Bioglasses derived from 45S5: effects of Nb2O5 or surface modification with Ca2+ on the glass structure and bioactivity

Author(s)

João Henrique Lopes

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Química
• Defense date: 2015-02-27

Examining board members

Celso Aparecido Bertran; Oscar Peitl Filho; Luiz Carlos Alves de Oliveira; Miguel Angel San Miguel Barrera; Richard Landers

• Advisor: Italo Odone Mazali; Celso Aparecido Bertran

Abstract

This thesis is divided into four chapters. Chapter I presents background information on the biomaterial and bioglasses. Chapter II is devoted to investigate the effects of adding niobium oxide (Nb2O5) on the physical properties, glass structure and bioactivity of two glasses series derived from the 45S5 Bioglass® (BG45S5). The chemical composition of BG45S5 was modified by replacing 1.3 and 2.6% of P2O5 with Nb2O5 and 1, 2.5, and 5% of SiO2 with Nb2O5, generating series (I) and (II), respectively (BGNs). Adding Nb2O5 significantly increases the density and the stability against devitrification as indicated by ?Txg = (Tx - Tg). The multinuclear 29Si, 31P, and 23Na solid-state MAS NMR spectra of the glasses, Raman spectroscopy, and the determination of some physical properties have generated insight into the structure of the glasses. For the series I glasses, the octahedral niobium take part in glasses network, sharing its corners with silicon tetrahedra forming O-Si-O-Nb-O-Si-O chains, whereas for the series II, NbO6 octahedra act as crosslinker for the silicates chains. Cell viability and metabolic activity were determined using the MTT assay. We investigated the in vitro effect of BGNs glasses on osteoblast viability and proliferation. No significant differences were found between BGNs and BG45S5. Furthermore, in vivo tests in Wistar rats have suggested that the presence of Nb2O5 might actually promote an increase in bioactivity of BGNs, increasing formation of cortical and cancellous bones. The chapter III covers research related to of the surface modification of BG45S5 bioglass (BG45Cas) and its effect on the surface structure, dissolution rate and calcium phosphate formation. BG45Cas were obtained by ion exchange method by immersion in molten salt bath containing calcium. The combination of Raman spectroscopy and atomic force microscopy (AFM) allowed the monitoring of the structural changes of BG45S5 bioglass submitted to increasing durations of immersion in the molten salt bath at 480 °C, whereas X-ray Fluorescence (XRF) was employed to derive the time evolution of Ca2+-Na+ ion exchange process. Structural rearrangements as a result of Ca2+-Na+ ion exchange have been investigated systematically on 45S5 bioglasses by FTIR and 29Si and 31P MAS NMR spectroscopies. Results show that the insertion of calcium ions in the glass structure is higher than the departure of sodium ions. The electroneutrality of the glass structure is preserved with local alterations, which lead to a higher degree of depolymerization of the silicate network. The formation of calcium phosphate layer chemically equivalent to hydroxyapatite (HA) on the bioglass surface was evaluated by immersing the bioglasses in the HEPES 50,69 mmol L-1 and simulated body fluid (SBF) for up to 2 days. This apatite layer was characterized by 31P MAS NMR spectroscopy. The growth kinetics of the apatite layer on the surface of the bioglasses demonstrated that modification of the glass surface (BG45Ca30) cause not only a reduction in time of the formation of HA, but also induced hydroxyapatite phase formation with a higher degree of crystallinity. Finally, chapter IV describes our contributions, final remarks and suggests some ideas for future works (AU)

• FAPESP's process: 10/05394-9 - Bioglasses derived from 45S5: effects of Nb2O5 or surface modification with Ca2+ on the glass structure and bioactivity
• Grantee: João Henrique Lopes
• Support Opportunities: Scholarships in Brazil - Doctorate