17-11-2012, 02:20 PM
Rapid Prototype Technique in Medical Field
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ABSTRACT:
Rapid Prototype is an innovative technology that has evolved within the design and manufacturing industries. In medical
industries the use of RP technology coupled with the other techniques has led to improvement in services offered to patients
by improvement in such areas as 3D visualization of a specific anatomy, surgical planning, implant design, prosthesis
production, and polymeric drug delivery devices. In this article we review the current technologies available in RPT and its
application in different fields of medicine and future trends in this area.
INTRODUCTION:
Rapid prototyping is the automatic construction of physical
objects using solid freeform fabrication. The first technique for
rapid prototyping became available in the late 1980s and was
used to produce models and prototype parts. Rapid prototyping
takes virtual designs from Computer Aided Design (CAD) or
animation modeling software, transforms them into thin,
virtual, horizontal cross-sections and then creates each crosssection
in physical space, one after the next until the model is
finished. However, each rapid prototyping platform uses the
same principles of slicing, layering and bonding to build parts.
Several research institutions and commercial organizations
have integrated Computer-aided Design (CAD) and Rapid
Prototyping (RP) systems with medical imaging systems to
fabricate medical devices or generate 3D hard copy of these
objects for use in surgical rehearsal, custom implant design and
casting. In manufacturing, models are planned and conceived
entirely on the computer screen, then converted to physical
reality. In bio-medical applications, the objects normally
already exist physically. Prior to building, this highly complex
data needs extensive pre-processing to provide a format that a
CAD program can utilize, before transferring to an RP system.
Stereo lithography (SLA):
Patented in 1986, this is the leading technology, with over 500
SLA machines installed worldwide, developed by 3-D Systems
Inc, of Valencia, CA. Stereo lithography creates 3-D models
out of acryl ate photopolymer or epoxy resin, by tracing a lowpowered
ultraviolet laser across a vat filled with resin.
The material is cured by the laser to create a solid thin slice.
The solid layer is then lowered just below the surface and
the next slice formed on top of it, until the object is
completed1-3. It is regarded as a benchmark by which other
technologies are judged. A recent development by Zeneca is
a translucent resin which changes to red when acted upon by
higher laser energy. This can be used to display local
regions of interest, and an obvious application would be for
the surgeon to draw round a tumor on the medical image
slices and have it to build into the model.Stereo lithography (SLA):
Patented in 1986, this is the leading technology, with over 500
SLA machines installed worldwide, developed by 3-D Systems
Inc, of Valencia, CA. Stereo lithography creates 3-D models
out of acryl ate photopolymer or epoxy resin, by tracing a lowpowered
ultraviolet laser across a vat filled with resin.
The material is cured by the laser to create a solid thin slice.
The solid layer is then lowered just below the surface and
the next slice formed on top of it, until the object is
completed1-3. It is regarded as a benchmark by which other
technologies are judged. A recent development by Zeneca is
a translucent resin which changes to red when acted upon by
higher laser energy. This can be used to display local
regions of interest, and an obvious application would be for
the surgeon to draw round a tumor on the medical image
slices and have it to build into the model.
Solid Ground Curing (SGC):
Developed by Cubital, solid ground curing (SGC) is somewhat
similar to stereolithography (SLA) in that both use ultraviolet
light to selectively harden photosensitive polymers. Unlike
SLA, SGC cures an entire layer at a time. It is also known as
the Solider process. First, photosensitive resin is sprayed on the
build platform. Next, the machine develops a photomask (like a
stencil) of the layer to be built. This photomask is printed on a
glass plate above the build platform using an electrostatic
process similar to that found in photocopiers. The mask is then
exposed to UV light, which only passes through the transparent
portions of the mask to selectively harden the shape of the
current layer. After the layer is cured, the machine vacuums up
the excess liquid resin and sprays wax in its place to support the
model during the build. The top surface is milled flat, and then
the process repeats to build the next layer. When the part is
complete, it must be de-waxed by immersing it in a solvent
bath. SGC machines are distributed in the U.S. by Cubital
America Inc. of Troy, MI. The machines are quite big and can
produce large models.
CONCLUSION:
RP technology can make significant impact in the field of
biomedical engineering and surgery. Physical models enable
correct identification of bone abnormality, intuitive
understanding of the anatomical issues for a surgeon, implant
designers and patients as well. A precise RP model facilitates
the pre-operative planning of am optimal surgical approach
and enables selection of correct or appropriate implants. In
the UK, RPT has been used to help plan treatment in more
than 20 patients; however, the cost of the modeling process is
currently a significant limitation to its use.