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Microcapsules Gain a New Power - Scavenging Reactive Oxygen Species


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Current natural and synthetic antioxidants lack biocompatibility and bioavailability, and they are chemically unstable. This means they have a limited capability to scavenge reactive oxygen species. The new microcapsules do not show these limitations, and they may provide a way to locally modulate oxidative stress.

Kharlampieva and colleagues describe the construction and properties of these new microcapsules in the paper “Manganoporphyrin-polyphenol multilayer capsules as radical and ROS scavengers,” published in Chemistry of Materials, a publication of the American Chemical Society.

The researchers have previous experience making and testing biocompatible microcapsules with alternating layers of tannic acid and poly(N-vinylpyrrolidone), or TA/PVPON. The layers are formed around a sacrificial core, such as solid silica, that is dissolved after the layers are complete.

Tannic acid is a natural antioxidant, and the TA/PVPON microcapsules have some reactive oxygen species-scavenging ability. However, they lose that ability and begin to degrade with prolonged exposure to the oxygen radicals.

So, the team explored adding a metalloporphyrin to the PVPON layer of the TA/PVPON microcapsules. Specifically, they devised a synthesis to covalently attach a manganoporphyrin to the PVPON. The addition of this pendant catalyst created an MnP-PVPON/TA capsule with the following characteristics: 1) the microcapsules synergistically remove reactive oxygen species, including superoxide and hydrogen peroxide, at dramatically increased rates compared to unmodified TA/PVPON microcapsules; 2) the microcapsule does not degrade with long exposure to reactive oxygen species; and 3) the microcapsules are nontoxic to mouse splenocytes.

Furthermore, the manganoporphyrin was stably contained within the microcapsule without release, and researchers showed that both manganoporphyrin and tannic acid were required for the synergistic scavenging of reactive oxygen species. The presence of the manganoporphyrin did not interfere with the alternate-layer construction of the microcapsules, and the MnP-PVPON/TA capsules had increased wettability compared to the PVPON/TA capsule, which may aid microcapsule maintenance in the blood. The microcapsules had five or five and a half bilayers placed around a 4-micrometer silica particle.

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Authors: Aaron Alford & al.