This research was supported by grant R01NS062842 from the National Institute of Neurological Disorders and Stroke, National Institutes of Health (V.V.D.) and by grants R21 NS064403 from the National Institute of Neurological Disorders and Stroke, National Institutes of Health through ARRA (V.V.D.) and R21 EB006301 National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health (V.V.D.).

The sections for the molecular machine-based detection should be prepared first because their preparation takes more time than the assembly of the molecular device. The construct works well with 5-6&mu;m-thick sections cut from paraformaldehyde-fixed, paraffin-embedded tissue blocks. Use slide brands which retain sections well, such as ProbeOn Plus charged and precleaned slides (Fisher Scientific) or similar. We recommend at first using a tissue with a well-known pattern of DNA damage which contains both DNase I- and DNase II-type breaks, such as dexamethasone-treated apoptotic rat thymus 13,14.
1. Preparation of sections
<ol>
	<li>Place the sections in a slide rack and dewax in xylene for 15 min, transfer to a fresh xylene bath for an additional 5 minutes.</li>
	<li>Rehydrate by passing through graded ethanol concentrations: 96% Ethanol -2x5min; 80% Ethanol - 5min; water - 2x5 min.</li>
	<li>Digest section with Proteinase K. Use 100&mu;L of a 50&mu;g/mL solution per section. Incubate 15' at room temperature (23&deg; C) in a humidified chamber. The time may need adjustment depending on the tissue type. Hard tissues might require longer digestion. Times of 15-25 min are usually used. Insufficient digestion may result in the weaker signal. Overdigestion on the other hand results in signal disappearance and section disruption.</li>
	<li>Rinse in distilled water for 2x10 min.</li>
	<li>Apply 100 &mu;L per section of 2% BSA for preblocking. Incubate for 15 min at room temperature (23&deg; C). During this time assemble the molecular machine.</li>
</ol>
2. Molecular machines assembly
All reagents are scaled for 25 &mu;L total volume, which is sufficient for a single detection in an average size tissue section (10x10mm). The volume can be scaled up as needed.
<ol>
	<li>Combine in a small plastic tube in this order:</li>
</ol>
<table border="1">
	<tbody>
		<tr>
			<td>
			<ol>
				<li>Bidistilled water;</li>
				<li>15% polyethylene glycol-8000;</li>
				<li>Solution of 66 mM-Tris HCl, pH 7.5, 5 mM MgCl2, 0.1 mM dithioerythritol, 1 mM ATP, (i.e. regular T4 DNA ligase buffer);</li>
				<li>70 pmoles of Oligonucleotide 1,</li>
				<li>215 pmoles (1.76 - 7.1 &mu;g) VACC TOPO</li>
				<li>10 units T4 DNA ligase (500 U/mL)</li>
			</ol>
			</td>
		</tr>
	</tbody>
</table>
<ol start="2">
	<li>Mix gently by pipetting. The molecular construct almost instantly self-assembles in this solution and can be used immediately at room temperature (23&deg; C). Increasing the temperature to 37&deg; C blocks the T4 DNA ligase-based component of the labeling.</li>
</ol>
3. Using molecular machines in tissue sections to dual label 5'OH and 5'PO4 DNA breaks
<ol>
	<li>Aspirate the preblocking solution and apply 25&mu;L of the full reaction mix containing 70 pmoles of Oligonucleotide 1, 53 - 215 pmoles (1.76 - 7.1 &mu;g) VACC TOPO and 10 units T4 DNA ligase (500 U/mL) in solution of 66 mM-Tris HCl, pH 7.5, 5mM MgCl2, 0.1 mM dithioerythritol, 1 mM ATP, and 15% polyethylene glycol-8000. The same sequence oligonucleotide carrying a single FITC label, Oligonucleotide 2, can be used instead for detection of a single type of DNA breaks. In such case omit ligase from the labeling reaction. Also in this situation a solution of 50mM Tris-HCL, pH 7.4, 15% PEG-8000 can be used instead of T4 DNA ligase buffer.</li>
