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Pipetting is surprisingly hard work – a fact one painfully learns when large sample series need to be processed and the hands, wrists, elbows, upper/lower arm or shoulders ache in the evening. These symptoms often develop insidiouslyover a period of months or years. Initial feelings of numbness or tingling sensations are later accompanied by pain, swelling and spasms. The situation is worsened by the fact that physiological accommodation to heavy workloads leads to increased muscle tension, which in turn places a strain on the parts of the body involved.
As far as pipetting is concerned, however, protecting oneself from the infamous RSI/RMI syndrome and staying fit for everyday lab work is not simply a matter of switching to lighter pipettes. It is important to understand that pipetting constitutes a labourintensive, repetitive activity and can thus be associated with occupational health risks.
One should also be aware that pipetting is strongly dependent on the technology deployed, especially at low volumes. Every variation made when executing iterative pipetting cycles can impact both pipetting accuracy and precision. Pain, for example, can compel a research scientist to vary the pipetting rhythm or alter the pressure on the plunger. Pain may even cause a situation where the liquid is not fully aspirated or dispensed. Accordingly, pipetting ergonomicsnot only affects worker wellbeingbut also impacts the accuracy and precision – and thus the reliability – of the experiment itself. To achieve ergonomically optimum pipetting, three aspects are ultimatelycrucial:
As part of its Good Pipetting Practice (GPPTM) programme, METTLER TOLEDO offers a module dedicated to learning all about pipetting techniques and ergonomics. This ergonomics training aims to help lab workers identify risk factors with an ergonomic element and provides a list of techniques designed to improve day-to-day pipetting in the lab. At the end of the day, good pipetting pays its way – for both lab worker health and research results.
What forces are involved in pipetting?
In pipetting work steps involving the application of considerable force, including the setting of the volume, the actuation of the plunger as well as the attachment and discarding of the tips, may require several kilograms of force. In all of these steps, the thumb does most of the work. If the thumb becomes overworked, then any other part of the body connected with the thumb via tendons, ligaments and muscles may be affected in tandem. These muscles , tendons and ligaments then suffer microscopic injuries that cannot heal properly since they are under chronic strain. Accordingly, relieving the burden on the thumb is a key step towards optimum pipetting ergonomics. To avoid overworking the thumb, the dynamic force applied should not exceed 30 % of the individual’s maximum physical strength: on average, this is about 3 kg of thumb pressure for a man and about 2.1 kg for a woman.
In the first step in the pipetting cycle – sample aspiration – the use of conventional air displacement pipettes results in combined dynamic and static forces of up to 3 kg. The application of even more force – about 4 kg – is required in the second phase, so as to dispense the sample and (in particular) for pipette tip blow-out. Although this value already exceeds the safety threshold, the last step really adds insult to injury: to attach a pipette tip to a conventional coni cal shaft, around 5.5 kg of force is required. The ejection force for a tip is also pro portional to the attachment force and is around 4 kg. The methods used to attach tips show considerable indivi dual variation, how ever: realworld observations have regularly recorded ejection forces of up to 10 kg, especially if the tip was ‘jammed’ onto the pipette or applied using the fingers. In addition, the ejection force is multi plied if multichannel pipettes with 8 or 12 tips are used.
Ergonomic pipetting solutions
For many years now, the developers of our Rainin pipettes have thus focused particularly on pipetting forces, to achieve contin uous improvements in pipette design.
Attaching the tips
The Rainin LiteTouch™ System (LTS) constitutes a key element in improving pipette ergonomics. The use of a cylindrical design for shaft and pipette tip (instead of the conventional conical form) substantially reduces the contact surface between shaft and pipette without impairing fluid tightness characteristics. LTS tips also feature a positive stop to ensure that the tip is always seated perfectly on the shaft and cannot be fitted too tightly. Studies comparing conventional tips with the LTS design have shown that merely 1 kg of force is required to fit LTS tips, whereas several kilograms of force are required to attach conical tips. This especially simplifies the handling of multichannel pipettes, which involve uniform, high-density tip fitting work.
Ejecting the tips
Ejection forces are critical, since they require the greatest application of force. With conical systems, ejection forces are proportional to fitting forces and therefore greatly exceed the forces recommended by ergonomics. By limiting the fitting force and ensuring that seal surfaces are clearly defined, the LTS system has made a decisive improvement here. Regardless of the fitting force, 200 μL LTS tips (e.g.) need an ejection force of just 0.6 kg – compared to almost 4 kg for conventional tips.
Another design feature also simplifies the ejection procedure: a silicone shock absorber ensures that the ejection mechanism cannot be suddenly depressed to its lowest position without any appreciable resistance, as the tip starts to detach itself from the shaft. As a result, the thumb’s powerful movementdoes not end abruptly, protecting both muscles and tendons. The relationship between tip loading and ejection forces – a traditional conical tip compared with a Rainin LTS tip.
Aspirating and dispensing the liquid
Pipettes work with two springs: the first is used to aspirate and dispense the sample, the second to blow out the pipette tip. The latter offers considerably more resistance, to ensure the operator can reliably feel and maintain the first stop point between the aspiration / despensing and blow-out position. While reducing this resistance could guard against RSI, it would unfortunately make the first stop less easy for the operator to identify, leading to a significant worsening of pipetting precision and accuracy. The solution: a magnetic assist feature helps the thumb reliably identify the first stop – i.e. the null position for aspiration – while permitting a reduction of the tensile forces involved in aspiration/dispensing and the blow-out operation, and all without impairing accuracy or reproducibility. These design features, coupled with a low weight, a special finger hook and an ergonomic handle, mean all Rainin pipettes in the Pipet-Lite XLS series feature optimised ergonomics.
The electronic single- and multichannel pipettes from the E4 XLS series offer maximum workflow simplification and protection against RMI disorders: the only pipetting step requiring force that remains is tip ejection – itself simplified by LTS. These pipettes also offer flexible programming options for streamlining especially repetitive pipetting tasks.
Repetitive pipetting of large-scale sample series
Due to their large number of repetitive work steps, large-scale sample series present a particular challenge in terms of ergonomics.Choosing the right set of instruments can significantly reduce the number of work steps, however, while also increasing pipetting efficiency. This ensures even the largest sample series stays “pain-free”:
Workplace and work posture
As with almost all programmes designed to improve ergonomics, posture forms a central element. The key to good posture is maintaining the natural S-curvature of the spine. Posture should be straight and erect, the shoulders should be lowered and in line with the ears.
When standing, the hips should be tilted slightly forwards, so as to form a continuous line with the ankles. Observing the correct height for working surfaces and seating prevents an unnatural, cramped posture and pressure points. Keep your elbows held as close as possible to the upper body and place objects that you require for your work within easy reach. The forearm and hand should form a continuous line and the wrist should not stay twisted or bent for long periods. To prevent physical fatigue, we also recommend alternating the individual’s working schedule and movement patterns experienced in the workplace. After 20 – 30 minutes, regular breaks should be taken so as to relax, to rejuvenate the overworked brain and to stretch the shoulders, arms and hands. Stretching and strengthening exercises should be a permanent fixture in the daily timetable. It also helps to integrate different types of tasks into work schedules.