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 thoroughly, degas the bubbles in a vacuum chamber, and then spread the mixed solution onto a micropatterned surface of the silicon wafer evenly within a foil casting dish.</li>
	<li>Place the silicon wafer onto a 65 &#176;C heated plate for 90 min on a flat surface to cure the PDMS.</li>
	<li>Remove the cured PDMS from the casting dish and the silicon wafer.</li>
	<li>Cut the edges of the PDMS and place it onto a 100-mm-diameter petri dish with the micropatterned side up.</li>
	<li>Wash the micropatterned cured PDMS on the petri dish using 70% ethanol and distilled water for primary sterilization. Then, dry them completely for 10 min in an oven at 65 &#176;C.</li>
	<li>Dissolve and mix O/N&#160;3 g of a powdered nonionic surfactant in 100 ml of distilled water, creating a 3% (w/v) coating solution.</li>
	<li>Place the micropatterned PDMS molds in a plasma cleaner and clean them for 1 min (85 W, 0.73 mbar) to create a hydrophilic surface, to facilitate the addition of aqueous liquids. Then, coat the surface of the PDMS with the 100 ml surfactant solution for at least&#160;3 hr (orO/N) using a laboratory rocker.</li>
	<li>Wash the surfactant solution from the PDMS molds and dry them completely in an oven at 65 &#176;C for 10 min. Then, sterilize each micropatterned mold by exposure to ultraviolet (UV) radiation over 30 min.</li>
</ol>
2. Prepare the Cell Suspension in a Hydrogel Precursor
<ol>
	<li>To prepare hydrogel precursor, dissolve 0.1 g of sodium alginate powder in 10 ml of phosphate buffered saline (PBS), creating a 1% (w/v) alginate precursor. To dissolve the powder completely, incubate and mix them O/N.</li>
	<li>Filter the solution through a 0.22&#160;&#181;m filter connected to a 1&#160;ml syringe.</li>
	<li>Culture the HepG2 cells in Dulbecco&#39;s modified Eagle&#39;s medium (DMEM) supplemented with 10% fetal bovine serum and 1% penicillin-streptomycin on a conventional tissue culture dish until 70% - 80% confluence in a 5% CO2 humidified incubator at 37 &#176;C.</li>
	<li>Wash the cells once using PBS, and then trypsinize them by adding 1 ml of 0.05% trypsin-EDTA for 4 min in a 5% CO2 humidified incubator at 37 &#176;C. Centrifuge the cells harvested from the culture dish at 250 x g for 3 min and resuspend using 1 ml of PBS following removal of the supernatant.</li>
	<li>Count the number of single distributed cells in PBS using an automated cell counter.</li>
	<li>Following centrifugation at 250 x g for 3 min and PBS removal, add 1 ml of the 1% (w/v) of sodium alginate solution to the remaining cell pellet and mix them gently using pipetting. The final seeding density of the cells should be 5 x 106&#160;- 107 cells/ml. Incubate the cell/hydrogel suspension in a 5% CO2 humidified incubator at 37 &#176;C.</li>
</ol>
3. Loading and Cross-linking of Cell/Hydrogel Suspension
<ol>
	<li>Dissolve 1.47 g of calcium chloride dehydrate in 100 ml of ddH2O to produce a cross-linking reagent (i.e., 100 mM CaCl2&#183;2H2O in ddH2O).</li>
	<li>Rinse out the interior of a humidifier with ultrasonic transducer using 70% ethanol, and fill it with 200 ml of cross-linking reagent. The humidifier is 110 mm wide, 300 mm long and 170 mm deep (i.e., 110 mm x&#160;300 mm x 170 mm (W x H x D)).</li>
	<li>Place the micropatterned PDMS molds in a plasma cleaner and clean them for 1 min at 85 W to create a hydrophilic surface.</li>
	<li>Steadily load 7.2 &#181;l of the well-mixed cell/hydrogel suspension at the edge of the micropattern in the mold. The example shown uses a liver lobule-like mesh pattern (Figure 1). The volume of the suspension depends on the topographic pattern.</li>
	<li>To achieve gelation of the cell/hydrogel suspension, turn on the humidifier and verify that the humidifier produces a mist of the cross-linking reagent. Spray the cross-linking reagent onto the hydrogel precursor for 5 min, covering the topographic surface of the PDMS molds within a range of 5 cm. 
	Note: Distances longer and shorter than 5 cm could cause incomplete and uneven gelation, respectively. Ensure that the humidifier has a spraying rate of 250 ml/hr, producing 20 ml of mist of the cross-linking reagent in 5 min.</li>
	<li>Following the cross-linking process, turn off the humidifier and fill the PDMS molds with PBS.</li>
</ol>
4. Handling of Single Modular Hydrogel Sheets
<ol>
	<li>Detach each hardened hydrogel sheet from the micropatterned molds via pipetting PBS gently around the hydrogel sheet using a 200&#160;&#181;l pipette tip.</li>
	<li>Pick up each floating hydrogel sheet using an end-cut 1,000&#160;&#181;l pipette tip end. Each liver lobule-like mesh hydrogel sheet has dimensions of 8 mm x 8.7 mm, and be 100 - 200 &#181;m thick.</li>
	<li>Transfer a single layer of the hydrogel sheet into 1 ml of DMEM in a 12-well plate, and culture the cells in vitro in a floating manner using the hydrogel construct as a unit component in the 12-well plate over a week in a 5% CO2 humidified incubator at 37 &#176;C. Exchange the culture medium every other day.</li>
</ol>
5. Assembly of Multi-layered Hydrogel Sheets
<ol>
	<li>Repeat steps 1.1 to 1.5 to produce a PDMS frame with dimensions of 18 mm x 18&#160;mm x 4 mm (W x H x D), and which contains 170-&#181;m-high pillar structures at the lower surface. Use 42 g of the mixture of PDMS and curing agent, with the same ratio as in step 1.2. Place a specialized polycarbonate mold on the silicon wafer for the PDMS frame to create an interior frame with dimensions of 8 mm x 9 mm x 2 mm (W x H x D).</li>
	<li>Sterilize the PDMS frame and 180-&#181;m-pore nylon filter papers&#160;submerged in distilled water and tweezers in an autoclave for 15 min at 121 &#176;C.</li>
	<li>Place the sterilized PDMS frame onto a quarter of a piece of nylon filter paper (with a diameter of 5 cm) in a 60-mm diameter&#160;petri dish.</li>
	<li>Transfer a modular hydrogel sheet into the interior of the PDMS frame using an end-cut 1,000&#160;&#181;l pipette tip. The hydrogel sheets used for assembly should be cultured for at least a day after they were fabricated.</li>
	<li>Align the edge of each modular hydrogel sheet with the PDMS frame using an empty 200&#160;&#181;l pipette tip.</li>
	<li>Repeat steps 5.4 and 5.5 using modular hydrogel sheets to form a stack of 4 - 6 layers.</li>
	<li>Remove the culture medium by flowing it out through the pillar structures at the bottom of the PDMS frame. Then add 2 &#181;l of alginate solution (2% w/v) at a corner of the multi-layer construct.</li>
	<li>Spray a mist of the cross-linking reagent for 30 sec onto the multi-layer construct to attach the edges of each layer with those of another. Use 2 ml of mist of the cross-linking reagent (at a spraying rate of 250 ml/hr).</li>
	<li>Rinse the multi-layered construct gently with 400 &#181;l DMEM and remove the PDMS frame using tweezers.</li>
	<li>Detach the multi-layered construct from the filter paper by gently wiping with a cell lifter following the addition of 4 ml of DMEM.</li>
	<li>Transfer the multi-layered construct to a 6-well plate containing 3 ml of DMEM using filter paper, and culture the cells in vitro in a floating manner, with the hydrogel construct as a multi-scale cellular scaffold in the 6-well plate over a week in a 5% CO2 humidified incubator at 37 &#176;C. Exchange the culture medium every other day.</li>
</ol>

