Name: three-dimensional biomimetic technology: novel biorubber creates defined micro- and macro-scale architectures in collagen hydrogels
Uploaded: 2016-02-12T14:00:00
Description: Watch this Scientific Journal Video about Three-dimensional Biomimetic Technology: Novel Biorubber Creates Defined Micro- and Macro-scale Architectures in Collagen Hydrogels at JoVE.com

This work was supported by NIH-NIDCR IRO1DE019355 (MJ Yost, PI), and NSF-EPSCoR (EPS-0903795).

1. Determine the Percentage of Solids in the Collagen Batch
<ol>
	<li>Extract the collagen following a previously published procedure13. Thaw a minimum of 20 ml of collagen. Determine the initial percentage of collagen solids in the batch in order to manipulate the collagen concentration in the formed hydrogels.
	<ol>
		<li>Cut three pieces of aluminum foil (about 6 x 6 cm) and shape each one as a pan by using the bottom of a 25 ml beaker. Record the weight of each pan.</li>
		<li>Add a small amount of colla...

<ol>
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Biofabrication is a highly multidisciplinary field in which biology and engineering principles merge to generate complex materials that mimic native tissue. In order to achieve this, there is a need to develop techniques that use the information gathered from in vivo tissue and translate it into an in vitro scaffold. In this way, a platform can be engineered that closely resembles the architectural, functional, and mechanical properties of the in vivo tissue. The optimal scaffolding material sh...

In the tissue engineering field the ability to fabricate tissue scaffolds is vital. A suitable tissue scaffold has a 3D structure, is composed of biocompatible materials, and mimics in vivo tissue architecture to facilitate cell and tissue growth and remodeling. This scaffold must allow the transport of nutrients and the removal of wastes1-4. One of the main obstacles in the production of these scaffolds is the ability to recapitulate specific geometrical features into a biocompatible material. Several biofabrication techniques have been reported to control the geometrical features of these scaffolds, examples are electrospinning5-8, solvent-casting9, stereolithography10, and 3D-printing11, among others. These techniques fall short in providing a relatively easy transfer of controllable internal and external architectural features, are expensive, are limited by their resolution and printability (e.g., nozzle gauge, material restriction), or require post-fabrication techniques which demands a long period of time to produce viable scaffolds12.
In many commercial fabrication systems, the creation of internal voids, channels, and features is achieved using sand or other suitable removable or sacrificial materials. The metal or plastic part is formed around the sand mold, and once it is solidified, the sand is removed. In much the same manner, the next generation of biomaterials needs the biosand equivalent. Therefore, the BSA rubber was developed as a substitute for biosand. The BSA rubber is a newly formulated material that consists of bovine serum albumin crosslinked with glutaraldehyde. The ultimate goal is to recreate specific architectural features into a biodegradable collagen scaffold. The characteristics of the sacrificial biorubber that maintains dimensional fidelity with the mold of the original tissue are described.
Several combinations of BSA and glutaraldehyde concentrations were tested using a variety of solvents. This material was created by the reaction between BSA and glutaraldehyde. BSA rubber can be reaction injected into the intricate geometries of the tissue molds. Crosslinked BSA is trypsin labile and readily digested by the enzyme at mild pH and temperature conditions. Conversely, intact type I collagen is very resistant to trypsin digestion. These features were capitalized to selectively remove the BSA rubber leaving the collagen behind. The present work consisted of determining the ideal parameters needed to obtain a labile mold that can deliver specific architectural features to a biocompatible scaffold. The specific features that were evaluated included mixability, enzyme digestion, load bearing, and ability to be reaction injected into a negative mold. The combination of 30% BSA and 3% glutaraldehyde fulfills these requirements. This protocol provides the necessary guidelines to create these three-dimensional scaffolds. The prototype consists of a collagen scaffold that represents a branched architecture with one inflow and two outflow channel with diameters of 4- and 3-mm, respectively. This technique has the potential to mimic macro- and micro-environments of the tissue of interest. This technology provides a viable technique to deliver a specific geometrical instructive to a biodegradable material in a relatively easy and timely matter with high fidelity, which can be tuned to mimic the in vivo tissue elasticity and other characteristics of the tissue of interest.

