Name: Capillary Force Lithography for Cardiac Tissue Engineering (Video) | JoVE Journal
Uploaded: 2014-06-10T13:00:00.000+00:00
Duration: 10 min 9 s
Description: Learn capillary force lithography for cardiac tissue engineering using biomimetic substrata. This scalable method enables precise patterning to study cardiomyocyte structure and function in vitro.

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D. H. Kim thanks the Department of Bioengineering at the University of Washington for the new faculty startup fund. D. H. Kim is also supported by the Perkins Coie Award for Discovery, the Wallace H. Coulter Foundation Translational Research Partnership Award, the Washington State Life Science Discovery Fund, and the American Heart Association Scientist Development Grant (13SDG14560076). J. Macadangdang and A. Jiao thank the support from the NIH Bioengineering Cardiovascular Training Grant Fellowship. &#160;Additional support for this work comes from the National Institutes of Health (NIH) grant R01HL111197 to M. Regnier.

All procedures are conducted at room temperature (~23 &#176;C) unless otherwise noted.
1. Fabrication of Silicon Master
<ol>
	<li>Clean silicon wafer with 100% ethanol or xylene and dry under O2/N2 gas.</li>
	<li>Place silicon wafer in spin-coater at rotation speeds of 2,000-4,000 rpm to produce a 0.3-0.5 &#181;m thick film.</li>
	<li>Pattern the photoresist film with the correct dimensions by using a photolithography system</li>
	<li>Fully immerse the patterned photoresist-coated silicon wafers in an appropriate volume of photoresist developing solution.</li>
	<li>Rinse the developed photoresist-coated silicon wafers with deionized water.</li>
	<li>To form arrays of sub-micron scale ridges with near vertical side walls, deep reactive ion etch the exposed silicon using an etching system.</li>
	<li>Remove the remaining photoresist by placing the silicon wafer in a plasma asher system.</li>
	<li>Cut the silicon wafers with a diamond-tipped cutter into the appropriately sized silicon masters for subsequent replica molding.</li>
</ol>
2. Fabrication of PUA Mold from Silicon Master
NOTE: Volume to be added to silicon master for nanofabrication will vary depending on the area of the nanopatterned master to be replicated as well as the viscosity of the polyurethane acrylate (PUA) solution.
<ol>
	<li>Clean silicon master surface with 100% ethanol or xylene and dry under O2/N2 gas.</li>
	<li>Place silicon master pattern side up in a Petri dish.</li>
	<li>For a silicon master with a 2 cm x 2 cm surface pattern, pipette 40 &#181;l of PUA to the pattern surface.</li>
	<li>Place a sheet of 4 cm x 4 cm transparent polyester (PET) film over the dispensed PUA.</li>
	<li>Press down on the PET sheet and spread the PUA underneath the sheet across the pattern face using a roller or flat edged surface (such as a card) so that the entire pattern is covered by the PUA prepolymer.</li>
	<li>Place silicon master, prepolymer, and PET approximately 10 cm below a 20 Watt (115 V) UV light (&#955; = 365 nm) for 50 sec. To be effective, the UV light wavelength can be anywhere between 310-400 nm. The intensity of the light is 10-15 mW/cm2 at the surface of the substrate.</li>
	<li>After curing, remove PET film slowly with forceps. PUA should attach to the PET film with a negative of the silicon master nanopattern.</li>
	<li>Cure PUA/PET nanopatterns under UV for at least 12 hr prior to use. Overexposure is not an issue.</li>
	<li>To clean silicon masters, place another film of PET on top of the master without the addition of PUA and expose to UV light (&#955; = 365 nm) for 50 sec and remove PET film. This will remove any unreacted monomers.</li>
	<li>Rinse silicon master with 100% ethanol or xylene and dry under O2/N2 gas.</li>
</ol>
3a. Nanopatterning Polyurethane Polymer
<ol>
	<li>Prepare 25 mm diameter circular glass slides by placing in an ozone treatment chamber for 10 min.</li>
	<li>Place ozone-treated glass slides onto small PDMS block for easy handling.</li>
	<li>Apply thin layer of surface adhesion promoter with paintbrush to glass slides. Air dry glass slides for 30 min.</li>
	<li>Place the glass slide on a piece of printer paper.</li>
	<li>Drop dispense 10 &#956;l of polyurethane (PU) pre-polymer (NOA 76) to center of glass slide. Make sure no bubbles are present after addition.</li>
	<li>Place PUA mold, pattern face down, onto the glass slide. Disperse the PU uniformly across the surface of the glass slide by rolling a rubber cylinder roller along the PUA mold. Printer paper will absorb polymer overflow.</li>
