Precision design of dissolving microneedles via mechanically induced micro-vent and Capillary-Controlled Molding: From fabrication to mechanical characterization

• Rheology-guided pre-curing physically suppresses capillary failures. • Mechanically induced micro-vents enable reliable microneedle casting. • A piecewise linear model defines coupled microneedle-skin mechanics. • Tip diameters below 25 µm enabled reliable insertion in layered skin. Dissolving microneedles with controlled geometry are difficult to fabricate reproducibly because liquid polydimethylsiloxane (PDMS) molding is prone to meniscus failure and bubble entrapment. Here, we formed a PDMS master mold by directly inserting metal needles into thermally pre–cured PDMS and used rheology to identify the insertion window for stable cavity replication. A modified Young–Laplace model described the capillary-dominated failure of liquid PDMS, whereas successful meniscus suppression occurred after PDMS entered a gel-like viscoelastic regime. Under our conditions, pre–curing for 6 min on a 100 °C hotplate enabled faithful cavity replication and the fabrication of gelatin microneedle arrays with heights of 500–1500 µm. As the gelatin concentration increased from 25 to 40 % (w/v), Young’s modulus increased from 0.286 to 1.826 GPa. Compression and insertion tests using a multilayer artificial skin model identified distinct insertion phases and showed that microneedles with tip diameters of up to 25 µm reliably penetrated the model. These results provide a simple PDMS mold fabrication route and a rheology-guided basis for designing and mechanically evaluating dissolving gelatin microneedles.