<table border="0" cellpadding="0" cellspacing="0" width="770">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:281px;">Collagen type I</td>
			<td style="width:156px;"></td>
			<td style="width:116px;"></td>
			<td style="width:217px;">Collagen extracted from calf hide</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hydrocloric Acid (HCl)</td>
			<td>Sigma-Aldrich</td>
			<td>7647-01-0</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Phosphate Buffer Solution (PBS Tablets)</td>
			<td>MP Biomedical</td>
			<td>U5378</td>
			<td>1 tablet per 100 mL makes 1XPBS</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Albumium from bovine serum (BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>A9647</td>
			<td></td>
		</tr>
		<tr height="19">
			<td height="19" style="height:19px;">Glutaraldehyde</td>
			<td>Sigma -Aldrich</td>
			<td>G5882</td>
			<td>Toxic</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Lard</td>
			<td>Fields</td>
			<td>3090</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Stainless Steel Molds</td>
			<td></td>
			<td></td>
			<td>Milled using Microlution Machine</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Air Brush Kit</td>
			<td>Central Pneumatic</td>
			<td>47791</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Mixing Tip for double syringe</td>
			<td>Medmix</td>
			<td>ML2.5-16-LLM</td>
			<td>Mixer, DN2,5X16, 4:1 brown, med</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Small O ring for double syringe</td>
			<td>Medmix</td>
			<td>PPB-X05-04-02SM</td>
			<td>Piston B, 5mL, 4:1, PE natural</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Double Syringe cap&#160;</td>
			<td>Medmix</td>
			<td>VLX002-SM</td>
			<td>Cap, 4:1/10:1, PE brown, med</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Big O ring for double syringe</td>
			<td>Medmix</td>
			<td>PPA-X05-04-02SM</td>
			<td>Piston A, 5 mL, 4:1</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Double Syringe&#160;</td>
			<td>Medmix</td>
			<td>SDL X05-04-50M</td>
			<td>Double syringe, 5 mL, 4:1</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Double Syringe Dispenser</td>
			<td>Medmix</td>
			<td>DL05-0400M</td>
			<td>Dispenser, 5 mL, 4:1, med , plain</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Laminim</td>
			<td></td>
			<td></td>
			<td>3.6 mg/mL- extracted USC lab</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">20 mL Syringe Luer Lock Tip</td>
			<td>BD</td>
			<td>302830</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Luer Lock Caps</td>
			<td>Fisher</td>
			<td>JGTCBLLX</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">HEPES</td>
			<td>Sigma -Aldrich</td>
			<td>H4034</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gibco Minimum Essential Media 10X (MEM)</td>
			<td>&#160;Life Technologies</td>
			<td>1143-030</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Trypsin</td>
			<td>Life Technologies</td>
			<td>27250-018</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">UV Crosslinker&#160;</td>
			<td>Spectroline UV</td>
			<td>XLE1000</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sodium Cloride (NaCl)</td>
			<td>Fisher</td>
			<td>S271-10</td>
			<td>To prepare Mosconas</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Potassium chloride (KCl)</td>
			<td>Sigma -Aldrich</td>
			<td>P5405-250</td>
			<td>To prepare Mosconas</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Sodium Bicarbonate (NaHCO3)</td>
			<td>Fisher</td>
			<td>BP328-500</td>
			<td>To prepare Mosconas</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Glucose</td>
			<td>Sigma -Aldrich</td>
			<td>G-8270</td>
			<td>To prepare Mosconas</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Sodium Phosphate didasic (NaH2PO4)</td>
			<td>Sigma-Aldrich</td>
			<td>S-7907</td>
			<td>To prepare Mosconas</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sterile Filter for syringes</td>
			<td>Corning</td>
			<td>431224</td>
			<td></td>
		</tr>
	</tbody>
</table>

three-dimensional biomimetic technology: novel biorubber creates defined micro- and macro-scale architectures in collagen hydrogels

