Medical Device Link.

Originally Published EMDM September 2004

ENGINEERING INSIGHT

The Gravitational Platelet Separation system features a finely tuned buoy mechanism, engineered to separate the plasma and red cell interface. The platelet-rich plasma is isolated above the buoy and then extracted with a syringe.

A next-generation platelet concentrator improves platelet gel–harvesting quality and efficiency. Designed and manufactured by Biomet Inc. (Warsaw, IN, USA), the Gravitational Platelet Separation (GPS) system uses single-spin technology to accelerate the procedure. An acrylic-based compound formulated by Cyro Industries (Rockaway, NJ, USA), which was used to mould a device component, played a key role in the successful development of the product.

Platelet concentrate is derived from the patient’s own blood, and then reintroduced to the wound to speed the body’s natural healing response. Platelet harvesting is typically performed in the operating room, so time is of great importance. The blood is taken from the patient and placed in a platelet concentrator. It is centrifuged twice to separate the buffy coat suspended in plasma from the red blood cell pack and the platelet-poor plasma fraction. Typically, this process can take half an hour and requires a full unit of blood.

The GPS system completes the cell-harvesting process in 12 minutes, and requires only 55 ml of blood for 6 ml of platelet-rich plasma. The process was simplified and accelerated thanks to the device’s unique construction. The unit uses a tube-and-buoy design that is tuned to the density of the red blood cells. The proprietary buoy mechanism is engineered to separate the plasma and red cell interface by reacting to the density of each layer. Under centrifugal forces, the tube expands, allowing the buoy to float freely. The buoy then separates the blood and feeds the red cells through the spacing between the buoy and the tube. When the centrifuge comes to a stop, the tube regains its original size, trapping the buoy and preventing cell movement.

Material selection was paramount for this application because of the precise tolerances and expansion rates required in the centrifuge. “The tube must consistently retain the exact mould shape without deviation,” explains Joel Higgins, director of resorbables engineering at Biomet. Shrinkage was a key mould factor, as the tube’s diameter must fit the buoy precisely in order to separate and trap the platelet-rich portion of the blood. 

The company tested several materials. Biomet required a clear material that is certified to ISO 10993 and meets USP Class VI guidelines. The polymer also had to adhere to tight mould tolerances and deliver consistent expansion and contraction rates. After many trials and processing tests, Biomet chose the Cyrolite Med 2 compound.

Sticky Problem 

Biomet was initially drawn to the acrylic for its alcohol and lipid resistance, which would improve the device’s durability. After testing, the company discovered that Cyrolite Med 2 offered an added benefit. The material improved platelet flow around the buoy, increasing platelet counts by 30–45%.

“Platelets tend to clump and adhere to materials,” says Higgins. Concentrated in large numbers, the platelets stuck to some of the polycarbonates the firm initially tested, cutting into overall yields. “The Cyrolite Med 2 compound was resistant to the adhesive quality of the platelets, providing better flow and higher counts,” says Higgins. “It provided excellent processing and consistent results in G force expansion. [The material was] easy to work with, and it consistently held the mould design without tapering.”

Copyright ©2003 European Medical Device Manufacturer