	<li>Incubate for 1 hr at room temperature (23&deg; C) in a humidified chamber with a plastic coverslip. Protect from light. Lowering of the temperature to 16&deg; C reduces the ligase-based signal; the temperature increase to 37&deg; C completely eliminates the ligase-based signal. A partial inhibition of ligase sometimes occurs in the reaction mix, possibly due to contaminants introduced with topoisomerase preparations. Therefore, longer incubation (2-4 hours) might be required especially when significant numbers of ligase-labeled breaks are present. Although both ligase and topo signals can be observed at this stage, in many instances the ligase signal can be further enhanced by re-application of the reaction mix without VACC TOPO and dual-labeled Oligonucleotide, but containing a hairpin shaped oligonucleotide (Oligonucleotide 3) (35 mg/mL) and T4 DNA ligase (250 U/mL). To enhance signal proceed to Step 3, to see the reaction without enhancement go to Step 5.</li>
	<li>Remove coverslips by gently immersing the slides vertically in a Coplin jar containing water at room temperature. Aspirate excess water.</li>
	<li>Enhance ligase signal by applying 25 &mu;L of reaction mix without VACC TOPO and Oligonucleotide 1, but containing Oligonucleotide 3: 66 mM-Tris HCl, pH 7.5, 5 mM MgCl2, 0.1 mM dithioerythritol, 1 mM ATP, and 15% polyethylene glycol-8000, 5 units T4 DNA ligase, 35 mg/mL Oligonucleotide 3 (blunt ended hairpin). The total volume of the labeling solution can be scaled up to accommodate the bigger sections. Incubate for 18 hr (overnight) at room temperature (23&deg; C) in a humidified chamber with a plastic coverslip.</li>
	<li>Remove coverslips by gently immersing the slides vertically in Coplin jar containing water at room temperature. Then wash section 3x10 min in distilled water.</li>
	<li>Rinse with sodium bicarbonate buffer. Alkaline solution rinse enhances FITC fluorescence, which is pH sensitive and is significantly reduced below pH 7.</li>
	<li>Cover section with an antifading solution (Vectashield with DAPI), coverslip and analyze the signal using a fluorescent microscope. Double-strand DNA breaks with 5'OH will fluoresce green, 5'PO4 breaks - will fluoresce red (Figure 2).</li>
</ol>
4. Representative Results
<img alt="Figure 2." src="/files/ftp_upload/3628/3628fig2.jpg" /> 
Figure 1. Semi-artificial molecular machine detects two types of DNA damage in situ. The fluorescent machine self-assembles when VACC TOPO binds to the double-hairpin 32-mer. The machine begins operation by splitting itself into two detector units via topoisomerase-made cut at the 3' end of the recognition sequence. This results in a cyclic process where the FITC-labeled unit continuously separates and religates back to the rhodamine-labeled unit. This persists until a detectable DNA break is encountered. When such an alternative acceptor (5'OH blunt end DNA break) is present in the tissue section, the FITC part will ligate to it. The remaining rhodamine part will attach to 5' PO4 DNA blunt end breaks with the help of T4 DNA ligase. Consequently, both types of DNA breaks are simultaneously detected.
<img alt="Figure 1." src="/files/ftp_upload/3628/3628fig1.jpg" />
 
