The Role of Polydimethylsiloxane in the Molecular Structure of Silica Xerogels Intended for Drug Carriers

Abstract

The aim of this study was to prepare and examine polymer/oxide xerogels with metronidazole (MT) as delivery systems for the local application of a drug to a bone. The nanoporous SiO2-CaO and PDMS-modified SiO2-CaO xerogel materials with different amounts of the polymer, polydimethylsiloxane (PDMS), were prepared by the sol-gel method. Characterization assays comprised the analysis of the composite materials by using Fourier transform infrared spectroscopy (FTIR), determining the specific surface area of solids (BET), using X-ray powder diffraction (XRD) and scanning electron microscope (SEM) techniques, and further monitoring in the ultraviolet and visible light regions (UV-Vis) of the in vitro release of the drug (metronidazole) over time. According to these results, the bioactive character and chemical stability of PDMS-modified silica xerogels have been proven. The release of MT from xerogels was strongly correlated with the composition of the matrix. In comparison with the pure oxide matrix, PDMS-modified matrices accelerated the release of the drug through its bigger pores, and additionally, on account of weaker interactions with the drug. The obtained results for the xerogel composites suggest that the metronidazole-loaded xerogels could be promising candidates for formulations in local delivery systems particularly to bone.

Keywords: Drug delivery systems; Ormosils; Sol-gel method.

Fig. 1

FTIR spectra of SiO₂-CaO, SiO₂-CaO-30%PDMS, and SiO₂-CaO-50%PDMS xerogels

Fig. 2

Nitrogen adsorption-desorption isotherms of xerogels: SiO₂-CaO (a), and SiO₂-CaO-30%PDMS (b), (insert map: BET isoterms of SiO₂-CaO-50%PDMS xerogel)

Fig. 3

SEM micrographs for SiO₂-CaO (a), SiO₂-CaO-30%PDMS (b), and SiO₂-CaO-50%PDMS (c) xerogels

Fig. 4

The chemical stability of the xerogels: (a) pH, and (b) conductivity of the SBF in which the xerogel samples were incubated for a period of three months

Fig. 5

FTIR spectra of all xerogel samples after soaking in SBF solution for 1 month

Fig. 6

The XRD patterns of the SiO₂-CaO xerogel before (a), and after (b) 1 month of soaking in SBF solution (insert map: XRD patterns of SiO₂-CaO-PDMS xerogels)

Fig. 7

The release profiles of MT from SiO₂-CaO, SiO₂-CaO-30% PDMS, and SiO₂-CaO-50% PDMS xerogel carriers