can be an effective molecule to enhance the peri-implant soft tissue seal. To overcome the limitations of the recombinant protein form of PDGF-BB, such as cost and the need for supraphysiological doses, we have developed and characterized a titanium surface that is rendered bioactive by coating it with polyethylenimine-plasmid DNA (pDNA) nanoplexes in the presence of sucrose. Human embryonic kidney 293T (HEK293T) cells and human primary gingival fibroblasts (GFs) were successfully transfected in culture with enhanced green fluorescent protein (EGFP)-encoding pDNA or platelet-derived growth factor subunit B (PDGFB)-encoding pDNA loaded into nanoplexes and coated onto titanium disks in a dose-dependent manner. GFs were shown to secrete PDGF-BB for at least 7 days after transfection and displayed both minimal viability loss and increased integrin-α2 expression 4 days posttransfection.

Mesenchymal stem cell-derived microvesicles mediate BMP2 gene delivery and enhance bone regeneration

Microvesicles–polyethyleneimine/pDNA formed via layer-by-layer self-assembly increase the delivery of hBMP2 plasmids and enhance bone repair.

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.

Eluted 25-hydroxyvitamin D3 from radially aligned nanofiber scaffolds enhances cathelicidin production while reducing inflammatory response in human immune system-engrafted mice

Vitamin D₃ modulates immune response, induces endogenous antimicrobial peptide production, and enhances innate immunity to defend against infections. These findings suggest that incorporating vitamin D₃ into medical devices or scaffolds could positively modulate host immune response and prevent infections. In the current study, we evaluated host responses and endogenous antimicrobial peptide production using 25-hydroxyvitamin D₃ (25(OH)D₃)-eluting radially aligned PCL nanofiber scaffolds in human immune system-engrafted mice. We transformed traditional 2D electrospun nanofiber membranes into radially aligned PCL nanofiber scaffolds using the concept of solid of revolution and an innovative gas-foaming technique. Such scaffolds can promote rapid cellular infiltration and neovascularization. The infiltrating immune cells within subcutaneously implanted 25(OH)D₃-containing scaffolds mainly consisted of human macrophages in the M1 phase (CCR7⁺), mice macrophages in the M2 phase (CD206⁺), and human cytotoxic T cells (CD8⁺) other than few human T-helper cells (CD4⁺). The 25(OH)D₃-eluting nanofiber scaffolds significantly inhibited the production of pro-inflammatory cytokines (TNF-α, IL-6), while accelerating the production of anti-inflammatory cytokines (IL-4, IL-10) within the scaffolds. Additionally, we observed increased expression of human cathelicidin LL-37 within the 25(OH)D₃-eluting scaffolds, while no LL-37 expression was observed in the control. Together, these findings support further work in the design of vitamin D₃-eluting medical devices or scaffolds for modulating immune response and promoting antimicrobial peptide production. This could potentially reduce the inflammatory response, prevent infections, and eventually improve success rates of implants. STATEMENT OF SIGNIFICANCE: Transplant failure of medical devices, grafts, scaffolds, and tissue-engineered constructs due to inflammation and infection causes not only economic losses but also sufferings of second operation to the patient. Positive modulation of the host response to implants, scaffolds, and tissue-engineered constructs is likely to reduce the failure rate. Vitamin D₃ plays an important role in modulating the immune response. It is able to not only reduce inflammation and induce endogenous antimicrobial peptide production but also prevent multidrug resistance and other side effects of traditional antibiotics. In this study, host responses to 25-hydroxyvitamin D₃ (25(OH)D₃)-eluting radially aligned PCL nanofiber scaffolds were evaluated in human immune system-engrafted mice. The 25(OH)D₃-eluting medical devices or scaffolds were able to modulate positive immune response and promote antimicrobial peptide production. This work presented an innate immunity-enhancing approach for reducing the inflammatory response and preventing infections, likely resulting in improvement of success rates of implants.

A bioactive collagen membrane that enhances bone regeneration

Membranes are an integral component of guided bone regeneration protocols. This pre-clinical study was aimed at enhancing the bioactivity of collagen membranes by incorporating plasmid DNA (pDNA) or chemically modified RNA (cmRNA) encoding bone morphogenetic protein-9 (BMP-9). In addition, we also endeavored to harness the regenerative potential of the periosteum by creating perforations in the membrane. Nanoplexes of polyethylenimine (PEI)-nucleic acids (PEI-pDNA or PEI-cmRNA encoding BMP-9) were incorporated into commercially obtained and perforated collagen membranes (PCM) to produce PCM-pDNA(BMP-9) or PCM-cmRNA(BMP-9). After structural characterization, the biodegradation kinetics of PCM, PCM-pDNA(BMP-9) and PCM-cmRNA(BMP-9) were assessed in simulated body fluid in vitro. Using a 24-well transwell plate system with bone marrow stromal cells (BMSCs) in the lower chamber and the PCM to be tested in the upper chamber, the in vitro bioactivity of different PCMs was evaluated by measuring various markers for osteogenesis in BMSCs. Alkaline phosphatase activity was assessed in BMSCs, after 7 and 11 days of exposure to PCM, PCM-pDNA(BMP-9), or PCM-cmRNA(BMP-9). Similarly, calcium deposition and Alizarin red staining in BMSCs were assessed after 14 days of exposure to the three different types of PCM. PCMs were then tested in vivo using the calvarial defect model in rats. After 4 weeks, animals were euthanized and bone specimens were harvested for micro-computed tomography and histological assessments. Incorporation of pDNA or cmRNA did not alter the biodegradation profile of PCMs. Alkaline phosphatase activity trended toward being higher in BMSCs exposed to PCM-cmRNA(BMP-9) or PCM-pDNA(BMP-9), when compared to BMSCs alone. Similar trends were observed when calcium deposition and alizarin red staining was evaluated. Calvarial bone defects treated with PCM-cmRNA(BMP-9) resulted in significantly higher bone volume/total volume % (BV/TV%), when compared to empty defects and trended toward being higher than defects treated with PCM-pDNA(BMP-9) and PCM alone. We demonstrate for the first time that resorbable PCM can be utilized to efficiently deliver pDNA and cmRNA of interest. The released pDNA and cmRNA encoding BMP-9 in this assessment was shown to be functional in vitro as well as in vivo. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1824-1832, 2019.