Figure 2. Molecular machine dual labels two types of DNA breaks in a tissue section of dexamethasone-treated thymus. Blunt-ended DNA breaks of DNase I- and DNase II-type are detected in the thymic cortical areas undergoing apoptosis. Green cytoplasmic fluorescence (5'OH DNA breaks) marks cortical macrophages digesting nuclear material of apoptotic thymocytes. This signal is produced by VACC TOPO, and localizes to phagolysosomes with DNA containing 5'OH double-strand breaks 11,12. Red fluorescence (5'PO4 breaks) labels nuclei of apoptotic thymocytes not engulfed by macrophages. Massive numbers of thymocytes simultaneously undergo apoptosis accompanied by generation of 5'PO4 double-strand breaks, visualized by ligase-based labeling. These breaks are located at the nuclear periphery, forming ring-shaped patterns. All cellular nuclei are visualized by counterstaining with DAPI (blue fluorescence).

<ol>
	<li>Meacham, G. C., Patterson, C., Zhang, W., Younger, J. M., Cyr, D. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Nature. Cell. Biol. 3, 100-105 (2001).</li><li>Schuldt, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamic+Pol+expeditions.">Dynamic Pol expeditions.</a> Nature. Cell. Biol. 4, E279-E279 (2002).</li><li>Urry, D. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+machines:+how+motion+and+other+functions+of+living+organisms+can+result+from+reversible+chemical+changes.">Molecular machines: how motion and other functions of living organisms can result from reversible chemical changes.</a> Angew. Chem. Int. Ed. Engl. 32, 819-841 (1993).</li><li>Schneider, T. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Theory+of+molecular+machines+I.+Channel+capacity+of+molecular+machines.">Theory of molecular machines I. Channel capacity of molecular machines.</a> J. Theor. Biol. 148, 83-123 (1991).</li><li>McClare, C. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+machines,+Maxwell's+demon+and+living+organisms.">Chemical machines, Maxwell's demon and living organisms.</a> J. Theor. Biol. 30, 1-34 (1971).</li><li>Spirin, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ribosome+as+a+molecular+machine.">Ribosome as a molecular machine.</a> FEBS Lett. 514, 2-10 (2002).</li><li>Fabbrizzi, L., Foti, F., Licchelli, M., Maccarini, P. 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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Semi-artificial+fluorescent+molecular+machine+for+DNA+damage+detection.">Semi-artificial fluorescent molecular machine for DNA damage detection.</a> Nano. Letters. 4, 2461-2466 (2004).</li><li>Didenko, V. V., Hornsby, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Presence+of+double-strand+breaks+with+single-base+3'+overhangs+in+cells+undergoing+apoptosis+but+not+necrosis.">Presence of double-strand breaks with single-base 3' overhangs in cells undergoing apoptosis but not necrosis.</a> J. Cell Biol. 135, 1369-1376 (1996).</li><li>Didenko, V. V., Tunstead, J. R., Hornsby, P. 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No conflicts of interest declared.

In this video, we demonstrate how to assemble and use a dual-labeling DNA damage sensor. The sensor is a molecular machine driven by bio-molecular engine, a virus-encoded protein VACC TOPO linked with artificial components. The presented development exemplifies a bio-enabled approach which advocates adapting biological structures, architectures and actual parts and components of cells to the design of non-toxic molecular scale devices 12,15. This approach resolves two issues inherent to the field of in viv...

