NPs can also interfere with the polymerization/crosslinking reactions. For instance, in situ formed CaP NPs reduced the probability of monomer interaction (i.e., DMAEMA/HEMA/DEGDMA) and weakened the material. Similarly, covalent conjugation of PDA NPs to a polymer backbone offered the advantage of their stable retention but, due to a decrease in the availability of functional groups otherwise involved in polymer crosslinking, it reduced the overall strength of the hydrogel. In the same manner, incorporation of PPy NPs into a COL/HAMA hydrogel was advantageous to endow the matrix with conductive and antioxidant properties. However, exceeding a certain amount, the black NPs hindered light penetration and UV-mediated crosslinking, leading to a drop in the storage modulus. Additionally, the geometry and the size of dispersed nano-objects can be determining factors.