Cell Disrupters: A Review


Apparatus and Techniques of Cell Disruption - A Review

by Tim Hopkins, (Updated 2023)

Practical aspects of mechanical cell and tissue disruption are discussed. Equipment sources and approximate prices are given. For a comprehensive review by the author see 'Purification and Analysis of Recombinant Proteins', Chapter 3, Seetharam and Sharma, editors, published by Marcel Dekker, Inc (New York), 1991.

Bead Mill Homogenizers

Over 40% of lab homogenizers are specifically used to disrupt cells (Lab Manager, December 2015).  In the general category of lab homogenizers, bead-milling, commonly called beadbeating, is the latest entry in this general category and leads traditional rotor-stator and ultrasonic methods as the method of choice for disruption of cells and tissue.

In bead-milling, a suspension of tissue or microorganisms is mixed with a large number of minute glass, ceramic, or steel beads and vigorously agitated by shaking or stirring. Cell disruption occurs by the crushing action of the beads as they collide with the cells. Compared to ultrasonic and high-pressure methods of cell disruption, bead milling is relatively low in shearing force. By selecting the correct-sized beads and modest shaking speed, recovery of cell membranes is high, and intact intracellular organelles can often be isolated. At higher shaking energies, beadbeating is considered the method of choice for disruption for spores, yeast, and fungi and performs successfully with tough-to-disrupt cells like cyanobacteria, mycobacteria, spores, and microalgae. More recently, bead mill homogenization has been applied to soil samples and to small samples of plant and animal tissue. If PCR techniques are employed, this homogenization method is one of the few that can totally avoid possible cross-contamination between samples -- primarily because both the vials and beads used in the method are disposable items.

The diameter of the beads used is important. The optimal size for bacteria and spores is 0.1 mm, 0.5 mm for yeast, mycelia, microalgae, and unicellular animal cells such as leucocytes or trypsinized tissue culture cells, and 1.0 or 2.5 mm for tissues such as brain, muscle, leaves, and skin. The speed of disruption is increased by about 50% by using like-sized, but heavier ceramic beads made of zirconia-silica or zirconia rather than glass. Disruption of really tough tissue sometimes requires chrome-steel beads - which are 5 times denser than glass beads.

While steel beads in microvials can be used with "shaking-type bead mills", they are too heavy to be used in "rotor-type bead mills".  And even then, in some high-energy shaking-type bead mills, steel beads may crack commonly available polypropylene microvials. To get around this microvial limitation, reinforced polypropylene microvials (branded ‘XXTuff’) or stainless steel microvials are available from BioSpec Products, Bartlesville, OK. There are reports that non-bead, sharp-edged particles made of silicon carbide or garnet, also do a good job of disrupting tough tissue. An adequate load of the beads in a vial is usually about 20-50% of the total vial volume. And, in the case of rotor-type bead beaters the bead load volume relative to the chamber volume is about 50%. Generally, the higher the volume ratio of beads to the cell suspension, the faster the rate of cell disruption. After homogenization in a bead mill, the beads quickly settle by gravity and the homogenate is removed by pipetting.

Microorganisms and tissue can be disrupted manually using the bead-mill technique: While this hand-held method is tedious and slow, it serves as an initial test of the bead mill method:  Microbial cells or tissue (pre-chopped into very small pieces) suspended in one ml of extraction media are added to a 2 mL microvial already preloaded with one ml of appropriately sized beads. Cap the microvial and agitate the mixture for ten minutes on a lab vortex mixer.

Shaking-type Bead Mills

The standard Shaking-type bead mill (aka Beadbeater) can process sample sizes up to 500 mg (wet weight) using 2 mL polypropylene screw-cap microvials. Bead mill accessories which hold 7 mL or larger tubes are also available.  Screw-caps must always be used because snap-top microvials can release aerosols of their contents during the high-energy shaking process. These bead mills hold the vials either in a vertical position or a more efficient near-horizontal position. Almost all machines shake the beads in the direction of the vial’s axis and the pattern of the vial shaking back and forth can be either linear or a compressed figure-8.  While there are some noticeable performance differences between different brands of bead mills, especially when disrupting tough cells or tissue, total disruption generally takes about 1-3 minutes and yields of intracellular biochemicals are very high. After beadbeating, the beads settle by gravity in seconds and the cell extract is easily removed by pipette.

