Prolonged Corrosion Stability of a Microchip Sensor Implant during In Vivo Exposure

Abstract

A microelectronic biosensor was subjected to in vivo exposure by implanting it in the vicinity of m. trapezii (Trapezius muscle) from cattle. The implant is intended for the continuous monitoring of glucose levels, and the study aimed at evaluating the biostability of exposed semiconductor surfaces. The sensor chip was a microelectromechanical system (MEMS) prepared using 0.25 µm complementary metal–oxide–semiconductor CMOS/BiCMOS technology. Sensing is based on the principle of affinity viscometry with a sensoric assay, which is separated by a semipermeable membrane from the tissue. Outer dimensions of the otherwise hermetically sealed biosensor system were 39 × 49 × 16 mm. The test system was implanted into cattle in a subcutaneous position without running it. After 17 months, the device was explanted and analyzed by comparing it with unexposed chips and systems. Investigations focused on the MEMS chip using SEM, TEM, and elemental analysis by EDX mapping. The sensor chip turned out to be uncorroded and no diminishing of the topmost passivation layer could be determined, which contrasts remarkably with previous results on CMOS biosensors. The negligible corrosive attack is understood to be a side effect of the semipermeable membrane separating the assay from the tissue. It is concluded that the separation has enabled a prolonged biostability of the chip, which will be of relevance for biosensor implants in general.

Continuously Operating Biosensor and Its Integration into a Hermetically Sealed Medical Implant

“…In addition, the development and test of implantable biosensors has to overcome high administrative obstacles, since human body implants are meaningfully subjected to strict regulations via various laws and enactments [ 10 ]. This holds in a comparable manner for animal models that are frequently used for preliminary tests of human medical implants [ 12 , 13 ]. One of these requirements relates to the sterilization of the implant that has to be demonstrated prior to any in vivo testing.…”

“…Previous investigations have shown that the exposed surfaces from TiN [ 16 , 17 ], SiO 2 , and SiON remain intact in vitro and would allow sensor chip operation in liquid environments for many months [ 13 , 18 ]. It is shown here how the developed BioMEMS can be integrated into a hermetically sealed implant.…”