Electrospinning of Ultrafine Conducting Polymer Composite Nanofibers with Diameter Less than 70 nm as High Sensitive Gas Sensor

Polyvinyl alcohol/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PVA/PEDOT:PSS) composite ultrafine fibers were successfully fabricated by high pressure airflow assisted electrospinning. The electrical properties of PVA/PEDOT:PSS nanofibers with different diameters were characterized. The average diameter of the nanofibers can be down to 68 nm. Due to its large specific surface area, ammonia sensing of the ultrafine nanofibers is more sensitive than the traditional electrospun fibers (average fiber diameter of 263 nm). The ammonia sensing properties of the samples were tested by impedance analysis. The results show that ultrafine PVA/PEDOT:PSS nanofibers are more suitable for detecting low concentrations of ammonia with higher sensitivity.

Mediating human stem cell behaviour via defined fibrous architectures by melt electrospinning writing

The architecture within which cells reside is key to mediating their specific functions within the body. In this study, we use melt electrospinning writing (MEW) to fabricate cell micro-environments with various fibrous architectures to study their effect on human stem cell behaviour. We designed, built and optimised a MEW apparatus and used it to fabricate four different platform designs of 10.4 ± 2 μm fibre diameter, with angles between fibres on adjacent layers of 90°, 45°, 10° and R (random). Mechanical characterisation was conducted via tensile testing, and human skeletal stem cells (hSSCs) were seeded to scaffolds to study the effect of architecture on cell morphology and mechanosensing (nuclear YAP). Cell morphology was significantly altered between groups, with cells on 90° scaffolds having a lower aspect ratio, greater spreading, greater cytoskeletal tension and nuclear YAP expression. Long term cell culture studies were then conducted to determine the differentiation potential of scaffolds in terms of alkaline phosphatase activity, collagen and mineral production. Across these studies, an increased cell spreading in 3-dimensions is seen with decreasing alignment of architecture correlated with enhanced osteogenesis. This study therefore highlights the critical role of fibrous architecture in regulating stem cell behaviour with implications for tissue engineering and disease progression.

STATEMENT OF SIGNIFICANCE

This is the first study which has investigated the effect of controlled fibrous architectures fabricated via melt electrospinning writing on stem cell behaviour and differentiation. After optimising the fabrication process and characterising scaffolds via SEM and mechanical testing, skeletal stem cells were seeded onto fibrous scaffolds with various micro-architectures. These architectures drove cell shape changes resulting in architecture dependent nuclear YAP localisation, suggesting altered mechanosensing at early time points. In agreement with these early markers, long term cell culture studies revealed for the first time that a 90° fibrous architecture is optimal for the osteogenic differentiation of skeletal stem cells.

Dimension-Based Design of Melt Electrowritten Scaffolds

The electrohydrodynamic stabilization of direct-written fluid jets is explored to design and manufacture tissue engineering scaffolds based on their desired fiber dimensions. It is demonstrated that melt electrowriting can fabricate a full spectrum of various fibers with discrete diameters (2-50 µm) using a single nozzle. This change in fiber diameter is digitally controlled by combining the mass flow rate to the nozzle with collector speed variations without changing the applied voltage. The greatest spectrum of fiber diameters was achieved by the simultaneous alteration of those parameters during printing. The highest placement accuracy could be achieved when maintaining the collector speed slightly above the critical translation speed. This permits the fabrication of medical-grade poly(ε-caprolactone) into complex multimodal and multiphasic scaffolds, using a single nozzle in a single print. This ability to control fiber diameter during printing opens new design opportunities for accurate scaffold fabrication for biomedical applications.

