Alternative Electrode Materials for Prototyping Cell Model-Specific Microelectrode Arrays

Mikroelektrodimatriisi (MEA, microelectrode array) on biologien käyttämä väline solujen sähköisen toiminnan mittaamiseen in vitro olosuhteissa. Pelkkien satunnaisten soluryppäiden ja yksikerroksisten soluviljelmien tutkimisen rinnalla yleistymässä ovat biologiset tutkimuskysymykset, joissa tutkitaan ohjatusti muodostettuja soluverkkoja tai yksittäisiä soluja. Nämä aiheet asettavat sellaisia erityisvaatimuksia elektrodien koolle ja sijainnille MEA-levyllä, sekä ylipäätään MEA-levyn suorituskyvylle, että kaupasta saatavat vakiomalliset MEA-levyt eivät yleensä niitä täytä. Räätälöidyille MEA-levyille onkin tarvetta monella sovellusalueella perussolubiologiasta ja tautimallien kehittämisestä myrkyllisyystutkimuksiin ja lääketestaukseen. Tässä väitöstyössä on valmistettu mikroelektrodeja, joiden materiaalina on käytetty titaania, atomikerroskasvatettua (atomic layer deposition, ALD) iridiumoksidia (IrOx) sekä ionisuihkuavusteiselle elektronisuihkuhöyrystyksellä (ion beam assisten e-beam deposition, IBAD) tuotettua titaaninitridiä (TiN). Elektrodit on karakterisoitu mm. niiden impedanssin, kohinatason ja pinnan morfologian osalta. Lisäksi bioyhteensopivuus ja toimivuus on varmistettu kokeilla, joissa on käytetty ihmisperäisistä kantasoluista johdettuja hermo- ja sydänsoluja. Näiden tutkimusten tarkoituksena on tarjota MEA-valmistukseen lisää vaihtoehtoja, mistä valita eri sovelluksiin parhaiten sopivat ja käytettävissä olevat resurssit parhaiten huomioivat elektrodimateriaalit. Titaanin käyttöä puhtaasti metallimuodossa on mikroelektrodimateriaalina yleisesti vältetty sen johtavuusominaisuuksia häiritsevän hapettumistaipumuksen vuoksi. Valmistukseen kuluva aika ja kustannukset voivat kuitenkin olla räätälöityjen MEA-prototyyppien kehittämisessä olennaisempia tekijöitä kuin prototyypin huippuunsa viritetty suorituskyky, jota usein arvioidaan 1 kHz taajuudella mitatun impedanssin avulla. Kuten odotettua, titaanielektrodien impedanssi oli huomattavan korkea (>1700 kΩ), mutta silti solumittauksissa sekä hermo- että sydänsolujen tuottamat kenttäpotentiaalisignaalit olivat erotettavissa kohinasta. Titaanin etuihin elektrodimateriaalina kuuluvat yleisimpiin vaihtoehtoihin verrattuna vähäisempien ja yksinkertaisempien prosessivaiheiden tarve sekä noin sata kertaa pienemmät raaka-aine kustannukset kultaan ja platinaan verrattuna. IrOx ja TiN ovat yleisesti käytettyjä elektrodien pinnoitusmateriaaleja, joiden tarkoitus on laskea esimerkiksi titaanista tehtyjen elektrodien impedanssia ja kohinatasoa. Tässä työssä tutkittiin mahdollisuutta tehdä pinnoitukset vaihtoehtoisilla, MEA sovelluksissa uusilla menetelmillä, ALD:llä ja IBAD:lla. Vaikka näillä menetelmillä pinnoitettujen 30 μm elektrodien impedanssit (450 kΩ ALD IrOx:lle ja ~90 kΩ IBAD TiN:lle) eivät aivan laskeneetkaan yleisesti käytettyjen sputteroidun TiN:n (30-50 kΩ) ja huokoisen platinan eli Pt black:n (20-30 kΩ) tasolle, niin solumittauksissa etenkään IBAD TiN elektrodien ja sputteroitujen TiN elektrodien välillä ei ollut käytännössä lainkaan havaittavaa eroa kohinatasossa ja signaalipiikkien korkeuksissa. Täten IBAD TiN onkin täysin varteenotettava materiaalivaihtoehto niille, jotka suosivat TiN elektrodeja, mutta joilla ei ole sputteriointiin sopivaa laitetta käytettävissä. ALD:n ja IrOx:n yleiset ominaisuudet sen sijaan puoltavat ALD IrOx:n sopimista erityisesti geometrialtaan haastaviin tapauksiin tai sovelluksiin, joissa elektrodeilta vaaditaan erinomaisia stimulointiominaisuuksia. Lopuksi tässä väitöstyössä kehitettiin esimerkkinä räätälöidyn MEA-levyn vaativasta sovelluksesta yksittäisten sydänsolujen mittaamiseen soveltuva MEA-levy. Tällainen MEA-levy tarjoaa yleisesti käytetylle, mutta työläälle patch-clamp menetelmälle ainutlaatuisen soluja vahingoittamattoman vaihtoehdon yksittäisten solujen tutkimiseksi, sekä mahdollistaa yksittäisen solun ominaisuuksien havainnoinnin paremmin, kuin usein varsin heterogeenisen soluviljelmän tutkiminen vakiomallisella MEA-levyllä. Ratkaisuna tähän oli elektrodien sijoittaminen lähelle solualueen ulkokehää sekä elektrodien halkaisijan kasvattaminen 80 μm:iin tavanomaisesta 30 μm:stä, mikä helpotti solujen asettamista elektrodeille ja mahdollisti solujen sähköisen sykesignaalin