Solvent Retention in Electrospun Fibers Affects Scaffold Mechanical Properties

Electrospinning is a robust material fabrication method allowing for fine control of mechanical, chemical, and functional properties in scaffold manufacturing. Electrospun fiber scaffolds have gained prominence for their potential in a variety of applications such as tissue engineering and textile manufacturing, yet none have assessed the impact of solvent retention in fibers on the scaffold’s mechanical properties. In this study, we hypothesized that retained electrospinning solvent acts as a plasticizer, and gradual solvent evaporation, by storing fibers in ambient air, will cause significant increases in electrospun fiber scaffold brittleness and stiffness, and a significant decrease in scaffold toughness. Thermogravimetric analysis indicated solvent retention in PGA, PLCL, and PET fibers, and not in PU and PCL fibers. Differential scanning calorimetry revealed that polymers that were electrospun below their glass transition temperature (Tg) retained solvent and polymers electrospun above Tg did not. Young’s moduli increased and yield strain decreased for solventretaining PGA, PLCL, and PET fiber scaffolds as solvent evaporated from the scaffolds over a period of 14 days. Toughness and failure strain decreased for PGA and PET scaffolds as solvent evaporated. No significant differences were observed in the mechanical properties of PU and PCL scaffolds that did not retain solvent. These observations highlight the need to consider solvent retention following electrospinning and its potential effects on scaffold mechanical properties.

Fabrication and Bioapplications of Magnetically Modified Chitosan-based Electrospun Nanofibers

The fabrication of magnetically modified electrospun nanocomposite fibers based on a naturally-derived biocompatible and biodegradable polysaccharide chitosan (CS) and the hydrophilic and biocompatible poly(vinylpyrrolidone) (PVP) is reported herein. The anchoring of magnetic nanoparticles (MNPs) onto the surfaces of the electrospun PVP/CS fibers was carried out by a post-magnetization process based on chemical coprecipitation, via immersing the produced fibrous mats in an aqueous solution containing Fe(II) and Fe(III) salts at appropriate molar ratios, followed by the addition of a weak base to yield MNPs. Electron microscopy revealed the presence of continuous micron and submicron fibers surface-decorated with MNPs. The magnetically modified PVP/CS fibers exhibited superparamagnetic behavior at ambient temperature. The magnetic fibrous nanocomposite carrier was employed for the immobilization of Saccharomyces cerevisiae cells and their use for sucrose hydrolysis, and Candida rugosa lipase and its use for artificial substrate hydrolysis.

Fabrication of radially aligned electrospun nanofibers in a three-dimensional conical shape

This paper reports on the rapid fabrication of radially-aligned, three-dimensional conical structures by electrospinning. Three different polymers, Polyvinylpyrrolidone, Polystyrene and Polyacrylonitrile were used to electrospin the cones. These cone structures are spreading out from a vertical conductive pillar, which can be arbitrarily placed on specific part of the collector. The lower part of the cone is clearly defined on the collector, and the cone has a relatively uniform radius around the pillar. The cones are constituted of fibers that are radially aligned towards the top of the pillar, but there is no apex and the fibers fall flat on the top of the pillar surface. A parametric study has been performed to investigate the effects of the pillar morphology (height and thickness) and the electrospinning parameters (applied voltage and working distance) on the overall shape and size of the cone structure, as well as the fiber alignment. The pillar morphology influences directly the cone diameter and height. The electrospinning parameters have little effect on the cone structure. The formation mechanism has been identified to be related to the shape of the electric field, which has been systematically simulated to understand the effect of the electric field lines on the final dimensions of the cone structure.

Electrospun polystyrene/Aliquat 336 for preconcentration and determination of thiocyanate in flow analysis

A new extracting polymer wool was prepared from polystyrene (PS) and the commercial extractant Aliquat 336 by electrospinning and its potential as a packing material for an online preconcentration column in an automated flow injection system was investigated for the determination of thiocyanate (SCN−). The formation of the wool fibres was confirmed by scanning electron microscopy (SEM). The polymer wool was inserted into a glass tube to prepare a column. SCN− solutions of different volumes (2-10 mL) were passed through the fibre-packed column where SCN− was extracted by the fibres. The columnwas then eluted with a small volume of 1MNaNO3 solution. The eluatewas mixed with an iron(III) solution and the resulting coloured complex (FeSCN2+) was detected colorimetrically. The system successfully achieved 21-fold preconcentration of SCN−. A linear calibration curve was obtained in the range from 0.02 to 1.0 mg L−1 SCN− with a sampling rate of 9 h−1. To the authors’ best knowledge this is the first time electrospun fibres containing a liquid extractant have been used for preconcentration in a flow analysis system.

