Page 28 - IJB-9-3

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

number and location of the gear teeth structures, promising are matters of concern [50,51] . To verify cytotoxicity, the
a novel ability to choose the stimuli interaction type beyond as-prepared MNIH samples were rinsed, disinfected,
4D programmability. The as-fabricated gripper MNIH and loaded with fibroblasts for viability evaluations
bent its arms with asymmetric gear teeth from a typical with the live-dead assay kit. Fluorescence microscopy
C-arm (Figure 3F2 and Video clip S3) to a higher-freedom images reflected the cell-culturing activities on MNIHs.
S-arm (Figure 3G1-G3, the arm bent in shifting directions Fibroblasts [51] spread (stained in green, Figure 4C)
to form S-shape closure/opening actions). Noticeably, we throughout the surfaces of the MNIHs with desirable
not only modified the arm bending configuration, but adhesion. The constantly-high cell viability values across
also selected the actuation conditions simultaneously the entire culture period (Figure 4B, >97.55%) suggested
as observed. C-armed gripper (Figure 3F2) was closed the availability of MNIHs as implantable bio-robotics or
by absorbing solvent, and in contrast, the S-arm gripper medical care.
(Figure 3G2 and G3) opened under the same condition, For actual usage, we need to investigate the self-
and was closed by evaporating solvent. Therefore, the gear [52-58]
teeth arrangement allowed MNIHs to select actuation repairing ability under extreme conditions. As known,
hydrogel nature bestowed MNIHs with an impact/shock-
stimuli, bringing the simple shape-reconfiguration to a absorbing ability superior to those non-deformable
higher level.
constructs, as plastic or metal structures were usually
After investigations were done considering MNIHs as decomposed into pieces if being deformed. To check this
mechanically-interconnect devices, we identified the shape ability in room conditions, we implemented a series of
reconfiguration of the nanometric unit, NWs, which was damage experiments on MNIHs. After being intentionally
the cornerstone for reprogrammed behavior (Figure 4). As poked or squeezed by externally-applied forces, MNIHs
described, TPP provided sub-200 nm line width and sub- would not disintegrate, instead, these damaged MNIHs
10 nm surficial roughness (Figure S8) of NWs to exceed spontaneously recovered (Figure 4F and G, the small
the optical diffraction limits [8,41] , therefore promising organic molecules PEG-400 penetrated MNIH as a mobile
novel hydrogel-nature photonic crystal applications based nano binder to automatically stitch up wounds), displaying
on nanowire structure. We separated NWs (without self-repairing function under harsh environments such as
interconnection) for interactive PCs with gradient accidental shock or destruction. For instance, a micro-
structure coloration. A riot of tunable coloration was structured “broken heart” MNIH (Figure 4F) self-fixed
realized for micro-scale anti-counterfeiting marks, optical itself after an intentional distortion caused by squeezing
information storage, or display (Figures 1, 4A and B). Their with the use of a hard tweezer. The “broken heart” MNIH
periodic structure became dynamic because hydrogel self-repaired and returned to the pre-designed symmetrical
NWs slightly swelled or shrunk to modulate its dielectric shape simply by absorbing PEG-400 molecules (structural
constant difference by the changeable solvent retention, similarity over 90%, Video clip S5), and avoided turning
tuning the photonic band gap [40,47] as multi-stage photon into waste after accidental damage. The reconstructed
filters. stiffness/Young’s modulus reached over 70% of the initial
We further found a light-deformable ability of the PEG/ state. Beneficially, no tedious surgical operation/diagnosis,
NIPAM/TAIC network inside MNIHs, which modulated fixation, or tools were necessary through the self-repairing
the local internal stress like photon-active muscles” for process.
clarity. The remote laser-irradiated local region thermally To in-depth verify the recovering ability, we forcibly
expanded according to the applied light. As evidence, poked an MNIH woodpile using a sharp needle, leaving
a fabricated free-standing frog-mimicking MNIH behind two through holes. Strikingly, the physically-
(dimension <100 × 100 × 40 μm ) became photoactive damaged hole absorbed PEG-400 molecules, and
3
[48]
but without liquid crystal elastomer (Figure S9), showing regenerated the pre-designed woodpile structure
the hybrid PEG/NIPAM/TAIC network as alternative without guidance, showcasing a typical shape-memory
photon-active materials. Photon-thermal conversion characteristic. As shown, the damaged area exposed more
redistributed the swelling-induced stress of the frog head, functional groups to capture organic (PEG-400) molecules
making the frog nod continuously (Videoclip S4) at a than the other areas. The strength of the intermolecular
frequency and amplitude relying on the laser radiation interaction between binder and MNIHs determined the
without fatigue over 10 actuation cycles. recovered strength. As confirmed, MNIHs possessed
4
In potential bio-chip applications [49] such as shape-memory characteristics, enabling the recovery
medical theranostics, or regenerative engineering, the process to happen toward the initial design, not to an
biocompatibility and human-friendliness of using MNIHs amorphous form.

Volume 9 Issue 3 (2023) 20 https://doi.org/10.18063/ijb.678