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Biomedical subjects

M Vert

Publications and source records attributed to M Vert.

At least 19 recordsLinked to original sources
PubMed2005

Interactions of GRF(1-29)NH2 with plasma proteins and their effects on the release of the peptide from a PLAGA matrix.

The administration of the GRF(1-29)NH2 Growth Hormone Releasing Hormone analog is known as relevant of the concept of drug delivery system using a bioresorbable matrix. However, the release of this peptide from poly(dl-lactic acid-co-glycolic acid) matrices is affected by its insolubility at neutral in salted media and in plasma as well. In order to investigate the origin and the nature of the insolubility in these media in more details, the precipitates collected when the peptide was set in contact with saline, isotonic pH=7.4 phosphate buffer and plasma were analyzed by various techniques, namely weighting, gel chromatography, 1D- and 2D-immunoelectrophoresis, and dialysis to discern the soluble from the insoluble or aggregated fractions. It is shown that precipitation in protein-free salted media is due to a salting out phenomenon complemented by the neutralization of the solubilizing electrostatic charges in the isotonic buffer. In contrast, the precipitation in plasma is due to inter polyelectrolyte-type complexation that involved polyanionic proteins having a rather low isoelectric point like albumin, transferin, haptoglobulin and IgG immunoglobulins. When a rather large quantity of GRF(1-29)NH2 was entrapped in bioresorbable pellets working at a percolating regime after subcutaneous implantation in rats, the peptide was slowly released despite the complexation with plasma proteins. However only a very small part of the peptide was found in blood, this small part being still large enough to cause a detectable increase of the circulating growth hormone concentration. Attempts made to increase the solubility of the peptide in plasma were successful when the peptide was combined with arginine, an amino acid known to promote the poor hormonal activity of injected GRF(1-29)NH2 solutions under clinical conditions.

Animals↗
PubMed2005

Fabrication using a rapid prototyping system and in vitro characterization of PEG-PCL-PLA scaffolds for tissue engineering.

In the field of tissue engineering new polymers are needed to fabricate scaffolds with specific properties depending on the targeted tissue. This work aimed at designing and developing a 3D scaffold with variable mechanical strength, fully interconnected porous network, controllable hydrophilicity and degradability. For this, a desktop-robot-based melt-extrusion rapid prototyping technique was applied to a novel tri-block co-polymer, namely poly(ethylene glycol)-block-poly(epsilon-caprolactone)-block-poly(DL-lactide), PEG-PCL-P(DL)LA. This co-polymer was melted by electrical heating and directly extruded out using computer-controlled rapid prototyping by means of compressed purified air to build porous scaffolds. Various lay-down patterns (0/30/60/90/120/150 degrees, 0/45/90/135 degrees, 0/60/120 degrees and 0/90 degrees) were produced by using appropriate positioning of the robotic control system. Scanning electron microscopy and micro-computed tomography were used to show that 3D scaffold architectures were honeycomb-like with completely interconnected and controlled channel characteristics. Compression tests were performed and the data obtained agreed well with the typical behavior of a porous material undergoing deformation. Preliminary cell response to the as-fabricated scaffolds has been studied with primary human fibroblasts. The results demonstrated the suitability of the process and the cell biocompatibility of the polymer, two important properties among the many required for effective clinical use and efficient tissue-engineering scaffolding.

Adult↗
PubMed2001

Protein release from physically crosslinked hydrogels of the PLA/PEO/PLA triblock copolymer-type.

