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At least 811 records · Page 45Linked to original sources
PubMed1985

The crystal structure of d(G-G-G-G-C-C-C-C). A model for poly(dG).poly(dC).

The structure of the DNA oligomer d(G-G-G-G-C-C-C-C) has been determined at a resolution of 2.5 A by single-crystal X-ray methods. There are two strands in the asymmetric unit, and these coil about each other to form a right-handed double-helix of the A-type with Watson-Crick hydrogen bonds between base-pairs. The helix has a shallow minor groove and a deep, water-filled major groove; almost all exposed functional groups on the DNA are hydrated, and 106 ordered solvent molecules have been found. The two d(G-G-G-G).d(C-C-C-C) segments in the octamer exhibit similar and uniform structures, but there is a slight discontinuity at the GpC step between them. A recurring feature of the structure is the overlap of adjacent guanine bases in each GpG step, with the five-membered ring of one guanine stacking on the six-membered ring of its neighbour. There is little or no overlap between adjacent cytosine rings. Conformational parameters for these GpG steps are compared with those from other single-crystal X-ray analyses. In general, GpG steps exhibit high slide, low roll and variable twist. Models for poly(dG).poly(dC) were generated by applying a simple rotation and translation to each of the unmodified d(G-G-G-G).d(C-C-C-C) units. Detailed features of these models are shown to be compatible with various assays of poly(dG).poly(dC) in solution, and are useful in understanding the polymorphic behaviour of this sequence under a variety of experimental conditions.

Chemical Phenomena↗
PubMed1995

Synthesis and properties of novel block copolymers containing poly(lactic-glycolic acid) and poly(ethyleneglycol) segments.

A synthetic process for obtaining high-molecular-weight block copolymers containing poly(lactic-glycolic acid) and poly(ethylene glycol) segments has been established. This process involves the reaction of poly(ethylene glycols) with phosgene, followed by polycondensation of the resulting alpha, omega-bis(chloroformates) with poly(lactic-glycolic acid) oligomers. The copolymers have been characterized for their molecular weight, solubility properties, water absorption and preliminarily thermal behaviour. All evidence points to the conclusion that the process described is a general one, enabling biodegradable polymers to be obtained tailor-made according to specific requirements.

Biocompatible Materials↗
PubMed1993

Spectrophotometric and kinetic studies of the binding of Ni2+, Co2+, and Mg2+ to poly(dG-dC).poly(dG-dC). Determination of the stoichiometry of the Ni2+-induced B--->Z transition.

Data are reported for the binding of Ni2+, Co2+, and Mg2+ to the B-form of double-stranded poly(dG-dC) at ionic strength conditions I = 0.001 M, 0.01 M, and 0.1 M. The apparent binding constants for Ni2+ and Co2+ are about the same and are 2- to 3-fold higher than those for Mg2+. Kinetic studies indicate that Mg2+ binds to the polynucleotide mainly (or solely) as a mobile cloud (electrostatically, outer-sphere), whereas the transition metal ions undergo site binding (inner-sphere coordination) with poly(dG-dC). The kinetic data suggest that an Ni2+ ion coordinates to more than one binding site at the polynucleotide, presumably to G-N7 and a phosphate group. At low ionic strength conditions the addition of Ni2+ induces a B-->Z conformational transition in poly(dG-dC). As demonstrated by UV absorption and DC spectroscopy, the transition occurs at I = 0.001 M already when 3 x 10(-5) - 7 x 10(-5) M of Ni2+ are added to 8 x 10(-5) M (in monomeric units) of poly(dG-dC), and at I = 0.01 M between 2.5 x 10(-4) M and 4.5 x 10(-4) M of Ni2+. Using murexide as an indicator of the concentration of free Ni2+ ions, the amount of Ni2+ which is bound to the polynucleotide could be determined. At I = 0.001 M it was established that the B-->Z transition begins when 1 Ni2+ is bound coordinatively per four base pairs, and the transition is complete when 1 Ni2+ is bound coordinatively per three base pairs. It is this coordinated Ni2+ which induces the B-->Z transition.

Binding Sites↗
PubMed1990

Acid-sensitive dissociation between poly(lysine) and histamine-modified poly(glutamate) as a model for drug-releasing from carriers in endosomes.