In 1979 BioSpec Products was the first to introduce lab-scale bead mill cell disrupters and it dominated the market for about 20 years.  This company now manufactures six models of high-energy, laboratory-scale bead mills.  The MiniBeadbeater-Plus holds a single 2 mL screw-cap microvial while the three other MiniBeadbeater models can process up to 16, 24, or 48 two mL microvials at a time.  The MiniBeadbeater-96 can also process samples in 96 deep-well microplates. They also offer a preparative lab beadbeater that processes up to 80 g (wet wt) of microbial cells.  Their newest addition, the SoniBeast, processes twelve 0.6 mL microtubes or three 2 mL microvials and, unlike the shaking-type bead beaters, agitates the beads using a patented ultra-high vortex motion driven by a 30,000 rpm (500 Hz) motor. The SoniBeast disrupts cells in seconds rather than minutes, making it the fastest bead mill cell disrupter on the market.

In the 40+ years since the introduction of the Beadbeater, numerous manufacturers currently offer similar bead mills designed specifically for cell disruption. In order of their introduction date, commercial shaking-type bead mill cell disrupters currently available are: Mini-BeadBeater-1, -16, -24, -96 and SoniBeast (BioSpec Products, Bartlesville, OK); Retsch Mixer MM 301 and MM400 (F. Kurt Retsch GmbH, Haan, Germany); FastPrep-24 and -96 (MP Biomedicals, Santa Ana, CA); Precellys Evolution, Precellys-24 and Minilys (Bertin Instruments, Montigny-le-Bretonneux, France); 2010 Geno/Grinder-2010, -2025, -2030 and 1600 MiniG (SPEX SamplePrep, Metuchen, NJ); MagNA Lyser (Roche Applied Science, Penzberg, Germany); Powerlyser-24 (MO BIO Laboratories, Carlsbad, CA); Bead Rupter-4, -12, -24 Elite and -96 (Omni International, Kennesaw, GA); TissueLyser (Qiagen Inc-USA, Valencia, CA); Talboys H.T.H. (Troemner, Thorofare, NJ); SpeedMill PLUS (Analytik Jena, Jena, Germany); HT Lysing Homogenizer (Ohaus Corporation, Parsippany-Troy Hills, NJ): Micro Smash MS-100 (Tomy Digital Biology, Tokyo, Japan) and UPHO (Geneye, Quarry Bay, Hong Kong). Other bead-stirring devices based primarily on vortex-type mixing are Disruptor-Genie (Scientific Industries, Bohemia, NY) and BulletBlender (Next Advance, Averill Park, NY).  Compared to the above shaking-type bead mills, these vortex-type bead mixers deliver lower mixing energies and, therefore, require considerably longer shaking times to get good cell disruption. The current price of shaking and vortexing bead mill cell disrupters ranges from $600 to $16,000.

Most of these disrupters are well-designed and fulfill the specifications needed for maximum cell disruption performance.  When shopping, look for machines that have a shaking speed of at least 2000 rpm; a throw (or displacement) of the vial of at least 3/4 inches, and a shaking orientation and pattern that maximizes bead circulation within the vial.  There are additional important factors influencing cell disruption performance and they are numerous and complex. Some manufacturers have chosen to combine shaking speed and the vial throw (displacement) of their machine into a "specification" having units of m/sec.  The term correlates with but does not define cell disruption efficiency.  It makes the objective comparison of operating parameters between different brands of bead mill cell disrupter difficult and the reproduction of published cell disruption protocols using different beadbeater brands questionable.  To get around this problem a time-study with a reference sample for 0.5, 1, 2, 3, and 5 minutes beadbeating, at the machine's maximum speed, will pinpoint its optimal disruption time...typically 1 - 3 minutes for total cell lysis.



