Control of surface interactions with ultra-violet/ozone modification at polystyrene surface.
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Surface interactions and reactivity are of critical importance in current biomedical technologies, for example, satisfactory cell attachment and long term viability are essential for optimal in vitro tissue culture and for successful implantation and stability of cardiovascular medical implants such as stents and grafts. To achieve this, the control of fundamental forces and the resulting molecular interactions between the relevant surface and absorbing or adhering species in the physiological system is compulsory. This work utilised the surface modification technique of Ultra-Violet/ Ozone to improve the polystyrene biocompatibility by oxidising the surface with additional polar oxygen functional groups without damaging the surface bulk property. UV/Ozone treatment utilised throughout this study produced controllable oxygen functional groups and led to an increase in surface atomic oxygen level to 41% on unwashed and 35% on washed polystyrene surfaces, washing resulted in the removal of low molecular weight oxidised materials. Surface energy was increased by the addition of oxygen functional groups with the combination of alcohol (C-OR), carbonyl (C=O) and carboxyl (O-C=O); Saturation state was reached after 300s of UV/Ozone treatment where no more oxygen functionalities were incorporated to the surface. Moreover, UV/ozone treatment did not show an effect on the surface roughness studied by atomic force microscopy. The biological responses of human endothelial umbilical vein cells (HUVECs) were studied at the different level of UV/Ozone treated surfaces. HUVEC adhesion, proliferation and migration were significantly improved by the treatment compared to untreated and tissue cultures plastics (TCPs). Among the levels of UV/ozone treatment studied, 120s and 180s were found to be the most effective and HUVEC proliferation did not seem to be affected by the high level of oxygen. Similarly, the surface oxygen level did not affect the migration over UV/Ozone treated over 60s. Hypoxic condition significantly increased HUVECs migration on UV/Ozone treated, TCPs and untreated surfaces compared to normoxia, the oxygen rich surface did not favour to HUVECs that underwent regulatory process to enable the cells to increase migration. Under laminar flow conditions, HUVECs did not only grow, proliferate and migrate but also showed standard responses on UV/Ozone treated polystyrene surface. A decrease in cell size was observed at all shear stress intensities studied (1 dyn/cm2, 9 dyn/cm2 and 25 dyn/cm2) and the decrease was more obvious at higher shear stress. High shear stress intensity also induced high cell turnovers, which may be related to air bubbles induced at high flow rate. The overall findings of this study clearly illustrate that UV/Ozone surface treatment can be applied on polystyrene to improve human endothelial cells functionalities in term of adhesion, proliferation and migration in both static and laminar flow environment.