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

Degradable copolymers were synthesized by ring opening polymerization of lactide in the presence of poly(ethylene glycol) (PEG), using CaH2 as a biocompatible initiator. The resulting PLA/PEO/PLA triblock copolymers were dissolved in a biocompatible solvent, namely tetraglycol. Physically crosslinked hydrogels were then prepared by introducing small amounts of water into the thus obtained solutions. Hydrolytic degradation of the highly swollen hydrogels was realized in 0.13 M pH=7.4 phosphate buffer, while the enzymatic degradation was carried out in 0.05 M pH=8.6 Tris buffer containing a PLA-degrading enzyme, proteinase K. In both cases, degradation was initially very fast with dramatic weight loss. The LA/EO ratio of the remaining material increased rapidly, in agreement with the release of PEO-rich segments. In a second phase, the degradation rate slowed down. The presence of proteinase K strongly accelerated the degradation rate of the hydrogels, indicating that the enzyme was able to penetrate inside and attack the PLA domains which constituted nanometric nodes in the gel network.
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PMID:Hydrolytic and enzymatic degradations of physically crosslinked hydrogels prepared from PLA/PEO/PLA triblock copolymers. 1534 10

For use in micro-patterned scaffolds in tissue engineering, novel diacrylated triblock macromers (PLA-b-PCL-b-PLA, PGA-b-PCL-b-PGA and PCL-b-PEO-b-PCL) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR) and gel permeation chromatography (GPC). All diacrylated polymers were designed as triblock copolymers and involved biodegradable blocks of relatively non-polar epsilon-caprolactone (CL) and polar monomers such as glycolide (GA), lactide (LA) or ethylene oxide (EO). All triblock polymers were prepared in molecular weights of a few kilo daltons via the anionic ring-opening polymerization (ROP) of the corresponding lactide, glycolide or caprolactone using stannous octoate [Sn(Oct)(2)] as catalyst. The polymers had low polydispersity indices, ranging from 1.23 to 1.56. Biodegradable polymeric networks were prepared with conversions of 72-84% via photopolymerization of the triblock diacrylated polymers with 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. PLA-b-PCL-b-PLA copolymers crumbled easily and were not suitable for micro-patterning. PGA-b-PCL-b-PGA copolymers had higher water contact angles than PCL-b-PEO-b-PCL and were also cytocompatible with Fibroblasts 3T3.
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PMID:Novel photopolymerizable biodegradable triblock polymers for tissue engineering scaffolds: synthesis and characterization. 1546 60

Poly(lactic acid) (PLA) was successfully grafted to both ends of Pluronic F127 block copolymers (PEO-PPO-PEO) to obtain amphiphilic PLA-F127-PLA block copolymers. The block composition and structure of PLA-F127-PLA block copolymers were studied by nuclear magnetic resonance (NMR), gel permeation chromatography (GPC), differential scanning calorimetric (DSC) and wide angle X-ray diffraction (WXRD) techniques. Data from DSC and WXRD measurements indicated that Tg and Tm of PLA blocks in PLA-F127-PLA block polymers are lower than those of PLA homopolymer. Furthermore, Tm and crystallinity of PLA blocks decrease with decreasing PLA block length in PLA-F127-PLA block copolymers. The release behaviors of both hydrophobic 9-(methylaminomethyl)anthracene (MAMA) and hydrophilic procaine hydrochloride (PrHy) model drugs from PLA-F127-PLA nanoparticles with vesicular structure in PBS solution at 37 degrees C were examined by UV spectroscopy. The release kinetics of both MAMA and PrHy model drugs from PLA-F127-PLA nanoparticles exhibit burst release characteristics, which are believed to be controlled by concentration gradient resulting from the slow hydrolytic degradation of PLA segments.
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PMID:Release kinetics of hydrophobic and hydrophilic model drugs from pluronic F127/poly(lactic acid) nanoparticles. 1571 May 1

