Name: design and synthesis of a reconfigurable dna accordion rack
Uploaded: 2018-08-15T15:00:00
Description: Watch this Scientific Journal Video about Design and Synthesis of a Reconfigurable DNA Accordion Rack at JoVE.com

This research was partially supported by the Global Research Development Center Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Science and ICT (MSIT) (2015K1A4A3047345) and Nano&#183;Material Technology Development Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science and ICT (MSIT) (2012M3A7A9671610). The Institute of Engineering Research at Seoul National University provided research facilities for this work. Authors acknowledge gratitude towards Tae-Young Yoon (Biological Sciences, Seoul National University) regarding the fluorescence spectroscopy for the FRET analysis.

1. Design of the 6 by 6 DNA Accordion Rack with caDNAno14
<ol>
	<li>Download and install caDNAno 2.0 software14 to design a DNA accordion rack (caDNAno 2.5 is also available on https://github.com/cadnano/cadnano2.5). Open caDNAno14 and click the Square Tool to add a new part with a square lattice.</li>
	<li>Number each beam of the accordion rack and draw on the left lattice panel of the caDNAno14 (<strong cl...

<ol>
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C., Lee, H., Kwon, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Reconfigurable+DNA+Accordion+Rack.">A Reconfigurable DNA Accordion Rack.</a> Angewandte Chemie International Edition. 57 (11), 2811-2815 (2018).</li><li>Chen, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Understanding+the+Mechanical+Properties+of+DNA+Origami+Tiles+and+Controlling+the+Kinetics+of+their+Folding+and+Unfolding+Reconfiguration.">Understanding the Mechanical Properties of DNA Origami Tiles and Controlling the Kinetics of their Folding and Unfolding Reconfiguration.</a> Journal of the American Chemical Society. 136 (19), 6995-7005 (2014).</li><li>Han, D., Pal, S., Liu, Y., Yan, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Folding+and+cutting+DNA+into+reconfigurable+topological+nanostructures.">Folding and cutting DNA into reconfigurable topological nanostructures.</a> Nature Nanotechnology. 5 (10), 712-717 (2010).</li><li>Douglas, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+prototyping+of+3D+DNA-origami+shapes+with+caDNAno.">Rapid prototyping of 3D DNA-origami shapes with caDNAno.</a> Nucleic Acids Research. 37 (15), 5001-5006 (2009).</li><li>Castro, C. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+primer+to+scaffolded+DNA+origami.">A primer to scaffolded DNA origami.</a> Nature methods. 8 (3), 221-229 (2011).</li><li>Ouldridge, T. E., Louis, A. A., Doye, J. P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=DNA+Nanotweezers+Studied+with+a+Coarse-Grained+Model+of+DNA.">DNA Nanotweezers Studied with a Coarse-Grained Model of DNA.</a> Physical Review Letters. 104 (17), 178101 (2010).</li><li>Snodin, B. E. K., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+Simulation+of+the+Self-Assembly+of+a+Small+DNA+Origami.">Direct Simulation of the Self-Assembly of a Small DNA Origami.</a> ACS Nano. 10 (2), 1724-1737 (2016).</li><li>Amir, Y., Abu-Horowitz, A., Bachelet, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Folding+and+Characterization+of+a+Bio-responsive+Robot+from+DNA+Origami.">Folding and Characterization of a Bio-responsive Robot from DNA Origami.</a> Journal of Visualized Experiments. (106), e51272 (2015).</li><li>Stahl, E., Martin, T. G., Praetorius, F., Dietz, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+and+Scalable+Preparation+of+Pure+and+Dense+DNA+Origami+Solutions.">Facile and Scalable Preparation of Pure and Dense DNA Origami Solutions.</a> Angewandte Chemie International Edition. 53 (47), 12735-12740 (2014).</li><li>Wei, B., Vhudzijena, M. K., Robaszewski, J., Yin, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Self-assembly+of+Complex+Two-dimensional+Shapes+from+Single-stranded+DNA+Tiles.">Self-assembly of Complex Two-dimensional Shapes from Single-stranded DNA Tiles.</a> Journal of Visualized Experiments. (99), e52486 (2015).</li><li>Clegg, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fluorescence+resonance+energy+transfer+and+nucleic+acids.">Fluorescence resonance energy transfer and nucleic acids.</a> Methods in enzymology. 211, 353-388 (1992).</li><li>Kopperger, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+self-assembled+nanoscale+robotic+arm+controlled+by+electric+fields.">A self-assembled nanoscale robotic arm controlled by electric fields.</a> Science. 359 (6373), 296-301 (2018).</li><li>Lauback, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Real-time+magnetic+actuation+of+DNA+nanodevices+via+modular+integration+with+stiff+micro-levers.">Real-time magnetic actuation of DNA nanodevices via modular integration with stiff micro-levers.</a> Nature Communications. 9 (1), 1446 (2018).</li></ol>