<ol><li>Hoffman, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Hydrogels+for+biomedical+applications%5BTitle%5D)+AND+%22Adv.+Drug+Deliv.+Rev%22%5BJournal%5D)">Hydrogels for biomedical applications.</a> Adv. Drug Deliv. Rev. 64 (Supplement), 18-23 (2012).</li>
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<li>Yamada, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Controlled+formation+of+heterotypic+hepatic+micro-organoids+in+anisotropic+hydrogel+microfibers+for+long-term+preservation+of+liver-specific+functions%5BTitle%5D)+AND+%22Biomaterials%22%5BJournal%5D)">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/pubmed?term=((Metre-long+cell-laden+microfibres+exhibit+tissue+morphologies+and+functions%5BTitle%5D)+AND+%22Nat.+Mater%22%5BJournal%5D)">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/pubmed?term=((Facile+and+Biocompatible+Fabrication+of+Chemically+Sol%E2%88%92Gel+Transitional+Hydrogel+Free-Standing+Microarchitectures%5BTitle%5D)+AND+%22%22%5BJournal%5D)">Facile and Biocompatible Fabrication of Chemically Sol−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/pubmed?term=((Cellular+hydrogel+biopaper+for+patterned+3D+cell+culture+and+modular+tissue+reconstruction%5BTitle%5D)+AND+%22Adv.+Healthcare+Mater%22%5BJournal%5D)">Cellular hydrogel biopaper for patterned 3D cell culture and modular tissue reconstruction.</a> Adv. Healthcare Mater. 1 (5), 635-639 (2012).</li>
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<li>Bruzewicz, D. A., McGuigan, A. P., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Fabrication+of+a+modular+tissue+construct+in+a+microfluidic+chip%5BTitle%5D)+AND+%22Lab+Chip%22%5BJournal%5D)">Fabrication of a modular tissue construct in a microfluidic chip.</a> Lab Chip. 8 (5), 663-671 (2008).</li>
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<li>Lee, B. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((In+situ+formation+and+collagen-alginate+composite+encapsulation+of+pancreatic+islet+spheroids%5BTitle%5D)+AND+%22Biomaterials%22%5BJournal%5D)">In situ formation and collagen-alginate composite encapsulation of pancreatic islet spheroids.</a> Biomaterials. 33 (3), 837-845 (2012).</li>
<li>Cabodi, M., Choi, N. W., Gleghorn, J. P., Lee, C. S., Bonassar, L. J., Stroock, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+microfluidic+biomaterial%5BTitle%5D)+AND+%22J.+Am.+Chem.+Soc%22%5BJournal%5D)">A microfluidic biomaterial.</a> J. Am. Chem. Soc. 127 (40), 13788-13789 (2005).</li>
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The authors have nothing to disclose.

