(I-359) Miniature, Battery-Powered Cell Culture Incubator for Resource Limited Settings

Introduction::

Acquiring biomarker data from large populations across diverse demographics—including race, ethnicity, gender, socioeconomic status, occupation, and more—allows researchers to elucidate connections between demographic markers, physiological variations, and disease risk. For instance, inflammatory dysregulation is linked to many cardiovascular and neurodegenerative diseases [1], as well as infectious diseases like HIV [2]. Cell culture assays can be used to provide insight into dynamic cellular responses correlating to the function of the active immune system rather than just the baseline immune function measured by traditional methods, such as dried blood spot sampling and serological screens [3]. However, these techniques require access to laboratory facilities with expensive incubators monitoring humidity and CO₂. For cell culture assays studying immune systems of populations in resource-limited settings, the McDade lab (Northwestern University) has developed a low-volume, cytokine-release assay that can be conducted on whole capillary blood samples from a finger prick and a simplified cell culture protocol that does not require laboratory conditions [4]. Unfortunately, currently available portable incubators are too bulky and expensive to be feasibly transported to remote settings to enable these tests. To address these challenges and expand cell culture access to diverse populations, we developed a miniature, battery-powered incubator that we call “mini-cube.” mini-cube is a shippable, easy-to-use device consisting of an insulated chamber, rechargeable batteries, and a control system that can hold samples at 37^°C (±0.5°C) for over 16 hours on a single charge. We hope mini-cube will provide researchers with a low-cost solution to population-based cell culture studies in resource-limited settings.

Materials and Methods::

Our device was designed to minimize size and weight while regulating the temperature of blood samples at 37°C with a tolerance of ±0.5 °C for a minimum of 6 hours. The size and weight of our incubator is less than 0.45 kg (1 lb) in weight and 5.86 x 8.61 x 14.64 cm or 738.66 cm³ in volume, making it suitable for inexpensive ground shipment to the study location. A 3D-printed plastic exterior houses a battery-powered electric heating and control system and polystyrene insulation to regulate the heat of samples in an aluminum sample tube holder (Figure 1A).

The device is powered by two protected, rechargeable, 18650 lithium-ion batteries. The small, ultra-low-power XIAO nRF52840 Seeedstudio microprocessor regulates heating of the brick through a resistive heating pad while minimizing size and energy requirements. The microcontroller receives input from a digitally integrated temperature sensor placed in contact with the aluminum block and, using a proportional integral derivative (PID) algorithm, provides proportional power to an n-channel MOSFET gating the heating pad (Figure 1B). The device’s electronics are housed on a custom printed circuit board in the battery compartment (Figure 1C).  In addition, the microprocessor controls a simple user interface consisting of a red, yellow, and green LED system which indicates to the user when the device is warming up (yellow), ready for incubation (green), and compromised (red).

Results, Conclusions, and Discussions::

We successfully created a functional prototype of the mini-cube. The current prototype of the final design successfully heated the samples to 37°C and regulated the temperature for over 6 hours (the time necessary for Dr. McDade’s incubation experiments). Incubation experiments involve heating cryogenic vials containing 100uL of blood, so to test the efficacy of the temperature regulation of the device, we monitored the temperature using external digital temperature probes embedded in the cryogenic vials containing 100uL of phosphate-buffered saline (PBS), to mimic blood samples. These tests were performed in a room temperature laboratory environment, and measured the temperature throughout the entire incubation, from device heating to battery discharge and device shutdown.

The current standard used by the McDade lab for small volume cytokine release assays is the Benchmark Scientific myBlock Mini Digital Dry Bath, a wall-powered benchtop incubator. We performed an identical test of the myBlock Mini incubator to compare our device to the current lab standard. Results of our initial tests of our most current prototype of the mini-cube as well the myBlock Mini revealed our device was able to maintain 37 °C within tolerance for over 16 hours on a single charge, while the myBlock Mini exhibited significant oscillations and did not maintain tolerance (Figure 2).

Future work will continue characterizing the incubator performance in varied environmental conditions, such as altered ambient temperature or airflow. These variations could affect temperature regulation as well as battery-life. Although development of the mini-cube is not complete, our initial testing provides a proof of concept that a battery-powered incubator can fulfill Dr. McDade's novel cell culture protocol requirements. 

          We have explored several different potential applications of this device, including traveling to Cape Town, South Africa to meet with Dr. Pieter Naudé, a neuroinflammation and HIV research expert, to identify research areas that could benefit from the mini-cube. One such research area is using the mini-cube to assess the HIV immunity status of HIV exposed, uninfected infants in rural South Africa. Regardless of the application, we envision the mini-cube will enable a new generation of advanced cell culture assays in expanded target populations. 

Acknowledgements (Optional): : We would like to acknowledge Dr. Thomas McDade of Northwestern University and Dr. Pieter Naudé of Cape Town University for guidance on this project, as well as Northwestern's Department of Biomedical Engineering for funding this project.

References (Optional): :

[1]   [1]    T. W. Mcdade, S. Williams, and J. J. Snodgrass, “What a Drop Can Do: Dried Blood Spots as a Minimally Invasive Method for Integrating Biomarkers Into Population-Based Research,” 2007. [Online]. Available: https://people.brandeis.edu/~rgodoy/

[4]   [2]    M. E. Williams, A. J. Van Rensburg, D. T. Loots, P. J. W. Naudé, and S. Mason, “Immune Dysregulation Is Associated with Neurodevelopment and Neurocognitive Performance in HIV Pediatric Populations—A Scoping Review,” Viruses, vol. 13, no. 12, p. 2543, Dec. 2021, doi: 10.3390/V13122543/S1.

[3]    S. Vardhana, L. Baldo, W. G. Morice, and E. J. Wherry, “Understanding T cell responses to COVID-19 is essential for informing public health strategies,” Sci Immunol, vol. 7, no. 71, May 2022, doi: 10.1126/SCIIMMUNOL.ABO1303.

[2]   [4]    T. W. McDade et al., “Out of the Laboratory and Into the Field: Validation of Portable Cell Culture Protocols,” Psychosom Med, vol. 83, no. 3, pp. 283–290, Apr. 2021, doi: 10.1097/PSY.0000000000000923.

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