Motor Selection for Bench-top Point-of-Care Testing Devices

Rapid and dependable sample testing results play a pivotal role in ensuring accurate medical care, as the ability to swiftly administer appropriate treatment can be the critical factor between life and death. Various sample testing procedures like blood and urine tests have historically required specialized labs outside of healthcare settings, relied on intricate equipment, and demanded highly trained technicians. This conventional testing approach presented hurdles in delivering prompt and dependable outcomes, encompassing challenges in sample transportation, the expertise required by technicians, and potential congestion at testing facilities. The COVID crisis underscored this issue, notably with PCR tests, where results could take several days to be received.

INTRODUCTION TO POINT-OF-CARE TESTING (POCT) DEVICES

The challenges described above can be addressed through Point-of-Care Testing (POCt) devices, which bring testing capabilities directly to patients or doctors. There are two primary types of POCt devices: handheld and bench-top devices. Handheld devices employ either manual actuation or simple single actuation and excel at performing simple tasks, but lack the adaptability required for complex tests that involve multiple steps. Bench-top devices, however, are single devices designed specifically to conduct complex tests rapidly; they are quite user-friendly, conveniently sized, and can be used directly in a doctor's office. This article will focus on bench-top POCt devices.

MOTOR TECHNOLOGY OPTIONS FOR BENCH-TOP POCT DEVICES

Selecting an appropriate miniature motor is crucial to a successful bench-top POCt device. Motors within this device are tasked with multiple functions, each with its distinct set of needs and specifications. While specific requirements differ for each task, certain principles apply across all motion systems. Reliability is critical to ensuring a consistent and maintenance-free operation throughout the device's lifespan, guaranteeing accurate test results. Given the potential presence of numerous motors—up to 20 within a single device—factors like size, high power density, and costeffectiveness are pivotal in creating a competitive device. Beyond these general criteria, diverse tasks within the device demand unique features such as high efficiency or robust holding capabilities.

Stepper Motors

Stepper motors provide an interesting motion solution for bench-top POCt devices, as most of the tasks powered by miniature motors require high torque and important (unenergized) holding torque rather than high speeds. A stepper’s important holding torque – while seen as a disadvantage in some applications – is a benefit for this application, as it drastically reduces battery usage for long term position holding. This cost-effective motor technology allows bench-top POCt devices, which may require a significant number of motors for various tasks, to maintain a competitive price point.

Brush DC Motors

The higher performance capabilities of brush DC motors makes this motor technology an ideal alternative motion solution for bench-top POCt devices. The higher power density of DC motors allows significant size reduction, facilitating the integration of a high number of motors in one bench-top POCt device. Higher efficiency reduces the battery life and consumption for applications with a high duty cycle. Thirdly is this technology’s simple velocity control and lack of complex electronics requirement, making these motors well-suited for POCt velocity applications while maintaining a competitive price position for the device.

Brushless DC Motors

POCt design engineers tend to employ stepper or brush DC motors in their device development, avoiding brushless DC technology due to pricing and complexity of control. However, with the latest developments in BLDC technology, this motor type is quickly evolving into a viable solution for new bench-top POCt devices. Brushless DC motors feature higher efficiency, higher power density, and longer lifetime than either brush DC or stepper motors, contributing to size reduction, improved battery usage, and longer device lifetime. Using BLDC motors has historically been cost-prohibitive due to the motor price and the need for complex controllers. However, new developments in production, control, and technology are contributing to a significant price reduction in brushless motors, leading to a rise in interest in this technology for POCt applications.

MOTOR APPLICATIONS IN BENCH-TOP POCT DEVICES

Various bench-top POCt applications employ miniature motors. Specific examples include:

•	Blister Bursting. To dispense chemicals into the testing device, POCt devices utilize chemical blisters that need to be burst. Linear stepper motors are an ideal technology for this application due to their precision and control in actuating the bursting mechanism. In such devices, this motor technology operates to precisely control the movement of a bursting element which punctures or opens the blister containing the reagents. Portescap’s 26DBM DLA is an ideal motion technology for this process.
•	Valve Actuation. Point-of-care testing devices are frequently built around the use of disposable cartridges with a high amount of microchannels. To control fluid distribution within the microchannels, a high number of valves are required. The ideal motor to actuate these valves is a small linear stepper motor, such as Portescap’s 20DAM digital linear actuator, thanks to its linear motion, holding force, and cost-efficiency.
•	Liquid Handling (Mixing & Pumping). Moving liquid within the testing device is critical and is accomplished using a small pump. As this task requires smooth, continuous rotation at a high speed, a brushless DC motor, such as the 12ECP48 Ultra ECTM motor, or a brush DC motor like the 12GS88 AthlonixTM motor, are optimal choices.
•	Sample Movement. Samples are generally inserted in the POCt device via a small opening and are required to either be automatically moved inside or ejected from the device at the end of the test. This is completed through linear or rotational movement, with a precise position control. Stepper motors are an excellent fit for this process, including Portescap’s 26M024 for rotational motion or 26DBM for linear motion.
•	Door Actuation and Lock. As POCt devices perform sensitive, complex tests while being used by non-qualified personnel, a door and/or lock system is typically required to prevent user tampering. High holding torque is critical for successful door actuation and locking, making stepper motors (with or without linear movement), including Portescap’s 35DBM and 35L048D can stack stepper motors, a good fit for this task.

CONCLUSION

While design engineers have traditionally favored stepper and DC motors, recent advancements have positioned BLDC motors as a promising alternative to DC motors in the realm of point-of-care testing. Each technology offers distinct advantages for these devices. Stepper motors excel in applications demanding holding torque and precise position control and a good choice for developers prioritizing cost-efficiency. On the other hand, brush DC and BLDC motors present themselves as optimal choices for high-duty cycle and velocity applications, as well as for those aiming to shrink device sizes. Considering the diversity of applications within POCt devices, collaborating with a motor supplier offering all three technologies in their portfolio can significantly aid in both the development and production phases.

CONTACT AN ENGINEER