Concave Microwell Formation Induced by PDMS Water Vapor Permeability for Spheroid Generation

This study introduces a novel method for the fabrication of concave microwells involving water vapor permeation through polydimethylsiloxane (PDMS). This method leverages the exceptional water vapor permeability of PDMS to enable a scalable and cost-effective fabrication process, addressing the limitations of existing techniques such as photolithography that are resource-intensive and complex. PDMS is more permeable to water vapor than to other gas molecules, resulting in the formation of microwells. Smooth-sloped concave microwells are formed by depositing droplets of 10% ethylene glycol on a PDMS substrate followed by curing at 70 °C and evaporation of water vapor. These microwells exhibit a unique structural gradient that is highly conducive for biological applications. Concave microwells were further used as a platform to generate animal cell spheroids, demonstrating their potential for three-dimensional cell culture. Unlike conventional methods, this approach allows precise control over microwell morphology by simply adjusting droplet size and curing conditions, offering enhanced tunability and reproducibility. The formation yield of these microwells is dependent on the volume of the water droplets, demonstrating the importance of droplet size in controlling microwell morphology. This approach provides a simple and effective method for creating microwells without complex lithographic processes, making it a highly promising tool for a range of biomedical applications, including tissue engineering, cancer research, and high-throughput drug screening.