Advancements in electrospinning of polymeric nanofibrous scaffolds for tissue engineering

Synthesis and characterization of new electrospun medical scaffold-based modified cellulose nanofiber and bioactive natural propolis for potential wound dressing applications

Recently, the design of polymer nanofibers using the electrospinning process has attracted much interest. Particularly the use of natural polymers has promoted many advantages in their biomedical applications. However, the combination of multiple natural polymers remains a great challenge in terms of electrospun production and applied performance. From this perspective, the current investigation highlights the study of the preparation of electrospun nanomaterial scaffolds based on combined natural polymers for improved wound healing performance. First, we have synthesized a crosslinked polymer by reacting microcrystalline cellulose (MC) and chitosan (CS) biopolymer via the intermediate of citric acid as a crosslinking agent. Then a natural propolis biomolecule was incorporated into the polymer network. Different MC/CS blend ratios of 90/10 and 70/30 were then used and various machine parameters were optimized to obtain nanofiber scaffolds with excellent strength and structures. SEM, IR, physicochemical, mechanical, and morpho-logical characterization were then performed. SEM evaluation revealed homogeneous and bead-free nanofibrous structures, with well-defined morphology and a random deposition that could accurately mimic the extracellular matrix of native skin. The calculated average nanofiber diameters for the MC/CS blend ratios at 90/10 and 70/30 were 431.4 and 441.2 nm, respectively. The results showed that when the chitosan amount increased, larger nanofibers with narrow diameter distribution appeared. The prepared nanomaterials had a significant and close water vapor permeability of about 1735.12 and 1698.52 g per m per day for the two blend ratios of 90/10 and 70/30, respectively. The examination of swelling behavior revealed a noteworthy enhancement in hydrophilicity, a necessary attribute for improved healing efficacy. FT-IR analysis confirmed the success and the stability of the chemical crosslinking reaction between the two biopolymers before nanofiber conception. Excellent mechanical properties were acquired, based on the chitosan content. Both developed nanofiber scaffolds exhibited high tensile strength and Young's modulus values. The incorporation of 30% chitosan versus 10% results in an increase in tensile strength of 11% and 14% in Young's modulus. Therefore, we could adjust the different mechanical properties simply by varying the mixing rate of the electrospun polymers. Using epithelial HepG2 cells, viability and kinetic cell adhesion assays were assessed to obtain biological evaluation. No cytotoxicity was observed and good cytocompatibility was confirmed. Functionalized nanofiber biomaterials with different MC/CS ratios substantiated significant bactericidal effectiveness against Gram-positive and Gram-negative bacterial culture strains. The novel functional electrospun wound dressing scaffold demonstrated effective and promising biomedical performance, healing both acute and chronic wounds.

Design and fabrication of dual-layer PCL nanofibrous scaffolds with inductive influence on vascular cell responses

Confronted with the profound threat of cardiovascular diseases to health, vascular tissue engineering presents potential beyond the limitations of autologous and allogeneic grafts, offering a promising solution. This study undertakes an initial exploration into the impact of a natural active protein, elastin, on vascular cell behavior, by incorporating with polycaprolactone to prepare fibrous tissue engineering scaffold. The results reveal that elastin serves to foster endothelial cell adhesion and proliferation, suppress smooth muscle cell proliferation, and induce macrophage polarization. Furthermore, the incorporation of elastin contributes to heightened scaffold strength, compliance, and elongation, concomitantly lowering the elastic modulus. Subsequently, a bilayer oriented polycaprolactone (PCL) scaffold infused with elastin is proposed. This design draws inspiration from the cellular arrangement of native blood vessels, leveraging oriented fibers to guide cell orientation. The resulting fiber scaffold exhibits commendable mechanical properties and cell infiltration capacity, imparting valuable insights for the rapid endothelialization of vascular scaffolds.

Preparation and performance evaluation of a novel orthodontic adhesive incorporating composite dimethylaminohexadecyl methacrylate-Polycaprolactone fibers

This study addressed enamel demineralization, a common complication in fixed orthodontic treatment, by evaluating a novel orthodontic adhesive with DMAHDM-PCL composite fibers. These fibers, produced through electrospinning, were incorporated into orthodontic adhesive to create experimental formulations at different concentrations and a control group. The study assessed antimicrobial properties, biosafety, and mechanical characteristics. New orthodontic adhesive exhibited significant bacteriostatic effects, reducing bacterial biofilm activity and concentrations. Incorporating 1% and 3% DMAHDM-PCL did not affect cytocompatibility. Animal tests confirmed no inflammatory irritation. Shear bond strength and adhesive residual index results indicated that antimicrobial fibers didn't impact bonding ability. In conclusion, orthodontic adhesives with 3% DMAHDM-PCL fibers are potential antimicrobial bonding materials, offering a comprehensive solution to enamel demineralization in orthodontic patients.

Silk fibroin/methacrylated gelatine/hydroxyapatite biomimetic nanofibrous membranes for guided bone regeneration

By mimicking in vivo bionic microenvironment and promoting osteogenic differentiation, the hybrid organic-inorganic nanofibrous membranes provide promising potential for guided bone regeneration (GBR) in the treatment of clinical bone defects. To develop a degradable and osteogenic membrane for GBR by combining the natural biomacromolecule silk fibroin (SF) and gelatine with the bioactive nano hydroxyapatite (nHA), the anhydride-modified gelatine-nano hydroxyapatite (GelMA-nHA) composites were synthesized in situ and introduced into silk fibroin to prepare nanofibrous membranes with different ratios using electrospinning and photocrosslinking. The nanofibrous membranes, particularly those with a mass ratio of 7:2:1, were found to exhibit satisfactory elongation at break up to 110 %, maintain the nanofibrous structure for up to 28 days, and rapidly form bone-like apatite within 3 days, thus offering advantages when it comes to guided bone regeneration. In vitro cell results showed that the SF/GelMA/nHA membranes had excellent biocompatibility and enhanced osteogenic differentiation of hBMSCs. In vivo studies revealed that the hybrid composite membranes can improve bone regeneration of critical-sized calvarial defects in rat model. Therefore, the novel hybrid nanofibrous membrane is proposed to be a alternative candidate for creating a bionic microenvironment that promotes bone regeneration, indicating their potential application to bone injury treatment.

A 3D-Printed Scaffold for Repairing Bone Defects

The treatment of bone defects has always posed challenges in the field of orthopedics. Scaffolds, as a vital component of bone tissue engineering, offer significant advantages in the research and treatment of clinical bone defects. This study aims to provide an overview of how 3D printing technology is applied in the production of bone repair scaffolds. Depending on the materials used, the 3D-printed scaffolds can be classified into two types: single-component scaffolds and composite scaffolds. We have conducted a comprehensive analysis of material composition, the characteristics of 3D printing, performance, advantages, disadvantages, and applications for each scaffold type. Furthermore, based on the current research status and progress, we offer suggestions for future research in this area. In conclusion, this review acts as a valuable reference for advancing the research in the field of bone repair scaffolds.

