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PubMed1987

Polymers for biodegradable medical devices. II. Hydroxybutyrate-hydroxyvalerate copolymers: hydrolytic degradation studies.

The hydrolytic degradation of poly(hydroxybutyrate) together with a series of hydroxybutyrate-hydroxyvalerate copolymers has been studied. The effects of copolymer composition and molecular weight are presented together with the results of varying pH and temperature on the degradation rate. Degradation has been monitored by weight loss and water uptake measurements together with goniophotometric, surface energy and scanning electron microscopic studies. Some comparisons with the more widely used so-called 'biodegradable' polymers, poly(glycolic acid), poly(dioxanone) and the glycolic-lactic acid (90:10) copolymers are presented together with the effect of blood plasma on the degradation process.

Biocompatible Materials↗
PubMed1989

Polymers for biodegradable medical devices. VI. Hydroxybutyrate-hydroxyvalerate copolymers: accelerated degradation of blends with polysaccharides.

The hydrolytic degradation of poly(hydroxybutyrate)-poly(hydroxyvalerate) (PHB-PHV) copolymers in the form of blends with the polysaccharides amylose, dextran, dextrin and sodium alginate, has been studied under a range of conditions (pH 2.3, 7.4 and 10.6 and at 37 degrees C and 70 degrees C). The hydrolytic degradation of the PHB-PHV copolymers was found to be dramatically affected by the presence of polysaccharides. Its progress was characterized by an initial increase in the wet weight, with concurrent decrease in the dry weight as the polysaccharides eroded from the matrix. Surface energy measurements and goniophotometry proved to be particularly useful in monitoring this stage of the degradation process. The concurrent increase in internal porosity leads to the eventual collapse of the matrix, a process which occurs, but less rapidly, in the degradation of the unblended PHB-PHV copolymers. Information obtained from molecular weight and crystallinity studies enabled a comprehensive profile of the overall degradation process to be built up.

Alginates↗
PubMed1990

XPS and SSIMS analysis of the surface chemical structure of poly(caprolactone) and poly(beta-hydroxybutyrate-beta-hydroxyvalerate) copolymers.

The surface chemical structures of poly(beta-hydroxybutyrate), poly(caprolactone) and poly(beta-hydroxybutyrate-co-beta-hydroxyvalerate) have been analysed using static secondary ion mass spectrometry and X-ray photoelectron spectroscopy. The X-ray photoelectron spectroscopy data confirm the purity of the polyester surfaces and there is close agreement between the stoichiometric and experimentally determined ratios of the peaks and different carbon environments within the C1s envelopes. The static secondary ion mass spectrometry analysis reveals general fragmentation pathways which permit the ready distinction between the different polyesters examined. The differentiation of the different monomer repeat units in the copolymer together with the detection of some ions representative of the random copolymer sequence are also possible in the static secondary ion mass spectrometry analysis.

Biocompatible Materials↗
PubMed1990

Polymers for biodegradable medical devices. VII. Hydroxybutyrate-hydroxyvalerate copolymers: degradation of copolymers and their blends with polysaccharides under in vitro physiological conditions.

The hydrolytic degradation of hydroxybutyrate-hydroxyvalerate copolymers was monitored in vitro at 37 degrees C and pH 7.4. Direct use of bulk properties such as weight loss and tensile strength did not reveal substantial changes in the polymer matrix over degradation periods of several months. Despite this, the polymers were demonstrated to undergo significant modification during this period, in ways that markedly influence their subsequent behaviour. Combined use of goniophotometry and surface energy measurements revealed that surface modification begins at an early stage and is accompanied by diffusion of water into the matrix and a progressive increase in polymer porosity. Relatively little change in the molecular weight and some increase in the crystallinity of the matrix occurred during these early months. As a result, the tensile strength of the polymer varies little in this period. As the porosity of the matrix increases, hydrolytic chain scission within the matrix and diffusion out of degradation products proceeds more effectively. Decrease in matrix molecular weight, increase in matrix erosion, weight loss and loss of tensile strength began at a much more dramatic rate. The apparent resistance of the polymer to degradation in the early months is followed by an accelerated degradation phase around and beyond 1 yr. The use of filters that can dissolve or hydrolytically degrade more rapidly than the hydroxybutyrate matrix accelerates the development of porosity within the matrix and thus enhances the decomposition process.

Biocompatible Materials↗
PubMed1991

Physico-mechanical properties of degradable polymers used in medical applications: a comparative study.

The physico-mechanical properties of degradable polymers used for medical applications have been characterized. The following polymers were included in this study: three samples of poly(ortho esters) derived from 3,9-bis(ethylidene 2,4,8,10-tetraoxaspiro[5,5]undecane) and various ratios of 1,6-hexanediol and trans-cyclohexane dimethanol, poly(glycolic acid), six samples of poly(L-lactic acid) and poly(D,L-lactic acid) with mol wt from 21,000 to 550,000, poly(epsilon-caprolactone), poly(beta-hydroxybutyrate) and three copolymers of beta-hydroxybutyric acid and various amounts of hydroxyvaleric acid, one sample each of two different types of poly(anhydrides), poly(trimethylene carbonate) and two different poly(imino-carbonates). For each polymer, the thermal properties (glass transition temperature, crystallization, melting and decomposition points) were determined by differential scanning calorimetry and by thermogravimetric analysis. The tensile properties (Young's modulus, tensile strength and elongation at yield and break) were determined by tensile testing on an Instron stress-strain tester. The flexural storage modulus as a function of temperature was determined by dynamic mechanical analysis.

Anhydrides↗
PubMed1991

In vivo and in vitro degradation of poly(3-hydroxybutyrate) in rat.

The inflammatory activity and biodegradation of poly(3-hydroxybutyrate) were examined. Poly(3-hydroxybutyrate) sheet did not cause any inflammation in the chorioallantoic membrane of the developing egg. The i.v. injection of 14C-labelled poly(3-hydroxybutyrate) granules showed that 86, 2.5 and 2.4% of the total radioactivity administered were distributed in the liver, spleen and lung, respectively, and the radioactivity decreased slowly but steadily in most tissues examined during 2 month. Crude extracts of rat tissues showed that the activity degraded the poly(3-hydroxybutyrate) granules in vitro.

Animals↗
PubMed1992

Modification of the biocompatible and haemocompatible properties of polymer substrates by plasma-deposited fluorocarbon coatings.

The polymerization of gases present in a low temperature plasma is a technique particularly well suited for biomedical material processing. Therefore, the possibilities this technique offers to increase the biocompatibility and haemocompatibility of polysulphone and poly(hydroxybutyrate) membranes to be used in a new bioartificial pancreas device were studied. The deposition of thin fluorocarbon coatings from an argon plasma containing perfluorohexane gave very smooth and hydrophobic surfaces without affecting the filtering properties of the treated membranes. Adding hydrogen increased the reaction yield, but gave rougher and less hydrophobic coatings. We characterized the biological properties of the treated surfaces and discussed the influence of the modified surface properties on the biological behaviour of the treated polymers. The good biocompatibility of the deposited coatings was established by following in vitro the insulin secretion of Langerhans islets cultured on the treated membranes and by examining the fibrous capsule that developed on plasma-treated polymer disks after three months of in vivo incubation in the peritoneum of Wistar rats. Rough and haemocompatible films of poly(hydroxybutyrate) and smoother, but more thrombogenic, polysulphone films were treated by perfluorohexane and perfluorohexane + H2 plasmas to study the relative influence of surface roughness and surface energy on polymer thrombogenicity. In vitro protein adsorption and total blood clotting tests proved that the surface roughness influences the thrombogenicity more than the other surface properties. This study seems to show that the plasma deposition of smooth and hydrophobic fluorocarbon coatings can increase the biocompatibility and reduce the surface thrombogenicity of the treated membranes without affecting their filtering properties.

Animals↗
PubMed1995

Enzymatic assay of hydroxybutyric acid monomer formation in poly(beta-hydroxybutyrate) degradation studies.

A novel method for monitoring the degradation of poly(beta-hydroxybutyrate) based on the enzymatic assay of beta-hydroxybutyrate (HBA) monomers has been developed. The method is particularly applicable to forms of the polymer, such as fibre and microcapsules, for which conventional surface and gravimetric monitoring techniques are not readily applicable. The method involves the use of enzyme HBA dehydrogenase in a reaction that converts nicotinamide adenine dinucleotide (NAD) to its reduced form (NADH). The conversion is associated with an increase in light absorption at 340 nm which thus serves to indicate the concentration of HBA monomer in the sample. The application of the methodology to the degradation of poly(beta-hydroxybutyrate) gel spun fibres has been used to demonstrate its potential use as a quantitative monitoring technique in the study of the hydrolysis of this polymer.

Hydrogen-Ion Concentration↗
PubMed1985

Fourier transform-infrared spectroscopic methods for microbial ecology: analysis of bacteria, bacteria-polymer mixtures and biofilms.

