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Alain Meunier

Publications and source records attributed to Alain Meunier.

12 recordsLinked to original sources
PubMed2006

Chemical signature of two Permian volcanic ash deposits within a bentonite bed from Melo, Uruguay.

A Permian bentonite deposit at Melo, Uruguay is composed of a calcite-cemented sandstone containing clay pseudomorphs of glass shards (0-0.50 m) overlying a pink massive clay deposit (0.50-2.10 m). The massive bed is composed of two layers containing quartz and smectite or pure smectite respectively. The smectite is remarkably homogeneous throughout the profile: it is a complex mixed layer composed of three layer types whose expandability with ethylene glycol (2EG 1EG or 0EG sheets in the interlayer zone which correspond to low-, medium- and high-charge layers respectively) varies with the cation saturating the interlayer zone. The smectite homogeneity through the profile is the signature of an early alteration process in a lagoonal water which was over saturated with respect to calcite. Compaction during burial has made the bentonite bed a K-depleted closed system in which diagenetic illitization was inhibited. Variations in major, REE and minor element abundances throughout the massive clay deposit suggest that it originated from two successive ash falls. The incompatible element abundances are consistent with that of a volcanic glass fractionated from a rhyolite magma formed in a subduction/collision geological context.

Journal Article↗
PubMed2005

Bovine BMP osteoinductive potential enhanced by functionalized dextran-derived hydrogels.

This study evaluated functionalized dextran-derived hydrogels as BMP carriers using both in vitro and in vivo models. In vitro release kinetics indicated that dextran-derived hydrogels could retain rhBMP-2 growth factor in a variable manner depending on their functionalization ratio. The potential of these hydrogels when combined with extracted bovine BMP to enhance the bone formation was evaluated in a rat ectopic model. The largest osteoinduction was found when using hydrogels exhibiting the highest growth factor retention capacity. In addition, some implanted hydrogels demonstrated a capacity to induce an in-vivo calcification certainly related to their chemical composition. These properties make these materials interesting osteoconductive BMP carriers, allowing to decrease the amount of implanted factor required for bone regeneration.

Animals↗
PubMed2005

Ceramics in total hip replacement.

Alumina-on-alumina total hip arthroplasty has been used for 32 years in Europe. The theoretical advantages of this combination are represented by its remarkable sliding characteristics, its very low wear debris generation, and its improved fracture toughness. These advantages are achieved if the material is processed properly with high density, high purity and small grains. We summarize the results obtained with the alumina-on-alumina combination concerning in vitro and in vivo wear behavior with special emphasis on wear debris characterization and quantification and histologic tissue examinations. Alumina-on-alumina seems to be one of the best choices in young and active patients provided that sound socket fixation is maintained in the long term.

Aluminum Oxide↗
PubMed2004

Effects of platelet lysates on select bone cell functions.

Although platelet-rich plasma and platelet concentrates have been used to promote bone healing in orthopaedic and maxillofacial surgery, the underlying cellular-level mechanisms remain poorly understood. The present in vitro study investigated the effects of human platelet lysate (PL) on selected functions of cultured bone cells. Cells from 18-day-old fetal rat calvaria were isolated by a collagenase digestion procedure. PL was added at different concentrations on pre- or post-confluent cell stage. After 1 day, bone cell proliferation was maximal and half-maximal in the presence of PL from 3 x 10(8) and 0.5 x 10(8) platelets/ml, respectively. During 17 h, the number of bone cells traversing the scrape border of a scrape wound model increased by 16-fold in the presence of PL from 3 x 10(8) platelets/ml. The presence of PL from 3 x 10(8) platelets/ml in pre-confluent bone cell cultures for 48 h resulted in a threefold decrease of alkaline phosphatase (ALP) specific activity. In the case of confluent bone cells, the presence of PL (from 1 x 10(6) to 3 x 10(8) platelets/ml) for 11 days, the ALP specific activity and total calcium content decreased in a PL dose-dependent manner and reached a minimum in the presence of PL from 3 x 10(8) platelets/ml. In summary, short-term PL exposure (up to 24 h) promotes the proliferative and chemotactic bone cell functions while long-term PL exposure results in a decrease of both ALP activity and mineral formation. These data show that the soluble components contained in PL may affect the bone healing process by modulating differently bone cell functions.

Alkaline Phosphatase↗
PubMed2004

A technique for creating critical-size defects in the metatarsus of sheep for use in investigation of healing of long-bone defects.

