Simulated tissue structures and methods of making them are disclosed. An elastic first material is placed in tension. An elastic second material is adhered to the first material while the first material is in tension. The adhered second material and the first material in tension forms a first shape of the simulated tissue structure. Tension on the first material is released. In releasing the tension of the first material, a force is exerted on the adhered second material bring the combination of the first material and the second material into a second shape. The first shape is maintained by a mold or mandrel and the second shape is the desired shape of the simulated tissue structure.