Novel P(3HB) Composite Films Containing Bioactive Glass Nanoparticles for Wound Healing Applications

Bioactive glass (BG) is considered an ideal material for haemostasis as it releases Ca2+ ions upon hydration, which is required to support thrombosis. In this study the effect of the presence of the BG nanoparticles in P(3HB) microsphere films on the structural properties, thermal properties and biocompatibility of the films were studied. The nanoscaled bioactive glass with a high surface area was also tested for its in vitro haemostatic efficacy and was found to be able to successfully reduce the clot detection time. In an effort to study the effect of the roughness induced by the formation of HA on the cellular functions such as cell adhesion, cell mobility and cell differentiation, the composite films were immersed in SBF for a period of 1, 3 and 7 days. From the SEM images the surface of the P(3HB)/n-BG composite microsphere films appeared fairly uniform and smooth on day 1, however on day 3 and day 7 a rough and uneven surface was observed. The presence of HA on the composite microsphere films on day 3 and day 7 influenced the surface roughness of the films. However, when the P(3HB)/n-BG composite microspheres with enhanced surface roughness were tested for biocompatibility, reduced amount of protein adsorption and cell adhesion were observed. This study thus revealed that there is an optimal surface roughness for the P(3HB) microsphere films for increased cell adhesion, beyond which it could be deleterious for cell adhesion and differentiation.

Structure dependencies for multiscale polymer composites using extrusion processes

Multiscale reinforcement, using carbon microfibers and multi-walled carbon nanotubes, of polymer matrix composites manufactured by twin-screw extrusion is investigated for enhanced mechanical and thermal properties with an emphasis on the use of a diverging flow in the die for fluid mechanical fiber manipulation. Using fillers at different length scales (microscale and nanoscale), synergistic combinations have been identified to produce distinct mechanical and thermal behavior. Fiber manipulation has been demonstrated experimentally and computationally, and has been shown to enhance thermal conductivity significantly. Finally, a new physics driven predictive model for thermal conductivity has been developed based on fiber orientation during flow, which is shown to successfully capture composite thermal conductivity.

Dynamic mechanical-thermal, microstructural and mechanical analysis of ultra-light polymer-metal composites: influence of forming

A really particular and innovative metal-polymer sandwich material is Hybrix. Hybrix is a product developed and manufactured by Lamera AB, Gothenburg, Sweden. This innovative hybrid material is composed by two relatively thin metal layers if compared to the core thickness. The most used metals are aluminum and stainless steel and are separated by a core of nylon fibres oriented perpendicularly to the metal plates. The core is then completed by adhesive layers applied at the PA66-metal interface that once cured maintain the nylon fibres in position. This special material is very light and formable. Moreover Hybrix, depending on the specific metal which is used, can achieve a good corrosion resistance and it can be cut and punched easily. Hybrix architecture itself provides extremely good bending stiffness, damping properties, insulation capability, etc., which again, of course, change in magnitude depending in the metal alloy which is used, its thickness and core thickness. For these reasons nowadays it shows potential for all the applications which have the above mentioned characteristic as a requirement. Finally Hybrix can be processed with tools used in regular metal sheet industry and can be handled as solid metal sheets. In this master thesis project, pre-formed parts of Hybrix were studied and characterized. Previous work on Hybrix was focused on analyze its market potential and different adhesive to be used in the core. All the tests were carried out on flat unformed specimens. However, in order to have a complete description of this material also the effect of the forming process must be taken into account. Thus the main activities of the present master thesis are the following: Dynamic Mechanical-Thermal Analysis (DMTA) on unformed Hybrix samples of different thickness and on pre-strained Hybrix samples, pure epoxy adhesive samples analysis and finally moisture effects evaluation on Hybrix composite structure.

Design, development, and analysis of hybrid metal-composite tube for industrial application

In the aerospace, automotive, printing, and sports industries, the development of hybrid Carbon Fiber Reinforced Polymer (CFRP)-metal components is becoming increasingly important. The coupling of metal with CFRP in axial symmetric components results in reduced production costs and increased mechanical properties such as bending, torsional stiffness, mass reduction, damping, and critical speed compared to the single material-built ones. In this thesis, thanks to a novel methodology involving a rubbery/viscoelastic interface layer, several hybrid aluminum-CFRP prototype tubes were produced. Besides, an innovative system for the cure of the CFRP part has been studied, analyzed, tested, and developed in the company that financed these research activities (Reglass SRL, Minerbio BO, Italy). The residual thermal stresses and strains have been investigated with numerical models based on the Finite Element Method (FEM) and compared with experimental tests. Thanks to numerical models, it was also possible to reduce residual thermal stresses by optimizing the lamination sequence of CFRP and determining the influence of the system parameters. A novel software and methodology for evaluating mechanical and damping properties of specimens and tubes made in CFRP were also developed. Moreover, to increase the component's damping properties, rubber nanofibers have been produced and interposed throughout the lamination of specimens. The promising results indicated that the nanofibrous mat could improve the material damping factor over 77% and be adopted in CFRP components with a negligible increment of weight or losing mechanical properties.

Advanced electrospun nanofibrous mats for hindering delamination, improving damping and for sensing of composite laminates

Carbon Fiber Reinforced Polymers (CFRPs) display high specific mechanical properties, allowing the creation of lightweight components and products by metals replacement. To reach outstanding mechanical performances, the use of stiff thermoset matrices, like epoxy, is preferred. Laminated composites are commonly used for their ease of manipulation during object manufacturing. However, the natural anisotropic structure of laminates makes them vulnerable toward delamination. Moreover, epoxy-based CFRPs are very stiff materials, thus showing low damping capacity, which results in unwanted vibrations and structure-borne noise that may contribute to delamination triggering. Hence, searching for systems able to limit these drawbacks is of primary importance for safety reasons, as well as for economic ones. In this experimental thesis, the production and integration of innovative rubbery nanofibrous mats into CFRP laminates are presented. A smart approach, based on single-needle electrospinning of rubber-containing blends, is proposed for producing dimensionally stable rubbery nanofibers without the need for rubber crosslinking. Nano-modified laminates aim at obtaining structural composites with improved delamination resistance and enhanced damping capacity, without significantly lowering other relevant mechanical properties. The possibility of producing nanofibers nano-reinforced with graphene to be applied for reinforcing composite laminates is also investigated. Moreover, the use of piezoelectric nanofibrous mats in hybrid composite laminates for achieving self-sensing capability is presented too as a different approach to prevent the catastrophic consequences of possible structural laminate failure. Finally, an accurate, systematic, and critical study concerning tensile testing of nonwovens, using electrospun Nylon 66 random nanofibrous mats as a case study, is proposed. Nanofibers diameter and specimen geometry were investigated to thoroughly describe the nanomat tensile behaviour, also considering the polymer thermal properties, and the number of nanofibers crossings as a function of the nanofibers diameter. Stress-strain data were also analysed using a phenomenological data fitting model to interpret the tensile behaviour better.

Smart tracking of composite parts: feasibility study and effect on mechanical behaviour

This research proposes a solution for integrating RFID - Radio Frequency Identification technology within a structure based on CFRPs - Carbon Fiber Reinforced Polymers. Therefore, the main objective is to use technology to monitor and track composite components during manufacturing and service life. The study can be divided into two macro-areas. The first portion of the research evaluates the impact of the composite materials used on transmitting the electromagnetic signal to and from the tag. RFID technology communicates through radio frequencies to to track and trace items associated with the tags. In the first instance, a feasibility study was carried out to assess using commercially available tags. Then, after evaluating different solutions, it was decided to incorporate the tags into coupons during production. The second portion of the research is focused on evaluating the impact on the composite material's resistance to tag embedding. It starts with designing tensile test specimens through the FEM model with different housing configurations. Subsequently, the best configuration was tested in the facilities of the In the Faculty of Aerospace Engineering at TU Delft, particularly in the Structure & Materials Laboratory, two tests were conducted: the first one based on ASTM D3039/D3039 - 14 - Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials, the second one dividing the path to failure into failure intervals in a load-unload-reload. Both tests were accompanied by instruments such as DIC, AE, C-Scan and Optical Microscopes. The expected result of the inclusion of RFID tags in composite components is that it brings added value to the parts with which it is associated without affecting too much its mechanical properties. This comes first from the automatic identification of RFID during the production cycle and its useful life. As a result, improvements were made in the design of production facilities.

