Polymeric Scaffold Based Gene Delivery Strategies to Improve Angiogenesis in Tissue Engineering: A Review

Scaffold-based non-viral CRISPR delivery platform for efficient and prolonged gene activation to accelerate tissue regeneration

Clustered regularly interspaced short palindromic repeat activation (CRISPRa) technology has emerged as a precise genome editing tool for activating endogenous transgene expression. While it holds promise for precise cell modification, its translation into tissue engineering has been hampered by biosafety concerns and suboptimal delivery methods. To address these challenges, we have developed a CRISPRa non-viral gene delivery platform by immobilizing non-viral CRISPRa complexes into a biocompatible hydrogel/nanofiber (Gel/NF) composite scaffold. The Gel/NF scaffold facilitates the controlled and sustained release of CRISPRa complexes and also promotes cell recruitment to the scaffold for efficient and localized transfection. As a proof of concept, we employed this CRISPRa delivery platform to activate the vascular endothelial growth factor (VEGF) gene in a rat model with full-thickness skin defects. Our results demonstrate sustained upregulation of VEGF expression even at 21 days post-implantation, resulting in enhanced angiogenesis and improved skin regeneration. These findings underscore the potential of the Gel/NF scaffold-based CRISPRa delivery platform as an efficient and durable strategy for gene activation, offering promising prospects for tissue regeneration. STATEMENT OF SIGNIFICANCE: Translation of clustered regularly interspaced short palindromic repeat activation (CRISPRa) therapy to tissue engineering is limited by biosafety concerns and unsatisfactory delivery strategy. To solve this issue, we have developed a CRISPRa non-viral gene delivery platform by immobilizing non-viral CRISPRa complexes into a biocompatible hydrogel/nanofiber (Gel/NF) composite scaffold. This scaffold enables controlled and sustained release of CRISPRa and can induce cell recruitment for localized transfection. As a proof of concept, we activated vascular endothelial growth factor (VEGF) in a rat model with full-thickness skin defects, leading to sustained upregulation of VEGF expression, enhanced angiogenesis and improved skin regeneration in vivo. These findings demonstrate the potential of this platform for gene activation, thereby offering promising prospects for tissue regeneration.

Spatiotemporal Delivery of pBMP2 and pVEGF by a Core-Sheath Structured Fiber-Hydrogel Gene-Activated Matrix Loaded with Peptide-Modified Nanoparticles for Critical-Sized Bone Defect Repair

The clinical translation of bioactive scaffolds for the treatment of large segmental bone defects remains a grand challenge. The gene-activated matrix (GAM) combining gene therapy and tissue engineering scaffold offers a promising strategy for the restoration of structure and function of damaged or dysfunctional tissues. Herein, a gene-activated biomimetic composite scaffold consisting of an electrospun poly(ε-caprolactone) fiber sheath and an alginate hydrogel core which carried plasmid DNA encoding bone morphogenetic protein 2 (pBMP2) and vascular endothelial growth factor (pVEGF), respectively, is developed. A peptide-modified polymeric nanocarrier with low cytotoxicity and high efficiency serves as the nonviral DNA delivery vector. The obtained GAM allows spatiotemporal release of pVEGF and pBMP2 and promotes osteogenic differentiation of preosteoblasts in vitro. In vivo evaluation using a critical-sized segmental femoral defect model in rats shows that the dual gene delivery system can significantly accelerate bone healing by activating angiogenesis and osteogenesis. These findings demonstrate the effectiveness of the developed dual gene-activated core-sheath structured fiber-hydrogel composite scaffold for critical-sized bone defect regeneration and the potential of cell-free scaffold-based gene therapy for tissue engineering.

Electrospun-Fibrous-Architecture-Mediated Non-Viral Gene Therapy Drug Delivery in Regenerative Medicine

Gene-based therapy represents the latest advancement in medical biotechnology. The principle behind this innovative approach is to introduce genetic material into specific cells and tissues to stimulate or inhibit key signaling pathways. Although enormous progress has been achieved in the field of gene-based therapy, challenges connected to some physiological impediments (e.g., low stability or the inability to pass the cell membrane and to transport to the desired intracellular compartments) still obstruct the exploitation of its full potential in clinical practices. The integration of gene delivery technologies with electrospun fibrous architectures represents a potent strategy that may tackle the problems of stability and local gene delivery, being capable to promote a controlled and proficient release and expression of therapeutic genes in the targeted cells, improving the therapeutic outcomes. This review aims to outline the impact of electrospun-fibrous-architecture-mediated gene therapy drug delivery, and it emphatically discusses the latest advancements in their formulation and the therapeutic outcomes of these systems in different fields of regenerative medicine, along with the main challenges faced towards the translation of promising academic results into tangible products with clinical application.

