Programmed multimaterial assembly by synergized 3D printing and freeform laser induction

Nature's efficient assembly of multimaterial structures inspires the development of multifunctional 3D objects. Traditional hybridized fabrication methods, such as producing multilayer 3D printed circuit boards (PCBs), are costly and unsustainable due to multiple processing steps and waste generation. While multimaterial 3D printing offers advantages like cost-effectiveness and reduced waste, existing techniques lack versatility in precisely placing functional materials and accessing a broader range of materials. Embedded 3D printing requires molds, limiting complex geometries. Core-shell 3D printing cannot deposit functional materials in predesigned locations. Multi-nozzle DIW often results in materials with low electrical conductivity and mechanical strength, and DLP is limited to photosensitive resins. Direct laser writing (DLW) provides versatility in patterning functional materials but is limited in fabricating these materials within 3D structures. Freeform laser induction (FLI) allows for 3D conformable electronics fabrication but struggles with spatially patterning functional materials within predesigned 3D structure locations. This paper addresses these challenges by introducing FMAP, a process that synergistically combines FLI, DIW, and FFF to seamlessly assemble structural and laser-processable functional materials into complex, multifunctional 3D objects.

The literature review highlights the limitations of existing multimaterial fabrication techniques. Traditional methods such as etching, lamination, and pressing for PCBs are inefficient and wasteful. Emerging techniques like multimaterial 3D printing offer improvements but face challenges. Embedded 3D printing restricts complex geometries, while core-shell 3D printing limits the placement of functional materials. Multi-nozzle DIW and DLP also present material limitations and processing inefficiencies. Direct laser writing shows promise but struggles with 3D integration. The researchers then position their FMAP approach as a solution to these challenges.

FMAP utilizes a 5-DOF platform integrating three linear and two rotational motions controlled by motors and harmonic gearboxes. Three end effectors—FFF, DIW, and a laser module—are strategically configured to prevent ink contact during extrusion. The laser (450 nm, 5 W max) converts FFF-printed material to laser-induced graphene (LIG) and DIW-deposited ink into functional materials. A 3D wireless LED fabrication is used as an example workflow. The process starts with FFF of a PC structure, followed by laser induction to create an LIG electrode. A silver precursor is deposited by DIW and laser-induced to form a highly conductive LIG/Ag electrode. Additional PC layers are printed, and the process can be adapted for different polymers (TPU, PETG) by using a lignin and silver citrate ink. Besides silver, other materials like Fe, Co, Ni, and CuO can be synthesized via laser induction to achieve diverse functionalities. The paper details the materials characterization techniques used, including SEM, EDS, Raman spectroscopy, and tensile testing, to analyze the properties of the fabricated materials and structures. The methodology also explains the fabrication process for a variety of devices like crossbar circuits for LEDs, capacitive sensors, a UV sensor, a 3D electromagnet, and an integrated microfluidic reactor with a Joule heater. Specific fabrication steps and parameters are provided for each device.

The FMAP platform successfully fabricates a range of functional 3D devices. The wireless LED demonstration showcased functionality on both rigid and flexible substrates. Material characterization revealed that the LIG/Ag composite has a sheet resistance as low as 2.75 Ω per square, and tensile testing showed that the mechanical properties of the PC are well maintained even with partial conversion to LIG. The fabrication of complex 3D structures with spatially patterned features was demonstrated. The crossbar circuit for LED display achieved individual LED control, enabling pattern display. The capacitive sensors (touchpad and slider) provided reliable and linear capacitive responses, with the slider demonstrating functionality on various surfaces. The UV sensor exhibited a linear relationship between photocurrent and UV light intensity. The strain-sensing spring and gripper showed consistent resistance change with displacement, suggesting potential for haptic applications. The 3D electromagnet functioned as a rotational encoder, accurately measuring rotational speed. Finally, the integrated microfluidic reactor with the Joule heater successfully synthesized ZIF-8 nanoparticles at elevated temperatures, as confirmed by TEM and XRD.

The findings demonstrate the effectiveness of FMAP in addressing the limitations of existing multimaterial fabrication methods. The ability to integrate various functional materials into complex 3D structures opens possibilities across various applications. The high linearity, accuracy, and rapid response of the fabricated sensors highlight FMAP's precision. The successful fabrication and testing of the diverse applications showcases the versatility and potential impact of FMAP. The seamless integration of FLI, DIW, and FFF into a single apparatus simplifies the fabrication process and improves material utilization.

FMAP provides a novel and versatile approach for programmed multimaterial assembly, enabling the creation of complex and multifunctional 3D objects. The platform simplifies fabrication, reduces waste, and broadens material options compared to existing methods. Future work will focus on improving processing speed through simultaneous operation of end effectors, enhancing resolution by upgrading the laser system, and expanding applications beyond electronics by integrating additional processes.

The current FMAP setup requires separate operation of FLI, DIW, and FFF processes, limiting the processing rate. While the current laser achieves a linewidth sufficient for many applications, higher resolution could be beneficial. The study primarily focuses on electronic applications; future research should explore diverse application areas.