This work was funded by the Research Foundation for the State University of New York (Award #: 71272) and the IMPACT Award of University at Buffalo (Award #: 000077).

NOTE: The hierarchical cloning protocol offered in this toolkit can be divided into three major steps: 1. Cloning part plasmids; 2. Cloning transcription units (TUs); 3. Cloning multi-gene plasmids (Figure 1). This protocol starts from the primer design and ends with applications of the cloned multi-gene plasmid.
1. Primer design for cloning the part plasmid (pYTK001):
<ol>
	<li>Design the forward and reverse primers containing flanking nucleotides TTT at the 5&...

The MoClo based cloning kit developed by Lee et al. provides an excellent resource for quick assembly of one to five transcription units into a multi-gene plasmid either for replication or integration into the yeast genome. The use of this kit eliminates the time-consuming cloning bottleneck that frequently exists for expressing multiple genes in yeast.
We tested five different conditions for the digestion/ligation cycles of Golden Gate cloning with T4 DNA ligase. We found that 30 cycles of di...

Synthetic biology aims to engineer biological systems with new functionalities useful for pharmaceutical, agricultural, and chemical industries. Assembling large numbers of DNA fragments in a high-throughput manner is a foundational technology in synthetic biology. Such a complicated process can break down into multiple levels with decreasing complexity, a concept borrowed from basic engineering sciences1,2. In synthetic biology, DNA fragments usually assemble hierarchically based on functionality: (i) Part level: &#34;parts&#34; refers to DNA fragments with a specific function, such as a promoter, a coding sequence, a terminator, an origin of replication; (ii) Transcription units (TU) level: a TU consists of a promoter, a coding sequence, and a terminator capable of transcribing a single gene; (iii) Multi-gene level: a multi-gene plasmid contains multiple TUs frequently comprised of an entire metabolic pathway. This hierarchical assembly pioneered by the BioBrick community is the foundational concept for the assembly of large sets of DNAs in synthetic biology3.
In the past decade4,5,6,7, the Golden Gate cloning technique has significantly facilitated hierarchical DNA assembly2. Many other multi-part cloning methods, such as Gibson cloning8, ligation-independent cloning (SLIC)9, uracil excision-based cloning (USER)10, the ligase cycling reaction (LCR)11, and in vivo recombination (DNA Assembler)12,13, have also been developed so far. But Golden Gate cloning is an ideal DNA assembly method because it is independent of gene-specific sequences, allowing scar-less, directional, and modular assembly in a one-pot reaction. Golden Gate cloning takes advantage of type IIS restriction enzymes that recognize a non-palindromic sequence to create staggered overhangs outside of the recognition site2. A ligase then joins the annealed DNA fragments to obtain a multi-part assembly. Applying this cloning strategy to the modular cloning (MoClo) system has enabled the assemble of up to 10 DNA fragments with over 90% transformants screened containing the correctly assembled construct4.
