Page 25 - IJB-9-3

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

Princeton) was used to detect the transmission/reflection force-to-weight ratio exceeded 1000 N/mg tested on
spectra of each PC sequentially for coloration at a resolution MNIHs. The relation of stress (load force) and displacement
of 0.2 nm. All optical observation or CCD profiling was exclusively presented variable hysteresis loops, validating
done by the digital microscope terminal of the laser system that MNIHs had at least two metastable phases while
(X81, Olympus). interacting with stimuli.

2.7. Micromechanics test Hydrophilicity/hydrophobicity switch of pure NIPAM
happened at its lower at the lower critical solution
In this case, a micromechanics tester (FT-MTA02) from temperature (LCST =32.4°C, Figures S4 and S5) ,
[21]
NIPAM
FemtoTools measured MNIH samples at the vertical and however, the hydrophilicity/hydrophobicity switch of MNIH
horizontal axes to detect stiffness/Young’s modulus, cohesive extended to more broad 30 – 42°C zone . In addition,
[21]
behavior, and output force amplitude. The equipped amphiphilicity of PEG-DA offered another privilege
[24]
Tungsten probe, which records the generated compressive to interact with oils, acrylates, and organic polar
and tensile force, was waterproof for contacting with solvents (such as DMSO, and IPA.), far beyond the
solvents at a micrometer tip radius (a fraction of 2 μm).
single water/humidity for shape mutation (Figure 2D).
3. Results and discussion Subsequently, based on the experiment, we concluded
that the material ratio affected the water-contact angle
The self-driven high-freedom MNIHs combined with (Figure 2E) noticeably, and the contact angle declined
edgy femtosecond laser fabrication technique and in the order of 63.35°→56.49°→46.25°→37.87°, which
advanced material sciences were studied via necessary was ascribed to the increased NIPAM: PEG-DA ratio in
characterization methods here. Surficial functional the order of 0.5:1→1:1→2:1→3:1. In the respect to shape
groups of MNIH matrix spontaneously perceived stimuli, reconfiguration, we numerically investigated a model on
interacted with organic matters or ions for diffusion, or cantilever beam shape through finite element framework
were remotely activated by light/heat radiation to transfer (Figures 2F and S6), 3D stress distribution confirmed that
heat. First, we freeze-dried a cantilever beam to observe the interconnecting arm released the mechanical energy
molecular-chain conformation. The linked network accumulated from the intermolecular force, and the
exhibited an interlaced, bumpy, nanofibrous tangled fixation pads bore the maximum residual stress, matching
conformation (Figure 2) instead of a stereotypical porous with the beam’s upward humping as described in SEM
network of hydrothermal synthesized PNIPAM, offering images (Figure 2F).
a sizeable contact area to load stimuli. Subsequently, we
conducted FTIR spectroscopic observation (Figure 2B, laser To meticulously regulate the spontaneous interaction
wavelength 532 nm, optical power 1 mW, and wavenumber between MNIHs and stimuli, we introduced a monolayer
range from 500 to 4000 cm ) to deduct molecular heterojunction nanostructure (Figure 3) based on
-1
structural transferring. MNIH spectrum contained the nanowires (NWs) by our high-precision laser scanning
[40]
-1
absorption peaks of amide bond (C=O at 1654.2 cm , method , modulating NWs’ interspacing and line
-1
N-H at 1560.1 cm ) from NIPAM, accompanied by ester width. After polymerization, the solidified NWs worked
-1
structure of PEG-DA (C-O at 1160.2 cm ). It could be as a skeleton, and the loosely-linked interspacing
understood that MNIH was crosslinked by NIPAM and provided unfolding space and a large quantity of
PEG-DA in pre-polymerization and TPP. survived functional groups. NWs connected each other
through interspacing, forming a high-quality monolayer
In situ micromechanics measurements (using hierarchical heterojunction at tight topological control.
FT-MTA02, FemtoTools, with 2-μm radius tungsten After simplifying the scanning path, we succeeded
probes and capacitive force sensor were used in the loading/ in manipulating the μ/n-scale mutation behaviors to
unloading process at 5 nN resolution, Figure 2C) elucidated break the freedom constraints of conventional methods
the MNIHs’ elasticity, guaranteeing structural integrity (Videoclips S2 and S3). The first evidence, a transparent
during violent mutation, which was pivotal to addressing “bracelet” (Figure 3A) with a horizontal expansion >120%,
challenges in bio-interconnects and soft machines/robots. lateral growth <8%, a longitudinal expansion >110%, and
We further identified the generated internal stress, stiffness, a curvature radius of 32 μm, was reversely constructed
and adhesion by circles of penetrating-in (compressive) from a simple monolayer planar MNIH (dimensions of
and pulling-out (tensile) operations. Stiffness of swelled 30 × 150 × 4 μm ).
3
MNIHs (<300 N/m) increased to >4,000 N/m after drying,
implying tunable Young’s modulus range [38,39] (from <10 Beyond this common conformal bending/extension,
MPa immersed in ethanol to >55 MPa after dehydration, the unique chiral torsional spirochete, which received ever-
Figure S3) well-suited for device-level applications. The increasing attention recently, was facilely reconstructed.

Volume 9 Issue 3 (2023) 17 https://doi.org/10.18063/ijb.678