Histamine was coupled to poly(L-glutamate) (PLG) to give a copolymer, poly(glutamylhistamineglutamate) (PHG), with approx. 40% of carboxyl groups in PLG being modified. Unlike either poly(L-histidine) (PLH) or PLG, PHG precipitated only in buffers with pH between 4 and 5. A complex was formed between PHG and poly(L-lysine) (PLL) at pH 7, but it was rapidly dissociated at pH 5 or lower. When PHG-linked transferrin (Tf-PHG) was used to deliver a PLL-conjugated [3H]methotrexate ([3H]MTX-PLL) in K562 leukemia cell cultures, an intracellular accumulation of the radioactivity was observed. These results suggest that a copolymer with both imidazole and carboxyl groups can be useful in the design of acid-sensitive, carrier-mediated drug delivery systems.

Cells, Cultured↗
PubMed1995

Polyamine-mediated conformational perturbations in DNA alter the binding of estrogen receptor to poly(dG-m5dC).poly(dG-m5dC) and a plasmid containing the estrogen response element.

The binding estrogen receptor (ER) to the upstream regions of estrogen-responsive genes, the estrogen response elements (ERE), is of fundamental importance in the regulation of gene expression by estradiol. Multiple cell-specific factors affect ER-ERE binding and modulate the responses of estradiol. We studied the role of polyamines in the recognition of ER, a ligand-activated transcription factor, with a left-handed Z-DNA forming polynucleotide as well as with a plasmid containing ERE. Polyamines are cellular organic cations with multiple functions in cell growth and differentiation. Polyamines induce Z-DNA conformation in alternating purine-pyrimidine sequences. To understand the role of polyamine-induced DNA conformational transition in ER-DNA interaction, we studied the binding of partially purified rabbit uterine ER to poly(dG-m5dC).poly(dG-m5dC). The induction of Z-DNA in the polynucleotide was monitored by circular dichroism and ultraviolet spectroscopic measurements. Binding of ER to poly(dG-m5dC).poly(dG-m5dC) increased from 15% to approx. 50-60% in the presence of 7.5 mM putrescine, 0.5 mM spermidine or 0.25 mM spermine. Maximal binding of ER to the polynucleotide was observed near the midpoint of the B-DNA to Z-DNA transition of the polynucleotide. N1-acetyl spermidine and N1-acetyl spermine facilitated the B-DNA to Z-DNA transition and the binding of ER although they were less effective than the unacetylated analog. Co(NH3)6(3+), a trivalent inorganic cation, also provoked the B-DNA to Z-DNA transition of the polynucleotide and increased its binding to ER. At higher polyamine concentrations, there was an inhibition of ER binding to the polynucleotide. In the presence of polyamines, the binding of ER to a plasmid containing ERE was 2-3-fold higher than that to a control plasmid devoid of ERE. Polyamine-induced facilitation of ER-ERE binding was also confirmed by gel mobility shift assay. Our data indicate that conformational perturbations, similar to that of the early stages of B-DNA to Z-DNA transition, are important in the recognition of ER and ERE.

Animals↗
PubMed2005

Incorporation and in vitro release of doxorubicin in thermally sensitive micelles made from poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide)-b-poly(D,L-lactide-co-glycolide) with varying compositions.

Thermally sensitive block copolymers, poly(N-isopropylacrylamide-co-N, N-dimethylacrylamide)-b-poly(d,l-lactide-co-glycolide) [P(NIPAAm-co-DMAAm)-b-poly(D,L-lactide-co-glycolide) (PLGA)] with different compositions and lengths of PLGA block are synthesized and utilized to fabricate micelles containing doxorubicin (DOX), a model anticancer drug, by a membrane dialysis method for targeted anticancer drug delivery. The critical association concentration (CAC) of the polymers ranges from 4.0 to 25.0 mg/L. An increased length of core-forming block PLGA leads to a decrease in the CAC. The clearly defined core-shell structure of micelles is proved by 1H-NMR analyses of the micelles in CDCl3 and D2O. The morphology of the micelles is analyzed by transmission electron microscopy, showing a spherical structure of both blank and drug-loaded micelles. The results obtained from dynamic light scattering show that the blank and drug-loaded micelles have an average size below 200 nm. The lower critical solution temperature (LCST) of the micelles made from the various polymers is similar, around 39 degrees C in phophate-buffered solution (PBS). The presence of serum in PBS does not alter the LCST significantly. The drug loading capacity varies depending on the PLGA block. The polymers are degradable, and the degradation of PLGA-based polymers is faster than that of poly(lactide) (PLA)-based polymer. The DOX-loaded micelles are stable in PBS containing serum at 37 degrees C but deform at 39.5 degrees C above the normal body temperature, thus triggering DOX release. It is revealed by confocal laser scanning microscopy that free DOX molecules enter cell nuclei very fast and DOX-loaded micelles accumulate mostly in cytoplasm after endocytosis. At a temperature above the LCST, more DOX molecules release from the micelles and enter the nuclei as compared to the temperature below the LCST. DOX-loaded micelles show greater cytotoxicity at a temperature above the LCST. The P(NIPAAm-co-DMAAm)-b-PLGA micelles developed may be a good carrier for anticancer drug delivery.