Larger capacity laboratory bead mill cell disrupters agitate the beads with a rotor rather than by shaking. Equipped with efficient cooling jackets, large sample volumes can be processed without overheating the homogenate. By far the most widely used rotor-type bead mill is the BeadBeater (BioSpec Products, Bartlesville, OK). In three to five minutes of operation, this compact laboratory-sized unit will disrupt a batch of up to 80 g (wet wt) of microbial cells suspended in 250 ml of disruption media or, with smaller chamber attachments, 50 or 15 mL batches of cell suspension. Cell suspension concentrations as high as forty percent (packed cell volume) can be used. VirTis Company (Gardiner, NY) offers an attachment for its line of high-speed rotary homogenizers which efficiently agitate glass beads in a special fluted flask.  These rotor-type homogenizer units cost about $600 and $800, respectively. Using a rotating spiral to agitate the beads rather than a rotor, the Spiral Mill (Caheravirane Schull Co., Cork, Ireland)  is priced at about $3000.  It can process up to 6 g (wet weight) of microbial cells.

Rotor-Stator Homogenizers (also called colloid mills or Willems homogenizers)

These homogenizers are well suited for homogenizing plant and animal tissue in liquid media volumes of 1 ml to a few liters.  They generally outperform cutting-blade-type Benders. Compared to a Blender, foaming, and aeration are minimized and much smaller sample volumes are easily accommodated. The cellular material is drawn into the apparatus by suction created by a rotor sited inside the end of a long static tube or probe (commonly called a stator). The material then centrifugally exits through slots or holes located near the tip of the stator. The tissue is repeatedly recycled, and because the rotor is turning at very high speeds, the tissue is reduced in size by a combination of liquid shear forces and mechanical scissor-like shearing occurring at the tip of the probe. Depending upon the toughness of the tissue sample, desired results are usually obtained in 5-60 seconds. For the recovery of intracellular organelles or receptor site complexes, shorter times and/or reduced rotor speeds are used. When using smaller-sized rotor-stator probes the tissue sample must be pre-chopped with a scalpel or razor blade into pieces less than 1 mm in cross-section prior to processing in order for the sample to be drawn inside the hole at the tip of the stator. If the sample has already been stored frozen, a cryopulverizer (a device that quickly powders tissue at liquid nitrogen temperatures - see below) can be used to break the tissue sample into small pieces without thawing. Some rotor-stator manufacturers offer probes having a saw-like circle of teeth at the tip of the stator which helps break up samples that were initially too large to enter the probe.  This feature is helpful but homogenization time can be slower.  Unlike many other types of mechanical cell disrupters, rotor-stators homogenizers generate essentially no heat during operation.  Additionally, rotor-stator homogenizers can not lyse microorganisms -- a property that is useful when studying microorganisms embedded in soil, feces, or the like.

Most laboratory rotor-stator homogenizers are top-driven with a compact, high-speed electric motor that turns at 8,000 to 35,000 rpm. The size of the rotor-stator probe (collectively called the generator) can vary from the diameter of a drinking straw for 0.5-50 mL sample volumes to much larger units capable of processing 10-liter batches or more. There is an important relationship between rotor speed and stator diameter. In principle, the top rotor speed of the homogenizer should double for each halving of the rotor diameter. It is not rpm per se, but the tip velocity of the rotor that is the important operating parameter. Ten to twenty meters per second (2000 to 4000 fpm) are acceptable tip speeds for tissue disruption. Unfortunately, most commercial rotor-stator homogenizers small enough to easily fit into a microtube fall short of this tip-speed standard. Other factors such as rotor-stator design (there are many), materials used in its construction, and ease of cleaning are also important to consider in selecting a rotor-stator homogenizer. Some manufacturers of rotor-stator homogenizers are BioSpec Products (Bartlesville, OK), Brinkmann Instruments (Westbury, NY), Charles Ross & Son Company (Hauppauge, NY), Craven Laboratories (Austin, TX), IKA Works (Cincinnati, OH), Omni International (Gainsville, VA), Pro Scientific (Monroe, CT), Silverson Machines (Bay Village, OH), and VirTis Company (Gardiner, NY). The cost of complete units (motor plus rotor-stator head or generator) ranges from $600 to $5000.