Controlled pVEGF delivery via a gene-activated matrix comprised of a peptide-modified non-viral vector and a nanofibrous scaffold for skin wound healing

Regulating cell function and tissue formation by combining gene delivery with functional scaffolds to create gene-activated matrices (GAMs) is a promising strategy for tissue engineering. However, fabrication of GAMs with low cytotoxicity, high transfection efficiency, and long-term gene delivery properties remains a challenge. In this study, a non-viral DNA delivery nanocomplex was developed by modifying poly (D, L-lactic-co-glycolic acid)/polyethylenimine (PLGA/PEI) nanoparticles with the cell-penetrating peptide KALA. Subsequently, the nanocomplex carrying plasmid DNA encoding vascular endothelial growth factor (pVEGF) was immobilized onto a polydopamine-coated electrospun alginate nanofibrous scaffold, resulting in a GAM for enhanced skin wound healing. The nanocomplex exhibited much lower cytotoxicity and comparable or even higher transfection efficiency compared with PEI. The GAM enabled sustained gene release and long-tern transgene expression of VEGF in vitro. In an excisional full-thickness skin wound rat model, the GAM could accelerate wound closure, promote complete re-epithelization, reduce inflammatory response, and enhance neovascularization, ultimately enhancing skin wound healing. The current GAM comprising a low-toxic gene delivery nanocomplex and a biocompatible 3D nanofibrous scaffold demonstrates great potential for mediating long-term cell functions and may become a powerful tool for gene delivery in tissue engineering. STATEMENT OF SIGNIFICANCE: Gene delivery is a promising strategy in promoting tissue regeneration as an effective alternative to growth factor delivery, but the study on three-dimensional gene-activated scaffolds remains in its infancy. Herein, a biodegradable nanofibrous gene-activated matrix integrating non-viral nanoparticle vector was designed and evaluated both in vitro and in vivo. The results show that the nanoparticle vector provided high transfection efficiency with minimal cytotoxicity. After surface immobilization of the nanocomplexes carrying plasmid DNA encoding vascular endothelial growth factor (pVEGF), the nanofibrous scaffold enabled sustained DNA release and long-term transgene expression in vitro. In a rat full-thickness skin wound model, the scaffold could accelerate wound healing. This innovative gene-activated matrix can be a promising candidate for tissue regeneration.

Nanomaterials in Skin Regeneration and Rejuvenation

Skin is the external part of the human body; thus, it is exposed to outer stimuli leading to injuries and damage, due to being the tissue mostly affected by wounds and aging that compromise its protective function. The recent extension of the average lifespan raises the interest in products capable of counteracting skin related health conditions. However, the skin barrier is not easy to permeate and could be influenced by different factors. In the last decades an innovative pharmacotherapeutic approach has been possible thanks to the advent of nanomedicine. Nanodevices can represent an appropriate formulation to enhance the passive penetration, modulate drug solubility and increase the thermodynamic activity of drugs. Here, we summarize the recent nanotechnological approaches to maintain and replace skin homeostasis, with particular attention to nanomaterials applications on wound healing, regeneration and rejuvenation of skin tissue. The different nanomaterials as nanofibers, hydrogels, nanosuspensions, and nanoparticles are described and in particular we highlight their main chemical features that are useful in drug delivery and tissue regeneration.

Nanocomposite scaffolds for accelerating chronic wound healing by enhancing angiogenesis

Skin is the body's first barrier against external pathogens that maintains the homeostasis of the body. Any serious damage to the skin could have an impact on human health and quality of life. Tissue engineering aims to improve the quality of damaged tissue regeneration. One of the most effective treatments for skin tissue regeneration is to improve angiogenesis during the healing period. Over the last decade, there has been an impressive growth of new potential applications for nanobiomaterials in tissue engineering. Various approaches have been developed to improve the rate and quality of the healing process using angiogenic nanomaterials. In this review, we focused on molecular mechanisms and key factors in angiogenesis, the role of nanobiomaterials in angiogenesis, and scaffold-based tissue engineering approaches for accelerated wound healing based on improved angiogenesis.

