Biomedical subjects

G Laroche

Publications and source records attributed to G Laroche.

At least 37 records · Page 2Linked to original sources

PubMed1997

In vitro and in vivo studies of a polyester arterial prosthesis with a warp-knitted sharkskin structure.

The present study was undertaken to assess the performance of a new knitted and gelatin-sealed polyester vascular graft that is believed to have greater dimensional stability than current commercial devices. Samples of the uncrimped, crimped, and sealed prosthesis were submitted to a series of in vitro and in vivo trials. Four commercial polyester knitted devices were included as controls for the in vitro tests, which included measurements of the textile and yarn structure and physical, chemical, and thermal properties of the graft, such as water permeability, dilatation, suture retention strength, melting point, and crystallinity index. The in vivo evaluation involved implanting the prototype device as a canine thoraco-abdominal bypass for periods ranging from 4 h to 1 year and assessing the biocompatibility, biofunctionality, and biostability of the explanted specimens. The warp-knitted structure of the prototype device has a unique sharkskin stitch that confers a superior dilatation resistance and suture retention strength to the prosthesis. The animal trial demonstrated that the gelatin ensures initial hemostasis without preclotting. The gelatin is bioresorbed during the first 2 weeks of implantation, which generates a temporary, moderate, acute inflammatory response. An external capsule of granulomatous tissue and an internal collagen capsule are formed between the first and third month. Analysis of the textile and physical properties of the explanted prostheses confirmed there was neither dilatation nor significant changes in structure or mechanical performance during implantation, thus confirming the biostability of this new prototype device and opening the way for clinical trials.

Anastomosis, Surgical↗

PubMed1997

Chemical inactivators as sterilization agents for bovine collagen materials.

The use of collagen as a biomedical implant raises safety issues with regard to viruses and prions. Specific chemical agents that inactivate prion infectivity could be applied to collagen implants. The physicochemical changes and the in vitro and in vivo biocompatibility of collagen treated by formic acid (FA), trifluoroacetic acid (TFA), tetrafluorethanol (TFE), and hexafluoroisopropanol (HFIP) were investigated. In addition, the effects of these treatments on nucleic acids incorporated in collagen were analyzed. The molecules of FA and, more important, of TFA remained within collagen. FA, TFA, and HFIP treatments modify the secondary structure of collagen, as shown by Fourier transform infrared spectroscopy, while TFE does not. Differential scanning calorimetry measurements showed a decrease in the denaturation temperature compared to untreated collagen. However, resistance to collagenase was modified only after HFIP treatment. In vitro, cell growth was not impaired; in vivo, implants induced a temporary inflammatory reaction that was prolonged with TFA and HFIP treatments. TFE and FA-treated collagen were thoroughly infiltrated by fibroblasts. On the other hand, FA and TFA resulted in extensive depurination of nucleic acids while HFIP and TFE did so to a lesser degree. Among the investigated chemical scrapie inactivators, FA treatment could offer a safe and biocompatible collagen-derived material for biomedical use.

Animals↗

PubMed1997

Vascugraft polyurethane arterial prosthesis as femoro-popliteal and femoro-peroneal bypasses in humans: pathological, structural and chemical analyses of four excised grafts.

Following positive results obtained in in vitro studies and in vivo implantations in animals, a clinical trial using the Vascugraft polyurethane arterial prosthesis as a below-knee substitute was undertaken in 15 patients. Eight grafts became occluded during the first year, and segments from four of them were explanted and made available for pathological, structural and chemical investigations. The implantation periods ranged from 21 to 358 days. Failures were associated with kinking (one case), possible anastomotic mismatch between the graft and the artery (one case), and poor run-off (two cases). No organized collagenous internal encapsulation was noted; however, endothelial-like cells were observed at the anastomotic site of one graft. No significant structural degradation of the prostheses was observed in those grafts implanted for 21, 38 and 46 days. Some deteriorations in the fibrous structure were observed on the external surface of the prosthesis implanted for 358 days. High-resolution carbon C1s analysis by ESCA demonstrated a 60 to 80% decrease in carbonate content on the surface of all explanted prostheses. Chemical analyses of each polyurethane graft by IR, SEC and DSC revealed no significant chemical changes. The clinical performance of the Vascugraft prosthesis for below-knee implantation proved to be no more impressive than that of expanded polytetrafluorethylene, the currently accepted reference. The decision by B. Braun Melsungen AG to end this program is therefore to be regarded as highly professional.

