Formation Mechanism And Biomimetic Mineralization Of Directly Electrospun Fibers Of Silica Based Sols

In this paper, three kinds of SiO2, SiO2-P2O5 and SiO2-CaO-P2O5 gel fibers were prepared by sol-gel method and electrospinning comnined technology (Abbreviated: Directly Electro-spinning of Sol, DESS). The test methods of conductivity, viscosity, and drawing capabilities were used to assess the processes of sol-gels and their influencing factors; TG-DSC, XRD, FTIR, SEM and TEM techniques were used to characterize silica-based gels and micro-morphologies and structures, formation mechanism, calcining process and products of DESS gel fibers. The SiO2-CaO-P2O5 gel and gel fibers obtained before and after calcination, mineralizated in the initial pH = 7.0, 5 times concentration of simulated body fluid (SBF) at 37℃for 10 days were assessed. Comprehensive analysis results shown as follows:(1) As the aging time increases, the conductivity of three silica-based sols firstly fell then rose, and corresponded to the two reactions of the TEOS hydrolysis process. The initial pH value has significant impact to the gelation time of SiO2-CaO-P2O5 sol. With the initial pH value decrease, the gelation time increased. With aging time increasing (<20h), the drawing length of silica-based sols increased very slow, but when the aging time further extends (>20h), the length increased fast to maxim value and then decreased rapidly. Under ambient conditions, the drawing length and viscosity of the three sols varyied in the same law with the aging time increasing. Therefore, the viscosity is able to be foundation of directly electrospinning of silica-based sols.(2) The micro-morphological variations of three DESS gel fibers with the viscosity followed the same law, but the occurrence of various morphological features shown some differences. With the viscosity increase (40-550mPa?s) of silica-based sols, the micro- morphological variations of the SiO2 DESS products shown as: beads→gel fibers with beads→smooth fibers→hollow beads; the micro-morphological variations of the SiO2-P2O5 DESS products shown as: beads→gel fibers with beads→spindle-shaped fibers→smooth fibers→gel fibers with hollow beads→hollow beads; the micro-morphological variations of SiO2-CaO-P2O5 DESS products shown as: beads→gel fibers with beads→spindle-shaped gel fibers→smooth fibers→hollow fibers. Under the given conditions of the sol compositions and electrospun parameters, the micro- morphologies of DESS products are also affected by environmental conditions, the micro-morphological characteristics are not necessarily all there, some kinds of them may overlap.(3) The main factor effects the micro-morphologies of DESS products is the sol viscosity, but sol compositions, electric field intensity and the environmental conditions can not be ignored, either. When the sol viscosity is 200-350mPa?s, the DESS gel fibers of smooth surface, uniform diameter will be available.(4) The SiO2-CaO-P2O5 gel hollow fibers by using single-tube jet and DESS technology were prepared firstly. TEM analysis shown that: the SiO2-CaO-P2O5 hollow fibers calcined at 700℃have obvious features of the hollow mass thickness and microcrystalline diffraction contrast.(5) The biomimetic mineralization research shown that: SiO2-CaO-P2O5 gel and gel fibers obtained before and after calcination have excellent performances of mineralization and biological activity.