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Trends in long-term encapsulation for BCI implants
Keywords: encapsulation, bci, implants
Several groups around the world are currently working on Brain Computer Interfaces (BCI). The objective is to read signals on the motor cortex or to stimulate various area of the human brain in order of restoring deficiencies in the central neuro system. To achieve these goals and have a good precision of the interface, BCI systems must be implanted. Some devices are already available, like Deep Brain Stimulation Systems (DBS), for treating Parkinson’s disease, also being studied for other applications like obesity, Tourette’s syndrome or other neurological disorders. DBS have electrodes implanted in the brain, but the implanted stimulator is currently placed in the pectoral area, mainly due to the large size of the device. Other considerable efforts are focuses on BCI for the decoding of cortical signals for the restoration of movements in cases of paralysis. Future BCI will have the electronics implanted above the neck, for example behind the ear, on the surface of the skull but beneath the scalp, similarly to cochlear implants. Above the neck implants presents several challenges, especially in terms of volume, thickness, transfer of energy and large flow of information. This presentation will address the specific issues related to above the neck implants. Conventional encapsulation methods, like hermetic titanium housings have shown their limitations, especially regarding incorporation of large number (more than 100) hermetic feedthroughs. Miniaturization of above the neck devices induces exploration of disruptive technologies, like CerMet feedthroughs developed by Heraeus Inc in Germany. Other trends regarding highly miniaturized assemblies will be covered, for example in the ways to attach cables and wires to hermetic housings. We will also discuss opportunities to replace titanium housings by other types of hermetic encapsulations, like ceramic, glass or sapphire. In a second part of the presentation, we will discuss the possibilities to move to so-called “near hermetic” encapsulations, using novel technologies to prevent moisture ingress over a sufficient implantation duration. Multi-layer conformal coatings or Atomic Layer Deposition (ALD) are growing in maturity and present promising solutions for long term implantation. Applying such technologies to highly miniaturized devices will open the way to ultra-thin subcutaneous devices to be placed on the skull without or minimal bone work. Such developments will redefine the assembly and test processes. New test methods will be needed to assess hermeticity, biostability, impact resistance and long-term stability. Specific methods must be developed for the validation of these new encapsulation systems. As new materials and joining of materials of different types are being introduced for human grade implants, innovative methods must be put in place in order of assessing long term stability through artificial aging. As the brain and Cerebro Spinal Fluid have unique characteristics, biostability of implants presents unexpected challenges, not only for the encapsulation of the electronics, but also for the body interface (penetrating electrodes, multi electrodes arrays, ECoGs…), lead cables and connectors. The presentation will cover the challenges of putting entire systems (body interface, lead cable, connector, encapsulated electronics, induction coil for energy transfer, RF antenna or optical communication) above the neck. We will also debate about the consequences of locating a BCI implant above the neck in terms of energy and large volume of data to be transferred. The presentation will focus on human applications and will show the limitations imposed by the very nature of the human body. Translational projects must clearly be assessed in the view of their feasibility. Step-by-step developments have a better chance to reach patients in a foreseeable future. The electronics applicable to high channel count BCIs is progressing extremely fast, but the “mechanical” aspects, like feedthroughs, connection, communication and energy transfer are not showing improvements in line with expectations. The presentation will identify the areas where special efforts are requested.
Claude Clement , CTO
Wyss Center for Bio and Neuroengineering
Geneve , CH
Switzerland


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