3D printing is a way of manufacturing physical objects directly from 3D computer models. 3D printers work in additive fashion, building an object layer upon layer, typically from resin or photopolymer, which may be pigmented for production of coloured objects. Even intricate forms can be produced quickly by this technology, making it ideal for one-off or short-run production.
3D printing is widely employed in product design, for rapid prototyping of such things as hand-held devices, car parts, jewellery or footwear designs, architectural or engineering components. In future it looks likely to extend into the manufacture of complex multi-part objects.
Amongst the most useful applications of this rapidly developing technology are in medicine, in the production of individually shaped items such as dental crowns and bridges, synthetic bones and joints, or artificial limbs and other prostheses.
Conventionally, prosthetic ears, eyes and noses have had to be individually hand-modelled and painted, a time-consuming process whose results have often been variable and unsatisfactory. For that reason Sheffield-based company Fripp Design and Research, who have extensive experience in 3D printing for industrial design, were keen to try and adapt the technology for prosthetic production. They identified a number of specific challenges:
"Creating fleshlike prostheses, as opposed to porcelain teeth or crowns, posed a unique set of challenges. The material used would have to be strong, flexible and biocompatible (unlikely to trigger a toxic or allergic reaction when inserted into human skin). The colour would have to match the patient's specific skin tone exactly, and the whole prosthesis would need to blend as invisibly as possible into the surrounding face."
In collaboration with researchers at Sheffield University and supported by The Wellcome Trust, Fripp have developed new ways of speeding production and improving the quality of soft-tissue prostheses. Key to the project has been the development of printable materials that are biologically inert, that can be safely worn in contact with human tissue and comply with relevant safety standards. After testing several materials, the research team found a starch powder that fit the bill and which can be combined with water-based resin and inks to produce a suitable printing medium.
The production process begins with 3D scanning of the part of the patient's face/ head to be augmented, along with 2D photos of skin tone and colour. Special CAD software is used to combine these datasets with a model of the new body part and to match the model's contours, tone and texture to the patient's face.
The resulting 3D file is output to the printer to make the prosthesis which, being quite brittle at first, has to be cured with a medical-grade silicone fluid to give it strength and pliability. Curing has a beneficial side effect: as the silicone drains off it forms a fine feathered edge that bonds seamlessly to the face.
The printed prosthesis is lighter in weight than a conventional hand-made one, and much more easily replaced when it wears out or gets damaged, as the stored product file can simply be reprinted.
This method of manufacture reduces the cost to the healthcare provider and delivers higher quality and consistency to the patient. The Sheffield researchers believe that the technology could be easily and inexpensively installed in centres across the developing world, making high-quality soft-tissue protheses widely available there.
(See also project report on Fripp Design website.)