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Stereolithography

Stereolithography is the name of a process used to make three-dimensional models from computer databases. Designers in manufacturing companies use the technique extensively to assist them in visualizing a plan for a new car part, an airplane component, or a small medical device. The general field of such work is called rapid prototyping. By using a series of photochemical reactions and a unique assembling system, designers can quickly replicate a computer representation as a plastic model or prototype. The prototype provides a simple visualization of what a part will actually look like in three dimensions.

Stereolithography uses a photochemical event, or more specifically, it uses small lasers and a series of photochemical events, to direct the formation of points of plastic on the surface of an easily solidified liquid. The computer (28) directs a laser (26) across the surface of a polymerizable plastic (to polymerize means to make large molecules from small ones – all common plastics are large, non-homogeneous molecules or polymers) converting the polymerizable material point by point into a solid. This is done, in this particular experimental setup, on a platform that is held a few millimeters under the surface of the photoreactive liquid (22). After the laser has converted to solid plastic all the points in one layer that are needed for the model, producing a two dimensional lithograph (30a) of fixed z dimension, z, the platform (29) is dropped a small increment and a second layer is built on top of the first. This process continues until each layer of the computer graphic, or plan, is converted to solid plastic. When the process is complete the model can be lifted from the plastic vat as an exact replica of the computer graphic.

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One of the most important uses of stereolithography is in making replicas of medical data, such as CT scans and MRI scans, for surgical planning. From the three dimensional model of the CT scan, one can obtain a better image of the actual medical problem to be encountered during the surgery.

A poignant example of the use of stereolithography in medical imaging was that in which models of two conjoint Egyptian twins were prepared prior to surgical procedures for their separation in October 2003. In the model, the areas of the skull at which the two twins were joined were shown in red.  Surgeons were able to practice the surgery on the models prior to performing it in the operating suite. Several years ago, alumni of the Center for Photochemical Sciences outlined the chemistry that made possible the medical modeling in multiple colors. In the late 1980s the Center produced the first ever medical model from a CT scan using stereolithography. Scientists were critical to the development of this important technique.

mummies found in the collections of the Toledo Museum of ArtAnother example of Center alumni work in this field involved making replicas of mummies found in the collections of the Toledo Museum of Art. This has often been reported in the press and in professional publications (see for example, A Mummy “Comes to Life” in Toledo, by Sandra E. Knudsen, KMT – A Modern Journal of Ancient Egypt, Vol. 12, Number 1, Spring 2001). Museum scientists wanted to date and identify critical body characteristics of two Egyptian mummies collected by friends of the Museum in the 19th century. To do this, the mummies were taken to a local hospital where their bodies were scanned in a large CT machine. From the CT scan, Center alumni working in a small business called Spectra Group Ltd., Inc. assembled models of the mummies, based on which forensic scientists were able to make apparent replicas of what the mummies might have looked like when alive more than 2,500 years ago.

Stereolithography, or the making of three-dimensional replicas from two-dimensional data, is an exciting new application of photochemical polymerization reactions. One can find out more about it by visiting the web site of the company founded by the inventors of stereolithography, 3D Systems Corporation.