One challenge facing researchers was learning how to control crystallization of the polymer. As similar shape-shifting materials are stretched or cooled, atomic strands of polymer molecules re-align, driving the object to stay in the "temporary" alignment. This process makes it more and more difficult to bring the object back to its "relaxed," original form. Individual "linkers" were used to connect the molecules, reducing the effects of crystallization in the new polymer. By carefully controlling the placement of the linking chains, researchers were able to precisely direct the turning point of the material. When the new polymer is removed from the...