Morphology of optically anisotropic agarose hydrogel prepared by directional freezing

Abstract

Agarose hydrogels which showed optical anisotropy were obtained by the directional freezing of starting isotropic gels under a temperature gradient. The directional freezing caused a crystallization of many isolated ice crystal phases, leaving a honeycomb-like gel phase with a higher polymer content. The crystallographic c-axis of the ice crystals was directed to the temperature gradient. X-ray and optical analyses showed that agarose chains had a strong planar orientation along the walls'side surfaces, which were parallel to the equatorial planes of the ice crystals. Scanning electron microscopy showed that the wall consisted of a large number of sheets stacked along the wall thickness; in each sheet, agarose fibrillar structures were found to be densely aligned. With the application of repeated freezing and thawing, the anisotropy of the segregated gel phases increased.

Structured Macroporous Hydrogels: Progress, Challenges, and Opportunities

“…In most cases, polymer precursor solutions are frozen and subsequently cryopolymerized through small molecule, [104,[119][120][121] UV, [122][123][124] or radiation [110,118,125] initiated methods; however, physically crosslinked gels have also been reported, [126] including PVA-based anisotropic hydrogels prepared via directional freeze-thawing. [107,109] The direction of ice crystal growth determines the orientation of the pore while the rate of freezing predominantly influences the dimensionality of the aligned structures generated, with slower cooling rates resulting in slower ice crystal growth and ultimately the formation of larger ice platelets and thus larger pores following lyophilization.…”

Influence of Gluten and Gum Additives and Cryogenic Treatment on Some Properties and Morphology of Wheat Starch Complex Gels

“…These pores pierce through the gel material, and the polymeric phase proper represents the walls of the macropores (in thin sections of FTGs the Lugol's solution stained the walls in dark violet). For the non-covalent (physical) gels, such pore formation is well-known and its phenomenology was explored in considerable detail, e.g., for the cases of freezing of starch [38] or agarose [39] gels. The presence of gluten and gums in the systems studied in our research was an additional factor that influenced the structure of the gels.…”

Micropatterned Carbon Nanotube–Gel Composite as Photothermal Material

“…4b). [27][28][29] Both dried films (nanotube-gel composite and ordinary agarose gel) are not destroyed even when rubbed with a cotton gauze, and continue to stick strongly with the slide glass (Fig. 4c), whereas the as-produced nanotube-gel composite without drying is readily destroyed when rubbed with a gauze.…”