Covalent biofunctionalisation of the inner surfaces of a hollow fibre capillary bundle using packed bed plasma ion implantation.

Hollow fiber capillary bundles are widely used in the production of medical devices for blood oxygenation and purification purposes such as in cardiopulmonary bypass, hemodialysis and hemofiltration but the blood interfacing inner surfaces of these capillaries provide poor hemocompatibility. Here we present a novel method of packed bed plasma ion implantation (PBPII) for the modification of the inner surfaces of polymeric hollow fiber bundles enclosed in a cassette. The method is simple and can be performed on an intact hollow fibre bundle cassette by placement of a hollow cylindrical electrode, connected to a negative high voltage pulse generator, around the cassette. The method does not require the insertion of electrodes inside the capillaries or the cassette. Nitrogen gas is fed into the capillaries inside the cassette by connecting the inlet of the cassette to a gas source. On application of negative high voltage bias pulses to the electrode, plasma is ignited inside the cassette, achieving surface modification of both the internal and external surfaces of the capillaries. FTIR-ATR spectroscopy of the PBPII treated capillaries revealed the formation of aromatic C=C bonds, indicating progressive carbonisation of the capillary surfaces. The PBPII treatment was found to be uniform along the capillaries and independent of radial position in the cassette. Atomic force microscopy (AFM) of cross-sections through the capillaries revealed that the increased stiffness associated with the carbonized layer on the inner surface of the PBPII treated capillary has a depth (~ 40 nm) consistent with that expected for ions accelerated by the bias voltage applied. The modified internal surfaces of the capillary bundle showed greatly increased wettability and could be biofunctionalized by covalently immobilising protein directly from buffer solution. Direct, reagent-free protein immobilisation was demonstrated using tropoelastin as an example protein. Covalent binding of the protein was confirmed by its resistance to removal in hot sodium dodecyl sulphate (SDS) detergent washing, which is known to disrupt physical binding.