Plasmid K401-BCCP-H6 was a gift from Dr. Zvonimir Dogic. This research was supported by Dr. Kun-Ta Wu's start-up fund in Worcester Polytechnic Institute. We thank Dr. Zvonimir Dogic for the protocols to purify and label tubulin and to synthesize active fluids. We are grateful to Dr. Marc Ridilla for his expertise in protein expression and purification. We thank Dr. William Benjamin Roger for assisting us with building the temperature-controlled stage. We acknowledge Brandeis MRSEC (NSF-MRSEC-1420382) for use of the Biological Materials Facility (BMF). We acknowledge the Royal Society of Chemistry for adapting the figures from Bate et al. on Soft Matter33.

1. Preparation of MTs
CAUTION: In this step we purify tubulins from bovine brain tissue. Bovine brain may cause variant Creutzfeldt-Jakob disease (vCJD)35. Therefore, the brain waste and related solutions, bottles, and pipette tips should be collected in a biowaste bag and disposed of as biohazardous waste according to the rules of the institution.
<ol>
	<li>Purify tubulins from bovine brain (modified from Castoldi et al.36).
	<ol>
		<li>Transp...

The authors have nothing to disclose.

Controlling active matter in situ opens the door to directed self-organization of active matter4,5,24,28,54. In this article, we present a protocol for using temperature to control kinesin-driven, MT-based active fluids in situ, based on the Arrhenius characteristic of the system29,30,<sup c...

Active matter is differentiated from conventional passive matter due to its capability to convert chemical energy into mechanical work. A material that possesses such capability can consist of living or non-living entities such as bacteria, insects, colloids, grains, and cytoskeletal filaments1,2,3,4,5,6,7,8,9,10. These material entities interact with their neighbors. At a larger scale, they self-organize into either turbulent-like vortices (active turbulence) or material flows11,12,13,14,15,16,17,18,19,20. An understanding of self-organization of active matter has led to various applications in molecular shuttles, optical devices, and parallel computation21,22,23. To bring applications to the next level requires control beyond self-organization. For example, Palacci et al. developed a hematite-encapsulated colloid that self-propelled only when exposed to manually controlled blue light, which led to the emergence of living crystals24. Morin et al. established the control of rolling Quincke colloids by using a tunable external electric field, resulting in colloidal flocking in a racetrack-like channel25. These previous works demonstrate the role of local control in applications and advance the knowledge base of active matter.
In this article, we focus on the controllability of kinesin-driven, microtubule (MT)-based 3D active fluids. The fluids consist of three main components: MTs, kinesin molecular motors, and depletants. The depletants induce a depletion force to bundle the MTs, which are later bridged by motor clusters. These motors walk along the MTstoward the plus end. When a pair of bridged MTsis antiparallel, the corresponding motors walk in opposite directions. However, the motors are bound in a cluster and are unable to walk apart, so they cooperatively slide apart pairs of MTs (interfilament sliding, Figure 1A). These sliding dynamics accumulate, causing bundles of MTsto extend until reaching their buckling instability point and break (extensile bundles, Figure 1B)26. The broken bundles are annealed by the depletion force, which subsequently extends again, and the dynamics repeat. During the process of the repeating dynamics, the bundle movements stir the nearby liquid, inducing flows that can be visualized by doping with micron-scale tracers (Figure 1C). Sanchez et al. and Henkin et al. have characterized the mean speeds of tracers, finding that the speeds were tunable by varying the concentrations of adenosine triphosphate (ATP), depletants, motor clusters, and MTs19,27. However, such tunability existed only prior to active fluid synthesis. After synthesis, the tunability was lost, and the fluids self-organized in their own way. To control active fluid activity after synthesis, Ross.et al. reported a method using the light-activated dimerization of motor proteins, allowing fluid activity to be tuned on and off using light28. While light control is convenient in terms of locally activating the fluids, the method requires redesigning the structures of motor proteins, along with modifying the optical paths in a microscope. Here, we provide an easy-to-use method for locally controlling fluid flows without microscope modification while keeping the motor structure intact.
