Role of Surfactant in Evaporation and Deposition of Bisolvent Biopolymer Droplets

Abstract

Inkjet printing of biopolymer droplets is gaining popularity because of its potential applications in regenerative medicine, particularly the fabrication of tissue-regenerative scaffolds. The quality of bioprinting, which affects cellular behaviors and the subsequent tissue formation, is determined by the solvent evaporation and deposition processes of biopolymer droplets, during which instantaneous local viscosity and surface tension changes occur because of the redistribution of the biopolymer inside the drop. Such dynamics is complex and not well understood. Most biopolymer inks also contain multiple solvents of distinct evaporation rates, further complicating the system dynamics. Using high-speed interferometry, we directly observe in real time the instantaneous drop shape of inkjetprinted picoliter gelatin drops containing glycerol and water. It is observed that, for bisolvent gelatin drops with surfactants, highly viscous gelatin and glycerol accumulated near the pinned contact line at an early stage suppress the evaporation-driven outward flow and create a stagnation zone near the contact line region. Lower surface tension at the contact line, because of its high local surfactant concentration, as compared to the drop apex induces a strong Marangoni recirculation, which in conjunction with a stagnation zone in the contact line region causes the instantaneous drop shape to transition from a spherical cap to a volcano shape during evaporation and resulting in a volcano-like deposition profile. In contrast, the suppressed evaporation outward flow together with a weak Marangoni flow leads to a domelike deposition for the case without surfactant. The role of surfactant in polymer drop deposition with water-only solvent is also investigated and compared against that of bisolvent drops. For the single-solvent case, the deposition profile is found to shift from a coffee-eye shape in the presence of surfactant to a uniform deposition without surfactant. The results reveal new insight into the complex role surfactant plays during polymer drop evaporation and deposition processes.

4D printing of self-folding and cell-encapsulating 3D microstructures as scaffolds for tissue-engineering applications

“…Inkjet-printing produces micropatterns by delivering droplets of water-based inks on to a substrate, where the droplets dry, become ink-spots, and assemble into the micropatterns. Environmental and manufacturing factors, such as temperature and the timing for firing the droplets, determine the final morphology of the ink-spots and thus the shape, swelling rate, and self-folding of the micropatterns [35]. We first studied the effects of these factors on the printing of a single ink-spot.…”

“…Assuming axisymmetry and the droplet forms a spherical cap, the volume may be tracked over time knowing the contact radius and contact angle. The thickness length scales during the late stages of evaporation for when the droplet turns into a film are acquired in-situ by a reflection interference microscopy technique [35]. When the substrate was at RT (25 • C), the volume of the deposited ink-spot decreases rapidly for about 1.2 s as the water evaporated from the ink-spot.…”

CLeANFIT – Contact‐Less Axial Nearfield‐Based Fluorescence Imaging Topography: A Method for 3D Micro‐ and Nanotopography Characterization

“…In the presence of surfactant and depending on the surfactant concentration, the local Marangoni flow increases which affects the droplet surface tension. [ 55,56 ] Equal magnitudes of two competitive forces of capillary and Marangoni flows at the droplet edge causes local Marangoni vortices near the contact edge, which generates the swirling motion rather than the back‐and‐forth motions, [ 57 ] pulling and redistributing the dyes upwards and inwards by swirling flow. It is known that the Marangoni flow is weak in water droplets.…”

“…Accumulation of dyes near the contact line in the presence of surfactant, creates a stagnation zone, where the Marangoni flow overcomes the capillary flow. [55] This results the inflection point occurring after 24 min, which allied to an inconstant pressure inside the droplet causes the droplet curvature at the interface. [59] Such a transition point is followed by contact line displacement and consequent deposition of dyes into contact rings.…”

Effect of Particle Concentration on Surfactant-Induced Alteration of the Contact Line Deposition in Evaporating Sessile Droplets

“…Zhong et al 33 recently investigated the effect of different surfactant concentrations on the wetting transition of an evaporative sessile droplet and could achieve exiting shapes of deposition. Kim et al, 34 by using surfactants in bisolvent gelatin drops, could induce strong Marangoni eddies, which in coexistence with a stagnation zone near the contact line changed the volcano-like depositions to dome-like depositions. Among the few studies that have taken the effect of successively increasing surfactant concentration into account, the valuable effort of Still et al 35 deserves mentioning.…”