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PubMed2003

Preparation, characterization and properties of poly(2,2-dimethyl trimethylene carbonate-co-epsilon-caprolactone)-block-poly(ethylene glycol).

Degradable terpolymers were synthesized by bulk copolymerization of 2,2-dimethyl trimethyle necarbonate (DTC), epsilon-caprolactone (CL) and poly(ethylene glycol) (PEG) using stannous octoate as catalyst at 140 degrees C for 36 h. The molar ratio in feed of DTC to CL was fixed at 20:80. The molecular weight and the mol% of PEG were varied in order to obtain copolymers with different properties. The copolymers were characterized by 1H-NMR, 13C-NMR, FT-IR, GPC and DSC. It was found that the hydrophilicity of these materials increased with increasing PEG content in the copolymers, according to the measurements of static contact angles of distilled water on the surface of polymer films. Mechanical tests and hydrolytic degradation assays showed that copolymers of different degradability and mechanical properties could be tailored by adjusting the compositions. For the copolymer T-4 (11.9 mol% of PEG with Mn 2000), the tensile strength and the elastic modulus could reach 6.2 MPa and 25 MPa, respectively. It took only 4 weeks for the copolymer T-4 to degrade to 83% (M(n,t)/M(n,0)) and 10 weeks to 63% in 0.1 M PBS at pH 7.4 and 37 degrees C. There was no obvious acceleration of degradation rate in vivo in comparison with that in vitro. These materials might be useful for nerve regeneration guides and other biomedical applications.

Biocompatible Materials↗
PubMed2003

Acid-initiated polymerization of epsilon-caprolactone under microwave irradiation and its application in the preparation of drug controlled release system.

Acid-initiated ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) was conducted under microwave irradiation (MI) at 2.45 GHz. At this frequency, metallic catalysts were no longer necessary. The effects of microwave power, irradiation time, epsilon-CL: acid molar ratio and acidity of acid on the polymerization were investigated. Both the rate of polymerization and the molar mass of polymer obtained were enhanced in comparison with conventional thermal method. Poly(epsilon-caprolactone) (PCL) with weight-average molar mass (Mw) over 12000 g/mol and Mw/Mn below 1.6 was synthesized in the presence of carboxylic acids such as maleic acid (MA), succinic acid (SA) and adipic acid (AA). The polymerization was also carried out when the monomer contained a certain amount of ibuprofen (IBU), by which, the IBU-PCL controlled release system was prepared directly. The release of IBU from the system was sustained from 12 h to 9 days with IBU content in weight increasing from 5 to 20%. It seems that this is a promising method to prepare drug controlled release systems.

Biocompatible Materials↗
PubMed2005

Properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) films modified with polyvinylpyrrolidone and behavior of MC3T3-E1 osteoblasts cultured on the blended films.

A series of composite films of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) modified with polyvinylpyrrolidone (PVP) was prepared by varying the ratio of constituents, and their properties and cytocompatibility were evaluated. The hydrophilicity of the blended materials surfaces increased and the amounts of fibronectin and laminin adsorbed on the materials surface increased remarkably compared with PHBHHx. FT-IR spectra of the blended films showed a new band, implying that a surface physical interpenetrating network structure had formed. Scanning electron microscopy showed that there were dense pits and holes on the blended films surface. For the films of PHBHHx with 20 wt% and 40 wt% PVP, MTT assay indicated that PVP enhanced cell adhesion and proliferation, but that the effects were impaired by excessive PVP. The results suggested that proper addition of PVP increased the cytocompatibility of PHBHHx because the material surface had increased hydrophilicity and presented an appropriate morphology.

3-Hydroxybutyric Acid↗
PubMed2005

In vitro and in vivo degradation of non-woven materials made of poly(epsilon-caprolactone) nanofibers prepared by electrospinning under different conditions.

