Local surface damage and material dissolution in 45S5 bioactive glass: Effect of the contact deformation Ding Li a , Mimi X. Yang b , Pavitra Muralidhar b , Connie Wu b , Fuqian Yang a, * a Department of Chemical and Materials Engineering, University of Kentucky, 161 Anderson Hall, Lexington, KY 40506, United States b MSTC Program, Paul Laurence Dunbar High School, Lexington, KY 40513, United States article info Article history: Received 13 March 2008 PACS: 61.43.Fs 62.20.mm 81.70.q Keywords: Bioglass Crack growth Indentation, Microindentation abstract Bioactive glasses react with the human physiological solution in control of their biofunctionality. The stress state in bioactive glasses determines the chemomechanical reaction and their biofunctionality. Using the microindentation technique, the effect of the indentation deformation on the surface damage and material dissolution of 45S5 bioglass was investigated. The indentation-induced local surface dam- age, including ring cracks and radial cracks, was revealed before and after the immersion tests in phos- phate buffer solution (PBS). There existed a critical load for the formation of the radial cracks, which emanated from the periphery of the outmost ring crack. The growth of the radial cracks in the PBS solu- tion displayed the stress-corrosion behavior with the crack-growth speed being a linear function of the indentation load. Fast dissolution occurred at the edges of the surface-damaged zone due to stress- assisted dissolution under the action of local tensile stress, which was different from the dissolution behavior of stress-free 45S5 bioglass. Ó 2009 Elsevier B.V. All rights reserved. 1. Introduction The control of material deformation and dissolution is one of the most concerns for the biomedical applications of bioactive materials in the reconstruction and substitution of bone and tooth. Localized stresses/strains through contact between materials are of biomedical and technological importance because their influence on local chemomechanical behavior affects the service life and per- formance of bioactive materials and the growth of bioactive struc- tures such as a biologically active apatite layer. The understanding of the deformation-induced chemomechanical behavior of bioac- tive materials plays an important role in the processing and man- ufacturing of bioactive materials, which generally requires that bioactive materials maintain reasonably mechanical strength and biofunctionality when subjected to external mechanical loading [1]. The biofunctionality of bioactive materials generally can be characterized in the phosphate buffer solution (PBS) and the simu- lated body fluid (SBF) and be determined by examining the growth rate of the apatite layer. Fazan and Marquis [2] evaluated the changes in crystallinity and surface topology of plasma-sprayed hydroxyapatite coatings over pure titanium and determined the dissolution behavior of the hydroxyapatite coating. Xue et al. [3] coated hydroxyapatite over the cortical bone, muscle, and marrow of adult dogs and used scanning electron microscope to in vivo examine the dissolution of the hydroxyapatite coatings. Most work reported in literature focused on either the dissolution or the mechanical response of bioactive materials. There are only a few studies on the dissolution of bioactive materials under the action of mechanical stresses. Han et al. [4] studied the effect of residual stresses on the dissolution of hydroxyapatite coatings on a tita- nium alloy. Reis et al. [5] observed the degradation of the hydroxy- apatite coatings on Ti–6Al–4V substrate through surface cracking and faster dissolution when subjected to cyclic bending. Bloyer et al. [6] evaluated the stress-corrosion crack growth of Si-based bioactive glasses in the SBF solution. Li et al. [1] recently studied the stress effect on the material dissolution of 45S5 bioglass in the PBS solution using the Vickers indentation. It is known that localized plastic deformation in a material can be created by the sharp-instrumented indentation. Such a localized deformation can change local chemomechanical response of a bio- active material and alter the local dissolution and biofunctionality of the material. It is the purpose of this work to study the indenta- tion deformation of 45S5 bioglass using a spherical, diamond in- denter and to examine the effect of the indentation deformation on the material dissolution of 45S5 bioglass in the PBS solution. Ring cracks, radial cracks and local surface damage due to the con- tact between the indenter and the 45S5 bioglass are revealed. The dependence of the growth of the radial cracks on the indentation load is also discussed. 0022-3093/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2009.04.026 * Corresponding author. Tel.: +1 859 257 2994; fax: +1 859 323 1929. E-mail address: fyang0@engr.uky.edu (F. Yang). Journal of Non-Crystalline Solids 355 (2009) 874–879 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol