Scaling of far-field wake angle of nonaxisymmetric pressure disturbance.

It has been recently emphasized that the angle of maximum wave amplitude α in the wake of a disturbance of finite size can be significantly narrower than the maximum value α_{K}=sin^{-1}(1/3)≃19.47^{∘} predicted by the classical analysis of Kelvin. For axisymmetric disturbance, a simple argument based on the Cauchy-Poisson initial-value problem suggests that the wake angle decreases following a Mach-like law at large velocity, α≃Fr_{L}^{-1}, where Fr_{L}=U/sqrt[gL] is the Froude number based on the disturbance velocity U, its size L, and gravity g. In this paper we extend this analysis to the case of nonaxisymmetric disturbances, relevant to real ships. We find that, for intermediate Froude numbers, the wake angle follows an intermediate scaling law α≃Fr_{L}^{-2}, in agreement with the recent prediction of Noblesse et al. [Eur. J. Mech. B/Fluids 46, 164 (2014)]. We show that beyond a critical Froude number, which scales as A^{1/2} (where A is the length-to-width aspect ratio of the disturbance), the asymptotic scaling α≃Fr_{B}^{-1} holds, where now Fr_{B}=A^{1/2}Fr_{L} is the Froude number based on the disturbance width. We propose a simple model for this transition, and provide a regime diagram of the scaling of the wake angle as a function of parameters (A,Fr_{L}).

Dynamics of grain ejection by sphere impact on a granular bed.

The dynamics of grain ejection consecutive to a sphere impacting a granular material is investigated experimentally and the variations of the characteristics of grain ejection with the control parameters are quantitatively studied. The time evolution of the corona formed by the ejected grains is reported, mainly in terms of its diameter and height, and favorably compared with a simple ballistic model. A key characteristic of the granular corona is that the angle formed by its edge with the horizontal granular surface remains constant during the ejection process, which again can be reproduced by the ballistic model. The number and the kinetic energy of the ejected grains are evaluated and allow for the calculation of an effective restitution coefficient characterizing the complex collision process between the impacting sphere and the fine granular target. The effective restitution coefficient is found to be constant when varying the control parameters.

Subcritical Kelvin-Helmholtz instability in a Hele-Shaw cell.

We investigate experimentally the subcritical behavior of the Kelvin-Helmholtz instability for a gas-liquid shearing flow in a Hele-Shaw cell. The subcritical curve separating the solutions of a stable plane interface and a fully saturated nonlinear wave train is determined. Experimental results are fitted by a fifth order complex Ginzburg-Landau equation whose linear coefficients are compared to theoretical ones.

Gap size effects for the Kelvin-Helmholtz instability in a Hele-Shaw cell.

We report experimental results for the Kelvin-Helmholtz instability between two immiscible fluids in parallel flow in a Hele-Shaw cell. We focus our interest on the influence of the gap size between the walls on the instability characteristics. Experimental results show that the instability threshold, the critical wavelength, the phase velocity, and the spatial growth rate depend on this gap size. These results are compared to both the previous two-dimensional analysis of Gondret and Rabaud [Phys. Fluids 9, 3267 (1997)] and the three-dimensional analysis recently derived by Plouraboué and Hinch [Phys. Fluids (to be published)], showing that the agreement is still not complete especially when gap size increases.

Biodegradable biocomposite non-woven matrices based on PDLLA- and elastin-solubilized proteins/elastin.