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper composition, targeted modulus, and well-defined architectural features. Biomaterials that recapitulate the intrinsic architecture of in vivo tissue are vital for studying diseases as well as to facilitate the regeneration of lost and malformed soft tissue. A novel biofabrication technique was developed which combines state of the art imaging, three-dimensional (3D) printing, and selective enzymatic activity to create a new generation of biomaterials for research and clinical application. The developed material, Bovine Serum Albumin rubber, is reaction injected into a mold that upholds specific geometrical features. This sacrificial material allows the adequate transfer of architectural features to a natural scaffold material. The prototype consists of a 3D collagen scaffold with 4 and 3 mm channels that represent a branched architecture. This paper emphasizes the use of this biofabrication technique for the generation of natural constructs. This protocol utilizes a computer-aided software (CAD) to manufacture a solid mold which will be reaction injected with BSA rubber followed by the enzymatic digestion of the rubber, leaving its architectural features within the scaffold material.

The results demonstrate that this biofabrication technique is efficient in generating 3D scaffolds that can mimic the spatial arrangement seen in in vivo tissue. The architectural features are vital parameters for tissue engineering application, playing a crucial role in the in vivo cell interaction and functionality of the tissue.
The consistency and mixability of the BSA rubber was an important parameter in p...

Watch this Scientific Journal Video about Three-dimensional Biomimetic Technology: Novel Biorubber Creates Defined Micro- and Macro-scale Architectures in Collagen Hydrogels at JoVE.com

Three-dimensional Biomimetic Technology: Novel Biorubber Creates Defined Micro- and Macro-scale Architectures in Collagen Hydrogels

An innovative biofabrication technique was developed to engineer three-dimensional constructs that resemble the architectural features, components, and mechanical properties of in vivo tissue. This technique features a newly developed sacrificial material, BSA rubber, which transfers detailed spatial features, reproducing the in vivo architectures of a wide variety of tissues.

Tissue scaffolds play a crucial role in the tissue regeneration process. The ideal scaffold must fulfill several requirements such as having proper ...

