  The quasi-equilibrium evolution of the helical fraction occurring in a
biopolymer network (gelatin gel) under an applied stress has been investigated
by observing modulation in its optical activity. Its variation with the imposed
chain extension is distinctly non-monotonic and corresponds to the transition
of initially coiled strands to induced left-handed helices. The experimental
results are in qualitative agreement with theoretical predictions of helices
induced on chain extension. This new effect of mechanically stimulated
helix-coil transition has been studied further as a function of the elastic
properties of the polymer network: crosslink density and network aging.
