In the present study, the synthesis of a semi-Interpenetrating Polymer Network (semi-IPN) incorporating linear poly-(epsilon-caprolactone) (PCL) into cross-linked poly-(2-hydroxyethylmethacrilate) (PHEMA) reinforced with hydroxyapatite (HA) has been described. The aim of this study was to improve the mechanical and biological performance of the PHEMA/PCL in the hydrated state, for orthopaedic applications. The swelling behaviour, mechanical (compressive and tensile) and surface chemical-physical (morphology, stoichiometric composition) characterisation of the novel HA reinforced composite based on PHEMA/PCL polymer matrix, PHEMA/PCL 70/30 (w/w) + 50% (w/w) HA (PHEMA/PCL/HA), were evaluated. Furthermore, a preliminary in vitro biological evaluation was also performed on the composite using a fully characterised primary human osteoblast-like (HOB) cell model. The inclusion of HA in the composite improved the mechanical performance in the swollen state, with values of elastic modulus in a similar range to that of trabecular bone. The composite surfaces showed a porous, irregular topography with the presence of: oxygen (O), carbon (C); phosphorous (P); calcium (Ca) where the Ca/P ratio was 1.78. Biological evaluation indicated undetectable weight loss of the sample, no release of toxic leachables from the composite and pH values within an acceptable range for cell growth. The results indicate that the novel PHEMA/PCL/HA composite is a promising candidate as filler or substitute for spongy bone for orthopaedic applications.