mittaamisen. Indiumtinaoksidi (ITO) elektrodien läpinäkyvyys mahdollisti lisäksi mekaanisen sykinnän analysoimisen kuvaan perustuvan mittaamisen avulla.A microelectrode array, MEA, is a tool used by biologists for measuring the electrical activity of cells in vitro. Instead of only studying random cell clusters and monolayers, an increasing number of biological research questions are aimed at studying well- defined cell networks or single cells. This places special demands on the location, size, and overall performance of the MEA electrodes, which the standard, commercially available layouts cannot usually meet. Therefore, custom-designed MEAs are needed for a wide range of applications from basic cell biology and disease model development to toxicity testing and drug screening. This thesis focuses on the fabrication of microelectrodes made of titanium, atomic layer deposited (ALD) iridium oxide (IrOx), and ion beam-assisted e-beam deposited (IBAD) titanium nitride (TiN). These MEAs are characterized, for example, in terms of their impedance, noise level, and surface morphology, and their biocompatibility and functionality are verified by simple experiments with human stem cell-derived neuronal cells and cardiomyocytes. The aim of these studies is to offer more alternatives for MEA fabrication, enabling researchers and practitioners to choose the electrode material that best fits their application from their available resources. Pure titanium is commonly disregarded as an electrode material because of its oxidation tendency, which destabilizes the electrical performance. However, when prototyping customised MEAs, the time and cost of fabricating the subsequent iterations of the prototype can be more decisive factors than the device’s ultimate electrical performance, which is typically evaluated by the impedance value at 1 kHz. As might be expected, although titanium electrodes underperformed in terms of impedance (>1700 kΩ), when used in the cell experiments, the field potentials from both neuronal cells and cardiomyocytes were still easily distinguishable from the noise. There are a number of benefits to using titanium as an electrode material. Besides the fact that it is about hundred times cheaper than other commonly-used materials, such as gold or platinum, it usually requires fewer and often simpler process steps than the most common alternatives. IrOx and TiN are common electrode coatings which, when applied on top of e.g. a titanium electrode, can lower the impedance and the noise level of the electrode. In this study, two alternative deposition methods, ALD and IBAD, were used for IrOx and TiN in MEA applications. Even if the impedance of these 30 μm electrodes (450 kΩ for ALD IrOx and ~90 kΩ for IBAD TiN) did not quite reach the impedance levels of the industry standards, i.e. sputtered TiN (30-50 kΩ) and Pt black (20-30 kΩ), in cell experiments the IBAD TiN electrodes in particular showed no tangible differences in peak amplitudes and noise levels compared with sputtered TiN electrodes. This makes IBAD TiN an attractive alternative material for those who prefer to use TiN electrodes, but do not have access to a sputter coater, for example. ALD IrOx, on the other hand, relies on the potential of the general properties of ALD and IrOx (yet unverified) to provide exceptional performance in designs requiring excellent step coverage or stimulation capability. Finally, as an application example of a custom-designed MEA, a version capable of measuring cardiomyocytes at the single-cell level was developed. The benefit of such an MEA is to offer a unique noninvasive method to study single cells without destroying them with the time-consuming patch clamp method, and without losing cell-specific information, which often occurs if the cell clusters studied with standard MEAs are too heterogenous. This was achieved with a number of innovations. For example, the electrodes were placed near the perimeter of the cell culturing area and had a larger diameter (80 μm) than the usual 30 μm electrodes. This simplified the plating of the cells to the electrodes and enabled the beating of the cells to be electrically recorded. It is also possible to combine that with image-based analysis of mechanical beating through transparent indium tin oxide (ITO) electrodes

Transparent Microelectrode Arrays Fabricated by Ion Beam Assisted Deposition for Neuronal Cell In Vitro Recordings

Microelectrode array (MEA) is a tool used for recording bioelectric signals from electrically active cells in vitro. In this paper, ion beam assisted electron beam deposition (IBAD) has been used for depositing indium tin oxide (ITO) and titanium nitride (TiN) thin films which are applied as transparent track and electrode materials in MEAs. In the first version, both tracks and electrodes were made of ITO to guarantee full transparency and thus optimal imaging capability. In the second version, very thin (20 nm) ITO electrodes were coated with a thin (40 nm) TiN layer to decrease the impedance of Ø30 µm electrodes to one third (1200 kΩ → 320 kΩ) while maintaining (partial) transparency. The third version was also composed of transparent ITO tracks, but the measurement properties were optimized by using thick (200 nm) opaque TiN electrodes. In addition to the impedance, the optical transmission and electric noise levels of all three versions were characterized and the functionality of the MEAs was successfully demonstrated using human pluripotent stem cell-derived neuronal cells. To understand more thoroughly the factors contributing to the impedance, MEAs with higher IBAD ITO thickness as well as commercial sputter-deposited and highly conductive ITO were fabricated for comparison. Even if the sheet-resistance of our IBAD ITO thin films is very high compared to the sputtered one, the impedances of the MEAs of each ITO grade were found to be practically equal (e.g., 300–370 kΩ for Ø30 µm electrodes with 40 nm TiN coating). This implies that the increased resistance of the tracks, either caused by lower thickness or lower conductivity, has hardly any contribution to the impedance of the MEA electrodes. The impedance is almost completely defined by the double-layer interface between the electrode top layer and the medium including cells

Ion Beam Assisted E-Beam Deposited TiN Microelectrodes—Applied to Neuronal Cell Culture Medium Evaluation

Microelectrode material and cell culture medium have significant roles in the signal-to-noise ratio and cell well-being in in vitro electrophysiological studies. Here, we report an ion beam assisted e-beam deposition (IBAD) based process as an alternative titanium nitride (TiN) deposition method for sputtering in the fabrication of state-of-the-art TiN microelectrode arrays (MEAs). The effects of evaporation and nitrogen flow rates were evaluated while developing the IBAD TiN deposition process. Moreover, the produced IBAD TiN microelectrodes were characterized by impedance, charge transfer capacity (CTC) and noise measurements for electrical properties, AFM and SEM for topological imaging, and EDS for material composition. The impedance (at 1 kHz) of brand new 30 μm IBAD TiN microelectrodes was found to be double but still below 100 kΩ compared with commercial reference MEAs with sputtered TiN microelectrodes of the same size. On the contrary, the noise level of IBAD TiN MEAs was lower compared with that of commercial sputtered TiN MEAs in equal conditions. In CTC IBAD TiN electrodes (3.3 mC/cm2) also outperformed the sputtered counterparts (2.0 mC/cm2). To verify the suitability of IBAD TiN microelectrodes for cell measurements, human pluripotent stem cell (hPSC)-derived neuronal networks were cultured on IBAD TiN MEAs and commercial sputtered TiN MEAs in two different media: neural differentiation medium (NDM) and BrainPhys (BPH). The effect of cell culture media to hPSC derived neuronal networks was evaluated to gain more stable and more active networks. Higher spontaneous activity levels were measured from the neuronal networks cultured in BPH compared with those in NDM in both MEA types. However, BPH caused more problems in cell survival in long-term cultures by inducing neuronal network retraction and clump formation after 1–2 weeks. In addition, BPH was found to corrode the Si3N4 insulator layer more than NDM medium. The developed IBAD TiN process gives MEA manufacturers more choices to choose which method to use to deposit TiN electrodes and the medium evaluation results remind that not only electrode material but also insulator layer and cell culturing medium have crucial role in successful long term MEA measurements

