Double-Network Hydrogel-Based Photonic Crystal Sensor for Mechanical Force Naked Eye Sensing and Its Application in Medical Compressive or Stretchy Instruments.

Herein, we coalesced a poly(acrylamide---Acryloyl phenylalanine)/polyacrylamide double-network (P(AM--APA)/PAM DN) hydrogel with a photonic crystal array, fabricating a mechanochromic sensor for application in flexible medical instruments by naked eye monitoring. The intensified mechanical properties of the DN hydrogel were proved by the mechanical property tests, which are attributed to the interactions of chemical bonds and hydrogen bonds between the two polymer networks. In the range of stress from 0 to 328 kPa, the reflected light wavelength of this sensor changed from 659 to 480 nm and the color changed from red to blue in response; in the range of pressure from 0 to 85 kPa, the sensor exhibited a spectrum changing from 658 nm to 467 nm, covering almost the whole visible color range. The prepared sensor was incorporated into medical instruments including the femoral artery hemostat and bandage to indicate pressure and tensile stress in practical applications. Within the appropriate pressure for wound recovery, the sensitivity and correlation between the external stimulus of pressure and wavelength of this integrated sensor were 5.58 nm·kPa and over 0.99, respectively. Ultimately, the sensor proved to be tough, sensitive, and durable, showing a broad prospect of a series of future applications.