Doug, I am not an expert but here is my opinion on your questions. 1) I think that your ultrasonic transducer operates at a frequency around 42 kHz and not 50/60 Hz. The bubbles that rupture are bubbles of gas. The liposome bubbles that form consist of a phospholipid shell with a water center. Since the liposome bubble is not gaseous it does not rupture in the same way that gas bubbles do. That does not mean that shear forces do not rupture some lipisomes but I expect that the liposomes reform after the shear forces go away.
2) The ultrasonic waves apply shear forces to break the lecithin into individual phospholipids that will then form liposomes See: http://en.wikipedia.org/wiki/Liposome "It should be noted that formation of liposomes and nanoliposomes is not a spontaneous process. Lipid vesicles are formed when phospholipids such as lecithin are placed in water and consequently form one bilayer or a series of bilayers, each separated by water molecules, once enough energy is supplied [8]. Liposomes can be created by sonicating phospholipids in water[3]. Low shear rates create multilamellar liposomes, which have many layers like an onion. Continued high-shear sonication tends to form smaller unilamellar liposomes. In this technique, the liposome contents are the same as the contents of the aqueous phase." As the article states, low shear rates create multilamellar liposomes, which have many layers like an onion. The goal is to generate high shear rates to create small liposomes. This can be done in small ultrasonic cleaners as well as in large ultrasonic cleaners. The shear rate is proportional to the energy in the solution and is usually defined by the watts/volume the transducer produces. You can adjust the watts/volume by simply by changing the amount of solution you put in the ultrasonic cleaner. The reason for the stirring is that standing waves generally form in the solution. This is evidenced by ripples on the top of the solution. If the ripples are stationary. Then the desired shear forces are not moving through the solution but are stationary. To evenly apply the shear forces to all the lecithin, you must then move the lecithin around by stirring. 3) The ultrasonic cleaner is a form of sonication. See: http://en.wikipedia.org/wiki/Sonication " Sonication is the act of applying sound (usually ultrasound) energy to agitate particles in a sample, for various purposes. In the laboratory, it is usually applied using an ultrasonic bath or an ultrasonic probe, colloquially known as a sonicator." 4) Yes, gas in the solution reduces the effectiveness of the process because the gas bubbles absorb some of the ultrasonic energy. I don't know how long it takes to degas a solution but using distilled water for the solution will reduce the amount of dissolved gasses in the solution you start with. - Steve N From: polo [mailto:dah...@centurytel.net] Sent: Wednesday, June 23, 2010 7:02 AM To: silver-list@eskimo.com Subject: CS>liposomes & ultrasonic cleaners I have been doing some study on the mechanics of ultrasonic cleaners in relation to liposomes and I am curious of some of the ramifications: 1) Ultrasonic cleaners work by producing alternating low and high sound waves. The unit I am using does 50/60 Hz. The low phase produces the bubble and the high phase implodes the bubbles which produces the cleaning action so desired in such cleaners. Question: I can see the low phase producing liposomes, but how are the liposomes immune to the high phase that normally ruptures bubbles? 2) Using the cheap harbor freight ultrasonic cleaner, it is recommended to stir the solution and that the more shallow the solution, the higher the quality of liposome. Is stirring really necessary as it is so time consuming? It seems to me that the solution has natural movement all by itself from the production of the ultrasonic waves. 3) It is suggested that the best cavitation of the solution in the ultrasonic cleaner occurs when the solution is warm, plus the cavittion produces heat too. How much danger is this produced heat from ultrasonic wave production to ascorbic acid or the ascorbates' integrity over a long period of time? Is it minimal? One would logically conclude that the more heat produced, the more energetic the cavitation---would one not? If this is true, would it not be more efficient to produce liposomes with specialized instruments like sonifiers (pulsing and placing the lipo-C in ice water to keep temps low)? 4) It sounds to me that the longer one can run your lipo-C solution in a ultrasonic cleaner the better the quality of liposomes according to some of Brooks' later posts, however there is what is known as "degassing" in ultrasonic cleaning. Many instruction manuals for cleaners will advise you to "de-gas" your solution from 5-10 minutes before actually starting the cleaning process. Degassing is the initial removal of gases present in the solution. Useful cavitation occurs after the gasses have been removed from the solution leaving a vacuum in the later formed bubbles as it is written in these manuals. So it seems to me on first glance after reading this, that one would not want to extend our Lipo-C solution cavitation much longer than the recommended 6 minutes as that would degas the solution, producing an "empty bubble". Is this true or am I missing some thing? 5) Finally, there seems to me, better ways to produce a liposome via sound waves. Would not lab devices known as sonifiers/sonicators/cell disruptors be a better choice since these devices produce an intense steady frequency unlike the ultrasonic cleaner? Agreed, this device would not be in the reach of the average home-made tech, but would it produce a smaller, better liposome than ultrasonic cleaners? I realize that heat generation would be a problem from such intense ultrasound involvement from a cell disruptor, but having the solution in ice and pulsing should over come this problem, eh? doug -- The Silver List is a moderated forum for discussing Colloidal Silver. 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