Preparation of PLA composites containing calcium carbonate with cotton wool-like structure for bone regeneration

摘要

Introduction: In our earlier work, fibrous siloxane-doped vaterite (SiV)/poly(L-lactic acid) (PLLA) composites (SiVPC) with the reusability of calcium and silicate ions, for enhancing bone formation, has been prepared. Animal test showed excellent bone formation around the fibers containing 47 vol% (60 wt%) of SiV. Recently, we have prepared cotton wool-like SiVPC as bone-void fillers, using an electrospinning method'2!. The fibers are relatively brittle due to the high SiV content. We hypothesized that the brittleness may be improved by coating the fiber with a thin poly(lactide-co-glycolide) (PLGA) layer. Materials and Methods: PLLA (Mw: 140 kDa) and PLGA (lactide/glycolide = 75/25; Mw: 195 kDa) were used. The SiV (spherical particles of ～1.4 μm in diameter) containing 2.6 wt% of siloxane were prepared, following our previous report. PLLA and SiV were kneaded at 200oC for 10 min. The resulting composites and PLGA were dissolved in chloroform for electrospinning using a concentrical nozzle, which was the 0.5 mm diameters of the core-side (SiVPC) nozzle and the 1.10 mm diameters of the shell-side (PLGA) one. A ground plate was soaked in ethanol. The impressed solution with core-shell-type structure flowed to the ground plate in the ethanol. The resulting fibers were collected and then washed with fresh ethanol, subsequently dried at room temperature, resulting in the formation of cotton wool-like materials. Results and Discussion: The diameters of the resulting fibers were ～10 μm. Many small-sized pits originating from the volatilization of solvent were observed on the surface. The cross-sectional view of the fiber fractured showed a core-shell-type structure, consisting of the core part of ～8 μm diameter and the PLGA coating layer of ～2 μm thickness. It can be imaged from the fracture face that the SWPC-core fractured catastrophically and the PLGA surface layer fractured after necking. SiVPC lost its recovering ability after the compression under 1.5 kPa of pressure due to its brittle fracture, while PLGA-coated SiVPC showed ～50 % in recovery ratio. PLGA-coated SiVPC showed the reusability of calcium and silicate ions in Tris buffer solution: within 32 days, 35-45 % of calcium and silicate ions were released. The good hydrophilicity and high degradation ability of the PLGA layer might allow the solution to permeate into the fibers. Cell culture test using mouse osteoblast-like MC3T3-E1 showed larger numbers of cells on PLGA-coated SiVPC than those on SiVPC. Since PLGA is more hydrophilic than PLLA, the initial attachment of cells would be improved. Fig. 1. SEM images of the resulting fibrous material. Inset is a fracture face after breaking the fiber in liquid nitrogen. Conclusions: Using a coaxial electrospinning technique, a PLGA thin layer of ～2 μm-thickness has been successfully coated on the surface of SiVPC fibers of ～8μm-diameter. Since the cotton wool-like material has highly-porous structure, good mechanical properties, and calcium/silicate ions- reusability, it is expected to have an excellent performance in use as bone-void fillers.