Microelectrode Array With Transparent ALD TiN Electrodes

Low noise platinum black or sputtered titanium nitride (TiN) microelectrodes are typically used for recording electrical activity of neuronal or cardiac cell cultures. Opaque electrodes and tracks, however, hinder the visibility of the cells when imaged with inverted microscope, which is the standard method of imaging cells plated on microelectrode array (MEA). Even though transparent indium tin oxide (ITO) electrodes exist, they cannot compete in impedance and noise performance with above-mentioned opaque counterparts. In this work, we propose atomic layer deposition (ALD) as the method to deposit TiN electrodes and tracks which are thin enough (25–65 nm) to be transparent (transmission ∼18–45%), but still benefit from the columnar structure of TiN, which is the key element to decrease noise and impedance of the electrodes. For ALD TiN electrodes (diameter 30 μm) impedances from 510 to 590 kΩ were measured at 1 kHz, which is less than the impedance of bare ITO electrodes. Human induced pluripotent stem cell (hiPSC)-derived cortical neurons were cultured on the ALD TiN MEAs for 14 days without observing any biocompatibility issues, and spontaneous electrical activity of the neurons was recorded successfully. The results show that transparent ALD TiN film is a suitable electrode material for producing functional MEAs

A modular brain-on-a-chip for modelling epileptic seizures with functionally connected human neuronal networks

Epilepsies are a group of neurological disorders characterised by recurrent epileptic seizures. Seizures, defined as abnormal transient discharges of neuronal activity, can affect the entire brain circuitry or remain more focal in the specific brain regions and neuronal networks. Human pluripotent stem cell (hPSC)-derived neurons are a promising option for modelling epilepsies, but as such, they do not model groups of connected neuronal networks or focal seizures. Our solution is a Modular Platform for Epilepsy Modelling In Vitro (MEMO), a lab-on-chip device, in which three hPSC-derived networks are separated by a novel microfluidic cell culture device that allows controlled network-to-network axonal connections through microtunnels. In this study, we show that the neuronal networks formed a functional circuitry that was successfully cultured in MEMO for up to 98 days. The spontaneous neuronal network activities were monitored with an integrated custom-made microelectrode array (MEA). The networks developed spontaneous burst activity that was synchronous both within and between the axonally connected networks, i.e. mimicking both local and circuitry functionality of the brain. A convulsant, kainic acid, increased bursts only in the specifically treated networks. The activity reduction by an anticonvulsant, phenytoin, was also localised to treated networks. Therefore, modelling focal seizures in human neuronal networks is now possible with the developed chip.acceptedVersionPeer reviewe

"Tää sen mielekkyyden tälle työlle antaa" : Haapaniemen päiväkodin henkilökunnan kokemuksia omahoitaja-työkäytännöstä

