Fractal-Based Stretchable Circuits via Electric-Field-Driven Microscale 3D Printing for Localized Heating of Shape Memory Polymers in 4D Printing

Abstract

Thermally responsive shape memory polymers (SMPs) used in 4D printing are often reported to be activated by external heat sources or embedded stiff heaters. However, such heating strategies impede the practical application of 4D printing due to the lack of precise control over heating or the limited ability to accommodate the stretching during shape programming. Herein, we propose a novel 4D printing paradigm by fabricating stretchable heating circuits with fractal motifs via electric-fielddriven microscale 3D printing of conductive paste for seamless integration into 3D printed structures with SMP components. By regulating the fractal order and printing/processing parameters, the overall electrical resistance and areal coverage of the circuits can be tuned to produce an efficient and uniform heating performance. Compared with serpentine structures, the resistance of fractal-based circuits remains relatively stable under both uniaxial and biaxial stretching. In practice, steady-state and transient heating modes can be respectively used during the shape programming and actuation phases. We demonstrate that this approach is suitable for 4D printed structures with shape programming by either uniaxial or biaxial stretching. Notably, the biaxial stretchability of fractal-based heating circuits enables the shape change between a planar structure and a 3D one with double curvature. The proposed strategy would offer more freedom in designing 4D printed structures and enable the manipulation of the latter in a controlled and selective manner.

Directly Printed Embedded Metal Mesh for Flexible Transparent Electrode via Liquid Substrate Electric‐Field‐Driven Jet

“…It adds the 4D "time" to the 3D printing structure to achieve the shape deformation of the 3D structure by changing the external environment such as thermal, electric, optical, and magnetic conditions. [53][54][55] Thermally responsive shape-memory polymers (SMPs) have become one of the most exciting materials due to their fast response time, large deformability, and high compatibility with multimaterial 3D printing. Currently, the most commonly used heating method for SMPs-based 4D printing is external heating, however, this heating method cannot accurately control the heating temperature of 4D printing structure, which hinders the further application of 4D printing.…”

3D Printing of a PDMS Cylindrical Microlens Array with 100% Fill-Factor

“…The printing module is the core of the proposed CMLA-manufacturing method, and its basic principle is based on the principle of EFD microscale 3D printing. 42 The positive pole of the HVDC power supply is directly connected to the conductive nozzle, and the negative pole is grounded. The system mainly includes two printing modes: a microextrusion mode and a continuous cone jet mode (for more details, see the Supporting Information, Figure S3).…”

“…As a result, there is no need to perform redundant vacuum defoaming procedures, which simplifies the process flow and facilitates the simple and efficient production of CMLAs (Figure S2). The printing module is the core of the proposed CMLA-manufacturing method, and its basic principle is based on the principle of EFD microscale 3D printing . The positive pole of the HVDC power supply is directly connected to the conductive nozzle, and the negative pole is grounded.…”

3D Printed High Performance Silver Mesh for Transparent Glass Heaters through Liquid Sacrificial Substrate Electric‐Field‐Driven Jet

“…More importantly, EFD microscale 3D printing also has considerable potential in micro/nanoscale 3D printing because a stable electric field can always be reformed between the nozzle and the printed object, ensuring stability and reliability of the 3D printing process. [57][58][59][60] In this work, we propose a new method for manufacturing high performance TGHs based on liquid sacrificial substrate electric-field-driven (LS-EFD) microscale 3D printing. First, a thin layer of liquid material was spin-coated on a glass substrate, and then the TFSP was printed directly onto the liquid film substrate using LS-EFD microscale 3D printing technology.…”