Effect of Porous and Nonporous Polycaprolactone Fiber Meshes on CaCO₃ Crystallization Through a Gas Diffusion Method

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 °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 nucleation 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.