Interfibrillar Spacing Research Articles

Stromal response to orthokeratology: an X‐ray diffraction study

Abstract Purpose: To examine the impact of overnight orthokeratology lens wear on stromal collagen fibril diameter and spacing using synchrotron X‐ray diffraction. Methods: Seven New Zealand White rabbits (10 eyes) wore orthokeratology lenses (Capricornia, Brisbane, Australia) overnight during a 2‐week period to determine the effect of corneal refractive therapy on stromal collagen fibrils. To verify the effectivity of treatment, corneal topography (Medmont, Brisbane, Australia), corneal thickness (Allergan Humphrey pachymetry) and refractive error (retinoscopy) were measured prior to and every 3‐4 days during the treatment period. Following completion of treatment, rabbits were euthanased and corneas immediately dissected and snap frozen for subsequent X‐ray diffraction analysis every 1mm over the central c.10mm horizontal corneal band. Results: Orthokeratology treatment induced an average change in refraction of 2.0 +/‐ 1.3DS, and a topography‐measured treatment zone diameter of 4.2 +/‐ 0.7mm. The results from X‐ray diffraction revealed no significant difference in collagen fibril diameter between treated and untreated eyes (p>0.05). Interfibrillar spacing (IFS) was positively correlated with tissue hydration but no significant association between the change in IFS and refraction was apparent. Conclusions: The magnitude and time course of refractive change induced by orthokeratology in the rabbit eye is similar to that reported in humans, producing significant rapid and characteristic changes in corneal topography. Such specific changes in topography seem limited to the epithelial layers, with no parallel topographic modification evident in the underlying stromal architecture.

Microscopic characterization of collagen modifications induced by low‐temperature diode‐laser welding of corneal tissue

Laser welding of corneal tissue that employs diode lasers (810 nm) at low power densities (12-20 W/cm(2)) in association with Indocyanine Green staining of the wound is a technique proposed as an alternative to conventional suturing procedures. The aim of this study is to evaluate, by means of light (LM) and transmission electron microscopy (TEM) analyses, the structural modifications induced in laser-welded corneal stroma. Experiments were carried out in 20 freshly enucleated pig eyes. A 3.5 mm in length full-thickness cut was produced in the cornea, and was then closed by laser welding. Birefringence modifications in samples stained with picrosirius red dye were analyzed by polarized LM to assess heat damage. TEM analysis was performed on ultra-thin slices, contrasted with uranyl acetate and lead citrate, in order to assess organization and size of type I collagen fibrils after laser welding. LM evidenced bridges of collagen bundles between the wound edges, with a loss of regular lamellar organization at the welded site. Polarized LM indicated that birefringence properties were mostly preserved after laser treatment. TEM examinations revealed the presence of quasi-ordered groups of fibrils across the wound edges preserving their interfibrillar spacing. These fibrils appeared morphologically comparable to those in the control tissue, indicating that type I collagen was not denatured during the diode laser corneal welding. The preservation of substantially intact, undenatured collagen fibrils in laser-welded corneal wounds supported the thermodynamic studies that we carried out recently, which indicated temperatures below 66 degrees C at the weld site under laser irradiation. This observation enabled us to hypothesize that the mechanism, proposed in the literature, of unwinding of collagen triple helixes followed by fibrils "interdigitation" is not likely to occur in the welding process that we set up for the corneal suturing.

Age-related changes in human macular Bruch's membrane as seen by quick-freeze/deep-etch