Commercializing Electrospun Scaffolds For Pluripotent Stem Cell-Based Tissue Engineering Applications

Tissue engineering, the process of combining bioactive scaffolds often with cells to produce replacements for damaged organs, represents an enormous market opportunity. This review critically evaluates the commercialization potential of electrospun scaffolds for applications in stem cell biology, including tissue engineering. First, it provides an overview of pluripotent stem cells (PSCs) and their defining properties, pluripotency and the ability to self-renew. These cells serve as an important tool for engineering tissues, including for clinical applications. Next, we review the technique of electrospinning and its promise for fabricating cell culture substrates and scaffolds for directing tissue formation from stem cells and compare these scaffolds to existing technologies, such as hydrogels. We address the associated market for electrospun scaffolds for PSCs and its potential for growth along with highlighting the importance of 3D cell culture substrates for PSCs by analyzing the net capital invested in this market and the associated growth rate. This review finishes by detailing the current state of commercializing electrospun scaffolds along with pathways for translating these scaffolds from research laboratories into successful start-up companies and the associated challenges with this process.

A review of electrospinning manipulation techniques to direct fiber deposition and maximize pore size

Electrospinning has been widely accepted for several decades by the tissue engineering and regenerative medicine community as a technique for nanofiber production. Owing to the inherent flexibility of the electrospinning process, a number of techniques can be easily implemented to control fiber deposition (i.e. electric/ magnetic field manipulation, use of alternating current, or air-based fiber focusing) and/or porosity (i.e. air impedance, sacrificial porogen/sacrificial fiber incorporation, cryo-electrospinning, or alternative techniques). The purpose of this review is to highlight some of the recent work using these techniques to create electrospun scaffolds appropriate for mimicking the structure of the native extracellular matrix, and to enhance the applicability of advanced electrospinning techniques in the field of tissue engineering.

Using Electrospun Scaffolds to Promote Macrophage Phenotypic Modulation and Support Wound Healing

The development of pressure ulcers in spinal cord injury patients is extremely common, often requiring extensive surgical procedures. Macrophages (MACs) play a crucial role in the innate immune system, contributing to wound healing and overall regeneration. MACs have been found to possess the potential to be activated by external factors from their M0 inactive state to an M1 proinflammatory or M2 regenerative state. This study conducted a comprehensive evaluation of MAC phenotype in response to electrospun scaffolds of varying material fiber/pore diameter, fiber stiffness, and +/− inclusion of platelet-rich plasma (PRP). Generally, itwas found that the addition of PRP resulted in decreased pore size, where 5 silk fibroin (SF) had the stiffest fibers. Furthermore, PRP scaffolds demonstrated an increased production of VEGF and chemotaxis. The polycaprolactone (PCL) and SF scaffolds had the largest cell infiltration and proliferation. Overall, it was found that 5% SF had both ideal fiber and pore structure, allowing for cell infiltration further enhanced by the presence of PRP. Additionally, this scaffold led to a reasonable production of VEGF while still allowing fibroblast proliferation to occur. These results suggest that such a scaffold could provide an off-the-shelf product capable of modifying the local MAC response.

Electrospun fibers/branched-clusters as building units for tissue engineering

Although electrospun templates are effective at mimicking the extracellular matrix (ECM) of native tissue due to the tailorability of parameters such as fiber diameter, polymer composition, and drug loading, these templates are often limited with regards to cell infiltration and the tailorability of the microenvironments within the structures. Thus, there remains a need for a flexible threedimensional template system which could be combined with cell suspensions to promote three-dimensional tissue regeneration, and ultimately allow cells to freely reorganize and modify their microenvironment. In this study, a mincing process was designed and optimized to create mixtures of electrospun fibers/branched-clusters for use as fundamental tissue engineering building units. These fiber/branched-cluster elements were characterized with regards to fiber and branch lengths, and a method was optimized to combine them with normal human dermal fibroblasts (nHDFs) in culture to create interconnected template constructs. Sectioning and imaging of these constructs revealed cell/fiber integration as well as even cell distribution throughout the construct interior. These fiber/branched-cluster elements represent an innovative flexible tissue regeneration template system.

Correlation between electrospinning parameters and magnetic properties of BiFeO3 nanofibers

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Decellularized extracellular matrices for tissue engineering applications

Decellularization removes cellular antigens while preserving the ultrastructure and composition of extracellular matrix (ECM). Decellularized ECM (DECM) scaffolds have been widely used in various tissue engineering applications with varying levels of success. The mechanical, architectural and bioactive properties of a DECM scaffold depend largely on the method of decellularization and dictate its clinical efficacy. This article highlights the advantages and challenges associated with the clinical use of DECM scaffolds. Poor mechanical strength is a significant disadvantage of some DECM scaffolds in the repair of load-bearing tissues as well as critical-size defects, where long-term mechanical support is required for the regenerating tissue. Combining DECM scaffolds with synthetic biocompatible polymers could provide a useful strategy to circumvent the issues of poor mechanical stability. This article reviews studies that have combined DECM scaffolds from various tissues with synthetic polymers to create hybrid scaffolds using electrospinning. These hybrid scaffolds provide a mechanical backbone while retaining the bioactive properties of DECM, thus offering a significant advantage for tissue engineering and regenerative medicine applications.