Name: construction of modular hydrogel sheets for micropatterned macro-scaled 3d cellular architecture
Uploaded: 2016-01-11T10:30:00
Description: Watch this Scientific Journal Video about Construction of Modular Hydrogel Sheets for Micropatterned Macro-scaled 3D Cellular Architecture at JoVE.com

This research was supported by a National Leading Research Laboratory Program (Grant NRF-2013R1A2A1A05006378) through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future Planning. The authors also acknowledge a KAIST Systems Healthcare Program.

&#160; &#160;1. Preparation of the Micropatterned Molds and Hydrogels
<ol>
	<li>Produce the desired micro-scale patterns using SU-8 photoresist on the surface of a silicon wafer via a standard two-step photolithography technique15,17 for casting PDMS molds. The example shown uses a liver lobule-like mesh pattern (Figure 1).</li>
	<li>Weigh out PDMS and a curing agent solution with a ratio of 1:5 (i.e., 12.5 g of PDMS and 2.5 g of curing agent).</li>
	<li>Mix the 15 g of the solution...

<ol>
	<li>Hoffman, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hydrogels+for+biomedical+applications.">Hydrogels for biomedical applications.</a> Adv. Drug Deliv. Rev. 64 (Supplement), 18-23 (2012).</li><li>Lan, S., Starly, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alginate+based+3D+hydrogels+as+an+in+vitro+co-culture+model+platform+for+the+toxicity+screening+of+new+chemical+entities.">Alginate based 3D hydrogels as an in vitro co-culture model platform for the toxicity screening of new chemical entities.</a> Toxicol. Appl. Pharm. 256 (1), 62-72 (2011).</li><li>Szot, C. S., Buchanan, C. F., Freeman, J. W., Rylander, M. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=3D+in+vitro+bioengineered+tumors+based+on+collagen+I+hydrogels.">3D in vitro bioengineered tumors based on collagen I hydrogels.</a> Biomaterials. 32 (31), 7905-7912 (2011).</li><li>Lim, F., Sun, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microencapsulated+islets+as+bioartificial+endocrine+pancreas.">Microencapsulated islets as bioartificial endocrine pancreas.</a> Science. 210 (4472), 908-910 (1980).</li><li>Koh, W. G., Itle, L. J., Pishko, M. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molding+of+hydrogel+microstructures+to+create+multiphenotype+cell+microarrays.">Molding of hydrogel microstructures to create multiphenotype cell microarrays.</a> Anal. Chem. 75 (21), 5783-5789 (2003).</li><li>Xu, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Microfluidic+Hydrogel+Capable+of+Cell+Preservation+without+Perfusion+Culture+under+Cell-Based+Assay+Conditions.">A Microfluidic Hydrogel Capable of Cell Preservation without Perfusion Culture under Cell-Based Assay Conditions.</a> Adv Mater. 22 (28), 3017-3021 (2010).</li><li>Um, E., Lee, D. S., Pyo, H. S., Park, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Continuous+generation+of+hydrogel+beads+and+encapsulation+of+biological+materials+using+a+microfluidic+droplet-merging+channel.">Continuous generation of hydrogel beads and encapsulation of biological materials using a microfluidic droplet-merging channel.</a> Microfluid. Nanofluid. 5 (4), 541-549 (2008).</li><li>Lee, D. H., Lee, W., E, U. m., Park, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbridge+structures+for+uniform+interval+control+of+flowing+droplets+in+microfluidic+networks.">Microbridge structures for uniform interval control of flowing droplets in microfluidic networks.</a> Biomicrofluidics. 5 (3), 034117 (2011).</li><li>Lee, D. H., Bae , C. Y., Han, J. I., Park, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+situ+analysis+of+heterogeneity+in+the+lipid+content+of+single+green+microalgae+in+alginate+hydrogel+microcapsules.">In situ analysis of heterogeneity in the lipid content of single green microalgae in alginate hydrogel microcapsules.</a> Anal. Chem. 85 (18), 8749-8756 (2013).</li><li>Yamada, M., Sugaya, S., Naganuma, Y., Seki, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+synthesis+of+chemically+and+physically+anisotropic+hydrogel+microfibers+for+guided+cell+growth+and+networking.">Microfluidic synthesis of chemically and physically anisotropic hydrogel microfibers for guided cell growth and networking.</a> Soft Matter. 8 (11), 3122-3130 (2012).</li><li>Yamada, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Controlled+formation+of+heterotypic+hepatic+micro-organoids+in+anisotropic+hydrogel+microfibers+for+long-term+preservation+of+liver-specific+functions.">Controlled formation of heterotypic hepatic micro-organoids in anisotropic hydrogel microfibers for long-term preservation of liver-specific functions.</a> Biomaterials. 33 (33), 8304-8315 (2012).</li><li>Onoe, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metre-long+cell-laden+microfibres+exhibit+tissue+morphologies+and+functions.">Metre-long cell-laden microfibres exhibit tissue morphologies and functions.</a> Nat. Mater. 12 (6), 584-590 (2013).</li><li>Lee, W., Son, J., Yoo, S. S., Park, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+and+Biocompatible+Fabrication+of+Chemically+Sol&#8722;Gel+Transitional+Hydrogel+Free-Standing+Microarchitectures.">Facile and Biocompatible Fabrication of Chemically Sol&#8722;Gel Transitional Hydrogel Free-Standing Microarchitectures.</a> 12 (1), 14-18 (2011).</li><li>Lee, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+hydrogel+biopaper+for+patterned+3D+cell+culture+and+modular+tissue+reconstruction.">Cellular hydrogel biopaper for patterned 3D cell culture and modular tissue reconstruction.</a> Adv. Healthcare Mater. 1 (5), 635-639 (2012).</li><li>Bae, C. Y., Min, M. K., Kim, H., Park, J. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Geometric+effect+of+the+hydrogel+grid+structure+on+in+vitro+formation+of+homogeneous+MIN6+cell+clusters.">Geometric effect of the hydrogel grid structure on in vitro formation of homogeneous MIN6 cell clusters.</a> Lab Chip. 14 (13), 2183-2190 (2014).</li><li>Bruzewicz, D. A., McGuigan, A. P., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+a+modular+tissue+construct+in+a+microfluidic+chip.">Fabrication of a modular tissue construct in a microfluidic chip.</a> Lab Chip. 8 (5), 663-671 (2008).</li><li>Choi, S., Park, J. 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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+microfluidic+biomaterial.">A microfluidic biomaterial.</a> J. Am. Chem. Soc. 127 (40), 13788-13789 (2005).</li><li>Choi, N. W., Cabodi, M., Held, B., Gleghorn, J. P., Bonassar, L. J., Stroock, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+scaffolds+for+tissue+engineering.">Microfluidic scaffolds for tissue engineering.</a> Nat. Mater. 6 (11), 908-915 (2007).</li><li>Rowley, J. A., Madlambayan, G., Mooney, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alginate+hydrogels+as+synthetic+extracellular+matrix+materials.">Alginate hydrogels as synthetic extracellular matrix materials.</a> Biomaterials. 20 (1), 45-53 (1999).</li></ol>

