# Deposition of Cell Culture Coatings Using a Cold Plasma Deposition Method
## 3 Results
### Characterization of the Plasma Discharge
Therefore, higher magnification SEM and AFM techniques were used to probe the surfaces in more detail. Figure 6A,B shows SEM images of the collagen delivered via plasma coating process or the wet chemical coating, respectively. There were no macroscopic features on any of the plates indicating that there is a continuous, uniform layer across the entire surface. Deposition results in subtle changes in the morphology compared to the pristine polystyrene, but surface texture modification is more noticeable from the wet chemical deposited film (Figure 6B). Figure 6C,D shows the AFM images of the plasma deposited collagen coating and the wet chemical coating, respectively. The plasma deposited collagen film displayed broad, textured features of 10 nm or less. This correlates with the SEM images and indicates a continuous coating of the collagen. Figure 6D shows that the film deposited using the wet chemical method has greater texturing and relatively larger features (80 nm compared to 10 nm) were observed across the surface. These images indicate that the underlying polystyrene plate was successfully coated with a layer of the collagen using either method. Surface ChemistryWater and hexadecane contact angle measurements were recorded on each surface and the surface energy was calculated using the method of [PERSON] and Wendt [26]. As shown in Table 1, the hexadecane readings were consistent across all surfaces, indicating that the dispersive component of surface energy was highly consistent. In contrast, the water contact angles varied significantly. Both coated surfaces were considerably more hydrophilic than the uncoated polystyrene. The wet chemical coating was slightly more hydrophilic than the plasma coating, which might be due to the higher level of collagen present, as determined gravimetrically. Figure 5: Mass of collagen deposited with increasing plasma exposure. The surface chemistry of plasma deposited collagen coatings and air-dried collagen coatings were probed using FTIR spectroscopy and typical spectra are shown in Figure 7. In accordance with previous reports [23; 25], the plasma appears to have no detectable effect on the chemical structure of the protein; there were no changes in peak heights or positions. The spectra collected from the two collagen coatings were effectively identical with no additional features or shifts evident in either spectrum. The spectra are dominated by the anticipated amide peaks at 3325, 3087, 1653, 1554, and 1241 cm\({}^{-1}\) along with the anticipated C-H\({}_{x}\) features below 3000 cm\({}^{-1}\)[32]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Substrate**} & **Water Contact** & **Hexadecane** & **Polar Component** & **Dispersive** & **Surface Energy** \\  & **Angle (\({}^{\circ}\))** & **Contact Angle (\({}^{\circ}\))** & **(mJ/m\({}^{2}\))** & **Component (mJ/m\({}^{2}\))** & **(mJ/m\({}^{2}\))** \\ \hline Polystyrene & \(84\pm 3\) & \(5\pm 1\) & 4 & 27 & 31 \\ Wet Chemical & \(27\pm 6\) & \(5\pm 1\) & 38 & 27 & 65 \\ Plasma Deposited & \(47\pm 4\) & \(5\pm 1\) & 26 & 27 & 53 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Surface Energy Measurements. Figure 6: (top) Scanning Electron Microscopy (SEM) images of 6-well plates with (**A**) plasma deposited rat tail collagen, (**B**) wet chemical deposition of rat tail collagen, and (bottom) Atomic Force Microscopy (AFM) images of 6-well plates with (**C**) plasma deposited rat tail collagen, (**D**) wet chemical deposition of rat tail collagen. Gel electrophoresis was used to investigate the effect of plasma on the protein structure. Collagen samples were sprayed into a solution of 0.02 M acetic acid with the plasma either turned off (sprayed liquid collagen sample) or with the plasma powered on (plasma deposited collagen). Undiluted collagen was also run as a control. Figure 8 shows that all samples displayed identical bands typical of a collagen molecule.