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PubMed2000

Abnormal elastic system fibers in fibrotic human liver.

The network of elastic system fibers in human fibrotic liver was investigated by histological methods, immunohistochemical staining, and electron microscopy. Type III collagen was seen not only in regions of portal fibrosis but also in the sinusoidal wall. However, elastic system fibers were not found in the Disse space of the sinusoidal wall. Elastic system fibers including oxytalan, elaunin, and elastic fibers were found successively in the course of elastogenesis. A few normal oxytalan fibers and abnormal oxytalan fibers were observed in the periportal tracts. Few normal elaunin and abnormal elaunin fibers were observed in regions of portal fibrosis but not in the surrounding margin. Elastic fibers, only in scarce amounts, were observed around the portal veins in the case of chronic active hepatitis but not in acute hepatitis. Abnormal oxytalan fibers were seen as a bundle of wavelike microfibrils and had an irregular arrangement. Abnormal elaunin fibers were not associated with bundles of microfibrils. Abnormal elaunin fibers in large amounts were found interspersed with spiraled collagen, which most likely indicates that the oxytalan fibers degenerated in the course of elastogenesis. Thus, in a fibrotic liver it is possible that synthesis of normal elaunin and elastic fibers does not occur or that the quantity of such fibers synthesized may be small because of the effect of the degenerated oxytalan fibers. As a characteristic of liver fibrosis, the composition of abnormal elastic system fibers and spiraled collagen differs from that in other fibrotic organs.

Adult↗
PubMed2006

A combined FEM/genetic algorithm for vascular soft tissue elasticity estimation.

Tissue elasticity reconstruction is a parameter estimation effort combining imaging, elastography, and computational modeling to build maps of soft tissue mechanical properties. One application is in the characterization of atherosclerotic plaques in diseased arteries, wherein the distribution of elastic properties is required for stress analysis and plaque stability assessment. In this paper, a computational scheme is proposed for elasticity reconstruction in soft tissues, combining finite element modeling (FEM) for mechanical analysis of soft tissues and a genetic algorithm (GA) for parameter estimation. With a model reduction of the discrete elasticity values into lumped material regions, namely the plaque constituents, a robust, adaptive strategy can be used to solve inverse elasticity problems involving complex and inhomogeneous solution spaces. An advantage of utilizing a GA is its insistence on global convergence. The algorithm is easily implemented and adaptable to more complex material models and geometries. It is meant to provide either accurate initial guesses of low-resolution elasticity values in a multi-resolution scheme or as a replacement for failing traditional elasticity estimation efforts.

Algorithms↗
PubMed1996

Morphological and biochemical studies of the elastic fibres in the craniomandibular joint articular disc of the tight-skin mouse.

The tight-skin (TSK) mouse is characterized by the hyperplasia of loose connective tissues, and of excessive growth of cartilage and of bones including the mandible. Since the fibroelastic connective tissues of the craniomandibular joint (CMJ) are essential to the functions of this joint, the present histological study compared the presence and general distribution of elastic fibres in CMJ discal tissues of TSK and normal mice. The excised CMJs were processed for light microscopy. The tissues were fixed, demineralized, embedded in paraffin, sectioned and then stained with resorcin-fuchsin to demonstrate elastic fibres. There were no obvious histological differences in either the amount or the distribution of elastic fibres in the discs from the two groups. In both groups, elastic fibres were found in the disc and in many of the attachments of the disc to the mandible and squamosal bone. In addition to the morphological preparations, articular discs and samples of lung tissue were excised from other mice and subjected to a radioimmunoassay for desmosine in order to estimate the amounts of elastin in these tissues; the amount of elastin was significantly reduced in the TSK lung, but the amounts of elastin in the TSK and normal CMJ discal tissues were not significantly different statistically. These morphological and histochemical results suggest that the distribution and quantity of elastic fibres in the TSK mouse disc are not significantly different from those in the normal mouse articular disc. Moreover, these data may be interpreted to either suggest a differential effect on the elastic fibres in different TSK tissues, or to support the suggestion that abnormal degradation of elastic fibres may not be characteristic of the TSK mouse.

