Metal-Imidazolate Cages as Porous Ionic Liquids: A Nitric Oxide Delivery Therapeutic Platform for Burn Wound Healing

Porous liquids (PLs) are a unique class of materials that combine intrinsic permanent porosity with fluidity, yet their synthesis remains challenging due to cost, sustainability, and scalability. In this work, two poly(ethylene glycol)-functionalized rhombic dodecahedral tetradecanuclear metal-imidazolate cages (denoted as 1 and 2) are reported, modified with diethylene glycol (PEG₂) and triethylene glycol (PEG₃) chains, respectively. Both cages are liquids at room temperature and are obtained via subcomponent self-assembly of 4-methyl-5-imidazolecarboxaldehyde, Ni²⁺, and NH₂-PEG₂ or NH₂-PEG₃. Both ionic PLs demonstrate higher nitric oxide (NO) adsorption capacities than their solid-state counterparts, with 1 showing the highest performance, capturing approximately eight NO molecules per cage. Upon aqueous stimulation, the cages rapidly release NO, effectively killing Escherichia coli and Staphylococcus aureus. To achieve sustained NO release, cage 1 is incorporated into a sodium alginate (SA) hydrogel composite (1@SA), which exhibits prolonged antibacterial activity while promoting angiogenesis and modulating inflammation in vitro. NO-loaded hydrogel films (NO@1@SA) are fabricated, demonstrating accelerated burn wound healing through slow NO release, which enhances angiogenesis while providing anti-inflammatory and antibacterial effects. This work not only demonstrates the high potential of metal-imidazolate cage-based PLs as exogenous NO delivery platforms but also paves the way for biomedical applications of porous liquids.