Responsive hydrogel technologies are currently being pursued in a range of applications, including tissue scaffolds, chemical release agents, biosensors, and artificial muscles. However, their efficacy has been severely restricted by an inability to introduce accurate and tunable response mechanisms in a controlled fashion. This is often attributable to the inherently ill-defined structure of most systems, with gelation based on spatially random cross-links within the material, or poorly formed solid phase domains distributed non-uniformly throughout the sample. The ultimate goal of the research activities proposed in this CAREER award is the successful generation of a new class of highly distensible, nanostructured hydrogels, capable of sophisticated and tunable responses to a range of external stimuli. The first generation of hydrogels are to be fabricated by exploiting the melt-state self-assembly of sphere forming block copolymer amphiphiles, as extremely versatile templates for more highly functioning materials. Our goal is to generate hydrogels with integrated functionality permitting one to continuously tune, through external stimuli (e.g., temperature, pH, light, etc.), the dimensions, geometry, and size distribution of both the solution and solid phases in these gels, all with exacting control. At the same time, we aim to incorporate internal triggers that can induce more drastic material responses to an external stimulus, such as rapid and discontinuous changes in volume, modulus, or domain permeability. Extension of these ideas to non-spherical morphologies is expected to provide access to materials in which anisotropic swelling control is possible. While the preliminary work proposed focuses on the synthesis of the basic hydrogels and evaluation of their inherent response characteristics, the predominance of the work will be focused on the integration of advanced response mechanisms through synthetic modifications to the constituent block copolymers at the molecular level. The proposed research will be instrumental in the advancement of knowledge concerning the design of next generation, "intelligent" or responsive materials, capable of multiple simultaneous stimulus-induced behaviors, including: dissolution, swelling anisotropy, continuous and discontinuous expansion (and contraction), bending (and unbending), reversible self-adhesion, shape recovery, and triggerable chemical release.
NON-TECHNICAL SUMMARY:
The research proposed in this CAREER award is directed at the successful generation of a new class of super-absorbent polymeric materials that possess the unique capability of changing their most basic characteristics, such as shape, size, toughness, and permeability in direct response to an applied stimulus, such as UV light, heat, or an electric field, to name just a few. These materials are anticipated to have direct implications in advanced drug delivery, improved implant compatibility, degradable tissue scaffolds, artificial muscles, chemical and biological sensors, and biocatalysis. Thus, the proposed research is expected to have broad impact in a number of technologically important areas in which societal quality of life can be deeply affected. These research activities will be integrated with student education in a range of capacities, in an effort to bring the element of discovery in learning to promising young researchers. For example, the extensive inclusion of undergraduate students as active researchers on this project, integration of the results directly into course curricula, and the dissemination of results through undergraduate, graduate, and departmental seminars around the country and world permit this cutting edge research to become a mainstream learning tool. In addition, this CAREER award is also being used to develop annual one-day interactive research workshops for regional (Colorado and Wyoming) high school science teachers, in which recent topics in nanotechnology, biotechnology, and biomaterials can be discussed with world experts. The goal of these workshops is to provide each of the teachers with the hands-on materials to bring the latest research to life in their own classrooms, such that high school students will be able to share the excitement of the latest research at Colorado State University and around the world.
The intellectual merit of this project is based on the formation of new and valuable hydrogel networks through the application of creative polymer chemistry. We were able to use molecular self-assembly to produce a unique class of polymer networks capable of absorbing large quantities of water, aqueous solutions, or other organic solvents while retaining outstanding mechanical properties. Such materials are of high value in applications involving membrane separations of biological molecules such as antibodies and proteins, light gas separations important to carbon dioxide capture from the environment, and transport control during localized drug delivery in the human body. Hydrogel systems are not unique in this regard, but an inability to accurately and reproducibly control both the network mesh size, the water content, and the various mechanical properties such as tensile strength or elastic modulus can severely retard their ability to function reliably in these types of applications. The scientific approach employed in this project exploited the concept of macromolecular self-assembly, or designing of molecules such that they are driven to organize themselves into very predictable patterns on the nano-scale, to overcome the typical flaws in most hydrogel systems. Several of the most significant outcomes of this project include the development of ultra elastic hydrogels of outstanding tensile strength, a new understanding of the origins of modulus in tethered sphere networks (the type of networks used for these hydrogels), light activated curing chemistry that allows trapping of very specific self-assembled patterns and transferring them into hydrogel networks, and methods to pattern hydrogel systems using simple photolithography type technology. The broader impacts of this study are numerous. Over the last five years, The principal investigator and his group have used this project as an opportunity to become engaged in a number of GK – 12 programs aimed at generating a passion for scientific discovery and creative problem solving that becomes a career driving force. At the local level, our group has been involved with Rivendell Elementary (Fort Collins) students in the K – 2 age range, where we have developed hands on activities accompanying 3-week study modules on "Solids, Liquids, & Gases", and "Light and Sound". With colleague Professor Matthew Kipper (Colorado State University), we have also developed a one week intensive summer camp as part of the Preston Elementary STEM Summer Institute for 5th – 8th graders called "Polymer Nano-Structures: Say What!?" Importantly, this program offers numerous scholarships to both female participants and students in need. The principal investigator also became a guest presenter ("The Polymer Show") in the Telluride Science Research Center’s Pinhead Punk Science Summer Program, which is dedicated to the providing the Telluride regional community with quality science education for children and their families. Importantly, bringing excitement for science to the rural mountain communities and inciting interest in the value of higher education opportunities will hopefully engender growing appreciation and community support of Colorado’s higher learning institutions. The PI also sued this project as a means to incorporate extensive undergraduate involvement in research, mentoring 12 undergraduates over the lifetime of the project. These undergraduates produced nine individual research presentations (poster and oral) at regional and national conferences in the last five years. These resulted in two awards in the regional (1st Place) and national (3rd Place) AIChE conference undergraduate student paper competitions.