Our method of locally tuning active fluid flow is based on the Arrhenius law because the kinesin-MT reaction has been reported to increase with temperature29,30,31,32. Our previous studies showed that the temperature dependence of the mean speed of an active fluid flow followed the Arrhenius equation: v = A exp(-Ea/RT), where A is a pre-exponential factor, R is the gas constant, Ea is the activation energy, and T is the system temperature33. Therefore, fluid activity is sensitive to the temperature environment, and the system temperature needs to be consistent to stabilize the motor performance, and consequently, the fluid flow speed34. In this article, we demonstrate the use of the motor&#39;s temperature dependence to continuously tune the flow speeds of active fluids by adjusting the system temperature. We also demonstrate the preparation of an active fluid sample, followed by mounting the sample on a microscope stage whose temperature is controlled via computer software. Increasing the temperature from 16 &#176;C to 36 &#176;C speeds up the mean flow speeds from 4 to 8 &#181;m/s. Additionally, the tunability is reversible: repeatedly increasing and decreasing the temperature sequentially accelerates and decelerates the flow. The demonstrated method is applicable to a wide range of systems where the main reactions obey the Arrhenius law, such as the MT gliding assay29,30,31,32.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>(&#177;)-6-Hydroxy-2,5,7,8-tetramethylchromane-2-carboxylic acid</td>
			<td>Sigma-Aldrich</td>
			<td>238813</td>
			<td>Trolox</td>
		</tr>
		<tr>
			<td>2-Mercaptoethanol</td>
			<td>Sigma-Aldrich</td>
			<td>M6250</td>
			<td></td>
		</tr>
		<tr>
			<td>3-(Trimethoxysilyl)propyl methacrylate, 98%, ACROS Organics</td>
			<td>Fisher Scientific</td>
			<td>AC216550050</td>
			<td></td>
		</tr>
		<tr>
			<td>3.2mm I.D. Tygon Tubing R-3603</td>
			<td>HACH</td>
			<td>2074038</td>
			<td>Water tubes</td>
		</tr>
		<tr>
			<td>31.75 mm diameter uncoated, sapphire window</td>
			<td>Edmund Optics</td>
			<td>43-637</td>
			<td>Sapphire disc</td>
		</tr>
		<tr>
			<td>3M 1181 Copper Tape - 1/2 IN Width X 18 YD Length - 2.6 MIL Total Thickness - 27551</td>
			<td>R.S. HUGHES</td>
			<td>054007-27551</td>
			<td>Copper tape</td>
		</tr>
		<tr>
			<td>Acetic Acid</td>
			<td>Sigma-Aldrich</td>
			<td>A6283</td>
			<td></td>
		</tr>
		<tr>
			<td>Acrylamide Solution (40%/Electrophoresis), Fisher BioReagents</td>
			<td>Fisher Scientific</td>
			<td>BP1402-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Adenosine 5&#39;-triphosphate dipotassium salt hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>A8937</td>
			<td>ATP</td>
		</tr>
		<tr>
			<td>Alexa Fluor 647 NHS Ester (Succinimidyl Ester)</td>
			<td>Thermo Fisher Scientific</td>
			<td>A20006</td>
			<td>Far-red fluorescent dye. Alexa 647 can be pre suspended in dimethylsulfoxide (DMSO) before mixing with microtubules (1.3.3.2.)</td>
		</tr>
		<tr>
			<td>Amicon Ultra-4 Centrifugal Filter Unit</td>
			<td>Sigma-Aldrich</td>
			<td>UFC801024</td>
			<td>Centrifugal filter tube. Cutoff molecular weight: 10 kDa</td>
		</tr>
		<tr>
			<td>Ammonium Persulfate, 100g, MP Biomedicals</td>