The aim of this study was to prepare non-woven materials from a biodegradable polymer, poly(epsilon-caprolactone) (PCL) by electrospinning. PCL was synthesized by ring-opening polymerization of epsilon-caprolactone in bulk using stannous octoate as the catalyst under nitrogen atmosphere. PCL was then processed into non-woven matrices composed of nanofibers by electrospinning of the polymer from its solution using a high voltage power supply. The effects of PCL concentration, composition of the solvent (a mixture of chloroform and DMF with different DMF content), applied voltage and tip-collector distance on fiber diameter and morphology were investigated. The diameter of fibers increased with the increase in the polymer concentration and decrease in the DMF content significantly. Applied voltage and tip-collector distance were found critical to control 'bead' formation. Elongation-at-break, ultimate strength and Young's modulus were obtained from the mechanical tests, which were all increased by increasing fiber diameter. The fiber diameter significantly influenced both in vitro degradation (performed in Ringer solution) and in vivo biodegradation (conducted in rats) rates. In vivo degradation was found to be faster than in vitro. Electrospun membranes were more hydrophobic than PCL solvent-casted ones; therefore, their degradation was a much slower process.

Absorbable Implants↗
PubMed2006

Initiator structure influence on thermal and rheological properties of oligo(epsilon-caprolactone).

Biodegradable thermoplastic oligomers have potential as biomaterials for tissue augmentation and drug-delivery applications. One means of obtaining such a biomaterial is through the ring-opening polymerization of epsilon-caprolactone using an alcohol initiator. In this paper we continue to examine the influence of the structure of the initiator used on the thermal and rheological properties of oligo(epsilon-caprolactone). Specifically, primary and secondary pentanol, and cis- and trans-pentenol were studied as initiators in the preparation of oligomers of constant molecular weight. In agreement with previous work, the secondary conformer yielded higher melt viscosities, lower degrees of crystallinity and lower glass transition temperatures. The cis conformer produced the lowest melt viscosity; however, the activation energy for flow was higher than obtained previously with oleyl alcohol. This result was attributed to the alkane chain lengths on either side of the cis double bond in the initiator. The order of melt viscosity increased with initiator conformer as follows: cis, trans, primary and secondary. The results were explained in terms of oligomer chain flexibility in the melt.

Biocompatible Materials↗
PubMed2006

Synthesis of trimethoxy- or triethoxysilane-endcapped polylactones via a bismuth(III)hexanoate-catalyzed one-pot-procedure.

It was shown that bismuth(III)hexanoate (Bi(OHex)3) efficiently and selectively catalyzes the addition of tetra(ethylene glycol) (TEG) onto the isocyanate group of 3-isocyanatopropyl triethoxysilane, IPTES. delta-Valerolactone (deltaVL), epsilon-caprolactone (epsilonCL) and D,L-lactide were polymerized by initiation with TEG/Bi(OHex)3. The resulting telechelic polyesters were in situ functionalized with IPTES or with 3-isocyanatopropyl trimethoxysilane, IPTMS. Using pentaerythritol as co-initiator of Bi(OHex)3 and epsilonCL as monomer, star-shaped polylactones having triethylsilyl end-groups were synthesized in a one-pot-procedure. All functionalized polyesters were characterized by 1H-NMR and 13C-NMR spectroscopy and by MALDI-TOF mass spectrometry. Bi(OHex)3 is a remarkable initiator and catalyst, because of its extraordinary low toxicity.

Bismuth↗
PubMed2006

Apatite formation in composites of alpha-TCP and degradable polyesters.

