Biocompatible Adhesive Applicable in Hair Transplantation

Biocompatible Adhesive Applicable to Hair Transplantation Medical adhesives are materials applicable to various fields such as wound healing, hemostasis, vascular anastomosis and tissue engineering. These adhesives are expected to make significant contributions to the development of minimally invasive surgery and organ transplantation. However, adhesives that possess high adhesive strength and low toxicity while simultaneously being degradable in the body are rare. Adhesives based on natural proteins such as fibrin and collagen have high biocompatibility but insufficient adhesive strength. Synthetic polymer adhesives based on urethane or acrylic, conversely, have greater adhesive strength but degrade poorly and can cause inflammatory reactions in the body. A collaborative research team led by Professor Myungeun Seo and Professor Haeshin Lee from the KAIST Chemistry Department developed an environmentally friendly adhesive from biocompatible polymers using tannic acid, the source of astringency in wine. The research team focused on tannic acid, a natural polyphenolic product. Tannic acid is a polyphenol found in large quantities in fruit peels, nuts and cocoa. It has high affinity and coating capability on other materials, and when tannic acid adheres to the surface of our tongue, we perceive the astringent taste in wine. When tannic acid is mixed with hydrophilic polymers, it forms coacervates or droplets of sinking gel-like liquids. If the polymers used are biocompatible, the mixture can be applied as a medical adhesive with low toxicity. However, coacervates are fundamentally fluid-like and cannot withstand large forces, which limits their adhesive properties. For this reason, although research into their use as adhesives is actively discussed, a biodegradable material exhibiting strong adhesion due to high shear strength has not yet been developed. The research team found a way to increase adhesion by mixing two biocompatible FDA-approved polymers, polyethylene glycol (PEG) and polylactic acid (PLA). PEG (commonly used in eye drops and creams) is hydrophilic, while PLA (a well-known bioplastic derived from lactic acid) is water-insoluble. By combining these two in a block copolymer, the team created hydrophilic PLA aggregates in water surrounded by PEG blocks. The coacervate formed by mixing micelles and tannic acid exhibited solid behavior due to the rigid PEG components and showed a thousand-fold improved elastic modulus compared to PEG, allowing it to demonstrate far greater resistance to force as an adhesive. The research team also observed that the material's mechanical properties could be improved more than a hundredfold through a heating and cooling process used to heat-treat metals. They also discovered that this resulted from forced interactions between the micelle and tannic acid sequences. Using the properties of minimal skin irritation and good degradation in the body, the research team demonstrated through animal experiments that the material could be used as an adhesive in hair transplantation. Professor Haeshin Lee, who pioneered various application areas such as medical adhesives, hemostatic agents and darkening shampoos, focused on the adhesive capacities and low toxicity of polyphenols such as tannic acid and eagerly anticipates improving the limitations imposed by current hair transplantation methods involving follicle transfer and difficult to replicate. The research was published online in the JACS Au journal under the title "Biodegradable Block Copolymer-Tannic Acid Glue." Academic Reference: Jongmin Park et al, Biodegradable Block Copolymer–Tannic Acid Glue, JACS Au (2022). DOI: 10.1021/jacsau.2c00241   Source