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International Journal of Bioprinting 4D heterojunction shape reconfiguration by two-photon polymerization

A B

C D

E F

Figure 2. (A) Inset figures display the laser-scanned cantilevers equilibrium, swelled and dried respectively. The zoomed-in SEM image exhibited an
intertwined 3D matrix. (B) Normalized FTIR spectra of precursor compositions and MNIHs, where PEG-DA spectrum displayed =C-H stretching
-1
-1
vibration (2970.1 cm ), a strong absorbing spectrum of ester bond C=O (1728.9 cm ). NIPAM spectrum manifested the stretching vibration of N-H
-1
-1
in acylamino (3283.2 cm ), C-H deformation vibration, and a stretching vibrational peak of C-O in ester (1367.5 cm ). (C) Inset illustration shows
mechanical tests on the nano-indentation principle, and the representative hysteresis loops imply the elasticity of hydrogel nature, which changes the loop
shape at different states. (D) The swelling ratios of MNIH absorbed different chemicals. (E) Dynamic water contact angles on the surfaces at varied material
ratios. (F) Inset SEM images show a hydrogel cantilever standing out from the substrate. 3D illustrations are finite element calculations to verify the shape-
morphing trends and stress, matching the practical results
We intentionally tilted the scanning direction (Figure 3B) due to unfoldable space (Figure S7, the buckled area
in forming the same planar, which transformed into a elevated over 7 μm at altitude). The compact area was
spirochete, rotated at three turns, otherwise, opened, anchored on the substrate and coordinated with the
and restored to its original shape as a chiral torsion smoothly crosslinked area to regulate the buckling duty
(Videoclip S2) in an oblique view and optical microscope cycle, forming a freestanding arch bridge landscape
images. Mechanics tests found the lateral swelling force (Figure 3F1 and F2). In 3D micrographs, the loose
2
exceeding 10 N at a small footprint area of 50 × 500 μm , interspacing region buckled out-plane and was evidenced
repeated deformation manifested a slight deviation of by laser scanning confocal microscopy (LSCM, LEXT
smaller than 5% in bending angle of 1080°, and the rotation OLS5000™, Olympus) cross-sectional view to evaluate
torsional moment by mechanics test reached 5 N·μm. profile at sub wavelength accuracy. The as-demonstrated
Consequently, monolayer design realized complex chiral reversible 2D-to-3D transforming geometries at different
torsion much easier than those tedious reciprocating freedom or positions all started from the same planar
scanning strategies, showcasing no mechanical mismatch shape.
or breaking. Holding or gripping motion meant an indispensable

To spatiotemporally program reconfiguration at function in microfluidics applications or intravascular
specific sites, we accurately manipulated a buckling surgery [12,46] . For creating monolayer biomimetic hands or
action by varying NWs’ density at segmented regions. grippers, we divided MNIH structural design accordingly,
Low-density regions preferentially buckled upward scanning at different directions and densities. As seen in

Volume 9 Issue 3 (2023) 18 https://doi.org/10.18063/ijb.678