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At least 667 records · Page 37Linked to original sources
PubMed2006

Finalizing the properties of porous scaffolds of aliphatic polyesters through radiation sterilization.

Porous scaffolds made of various L,L-lactide (LLA), 1,5-dioxepane-2-one (DXO) and epsilon-caprolactone (CL) copolymers were sterilized by EB- and gamma-irradiation. Differences in the comonomers, composition and the microstructure of the starting materials were used to influence the degradation mechanism and susceptibility towards irradiation and by this means to achieve sterilized scaffolds with predicted end-properties. The chemical changes and the formation of low-molecular-weight products were determined by SEC, 1H nuclear magnetic resonance (NMR), 13C NMR and gas chromatography-mass spectrometry (GC-MS). The degradation mechanism changed from random chain scission to cross-linking depending on the choice of monomers, the copolymer composition and the monomer sequences. Copolymerization of LLA with small amounts of CL or DXO increased the stability compared to that of the LLA homopolymer. Changing DXO to CL in a LLA copolymer also increased the stability. The type of radiation and the microstructure of the copolymer chains determined which of the monomer sequences were more prone to degrade. The most abundant low-molecular-weight product identified after sterilization was DXO monomer. Traces of LLA and CL monomers were also identified. Modification of the copolyester microstructure changed the degradation mechanism and the susceptibility towards irradiation. This allows the use of radiation sterilization to finalize the scaffold properties.

Biocompatible Materials↗
PubMed2004

Influence of the co-encapsulation of different excipients on the properties of polyester microparticle-based vaccine against brucellosis.

This work evaluates the influence of different pharmaceutical auxiliaries (Pluronic F68, polyvinylpyrrolidone [PVP] or Tween 20), when mixed with an antigenic extract from Brucella ovis (hot saline; HS), on the characteristics of the resulting poly(epsilon-caprolactone) (PEC) and poly(lactide-co-glycolide) (PLGA) microparticles. In all cases, PEC microparticles were smaller than PLGA ones. Concerning the HS loading, PLGA microparticles were highly dependent on the type of the excipient used, whereas all the PEC formulations displayed similar encapsulation efficiencies. For both types of microparticles, the presence of PVP induced a burst release effect. On the contrary, the use of Tween 20 or Pluronic F68 dramatically modified this profile. For PLGA-Tween 20 and PEC-Pluronic F68 microparticles, the HS was released in a pulsatil way during the first 7 days followed by a continuous release for at least 3 weeks. The antigenicity of the HS components was kept in all cases. Phagocytosis by murine monocytes showed a clear difference based just on the hydrophobicity of the polymer, being PEC microparticles better engulfed. Cell activation quantified by the release of H2O2 did not showed major differences between batches, however, microparticles of PEC and Pluronic F68 induced the highest nitric oxide production. Together, these results confirm the advantageous qualities of the "HS-PEC-Pluronic F68 microparticles" as favorable candidate for vaccine purposes against brucellosis.

Animals↗
PubMed2004

Sustained delivery and expression of plasmid DNA based on biodegradable polyester, poly(D,L-lactide-co-4-hydroxy-L-proline).

Gene expression mediated by a non-viral vector usually lasts only a few days. The objective of this study was to synthesize and characterize a non-toxic, polymeric gene carrier, poly(D,L-lactide-co-4-hydroxy-L-proline) (PLHP) for sustained gene delivery. The copolymer was synthesized by ring-opening polymerization of D,L-lactide (DLLA) with N-cbz-4-hydroxy-L-proline (HP) in the presence of stannous octoate (Sn(Oct)(2)). The resulting copolymer was characterized by (1)H nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC). Degradation of PLHP was examined by monitoring the medium pH change and molecular weight (MW) of the remaining polymer. It showed a rapid initial degradation and followed by a slower degradation for about 30 days at 37 degrees C. The cytotoxicity of copolymer was significantly lower than polyethylenimine (PEI) and poly-L-lysine hydrochloride (PLL) by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The plasmid DNA (pDNA)-loaded microspheres based on the copolymer were prepared by a water-oil-water (w/o/w) solvent evaporation emulsion method. The release profile of pDNA from PLHP microspheres showed an initial burst release, and then a slower and continuous release for about 18 days at 37 degrees C. Gene transfer efficiency of PLHP/pDNA delivery system showed a sustained activity (over a week) when compared with PEI and PLL, and can be further improved by the addition of cationic liposomes. The results suggest that PLHP is a promising candidate for long-term gene delivery with good biocompatibility and biodegradability.

Cell Survival↗
PubMed2005

Apoplastic polyesters in Arabidopsis surface tissues--a typical suberin and a particular cutin.