Aged↗

PubMed1997

Are intraaortic balloons suitable for reuse? A survey study of 112 used intraaortic balloons.

To assess the safety of reusing single-use intraaortic balloon devices (IABs), 112 used devices were investigated in terms of physical integrity, gas leakage inspection, mechanical performance, surface chemistry and morphology, and physical stability. These IABs were all used clinically only once, and the duration of the IABs in vivo ranged from 6 to 312 h. Macroscopic examination of the balloons and the outer catheters revealed no obvious change in either shape or color. No discernible abrasions or cracks were observed on the balloons. However, 61% of the balloons were creased, and 40% of the central lumens and 21% of the sheaths showed visible bending flaws. Moreover, 65% of the balloons and 38% of the central lumens were contaminated by visible residual organic debris. The physical integrity of each device was verified in a specially designed leakage-fatigue tester for 72 h. Ninety-seven percent of the devices passed the leakage inspection. Stress-strain testing, differential scanning calorimetry, attenuated total reflection-Fourier transform infrared, and scanning electron microscopy analyses clearly indicated that there were no significant differences in the mechanical properties, bulk material morphology, surface chemistry, and external surface morphology between the used balloons and virgin controls. Although some surface modifications occurred on the internal side of the balloons, the external surfaces of most balloons suffered no trauma. Most of the used IABs examined in this study maintained physical and mechanical properties similar to those of the virgin devices. The chemistry of the balloon material was stable after short-term in vivo use. However, it does not seem possible to establish a rigorous protocol of cleaning, sterilization, and inspection to guarantee a safer reuse of these devices. The presence of residual organic debris that cannot be eliminated results in an imperative preclusion not to reuse the IABs.

Calibration↗

PubMed1996

In vitro characterization of a fluoropassivated gelatin-impregnated polyester mesh for hernia repair.

The surgical management of abdominal hernias requires prosthetic grafting in situations where the defect is too large or the surrounding tissue is not available for repair. Flat patches made of different biomaterials have been used in textile or microporous forms. The present work describes the results of an in vitro study comparing the morphological, mechanical, and chemical characteristics of a new textile prototype, Fluoropassiv, made of polyester fibers treated with a fluoropolymer and impregnated with gelatin to those of seven existing commercial meshes and patches made from polypropylene, polyester, polytetrafluoroethylene (PTFE) yarns, and expanded microporous PTFE graft. The morphological study revealed a diversity of structures having a minimal relative porosity of 70%, high bursting, and suture retention strengths in comparison with natural muscular tissue. Elasticmoduli proved to depend more on the direction of the textile the rigidity was higher for those materials having tight structure, like the Fluoropassiv and the Surgipro meshes (> 30 MPa), whereas those with more open structures, such as the Marlex, Trelex, Lars, Bard Teflon, and GoreTex structures, showed lower elastic modulus (10 mPa). In addition, chemical analyses confirmed no irregularities in the polymers used in all prostheses and demonstrated that the fluoropolymer coating of the Fluoropassiv was uniformly distributed. The innovative aspects in the construction of the knitted fabric Fluoropassiv appears to make it suitable for repairing hernias, and the inclusion of both continuous fluoropolymer surface treatment of polyester fibers and gelatin impregnation appears to improve the healing process.

Biocompatible Materials↗

PubMed1996

In vivo characterization of a fluoropassivated gelatin-impregnated polyester mesh for hernia repair.

