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SUMMARY:Fracture mechanics of biological protein materials: Robustness\, s
 trength and adaptability - Markus J. Buehler\, Laboratory for Atomistic an
 d Molecular Mechanics\, Department of Civil and Environmental Engineering\
 , Massachusetts Institute of Technology\, 77 Massachusetts Avenue\, Room 1
 -272\, Cambridge\, Massachusetts 02139\, USA
DTSTART:20080313T160000Z
DTEND:20080313T170000Z
UID:TALK11071@talks.cam.ac.uk
CONTACT:Michelle L. Oyen
DESCRIPTION:Proteins constitute critical building blocks of life\, forming
  biological materials such as hair\, bone\, skin\, spider silk or cells\, 
 which play an important role in providing key mechanical functions in biol
 ogical systems.  The fundamental deformation and fracture mechanisms of bi
 ological protein materials remain largely unknown\, partly due to a lack o
 f understanding of how individual protein building blocks respond to mecha
 nical load and how they participate in the function of the overall biologi
 cal system.  However\, such understanding is vital to advance models of di
 seases\, the understanding of biological processes such as mechanotransduc
 tion\, or the development of biomimetic materials.  Recent theoretical and
  computational progress provides us with the first insight into such mecha
 nisms and clarifies how biology ‘works’ at the ultimate\, molecular sc
 ale\, and how this relates with macroscopic phenomena such as cell mechani
 cs or tissue behavior\, across multiple hierarchical scales.  Here we revi
 ew how molecular dynamics (MD) simulations implemented on ultra-large comp
 uting facilities\, combined with statistical theories\, is used to develop
  predictive models of the deformation and fracture behavior of protein mat
 erials.  This approach explicitly considers the hierarchical architecture 
 of proteins\, including the details of their chemical bonding\, capable of
  accurately predicting their unfolding behavior and thereby providing a ri
 gorous structure-property relationship.  We exemplify the approach in the 
 analysis of the deformation mechanisms of beta-sheets and alpha-helices\, 
 two prominent protein motifs that form the basis of many protein materials
 \, including spider silk and intermediate filaments.  Spider silk is a pro
 tein material that can reach the strength of steel cables\, despite the pr
 edominant weak hydrogen bonding.  Intermediate filaments are an important 
 class of structural proteins responsible for the mechanical integrity of e
 ukaryotic cells\, which\, if flawed\, can cause serious diseases such as t
 he rapid aging disease progeria or muscle dystrophy.  For both examples\, 
 our studies elucidate intriguing material concepts that enable them to bal
 ance strength\, energy dissipation and robustness by selecting nanopattern
 ed\, hierarchical features. We present an analysis that reveals that the u
 tilization of such hierarchical features in protein materials is vital to 
 synthesize materials that combine seemingly incompatible material properti
 es such as strength and robustness\, self-adaptation and adaptability\, by
  overcoming the physical limitations of conventional material design.   We
  discuss the general implications of our work for the science of multi-sca
 le interactions and how this knowledge can be utilized to develop de novo 
 biomimetic materials based on a bottom-up structural design.  
LOCATION:Engineering Department - Room LR 6
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