	<li>Watt UV lamp. Polymerization time of the PU is dependent on power of UV source.</li>
	<li>Remove the sample from UV light source and carefully peel the PUA mold from PU coated glass slide. Polymerization of the PU is considered complete when the PUA mold peels cleanly away from the sample and the PU glass slide has an iridescent appearance.</li>
	<li>Place finished samples in desiccator for storage for as long as a month.</li>
</ol>
3b. Nanopatterning Poly(Lactide-Co-Glycolide) Hydrogel
<ol>
	<li>Create a flat PDMS mold by vigorously mixing silicone elastomer base and silicone elastomer curing agent in a 10:1 ratio.</li>
	<li>Pour mixed PDMS precursor solution into a Petri dish so that the PDMS precursor reaches 5 mm up the edge of the dish (i.e. so that the PDMS is 5 mm thick).</li>
	<li>Place Petri dish and PDMS precursor in a desiccator for 1 hr to degas.</li>
	<li>Move Petri dish and PDMS precursor into a 65 &#176;C oven for at least 2 hr to cure.</li>
	<li>After PDMS is cured, use a razor to cut the flat PDMS into 3 cm x 3 cm square sections. These will be the flat PDMS molds used later in the patterning process.</li>
	<li>Clean 25 mm diameter circular glass slides by placing in isopropyl alcohol for 30 min in a water sonicator.</li>
	<li>Dry cleaned glass slides under O2/N2 gas.</li>
	<li>Drop dispense 100 &#956;l of PLGA solution (15% w/v PLGA in chloroform) onto glass slide.</li>
	<li>Place a flat PDMS mold on top of the dispensed PLGA to absorb the solvent and obtain a flat PLGA surface. Apply a light pressure (~10 kPa) by placing a 200 g weight on top of the PDMS for 5 min.</li>
	<li>Slowly peel away flat PDMS mold and place the cover glass on a preheated plate (120 &#176;C) for 5 min to remove residual solvent and increase adhesion between the PLGA and the cover glass.</li>
	<li>Place the NP PUA mold on top of the flat PLGA and apply constant pressure (~100 kPa) and heat (120 &#176;C) by placing a 1 kg weight on top of the PUA mold while on the heating plate for 15 min.</li>
	<li>Remove the weight from PLGA cover slide and allow the substrata to cool to room temperature. Do not remove PUA mold until the substrata have been cooled.</li>
	<li>Once the substrata have sufficiently cooled, carefully peel away the NP PUA mold, revealing the NP PLGA substratum. The NP PLGA substratum should have an iridescent appearance.</li>
	<li>Place finished samples in desiccator for storage for as long as a month.</li>
</ol>
4. Cell Seeding and Culture
NOTE: This protocol describes the culture of neonatal rat ventricular myocytes (NRVMs) and H7 human embryonic stem cell-derived cardiomyocytes (hESC-CMs) but other cell sources may be used.
<ol>
	<li>Attach the ANFS coverslips (PU or PLGA) to a 35 mm tissue culture polystyrene dish. Pipette 20 &#181;l of Norland Optical Adhesive (NOA83H) to the bottom of the dish and gently place the ANFS coverslip on top of the NOA. Allow glue to spread out and cover entire coverslip bottom. Cure NOA by exposing dish to UV for 10 min.</li>
	<li>Sterilize ANFS by rinsing with 2 ml of 70% aqueous ethanol solution for 5 min, twice. Remove ethanol by aspiration. Allow ANFS to completely air dry for ~1 hr under the UV sterilization lamp (&#955; = 200-290 nm) in the biological safety cabinet.</li>
	<li>Cellular adhesion is enhanced by coating the ANFS in fibronectin overnight. Dilute fibronectin in DI water to 5 &#181;g/ml. Pipette 2 ml of fibronectin solution into dish. Place in incubator at 37 &#176;C and 5% CO2 overnight (at least 6 hr).</li>
	<li>Obtain NRVMs, hESC-CMs, or other cardiac cells of interest according to previous protocols22.</li>
	<li>Centrifuge cell sample at 1,000 rpm for 3 min to pellet the cells.</li>
	<li>Carefully remove the supernatant by aspiration. Make sure not to disturb the pellet.</li>
	<li>Resuspend cells in appropriate culture media to a concentration of 4.6 x 106 cells/ml.</li>
	<li>Carefully pipette 200 &#181;l of cell suspension onto sterilized ANFS. Make sure cell suspension remains on the coverslip.</li>
	<li>Place cells in incubator at 37 &#176;C and 5% CO2 for 4 hr to allow cells to attach to ANFS.</li>
	<li>Add 2 ml of warm culture media to dish and replace cells in incubator under the same conditions.</li>
	<li>After 24 hr, remove media and wash with 2 ml of DPBS twice to remove excess cells.</li>
	<li>Add 2 ml of warm culture media to dish and replace cells in incubator under the same conditions. Culture the cells to confluence. Replace media every other day.</li>
</ol>