Opinnäytetyössä tutkittiin Haapaniemen päiväkodin henkilökunnan kokemuksia oma-hoitaja-työkäytännössä. Tutkimuksen tarkoituksena oli toimia avoimena foorumina, jonka kautta henkilökunta pääsee kertomaan mielipiteensä työmenetelmästä. Opinnäytetyö on kvalitatiivinen tutkimus. Teoreettisena viitekehyksenä toimi John Bowlbyn luoma kiintymyssuhdeteoria, sekä kasvatuskumppanuuden neljä kantavaa periaatetta. Ai-neiston kerättiin yksilökohtaisilla teemahaastatteluilla. Kohdejoukkona tutkimuksessa toimi seitsemän Haapaniemen päiväkodin työntekijää, kolme oli nimikkeeltään lastentarhanopettajia ja neljä lastenhoitajia. Aineiston analyysissa käytettiin aineistolähtöistä sisällönanalyysia. Tutkimuksessa omahoitajuus koettiin hyväksi, joskin haavoittuvaiseksi työmenetelmäksi. Omahoitajuuden avulla voidaan tukea lapsen kasvua ja kehitystä, sekä helpottaa lapsen päivähoidon aloitusta. Lapsen ja omahoitajan välille muodostuu hyvä ja tiivis suhde. Omahoitajuus parantaa työntekijöiden lapsituntemusta. Omahoitajuuden myötä omahoitajan ja lapsen vanhempien välinen suhde muuttuu läheisemmäksi. Omahoitajuus selkeyttää ryhmän toimintaa ja henkilöstön työnjakoa. Menetelmä on altis muutoksille ja sen toteuttamista hankaloittavat esimerkiksi sairaspoissaolot ja sijaisten huono saatavuus. Haasteita työkäytännön toteuttamiselle aiheuttavat myös henkilöstön sitoutuminen omahoitajuuteen, ammatillisuuden säilyttäminen sekä oikeanlaisen toteutustavan löytäminen. Koska tutkimuksessa käsiteltiin ainoastaan työntekijöiden kokemuksia omahoitajuudesta, olisi tarpeen selvittää myös lasten vanhempien kokemuksia työmenetelmästä. Tämän myötä voitaisiin saada lisää arvokasta tietoa menetelmän toimivuudesta.The thesis was about to study the experiences of the staff in Haapaniemi day care centre about the personal carer practice. The purpose of the research was to function as an open forum for the staff so that they could share their experiences openly about the working method. The thesis is a qualitative research. The theoretical context consisted of Attachment theory that was created by John Bowlby and also the four principles of early childhood education and care partnership. The material was gathered through individual thematic interviews. The target group of the research comprehended seven employees from Haapaniemi daycarecentre, three of them were kindergarden teachers and four of them were nurses. Material-based contents analysis was used in analysis of this research. In research the personal carer practice was considered as a good, but at the same time a very vulnerable working method. With the personal carer practice, it is possible to support childrens growth and development and also to make it easier for the children to start the daycare. A good and solid relationship is built up between the child and the carer. The per-sonal carer practice improves staffs knowledge about the children. The relationships be-tween the staff and children’s parents are getting closer through the personal carer practice. The personal carer practice simplifies the fuctions of the group and the work distribution of the staff. The working method is vulnerable for changes and its execution is being compli-cated by for example absences due to sickness and poor availability of substitutes. Other challenges in personal carer practice are the staffs’ commitment to the practice, preserving professional approach and finding the right way to execute the practice. Because the thesis dealt with experiences of the staff about the personal carer practice, it’s considered important to examine the parents’ experiences of the working method. By this it would be possible to gain valuable information about the personal carer practice

Transparent Microelectrode Arrays Fabricated by Ion Beam Assisted Deposition for Neuronal Cell In Vitro Recordings

Microelectrode array (MEA) is a tool used for recording bioelectric signals from electrically active cells in vitro. In this paper, ion beam assisted electron beam deposition (IBAD) has been used for depositing indium tin oxide (ITO) and titanium nitride (TiN) thin films which are applied as transparent track and electrode materials in MEAs. In the first version, both tracks and electrodes were made of ITO to guarantee full transparency and thus optimal imaging capability. In the second version, very thin (20 nm) ITO electrodes were coated with a thin (40 nm) TiN layer to decrease the impedance of Ø30 µm electrodes to one third (1200 kΩ → 320 kΩ) while maintaining (partial) transparency. The third version was also composed of transparent ITO tracks, but the measurement properties were optimized by using thick (200 nm) opaque TiN electrodes. In addition to the impedance, the optical transmission and electric noise levels of all three versions were characterized and the functionality of the MEAs was successfully demonstrated using human pluripotent stem cell-derived neuronal cells. To understand more thoroughly the factors contributing to the impedance, MEAs with higher IBAD ITO thickness as well as commercial sputter-deposited and highly conductive ITO were fabricated for comparison. Even if the sheet-resistance of our IBAD ITO thin films is very high compared to the sputtered one, the impedances of the MEAs of each ITO grade were found to be practically equal (e.g., 300–370 kΩ for Ø30 µm electrodes with 40 nm TiN coating). This implies that the increased resistance of the tracks, either caused by lower thickness or lower conductivity, has hardly any contribution to the impedance of the MEA electrodes. The impedance is almost completely defined by the double-layer interface between the electrode top layer and the medium including cells

Alternative Electrode Materials for Prototyping Cell Model-Specific Microelectrode Arrays

