Medical Polymers and Processing Lab

Principal investigator:

Kenneth J. Wynne, Ph.D.
Phone: (804) 828-9303
Email: kjwynne@vcu.edu
Lab: Rooms 437, 443
Research: Polymer surface modifiers
Acknowledgment: Funding from the National Science Foundation, Division of Materials Research, is gratefully acknowledged.

Research in this lab is aimed at modifying the surface properties of commodity polymers by the addition of a small amount of polymer surface modifier that confers a desired surface property (Figure 1). As an example, the summary below illustrates how novel wetting behavior resulted from molecular characterization and design of a new PSM “water makes it water repellant.”

Figure 1. Coating cross section with a PSM.

Contraphilic wetting behavior

Ordinarily, when a polymeric surface becomes wet, the surface responds to water and becomes more hydrophilic. This behavior is conventional “amphiphilic.” A recent Langmuir letter1 describes a new hydrophobic/hydrophilic switching phenomenon. A novel polyurethane soft block resulted in “contraphilic” wetting, that is, the dry surface is hydrophilic while the wetted surface is hydrophobic (Figure 2). This report received attention by ScienceNOW,2 which led to other Web-based reports. According to the Langmuir website, this paper is the eighth most frequently referenced paper during the period January through June 2005. The new surface wetting phenomenon may have applications in diverse areas such as fabrics and microfluidic devices.

Figure 2. Photograph of the water drop profile for 1 as reported in Langmuir.1 Left, dry; right, wet.

References

  1. Makal, U.; Wynne, K. J. Langmuir 2005, 21, 3742-3745.
  2. Marshall, J. In ScienceNOW 2005; Vol. 26 April.
  3. Makal, U.; Wood, L.; Ohman, D.; Wynne, K. J. Biomaterials 2005, doi:10.1016/j.biomaterials.2005.08.038.

Biocidal polymeric surface modifiers

We have recently developed a new biocidal polyurethane PSM.1 Testing of the new PSM concept was done in collaboration with professor Dennis Ohman and Dr. Lynn Wood in VCU’s Department of Microbiology and Immunology. Biocidal activity was assessed by a modified AATCC-100 protocol that involved sandwiching a challenge of 107 colony-forming units per mL of Pseudomonas aeruginosa between two coated cover slips. Recovered bacteria were tested for activity. Figure 3 shows no CFUs were detected on a coating with only 2 percent biocidal PSM, while control coatings showed expected growth. Several trials showed no surviving CFUs after the shortest practical time (15 minutes). Following this protocol the percent kill/deactivation is 99.9 percent (>3.3 log reduction). Similar test results were obtained against challenges of E. coli and Staphylococcus aureus. These results attest to the validity of the model shown in Figure 1 for the new biocidal PSMs.

Figure 3. Test plates after 15 min challenge of P. aeruginosa demonstrate > 5.1 log reduction.

References

  1. Makal, U.; Wood, L.; Ohman, D.; Wynne, K.J. Biomaterials 2005, doi:10.1016/j.biomaterials.2005.08.038.