ROBOTIC BIOPRINTER

Biswajeet Champaty

Department of Biotechnology & Medical Engineering, National Institute of Technology,

Rourkela-769008, Odisha, India.

ABSTRACT

Tissue/organ printing aims to recapitulate the intrinsic complexity of native tissues. For a number

of tissues, in particular those of musculoskeletal origin, adequate mechanical characteristics are

an important prerequisite for their initial handling and stability, as well as long-lasting

functioning. Hence, organized implants, possessing mechanical characteristics similar to the

native tissue, may result in improved clinical outcomes of regenerative approaches. Using a

bioprinter, grafts were constructed by alternate deposition of thermoplastic fibers and (cell-laden)

hydrogels. Present efforts in tissue engineering are aimed at building living structures by

employing the self-organizing properties of cells and tissues and automated technologies. One

such technology is bioprinting that utilizes three-dimensional delivery devices for the rapid and

accurate placement of biological materials into biocompatible environments, where post-printing

self-assembly takes place. This Application article summarizes the scientific basis of this

approach and some of the recent developments.

1. INTRODUCTION

Bioprinting is a new emerging technology,that aims at achieving to develop new tissues and

eventually organs. It is in the research phase as with any technology that takes time to

completely develop. Currently, there is a lot of research being done on bioprinters.

In bioprinting, devices are printed by feeding biological materials as deposits. With an ink jet

printer instead of ink, cells are printed or deposited on a surface layer by layer. And in this way a

full organ can be produced. Bioprinting is a huge shift from the traditional approaches adopted so

far in tissue engineering. It does not aim at seeding cells on a biodegradable scaffold. It aims at

organizing the elements of the tissue during the fabrication step individually through the process

of depositing layers of biologically important components.

Bioprinting is a new area of research and engineering that involves printing devices that

deposit biological material. The long-term goal is that the technology could be used to create

replacement organs or even entire organisms from raw biological materials. Today, bioprinters

are in the development stage and primarily are used as scientific tools. They lack the speed and

fine-tuning necessary for commercial deployment, though that day might not be far off. The first

bioprinters deposited drops as small as 100 picoliters (by comparison, the volume of a cell is

around 3 picoliters and the best inkjet printers can deposit drops 1-5 picoliters in volume) at a

rate of tens of thousands per second. More recent bioprinters can extrude individual cells from

a micropipette at a lower speed.

A bioprinter developed by Gabor Forgacs, a biophysicist at the University of Missouri in

Columbia, used combinations of "bioink" and "biopaper" to print complex 3D structures, albeit

not at cellular resolution. Operating at 10,000 dots per second (10 kHz), a 100 picoliter printer

can produce 60 microliters of tissue each minute, or 86 milliliters per day, a quantity of tissue

that could almost fill a typical test tube. The downside of the 100 picoliter printer is its low

resolution - most organic tissue we're familiar with requires precise cell-level organization in

order to operate properly.

2. BACKGROUND

Previous tissue engineering scaffold-based approaches have aimed to induce tissue self-assembly

in applications such as cell-sheet engineering, centrifugal casting and magnetically driven

approaches. Manipulating the cellular environment (i.e. surface tension, restricted geometry etc)

may stimulate cells to self-aggregate to desirable geometrical shapes or migrate such as is done

in rotating-culture systems and hanging-drop method. These concepts have been extended to

other areas of research; utilizing micro fluidics, for example, for the high throughput generation

and screening of compact spheroids and cell encapsulation. The emphasis of understanding the

process by which cells self-assemble to 3D constructs has continued to grow to be central to

comprehending morphogenesis and the development of living tissues. Evolving from tissue

engineering, self-assembly processes have reached to other areas of research with increasing

speed.

