Intrinsic Antibacterial Borosilicate Glasses for Bone Tissue Engineering Applications Joa ̃ o S. Fernandes,* ,†,‡ Margarida Martins, †,‡ Nuno M. Neves, †,‡ Maria H. V. Fernandes, § Rui L. Reis, †,‡ and Ricardo A. Pires* ,†,‡ † 3B’s Research Group - Biomaterials, Biodegradables and Biomimetics, University of Minho, Headquarters of the European Institute of Excellence on Tissue Engineering and Regenerative Medicine, AvePark-Parque de Ciê ncia e Tecnologia, Zona Industrial da Gandra, 4805-017 Barco GMR, Portugal ‡ ICVS/3B’s - PT Government Associate Laboratory, Braga/Guimarã es, 4710-057 Portugal § Materials and Ceramic Engineering Department, CICECO - Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal ABSTRACT: Three novel borosilicate bioactive glasses (BBGs) were prepared and used to investigate their bioactive and antibacterial properties. The BBGs were prepared by melt-quenching using different glass modifiers, i.e. Mg 2+ , Ca 2+ , and Sr 2+ , and their amorphous nature was confirmed by X-ray diffraction. Scanning electron microscopy with energy dispersive X-ray spectroscopy allowed the visualization of apatite-like structures upon 7 days of immersion in simulated body fluid. BBG-Ca generated surface structures with a Ca/P ratio ≈1.67, while the surface of the BBG-Sr was populated with structures with a Sr/P ratio ≈1.7. Moreover, bacterial tests showed that the BBG-Mg and BBG-Sr glasses (at concentrations of 9, 18, 36, and 72 mg/ mL) present antibacterial characteristics. In particular, BBG-Sr, at concentrations of 9 mg/mL, exhibited bacteriostatic activity against Pseudomonas aeruginosa, and at concentrations ≥18 mg/mL it was able to eradicate this bacterium. These results evidence an antibacterial activity dependent on the BBGs composition, concentration, and bacterial species. Cellular studies showed that the developed BBGs do not present a statistically significant cytotoxic effect against Saos-2 cells after 3 days of culture, showing better performance (in the cases of BBG-Ca and BBG-Sr) than commercial 45S5 Bioglass up to 7 days of culture. Overall, this study demonstrates that BBGs can be effectively designed to combine bioactivity and intrinsic antibacterial activity targeting bone tissue engineering applications. KEYWORDS: borosilicate bioactive glasses, glass modifiers, Sr-containing glasses, Mg-containing glasses, antibacterial activity 1. INTRODUCTION In recent years, tissue engineering has shown great promise for the repair, replacement, and even regeneration of bone defects. A large diversity of bioactive glasses (BGs) has been reported. Usually they present enhanced capacity to interact with bone due to their capability to form a hydroxyapatite layer (HA) under simulated physiological conditions. 1 The CaO:- SiO 2 :Na 2 O:P 2 O 5 system (45S5 Bioglass) 1 has been the gold standard for BGs, but it has limitations, namely related with its degradation rates. When transformed into glass ceramics, these silica based BGs have slow degradation rates, after being implanted, which makes it difficult to match with the rate of new tissue formation. 2,3 The conversion of the BGs to a bone- like HA is slow and often incomplete. 2 Moreover, the huge increase in joint and bone implant surgeries is usually accompanied by an increase in the incidence of implant-related bacterial infections. This can lead to the failure of the implanta growing public health concern in developed countries. 4,5 A broad spectrum of bacterial species can be found at implant sites, including Pseudomonas aeruginosa, Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis. These Received: March 22, 2016 Accepted: June 16, 2016 Published: June 16, 2016 Article pubs.acs.org/journal/abseba © 2016 American Chemical Society 1143 DOI: 10.1021/acsbiomaterials.6b00162 ACS Biomater. Sci. Eng. 2016, 2, 1143-1150