Laboratory-sized homogenizers function properly only with liquid samples in the low to medium viscosity range (<10,000 cps). The speed and efficiency of homogenization is compromised by using too small a unit, and the volume range over which a given homogenizer's rotor-stator probe size will function efficiently is only about ten-fold. Foaming and aerosols can be a problem with rotor-stator homogenizers. Keeping the tip of the homogenizer well submerged in the media and the use of properly sized vessels helps with the first problem. Square-shaped homogenization vessels give better results than round vessels and it is also beneficial to hold the immersed probe off-center. Aerosols can be minimized, but not completely eliminated, by using properly covered vessels (VirTis, Brinkmann, and Omni). Even though a number of laboratory rotor-stator homogenizers use fully enclosed motors, none of the motors are explosion-proof. Therefore, due caution should be followed when using flammable organic solvents such as acetone, alcohol, or chloroform by conducting the homogenization in a well-ventilated hood.

Bottom-driven laboratory rotor-stator homogenizers are a new entry to the laboratory. The rotor-stator assembly is usually placed within a sealed chamber or container, fits blender motor bases, and has working volumes of 100-1000 mL. They cost about $250 to $400 and are available from BioSpec Products (Bartlesville, OK) and Eberbach Corporation (Ann Arbor, MI).

Dispersers

Closely related to rotor-stator homogenizers, dispersers are used for preparing large volumes of crude plant and animal aqueous extract. Constructed like a household garbage disposal unit, the rotor-stator mechanism quickly homogenizes and liquefies kilogram quantities of biomass. The sample is suspended in one or more liters of media, loaded into its top reservoir and homogenized either in a continuous- or batch-mode. Costing $600 to $7000, two manufacturers are BioSpec Products and IKA Works.

Blade Homogenizers

Although less efficient than rotor-stator homogenizers, and aeration and foaming can be a problem, blade homogenizers (commonly called blenders) have been used for years to produce fine brie and extracts from plant and animal tissue. Blenders cannot efficiently disrupt microorganisms. In this class of homogenizers, a set of stainless steel cutting blades rotate at speeds of 6,000-50,000 rpm inside a glass, plastic or stainless steel container. The blades can be either bottom- or top-driven. As determined by flow cytometric analysis, some of the higher-speed homogenizers can reduce tissue samples to a consistent particulate size with distributions as small as 4 microns. After blending, some plant tissue homogenates undergo enzymatic browning -- an oxidation and chemical cross-linking process which can complicate subsequent separation procedures. Enzymatic browning is minimized by carrying out the extraction in the absence of oxygen or in the presence of oxygen-scavenging thiol compounds such as mercaptoethanol. The addition of polyethyleneimine, metal chelators, or certain mild detergents such as Triton X-100 or Tween 80 also minimizes enzymatic browning.

When using a blender, use caution when blending with flammable solvents such as alcohol or acetone. Blenders use brush motors to achieve their high speeds and, therefore, spark during operation. Also, aerosols readily form while blending. When homogenizing diseased tissues use a sealed blender container and operate it in a well-ventilated safety hood.

Blade homogenizers can process liquid suspensions in container sizes from 2 ml to one gallon. Accessories for blenders include cooling jackets for temperature control, closed containers to minimize aerosol formation,  vessels made of stainless steel, semi-micro containers, and insulated vessels for use with cryogenic solvents (see Freeze fracturing). Manufactures of a scientific line of blenders include British Medical Enterprises (London, England), ESGE (Basel, Switzerland), Hamilton Beach Commercial (Washington, NC), Omni International (Waterbury, CT), The VirTis Company (Gardiner, NY) and the Waring Products Division (New Hartford, CT). Accessory vessels for Hamilton-Beach brand blenders are manufactured by BioSpec Products (Bartlesville, OK). And, Eberbach Corporation (Ann Arbor, MI) makes accessories for Waring brand blenders. Prices for blade homogenizers range from about $100 to $2000.

