Overview   |   Catalytic Synthesis   |   Biomimetic Design   |   Functional Biomaterial
Biomimetic Materials
1. Bio-inspired Self-healing Materials
The ability to spontaneously heal injury is a key biomaterial feature that increases the survivability and lifetime of most plants and animals. In sharp contrast, synthetic materials usually fail after damage or fracture. To improve the safety, lifetime, and energy efficiency of manmade materials, there has been a recent push from researchers around the world to imbue self-healing properties into synthetic materials. A major challenge in self-healing materials design is the inherent tradeoff between robust mechanical properties and self-healing efficiency. Our lab has successfully addressed this challenge by developing a multiphasic design, in which the hard nano-phase provides stiffness and strength while the continuous dynamic phase enables spontaneous self-healing. A number of supramolecular healing motifs, including dynamic hydrogen-bonds and metal-ligand interactions, are employed in our designs.
In addition to supramolecular interactions, we have also developed self-healing materials using dynamic covalent interactions. For example, we impregnated cross-linked commercial polybutadiene rubber with very low quantities of Grubbs second-generation olefin metathesis catalyst for self-healing through dynamic remodeling of the network via olefin cross-metathesis. This simple design showed fast and quantitative healing at ambient temperature and remains, to our knowledge, the only example of near quantitative healing at sub-ambient temperatures.
Representative publications:
1.
Self-Healing Multiphase Polymers via Dynamic Metal-Ligand Interactions. Mozhdehi, D. ; Ayala, S.; Cromwell, O. R.; Guan, Z. J. Am. Chem. Soc. 2014, 136, 16128-16131.
2.
Self-Healing Supramolecular Block Copolymers. Henstschel, J.; Kushner, A. M.; Ziller, J.; Guan, Z. Angew. Chem. Int. Ed. 2012, 51, 10561-10565.
3.
Olefin Metathesis for Effective Polymer Healing via Dynamic Exchange of Strong Carbon-Carbon Double Bonds. Lu, Y.-X.; Guan, Z. J. Am. Chem. Soc. 2012, 134, 14226-14231.
4.
Multiphase Design of Autonomic Self-Healing Thermoplastic Elastomers. Chen, Y.; Kushner, A. M.; Williams, G. A.; Guan, Z. Nature Chem. 2012, 4, 467-472.
2. Biomimetic Modular Polymer Design
One major contrast between natural and synthetic macromolecules is that the latter usually lack well-defined high order structures. Following nature's strategy, we are introducing weak molecular forces into synthetic macromolecules to guide the formation of high order structures. Following a common structural feature observed in natural polymers, the repetitive modular design, we have designed modular multidomain polymers that can combine strength, toughness, and elasticity. Drawing various inspirations from nature, we are programming covalent and subtle non-covalent molecular forces to create a plethora of biomimetic materials showing dynamic, responsive, shape-memory, and self-healing properties.
To elucidate the molecular origin for material properties and build fundamental structure-property correlations, we are also investigating material properties at various length scales ranging from single molecule to bulk level. For example, we performed single molecule force spectroscopy (SMFS) of individual polymer chains using Atomic Force Microscopy (AFM), allowing quantitative derivation of the energy landscape of single module behavior in our modular polymers. This provided for the first time the direct correlation between single molecule nano-mechanical properties to bulk mechanical performance.
Representative publications:
1.
Direct correlation of single-molecule properties with bulk mechanical performance for the biomimetic design of polymers. Chung, J.; Kushner, A. M.; Weisman, A. C.; Guan, Z. Nature Mater.. 2014, 13, 1055-1062.
2.
Modular Design in Natural and Biomimetic Soft Materials. Kushner, A. M.; Guan, Z. Angew. Chem. Int. Ed. 2011, 50, 9026-9057.
3.
Computational and Single-Molecule Force Studies of a Macro Domain Protein Reveal a Key Molecular Determinant for Mechanical Stability. Guzman, D.; Randall, A. Z.; Baldi, P.; Guan, Z. Proc. Natl. Acad. Sci. USA. 2010, 107, 1989-1994.
4.
A Biomimetic Modular Polymer with Tough and Adaptive Properties. Kushner, A. M.; Vossler, J.; Williams, G. A., and Guan, Z. J. Am. Chem. Soc. 2009, 131, 8766-8768.
5.
Cycloaddition-Promoted Self-assembly of a Polymer into Well-Defined beta-Sheet and Hierarchical Nanofibrils. Yu, T. B.; Bai, Z.; Guan, Z. Angew. Chem. Int. Ed. 2009, 48, 1097-1101.