Nanofiber-based 3D cell carrier and cryopreservation systems for adherent cells

Significant efforts have been recently made to develop advanced cell-based lab-on-a-chip devices using electrochemical sensors. However, current systems are still not suitable for a ready-to-use format as the cells inside the device need incubator conditions (CO2, nutrients, etc.) for survival during conventional transportation. Herein we propose a strategy called on-sensor cryopreservation (OSC), which enables the adherent cells to be preserved by freezing (-80°C) on a sensor surface, such as the light-addressable potentiometric sensor (LAPS). Adherent cells on the LAPS surface were prone to cryo-injury; thus, the surface was modified to enhance the cell recovery for OSC. It relies on i) the integration of elastic electrospun fibers composed of polyethylene vinyl acetate (PEVA), which has a high thermal expansion coefficient and low glass-transition temperature, and ii) the treatment with O2 plasma. The modified sensor is integrated into a microfluidic chip system not only to decrease the thermal mass, which is critical for fast thawing, but also to provide a precisely controlled micro-environment. This novel cryo-chip system is effective for keeping cells viable during OSC. As a proof-of-concept application, the extracellular acidification of cancer cells (CHO-K1) was evaluated by differential LAPS measurements. Results show, for the first time, that our strategy based on OSC using the cryo-chip allows label-free and quantitative measurements directly after thawing, which eliminates additional post-thaw culturing steps. The freezing of the chips containing cells at the manufacturing stage and sending them via a cold-chain transport could open up a new possibility for the ready-to-use on-site format. Moreover, this strategy is potentially adaptable to other cell-based lab-on-a-chip devices in the future.