Nanofibrous scaffolds for the healing of the fibrocartilaginous enthesis: advances and prospects

With the current developmental advancements in nanotechnology, nanofibrous scaffolds are being widely used. The healing of fibrocartilaginous enthesis is a slow and complex process, and while existing treatments have a certain effect on promoting their healing, these are associated with some limitations. The nanofibrous scaffold has the advantages of easy preparation, wide source of raw materials, easy adjustment, easy modification, can mimic the natural structure and morphology of the fibrocartilaginous enthesis, and has good biocompatibility, which can compensate for existing treatments and be combined with them to promote the repair of fibrocartilaginous enthesis. The nanofibrous scaffold can promote the healing of fibrocartilaginous enthesis by controlling the morphology and ensuring controlled drug release. Hence, the use of nanofibrous scaffold with stimulative response features in the musculoskeletal system has led us to imagine its potential application in fibrocartilaginous enthesis. Therefore, the healing of fibrocartilaginous enthesis based on a nanofibrous scaffold may be a novel therapeutic approach.

Tideglusib-incorporated nanofibrous scaffolds potently induce odontogenic differentiation

Pulp-Dentin regeneration is a key aspect of maintain tooth vitality and enabling good oral-systemic health. This study aimed to investigate a nanofibrous scaffold loaded with a small molecule i.e. Tideglusib to promote odontogenic differentiation. Tideglusib (GSK-3β inhibitor) interaction with GSK-3β was determined using molecular docking and stabilization of β-catenin was examined by confocal microscopy. 3D nanofibrous scaffolds were fabricated through electrospinning and their physicochemical characterizations were performed. Scaffolds were seeded with mesenchymal stem cells or pre-odontoblast cells to determine the cells proliferation and odontogenic differentiation. Our results showed that Tideglusib (TG) binds with GSK-3β at Cys199 residue. Stabilization and nuclear translocation of β-catenin was increased in the odontoblast cells treated with TG. SEM analysis revealed that nanofibers exhibited controlled architectural features that effectively mimicked the natural ECM. UV-Vis spectroscopy demonstrated that TG was incorporated successfully and released in a controlled manner. Both kinds of biomimetic nanofibrous matrices (PCLF-TG100, PCLF-TG1000) significantly stimulated cells proliferation. Furthermore, these scaffolds significantly induced dentinogenic markers (ALP, and DSPP) expression and biomineralization. In contrast to current pulp capping material driving dentin repair, the sophisticated, polymeric scaffold systems with soluble and insoluble spatiotemporal cues described here can direct stem cell differentiation and dentin regeneration. Hence, bioactive small molecule-incorporated nanofibrous scaffold suggests an innovative clinical tool for dentin tissue engineering.

Preclinical animal study of electrospun poly (l-lactide-co-caprolactone) and formulated porcine fibrinogen for full-thickness diabetic wound regeneration

Diabetic foot ulcer is one of the most serious chronic complications of diabetes mellitus. It may lead to amputation of the lower extremities for diabetics. Our study was to evaluate the effect of electrospun poly (L-lactide-co-caprolactone) and formulated porcine fibrinogen (PLCL/Fg) wound dressing on animal wound model. A blend ratio of PLCL/Fg scaffold was 4 (PLCL):1 (Fg). The scanning electron microscopy findings showed that the fibers' diameter was 122.5 ± 80.3 nm, and the tensile strength was 9.2 ± 0.2 MPa. In-vivo study of the hog normal model demonstrated that PLCL/Fg dressing had better biocompatibility, degradability, and ability to restore the skin's normal structure. We evaluated the wound healing processes in the rat diabetic model by macroscopic observation and histological observation at 1, 2, and 3 post-operation weeks. In our study, the PLCL/Fg group performed better 3 weeks after surgery, in terms of macroscopic healing and scarring. After surgery, the PLCL/Fg group showed better fibroblast accumulation, tissue granulation, and collagen expression than the control group. Topical treatment with PLCL/Fg dressing effectively enhanced wound healing in both normal and hyperglycemic conditions, suggesting that it may possess wound-healing potential.

The Delivery and Activation of Growth Factors Using Nanomaterials for Bone Repair

Bone regeneration is a comprehensive process that involves different stages, and various growth factors (GFs) play crucial roles in the entire process. GFs are currently widely used in clinical settings to promote bone repair; however, the direct application of GFs is often limited by their fast degradation and short local residual time. Additionally, GFs are expensive, and their use may carry risks of ectopic osteogenesis and potential tumor formation. Nanomaterials have recently shown great promise in delivering GFs for bone regeneration, as they can protect fragile GFs and control their release. Moreover, functional nanomaterials can directly activate endogenous GFs, modulating the regeneration process. This review provides a summary of the latest advances in using nanomaterials to deliver exogenous GFs and activate endogenous GFs to promote bone regeneration. We also discuss the potential for synergistic applications of nanomaterials and GFs in bone regeneration, along with the challenges and future directions that need to be addressed.

Response of mesenchymal stem cells to surface topography of scaffolds and the underlying mechanisms

Mesenchymal stem/stromal cells (MSCs) serve as essential components of regenerative medicine. Their destiny is influenced by the interaction of the cells with the external environment. In addition to the biochemical cues in a microenvironment, physical cues of the topography of the surrounding materials such as the extracellular matrix emerge as a crucial regulator of stem cell destiny and function. With recent advances in technologies of materials production and surface modification, surfaces with micro/nanotopographical characteristics can be fabricated to mimic the micro/nanoscale mechanical stimuli of the extracellular matrix environment and regulate the biological behavior of cells. Understanding the interaction of cells with the topography of a surface is conducive to the control of stem cell fate for application in regenerative medicine. However, the mechanisms by which topography affects the biological behavior of stem cells have not been fully elucidated. This review will present the effects of surface topography at the nano/micrometer scale on stem cell adhesion, morphology, proliferation, migration, and differentiation. It also focuses on discussing current theories about the sensing and recognition of surface topology cues, the transduction of the extracellular cues into plasma, and the final activation of related signaling pathways and downstream gene expression in MSCs. These insights will provide a theoretical basis for the future design of biomaterial scaffolds for application in regenerative medicine and tissue engineering.

Antioxidant and Antimicrobial Properties of Hydrolysed Collagen Nanofibers Loaded with Ginger Essential Oil

Hydrolysed collagen obtained from bovine leather by-products were loaded with ginger essential oil and processed by the electrospinning technique for obtaining bioactive nanofibers. Particle size measurements of hydrolysed collagen, GC-MS analysis of ginger essential oil (EO), and structural and SEM examinations of collagen nanofibers loaded with ginger essential oil collected on waxed paper, cotton, and leather supports were performed. Antioxidant and antibacterial activities against Staphylococcus aureus and Escherichia coli and antifungal activity against Candida albicans were also determined. Data show that the hydrolysed collagen nanofibers loaded with ginger EO can be used in the medical, pharmaceutical, cosmetic, or niche fields.