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 reagent using a humidifier in the form of a mist. Without this cross-linking process, the micro-scale patterns could not be generated in the form of a thin hydrogel construct with the limited diffusive depth (100 - 200 &#181;m), which has high diffusive permeability to metabolites and nutrients. Furthermore, compared with existing diffusion-based methods, which require 30 - 60 min,18&#8722;20 the cross-linking time was relatively short (3 - 5 min).
Moreover, it was also challenging to manipulate the thin hydrogel sheets, which were mechanically stable only in a liquid medium. As shown in Figure 1, the thin hydrogel structure was simply and stably handled and manipulated using an end-cut conventional tip for transferal between different culturing conditions. Using generation and manipulation techniques, we could provide not only a single-layer sheet in a floating manner for potential applications in drug assays but also stacked multi-layer structures, with potential applications as scaffolds for tissue-like constructs.
Multi-layered cellular architectures can be generated by stacking the modular single-layer hydrogel sheets (Figure 3A). Each modular hydrogel sheet may contain differing cell types, and may be exposed to different culture conditions. These multi-layer constructs may then be selectively assembled. However, simply stacking hydrogel sheets may lead to cell necrosis inside the assembled structure when the total depth exceeds the limited diffusive depth (Figure 3C). To overcome this problem, it would be necessary to align micromesh patterns, such as liver lobule-like meshes, when the multi-layer hydrogel sheets are assembled. We therefore require a PDMS frame with the same interior pattern as the border of the hydrogel sheet to align the stacked hydrogel sheets. Thus, aligned hole-array micropatterns in the assembled mesh hydrogel sheets could be used to form expanded pipeline structures, facilitating more efficient nutrient transport for improved cell viability (Figure 3B).
One limitation of this technique is the absence of cell&#8211;matrix interactions in the alginate hydrogel. Alginate cannot provide cell adhesion ligands for in vivo-like cell&#8211;matrix interactions;21 however, it does offer mechanical and geometrical effects as a 3D cell-encapsulating scaffold with cell&#8211;cell interactions. For primary cells and stem cells, alginate could be used following modification with RGD-containing peptides,21 or in combination with collagen or gelatin.14,18 Another limitation is that, once the cell-embedded hydrogel sheets are fabricated with low cell density below 5 x 106 cells/ml, construction of multi-layered structure could cause weak attachments between the hydrogel sheets because only the edge of the structure is fixed by use of additional alginate. However, the layers can be stacked compactly as a single scaffold via drainage structure under the PDMS frame. In addition, higher density of cells in the hydrogel sheets could proliferate on the surface as well as within the layer after one day culture, which would help attachments between layers as shown in Figure 3A.
The hydrogel sheet fabrication and manipulation technique described here may be adapted to the in vitro culture systems and tissue-like cellular models to provide an in vivo-like microenvironment for applications, including cellular assays and engineering artificial organs. This technique could be applied to cell-based drug assays and biological studies that require geometrically different 3D cellular micro- and macroenvironments that incorporate various cells or hydrogel types.