			<td>Fisher Scientific</td>
			<td>ICN802829</td>
			<td>APS</td>
		</tr>
		<tr>
			<td>Ampicillin Sodium Salt (Crystalline Powder), Fisher BioReagents</td>
			<td>Fisher Scientific</td>
			<td>BP1760</td>
			<td>Ampicillin</td>
		</tr>
		<tr>
			<td>Antivibration Table</td>
			<td>Nikon</td>
			<td>63-7590S</td>
			<td></td>
		</tr>
		<tr>
			<td>Avanti J-E Centrifuge</td>
			<td>Beckman Coulter</td>
			<td>369001</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Agar Soldifying Agent, BD Diagnostics</td>
			<td>VWR</td>
			<td>90000-760</td>
			<td>Agar</td>
		</tr>
		<tr>
			<td>Biotin</td>
			<td>Alfa Aesar</td>
			<td>A14207</td>
			<td></td>
		</tr>
		<tr>
			<td>Bucket-plastic white - 2 gallon</td>
			<td>Bon</td>
			<td>84-715</td>
			<td>Water bucket</td>
		</tr>
		<tr>
			<td>Calcium Chloride</td>
			<td>Sigma-Aldrich</td>
			<td>746495</td>
			<td>CaCl2</td>
		</tr>
		<tr>
			<td>Catalase from bovine liver</td>
			<td>Sigma-Aldrich</td>
			<td>C40</td>
			<td></td>
		</tr>
		<tr>
			<td>CFI Plan Apo Lambda 4x Obj</td>
			<td>Nikon</td>
			<td>MRD00045</td>
			<td>4x air objective</td>
		</tr>
		<tr>
			<td>C-FLLL-FOV GFP HC HC HISN ero Shift</td>
			<td>Nikon</td>
			<td>96372</td>
			<td>GFP filter cube</td>
		</tr>
		<tr>
			<td>CH-109-1.4-1.5</td>
			<td>TE Technology</td>
			<td>CH-109-1.4-1.5</td>
			<td>Thermoelectric Cooler (TEC)</td>
		</tr>
		<tr>
			<td>Chloramphenicol, 98%, ACROS Organics</td>
			<td>Fisher Scientific</td>
			<td>C0378</td>
			<td></td>
		</tr>
		<tr>
			<td>Cooling block</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Custom milled aluminum</td>
		</tr>
		<tr>
			<td>Coomassie Brilliant Blue R-250 #1610400</td>
			<td>Bio-Rad</td>
			<td>1610400</td>
			<td>Triphenylmethane dye</td>
		</tr>
		<tr>
			<td>D-(+)-Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G7528</td>
			<td></td>
		</tr>
		<tr>
			<td>Dimethyl Sulfoxide (Certified ACS), Fisher Chemical</td>
			<td>Fisher Scientific</td>
			<td>D128</td>
			<td>DMSO</td>
		</tr>
		<tr>
			<td>DL-1,4-Dithiothreitol, 99%, for biochemistry, ACROS Organics</td>
			<td>Fisher Scientific</td>
			<td>AC165680050</td>
			<td>DTT</td>
		</tr>
		<tr>
			<td>DOWSIL 340 Heat Sink Compound</td>
			<td>Dow</td>
			<td>1446622</td>
			<td>Thermal paste</td>
		</tr>
		<tr>
			<td>ETHYL ALCOHOL, 200 PROOF ACS/USP/NF GRADE 5 GALLON POLY CUBE</td>
			<td>Pharmco by Greenfield Global</td>
			<td>111000200CB05</td>
			<td>Ethanol</td>
		</tr>
		<tr>
			<td>Ethylene glycol-bis(2-aminoethylether)-N,N,N&#39;,N&#39;-tetraacetic acid</td>
			<td>Sigma-Aldrich</td>
			<td>E3889</td>
			<td>EGTA</td>
		</tr>
		<tr>
			<td>Ethylenediaminetetraacetic acid</td>
			<td>Sigma-Aldrich</td>
			<td>798681</td>
			<td>EDTA</td>
		</tr>
		<tr>
			<td>Fisher BioReagents Microbiology Media Additives: Tryptone</td>
			<td>Fisher Scientific</td>
			<td>BP1421</td>
			<td>Tryptone</td>
		</tr>
		<tr>
			<td>Fisher BioReagents Microbiology Media Additives: Yeast Extract</td>
			<td>Fisher Scientific</td>
			<td>BP1422</td>
			<td>Yeast extract</td>
		</tr>
		<tr>
			<td>Fluoresbrite YG Microspheres, Calibration Grade 3.00 &#181;m</td>
			<td>Polysciences</td>
			<td>18861</td>
			<td>Tracer particles</td>
