Tis work was supported by the National Key Research and Development Program of China (2022YFA1104600), and the Zhejiang Provincial Natural Science Foundation of China (LQ23H160011).

1. Fabrication of the 3D acoustic assembly device
<ol>
	<li>Begin by preparing four 1 mm thick PMMA sheets through laser cutting30, and then proceed to glue them together to form a square chamber with an inner width of 21 mm and a height of 10 mm.</li>
	<li>Next, attach another 1 mm thick PMMA sheet to the bottom of the chamber to serve as a holder for the bioink.</li>
	<li>Carefully affix three lead zirconate titanate (PZT) transducers (each measuring 20 mm in length, 10 mm in width, 0.7 mm in thickness, and with a primary resonant frequency of 3 MHz, see Table of Materials) to the exterior of the three orthogonal walls of the chamber, respectively. Ensure that the bottom PZT transducer is centered beneath the chamber.</li>
	<li>Solder wires to the two conductive areas of each PZT transducer.</li>
	<li>Finally, secure the device onto a hollow base to prevent the bottom PZT from coming into contact with other countertops.</li>
</ol>
2. Setting up the acoustic assembly system
<ol>
	<li>Begin by mounting the acoustic device onto a microscope stage, allowing for top-view observation of the chamber&#39;s interior.</li>
	<li>Position a digital microscope on the side of the device that is free from PZT transducers, enabling side-view observation of the chamber&#39;s interior.</li>
	<li>Independently connect the wires from the three PZT transducers in series to three power amplifiers and three output channels of function generators (see Table of Materials).</li>
	<li>Program the settings on the function generators for each PZT transducer, specifying parameters such as sinusoidal waveform, frequency, and amplitude.</li>
	<li>To ensure sterilization, fill the chamber of the acoustic device with 75% alcohol for 5 min, followed by a thorough cleaning with sterile PBS solution. Subsequently, irradiate the chamber with UV light in a clean bench for a minimum of 1 h.</li>
</ol>
3. Cell culture and harvest procedure
<ol>
	<li>Begin by culturing C3A cells, a human hepatocellular carcinoma cell line, in a T25 cell culture flask using Dulbecco&#39;s modified Eagle medium (DMEM) supplemented with 10% fetal bovine serum and 1% penicillin-streptomycin (see Table of Materials).</li>
	<li>When the C3A cells reach approximately 80% confluence, perform cell passage as follows: firstly, wash the bottom of the culture flask twice with PBS. Then, add 2 mL of 0.05% trypsin-EDTA to the cell culture flask and incubate at 37 &#176;C to facilitate cell detachment. Stop the trypsinization process by adding 2 mL of complete culture medium.</li>
	<li>Transfer the cell solution to a 15 mL tube, and centrifuge it at 200 &#215; g for 5 min at room temperature to obtain a cell pellet.</li>
</ol>
4. Preparation of the bioink
<ol>
	<li>Prepare a 6% (w/v) GelMA solution containing 0.5% (w/v) lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) by dissolving 0.3 g of GelMA and 0.025 g of LAP (see Table of Materials) in 5 mL of phosphate buffer solution (PBS). Allow the mixture to sit in a 47 &#176;C water bath for 1 h.</li>
	<li>Before mixing with cells, pass the GelMA solution through a 0.22 &#181;m filter (see Table of Materials) for sterilization.</li>
	<li>Resuspend the cell pellet mentioned above (step 3.3) in cell culture medium. Stain a small volume of cells with a 0.4% trypan blue solution and then use a clean hemocytometer for cell counting.</li>
	<li>Mix an appropriate amount of C3A cells, calculated based on the cell density obtained above, with the sterilized GelMA solution to prepare the bioink with a cell density of 2 &#215; 106 cells/mL.</li>