The MoClo system offers tremendous advantages that have accelerated the design-build-test cycle of synthetic biology. Firstly, the interchangeable parts enable combinatorial cloning to test a large space of parameters rapidly. For example, optimizing a metabolic pathway usually requires cycling through many promoters for each gene to balance the pathway flux. The MoClo system can easily handle such demanding cloning tasks. Secondly, one needs to sequence the part plasmid but typically not the TU or the multi-gene plasmids. In most cases, screening by colony PCR or restriction digestion is sufficient for verification at the TU and multi-gene plasmid level. This is because cloning the part plasmid is the only step requiring PCR, which frequently introduces mutations. Thirdly, the MoClo system is ideal for building multi-gene complex metabolic pathways. Lastly, because of the universal overhangs, the part plasmids can be reused and shared with the entire bioengineering community. Currently, MoClo kits are available for plants14,15,5,16,17, fungi6,18,19,20,21,22, bacteria7,23,24,25,26,27, and animals28,29. A multi-kingdom MoClo platform has also been introduced recently30.
For Saccharomyces cerevisiae, Lee et al.6 have developed a versatile MoClo toolkit, an excellent resource for the yeast synthetic biology community. This kit comes in a convenient 96-well format and defines eight types of interchangeable DNA parts with a diverse collection of well-characterized promoters, fluorescent proteins, terminators, peptide tags, selection markers, origin of replication, and genome editing tools. This toolkit allows the assembly of up to five transcription units into a multi-gene plasmid. These features are valuable for yeast metabolic engineering, in which partial or entire pathways are over-expressed to produce targeted chemicals. Using this kit, researchers have optimized the production of geraniol, linalool31, penicillin32, muconic acid33, indigo34, and betalain35 in yeast.
Here we provide a detailed, step-by-step protocol to guide the use of the MoClo toolkit to generate multi-gene pathways for either episomal or genomic expression. Through extensive use of this kit, we have found that the accurate measurement of DNA concentrations is key to ensuring the equimolar distribution of each part in the Golden Gate reaction. We also recommend the T4 DNA ligase over the T7 DNA ligase because the former works better with larger numbers of overhangs36. Lastly, any internal recognition sites of BsmBI and BsaI must be removed or domesticated prior to assembly. Alternatively, one may consider synthesizing parts to remove multiple internal sites and to achieve simultaneous codon optimization. We demonstrate how to use this toolkit by expressing a five-gene pathway for &#946;-carotene and lycopene production in S. cerevisiae. We further show how to knock out the ADE2 locus using the genome-editing tools from this kit. These color-based experiments were selected for easy visualization. We also demonstrate how to generate fusion proteins and to create amino acid mutations using Golden Gate cloning.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.5 mm Glass beads</td>
			<td>RPI research products</td>
			<td>9831</td>
			<td>For lysing yeast cells</td>
		</tr>
		<tr>
			<td>Bacto Agar</td>
			<td>BD &#38; Company</td>
			<td>214010</td>
			<td>Component of the yeast complete synthetic medium (CSM)</td>
		</tr>
		<tr>
			<td>Bacto Peptone</td>
			<td>BD&#38; Company</td>
			<td>211677</td>
			<td>Component of the yeast extract peptone dextrose medium (YPD)</td>
		</tr>
		<tr>
			<td>BsaI-HFv2</td>
			<td>New England Biolabs</td>
			<td>R3733S</td>
			<td>a highly efficient version of BsaI restriction enzyme</td>
		</tr>
		<tr>
			<td>Carbenicillin</td>
			<td>Fisher Bioreagents</td>
			<td>4800-94-6</td>
			<td>Antibiotic for screening at the transcription unit level</td>
		</tr>
		<tr>
			<td>Chloramphenicol</td>
			<td>Fisher Bioreagents</td>
			<td>56-75-7</td>
			<td>Antibiotic for screening at the entry vector level</td>
		</tr>
		<tr>
			<td>CSM-His</td>
			<td>Sunrise Sciences</td>
			<td>1006-010</td>
			<td>Amino acid supplement of the yeast complete synthetic medium (CSM)</td>
