According to the papers published in Advanced Healthcare Materials magazine,The team's approach is to strongly glue a layer of hydrogel, a soft, smooth polymer made of water, to common soft materials, such as latex, rubber, and silica gel. After bonding, we get soft, stretchable, smooth, and no leakage of viruses and other small molecules, "hydrogel stack".

　　Besides, embedding compounds into hydrogel coatings can also make them have the function of detecting pathological molecules. At the same time, drugs can also be embedded in hydrogels and released slowly from hydrogel coatings, so as to better treat diseases in vivo.

　　Dr. Zhao Xuanhe, an associate professor of mechanical engineering at the Massachusetts Institute of Technology, and the leader of the team, said the hydrogel coating was glued to various flexible medical devices, such as catheters and intravenous tubes. After being tested by bending and twisting, the coating still has no problem of cracking, and it is very durable. The coating is very smooth, friction is much smaller than the uncoated standard catheter, thereby reducing patient discomfort.

　　The team also applied this hydrogel coating to another widely used flexible product: condom. In addition to reducing the comfort of existing latex condoms by reducing friction, the researchers say, the gel coating can also be embedded in latex allergy drugs to improve the safety of the condoms.

　　"We have proved that hydrogels do have the possibility of replacing ordinary flexible materials," Zhao Xuanhe said. "Now we have a way of combining the hydrogels with other materials, which will probably be applied to various medical devices that are in contact with the body."

　　"Seventy-two changes" of hydrogels

　　Zhao Xuanhe's team has invented a new method before making a mixture of large amounts of water and a small amount of polymer to make tough and stretchable hydrogels. On this basis, another technique is developed. First, two phenyl ketones are used to treat the surface of the flexible materials such as rubber and silica gel, and then the hydrogel is glued to these flexible materials. When the molecular solution of two phenyl ketone is exposed to ultraviolet light, a strong chemical bond is formed between the flexible and the hydrogels.

　　The researchers used these technologies to create hydrogel laminates: two layers of hydrogels were sandwiched with a flexible sandwich structure. They then carried out a series of mechanical tests on the laminated structure and found that the structure would not be tearing or cracking even when it was stretched several times, but was able to keep it strong and durable.

　　The team also placed the stacked structure in double chamber containers, one side filled with deionized water and the other side filled with molecular dyes. A few hours later, the laminates still can effectively prevent dyes from infiltrating from one side to the other side. Compared with only one layer of hydrogel, dyes can easily pass through. They concluded that the flexible material in the stack made the whole structure anti permeable - they speculated that the structure could also prevent the virus and other small molecules from passing.

　　In another test, the team mixed pH sensitive molecules into a hydrogel coating coated on one side of the flexible material and mixed green food dyes into the hydrogel coating on the other side. This time, they immersed the entire laminated structure into two chamber containers filled with deionized water.

　　When changing the acidity of water in the container, the researchers observed that the hydrogel coating containing pH indicator was brightened. Meanwhile, the green dye penetrated slowly from the hydrogel coating to the other side of the water. German Parada, a researcher involved, said: "we can mix pH sensitive molecules into hydrogels, and we can also mix drugs that need to be gradually released into the hydrogel. In conclusion, the characteristics of gels can be adjusted to meet different application needs.

　　Broad application prospect

　　The researchers first applied the hydrogel stack to the flexible instruments, which used previously developed techniques to coating hydrogels on various flexible instruments, such as silicone tubes, Foley catheters and condoms.

　　"The first thing we care about is catheters," Parada said. "They are rough, hard, easy to cause discomfort, and catheterization can cause about 50% of patients to be admitted again. Second, we think it can be used in condoms, because the existing latex condoms will cause a large number of problems related to sensitivity and allergies, and if the drug can be mixed into the hydrogel condoms, the human body can be better protected. "

　　The researchers found that even if the hydrogel coated ducts were flexed, folded and formed, the hydrogel coating could still be firmly adhered to the catheter without cracking. The same is true when inflating the coated urethral catheter and the condom.

　　Parada said that the size of hydrogel laminate can be adjusted to adapt to different devices. For example, scientists can choose a thicker flexible material to enhance the strength of the stack, or select a thicker hydrogel coating to add more drug molecules or sensors. It can also change the design of hydrogel according to the size of the required friction, so as to change the smoothness of lamination.

　　"We can build large-scale hydrogels that can be coated with medical devices, and this hydrogel will not stimulate the body," Zhao Xuanhe said. "It can be thought of how extensive the application is based on this technology platform."