This work was supported by Government Support under Grant No. EPS-0903795 awarded by the National Science Foundation, NIH NIDCR R01-DE019355 (MJY PI), and Grant 8P20 GM103444 (YM PI).

1. Preparation of Gelatin Containing Substrate for Three-Dimensional Bioprinting of Alginate Hydrogels
<ol>
	<li>Prepare the calcium/gelatin substrate following the calcium/gelatin substrate method described by Pataky et al11 to avoid reduced viability associated with high content. The calcium/gelatin substrate method is listed below.
	<ol>
		<li>Combine calcium chloride dehydrate (1.5 wt%), sodium chloride (0.9 wt%), and porcine gelatin (2 wt%) in distilled water and boil for 2 min&#160;to create a...

<ol>
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The primary focus of tissue engineering is to bridge the gap between organ shortages and transplantation needs by developing biological substitutes capable of restoring, maintaining, or improving native tissue functio. This has led to the direct fabrication of scaffolds with a complex, anatomically correct external geometry, and precise control over the internal geometr. Three-dimensional bioprinting is a methodology used for generating three-dimensional constructs of various sizes and shapes from a digital model using a...

Tissue engineering uses the principles of biology and engineering in the development of functional substitutes to maintain, restore, or enhance native tissue and . The capability of generating three-dimensional biomimetic constructs on demand would facilitate scientific and technological advances in tissue engineering as well as in cell-based sensors, drug/toxicity screening, tissue or tumor models, and other . The three-dimensional organization of tissue-engineered constructs is a fundamental component of the fabrication method because it must closely mimic the highly organized interaction of cells and extracellular matrix in native tissue.
Biodegradable and shape-forming three-dimensional scaffolds are critical factors in generating novel tissue constructs because cells migrate to form a two-dimensional layer of cells, but lack the ability to grow in favored three-dimensional . The scaffold serves as a temporary foundation for cell attachment and proliferation, so it must be constructed from materials with controllable porosity and biodegradability, and sufficient mechanical integrit. The scaffold materials should not be cytotoxic or create an adverse response from the host. Hydrogels have been commonly used in tissue engineering techniques, and due to their hydrophilicity, hydrogels permit fluid and gas exchange throughout the structur. By combining different hydrogels, the synthesized hydrogel&#8217;s properties are modifiable to meet distinct application requirement.
The conventional tissue engineering approach involves the creation of acellular porous sacrificial scaffolds that are seeded with cells post-fabricatio. Many techniques have been employed, such as fiber bonding, solvent casting, and melt molding, but proved to be minimally successful for tissue engineering applications. Fiber bonding methods allow fibers to be aligned in specific shapes, but they are only capable of producing very thin scaffold. Solvent casting methods produced highly porous constructs, however the largest produced membrane was only 3-mm thic. Therefore, creating three-dimensional constructs is not feasible using these techniques. Melt molding techniques proved successful in producing three-dimensional scaffolds, but such high temperatures are required that biological materials cannot be incorporated during the production proces. Scaffolds seeded post-fabrication are limited in their ability to meet the requirements of tissue engineering to produce three-dimensional scaffolds with pre-defined or controllable microstructures and . Another major issue with solid scaffold seeding technologies is the deficiency of vascularization and poor mechanical .
Bioprinting has since been extended to three dimensions through the use of nontoxic, biodegradable, thermo-reversible gels to overcome the disadvantages of conventional . A few of the solid freeform fabrication techniques currently being employed are laser-assisted bioprinting and inkjet printing. Laser-assisted bioprinting techniques use a pulsed laser source, a target plate, and a receiving substrate to generate three-dimensional . However, this technique is limited due to low throughput, low cell viability, and can only produce limited arrangements of fabricated structures because only photocrosslinkable prepolymers can be used to form a crosslinked hydrogel . Inkjet printing was developed as a non-contact methodology that reproduces digital image data on a substrate by depositing picoliter ink . However, inkjet printing does not produce a high-resolution construct, constructs experience rapid protein denaturation, and many of the cells are lysed during the deposition .
