Fabrication of 3D Ordered Structures with Multiple Materials via Macroscopic Supramolecular Assembly

Abstract Integration of diverse materials into 3D ordered structures is urgently required for advanced manufacture owing to increase in demand for high‐performance products. Most additive manufacturing techniques mainly focus on simply combining different equipment, while interfacial binding of distinctive materials remains a fundamental problem. Increasing studies on macroscopic supramolecular assembly (MSA) have revealed efficient interfacial interactions based on multivalency of supramolecular interactions facilitated by a “flexible spacing coating.” To demonstrate facile fabrication of 3D heterogeneous ordered structures, the combination of MSA and magnetic field‐assisted alignment has been developed as a new methodology for in situ integration of a wide range of materials, including elastomer, resin, plastics, metal, and quartz glass, with modulus ranging from tens of MPa to over 70 GPa. Assembly of single material, coassembly of two to four distinctive materials, and 3D alignment of “bridge‐like” and “cross‐stacked” heterogeneous structures are demonstrated. This methodology has provided a new solution to mild and efficient assembly of multiple materials at the macroscopic scale, which holds promise for advanced fabrication in fields of tissue engineering, electronic devices, and actuators.

Video S1. Stepwise demonstration of the MSA-AM method to construct a 3D ordered structure.
Ltd., carboxyl-functionalized Fe3O4 magnetic nanoparticles with an average diameter of 240 nm from Shanghai So-Fe Biomedicine Co., Ltd. PAA-CD and PAA-Azo were synthesized as following a previous report [1] .
The glass transition temperature of polyelectrolyte multilayers was measured with a differential scanning calorimetry (DSC) method (Mettler-Toledo DCS1). The elastic modulus of used polymer materials was characterized on a universal test machine with tension testing mode. The modulus values of Al and Glass were taken from handbook. Elastic modulus of polyelectrolyte multilayers was measured within deionized water and calculated from forcedistance curves obtained from an atomic force microscope (JPK Nanowizard 4, Bruker). Optical photos were taken with a Nikon D5000 camera. Force measurements were performed on a Dynamic Contact Angle Measuring Device and Tensionmeter (DCAT21, Dataphysics).
Scanning electron microscopy Zeiss SUPRA55 was used to characterize the morphology of heterogeneous 3D structures at 20 kV, and energy dispersive spectrometer for elemental mapping was conducted with INCA Energy 350 from Oxford Instruments. The 3D profiled images were obtained on a 3D microscope contour GT-X (Bruker).

S1. MSA experiments and assembly of control groups without flexible spacing coatings
MSA experiments were conducted by placing building blocks modified with interactive groups in a container with about 15 mL deionized water and shaken on a rotating shaker at a speed of 180 r/min for 5 min (Scheme S1). For every result, at least five independent assembly experiments were repeated. We used cubic building blocks of diverse materials with different

S2. Fabrication of the flexible spacing coating and its properties
Fabrication. The flexible spacing coating and supramolecular groups were modified onto building blocks of cubic PU, PE, PP, ABS, PS, Al and quartz glass via a facile layer-by-layer (LbL) method (Figure 1c). Taking quartz glass building blocks as an example, firstly, the quartz glass cubes were cleaned with a piranha solution for 30 min and washed with deionized water, followed by immersion in a PEI solution (aq, 1 mg/mL) overnight. Building blocks of other materials were washed with ethanol and deionized water, followed by plasma treatment for 2 min and immersion in a PEI (aq, 1 mg/mL) solution overnight. Subsequently, the building blocks were alternately immersed in PAA (aq, 1 mg/mL) and PEI (aq, 1 mg/mL) solutions for 2 min, between each of which they were rinsed with copious water. The alternate cycles were repeated until designated number (n) of multilayers, noted as (PEI/PAA)n. Afterwards, the building blocks were LbL assembled in PDDA (aq, 1 mg/mL) and PSS (aq, 1 mg/mL) for 5 min each, leading to multilayers of (PDDA/PSS)n. Finally, via LbL in PDDA (aq, 1 mg/mL) and PAA-CD (aq, 1mg/mL) or PAA-Azo (aq, 1mg/mL) for 5 min each, the building blocks Glass transition temperature (Tg). We obtained the Tg of the composite multilayers of (PEI/PAA)20 and (PEI/PAA)20-(PDDA/PSS)20 with DSC measurements. The samples for DSC tests were prepared following the reported procedure [2] . The films were deposited onto polytetrafluoroethylene substrates, which allows for the easy peeling-off and collection of the films in water. The as-collected films after removing apparent water were used for DSC tests by referring to the reported test methods [3,4] . About 5 mg of collected films in a hydrated state were sealed in the pan of the DSC instrument and equilibrated at 0 °C for 5 min, and then ramped from 0 to 115 °C at a rate of 2 °C/min; the thermal cycle was repeated two times and the results of the second heating scans were taken as shown in Figure S2.

