Control of uniformity of plasma-surface modification inside of small-diameter polyethylene tubing using microplasma diagnostics

The realization of small scale biomedical devices will be closely related to the non-fouling/biocompatible properties of the exposed surfaces and the uniformity of the surface treatment throughout the device. The use of biomaterials for vascular grafts to replace diseased human blood vessels has increased tremendously over the past 30 years. In contrast to large-diameter vascular grafts, (i.e., larger than 5mm) which remain excellent for more than 10 years after implantation, small-diameter vascular grafts occlude rapidly after implantation. In this work, we apply a new approach for treating small-diameter polymer tubing and we make use of two microplasma diagnostics to monitor the plasma properties during the treatment process. A hollowcathode microplasma was used to modified the lumenal surface of small-diameter polyethylene (PE) tubing. A microwave-cavity diagnostic was used to measure the plasma density of the microplasma. Emitted light from the plasma was fed into a monochromator at various positions along the PE tube to assess uniformity of the microplasma. Effectiveness of oxygen and argon plasma treatments were evaluated using the capillary rise method at various positions along the tubing. We are able to show a correlation between the properties of the inner surface of the PE tubing and the light emitted from the plasma. Thrombus formation and embolization are significant problems for blood-contacting biomedical devices. To minimize these affects, a Poly(ethylene oxide) (PEO) surfactant was immobilized to the lumenal surface of the PE tubing. The plasma immobilization technique consists of a two-step process; first, a surfactant is coated to the inner surface of the PE tubing followed by exposing the precoated surface to an argon gas discharge. To test hematocompatibility, a blood flow loop circulated heparinized human blood through both a plasma-treated and untreated PE tubes, simultaneously. After blood exposure, the tubes were examined with a scanning electron microscope to assess the density of adhering platelets along the length of the tubes. The plasma-treated tubing showed fewer blood adherents than the untreated tubing. By modifying the plasma parameters, the uniformity of the microplasma treatment along the tubing can be optimized.