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At least 937 records · Page 52Linked to original sources
PubMed2005

Preparation and characterization of intelligent core-shell nanoparticles based on poly(D,L-lactide)-g-poly(N-isopropyl acrylamide-co-methacrylic acid).

New thermo-responsive, pH-responsive, and biodegradable nanoparticles comprised of poly(D,L-lactide)-graft-poly(N-isopropyl acrylamide-co-methacrylic acid) (PLA-g-P(NIPAm-co-MAA)) were developed by grafting biodegradable poly(D,L-lactide) onto N-isopropyl acrylamide and methacrylic acid. A core-shell type nano-structure was formed with a hydrophilic outer shell and a hydrophobic inner core, which exhibited a phase transition temperature above 37 degrees C suitable for biomedical application. Upon heating above the phase transition temperature, PLA-g-P(NIPAm-co-MAA) nanoparticle showed a polarity increase of pyrene in either buffer solution or intra-hepato-carcinoma cells as determined by fluorescence measurement, indicating that the structure of nanoparticles caused leakages from outer shell copolymers aggregation and collapsed. The drug loading level of 5-fluorouracil (5-FU) encapsulated in the PLA-g-P(NIPAm-co-MAA) nanoparticles can be as high as 20%. The release of 5-FU from nanoparticles was strongly controlled by the pH in the aqueous solution. Based on these results, PLA-g-P(NIPAm-co-MAA) nanoparticles can be used as a drug carrier for intracellular delivery of anti-cancer drug.

Acrylamides↗
PubMed2000

Phase separation in the mixture of schizophyllan and poly(ethylene oxide) in aqueous solution driven by a specific interaction between the glucose side chain and poly(ethylene oxide).

We found that the mixture of schizophyllan and poly(ethylene oxide) in aqueous solution underwent phase separation at around 3-4 degrees C, and this temperature was independent of both polymer concentration and the difference in poly(ethylene oxide) molecular weight (Mw 6000 and 70,000). The phase-separation took place at the same temperature at which the optical rotation changed. Since the optical rotation change is ascribed to the difference in the nature of hydrogen bonding between the schizophyllan side chain and water, the phase separation is also considered to be due to an interaction between poly(ethylene oxide) and schizophyllan. The phase-separation temperature increased on changing H2O to D2O in accordance with a change in the optical rotation, confirming the specific interaction essential for the phase separation.

Chemical Phenomena↗
PubMed2003

Biodegradable poly(L-lactide)-poly(ethylene glycol) multiblock copolymer: synthesis and evaluation of cell affinity.

A series of poly(L-lactide)-poly(ethylene glycol) multiblock copolymers (Multi-PLE) with high molecular weight were synthesized and successfully used to fabricate three-dimensional scaffolds. Using mouse NIH 3T3 fibroblasts as model cells, the cell affinity of various Multi-PLE copolymers was evaluated and compared with that of poly(L-lactide) (PLLA) by means of cell attachment efficiency measurement, scanning electron microscopy observation and MTT assay. On one hand, the results showed that the cell attachment efficiency on Multi-PLE 4/1(4/1 refers to the molar ratio of lactidyl units to ethylene oxide units) films was close to that on PLLA film, however, the other Multi-PLE films exhibited much lower cell attachment efficiency than PLLA film, such as Multi-PLE 2/1 and Multi-PLE 1/1, which had higher PEG content. On the other hand, it was interesting to find that cell proliferation on Multi-PLE4/1 and Multi-PLE2/1 scaffolds was better than that on PLLA scaffold, which was closely related to the improved hydrophilicity of Multi-PLE copolymers due to the incorporation of PEG in comparison with pure PLLA. The Multi-PLE copolymer scaffolds with appropriate hydrophilicity were in favor of mass transportation, and then of cell proliferation and cell affinity. It meant that the cell proliferation would be much improved by increasing the hydrophilicity of the three-dimensional scaffolds, which even outweighed the disadvantages of the cell attachment efficiency reduction with the incorporation of PEG.

3T3 Cells↗
PubMed1997

Erosion of biodegradable block copolymers made of poly(D,L-lactic acid) and poly(ethylene glycol).

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.

Biocompatible Materials↗
PubMed2003

Relative aggregation state and hemolytic activity of amphotericin B encapsulated by poly(ethylene oxide)-block-poly(N-hexyl-L-aspartamide)-acyl conjugate micelles: effects of acyl chain length.

