Vaso-occlusive devices for occluding a body cavity include an internal element located within a lumen of the device. The internal element may include an active element configured to stiffen the coil in-situ made from a material that can expand to a desired size, thereby inducing a radial stress to the coil to stiffen the occlusive device. Alternatively, the active element is secured to two points on the occlusive device, and is made from a material that contracts, thereby inducing a compression to stiffen the device. The internal element may additionally include an agent carrier that comprises a bioactive material capable of eliciting a biological reaction after the device is placed in-situ. For example, the bioactive material can be a part of a composition of the agent carrier, absorbed by the agent carrier, or coated as a layer on the agent carrier.