Drug loaded on the injectable polymer hydrogels to reach safely to the targeted site and elute slowly has significant advantages. For this purpose, many techniques have developed for crosslinking (CL) of the polymers chain including physical and chemical CL. Chemical CL (covalent CL) is more effective approach because it provides significant mechanical strength as compared to physically crosslinked hydrogel. There are a number of factors including light, pH, electric current, and glucose are used to stimulate the loaded drug release. For this purpose, various modifications have been made in the hydrogels by changing the CL strategies. In this chapter, a variety of CL techniques have been described along with its advantages and limitations including physically CL, chemically CL, hydrogen-bonding interaction etc. Moreover, the response of hydrogels to different stimuli in environment like temperature, pH, electric current, light and glucose sensitivity are also explained with few examples reported in the previous literature. Composite materials (CT) is one of the most emerging materials in various scientific and technological sectors and are effective in various biological applications. Therefore, the CT based hydrogels, are also included in the discussion of this chapter. The role of dexamethasone, methylene blue and vitamin B12 loading and release via CT based hydrogel are described in this chapter.