Lamellar Preparation Research Articles

The lamellar preparation of continuous porosity-graded Si3N4 ceramics without obvious interfaces for broadband radome application

Traditional layered broadband radomes are challenging to meet the needs of the high-temperature application, due to thermal mismatch between their layers. In this study, porous Si3N4 ceramics with a novel continuous porosity gradient from 54.7% to 82.4% were achieved by lamellar gel-casting, freeze-drying, and subsequent sintering process. The porosity-graded structure in Si3N4 ceramics shows no failure or cracks after sintering, benefiting from the low shrinkage after sintering at 1900 °C with the rapid sintering rate. The continuous porosity-graded structure without obvious interfaces was architected by ice crystal growth during solidification and the growth of rodlike β-Si3N4 grains across the interfaces during sintering. This approach can be beneficial to designing high wave transmission performance at specific broadband for radome.

Indications for intraoperative anterior segment optical coherence tomography in corneal surgery

PurposeRecently, intraoperative optical coherence tomography (iOCT) has evolved in the field of ophthalmic surgery. So far, the use of iOCT was mainly focused to lamellar keratoplasty, especially deep anterior lamellar keratoplasty (DALK) and Descemet membrane endothelial keratoplasty (DMEK). The aim of this study was to report our experiences with iOCT to introduce new possibilities of this application.MethodsWe used iOCT in 18 patients who underwent the following surgeries: DALK, DMEK, penetrating keratoplasty, autologous limbal transplantation, transscleral suture fixation of a posterior chamber lens, pannus removal on corneal surface and newborn investigation in Peters’ anomaly. We obtained qualitative video data for all procedures.ResultsWith the iOCT, the cannula placement during DALK preparation of the recipient cornea and bubble formation could be visualized to improve the success rate of the big bubble injection. In DMEK, the iOCT enables the visualization of Descemet’s membrane removal in the recipient and graft orientation as well as better control of graft attachment. The iOCT enables intraoperative visualization of the graft–host interface during penetrating keratoplasty. During autologous limbal transplantation, transscleral suture fixation of a posterior chamber lens and removal of corneal surface pannus the iOCT is capable of showing the thickness of lamellar preparations to avoid penetrations and to save healthy recipient’s tissue.ConclusionThe iOCT is a helpful device for intraoperative anterior segment imaging not only for DALK and DMEK. It is also beneficial in penetrating keratoplasty and every other form of lamellar preparation during corneoscleral surgery.

Modified lipid and protein dynamics in nanodiscs

For membrane protein studies, nanodiscs have been shown to hold great potential in terms of preparing soluble samples while maintaining a lipid environment. Here, we describe the differences in lipid order and protein dynamics in MSP1 nanodiscs compared to lamellar preparations by solid-state NMR. For DMPC, an increase of the dipolar C-H lipid acyl chain order parameters in nanodiscs is observed in both gel- and liquid crystalline phases. Incorporating proteorhodopsin in these nanodiscs resulted in a significantly longer rotating frame spin-lattice relaxation time for 13C leerzeichen and better cross polarisation efficiency due to restricted protein dynamics. A comparison of 13C–13C correlation spectra revealed no structural differences. The incorporation of proteorhodopsin into nanodiscs has been optimised with respect to detergent and to protein/scaffold protein/lipid stoichiometries. Its functional state was probed by time-resolved optical spectroscopy revealing only minor differences between lamellar and nanodisc preparations. Our observations show remarkable dynamic effects between membrane proteins, lipids and scaffold protein. The potential use of nanodiscs for solid-state NMR applications is discussed.

Endothelial quality of pre-cut posterior corneal lamellae for Descemet membrane endothelial keratoplasty with a stromal rim (DMEK-S): two-year outcome of manual preparation in an ocular tissue bank

To assess the quantitative and qualitative parameters of pre-cut posterior corneal lamellae for Descemet membrane endothelial keratoplasty with a stromal rim (DMEK-S) prepared manually in the Ocular Tissue Bank Prague. All 65 successfully prepared pre-cut posterior corneal lamellae provided for grafting during a 2-year period were analyzed retrospectively. The lamellae, consisting of a central zone of endothelium-Descemet membrane surrounded by a supporting peripheral stromal rim, were prepared manually from corneoscleral buttons having an endothelial cell density higher than 2,500 cells/mm(2). The live endothelial cell density, the percentage of dead cells, the hexagonality and the coefficient of variation were assessed before and immediately after preparation as well as after 2 days of organ culture storage at 31 °C. Altogether, the endothelium of 57 lamellae was assessed. Immediately after preparation, the mean live endothelial cell density was 2,835 cells/mm(2) and, on average, 1.8 % of dead cells were found. After 2 days of storage, the cell density decreased significantly to 2,757 cells/mm(2) and the percentage of dead cells to 1.0 %. There was a significant change in the mean hexagonality and the coefficient of variation after lamellar preparation and subsequent storage. The amount of tissue wasted during the preparation was 23 %. The endothelial cell density of posterior corneal lamellae sent for DMEK-S was higher than 2,700 cells/mm(2) in average with a low percentage of dead cells; 65 pre-cut tissues were used for grafting during a 2-year period.

