An intra-articular device comprises a membrane shaped like a cap having a peripheral geometry similar to that of a head of a bone for a joint to be restored and an open end sized to be applied over the bone proximate the head, so that the open end can be stretched over the head of the bone and held in position on the bone interposed between the head and its corresponding articular component of the joint. The membrane is made of a polyether-urethane-urea material selected to have a property of absorbing the joint's own synovial fluid so as to swell and have a viscoelastic property similar to the body's own articular hyaline cartilage. In a preferred embodiment, the membrane cap is adapted for use on a femoral bone for restoring a hip joint. A related method of installing an intra-articular device as artificial cartilage comprises forming a membrane cap to be applied over the head of the bone of the joint, surgically exposing the head of the bone, installing the membrane cap over the head of the bone, then repositioning the capped head of the bone back in its place in the joint with the membrane interposed as artificial cartilage.