Parylene C is a promising material for constructing flexible, biocompatible and corrosion-resistant microelectromechanical systems (MEMS) devices. Historically, Parylene C has been employed as an encapsulation material for medical implants, such as stents and pacemakers, due to its strong barrier properties and biocompatibility. In the past few decades, the adaptation of planar microfabrication processes to thin film Parylene C has encouraged its use as an insulator, structural and substrate material for MEMS and other microelectronic devices. However, Parylene C presents unique challenges during microfabrication and during use with liquids, especially for flexible, thin film electronic devices. In particular, the flexibility and low thermal budget of Parylene C require modification of the fabrication techniques inherited from silicon MEMS, and poor adhesion at Parylene-Parylene and Parylene-metal interfaces causes device failure under prolonged use in wet environments. Here, we discuss in detail the promises and challenges inherent to Parylene C and present our experience in developing thin-film Parylene MEMS devices.

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This work represents one of the first examples of a penetrating polymer probe array that records from individual neurons in structures that lie deep within the brain.

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Obtaining multiple single-unit recordings in particular neural networks from behaving animals is crucial for the understanding of cognitive functions of the brain. Attaining stable, chronic recordings from the brain is also the foundation to develop effective cortical prosthetic devices. However, severe immune response caused by micromotion between stiff implants and surrounding brain tissue often limits the lifetime of penetrating, neural recording devices. To reduce the stiffness mismatch between recording devices and brain tissue, we developed a flexible, polymer based multi-electrode array for recording single neuron activities from the rat hippocampus, a major subcortical structure of the rat brain. Parylene C, a biocompatible polymer, was used as the structural and insulation material of the multi-electrode array. 64 platinum (Pt) recording electrodes were placed in groups along each shank to conform to the anatomical distribution of hippocampal principle neurons. The multi-electrode array was chronically implanted in three animals. After recovery, neural activity together with movement traces were collected from the behaving animals.