Three single-use fluid management components joined with plastic welding

Single-use fluid management cassettes for dialysis and blood separation are injection-molded components that are joined through plastic welding.

By Kun Wang, Branson Welding and Assembly at Emerson

At-home peritoneal dialysis (PD) systems, blood separator units and wearable kidney devices all use disposable components for fluid management.

These injection-molded cassettes and cartridges are assembled with the use of plastic welding methods. Here’s more about each of these disposable components and the best plastic welding technique for their particular design.

Automated peritoneal dialysis fluid management cassettes

Automated peritoneal dialysis (APD) is a huge market for single-use products, since patients must use a fresh, sterile set of fluid connections to perform regular dialysis while preventing the risk of peritonitis.

To ensure that home-based patients make essential fluid connections properly — from their own peritoneal catheter to PD fluid bags and to the APD machine (cycler) itself — manufacturers have developed precise, but inexpensive, single-use plastic cassettes.

These cassettes snap into the APD cycler at the and are disposed of when the daily PD procedure is complete. Externally, the cassettes provide an easy interface to the APD cycler, offering external connection ports for flexible tubes, while internally, they include a variety of fluid paths, chambers and valves.

Typical APD cassettes are assembled when two injection-molded halves are welded together. Assembling these cassettes together is a challenge, since each part must be made of a transparent, biocompatible plastic and their internal plastic features must join cleanly and consistently to form fluid channels or circuits, each connected to external tubes that serve different fluid flows in each part of the APD process.

Blood separator cassettes

While this disposable part is associated with a hospital-grade blood separation unit, its single-use cassette design reflects the same design imperatives as point-of-care-type products.

The cassette accepts a number of flexible tubes that, together with the separator machine, process fluid flows to separate various blood components.

Cassettes from a blood separator unit are assembled by joining matching injection-molded parts using hot-plate welding.

Wearable kidney

A “wearable kidney” is now in clinical trials. It is a portable device consisting of a small infusion machine and a special, disposable adsorbing cartridge. The device is designed to enable continuous, tidal peritoneal dialysis using a 2 L or less of dialysate solution, a fraction of the typical volume for PD.

After infusion of dialysate fluid, small amounts of the dwelling dialysate fluid are passed through the adsorbing cartridge, in which thin, absorptive membranes capture and remove uremic toxins from the spent fluid. Then, the infusion machine reconstitutes the fluid by infusing it with minerals and glucose to desired levels, so that it can be reinfused. By continuously draining, cleansing, reconstituting and reinfusing small amounts of fluid, continuous tidal PD is possible.

The wearable kidney relies on a laser-welded plastic assembly. Laser welding is used because it can hermetically seal the cassette while offering exceptional control over heat inputs.

More from Kun Wang: Plastic welding technologies for joining single-use medical flow management devices

Kun Wang is the business development manager for medical and electronics, Branson Welding and Assembly at Emerson. With over a decade of experience in plastics joining, he applies his expertise to deliver value to customers in the medical and electronics markets. Wang is a graduate of Jiao Tong University in Shanghai.

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The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design & Outsourcing or its employees.