Poly(D,L-lactide) (PDLLA) was synthesized by ring-opening polymerization of D,L-lactide. Non-woven PDLLA matrices were prepared by an extrusion/winding process. The process conditions were optimized and the surfaces of these matrices were modified by glow-discharge treatment and/or glutaraldehyde incorporation for immobilization of elastin-derived proteins (ESP) to the matrix to increase the biocompatibility and also to improve the bioactivity of the matrix. Glow-discharge conditions were optimized. Ethylene diamine (EDA) and Ar were used as the active monomers in the plasma phase. When EDA was used, the glow-discharge treated PDLLA matrices were first allowed to be reacted with glutaraldehyde, although, when Ar used, the treated matrices were used directly for ESP immobilization. The higher degree of immobilization was obtained for EDA and glutaraldehyde. The ESP-incorporated PDLLA matrices were further treated with elastin by cross-reaction of the ESP molecules on the matrix surfaces with elastin. Scanning electron microscopy (SEM) studies showed that ESP were homogeneously deposited the surface of the matrix.

Elastin-derived protein coating onto poly(ethylene terephthalate). Technical, microstructural and biological studies.

Recently, it has been shown in our laboratory that certain proteins solubilized from elastin (ESP) formed a tight association with certain polymers such as elastin or polyethylene glycol terephthalate (PET) ... . The present paper deals with the description of the optimal chemical conditions of this unexpected association, its microstructure and its biological properties. A microstructural study of the composite ESP-PET material was performed using scanning and transmission electron microscopy. The thickness of the yield composite was evaluated (0.4-2 microm) but its imperviousness was unsatisfactory using ESP alone. So, we tentatively coated PET with the elastin-ESP complex. The microscopic views confirmed that the polymer was better filled by the organic matrix, the thickness of the layer being markedly improved (3 microm). Simultaneously, we attempted to verify whether the yielded composite retains the biological properties previously demonstrated with the 'Biopatches' and probably due to ESP. Thus, the culture of endothelial cells on an ESP-coating (with elastin or not) showed that a 100 microg/cm2 ESP concentration was able to promote endothelial cell growth in perfect conditions, maintaining their phenotypic character. While several physico-chemical determinations are in progress in our laboratory to identify and characterize the protein involved, a prototype of small-calibre vascular prosthesis was elaborated with elastin-ESP-PET composite and will be placed in a dog at the abdominal femoral junction to evaluate the in vivo performance of such an attractive material in artery restoration.

Unexpected original property of elastin derived proteins: spontaneous tight coupling with natural and synthetic polymers.

Elastin fibres can be decomposed into their constituting proteins using several processes; in particular by saponification of some bonds with KOH in aqueous tertiobutyl alcohol, elastin solubilized proteins - ESP- of 10 to 200 KDa were produced with a good yield (70-80%). It is demonstrated that some of these proteins were capable of tightly re-associating with the native elastin fibres and remained bound on the fibres, in spite of several drastic washes using 1 M Guanidinium, HCl at 37 degrees C for 1 h. At pH 4-5, approximately 30-40 microg ESP were retained per mg elastin. The same association is also shown to occur, under similar conditions, with Poly-ethylene-terephthalate, Poly-hexamethylene diamine-adipic acid but not with polyurethanes. The optimal conditions of the coupling were described as depending on ESP concentration, time, pH, ionic strength and Ca++. It was also shown that opposite pH conditions, i.e. pH 14, 0.5 M NaOH, could allow the retained proteins to desorb from polyesters. Hence, it will be possible to determine the sort of proteins which could be involved. This property of ESP allows us (1) to better understand the exceptional capacity of tissue repair certainly due to adhesive properties of the artificial connective matrices containing elastin or ESP, developed in our laboratory, (2) to provide a new approach for elucidating elastin microstructure and function, (3) especially to provide a new mode for coating certain fibres, yielding materials with bioactive and biofunctional qualities.

Rejection of islets differing by a single antigen is dependent on donor MHC.

