Centrifuge vs Laminar Wash HT2000 Time-Motion Study

This time-motion study aims to assess and compare features of two different cell sample preparation methods, namely the conventional centrifugation method and the centrifuge-less Laminar Wash™ method. Traits such as the hands-on and walk-away times, as well as the complexity of movements required to interact with the instruments were evaluated.

Materials and Methods

Equivalent single wash steps are performed on either of the two types of cell sample preparation methods:

• Centrifuge—three rounds using 96-well microtiter plates
• Laminar Wash HT2000 system—nine cycles using Laminar Wash 96-well plates (LW96)

Run-time definitions (study begins at ubiquitous post-incubation with antibody stain step):

• Centrifuge—from the addition of buffer to supernatant removal after three rounds of washing
• HT2000—from loading the LW96 plate onto the instrument to plate retrieval after nine wash cycles
• Total hands-on time—operator is actively handling samples and/or interacting with the instrument
• Total walk-away time—operator is not actively engaged (i.e., automation time)

A complexity score (1—5 scale, 1=uncomplicated, 5=complicated) was used to evaluate steps involved in using the instruments. Factors involved in score assignments included risks of mistakes and contamination, instrument user friendliness, and results integrity.

Lastly, the time required for the necessary maintenance, instrument setup, and shutdown were recorded for both sample preparation methods, where applicable.

Results and Discussion

Table 1: Run-time measurements

Table 1 indicates that total run time is notably longer for the centrifuge (~25 min) compared to the HT2000 (~5 min). Operator hands-on time is also more involved on the centrifuge compared to the Laminar Wash method, both in terms of absolute time (~10 min vs <1 min), as well as a percentage of the total run time (40.2% vs 10.5%). The Laminar Wash method substantially increases the fraction of walk-away time, representing ~90% of the total run time vs ~60% for the conventional centrifuge. Taken together, these results strongly suggest that using the HT2000 largely transforms cell sample prep into an automated process requiring little activity on behalf of the operator. 

Table 2: Instrument complexity scoring¹

¹Complexity scale: 1 = uncomplicated task, 2 = slightly less complicated, 3 = neutral, 4 = slightly more complicated, 5 = complicated.

Table 2 indicates that the centrifuge is slightly more complicated to use than the HT2000, with instrument complexity scores of 2.5 and 2, respectively. A notable difference amongst the two instruments is the washing step (i.e., the most hands-on step), which is a high score of 5 for the centrifuge, versus a complexity score of 2 the HT2000.  Post-centrifugation decanting or flicking to remove supernatant are hands-on steps prone to inter-operator variability and contamination risk. This step is highly complex and dependent on operator experience and technique, which varies across individuals. Therefore, manual handling involved in the cell washing steps can lead to inconsistencies in data.

On the other hand, the HT2000 is less complicated due to reduced manual handling. Fluidics on the LW HT dispense and aspirate a continuous buffer exchange, thus automating the decanting or flicking steps required for centrifugation. Improved data quality with lower coefficients of variation (CVs) may be expected.

Table 3: Operator and instrument interactions

²Plate balancing, per round of centrifugation

The Laminar Wash method requires routine maintenance, system set up, and shut down. The HT2000 is maintained by a daily calibration taking 1:57. Before and after using the HT2000, priming and reverse-priming steps are required, respectively, each taking 5:22. The timings for these steps are not included in the total run time, as they are only to be performed at the start and end of the day, and largely may be considered walk-away time, similar to the cell washing executions. Included among the instrument setup for the centrifuge is a plate balancing step required prior to each run, which took us 30 seconds. These steps may take longer or shorter, depending on the balancing needed, and can add up over the course of a day.

Limitation

This is a crude time-motion study performed without trained time-motion analysts. The timings taken are based on a single wash protocol by a single operator, and hence are limited in representation.

Conclusion

Preparing cell suspensions for downstream applications with the automated Laminar Wash method affords notable time savings with fewer manual steps, compared to traditional centrifugation, leading to more consistent cell sample preparation across different operators, locations, and times. However, Laminar Wash instruments require daily maintenance and set up interactions unique to the method. Researchers should consider all factors described herein when aligning goals and needs of the laboratory to decide on the best-suited method for cell sample preparation.