Dental adhesives modified by TiO2 nanotubes as carriers of enzyme inhibitors: synthesis, functionalization and incorporation of nanotubes and evaluation of enzymatic activity physico-chemical, mechanical and biological properties

Abstract

TiO2 nanotubes have recently been used for drug delivery due to their excellent properties such as reduced size, high surface area and functionable structure. An application of these nanotubes that has not yet been studied concerns the loading and distribution of enzyme inhibitors of matrix metalloproteinase enzymes (MMPs) and cysteine-cathepsins (CCs) in dentin adhesives aiming the increase of the longevity of the interface between dental substrate and polymeric restorative materials. The purposes of this study are the alkaline synthesis, APTMS functionalization and characterization of TiO2 nanotubes to work as carriers of the enzyme inhibitors Chlorhexidine (CHX) and Doxycycline (DOX) in a commercially available universal adhesive (Single Bond Universal, 3M ESPE). TiO2 nanotubes will be obtained through alkaline synthesis, functionalized or not with organosilane (APTMS) and, at first, submitted to the characterization through X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Energy Dispersive Spectroscopy (EDS), Scanning Electron Microscopy (SEM), Transmission Electronic Microscopy (TEM) and Thermogravimetric Analysis (TGA), in order to evaluate the molecular structures of the samples, confirm the effectiveness of the functionalization and the incorporation of the inhibitors and the surface potential of the samples. After characterization, CHX and DOX solutions will be prepared for TiO2 nanotubes. Loading efficiency of the nanotubes will be evaluated by liquid chromatography, and tests for the evaluation of release/desorption of the inhibitors will be carried out using UV-Vis. The modified adhesives will be subjected to degree of conversion test using Fourier Transform Infrared Spectroscopy (FTIR) with uncured adhesives (n = 3). In addition, the degree of conversion in situ will be evaluated in dentin disks (n = 3). Dentin slices will be hybridized with the proposed adhesive protocols. The surfaces will be evaluated through FTIR-ATR. For microtensile bond strength test, the modified adhesives will be applied in etch-and-rinse and self-etching modes 0.4 mm thick (n =10) in dentin discs obtained from extracted human molars, and the teeth will be cut to 0.64 mm2 beams, which will be tested in a universal testing machine, where tensile force perpendicular to the adhesive interface will be applied at a speed of 0.5 mm/min until failure. The fractured surfaces of the specimens will be visually examined with a stereomicroscope and the failures will be classified as adhesive, cohesive or mixed. For enzymatic activity analysis, total MMP activity will be performed. Subsequently, transdentinal cytotoxicity test will be carried out, human pulp culture cells (HDPC) will be cultured on the pulp face of dentin discs (0.4 mm thick) adapted to Trans-wells (n = 6/group) in duplicate. The adhesive system will be applied to the occlusal surface, followed by incubation for 24 h. Cell viability and morphology will be evaluated by Alamar Blue test and Scanning Electron Microscopy (SEM), respectively. Afterwards, a Live/Dead test will be performed to obtain the percentage of viable cells and dead cells. The data obtained will be submitted to analysis of variance followed by multiple comparisons test with significance level of 5%. (AU)