In vitro production of polyhydroxyalkanoates: achievements and applications

The mechanisms of polyhydroxyalkanoate (PHA) production have been studied for over half a century. However, despite numerous improvements in the control of monomer composition, genetically‐engineered host organisms, fermentation strategies and polymer recovery processes they remain uncompetitive compared with petrochemical plastics. Recently, interest has developed in the enzyme‐catalysed production of PHAs in vitro. This has allowed the study of enzyme kinetics and properties, and represents another strategy for the economic production of PHAs on the industrial scale. It also presents an opportunity to coat other materials in thin films of PHA so as to modify the surface properties. In vitro production offers advantages over in vivo methods as it enables greater control over monomer composition and molecular weight, does not require a biomass‐accumulation phase, simplifies downstream processing and can utilise a wider range of monomeric subunits. Copyright © 2009 Society of Chemical Industry     

Polyhydroxyalkanoates,a family of natural polymers,and their applications in drug delivery

Polyhydroxyalkanoates (PHAs) are natural biopolymers produced by various microorganisms as a reserve of carbon and energy. PHA synthesis generally occurs during fermentation under nutrient limiting conditions with excess carbon. There are two main types of PHAs, short chain length PHAs (scl‐PHAs) and medium chain length PHAs (mcl‐PHAs). The mechanical and thermal properties of PHAs depend mainly on the number of carbons in the monomer unit and its molecular weight. PHAs are promising materials for biomedical applications because they are biodegradable, non‐toxic and biocompatible. The large range of PHAs, along with their varying physical properties and high biocompatibility, make them highly attractive biomaterials for use in drug delivery. They can be used to produce tablets, micro‐ and nanoparticles as well as drug eluting scaffolds. A large range of different PHAs have been explored and the results obtained suggest that PHAs are excellent candidates for controlled and targeted drug delivery systems. © 2015 Society of Chemical Industry     

Ralstonia eutropha PHB－4重组菌合成PHA共聚物及性质测定

A series of polyhydroxyalkanoate（PHA）copolymers consisting of short-chain-length（SCL）and medium-chain-length（MCL）3-hydroxyalkanoate（3HA）monomers were synthesized in the recombinant Ralstonia eutropha PHB - 4 harboring a low-substrate-specificity PHA synthase PhaC2Ps from Pseudomonas stutzeri 1317. These polyesters,whose monomer compositions varied widely in chain length,were purified and characterized by acetone fractionation,nuclear magnetic resonance（NMR）,gel-permeation chromatography（GPC）,and differential scanning calorimetry（DSC）.This was the first time that the physical properties of PHA copolymers polymerized by PhaC2Ps were characterized.The results indicated that the variation in MCL 3HA contents did not have an obvious influence on the molecular weights of these PHA copolymers but was effective in changing their physical properties. The variation in the thermal property of PHA copolymers with 3-hydroxyoctanoate（3HO） content was also investigated in this study.     

A novel and wide substrate specific polyhydroxyalkanoate (PHA) synthase from unculturable bacteria found in mangrove soil

This study reports the discovery of a polyhydroxyalkanoate (PHA) synthase (PhaC) possessing very wide substrate specificity from a mangrove soil metagenome. For the first time, putative PhaCs were identified from a metagenome using next-generation sequencing (NGS) and bioinformatic approaches. High-throughput shotgun metagenomic sequencing was conducted using the Illumina HiSeq 2000 platform. Sequence annotation and bioinformatic analyses were performed using the MG-RAST metagenomic pipeline. Reads annotated as PhaC against the NCBI RefSeq database were retrieved using the MG-RAST RESTful API (Application Programming Interface). PhaC gene sequence assembly was accomplished using the SPAdes assembler. A total of two de novo assembled contigs were subjected to sequence verification. A putative PhaC sequence, “BP-M-CPF4”, was selected for functional assessment by in vivo PHA biosynthesis in a PHA-negative mutant. An artificial stop codon was added at the 3′-end of the incomplete coding gene sequence. This novel PhaC showed very broad substrate specificity with the ability to incorporate six types of PHA monomers, 3-hydroxybutyrate (3HB), 3-hydroxyvalerate (3HV), 4-hydroxybutyrate (4HB), 3-hydroxy-4-methylvalerate (3H4MV), 5-hydroxyvalerate (5HV) and 3-hydroxyhexanoate (3HHx) in the presence of suitable precursors. This PHA synthase is suitable for the biosynthesis of PHAs that can be used in various biomedical applications due to its ability to incorporate the lipase-degradable monomer sequences of 4HB and 5HV. This study demonstrates that a functional metagenomic approach using next-generation sequencing can be used to mine novel PHA synthases with interesting substrate specificities from unculturable microorganisms.     

