Electrospinning as a route to advanced carbon fibre materials for selected low-temperature electrochemical devices: a review

Electrospinning has been proven as a highly versatile fabrication method for producing nano-structured fibres with controllable morphology, of both the fibres themselves and the void structure of the mats. Additionally, it is possible to use heteroatom doped polymers or to include catalytic precursors in the electrospinning solution to control the surface properties of the fibres. These factors make it an ideal method for the production of electrodes and flow media for a variety of electrochemical devices, enabling reduction in mass transport and activation overpotentials and therefore increasing efficiency. Moreover, the use of biomass as a polymer source has recently gained attention for the ability to embed sustainable principles in the materials of electrochemical devices, complementing their ability to allow an increase in the use of renewable electricity via their application. In this review, the historical and recent developments of electrospun materials for application in redox flow batteries, fuel cells, metal air batteries and supercapacitors are thoroughly reviewed, including an overview of the electrospinning process and a guide to best practice. Finally, we provide an outlook for the emerging use of this process in the field of electrochemical energy devices with the hope that the combination of tailored microstructure, surface functionality and computer modelling will herald a new era of bespoke functional materials that can significantly improve the performance of the devices in which they are used

Engineering an in vitro model of the haematopoietic stem cell niche

This project designed and developed a novel in vitro model of the haematopoietic stem cell niche. Components of the endosteal niche and the perivascular niche, essential in the bone marrow haematopoietic stem cell niche microenvironment, were integrated in a single platform using a multiphasic approach that combined melt electrospun written scaffolds with starPEG-heparin hydrogels. Haematopoietic stem cell response was analysed after 3D co-culture with the tissue engineering niches

Design and fabrication of scaffolds via melt electrospinning for applications in tissue engineering

Melt electrospinning is a manufacturing technique that can be adapted into a direct writing process, similar to those based on melt extrusion. The resultant product is a three-dimensional (3D) scaffold with significantly reduced filament resolution compared to melt extrusion direct writing approaches. While the argument for using melt electrospinning in applications such as textiles and membranes is problematic due to scale-up requirements, it has a promising future for tissue and tumour engineering applications, as the scaffolds are cell invasive and provide an environment upon which cells can deposit ECM. This emerging processing technology should prosper with more in-depth research, as early results demonstrate excellent in vitro and in vivo biocompatibility

5.11 Engineering the haematopoietic stem cell niche in vitro

In vitro models recapitulate tissue-specific microenvironments of the human body in an experimental setting to study cell functions and responses in a holistic approach and to develop improved therapeutics. The hematopoietic stem cell (HSC) niche is located in the bone marrow in two main compartments: the endosteal niche, next to the inner face of the bone, and the perivascular niche, next to bone marrow sinusoids. Current in vitro models of the HSC niche introduce elements of only one of these two compartments. Tissue engineering strategies can advance our understanding of the HSC niche and current treatments of blood-related diseases. Herein, we describe a novel multiphasic tissue-engineered construct that incorporates elements of both compartments. To recreate the endosteal niche, primary human osteoblasts are grown on medical grade polycaprolactone scaffolds produced by melt electrospinning under osteogenic conditions to allow the deposition of a dense bone matrix. To recreate the perivascular niche, human umbilical vein endothelial cells and placenta-derived mesenchymal stem cells are embedded in star-shaped polyethylene glycol-heparin-based hydrogels to allow the formation of capillary-like networks. The multiphasic tissue-engineering construct is built by aligning the bone matrix with the capillary-like networks to enable the short-term culture and expansion of CD34 cells. To our knowledge, this is the first in vitro model of the HSC niche that aligns elements of both the endosteal and the perivascular niche in a single culture system

Production of scaffolds using melt electrospinning writing and cell seeding

Melt electrospinning writing (MEW) is a solvent-free fabrication method for making polymer fiber scaffolds with features which include large surface area, high porosity, and controlled deposition of the fibers. These scaffolds are ideal for tissue engineering applications. Here we describe how to produce scaffolds made from poly(ε-caprolactone) using MEW and the seeding of primary human-derived dermal fibroblasts to create cell-scaffold constructs. The same methodology could be used with any number of cell types and MEW scaffold designs.</p

Out-of-Plane 3D-Printed Microfibers Improve the Shear Properties of Hydrogel Composites

One challenge in biofabrication is to fabricate a matrix that is soft enough to elicit optimal cell behavior while possessing the strength required to withstand the mechanical load that the matrix is subjected to once implanted in the body. Here, melt electrowriting (MEW) is used to direct-write poly(ε-caprolactone) fibers "out-of-plane" by design. These out-of-plane fibers are specifically intended to stabilize an existing structure and subsequently improve the shear modulus of hydrogel-fiber composites. The stabilizing fibers (diameter = 13.3 ± 0.3 μm) are sinusoidally direct-written over an existing MEW wall-like structure (330 μm height). The printed constructs are embedded in different hydrogels (5, 10, and 15 wt% polyacrylamide; 65% poly(2-hydroxyethyl methacrylate) (pHEMA)) and a frequency sweep test (0.05-500 rad s-1, 0.01% strain, n = 5) is performed to measure the complex shear modulus. For the rheological measurements, stabilizing fibers are deposited with a radial-architecture prior to embedding to correspond to the direction of the stabilizing fibers with the loading of the rheometer. Stabilizing fibers increase the complex shear modulus irrespective of the percentage of gel or crosslinking density. The capacity of MEW to produce well-defined out-of-plane fibers and the ability to increase the shear properties of fiber-reinforced hydrogel composites are highlighted