Melt Electrospinning Writing of Highly Ordered Large Volume Scaffold Architectures

The additive manufacturing of highly ordered, micrometer-scale scaffolds is at the forefront of tissue engineering and regenerative medicine research. The fabrication of scaffolds for the regeneration of larger tissue volumes, in particular, remains a major challenge. A technology at the convergence of additive manufacturing and electrospinning-melt electrospinning writing (MEW)-is also limited in thickness/volume due to the accumulation of excess charge from the deposited material repelling and hence, distorting scaffold architectures. The underlying physical principles are studied that constrain MEW of thick, large volume scaffolds. Through computational modeling, numerical values variable working distances are established respectively, which maintain the electrostatic force at a constant level during the printing process. Based on the computational simulations, three voltage profiles are applied to determine the maximum height (exceeding 7 mm) of a highly ordered large volume scaffold. These thick MEW scaffolds have fully interconnected pores and allow cells to migrate and proliferate. To the best of the authors knowledge, this is the first study to report that z-axis adjustment and increasing the voltage during the MEW process allows for the fabrication of high-volume scaffolds with uniform morphologies and fiber diameters.

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.

Development of Endothelial Cell Networks in 3D Tissues by Combination of Melt Electrospinning Writing with Cell-Accumulation Technology

A remaining challenge in tissue engineering approaches is the in vitro vascularization of engineered constructs or tissues. Current approaches in engineered vascularized constructs are often limited in the control of initial vascular network geometry, which is crucial to ensure full functionality of these constructs with regard to cell survival, metabolic activity, and potential differentiation ability. Herein, the combination of 3D-printed poly-ε-caprolactone scaffolds via melt electrospinning writing with the cell-accumulation technique to enable the formation and control of capillary-like network structures is reported. The cell-accumulation technique is already proven itself to be a powerful tool in obtaining thick (50 µm) tissues and its main advantage is the rapid production of tissues and its ease of performance. However, the applied combination yields tissue thicknesses that are doubled, which is of outstanding importance for an improved handling of the scaffolds and the generation of clinically relevant sample volumes. Moreover, a correlation of increasing vascular endothelial growth factor secretion to hypoxic conditions with increasing pore sizes and an assessment of the formation of neovascular like structures are included.

3D Bioprinting for Cartilage and Osteochondral Tissue Engineering

Significant progress has been made in the field of cartilage and bone tissue engineering over the last two decades. As a result, there is real promise that strategies to regenerate rather than replace damaged or diseased bones and joints will one day reach the clinic however, a number of major challenges must still be addressed before this becomes a reality. These include vascularization in the context of large bone defect repair, engineering complex gradients for bone-soft tissue interface regeneration and recapitulating the stratified zonal architecture present in many adult tissues such as articular cartilage. Tissue engineered constructs typically lack such spatial complexity in cell types and tissue organization, which may explain their relatively limited success to date. This has led to increased interest in bioprinting technologies in the field of musculoskeletal tissue engineering. The additive, layer by layer nature of such biofabrication strategies makes it possible to generate zonal distributions of cells, matrix and bioactive cues in 3D. The adoption of biofabrication technology in musculoskeletal tissue engineering may therefore make it possible to produce the next generation of biological implants capable of treating a range of conditions. Here, advances in bioprinting for cartilage and osteochondral tissue engineering are reviewed.

Recent advances in electrospun nanofibers for wound healing

Electrospun nanofibers represent a novel class of materials that show great potential in many biomedical applications including biosensing, regenerative medicine, tissue engineering, drug delivery and wound healing. In this work, we review recent advances in electrospun nanofibers for wound healing. This article begins with a brief introduction on the wound, and then discusses the unique features of electrospun nanofibers critical for wound healing. It further highlights recent studies that have used electrospun nanofibers for wound healing applications and devices, including sutures, multifunctional dressings, dermal substitutes, engineered epidermis and full-thickness skin regeneration. Finally, we finish with conclusions and future perspective in this field.

Additive manufacturing with polypropylene microfibers

The additive manufacturing of small diameter polypropylene microfibers is described, achieved using a technique termed melt electrospinning writing. Sequential fiber layering, which is important for accurate three-dimensional fabrication, was achieved with the smallest fiber diameter of 16.4±0.2μm obtained. The collector speed, temperature and melt flow rate to the nozzle were optimized for quality and minimal fiber pulsing. Of particular importance to the success of this method is appropriate heating of the collector plate, so that the electrostatically drawn filament adheres during the direct-writing process. By demonstrating the direct-writing of polypropylene, new applications exploiting the favorable mechanical, stability and biocompatible properties of this polymer are envisaged.