A 2-chain can interlock with a k-chain
  One of the open problems posed in [3] is: what is the minimal number k such that an open, flexible k-chain can interlock with a flexible 2-chain? In this paper, we establish the assumption behind this problem, that there is indeed some k that achieves interlocking. We prove that a flexible 2-chain can interlock with a flexible, open 16-chain. 
Julie Glass, Stefan Langerman, Joseph O'Rourke, Jack Snoeyink,   Jianyuan K. Zhong