The default material used for Mechanical is structural. We need to change it to the new material we defined earlier (Tissue). In the outline window, expand Geometry and highlight Solid 1. The bone model will now be highlighted in green, meaning it is being selected. Right below the outline window you will see "Details of Solid 1". Expand Material, and change the assignment to Tissue. The material properties we defined for Tissue will now be assigned to the bone model.