A series of PLA/PEO/PLA triblock copolymers was prepared by ring opening polymerization of rac-lactide in the presence of various di-hydroxyl poly (ethylene glycol)s, using CaH2 as a biocompatible initiator. Hydrogels were prepared by a phase separation method consisting of introducing small amounts of water over solutions of the copolymers in a biocompatible organic solvent, namely tetraglycol [poly(ethylene glycol monotetrahydrofurfuryl ether)]. The resulting hydrogels appeared much more hydrophilic than the rather tough hydrogels formed by swelling of dry tablets or films processed from the same copolymers. The phase separation-derived hydrogels were soft enough to be injected through a trochar. Two proteins, namely bovine serum albumine (BSA) and fibrinogen, were physically entrapped in these hydrogels by mixing with the polymer solutions before gel formation. This procedure appeared to be protein-respecting according to circular dichroism analysis on the released BSA. Dramatically different release profiles were obtained for the two proteins. In the case of BSA, the release depended on the quantity of protein incorporated in the hydrogel and presented a parabolic-type profile, in agreement with the behaviors of diffusion-controlled monolitic drug delivery devices. In contrast, almost linear release profiles were observed in the case of fibrinogen, the hydrogels behaving like a reservoir drug delivery system. These findings are tentatively interpreted in terms of gel-protein compatibility in the case of BSA and gel-protein incompatibility in the case of fibrinogen.

Hydrogels↗
PubMed2001

Biodegradation of [(3)H]poly(epsilon-caprolactone) in the presence of active sludge extracts.

Poly(epsilon-caprolactone), PCL, is a commercial biodegradable and biocompatible polyester that can be bioassimilated by outdoor microorganisms. For biomedical and environmental applications, monitoring the fate of degradation products in vivo or under environmental conditions is one of the critical steps to evaluate degradation characteristics. [(3)H] radiolabeling is the best method to monitor the fate of degradable polymer chains in contact with complex living systems and to show bioassimilation. Therefore, tritiated PCL was synthesized by chemical modification using anionic activation by reaction with lithium diisopropylamide. The resulting radioactive polymer was characterized and allowed to degrade at 37 degrees C under aerobic conditions in the presence of active sludge. Comparison was made with abiotic hydrolytic degradation in pH = 7.4, 0.13 M phosphate buffer at 37 degrees C. Water-soluble degradation products were assessed by measuring radioactivity in the solution phase. It was shown that biodegradation of PCL started after a few hours and proceeded up to the ultimate stage over ca. 72 days, giving tritiated water (80-90%) and biomass. Radioactivity detection appeared much more sensitive than measurement of CO(2) production or consumption to monitor degradation phenomena. In particular, it showed that the onset of biodegradation occurs earlier than that reported using respirometry.

Bacteria, Aerobic↗
PubMed2001

Novel degradable polymers combining D-gluconic acid, a sugar of vegetal origin, with lactic and glycolic acids.

To synthesize functionalized poly(lactic acid-co-glycolic acid)-based polyesters for biomedical and pharmaceutical applications such as controlled drug delivery, D-gluconic acid was considered as an interesting source of comonomer. Accordingly D-gluconic acid was used to synthesize novel 1,4-dioxane-2,5-diones with protected hydroxyl groups, namely 3-(1,2:3,4-tetraoxobutyl-di-O-isopropylidene)-dioxane-2,5-dione (5a) and 3-methyl-6-(1,2:3,4-tetraoxobutyl-di-O-isopropylidene)-dioxane-2,5-dione (5b). The ring-opening homopolymerization and copolymerization of these cyclic dilactones with DL-lactide provided novel degradable polyesters with higher glass transition temperatures than poly(lactic acid-co-glycolic acid) polymers.

Biocompatible Materials↗
PubMed2001

Biodistribution of long-circulating PEG-grafted nanocapsules in mice: effects of PEG chain length and density.

PURPOSE: To study the pharmacokinetics and biodistribution of novel polyethyleneglycol (PEG) surface-modified poly(rac-lactide) (PLA) nanocapsules (NCs) and to investigate the influence of PEG chain length and content. METHODS: The biodistribution and plasma clearance in mice of different NC formulations were studied with [3H]-PLA. PLA-PEG copolymers were used in NC preparations at different chain lengths (5 kDa and 20 kDa) and PEG contents (10% and 30% w/w of total polymer). In vitro and in vivo stability were also checked. RESULTS: Limited [3H]-PLA degradation was observed after incubation in mouse plasma for 1 h, probably because of to the large surface area and thin polymer wall. After injection into mice. NCs prepared with PLA-PEG copolymers showed an altered distribution compared to poloxamer-coated PLA NCs. An increased concentration in plasma was also observed for PLA-PEG NCs. even after 24 h. A dramatic difference in the pharmacokinetic parameters of PLA-PEG 45-20 30% NCs compared to poloxamer-coated NCs indicates that covalent attachment, longer PEG chain lengths, and higher densities are necessary to produce an increased half-life of NCs in vivo. CONCLUSIONS: Covalently attached PEG on the surface of NCs substantially can reduce their clearance from the blood compartment and alter their biodistribution.