The objective of this study was to investigate the conversion of alpha-Ca3(PO4)2 (alpha-TCP) in composite bone cements based on a water-degradable polyester matrix as a function of the polymer formulation and the alpha-TCP filler content. Cross-linkable dimethacrylates of epsilon-caprolactone/ D,L-lactide co-polymer or of epsilon-caprolactone/glycolide co-polymer were mixed with hydroxyethylmethacrylate, a photo-initiator and alpha-TCP to obtain composites with a filler content of 80 or 40 wt% alpha-TCP. The disk shaped composite samples were set by visible light irradiation and immersed in HEPES at 37 degrees C. At selected times the samples were removed from the solution and analysed with X-ray diffractometry and infrared spectroscopy. Conversion of alpha-TCP into calcium-deficient hydroxyapatite (CDHAp) was observed for all composites, but the reaction was not completed after 8 weeks immersion. The conversion rate of alpha-TCP and the crystallinity of the formed apatite apparently were not affected by the type of polyester used, but significantly depended on the alpha-TCP content of the composites. An increase of the amount of alpha-TCP in the composite resulted in a slower formation of CDHAp with a higher crystallinity.

Apatites↗
PubMed1973

Synthesis of essential amino acids from their alpha-keto analogues by perfused rat liver and muscle.

Most essential amino acids can be replaced by their alpha-keto-analogues in the diet. These ketoacids have therefore been proposed as substitutes for dietary protein. In order to determine their fate in tissues of normal animals, isolated rat liver and hindquarter (muscle) preparations were perfused with keto-analogues of valine, leucine, isoleucine, methionine, or phenylalanine. When perfused at 1.5-2.0 mM, all five compounds were utilized rapidly by the liver of 48-h starved rats, at rates varying from 49 to 155 mumol/h per 200g rat. The corresponding amino acids appeared in the medium in significantly increased concentrations. Perfusion with phenylpyruvate also led to the appearance of tyrosine. Urea release was unaltered. Measurement of metabolite concentrations in freeze-clamped liver revealed two abnormalities, particularly at ketoacid concentrations of 5 mM or above: a large increase in alpha-ketoglutarate, and a moderate to marked decrease in tissue glutamine. This decrease was quantitatively sufficient to account for nitrogen appearing in newly synthesized amino acids. Isolated hindquarters of fed rats were perfused with the same ketoacids at concentrations of 1.3-8.0 mM. All were utilized at rates varying from 1.4 to 7.0 mumol/h per g muscle perfused. The corresponding amino acids were released at greatly increased rates. Alanine and glutamate levels fell in some perfusions, but the principal nitrogen donor in muscle was not identified; the content of glutamine in tissue, and its rate of release into the perfusate remained constant.

Acetoacetates↗
PubMed1985

Adsorption of zirconyl salts and their acids on hydroxyapatite: use of the salts as coupling agents to dental polymer composites.

Zirconyl methacrylate (I) and zirconyl-2-ethylhexanoate (II) were synthesized, and their adsorption isotherms from solutions onto synthetic hydroxyapatite were studied. The isotherms of methacrylic and 2-ethylhexanoic acids were also determined from the same solvents. The adsorption of I was irreversible from methylene chloride, and that of II was irreversible from cyclohexane. The adsorption in both cases was constant from solutions above a certain concentration, and exhaustive below this threshold concentration. Both compounds rendered the dried apatite powder extremely hydrophobic; however, the adsorbate was slowly washed off by excess water. The configuration of the adsorbate molecules, deduced from the maximum adsorption and other adsorption characteristics of the two compounds, indicated that: (i) in both cases the adsorbate may be held to the surface by concerted hydrogen bonding of the carboxylate and zirconyl oxygen atoms; and (ii) the hydrocarbon moieties in both adsorbates expose themselves toward the solution, thereby making the dried surface hydrophobic. The adsorptive behavior of the respective acids was similar to that of the salts. Polymer, filled with synthetic hydroxyapatite covered with irreversibly adsorbed I, had a diametral tensile strength about 50% greater than that of the polymer filled with untreated apatite. The strength of the composite was not affected by treatment of the apatite with II or with the acids.

Acids↗
PubMed1994

Acid profiles and pH of carious dentin in active and arrested lesions.

