A system for forming a looped suture is provided. The accessory component includes a component body having first and second ends. The ground contacting element contains a plurality of projections, with the projections divided into at least two sets. The second component is an acid that is capable of initiating polymerization of the resin. Uses of such crystals, crystal structures and models are also disclosed, including structure based drug design and therapeutic compositions. The sensor comprises an array of pixels, each of which comprises a negative-feedback avalanche diode and a read-out circuit that includes a counter.