Abstract
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.
Highlights
Numerous works on bone regeneration using bioactive materials have been reported
Hench et al reviewed that calcium and silicate ions released from bioactive glasses implanted in bone voids have a stimulatory effect on bone regeneration [4,5]
Xynos et al reported that calcium and silicate ions increase the proliferation of human osteoblasts through gene activation [7,8]
Summary
Numerous works on bone regeneration using bioactive materials have been reported. Recently, significant attention has been devoted to bone tissue engineering [1]. The composite containing PLGA as the matrix polymer exhibited better mechanical properties than the SiVPC with the PLLA matrix, almost all silicate ions initially dissolved in a burst-release fashion after being soaked in aqueous solution [14]. This may originate from the high hydrophilicity and degradability of PLGA. We hypothesized that coating a SiVPC fiber containing 47 vol % of SiV with a thin PLGA layer, i.e., preparing a so-called “core-shell”-type structure, may resolve the issues described above; as the thin PLGA layer could prevent the direct contact of the SiVPC with water immediately after soaking the fiber in aqueous solution, the burst release of silicate ions might be inhibited, and the mechanical properties might concurrently improve. The preparation method, mechanical properties, and ion-release behavior of the cotton-wool-like materials are discussed here
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