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<li>Badrossamay, M. R., McIlwee, H. A., Goss, J. A., Parker, K. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Nanofiber+Assembly+by+Rotary+Jet-Spinning%5BTitle%5D)+AND+%22Nano+Lett%22%5BJournal%5D)">Nanofiber Assembly by Rotary Jet-Spinning.</a> Nano Lett. 10, 2257-2261 (2010).</li>
<li>Rao, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+effect+of+microgrooved+culture+substrates+on+calcium+cycling+of+cardiac+myocytes+derived+from+human+induced+pluripotent+stem+cells%5BTitle%5D)+AND+%22Biomaterials%22%5BJournal%5D)">The effect of microgrooved culture substrates on calcium cycling of cardiac myocytes derived from human induced pluripotent stem cells.</a> Biomaterials. 34, 2399-2411 (2013).</li>
</ol>

Authors have nothing to disclose.

Functionally mature cardiac tissues are lacking for both in vivo and in vitro applications of cardiac tissue engineering. The CFL nanofabrication methods described here are robust techniques for achieving cellular alignment and influencing macroscopic tissue function due to the scalability of the system. Large areas can easily be patterned and used for cell culture. Macroscopic cellular alignment is essential in cardiac tissue engineering in order to create biomimetic, functional tissue as it influences...

Cardiovascular disease is the leading cause of morbidity and mortality in the world and present a weighty socio-economic burden on an already strained global health system1,17. Cardiac tissue engineering has two distinct goals: (1) to regenerate damaged myocardium after ischemic disease or cardiomyopathy or (2) to create a high fidelity model of the heart for in vitro drug screening or disease modeling.
The heart is a complex organ that must work constantly to supply blood to the body. Densely packed laminar structures of cardiomyocytes and supportive tissues are arranged in helical patterns throughout the heart wall18,19. The heart is also electromechanically coupled20 in a highly coordinated fashion to efficiently eject blood to the body21. Several major hurdles remain to be addressed, however, before nature&#8217;s intricate design can reliably be recapitulated in vitro. First, although robust cardiomyocyte differentiation methods continue to be developed22, hPSC-CMs still exhibit rather immature phenotypes. Their electromechanical properties and morphology most closely match fetal levels23. Second, when kept in traditional culture conditions, both stem cell-derived and primary cardiomyocytes fail to assemble into native, tissue-like structures. Rather, cells become randomly oriented and do not exhibit the banded rod-shaped appearance of adult myocardium24.
The extracellular matrix (ECM) environment with which cells interact plays a significant role in numerous cellular processes11,13,25. The ECM consists of complex, well-defined molecular and topographical cues that significantly influence the structure and function of cells6,26. Within the heart, cellular alignment closely follows the underlying nanometer scale ECM fibers2. The impact of these nanotopographical cues on cell and tissue function, however, is far from completely understood. Preliminary studies of nanometer scale cell-biomaterial interaction indicate the potential importance and impact of sub-micron topographical cues for cell signaling27, adhesion28-30, growth31, and differentiation32,33. However, due to the difficulty in developing reproducible and scalable nanofabricated substrates, such studies could not reproduce the multi-scale cellular effects of the complex in vivo ECM environment. In this protocol, a straightforward and cost-effective nanofabrication technique to produce cell culture scaffolds mimicking native cardiac ECM fiber alignment is described, allowing for a wide range of novel investigations of cardiomyocyte-biomaterial interactions. Understanding how cardiomyocytes interact with the nanoscale ECM environment could allow for the ability to control cellular behavior to more closely mimic native tissue function. Furthermore, cell monolayers are a simplified experimental system compared to 3D structures but still exhibit complex multi-cellular behavior for insightful investigations and functional screening2,34-36. Finally, such scaffolds could be used to improve cellular graft function when implanted into the heart for regenerative purposes37.