<ol>
 <li>Xylene</li>
 <li>80 and 96% Ethanol.</li>
 <li>2% solution of bovine serum albumin (BSA) in distilled water.</li>
 <li>Oligonucleotide 1: a double-hairpin, dual labeled with fluorescein and tetramethylrhodamine:</li>
</ol>
5'-AAG GGA CCT GCF GCA GGT CCC TTA ACG CAT RAT GCG TT- 3'; F - FITC-dT; R - Tetramethylrhodamine-dT. Other red-shifted fluorophores such as BODIPY TR, rhodamine or TAMRA can be used instead of tetramethylrhodamine as R.
Alternatively you can use Oligonucleotide 2 - a double-hairpin single labeled with fluorescein (for detection of a single type of DNA breaks (DNase II-type only). The single-fluorophore-carrying probe is considerably less expensive and is convenient whenever a single type of DNA break is to be labeled: 5'-AAG GGA CCT GCF GCA GGT CCC TTA ACG CAT ATG CGT T-3'; F - FITC-dT
<ol start="5">
 <li>Oligonucleotide 3. Blunt-ended rhodamine-labeled hairpin for enhancement of in situ ligation signal with T4 DNA ligase: 5'-GCG CTA GAC CRG GTC TAG CGC-3'; R - Tetramethylrhodamine-dT</li>
 <li>Vaccinia DNA topoisomerase l (VACC TOPO) - 3000 U/&mu;L (Vivid Technologies). In the initial experiments we used 215 pmoles (7.1 &mu;g) of the VACC TOPO per every 25 &mu;L of the reaction mix. However, the topoisomerase concentration can be significantly reduced without the loss of sensitivity. We later used a four times lesser amount of VACC TOPO per section (1.76 &mu;g in 25 &mu;L of the reaction mix per section) with similar results. Reducing amount of the enzyme to 880 ng (in 25 &mu;L of the reaction mix) resulted in a weaker signal and 8.8 ng of VACC TOPO produced no detectable signal.</li>
 <li>T4 DNA ligase 5 U/&mu;L (Roche). This highly concentrated ligase preparation gives the best signal in our experimental conditions.</li>
 <li>10 x reaction buffer for T4 DNA ligase: 660 mM Tris-HCl, 50 mM MgCl2, 10 mM dithioerythritol, 10 mM ATP, pH 7.5 (20&deg; C) (Roche) . ATP in reaction buffer is easily destroyed in repetitive cycles of thawing-freezing. Aliquot the buffer in small 15-20 &mu;L portions and store at - 20&deg; C. Use once.</li>
 <li>30% (w/v) solution of PEG-8000 (Sigma) in bidistilled water. 15 % PEG-8000 in the reaction mix strongly stimulates the detection, increasing the effective concentrations of its constituents by volume exclusion.</li>
 <li>Proteinase K (Roche) 20 mg/mL stock solution in distilled water. Store at - 20&deg; C. In the reaction use 50mg/mL solution in PBS, prepared from the stock. Do not reuse.</li>
 <li>Vectashield with DAPI (Vector Laboratories).</li>
 <li>Sodium bicarbonate buffer: 50mM NaHCO3, 15mM NaCl, pH 8.2.</li>
 <li>22x22mm or 22x40mm glass or plastic coverslips. Plastic coverslips are preferable during the reaction, as they are easier to remove from the section.</li>
</ol>

in vitro assembly of semi-artificial molecular machine and its use for detection of dna damage

Naturally occurring bio-molecular machines work in every living cell and display a variety of designs 1-6. Yet the development of artificial molecular machines centers on devices capable of directional motion, i.e. molecular motors, and on their scaled-down mechanical parts (wheels, axels, pendants etc) 7-9. This imitates the macro-machines, even though the physical properties essential for these devices, such as inertia and momentum conservation, are not usable in the nanoworld environments 10. Alternative designs, which do not follow the mechanical macromachines schemes and use mechanisms developed in the evolution of biological molecules, can take advantage of the specific conditions of the nanoworld. Besides, adapting actual biological molecules for the purposes of nano-design reduces potential dangers the nanotechnology products may pose. Here we demonstrate the assembly and application of one such bio-enabled construct, a semi-artificial molecular device which combines a naturally-occurring molecular machine with artificial components. From the enzymology point of view, our construct is a designer fluorescent enzyme-substrate complex put together to perform a specific useful function. This assembly is by definition a molecular machine, as it contains one 12. Yet, its integration with the engineered part - fluorescent dual hairpin - re-directs it to a new task of labeling DNA damage12.
Our construct assembles out of a 32-mer DNA and an enzyme vaccinia topoisomerase I (VACC TOPO). The machine then uses its own material to fabricate two fluorescently labeled detector units (Figure 1). One of the units (green fluorescence) carries VACC TOPO covalently attached to its 3'end and another unit (red fluorescence) is a free hairpin with a terminal 3'OH. The units are short-lived and quickly reassemble back into the original construct, which subsequently recleaves. In the absence of DNA breaks these two units continuously separate and religate in a cyclic manner. In tissue sections with DNA damage, the topoisomerase-carrying detector unit selectively attaches to blunt-ended DNA breaks with 5'OH (DNase II-type breaks)11,12, fluorescently labeling them. The second, enzyme-free hairpin formed after oligonucleotide cleavage, will ligate to a 5'PO4 blunt-ended break (DNase I-type breaks)11,12, if T4 DNA ligase is present in the solution 13,14 . When T4 DNA ligase is added to a tissue section or a solution containing DNA with 5'PO4 blunt-ended breaks, the ligase reacts with 5'PO4 DNA ends, forming semi-stable enzyme-DNA complexes. The blunt ended hairpins will interact with these complexes releasing ligase and covalently linking hairpins to DNA, thus labeling 5'PO4 blunt-ended DNA breaks.
This development exemplifies a new practical approach to the design of molecular machines and provides a useful sensor for detection of apoptosis and DNA damage in fixed cells and tissues.