Hydrogel-based microenvironment engineering of haematopoietic stem cells

Haematopoietic Stem cells (HSCs) have the potential for self-renewal and multilineage differentiation, and their behaviours are finely tuned by the microenvironment. HSC transplantation (HSCT) is widely used in the treatment of haematologic malignancies while limited by the quantity of available HSCs. With the development of tissue engineering, hydrogels have been deployed to mimic the HSC microenvironment in vitro. Engineered hydrogels influence HSC behaviour by regulating mechanical strength, extracellular matrix microstructure, cellular ligands and cytokines, cell-cell interaction, and oxygen concentration, which ultimately facilitate the acquisition of sufficient HSCs. Here, we review recent advances in the application of hydrogel-based microenvironment engineering of HSCs, and provide future perspectives on challenges in basic research and clinical practice.

Preparation and performance of random- and oriented-fiber membranes with core-shell structures via coaxial electrospinning

The cells and tissue in the human body are orderly and directionally arranged, and constructing an ideal biomimetic extracellular matrix is still a major problem to be solved in tissue engineering. In the field of the bioresorbable vascular grafts, the long-term functional prognosis requires that cells first migrate and grow along the physiological arrangement direction of the vessel itself. Moreover, the graft is required to promote the formation of neointima and the development of the vessel walls while ensuring that the whole repair process does not form a thrombus. In this study, poly (l-lactide-co-ε-caprolactone) (PLCL) shell layers and polyethylene oxide (PEO) core layers with different microstructures and loaded with sodium tanshinone IIA sulfonate (STS) were prepared by coaxial electrospinning. The mechanical properties proved that the fiber membranes had good mechanical support, higher than that of the human aorta, as well as great suture retention strengths. The hydrophilicity of the oriented-fiber membranes was greatly improved compared with that of the random-fiber membranes. Furthermore, we investigated the biocompatibility and hemocompatibility of different functional fiber membranes, and the results showed that the oriented-fiber membranes containing sodium tanshinone IIA sulfonate had an excellent antiplatelet adhesion effect compared to other fiber membranes. Cytological analysis confirmed that the functional fiber membranes were non-cytotoxic and had significant cell proliferation capacities. The oriented-fiber membranes induced cell growth along the orientation direction. Degradation tests showed that the pH variation range had little change, the material mass was gradually reduced, and the fiber morphology was slowly destroyed. Thus, results indicated the degradation rate of the oriented-fiber graft likely is suitable for the process of new tissue regeneration, while the random-fiber graft with a low degradation rate may cause the material to reside in the tissue for too long, which would impede new tissue reconstitution. In summary, the oriented-functional-fiber membranes possessing core-shell structures with sodium tanshinone IIA sulfonate/polyethylene oxide loading could be used as tissue engineering materials for applications such as vascular grafts with good prospects, and their clinical application potential will be further explored in future research.

Nanofibrous insulin/vildagliptin core-shell PLGA scaffold promotes diabetic wound healing

Introduction: Slow wound repair in diabetes is a serious adverse event that often results in loss of a limb or disability. An advanced and encouraging vehicle is wanted to enhance clinically applicable diabetic wound care. Nanofibrous insulin/vildagliptin core-shell biodegradable poly (lactic-co-glycolic acid) (PLGA) scaffolds to prolong the effective drug delivery of vildagliptin and insulin for the repair of diabetic wounds were prepared. Methods: To fabricate core-shell nanofibrous membranes, vildagliptin mixture with PLGA, and insulin solution were pumped via separate pumps into two differently sized capillary tubes that were coaxially electrospun. Results and Discussion: Nanofibrous core-shell scaffolds slowly released effective vildagliptin and insulin over 2 weeks in vitro migration assay and in vivo wound-healing models. Water contact angle (68.3 ± 8.5° vs. 121.4 ± 2.0°, p = 0.006) and peaked water absorbent capacity (376% ± 9% vs. 283% ± 24%, p = 0.003) of the insulin/vildagliptin core-shell nanofibrous membranes remarkably exceeded those of a control group. The insulin/vildagliptin-loaded core-shell nanofibers improved endothelial progenitor cells migration in vitro (762 ± 77 cells/mm² vs. 424.4 ± 23 cells/mm², p < 0.001), reduced the α-smooth muscle actin content in vivo (0.72 ± 0.23 vs. 2.07 ± 0.37, p < 0.001), and increased diabetic would recovery (1.9 ± 0.3 mm² vs. 8.0 ± 1.4 mm², p = 0.002). Core-shell insulin/vildagliptin-loaded nanofibers extend the drug delivery of insulin and vildagliptin and accelerate the repair of wounds associated with diabetes.

Electrospun Polymer Nanofibers: Processing, Properties, and Applications

Electrospun polymer nanofibers (EPNF) constitute one of the most important nanomaterials with diverse applications. An overall review of EPNF is presented here, starting with an introduction to the most attractive features of these materials, which include the high aspect ratio and area to volume ratio as well as excellent processability through various production techniques. A review of these techniques is featured with a focus on electrospinning, which is the most widely used, with a detailed description and different types of the process. Polymers used in electrospinning are also reviewed with the solvent effect highlighted, followed by a discussion of the parameters of the electrospinning process. The mechanical properties of EPNF are discussed in detail with a focus on tests and techniques used for determining them, followed by a section for other properties including electrical, chemical, and optical properties. The final section is dedicated to the most important applications for EPNF, which constitute the driver for the relentless pursuit of their continuous development and improvement. These applications include biomedical application such as tissue engineering, wound healing and dressing, and drug delivery systems. In addition, sensors and biosensors applications, air filtration, defense applications, and energy devices are reviewed. A brief conclusion is presented at the end with the most important findings and directions for future research.

Absorbable Electrospun Poly-4-hydroxybutyrate Scaffolds as a Potential Solution for Pelvic Organ Prolapse Surgery

Women with pelvic organ prolapse (POP) have bothersome complaints that significantly affect their quality of life. While native tissue repair is associated with high recurrence rates, polypropylene knitted implants have caused specific implant-related adverse events that have detrimental, often irreversible, effects. We hypothesize that surgical outcome can be improved with a tissue-engineered solution using an absorbable implant that mimics the natural extracellular matrix (ECM) structure, releases estrogen, and activates collagen metabolism by fibroblasts as the main regulators of wound healing. To this aim, we produced electrospun poly-4-hydroxybutyrate (P4HB) scaffolds and biofunctionalized them with estradiol (E2). The cell-implant interactions relevant for POP repair were assessed by seeding primary POP vaginal fibroblasts isolated from patients on electrospun P4HB scaffolds with 1%, 2%, or 5% E2 and without E2. To test our hypothesis on whether ECM mimicking structures should improve regeneration, electrospun P4HB was compared to knitted P4HB implants. We evaluated vaginal fibroblast proliferation, ECM deposition, and metabolism by quantification of collagen, elastin, and matrix metalloproteinases and by gene expression analysis for 28 days. We established effective E2 drug loading with a steady release over time. Significantly higher cell proliferation, collagen-, and elastin deposition were observed on electrospun P4HB scaffolds as compared to knitted P4HB. For this study, physical properties of the scaffolds were more determinant on the cell response than the release of E2. These results indicate that making these electrospun P4HB scaffolds E2-releasing appears to be technically feasible. In addition, electrospun P4HB scaffolds promote the cellular response of vaginal fibroblasts and further studies are merited to assess if their use results in improved surgical outcomes in case of POP repair.

