Projection Micro Stereolithography (PμSL) is a high-resolution (up to 0.6 μm) 3D printing technology based on area projection triggered photopolymerization, and capable of fabricating complex 3D architectures covering multiple scales and with multiple materials. This paper reviews the recent development of the PμSL based 3D printing technologies, together with the related applications. It introduces the working principle, the commercialized products, and the recent multiscale, multimaterial printing capability of PμSL as well as some functional photopolymers that are suitable to PμSL. This review paper also summarizes a few typical applications of PμSL including mechanical metamaterials, optical components, 4D printing, bioinspired materials and biomedical applications, and offers perspectives on the directions of the further development of PμSL based 3D printing technology.

https://iopscience.iop.org/article/10.1088/2631-7990/ab8d9a/pdf

Projection micro stereolithography based 3D printing and its applications

Hydrogel-polymer hybrids have been widely used for various applications such as biomedical devices and flexible electronics. However, the current technologies constrain the geometries of hydrogel-polymer hybrid to laminates consisting of hydrogel with silicone rubbers. This greatly limits functionality and performance of hydrogel-polymer-based devices and machines. Here, we report a simple yet versatile multimaterial 3D printing approach to fabricate complex hybrid 3D structures consisting of highly stretchable and high-water content acrylamide-PEGDA (AP) hydrogels covalently bonded with diverse UV curable polymers. The hybrid structures are printed on a self-built DLP-based multimaterial 3D printer. We realize covalent bonding between AP hydrogel and other polymers through incomplete polymerization of AP hydrogel initiated by the water-soluble photoinitiator TPO nanoparticles. We demonstrate a few applications taking advantage of this approach. The proposed approach paves a new way to realize multifunctional soft devices and machines by bonding hydrogel with other polymers in 3D forms.

3D printing of highly stretchable hydrogel with diverse UV curable polymers.

Conductive hydrogels are widely used in various applications, such as artificial skin, flexible and implantable bioelectronics, and tissue engineering. However, it is still a challenge to formulate...

/pdf/functional-conductive-hydrogels-for-bioelectronics-85j8dhgfm5.pdf

Functional Conductive Hydrogels for Bioelectronics

Inspired by physically adaptive, agile, reconfigurable and multifunctional soft-bodied animals and human muscles, soft actuators have been developed for a variety of applications, including soft grippers, artificial muscles, wearables, haptic devices and medical devices. However, the complex performance of biological systems cannot yet be fully replicated in synthetic designs. In this Review, we discuss new materials and structural designs for the engineering of soft actuators with physical intelligence and advanced properties, such as adaptability, multimodal locomotion, self-healing and multi-responsiveness. We examine how performance can be improved and multifunctionality implemented by using programmable soft materials, and highlight important real-world applications of soft actuators. Finally, we discuss the challenges and opportunities for next-generation soft actuators, including physical intelligence, adaptability, manufacturing scalability and reproducibility, extended lifetime and end-of-life strategies. Soft actuators are flexible and compliant and thus perfectly suited to interact with the human body. This Review discusses tethered, untethered and biohybrid soft actuation strategies, highlights promising real-world applications of soft robots and identifies key future challenges, such as implementing physical intelligence and end-of-life strategies.

Soft actuators for real-world applications

Closed-loop 4D-printed soft robots

Miniature Pneumatic Actuators for Soft Robots by High-Resolution Multimaterial 3D Printing

A microlens array has become an important micro-optics device in various applications. Compared with traditional manufacturing approaches, digital light processing (DLP)-based printing enables fabrication of complex three-dimensional (3D) geometries and is a possible manufacturing approach for microlens arrays. However, the nature of 3D printing objects by stacking successive 2D patterns formed by discrete pixels leads to coarse surface roughness and makes DLP-based printing unsuccessful in fabricating optical components. Here, we report an oscillation-assisted DLP-based printing approach for fabrication of microlens arrays. An optically smooth surface (about 1 nm surface roughness) is achieved by mechanical oscillation that eliminates the jagged surface formed by discrete pixels, and a 1-3 s single grayscale ultraviolet (UV) exposure that removes the staircase effect. Moreover, computationally designed grayscale UV patterns allow us to fabricate microlenses with various profiles. The proposed approach paves a way to 3D print optical components with high quality, fast speed, and vast flexibility.

Ultrafast Three-Dimensional Printing of Optically Smooth Microlens Arrays by Oscillation-Assisted Digital Light Processing

https://onlinelibrary.wiley.com/doi/pdf/10.1002/admt.201970054

Colin Ju‐Xiang Ng

Papers

Miniature Pneumatic Actuators for Soft Robots by High-Resolution Multimaterial 3D Printing

Ultrafast Three-Dimensional Printing of Optically Smooth Microlens Arrays by Oscillation-Assisted Digital Light Processing

Soft Robotics: Miniature Pneumatic Actuators for Soft Robots by High-Resolution Multimaterial 3D Printing (Adv. Mater. Technol. 10/2019)