Juri Belcari

Nanovascularization of polymer matrix: generation of nanochannels and nanotubes by sacrificial electrospun fibers.

Several methods for creating vascular structures, made of either discrete or interconnected channels have been developed. The currently employed methods enable the formation of channels with diameters in the millimetric and micrometric scale. However, the formation of an interconnected three-dimensional (3D) vasculature by using a rapid and scalable process is a challenge and largely limits the fields of applicability of these innovative materials. Here, we propose the use of electrospun nonwoven mats as sacrificial fibers to easily generate 3D macroscale vascularized composites containing interconnected networks with channels and tubes having submicrometric and nanometric diameters. The novel approach has the potentialities to give rise to a novel generation of composites potentially displaying new and enhanced functionalities thanks to the nanoscale features of the cavities.

Interaction between Polyaramidic Electrospun Nanofibers and Epoxy Resin for Composite Materials Reinforcement

Interaction between poly (m-phenylene isophtalamide) (PMIA) electrospun nanofibers and commercial epoxy resin precursor during the cross-linking process was investigated, in order to use such polyaramidic nanofibers for composite materials reinforcement. Hence nanofibrous PMIA mats were produced via electrospinning technique to be used for the functional modification of the epoxy matrix composite properties. When adding such fibers to an epoxy resin precursor, it was observed a strong influence on the kinetics of its curing process. The final results, however, demonstrates that boosting the reaction condition (raising the temperature and the reaction time) the curing is pushed to completion, indicating that the cross-linking process of the resin is just delayed and not completely hampered. It will be therefore necessary to rethink the composite cure cycle when PMIA nanofibers are added to the composite material, in order to attain significant improvement of the final composite performance.

Poly-m-aramid nanofiber mats: Production for application as structural modifiers in CFRP laminates

Poly(m-phenylene isophtalamide) electrospun nanofibrous membranes were produced to be used as structural reinforcements for carbon fiber reinforced composites production. In order for the polymer to be electrospun, it needs however to be fully solubilized, so the addition of some salts is required to help disrupt the tight macromolecular packing based on intra- and inter-molecular hydrogen bonding. Such salts may also contribute to the electrospinnability of the overall solution, since the provide it with a higher conductivity, whatever the solvent might be. The salt haobwever stays in the final nanofibrous mat. The membranes containing the salt are also observed to be highly hygroscopic, with a water content up to 26%, in the presence of 20%wt LiCl in the nanofibrous mat. When those membranes were interleaved among prepregs to produce a laminates, the obtained composite displayed thermal properties comparable to those of a reference nanofiber-free composite, though the former showed also easier delaminat...

Electrospinning: A versatile technique for energy storage and sensor applications

The possibility to produce materials for energy storage and piezoelectric sensor applications through the electrospinning technique is here investigated. Electrospun lithium-ion battery separators, piezoelectric sensors are characterized and tested in order to exhibit the outstanding properties of such nanostructured materials which can be successfully implemented on the market.

High-resolution x-ray tomographic morphological characterisation of electrospun nanofibrous bundles for tendon and ligament regeneration and replacement: X-RAY TOMOGRAPHIC MORPHOLOGICAL CHARACTERISATION OF ELECTROSPUN NANOFIBROUS BUNDLES

Repair of ligaments and tendons requires scaffolds mimicking the spatial organisation of collagen in the natural tissue. Electrospinning is a promising technique to produce nanofibres of both resorbable and biostable polymers with desired structural and morphological features. The aim of this study was to perform high‐resolution x‐ray tomography (XCT) scans of bundles of Nylon6.6, pure PLLA and PLLA‐Collagen blends, where the nanofibres were meant to have a predominant direction. Characterisation was carried out via a dedicated methodology to firmly hold the specimen during the scan and a workflow to quantify the directionality of the nanofibres in the bundle. XCT scans with 0.4 and 1.0 μm voxel size were successfully collected for all bundle compositions. Better image quality was achieved for those bundles formed by thicker nanofibres (i.e. 0.59 μm for pure PLLA), whereas partial volume effect was more pronounced for thinner nanofibres (i.e. 0.26 μm for Nylon6.6). As expected, the nanofibres had a predominant orientation along the axis of the bundles (more than 20% of the nanofibres within 3° and more than 60% within 18° from the bundle axis), with a Gaussian‐like dispersion in the other directions. The directionality assessment was validated by comparison against a similar analysis performed on SEM images: the XCT analysis overestimated the amount of nanofibres very close to the bundle axis, especially for the materials with thinnest nanofibres, but adequately identified the amount of nanofibres within 12°.

A variable stiffness joint with electrospun P(VDF-TrFE-CTFE) variable stiffness springs

This letter presents a novel rotational variable stiffness joint that relies on one motor and a set of variable stiffness springs. The variable stiffness springs are leaf springs with a layered design, i.e., an electro-active layer of electrospun aligned nanofibers of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) [P(VDF-TrFE-CTFE)] surrounded by two electrodes of aluminum and held together by inactive material. To achieve a variable stiffness, different voltages and, therefore, different electric fields, are applied to the springs. The variable stiffness springs are electromechanically analyzed to highlight the voltage-deflection and force-deflection characteristics. Finally, the springs are used in the design of a proof-of-concept variable stiffness joint prototype. Experimental results on the variable stiffness joint confirm the viability of the proposed solution.

Vibration energy harvesting using electrospun nanofibrous PVdF-TrFE

This work is focused on the study of the electromechanical response of fibrous materials produced by means of electrospinning. Such structures are considered an emerging technology for energy harvesting. In particular, PVdF-TrFe co-polymer nanofibers were electrospun and subjected to mechanical vibrations produced by an eccentric shaft. Experimental results showed that the specific electric response to mechanical vibrations, in the frequency range from 15 Hz to 37 Hz, is very high. Moreover, frequency response well follows the vibration source. Cost reduction and a simpler manufacturing technique represent other advantages of the electrospinning process compared to conventional production technologies.

Electrospun PVdF with enhanced piezoelectric behavior

This paper deals with electromechanical response of piezoelectric nanofibrous materials based on PVdF-TrFe co-polymer obtained by means of electrospinning. This technique, providing electrical poling and mechanical stretching during material processing, should increase the beta crystalline phase and thus piezoelectric effect. Two fiber patterns were analyzed, i.e. aligned and random. Experimental results showed that the electric response to mechanical vibrations, in the frequency range from 30 Hz to 200 Hz, is significantly larger for samples with aligned fiber pattern with respect to both commercial films and random fiber specimens. These latters, in fact, show lower beta phase with respect to the aligned-fiber samples.