Design of vascular prostheses by melt electrospinning-structural characterizations

Electrospinning technologies for the delivery of Biopharmaceuticals: Current status and future trends

This review provides an in-depth exploration of electrospinning techniques employed to produce micro- or nanofibres of biopharmaceuticals using polymeric solutions or melts with high-voltage electricity. Distinct from prior reviews, the current work narrows its focus on the recent developments and advanced applications in biopharmaceutical formulations. It begins with an overview of electrospinning principles, covering both solution and melt modes. Various methods for incorporating biopharmaceuticals into electrospun fibres, such as surface adsorption, blending, emulsion, co-axial, and high-throughput electrospinning, are elaborated. The review also surveys a wide array of biopharmaceuticals formulated through electrospinning, thereby identifying both opportunities and challenges in this emerging field. Moreover, it outlines the analytical techniques for characterizing electrospun fibres and discusses the legal and regulatory requirements for their production. This work aims to offer valuable insights into the evolving realm of electrospun biopharmaceutical delivery systems.

Advances of polyolefins from fiber to nanofiber: fabrication and recent applications

Polyolefins are a widely accepted commodity polymer made from olefinic monomer consisting of carbon and hydrogen. This thermoplastic polymeric material is formed through reactive double bonds of olefins by the addition polymerization technique and it possesses a diverse range of unique features for a large variety of applications. Among the various types, polyethylene and polypropylene are the prominent classes of polyolefins that can be crafted and manipulated into diversified products for numerous applications. Research on polyolefins has boomed tremendously in recent times owing to the abundance of raw materials, low cost, lightweight, high chemical resistance, diverse functionalities, and outstanding physical characteristics. Polyolefins have also evidenced their potentiality as a fiber in micro to nanoscale and emerged as a fascinating material for widespread high-performance use. This review aims to provide an elucidation of the breakthroughs in polyolefins, namely as fibers, filaments, and yarns, and their applications in many domains such as medicine, body armor, and load-bearing industries. Moreover, the development of electrospun polyolefin nanofibers employing cutting-edge techniques and their prospective utilization in filtration, biomedical engineering, protective textiles, and lithium-ion batteries has been illustrated meticulously. Besides, this review delineates the challenges associated with the formation of polyolefin nanofiber using different techniques and critically analyzes overcoming the difficulties in forming functional nanofibers for the innovative field of applications.

Poly(lactic acid)-Based Electrospun Fibrous Structures for Biomedical Applications

Poly(lactic acid)(PLA) is an aliphatic polyester that can be derived from natural and renewable resources. Owing to favorable features, such as biocompatibility, biodegradability, good thermal and mechanical performance, and processability, PLA has been considered as one of the most promising biopolymers for biomedical applications. Particularly, electrospun PLA nanofibers with distinguishing characteristics, such as similarity to the extracellular matrix, large specific surface area and high porosity with small pore size and tunable mechanical properties for diverse applications, have recently given rise to advanced spillovers in the medical area. A variety of PLA-based nanofibrous structures have been explored for biomedical purposes, such as wound dressing, drug delivery systems, and tissue engineering scaffolds. This review highlights the recent advances in electrospinning of PLA-based structures for biomedical applications. It also gives a comprehensive discussion about the promising approaches suggested for optimizing the electrospun PLA nanofibrous structures towards the design of specific medical devices with appropriate physical, mechanical and biological functions.

Biofabrication of small diameter tissue-engineered vascular grafts

Current clinical treatment strategies for the bypassing of small diameter (<6 mm) blood vessels in the management of cardiovascular disease frequently fail due to a lack of suitable autologous grafts, as well as infection, thrombosis, and intimal hyperplasia associated with synthetic grafts. The rapid advancement of 3D printing and regenerative medicine technologies enabling the manufacture of biological, tissue-engineered vascular grafts (TEVGs) with the ability to integrate, remodel, and repair in vivo, promises a paradigm shift in cardiovascular disease management. This review comprehensively covers current state-of-the-art biofabrication technologies for the development of biomimetic TEVGs. Various scaffold based additive manufacturing methods used in vascular tissue engineering, including 3D printing, bioprinting, electrospinning and melt electrowriting, are discussed and assessed against the biomechanical and functional requirements of human vasculature, while the efficacy of decellularization protocols currently applied to engineered and native vessels are evaluated. Further, we provide interdisciplinary insight into the outlook of regenerative medicine for the development of vascular grafts, exploring key considerations and perspectives for the successful clinical integration of evolving technologies. It is expected that continued advancements in microscale additive manufacturing, biofabrication, tissue engineering and decellularization will culminate in the development of clinically viable, off-the-shelf TEVGs for small diameter applications in the near future. STATEMENT OF SIGNIFICANCE: Current clinical strategies for the management of cardiovascular disease using small diameter vessel bypassing procedures are inadequate, with up to 75% of synthetic grafts failing within 3 years of implantation. It is this critically important clinical problem that researchers in the field of vascular tissue engineering and regenerative medicine aim to alleviate using biofabrication methods combining additive manufacturing, biomaterials science and advanced cellular biology. While many approaches facilitate the development of bioengineered constructs which mimic the structure and function of native blood vessels, several challenges must still be overcome for clinical translation of the next generation of tissue-engineered 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.

