Abstract

Drawing inspiration from the doubly reentrant microstructures on springtail skins, surfaces exhibiting repellency to liquids with very low surface tension, are well developed. However, utilizing doubly reentrant microstructures for controllable wettability switching, especially for liquids with low surface tensions, still remains a challenge. Herein, a strategy is presented involving two-photon lithography-assisted molding to fabricate doubly reentrant soft microstructures (DRSMs) with real-time magnetic responsiveness. Owing to the high spatial resolution enabled by two-photon absorption and the dissolvable molding template, the 3D reentrant features are well preserved in the DRSMs based on the magnetic elastomer. Accordingly, the fabricated magnetic DRSMs exhibit switchable repellency for nearly all commonly used solvents within 1 s. Furthermore, the additional doubly reentrant micro-fence design surrounding the doubly reentrant micropillars allows the DRSMs to switch wettability even when fully immersed in liquids. These DRSMs demonstrate sufficient abilities for on-demand analyte enrichment and drug release. This work may not only serve as a design strategy to enhance the responsiveness of DRSMs but also significantly simplify the wetting switching system, which is highly attractive across various fields in biomedical and microelectronic applications.

Figure 1. Design of the magnetically actuated DRSMs inspired by the springtail cuticle. a) Hand-drawn sketch of a springtail and magnified views of the doubly reentrant microstructures on its skin. b) Schematics of the TPLAM processes and the magnetic actuation of the DRSMs. c) Functionalities of the magnetically switchable wettability of DRSMs and their potential applications in on-demand analyte enrichment and drug release.

Figure 2. Micropillar arrays with different geometric designs and their corresponding liquid repellency. a–c) SEM images of the FMA, SRMA, and DRMA, and the corresponding repellency behaviors toward deionized water (DIW), n-hexadecane (OIL), and ethanol (EtOH). d) Photograph of a drop of dyed water (γ = 72.8 mN m−1, blue), ethylene glycol (γ = 46.5 mN m−1, yellow), n-hexadecane (γ = 27.2 mN m−1, white), and ethanol (γ = 22.3 mN m−1, pink) deposited on DRMA. e) The measured dynamic and static contact angles of different liquids on DRMA.

https://doi.org/10.1002/adfm.202510215