		</tr>
		<tr>
			<td>Glucose Oxidase from Aspergillus niger</td>
			<td>Sigma-Aldrich</td>
			<td>G2133</td>
			<td></td>
		</tr>
		<tr>
			<td>Glycerol</td>
			<td>Sigma-Aldrich</td>
			<td>G5516</td>
			<td></td>
		</tr>
		<tr>
			<td>GpCpp</td>
			<td>Jena Bioscience</td>
			<td>NU-405L</td>
			<td>Guanosine-5'[(&#945;,&#946;)-methyleno]triphosphate (GMPCPP)</td>
		</tr>
		<tr>
			<td>GS Power&#39;s 18 Gauge (True American Wire Ga), 100 feet, 99.9% Stranded Oxygen Free Copper OFC, Red/Black 2 Conductor Bonded Zip Cord Power/Speaker Electrical Cable for Car, Audio, Home Theater</td>
			<td>Amazon</td>
			<td>B07428NBCW</td>
			<td>Copper wire</td>
		</tr>
		<tr>
			<td>Guanosine 5&#39;-triphosphate sodium salt hydrate</td>
			<td>Sigma-Aldrich</td>
			<td>G8877</td>
			<td>GTP</td>
		</tr>
		<tr>
			<td>Hellmanex III</td>
			<td>Sigma-Aldrich</td>
			<td>Z805939</td>
			<td>Detergent</td>
		</tr>
		<tr>
			<td>HEPES Sodium Salt (White Powder), Fisher BioReagents</td>
			<td>Fisher Scientific</td>
			<td>BP410</td>
			<td>NaHEPES</td>
		</tr>
		<tr>
			<td>High performance blender machine</td>
			<td>AIMORES</td>
			<td>AS-UP1250</td>
			<td>Blender</td>
		</tr>
		<tr>
			<td>His GraviTrap</td>
			<td>GE Healthcare</td>
			<td>11003399</td>
			<td>Gravity Column</td>
		</tr>
		<tr>
			<td>Imidazole</td>
			<td>Sigma-Aldrich</td>
			<td>I5513</td>
			<td></td>
		</tr>
		<tr>
			<td>IPTG</td>
			<td>Sigma-Aldrich</td>
			<td>I6758</td>
			<td>Isopropyl &#946;-D-1-thiogalactopyranoside</td>
		</tr>
		<tr>
			<td>Isopropyl Alcohol 99%</td>
			<td>Pharmco by Greenfield Global</td>
			<td>231000099</td>
			<td>Isopropanol</td>
		</tr>
		<tr>
			<td>JA-10 rotor</td>
			<td>Beckman Coulter</td>
			<td>369687</td>
			<td></td>
		</tr>
		<tr>
			<td>L-Glutamic acid potassium salt monohydrate</td>
			<td>Sigma-Aldrich</td>
			<td>G1501</td>
			<td>K-Glutamate</td>
		</tr>
		<tr>
			<td>Lysozyme from chicken egg white</td>
			<td>Sigma-Aldrich</td>
			<td>L6876</td>
			<td></td>
		</tr>
		<tr>
			<td>Magnesium chloride hexahydrate</td>
			<td>Sigma-Aldrich</td>
			<td>M2670</td>
			<td>MgCl2&#8226;6H2O</td>
		</tr>
		<tr>
			<td>MES sodium salt</td>
			<td>Sigma-Aldrich</td>
			<td>M5057</td>
			<td>2-(N-Morpholino)ethanesulfonic acid sodium salt</td>
		</tr>
		<tr>
			<td>MOPS</td>
			<td>Sigma-Aldrich</td>
			<td>M1254</td>
			<td>3-(N-Morpholino)propanesulfonic acid</td>
		</tr>
		<tr>
			<td>MP-3022</td>
			<td>TE Technology</td>
			<td>MP-3022</td>
			<td>Thermocouple</td>
		</tr>
		<tr>
			<td>N,N,N&#39;,N&#39;-Tetramethylethylenediamine 99%, ACROS Organics</td>
			<td>Fisher Scientific</td>
			<td>AC138450500</td>
			<td>TEMED</td>
		</tr>
		<tr>
			<td>Nanodrop 2000c UV-VIS Spectrophotometer</td>
			<td>Thermo Fisher Scientific</td>
			<td>E112352</td>
			<td>Spectrometer</td>
		</tr>
		<tr>
			<td>Nikon Ti2-E Nikon Inverted Microscope</td>
			<td>Nikon</td>
			<td>MEA54000</td>
			<td></td>
		</tr>
		<tr>
			<td>Norland Optical Adhesive 81</td>
			<td>Norland Products</td>
			<td>NOA81</td>
			<td>UV glue</td>
		</tr>
		<tr>
			<td>Novex Sharp Pre-stained Protein Standard</td>
			<td>Thermo Fisher Scientific</td>
			<td>LC5800</td>
			<td>Protein standard ladder</td>
