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Biomedical subjects

S Weiner

Publications and source records attributed to S Weiner.

At least 19 recordsLinked to original sources
PubMed1992

Phosphatic shell plate of the barnacle Ibla (Cirripedia): a bone-like structure.

The carbonate apatite crystals and the segmented structure of the shell plates of the barnacles in the genus Ibla distinguish them from the shell plates of all other barnacles, which are coherent calcitic structures. A detailed study of the hierarchical organization of one of the two shell plate types, the tergum, reveals a remarkably complex structure. Cylinders composed of a chitin-protein complex and nodes of plate-shaped crystals constitute the basic building blocks. The crystals are organized into layered stacks in which the c crystallographic axes are all aligned perpendicular to a 25-nm banded structure. The cylinders are, in turn, ordered in arrays such that parts of each cylinder are aligned in a plane, and parts form arcuate out-of-plane structures. The overall result is a lamellar structure, with a plywood-like motif, that is present throughout an individual segment. A series of segments forms an interlocking mineralized core, which is enclosed within a thick organic envelope. The flexible and complex skeletal structure of the tergum shows some marked similarities to the structure of lamellar bone. Although this is undoubtably a product of convergent evolution, the iblid tergum provides a unique perspective on bone structure, which was heretofore unavailable.

Amino Acids↗
PubMed1992

Bone structure: from angstroms to microns.

Bone has a complex hierarchical structure, which despite much investigation, is still not well understood. Here we bring together pieces of this complicated puzzle, albeit from different sources, to present a tentative overview of bone structure. The basic building blocks are the extremely small plate-shaped crystals of carbonate apatite, just hundreds of angstroms long and wide and some 20-30 A thick. They are arranged in parallel layers within the collagenous framework. At the next hierarchical level these mineral-filled collagen fibrils are ordered into arrays in which the fibril axes and the crystal layers are all organized into a 3-dimensional structure that makes up a single layer or lamella of bone a few microns thick. The orientations of the collagen fibrils and the crystal layers in alternating lamellae of rat bone differ such that in the thinner lamellae, the fibrils and the crystal layers are parallel to the lamellar boundaries. In the thicker lamellae the fibrils are parallel to the boundary, but the crystal layers are rotated out of the plane of the boundary. In many bones these alternating lamellae are organized into even larger ordered structures to produce what is truly a remarkably ordered material, all the way from the molecular scale to the macroscopic product.

Animals↗
PubMed1992

Interactions between acidic matrix macromolecules and calcium phosphate ester crystals: relevance to carbonate apatite formation in biomineralization.

Control over crystal growth by acidic matrix macromolecules is an important process in the formation of many mineralized tissues. Earlier studies on the interactions between acidic macromolecules and carboxylate- and carbonate-containing crystals showed that the proteins recognize a specific stereochemical motif on the interacting plane. Here we show that a similar stereochemical motif is recognized by acidic mollusc shell macromolecules interacting with four different organic calcium phosphate-containing crystals. In addition, an acidic protein from vertebrate tooth dentin was also observed to recognize a similar structural motif in one of the crystals. The characteristic motif recognized is composed of rows of calcium ions and phosphates arranged in a plane defined by two free oxygens and a phosphorus atom emerging perpendicular to the affected face. These observations may have a direct bearing on the manner in which control over crystal growth is exerted on carbonate apatite crystals commonly found in vertebrate tissues.

Animals↗
PubMed1992

On the relationship between the microstructure of bone and its mechanical stiffness.

