Network Bonding

　　Hydrogels have various classification methods. According to the bonding of hydrogel networks, they can be divided into physical gels and chemical gels. Physical gels are formed by physical forces such as electrostatic interactions, hydrogen bonding, chain twisting, etc. These gels are non-permanent and can be converted to a solution by heating the gel, so they are also called pseudo gels or heat. Reversible gel. Many natural polymers exhibit a stable gel state at room temperature, such as k2 carrageenan, agar, and the like. Among synthetic polymers, polyvinyl alcohol (PVA) is a typical example and can be obtained by freezing and thawing. Hydrogels stable below 60°C. Chemical gels are three-dimensional network polymers formed by chemical bonds and are permanent, also known as true gels.

　　Size and shape

　　According to the size and shape of the hydrogel, there are macroscopic gels and microscopic gels (microspheres). According to the shape of the macrogels, they can be classified into columnar, porous sponge, fibrous, membrane, and spherical. The prepared microspheres are divided into micrometer and nanometer scale.

　　External stimuli

　　According to the response of hydrogel to external stimuli, it can be divided into traditional hydrogels and environmentally sensitive hydrogels. Traditional hydrogels are not sensitive to changes in the environment such as changes in temperature or pH, while environmentally sensitive hydrogels are those that can perceive small changes in the external environment (such as temperature, pH, light, electricity, pressure, etc.) or Stimulates and produces a series of polymer gels with corresponding changes in physical structure and chemical properties or even mutations. The salient feature of this type of gel is its remarkable swelling behavior in response to the environment. Using this stimuli response characteristics it can be used as a sensor, controlled release switch, etc. This is the most sincere in 1985 One of the topics of interest.

　　Synthetic material

　　According to different synthetic materials, hydrogels are divided into synthetic polymer hydrogels and natural polymer hydrogels. Due to its better biocompatibility, sensitivity to the environment, abundant sources, and low prices, natural polymers are attracting more and more attention from scholars. However, natural polymer materials have poor stability and are easily degraded.