PECASE: Molecular Design and Nanomechanical Testing of High-Toughness Biomimetic Polymeric Systems

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The research component of this CAREER proposal involves the design and nanomechanical testing of biomimetic, "modular" polymeric systems with highly controlled mechanical properties at the molecular level. A general design strategy for improving the molecular toughness of synthetic macromolecules is proposed which involves the nonspecific, noncovalent complexation of a synthetic "host" polymer with smaller, nanometer-size, shape-persistant "guests." The research will begin by studying a model system which involves the well-studied complexation of poly(ethylene oxide) (PEO), -[CH2-CH2-O]n- and the small globular protein, human serum albumin (HSA). Chemical attachment of one PEO chain end to a surface and sufficiently low chain grafting densities will be achieved using a mixed monolayer technique involving the co-chemisorption of mono(thiol)-functionalized PEO and a self-assembling alkanethiol monolayer (SAM) on gold. The PEO substrates will then be incubated in an HSA solution to form surface-immobilized macromolecular complexes. High-resolution force spectroscopy will be employed to tether the individual macromolecular complexes to a probe tip via nonspecific, physisorption interactions and the extensional nanomechanical properties (e.g. force, F, versus separation distance, D) will be measured in aqueous solution. A variety of parameters will be studied in order to control the molecular elasticity and toughness, such as the host polymer molecular weight, the length of host chain segment between two neighboring guests, pH, and ionic strength. In the long-term, this research project will be expanded to include other general classes of "guests" including dendrimers, SAM-functionalized nanoparticles, and complementary oligomer-clothed nanoparticles.%%%The educational activities described in this CAREER proposal are strongly integrated with the research objectives and will expose materials science students to the molecular origins of material properties and behavior. A secondary goal is to show students from a variety of disciplines some of the latest, most exciting scientific discoveries in the field of nanotechnology and to encourage them to take up undergraduate research projects, apply to graduate school, and / or pursue a career in research and academia. This will be achieved through the continuing development of a new semester-long undergraduate course entitled "Nanomechanics of Materials and Biomaterials," the creation of a special 4-week undergraduate course during our "independent activities period" entitled " Nanotechnology Science and Engineering," the creation of a week-long, graduate-level laboratory summer course entitled " High-Resolution Force Spectroscopy," and outreach to high school teachers.