We systematically altered the chemical structure of the core-forming poly(L-amino acid) block of an amphiphilic diblock copolymer series based on poly(ethylene oxide)-block-poly(N-hexyl-L-aspartamide), PEO-b-p(N-HA), acyl esters by varying the length of the attached acyl side chain. Drug-loaded micelles were prepared in good yield by a modified solvent evaporation procedure. In addition, the relative aggregation state and hemolytic activity of encapsulated amphotericin B (AmB) were analyzed by absorption spectroscopy. The length of the attached acyl side chain in PEO-b-p(N-HA) acyl ester micelles modulates the relative aggregation state of encapsulated AmB. Furthermore, acyl chain length appears to have a profound influence on the time-dependent hemolytic profile of encapsulated AmB toward bovine erythrocytes. For all acyl conjugate micelle-AmB formulations, the onset of hemolysis is delayed relative to free AmB. Particularly in the case of stearate ester micelles, the incomplete and gradual build-up of hemolysis might reflect the sustained release of drug over a period of 24 h. Based on the corresponding absorption spectrum, we speculate that encapsulated AmB may interact strongly with stearate side chains, resulting in sustained release. Via chemical manipulation of the core-forming region, it may be possible to fine-tune the release of encapsulated AmB from PEO-b-p(N-HA)-acyl ester micelles.

Amphotericin B↗
PubMed1998

Biocompatibility testing of ABA triblock copolymers consisting of poly(L-lactic-co-glycolic acid) A blocks attached to a central poly(ethylene oxide) B block under in vitro conditions using different L929 mouse fibroblasts cell culture models.

The biocompatibility of ABA triblock copolymers consisting of poly(L-lactide-co-glycolide) A blocks attached to a central poly(ethylene oxide), (PEO), B block was investigated under in vitro conditions. The ABA triblock copolymer was compared to commercially available Poly(D,L-lactide-co-glycolide) (PLGA) and reference materials in different L929 cell culture models according to the procedure recommended by the International Standard Organization (ISO). Different preparation methods: namely extraction, indirect contact and direct contact with polymer samples were compared. The extraction method seems to be the most sensitive assay, allowing estimates of IC50 values. ABA and PLGA polymers showed excellent compatibility with L929 fibroblasts with all preparation techniques used. The influence of polymer composition and molecular weight on degradation rate as well as in vitro biocompatibility was then investigated. Changes in pH and osmolarity as well as lactic acid content of the extracts were determined and compared to in vitro degradation data of polymer films in phosphate buffered saline at 37 degreesC evaluating molecular weight (GPC) and massloss (gravimetry). An acceleration of the degradation rate of the ABA triblock copolymers with increasing PEO content was observed. The in vitro cytotoxicity studies demonstrated that the three ABA polymers were well tolerated by fibroblasts in cell culture. One ABA polymer batch ABA2 showed unusual in vitro cytotoxicity in L929 fibroblasts, possibly related to the molecular weight of the PEO used for this particular batch or residual glycolic acid. Cell culture models for biocompatibility testing of polymers according to ISO are useful as screening models in characterizing biodegradable polymers, but they cannot replace animal testing. The extraction method in combination with the MTT assay allows quantitative ranking of cytotoxic properties with high sensitivity.

Animals↗
PubMed1999

Investigation on process parameters involved in preparation of poly-DL-lactide-poly(ethylene glycol) microspheres containing Leptospira Interrogans antigens.

Block copolymer, poly-DL-lactide-poly(ethylene glycol) (PELA) with 11.5% of poly(ethylene glycol) (PEG) content was prepared by bulk ring-opening polymerization using stannous chloride as initiator. PELA microspheres with entrapped Leptospira Interrogans antigens, outer membrane protein (OMP) were elaborated by solvent extraction method based on the formation of multiple w/o/w emulsion, and the resulting microspheres were characterized with respect to particle size, OMP entrapment and morphology characteristics. The purpose of the present study is to perform the optimization of preparative parameters for OMP-loaded PELA micropsheres to control particle size and improve the OMP encapsulation efficiency. Of all the parameters investigated, the polymer concentration of organic phase and the external aqueous phase volume play major roles on particle size, while the organic phase volume, internal aqueous phase volume and the addition of surfactant into the internal aqueous phase display considerable effects on OMP loading efficiency. A small volume of internal aqueous phase and intermediate volumes of organic phase and external aqueous phase were favorable to achieve micropsheres with a size of 1-2 microns and high antigen encapsulation efficiency (70-80%). In vitro OMP release profiles from PELA microspheres consist of a small burst release followed by a gradual release phase. The OMP release rate shows some relations with the porous and water-swollen inner structure of the microspheres matrix. The presence of surfactant in microspheres accelerates OMP release, but the OMP entrapment within microspheres shows limited effects on the release profile.

