More than 300 million major surgeries are conducted around the world, every year. During these surgeries, the surgeons have to use sutures to close the wounds or incisions which can themselves be problematic. They delay the healing of the damaged tissue and can cause infections. They can also cause pain, induce stress on the tissue and leave scars on the skin. To ease the healing process, researchers are coming up with new ways in which the wounds can be closed, which are superior alternatives to staples. sutures. stitches or wires. In the hard to reach areas of the body, this is also a tricky process that requires an expert hand. For over thousands of years. there have been no innovations or improvements in this department. A suitable surgical glue would have to be fast acting, strong, easily removable, non toxic (or biocompatible), flexible and work with moving organs. It is only recently that such adhesives are being developed.
STICKY TAPE SKIN GLUE
Researchers from MIT have been developing a sticky tape made specifically for surgeries. The tape works through the wet surfaces of the inter-nal tissues and can even be used on sensitive and delicate organs like the heart. Unlike previous tissue glues. the tape works rapidly even on the wet surfaces. This glues offer tougher adhesion skin glue than the alternatives found in nature such as the ones used by barnacles or mussels to stick to un-derwater rocks. The tape is inspired by the sticky material used by spiders to make their webs. The spider's web works by removing water from a small patch of the skin of the insect stuck in the web, allowing the adhesion to form quickly.
To absorb the water from the surface of the tissue, the researchers used poly acrylic acid, which is the same substance that is also used in diapers. As soon as the poly acrylic acid absorbs the water, another type of chemicals called NHS esters are used to stick the two surfaces together, through the formation of strong covalent bonds. Then, the researchers had to make this glue last for long periods within the body. To do this, they used gelatin, orchirosan, which is a hard substance found in the shells of insects. BY infusing the adhesive with these substances. the shape of the tape is retained within the body even after the surgical procedure is complete.
By varying the concentration of these substances within the adhesive, the researchers can control how long the tape can last. While gelatin dissolves within a few days or weeks, the chitosan can last many months, even a year if necessary. Apart from the surgical procedures. the tape can also be used to attach medical devices and sensors on the surface of organs.
There was however, a problem with this tape. The NHS esters formed such strong bonds that the underlyiug tissue could be damaged if it was necessary to subsequently remove the tape. To tackle this problem, the researchers first modified the chemical mixup in the original tape. and included disulfide. a substance that forms strong bonds but can be easily removed with a reducing substance. That substance was a biocompatible antioxidant known as glutathione which is found in human bodies naturally. With this combination. the tape could be removed when required. The tape has been tested on pig hearts, intestines and lungs.
METRO
To tackle the problem of keeping to gether fragile tissues like the breathing heart, moving lungs or pulsing blood vessels, an international team of researchers from many universities have created hydrogel-based adhesives that can be simply squirted on to the required area. Normally these organs are always moving and the motion can cause further stress on the organs depending on the method used to close the would. The constant motion also means that more conventional adhesives are likely to simply be ineffectiveor wear out quicker. The required solution has to be incredibly elastic, and strong at the same time. The range of hydrogel adhesives that promise to solve the problem, called MeTro are all developed for particular applications within the body, and use a range of substances. A seaweed
extract used to thicken foodstuff. known as alginate as well as the main material for soft contact lenses called polyacrylamide are both used to make hydrogel adhesives.
Another hydrogel adhesive uses elastin for the sealant which is the same nmaterial naturally found in
elastic tissues such as veins and lungs. Chitosan is also used to give tensile strength to these adhesives.
These hydrogels stay in the place of application without moving within the body. Additionally, the
formulations can be "cured" with UV light which makes them solidify in place stronger, making the procedure more effective. The potential applications for these adhesives are wide ranging, from the emergency wards to treat automobile accidents, to the injuries of soldiers in war zones. The ease of application and the fast action helps in both these situations. In the stress tests for MeTro adhesives, they were shown to outperform existing adhesives and stretch up to 20 times its length before breaking. They can withstand up to three times the stress of conventional medical adhesives before breaking.
The delicate organs are often soaked in liquid or blood, which makes the action of conventional ad-
hesives difficult. Existing adhesives aiso work in tandem with staples or sutures, and do not work at all
without them. The MeTro adhesives however are strong enough to work in these demanding environments, independently of support from other tissue mending procedures. When treated with the UV light. MeTro sets within a minute, which is incredibly fast for such strong adhesives. The process is similar to the silicon sealants used to repair plumbing in bathrooms and kitchens, but for the human body. Before the curing process, MeTro behaves like a viscous liquid filling in the gaps and moulding itself to the surface of the tissue. For healing cuts, the procedure can be as simple as squirting the MeTro gel onto the open wound with a syringe. The gel stays in place for as long as the delicate organs that it is applied on require to heal. When it eventually degrades, it does so without any toxicity in the human body. MeTro adhesives have already been tested on rats and pigs, and are moving to human trials.