This protocol introduces the entire process from design, simulation, synthesis, and analysis of the basic 2D DNA accordion rack. The modified design and simulation rules have been described because the design rule differs from that of standard DNA origami, in that the DNA accordion rack has additional nucleotides at the crossovers for flexibility14,15. From this, we expect that the protocol can accelerate various researches using DNA accordion racks. In addition,...

Mechanical systems based on DNA nanostructures or DNA nanomachines1,2,3,4,5 are unique because they produce complex nanoscale motion in 2D and 3D in the nanometer to &#229;ngstr&#246;m resolution, according to various biomolecular stimuli2,3,6. By attaching functional materials on these structures and controlling their positions, these structures can be applied to various areas. For example, DNA nanomachines have been proposed for a molecular reactor7, drug delivery8, and nanoplasmonic systems9,10.
Previously, we introduced the reconfigurable DNA accordion rack, which can manipulate a 2D or 3D nanoscale network of elements11 (Figure 1A). Unlike other DNA nanomachines that only control a few elements, the platform can collectively manipulate periodically arrayed 2D or 3D elements into various stages. We anticipate that a programmable chemical and biological reaction network or a molecular computing system can be built from our system, by increasing the number of controllable elements. The DNA accordion rack is a structure, in which the network of multiple DNA beams is connected to joints composed of single-stranded DNA (Figure 1B). The accordion rack generated by the DNA beams is reconfigured by the DNA locks, which hybridize to the sticky part of beams and change the angle between the beams according to the length of the bridging part of the locks (locked state). In addition, multi-step reconfiguration is demonstrated by adding new locks after formation of the free state by detaching DNA locks through toehold-based strand displacement12,13.
In this protocol, we describe the entire design and synthesis process of the reconfigurable DNA accordion rack. The protocol includes design, simulation, wet-lab experiments, and analysis for the synthesis of the DNA accordion rack of 6 by 6 meshes and a reconfiguration of these. The structure covered in the protocol is the basic model of the previous research11 and is 65 nm by 65 nm in size, consisting of 14 beams. In terms of the design and simulation, the structural design of the accordion rack is different from conventional DNA origami14,15 (i.e., tightly packed). Therefore, the design rule and molecular simulation have been modified from traditional methods. To demonstrate, we show the design technique using the modified approach of caDNAno14 and the simulation of the accordion rack using oxDNA16,17 with additional scripts. Finally, both protocols of TEM and FRET for analysis of configured accordion rack structures are described.

<table>
	<tbody>
		<tr>
			<td>M13mp18 Single-stranded DNA</td>
			<td>NEB</td>
			<td>N4040s</td>
			<td></td>
		</tr>
		<tr>
			<td>1M MgCl2 Solution</td>
			<td>Biosesang</td>
			<td>M2001</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris-EDTA buffer</td>
			<td>Biosesang</td>
			<td>T2142</td>
			<td></td>
		</tr>
		<tr>
			<td>Nuclease-Free Water</td>
			<td>Qiagen</td>
			<td>129114</td>
			<td></td>
		</tr>
		<tr>
			<td>5M Sodium Chloride solution</td>
			<td>Biosesang</td>
			<td>s2007</td>
			<td></td>
		</tr>
		<tr>
			<td>PEG 8000</td>
			<td>Sigma Aldrich</td>
			<td>1546605</td>
			<td></td>
		</tr>
		<tr>
			<td>10N NaOH</td>
			<td>Biosesang</td>
			<td>S2038</td>
			<td></td>
		</tr>
		<tr>
			<td>Uranyl formate</td>
			<td>Thomas Science</td>
			<td>C993L42</td>
			<td></td>
		</tr>
		<tr>
			<td>Thermal cycler C1000</td>
			<td>Biorad</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Nanodropic 2000</td>
			<td>Thermo Fisher Scientific</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>TEM (LIBRA 120)&#160;&#160;</td>
			<td>Carl Zeiss</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorometer Enspire 2300</td>
			<td>Perkin-Elmer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Labogene</td>
			<td>LZ-1580</td>
			<td></td>
		</tr>
	</tbody>
</table>