Algorithms↗
PubMed2000

Interactions between red blood cells and a lethal, partly quaternized tertiary polyamine.

Partially quaternized poly[thio-1-(N,N-diethyl-aminomethyl) ethylene]s, Q-P(TDAE)(x) with x indicating the percentage of quaternized subunits, have been proposed as potential carriers for drugs insoluble in water. However these cationic polyelectrolytes form emboli upon intravenous administration. In order to study the mechanism, Q-P(TDAE)(11) was incubated in vitro with red blood cells (RBCs) suspended in various aqueous media such as autologous plasma, autologous serum, albumin dissolved in phosphate buffer, plasma-serum mixtures and Tris buffer. The deformability of the RBC membrane studied by viscometry was not affected by the polycation. Q-P(TDAE)(11)-induced hemagglutination was studied by optical microscopy. It depended on the polymer concentration and on the presence of plasma proteins. As ghosts were formed in some cases, hemolysis was investigated by measuring potassium and hemoglobin released from RBCs. Fibrinogen and serum proteins, except albumin, protected RBCs from hemolysis. Moreover the order of addition of the suspension components modulated dramatically the Q-P(TDAE)(11)-induced hemolysis. Addition of Q-P(TDAE)(11) to whole blood caused hemolysis whereas addition of the polymer to plasma prior to contact with RBCs did not affect the cell integrity. In contrast, addition of the polymer to RBCs suspended in albumin solution caused greater hemolysis than the addition to whole blood, and the contact between Q-P(TDAE)(11) and albumin prior to RBC addition still enhanced cell lysis. Two conclusions can be drawn from these observations: (i) Q-P(TDAE)(11) induces both hemagglutination, probably through electrostatic interaction, and hemolysis, because Q-P(TDAE)(11) disrupted the RBC lipid bilayer; (ii) proteins can decrease or increase the deleterious effects of Q-P(TDAE)(11) on RBCs.

Blood Proteins↗
PubMed2000

Mechanism and rate of degradation of polyhydroxyoctanoate films in aqueous media: A long-term in vitro study.

The present study investigated the in vitro mechanism and degradation rate of polyhydroxyoctanoate (PHO). Solution-cast PHO films were incubated in either water or isoosmotic phosphate-buffered saline (PBS) for periods ranging from 1 to 24 months. Physical characterization included weight loss, water absorption, pH change, tensile strength, and scanning electron microscopy (SEM) studies. Analytical investigations including electron spectroscopy for chemical analysis, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), wide-angle X-ray diffraction, and size exclusion chromatography were also performed to assess chemical and morphological changes to the structure of the PHO. The results show that the PHO-cast films incubated in either water or isoosmotic PBS underwent a simple hydrolytic degradation process characterized by water absorption, gradual molecular weight decrease, and negligible mass loss after 24 months of incubation. DSC results suggest that degradation occurred in the amorphous zone, followed by an attack in the crystalline domain. An increase in the vibration stretching of OH after 24 months of incubation, as revealed by FTIR, may indicate that the degradation process began internally, moving outwardly toward the surface of the PHO films. This process was more rapid in the films incubated in PBS than in those incubated in water. However, no significant changes in the morphology of the films were detected by SEM. This study demonstrated that the in vitro degradation of PHO in water or in PBS is a very slow hydrolytic process, exceeding 2 years. Our findings also suggest that the internal degradation mechanism is faster in PBS because of the ionic strength of the medium and that this internal process surface moves gradually toward the surface.

Biocompatible Materials↗
PubMed2000

Selective enzymatic degradations of poly(L-lactide) and poly(epsilon-caprolactone) blend films.

