Fabrication of Stiffness Gradient Nanocomposite Hydrogels for Mimicking Cell Microenvironment

It has attracted much attention to develop a gradient hydrogel for real mimic of the extracellular matrix. Despite simplicity and ease of electrophoresis preparation method, some drawbacks limit the application of the method including toxic organic crosslinker residual, specific ionic monomer types, as well as narrow gradient gaps. In this work, we successfully prepared gradiently crosslinked nonionic PNIPAm/Laponite nanocomposite (NC) hydrogels with controllable gradient structures by adjusting the intensity of the direct current electric field. The results showed that the stiffness, surface property and thermosensitivity of the hydrogel changed with gradient distributions of Laponite. The average stiffness gradients varied from 0.18 kPa/mm, 0.41 kPa/mm to 1.28 kPa/mm by simply adjusting the intensity of the direct current electric field from 0.13 V/mm, 0.20 V/mm to 0.27 V/mm accordingly. The stiffness reached in a range of 13.8∼33.0 kPa. The growth behaviors of human cervical cancer cells (HeLa cells) on the gradient NC hydrogel surface were discussed. Spreading and proliferation, as well as morphology of HeLa cells were closely related to the stiffness of the gradient NC hydrogels. This work develops a stiffness-controllable gradient NC hydrogel and opens up a new insight into the better understanding of cells behaviors in different tissues and organs in vivo.