design and synthesis of a reconfigurable dna accordion rack

DNA nanostructure-based mechanical systems or DNA nanomachines, which produce complex nanoscale motion in 2D and 3D in the nanometer to &#229;ngstr&#246;m resolution, show great potential in various fields of nanotechnology such as the molecular reactors, drug delivery, and nanoplasmonic systems. The reconfigurable DNA accordion rack, which can collectively manipulate a 2D or 3D nanoscale network of elements, in multiple stages in response to the DNA inputs, is described. The platform has potential to increase the number of elements that DNA nanomachines can control from a few elements to a network scale with multiple stages of reconfiguration.
In this protocol, we describe the entire experimental process of the reconfigurable DNA accordion rack of 6 by 6 meshes. The protocol includes a design rule and simulation procedure of the structures and a wet-lab experiment for synthesis and reconfiguration. In addition, analysis of the structure using TEM (transmission electron microscopy) and FRET (fluorescence resonance energy transfer) is included in the protocol. The novel design and simulation methods covered in this protocol will assist researchers to use the DNA accordion rack for further applications.

The designed 6 by 6 DNA accordion rack is simulated from the oxDNA16,17 and the results are shown in Figure 6. From the simulation result, it was confirmed that the intended structure is formed without distortion of the structure.
The TEM images in Figure 7 are images of configured structures with a lock length ...

Watch this Scientific Journal Video about Design and Synthesis of a Reconfigurable DNA Accordion Rack at JoVE.com

Design and Synthesis of a Reconfigurable DNA Accordion Rack

We describe the detailed protocol for design, simulation, wet-lab experiments, and analysis for a reconfigurable DNA accordion rack of 6 by 6 meshes.

DNA nanostructure-based mechanical systems or DNA nanomachines, which produce complex nanoscale motion in 2D and 3D in the nanometer to &#229;ngstr&#246;m ...

