Polymer 191 (2020) 122283 Available online 15 February 2020 0032-3861/© 2020 Elsevier Ltd. All rights reserved. Fractal analysis of the formation process and morphologies of hyaluronan/ chitosan nanoflms in layer-by-layer assembly J. Hernandez-Montelongo a, b, * , V.F. Nascimento c , R. Hern� andez-Montelongo d , M.M. Beppu c , M. A. Cotta a a Departamento de Física Aplicada, Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, 13083-859, Campinas, SP, Brazil b Núcleo de Investigaci� on en Bioproductos y Materiales Avanzados, Facultad de Ingeniería, Universidad Cat� olica de Temuco, 4813302, Temuco, La Araucanía, Chile c Faculdade de Engenharia Química, Universidade Estadual de Campinas, 13083-852, Campinas, SP, Brazil d Departamento de Electr� onica, Centro Universitario de Ciencias Exactas e Ingenierías, Universidad de Guadalajara, 44430, Guadalajara, Jalisco, Mexico A R T I C L E INFO Keywords: Fractal analysis Hyaluronan/chitosan nanoflms Layer-by-layer ABSTRACT In the last decade, hyaluronan (HA, polyanion) and chitosan (CHI, polycation) biopolymers have been assembled by layer-by-layer (LbL) for the synthesis of antibacterial coatings. As electrostatic interactions are the main driving force for the formation of LbL flms, pH and ionic strength (IS) are important critical variables of syn- thesis. In this context, we used surface fractal analysis of HA/CHI flms to characterize the growth process for different bilayers obtained with two pH (5 and 3) and IS values (0 and 0.1 M NaCl). Our results showed that the HA/CHI assembling is mainly affected by changes in the pH than IS. Fractal dimension (D f ) of pH 5 series presented values ~2.2, indicating that irregularities from the initial random adsorption process are minimized. However, when pH decreased to 3, D f increases up to ~2.5, suggesting a transition to diffusion-limited aggregation. 1. Introduction Research and development of smart nanostructured materials gov- erned by their surface properties is a rapidly growing feld [1]. Layer-by-layer (LbL) assembly is a simple bottom-up technique to modify surfaces, synthesize nanocomposites and thin flms of different materials [2,3]. This method consists of alternating physisorption of oppositely charged polyelectrolytes, whereby electrostatic is one of the most critical interactions between molecules [4]. Due to its simplicity, cost-effectivity and versatility to tailor the physicochemical properties and structure of several materials [2,3], the LbL technique has been used in a wide range of applications such as adhesives [5,6], separation [7,8], catalysis [9,10], sensing [11,12], food industry [13], bioelectronics [14, 15], drug delivery [16,17], biomineralization [18,19], cell adhesion [20,21], tissue engineering [22,23], blood vessel models [24], and many others. Notably, in the last decade, hyaluronan (HA, a polyanion) and chi- tosan (CHI, a polycation), two biocompatible and biodegradable poly- electrolytes, have been assembled by LbL for the synthesis of antibacterial coatings: HA provides compression strength and lubrica- tion, whereas CHI presents the antimicrobial properties. Most of the representative works were performed by Richert et al. these authors characterized HA/CHI flms, which reduced the population of E. coli bacteria by 80% after 30 min of culture [20]; Chua et al. functionalized Ti with HA/CHI flms and immobilized RGD peptides on the surface, obtaining a 80% reduction of S. aureus after 4 h of culture [25]; Cui et al. synthetized HA/CHI microcapsules and could reduce by around 100% the population of E. coli bacteria after 4 h of incubation [26]; Hernandez-Montelongo et al. showed the antibacterial effect of HA/CHI nanoflms against X. fastidiosa, one of the top 10 plant pathogenic bac- teria in molecular plant pathology, for up to 8 days [27]; Hernandez-Montelongo et al. optimized the synthesis of HA/CHI nanoflms obtaining around 100% reduction of S. aureus after 8 h of culture [28]; and Nascimento et al. studied the infuence of pH and ionic strength on the antibacterial effect of HA/CHI nanoflms against S. aureus, obtaining almost 100% of reduction after 24 h of incubation [29]. In spite of the extensive studies regarding the formation process of * Corresponding author. Departamento de Física Aplicada, Instituto de Física Gleb Wataghin, Universidade Estadual de Campinas, 13083-859, Campinas, SP, Brazil. E-mail address: jacobo.hernandez@uct.cl (J. Hernandez-Montelongo). Contents lists available at ScienceDirect Polymer journal homepage: http://www.elsevier.com/locate/polymer https://doi.org/10.1016/j.polymer.2020.122283 Received 5 December 2019; Received in revised form 1 February 2020; Accepted 12 February 2020