Pseudo-knots in helical structures

It is generally accepted that physical entanglements are essential to explain some mechanical properties of polymers, like viscoelasticity. The current view is that entanglements behave as dynamic links that are destroyed and created in time. It is less clear whether entanglements could alternatively produce local and stable links, with similar effects to chemical bonds. Here we show that local and stable entanglements, that we call physical pseudo-knots, exist and are formed with high probability in helical structures. The energies required to create and destroy physical pseudo-knots can differ by at least one order of magnitude. Together with their localized nature this makes them controllable, opening the possibility for a wide range of applications in material science, nano- and biotechnology. Physical pseudo-knots can also have implications in living systems, that may use them, or try to avoid them and hence be related to disease.