This method can help answer key questions in the nano molecules field, such as DNA nano technology, nano molecular circuits, and nano medicine. The main advantage of this technique is that it dramatically increases the category of controlling periodically irate elements in both two and three dimensions. To begin, download and install Cadnano software to design a DNA accordion rack.Open Cadnano and click the square tool to add a new part with a square lattice. Click the pencil tool and draw each beam on the right edit panel of Cadnano. Break beams every 32 base pairs for joints between adjacent beams.Place staple crossovers in the same position as the joints. Use the insert tool and the pencil tool in Cadnano to let the joints have additional single stranded crossovers. Now, click the break tool.Break the strands where staple strands are circular or longer than 60 base pairs. To design the DNA lockstrands, click the break tool. Break eight base pairs of a staple DNA region to make a sticky part and delete eight base pairs of a staple DNA region.There are 18 sticky parts in the six by six accordion rack. Place sequences that are reverse complimentary to the sticky parts at both ends of lockstrands and connect them by a bridging region, which consists of poly T strands of the desired length. For the reconfiguration, add eight base pairs of toehold sequences at the end of the DNA locks for strand displacement.Design strands that are reverse complimentary to the DNA locks for the reconfiguration experiment. Generate a topology file and configuration file using OxDNA as described in the text protocol. The topology file includes how many strands and nucleotides are in the structure and information regarding backbone-backbone bonds between nucleotides.The configuration file includes general information, such as time step, box size, and energy. Orientation information, such as position vector, backbone-base vector, normal vector, velocity and angular velocity of nucleotides is also included. Change the information in the topology and configuration file from Cadnano to make them reflect the real structural information of the accordion rack.Then, run the molecular dynamics program as described in the text protocol. To visualize the structures, run the Cogli program with the topology and configuration files from the OxDNA simulation. Hide the box by pressing B.Purchase the design DNA staples and prepare them as described in the text protocol.Combine staple DNA, magnesium chloride solution, tris EDTA solution, nuclease free water, and scaffold DNA to make 20 micro liters of mixed stock with the final concentrations listed in the text protocol. Now, rapidly heat the mixed stock solution in a thermal cycler to 80 degrees Celsius. Cool the solution to 60 degrees Celsius, at a rate of four minutes per degree Celsius.Then, cool from 60 degrees Celsius to four degrees Celsius at a rate of 40 minutes per degree Celsius. To purify the structure, mix 20 micro liters of the synthesized structure in 20 micro liters of precipitation buffer. Then, spin the mixed stock at 16, 000 times G and four degrees celsius.Remove the super natant and dissolve pellet in the target buffer. To reconfigure the accordion rack from a free state to a locked state, first add two micro liters of DNA lockstrands of the desired length into 20 micro liters of the synthesized structure. Incubate the sample for 100 minutes at 50 degrees Celsius for 30 minutes and slowly cool down to 25 degrees Celsius at a rate of 0.33 degrees Celsius per minute.To reconfigure the accordion rack from a locked state to a free state, add two micro liters of strands that are reverse complimentary to the locked strands of the desired length into 20 microliters of synthesized structure. Incubate the sample for 12, 60, 120, and 240 minutes by rapidly heating the sample to 40 degrees Celsius and slowly cooling down to 20 degrees Celsius for the time corresponding to each. Right after the detaching step, rapidly cool down the sample to four degrees Celsius to prevent unwanted denaturation.To perform FRET analysis, synthesize the structure as before, expect with fluorescently labeled strands. Measure the concentration of the purified sample. After normalizing the sample to 10 nano molar, load 50 micro liters to a well in a 384 well micro plate.Measure the fluorescence of the sample with donor and acceptor dyes, as well as the donor only sample by exciting at 550 nano meters and measuring the fluorescent spectrum from 570 nano meters to 800 nano meters with a fluorometer. To measure the concentration of the acceptor, excite the dyes of the sample at 650 nano meters and measure the fluorescent spectrum from 670 nano meters to 800 nanometers. Then, calculate the FRET efficiency as described in the text protocol.A simulation result from OxDNA is visualized here by Cogli. The accordion rack is shown with DNA locks, of which the lengths are two, eight, 13, and 20 base pairs. The angle of the accordion rack, comprised of six by six meshes, was controlled by the length of the DNA locks.By adding DNA locks with lengths of two, eight, 13, and 20 base pairs to the 18 locking sights of the accordion rack, the angle is configured as seen in the representative transmission electron microscopy, or TEM images. The dye pair is attached to the structure for FRET efficiency analysis. Shown here are representative TEM images of configured six by six DNA accordion racks with different DNA lock lengths.After its development, this technique paved the way for researchers in the field of DNA nano technology to explore interactions of different molecules in a collectively controlled system.

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Bioengineering

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic valve leaflets are composed of interstitial cells suspended within an extracellular matrix (ECM) and are lined with an endothelial cell monolayer. The valve withstands a harsh, dynamic environment and is constantly exposed to shear, flexion, tension, and compression. Research has shown calcific lesions in diseased valves occur in areas of high mechanical stress as a result of endothelial disruption or interstitial matrix damage1-3. Hence, it is not surprising that epidemiological studies have shown high blood pressure to be a leading risk factor in the onset of aortic valve disease4. 
The only treatment option currently available for valve disease is surgical replacement of the diseased valve with a bioprosthetic or mechanical valve5. Improved understanding of valve biology in response to physical stresses would help elucidate the mechanisms of valve pathogenesis. In turn, this could help in the development of non-invasive therapies such as pharmaceutical intervention or prevention. Several bioreactors have been previously developed to study the mechanobiology of native or engineered heart valves6-9. Pulsatile bioreactors have also been developed to study a range of tissues including cartilage10, bone11 and bladder12. The aim of this work was to develop a cyclic pressure system that could be used to elucidate the biological response of aortic valve leaflets to increased pressure loads. 
The system consisted of an acrylic chamber in which to place samples and produce cyclic pressure, viton diaphragm solenoid valves to control the timing of the pressure cycle, and a computer to control electrical devices. The pressure was monitored using a pressure transducer, and the signal was conditioned using a load cell conditioner. A LabVIEW program regulated the pressure using an analog device to pump compressed air into the system at the appropriate rate. The system mimicked the dynamic transvalvular pressure levels associated with the aortic valve; a saw tooth wave produced a gradual increase in pressure, typical of the transvalvular pressure gradient that is present across the valve during diastole, followed by a sharp pressure drop depicting valve opening in systole. The LabVIEW program allowed users to control the magnitude and frequency of cyclic pressure. The system was able to subject tissue samples to physiological and pathological pressure conditions. This device can be used to increase our understanding of how heart valves respond to changes in the local mechanical environment.

