{HEAD ~ The purpose} of the activation mechanism is to stiffen {TAIL ~ the leaflets} to the same level as in the passive version, i.e., to provide the stiffness necessary to resist flow until the desired threshold pressure level is reached 
is to stiffen
{ HEAD ~ The purpose } of the activation mechanism is to stiffen { TAIL ~ the leaflets } to the same level as in the passive version , i.e. , to provide the stiffness necessary to resist flow until the desired threshold pressure level is reached
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH