Citation: Arkas, M.; Bompotis, T.; Giannakopoulos, K.; Favvas, E.P.; Arvanitopoulou, M.; Arvanitopoulos, K.; Arvanitopoulos, L.; Kythreoti, G.; Vardavoulias, M.; Giannakoudakis, D.A.; et al. Hybrid Silica Xerogel and Titania/Silica Xerogel Dispersions Reinforcing Hydrophilicity and Antimicrobial Resistance of Leathers. Gels 2023, 9, 685. https://doi.org/ 10.3390/gels9090685 Academic Editors: Francesco Caridi, Giuseppe Paladini and Andrea Fiorati Received: 23 July 2023 Revised: 19 August 2023 Accepted: 21 August 2023 Published: 25 August 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). gels Article Hybrid Silica Xerogel and Titania/Silica Xerogel Dispersions Reinforcing Hydrophilicity and Antimicrobial Resistance of Leathers Michael Arkas 1, * , Theofanis Bompotis 1 , Konstantinos Giannakopoulos 1 , Evangelos P. Favvas 1 , Marina Arvanitopoulou 1 , Konstantinos Arvanitopoulos 2 , Labros Arvanitopoulos 2 , Georgia Kythreoti 3,4 , Michail Vardavoulias 5 , Dimitrios A. Giannakoudakis 6 , Laura Castellsagués 7 and Sara Maria Soto González 7,8 1 Institute of Nanoscience Nanotechnology, NCSR “Demokritos”, Patriarchou Gregoriou Street, 15310 Athens, Greece; fanisbobotis@gmail.com (T.B.); k.giannakopoulos@inn.demokritos.gr (K.G.); e.favvas@inn.demokritos.gr (E.P.F.); marinaarva3@gmail.com (M.A.) 2 DARVICHEM Alexandrou, Papagou 5, 18233 Agios Ioannis Rentis, Greece; darvichem@hol.gr (K.A.); info@darvichem.gr (L.A.) 3 Institute of Bioscience and Applications, NCSR “Demokritos”, Patriarchou Gregoriou Street, 15310 Athens, Greece; gkythreoti@acg.edu 4 Department of Science and Mathematics, School of Liberal Arts and Sciences, The American College of Greece, Deree, Gravias 6, 15342 Athens, Greece 5 PYROGENESIS S.A., Technological Park 1, Athinon Avenue, 19500 Attica, Greece; mvardavoulias@pyrogenesis-sa.gr 6 Department Chemistry, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece; dagchem@gmail.com 7 Barcelona Institute for Global Health (ISGlobal), Universitat de Barcelona, 08036 Barcelona, Spain; laura.castellsagues@isglobal.org (L.C.); sara.soto@isglobal.org (S.M.S.G.) 8 CIBER Enfermedades Infecciosas (CIBERINFEC), Instituto de Salud Carlos III, 28029 Madrid, Spain * Correspondence: m.arkas@inn.demokritos.gr; Tel.: +30-210-6503669 Abstract: Four leather substrates from different animals were treated by dispersions containing hydrophilic composite silica-hyperbranched poly(ethylene imine) xerogels. Antimicrobial activity was introduced by incorporating silver nanoparticles and/or benzalkonium chloride. The gel pre- cursor solutions were also infused before gelation to titanium oxide powders typically employed for induction of self-cleaning properties. The dispersions from these biomimetically premade xe- rogels integrate environmentally friendly materials with short coating times. Scanning electron microscopy (SEM) provided information on the powder distribution onto the leathers. Substrate and coating composition were estimated by infrared spectroscopy (IR) and energy-dispersive X-ray spectroscopy (EDS). Surface hydrophilicity and water permeability were assessed by water-contact angle experiments. The diffusion of the leather’s initial components and xerogel additives into the water were measured by Ultraviolet-Visible (UV-Vis) spectroscopy. Protection against GRAM- bacteria was tested for Escherichia coli, Pseudomonas aeruginosa, and Klebsiella Pneumoniae against GRAM+ bacteria for Staphylococcus aureus and Enterococcus faecalis and against fungi for Candida albicans. Antibiofilm capacity experiments were performed against Staphylococcus aureus, Klebsiella Pneumoniae, Enterococcus faecalis, and Candida albicans. The application of xerogel dispersions proved an adequate and economically feasible alternative to the direct gel formation into the substrate’s pores for the preparation of leathers intended for medical uses. Keywords: titanium oxide; antibacterial; antifungal; antibiofilm; hyperbranched; dendrimers; polyethylene imine; IR spectroscopy; contact angle; electron dispersion spectroscopy 1. Introduction The hides of killed animals were the obvious and abundant raw material used by humanoids for protection against cold and other adverse environmental challenges. As Gels 2023, 9, 685. https://doi.org/10.3390/gels9090685 https://www.mdpi.com/journal/gels