Design of pastes for direct ink writing of zirconia parts with medical applications

Abstract

Direct ink writing (DIW) is an extrusion additive manufacturing (AM) technique in which inks are extruded through a nozzle and then deposited layer-by-layer. This technology allows 3D printing many different materials such as ceramics, metals, food, etc. In this work, the performance of zirconia pastes is addressed. The pastes are composed of zirconia powder and a polymeric binder. The content of the different components of the paste is varied and they are characterized, both regarding the printability of the paste and the and the quality of the 3D printed parts, specifically their dimensional accuracy and their surface finish. In the tests, the content of the different components of the pastes was varied with design of experiments, considering that the ceramic percentage is limited by the pressing force of the plunger that is used to extrude the pastes. On the other hand, the binder concentration is also limited, because it requires to be in a gel form in order to be properly extruded. In this work, 3D printing of cylindrical parts was considered. However, in the future, the pastes will be used to extrude more complex parts with medical applications. For example, zirconia is a usual material in hip prostheses, especially regarding the acetabulum. This part has a hemispherical shape. It requires a smooth internal surface, in contact with the femoral head, and a porous external area which allows fixing the prostheses by means of osseointegration. AM extrusion processes constitute a possible way to overcome the difficulties to obtain such geometries with conventional methods such as machining, in which zirconia parts can break due to their brittleness. Thus, the results of this work will help to manufacture complex shapes with porous areas in zirconia, when the DIW technology is employed.