The chemomechanical properties of microbial polyhydroxyalkanoates

Microbially produced polyhydroxyalkanoates (PHAs) are fully biodegradable biopolyesters that have attracted much attention recently as alternative polymeric materials that can be produced from biorenewable and biowaste resources. The properties of these biological polymers are affected by the same fundamental principles as those of fossil-fuel derived polyolefins, with a broad range of compositions available based on the incorporation of different monomers into the PHA polymer structure, and with this broad range tailoring subsequent properties. This review comprehensively covers current understanding with respect to PHA biosynthesis and crystallinity, and the effect of composition, microstructure and supramacromolecular structures on chemomechanical properties. While polymer composition and microstructure are shown to affect these properties, the review also finds that a key driver for determining polymer performance properties is compositional distribution. From this review it follows that PHA–PHA blend compositions are industrially important, and the performance properties of such blends are discussed. A particular need is identified for further research into the effect of chemical compositional distribution on macromolecular structure and end-use properties, advanced modeling of the PHA accumulation process and chain growth kinetics for better process control.     

聚羟基烷酸酯的生物合成研究进展

聚羟基烷酸酯（PHA）是一类在众多微生物细胞内可合成的聚酯,由于其可完全生物降解,是一类可替代传统塑料的新型生物材料。该类聚酯在不同的微生物细胞内的生物合成途径已经被广泛和深入地研究。为降低其生产成本,实现工业化生产,筛选更高产的菌株和利用廉价碳源来合成PHA成为近年来的研究重点。本文介绍了PHA的在微生物细胞内的合成途径以及最近几年来生物合成PHA的研究进展。     

聚羟基烷基酸酯及其改性研究

介绍了聚羟基烷基酸酯的化学结构,物理性质,详细论述了用天然高分子,化学合成高聚物及生物技术改性聚羟基烷基酸酯的研究进展。     

Synthetic hydrogels. 1. Effects of solvent on poly(acrylamide) networks

Acrylamide hydrogels were synthesized in a series of hydro-organic solvents to examine how solvent affects the network structure by influencing properties of the first formed polymer in the reaction mixture. The looser and more heterogeneous network structure of gels formed in aqueous solutions of ethylene glycol or propylene glycol was found to be largely due to the reduced chain lengths of the primary polymer molecules. Results from NMR analysis of the monomer, and intrinsic viscosity measurements of the polymer in various solvents indicate that solvent effects on the reactivity of the monomer and the propagating radical impose an overriding control over properties of the resultant networks.     

A physical insight into sonochemical emulsion polymerization with cavitation bubble dynamics

This paper tries to explain the physical features of the sonochemical emulsion polymerization process by coupling experiments with different conditions (such as monomer type, saturation level of the medium and the type of bubbling gas) with a mathematical model for the radial motion of cavitation bubble. Experiments have been performed without any added chemical initiator or surfactant. Time variation of the mean size and size distribution of polymer particles in the emulsion have been used as a measure for the analysis. This measure is found to be governed by various parameters such as rate of radical production from the cavitation bubbles, magnitude of the microturbulence and shock waves produced by the cavitation bubbles, glass transition temperature of polymer and the population density of polymer particles. The relative magnitudes of these parameters vary significantly with the experimental conditions. This variation has been explained on the basis of results of simulation of radial motion of cavitation bubble. It is revealed that the mean particle size and size distribution of particles are manifestation of simultaneous and resultant influence of these parameters.     

Synthesis and characterization of polymer light conduits

Summary Large diameter polymer light conduits are prepared for the first time by UV-curing. The polymer cores of the polymer light conduits are prepared from the copolymerization of various monomer mixtures in FEP tubes by UV curing, where FEP is used as the polymer cladding. The monomer mixtures consist of a multifunctional monomer for adjusting the heat resistance of the polymer cores and a monofunctional monomer for adjusting the flexibility. Experimental results indicate that the properties of the prepared polymer light conduits can be significantly modified by the formulations of the reactant mixtures. The onset thermal decomposition temperatures of the prepared polymer cores are 50°C to 79°C higher than that of the PMMA core. The glass transition temperatures and the refractive indices of the prepared polymer cores decrease from 78°C to -34°C and 1.490 to 1.474, respectively, when the contents of 2-ethyl-hexyl acrylate in the monomer mixtures increase from 0% to 70%. The prepared polymer light conduits conduits have large numerical apertures suitable for wide angle illumination applications.     