Solution cast films were prepared from poly(L-lactide) (PLLA) and poly(epsilon-caprolactone) (PCL) as well as from three blends, namely B75, B50, and B25 with PLLA/PCL proportions of 75/25, 50/50, and 25/75, respectively. The enzymatic degradation of square samples (10 x 10 x 0.2 mm) cut from the films was investigated at 37 degrees C in a pH = 8.6 Tris buffer containing proteinase K or in a pH = 7.0 phosphate buffer containing Pseudomonas lipase. It was confirmed that proteinase K can degrade amorphous domains of PLLA, but cannot degrade crystalline PLLA or PCL. In contrast, Pseudomonas lipase can degrade both amorphous and crystalline PCL but cannot degrade PLLA. The two faces of solution cast films showed different morphologies due to the solvent evaporation process. The lower face appeared more crystalline than the upper face because of the plasticizing effect of solvent entrapped inside which allowed crystallization to proceed. Therefore, the lower face was more resistant to enzymatic attack by proteinase K in the cases of PLLA and the blends. The two polymers in the blends exhibited well separated crystalline domains. PCL seemed to constitute the continuous phase of the blends with formation of large size spherulites when the PCL content was over 50%. The selective degradation of PCL or PLLA components revealed the inner morphology of the blends where microspherelike or islandlike patterns were observed.

Calorimetry, Differential Scanning↗
PubMed2000

A novel route to poly(epsilon-caprolactone)-based copolymers via anionic derivatization.

Poly(epsilon-caprolactone) (PCL) is known to biodegrade under composting or water sewage plant conditions. However, as compared with poly(alpha-hydroxy acids) derived from lactic and glycolic acids, PCL is much more resistant to chemical hydrolysis and is achiral, a feature that limits very much the possibility of property modulation through the configurational structure of polymer chains. For the sake of enlarging the family of PCL-type polymers, a novel method is proposed which is based on the anionic activation of PCL chain by the removal of a proton from the methylene group in alpha-position of the ester carbonyl present in the main chain, using a nonnucleophilic base such as lithium diisopropyl amide (LDA). This activation leads to a polycarbanion onto which various electrophile groups can be attached. The feasibility of the process was first shown on poly(methyl acrylate), (PMA), whose polyacrylic main chain is resistant to strong bases. The PMA polycarbanion was modified by various electrophiles, namely benzaldehyde, naphthoyl chloride, benzyl chloroformate, and iodomethane. In a second stage, the same reactions were performed successfully on PCL. The degree of substitution depended on the experimental conditions. PCL underwent main chain degradation during the formation of the polycarbanion whereas the reaction with the electrophiles did not cause any further main chain cleavages. The degradation of PCL chains can be limited enough to give access to novel functional PCL polymers.

Algorithms↗
PubMed2000

Poly(ethylene glycol): protein-repulsive or albumin-compatible?

In the literature, many papers deal with the behavior of proteins in aqueous media in the presence of poly(ethylene glycol) (PEG) molecules or poly(ethylene oxide) (PEO) segments, physically adsorbed onto, or covalently attached to, macromolecules or to solid surfaces. In particular, it is well known that PEO segments make foreign materials stealthy, i.e. they are much less detected by the immune system either through humoral reactions or, at the cell level, through opsonins. Revisiting the literature led us to challenge the largely accepted opinion that the decreased recognition of PEO segment-bearing foreign macromolecules and particles by the mononuclear phagocyte system is primarily the consequence of the repulsion of all blood proteins by PEG segments through the excluded volume effect. This challenge is based on the finding that albumin and PEG are compatible in phosphate-buffered saline at room temperature and at concentrations comparable to those measured by others on the surface of PEO segment-bearing species, whereas fibrinogen and PEG phase-separated and were incompatible despite the much lower concentration of the latter protein. According to literature and to these observations, it is proposed that the stealth effect induced by PEO segments is primarily due to the compatibility between PEO segments of intermediate molar mass and albumin, thus rendering PEO-bearing macromolecules or surfaces to look like native albumin. Under such conditions, the hospitality offered by PEG macromolecules or PEO segments to albumin, the dominant plasma protein, results in a 'chameleon' effect that prevents the activation of other PEG-compatible or -incompatible plasma proteins or cells involved in foreign body recognition and elimination. PEG with molar masses > or = 8000 did not accommodate albumin in agreement with the excluded volume phenomenon.

