How macroscopic materials properties depend on their microscopic structure and dynamics is an illustrative case of complexity. Issues like metal fatigue, mechanical strength of materials and transport properties are of key importance from a fundamental point of view as well as for many applications in technology and industry. The presence of grain boundaries, dislocations and various other types of defects in many materials lie at the heart of these issues. Colloidal systems provide an excellent model playground to address such problems, as they are relatively rich in defects due to their slow dynamics and intrinsic polydispersity. In addition, colloidal systems are easily deformed and manipulated using optical laser tweezers, while their macroscopic properties can be conveniently characterized using rheology. At the same time, the colloidal ‘atoms’ are sufficiently large to be imaged by video- and/or confocal microscopy and their properties can be tuned using advanced chemical methods.