This thesis analyses the possibility of using topology optimization for the design of cores in composite sandwich structures, with the aim of reducing weight compared to existing materials. The initial part of the thesis introduces the problem and theoretical background, followed by a description of the work through various topology optimization approaches. The conclusion of the thesis includes an analysis and comparison of the newly designed structures with existing ones using finite element method simulations. The results indicate that the application of topology optimization in this field is feasible and opens up possibilities for further research.