Lipid-containing inclusions have been observed in human Bruch's membrane (BrM) and are postulated to be associated with age-related maculopathy (ARM), a major cause of legal blindness in developed countries. The dehydration associated with specimen preparation for thin-section transmission electron microscopy causes loss of these inclusions. Better preservation of the ultrastructure of the inclusions and tissue is achieved by using a quick-freeze/deep-etch preparation. We use this technique to examine normal human macular BrM in order to characterize the deposition of the lipid-rich inclusions and their age-related accumulation within different layers of the tissue. We find that various inclusions mentioned in other studies can be formed by combinations of three basic structures: lipoprotein-like particles (LLPs), small granules (SGs) and membrane-like structures. These inclusions are associated with collagen and elastic fibrils by fine filaments. In younger eyes, these inclusions are found mostly in the elastic (EL) and outer collageneous layer (OCL) and occupy a small fraction of the interfibrillar spacing. As age increases, LLPs and SGs gradually fill the interfibrillar spacing of the EL and inner collageneous layer (ICL) of the tissue, and later form a new sublayer, the lipid wall, within the boundary region between the basal lamina of retinal pigment epithelium (RPE) and ICL. Because the formation of the lipid wall only occurs after these inclusions fill the ICL, and it seems unlikely that the LLPs can pass through the packed layer, this result suggests a possible RPE origin of the LLPs that make up the lipid wall.

Small-angle fibre diffraction studies of corneal matrix structure: a depth-profiled investigation of the human eye-bank cornea

In the cornea of the eye light transmission is facilitated by the regular arrangement and uniform diameter of collagen fibrils that constitute the bulk of the extracellular corneal matrix. Matrix architecture, in turn, is believed to be governed by interactions between collagen fibrils and proteoglycan molecules modified with sulfated glycosaminoglycan side chains. Here, we outline the contribution made by small-angle X-ray scattering studies of the cornea in understanding the role of sulfated glycosaminoglycans in the control of collagen architecture in cornea, and present new depth-profiled microbeam data from swollen human eye-bank corneas that indicate no significant change in collagen fibril diameter throughout the tissue, but a lower collagen interfibrillar spacing in the anterior-most stromal regions compared with the ultrastructure of the deeper cornea.

Analysis of histologic and clinical changes associated with Polaris WR treatment of facial wrinkles

The Polaris WR is a device that combines laser energy with radiofrequency (RF) treatment to provide more focused RF energy on the skin to reduce wrinkles and/or tighten skin. Clinical results have varied from highly visible to no obvious reduction in wrinkles. This prospective study investigated whether there was any corollary between clinical results, standardized VISIA (Canfield Imaging Systems, Fairfield, NJ) and digital photographs, and skin biopsy analysis after the treatment of facial wrinkles with the Polaris WR device. Fifteen patients received four full-face treatments. Biopsy of the treated skin was performed before and 1 and 3 months after their last treatment. A VISIA computer analysis of facial wrinkle density and depth was performed before any treatment and then 3 months after the last treatment. Digital photographs were reviewed by four surgeons to evaluate wrinkle reduction at 3 and 6 months after the four treatments. Physicians' ratings of these digital images revealed that 58% of the patients were improved at 3 months after treatment, and 42% were still improved at 6 months. The patient questionnaire responses revealed that 75% of patients felt that they looked better at 3 months, and 67% felt that they remained improved 6 months after their last treatment. VISIA photographic analysis demonstrated that 67% of the patients had fewer and/or shallower wrinkles at their 3-month visit. The average degree of improvement with VISIA analysis was 30%. Biopsy specimens in the group of patients that were defined as improved by VISIA assessment showed a greater dermal thickness and interfibrillar spacing P < .024). Two patients received superficial second-degree burns that did not require corrective treatment. Improvement in skin wrinkling after Polaris WR therapy was confirmed in patients at 3 months after treatment by physician assessment, VISIA analysis, and patient assessment, with a lower rate of improvement at 6 months after treatment. VISIA analysis tended to confirm patient assessments. Physician assessments of improvement tended to be lower.

Decorin Modulates Fibrin Assembly and Structure

Emerging evidence indicates that fibrin clotting is regulated by different external factors. We demonstrated recently that decorin, a regulator of collagen fibrillogenesis and transforming growth factor-beta activity, binds to the D regions of fibrinogen (Dugan, T.A., Yang, V. W.-C., McQuillan, D.J., and Höök, M. (2003) J. Biol. Chem. 278, 13655-13662). We now report that the decorin-fibrinogen interaction alters the assembly, structure, and clearance of fibrin fibers. Relative to fibrinogen, substoichiometric amounts of decorin core protein modulated clotting, whereas an excess of an active decorin peptide was necessary for similar activity. These concentration-dependent effects suggest that decorin bound to the D regions sterically modulates fibrin assembly. Scanning electron microscopy images of fibrin clotted in the presence of increasing concentrations of decorin core protein showed progressively decreasing fiber diameter. The sequestration of Zn(2+) ions from the N-terminal fibrinogen-binding region abrogated decorin incorporation into the fibrin network. Compared with linear thicker fibrin fibers, the curving thin fibers formed with decorin underwent accelerated tissue-type plasminogen activator-dependent fibrinolysis. Collectively, these data demonstrate that decorin can regulate fibrin organization and reveal a novel mechanism by which extracellular matrix components can participate in hemostasis, thrombosis, and wound repair.

Matrix morphogenesis in cornea is mediated by the modification of keratan sulfate by GlcNAc 6- O -sulfotransferase

Matrix assembly and homeostasis in collagen-rich tissues are mediated by interactions with proteoglycans (PGs) substituted with sulfated glycosaminoglycans (GAGs). The major GAG in cornea is keratan sulfate (KS), which is N-linked to one of three PG core proteins. To ascertain the importance of the carbohydrate chain sulfation step in KS functionality, we generated a strain of mice with a targeted gene deletion in Chst5, which encodes an N-acetylglucosamine-6-O-sulfotransferase that is integral to the sulfation of KS chains. Corneas of homozygous mutants were significantly thinner than those of WT or heterozygous mice. They lacked high-sulfated KS, but contained the core protein of the major corneal KSPG, lumican. Histochemically stained KSPGs coassociated with fibrillar collagen in WT corneas, but were not identified in the Chst5-null tissue. Conversely, abnormally large chondroitin sulfate/dermatan sulfate PG complexes were abundant throughout the Chst5-deficient cornea, indicating an alteration of controlled PG production in the mutant cornea. The corneal stroma of the Chst5-null mouse exhibited widespread structural alterations in collagen fibrillar architecture, including decreased interfibrillar spacing and a more spatially disorganized collagen array. The enzymatic sulfation of KS GAG chains is thus identified as a key requirement for PG biosynthesis and collagen matrix organization.

Neonatal Development of the Corneal Stroma in Wild-Type and Lumican-Null Mice

Between days 8 and 14 of neonatal development, the corneal stroma of the mouse undergoes critical changes in tissue thickness, cell density, and light scattering. The authors investigate the stromal matrix structure in wild-type and lumican-deficient corneas in this developmental phase. Wild-type (n = 44) and lumican-deficient (n = 42) mouse corneas at neonatal days 8, 10, 12, and 14 were investigated by synchrotron x-ray diffraction to establish the average collagen fibril spacing, average collagen fibril diameter, and level of fibrillar organization in the stromal matrix. Collagen interfibrillar spacing in the normal mouse cornea became more closely packed between days 8 and 14, though not significantly so. In lumican-null mice, interfibrillar spacing was significantly elevated at days 8, 10, and 12, but not day 14, compared with that in wild-type mice. At all stages investigated, collagen fibrils were, on average, marginally thinner than normal in lumican-null mutants, and the spatial distribution of the fibrils was less well organized. Transient thickening of the corneal stroma of the normal mouse at eye opening is probably not caused by widespread, homogeneous rearrangement of collagen fibrils but more likely by a temporary increase in cell or stromal "lake" volume. Lumican, structurally influential in adult mouse corneas, is also a key molecule in the neonatal development of the stromal matrix.

An ultrastructural investigation of dermatopontin‐knockout mouse corneas

Introduction The corneal stroma is composed of a network of heterotypic collagen fibrils, proteoglycans and matrix proteins. Transparency of the tissue principally requires the uniformity of fibril diameters and interfibrillar distances and the presence of a quasi‐hexagonal lattice arrangement of parallel fibrils. Keratan sulfate proteoglycans (KSPGs) have a crucial role and the KS chains are clearly required for the maintenance of transparency. Undersulfation of corneal KS results in tissue opacity and the lumican (a KSPG) knockout mouse shows corneal opacity and the disruption of collagen fibril diameters and interfibrillar distances (Chakravarti et al. 1998). Biochemical analysis has shown that dermatopontin is an abundant component of the extracellular matrix and that it interacts with KSPGs via the KS chains. This study aims to determine whether dermatopontin has a direct role in corneal matrix organization by investigating the corneal ultrastructure of dermatopontin‐null (dpt–/–) mouse corneas.Materials and methods Conventional light microscopy was used to compare the corneal thickness of dpt–/– mice (Takeda et al. 2002) with that of the wild‐type. Collagen fibril distribution was studied using transmission electron microscopy and the datasets analysed using SIS‐pro image analysis software to determine fibrillar volume, shape factor, fibril diameter and spacing.Results Light microscopy demonstrated that dpt–/– corneas show a 24% reduction in average stromal thickness compared to wild‐type (P &lt; 0.001). The epithelium and Descemet's membrane appear normal. Examination of dpt–/– stroma by transmission electron microscopy indicates a significant disruption to lamellar organization in the posterior region while the central and anterior regions appear largely unaffected compared to wild‐type. The collagen fibrils in dpt–/– stroma show a pronounced increase in interfibrillar spacing as well as exhibiting a lower fibril volume fraction. There is no apparent difference in fibril diameter between dpt–/– and wild‐type mice.Discussion Collectively, these data suggest that dermatopontin plays a key role in collagen fibril organization and deposition. Like the cornea from lumican‐knockout mice (Chakravarti et al. 1998), the defects in collagen organization in dpt–/– cornea appear to be most severe in the posterior stroma. It is likely that dermatopontin interacts with the KS chains on lumican and this interaction is involved in the maintenance of stromal architecture.

Proteomics of tendon ECM assembly

Introduction The ability of tendon to transduce tensile force to the skeleton relies on 10s of 1000s of long (&gt;100 microns) extracellular collagen fibrils that are in parallel register with the long axis of the tendon. Electron microscopy studies of developing mouse‐tail tendon show that at E13.5, the tissue is predominantly composed of cells with little or no matrix. By E15.5, intracellular fibrils can be seen. The long collagen fibrils are deposited one‐by‐one by ‘finger‐like’ projections of the plasma membrane into hexagonally packed bundles of the fibrils. Moreover, the fibrils have a precise interfibrillar spacing of approximately 30 nm. The aim of this work was to identify proteins whose patterns of expression change during tail development in order to understand better the molecular basis of intracellular collagen fibril assembly, tubule trafficking and supramolecular organization of the fibrils in the embryonic mouse tendon.Materials and methods Fresh embryonic tail tissue was harvested and proteins extracted into buffer containing urea, thiourea, detergent and DTT (DL‐dithiothreitol). Proteins (approximately 100 µg) were first separated by isoelectrofocusing on 24 cm, linear immobilized pH gradient strips (pH 4–7). Strips were reduced with 1% DTT and alkylated with 5% iodoacetamide before second dimension separation by SDS‐PAGE on an 11% gel. Gels were stained with either 0.1% colloidal Coomassie Blue or silver nitrate.Coomassie‐stained gels were used for MS analysis. Protein spots of interest were excised from the 2D gel, destained, reduced, alkylated and digested overnight with trypsin. The resulting peptides were then extracted and analysed by LC‐MS/MS. The data were used to search against SWISSPROT and Tremblnew public protein databases.Results We have established reproducible extraction conditions and separation methods to obtain 2D gels containing &gt;500 protein ‘spots’ that are visible by Coomassie Blue staining.Discussion Our approach is to extract proteins from whole embryonic tail from both E13.5 and E15.5 tissues, separate the proteins by 2D‐gel electrophoresis, highlight key changes in the spot profile and identify these proteins by trypsin digestion, q‐TOF mass spectrometry and database matching. A surprising observation was the abundance of intracellular proteins involved in protein folding and trafficking. A poster will be presented that lists the first proteins that we have identified.

Effect of morpholino antisense oligonucleotide against lumican mRNA in human embryonic kidney (HEK) 293 cells.

Lumican is a member of the small-leucine-rich proteoglycan (SLRP) family and is overexpressed during wound healing of the cornea, in ischemic and reperfused heart, and in several cancer tissues. Lumican is considered to regulate the collagen fibril diameter and interfibrillar spacing. However, the effect of lumican on cell growth has not been adequately examined. In the present study, we attempted to clarify whether lumican contributes to human embryonic kidney (HEK) 293 cell growth, using the morpholino antisense oligonucleotide (m-anti oligo) against lumican mRNA. M-anti oligo is a novel oligonucleotide and exhibits a higher antisense activity, higher water solubility, and greater resistance to nucleases in target cells than phosphorothioate types of oligonucleotide. After delivery of m-anti oligo against lumican mRNA, the fluorescein 5-isothiocyanate (FITC) conjugated oligonucleotides were observed in the cytoplasm and nucleus of HEK 293 cells at 24 h by confocal laser microscopy. M-anti oligo for lumican mRNA strongly inhibited the synthesis of lumican protein in the HEK 293 cells, and the HEK cell growth rate was higher than those in the control groups. These findings may indicate that lumican protein has an inhibitory effect on HEK 293 cell growth in vitro.

Collagens and proteoglycans of the corneal extracellular matrix.

The cornea is a curved and transparent structure that provides the initial focusing of a light image into the eye. It consists of a central stroma that constitutes 90% of the corneal depth, covered anteriorly with epithelium and posteriorly with endothelium. Its transparency is the result of the regular spacing of collagen fibers with remarkably uniform diameter and interfibrillar space. Corneal collagen is composed of heterotypic fibrils consisting of type I and type V collagen molecules. The cornea also contains unusually high amounts of type VI collagen, which form microfibrillar structures, FACIT collagens (XII and XIV), and other nonfibrillar collagens (XIII and XVIII). FACIT collagens and other molecules, such as leucine-rich repeat proteoglycans, play important roles in modifying the structure and function of collagen fibrils.Proteoglycans are macromolecules composed of a protein core with covalently linked glycosaminoglycan side chains. Four leucine-rich repeat proteoglycans are present in the extracellular matrix of corneal stroma: decorin, lumican, mimecan and keratocan. The first is a dermatan sulfate proteoglycan, and the other three are keratan sulfate proteoglycans. Experimental evidence indicates that the keratan sulfate proteoglycans are involved in the regulation of collagen fibril diameter, and dermatan sulfate proteoglycan participates in the control of interfibrillar spacing and in the lamellar adhesion properties of corneal collagens. Heparan sulfate proteoglycans are minor components of the cornea, and are synthesized mainly by epithelial cells. The effect of injuries on proteoglycan synthesis is discussed.

Persistent haze and disorganization of anterior stromal collagen appear unrelated following phototherapeutic keratectomy.

The theoretical effects on corneal transparency induced by changes in collagen fibril packing following phototherapeutic keratectomy were compared to changes in objective measurements of haze. Phototherapeutic keratectomy was performed on the right eyes of four young rabbits; left eyes were used as controls. Postoperative slit-lamp measurements of haze were taken at regular intervals up to 19 months. Wounded stromas were studied by synchrotron x-ray diffraction to calculate the average interfibrillar spacing of the collagen fibrils. These data were combined with transmission electron microscope measurements, and the summation of scattered fields method was used to predict the transmission of visible light. Objective measurements of haze were higher than the baseline control throughout the study. Electron micrographs of anterior stroma in 8-month-old wounds displayed irregularly spaced and poorly organized fibrils and x-ray diffraction indicated larger mean interfibrillar spacing compared to the controls. However, the predicted transmission of visible light through the anterior stromal scar tissue was not significantly different than normal. Following phototherapeutic keratectomy, anterior corneal collagen fibrils were more widely spaced and unevenly organized than in the normal rabbit cornea. However, this did not cause a significant loss of transparency and was therefore unlikely to contribute to haze.

Annulus of collagen fibrils in mouse cornea and structural matrix alterations in a murine-specific keratopathy.

Mouse corneas were investigated to see whether a limbal annulus of corneal collagen exists as in humans. Mice with corneas predisposed to topographical changes (the SKC strain) were also examined, to establish the size and spacing of stromal collagen fibrils and the integrity of the annulus. X-ray diffraction was used to measure collagen fibril spacing and diameter in normal (the BALB/c strain; four male, two female) and SKC (six male and six female) corneas and to identify the degree of preferred collagen orientation at 200- microm intervals across two BALB/c and four SKC corneas. The average collagen fibril diameter measured 35.5 nm in 3-month-old BALB/c corneas, and 36.9 nm and 37.0 nm, respectively, in corneas of age-matched male and female SKC mice. In male and female SKC corneas, average collagen interfibrillar Bragg spacing was significantly higher (64.5 and 59.9 nm, respectively) than in corneas of BALB/c mice (49.7 nm). Circumferentially aligned collagen, indicative of a limbal annulus of fibrillar collagen 2.2 mm in diameter, was identified in mouse cornea. On occasion, this was disturbed in the SKC phenotype. Collagen fibrils are marginally larger in the corneas of SKC mice than in the corneas of BALB/c mice and are considerably more widely spaced. An annulus of fibrillar collagen probably exists near the limbus of the normal mouse cornea that may help promote biomechanical stability and maintain corneal shape. A loss of structural integrity in the annulus of some SKC mice may predispose the corneas to biomechanical instability and shape changes.

Roles of lumican and keratocan on corneal transparency.

Lumican and keratocan are members of the small leucine-rich proteoglycan (SLRP) family, and are the major keratan sulfate (KS) proteoglycans in corneal stroma. Both lumican and keratocan are essential for normal cornea morphogenesis during embryonic development and maintenance of corneal topography in adults. This is attributed to their bi-functional characteristic (protein moiety binding collagen fibrils to regulate collagen fibril diameters, and highly charged glycosaminoglycan (GAG) chains extending out to regulate interfibrillar spacings) that contributes to their regulatory role in extracellular matrix assembly. The absence of lumican leads to formation of cloudy corneas in homozygous knockout mice due to altered collagenous matrix characterized by larger fibril diameters and disorganized fibril spacing. In contrast, keratocan knockout mice exhibit thin but clear cornea with insignificant alteration of stromal collaegenous matrix. Mutations of keratocan cause cornea plana in human, which is often associated with glaucoma. These observations suggest that lumican and keratocan have different roles in regulating formation of stromal extracellular matrix. Experimental evidence indicates that lumican may have additional biological functions, such as modulation of cell migration and epithelium-mesenchyme transition in wound healing and tumorgenesis, besides regulating collagen fibrillogenesis.

Ultrastructural morphology and expression of proteoglycans, βig-h3, tenascin-C, fibrillin-1, and fibronectin in bullous keratopathy

AIMSTo investigate the ultrastructural localisation of proteoglycans (PG), βig-h3 (keratoepithelin), tenascin-C (TN-C)), fibrillin, and fibronectin in bullous keratopathy (BK) corneas.METHODSFive corneas from cases of pseudophakic bullous keratopathy (BK) were examined...

Collagen as a model system to investigate the use of aspirin as an inhibitor of protein glycation and crosslinking

