Fabrication of Omega-Shaped Microwells via OSTE Single-Step Lithography

Curved microwells have become increasingly important in three-dimensional (3D) cell culture because their concave geometry better represents the native cellular microenvironment, promotes spontaneous cell aggregation, and supports tissue-like organization compared to conventional flat substrates. However, traditional fabrication of such curved microwells often relies on complex, multistep processes that require cleanroom facilities, customized masks, or specialized equipment. Here, we present a simple, cost-effective, and single-step lithographic method using off-stoichiometry thiol-ene (OSTE) polymer to produce micropillar arrays with omega ($\Omega$)-shaped tops, which serve as masters for replica-molding polydimethylsiloxane (PDMS) microwells. Our approach uses a porous, carbon-loaded PDMS membrane templated from processor pins as a combined mold and light-shielding layer. OSTE precursor is filled into the membrane pores and cured under a single diffused UV exposure through a glass diffuser, simultaneously forming both the pillars and their curved tops without the need for chrome masks or photolithographic tools. The resulting OSTE micropillar arrays exhibit tunable top diameters (666–1151 $\mathsf{\mu }$m) controlled by UV exposure time, and show hydrophobic surface properties (contact angles up to ∼135${}^{\circ }$). PDMS replica casting faithfully reproduces the $\Omega$-shaped geometry, yielding smooth, biocompatible microwells potentially suitable for 3D cell culture. This method significantly reduces fabrication complexity, time, and cost, offering a practical and scalable route to curved microstructures for tissue engineering and organoid applications.