Amniotic membrane has been used as a biomaterial in basic and clinical applications for many years. As early as the 20th century, fetal membrane donor grafts containing amniotic membrane were reported for burns and ulcerated wounds, followed by cranio-cerebral surgery, abdominal surgery, obstetrics and gynecology, and ophthalmology. With the development of bioengineering and tissue engineering technologies, the application of amniotic membrane has become more widespread and the research has become more in-depth. 1, amniotic membrane structure and function The normal human amniotic membrane tissue structure is divided into epithelial cell layer, basement membrane, dense layer, fiber cell layer and spongy layer. Usually the prepared amniotic membrane contains only 3 layers: epithelial cell layer, basement membrane and dense layer, while the fibrous cell layer and spongy layer are stripped off during preparation. The epithelial layer contains amniotic epithelial cells and a variety of growth factors secreted by the amniotic epithelial cells. 2. Characteristics of amniotic membranes prepared by different methods The amniotic membranes used for basic and clinical research are broadly fresh amniotic membranes, frozen amniotic membranes and amniotic extracellular matrix, each of which has its own characteristics [6]. 2.1 Fresh amniotic membrane This type of amniotic membrane is made by washing the fresh amniotic membrane under aseptic conditions to remove blood, peeling off the amniotic membrane, and storing it in a refrigerator at 4°C for use within 24h. Fresh amniotic membrane retains amniotic epithelial cells and cytokines, which is beneficial for ocular surface reconstruction when used for the treatment of ocular surface diseases. However, it is not convenient to use because it contains cellular components and is slightly antigenic, and the storage time is short. 2.2 Cryopreservation of amniotic membrane Fresh amniotic membrane was prepared, dehydrated in 100% glycerol at 4℃, and changed once every 24 hours for 3 times. Store in a constant temperature refrigerator at 4℃ for backup. The dehydrated amniotic membranes were removed and soaked in 100% glycerol:DMEM solution (1:1) containing chondroitin sulfate and stored at -80℃ in an ultra-low temperature refrigerator for 6 months. Compared with fresh amniotic membrane, the storage time is longer and more convenient to use. 2.3 Amniotic membrane extracellular matrix was removed from the amniotic membrane after glycerol dehydration, hydrated with PBS solution, added with 0125% trypsin, digested at 37℃ at room temperature, and then scraped with a cell scraper to remove the remaining amniotic membrane epithelial cells under an inverted phase contrast microscope to confirm the absence of cells after the amniotic membrane epithelial side up on acetate film paper, added with 100% glycerol:DMEM solution containing chondroitin sulfate (1:1) They were soaked in 100% glycerol:DMEM solution containing chondroitin sulfate (1:1) and stored at 4℃ in a constant temperature refrigerator for 1 week, or at -80℃ for 6 months at ultra-low temperature. One researcher cross-linked the saline rinsed amniotic membrane with 012% glutaraldehyde, 015% sodium dodecyl sulfate, 0125% trypsin decellularization, rinsed repeatedly, freeze-dried, sealed in separate packages, and sterilized with ethylene oxide [7]. This material removes the cellular and soluble protein components and retains only the insoluble components of the original tissue, mainly including collagen, elastin, aminoglucan and structural proteins, etc. It can be used as a scaffold for cell growth and promote cell adhesion, and also has a long storage time and is easy to use.