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.     

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.     

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.