This protocol provides a simple method of fabricating modular hydrogel sheets, and assembling them to form 3D cellular scaffolds.
To construct clear-cut patterned alginate structures in a short time, we should identify a cross-linking process that can create sufficiently rigid structures to maintain the complex micropatterns from the mold, as well as maintain cell viability and metabolism. We have developed a cross-linking process, including a sol&#8211;gel transition, to spray a cross-linking...

Hydrogels are particularly promising biomaterials, and are expected to be important in basic biology, pharmacological assays and medicine.1 Biofabrication of hydrogel-based cellular constructs has been suggested to reduce the use of animal experiments,2,3 replace transplantable tissues,4 and improve cell-based assays.5,6 Water-containing (hydro-) viscoelastic materials (gels) allow a large number of cells to be encapsulated and maintained in a scaffold structure to control the 3D cellular microenvironment. In combination with the guidance of microfluidic or micropatterning technologies, the geometry of the hydrogel constructs can be precisely controlled at the cellular scale. To date, a variety of shapes of hydrogels, including particles,7-9 fibers,10-12 and sheets,13-15 have been used as building units in bottom-up approaches to the fabrication of macro-scale multi-cellular architectures.
Both hydrogel-based particles and fibers have been readily and rapidly fabricated for applications as micro-scale cellular environments, with fluidic controls using microfluidic devices. However, as the basic units of engineered tissues, it would be complicated to rearrange them and to enlarge their volume as macro-scale constructs.16 It is more difficult to achieve macro-scaled constructs than to produce micron-sized basic modules. Sheet-like units of hydrogel-based constructs can be used to increase the volume of scaffolds via a simple assembly process. Consequentially, stacked layers of hydrogel sheets provide not only a volumetric increase but also a geometric extension in a 3D space.
We have previously reported a method of fabricating micropatterned hydrogel sheets,13-15 together with their assembly into multi-layered cellular architectures. The technique enables complex micropatterning&#160;and modular design of cellular constructs via a stacking process of multi-layered structures. Through the fabrication of stacked modular hydrogel sheets, which are micropatterned, a 3D cell culture system with a controlled macro-scale cellular microenvironment can be realized. This video protocol describes a simple yet powerful fabrication method that can be used to construct modular hydrogel sheets, based on the human liver carcinoma cell line (HepG2). We demonstrate herein simple manipulation of these patterned modular hydrogel sheets, and their assembly into a multi-layered structure.