The gamma-ray-induced crosslinking of polyacrylamide

The gamma-ray-induced crosslinking of polyacrylamide was carried out under various conditions. The molecular weight of the polymer before inrradiation was found to be the most important factor for crosslinking. When polymers have low molecular weights such as 80,000, the intensity of radiation, the external pressure applied, and the water content of the polymer powder became important for crosslinking. Although the polycrylamide hydrogel can be obtained directly by irradiating the monomer, it was obtained more conveniently by the irradiation of monomer—polymer mixtures. The hydrogels obtained by the radiation with a dose of over 50 kgray, absorb water by 1000–1500 wt %.     

In-situ polymerization of styrene in AAO nanocavities

One of the most promising aspects of the anodic aluminium oxide (AAO) template is the ability to generate a variety of different hierarchical one-dimensional (1D) polymer morphologies with structural definition on the nanometric scale. In-situ polymerization of monomers in reduced space of porous AAO template nanocavities can give rise to the direct production of versatile polymer nanostructures. In this work, porous AAO devices of 35 nm of diameter have been obtained by a two-step electrochemical anodization process and used as a nanoreactor to study the radical polymerization kinetics of styrene (St) in confinement and the results compared to those of polymerization in bulk. SEM morphological study has been conducted to establish the final structure of obtained polymer nanostructures. Confocal Raman microscopy has been performed to study the formation of the polymer through the AAO cavities as a function of time and with this methodology it has been possible to establish the monomer conversion for styrenic polymerization in AAO devices. Polystyrene obtained in the nanoreactor was characterized by SEC, NMR, TGA and DSC and the properties compared with those of bulk polymer. It was found that both the average molecular weights and polydispersity index of nanostructured polymer are lower than those obtained for bulk polymer. NMR studies have shown that the use of a reactor with nanometric size dimensions gave the obtained polystyrene greater stereospecificity than that obtained in bulk. Thermal stability and glass transition temperature (T_g) values are higher for nanostructured than bulk polymers. Moreover, the methodology proposed in this work, using AAO nanocavities as nanoreactors for polymerization reaction, can be generalized and applied to obtain polymer nanostructures of very different chemical nature and morphology by choosing the appropriate monomer or monomer reactants and by tailoring the dimension of AAO cylindrical nanocavities, that is, diameter from 20 to 400 nm and length from a few to hundreds of microns.     

Lignocellulosic and marine biomass as resource for production of polyhydroxyalkanoates

Polyhydroxyalkanoates (PHAs) are considered as sustainable ‘green/bio plastics’ because they have potential to replace their depleting petroleum-based competitors in the recent future. To reach this goal, PHAs must be able to compete with the established petroleum-based plastics in both technical and economic aspects. The current PHA production is based on high-priced substrates of high nutritional value and simple carbon sources such as glucose, sucrose, starch, or vegetable oils. Non-food based carbon-rich complex polysaccharides of lignocellulosic and marine biomass can be used as alternative and suitable feedstock through consolidated bioprocessing (CBP). CBP is a promising strategy that involves the production of lytic enzymes, hydrolysis of biomass, and fermentation of resulting sugars to desired products in a single process step. CBP offers very large cost reductions if microorganisms possessing the abilities are found or microbial processes are developed to utilize substrate and simultaneously produce products. This review focuses on possible available complex polysaccharides of lignocellulosic and marine biomass that can be used as resources to produce PHAs in biorefineries, including CBP.     

Acyclic diene metathesis polymerization: History,methods and applications

Acyclic Diene Metathesis (ADMET) polymerization was established decades ago and has since developed into a robust and reliable technique. A wide range of different, new materials exhibiting unique properties has been produced via ADMET polymerization since its development. This versatile technique allows, through the right combination of monomer design and choice of catalyst, the synthesis of various functional polymers in addition to a precise control over primary structure. Systematic studies on precise ADMET polymers have greatly contributed to a better understanding of how branch identity and its distribution along the polymer backbone affect the thermal/electronic properties, crystallization, molecular dynamics and morphology of different materials. This article presents an extensive review of how ADMET started, the mechanism that underlies the structural features of ADMET polymers and the different strategies and techniques that have been developed over the years to overcome common synthetic challenges. Monomer synthesis methods are also discussed in detail, providing an important overview of the limitations and advantages of using ADMET as a polymerization technique. Many examples are given of functional ADMET polymers that have been developed by research groups all over the world.     

