A Wirelessly–activated Parylene Electrothermal Valve for Mapping Brain Function in Freely Moving Subjects

Abstract

The first normally-closed Parylene valve operating on electrothermal principles for rapid and wireless drug delivery was designed, fabricated, modeled, and tested. This valve is a key component of an implantable microbolus infusion pump (MIP) for neuroimaging in freely-moving untethered animals. This low-power, lightweight MEMS valve enables an MIP suitable for studying functional brain activation in genetically engineered mice by replacing a large conventional solenoid valve used previously in larger animals.

A Parylene Bellows Electrochemical Actuator

“…In addition, Parylene has low Young's modulus which grants large displacement in fabricated diaphragms with low applied pressure. Several Parylene diaphragm geometries have been investigated: flat [15]–[17], dome [18], corrugated [13], [15], [19], [20], and bellows [21], [22]. Among them, corrugated diaphragms and bellows provide the largest deflections (> 1 mm), possess low intrinsic stress, and thus are less likely to undergo plastic deformation compared to flat and dome diaphragms.…”

Parylene C Aging Studies.

“…The following remarks provide the context for an in-depth analysis of the current accelerated aging data and also provide thoughts for future experimental designs and conditions to make robust lifetime predictions for Parylene C. Consistent with the current work as well as with earlier polymer accelerated aging studies, Parylene C too is noted for its unsuitability to the Arrhenius approach for making lifetime predictions, [25] since the polymer has been observed to undergo degradation at much lower temperatures compared to theory. [25][26][27][28] Thin films of Parylenes N and C were reported to undergo thermal-oxidation at temperatures ranging from 68 °C and 125 °C. [25] There are conflicting reports on changes to film thickness, [20] length and adhesion strength (interestingly with Silquest A-174 promoter, as used in the present study) of Parylenes depending on (annealing) temperature where the polymer folds into several lamellae before turning into spherulites as a consequence of transitioning from crystallization to glass transition temperatures.…”

Implantable MEMS drug delivery pumps for small animal research

“…Effective gating of pressurized reservoirs for on-demand delivery was achieved through a similar valve with [7], [11]. In this specific application, rapid and on-demand intravenous delivery of a relatively large volume (~200 μL) was required.…”

“…For example, on-demand and rapid delivery is desirable in applications such as tracer introduction in neuroimaging in animals [5]- [7]. Implantable systems that operate wirelessly and do not interfere with normal animal behavior are crucial requirements in this application.…”