Home About us Contact
|
Home About us Contact | ||
|
|
||
Hydrolytic Degradation (hydrolytic + degradation)
Selected AbstractsKnowledge-Based Approach towards Hydrolytic Degradation of Polymer-Based BiomaterialsADVANCED MATERIALS, Issue 32-33 2009Dieter Hofmann Abstract The concept of hydrolytically degradable biomaterials was developed to enable the design of temporary implants that substitute or fulfill a certain function as long as required to support (wound) healing processes or to control the release of drugs. Examples are surgical implants, e.g., sutures, or implantable drug depots for treatment of cancer. In both cases degradability can help to avoid a second surgical procedure for explanation. Although degradable surgical sutures are established in the clinical practice for more than 30 years, still more than 40% of surgical sutures applied in clinics today are nondegradable.1 A major limitation of the established degradable suture materials is the fact that their degradation behavior cannot reliably be predicted by applying existing experimental methodologies. Similar concerns also apply to other degradable implants. Therefore, a knowledge-based approach is clearly needed to overcome the described problems and to enable the tailored design of biodegradable polymer materials. In this Progress Report we describe two methods (as examples for tools for this fundamental approach): molecular modeling combining atomistic bulk interface models with quantum chemical studies and experimental investigations of macromolecule degradation in monolayers on Langmuir,Blodgett (LB) troughs. Finally, an outlook on related future research strategies is provided. [source] Assessment of the Oxidative and Hydrolytic Degradation of Oils Used as Liquid Medium of In-oil Preserved VegetablesJOURNAL OF FOOD SCIENCE, Issue 1 2003F. Caponio ABSTRACT: An experimental investigation was carried out on several in-oil preserved vegetables to evaluate the quality and genuineness of different oils used as liquid medium. The results obtained showed that the lipids released by vegetables to the oils are negligible, and that the routine analyses are not fully effective to assess the quality of the oils. More reliable results may be achieved from the percent determination of trans isomers, and from the classes of oxidation, polymerization, and hydrolysis substances contained in the polar compounds. In sunflower seed oils, much higher contents of trans isomers (p < 0.001), triglyceride oligopolymers, and oxidized triglycerides (p < 0.01) have been observed as compared to olive and extra virgin olive oils. [source] Hydrolytic Degradation and Monomer Recovery of Poly(butylene succinate) and Poly(butylene succinate/adipate) in the MeltMACROMOLECULAR REACTION ENGINEERING, Issue 6 2008Hideto Tsuji Abstract Aliphatic dicarboxylic acid/aliphatic diol-derived polyesters, poly(butylene succinate) and poly(butylene succinate/adipate), have been hydrolytically degraded in the melt in high-temperature and high-pressure water over a wide temperature range of 180,300,°C for periods of up to 30 min. The formation/decomposition of succinic acid (SA), adipic acid (AA), and butane-1,4-diol (BD), plus the molecular weight change of PBS and PBSA were then investigated. SA and AA were recovered at maximum yields of 65,80%, whereas BD was recovered at a maximum yield of only 30%, probably because of its decomposition. The obtained results were compared with those reported for aliphatic hydroxycarboxylic acid-derived polyesters and aromatic dicarboxylic acid/aliphatic diol-derived polyesters. [source] Degradation of aramid fibers under alkaline and neutral conditions: Relations between the chemical characteristics and mechanical propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010G. Derombise Abstract Aramid fibers are high-performance materials that have been used in various applications such as heat and cut protection, composites, rubber reinforcement, ropes and cables, and fabrics; today their use is proposed in geotextiles for alkaline ground reinforcement, and they have been used in cables for marine applications for a few years. However, there is a lack of experience with the long-term behavior of aramid fibers in wet and alkaline environments. Aging studies were therefore performed on Twaron 1000 fibers under different conditions (sea water, deionized water, pH 9, and pH 11). Hydrolytic degradation was evaluated with Fourier transform infrared and viscosimetry measurements, which were correlated with tensile test measurements. The tensile strength followed a logarithmic evolution with the aging time, whereas the modulus remained constant. A linear relation between the tensile strength and the reduced viscosity of the hydrolytically aged fibers is highlighted. Aging indicators are proposed that allow the hydrolytic degradation to be quantified. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Hydrolytic degradation of poly(ethylene terephthalate)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Seyed Saeid Hosseini Abstract Molecular weight is an important factor in the processing of polymer materials, and it should be well controlled to obtain desired physical properties in final products for end-use applications. Degradation processes of all kinds, including hydrolytic, thermal, and oxidative degradations, cause chain scission in macromolecules and a reduction in molecular weight. The main purpose of this research is to illustrate the importance of degradation in the drying of poly(ethylene terephthalate) (PET) before processing and the loss of weight and mechanical properties in textile materials during washing. Several techniques were used to investigate the hydrolytic degradation of PET and its effect on changes in molecular weight. Hydrolytic conditions were used to expose fiber-grade PET chips in water at 85°C for different periods of time. Solution viscometry and end-group analysis were used as the main methods for determining the extent of degradation. The experimental results show that PET is susceptible to hydrolysis. Also, we that as the time of retention in hydrolytic condition increased, the molecular weight decreases, but the rate of chain cleavage decreased to some extent, at which point there was no more sensible degradation. The obtained moisture content data confirmed the end-group analysis and viscometry results. Predictive analytical relationships for the estimation of the extent of degradation based on solution viscosity and end-group analysis are presented. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2304,2309, 2007 [source] Degradation of aramid fibers under alkaline and neutral conditions: Relations between the chemical characteristics and mechanical propertiesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2010G. Derombise Abstract Aramid fibers are high-performance materials that have been used in various applications such as heat and cut protection, composites, rubber reinforcement, ropes and cables, and fabrics; today their use is proposed in geotextiles for alkaline ground reinforcement, and they have been used in cables for marine applications for a few years. However, there is a lack of experience with the long-term behavior of aramid fibers in wet and alkaline environments. Aging studies were therefore performed on Twaron 1000 fibers under different conditions (sea water, deionized water, pH 9, and pH 11). Hydrolytic degradation was evaluated with Fourier transform infrared and viscosimetry measurements, which were correlated with tensile test measurements. The tensile strength followed a logarithmic evolution with the aging time, whereas the modulus remained constant. A linear relation between the tensile strength and the reduced viscosity of the hydrolytically aged fibers is highlighted. Aging indicators are proposed that allow the hydrolytic degradation to be quantified. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Effect of process parameters on properties of wet-spun poly(L,D -lactide) copolymer multifilament fibersJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2009Marja Rissanen Abstract Poly(L,D -lactide) [P(L,D)LA], LL/D ratio 96/4, and poly(L,DL -lactide) [P(L,DL)LA], L/DL ratio 70/30, multifilament fibers were prepared by wet-spinning and the effects of the spin draw ratio and the coagulant on the morphological, thermal, and mechanical properties of the filaments were studied. The hydrolytic degradation of filaments was studied in vitro. The filament diameter and the mechanical properties of filaments were highly dependent on the spin draw ratio, whereas the coagulant had no or minor effect. The filament diameters were in the range of 11,36 ,m and the maximum tenacity of 150 MPa was obtained at the spin draw ratio of 7.0 for both copolymers. The copolymer had the main importance on the crystallinity of filaments, but it was also affected by the duration of the coagulation process. The crystallinities of P(L,D)LA 96/4 filaments were in the range of 5,16%, whereas P(L,DL)LA 70/30 filaments were totally amorphous. The degree of crystallinity had effect on the hydrolytic degradation of filaments. The tenacity loss of P(L,D)LA 96/4 filaments was about 10% and that of P(L,DL)LA 70/30 filaments was as high as 50% after 24 weeks in vitro. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Comparative study of the hydrolytic degradation of glycolide/L -lactide/,-caprolactone terpolymers initiated by zirconium(IV) acetylacetonate or stannous octoateJOURNAL OF APPLIED POLYMER SCIENCE, Issue 5 2008Janusz Kasperczyk Abstract A series of copolymers have been synthesized by the ring-opening polymerization of glycolide, L -lactide, and ,-caprolactone with zirconium(IV) acetylacetonate [Zr(Acac)4] or stannous octoate [Sn(Oct)2] as the catalyst. The resulting terpolymers have been characterized by analytical techniques such as proton nuclear magnetic resonance, size exclusion chromatography, and differential scanning calorimetry. Data have confirmed that Sn(Oct)2 leads to less transesterification of polymer chains than Zr(Acac)4 under similar conditions. The various copolymers have been compression-molded and allowed to degrade in a pH 7.4 phosphate buffer at 37°C. The results show that the degradation rate depends not only on the copolymer composition but also on the chain microstructure, the Sn(Oct)2 -initiated copolymers degrading less rapidly than Zr(Acac)4 -initiated ones with more random chain structures. The caproyl component appears the most resistant to degradation as its content increases in almost all cases. Moreover, caproyl units exhibit a protecting effect on neighboring lactyl or glycolyl units. The glycolyl content exhibits different features: it decreases because of faster degradation of glycolyl units, which are more hydrophilic than caproyl and lactyl ones, remains stable in the case of abundant CGC sequences, which are very resistant to degradation, or even increases because of the formation of polyglycolide crystallites. Terpolymers can crystallize during degradation if the block length of one of the components is sufficiently long, even though they are amorphous initially. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] In vitro monitoring of surface mechanical properties of poly(L -lactic acid) using microhardnessJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2007C. Saiz-Arroyo Abstract Poly(L -lactic acid) (PLLA) was immersed in a simulated body fluid (SBF) solution at 37.5°C for distinct times. The variation of the surface mechanical properties of PLLA samples with immersion time was followed by microhardness. These measurements showed that PLLA microhardness decreased significantly (, 60%) after only 30 days of immersion. The results were explained in terms of hydrolytic degradation of the samples. The dependence of microhardness with the applied dwell time was also analyzed. The creep curves were successfully described by a power law. A decrease of the creep constant k as the immersion time increased was found. Differential scanning calorimetry was also used to analyze the changes in the physical properties of PLLA, namely in crystallinity degree (Xc) and glass transition temperature (Tg), as a function of the immersion time in SBF. A significant variation in the crystallinity degree of PLLA, initially nearly amorphous (Xc = 9%), was detected after only 3 days of immersion (Xc = 37%). The interpretation of this behavior was based on the hydrolysis process suffered by PLLA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007 [source] Hydrolytic degradation of poly(ethylene terephthalate)JOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Seyed Saeid Hosseini Abstract Molecular weight is an important factor in the processing of polymer materials, and it should be well controlled to obtain desired physical properties in final products for end-use applications. Degradation processes of all kinds, including hydrolytic, thermal, and oxidative degradations, cause chain scission in macromolecules and a reduction in molecular weight. The main purpose of this research is to illustrate the importance of degradation in the drying of poly(ethylene terephthalate) (PET) before processing and the loss of weight and mechanical properties in textile materials during washing. Several techniques were used to investigate the hydrolytic degradation of PET and its effect on changes in molecular weight. Hydrolytic conditions were used to expose fiber-grade PET chips in water at 85°C for different periods of time. Solution viscometry and end-group analysis were used as the main methods for determining the extent of degradation. The experimental results show that PET is susceptible to hydrolysis. Also, we that as the time of retention in hydrolytic condition increased, the molecular weight decreases, but the rate of chain cleavage decreased to some extent, at which point there was no more sensible degradation. The obtained moisture content data confirmed the end-group analysis and viscometry results. Predictive analytical relationships for the estimation of the extent of degradation based on solution viscosity and end-group analysis are presented. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2304,2309, 2007 [source] Development of a nanofiltration process to improve the stability of a novel anti-MRSA carbapenem drug candidateJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 4 2002V. Antonucci Abstract The benzenesulfonate salt of an anti-methicillin-resistant Staphylococcus aureus carbapenem antibiotic studied is a crystalline, nonhygroscopic powder which is stable at room temperature, making it an ideal compound for long-term storage. However, the limited aqueous solubility of this salt prohibits parenteral administration. Conversely, the chloride salt of this carbapenem demonstrates opposing characteristics; it is quantitatively soluble in water, however is amorphous and subject to significant hydrolytic degradation in the solid state. Given two such extreme alternatives for pharmaceutical salt selection, a common approach taken is to develop the bioavailable salt and devise manufacturing and storage conditions that minimize degradation. This report describes a different approach to this manufacturing dilemma via the application of a simple and efficient nanofiltration process to convert the benzenesulfonate salt (storage entity) to the chloride salt (formulated drug product). Such an approach combines the positive attributes of these two salt forms into a single scalable process that reduces processing cycle times via elimination of redundant unit operations, increases the flexibility in manufacturing schedule, and improves overall product quality. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 923,932, 2002 [source] Cationic polymerization of L,L -lactideJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2010gorzata Ba Abstract Cationic bulk polymerization of L,L- lactide (LA) initiated by trifluromethanesulfonic acid [triflic acid (TfA)] has been studied. At temperatures 120,160 °C, polymerization proceeded to high conversion (>90% within ,8 h) giving polymers with Mn , 2 × 104 and relatively high dispersity. Thermogravimetric analysis of resulting polylactide (PLA) indicated that its thermal stability was considerably higher than the thermal stability of linear PLA of comparable molecular weight obtained with ROH/Sn(Oct)2 initiating system. Also hydrolytic stability of cationically prepared PLA was significantly higher than hydrolytic stability of linear PLA. Because thermal or hydrolytic degradation of PLA starting from end-groups is considerably faster than random chain scission, both thermal and hydrolytic stability depend on molecular weight of the polymer. High thermal and hydrolytic stability, in spite of moderate molecular weight of cationically prepared PLA, indicate that the fraction of end-groups is considerably lower than in linear PLA of comparable molecular weight. According to proposed mechanism of cationic LA polymerization growing macromolecules are fitted with terminal OH and C(O)OSO2CF3 end-groups. The presence of those groups allows efficient end-to-end cyclization. Cyclic nature of resulting PLA explains its higher thermal and hydrolytic stability as compared with linear PLA. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2650,2658, 2010 [source] Synthesis, characterization, and in vitro degradation of liquid-crystalline terpolyesters of 4-hydroxyphenylacetic acid/3-(4-hydroxyphenyl)propionic acid with terephthalic acid and 2,6-naphthalene diolJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 11 2002V. S. Prasad Abstract Melt-processable liquid-crystalline terpolyesters of 4-hydroxyphenylacetic acid (HPAA) and 3-(4-hydroxyphenyl)propionic acid (HPPA) with terephthalic acid and 2,6-naphthalene diol were synthesized by one-step acidolysis melt polycondensation followed by postpolymerization and were characterized with viscosity studies, Fourier transform infrared (FTIR) and NMR spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), polarized light microscopy, and wide-angle X-ray diffraction. The melting behaviors and liquid-crystalline transition