1-Jahres-Ergebnisse nach posteriorer lamellärer Keratoplastik mit manuell disseziertem Spendermaterial

Posterior lamellar keratoplasty (PLK) is a reasonable alternative to penetrating keratoplasty (PK) for pathological changes of the corneal endothelium. The lamellar preparation of the donor tissue can be done in an automated fashion with a microkeratome, Descemet Stripping Automated Keratoplasty (DSAEK) or manually, Descemet Stripping Endothelial Keratoplasty (DSEK). Here, we describe our clinical results with one year follow-up using manually dissected donor lamellae for PLK. For 28 eyes (28 patients) best-corrected visual acuity, corneal topography, esthesiometry, pachymetry, as well as endothelial cell count were measured before, 1 day, 1 and 6 weeks, as well as 3, 6 and 12 months after surgery. 3 of 28 grafts showed primary graft failure. For 19 eyes (no other vision-limiting diseases), the best-corrected visual acuity rose on average from 1.0 +/- 0.53 to 0.4 +/- 0.20 (logMAR) 1 year after surgery. The surgically induced astigmatism changed from 3.8 +/- 2.8 dpt preoperatively to 1.4 +/- 1.0 dpt 12 months after DSEK. The pachymetry measured by slit lamp showed an averaged thickness of 649 +/- 54 mm pre- and 776 +/- 75 mm one week and 636 +/- 79 mm 1 year after surgery was performed. The endothelial cell count of the grafts was 2615 +/- 156 cells/mm (2), after one year postoperatively the mean endothelial cell count was 2084 +/- 536 cells/mm (2). The esthesiometry showed a slight rise from 0.96 +/- 0.34 g/mm (2) pre- to 0.96 +/- 0.03 g/mm (2) one year post-surgery. The postoperative course of our patients shows that improvement of visual acuity by PLK with manually dissected donor tissue is possible.

Optische lamellär-perforierende Keratoplastik mit Stammzelltransplantation bei Risikofällen

Stem cells of the corneal epithelium are located mainly at the sclerocorneal limbus, and are essential for the maintenance of a healthy corneal surface. Limbal stem cell deficiency leads--depending on intensity and extension--to several corneal alterations. The appearance of limbal stem cell deficiency is chiefly concentrated on pemphigoids, Herpes relapses and alkali burns and represents the main part of high-risk keratoplasty. The different types of limbal stem cell deficiency (partial or total) are usually treated with several surgical techniques. Total limbal deficiency can be treated with limbal transplantation, either of the healthy eye (limbal autograft), or using material of another donor (limbal allograft). Lamellar-penetrating keratoplasty (L-P-KP) has been carried out in five patients. Unlike recent surgical techniques containing ring-shaped or circular transplantations, a stripe-like lamellar preparation was performed. L-P-KP involves a peripheral lamellar and a central penetrating keratoplasty combined with limbal stem cell transplantation. In four of six cases, the transplant has been successfully kept clear without the occurrence of corneal decompensation or ulceration. No major changes could be seen between pre- and postoperative visual acuity. The mean observation period was 24 months. L-P-KP offers a new surgical opportunity in the treatment of high-risk cases of limbal deficiency.

