综述：面向集成功能器件的多材料槽式光聚合

《Polymer》：Multi-Material Vat Photopolymerization Toward Integrated Functional Devices

　　

槽式光聚合（VAT photopolymerization, VPP）已成为一种领先的增材制造平台，用于制造具有高空间分辨率和吞吐量的复杂三维结构。将VPP扩展至多材料制造，能够在单个打印对象内实现不同化学成分和功能特性的空间编码，为软机器人、生物电子学、组织工程、智能材料以及更广泛的集成功能器件开辟了新的机遇。本综述考察了为多材料VPP开发的主要策略，这些策略大致可分为硬件驱动方法（包括VAT切换系统和动态树脂输送平台）以及基于正交光聚合的化学驱动单VAT方法。针对每种策略，研究人员讨论了其基本工作原理、材料要求、代表性实现和关键局限性，包括交叉污染、界面不相容性以及受限的波长正交性。混合和过程驱动方法，包括挤出-光集成、磁场辅助打印和温度调制光聚合，也被探索为增强功能复杂性的补充途径。最后，研究人员讨论了将多材料VPP从实验室规模演示转化为可扩展且具有工业相关性的制造平台所面临的剩余挑战和未来前景。

Light-based printing has emerged as one of the most powerful additive manufacturing processes, enabling the rapid fabrication of complex three-dimensional structures with high spatial resolution, speed, scalability, and throughput. Light-based 3D printing encompasses a family of additive manufacturing technologies in which a polymeric photoreactive resin is selectively solidified upon exposure to patterned light, a process often referred to as VAT photopolymerization. In stereolithography, a laser scans directly across the resin surface; in masked stereolithography, LEDs are filtered through an LCD screen; in digital light processing, a digital micromirror device projects the image directly onto the resin. VPP systems also differ by build orientation, with bottom-up and top-down configurations. Multi-material VPP extends printing by encoding spatial chemical cues into fabrication, allowing composition and geometry to be controlled at high resolution within a single print, with applications in scaffolds, bioelectronics, and complex architectures. However, the field remains fragmented, as material design, printing strategies, and device-level requirements have advanced in isolation, and a unified framework is still missing. This review examines emerging strategies for multi-material VPP, including VAT-switching, dynamic resin delivery, and wavelength-selective photopolymerization, bridging materials science and engineering.

Multi-material VPP enables the fabrication of complex architectures by integrating distinct photocurable resins within a single printing process. Existing approaches are classified into hardware-driven systems, where material exchange is physically managed through VAT switching or dynamic resin delivery, and chemistry-driven systems, where multiple materials are encoded within a single VAT and selectively activated through orthogonal polymerization pathways. Other methods rely on external triggers such as temperature, capillary forces, or magnetic fields. Critical challenges remain: cross-contamination and material waste during resin switching; setup limitations such as interlayer misalignment, reduced printing area, or restricted material compatibility; wavelength orthogonality issues due to spectral overlap; and interfacial engineering problems including reduced adhesion, non-uniform shrinkage, and loss of structural integrity. Advancing multi-material VPP requires simultaneous progress in resolution, material scope, spatial control, part stability, interfacial bonding, scalability, and reproducibility.

Photopolymerization mechanisms in VPP are predominantly free-radical polymerization of (meth)acrylate-based monomers, offering rapid curing and broad compatibility but suffering from oxygen inhibition. Cationic polymerization of epoxides, oxetanes, or vinyl ethers is less oxygen-sensitive, requires higher UV photon energies, and can continue in the dark, though with slower kinetics and narrower versatility. Chemistry-driven approaches exploit this wavelength sensitivity: visible light triggers radical polymerization of acrylates, while UV activates cationic polymerization of epoxides. Other chemistries include thiol–ene, thiol–yne, mixed-mode thiol–acrylate, and hybrid dual-cure networks. Acrylate systems provide tunable compliance and hydrogels for biomedical use; epoxy systems offer strength and thermal stability; hybrid acrylate–epoxy formulations form interpenetrating networks; thiol-based systems reduce oxygen inhibition and shrinkage; biobased platforms use renewable feedstocks; dynamic covalent bonds such as thiourethane and imine bonds enable reshaping, repair, and recycling. Resin viscosity critically affects flow behavior, layer recoating, and feature resolution, directly conditioning the switching mechanism in hardware-driven systems: low-viscosity resins enable rapid exchange and high resolution, while high-viscosity resins require pressure-assisted dispensing or elevated-temperature processing.

Hardware-driven multi-material VPP is organized around VAT-switching and dynamic resin delivery. In VAT-switching approaches, multiple resin reservoirs are exchanged manually, linearly, or rotationally, with integrated cleaning strategies such as scrapers, rotational stages, air-jet systems, or mechanical interfaces. Early systems evolved from compositional control of monomer-to-crosslinker ratios to fully automated platforms. One landmark system combined a bottom-up DLP setup with syringe-based dispensing of discrete monomer droplets in a linear carousel, achieving a pixel size down to 15 μm at 405 nm, with PTFE-coated glass to reduce adhesion, followed by air-assisted purging. Applications included drug delivery devices, ionic conductive elastomers, and electronically conductive hydrogel-elastomer hybrids. A centrifugal-controlled