Development of 3D culture scaffolds for directional neuronal growth using 2-photon lithography

Conventional applications of transplant technology, applied to severe traumatic injuries of the nervous system, have met limited success in the clinics due to the complexity of restoring function to the damaged tissue. Neural tissue engineering aims to deploy scaffolds mimicking the physiological properties of the extracellular matrix to facilitate the elongation of axons and the repair of damaged nerves. However, the fabrication of ideal scaffolds with precisely controlled thickness, texture, porosity, alignment, and with the required mechanical strength, features needed for effective clinical applications, remains technically challenging. We took advantage of state-of-the-art 2-photon photolithography to fabricate highly ordered and biocompatible 3D nanogrid structures to enhance neuronal directional growth. First, we characterized the physical and chemical properties and proved the biocompatibility of said scaffolds by successfully culturing primary sensory and motor neurons on their surface. Interestingly, axons extended along the fibers with a high degree of alignment to the pattern of the nanogrid, as opposed to the lack of directionality observed on flat glass or polymeric surfaces, and could grow in 3D between different layers of the scaffold. The axonal growth pattern observed is highly desirable for the treatment of traumatic nerve damage occurring during peripheral and spinal cord injuries. Thus, our findings provide a proof of concept and explore the possibility of deploying aligned fibrous 3D scaffold/implants for the directed growth of axons, and could be used in the design of scaffolds targeted towards the restoration and repair of lost neuronal connections

Miniaturized hybrid inductors and transformers

In the frame of this thesis, we have developed a novel batch-type technology for the realization of three-dimensional millimeter-size transformers for ultra-small low-power (0.1-1 Watt) applications. The technology is based on the three-dimensional micropatterning of 0.5, 0.75 and 1 mm thick ferrite wafers by powder blasting to form the magnetic cores of the inductive devices, and the combination of these cores with electrical windings realized in flex-foil printed circuit board technology. Microfabrication and assembly of the parts can be done in a batch-process on a wafer/foil level, opening the way to further size reduction of the components. The coils are realized using an in-house developed high-resolution polyimide spinning and Cu electroplating process. Winding widths down to 5 μm have been obtained and total device volumes are ranging between 1.5 and 10 mm3. We have measured the inductive and resistive properties of our devices as a function of frequency and device geometry. The results clearly show the high potential of our technology for power applications, in which miniaturization and small-size is an issue. In the domain of RF frequencies, efforts are being made to improve the quality factor by multilayer techniques and leaving a space between the substrate and the conducting lines. Magnetic components operating at high frequencies rapidly increase eddy current and hysteresis losses in the magnetic core as the operating frequency increases. The micromachining techniques provide several approaches for the miniaturization of inductors operating at high frequencies. In the present work, we have realized millimeter-size RF inductors on silicon using the same coil as before and Ni-Zn ferrite plates. The coils are assembled with magnetic cover plates of commercially available bulk Ni-Zn ferrites of high resistivity. Using the magnetic flux-amplifying ferrite plates, we obtain a 40 % enhancement of the inductance and a 25 % enhancement of the quality factor (Q=10-20) for frequencies up to 0.2 GHz

Rotating Circular Micro-Platform with Integrated Waveguides and Latching Arm for Reconfigurable Integrated Optics

This work presents a laterally rotating micromachined platform integrated under optical waveguides to control the in-plane propagation direction of light within a die to select one of multiple outputs. The platform is designed to exhibit low constant optical losses throughout the motion range and is actuated electrostatically using an optimized circular comb drive. An angular motion of ±9.5° using 180 V is demonstrated. To minimize the optical losses between the moving and fixed parts, a gap-closing mechanism is implemented to reduce the initial air gap to submicron values. A latch structure is implemented to hold the platform in place with a resolution of 0.25° over the entire motion range. The platform was integrated with silicon nitride waveguides to create a crossbar switch and preliminary optical measurements are reported. In the bar state, the loss was measured to be 14.8 dB with the gap closed whereas in the cross state it was 12.2 dB. To the authors’ knowledge, this is the first optical switch based on a rotating microelectromechanical device with integrated silicon nitride waveguides reported to date

Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients

International audienceThe aim of this study was to estimate the incidence of COVID-19 disease in the French national population of dialysis patients, their course of illness and to identify the risk factors associated with mortality. Our study included all patients on dialysis recorded in the French REIN Registry in April 2020. Clinical characteristics at last follow-up and the evolution of COVID-19 illness severity over time were recorded for diagnosed cases (either suspicious clinical symptoms, characteristic signs on the chest scan or a positive reverse transcription polymerase chain reaction) for SARS-CoV-2. A total of 1,621 infected patients were reported on the REIN registry from March 16th, 2020 to May 4th, 2020. Of these, 344 died. The prevalence of COVID-19 patients varied from less than 1% to 10% between regions. The probability of being a case was higher in males, patients with diabetes, those in need of assistance for transfer or treated at a self-care unit. Dialysis at home was associated with a lower probability of being infected as was being a smoker, a former smoker, having an active malignancy, or peripheral vascular disease. Mortality in diagnosed cases (21%) was associated with the same causes as in the general population. Higher age, hypoalbuminemia and the presence of an ischemic heart disease were statistically independently associated with a higher risk of death. Being treated at a selfcare unit was associated with a lower risk. Thus, our study showed a relatively low frequency of COVID-19 among dialysis patients contrary to what might have been assumed