A multipurpose specimen-carrier for handling small biological objects through critical point drying

Micro-Patterning of PEG-Based Hydrogels With Gold Nanoparticles Using a Reactive Micro-Contact-Printing Approach

In this work a novel, relatively simple, and fast method for patterning of gold nanoparticles (Au NPs) on poly(ethylene glycol) (PEG)-based hydrogels is presented. In the hereby exploited reactive micro-contact printing (reactive-μ-CP) process, the surface of a micro-relief patterned PDMS-stamp is first functionalized with an amino-silane self-assembled monolayer (SAM), which is then inked with Au NPs. The stamp is subsequently brought into conformal contact with thiol-functionalized PEG-based hydrogel films. Due to the strong gold-thiol interactions the Au NPs are adequately and easily transferred onto the surfaces of these soft, multifunctional PEG hydrogels. In this way, defined μ-patterns of Au NPs on PEG hydrogels are achieved. These Au NPs patterns allow specific biomolecular interactions on PEG surfaces, and cell adhesion has been studied. Cells were found to effectively adhere only on Au NPs micro-patterns and to avoid the anti-adhesive PEG background. Besides the cell adhesion studies, these Au NPs μ-patterns can be potentially applied as biosensors in plasmon-based spectroscopic devices or in medicine, e.g., for drug delivery systems or photothermal therapies.

Effect of cyclosporine during initiation of transplant arteriosclerosis. An ultrastructural study in the aorta-transplanted rabbit

The immunosuppressant cyclosporine protects against the development of experimental transplant arteriosclerosis. To investigate the mechanism underlying this effect, aorta-allografted rabbits were randomly assigned to cyclosporine (n = 6) in the human therapeutic range or to its vehicle (n = 5). Perfusion fixation was performed 2 weeks after the transplantation, followed by light, scanning and transmission electron microscopy examination. Intimal proliferation was absent in native aortas, present in all grafts from vehicle-treated animals, and either absent or sparse in grafts from cyclosporine-treated rabbits. The endothelium of native aortas from both vehicle- and cyclosporine-treated rabbits was normal. Aortic allografts from cyclosporine-treated rabbits exhibited a normal endothelium with only a few adhering mononuclear cells, whereas aortic allografts from vehicle-treated rabbits exhibited an endothelial surface ranging from near-normal with only few adhering platelets and mononuclear cells, to an almost destroyed endothelium, lined with lymphocyte-like cells, monocytes/macrophages, platelets, erythrocytes and fibrin; in the subendothelial layer, mononuclear cells and smooth muscle cells were abundant. These results suggest that damage to the endothelial cells as well as invasion of lymphocytes, monocytes/macrophages and smooth muscle cells into the subendothelial space are important events during initiation of transplant arteriosclerosis, and that cyclosporine largely attenuates these early pathological changes.

Fine structure of the endolymphatic duct in the rat. A scanning and transmission electron microscopy study

To investigate the surface morphology of the endolymphatic duct epithelium, 8 rats were vascularly perfused with glutaraldehyde in a buffered and oxygenated blood substitute. Optimal preservation of the epithelium for scanning electron microscopy was attained by coating of the specimens with OsO4 and thiocarbohydrazide followed by a continuous dehydration procedure. Three types of cells were identified with the scanning electron microscope: A polygonal and oblong epithelial cell was observed in the largest number throughout the duct, whereas in the juxta-saccular half of the duct two additional types of epithelial cells were observed. The scanning electron microscopical observations are compared and discussed with reference to transmission electron microscopical observations of the endolymphatic duct.

Surface morphology of the endolymphatic duct in the rat. A scanning electron microscopy study

Following intracardiac vascular perfusion fixation of 8 rats with glutaraldehyde in a buffered and oxygenated blood substitute, the vestibular aqueduct and endolymphatic duct were opened by microsurgery of the resulting 16 temporal bones. Optimum preservation of the epithelium for scanning electron microscopy was attained by coating of the specimens with osmium tetroxide and thiocarbohydrazide followed by a continuous dehydration procedure. This technique permitted, for the first time, an investigation of the surface morphology of the epithelial cells in the endolymphatic duct. Three types of cells were identified with the scanning electron microscope. A polygonal and oblong epithelial cell was observed in the largest number throughout the duct, and in the juxtasaccular half of the duct, two additional types of epithelial cells were observed. The scanning electron microscopic observations are compared and discussed with reference to previous transmission electron microscopic studies of the endolymphatic duct.

Mesothelium of Reissner's membrane in guinea pigs: an electron microscopic study

The mesothelial cells of Reissner's membrane in guinea pigs were found to be connected by junctional complexes. No cell discontinuities or gaps were observed by scanning or transmission electron microscopy. These results are not in accordance with previous studies. They were achieved by in vivo vascular perfusion fixation, handling of cochleae in protective specimen carriers, thiocarbohydrazide treatment and continuous dehydration. Findings in the present study indicate that the interepithelial space between the epithelial and mesothelial cell layers constitutes a specific compartment which must be considered when examining solute transport over Reissner's membrane.