The present study was undertaken to evaluate a new prototype mesh that consists of a knitted polyester structure treated with a fluoropolymer and impregnated with gelatin. The Fluoropassiv mesh, as well as two controls, the Surgipro polypropylene mesh and the Gore-Tex expanded polytetrafluoroethylene patch, were used for the repair of experimentally induced abdominal hernias in piglets and followed for scheduled implantation periods of 4, 15, and 60 days. At the sacrifice the mesh and surrounding tissue were excised for histological assessment of the healing sequence, for the identification of changes in hematologic and immunological characteristics, and for the measurement of the mechanical properties. After cleaning to remove the encroaching tissue, the explanted devices were monitored for biostability by infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The present study has demonstrated that the Fluoropassiv mesh provides adequate mechanical strength and compares favorably with the two controls. No exacerbated systemic or in situ hematologic or immunological reactions were observed with either the meshes of the patch material. Histological studies revealed that thick collagenous and vascularized tissue were well anchored to the three biomaterials as early as 15 days after implantation. The degree of tissue penetration differed depending on the device. Chemically, they proved stable over time.

Abdominal Muscles↗

PubMed1996

Selecting valid in vitro biocompatibility tests that predict the in vivo healing response of synthetic vascular prostheses.

We have investigated the usefulness of six in vitro biocompatibility tests in predicting the healing performance of polyester vascular prostheses as observed in previous canine in vivo trials. Vascular grafts were evaluated by using (i) a direct contact (DC) assay, (ii) an extract dilution (ED) assay on murine fibroblast cells, (iii) a DC assay on endothelial cells, (iv) a complement activation study, (v) a leucocyte activation study of CD18 integrin subunit expression on human polymorphonuclear cells (PMNs) and (vi) interleukin-2 receptor expression on lymphocytes. Uncleaned polyester grafts had previously been associated with poor healing and gelatin-impregnated polyester grafts with delayed but satisfactory healing, whereas commercially cleaned polyester grafts had demonstrated excellent healing. Lightweight and heavyweight knitted and woven polyester grafts supplied specifically for this project were studied, each with a different surface condition, i.e. commercially available (CP), uncleaned (UP) and impregnated with gelatin (GP). The UP grafts induced fibroblast cytotoxicity according to the ED assay, poor migration and viability of endothelial cells, and an elevated expression of CD18 and interleukin-2 receptor on PMNs and lymphocytes, respectively. In contrast, the CP grafts promoted good endothelial cell growth, no evidence of cytotoxicity and a weaker cell activation, and the GP grafts were found to be non-cytotoxic, to exhibit a good cellular response and to moderate cell activation. The complement activation assay and the DC assay on fibroblasts were found to be less useful and less discriminating. From this, it is concluded that the two cell activation measurements, the DC assay on endothelial cells and ED assay on fibroblasts, are useful in predicting the in vivo healing response of arterial polyester substitutes.

Analysis of Variance↗

PubMed1996

Chemical and morphological analysis of explanted polyurethane vascular prostheses: the challenge of removing fixed adhering tissue.

During in vivo experiments to evaluate the biocompatibility and biostability of alternative biomaterials, the ideal protocol for the handling and preservation of the explanted material is often compromised in order to meet the needs of both the pathologist and the materials scientist. Explants surrounded by tissue are often fixed in formalin or glutaraldehyde to facilitate later pathological and histological analysis, but the subsequent removal of such fixed tissue from thermally sensitive and less chemically stable polymers, such as polyurethanes, poses major problems for the materials scientist, who does not wish to modify the chemical, physical or morphological characteristics of the underlying biomaterial. The present study has attempted to find a solution to this problem by exposing virgin specimens of the microporous polyurethane Vascugraft vascular prosthesis to six different cleaning conditions, all known to be effective in removing fixed tissue. These conditions included the use of 20% aqueous potassium hydroxide solution for 48 h at room temperature, 5% sodium bicarbonate solution for 5 min at the boil, and 9, 10, 11 and 12N hydrochloric acid for 48 h at room temperature. The appearance and chemical properties of the virgin and treated specimens were compared using electron spectroscopy for chemical analysis, Fourier transform infrared spectroscopy, gel permeation chromatography for molecular weight and differential scanning calorimetry techniques. The use of temperatures close to the boil resulted in the formation of a translucent, rubbery material with gross changes in the microporous and microfibrous structure. The strongly acidic and alkaline conditions caused a loss in the surface carbonate group content. In addition, 12N hydrochloric acid reduced the molecular weight and urethane content. Consequently, 9N hydrochloric acid is recommended as the cleaning agent of choice for removing fixed tissue from this type of microporous polyurethane. Control experiments on virgin material should also be included in any cleaning protocol.