<table border="0" cellpadding="0" cellspacing="0" width="958">
	<tbody>
		<tr height="42">
			<td height="42" style="height:42px;width:288px;">Sylgard 184 Silicone Elastomer Kit</td>
			<td style="width:111px;">Dow Corning Corporation</td>
			<td style="width:163px;">000000000001064291</td>
			<td style="width:397px;"></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:288px;">Pluronic F-127</td>
			<td style="width:111px;">Sigma-Aldrich</td>
			<td style="width:163px;">P2443</td>
			<td>Powdered nonionic surfactant&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Alginic acid sodium salt, low viscosity</td>
			<td style="width:111px;">Alfa Aesar</td>
			<td style="width:163px;">B25266</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Calcium chloride dihydrate</td>
			<td style="width:111px;">Sigma-Aldrich</td>
			<td style="width:163px;">C7902</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Ultrasonic humidifier</td>
			<td style="width:111px;">MediHeim</td>
			<td style="width:163px;">MH-2800</td>
			<td>Modified equipment, Maximum sprayed rate: 250 mL/h</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;width:288px;">Nylon net filter hydrofilic, 180 &#956;m</td>
			<td style="width:111px;">EMD Millipore</td>
			<td style="width:163px;">NY8H04700</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:288px;">Polycarbonate mold</td>
			<td style="width:111px;"></td>
			<td style="width:163px;"></td>
			<td>Customized mold for fabrication of a PDMS frame pattern</td>
		</tr>
	</tbody>
</table>

construction of modular hydrogel sheets for micropatterned macro-scaled 3d cellular architecture

Hydrogels can be patterned at the micro-scale using microfluidic or micropatterning technologies to provide an in vivo-like three-dimensional (3D) tissue geometry. The resulting 3D hydrogel-based cellular constructs have been introduced as an alternative to animal experiments for advanced biological studies, pharmacological assays and organ transplant applications. Although hydrogel-based particles and fibers can be easily fabricated, it is difficult to manipulate them for tissue reconstruction. In this video, we describe a fabrication method for micropatterned alginate hydrogel sheets, together with their assembly to form a macro-scale 3D cell culture system with a controlled cellular microenvironment. Using a mist form of the calcium gelling agent, thin hydrogel sheets are easily generated with a thickness in the range of 100 - 200 &#181;m, and with precise micropatterns. Cells can then be cultured with the geometric guidance of the hydrogel sheets in freestanding conditions. Furthermore, the hydrogel sheets can be readily manipulated using a micropipette with an end-cut tip, and can be assembled into multi-layered structures by stacking them using a patterned polydimethylsiloxane (PDMS) frame. These modular hydrogel sheets, which can be fabricated using a facile process, have potential applications of in vitro drug assays and biological studies, including functional studies of micro- and macrostructure and tissue reconstruction.

We have described the fabrication and manipulation of freestanding cellular hydrogel sheets. As shown in Figure 1, we fabricated micropatterned PDMS molds, and cell-containing hydrogel was loaded onto the hydrophilic surface of these molds and cross-linked using a humidifier to generate an aerosolized mist of gelling agent. Following release from the molds, HepG2 cells were cultured in freestanding hydrogel sheets with various patterns (Figure 2). Thus, t...

Watch this Scientific Journal Video about Construction of Modular Hydrogel Sheets for Micropatterned Macro-scaled 3D Cellular Architecture at JoVE.com

Construction of Modular Hydrogel Sheets for Micropatterned Macro-scaled 3D Cellular Architecture

We describe the fabrication of micropatterned hydrogel sheets using a simple process, which can be assembled and manipulated in a freestanding form. Using these modular hydrogel sheets, a simple macro-scaled 3D cell culture system can be generated with a controlled cellular microenvironment.

Hydrogels can be patterned at the micro-scale using microfluidic or micropatterning technologies to provide an in vivo-like three-dimensional (3D) tissue ...

