A pH-Responsive Hydrogel of Controlled Drug Release as a Strain Sensor

Intelligent response hydrogels, such as those sensitive to pH and strain, have been applied in biomedical and health fields. However, how to set up a bridge between pH and strain responsiveness to develop one product with versatility in a wide concept of health is attracting great interest. In this work, a pH-responsive hydrogel was synthesized via free-radical polymerization of acrylic acid (AA), hydroxyethyl methacrylate (HEMA), and sodium styrenesulfonate (SSS) in poly(vinyl alcohol) (PVA) solution. The AA component provided pH-responsiveness, HEMA part formed microhydrophobic domains that balanced swelling and enhanced the mechanical properties of networks based on PVA, while SSS segment served as a conductive dopant to achieve sensing capability. The optimal hydrogel exhibited good mechanical properties, including an elongation at breakage of 810%, tensile strength of 0.31 MPa, toughness of 1.48 MJ/m3, Young’s modulus of 0.03 MPa, and stable cyclic tensile behavior. The hydrogel showed distinct pH-dependent swelling characteristics and functioned as a drug-loaded vehicle to control drug release. The release process conformed to Fick diffusion. Meanwhile, the pH-responsive hydrogel could detect continuous variations in strain levels with a gauge factor (GF) of 7.12 and response and recovery times of 0.26 s and 0.28 s, respectively. After loading the drug, it was also integrated into a sensor to monitor various joint movements well, exhibiting satisfactory biocompatibility. In the big health industry, this multifunctional hydrogel can facilitate healthy living by detecting limb movements and protect joint health through transdermal drug delivery.