Mikroelektrodimatriisi (MEA, microelectrode array) on biologien käyttämä väline solujen sähköisen toiminnan mittaamiseen in vitro olosuhteissa. Pelkkien satunnaisten soluryppäiden ja yksikerroksisten soluviljelmien tutkimisen rinnalla yleistymässä ovat biologiset tutkimuskysymykset, joissa tutkitaan ohjatusti muodostettuja soluverkkoja tai yksittäisiä soluja. Nämä aiheet asettavat sellaisia erityisvaatimuksia elektrodien koolle ja sijainnille MEA-levyllä, sekä ylipäätään MEA-levyn suorituskyvylle, että kaupasta saatavat vakiomalliset MEA-levyt eivät yleensä niitä täytä. Räätälöidyille MEA-levyille onkin tarvetta monella sovellusalueella perussolubiologiasta ja tautimallien kehittämisestä myrkyllisyystutkimuksiin ja lääketestaukseen. Tässä väitöstyössä on valmistettu mikroelektrodeja, joiden materiaalina on käytetty titaania, atomikerroskasvatettua (atomic layer deposition, ALD) iridiumoksidia (IrOx) sekä ionisuihkuavusteiselle elektronisuihkuhöyrystyksellä (ion beam assisten e-beam deposition, IBAD) tuotettua titaaninitridiä (TiN). Elektrodit on karakterisoitu mm. niiden impedanssin, kohinatason ja pinnan morfologian osalta. Lisäksi bioyhteensopivuus ja toimivuus on varmistettu kokeilla, joissa on käytetty ihmisperäisistä kantasoluista johdettuja hermo- ja sydänsoluja. Näiden tutkimusten tarkoituksena on tarjota MEA-valmistukseen lisää vaihtoehtoja, mistä valita eri sovelluksiin parhaiten sopivat ja käytettävissä olevat resurssit parhaiten huomioivat elektrodimateriaalit. Titaanin käyttöä puhtaasti metallimuodossa on mikroelektrodimateriaalina yleisesti vältetty sen johtavuusominaisuuksia häiritsevän hapettumistaipumuksen vuoksi. Valmistukseen kuluva aika ja kustannukset voivat kuitenkin olla räätälöityjen MEA-prototyyppien kehittämisessä olennaisempia tekijöitä kuin prototyypin huippuunsa viritetty suorituskyky, jota usein arvioidaan 1 kHz taajuudella mitatun impedanssin avulla. Kuten odotettua, titaanielektrodien impedanssi oli huomattavan korkea (>1700 kΩ), mutta silti solumittauksissa sekä hermo- että sydänsolujen tuottamat kenttäpotentiaalisignaalit olivat erotettavissa kohinasta. Titaanin etuihin elektrodimateriaalina kuuluvat yleisimpiin vaihtoehtoihin verrattuna vähäisempien ja yksinkertaisempien prosessivaiheiden tarve sekä noin sata kertaa pienemmät raaka-aine kustannukset kultaan ja platinaan verrattuna. IrOx ja TiN ovat yleisesti käytettyjä elektrodien pinnoitusmateriaaleja, joiden tarkoitus on laskea esimerkiksi titaanista tehtyjen elektrodien impedanssia ja kohinatasoa. Tässä työssä tutkittiin mahdollisuutta tehdä pinnoitukset vaihtoehtoisilla, MEA sovelluksissa uusilla menetelmillä, ALD:llä ja IBAD:lla. Vaikka näillä menetelmillä pinnoitettujen 30 μm elektrodien impedanssit (450 kΩ ALD IrOx:lle ja ~90 kΩ IBAD TiN:lle) eivät aivan laskeneetkaan yleisesti käytettyjen sputteroidun TiN:n (30-50 kΩ) ja huokoisen platinan eli Pt black:n (20-30 kΩ) tasolle, niin solumittauksissa etenkään IBAD TiN elektrodien ja sputteroitujen TiN elektrodien välillä ei ollut käytännössä lainkaan havaittavaa eroa kohinatasossa ja signaalipiikkien korkeuksissa. Täten IBAD TiN onkin täysin varteenotettava materiaalivaihtoehto niille, jotka suosivat TiN elektrodeja, mutta joilla ei ole sputteriointiin sopivaa laitetta käytettävissä. ALD:n ja IrOx:n yleiset ominaisuudet sen sijaan puoltavat ALD IrOx:n sopimista erityisesti geometrialtaan haastaviin tapauksiin tai sovelluksiin, joissa elektrodeilta vaaditaan erinomaisia stimulointiominaisuuksia. Lopuksi tässä väitöstyössä kehitettiin esimerkkinä räätälöidyn MEA-levyn vaativasta sovelluksesta yksittäisten sydänsolujen mittaamiseen soveltuva MEA-levy. Tällainen MEA-levy tarjoaa yleisesti käytetylle, mutta työläälle patch-clamp menetelmälle ainutlaatuisen soluja vahingoittamattoman vaihtoehdon yksittäisten solujen tutkimiseksi, sekä mahdollistaa yksittäisen solun ominaisuuksien havainnoinnin paremmin, kuin usein varsin heterogeenisen soluviljelmän tutkiminen vakiomallisella MEA-levyllä. Ratkaisuna tähän oli elektrodien sijoittaminen lähelle solualueen ulkokehää sekä elektrodien halkaisijan kasvattaminen 80 μm:iin tavanomaisesta 30 μm:stä, mikä helpotti solujen asettamista elektrodeille ja mahdollisti solujen sähköisen sykesignaalin mittaamisen. Indiumtinaoksidi (ITO) elektrodien