Critical-point drying versus freeze drying for scanning electron microscopy: a quantitative and qualitative study on isolated hepatocytes

Critical-point drying and freeze drying were compared both quantitatively and qualitatively as preparative procedures for scanning electron microscopy. Isolated hepatocytes were used as model cells. Nomarski differential interference contrast microscopy was used for light microscopic measurements of the hepatocytes in the unfixed, the glutaraldehyde fixed, the glutaraldehyde + OsO4 fixed, the critical-point dried and the freeze dried states. Critical-point dried hepatocytes were found to shrink to 38% of glutaraldehyde + OsO4 fixed volume, whereas optimal freeze dried hepatocytes (frozen in water saturated with chloroform and freeze dried at 183 K for 84 h) were found to shrink to 51% of glutaraldehyde + OsO4 fixed volume. Transmission and scanning electron micrographs of the critical-point dried cells showed well-preserved ultrastructure and surface structure. Micrographs of the freeze dried cells showed ultrastructure destroyed by internal ice crystals and surface structure destroyed by external ice crystals. Double-fixed isolated hepatocytes were shown to swell during storage in buffer and to shrink during storage after critical-point drying. For low magnification scanning electron microscopy (up to about 3000 times) both critical-point drying and freeze drying can be used. However, for high magnification scanning electron microscopy, critical-point drying is superior to freeze drying.

Scanning electron microscopy of the oocyst and sporocyst of Toxoplasma gondii

Oocysts and sporocysts of T. gondii were examined with the scanning electron microscope. The oocysts were slightly ellipsoidal in shape with a smooth outline. The sporocysts were also ellipsoidal with a smooth surface on which there were a number of raised ridges. The ridges represent the junctions between the four plates comprising the sporocyst wall. From the distribution of the ridges it was concluded that the wall consisted of two upper and two lower plates which were at an angle to each other and which interlocked along the mid-line suture. The specific orientation of the plates would provide a structure extremely resistant to mechanical disruption. During excystation, an infolding of the surface was observed along the suture lines between the plates of the sporocyst wall.

Improved handling of structural fragile cell-biological specimens during electron microscopic preparation by the exchange method

An exact method of preparation of soft biological specimens for electron microscopic analysis of surface fine structures is described. It allows routine preparations of fragile specimens for SEM and TEM imaging modes. With this procedure physical preparation parameters such as mechanical loads on the specimen surface or changes of temperature are controlled. The wet specimens are premounted in cheap disposable BEEM-containers or glass boats and are constantly kept under liquid in a closed system. The exchange of preparation media is performed continuously and, if necessary, over gradients. For comparative investigations with different EM-modes, at each step of the procedure parts of the specimens may be removed for individual processing. Conventionally prepared critical-point dried specimens are compared to those processed by the exchange technique and preservation of surface fine structures is demonstrated. Shadow-casted clathrin cages and stereo-replicas of virus infected cell cultures are shown in TEM preparations. For SEM, coverslip cell cultures and isolated glomerulus basement membranes are prepared and an additional flat embedding for TEM ultrathin sections is demonstrated.

Hemoglobin-depleted human erythrocyte ghosts: characterization of morphology and transport functions

A method of preparing hemoglobin-depleted resealed ghosts with an extremely low hemoglobin content is described. The membrane morphology, the crossed immunoelectrophoresis pattern of the membrane proteins, and the transport function of these ghosts have been examined. Electron microscopic examination of the ghosts on hydrophilic as well as hydrophobic grid surfaces revealed a faint filamentous network (spectrin) associated with the membrane. The ghosts were found to have permeabilities towards small polar molecules (water and mannitol) and ions (chloride, sodium, and potassium) which are quantitatively very close to those of intact red cells. It is concluded that white ghosts prepared by the present method are well suited for simultaneous studies of morphology, membrane biochemistry, and membrane transport functions.

A simple low-cost critical point dryer with continuous flow dehydration attachment

A simple low-cost critical point dryer with continuous flow dehydration attachment is described. By using the critical point pressure chamber for all fluid exchanges, loss of material and air-drying artefacts due to specimen handling are reduced. An operating schedule that allows the optimum path around the critical point process to be followed is proposed.

A method for handling free cells through critical point drying

A method is described in which free cells were dehydrated in suspension, put one double-coated tape attached to a specimen stub and dried from CO2. The method provides a simple, fast means of handling free cells when using the critical point method of drying.

Simple magnetic holders for critical point drying of microspecimen suspensions

Microspecimens can be critical point dried from suspension in holders consisting of three magnets and two filters. These holders are inexpensive, require no construction, and are easily assembled and disassembled.