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

Heterostereocomplexes between d-PLA and l-peptides, obtained by spontaneous precipitation from acetonitrile solution, were characterized by thermal analysis and microscopic techniques. Differential scanning calorimetry showed two transition endotherms, one for the alpha form that melts at 178 degrees C and one for the beta form of PLA that melts at 169 degrees C. A linear correlation was found between the enthalpy of both melt temperatures and the peptide concentration. The complexation was monitored by a change in morphology, which was imaged by AFM-tapping mode. The initial fibrous network of d-PLA changed to uniform disks of 100 nm in diameter and 2.5 nm in height of the heterostereocomplex. Rhodamine B labeled leuprolide was complexed selectively to d-PLA, which was chemically bound onto mica plates. Addition of l-PLA to the complex enabled displacement of the peptide, which was observed by fluorescent spectrometry and confocal microscopy. These results provide a method, which enables one to obtain an expression for the relative interaction strength between various stereoselective polymers and polypeptides with opposite enantiomeric configuration.
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PMID:Heterostereocomplexes prepared from d-poly(lactide) and leuprolide. I. Characterization. 1295 99

In the study, poly(gamma-glutamic acid) (gamma-PGA) and poly(lactide) (PLA) were used to synthesize block copolymers via a simple coupling reaction between gamma-PGA and PLA to prepare self-assembled nanoparticles. For the potential of targeting liver cancer cells, galactosamine was further conjugated on the prepared nanoparticles as a targeting moiety. gamma-PGA, a water-soluble, biodegradable, and non-toxic compound, was produced by microbial fermentation (Bacillus licheniformis, ATCC 9945a) and then was hydrolyzed. The hydrolyzed gamma-PGA with a molecular weight of 4 kDa and a polydispersity of 1.3 was used, together with PLA (10 kDa, polydispersity 1.1), to synthesize block copolymers. The prepared nanoparticles had a mean particle size of about 140 nm with a zeta potential of about -20 mV. The results obtained by the TEM and AFM examinations showed that the morphology of the prepared nanoparticles was spherical in shape with a smooth surface. In the stability study, no aggregation or precipitation of nanoparticles was observed during storage for up to 1 month, as a result of the electrostatic repulsion between the negatively charged nanoparticles. With increasing the galactosamine content conjugated on the rhodamine-123-containing nanoparticles, the intensity of fluorescence observed in HepG2 cells increased significantly. Additionally, the intensity of fluorescence observed in HepG2 cells incubated with the nanoparticles with or without galactosamine conjugated increased approximately linearly with increasing the duration of incubation. In contrast, there was no fluorescence observed in Hs68 cells (without ASGP receptors) incubated with the nanoparticles with galactosamine conjugated. The aforementioned results indicated that the galactosylated nanoparticles prepared in the study had a specific interaction with HepG2 cells via ligand-receptor recognition.
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PMID:Preparation of nanoparticles composed of poly(gamma-glutamic acid)-poly(lactide) block copolymers and evaluation of their uptake by HepG2 cells. 1591 30

The poly(D,L-lactic acid)-block-(ligand-tethered poly(ethylene glycol)) copolymer was explored to engineer poly(D,L-lactic acid) (PLA) material to promote chondrocyte attachment and growth. The poly(D,L-lactic acid)-block-poly(ethylene glycol) copolymer (PLE) was synthesized by a coupling reaction between PLA and poly(ethylene glycol) (PEG) (M(n) 1000, 2000, and 4000 respectively), with the use of 4,4'-methylenediphenyl diisocyanate (MDI). Then the PLE was activated by methyl sulfonyl chloride and the amino acids or arginine-glycine-aspartic acid tripeptide (RGD) was attached, which was verified by the ninhydrin-UV method. The modified PLA films were simply prepared by blending PLA with PLE derivatives. ATR-FTIR, XPS, contact angle, and AFM results clearly showed that the PEG chain stably enriched on the surface of PLE-modified PLA films. The chondrocyte cytocompatibility test showed the modified PLA films could significantly improve chondrocyte attachment and proliferation.
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PMID:Poly(D,L-lactic acid)-block-(ligand-tethered poly(ethylene glycol)) copolymers as surface additives for promoting chondrocyte attachment and growth. 1613 Jan 43

The aim of this study was to synthesize novel biodegradable charged polymers to be used in DNA complexation for genetic delivery in different diseases. A new copolymer of PLA and complexed Schiff bases was synthesized in a several steps. This copolymer will be used as a nanocarrier. Also, AFM comparative studies in tapping mode were performed; on cationic copolymer and on PLA-Schiff base copolymer, on non-oriented and oriented film and on the DNA-cationic complex. The results indicated a difference in the topology and on phase picture of AFM film with or without cationic charge.
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PMID:AFM study of a new carrier based on PLA and salen copolymers for gene therapy. 1800 80

