Doctoral dissertation

Custom-designed microelectrodes for stem cell researchers

Tomi Ryynänen
In the Centre of Excellence in Body-on-Chip Research (CoEBoC) at Tampere University, the biologists and the engineers co-operate to develop novel stem cell-based cell models and enabling tecnologies for culturing and studing the models. In his doctoral thesis in the field of biomedical engineering, physicist Tomi Ryynänen studied alternative materials for microelectrode arrays (MEAs) which are used for measuring the cell activity electrically, as well as, cost-effective fabrication of custom-designed MEA-prototypes for advanced cell models.

Stem cell-based cell models can be used for studying mechanisms of various diseases and traumas. In the future, they may also replace animal experiments in drug screening and toxicity testing, or even act as a tool for patient-specific treaments.

In the past, the biologists managed with cell culture plates, pipettes and microscopes, but the more advanced the cell models get, the more need there is for additional techical tools. Microtunnels guide cells to form cell networks of specific shape, sensors monitor the cell culture conditions, controlled perfusion of drugs and gases can be implemented and so on.

"And of course, one wants to know how changing the conditions  or a drug affects e.g. to the beating of the cardiac cells or to the communication between the cells in the neuronal cell network. One common method for this is to use microelectrodes located on the bottom of the cell culture plate to record the cell-generated voltage signals", Tomi Ryynänen says.

Commercial standard MEA plates are fine for simple cell cultures, but when the cell models get more complex and more technical add-ons are applied, getting the best results require MEAs that are custom-designed for the cell model.

That was the acknowledged also in Tampere more than 10 years ago when the biology and engineering groups that form the current Centre of Excellence in Body-on-Chip Research started their co-operation. That was also when Mr. Ryynänen started to develop in-house processes for MEA prototype fabrication and small-scale production.

However, at that time, his department was far from having the full set of microfabrication equipment needed for MEA fabrication. The availability of lacking thin film processes, their compatibility with the other process steps, cost factors, and, of course, opportunistic publishing prospects made him interested in the electrode materials or their deposition methods not applied to MEAs before, instead of sticking to conventional electrode materials.

The results gained from titanium, atomic layer deposited (ALD) iridium oxide, and ion beam assisted electron beam deposited (IBAD) titanium nitride as microelectrode materials benefit not only CoEBoC’s in-house MEA production, but especially other research groups starting their own MEA fabrication activities with limited resources. In addition, these kind of alternative materials and methods may well turn out valuable when integrating future 3D-multi-tissue models with the required technical add-ons.

Finally, as an example of the need for custom-designed MEAs, Mr. Ryynänen fulfilled in his thesis cardiac cell researchers’ wish of getting an easy-to-use and long-term measurements enabling alternative for laborous and cell-damaging patch clamp method in studying cardiac cells at single cell level.

Tomi Ryynänen hails from Keuruu and currently he works as a researcher in the Centre of Excellence in Body-on-Chip Research at Tampere University.

The doctoral dissertation of MSc. Tomi Ryynänen in the field of biomedical engineering titled with Alternative Electrode Materials for Prototyping Cell Model-Specific Microelectrode Arrays will be publicly examined in the Faculty of Medicine and Health Technology at Tampere University at 12 o’clock on Friday 8.11.2019 in the auditorium TB109 of the Tietotalo building in Hervanta campus, Korkeakoulunkatu 1. The opponent will be professor Andreas Offenhäusser from the Research Centre Jülich, Germany. The custos will be professor emeritus Jukka Lekkala from the Faculty of Medicine and Health Technology, Tampere University.

The dissertation is available online at

Photo: Esa Ryynänen