Fundamentally, bioprinting emphasizes the use of computer-aided technology and

principles such as tissue self-assembly, synthesis and remodeling. Marketing an idea of "directed

tissue self-assembly", organ printing utilizes these rapid prototyping technologies and biological

principles to influence tissue development. Computer-aided design enables the precise and

controlled placement and layer-by-layer deposition (also known as solid free-form fabrication) of

cells, cell aggregates, cell-encapsulated hydrogels or any biologically related complex 3D

structure along with other important chemical components such as nutrients and growth factors.

With the simultaneous delivery of these cells, the natural autonomous organization of cells may

potentially lead to the controlled patterning and assembly of complex 3D constructs.

Fig.1 Biopaper, Bioink, Bioprinter

Fig .2 Bioink deposited from bioprinter onto hydrogel biopaper. Alternating layers of printed ring structure and gel

(acts like a matrix) eventually form a smooth cylinder after gel relaxes and layers merge.

Theoretically, bioprinting technology consists of six essential components: A CAD

drawing of the desired engineered organ (blueprint); cells, cell aggregates or cell-encapsulated

hydrogels capable of natural self-assembly (bioink); robotic-aided device for delivering the

bioink (bioprinter); a container enclosed of the material to be deposited (biocartridge); a

bioprocessible biomimetic hydrogel to transfer material on (biopaper); and a perfused container

containing the resulting printed 3D tissue construct capable of post-conditioning (bioreactor).

While only in the early stages of development, bioprinting has many potential applications and

can be divided into three steps: pre-processing, processing and post-processing.

3. BIOPRINTING PIONEERS

Several experimental bioprinters have already been built. For example, in 2002 Professor

Makoto Nakamura realized that the droplets of ink in a standard inkjet printer are about the same

size as human cells. He therefore decided to adapt the technology, and by 2008 had created a

working bioprinter that can print out biotubing similar to a blood vessel. In time, Professor

Nakamura hopes to be able to print entire replacement human organs ready for transplant. You

can learn more about this groundbreaking work here orread this message from Professor

Nakamura. The movie below shows in real-time the biofabrication of a section of biotubing

using his modified inkjet technology.

Another bioprinting pioneer is Organovo. This company was set up by a research group

lead by Professor Gabor Forgacs from the University of Missouri, and in March 2008 managed

to bioprint functional blood vessels and cardiac tissue using cells obtained from a chicken. Their

work relied on a prototype bioprinter with three print heads. The first two of these output cardiac

and endothelial cells, while the third dispensed a collagen scaffold -- now termed 'bio-paper' -- to

support the cells during printing.

Since 2008, Organovo has worked with a company called Invetech to create a

commercial bioprinter called the NovoGen MMX. This is loaded with bioink spheroids that each

contain an aggregate of tens of thousands of cells. To create its output, the NovoGen first lays

down a single layer of a water-based bio-paper made from collagen, gelatin or other hydrogels.

Bioink spheroids are then injected into this water-based material. As illustrated below, more

layers are subsequently added to build up the final object. Amazingly, Nature then takes over and

the bioink spheroids slowly fuse together. As this occurs, the biopaper dissolves away or is

otherwise removed, thereby leaving a final bioprinted body part or tissue.

As Organovo have demonstrated, using their bioink printing process it is not necessary to

print all of the details of an organ with a bioprinter, as once the relevant cells are placed in

roughly the right place Nature completes the job. This point is powerfully illustrated by the fact

that the cells contained in a bioink spheroid are capable of rearranging themselves after printing.

For example, experimental blood vessels have been bioprinted using bioink spheroids comprised

of an aggregate mix of endothelial, smooth muscle and fibroblast cells. Once placed in position

by the bioprint head, and with no technological intervention, the endothelial cells migrate to the

inside of the bioprinted blood vessel, the smooth muscle cells move to the middle, and the

fibroblasts migrate to the outside.

In more complex bioprinted materials, intricate capillaries and other internal structures

also naturally form after printing has taken place. The process may sound almost magical.

However, as Professor Forgacs explains, it is no different to the cells in an embryo knowing how

to configure into complicated organs. Nature has been evolving this amazing capability for

millions of years. Once in the right places, appropriate cell types somehow just know what to do.

