Osmotic squat actuation in stiffness adjustable bacterial cellulose composite hydrogel
Mechanically adaptive hydrogels can change their mechanical characteristics in response to external stimuli and show potential applications in biomechanical fields. To eliminate the undesired swelling/shrinkage in the responding process, poly(acrylic acid) (PAA) was grafted to acryloyl chloride (AC)-modified bacterial cellulose (BC) by free-radical polymerization. The obtained BC-g-PAA composite hydrogels showed adjustable stiffness in compression, kept soft at pH lower than 6 (compression strain over 49% at a stress of 0.1 MPa), and stiffened when pH reached 7 (compression strain lower than 27% at a stress of 0.1 MPa), while the volume change ratio was consistently lower than 15%. Based on this, the hydrogel showed interesting squat actuation to lift a weight. The BC composite hydrogel exhibited dual pH-responsiveness after grafting PAA with poly[2-(dimethylamino)ethyl methacrylate], confirmed the general availability of this strategy in fabricating volumetrically stable and mechanically adaptive hydrogels. The surrounding solution-independent softening of BC-g-PAA hydrogel was observed in 8 min under UV irradiation via a photo-triggered pH jump reaction. By virtue of the selective UV irritation, the spatiotemporally controllable softening with actuation in BC-g-PAA hydrogel was realized. The developed pH-responsive mechanically adaptive BC composite hydrogels with high dimensional stability and UV-activated spatiotemporal squat actuating capability are expected to provide more options in developing novel bioimplants and smart structures.
- This article is part of the themed collection: Journal of Materials Chemistry B HOT Papers