Hidrojeller özellikle biyomalzemeler umut vericidir, ve temel biyoloji, farmakolojik deneyleri ve tıpta önemli olması beklenmektedir. 1 hidrojel tabanlı hücresel yapıları Biofabrication hayvan deneyleri kullanımını azaltmak için ileri sürülmüştür, 2,3, 4 transplante dokuların yerini ve geliştirmek Hücre bazlı deneyler. 5,6 su-ihtiva eden (hidro) viskoelâstik malzemelerin (jeller), hücrelerin geniş bir sayısı kapsüllenmiş ve 3B, hücresel mikro-kontrol etmek için bir iskele yapısı içinde muhafaza edilmesini sağlar. Mikroakışkan ya micropatterning teknolojileri yönlendirmesi ile birlikte, hidrojel yapıları geometrisi kesin hücresel ölçekte kontrol edilebilir. Tarih, parçacıkların dahil hidrojellerin şekiller, çeşitli, 7-9 lifler, 10-12 ve levhalar, 13-15 aşağıdan yukarıya beğenme yapı birimi olarak kullanılmıştırMakro ölçekli çok hücreli mimarilerinin imalat için ağrıyor. Hidrojel-bazlı partiküller ve elyaflar Hem mikroakışkan cihazlar kullanılarak akışkan kontrol grubu ile, mikro ölçekli hücre ortamları gibi uygulamalar için kolaylıkla ve hızlı bir şekilde imal olmuştur. Bununla birlikte, mühendislik dokuların temel birimleri olarak, onları yeniden düzenlemek ve makro ölçekli yapıları olarak hacmini büyütmek için. 16 mikron büyüklüğünde temel modülleri üretmek için daha Makro ölçekli yapıları elde etmek daha zordur karmaşık olacaktır. Hidrojel-bazlı yapıların Levha benzeri birimler basit bir montaj işlemi ile iskeleler hacmini artırmak için de kullanılabilir. Neticesinde, hidrojel levha istiflenmiş katmanları bir hacimsel artış, aynı zamanda 3D uzayda geometrik uzantısı sadece sağlar. Çoklu yumurtlama içine montajı ile birlikte 15 - Daha önce, 13 micropatterned hidrojel tabakaları imal edilmesi için bir yöntem bildirmiştirola- rak hücresel mimarileri. Teknik, çok katmanlı yapıların istifleme işlemi yoluyla karmaşık micropatterning ve hücresel yapıları modüler tasarımı sağlar. Micropatterned edilir istiflenmiş modüler hidrojel levha, imalatı ile, kontrollü bir makro-ölçekte, hücresel mikro-3 boyutlu bir hücre kültür sistemi gerçekleştirilebilir. Bu video protokol insan karaciğer karsinoma hücre hattında (HepG2) göre modüler hidrojel tabakaları oluşturmak için kullanılabilen basit ama güçlü bir üretim yöntemi açıklanmaktadır. Bu tarifnamede, basit olan bu desenli modüler hidrojel tabakaların manipülasyonu ve bir çok-tabakalı yapı halinde asamblajı göstermektedir.

<table><tbody><tr><td>Sylgard 184 Silicone Elastomer Kit</td><td>Dow Corning Corporation</td><td>000000000001064291</td><td></td></tr><tr><td>Pluronic F-127</td><td>Sigma-Aldrich</td><td>P2443</td><td>Powdered nonionic surfactant&amp;nbsp;</td></tr><tr><td>Alginic acid sodium salt, low viscosity</td><td>Alfa Aesar</td><td>B25266</td><td></td></tr><tr><td>Calcium chloride dihydrate</td><td>Sigma-Aldrich</td><td>C7902</td><td></td></tr><tr><td>Ultrasonic humidifier</td><td>MediHeim</td><td>MH-2800</td><td>Modified equipment, Maximum sprayed rate: 250 ml/hr</td></tr><tr><td>Nylon net filter hydrofilic, 180 &amp;mu;m</td><td>EMD Millipore</td><td>NY8H04700</td><td></td></tr><tr><td>Polycarbonate mold</td><td></td><td></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

