Controlling barrier penetration via exothermic iron oxidation

Area of Science:

• Materials Science
• Chemical Engineering
• Physical Chemistry

Background:

• Exothermic iron oxidation offers a controllable method for heat generation.
• Understanding the kinetics of heat release is crucial for modulating barrier properties.
• Polymer gels, like carboxymethyl cellulose (CMC), exhibit temperature-dependent water adsorption.

Purpose of the Study:

• To investigate the influence of temperature change kinetics from exothermic iron oxidation on barrier diffusion rates.
• To compare lidocaine transport through a CMC gel under different iron oxidation reaction conditions.
• To elucidate the relationship between temperature-induced structural changes in CMC and drug diffusion.

Main Methods:

• Utilized two rapid iron oxidation reactions initiated by water (ExoRap) and one slower reaction initiated by oxygen (ExoSl).
• Measured maximum temperature (Tmax) and time to maximum temperature (tmax) for each reaction.
• Quantified lidocaine transport through CMC gel using diffusion assays under varying thermal conditions.

Main Results:

• Rapid water-initiated reactions (ExoRap) resulted in significantly higher lidocaine diffusion rates (555.61–663.1 μg/cm²/h) compared to the slower oxygen-initiated reaction (ExoSl, 159.36 μg/cm²/h).
• Despite ExoSl inducing a greater overall temperature change over a longer period, the *kinetics* of temperature increase in ExoRap were more influential on diffusion.
• Lidocaine diffusion correlated strongly with the rate of temperature change, suggesting temperature-induced alterations in CMC structure are key.

Conclusions:

• The kinetics of temperature change, not just the magnitude, critically affects barrier diffusion rates.
• Temperature-induced changes in polymer hydration, specifically CMC's increased water adsorption with moderate temperature rises, are primary determinants of lidocaine transport.
• Controlled exothermic reactions can be leveraged to modulate drug diffusion through polymer-based barriers.