The time effect of pressure on tissue viability: investigation using an experimental rat model

An experimental rat model was used to investigate the time-pressure effect on tissue viability. External loading equivalent to 13.3 kPa (100 mm Hg) of pressure was applied to the greater trochanter and tibialis area of Sprague-Dawley rats using pneumatic indentors for duration of 6 hrs each day for 1 to 4 days. It was observed that postocclusive hyperemic responses were gradually increased at the trochanter throughout the 4 days of loading, whereas for the tibia there was a significant increase (P = 0.04) in postocclusive hyperemic flow between Days 2 and 3. In histologic evaluations, cutaneous tissue damage was observed at the trochanter area but not at the tibialis area after 2 consecutive days of load application. In contrast, degeneration of muscle cells characterized by numerous increases of nuclei occupying the central of the muscle fibers was observed after 2 days of load application at the tibialis. The situation was found to progress with time (P = 0.17). The presence of other histologic signs, including the internalization of peripherally located nuclei, replacement of muscle cells by fibrosis and adipose tissues, and the presence of pyknotic nuclei as well as karyorrhexis, confirmed that the affected tissues were damaged. These findings suggest that postocclusive hyperemia and the distress of tissues under loading could be closely related.     

The effect ofin ovo boron supplementation on bone mineralization of the vitamin D-deficient chicken embryo

It has been hypothesized that boron (B) is an essential element for animals, but its action will vary greatly depending on the nutriture of the organism. One of the nutrients implicated as having an interaction with boron is cholecalciferol (Vit D3). This study was carried out to determine if such an interaction exists. The study was conducted utilizing vitamin D-deficient chicken embryos that were injected through the shell at 8 d of embryogenesis with carrier (NaCl and/or acetone), B (0.5 mg), B + Vit D3 (0.5 mg and 0.3 microgram, respectively), or Vit D3 (0.3 or 1.5 micrograms). The in ovo concomitant administration of boron and vitamin D enhanced (p less than 0.05) the hatchability of the vitamin D-deficient embryos. Furthermore, boron and/or vitamin D3 increased (p less than 0.05) the percent of bone ash and decreased (p less than 0.05) the exaggerated height of the proliferative zone of the epiphyseal growth plate normally observed in vitamin D deficiency, suggesting a more rapid bone formation. The results provide further evidence supporting the hypothesis that boron plays a role in bone mineralization through an interaction with vitamin D.     

The effect of strain rate on the mechanical properties of human cortical bone

Bone mechanical properties are typically evaluated at relatively low strain rates. However, the strain rate related to traumatic failure is likely to be orders of magnitude higher and this higher strain rate is likely to affect the mechanical properties. Previous work reporting on the effect of strain rate on the mechanical properties of bone predominantly used nonhuman bone. In the work reported here, the effect of strain rate on the tensile and compressive properties of human bone was investigated. Human femoral cortical bone was tested longitudinally at strain rates ranging between 0.14-29.1 s(-1) in compression and 0.08-17 s(-1) in tension. Young's modulus generally increased, across this strain rate range, for both tension and compression. Strength and strain (at maximum load) increased slightly in compression and decreased (for strain rates beyond 1 s(-1)) in tension. Stress and strain at yield decreased (for strain rates beyond 1 s(-1)) for both tension and compression. In general, there seemed to be a relatively simple linear relationship between yield properties and strain rate, but the relationships between postyield properties and strain rate were more complicated and indicated that strain rate has a stronger effect on postyield deformation than on initiation of yielding. The behavior seen in compression is broadly in agreement with past literature, while the behavior observed in tension may be explained by a ductile to brittle transition of bone at moderate to high strain rates.     

Analysis of the effect of using two different strain rates on the acoustic emission in bone

To study the effect of strain rate on the acoustic emission amplitude signature of bone, bovine cortical bone was milled into standard tensile specimens which were tested at two different strain rates while being monitored with acoustic emission equipment. It was demonstrated that the amplitude distribution of the acoustic events in bone is dependent on strain rate. Greater numbers of events occurred with the slower strain rate (0.0001 s-1), but these events were of lower amplitude than those emitted during the more rapid strain rate (0.01 s-1). The plot of the cumulative event amplitude distribution followed the power-law model, and the slope of this output, the b-value, represented a signature of the amplitude distribution. The mechanical test results were consistent with the behavior of a viscoelastic multi-phase composite material.     

The vascularized pig fibula bone flap model: effect of segmental osteotomies and internal fixation on blood flow

The free fibular flap is the flap of choice for reconstruction of complex mandibular defects, although two or more osteotomies may be required to recreate the normal mandibular contour. The effect of these surgical manipulations on the fibula has not been adequately investigated. This study was designed to study the effect of multiple segmental osteotomies and internal fixation techniques on blood flow in the vascularized pig fibula bone flap model. The hindlimbs of 15 Yorkshire pigs were randomized into 1 of 5 groups (n = 6 fibulae per group) consisting of: (1) a nonoperated, in situ fibula; (2) an elevated fibula flap; (3) an elevated fibula flap with two segmental osteotomies; (4) an elevated fibula with two segmental closing osteotomies rigidly fixed with 2-mm miniplates; (5) an elevated fibula with two segmental closing osteotomies rigidly fixed with 2-mm lag screws. Total and gradient blood flow was measured in the bone and soft-tissue components of these flaps using the 15-microm radioactive microsphere technique. The creation of two segmental osteotomies in the vascularized pig fibula bone flap model resulted in a significant decrease (p<0.05) in the gradient blood flow in the segment of bone distal to the second osteotomy. Application of miniplates or lag screws across closing osteotomies resulted in a significant decrease (p<0.05) in total and gradient blood flow to the bone component of the fibulae, as compared with the elevated and osteotomized fibulae groups. An increase in blood flow suggesting a hyperemic response was noted in the bone and soft tissue in the elevated and osteotomized flap groups as compared with the in situ, nonoperated controls. This study established the validity of the pig fibula as a suitable model for investigating the pathophysiology of blood flow changes in the face of standard surgical maneuvers necessary for the restoration of mandibular form and function. The results demonstrated that the creation of multiple segmental osteotomies and the application of internal fixation significantly decreases (p<0.05) blood flow to the distal portion of the flap. The effects of segmental osteotomies and internal fixation on healing and growth of the pig fibula bone flap model are investigated in a separate study.     

An investigation into the internal and external variables acting on crystallinity index using Fourier Transform Infrared Spectroscopy on unaltered and burned bone

The Crystallinity Index is a measure of structural order in bone and is potentially an extremely useful tool in bioarchaeology since it can assist in sequencing bones into chronological and/or stratigraphic order, act as an indicator for preservation, and assist in reconstructing burning events. Unfortunately, concerns over influencing variables and bone sampling issues inhibit full and wide-spread adoption of this approach. An attempt has been made to determine the influence of a number of internal and external variables on bone crystallinity changes. CI, C/P and C/C were calculated using Fourier Transform Infrared Spectroscopy – Attenuated Total Reflectance (FTIR-ATR) on modern burned and unburned faunal bone. Samples were taken systematically across bone elements and on the internal and external surfaces. The CI results support previous work and show increases with burning intensity. It is also shown that extrinsic variables (such as temperature and duration of burning) have more of a significant influence on CI values than intrinsic variables (such as location of sample site on the bone). A sampling strategy is suggested for those wishing to use the CI on bone in archaeological contexts.     

The effect of mechanical strain on soft (cardiovascular) and hard (bone) tissues

Mechanical stress plays a pivotal role in developing and maintaining tissues functionalities. Cells are constantly subjected to strain and compressive forces that are sensed by specialized membrane mechanosensors and converted in biochemical signals able to differently influence cellular behavior in terms of surviving, differentiation and extracellular matrix remodeling. This review focuses on the effects of mechanical strain on soft and hard tissues.

Unexpectedly, different cells share almost the same membrane mechanosensors and the relative intracellular pathways, but to ultimately obtain very different biological effects. The events occurring in cardiovascular and bone tissues are treated in details, showing that integrins, cadherins, growth factor receptors and ions channels specifically expressed in the different tissues are the major actors of the sight. However, MAPkinases and RhoGTPases are mainly involved in the biochemical intracellular signaling directed to nuclear modifications.     

The effect of strain rate on the failure stress and toughness of bone of different mineral densities

The risk of low energy fracture of the bone increases with age and osteoporosis. This paper investigates the effect of strain rate and mineral level on the peak stress and toughness of whole ovine bones.     

The correlation between craniofacial and long bone growth: an experimental investigation in normal rabbits

The present study was undertaken to elucidate the relationships between craniofacial and long-bone growth. Nine male New Zealand white rabbits received spherical tantalum bone markers in the tibial epiphyses and in the nasal, frontal, and parietal bones. The animals were followed from 30 to 143 days of age. Growth changes were calculated with a roentgen stereometric system, and the results statistically evaluated. Except for the final interval when all variables varied at random, high correlations between tibial and frontonasal or coronal sutural growth were demonstrated; and the respective linear regression lines were homogeneously assembled. The relationship between the tibia and the sagittal suture displayed great variations between individual animals as well as between the suture's parts, although growth at the interfrontal suture was clearly correlated to tibial growth upon exclusion of the time factor. The first principal component of the three neurocranial sutures was calculated and seemed accurately correlated to long-bone growth. The present study concluded that growth at the frontonasal and coronal sutures normally seems to parallel general somatic development, while growth at the sagittal suture appears individually displaced in time. Nevertheless, when the principal component of the combination of the coronal suture and the neurocranial section of the sagittal suture was computed, this was highly correlated to body growth.     

