Pump-Free Insulin Delivery via an SLA-Printed Hollow Microneedle Patch with an Integrated Self-Sealing Reservoir

Hollow microneedle (HMN) systems can deliver insulin with minimal pain, but most rely on external pumps that add bulk, cost, and failure modes. This paper reports the design, fabrication, and mechanical characterisation of a pump-free, refillable HMN patch that integrates a syringe-loadable, self-sealing reservoir and delivers by passive diffusion. A 3 × 4 array of side-orifice conical HMNs with a target height of 1 mm and a bore of 0.8 mm was stereolithography-printed in dental-grade resin and coupled to an elastic-grade resin septum that maintains a leak-free seal after repeated needle puncture. A surface-response design of experiments (DoE) probed wall thickness of 0.10-0.20 mm, post-cure time of 20-60 min, and temperatures of 35-80 °C. The microneedle characteristics include geometric fidelity, insertion into multilayer Parafilm, and axial compression to 150 N. All patches were printed with a hollow channel and side orifices with tips were slightly blunted. Relative to the original design, height undershoot was from -24.5% to -60.5% while base diameters were within -11% to +20%. Parafilm insertion exhibited a peak then force drop at about 0.22 mm displacement with 1.2-1.5 N pierced the first layer. It was found that about 90% of needles penetrated about 381 µm and more than 20% reached 635 µm. Patches withstood 150 N without fracture with strains of 9.7-15.6% and modulus of 8-48 MPa. ANOVA identified wall thickness as a significant factor, with curing temperature not being significant. Contour analysis defined an operating window near a 0.15 mm wall and about 40 min post-cure balancing dimensional fidelity and post-compression height retention. These results define a manufacturable path to compact, pump-free insulin patches with low insertion force and robust mechanics, opening a clinically scalable route to simpler everyday insulin therapy.