Plasticised poly(vinyl chloride) : significance of plasticiser and surface modification for protein adsorption
Plasticised poly(vinyl chloride)(PVC-P) remains the most widely used bloodcontacting biomaterial. With respect to the blood compatibility of PVC-P, the plasticiser plays a more important role than the PVC polymer itself, since the blood contacting surface is highly distributed with plasticiser. Therefore, the objective of this project was to study the significance of the plasticiser on protein adsorption onto PVC-P, where the features of plasticiser considered were plasticiser selection (nature of plasticiser), the plasticiser surface level and plasticiser surface distribution. To evaluate this, three types of medical grade PVC-P, plasticised with 2-diethylhexyl phthalate (DEHP), tri-(2-ethylhexyl) trimellitate (TEHTM) and n-butyryl-tri-n-hexyl citrate (BTHC) respectively in sheet form with the same softness, were selected. Protein adsorption was carried out using 1251 radiolabelled human fibrinogen and bovine serum albumin. The in vitro protein Imaterial contact was achieved with a modified 24-well incubation test cell. A reduced plasticiser surface level was obtained with methanol surface treatment. Surface characterisation was carried out using ATRFTIR and UV-spectrophotometer. Results obtained indicate that fibrinogen adsorption on PVC-P strongly correlates with the plasticiser surface level. A reduced plasticiser level can reduce fibrinogen adsorption and increase albumin adsorption. However, excess surface washing might lead to a surface topographical change, initiating an increased fibrinogen adsorption. Protein adsorption is also dependent on the plasticiser nature and plasticiser surface distribution. A high level of plasticiser does not necessarily mean a high reactivity towards fibrinogen adsorption. Based on this study, surface modification of PVC-P was carried out using cyclodextrins (CDs) by blending. The combination of CDs with polyethylene oxide (PEO) or polyethylene (PEO)-poly(propylene oxide) (PPO) triblock copolymer (pluronic surfactant) was also studied. Protein adsorption results indicate that the surface enriched CDs, CDIPEO, CD/Pluronic physical mixture or CD inclusion complex (CIC) can achieve a reduced protein adsorption. Finally, a possible mechanism was hypothesised and a proposal was made for a novel form of surface modification.