läpinäkyvyys mahdollisti lisäksi mekaanisen sykinnän analysoimisen kuvaan perustuvan mittaamisen avulla.A microelectrode array, MEA, is a tool used by biologists for measuring the electrical activity of cells in vitro. Instead of only studying random cell clusters and monolayers, an increasing number of biological research questions are aimed at studying well- defined cell networks or single cells. This places special demands on the location, size, and overall performance of the MEA electrodes, which the standard, commercially available layouts cannot usually meet. Therefore, custom-designed MEAs are needed for a wide range of applications from basic cell biology and disease model development to toxicity testing and drug screening. This thesis focuses on the fabrication of microelectrodes made of titanium, atomic layer deposited (ALD) iridium oxide (IrOx), and ion beam-assisted e-beam deposited (IBAD) titanium nitride (TiN). These MEAs are characterized, for example, in terms of their impedance, noise level, and surface morphology, and their biocompatibility and functionality are verified by simple experiments with human stem cell-derived neuronal cells and cardiomyocytes. The aim of these studies is to offer more alternatives for MEA fabrication, enabling researchers and practitioners to choose the electrode material that best fits their application from their available resources. Pure titanium is commonly disregarded as an electrode material because of its oxidation tendency, which destabilizes the electrical performance. However, when prototyping customised MEAs, the time and cost of fabricating the subsequent iterations of the prototype can be more decisive factors than the device’s ultimate electrical performance, which is typically evaluated by the impedance value at 1 kHz. As might be expected, although titanium electrodes underperformed in terms of impedance (>1700 kΩ), when used in the cell experiments, the field potentials from both neuronal cells and cardiomyocytes were still easily distinguishable from the noise. There are a number of benefits to using titanium as an electrode material. Besides the fact that it is about hundred times cheaper than other commonly-used materials, such as gold or platinum, it usually requires fewer and often simpler process steps than the most common alternatives. IrOx and TiN are common electrode coatings which, when applied on top of e.g. a titanium electrode, can lower the impedance and the noise level of the electrode. In this study, two alternative deposition methods, ALD and IBAD, were used for IrOx and TiN in MEA applications. Even if the impedance of these 30 μm electrodes (450 kΩ for ALD IrOx and ~90 kΩ for IBAD TiN) did not quite reach the impedance levels of the industry standards, i.e. sputtered TiN (30-50 kΩ) and Pt black (20-30 kΩ), in cell experiments the IBAD TiN electrodes in particular showed no tangible differences in peak amplitudes and noise levels compared with sputtered TiN electrodes. This makes IBAD TiN an attractive alternative material for those who prefer to use TiN electrodes, but do not have access to a sputter coater, for example. ALD IrOx, on the other hand, relies on the potential of the general properties of ALD and IrOx (yet unverified) to provide exceptional performance in designs requiring excellent step coverage or stimulation capability. Finally, as an application example of a custom-designed MEA, a version capable of measuring cardiomyocytes at the single-cell level was developed. The benefit of such an MEA is to offer a unique noninvasive method to study single cells without destroying them with the time-consuming patch clamp method, and without losing cell-specific information, which often occurs if the cell clusters studied with standard MEAs are too heterogenous. This was achieved with a number of innovations. For example, the electrodes were placed near the perimeter of the cell culturing area and had a larger diameter (80 μm) than the usual 30 μm electrodes. This simplified the plating of the cells to the electrodes and enabled the beating of the cells to be electrically recorded. It is also possible to combine that with image-based analysis of mechanical beating through transparent indium tin oxide (ITO) electrodes