Adhesiveness↗

PubMed1995

Polyvinylidene fluoride (PVDF) as a biomaterial: from polymeric raw material to monofilament vascular suture.

This study identified the effects of various manufacturing processes on the crystalline microstructure, mechanical properties, and biocompatibility of a polyvinylidene fluoride (PVDF) suture. To achieve this, changes in the crystalline microstructure and the tensile behavior of PVDF monofilaments were monitored in vitro after different thermal processing, coloration, and sterilization treatments. In addition, the in vivo biocompatibility of the manufactured and sterilized PVDF suture was assessed by using it to anastomose a preclotted polyester vascular prosthesis as a thoracoabdominal bypass in a series of dogs. The tissue response was followed by histologic and scanning electron microscopy over implantation periods ranging from 4 h to 6 months. Differential scanning calorimetry and infrared spectroscopy (FTIR-ATR) showed that thermal processing and the addition of a coloring agent had a direct effect on modifying the crystalline microstructure and hence changing the mechanical properties. For example, thermal processing converted some of the alpha phase into the beta and gamma polymorphs, whereas coloration led only to a major increase in the beta-to-alpha ratio. The tensile properties were found to be optimized when the relative proportion of the beta and gamma phases combined compared to the alpha form gave rise to an FTIR A509/A532 absorption ratio between 4.0 and 4.5. Sterilization was found to cause some modifications to the crystalline microstructure near the surface of the monofilaments, but it did not change their mechanical properties. Pathologic examination of the anastomotic regions after different periods of implantation revealed a minimal cellular response, with no mineralization, intimal hyperplasia, or excessive fibrous tissue reaction. This good biocompatibility, together with other desirable characteristics such as ease of manipulation and satisfactory mechanical strength, makes PVDF an attractive alternative monofilament suture material for cardiovascular surgery.

Animals↗

PubMed1995

Removing fresh tissue from explanted polyurethane prostheses: which approach facilitates physico-chemical analysis?

Chemical, physical and structural analyses of polymers from explanted vascular prostheses are frequently jeopardized because of incomplete removal of the encroaching host tissue. In this study, microporous polyurethane arterial prostheses implanted as a canine thoraco-abdominal bypass were explanted after 1 and 12 months and were cleaned without fixation using four different digesting enzyme treatments, including collagenase, pancreatin and trypsin alone and collagenase and pancreatin in series, followed by washing in a solution of Triton X-100 detergent. By following this approach all the fresh tissue attached to the external and internal walls of the prostheses was removed with minimal damage to the underlying synthetic polymer. The morphology of the explanted and cleaned polyurethane prostheses could be obtained readily by light and scanning electron microscopy. Surface microporous features and the presence of polyurethane microfibres that had experienced in vivo biodegradation could therefore be identified easily. The surface and bulk physico-chemical properties of the polyurethane polymer were determined by electron spectroscopy for chemical analysis, attenuated total reflectance-Fourier transform infrared spectroscopy and differential scanning calorimetry. It was found that the most successful approach for removing fresh tissue and exposing a clean and uncontaminated polyurethane surface was to incubate the explanted samples first in collagenase followed by digestion in pancreatin. This particular cleaning technique has proved valuable in enabling us to monitor small in vivo changes in the surface chemistry and in the bulk microphase segmented structure of polyurethane biomaterials.

Animals↗

PubMed1995

Polyvinylidene fluoride monofilament sutures: can they be used safely for long-term anastomoses in the thoracic aorta?

