Band 36, Heft 8

In the present work, levofloxacin in situ gel formulation was developed using gelrite as a gelling agent in combination with hydroxy propyl methyl cellulose. The developed formulations were evaluated for physicochemical parameters, in vitro release, ex vivo transcorneal study, sterility testing, antimicrobial efficacy, ocular irritation study, histopathological and stability evaluation. The in vitro drug release study showed the extended drug release up to 12 h, and the best fit kinetic model was found to be Peppas model ( R 2 =0.9654), suggesting a Fickian diffusion process. The developed formulations showed optimized physicochemical results for all parameters. The optimized formulation showed therapeutically efficacious antimicrobial activity. Hens egg test-chorioallantoin membrane assay (HET-CAM) showed a mean score of 0.33 up to 24 h, which indicated the non-irritant property of the developed formulation. This non-irritant and stable in situ gel formulation of levofloxacin was found to be promising and safe for use as ocular delivery. The degradation rate constant and shelf life of developed optimized formulation (F14) were found to be low (1.213×10 -4 at 25°C) and 2.14 years, respectively. This renders them favorable for ocular use as they would gel once in contact with the tear fluid, thus reducing nasolacrimal drainage, but would thin upon shearing, preventing ocular irritation and therefore induced lacrimation.

Poly(vinyl alcohol) reinforced with nanohydroxyapatite (PVA-nHA) composite scaffolds were developed by varying the nHA (1%, 2%, 3%, 4%, and 5%, w/v) composition in the PVA matrix by solvent casting technique. The developed composite scaffolds were characterized using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, and contact angle measurement. The stability of the composite scaffolds in physiological environment was evaluated by swelling and degradation studies. Further, these composite scaffolds were tested for in vitro bioactivity, hemolysis, biocompatibility, and mechanical strength. SEM micrographs showed a homogenous distribution of nHA (3%, w/v) in the PVA matrix. XRD and ATR-FTIR analysis confirmed no phase contamination and the existence of the chemical bond between PVA-nHA at approximately 2474 cm -1 . PVA-nHA composite scaffolds with 3% (w/v) concentration of nHA showed nominal swelling and degradation behavior with good mechanical strength. The mechanical strength and degradation properties of the scaffold above 3% (w/v) of nHA was found to deteriorate, which is due to the agglomeration of nHA. The in vitro bioactivity and hemolysis studies showed improved apatite formation and hemocompatibility of the developed scaffolds. In vitro cell adhesion, proliferation, alkaline phosphatase activity, and Alizarin red S staining confirmed the biocompatibility of the composite scaffolds.

This study aimed (1) to use scanning electron microscopy associated with energy-dispersive spectroscopy (SEM-EDS) to characterize the surface of dental resins after nonthermal plasma (NTP) treatment and (2) to use surface energy analysis to evaluate whether NTP treatment protects the microhardness of the resins against the degradative effects of saliva. Twenty-eight acrylic and composite resin discs were fabricated and divided into four groups. Two groups received no surface treatment [control acrylic resin (Co/AR) and control composite resin (Co/CR] and two groups [NTP-treated acrylic resin (NTP/AR) and NTP-treated composite resin (NTP/CR)] were treated with NTP. One disc from each group was analyzed using SEM-EDS. Ten discs were subjected to surface energy analysis (before and after NTP) and microhardness assessments (at various time points). p<0.05 was used to determine statistical significance. Surface energy decreased after NTP treatment. Microhardness was reduced after 30 days in the Co/AR group and between 15 and 30 days in the NTP/AR group. Microhardness decreased in the Co/CR group after 15 and 30 days, whereas there was no difference after 30 days in the NTP/CR group. SEM images showed the presence of cracks and holes after 30 days in both Co/AR and NTP/AR groups. Cracks and silicon particles were observed after 30 days in the Co/CR group. Both the acrylic and composite resins exhibited hydrophobic properties after NTP treatment. The reduction in microhardness of the acrylic resin after NTP treatment was lower than that of the composite resin.

In this study, hydroxyapatite/polyvinyl alcohol (HAp-PVA) biocomposites were prepared using a spray drying method. HAp-PVA solutions fed to spray dryer were prepared by two different routes, namely, physical and in situ biomimetric methods. In the former method, HAp was synthesized without the presence of polymer and then HAp particles were incorporated into a PVA solution. In the second one, hydroxyapatite was in situ synthesized in the presence of PVA. Experiments were also run to investigate the effect of the molecular weight of PVA on the structure of spray-dried biocomposites. Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and particle size analyses were performed to characterize the produced HAp-PVA composites.

The thermal stability and ablation properties of silicone rubber composites filled with Fe 2 O 3 , SnO 2 , CuO, MgO, and Al 2 O 3 were researched using thermogravimetric analysis (TGA) and the oxyacetylene torch test. The effecting laws of metallic oxide on the thermal stability and ablation properties of silicone rubber composites were analyzed by uniform design method. TGA indicated that the thermal degradation process of silicone rubber composites took a two mass loss steps. The effecting order of metallic oxide on enhancing thermal stability property of silicone rubber composites in step 1 was MgO>SnO 2 > Fe 2 O 3 >Al 2 O 3 >CuO, whereas the order in step 2 was CuO> SnO 2 >MgO>Fe 2 O 3 >Al 2 O 3 . Furthermore, Fe 2 O 3 and SnO 2 had an evident synergistic effect on enhancing the thermal stability property and residual carbon of silicone rubber composites. The oxyacetylene torch test showed that the effecting order of metallic oxide on increasing ablation resistance property of silicone rubber composites in ablation process was CuO>MgO>Fe 2 O 3 >SnO 2 >Al 2 O 3 . Moreover, the line ablation rate of specimen 2 was 0.0499, which indicated that it had the best ablation resistance among all uniform samples. Furthermore, scanning electron microscopy also showed that the porous ceramic layer became much denser after the ablation process, and this will significantly improve the ablation resistance property.

Butyl acrylate-α-methyl methacrylate-glycidyl methacrylate (BA-MMA-GMA) terpolymer was successfully grafted onto carbon nanotubes (CNTs) via a facile grafting functionalization approach, affording an organically functionalized multiwalled CNTs (O-MWCNTs), which show improved mechanical and thermal properties in natural rubber/styrene-butadiene rubber (NR/SBR) composites. Under optimized conditions, the result of elongation at break of NR/SBR composites combined with 1.5 parts per hundred rubber (phr) O-MWCNTs is 450% compared to 376% of pristine NR/SBR composites, which is proportional to tensile strength due to the mixed O-MWCNTs in the rubber matrix. Transmission electron microscopy study shows that O-MWCNTs (1.5 phr) can disperse uniformly in NR/SBR/O-MWCNT composites. A scanning electron microscopy study on the fractured surface morphology of the optimized composites reveals that a BA-MMA-GMA terpolymer can interact with the rubber matrix strongly. The decreased height of the maximum tanδ peak shows that O-MWCNTs can reduce the heat buildup and damping capability of NR/SBR/O-MWCNT composites. The largest enhancement observed in the thermal degradation curves of composites is, for the first time, about 70°C, which can be attributed to enhanced interfacial interaction between MWCNTs and the rubber matrix.

Coatings from poly(glycidoxy siloxane) resins were developed and their mechanical properties examined. Three different resins with varying numbers of methyl siloxane and glycidyl siloxane units were tested. Crystallinity was found to be a very important indicator of the mechanical properties of coatings, as the parameters such as cupping and hardness were linearly dependent on the degree of crystallinity of coatings. The method involving the spectrophotometric determination of unbounded amine curing agent was successfully applied as a way of optimizing the curing process both for expected mechanical properties and for ecological aspect. It was found that the resin with 50 methyl siloxane and 25 glycidyl siloxane units was the most appropriate for technological use because of the preferred mechanical properties and stability of technological parameters. Interestingly, this type of resin was characterized by the lowest degree of crystallinity. The curing conditions leading to the optimal product corresponded to 30 min of curing at 120°C or 20 min at 140°C. Under such conditions, the amount of released unbounded amine was the lowest. It was also found that poly(glycidoxy) siloxane resins may be ecologically valuable since the release of amine from this type of resins is smaller than that from a typical epoxy resin.