OBJECTIVE: To develop a technique for use in investigation of healing of long-bone defects by creation of a critical-size defect in the left metarsal III and IV bone (metatarsus) of sheep. ANIMALS: 18 healthy adult sheep. PROCEDURE: Sheep were allocated to 4 groups (3, 3, 5, and 7 sheep in groups 1 to 4, respectively). An ostectomy with various segmental length-to-diaphyseal diameter ratios (0.5, 1.0, 2.0, and 2.0 for groups 1 to 4, respectively) was performed on the left metatarsus of each sheep. The defect was left empty in sheep of groups 1, 2, and 3, whereas the defect was filled with a massive corticocancellous bone autograft in sheep of group 4. RESULTS: All sheep tolerated the surgical procedure well and were able to use the affected limb the day after surgery. Radiographic and histologic examinations conducted 16 weeks after surgery revealed nonunion in all sheep of groups 1, 2, and 3, whereas consistent bone healing with abundant bone formation was observed in all sheep of group 4. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of these findings suggests that the sheep metatarsal model is a critical-size defect model with low morbidity. It should allow the assessment of new technologies for bone regeneration in conditions closely mimicking the clinical setting. IMPACT FOR HUMAN MEDICINE: Use of this technique in sheep should be of benefit for the preclinical study of osteoconductive, osteoinductive, or osteogenic biomaterials for use in humans.

Animals↗
PubMed2003

Fractures of ceramic bearings: history and present status.

During a period of 25 years (1977 to 2001), 13 fractures of an alumina component were recorded retrospectively. During the same period, approximately 5500 alumina components were implanted (3300 with all-alumina bearings and 1200 with alumina-on-polyethylene). These events occurred in seven women and six men, with a mean age of 59 years and a mean weight of 71 kg. There were eight fractures of the femoral head and five fractures of the socket component. Three fractures clearly were related to trauma (two fractures of the socket and one fracture of the head) and two were related to an abnormal design (one 22-mm head and one extra-long neck). Five fractures occurred without any rational explanation, but two fractures that occurred in the early phase could have been caused by a weaker alumina material. Finally three recent fractures of the liner were related to a change in the design of the material. This has been corrected and no additional fractures were observed. Although this dramatic event is of concern, it is infrequent and easy to solve by a limited revision procedure if done emergently. This rare complication should be balanced with the other complications of THR, including mechanical failures and osteolysis, often described with metal-on-polyethylene prostheses.

Adult↗
PubMed2003

Cyclic pressure affects osteoblast functions pertinent to osteogenesis.

In an attempt to elucidate the cellular/molecular correlations between mechanical stimuli and new bone formation, the present in vitro study used a custom-made laboratory setup and examined the effects of cyclic pressure on select functions of osteoblasts pertinent to osteogenesis. The results demonstrated that, compared to controls (no pressure), mRNA expression for type-I collagen (the main constituent of the organic phase of bone) was enhanced when osteoblasts were exposed to cyclic pressure (10-40 kPa at 1.0 Hz) for 1 h daily for up to 19 consecutive days. In addition, compared to controls, both deposition of collagen and accumulation of calcium (one of the major components of the inorganic phase of bone) increased significantly (p<0.05) following exposure of osteoblast cultures to cyclic pressure for 19 days. Since the amounts of total DNA in controls and in osteoblast cultures exposed to cyclic pressure were similar at all time points tested, it was concluded that increased collagen and calcium concentrations in cultures resulted from enhanced osteoblast function (and not from increased number of cells); the presence of increased amounts of collagen affected the subsequent increased accumulation of calcium. These results provide evidence that daily exposure to cyclic pressure for various time periods (up to 19 days) affect osteoblast functions pertinent to bone formation.

Animals↗
PubMed2003

In vitro acoustic waves propagation in human and bovine cancellous bone.

UNLABELLED: The acoustic behavior of cancellous bone with regard to its complex poroelastic nature has been investigated. The existence of two longitudinal modes of propagation is demonstrated in both bovine and human cancellous bone. Failure to take into account the presence of these two waves may result in inaccurate material characterization. INTRODUCTION: Acoustic wave propagation is now a commonly used nondestructive method for cancellous bone characterization. However, wave propagation in this material may be affected by fluid-solid interactions inherent to its poroelastic nature, resulting in two different longitudinal waves. This phenomenon has been demonstrated in previous studies and is in agreement with Biot's theory. The purpose of this paper is to extend these findings to human trabecular bone and to thoroughly investigate these two waves. MATERIALS AND METHODS: Sixty human and 14 bovine cancellous bone cubic specimens were tested in vitro in three different directions using an immersion acoustic transmission method. Original procedures were developed to quantify both velocity and attenuation characteristics of each wave. In term of attenuation, a modified broadband ultrasound attenuation (BUA), describing the rate of change of the frequency-dependent attenuation, was defined for each wave (FDUA). RESULTS: Both waves were identified in most of the specimens. The fast wave velocities demonstrated a negative linear correlation with porosity (1500-2300 m/s, R2 = 0.44, p < 10(-3)), whereas the slow wave velocities exhibited two different behaviors: (1) a first set of data clearly dependent on porosity showing a positive linear correlation (1150-1450 m/s, R2 = 0.26, p < 10(-3)) and (2) a second group independent on porosity. The fast wave FDUA (20-140 dB/cmMHz) showed a parabolic behavior and reached a maximum for 75% porosity (second degree relationship R2 = 0.41,p < 10(-3)), whereas a positive linear behavior was observed for the slow wave FDUA (15-40 dB/cmMHz; R2 = 0.15, p < 10(-2)). CONCLUSIONS: Existence of two wave propagation modes were demonstrated in human cancellous bone. Our data suggest that, in some cases, the amplitude of the slow wave is much larger than the amplitude of the fast wave. For this reason, care should be taken when using measurement systems that incorporate simple threshold detection because the fast wave could remain undetected. Moreover, failure to consider the presence of these two waves could result in an inaccurate quantification of cancellous bone physical properties.

