Although the huge progress in traditional top-down tissue engineering (TE) (seeding cells onto scaffolds), the complex histoarchitecture of tissues can hardly be achieved and the engineered constructs are limited in size due to diffusion limitations. In this regard, the engineering of ‘vascularized’ constructs is mandatory. Recently, ‘modular’ or ‘bottom-up’ TE is introduced as an alternative that would overcome these limits. In this project, microtissues or building blocks will be formed followed by directed assembling into tailor-made complex (a)vacularized tissues based on cellular self-assembly. Dependent on the tissue type (cartilage, bone) to be engineered, homo- and heterocellular aggregates will be formed in a cell-driven, scaffold-free way. Vascularized tissues will be assembled by the combination of tissue-specific spheroids and vascularized spheroids. After cell aggregation, maturation of the building blocks (either differentiation or cellular reorganization to obtain different levels in ‘vessel’ organization) is needed. To achieve a specific histoarchitecture, the building blocks will be directly assembled with a 3D bioprinter. The aid of biomaterials will be necessary for further structural support until fusion and maturation of the building blocks is achieved. Finally, as a proof of concept, the obtained constructs will be evaluated in nude mice and sheep. Special attention will be given on the viability of the constructs and the blood vessel formation.