Funding: U.S. Army Medical Research &#38; Materiel Command (USAMRMC) and managed by the Telemedicine &#38; Advanced Technology Research Center.&#160; Shunxi Ji contributed the modification of the syringes as described here.

1. System Set-up
The system consists of a holding and concentrating tank (HCT) fitted with a single stage mixer, an in-line high shear homogenizer, a roller pump to move fluid between the HCT and the homogenizer, and a heat-exchanger (Figure 1).
<ol>
	<li>Place a sterilized, wide-mouthed 4 L glass collection vessel fitted with 2 base ports and 3 side ports beneath the single stage mixer. Lower the mixer head to the mouth of the vessel and ensure a gas-tight fitting using rubber seals or tape (in order to prevent ambient air from contaminating the head space).</li>
	<li>Fit one of the base ports (Figure 1, port #1) of the HCT with sterile 3/8&#8221; (ID) clear tubing, approximately 10&#8221; long, fitted with a 3-way stopcock at the tip for collection of the concentrated emulsion.</li>
	<li>Fit the second base port (Figure 1, port #2) with sterile 3/8&#8221; (ID) tubing, approximately 36&#8221; in length. Feed this tubing through a roller pump. Fit the inlet of the high shear homogenizer with a T-piece including two ports and connect as follows: connect tubing from port #2, through the roller pump and connect to the side port of the T-piece. Attach the other port to an oxygen tank using a low-flow oxygen gas flowmeter.</li>
	<li>Connect the outlet port of the high shear homogenizer to the inlet port of an in-line heat exchanger maintained at 4 &#176;C. Connect the outlet port of the heat exchanger to the return port of the HCT (Figure 1, port #3), creating a closed loop system.</li>
	<li>Attach an oxygen tank (via a flowmeter) to the HCT (Figure 1, port #4). Attach a gas composition monitor that is open to atmosphere to the top port of the HCT (Figure 1, port #5).</li>
	<li>If sterility is desired, sterilize the glass and metal components before each use by autoclave. Sterilize the tubing components and plastic connectors by ethylene oxide before each use. This is especially important if the product is to be tested in vivo.</li>
</ol>
2. LOM Manufacture
<ol>
	<li>Place 20 g of GMP 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and 10 g of cholesterol in the base of the HCT. Add 1 L of Plasma-Lyte A to the HCT and hand stir for 1 min, integrating as much lipid as possible into aqueous phase.</li>
	<li>Lower the single stage mixer into the aqueous phase, ensuring that the entire mixer head is covered by the aqueous phase. Ensure that the top of the HCT is gas tight (see Step 1.1 above) and that there are no open side ports. Turn on the gas source attached to port #4 and wait until the oxygen fraction of the HCT headspace reaches &#62;95%. At 10 L/min&#160;(LPM), this should take ~10 min.</li>
	<li>Using the single stage mixer, mix the precursor emulsion for 5 min at 5,000 rpm. The resulting mixture should appear pale white and contain no visible lipid clumps. Once mixed, unused lipid-water mixture can be stored at 4 &#186;C for up to 30 days before single use.</li>
	<li>Prime the entire closed loop system with the precursor emulsion by turning on the roller pump at 1.3 LPM. Once the system is primed, keep the pump on at 1.3 LPM.</li>
	<li>To begin manufacture of the LOMs, turn on the in-line high shear homogenizer to 7,500 rpm. Immediately thereafter, turn on oxygen flow to the inlet portion of the homogenizer at 0.5 LPM. Keep the single stage mixer (in the HCT) on at 3,500 rpm. LOMs are formed at the interface of rotor blades and the emulsor screens within the in-line homogenizer (Figure 2). Within&#160;minutes, fluid should become visibly more viscous. A more rigorous approach is to determine viscosity as a function of time, which can be done by removing aliquots from Port 1 during fabrication and analyzing with a viscometer. 
	Note: If visible air bubbles are present in the tubing exiting the mixer, oxygen flow to the in-line homogenizer is too high. Titrate down gas flow until fluid is opaque and contains no visible gas bubbles.</li>
	<li>Run the system for 15 min, and then turn off the high shear homogenizer and the oxygen inlet to it. Continue to run the single stage mixer in the HCT until the emulsion is removed; this mitigates phase separation and keeps the product relatively uniform within the HCT. 
	Note: The volume of the gas-filled emulsion should increase approximately 2-3x&#160;during the serial concentration phase. If it does not, check to ensure that oxygen is flowing into the high shear homogenizer and that lipid concentrations in the precursor emulsion are correct. Efficiency of production decreases as lipid concentration decreases.</li>
</ol>
3. Collection, Concentration, Assessment, and Storage of LOMs
<ol>
	<li>Attach a sterile, modified 140 ml luer-lock syringe to the stopcock attached to base port #1 on the collection vessel. Draw up 100 ml of fluid. Tightly cap syringe and repeat until all fluid has been removed.
	<ol>
		<li>Modify syringes by withdrawing 100 ml of air into the syringe and then sawing off the excess plunger and syringe material above the 140 ml mark. Fill and empty syringes using toothed forceps to draw up the plunger. This modification allows easier centrifugation.</li>
	</ol>
	</li>
	<li>Centrifuge syringes with the capped end oriented downward in a refrigerated (4 &#186;C) bucket centrifuge at 225 x g for 10 min.</li>
	<li>Three layers of material will appear after centrifugation. Expel the bottom layer of excess cloudy aqueous phase and discard. The second layer is bright white and contains concentrated LOMs. Transfer concentrated foam to a gas-impermeable syringe using a three-way stopcock to prevent ambient gas contamination. Discard the final layer, which contains free oxygen gas from ruptured LOMs.</li>
	<li>Foam quality can be assessed by reaching &#8805;90% gas of concentrated foam. Calculate gas concentration as follows: 
	Volume % gas = [(Foam weight/ Foam volume)- 1] x 100
	<ol>
		<li>As a second quality control, size microbubbles by light obscuration to determine if particle size is within the expected range. It should be noted that a change in homogenization time or formulation might alter bubble size.</li>
	</ol>
	</li>
	<li>Tightly cap the glass syringe with a luer-lock fitting. Concentrated LOMs can be diluted with Plasma-Lyte A at the time of use. Syringes can be stored at 22, 4, or -20 &#186;C; colder temperatures may provide enhanced shelf-life stability7.</li>
</ol>