	<li>For visualization of the assembled cell spheroids, pre-stain C3A cells by incubating them with 2 &#181;M cell tracker (DiO dye, see Table of Materials) at 37 &#176;C for 20 min. Subsequently, wash the labeled cells with fresh cell culture medium three times before use.</li>
</ol>
5. Assembling the cell spheroids using the acoustic device
<ol>
	<li>Pipette more than 1 mL of the bioink into the sterilized chamber. Ensure that the face-to-face distance between the liquid surface and the chamber bottom is an integer multiple of half the acoustic wavelength. 
	NOTE: One can control this distance by adjusting the volume of bioink added. The acoustic wavelength (&#955;) can be estimated using the formula &#955; = c/f, where c represents the speed of sound in the medium, and f is the frequency of the PZT transducer.</li>
	<li>Turn on the function generator and power amplifier to initiate the actuation of each PZT transducer. 
	NOTE: It is recommended to individually actuate each PZT transducer first to achieve the optimal parallel-line cellular pattern. This can be achieved by conducting a frequency sweep with a step size of 0.001 MHz near the primary resonant frequency for each PZT transducer. Afterward, simultaneously apply these optimal signals to all three PZT transducers to obtain the expected 3D-dot cellular pattern. Before applying each input signal, ensure that the cells are evenly dispersed in the bioink by gently agitating.</li>
	<li>Crosslink the bioink using blue light (405 nm, 60 mW/cm2, 30 s) to create a 3D hydrogel scaffold that encapsulates the cell aggregates assembled acoustically. Afterward, turn off the function generator and power amplifier.</li>
	<li>Carefully transfer the 3D hydrogel scaffold from the chamber into a Petri dish and cut it into small pieces (e.g., 2 mm &#215; 2 mm &#215; 2 mm) using a clean razor.</li>
	<li>Add cell culture medium for cultivation. 
	&#8203;NOTE: Remember to change the culture medium every day.</li>
</ol>
6. Retrieving cell spheroids
<ol>
	<li>Begin by observing spheroid formation at different layers of the scaffolds using an inverted microscope.</li>
	<li>After 3 days of culture, remove the culture medium and thoroughly wash the hydrogel scaffolds twice with PBS.</li>
	<li>Incubate the scaffolds with more than 2 mL of GelMA lysis buffer at a 1: 200 dilution with cell culture medium for 30 min in a cell incubator. This step aims to dissolve the hydrogel scaffolds.</li>
	<li>Transfer the solution from the previous step into a tube and then centrifuge it at 200 &#215; g for 5 min at room temperature to obtain the cell spheroid pellet.</li>
	<li>Discard the supernatant and resuspend the pellet in fresh culture medium for downstream applications.</li>
</ol>
7. Spheroid viability analysis
<ol>
	<li>Assess the viability of cell spheroids either within the hydrogel scaffolds or in the retrieved spheroids using a live/dead staining kit (see Table of Materials).</li>
	<li>Incubate the samples at different culture time points with 1 mL of PBS solution containing 1 &#181;L of Calcein-AM and 2 &#181;L of Propidium Iodide (PI) for 15 min at 37 &#176;C.</li>
	<li>For samples within the hydrogel scaffolds, wash them directly with PBS twice. For retrieved spheroids, centrifuge at 200 &#215; g for 5 min at roomtemperature to obtain a spheroid pellet, and wash it twice before observation.</li>
	<li>Observe the samples using a fluorescence microscope and capture the fluorescence images.</li>
	<li>Calculate the ratio of the area stained with Calcein-AM to the total area stained with both Calcein-AM and PI using ImageJ to determine spheroid viability.</li>
</ol>

