Hydrogel‐Reactive‐Microenvironment Powering Reconfiguration of Polymer Architectures

Abstract Reconfiguration of architected structures has great significance for achieving new topologies and functions of engineering materials. Existing reconfigurable strategies have been reported, including approaches based on heat, mechanical instability, swelling, origami/kirigami designs, and electromagnetic actuation. However, these approaches mainly involve physical interactions between the host materials and the relevant stimuli. Herein, a novel, easy‐manipulated, and controllable reconfiguration strategy for polymer architectures is proposed by using a chemical reaction of host material within a hydrogel reactive microenvironment. 3D printed polycaprolactone (PCL) lattices transformed in an aqueous polyacrylamide (PAAm) hydrogel precursor solution, in which ultraviolet (UV) light triggered heterogeneous grafting polymerization between PCL and AAm. In situ microscopy shows that PCL beams go through volumetric expansion and cooperative buckling, resulting in transformation of PCL lattices into sinusoidal patterns. The transformation process can be tuned easily and patterned through the adjustment of the PCL beam diameter, unit cell width, and UV light on–off state. Controlling domain formation is achieved by using UV masks. This framework enables the design, fabrication, and programming of architected materials and inspires the development of novel 4D printing approaches.


Figures S1 to S14
Table S1 Captions for Movies S1 to S8 Other Supplementary Materials for this manuscript include the following:

In situ optical microscopy setup
In situ optical microscopy setup included an optical microscope (Nikon, Eclipse TS100), an ultraviolet (UV) light resource (365 nm, 10%, XM230, Shanghai Aventk Co. Ltd.), and a tablet connected to the optical microscope.UV light was used to irradiate the sealed device embedded with PCL architectures and PAAm precursor solution and trigger the deformation of the polymeric lattice.The tablet was used to observe, take snapshots, and record videoes of the deformation process.

Statistical analysis of the expansion ratio of PCL beams and PCL lattices
The expansion ratio of the PCL beams, including the radial growth ratio and axial elongation ratio, was calculated.The relative lengths of the PCL beams exposed to UV light for different durations were measured using the image analysis software ImageJ 1.40G (http://rsb.info.nih.gov/ij/download.html).The axial length elongation ratio of the PCL beams was calculated using the following expression: where θ represents the axial length elongation ratio, and L0 and Lt represent the lengths of the PCL beams exposed to UV light for 0 and t s, respectively.The schematic of L0 and Lt measurements is shown in Figure S2.
The radial expansion ratio of the PCL beams was calculated as where β represents the radial expansion ratio, and D0 and Dt represent the diameters of the PCL beams exposed to UV light for 0 and t s, respectively.The measurement procedures of D0 and Dt were similar to those of L0 and Lt.
The expansion ratio of the PCL lattice was calculated using Equation (1), in which L0 and Lt represent the node X-Y lengths of the initial and deformed lattices, respectively.
Equation (2) was not applied to calculate the expansion ratio of the PCL lattice because the lattice was composed of eight layers of the PCL beams, which may be misplaced after deformation, resulting in inaccurate diameter measurement.were drawn and measured using the 'segmented line' tool in ImageJ 1.40G.For the tetragonal PCL lattice, the red lines were drawn along the outer edge of the PCL beams between two nodes.Formula (1) was used for calculation.

Fabrication of a triangular PCL lattice and its reconfigurability
A triangular PCL lattice was prepared via MEW.The fabrication process parameters were similar to those of the tetragonal PCL lattice.One triangular sample contained eight layers of PCL beams, and the distance between adjacent beams was 500 m (Figure S3a).Under UV light, the original triangular lattice in the PAAm hydrogel precursor solution underwent deformation (Figure S3b).

Fabrication of a tetragonal polylactic acid lattice and its reconfigurability
To verify our photochemical reaction-induced expansion theory and extend its application fields, polylactic acid (PLA, Nature works 4032D, USA) was used to fabricate a tetragonal lattice via MEW (Figure S4a).The lattice was subjected to the same treatment as that of the PCL lattice and underwent deformation (Figure S4b).Different from the tetragonal PCL lattice, the deformed PLA lattice (with initial unit cell width of 500 m) exhibited nonuniform sinusoidal curves.Thus, our proposed strategy can be applied to other UV-initiated graft polymerization material systems.

Figure S1 .
Figure S1.Images of the in situ optical microscopy setup and a sealed device embedded with a reconfigured PCL lattice (Figure 1e) and transparent PAAm hydrogel.

Figure S2 .
Figure S2.Schematics of length measurement for the initial and deformed (a, b) PCL beams and (c, d) PCL lattices for expansion ratio calculation.The red lines along the PCL beams

Figure S3 .
Figure S3.Optical images of a triangular PCL lattice (a) before and (b) after deformation.

Figure S4 .
Figure S4.Optical images of a tetragonal PLA lattice (a) before and (b) after deformation.

Figure S8 .
Figure S8.Finite-element modelling of triangular PCL lattices.Geometries of (a) simulated and (b) experimental PCL lattices with different axial elongation ratios over the deformation period.(c) Experimental axial elongation ratio versus time over the deformation period.

Figure S11 .
Figure S11.Illustration of a potential application scenario for information steganography with 'Taiji-information' as a model.

Figure S12 .
Figure S12.(a) Schematic diagram of the fabrication process for the UV-environmentally adaptive materials, such as a kind of UV-responsive smart glass.(b) An image of a PCL lattice with a blurred zone after UV exposure and a blank zone without UV exposure.

Figure S13 .
Figure S13.(a) Images of PCL beams and the corresponding surfaces before and after reconfiguration.(b) Schematic diagram of a controlled drug-release systems by using the expansion of PCL beams and cracks formation on the surface of PCL beams.

Figure S14 .
Figure S14.Optical image of a tetragonal PCL lattice with a length of 21 cm.

Table S1
Length-relative error chart of reconfigurable architected materials.