Tomi Ryynänen

Atomic layer deposited iridium oxide thin film as microelectrode coating in stem cell applications

Microelectrodes of microelectrode arrays (MEAs) used in cellular electrophysiology studies were coated with iridium oxide (IrOx) thin film using atomic layer deposition (ALD). This work was motivated by the need to find a practical alternative to commercially used titanium nitride (TiN) microelectrode coating. The advantages of ALD IrOx coating include decreased impedance and noise levels and improved stimulation capability of the microelectrodes compared to uncoated microelectrodes. The authors’ process also takes advantage of ALD’s exact process control and relatively low source material start costs compared to traditionally used sputtering and electrochemical methods. Biocompatibility and suitability of ALD IrOx microelectrodes for stem cell research applications were verified by culturing human embryonic stem cell derived neuronal cells for 28 days on ALD IrOx MEAs and successfully measuring electrical activity of the cell network. Electrode impedance of 450 kΩ at 1 kHz was achieved with ALD IrOx in t...

All Titanium Microelectrode Array for Field Potential Measurements from Neurons and Cardiomyocytes—A Feasibility Study

In this paper, we describe our all-titanium microelectrode array (tMEA) fabrication process and show that uncoated titanium microelectrodes are fully applicable to measuring field potentials (FPs) from neurons and cardiomyocytes. Many novel research questions require custom designed microelectrode configurations different from the few commercially available ones. As several different configurations may be needed especially in a prototyping phase, considerable time and cost savings in MEA fabrication can be achieved by omitting the additional low impedance microelectrode coating, usually made of titanium nitride (TiN) or platinum black, and have a simplified and easily processable MEA structure instead. Noise, impedance, and atomic force microscopy (AFM) characterization were performed to our uncoated titanium microelectrodes and commercial TiN coated microelectrodes and were supplemented by FP measurements from neurons and cardiomyocytes on both platforms. Despite the increased noise levels compared to commercial MEAs our tMEAs produced good FP measurements from neurons and cardiomyocytes. Thus, tMEAs offer a cost effective platform to develop custom designed electrode configurations and more complex monitoring environments.

Indirect Temperature Measurement and Control Method for Cell Culture Devices

Microfluidic devices are promising tools with which to create an environment that mimics a cell’s natural microenvironment more closely than traditional macroscopic cell culture approaches. In these devices, temperature is one of the most important environmental factors to monitor and control. However, direct temperature measurement at the cell area can disturb cell growth and potentially prevent optical monitoring, and is typically difficult to implement. On the other hand, indirect measurement could overcome these challenges. Therefore, using the system identification method, we have developed models to estimate the cell area temperature from external measurements without interfering cells. In order to validate the proposed models, we performed large sets of experiments. The results show that the models are able to catch the dynamics of temperature in a desired area with a high level of accuracy, which means that indirect temperature measurement using the model can be implemented in the future cell culture studies. The usefulness of the model is also demonstrated by simulations that use estimated temperature as a feedback signal in a closed-loop system. We also present tuning of a model-based controller and a noise study, which shows that the tuned controller is robust for typical ambient room temperature variations.Note to Practitioners—In this paper, we tackle the problem related to temperature measurement in microfluidic devices, especially but not only concerning cell culture environments. Even though it would be desirable to place a temperature sensor as close as possible to the location of interest, practical limits usually prevent this; for instance, limited space and requirements for optical monitoring. To overcome these problems in microfluidic devices, we present a novel indirect temperature measurement approach using the system identification method. The idea is to create a model that estimates temperature on the area of interest using measured outside temperature. Because it is required to measure both model input and output signals for the model development, we first fabricated a temperature sensor plate, combined it with our heating system, and measured required temperatures on several experiments. Then, we developed third-order discrete state-space models using measured temperatures and System Identification Toolbox in MATLAB. Model performances were examined and compared with measurements. Furthermore, we created a closed-loop Simulink (from MATLAB) model, and showed how desired temperature could be controlled using only measured outside temperature and the developed model. In the future research, we will implement the designed closed-loop system to our cell culture system to precisely control temperature in the cell area.

A Portable Microscale Cell Culture System with Indirect Temperature Control

A physiologically relevant environment is essential for successful long-term cell culturing in vitro. Precise control of temperature, one of the most crucial environmental parameters in cell cultures, increases the fidelity and repeatability of the experiments. Unfortunately, direct temperature measurement can interfere with the cultures or prevent imaging of the cells. Furthermore, the assessment of dynamic temperature variations in the cell culture area is challenging with the methods traditionally used for measuring temperature in cell culture systems. To overcome these challenges, we integrated a microscale cell culture environment together with live-cell imaging and a precise local temperature control that is based on an indirect measurement. The control method uses a remote temperature measurement and a mathematical model for estimating temperature at the desired area. The system maintained the temperature at 37±0.3 °C for more than 4 days. We also showed that the system precisely controls the culture temperature during temperature transients and compensates for the disturbance when changing the cell cultivation medium, and presented the portability of the heating system. Finally, we demonstrated a successful long-term culturing of human induced stem cell–derived beating cardiomyocytes, and analyzed their beating rates at different temperatures.

Temperature effect on the baseline noise in MEA measurements

It is a well known fact that increasing temperature increases noise in all kind of electronics, which applies also to cell and tissue measurements by microelectrode arrays (MEAs). We show that ambient temperature may have a surprisingly big role in the noise level of MEA measurements. To study that we measured the baseline noise when the MEA amplifier was subject to temperature variations, either in a temperature chamber or by preventing amplifier unit’s normal heat exchange. Around room temperature (+24°C) the RMS value of the baseline noise was found to increase approximately 0.14 µV/°C, which is a huge variation as the default RMS noise at that temperature with our setup was only around 5.5 µV. Additional cooling of the MEA amplifier could thus be a clever way to decrease the noise level at very sensitive measurements and on the other hand, one should not interfere the amplifier’s normal heat exchange to the ambient air in order to avoid additional warming and thus increasing the noise level.

Design and simulation of a thermal flow sensor for gravity-driven microfluidic applications

Gravity-driven flow is an attractive approach to develop simpler microfluidic systems. Because clogged microchannels could easily lead to fatal operational failures, it is crucial to monitor flow rate in these systems. Therefore, we propose here for the first time a numerical model that combines a calorimetric flow sensor and a gravity-driven system. With the validated model, we studied the flow behavior in a gravity-driven system. Furthermore, we were able to improve the sensitivity of the measurement based on simulation results. This demonstrates, how the model could be used as an effective optimization tool in the gravity-driven system including calorimetric flow measurement.

Backside Detection of Photoresist Development Endpoint Using Surface Plasmon Resonance

Simulations and experiments done for a simple photoresist on metallized glass wafer structure show that surface plasmon resonance, a method commonly used in biosensing, is suitable for monitoring photoresist development. End-point can be detected very easily and according to simulations, the detection sensitivity is highest close to the endpoint, which indicates high potential for closer study of development process even down to monolayer thicknesses. The method allows instrumentation to be placed on the backside of the wafer leaving the photoresist development process undisturbed.