The synthesis of doxorubicin‐loaded metal–organic framework nanoparticles (NMOFs) coated with a stimuli‐responsive nucleic acid‐based polyacrylamide hydrogel is described. The formation of the hydrogel is stimulated by the crosslinking of two polyacrylamide chains, PA and PB, that are functionalized with two nucleic acid hairpins (4) and (5) using the strand‐induced hybridization chain reaction. The resulting duplex‐bridged polyacrylamide hydrogel includes the anti‐ATP (adenosine triphosphate) aptamer sequence in a caged configuration. The drug encapsulated in the NMOFs is locked by the hydrogel coating. In the presence of ATP that is overexpressed in cancer cells, the hydrogel coating is degraded via the formation of the ATP–aptamer complex, resulting in the release of doxorubicin drug. In addition to the introduction of a general means to synthesize drug‐loaded stimuli‐responsive nucleic acid‐based polyacrylamide hydrogel‐coated NMOFs hybrids, the functionalized NMOFs resolve significant limitations associated with the recently reported nucleic acid‐gated drug‐loaded NMOFs. The study reveals substantially higher loading of the drug in the hydrogel‐coated NMOFs as compared to the nucleic acid‐gated NMOFs and overcomes the nonspecific leakage of the drug observed with the nucleic‐acid‐protected NMOFs. The doxorubicin‐loaded, ATP‐responsive, hydrogel‐coated NMOFs reveal selective and effective cytotoxicity toward MDA‐MB‐231 breast cancer cells, as compared to normal MCF‐10A epithelial breast cells.
DNA-tethered poly-N-isopropylacrylamide copolymer chains, pNIPAM, that include nucleic acid tethers have been synthesized. They are capable of inducing pH-stimulated crosslinking of the chains by i-motif structures or to be bridged by Ag(+) ions to form duplexes. The solutions of pNIPAM chains undergo crosslinking at pH 5.2 or in the presence of Ag(+) ions to form hydrogels. The hydrogels reveal switchable hydrogel-to-solution transitions by the reversible crosslinking of the chains at pH 5.2 and the separation of the crosslinking units at pH 7.5, or by the Ag(+) ion-stimulated crosslinking of the chains and the reverse dissolution of the hydrogel by the cysteamine-induced elimination of the Ag(+) ions. The DNA-crosslinked hydrogels are thermosensitive and undergo reversible temperature-controlled hydrogel-to-solid transitions. The solid pNIPAM matrices are protected against the OH(-) or cysteamine-stimulated dissociation to the respective polymer solutions.
We present the assembly of asymmetric two-layer hybrid DNA-based hydrogels revealing stimuli-triggered reversibly modulated shape transitions. Asymmetric, linear hydrogels that include layer-selective switchable stimuli-responsive elements that control the hydrogel stiffness are designed. Trigger-induced stress in one of the layers results in the bending of the linear hybrid structure, thereby minimizing the elastic free energy of the systems. The removal of the stress by a counter-trigger restores the original linear bilayer hydrogel. The stiffness of the DNA hydrogel layers is controlled by thermal, pH (i-motif), K ion/crown ether (G-quadruplexes), chemical (pH-doped polyaniline), or biocatalytic (glucose oxidase/urease) triggers. A theoretical model relating the experimental bending radius of curvatures of the hydrogels with the Young's moduli and geometrical parameters of the hydrogels is provided. Promising applications of shape-regulated stimuli-responsive asymmetric hydrogels include their use as valves, actuators, sensors, and drug delivery devices.
Stimuli-responsive polyacrylamide hydrogels crosslinked by glucosamine–boronate/G-quadruplexes or azobenzene-functionalized DNA reveal controlled stiffness using chemical or photochemical triggers.
Gold nanoparticles
(AuNPs) or gold nanorods (AuNRs) are loaded
in polyacrylamide hydrogels cooperatively cross-linked by bis-acrylamide
and nucleic acid duplexes or boronate ester–glucosamine and
nucleic acid duplexes. The thermoplasmonic properties of AuNPs and
AuNRs are used to control the stiffness of the hydrogels. The irradiation
of the AuNP-loaded (λ = 532 nm) or the AuNR-loaded (λ
= 808 nm) hydrogels leads to thermoplasmonic heating of the hydrogels,
the dehybridization of the DNA duplexes, and the formation of hydrogels
with lower stiffness. By ON/OFF irradiation, the hydrogels are switched
between low- and high-stiffness states. The reversible control over
the stiffness properties of the hydrogels is used to develop shape-memory
hydrogels and self-healing soft materials and to tailor thermoplasmonic
switchable drug release. In addition, by designing bilayer composites
of AuNP- and AuNR-loaded hydrogels, a reversible thermoplasmonic,
light-induced bending is demonstrated, where the bending direction
is controlled by the stress generated in the respective bilayer composite.
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