Production of polyhydroxyalkanoates: the future green materials of choice

Polyhydroxyalkanoates (PHAs) have recently been the focus of attention as a biodegradable and biocompatible substitute for conventional non degradable plastics. The cost of large‐scale production of these polymers has inhibited its widespread use. Thus, economical, large‐scale production of PHAs is currently being studied intensively. Various bacterial strains, either wild‐type or recombinant have been utilized with a wide spectrum of utilizable carbon sources. New fermentation strategies have been developed for the efficient production of PHAs at high concentration and productivity. With the current advances, PHAs can now be produced to a concentration of 80 g L^?1 with productivities greater than 4 g PHA L^?1 h^?1. These advances will further lower the production cost of PHAs and allow this family of polymers to become a leading biodegradable polymer in the near future. This review describes the properties of PHAs, their uses, the various attempts towards the production of PHAs, focusing on the utilization of cheap substrates and the development of different fermentation strategies for the production of these polymers, an essential step forward towards their widespread use. Copyright © 2010 Society of Chemical Industry     

Polyhydroxyalkanoates: Recent Advances in Their Synthesis and Applications

Polyhydroxyalkanoates (PHAs) are microbial biopolymers (polyesters) that have a wide range of functions and applications. They serve in nature mainly as carbon and energy storage materials for a variety of microorganisms. In past decades, their utilization has attracted much attention, from commodities and degradable plastics to specialty performance materials in medicine. PHA biosynthesis has been well understood, and it is now possible to design bacterial strands to produce PHAs with desired properties. The substrates for the fermentative production of PHAs are very manifold: some are derived from food‐based carbon sources (e.g., fats and oils (triglycerids)), thus raising concerns with regard to the sustainability of their productions in terms of crop area and food. In addition, hemicellulose hydrolysates, crude glycerol, and methanol are very promising carbon sources for the sustainable production of PHAs. The integration of PHA production within a modern biorefinery is an important issue and can result in a simultaneous production of biofuels and bioplastics. Furthermore, many chemical‐synthetic procedures by means of efficient catalysts can give access to a variety of PHAs. This article summarizes recent developments in these fields and emphasizes the importance of a sustainable PHA‐based industry. Practical Applications: Practical applications of the microbial polyesters PHAs are, for example, a variety of sustainably produced commodities as well as special applications in (bio)medicine, for example, tissue engineering.     

Synthesis and Swelling Properties of Hydrolyzed Cottonseed Protein Composite Superabsorbent Hydrogel

A novel protein-based superabsorbent hydrogel was synthesized by graft copolymerization of hydrolyzed cottonseed protein (HCP) and acrylic acid (AA) monomer. This hydrogel was synthesized by solution-based copolymerization, using N,N-methylene bisacrylamide as a crosslinking agent, potassium persulphate and sodium sulfite as the initiators. The effects of the certain variables of the graft copolymerization on the swelling capacity of the hydrogel were measured and its swelling properties in different solutions were investigated as well. This new approach is a promising method in utilizing hydrolyzed cottonseed protein in the production of a superabsorbent polymer with excellent water absorbency and potential use in various applications.     

Tailoring Silica Surface Properties by Plasma Polymerization for Elastomer Applications

