Page 285 - IJB-9-3

International Journal of Bioprinting 3D-printed thermosensitive hydrogel based microrobots

Figure 5. (a) SEM spectra of PNAGA-100 in helix shape. (b) SEM spectra of PNAGA-100 in five-pointed star pattern. (c) SEM spectra of PNAGA-100
hexagonal pattern.

3.3.2. Scanning electron microscopy by increasing the monomer NAGA amount from 50 mg
Figure 5 shows the scanning electron microscopy (SEM) (PNAGA-50) to 100 mg (PNAGA-100). However,
images of PNAGA-100 microstructures prepared by 2PP they decreased sharply when the NAGA amount was
method. Structure design with CAD software incorporated further increased to 200 mg (PNAGA-200) and 300 mg
with advanced 3D printing technology makes it possible (PNAGA-300), indicating that NAGA concentration plays
to obtain diverse shapes of PNAGA hydrogels with high a vital role in modulating the thermosensitive performance
resolution, high precision, and compact morphologies of these materials. Noticeably, the optimized growth rate
(Figure 5a). Helix, five-pointed star (Figure 5b), and of PNAGA-100 was 22.5% when it was incubated in DI
hexagonal patterns (Figure 5c) of PNAGA-100-based water at 45°C for 12 h. PNAGA-100 reached a growth rate
microrobots were designed and successfully 3D-printed, of 20.8% in the shortest time (6 h), which demonstrates the
and their sizes can be adjusted according to different best thermosensitive performance among these hydrogels.
application situations. Furthermore, it is hard to evaluate the thermosensitive
performance of PNAGA-300 after it was incubated in DI
3.4. Thermosensitive properties of 3D-printed water at 45°C for 24 h owing to its preference for bending
PNAGA microstructures because of swelling (Figure S5).
First, we prepared PNAGA microstructures with different
NAGA loadings via the 2PP method to estimate the Although we lack a comprehensive theory to explain
thermosensitive properties of materials (Table 1). As shown why PNAGA-100 exhibits better thermosensitive
in Figure 6, the thermosensitive properties of these hydrogels performance than others, we rationalized this by the
were evaluated with different duration times (6 h; 12 h; variations of PNAGA polymer structures induced by
24 h) at room temperature (25°C) and 45°C, respectively. NAGA monomer concentrations. In detail, PNAGA has
The growth rates of these hydrogels were measured for the dual H-bonding donors (D) and dual H-bonding acceptors
sake of evaluating their swelling performance. In detail, the (A), which feature an ADAD hydrogen network (Figure 7).
growth rates of these hydrogels were much higher at 45°C Based on the NAGA concentrations, the phase diagrams
[44]
(close to body temperature) than that at 25°C, revealing of PNAGA are mainly divided into two regions . Region
that all these PNAGA-based microrobots exhibit better 1 has medium NAGA concentration, and swellable and
thermosensitive performance under 45°C. In addition, thermosensitive hydrogels are observed with a gel-like
the growth rates of these microstructures were enhanced behavior in this region. PNAGA-100 with higher NAGA

Volume 9 Issue 3 (2023) 277 https://doi.org/10.18063/ijb.709