Preparation and Evaluation of Aminomalononitrile-Coated Ca–Sr Metal–Organic Frameworks as Drug Delivery Carriers for Antibacterial Applications

[Image: see text] After orthopedic surgery, antibiotics are usually employed to reduce the risk of infection. If it is possible to enhance antimicrobial functionality and incorporate antimicrobial agents into the bone-filling matrix, not only it can promote bone tissue regeneration, but it can also enable localized administration of medication to elevate antibacterial efficacy. Meanwhile, previous studies have shown that calcium and strontium can support the growth of osteoblastic cells and diminish bone resorption or deterioration. In the past few years, metal–organic frameworks (MOFs) have been widely used as drug carriers owing to their characteristic advantages. In this study, a MOF was prepared in an aqueous solution by a simple coprecipitation method with the organic ligand 1,3,5-tricarboxylic benzene (H(3)BTC) as a linker to form Ca–Sr–MOF. Furthermore, the Ca–Sr–MOF was coated with aminomalononitrile (AMN), which adhered through the electrostatic interactions between H(3)BTC and AMN. With this MOF (Ca–Sr–AMN–MOF), AMN polymerization reactions can occur in aqueous environments, and a polymer layer was observed on the MOF surface with moderate hydrophilicity. The prepared Ca–Sr–MOF and Ca–Sr–AMN–MOF were characterized by Fourier transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and UV–visible spectroscopy. Finally, tetracycline (TC) was selected as the model drug to measure the drug loading efficiency, release profile, and antibiotic activity. The percent cumulative drug release of TC from Ca–Sr–MOF and Ca–Sr–AMN–MOF was 55.15 and 9.1%, respectively. The antibacterial effectiveness of TC-loaded MOF against Gram-negative Escherichia coli bacteria was evaluated, revealing the remarkable antimicrobial performance of these substances.