MOFs, carbon, composite, drug delivery, antibiotics, amoxicillin

Amoxicillin, a widely used β-lactam antibiotic, exerts its bactericidal effect by inhibiting bacterial cell membrane synthesis through binding to penicillin-binding proteins (PBPs), thereby preventing bacterial proliferation, as observed with other penicillin-type antibiotics [1]. Although it is typically administered orally in tablet form, research has revealed that amoxicillin is chemically unstable in acidic environments [2], which compromises its therapeutic efficacy in the gastric milieu. To overcome this limitation, drug delivery systems capable of protecting the active compound during transit through the stomach are essential. In recent years, targeted drug delivery systems have gained significant attention as a highly promising strategy in modern healthcare. This approach enables the transport of therapeutic agents directly to specific sites within the body, maintaining the drug in its active form and at optimal concentrations while minimizing release outside the intended area of action [3]. A variety of materials, including organic polymers and inorganic porous structures, have been explored as potential biocompatible carriers. Despite their advantages, these systems often face challenges such as limited drugloading capacity and insufficient control over the release profile [4]. This study explores the application of composite systems based on hierarchically porous carbon monoliths (HPCM) integrated with metal-organic frameworks (MOFs), specifically UiO-66 and UiO-66-NH₂, as potential carriers for amoxicillin. The composites were synthesized using an in-situ technique, allowing MOF crystals to form directly within the pore structure of the carbon monolith during synthesis. The materials were characterized by several methods including scanning electron microscopy (SEM) as can be seen in Figure 1 (A, B). From these images, it can be seen that the MOF present on the surface of the carbon is situated in the form of microcrystals covering the entire surface of the carbon. From the pictures it can be seen that the types of MOFs are slightly different, while UiO-66-NH2 smoothly follows the surface of the carbon, UiO-66 also fills the pores of the carbon. Sorption and then release of amoxicillin was performed on the prepared composites at 37 °C and 42 °C and 2 different pHs: pH - 2, simulating the gastric fluid environment, and pH - 7-8, indicating the intravenous fluid/small intestine medium. The amount of amoxicillin released was determined at time intervals of 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 5, 6 and 24 hours and analysed by UV spectroscopy. The amount of drug released was determined using a calibration line. The measured data show that at pH - 2, there is a slow and continuous release of the drug from the composites. At the same time, it can be observed that at this pH the amount of drug released from the composites was much lower, approximately 20%, at both measured temperatures compared to the pure MOF materials, from which almost 100% of the drug was released in the acidic environment, while the drug is unstable in the acidic environment and loses its effect. At pH - 7-8, i.e., in a small intestine mimicking environment, the trend remains the same, with the drug released continuously, with the amount of drug released remaining around 20% for the composites, but decreasing to 20-50% for the pure MOF materials. These results suggest that the composite materials, due to their unique structural and chemical properties, have the ability to retain amoxicillin when transported through the acidic environment of gastric fluids, thereby increasing its stability and efficacy in the intestine compared to pure MOF materials. This study also focuses on the potential to increase the amount of drug released from the composites in the gut environment, which is the main site of absorption and subsequent action of the drug in the body.