PHBHHx

Rasal, R.M. and Hirt, D.E. 2008. Toughness decrease of PLA-PHBHHx blend films upon surface-confined photopolymerization. Journal of Biomedical Materials Research Part A 88 1079-1086. 

Cheng Mei-Ling, Chen Po-Ya, Lan Chin-Hung, Sun Yi-Ming, Structure, mechanical properties and degradation behaviors of the electrospun fibrous blends of PHBHHx/ PDLLA. Polym. 2011, doi 10.1016/j.polymer.2011.01.039 in press. 

PHBHHx Nonwoven scaffold TE In vitro hMSCs culture, flucvescence stain. M i l assay, alizarin red S stain (Yuetal. 2008)... 

PHB/PHBHHx PHB/P3HB4HB Nonwoven scaffold TE SEM, Wide Angle X-ray Dififraclion (WAXD), density test, mechanical (Li et al. 2008) test, assay of cell attachment and viability ... 

Qu XH, Wu Q, Liang J, Qu X, Wang SG, Chen GQ (2005) Enhanced vascular-related cellular affinity on surface modified copolyesters of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx). Biomaterials 26 6991-7001... 

Cheng, Mei-Ling, Chen, Po-Ya., Lan Chin-Hung, Sun Yi-Ming. (2011). Structure, Mechanical Properties and Degradation Behaviors of the Electrospun Fibrous Blends of PHBHHx/PDLLA. Polymer, 52, 6587-6594. 

The second PHA synthesis pathway (pathway II) is related to fatty acid uptake by microorganisms. After fatty acid P-oxidation, acyl-CoA enters the PHA monomer synthesis process. Enzymes including 3-ketoacyl-CoA reductase, epimerase, (I )-enoyI-CoA hydratase/enoyl-CoA hydratase I, acyl-CoA oxidase (putative), and enoyl-CoA hydratase I (putative) were found to be involved in supplying the PHA precursor 3-hydroxyacyl-CoA for PHA synthesis. Pseudomonas putida, Pesudomonas aeruginosa, and A. hydrophila are able to use pathway n to synthesize medium-chain-length (mcl) PHA or copolymers of (/ )-3-hydroxybutyrate (R3HB) and (R)-3-hydroxyhexanoate (PHBHHx). 

Copolymers of scl and mcl PHA possess useful and flexible mechanical properties they are the preferred materials for application development. A successful example is the PHBHHx that was produced on an industrial scale (Chen 2009b). US-based Procter Gamble has trademarked scl and mcl PHA copolymers of C and Cg-Cj2 as Nodax (Noda et al. 2009). 

Only several PHA, including PHB, PHBV, P4HB, PHBHHx, and PHO, are available in sufficient quantities for application research (Hrabak 1992 Byrom 1992 Chen et al. 2001). This is why most of the application research, including tissue engineering and controlled drug release, is based on the above-mentioned PHA. 

Aeromonas hydrophila is a heterotrophic bacterium found in warm climates, and in fresh, salty, marine, estuarine, chlorinated, and unchlorinated water. In addition, it is resistant to refrigeration and cold temperatures. This bacterium produces a PHA copolyester consisting of (/ )-3-hydroxybutyrate and (/ )-3-hydroxyhexanoate (PHBHHx Chen et al. 2001). To understand the relationship between enhanced survival abihty and PHA accumulation of A. hydrophila, the physiological behaviors of a wild type and a phaC mutant were compared. The ability of the phaC mutant to survive UV irradiation, heat and cold treatment, ethanol, osmotic pressure, and oxidative stress was significantly impaired as compared with that of the wild type. Thus, PHBHHx synthesis and accumulation in A. hydrophila is another example of positive correlation between resistance to environmental stresses and PHA accumulation (Zhao et al. 2007). 

An enhanced expression of rpoS in A. hydrophila has been linked to the enhanced resistance to environmental stress conferred by PHBHHx (Zhao et al. 2007). In P. oleovorans, the increase of the intracellular concentration of RpoS during PHA depolymerization was related to an enhanced cross-tolerance to different stress agents (Ruiz et al. 2004). Interestingly, under PHA accumulation and nonaccumulation conditions, an rpoS mutant of P. putida had similar and lower survival under oxidative stress, respectively, as compared with the wild-type strain (Raiger-Iustman and Ruiz 2008). 

Jiangmen Biotech Center, China PHBHHx Unknown 1990s Raw materials... 

The current production cost for PHBHHx is stiU too high for real commercial application. However, many efforts have been made to improve the production process for PHBHHx, including the downstream process technology. Most efforts have been focused on increasing cell density and simplifying the downstream process. A better production strain able to utilize glucose will be one of the most important issues for reducing the PHBHHx production costs. 

An attempt was also made to manipulate PHBHHx production in E. coli (Lu et al. 2003). The acyl-CoA dehydrogenase gene (yaJH) of E. coli was expressed together... 

FIGURE 1 Crystallinity as a function of comonomer composition in a series of PHAs samples (a) PHBV, (b) PHBB and (c) PHBHHx. The dash curve in (a) and (b) is for visual aid. Solid marker indicates second heating after isothermal crystallization at preselected T. Open marker indicates second heating under non-isothermal. 

FIGURE 10 Activation energy of isothermal crystallization [calculated after Equation (8)] of PHBHHx as a function of comonomer composition. 

It was noted in early session that sphemlitic structure of a polymer affects the mechanical properties of the polymer. Micrographs of PHB and PHB12 V crystals stractrrre, revealed using POM, are shown in Figure 12. The PHB V and PHBHHx show fine fibrillar structure of spherulites while PHB shows circular ring banded spherulites, both types of crystals display Maltese cross. 

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