# Deposition of Cell Culture Coatings Using a Cold Plasma Deposition Method
## 3 Results
### Characterization of the Plasma Discharge
The chromatographs are dominated by the pair of \(\alpha\) chains, a strong band associated with the \(\beta\)-sheet, and a \(\gamma\) component. The increased intensity of the bands in lane 3 were associated with the undiluted collagen control sample. No additional features or alterations of the plasma treated sample were observed in the gel, indicating that this protein structure is not altered by the plasma process. _Electrochemical Properties of film_. In order to investigate the effect of the underlying substrate on the film morphology and to facilitate electrochemical measurements, collagen films were deposited using the plasma process and the wet chemical method on gold on silicon electrodes. Figure 9A,B shows the SEM images of the plasma deposition method and the wet chemical method on gold, respectively. For the plasma deposited collagen film, similar shadowing to the polystyrene plates was observed on the surface, indicating a similar change in the texture occurred on both substrates. For the wet chemical deposition, the shadowing was also present, but additional larger features are present perhaps due to some aggregation of collagen fibrils in the deposition solution. Figure 9C,D shows the AFM images of the plasma deposition and wet chemical deposition, respectively, on a gold surface. The plasma deposited film shows a continuous layer with features less than 10 nm in height and was very similar to the plasma deposited collagen film on the polystyrene substrate. The wet chemical film on gold again produced rougher features of 50-60 nm in height. Overall, the SEM and AFM imaging confirm the presence of continuous collagen films on both the polystyrene and gold surfaces but that the plasma deposited films contain less protein aggregates and they are of a smaller size than the wet chemical method. Figure 7: Fourier transform infra-red (FTIR) spectra of collagen coating deposited using traditional wet chemical technique and plasma deposited collagen. Figure 8: Gel electrophoresis collected from sprayed liquid collagen without plasma (1), plasma deposited collagen (2), and concentrated collagen control sample (3). Figure 9: (top) Scanning Electron Microscopy (SEM) images of gold-coated silicon wafers with (**A**) plasma deposited rat tail collagen, (**B**) wet chemical deposition of rat tail collagen. (bottom) Atomic Force Microscopy (AFM) images of gold-coated silicon wafers with (**C**) plasma deposited rat tail collagen, (**D**) wet chemical deposition of rat tail collagen. By using redox probes in solution that have different physical dimensions and charges, electrochemical techniques such as cyclic voltammetry can provide powerful insights into the coverage of thin films and their barrier properties. For example, the isoelectric potential of collagen is typically approximately 4.7 [33] so that at the neutral pH used here, it is expected to be negatively charged and so the film is likely to repel the negatively charged ferrocyanide probe and perhaps preconcentrate the positively charged ruthenium hexamine probe. Ferricyanide [Fe(CN)\({}_{6}\)]\({}^{4-/5-}\), ferrocene methanol [FeMeOH]\({}^{0/1+}\), and ruthenium hexamine [Ru(NH\({}_{3}\))\({}_{6}\)]\({}^{2+/3+}\) were used to investigate size and charge effects. As well as the barrier properties, by varying the scan rate, the rate of heterogeneous electron transfer across the electrode/film interface can be measured which depends strongly on the interfacial properties [34]. At bare gold, each of the electroactive probes gave voltammetric responses that were consistent with those expected for reversible electron transfer reactions involving a solution phase reagent. These voltammograms were fitted to a reversible model under semi-infinite linear diffusion control by varying the standard heterogeneous electron transfer rate constant, k\({}^{o^{\prime}}\), so as to minimize the sum square residuals between the experimental and model currents.