Compartmentalization of synthetic body fluid constituents for coating electrospun PCL nanofiber mats with different calcium phosphate phases

Abstract

Bone tissue engineering scaffolds produced by electrospinning of biocompatible and biodegradable polymers like PCL have proven themselves in promoting adhesion and proliferation of cells due to the resemblance of their physical nanofeatures to natural extracellular matrix. Hybridization of nanofibers with biomimetic calcium phosphates is another avenue, in which the osteoconductive properties of polymers can be improved and polymer matrix resorption and degradation can be tailored with definite enhancements in cell adhesion, proliferation and differentiation. Different calcium phosphate phases can have different dissolution rates in the body environment depending on their phase constitution. A phase mixture that would provide variable dissolution rate is generally accepted to be more beneficial in tissue engineering approaches. Biomimetic calcium phosphates have been coated on two dimensional nanofiber mats that are laid in a synthetic body fluid medium with one surface facing the solution. Therefore the biological activity tests have generally been limited with observations made on the coated surfaces of mats. In most of the cases these were single phase calcium phosphates with a single dissolution rate. Here a method to coat both sides of a nanofiber mat will be introduced. In addition, this method not only allows a coating on both the surfaces of the mat, but also provides the means of forming a continuous coating along the whole cross section. The ability to control the calcium phosphate phases that are going to form on the surfaces of the mat is another merit, which serves the means of forming a phase graded mat cross section. Synthetic body fluids (SBF) have been widely used to form biomimetic coatings on different substrates. They are generally formulized such that they mimic the mineral constituents of the blood plasma. Here the low pH constituents of SBFs are separated from the high pH constituents by the nanofiber mat that is to be coated. As the ions in compartments on both sides of the mat start to diffuse, they start to supersaturate different calcium phosphate phases on either side of the mat providing a novel coating and phase grading strategy. By changing the compartment concentrations, and the target concentration, not only the density of coatings could effectively be changed but also the compartment concentration limits that provide a single phase or two phase coating were found.