Effect of low-temperature plasma treatment of electrospun polycaprolactone fibrous scaffolds on calcium carbonate mineralisation

Abstract

This article reports on a study of the mineralisation behaviour of CaCO₃ deposited on electrospun poly(ε-caprolactone) (PCL) scaffolds preliminarily treated with low-temperature plasma. This work was aimed at developing an approach that improves the wettability and permeability of PCL scaffolds in order to obtain a superior composite coated with highly porous CaCO₃, which is a prerequisite for biomedical scaffolds used for drug delivery. Since PCL is a synthetic polymer that lacks functional groups, plasma processing of PCL scaffolds in O₂, NH₃, and Ar atmospheres enables introduction of highly reactive chemical groups, which influence the interaction between organic and inorganic phases and govern the nucleation, crystal growth, particle morphology, and phase composition of the CaCO₃ coating. Our studies showed that the plasma treatment induced the formation of O- and N-containing polar functional groups on the scaffold surface, which caused an increase in the PCL surface hydrophilicity. Mineralisation of the PCL scaffolds was performed by inducing precipitation of CaCO₃ particles on the surface of polymer fibres from a mixture of CaCl₂- and Na₂CO₃-saturated solutions. The presence of highly porous vaterite and nonporous calcite crystal phases in the obtained coating was established. Our findings confirmed that preferential growth of the vaterite phase occurred in the O₂-plasma-treated PCL scaffold and that the coating formed on this scaffold was smoother and more homogenous than those formed on the untreated PCL scaffold and the Ar- and NH₃-plasma-treated PCL scaffolds. A more detailed three-dimensional assessment of the penetration depth of CaCO₃ into the PCL scaffold was performed by high-resolution micro-computed tomography. The assessment revealed that O₂-plasma treatment of the PCL scaffold caused CaCO₃ to nucleate and precipitate much deeper inside the porous structure. From our findings, we conclude that O₂-plasma treatment is preferable for PCL scaffold surface modification from the viewpoint of use of the PCL/CaCO₃ composite as a drug delivery platform for tissue engineering.