Hydroxyapatite and pore former effects on the microstructure and mechanical strength of porous pellets loaded with Lactobacillus

Abstract

Porous hydroxyapatite (HAP) pellets were prepared by extrusion/spheronization/sintering and loaded with Lactobacillus (La-5). Micronized (PFm) or coarse size (PFc) microcrystalline cellulose were the pore formers, while HAP grades from Budenheim (Tri-cafos®) and Sigma-Aldrich with different specific surface (Sw) were the substrates. Green pellets were heated to sublime microcrystalline cellulose, followed by sintering to form porous pellets. These were characterized by electron/optical microscopy/image analysis, porosimetry, nitrogen sorption and mechanically. Stronger pellets resulted from the high Sw HAP and PFm, and larger pores from the low Sw HAP and PFc. HAP origin impacted on pellet strength. Two loading methods were applied: (i) immersion of pellets in La-5 suspension and (ii) injection of suspension into pellets under vacuum. The latter gave 3-x higher loading, which was maximum for the Tri-cafos® 250 HAP/PFc pellets with larger pores that allowed entrance of bacteria, but adequate strength to resist disintegration during loading. La-5 viability in 250 HAP/PFc pellets was 1.2 × 108 CFU/g.