		</tr>
		<tr>
			<td>Dextrose</td>
			<td>Fisher Chemical</td>
			<td>D16-500</td>
			<td>Carbon source of the yeast complete synthetic medium (CSM)</td>
		</tr>
		<tr>
			<td>Difco Yeast Nitrogen Base w/o Amino Acids</td>
			<td>BD &#38; Company</td>
			<td>291940</td>
			<td>Nitrogen source of the yeast complete synthetic medium (CSM)</td>
		</tr>
		<tr>
			<td>dNTP mix</td>
			<td>Promega</td>
			<td>U1515</td>
			<td>dNTPs for PCR</td>
		</tr>
		<tr>
			<td>Esp3I</td>
			<td>New England Biolabs</td>
			<td>R0734S</td>
			<td>a highly efficient isoschizomer of BsmBI</td>
		</tr>
		<tr>
			<td>Frozen-EZ Yeast Trasformation II Kit</td>
			<td>Zymo Research</td>
			<td>T2001</td>
			<td>For yeast transformation</td>
		</tr>
		<tr>
			<td>Hexanes</td>
			<td>Fisher Chemical</td>
			<td>H302-1</td>
			<td>For carotenoid extraction from yeast cells</td>
		</tr>
		<tr>
			<td>Kanamycin</td>
			<td>Fisher Bioreagents</td>
			<td>25389-94-0</td>
			<td>Antibiotic for screening at the multigene plasmid level</td>
		</tr>
		<tr>
			<td>LB Agar, Miller</td>
			<td>Fisher Bioreagents</td>
			<td>BP1425-2</td>
			<td>Lysogenic agar medium for E. coli culturing</td>
		</tr>
		<tr>
			<td>LB Broth, Miller</td>
			<td>Fisher Bioreagents</td>
			<td>BP1426-2</td>
			<td>Lysogenic liquid medium for E. coli culturing</td>
		</tr>
		<tr>
			<td>Lycopene</td>
			<td>Cayman chemicals</td>
			<td>NC1142173</td>
			<td>For lycopene quantification</td>
		</tr>
		<tr>
			<td>MoClo YTK</td>
			<td>Addgene</td>
			<td>1000000061</td>
			<td>Depositing Lab: John Deuber</td>
		</tr>
		<tr>
			<td>Monarch Plasmid Miniprep Kit</td>
			<td>New England Biolabs</td>
			<td>T1010L</td>
			<td>For plasmid purification from E.coli</td>
		</tr>
		<tr>
			<td>Nanodrop Spectrophotometer</td>
			<td>Thermo Scientific</td>
			<td>ND2000c</td>
			<td>For measuring accurate DNA concentrations</td>
		</tr>
		<tr>
			<td>NotI-HF</td>
			<td>New England Biolabs</td>
			<td>R3189S</td>
			<td>Restriction enzyme for integrative multigene plasmid linearization</td>
		</tr>
		<tr>
			<td>Nourseothricin Sulphate</td>
			<td>Goldbio</td>
			<td>N-500-100</td>
			<td>Antibiotic Selection marker for the pCAS plasmid used in this study</td>
		</tr>
		<tr>
			<td>Phusion HF reaction Buffer (5X)</td>
			<td>New England Biolabs</td>
			<td>B0518S</td>
			<td>Buffer for PCR using Phusion polymerase</td>
		</tr>
		<tr>
			<td>Phusion High Fidelity DNA Polymerase</td>
			<td>New England Biolabs</td>
			<td>M0530S</td>
			<td>High fidelity polymerase for all the PCR reactions</td>
		</tr>
		<tr>
			<td>pLM494</td>
			<td>Addgene</td>
			<td>100539</td>
			<td>Plasmid used to amplify crtI, crtYB and crtE used in this study</td>
		</tr>
		<tr>
			<td>Quartz Cuvette</td>
			<td>Thermo Electron</td>
			<td>10050801</td>
			<td>For quantifing carotenoids</td>
		</tr>
		<tr>
			<td>T4 ligase</td>
			<td>New England Biolabs</td>
			<td>M0202S</td>
			<td>Ligase for Golden Gate cloning</td>
		</tr>
		<tr>
			<td>Thermocycler</td>
			<td>BIO-RAD</td>
			<td>1851148</td>
			<td>For performing all the PCR and cloning reactions</td>
		</tr>
		<tr>
			<td>Tissue Homogenizer</td>
			<td>Bullet Blender</td>
			<td>Model: BBX24</td>
			<td>For homogenization of yeast cells</td>
		</tr>
		<tr>
			<td>UV-Vis Spectrophotometer</td>
			<td>Thermo Scientific</td>
			<td>Genesys 150</td>
			<td>For quantifing carotenoids</td>
		</tr>
		<tr>
			<td>Yeast Extract</td>
			<td>Fisher Bioreagents</td>
			<td>BP1422-500</td>
			<td>Component of the yeast extract peptone dextrose medium (YPD)</td>
		</tr>
		<tr>
			<td>&#946;-carotene</td>
			<td>Alfa Aesar</td>
			<td>AAH6010603</td>
			<td>For &#946;-carotene quantification</td>
		</tr>
	</tbody>
</table>

