| 摘要 |
An article, for example a dental point, formed of a hydrophilic plastics material is capable of undergoing controlled radial expansion (d<SB>1</SB> to d<SB>2</SB>) upon hydration by aqueous media including body fluids without appreciable axial expansion. The hydrophilic plastics material is pre-stressed by application of pressure to its unhydrated form at a temperature in the range 100 to 160{C. It is then cooled to 40{C or less before release of the applied pressure. After cooling, the material may be machined to shape. Alternatively, pre-stressing can be carried out after shaping. Preferably, the pressure is applied by extruding the material through a die which may be maintained at the same temperature as that of the polymeric material. The article may also be used in engineering to develop gaskets for underwater use or as a tube or sleeve for sealing ruptured pipes; in electrical applications as a sleeve for sliding over electrical connectors; in medicine as a tube for sliding over limbs to immobilise broken bones and in vascular therapy as a tube or sleeve for sliding over arteries or for insertion into blood vessels or other body passages and cavities for opening up constrictions. |