A recent study of bone structure shows that the plate-shaped carbonate apatite crystals in individual lamellae are arranged in layers across the lamellae, and that the orientation of these layers are different in alternate lamellae. Based on these findings, a new micromechanical model for the Young's modulus of bone is proposed, which accounts for the anisotropy and geometrical characteristics of the material. The model incorporates the platelet-like geometry of the basic reinforcing unit, the presence of alternating thin and thick lamellae, and the orientations of the crystal platelets in the lamellae. The thin and thick lamellae are modeled as orthotropic composite layers made up of thin rectangular apatite platelets within a collagen matrix, and classical orthotropic elasticity theory is used to calculate the Young's modulus of the lamellae. Bone is viewed as an assembly of such orthotropic lamellae bent into cylindrical structures, and having a constant, alternating angle between successive lamellae. The micromechanical model employs a modified rule-of-mixtures to account for the two types of lamellae. The model provides a curve similar to the published experimental data on the angular dependence of Young's modulus, including a local maximum at an angle between 0 and 90 degrees. A rigorous testing of the model awaits additional experimental data.

Animals↗
PubMed1992

A comparative study of ceramic crown margins constructed using different techniques.

This study compares three variations of the direct lift-off technique utilizing porcelain materials with thermoplastic, modeling liquid, and visible light-cured resin carriers. Three commercially available materials were evaluated. Vita, Ducera, and Dentsply Spectrum. Measurements were made of the width of the marginal gap for three sites at each of four stages: (1) after the shoulder firing, (2) after the body-incisal firing, (3) after the glaze firing, and (4) after a correction firing. All techniques produced marginal gaps in the clinically acceptable range. Use of the Vita thermoplastic carrier porcelain material resulted in the smallest marginal gap at all but the body-incisal stage. Crowns done with the Ducera and Spectrum materials had statistically similar marginal gaps at all but the glaze stage, where the Ducera material crowns demonstrated the largest marginal gaps.

Ceramics↗
PubMed1992

Treatment of non-small cell lung cancer with external beam radiotherapy and high dose rate brachytherapy.

Between August 1985 and September 1989, 62 patients with medically inoperable or surgically unresectable, non-small cell lung cancer were treated with both external beam radiotherapy and high dose rate bronchial brachytherapy. Treatment consisted of external beam radiotherapy (5000-6000 cGy in 5-6 1/2 weeks) and weekly high dose rate bronchial brachytherapy (three to five fractions, 500 cGy at 1 cm from the source) delivered either concurrently or sequentially. Median survival for all patients was 13 months (m). Stage I and Stage IIIA-B patients had median survivals of 20 m and 10 m, respectively. Patients without nodal disease (No) had a significantly longer median survival compared to patients with regional node metastases (N1-3), 17 m versus 9 m. A total of 54 patients were evaluable for local tumor control analysis. Local tumor control was achieved in six of eight patients who had a normal pre-treatment radiograph. Patients with measurable tumor on the pre-treatment radiograph and negative regional nodes had local tumor control in eight of twenty-two (36%) cases. In patients with regional lymphadenopathy, loco-regional tumor control was achieved in four of eight cases. Additionally, there were sixteen patients with non-measurable tumor due to associated effusion, atelectasis and/or infiltrate. Four of these (25%) were considered to have local tumor control. Of 60 evaluable patients, there were nine occurrences of fatal hemorrhage, one of whom was disease-free (NED) at autopsy. The remaining eight patients had either clinical or pathological evidence of recurrent or persistent tumor. Patients who had follow up bronchoscopies were found to have varying degrees of concentric narrowing in the treated areas. One such patient had total lung collapse with no evidence of tumor. While this form of treatment may yield high local control rates in earlier stages, this study suggests the potential risk of fatal complication. Additional studies are warranted to further investigate the use of this modality in the treatment of lung cancer.

Adenocarcinoma↗
PubMed1992

The effect of improvement of umbilical artery absent end-diastolic velocity on perinatal outcome.

