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Two-photon lithography (2 PL) has been proposed as an additive manufacturing method to fabricate structures at the microscale, including curing protein-based bioinks. In this study, we explored the use of 2 PL for biomedical applications to photo-cross-link silk fibroin solution into a solid hydrogel with directly tuneable physico-chemical properties. 2 PL allowed control of the cross-linking degree and the porosity of the resulting hydrogel at the micrometric scale by regulating the intensity of the IR laser exposure, tested between 800 and 2400 mW, during the 3D printing process. The regulation of the cross-linking degree in this way allowed for the production of hydrogels with significantly different degradation rates, ranging from 0.5 to 2 h during accelerated enzymatic degradation assay, while their β-sheet content, assessed by Fourier-transform infra-red spectroscopy (FTIR), did not show significant changes. The hydrogels Young’s modulus, assessed by quantitative microelastography, could also be controlled within a 9.6 to 47.2 kPa range and was found to increase with the rate of cross-linking. When human dermal fibroblasts were included in the silk fibroin solution for bioprinting testing at different laser exposures, cell viability was assessed over 95% during 21 days of in vitro culture. Moreover, cells showed a higher proliferation rate in less cross-linked hydrogels and were able to align and migrate to areas of increased stiffness printed in gradient hydrogels. Overall, this versatile additive manufacturing method represents an advancement of silk fibroin biomaterials for soft tissue engineering, enabling control of the microstructure and degradation rate of the products and the proliferation of the engrafted cells.

Micro/nano electrodes employing nanotubes has attracted paramount attention in recent years due to their inherent superior mechanical and structural properties. Electrical interfaces with different geometries and sizes have been developed as electrodes for measuring action potentials and investigating neural information processing in neural networks. In this work, we investigated the possibility of using TiO2 nanotube arrays that were grown using electrochemical anodization technique, as a micro/nano electrode for neural interfacing. The morphology of fabricated nanotube arrays were found to be significantly affected by the applied voltage. Annealing and doping of TiO2 nanotube arrays has been performed to improve the structural and electrical properties of the nanotube arrays. It was found that the annealing and doping with nitrogen improve the electrical conductivity of the nanotube arrays. Moreover, the tube diameter and length can be controlled by changing the applied voltage and that can significantly affect the biocompatibility of the nanotube arrays. It was observed that nitrogen doped nanotubes with morphology consisting of 61nm diameter, 25nm wall thickness and tube length of 2.25μm could be good candidate to be used as electrodes for biological interfacing. This is due to the fact that the nitrogen doped nanotubes with aforementioned morphology possess great properties necessary for effective biological interfacing such as low impedance, high capacitance and good biocompatibility.

Low interface strength is a common challenge in taking full advantage of excellent physical performances of carbon fibre (CF) reinforced polymer composites. Herein, for the first time, we have used amino-functionalized nanoclay as a linkage between CF surface and epoxy matrix, which by a cation exchange process was grafted on the CF surface. Amino-functionalized nanoclay significantly increased surface roughness, coefficient of friction, and BET surface area of CF. The results showed that nanoclay-based modification does not change the tensile strength and Weibull modulus of CF significantly however, both specific and dispersive surface energies, obtained by inverse gas chromatography technique, were increased. A high compatibility of nanoclay-based modified CF (clay@CF) with epoxy resin was also observed by analysing the contact angle between epoxy droplets and fibre surface. Moreover, single fibre fragmentation tests (SFFT) alongside fractographic observations showed that the length of fibre pull-out and the size of cracks between the fibre and matrix were outstandingly reduced in clay@CF in comparison to untreated CF, demonstrating that the stress transfer and interfacial shear strength (IFSS) have been significantly improved.

Preparation of high-value pitch-based carbon fibres (CFs) from mesophase pitch precursor is of great importance towards low-cost CFs. Herein, we developed a method to reduce the cost of CFs precursor through incorporating high loading of coal tar pitch (CTP) into polyacrylonitrile (PAN) polymer solution. The CTP with a loading of 25% and 50% was blended with PAN and their spinnability was examined by electrospinning process. The effect of CTP on thermal stabilization and carbonisation of PAN fibres was investigated by thermal analyses methods. Moreover, electrospun PAN/CTP fibres were carbonised at two different temperatures i.e., 850 &deg, C and 1200 &deg, C and their crystallographic structures of resulting such low-cost PAN/CTP CFs were studied through X-ray diffraction (XRD) and Raman analyses. Compared to pure PAN CFs, the electrical resistivity of PAN/25% CTP CFs significantly decreased by 92%, reaching 1.6 k&Omega, /sq. The overall results showed that PAN precursor containing 25% CTP resulted in balanced properties in terms of spinnability, thermal and structural properties. It is believed that CTP has a great potential to be used as an additive for PAN precursor and will pave the way for cost-reduced and high-performance CFs.

