Dr Mark Fretz



Mark is a senior R&D research engineer and project manager at CSEM and has been a member of the Optics & Packaging group since November 2012. He worked on and managed numerous projects concerning electronic and medical packaging as well as optical systems such as long-term implantable pressure sensors, fabrics inspection systems for looms and gas flow sensors.

Previously, Mark worked for Implant Systems, NICTA, in Australia from 2009 to 2012, where he focused on biocompatibility and –stability issues of spinal cord stimulator leads, and gained insight into developing long-term implantable devices.

Mark received his Diploma in Physics from the Federal Institute of Technology Zurich (ETHZ) in 2005 and a PhD from the University of Neuchâtel, Switzerland, in 2009 for his work on ‘Flip Chip Bonding Technologies for Hybrid Integration’ conducted at CSEM from 2005 to 2009. He was involved in developing novel packaging concepts for electronic devices and in testing new micro-joining techniques.

As a master student, Mark researched in the field of photorefractive crystals for laser beam quality improvement, which is a branch of nonlinear optics.

He co-authored several patents (some pending) concerning medical and electronic packaging, (co-) wrote several publications and presented at various conferences.


ACTION - ACTive Implant for Optoacoustic Natural sound enhancement

The EU-project ACTION builds on the recent discovery that relatively low levels of pulsed infrared laser light are capable of triggering activity in hair cells of the partially hearing (hearing impaired) cochlea and vestibule. So far the excessively large volume of optical fibre systems and external light sources used for animal studies prevented the practical use of this discovery for long term animal research devices or for human grade implants. ACTION aims to develop a self-contained, smart, miniaturised system to provide optoacoustic stimuli directly from the electrode array of a cochlear implant. In-vivo measurements in guinea pig confirmed our hypothesis that the generated compound action potentials are indeed explained by the optoacoustic effect in the cochlea: IR-light from a tiny VCSEL- absorbed by a small volume of the cochlear fluid- generates heat and causes this volume to expand quickly. The volume/pressure change propagates through the cochlea and stimulates the hair cells.

A new miniaturised device sufficiently small for in-vivo chronic cat experiments will be available by the end of the project. The external part is a belt-worn box which runs autonomously for at least 24 hours. Acquired data is transferred wirelessly to a nearby computer. Two insertable stimulators have been fabricated: The first device is suitable for short term in-vivo tests (less than 29 days) and is based on a commercially available flexible PCB. The VCSEL is directly attached. The entire device is coated with a layer of silicone. The second device is exclusively made of biocompatible materials. The VCSEL is hermetically sealed inside a sapphire box. This device has slightly larger dimensions and was, therefore, not tested in in-vivo trials.

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