A vaso-occlusive device includes an inner coil made from inner coil wire having a first diameter and formed from a first material, and an outer coil disposed at least partially around the inner coil and made from outer coil wire having a second diameter and formed from a second material. The inner coil has a first pitch and the outer coil has a second pitch. The first diameter, material, and pitch are different from the second diameter, material, and pitch, respectively. The outer coil defines a lumen and the inner coil is disposed at least partially in the lumen. The vaso-occlusive device also includes an intermediate layer disposed between the inner coil and the outer coil, where the intermediate layer includes a biocompatible metal or a biocompatible, swellable polymer.