S3. In situ measurement of the interactive forces
The interactive forces between building blocks were in situ measured in water based on a controlled contact-detachment process between interactive pairs ( Figure S5a) with a DCAT apparatus ( Figure S5b). As schematically illustrated in Figure S5a, the measurement consists of a force sensor at the top, a cell containing water and building blocks for measurements, and a motor-driven stage with controlled moving velocity of 0.5 mm/s. The cube and the sheet were an interactive pair modified with designated multilayers to ensure a constant contacting area in each contact-detachment test. To increase the density of the cube for immersion in water for stable tests, extra PDMS cubes loaded with metal are added (Figure S5b). The whole test process was conducted within water. In the beginning, the cube and sheet building blocks were separate and the force sensor was adjusted to a zero state to indicate a balanced force exerted on the cube. The tension of the soft thread reflects the force changes on the suspended green cubic building block: the tension T0 is balanced with gravity and buoyancy, which could be taken as a reference; subsequently, the motor drives the container of the other red building block upward to approach and contact the green cube, during which the cube is totally supported by the stage and the thread lost its tension and thus the two building blocks could have sufficient molecular recognition; afterwards, the motor drives downward to result in the detachment and sepration at a critical point that reveals the adhesion strength (Fadhesion) between the two building blocks; finally these building blocks are totally separated and back to the original state. With reference to T0 and the recorded Td values, the adhesion strength (Fadhesion) could be obtained from a typical force curve in one test (Figure S5c). We normalized this value relative to interacted surface area and obtained the results of binding between distinctive materials in     PDMS, PET and Ti were prepared into a dimension of 150 μm × 100 μm × 2 mm, 130 μm × 100 μm × 2 mm and 50 μm × 60 μm × 2 mm, correspondingly, following the procedures shown in Figure S9. To be specific, degassed mixture of PDMS pre-polymer and its curing agent (the weight ratio is 10:1) was poured between two hydrophobic glass slides sandwiched by cover glasses with a thickness of 150 μm, followed by curing at 70 ℃ for 1 h. PET and Ti films with a thickness of 130 μm and 50 μm are commercially available. Thin films of PDMS and PET were pre-cut into sheets with a size of 2 mm × 2 mm with blades and further cut into strips with a width of 100 μm with a freezing microtome. The Ti film was machined via femtosecond laser micromachining techniques.
For the fabrication of magnetic-responsive PDMS building blocks, dry particles of Fe3O4 MNPS were incorporated via directly mixing in the prepolymer mixture before curing. For PET and Ti, we applied the LbL method to deposit multilayers of PDDA and carboxyl-functionalized

S7. 3D profile of the 3D ordered structures
The assembly precision of the 3D structure fabricated by the MSA-AM method is characterized by a 3D profiler ( Figure S12) with calculations of location and angular deviation of the building blocks. For example, for the first layer with four parallel strip building blocks, the center-tocenter distance of two adjacent building blocks was measured, leading to an averaged location deviation of about 3.33 μm. We took the first strip building block as reference, and measured the angular deviation of the subsequent three building blocks, leading to an averaged deviation value of about 0.87°. Figure S12. 3D profile images of heterogeneous 3D structures with alignment of one, two and three layers.