No abstract

One of the most important aspects of dental resin composites is the ability to improve mechanical properties by adding reinforcing filler particles. TiO2 nanotubes are expected to improve the physical and mechanical properties of silica micro-filled dental composite. Therefore, TiO2 nanotubes were synthesized using an alkaline hydrothermal process and then functionalized with 3-methacryloxypropyl-trimethoxysilane. TiO2 nanotubes were characterized by scanning and transmission electron microscopies, X-ray diffraction and Fourier transform infrared spectroscopy. Different quantities of TiO2 nanotubes and silica microparticles were reinforced in bisphenol A-glycidyl methacrylate (Bis-GMA) and tri-ethylene glycol dimethacrylate to prepare dental composite samples. Thereafter, the flexural strength and modulus, compressive strength, degree of conversion of monomers, wear resistance and water sorption were utlized to examine the prepared composites. The flexural strength and wear resistance of composites with 3 wt% TiO2 nanotubes significantly increased in comparison with other composites. On the other hand, due to the stability of composite, the water sorption was decreased. Therefore, TiO2 nanotubes reinforcement could be a promising solution for the improvement of mechanical properties in dental composites.

No abstract

In this study, antibacterial activity and long-lasting release of silver for clinical applications were achieved by utilizing silver nanoparticles on the Titania nanotubes (TNTs) through in situ polymerization of polydopamine (PDA). TNTs were synthesized with the hydrothermal process from Titania nanoparticles. Then the surface modification of TNTs was accomplished by in situ polymerization of PDA and silver ions were reduced on the PDA surface. The feature of obtained samples was characterized using transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FTIR) and atomic absorption spectrophotometry (AAS). The results showed that PDA layer formed on the synthesized anatase TNTs surface. This used as reduction agent for silver ions as well as an adhesive layer to tethering the silver nanoparticles on TNTs surface. AAS results indicated that silver ions reduction to silver nanoparticles on the TNTs surface increased from 3.1 wt.% to 9.6 wt.% in presence of PDA. Also, the results of silver release revealed that PDA worked as an adhesive layer by chelating silver nanoparticles on TNTs and slowing silver ions release rate which implying the possible long-term antibacterial activity of PDA coated TNTs. Besides that, TNTs showed 33% antibacterial activity which is half than silver loaded TNTs-PDA samples. This confirms that PDA have extraordinary effect on the antibacterial activity. This work offers a facile process for the preparation of long-lasting silver based antibacterial activity and facilitates their clinical application in the modern biomedical fields.

Residual stresses, local mechanical properties, and microstructural evolution in terms of grain structures and precipitation distribution have been studied in friction stir welding of AA2017 in T4 and T6 conditions. Microstructural studies including optical and electron microscopy were made to characterize the developed microstructures in different zones of the weldment. Furthermore, X-ray diffraction technique and digital image correlation technique were also utilized to assess residual stress and mechanical properties of the welded alloy. The results show that coarsening of semi-coherent plate-shaped precipitates and formation of incoherent spherical-shaped particles occur in heat affected and thermomechanical affected zones while a non-uniform grain size distribution is formed in the stir zone because of asymmetric distributions of strain rate and temperature. Moreover, the developed residual stresses in the welded samples significantly enhance the effect of subsequent natural aging.