Additive Manufacturing of Mechanically Stable, Hollow, Polymer Microneedles onto Microfluidic Chips

Traditional microneedle (MN) devices face significant biocompatibility challenges,¹ for instance, when based on silicon.² 3D printing offers flexibility in material choice and rapid prototyping capabilities while accessing complex geometries. Here, we demonstrate the 3D printing of hollow and polymer-based MNs onto silicon microfluidics from standard cleanroom processes using two-photon polymerization. Our FEM-simulation-driven microneedle design underwent mechanical and fluidic characterization. The fabricated microneedles exhibited high replicability in length, centerline alignment, and feature size. Mechanical testing confirmed that the MN arrays could withstand compressive forces exceeding those required for insertion into simulated skin and human subjects. We successfully extracted interstitial fluid (ISF) from a human subject and conducted a 72-hour in-vivo biocompatibility test, which yielded positive results, demonstrating the system's potential for continuous health monitoring. This platform's capability for minimally invasive, continuous monitoring of ISF offers a promising avenue for enhancing personalized medical treatments as it presents a rich source of biomarkers.³

1 Liu, G.-S. et al. Microneedles for transdermal diagnostics: Recent advances and new horizons. Biomaterials 232, 119740 (2020). https://doi.org/https://doi.org/10.1016/j.biomaterials.2019.119740
2 Larrañeta, E., Lutton, R. E. M., Woolfson, A. D. & Donnelly, R. F. Microneedle arrays as transdermal and intradermal drug delivery systems: Materials science, manufacture and commercial development. Materials Science and Engineering: R: Reports 104, 1-32 (2016). https://doi.org/https://doi.org/10.1016/j.mser.2016.03.001
3 Wu, Z. et al. Interstitial fluid-based wearable biosensors for minimally invasive healthcare and biomedical applications. Communications Materials 5, 33 (2024). https://doi.org/10.1038/s43246-024-00468-6