The overall goal of this protocol is to engineer three dimensional collagen scaffolds that can resemble the architectural features, composition, and mechanical properties of in-vivo tissue. This method can help answer key questions in the tissue engineering field, such as ECM cell interactions, the influence of architectural features in the creation of engineered tissues, and the development of tissue replacements, among others. The main advantage of this technique is that it provides a viable procedure to recapitulate the microgeometry of interior flow channels and paths with high fidelity in a biodegradable material.Demonstrating the procedure will be Veronica Rodriguez-Rivera, a post-doctoral associate in my laboratory. The materials used to prepare the BSA rubber must be stored and kept cold until they are ready to use so that the BSA rubber does not prematurely set. Sterility is also very important to this procedure.First, sterilize the dispenser. In a non-cell culture hood, lay out the O rings, the syringe, its cap, the mix tip, and the four-to-one dispenser. UV sterilize these materials for 30 minutes.First, screw the two stainless steel mold pieces together and attach the Luer lock. Before assembling the dispenser, spray pipettes and reagents prior to introducing them to the hood with 70%ethanol. First attach the tip cap to the solution holder.Next, load the 30%BSA solution into the larger chamber without contaminating the other chamber. Leave enough room to attach the O ring. Then, load the smaller dispenser chamber with three percent glutaraldehyde and attach another O ring.Now, attach the syringe to the dispenser. Then tilt the assembly so the cap is on top, and replace the cap with a mixing tip. Then gently tap the sides to allow the air bubbles to travel upwards.Next, place the dispenser inside of an autoclaved bag to contain the exhaust solution. In the bag, with the dispenser upright, dispense a small amount of solution to clear all the air from the syringe. Removing the air is very important.Then, quickly, attach the stainless steel Y mold's Luer lock to the syringe tip. Now, with the mold in your non-dominant hand, alternate ejecting solution into the left and right exhausts of the outflow channels. Press the exhausts, thus filling the internal voids with solution.Then, position the mold horizontally and inject it with more solution until half the dispenser volume has been used. The mold should now be placed into a dish, wrapped in parafilm, and stored at four degrees Celsius overnight. This procedure is scaled to four grams of acidified collagen.Keep it chilled until it is used. After the collagen has been weighted, proceed to sterilize the solution by gamma radiation. In preparation, make fresh 0.2 normal HEPES solution in water.Then transfer the contents to a 50 milliliter conical tube. Adjust the pH to nine using concentrated sodium hydroxide. Be sure to UV-sterilize the hood and autoclave the forceps, spatula, and scalpel.In the hood, mix 1.5 milliliters of the HEPES solution with 1.5 milliliters of 10x MEM. Store this mixture on ice. Also, chill a 12 well plate and a 20 milliliter syringe in the freezer for 10 minutes.For added sterility, spray the tubes and plates involved with 70%ethanol prior to placing them in the hood. Spray the mold plate, and place it in the hood. Then, remove the BSA rubber molds with forceps.Then, cut the exhaust channels off the mold using a scalpel. Next, briefly vortex the HEPES-MEM mixture and add one milliliter to the collagen. Then, thoroughly mix the solution with a sterile spatula.Follow with a brief vortex, and quickly transfer the solution to the cold, 20 milliliter syringe. Now, while securing the BSA rubber inside of the well, dispense half the collagen hydrogel solution into the well bottom. Next, using tweezers, position the mold so that the rubber inflow and outflow ends are touching the walls of the well.Then, cover the mold with collagen hydrogel. Now, seal the well with parafilm, and load the plate into a 37 degree Celsius incubator. Allow one hour for the collagen to polymerize.During this time, keep the UV light in the hood on. Also, set the UV crosslinking apparatus to deliver 630, 000 microjoules per square centimeter. Now, spray down your gloved hands with 70%ethanol, and load the plate with the collagen covered molds into the crosslinker, and start the irradiation process.After the irradiation, spray your gloves again, and unload the plate from the crosslinker. Then, using a sterile spatula, remove the gel from the well flip it over, and crosslink the bottom of the hydrogel. After the final crosslinking cycle, proceed with the enzyme digestion.To remove the BSA rubber without disturbing the collagen scaffold, use sterile 0.25%trypsin solution at pH 7.8 and press it through a 0.20 micron filter. Transfer enough filtered trypsin solution to a new 50 milliliter conical tube. Then, transfer the collagen hydrogel to the conical tube that contains the enzyme solution.Make sure that the hydrogel is completely covered with the solution. Seal the tube with parafilm, and vortex it gently for about a minute. Then, incubate the tube at 30 degrees Celsius and let the digestion go for 15 to 24 hours.For the first four hours, remove the tube every 15 to 30 minutes and gently vortex it to help complete the BSA rubber digestion. The next day, the digestion is considered complete when no rubber floats in the solution or there are no broken down pieces of the rubber in the hydrogel. Now, replace the trypsin solution with sterile Mosconas solution, and let the tube shake at four degrees Celsius for 30 minutes.Later, aspirate the Mosconas solution and repeat this step two more times to fully clean the collagen scaffold. An extensive number of tests were used to optimize the use of the biorubber and described in detail in the text protocol. Using the optimized protocol and three solid mold pieces, collagen hydrogels were fabricated and examined in detail.The Y mold needed was crafted on a Microlution machine. The Y mold was injected with 30%BSA and three percent glutaraldehyde, which reacted overnight at four degrees Celsius. Next, the BSA rubber was casted with the collagen and heated to 37 degrees Celsius for an hour.The rubber was enzyme digested for 15 hours, which weakened it to the point of falling off without affecting the geometry of the collagen hydrogel. The four millimeter inflow channel cast by the mold was measured with calipers to be precisely four millimeters in the collagen hydrogel. Testing the stability of the mold, it was found that dimensions as small as 300 microns could be reliably engineered.In addition, the scaffolds were tested for residual glutaraldehyde after the Mosconas washes, and no residue was found. After watching this video, you should have a good understanding of how to fabricate 3D collagen scaffolds with the potential to mimic in-vivo geometries. Following this procedure, other methods that complement this technique, such as creating 3D models of in-vivo tissues and fabricating molds with specific architectural features can be performed to answer additional questions.After its development, this technique paved the way for researchers in the field of tissue engineering to explore the interaction between internal architectural features and matrix components with cells in in-vitro models.