The overall goal of this procedure is to demonstrate the simple fabrication, manipulation, and assembly of modular hydrogel sheets for a 3D cell culture system. This method can help answer key questions in the tissue engineering field such as how to create more in vivo-like functional engineered tissues with cultured micro-environments. The main advantage of this technique is that cellular hydrogel constructs can be generated without any costly increment.The 3D cell culture conditions will depend on each modular hydrogel sheet. The implications of this technique extend toward improved cell-based assays and biological studies because the technique can provide various geometries and composition of 3D cellular micro-and macro-environments. Though this method can provide insight into in vitro cell-based assays, it can also be applied to another system such as transplantable scaffold of 3D tissue model.Begin by producing the desired microscale patterns using standard photolithography techniques. The example shown in this video will use a liver lobule-like mesh pattern like the one shown here. Next weigh out 2.5 grams of PDMS and 2.5 grams of the curing agent solution and mix the components together thoroughly.De-gas the solution in a vacuum chamber and then spread the mixed solution onto the micropattern surface of the silicon wafer evenly within a foil casting dish. Next, cure the PDMS by placing the dish onto the flat surface of a 65-degree Celsius heated plate for 90 minutes. Once cured, remove the PDMS from the casting dish and carefully peel it away from the silicon wafer.Cut away the edges of the PDMS and place the patterned portion onto a 100-millimeter diameter Petri dish so that the micropattern side faces up. Then, wash the micropatterned PDMS with 70%ethanol, followed by distilled water, for primary sterilization. Afterwards, dry the setup completely for 10 minutes in an oven at 65 degrees Celsius.Next, place the micropatterned PDMS mold into a plasma cleaner and clean them for one minute in order to create a hydrophilic surface. This will facilitate the loading of aqueous liquids. Then coat the surface of the PDMS with 100 milliliters of the surfactant solution listed in the Table of Materials.Incubate the samples on a laboratory rocker for at least three hours. Next, wash the surfactant solution from the PDMS molds using sterile water, and dry them completely in an oven at 65 degrees Celsius for 10 minutes. Then, sterilize each micropatterned mold by exposing it to ultraviolet radiation for 30 minutes.Begin by culturing hepg2 cells using standard techniques. Once the cells are 70%to 80%confluent, wash the cells once using PBS. Then, harvest the cells by adding one millileter of 05%tripsin edta and incubating them for four minutes at 37 degrees Celsius.Once detached, collect the cells in a centrifuge tube and pellet them at 250 g for three minutes. Remove the supernatant and then resuspend the cells in one millileter of PBS. Count the number of single distributed cells in PBS using an automated cell counter.Then, pellet the cells again at 250 g for three minutes. Remove the PBS supernatant and add enough of a one percent sodium alginate solution to the cells so that the final seeding density is between five and ten million cells per millileter. Mix the cell solution gently using a pipette and then incubate the cell hydrogel suspension in a five percent CO2 humidified incubator at 37 degrees Celsius.While the cells incubate, place the micropatterned PDMS molds into a plasma cleaner and clean them for one minute at 85 watts to create a hydrophilic surface. Mix the cell hydrogel suspension by gently pipetting up and down and then steadily load 7.2 microliters of the suspension at the edge of the micropattern in the mold. Then, gel the cell hydrogel suspension by producing a mist of the cross-linking reagent with the humidifier at a rate of 250 milliliters per hour and spraying it onto the hydrogel precursor for five minutes.Ensure that this procedure covers the topographic surface of the PDMS mold within a range of five centimeters. Following the cross-linking process, turn off the humidifier and fill the PDMS mold with PBS. Using a 200-microliter pipette, dispense PBS gently around the edge of the hardened hydrogel sheets in order to detach each of the hydrogels.Then, pick up each floating hydrogel sheet, using an end-cut, 1, 000-microliter pipette tip. Transfer each sheet of the hydrogel into individual wells of a 12-well plate containing one millileter of pre-warmed DMEM so that they float on the surface of the media. Culture the cells like this for one week, exchanging the culture medium every other day.Next, produce a PDMS frame, which contains 170-micron high pillar structures at the lower surface as described in the accompanying text protocol. During fabrication, place a specialized polycarbonate mold on the silicon wafer for the PDMS frame to create an interior frame with a wide of eight millimeters, a height of nine millimeters, and a depth of two millimeters. Once sterilized, place the PDMS frame onto a quarter of a piece of nylon filter paper set in a 60-millimeter Petri dish.Remove the hydrogel sheets from the incubator and transfer the first of the modular hydrogel sheets into the interior of the PDMS frame using an end-cut 1, 000-microliter pipette tip. Align the edge of the modular hydrogel sheet with the PDMS frame using an empty 200-microliter pipette tip. Repeat this process with additional hydrogel sheets until a stack of four to six layers is achieved.Next, remove the culture medium by flowing it through the pillar structures at the bottom of the PDMS frame. Then, add two microliters of a two percent alginate solution at one corner of the multi-layer construct. Using a humidifier, spray a mist of the cross-linking reagent at a rate of 250 milliters per hour onto the multi-layer construct for thirty seconds to attach the edges of each layer together.Then, rinse the multi-layered construct gently with 400 microliters of DMEM and remove the PDMS frame using a tweezer. Then, add an additional four milliliters of DMEM. Detach the multi-layered construct with the filter paper by gently wiping it with a cell lifter and then use filter paper to transfer it to a six-well plate containing three milliliters of DMEM.Culture the cells in a floating manner with a hydrogel construct as a multi-scale cellular scaffold in the six-well plate for at least one week. Exchange the culture medium every other day. The result of a layer-by-layer assembly of liver lobule-like micropattered hydrogel sheets is shown here, where human liver carcinoma cells fluorescing green and NIH-3T3 fibroblasts fluorescing red were grown together in co-culture on a combined mesh.Using the technique presented here, many pattern variations can be created, including hexagonal pillars, thin meshes, whole arrays, and multiple microcomb-like microfibers in the form a thin hydrogel construct on the order of 100 to 200 micrometers. These structures provide a rich 3D culture environment for many different cell types. After watching this video, you should have a good understanding of how to create cellular hydrogel sheets for engineering in vivo-like 3D culture systems from the bottom up.

