This segment will detail the prototyping of a microtube capper derived from the aforementioned design, alongside evaluations of mechanical functionality and usability, ensuring compliance with the specified requirements and conditions.
Prototype model
Figure 6 presents a prototype of the proposed manually operated microtube automatic capper/decapper system, conforming to the mechanical design outlined earlier. The front panel hosts the mini box PC switch, with the power supply connector and switch positioned at the rear. The stopper for a 2 mL microtube is placed on the back side. The prototype’s total weight is approximately 1,330 g, underscoring its compact and lightweight nature for facile transportation within a biological safety cabinet. It facilitates direct visual inspection of the microtube’s interior, whether the cap is open or closed. The exposed metal parts are primarily constructed from anodized aluminum alloy or stainless steel, and the covers are 3D-printed parts (printed by Stratasys F170, 333-60300 ABS-M30 (Ivory)). Particular damage was not observed after wiping and spraying with disinfectant alcohol.
Figure 6 Overview of a prototype of the proposed manually operated microtube automatic capper/decapper system
Evaluation of opening and closing cap function
The function of the opening and closing cap of the microtube was evaluated. The microtubes used this time were Thermo Fisher #3448 (1.5 ml) and Greiner 623201 (2 ml). We verified that when the microtube capper/decapper was powered by a 15 to 24 V DC supply, connected through an AC–DC converter from a 100 V AC source, and linked to a mini box PC, the device’s operating program for manual capping and decapping automatically initiated. It executed a return-to-origin operation and then entered a standby state. It took about 30 s from powering on the mini box PC to the standby state. Furthermore, we confirmed that a series of operations, such as Procedures A–C, can be performed by pressing the open and close buttons as appropriate after setting the microtube in the standby state. Figure 7 shows a series of opening and closing operations using the manual microtube capper (Procedure A). We also confirmed smooth opening and closing operations. The time from pressing the button to completing the opening and closing operations were 5.4 and 4.9 s each. The operation could be stopped immediately by pressing the stop button. Furthermore, it was driven in the same way by a mobile battery designed for notebook PCs (SANWA SUPPLY INC., 700-BTL033BK, DC12 V, 16 V, 19 V (3.6A) 17400mAh, 62.64Wh, and 700-BTL049 DC12 V (3.6A) 17400mAh, 62.64Wh).
Figure 7 Opening and closing cap motion (Procedure A)
Evaluation of the operation time of pipetting tasks
The working times were compared between the full manual operation and the manual operation using the microtube capper/decapper. The comparison tasks were determined with reference to the procedures performed in the sample pretreatment process of the PCR-based diagnosis. Figure 8 shows the pipetting task sequences of full manual operation and manual operation using the microtube capper/decapper. The evaluation pipetting task involves dispensing 150 μL from a cryopreservation tube (SARSTEDT 72. 694. 100. 02) containing 1,000 μL of tap water to a microtube: Thermo Fisher #3448 (1.5 ml) containing 600 μL of tap water. One lot is 12 pieces. Figure 9 shows the arrangement of cryopreservation tubes and microtubes and opening/closing cap and aspiration/dispensing position. The tubes before aspiration/dispensing are arranged on the right side, and the tubes after aspiration/dispensing are arranged on the left side.
The experimental setup is shown in Figure 10. Before starting the experiment, a subject (right-handed, nonprofessional), one of the authors, was required to familiarize himself with the pipetting task. The subject ran four trials (12 pieces × 4 lots) for each condition, each of which was video-recorded. Each operation time shown in Fig. 8 (handling and opening cap time, pipetting time and closing cap and the handling time) was retrieved based on the video.
