# Real-Time Monitoring of the Formation and Culture of Hybrid Cell-Microbiomaterial Spheroids Using Non-Faradaic Electrical Impedance Spectroscopy

## TL;DR

A new microfluidic device uses electrical impedance to monitor cell spheroid formation and culture in real time.

## Contribution

A novel microfluidic bioreactor with non-Faradaic EIS for nondestructive real-time monitoring of hybrid cell-microbiomaterial spheroids.

## Key findings

- The device can distinguish between 2D cultures, spheroids, and hybrid spheroids using impedance and capacitance data.
- Differences in electrical properties were observed based on culture duration and the presence of biomaterials.
- The system can detect the spatial arrangement of cells and micro-sized biomaterials over time.

## Abstract

Cellular spheroids are considered a popular option for
modeling
healthy and diseased tissues in vitro and as injectable
therapies. The formation and culture of spheroids can make use of
different three-dimensional (3D) culture platforms, but the spheroids’
analysis often has to rely on endpoint assays. In this study, we propose
a microfluidic bioreactor to culture and nondestructively monitor
human mesenchymal stem cell (hMSC) spheroids over time using non-Faradaic
electr­(ochem)­ical impedance spectroscopy (EIS). For this, an array
of porous microwells thermoformed from ion track-etched thin films
and a pair of sensing electrodes from transparent indium tin oxide
are integrated into the flow and culture chamber of the bioreactor.
To measure the spheroid’s electrical properties, the electrodes
are connected to a frequency response analyzer (FRA), with a multiplexer
in between to enable the operation of more than one bioreactor at
the FRA at the same time. We find differences between the complex
resistance/impedance and/or capacitance data of a reference condition
without cells, a two-dimensional (2D) hMSC culture, hMSC spheroids,
and hybrid spheroids aggregated from hMSCs and titanium or hydroxyapatite
microparticles. We also found differences between different culture
durations. These results suggest that our device can sense the presence
and spatial arrangement of cells and micro­(sized) biomaterials as
a function of time.