Design of a Cyclic Pressure Bioreactor for the Ex Vivo Study of Aortic Heart Valves

A cyclic pressure bioreactor capable of subjecting heart valve tissue to physiological and pathological pressure conditions has been designed. A LabVIEW program allows users to control pressure magnitude, amplitude and frequency. This device can be used to study the mechanobiology of heart valve tissue or isolated cells.

The aortic valve, located between the left ventricle and the aorta, allows for unidirectional blood flow, preventing backflow into the ventricle. Aortic ...

Gold Nanostar Synthesis with a Silver Seed Mediated Growth Method

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest in using nano-colloids for photo-thermal ablation, drug delivery and many other biomedical applications 6. Gold is particularly used because of its low toxicity 7-9. A property of metal nano-colloids is that they can have a strong surface plasmon resonance 10. The peak of the surface plasmon resonance mode depends on the structure and composition of the metal nano-colloids. Since the surface plasmon resonance mode is stimulated with light there is a need to have the peak absorbance in the near infrared where biological tissue transmissivity is maximal 11, 12.
We present a method to synthesize star shaped colloidal gold, also known as star shaped nanoparticles 13-15 or nanostars 16. This method is based on a solution containing silver seeds that are used as the nucleating agent for anisotropic growth of gold colloids 17-22. Scanning electron microscopy (SEM) analysis of the resulting gold colloid showed that 70 % of the nanostructures were nanostars. The other 30 % of the particles were amorphous clusters of decahedra and rhomboids. The absorbance peak of the nanostars was detected to be in the near infrared (840 nm). Thus, our method produces gold nanostars suitable for biomedical applications, particularly for photo-thermal ablation.

We synthesized star shaped gold nanostars using a silver seed mediated growth method. The diameter of the nanostars ranges from 200 to 300 nm and the number of tips vary from 7 to 10. The nanoparticles have a broad surface plasmon resonance mode centered in the near infrared.

The physical, chemical and optical properties of nano-scale colloids depend on their material composition, size and shape 1-5. There is a great interest ...

Design of a Biaxial Mechanical Loading Bioreactor for Tissue Engineering

We designed a loading device that is capable of applying uniaxial or biaxial mechanical strain to a tissue engineered biocomposites fabricated for transplantation. While the device primarily functions as a bioreactor that mimics the native mechanical strains, it is also outfitted with a load cell for providing force feedback or mechanical testing of the constructs. The device subjects engineered cartilage constructs to biaxial mechanical loading with great precision of loading dose (amplitude and frequency) and is compact enough to fit inside a standard tissue culture incubator. It loads samples directly in a tissue culture plate, and multiple plate sizes are compatible with the system. The device has been designed using components manufactured for precision-guided laser applications. Bi-axial loading is accomplished by two orthogonal stages. The stages have a 50 mm travel range and are driven independently by stepper motor actuators, controlled by a closed-loop stepper motor driver that features micro-stepping capabilities, enabling step sizes of less than 50 nm. A polysulfone loading platen is coupled to the bi-axial moving platform. Movements of the stages are controlled by Thor-labs Advanced Positioning Technology (APT) software. The stepper motor driver is used with the software to adjust load parameters of frequency and amplitude of both shear and compression independently and simultaneously. Positional feedback is provided by linear optical encoders that have a bidirectional repeatability of 0.1 &mu;m and a resolution of 20 nm, translating to a positional accuracy of less than 3 &mu;m over the full 50 mm of travel. These encoders provide the necessary position feedback to the drive electronics to ensure true nanopositioning capabilities. In order to provide the force feedback to detect contact and evaluate loading responses, a precision miniature load cell is positioned between the loading platen and the moving platform. The load cell has high accuracies of 0.15% to 0.25% full scale.