Acrylamides↗
PubMed2005

Synthesis and characterizations of biodegradable and crosslinkable poly(epsilon-caprolactone fumarate), poly(ethylene glycol fumarate), and their amphiphilic copolymer.

A series of self-crosslinkable and biodegradable polymers, poly(caprolactone fumarate) (PCLF), poly(ethylene glycol fumarate) (PEGF), and their copolymer PEGF-co-PCLF, has been developed for tissue engineering applications using a novel synthesis method. The current method employs potassium carbonate (K2CO3), other than the previously reported triethylamine, as the proton scavenger. The new synthetic route is more convenient and less time-consuming to carry out, and the synthesized polymers have a much lighter color, which renders them more suitable for self-crosslinking via photo-initiation. This group of polymers are essentially copolymers of fumaryl chloride, which contains double bonds for in situ crosslinking, with poly(epsilon-caprolactone) (PCL) or/and poly(ethylene glycol) (PEG) that has a flexible chain to facilitate self-crosslinking. Both PCLF and PEGF, and their amphiphilic copolymer PEGF-co-PCLF could be self-crosslinked or photocrosslinked to produce scaffolds without the use of a crosslinking agent. Our results suggest that these polymers are potentially useful as injectable, self-crosslinkable, and photo-crosslinkable materials for diverse tissue engineering applications.

Biocompatible Materials↗
PubMed2004

Albumin loaded microsphere of amphiphilic poly(ethylene glycol)/ poly(alpha-ester) multiblock copolymer.

The purpose of this study is to investigate the microspheres (MS) based on (AB)(n) type amphiphilic multiblock copolymers for sustained and complete release of a model protein, bovine serum albumin (BSA). The MS were prepared by a modified water-in-oil-in-water (W/O/W) double emulsion method using amphiphilic multiblock copolymers consisting of poly(ethylene glycol) (PEG) and a poly(alpha-ester), poly(epsilon-caprolactone) (PCL) or poly(l-lactic acid) (PLLA). The size of MS and encapsulation efficiency of BSA within MS were not noticeably influenced by the copolymer composition used in this experiment. While BSA was completely released from PEG/PLLA MS through matrix erosion and the diffusion of BSA, it was released only to an extent of 60% from PEG/PCL MS solely through the diffusion process. However, the release of BSA from PEG/PCL MS dramatically increased and then reached 100% release in 10 days after thermal treatment of the MS at 50 degrees C for 30 min in the middle of release test (on day 15).

Delayed-Action Preparations↗
PubMed2005

Enhancement of oral bioavailability of poorly water-soluble drugs by poly(ethylene glycol)-block-poly(alkyl acrylate-co-methacrylic acid) self-assemblies.

The purpose of the present study was to determine whether pH-sensitive polymeric micelles could improve the oral bioavailability of a poorly water-soluble drug. Poly(ethylene glycol)-block-poly(alkyl acrylate-co-methacrylic acid)s were synthesized by atom transfer radical polymerization and the composition of the ionizable polymer block was varied to maximize drug loading and pH-dependent release. Poorly water-soluble model drugs viz. fenofibrate (FNB) and progesterone (PRG) were incorporated in the self-assemblies by the oil-in-water emulsion or film casting methods. The pH-dependent release of several formulations was studied in vitro and the oral bioavailabilities of FNB-loaded micelles, Lipidil Micro and FNB coarse suspension were assessed in Sprague-Dawley rats at a dose of 7.5 mg/kg. Entrapment efficiency (defined as the ratio of experimental drug loading in self-assemblies to the initial amount of drug added) ranged between 55-75% and was dependent on polymer composition and drug-loading method. Hydrophobic chain composition of the polymer had tremendous impact on in vitro release kinetics, with only poly(ethylene glycol)-block-poly(n-butyl acrylate(17)-co-methacrylic acid(17)) micelles showing the desired pH-dependent drug-release profile. The oral bioavailability of FNB from these self-assemblies revealed 156% and 15% increases vs. FNB coarse suspension and Lipidil Micro, respectively. The results suggest that these pH-sensitive self-assemblies have potential for improving the oral bioavailability of poorly water-soluble drugs.

Acrylates↗
PubMed2006

Paclitaxel releasing films consisting of poly(vinyl alcohol)-graft-poly(lactide-co-glycolide) and their potential as biodegradable stent coatings.

Although substantial progress in catheter and stent design has contributed to the success of percutaneous transluminal angioplasty (PTA) of atherosclerotic disease, the incidence of restenosis caused by in-stent neointimal hyperplasia remains a serious problem. Therefore, stents with a non-degradable polymer coating showing controlled release of active ingredients have become an attractive option for the site-specific delivery of anti-restenotic agents. Biodegradable coatings using polyesters, namely poly(lactic-co-glycolic acid) (PLGA) and different poly(vinyl alcohol)-graft-poly(lactic-co-glycolic acid) (PVA-g-PLGA) as paclitaxel-eluting stent coating materials were investigated here to evaluate their influence on the release kinetic. Whereas PLGA showed sigmoid release behavior, the paclitaxel release from PVA-g-PLGA films was continuous over 40 days without initial drug burst. Wide angle X-ray diffraction confirmed that paclitaxel is dissolved in the polymer matrix. Paclitaxel crystallization can be observed at a drug load of > or =10%. The effect of drug loading on polymer degradation was studied in films prepared from PVA300-g-PLGA30 with paclitaxel loadings of 5% and 15% over a time period of 6 weeks. The results suggest a surface-like erosion mechanism in films. A model stent (Jostent peripheral) coated with Parylene N, a poly(p-xylylene) (PPX) derivate, was covered with a second layer of PVA300-g-PLGA15, and PVA300-g-PLGA30 by using airbrush method. Morphology of coated stents, and film integrity after expansion from 3.12 to 5 mm was investigated by scanning electron microscopy (SEM). The devices resisted mechanical stress during stent expansion and merit further investigation under in vivo conditions.

Antineoplastic Agents, Phytogenic↗
PubMed1988

Chromatographic resolution of dipeptide enantiomers and diastereomers on chiral stationary phases from poly(L-leucine) or poly(L-phenylalanine).

Two types of chiral stationary phase, polymer-bonded and non-bonded, containing poly(L-leucine) and poly(L-phenylalanine) were prepared. These stationary phases gave higher enantioselectivity for the optical resolution of various derivatives of leucylphenylalanine methyl ester by liquid chromatography than did poly(L-alanine) and poly(L-glutamate).

Chromatography, Liquid↗
PubMed2003

Effect of the nature of the counterion on the interaction between cesium and tetraalkylammonium dodecylsulfates and poly(ethylene oxide) or poly(vinylpyrolidone).

The interaction between poly(ethylene oxide) or poly(vinylpyrrolidone) and cesium and tetraalkylammonium (tetramethyl to tetrabutyl ammonium) dodecylsulfate has been investigated by means of electrical conductivity measurements to determine the critical aggregation concentration (cac) of the surfactants in the presence of polymer. The cac values were compared to the values of the critical micellization concentration (cmc) of the surfactants in the absence of polymer. The value of the cac/cmc ratio increased with the radius of the counterion in the sequence: Na(+)<Cs(+)<tetramethylammonium(+)<tetraethylammonium(+)=tetrapropylammonium(+)=tetrabutylammonium(+)=1.0. This result indicates that the strength of the interaction decreases upon increasing counterion radius. For the last three tetraalkylammonium ions the value cac/cmc=1 indicates the absence of interaction. The results are discussed in an attempt to gain a better understanding of the mechanism of formation of surfactant aggregates bound to water-soluble polymers such as poly(ethylene oxide) or poly(vinylpyrrolidone).

Alkanesulfonic Acids↗
PubMed2001

Poly(L-lysine)-GRGDS as a biomimetic surface modifier for poly(lactic acid).

