Conversion of marine waste and carbonated water into hydrogels by CO₂ emission behavior

Hydrogels are soft materials made of cross-linked polymer networks filled with water and have a wide range of applications, from wound dressings to enriching soil moisture for plant growth. They are formed through a process called gelation, in which polymers in solution bond with each other to form a gel.

Biopolymers such as polysaccharides and proteins often require the addition of acidic substances for this gelation process. However, these drugs can remain within the hydrogel, potentially posing a risk for biological applications. To address this issue, new gelling methods use carbon dioxide (CO2) instead of acidic substances. CO2 acts as an acidic agent during gelation and escapes into the atmosphere once the hydrogel is formed.

A study led by Professor Hidenori Otsuka and Professor Ryota Teshima from Tokyo University of Science investigated the effect of CO2 release on the properties of hydrogels. Their findings, published in the journal Materials Advances, provide valuable insights for synthesizing hydrogels suitable for medical applications.

“The degree of crosslinking in hydrogels is usually controlled by ‘pre-gelling parameters’ such as the concentration of polymers and crosslinkers. However, the degree of crosslinking in hydrogels prepared using carbon dioxide as the acidic agent is “We have demonstrated that the conditions are met even after gelation,” say Professor Otsuka and Teshima.

The researchers synthesized a hydrogel called Alg gel from alginate, a polymer derived from brown algae. They mixed alginate with calcium carbonate (CaCO3) and added carbonated water, resulting in a porous hydrogel in which alginate chains were cross-linked by calcium ions.

Two samples were prepared to control the CO2 release from Alg gels. One was cultured in a Petri dish with only the top surface exposed to air, and the other was on a wire mesh with the entire surface exposed. The rate of CO2 release was monitored using bromothymol blue (BTB), a pH indicator that changes color depending on acidity (yellow for acidic conditions, green for neutral, and blue for alkaline conditions).

The gel in the Petri dish gradually turned green (neutral) over 60 minutes, indicating slow CO2 release, and turned completely blue after 5 hours. In contrast, the gel on the wire mesh released CO2 much faster, turning completely blue in 40 minutes and releasing all the CO2 in just 90 minutes.

The rapid release of CO2 immediately after gel formation prevents calcium carbonate from completely dissolving into solution, leaving fewer calcium ions available to bind the polymer chains.

“The rapid release of CO2 from the hydrogel after gelation increases the pH of the system and reduces the degree of cross-linking,” explain Professors Otsuka and Teshima.

When both samples were subjected to compression tests, the disk stiffness, fracture stress, and energy required to fracture the disk were higher for the sample cultured in Petri dishes compared to the sample cultured on wire mesh. Ta.

This study improves our understanding of how CO2 release after gel formation affects the degree of crosslinking and mechanical properties of hydrogels, and provides insight into creating hydrogels using CO2 . Additionally, marine waste-derived alginate can be used to convert the waste into high-value hydrogels that can be used for medical applications such as tissue engineering, including wound healing and organ regeneration.