Facile and innovative method for bioglass surface modification: Optimization studies João Henrique Lopes a,1 , Emanuella Maria Barreto Fonseca b , Italo O. Mazali a , Alviclér Magalhães a , Richard Landers c , Celso Aparecido Bertran a, ⁎ ,1 a Institute of Chemistry, University of Campinas – UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil b Laboratory of Bioassays and Signal Transduction, Department of Biochemistry and Tissue Biology, Institute of Biology, University of Campinas, SP 13083-862, Brazil c Institute of Physics Gleb Wataghin, University of Campinas, Campinas 13083-859, Brazil abstract article info Article history: Received 4 July 2016 Received in revised form 10 October 2016 Accepted 13 November 2016 Available online 16 November 2016 In this work it is presented a facile and novel method for modification of bioglass surface based on (Ca molten salt bath 2+ | Na glass + ) ion exchange by immersion in molten salt bath. This method allows changing selectively the chemical composition of a surface layer of glass, creating a new and more reactive bioglass in a shell that sur- rounds the unchanged bulk of the original BG45S5 bioglass (core-shell type system). The modified bioglass con- serves the non-crystalline structure of BG45S5 bioglass and presents a significant increase of surface reactivity in comparison with BG45S5. Melt-derived bioactive glasses BG45S5 with the nominal composition of 46.1 mol% SiO 2 , 24.4 mol% Na 2 O, 26.9 mol% CaO, and 2.6 mol% P 2 O 5 have been subjected to ion exchange at 480 °C in molten mixture of Ca(NO 3 ) 2 and NaNO 3 with molar ratio of 70:30 for different time periods ranging from 0 to 60 min. The optimization studies by using XRF and XRD showed that ion exchange time of 30 min is enough to achieve higher changes on the glass surface without alters its non-crystalline structure. The chemical composition, morphology and structure of BG45S5 and bioglass with modified surface were studied by using several analytical techniques. FTIR and O 1s XPS results showed that the modification of glass surface favors the formation of Si-O NBO groups at the expense of Si \\ O BO \\ Si bonds. 29 Si MAS-NMR studies showed that the connectivity of Si Q n species decreases from cross-linked Si Q 3 units to chain-like Si Q 2 units and finally to depolymerized Si Q 1 and Si Q 0 units after ion ex- change. This result is consistent with the chemical model based on the enrichment with calcium ions of the bioglass surface such that the excess of positive charges is balanced by depolymerization of silicate network. The pH changes in the early steps of reaction of bioactive glasses BG45S5 and BG45Ca30, in deionized water or solutions buffered with HEPES were investigated. BG45Ca30 bioactive glass exhibited a significant increase in the pH during the early steps of the reaction compared to BG45S5. © 2016 Published by Elsevier B.V. Keywords: 45S5 bioglass Bioactivity Ion exchange Calcium ion Silicate glass Surface modification 1. Introduction The evolution of the biomaterials science over the years experienced a breakthrough in the late 60's, which represented a paradigm shift with the genesis of a new biomaterial class defined as being bioactive [1–4]. The bioactivity was first observed for the bioactive glasses, specifically 45S5 Bioglass® composition, which showed the ability of combine with both soft and hard tissues through the formation of a strong inter- facial bond between the glass and the surrounding living tissues by means of the development of an apatite phase [1,2,5–8]. Consequently, bioactive glasses have attracted increasing interest during the past few decades, in particular, in the field of development and study of new glass compositions [1,5], as well as devices potentially suitable for med- ical purposes, such as bone graft substitute in various clinical applica- tions [9]. The physicochemical reactions occurring at the surface of bioactive glasses have been exhaustively discussed by several articles in recent decades [10–13]. In general, most of the work has been limited to study the ability of certain compositions to form the apatite layer, disregarding an understanding of kinetic factors that can be decisive and highly needed to support further progress in this field. The reactivity and bioactivity of surface-active glass are commonly described in terms of their composition and connectivity network, i.e., crosslink density of the glass matrix [14]. It is widely recognized that glasses composition containing large amounts of sodium and calcium modifier cations leads to high concentration of nonbridging oxygen (NBO), and thus decreasing the bioglass connectivity network [6,15,16]. Glasses characterized by a highly fragmented network definitely re- acts faster in a physiological aqueous environment owing to favorable Materials Science and Engineering C 72 (2017) 86–97 ⁎ Corresponding author. E-mail addresses: henriquelopez@gmail.com (J.H. Lopes), emanuella.fonseca@gmail.com (E.M.B. Fonseca), mazali@iqm.unicamp.br (I.O. Mazali), alvicler@uol.com.br (A. Magalhães), landers@ifi.unicamp.br (R. Landers), bertran@iqm.unicamp.br (C.A. Bertran). 1 These authors contributed equally. http://dx.doi.org/10.1016/j.msec.2016.11.044 0928-4931/© 2016 Published by Elsevier B.V. Contents lists available at ScienceDirect Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec