3D conformal printing has emerged as one of the most promising strategies for constructing micropatterns or microstructures on large-area curved surfaces, enabling innovative applications such as electromagnetic metamaterials and electronic devices. The robotic conformal electrohydrodynamic (EHD) printing (RE-printing) technique is highly appealing in this respect because of its capability for submicron-scale patterning and compatibility with a broad range of ink viscosities. However, maintaining a steady electric field to ensure uniform deposition on curved and rough surfaces is challenging. Here, we propose an eye-inlaid printhead with a ‘neighborhood’ path compensation algorithm and a self-stabilizing electric field mechanism to significantly improve the accuracy of RE printing and find that a steady electric field strength, rather than a constant printing height, affects the uniformity of EHD-printed patterns more. This printhead integrates a camera for tangent plane positioning alongside a laser displacement sensor for measuring normal displacement and facilitates precise 3D positioning. The path compensation algorithm can maintain the electric field strength during the printing process by calculating the average local nozzle-to-substrate distance through in situ measurements of the printing height. This approach can not only stabilize the electric field but also reduce the robotic vibration caused by a fluctuating path on rough surfaces, reducing the electric field strength fluctuations from 20% to 5% and the vibration amplitude from 55 μm to nearly 0 μm compared with those of the traditional ‘point–to–point’ path compensation technique. In addition, it can adaptively correct substrate model errors, frame deviations, and robot motion inaccuracies. The mean absolute deviation of the nozzle-to-substrate distance can be reduced to 20 μm, presenting an enhancement in printing precision by 77.23% compared with that of the ‘point–to–point’ path compensation strategy. As a result, this approach achieves consistent line width and electrical resistance on curved substrates, supporting high-resolution conformal printing on surfaces with curvature radii as small as 1 mm and resolutions up to 5 μm. Finally, de-icing heaters have been conformally fabricated on an airplane wing, and their performance has been confirmed through subsequent de-icing trials. This approach promises a versatile solution for the RE printing of large-area 3D conformal electronic devices.

Real-time analysis and prediction of flow field characteristics are essential for flight safety and necessitating in-flight data acquisition, an almost impossible task for traditional techniques such as temperature/pressure-sensitive paints. Flexible smart skins demonstrate great promise for acquiring in-flight data. Nevertheless, the multi-physical data collected are usually sparsely in distribution and limited in quantity, making it difficult to accurately identify transition and stall locations. To overcome this limitation, we introduce a novel method for rapidly reconstructing high-resolution flow fields around aircraft wings from sparse data. Leveraging the flow fields computed by CFL3D, a dual-branch attention fusion model is developed based on an encoder-decoder network. This model facilitates rapid prediction of 2D flow fields for 52 types of NACA airfoils under 156 different freestream conditions, achieving an average relative error of 3.68% and providing a substantial amount of high-fidelity training data for the reconstruction process. Furthermore, using flow fields around the M6 airfoil generated by the rapid prediction model, a flow field reconstruction model is developed based on a shallow neural network. This model fulfills rapid reconstruction of high-resolution flow fields with a relative error of 2.73%. This work establishes a valuable data foundation for the in-flight application of smart skins, enhancing real-time monitoring capabilities and improving flight safety through accurate flow field reconstructions and insights.

Multi-material 3D fabrication at the nanoscale has been a long-sought goal in additive manufacturing, with great potential for the direct construction of functional micro/nanosystems rather than just arbitrary 3D structures. To achieve this goal, researchers have introduced several nanoscale 3D printing principles, explored various multi-material switching and combination strategies, and demonstrated their potential applications in 3D integrated circuits, optoelectronics, biological devices, micro/nanorobots, etc. Although some progress has been made, it is still at the primary stage, and a serious breakthrough is needed to directly construct functional micro/nano systems. In this perspective, the development, current status and prospects of multi-material 3D nanoprinting are presented. We envision that this 3D printing will unlock innovative solutions and make significant contributions to various technologies and industries in the near future.

Inorganic-based micro light-emitting diodes (microLEDs) offer more fascinating properties and unique demands in next-generation displays. However, the small size of the microLED chip (1–100 µm) makes it extremely challenging for high efficiency and low cost to accurately, selectively, integrate millions of microLED chips. Recent impressive technological advances have overcome the drawbacks of traditional pick-and-place techniques when they were utilized in the assembly of microLED display, including the most broadly recognized laser lift-off technique, contact micro-transfer printing (µTP) technique, laser non-contact µTP technique, and self-assembly technique. Herein, we firstly review the key developments in mass transfer technique and highlight their potential value, covering both the state-of-the-art devices and requirements for mass transfer in the assembly of the ultra-large-area display and virtual reality glasses. We begin with the significant challenges and the brief history of mass transfer technique, and expand that mass transfer technique is composed of two major techniques, namely, the epitaxial Lift-off technique and the pick-and-place technique. The basic concept and transfer effects for each representative epitaxial Lift-off and pick-and-place technique in mass transfer are then overviewed separately. Finally, the potential challenges and future research directions of mass transfer are discussed.

Large, 3D curved electronics are a trend of the microelectronic industry due to their unique ability to conformally coexist with complex surfaces while retaining the electronic functions of 2D planar integrated circuit technologies. However, these curved electronics present great challenges to the fabrication processes. Here, we propose a reconfigurable, mask-free, conformal fabrication strategy with a robot-like system, called robotized ‘transfer-and-jet’ printing, to assemble diverse electronic devices on complex surfaces. This novel method is a ground-breaking advance with the unique capability to integrate rigid chips, flexible electronics, and conformal circuits on complex surfaces. Critically, each process, including transfer printing, inkjet printing, and plasma treating, are mask-free, digitalized, and programmable. The robotization techniques, including measurement, surface reconstruction and localization, and path programming, break through the fundamental constraints of 2D planar microfabrication in the context of geometric shape and size. The transfer printing begins with the laser lift-off of rigid chips or flexible electronics from donor substrates, which are then transferred onto a curved surface via a dexterous robotic palm. Then the robotic electrohydrodynamic printing directly writes submicrometer structures on the curved surface. Their permutation and combination allow versatile conformal microfabrication. Finally, robotized hybrid printing is utilized to successfully fabricate a conformal heater and antenna on a spherical surface and a flexible smart sensing skin on a winged model, where the curved circuit, flexible capacitive and piezoelectric sensor arrays, and rigid digital–analog conversion chips are assembled. Robotized hybrid printing is an innovative printing technology, enabling additive, noncontact and digital microfabrication for 3D curved electronics.