Figure 8 Pipetting task sequences of full manual operation and manual operation using the microtube capper/decapper
Figure 9 Arrangement of cryopreservation tubes and microtubes and opening/closing cap and aspiration/dispensing position
Figure 10 Experimental setup for evaluation of operating time of pipetting tasks
Figure 11 shows the experimental results of handling and opening cap time, pipetting time and closing cap and handling time by box plots, and the average operation time of one piece by bar graph. Due to some operational sequence errors in the first trial, the box plot data excluded the operation times affected by these errors. However, it was included in the average working time per piece. The first trial had a large variation, but the second to fourth trials had a smaller variation by learning curve. The time required to open and close the cap, including tube handling, was approximately 1–2 s longer when using the microtube capper/decapper relative to the full manual operation. No significant difference existed in dispensing time. The time taken to open and close the cap using the microtube capper was about 5 s each, but if parallel operations are possible during the opening and closing operations, the impact on the overall operation time is small, so the opening and closing time of the cap using the microtube capper is acceptable. Furthermore, the capper can markedly reduce the burden on the operator when opening and closing the microtube cap.
Figure 11 Experimental results of handling and opening cap time, pipetting time, closing cap and handling time and average operation time of one piece.
Evaluation of the cooling function
The cooling function using the cooling boxes was evaluated. The cooling box was prototyped by a 3D printer (printed by Formlabs Form 3, Resin Rigid 4000 V1). The capacities of the small and large cooling boxes were 32.3 mL and 55.5 mL, respectively. Figure 12 shows the experimental conditions for the cooling function. The experiments were conducted under four conditions: (1) No-cooling box sample, (2) Small cooling box sample (Tap water ice), (3) Small cooling box sample (frozen gel), and (4) Large cooling box sample (Tap water ice). Furthermore, under all experimental conditions, room temperature and left indoor samples were simultaneously measured. The temperature was measured by K-Thermocouple (HIOKI 9810) in the microtube bottom and middle position and recorded by a data logger (HIOKI LR8431). An hour of data was acquired. Tap water ice or frozen gel was used as the cooling material. After putting tap water or gel (Contents of Snow Pack R-20 by MIE Chemical Industry) in the cooling box and cooling it in a freezer (−17℃) to freeze, experiments of the cooling functions were conducted. A 1,000 μL of tap water in the microtube: Thermo Fisher #3448 (1.5 ml) was cooled to approximately 0°C–4°C with crushed ice. Figure 13 shows the experimental setup for the cooling functions.
Figure 14 shows the experimental results of the cooling functions as the average value of time series data acquired three times under the same conditions. The room temperatures were 22°C −23°C in all cases, and the experiments were conducted in almost the same temperature environment. In the case of the no-cooling function, the temperature rises after the measurement starts, rising to about 35℃ in 20–30 min, and then remaining almost constant. The heat sources are thought to be the mini box PC and motor position control system (Maxon EPOS2 24/2). In contrast, using the cooling box caused the temperature of the tap water in the microtube to be maintained at about 5℃ or less for about 20–40 min. Although no noticeable difference was observed between the tap water ice and the frozen gel, the cooling function was maintained for a long time, depending on the difference in capacity between large and small boxes. While precise temperature control over long periods proved challenging with a cooling box–based cooling function, it effectively sustained the coolness of the microtube contents for short durations. The cooling performance is expected to improve through methods such as inserting a heat-insulating material between heat sources (the mini box PC and the Maxon EPOS2 24/2) and placing cooling material under the microtube.
Figure 12 Experimental conditions for cooling function
Figure 13 Experimental setup for cooling function
Figure 14 Experimental results of the cooling functions.
Discussion on required specifications and preconditions
The considerations for the abovementioned requirement specifications and preconditions are summarized below.
(1) Operators can manually insert and remove microtubes from the capper/decapper.
(2) The device accommodates the opening and closing of caps on both 1.5 mL and 2 mL microtubes.
(3) Using procedures A, B, and C, microtubes can be inserted and removed with their caps in both the open and closed states.
(4) The size, weight, and power source of the device are compatible for use within a biological safety cabinet, and the device is easy to carry (easy to put in and take out of the cabinet)
(5) The operating procedures are straightforward and simple, with only pushing buttons.
(6) This device allows visual observation of the microtube’s interior when the cap is in open and closed positions.
(7) The device is operable with a mobile battery.
(8) It is cleanable with alcohol or similar disinfectants.
(9) The device has a cooling function for specimens and reagents within the microtube.
(10) Quantitative evaluations of the risk of contamination from specimen scattering, virus exposure, and aerosol generation during cap manipulation are currently being conducted and will be reported separately.