The surface properties of reinforcing fillers are a crucial factor for dispersion and filler–polymer interaction in rubber compounds, as they strongly influence the final vulcanized properties of the rubber article. Silica is gaining more and more importance as reinforcing filler for rubbers, as it allows for a reduction of rolling resistance and thus energy losses in tires, compared to the use of carbon black as filler. However, silica and common elastomers differ greatly in polarity and, therefore, are difficult to mix and thus have little interaction. In the present study plasma-coating of silica-filler with acetylene, thiophene and pyrrole is applied, and the surface-treated silicas are blended with S-SBR rubber, in an attempt to enhance the compatibility between the two. The dispersion and reinforcing effects of the modified silicas are investigated and compared with untreated and silanized silica. The relative rankings of the various coatings in reduction of filler–filler interaction, improved dispersion, enhanced polymer–filler interaction, apparent crosslink density and tensile mechanical properties are mutually different. Where the best silica dispersion and largest reduction in filler–filler interaction are obtained with polyacetylene coating and the worst with polythiophene coating, but the tensile properties achieved with the polythiophene coating are far better than all others. Apparently, the sulfur contained in the thiophene-moiety enhances the filler–polymer interaction and contributes to the degree of crosslinking. Unmodified silica performs worst in all aspects, also because its acidic nature harms the preferably alkaline vulcanization process. Silane treatment of silica has a positive effect on reduction of filler–filler interaction and improved dispersion, but has little effect on polymer–filler interaction in the still unvulcanized state. Its tensile properties after vulcanization are comparable with polyacetylene- or polypyrrole-coated silica. This investigation shows that the compatibility and interaction of silica with a polymer can be controlled by tailoring the surface energy of the filler by coating with plasma polymers. An appropriate monomer for the plasma polymerization process allows to improve the cured rubber properties.     

The thermal step technique: an advanced method for studying the properties and testing the quality of polymers

It is well known that the physical properties of a polymer alter with time. This phenomenon—ageing—is strongly related to the external factors acting upon the polymer and to the manufacturing process. An appropriate process could prevent the premature and undesired changes in the characteristics of a polymeric material. For this reason, considerable efforts are made to understand the mechanism of polymer degradation. Past studies have shown that the existence of electrical charges in the bulk of polymers can affect their properties significantly. These charges—usually called space charges or space charge—were first observed in polymers used for electrical insulation and therefore submitted to high electric fields. Some recent studies, particularly those presented in this paper, proved that space charge exists in almost every polymer. It has been shown that space charge can be present within the material from the very manufacturing process, without previous submission to stress. The increase of the amount of the space charge seems strongly related to the deterioration of the physical properties of polymers. Space charge measurements can therefore be considered as a test of quality for polymers. This paper is dedicated to a method for measuring space charge: the Thermal Step Method (TSM). The physical basis of the technique, as well as its applications, are presented. Results obtained on various polymers are presented and discussed. The results show that the features of this technique, particularly its high sensitivity, make it an appropriate tool for the characterization of a wide variety of materials. The TSM could also be associated with other physical, chemical or physico-chemical techniques. © 1998 SCI.     

Vinyl monomers bearing chromophore moieties and their polymers. VI. Synthesis and photochemical behavior of acrylic monomer bearing phenoxazine moiety and its polymer

An acrylic monomer having phenoxazine moiety, i.e., N-acryloylphenoxazine (APO), has been synthesized by dehydrochlorination of N-(3-chloropropionyl)phenoxazine with 1,5-diazabicyclo[5.4.0]undec-5-ene in dimethyl sulfoxide. The monomer can be polymerized with AIBN as an initiator. The photochemical behavior, including the fluorescence and photosensitizing properties of this monomer and its polymer, has been studied. It has been recorded that the absorption spectrum of polymer P(APO) displays a few blue shifts compared with its monomer APO. It has also been observed that the fluorescence emission intensity of the monomer is dramatically lower than that of its polymer at the same chromophore concentration. This may be ascribed to the charge transfer interacting between the coexisting electron-accepting acrylic carbon-carbon double bond and the electron-donation phenoxazine moiety in APO, intramolecularly or intermolecularly on excitation. The fluorescence of the APO polymer, which does not have carbon-carbon double bond, can be quenched by electron-deficient unsaturated nitriles and esters, clarifying that the electron-deficient carbon-carbon double bond does play an important role for the fluorescence quenching of the monomer. Thus, we term such phenomena as structural self-quenching effect, differing from the concentrational self-quenching effect, which is caused mainly by concentrational factors. The fluorescence quenching of P(APO) by C₆₀ has also been demonstrated. The formation of the charge transfer complex of P(APO) with C₆₀ in the ground state is revealed by the upward deviation from the linearity of the Stern-Volmer plot. APO can act as a photoinitiator to sensitize the photopolymerization of vinyl monomers such as acrylonitrile in dimethyl formamide and pursued kinetically. From the ultraviolet analysis of the PAN sensitized by APO, it is proved that APO not only sensitizes the photopolymerization of AN, but also incorporates in the PAN chain. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:481–489, 1997