Micro Sponge Balls: Preparation and Characterization of Sponge-like Cryogel Particles of Poly(2-hydroxyethyl methacrylate) via the Inverse Leidenfrost Effect

Abstract

Here, we report a method to prepare cryogel particles with sponge-like mechanical properties, including high porosity and high elasticity. The preparation process of the cryogel particles of poly(2-hydroxythyl methacrylate) can be summarized in the two following steps: preparation of frozen droplets using the inverse Leidenfrost effect, followed by cryo-gelation by frozen polymerization. First, a polymer precursor was dropwise added into bulk liquid nitrogen (−196 °C). Then, frozen droplets were created by the inverse Leidenfrost effect, which were subsequently polymerized in liquid paraffine (−15 °C). After thawing and drying, the cryogel particles were obtained. The monolithic super-macroporous structure was observed by scanning electron microscopy (SEM). The mechanical properties of the cryogel particles were studied via compression−swelling tests. At maximum compression, the particles achieved 94.3% degree of deformation; remarkably, they returned to their original shape under the swelling state. The strategy proposed herein, which combines the inverse Leidenfrost effect with a cryopolymerization technique, could be applied to prepare various polymer particles without employing surfactants.

Versatility of the Preparation Method for Macroporous Cryogel Particles Utilizing the Inverse Leidenfrost Effect

“…Hence, the choice of the monomers for the synthetic polymer and cross-linker and the natural polymer itself is a key factor in obtaining the appropriate materials for their specific application. We prepared five kinds of cryogel particles by selecting four synthetic polymers with different monomers and a natural polymer as case studies in order to prove the versatility of our previous method including the two-step preparation process . All the experimental conditions and results for the polymer particles are summarized in Table and Figures and , together with the Supporting Information. …”

“…We prepared five kinds of cryogel particles by selecting four synthetic polymers with different monomers and a natural polymer as case studies in order to prove the versatility of our previous method including the two-step preparation process. 21 All the experimental conditions and results for the polymer particles are summarized in Table 1 and Figures 1 and 2 , together with the Supporting Information .…”

“…In addition to the beneficial aspect of various properties of the cryogels being flexibly designed, the shape of cryogel particles is difficult to be controlled without the use of a detergent, where the emulsion without any detergent for the cryo-polymerization at the frozen temperature becomes unstable, and therefore, the colloidal coalescence occurs . We have recently reported the novel preparation method via a two-step process for cryogel particles without any detergent, where (1) the inverse-Leidenfrost effect and (2) the cryo-polymerization method were adopted stepwisely . The polymer particles with spherical shapes can be easily formed on the liquid nitrogen because the boiling film coats the surface of the water droplet including polymer precursors and the included water droplets contribute to the formation of the macroporous structure in the polymer particle via cryo-polymerization.…”

“… 20 We have recently reported the novel preparation method via a two-step process for cryogel particles without any detergent, where (1) the inverse-Leidenfrost effect and (2) the cryo-polymerization method were adopted stepwisely. 21 The polymer particles with spherical shapes can be easily formed on the liquid nitrogen because the boiling film coats the surface of the water droplet including polymer precursors and the included water droplets contribute to the formation of the macroporous structure in the polymer particle via cryo-polymerization.…”

A Breathable, Passive‐Cooling, Non‐Inflammatory, and Biodegradable Aerogel Electronic Skin for Wearable Physical‐Electrophysiological‐Chemical Analysis

“…Motivated by these previously reported literatures that validate the impact of low-temperature using liquid nitrogen on the flexibility of other polymers (i.e., poly(2-hydroxyethyl methacrylate) cryogels, [54] alginate (or cellulose)-based cryogels, [55,56] and cellulose-chitosan aerogels [57] ), we firstly employed such liquid nitrogen-assisted strategy to make GelMA aerogel flexible, which has not been studied previously.…”