Surgical prototypes a cut above the rest

Prototypes and medical models can be made by ink jetting two different materials at the same time. Tom Shelley reports



New ink-jet printing techniques mean internal organs can now be seen and studied, prior to attempting surgery.
By ink jet printing two entirely different polymers, combinations of hard and soft material, or grey-scale colours, can be laid down in such a way as to produce remarkable rapid prototypes and realistic medical models.
The technique – dubbed PolyJet Matrix technology – has been developed by Objet Geometries, headquartered in Israel, with several machines already sold worldwide, according to region manager Haim Levy.
Eureka first came across one of the machines at SolidWorks World, printing a part that was part hard plastic and part elastomer. But it was not until the recent Hanover Fair that we were able to see some of the results up close.
In the process, each material is funnelled to a dedicated liquid system connected to a matrix block, which contains eight printing heads. Two heads are designated for each material, including the support material. Model materials can be blended mixtures called ‘Digital material’, which can be chosen to provide specific values of tensile strength, elongation to break, heat distortion temperature (HDT) and Shore A flexibility. There are six base materials: transparent, opaque white, opaque blue, opaque black, grey rubber-like and black rubber-like. However, 21 types of composite materials can be generated on the fly.
Each layer is cured by UV light immediately after it has been jetted, producing fully cured models that can be handled and used. Hand or water jetting easily removes the gel-like support material.
The ability to print two materials simultaneously not only means it is possible to rapid prototype products such as hair brushes, rubber ended mallets and consumer products with elastomer enhanced handles, but also - by interspersing, for example, black and white materials on a micro scale - it is possible to create greyscales. These are mainly of interest to produce visual effects, but could also be used to create components whose materials have graded properties, providing transitions between hard and soft elements. Alternatively, such compontents could provide a wear-resistant or cutting surface on otherwise soft products.
Furthermore, by combining transparent and opaque materials, transparent medical models can be printed that show nerves, tumours and other details. These can be used for teaching purposes or as an aid to planning difficult surgical operations before they are undertaken. This is in addition to rapid prototyping products, such as MP3 players and mobile phones with built-in screens.
The Connex500 machine - the first produced by the company to take advantage of the new technology - has a net build size of 490mm x 390mm x 200mm, and horizontal build layers can be as thin as 16 microns. There are three printing modes: DM printing mode produces multiple model materials and digital materials; high quality (HQ) printing mode is for single material printing as 12mm/h/strip, with a 16 micron layer thickness; and high-speed (HS) printing mode is for single material printing at 20mm/h/strip, with a 30 micron layer thickness. Walls can be as thin as 0.6mm.


Pointers

* PolyJet Matrix technology allows two materials to be laid down at once, each of which can be blended on the fly to produce particular mechanical properties

* Materials can be of different colours and mechanical properties, or one can be transparent and the other opaque

Author
Tom Shelley

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