construction-modular-hydrogel-sheets-for-micropatterned-macro-scaled

Research

JoVE Journal

Bioengineering

Tissue Engineering: Construction of a Multicellular 3D Scaffold for the Delivery of Layered Cell Sheets

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.2,3 Strategies in tissue engineering propose innovations to assist the body in recovery and repair. For example, TE approaches may be able to attenuate heart remodeling after myocardial infarction (MI) and possibly increase total heart function to a near normal pre-MI level.4 As with any functional tissue, successful regeneration of cardiac tissue involves the proper delivery of multiple cell types with environmental cues favoring integration and survival of the implanted cell/tissue graft. Engineered tissues should address multiple parameters including: soluble signals, cell-to-cell interactions, and matrix materials evaluated as delivery vehicles, their effects on cell survival, material strength, and facilitation of cell-to-tissue organization. Studies employing the direct injection of graft cells only ignore these essential elements.2,5,6 A tissue design combining these ingredients has yet to be developed. Here, we present an example of integrated designs using layering of patterned cell sheets with two distinct types of biological-derived materials containing the target organ cell type and endothelial cells for enhancing new vessels formation in the &#8220;tissue&#8221;. Although these studies focus on the generation of heart-like tissue, this tissue design can be applied to many organs other than heart with minimal design and material changes, and is meant to be an off-the-shelf product for regenerative therapies. The protocol contains five detailed steps. A temperature sensitive Poly(N-isopropylacrylamide) (pNIPAAM) is used to coat tissue culture dishes. Then, tissue specific cells are cultured on the surface of the coated plates/micropattern surfaces to form cell sheets with strong lateral adhesions. Thirdly, a base matrix is created for the tissue by combining porous matrix with neovascular permissive hydrogels and endothelial cells. Finally, the cell sheets are lifted from the pNIPAAM coated dishes and transferred to the base element, making the complete construct.

For creation of highly organized structures of complex tissue, one must assemble multiple material and cell types into an integrated composite. This combinatorial design incorporates organ-specific layered cell sheets with two distinct biologically-derived materials containing a strong fibrous matrix base, and endothelial cells for enhancing new vessels formation.

Many tissues, such as the adult human hearts, are unable to adequately regenerate after damage.2,3 Strategies in tissue engineering propose innovations to ...

The Encapsulation of Cell-free Transcription and Translation Machinery in Vesicles for the Construction of Cellular Mimics

As interest shifts from individual molecules to systems of molecules, an increasing number of laboratories have sought to build from the bottom up cellular mimics that better represent the complexity of cellular life. To date there are a number of paths that could be taken to build compartmentalized cellular mimics, including the exploitation of water-in-oil emulsions, microfluidic devices, and vesicles. Each of the available options has specific advantages and disadvantages. For example, water-in-oil emulsions give high encapsulation efficiency but do not mimic well the permeability barrier of living cells. The primary advantage of the methods described herein is that they are all easy and cheap to implement. Transcription-translation machinery is encapsulated inside of phospholipid vesicles through a process that exploits common instrumentation, such as a centrifugal evaporator and an extruder. Reactions are monitored by fluorescence spectroscopy. The protocols can be adapted for recombinant protein expression, the construction of cellular mimics, the exploration of the minimum requirements for cellular life, or the assembly of genetic circuitry.

