Bio-inspired and sustainable approaches in cultural heritage conservation: chitosan-based nanoparticles for archaeological wood preservation

The development of bio-inspired and sustainable products is becoming a central topic in cultural heritage conservation. Biopolymers and bio-based polymers are among the most studied products, which have proven to be useful and reliable alternatives to non-green consolidants, protectives and biocides, commonly used in restoration [1]. Among them, chitosan, a polysaccharide resulting from the deacetylation of chitin, is attracting the attention of researchers for its non-toxicity, biocompatibility, biodegradability and its biocidal properties. Chitosan has already been tested as a consolidant on archaeological wood, and the results obtained are very interesting [2], both for the effectiveness of the treatment and for the reduced side effects compared to products currently used. Another remarkable characteristic of chitosan consists in its ability in forming nanoparticles (NPs) via ionic gelation, a straightforward and harmless process that involves the electrostatic interactions between the positively charged -NH3+ groups of chitosan an the negatively charged groups of an anionic crosslinker, typically sodium tripolyphosphate (TPP) [3]. Such NPs can be loaded and functionalized with different substances, included essential oils and their main components; the latter already demonstrated to be valid substitutes for chemical biocides in numerous studies [4]. In this perspective, this research is aimed to synthesize chitosan NPs loaded with R-(+)-pulegone (ChNPs-Pu), a selected component from C. nepeta essential oil [5], as a consolidant and biocidal product to preserve archeological wood, —a material particularly prone to mechanical and biological deterioration. The synthesis of ChNPs involved adjustments to the experimental setup to optimize particle size, zeta potential, and loading capacity, thus enhancing system performance. Analytical characterization of ChNPs-Pu encompassed techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS). Subsequently, the efficacy of ChNPs-Pu against Aspergillus niger, a fungus responsible for soft-rot disease, was assessed both in vitro and on biocolonized wooden samples, revealing promising outcomes. The research is ongoing, with further investigation focused on evaluating the consolidating effects of ChNPs-Pu on archaeological wooden samples through non-invasive and non-destructive methods, utilizing portable nuclear magnetic resonance (NMR) measurements. [1] M.R. Caruso et al., J Mater Sci 58(32), 2023, 12954–12975. [2] J.M.K. Wakefield et al., EBJ 49(8), 2020, 781-789. [3] L. Keawchaoon, R. Yoksan, Colloids Surf. B, 84(1), 2011,163-171. [4] C. Genova et al, Coatings, 10 (3), 2020, 295. [5] M. Božovic, R. Ragno, Molecules, 22(2), 2017, 290.