OBJECTIVES: The purpose of this study was to analyze cases in which antenatal improvement of absent fetal umbilical artery end-diastolic velocity was detected and to correlate improvement with perinatal outcome. STUDY DESIGN: Forty cases of umbilical artery absent end-diastolic velocity in singleton pregnancies were retrospectively reviewed. Maternal characteristics and perinatal outcomes were compared in cases where improvement of end-diastolic velocity was diagnosed and those in which no improvement was detected. RESULTS: Eleven cases of absent end-diastolic velocity showed antenatal improvement and were associated with more advanced gestational age at delivery, longer diagnosis-to-delivery interval, larger birth weights, and a lower incidence of neonatal death than those fetuses without antenatal improvement. CONCLUSION: Improvement of umbilical artery absent end-diastolic velocity can occur and is associated with improved pregnancy outcome when compared with patients without antenatal improvement of diastolic velocity.

Blood Flow Velocity↗
PubMed1992

Origin of mineral crystal growth in collagen fibrils.

Collagen fibrils from young turkey-leg tendons, just beginning to mineralize, were stained with uranyl acetate and examined by electron microscopy. Small needle-like mineral crystals were observed and located, in relation to the collagen banding pattern, as originating at the e band in the gap region and near the surface of the fibrils. These are evidently the sites of crystal nucleation. They lie near binding locations on collagen fibrils of two glycosylated proteins believed to be implicated in the mineralization process, as well as the sites of early crystals in embryonic fowl bones.

Animals↗
PubMed1992

Efficacy of first trimester transvaginal sonography in detecting normal fetal development.

The transvaginal probe is now commonly used by the obstetrician/gynecologist. The improved resolution offered by the probe makes it easier to study the anatomic development of the first trimester fetus in greater detail. The aim of this study was to define the gestational age at which certain fetal structures become apparent by ultrasound and to screen pregnancies at high risk for development of fetal anomalies that could be detected in the first trimester. Endovaginal ultrasound was performed on 60 pregnant women at 8 to 13 menstrual weeks. Clinical follow-up disclosed 36 normally developed fetuses at delivery, five abnormal scans, and 19 ongoing pregnancies. The results of this study show that it is possible to demonstrate most of the major fetal structures by 13 weeks' gestation. By imaging the fetus transvaginally, detection of fetal anomalies can be accomplished much earlier than with the transabdominal scanning alone.

Adult↗
PubMed1992

Growth of mineral crystals in turkey tendon collagen fibers.

Bone and several other vertebrate mineralized tissues are formed by the organized growth of crystals of carbonated apatite within a matrix of type 1 collagen fibers. The development of this process in isolated fibrils of young turkey leg tendons has been studied by transmission electron microscopy. Collagen banding, presumably due to ion concentration, precedes the appearance of any crystals. The smallest crystals observed are short needles in bands near the surface of the fibrils. Longer needles, up to the length of the collagen gap regions, were also seen, and, evidently at a later stage, single crystal belts extending partly or wholly through the fibrils. Finally, in mature tendon crystal platelets, seemingly derived from the cracking of belts, extend partly into the collagen overlap zone. In the least mineralized tendon, extrafibrillar mineral-containing vesicles have occasionally been observed adjacent to regions of radiating needle crystal growth in the fibrils, and, more commonly, smaller particles adjacent to bands of very small needles.

Aging↗
PubMed1991

Crystal organization in rat bone lamellae.

The plate-shaped crystals of rat bone are arranged in parallel layers that form coherent structures up to the level of individual lamellae. The crystal layers of the thin lamellae are parallel to the lamellar boundary, whereas those of the thicker lamellae are oblique to the boundary. The basic structure of rat bone can be described as 'rotated plywood'; a structure hitherto unrecognized in either biologic or synthetic materials.

Animals↗
PubMed1991

The normal fetus of an acardiac twin pregnancy: perinatal management based on echocardiographic and sonographic evaluation.

Experience with three prenatally diagnosed pregnancies complicated by an acardiac twin reveals that ultrasonography and echocardiography are helpful in detecting early signs of in-utero congestive heart failure in the normal twin. The use of Doppler blood flow analysis to determine direction of blood flow, post-mortem placental and fetal angiography, and umbilical cord blood gas determination provided proof that retrograde arterial perfusion occurs in the acardiac fetus. In a fourth pregnancy, an experimental approach to occlude the acardiac twin's umbilical cord was attempted, but was unsuccessful.

Adult↗
PubMed1991

Venous Doppler ultrasonography in the fetus with nonimmune hydrops.

Eighteen pregnancies with nonimmune hydrops fetalis were referred for fetal echocardiography to rule out congenital heart disease. In 14 of these cases, pulsating blood velocities were recorded in the umbilical vein, which in a normal population had a nonpulsatile blood velocity pattern. The four cases without pulsations in the umbilical vein were found to have intrauterine viral infections. In the last 10 cases examined, the umbilical venous pulsations were found to reflect abnormal central venous pulsations during atrial systole suggesting increased fetal central venous pressure. Right ventricular shortening fraction was significantly decreased in the group with umbilical venous pulsations compared with those without (0.18 versus 0.32, p less than 0.05). All the fetuses without venous pulsations survived, but only four of the 14 with pulsations survived (p less than 0.05). The results suggest that blood velocity recordings in the umbilical and central veins of the fetus can give valuable clinical information with regard to the presence of fetal congestive heart failure and differentiate between this physiologic state and other causes of nonimmune hydrops fetalis. This may have implications for fetal diagnostic work-up and prognosis.

Blood Flow Velocity↗
PubMed1991

Effects of thermocycling on the margins of transitional acrylic resin crowns.

Transitional resin crowns were subjected to thermocycling and examined for marginal integrity since disturbance of the marginal seal is detrimental. Two groups of 10 crowns, one with a chamfer and the second with a shoulder finish line, were subjected to two series of 2500 thermocycles. In the first series, the crowns received cold thermocycling and in the second, hot thermocycling. Impressions were made of the facial margins before thermocycling, after cold thermocycling, and after hot thermocycling. The impressions were analyzed for loss of marginal integrity and changes in axial contour. Cold thermocycling resulted in only limited deterioration, but the changes after hot thermocycling were more pronounced. Tooth preparation designs did not influence the effects of thermocycling.

Cold Temperature↗
PubMed1991

Effects of temperature on color stability of porcelain stains.

The effects of oven firing on the color stability of extrinsic stains used for characterization and color modification of metal ceramic restorations were studied by comparing the color of the stain as initially applied with that observed after it was fired to the fusion temperature. Perceptible changes were noted for all stains studied. Multiple firings of the stain showed only minor effects on the observed color. The effects at fusion temperatures of 1700 degrees F and 1775 degrees F appeared similar. Finally, there appeared to be no marked differences between the color change observed with the use of autoglazing and overglazing techniques.

Analysis of Variance↗
PubMed1991

Enkephalinergic involvement in periaqueductal gray control of hypothalamically elicited predatory attack in the cat.

The effects of central infusion of naloxone into the midbrain periaqueductal gray (PAG) upon predatory attack behavior in the cat were studied in 12 cats. Initially, quiet biting attack was elicited by electrical stimulation of sites within the lateral hypothalamus using monopolar electrodes. Then cannula-electrodes were implanted into sites within the PAG from which electrical stimulation facilitated or suppressed the attack response. Following identification of modulatory sites within the PAG, naloxone (1.0 micrograms/0.5 microliter) was microinjected into those sites and the effects upon hypothalamically elicited attack were assessed. At nine of twelve sites in the PAG where suppression was obtained, administration of naloxone served to block those effects. Similarly, at six of eight facilitatory sites within the PAG, naloxone also blocked the modulatory effects of PAG stimulation. However, vehicle (isotonic saline) alone did not alter the modulatory effects of PAG stimulation. Administration of DAME (250 ng/0.3 microliter) into PAG modulatory sites in four cats, two which facilitated and two that suppressed the attack response, reversed the effects of naloxone at these sites. These results demonstrate that opioid peptides within the PAG play a complex role in the expression of predatory attack behavior in the cat.

Aggression↗