Antigens, Bacterial↗
PubMed2001

The effect of alkyl core structure on micellar properties of poly(ethylene oxide)-block-poly(L-aspartamide) derivatives.

Block copolymers based on fatty acid esters of poly(ethylene oxide)-block-poly(hydroxy alkyl L-aspartamide) were prepared and characterized by 1H-NMR. The structure of the core-forming block was changed through application of different lengths of the poly(L-aspartamide) (PLAA) block, spacer group or fatty acid and varying the substitution level of the side chain on the polymeric backbone. Transmission electron microscopy and fluorescent probe studies provided evidence for the formation of supramolecular core/shell architectures with nanoscopic dimensions. The same techniques were used to study the effect of hydrophobic block structure on micellar size, critical micelle concentration (CMC), core polarity and viscosity of the polymeric micelles. Among the structural factors studied, it was revealed that the length of the PLAA block and the level of fatty acid attached to the polymeric backbone are the major factors affecting micellar properties. An increase in micellar size and reduction in CMC were observed when the level of fatty acid attachment to the polymeric backbone was raised. The elongation of the PLAA block, on the other hand, resulted in an increase in micellar size and core viscosity. Micellar size was the only characteristic being affected by the length of the attached fatty acid. However, a decrease in microviscosity was revealed when behenic acid (22 carbons) was attached to the core-forming block in a high level of substitution. The length of spacer group was also found to be a useful means by which the level of side chain attachment could be controlled. Chemical tailoring of the core structure in polymeric micelles may be used as an efficient means to change micellar properties. As a result, nanoscopic, spherical and stable micelles with improved core properties may be achieved to insure efficient loading and controlled release of an individual drug from the delivery system.

Journal Article↗
PubMed2006

Grafting of poly(ethylene glycol) onto poly(acrylic acid)-coated glass for a protein-resistant surface.

The surface of solid glass supports for samples in optical microscopy and for biosensors needs to be protein-resistant. A coating of a poly(ethylene glycol) monomethyl ether (mPEG) on the surface of the glass is one promising method for preventing the nonspecific adsorption of proteins. In this study, we have developed a novel technique for achieving an optimal coverage of a glass surface with mPEG to prevent protein adhesion. A clean glass substrate previously treated with (3-aminopropyl)dimethylethoxysilane (APDMES) was treated sequentially with poly(acrylic acid) and subsequently a primary amine derivative of mPEG in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. The resultant glass surface was demonstrated to be highly protein-resistant, and the adsorption of bovine serum albumin decreased to only a few percentage points of that on a glass surface treated with APDMES alone. Furthermore, to extend the present method, we also prepared a glass substrate on which biotinylated poly(ethylene glycol) was cografted with mPEG, and biotinylated myosin subfragment-1 (biotin-S1) was subsequently immobilized on this substrate by biotin/avidin chemistry. Actin filaments were observed to glide on the biotin-S1-coated glass surface in the presence of ATP, and thus, the method is capable of immobilizing the protein specifically without any loss in its biological function.

Acrylic Resins↗
PubMed2000

Phosphorescent oxygen sensors utilizing sulfur-nitrogen-phosphorous polymer matrixes: synthesis, characterization, and evaluation of poly(thionylphosphazene)-b-poly(tetrahydrofuran) block copolymers