Watch this Scientific Journal Video about In vitro Assembly of Semi-artificial Molecular Machine and its Use for Detection of DNA Damage at JoVE.com

In vitro Assembly of Semi-artificial Molecular Machine and its Use for Detection of DNA Damage

We demonstrate the assembly and application of a molecular-scale device powered by a topoisomerase protein. The construct is a bio-molecular sensor which labels two major types of DNA breaks in tissue sections by attaching two different fluorophores to their ends.

In vitro Assembly of Semi-artificial Molecular Machine and its Use for Detection of DNA Damage

Naturally occurring bio-molecular machines work in every living cell and display a variety of designs 1-6. Yet the development of artificial molecular ...

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11.5K Görüntüleme.  Baylor College of Medicine. Biz topoizomeraz bir protein tarafından desteklenmektedir moleküler ölçekli cihaz montaj ve uygulama göstermektedir. Inşa uçları iki farklı fluorophores ekleyerek doku kesitlerinde DNA kırıkları başlıca iki tipi etiketler moleküler biyo-sensör.

Video: In vitro Assembly of Semi-artificial Molecular Machine and its Use for Detection of DNA Damage

Fabrication of Electrochemical-DNA Biosensors for the Reagentless Detection of Nucleic Acids, Proteins and Small Molecules

As medicine is currently practiced, doctors send specimens to a central laboratory for testing and thus must wait hours or days to 
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"E-DNA" sensors, reagentless, electrochemical biosensors that perform well even when challenged directly in blood and other complex matrices, have been adapted to the detection of a wide range of nucleic acid, protein and small molecule analytes. Here we present a general procedure for the fabrication and use of such sensors.

As medicine is currently practiced, doctors send specimens to a central laboratory for testing and thus must wait hours or days to 
receive the results. ...

CometChip: A High-throughput 96-Well Platform for Measuring DNA Damage in Microarrayed Human Cells

DNA damaging agents can promote aging, disease and cancer and they are ubiquitous in the environment and produced within human cells as normal cellular metabolites. Ironically, at high doses DNA damaging agents are also used to treat cancer. The ability to quantify DNA damage responses is thus critical in the public health, pharmaceutical and clinical domains. Here, we describe a novel platform that exploits microfabrication techniques to pattern cells in a fixed microarray. The &#8216;CometChip&#8217; is based upon the well-established single cell gel electrophoresis assay (a.k.a. the comet assay), which estimates the level of DNA damage by evaluating the extent of DNA migration through a matrix in an electrical field. The type of damage measured by this assay includes abasic sites, crosslinks, and strand breaks. Instead of being randomly dispersed in agarose in the traditional assay, cells are captured into an agarose microwell array by gravity. The platform also expands from the size of a standard microscope slide to a 96-well format, enabling parallel processing. Here we describe the protocols of using the chip to evaluate DNA damage caused by known genotoxic agents and the cellular repair response followed after exposure. Through the integration of biological and engineering principles, this method potentiates robust and sensitive measurements of DNA damage in human cells and provides the necessary throughput for genotoxicity testing, drug development, epidemiological studies and clinical assays.

We describe here a platform that allows comet assay detection of DNA damage with unprecedented throughput. The device patterns mammalian cells into a microarray and enables parallel processing of 96 samples. The approach facilitates analysis of base level DNA damage, exposure-induced DNA damage and DNA repair kinetics.

DNA damaging agents can promote aging, disease and cancer and they are ubiquitous in the environment and produced within human cells as normal cellular ...