<table><tbody><tr><td>Fibronectin</td><td>BD Biosciences</td><td>354008</td><td></td></tr><tr><td>NOA 76</td><td>Norland Products, Inc.</td><td>7606B</td><td></td></tr><tr><td>Surface Adhesion Promotor (Glass Primer)</td><td>Minuta Tech</td><td></td><td></td></tr><tr><td>PUA</td><td>Minuta Tech</td><td>MINS-311RM</td><td></td></tr><tr><td>Soft Rubber Roller</td><td>Speedball</td><td></td><td></td></tr><tr><td>Silicon Wafers</td><td>NOVA Electronic Materials</td><td>FA01-9900</td><td></td></tr><tr><td>Photoresist</td><td>Shipley</td><td>SPRT510</td><td></td></tr><tr><td>Photoresist Developer</td><td>Shipley</td><td>MF320</td><td></td></tr><tr><td>Electron-Beam Lithography System</td><td>JEOL</td><td>JBX-9300FS</td><td></td></tr><tr><td>Etching System</td><td>Surface Technology Systems</td><td>NP10 8UJ</td><td></td></tr><tr><td>Plasma Asher System</td><td>BMR Technology Co.</td><td>DSF-200</td><td></td></tr><tr><td>Ozone Cure System</td><td>Minuta Tech</td><td>MT-UV-O- 08</td><td></td></tr><tr><td>Fusion Cure System</td><td>Minuta Tech</td><td>MT-UV-A 11</td><td></td></tr><tr><td>NOA 83H</td><td>Norland Products, Inc.</td><td>8301</td><td></td></tr><tr><td>Spin Coater</td><td>Laurel Technology</td><td>WS-400-6NPP</td><td></td></tr><tr><td>Skyrol PET Film</td><td>SKC Co., Ltd.</td><td>23038-59-9</td><td></td></tr><tr><td>25 mm Glass Slides</td><td>Corning</td><td>2948</td><td></td></tr><tr><td>Sylgard 184 Silicone Elastomer Kit</td><td>Dow Corning</td><td>6/5/2553</td><td></td></tr><tr><td>Poly(D,L-lactide-co-glycolide)</td><td>Sigma-Aldrich</td><td>P2191-1G</td><td></td></tr><tr><td>Chloroform</td><td>Sigma-Aldrich</td><td>372978-1L</td><td></td></tr><tr><td>500 g Weights</td><td>Global Insustrial</td><td>T9FB503120</td><td></td></tr><tr><td>Isopropyl Alcohol</td><td>EMD Millipore</td><td>PX1835-2</td><td></td></tr><tr><td>Hot Plate</td><td>Corning</td><td>PC-420D</td><td></td></tr><tr><td>Sonicator</td><td>Branson</td><td>B2510MTH</td><td></td></tr></tbody></table>

