Topologically, loops and knots cannot be converted one to the other through simple twisting or stretching. These differences make knots and loops interesting objects to study, but it can be difficult to manipulate polymers into predefined shapes. Tkalec et al. (p. 62; see the Perspective by Kamien) immersed surface-treated colloidal particles in a chiral nematic liquid crystal. When the liquid crystal molecules were aligned normal to the surface of the particles, defect lines formed around each particle. By choosing different arrays of colloidal particles that could be manipulated using optical tweezers, structures where neighboring defect loops cross each other were generated allowing the production of knots of arbitrary complexity.
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