Controlling the bone regeneration properties of bioactive glass: Effect of particle shape and size.

The ability of particulate bioactive glass to function as an effective bone graft material is directly related to its in vivo dissolution, ion release, and interparticle spacing (area associated with bone in-growth). A spherical shape represents an optimal geometry to control bioactive glass bone formation properties. Spherical particles were fabricated from 45S5 bioactive glass with unimodal (90-180, 180-355, and 355-500 μm) and bimodal size ranges (180-355/355-500 and 90-180/355-500 μm). Particles were formed into bone graft putties and compared to a commercially available product composed of irregular 45S5 bioactive glass particles (32-710 μm). Scanning electron microscopy characterization of spherical particles showed a relatively uniform sphere shape and smooth surfaces. Irregular particles were characterized by random shapes with flat surfaces and sharp edges. X-ray fluorescence and X-ray diffraction indicated that the spheroidization process maintained the properties of 45S5 bioactive glass. Cross-sectional micro-computed tomography imaging of the putty samples demonstrated that smaller spheres and irregular particles resulted denser packing patterns compared to the larger spheres. Isolated particles were immersed in simulated body fluid for 14 days to measure silicon ion release and bioactivity. Inductively coupled plasma spectroscopy showed faster ion release from smaller particles due to increased surface area. Bioactivity characterization of 14-day simulated body fluid exposed particle surfaces showed the presence of a hydroxycarbanoapatite mineral layer (characteristic of 45S5 bioactive glass) on all bioactive glass particles. Results demonstrated that spherical particles maintained the properties of the starting 45S5 bioactive glass, and that particle shape and size directly affected short-term glass dissolution, ion release, and interparticle spacing.