Thermoresponsive PEDOT:PSS/PNIPAM conductive hydrogels as wearable resistive sensors for breathing pattern detection

This study investigated a sustainable method for preparing PEDOT:PSS/PNIPAM conductive hydrogels. The free radical polymerization of NIPAM to PNIPAM was simply initiated by ultrasonication in an ice bath. This was done in open air rather than spending hours under an N2 purge. The resulting conductive hydrogel had a uniform texture and good flexibility for rapid resistance and color changes when exposed to temperature stimulations. Furthermore, the dual actions of hydrogen bonding and hydrophobic aggregation weaken the Coulomb interaction between PEDOT+ and PSS− for better conductivity. When interacting and aligning with the PNIPAM chain, the partial growth of the conjugation of PEDOT+ molecules was evidenced by the redshift of the PEDOT:PSS characteristic peak of Raman spectra for better resistance-temperature responses. The temperature correspondences of the resistance and transparency of the hydrogel were distinctly inversed due to the transition of hydrophilic-hydrophobic interactions when the temperature was changed through the phase transition temperature (PTT). The unique R-T relationship of the thermosensitive conductive hydrogel was used as a wearable sensor to continuously monitor breathing patterns for sleeping patients.