Microelectrode arrays on polydimethylsiloxane substrate

Abstract

Microelectrode arrays (MEAs) have emerged as innovative electronic tools that can be used in laboratory environments to study electrically active cells. MEAs fabricated on compliant substrates, such as polydimethylsiloxane (PDMS), offer improved biocompatibility compared to MEAs constructed on rigid substrates, since PDMS as an elastic material can conform to tissue surfaces. The enhanced ability of MEAs on PDMS to acquire electrical signals from biological specimen, attributed to the formation of a tight tissue-electrode interface due to the elasticity of PDMS, offers an approach to develop more precise diagnostics and treatment methods for cardiovascular diseases and neural disorders compared to MEAs fabricated on rigid substrates. The aim of this bachelor’s thesis is to present fabrication processes by which MEAs exhibiting both biocompatible and optimal electrical characteristics on PDMS can be fabricated, since MEAs constructed on PDMS are seen to be at the forefront of developing innovative treatment approaches and advancing biomedical research. Due to its optimal mechanical properties, PDMS is also utilized as a substrate material in systems integrating electronics and microfluidic channels. These organ-on-chips mimic human physiology with utmost accuracy in vitro, which emphasizes the significance of PDMS as a substrate material within the biomedical field. In this literature review, the material properties of PDMS and their importance in biomedical applications are first introduced. Subsequently, both rigid and flexible MEAs and the standard microfabrication processes applied to fabricate planar MEAs are presented. Thereafter, the focus of the thesis is on diverse fabrication processes by which MEAs on PDMS are fabricated. The fabrication processes employed to construct MEAs on PDMS can be roughly divided into three categories, determined by whether the fabrication of microelectrodes is based on photolithography, ink-jet printing, or principles of stretchable electronics. Principles of stretchable electronics are typically applied in MEA fabrication via manufacturing polymeric conductive microelectrodes, the wavy electrode configuration of which enables the stretching of the MEA. However, the material properties of the PDMS substrate pose challenges that complicate the fabrication process. As a result, standard microfabrication techniques may not be applicable in fabrication processes where PDMS is utilized as the substrate material. The elasticity of PDMS may cause the properties of the PDMS substrate to change during processing and hydrophobicity of the substrate complicates the introduction of hydrophilic materials to PDMS. Thus, to minimize the drawbacks occurring in PDMS during processing and enable the construction of MEAs with optimal electrical characteristics, novel fabrication processes are required. Since the elasticity of PDMS poses challenges in MEA fabrication especially in traditional photolithographical fabrication processes, ink-jet printing of microelectrodes, where the elasticity of the PDMS substrate is not problematic, is being developed. To address the challenges caused by the hydrophobic nature of PDMS, resources are directed towards researching oxidizing agents to modify the material properties and surface energy of PDMS. However, regardless of the differences between the manufacturing techniques, all fabrication processes aim to produce a biocompatible MEA with a tight electrode-tissue interface in a time- and cost-efficient manner.