Fabrication of PCL nanofibrous scaffold with tuned porosity for neural cell culture.

In tissue engineering, the structure of nanofibrous scaffolds and optimization of their properties play important role in the enhancement of cell growth and proliferation. Therefore, the basic idea of the current study is to find a proper method for tuning the extent of porosity of the scaffold, study the effect of porosity on the cell growth, and optimize the extent of porosity with the aim of achieving the maximum cell growth. To tune the scaffold's porosity, four types of metal mesh with different mesh sizes were employed as collectors. For this purpose, the structural properties of polycaprolactone nanofibrous layers which were electrospun on collectors, and the level of neural A-172 cell growth on layers were investigated, and the results were compared with the results attained for the fabricated nanofibrous layer on a flat aluminum collector. It was found that upon changing the porosity of the metal mesh as collector, the fibers' diameter would be inevitably changed, albeit insignificantly, and following no specific trends. However, changing the mesh size has shown a significant effect on the thickness and porosity of nanofibrous layer. According to the MTT assay results, the optimum neural cell growth was observed for the electrospun nanofibrous scaffold with the porosity of 96% and pore size of (0.42-23 µm) which has been fabricated on the type-4 collector having a mesh size of 10. The fabricated scaffold using this mesh with the optimum extent of porosity (58%) resulted in 44% enhancement in the cell growth as compared with the fabricated layer on the flat collector.

Incorporation of F-MWCNTs into electrospun nanofibers regulates osteogenesis through stiffness and nanotopography.

Nanotopography and stiffness are major physical cues affecting cell fate. However, the current nanofiber modifications techniques are limited by their ability to control these two physical cues irrespective of each other without changing the materials' surface chemistry. For this reason, the isolated effects of topography and stiffness on osteogenic regulation in electrospun nanofibers have been studied incompletely. Here, we investigated 1. how functionalized multiwall carbon nanotubes (F-MWCNTs) loaded in Polycaprolactone (PCL) nanofibers control their physical properties and 2. whether the resulting unique structures lead to distinctive phenotypes in bone progenitor cells. Changes in material properties were measured by high-resolution electron microscopes, protein adsorption and tensile tests. The effect of the developed structures on human mesenchymal stem cell (MSC) osteogenic differentiation was determined by extensive quantification of early and late osteogenic marker genes. It was found that F-MWCNT loading was an effective method to independently control the PCL nanofiber surface nanoroughness or stiffness, depending on the applied F-MWCNT concentration. Collectively, this suggests that stiffness and topography activate distinct osteogenic signaling pathway. The current strategy can help our further understanding of the mechano-biological responses in osteoprogenitor cells, which could ultimately lead to improved design of bone substitute biomaterials.

Mathematical Modeling and Experimental Evaluation for the predication of single nanofiber modulus.

Electrospun nanofiber matrices are widely used as scaffolds for the regeneration of different tissues due to similarities with fibrous components of the extracellular matrix. These scaffolds could act as a substrate for inducing mechanical stimuli to cells. The main mechanical stimuli factor in nanofiber scaffolds for determining the cell behaviors is stiffness of single nanofibers. This paper especially highlights the finding that the young's modulus of single nanofibers can be obtained from aligned nanofibers matrix. It is assume that, the modulus of single nanofibers are equal to modulus of completely aligned nanofibers. However, due to difficulty of producing completely aligned nanofibers, the obtained modulus of single nanofiber wouldn't have significant value. Therefore, we propose a new mathematical model to predict the stiffness of single nanofibers from non-perfectly aligned nanofibers matrix.

Drug release profile in core-shell nanofibrous structures: a study on Peppas equation and artificial neural network modeling.

Release profile of drug constituent encapsulated in electrospun core-shell nanofibrous mats was modeled by Peppas equation and artificial neural network. Core-shell fibers were fabricated by co-axial electrospinning process using tetracycline hydrochloride (TCH) as the core and poly(l-lactide-co-glycolide) (PLGA) or polycaprolactone (PCL) as the shell materials. The density and hydrophilicity of the shell polymers, feed rates and concentrations of core and shell phases, the contribution of TCH in core material and electrical field were the parameters fed to the perceptron network to predict Peppas constants in order to derive release pattern. This study demonstrated the viability of the prediction tool in determining drug release profile of electrospun core-shell nanofibrous scaffolds.

The influence of surface nanoroughness of electrospun PLGA nanofibrous scaffold on nerve cell adhesion and proliferation.

Electrospun nanofibrous scaffolds in neural tissue engineering provide an alternative approach for neural regeneration. Since the topography of a surface affects the microscopic behaviour of material; the creation of nanoscale surface features, which mimic the natural roughness of live tissue, on polymer surfaces can promote an appropriate cell growth and proliferation. In this research, a unique PLGA nanofibrous structure was fabricated without any post-electrospinning treatment. Scaffolds were prepared in two general groups: cylindrical and ribbon-shaped electrospun fibres, with smooth and rough (porous and grooved) surfaces. The experiments about nerve cell culture have demonstrated that the nanoroughness of PLGA electrospun scaffolds can increase the cell growing rate to 50 % in comparison with smooth and conventional electrospun scaffolds. SEM and AFM images and MTT assay results have shown that the roughened cylindrical scaffolds enhance the nerve growth and proliferation compared to smooth and ribbon-shaped nanofibrous scaffolds. A linear interaction has been found between cell proliferation and surface features. This helps to approximate MTT assay results by roughness parameters.

Effect of accelerated aging on the color and opacity of resin cements.

STATEMENT OF THE PROBLEM: The color stability of resin cements plays a major role in the esthetic performance of porcelain laminate veneers. Some dual-polymerizable resin cements used to bond porcelain laminates were shown to undergo color changes during service. Some recently produced cements are described as being color stable, but scientific data are not available. PURPOSE: The current study evaluated the effect of accelerated aging on the color and opacity of resin cements. The hypothesis was that the auto-polymerizing cements would show less color and opacity stability. MATERIALS AND METHODS: Forty (0.7 x 18 mm) feldspathic porcelain disks were prepared and divided into four equal groups. The resin cements were bonded to the disks by application of an identical load of 2.5 kilograms, and they were polymerized according to the manufacturer's instructions. The groups were: Variolink Veneer (light-polymerizing), Variolink II (light-polymerizing), Variolink II (dual-polymerizing) and Multilink (auto-polymerizing). A spectrophotometer was used to measure the following color parameters in the CIE L*a*b* color space on a black and white background: deltaa*, deltab*, deltaL*, deltaC, deltaH, deltaE and deltaCR (contrast ratio). The measurements were performed before and after aging. Paired t- and one-way ANOVA tests were used to analyze the data (alpha = .05). RESULTS: None of the groups showed significant differences in deltaE before and after aging (p > .05); deltaE remained in the range of clinical acceptance (deltaE < 3.3). All of the cements became more opaque, while deltaCR (difference in contrast ratio) was significantly different (p = .004). The auto-polymerized cement showed an increase in opacity. CONCLUSIONS: The studied cements behaved acceptably according to deltaE, but they became more opaque after aging. CLINICAL IMPLICATIONS: The studied cements can ensure color stability when used to cement porcelain laminate veneers, but the change in opacity can affect clinical results. Auto polymerizing cements become more opaque with aging; therefore, porcelain restorations may lose their match with other teeth.