Force-sensor-integrated soft microfinger for mechanical stimulation and generated force evaluation of zebrafish larvae.

Zebrafish exhibit specific locomotor patterns during the early embryonic and larval stages, which has established them as a widely used vertebrate model for locomotor and behavioral research. In movement- and motor disorders-related analyses, touch-evoked response experiments are commonly used to trigger reflex behaviors in a zebrafish. Traditionally, these experiments have been performed manually using metal instruments such as tweezers or needles. However, this method carries a risk of physical injury to the larvae and poses considerable limitations in terms of stimulation repeatability and quantitative control. Recently, automated systems for touch response experiments have been developed to overcome these limitations; however, metal instruments are still predominantly used. To address this gap, this study introduces a novel microrobotic platform for stimulus delivery and response evaluation, featuring a microfinger equipped with integrated force sensors that enable flexible and safe contact. For tail stimulation using the microfinger, only the head of the zebrafish larva required immobilization to ensure efficient transmission of the applied force, which necessitated the development of a head restraint chamber device. The resulting touch response experimental system, comprising the microfinger and the fixation apparatus, effectively elicited reflex responses. This system can provide a new platform for performing zebrafish touch response experiments.