Dure-mère | EPFL Graph Search

La dure-mère (ou les pachyméninges) est une membrane fibreuse, dure et rigide, qui entoure le cerveau, la moelle épinière, les racines des nerfs crâniens et spinaux et le filum terminal. Le mot vient du latin médiéval dura mater cerebri, signifiant « la mère dure du cerveau » qui serait un emprunt à l'arabe : umm al-dimagh as-safiqa. En arabe les mots « père », « mère » et « fils » sont souvent utilisés pour marquer une relation entre les objets. La dure-mère est la plus externe des trois membranes constituant les méninges avec la pie-mère et l'arachnoïde. Elle se compose de deux feuillets de tissu conjonctif dense : le feuillet externe attaché au périoste et le feuillet interne, qui se prolonge dans le canal vertébral, formant la dure-mère spinale. Les deux feuillets sont soudés, sauf dans les endroits où ils enveloppent les sinus de la dure-mère recueillant le sang veineux de l'encéphale dirigé dans les veines jugulaires internes du cou. La dure-mère s'étend du sommet de la cavité crânienne jusqu'au niveau des vertèbres S2 et S3 du sacrum (cul-de-sac dural). Elle adhère à l'os dans la cavité crânienne, ce qui n'est pas le cas au niveau rachidien où sa structure diffère. La dure-mère spinale, en continuité avec sa partie crânienne, constitue une membrane fibreuse épaisse et résistante, d'un blanc nacré, formant un sac inextensible autour de la moelle spinale, nommé le sac dural. Elle forme des cloisons : tente du cervelet : qui délimite 2 loges : loge cérébrale et loge cérébelleuse ; faux du cerveau : qui sépare les deux hémisphères cérébraux au niveau de la scissure inter-hémisphérique ; faux du cervelet : qui sépare les deux hémisphères cérébelleux ; tente de l'hypophyse : recouvrant la selle turcique, elle est tendue entre les apophyses clinoïdes antérieur et postérieur, elle est perforée par la tige pituitaire. Comme toutes les membranes fibreuses, la dure-mère est très peu vascularisée. Les artères sont situés entre la dure-mère et la lame interne des os de la voûte du crâne.

Spatiotemporal stimulation strategies in neuroprostheses to improve locomotion after spinal cord injury

Jérôme Gandar

Spinal cord injury (SCI) disrupts communication within central nervous system and lead to range of neurological disorders including paralysis. Current rehabilitation strategies to restore locomotion are poorly effective in people with severe SCI. Epidural electrical stimulation (EES) showed promising results in animal models and humans to improve recovery. However, EES protocols have remained empirical, which has limited the efficacy of this paradigm. In this thesis, I report my contribution to the development of EES related software and hardware that were driven by the under- standing of the mechanisms underlying EES. These neurotechnologies showed a remarkable efficacy to reestablish locomotion in animal models of leg paralysis. EES protocols have primarily been delivered with continuous stimulations applied over the middle of the spinal cord, independently of current limb positions. However the natural activity of the spinal cord does not correspond to this limited monotone modulation. In the first part of this thesis, we developed spatiotemporal stimulation protocols that seek to reproduce the natural activity of the spinal cord during walking. Using computational models, we identified optimal electrode locations that target individual posterior roots. These simulations steered the design of spatially selective spinal implants. Control software triggered stimulation trains in real-time to engage extensor and flexor synergies according to limb positions. This spatiotemporal neuro- modulation therapy enhanced locomotor performances in rats with severe SCI. However, these spatiotemporal neuromodulation protocols were controlled via an external computer. The animal had no control over the occurrence of the stimulation. To remedy this limitation, we designed a brain-spine interface. We linked motor states decoded from leg motor cortex activity to spinal cord stimulation protocols to elicited the intended movements. We implemented this brain-spine interface in a nonhuman primate models of transient unilateral leg paralysis. All the animals immediately regained movements of the paralyzed leg. There is often a mechanical mismatch between current stiff implants and the soft neural tissues of the host. The third part of this thesis is dedicated to the design and fabrication of soft neural implants that present the same elasticity as the dura mater. These implants maintain the ability to deliver electrochemical stimulation while being stretched. Such interfaces can be applied to multiple neuroprosthetic applications, including the restoration of locomotion in paralyzed rats. In the last part of this thesis, I addressed the current limitations of spinal implant specificity. We found that EES activates the large afferent fibers within the dorsal rots and developed novel implants that take advantage of the known trajectories of the dorsal roots to increase the specificity of EES. First, we built a precise anatomical computational model of the lumbosacral roots. We then ran simulations that identi- fied multipolar electrode configurations capable of steering the current specifcally. These results drove the fabrication of soft neural implants that we inserted chronically in rat models of severe SCI. Experiments showed that multipolar EES increases the specificity of the stimulation compared to conventional protocols. All the concepts developed and validated in my thesis are already applied or are steering applications in humans with SCI.

EPFL2019

Electronic dura mater soft, multimodal neural interfaces

Arthur Edouard Hirsch

Neuroprosthetic devices are engineered to study, support or replace impaired functions of the nervous system. The neural interface is an essential element of neuroprosthetic systems as it allows for transduction of signals and stimuli of desired functions (recording, stimulation, neuromodulation). A persistent challenge for translating neuroprosthetics from the laboratory to the clinic is the lack of long-term biointegration of neural interfaces. This thesis aims at improving biointegration of neural interfaces by reducing the mechanical mismatch between implant and neural tissue. In this thesis, the design, fabrication and characterization of soft surface neural interfaces is described. These soft neural interfaces, termed electronic dura mater or e-dura, were designed to mimic the mechanical properties of dura mater. In contrast with conventional neural technologies, e-dura neural interfaces were made of soft and compliant materials. They conform to the circumvolutions of the brain and spinal cord and follow their dynamic deformation without damaging the surrounding neural tissues. These soft multimodal neural interfaces were fabricated on silicone substrates using techniques imported from the microfabrication industry and incorporate compliant electrodes, stretchable electrical interconnects and a micro-catheter for drug delivery. Evaluation of the e-dura biointegration with spinal tissues demonstrated reduced foreign body reaction, compared to stiff polyimide based implants. Additionally, mechanical tests on an in-vitro spinal surrogate provided insights on the complex biomechanical coupling between implants and neural tissue. E-dura interfaces, implanted in rodents, maintained their functionality over extended periods and provided high-resolution neuronal recordings and concurrent delivery of electrical and chemical neuromodulation. Eventually, the use of gallium thin films was explored to create highly conductive and stretchable interconnects for integration of active electronic components in e-dura neural interfaces.

EPFL2018