capillary force lithography for cardiac tissue engineering

Capillary Force Lithography for Cardiac Tissue Engineering

Cardiovascular disease remains the leading cause of death worldwide1. Cardiac tissue engineering holds much promise to deliver groundbreaking medical discoveries with the aims of developing functional tissues for cardiac regeneration as well as in vitro screening assays. However, the ability to create high-fidelity models of heart tissue has proven difficult. The heart&#8217;s extracellular matrix (ECM) is a complex structure consisting of both biochemical and biomechanical signals ranging from the micro- to the nanometer scale2. Local mechanical loading conditions and cell-ECM interactions have recently been recognized as vital components in cardiac tissue engineering3-5.
A large portion of the cardiac ECM is composed of aligned collagen fibers with nano-scale diameters that significantly influences tissue architecture and electromechanical coupling2. Unfortunately, few methods have been able to mimic the organization of ECM fibers down to the nanometer scale. Recent advancements in nanofabrication techniques, however, have enabled the design and fabrication of scalable scaffolds that mimic the in vivo structural and substrate stiffness cues of the ECM in the heart6-9.
Here we present the development of two reproducible, cost-effective, and scalable nanopatterning processes for the functional alignment of cardiac cells using the biocompatible polymer poly(lactide-co-glycolide) (PLGA)8 and a polyurethane (PU) based polymer. These anisotropically nanofabricated substrata (ANFS) mimic the underlying ECM of well-organized, aligned tissues and can be used to investigate the role of nanotopography on cell morphology and function10-14.
Using a nanopatterned (NP) silicon master as a template, a polyurethane acrylate (PUA) mold is fabricated. This PUA mold is then used to pattern the PU or PLGA hydrogel via UV-assisted or solvent-mediated capillary force lithography (CFL), respectively15,16. Briefly, PU or PLGA pre-polymer is drop dispensed onto a glass coverslip and the PUA mold is placed on top. For UV-assisted CFL, the PU is then exposed to UV radiation (&#955; = 250-400 nm) for curing. For solvent-mediated CFL, the PLGA is embossed using heat (120 &#176;C) and pressure (100 kPa). After curing, the PUA mold is peeled off, leaving behind an ANFS for cell culture. Primary cells, such as neonatal rat ventricular myocytes, as well as human pluripotent stem cell-derived cardiomyocytes, can be maintained on the ANFS2.

Figure 1 is a schematic overview of the production process for the two fabrication methods. Due to the diffraction of light caused by the nanoscale topography, nanopatterning should result in an iridescent surface to the ANFS. Figure 2 depicts this iridescent surface on a well-patterned 25 mm NP-PU coverslip (Figure 2A) with 800 nm ridge and groove width (Figure 2B). The iridescent appearance of the ANFS will vary slightly depending on the ridge and groo...

In this protocol, we demonstrate the fabrication of biomimetic cardiac cell culture substrata made from two distinct polymeric materials using capillary force lithography. The described methods provide a scalable, cost-effective technique to engineer the structure and function of macroscopic cardiac tissues for in vitro and in vivo applications.

Cardiovascular disease remains the leading cause of death worldwide1. Cardiac tissue engineering holds much promise to deliver groundbreaking medical ...

The overall goal of this procedure is to produce biomimetic cell culture substrata to engineer the structure and function of macroscopic cardiac tissues. This is accomplished by first fabricating a silicone master with the desired topographic architecture by deep reactive ion etching. The second step is to transfer the desired topographic pattern from the silicon master to a PUA mold using UV assisted capillary force lithography.Next, the PUA mold is used as a template to fabricate cell culture substrata out of various polymeric materials depending on the desired application via UV assisted or solvent mediated capillary force lithography. The final step is to plate either primary or stem cell derived cardiomyocytes onto the nano pattern cell culture substrata for subsequent analysis. Ultimately, bright field and immunofluorescence microscopy are used to show changes in cell morphology and contractual protein arrangement within the cardiomyocytes.The main advantage of this technique over existing methods, such as micro contact printing, is that capillary force lithography produces nano pattern cell culture substrata that can induce structural alignment of cardiac tissue monolayers w

capillary-force-lithography-for-cardiac-tissue-engineering

Research

JoVE Journal

Bioengineering

The generation of aligned myocardial tissue is a key requirement for adapting the recent advances in stem cell biology to clinically useful purposes. Herein we describe a microcontact printing approach for the precise control of cell shape and function. Using highly purified populations of embryonic stem cell derived cardiac progenitors, we then generate anisotropic functional myocardial tissue.

