The Trak Male Fertility System is a microfluidic device which uses Topas 8007S-04 in a disposable cartridge due to its low moisture vapour transmission rate (MVTR), decreased water absorption, and biocompatibility. The sample is transferred into a cartridge using a dropper and the cartridge is pressed onto a centrifuge which spins to initiate the microfluidic process.
Sandstone Diagnostics began work on the male fertility point-of-care (POC) testing device in 2012. The company tested numerous materials and eventually selected Topas resin for its superior material properties which enhanced the design and functionality of its initial system. The Topas material was one of three polymers that Sandstone tested in the early development stage. Ulrich Schaff, co-founder and chief technology officer at Sandstone, explained that other material options such as PC, PS, and clear ABS were considered but lacked the adequate barrier properties. The main issue was that these materials absorbed fluid and transmitted vapour over time, according to Schaff.
“Storage of materials that are moisture sensitive or trying to keep fluid in can be a real challenge,” said Schaff. “We needed to store a small amount of fluid, less than 1/10ml, which pushed the limits for what you can store long-term. Most plastics aren’t suitable for storing fluids for an extended period, but the Topas material performed very well.”
Additionally, the Topas resin provided adequate durability compared with polystyrene, along with better dimensional stability than PC, resulting in flat injection moulded parts which were tough enough for the mechanical processes of the application. COC also delivered strong biocompatibility with the reagents that were used, resulting in no leaching.
The disposable cartridge also required high transparency and low autofluorescence for efficient sample analysis. Because COC is an amorphous material, a solid ultrasonic weld of the two sections of the cartridge was achieved, according to Schaff. Among the polymers tested, the Topas material offered the best control in welding.
COC did present one challenge in pad printing. The company overcame the ink’s non-adherence by using a low-powered corona treatment combined with ink formulated for polyolefins.