Researchers from Tokyo University of Science found that the gelation process impacts the properties of hydrogels and their medical applications
Researchers from Tokyo University of Science have found that the properties of hydrogels change depending on the rate at which carbon dioxide (CO₂) is released after gelation.
Hydrogels are soft materials made of water-filled, crosslinked polymer networks that are particularly useful for medical applications such as wound dressings and organ regeneration. Gelation is the process through which hydrogels are formed.
“The degree of crosslinking in hydrogels is typically controlled by 'pre-gelation parameters,' such as polymer and crosslinker concentrations, said study leaders professor Hidenori Otsuka and Mr Ryota Teshima of Tokyo University of Science.
“However, we demonstrate that the crosslinking degree of hydrogels prepared using carbon dioxide as the acidic agent is also influenced by post-gelation conditions.”
During gelation, biopolymers, such as polysaccharides and proteins often require the addition of acidic agents. However, these agents can remain behind in the hydrogel, which is risky for biological applications. This is why a new method uses CO₂ that escapes into the atmosphere once the gel is formed.
To test the impact of CO₂ release on hydrogel properties, researchers first synthesised hydrogels called alg-gels from alginate, a polymer derived from brown seaweed. They then mixed alginate with calcium carbonate (CaCO₃) and added carbonated water to create a porous hydrogel where alginate chains were crosslinked by calcium ions.
Researchers controlled the rate at which CO₂ was released across two samples. One incubated in a Petri dish where only the top surface was exposed to the air, while the other was on a wire mesh, exposing the entire surface.
The rate of CO₂ release was monitored using bromothymol blue (BTB), a pH indicator that changes colour with the level of acidity. Yellow indicates acidic conditions, green is neutral and blue indicates alkaline conditions. The faster CO₂ is released, the faster the gel turns blue.
The gel in the Petri dish became blue after five hours, while the gel on the wire mesh only took 40 minutes to turn blue, showing that the release of CO₂ was much quicker with more exposure to the air.
The rapid release of CO₂ after gel formation prevented the calcium carbonate from completely dissolving, leaving fewer calcium ions to link the polymer chains.
When both samples underwent a compression test, the stiffness, breaking stress and energy required to break the disks were higher for the gel from the Petri dish.
The significance of these findings lies in the use of hydrogel as a medical tool to encourage wound healing and organ regeneration.
Researchers now know that the way hydrogel is made can impact its effectiveness in these areas, with the rapid release of CO₂ posing more risks due to the increased pH levels and decreased crosslinking.
