TH‐11, a bacterial strain with strong depolymerase activity that breaks down aliphatic esters such as poly(3‐hydroxybutyrate) (PHB) and poly(ethylene succinate) (PES) was isolated from a soil sample collected from the sediment of Tou‐Chain River, Taiwan, R.O.C. It was phenotypically and genetically characterized to be a Streptomyces strain. The degradation of PHB and PES were tested both using emulsified polymers in solid agar and thin polymer films in liquid culture media. The degradations were measured by clear‐zone formation on solid agar plates, or direct weight measurements and electromicroscope inspection of the incubated polymer films in the liquid culture. The depolymerase activities can be detected in the cell‐free preparation of the culture medium, and can be enhanced by gelatin. 相似文献
The synthesis of multi‐arm poly([R]‐3‐hydroxybutyrate) (PHB)‐based triblock copolymers (poly([R]‐3‐hydroxybutyrate)‐b‐poly(N‐isopropylacrylamide)‐b‐[[poly(methyl ether methacrylate)‐g‐poly(ethylene glycol)]‐co‐[poly(methacrylate)‐g‐poly(propylene glycol)]], PHB‐b‐PNIPAAM‐b‐(PPEGMEMA‐co‐PPPGMA), and their subsequent self‐assembly into thermo‐responsive hydrogels is described. Atom transfer radical polymerization (ATRP) of N‐isopropylacrylamide (NIPAAM) followed by poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and poly(propylene glycol) methacrylate (PPGMA) was achieved from bromoesterified multi‐arm PHB macroinitiators. The composition of the resulting copolymers was investigated by 1H and 13C J‐MOD NMR spectroscopy as well as size‐exclusion chromatography (SEC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The copolymers featuring different architectures and distinct hydrophilic/hydrophobic contents were found to self‐assemble into thermo‐responsive gels in aqueous solution. Rheological studies indicated that the linear one‐arm PHB‐based copolymer tend to form a micellar solution, whereas the two‐ and four‐arm PHB‐based copolymers afforded gels with enhanced mechanical properties and solid‐like behavior. These investigations are the first to correlate the gelation properties to the arm number of a PHB‐based copolymer. All copolymers revealed a double thermo‐responsive behavior due to the NIPAAM and PPGMA blocks, thus allowing first the copolymer self‐assembly at room temperature, and then the delivery of a drug at body temperature (37 °C). The non‐significant toxic response of the gels, as assessed by the cell viability of the CCD‐112CoN human fibroblast cell line with different concentrations of the triblock copolymers ranging from 0.03 to 1 mg mL?1, suggest that these PHB‐based thermo‐responsive gels are promising candidate biomaterials for drug‐delivery applications. 相似文献
Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using 1H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the Tg of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as αS and αH, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains. 相似文献
Abstract A new pretreatment method for the gas chromatographic determination of poly(3‐hydroxybutyrate) (PHB) was developed based on a combination of alkaline hydrolysis and acid esterification. The determination principle is as follows: PHB is hydrolyzed to its monomer 3‐hydroxybutyrate by alkaline solution, followed by the esterification with methanol to generate the methyl ester of 3‐hydroxybutyrate catalyzed by acid, which is detected by a gas chromatography. From the comparison of effects of alkali and acid on PHB hydrolysis and 3‐hydroxybutyrate esterification, alkali resulted in a better performance for the hydrolysis, while acid was better for the esterification. The pretreatment conditions for PHB were optimized and the determination performance was characterized. 相似文献
A series of telechelic oligo[(R,S)‐3‐hydroxybutyrate]‐diols (PHB‐diols) was synthesized from ethyl (R,S)‐3‐hydroxybutyrate (ethyl (HB)) and four different aliphatic diols, namely, 1,4‐butanediol, 1,6‐hexanediol, 1,8‐octanediol and 1,10‐decanediol by transesterification and condensation in bulk. The structures of the synthesized oligomers were confirmed by 1H NMR spectroscopy and MALDI‐TOF mass spectroscopy. The use of 1,4‐butanediol results in an oligoester with hydroxyl functionality of approximately 2. In the case of the higher aliphatic diols, the number average functionalities were found to be lower than 2. These differences were ascribed to side reactions which occur during polymerization, yielding unreactive end groups. Other novel families of biodegradable poly(ester‐urethane)s were synthesized either from PHB‐diol alone, or PHB‐diol mixed with poly(ε‐caprolactone)‐diol (PCL‐diol), poly(butylene adipate)‐diol (PBA‐diol) or poly(diethylene glycol adipate)‐diol (PDEGA‐diol). In each case, 1,6‐hexamethylene diisocyanate was used as a nontoxic connecting agent. The homopolymers prepared from PCL‐diol, PBA‐diol and PDEGA‐diol were also synthesized for the sake of comparison. All the prepared copolymers possess high molecular weight with glass transition temperature (Tg) values varying from –54 to –23°C. Some of the prepared copoly(ester‐urethane)s are partially crystalline with melting temperatures (Tm's) varying from 37 to 56°C. 相似文献
The defect Gibbs energy of hydroxyvalerate comonomer inclusions into the crystals made up by random copolymers of poly(β‐hydroxybutyrate‐co‐β‐hydroxyvalerate) (PHB/HV) is calculated by means of the thermodynamic integration approach. The result obtained for a single inclusion is in excellent agreement with those obtained by fitting experimental melting temperature and cocrystal composition data. Lattice model calculations that cover the whole range of copolymer composition were carried out based on calculations of double inclusion, which revealed a decrease of the average defect Gibbs energy in adjacent defects. On decomposing the Gibbs energy, it is found that the configurational entropy contributes the dominant part of the defect Gibbs energy. 相似文献