We designed a novel mechanical loading bioreactor that can apply uniaxial or biaxial mechanical strain to a cartilage biocomposite prior to transplantation into an articular cartilage defect.

We  designed a loading device that is capable of applying uniaxial or biaxial  mechanical strain to a tissue engineered biocomposites fabricated for  ...

Millifluidics for Chemical Synthesis and Time-resolved Mechanistic Studies

Procedures utilizing millifluidic devices for chemical synthesis and time-resolved mechanistic studies are described by taking three examples. In the first, synthesis of ultra-small copper nanoclusters is described. The second example provides their utility for investigating time resolved kinetics of chemical reactions by analyzing gold nanoparticle formation using in situ X-ray absorption spectroscopy. The final example demonstrates continuous flow catalysis of reactions inside millifluidic channel coated with nanostructured catalyst.

Millifluidic devices are utilized for controlled synthesis of nanomaterials, time-resolved analysis of reaction mechanisms and continuous flow catalysis.

Procedures utilizing millifluidic devices for chemical synthesis and time-resolved mechanistic studies are described by taking three examples. In the ...

Synthesis of an Intein-mediated Artificial Protein Hydrogel

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of this hydrogel are two protein block-copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. A highly hydrophilic random coil is inserted into one of the block-copolymers for water retention. Mixing of the two protein block copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit with crosslinkers at either end that rapidly self-assembles into a hydrogel. This hydrogel is very stable under both acidic and basic conditions, at temperatures up to 50 &#176;C, and in organic solvents. The hydrogel rapidly reforms after shear-induced rupture. Incorporation of a &#34;docking station peptide&#34; into the hydrogel building block enables convenient incorporation of &#34;docking protein&#34;-tagged target proteins. The hydrogel is compatible with tissue culture growth media, supports the diffusion of 20 kDa molecules, and enables the immobilization of bioactive globular proteins. The application of the intein-mediated protein hydrogel as an organic-solvent-compatible biocatalyst was demonstrated by encapsulating the horseradish peroxidase enzyme and corroborating its activity.

We present the synthesis of a split-intein-mediated protein hydrogel. The building blocks of this hydrogel are two protein copolymers each containing a subunit of a trimeric protein that serves as a crosslinker and one half of a split intein. Mixing of the two protein copolymers triggers an intein trans-splicing reaction, yielding a polypeptide unit that self-assembles into a hydrogel. This hydrogel is highly pH- and temperature-stable, compatible with organic solvents, and easily incorporates functional globular proteins.

We present the synthesis of a highly stable protein hydrogel mediated by a split-intein-catalyzed protein trans-splicing reaction. The building blocks of ...

Synthesis of Keratin-based Nanofiber for Biomedical Engineering

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of these porous nanofibers is of great interest due to their unique physiochemical properties. Here we elaborate on the fabrication of keratin containing poly (&#949;-caprolactone) (PCL) nanofibers (i.e., PCL/keratin composite fiber). Water soluble keratin was first extracted from human hair and mixed with PCL in different ratios. The blended solution of PCL/keratin was transformed into nanofibrous membranes using a laboratory designed electrospinning set up. Fiber morphology and mechanical properties of the obtained nanofiber were observed and measured using scanning electron microscopy and tensile tester. Furthermore, degradability and chemical properties of the nanofiber were studied by FTIR. SEM images showed uniform surface morphology for PCL/keratin fibers of different compositions. These PCL/keratin fibers also showed excellent mechanical properties such as Young&#39;s modulus and failure point. Fibroblast cells were able to attach and proliferate thus proving good cell viability. Based on the characteristics discussed above, we can strongly argue that the blended nanofibers of natural and synthetic polymers can represent an excellent development of composite materials that can be used for different biomedical applications.

Electrospun nanofibers have a high surface area to weight ratio, excellent mechanical integrity, and support cell growth and proliferation. These nanofibers have a wide range of biomedical applications. Here we fabricate keratin/ PCL nanofibers, using the electrospinning technique, and characterize the fibers for possible applications in tissue engineering.

Electrospinning, due to its versatility and potential for applications in various fields, is being frequently used to fabricate nanofibers. Production of ...

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; ...

