Spin-coated epoxy resin embedding technique enables facile SEM/FIB thickness determination of porous metal oxide ultra-thin films.

A facile nonsubjective method was designed to measure porous nonconductive iron oxide film thickness using a combination of a focused ion beam (FIB) and scanning electron microscopy. Iron oxide films are inherently nonconductive and porous, therefore the objective of this investigation was to optimize a methodology that would increase the conductivity of the film to facilitate high resolution imaging with a scanning electron microscopy and to preserve the porous nature of the film that could potentially be damaged by the energy of the FIB. Sputter coating the sample with a thin layer of iridium before creating the cross section with the FIB decreased sample charging and drifting, but differentiating the iron layer from the iridium coating with backscattered electron imaging was not definitive, making accurate assumptions of the delineation between the two metals difficult. Moreover, the porous nature of the film was lost due to beam damage following the FIB process. A thin layer plastication technique was therefore used to embed the porous film in epoxy resin that would provide support for the film during the FIB process. However, the thickness of the resin created using conventional thin layer plastication processing varied across the sample, making the measuring process only possible in areas where the resin layer was at its thinnest. Such variation required navigating the area for ideal milling areas, which increased the subjectivity of the process. We present a method to create uniform thin resin layers, of controlled thickness, that are ideal for quantifying the thickness of porous nonconductive films with FIB/scanning electron microscopy.

A PLGA membrane controlling cell behaviour for promoting tissue regeneration.

Barrier membranes are used in periodontal applications with the aim of supporting bone regeneration by physically blocking migrating epithelial cells. We report a membrane design that has a surface topography that can inhibit epithelial cell migration and proliferation on one side and a topography that guides osteoblast migration to a desired area. A PLGA copolymer (85:15) blended with MePEG, was cast to have surfaces with smooth, grooved or sandblasted-acid-etched topographies. Epithelial cells spread on smooth surfaces after 24 h, and cell numbers increased after 5 days. Cells on the smooth surface exhibited no preferred direction of migration. On the sandblasted-acid-etched topography epithelial cells spread but the cell number did not significantly increase after 5 days. Cell migration was inhibited on this surface. Osteoblasts spread on both grooved and smooth surfaces and cell number increased after 5 days on all surfaces. The cells that adhered in the grooves migrated preferentially in the direction of the grooves. Positive alkaline phosphatase staining was seen on all surfaces within 4 weeks and positive Von Kossa nodule staining within 6 weeks. These results suggest that surface topographies replicated on opposite sides of a biodegradable polymers membrane can inhibit proliferation and migration of the epithelial cells, and promote proliferation and directional migration of osteoblasts. Addition of appropriate surface topographies to membranes used in guided tissue regeneration has the possibility of improving clinical performance in periodontal tissue regeneration procedures.

Focal adhesion quantification - a new assay of material biocompatibility? Review.

The development of novel synthetic biomaterials is necessitated by the increasing demand for accelerated healing of tissues following surgical intervention. Strict testing of such materials is necessary before application. Currently, before any material can be marketed, approval by regulatory organisations such as the FDA is required. Presently, in vitro testing is performed as a prerequisite to in vivo evaluation. The in vitro techniques currently employed do not reflect the progress in our understanding of extra and intra-cellular processes, with far more sensitive in vitro evaluations now available. Obtaining quantifiable data is increasingly relevant to evaluating events occurring in vivo. Quantifying cell adhesion to surfaces provides some of this data as an initial assessment method. Major developments in this field are occurring but many investigators still use less than optimal methods for assessing biomaterials. The relevance of using cell adhesion assays to help determine biomaterial biocompatibility is reviewed. Additionally, current in vitro methods of evaluating biomaterials are discussed in the context of novel testing concepts developed by the authors.

Variation in cell-substratum adhesion in relation to cell cycle phases.

The quantification of focal adhesion sites offers an assessable method of measuring cell-substrate adhesion. Such measurement can be hindered by intra-sample variation that may be cell cycle derived. A combination of autoradiography and immunolabelling techniques, for scanning electron microscopy (SEM), were utilised simultaneously to identify both S-phase cells and their focal adhesion sites. Electron-energy 'sectioning' of the sample, by varying the accelerating voltage of the electron beam, combined with backscattered electron (BSE) imaging, allowed for S-phase cell identification in one energy 'plane' image and quantitation of immunogold label in another. As a result, it was possible simultaneously to identify S-phase cells and their immunogold-labelled focal adhesions sites on the same cell. The focal adhesion densities were calculated both for identified S-phase cells and the remaining non-S-phase cells present. The results indicated that the cell cycle phase was a significant factor in determining the density of focal adhesions, with non-S-phase cells showing a larger adhesion density than S-phase cells. Focal adhesion morphology was also seen to correspond to cell cycle phase; with 'dot' adhesions being more prevalent on smaller non-S-phase and the mature 'dash' type on larger S-phase cells. This study demonstrated that when quantitation of focal adhesion sites is required, it is necessary to consider the influence of cell cycle phases on any data collected.

Simultaneously identifying S-phase labelled cells and immunogold-labelling of vinculin in focal adhesions.

A new combination of autoradiography and immunolabelling techniques is presented that allows the simultaneous identification of both S-phase cells and their focal adhesions using scanning electron microscopy. The technique allows both labels to be discerned visually by their unique shapes and location within and on the cell. S-phase cells were radio-labelled with a pulse of tritiated thymidine, selectively incorporated into synthesizing DNA. The cells were then immunogold-labelled for the focal adhesion protein, vinculin, prepared for autoradiography, and embedded in resin. The resin was then polymerized before removing the substrate, to expose the embedded cell undersurface. Electron-energy 'sectioning' of the sample by varying the accelerating voltage of the electron beam allowed separate S-phase cell identification in one electron-energy 'section' and visualization of immunogold label in another 'section', within the same cell. As a result of applying this technique it was possible to positively identify S-phase cells and immunogold-labelled focal adhesions on the same cell simultaneously, which could be used to quantify focal adhesion sites on different substrates.