Melanin is a natural polymeric biomaterial found in microorganisms, animals, and plants. Melanin has a diverse range of functionalities, including but not limited to UV radiation protection in human skin, structural coloration in bird feathers, and material strength enhancement in fungi. Many structural features account for melanin’s ubiquitous nature. Notably, melanin has strong intermolecular hydrogen-bonding, pi-pi stacking, and covalent interactions, which allow it to bind to and adsorb organic molecules. Melanin produced in certain animals has been demonstrated to adsorb harmful or toxic small molecules and metals to protect against environmental pollutants, as in turtleheaded seasnakes and British peppered moths, Biston betularia, or prevent self-poisoning, as in butter clams. Despite its advantageous adsorption capabilities, no natural porous melanins are known. The structural properties of melanin coupled with its adsorption capabilities makes synthetic porous melanin an alluring candidate for the remediation of chemical warfare agents.
Motivated by its potential for chemical warfare remediation, porous versions of melanin were synthesized to enhance melanin’s natural adsorbent and structural properties. The most commonly used melanin mimic is derived from a dopamine monomer, which is oxidatively polymerized to form polydopamine (PDA). Utilizing a templation strategy, micro- and mesoporosity were easily introduced into PDA nanoparticles using a sacrificial mesoporous silica template. The resulting synthetic porous melanin (SPM) nanoparticles had the highest measured surface area of any known polydopamine-based material. The prepared SPM was effective for the uptake of various gases, with the material exhibiting high selectivity for CO₂ over CH₄, and high potential for ammonia capture. Additionally, SPM had high adsorption capabilities for chemical warfare agent (CWA) simulants both in solution and when coated on fabric. These versatile biomimetic nanomaterials could be used to combat the threat of chemical warfare agents by adsorbing and degrading CWAs.

<b>Figure 1.</b> Templated synthesis of synthetic porous melanin (SPM).

Figure 1. Templated synthesis of synthetic porous melanin (SPM).

Dr. Brandy Johnson

Director (Acting), Center for Bio/Molecular Science &amp; Engineering, US Naval Research Laboratory

Appearances

Director (Acting), Center for Bio/Molecular Science & Engineering, US Naval Research Laboratory