Melt Electrospinning of Polymers: Blends, Nanocomposites, Additives and Applications

Melt electrospinning has been developed in the last decade as an eco-friendly and solvent-free process to fill the gap between the advantages of solution electrospinning and the need of a cost-effective technique for industrial applications. Although the benefits of using melt electrospinning compared to solution electrospinning are impressive, there are still challenges that should be solved. These mainly concern to the improvement of polymer melt processability with reduction of polymer degradation and enhancement of fiber stability; and the achievement of a good control over the fiber size and especially for the production of large scale ultrafine fibers. This review is focused in the last research works discussing the different melt processing techniques, the most significant melt processing parameters, the incorporation of different additives (e.g., viscosity and conductivity modifiers), the development of polymer blends and nanocomposites, the new potential applications and the use of drug-loaded melt electrospun scaffolds for biomedical applications.

Nonwoven Materials Produced by Melt Electrospinning of Polypropylene Filled with Calcium Carbonate

Nowadays, polypropylene-based nonwovens are used in many areas, from filtration to medicine. One of the methods for obtaining such materials is melt electrospinning. In some cases, it is especially interesting to produce composite fibers with a high degree of filling. In this work, the influence of the filling degree of isotactic polypropylene with calcium carbonate on the structure and properties of nonwoven materials obtained by melt electrospinning was studied. It was shown that electrospinning is possible, even at a filler content of 50%, while the average diameter of the fibers increases with the growth in the content of calcium carbonate. The addition of sodium stearate significantly reduces the diameter of the fibers (from 10–65 to 2–10 microns) due to reducing viscosity and increasing the electrical conductivity of the melt. Wide-angle X-ray diffraction analysis and IR spectroscopy reveal that the initial polymer and composites are characterized by the presence of stable α-form crystals, while nonwovens show a predominance of smectic mesophase. The addition of calcium carbonate leads to an increase in the hydrophobicity of the composite films, the addition of sodium stearate results in a decrease of hydrophobicity, while all nonwovens demonstrate superhydrophobic properties.

Pilot-scale production of polylactic acid nanofibers by melt electrospinning

Melt electrospinning has been used to manufacture fibers with diameters in the low micrometer range, but the production of submicrometer fibers has proven more challenging. In this study, we investigated the feasibility of fabricating polylactic acid nanofibers using polymer grades with the increasing melt flow rates (15–85 g/10 min at 210°C) by melt electrospinning with a 600-nozzle pilot-scale device featuring an integrated climate control system realized as a glass chamber around the spinneret. Previous experiments using this device without appropriate climate control produced fibers exceeding 1 µm in diameter because the drawing of fibers was inhibited by the rapid cooling of the polymer melt. The integrated glass chamber created a temperature gradient exceeding the glass transition temperature of the polymer, which enhanced the drawing of fibers below the spinneret. An average fiber diameter of 810 nm was achieved using Ingeo Biopolymer 6252, and the finest individual fiber (420 nm in diameter) was produced at a spin pump speed of 5 rpm and a spinneret set temperature of 230°C. We have therefore demonstrated the innovative performance of our pilot-scale melt-electrospinning device, which bridges the gap between laboratory-scale and pilot-scale manufacturing and achieves fiber diameters comparable to those produced by conventional solution electrospinning.

Biobased Dyes as Conductive Additives to Reduce the Diameter of Polylactic Acid Fibers during Melt Electrospinning

Electrospinning is widely used for the manufacture of fibers in the low-micrometer to nanometer range, allowing the fabrication of flexible materials with a high surface area. A distinction is made between solution and melt electrospinning. The former produces thinner fibers but requires hazardous solvents; whereas the latter is more environmentally sustainable because solvents are not required. However, the viscous melt requires high process temperatures and its low conductivity leads to thicker fibers. Here, we describe the first use of the biobased dyes alizarin; hematoxylin and quercetin as conductive additives to reduce the diameter of polylactic acid (PLA) fibers produced by melt electrospinning; combined with a biobased plasticizer to reduce the melt viscosity. The formation of a Taylor cone followed by continuous fiber deposition was observed for all PLA compounds; reducing the fiber diameter by up to 77% compared to pure PLA. The smallest average fiber diameter of 16.04 µm was achieved by adding 2% (w/w) hematoxylin. Comparative analysis revealed that the melt-electrospun fibers had a low degree of crystallinity compared to drawn filament controls—resembling partially oriented filaments. Our results form the basis of an economical and environmentally friendly process that could ultimately, provide an alternative to industrial solution electrospinning