Technological advances in ocular trabecular meshwork in vitro models for glaucoma research

Glaucoma is the leading cause of irreversible blindness worldwide and is characterized by the progressive degeneration of the optic nerve. Intraocular pressure (IOP), which is considered to be the main risk factor for glaucoma development, builds up in response to the resistance (resistance to what?) provided by the trabecular meshwork (TM) to aqueous humor (AH) outflow. Although the TM and its relationship to AH outflow have remained at the forefront of scientific interest, researchers remain uncertain regarding which mechanisms drive the deterioration of the TM. Current tissue-engineering fabrication techniques have come up with promising approaches to successfully recreate the TM. Nonetheless, more accurate models are needed to understand the factors that make glaucoma arise. In this review, we provide a chronological evaluation of the technological milestones that have taken place in the field of glaucoma research, and we conduct a comprehensive comparison of available TM fabrication technologies. Additionally, we also discuss AH perfusion platforms, since they are essential for the validation of these scaffolds, as well as pressure-outflow relationship studies and the discovery of new IOP-reduction therapies.

Topographic Orientation of Scaffolds for Tissue Regeneration: Recent Advances in Biomaterial Design and Applications

Tissue engineering to develop alternatives for the maintenance, restoration, or enhancement of injured tissues and organs is gaining more and more attention. In tissue engineering, the scaffold used is one of the most critical elements. Its characteristics are expected to mimic the native extracellular matrix and its unique topographical structures. Recently, the topographies of scaffolds have received increasing attention, not least because different topographies, such as aligned and random, have different repair effects on various tissues. In this review, we have focused on various technologies (electrospinning, directional freeze-drying, magnetic freeze-casting, etching, and 3-D printing) to fabricate scaffolds with different topographic orientations, as well as discussed the physicochemical (mechanical properties, porosity, hydrophilicity, and degradation) and biological properties (morphology, distribution, adhesion, proliferation, and migration) of different topographies. Subsequently, we have compiled the effect of scaffold orientation on the regeneration of vessels, skin, neural tissue, bone, articular cartilage, ligaments, tendons, cardiac tissue, corneas, skeletal muscle, and smooth muscle. The compiled information in this review will facilitate the future development of optimal topographical scaffolds for the regeneration of certain tissues. In the majority of tissues, aligned scaffolds are more suitable than random scaffolds for tissue repair and regeneration. The underlying mechanism explaining the various effects of aligned and random orientation might be the differences in “contact guidance”, which stimulate certain biological responses in cells.

Polymeric biomaterials for wound healing applications: a comprehensive review

Chronic wounds have been a global health threat over the past few decades, requiring urgent medical and research attention. The factors delaying the wound-healing process include obesity, stress, microbial infection, aging, edema, inadequate nutrition, poor oxygenation, diabetes, and implant complications. Biomaterials are being developed and fabricated to accelerate the healing of chronic wounds, including hydrogels, nanofibrous, composite, foam, spongy, bilayered, and trilayered scaffolds. Some recent advances in biomaterials development for healing both chronic and acute wounds are extensively compiled here. In addition, various properties of biomaterials for wound-healing applications and how they affect their performance are reviewed. Based on the recent literature, trilayered constructs appear to be a convincing candidate for the healing of chronic wounds and complete skin regeneration because they mimic the full thickness of skin: epidermis, dermis, and the hypodermis. This type of scaffold provides a dense superficial layer, a bioactive middle layer, and a porous lower layer to aid the wound-healing process. The hydrophilicity of scaffolds aids cell attachment, cell proliferation, and protein adhesion. Other scaffold characteristics such as porosity, biodegradability, mechanical properties, and gas permeability help with cell accommodation, proliferation, migration, differentiation, and the release of bioactive factors.

Bone Mineralization in Electrospun-Based Bone Tissue Engineering

Increasing the demand for bone substitutes in the management of bone fractures, including osteoporotic fractures, makes bone tissue engineering (BTE) an ideal strategy for solving the constant shortage of bone grafts. Electrospun-based scaffolds have gained popularity in BTE because of their unique features, such as high porosity, a large surface-area-to-volume ratio, and their structural similarity to the native bone extracellular matrix (ECM). To imitate native bone mineralization through which bone minerals are deposited onto the bone matrix, a simple but robust post-treatment using a simulated body fluid (SBF) has been employed, thereby improving the osteogenic potential of these synthetic bone grafts. This study highlights recent electrospinning technologies that are helpful in creating more bone-like scaffolds, and addresses the progress of SBF development. Biomineralized electrospun bone scaffolds are also reviewed, based on the importance of bone mineralization in bone regeneration. This review summarizes the potential of SBF treatments for conferring the biphasic features of native bone ECM architectures onto electrospun-based bone scaffolds.

Cross-Linking Agents for Electrospinning-Based Bone Tissue Engineering

Electrospun nanofibers are promising bone tissue scaffolds that support bone healing due to the body’s structural similarity to the extracellular matrix (ECM). However, the insufficient mechanical properties often limit their potential in bone tissue regeneration. Cross-linking agents that chemically interconnect as-spun electrospun nanofibers are a simple but effective strategy for improving electrospun nanofibers’ mechanical, biological, and degradation properties. To improve the mechanical characteristic of the nanofibrous bone scaffolds, two of the most common types of cross-linking agents are used to chemically crosslink electrospun nanofibers: synthetic and natural. Glutaraldehyde (GTA) is a typical synthetic agent for electrospun nanofibers, while genipin (GP) is a natural cross-linking agent isolated from gardenia fruit extracts. GP has gradually gained attention since GP has superior biocompatibility to synthetic ones. In recent studies, much more progress has been made in utilizing crosslinking strategies, including citric acid (CA), a natural cross-linking agent. This review summarizes both cross-linking agents commonly used to improve electrospun-based scaffolds in bone tissue engineering, explains recent progress, and attempts to expand the potential of this straightforward method for electrospinning-based bone tissue engineering.

Implantable nerve guidance conduits: Material combinations, multi-functional strategies and advanced engineering innovations

Nerve guidance conduits (NGCs) have attracted much attention due to their great necessity and applicability in clinical use for the peripheral nerve repair. Great efforts in recent years have been devoted to the development of high-performance NGCs using various materials and strategies. The present review provides a comprehensive overview of progress in the material innovation, structural design, advanced engineering technologies and multi functionalization of state-of-the-art nerve guidance conduits NGCs. Abundant advanced engineering technologies including extrusion-based system, laser-based system, and novel textile forming techniques in terms of weaving, knitting, braiding, and electrospinning techniques were also analyzed in detail. Findings arising from this review indicate that the structural mimetic NGCs combined with natural and synthetic materials using advanced manufacturing technologies can make full use of their complementary advantages, acquiring better biomechanical properties, chemical stability and biocompatibility. Finally, the existing challenges and future opportunities of NGCs were put forward aiming for further research and applications of NGCs.

