bioprinting, the technology of tomorrow - duke...
TRANSCRIPT
2016
Bioprinting, the Technology of Tomorrow
Understanding Bioprinting
Abdulla Shahid Math89S: MAthematics of the universe Dr.HuberT Bray Paper OnE
Introduction:
Every ten seconds, a person is added to the organ transplant list. Currently, there are around
120,000 people on the organ transplant list, and every day, twenty-two people on that list die due
to the shortage of organs. Countries have tried implementing different policies to increase the
amount of organ donors, however, the incentives offered are not enough to motivate individuals
to donate organs. The demand for organs significantly exceeds the supply, in fact, by the time
you read this sentence, two people will have been added to the organ transplant list. With our
current solutions, we are unable to meet the demand for organs, however, thanks to modern
technology, in specific bioprinting, we can.
What is Bioprinting?
According to the Oxford Dictionary, bioprinting is defined as “The use of 3D printing
technology with materials that incorporate viable living cells”. As you can conclude from the
definition above, bioprinting is the process of using cells to create different tissues which can
ultimately be used together to create vital organs.
How does Bioprinting work:
The process of bioprinting can be divided into three sections: Imaging and Design, Material and
Cell selection, and Bioprinting.
Below is a detailed explanation of the three different processes:
Imaging and Design
When trying to replicate the intricate, heterogeneous architecture of tissues and organs it is
imperative that one has a comprehensive understanding of the desired organ’s components.
Thanks to medical imaging technology, such as MRIs or CT scans, bioprinting engineers are able
to gain information about the desired organ on both a cellular and tissue level. Once the medical
image has been captured from one of the said medical imaging modalities, the data must be
processed using tomographic reconstruction to produce 2D cross-sectional images which are
later translated to 3D anatomical representations. In terms of creating these 3D anatomical
representations, there are multiple Computer Aided Design (CAD) programs that can be used to
create them, the most effective technique has been using mathematic modeling methods in
addition to CAD programs to create these representations (Jakab). Using the following method
ultimately enables engineers to view the anatomy of the organ while retaining the voxel1
information which can later be used for interpreting the volume of the organ. One important
concept to understand is that when an organ is being bioprinted, the 3D representations being
created should not be an exact match of the organ that is being duplicated. This is because the
person seeking an organ transplant might have some form of an injury or a disease that is altering
the shape of their organ. In such scenarios, computer modeling techniques are employed to alter
the medical image of the defected organ to create representations of how the organ would appear
if it was healthy. Once the final model of the tissue or organ has been completed, the tissue or
organ begins to prep for manufacturing. This is achieved by dividing the 3D rendered model by
2D horizontal slices that are ultimately imported to the bioprinter (Murphy 775). In order to
better understand this process, I created an infographic2 below that explains the technique:
1 A voxel is a value on a 3-D grid2 Image Created by me on Inkskape
In the above image, I am trying to bioprint my least favorite candy a “Mega Bruiser Jawbreaker”
which can be seen in Image 1. Using tomographic reconstruction on the Jawbreaker, 2D
horizontal cross sectionals are created which can be seen in Image 2, in actual practice, the 2D
horizontal cross sectionals are far smaller, however, in the diagram above I only drew four cross
sectionals to demonstrate the main idea. Then those cross sectionals, which can be seen in Image
3, are imported to the bioprinter. Finally, once the Material/Cell process (explained further
down) is completed, the bioprinter prints each cross sectionals successively on top of each other
which ultimately produces Image 4, a replicated version of the original jawbreaker.
Material and Cell Selection
When a tissue or organ is being bioprinted, there are various techniques that can be used to
bioprint the tissue or organ3. Some systems (bioprinter) deposit a continuous bead of bioink4 to
form a 3D structure while other times, a system might deposit materials in defined spaces. The
technique used is dictated by the material and cells that are chosen to create the bioink. Initially,
3D printers were not designed for biological applications and non-biological materials were used
as the ink to create the different objects. Thus one of the main challenges in the field bioprinting
has been finding a material that can provide the desired mechanical and functional properties of a
tissue but also be compatible with biological materials.