Currently, new additive manufacturing bioprinting methods have been developed. In these systems cells, proteins, growth factors, and biomimetic hydrogels are typically integrated into matrix materials during the fabrication process and concurrently deposited using computer-controlled actuators to generate three-dimensional scaffold-based cell-laden constructs that closely mimic the microarchitecture of native . The cell-laden hydrogels constitute the bioink, which can be heterogeneous, consisting of multiple cell types, or homogeneous. Additive manufacturing systems deposit bioink drop-by-drop or layer-by-layer via disposable syringes and tips onto a computer-controlled stage capable of moving in the x, y, and z directions. Through computer software, the architecture of printed scaffolds can be easily manipulated depending on requirements of the application. Unlike conventional techniques, three-dimensional medical technologies (magnetic resonance imaging, computer tomography) can be incorporated into the designs, generating patient-specific construct. These methods also allow the possibility of producing vascularized replacements because constructs are produced with a higher local cell density, allowing cell-cell interactions and improving the likelihood of post-implantation surviva.
The Palmetto Printer is a custom built three-dimensional multi-dispenser system that uses programmable robotic manufacturing methods to generate three-dimensional heterogeneous tissue constructs (Figure 1). It allows the use of a plurality of materials in unique combinations to produce heterogeneous structures. The initialization of the bioprinter is one of the most important steps in bioprinting because it allows you to set a variety of parameters to optimize the printability of the bioprinted constructs.
The bioprinter comprises a batch type process with startup, operation and shutdown sequences controlled by a programmable logic controller (PLC), which the user operates through an interactive touch screen control panel (Figure 1,&#160;A). To prevent contamination of biological materials the bioprinter is enclosed in a positively-pressured poly(methyl methacrylate) (PMMA) chamber with a high-efficiency particulate arrestance (HEPA)-filtered air circulation system (Figure 1, B,C). The interior of the printer can be sterilized using the built-in ultraviolet light sources (Figure 1, D). The central component of the bioprinter is a fully programmable positioning robot that can reproducibly place a dispenser tip with an accuracy of 10 micrometers (Figure 1, E). There are three dispensers, which are able to deposit volumes as small as 230 nl using a rotary screw (Figure 1, F). They are independently programmable using separate computers that govern printing parameters for each dispenser (Figure 1, G). Rotary-screw dispensing utilizes the rotation of a motor-driven screw to move bioink down a syringe and out of the syringe tip. These dispensers are mounted onto a pneumatically controlled Tool Nest (Figure 2A, B), allowing the robot to switch dispenser mounted onto the Z-axis robotic arm under programmed control (Figure 1, H).
The XYZ robot receives printing instructions from a computer running design software (Figure 1, I). Each program contains dispensing locations, calibration routines, and dispenser-changing protocols. The design of generated constructs primarily consists of the XYZ coordinates where each dispenser will deposit material. The bioprinter comprises two optical light sensors (Figure 2C) that determine the XYZ coordinates of the syringe tip end. These sensors send coordinate information to the robot, which uses these to calculate positions of the dispenser tip ends. There is an additional displacement laser (Figure 2D) that projects a 633 nm diode red laser beam of spot size 30 x 100 micrometers to measure distance with an accuracy of 0.1 micrometers. When the beam is highly focused the robot determines the Z distance of the printing surface. This measurement, and the optical light sensors measurement of the tip end in Z, allows calculation of accurate Z coordinates used to place the dispenser tip in relation to the printing surface. The dispenser tips move laterally and vertically through the X-axis oriented optical light sensor to find the Y and Z centers, and laterally through a Y-axis sensor to find the center of the X-axis. The printing surface is mapped using the formula for a flat plane in xyz space: ax + by +cz = d to determine where the surface is relative to the position of the dispensing tip end. The printer stage (Figure 1, J) holds a sample Petri dish up to 80 mm in diameter and uses a recirculating water bath to maintain the set temperature (Figure 1, K). Stage temperature can be set within a range of -20 and remains stable within . There is a USB camera mounted onto the robot Z-arm to provide a magnified view of the dispensing tip during the printing process (Figure 1, L). There is a second camera mounted towards the top of the chamber interior that provides a complete view of the bioprinter during the printing process (Figure 1, L).
