Ultrasonic Cell Disrupters, also called Sonicators or Sonifiers® operate on a different principle than mechanical shear homogenizers.  They are extremely effective on hard to disrupt samples and for producing smaller particle size distribution within a sample.  Some of the samples that are typically sonicated or sonified are bacteria, spores, tough animal tissue, soil samples, nanostructures, and liposomes.

There are three main components of a laboratory Ultrasonic Homogenizer; an electronic generator which provides the power, a transducer which converts the signal to mechanical energy and a horn or probe where the processing takes place.

The electronic generator which located in the base of the unit gets its power from an AC line.  The generator transforms this electrical power to a 20 KHz signal that drives the transducer or converter. This signal is outside of normal human hearing ranges so it is not audible in this form of energy.

The converter or transducer contains piezoelectric crystals.  These crystals are able to convert the electrical signal that the generator produces into a mechanical energy or vibration.  This mechanical vibration is amplified and is used to drive the horn.

The vibration of the crystals is transmitted down the length of the horn or probe causing it to longitudinally expand and contract all the way to the end of the probe.  The tip of the probe is the area where the highest level of activity will be occurring.  The longitudinal vibration in the tip causes the sample to cavitate meaning thousands of tiny bubbles form and collapse as the tip continues to vibrate.  This cavitation creates the energy that causes the sample to disrupt and break down into smaller particles which is responsible for the sound that is heard during sonication.

The probes are typically manufactured out of titanium as this metal can withstand the expansion and contraction caused by the longitudinal vibration.  As with any metal, over time the probe can begin to erode or become pitted.  It is important to clean the probe after each use and dry it to keep it from eroding.  Erosion or pitting on a probe can decrease the effectiveness of the sonication so it is important to inspect the probe after 8-10 hours of use and polish it with a fine emery cloth.

Probes come in different diameter tip sizes to enable very small to large samples to be processed.  A tip with a very small diameter will have a very high intensity for processing as all the energy is focused on a very small area.  However, the size of the tip will limit the area of the cavitation and which will limit the sample size.  A larger tip will have a lower intensity as the energy is spread out over a larger surface area.  However, the area of cavitation or processing area is larger thus allowing for more sample to be processed.

When looking at what type of sonicator is needed for an application, it is important to look at power output along with probe size.  Power is measured in Watts or Wattage and the higher the wattage the more power the Ultrasonic Homogenizer can produce.  Small samples will not need high power because the size of the probe will be small and the intensity of the smaller probes is much higher than the larger probes.  Large samples or samples with higher viscosities may require higher power to produce results as the Ultrasonic has to drive a larger probe with less intensity or energy at the tip.

In my last blog I wrote that I would be back with some Ultrasonic Homogenizer Applications and here I am, back again, trying to fill the Ultrasonic void.

Although Ultrasonic Homogenization is most widely known for disruption of cells and tissue, there are many other uses for it that covers a wide range of applications.

Emulsifications

Water in oil emulsions are well suited for sonication because there is little danger of the sample being ruined by inversion and the process is considerably faster than traditional mixing methods.  The cosmetic industry uses Ultrasonic Homogenization for liquid make-up in order to disperse the pigments uniformly.  It is also widely used by lotion and toothpaste manufacturers as the final product has a much longer shelf life and is a higher quality product.

Environmental

Sonication is used in environmental testing labs for testing of water, soil and sediment samples.  Testing that was done prior to Ultrasonic Homogenization was very time consuming and required high volumes of solvents. The use of Ultrasonics cut the testing time by many hours down to 5-10 minutes making the environmental labs more efficient and reduced solvent waste products.

Pharmaceutical

Pharmaceutical research covers a wide range of applications for Ultrasonics.  Common uses are mixing of powders and solutions, the making of smaller crystals for drug compounds, and degassing samples.  The production of liposomes or lipid vesicles that are used to study mechanisms for drug discovery are also critical in this industry along with putting complex compounds into solution for analysis via chromatography.

Focused Cleaning

This may be the least well known application for Ultrasonic Homogenizers.  In an Ultrasonic Bath the strength of the sonication waves are limited for this type of application.  It takes much more time to clean items in a bath than it would if using a probe type Ultrasonic.  The benefits of this are apparent when trying to clean items with very small openings such as needle or wire dies and electronic components as the energy can be focused and directed by moving the probe.

Check back in a few weeks for part III of the Ultrasonic Blog, “What Equipment in Right for You” and in the meantime have a Happy, Healthy and Safe Holiday and New Year!

Many customers who are just starting to investigate laboratory homogenization techniques call us and ask what the difference is between Ultrasonic Homogenization and Mechanical Shear or Rotor/Stator Homogenization.  As we offer both products, it is fairly simple for us to meet the requirements of all the customers whether they need sonication or mechanical shear technology.  Although you may be able to get similar results from both ultrasonic and mechanical homogenizers, the way they create the energy to process the sample is different and can have distinctive effects on the sample and the end result.

Ultrasonic homogenization is created by power that is supplied by electrical energy that is transferred to a probe, usually titanium, where it is converted to mechanical energy.  This mechanical energy shows up as longitudinal vibrations at the tip of the probe.  Once the energy reaches the tip it causes microscopic vapor bubbles that implode and cause shock waves throughout the sample that cause the processing effect or what is called cavitation.

Ultrasonic probes are solid so they have no tearing or cutting capabilities however they are extremely effective on very small samples as the sample has no chance of hiding in a blade assembly.  Sonicators are more effective at processing bacteria and spores along with soil and sediment samples as they have more of an impact effect for breaking the hard walls of these samples. Ultrasonic Homogenizers are also very effective for DNA shearing.  However, they do generate more heat than Mechanical Shear Homogenizers so heat sensitive samples must sometimes be cooled.

Rotor/Stator Homogenization is driven by an electrical motor that is used to drive a long shaft with a rotor/stator (blade assembly) attached to the bottom of it.  This motor causes rotation of the blade assembly at very high speeds anywhere from 5,000 rpm’s all the way up to 75,000 rpm’s.  The blade (rotor) which is rotating pulls the sample into the processing area and then forces it through very sharp windows in the outer blade assembly (stator) to fully and continuously process the sample.

Mechanical shear homogenization is usually better suited to samples that need a tearing or cutting effect on them.  Examples of these samples include animal tissue and cells such as mouse organs, tumors, and muscle.  It is also very useful for making emulsions and combining powders and liquids along with other general lab applications.

Did you like this article? Stand by, our newest Ultrasonic article entitled “Getting Specific: Ultrasonic Homogenizer Applications” is coming soon!