Fig. 3
Mechanical robustness of the ingestible hydrogel device. a True stress–stretch curves of the polyvinyl alcohol hydrogel membranes with and without pores, which have been immersed in SGF (pH 3) at 37 °C for 12 h. b Tensile strength of the hydrogel membranes with (open) and without (filled) pores, which have been immersed in water or SGF (pH 3) at 37 °C for 0–15 days. c Fracture toughness of the hydrogel membranes, which have been immersed in water or SGF (pH 3) at 37 °C for 0–15 days. d Time-lapse images of an SGF (pH 3)-saturated hydrogel device (diameter ~3.6 cm at undeformed state) exposed to a maximum compressive force of 70 N and a strain of 90%. e Force–strain curves of the SGF (pH 3)-saturated hydrogel device exposed to a maximum compressive force of 70 N and a strain of 90% for two cycles. f Measured compressive forces applied to a hydrogel device (diameter ~4.8 cm at undeformed state) on day 14 (the hydrogel device was immersed in SGF (pH 3), and sustained 1920 cycles of 40% compressive strains for 8 h per day). g Measured mass of the hydrogel device after 1920 cycles of 40% compressive strain for 8 h per day over 14 days. Scale bars are 10 mm in (d). Data in (b, c, g) represent the mean ± s.d. (N = 3)