Development of new chemical approaches for preparation of engineered carbon-based fillers is critical for high-performance applications. Herein, an efficient method for covalent functionalization of polyacrylonitrile-based carbon fibre through azo radical addition under mild condition is demonstrated. In this way, isobutyronitrile radicals in situ produced from thermal decomposition of 2,2′-azobisisobutyronitrile (AIBN), were covalently grafted on milled carbon fibre (MCF) surface, assisted by microwave irradiation, as evidenced by FTIR, Raman, and TGA analysis. The grafted isobutyronitriles on MCF surface ( n -MCF) were applied for further MCF amino-functionalization ( a -MCF) via nucleophilic reaction of an amine-rich compound. Then, both pure MCF and a -MCF were incorporated into epoxy matrix; and its curing process and thermo-physical properties were investigated using DSC, rheometry, DMA, TGA, and flexural analysis. The T g and flexural strength of epoxy/ a -MCF composites, compared to epoxy/MCF, increased by ∼3.5% and ∼10.2%, resulting from good adhesion between a -MCF and epoxy matrix which confirmed by SEM observations.

The electrical conductivity of biodegradable polymeric scaffolds has shown promising results in tissue engineering, particularly for electrically excitable tissues such as muscles and nerves. Herein, we demonstrate a novel processing approach to produce electroactive nanofibres. Electrically conducting, robust nanofibres comprising both a biodegradable component using poly(e-caprolactone) (PCL) and a conducting component, polypyrrole (PPy), have been produced by electrospinning and vapour phase polymerization. The PCL/PPy nanofibres were characterised in terms of morphology, electrical conductivity, and dimensional stability. The as-prepared nanofibres were found to be cytocompatible with good electrical conductivity and mechanical properties. It was found that electrical conductivity of the PPy coated PCL nanofibre was 1.9 S/cm, which is much higher than that of PCL mixed with PPy in other studies. Cell viability on the scaffolds were firstly examined by in vitro culturing the L929 fibroblast cells for 24 h, revealing viability of 97.6 ± 2.7 %. Then PC12 cells differentiation observed by neurite outgrowth which occurred after 4 days of culture on the scaffolds. Significantly larger areas of the PPy coated PCL were covered by cells compared to PCL without coating. The obtained results from filament staining suggested the high potentials of the conducting scaffold for use in neural tissue engineering.

Electrically conductive scaffolds are of significant interest in tissue regeneration. However, the chemistry of the existing scaffolds usually lacks the bioactive features for effective interaction with cells. In this study, poly(ε-caprolactone) was electrospun into aligned nanofibers with 0.58 µm average diameter. Electrospinning was followed by polypyrrole coating on the surface of the fibers, which resulted in 48 kΩ/sq surface resistivity. An oxygen plasma treatment was conducted to change the hydrophobic surface of the fiber mats into a hydrophilic substrate. The water contact angle was reduced from 136° to 0°, and this change remained on the surface of the material even after one year. An indirect cytotoxicity test was conducted, which showed cytocompatibility of the fibrous scaffolds. To measure the cell growth on samples, fibroblast cells were cultured on fibers for 7 days. The cell distribution and density were observed and calculated based on confocal images taken of the cell culture experiment. The number of cells on the plasma-treated sample was more than double than that of sample without plasma treatment. The long-lasting hydrophilicity of the plasma treated fibers with conductive coating is the significant contribution of this work for regeneration of electrically excitable tissues.

The demand for wearable electronics has resulted in an increasing interest in the development of functional fibers, with a specific focus upon the development of electrically conductive fibers incorporable into garments. However, the production of thermally conductive fibers for heat dissipation has been largely neglected. Owing to the very rapid development of miniaturized wearable electronics, there is an increasing need for the development of thermally conductive fibers as heat sinks and thermal management processes. In this study, thermally conductive but electrically insulating boron nitride nanopowder (BNNP) fillers are used to effectively enhance the thermal conductivity and mechanical properties of elastomeric polyurethane fibers. Thermal conductivity enhancement of more than 160% is achieved at very low loadings of BNNP (less than 5 wt%) with an improvement in the mechanical properties of the unmodified fiber. These thermally conductive fibers are also incorporated into 3D textile structures as a proof of processability.