rapid assembly of multi-gene constructs using modular golden gate cloning

The Golden Gate cloning method enables the rapid assembly of multiple genes in any user-defined arrangement. It utilizes type IIS restriction enzymes that cut outside of their recognition sites and create a short overhang. This modular cloning (MoClo) system uses a hierarchical workflow in which different DNA parts, such as promoters, coding sequences (CDS), and terminators, are first cloned into an entry vector. Multiple entry vectors then assemble into transcription units. Several transcription units then connect into a multi-gene plasmid. The Golden Gate cloning strategy is of tremendous advantage because it allows scar-less, directional, and modular assembly in a one-pot reaction. The hierarchical workflow typically enables the facile cloning of a large variety of multi-gene constructs with no need for sequencing beyond entry vectors. The use of fluorescent protein dropouts enables easy visual screening. This work provides a detailed, step-by-step protocol for assembling multi-gene plasmids using the yeast modular cloning (MoClo) kit. We show optimal and suboptimal results of multi-gene plasmid assembly and provide a guide for screening for colonies. This cloning strategy is highly applicable for yeast metabolic engineering and other situations in which multi-gene plasmid cloning is required.

Here the results of four replicative multi-gene plasmids for &#946;-carotene (yellow) and lycopene (red) production. One integrative multi-gene plasmid for disrupting the ADE2 locus was constructed, the colonies of which are red.
Cloning CDSs into the entry vector (pYTK001) 
ERG20 was amplified from the yeast genome and the three carotenoid genes crtE, crtYB, crtI</em...

Watch this Scientific Journal Video about Rapid Assembly of Multi-Gene Constructs using Modular Golden Gate Cloning at JoVE.com

Rapid Assembly of Multi-Gene Constructs using Modular Golden Gate Cloning

The goal of this protocol is to provide a detailed, step-by-step guide for assembling multi-gene constructs using the modular cloning system based on Golden Gate cloning. It also gives recommendations on critical steps to ensure optimal assembly based on our experiences.

The Golden Gate cloning method enables the rapid assembly of multiple genes in any user-defined arrangement. It utilizes type IIS restriction enzymes that ...

