Another important area in additive fabrication is material selection. Currently, commercial printers exist for a wide variety of materials, ranging from thermoplastics, optical-cured polymers, ceramics, metals, biomaterials, and even food. These printers use a selection of different techniques for solidifying the material, such as thermal, optical, and chemical curing methods.
Currently, most printers still function with a single primary material. In the future, however, multimaterial printers will become the standard rather than the exception that they are today. For commercial printers, the small subset of multimaterial printers are limited to mainly optically cured photopolymers. Stratasys is a leader in this field and its top printer models presently can print using a mixture of three resin types, in addition to support material used for generating overhanging features. These multimaterial machines use inkjet deposition heads and can print mixtures of the three selected resins to allow for gradient material properties. The material gradients can vary in properties such as stiffness, color, and translucency. A relevant example using the Stratasys Objet500 Connex3 printer is a recent chaise lounge designed by Dr. Neri Oxman and Dr. W. Craig Carter, as illustrated in Figure 18-11. It was based on the functional goal of an acoustically quiet orb. As seen in the lower portion of the figure, gradients of color and elasticity were designed to inform the aesthetic and acoustical properties of the chair. The printer uses a 16 pm voxel (volumetric pixel) size to accommodate spatial variations throughout the printed parts. The chaise lounge uses a milled wood back panel for support and is an example of combining both additive and subtractive fabrication modes.