A new poly(ethylene glycol) (PEG)-modified poly(D,L-lactic acid) (PLA) was synthesized by grafting maleic anhydride onto PLA and subsequently amidating with O,O'-bis-(2-aminopropyl) polypropylene glycol-block-polyethylene oxide-block-polypropylene glycol (H2N-PEG-NH2, Mw: 600). Its structure was confirmed by FTIR, DSC, 1H NMR, GPC, and ninhydrin test. The polymer is more hydrophilic compared with PLA according to contact angle tests, and is degradable as determined from its pH and mass changes during degradation. The polymer shows a 62.7% decrease in BSA absorption compared with PLA when dried in air, and a 82.76% decrease when dried under 65% humidity, as measured by fluorospectrophotometry. The polymer promotes adhesion and proliferation of osteoblasts, determined by MTT assay. With this new polymer, spherical nanoscale aggregates encapsulated with or without hydrophilic dye are formed spontaneously in water, visualized by inverted microscope and AFM. The particle size is concentration dependent as confirmed by dynamic light scattering, and its critical micelle concentration was 1.124 microg/mL as determined by a fluorescence method. The good hydrophilicity, degradability, cellular compatibility, protein-resistance, self-aggregation, and reactivity of the polymer may lead to its potential applications in drug delivery.
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PMID:Development of a new poly(ethylene glycol)-graft-poly(D,L-lactic acid) as potential drug carriers. 1843 84

Previous nanoscale investigations of the gel-state membrane surface structure under the action of phospholipase A(2) (PLA(2)) suggest that single enzymes at work scoot on the membrane surface from the observed defects, which creates nanosized channels oriented along the lipid crystal-packing structure. To date, however, there have been no reports of direct observation of PLA(2) at the single-molecule level focusing on how the enzymes interact with the defects. Herein, we report a single-molecule fluorescence microscopy study on the action of enzymatically active rhodamine B-labeled cobra PLA(2) on a supported lipid membrane with visible packing defects on a glass substrate. Working with a gel-state phospholipid bilayer, the low-activity period (lag phase) of PLA(2) action is followed by the burst binding of PLA(2) molecules from aqueous solution on a few newly created active sites. These active sites are distinguished by a spatial resolution of approximately 40 nm, which is below the diffraction limit. The rate of active-site propagation as reflected by new PLA(2) binding on the membrane surface is estimated to be approximately 5 nm min(-1). This rate is about two orders of magnitude slower than the propagation rate of hydrolyzed channels estimated by AFM studies on bee venom PLA(2) on a similar membrane surface. This direct observation of PLA(2) molecules allows the visualization of different PLA(2) binding modes on the membrane surface and on the membrane boundary.
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PMID:Fluorescence single-molecule study of cobra phospholipase A2 action on a supported gel-phase lipid bilayer. 1914 25

In order to evaluate the solubility effect of grafted moiety on the physicochemical properties of poly(d,l-lactide) (PLA) based nanoparticles (NPs), two materials of completely different aqueous solubility, polyethylene glycol (PEG) and palmitic acid were grafted on PLA backbone at nearly the same grafting density, 2.5% (mol of grafted moiety/mol of lactic acid monomer). Blank and ibuprofen-loaded NPs were fabricated from both polymers and their properties were compared to PLA homopolymer NPs as a control. NPs were analyzed for major physicochemical parameters such as encapsulation efficiency, size and size distribution, surface charge, thermal properties, surface chemistry, % poly(vinyl alcohol) (PVA) adsorbed at the surface of NPs, and drug release pattern. Encapsulation efficiency of ibuprofen was found to be nearly the same for both polymers approximately 36% and 39% for PEG2.5%-g-PLA and palmitic acid2.5%-g-PLA NPs, respectively. Lyophilized NPs of palmitic acid2.5%-g-PLA either blank or loaded showed larger hydrodynamic diameter ( approximately 180nm) than PEG2.5%-g-PLA NPs ( approximately 135nm). PEG2.5%-g-PLA NPs showed lower % of PVA adsorbed at their surface ( approximately 5%, w/w) than palmitic acid2.5%-g-PLA NPs ( approximately 10%, w/w). Surface charge of palmitic acid2.5%-g-PLA NPs seems to be influenced by the large amount of PVA remains associated within their matrix. Thermal analysis using DSC revealed possible drug crystallization inside NPs. Both AFM phase imaging and XPS studies revealed the tendency of PEG chains to migrate towards the surface of PEG2.5%-g-PLA NPs. While, XPS analysis of palmitic acid2.5%-g-PLA NPs showed the tendency of palmitate chains to position themselves into the inner core of the forming particle avoiding facing the aqueous phase during NPs preparation using O/W emulsion method. The in vitro release pattern showed that PEG2.5%-g-PLA NPs exhibited faster release rates than palmitic acid2.5%-g-PLA NPs. PEG and palmitate chains when grafted onto PLA backbone, different modes of chain organization during NPs formation were obtained, affecting the physicochemical properties of the obtained NPs. The obtained results suggest that the properties of PLA-based NPs can be tuned by judicious selection of both chemistry and solubility profile of grafted material over PLA backbone.
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PMID:Effect of aqueous solubility of grafted moiety on the physicochemical properties of poly(d,l-lactide) (PLA) based nanoparticles. 2006 Apr 50