Humic acid effect on pyrene degradation: finding an optimal range for pyrene solubility and mineralization enhancement

The addition of humic acid (HA) to polycyclic aromatic hydrocarbon (PAH) contaminated systems has been shown to enhance, inhibit, or have no effect on the biodegradation of these PAHs. In this study, the surfactant effects of Elliott soil HA (ESHA) at two pH values were tested. At pH 7.0, ESHA did not behave as a surfactant. At pH 11.8, ESHA acted as a surfactant, as displayed by a decrease in surface tension with increasing concentrations of ESHA. The effect of ESHA on pyrene solubility was tested by adding 0 to 800 μg ESHA/g soil to soil-slurries. Enhancement of pyrene apparent solubility demonstrated a dose- and time-related effect. Broader doses from 0 to 10,080 μg ESHA/g soil and three higher doses from 3,360 to 10,080 μg ESHA/g soil were tested for their effects on pyrene mineralization by indigenous soil microorganisms and a novel PAH-degrading Mycobacterium sp. KMS in soil microcosms, respectively. ESHA amendments between 20 and 200 μg ESHA/g soil were found to consistently increase pyrene mineralization by indigenous microorganisms, while the 10,080 μg ESHA/g soil produced inhibition and all other doses presented no effects. Pyrene degradation by M. KMS was significantly inhibited by the addition of the highest dose of ESHA.     

The photoreaction of active-site-methylated bacteriorhodopsin: an investigation using static and time-resolved infrared difference spectroscopy

The photoreaction of active-site-methylated, permethylated bacteriorhodopsin has been investigated by static and time-resolved UV-vis and infrared difference spectroscopy. Additional information on the isomeric composition of the initial state and of photoproducts was obtained by retinal extraction and subsequent HPLC analysis. The data show that the dark-adapted state contains only all-trans-retinal. Prolonged illumination produces a metastable state which contains essentially only 9-cis-retinal and which decays back to the dark-adapted initial state within 8 h. The time-resolved infrared difference spectra clearly demonstrate that laser flash excitation produces an intermediate that has all the characteristics of the L intermediate. It is demonstrated that the methyl group at the Schiff base nitrogen introduces a steric hindrance with the protein which inhibits a photoreaction at 80 K, but which allows the generation of an L-like intermediate at room temperature and 173 K.     

The effect of rigid fixation on the survival of onlay bone grafts: an experimental study

Much attention has recently been focused on rigid fixation as a method of improving fracture healing. Whether such fixation, when applied to onlay grafting, improves graft take and volume is unknown. To examine this question, we compared survival of both endochondral and membranous grafts fixed rigidly and nonrigidly in areas of low motion (snout) and high motion (femur) in a rabbit model. Gross morphology, histologic analysis, and graft volume kinetics were evaluated. Findings demonstrate that in areas of high motion, the application of rigid fixation improves graft survival, whereas in a low-motion region, no differences in graft volume retention as a function of fixation were observed. Histologically, no differences with the method of fixation employed were seen, and similar revascularization patterns were noted. By kinetic analysis, rigid fixation appears to exert its most profound effect early in the postgraft period. Membranous bone grafts remain superior to endochondral grafts under all circumstances. From these studies, we conclude that rigid fixation is the method of choice in all circumstances where onlay bone grafts may be exposed to motion, shear, and torsional forces.     

Observations on the internal and surface morphology of malaria infected blood cells using optical and atomic force microscopy

We describe a simple and fast method to probe the morphological changes on the exterior and interior of a malaria infected erythrocyte at different stages of parasite development. This involves the imaging and scanning of Giemsa stained malaria infected erythrocytes using optical microscopy and atomic force microscopy, respectively.     

Studying the effect of a charged surface on the interaction of bleomycin with DNA using an atomic force microscope

The cleavage of DNA caused by the antitumoral drug bleomycin has been investigated using atomic force microscopy (AFM). This work deals with the effect that adsorbing DNA onto a positively- or negatively-charged surface has on the double-strand cleavage of DNA by Fe(III)/bleomycin. Quantitative analysis of the number of breaks per DNA molecule, in bulk and at the surface of the mica substrate, has been performed by analyzing AFM images. It turns out that the cleavage of DNA is strongly inhibited by a positively-charged surface. Our experiments can be interpreted using a simple electrostatic model. This paper is a first step in the study of DNA accessibility to ligand such as bleomycin, using AFM in liquids.Olivier Piétrement and David Pastré have contributed equally to the work.