Freeze Fracturing or Cryopulverization

Microbial paste and plant and animal tissue can be frozen in liquid nitrogen and then ground with a mortar and pestle at the same low temperature. The hard frozen cells are fractured because of their brittle nature. Also, at these low temperatures, internal ice crystals may act as an abrasive.  The end product of this process can range from very small pieces of tissue the size of grains of salt to preparations with almost all of the cells disrupted.  With respect to the latter, cryopulverization is a unique mechanical cell disruption method capable of delivering very high molecular weight DNA.

A ceramic mortar and pestle precooled to liquid nitrogen temperatures can be a cryopulverizer.  BioSpec Products (Bartlesville, OK) makes an improved version of this simple tool specifically targeted for cryopulverization.  It is called a Cryo-cup Grinder. There are additional devices designed to cryopulverize tissue samples. Caheravirane Schull Co. (Cork, Ireland), Spectrum Medical Industries (Carson, CA) and BioSpec Products manufacture freeze fracturing devices called, respectively, CellCrusher, Bessman Tissue Pulverizer, and BioPulverizer.  These freeze-fracturing devices fragment 10 mg to 10 g quantities of soft or fibrous tissue such as skin or cartilage to the size of grains of salt. This ground material is then easily and quickly homogenized by other cell disruption methods. Looking somewhat like a tablet press, these pulverizers consist of a hole machined into a stainless steel base into which fits a piston or rod.  Each differs in structural details of the hole and/or piston. The base and piston are pre-cooled to liquid nitrogen temperatures. The hard frozen animal or plant tissue is placed in the chilled hole, the chilled piston is placed in the hole, and given one or two sharp blows with a hammer. The resulting frozen, powder-like material can be further processed by Pestle and Tube, Bead Mill, Rotor-stator homogenizer, Sonicator, etc.  Cryopulverizers come in several sizes and cost $400 to $700. Two other "hammerless" cryopulverizers, available from BioSpec Products, are the MicroCryoCrusher, a hand-operated screw press that is especially suited for cryopulverizing small samples of fresh bone or teeth, and the CryogenicTissueGrinder, a high-speed blade mill that cryopulverizes 0.5 - 10 grams of microbial, plant or animal tissue to a fine powder in the presence of dry ice.  Both cost about $100.

Grinders

Grinding biological material in a mortar or tube containing sand, alumina or glass powder is roughly the equivalent of bead-milling (see above). The method works reasonably well with all types of biomass but is strictly small-scale and labor-intensive. Microbial cell paste or prechopped tissue,  a minimum volume of buffer, and a 0.5-1 volume of grinding media is mixed and ground with a mortar and pestle. Disruption efficiency is poor if too much media is added or smaller charges of grinding media are used. Also, the grinding powder has a high surface area and may bind significant amounts of charged biomolecules such as nucleic acids and proteins.

Pestle and Tube Homogenizers (also called tissue grinders)

Are used to disrupt fresh animal tissue. While variations of the pestle and tube homogenizer have names like Potter, Potter-Elvehjem, Dounce, and Ten Broeck, as a group they consist of test tubes made of glass, inert plastic, or stainless steel into which is inserted a tight-fitting pestle made of like materials with clearance about 0.1-0.2 mm. The walls of the test tube and pestle can be smooth or have a ground finish. Most tissues must be cut or chopped into small pieces (~1 mm in cross-section) with scissors or a single-edge razor blade before being suspended in a 3-10 fold volume excess of a medium in the test-tube). The pestle is manually worked to the bottom of the tube, thus tearing and crushing tissue as it is forced to flow between the tight-fitting sides of the pestle and the wall of the tube. The grinding action occurs again as the pestle is withdrawn. Five to thirty repetitions of this low-shear method are required to homogenize most tissues. The process is speeded up by rotation of the pestle at about 500-1000 rpm attached to an electric motor while the test tube is manually raised and lowered. While pestle and tube homogenization is simple and the equipment used is usually inexpensive, the process is labor-intensive and, when using fragile glass homogenizers, potentially dangerous. Even so, this homogenizer continues to be popular because of its extremely gentle action. Often it is the method of choice for the preparation of small quantities of subcellular organelles from soft animal tissues such as the brain or liver. Microorganisms cannot be disrupted with pestle homogenizers.

