A range of semi-interpenetrating polymer networks (semi-IPNs) based on polyurethane (PU) and poly(vinyl pyrrolidone) (PVP) have been synthesized and characterized with respect to their thermodynamic characteristics, morphology, mechanical properties, surface properties, water sorption and bacterial adhesion. The free energies of mixing of PU and PVP in semi-IPNs have been determined by the vapor sorption method and were shown to be positive for all compositions. The surface properties of semi-IPNs were investigated using the dynamic contact angle analysis. It was shown that the advancing contact angle changes from 83.1degrees to 65.3degrees with increasing PVP from 7.05% to 57.38%. Scanning electron microscopy demonstrated that the semi-IPNs are two-phase systems with incomplete phase separation. The mechanical properties reflect the changes in structure of semi-IPNs with increasing of amounts of PVP in the system. Incorporation of PVP into the semi-IPN with PU restricts the ability of PVP to sorb water. As infection is likely to be caused by bacterial adherence to biomedical implants, the bacterial adhesion data suggests that the semi-IPNs with PVP content below 22.52% may be useful for biomedical material applications.