title: Toughened hydrogels inspired by aquatic caddisworm silk.
abstract: Aquatic caddisworm silk is a tough adhesive fiber. Part of the toughening mechanism resides in serial, Ca(2+)-phosphate crosslinked nano-domains that comprise H-fibroin, the major structural protein. To mimic the toughening mechanism, a synthetic phosphate-graft-methacrylate prepolymer, as a simple H-fibroin analog, was copolymerized within a covalent elastic network of polyacrylamide. Above a critical phosphate sidechain density, hydrogels equilibrated with Ca(2+) or Zn(2+) ions displayed greatly increased initial stiffness, strain-rate dependent yield behavior, and required 100 times more work to fracture than hydrogels equilibrated with Mg(2+) or Na(+) ions. Conceptually, the enhanced toughness is attributed to energy-dissipating, viscous unfolding of clustered phosphate-metal ion crosslinks at a critical stress. The toughness of the bioinspired hydrogels exceeds the toughness of cartilage and meniscus suggesting potential application as prosthetic biomaterials. The tough hydrogels also provide a simplified model to test hypotheses about caddisworm silk architecture, phosphate metal ion interactions, and mechanochemical toughening mechanisms.
authors.affiliation: Department of Bioengineering, University of Utah, Salt Lake City, UT 84112, USA. russell.stewart@utah.edu.
authors.forename: Dwight D
authors.initials: DD
authors.lastname: Lane
authors.forename: Sarbjit
authors.initials: S
authors.lastname: Kaur
authors.forename: G Mahika
authors.initials: GM
authors.lastname: Weerasakare
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Stewart
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry; D005349:Fibroins / Q000737:chemistry*; D020100:Hydrogels / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry; D012964:Sodium / Q000737:chemistry; D014783:Viscosity; D000099166:Polyacrylamides
chemical_list: D000180:Acrylic Resins; D005349:Fibroins; D020100:Hydrogels; D008274:Magnesium; D012964:Sodium; D000099166:Polyacrylamides