Synthesis and characterization of carboxylic- and amine-grafted FAU zeolites as inorganic fillers to design biocompatible composites

Abstract

Zeolites have been used for decades in industry owing their large surface area, high stability and well-defined crystalline structure. Therefore, numerous synthesis routes have been developed to tune the morphology and the physical chemical properties of the final zeolite. In particular in the biomedical field, zeolites were used as drug carriers, and even as transporters to penetrate directly into the cells. The aim of this study was to develop zeolite-based composites which involved a gelatin matrix covalently bonded to zeolites. Nanosized faujasites (FAU) were synthesized leading to a colloidal suspension prior to mixing with gelatin solutions at different FAU-to-gelatin weight percentages. FAU morphologies and size distribution were investigated by SEM and DLS focusing on the aggregation propensity in response to different pH and ionic strength. Zeolite surfaces were then functionalized to graft either amine, or carboxylic groups, using the well-known 3-(aminopropyl)triethoxysilane (APTES) for amine, and 5-(triethoxysilyl)pentanoic acid (TESPA) for carboxylic groups for the first time. According to these strategies, zeolites were covalently linked to gelatin chains via EDC/NHS coupling widely used in biology. The successful surface functionalization was assessed by ATR-FTIR, XPS, and zeta potential measurements. The resulting composites were found stable under physiological temperature compared to gelatin alone, as confirmed by DSC analysis. Lastly, in order to get a first glimpse of the potential use of these composites in biology, gels were incubated in culture media prior to be poured onto macrophage-derived THP-1 cells, showing good viability. FAU zeolite crystals could therefore be used as fillers to improve thermal properties of gelatin hydrogels, using a novel surface functionalization strategy, being thus promising candidates as scaffolds for tissue engineering, or even wound dressing.