Bio-inspired flow-driven chitosan chemical gardens

Abstract

Organic chemical gardens of chitosan hydrogel develop upon injecting an acidic chitosan solution into an alkaline solution. Besides complex and budding structures, tubular hydrogel formations develop that exhibit periodic surface...

Flow‐driven Surface Instabilities of Tubular Chitosan Hydrogel

“…The deformations take place along the direction of the tube head with π phase shifting at the boundaries (Figure 4a, VideoS2 in SI), similarly to that observed using LMW chitosan. [36] The characteristic wavelength in Figure 4(b) indicates the linear scaling as a function of tube depth, h, analogously to previous studies of wrinkling where wavelength is dependent on the thickness of the gel. [12] We have also found that the increase in the alkaline concentration increases the wavelength of surface deformations (cf.…”

“…Since this wrinkle-to-fold transition is responsible for the appearance of the periodic bands, one expects that the wavelength of the wrinkles will determine the periodicity of folds as well. Indeed, the characteristic wavelength of the folds in Figure 3(f) is a linear function of the tube depth, h (see work where we reported that the wavelength of wrinkling patterns on low molecular weight (LMW) tubes scales linearly with h. [36] The same dependence is observed for the fold amplitude (A h ), defined in Figure 1(b), in Figure 3(f). Further increase of the flow rate increases the amplitude of local wrinkles which affects the tube deformation by allowing the coexistence of wrinkles and folds (see triangular markers in Figure 2).…”

“…Despite the different tube characteristics, the slope of the R À Q straight line is near unity for all the concentrations and molecular weights (for MMW: 1.03 � 0.03 and for HMW: 0.98 � 0.07). Thus, likewise the LMW scenario, [36] there is no significant liquid transfer through the hydrogel membrane.…”

“…An upward growing closed tube develops which adheres to the glass wall in accordance with our previous work. [36] At slow injection rates and high NaOH concentration, tubes with a smooth surface evolves as shown with filled circles in the dynamical phase diagram in Figure 2. When the alkaline concentration is decreased and the flow rate is increased, narrow dark stripes appear on the tube transverse with right angle to the flow (open circles in Figure 2).…”

“…Previously we have designed a method, utilizing laminar flow, to create chitosan gels in various structures resembling soft chemical gardens. [36] We have also determined the experimental conditions where the developing gel interface between acidic and alkaline solutions can go through spontaneous symmetry breaking of the smooth surface and chitosan tubes exhibiting well-defined periodic wrinkles arise. In this work, we apply the same flow-driven approach to explore the types of surface instabilities inherent in the system for chitosan tubes of various molecular weights.…”