Effect Of Composite Containing An Iodonium Salt On The Bond Strength Of Brackets To Bovine Enamel.

This study investigated the effect of the incorporation of an iodonium salt in experimental composites, on the bond strength of metallic brackets bonded to bovine teeth. Two hundred and seventy bovine teeth were embedded in self-curing acrylic resin and divided into 18 groups (n=15), according to the experimental composite with an iodonium salt at molar concentrations 0 (control), 0.5, or 1%; the light-activation times (8, 20 and 40 s); and the storage times (10 min or 24 h). Metallic brackets were fixed on the tooth surface using experimental composites. Photoactivation was performed with a quartz-tungsten-halogen light-curing unit curing unit for 8, 20 and 40 s. The specimens were stored in distilled water at 37 °C for 10 min or 24 h and submitted to bond strength test at 0.5 mm/min. The data were subjected to three-way ANOVA and Tukey's test (α=0.05). The Adhesive Remnant Index (ARI) was used to classify the failure modes. The shear bond strengths (MPa) at 10 min for light-activation times of 8, 20 and 40 s were: G1 - 4.6, 6.9 and 7.1; G2 - 8.1, 9.2 and 9.9; G3 - 9.1, 10.4 and 10.7; and at 24 h were: G1 - 10.9, 11.1 and 11.7; G2 - 11.8, 12.7 and 14.2; G3 - 12.1, 14.4 and 15.8. There was a predominance of ARI score 3 for groups with 10 min storage time, and ARI score 2 for groups with 24 h storage time. In conclusion, the addition of iodonium salt (C05 and C1) to the experimental composite may increase the bond strength of brackets to bovine enamel using reduced light exposure times.

Influence Of Successive Light-activation On Degree Of Conversion And Knoop Hardness Of The First Layered Composite Increment.

To evaluate the influence of light-activation of second, third and fourth increments on degree of conversion (DC) and microhardness (KHN) of the top (T) and bottom (B) surface of the first increment. Forty samples (n = 5) were prepared. In groups 1-4, after each increment light-activation (multiple irradiation), T and B of the first increment were measured in DC and KHN. In groups 5-8, only the first increment was made (single irradiation) and measurements of DC and KHN were taken at 15 min intervals. The light-activation modes were (XL) 500 mW/cm(2) × 38 s (G1/G5); (S) 1000 mW/cm(2) × 19 s (G2/G6), (HP) 1400 mW/cm(2) × 14 s (G3/G7); (PE) 3200 mW/cm(2) × 6 s (G4/G8). Data for DC and KHN were analyzed separately by using PROC MIXED for repeated measures and Tukey-Kramer test (α = 0.05). For KHN, B showed lower values than T. PE resulted in lower values of KHN in B surface. For single and multiple irradiations, T and B of first measurement showed the lowest KHN and the fourth measurement showed the highest, with significant difference between them. For single irradiation, first and second increments presented similar KHN, different from the third and fourth increment, which did not differ between them. For multiple irradiations, the second light-activation resulted in KHN similar to first, third and fourth increments. For DC, except QTH, T presented higher DC than B. The light-activation of successive increments was not able to influence the KHN and DC of the first increment.