Poly(lactic acid) (PLA) was successfully grafted to both ends of Pluronic F127 block copolymer (PEO-PPO-PEO) to obtain amphiphilic PLA-F127-PLA block copolymers. The effect of enzymatic degradation on the release behaviors of hydrophobic model drug 9-(methylaminomethyl)anthracene (MAMA) from PLA-F127-PLA nano-particles with vesicular structure was studied by UV-Vis spectroscopy. It was observed that the release rate of MAMA from PLA-F127-PLA nano-particles with the enzymatic degradation varied with temperature due to the activity of the enzyme with temperature. However, the enzyme concentration has negligible effect on the release rates of MAMA.
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PMID:Effect of enzymatic degradation on the release kinetics of model drug from Pluronic F127/poly(lactic acid) nano-particles. 1619 6

In this paper, we report a novel synthesis of poly(ethylene oxide monooleate-block-DL-lactide) (MOPEO-PLA) in the presence of stannous 2-ethylhexanoate catalyst. By utilizing the surfactant property and the reactive double bond of the amphiphilic MOPEO-PLA, various characteristics of PLA microspheres, such as surface and internal structure, surface morphology, release property, and so on, may potentially be controlled. MOPEO-PLA was found to be hydrophobic enough to prevent loss by dissolution into aqueous solution, which is often a problem for MOPEO. Furthermore, the interfacial tension measurements of a MOPEO-PLA/toluene/water system revealed that MOPEO-PLA had a good surface activity almost equal to that of MOPEO. The MOPEO-PLA/PLA blend films were prepared by solvent casting on a water layer. Contact-angle measurements of MOPEO-PLA/PLA blend films confirmed that the hydrophilic PEO segments were selectivity accumulated at the oil/water interface. Moreover, the surface free energy on the 'water side' of the MOPEO-PLA/PLA blend films was increased because of the increase in polar components as a result of the ether bonds of the PEO segments. Schematic illustration of the adsorption property of a) MOPEO-PLA with a high-molecular-weight PLA segment and b) MOPEO-PLA with a low-molecular-weight PLA segment at an ethyl acetate/water interface.
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PMID:Preparation and interfacial properties of a novel biodegradable polymer surfactant: poly(ethylene oxide monooleate-block-DL-lactide). 1624 72

Four-armed (star-branched) block copolymers of l-PLA and PEO were synthesized using ring opening polymerization with different LA/EO ratio. Micellar aggregates were prepared from these block copolymers and characterized. Some surface segregation of PEG was found : the extent depends on the state of the material (whether it is in film or particle form), as well as on molecular geometry. The degradation behavior of star-shaped copolymer was studied over a three week period and compared to its linear counterpart. Anti-cancer drugs 5-FU and paclitaxel were loaded into the micellar nanoparticles. The drug release profile showed that the release of paclitaxel from these polymers could be controlled over 2 weeks. The kinetics of drug release for star-branched, tri- and di-block copolymers were compared. The micelles from star-shaped branch showed more complete release of drug than the diblock copolymers; also, the lower hydrodynamic radius of star-shaped polymers may result in better clearance of the carrier polymer from the body.
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PMID:Micelle-like nanoparticles of star-branched PEO-PLA copolymers as chemotherapeutic carrier. 1628 21

Poly(lactic acid) (PLA) and poly(lactic/glycolic acid) copolymers (PLGA) are biodegradable drug carriers of great importance, although successful pharmaceutical application requires adjustment of the surface properties of the polymeric drug delivery system to be compatible with the biological environment. For that reason, reduction of the original hydrophobicity of the PLA or PLGA surfaces was performed by applying a hydrophilic polymer poly(ethylene oxide) (PEO) with the aim to improve biocompatibility of the original polymer. PEO-containing surfaces were prepared by incorporation of block copolymeric surfactants, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic), into the hydrophobic surface. Films of polymer blends from PLA or PLGA (with lactic/glycolic acid ratios of 75/25 and 50/50) and from Pluronics (PE6800, PE6400, and PE6100) were obtained by the solvent casting method, applying the Pluronics at different concentrations between 1 and 9.1% w/w. Wettability was measured to monitor the change in surface hydrophobicity, while X-ray photoelectron spectroscopy (XPS) was applied to determine the composition and chemical structure of the polymer surface and its change with surface modification. Substantial reduction of surface hydrophobicity was achieved on both the PLA homopolymer and the PLGA copolymers by applying the Pluronics at various concentrations. In accordance with the wettability changes the accumulation of Pluronics in the surface layer was greatly affected by the initial hydrophobicity of the polymer, namely, by the lactide content of the copolymer. The extent of surface modification was also found to be dependent on the type of blended Pluronics. Surface activity of the modifying Pluronic component was interpreted by using the solubility parameters.
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PMID:XPS and wettability characterization of modified poly(lactic acid) and poly(lactic/glycolic acid) films. 1629 Mar 40

