Stiffness‐Switchable, Biocatalytic pH‐Responsive DNA‐Functionalized Polyacrylamide Cryogels and their Mechanical Applications

Abstract The large‐pore interconnected channels in cryogels, allow convectional flow and rapid mass‐transport of solute constituents between the solution and cryogel polymer framework, as compared to slower, diffusionally‐controlled mass‐transport in small‐pore hydrogels. These features are applied to develop enzyme‐loaded polyacrylamide (pAAm) cryogels, and glucose oxidase (GOx)‐loaded pH‐responsive DNA‐based pAAm cryogels, revealing enhanced biocatalytic transformations, enhanced temporal stiffness changes, and mechanical bending functions, as compared to analog hydrogels. DNA‐based pAAm cryogel/hydrogel matrices, revealing pH‐switchable stiffness properties through reversible reconfiguration of DNA‐bridging units into i‐motif structures, are introduced. Enhanced switchable stiffness changes of DNA‐based pAAm cryogels, as compared to analog hydrogels, are demonstrated upon subjecting the cryogel/hydrogel matrices to auxiliary pH‐changes, or by integration of GOx into the frameworks, and driving pH‐changes through GOx‐catalyzed aerobic oxidation of glucose to gluconic acid. Enhanced stiffness changes of pAAm cryogels represent a major advance to control the mechanical properties of cryogels and are attributed to the convectionally‐controlled mass‐transport in the cryogel matrices. Moreover, bilayer constructs consisting of poly‐N‐isopropylacrylamide (pNIPAM) cryogels and pH‐responsive DNA‐based pAAm cryogel or hydrogel structures are constructed. Enhanced pH/glucose triggered mechanical bending rates of the pNIPAM cryogel/pAAm cryogel or pNIPAM cryogel/GOx‐loaded pAAm cryogel, as compared to analog pNIPAM cryogel/pAAm hydrogel frameworks are demonstrated.