Tomographic imaging of hydrogels by digital holography microscopy

Hydrogels are very similar to natural tissues; therefore they have been used as artificial materials for repairing and regenerating a wide variety of tissues and organs. It is important to study the microstructure of hydrogels, for determining their physical and mechanical properties. However, there are few imaging methods which can be used to characterize the microstructure of hydrogels immerged in liquids. Digital holography allows measurements of immerged samples and this makes it as an ideal tool for hydrogel microstructures investigation. In our setup, a short coherent cw laser diode is used as the light source. Each layer of the sample is scanned and recorded with micrometer axis resolution by varying the path length of the reference beam. By processing a series of two dimensional reconstructions with fitting algorithms, we get the three-dimensional distributions of phase and intensity. The method can be applied for various investigations such as monitoring optical and mechanical properties under mechanical stress or temperature.