Hidrojeller, bir in vivo benzeri üç boyutlu (3D), doku yapısının sağlanması için mikro-akışkan veya micropatterning teknolojileri kullanılarak mikro ölçekte desenli olabilir. Elde edilen 3D hidrojel-bazlı hücresel yapılar gelişmiş biyolojik çalışmalar, farmakolojik tahliller ve organ nakli uygulamaları için hayvan deneylerinde alternatif olarak sunulmuştur. Hidrojel-bazlı partiküller ve elyaflar, kolayca imal edilebilir, ancak, bu doku onarımı için bunları işlemek oldukça zordur. Bu videoda, biz kontrollü hücresel mikroçevresinin ile makro ölçekli 3D hücre kültürü sistemi oluşturmak için kendi montaj ile birlikte, micropatterned aljinat hidrojel sayfaları için bir fabrikasyon yöntem açıklanmaktadır. 200 um ve hassas micropatterns ile - kalsiyum jelleştirme maddesinin bir sis formu, ince hidrojel levha kolayca 100 aralığı içinde bir kalınlığa sahip olarak oluşturulur. Hücreler daha sonra hidrojel yaprak geometrik rehberlik ile kültüre edilebilirduran koşullar. Ayrıca, hidrojel levha hali hazırda bir uç kesim ucu ile bir mikropipet kullanılarak manipüle edilebilir ve desenli bir polidimetilsiloksan (PDMS) kare kullanarak istifleme tarafından çok tabakalı yapılar halinde monte edilebilir. , Basit bir işlem kullanılarak imal edilebilir Bu modüler hidrojel levha, mikro ve makro ve doku yeniden üzerindeki fonksiyonel çalışmalarda da dahil olmak üzere in vitro ilaç deneylerinde ve biyolojik çalışmalar, potansiyel uygulamaya sahiptir.

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, the thin hydrogel sheets provided a 3D culture environment. Furthermore, modular hydrogel sheets may be assembled by layering the sheets using a micropipette with an end-cut tip, and using a PDMS frame, which enables 3D macro-scale cell culture (Figure 3).
<img alt="Figure 1" src="/files/ftp_upload/53475/53475fig1.jpg" /> 
Figure 1. Flow Chart Showing the Fabrication of a Hydrogel Sheet and Multi-layer Hydrogel Sheets. <a href="https://www.jove.com/files/ftp_upload/53475/53475fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/53475/53475fig2.jpg" /> 
Figure 2. Freestanding 3D Cell Culture in Various Hydrogel Sheets. The fabrication method of spraying cross-linking reagent enabled precise patterning of alginate hydrogel at the micro-scale. Furthermore, the fabricated hydrogel sheets could be harvested from the mold and manipulated easily in freestanding conditions. HepG2 cells were patterned and cultured in a flat hydrogel sheet (A), hydrogel sheets with hexagonal pillars (B), mesh (C), liver lobule-like mesh (D), an array of holes (E), and multiple microcomb-like microfibers (F). The scale bars are as follows: 500 &#181;m (A, D, F), 100 &#181;m (B, C), and 2 mm (E). <a href="https://www.jove.com/files/ftp_upload/53475/53475fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/53475/53475fig3.jpg" /> 
Figure 3. Assembly of Micropatterned Hydrogel Sheets for Macro-scale Cellular Constructs. Various types of hydrogel sheet could be assembled via layer-by-layer stacking with alignment, including the assembly of five hydrogel sheets containing HepG2 cells stained with green fluorescence and NIH3T3 cells stained with red fluorescence (A). An assembly of micropatterned hydrogel sheets with expanded pipeline structure (B) provided higher cell viability than that of non-patterned hydrogel sheets (C) after 7 days. The viability was assessed by staining HepG2 cells with calcein-AM (live cells shown as green) and ethidium homodimer-1 (dead cells shown as red). Scale bars: 500 &#181;m (A) and 200 &#181;m (B, C). <a href="https://www.jove.com/files/ftp_upload/53475/53475fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

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.

Micropatterned Makro ölçekli 3D Hücresel Mimarlık Modüler Hidrojel Levhaların İnşaatı

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

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

Nanyang Technological University

Research

JoVE Journal

Bioengineering

10.3K Görüntüleme.  Korea Advanced Institute of Science and Technology (KAIST). 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. 