Organic acids in caries lesions play important roles in initiation and progress of dental caries. We investigated relationships between clinical types of dentin caries and acid profile or pH in the lesions. Caries lesions in dentin from 76 permanent teeth were classified into active, arrested, situated beneath a restoration, and unclassified types. The pH of carious dentin was distinctly lower than that of sound dentin (p < 0.001). Carious dentin with a high percentage of lactate had a lower pH than that with a high percentage of acetate and propionate (p < 0.001). Dentin from active lesions showed a mean pH of 4.9, and the dominant acid was lactate (mean percentage, 88.2). In contrast, carious dentin from arrested lesions showed a higher pH, 5.7, with acetate and propionate as the dominant acids (mean percentages of acetate and propionate, 64.0 and 18.2, respectively). The acid profile (mean percentages of acetate and propionate, 54.0 and 27.7, respectively) and pH (mean 5.8) of carious dentin sampled from lesions beneath a restoration were similar to those of dentin from arrested lesions. This study showed a clear relationship between clinical classification of dentin caries and acid profile and pH, suggesting that both factors are important in dentin caries etiology.

Acetates↗
PubMed2004

Fibrin/Schwann cell matrix in poly-epsilon-caprolactone conduits enhances guided nerve regeneration.

The goal of this study was to investigate if a three dimensional matrix, loaded homogeneously with Schwann cells and the neurotrophic factor LIF (leukemia inhibitory factor), enhances regeneration in a biodegradable nerve guidance channel as compared to non-structured cell suspensions. Therefore a 10 mm nerve gap in the buccal branch of the rat's facial nerve was bridged with tubular PCL (poly-epsilon-caprolactone) conduits filled with no matrix, Schwann cells, the three dimensional fibrin/Schwann cell matrix or the fibrin/Schwann cell matrix added with LIF Four weeks after the nerve defects were bridged histological and morphometric analyses of the implants were performed. In conclusion, the three dimensional fibrin/Schwann cells matrix enhanced the quantity and the quality of peripheral nerve regeneration through PCL conduits. The application of LIF prevented hyperneurotization. Therefore, tissue engineered fibrin/Schwann cells matrices are new invented biocompatible and biodegradable devices for enhancing peripheral nerve regeneration as compared to non-structured cell suspensions without neurotrophic factors.

Analysis of Variance↗
PubMed2006

In vitro bioactivity of poly(epsilon-caprolactone)-apatite (PCL-AP) scaffolds for bone tissue engineering: the influence of the PCL/AP ratio.

Porous poly(epsilon-caprolactone) (PCL) is used as long-term bioresorbable scaffold for bone tissue engineering. The bone regeneration process can be enhanced by addition of carbonated apatites (AP). This study was aimed at evaluating the influence of the PCL/AP ratio on the in vitro degradation and bioactivity of PCL-AP composites. To this purpose, PCL-AP samples were synthesised with the following PCL/AP weight/weight ratios: 50/50, 60/40 and 75/25. Vibrational IR and Raman spectroscopies coupled to thermogravimetry (TG) and differential scanning calorimetry (DSC) were used to investigate the in vitro degradation mechanism in different media: 0.01 M NaOH solution (pH=12), saline phosphate buffer at pH 7.5 (SPB), esterase in SPB and simulated body fluid (SBF) at pH 7.5. The latter medium was used to evaluate the bioactivity of the composites. A control PCL sample was analysed before the addition of the AP component. As regards the untreated samples, the method of synthesis utilised for preparing the composite was found to enhance the crystallinity degree. The AP component revealed to be constituted of a B-type carbonated hydroxyapatite with a 3% carbonate content. After 28 days of treatment, the samples showed different degradation patterns and extents depending on the degradation medium, the starting PCL crystallinity and composite composition. Weight measurements, Raman and TG analyses revealed deposition of an apatitic phase on all the composites immersed in SBF. Therefore, all the samples displayed a good bioactivity; the sample which showed the most pronounced apatitic deposition was 50/50, i.e. that containing the highest amount of AP.

Apatites↗
PubMed1996

CYP enzymes catalyze the formation of a terminal olefin from 2-ethylhexanoic acid in rat and human liver.