Advances in microfabrication technologies in tissue engineering and regenerative medicine

BACKGROUND

Tissue engineering provides various strategies to fabricate an appropriate microenvironment to support the repair and regeneration of lost or damaged tissues. In this matter, several technologies have been implemented to construct close-to-native three-dimensional structures at numerous physiological scales, which are essential to confer the functional characteristics of living tissues.

METHODS

In this article, we review a variety of microfabrication technologies that are currently utilized for several tissue engineering applications, such as soft lithography, microneedles, templated and self-assembly of microstructures, microfluidics, fiber spinning, and bioprinting.

RESULTS

These technologies have considerably helped us to precisely manipulate cells or cellular constructs for the fabrication of biomimetic tissues and organs. Although currently available tissues still lack some crucial functionalities, including vascular networks, innervation, and lymphatic system, microfabrication strategies are being proposed to overcome these issues. Moreover, the microfabrication techniques that have progressed to the preclinical stage are also discussed.

CONCLUSIONS

This article aims to highlight the advantages and drawbacks of each technique and areas of further research for a more comprehensive and evolving understanding of microfabrication techniques in terms of tissue engineering and regenerative medicine applications.

Applications of electrospun scaffolds with enlarged pores in tissue engineering

Despite electrospinning has multiple advantages over other methods such as creating materials with superfine fiber diameter, high specific surface area, and good mechanical properties, the pore diameter of scaffolds prepared...

Prevention of Postsurgical Abdominal Adhesion Using Electrospun TPU Nanofibers in Rat Model

Intra-abdominal adhesions following surgery are a challenging problem in surgical practice. This study fabricated different thermoplastic polyurethane (TPU) nanofibers with different average diameters using the electrospinning method. The conditions were evaluated by scanning electron microscopy (SEM), atomic force microscope (AFM), and Fourier transform infrared spectrometer (FTIR) analysis. A static tensile test was applied using a strength testing device to assess the mechanical properties of the electrospun scaffolds. By changing the effective electrospinning parameters, the best quality of nanofibers could be achieved with the lowest bead numbers. The electrospun nanofibers were evaluated in vivo using a rat cecal abrasion model. The macroscopic evaluation and the microscopic study, including the degree of adhesion and inflammation, were investigated after three and five weeks. The resultant electrospun TPU nanofibers had diameters ranging from about 200 to 1000 nm. The diameters and morphology of the nanofibers were significantly affected by the concentration of polymer. Uniform TPU nanofibers without beads could be prepared by electrospinning through reasonable control of the process concentration. These nanofibers' biodegradability and antibacterial properties were investigated by weight loss measurement and microdilution methods, respectively. The purpose of this study was to provide electrospun nanofibers having biodegradability and antibacterial properties that prevent any adhesions or inflammation after pelvic and abdominal surgeries. The in vivo experiments revealed that electrospun TPU nanofibers reduced the degree of abdominal adhesions. The histopathological study confirmed only a small extent of inflammatory cell infiltration in the 8% and 10% TPU. Conclusively, nanofibers containing 8% TPU significantly decreased the incidence and severity of postsurgical adhesions, and it is expected to be used in clinical applications in the future.

Endothelial Cell Migration Regulated by Surface Topography of Poly(ε-caprolactone) Nanofibers

The study of cell migration on biomaterials is of great significance in tissue engineering and regenerative medicine. In recent years, there has been increasing evidence that the physical properties of the extracellular matrix (ECM), such as surface topography, affect various cellular behaviors such as proliferation, adhesion, and migration. However, the biological mechanism of surface topography influencing cellular behavior is still unclear. In this study, we prepared polycaprolactone (PCL) fibrous materials with different surface microstructures by solvent casting, electrospinning, and self-induced crystallization. The corresponding topographical structure obtained is a two-dimensional (2D) flat surface, 2.5-dimensional (2.5D) fibers, and three-dimensional (3D) fibers with a multilevel microstructure. We then investigated the effects of the complex topographical structure on endothelial cell migration. Our study demonstrates that cells can sense the changes of micro- and nanomorphology on the surface of materials, adapt to the physical environment through biochemical reactions, and regulate actin polymerization and directional migration through Rac1 and Cdc42. The cells on the nanofibers are elongated spindles, and the positive feedback of cell adhesion and actin polymerization along the fiber direction makes the plasma membrane continue to protrude, promoting cell polarization and directional migration. This study might provide new insights into the biomaterial design, especially those used for artificial vascular grafts.

Renal Biology Driven Macro- and Microscale Design Strategies for Creating an Artificial Proximal Tubule Using Fiber-Based Technologies

Chronic kidney disease affects one in six people worldwide. Due to the scarcity of donor kidneys and the complications associated with hemodialysis (HD), a cell-based bioartificial kidney (BAK) device is desired. One of the shortcomings of HD is the lack of active transport of solutes that would normally be performed by membrane transporters in kidney epithelial cells. Specifically, proximal tubule (PT) epithelial cells play a major role in the active transport of metabolic waste products. Therefore, a BAK containing an artificial PT to actively transport solutes between the blood and the filtrate could provide major therapeutic advances. Creating such an artificial PT requires a biocompatible tubular structure which supports the adhesion and function of PT-specific epithelial cells. Ideally, this scaffold should structurally replicate the natural PT basement membrane which consists mainly of collagen fibers. Fiber-based technologies such as electrospinning are therefore especially promising for PT scaffold manufacturing. This review discusses the use of electrospinning technologies to generate an artificial PT scaffold for ex vivo/in vivo cellularization. We offer a comparison of currently available electrospinning technologies and outline the desired scaffold properties required to serve as a PT scaffold. Discussed also are the potential technologies that may converge in the future, enabling the effective and biomimetic incorporation of synthetic PTs in to BAK devices and beyond.

Electrospinning of Polyepychlorhydrin and Polyacrylonitrile Anionic Exchange Membranes for Reverse Electrodialysis

The saline gradient present in river mouths can be exploited using ion-exchange membranes in reverse electrodialysis (RED) for energy generation. However, significant improvements in the fabrication processes of these IEMs are necessary to increase the overall performance of the RED technology. This work proposes an innovative technique for synthesizing anion exchange membranes (AEMs) via electrospinning. The AEM synthesis was carried out by applying a high voltage while ejecting a mixture of polyepichlorohydrin (PECH), 1,4-diazabicyclo [2.2.2] octane (DABCO® 33-LV) and polyacrylonitrile (PAN) at room temperature. Different ejection parameters were used, and the effects of various thermal treatments were tested on the resulting membranes. The AEMs presented crosslinking between the polymers and significant fiber homogeneity with diameters between 1400 and 1510 nm, with and without thermal treatment. Good chemical resistance was measured, and all synthesized membranes were of hydrophobic character. The thickness, roughness, swelling degree, specific fixed-charge density and ion-exchange capacity were improved over equivalent membranes produced by casting, and also when compared with commercial membranes. Finally, the results of the study of the electrospinning parameters indicate that a better performance in electrochemical properties was produced from fibers generated at ambient humidity conditions, with low flow velocity and voltage, and high collector rotation velocity.

