Portable cell culture device for maintaining low oxygen environment: CASE STUDY - proliferation of fibroblasts under hypoxic conditions

Here we present a portable cell culture instrument that increase the biomimicry of traditional cell research applying and maintaining low oxygen or hypoxic environment around the custom made culture chambers. It is well known that most of the cells in vivo experience considerably less than 10 % oxygen concentration and some cells/organs even less than 1 % [1]. It is also well known that cells behave significantly differently when exposed to lower oxygen than normal incubator condition (~19 % O2) [1]. Even though researchers are aware of the drastic effect of low oxygen and hypoxic condition for the cells these conditions are not widely applied in basic biological studies.

One reason for low number of hypoxia studies is lack of commercial tools and devices available to maintain the low oxygen conditions in a chip/dish. For example, to use a normal Petri dish and in a stationary hypoxia incubator or large hypoxia workstation might be difficult to perform high quality or long-term imaging studies. Taking the Petri dish out from the incubator/workstation expose the culture immediately to reoxygenation (oxygen level increase) and increasing temperature, which could affect remarkably to cell behavior. Furthermore, these stationary systems reserve large space from the lab, which might be a huge cost issue as well. In addition to these stationary systems, there are few commercial portable systems available. However, they typically lack of temperature and/or oxygen control and therefore are difficult to maintain for example under long-term microscopy.

In this study, we present the portable cell culture instrument that include battery to maintain the temperature control and preloaded gas containers to maintain the predefined oxygen level inside the six individual culture chambers (See Figure 1). The flow divider unit can be extended from the base unit while maintaining temperature and gas supply. This enables the use microscope for extensive study of live cell imaging without affecting to the cell culture environment. Furthermore, the cells in the chambers can be cultured and maintained in hypoxic conditions. The dynamics of oxygen conditions inside the chamber was studied with in house build non-invasive optical oxygen sensor [2] while maintaining temperature at 37 °C. We also demonstrated the effect of hypoxia on proliferation of mouse embryonic fibroblasts (MEFs) under different oxygen levels (1 %, 5 % and 19 %; each containing 5% CO2; 19 % O2 mimicking incubator conditions). MEFs were cultured in the instrument and image ones per day to determine the proliferation rate in hypoxic conditions. Zeiss Observer Z1 microscope was utilized to automatically image entire culture area (16mm in diameter) by tiling and stitching 96 single images to one large image. This allow us to analyze the entire culture area and thus avoiding poorly selected random shots around the well, which might finally be misleading. Images were processed using MATLAB to obtain relative proliferation growth rate data that is based on area cell are covering (See Figure 2). The results showed that the proliferation rate is enhanced in 5 % oxygen compared to 1% and 19 % oxygen conditions (See Figure 3). This also demonstrate that cells are vital in all gas concentrations and reach confluent after 3 days. Therefore, our portable culture instrument can be utilized in physiologically more relevant low oxygen studies in different cell- and organ-on-a-chip applications.