		</tr>
		<tr>
			<td>NuPAGE 4-12% Bis-Tris Protein Gels, 1.5 mm, 10-well</td>
			<td>Thermo Fisher Scientific</td>
			<td>NP0335BOX</td>
			<td>SDS gel</td>
		</tr>
		<tr>
			<td>Optima L-90K Ultracentrifuge</td>
			<td>Beckman Coulter</td>
			<td>365672</td>
			<td></td>
		</tr>
		<tr>
			<td>Parafilm PM996 Wrap , 4&#34; Wide; 125 Ft/Roll</td>
			<td>Cole-Parmer</td>
			<td>EW-06720-40</td>
			<td>Wax film</td>
		</tr>
		<tr>
			<td>Pe 300 ultra Illumination System Single 
			Band , 3mm Light Guide control Pod 
			power supply</td>
			<td>Nikon</td>
			<td>PE-300-UT-L-SB-40</td>
			<td>Cool LED Illuminator</td>
		</tr>
		<tr>
			<td>Phenylmethanesulfonyl fluoride</td>
			<td>Sigma-Aldrich</td>
			<td>78830</td>
			<td>PMSF</td>
		</tr>
		<tr>
			<td>Phosphoenolpyruvic acid monopotassium salt, 99%</td>
			<td>BeanTown Chemical</td>
			<td>129745</td>
			<td>PEP</td>
		</tr>
		<tr>
			<td>Pierce Coomassie (Bradford) Protein Assay Kit</td>
			<td>Thermo Fisher Scientific</td>
			<td>23200</td>
			<td></td>
		</tr>
		<tr>
			<td>Pierce Protease Inhibitor Mini Tablets</td>
			<td>Thermo Fisher Scientific</td>
			<td>A32953</td>
			<td></td>
		</tr>
		<tr>
			<td>PIPES</td>
			<td>Sigma-Aldrich</td>
			<td>P6757</td>
			<td>1,4-Piperazinediethanesulfonic acid</td>
		</tr>
		<tr>
			<td>Pluronic F-127</td>
			<td>Sigma-Aldrich</td>
			<td>P2443</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(ethylene glycol)</td>
			<td>Sigma-Aldrich</td>
			<td>81300</td>
			<td>PEG. Average molecular weight 20,000 Da</td>
		</tr>
		<tr>
			<td>Potassium Hydroxide (Pellets/Certified ACS), Fisher Chemical</td>
			<td>Fisher Scientific</td>
			<td>P250-500</td>
			<td>KOH</td>
		</tr>
		<tr>
			<td>PowerEase 300W Power Supply (115 VAC)</td>
			<td>ThermoFisher Scientific</td>
			<td>PS0300</td>
			<td>DC power supply of the gel box</td>
		</tr>
		<tr>
			<td>PS-12-8.4A</td>
			<td>TE Technology</td>
			<td>PS-12-8.4A</td>
			<td>DC power supply of the temperature controller</td>
		</tr>
		<tr>
			<td>Pyruvate Kinase/Lactic Dehydrogenase enzymes from rabbit muscle</td>
			<td>Sigma-Aldrich</td>
			<td>P-0294</td>
			<td>PK/LDH</td>
		</tr>
		<tr>
			<td>Quiet One Lifegard Fountain Pump, 296-Gallon Per Hour</td>
			<td>Amazon</td>
			<td>B005JWA612</td>
			<td>Fish tank pump</td>
		</tr>
		<tr>
			<td>Rosetta 2(DE3)pLysS Competent Cells - Novagen</td>
			<td>Millipore Sigma</td>
			<td>71403</td>
			<td>Competent cells</td>
		</tr>
		<tr>
			<td>Sharp Microwave ZSMC0912BS Sharp 900W Countertop Microwave Oven, 0.9 Cubic Foot, Stainless Steel</td>
			<td>Amazon</td>
			<td>B01MT6JZMR</td>
			<td>Microwave for boiling the water</td>
		</tr>
		<tr>
			<td>Sodium Chloride (Crystalline/Certified ACS), Fisher Chemical</td>
			<td>Fisher Scientific</td>
			<td>S271-500</td>
			<td>NaCl</td>
		</tr>
		<tr>
			<td>Sodium dodecyl sulfate</td>
			<td>Sigma-Aldrich</td>
			<td>L3771</td>
			<td>SDS</td>
		</tr>
		<tr>
			<td>Sodium phosphate monobasic</td>
			<td>Sigma-Aldrich</td>
			<td>S8282</td>
			<td>NaH2PO4</td>
		</tr>
		<tr>
			<td>Streptavidin Protein</td>
			<td>Thermo Fisher Scientific</td>
			<td>21122</td>
			<td></td>
		</tr>
		<tr>
			<td>Sucrose</td>
			<td>Sigma-Aldrich</td>