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Research

JoVE Journal

Bioengineering

Fabrication of Micro-tissues using Modules of Collagen Gel Containing Cells

This protocol describes the fabrication of a type of micro-tissues called modules.  The module approach generates uniform, scalable and vascularized tissues.  The modules can be made of collagen as well as other gelable or crosslinkable materials.  They are approximately 2 mm in length and 0.7 mm in diameter upon fabrication but shrink in size with embedded cells or when the modules are coated with endothelial cells.  The modules individually are small enough that the embedded cells are within the diffusion limit of oxygen and other nutrients but modules can be packed together to form larger tissues that are perfusable.  These tissues are modular in construction because different cell types can be embedded in or coated on the modules before they are packed together to form complex tissues.  There are three main steps to making the modules: (1) neutralizing the collagen and embedding cells in it, (2) gelling the collagen in the tube and cutting the modules and (3) coating the modules with endothelial cells.

Creation of micro-tissues using cylindrical collagen gels, called modules, that contain embedded cells and which surface is coated with endothelial cells.

This protocol describes the fabrication of a type of micro-tissues called modules.  The module approach generates uniform, scalable and vascularized ...

Three-dimensional Optical-resolution Photoacoustic Microscopy

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As the mainstays of in vivo three-dimensional (3-D) optical microscopy, single-/multi-photon fluorescence microscopy and optical coherence tomography (OCT) have demonstrated their extraordinary sensitivities to fluorescence and optical scattering contrasts, respectively. However, the optical absorption contrast of biological tissues, which encodes essential physiological/pathological information, has not yet been assessable. 
The emergence of biomedical photoacoustics has led to a new branch of optical microscopy optical-resolution photoacoustic microscopy (OR-PAM)1, where the optical irradiation is focused to the diffraction limit to achieve cellular1 or even subcellular2 level lateral resolution. As a valuable complement to existing optical microscopy technologies, OR-PAM brings in at least two novelties. First and most importantly, OR-PAM detects optical absorption contrasts with extraordinary sensitivity (i.e., 100%). Combining OR-PAM with fluorescence microscopy3 or with optical-scattering-based OCT4 (or with both) provides comprehensive optical properties of biological tissues. Second, OR-PAM encodes optical absorption into acoustic waves, in contrast to the pure optical processes in fluorescence microscopy and OCT, and provides background-free detection. The acoustic detection in OR-PAM mitigates the impacts of optical scattering on signal degradation and naturally eliminates possible interferences (i.e., crosstalks) between excitation and detection, which is a common problem in fluorescence microscopy due to the overlap between the excitation and fluorescence spectra. 
Unique for optical absorption imaging, OR-PAM has demonstrated broad biomedical applications since its invention, including, but not limited to, neurology5, 6, ophthalmology7, 8, vascular biology9, and dermatology10. In this video, we teach the system configuration and alignment of OR-PAM as well as the experimental procedures for in vivo functional microvascular imaging.

Optical-resolution photoacoustic microscopy (OR-PAM) is an emerging technology capable of imaging optical absorption contrasts in vivo with cellular resolution and sensitivity. Here, we provide a visualized instruction on the experimental protocols of OR-PAM, including system configuration, system alignment, typical in vivo experimental procedures, and functional imaging schemes.

Optical microscopy, providing valuable insights at the cellular and organelle levels, has been widely recognized as an enabling biomedical technology. As ...