Nanofiber as a novel vehicle for transdermal delivery of therapeutic agents: challenges and opportunities

Background

Transdermal delivery of drugs is a quite challenging task for pharmaceutical scientists. The transdermal route is preferred over the oral route due to various advantages like avoidance of the first-pass effect, non-invasiveness, and high patient compliance. Therefore, it is necessary to develop an effective carrier system that enables the effective passage of the drug through the dermal barrier.

Main body of abstract

Various novel drug delivery systems are used to enhance the permeation of a variety of drugs through the skin barrier. Researchers around the globe have explored nanofibers for the transdermal delivery of various therapeutic agents. Nanofibers are designed to have a high concentration of therapeutic agents in them promoting their flux through various skin layers. Polymeric nanofibers can be explored for the loading of both hydrophilic and lipophilic drugs. Biopolymer-based nanofibers have been also explored for transdermal delivery. They are capable of controlling the release of therapeutic agents for a prolonged time.

Short conclusion

The literature presented in this review paper provides significant proof that nanofibers will have an intense impact on the transdermal delivery of different bioactive molecules in the future.

Graphic abstract

PEDOT:PSS-Coated Polybenzimidazole Electroconductive Nanofibers for Biomedical Applications

Bioelectricity drives several processes in the human body. The development of new materials that can deliver electrical stimuli is gaining increasing attention in the field of tissue engineering. In this work, novel, highly electrically conductive nanofibers made of poly [2,2′-m-(phenylene)-5,5′-bibenzimidazole] (PBI) have been manufactured by electrospinning and then coated with cross-linked poly (3,4-ethylenedioxythiophene) doped with poly (styrene sulfonic acid) (PEDOT:PSS) by spin coating or dip coating. These scaffolds have been characterized by scanning electron microscopy (SEM) imaging and attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy. The electrical conductivity was measured by the four-probe method at values of 28.3 S·m⁻¹ for spin coated fibers and 147 S·m⁻¹ for dip coated samples, which correspond, respectively, to an increase of about 10⁵ and 10⁶ times in relation to the electrical conductivity of PBI fibers. Human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) cultured on the produced scaffolds for one week showed high viability, typical morphology and proliferative capacity, as demonstrated by calcein fluorescence staining, 4′,6-diamidino-2-phenylindole (DAPI)/Phalloidin staining and MTT [3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyl tetrazolium bromide] assay. Therefore, all fiber samples demonstrated biocompatibility. Overall, our findings highlight the great potential of PEDOT:PSS-coated PBI electrospun scaffolds for a wide variety of biomedical applications, including their use as reliable in vitro models to study pathologies and the development of strategies for the regeneration of electroactive tissues or in the design of new electrodes for in vivo electrical stimulation protocols.

In vitro and in vivo advancement of multifunctional electrospun nanofiber scaffolds in wound healing applications: Innovative nanofiber designs, stem cell approaches, and future perspectives

The skin is one of the most essential tissues in the human body, interacting with the outside environment and shielding the body from diseases and excessive water loss. Hydrogels, decellularized porcine dermal matrix, and lyophilized polymer scaffolds have all been used in studies of skin wound repair, wound dressing, and skin tissue engineering, however, these materials cannot replicate the nanofibrous architecture of the skin's native extracellular matrix (ECM). Electrospun nanofibers are a fascinating new form of nanomaterials with tremendous potential across a broad spectrum of applications in the biomedical field, including wound dressings, wound healing scaffolds, regenerative medicine, bioengineering of skin tissue, and multifaceted drug delivery. This article reviews recent in vitro and in vivo developments in multifunctional electrospun nanofibers (MENs) for wound healing. This review begins with an introduction to the electrospinning process, its principle, and the processing parameters which have a significant impact on the nanofiber properties. It then discusses the various geometries and advantages of MEN scaffolds produced by different innovative electrospinning techniques for wound healing applications when used in combination with stem cells. This review also discusses some of the possible future nanofiber-based models that could be used. Finally, we conclude with potential perspectives and conclusions in this area.

Effect of Pore Size of Honeycomb-Patterned Polymer Film on Spontaneous Formation of 2D Micronetworks by Coculture of Human Umbilical Vein Endothelial Cells and Mesenchymal Stem Cells

The geometrical control of micronetwork structures ( μ NSs) formed by endothelial cells is an important topic in tissue engineering, cell-based assays, and fundamental biological studies. In this study, μ NSs are formed using human umbilical vein endothelial cells (HUVECs) by the coculture of HUVECs and human mesenchymal stem cells (MSCs) confined in a honeycomb-patterned poly-l-lactic acid film (honeycomb film (HCF)), which is a novel cell culture scaffold. The HCF is produced using the breath figure method, which uses condensed water droplets as pore templates. The confinement of the HUVECs and MSCs in the HCF along with the application of centrifugal force results in μ NS formation when the pore size is more than 20  μ m. Furthermore, μ NS development is geometrically restricted by the hexagonally packed and connected pores in the horizontal direction of the HCF. Network density is also controlled by changing the seeding density of the HUVECs and MSCs. The threshold pore size indicates that μ NSs can be formed spontaneously by using an HCF with a perfectly uniform porous structure. This result provides an important design guideline for the structure of porous cell culture scaffolds by applying a blood vessel model in vitro.

Growth factor delivery using extracellular matrix-mimicking substrates for musculoskeletal tissue engineering and repair

Therapeutic approaches for musculoskeletal tissue regeneration commonly employ growth factors (GFs) to influence neighboring cells and promote migration, proliferation, or differentiation. Despite promising results in preclinical models, the use of inductive biomacromolecules has achieved limited success in translation to the clinic. The field has yet to sufficiently overcome substantial hurdles such as poor spatiotemporal control and supraphysiological dosages, which commonly result in detrimental side effects. Physiological presentation and retention of biomacromolecules is regulated by the extracellular matrix (ECM), which acts as a reservoir for GFs via electrostatic interactions. Advances in the manipulation of extracellular proteins, decellularized tissues, and synthetic ECM-mimetic applications across a range of biomaterials have increased the ability to direct the presentation of GFs. Successful application of biomaterial technologies utilizing ECM mimetics increases tissue regeneration without the reliance on supraphysiological doses of inductive biomacromolecules. This review describes recent strategies to manage GF presentation using ECM-mimetic substrates for the regeneration of bone, cartilage, and muscle.

