3D printing: artificial
limbs and biomaterials go main stream
Introduction:
Can
the human race imagine being modified, rectified or substituted in a clinical
environment using body parts better than those we were born with? Yes, that is
likely to happen between now and 2020 according to (Canton 2014). For this innovative transformation to happen
technological advancements need to evolve in 3 dimensional printing (3D). Currently, 3D printing is in its trial and
infancy stage. 3D printing offers huge potential and hope to medicine and the
human race at large. In a nutshell, it’s to print out a part of the human body
in 3D spatial orientation. It might be a bit hard to imagine now, that we have
seen only 2D printers at work.
Printing,
as we know now when founded in the 15th century had revolutionary
effect on all spheres of society (Atala &
Murphy 2014) likewise 3 D printing is all poised to transform the way we
live and think. At present 3D printing is confined to prototyping,
manufacturing industry and customised production of goods such as jewellery and
motor parts (Malone & Lipson 2007).
Twenty to thirty motor parts for the present day cars are produced using 3 D
printing. Its impact on science and education is immense. It allows for
educationalists to create a prototype of rare artifacts which aid in knowledge
transfer by helping to feel and visualize in real space (Allard et al. 2007, Gomez et al 2012)
3D
printing was first coined by Charles W. Hull using a principle called stereolithography.
This included multiple layers being printed to a surface using materials that
can be cured by ultra violet light (Hoffman
2011)) These were later used to create 3D scaffold on to which now, using 3D
bio printing and tissue engineering, cell tissues are being printed. Another
phrase used synonymously with 3D printing is Rapid prototyping (RP) (Narayan 2014)
It
is noteworthy to understand the challenges faced by 3D printing. The
researchers are still finding ways to adapt hardware which can only use molten
plastic and metals to utilise sensitive living biological material. The main
idea is to recreate the extra cellular matrix and reproduce its complex architecture
so as to enable its biological function (Atala
&Murphy 2014)
Technology
utilised in 3D can be classified in to three major heading, approaches, design
and strategies (Atala & Murphy 2014). The main three methods used are
·
Bio mimicry: this approach
is highly advanced and requires identical replication of cellular and extra cellular
environment. The cellular components should be able to perform its functions,
hence, the intra cellular and extracellular forces’ knowledge is paramount (Ingber 2006). The hurdle in this
approach is the lack of in-depth knowledge at the micro-finite level.
·
Autonomous self-assembly:
here the technology uses embryonic development principles whereby basic stem
cells are printed and from there on these cells regenerate in to tissues and
organs (Marga et al. 2007). This is
good in case of tissue mass generation unlike specific shaped organs e.g. Liver
tissue can be prototyped using this approach, however it fails if skull bones
or specifically structured parts of the body has to be created.
·
Mini tissues: This is a
mid-micro level which encompasses of tissue building blocks such as muscle fibres
(Kelm et al. 2010) and they self-assemble
themselves with substrate they are printed. These need accurate tissue level
biological data replicated to form a condusive environment.
Imaging
is the first step in 3D printing. Images have to be captured to the exact
dimensions of what is being produced. The surfaces, borders and angles of the
product are captured using various methods, namely X-rays, CT scans or MRI
scans. The whole idea is to achieve
layered 2 dimensional sliced images of the part to be reconstructed. This data
is then converted to a 3D design using CAD. This design is transformed in to a
manufacturing data using CAM which is the printer’s language. Both CAD and CAM
are mathematical modelling techniques (Atala
& Murphy 2014). Imaging, in fact, has two major purposes, it helps us
to replicate structurally and also gives a detailed idea of the biological
environment around and within the part
that is to be replicated. The 2D layered information is used by the printer to
deposit tissue material in layers while printing.
Different
techniques are used in 3D printing; however they all follow the basic principle
of building layer by layer. Starting from the bottom layer, layers are laid on
top of each other and bonded together in the end. Some of the techniques are
inkjet printing, micro extrusion and laser assisted printing. Which one is used
is decided by surface resolution of design, cell viability of the tissue being
constructed and type of biological material used (Atala & Murphy 2014).