Fourier transform-infrared (FT-IR) spectroscopy has been used to rapidly and nondestructively analyze bacteria, bacteria-polymer mixtures, digester samples and microbial biofilms. Diffuse reflectance FT-IR (DRIFT) analysis of freeze-dried, powdered samples offered a means of obtaining structural information. The bacteria examined were divided into two groups. The first group was characterized by a dominant amide I band and the second group of organisms displayed an additional strong carbonyl stretch at approximately 1740 cm-1. The differences illustrated by the subtraction spectra obtained for microbes of the two groups suggest that FT-IR spectroscopy can be utilized to recognize differences in microbial community structure. Calculation of specific band ratios has enabled the composition of bacteria and extracellular or intracellular storage product polymer mixtures to be determined for bacteria-gum arabic (amide I/carbohydrate C-O approximately 1150 cm-1) and bacteria-poly-beta-hydroxybutyrate (amide I/carbonyl approximately 1740 cm-1). The key band ratios correlate with the compositions of the material and provide useful information for the application of FT-IR spectroscopy to environmental biofilm samples and for distinguishing bacteria grown under differing nutrient conditions. DRIFT spectra have been obtained for biofilms produced by Vibrio natriegens on stainless steel disks. Between 48 and 144 h, an increase in bands at approximately 1440 and 1090 cm-1 was seen in FT-IR spectra of the V. natriegens biofilm. DRIFT spectra of mixed culture effluents of anaerobic digesters show differences induced by shifts in input feedstocks. The use of flow-through attenuated total reflectance has permitted in situ real-time changes in biofilm formation to be monitored and provides a powerful tool for understanding the interactions within adherent microbial consortia.

Bacterial Physiological Phenomena↗
PubMed1993

Stability of r-microbes: stabilization of plasmid vectors by the partitioning function of broad-host-range plasmid RP4.

The genes for biosynthesis of the biodegradable polymer poly-beta-hydroxybutyric acid (PHB) cloned from Alcaligenes eutrophus H16 were used for synthesis of PHB with recombinant Escherichia coli strains. It was recognized that the PHB-biosynthesis genes cause segregational instability to the plasmids used as vectors. Recombinant PHB-plasmids are rapidly lost from host cells and plasmid-free cells occur at high rates, even under conditions of selection for the plasmids. Cloning the partitioning region of plasmid RP4 onto such plasmids resulted in a high degree of stabilization. These par-stabilized recombinant PHB-plasmids could be maintained quite efficiently in batch cultivation experiments in the absence of any selection pressure.

Alcaligenes↗
PubMed1994

Construction of plasmids, estimation of plasmid stability, and use of stable plasmids for the production of poly(3-hydroxybutyric acid) by recombinant Escherichia coli.

Plasmids containing the Alcaligenes eutrophus poly(3-hydroxybutyric acid) (PHB) biosynthetic genes were constructed for the production of PHB in Escherichia coli and plasmid stability was investigated by repeated subculturing without antibiotic pressure. Both pSYL101 (high copy) and pSYL102 (medium copy) were unstable during the subcultures. Higher instability was observed when cells were accumulating PHB. Segregational instability was aggravated by the faster growth of plasmid-free cells and by appearance of non-dividing cells harboring large amount of PHB during the fed-batch culture. Two derivatives, pSYL103 and pSYL104, were then developed by cloning the parB locus of plasmid R1 into pSYL102 and pSYL101, respectively. They showed 100% stability even during PHB synthesis and accumulation over 110 generations. All four plasmids were structurally stable. The final cell mass, PHB concentration, and PHB per dry cell weight (P/X, w/w, %) of 101.4 g l-1, 81.2 g l-1, and 80.1%, respectively, were obtained in 39 h by high cell density culture of XL1-Blue (pSYL104). The final PHB concentration was lower using XL1-Blue (pSYL103), which suggested that high gene dosage was required for the synthesis and accumulation of PHB to a high concentration in E. coli.

Escherichia coli↗
PubMed1986

Degradation of poly(3-hydroxybutyrate) by poly(3-hydroxybutyrate) depolymerase from Alcaligenes faecalis T1.

The extracellular poly(3-hydroxybutyrate) depolymerase purified from Alcaligenes faecalis T1 has two disulfide bonds, one of which appears to be necessary for the full enzyme activity. This depolymerase hydrolyzed not only hydrophobic poly(3-hydroxybutyrate) but also water-soluble trimer and larger oligomers of D-(-)-3-hydroxybutyrate, regardless of their solubilities in water. Kinetic analyses with oligomers of various sizes indicated that the substrate cleaving site of the enzyme consisted of four subsites with individual affinities for monomer units of the substrate. Analyses of the hydrolytic products of oligomers, which had labeled D-(-)-3-hydroxybutyrate at the hydroxy terminus, showed that the enzyme cleaved only the second ester linkage from the hydroxy terminus of the trimer and tetramer, and acted as an endo-type hydrolase toward the pentamer and higher oligomers. The enzyme appeared to have a hydrophobic site which interacted with poly(3-hydroxybutyrate) and determined the affinity of the enzyme toward the hydrophobic substrate.