Commercially available glass or plastic pestle homogenizers with batch capacities of 0.1-50 mL generally cost $15-$100 and are available from many manufacturers including Ace Glass (Vineland, NJ), Bell-Art Products (Wayne, NJ), Bellco Glass (Vineland, NJ), BioSpec Products (Bartlesville, OK), Kontes (Vineland, NJ), Thomas Scientific (Swedesboro, NJ), Tri-R Instruments (Rockville Center, NY), Sage Products (Crystal Lake, IL), Research Products International (Prospect, IL) and Wheaton Industries (Millville, NJ).  Stainless steel tissue grinders, while more expensive ($200 - $250, BioSpec Products and Wheaton), can be efficiently cooled and tolerate vigorous homogenization without risk of shattering.

A hand-held, battery-powered motor unit called a BioRotator, is designed to rotate a disposable plastic pestle in a 1.5 ml conical microcentrifuge tube at high speed.  It is made by BioSpec Products and Bell-Arts Products ($50-80). BioSpec Products has improved the efficiency of the classic plastic pestle by molding spiral grooves on the pestle's surface.  The grooves greatly enhance the circulation of the tissue being processed by the BioRotator. Furthermore, by also adding a pinch of 0.5 mm dia glass grinding beads to the microtube, cell disruption of microorganisms is possible.

Solid Tissue Presses and Dispersers

There are several mechanical devices that reduce soft tissue to a much smaller size by forcing the solid tissue sample through an array of small holes or a stainless steel screen.  In most cases, no liquid media is added to the sample prior to homogenization, and, depending on the press used, the exiting, dispersed tissue can have a texture varying from hamburger meat to paste-like liver pate. While it is not an effective way to disrupt cells per se, it is used as a preliminary step for complete homogenization using other physical, chemical or enzymatic methods.

The well-known household meat grinder or mincer has been used for decades for the preparation of dispersed animal tissue. The tissue is mechanically pushed through small holes in a metal sieve plate while rotating blades slowly sweep across the face of the sieve plate and cut the extruded meat into 0.3 - 0.5 mm fragments.  Meat grinders cut flexible tissue like muscle better if the tissue is processed slightly frozen.

For smaller tissue samples, BioSpec Products (Bartlesville, OK) manufactures hand-operated tissue presses for the preparation of highly dispersed tissue as does EDCO Scientific (Chapel Hill, NC). There are several models of these mechanical presses, all capable of generating considerable pushing force.  Sample sizes from 0.1 grams up to 50 grams of soft tissue are pushed through sieve plates having 0.5 to 3 mm holes, much like the action of a common kitchen garlic press. Compared to other mechanical cell dispersion methods, they excel in producing a significant proportion of viable single tissue cells (10-40%).  Hard or fibrous tissue like tendons, skin, leaves, and seeds cannot pass through these presses. The devices cost from $35 to $400. Fred S. Carver (Wabash, IN) has a compact hydraulic laboratory tissue press for the extraction of intracellular liquids and oils for about $1600.  The insoluble plant fibers and cell debris is discarded.  On a much smaller scale, BioSpec Products makes a simple, hand-operated plant leaf press. Combined with a special Plant Leaf Collection Card containing cellulose filter paper, it is primarily used for the isolation and preservation of nucleic acids, microbes, viruses, and soluble protein pressed from intact leaves while in the field, distant from an analytical facility.

