Surface modification of cotton-wool-like bone void fillers consisting of biodegradable polymer-based composite fibers containing calcium-salt particles

A cotton-wool-like bone-void-filling material, an aggregate of tangled fibers consisting of biodegradable polymer (poly(lactic-co-glycolic acid); PLGA) with calcium-salt particles, such as calcium carbonate and β-type tricalcium phosphate, is advantageous because it can be easily mixed with autologous blood and/or bone marrow aspirate (BMA), just before implantation into the defect area during surgery. The composite fibers are hydrophobic because of the PLGA phase around the surface, so hydrophilicity of the fiber surface should be improved to allow blood or BMA to rapidly mix with this cotton-wool-like material. In this work, a simple method for rapidly forming a thin water-soluble layer on the surface of the fibrous composite material was developed to impart hydrophilicity and improve the metabolic activity of osteoblast-like cells. The composite fibers were mechanically mixed with calcium carbonate (vaterite) particles to charge them triboelectrically. The particles were attached densely onto the fiber surface and then heated for 10 min at 60 °C to fix them to the surface using viscous-flowing PLGA. The resulting fibers were immersed in a 0.2 mM Na2HPO4 aqueous solution for 5 min at 37 °C. After this treatment, leaf-like and irregularly shaped amorphous phases formed not only on the fixed vaterite particles but also on the fiber surface, as a layer with <∼1 μm in thickness. The resulting cotton-wool-like material showed high hydrophilicity. This newly formed layer consisted predominantly of an amorphous sodium calcium silicophosphate phase. The resulting layer was gradually dissolved via immersion in a Tris-HCl buffer solution. A cell culture test using mouse-derived osteoblast-like cells MC3T3-E1 on a cotton-wool-like material after hydrophilic treatment showed significantly higher metabolic activity.