Temperature-mediated construction of a plantar pressure-relieving, thermally insulating, and biodegradable thick-walled cellulose sponge insole

Plantar pressure can be reduced and wearing comfort can be improved by using cushioning materials such as insoles. However, the biodegradation of most commercial insoles is difficult, incurring high disposal costs both economically and environmentally. Herein, we present a temperature-mediated approach for constructing a plantar pressure reducing, thermally insulating, and biodegradable thick-walled cellulose sponge (TWCS) insole from cotton linters. 3D Raman imaging and crystallographic test results demonstrated that freezing temperature affected the packing behavior of the dispersed cellulose at the ice crystal boundary, resulting in a marked distinction between wall thicknesses and crystallinity of sponges, from 0.36 μm and 0.39 to 7.74 μm and 0.46, at distinguishing temperatures (−25 ˚C, −78 ˚C, and − 198 ˚C). Benefiting from the thick-walled structure generated during the temperature-mediated interfacial assembly, the mechanical strength of the TWCS was significantly increased by 5.6 times to 569 kPa, accompanied by significantly enhanced structural stability, pressure-relieving, and thermal insulating characteristics. Subsequently, we designed TWCS as a biomass insole, and its performance was thoroughly examined using plantar pressure testing, thermal performance assessment, finite element simulation, and degradability investigations. The results demonstrate that TWCS can effectively decompress (1-fold pressure reduction), disperse external stresses, prevent heat loss and complete degradation within 50 days under biological conditions, and can potentially replace traditional petroleum-based sponge insoles.