  We show that polarons can sustain loop-like configurations in flexible
bio-polymers and that the size of the loops depend on both the flexural
rigidity of the polymer and the electron-phonon coupling constant. In
particular we show that for single stranded DNA (ssDNA) such loops can have as
little as 10 base pairs. For polyacetylene the shortest loop must have at least
12 nodes. We also show that these configurations are very stable under thermal
fluctuations and can facilitate the formation of hairpin-loops of ssDNA.
