Could wound healing dressings adhere better, and drug delivery patches become more sophisticated? A KAIST research team has developed a technology that leverages natural ingredients derived from plants to increase the strength of seaweed-based hydrogel (a gel material that contains a large amount of water while maintaining its shape) by more than fivefold, while also controlling its adhesiveness and degradation rate.
KAIST announced on June 9th that a research team led by Professor Haeshin Lee from the Department of Chemistry has developed a new material design strategy that utilizes tannic acid—a type of polyphenol, which is a natural antioxidant abundant in tea and fruits—to enhance the mechanical strength and adhesiveness of seaweed-derived hydrogel and to control its degradation rate.
Hydrogel is a high-moisture gel material used in contact lenses, acne patches, mask packs, and wound healing dressings. Because it can adhere closely to the skin while holding drugs or active ingredients, it is being utilized in various bio and healthcare fields, such as drug delivery systems (materials that effectively deliver drugs to desired sites), wound dressings (medical dressings that protect wounds and aid healing), tissue engineering scaffolds (structures that help regenerate artificial tissue), and cosmetic materials.
Among various hydrogel materials, the research team focused on 'κ-Carrageenan'. κ-Carrageenan is a natural polymer extracted from red seaweed (rhodophytes) such as agar-agar, and it is a familiar food ingredient used to increase the viscosity and maintain the shape of jellies and sauces. However, there were limitations to improving the performance of hydrogels made with κ-Carrageenan. The κ-Carrageenan molecule contains many structures called sulfate groups, which create intermolecular repulsion—much like magnets of the same pole pushing each other away—and prevent the formation of a dense structure. For this reason, it was difficult to increase the strength and adhesiveness of the hydrogel or to adjust the degradation rate to a desired level.
To solve this problem, the research team focused on finding a natural substance that could effectively interact with the sulfate groups. As a result, they determined that tannic acid, a natural polyphenol abundant in tea and fruits, could be a promising candidate.
Polyphenols are natural ingredients produced by plants to protect themselves from external environments such as ultraviolet rays or pests, and they have the characteristic of being able to bind with multiple substances simultaneously. In particular, tannic acid has multiple binding sites (galloyl groups), so it was expected to interact strongly with the sulfate groups of κ-Carrageenan and connect the molecules together. The research team believed that this characteristic could be utilized to reinforce the hydrogel structure.
As a result of the study, it was confirmed that the sulfate group, which was previously considered a factor hindering hydrogel formation, actually acts as a core binding site with tannic acid. In other words, the structure that was previously considered a "weakness" played a role in making the hydrogel even firmer upon meeting tannic acid.
In fact, the storage modulus (an index representing the firmness and elasticity of a gel) of the κ-Carrageenan hydrogel with added tannic acid was approximately 1,632 Pa, showing an improvement of more than fivefold compared to the pure κ-Carrageenan hydrogel (approximately 294 Pa). This means that the hydrogel can maintain its shape more stably even under external pressure or deformation, demonstrating that it can increase the durability and usability of wound healing dressings or drug delivery patches.
In addition, the research team confirmed that tannic acid stably reinforces the internal network structure (gel network) of the already formed hydrogel, regardless of the point in time when the tannic acid is added. This implies that tannic acid connects molecules at multiple points, allowing the internal structure of the hydrogel to remain consistently firm.
Notably, the research team succeeded in implementing rapid degradability and strong adhesiveness simultaneously. In experiments simulating the human stomach and intestinal environments, the hydrogel containing tannic acid degraded relatively quickly while adhering strongly to the skin and rough surfaces. This means that wound healing dressings will not easily fall off during use but can naturally degrade after completing their role, and drug delivery patches can be utilized to stably deliver drugs for a desired period.
This study is meaningful in that it presented a design principle capable of simultaneously controlling the strength, adhesiveness, and degradation rate of hydrogel using only food-grade natural ingredients without complex chemical synthesis processes. The research team expects this technology to be utilized in various bio and healthcare fields, such as capsules and coating materials for food and functional foods, skin-adhering cosmetics and skincare products, wound dressings, drug delivery patches, and tissue engineering scaffolds.
Professor Haeshin Lee said, "This study is an example showing that the mechanical strength, adhesiveness, and degradation behavior of hydrogel can be designed together using only naturally derived materials," adding, "It can be expanded into a safer and simpler natural polymer gel platform in the fields of food, cosmetics, and biomaterials."
This study, in which PhD student Han-Yeol Yang participated as the first author, was published on April 21st in 'Biomimetics', an international academic journal in the field of biomimetics. ※ Paper Title: Adhesive κ-Carrageenan Hydrogels by Polyphenol Intervention, DOI: 10.3390/biomimetics11040290
Meanwhile, this research was conducted with research funding support from Polyphenol Factory Inc., a faculty-led startup enterprise of KAIST.