The immobilization of adhesion peptide sequences (such as RGD) at the surfaces of poly(alpha-hydroxyacid)s, including poly(lactic acid) (PLA), is complicated by an absence of functional groups to support covalent attachment. We demonstrate a method to overcome this problem, by attaching the peptide to poly(L-lysine) (PLL), which immobilizes the sequence through adsorption at the poly(alpha-hydroxyacid) surface. When coated using a 0.01% w/v solution of PLL-GRGDS, bovine aortic endothelial cells seeded upon the modified PLA showed a marked increase in spreading over unmodified PLA. However, inhibition of the cell-spreading effect occurred when using higher concentrations of PLL-GRGDS, which we attribute to the PLL component. This inhibitory effect can be challenged by increasing the amount of GRGDS attached to each PLL molecule. Potentially, this is a flexible method of surface modification that can engineer many different types of tissue engineering scaffolds with a variety of biomolecules, thus allowing initial cell adhesion to be controlled.

Animals↗
PubMed2001

Biodegradable microspheres of novel segmented poly(ether-ester-amide)s based on poly(epsilon-caprolactone) for the delivery of bioactive compounds.

A novel class of multiblock poly(epsilon-caprolactone)-based polymers containing hydrophilic trioxyethylene segments and potentially relevant to the delivery of drugs is described in this work. L-phenylalanine residues may also be inserted into the hydrophilic blocks to generate peptide bonds susceptible to enzymatic attack. The investigated polymers were poly(ether-ester-amide)s (PEEAs) obtained by a two-step polymerization procedure from OH-end capped low molecular weight poly(epsilon-caprolactone), sebacoyl chloride and either 4,7,10-trioxa-1,13-tridecanediamine (PEEA1) or 1,13-di(L-phenylalaninamido)-4,7,10-trioxatridecane (PEEA2). PEEAs were characterized by 1H-NMR spectroscopy, differential scanning calorimetry, gel permeation chromatography and were tested for their suitability in producing microspheres. Particles obtained by the single emulsion-solvent evaporation technique were regular and smooth (SEM analysis) showing a monomodal distribution of dimensions. To assess the potentiality of PEEAs in the oral delivery of drugs, three model compounds with different pKa and solubilities--diclofenac, nicardipine and dicumarol--were encapsulated within PEEA microspheres. For the sake of comparison, microspheres prepared from poly(epsilon-caprolactone) (PCL) with a molecular weight similar to PEEAs were also prepared and tested. The release of diclofenac from all the microspheres was very rapid (100% released within 2 h) whereas nicardipine release was slower and biphasic. The initial phase approximated a near zero-order release, being the fraction of nicardipine released after 8 h from PEEA microspheres higher with respect to PCL particles (about 70 vs. 30%). This result was ascribed to the lower crystallinity of PEEAs with respect to PCL which results in a facilitated access of water molecules through the polymer matrix. The lipophilic-unionizable dicumarol was released from PEEA microspheres at a very slow rate. Therefore, dicumarol-loaded PEEA2 microspheres allowed the study of the influence on the release rate of the insertion into the polymer chain of enzymatically degradable bonds. PEEA2 microspheres released dicumarol at the same rate in a medium with or without the proteolitic enzyme alpha-chymotrypsin. Although the insertion of an isolated amino acid was not sufficient to confer enzyme susceptibility to the polymer, the distinctive properties of PEEAs make their use very attractive in the field of controlled release.

Amides↗
PubMed2003

Preparation and drug release behaviors of nimodipine-loaded poly(caprolactone)-poly(ethylene oxide)-polylactide amphiphilic copolymer nanoparticles.

Amphiphilic block copolymers, poly(caprolactone)-poly(ethylene glycol)-poly(lactide) (PCELA), were synthesized by ring opening polymerization of caprolactone and lactide initiated with the hydroxyl groups of poly(ethylene glycol) (PEG). These copolymers could form micelle-like nanoparticles due to their amphiphilic characteristic. From the observation of transmission electron microscopy (TEM), the nanoparticles exhibited a regular spherical shape with core-shell structure. The critical micelle concentrations (CMC) of these nanoparticles in water were decreased as molecular weight of PEG decreased. The particle sizes obtained by dynamic light scattering of these nanoparticles were in the range of 100-200 nm, and increased as the hydrophobic property of the nanoparticles increased. Nimodipine as a model drug was loaded in these nanoparticles to investigate the drug release behavior. It was found that the chemical composition of the nanoparticles was a key factor in controlling nanoparticle size, nanoparticle yields, drug-entrapment efficiency, and drug release behavior. When the PEG content is about 2% (wt), the release profile of PCELA nanoparticles appeared to follow zero-order kinetics.

Absorbable Implants↗
PubMed2003

The use of poly(ethylene glycol)-block-poly(lactic acid) derived copolymers for the rapid creation of biomimetic surfaces.

