A Simple and Fast Compression‐Based Method to Fabricate Responsive Gold‐pNIPAM Hybrid Materials: From Thin Films to Anisotropic Microgels

Abstract

In recent years, hydrogel‐based soft materials with hybrid properties have found widespread use in various technological fields, including tissue engineering, soft actuators, and flexible electronics. The proper implementation of these smart multifunctional materials into real‐world applications requires the development of simple, cost‐effective, and large‐scale fabrication methods. Herein, a simple compression‐ and colloid‐based method is presented to fabricate responsive Au‐poly(N‐isopropylacrylamide) (pNIPAM) hybrid films using photopolymerizable resin containing Au‐pNIPAM core–shell microgels as building blocks. Uniform Au‐pNIPAM hybrid films of 25 × 25 mm with adjustable thickness in the micron‐size range (2.3–1.2 µm) w ere successfully fabricated on glass substrates and flexible commercial acetate sheets. The resulting flexible Au‐pNIPAM films exhibit robust optical and mechanical properties, even after repeated edge‐to‐edge bending cycle tests. Additionally, using patterned light to polymerize the Au‐pNIPAM films allows synthesizing of anisotropic Au‐pNIPAM microgels with high width‐to‐height aspect ratios, such as square, circular, and rectangular microgels, adding a new dimension to the proposed fabrication method.

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“…Ultimately, uniform Au-pNIPAM films were fabricated by employing two distinct fabrication methods depending on the desired film thickness range (Figure A-3). On the one hand, the films were prepared following a recently published fabrication method for thin Au-pNIPAM films of less than 3 μm in thickness . This method relies on compressing and photopolymerizing a thin layer of the photoresin over a 3-MPS-functionalized substrate (Figure A-3, top).…”

“…The Au-pNIPAM film firmly adheres to the substrate due to the chemical bonding between the pNIPAM hydrogel and the methacrylate functional groups of the substrate. , Notably, the thickness of the films can be easily adjusted by varying the applied compression pressure during the fabrication process. More details about the fabrication method can be found in the Experimental Section, as well as in ref . On the other hand, thicker Au-pNIPAM films were achieved through a capillary-driven approach by using Parafilm tape as a spacer to form a microchannel with a given thickness, as illustrated in Figure A-3 (bottom).…”

“…On the one hand, the films were prepared following a recently published fabrication method for thin Au-pNIPAM films of less than 3 μm in thickness. 39 This method relies on compressing and photopolymerizing a thin layer of the photoresin over a 3-MPS-functionalized substrate (Figure 1A-3, top). The Au-pNIPAM film firmly adheres to the substrate due to the chemical bonding between the pNIPAM hydrogel and the methacrylate functional groups of the substrate.…”

“…Thin light-sensitive Au-pNIPAM films were fabricated through a recently published simple compression-and colloid-based method. 39 Briefly, in a custom-made photopolymerization setup, 14 μL of photoresin was directly pipetted onto the 3-MPS-functionalized substrate (glass or acetate) and compressed with a piranha-cleaned glass substrate to uniformly spread the photoresin over the surface. After 3 min of photopolymerization at 405 nm, the upper piranha-cleaned glass was gently peeled off.…”

“…To this end, several Au-pNIPAM hybrid films with varying thicknesses in the micrometer range were fabricated using a recently published fabrication method. 39 This method involves the compression and subsequent photopolymerization of a pNIPAM-based resin containing Au-pNIPAM core−shell microgels as light-sensitive building blocks. The temperature increase produced by Au-pNIPAM films with different thicknesses and containing 15 nm gold nanoparticles upon light excitation at 520 nm was experimentally characterized through thermal images captured with an infrared camera.…”