Name: printing thermoresponsive reverse molds for the creation of patterned two-component hydrogels for 3d cell culture
Uploaded: 2013-07-10T14:00:00
Description: Watch this Scientific Journal Video about Printing Thermoresponsive Reverse Molds for the Creation of Patterned Two-component Hydrogels for 3D Cell Culture at JoVE.com

We thank Deborah Studer for the help with the bioprinter.
The work was funded by the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n&deg;NMP4-SL-2009-229292.

1. Preparation of the Poloxamer 407 Solution
If available, perform the preparation of the poloxamer solution in a cold room (4 &deg;C). If not available, place a glass bottle in a beaker filled with ice-cold water. At higher temperatures the poloxamer will be above the gel point and will not dissolve properly.
<ol>
	<li>Add 60 ml of ice cold PBS solution into a glass bottle and stir vigorously using a magnetic stirrer.</li>
	<li>Weigh 24.5 grams of poloxamer and add it in small amounts t...

<ol>
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Here we present, for the first time, the use of a thermoresponsive polymer for a sacrificial mold that can be quickly eluted in cold water due to the gel-sol transition of poloxamer of ~20 &deg;C. The speed of the entire process makes poloxamer interesting for the rapid creation of biopolymer structures which cannot be printed with adequate resolution. The technique described here can be used for patterning one hydrogel within another hydrogel or for the creation of microfluidic channels as has been previously reported f...

Tissue engineering approaches have made much progress over the last years with respect to regeneration of human tissues and organs19,20. However, until now, the focus of tissue engineering has been often limited to tissues that have a simple structure or small dimensions such as the bladder21,22 or the skin23-25. The human body, however, contains many complex three-dimensional tissues where cells and extracellular matrix are arranged in a spatially defined manner. To manufacture these tissues, a technique is required that can place cells and extracellular matrix scaffolding within a three-dimensional construct at specified positions. Bioprinting has the potential to be such a technique where the vision of manufacturing complex three-dimensional tissues can be realized10,11,26-28.
Bioprinting is defined as "the use of material transfer processes for patterning and assembling biologically relevant materials - molecules, cells, tissues, and biodegradable biomaterials - with a prescribed organization to accomplish one or more biological functions"4. It encompasses several different techniques that work at different resolutions and length scales, ranging from the sub-micron resolution of two-photon polymerization29 to a resolution of 150 &mu;m to 420 &mu;m for extrusion printing1,12,30. Not a single material or material combination will satisfy the requirements of each method31. For extrusion printing, the key parameters are viscosity and gelation time32, where high viscosity and rapid gelation are desirable.
3D printing is a technique which allows the easy creation of sacrificial molds for creating complex geometries30,33,34. This process is based on the construction of a mold using a rapid prototyping technique such as an extrusion bioprinter. The created sacrificial mold is used to form complex structures from materials which are difficult to print due to their low viscosity and slow gelation time. The method presented here involves the creation of a sacrificial mold consisting of a material that dissolves quickly at low temperature and can be extruded accurately. The block copolymer poly(ethylene glycol)99-poly(propylene glycol)67-poly(ethylene glycol)99 (also known as Pluronic F127 or poloxamer 407) fulfills these requirements. It has already been used in a modified version in extrusion printing1 but, to our knowledge, has never been used for printing in its unmodified version due to its instability in liquid environments. Poloxamer 407 also shows an inverse thermal responsive behavior18 i.e. it changes from a gel to a sol upon cooling. Most importantly, it can be printed into complex arbitrarily curved structures with very high fidelity. This allows the creation of a structured hydrogel from a low viscosity material, in this case slow gelling agarose, by pipetting the solution into the printed sacrificial mold. The combination of printing the sacrificial mold with high fidelity and its quick elution from the casted structured hydrogel makes it a fast and flexible method to create molds with different geometries without the use of a mask or a stamp as it is often required in lithographic methods. The casted structured hydrogel can be further filled with another material that is not suitable for extrusion printing due to its low viscosity. This is in our case a low viscosity alginate methacrylate solution. Here we present the method of thermoresponsive reverse sacrificial molds for hydrogel patterning using the example of a pillar array.

