Browsing by Subject "polymerization"

Now showing 1 - 3 of 3
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    In vitro evaluation of polymerization energy for bulk fill composites
    (2016-05) AlRasheed, Rawan S.; Platt, Jeffery A.; Wallace, Joseph; Matis, Bruce A.; Cook, Norman Blaine; Chu, Tien-Min Gabriel
    Recently, the concept of “bulk-fill” resin-based composites (RBCs) has been re-emphasized, with claimed improvements in depth of cure (DOC) with similar mechanical properties and comparable adaptation to walls and margins relative to conventional composite. More research is needed to carefully examine the properties of these new materials. The objective of this study was to measure the light energy, microhardness (VHN), and elastic modulus across the depth of one conventional and three bulk-fill RBCs. Materials and Methods: Three commercially available bulk-fill RBCs (Tetric EvoCeram Bulk Fill [TE], SonicFill [SF], X-tra fill[XF]) and one conventional RBC (Premise [PR]) were evaluated (n = 10). DOC (using Vickers’s microhardness), elastic modulus (using atomic force microscopy), and the mean irradiance and total light energy transmitted through different thicknesses of RBC were measured by a spectrometer. The effects of group, location, and curing depth on VHN were analyzed using mixed-model ANOVA. Elastic modulus and light energy comparisons were made using two-way ANOVA, with a significance level of 5 percent. Results: There was a significant difference in the depths for the mean irradiance and total energy between different depths in all materials. All materials achieved the manufacturers’ claimed DOC. XF had the highest DOC with 7 mm and a light energy of 0.56± 0.02 J/cm2 at 7 mm. PR had the lowest DOC with 3 mm and a light energy of 0.84 ±0.12 J/cm2 at 3 mm. The elastic modulus showed significant variation in depth profiles that were different than the DOC. Significance: The manufacturers’ claims for bulk-fill DOC were achieved using a microhardness method. However, this method failed to detect the quality of the polymerization. Assessment of the elastic modulus using AFM is a promising method for greater understanding of the polymerization.
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    Modular crosslinking of gelatin based thiol-norbornene hydrogels for in vitro 3D culture of hepatic cells
    (ACS Biomaterials Science and Engineering, 2015-10-21) Greene, Tanja L.; Lin, Chien-Chi; Xie, Dong; Dai, Guoli; Yoshida, Ken
    As liver disease becomes more prevalent, the development of an in vitro culture system to study disease progression and its repair mechanisms is essential. Typically, 2D cultures are used to investigate liver cell (e.g., hepatocyte) function in vitro; however, hepatocytes lose function rapidly when they were isolated from the liver. This has promoted researchers to develop 3D scaffolds to recreate the natural microenvironment of hepatic cells. For example, gelatin-based hydrogels have been increasingly used to promote cell fate processes in 3D. Most gelatin-based systems require the use of physical gelation or non-specific chemical crosslinking. Both of these methods yield gelatin hydrogels with highly interdependent material properties (e.g., bioactivity and matrix stiffness). The purpose of this thesis research was to prepare modularly crosslinked gelatin-based hydrogels for studying the influence of independent matrix properties on hepatic cell fate in 3D. The first objective was to establish tunable gelatin-based thiol-norbornene hydrogels and to demonstrate that the mechanical and biological properties of gelatin hydrogels can be independently adjusted. Furthermore, norbornene and heparin dual-functionalized gelatin (i.e., GelNB-Hep) was prepared and used to sequester and slowly release hepatocyte growth factor (HGF). The second objective was to investigate the viability and functions of hepatocytes encapsulated in gelatin-based hydrogels. Hepatocellular carcinoma cells, Huh7, were used as a model cell type to demonstrate the cytocompatibility of the system. The properties of GelNB hydrogels were modularly tuned to systematically evaluate the effects of matrix properties on cell viability and functions, including CYP3A4 activity and urea secretion. The last objective was to examine the effect of heparin immobilization on hepatocyte viability and functions. The conjugation of heparin onto GelNB led to suppressed Huh7 cell metabolic activity and improved hepatocellular functions. This hybrid hydrogel system should provide a promising 3D cell culture platform for studying cell fate processes.
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    Photo-Curing Through Single Apertures: The Phenomenon and Its Influence On Polymerization
    (2013) MacPherson, Meoghan Elizabeth; Chu, Tien-Min Gabriel; Brown, David T.; Naumann, Christoph A.; Moore, B. Keith; Platt, Jeffrey A., 1958-
    Reduction of the polymerization shrinkage stress inherent of dimethacrylate-based resin composites has been a work in progress since the phenomenon was first described by Dr. Rafael L. Bowen in 1967. Contemporary efforts to modify the composites or the curing protocols for polymerization have proven a challenging task with controversial results. Influenced by existing mathematical models relating exposure, curing time and depth of cure of resin composites, a novel method for the reduction of polymerization shrinkage stress is proposed. By polymerizing through a single aperture mask, a dental light curing unit is transformed from a planar light source to a point light source, and a fully cured, three-dimensional “bullet” shaped curing front is predicted for the cured resin below. So long as the edges of the bullet do not touch the cavity walls or floor, the shrinkage stress of the bullet is not transferred. Follow-up with an unmasked curing unit then fully polymerizes the restoration. By reducing the volume of uncured composite in contact with the cavity walls and floor, shrinkage stress of the restoration is also reduced. The objective of the present study was to demonstrate this curing phenomenon with a model resin composite using masks with aperture diameters of 0.5, 0.4, and 0.25 mm and curing times of 10, 20, 30, and 40 seconds. The resulting curing front was evaluated quantitatively and qualitatively. From this, mathematical models of the curing front were derived. Selected combinations of aperture mask and curing time were then investigated to evaluate the influence of this phenomenon on the degree of conversion, Knoop hardness, and polymerization shrinkage stress of the same model resin composite. Group differences were analyzed using a one-way ANOVA at 5% significance.