Functional incorporation of G protein‐coupled receptors into reconstituted HDL

High density lipoproteins (HDL) are lipid-protein complexes that are involved in the reverse transport of cholesterol. When HDL is first formed in the body, it is disc shaped, with a diameter of 10–12 nm. It is comprised of a dimer of amphipathic, helically structured apolipoprotein A-I (apoA-I) wrapped around a phospholipid bilayer. The HDL complex can be reconstituted in vitro by combining purified apoA-I with phospholipid micelles. We are developing a system whereby we incorporate G protein-coupled receptors (GPCRs) into the phospholipid bilayer of rHDL. We have succeeded in functionally incorporating the two prototypic GPCRs into rHDL: the β2 adrenergic receptor (β2AR) and rhodopsin. β2AR incorporated into reconstituted HDL (rHDL) binds [3H]dihydroalprenolol with a Kd~0.5 nM, representing a ten-fold higher affinity than observed in detergent micelles and more consistent with the Kd values found with β2AR in cellular membranes. In addition, the receptor exhibits both high affinity agonist binding and agonist-stimulated guanine nucleotide exchange. Rhodpsin incorporated into rHDL comprised of unsaturated lipids converts to the active metarhodopsin II conformation with properties consistent with that seen in rod outer segment membranes upon light activation. In the case of both receptors, alterations in the lipid composition have dramatic consequences on the efficiency of receptor incorporation and function, consistent with similar studies using phospholipid vesicles or lamellar preparations. With this approach both the disc size and phospholipid composition may be controlled giving this powerful technique the potential to be applied to both the structural and functional characterization of membrane proteins in general. Supported by NIH RO1 GM-068603

Lamellar preparations as adjunctive therapy in the treatment of atopic dermatitis

Lamellar preparations as adjunctive therapy in the treatment of atopic dermatitis

Putschkowaskaja corneal protection

Excessive cornea defects after chemical, thermal and microbiological damages respectively trophic disturbances often demand measures for conservation of the bulbus. In the time between 1969 and 1993 22 patients were provided with a "Keratoplasty according to Putschkowskaja": circular cut at the recipient eye 0.15 mm deep, trepan diameter 8.5 to 13 mm, without lamellar preparation, covering with a donor cornea of normal thickness by silk single sutures. In 19 eyes the primary aim, the conservation of the bulbus, could be achieved. The complete transplant was mostly rejected after several months, only in two patients it healed by vascularisation. In one patient an abscess arose between recipient--cornea and transplant, which made explantation necessary. The histological examination of the transplant showed a purulent inflammation, swelling of the parenchym, partly absence of keratocytes and endothel cells, and a defect in the Bowman membrane. The "Keratoplasty according to Putschkowskaja" can be useful as "living contact lens" besides other surgical measures for treatment (primary conservation of the bulbus) of excessive cornea defects. It seems that the existence of Bowman and Descemet membrane in the transplant prevents the decomposition of the donor cornea for a rather long time. By then the cornea defect has often healed leaving scars.

Imaging of polyethylene films by diffraction contrast

The technique of crystalline diffraction contrast imaging of lamellae in spherulitic and oriented thin films of polyethylene is illustrated for both conventional transmission and scanning transmission electron microscopY. Bright-field “ghost” imaging permits real space crystallography of the specimen and reveals the occurrence of variable chain inclination in a given lamellar preparation. N beam annular dark-field scanning transmission microscopy is useful for distinguishing between curved lamellae and mosaic blocks as well as for the direct imaging of the amorphous regions between lamellae.

Comparative studies of cytochrome c redox reactions by photochemical lamellar preparations obtained from blue-green, red, and green algae, and spinach chloroplasts

Sonic-treated lamellar preparations of Anabaena cylindrica, Anacystis nidulans, Porphyridium cruentum, Chlamydomonas reinhardi, and spinach chloroplasts were active in cytochrome c redox reactions, though they lost Hill reaction activity. All preparations gave the same anaerobic redox reactions: cytochrome c was oxidized in the light and reduced to the original redox level in the subsequent dark period. Buffer extracts obtained from the acetone-treated preparations of all organisms tested had the same heat-stable factor with activity for stimulating the anaerobic redox reactions by Anabaena-extracted preparations. Results were taken as evidence that occurrence of a large amount of redox substance (CRS) at system 1 level is a common feature of the photosynthetic systems in these organisms.

Cytochrome c redox reactions induced by photochemical system 1 in sonicated preparations of Anabaena cylindrica

Sonicated preparations of Anabaena cylindrica were highly active in cytochrome c redox reaction, though they had negligible activity for 2,6-dichlorophenol indophenol-Hill reaction. The anaerobic redox reactions (light oxidation and dark reduction) were observed in the present preparation just as in the previous preparations which retained Hill reaction activity. Hence the hypothetical substance, CRS, which is reduced at the level of photochemical system 1, is retained in the sonicated lamellar preparation. Washing, dialyzing, detergent, or Sephadex treatments did not affect the rates or magnitudes of anaerobic redox reactions, indicating that CRS is tightly bound to the photoreactive lamellar fragments. The heat-stable factor which stimulates anaerobic redox reaction was partially separated from the lamellar fragments by buffer extraction after acetone treatment. The substance is heat-stable and not soluble in acetone, chloroform, or an acetonehexane mixture. Sephadex filtration suggested that the substance is a large molecule.