William Y. Bender
March 21, 2017
Since the last blog, we have been able to characterize the mechanical (bulk) and surface properties of the newly synthesized materials of crosslinked vinyl-terminated poly(dimethylsiloxane) (v-PDMS) and hydridosiloxanes (Figure 1). The hope is to prepare materials that have antimicrobial properties. In other words, biofilms will be unable to grow on them. So far, we have mixed the two polymers in different ratios in order to change the mechanical properties of the silicone materials. We know from previous work that the mechanical properties have an important role on how cell growth will proceed on the surface. Additionally, we have looked at the effects of different additives on the pdroperties. For example, we have found that including zinc chloride powder into the material increases the Young’s modulus, and therefore creates materials that are “stiffer”. This is unsurprising since salts, like zinc chloride, are very hard. Surprisingly, the addition of titanium dioxide nanoparticles has the opposite effect, and softened the materials. These effects and be seen by the slope of the line in the stress-strain curves for these materials (Figure 2), where a higher slope means the material is “stiffer.” In contrast to the mechanical properties, the surface properties of these materials show little change with respect to additive, as seen through contact angle analysis.
Figure 1. Hydrosilyation reaction of vinyl-terminated PDMS and hydridomethylsiloxanes to make robust crosslinked, silicone materials.
Figure 2. Stress-strain curves for pure silicone (left), zinc chloride-filled silicone (middle), and titanium dioxide filled silicone (right). Young’s moduli for each of these is 359 mPa, 1,560 mPa, and 234 mPa, respectively.
Currently, we have begun preliminary testing of the antimicrobial properties of films of these materials in collaboration with Dr. Andrew Wier’s research group in Biology. Figure 3 shows biofilm growth (stained purple for ease of viewing) on a number of different silicone materials and composites. While these are purely preliminary and too early to draw real conclusions, there seems to be differences in the amount of biofilm growth on the different samples, which is hopeful for future experiments.
Figure 3. Biofilm growth on various silicone materials
Also during this past semester, I had the opportunity to present what we had been working on at the thirty-sixth annual meeting of the Society of Fellows of Dyson College in March. It was an eye-opening experience, and it exhibited just how much forward-thinking research happens at Pace. Further, I am once again honored to be afforded this research opportunity by the UGR program, considering the quality of the research I saw there.
In summary, we have shown that the mechanical properties of the materials can be altered through the addition of different compounds into the silicone without changing the surface properties. We plan to continue testing materials, including silicone-organic hybrid materials, and their effects on biofilm growth. We look forward to reporting our results on the next blog!