Composite hydrogels were obtained by the entrapment of chitosan, pectin or kappa-carrageenan within methacrylate-based hydrogels to improve their swelling and the mechanical properties. The results indicated that the water uptake (WU) of kappa-carrageenan and chitosan hydrogels were until 3.5 and 2.2 times higher than the WU of the synthetic hydrogel, respectively. The surface morphologies of the hydrogels showed that the pectin and kappa-carrageenan favors the formation of larger and more defined pores. The mechanical properties indicated that the pectin increased slightly the mechanical properties and the kappa-carrageenan improves the mechanical properties of the synthetic hydrogel reaching up 400 N of compression load. Therefore, the entrapment of kappa-carrageenan within synthetic hydrogels improved both the swelling and the mechanical properties. The biocompatibility of the hydrogels was evaluated with in vitro cytotoxicity assays and the results indicated that they could be considered as candidates for biomedical use.