<ol>
	<li>Lentacker, I., De Smedt, S. C., Sanders, N. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Drug+loaded+microbubble+design+for+ultrasound+triggered+delivery.">Drug loaded microbubble design for ultrasound triggered delivery.</a> Soft Matter. 5 (11), 2161-2170 (2009).</li><li>Ren, J. L., 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+Novel+Ultrasound+Microbubble+Carrying+Gene+and+Tat+Peptide:+Preparation+and+Characterization.">A Novel Ultrasound Microbubble Carrying Gene and Tat Peptide: Preparation and Characterization.</a> Academic Radiology. 16 (12), 1457-1465 (2009).</li><li>Tinkov, 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=Microbubbles+as+Ultrasound+Triggered+Drug+Carriers.">Microbubbles as Ultrasound Triggered Drug Carriers.</a> Journal of Pharmaceutical Sciences. 98 (6), 1935-1961 (2009).</li><li>Hernot, S., Klibanov, A. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microbubbles+in+ultrasound-triggered+drug+and+gene+delivery.">Microbubbles in ultrasound-triggered drug and gene delivery.</a> Advanced Drug Delivery Reviews. 60 (10), 1153-1166 (2008).</li><li>Lanza, G. 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=A+novel+site-targeted+ultrasonic+contrast+agent+with+broad+biomedical+application.">A novel site-targeted ultrasonic contrast agent with broad biomedical application.</a> Circulation. 94 (12), 3334-3340 (1996).</li><li>Cavalli, R., 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=Preparation+and+characterization+of+dextran+nanobubbles+for+oxygen+delivery.">Preparation and characterization of dextran nanobubbles for oxygen delivery.</a> International Journal of Pharmaceutics. 381 (2), 160-165 (2009).</li><li>Kheir, J. N., 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=Oxygen+Gas-Filled+Microparticles+Provide+Intravenous+Oxygen+Delivery.">Oxygen Gas-Filled Microparticles Provide Intravenous Oxygen Delivery.</a> Science Translational Medicine. 4 (140), (2012).</li><li>Lindner, J. R., 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=Microvascular+rheology+of+definity+microbubbles+after+intra-arterial+and+intravenous+administration.">Microvascular rheology of definity microbubbles after intra-arterial and intravenous administration.</a> Journal of the American Society of Echocardiography. 15 (5), 396-403 (2002).</li><li>Zhao, Y. Z., 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=Preparation,+characterization+and+in+vivo+observation+of+phospholipid-based+gas-filled+microbubbles+containing+hirudin.">Preparation, characterization and in vivo observation of phospholipid-based gas-filled microbubbles containing hirudin.</a> Ultrasound in Medicine and Biology. 31 (9), 1237-1243 (2005).</li><li>Seo, 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=Microfluidic+Assembly+of+Monodisperse,+Nanoparticle-Incorporated+Perfluorocarbon+Microbubbles+for+Medical+Imaging+and+Therapy.">Microfluidic Assembly of Monodisperse, Nanoparticle-Incorporated Perfluorocarbon Microbubbles for Medical Imaging and Therapy.</a> Langmuir. 26 (17), 13855-13860 (2010).</li><li>Wan, J. D., Stone, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coated+Gas+Bubbles+for+the+Continuous+Synthesis+of+Hollow+Inorganic+Particles.">Coated Gas Bubbles for the Continuous Synthesis of Hollow Inorganic Particles.</a> Langmuir. 28 (1), 37-41 (2012).</li><li>Duncanson, W. J., 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=Monodisperse+Gas-Filled+Microparticles+from+Reactions+in+Double+Emulsions.">Monodisperse Gas-Filled Microparticles from Reactions in Double Emulsions.</a> Langmuir. 28 (17), 6742-6745 (2012).</li><li>Kendall, M. R., 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=Scaled-Up+Production+of+Monodisperse,+Dual+Layer+Microbubbles+Using+Multi-Array+Microfluidic+Module+for+Medical+Imaging+and+Drug+Delivery.">Scaled-Up Production of Monodisperse, Dual Layer Microbubbles Using Multi-Array Microfluidic Module for Medical Imaging and Drug Delivery.</a> Bubble Science Engineering and Technology. 4 (1), 12-20 (2012).</li><li>Szijjarto, C., 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=Effects+of+Perfluorocarbon+Gases+on+the+Size+and+Stability+Characteristics+of+Phospholipid-Coated+Microbubbles:+Osmotic+Effect+versus+Interfacial+Film+Stabilization.">Effects of Perfluorocarbon Gases on the Size and Stability Characteristics of Phospholipid-Coated Microbubbles: Osmotic Effect versus Interfacial Film Stabilization.</a> Langmuir. 28 (2), 1182-1189 (2012).</li><li>Rossi, S., Waton, G., Krafft, M. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phospholipid-Coated+Gas+Bubble+Engineering:+Key+Parameters+for+Size+and+Stability+Control,+as+Determined+by+an+Acoustical+Method.">Phospholipid-Coated Gas Bubble Engineering: Key Parameters for Size and Stability Control, as Determined by an Acoustical Method.</a> Langmuir. 26 (3), 1649-1655 (2010).</li><li>Swanson, E. J., 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=Phospholipid-Stabilized+Microbubble+Foam+for+Injectable+Oxygen+Delivery.">Phospholipid-Stabilized Microbubble Foam for Injectable Oxygen Delivery.</a> Langmuir. 26 (20), 15726-15729 (2010).</li><li>Kv&#229;le, 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=Size+fractionation+of+gas-filled+microspheres+by+flotation.">Size fractionation of gas-filled microspheres by flotation.</a> Separations Technology. 6 (4), 219-226 (1996).</li><li>Dressaire, 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=Interfacial+polygonal+nanopatterning+of+stable+microbubbles.">Interfacial polygonal nanopatterning of stable microbubbles.</a> Science. 320 (5880), 1198-1201 (2008).</li><li>Kheir, J. N., 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=Bulk+Manufacture+of+Concentrated+Oxygen+Gas-Filled+Microparticles+for+Intravenous+Oxygen+Delivery.">Bulk Manufacture of Concentrated Oxygen Gas-Filled Microparticles for Intravenous Oxygen Delivery.</a> Advanced Healthcare Materials. , (2013).</li></ol>

