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

Abstract

We have investigated the versatility of a two-step preparation method, without a detergent, that combines both the inverse Leidenfrost effect and the cryogelation technique by using the macroporous particles of different kinds of monomers (four vinyl monomers) or a natural polymer (agarose). First, the precursor of polymers was dropped into liquid nitrogen to prepare the spherical frozen droplet by the inverse Leidenfrost effect. Second, the frozen droplets were cryo-polymerized at the frozen temperature; then, cryogel particles were prepared after thawing. Subsequently, the basic characteristics of the macroporous polymer particles obtained above were compared, focusing on the appearances, porous morphologies, and mechanical properties. It was found that the similar polymer particles could be obtained by the two-step preparation method, while there was a slight difference in their characteristics, depending on the type of monomers. Especially for the mechanical properties, the cryogel particles of the hydrophilic polymer exhibited a shape memory function with sponge-like elasticity, whereas the hydrophobic polymer particles were observed to be cracked after compression (i.e., no shape memory function). This work provides a versatile method of adopting various kinds of monomers and natural polymers for the preparation of macroporous particles. Hence, the method possibly has a potential to prepare and design "tailor-made" macroporous polymer particles for the application purpose.

Preparation and Characterization of Biodegradable Sponge-like Cryogel Particles of Chitosan via the Inverse Leidenfrost (iLF) Effect

“…This might have occurred because the chitosan cryogel particles were made from natural polymers with different mechanical properties compared to those of synthetic polymers. A similar result could also be found in agarose cryogels, where the shape of the particle changed after compression . On the other hand, cryogel made from synthetic polymers like poly­(2-hydroxyethyl methacrylate) could withstand up to 13 cycles without losing its original form .…”

“…The porogen's size contributed to the pore's difference in size between the surface and cross section. 25 Sponge-like Mechanical Properties. The deformation study of the cryogel particles produced here was examined by performing mechanical compression-release tests in a micro syringe, as shown in Figure 8a.…”

“…The addition of glutaraldehyde caused the primary amino groups of chitosan to react with aldehyde groups in a condensation reaction, resulting in the formation of Schiff’s bases. , Moreover, the change in viscosity of the solution after the addition of glutaraldehyde indicated the cross-linking reaction had happened . The cryogel particles were prepared by combining the iLF effect and cryo-polymerization technique (iLF cryo-method). ,, Figure shows the observation of cryogel particles with varied amounts of acetic acid (0.01, 0.02, 0.03, and 0.04 mol) as a frozen droplet, after cryogelation and lyophilization. As shown in Figure a3–d3, the cryogel particles had a spherical shape with a yellow color.…”

“…Therefore, the porogen should be larger in the cross section. The porogen’s size contributed to the pore’s difference in size between the surface and cross section …”

“…The cryogel particles were created by polymerization under freezing conditions. ,, Ice crystals were used as porogens in the polymerization process after being templated in a polymer precursor. The cryogel particles in this study were created by using the droplet method and the iLF effect.…”