A simple microindentation technique for mapping the microscale compliance of soft hydrated materials and tissues

Several recent studies have shown that cells respond to the elastic modulus and elasticity gradients on soft substrates. However, traditional macroscale methods for measuring elastic modulus cannot resolve elastic gradients or differences between the macroscale and microscale elastic modulus of layered tissues. Here, we present a technique for measurement of the microscale elastic modulus of soft, hydrated gels and tissues. This technique requires less equipment than equivalent atomic force microscopy (AFM) and can easily measure larger samples with high adhesiveness. We validate this technique by measuring the microscale modulus of a hydrogel with elasticity that does not depend on measurement scale. We show that the elastic modulus measured using microindentation correlates with measurements using AFM and the macroscale tensile modulus. We verified the ability of this technique to characterize a hydrogel with an elastic gradient of 2.2 kPa/mm across 19 mm and to measure the microscale elastic modulus of the endothelial side of human greater saphenous vein, which is an order of magnitude less than the whole vein macroscale modulus. This simple, inexpensive system allows the measurement of the spatial organization of microscale elastic properties of fully hydrated, soft gels and tissues as a routine laboratory technique.