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

Fabrication of Micropatterned Hydrogels for Neural Culture Systems using Dynamic Mask Projection Photolithography

Increasingly, patterned cell culture environments are becoming a relevant technique to study cellular characteristics, and many researchers believe in the need for 3D environments to represent in vitro experiments which better mimic in vivo qualities 1-3. Studies in fields such as cancer research 4, neural engineering 5, cardiac physiology 6, and cell-matrix interaction7,8have shown cell behavior differs substantially between traditional monolayer cultures and 3D constructs.
Hydrogels are used as 3D environments because of their variety, versatility and ability to tailor molecular composition through functionalization 9-12. Numerous techniques exist for creation of constructs as cell-supportive matrices, including electrospinning13, elastomer stamps14, inkjet printing15, additive photopatterning16, static photomask projection-lithography17, and dynamic mask microstereolithography18. Unfortunately, these methods involve multiple production steps and/or equipment not readily adaptable to conventional cell and tissue culture methods. The technique employed in this protocol adapts the latter two methods, using a digital micromirror device (DMD) to create dynamic photomasks for crosslinking geometrically specific poly-(ethylene glycol) (PEG) hydrogels, induced through UV initiated free radical polymerization. The resulting "2.5D" structures provide a constrained 3D environment for neural growth. We employ a dual-hydrogel approach, where PEG serves as a cell-restrictive region supplying structure to an otherwise shapeless but cell-permissive self-assembling gel made from either Puramatrix or agarose. The process is a quick simple one step fabrication which is highly reproducible and easily adapted for use with conventional cell culture methods and substrates.
Whole tissue explants, such as embryonic dorsal root ganglia (DRG), can be incorporated into the dual hydrogel constructs for experimental assays such as neurite outgrowth. Additionally, dissociated cells can be encapsulated in the photocrosslinkable or self polymerizing hydrogel, or selectively adhered to the permeable support membrane using cell-restrictive photopatterning. Using the DMD, we created hydrogel constructs up to ~1mm thick, but thin film (&lt;200 &mu;m) PEG structures were limited by oxygen quenching of the free radical polymerization reaction. We subsequently developed a technique utilizing a layer of oil above the polymerization liquid which allowed thin PEG structure polymerization.
In this protocol, we describe the expeditious creation of 3D hydrogel systems for production of microfabricated neural cell and tissue cultures. The dual hydrogel constructs demonstrated herein represent versatile in vitro models that may prove useful for studies in neuroscience involving cell survival, migration, and/or neurite growth and guidance. Moreover, as the protocol can work for many types of hydrogels and cells, the potential applications are both varied and vast.

Simple techniques are described for the rapid production of microfabricated neural culture systems using a digital micromirror device for dynamic mask projection lithography on regular cell culture substrates. These culture systems may be more representative of natural biological architecture, and the techniques described could be adapted for numerous applications.

Dinamik Maske Projeksiyon Fotolitografi kullanarak Sinir Kültür Sistemleri Micropatterned Hidrojeller Fabrikasyon

Increasingly, patterned cell culture environments are becoming a relevant technique to study cellular characteristics, and many researchers believe in the ...

Biyomühendislik

Easy Manipulation of Architectures in Protein-based Hydrogels for Cell Culture Applications

Hydrogels are recognized as promising materials for cell culture applications due to their ability to provide highly hydrated cell environments. The field of 3D templates is rising due to the potential resemblance of those materials to the natural extracellular matrix. Protein-based hydrogels are particularly promising because they can easily be functionalized and can achieve defined structures with adjustable physicochemical properties. However, the production of macroporous 3D templates for cell culture applications using natural materials is often limited by their weaker mechanical properties compared to those of synthetic materials. Here, different methods were evaluated to produce macroporous bovine serum albumin (BSA)-based hydrogel systems, with adjustable pore sizes in the range of 10 to 70 &#181;m in radius. Furthermore, a method to generate channels in this protein-based material that are several hundred microns long was established. The different methods to produce pores, as well as the influence of pore size on material properties such as swelling ratio, pH, temperature stability, and enzymatic degradation behavior, were analyzed. Pore sizes were investigated in the native, swollen state of the hydrogels using confocal laser scanning microscopy. The feasibility for cell culture applications was evaluated using a cell-adhesive RGD peptide modification of the protein system and two model cell lines: human breast cancer cells (A549) and adenocarcinomic human alveolar basal epithelial cells (MCF7).

Different methods to manipulate three-dimensional architecture in protein-based hydrogels are evaluated here with respect to material properties. The macroporous networks are functionalized with a cell-adhesive peptide, and their feasibility in cell culture is evaluated using two different model cell lines.

Protein bazlı Hydrogels mimarilerde kolayca idare hücre kültür uygulamaları için

Hydrogels are recognized as promising materials for cell culture applications due to their ability to provide highly hydrated cell environments. The field ...

Biyokimya

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

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

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

Desenli ve Yaratılış 3D Hücre Kültürü için iki bileşenli Hidrojeller için Thermoresponsive Ters Kalıpları Baskı

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

İmmünoloji ve Enfeksiyon

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.

