Dynamic Autofocus 3D Pulsed Laser Micro-machining Technology

01 Introduction

Next-generation wearable or implantable bioelectronic devices are advancing toward flexibility, miniaturization, and seamless integration with biological tissues (skin or internal organs). However, conventional fabrication approaches, primarily based on ultraviolet (UV) photolithography, soft lithography, or transfer printing, are typically limited to planar, layered architectures and rely on complex wet-chemical procedures, making it difficult to achieve compatibility with complex three-dimensional (3D) curved surfaces. Although ultrashort pulse laser micromachining has been widely applied due to its high resolution and low thermal effects, current implementations are mostly restricted to single-layer or multilayer planar systems or require post-processing mechanical reshaping to conform to tissue curvature. To overcome these limitations, this study proposes a “dynamic auto-focusing 3D pulsed laser micromachining (d-3DPLM)” technique based on nanosecond pulsed near-infrared (NIR) lasers. By continuously adjusting the focal plane in real time to match a pre-defined 3D surface contour, this method enables direct, monolithic, mask-free micro-/nanofabrication on various curved and non-planar substrates, providing a novel fabrication route for highly conformal and high-performance bioelectronic interfaces.

02 Overview

This work systematically investigates its processing capacity and application potential across both soft and rigid materials. Using a 1064 nm nanosecond pulsed laser, the research team dynamically controlled the laser focal depth to overcome the Rayleigh-length-limited focusing depth in traditional laser machining, achieving high-resolution patterning on highly curved surfaces (lateral resolution ~10–25 µm, vertical resolution ~5–10 µm).
The versatility of d-3DPLM is demonstrated through three representative applications:
(1) Electrotactile wearable patch: 3D microneedle electrodes were integrated on flexible substrates, significantly reducing skin–electrode impedance and improving tactile stimulation efficiency.
(2) Highly tunable 3D microelectrode arrays (MEAs): A highly customizable 3D microneedle electrode array was fabricated for non-invasive recording from brain organoids. The device conformed to complex organoid geometries and enabled high-quality electrophysiological signal acquisition.
Overall, this work expands the technological toolbox of laser microfabrication for bioelectronics and establishes a foundation for rapid prototyping and personalized medical device manufacturing.

03 Figure Analysis

Figure 1 visually illustrates the core working principle of d-3DPLM. As shown, unlike traditional laser processing with a fixed focal plane, the focal point of d-3DPLM dynamically adjusts according to a pre-set 3D contour. This method maintains continuous laser focusing on the material surface. The technique enables direct sculpting of 3D structures on bulk materials as well as precise patterned etching on coated or pre-formed 3D substrates, achieving true monolithic 3D fabrication.

Figure 1. Schematic diagram of the principle of dynamic autofocus 3D pulsed laser micromachining (d-3DPLM). (a) The laser focus follows the contour of the 3D envelope surface for processing; (b) 3D structures are processed on the surface of bulk materials; (c) Patterning is performed on a pre-formed 3D substrate coating.

Figure 2 demonstrates the dimensional machining capability and resolution characterization of the d-3DPLM process. Tests were conducted on stainless steel and Au/poly-parylene films. Figures 2e and 2f particularly highlight the ability to process hemispherical surfaces, confirming that the technique maintains high angular resolution (~35°–42°) while overcoming large-curvature defocusing issues. Unlike conventional 2D machining that suffers severe resolution degradation near curved edges, d-3DPLM maintains consistent feature size over the entire surface, showcasing its unique advantage in non-planar micro-/nanofabrication.

Figure 2. Characterization of NIR laser ablation process and d-3DPLM.

Figure 3 presents d-3DPLM-fabricated electrotactile patches with microneedle electrodes and their performance. By patterning Ti/Au thin films and integrating 3D-printed microneedles, the fabricated 3D electrodes exhibit significantly lower contact impedance under pressure compared to conventional 2D flat electrodes. Figure 2f shows that during human skin testing, the 3D electrodes feature a markedly lower perceptual current threshold, indicating more efficient charge injection and improved tactile stimulation precision.

Figure 3. Microneedle electrode electrotactile patches fabricated by d-3DPLM for tactile stimulation.

Figure 4 shows the highly tunable 3D microelectrode arrays (MEAs) for in-vitro organoid recording. Due to the spherical geometry of human brain organoids, traditional planar MEAs fail to capture comprehensive neural signals. Using d-3DPLM, a customizable stainless-steel microneedle array was fabricated, where electrode height was tailored to organoid morphology (Figure 4b). Electrophysiological recordings (Figures 4i and 4j) show that, compared with planar electrodes, the 3D MEA detects broader spatially distributed and higher-signal-to-noise local field potentials (LFPs), proving its capability to monitor deep neural activity while preserving organoid 3D structure.

Figure 4. Adjustable height 3D MEAs fabricated by d-3DPLM for in vitro recording of organoids.

04 Conclusion

This study introduces a universal dynamic auto-focusing 3D laser micromachining strategy (d-3DPLM) that combines nanosecond pulsed lasers with real-time focal tracking, successfully overcoming planar constraints of conventional lithography and laser processing. The technique offers mask-free, solvent-free, and non-contact machining and is compatible with diverse materials including metals and polymers. Through demonstrations in electrotactile patches and organoid MEAs, the research team highlights d-3DPLM’s significant potential for fabricating complex 3D bioelectronic devices: it not only enhances mechanical conformity with biological tissues but also optimizes electrical performance (e.g., reduced impedance, improved wireless transmission efficiency). Although challenges still exist regarding extreme resolution and high-volume automation, hybrid use with femtosecond lasers (as applied in MEA fabrication) suggests a feasible path toward high-precision and customizable 3D bioelectronic manufacturing. This advance provides a powerful manufacturing tool for innovations in neuroscience, ophthalmologic treatment, and human–machine interaction interfaces.

**--Cite the article published by 高能束加工技术 on November 26, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."