Drug-Eluting Medical Textiles: From Fiber Production and Textile Fabrication to Drug Loading and Delivery

Drug-eluting medical textiles have recently gained great attention to be used in different applications due to their cost effectiveness and unique physical and chemical properties. Using various fiber production and textile fabrication technologies, fibrous constructs with the required properties for the target drug delivery systems can be designed and fabricated. This review summarizes the current advances in the fabrication of drug-eluting medical textiles. Different fiber production methods such as melt-, wet-, and electro-spinning, and textile fabrication techniques such as knitting and weaving are explained. Moreover, various loading processes of bioactive agents to obtain drug-loaded fibrous structures with required physicochemical and morphological properties, drug delivery mechanisms, and drug release kinetics are discussed. Finally, the current applications of drug-eluting fibrous systems in wound care, tissue engineering, and transdermal drug delivery are highlighted.

Advances in Fabricating the Electrospun Biopolymer-Based Biomaterials

Biopolymers formed into a fibrous morphology through electrospinning are of increasing interest in the field of biomedicine due to their intrinsic biocompatibility and biodegradability and their ability to be biomimetic to various fibrous structures present in animal tissues. However, their mechanical properties are often unsatisfactory and their processing may be troublesome. Thus, extensive research interest is focused on improving these qualities. This review article presents the selection of the recent advances in techniques aimed to improve the electrospinnability of various biopolymers (polysaccharides, polynucleotides, peptides, and phospholipids). The electrospinning of single materials, and the variety of co-polymers, with and without additives, is covered. Additionally, various crosslinking strategies are presented. Examples of cytocompatibility, biocompatibility, and antimicrobial properties are analyzed. Special attention is given to whey protein isolate as an example of a novel, promising, green material with good potential in the field of biomedicine. This review ends with a brief summary and outlook for the biomedical applicability of electrospinnable biopolymers.

Electrospinning of small diameter vascular grafts with preferential fiber directions and comparison of their mechanical behavior with native rat aortas

Conventional electrospun small diameter vascular grafts have a random fiber orientation. In order to achieve mechanical characteristics similar to a native blood vessel, a controllable fiber orientation is of interest. In this study the electrospinning jet was directly controlled by means of an auxiliary, changeable electrostatic field, so that the fibers could be deposited in adjustable orientations. Prostheses with circumferentially, axially, fenestrated and randomly aligned fibers were electrospun on Ø2mm mandrels out of a thermoplastic polyurethane (PUR) and a polylactid acid (PLLA). The impact of the materials and the various preferential fiber orientations on the resulting biomechanics was investigated and compared with that of the native rat aorta in quasistatic and dynamic hoop tensile tests. The test protocol included 3000 dynamic loading cycles in the physiological blood pressure range and ended with a quasistatic tensile test. Any orientation of the fibers in a particular direction resulted in a significant reduction in scaffold porosity for both materials. The standard randomly oriented PUR grafts showed the highest compliance of 29.7 ± 5.5 [%/100 mmHg] and were thus closest to the compliance of the rat aortas, which was 37.2 ± 6.5 [%/100 mmHg]. The maximum tensile force was increased at least 6 times compared to randomly spun grafts by orienting the fibers in the circumferential direction. During the 3000 loading cycles, creeping of the native rat aorta was below 1% whereas the electrospun grafts showed creeping up to 2.4 ± 1.2%. Although the preferred fiber orientations were only partially visible in the scanning electron micrographs, the mechanical effects were evident. The investigations suggest a multi-layer wall structure of the vascular prosthesis, since none of the preferred fiber directions and the materials used could imitate the typical j-shaped mechanical characteristics of the rat aorta.

bFGF and SDF-1α Improve In Vivo Performance of VEGF-Incorporating Small-Diameter Vascular Grafts

Tissue-engineered vascular grafts are widely tested as a promising substitute for both arterial bypass and replacement surgery. We previously demonstrated that incorporation of VEGF into electrospun tubular scaffolds from poly(3-hydroxybutyrate-co-3-hydroxyvalerate)/poly(ε-caprolactone) enhances formation of an endothelial cell monolayer. However, an overdose of VEGF can induce tumor-like vasculature; thereby, other bioactive factors are needed to support VEGF-driven endothelialization and successful recruitment of smooth muscle cells. Utilizing emulsion electrospinning, we fabricated one-layer vascular grafts with either VEGF, bFGF, or SDF-1α, and two-layer vascular grafts with VEGF incorporated into the inner layer and bFGF and SDF-1α incorporated into the outer layer with the following structural evaluation, tensile testing, and in vivo testing using a rat abdominal aorta replacement model. The latter graft prototype showed higher primary patency rate. We found that the two-layer structure improved surface topography and mechanical properties of the grafts. Further, the combination of bFGF, SDF-1α, and VEGF improved endothelialization compared with VEGF alone, while bFGF induced a rapid formation of a smooth muscle cell layer. Taken together, these findings show that the two-layer structure and incorporation of bFGF and SDF-1α into the vascular grafts in combination with VEGF provide a higher primary patency and therefore improved in vivo performance.

Electrospinning cellulose acetate/silk fibroin/Au-Ag hybrid composite nanofiber for enhanced biocidal activity against MCF-7 breast cancer cell

The development of multifunctional nanomaterials with enhanced biocompatible potential is crucial for effective biomedical applications. Herein we propose electrospun silk fibroin/cellulose acetate/gold-silver nanoparticles (CA/SF/Au-Ag) composite nanofiber for anticancer applications. The silk fibroin and cellulose acetate serving as the reducing and stabilizing agent for Ag⁺ and Au⁺ ions with improved biocompatibility. The fabricated CA/SF/Au-Ag nanofiber was studied with different functional, surface and crystallographic techniques. The CA/SF polymer matrix was formed in the needle and rod-shaped morphology with the range of 86.02 ± 57.35 nm in diameter and the Au and Ag NPs were embedded on the fiber matrix with an average size of 17.32 nm and 53.21 nm respectively. Further, it strongly triggers the cytotoxic effects against MCF-7 and MDA-MB-231 human breast cancer cells with an effective IC₅₀ value. Our findings implied that CA/SF/Au-Ag composite nanofibers are an effective material for safer anticancer applications.

Surfactant location and internal phase volume fraction dictate emulsion electrospun fiber morphology and modulate drug release and cell response

Emulsion electrospinning is a versatile technique used to create fibrous meshes for applications in drug delivery and tissue engineering. In this study, the effects of surfactant and increasing internal phase volume fraction on emulsion electrospun fiber morphology were investigated. The fiber diameter, surface topography, internal architecture, mesh hydrophobicity, and fiber volume fraction were all characterized and the resulting effects on model drug release and cell response were determined. Surfactant relocation to the fiber surface resulted in alterations to fiber surface topography and internal morphology, increased rate of water adsorption into the mesh, and reduced burst effects of drug release. Increasing the internal phase volume fraction within the emulsion resulted in minimal change to fiber diameter, surface morphology, fiber volume fraction, and rate of water adsorption illustrating the ability to increase drug loading without affecting fiber properties. Lastly, all meshes promoted cell adhesion and good viability with a trend of increased MTT absorbance from cells on the surfactant and emulsion fibers possibly suggesting that an increase in surface area via smaller fiber diameter and fiber volume fraction increases metabolic activity. Overall, these studies indicate that fiber morphology and mesh hydrophobicity can be tuned by controlling surfactant location within fibers and internal phase volume fraction. Modulating fiber properties within the emulsion electrospun mesh is important to achieve controlled drug release and cell response for tissue engineering applications.