Generation of Aligned Functional Myocardial Tissue Through Microcontact Printing

We present a method for microfluidic deposition of patterned genipin and fibronectin on PDMS substrates, allowing extended viability of vascular smooth muscle cell-dense tissues. This tissue fabrication method is combined with previous vascular muscular thin film technology to measure vascular contractility over disease-relevant time courses.

Microfluidic Genipin Deposition Technique for Extended Culture of Micropatterned Vascular Muscular Thin Films

This manuscript describes the creation of defined engineered cardiac tissues using surface marker expression and cell sorting. The defined tissues can then be used in a multi-tissue bioreactor to investigate mechanisms of cardiac cell therapy in order to provide a functional, yet controlled, model system of the human heart.

Construction of Defined Human Engineered Cardiac Tissues to Study Mechanisms of Cardiac Cell Therapy

This protocol describes 3D bioprinting of cardiac tissue without the use of biomaterials. 3D bioprinted cardiac patches exhibit mechanical integration of component spheroids and are highly promising in cardiac tissue regeneration and as 3D models of heart disease.

Creation of Cardiac Tissue Exhibiting Mechanical Integration of Spheroids Using 3D Bioprinting

We provide a generalized protocol based on a microfluidic bioprinting strategy for engineering a microfibrous vascular bed, where a secondary cell type could be further seeded into the interstitial space of this microfibrous structure to generate vascularized tissues and organoids.

Microfluidic Bioprinting for Engineering Vascularized Tissues and Organoids

This protocol introduces a lithography-free micropatterning method that is simple and accessible to those with a limited bioengineering background. This method utilizes customized laser-cut stencils to micropattern extracellular matrix proteins in a shape of interest for modulating cell morphologies. The procedure for micropatterning is demonstrated using induced pluripotent stem cell derived cardiomyocytes.

Simple Lithography-Free Single Cell Micropatterning using Laser-Cut Stencils

Engineered tissues heavily rely on proper vascular networks to provide vital nutrients and gases and remove metabolic waste. In this work, a stepwise seeding protocol of endothelial cells and support cells creates highly organized vascular networks in a high-throughput platform for studying developing vessel behavior in a controlled 3D environment.

Stepwise Cell Seeding on Tessellated Scaffolds to Study Sprouting Blood Vessels

Three-dimensional cardiac tissues bioengineered using stem-cell-derived cardiomyocytes have emerged as promising models for studying healthy and diseased human myocardium in vitro while recapitulating key aspects of the native cardiac niche. This manuscript describes a protocol for fabricating and analyzing high-content engineered cardiac tissues generated from human induced pluripotent stem-cell-derived cardiomyocytes.

Designing a Bioreactor to Improve Data Acquisition and Model Throughput of Engineered Cardiac Tissues

Using light to control cardiac cells and tissue enables non-contact stimulation, thereby preserving the natural state and function of the cells, making it a valuable approach for both basic research and therapeutic applications.

A Cardiac Microphysiological System for Studying Ca2+ Propagation via Non-genetic Optical Stimulation

A reproducible method is presented to generate 3D myocardial tissues combining melt electrospinning writing (MEW) polycaprolactone (PCL) scaffolds and fibrin hydrogels with hiPSC-derived cardiomyocytes and fibroblasts. This technique offers precise control over scaffold architecture and can be applied in preclinical drug testing and cardiac disease modeling.

3D Human Myocardial Tissue Generation Using Melt Electrospinning Writing of Polycaprolactone Scaffolds and hiPSC-Derived Cardiac Cells

Learn capillary force lithography for cardiac tissue engineering using biomimetic substrata. This scalable method enables precise patterning to study cardiomyocyte structure and function in vitro.

Capillary Force Lithography for Cardiac Tissue Engineering

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