Designed to Save Time, Improve Yield, and Eliminate Cross-Contamination
by Karl Jahn
Rotor–stator technology is a highly efficient method utilized by many laboratories to homogenize, disrupt, emulsify, and blend a broad range of samples, including tissue samples. As a result, rotor–stator homogenizers are used whenever possible for most laboratory homogenizing tasks. Sample processing times are generally very short, homogenization is fast and efficient, and sample temperature rise is minimized or eliminated. First invented by Prof. Peter Willems in 1957, rotor–stator homogenizing remained relatively unchanged for nearly 35 years.
Plastic Homogenizing Probes
In 1992, Omni International, Inc. (Marietta, GA) invented the first plastic rotor– stator homogenizing probes, known as the Omni Tips™ (Figure 1). This marked the first significant improvement to this venerable technology and completely revolutionized rotor–stator homogenization (patent numbers 6,398,402 B1 and 6,863,431). Stainless steel homogenizing probes, still used in many laboratories, usually require a tedious cleaning step between samples. This may involve complete probe disassembly, especially if autoclaving is necessary. After cleaning, the probes must be carefully dried and reassembled. Even when meticulously cleaned, sample-to-sample contamination cannot be totally eliminated, and the complex geometry of stainless steel probes leaves many places for contaminants to hide. Plastic Omni Tip probes, on the other hand, can be disposed of after use, thereby eliminating the possibility of cross- contamination. Further, the use of modern engineering plastics enables the probes to be cleaned and reused. When chemically cleaned, Omni Tips can be reused dozens of times, and can be autoclaved up to seven times. The probes require no bearings, and simple two-piece construction allows for easy disassembly and cleaning. This simple construction also reduces the potential for cross-contamination by a factor of four when compared to stainless steel probes.
With a trend toward smaller and more valuable samples, sample loss can be a real source of concern for some laboratories. The design of Omni Tip plastic probes offers the additional benefit of a clear outer tube, thereby keeping the entire sample visible during the homogenization process and ensuring that sample is not lost within the probe. A second trend, particularly in laboratories with scarce financial resources, is equipment sharing. With stainless steel probes researchers are never quite sure what was most recently processed, or how clean the probe is. The low acquisition cost of Omni Tip plastic probes means that laboratory homogenizer motors can now be easily shared, while each researcher can use his or her own Omni Tip probes. Further, stainless steel probes can easily cost more than a thousand dollars, and can be damaged if not effectively maintained and cleaned. A mere six-inch drop can permanently damage a stainless steel probe. The Omni Tips can readily survive a drop in excess of six feet and remain fully functional. Many laboratories also value consistent sample-to-sample processing. Stainless steel probes wear with use, particularly in the lower bearing area. The PTFE lower bearing is responsible for centering the probe knife during processing.
As the soft PTFE material wears, the spacing between the rotating knife and the stator begins to change, leading to variable processing results. Omni Tips are molded to rigid standards with virtually no dimensional probe-to-probe variability. As a result, they tend to yield highly repeatable processing results.
The plastic probes are available in a soft tissue version for sensitive cell disruption and in a hard tissue version, tough enough to process frozen tissue as well as most other applications that previously required stainless steel probes. Omni Tips spin at 35,000 rpm, which is the same speed as their stainless steel counterparts. For aerosol containment, a broad range of sealed tube solutions is available to work with the probes.
Omni Tips are very economical to own and use. Their acquisition cost is about 1% of stainless steel probes, which can be significantly reduced when cleaned and reused. This low cost makes batch processing a highly efficient method for homogenization. Samples can be quickly homogenized, and the probes subsequently disposed of, or batch cleaned for reuse. Elimination of the cleaning step between samples also creates an ideal platform for automation, as with the Omni Prep™ homogenizing workstation (Omni International), which is capable of processing six samples simultaneously, with a capacity of up to 250 samples per hour.
The Omni Prep programmable homogenizing system (Figure 3) is designed to eliminate homogenizing processing bottlenecks, while also addressing the shortcomings of existing approaches to rotor–stator homogenizing methods. The system is small enough to easily fit into a fumehood, and also preserves precious laboratory bench space. It is designed around a rack system that allows six samples to be processed simultaneously. By utilizing a second processing rack, six more samples can be prepared while the first rack is processing, permitting a single operator to process up to 250 samples per hour. Operator fatigue and repetitive motion injuries that can result from homogenizing a large number of samples per day by hand are also eliminated, while a single technician can now perform the work of six. The racks are designed to accommodate a broad range of tube sizes from 1.5-mL microcentrifuge tubes up to 50-mL conical bottom tubes, and are available in fixed or movable configurations. The fixed rack is well suited for processing samples that require sealed tubes, while the movable version is intended for processing larger sample volumes that require probe mobility within the sample. The recommended processing volume for the Omni Prep is .25 mL up to 30 mL. A cooling tray is also offered to keep sensitive or frozen samples cold during the homogenization step. A clear plastic door protects the operator from accidental splashing, and a fan-driven positive airflow pattern move air away from the front of the instrument for exhaustion into a fumehood or through a HEPA filter.
1. Mace, B.E.; Sullivan, P.M. The Use of Steel Homogenizer Probe Results in Sample Carryover Contamination. Duke University
Medical Center, Durham, NC, 1997.