This is a detailed protocol for assembling multi-gene plasmids using the Yeast MoClo kit. This method enables the convenient cloning of a variety of multi-gene classmates. It is ideal for generating a big library of related parts.Begin by setting up the Golden Gate reaction mix. Add 20 femtomoles of each PCR product and the entry vector, one microliter of 10X T4 Ligase buffer, 0.5 microliters of Esp3I, and 0.5 microliters of T4 ligase. Add double-distilled water to bring the total volume to 10 microliters.Then, run the cloning reaction. Transform the entire reaction mix into the DH5 alpha strain or equivalent Escherichia coli chemically competent cells by heat shock. Spread the cells on an lb plate with 35 micrograms per milliliter chloramphenicol.Then incubate the plate at 37 degrees Celsius overnight. After 16 to 18 hours, take the plate out of the incubator and leave it at four degrees Celsius for about five hours to let the superfolder green fluorescent protein or sfGFP develop for a more intense green color. To screen the plate, place it on an ultra-violet or blue light transilluminator.The sfGFP containing colonies will fluoresce under the UV light. The green colonies are negative because they contain the uncut part plasmid. The white colonies are likely positive.The cloning is successful if there are 30 to 100%white colonies. Assemble an intermediate vector with the left connector, the sfGFP dropout, the right connector, a yeast selection marker, a yeast origin of replication, and the part plasmid with an mRFP1, an E.coli origin, and the ampicillin resistant gene. Perform the cloning reaction as described in the text manuscript.Transform the entire reaction mix into the DH5 alpha strain then spread the cells on an lb plate with 50 micrograms per milliliter carbenicillin or ampicillin. Incubate at 37 degrees Celsius overnight. After 16 to 18 hours, take the plate out of the incubator.The plate will contain both pale red and pale green colonies. Keep it at four degrees Celsius for about five hours to let the mRFP1 and sfGFP mature. Use a UV or blue light transilluminator to identify the green colonies which contain the potentially correct intermediate vector.Streak out the green colonies on an lb carbenicillin plate and incubate at 37 degrees Celsius overnight. On the next day, streak them out again on a chloramphenicol plate and incubate at 37 degrees Celsius overnight. The colonies growing on chloramphenicol plates contain misassembled plasmids.Once the intermediate vector has been successfully assembled, proceed with assembling the transcription units. This four-piece assembly contains the intermediate vector, a promoter, a CDS, and determinator. Purify the plasmids, record their concentrations, and dilute each plasmid to 20 femtomoles of DNA per microliter.After performing the cloning reaction, transform the entire cloning reaction mix into the DH5 alpha or equivalent E.coli competent cells and plate them on LBN carbenicillin. Then incubate the plate at 37 degrees Celsius overnight. After 16 to 18 hours, take the plate out of the incubator and keep it at four degrees Celsius for about five hours to let the sfGFP mature.Use a UV or a blue light transilluminator to identify the non-fluorescent white colonies which contain the potentially correct transcription units. Assemble an intermediate vector for the multi-gene plasmids as described in the text manuscript. Then transform the entire cloning reaction mix into DH5 alpha cells and plate them on lb with 50 micrograms per milliliter kanamycin.Incubate the plate at 37 degrees Celsius overnight. Perform red and green color-based screening, then streak and grow the green colonies on an lb kanamycin plate to screen for misassemblies as previously demonstrated. Next, assemble the multi-gene plasmid by setting up a cloning reaction as described in the text manuscript.Transform the entire cloning reaction mix into DH5 alpha cells and plate them on lb kanamycin. Incubate the plate at 37 degrees Celsius overnight. Then perform the green and white screening as previously described.This protocol was used to construct one integrative multi-gene plasmid for disrupting the ADE2 locus. Four replicative and one integrative multi-gene plasmids were assembled. The ratio of potentially correct colonies for the intermediate vector cloning was 1.83%Once the intermediate plasmid was cloned, the success rate of assembling multi-gene plasmids from the intermediate was 93.77%The negligible numbers of positive white colonies demonstrate a suboptimal assembly of multi-gene plasmids.After transforming into yeast, colonies producing beta-carotene and lycopene grew on day three. Four colonies from each plate were streaked out onto fresh plates and grown for two more days. The carotenoids were extracted and quantified by UV-Vis spectrophotometry.BTS1/ERG20 leads to 35 fold higher production of beta-carotene compared to the strain with ERG20 alone. Likewise, the production of lycopene is approximately 16.5 fold higher in the strain with BTS1/ERG20 compared to ERG20 alone. The multi-gene integrative plasmid was used for the disruption of the ADE2 locus, either with a gRNA and no helper DNA or with gRNA and a multi-gene integrative plasmid as helper DNA.After three to four days, red colonies were observed on the YPD plate with Nourseothricin, indicating that ADE2 had been successfully disrupted. While attempting this method, the most important thing to remember is to measure the DNA concentrations accurately and pipette carefully while setting up this reaction mix. This technique allows researchers in the field of Yeast Metabolic Engineering to survey a large number of genes and promoters for maximized product yield.

rapid-assembly-multi-gene-constructs-using-modular-golden-gate

Research

JoVE Journal

Bioengineering

ECM Protein Nanofibers and Nanostructures Engineered Using Surface-initiated Assembly

The extracellular matrix (ECM) in tissues is synthesized and assembled by cells to form a 3D fibrillar, protein network with tightly regulated fiber diameter, composition and organization. In addition to providing structural support, the physical and chemical properties of the ECM play an important role in multiple cellular processes including adhesion, differentiation, and apoptosis. In vivo, the ECM is assembled by exposing cryptic self-assembly (fibrillogenesis) sites within proteins. This process varies for different proteins, but fibronectin (FN) fibrillogenesis is well-characterized and serves as a model system for cell-mediated ECM assembly. Specifically, cells use integrin receptors on the cell membrane to bind FN dimers and actomyosin-generated contractile forces to unfold and expose binding sites for assembly into insoluble fibers. This receptor-mediated process enables cells to assemble and organize the ECM from the cellular to tissue scales. Here, we present a method termed surface-initiated assembly (SIA), which recapitulates cell-mediated matrix assembly using protein-surface interactions to unfold ECM proteins and assemble them into insoluble fibers. First, ECM proteins are adsorbed onto a hydrophobic polydimethylsiloxane (PDMS) surface where they partially denature (unfold) and expose cryptic binding domains. The unfolded proteins are then transferred in well-defined micro- and nanopatterns through microcontact printing onto a thermally responsive poly(N-isopropylacrylamide) (PIPAAm) surface. Thermally-triggered dissolution of the PIPAAm leads to final assembly and release of insoluble ECM protein nanofibers and nanostructures with well-defined geometries. Complex architectures are possible by engineering defined patterns on the PDMS stamps used for microcontact printing. In addition to FN, the SIA process can be used with laminin, fibrinogen and collagens type I and IV to create multi-component ECM nanostructures. Thus, SIA can be used to engineer ECM protein-based materials with precise control over the protein composition, fiber geometry and scaffold architecture in order to recapitulate the structure and composition of the ECM in vivo.