The authors declare that they have no competing financial interests.

The most important steps to creating concentrated, highly oxygenated LOMs include: 1) ensuring that the headspace within the HCT remains fully oxygenated; 2) ensuring that the purity of the lipid excipients is optimal (including storage conditions and use of GMP products); 3) ensuring that the powdered lipids mix completely with the aqueous phase prior to priming the system; and 4) paying close attention to the increase in gas fraction within the HCT to ensure that the volume fraction of gas does not exceed 70%.
<p c...

Microbubbles composed of protein, polymer, and lipid shells have been developed as vectors for drug delivery, gene therapy, and ultrasound contrast agents1-5. Because these therapeutic uses require intravascular microbubble persistence, such microbubbles are commonly filled with inert, high molecular-weight gases such as perfluorocarbons6, which have low solubility in blood and stabilize the bubble3,4.
Recently, lipid-based oxygen microbubbles (LOMs) have been designed to deliver therapeutic doses of oxygen, which may preserve end-organ oxygen delivery and prevent hemodynamic instability during periods of airway obstruction or hypoxemia7. Emulsions designed for intravenous gas delivery require different design features than those used for ultrasound contrast agents or targeted drug delivery. First, because the body consumes large volumes of oxygen gas (~200 ml/min), LOMs must be produced and injected on a large scale. This requires that the manufacturing process be efficient. Second, the manufacturing process should be closed-loop in order to avoid nitrogen contamination through the exposure of LOMs (which should be filled with 100% oxygen) to ambient air. Third, because the purpose of LOMs is intravenous gas delivery, the gas fraction of LOMs should be maximized, recognizing the limitations imposed by emulsion viscosity7. Finally, as with any intravenous injectable, precise control over particle size distribution is essential to avoiding microvascular obstruction8.
There are several established methods for microbubble manufacture. Sonication utilizes high intensity, low-frequency ultrasound applied to the air-fluid interface of an emulsion which includes a surfactant, such as an amphipathic phospholipid, in the presence of a gas headspace to produce microbubbles7,9. This process is controllable by varying ultrasound frequency, power and pulse duration, and the resulting size distribution can be tailored to produce microbubbles of a specific size distribution, though sonication is rarely used in the manufacture of clinically-used microbubbles. Amalgamation is the intense mechanical agitation of a surfactant and gas in a closed system, which is also difficult to scale up to accommodate large volumes2. Droplet-based microfluidics allows precise control of microbubble size distribution10-13. Though traditionally difficult to scale up, multi-channel, high-speed microfluidics have been described which increase microbubble production efficiency13. Microbubbles manufactured using any of these methods may require post-manufacture size-reduction processes, such as centrifugal fractionation14,15 and microbubble flotation16,17.
Another established method for the manufacture of highly stable microbubbles is shear homogenization6, which can result in a stabilizing hexagonal phospholipid pattern on the microbubble surface18. Building on this concept, we describe the incorporation of an in-line high shear homogenizer to create self-assembling LOMs19. In this process, the homogenizer utilizes rapidly rotating blades in close proximity to dual fine mesh emulsor screens, creating high mechanical and hydraulic shear for the creation of microbubbles. Serial concentration of the lipid emulsion through this system yields an increasingly concentrated gas fraction, which can be even further concentrated by centrifugation.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr height="42">