Durabilidade de compósito biomassa vegetal-cimento modificado por polímero

The durability of the cellulose-cement composites is a decisive factor to introduce such material in the market. Polymers have been used in concrete and mortar production to increase its durability. The goal of this work was the physical and mechanical characterization of cellulose-cement composites modified by a polymer and the subsequent durability evaluation. The work also evaluated the dispersion of acrylic polymer in composites made of Pinus caribaea residues. The physical properties observed were water absorption by immersion and bulk density. Rupture modulus and toughness were determined by flexural test. The specimens were obtained from pads, produced by pressing and wet curing. Samples were subjected to accelerated aging tests by repeated wetting and drying cycles and hot-water bath and natural aging. The scanning electron microscopy (SEM) allowed verifying the fiber and composite characteristics along the time. For the composite range analyzed, it was observed the polymer improved the mechanical properties of composites besides a significant decreasing in water absorption. The use of polymer improved the performance of vegetable fiber-cement composites when compared to the conventional mortar, due to water absorption decreasing.

Fracture resistance of weakened roots restored with composite resin and glass fiber post

This study evaluated the fracture resistance of weakened roots restored with glass fiber posts, composite resin cores and complete metal crowns. Thirty maxillary canines were randomly divided into 3 groups of 10 teeth each: teeth without weakened roots (control); teeth with partially weakened roots (PWR) and teeth with and largely weakened roots (LWR). The control group was restored with glass fiber posts and a composite resin core. Teeth in the PWR and LWR groups were flared internally to standardized dimensions in order to simulate root weakness. Thereafter, the roots were partially filled with composite resin and restored in the same way as in the control group. The specimens were exposed to 250,000 cycles in a controlled chewing simulator. All intact specimens were subjected to a static load (N) in a universal testing machine at 45 degrees to the long axis of the tooth until failure. Data were analyzed by one-way ANOVA and Dunnett's test for multiple comparisons (p=0.05). There were statistically significant difference differences (p<0.01) among the groups (control group = 566.73 N; PWR = 409.64 N; and LWR = 410.91 N), with significantly higher fracture strength for the control group. There was no statistically significant difference (p>0.05) between the weakened groups. The results of this study showed that thicker root dentin walls significantly increase the fracture resistance of endodontically treated teeth.

Effects of light-curing time on the cytotoxicity of a restorative composite resin on odontoblast-like cells

This in vitro study evaluated the cytotoxicity of an experimental restorative composite resin subjected to different light-curing regimens. METHODS: Forty round-shaped specimens were prepared and randomly assigned to four experimental groups (n=10), as follows: in Group 1, no light-curing; in Groups 2, 3 and 4, the composite resin specimens were light-cured for 20, 40 or 60 s, respectively. In Group 5, filter paper discs soaked in 5 µL PBS were used as negative controls. The resin specimens and paper discs were placed in wells of 24-well plates in which the odontoblast-like cells MDPC-23 (30,000 cells/cm²) were plated and incubated in a humidified incubator with 5% CO2 and 95% air at 37ºC for 72 h. The cytotoxicity was evaluated by the cell metabolism (MTT assay) and cell morphology (SEM). The data were analyzed statistically by Kruskal-Wallis and Mann-Whitney tests (p<0.05). RESULTS: In G1, cell metabolism decreased by 86.2%, indicating a severe cytotoxicity of the non-light-cured composite resin. On the other hand, cell metabolism decreased by only 13.3% and 13.5% in G2 and G3, respectively. No cytotoxic effects were observed in G4 and G5. In G1, only a few round-shaped cells with short processes on their cytoplasmic membrane were observed. In the other experimental groups as well as in control group, a number of spindle-shaped cells with long cytoplasmic processes were found. CONCLUSION: Regardless of the photoactivation time used in the present investigation, the experimental composite resin presented mild to no toxic effects to the odontoblast-like MDPC-23 cells. However, intense cytotoxic effects occurred when no light-curing was performed.

