Fig. 6: Changes of the impedance phase of MSCs and HUVECs cultured on collagen thin films with concentrations of 250 \(\mu g/mL\), 500\(\mu g/mL\), 1000 \(\mu g/mL\) over time.
Effect of the collagen thin films on the MDA-MB-231 cells
In the second step of the research, tests were accomplished on the MDA-MB-231 to explore the effect of the collagen thin film concentration on the growth and proliferation of the cancer cells. This experiment was performed twice for four concentrations and five samples from each concentration. These cells did not attach to the collagen thin films in any of the samples and died. In general, cancer cells produce collagenase. Collagenase is an enzyme that dissolves and destroys collagen. In particular, MDA-MB-231 cells, which are aggressive and malignant, show this behavior more strongly. Three mammalian collagenases (MMP-1, MMP-8, MMP-13) [42] appertain to the group of matrix metalloproteinases and can cleave and destroy the extracellular collagen matrix [42]. In addition to the fibrillar collagens, collagenases can cleave and destroy some other extracellular matrices and non-matrix proteins, including growth factors[42]. MMPs are commonly thought of as tumor growth enzymes because they destroy extracellular matrix components and thus increase the invasive power of the cancerous cells[43]. It seems that due to the fact that these collagenases have been observed in breast cancerous cells[44], they can destroy the thin layers of the collagen. By destroying these thin layers, which are considered as a bed for the cell attachment, the cells do not found an appropriate substrate to attach and die.
Bioimpedance assessment of the collagen thin films concentration on the HUVECs proliferation rate
In the third step of the research, collagen thin films were created on the surface of the alkanethiol-treated IDEs and the role of the concentration of the collagen thin films on the growth and proliferation of the HUVECs was quantitatively investigated using impedance measurements. Like the MSCs, viability assessment of HUVECs showed no remarkable discrepancy among the viability of HUVECs cultured on the collagen thin films with different concentrations. The HUVECs cultured on the collagen thin films with various concentrations had a viability of over 99%. As well, obtained impedance results were analogous with the results of the MSCs.
3.4.1 Bioimpedance magnitude of the HUVECs cultured on the collagen thin films
The impedance measurement results of the HUVECs were similar to that of the MSCs. Fig. 4 (D-F) shows the magnitude diagram of the measured impedances of the HUVECs cultured on the collagen thin films with different concentrations during the time. As shown in the figure, the magnitude of the measured bioimpedance at different concentrations of collagen thin films has increased over time. This increase in the impedance in the first hours results from the cell attachment. After 48 h, the increased impedance magnitude is due to the cell proliferation since the cell numbers have been increased because cells doubling time has elapsed. The diagram of the measured differential bioimpedance for different concentrations after 48 h is also shown in Fig. 5 (B). We can see in this figure that after 48 h, when the doubling time (about 36 h) of the HUVECs has elapsed, the amount of increase in impedance at lower concentrations is higher than that of the higher concentrations, which may indicate more cell growth on the collagen thin films with lower concentration.