			<td height="42" style="height:43px;width:239px;">Name of Material/ Equipment</td>
			<td style="width:141px;">Company</td>
			<td style="width:119px;">Catalog Number</td>
			<td style="width:405px;">Comments/Description</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:239px;">1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)</td>
			<td style="width:141px;">Avanti Polar Lipids</td>
			<td style="width:119px;">770365</td>
			<td>Alternate product: non-GMP from NOF America (Coatsome MC-8080)</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:239px;">Cholesterol</td>
			<td style="width:141px;">Sigma Aldrich</td>
			<td style="width:119px;">C75209</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:239px;">Plasma-Lyte A</td>
			<td style="width:141px;">VWR</td>
			<td style="width:119px;">80089-818</td>
			<td>Alternatively can use NaCl</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:239px;">Glass collection vessel</td>
			<td style="width:141px;">Specialty Glass, Inc.</td>
			<td style="width:119px;">Custom</td>
			<td>Contact: Pam Zurbrick - 281-595-2210</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:239px;">Gas composition (oxygen) monitor</td>
			<td style="width:141px;">Precision Medical</td>
			<td style="width:119px;">PM5900L</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:239px;">Sarns 8000 roller pump</td>
			<td style="width:141px;">Calicut Medical</td>
			<td style="width:119px;">16407</td>
			<td>Part of a modular perfusion system</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:239px;">BIOtherm Heat Exchanger</td>
			<td style="width:141px;">Medtronic</td>
			<td style="width:119px;">ECMOtherm-II</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:239px;">Verso laboratory in-line mixer</td>
			<td style="width:141px;">Silverson Machines, Inc</td>
			<td style="width:119px;">TH-IL-102-VERSO</td>
			<td>Use multistage workheads and front-end extension with T piece</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:239px;">T-piece for Silverson Verso inlet port</td>
			<td style="width:141px;">Process Innovations</td>
			<td style="width:119px;">Custom</td>
			<td>Contact: Brian Leavitt - 508-423-2266</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:239px;">L5M-A laboratory mixer</td>
			<td style="width:141px;">Silverson Machines, Inc</td>
			<td style="width:119px;">NC0136483</td>
			<td>Use mesh emulsor screen (fine)</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:239px;">Rochester-Ochsner toothed forceps</td>
			<td style="width:141px;">Fisher Scientific</td>
			<td style="width:119px;">13-812-18</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:239px;">140 mL syringe</td>
			<td style="width:141px;">Kendall Healthcare Monoject&#160;</td>
			<td style="width:119px;">8881114030</td>
			<td>Ensure there is a luer lock.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:239px;">IX71 Inverted light microscope</td>
			<td style="width:141px;">Olympus</td>
			<td style="width:119px;">IX71</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:239px;">Retiga-2000R microscope camera</td>
			<td style="width:141px;">QImaging</td>
			<td style="width:119px;">RET-2000R-F-M-12</td>
			<td></td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:239px;">Accusizer 780A Autodilution</td>
			<td style="width:141px;">PSS-NICOMP Particle Sizing Systems</td>
			<td style="width:119px;">Out of production</td>
			<td></td>
		</tr>
	</tbody>
</table>