Currently, the materials being used for regenerative medicine are predominately based on
either naturally derived polymers such as alginate, gelatin, collagen and hyaluronic acid or
synthetic molecules such as polyethylene glycol or PEG112. Both materials, natural polymers and
synthetic molecules, have their advantages and disadvantages when being used in the field of
bioprinting. Some benefits of natural polymers are their inherent bioactivity and their similarity
3 Different Techniques will be discussed later, in the last section- “Bioprinting”4 Ink that is used to create the organs-combination of the material and cells selected
to human ECM5. In comparison, the main advantage of using synthetic polymers is that they can
be “tailored with specific physical properties to suit particular applications” which ultimately
make them the better choice bioprinting as it easy for engineers to control their physical
properties during synthesis (Murphy 775). However, there are drawbacks to using synthetic
polymers such as having poor biocompatibility and that during the degradation of the polymer, it
loses some of its mechanical properties. Overall as the variety of biological materials for
bioprinting is increasing, the list of “desired traits” has also become more specific and complex.
Some of the qualities that these materials must now possess are “suitable crosslinking
mechanisms to facilitate bioprinter depositions, higher levels of biocompatibility, and short-term
stability” (Murphy 776).
Once the material for the bioink has been selected, the next step is to choose the cells.
The choice of cells for a tissue or organ is crucial for correct function of the fabricated construct.
Tissues and organs consist of an array of cell types that must be recapitulated in the transplanted
tissue in order to achieve correct functionality (Atala 776).
Bioprinting:
Once the Imaging/Design phase and the Material/Cell phase have been completed, the next step
is to begin printing. There are three different methods to bioprint organs: Inkjet, Microextrusion,
and Laser Assisted bioprinting. All three strategies are explained in detail below:
Inkjet:
Currently, inkjet printers are the most commonly used printers for both biological and non-
biological applications. The main idea of inkjet printers is that they deposit controlled volumes
of ink on predefined locations. When trying to understand how inkjet bioprinting works, the
5 Extracellular Matrix- The non-cellular portion of a tissue produced by cells and used to provide support
easiest way to understand it is by thinking about the printers you use at libraries which are
typically inkjet printers. The difference for bioprinting is you replace the ink with biological
materials (discussed in Materials and Cell selection section) and you replace the paper with a
stage on which a 3D object can be printed on (you now have an X, Y, and Z axis). There are two
forces that are primarily used when dealing with inkjet bioprinting, thermal and acoustic forces.
Thermal inkjet printers function by electrically heating the nozzle of the ink dispenser which
ultimately produces “pulses of pressure that force
droplets from the nozzle”. Acoustic inkjet
printers, on the other hand, have a piezoelectric
crystal that “creates an acoustic wave inside the
had to break the liquid intro droplets at regular
intervals” (Murphy 778). The image6 on the right
shows the two kinds of inkjet printing, thermal
and acoustic (piezoelectric):
Microextrusion:
Microextrusion is the most common and affordable non-biological 3D printer being used today.
These kinds of printers are commonly composed of a “temperature-controlled material handling
and dispensing system and a stage” (Murphy 777). Microextrusion printer function by creating
extrusions7 of a material which is then stored in a nozzle which ultimately deposits the material
onto a substrate. Unlike inkjet printing which prints out liquid droplets, Microextrusion printing
prints continuous beads of bioink along the Z-axis of the stage. There are ultimately two different
methods that can be employed to extrude biological materials for bioprinting, pneumatic and
6 Image was adapted from Katie Vicari/Nature Publishing Group7 Extrusion- process to create objects at a fixed cross-sectional
mechanical. Pneumatically driven printers are advantageous in the sense that they have simple
mechanism components8 as the force is only limited by air-pressure capabilities of the system.
On the other hand, mechanically driven mechanisms have more intricate components (piston,
screw, and valve) that work in tandem, ultimately making it more complex. It is this complexity
of the system however, that ultimately allows for this system to provide greater spatial control of
the ink being deposited (Atala 778). The image9 below shows the two kinds of microextrusion
printing, Pneumatically and Mechanical:
Laser-Assisted:
Laser-assisted bioprinting revolves around the concept of “Laser-Induced Forward Transfer” 10 to
make copies of the original organ or tissue. The transfer in LIFT is induced by focusing one or
more laser “pulses onto the support film interface (energy absorbing layer in the image below),
where heating and phase change of the film provide the propulsion to propel material to a
receiving substrate place nearby” (Eason). Laser-assisted bioprinting is not heavily employed by
bioprinting engineers, as there are multiple factors that reduce the quality of the replicated tissue.
Some of these factors are surface tension, the wettability of the substrate and the viscosity of the
8 Simple in the sense that the only factor involved is air pressure 9 Image was adapted from Katie Vicari/Nature Publishing Group 10 LIFT- involves the pixelated transfer of material from a thin film onto the rear side of a transparent support substrate(Eason)
biological material/layer (Eason). Ultimately problems in the resolution of the printed organ lead
to said organ being less functional hence making it inefficient to use. Despite these problems,
there are also some advantages to using LAB (laser-assisted bioprinting) when printing tissues or
organs. One benefit is that LAB is nozzle free, therefore
there are no chances of nozzle being clogged. Overall,
while LAB could produce promising tissues and organs, we
currently lack the technology to fix the problems that
occur with the resolution of the printed organ. The
image11 on the right shows Laser-assisted bioprinting:
Summary:
The chart below12 summarizes the information above by showing all the steps (Imaging/Design,
Material/Cell selection, and Bioprinting).
