Ice modulatory effect of the polysaccharide FucoPol in directional freezing

Abstract

Directional freezing harnesses crystal growth development to create aligned solid structures or etchable patterns, useful for directed ice growth in cryobiology and cryoprinting for tissue engineering. We have delved into the ice-modulating properties of FucoPol, a fucose-rich, bio-based polysaccharide. Previous research on FucoPol revealed its non-colligative hysteresis in kinetic freezing point, reduced crystal dimensions and cryoprotective effect. Here, FucoPol reshaped developing sharp, anisotropic obloid ice dendrites into linearly-aligned, thin, isotropic spicules or tubules (cooling rate-dependent morphology). The effect was enhanced by increased concentration and decreased cooling rate, but major reshaping was observed with 5 μM and below. These structures boasted remarkable enhancements: uniform alignment (3-fold), tip symmetry (5.9-fold) and reduced thickness (5.3-fold). The ice-modulating capability of FucoPol resembles the Gibbs–Thomson effect of antifreeze proteins, in particular the ice reshaping profiles of type I antifreeze proteins and rattlesnake venom lectins, evidenced by a 52.6 ± 2.2° contact angle (θ) and spicular structure generation. The high viscosity of FucoPol solutions, notably higher than that of sucrose, plays a crucial role. This viscosity dynamically intensifies during directional freezing, leading to a diffusion-limited impediment that influences dendritic formation. Essentially, the ice-modulating prowess of FucoPol not only reinforces its established cryoprotective qualities but also hints at its potential utility in applications that harness advantageous ice growth for intentional structuring. For instance, its potential in cryobioprinting is noteworthy, offering an economical, biodegradable resource, of easy removal, sidestepping the need for toxic reagents. Moreover, FucoPol fine-tunes resulting ice structures, enabling the ice-etching of biologically relevant patterns within biocompatible matrices for advanced tissue engineering endeavors.