temperatures of the terpolyesters were dependent on the composition of the HPAA/HPPA content. The transition temperatures of the polyesters could be effectively reduced by the introduction of an even number of built-in short methylene spacers in combination with the 2,6-naphthalene offset structure. A terpolyester with an HPPA content of 33% (NTP33) showed optimum properties for the glass-transition temperature, around 71 °C, and the melting temperature, near 240 °C, with a Schlieren nematic texture. The polymer showed excellent flow behavior in a Brabender plasticorder. It was also thermally stable up to 400 °C. NTP33 showed 2.5% in vitro hydrolytic degradation in buffer solutions of pH 10 at 60 °C after 540 h. Considerable enzymatic degradation was also observed with porcine pancreas lipase/buffer solutions in comparison with Candida rugosa lipase after 60 days. The degradation was also followed with FTIR, DSC, and TGA. Apart from the temperature and pH of the buffer solution, several structural parameters, such as the aromatic content, crystallinity percentage, and composition of the polymer, affected the degradation behavior. FTIR studies indicated the involvement of chain scission during degradation. Scanning electron microscopy studies further showed that surface erosion also played a major role in the degradation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1845,1857, 2002 [source] Synthesis and specific biodegradation of novel polyesteramides containing amino acid residuesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 9 2001Yujiang Fan Abstract Novel polyesteramides were synthesized from p -nitrophenyl esters of sebacic or adipic acids and diamines containing ,-amino acid ester groups. The optimal polymerization condition was 60 °C in N,N -dimethylformamide. The structures of these polymers were confirmed by IR and NMR. The number-average molecular weights of these polyesteramides ranged from 2280 to 23,600 (except for the polymers containing glycine residues), depending on the nature of the amino acid used. The biodegradability of the polyesteramides was investigated by in vitro hydrolysis with proteases and a lipase as catalysts in borate buffer solutions. The results indicated that the polymers containing L -phenylalanine were hydrolyzed most effectively by ,-chymotrypsin, subtilisin Carlsberg, and subtilisin BPN,. The polyesteramides containing other amino acid residues also underwent hydrolysis to different extents, reflecting the substrate specificity of the proteases. Lipase had almost no effect on the hydrolytic degradation of these polyesteramides. The polymers containing glycine residues were hardly decomposed by any of the enzymes used. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1318,1328, 2001 [source] in vitro Evaluation of Biodegradable Poly(butylene succinate) as a Novel BiomaterialMACROMOLECULAR BIOSCIENCE, Issue 5 2005Haiyan Li Abstract Summary: Poly(butylene succinate) (PBSU) can be easily synthesized by condensation polymerization of the starting materials of succinic acid and butan-1,4-diol. It has good degradability and possesses excellent processability. Due to these advantages, PBSU was first evaluated in the present study for its potential application as a novel biomaterial. The in vitro biocompatibility of the PBSU was evaluated by monitoring proliferation and differentiation of osteoblasts cultured on the PBSU film substrates for different periods. The results showed that the PBSU was biocompatible as the osteoblasts could proliferate and differentiate on the PBSU plates. In addition, the hydrolytic degradation behavior of the PBSU films in the phosphate-buffered saline (PBS) was also investigated and the results suggested that the PBSU degraded in the PBS solution with the same behavior as that of the degradable poly(, -hydroxyesters). In addition to the biocompatibility and hydrolytic degradation, some physical properties, including hydrophilicity, and mechanical and thermal properties of the PBSU substrates, were also determined and the results revealed that the PBSU was hydrophilic and ductile with excellent processability. The biocompatibility of the PBSU, together with the advantages of hydrolytic degradability, hydrophilicity, and excellent processability, indicated that PBSU has the potential to be used as a biomaterial for tissue repair. Alkaline phosphate activity of osteoblasts cultured on PBSU and TCPS substrates for different time periods. [source] Biodegradable Water Absorbent Synthesized from Bacterial Poly(amino acid)sMACROMOLECULAR BIOSCIENCE, Issue 3 2004Masao Kunioka Abstract Summary: Biodegradable hydrogels prepared by , -irradiation from microbial poly(amino acid)s have been studied. pH-Sensitive hydrogels were prepared by the , -irradiation of poly(, -glutamic acid) (PGA) produced by Bacillus subtilis and poly(, -lysine) (PL) produced by Streptomyces albulus in aqueous solutions. When the , -irradiation dose was 19 kGy or more, and the concentration of PGA in water was 2 wt.