1. Inkjet
printing: in a 3D inkjet printer, the basic principles remain the same as that
of a 2D printer. It uses a drop on demand feature. The printing material (ink)
in the normal printers is replaced by biological material. The substrates on
which materials are deposited are made up of electronically precise lift
mechanism. This helps the material to be deposited in all the three axes (Xu et al. 2008). One of the major
drawbacks of such printers lies in the potential danger caused to the material
printed as these printers heat up to 200-300 degree Celsius (Okamoto et al. 2000). However, recent
study results look encouraging as there is no evidence of negative effects on
the stability of the biological molecule (Cui
et al. 2010). Owing to its nature of
substance used in such printers, the scope is limited at present. The material
needs to be in the liquid form while printing and should solidify later on but
while do so, it should maintain the biological properties. Yet the major advantage
of such printers is fast printing, low cost and easy availability of printers.
2. Micro
extrusion printing: they work by automated extrusion of tissue and depositing
them on to a bio viable substrate. Micro extrusion printing varies in sizes
from large industrial one’s to small laboratory ones. The deposits are made in
2D format as continuous beads of substance rather than liquid droplets as used
in inkjet printers (Atala & murphy).
The main advantage of these printers is the fact that printing substance need
not to be in a liquid form and is a win- win scenario especially in tissue
printing. They can be used to fill in tissue scaffoldings or can be placed in
strategically calculated positions when then fills up the space by self-assembly.
However, the drawback of micro extrusion is the cell viability when compared to
inkjet printing (Chang et al. 2008).
Therefore, usually, it is used for structural reproduction such as Heart valves
or vascular tissues rather than tissue reproduction.
3. Laser
assisted bio printing: these are less commonly used than other forms. LAB uses
pulsed laser beam to propel bubbled cellular components in a substrate space.
The laser beams are received by laser absorbing layer of metal such as titanium
or gold which acts as a guide to deposit tissues. Main advantage is the nozzle
less mechanism compared to other printers. However due to the complexity of the
process and lack of versatility. The printers are still in the early phase of
development.
In
general there are numerous software’s and interfaces, however commonly used
ones are OpenGL and DirectX. OpenGL is used by everyone and Direct X is backed
by Microsoft. 3D library based on Java
is called java 3D which is a low level application programming interface using
java and sits on top of OpenGL, thus allowing Java applications such as ImageJ
to interoperate with graphics card of computer.
Since bioinformatics and bio 3D involves predominantly human body parts,
its design phase definitely includes image capture and then designing. Image processing software in the medical
industry are numerous and either free or commercial such as Amira, Visage
Imaging; MeVisLab, Mevis etc (Schmid et
al. 2010). Design software can be an entry level such as Tinker Cad ( a
free web based application) or an intermediate level sketch up (owned by google until 2012) or advanced blenders used for animation and movies( Griffey 2014). Many open source software
are available for designing and construction. Scotland has a fully functioning
Rapid Design and Manufacturing centre that focuses on prosthetic body parts.
They use tracerCad premier prosthetic system to do the initial scan of the limb
of which they aim to produce the prosthesis. They scan the limb both
horizontally and vertically. This digital data which holds surface data of the
limb structure is transported back from the tracerCad software in DXF format
and printed using Solid view pro a CAD package( Herbert et al. 2005).
One
of the latest software launched in the area of 3D printing consists of two software
combined together. Go!SCAN 3D white-light 3D scanners and VX model (a 3D scan
to print software). The VX model software helps designers to avoid post scan
adjustment steps and quickly produce a 3D printer ready file. Another advantage
of this software is its seamless fit with CAD software and 3D printers (Knox 2014).
Most
commonly used in the bioinformatics is CAD or computer assisted design. CAD’s
generate digital data of sliced images in STL format. STL or sterolithography format
are mathematical representation of sliced 3D image. They are not by far the
best, but due to the ability to represent triangulation, they do perform well
in bio 3D printing. Another form of 3D printable data is G Code format.
These
data are then analysed by software such as Replicator G. They act as the
interface between design phase and the 3D printer. Replicator G takes on both
STL and G code data formats and is most commonly used open software in 3D
printing.
Conclusion
3D
printing has come a long way in the last two decades and rightly so the
Economist quoted 3D printing as the “third industrial revolution.”(The
economist, 2012) and the forecasted implications are overwhelming. Bio
informatics takes its lessons from the generic 3D printing technology and
customizes it to meet the medical demands.
3D printing has proven to be a life saver in re-constructional surgeries
after accidents or anticancer treatments. Three areas are still to be explored
and they are more robust imaging and designing techniques, printing hardware
and material development which would approximate artificial and natural
differences in materials.
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