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SUMMARY:How to beat biology: fine-tuning mechanical and structural propert
 ies on the macroscale through programmable nanomaterials - David Smith\, F
 raunhofer Institute for Cell Therapy and Immunology\, Leipzig.
DTSTART:20150605T131500Z
DTEND:20150605T141500Z
UID:TALK59166@talks.cam.ac.uk
CONTACT:Lucy Colwell
DESCRIPTION:Biologically evolved materials are often used as inspiration i
 n the design and development of new materials as well as examinations into
  the underlying physical principles governing their behavior. For instance
 \, the biopolymer constituents of the highly dynamic cellular cytoskeleton
 \, including actin filaments and the associated set of crosslinkers and mo
 lecular motors\, have inspired a deep understanding of soft polymer-based 
 materials on both the experimental and theoretical levels. However\, the m
 olecular toolbox provided by biological systems has been evolutionarily op
 timized to carry out the necessary functions of cells.  The resulting inab
 ility to systematically modify basic properties such as biopolymer stiffne
 ss or crosslink affinity in experimentally available model systems hinders
  a meticulous examination of parameter space. Using the actin cytoskeleton
  as inspiration\, we circumvent these limitations using model systems asse
 mbled from programmable materials such as DNA. Filaments with comparable\,
  but controllable dimensions and mechanical properties as actin can be con
 structed from small sets of specially designed DNA strands. In entangled n
 etworks at low density\, these allow us to experimentally determine the de
 pendence of macroscopic mechanical properties on previously inaccessible p
 arameters such as filament stiffness.  While bulk characterization of stre
 ss-strain response and microscopic single-filament analysis of snake-like 
 reptation are consistent with established models for entangled networks of
  semiflexible polymers\, deviating mechanical behavior with respect to the
  systematic variation of filament stiffness points towards a possible brea
 kdown of fundamental assumptions.  At higher concentrations in the presenc
 e of local attractive forces\, we see a transition to highly-ordered bundl
 ed and "aster" phases with microscale patterning similar to those previous
 ly characterized in systems of actin or microtubules.  In addition to prov
 iding a methodology for the more comprehensive characterization of soft po
 lymer-based materials on both the micro- and macroscale\, we expect this t
 o potentially be a powerful tool for the design of mechanically tunable an
 d switchable biomaterials.
LOCATION:Todd Hamied Room\, Dept. of Chemistry
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