The adsorption behaviour of a tetrafunctional copolymer of poly (ethylene oxide)-poly (propylene oxide) ethylene diamine (commercially available as Poloxamine 908) and a diblock copolymer of poly (lactic acid)-poly (ethylene oxide) (PLA/PEG 2:5) onto a model colloidal drug carrier (156 nm sized polystyrene latex) is described. The adsorption isotherm, hydrodynamic thickness of the adsorbed layers and enthalpy of the adsorption were assessed. The close similarity in the conformation of the poly (ethylene oxide) (PEO) chains (molecular weight 5,000 Da) in the adsorbed layers of these two copolymers was demonstrated by combining the adsorption data with the adsorbed layer thickness data. In contrast, the results from isothermal titration microcalorimetry indicated a distinct difference in the interaction of the copolymers with the polystyrene colloid surface. Poloxamine 908 adsorption to polystyrene nanoparticles is dominated by an endothermic heat effect, whereas, PLA/PEG 2:5 adsorption is entirely an exothermic process. This difference in adsorption behaviour could provide an explanation for differences in the biodistribution of Poloxamine 908 and PLA/PEG 2:5 coated polystyrene nanoparticles observed in previous studies. A comparison with the interaction enthalpy for several other PEO-containing copolymers onto the same polystyrene colloid was made. The results demonstrate the importance of the nature of the anchoring moiety on the interaction of the adsorbing copolymer with the colloid surface. An endothermic contribution is found when an adsorbing molecule contains a poly (propylene oxide) (PPO) moiety (e.g. Poloxamine 908), whilst the adsorption is exothermic (i.e. enthalpy driven) for PEO copolymers with polylactide (PLA/PEG 2:5) or alkyl moieties.
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PMID:Differences in the adsorption behaviour of poly(ethylene oxide) copolymers onto model polystyrene nanoparticles assessed by isothermal titration microcalorimetry correspond to the biological differences. 1633 70

We have achieved nearly zero order sustained release behavior for periods up to 10-20 days for two hydrophobic drugs, sulindac and tetracaine, from 5wt.% micellar solutions of poly(lactide)-poly(ethylene oxide)-poly(lactide) (PLA-PEO-PLA) triblock copolymer. The effect of PLA block length and crystallinity on the drug release profiles was studied. A series of polymers with constant PEO molecular weight of 8900Da and PLA molecular weight varying in the range of 4100-6500Da were examined. Drug release was found to be much faster for polymers with crystalline PLA blocks as compared to those with amorphous PLA blocks. The drug release rate also depends significantly on the length of the PLA block. Sustained release of sulindac was observed up to 20 days, and for tetracaine up to 10 days. By comparison, release of these drugs without polymeric carriers occurs over 4-6h. This result, along with a proposed mechanism for drug release, suggests that polymer-drug interactions significantly impact release profiles, causing slow and sustained release of the drug.
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PMID:Novel drug release profiles from micellar solutions of PLA-PEO-PLA triblock copolymers. 1650 25

Poly(p-xylylene) (PPX) was deposited by chemical vapor deposition (CVD) on stainless steel substrates. These PPX films were coated by solution casting of poly(lactide)-poly(ethylene oxide)-poly(lactide) triblock copolymers (PLA-PEO-PLA) loaded with 14C-labeled paclitaxel. Adhesion of PLA-PEO-PLA on PPX substrate coatings was measured using the blister test method. Excellent adhesion of the block copolymers on PPX substrates was found. Stress behavior and film integrity of PLA-PEO-PLA was compared to pure PLA on unexpanded and expanded stent bodies and was found to be superior for the block copolymers. The release of paclitaxel from the biodegradable coatings was studied under physiological conditions using the scintillation counter method. Burst release of paclitaxel was observed from PLA-PEO-PLA layers regardless of composition, but an increase in paclitaxel loading was observed with increasing content of PEO.
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PMID:Coating of poly(p-xylylene) by PLA-PEO-PLA triblock copolymers with excellent polymer-polymer adhesion for stent applications. 1682 74


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