Electrospun PVP Fibers as Carriers of Ca2+ Ions to Improve the Osteoinductivity of Titanium-Based Dental Implants

Abstract

Although titanium and its alloys are widely used as dental implants, they cannot induce the formation of new bone around the implant, which is a basis for the functional integrity and long-term stability of implants. This study focused on the functionalization of the titanium/titanium oxide surface as the gold standard for dental implants, with electrospun composite fibers consisting of polyvinylpyrrolidone and Ca²⁺ ions. Polymer fibers as carriers of Ca²⁺ ions should gradually dissolve, releasing Ca²⁺ ions into the environment of the implant when it is immersed in a model electrolyte of artificial saliva. Scanning electron microscopy, energy dispersive X-ray spectroscopy and attenuated total reflectance Fourier transform infrared spectroscopy confirmed the successful formation of a porous network of composite fibers on the titanium/titanium oxide surface. The mechanism of the formation of the composite fibers was investigated in detail by quantum chemical calculations at the density functional theory level based on the simulation of possible molecular interactions between Ca²⁺ ions, polymer fibers and titanium substrate. During the 7-day immersion of the functionalized titanium in artificial saliva, the processes on the titanium/titanium oxide/composite fibers/artificial saliva interface were monitored by electrochemical impedance spectroscopy. It can be concluded from all the results that the composite fibers formed on titanium have application potential for the development of osteoinductive and thus more biocompatible dental implants.

Keywords: Ca2+ ions; DFT; EIS; electrospinning; polyvinylpyrrolidone; titanium.

Figure 1

The ATR-FTIR spectra of (a) CaCl₂ salt, PVP and (PVP+Ca²⁺) fibers; (b) freshly prepared Ti, Ti modified with thermally prepared oxide film (Ti/Ti oxide) and Ti modified with the composite fibers [Ti/Ti oxide/(PVP+Ca²⁺) fibers].

Figure 2

The SEM images and corresponding EDS spectra of (a,b) (PVP+Ca²⁺) fibers; (c,d) Ti modified with thermally prepared oxide film (Ti/Ti oxide) and (e,f) Ti modified with the composite fibers [Ti/Ti oxide/(PVP+Ca²⁺) fibers].

Figure 3

The optimized structures of (a) PVP-Ca-I, in which the PVP-Ca bond is established via a nitrogen atom; (b) PVP-Ca-II, in which the PVP-Ca bond is established via oxygen atoms of the carbonyl groups. The bond distances are given in Å. The bond energies are given in kcal mol⁻¹. O—red, C—gray, N—blue, H—white, Ca—yellow-green.

Figure 4

The optimized structures of (a) PVP-Ca-TiO₂-I, in which the Ca²⁺ is complexed in between PVP layer and TiO₂ surface, (b) PVP-Ca-TiO₂-II, in which the Ca²⁺ is bound on the top of PVP layer. The bond distances are given in Å. The bond energies are given in kcal mol⁻¹. O—red, C—gray, N—blue, H—white, Ca—yellow-green.

Figure 5

The EIS plots in the form of (a) magnitude vs. log f, (b) phase angle vs. log f recorded on the [Ti/Ti oxide/(PVP+Ca²⁺) fibers] sample at open circuit potential after 1 h, 2 days and 7 days of immersion in artificial saliva, pH = 6.8.

Figure 6

The SEM images and corresponding EDS spectra of (a,b) freshly electrospun (PVP+Ca²⁺) fibers on Al foil; (c,d) the Al foil surface with residual fibers after 7 days of immersion in artificial saliva, pH = 6.8. Fe, visible in the spectrum (d), originates from Al foil.

Figure 7

The photographs of (a) the freshly abraded and degreased surface of the Ti samples; (b) the thermally generated oxide film on the Ti (Ti/Ti oxide); and (c) the (PVP+Ca²⁺) fibers on the Ti/Ti oxide sample.