Gradient semi-interpenetrating polymer networks (gradient semi-IPNs) as well as the traditional semi-interpenetrating polymer networks (semi-IPNs) were synthesized using polyurethane (PU) and poly(2-hydroxyethyl methacrylate) (PHEMA). The materials were characterized with respect to thermodynamic miscibility, NIR imaging, mechanical properties and morphological structure by tapping mode atomic force microscopy (TM AFM). The positive values of Gibbs free energy indicated that polymeric systems were thermodynamically immiscible. The dynamic mechanical analysis as well as TM AFM demonstrated that the systems under investigation were two-phase systems with incomplete phase separation. The gradient semi-IPNs were shown to have unique mechanical properties dependent on the composition and on the degree of microphase separation. The ability to create a layer of biocompatible polymer, such as PHEMA, at the surface, or create nanostructured surface consisting of nanodomains of different polymeric compositions, and engineer the improvements in the mechanical properties of the materials through the use of gradient systems should allow the creation of novel materials for biomedical application through the optimisation of mechanical properties, surface chemistry and biological properties.