We examine the use of thionylphosphazene-based block copolymers as matrixes for oxygen sensor applications. Poly(aminothionylphosphazene)-b-poly(tetrahydrofuran) (PATPy-PTHFx) block copolymers were prepared via reaction of ring-opened poly(chlorothionylphosphazene) with THF and subsequently with excess n-butylamine (to form PBATPy-PTHFx) or methylamine (to form PMATPy-PTHFx). The block copolymers were characterized by NMR, gel permeation chromatography, and differential scanning calorimetry. Films of PBATPy-PTHFx block copolymers containing platinum octaethylporphyrin or [Ru(dpp)3]Cl2 (dpp = 4,7-diphenyl-1,10-phenanthroline) as the oxygen-sensitive chromophore were prepared, and time-scan experiments were carried out to determine the diffusion coefficients, Do2, and solubilities, So2, of oxygen therein. Despite microphase separation, the data fit well to a simple Fick's law description of oxygen diffusion and gave Do2 values smaller than that for the n-butylamino-substituted PBATP635. For films freshly annealed above the melting point of PTHFx, the Do2 values were 35-50% (dye-dependent) larger than after aging 3 days at room temperature. Films with [Ru(dpp)3]Cl2 as the dye were evaluated as media for phosphorescent pressure-sensing. The dye-containing polymer films exhibit linear Stern-Volmer-like plots, even at high dye concentrations, as well as good photostability, and significantly higher sensitivity to oxygen quenching than simple mixtures of the analogous homopolymers.

Journal Article↗
PubMedDate not supplied

Self-assembling nanocomplexes from insulin and water-soluble branched polyesters, poly[(vinyl-3-(diethylamino)- propylcarbamate-co-(vinyl acetate)-co-(vinyl alcohol)]-graft- poly(L-lactic acid): a novel carrier for transmucosal delivery of peptides.

The design of carriers for protein delivery that provide protection against enzymatic degradation and facilitate protein transport across epithelial surfaces, thus avoiding parenteral administration, remains a challenge. Self-assembling nanoscale protein/polymer complexes might present a promising approach. We synthesized water-soluble, amphiphilic polyesters, poly[(vinyl-3-(diethylamino)-propylcarbamate-co-(vinyl acetate)-co-(vinyl alcohol)]-graft-poly(L-lactic acid), containing a positively charged backbone, and studied the spontaneous formation of nanocomplexes (NC) with insulin. NC were characterized using dynamic light scattering, zeta-potential measurements, and atomic force microscopy (AFM). Insulin loading was determined with HPLC, and the binding constants were obtained by isothermal titration calorimetry (ITC). The NC formation was followed using nephelometric and light scattering techniques. Water-soluble, positively charged, branched polyesters with amphiphilic properties were obtained in a three-step polymer-analogous reaction. The degree of amine substitution, DS, in the PVAL backbone was varied between 0.04 and 0.5, and grafting this backbone with L-lactide increased the molecular weight from 18 kDa to 81 kDa. The polymer composition was optimized to facilitate NC formation with insulin resulting in a DS of 0.09 and a poly(L-lactide) side chain substitution of 0.5 with an average chain length of two lactic acids. Depending on polymer composition, stable NC of 200-500 nm diameter were formed with insulin, and the binding constants ranged from 4.7 x 10(5) to 9.5 x 10(6) M(-1). Positively charged surface charges ranging from +5 to +35mV and an insulin loading up to 98% of 33 IU/mL were obtained. The NC visualized by AFM revealed spheroidal particles with an entangled internal structure. It was demonstrated that this class of multifunctional polymers is capable of self-assembly with a peptidic substrate. The resulting nanosized complexes offer the potential for mucosal insulin/protein delivery and merit further investigations under in vivo conditions.

Biological Transport↗
PubMedDate not supplied

Polycationic block copolymers of poly(ethylene oxide) and poly(propylene oxide) for cell transfection.

A facile, one-step synthesis of cationic block copolymers of poly(2-N-(dimethylaminoethyl) methacrylate) (pDMAEMA) and copolymers of poly(propylene oxide) (PPO) and poly(ethylene oxide) (PEO) has been developed. The PEO-PPO-PEO-pDMAEMA (L92-pDMAEMA) and PEO-pDMAEMA copolymers were obtained via free radical polymerization of DMAEMA initiated by polyether radicals generated by cerium(IV). Over 95% of the copolymer fraction was of molecular mass ranging from 6.9 to 7.1 kDa in size, indicating the prevalence of the polyether-monoradical initiation mechanism. The L92-pDMAEMA copolymers possess parent surfactant-like surface activity. In contrast, the PEO-pDMAEMA copolymers lack significant surface activity. Both copolymers can complex with DNA. Hydrodynamic radii of the complexes of the L92-pDMAEMA and PEO-pDMAEMA with plasmid DNA ranged in size from 60 to 400 nm, depending on the copolymer/DNA ratio. Addition of Pluronic P123 to the L92-pDMAEMA complexes with DNA masked charges and decreased the tendency of the complex to aggregate, even at stoichiometric polycation/DNA ratios. The transfection efficiency of the L92-pDMAEMA copolymer was by far greater than that of the PEO-pDMAEMA copolymer. An extra added Pluronic P123 further increased the transfecton efficacy of L92-pDMAEMA, but did not affect that of PEO-pDMAEMA.

