Poly-3-hydroxyoctanoate

In order to develop a tissue-engineered heart valve, a group at Children s Hospital in Boston evaluated several synthetic absorbable polyesters as potential scaffolding materials for heart valves. Unfoitu-nately, the most synthetic polyesters proved to be too stiff to be function as flexible leaflets inside a tri-leaflet valve. " In the late 1990s, a much more flexible PHAs called poly-3-hydroxyoctanoate-co-3-hydroxyhexanoate (PHO) was used as the scaffold material for the valve leaflet, and then the entire heart valve. ... 

The vast majority of these interesting biopolyesters have been studied and produced only on the laboratory scale. However, there have been several attempts to develop pilot scale processes, and these provide some insight into the production economics of poly(3HAMCL)s other than poly(3HB) and poly(3HB-co-3HV). These processes utilize diverse fermentation strategies to control the monomer composition of the polymer, enabling the tailoring of polymer material properties to some extent. The best studied of these is poly(3-hydroxyoctano-ate) (poly(3HO)), which contains about 90% 3-hydroxyoctanoate. This biopolyester has been produced on the pilot scale and is now being used in several experimental applications. 

Injectable liquid polyhydroxyalkanoate compositions consisting of the transesterification product of poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) with 1,3-butanediol were prepared by Williams et al. (3) and used in soft tissue repair, augmentation, and viscosupplementation in humans. 

It is interesting to investigate effects of long side chains on the molecular dynamics and related physical properties of poly(hydroxyalkanoic acid)s. The poly(hydroxyalkanoic acid)s with longer side chains, such as poly(3-hydroxyoctanoic acid) [P(3HO)], have quite different mechanical properties from P(3HB) and P(3HB-co-3HV), being thermal elastmers with low glass transition temperatures ranging from -25 to — 40°C [88] and a much lower crystallinity of about 25-33% [89]. 

Figure 10.1 Chemical structures of (a) poly(3-hydroxybutyric acid), (b) poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) and (c) poly(3-hydroxyoctanoic acid).

PHB-co-PHV [54] is obtained from Azotobacter chroococcum [58, 63). The biodegradation is slower for the copolymers than poly-3-hydroxybutyrate. 3-hydroxy-n-phenylalkanoic acids and 3-hydroxyaliphatic acids are obtained from Pseudomonas putida [59]. Poly (3-hydroxyoctanoic acid) and poly (6-hydroxyhexanoic acid) and poly (3-hydroxyoctanoic acid) [64], Poly-(R)-3-hydroxybutyrate/polyphosphate (PHB/polyP) complexes are isolated from the plasma membranes of bacteria [65,66]. Polyhydroxyoctanoate is produced by feeding octanoic acid to Pseudomonas oleovorans [67]. 

PHAs containing pendant diol groups were synthesized from unsaturated polymers poly[(/ )-3-hydroxyoctanoate-ct)-(/ )-3-hydroxyundecenoate] by treatment with KMnO in cold alkaline solution (pH 8-9) at 20°C (Lee et al. 2000b). The chemical reaction did not cause PHA hydrolysis (or at least not to a high extent) since no severe rednction in molecular weight was observed. The hydroxylated polymers had a considerably enhanced hydrophilicity since they showed increased solnbility in polar solvents such as an acetone/water mixture, methanol and dimethyl sulphox-ide (Lee et al. 2000b). 

Kurth et al. 2002 Stigers and Tew 2003). One of them involves the oxidation of unsaturated PHAs i.e. poly[(/ )-3-hydroxyoctanoate-co-(/ )-3-hydroxyundecenoate] with KMnO in the presence of NaHCOj (Lee and Park 2000). Although it allowed the transformation of 50% of the olefins into carboxylic functions, this method involves a decrease in the molecular weight of the polymer. 

Largely unsaturated PHAs have been cross-linked by a very slow chemical procedure (it usually takes days), which implies the conversion of double bonds into epoxy groups and exposure to air (Ashby et al. 20(X)). Other epoxidized bacterial copolyesters, poly[(/ )-3-hydroxyoctanoate-co-(/ )-3-hydroxy-10,ll-epoxyunde-canoate], were cross-linked with succinic anhydride in the presence of 2-ethyM-methylimidazole or with hexamethylene diamine without a catalyst at 90°C (Lee et al. 1999a Lee and Park 1999). 

Timbart L, Renard E, Langlois V, Guerin P (2004) Novel biodegradable copolyesters containing blocks of poly(3-hydroxyoctanoate) and poly(8-caprolactone) synthesis and characterization. Macromol Biosd 4 1014—1020... 

PHO poly(3-hydroxyocatanoate), HO 3-hydroxyocatanoate, PHOU poly(3-hydroxyoctanoate-co-3-hydroxy-lO-undecenoate), PHUE poly(3-hydioxy-10-undecenoate), PHDD poly(3-hydroxydo-decanoate), HDD 3-hydroxydodecanoate, PHTD poly(3-hydroxytetradecanoate), HTD 3-hydroxytetradecanoate, ND not determined, NE nonexistent... 

Schirmer A, Jendrossek D, ScUegel HG (1993) Degradation of poly(3-hydroxyoctanoic add) [P(3HO)] by bacteria purification tmd properties of a P(3HO) depolymerase fmm Pseudomonas fluorescens GK13. Appl Environ Microbiol 59 1220 Schirmer A, Matz C, Jendrossek D (1995) Substrate spedfidties of poly(hydroxyalkanoate)-degrading bacteria and active site studies on the extracellular poly(3-hydroxyoctanoic add) depolymerase of Pseudmnonas fluorescens GK13. Can J Microbiol 41 170-179 Schmid A, KoUmer A, Sonnleitner B, Witholt B (1999) Development of equipment and procedures for the safe operation of aerobic bacterid bioprocesses in the presence of bulk amounts of flammable oiganic solvents. Bioprocess Eng 20 91-100 Schmid A, Dordick JS, Hauer B, Kiener A, Wubbolts M, Witholt B (2001) Industrial biocatalysis today and tomorrow. Nature 409 258-268... 

Rhee YA, Kim YH, SMn KS (2006) Characterization of an extracellular poly(3-hydroxyoctano-ate) depolymerase from the marine isolate Pseudomonas luteola Ml3-4. Enzyme Microb Technol 38 529-535... 

A latex of poly(/3-hydroxyoctanoate) can be obtained from the bacterium Pseudomonas oleovorans grown on sodium octanoate at a high cell density (22). In the course of purification sodium hypochlorite was used. It was observed that latex stabilization occurred spontaneously due to the persistence around the polymer granules of the murein sacculus, which envelopes the bacterial ceU. It was shown that the optimal conditions for the bacteria digestion correspond to a sodium h ochlorite concentration of 21-26 mmolg. ... 

The resulting films display the t ical properties of a thermoplastic elastomer. Depending on the conditions of purification, also fully amorphous poly(/3-hydroxyoctanoate) films can be obtained. Nanocomposite materials can be prepared when using this latex as a matrix and using in addition a colloidal suspension of hydrolyzed starch or cellulose whiskers as a natural and biodegradable filler. The properties are strongly dependent on the aspect ratio of the whiskers (23). 

Poly(3-hydroxyoctanoate) with pendant carboxylic groups have been prepared by the chemical modification of unsaturated bacterial polyesters. The oxidation of the pendant alkene groups is complete and thereby a loss in molecular weight of polymer was observed. The introduction of pendant carboxylic groups enhances the hydrophilic character of the polymers (24). 

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