Scalable Generation of Uniform Cell Spheroids Using a 3D Acoustic Assembly Device

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The authors have nothing to disclose.

Efficient and stable fabrication of cell spheroids with high throughput using technologies like the 3D acoustic assembly device holds great promise for advancing biomedical engineering and drug screening1,2,3. This approach simplifies the mass production of cell spheroids through straightforward procedures.
However, there are critical factors to consider when using this acoustic device. The creation o...

3D in vitro culture models, which provide more in vivo-like structural and morphological characteristics compared to conventional 2D culture models, have been recognized as promising systems in various biomedical applications such as tissue engineering, disease modeling, and drug screening1,2,3. As one type of 3D culture model, cell spheroids typically refer to cell aggregation, creating 3D spheroidal structures characterized by enhanced cell-cell and cell-matrix interactions4,5,6. Therefore, fabricating cell spheroids has become a powerful tool for enabling diverse biological studies.
Various techniques, including hanging drop7, non-adhesive plates8, or microwell devices9, have been developed to obtain spheroids. In principle, these methods commonly facilitate cell assembly by utilizing physical forces such as gravitational force while minimizing interactions between cells and the substrate. However, they often involve labor-intensive processes, have low productivity, and pose challenges for controlling spheroid size10,11. Importantly, the production of spheroids with the desired size and uniformity in sufficient quantity is of utmost importance to satisfy specific biological applications. In contrast to the above-mentioned methods, acoustic waves, as one type of external-force-driven technique12,13,14, have shown potential for mass manufacturing of cell spheroids with high quality and throughput, based on the principle of enhancing cell aggregation through external forces15,16,17,18. Unlike electromagnetic or magnetic forces, acoustic-based cell manipulation techniques are non-invasive and label-free, enabling spheroid formation with excellent biocompatibility19,20.
Commonly, standing surface acoustic waves (SAWs) and bulk acoustic waves (BAWs)-based devices have been developed to generate spheroids, utilizing the acoustic nodes (ANs) produced by corresponding standing acoustic fields21,22,23. Particularly, acoustic assembly devices based on BAWs, with the merits of convenient manufacture, easy operation, and excellent scalability, have gained attention for fabricating cell spheroids24,25. We have recently developed a facile BAWs-based acoustic assembly device with the ability to generate spheroids with high throughput26. The proposed device consists of a square polymethyl methacrylate (PMMA) chamber with three lead zirconate titanate (PZT) transducers arranged respectively in the X/Y/Z plane. This arrangement enables the creation of a 3D dot-array pattern of levitated acoustic nodes (LANs) for driving cell assembly. Compared to previously reported BAWs- or SAWs-based devices, which can only create a 1D or 2D array of ANs27,28,29, the present device enables a 3D dot-array of LANs for rapid cell aggregate formation within the gelatin methacryloyl (GelMA) solution. Subsequently, cell aggregates matured into spheroids with high viability within the photocured GelMA scaffolds after three days of cultivation. Finally, a large number of spheroids with uniform size were easily obtained from the GelMA scaffolds for downstream applications.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.22-&#956;m filter</td>
			<td>Merck</td>
			<td>SLGSM33SS</td>
			<td>Used for GelMA solution sterilization</td>
		</tr>
		<tr>
			<td>35 mm-cell culture dish</td>
			<td>Corning</td>
			<td>430165</td>
			<td>Used for culturing cells</td>
		</tr>
		<tr>
			<td>Confocal microscope</td>
			<td>Nikon</td>
			<td>A1RHD25</td>
			<td>Fluorescent cell observation</td>
		</tr>
		<tr>
			<td>DiO dye</td>
			<td>Beyotime</td>
			<td>C1038</td>
			<td>Dye used to stain cells</td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Gibco</td>
			<td>12430054</td>
			<td>Cell culture media</td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Gibco</td>
			<td>10099141C</td>
			<td>Cell culture media supplement</td>
		</tr>
		<tr>
			<td>Function generator</td>
			<td>Rigol</td>
			<td>DG5352</td>
			<td>For RF signal generation</td>
		</tr>
		<tr>
			<td>GelMA</td>
			<td>Regenovo</td>
			<td>none</td>
			<td>Used to prepare bioink</td>
		</tr>
		<tr>
			<td>GelMA lysis buffer</td>
			<td>EFL</td>
			<td>EFL-GM-LS-001</td>
			<td>Used to dissolve GelMA scaffolds</td>
		</tr>
		<tr>
			<td>Inverted microscope</td>
			<td>Nikon</td>
			<td>Ti-U</td>
			<td>Cell observation</td>
		</tr>
		<tr>
			<td>LAP</td>
			<td>Sigma-Aldrich</td>
			<td>900889</td>
			<td>Used as photoinitiator</td>
		</tr>
		<tr>
			<td>Live-Dead kit</td>
			<td>Beyotime</td>
			<td>C2015M</td>
			<td>Cell vability analysis</td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Gibco</td>
			<td>10010002</td>
			<td>Used as buffer</td>
		</tr>
		<tr>
			<td>Penicillin-streptomycin</td>
			<td>Gibco</td>
			<td>15070063</td>
			<td>Prevent cell culture contamination</td>
		</tr>
		<tr>
			<td>Power amplifer</td>
			<td>Minicircuit</td>
			<td>LCY-22+</td>
			<td>Increase the voltage amplitude of the RF signal</td>
		</tr>
		<tr>
			<td>PZT transducers</td>
			<td>Yantai Xingzhiwen Trading Co.,Ltd.</td>
			<td>PZT-41</td>
			<td>Functional units for acoustic assembly device</td>
		</tr>
		<tr>
			<td>T25 cell culture flask</td>
			<td>Corning</td>
			<td>430639</td>
			<td>Used for culturing cells</td>
		</tr>
		<tr>
			<td>Trypan blue&#160;</td>
			<td>Gibco</td>
			<td>15250061</td>
			<td>Cell counting</td>
		</tr>
		<tr>
			<td>Trypsin-EDTA&#160;</td>
			<td>Gibco</td>
			<td>25200056</td>
			<td>Cell dissociation enzyme</td>
		</tr>
	</tbody>
</table>

three-dimensional acoustic assembly device for mass manufacturing of cell spheroids

