## 3 Results and Discussion
### Hardness  
The hardness measurements are shown in Tables 2 and 3. The initial maximum hardness measurements were taken immediately after the durometer was pressed to the polymer and are shown in Table 2. These measurements were considered the 'peak' values, as the maximum value was reached right after the durometer was secured in place. As the durometer was held in place, the needle on the tip of the durometer began to penetrate through more of the surface of the plastic. Given this, another hardness value was then recorded after 15 s of holding the durometer in place. The measured hardness values after the durometer were held into the polymer for 15 s, as can be seen in Table 3.  
There was no significant change to the maximum hardness values. However, there did appear to be some small increase in the 15 s depression values. Modifying and improving the hardness of polymers has been shown to be possible with some plasma sources [14; 19; 27]. The increase in hardness is related to the amount of crosslinking of the polymer chains at the surface [14]. This crosslinking comes when the free radicals on different polymer chains interact and combine [14]. As was discovered from the increase in the hydrophilicity and roughness, there were likely some free radicals that were created on the polymer surface, and thus, the treatment may have created a small amount of crosslinking that could account for the small changes in the hardness values, as shown in Tables 2 and 3. To summarize the results of CAP plasma treatment on the surface of the UHMWPE polymer, it was found that there were significant increases in both the hydrophilicity and roughness with increasing treatment time, specifically at the higher 2.5 L/min flow rate. This trend has positive effects when incorporating a polymer into a joint replacement. First, the increase in the hydrophilicity of the polymer leads to a better interaction with the synovial fluid in a joint and to increased adhesion to the bone [10; 12]. Secondly, the increase in surface roughness could lead to better adhesion because of the increase in the surface area of the polymer [6; 28; 29]. Finally, although there was no measurable change in the surface hardness to relate to an increase in wear resistance, the increased lubrication and adhesion from the improvement of the other surface properties did lead to a material with a more biocompatible surface. However, one point of caution that should be noted is that there are both advantages and disadvantages to increasing the surface roughness. For example, although a rougher surface does lead to better adhesion and there is less chance of the implant loosening from a surface area perspective, it could also lead to more wear of small particles off of the polymer surface, causing negative long-term effects in the joint [10; 29]. This could perhaps be avoided by treating the polymer for lower treatment times, given that, for the UHMWPE examined, after just a 1-min treatment time, the \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Treatment Time (min)**} & \multicolumn{3}{c}{**Hardness (Shore-D) [duro]**} \\  & **Base FR:1 L/min** & **Base FR: 2.5 L/min** & **Tip FR: 2.5 L/min** \\ \hline
0 & 68.7 & 68.7 & 68.7 \\
1 & 70.5 & 69 & 70 \\
6 & 70.5 & 70 & 70 \\
26 & 70.5 & 69 & 69 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Maximum hardness readings. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Treatment Time (min)**} & \multicolumn{3}{c}{**Hardness (Shore-D) [duro]**} \\  & **Base FR:1 L/min** & **Base FR: 2.5 L/min** & **Tip FR: 2.5 L/min** \\ \hline
0 & 64.7 & 64.7 & 64.7 \\
1 & 67 & 64 & 65 \\
6 & 67.5 & 65 & 66 \\
26 & 67 & 65 & 67 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Hardness measurements after 15 s of depression. samples showed a significant decrease in the contact angle without significantly affecting the roughness.