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

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. Enhanced mechanical bending of pH-responsive bilayer cryogel-pNIPAM/DNA-based-polyacrylamide cryogel structures, as compared to cryogel-pNIPAM/DNA-based-polyacrylamide hydrogel is demonstrated using auxiliary pH triggers or pH-changes stimulated by the glucose oxidase biocatalyzed aerobic oxidation of glucose. The phenomenon originates from enhanced convectional mass-transport in the cryogel framework.image