Cell spheroids are promising three-dimensional (3D) models that have gained wide applications in many biological fields. This protocol presents a method for manufacturing high-quality and high-throughput cell spheroids using a 3D acoustic assembly device through maneuverable procedures. The acoustic assembly device consists of three lead zirconate titanate (PZT) transducers, each arranged in the X/Y/Z plane of a square polymethyl methacrylate (PMMA) chamber. This configuration enables the generation of a 3D dot-array pattern of levitated acoustic nodes (LANs) when three signals are applied. As a result, cells in the gelatin methacryloyl (GelMA) solution can be driven to the LANs, forming uniform cell aggregates in three dimensions. The GelMA solution is then UV-photocured and crosslinked to serve as a scaffold that supports the growth of cell aggregates. Finally, masses of matured spheroids are obtained and retrieved by subsequently dissolving the GelMA scaffolds under mild conditions. The proposed new 3D acoustic cell assembly device will enable the scale-up fabrication of cell spheroids, and even organoids, offering great potential technology in the biological field.

This study designed a 3D acoustic assembly device for mass manufacturing of cell spheroids. The acoustic device comprised a square chamber with two PZT transducers attached to the X-plane and Y-plane on the outer surface of the chamber and one PZT transducer on the chamber&#39;s bottom (Figure 1A,B). Three output channels from two function generators were connected to three power amplifiers to generate three independently sinusoidal signals to actuate the PZT transducers (<s...

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Author Spotlight: Development of a Scaffold-Free Acoustic Assembly Method for High-Quality 3D Cell Spheroid Culture 

Cell spheroids have been considered one potential model in the field of biological applications. This article describes protocols for scalably generating cell spheroids using a 3D acoustic assembly device, which provides an efficient method for the robust and rapid fabrication of uniform cell spheroids.

Three-Dimensional Acoustic Assembly Device for Mass Manufacturing of Cell Spheroids

Cell spheroids are promising three-dimensional (3D) models that have gained wide applications in many biological fields. This protocol presents a method ...

3D in vitro culture models, like cell spheroids, have been widely used in the fields of tissue engineering, disease modeling, and drug screening. Our research focuses on developing and invest per engineering method to fabricate spheroids or other 3D in vitro culture models with high quality for diverse biological studies. In the current protocol, the spheroids grew within the GelMA scaffold and are retrieved at the final layback, dissolving the scaffold, causing additional procedures.We will try to acoustically assemble cell aggregates in a cultural medium to enable them to grow within spheroids without scaffold. Compared to magnetic assembly techniques, acoustic waves can directly assemble cells in a label-free manner without potential toxic effects on cells. Besides, our protocol enables cell spheroids to be assembled in a three-dimensional array, substantially increasing throughput.

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Research

JoVE Journal

Bioengineering

1.0K Views.  Hangzhou Dianzi University. 3D in vitro culture models, like cell spheroids, have been widely used in the fields of tissue engineering, disease modeling, and drug screening. Our research focuses on developing and invest per engineering method to fabricate spheroids or other 3D in vitro culture models with high quality for diverse biological studies. In the current protocol, the spheroids grew within the GelMA scaffold and are retrieved at the final layback, dissolving the scaffold, causing additional procedures.W...

Video: Author Spotlight: Development of a Scaffold-Free Acoustic Assembly Method for High-Quality 3D Cell Spheroid Culture 

Planar and Three-Dimensional Printing of Conductive Inks

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

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

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

Three-dimensional Cell Culture Model for Measuring the Effects of Interstitial Fluid Flow on Tumor Cell Invasion