Alginate Hydrogels for Three-Dimensional Organ Culture of Ovaries and Oviducts

Ovarian cancer is the fifth leading cause of cancer deaths in women and has a 63% mortality rate in the United States1. The cell type of origin for ovarian cancers is still in question and might be either the ovarian surface epithelium (OSE) or the distal epithelium of the fallopian tube fimbriae2,3. Culturing the normal cells as a primary culture in vitro will enable scientists to model specific changes that might lead to ovarian cancer in the distinct epithelium, thereby definitively determining the cell type of origin. This will allow development of more accurate biomarkers, animal models with tissue-specific gene changes, and better prevention strategies targeted to this disease.
Maintaining normal cells in alginate hydrogels promotes short term in vitro culture of cells in their three-dimensional context and permits introduction of plasmid DNA, siRNA, and small molecules. By culturing organs in pieces that are derived from strategic cuts using a scalpel, several cultures from a single organ can be generated, increasing the number of experiments from a single animal. These cuts model aspects of ovulation leading to proliferation of the OSE, which is associated with ovarian cancer formation. Cell types such as the OSE that do not grow well on plastic surfaces can be cultured using this method and facilitate investigation into normal cellular processes or the earliest events in cancer formation4.
Alginate hydrogels can be used to support the growth of many types of tissues5. Alginate is a linear polysaccharide composed of repeating units of &beta;-D-mannuronic acid and &alpha;-L-guluronic acid that can be crosslinked with calcium ions, resulting in a gentle gelling action that does not damage tissues6,7. Like other three-dimensional cell culture matrices such as Matrigel, alginate provides mechanical support for tissues; however, proteins are not reactive with the alginate matrix, and therefore alginate functions as a synthetic extracellular matrix that does not initiate cell signaling5. The alginate hydrogel floats in standard cell culture medium and supports the architecture of the tissue growth in vitro.
A method is presented for the preparation, separation, and embedding of ovarian and oviductal organ pieces into alginate hydrogels, which can be maintained in culture for up to two weeks. The enzymatic release of cells for analysis of proteins and RNA samples from the organ culture is also described. Finally, the growth of primary cell types is possible without genetic immortalization from mice and permits investigators to use knockout and transgenic mice.

Culture of normal cells in their three-dimensional context represents an alternative method to study early events required for cellular transformation and tumorigenesis. This method is used to grow normal ovarian and oviductal cells to study early events in ovarian cancer formation.

Ovarian cancer is the fifth leading cause of cancer deaths in women and has a 63% mortality rate in the United States1. The cell type of origin for ...

Planar and Three-Dimensional Printing of Conductive Inks

Printed electronics rely on low-cost, large-area fabrication routes to create flexible or multidimensional electronic, optoelectronic, and biomedical devices1-3. In this paper, we focus on one- (1D), two- (2D), and three-dimensional (3D) printing of conductive metallic inks in the form of flexible, stretchable, and spanning microelectrodes.
Direct-write assembly4,5 is a 1-to-3D printing technique that enables the fabrication of features ranging from simple lines to complex structures by the deposition of concentrated inks through fine nozzles (~0.1 - 250 &mu;m). This printing method consists of a computer-controlled 3-axis translation stage, an ink reservoir and nozzle, and 10x telescopic lens for visualization. Unlike inkjet printing, a droplet-based process, direct-write assembly involves the extrusion of ink filaments either in- or out-of-plane. The printed filaments typically conform to the nozzle size. Hence, microscale features (&lt; 1 &mu;m) can be patterned and assembled into larger arrays and multidimensional architectures.
In this paper, we first synthesize a highly concentrated silver nanoparticle ink for planar and 3D printing via direct-write assembly. Next, a standard protocol for printing microelectrodes in multidimensional motifs is demonstrated. Finally, applications of printed microelectrodes for electrically small antennas, solar cells, and light-emitting diodes are highlighted.

Planar and three-dimensional printing of conductive metallic inks is described. Our approach provides new avenues for fabricating printed electronic, optoelectronic, and biomedical devices in unusual layouts at the microscale.

Printed electronics rely on low-cost, large-area fabrication routes to create flexible or multidimensional electronic, optoelectronic, and biomedical ...

Cell Patterning on Photolithographically Defined 
Parylene-C: SiO2 Substrates

Cell patterning platforms support broad research goals, such as construction of predefined in vitro neuronal networks and the exploration of certain central aspects of cellular physiology. To easily combine cell patterning with Multi-Electrode Arrays (MEAs) and silicon-based &#8216;lab on a chip&#8217; technologies, a microfabrication-compatible protocol is required. We describe a method that utilizes deposition of the polymer parylene-C on SiO2&#160;wafers. Photolithography enables accurate and reliable patterning of parylene-C at micron-level resolution. Subsequent activation by immersion in fetal bovine serum (or another specific activation solution) results in a substrate in which cultured cells adhere to, or are repulsed by, parylene or SiO2 regions respectively. This technique has allowed patterning of a broad range of cell types (including primary murine hippocampal cells, HEK 293 cell line, human neuron-like teratocarcinoma cell line, primary murine cerebellar granule cells, and primary human glioma-derived stem-like cells). Interestingly, however, the platform is not universal; reflecting the importance of cell-specific adhesion molecules. This cell patterning process is cost effective, reliable, and importantly can be incorporated into standard microfabrication (chip manufacturing) protocols, paving the way for integration of microelectronic technology.