Recent Approaches for Angiogenesis in Search of Successful Tissue Engineering and Regeneration

Angiogenesis plays a central role in human physiology from reproduction and fetal development to wound healing and tissue repair/regeneration. Clinically relevant therapies are needed for promoting angiogenesis in order to supply oxygen and nutrients after transplantation, thus relieving the symptoms of ischemia. Increase in angiogenesis can lead to the restoration of damaged tissues, thereby leading the way for successful tissue regeneration. Tissue regeneration is a broad field that has shown the convergence of various interdisciplinary fields, wherein living cells in conjugation with biomaterials have been tried and tested on to the human body. Although there is a prevalence of various approaches that hypothesize enhanced tissue regeneration via angiogenesis, none of them have been successful in gaining clinical relevance. Hence, the current review summarizes the recent cell-based and cell free (exosomes, extracellular vesicles, micro-RNAs) therapies, gene and biomaterial-based approaches that have been used for angiogenesis-mediated tissue regeneration and have been applied in treating disease models like ischemic heart, brain stroke, bone defects and corneal defects. This review also puts forward a concise report of the pre-clinical and clinical studies that have been performed so far; thereby presenting the credible impact of the development of biomaterials and their 3D concepts in the field of tissue engineering and regeneration, which would lead to the probable ways for heralding the successful future of angiogenesis-mediated approaches in the greater perspective of tissue engineering and regenerative medicine.

Fabrication of a self-assembled honeycomb nanofibrous scaffold to guide endothelial morphogenesis

Controlling angiogenesis within tissue engineered constructs remains a critical challenge, especially with regard to the guidance of pre-vascular network formation. Here, we aimed to regulate angiogenesis on a self-assembled honeycomb nanofibrous scaffold. Scaffolds with honeycombs patterns have several desirable properties for tissue engineering, including large surface area, high structural stability and good permeability. Furthermore, the honeycomb pattern resembles early vascular network formation. The self-assembly electrospinning approach to honeycomb scaffolds is a technically simple, rapid, and direct way to realize selective deposition of nanofibers. To evaluate cell compatibility, spreading, proliferation and tube formation, human umbilical vein endothelial cells (HUVECs) were cultured on honeycomb scaffolds, as well as on random scaffolds for comparison. The optimized honeycomb nanofibrous scaffolds were observed to better support cell proliferation and network formation, which can facilitate angiogenesis. Moreover, HUVECs cultured on the honeycomb scaffolds were observed to reorganize their cell bodies into tube-like structures containing a central lumen, while this was not observed on random scaffolds. This work has shown that the angiogenic response can be guided by honeycomb scaffolds, allowing improved early HUVECs organization. The guided organization via honeycomb scaffolds can be utilized for tissue engineering applications that require the formation of microvascular networks.

Electrospun Biomaterials in the Treatment and Prevention of Scars in Skin Wound Healing

Electrospinning is a promising method for the rapid and cost-effective production of nanofibers from a wide variety of polymers given the high surface area morphology of these nanofibers, they make excellent wound dressings, and so have significant potential in the prevention and treatment of scars. Wound healing and the resulting scar formation are exceptionally well-characterized on a molecular and cellular level. Despite this, novel effective anti-scarring treatments which exploit this knowledge are still clinically absent. As the process of electrospinning can produce fibers from a variety of polymers, the treatment avenues for scars are vast, with therapeutic potential in choice of polymers, drug incorporation, and cell-seeded scaffolds. It is essential to show the new advances in this field; thus, this review will investigate the molecular processes of wound healing and scar tissue formation, the process of electrospinning, and examine how electrospun biomaterials can be utilized and adapted to wound repair in the hope of reducing scar tissue formation and conferring an enhanced tensile strength of the skin. Future directions of the research will explore potential novel electrospun treatments, such as gene therapies, as targets for enhanced tissue repair applications. With this class of biomaterial gaining such momentum and having such promise, it is necessary to refine our understanding of its process to be able to combine this technology with cutting-edge therapies to relieve the burden scars place on world healthcare systems.

Strategies to Improve Nanofibrous Scaffolds for Vascular Tissue Engineering

The biofabrication of biomimetic scaffolds for tissue engineering applications is a field in continuous expansion. Of particular interest, nanofibrous scaffolds can mimic the mechanical and structural properties (e.g., collagen fibers) of the natural extracellular matrix (ECM) and have shown high potential in tissue engineering and regenerative medicine. This review presents a general overview on nanofiber fabrication, with a specific focus on the design and application of electrospun nanofibrous scaffolds for vascular regeneration. The main nanofiber fabrication approaches, including self-assembly, thermally induced phase separation, and electrospinning are described. We also address nanofibrous scaffold design, including nanofiber structuring and surface functionalization, to improve scaffolds' properties. Scaffolds for vascular regeneration with enhanced functional properties, given by providing cells with structural or bioactive cues, are discussed. Finally, current in vivo evaluation strategies of these nanofibrous scaffolds are introduced as the final step, before their potential application in clinical vascular tissue engineering can be further assessed.

