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Abstract: We have explored the use of X-ray microcomputed tomography (μCT) for assessing cell adhesion and proliferation in polymer scaffolds. Common methods for examining cells in scaffolds include fluorescence microscopy and soluble assays for cell components such as enzymes, protein or DNA. Fluorescence microscopy is generally qualitative and cannot visualize the scaffold interior. Soluble assays quantitatively measure cell number but do not yield information on cell spatial distribution. Herein, the ability of μCT to detect cells in scaffolds was compared with fluorescence microscopy and a soluble DNA assay. Comparisons were performed using polymer scaffolds that were seeded with cells at different densities and cultured for different times. The results showed that fluorescence microscopy had better resolution than μCT and that the soluble DNA assay was approximately 5× more sensitive than μCT under the conditions tested. However, μCT was able to image through opaque scaffolds to yield quantitative 3D imaging and analysis via a single, non-invasive modality. Quantitative μCT analysis of cell penetration into scaffolds was demonstrated. Further, quantitative μCT volume analysis required that the cell density in the scaffolds be greater than 1 million cells per mL indicating that μCT is best suited for quantifying cells at relatively high density during culture in scaffolds. In sum, the results demonstrate the benefits and limitations of using μCT for 3D imaging and analysis of cell adhesion and proliferation in polymer scaffolds. [Copyright &y& Elsevier]

Abstract: Objectives: The main objective of this study was to assess the feasibility of using X-ray microcomputed tomography (μCT) as a viable technique for accurate measurements of composite volumetric changes due to polymerization. Methods: μCT, a non-destructive 3D imaging technique that measures the intensity of content at each voxel, was used to determine the volume of experimental and commercial polymeric dental composites before and after photopolymerization. The experimental composites consisted of various mass ratios of 2,2-bis(4-(2-hydroxy-3-methacryloxypropoxy)-phenyl]propane (BisGMA) and triethylene glycol dimethacrylate (TEGDMA) filled with various amounts of barium boroaluminosilicate glass and fumed amorphous silica. Polymerization shrinkage was determined using μCT and shrinkage calculated based on density measurements. Results: μCT was successfully used to calculate volumetric shrinkage of dental composites. Results agreed well with shrinkage obtained via density measurements of the same sample. The addition of radio opaque filler was necessary to achieve sufficient contrast between the sample and background. Appropriate image analysis procedures were needed to obtain the volumes of sample specimens. Significance: μCT enables the characterization of polymerization shrinkage under clinically relevant conditions. In particular, the sample geometry and the physical state (liquid or solid) are flexible. The current test allowed multiple samples to be measured at the same time. In addition, the ability to accurately measure the size and shape of the object will allow multiple properties to be determined simultaneously. [Copyright &y& Elsevier]

Abstract: Objective: Use X-ray microcomputed tomography (μCT), to test the hypothesis that composite shrinkage and sites of potential leakage in human teeth are non-uniformly distributed and depend on cavity geometry and C-factor. Methods: Two holes of equal volume but different dimensions were drilled into the exposed dentin of extracted human molars. The cavities were filled with composite and teeth were scanned, before and after curing, using μCT. Three-dimensional (3D) reconstructions of the data were prepared and analyzed using image analysis software. Results: 3D reconstructions showed that cavity geometry did not affect the polymerization shrinkage. The shrinkage for all restorations was 2.66±0.59%, and cavity dimensions did not affect the volume lost, either in quantity or location on the sample. Potential leakage sites were identified by gap formations and found to be non-uniformly distributed along the tooth–composite interface. Leakage in regions calculated by μCT was confirmed by visualization of sectioned samples with confocal laser scanning microscopy. Significance: μCT evaluation will add tremendous value as part of a suite of tests to characterize various properties of dental materials. The non-uniform distribution of potential leakage sites about the cavities that was determined by μCT emphasizes the inadequacy of traditional methods of determining leakage, which are capable of analyzing only limited areas. Additionally, μCT evaluation can produce quantitative analyses of shrinkage and leakage, compared to the conventional methods, which are qualitative or semi-quantitative. Finally, experimentally determined shrinkage and leakage of composite in extracted teeth agrees with the results of similar experiments in model cavities, confirming the validity of those models. [Copyright &y& Elsevier]

Abstract: We have developed a combinatorial method for determining optimum tissue scaffold composition for several X-ray imaging techniques. X-ray radiography and X-ray microcomputed tomography enable non-invasive imaging of implants in vivo and in vitro. However, highly porous polymeric scaffolds do not always possess sufficient X-ray contrast and are therefore difficult to image with X-ray-based techniques. Incorporation of high radiocontrast atoms, such as iodine, into the polymer structure improves X-ray radiopacity but also affects physicochemical properties and material performance. Thus, we have developed a combinatorial library approach to efficiently determine the minimum amount of contrast agent necessary for X-ray-based imaging. The combinatorial approach is demonstrated in a polymer blend scaffold system where X-ray imaging of poly(desaminotyrosyl-tyrosine ethyl ester carbonate) (pDTEc) scaffolds is improved through a controlled composition variation with an iodinated-pDTEc analog (pI2DTEc). The results show that pDTEc scaffolds must include at least 9%, 16%, 38% or 46% pI2DTEc (by mass) to enable effective imaging by microradiography, dental radiography, dental radiography through 0.75cm of muscle tissue or microcomputed tomography, respectively. Only two scaffold libraries were required to determine these minimum pI2DTEc percentages required for X-ray imaging, which demonstrates the efficiency of this new combinatorial approach for optimizing scaffold formulations. [Copyright &y& Elsevier]