manufacture of concentrated, lipid-based oxygen microbubble emulsions by high shear homogenization and serial concentration

Gas-filled microbubbles have been developed as ultrasound contrast and drug delivery agents. Microbubbles can be produced by processing surfactants using sonication, mechanical agitation, microfluidic devices, or homogenization. Recently, lipid-based oxygen microbubbles (LOMs) have been designed to deliver oxygen intravenously during medical emergencies, reversing life-threatening hypoxemia, and preventing subsequent organ injury, cardiac arrest, and death. We present methods for scaled-up production of highly oxygenated microbubbles using a closed-loop high-shear homogenizer. The process can produce 2 L of concentrated LOMs (90% by volume) in 90 min. Resulting bubbles have a mean diameter of ~2 &#956;m, and a rheologic profile consistent with that of blood when diluted to 60 volume %. This technique produces LOMs in high capacity and with high oxygen purity, suggesting that this technique may be useful for translational research labs.

High shear homogenization enables the efficient (i.e. within one afternoon) production of sufficient LOMs for an animal study and does not require technical expertise. Once proficient, up to 2 L of concentrated LOMs can be manufactured in 90 min.
Microbubble size and morphology was assessed by light microscopy and by light obscuration. When a 10 &#956;l sample of LOMs was visualized, spherical LOMs were noted, as well as a relative paucity of lipid debris (Figure 3A)....

Watch this Scientific Journal Video about Manufacture of Concentrated, Lipid-based Oxygen Microbubble Emulsions by High Shear Homogenization and Serial Concentration at JoVE.com

Manufacture of Concentrated, Lipid-based Oxygen Microbubble Emulsions by High Shear Homogenization and Serial Concentration

We describe methods for the manufacture of large volumes of lipid-based oxygen microbubbles (LOMs) designed for intravenous oxygen delivery using high-shear homogenization and serial concentration.

Gas-filled microbubbles have been developed as ultrasound contrast and drug delivery agents. Microbubbles can be produced by processing surfactants using ...

manufacture-concentrated-lipid-based-oxygen-microbubble-emulsions

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JoVE Journal

Bioengineering

14.9K Views.  Harvard Medical School. We describe methods for the manufacture of large volumes of lipid-based oxygen microbubbles (LOMs) designed for intravenous oxygen delivery using high-shear homogenization and serial concentration.

Video: Manufacture of Concentrated, Lipid-based Oxygen Microbubble Emulsions by High Shear Homogenization and Serial Concentration

Introduction to the Ultrasound Targeted Microbubble Destruction Technique

In UTMD, bioactive molecules, such as negatively charged plasmid DNA vectors encoding a gene of interest, are added to the cationic shells of lipid microbubble contrast agents7-9. In mice these vector-carrying microbubbles can be administered intravenously or directly to the left ventricle of the heart. In larger animals they can also be infused through an intracoronary catheter. The subsequent delivery from the circulation to a target organ occurs by acoustic cavitation at a resonant frequency of the microbubbles. It seems likely that the mechanical energy generated by the microbubble destruction results in transient pore formation in or between the endothelial cells of the microvasculature of the targeted region10. As a result of this sonoporation effect, the transfection efficiency into and across the endothelial cells is enhanced, and transgene-encoding vectors are deposited into the surrounding tissue. Plasmid DNA remaining in the circulation is rapidly degraded by nucleases in the blood, which further reduces the likelihood of delivery to non-sonicated tissues and leads to highly specific target-organ transfection.