The growth and progression of most solid tumors depend on the initial transformation of the cancer cells and their response to stroma-associated signaling in the tumor microenvironment 1. Previously, research on the tumor microenvironment has focused primarily on tumor-stromal interactions 1-2. However, the tumor microenvironment also includes a variety of biophysical forces, whose effects remain poorly understood. These forces are biomechanical consequences of tumor growth that lead to changes in gene expression, cell division, differentiation and invasion3. Matrix density 4, stiffness 5-6, and structure 6-7, interstitial fluid pressure 8, and interstitial fluid flow 8 are all altered during cancer progression.
Interstitial fluid flow in particular is higher in tumors compared to normal tissues 8-10. The estimated interstitial fluid flow velocities were measured and found to be in the range of 0.1-3 &mu;m s-1, depending on tumor size and differentiation 9, 11. This is due to elevated interstitial fluid pressure caused by tumor-induced angiogenesis and increased vascular permeability 12. Interstitial fluid flow has been shown to increase invasion of cancer cells 13-14, vascular fibroblasts and smooth muscle cells 15. This invasion may be due to autologous chemotactic gradients created around cells in 3-D 16 or increased matrix metalloproteinase (MMP) expression 15, chemokine secretion and cell adhesion molecule expression 17. However, the mechanism by which cells sense fluid flow is not well understood. In addition to altering tumor cell behavior, interstitial fluid flow modulates the activity of other cells in the tumor microenvironment. It is associated with (a) driving differentiation of fibroblasts into tumor-promoting myofibroblasts 18, (b) transporting of antigens and other soluble factors to lymph nodes 19, and (c) modulating lymphatic endothelial cell morphogenesis 20.
The technique presented here imposes interstitial fluid flow on cells in vitro and quantifies its effects on invasion (Figure 1). This method has been published in multiple studies to measure the effects of fluid flow on stromal and cancer cell invasion 13-15, 17. By changing the matrix composition, cell type, and cell concentration, this method can be applied to other diseases and physiological systems to study the effects of interstitial flow on cellular processes such as invasion, differentiation, proliferation, and gene expression.

Interstitial fluid flow is elevated in solid tumors and can modulate tumor cell invasion. Here we describe a technique to apply interstitial fluid flow to cells embedded in a matrix and then measure its effects on cell invasion. This technique can be easily adapted to study other systems.

The growth and progression of most solid tumors depend on the initial transformation of the cancer cells and their response to stroma-associated signaling ...

A Novel Three-dimensional Flow Chamber Device to Study Chemokine-directed Extravasation of Cells Circulating under Physiological Flow Conditions

Extravasation of circulating cells from the bloodstream plays a central role in many physiological and pathophysiological processes, including stem cell homing and tumor metastasis. The three-dimensional flow chamber device (hereafter the 3D device) is a novel in vitro technology that recreates physiological shear stress and allows each step of the cell extravasation cascade to be quantified. The 3D device consists of an upper compartment in which the cells of interest circulate under shear stress, and a lower compartment of static wells that contain the chemoattractants of interest. The two compartments are separated by porous inserts coated with a monolayer of endothelial cells (EC). An optional second insert with microenvironmental cells of interest can be placed immediately beneath the EC layer. A gas exchange unit allows the optimal CO2 tension to be maintained and provides an access point to add or withdraw cells or compounds during the experiment. The test cells circulate in the upper compartment at the desired shear stress (flow rate) controlled by a peristaltic pump. At the end of the experiment, the circulating and migrated cells are collected for further analyses. The 3D device can be used to examine cell rolling on and adhesion to EC under shear stress, transmigration in response to chemokine gradients, resistance to shear stress, cluster formation, and cell survival. In addition, the optional second insert allows the effects of crosstalk between EC and microenvironmental cells to be examined. The translational applications of the 3D device include testing of drug candidates that target cell migration and predicting the in vivo behavior of cells after intravenous injection. Thus, the novel 3D device is a versatile and inexpensive tool to study the molecular mechanisms that mediate cellular extravasation.

The three-dimensional flow chamber device is a novel in vitro technology for the quantitative and step-wise evaluation of the extravasation cascade of cells circulating under conditions of physiological shear stress. The device therefore fills a critical need for basic, preclinical, and clinical studies of cell migration.

Extravasation of circulating cells from the bloodstream plays a central role in many physiological and pathophysiological processes, including stem cell ...

