Improving the Laboratory Work Experience When Homogenizing

It is no secret to researchers who homogenize tissue samples as part of their regular laboratory routine that the job can be messy and loud, and produce results that are sometimes inconsistent. To improve the laboratory work experience, Omni International (Marietta, GA) took a fresh look at the factors that matter most to those who use homogenizers. These factors include sample processing results, repeatability, ease of cleaning, cross-contamination concerns, product noise, time, ease of use, product weight (for handheld applications), reliability, the need for sharing equipment in the laboratory, and environmental impact.

This analysis resulted in the creation of Whisper Drive Technology™, which is built into the Omni THQ, UltraShear, and Omni Prep product lines. The Omni THQ is a lightweight handheld tissue homogenizer. Omni UltraShear homogenizers use magnetic drive technology to process a variety of sample sizes. The Omni Prep is a multisample homogenizer that can homogenize up to six samples at a time. The products make traditional rotor-stator homogenization more productive and more comfortable for the user.

Tissue homogenization is most commonly and easily achieved using mechanical shear homogenizers, also known as rotor-stator homogenizers. They generally consist of a motor and a processing probe or generator probe. Rotor-stator generator probes are usually composed of a tube and collar assembly, shaft, knife, and an upper and lower bearing. The rotating knife comprises the rotor portion of the rotor-stator generator probe. The tube and collar assembly attaches to the motor housing, but does not spin, and is therefore called the stator. As the knife spins within the stator, it creates a pumping action that pulls liquid into the open end of the generator probe. The probe then forces the liquid out through windows in the stator portion of the generator probe. The interaction of the knife with these windows sets up a shearing action, much like a pair of scissors. It thereby works to reduce the particle size of sample being forced through the windows.

The vast majority of today’s rotor-stator homogenizers are powered by motors that require carbon brushes to make them operate. This technology has been around for many years, and while it is quite suitable for occasional use, it has a number of drawbacks when compared to Whisper Drive Technology brushless motors.

Figure 1 - Omni THQ digital tissue homogenizer.

Brushless motors are significantly more efficient than their brush motor counterparts. For instance, the Omni THQ (see Figure 1) with brushless Whisper Drive Technology uses 80% less electricity to drive a 7-mm generator probe than does the traditional brush motor Omni TH model. The motor itself is significantly smaller and lighter, allowing the THQ to weigh only 10.8 oz (306 g), or 66% of the weight of the standard Omni TH. These motors also run much quieter, allowing the THQ to be 80% quieter than the TH when both are running at 35,000 rpm. This sound level is roughly equivalent to the sound of a moderate rainfall. Furthermore, since no brushes are used, no carbon dust is created. Like all of the Whisper Drive products, the motor is maintenance-free, which makes it more convenient for the user and results in a longer product warranty.

Another benefit of Whisper Drive Technology is that the motor consistently runs at its set speed. A brush motor’s speed will fluctuate as sample viscosity changes, or as sample particle size varies, affecting repeatability and accuracy. However, the Whisper Drive motors are able to hold their speeds throughout the entire operating cycle. Accuracy and repeatability are ensured when the motors are coupled with a digital speed readout, as with the THQ, UltraShear M, and Omni Prep.

Another development that complements two of the Whisper Drive homogenizers are the Omni Tip™ plastic generator probes (patent no. 6,398,402 and 6,863,431). Prior to Omni Tips, rotor-stator probes were almost exclusively constructed from stainless steel. These stainless steel probes can cost from $700 to well over $1000. They can consist of six or more parts, including two wearable bearings that require regular maintenance. Disassembly for cleaning and subsequent reassembly generally require one or more tools, and usually take much longer than it actually takes to homogenize the sample. This cleaning step often has to be applied between each processed sample. Omni Tips, on the other hand, consist of only two pieces, have no bearings, and disassemble and reassemble in seconds. There are no hidden areas in which leftover sample can hide. This not only facilitates cleaning, but also reduces the potential for sample loss during processing. To ensure that the entire sample is fully recovered, the stator portion of each probe is clear and the sample always remains visible. Patented shaft geometry further ensures that sample is not lost in the shaft while processing. While Omni Tips reduce cleaning time, and are in fact autoclavable, there are some applications that simply cannot tolerate any cross-contamination. For these applications, the probes are inexpensive enough to be disposed of after use.

In many research laboratories, equipment is shared among a number of co-workers. As previously mentioned, stainless steel probes are both very expensive and very fragile. The fact that they are opaque makes it impossible to determine if they are clean without actually disassembling and reassembling the probe. Lack of cleaning after use can actually lead to product failure due to corrosion, and a dropped probe can bend the stator, making it nonfunctional. These problems are easily resolved when using Omni Tip plastic probes. Since they cost less than 1% of stainless steel probes, multiple users can own their own probes, which can be autoclaved or chemically cleaned for repeated use. In addition, if an Omni Tip is dropped from a tabletop, it still works like new.

For laboratories that process five, ten, or more samples per day, the tedium of cleaning between sample processing can be completely eliminated. The low cost of Omni Tips allows multiple probes to be purchased. Rather than cleaning stainless steel probes after each homogenizing step, all samples can be processed, and the probes can be collected for batch cleaning at the end of the work period.

Figure 2 - Omni Prep multisample homogenizer.

The Omni Prep multisample homogenizer (see Figure 2) takes full advantage of the benefits of Omni Tips. It uses Whisper Drive Technology to process up to six samples simultaneously. Sample tubes and Omni Tips are loaded onto a specially designed processing rack, similar in concept to a centrifuge rotor, and then processed all at once, again much like in a centrifuge. This saves time and significantly reduces energy costs, since less than 10% of the power required to process six samples individually with a traditional brush motor homogenizer is required to process six samples simultaneously with the Omni Prep. The homogenizer is also suitable for sharing. As with a multisample centrifuge, an Omni Prep in the laboratory can elevate productivity and improve work flow.

Figure 3 - Omni UltraShear M magnetic homogenizer.

While the THQ and Omni Prep are designed to handle sample volume of 1.5 mL to 50 mL, the UltraShear M (see Figure 3) was designed to quietly process up to 2 L of sample. Its patented drive technology is not only brushless, but also magnetic. The rotating shaft of the generator probe actually becomes part of the motor itself. This magnetic coupling eliminates all coupling noise or wear, but most importantly makes the generator probe a completely sealed assembly, ensuring that there is no possible path for escape of sample or aerosol for critical sealed sample processing. Also, like other Whisper Drive products, the UltraShear’s low power usage makes it more ecofriendly than traditional homogenizers, while its quiet motor makes it more researcher friendly.

Mr. Jahn is President, Omni International, Inc., 1000 Williams Dr., Ste. 1024, Marietta, GA 30066, U.S.A.; tel.: 800-776-4431; fax: 770-421-0206; e-mail: omni@omni-inc.com.

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