Ultrasound Targeted Microbubble Destruction (UTMD) can be used to direct site-specific delivery of bioactive molecules, including therapeutic genes, to target organs accessible to ultrasound, such as the heart and liver1-6.

In UTMD, bioactive molecules, such as negatively charged plasmid DNA vectors encoding a gene of interest, are added to the cationic shells of lipid ...

Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer several advantages over traditional microsphere fabrication techniques. Contrary to emulsion, suspension, and dispersion techniques, microgels formed by precipitation are of uniform shape and size, i.e.&#160;low polydispersity index, without the use of organic solvents or stabilizers. The mild conditions of the precipitation reaction, customizable properties of the microgels, and low viscosity for injections make them applicable for in vivo purposes. Unlike other fabrication techniques, microgel characteristics can be modified by changing the starting polymer molecular weight. Increasing the starting PEG molecular weight increased microgel diameter and swelling ratio. Further modifications are suggested such as encapsulating molecules during microgel crosslinking. Simple adaptations to the PEG microgel building blocks are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds.

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Increasing the PEG molecular weight increased microgel diameter and swelling ratio. Simple adaptations to the PEG microgel precipitation reaction are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds.

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer ...

Generation of Shear Adhesion Map Using SynVivo Synthetic Microvascular Networks

Cell/particle adhesion assays are critical to understanding the biochemical interactions involved in disease pathophysiology and have important applications in the quest for the development of novel therapeutics. Assays using static conditions fail to capture the dependence of adhesion on shear, limiting their correlation with in vivo environment. Parallel plate flow chambers that quantify adhesion under physiological fluid flow need multiple experiments for the generation of a shear adhesion map. In addition, they do not represent the in vivo scale and morphology and require large volumes (~ml) of reagents for experiments. In this study, we demonstrate the generation of shear adhesion map from a single experiment using a microvascular network based microfluidic device, SynVivo-SMN. This device recreates the complex in vivo vasculature including geometric scale, morphological elements, flow features and cellular interactions in an in vitro format, thereby providing a biologically realistic environment for basic and applied research in cellular behavior, drug delivery, and drug discovery. The assay was demonstrated by studying the interaction of the 2 &#181;m biotin-coated particles with avidin-coated surfaces of the microchip. The entire range of shear observed in the microvasculature is obtained in a single assay enabling adhesion vs. shear map for the particles under physiological conditions.

Flow chambers used in adhesion experiments typically consist of linear flow paths and require multiple experiments at different flow rates to generate a shear adhesion map. SynVivo-SMN enables the generation of shear adhesion map using a single experiment utilizing microliter volumes resulting in significant savings in time and consumables.

Cell/particle adhesion assays are critical to understanding the biochemical interactions involved in disease pathophysiology and have important ...

High-resolution Spatiotemporal Analysis of Receptor Dynamics by Single-molecule Fluorescence Microscopy

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., kinetics, coexistence of different states and populations, transient interactions), which are typically hidden in ensemble measurements, such as those obtained with standard biochemical or microscopy methods. Thus, dynamic events, such as receptor-receptor interactions, can be followed in real time in a living cell with high spatiotemporal resolution. This protocol describes a method based on labeling with small and bright organic fluorophores and total internal reflection fluorescence (TIRF) microscopy to directly visualize single receptors on the surface of living cells. This approach allows one to precisely localize receptors, measure the size of receptor complexes, and capture dynamic events such as transient receptor-receptor interactions. The protocol provides a detailed description of how to perform a single-molecule experiment, including sample preparation, image acquisition and image analysis. As an example, the application of this method to analyze two G-protein-coupled receptors, i.e., &#946;2-adrenergic and &#947;-aminobutyric acid type B (GABAB) receptor, is reported. The protocol can be adapted to other membrane proteins and different cell models, transfection methods and labeling strategies.

This protocol describes how to use total internal reflection fluorescence microscopy to visualize and track single receptors on the surface of living cells and thereby analyze receptor lateral mobility, size of receptor complexes as well as to visualize transient receptor-receptor interactions. This protocol can be extended to other membrane proteins.