Animals↗
PubMedDate not supplied

An adduct of cis-diamminedichloroplatinum(II) and poly(ethylene glycol)poly(L-lysine)-succinate: synthesis and cytotoxic properties.

A noncovalent adduct of the antineoplastic drug cis-diamminedichloroplatinum (cDDP) and a biocompatible graft copolymer of poly(L-lysine) and methylpoly(ethylene glycol) succinate is described. Upon incubation of cDDP with [O-methylpoly(ethylene glycol)-O'-succinyl]-N- epsilon-poly(L-lysine)n-N-epsilon-succinate, n = 250-270, highly soluble, long circulating adducts were formed which contained 4.3% of platinum by weight. Approximately 60% of the polymer-associated drug was released during dialysis against saline or serum albumin containing saline, with a half-time of release of 63 h. The adducts showed a pronounced antineoplastic effect in BT-20 human adenocarcinoma cell cultures. In cell proliferation assays, the concentration of half-inhibition of [3H]thymidine uptake was 0.9 +/- 0.2 microM for the drug-copolymer adduct compared to 0.3 +/- 0.1 microM for free cDDP. The adduct showed a long blood half-life (ca. 14 h in rats) and accumulated in experimental mammary adenocarcinomas at 2.5-3.5% injected dose per gram of tissue. A control adduct of cDDP with the backbone portion of the copolymer, poly(L-lysine)-N-epsilon-succinate, had a short half-life in the bloodstream (ca. 30 min) and low accumulation (0.5% injected dose per gram) in tumor. A dual therapeutical effect of methylpoly(ethylene glycol)succinylpoly(L-lysine)-succinate as a carrier of cDDP is suggested: (1) as a carrier for systemic release of the active drug from the macromolecule while it circulates in the bloodstream and (2) as a carrier for on-site delivery which results from the release of the drug in the tumor as a consequence of accumulation of the copolymer in the tumor.

Adenocarcinoma↗
PubMedDate not supplied

Study of blood compatibility with poly(2-methoxyethyl acrylate). Relationship between water structure and platelet compatibility in poly(2-methoxyethylacrylate-co-2-hydroxyethylmethacrylate).

Previously, we reported that poly(2-methoxyethylacrylate) (PMEA) showed excellent blood compatibility and implied that the water structure in PMEA contributed to the blood compatibility. In this study, the relationship between the water structure and the blood compatibility is clarified by studying the influence of the monomer composition of poly(MEA-co-HEMA) on the water structure and the blood compatibility of the copolymers. The water in the polymer was classified into three types: free water, freezing bound water, and nonfreezing water. The polymers with 0-30 mol % of HEMA content had a significant amount of freezing bound water, and the amount decreases greatly when the composition of HEMA exceeded 30 mol %. On the other hand, the amount of other water increased simply with an increase of HEMA content. The evaluation of the platelet compatibility of poly(MEA-co-HEMA) revealed that the adhesion number and the morphological change of platelet on the copolymer surface were least when the HEMA content was 0-20 mol %. These two results strongly suggest that the freezing bound water relates to the platelet compatibility of the polymers.

Acrylates↗
PubMedDate not supplied

Synthesis and self-association behavior of biodegradable amphiphilic poly[bis(ethyl glycinat-N-yl)phosphazene]- poly(ethylene oxide) block copolymers.

Amphiphilic diblock copolymers with varying compositions of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly[bis(ethyl glycinat-N-yl)phosphazene] (PNgly) were synthesized via the controlled cationic-induced polymerization of a phosphoranimine (Cl(3)P=NSiMe(3)) at ambient temperature using a PEO-phosphoranimine macroinitiator. The aqueous-phase transition behavior of PEO-PNgly-3 (M(n) = 10,000) and micelle formation of both PEO-PNgly-3 and PEO-PNgly-4 (M(n) = 8,500) were investigated using fluorescence techniques and dynamic light scattering. The critical micelle concentrations (cmc's) of PEO-PNgly-3 and PEO-PNgly-4 were determined to be 3 and 12 mg/L with the mean diameters of micelles being 120 and 130 nm, respectively. The hydrolytic degradation of these diblock copolymers was also studied in solution. These studies coupled with the biodegradability of the poly[bis(ethyl glycinat-N-yl)phosphazene] block to give benign products make PEO-PNgly copolymers well-suited for a wide variety of biomedical applications including novel biodegradable drug-delivery systems.