Current approaches and future prospects of nanofibers: a special focus on antimicrobial drug delivery

Antibacterial nanofibers have a great potential for effective treatment of infections. They act as drug reservoir systems that release higher quantities of antibacterial agents/drug in a controlled manner at infection sites and prevent drug resistance, while concomitantly decreasing the systemic toxicity. With this drug delivery system, it is also possible to achieve multiple drug entrapment and also simultaneous or sequential release kinetics at the site of action. Therefore, advances in antibacterial nanofibers as drug delivery systems were overviewed within this article. Recently published data on antibacterial drug delivery was also summarised to provide a view of the current state of art in this field. Although antibacterial use seems to be limited and one can ask that 'what is left to be discovered?'; recent update literatures in this field highlighted the use of nanofibers from very different perspectives. We believe that readers will be benefiting this review for enlightening of novel ideas.

Surface-Modified Highly Biocompatible Bacterial-poly(3-hydroxybutyrate-co-4-hydroxybutyrate): A Review on the Promising Next-Generation Biomaterial

Polyhydroxyalkanoates (PHAs) are bacteria derived bio-based polymers that are synthesised under limited conditions of nutritional elements with excess carbon sources. Among the members of PHAs, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [(P(3HB-co-4HB)] emerges as an attractive biomaterial to be applied in medical applications owing to its desirable mechanical and physical properties, non-genotoxicity and biocompatibility eliciting appropriate host tissue responses. The tailorable physical and chemical properties and easy surface functionalisation of P(3HB-co-4HB) increase its practicality to be developed as functional medical substitutes. However, its applicability is sometimes limited due to its hydrophobic nature due to fewer bio-recognition sites. In this review, we demonstrate how surface modifications of PHAs, mainly P(3HB-co-4HB), will overcome these limitations and facilitate their use in diverse medical applications. The integration of nanotechnology has drastically enhanced the functionality of P(3HB-co-4HB) biomaterials for application in complex biological environments of the human body. The design of versatile P(3HB-co-4HB) materials with surface modifications promise a non-cytotoxic and biocompatible material without inducing severe inflammatory responses for enhanced effective alternatives in healthcare biotechnology. The enticing work carried out with P(3HB-co-4HB) promises to be one of the next-generation materials in biomedicines which will facilitate translation into the clinic in the future.

Functionally graded biomaterials for use as model systems and replacement tissues

The heterogeneity of native tissues requires complex materials to provide suitable substitutes for model systems and replacement tissues. Functionally graded materials have the potential to address this challenge by mimicking the gradients in heterogeneous tissues such as porosity, mineralization, and fiber alignment to influence strength, ductility, and cell signaling. Advancements in microfluidics, electrospinning, and 3D printing enable the creation of increasingly complex gradient materials that further our understanding of physiological gradients. The combination of these methods enables rapid prototyping of constructs with high spatial resolution. However, successful translation of these gradients requires both spatial and temporal presentation of cues to model the complexity of native tissues that few materials have demonstrated. This review highlights recent strategies to engineer functionally graded materials for the modeling and repair of heterogeneous tissues, together with a description of how cells interact with various gradients.

Tissue-engineered vessel derived from human fibroblasts with an electrospun scaffold

Advanced cardiovascular disease often requires surgical revascularization for small diameter arterial bypass procedures, and there is a need for alternative grafts in those patients lacking autologous vein. A decellularized biological vessel with the characteristics of a small artery and the ability to remodel in vivo could replace currently available bypass grafts. In this study, a biodegradable electrospun scaffold was specifically designed to be placed in a biomimetic perfusion system to generate a tissue-engineered vessel from human dermal fibroblasts. The polyglycolic acid electrospun scaffold was co-electrosprayed with a sacrificial porogen microparticle, polyethylene oxide, to increase porosity and pore size. After a 10-week culture period in the biomimetic system, the tissue-engineered vessel derived from human fibroblasts was further processed with decellularization to form an allogeneic tissue-engineered vessel. The tissue-engineered vessel had a similar morphology by histological staining for collagen and elastin before and after decellularization. The mechanical properties (burst pressure, ultimate tensile strength, and elastic modulus) remained stable after decellularization and were on the same magnitude as a human saphenous vein. The decellularization processing demonstrated no loss of collagen, near complete removal of DNA, and no presence of intracellular proteins. The decellularized tissue-engineered vessel supported the growth of endothelial cells on the surface, and fibroblasts were able to migrate into the midportion of the matrix. Therefore, an electrospun scaffold provides a versatile biomaterial to create a decellularized tissue-engineered vessel derived from human dermal fibroblasts with morphological and mechanical properties for use as a small diameter vascular graft.

Biocompatibility evaluation of heparin-conjugated poly(ε-caprolactone) scaffolds in a rat subcutaneous implantation model

Vascular grafts prepared from synthetic polymers have serious shortcomings that can be resolved by surface modification, such as by immobilizing heparin. In this study, the mechanical properties, biocompatibility, anticoagulation property, and water contact angle of two heparin-conjugated poly(ε-caprolactone) scaffolds (PCL-hexamethylendiamine-heparin, PCL-HMD-H. PCL-lysine-heparin, PCL-LYS-H) were compared to identify a preferred heparin conjugation method. An evaluation of the subcutaneous tissue biocompatibility of the scaffolds demonstrated that PCL-HMD-H had better endothelial cell proliferation than the PCL-LYS-H and was therefore a promising scaffold candidate for use in vascular tissue-engineering.

Potential Implantable Nanofibrous Biomaterials Combined with Stem Cells for Subchondral Bone Regeneration

The treatment of osteochondral defects remains a challenge. Four scaffolds were produced using Food and Drug Administration (FDA)-approved polymers to investigate their therapeutic potential for the regeneration of the osteochondral unit. Polycaprolactone (PCL) and poly(vinyl-pyrrolidone) (PVP) scaffolds were made by electrohydrodynamic techniques. Hydroxyapatite (HAp) and/or sodium hyaluronate (HA) can be then loaded to PCL nanofibers and/or PVP particles. The purpose of adding hydroxyapatite and sodium hyaluronate into PCL/PVP scaffolds is to increase the regenerative ability for subchondral bone and joint cartilage, respectively. Human bone marrow-derived mesenchymal stem cells (hBM-MSCs) were seeded on these biomaterials. The biocompatibility of these biomaterials in vitro and in vivo, as well as their potential to support MSC differentiation under specific chondrogenic or osteogenic conditions, were evaluated. We show here that hBM-MSCs could proliferate and differentiate both in vitro and in vivo on these biomaterials. In addition, the PCL-HAp could effectively increase the mineralization and induce the differentiation of MSCs into osteoblasts in an osteogenic condition. These results indicate that PCL-HAp biomaterials combined with MSCs could be a beneficial candidate for subchondral bone regeneration.