Analysis of Cell Migration within a Three-dimensional Collagen Matrix

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

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

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

Micropatterning and Assembly of 3D Microvessels

In vitro platforms to study endothelial cells and vascular biology are largely limited to 2D endothelial cell culture, flow chambers with polymer or glass based substrates, and hydrogel-based tube formation assays. These assays, while informative, do not recapitulate lumen geometry, proper extracellular matrix, and multi-cellular proximity, which play key roles in modulating vascular function. This manuscript describes an injection molding method to generate engineered vessels with diameters on the order of 100 &#181;m. Microvessels are fabricated by seeding endothelial cells in a microfluidic channel embedded within a native type I collagen hydrogel. By incorporating parenchymal cells within the collagen matrix prior to channel formation, specific tissue microenvironments can be modeled and studied. Additional modulations of hydrodynamic properties and media composition allow for control of complex vascular function within the desired microenvironment. This platform allows for the study of perivascular cell recruitment, blood-endothelium interactions, flow response, and tissue-microvascular interactions. Engineered microvessels offer the ability to isolate the influence from individual components of a vascular niche and precisely control its chemical, mechanical, and biological properties to study vascular biology in both health and disease.

This manuscript presents an injection molding method to engineer microvessels that recapitulate physiological properties of endothelium. The microfluidic-based process creates patent 3D vascular networks with tailorable conditions, such as flow, cellular composition, geometry, and biochemical gradients. The fabrication process and examples of potential applications are described.

In vitro platforms to study endothelial cells and vascular biology are largely limited to 2D endothelial cell culture, flow chambers with polymer or glass ...

Characterizing Cell Migration Within Three-dimensional In Vitro Wound Environments

Currently, most in vitro models of wound healing, such as well-established scratch assays, involve studying cell migration and wound closure on two-dimensional surfaces. However, the physiological environment in which in vivo wound healing takes place is three-dimensional rather than two-dimensional. It is becoming increasingly clear that cell behavior differs greatly in two-dimensional vs. three-dimensional environments; therefore, there is a need for more physiologically relevant in vitro models for studying cell migration behaviors in wound closure. The method described herein allows for the study of cell migration in a three-dimensional model that better reflects physiological conditions than previously established two-dimensional scratch assays. The purpose of this model is to evaluate cell outgrowth via the examination of cell migration away from a spheroid body embedded within a fibrin matrix in the presence of pro- or anti-migratory factors. Using this method, cell outgrowth from the spheroid body in a three-dimensional matrix can be observed and is easily quantifiable over time via brightfield microscopy and analysis of spheroid body area. The effect of pro-migratory and/or inhibitory factors on cell migration can also be evaluated in this system. This method provides researchers with a simple method of analyzing cell migration in three-dimensional wound associated matrices in vitro, thus increasing the relevance of in vitro cell studies prior to the use of in vivo animal models.

Characterizing Cell Migration Within Three-dimensional In Vitro Wound Environments

The goal of this protocol is to evaluate the effect of pro- and anti-migratory factors on cell migration within a three-dimensional fibrin matrix.

Currently, most in vitro models of wound healing, such as well-established scratch assays, involve studying cell migration and wound closure on ...

Evaluation of Keratinocyte Proliferation on Two- and Three-dimensional Type I Collagen Substrates

Type I collagen, useful as a substrate for cell culture, exists in two forms: the two-dimensional, non-fibrous form and three-dimensional, fibril form. Both forms can be prepared with the same type I collagen. In general, the non-fibrous form promotes cell adhesion and proliferation. The fibril form (gels) provides more physiological conditions in many types of cells; therefore, gel culture is useful for examining physiological behaviors of cells, such as drug efficacy.
Researchers can select the appropriate form according to the purpose of its use. For example, in the case of keratinocytes, on-gel culture has been used as a wound healing model. FEPE1L-8, a keratinocyte cell line cultured on the non-fibrous form of type I collagen, promote cell adhesion. Notably, keratinocyte proliferation is slower on the fibril form than the non-fibrous form. Protocols for the preparation of type I collagen for cell culture are simple and have wide applications depending on the experimental needs.

Here, we present a protocol for the preparation of two different forms of culture substrates utilizing type I collagen. Depending on how collagen is handled, collagen molecules either maintain two-dimensional, non-fibrous form or reassemble into three-dimensional, fibril form. Cell proliferation on type I collagen is drastically affected by fibril formation.

Type I collagen, useful as a substrate for cell culture, exists in two forms: the two-dimensional, non-fibrous form and three-dimensional, fibril form. ...