Herein we describe simple methods for the preparation of vesicles, the encapsulation of transcription and translation machinery, and the monitoring of protein production. The resulting cell-free systems can be used as a starting point from which to build increasingly complex cellular mimics.

As interest shifts from individual molecules to systems of molecules, an increasing number of laboratories have sought to build from the bottom up ...

3D Hydrogel Scaffolds for Articular Chondrocyte Culture and Cartilage Generation

Human articular cartilage is highly susceptible to damage and has limited self-repair and regeneration potential. Cell-based strategies to engineer cartilage tissue offer a promising solution to repair articular cartilage. To select the optimal cell source for tissue repair, it is important to develop an appropriate culture platform to systematically examine the biological and biomechanical differences in the tissue-engineered cartilage by different cell sources. Here we applied a three-dimensional (3D) biomimetic hydrogel culture platform to systematically examine cartilage regeneration potential of juvenile, adult, and osteoarthritic (OA) chondrocytes. The 3D biomimetic hydrogel consisted of synthetic component poly(ethylene glycol) and bioactive component chondroitin sulfate, which provides a physiologically relevant microenvironment for in vitro culture of chondrocytes. In addition, the scaffold may be potentially used for cell delivery for cartilage repair in vivo. Cartilage tissue engineered in the scaffold can be evaluated using quantitative gene expression, immunofluorescence staining, biochemical assays, and mechanical testing. Utilizing these outcomes, we were able to characterize the differential regenerative potential of chondrocytes of varying age, both at the gene expression level and in the biochemical and biomechanical properties of the engineered cartilage tissue. The 3D culture model could be applied to investigate the molecular and functional differences among chondrocytes and progenitor cells from different stages of normal or aberrant development.

Cartilage repair represents an unmet medical challenge and cell-based approaches to engineer human articular cartilage are a promising solution. Here, we describe three-dimensional (3D) biomimetic hydrogels as an ideal tool for the expansion and maturation of human articular chondrocytes.

Human articular cartilage is highly susceptible to damage and has limited self-repair and regeneration potential. Cell-based strategies to engineer ...

Gradient Strain Chip for Stimulating Cellular Behaviors in Cell-laden Hydrogel

Artificial guidance for cellular alignment is a hot topic in the field of tissue engineering. Most of the previous research has investigated single strain-induced cellular alignment on a cell-laden hydrogel by using complex experimental processes and mass controlling systems, which are usually associated with contamination issues. Thus, in this article, we propose a simple approach to building a gradient static strain using a fluidic chip with a plastic PDMS cover and a UV transparent glass substrate for the stimulation of cellular behavior in a 3D hydrogel. Overloading photo-patternable cell prepolymer in the fluidic chamber can generate a convex curved PDMS membrane on the cover. After UV crosslinking, through a concentric circular micropattern under the curved PDMS membrane, and buffer washing, a microenvironment for investigating cell behaviors under a variety of gradient strains is self-established in a single fluidic chip, without external instruments. NIH3T3 cells were demonstrated after observing the change in the cellular alignment trend under geometry guidance, in cooperation with strain stimulation, which varied from 15 - 65% on hydrogels. After a 3-day incubation, the hydrogel geometry dominated the cell alignment under low compressive strain, where cells aligned along the hydrogel elongation direction under high compressive strain. Between these, the cells showed random alignment due to the dissipation of the radical guidance of hydrogel elongation and the geometry guidance of the patterned hydrogel.

This article introduces a simple approach to providing non-continuous gradient static strains on a concentric cell-laden hydrogel to regulate cell alignment for tissue engineering.

Artificial guidance for cellular alignment is a hot topic in the field of tissue engineering. Most of the previous research has investigated single ...

