Preparation and characterisation of zwitterionic sulfobetaine containing siloxane-based biostable polyurethanes

Siloxane-based biostable polycarbonateurethanes (PCUs) with varying [PDMS]/([PDMS] + [PCDL]) were synthesized by a two-step solution polymerisation method. As potential blood-contact biomaterials, their biocompatibility was further improved by inserting sulfobetaine via three synthetic protocols. It was found that Mn was progressively decreased from 4.50 × 10⁴ to 3.23 × 10⁴ with increasing PDMS content and the PDI was kept below 2.0 after the zwitterionic modification. At the same time, the Mn was reduced from 3.78 × 10⁴ for a 20 mol% PDMS containing PU to around 2.38 × 10⁴ for these zwitterion modified PUs while the PDI was dropped below 1.61. Accordingly, the tensile stress was dropped from 43.1 MPa to about 25.3 MPa and the fracture energy was decreased from 146.4 MN m⁻¹ to about 69.8 MN m⁻¹. Thanks to the enrichment of PDMS on the surface as evidenced by XPS analysis, the water contact angle (WCA) was increased from 106.2° to 116.8°, whereas this value was again decreased to about 94.6° after inserting sulfobetaine. Compared to siloxane-based PCUs, the fibrinogen absorption on and platelet adhesion to the surface of these zwitterionic modified ones were markedly retarded. This suggested that there is a trade-off between the mechanical properties and biocompatibility for the zwitterion containing siloxane-based biostable PCUs applied as blood-contacting biomaterials.