Copy Link
Add to Bookmark
Report
Greeny World Domination 084
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.
-----------------------------<GwD Command Centers>------------------------------
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. Box 16038 - Lubbock, Texas 79490 *
--------------------------------------------------------------------------------
"Payin' mental rent to corporate presidents." - Public Enemy, "He Got Game"
--------------------------------------------------------------------------------
-+- F Y M -+-
GR33NY LIK3S mash3d p0tat03s
MORE THAN FIVE YEARS of ABSOLUTE CRAP! /---------------\
copyright (c) MM Otis/GwD Publications :PRIME THE PUMPS:
copyright (c) MM GwD, Inc. : GwD :
All rights reserved \---------------/
GwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwDGwD84