Electrospun Fibrous Scaffolds for Small-Diameter Blood Vessels: A Review

Small-diameter blood vessels (SDBVs) are still a challenging task to prepare due to the occurrence of thrombosis formation, intimal hyperplasia, and aneurysmal dilation. Electrospinning technique, as a promising tissue engineering approach, can fabricate polymer fibrous scaffolds that satisfy requirements on the construction of extracellular matrix (ECM) of native blood vessel and promote the adhesion, proliferation, and growth of cells. In this review, we summarize the polymers that are deployed for the fabrication of SDBVs and classify them into three categories, synthetic polymers, natural polymers, and hybrid polymers. Furthermore, the biomechanical properties and the biological activities of the electrospun SBVs including anti-thrombogenic ability and cell response are discussed. Polymer blends seem to be a strategic way to fabricate SDBVs because it combines both suitable biomechanical properties coming from synthetic polymers and favorable sites to cell attachment coming from natural polymers.

Melt electrospinning vs. solution electrospinning: A comparative study of drug-loaded poly (ε-caprolactone) fibres

Curcumin-loaded poly (ε-caprolactone) (PCL) fibres prepared by melt and solution electrospinning methods were both fabricated to investigate their difference in characterization and drug release behaviour. The increasing curcumin content did not influence the morphologies of melt electrospun fibre, but enhanced the range of diameter distribution of solution electrospun fibre owing to the curcumin aggregates in the spinning solution which disturbed the stability of jet. Moreover, a large amount of curcumin with amorphous state could be loaded in the melt electrospun fibre. Whereas the limited solubility of curcumin in the solvent led to the drug aggregates dispersing within the solution electrospun fibre. In addition, the melt electrospun fibres had low drug release rate without burst release on the profiles due to the high crystallinity in the fibre, but high drug release rate and burst release occurred on the release profiles of the solution electrospun fibres because of their low crystallinity, porous structure and roughness surface.

Polymer Bioprocessing to Fabricate 3D Scaffolds for Tissue Engineering

Traditional methods for polymer processing involve the use of hazardous organic solvents which may compromise the biological function of scaffolds in tissue engineering. Indeed, the toxic effect of them on biological microenvironment has a tremendous impact on cell fate so altering the main activities involved in in vitro tissue formation. To date, extensive researches focus on seeking newer methods for bio-safely processing polymeric biomaterials to be implanted in the human body. Here, we aim at over viewing two approaches based on solvent free or green solvent based processes in order to identify alternative solutions to fabricate bio-inspired scaffolds to be successfully used in regenerative and degenerative medicine.

Micro/nanoscale electrohydrodynamic printing: from 2D to 3D

Electrohydrodynamic printing (EHDP), based on the electrohydrodynamically induced flow of materials, enables the production of micro/nanoscale fibers or droplets and has recently attracted extensive interest to fabricate user-specific patterns in a controlled and high-efficiency manner. However, most of the existing EHDP techniques can only print two-dimensional (2D) micropatterns which cannot meet the increasing demands for the direct fabrication of three-dimensional (3D) microdevices. The integration of EHDP techniques with the layer-by-layer stacking principle of additive manufacturing has emerged as a promising solution to this limitation. Here we present a state-of-the-art review on the translation of 2D EHDP technique into a viable micro/nanoscale 3D printing strategy. The working principle, essential components as well as critical process parameters for EHDP are discussed. We highlight recent explorations on both solution-based and melt-based 3D EHDP techniques in cone-jet and microdripping modes for the fabrication of multimaterial structures, microelectronics and biological constructs. Finally, we discuss the major challenges as well as possible solutions with regard to translating the 3D EHDP process into a real micro/nanoscale additive manufacturing strategy for the freeform fabrication of 3D structures.

Electrospinning thermoplastic polyurethane/graphene oxide scaffolds for small diameter vascular graft applications

Fabrication of small diameter vascular grafts plays an important role in vascular tissue engineering. In this study, thermoplastic polyurethane (TPU)/graphene oxide (GO) scaffolds were fabricated via electrospinning at different GO contents as potential candidates for small diameter vascular grafts. In terms of mechanical and surface properties, the tensile strength, Young's modulus, and hydrophilicity of the scaffolds increased with an increase of GO content while plasma treatment dramatically improved the scaffold hydrophilicity. Mouse fibroblast (3T3) and human umbilical vein endothelial cells (HUVECs) were cultured on the scaffolds separately to study their biocompatibility and potential to be used as vascular grafts. It was found that cell viability for both types of cells, fibroblast proliferation, and HUVEC attachment were the highest at a 0.5wt.% GO loading whereas oxygen plasma treatment also enhanced HUVEC viability and attachment significantly. In addition, the suture retention strength and burst pressure of tubular TPU/GO scaffolds containing 0.5wt.% GO were found to meet the requirements of human blood vessels, and endothelial cells were able to attach to the inner surface of the tubular scaffolds. Platelet adhesion tests using mice blood indicated that vascular scaffolds containing 0.5% GO had low platelet adhesion and activation. Therefore, the electrospun TPU/GO tubular scaffolds have the potential to be used in vascular tissue engineering.