In previous works, we reported the fabrication of cotton-wool-like composites consisting
of siloxane-doped vaterite and poly(L-lactic acid) (SiVPCs). Various irregularly shaped bone voids
can be filled with the composite, which effectively supplies calcium and silicate ions, enhancing
the bone formation by stimulating the cells. The composites, however, were brittle and showed an
initial burst release of ions. In the present work, to improve the mechanical flexibility and ion release,
the composite fiber was coated with a soft, thin layer consisting of poly(D,L-lactic-co-glycolic acid)
(PLGA). A coaxial electrospinning technique was used to prepare a cotton-wool-like material
comprising “core-shell”-type fibers with a diameter of ~12 µm. The fibers, which consisted of
SiVPC coated with a ~2-µm-thick PLGA layer, were mechanically flexible; even under a uniaxial
compressive load of 1.5 kPa, the cotton-wool-like material did not exhibit fracture of the fibers and,
after removing the load, showed a ~60% recovery. In Tris buffer solution, the initial burst release
of calcium and silicate ions from the “core-shell”-type fibers was effectively controlled, and the ions
were slowly released after one day. Thus, the mechanical flexibility and ion-release behavior of the
composites were drastically improved by the thin PLGA coating.