Acoustics↗
PubMed2002

Interaction of specifically chemically modified dextrans with transforming growth factor beta1: potentiation of its biological activity.

Transforming growth factor beta (TGFbeta), a potent multifunctional cytokine, is well known to demonstrate heparin binding ability. This study investigated the binding capacity of heparin-like family of chemically modified dextrans to TGFbeta1. Dextran derivatives with various substitution contents in carboxymethyl, benzylamide and sulfate groups were evaluated using a gel mobility shift assay. This structure-function study indicated that a synergistic role of benzylamide and sulfate substituents resulted in an optimal interaction with the growth factor. The effect of these polymers on the biological response of TGFbeta1 was assessed using mink lung epithelial cells transfected with a plasminogen activator inhibitor-1 promoter-luciferase construct (PAI/Luc). When the growth factor was mixed with 250 microg/mL of carboxymethyl-benzylamide-dextran (DCMB) or carboxymethyl-benzylamide-sulfate-dextran (DCMBSu), the luciferase gene expression was enhanced. Only polymers exhibiting TGFbeta1 binding demonstrated a biological potentiating effect. However, this effect was strongly amplified as the cell plating time increased (35-fold increase with a 2 days plating time versus 1.1-fold increase with a 4 hr plating time at a 0.25 ng/mL concentration of TGFbeta1). TGFbeta1 induced the PAI/Luc construct in a dose-dependent fashion but its effect diminished when added to cells previously cultured for 24 and 48 hr. The results indicated that the potentiating effect required a complex formation between TGFbeta1 and polymers, the action of which seeming to locally maintain TGFbeta1 in an active form. TGFbeta isoforms playing a key role in the process of bone repair, specifically designed functionalized dextrans could potentiate the in vivo TGFbeta1 biological effect and be used in the field of wound healing applications.

Animals↗
PubMed2002

Interrelations between elastic energy and strain in a tensegrity model: contribution to the analysis of the mechanical response in living cells.

Interactions between the physical and physiological properties of cellular sub-units result in changes in the shape and mechanical behaviour of living tissues. To understand the mechanotransmission processes, models are needed to describe the complex interrelations between the elements and the cytoskeletal structure. In this study, we used a 30-element tensegrity structure to analyse the influence of the type of loading on the mechanical response and shape changes of the cell. Our numerical results, expressed in terms of strain energy as a function of the overall deformation of the tensegrity structure, suggest that changes in cell functions during mechanical stimuli for a given potential energy are correlated to the type of loading applied, which determines the resultant changes in cell shape. The analysis of these cellular deformations may explain the large variability in the response of bone cells submitted to different types of mechanical loading.

Cells↗
PubMed2002

Effects of cyclic pressure on bone marrow cell cultures.

The present in-vitro study used bone marrow cell cultures and investigated the effects of cyclic pressure on osteoclastic bone resorption. Compared to control (cells maintained under static conditions), the number of tartrate resistant acid phosphatase (TRAP)-positive, osteoclastic cells was significantly (p<0.05) lower when, immediately upon harvesting, bone marrow cells were exposed to cyclic pressure (10-40 kPa at 1.0 Hz). In contrast, once precursors in bone marrow cells differentiated into osteoclastic cells under static culture conditions for 7 days, subsequent exposure to the cyclic pressure of interest to the present study did not affect the number of osteoclastic cells. Most important, exposure of bone marrow cells to cyclic pressure for 1 h daily for 7 consecutive days resulted in significantly (p<0.05) lower osteoclastic bone resorption and in lowered mRNA expression for interleukin-1 (IL-1) and tumor necrosisfactor-a (TNF-a), cytokines that are known activators of osteoclast function. In addition to unique contributions to osteoclast physiology, the present study provided new evidence of a correlation between mechanical loading and bone homeostasis as well as insight into the molecular mechanisms of bone adaptation to mechanical loading, namely cytokine-mediated control of osteoclast functions.

Acid Phosphatase↗