title: Facile and innovative method for bioglass surface modification: Optimization studies.
abstract: In this work it is presented a facile and novel method for modification of bioglass surface based on (Camolten salt bath2+|Naglass+) 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 surrounds the unchanged bulk of the original BG45S5 bioglass (core-shell type system). The modified bioglass conserves 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 46.1mol% SiO2, 24.4mol% Na2O, 26.9mol% CaO, and 2.6mol% P2O5have been subjected to ion exchange at 480°C in molten mixture of Ca(NO3)2and NaNO3with molar ratio of 70:30 for different time periods ranging from 0 to 60min. The optimization studies by using XRF and XRD showed that ion exchange time of 30min 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 O1sXPS results showed that the modification of glass surface favors the formation of Si-ONBOgroups at the expense of SiOBOSi bonds.29Si MAS-NMR studies showed that the connectivity ofSiQnspecies decreases from cross-linkedSiQ3units to chain-likeSiQ2units and finally to depolymerizedSiQ1andSiQ0units after ion exchange. 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.
authors.affiliation: Institute of Chemistry, University of Campinas - UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil. Electronic address: henriquelopez@gmail.com.
authors.forename: João Henrique
authors.initials: JH
authors.lastname: Lopes
authors.affiliation: Laboratory of Bioassays and Signal Transduction, Department of Biochemistry and Tissue Biology, Institute of Biology, University of Campinas, SP 13083-862, Brazil. Electronic address: emanuella.fonseca@gmail.com.
authors.forename: Emanuella Maria Barreto
authors.initials: EMB
authors.lastname: Fonseca
authors.affiliation: Institute of Chemistry, University of Campinas - UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil. Electronic address: mazali@iqm.unicamp.br.
authors.forename: Italo O
authors.initials: IO
authors.lastname: Mazali
authors.affiliation: Institute of Chemistry, University of Campinas - UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil. Electronic address: alvicler@uol.com.br.
authors.forename: Alviclér
authors.initials: A
authors.lastname: Magalhães
authors.affiliation: Institute of Physics Gleb Wataghin, University of Campinas, Campinas 13083-859, Brazil. Electronic address: landers@ifi.unicamp.br.
authors.forename: Richard
authors.initials: R
authors.lastname: Landers
authors.affiliation: Institute of Chemistry, University of Campinas - UNICAMP, P.O. Box 6154, 13083-970 Campinas, SP, Brazil. Electronic address: bertran@iqm.unicamp.br.
authors.forename: Celso Aparecido
authors.initials: CA
authors.lastname: Bertran
mesh_terms: D002118:Calcium / Q000737:chemistry; D002152:Calorimetry, Differential Scanning; D002516:Ceramics / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D018625:Microscopy, Atomic Force; D056951:Photoelectron Spectroscopy; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties
chemical_list: C022107:Bioglass; D002118:Calcium
keywords: 45S5 bioglass; Bioactivity; Calcium ion; Ion exchange; Silicate glass; Surface modification