Animals↗
PubMed1987

Three-dimensional architecture of elastic tissue in athero-arteriosclerotic lesions of the rat aorta.

The overall three-dimensional architecture of elastic tissue in athero-arteriosclerotic lesions of the ascending aorta of the rat was studied, using scanning electron microscopy (SEM), after hot-formic acid extraction followed by a freeze-drying method. The lesions were induced by feeding the rats a diet containing 2% cholesterol for 6 weeks and administering massive doses of vitamin D2 for the first 4 days. SEM revealed the synthesis of elastins mainly in the intima and the degradation in the internal elastic lamina (IEL) and medial concentric elastic lamellae. Intimal elastic elements involved in atherosclerotic lesions were composed of an intricately tangled network of fibrous elastins or a row of elastic laminae that surrounded many rectangular compartments, which were separated by fenestrated septum-like elastins and were assumed to be the sites of smooth-muscle-cell proliferation. These observations indicated remodelling of the elastic laminae in the intima. Degradation in the IEL and media was attributed to either vitamin D2 intoxication, which was characterized by the formation of a large degraded portion, or an enhanced elastolytic process. These alterations of elastic elements probably reflect the exact frame of the modes of migration of aortic smooth muscle cells in the development of athero-arteriosclerotic lesions, thereby indicating the role of smooth muscle cells in the progress of atherosclerosis.

Animals↗
PubMed1987

Elastic fibers in tunica propria of undescended and contralateral scrotal testes from cryptorchid patients.

Elastic fibers in the tunica propria of the testes from cryptorchid patients and normal fertile adults were examined by light (Weigert resorcin-fuchsin stain) and electron microscopic techniques. In the testes from normal fertile adults, elastic fibers were proved to exist in the tunica propria by light and electron microscopy, and were located in the fibrous and cellular layers of the tunica propria. In the undescended testes from the cryptorchid patients, during prepubertal and pubertal periods, elastic fibers could not be visualized in the tunica propria, but were found after puberty. The positive Weigert reaction of the tunica propria in the undescended testes from postpubertal cryptorchid patients, however, was markedly weaker than that in normal control patients, suggesting diminution of elastic fibers. This diminution of elastic fibers in the undescended testes from postpubertal cryptorchid patients was also substantiated by electron microscopy. However, in the contralateral scrotal testes, elastic fibers appeared during puberty and were observed after puberty in the same manner as in normal testes. Thus, the present study suggested retarded appearance of elastic fibers in puberty and impaired development of those fibers after puberty, in the undescended testes of cryptorchid patients.

Adolescent↗
PubMed2006

Impact of oxidative stress on arterial elasticity in patients with atherosclerosis.

BACKGROUND: Alterations in the elastic behavior of arteries is an early sign of vascular damage in atherogenesis and may be promoted by oxidative stress (OxS). However, studies designed for simultaneous assessment of arterial elasticity and OxS status in patients with peripheral arterial disease (PAD) are absent. The purpose of this study was to assess large (C1) and small artery elasticity (C2) and indices of OxS in patients with PAD as well as to investigate possible relationships between these parameters. METHODS: Arterial elasticity was assessed noninvasively by pulse wave analysis (PWA) and biochemical measurements were taken from 38 patients with PAD and from 28 matched control subjects. The elasticity indices of the arteries were derived from PWA based on the modified Windkessel model and the OxS status was measured using urinary 8-iso-prostaglandin F2alpha (F2-IsoPs) and plasma baseline diene conjugates of low-density lipoproteins (LDL-BDC). RESULTS: Patients with PAD showed significantly reduced C1 and C2 and increased values of F2-IsoPs and LDL-BDC. There was an inverse association between C1 and F2-IsoPs, as well as between C2 and F2-IsoPs (R=-.3, P=.04; R=-.49, P=.002, respectively) in the patient group, but not in the controls. After controlling for potential confounders in a multiple regression model, the associations between C2 and F2-IsoPs remained significant in the patient group (P<.001). CONCLUSIONS: The possible link between arterial elasticity and F2-IsoPs in patients with PAD suggests that oxidative modifications may be involved in alterations of arterial elastic properties in atherosclerosis.

Aged↗
PubMed2006

Age-related changes in hardness and modulus of elasticity of dentine.

OBJECTIVES: Little knowledge has been clarified about the relationship between the morphological and physical changes of dentine during aging. The purpose of this study was to clarify the modulus of elasticity and hardness related to the morphological changes of dentine by aging using a transmitted light microscope (TLM) and a nano-hardness tester (NHT). METHODS: Aged human molars and young third molars were used. The dentine morphology was observed under a TLM. The hardness and Young's modulus of elasticity related to the morphologic study were evaluated with an NHT. RESULTS: The thickness of mantle dentine and globular dentine of aged teeth were less than that of young teeth. Transparent dentine was observed only underneath the attrition of young teeth. Reactionary tertiary dentine formed and a "dark zone" was found at the junction between physiologic secondary and reactionary dentine only in aged teeth. At the mantle dentine, hardness and modulus of elasticity of aged dentine were higher than those of young dentine. The reactionary dentine in aged teeth and newly developed secondary dentine in young teeth demonstrated lower modulus of elasticity and hardness than those of other circumpulpal dentine. Relatively low modulus of elasticity and hardness were observed at the zone between secondary and reactionary dentine. CONCLUSIONS: Changes in dentine due to aging resulted in transformation of morphological features causing changes to their hardness and modulus of elasticity at the explicit areas such as the increase of hardness and modulus of elasticity at mantle dentin and the reduction of these properties at the "dark zone" that found in aged teeth.

Adolescent↗
PubMed2004

Neointima formation on vascular elastic laminae and collagen matrices scaffolds implanted in the rat aortae.

Synthetic polymers, including polytetrafluoroethylene and Dacron, and biomatrix proteins, including collagen and fibrin, have been used for the construction of vascular substitutes. However, these materials induce inflammatory reactions, contributing to thrombosis, smooth muscle cell (SMC) proliferation, and neointima formation, processes leading to the failure of vascular substitutes. Thus, a pressing issue in vascular reconstruction is to construct vascular substitutes with surface materials that are inflammation-resistant. Here, we demonstrate that the vascular elastic laminae exhibit such a property. Aortic specimens from donor rats were treated with 0.1M NaOH for various times, resulting in elastic lamina-collagen matrix scaffolds with and without the basal lamina. Matrix scaffolds were implanted into the host aorta with three different surface materials, including the elastic lamina, basal lamina, and adventitial collagen, and observed for leukocyte adhesion, endothelial migration, cell proliferation, and neointimal formation on these surfaces. It was found that the elastic lamina was associated with significantly lower leukocyte adhesion, BrdU incorporation, and neointima formation than the basal lamina and adventitial collagen, while the migration of endothelial cells was comparable on all three surfaces. The adventitial collagen matrix was associated with leukocyte infiltration from blood and subsequent SMC migration from the host aorta, whereas the elastic laminae were resistant to such processes. The morphology of the implanted elastic laminae appeared normal at all times. These observations suggest that the vascular elastic laminae exhibit inflammation-resistant properties and inhibit SMC mitogenic activities compared with collagen-containing matrices and may be considered a potential surface material for vascular reconstruction.

Animals↗
PubMed2004

Skin elasticity meter or subjective evaluation in scars: a reliability assessment.

UNLABELLED: Various methods are available for evaluating the elasticity of scars. However, the reliability and validity of these methods have been sparsely examined. The aim of this study was to examine the reliability of the subjective evaluation of scar pliability, while at the same time testing the reliability of the measurements of a non-invasive suction device (Cutometer Skin Elasticity Meter 575) on scars. Four observers assessed 49 scar areas of 20 patients with a subjective assessment of pliability. Subsequently, each observer measured the scar areas with the Cutometer. The intraclass correlation coefficients (ICC) of the elasticity (Ue) and extension (Uf) parameters of the Cutometer were acceptable (r = 0.76 and 0.74, respectively) when a single observer carried out the measurements. The subjective assessment of pliability needs to be completed by two or more observers to make the evaluation reliable (r = 0.79). The concurrent validities between the subjective pliability-assessment and each of the Cutometer parameters were statistically significant and ranged from r = 0.29-0.53. The correlations between each of the Cutometer parameters were high and statistically significant (r > or = 0.71). CONCLUSION: A single observer can reliably use the Cutometer for the elasticity measurements of scars. Furthermore, either Ue or Uf, instead of all five elasticity values provided by the Cutometer, can be adequately used for the elasticity measurements of scars. The subjective assessment of pliability of scars can only be assessed reliably when completed by two or more observers. The concurrent validity showed that all Cutometer parameters, except for visco-elasticity (Uv), and the subjective assessment of pliability measured the same characteristic of a scar.

Adolescent↗
PubMed2005

Dynamic visco-elastic properties of dental composite resins.

OBJECTIVES: This study aimed to examine the visco-elastic properties of dental composites by dynamic mechanical analysis under the influence of clinically relevant temperatures and variable frequencies, after being stored in air or distilled water for up to 3 months. METHODS: Two direct (Diamond Lite and Grandio) and two indirect (Artglass and Vita Zeta LC) composites were used. Samples were immediately tested (baseline) or stored at 37 degrees C, either in air or distilled water for 1 day, 7 or 90 days before testing. During dynamic testing, elastic modulus, viscous modulus and loss tangent were determined over a frequency range from 0.1 to 10 Hz at constant temperatures between 5 and 55 degrees C. RESULTS: Results were analyzed by one-way ANOVA and Turkey's-test. Elastic and viscous moduli were higher for direct than for indirect composites. No such evidence was found for loss tangent. Only the elastic modulus showed statistically relevant differences in the direct and indirect materials groups: Grandio showed higher modulus than Diamond Lite, while Artglass had higher modulus than Vita Zeta LC. The elastic modulus reduced with increasing temperature and decreasing frequency, while the loss tangent showed the opposite trend. The influence of temperature and frequency on viscous modulus was not conclusive. The elastic modulus was more sensitive to moisture than viscous modulus and loss tangent but all three properties showed no overall consistent trend in the results following the storage periods. SIGNIFICANCE: Dynamic mechanical analysis was a valuable tool to characterize the visco-elastic properties of dental composites, thus giving us a greater insight into material behavior.

Air↗
PubMed1996

Nonuniform elasticity of titin in cardiac myocytes: a study using immunoelectron microscopy and cellular mechanics.

Titin (also known as connectin) is a muscle-specific giant protein found inside the sarcomere, spanning from the Z-line to the M-line. The I-band segment of titin is considered to function as a molecular spring that develops tension when sarcomeres are stretched (passive tension). Recent studies on skeletal muscle indicate that it is not the entire I-band segment of titin that behaves as a spring; some sections are inelastic and do not take part in the development of passive tension. To better understand the mechanism of passive tension development in the heart, where passive tension plays an essential role in the pumping function, we investigated titin's elastic segment in cardiac myocytes using structural and mechanical techniques. Single cardiac myocytes were stretched by various amounts and then immunolabeled and processed for electron microscopy in the stretched state. Monoclonal antibodies that recognize different titin epitopes were used, and the locations of the titin epitopes in the sarcomere were studied as a function of sarcomere length. We found that only a small region of the I-band segment of titin is elastic; its contour length is estimated at approximately 75 nm, which is only approximately 40% of the total I-band segment of titin. Passive tension measurements indicated that the fundamental determinant of how much passive tension the heart develops is the strain of titin's elastic segment. Furthermore, we found evidence that in sarcomeres that are slack (length, approximately 1.85 microns) the elastic titin segment is highly folded on top of itself. Based on the data, we propose a two-stage mechanism of passive tension development in the heart, in which, between sarcomere lengths of approximately 1.85 microns and approximately 2.0 microns, titin's elastic segment straightens and, at lengths longer than approximately 2.0 microns, the molecular domains that make up titin's elastic segment unravel. Sarcomere shortening to lengths below slack (approximately 1.85 microns) also results in straightening of the elastic titin segment, giving rise to a force that opposes shortening and that tends to bring sarcomeres back to their slack length.

Animals↗
PubMed1997

Phosphatidylcholine acyl unsaturation modulates the decrease in interfacial elasticity induced by cholesterol.

The effect of cholesterol on the interfacial elastic packing interactions of various molecular species of phosphatidylcholines (PCs) has been investigated by using a Langmuir-type film balance and analyzing the elastic area compressibility moduli (Cs(-1)) as a function of average cross-sectional molecular area. Emphasis was on the high surface pressure regions (pi > or = 30 mN/m) which are thought to mimic biomembrane conditions. Increasing levels of cholesterol generally caused the in-plane elasticity of the mixed monolayers to decrease. Yet, the magnitude of the cholesterol-induced changes was markedly dependent upon PC hydrocarbon structure. Among PC species with a saturated sn-1 chain but different sn-2 chain cis unsaturation levels [e.g., myristate (14:0), oleate (18:1delta9(c), linoleate (18:2delta9,12(c), arachidonate (20:4delta5,8,11,14(c), or docosahexenoate (22:6delta4,7,10,13,16,19(c)], the in-plane elasticity moduli of PC species with higher sn-2 unsaturation levels were less affected by high cholesterol mol fractions (e.g., >30 mol %) than were the more saturated PC species. The largest cholesterol-induced decreases in the in-plane elasticity were observed when both chains of PC were saturated (e.g., di-14:0 PC). When both acyl chains were identically unsaturated, the resulting PCs were 20-25% more elastic in the presence of cholesterol than when their sn-1 chains were long and saturated (e.g., palmitate). The mixing of cholesterol with PC was found to diminish the in-plane elasticity of the films beyond what was predicted from the additive behavior of the individual lipid components apportioned by mole and area fraction. Deviations from additivity were greatest for di-14:0 PC and were least for diarachidonoyl PC and didocosahexenoyl PC. In contrast to Cs(-1) analyses, sterol-induced area condensations were relatively unresponsive to subtle structural differences in the PCs at high surface pressures. Cs(-1) versus average area plots also indicated the presence of cholesterol concentration-dependent, low-pressure (<14 mN/m) phase boundaries that became more prominent as PC acyl chain unsaturation increased. Hence, area condensations measured at low surface pressures often do not accurately portray which lipid structural features are important in the lipid-sterol interactions that occur at high membrane-like surface pressures.

Cholesterol↗
PubMed2001

Endothelial, cardiac muscle and skeletal muscle exhibit different viscous and elastic properties as determined by atomic force microscopy.

This study evaluated the hypothesis that, due to functional and structural differences, the apparent elastic modulus and viscous behavior of cardiac and skeletal muscle and vascular endothelium would differ. To accurately determine the elastic modulus, the contribution of probe velocity, indentation depth, and the assumed shape of the probe were examined. Hysteresis was observed at high indentation velocities arising from viscous effects. Irreversible deformation was not observed for endothelial cells and hysteresis was negligible below 1 microm/s. For skeletal muscle and cardiac muscle cells, hysteresis was negligible below 0.25 microm/s. Viscous dissipation for endothelial and cardiac muscle cells was higher than for skeletal muscle cells. The calculated elastic modulus was most sensitive to the assumed probe geometry for the first 60 nm of indentation for the three cell types. Modeling the probe as a blunt cone-spherical cap resulted in variation in elastic modulus with indentation depth that was less than that calculated by treating the probe as a conical tip. Substrate contributions were negligible since the elastic modulus reached a steady value for indentations above 60 nm and the probe never indented more than 10% of the cell thickness. Cardiac cells were the stiffest (100.3+/-10.7 kPa), the skeletal muscle cells were intermediate (24.7+/-3.5 kPa), and the endothelial cells were the softest with a range of elastic moduli (1.4+/-0.1 to 6.8+/-0.4 kPa) depending on the location of the cell surface tested. Cardiac and skeletal muscle exhibited nonlinear elastic behavior. These passive mechanical properties are generally consistent with the function of these different cell types.

Animals↗
PubMed2003

The dependence of the elastic properties of osteoporotic cancellous bone on volume fraction and fabric.

Osteoporosis is a progressive systemic skeletal condition characterized by low bone mass and microarchitectural deterioration, with a consequent increase in susceptibility to fracture. Hence, osteoporosis would be best diagnosed by in vivo measurements of bone strength. As this is not clinically feasible, our goal is to estimate bone strength through the assessment of elastic properties, which are highly correlated to strength. Previously established relations between morphological parameters (volume fraction and fabric) and elastic constants could be applied to estimate cancellous bone stiffness in vivo. However, these relations were determined for normal cancellous bone. Cancellous bone from osteoporotic patients may require different relations. In this study we set out to answer two questions. First, can the elastic properties of osteoporotic cancellous bone be estimated from morphological parameters? Second, do the relations between morphological parameters and elastic constants, determined for normal bone, apply to osteoporotic bone as well? To answer these questions we used cancellous bone cubes from femoral heads of patients with (n=26) and without (n=32) hip fractures. The elastic properties of the cubes were determined using micro-finite element analysis, assuming equal tissue moduli for all specimens. The morphological parameters were determined using microcomputed tomography. Our results showed that, for equal tissue properties, the elastic properties of cancellous bone from fracture patients could indeed be estimated from morphological parameters. The morphology-based relations used to estimate the elastic properties of cancellous bone are not different for women with or without fractures.

Bone and Bones↗
PubMed1990

Role of elastic fiber degradation in emphysema-like lesions of pulmonary lymphangiomyomatosis.

To study the pulmonary structural remodeling in pulmonary lymphangiomyomatosis, electron microscopy and light and electron microscopic immunohistochemical observations for elastin and alpha 1-antitrypsin were performed on five open lung biopsy samples. Lung specimens showed emphysema-like changes in areas of abnormally accumulated smooth muscle cells. In the alveolar walls having accumulated smooth muscle cells, elastic fibers were decreased in number, disrupted, granular, and occasionally accumulated. Ultrastructurally, elastic fibers in areas of smooth muscle cell accumulation showed poorly outlined amorphous components and a few microfibrils, and occasionally showed electron-dense granular deposits in and around the amorphous components. Spiraling collagen fibrils were frequently found associated with these abnormal elastic fibers. Immunohistochemistry for elastin showed even staining of amorphous components of elastic fibers in the areas of smooth muscle cell accumulation. alpha 1-Antitrypsin was also detected evenly in amorphous components of elastic fibers in the areas of smooth muscle cell accumulation. It is proposed that the emphysema-like lesions of lymphangiomyomatosis are mediated by the degradation of elastic fibers, and these degraded elastic fibers are related to an imbalance of the elastase/alpha 1-antitrypsin system similar to the probable pathogenesis of emphysema.

Adult↗
PubMed1999

Actinically degenerate elastic tissue is the likely antigenic basis of actinic granuloma of the skin and of temporal arteritis.

Staining technique is paramount for detecting and assessing the severe degeneration that occurs in the elastic tissues of the skin and its arteries in response to prolonged exposure to actinic radiation. With a selective "controlled" hematoxylin-and-eosin stain, actinically damaged ("elastotic") elastic tissue stains blue, as Unna described, and contrasts with normal and simply hyperplastic elastic tissue, which stains red. "Special" elastic stains such as Orcein and Verhoeff do not demonstrate this difference. When resorptive (elastolytic) giant cell reactions develop in relation to actinically degenerate elastic tissue of the skin, the papules that arise tend to form expanding, annular rings. A previously used and appropriate name for these autoimmune lesions in the skin is actinic granuloma because this name highlights the likely actinic origin and pathogenesis of many such lesions. Granulomatous inflammation in connection with actinically degenerate internal elastic lamina appears to be the basis of temporal arteritis. Actinic granulomas may occur in the skin concurrently with temporal arteritis. A recent study of temporal arteritis strongly relates its elastic tissue changes to those of "accelerated" atherosclerosis.

Adolescent↗
PubMed1996

Imaging of the elastic properties of tissue--a review.

Recently, a number of methods have been developed that make it possible to image the elastic properties of soft tissues. Because certain types of tissues such as malignant lesions, for example, have elastic properties that are markedly different from surrounding tissues, elasticity imaging could provide a significant adjunct to current diagnostic ultrasonic methods. Further, elasticity imaging techniques could be used to augment the study of tissues that change their elastic properties, such as skeletal and cardiac muscle. In this paper, we survey some of the previous work done in the related field of biomechanics, and we review measurement techniques from the 1950s to the 1980s. Different approaches to elastic imaging and signal processing are then discussed and a lexicography for elastic imaging is introduced. It is hoped that this nomenclature will provide a meaningful categorization of various approaches and will make evident the inherent parameters displayed and conditions applied in deriving the resulting images. Key assumptions and signal processing approaches are also reviewed. Finally, directions for future work are suggested.

Animals↗
PubMed2001

Elasticity of vesicles assessed by electron spin resonance, electron microscopy and extrusion measurements.

The composition of vesicles determines the physical state and elasticity of their bilayers. Fatty acid spin labels were incorporated into vesicles, composed of the single chain non-ionic surfactant octaoxyethylenelaurate-ester (PEG-8-L), the sucrose laurate-ester L-595 and cholesterol sulfate (CS) to monitor local dynamic properties of lipid molecules in vesicle bilayers and to study the elasticity of vesicle bilayers. Studies with the spin label probes 5-, 12- and 16-doxyl stearic acid (DSA) indicated that both the order parameter and the rotational correlation times increased when the doxyl group was positioned closer to the headgroup region. These findings indicate that the fluidity of membranes decreased near the headgroup region. Comparing 16-DSA incorporated in vesicle formulations with either 30 or 70 mol% showed no difference in alkyl chain mobility as was reflected by the order parameter. The rotational correlation times, however, showed a slowdown from 0.38 to 0.71 and 1.13 ns when the PEG-8-L molar content was decreased from 100 to 70 and 30 mol% for PEG-8-L:L-595:CS vesicles, respectively. Extrusion measurements indicated an increase in elasticity of vesicle bilayers as the molar content of PEG-8-L was increased from 10 to 90 mol%. Incorporation of cholesterol sulfate stabilizes vesicles and thereby, decreases the elasticity. The increased elasticity correlated excellent with a reduction in the rotational correlation times observed. In conclusion, these results demonstrate that when the molar content of the single chain non-ionic surfactant PEG-8-L in vesicles is increased the elasticity is enhanced and the rotational correlation time is reduced. The enhanced elasticity might contribute to an optimal design of vesicles as drug carriers for transdermal application.

Caprylates↗