Enhancing Temperature Responsiveness of PNIPAM Through 3D‐Printed Hierarchical Porosity

Materials with ultra-fast responsive properties are essential for variousapplications. Among the responsive materials, poly(N-isopropylacrylamide)(PNIPAM) stands out due to its well-studied temperature-responsiveproperties. Improving the kinetics of the responsive properties of PNIPAMis, however, still essential for advancing its practical use. Here, the responsiverate of PNIPAM hydrogels is enhanced by first incorporating sub-micrometerporosity into the material through polymerization-induced phase separation(PIPS), followed by introducing millimeter scale pores via 3D printing, therebyrendering the material with hierarchical porosity. The 3D-printed porousPNIPAM structures show accelerated swelling and deswelling, when comparedto non-porous PNIPAM structures, due to enhanced water permeability asso-ciated with the continuous network of micrometer to millimeter-sized pores.Additionally, thinner polymer structures result in faster temperature responserates. At the same time, the mechanical strength of PNIPAM hydrogels withhigh porosity and thinner polymer walls is not compromised, overcomingthe common trade-off between swelling and mechanical properties.