DNA fragment translocation through the lipid membrane assisted by carbon nanotube

DNA delivery through cell membrane is a fundamental step for efficiency gene therapy. As a potential DNA carrier, carbon nanotubes (CNTs) have been extensively studied due to its unique properties. However, the mechanism of DNA translocation with CNTs through cell membrane is still not well understood. In this study, the DNA translocation process through POPC (1-palmitoyl-2-oleoylphosphatidylcholine) membrane with the assistance of CNTs was explored by molecular dynamics (MD) simulation. Our simulation results demonstrated that the CNTs could insert steadily into the POPC membrane, and DNA molecules tends to insert into the inner space of CNTs. With the assistance of CNTs, the free energy of nucleotides passing through the POPC membrane decreases. Moreover, the free energy of nucleotides (DA (deoxyadenosine), DT (deoxythymidine), DC (deoxycytidine), and DG (deoxyguanosine)) passing through POPC membrane follows the order: DA (deoxyadenosine) > DG (deoxyguanosine) > DC (deoxycytidine) > DT (deoxythymidine). These results may promote the design and application of CNT-based gene delivery system.

Bioprinting of Vascularized Tissue Scaffolds: Influence of Biopolymer, Cells, Growth Factors, and Gene Delivery

Over the past decades, tissue regeneration with scaffolds has achieved significant progress that would eventually be able to solve the worldwide crisis of tissue and organ regeneration. While the recent advancement in additive manufacturing technique has facilitated the biofabrication of scaffolds mimicking the host tissue, thick tissue regeneration remains challenging to date due to the growing complexity of interconnected, stable, and functional vascular network within the scaffold. Since the biological performance of scaffolds affects the blood vessel regeneration process, perfect selection and manipulation of biological factors (i.e., biopolymers, cells, growth factors, and gene delivery) are required to grow capillary and macro blood vessels. Therefore, in this study, a brief review has been presented regarding the recent progress in vasculature formation using single, dual, or multiple biological factors. Besides, a number of ways have been presented to incorporate these factors into scaffolds. The merits and shortcomings associated with the application of each factor have been highlighted, and future research direction has been suggested.

Potential core-shell designed scaffolds with a gelatin-based shell in achieving controllable release rates of proteins for tissue engineering approaches

The biomaterials design as core-shell structures opens a new door to the release of susceptible biomolecules in a controllable manner and enables to place natural biomaterials as shell layers to impart the effective biofunctional features at surfaces. In this study, core-shell designed scaffolds were prepared using coaxial electrospinning with hybrid of gelatin (GT)/polycaprolactone (PCL) at different weight ratios as their shell and protein solution as their core, followed by cross-linking to impart controllable release rates, tunable mechanical properties, and enhanced cytocompatibility. SEM, FM, and TEM confirmed the successful production of uniform core-shell nanofibers and homogeneous protein distribution. Results showed that an increase in GT proportion in the shell resulted in a decrease in fiber diameter, an increase of Young's modulus, and an intense burst release of BSA 0.2% which could be controlled through cross-linking. The mechanical tests revealed that the GT/PCL combining and cross-linking improved mechanical properties which correlated with an increase in spreading and proliferation of HUVECs. A slight burst release was also detected from BSA 0.05% and EGF encapsulated GT73P-cross-linked scaffold which demonstrated their applicability for a controlled release of dilute proteins. We were able to successfully incorporate two types of protein with different concentrations without supporting polymer into the GT shell to provide scaffolds possessing tunable mechanical properties and controllable release rates through blending with PCL at different ratios and/or cross-linking. These findings are promising to promote delivery systems of angiogenic growth factors that are needed a sustained release with different rates at each angiogenesis stage. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2019.

Functional electrospun fibrous scaffolds with dextran-g-poly(l-lysine)-VAPG/microRNA-145 to specially modulate vascular SMCs

Functional electrospun membranes loaded with Dex-g-PLL-VAPG/miR-145 complexes exhibit the excellent ability to modulate SMC phenotype and proliferation locally.