Cutinized and suberized cell walls form physiological important plant-environment interfaces as they act as barriers limiting water and nutrient loss and protect from radiation and invasion by pathogens. Due to the lack of protocols for the isolation and analysis of cutin and suberin in Arabidopsis, the model plant for molecular biology, mutants and transgenic plants with a defined altered cutin or suberin composition are unavailable, causing that structure and function of these apoplastic barriers are still poorly understood. Transmission electron microscopy (TEM) revealed that Arabidopsis leaf cuticle thickness ranges from only 22 nm in leaf blades to 45 nm on petioles, causing the difficulty in cuticular membrane isolation. We report the use of polysaccharide hydrolases to isolate Arabidopsis cuticular membranes, suitable for depolymerization and subsequent compositional analysis. Although cutin characteristic omega-hydroxy acids (7%) and mid-chain hydroxylated fatty acids (8%) were detected, the discovery of alpha,omega-diacids (40%) and 2-hydroxy acids (14%) as major depolymerization products reveals a so far novel monomer composition in Arabidopsis cutin, but with chemical analogy to root suberin. Histochemical and TEM analysis revealed that suberin depositions were localized to the cell walls in the endodermis of primary roots and the periderm of mature roots of Arabidopsis. Enzyme digested and solvent extracted root cell walls when subjected to suberin depolymerization conditions released omega-hydroxy acids (43%) and alpha,omega-diacids (24%) as major components together with carboxylic acids (9%), alcohols (6%) and 2-hydroxyacids (0.1%). This similarity to suberin of other species indicates that Arabidopsis roots can serve as a model for suberized tissue in general.

Arabidopsis↗
PubMedDate not supplied

Use of polyester leukocyte elimination filters in blood filterability research.

We tested a new routine to eliminate leukocytes for blood rheology measurements using commercial leukocyte absorbing filters (here PALL RC400). These filters were punched out and fitted in smaller chambers through which blood was filtered under controlled suction pressure (< 30 mm Hg). This technique resulted in a very effective leukocyte elimination to 0.0022% but also a platelet reduction to 0.2%. The process causes a small but significant hemolysis with free hemoglobin, of the order of 0.06% of the filtered erythrocytes. A small fraction of the erythrocytes were retained in the filter, versus plasma, to reduce the hematocrit on the order of 1.4%. The leukocyte filtration did not cause any detectable functional trauma to the erythrocytes, measured as micro-pore filterability of normal and glutaraldehyde (GA) hardened erythrocytes. However, when 10% of the erythrocytes were hardened with GA, which caused an increase in pore clogging slope (p < 0.05), the additional passage through the leukocyte elimination filter removed this measured change in clogging. This observation suggests that the leukocyte elimination filter may selectively remove, not only leukocytes and platelets, but also hardened erythrocytes. Reticulocyte counting did not reveal any selective removal of young erythrocytes. In general, we find the presented method reproducible, efficient and easy for eliminating leukocytes for blood rheology research although the risk of removing undeformable erythrocytes must be considered.

Adult↗
PubMed2001

Blends of aliphatic polyesters. VI. Lipase-catalyzed hydrolysis and visualized phase structure of biodegradable blends from poly(epsilon-caprolactone) and poly(L-lactide).

Phase-separated biodegradable polymer blends were prepared from poly(epsilon-caprolactone) (PCL) and poly(L-lactide) (PLLA), and Rhizopus arrhizus lipase-catalyzed hydrolysis and phase structure of the blend films were investigated. Gravimetry revealed that the lipase-catalyzed hydrolysis of PCL in PCL- and PLLA-rich phases is disturbed by the presence of PLLA. Polarimetry confirmed the occurrence of a predominant hydrolysis of PCL and subsequent removal of the hydrolyzed water-soluble PCL oligomers in the blend films. Gravimetry and gel permeation chromatography of the non-blended PLLA film indicated that R. arrhizus lipase has no catalytic effect on the hydrolysis of PLLA. The phase structure of the blend films could be visualized by selective enzymatic removal of one component and subsequent scanning electron microscopic observation.

Biocompatible Materials↗
PubMed2003

Carbonated calcium phosphates are suitable pH-stabilising fillers for biodegradable polyesters.

Carbonated amorphous calcium phosphates were prepared with different carbonate content. Their ability to neutralise acidity was probed by time-resolved titration experiments with lactic acid, the monomer that results from degradation of polylactide. The results show that although calcium phosphate as such can reduce acidity, their buffering range lies at a pH of about 4, i.e. outside the physiological range. This is not related to the rate of dissolution. Carbonated calcium phosphates as well as calcium carbonate (calcite) alone are able to keep the pH around 7.4. Consequently, carbonated calcium phosphates are suitable basic filler materials as they are able to compensate acidity, and to buffer within the physiological pH-range.

Biocompatible Materials↗