Hücre yüklü hidrojel uyarıcı hücresel davranışları için degrade zorlanma çip

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

Light-mediated Formation and Patterning of Hydrogels for Cell Culture Applications

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In particular, light-mediated click reactions, such as photoinitiated thiol&#8722;ene and thiol&#8722;yne reactions, afford spatiotemporal control over material properties and allow the design of systems with a high degree of user-directed property control. Fabrication and modification of hydrogel-based biomaterials using the precision afforded by light and the versatility offered by these thiol&#8722;X photoclick chemistries are of growing interest, particularly for the culture of cells within well-defined, biomimetic microenvironments. Here, we describe methods for the photoencapsulation of cells and subsequent photopatterning of biochemical cues within hydrogel matrices using versatile and modular building blocks polymerized by a thiol&#8722;ene photoclick reaction. Specifically, an approach is presented for constructing hydrogels from allyloxycarbonyl (Alloc)-functionalized peptide crosslinks and pendant peptide moieties and thiol-functionalized poly(ethylene glycol) (PEG) that rapidly polymerize in the presence of lithium acylphosphinate photoinitiator and cytocompatible doses of long wavelength ultraviolet (UV) light. Facile techniques to visualize photopatterning and quantify the concentration of peptides added are described. Additionally, methods are established for encapsulating cells, specifically human mesenchymal stem cells, and determining their viability and activity. While the formation and initial patterning of thiol-alloc hydrogels are shown here, these techniques broadly may be applied to a number of other light and radical-initiated material systems (e.g., thiol-norbornene, thiol-acrylate) to generate patterned substrates.

We describe a sequential process for light-mediated formation and subsequent biochemical patterning of synthetic hydrogel matrices for three-dimensional cell culture applications. The construction and modification of hydrogels with cytocompatible photoclick chemistry is demonstrated. Additionally, facile techniques to quantify and observe patterns and determine cell viability within these hydrogels are presented.

Hücre Kültürü Uygulamaları için Hidrojeller Işık aracılı Oluşumu ve Desenlendirme

Click chemistries have been investigated for use in numerous biomaterials applications, including drug delivery, tissue engineering, and cell culture. In ...

A Versatile Method of Patterning Proteins and Cells

Substrate and cell patterning techniques are widely used in cell biology to study cell-to-cell and cell-to-substrate interactions. Conventional patterning techniques work well only with simple shapes, small areas and selected bio-materials. This article describes a method to distribute cell suspensions as well as substrate solutions into complex, long, closed (dead-end) polydimethylsiloxane (PDMS) microchannels using negative pressure. This method enables researchers to pattern multiple substrates including fibronectin, collagen, antibodies (Sal-1), poly-D-lysine (PDL), and laminin. Patterning of substrates allows one to indirectly pattern a variety of cells. We have tested C2C12 myoblasts, the PC12 neuronal cell line, embryonic rat cortical neurons, and amphibian retinal neurons. In addition, we demonstrate that this technique can directly pattern fibroblasts in microfluidic channels via brief application of a low vacuum on cell suspensions. The low vacuum does not significantly decrease cell viability as shown by cell viability assays. Modifications are discussed for application of the method to different cell and substrate types. This technique allows researchers to pattern cells and proteins in specific patterns without the need for exotic materials or equipment and can be done in any laboratory with a vacuum.

This report describes a simple, easy to perform technique, using low pressure vacuum, to fill microfluidic channels with cells and substrates for biological research.

Desenlendirme Proteinlerin ve Hücreleri Çok Yönlü Yöntemi

Substrate and cell patterning techniques are widely used in cell biology to study cell-to-cell and cell-to-substrate interactions. Conventional patterning ...

An Additive Manufacturing Technique for the Facile and Rapid Fabrication of Hydrogel-based Micromachines with Magnetically Responsive Components

Polyethylene glycol (PEG)-based hydrogels are biocompatible hydrogels that have been approved for use in humans by the FDA. Typical PEG-based hydrogels have simple monolithic architectures and often function as scaffolding materials for tissue engineering applications. More sophisticated structures typically take a long time to fabricate and do not contain moving components. This protocol describes a photolithography method that allows for facile and rapid microfabrication of PEG structures and devices. This strategy involves an in-house developed fabrication stage that allows for the rapid fabrication of 3D structures by building upwards in a layer-by-layer fashion. Independent moving components can also be aligned and assembled onto support structures to form integrated devices. These independent components are doped with superparamagnetic iron oxide nanoparticles that are sensitive to magnetic actuation. In this manner, the fabricated devices can be actuated using external magnets to yield movement of the components within. Hence, this technique allows for the fabrication of sophisticated MEMS-like devices (micromachines) that are composed entirely out of a biocompatible hydrogel, able to function without an onboard power source, and respond to a contact-less method of actuation. This manuscript describes the fabrication of both the fabrication set-up as well as the step-by-step method for the microfabrication of these hydrogels-based MEMS-like devices.

