Unlike central laboratory diagnostic instrument systems where consumables are generally passive elements, consumables for Point of Care Testing (POCT) devices are not only an active component, they are often the heart of the system.
Consumables for Point of Care systems frequently need to incorporate complex functionality in a simple manner, and in as small a footprint as possible. This typically results in the consumable taking the form of a high-precision microfluidic cartridge.
Key considerations in developing microfluidic cartridges for POCT devices
Since microfluidic cartridge design plays a key role in the successful development of a complete in vitro diagnostic (IVD) instrument system where ease-of-use, throughput, and cost per test are critical factors, it is particularly important for the microfluidic cartridge design to mature ahead of the instrument. This provides the design freedom needed to, 1) balance all the commercial program success factors with the cartridge design effort as early as possible, and 2) to deliver a simpler and more effective cartridge concept that is more likely to meet the desired cost of goods target.
When designing microfluidic cartridges for POCT devices, below are some key considerations that will help contribute to a more successful instrument development program.
Balance competing technical and commercial priorities
Microfluidic cartridge design needs to accommodate many factors, including cost of goods, functionality, usability and development cost. Arriving at the right balance has a direct effect on the microfluidic cartridge’s complexity. The development effort required – both in cartridge design and assembly process development – is proportional to that complexity and should be figured in when making trade-off decisions.
Estimating the cartridge cost at various assembly volumes and evaluating the assembly methodology options for commercial ramp-up also help in planning and executing a POCT production scale-up strategy that balances capital investment with demand forecasts.
Develop the microfluidic cartridge manufacturing process
Determining the correct processes for the cartridge assembly, the best method for executing those processes, and the capability of the process to meet design requirements are critical for the commercial success of the product.
Some elements to consider include:
Anticipated annual production volumes (1,000s or 1,000,000s),
The number of components within the cartridge itself,
The total number of assembly process steps,
The cycle time for each process step, and
The number of process steps that are unique.
Identifying these manufacturing process parameters can also provide insight into potential risks associated with microfluidic cartridge assembly and strategies to mitigate those risks, such as evaluation of process alternatives or minor cartridge design refinements.
Assure in-process quality
It is critical that each step of the cartridge assembly process can be executed consistently and correctly at production volume levels. Determining in advance the number of Critical to Quality or Critical to Performance steps in the assembly process is key to the planning and execution of the cartridge development program.
Cartridge manufacturing, even at a prototype level, may also require specific environmental controls, such as cleanroom conditions and humidity and/or temperature controls, to maintain consistent quality and performance as well as to assess the potential impact of these variables on the performance of the cartridge.
Design for the context of use
Microfluidic cartridges for Point of Care systems need to potentially withstand multiple environmental conditions all while maintaining appropriate functionality. These can range from temperature extremes (both hot and cold) during shipment and storage, to vibration, heat, and pressure during operation.
It is also critical that the functionality of the cartridge, as well as its key interfaces with the user and the instrument, are well defined early in the development. This holistic view of the microfluidic cartridge design allows for material selection to accommodate use conditions, anticipated shelf life, and manufacturing suitability.
Replicate “the bench”
Often within a POCT system, the cartridge must automate complex workflows within limited dimensions and perform flawlessly 100 percent of the time. Careful upfront thought needs to be given to the valves, pressure, and onboard reagent storage and reconstitution required to replicate the bench assay. Bringing together material science, microfluidics and thermodynamics considerations early in the development process allows for evaluation of the overall cartridge design in terms of its manufacturability and balancing any trade-offs between cost and overall assay performance parameters.
Start early to ensure success
Focusing on the design of the microfluidic cartridge upfront, will pay the biggest dividends in the POCT product development process and the overall success of the IVD system. Giving the cartridge design team the maximum flexibility to create a design that balances all the commercial program success factors, user interactions, and assembly processes and equipment, enables them to develop the simplest possible cartridge design that provides the needed functionality.
Given its central role, honing in on the optimal microfluidic cartridge design at the start of a project is key to the successful development and ultimately commercial success of the complete POCT system.
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Marjorie Toth is a program manager for Invetech’s diagnostics business group. Marjorie has over 15 years of experience in product development and design transfer in the life science and medical device industry. She has successfully transferred multiple instrument systems into production (including three novel technology platforms) and has served as program team leader/member for multiple POC development programs.
Andrew Guy is the Manager of Invetech's Hardware Resource Group in San Diego.