A dual-transduction-integrated biosensing system to examine the 3D cell-culture for bone regeneration

Three-dimensional (3D) cell cultures developed with living cells and scaffolds have demonstrated outstanding potential for tissue engineering and regenerative medicine applications. However, no suitable tools are available to monitor dynamically variable cell behavior in such a complex microenvironment. In particular, simultaneously assessing cell behavior, cell secretion, and the general state of a 3D culture system is of a really challenging task. This paper presents our development of a dual-transduction-integrated biosensing system that assesses electrical impedance in conjunction with imaging techniques to simultaneously investigate the 3D cell-culture for bone regeneration. First, we created models to mimic the dynamic deposition of the extracellular matrix (ECM) in 3D culture, which underwent osteogenesis by incorporating different amounts of bone-ECM components (collagen, hydroxyapatite [HAp], and hyaluronic acid [HA]) into alginate-based hydrogels. The formed models were investigated by means of electrical impedance spectroscopy (EIS), with the results showing that the impedances increased linearly with collagen and hyaluronan, but changed in a more complex manner with HAp. Thereafter, we created two models that consisted of primary osteoblast cells (OBs), which expressed the enhanced green fluorescent protein (EGFP), and 4T1 cells, which secreted the EGFP-HA, in the alginate hydrogel. We found the capacitance (associated with impedance and measured by EIS) increased with the increases in initial embedded OBs, and also confirmed the cell proliferation over 3 days with the EGFP signal as monitored by the fluorescent imaging component in our system. Interestingly, the change in capacitance is found to be associated with OB migration following stimulation. Also, we show higher capacitance in 4T1 cells that secret HA when compared to control 4T1 cells after a 3-day culture. Taken together, we demonstrate that our biosensing system is able to investigate the dynamic process of 3D culture in a non-invasive and real-time manner.