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.