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Query: UNIPROT:P00750 (PLA)
 16,800 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nanoparticles were prepared from methoxy poly(ethylene glycol)poly(d,l-lactic acid) block copolymers (Me.PEG-PLA) or blends of Me.PEG-PLA and PLA by the precipitation-solvent diffusion method. These nanoparticles, labeled by introducing [14C]PLA in the formulation, were shown to be more slowly captured by cultured THP-1 monocytes than F68-coated PLA nanoparticles, in a PEG chain-length-dependent manner. In vivo, the half-life in plasma of the Me.PEG-PLA nanoparticles that were intravenously administered to rats is increased by a factor 180 compared with the F68-coated PLA nanoparticles. This mononuclear phagocytes system avoidance was explained according to a conformation model in which the PEG density at the surface of the particles is a key parameter.
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PMID:Stealth Me.PEG-PLA nanoparticles avoid uptake by the mononuclear phagocytes system. 762 43

The modification of surface properties of biodegradable poly(lactide-co- glycolide) (PLGA) and model polystyrene nanospheres by poly(lactide)-poly(ethylene glycol) (PLA:PEG) copolymers has been assessed using a range of in vitro characterization methods followed by in vivo studies of the nanospheres biodistribution after intravenous injection into rats. Coating polymers with PLA:PEG ratio of 2:5 and 3:4 (PEG chains of 5000 and 2000 Da. respectively) were studied. The results reveal the formation of a PLA:PEG coating layer on the particle surface resulting in an increase in the surface hydrophilicity and decrease in the surface charge of the nanospheres. The effects of addition of electrolyte and changes in pH on stability of the nanosphere dispersions confirm that uncoated particles are electrostatically stabilized, while in the presence of the copolymers, steric repulsions are responsible for the stability. The PLA:PEG coating also prevented albumin adsorption onto the colloid surface. The evidence that this effect was observed for the PLA:PEG 3:4 coated nanospheres may indicate that a poly(ethylene glycol) chain of 2000 Da can provide an effective repulsive barrier to albumin adsorption. The in vivo results reveal that coating of PLGA nanospheres with PLA:PEG copolymers can alter the biodistribution in comparison to uncoated PLGA nanospheres. Coating of the model polystyrene nanospheres with PLA:PEG copolymers resulted in an initial high circulation level, but after 3 hours the organ deposition data showed values similar to uncoated polystyrene spheres. The difference in the biological behaviour of coated PLGA and polystyrene nanospheres may suggest a different stability of the adsorbed layers on these two systems.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Surface modification of poly(lactide-co-glycolide) nanospheres by biodegradable poly(lactide)-poly(ethylene glycol) copolymers. 789 46

ABA block copolymers of polyethylene glycol and poly-DL-lactic acid were prepared by ring-opening polymerization of DL-dilactide with alpha,omega-dihydroxy polyethylene glycol, Mn 1000 or 2000. The morphology of the resulting copolymers, with PEG:PLA ratios(mol/mol) of 1:2, 1:3 and 1:4, was characterized by DSC and ESR spectroscopy. The rate of water uptake was biphasic, reflecting the contribution of two processes: rapid diffusion of water into the initially miscible PEG and PLA blocks; then a slower rate of hydration possibly due to phase separation and hydrolytic cleavage of the PLA blocks. The rate of hydrolytic degradation of the block copolymers in DI water at 37 degrees C was measured by two methods: weight loss and colorimetric analysis of the carboxy end group concentration resulting from chain scission of PLA blocks. As a result of phase separation, the rate of scission of PLA blocks in the copolymers was similar to that of the PLA homopolymer. The more rapid onset of weight loss of the copolymers, relative to PLA, is attributed to the greater water solubility of PEG-PLA oligomers and their greater diffusivity in the more highly hydrated copolymers.
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PMID:Poly-DL-lactic acid: polyethylene glycol block copolymers. The influence of polyethylene glycol on the degradation of poly-DL-lactic acid. 803 37

