ИСТИНА

New composite biopolymer-based aerogels have been synthesized from cellulose and chitosan and ultrafine CeO2 and WO3 nanoparticles. Sol-gel synthesis of hydrogels was followed by solvent exchange and drying in supercritical CO2. Obtained aerogels have high surface areas (200-260 m2/g) and low geometric densities (0.05–0.005 g/cm3). The aerogels containing WO3 exhibited reversible photochromism. UV-irradiation causes coloration of the aerogels, storage of the samples in air leads to de-coloration. One of the highly important challenges of modern medicine and chemistry is development of functional wound dressing materials with wound healing and antimicrobial properties. Currently, different metal and metal oxide nanoparticles are used as components of biopolymer-based composites for wound dressing [1]. The crucial advantage of inorganic nanoparticles is their activity against antibiotic-resistant bacteria. CeO2 and WO3 have low toxicity to human cells and provide anti-inflammatory, antibacterial and antioxidant effects [2, 3]. Biopolymers are convenient precursors for synthesis of composites, because they firmly immobilize inorganic nanoparticles and form bulk materials. In the present work, new bulk composite materials based on biopolymers (cellulose and chitosan) modified with inorganic nanoparticles (CeO2 or WO3) were synthesized. Cellulose and chitosan are non-toxic for human cells. These polymers efficiently stabilize various metal oxide nanoparticles and form flexible transparent films and low-density monolithic aerogels. Obtained bulk composites have potential as materials for biomedicine because of antibacterial properties of CeO2 and WO3. An aqueous sol of ultrafine CeO2 nanoparticles was synthesized by hydrothermal method from ammonium cerium (IV) nitrate ((NH4)2Ce(NO3)6). An aqueous sol of ultrafine WO3 nanoparticles was obtained from sodium tungstate (Na2WO4) on a cation exchange resin. Nanocrystalline cellulose was transformed in carboxylated polyanion form by soft TEMPO-mediated oxidation. The polyanionic cellulose was able to immobilize nanoceria, forming a hydrogel. Cellulose modified with aldehyde groups was obtained by oxidation of nanocrystalline cellulose with sodium periodate. The carbonyl groups of cellulose formed Schiff base with amino groups of chitosan. The crosslinked gel of cellulose and chitosan effectively stabilized WO3 nanoparticles. Drying of hydrogels under ambient conditions resulted in nanocomposite transparent flexible films. Although the films swelled slightly in water, the nanoparticles remained absorbed in the polymer matrices and could not be re-dissolved in water. The hydrogels were transformed to alcogels by solvent exchange and then dried in supercritical CO2. The obtained monolithic aerogels based on cellulose and chitosan modified with CeO2 and WO3 nanoparticles had porous network structure of cellulose nano whiskers. The aerogels had low geometric densities (0.05–0.005 g/cm3) and high surface areas (200–260 m2/g). The films and aerogels modified with tungsten trioxide demonstrated reversible photochromism. UV-irradiation (200-400 nm) of the composites caused blue-coloration as a result of photo-induced reduction of tungsten (W+6 → W+5). Air storage of the composites in dark led to oxidation of tungsten and de-coloration of the samples. All the synthesized materials were studied using different analytical techniques (XRD-analysis, low-temperature nitrogen absorption, thermal analysis, SEM, IR- and UV-vis-spectroscopy). 1. Nethi S. K. et al. Recent advances in inorganic nanomaterials for wound-healing applications. // Biomaterials Science. 2019. V. 7. N. 7. P. 2652–2674. 2. Duan G. et al. Robust Antibacterial Activity of Tungsten Oxide (WO3-x) Nanodots // Chem. Res. Toxicol. 2019. V. 32. N. 7. P. 1357−1366. 3. Shcherbakov A.B. et al. Nanocrystalline ceria based materials - Perspectives for biomedical application // Biophysics. 2011. V. 56. N. 3. P. 987–1004. S.V. Kameneva thanks the Council for Grants of the President of the Russian Federation for the support of the study (No. SP-4398.2021.4). CeO2/cellulose composites were synthesised within the project (19-13-00416) supported by Russian Science Foundation.