Cell Patterning on Photolithographically Defined 
Parylene-C: SiO2 Substrates

This protocol describes a microfabrication-compatible method for cell patterning on SiO2. A predefined parylene-C design is photolithographically printed on SiO2 wafers. Following incubation with serum (or other activation solution) cells adhere specifically to (and grow according to the conformity of) underlying parylene-C, whilst being repulsed by SiO2 regions.

Cell patterning platforms support broad research goals, such as construction of predefined in vitro neuronal networks and the exploration of certain ...

Human Cartilage Tissue Fabrication Using Three-dimensional Inkjet Printing Technology

Bioprinting, which is based on thermal inkjet printing, is one of the most attractive enabling technologies in the field of tissue engineering and regenerative medicine. With digital control&#160;cells, scaffolds, and growth factors can be precisely deposited to the desired two-dimensional (2D) and three-dimensional (3D) locations rapidly. Therefore, this technology is an ideal approach to fabricate tissues mimicking their native anatomic structures. In order to engineer cartilage with native zonal organization, extracellular matrix composition (ECM), and mechanical properties, we developed a bioprinting platform using a commercial inkjet printer with simultaneous photopolymerization capable for 3D cartilage tissue engineering. Human chondrocytes suspended in poly(ethylene glycol) diacrylate (PEGDA) were printed for 3D neocartilage construction via layer-by-layer assembly. The printed cells were fixed at their original deposited positions, supported by the surrounding scaffold in simultaneous photopolymerization. The mechanical properties of the printed tissue were similar to the native cartilage. Compared to conventional tissue fabrication, which requires longer UV exposure, the viability of the printed cells with simultaneous photopolymerization was significantly higher. Printed neocartilage demonstrated excellent glycosaminoglycan (GAG) and collagen type II production, which was consistent with gene expression. Therefore, this platform is ideal for accurate cell distribution and arrangement for anatomic tissue engineering.

The methods described in this paper show how to convert a commercial inkjet printer into a bioprinter with simultaneous UV polymerization. The printer is capable of constructing 3D tissue structure with cells and biomaterials. The study demonstrated here constructed a 3D neocartilage.

Bioprinting, which is based on thermal inkjet printing, is one of the most attractive enabling technologies in the field of tissue engineering and ...

Analysis of Cell Migration within a Three-dimensional Collagen Matrix

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic development, wound healing, and immune responses. However, cell migration is also a key mechanism in cancer enabling these cancer cells to detach from the primary tumor to start metastatic spreading. Within the past years various cell migration assays have been developed to analyze the migratory behavior of different cell types. Because the locomotory behavior of cells markedly differs between a two-dimensional (2D) and three-dimensional (3D) environment it can be assumed that the analysis of the migration of cells that are embedded within a 3D environment would yield in more significant cell migration data. The advantage of the described 3D collagen matrix migration assay is that cells are embedded within a physiological 3D network of collagen fibers representing the major component of the extracellular matrix. Due to time-lapse video microscopy real cell migration is measured allowing the determination of several migration parameters as well as their alterations in response to pro-migratory factors or inhibitors. Various cell types could be analyzed using this technique, including lymphocytes/leukocytes, stem cells, and tumor cells. Likewise, also cell clusters or spheroids could be embedded within the collagen matrix concomitant with analysis of the emigration of single cells from the cell cluster/ spheroid into the collagen lattice. We conclude that the 3D collagen matrix migration assay is a versatile method to analyze the migration of cells within a physiological-like 3D environment.

Cell migration is a biological phenomenon that is involved in a plethora of physiological, such as wound healing and immune responses, and pathophysiological processes, like cancer. The 3D-collagen matrix migration assay is a versatile tool to analyze the migratory properties of different cell types within in a 3D physiological-like environment.

The ability to migrate is a hallmark of various cell types and plays a crucial role in several physiological processes, including&#160;embryonic ...