We developed adequate delivery systems for bone morphogenetic protein (BMP) to express its bone-inducing activity by combining it with biodegradable synthetic polymers, these causing no unfavorable tissue reaction or anti-BMP effect. Their efficacy was tested for ectopic bone formation in mice and reconstruction of large segmental bone defects of the tibiae in rabbits. Composites of semipurified BMP and polylactic acid--polyethylene glycol block copolymer (PLA-PEG), and composites of BMP, PLA-PEG and lactic acid--glycolic acid copolymer (PLGA) were implanted under the fasciae of the dorsal muscles of mice. Three weeks after implantation, both the BMP/PLA-PEG and BMP/PLA-PEG/PLGA composites were completely absorbed and replaced by newly induced bone with hematopoietic marrow. Because the BMP/PLA-PEG composite is a viscous semiliquid and the BMP/PLA-PEG/PLGA composite is a plastic and moldable, the former can be used as an injectable bone-inducing material and the latter as a plastic mold. The BMP/PLA-PEG/PLGA composites were implanted in large segmental bone defects in the tibiae in rabbits. Twelve weeks after implantation, the bone defect was completely restored by a newly formed bone mass of the original thickness and structure.
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PMID:Bone induction and bone repair by composites of bone morphogenetic protein and biodegradable synthetic polymers. 815 40

A new biodegradable polymer, a polylactic acid-polyethylene glycol (PLA-PEG) block copolymer, proved to be an effective and suitable carrier for bone morphogenetic protein (BMP). Composites of semipurified BMP and PLA-PEG consisting of a PLA segment with a molecular weight (MW) of 650 d and a PEG segment with a MW of 200 d (PLA-PEG 650-200) were implanted under the fasciae of the dorsal muscles of mice. Three weeks after implantation, the PLA-PEG 650-200/BMP composites were completely absorbed and replaced by newly induced bone with hematopoietic marrow. The composites induced twice as much bone as composites of BMP and a 650-d PLA homopolymer. Results indicate that of all the biodegradable synthetic polymers the authors have tested, PLA-PEG 650-200 is the most suitable and effective BMP carrier. Composites of PLA-PEG 650-200/BMP and hydroxyapatite powder (HAP) also induced ectopic bone formation. Because PLA-PEG 650-200/BMP is viscous and semiliquid and PLA-PEG 650-200/BMP/HAP is doughy and plastic, the former can be used as an injectable osteoinductive material and the latter as a plastic mold.
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PMID:Polylactic acid-polyethylene glycol block copolymer. A new biodegradable synthetic carrier for bone morphogenetic protein. 835 39

Hexadecafluoro zinc phthalocyanine (ZnPcF16), a second-generation sensitizer for the photodynamic therapy (PDT) of cancer, was formulated in polyethylene-glycol-coated poly(lactic acid) nanoparticles (PEG-coated PLA-NP) and tested in EMT-6 tumour-bearing mice for its photodynamic activity. The tumour response was compared to that induced by the same dye formulated as a Cremophor EL (CRM) emulsion. Formulation in the biodegradable NP improved PDT response of the tumour while providing prolonged tumour sensitivity towards PDT.
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PMID:Photodynamic therapy of tumours with hexadecafluoro zinc phthalocynine formulated in PEG-coated poly(lactic acid) nanoparticles. 864 56

Nanoparticles composed of diblock poly(D,L-lactide-co-glycolide)-poly(ethylene glycol) (PLGA-PEG) or a branched, multiblock PLA-(PEG)3 were prepared by the single emulsion technique. Results of previous studies of these nanoparticles suggested that their structure is of the core-corona type with a polyester core and an outer PEG coating. In the present study, 1H NMR spectroscopy was utilized to provide direct evidence of the structure of these nanoparticles suspended in an aqueous environment. The results confirm the existence of the core-corona structure under these conditions, and show that the PEG moieties extend out from the nanoparticle core into the aqueous environment, and exhibit chain mobility similar to that of PEG in solution.
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PMID:Nanotechnology for biomaterials engineering: structural characterization of amphiphilic polymeric nanoparticles by 1H NMR spectroscopy. 900 93

