Microfluidic\nDevice with an Oxygen Gradient Generator\nfor Investigating Effects of Specific Hypoxia Conditions on Responses\nof Tumor Cells

The oxygen level in the tumor microenvironment (TME)\nplays a critical\nrole in regulating cell fates such as proliferation, migration, apoptosis,\nand so forth. To better elucidate how hypoxia affects tumor cell behaviors,\na series of microfluidic strategies have been utilized to generate\nan oxygen gradient covering both hypoxia and normoxia conditions.\nHowever, in most studies, some chemicals are introduced into microfluidic\nchips, causing the potential of their poor biocompatibility. The common\noxygen gradient with linear variation does not allow the effects of\nspecific oxygen concentrations on tumor cells to be analyzed accurately.\nIn this paper, based on the physical method of gas diffusion, a microfluidic\ndevice integrated with an oxygen gradient generator is proposed for\ninvestigating effects of different hypoxia levels on responses of\ntumor cells. This device consists of three layers, i.e., upper layer,\nthin film layer, and bottom layer. The upper layer is used for introducing\nthe initial gas and generating an oxygen gradient in the form of gas.\nThe bottom layer is used for introducing cells and culture medium.\nThe thin film layer separates the former two layers, allowing the\ngas to diffuse from the top to the bottom through it. The oxygen gradient\nin the bottom layer is finally generated in the form of dissolved\noxygen. The device is fabricated using microfabrication technology.\nThe effects of structural and working parameters of the device on\nthe oxygen gradient are evaluated by finite element simulation. The\noxygen gradient in cell culture channels is characterized by using\noxygen-sensitive fluorescence materials. The proliferation and morphology\nof HeLa cells under specific oxygen levels are compared after culturing\nfor 48 h. The oxygen gradient with a ladder-like distribution demonstrates\nthat this microfluidic device can provide a prospective experimental\nplatform for in vitro cell studies and revelation of the mechanism\nof tumor metastasis associated with a specific hypoxic microenvironment.