Effect of porous and nonporous polycaprolactone fiber meshes on CaCO3 crystallization through a gas diffusion method

Abstract

The effect of nonporous (NP-PCL) and porous (P-PCL) fibrous polycaprolactone (PCL) meshes, used as templates, on in vitro CaCO3 crystallization via a gas diffusion (GD) method at 20 degrees C for 24 h was studied. The nonporous random (NPR-PCL) and porous random (PR-PCL) and the nonporous-aligned (NPA-PCL) and porous-aligned (PA-PCL) fibrous PCL meshes were directly spun on flat or rotary collectors from 18% PCL solutions using ethyl acetate/acetone or ethyl acetate/dimethyl sulfoxide, respectively. The morphology and type of CaCO3 crystal grown on PCL fiber scaffolds were analyzed by Fourier transform infrared spectroscopy (FTIR), contact angle measurements, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS), focused ion beam combined with scanning electron microscopy (FIB-SEM), and X-ray diffraction (XRD) techniques. The PCL fibers distributions affected the nudeation and stabilized calcite and vaterite polymorphs of CaCO3 with different crystal population densities. The crystal density of vaterite was higher than calcite (2:1) when the NPA-PCL and PA-PCL fibers were used as a template, but calcite predominated (2:1) on P-PCL fiber mesh with respect to the NP-PCL fiber mesh. We found that CaCO3 crystals covered the surface of PCL fibers, and some of them grown from inside of the PCL fibers showed that PCL fibers were occluded inside the CaCO3 crystals during the GD crystallization. The nano- and microscale topological features of PCL scaffolds control the diffusion of carbon dioxide (CO2) gas through PCL fiber meshes in the soaking of PCL meshes into a calcium chloride (CaCl2) solution during the GD crystallization affecting subsequently the nucleation and growth of CaCO3 crystals. Indeed, pore size feature of the micrometric A-PCL and nanometric R-PCL fiber meshes affected the intensities of the crystallographic faces of calcite and vaterite as observed by XRD. Contact angle measurements of the aqueous and crystallization liquid droplet on NPR-PCL, PR-PCL and A-PCL fibrous showed different hydrophobic character of the PCL meshes. This study shows the role of the nano- and microscale topological features and the presence of pores on PCL fiber scaffolds on the mineralization behavior of CaCO3 deposited on R-PCL and A-PCL fiber scaffolds, and by this approach various aspects of controlled CaCO3 crystallization such as nucleation and crystal growth of biomaterials based on CaCO3 can be studied with potential biotech applications.