(PEG)(3)-PLA copolymer has been explored for the formation of polymersomes. For this, three chains of methoxy-PEG(1100) were directly attached to citric acid by esterification. (Methoxy-PEG(1100))(3)-citrate was then reacted at its hydroxyl terminal with different moles of d,l-lactide by ring-opening polymerization to obtain polymers with five different PEG-to-PLA ratios ranging from 10:90 to 90:10. Polymers were characterized by GPC, FTIR, (1)H NMR, and DSC, films were characterized for hydrophilicity by contact angle, and surface topography was observed by SEM and AFM. All five polymers were evaluated for the formation of polymersomes. Among these, polymers with PEG content of 10-30% were able to self-assemble into polymersomes. To affirm their self-arrangement and drug carrier properties, hydrophilic and hydrophobic dyes were simultaneously encapsulated in these structures. SEM and TEM analysis of the blank polymersomes confirmed the vesicular nature of the polymersomes, whereas CLSM analysis of dye-loaded polymersomes demonstrated the presence of two separate regions viz. hydrophilic core and hydrophobic wall. Hydrophobic dye, fluorescein was released relatively faster from the wall of polymersomes, whereas hydrophilic dye, propidium iodide, was released in controlled fashion up to 18 days. It is expected that these systems may serve as a suitable carrier for simultaneous or separate delivery of drug molecules with varying physicochemical properties.
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PMID:Self assembly of amphiphilic (PEG)(3)-PLA copolymer as polymersomes: preparation, characterization, and their evaluation as drug carrier. 2017 78

The aim of the present study is to evaluate the effect of polyethylene glycol (PEG) chain organization on various physicochemical aspects of drug delivery from poly(D, L-lactide) (PLA) based nanoparticles (NPs). To reach that goal, two different pegylated polymers of poly(D, L-lactide) (PLA) were synthesized. Polymers used in this study are grafted ones in which PEG was grafted on PLA backbone at 7% (mol/mol of lactic acid monomer), PEG7%-g-PLA, and multiblock copolymer of both PLA and PEG, (PLA-PEG-PLA)n with nearly similar PEG insertion ratio and the same PEG chain length. Blank and ibuprofen-loaded NPs were prepared from both polymers and their properties were compared to PLA homopolymer NPs as a control. Encapsulation efficiency of ibuprofen was found to be approximately 25% for (PLA-PEG-PLA)n NPs and approximately 80% for PEG7%-g-PLA NPs. (PLA-PEG-PLA)n NPs either blank or loaded showed larger hydrodynamic diameter (approximately 200 nm) than PEG7%-g-PLA NPs (approximately 135 nm). A significant difference was observed in the amount of PVA associated with the surface of both NPs where 3.6% and 0.4% (wt/wt) were found on the surface of PEG7%-g-PLA and (PLA-PEG-PLA)n NPs, respectively. No observed difference in zeta potential values for both NPs formulations was found. DSC showed the existence of the drug in a crystalline state inside NPs matrix irrespective of the type of polymer used with either shifting or/and broadening of the drug melting endotherm. Both AFM phase imaging and XPS studies revealed the possibility of existence of more PEG chains at the surface of grafted polymer NPs than (PLA-PEG-PLA)n during NPs formation. The in vitro release behavior showed that (PLA-PEG-PLA)n NPs exhibited faster release rates than PEG7%-g-PLA NPs. The physicochemical differences obtained between both polymers were probably due to different chain organization during NPs formulation. Such pegylated NPs made from these two different polymers might find many applications, being able to convert poorly soluble, poorly absorbed substances into promising drugs, improving their therapeutic performance, and helping them reach adequately their target area. Our results suggest that the properties of pegylated PLA-based NPs can be tuned by proper selection of both polymer composition and polymer architecture.
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PMID:Effect of polyethylene glycol (PEG) chain organization on the physicochemical properties of poly(D, L-lactide) (PLA) based nanoparticles. 2021 27

We show that vesicles made of block copolymers with aldehyde end groups can be covalently attached to aminated and non-aminated, untreated glass surfaces. The attached vesicles were sufficiently stable to allow a detailed investigation of vesicle shapes by confocal laser scanning microscopy (CLSM) and AFM in aqueous solutions allowing reconstruction of 3D images of the vesicle structure. Covalently attached PCL-PEO, PLA-PEO, and PI-PEO block copolymer vesicles have different footprint areas and different shapes due to their differences in bilayer stiffness.
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PMID:Covalent attachment of polymersomes to surfaces. 2035 8


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