A method to obtain nanofibers and complex nanostructures from single or multiple extracellular matrix proteins is described. This method uses protein-surface interactions to create free-standing protein-based materials with tunable composition and architecture for use in a variety of tissue engineering and biotechnology applications.

The extracellular matrix (ECM) in tissues is synthesized and assembled by cells to form a 3D fibrillar, protein network with tightly regulated fiber ...

Cloning and Large-Scale Production of High-Capacity Adenoviral Vectors Based on the Human Adenovirus Type 5

High-capacity adenoviral vectors (HCAdV) devoid of all viral coding sequences represent one of the most advanced gene delivery vectors due to their high packaging capacity (up to 35 kb), low immunogenicity, and low toxicity. However, for many laboratories the use of HCAdV is hampered by the complicated procedure for vector genome construction and virus production. Here, a detailed protocol for efficient cloning and production of HCAdV based on the plasmid pAdFTC containing the HCAdV genome is described. The construction of HCAdV genomes is based on a cloning vector system utilizing homing endonucleases (I-CeuI and PI-SceI). Any gene of interest of up to 14 kb can be subcloned into the shuttle vector pHM5, which contains a multiple cloning site flanked by I-CeuI and PI-SceI. After I-CeuI and PI-SceI-mediated release of the transgene from the shuttle vector the transgene can be inserted into the HCAdV cloning vector pAdFTC. Because of the large size of the pAdFTC plasmid and the long recognition sites of the used enzymes associated with strong DNA binding, careful handling of the cloning fragments is needed. For virus production, the HCAdV genome is released by NotI digest and transfected into a HEK293 based producer cell line stably expressing Cre recombinase. To provide all adenoviral genes for adenovirus amplification, co-infection with a helper virus containing a packing signal flanked by loxP sites is required. Pre-amplification of the vector is performed in producer cells grown on surfaces and large-scale amplification of the vector is conducted in spinner flasks with producer cells grown in suspension. For virus purification, two ultracentrifugation steps based on cesium chloride gradients are performed followed by dialysis. Here tips, tricks, and shortcuts developed over the past years working with this HCAdV vector system are presented.

A protocol for generation of high-capacity adenoviral vectors lacking all viral coding sequences is presented. Cloning of transgenes contained in the vector genome is based on homing endonucleases. Virus amplification in producer cells grown as adherent cells and in suspension relies on a helper virus providing viral genes in trans.

High-capacity adenoviral vectors (HCAdV) devoid of all viral coding sequences represent one of the most advanced gene delivery vectors due to their high ...

Viability of Bioprinted Cellular Constructs Using a Three Dispenser Cartesian Printer

Tissue engineering has centralized its focus on the construction of replacements for non-functional or damaged tissue. The utilization of three-dimensional bioprinting in tissue engineering has generated new methods for the printing of cells and matrix to fabricate biomimetic tissue constructs. The solid freeform fabrication (SFF) method developed for three-dimensional bioprinting uses an additive manufacturing approach by depositing droplets of cells and hydrogels in a layer-by-layer fashion. Bioprinting fabrication is dependent on the specific placement of biological materials into three-dimensional architectures, and the printed constructs should closely mimic the complex organization of cells and extracellular matrices in native tissue. This paper highlights the use of the Palmetto Printer, a Cartesian bioprinter, as well as the process of producing spatially organized, viable constructs while simultaneously allowing control of environmental factors. This methodology utilizes computer-aided design and computer-aided manufacturing to produce these specific and complex geometries. Finally, this approach allows for the reproducible production of fabricated constructs optimized by controllable printing parameters.

A Cartesian bioprinter was designed and fabricated to allow multi-material deposition in precise, reproducible geometries, while also allowing control of environmental factors. Utilizing the three-dimensional bioprinter, complex and viable constructs may be printed and easily reproduced.

Tissue engineering has centralized its focus on the construction of replacements for non-functional or damaged tissue. The utilization of ...

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 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 ...

Bioprinting Cellularized Constructs Using a Tissue-specific Hydrogel Bioink

Bioprinting has emerged as a versatile biofabrication approach for creating tissue engineered organ constructs. These constructs have potential use as organ replacements for implantation in patients, and also, when created on a smaller size scale as model "organoids" that can be used in in vitro systems for drug and toxicology screening.
Despite development of a wide variety of bioprinting devices, application of bioprinting technology can be limited by the availability of materials that both expedite bioprinting procedures and support cell viability and function by providing tissue-specific cues. Here we describe a versatile hyaluronic acid (HA) and gelatin-based hydrogel system comprised of a multi-crosslinker, 2-stage crosslinking protocol, which can provide tissue specific biochemical signals and mimic the mechanical properties of in vivo tissues. 
Biochemical factors are provided by incorporating tissue-derived extracellular matrix materials, which include potent growth factors. Tissue mechanical properties are controlled combinations of PEG-based crosslinkers with varying molecular weights, geometries (linear or multi-arm), and functional groups to yield extrudable bioinks and final construct shear stiffness values over a wide range (100 Pa to 20 kPa). Using these parameters, hydrogel bioinks were used to bioprint primary liver spheroids in a liver-specific bioink to create in vitro liver constructs with high cell viability and measurable functional albumin and urea output. This methodology provides a general framework that can be adapted for future customization of hydrogels for biofabrication of a wide range of tissue construct types.

We describe a set of protocols that together provide a tissue-mimicking hydrogel bioink with which functional and viable 3-D tissue constructs can be bioprinted for use in in vitro screening applications.

Bioprinting has emerged as a versatile biofabrication approach for creating tissue engineered organ constructs. These constructs have potential use as ...

Layered Alginate Constructs: A Platform for Co-culture of Heterogeneous Cell Populations

Many load bearing tissues possess structurally and functionally distinct regions, typically accompanied by different cell phenotypes with differential mechanosensing characteristics. Engineering and analysis of these tissue types remain a challenge. Layered hydrogel constructs provide an opportunity for investigating the interactions among multiple cell populations within single constructs. Alginate hydrogels are both biocompatible and allow for easy isolation of cells after experimentation. Here, we describe a method for the development of small sized dual layered alginate hydrogel discs. This process maintains high cell viability of human mesenchymal stem cells during the formation process and these layered discs can withstand unconfined cyclic compression, commonly used for stimulation of hMSCs undergoing chondrogenesis. These layered constructs can potentially be scaled up to include additional levels, and also be used to segregate cell populations initially after layering. This dual layer alginate hydrogel culture platform can be used for many different applications including engineering and analysis of cells of load bearing tissues and co-cultures of other cell types.

Engineering and analysis of load bearing tissues with heterogeneous cell populations are still a challenge. Here, we describe a method for creating bi-layered alginate hydrogel discs as a platform for co-culture of diverse cell populations within one construct.

Many load bearing tissues possess structurally and functionally distinct regions, typically accompanied by different cell phenotypes with differential ...

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 ...

Automated Robotic Liquid Handling Assembly of Modular DNA Devices

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; represented by &#34;devices&#34; created as combinations of individual genetic components. However, manual assembly of such large numbers of devices is time-intensive, error-prone, and costly. The increasing sophistication and scale of synthetic biology research necessitates an efficient, reproducible way to accommodate large-scale, complex, and high throughput device construction.
Here, a DNA assembly protocol using the Type-IIS restriction endonuclease based Modular Cloning (MoClo) technique is automated on two liquid-handling robotic platforms. Automated liquid-handling robots require careful, often times tedious optimization of pipetting parameters for liquids of different viscosities (e.g. enzymes, DNA, water, buffers), as well as explicit programming to ensure correct aspiration and dispensing of DNA parts and reagents. This makes manual script writing for complex assemblies just as problematic as manual DNA assembly, and necessitates a software tool that can automate script generation. To this end, we have developed a web-based software tool, http://mocloassembly.com, for generating combinatorial DNA device libraries from basic DNA parts uploaded as Genbank files. We provide access to the tool, and an export file from our liquid handler software which includes optimized liquid classes, labware parameters, and deck layout. All DNA parts used are available through Addgene, and their digital maps can be accessed via the Boston University BDC ICE Registry. Together, these elements provide a foundation for other organizations to automate modular cloning experiments and similar protocols.
The automated DNA assembly workflow presented here enables the repeatable, automated, high-throughput production of DNA devices, and reduces the risk of human error arising from repetitive manual pipetting. Sequencing data show the automated DNA assembly reactions generated from this workflow are ~95% correct and require as little as 4% as much hands-on time, compared to manual reaction preparation.

Here, an automated workflow to perform modular DNA &#34;device&#34; assembly using a modular cloning DNA assembly method on liquid-handling robots is presented. The protocol uses an intuitive software tool for generating liquid handler picklists for combinatorial DNA device library generation, which we demonstrate using two liquid handling platforms.

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; ...

Synthesis of Cationized Magnetoferritin for Ultra-fast Magnetization of Cells

Many important biomedical applications, such as cell imaging and remote manipulation, can be achieved by labeling cells with superparamagnetic iron oxide nanoparticles (SPIONs). Achieving sufficient cellular uptake of SPIONs is a challenge that has traditionally been met by exposing cells to elevated concentrations of SPIONs or by prolonging exposure times (up to 72 hr). However, these strategies are likely to mediate toxicity. Here, we present the synthesis of the protein-based SPION magnetoferritin as well as a facile surface functionalization protocol that enables rapid cell magnetization using low exposure concentrations. The SPION core of magnetoferritin consists of cobalt-doped iron oxide with an average particle diameter of 8.2 nm mineralized inside the cavity of horse spleen apo-ferritin. Chemical cationization of magnetoferritin produced a novel, highly membrane-active SPION that magnetized human mesenchymal stem cells (hMSCs) using incubation times as short as one minute and iron concentrations as lows as 0.2 mM.

A protocol for the synthesis and cationization of cobalt-doped magnetoferritin is presented, as well as a method to rapidly magnetize stem cells with cationized magnetoferritin.

Many important biomedical applications, such as cell imaging and remote manipulation, can be achieved by labeling cells with superparamagnetic iron oxide ...

Treatment of Ligament Constructs with Exercise-conditioned Serum: A Translational Tissue Engineering Model

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, and translation of findings is often poor. Thus, there is ample opportunity for alternative experimental approaches. Here we present an approach in which human cells are isolated from human anterior cruciate ligament tissue remnants, expanded in culture, and used to form engineered ligaments. Exercise alters the biochemical milieu in the blood such that the function of many tissues, organs and bodily processes are improved. In this experiment, ligament construct culture media was supplemented with experimental human serum that has been &#39;conditioned&#39; by exercise. Thus the intervention is more biologically relevant since an experimental tissue is exposed to the full endogenous biochemical milieu, including binding proteins and adjunct compounds that may be altered in tandem with the activity of an unknown agent of interest. After treatment, engineered ligaments can be analyzed for mechanical function, collagen content, morphology, and cellular biochemistry. Overall, there are four major advantages versus traditional monolayer culture and animal models, of the physiological model of ligament tissue that is presented here. First, ligament constructs are three-dimensional, allowing for mechanical properties (i.e., function) such as ultimate tensile stress, maximal tensile load, and modulus, to be quantified. Second, the enthesis, the interface between boney and sinew elements, can be examined in detail and within functional context. Third, preparing media with post-exercise serum allows for the effects of the exercise-induced biochemical milieu, which is responsible for the wide range of health benefits of exercise, to be investigated in an unbiased manner. Finally, this experimental model advances scientific research in a humane and ethical manner by replacing the use of animals, a core mandate of the National Institutes of Health, the Center for Disease Control, and the Food and Drug Administration.

We present a model of ligament tissue in which three-dimensional constructs are treated with the human exercise-conditioned serum and analyzed for collagen content, function, and cellular biochemistry.

In vitro experiments are essential to understand biological mechanisms; however, the gap between monolayer tissue culture and human physiology is large, ...