Smart Materials by Extrusion Solid Freeform Fabrication. Brief Annotations

摘要

Extrusion freeform fabrication allows materials to be built layer by layer to form a solid. By combining different materials it is possible to attain new combinations of properties and to design the response of a material for the local stresses on a part. Most biological structures are built layer by layer and show excellent adaption of structure to function. This method has been used to form hydrogels and then mineralize them to very volume fractions of inorganic material. The resulting composites are tough, stiff and strong. The approach has also been used to make electrically stimulated muscle-like actuators of two types of hydrogel, crosslinked polyacrylic acid and crosslinked polyacrylamide. One layer of gel contracts in the applied field, the other layer acts as a passive, soft reservoir which takes up the extruded water without limiting contraction of the active layer. This system has been adapted to make an electrically-driven reversible gel 'jack'. When a field is applied the sample changes thickness by 10% in about 60 seconds and then returns to the original state when the field is reversed. This is close to what would be needed for a synthetic electrical muscle in that it provides a large, reversible linear expansion at constant volume.