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., ...

Synthesis of Gold Nanoparticle Integrated Photo-responsive Liposomes and Measurement of Their Microbubble Cavitation upon Pulse Laser Excitation

Photo-responsive nanoparticles (NPs) have received considerable attention because of their potential in providing spatial, temporal, and dosage control over the drug release. However, most of the relevant technologies are still in the development process and are unprocurable by clinics. Here, we describe a facile fabrication of these photo-responsive NPs with commercially available gold NPs and thermo-responsive liposomes. Calcein is used as a model drug to evaluate the encapsulation efficiency and the release kinetic profile upon heat/light stimulation. Finally, we show that this photo-triggered release is due to the membrane disruption caused by microbubble cavitation, which can be measured with hydrophone.

This protocol describes a simple preparation method for gold nanoparticle integrated photo-responsive liposomes with the commercially available materials. It also shows how to measure the microbubble cavitation process of the synthesized liposomes upon the treatment of pulsed laser.

Photo-responsive nanoparticles (NPs) have received considerable attention because of their potential in providing spatial, temporal, and dosage control ...

Manufacture and Drug Delivery Applications of Silk Nanoparticles

Silk is a promising biopolymer for biomedical and pharmaceutical applications due to its outstanding mechanical properties, biocompatibility and biodegradability, as well its ability to protect and subsequently release its payload in response to a trigger. While silk can be formulated into various material formats, silk nanoparticles are emerging as promising drug delivery systems. Therefore, this article covers the procedures for reverse engineering silk cocoons to yield a regenerated silk solution that can be used to generate stable silk nanoparticles. These nanoparticles are subsequently characterized, drug loaded and explored as a potential anticancer drug delivery system. Briefly, silk cocoons are reverse engineered first by degumming the cocoons, followed by silk dissolution and clean up, to yield an aqueous silk solution. Next, the regenerated silk solution is subjected to nanoprecipitation to yield silk nanoparticles &#8211; a simple but powerful method that generates uniform nanoparticles. The silk nanoparticles are characterized according to their size, zeta potential, morphology and stability in aqueous media, as well as their ability to entrap a chemotherapeutic payload and kill human breast cancer cells. Overall, the described methodology yields uniform silk nanoparticles that can be readily explored for a myriad of applications, including their use as a potential nanomedicine.

Nanoparticles are emerging as promising drug delivery systems for a broad range of indications. Here, we describe a simple yet powerful method to manufacture silk nanoparticles using reverse engineered Bombyx mori silk. These silk nanoparticles can be readily loaded with a therapeutic payload and subsequently explored for drug delivery applications.

Silk is a promising biopolymer for biomedical and pharmaceutical applications due to its outstanding mechanical properties, biocompatibility and ...

Quantifying Intermembrane Distances with Serial Image Dilations

A recently-described extracellular nanodomain, termed the perinexus, has been implicated in ephaptic coupling, which is an alternative mechanism for electrical conduction between cardiomyocytes. The current method for quantifying this space by manual segmentation is slow and has low spatial resolution.We developed an algorithm that uses serial image dilations of a binary outline to count the number of pixels between two opposing 2 dimensional edges.This algorithm requires fewer man hours and has a higher spatial resolution than the manual method while preserving the reproducibility of the manual process.In fact, experienced and novice investigators were able to recapitulate the results of a previous study with this new algorithm.The algorithm is limited by the human input needed to manually outline the perinexus and computational power mainly encumbered by a pre-existing pathfinding algorithm.However, the algorithm&#39;s high-throughput capabilities, high spatial resolution and reproducibility make it a versatile and robust measurement tool for use across a variety of applications requiring the measurement of the distance between any 2-dimensional (2D) edges.

The purpose of this algorithm is to continuously measure the distance between two 2-dimensional edges using serial image dilations and pathfinding. This algorithm can be applied to a variety of fields such as cardiac structural biology, vascular biology, and civil engineering.

A recently-described extracellular nanodomain, termed the perinexus, has been implicated in ephaptic coupling, which is an alternative mechanism for ...

