INTELLECTUAL MERIT: The proposal aims to identify engineering design rules for controlling protein and cell interactions with biomaterials. A central and persistent problem confronting biomaterials design is the uncontrolled adsorption of proteins to material surfaces. There is currently no general consensus on how to design a protein-resistant coating. A major gap in current knowledge is the limited understanding of the basic mechanisms of protein adsorption to polymer interfaces in aqueous media. Absent this information, it is difficult to define engineering approaches to control specific behavior. This research plan will address this knowledge gap by using a combination of synthetic chemistry and complementary experimental approaches that probe the mechanisms by which proteins interact with grafted polymers. In Objective 1, polymer gradients will be used as high throughput screening platforms to identify polymer brush properties that support protein adsorption. In Objective 2, a combination of fluorescence techniques will quantify the diffusivity of adsorbed proteins as a function of the brush parameters. In Objective 3, neutron reflectivity measurements with deuterated proteins will determine where adsorbed proteins localize relative to the polymer brush. Finally, Objective 4 will quantify the magnitude and range of attractive and repulsive forces between proteins and polymers that are responsible for protein adsorption behavior. The work will help to develop an understanding of the interactions of proteins with polymer brushes and could advance the design and preparation of surfaces resistant to protein adsorption and biofouling.
BROADER IMPACTS: Success of this project will shed new and useful light on the mechanisms by which polymer brush coatings may protect surfaces from unwanted protein adsorption. With respect to broadening participation, the project will continue the PI's on-going efforts to involve students from underrepresented groups in science and engineering in the research endeavor. These efforts will include inclusion of females and underrepresented minorities in graduate level research and participation in the Summer Research Opportunity Program that provides opportunities for minority undergraduate students to participate in research.
This grant identified a new mechanism underlying the temperature-dependent, reversible adhesion of biological molecules and cells onto thin poly(N-isopropylacrylamide) (PNIPAM) coatings, and the underlying polymer properties that determine this behavior. PNIPAM is a temperature responsive "smart" polymer with potentially widespread uses in biotechnology. An attractive property of this polymer is that it becomes sticky to cells and proteins above 32°C, which is close to body temperature (37°), but the polymer repels proteins and cells below this temperature. This polymer can be used as a temperature-controlled on/off switch for the binding and release of proteins or cells. Several applications attempt to exploit this thermal switching, in order to control the efficient capture and release of proteins or cells. However, results are often variable. This was partly due to the incomplete understanding of the properties of the polymer coatings that control the thermal switching, and the mechanism of bio-adhesion to the films above 32°C Our research directly addressed this knowledge gap and may transform the field. The intellectual merit of the work is that our findings disproved a commonly held view of the underlying mechanism of biological adhesion to PNIPAM. However, we demonstrated an alternative mechanism, and we identified the polymer properties that regulate this alternative mechanism. These findings are potentially transformative because they will dramatically alter current thinking regarding how this material interacts with biological molecules above and below the switching temperature. We further proposed general guidelines for achieving reproducible results with different PNIPAM coatings. This research will have broad impact because PNIPAM is used in a range of applications including, for example, self-cleaning coatings, protein purification, drug delivery, and tissue regeneration. A second major finding is that the material onto which the PNIPAM coatings are attached can also influence the temperature-dependent bioadhesive switching. This was another source of inconsistent results obtained with PNIPAM coatings. The intellectual merit of our findings is that we demonstrated how the coating substrate alters the bioadsorption mechanisms. We then demonstrated how to fabricate PNIPAM coatings, which reproducibly achieve the desired performance of these smart PNIPAM coating, regardless of the underlying substrate. Because PNIPAM is a prototype of a larger class of water-soluble polymers, our findings should have broad implications for the design of other thermally responsive, neutral water-soluble polymer coatings. Finally, we broadened this impact of this research by participating in outreach that targets girls in STEM disciplines. We developed and guided a hands-on learning module for the Girls Adventures in Mathematics and Engineering summer camp (GAMES). Our module introduced middle school girl campers to concepts of cell adhesion and migration on biocompatible materials, and the importance of these concepts in tissue engineering. Girls learned how to image migrating cells and how to quantify migration speeds. We then discussed how these parameters affect wound healing and tissue regeneration. Through these activities we broadened girls’ awareness of interesting, socially relevant problems in science and engineering.