Aspirin has been shown to be a powerful inhibitor of post-Amadori Maillard reactions, although the exact mechanism of this action remains unclear. We have used corneal and scleral collagen as a model system: (i) to assess how aspirin, either alone or in combination with sugars, affects the surface charge distribution along the collagen fibrils; (ii) to see how sugars and/or aspirin affect the swelling properties of the cornea; and (iii) to see if sugars and/or aspirin change the distribution of water within the corneal stroma as the tissue swells. Charge changes were detected by examining changes in the uptake of phosphotungstate ions as seen in the electron microscope. Swelling was measured by monitoring the uptake of water as a function of swelling time, and water distribution was determined by using synchrotron X-ray diffraction to follow changes in the interfibrillar Bragg spacing as the cornea swells. Aspirin has a marked effect on the positive staining pattern of scleral collagen. This is different to the changes in stain uptake produced by glycation. Incubation with both sugars and aspirin showed that the sugar binding takes precedence over the effects of aspirin which, in turn, suggests that protein acetylation by aspirin is unlikely under these circumstances. However, aspirin completely suppresses corneal swelling. Even when the aspirin is removed, swelling in distilled water is reduced, and this is accompanied by changes in the water distribution. The results suggest that water is more evenly distributed in aspirin-treated corneas that are subsequently swollen than in swollen glycated corneas. Fructation, glucation and ribation on their own have little effect on the uptake of water as the cornea swells. This suggests that any sugar-derived crosslinks formed at this stage do not limit swelling.

Swelling Studies on the Cornea and Sclera: The Effects of pH and Ionic Strength

The biophysical properties of the cornea and sclera depend on the precise maintenance of tissue hydration. We have studied the swelling of the tissues as a function of pH and ionic strength of the bathing medium, using an equilibration technique that prevents the loss of proteoglycans during swelling. Synchrotron x-ray diffraction was used to measure the average intermolecular and interfibrillar spacings, the fibril diameters, and the collagen D-periodicity. We found that both tissues swelled least near pH 4, that higher hydrations were achieved at lower ionic strengths, and that sclera swelled about one-third as much as cornea under most conditions. In the corneal stroma, the interfibrillar spacing increased most with hydration at pH values near 7. Fibril diameters and D-periodicity were independent of tissue hydration and pH at hydrations above 1. Intermolecular spacings in both tissues decreased as the ionic strength was increased, and there was a significant difference between cornea and sclera. Finally, we observed that corneas swollen near pH 7 transmitted significantly more light than those swollen at lower pH levels. The results indicate that the isoelectric points of both tissues are close to pH 4. The effects of ionic strength can be explained in terms of chloride binding within the tissues. The higher light transmission achieved in corneas swollen at neutral pH may be related to the fact that the interfibrillar fluid is more evenly distributed under these conditions.

Lamellar structure and properties in poly(ethylene terephthalate) fibers

The fibrillar and the lamellar structures in a range of poly(ethylene terephthalate) fibers were studied by small-angle X-ray scattering. The intensity maxima in the lamellar peaks lie on a curve that can be described as an ellipse. Therefore, the two-dimensional images were analyzed in elliptical coordinates. The dimensions of the coherently diffracting lamellar stack, the dimensions of the fibrils, the interfibrillar spacing, and the orientation of the lamellar surfaces were measured in addition to the lamellar spacing. The orientation of the lamellar planes and the size of the lamellar stacks had a better correlation with mechanical properties of the fibers than did the lamellar spacing. In particular, longer and wider lamellar stacks reduced fiber shrinkage, as did the closer alignment of the lamellar normal to the fiber axis. These structural features were also associated with lower tenacity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2527–2538, 1998

Lamellar structure and properties in poly(ethylene terephthalate) fibers

The fibrillar and the lamellar structures in a range of poly(ethylene terephthalate) fibers were studied by small-angle X-ray scattering. The intensity maxima in the lamellar peaks lie on a curve that can be described as an ellipse. Therefore, the two-dimensional images were analyzed in elliptical coordinates. The dimensions of the coherently diffracting lamellar stack, the dimensions of the fibrils, the interfibrillar spacing, and the orientation of the lamellar surfaces were measured in addition to the lamellar spacing. The orientation of the lamellar planes and the size of the lamellar stacks had a better correlation with mechanical properties of the fibers than did the lamellar spacing. In particular, longer and wider lamellar stacks reduced fiber shrinkage, as did the closer alignment of the lamellar normal to the fiber axis. These structural features were also associated with lower tenacity. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2527–2538, 1998