The team is developing a biocompatible glue suitable for hair transplants

Medical adhesives are materials that can be applied for various purposes, such as wound healing, hemostasis, vascular anastomosis, and tissue engineering, and are expected to greatly contribute to the development of minimally invasive surgery and organ transplantation. However, glues that have high adhesion and low toxicity, and are able to decompose in the body, are rare.

Adhesives based on natural proteins, such as fibrin and collagen, have high biocompatibility, but insufficient adhesive strength. Synthetic polymer glue on the basis of urethane or acrylic have greater adhesion, but do not decompose well and can cause an inflammatory reaction in the body.

A joint research team led by Prof. Myungeun Seo and Prof. Haeshin Lee from the Department of Chemistry at KAIST has developed a bio-adhesive from biocompatible polymers using tannic acidssource of astringency in wine.

The research team focused on tannic acid, a natural polyphenolic product. Tannic acid is a polyphenol that is abundant in the skins of fruits, nuts, and cocoa. He has a high affinity and the ability to coat other substances and we experience the astringent taste of wine as the tannic acid adheres to the surface of our tongue. When tannic acid is mixed with hydrophilic polymers, they form coacervates, or small droplets of a jelly-like liquid that sink.

If the polymers used are biocompatible, the mixture can be used as a medical adhesive with low toxicity. However, coacervates are essentially liquid-like and cannot withstand large forces, which limits their adhesive capabilities. Therefore, while research on its use as an adhesive is actively debated, a biodegradable material that has strong adhesion due to its high shear strength has yet to be developed.

(a) Overview of a hair transplantation method using a biodegradable adhesive (right) compared to a conventional hair transplantation method (left), which transplants hair containing hair follicles. After the glue is applied to the tip of the hair, it is fixed to the skin by implantation through a subcutaneous injection, and repeated treatments are possible. (b) Initial results from animal testing. A day after 15 hair transplants, 12 strands of hair remain. If you pull the 3 strands of hair, you will see that the entire body is pulled up, indicating that they are deeply rooted in the skin. All strands of hair applied without the new adhesive material fell out, and in the case of glue without heat treatment, the efficiency was 1/7. credit: JACS Au (2022). DOI: 10.1021/jacsau.2c00241

A research team found a way to increase adhesion by mixing two FDA-approved biocompatible polymers, polyethylene glycol (PEG) and polylactic acid (PLA). While PEG (which is widely used in eye drops and creams) is hydrophilic, PLA (a well-known bioplastic derived from lactic acid) does not dissolve in water.

The team combined them into a block copolymer that formed hydrophilic PLA aggregates in water with the PEG blocks surrounding them. The coacervate created by mixing micelles and tannic acid behaved as a solid due to the solid components of PLA and exhibited modulus of elasticity improved a thousand times over PEG, allowing it to withstand much greater strength as an adhesive.

In addition, the research team noticed that the mechanical properties of the material could be improved by more than a hundred times through the heating and cooling process used to heat treat metals. They also found that this is due to a coercive interaction between the micelle and tannic acid arrays.

The research team used the fact that the material has minimal skin irritation and breaks down well in the body to demonstrate its possible use as an adhesive for hair transplants through an animal experiment. Professor Heshin Li, who has pioneered a variety of applications including medical adhesives, hemostatic agents and anti-brown shampoo, has focused on the adhesive power and low toxicity of polyphenols such as tannic acid, which he now hopes will improve the limitations of current hair transplant techniques , which still involve follicle transfer and are difficult to replicate

The study was published online Aug. 22 in the journal JACS Au entitled “Biodegradable Block Copolymer Tannic Acid”.