Fig. 2: Characterizations of multimaterial cryogenic printing technique.
From: Multimaterial cryogenic printing of three-dimensional soft hydrogel machines
a–e Cryogenic printing: a Schematic diagram of printing high-resolution 3D structures enabled by instant solidification against capillarity- and gravity-driven instability. b In-situ observations of instant ink-solvent solidification and SEM cross-sectional image of printed filamentary hydrogels. Scale bars, 200 μm (optical images), 5 μm (SEM image). c The kinetic predictions on printed linewidth compared to experimental measurements under varying platform moving speeds and extrusion pressures. Pred. prediction. d The kinetic prediction errors on the layer thickness of thin walls compared to experimental measurements, by using multiple hydrogel inks like PEDOT:PSS-PVA, PVA, and SA. e The generalized resolution improvement on multiple hydrogel choices and printing substrates by using cryogenic printing. RTP room-temperature printing, PI polyimide, PDMS polydimethylsiloxane, PET polyethylene terephthalate. The comparisons use the same 32 G nozzles for printing hydrogel inks. f–j Cryogenic cross-linking: f Schematic diagram of cryogenic cross-linking reactions at the synchronously melting ice-water interfaces. g Differential scanning calorimetry (DSC) curves of typical hydrogel inks and cross-linking baths. The cross-linking process is designed to react within the temperature window between the melting temperature of frozen inks and the solidification temperature of baths. h Raman spectra of frozen PVA structures after immersing in cross-linking baths show the reaction process at −5 °C. i Uniaxial tensile tests of the printed multimaterial hydrogel samples and corresponding composed single-material samples. Typical snapshots of the heterogeneous samples are inserted within this panel. @, heterogeneous sample. j Printing performance comparisons on mechanical tunability (the ratio of maximum and minimum Young’s modulus, Ymax/Ymin) and extreme aspect ratio (the ratio of structural height to resolution) with existing approaches. DIW direct-ink-writing. Error bars indicate one standard deviation from the mean over three samples.