-% or more, transparent hydrogels could be produced. For the 19 kGy dose, the produced hydrogel was very weak, however, the specific water content (wt. of absorbed water/wt. of dry hydrogel) of this PGA hydrogel was approximately 3,500. The specific water content decreased to 200, increasing when the , -irradiation dose was over 100 kGy. Under acid conditions or upon the addition of electrolytes, the PGA hydrogels shrunk. The PGA hydrogel was pH-sensitive and the change in the volume of the hydrogel depended on the pH value outside the hydrogel in the swelling medium. This PGA hydrogel was hydrodegradable and biodegradable. A new novel purifier reagent (coagulant), made from the PGA hydrogels, for contaminated turbid water has been found and developed by Japanese companies. A very small amount of this coagulant (only 2 ppm in turbid water) with poly(aluminum chloride) can be used for the purification of turbid water. A PL aqueous solution also can change into a hydrogel by , -irradiation. The specific water content of the PL hyrdogel ranged from 20 to 160 depending on the preparation conditions. Under acid conditions, the PL hydrogel swelled because of the ionic repulsion of the protonated amino groups in the PL molecules. The rate of enzymatic degradation of the respective PL hydrogels by a neutral protease was much faster than the rate of simple hydrolytic degradation. [source] Hydroxylated Linear Polyurethanes Derived from Sugar AlditolsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2009Romina Marín Abstract A set of linear [m,n]-type polyurethanes was synthesized by reaction of HDI or MDI with conveniently protected sugar alditols L -threitol (LTh), L -arabinitol (LAr) and xylitol (Xy). of the resulting polyurethanes ranged between 10,000 and 60,000 with polydispersities around 2. They were thermally stable, showing no decomposition up to temperatures near 300,°C. They all were amorphous polymers with Tg highly dependent on the constitution of the diisocyanate, but scarcely dependent on the structure of the alditol. Hydrogenation of the LThBn-HDI polyurethane yielded partially debenzylated products with Tg values ranging between 20 and 30,°C. Fully benzylated polyurethanes showed high resistance to hydrolytic degradation, whereas polyurethane with free hydroxyl side groups degraded significantly in saline buffer at pH,=,10 and 37,°C. [source] Polymeric Toughening of Particle Filled Cyanate Ester CompositesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 10 2005Tim J. Wooster Abstract Summary: The present study examines the effect of polymeric tougheners on the performance of silica filled cyanate ester composites. The polymeric tougheners used have been shown to enhance cyanate ester tougheners in binary toughener/matrix systems. Tougheners that were able to form a favourable phase-separated morphology resulted in the greatest increase in crack resistance. The addition of these tougheners resulted in minimal loss of strength, and a slight decrease in modulus. Importantly the viscosity of the compounded systems was low enough for them to be readily processable. Whilst conserving most secondary properties, toughener addition did result in a slight increase in composite hydrolytic degradation. This issue was linked to the additive/ additive compounding processes. Removal of this extra moisture should eliminate this concern, permitting the used of these composites in electronic applications. Effect of ETBN content on the crack resistance of particle filled cyanate ester composites and SEM image of 15 matrix wt.