Fibrinogen↗
PubMed2000

Synthesis, characterisation and in vivo behaviour of a norfloxacin-poly(L-lysine citramide imide) conjugate bearing mannosyl residues.

With the aim of promoting the targeting of macrophage mannose receptors and the internalisation of the norfloxacin antibiotic, which is active against some intracellular bacteria, a macromolecular prodrug was synthesised where the antibiotic and mannosyl moieties were coupled to a polymeric carrier, namely poly(L-lysine citramide imide). This carrier, which derived from two metabolites, citric acid and L-lysine, is known to be biocompatible and slowly degradable under slight acidic conditions. Norfloxacin was coupled onto the acid groups present along the polymer chains, and conjugates were characterised by UV, TLC and SEC. The mannosyl groups selected to promote the targeting of the mannose-specific lectin present on the outer membrane of macrophages were incorporated through a biodegradable glycolic spacer arm. Two different strategies were considered to synthesise the full conjugates, namely coupling norfloxacin onto mannosylated conjugates, and coupling mannose onto PLCAI/Nflx conjugates. The second pathway led to better results regarding mannosylation. The presence of norfloxacin and mannose caused chain aggregation, especially for conjugates with a high content of mannosyl residues. The targeting ability of the prodrug was investigated using a method based on the competition between the mannosylated macromolecules and glucose oxidase, a mannosyl-bearing non-human protein. This method showed that prodrug macromolecules competed effectively with glucose oxidase and thus should be able to bring the drug up to the mannosyl receptor-bearing membranes of macrophages infected by intracellular bacteria.

Animals↗
PubMed1999

Capillary zone electrophoretic analysis of positively charged poly(ethylene oxide) macromolecules using non-covalent polycation-coated fused-silica capillary and indirect UV detection.

Capillary zone electrophoresis was used to show the coupling between NH2-terminated poly(ethylene oxide) and oligomers of lactic acid activated by transforming carboxyl chain ends to acyl chloride ones. The demonstration was based on the use of fused-silica capillary physically modified by pre-adsorption of polycations in the reversed polarity mode. As poly(ethylene oxide) macromolecules are UV transparent, indirect UV detection was used. A creatinine solution at pH 4.8 was selected as background electrolyte. Commercially available polycations with different structures were tested. It was shown that the reversed electroosmosis could be modulated according to the structure of the polycation. The method was then applied to analyse a commercial alpha,omega-diamino poly(ethylene oxide), namely Jeffamine ED 600 characterised by a broad mass dispersion. Data showed that the method can detect and separate amino poly(ethylene oxide) of different structures. When applied to analyse post coupling products, no free NH2-terminated poly(ethylene oxide) segments were detected. Moreover, the method allowed detection of water-soluble oligomers generated by partial degradation of lactic segments during the reaction.

Electrochemistry↗
PubMed1999

Alkylated poly(L-lysine citramide) as models to investigate the ability of amphiphilic macromolecular drug carriers to physically entrap lipophilic compounds in aqueous media.

Poly(L-lysine citramide) was synthesized to serve as a polymeric bioresorbable drug carrier. It was previously shown that low molecular weight poly(L-lysine citramide) hydrophobized with heptyl and lauryl side chains (PLCA-C7(p) with p=43 and 60%; and PLCA-C12(p), with p=68, 75 and 100%) formed aggregates in aqueous media. The size of these aggregates was found to depend on the balance between repulsive electrostatic charges and attractive hydrophobic interactions, on the degree of ionization, and on the ionic strength. In this paper, the formation of these aggregates was further investigated by fluorescence probing, using two polarity sensitive molecules, pyrene and Nile Red, which were physically entrapped within the lipophilic core of the aggregates. In contrast to other micellar structures formed by surfactants and amphiphilic block copolymers, aggregates were observed even at very low polymer concentrations. The capacity of the hydrophobic domains to accommodate lipophilic molecules via physical entrapment was demonstrated with progesterone.

Absorption↗