This work is a review of the results of biomedical studies of polymer devices (films, fibers, microparticles, 3D implants) made from resorbable PHAs synthesized by the bacterium Wautersia (Ralstonia) eutropha B5786, using the technology developed at the Institute of Biophysics of the Siberian Branch of the Russian Academy of Sciences. Two types of PHAs – polyhydroxybutyrate (PHB) and a hydroxybutyrate/hydroxyvalerate copolymer (PHB/PHV) – have been proven to be biocompatible in vitro in cultures of fibroblasts, endothelial cells, hepatocytes, and osteoblasts, and in short- and long-duration experiments on animals. Polymer films and membranes have been found to be usable as scaffolds for functioning cells and monofilament suture fibers – for stitching muscular-fascial wounds and in abdominal surgery. Ectopic bone formation assay and experiments with the model of segmental osteotomy showed that 3D PHB and PHB/HA implants can be used for reparative osteogenesis. The paper reports beneficial results of using polymers to repair bone defects in oral surgery. 相似文献
Summary: Liquid‐nitrogen quenching was applied to study the enthalpy effect on the stress‐induced crystallization of microbial polyesters. Crystallization bands of poly(3‐hydroxybutyrate) exhibited the potential to reveal the stress distribution in the melt; while crystallization of poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] gave shish‐kebab structures. Polarized‐light micrographs confirmed that the enhanced nucleation was attributed to the tensile stress. Furthermore, control of the quenching direction provides a method to direct the lamellar growth.
Polarized‐light micrographs of PHB film crystallized at 90 °C after quenching in liquid nitrogen from the melt. The normal of the bands, namely the lamellar growth direction, runs predominantly parallel to the stress direction. 相似文献
In this study, uracil has been introduced as the nucleating agent (NA) for bacterially synthesized poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] (PHBHHx) copolymers with HHx content of 5, 10, 18 mol‐%, and poly(3‐hydroxybutyrate) (PHB) homopolymer for the first time. Its effect was compared with the conventional NA of PHB, that is, boron nitride (BN), and two other naturally occurring pyrimidine derivatives, i.e., thymine and cytosine. The effects of uracil on the crystallization kinetics, melting behavior, spherulite morphology, and crystalline structure of PHBHHx and PHB were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Uracil and BN exhibit the comparable nucleation efficiency on the crystallization of PHB, whereas uracil shows much more effective nucleation ability than BN for PHBHHx copolymers. With incorporation of 1 wt.‐% uracil, PHBHHx with 0–10 mol‐% HHx units can finish crystallization upon cooling at 10 °C · min?1. The crystallization half‐times (t1/2) of all the PHB and PHBHHx samples decrease significantly with presence of uracil. The crystallization rate of polymers further enhances with increase in uracil concentration. With addition of 1 wt.‐% uracil, the t1/2 value of PHBHHx with 10 mol‐% HHx units melt‐crystallizing at 80 °C decreases to ≈4.0% of the neat polymer, and the nucleation density increases by 3–4 orders of magnitude. The incorporation of uracil has no discernable effect on the crystalline structure of PHBHHx, as evidenced by WAXD results. It was proposed that the nucleation mechanism of the uracil/PHBHHx (or PHB) system might be the epitaxial nucleation.
Abstract A combination of enzyme‐based spectrophotometric analysis and alkaline hydrolysis was developed for the measurement of poly(3‐hydroxybutyrate) (PHB). The principle of the determination is as follows: alkaline hydrolysis decomposes PHB into its monomer product 3‐hydroxybutyrate, which is followed with enzymatic reaction catalyzed by 3‐hydroxybutyrate dehydrogenase in the presence of nicotinamide adenosine dinucleotide (NAD). The product, nicotinamide adenosine dinucleotide with hydrogen (NADH) results in a spectrophotometric signal at 340 nm. This method shows high performance characteristics with simple operations. 相似文献
The aim of this work was to obtain biodegradable polymeric systems based on poly(hydroxybutyrate) (PHB) for use in the controlled release of agrochemicals and to analyze the relationship between the properties of polymers and the rates of release of active compounds. Two types of systems were obtained: one using nitrogen, phosphorous, and potassium (NPK) fertilizer directly mixed within the polymer matrix and another with the fertilizer previously incorporated in bentonite (Bent) and mixed with the polymer. The systems were obtained by melt processing and then evaluated by their properties. The release of the active compounds was analyzed by conductometric analysis using an aqueous solution as release medium for 240 hours. The obtained results were correlated with the biodegradation process of PHB. All of the systems presented a significant reduction in the active compounds released to the environment as compared with the direct application of NPK. The PHB/NPK systems showed a release of up to 37% of the compounds, while the PHB/m‐Bent showed greater control, with a release between 4% and 11% after 240 hours. In addition, the properties of the polymer systems presented a direct relationship with the rate of active compounds released. The type of production process, properties, and biodegradability indicate interesting potential of these systems for application in the controlled release of active compounds. 相似文献