Image: The finished PCU venous valve prosthesis (Photo courtesy of Aachen University).

Patients suffering from chronic venous insufficiency (CVI) may soon be able to receive an implant that will assume the function of damaged atrioventricular valves.

Researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation (IPA; Stuttgart, Germany), Aachen University (Germany), and four industrial partners have developed an automated production facility that can make venous valve prostheses from polycarbonate-urethane (PCU), a particularly strong and flexible plastic which can be made in very thin layers, and is also easy to sew surgically into surrounding tissue. The automated manufacturing process is based on a three-dimensional (3D) droplet-dispensing tool, which enables the researchers to precisely apply a particular polymer onto freeform surfaces, while at the same time combining various grades of polymer hardness--called Shore hardnesses.

The process involves dissolving the polymers in a solvent, which is then deposited onto a venous valve prosthetic mold one droplet at a time, using the new dispensing tool. The system is accurate to within 25 micrometers, and can deliver up to 100 droplets per second, each with a volume of 2-60 nanoliters. A six-axis kinematic system positions the piezo-feeder precisely above the mold. Once it is fully coated with droplets, the mold is bathed in a warm stream of nitrogen. This causes the solvent to evaporate, leaving the polymer behind. Further layers are applied by repeating the dispensing process, and in the end, the polymer prosthesis can simply be peeled from the mold. Doctors can then take the finished replacement valves and implant them into the veins of the leg via percutaneous access.

“3D droplet dispensing technology is an additive procedure that allows three-dimensional geometries to be created layer by layer using a polymer,” said Oliver Schwarz, PhD, group manager at the IPA. “By using PCU in combination with our 3D dispensing kinematics, we can achieve seamless transitions within the material between six different grades of elasticity and hardness - without any breaking points whatsoever. This technique mirrors the design of highly stressed structures in nature. It can't be done using injection molding.”
 

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