<table border="1">
 <tbody>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>REAGENTS</td>
 </tr>
 <tr>
 <td>Poloxamer (Pluronic F127)</td>
 <td>Sigma</td>
 <td>P2443</td>
 <td ></td>
 </tr>
 <tr>
 <td>PBS</td>
 <td>Invitrogen</td>
 <td><a href="http://products.invitrogen.com/ivgn/en/US/adirect/invitrogen?cmd=catProductDetail&amp;productID=10010015" target="_blank">10010-015</a></td>
 <td ></td>
 </tr>
 <tr>
 <td>CAD software</td>
 <td>regenHU</td>
 <td>BioCAD</td>
 <td ></td>
 </tr>
 <tr>
 <td>Alginate methacrylate</td>
 <td>Innovent e.V Technologieentwicklung Jena</td>
 <td></td>
 <td >Synthesized by Innovent for the FP7 Project Nr NMP4-SL-2009-229292</td>
 </tr>
 <tr>
 <td>Fibrinogen From Human Plasma, Alexa Fluor 488 Conjugate</td>
 <td>Invitrogen</td>
 <td>F13191</td>
 <td ></td>
 </tr>
 <tr>
 <td>Lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP)</td>
 <td>Innovent e.V Technologieentwicklung Jena</td>
 <td></td>
 <td >Synthesized by Innovent for the FP7 Project Nr NMP4-SL-2009-229292</td>
 </tr>
 <tr>
 <td>Agarose</td>
 <td>Lonza</td>
 <td>50004</td>
 <td ></td>
 </tr>
 <tr>
 <td></td>
 <td></td>
 <td></td>
 <td>EQUIPMENT</td>
 </tr>
 <tr>
 <td>Bioprinter</td>
 <td>regenHU</td>
 <td>Biofactory</td>
 <td ></td>
 </tr>
 <tr>
 <td>Valve</td>
 <td>regenHU</td>
 <td>300 &mu;m Nozzel Diameter</td>
 <td ></td>
 </tr>
 <tr>
 <td>Needle</td>
 <td>regenHU</td>
 <td>150 &mu;m Inner Diameter</td>
 <td ></td>
 </tr>
 <tr>
 <td>Zeiss Axioobserver with ApoTome</td>
 <td>Zeiss</td>
 <td></td>
 <td ></td>
 </tr>
 <tr>
 <td>UV Light Source</td>
 <td>UVP</td>
 <td>Blak-Ray B-100AP High Intensity UV Lamp</td>
 <td>100 W</td>
 </tr>
 </tbody>
</table>

printing thermoresponsive reverse molds for the creation of patterned two-component hydrogels for 3d cell culture

Bioprinting is an emerging technology that has its origins in the rapid prototyping industry. The different printing processes can be divided into contact bioprinting1-4 (extrusion, dip pen and soft lithography), contactless bioprinting5-7 (laser forward transfer, ink-jet deposition) and laser based techniques such as two photon photopolymerization8. It can be used for many applications such as tissue engineering9-13, biosensor microfabrication14-16 and as a tool to answer basic biological questions such as influences of co-culturing of different cell types17. Unlike common photolithographic or soft-lithographic methods, extrusion bioprinting has the advantage that it does not require a separate mask or stamp. Using CAD software, the design of the structure can quickly be changed and adjusted according to the requirements of the operator. This makes bioprinting more flexible than lithography-based approaches.
Here we demonstrate the printing of a sacrificial mold to create a multi-material 3D structure using an array of pillars within a hydrogel as an example. These pillars could represent hollow structures for a vascular network or the tubes within a nerve guide conduit. The material chosen for the sacrificial mold was poloxamer 407, a thermoresponsive polymer with excellent printing properties which is liquid at 4 &deg;C and a solid above its gelation temperature ~20 &deg;C for 24.5% w/v solutions18. This property allows the poloxamer-based sacrificial mold to be eluted on demand and has advantages over the slow dissolution of a solid material especially for narrow geometries. Poloxamer was printed on microscope glass slides to create the sacrificial mold. Agarose was pipetted into the mold and cooled until gelation. After elution of the poloxamer in ice cold water, the voids in the agarose mold were filled with alginate methacrylate spiked with FITC labeled fibrinogen. The filled voids were then cross-linked with UV and the construct was imaged with an epi-fluorescence microscope.

The representative results show that the reverse mold technique (depicted in Figure 2) will create a structured gel that can be filled with a second material. At the beginning of every printing process the printing parameters are first optimized. Step-wise adjustments of the parameters will result in printed multilayered constructs depicted in Figure 3 and Figure 4 when single lines are printed. If the layer thickness (the needle lift after one printed layer) is too low,...

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Printing Thermoresponsive Reverse Molds for the Creation of Patterned Two-component Hydrogels for 3D Cell Culture

A bioprinter was used to create patterned hydrogels based on a sacrificial mold. The poloxamer mold was backfilled with a second hydrogel and then eluted, leaving voids which were filled with a third hydrogel. This method uses fast elution and good printability of poloxamer to generate complex architectures from biopolymers.

Bioprinting is an emerging technology that has its origins in the rapid prototyping industry. The different printing processes can be divided into contact ...

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