Glass - Back to the Future!



Presenting Author:
Bryan Stuart
<epxbs4@nottingham.ac.uk>

article posted 31 March 2016


Bryan Stuart Following the completion of his undergraduate degree in Mechanical Engineering at The University of Nottingham in 2013, Bryan Stuart has been completing a PhD in Biomaterials and Manufacturing Engineering. His specific expertise lies in the production and characterisation of phosphate and silicate glasses by both melt quenching and vapour deposition.






Structural Variability and Dissolution Characteristics of RF Magnetron Sputtered Ion-Doped Phosphate Based Glass Coatings

Bryan W. Stuart, M. Gimeno-Fabra, J. Segal, I. Ahmed and D.M. Grant
Department of Mechanical, Materials and Manufacturing Engineering, University of Nottingham, England, epxbs4@nottingham.ac.uk


Resorbable phosphate based glasses (PBG) can be tailored to deliver a controlled release of therapeutic ions, and have been applied as thin-film coatings to facilitate osseointegration of orthopaedic implants. Quinternary PBG targets containing Ca, Na, Mg and Fe or Ti were produced by melt-quenching and were subsequently used as targets for RF magnetron sputtering onto borosilicate glass cover slips and Ti6Al4V discs 1. FTIR, XPS and NMR were used to investigate the short-range structural relationship between coatings and melt quenched glasses of similar elemental composition prior to exploring their dissolution behaviours in distilled water; phosphate buffered saline and simulated body fluid.



slip (insert) Uncoated and coated Ti6Al4V (B) Elemental mapping for phosphorous within the cross sectional layer. Figure 1: (A) Cross sectional micrograph of a 20 Ám coating on a borosilicate cover

Cross sectional micrographs suggested that the coatings were uniformly deposited and followed the topographical features of their substrates, whilst forming an adherent featureless interface (Figure 1A and B). XPS surface characterisation (Figure 2) and bulk analysis by NMR suggested that vapour deposited glasses were structurally unique, showing that coatings were highly polymerised in comparison to conventional glasses leading to their greater solubility. Coatings of 2.7 Ám in thickness containing 4.0 mol% Fe2O3 were found to fully degrade in distilled water, showing a t1/2 degradation profile in the first 2 hours, followed by a linear dependence from 2-24 hours until the coating was entirely degraded by the 48 h time point 2. Coatings containing 5.5 mol% TiO2 showed remarkable stability, degrading over a period of 14 days, exhibiting the flexibility associated with compositional variations.

An enhanced hydration ability of the sputtered coatings was confirmed by contact angles <1░ with distilled water in comparison to 25░ for melt quenched glass. XPS results suggested an increased ratio of (P-O-P) to (PO- /P=O) and mostly (PO3)- Q2 surface species, in comparison to the melt quenched counterpart which contained mostly (PO4)3- Q0 species and (P2O7)4- Q1 species, which may be responsible for the early t1/2 dissolution profile 2 (Figure 2).



Figure 2: Deconvolution of the P 2p (A and C) and O 1s (B and D) peaks showing majority Q0 and Q1 species within the surface of the melt quenched glasses as compared to majority Q2 on the surface of vapour deposited glass coatings. Additional the ratio of bridging to non-bridging oxygen as shown by the O 1s was observed.

References

1. Stuart, B.; Gimeno-Fabra, M.; Segal, J.; Ahmed, I.; Grant, D. M., Preferential Sputtering in Phosphate Glass Systems for the Processing of Bioactive Coatings. Thin Solid Films 2015.

2. Stuart, B. W.; Gimeno-Fabra, M.; Segal, J.; Ahmed, I.; Grant, D. M., Degradation and Characterization of Resorbable Phosphate-Based Glass Thin-Film Coatings Applied by Radio-Frequency Magnetron Sputtering. ACS applied materials & interfaces 2015, 7 (49), 27362-27372.