Use of a High-throughput In Vitro Microfluidic System to Develop Oral Multi-species Biofilms

There are few high-throughput in vitro systems which facilitate the development of multi-species biofilms that contain numerous species commonly detected within in vivo oral biofilms. Furthermore, a system that uses natural human saliva as the nutrient source, instead of artificial media, is particularly desirable in order to support the expression of cellular and biofilm-specific properties that mimic the in vivo communities. We describe a method for the development of multi-species oral biofilms that are comparable, with respect to species composition, to supragingival dental plaque, under conditions similar to the human oral cavity. Specifically, this methods article will describe how a commercially available microfluidic system can be adapted to facilitate the development of multi-species oral biofilms derived from and grown within pooled saliva. Furthermore, a description of how the system can be used in conjunction with a confocal laser scanning microscope to generate 3-D biofilm reconstructions for architectural and viability analyses will be presented. Given the broad diversity of microorganisms that grow within biofilms in the microfluidic system (including Streptococcus, Neisseria, Veillonella, Gemella, and Porphyromonas), a protocol will also be presented describing how to harvest the biofilm cells for further subculture&#160;or DNA extraction and analysis. The limits of both the microfluidic biofilm system and the current state-of-the-art data analyses will be addressed. Ultimately, it is envisioned that this article will provide a baseline technique that will improve the study of oral biofilms and aid in the development of additional technologies that can be integrated with the microfluidic platform.

Use of a High-throughput In Vitro Microfluidic System to Develop Oral Multi-species Biofilms

The goal of this methods paper is to describe the use of a microfluidic system for the development of multi-species biofilms that contain species typically identified in human supragingival dental plaque.&#160;Methods to describe biofilm architecture, biofilm viability, and an approach to harvest biofilm for culture-dependent or culture-independent analyses are highlighted.

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Eye Irritation Test (EIT) for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial (RhCE) Tissue Model

To comply with the Seventh Amendment to the EU Cosmetics Directive and EU REACH legislation, validated non-animal alternative methods for reliable and accurate assessment of ocular toxicity in man are needed. To address this need, we have developed an eye irritation test (EIT) which utilizes a three dimensional reconstructed human cornea-like epithelial (RhCE) tissue model that is based on normal human cells. The EIT is able to separate ocular&#160;irritants and corrosives (GHS Categories 1 and 2 combined) and those that do not require labeling (GHS No Category). The test utilizes two separate protocols, one designed for liquid chemicals and a second, similar protocol for solid test articles. The EIT prediction model uses a single exposure period (30 min for liquids, 6 hr for solids) and a single tissue viability cut-off (60.0% as determined by the MTT assay). Based on the results for 83 chemicals (44 liquids and 39 solids) EIT achieved 95.5/68.2/ and 81.8% sensitivity/specificity and accuracy (SS&#38;A) for liquids, 100.0/68.4/ and 84.6% SS&#38;A for solids, and 97.6/68.3/ and 83.1% for overall SS&#38;A. The EIT will contribute significantly to classifying the ocular irritation potential of a wide range of liquid and solid chemicals without the use of animals to meet regulatory testing requirements. The EpiOcular EIT method was implemented in 2015 into the OECD Test Guidelines as TG 492.

Eye Irritation Test EIT for Hazard Identification of Eye Irritating Chemicals using Reconstructed Human Cornea-like Epithelial RhCE Tissue Model

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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.

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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 ...

Construction and Use of an Electrical Stimulation Chamber for Enhancing Osteogenic Differentiation in Mesenchymal Stem/Stromal Cells In Vitro

Mesenchymal stem/stromal cells (MSCs) have been used extensively to promote bone healing in tissue engineering approaches. Electrical stimulation (EStim) has been demonstrated to increase MSC osteogenic differentiation in vitro and promote bone healing in clinical settings. Here we describe the construction of an EStim cell culture chamber and its use in treating rat bone-marrow-derived MSC to enhance osteogenic differentiation. We found that treating MSCs with EStim for 7 days results in a significant increase in the osteogenic differentiation, and importantly, this pro-osteogenic effect persists long after (7 days) EStim is discontinued. This approach of pretreating MSCs with EStim to enhance osteogenic differentiation could be used to optimize bone tissue engineering treatment outcomes and, thus, help them to achieve their full therapeutic potential. In addition to this application, this EStim cell culture chamber and protocol can also be used to investigate other EStim-sensitive cell behaviors, such as migration, proliferation, apoptosis, and scaffold attachment.

Here we present a protocol for the construction of a cell culture chamber designed to expose cells to various types of electrical stimulation, and its use in treating mesenchymal stem cells to enhance osteogenic differentiation.

Mesenchymal stem/stromal cells (MSCs) have been used extensively to promote bone healing in tissue engineering approaches. Electrical stimulation (EStim) ...

Bioparticle Microarrays for Chemotactic and Molecular Analysis of Human Neutrophil Swarming in vitro

Neutrophil swarming is a cooperative process by which neutrophils seal off a site of infection and promote tissue reorganization. Swarming has classically been studied in vivo in animal models showing characteristic patterns of cell migration. However, in vivo models have several limitations, including intercellular mediators that are difficult to access and analyze, as well as the inability to directly analyze human neutrophils. Because of these limitations, there is a need for an in vitro platform that studies swarming with human neutrophils and provides easy access to the molecular signals generated during swarming. Here, a multistep microstamping process is used to generate a bioparticle microarray that stimulates swarming by mimicking an in vivo infection. The bioparticle microarray induces neutrophils to swarm in a controlled and stable manner. On the microarray, neutrophils increase in speed and form stable swarms around bioparticle clusters. Additionally, supernatant generated by the neutrophils was analyzed and 16 proteins were discovered to have been differentially expressed over the course of swarming. This in vitro swarming platform facilitates direct analysis of neutrophil migration and protein release in a reproducible, spatially controlled manner.

This protocol generates bioparticle microarrays that provide spatially controlled neutrophil swarming. It provides easy access to the mediators that neutrophils release during migration and allows for quantitative imaging analysis.

Neutrophil swarming is a cooperative process by which neutrophils seal off a site of infection and promote tissue reorganization. Swarming has classically ...

Advanced 3D Liver Models for In vitro Genotoxicity Testing Following Long-Term Nanomaterial Exposure

Due to the rapid development and implementation of a diverse array of engineered nanomaterials (ENM), exposure to ENM is inevitable and the development of robust, predictive in vitro test systems is essential. Hepatic toxicology is key when considering ENM exposure, as the liver serves a vital role in metabolic homeostasis and detoxification as well as being a major site of ENM accumulation post exposure. Based upon this and the accepted understanding that 2D hepatocyte models do not accurately mimic the complexities of intricate multi-cellular interactions and metabolic activity observed in vivo, there is a greater focus on the development of physiologically relevant 3D liver models tailored for ENM hazard assessment purposes in vitro. In line with the principles of the 3Rs to replace, reduce and refine animal experimentation, a 3D HepG2 cell-line based liver model has been developed, which is a user friendly, cost effective system that can support both extended and repeated ENM exposure regimes (&#8804;14 days). These spheroid models (&#8805;500 &#181;m in diameter) retain their proliferative capacity (i.e., dividing cell models) allowing them to be coupled with the &#8216;gold standard&#8217; micronucleus assay to effectively assess genotoxicity in vitro. Their ability to report on a range of toxicological endpoints (e.g., liver function, (pro-)inflammatory response, cytotoxicity and genotoxicity) has been characterized using several ENMs across both acute (24 h) and long-term (120 h) exposure regimes. This 3D in vitro hepatic model has the capacity to be utilized for evaluating more realistic ENM exposures, thereby providing a future in vitro approach to better support ENM hazard assessment in a routine and easily accessible manner.

This procedure was established to be used for developing advanced 3D hepatic cultures in vitro, which can provide a more physiologically relevant assessment of the genotoxic hazards associated with nanomaterial exposures over both an acute or long-term, repeated dose regimes.

Due to the rapid development and implementation of a diverse array of engineered nanomaterials (ENM), exposure to ENM is inevitable and the development of ...