Reconfigurable Microfluidic Channel with Pin-discretized Sidewalls

Microfluidic components need to have various shapes to realize different key microfluidic functions such as mixing, separation, particle trapping, or reactions. A microfluidic channel that deforms even after fabrication while retaining the channel shape enables high spatiotemporal reconfigurability. This reconfigurability is required in such key microfluidic functions that are difficult to achieve in existing "reconfigurable" or "integrated" microfluidic systems. We describe a method for the fabrication of a microfluidic channel with a deformable sidewall consisting of a laterally aligned array of the ends of rectangular pins. Actuating the pins in their longitudinal directions changes the pins' end positions, and thus, the shape of discretized channel sidewalls.Pin gaps can cause unwanted leakage or adhesion to adjacent pins caused by meniscus forces. To close the pin gaps, we have introduced hydrocarbon-fluoropolymer suspension-based gap filler accompanied by an elastomeric barrier. This reconfigurable microfluidic device can generate strong temporal in-channel displacement flow, or can stop the flow in any region of the channel. This feature will facilitate, on demand, the handling of cells, viscous liquids, gas bubbles, and non-fluids, even if their existence or behavior is unknown at the time of fabrication.

A microfluidic channel with deformable sidewalls offers flow control, particle handling, channel dimension customization and other reconfigurations while in use. We describe a method for fabricating a microfluidic channel with sidewalls made of an array of pins that allows their shape to change.

Microfluidic components need to have various shapes to realize different key microfluidic functions such as mixing, separation, particle trapping, or ...

In Vesiculo Synthesis of Peptide Membrane Precursors for Autonomous Vesicle Growth

Compartmentalization of biochemical reactions is a central aspect of synthetic cells. For this purpose, peptide-based reaction compartments serve as an attractive alternative to liposomes or fatty acid-based vesicles. Externally or within the vesicles, peptides can be easily expressed and simplify the synthesis of membrane precursors. Provided here is a protocol for the creation of vesicles with diameters of ~200 nm based on the amphiphilic elastin-like polypeptides (ELP) utilizing dehydration-rehydration from glass beads. Also presented are protocols for bacterial ELP expression and purification via inverse temperature cycling, as well as their covalent functionalization with fluorescent dyes. Furthermore, this report describes a protocol to enable the transcription of RNA aptamer dBroccoli inside ELP vesicles as a less complex example for a biochemical reaction. Finally, a protocol is provided, which allows in vesiculo expression of fluorescent proteins and the membrane peptide, whereas synthesis of the latter results in vesicle growth.

Presented here are protocols for the creation of peptide-based small unilamellar vesicles capable of growth. To facilitate in vesiculo production of the membrane peptide, these vesicles are equipped with a transcription-translation system and the peptide-encoding plasmid.

Compartmentalization of biochemical reactions is a central aspect of synthetic cells. For this purpose, peptide-based reaction compartments serve as an ...

Design of an Open-Source, Low-Cost Bioink and Food Melt Extrusion 3D Printer

Three-dimensional (3D) printing is an increasingly popular manufacturing technique that allows highly complex objects to be fabricated with no retooling costs. This increasing popularity is partly driven by falling barriers to entry such as system set-up costs and ease of operation. The following protocol presents the design and construction of an Additive Manufacturing Melt Extrusion (ADDME) 3D printer for the fabrication of custom parts and components. ADDME has been designed with a combination of 3D-printed, laser-cut, and online-sourced components. The protocol is arranged into easy-to-follow sections, with detailed diagrams and parts lists under the headings of framing, y-axis and bed, x-axis, extrusion, electronics, and software. The performance of ADDME is evaluated through extrusion testing and 3D printing of complex objects using viscous cream, chocolate, and Pluronic F-127 (a model for bioinks). The results indicate that ADDME is a capable platform for the fabrication of materials and constructs for use in a wide range of industries. The combination of detailed diagrams and video content facilitates access to low-cost, easy-to-operate equipment for individuals interested in 3D printing of complex objects from a wide range of materials.

The aim of this work is to design and construct a reservoir-based melt extrusion three-dimensional printer made from open-source and low-cost components for applications in the biomedical and food printing industries.

Three-dimensional (3D) printing is an increasingly popular manufacturing technique that allows highly complex objects to be fabricated with no retooling ...