Alcaligenes↗
PubMed1989

Poly-beta-hydroxybutyric acid in staphylococci.

Poly-beta-hydroxybutyric acid (PHB) was extracted from various species of staphylococci isolated from different sources. IR and UV spectrophotometry and NMR analysis revealed that the compound consisted only of the beta-hydroxybutyrate. The PHB level in the richest strain among investigated staphylococci is about 64-fold less than in bacilli. The intrinsic viscosity number of this polymer is more than twice greater in the case of the staphylococcal product than that of bacilli.

Hydroxybutyrates↗
PubMed1990

Cyclic nature of poly(3-hydroxyalkanoate) metabolism in Alcaligenes eutrophus.

The cyclic process of biosynthesis and degradation of poly(3-hydroxyalkanoate) (PHA) was studied in Alcaligenes eutrophus under conditions of nitrogen-limitation of growth. A. eutrophus cells, which had accumulated poly(3-hydroxybutyrate) (PHB) of 55 wt% content within cells from butyric acid, were transferred into a nitrogen-free medium containing pentanoic acid as the sole carbon source and cultivated at 30 degrees C and pH 7.5. The content of PHB in A. eutrophus cells decreased with time, whereas a copolyester of 3-hydroxybutyrate (HB) and 3-hydroxyvalerate (HV) units, P(HB-co-HV), was accumulated in the presence of pentanoic acid. Conversely, when A. eutrophus cells with 50 wt% content of P(HB-co-56% HV) were incubated in a nitrogen-free medium containing butyric acid, the content of P(HB-co-56% HV) decreased with time, whereas PHB was accumulated. These results indicate the cyclic nature of PHA metabolism in A. eutrophus under these conditions.

Alcaligenes↗
PubMed1992

Isolation and identification of granule-associated proteins relevant for poly(3-hydroxyalkanoic acid) biosynthesis in Chromatium vinosum D.

Poly(3-hydroxybutyric acid) granules, which harbored only four major granule-associated proteins as revealed by SDS polyacrylamide gel electrophoresis, were isolated from crude cellular extracts of Chromatium vinosum D by centrifugation in a linear sucrose gradient. N-Terminal amino acid sequence determination identified two proteins of M(r) 41,000 and M(r) 40,000 as the phaECv and phaCCv translational products, respectively, of C. vinosum D. In a previous study it was shown that both proteins are required for the expression of poly(3-hydroxyalkanoic acid) synthase activity. The N-terminus of the third protein (M(r) 17,000) exhibited no homology to other proteins. Lysozyme, which was added during purification of the granules, exhibited a strong affinity to PHB granules and was identified as the fourth protein enriched with the granules.

Acyltransferases↗
PubMed1992

Polyhydroxyalkanoate production in recombinant Escherichia coli.

The bacterial species Escherichia coli has proven to be a powerful tool in the molecular analysis of polyhydroxyalkanoate (PHA) biosynthesis. In addition, E. coli holds promise as a source for economical PHA production. Using this microorganism, clones have been developed in our laboratory which direct the synthesis of poly-beta-hydroxybutyrate (PHB) to levels as high as 95% of the cell dry weight. These clones have been further enhanced by the addition of a genetically mediated lysis system that allows the PHB granules to be released gently and efficiently. This paper describes these developments, as well as the use of an E. coli strain to produce the copolymer poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-co-3HV).

Escherichia coli↗
PubMed1992

Intracellular degradation of poly(3-hydroxybutyrate) granules of Zoogloea ramigera I-16-M.

Intracellular degradation of poly(3-hydroxybutyrate) (PHB) in bacteria is not yet clear. The properties of the autodigestion of native PHB granules from Zoogloea ramigera I-16-M were examined. The release of D(-)-3-hydroxybutyrate was observed only at pH values higher than about 8.5 and at relatively high ionic strength (optimal concentration 200 mM NaCl). Triton X-100 and diisopropylfluorophosphate inhibited this reaction. Addition of the supernatant fraction of Z. ramigera did not increase the release of D(-)-3-hydroxybutyrate from the native PHB granules. On the other hand, using the protease-treated PHB granules from Alcaligenes eutrophus as a substrate, PHB depolymerase activity was detected in the supernatant fraction of Z. ramigera cells. The soluble PHB depolymerase showed similar properties to the enzyme in the PHB granules. Since PHB depolymerase activity was found in fractions containing D(-)-3-hydroxybutyrate oligomer hydrolase activity, which were separated by DEAE-Toyopearl or by Sephacryl S-100, it is possible that the intracellular PHB depolymerase is identical to the oligomer hydrolase which has been purified already.

Biodegradation, Environmental↗