In December 2010, Organovo create the first blood vessels to be bioprinted using cells cultured

from a single person. The company has also successfully implanted bioprinted nerve grafts into

rats, and anticipates human trials of bioprinted tissues by 2015. However, it also expects that the

first commercial application of its bioprinters will be to produce simple human tissue structures

for toxicology tests. These will enable medical researchers to test drugs on bioprinted models of

the liver and other organs, thereby reducing the need for animal tests.

In time, and once human trials are complete, Organovo hopes that its bioprinters will be

used to produce blood vessel grafts for use in heart bypass surgery. The intention is then to

develop a wider range of tissue-on-demand and organs-on-demand technologies. To this end,

researchers are now working on tiny mechanical devices that can artificially exercise and hence

strengthen bioprinted muscle tissue before it is implanted into a patient.

Organovo anticipates that its first artificial human organ will be a kidney. This is because,

in functional terms, kidneys are one of the more straight-forward parts of the body. The first

bioprinted kidney may in fact not even need to look just like its natural counterpart or duplicate

all of its features. Rather, it will simply have to be capable of cleaning waste products from the

blood. You can read more about the work of Organovo and Professor Forgac's in this article from

Nature.

4. BIOPRINTING

Manipulation of picoliter to nanoliter droplets has been a challenge for several applications

including biochemical surface patterning, tissue engineering, and direct placement of cells and

biomaterials for wound dressing applications [1–4]. In this regard, ejecting droplets via an

actuator has emerged as a valuable technological advance addressing the issue of precise

manipulation and deposition. Bioprinting is defined as the use of printing technology to deposit

living cells, extracellular matrix (ECM) components, biochemical factors, proteins, drugs, and

biomaterials on a receiving solid or gel substrate or liquid reservoir [5–8]. In recent years, there

has been a growing interest in bioprinting due to its various advantages over existing patterning

methods such as photolithography, soft-lithography, and stamping. Among these advantages are:

(i) simple to use; (ii) enabling researchers to generate geometrically well-defined scaffolds in a

rapid and inexpensive manner using polymers or ceramics and other cell stimulating factors

providing support and induction for seeded cells [9]; (iii) allowing high-throughput generation of

replicas of spatially and temporally well-controlled complex constructs [10]; and (iv) providing

3D complexity by multilayer printing [6,7,10]. By using conventional single-step lithography

and stamp printing methods, building 3D constructs at high-throughput is challenging because

fabricated 2D layers have to be merged. Existing co-culture approaches either lack high-

throughput (e.g., conventional multiwell plate co-culture) or require complex fabrication steps

and peripheral systems (e.g., microfluidic co-culture).

Emerging methods to pattern and assemble microscale hydrogels fabricated by

photolithography are promising in terms of mimicking the complexity of the native

microenvironment [11–15]. Although bioprinting is a young field, it has experienced a rapid

growth despite the initial challenges that an emerging field experiences. First, biological

challenges for bioprinting have been cell viability and long-term functionality post-printing.

Concerns regarding potential apoptotic effects after and during bioprinting have been raised by

the potential future end-users of this technology such as biologists, who consider bioprinting as

an enabling technology for various applications. These biological requirements have set

standards on the technology, leading to the development of several bioprinting technologies

focusing on cytocompatibility issues maintaining a control over cell positioning in 2D and 3D

microenvironments. Among these bioprinting technologies are inkjet-based printing [16,17],

laser printing [18–22], acoustic cell encapsulation [5,23], and valve-based printing [7,24–26]. In

recent years, there has been an increasing interest in the use of bioprinting for applications in

biology and medicine. An emerging area is integration of bioprinting technologies with stem cell

research. Microenvironments with spatially controlled gradients of immobilized macromolecules

have been engineered to direct stem cell fate [27–33]. Stem cells such as embryonic stem cells

(ESCs), human bone marrow stem cells, and adipose-derived stem cells (ASCs) have been also

directly bioprinted onto substrates [34–37].

