Revealing Microscale Hydrogel 3D Structural Features at Ambient Conditions Using Ptychographic X-ray Computed Tomography

Hydrogels and microscale hydrogels containing micron-scale pores are extensively utilized in diverse fields because of their superior mass transport properties, large surface area, and strong resemblance to biological tissues, making them especially valuable in biomedical applications and devices. For this reason, accurately characterizing their porosity and pore interconnectivity under realistic ambient conditions─rather than the vacuum environments often used in conventional studies─is essential. In this work, the nano- and microstructural features of hydrogels are investigated using ptychographic X-ray computed tomography (PXCT), achieving a spatial resolution of 127 nm and covering a field of view of approximately 100 × 30 μm 2 under ambient conditions. The hydrogel microscopic samples exhibited a modification of the bulk pore size (from ∼0.9 μm) and porosity (from ∼20%) with decreasing thickness (toward ∼0.7 μm and 5%, respectively) and with increasing departure from the bulk region (toward ∼1.2 μm and 30%, respectively). Furthermore, pore throat sizes are estimated to fall mainly below ∼200 nm for narrower connections and 400–500 nm for wider ones. Notably, pore connectivity─and thus transport efficiency─is greater in the out-of-plane direction than in-plane. These findings are critical for understanding transport behavior and performance in real biological environments.