For many tissue engineering applications biomimetic or bioactive polymers would allow for a more precise control of cell behavior in growing tissues than has so far been possible. For this application recently developed amine reactive diblock copolymers (N-succinimidyl tartrate monoamine poly(ethylene glycol)-block-poly(D,L-lactic acid) [ST-NH-PEGxPLAy]) were investigated concerning their reactivity in binding model substances. Their ability to covalently immobilize proteins on their surfaces was examined using polymer films with amine reactive surfaces. Furthermore, thiol reactive polymers were obtained by attaching N-succinimidyl 3-maleinimido propionate, a thiol reactive linker to monoamine poly(ethylene glycol)-block-poly(D,L-lactic acid) [H2N-PEGxPLAy]. This allowed the immobilization of proteins carrying free thiol groups. The amine and thiol reactive polymers were characterized by 1H-NMR spectroscopy and gel permeation chromatography (GPC). Investigation of glass transitions temperatures using modulated differential scanning calorimetry proved suitability for the fabrication of polymeric scaffolds for tissue engineering applications. The functionality of the polymers was demonstrated by investigating their ability to bind model amines, like the fluorescent dye EDANS. Moreover, insulin and somatostatin were covalently attached to the active linker groups via amine and thiol groups. The polymers will permit covalently attaching different bioactive molecules, such as growth and differentiation factors, with fast and gentle procedures securing their biological activity.

Amino Acid Sequence↗
PubMed2004

Biodegradable poly(ether ester urethane)urea elastomers based on poly(ether ester) triblock copolymers and putrescine: synthesis, characterization and cytocompatibility.

Polymers with elastomeric mechanical properties, tunable biodegradation properties and cytocompatibility would be desirable for numerous biomedical applications. Toward this end a series of biodegradable poly(ether ester urethane)urea elastomers (PEEUUs) based on poly(ether ester) triblock copolymers were synthesized and characterized. Poly(ether ester) triblock copolymers were synthesized by ring-opening polymerization of epsilon-caprolactone with polyethylene glycol (PEG). PEEUUs were synthesized from these triblock copolymers and butyl diisocyanate, with putrescine as a chain extender. PEEUUs exhibited low glass transition temperatures and possessed tensile strengths ranging from 8 to 20MPa and breaking strains from 325% to 560%. Increasing PEG length or decreasing poly(caprolactone) length in the triblock segment increased PEEUU water absorption and biodegradation rate. Human umbilical vein endothelial cells cultured in a medium supplemented with PEEUU biodegradation solution suggested a lack of degradation product cytotoxicity. Endothelial cell adhesion to PEEUUs was less than 60% of tissue culture polystyrene and was inversely related to PEEUU hydrophilicity. Surface modification of PEEUUs with ammonia gas radio-frequency glow discharge and subsequent immobilization of the cell adhesion peptide Arg-Gly-Asp-Ser increased endothelial adhesion to a level equivalent to tissue culture polystyrene. These biodegradable PEEUUs thus possessed properties that would be amenable to applications where high strength and flexibility would be desirable and exhibited the potential for tuning with appropriate triblock segment selection and surface modification.

Absorbable Implants↗
PubMed1997

Effect of thermal treatment on sterility, molecular and mechanical properties of various polylactides. 2. Poly(L/D-lactide) and poly(L/DL-lactide).

Pins for orthopaedic applications injection-moulded from as-supplied poly(L/D-lactide) 95/5% and poly(L/DL-lactide) 95/5%, raw as-supplied polymers or raw methanol-extracted polymers were heat-treated for a predetermined time at 135 degrees C under moisture-free argon. The sterility, molecular weight, polydispersity, mechanical properties, and crystallinity of the heat-treated samples were evaluated. All the samples heat treated under argon were sterile after 2 h exposure to heat. The heat-treated pins and raw as-supplied polymers showed a continuous decrease in molecular weight over the entire 50 h of heating, the decrease being more substantial for poly(L/D-lactide) than poly(L/DL-lactide). Raw methanol-extracted polymers showed an increase of molecular weight after 2 h of heat treatment, followed by a gradual decrease of molecular weight up to 50 h. A drop in the bending strength, an increase in the bending moduli, and no change in the shear strength was observed for polylactide pins during the first 5 h of thermal treatment. For both the polymers, there was a progressive increase in crystallinity over time of thermal treatment, and practically no change in the melting temperature.

Bone Nails↗