Evaluation of the Antimicrobial Protection of Pharmaceutical Kaolin and Talc Modified with Copper and Zinc

Abstract

Six pharmaceutical pastes were prepared using chemically modified kaolin and talc powders. Tests were conducted to determine their structural and chemical characteristics as well as their antimicrobial protection, thus rendering them suitable for cosmetic and pharmaceutical uses. Kaolin and talc were treated chemically via the cation exchange method to load the clay particles with copper and zinc ions, two cations well known for their antimicrobial properties. Mineralogical analyses were conducted by using X-ray diffraction (XRD) before and after the modification, confirming the mineralogical purity of the samples. Scanning electron microscopy was also used in conjunction with energy dispersed spectroscopy (SEM-EDS) to obtain chemical mapping images, revealing the dispersion of the added metals upon the clay minerals surfaces. Moreover, chemical analysis has been performed (XRF) to validate the enrichment of the clays with each metal utilizing the cation exchange capacity. All modified samples showed the expected elevated concentration in copper or zinc in comparison to their unmodified versions. From the X-ray photoelectron spectroscopy (XPS), the chemical state of the samples’ surfaces was investigated, revealing the presence of salt compounds and indicating the oxidation state of adsorbed metals. Finally, the resistance of pastes in microbial growth when challenged with bacteria, molds, and yeasts was assessed. The evaluation is based on the European Pharmacopeia (EP) criteria.

The Antimicrobial Properties of Modified Pharmaceutical Bentonite with Zinc and Copper

“…There are several PET Protocols, like the compendial methods of European and U.S. Pharmacopoeia, or ISO 11930. During this study, an alternative PET Protocol has been used, known as mixed Protocol, which is based on the compendial protocols but is more demanding [ 56 ]. The mixed protocol is based on the compendia methods and includes eleven (11) Gram-positive and Gram-negative bacteria, yeast, and molds ( Table 3 ).…”

“…Moreover, this result is corroborated by other authors like Jou et al, (2016) [ 67 ] and Holesova et al, (2013) [ 68 ] which reported that natural clay minerals show no antibacterial effect. Therefore, the antibacterial properties of clay minerals are attributed to coexisting inorganic species such as Zn [ 56 , 69 , 70 ] and Cu ions [ 56 , 71 , 72 , 73 ].…”

“…Moreover, this result is corroborated by other authors like Jou et al, (2016) [67] and Holesova et al, (2013) [68] which reported that natural clay minerals show no antibacterial effect. Therefore, the antibacterial properties of clay minerals are attributed to coexisting inorganic species such as Zn [56,69,70] and Cu ions [56,[71][72][73]. The total count of bacteria, molds, and yeasts starting from the initial inoculation at the predetermined time intervals are summarized in Table 6, while the logarithmic reduction of CFU and the score for each sample according to the relevant criteria are presented in Table 7.…”

“…However, due to the high cost of silver [ 50 , 51 ], its high cytotoxicity [ 52 , 53 , 54 ], and the problem of 'argyria' after continuous use of silver [ 55 ], new metals may be considered. Recently, Cu-loaded kaolinite showed excellent preservation activity against bacteria and adequate population reduction for molds, while Zn-loaded talc demonstrated significant antimicrobial protection on yeasts [ 56 ]. Modified bentonite with metals like zinc or copper, which do not display the above-mentioned negative properties of silver, has not been tested until now for the evaluation of antimicrobial protection in topical use.…”

Τροποποίηση Αργιλικών Ορυκτών Για Χρήση Σε Καλλυντικά Και Φαρμακευτικά Σκευάσματα Τοπικής Χορήγησης

“… 10 1 cfu : μέγιστος αριθμός αποδοχής = 20 Συγκεκριμένα, σχετικά χαμηλές κορυφές που υποδεικνύουν μικρές ποσότητες περίπου 4% (χαμηλές ανακλάσεις), πιθανώς οξειδίων χαλκού και ψευδαργύρου αντίστοιχα. (Martsouka et al, 2021a). Τέλος, οι πειραματικές διαδικασίες με αιθυλενογλυκόλη, επιβεβαίωσαν τα αποτελέσματα των ορυκτολογικών αναλύσεων (Εικόνα 4Β).…”