Dr. Juan S. Ordonez
Oktober 2015 - Juli 2016
Juan Sebastian Ordonez studied Microsystems Engineering at the University of Freiburg. At a very early career stage he joined the Laboratory for Biomedical Microtechnology, headed by Prof. Dr. Thomas Stieglitz to pursue his deep interest in neuroprostheses’ development. During two research internships at the Australian Vision Prostheses Group in Newcastle (2006) and Sydney (2008/2009) he strongly focused on the material-scientific aspects defining the reliability and longevity of implantable devices. This perspective, combined with his background in microsystems engineering and its modern methods, together with the research topics addressed in Freiburg merged into his main challenge: understanding the material-related aspects that delineate the stability of miniaturized prostheses. During his PhD, he investigated the failure of thin-film based electrode arrays caused by the lack of adhesion. Improvements regarding delamination, as well as the development of micro packages for miniaturized implants were combined to a miniature prototype of a vision prosthesis with 232-channels. His technological expertise expands across the methods and disciplines related to the fabrication of implantable devices, including the microelectrodes, electronics packaging and the respective interconnection technologies. Furthermore, his work on device reliability improvement has been awarded across disciplines at the International Engineering in Medicine and Biology Society (IEEE EMBS, 2012), at the German Biomedical Engineering Society (DG-BMT, 2012) and at the International Microelectronics Packaging Society (IMAPS – UK, 2013)
- Ordonez, J.S., Schuettler, M., Boehler, C., Boretius, T., Stieglitz, T., "Thin-films and microelectrode arrays for neuroprosthetics" MRS Bulletin, vol. 37(6), pp. 590-598, (2012).
- Ordonez J.S., Stieglitz, T., “Electrochemical Strain of thin-film electrodes for electrical stimulation” Proceedings of the IEEE Engineering in Medicine and Biology Society Conference (2015) – accepted; in print
- Ordonez, J.S., Stieglitz, T.: „Thermal stress in thin-film electrode arrays”, Proceedings of Biomedical Microtechnology (BMT) Conference, (2014)
- Ordonez, J.S., Boehler, C., Schuettler, M., Stieglitz, T.: "Improved Polyimide Thin-Film Electrodes for Neural Implants", Proceedings of the IEEE Engineering in Medicine and Biology Society Conference, pp. 5134-5137 (2012).
- Ordonez, J.S., Schuettler, M., Ortmanns, M., Stieglitz, T.: "A 232-Channel Retinal Prosthesis with a Miniaturized Hermetic Package", Proceedings of the IEEE Engineering in Medicine and Biology Society Conference, pp. 2796-2799 (2012).
A novel mechanical model for safe electrical stimulation
Electrical stimulation of the nervous system belongs to the state of the art in contemporary medical therapies and is used to treat medical conditions to which conventional medical therapies have no solution. Modern neuroprostheses implement thin-film (micro) technologies to fabricate smallest electrode arrays required to interface with delicate nervous tissue. Such microsystems, however, tend to fail quickly during stimulation, impairing their long-term use. Recent findings by the author indicate that the failure mechanism is of mechanical nature and inherent to the unavoidable electrochemical processes involved during electrical stimulation at the electrode’s surface. A structural expansion of the metallic surface subjected to stimulation was measured to reach over 25% of the initial size. This result provides a new perspective on the failure of implantable micro-devices. Within this proposal, based on the combined knowledge derived from electrochemistry and material sciences a mechanical and mathematical model for this phenomenon shall be established. The strain arising from the lattices of platinum and iridium while changing electrochemical states during stimulation, as well as the fatigue behaviour for different structures will be modeled. The models will be validated by driving platinum and iridium membranes of known geometry into specific electrochemical states and measuring the induced expansions. This model shall allow the design of electrode geometries with minimized mechanical stress under known stimulation conditions. It will help increase the longevity and reliability of electrodes used in neural intervention.