Green synthesis of zinc oxide nanoparticles using Ilex paraguariensis leaves for application in antimicrobial polyelectrolyte biomaterials

Abstract

This research aims to develop and characterize antimicrobial polymer biomaterials containing zinc oxide nanoparticles (ZnONPs) obtained using Ilex paraguariensis (IP) leaf extract by green synthesis. The biomaterials were investigated for biomedical device coating and tissue regeneration applications, considering that infections are one of the major complications in this field. The biomaterials were synthesized using the polyelectrolytes polyallylamine hydrochloride (PAH) and polyacrylic acid (PAA) and characterized according to their morphology, composition, and antimicrobial activity. The green synthesis of ZnONPs was optimized by evaluating the influence of ethanolic and aqueous plant extract and the zinc source on the morphological properties of the nanomaterial. Overall, ZnONPs exhibited hexagonal crystalline structure while the size and shape varied depending on the extract and zinc salt used. The most uniform and smallest ZnONPs were obtained using ethanolic extract and zinc nitrate, being spherical in shape and with a diameter of ̴18nm. An investigation of the mechanism route for the green synthesis indicated that the formation of ZnONPs occurred due to the complexation of Zn(II) ions by antioxidants compounds present in the IP extract and further thermal degradation of the complexes. Cytotoxic analysis showed that L929 cell viability decreased in a dose dependent manner for all ZnONPs samples. However, the nanomaterial with reduced size and uniform shape exhibited no cytotoxic effects up to a concentration of 10 μg mL-1 and was chosen to be incorporated in the polymeric biomaterials. Gram-positive bacteria were more vulnerable to the ZnONPs than Gram-negative, presenting a minimum inhibitory concentration of 45 μg mL-1 , while the Gram-negative bacteria showed only 10% inhibition at the same concentration. The thin films were characterized according to their morphology, ZnONPs content, and antimicrobial activity. The film composition was found to be dependent on the PAH pH and the IP concentration, where a more basic pH and lower IP extract concentration resulted in higher adsorption of ZnONPs, following a linear mathematical model. The thin films displayed no significant antimicrobial inhibition; however, many possibilities were addressed for this outcome. Conversely, the electrospun fibres containing ZnONPs presented a high antimicrobial activity against both S. aureus and E. coli bacteria strains, which is related to a higher content of ZnONPs. Also, morphological analysis of the fibre scaffold showed a three-dimensional structure formed by uniform fibres with a 230 nm diameter that mimics the extracellular matrix of natural tissue. Thus, ZnONPs were successfully synthesized using a green synthesis route and incorporated in two different biomaterials. While further studies need to be performed for the development of the thin film, the electrospun fibres showed promising properties for wound dressing applications,