A computer-aided design drawing software determines the deposition pattern and permits the user to generate incrementally spaced droplets and complex structures (Figure 3). Three-dimensional pathways can be manually coded into the printer-compatible design software or imported from a separate computer-aided design drawing software (Figure 4, Table 1). The printer-compatible software allows variations of printing parameters such as the deposition method (single droplet deposition or continuous pathway deposition), three-dimensional geometry of the pathways, deposition rate, distance between the syringe tip end and substrate printing surface, the amount of time to deposit an individual drop, and the height and speed the syringe is lifted between deposition of the drops. Each program contains XYZ dispensing locations, tip calibration routines, and dispenser-changing protocols to provide a sterile environment, without operator intervention, during printing. The programmable logic controller (PLC) of the robot receives instructions from the computer running the design software and controls the timing of events from the external controllers (e.g.,&#160;the dispensers). To do this, the PLC uses a looping mechanism to control the dispensers, robotic positioning device, and environmental factors.
Three-dimensional direct-write bioprinting utilizing a rotary-screw, liquid-dispensing system allows the process of depositing cells to be more efficient, accurate, and easier than previous methods. This study shows the custom built bioprinter is capable of generating cell-laden hydrogel constructs with high cell viability.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Positioning Robot (JR2000 XYZ)</td>
			<td>Janome&#160;</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Dispensers: SDAV Linear Drive SmartDispensers</td>
			<td>Fishman Corporation</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Optical Light Sensors:&#160;</td>
			<td>Keyensce</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Displacement Laser: OD Mini</td>
			<td>SICK</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Recirculating Water Bath: Polystat</td>
			<td>Cole-Parmer</td>
			<td>EW-12122-02</td>
			<td></td>
		</tr>
		<tr>
			<td>USB Cameras: Dino-Lite Premier 5MP</td>
			<td>AnMo Electrionics/YSC Technologies</td>
			<td>AD7013MT</td>
			<td></td>
		</tr>
		<tr>
			<td>Printer-Compatible Computer Design Software: JR-C Points</td>
			<td>Janome</td>
			<td></td>
			<td>Comes with purchase of Janome Robot</td>
		</tr>
		<tr>
			<td>Computer-Aided Design Drawing Software: Visual PathBuilder</td>
			<td>RatioServ</td>
			<td></td>
			<td>Can be downloaded at: www.ratioserv.com/index.php/downloads</td>
		</tr>
		<tr>
			<td>Printer 3 cc Syringes:&#160;</td>
			<td>Fishman Corporation</td>
			<td>122051</td>
			<td></td>
		</tr>
		<tr>
			<td>22 G Dispenser Tips</td>
			<td>Fishman Corporation</td>
			<td>Z520122&#160;</td>
			<td></td>
		</tr>
		<tr>
			<td>Calcium Chloride Dihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>10035-04-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Chloride</td>
			<td>Sigma-Aldrich</td>
			<td>7647-14-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Porcine Gelatin</td>
			<td>Sigma-Aldrich</td>
			<td>9000-70-8</td>
			<td></td>
		</tr>
		<tr>
			<td>Titanium Dioxide</td>
			<td>Sigma-Aldrich</td>
			<td>13462-67-7</td>
			<td></td>
		</tr>
		<tr>
			<td>Protanal LF 20/40 Alginate (Sodium Alginate)</td>
			<td>FMC BioPolymer</td>
			<td>9005-38-3</td>
			<td></td>
		</tr>
		<tr>
			<td>Hydrochloric Acid</td>
			<td>Sigma-Aldrich</td>
			<td>7647-01-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethylene Glycol</td>
			<td>Mallinckrodt Baker, Inc</td>
			<td>9300-01</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium Periodate</td>
			<td>Sigma-Aldrich</td>
			<td>7790-28-5</td>
			<td></td>
		</tr>
		<tr>
			<td>hADSC</td>
			<td>Lonza</td>
			<td>PT-5006</td>
			<td>Store in vials in liquid nitrogen until use.</td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle&#39;s Medium</td>
			<td>Gibco Life Technologies</td>
			<td>11965-092</td>
			<td>Warm in 37&#176;C water before use.</td>
		</tr>
		<tr>
			<td>Trypsin/EDTA</td>
			<td>Lonza</td>
			<td>CC-5012</td>
			<td>Warm in 37&#176;C water before use.</td>
		</tr>
		<tr>
			<td>Calcein AM</td>
			<td>Gibco Life Technologies</td>
			<td>C3100MP</td>
			<td>Store in the dark at -80&#176;C until use.</td>
		</tr>
		<tr>
			<td>Live/Dead Mammalian Viability Assay Kit</td>
			<td>Invitrogen Life Technologies</td>
			<td>L-3224</td>
			<td>Store in the dark at -80&#176;C until use.</td>
		</tr>
		<tr>
			<td>MES Hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>M2933</td>
			<td></td>
		</tr>
		<tr>
			<td>N-Hydroxysuccinimide</td>
			<td>Sigma-Aldrich</td>
			<td>130672</td>
			<td></td>
		</tr>
		<tr>
			<td>1-ethyl-(dimethylaminopropyl) carbodiimide (EDC)</td>
			<td>Sigma-Aldrich</td>
			<td>E1769&#160;</td>
			<td>10 G</td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Phosphate-Buffered Saline, +Calcium, +Magnesium</td>
			<td>Life Technologies</td>
			<td>14040133</td>
			<td>Warm in 37&#176;C water before use.</td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Phosphate-Buffered Saline, -Calcium, -Magnesium</td>
			<td>Life Technologies</td>
			<td>14190144</td>
			<td>Warm in 37&#176;C water before use.</td>
		</tr>
		<tr>
			<td>RGD Peptides</td>
			<td>International Peptides</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Alexa Fluor 546 Phalloidin Stain</td>
			<td>Invitrogen Life Technologies</td>
			<td>A22283</td>
			<td>Store at -20&#176;C until use</td>
		</tr>
		<tr>
			<td>(4&#8217;, 6-Diamidino-2-Phenylindole, Dihydrochloride) (DAPI) Stain</td>
			<td>Life Technologies</td>
			<td>R37606</td>
			<td>Store at -20&#176;C until use</td>
		</tr>
	</tbody>
</table>

