MiniVStimA: A miniaturized easy to use implantable electrical stimulator for small laboratory animals

According to PubMed, roughly 10% of the annually added publications are describing findings from the small animal model (mice and rats), including investigations in the field of muscle physiology and training. A subset of this research requires neural stimulation with flexible adjustments of stimulation parameters, highlighting the need for reliable implantable electrical stimulators, small enough (~1 cm3), that even mice can tolerate them without impairing their movement. The MiniVStimA is a battery-powered implant for nerve stimulation with an outer diameter of 15 mm and an encapsulated volume of 1.2 cm3 in its smallest variation. It can be pre-programmed according to the experimental protocol and controlled after implantation with a magnet. It delivers constant current charge-balanced monophasic rectangular pulses up to 2 mA and 1 ms phase width (1 kΩ load). The circuitry is optimized for small volume and energy efficiency. Due to the variation of the internal oscillator (31 kHz ± 10%), calibration measures must be implemented during the manufacturing process, which can reduce the deviation of the frequency related parameters down to ± 1%. The expected lifetime of the smaller (larger) version is 100 (480) days for stimulation with 7 Hz all day and 10 (48) days for stimulation with 100 Hz. Devices with complex stimulation patterns for nerve stimulation have been successfully used in two in-vivo studies, lasting up to nine weeks. The implant worked fully self-contained while the animal stayed in its familiar environment. External components are not required during the entire time.