A brace for a part of a body includes a first conductive fiber associated with a first polarity, and a second conductive fiber associated with a second polarity different from the first polarity. The second fiber is woven together with the first fiber and insulated from the first fiber. The brace also includes a selectively electrically activated cross-linking agent between the first and second fibers. The agent is constructed to cross-link in a first active mode when the first and second fibers are electrified and is constructed to not cross-link in a second inactive mode when the first and second fibers are not electrified. The brace surrounds a body part, such as a knee or neck. The agent can include an ER fluid and/or EAP. A brace system includes a selectively electrically activated brace for the part of the body.