Fig.3 Principles of bioprinting technology: a) bioprinter (general view); b) multiple bioprinter nozzles; c) tissue

spheroids before dispensing; d) tissue spheroids during dispensing; e) continuous dispensing in air; f) continuous

dispensing in fluid; g) digital dispensing in air; h) digital dispensing in fluid; i) scheme of bioassembly of tubular

tissue construct using bioprinting of self-assembled tissue spheroids illustrating sequential steps of layer-by-layer

tissue spheroid deposition and tissue fusion process.

5. BIOPRINTING TECHNOLOGIES: ROBOTIC APPROACH

Bioprinting helps to replicate human organs. The long term goal is to create a whole organ.

However, this technology is in its rudimentary stage. As the system still lacks fine-tuning, it is

not yet well-accepted in the mainstream medical field. With a regular ink-jet printer a cartridge is

moved back and forth on a petri dish. A liquid is kept in the petri dish and the cartridges have

cells inside them instead of ink. Inside, it has a crosslinker for binding. The crosslinker turns the

liquid into a gel like substance over which the cells are deposited. This process is repeated with

addition of liquid and more layers of cells. In this way, cells are structured for the formation of

an organ. Newly developed bioprinters work at lower speed and can extrude cells individually

from a micropipette.

Fig.4 Sketch of bioprinting technologies. (a) Thermal and piezoelectric ink-jet printing. Two major methods to jet the bio-ink are demonstrated. The thermal technique heats a resistor and expands an air bubble. The piezoelectric

technique charges crystals that expand. (b) Setup for acoustic pico-liter droplet generation. Droplets can be

deposited drop-on-demand with predetermined separation and locations. Periodically spaced interdigitated gold

rings of an acoustic picoliter droplet ejector are demonstrated. The wavelength of the acoustic wave (low ‘f’) is

much larger than the cell size resulting in harmless ejection of cells [5]. (c) Sketch of the valvebased printing setup

[7,24–26]. (d) Sketch of the laser printing setup. (Left) Laser-guided direct cell printing [18,39]. The laser is focused

into a cell suspension and the force due to the difference in refractive indexes moves the cells onto an acceptor

substrate. (Right) The cell–hydrogel compound is propelled forward as a jet by the pressure of a laser-induced vapor

bubble.

Several bioprinting methods have been developed to deposit cells including acoustic

[5,23], inkjet [16,17], valve-based [7,24–26], and laser printing technologies [18–22].

Initially,commercially available desktop inkjet printers have been modified and used as cell

printers [38]. In these systems, cell suspensions are placed in a printer cartridge, and a computer

controls the printing pattern. Another technique to generate cell-encapsulating hydrogel droplets

is the valve-based droplet ejection method [24,25]. In this method, cell-encapsulating hydrogel

droplets are ejected onto a surface drop-on-demand. Size and number of cells in a single droplet

and amount of droplets are controlled by the valve opening duration and actuation frequency

[26].

In the laser-guided direct writing method, photons from a laser beam trap and guide cells

by exploiting the differences in refractive indexes of cells and cell media [18,39]. Exposure of

excessive thermal energy via laser light onto the cell biolayer and overheating of the cell can be

one of the challenges. To overcome these challenges, near-infrared wavelengths (700–1000 nm)

have been used [39]. Photons in the near-infrared lack the energy to generate free radicals and

are not absorbed by DNA. Hence, laserguided direct printing is described to be unlikely to cause

mutations or trigger apoptosis, although wavelength optimization remains an open issue [39]. As

an alternative to laser-guided direct printing, a cell-encapsulating donor film is previously

deposited onto a substrate, and placed in parallel facing the receiving substrate [19,21,40]. The

heat transfer from the laser pulse to the cellencapsulating donor film leads to the transfer of

material from the donor film to the receiving substrate. Patterning is performed on the receiving

substrate that is usually fixed on a computerized stage and coated with a cell culture medium or a

biopolymer layer for cellular adhesion. Among these methods are laser-induced forward transfer

(LIFT), absorbing film-assisted laser-induced forward transfer (AFA-LIFT), biological laser

processing (BioLP), and matrix-assisted pulsed laser evaporation direct writing (MAPLE DW)

[42].

Table I. Comparison of commonly used bioprinting technologies based on performance

Performance metric Valve-based

bioprinting

[7,24–26]

Laser –induced

bioprinting (LIFT,

BioLP, MAPLE)

[19,21,40–44]

Laser-guided

bioprinting

[18,39]

Inkjet

bioprinting

[16,17]

Acoustic

bioprinting

[5,23]

Throughput Medium Medium Low High High

Droplet size 100µm–1 mm >20 µm >10 µm 50–300 µm 10–500 µm

Spatial resolution Medium Medium High Medium Medium

Single Cell Control Medium Medium High Low High

A picoliter droplet-based cell encapsulation technology via acoustics has been developed

[5,23,42]. Acoustic droplet formation rate can reach up to 100 000 droplets per second [5] with

high cell viability. Among the advantages of this technology over other printing approaches are:

(i) no nozzle is required for droplet generation because droplets are created from an open liquid

reservoir, which circumvents complications that may be related to shear or clogging; (ii) acoustic

waves do not harm cells due to low power droplet generation with only a few microseconds of

pulse duration; and (iii) acoustic ejectors can be combined in an adjustable array format as

multiple ejectors [41]. This would allow to enhance the rate of printing and to deposit multiple

cell and ECM types. These ejectors could potentially print several biomaterials such as living

cells, ECM proteins, nutrients, therapeutic drugs, and growth factors (GFs) simultaneously from

the same platform by integrating microfluidic systems into these ejectors [42]. To obtain

reproducible results for the deposition of cell-encapsulating droplets, bioprinting spatial

precision should be comparable to the cell size, for example, 10–20 µm in suspension [5].

6. APPLICATIONS AND RECENT ADVANCES

6.1 Regenerative Scaffolds and Bones

A further research team with the long-term goal of producing human organs-on-demand has

created the Envisiontec Bioplotter. Like Organovo's NovoGen MMX, this outputs bio-ink 'tissue

spheroids' and supportive scaffold materials including fibrin and collagen hydrogels. But in

addition, the Envisontech can also print a wider range of biomaterials. These include

biodegradable polymers and ceramics that may be used to support and help form artificial

organs, and which may even be used as bioprinting substitutes for bone.

Talking of bone, a team lead by Jeremy Mao at the Tissue Engineering and Regenerative

Medicine Lab at Columbia University is working on the application of bioprinting in dental and

bone repairs. Already, a bioprinted, mesh-like 3D scaffold in the shape of an incisor has been

implanted into the jaw bone of a rat. This featured tiny, interconnecting microchannels that

contained 'stem cell-recruiting substances'. In just nine weeks after implantation, these triggered

the growth of fresh periodontal ligaments and newly formed alveolar bone. In time, this research

may enable people to be fitted with living, bioprinted teeth, or else scaffolds that will cause the

body to grow new teeth all by itself. You can read more about this development in this article

from The Engineer.

I n another experient, Mao's team implanted bioprinted scaffolds in the place of the hip

bones of several rabbits. Again these were infused with growth factors. As reported inThe Lancet,

over a four month period the rabbits all grew new and fully-functional joints around the mesh.

Some even began to walk and otherwise place weight on their new joints only a few weeks after

surgery. Sometime next decade, human patients may therefore be fitted with bioprinted scaffolds

that will trigger the grown of replacement hip and other bones. In a similar development, a team

from Washington State Universityhave also recently reported on four years of work using 3D

printers to create a bone-like material that may in the future be used to repair injuries to human

bones.

6.2 In Situ Bioprinting

The aforementioned research progress will in time permit organs to be bioprinted in a lab from a

culture of a patient's own cells. Such developments could therefore spark a medical revolution.

Nevertheless, others are already trying to go further by developing techniques that will enable

cells to be printed directly onto or into the human body in situ. Sometime next decade, doctors

may therefore be able to scan wounds and spray on layers of cells to very rapidly heal them.

Fig.5. Robotic bioprinter for in situ bioprinting

Already a team of bioprinting researchers lead by Anthony Alata at the Wake Forrest School of

Medicine have developed a skin printer. In initial experiments they have taken 3D scans of test

injuries inflicted on some mice and have used the data to control a bioprint head that has sprayed

skin cells, a coagulant and collagen onto the wounds. The results are also very promising, with

the wounds healing in just two or three weeks compared to about five or six weeks in a control

group. Funding for the skin-printing project is coming in part from the US military who are keen

to develop in situ bioprinting to help heal wounds on the battlefield. At present the work is still

in a pre-clinical phase with Alata progressing his research usig pigs. However, trials of with

human burn victims could be a little as five years away.

The potential to use bioprinters to repair our bodies in situ is pretty mind blowing. In

perhaps no more than a few decades it may be possible for robotic surgical arms tipped with

bioprint heads to enter the body, repair damage at the cellular level, and then also repair their

point of entry on their way out. Patients would still need to rest and recuperate for a few days as

bioprinted materials fully fused into mature living tissue. However, most patients could

potentially recover from very major surgery in less than a week.

6.3 Cosmetic Applications

As well as allowing keyhole bioprinters to repair organs inside a patient during an operation, in

situ bioprinting could also have cosmetic applications. For example, face printers may be

created. These would evaporate existing flesh and simultaneously replace it with new cells to

exact patient specification. People could therefore download a face scan from the Internet and

have it applied to themselves. Alternatively, some teenagers may have their own face scanned,

and then reapplied every few years to achieve apparent perpetual youth.

Fig.6. face bioprinter

The idea of having the cells of your face slowly burnt away by a laser and reprinted to order may

sound like a nightmare that nobody would ever choose to endure. However, as we all know,

many people today go under the knife to achieve far less cosmetically. When the technology is

available to create them, face printers capable of printing new muscles without the hassle of

exercise.

6.4 3D Bio-printer to create arteries and organs

An engineering firm has developed a 3D bio-printer that could one day be used to create organs

on demand for organ replacement surgery. The device is already capable of growing arteries and

its creators say that arteries "printed" by the device could be used in heart bypass surgery in as

little as five years. Meanwhile, more complex organs such as hearts, and teeth and bone should

be possible within ten years.

The 3D bio-printer allows scientists to place cells of almost any type into a desired 3D

pattern. It includes two print heads, one for placing human cells, and the other for placing a

hydrogel, scaffold, or support matrix. The cells used by the device need to be the cells of what is

being regenerated – building an artery requires arterial cells for example. Because the patient’s

own cells are used the new organ will not be rejected by the body. The printer fits inside a

standard biosafety cabinet for sterile use.

Fig.7. 3D robotic bio-printers

Its creators say that one of the most complex challenges in the development of the printer

was being able to repeatedly position the capillary tip, attached to the print head, to within

microns. This was essential to ensure that the cells are placed in exactly the right position. A

computer controlled, laser-based calibration system was developed to achieve the required

repeatability. The 3D bio-printers include a software interface that allows engineers to build a

model of the tissue construct before the printer commences the physical constructions of the

organs cell-by-cell using the automated, laser-calibrated print heads.

Researchers can place liver cells on a preformed scaffold, support kidney cells with a co-

printed scaffold, or form adjacent layers of epithelial and stromal soft tissue that grow into a

mature tooth. Ultimately the idea would be for surgeons to have tissue on demand for various

uses, and the best way to do that is get a number of bio-printers into the hands of researchers and

give them the ability to make three dimensional tissues on demand.

7. FUTURE CHALLENGES

Although the idea of building tissues and organs has long been envisioned, bioprinting is still a

very new process. While the concept seems possible, its full potential has yet to be fully

demonstrated. Despite much progress and a number of breakthroughs in this area, researchers

have met many challenges. There are many design considerations, only a few are discussed

below, to factor in the design and development of the process and bioprinting devices. Utilizing

emerging technologies and advances (in all fields) and optimizing the current state-of-the-art

process and tools will progress bioprinting further.

An organ blueprint should not only provide an accurate representation of the desired

tissue, but also factor in dynamic events such as tissue fusion, compaction and retraction and

constant remodeling. However, designing a bioprint to consider post-processing fusion,

remodeling, retraction and compaction after printing and solidification is a challenging task. To

resolve this, one modification to the blueprint would require it to be larger and slightly shaped

differently from the final desired tissue structure. The CAD drawing may also need to include

coefficients that estimate these remodeling factors. Furthermore, to accurately capture and

simulate dynamic tissue self-assembly and post-processing remodeling, computer simulations

must be improved in order to be utilized in the organ printing process. However, novel software

and blueprints may lead to more effective solutions.

There are also challenges to improving and optimizing the biofabrication process.

Currently, biopaper is characterized as a bioprocessible biomimetic hydrogel that have been

generally used as matrices or scaffolds for bioprinting. Ideally, biopaper must be capable of rapid

solidification, be dispensible, functional with growth factors, non-toxic to enable high cell

viability (biocompatible), stimuli-sensitive and cross-linkable, capable of tissue fusion,

hydrophilic and able to maintain shape, biodegradable and low cost. Thus far, naturally derived

hydrogels such as collagen have been used. Improvements in the biomaterials used as bioinks

and biopaper are needed before real clinical application potential can be realized. It is necessary

to optimize bioinks such as their deformation and fluidic (rheological) and surface properties.

While studies have demonstrated the potential of dispensing and depositing single cells,

more difficulty lies in developing a standardized scalable fabrication method for the robotic

delivery of cell aggregates or tissue spheroids. Following that, biocartridge designs must also be

modified. There are important challenges in designing and fabricating a bioprinter that is

biologically "friendly" with rapid prototyping capabilities. Possible solutions that may address

and answer these challenges include the use of temporary, removable porous needles. These type

of needles may provide temporary mechanical support and perfusion of the printed scaffold

essential in the post-processing step. In addition, enhancing the ability to develop vascular

systems, these needles may enable the automatic printing of vascular-like tubular structures from

self-assembling cell aggregates or fused vascular spheroids.

It is not enough to be able to print an organ. It is necessary for the printed tissue construct

to undergo post-conditioning to acquire properties similar to native tissue. Bioreactors used in

classical tissue engineering research differ from the ideal bioreactor for bioprinting. The

bioreactor must meet a number of challenges including continuous perfusion, enabling

accelerated tissue maturation and functionality for intravascular perfusion initiation, maintaining

cell viability and vascularization, and dynamic biomechanical conditioning. Ideally, all

components in the biofabrication process should be smoothly integrated to allow for easy

transitioning of the tissue construct from the printed state (in a wet environment) to the post-

conditioning state (transfer to bioreactor). The use of modern software and manufacutring device

and process improvements with the aid of robotic biofabrication equipment may lead to

revolutionary changes in this area.

8. DISCUSSION

As bioprinters enter medical application, so replacement organs will be output to individual

patient specification. As every item printed will be created from a culture of a patient's own cells,

the risk of transplant organ rejection should be very low indeed. Together with developments

in nanotechnology and genetic engineering, bioprinting may also prove a powerful tool for those

in pursuit of life extension. Mainstream bioprinting will also inevitably drive further the New

Industrial Convergence, with doctors, engineers and computer scientists all increasingly learning

to manipulate living tissue at its most basic cellular level.

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