PDMS-Parylene Adhesion Improvement via Ceramic Interlayers to Strengthen the Encapsulation of Active Neural Implants

Abstract

Parylene-C has been used as a substrate and encapsulation material for many implantable medical devices. However, to ensure the flexibility required in some applications, minimize tissue reaction, and protect parylene from degradation in vivo an additional outmost layer of polydimethylsiloxane (PDMS) is desired. In such a scenario, the adhesion of PDMS to parylene is of critical importance to prevent early failure caused by delamination in the harsh environment of the human body. Towards this goal, we propose a method based on creating chemical covalent bonds using intermediate ceramic layers as adhesion promoters between PDMS and parylene. To evaluate our concept, we prepared three different sets of samples with PDMS on parylene without and with oxygen plasma treatment (the most commonly employed method to increase adhesion), and samples with our proposed ceramic intermediate layers of silicon carbide (SiC) and silicon dioxide (SiO2). The samples were soaked in phosphate-buffered saline (PBS) solution at room temperature and were inspected under an optical microscope. To investigate the adhesion property, cross-cut tape tests and peel tests were performed. The results showed a significant improvement of the adhesion and in-soak long-term performance of our proposed encapsulation stack compared with PDMS on parylene and PDMS on plasmatreated parylene. We aim to use the proposed solution to package bare silicon chips on active implants.

Hybrid fabrication of multimodal intracranial implants for electrophysiology and local drug delivery

“…A further drawback of classic microfabrication approach is the demand for an adhesion promotor between PDMS and PAC. 39 Without a promotor the two layers are detachable by hand. A bonding of a PAC sheet onto cured PDMS, in an analogous manner to the here reported bonding to a resin, is by best of our knowledge not reported.…”

Thin Film Encapsulation for LCP-Based Flexible Bioelectronic Implants: Comparison of Different Coating Materials Using Test Methodologies for Life-Time Estimation

“…Thus, further improvement at the interface between Parylene C and silicone is needed. This could be achieved by the addition of PECVD ceramic interlayers [42,43]. Alternatively, TFE2 could be modified to finish at one of the Al 2 O 3 and TiO 2 ALD layers instead of Parylene C.…”

Cold Laser Micro-Machining of PDMS as an Encapsulation Layer for Soft Implantable Neural Interface

“…PDMS film has been proven to act as an excellent barrier to implantable microelectrodes or as high-quality dielectrics with minimal resistive power loss [13,14]. As an encapsulation layer for implantable neural interface, PDMS can increase the flexibility required for the application and minimize tissue response [15]. Joint research on other materials of PDMS provides a new idea for the further development of implantable neural interfaces [16].…”