An experimental study to observe the change in impact response of rigid polyurethane foam due to γ irradiation is presented. The foam samples were irradiated using a 60 Co based γ irradiator, γ Chamber 5000. Dynamic tests were performed on unirradiated and irradiated cubical foam specimens in a drop weight testing machine to characterize the mechanical properties. Structural characterization was performed using phase-contrast X-ray imaging and scanning electron microscopy (SEM). The results reveal a significant change in the dynamic response of polyurethane foam after irradiation due to change in structure. The response of foam gets stiffer in the initial linear phase, and densification (lockup) occurs well below the strains at which lockup occurs for an unirradiated foam. The ramifications of this study towards the application of polyurethane foam as an impact limiter in nuclear shipping casks are discussed.

In this study, the fiber extracted from the fruit of a luffa plant was used as a reinforcement to an unsaturated polyester resin matrix under two different fiber conditions. The untreated and alkali-treated fibers were impregnated and pressed to produce laminates. Composites were made with an optimal compression pressure of 5 MPa for 12 h of curing at room temperature. Ejected samples were cut according to the dimensions specified by the ASTM test specifications. To investigate the effects of fiber surface treatment on the frictional behavior of the produced composites under dry sliding wear conditions, wear test was conducted in a pin-on-disc equipment as per ASTM G99 at varying sliding velocities. In addition, hardness and un-notched impact strengths were measured and discussed. Results showed that the change in fiber surface morphology significantly changed the coefficient of friction of the composites. Moreover, the sliding distance had a prominent influence in increasing the friction between the composite and the counter face.

Silica fume was modified by a silane coupling agent (KH-550). The modified silica fume was further investigated to reinforce polyurethane (PU) composites. Unmodified and modified silica fume reinforced PU composites were prepared. Through the comparisons of Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM) of unmodified and modified silica fume, the agglomerations of silica fume particles were effectively prevented as KH-550 was grafted. The compressive strength of the modified silica fume/PU composites was largely improved, because KH-550 could react with both silica fume and PU. Meanwhile, modified silica fume turned from hydrophilic to hydrophobic; a better dispersion was realized in the PU elastomers compared to the unmodified silica fume. The reinforcement effects were evaluated based on the results of a universal test machine in comparison with unmodified silica fume/PU composites.

Since polyethylene (PE) has been widely accepted for the production of high-pressure fluid conveying pipelines, studies devoted to weldability of PE connections were always of major importance. In this study, two industrial PE grades designed for pipe production, namely PE80 and PE100, were injection molded, cut, and then welded as PE100-PE100, PE100-PE80, and PE80-PE80. The heat-welded joints were assessed by differential scanning calorimetry and tensile measurements. The results obtained from thermal and mechanical analyses were compared with equivalents for aged samples. Thermal analysis revealed that the melting point of the PE100-PE100 sample is obviously larger than the one for the PE80-PE80 joint, for the PE80 chains deteriorate the crystallization of PE100. Further, the PE80-PE80 sample showed the lowest lamellar thickness and crystalline molecular weight among the studied joints. The aging process was found to increase lamellar thickness and molecular weight, though in the PE100-PE100 sample such quantities very limitedly increased. The yield stress of aged joints was higher than that for just-prepared samples, while an inverse trend was seen for strain at break. From a practical viewpoint, the PE100-PE100 welds offer better properties.

This paper presents a study of the characteristics of axial vibration of a screw in the filling process for a novel dynamic injection molding machine. By simplifying a generalized model of the injection screw, physical and mathematic models are established to describe the dynamic response of the axial vibration of a screw using the method of lumped-mass. The damping coefficient of the screw is calculated in the dynamic filling process. The amplitude-frequency characteristics are analyzed by the simulation and experimental test of polypropylene. The results show that the amplitude of a dynamic injection molding machine is not only is related to structure parameters of the screw and performance of the material, such as non-Newtonian index, but also depends on the processing parameters, such as vibration intensity and injection speed.