# The Effect of Human Blood Plasma Conditioning Films on Platelet Tungsten Bag Surface Properties
## 4 Discussion  
It is known that under environmental conditions that surfaces will adsorb molecules from their surroundings, which can alter surface properties and hence bacterial retention. From the results it was apparent that the application of a CF can have significant effects on the surface properties of the three surfaces used in this study. When physical properties were tested, the human plasma CF appeared to have the most significant effect on the rough surface, with the SEM results demonstrating visible increases of material on the rough surface from 1 h to 24 h, likely caused by a continuous building up of molecules being adsorbed onto the surface and onto other molecules already adsorbed [12]. This was only apparent on the rough surface, as both the smooth and flat did not appear to demonstrate any significant differences between the time points. This is in agreement with work by [PERSON] et al. (2016) who found that bacterial adhesion and biofilm  
Figure 5: MATH assay of (**a**) _Ser. marcescens_ and (**b**) _S. epidermidis_ with and without the presence of a human plasma conditioning film. (\(n=3\)). Data presented as mean \(\pm\) SE. formation were significantly higher on the rough surfaces of platelet bags compared to the smooth surfaces [24]. The effect likely appeared on the rough surface due to the pits within the surface which made it harder to wash away the excess CF and became filled with organic material. In support of this, it has been shown that surface roughness on the scale of bacterial size promotes their adhesion by increasing the contact area between the material and bacteria and by protecting the bacteria from shear forces [25]. This was supported by the optical surface profile data, which also demonstrated the most significant changes with the rough surface. The CF that had the greatest effect on the surface roughness was the human plasma CF, with both 1 h and 24 h incubations significantly reducing the roughness values. The reduction in roughness was likely to be caused by polymeric materials in the human plasma adsorbing and aggregating onto the surface. Further, it has previously been demonstrated that the addition of a CF can drastically reduce surface roughness of glass [12]. On the smooth surface, human plasma had no significant effect after 1 h, but after 24 h a reduction in surface roughness was observed. Whilst the smooth surface did not have the pits that were present on the rough surface, it still had a greater surface roughness than the flattened surface which could have been smoothed out by adsorption and aggregation of polymeric materials. Finally, on the flat surface a slight increase in roughness was observed after 1 h but this change was not sustained when assessing at 24 h. This could potentially be due to an uneven adsorption/aggregation of material onto the surface after 1 h, causing more irregularity in the surface features, but was smoothed out as more material was adsorbed/aggregated onto the surface. It may be suggested that these findings are due in part to the Vroman effect. Protein adsorption generally involves rapid monolayer adsorption with an almost flat orientation followed by a slow conformational and orientational rearrangement of previously adsorbed molecules known as the Vroman effect [26]. The adsorbed proteins can form different thicknesses (2-10,000 nm), which affects protein conformation, and this may affect the physicochemistry of what was determined on the surfaces. Many physical interactions at the surface interface influence both initial protein attachment and subsequent conformational rearrangement, as was demonstrated by the rough surfaces. In addition, the _Ser. marcescens_ and human plasma demonstrated different physicochemical results than the human plasma, _S. epidermidis_ and human plasma conditioning films, and it may be that the more hydrophilic nature of the _Ser. marcescens_ demonstrated in the MATH assay contributed to the different physicochemical results observed.