Supramolecular metal-phenolic foams with monodisperse microstructure

Monodisperse foams are desirable in applications that require structural control, for example, in biomedical scaffolds, catalysis, insulative and acoustic materials. This study presents a novel approach for the fabrication of self-supporting metal-phenolic network (MPN) foams produced with a microfluidic flow-focusing system. For this purpose, tannic acid (TA) and titanium ions (Ti 4+ ) were used to generate stable, monodisperse liquid foams, which were subsequently dried in ambient condition resulting in solid foams. We investigated the effects of gas pressure and Ti 4+ concentration on foam formation. Rheological analysis confirmed an increase in viscosity with Ti 4+ addition, with an upper threshold at n Ti/ n TA = 0.4, beyond which fast gelation hindered microfluidic processing. The bubble size of the liquid foam templates ranged from 200 to 310 μm in diameter, depending on the gas pressure (100–200 mbar) and Ti 4+ concentration. After ambient drying we obtained open-cell solid foams with pore sizes approximately twice the initial bubble diameter, attributed to gas uptake during drying. Uniaxial compression testing showed a negative correlation between pore size and mechanical strength, with ultimate compressive strength values ranging from 5 to 25 kPa. The strongest foams were obtained at n Ti/ n TA = 0.3, balancing crosslinking density and structural integrity. Our proposed green approach provides a platform for morphological control of functional MPN foams, opening their potential for sustainable, cell seeding scaffolds, drug delivery or catalysis, among other.