			<td>S7903</td>
			<td></td>
		</tr>
		<tr>
			<td>TC-720</td>
			<td>TE Technology</td>
			<td>TC-720</td>
			<td>Temperature controller</td>
		</tr>
		<tr>
			<td>Tris Base, Molecular Biology Grade - CAS 77-86-1 - Calbiochem</td>
			<td>Sigma-Aldrich</td>
			<td>648310</td>
			<td>Tris-HCL</td>
		</tr>
		<tr>
			<td>Type 45 Ti rotor</td>
			<td>Beckman Coulter</td>
			<td>339160</td>
			<td></td>
		</tr>
		<tr>
			<td>Type 70 Ti rotor</td>
			<td>Beckman Coulter</td>
			<td>337922</td>
			<td></td>
		</tr>
		<tr>
			<td>Type 70.1 Ti rotor</td>
			<td>Beckman Coulter</td>
			<td>342184</td>
			<td></td>
		</tr>
		<tr>
			<td>VWR General-Purpose Laboratory Labeling Tape</td>
			<td>VWR</td>
			<td>89097-916</td>
			<td>Paper tapes</td>
		</tr>
		<tr>
			<td>VWR Micro Cover Glasses, Square, No. 1 1/2</td>
			<td>VWR</td>
			<td>48366-227</td>
			<td>Glass coverslips</td>
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			<td>VWR Plain and Frosted Micro Slides, Premium</td>
			<td>VWR</td>
			<td>75799-268</td>
			<td>Glass slides</td>
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			<td>XCell SureLock Mini-Cell</td>
			<td>ThermoFisher Scientific</td>
			<td>EI0001</td>
			<td>Gel box</td>
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			<td>ZYLA 5.5 USB3.0 Camera</td>
			<td>Nikon</td>
			<td>ZYLA5.5-USB3</td>
			<td>Monochrome CCD camera</td>
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controlling flow speeds of microtubule-based 3d active fluids using temperature

We present a method for using temperature to tune the flow speeds of kinesin-driven, microtubule-based three-dimensional (3D) active fluids. This method allows for tuning the speeds in situ without the need to manufacture new samples to reach different desired speeds. Moreover, this method enables the dynamic control of speed. Cycling the temperature leads the fluids to flow fast and slow, periodically. This controllability is based on the Arrhenius characteristic of the kinesin-microtubule reaction, demonstrating a controlled mean flow speed range of 4&#8211;8 &#181;m/s. The presented method will open the door to the design of microfluidic devices where the flow rates in the channel are locally tunable without the need for a valve.

Preparing the kinesin-driven, MT-based active fluids requires both kinesin and MTs. The MTs were polymerized from labeled tubulins (steps 1.3 and 1.4) that were purified from bovine brains (step 1.1, Figure 2A), followed by recycling to enhance purity (step 1.2, Figure 2B). The kinesin motor proteins were expressed in and purified from E. coli (steps 2.1 and 2.2, Figure 2B)...

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Controlling Flow Speeds of Microtubule-Based 3D Active Fluids Using Temperature

The goal of this protocol is to use temperature to control the flow speeds of three-dimensional active fluids. The advantage of this method not only allows for regulating flow speeds in situ but also enables dynamic control, such as periodically tuning flow speeds up and down.

We present a method for using temperature to tune the flow speeds of kinesin-driven, microtubule-based three-dimensional (3D) active fluids. This method ...

