GwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwD T h e G R E E N Y w o r l d D o m i n a t i o n T a s k F o r c e , I n c o r p o r a t e d Presents: __ __ 888888888 444 _____ ____ _| |__| |_ 888 888 44 44 // | \ |_ __ _| 888 888 44 44 || ____ | || | | | | | 888888888 44444444444 || || \ / | || | _| |__| |_ 888 888 44 \\___// \/\/ |____/ |_ __ _| 888 888 44 |__| |__| 888 888 44 888888888 4444 "Medical Applications of Selective Laser Sintering (SLS)" by Otis ----- GwD: The American Dream with a Twist -- of Lime ***** Issue #84 ----- ----- release date: 01-03-01 ***** ISSN 1523-1585 ----- Fields of knowledge that were once completely diverse and unrelated have begun to come together. Among the most important of these for humanity as a whole are the multitude of (relatively) new links between medicine and other disciplines. Medicine is influencing the legal process: the advent of DNA evidence is a major step in the field of law enforcement. Computers are being used more frequently in the diagnosis of illness. Even materials engineering has contributed to some recent advances in medicine: the development of rapid prototyping technologies such as Selective Laser Sintering offer new hope to many due to their vast array of medical uses. The Selective Laser Sintering (SLS) process was developed at the University of Texas at Austin and is a patented process of DTM Corporation. It is like other sintering processes in that "materials are manufactured into useful shapes...by a high temperature treatment [a CO2 laser, in this case] that causes particles to join together and gradually reduces the volume of pore space between them" (Askeland 126). However, while many rapid prototyping processes "create parts within a vat of liquid resin," SLS "sinters - or fuses...[powdered materials] with a precisely guided laser to form solid, three-dimensional parts" (DTM). The process itself (see Figure 1) is similar to other rapid prototyping processes: "a laser sinters selected areas causing the particles to melt and then solidify" (Dolenc). The laser thus fuses the particles into whatever shape is desired, even allowing for excellent dimensional tolerances (depending on the size and complexity of the object formed, of course). The shape is specified in a "solid model 3-D CAD file, using the [international] industry standard STL format" (DTM). This allows intricate 3-D geometries to be formed from a large number of materials. In fact, "extremely complex geometries that could not otherwise be machined, cast or molded" can be produced through the use of SLS ("Growing Parts"). The powdered material requirement of SLS also allows for the creation of a material or combination of materials "appropriate for virtually any manufacturing application" (DTM). Selective Laser Sintering is a quite useful technique. For the most part, SLS has been used in industrial rapid prototyping. It allows engineers to develop models of parts before mass production begins. These models can be analyzed and flaws can be determined before the actual manufacturing process has begun. Interestingly enough, the production of models was the impetus behind SLS's use in non-traditional manufacturing processes. Within the last few years, SLS (along with other rapid prototyping methods) has found a place in the medical field. According to Andy Christensen, general manager at Medical Modeling Corp., "'models are used for preoperative planning and surgical simulation, for communication with the patient and other surgeons, and for customization of off-the-shelf implants'" (Raplee 52). These models can be of either soft or hard tissue surgeries, showing the great flexibility of the SLS technology. Surgical planning is one of the main applications of SLS in medicine. Models built for this purpose allow surgeons to "rehearse incisions, measure grafts, and fit surgical resections before they operate," (Raplee 52) thus saving time during the actual procedure. The time saved reduces the patients' exposure to anesthesia and possibly decreases blood loss. Doctors often use these models to practice intricate surgeries. They are used for determination purposes, such as to find the least traumatic angle and position of entry for removal of tumors in the skull, near the eye (Ashley 53). Through use of these models, "doctors can literally practice removing a tumor on an accurate representation of the patient" (Crockett). The benefits to the patient of the doctor(s) practicing the surgery before operating are obvious but immeasurable. Also, the fact that SLS allows for composites of materials to be sintered permits the construction of "semitransparent and two-color models. Semitrans- parent models can illustrate...body and bone cavities. Two-color models can help a surgeon visualize radiopaque density differences...where a perceptible difference may be critical to the operation" (Raplee 52). There are indeed many effects of SLS and other rapid prototyping technologies on pre-surgical planning. The SLS technology has also been used to model and manufacture prosthetic limbs for amputees. The University of Texas "has developed a high-speed laser scanner for amputees called the UT Prosthetic Imager. This three-dimensional laser scanner and digitizer images a patient's residual limb in 10 seconds, acquiring a three-dimensional data file that describes the limb" (Ashley 51). The file is then adjusted by a prosthetist to improve fit, comfort, and stability. An SLS system then interprets the CAD files and manufactures a replacement prosthetic limb. Bill Rogers, a professor of Rehabilitation Medicine at the University of Texas Health Science Center in San Antonio, says that "'Rapid prototyping allows us to design in an integral fitting, which means you don't have to