Improved 3D Hydrogel Cultures of Primary Glial Cells for In Vitro Modelling of Neuroinflammation

In the central nervous system, numerous acute injuries and neurodegenerative disorders, as well as implanted devices or biomaterials engineered to enhance function result in the same outcome: excess inflammation leads to gliosis, cytotoxicity, and/or formation of a glial scar that collectively exacerbate injury or prevent healthy recovery. With the intent of creating a system to model glial scar formation and study inflammatory processes, we have generated a 3D cell scaffold capable of housing primary cultured glial cells: microglia that regulate the foreign body response and initiate the inflammatory event, astrocytes that respond to form a fibrous scar, and oligodendrocytes that are typically vulnerable to inflammatory injury. The present work provides a detailed step-by-step method for the fabrication, culture, and microscopic characterization of a hyaluronic acid-based 3D hydrogel scaffold with encapsulated rat brain-derived glial cells. Further, protocols for characterization of cell encapsulation and the hydrogel scaffold by confocal immunofluorescence and scanning electron microscopy are demonstrated, as well as the capacity to modify the scaffold with bioactive substrates, with incorporation of a commercial basal lamina mixture to improved cell integration.

Improved 3D Hydrogel Cultures of Primary Glial Cells for In Vitro Modelling of Neuroinflammation

Herein, we present a protocol for the 3D culture of rat brain-derived glia cells, including astrocytes, microglia, and oligodendrocytes. We demonstrate primary cell culture, methacrylated hyaluronic acid (HAMA) hydrogel synthesis, HAMAphoto-polymerization and cell encapsulation, and sample processing for confocal and scanning electron microscopic imaging.

In the central nervous system, numerous acute injuries and neurodegenerative disorders, as well as implanted devices or biomaterials engineered to enhance ...

Construction of a Multilayered Mesenchymal Stem Cell Sheet with a 3D Dynamic Culture System

Stem cell therapy shows a promising future in regenerating injured organ and tissues, and the cell sheet technique has been developed to improve the low cell retention and poor survival within the target zone. However, during the in vitro construction process, a solution for maintaining stem cell bioactivity and increasing the cell amount within the cell sheet is urgently needed. Here, this protocol presents a method for constructing a multilayered cell sheet with favorable stem cell bioactivity and optimal operability. Decellularized porcine pericardium (DPP) is prepared by phospholipase A2 (PLA2) decellularization method as the cell sheet scaffold, and rat bone marrow mesenchymal stem cells (BMSCs) are isolated and expanded as the seeded cells. The temporary multilayered cell sheet structure is constructed by using RAD16-I peptide hydrogel. Finally, the cell sheet is cultured with a dynamic perfusion system to stabilize the three-dimensional (3D) structure, and the cell sheet could be obtained following a 48-hour culture in vitro. This protocol provides an efficient and feasible method for constructing a multilayered stem cell sheet, and the cell sheet could be developed as a favorable stem cell therapy product in the future.

This article provides an efficient and feasible method for constructing multilayered stem cell sheets with favorable stem cell property.

Stem cell therapy shows a promising future in regenerating injured organ and tissues, and the cell sheet technique has been developed to improve the low ...

3D Analysis of Multi-cellular Responses to Chemoattractant Gradients

Various limitations of 2D cell culture systems have sparked interest in 3D cell culture and analysis platforms, which would better mimic the spatial and chemical complexity of living tissues and mimic in vivo tissue functions. Recent advances in microfabrication technologies have facilitated the development of 3D in vitro environments in which cells can be integrated into a well-defined extracellular matrix (ECM) and a defined set of soluble or matrix associated biomolecules. However, technological barriers have limited their widespread use in research laboratories. Here, we describe a method to construct simple devices for 3D culture and experimentation with cells and multicellular organoids in 3D microenvironments with a defined chemoattractant gradient. We illustrate the use of this platform for analysis of the response of epithelial cells and organoids to gradients of growth factors, such as epidermal growth factor (EGF). EGF gradients were stable in the devices for several days leading to directed branch formation in breast organoids. This analysis allowed us to conclude that collective gradient sensing by groups of cells is more sensitive vs. single cells. We also describe the fabrication method, which does not require photolithography facilities nor advanced soft lithography techniques. This method will be helpful to study 3D cellular behaviors in the context of the analysis of development and pathological states, including cancer.

We describe a method to construct devices for 3D culture and experimentation with cells and multicellular organoids. This device allows analysis of cellular responses to soluble signals in 3D microenvironments with defined chemoattractant gradients. Organoids are better than single cells at detection of weak noisy inputs.

Various limitations of 2D cell culture systems have sparked interest in 3D cell culture and analysis platforms, which would better mimic the spatial and ...