-% ETBN. [source] In vitro hydrolytic degradation of centrifugally spun polyhydroxybutyrate,pectin composite fibresPOLYMER INTERNATIONAL, Issue 12 2009L John R Foster Abstract BACKGROUND: Centrifugal spinning is a novel fibre-forming process that readily permits the incorporation of additives while avoiding the thermal damage often associated with conventional melt spinning. Centrifugal spinning of a viscous solution of poly(3-hydroxybutyrate) (PHB) mixed with pectin was used to fabricate a range of fibres containing different concentrations of this biologically active agent. The influence of this blending on fibre morphology and in vitro degradation in an accelerated hydrolytic model at 70 °C and pH of 10.6 is reported. RESULTS: Blending influenced the physiochemical properties of the fibres, and this significantly affected the degradation profile of both the fibre and its PHB constituent. A greater influence on degradation was exerted by the type of pectin and its degree of esterification than by variations in its loading. CONCLUSION: Centrifugal spinning permits the fabrication of composite fibrous matrices from PHB and pectin. Incorporation of the polysaccharide into the fibres can be used to manipulate degradation behaviour and demonstrates a model for doping of matrices with active biological constituents. The unique features of the centrifugal spinning process, as illustrated by the structure of the fibres and the degradation profiles, suggest possible applications of centrifugally spun biopolymers as wound scaffolding devices and in tissue engineering. Copyright © 2009 Society of Chemical Industry [source] Preparation and characterization of novel poly[cyclotriphosphazene- co -(4,4,-sulfonyldiphenol)] nanofiber matricesPOLYMER INTERNATIONAL, Issue 12 2006Zhu Lu Abstract Novel poly[cyclotriphosphazene- co -(4,4,-sulfonyldiphenol)] nanofiber matrices were synthesized via a facile one-pot polymerization. The fibers are 20,50 nm in diameter and 500 nm or more in length. Uniform nanoscale fibers linked covalently with each other and formed three-dimensional matrices. The highly cross-linked chemical structure of the nanofiber matrices was measured by means of Fourier transform infrared and quantitative solid-state NMR spectroscopy. Experiments show the pH had an effect on the hydrolytic degradation of the polymer. The hydrolysis of the matrices could be accelerated by alkaline conditions. The as-synthesized nanofiber matrices have potential applications in tissue engineering materials. Copyright © 2006 Society of Chemical Industry [source] Atomic resolution studies of haloalkane dehalogenases DhaA04, DhaA14 and DhaA15 with engineered access tunnelsACTA CRYSTALLOGRAPHICA SECTION D, Issue 9 2010A. Stsiapanava The haloalkane dehalogenase DhaA from Rhodococcus rhodochrous NCIMB 13064 is a bacterial enzyme that shows catalytic activity for the hydrolytic degradation of the highly toxic industrial pollutant 1,2,3-trichloropropane (TCP). Mutagenesis focused on the access tunnels of DhaA produced protein variants with significantly improved activity towards TCP. Three mutants of DhaA named DhaA04 (C176Y), DhaA14 (I135F) and DhaA15 (C176Y + I135F) were constructed in order to study the functional relevance of the tunnels connecting the buried active site of the protein with the surrounding solvent. All three protein variants were crystallized using the sitting-drop vapour-diffusion technique. The crystals of DhaA04 belonged to the orthorhombic space group P212121, while the crystals of DhaA14 and DhaA15 had triclinic symmetry in space group P1. The crystal structures of DhaA04, DhaA14 and DhaA15 with ligands present in the active site were solved and refined using diffraction data to 1.23, 0.95 and 1.22,Å, resolution, respectively. Structural comparisons of the wild type and the three mutants suggest that the tunnels play a key role in the processes of ligand exchange between the buried active site and the surrounding solvent. [source] Crystallization and preliminary X-ray crystallographic analysis of BxlA, an intracellular ,- d -xylosidase from Streptomyces thermoviolaceus OPC-520ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 7 2010Hideaki Morioka BxlA from Streptomyces thermoviolaceus OPC-520, together with the extracellular BxlE and the integral membrane proteins BxlF and BxlG, constitutes a xylanolytic system that participates in the intracellular transport of xylan-degradation products and the production of xylose. To elucidate the mechanism of the hydrolytic degradation of xylooligosaccharides to xylose at the atomic level, X-ray structural analysis of BxlA was attempted. The recombinant BxlA protein (molecular weight 82,kDa) was crystallized by the hanging-drop vapour-diffusion method at 289,K. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 142.2, b = 129.5, c = 101.4,Å, , = 119.8°, and contained two molecules per asymmetric unit (VM = 2.47,Å3,Da,1). Diffraction data were collected to a resolution to 2.50,Å and provided a data set with an overall Rmerge of 8.3%. [source] | |||||||||||||