Biomimetic hydrogel-CNT network induced enhancement of fluid-structure interactions for ultrasensitive nanosensors

Flexible, self-powered, miniaturized, ultrasensitive flow sensors are in high demand for human motion detection, myoelectric prosthesis, biomedical robots, and health-monitoring devices. This paper reports a biomimetic nanoelectromechanical system (NEMS) flow sensor featuring a PVDF nanofiber sensing membrane with a hydrogel infused, vertically aligned carbon nanotube (VACNT) bundle that mechanically interacts with the flow. The hydrogel-VACNT structure mimics the cupula structure in biological flow sensors and gives the NEMS flow sensor ultrahigh sensitivity via a material-induced drag force enhancement mechanism. Through hydrodynamic experimental flow characterization, this work investigates the contributions of the mechanical and structural properties of the hydrogel in offering a sensing performance superior to that of conventional sensors. The ultrahigh sensitivity of the developed sensor enabled the detection of minute flows generated during human motion and micro-droplet propagation. The novel fabrication strategies and combination of materials used in the biomimetic NEMS sensor fabrication may guide the development of several wearable, flexible, and self-powered nanosensors in the future. An artificial sensor that mimics the simple biological flow sensors found in some fishes has been developed by researchers in Singapore and the USA. Fishes feature soft polymer-like structures with embedded sensing elements that are sensitive to the flow of surrounding water, and help them to navigate. By mimicking this idea, Meghali Bora and Ajay Giri Prakash Kottapalli from the Singapore–MIT Alliance for Research and Technology and co-workers have created a flow sensor that is self-powered, flexible and highly sensitive. Specifically, they made hydrogel-infused bundles of carbon nanotube ‘hairs’ on a ‘hair-cell’ membrane made of electrospun polyvinylidene fluoride nanofibers. The hydrogel mechanically couples external flow stimuli to the nanotubes and improves the sensing performance of the sensor. Moreover, the device does not require a power supply. A new class of self-powered and flexible biomimetic NEMS flow sensor is developed that can detect minute fluid flows with ultrahigh sensitivity. The hydrogel-VACNT structure closely mimics the mechanical and material properties of the gelatinous cupula found in many biological flow sensors. This work illustrates how such a nature-inspired design when implemented in NEMS sensor through nanofabrication enhances the sensitivity of the flow sensor.