Scheme of hydrogel biofunctionalization. The osteogenic properties of hydrogels are enhanced by various modifications including bioconjugation, composite formation, and encapsulation of osteogenic components. Bioconjugation enables covalent tethering of numerous functional groups. Composite hydrogel allows non-covalent incorporation of functional organic or inorganic fillers. Moreover, diverse osteogenic components (proteins, cells, genes, small molecules, or bone grafts) can be encapsulated into hydrogel network.