Biocompatible Materials↗
PubMedDate not supplied

Morphology control in co-continuous poly(L-lactide)/polystyrene blends: a route towards highly structured and interconnected porosity in poly(L-lactide) materials.

Poly(L-lactide) is a biodegradable polymer primarily used in biomedical applications. In this paper, both the microstructure and the region of dual-phase continuity are examined for binary and compatibilized poly(L-lactide)/polystyrene blends (PLLA/PS) prepared by melt mixing. The blends are shown to be completely immiscible with an interfacial tension of 6.1 mN/m. The PS-b-PLLA (24,000-b-28,000) diblock copolymer compatibilizer has an asymmetric effect on the blend. It is effective at compatibilizing 50/50 PLLA/PS blends but is only a marginal emulsifier for blends where PLLA is the dominant matrix. Percent continuity, as estimated by solvent extraction/gravimetry and also torque/composition diagrams clearly indicate an onset of the region of dual-phase continuity at 40-45%PS. It is demonstrated that highly percolated blends of the above materials exist from 40 to 75% PS and 40 to 60% PS for the binary and compatibilized blends, respectively. The scale of the microstructure of the continuous morphology is measured using BET and mercury intrusion porosimetry techniques, after extraction of the PS phase. Both the pore size and extent of continuity can be controlled through composition and interfacial modification. Static annealing of the blend after melt mixing can also be used to substantially increase the pore size of the system. Extraction of the PS phase in the blend, carried out after the above preparation protocols, is a route to generating completely interconnected porosity of highly controlled morphologies (pore size, void volume) in poly(L-lactide) materials. In this study, the pore diameter was controlled from 0.9 to 72 microm for a constant void volume of 45-47%, and the void volume was modified from 35 to 74% depending on the blend composition.

Biocompatible Materials↗
PubMedDate not supplied

Lipase-catalyzed transformation of poly(butylene adipate) and poly(butylene succinate) into repolymerizable cyclic oligomers.

The enzymatic degradation and repolymerization were carried out with the objectives of developing the chemical recycling of aliphatic polyester-type plastics, such as the poly(butylene adipate) (PBA), poly(butylene succinate), and poly(butylene adipate-co-succinate) copolymers which are typical biodegradable plastics. They were degraded by lipase in an organic solvent solution containing a small amount of water to produce cyclic oligomers mainly consisting of the cyclic diester. The produced cyclic oligomer was readily repolymerized by lipase to produce a polyester having an equal or higher molecular weight compared to the parent polymer. As an example, PBA having an Mw of 22,000 was almost quantitatively transformed by lipase CA (Novozym 435) in water-containing toluene at 50 degrees C into the corresponding cyclic oligomers mainly consisting of dimers. Thus, the obtained oligomers were readily polymerized by lipase CA to produce the PBA with an Mw of 52,000.

Adipates↗
PubMedDate not supplied

New amphiphilic poly(2-ethyl-2-oxazoline)/ poly(L-lactide) triblock copolymers.

A new series of cationic, thermo-sensitive, and biodegradable poly(L-lactide)-poly(2-ethyl-2-oxazoline)-poly(L-lactide) (PLLA-PEOz-PLLA) triblock copolymers were synthesized by ring-opening polymerization. With increasing molecular weight and crystallinity of hydrophobic PLLA blocks, the critical micellization concentrations (CMC) occurred at lower concentration. The PLLA-PEOz-PLLA aqueous solution was transparent at room temperature. Heating the solution resulted in precipitations, which were caused by the combination of dehydration of water around PEOz and the aggregations of PLLA segments. Acid/base titration profiles indicated that PLLA-PEOz-PLLA were protonated at neutral and acidic conditions. Considerable buffering capacity was found over the entire pH range. The specific PLLA-PEOz-PLLA triblock copolymers with thermal- and pH-sensitive properties can be tailored by varying the compositions and can be applied as controlled release carries for biomedical applications.

Biocompatible Materials↗