To study the effect of expression of a single foreign antigen on the outcome of otherwise compatible mouse islet grafts, we have used transgenic mice expressing the human complement receptor 2 (CR2, CD21, C3d/EBV receptor) on their pancreatic beta-cells (RIP-CR2 mice). Donors were RIP-CR2 mice, typed at the major histocompatibility complex (MHC) as H-2(k), H-2(b), or H-2(bxk), and recipients were streptozotocin-treated nontransgenic B6 x CBA F1 mice (H-2(bxk)). H-2(b) or H-2(bxk) CR2-expressing islets were not rejected (mean survival time [MST] >100 days) but induced a peri-insulitis and an antibody response to CR2. In contrast, H-2(k) CR2-expressing islets were rejected in 80% of the cases with a MST of 65 +/- 23 days and were massively infiltrated by a destructive insulitis. In both cases, the infiltrate was mainly made of CD4+ cells, with few CD8+ cells. The isotype of IgG antibody response to CR2 was studied: recipients of H-2(k) grafts had a predominantly IgG1 response, while recipients of H-2(b) grafts had a balanced IgG2a and IgG1 response. To further evaluate the mechanism of differential rejection of the two types of grafts, recipients were immunized with CR2-expressing rat insulinoma cells before transplantation. Preimmunization with CR2 did not affect the outcome of H-2(b) grafts but greatly accelerated the rejection of H-2(k) grafts. These experiments indicate that expression of a single foreign antigen on beta-cells triggers an immune response leading to rejection or to peri-insulitis, depending on the MHC of donor islets.

Evaluation of bioabsorbable elastin-fibrin matrix as a barrier in surgical periodontal treatment.

The purpose of this investigation was to test clinically the efficiency of a recently described bioabsorbable matrix as a guided tissue regeneration membrane. This matrix was prepared from an original reaction between elastin and fibrin monomers and is now extensively used in several domains of surgery. The study group was composed of 26 patients, with a total of 35 lesions (22 intrabony defects, 8 Class II furcations and 5 Class III furcations) presenting moderate to advanced adult periodontitis. After initial therapy, measurements were made with a calibrated periodontal probe. Probing depth (PD) and gingival margin location (GM) measurements were taken twice: immediately before surgery and after 6 months before re-entry. Clinical attachment level (CAL), vertical osseous level (VOL) and alveolar crest location (AC) measurements were taken during surgery and after 6 months with re-entry procedures for all the patients. Color change of the gingival margin was only observed in 4 defects and device exposure occurred in the proportion of 2 out of the 35 defects. No foreign body reaction was observed in any case. At the intrabony defects mean PD reduction was 5 mm (P < 0.001), and mean gain of CAL was 4 mm (P < 0.001). Mean VOL was 4.3 mm (P < 0.001), mean gingival recession was 0.9 mm (P < 0.05) and mean AC was 0.2 mm (NS). At the Class II furcation defects the mean PD reduction was 4.5 mm (P < 0.001), mean gain CAL vertical was 3.2 mm and CAL horizontal was 4.5 mm (P < 0.001). Gingival recession averaged 1 mm (NS). A complete closure was observed in 2 out of the 8 defects. At the Class III furcation defects the mean PD reduction was 3.6 mm (P < 0.05) and mean CAL-V gain was 1.5 mm (P < 0.02). However the 5 sites showed no horizontal attachment gain and none were unchanged. A very low gingival recession, gingival reaction, crestal bone loss, and device exposure occurred during this study. This preliminary study suggests that the use of a biosynthetic barrier may have beneficial effects in the treatment of intrabony defects and Class II furcation defects. Randomized controlled trials are necessary to evaluate the efficacy and safety of this bioabsorbable membrane in periodontal therapy.

New preparation and microstructure of the EndoPatch elastin-collagen containing glycosaminoglycans.

Several improvements of the basic reaction between elastin-solubilized peptides and type I + III collagens are presented. They concern the prior incubation of the proteins in an adequate medium as well as the addition of heparan sulphate or hyaluronic acid (HA) and the consequent effects on the physical properties of yielded matrices. The addition of HA in small amounts enabled us to make membranes with good performances.

Colonization of a calcium phosphate/elastin-solubilized peptide-collagen composite material by human osteoblasts.

