Varying Simulated Body Fluid Formulation to Control Calcium Phosphate Mineralization of Electrospun Fibers

The current gold standard in treating large bone defects are autografts which are limited by their availability, donor site morbidity, and other issues. Bone tissue engineering aims to combine cells, biomolecules, and biomaterials to regenerate functional bone tissue. Here, a method of mineralizing electrospun fibers to mimic the hydroxyapatite found in native bone was developed for use as a scaffold for bone repair. Two materials were chosen: polycaprolactone (PCL) and norbornene-functionalized cellulose acetate (nor-CA). PCL was selected because of its common usage in biomaterial scaffolds as a medical grade and FDA approved polymer. Nor-CA was selected because of the combination of handleability and presence of a norbornene group which enables thiol-ene click chemistry. PCL fibers were prepared for mineralization by an activation step using sodium hydroxide and calcium phosphate. Conversely, nor-CA was prepared for mineralization through the conjugation of a calcium-binding peptide to the scaffold. Three types of simulated body fluid (SBF) were chosen for PCL incubation: conventional (C-SBF), revised (R-SBF), and 4x revised (4x R-SBF). For nor-CA, the concentration of peptide on the scaffold was varied and all samples were incubated in C-SBF. Energy dispersive x-ray spectroscopy (EDX/S) was used to quantify the mineral compositions on the mineralized fibers. For PCL, calcium phosphate and sodium chloride-based mineralization was observed for all SBF formulations. The calcium phosphate ratio most like hydroxyapatite was found the 4x R-SBF group. The ratio of calcium to sodium was highest in the C-SBF group. SEM imaging showed distinct regions of calcium phosphate and sodium chloride mineralization for the 4x R-SBF group. In nor-CA, as peptide concentration increased, the amount of calcium deposition also increased. Future studies will explore the mineralization of nor-CA in other SBF formulations and the creation of mineral gradients on the surface of nor-CA through variable peptide concentrations along a singular scaffold.