Lab-on-a-CD Platform for Generating Multicellular Three-dimensional Spheroids

A three-dimensional spheroid cell culture can obtain more useful results in cell experiments because it can better simulate cell microenvironments of the living body than two-dimensional cell culture. In this study, we fabricated an electrical motor-driven lab-on-a-CD (compact disc) platform, called a centrifugal microfluidic-based spheroid (CMS) culture system, to create three-dimensional (3D) cell spheroids implementing high centrifugal force. This device can vary rotation speeds to generate gravity conditions from 1 x g to 521 x g. The CMS system is 6 cm in diameter, has one hundred 400 &#956;m microwells, and is made by molding with polydimethylsiloxane in a polycarbonate mold premade by a computer numerical control machine. A barrier wall at the channel entrance of the CMS system uses centrifugal force to spread cells evenly inside the chip. At the end of the channel, there is a slide region that allows the cells to enter the microwells. As a demonstration, spheroids were generated by monoculture and coculture of human adipose-derived stem cells and human lung fibroblasts under high gravity conditions using the system. The CMS system used a simple operation scheme to produce coculture spheroids of various structures of concentric, Janus, and sandwich. The CMS system will be useful in cell biology and tissue engineering studies that require spheroids and organoid culture of single or multiple cell types.

We present a motor-powered centrifugal microfluidic device that can cultivate cell spheroids. Using this device, spheroids of single or multiple cell types could be easily cocultured under high gravity conditions.

A three-dimensional spheroid cell culture can obtain more useful results in cell experiments because it can better simulate cell microenvironments of the ...

Using Multilayered Hydrogel Bioink in Three-Dimensional Bioprinting for Homogeneous Cell Distribution

During the extrusion-based three-dimensional bioprinting process, liquid-like bioinks with low viscosity can protect cells from membrane damage induced by shear stress and improve the survival of the encapsulated cells. However, rapid gravity-driven cell sedimentation in the reservoir could lead to an inhomogeneous cell distribution in bioprinted structures and therefore hinder the application of liquid-like bioinks. Here, we developed a novel multilayered modified strategy for liquid-like bioinks (e.g., gelatin methacryloyl with low viscosity) to prevent the sedimentation of encapsulated cells. Multiple liquid interfaces were manipulated in the multilayered bioink to provide interfacial retention. Consequently, the cell sedimentation action going across adjacent layers in the multilayered system was retarded in the bioink reservoir. It was found that the interfacial retention was much higher than the sedimental pull of cells, demonstrating a critical role of the interfacial retention in preventing cell sedimentation and promoting a more homogeneous dispersion of cells in the multilayered bioink.

Here, we developed a novel multilayered modified strategy for liquid-like bioinks (gelatin methacryloyl with low viscosity) to prevent the sedimentation of encapsulated cells.

During the extrusion-based three-dimensional bioprinting process, liquid-like bioinks with low viscosity can protect cells from membrane damage induced by ...

Generation of Multicue Cellular Microenvironments by UV-Photopatterning of Three-Dimensional Cell Culture Substrates

The extracellular matrix is an important regulator of cell function. Environmental cues existing in the cellular microenvironment, such as ligand distribution and tissue geometry, have been increasingly shown to play critical roles in governing cell phenotype and behavior. However, these environmental cues and their effects on cells are often studied separately using in vitro platforms that isolate individual cues, a strategy that heavily oversimplifies the complex in vivo situation of multiple cues. Engineering approaches can be particularly useful to bridge this gap, by developing experimental setups that capture the complexity of the in vivo microenvironment, yet retain the degree of precision and manipulability of in vitro systems.
This study highlights an approach combining ultraviolet (UV)-based protein patterning and lithography-based substrate microfabrication, which together enable high-throughput investigation into cell behaviors in multicue environments. By means of maskless UV-photopatterning, it is possible to create complex, adhesive protein distributions on three-dimensional (3D) cell culture substrates on chips that contain a variety of well-defined geometrical cues. The proposed technique can be employed for culture substrates made from different polymeric materials and combined with adhesive patterned areas of a broad range of proteins. With this approach, single cells, as well as monolayers, can be subjected to combinations of geometrical cues and contact guidance cues presented by the patterned substrates. Systematic research using combinations of chip materials, protein patterns, and cell types can thus provide fundamental insights into cellular responses to multicue environments.

Traditionally, cell culture is performed on planar substrates that poorly mimic the natural environment of cells in vivo. Here we describe a method to produce cell culture substrates with physiologically relevant curved geometries and micropatterned extracellular proteins, allowing systematic investigations into cellular sensing of these extracellular cues.