Hydrogel is cross-linked polymeric network containing more than 90% water. They have been extensively applied in organ reconstruction, soft tissue prosthesis,cell culturing substrate, and controlled drug release. In addition to their good biocompatibility, they share remarkable resemblance to the structures of many living organisms’ tissues, such as muscles, cartilages, corneas and the skin; one key property of hydrogel is that it can be easily integrated with other functional materials to play a synergistic role, which greatly extends the application in many areas. For instance, the hydrogel containing magnetic nanoparticles can take other special effects besides the role of tissue prosthesis in postoperative organ reconstruction after excision of tumor. Thus, they are more suitable for materials of living tissues than any other artificial ones. However, compared with the biological soft tissue, conventional synthetic hydrogels show isotropic structure at the molecular and macroscopic level, lacking ordered structures, which leads to limitations in practical applications. The synthesis of anisotropic hydrogels, to some degree, solves this problem. In this paper, we mainly focus on the preparation methods of anisotropic hydrogels and the classifications of anisotropic properties. The factors influencing the anisotropy are summarized.The existing problems and further research directions are also discussed.

Contents
1 Introduction
2 The property of the anisotropic hydrogel
2.1 Magnetic property of anisotropic hydrogel
2.2 Mechanical property of anisotropic hydrogel
2.3 Optical property of anisotropic hydrogel
2.4 Swelling property of anisotropic hydrogel
3 The preparation of anisotropic hydrogel
3.1 Anisotropic hydrogel synthesized by template method
3.2 Anisotropic hydrogel synthesized by magnetic field
3.3 Anisotropic hydrogel synthesized by self-assembly
4 Conclusion