Name: manufacture of concentrated, lipid-based oxygen microbubble emulsions by high shear homogenization and serial concentration
Uploaded: 2014-05-26T14:00:00
Description: Watch this Scientific Journal Video about Manufacture of Concentrated, Lipid-based Oxygen Microbubble Emulsions by High Shear Homogenization and Serial Concentration at JoVE.com

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 rub...

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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%.
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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 ...

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