distort the end of the socket. It also means you can include the patient's specific alignment characteristics in the socket design'" (Ashley 51). The rapid prototyping described by Dr. Rogers only refers to exterior prosthetics. There has also been work relating to surgical implants made by rapid prototyping, though not specifically by SLS. Stereolithography, another rapid prototyping technique that is similar to SLS in many ways (it is a sintering process that interprets CAD files directly) has been used extensively in the development of surgical implants (Ashley, Raplee). Another obvious use of SLS in medicine is the modeling and manufacture of artificial bones. The hard bone material is somewhat similar to other materials that are used in the SLS process. Researchers at the University of Leeds were some of the first to realize the medical applications of SLS. By 1995, the researchers had formed complete human adult and child skulls using the SLS technology. The skulls were scanned using computer tomography (CT). These scans were translated into the STL format, and the skulls were manufactured (Berry 91-96). These initial models were quite accurate. Use of SLS and other rapid prototyping techniques to model bones has continued in recent years. The Milwaukee School of Engineering and the Medical College of Wisconsin have been working on models of vertebrae for use in extremely human-like crash test dummies: "human vertebrae...consist of hard, dense cortical bone surrounding a soft, spongy trabecular bone. Creating a model of such a complex structure is now possible by linking CT imaging with RP [rapid prototyping] technology" (Crockett). Perhaps these artificial vertebrae (or further generations of artificial vertebrae developed in this manner) can one day be used to replace vertebrae in people. It is likely that work will continue in the area of rapid prototyping bones. While there are many benefits medical benefits of SLS and other rapid prototyping techniques, there are also many drawbacks. The problems the Leeds researchers encountered with translating CT data into STL format seem to have been lessened, but not completely overcome in the past few years. Raplee notes (quoting Christensen) that "Each year, thousands of surgeries are performed that could benefit from the use of models, yet 'models of the craniofacial skeleton, for instance, are sold for an average cost of $1,500 to $3,000,'...'Despite the benefits of its use, it can be a hard sell'" (53). These models are quite costly, and one can hardly blame a patient for not wanting to pay. Perhaps with the improvement of the technology (to incorporate CT data more easily) and the hardware required to build the models decreases in price (in general, technology tends to decrease in price over time), SLS-created models will be more commonplace in the hospitals of America. Possibly in the future, SLS and other rapid prototyping techniques can be used to manufacture models of soft tissues, as well as continuing to produce and improve prosthetics and artificial bones. The Leeds professors predicted the development of soft tissue models using SLS (Berry 95): "Possible future uses include building models of soft tissue organs such as the heart and vessels." However, the literature regarding such soft tissue models is rather scant. This is likely because research into these areas has not yet been published. SLS and other rapid prototyping techniques have a wide variety of medical applications. As time goes on, more applications will be available for rapid prototyped models in the hospitals and doctors' offices of America and the world. Millions of patients could benefit from this technology. Christensen states that, "'The future almost guarantees that growth will be seen in this area with better, faster, and cheaper machines and materials'...'One day we may see every patient who could benefit from this service get it'" (Raplee 53). Christensen's prediction for the future does not seem far-fetched at all. Mankind has already brought diverse fields such as materials engineering and medicine together; allowing everyone to benefit from this coupling cannot be far behind. Works Cited Ashley, Steven. "Rapid prototyping for artificial body parts." _Mechanical Engineering: The Journal of the American Society of Mechanical Engineers_ vol. 115, no. 5 (May 1993): 50-53. Askeland, Donald R. The Science and Engineering of Materials. Third edition. Boston, PWS Publishing Company, 1994. Berry, E., et al. "Preliminary experience with medical applications of rapid prototyping by selective laser sintering." _Medical Engineering & Physics_ vol.19, no. 1 (January 1997): 90-96. Crockett, Robert. "Building the Future, One Layer at a Time." The World & I. July 1999. http://www.worldandi.com/archive/nsjul99.htm. (15 April 2000). Dolenc, Andre. "Selective laser sintering." 24 July 1994. http://www.cs.hut.fi/~ado/rp/subsection3_6_3.html. (2 May 2000) DTM Corporation. "A Process With Material Advantages." Austin, DTM Corporation, 1996. "Growing Parts." Los Alamos National Laboratory Daily Newsbulletin. 15 January 1998. http://www.lanl.gov/orgs/pa/News/011598.html. (1 May 2000). Raplee, Jack. "Saving face: Rapid prototyping in the operating room ranges from the planning of bone cuts to the custom fit of implants." _Mechanical Engineering: The Journal of the American Society of Mechanical Engineers_ vol. 121, no. 6 (June 1999): 52-53. ----------------------------------------------------------- GwDweb: http://www.GREENY.org/ GwD Publications: http://gwd.mit.edu/ ftp://ftp.GREENY.org/gwd/ GwD BBSes: C.H.A.O.S. - http://chaos.GREENY.org/ Snake's Den - http://www.snakeden.org/ E-Mail: gwd@GREENY.org * GwD, Inc. - P.O. 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