**7. 3D colour printing**

intensity (from white to black), computer software can control the depth of imperfections over a skin surface. An original skin depth map is shown in **Figure 7 (a)** and can be used to add texture over a flat surface. Surface topography changes according to the grey level intensity and the positioning of individual pores and wrinkles is shown in (b). The resultant mesh can

**Figure 7.** (a) Depth map of skin showing pores and fine wrinkles as dark areas. (b) Software‐induced texture mapping over a flat surface using the depth map from (a). (c) 3D printed surface with pores and wrinkles clearly visible on the

Given the flexibility of such software, texture can be mapped not only onto flat surfaces but also over complex 3D shapes. An example of this texture mapping over a nose model with

However, the detail provided in the final prosthesis is dependent not only on the resolution of 3D data obtained but also the resolution of the 3D printer and characteristics of the powder and binder type used within the process. The use of course powder in the printing process will reduce the detail of the texture derived from the height‐field mapping even though such detail can be mapped within the CAD process. In contrast, using finer powder will enable the

be 3D printed, producing a skin‐like texture over a flat surface (c).

**Figure 8.** Illustrations detailing texture mapping. (Approx. part Dim: 70 × 61 × 29 mm).

addition of very fine details over the printed prosthesis.

surface (Approx. part Dim: 38 × 38 × 3 mm).

100 New Trends in 3D Printing

varying pore depths is show in **Figure 8**.

Full colour 3D printing is considered advanced technology with different 3D colour printing technologies continually being developed and evolving. One common full colour 3D printing technology is 3DPTM printing, also known as powder–binder printing. Developed at Massa‐ chusetts Institute of Technology [33] and licensed to Z Corporation and 3D Systems, the process itself is based on inkjet printing, with the powder being deposited in consecutive layers, which are then selectively joined by ink‐jetting with coloured binder. Three (CMY) or four (CMYK) coloured binders together with a clear binder are mixed to print powder material in a full colour spectrum, layer by layer. After 3D printing, post‐processing, including the removal of excessive unused powder and infiltration, often needs to be conducted in order to produce the final model (**Figure 10**). The powders can be made of different kinds of materials. Gypsum is primarily used in combination with plastic powder. However, starch, ceramic, glass and other powdered materials can also be processed as well. For manufacturing facial prostheses, 3D printers including the Z Corp Z510 3D printer (3D Systems Inc., Rock Hill, SC, USA) can be used to print colour into biocompatible starch powder. Post‐printing processing is then required. Infiltrating with suitable elastomeric polymer can then be undertaken to produce a flexible, lightweight and lifelike soft tissue prosthesis. More recently there has been the development of other elastomeric 3D printing processes including direct deposition and filament printing. However, their main drawback is the limited spectrum of colour they can print in.