1. The metabolism of 2-ethylhexanoic acid (2-EHA) was studied in rat, mouse and human liver microsomes in vitro. The metabolites of 2-EHA were identified as methylated derivatives by gas chromatography-mass spectrometry. 2. 2-Ethyl-1,6-hexanedioic acid was the main metabolite produced in rat, mouse and human liver microsomes. Unsaturated 2-ethyl-5-hexenoic acid, a terminal olefin, was produced only in human liver microsomes and phenobarbital-induced rat liver microsomes. The cytochrome P450 (CYP) inhibitors metyrapone, SKF 525A, triacetyloleandomycin (TAO), quinidine and the cytochrome P450 reductase antibody abolished its formation both in rat and human microsomes. 3. The metabolites were analyzed also in vivo in urine of 2-EHA-exposed rats and in urine of sawmill workers exposed occupationally to 2-EHA. Both rat and human urine contained 2-ethyl-1,6-hexanedioic acid as the main metabolite and also 2-ethyl-5-hexenoic acid. Metyrapone, SKF 525A and TAO all decreased drastically the formation of 2-ethyl-5-hexenoic acid in the rat. 4. The data indicate that (1) several CYP families (CYP2A, CYP2B, CYP2D and CYP3A) could be responsible for the hepatic metabolism of 2-EHA, (2) the same metabolites were formed in rats and man and (3) an unsaturated terminal olefin, 2-ethyl-5-hexenoic acid is formed in the liver.

Aged↗
PubMed2006

In vitro studies on the release of isoniazid incorporated in poly(epsilon-caprolactone).

A polymeric micro- and nanosphere formulation using poly (epsilon-caprolactone) (PCL) to entrap an antituberculosis drug, isoniazid (INH), was developed and characterized. The microspheres were prepared by a solvent evaporation method using ethyl acetate, PCL and INH as the organic phase and water and Tween 40 as the aqueous phase. The nanospheres were prepared by a spontaneous emulsification solvent diffusion method using 40% ethanol in acetone (v/v), PCL and INH as the organic phase and water and Tween 40 as the aqueous phase. After freeze-drying, these systems were characterized by scanning electron microscopy (SEM), particle size analysis, determination of entrapped INH content, in vitro INH release and brine shrimp toxicity bioassay.

Animals↗
PubMed2002

SREBP-1 integrates the actions of thyroid hormone, insulin, cAMP, and medium-chain fatty acids on ACCalpha transcription in hepatocytes.

In chick embryo hepatocytes, activation of acetyl-CoA carboxylase-alpha (ACCalpha) transcription by 3,5,3'-triiodothyronine (T3) is mediated by a cis-acting regulatory unit (-101 to -71 bp) that binds the nuclear T3 receptor (TR) and sterol regulatory element-binding protein-1 (SREBP-1). SREBP-1 directly interacts with TR on the ACCalpha gene to enhance T3-induced transcription. Here, we show that treating hepatocytes with T3 or insulin stimulates a 4-fold increase in the concentration of the mature, active form of SREBP-1. When T3 and insulin are added together, a 7-fold increase in the mature SREBP-1 concentration is observed. Time course studies indicate that the T3-induced increase in mature SREBP-1 abundance is closely associated with changes in ACCalpha transcription and that the mechanism mediating the effect of T3 on mature SREBP-1 is distinct from that mediating the effect of insulin. Transfection analyses indicate that inhibition of ACCalpha transcription by cAMP or hexanoate is mediated by ACCalpha sequences between -101 and -71 bp. Treatment with cAMP or hexanoate suppresses the increase in mature SREBP-1 abundance caused by T3 and insulin. These results establish a new interaction between the SREBP-1 and TR signaling pathways and provide evidence that SREBP-1 plays an active role in mediating the effects of T3, insulin, cAMP, and hexanoate on ACCalpha transcription.

Acetyl-CoA Carboxylase↗