In vitro bioactivity evaluation, mechanical properties and microstructural characterization of Na 2 O–CaO–B 2 O 3 –P 2 O 5 glasses Sherief M. Abo-Naf a,⇑ , El-Sayed M. Khalil b , El-Sayed M. El-Sayed c , Hamdia A. Zayed d , Rasha A. Youness b a Glass Research Department, National Research Centre (NRC), El-behoos Str., Dokki, 12622 Cairo, Egypt b Spectroscopy Department, National Research Centre (NRC), El-behoos Str., Dokki, 12622 Cairo, Egypt c Physics Department, Faculty of Science, Ain-Shams University, Cairo, Egypt d Physics Department, Faculty of Girls, Ain-Shams University, Cairo, Egypt highlights  In vitro bioactivity of Ca- borophosphate glasses was tested by soaking in the SBF.  Density, Vickers microhardness and fracture toughness of the glasses were measured.  Nano-HA formation on fine glass grains was analyzed by XRD, FTIR, TEM and ICP-AES.  Formation of HA surface layer on glass bulk slabs was characterized by SEM-EDAX.  Increasing B 2 O 3 content in glass composition enhances the bioactivity of glasses. graphical abstract TEM images of the nano-HA formed on surface of glass grains after soaking in the SBF for 1 month: (a) glass sample B5, (b) B15 and (c) B30. article info Article history: Received 9 October 2014 Received in revised form 28 December 2014 Accepted 18 February 2015 Available online 26 February 2015 Keywords: Bioactive glass In vitro bioactivity XRD FTIR TEM ICP abstract Na 2 O–CaO–B 2 O 3 –P 2 O 5 glasses have been prepared by the melt-quenching method. B 2 O 3 content was sys- tematically increased from 5 to 30 mol%, at the expense of P 2 O 5 , in the chemical composition of these glasses. Density, Vickers microhardness and fracture toughness of the prepared glasses were measured. In vitro bioactivity of the glasses was assessed by soaking in the simulated body fluid (SBF) at 37 ± 0.5 °C for 3, 7, 14 and 30 days. The glasses were tested in the form of glass grains as well as bulk slabs. The struc- ture and composition of the solid reaction products were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). The kinetics of degradation of the glass particles were monitored by measuring the weight loss of the particles and the ionic concentra- tion of Ca, P and B in the SBF solution using inductive coupled plasma-atomic emission spectroscopy (ICP- AES). The obtained results revealed the formation of a bioactive hydroxyapatite (HA) layer, composed of nano-crystallites, on the surface of glass grains after the in vitro assays. The results have been used to understand the formation of HA as a function of glass composition and soaking time in the SBF. It can be pointed out that increasing B 2 O 3 content in glass composition enhances the bioactivity of glasses. The nanometric particle size of the formed HA and in vitro bioactivity of the studied glasses make them possible candidates for tissue engineering application. Ó 2015 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2015.02.076 1386-1425/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +20 2 33335971; fax: +20 2 33370931. E-mail address: sheriefabonaf@yahoo.com (S.M. Abo-Naf). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 144 (2015) 88–98 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa