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-co-N-Acryloyl phenylalanine)/polyacrylamide double-network (P(AM-co-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-1 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.

Responsive hydrogel-based three-dimensional photonic crystal sensor for lactic acid detection.

The determination of lactic acid content has a guiding significance for disease diagnosis or food supervision. Herein, a hydrogel-based three-dimensional photonic crystal (PC) sensor for specific detection of lactic acid is introduced. The hydrogel was prepared by one-step copolymerization of N-isopropylacrylamide and acrylamide in the presence of oxamate derivative 2-((6-acrylamidohexyl) amino)-2-oxoacetic acid (AOA). An obvious color change from orange-red to purple and a 45-nm redshift of the reflection peak were obtained in 3 min when lactic acid concentration increased from 0 to 20 mM. The detection limit was confirmed as 0.1 mM, and the prepared sensor can be reused more than 20 times. Moreover, the affinity and selectivity of AOA to lactic acid were proven by both the interaction energy from density functional theory (DFT) study and the comparison to those of pyruvate and propionic acid. This sensor was proven to be cost-effective and convenient with rapid response time, good reusability, and selectivity.