The evaluation of the suitability of a new biomaterial as a possible substitute for bone tissue is described here. This biomaterial is based on calcium phosphate particles linked to an artificial connective matrix, the elastin-solubilized peptides (ESP) associated with type I and III collagens. This work demonstrates the feasibility of shaping this composite material into discs, describes its microstructural characteristics, and evaluates its capacity as a substrate for the proliferation of human osteoblasts without loss of their phenotypic expression.

Use of a biodegradable elastin-fibrin material, Neuroplast, as a dural substitute.

Since the new Neuroplast biomaterial is now commonly used in several domains of restorative and curative surgery, its preliminary evaluation as a dura mater substitute in the rabbit was performed and is described herein. Whereas the importance of prosthesis thickness was implicated and solved (0.2 rather than 1.0 mm), both macroscopic examination and histological studies revealed for the neotissue an effective patency, a good continuity and especially no or almost no adherence at all. As Neuroplast is now available for use everywhere in humans, this material is being developed in several fields of neurosurgery.

New artificial connective matrix made of fibrin monomers, elastin peptides and type I + III collagens: structural study, biocompatibility and use as tympanic membranes in rabbit.

Experiments leading to the conception and development of a new artificial connective matrix based on collagen-elastin-fibrin associations are presented. Preliminary evaluation of this biomaterial as an artificial tympanic membrane is described. Morphological evaluation was performed by histopathological and scanning electron microscopic studies. Biocompatibility was documented by subcutaneous implantation and experimental grafting in rabbits was performed with histopathological studies of the tympanic grafted membranes. The positive results obtained in this experimental study enable future studies in humans to be prepared.

New bioactivation mode for vascular prostheses made of Dacron polyester.

The performance of vascular prostheses, especially those of small calibre, still presents several problems. The use of polyesters such as the well-known poly(ethylene terephthalate) (Dacron) and, more recently, poly(tetrafluoroethylene) and polyurethanes provides a marked improvement. We have developed a process to increase the efficiency of such prostheses, using the ability of the Dacron polyester to be covalently modified by proteins under mild chemical conditions. The biomaterial is obtained from the particular interaction of elastin-solubilized peptides with type I + III collagens under very precise conditions. We have obtained an irreversible covalent bonding on Dacron. These biological conditions and the addition of connective proteins and glycosaminoglycans conferred on the resulting material a composition and a three-dimensional structure equivalent to the subendothelium, providing bioactive properties suitable for the development of a vascular prosthesis.

[Development of artificial collagen-elastin conjunctive matrix for tympanoplasty. Concept and 1st results of animal experiments]. / Développement d'une matrice conjonctive artificielle "collagène-élastine" comme matériau de tympanoplastie. Conception et premiers résultats expérimentaux chez l'Animal.

We developed a new biomaterial designed to replaced loss of tympanic tissue. This new material has an original collagen-elastin structure which can be used to create an new artificial conjunctive matrix. The concept and the first experimental results are reported.

[Preliminary results of the evaluation of the Endopatch E-F in digestive surgery]. / Résultats préliminaires de l'évaluation de l'Endopatch E-F en chirurgie digestive.

Endopatch E-F is a new product elaborated with natural human and animal proteins. Its synthesis originates in a covalent link between elastin and fibrin monomers. Numerous experimental studies carried out in animal have previously shown its ability to reinforce healing process of digestive wall. The results reported herein have been obtained in very selected patients in whom a digestive anastomosis had to be done in spite of unfavorable circumstances, such as intra-abdominal infection, radiated bowel or ascitis. From October 1990 to October 1992, 21 digestive anastomosis have been performed in 18 patients. All were reinforced by Endopatch E-F. Two deaths have been observed (mortality: 11.1%), which do not look like a consequence of the use of the product (One myocardial infarction and one cirrhotic failure). There were 2 post-operative fistulas (9.5% of the whole anastomosis). No patients had any reaction of intolerance. These preliminary results confirm experimental data, and suggest that Endopatch EF can be used in order to reinforce digestive sutures when performed under unfavorable circumstances.