Active matter has been used in various applications like molecular shadows. To bring the application to the next level, we need to develop the ability to control the active matter locally. We provide an easy to use method that doesn't require modification of the active fluid.Nor the need to modify the optical path of microscope to achieve the local control of the active fluid. Our method can be applied to a wide range of systems where the main reactions obey the erroneous law such as the microtubule gliding assay or enzyme based systems. The setup involves a water circulation system.If leaks occur, water can damage the microscope. Therefore, before adopting our protocol, it is important to ensure the system is leak free. Our protocol requires mounting the glass sample on a temperature stage.While the manuscript describes the mounting procedure, it lacks mechanical subtleties such as securing the sample to the stage. Demonstrating the procedure, will be Teagan Bate, Edward Jarvis, and Megan Varney. Teagan and Edward are graduate students, and Megan is an undergraduate student from a laboratory.To prepare active fluids in an Eppendorf tube, mix 16 point seven microliters of eight milligrams per milliliter microtubules with six point seven microliters of one point eight micromolar kinesin motor clusters, and one point one microliters of 500 millimolar DTT in high-salt M2B. Bundle microtubules by adding 11 point four microliters of seven percent weight by weight polyethylene glycol. Then activate kinesin motors by adding two point eight microliters of 50 millimolar ATP.Maintain the ATP concentrations by adding two point eight microliters of stock pyruvate kinase/lactate dehydrogenase, and 13 point three microliters of 200 millimolar phosphenol pyruvate. Reduce the photo bleaching effect by adding 10 microliters of 20 millimolar Trolox, one point one microliters of three point five milligrams per milliliter catalase, one point one microliters of 20 milligrams per milliliter glucose oxidase, and one point one microliters of 300 milligrams per milliliter glucose. Track the motion of the fluid by adding one point six microliters of zero point zero two five percent volume by volume tracer particles.Add high-salt M2B to achieve a total volume of 100 microliters. Next, rinse a polyacrylamide coated glass slide and cover slip with DI water. Dry the glasses with pressurized air.Place the glasses on a clean, flat surface. Cut a three millimeter wide channel in the wax film. The total width is the same width as the glass cover slip at 20 millimeters.Insert the wax between the slide and cover slip to form a flow cell channel for fluid. Adhere the glass to the wax film by placing the glass wax complex on an 80 degree Celsius hot plate to melt the wax. During the melting, press the cover slip gently with a pipette tip to uniformly adhere the wax film to the glass surfaces.After adhesion, cool the glass complex to room temperature. Promptly load the prepared active fluids to the flow channel with the pipette tip at an angle away from the channel opening and in contact with the glass slide surface. Seal the channel with UV glue.After building a temperature control setup, place the active fluid sample on the sapphire surface with the slide side contacting the surface. Secure the glass slide with paper tape. Using copper tape, attach the ThermoSensor to the cover slip surface.To mount the setup on a microscope stage, with the cover slip slide facing toward the objectives, secure the setup with microscope stage needle clamps. Turn on the temperature controller and fish tank pump. Follow the manufacturers guide to set the target temperature.Enable temperature control. And record ThermoSensor temperature data. Image the sample with a constant time interval on a fluorescent microscopy equipped with a GFP filter cube to monitor the Alexa 488 labeled tracer particles in the active mix.Adjust the time interval to allow the tracer displacement between frames to be within nine pixels. For imaging tracers moving at 10 micrometers per second, using a four times objective, the time interval is recommended to be one to five seconds. Save the images as TIF files, name the files based on frame number, and store them in a separate folder.For this kinesin driven microtubule based active fluids, the temperature was controlled at 10, 20, 30, and 40 degrees Celsius. The fluctuation in temperature was within zero point one to zero point three degrees Celsius for four hours demonstrating the stability and reliability of this temperature control setup. The tracers were imaged every two seconds, which the sequential images allowed for tracking tracer trajectories.The mean speeds measured at 20 to 36 degrees Celsius, appeared to be nearly time independent at zero to two hours. Where as at 10 and 40 degrees Celsius, the mean speeds decayed quickly caused by microtubule depolymerization below 16 degrees Celsius and the kinesin clusters malfunctioning above 36 degrees Celsius respectively. When the system temperatures were alternated between 20 and 30 degrees Celsius every 30 minutes, the mean speeds of the active fluids did not only accelerate and decelerate accordingly, but they also responded to the temperature change within 10 seconds.Active fluids begin to malfunction, when cooled below 16 or heated above 36 degrees. So when manipulating the temperature controller, ensure the temperature is between 16 and 36 degrees. The ability of tuning active fluid locally, allows for directing the fluid power such as delivering cargos from point A to point B or developing a microfluidity device that doesn't require a physical valve.The acrylamide used to coat glassware is a neurotoxin which can absorb through the skin. Wear proper protective equipment such as gloves, lab coats and safety goggles to minimize risk.

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