3D Printed Porous Cellulose Nanocomposite Hydrogel Scaffolds

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with controlled pore structure and mechanical properties. Cellulose nanocrystals (CNCs, 69.62 wt%) based hydrogel ink with matrix (sodium alginate and gelatin) was developed and 3D printed into scaffolds with uniform and gradient pore structure (110-1,100 &#181;m). The scaffolds showed compression modulus in the range of 0.20-0.45 MPa when tested in simulated in vivo conditions (in distilled water at 37 &#176;C). The pore sizes and the compression modulus of the 3D scaffolds matched with the requirements needed for cartilage regeneration applications. This work demonstrates that the consistency of the ink can be controlled by the concentration of the precursors and porosity can be controlled by the 3D printing process and both of these factors in return defines the mechanical properties of the 3D printed porous hydrogel scaffold. This process method can therefore be used to fabricate structurally and compositionally customized scaffolds according to the specific needs of patients.&#160;

The three critical steps of this protocol are i) developing the right composition and consistency of the cellulose hydrogel ink, ii) 3D printing of scaffolds into various pore structures with good shape fidelity and dimensions and iii) demonstration of the mechanical properties in simulated body conditions for cartilage regeneration.

This work demonstrates the use of three-dimensional (3D) printing to produce porous cubic scaffolds using cellulose nanocomposite hydrogel ink, with ...

Protocols of 3D Bioprinting of Gelatin Methacryloyl Hydrogel Based Bioinks

Gelatin methacryloyl (GelMA) has become a popular biomaterial in the field of bioprinting. The derivation of this material is gelatin, which is hydrolyzed from mammal collagen. Thus, the arginine-glycine-aspartic acid (RGD) sequences and target motifs of matrix metalloproteinase (MMP) remain on the molecular chains, which help achieve cell attachment and degradation. Furthermore, formation properties of GelMA are versatile. The methacrylamide groups allow a material to become rapidly crosslinked under light irradiation in the presence of a photoinitiator. Therefore, it makes great sense to establish suitable methods for synthesizing three-dimensional (3D) structures with this promising material. However, its low viscosity restricts GelMA's printability. Presented here are methods to carry out 3D bioprinting of GelMA hydrogels, namely the fabrication of GelMA microspheres, GelMA fibers, GelMA complex structures, and GelMA-based microfluidic chips. The resulting structures and biocompatibility of the materials as well as the printing methods are discussed. It is believed that this protocol may serve as a bridge between previously applied biomaterials and GelMA as well as contribute to the establishment of GelMA-based 3D architectures for biomedical applications.

Presented here is a method for the 3D bioprinting of gelatin methacryloyl.

Gelatin methacryloyl (GelMA) has become a popular biomaterial in the field of bioprinting. The derivation of this material is gelatin, which is hydrolyzed ...

Simple, Affordable, and Modular Patterning of Cells using DNA

The relative positioning of cells is a key feature of the microenvironment that organizes cell-cell interactions. To study the interactions between cells of the same or different type, micropatterning techniques have proved useful. DNA Programmed Assembly of Cells (DPAC) is a micropatterning technique that targets the adhesion of cells to a substrate or other cells using DNA hybridization. The most basic operations in DPAC begin with decorating cell membranes with lipid-modified oligonucleotides, then flowing them over a substrate that has been patterned with complementary DNA sequences. Cells adhere selectively to the substrate only where they find a complementary DNA sequence. Non-adherent cells are washed away, revealing a pattern of adherent cells. Additional operations include further rounds of cell-substrate or cell-cell adhesion, as well as transferring the patterns formed by DPAC to an embedding hydrogel for long-term culture. Previously, methods for patterning oligonucleotides on surfaces and decorating cells with DNA sequences required specialized equipment and custom DNA synthesis, respectively. We report an updated version of the protocol, utilizing an inexpensive benchtop photolithography setup and commercially available cholesterol modified oligonucleotides (CMOs) deployed using a modular format. CMO-labeled cells adhere with high efficiency to DNA-patterned substrates. This approach can be used to pattern multiple cell types at once with high precision and to create arrays of microtissues embedded within an extracellular matrix. Advantages of this method include its high resolution, ability to embed cells into a three-dimensional microenvironment without disrupting the micropattern, and flexibility in patterning any cell type.

Here we present a protocol to micropattern cells at single-cell resolution using DNA-programmed adhesion. This protocol uses a benchtop photolithography platform to create patterns of DNA oligonucleotides on a glass slide and then labels cell membranes with commercially available complementary oligonucleotides. Hybridization of the oligos results in programmed cell adhesion.

The relative positioning of cells is a key feature of the microenvironment that organizes cell-cell interactions. To study the interactions between cells ...