Another group of devices designed to disperse solid tissue differs from the above presses or grinders.  Bioreba (Chapel Hill, NC) makes a hand-held crusher designed for whole, fresh plant leaves.  It consists of a circular array of steel balls, inside a tough Mylar plastic bag, that manually crushes a few leaves in a minimal amount of extraction media. The grinder and bags cost about $200.  Several overseas companies make Paddle- or Bag-Blenders [Seward Laboratories (West Sussex, UK), IUL Instruments (Barcelona, Spain), Synbiosis (Cambridge, UK), Interscience Laboratories (Saint Nom la Breteche, France), bioMerleux Industry (Marcy l'Etroile, France), Corning Gosselin (Hazebrouck Cedex, France)].  These motor-driven machines reduce processed food, soil samples, feces, and intact, soft plant and animal tissue to a suspension suitable for microbial testing.  The solid sample is placed in a nylon or polyethylene bag and a minimal amount of extraction media is added. The top of the plastic bag is sealed by a clamp built into the door of the paddle blender and the bag contents are repetitively smashed with two flat paddles rapidly alternating back and forth against the bag and door surface at speeds of 5-10 strokes per second.  In less than a minute, the bag's contents are dispersed and homogenized.  Current Paddle Blenders are designed to work with multi-gram quantities of bio-material and are priced from $3000 to $6000.

Ultrasonic Disintegrators

These devices generate intense sonic pressure waves in liquid media and are widely used to disrupt cells. Under the right conditions, the high-pressure waves form transient microbubbles near the face of the ultrasonic probe that grow and collapse violently. Called cavitation, the implosion generates a shock wave with enough energy to tear cell membranes and can even break covalent bonds.

Modern ultrasonic processors use piezoelectric generators made of lead zirconate titanate crystals. The vibrations are transmitted down a titanium metal horn or probe that is tuned to make the processor unit resonate at 15-25 kHz. The rated power output of ultrasonic processors varies from 10 to 375 Watts. What really counts is the power density at the probe tip. As expected,  higher output power is required to sustain good performance in large-sized probes. For cell disruption, probe densities should be at least 100 W/cm2, and the larger the better for tip vibration amplitude (typical range: 30-250 microns). Some manufacturers of ultrasonic disintegrators are Artek Systems (Farmington, NY), Branson Sonic Power Company (Danbury, CT), Hielscher Technology (Teltow, Germany), RIA Research Corp. (Hauppauge, NY), Sonic Systems (Newton, PA), Ultrasonic Power Corporation (Freeport, IL) and VirTis Company (Gardiner, NY).

Ultrasonic disintegrators generate considerable heat during processing. For this reason, the sample should be kept ice cold. For microorganisms, the addition of 0.1 - 0.5 mm diameter glass beads in a ratio of one volume beads to two volumes liquid is recommended, although this modification eventually erodes the sonicator tip. Tough tissues like skin or tendon should be pre-chopped or macerated first in a tissue press, grinder, or pulverized in liquid nitrogen (see details above). Use small vessels during ultrasonic treatment and place the probe tip deep enough into the sample suspension to avoid foaming. Finally, one should be aware that free radicals can be generated during sonication and that these radicals can react with most biomolecules. Damaging oxidative free radicals can be minimized by flushing the reaction solution with nitrogen gas and/or including radial scavengers like cysteine, dithiothreitol, or other -SH compounds in the media.

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A comprehensive discussion of cell disruption equipment and methods is covered by the author in Chapter 3 of Purification and Analysis of Recombinant Proteins, Seetharam and Sharma, editors, published by Marcel Dekker, Inc., 1991.  Additional cell disruption methods discussed include High-Pressure Homogenizers, Autolysis, Enzymatic lysis, Dehydration, Chemical lysis, Solvent lysis and Programmed self-destruction.  [The relevant Chapter is available on the internet.  It can be read but, unfortunately, not copied].