Effect of deproteinization and tubular occlusion on microtensile bond strength and marginal microleakage of resin composite restorations

Dentin adhesion procedure presents limitations, especially regarding to lifetime stability of formed hybrid layer. Alternative procedures have been studied in order to improve adhesion to dentin. OBJECTIVE: The aim of this study was to evaluate in vitro the influence of deproteinization or dentin tubular occlusion, as well as the combination of both techniques, on microtensile bond strength (µTBS) and marginal microleakage of composite resin restorations. MATERIAL AND METHODS: Extracted erupted human third molars were randomly divided into 4 groups. Dentin surfaces were treated with one of the following procedures: (A) 35% phosphoric acid gel (PA) + adhesive system (AS); (B) PA + 10% NaOCl + AS; (C) PA + oxalate + AS and (D) PA + oxalate + 10% NaOCl + AS. Bond strength data were analyzed statistically by two-way ANOVA and Tukey's test. The microleakage scores were analyzed using Kruskal-Wallis and Mann-Whitney non-parametric tests. Significance level was set at 0.05 for all analyses. RESULTS: µTBS data presented statistically lower values for groups D and B, ranking data as A>C>B>D. The use of oxalic acid resulted in microleakage reduction along the tooth/restoration interface, being significant when used alone. On the other hand, the use of 10% NaOCl alone or in combination with oxalic acid, resulted in increased microleakage. CONCLUSIONS: Dentin deproteinization with 10% NaOCl or in combination with oxalate significantly compromised both the adhesive bond strength and the microleakage at interface. Tubular occlusion prior to adhesive system application seems to be a useful technique to reduce marginal microleakage.

Impact and fracture resistance of an experimental acrylic polymer with elastomer in different proportions

The purpose of this study was to evaluate the impact and fracture resistance of acrylic resins: a heat-polymerized resin, a high-impact resin and an experimental polymethyl methacrylate with elastomer in different proportions (10, 20, 40 and 60%). 120 specimens were fabricated and submitted to conventional heat-polymerization. For impact test, a Charpy-type impact tester was used. Fracture resistance was assessed with a 3-point bending test by using a mechanical testing machine. Ten specimens were used for each test. Fracture (MPa) and impact resistance values (J.m-1) were submitted to ANOVA - Bonferroni's test - 5% significance level. Materials with higher amount of elastomer had statistically significant differences regarding to impact resistance (p < 0.05). Fracture resistance was superior (p < 0.01) for high-resistance acrylic resin. The increase in elastomer concentration added to polymethyl methacrylate raised the impact resistance and decreased the fracture resistance. Processing the material by injection decreased its resistance to impact and fracture.

Abrasion wear resistance of different artificial teeth opposed to metal and composite antagonists

One of the most important properties of artificial teeth is the abrasion wear resistance, which is determinant in the maintenance of the rehabilitation's occlusal pattern. OBJECTIVES: This in vitro study aims to evaluate the abrasion wear resistance of 7 brands of artificial teeth opposed to two types of antagonists. MATERIAL AND METHODS: Seven groups were prepared with 12 specimens each (BIOLUX & BL, TRILUX & TR, BLUE DENT & BD, BIOCLER & BC, POSTARIS & PO, ORTHOSIT & OR, GNATHOSTAR & GN), opposed to metallic (M & nickel-chromium alloy), and to composite antagonists (C & Solidex indirect composite). A mechanical loading device was used (240 cycles/min, 4 Hz speed, 10 mm antagonist course). Initial and final contours of each specimen were registered with aid of a profile projector (20x magnification). The linear difference between the two profiles was measured and the registered values were subjected to ANOVA and Tukey's test. RESULTS: Regarding the antagonists, only OR (M = 10.45 ± 1.42 µm and C = 2.77 ± 0.69 µm) and BC (M = 6.70 ± 1.37 µm and C = 4.48 ± 0.80 µm) presented statistically significant differences (p < 0.05). Best results were obtained with PO (C = 2.33 ± 0.91 µm and M = 1.78 ± 0.42 µm), followed by BL (C = 3.70 ± 1.32 µm and M = 3.70 ± 0.61 µm), statistically similar for both antagonists (p>0.05). Greater result variance was obtained with OR, which presented the worse results opposed to Ni-Cr (10.45 ± 1.42 µm), and results similar to the best ones against composite (2.77 ± 0.69 µm). CONCLUSIONS: Within the limitations of this study, it may be concluded that the antagonist material is a factor of major importance to be considered in the choice of the artificial teeth to be used in the prosthesis.