Generation of a Three-dimensional Full Thickness Skin Equivalent and Automated Wounding

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models reflect the human wound situation better than animal models. Although two-dimensional models are widely used to investigate processes such as cellular migration and proliferation, models that are more complex are required to gain a deeper knowledge about wound healing. Besides a suitable model system, the generation of precise and reproducible wounds is crucial to ensure comparable results between different test runs. In this study, the generation of a three-dimensional full thickness skin equivalent to study wound healing is shown. The dermal part of the models is comprised of human dermal fibroblast embedded in a rat-tail collagen type I hydrogel. Following the inoculation with human epidermal keratinocytes and consequent culture at the air-liquid interface, a multilayered epidermis is formed on top of the models. To study the wound healing process, we additionally developed an automated wounding device, which generates standardized wounds in a sterile atmosphere.

The goal of this protocol is to build up a three-dimensional full thickness skin equivalent, which resembles natural skin. With a specifically constructed automated wounding device, precise and reproducible wounds can be generated under maintenance of sterility.

In vitro models are a cost effective and ethical alternative to study cutaneous wound healing processes. Moreover, by using human cells, these models ...

Melt Electrospinning Writing of Three-dimensional Poly(&#949;-caprolactone) Scaffolds with Controllable Morphologies for Tissue Engineering Applications

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology with great potential for biomedical applications. The technique facilitates the direct deposition of biocompatible polymer fibers to fabricate well-ordered scaffolds in the sub-micron to micro scale range. The establishment of a stable, viscoelastic, polymer jet between a spinneret and a collector is achieved using an applied voltage and can be direct-written. A significant benefit of a typical porous scaffold is a high surface-to-volume ratio which provides increased effective adhesion sites for cell attachment and growth. Controlling the printing process by fine-tuning the system parameters enables high reproducibility in the quality of the printed scaffolds. It also provides a flexible manufacturing platform for users to tailor the morphological structures of the scaffolds to their specific requirements. For this purpose, we present a protocol to obtain different fiber diameters using melt electrospinning writing (MEW) with a guided amendment of the parameters, including flow rate, voltage and collection speed. Furthermore, we demonstrate how to optimize the jet, discuss often experienced technical challenges, explain troubleshooting techniques and showcase a wide range of printable scaffold architectures.

This protocol serves as a comprehensive guideline to fabricate scaffolds via electrospinning with polymer melts in a direct writing mode. We systematically outline the process and define the appropriate parameter settings for achieving targeted scaffold architectures.

This tutorial reflects on the fundamental principles and guidelines for electrospinning writing with polymer melts, an additive manufacturing technology ...

Ultrathin Porated Elastic Hydrogels As a Biomimetic Basement Membrane for Dual Cell Culture

The basement membrane is a critical component of cellular bilayers that can vary in stiffness, composition, architecture, and porosity. In vitro studies of endothelial-epithelial bilayers have traditionally relied on permeable support models that enable bilayer culture, but permeable supports are limited in their ability to replicate the diversity of human basement membranes. In contrast, hydrogel models that require chemical synthesis are highly tunable and allow for modifications of both the material stiffness and the biochemical composition via incorporation of biomimetic peptides or proteins. However, traditional hydrogel models are limited in functionality because they lack pores for cell-cell contacts and functional in vitro migration studies. Additionally, due to the thickness of traditional hydrogels, incorporation of pores that span the entire thickness of hydrogels has been challenging. In the present study, we use poly-(ethylene-glycol) (PEG) hydrogels and a novel zinc oxide templating method to address the previous shortcomings of biomimetic hydrogels. As a result, we present an ultrathin, basement membrane-like hydrogel that permits the culture of confluent cellular bilayers on a customizable scaffold with variable pore architectures, mechanical properties, and biochemical composition.

Current bilayer culture models do not allow for functional in vitro studies that mimic in vivo microenvironments. Using polyethylene glycol and a zinc oxide templating method, this protocol describes the development of an ultrathin biomimetic basement membrane with tunable stiffness, porosity, and biochemical composition that closely mimics in vivo extracellular matrices.

The basement membrane is a critical component of cellular bilayers that can vary in stiffness, composition, architecture, and porosity. In vitro studies ...