Innovative ceramic-matrix composite substrates with tunable electrical conductivity for high-power applications.

A wide band gap semiconductor power module can operate at higher voltages as compared with its traditional silicon counterpart. However, its insulating system undergoes stronger electric fields at the triple point between the ceramic substrate, the metallic tracks and the encapsulating polymer, which can dramatically reduce its lifespan. Here we report an original concept based on the local modification of the substrate properties to mitigate such electrical stress. Numerical simulations revealed its potential to reduce this constraint by up to 50%. This concept was realized by developing, through a practical approach, a novel substrate made of an AlN-based ceramic (material A) integrating a nanocomposite volume endowed with controlled properties and geometry. This approach implies first the spark plasma sintering of the AlN powder with additives (Y2O3, CaF2) to endow the material A with a very low electrical conductivity (σ) and high thermal conductivity (k). Graphene nanoplatelets (GNP) were incorporated within this material to fabricate a nanocomposite with a controlled σ anisotropy that otherwise reached a striking ratio of 106 at 20°C for 1.25 vol% GNP. Our approach secondly aimed at developing an effective process allowing to integrate this nanocomposite into the material A with a very high degree of reproducibility. It finally consisted in establishing the electrical contacts on the achieved substrate and encapsulating it for breakdown testing. The novel substrate enabled a mitigation of the electrical constraint by diminishing its intensity and shifting it from the triple point to a less constrained area. It already brought an improvement in breakdown voltage (VB) by 15% as compared to the traditional substrate, and revealed the potential for achieving higher VB as well. This work lays the foundation for the development of novel multifunctional ceramic-matrix composite substrates sought for power electronics as well as for other potential applications.

Skin electroporation for transdermal drug delivery: Electrical measurements, numerical model and molecule delivery.

Skin electroporation for drug delivery involves the application of Pulsed Electric Fields (PEFs) on the skin to disrupt its barrier function in a temporary and non-invasive manner, increasing the uptake of drugs. It represents a potential alternative to delivery methods that are invasive (e.g. injections) or limited. We have developed a drug delivery system comprising nanocomposite hydrogels which act as a reservoir for the drug and an electrode for applying electric pulses on the skin. In this study, we employed a multi-scale approach to investigate the drug delivery system on a mouse skin model, through electrical measurements, numerical modeling and fluorescence microscopy. The Electrical properties indicated a highly non-linear skin conductivity behavior and were used to fine-tune the simulations and study skin recovery after electroporation. Simulation of electric field distribution in the skin showed amplitudes in the range of reversible tissue electroporation (400-1200 V/cm), for 300 V PEF. Fluorescence microscopy revealed increased uptake of fluorescent molecules compared to the non-pulsed control. We reported two reversible electroporation domains for our configuration: (1) at 100 V PEF the first local transport regions appear in the extracellular lipids of the stratum corneum, demonstrated by a rapid increase in the skin's conductivity and an increased uptake of lucifer yellow, a small hydrophilic fluorophore and (2) at 300 V PEF, the first permeabilization of nucleated cells occurred, evidenced by the increased fluorescence of propidium iodide, a membrane-impermeable, DNA intercalating agent.

Hydrogels with electrically conductive nanomaterials for biomedical applications.

Hydrogels, soft 3D materials of cross-linked hydrophilic polymer chains with a high water content, have found numerous applications in biomedicine because of their similarity to native tissue, biocompatibility and tuneable properties. In general, hydrogels are poor conductors of electric current, due to the insulating nature of commonly-used hydrophilic polymer chains. A number of biomedical applications require or benefit from an increased electrical conductivity. These include hydrogels used as scaffolds for tissue engineering of electroactive cells, as strain-sensitive sensors and as platforms for controlled drug delivery. The incorporation of conductive nanomaterials in hydrogels results in nanocomposite materials which combine electrical conductivity with the soft nature, flexibility and high water content of hydrogels. Here, we review the state of the art of such materials, describing the theories of current conduction in nanocomposite hydrogels, outlining their limitations and highlighting methods for improving their electrical conductivity.

Nonlinear Electrical Conduction in Polymer Composites for Field Grading in High-Voltage Applications: A Review.

Applications of polymeric materials in electrical engineering increasingly require improvements in operating voltages, performance, reliability, and size reduction. However, the resulting increase on the electric field in electrical systems can prevent achieving these goals. Polymer composites, functionalized with conductive or semiconductive particles, can allow us to reduce the electric field, thus grading the field within the system. In this paper, a comprehensive review of field-grading materials, their properties, and recent developments and applications is provided to realize high-performance high-voltage engineering applications.

Heart rate variability biofeedback intero-nociceptive emotion exposure therapy for adverse childhood experiences.

Background: Psychiatric patients with adverse childhood experiences (ACE) tend to have dysfunctions in the interoceptive part of their emotional experience. The integration of interoceptive emotional activity in the insular and cingulate cortices is linked to the regulation of sympathovagal balance. This makes heart rate variability (HRV) an ideal measure for providing feedback on emotion regulation in real-time. Methods: A sample of one hundred (n=100) outpatients was evaluated. Participants underwent eight 30-minutes ACE exposure sessions during which patients were guided to experience bodily sensations related to ACE while their HRV was monitored using a commercial biofeedback device. Results: Comparing the results of the first to last therapeutic session, a significant decrease in heart rate and an increase in HRV at the onset of the session were observed. Conclusions: This study suggests a physiological impact of therapeutic interventions on autonomic balance and underlines the interest in HRV biofeedback as clinical practice.