Polyvinylidene fluoride (PVDF) represents an attractive alternative to polypropylene as a monofilament vascular suture because of its satisfactory physicochemical properties, it ease of handling, and its good biocompatibility. However, the polymer's ability to remain mechanically and chemically stable when exposed to a mild hydrolytic environment over the long term has yet to be demonstrated. One in vitro study involved the comparison of the long-term relative resistance of PVDF and polypropylene sutures to hydrolysis for a period of 9 years. The PVDF suture showed major molecular rearrangements from the original ratio of three crystalline structures to the single beta crystalline phase. The observation of some surface oxidation and water inhibition did not significantly modify the tensile strength of the PVDF suture, which retained 92.5% of its original value. In contrast, the polypropylene sample did not undergo any recrystallization but was associated with more oxidation byproducts and more water molecules near the surface, which contributed to a 46.6% loss in initial tensile strength. An in vivo study confirmed that PVDF sutures are biocompatible and are able to maintain satisfactory biostability when used to anastomose thoracic aortic allografts for a period of 6 months in the dog. The cellular reaction of fresh allografts as well as the control autografts to PVDF sutures was minimal. In other allografts that had been preserved in a supplemented medium for 1 week prior to implantation, the PVDF sutures healed satisfactorily with the formation of neocollagen and few macrophages surrounding the monofilament. No evidence of instability at the allograft-host artery junction was observed, confirming that the PVDF sutures were able to ensure a secure anastomosis in the thoracic aorta. PVDF sutures have demonstrated superior long-term biostability in vitro and minimal tissue response in vivo. These are two essential requirements when evaluating the use of a suture for vascular surgery in general and thoracic aortic surgery in particular.

Anastomosis, Surgical↗

PubMed1995

Intracerebral implantation of hydrogel-coupled adhesion peptides: tissue reaction.

Arg-Gly-Asp peptides (RGD) were synthesized and chemically coupled to the bulk of N-(2-hydroxypropyl) methacrylamide-based polymer hydrogels. Fourier Transform Infrared Spectroscopy (FTIR) and amino acid analysis confirmed the peptide coupling to the polymer. Activated and control (unmodified) polymer matrices were stereotaxically implanted in the striata of rat brains, and two months later the brains were processed for immunohistochemistry using antibodies for glial acidic fibrillary protein (GFAP), laminin and neurofilaments. RGD-containing polymer matrices promoted stronger adhesion to the host tissue than the unmodified polymer matrices. In addition, the RGD-grafted polymer implants promoted and supported the growth and spread of GFAP-positive glial tissue onto and into the hydrogels. Neurofilament-positive fibers were also seen running along the surface of the polymer and, in some instances, penetrating the matrix. These findings are discussed in the context of using bioactive polymers as a new approach for promoting tissue repair and axonal regeneration of damaged structures of the central nervous system.

Adhesives↗

PubMed1995

The gelweave polyester arterial prosthesis.

OBJECTIVE: To determine the effect of the gelatin coating on the efficacy of Gelweave, a new gelatin-sealed woven polyester graft material, as an arterial prosthesis. DESIGN: In-vitro and in-vivo studies of the prosthesis. SETTING: A laboratory of experimental surgery in a university teaching institution. SUBJECTS: After in-vitro testing of the material, eight dogs were subjected to a series of in-vivo tests to evaluate the properties of Gelweave in comparison with its unsealed precursor and a commerically available collagen-coated woven polyester prosthesis. INTERVENTION: Implantation of the prosthesis as a thoracoabdominal bypass for prescheduled periods ranging from 4 hours to 6 months. MAIN OUTCOME MEASURES: Physical and chemical properties of the virgin prosthesis compared with the other two prostheses, effects of the gelatin-sealed prosthesis on healing, the hematologic characteristics of the dogs before operation and at sacrifice, microscopic studies, fibrin and platelet uptakes, prostaglandin secretion, and properties of the Gelweave grafts removed at varying periods after implantation. RESULTS: The gelatin sealant in the Gelweave prosthesis effectively reduced the water permeability of the new prototype to zero. Neither blood loss at implantation nor infection during the postimplantation period was observed. The gelatin impregnation did not cause any adverse response in the dogs and was completely lysed within 2 weeks, thus allowing encapsulation and graft healing to progress satisfactorily. After 2 weeks, the prostacyclin:thromboxane ratio was greater than 1.0, whereas the fibrin and platelet uptakes on the luminal surface of the Gelweave grafts remained low, regardless of the period of implantation. Analysis of the explanted grafts confirmed that this gelatin-sealed prototype prosthesis healed satisfactorily and no adverse biologic response occurred as a result of the gelatin coating. It maintained its biostability during 6 months in situ. CONCLUSION: The new Gelweave arterial prosthesis is ready for clinical use as a thoracic and abdominal vascular substitute.

Animals↗

PubMed1994

Porosity and biological properties of polyethylene glycol-conjugated collagen materials.

Collagen-based materials can be designed for use as scaffolds for connective tissue reconstruction. The goal of the present study was to evaluate the behavior of collagen materials as well as cell and tissue reactions after the conjugation of activated polyethylene glycols (PEGs) with collagen. It is known that proteins conjugated with PEGs exhibit a decrease in their biodegradation rate and their immunogenicity. Different concentrations and molecular weights of activated PEGs (PEG-750 and PEG-5000) were conjugated to collagen materials (films or sponges) which were then investigated by collagenase assay, fibroblast cell culture, and subcutaneous implantation. PEG-conjugated collagen sponge degradation by collagenase was delayed in comparison to untreated sponges. In culture, fibroblasts with a normal morphology reached confluency on PEG-conjugated collagen films. In vivo, the porous structure of non-modified sponges collapsed by day 15 with a few observable fibroblasts between the collagen fibers. In PEG-modified collagen sponges, the porous structure remained stable for 30 days. Cell infiltration was particularly enhanced in PEG-750-conjugated collagen sponges. In conclusion, PEGs conjugated onto collagen sponges stabilize the porous structure without deactivating the biological properties of collagen. These porous composite materials could function as a scaffold to organize tissue ingrowth.

Animals↗

PubMed1992

Characterization by infrared spectroscopy of the interaction of a cardiotoxin with phosphatidic acid and with binary mixtures of phosphatidic acid and phosphatidylcholine.

The effect of cardiotoxin IIa from Naja mossambica mossambica, a small basic protein extracted from snake venom, on dimyristoylphosphatidic acid (DMPA) and on equimolar mixtures of DMPA and dimyristoylphosphatidylcholine (DMPC) has been studied by Fourier transform infrared spectroscopy. The interaction of cardiotoxin with DMPA dispersions decreases both the cooperativity of the phase transition of the lipid and the molecular order of the lipid acyl chains in the gel phase. This effect increases with the proportion of the toxin in the complexes and leads to the total abolition of the phase transition of DMPA at a lipid-to-protein molar ratio of 5. Small-angle X-ray results demonstrate that the structure of the lipid-protein complexes is poorly ordered and gives rise to broad diffusion peaks rather than to well-resolved diffraction patterns. Infrared spectra of oriented cardiotoxin-DMPA films show that the protein is not homogeneously oriented with respect to the bilayer surface. The destabilization of the gel-phase structure of DMPA by cardiotoxin also results in a deeper water penetration in the interfacial region of the lipid since more carbonyl ester groups appear to be hydrogen bonded in the presence of the toxin. The infrared results on the phosphate group vibrations also indicate clearly that the basic residues of cardiotoxin interact strongly with the phosphate group of DMPA that becomes partly ionized at a pH as low as 6.5. The results obtained on the interaction of cardiotoxin with an equimolar mixture of DMPA and DMPC clearly demonstrate the ability of this toxin to induce lateral phase separation in this mixture with one phase containing DMPA-rich domains perturbed by cardiotoxin while the second phase is composed of regions enriched in DMPC. Comparison of the results of the current study with those obtained on other basic proteins and polypeptides suggests that charge-induced phase separation occurs only when the charge density on certain regions of the protein structure is high enough to lead to efficient electrostatic interactions with anionic phospholipids. This condition occurs only when the conformation of the protein or polypeptide is well-ordered at the lipid interface.

Cobra Cardiotoxin Proteins↗

PubMed1991

Structure and dynamics of dimyristoylphosphatidic acid/calcium complexes by 2H NMR, infrared, spectroscopies and small-angle x-ray diffraction.

The structural and dynamic properties of complexes of dimyristoylphosphatidic acid (DMPA) and calcium ions have been characterized by 2H NMR, Raman, and infrared spectroscopies and small-angle X-ray diffraction. All techniques used show that these complexes do not undergo a cooperative thermotropic phase transition. Small-angle X-ray diffraction unambiguously demonstrates that the structure of the lipid molecules of the DMPA/Ca2+ complexes remains lamellar even at a temperature as high as 85 degrees C. Raman results indicate that within this temperature range, only a few trans-gauche isomerizations of the C-C bonds of the phospholipid acyl chains arise in this system. The 2H NMR spectra indicate that the DMPA chains are highly motionally restricted up to 65 degrees C and that higher temperatures might activate some low-frequency overall motions of entire lamellar domains. Small-angle X-ray scattering and 2H NMR spectroscopy of 2H2O also show that the interaction of calcium with DMPA promotes an important dehydration of the lipid assembly, even though the latter technique clearly demonstrates that some water molecules remain strongly bond in the DMPA/Ca2+ complexes. The carbonyl stretching mode region of the infrared spectrum of DMPA/Ca2+ complexes suggests that these water molecules are trapped near the interfacial region of the lipid membrane and are hydrogen bonded with the carbonyl groups of the lipid. Finally, comparison of the phosphate stretching mode region of the infrared spectra of complexes of DMPA with calcium ions with those of model compounds provides strong evidence that calcium ions bind to both charges of the phosphate group of DMPA and form bridges between adjacent bilayers.

Glycerophospholipids↗

PubMed1991

Bifidobacterium from fermented milks: survival during gastric transit.

Two Bifidobacterium strains contained in two different fermented milks behave very differently when exposed to an in vitro simulated gastric environment. One strain survives very well during at least 90 min (greater than 10(7)/g), but the second strain studied is much less resistant. These in vitro results, with slight differences, were confirmed by an in vivo study in humans. The assessment of the gastric emptying rate of these products allows an estimation of the amount of Bifidobacterium that may pass into the small intestine.

Adult↗

PubMed1990

Coupled changes between lipid order and polypeptide conformation at the membrane surface. A 2H NMR and Raman study of polylysine-phosphatidic acid systems.

Thermotropism and segmental chain order parameters of sn-2-perdeuteriated dimyristoyl-phosphatidic acid (DMPA)-water dispersions, with and without poly(L-lysine) (PLL) of different molecular weights, have been investigated by solid-state deuterium NMR spectroscopy. The segmental chain order parameter profile of this negatively charged lipid is similar to that already found for other lipids. Addition of long PLL (MW = 200,000) increases the temperature, Tc, of the lipid gel-to-fluid phase transition, whereas short PLL (MW = 4000) has practically no effect on Tc. In the fluid phase both varieties of PLL increase the "plateau" character of segmental order parameters up to carbon position 10. At the same reduced temperature, long PLL more significantly increases the segmental ordering, especially at the methyl terminal position. This leads to the conclusion that polar head-group capping and charge neutralization by PLL induce severe changes in lipid chain ordering, even down to the bilayer core. The structure of PLL bound to the lipid bilayer surface was monitored by Raman spectroscopy, following the amide I bands. Results show that the lipid gel-to-fluid phase transition triggers a conformational transition from ordered beta-sheet to random structure of short PLL, while it does not affect the strongly stabilized beta-sheet structure of long PLL. It is concluded that both short and long PLL can efficiently cap and neutralize lipid head groups, whatever their structure, and that peptide length is a key parameter in whether lipids or peptides are the driving force in conformationally coupled changes of both partners in the membrane.

Chemical Phenomena↗