An additive manufacturing strategy for processing UV-crosslinkable hydrogels has been developed. This strategy allows for the layer-by-layer assembly of microfabricated hydrogel structures as well as the assembly of independent components, yielding integrated devices containing moving components that are responsive to magnetic actuation.

Teknik hidrojel tabanlı Micromachines manyetik olarak duyarlı bileşenleri ile Facile ve hızlı üretim için üretim bir katkı

Polyethylene glycol (PEG)-based hydrogels are biocompatible hydrogels that have been approved for use in humans by the FDA. Typical PEG-based hydrogels ...

Initial 3D Cell Cluster Control in a Hybrid Gel Cube Device for Repeatable Pattern Formations

The importance of in vitro 3D cultures is considerably emphasized in cell/tissue culture. However, the lack of experimental repeatability is one of its restrictions. Producing few repeatable results of pattern formation deteriorates the analysis of the mechanisms underlying the self-organization. Reducing variation in initial culture conditions, such as the cell density and distribution in the extracellular matrix (ECM), is crucial to enhance the repeatability of a 3D culture. In this article, we demonstrate a simple but robust procedure for controlling the initial cell cluster shape in a 3D extracellular matrix to obtain highly repeatable pattern formations. A micromold with a desired shape was fabricated by using photolithography or a machining process, and it formed a 3D pocket in the ECM contained in a hybrid gel cube (HGC). Highly concentrated cells were then injected in the pocket so that the cell cluster shape matched with the fabricated mold shape. The employed HGC allowed multi-directional scanning by its rotation, which enabled high-resolution imaging and the capture of the entire tissue structure even though a low-magnification lens was used. Normal human bronchial epithelial cells were used to demonstrate the methodology.&#160;

We present a procedure for controlling the initial cell cluster shape in a 3D extracellular matrix to obtain a repeatable pattern formation. A cubic device containing two different hydrogels is employed to achieve multi-directional imaging for tissue pattern formation.

İlk 3D hücre küme denetimi içinde a Hybrid jel küp aygıt için tekrarlanabilir model oluşumları

The importance of in vitro 3D cultures is considerably emphasized in cell/tissue culture. However, the lack of experimental repeatability is one of its ...

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.

Jelatin Metacryloyl Hidrojel Bazlı Bioinks 3D Biyobaskı Protokolleri

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

Interlinked Macroporous 3D Scaffolds from Microgel Rods

A two-component system of functionalized microgels from microfluidics allows for fast interlinking into 3D macroporous constructs in aqueous solutions without further additives. Continuous photoinitiated on-chip gelation enables variation of the microgel aspect ratio, which determines the building block properties for the obtained constructs. Glycidyl methacrylate (GMA) or 2-aminoethyl methacrylate (AMA) monomers are copolymerized into the microgel network based on polyethylene glycol (PEG) star-polymers to achieve either epoxy or amine functionality. A focusing oil flow is introduced into the microfluidic outlet structure to ensure continuous collection of the functionalized microgel rods. Based on a recent publication, microgel rod-based constructs result in larger pores of several hundred micrometers and, at the same time, lead to overall higher scaffold stability in comparison to a spherical-based model. In this way, it is possible to produce higher-volume constructs with more free volume while reducing the amount of material required. The interlinked macroporous scaffolds can be picked up and transported without damage or disintegration. Amine and epoxy groups not involved in interlinking remain active and can be used independently for post-modification. This protocol describes an optimized method for the fabrication of microgel rods to form macroporous interlinked scaffolds that can be utilized for subsequent cell experiments.

Microgel rods with complementary reactive groups are produced via microfluidics with the ability to interlink in aqueous solution. The anisometric microgels jam and interlink into stable constructs with larger pores compared to spherical-based systems. Microgels modified with GRGDS-PC form macroporous 3D constructs that can be used for cell culture.

Mikrojel Çubuklardan Birbirine Bağlı Makrogözenekli 3D İskeleler

A two-component system of functionalized microgels from microfluidics allows for fast interlinking into 3D macroporous constructs in aqueous solutions ...