Biocompatibility is the basic requirement for the tissue engineering scaffolds. The most distinct difference between the tissue engineering scaffolds and other functional materials is that they must possess satisfactory biocompatibility, which can ensure that the tissue defect or loss is without causing any inflammation. At the time of scaffold material selection, its biocompatibility should be primarily considered. If the biologically incompatible materials were implanted into the human body, they would definitely bring about inflammatory or foreign-body responses that eventually lead to rejection and/or necrosis. On the other hand, the scaffold must elicit a negligible immune reaction or clinically detected foreign body reactions to prevent the rejection of the body. Moreover, each material, which the scaffolds are made of, should support the appropriate regulation of cell behaviors, such as adhesion, proliferation, migration, differentiation, biomineralization, etc., directly based on its specific physicochemical propertie or by multiple stirring interactions with the bioactive factors in vivo  so that the new desired functional tissue can form. In most cases, the tissue engineering scaffolds are made of several components to get optimized biocompatibility by utilizing the coordination between the components. For example, Li et al.  prepared poly-L-lactic acid (PLLA)/ chitin scaffolds, in which there was a good coordination between PLLA and chitin. The alkaline degradation products of the chitin could neutralize the acidity caused by PLLA degradation, thus providing a better environment for the growth of cells and tissues than PLLA or chitin alone.