Future of Bioprinting: n terms of bioprinting applications today, we have been able to replicate
some tissues, however we are still far away from being able to print out complex organs such as
11 Image was adapted from Katie Vicari/Nature Publishing Group12 Image Citation: Massachusetts Medical Society
a kidney or a heart. The graphic below shows a timeline of what human body parts we will be
able to create in the upcoming years13. This graphic was created in 2011 so we are currently in
the “very soon” stage:
Treatment vs. Enhancements:
This section of the paper begins to investigate the implications in the future once bioprinting
becomes possible. One of the main reasons why people disagree with the idea of bioprinting
organs is because of the idea of treatment vs enhancement. People believe that instead of printing
out organs for life-sustaining purposes, people will print out organs to enhance themselves
whether it be internally or cosmetically (bioprinting body parts). For example, a cross-country
runner might bioprint a new lung for himself so that he can become a better long distance runner.
Many people find this to be unethical and believe enhancements ultimately corrupt the innate
purpose of bioprinting. Some people might abuse themselves as they realize if any of their
organs fail they can print out a new one (example would be an alcoholic continuously drinking).
Overall, while there are advantages present with bioprinting, there are also some possible
consequences that can result from its development. 13 Image citation: University of Pittsburgh; developmental biologist Vladimir Mironov
Other Solutions:
While there is large support for bioprinting, there are still many people who are against it. They
believe that there are other solutions available that will be able to increase the supply of organs
available for an organ transplant. Many countries have tested programs that offer organ donors
stipends, tax breaks, and other financial incentives, but almost all have proven to be ineffective.
One plan that has to be proven to be effective is the current plan being implemented by Israel.
Israel’s organ donation plan relies on the concept of self-preservation. The program prioritizes
organ allocation based upon willingness to be a donor, “If two people on the organ transplant
waiting list are medically equally well matched as potential recipients, the organ will go to the
person who previously agreed to be an organ donor” (Aptekar). This rule ultimately encourages
people to become organ donors as by becoming an organ donor, in the event of them needing an
organ, they would have a higher chance of receiving a transplant. This plan has been active in
Israel for the past three years however, the results are showing a strong increase in the number of
registered organ donors. While this may seem like an “answer”, this still does not truly erase the
gap between the demand for organs and the supply of organs for transplants as it still depends on
humans to provide the organs.
Conclusion:
Overall, while there are programs that encourage organ donations, I believe it is important to
continue investing our resources into the field of bioprinting. Bioprinting would ultimately allow
us to create organs for those in need in a time and cost efficient manner. In addition, it would
ultimately enable us to expand further in the field of medicine which could benefit a variety of
people, ranging from people with congenital organ defects to individuals with lifetime injuries.
While we might still be far from being able to bioprint an organ, it is important to realize how
great of an impact bioprinting can have as it has the “[bioprinting has the] potential to change the
world”14.
Works Cited
Aptekar. "How Can Organ Donation Rates Be Improved?" The Huffington Post.
TheHuffingtonPost.com, n.d. Web. 27 Sept. 2016.
Eason, Rob. "IN THIS SECTION." Laser-Induced Forward Transfer. N.p., n.d. Web. 25 Sept.
2016.
14 Direct Quote: Jeff Kowalski, CTO of Autodesk
F, Jeffery. "3D Bioprinting Becoming Economically Feasible." National University of
Singapore, n.d. Web. 25 Sept. 2016.
Jakab, Karoly, Francoise Marga, Cyrille Norotte, Keith Murphy, Gordana Vunjak-Novakovic,
and Gabor Forgacs. "Tissue Engineering by Self-assembly and Bio-printing of Living
Cells." Biofabrication. U.S. National Library of Medicine, June 2010. Web. 25 Sept.
2016.
Murphy, Sean, Atala, Anthony. "3D Bioprinting of Tissues and Organs." Biotechnolgy. Nature,
25 June 2014. Web. 25 Sept. 2016.
Papavulur, Alexander. LASER INDUCED FORWARD TRANSFER FOR MATERIALS
PATTERNING (n.d.): n. pag. Web. 25 Sept. 2016.