Design of air aging induced surface patterns on 45S5 Bioglass® compacted by spark plasma sintering

• We report the first investigation into air aging induced surface patterns on spark plasma sintered 45S5 Bioglass® pellets.
• The morphology of Na2CO3 surface patterns could be conveniently designed by tuning the processing parameters.
• Flower-like structures with appealing radial symmetry could be obtained on wet-ground amorphous 45S5 Bioglass® pellets.
• Formation of a layer rich in Si, Ca and P is possibly faster for air aged 45S5 Bioglass® pellets in aqueous solutions.

The past few decades have witnessed the widespread successful application of 45S5 Bioglass® for hard tissue repair and replacement, as well as a vast quantity of efforts devoted to the investigation into its bioactivity and degradability. In this regard, the current study attempts to examine the evolving surface patterns on sintered 45S5 Bioglass® pellets and explore the mechanisms for their formation. Highly compact samples were fabricated by spark plasma sintering at 500–600 °C under 50/70 MPa, ground with/without water, and aged in air for 10–30 days. Sample characterization was carried out by X-ray diffraction, field emission scanning electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy. It was found that the microscopic surface patterns could be designed by simply tuning the sintering parameters, grinding medium, and aging time, and that the surface patterns consisted mainly of Na2CO3 regardless of the processing route used. It was discovered that beautiful flower-like patterns could be obtained by aging wet-ground pellets sintered at 500 °C under 70 MPa for 30 days as a result of the growth of Na2CO3 in preferential orientations. The higher Si, Ca and P concentrations in the pellet matrix might be able to expedite the crystallization of the Ca-P layer on the pellet surface and hence lead to higher bioactivity in aqueous solutions. It is believed that these interesting findings are helpful in understanding the degradation behavior of 45S5 Bioglass® and planning appropriate processing routes to fully exploit its outstanding bioactivity.