viability of bioprinted cellular constructs using a three dispenser cartesian printer

Tissue engineering has centralized its focus on the construction of replacements for non-functional or damaged tissue. The utilization of three-dimensional bioprinting in tissue engineering has generated new methods for the printing of cells and matrix to fabricate biomimetic tissue constructs. The solid freeform fabrication (SFF) method developed for three-dimensional bioprinting uses an additive manufacturing approach by depositing droplets of cells and hydrogels in a layer-by-layer fashion. Bioprinting fabrication is dependent on the specific placement of biological materials into three-dimensional architectures, and the printed constructs should closely mimic the complex organization of cells and extracellular matrices in native tissue. This paper highlights the use of the Palmetto Printer, a Cartesian bioprinter, as well as the process of producing spatially organized, viable constructs while simultaneously allowing control of environmental factors. This methodology utilizes computer-aided design and computer-aided manufacturing to produce these specific and complex geometries. Finally, this approach allows for the reproducible production of fabricated constructs optimized by controllable printing parameters.

The results demonstrate the bioprinter is capable of depositing cell-laden hydrogels in specific three-dimensional locations accurately and consistently using computer-aided software. These softwares determine the placement of each droplet and control many of the parameters for dispensing (Figure 3,4). The repeatability of the bioprinter to appropriately deposit biomaterials is fundamental to its success in tissue engineering applications.
Cell viability, one of the requiremen...

Watch this Scientific Journal Video about Viability of Bioprinted Cellular Constructs Using a Three Dispenser Cartesian Printer at JoVE.com

Viability of Bioprinted Cellular Constructs Using a Three Dispenser Cartesian Printer

A Cartesian bioprinter was designed and fabricated to allow multi-material deposition in precise, reproducible geometries, while also allowing control of environmental factors. Utilizing the three-dimensional bioprinter, complex and viable constructs may be printed and easily reproduced.

Tissue engineering has centralized its focus on the construction of replacements for non-functional or damaged tissue. The utilization of ...

viability-bioprinted-cellular-constructs-using-three-dispenser

Research

JoVE Journal

Bioengineering

9.9K vistas.  Medical University of South Carolina. A Cartesian bioprinter was designed and fabricated to allow multi-material deposition in precise, reproducible geometries, while also allowing control of environmental factors. Utilizing the three-dimensional bioprinter, complex and viable constructs may be printed and easily reproduced.