The design of biodegradable microparticle drug delivery systems with precisely tailored surface properties requires surface analytical methods that can relate polymer chemistry and fabrication parameters to the final surface chemistry of the microparticles. We demonstrate using X-ray photoelectron spectroscopy (XPS) that it is possible to identify significant variations in the surface chemistry of microparticles composed of poly(lactic acid) (PLA), poly(lactide-co-glycolide) (PLGA), or block copolymers of PLA or PLGA with poly(ethylene glycol) (PEG). These variations are related to the mechanism by which the microparticle/water interface is stabilized. This, in turn, is controlled by the interfacial surface tensions of the polymers within aqueous environments. For PEG containing block copolymers, adsorption of a surfactant, poly(vinyl alcohol) (PVA), from the aqueous medium onto the polymer is reduced compared with the PLA and PLGA polymers. This reduction is achieved because the PEG segments, within the copolymer structure, stabilize the polymer/water interface. Estimates of the relative amounts of lactide, lactide-co-glycolide, vinyl alcohol, and ethylene glycol monomer units at the microparticle surfaces are presented based on curve-fitting analysis of the XPS data.
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PMID:The Adsorption of Poly(vinyl alcohol) to Biodegradable Microparticles Studied by X-Ray Photoelectron Spectroscopy (XPS) 902 8

Biodegradable block copolymers made of poly(ethylene glycol) monomethylether (Me.PEG) and poly(D,L-lactic acid) (PLA) were investigated for their erosion properties. Wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) investigations prior to erosion revealed that despite the low content of crystallizable Me.PEG of 10%, Me.PEG5-PLA45 is a partially crystalline polymer. The erosion of the polymer was investigated using cylindrical polymer matrix discs with a diameter of 8 mm and a height of 1.5 mm. WAXD and DSC spectra obtained from eroded polymer matrix discs suggest that both polymer blocks separate completely during erosion. The crystallinity of Me.PEG5-PLA45 was found to increase during erosion, which is probably due to the improved mobility of Me.PEG inside the polymer with a progressive degree of degradation. The erosion kinetics were found to be similar to that of PLA or poly(lactic-co-glycolic acid). During erosion the polymer matrix weight of dried samples remains constant for 11 weeks after which erosion sets in rapidly. From this observation one can conclude that the impact of the relatively small Me.PEG chains on Me.PEG5-PLA45 erosion is not pronounced. This is beneficial for all those applications that require the stability of the polymer matrix and in which the Me.PEG chain is intended to bring about other effects such as the modification of the surface properties of PLA polymers.
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PMID:Erosion of biodegradable block copolymers made of poly(D,L-lactic acid) and poly(ethylene glycol). 961 7

Isradipine, an antihypertensive agent, was encapsulated by the nanoprecipitation method using polymers including poly(epsilon-caprolactone), poly(D,L-lactide) and poly(d, L-lactide-co-glycolide). In vitro scanning electron microscopy and differential scanning calorimetry were used to characterize the nanoparticles. The average diameters of the nanoparticles ranged from 110 nm to 208 nm. PCL nanoparticles were larger than nanoparticles prepared with the other polymers. The zeta potential of the nanoparticles was negative, with values of about -25 mV which promoted good stabilization of the particles. The amorphous state of PLA and PLAGA non-loaded nanoparticles and the semi-crystalline state of PCL were demonstrated with X-ray diffraction and differential scanning calorimetry. For all nanoparticles, isradipine was found to be totally amorphous in the polymer which suggested that the drug was molecularly dispersed in the matrix. The colloidal suspensions displayed a sustained release profile in comparison with the drug release profile of isradipine in a PEG solution. Results from this investigation suggest that these nanospheres will be a good candidate delivery system for oral administration, to reduce the initial hypotensive peak and to prolong the antihypertensive effect of the drug.
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PMID:Preparation and characterization of nanoparticles containing an antihypertensive agent. 979 32


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