Catalytic Scavenging of Plant Reactive Oxygen Species In Vivo by Anionic Cerium Oxide Nanoparticles

Reactive oxygen species (ROS) accumulation is a hallmark of plant abiotic stress response. ROS play&#160;a dual role in plants by acting as signaling molecules at low levels and damaging molecules at high levels. Accumulation of ROS in stressed plants can damage metabolites, enzymes, lipids, and DNA, causing a reduction of plant growth and yield. The ability of cerium oxide nanoparticles (nanoceria) to catalytically scavenge ROS in vivo provides a unique tool to understand and bioengineer plant abiotic stress tolerance. Here, we present a protocol to synthesize and characterize poly (acrylic) acid coated nanoceria (PNC), interface the nanoparticles with plants via leaf lamina infiltration, and monitor their distribution and ROS scavenging in vivo using confocal microscopy. Current molecular tools for manipulating ROS accumulation in plants are limited to model species and require laborious transformation methods. This protocol for in vivo ROS scavenging has the potential to be applied to wild type plants with broad leaves and leaf structure like Arabidopsis thaliana.

Catalytic Scavenging of Plant Reactive Oxygen Species In Vivo by Anionic Cerium Oxide Nanoparticles

Here, we present a protocol for the synthesis and characterization of cerium oxide nanoparticles (nanoceria) for ROS (reactive oxygen species) scavenging in vivo, nanoceria imaging in plant tissues by confocal microscopy, and in vivo monitoring of nanoceria ROS scavenging by confocal microscopy.

Reactive oxygen species (ROS) accumulation is a hallmark of plant abiotic stress response. ROS play&#160;a dual role in plants by acting as signaling ...

Detection of Endotoxin in Nano-formulations Using Limulus Amoebocyte Lysate (LAL) Assays

When present in pharmaceutical products, a Gram-negative bacterial cell wall component endotoxin (often also called lipopolysaccharide) can cause inflammation, fever, hypo- or hypertension, and, in extreme cases, can lead to tissue and organ damage that may become fatal. The amounts of endotoxin in pharmaceutical products, therefore, are strictly regulated. Among the methods available for endotoxin detection and quantification, the Limulus Amoebocyte Lysate (LAL) assay is commonly used worldwide. While any pharmaceutical product can interfere with the LAL assay, nano-formulations represent a particular challenge due to their complexity. The purpose of this paper is to provide a practical guide to researchers inexperienced in estimating endotoxins in engineered nanomaterials and nanoparticle-formulated drugs. Herein, practical recommendations for performing three LAL formats including turbidity, chromogenic and gel-clot assays are discussed. These assays can be used to determine endotoxin contamination in nanotechnology-based drug products, vaccines, and adjuvants.

Detection of Endotoxin in Nano-formulations Using Limulus Amoebocyte Lysate LAL Assays

Detection of endotoxins in engineered nanomaterials represents one of the grand challenges in the field of nanomedicine. Here, we present a case study that describes the framework composed of three different LAL formats to estimate potential endotoxin contamination in nanoparticles.

When present in pharmaceutical products, a Gram-negative bacterial cell wall component endotoxin (often also called lipopolysaccharide) can cause ...

Fabrication of Zero Mode Waveguides for High Concentration Single Molecule Microscopy

In single molecule fluorescence enzymology, background fluorescence from labeled substrates in solution often limits fluorophore concentration to pico- to nanomolar ranges, several orders of magnitude less than many physiological ligand concentrations. Optical nanostructures called zero mode waveguides (ZMWs), which are 100&#8722;200 nm in diameter apertures fabricated in a thin conducting metal such as aluminum or gold, allow imaging of individual molecules at micromolar concentrations of fluorophores by confining visible light excitation to zeptoliter effective volumes. However, the need for expensive and specialized nanofabrication equipment has precluded the widespread use of ZMWs. Typically, nanostructures such as ZMWs are obtained by direct writing using electron beam lithography, which is sequential and slow. Here, colloidal, or nanosphere, lithography is used as an alternative strategy to create nanometer-scale masks for waveguide fabrication. This report describes the approach in detail, with practical considerations for each phase. The method allows thousands of aluminum or gold ZMWs to be made in parallel, with final waveguide diameters and depths of 100&#8722;200 nm. Only common lab equipment and a thermal evaporator for metal deposition are required. By making ZMWs more accessible to the biochemical community, this method can facilitate the study of molecular processes at cellular concentrations and rates.

Described here is a nanosphere lithography method for parallel fabrication of zero mode waveguides, which are arrays of nanoapertures in a metal-clad glass microscopy coverslip for single molecule imaging at nano- to micromolar concentrations of fluorophores. The method takes advantage of colloidal crystal self-assembly to create a waveguide template.

In single molecule fluorescence enzymology, background fluorescence from labeled substrates in solution often limits fluorophore concentration to pico- to ...