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PubMedDate not supplied

Studies on comonomer compositional distribution of bacterial poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)s and thermal characteristics of their factions.

The comonomer-unit compositional distributions have been investigated for bacterial poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HH)] samples with 3HH unit content of 13.8, 18.0, 22.0, and 54.0 mol %. They were comonomer compositionally fractionated using chloroform/n-heptane mixed solvent at ambient temperature. The fractionation of P(3HB-co-18.0 mol %3HH) and P(3HB-co-22.0 mol % 3HH), which could not be carried out effectively at room temperature, were refractionated at 70 degrees C in the mixed solvent. Fractions with different 3HH unit content in a wide range (from 4.4 to 80.7 mol %) were obtained. By use of these fractions with narrow compositional distribution, the comonomer composition dependence of thermal properties was investigated by differential scanning calorimetry. The melting point (T(m)) and heat of fusion (DeltaH) decreased as the 3HH unit content increased in the range of low 3HH content (<40 mol %), while they increased as the 3HH unit content increased in the high 3HH content range (>70 mol %). The minimum T(m) and DeltaH values were found to exist at 3HH unit content of about 60 mol %. The glass transition temperature (T(g)) decreased linearly with the increase of 3HH unit content. The values of T(m), DeltaH, and T(g) of P(3HB-co-3HH)s were compared with those of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and the effects of comonomer types on the thermal properties were revealed.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Polycaprolactone-poly(ethylene glycol) multiblock copolymers as potential substitutes for di(ethylhexyl) phthalate in flexible poly(vinyl chloride) formulations.

New high-molecular-weight hydrophobic/hydrophilic segmented copolymers of poly(ester ether carbonate) structure, containing poly(epsilon-caprolactone) (PCL) and poly(ethylene glycol) (PEG) segments in their main chain, were synthesized and characterized. These copolymers were obtained by a two-step chain-extension reaction carried out in the presence of alpha,omega-dihydroxy-oligoPCL of molecular weight 1250 and PEG samples of molecular weight 150, 400, 600, 1000, and 2000. The molecular structures of all synthesized materials were characterized by means of (1)H NMR and (13)C NMR spectroscopy, their molecular weights were determined by means of size exclusion chromatography, and their thermal properties were obtained by means of differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The poly(ester ether carbonate)s of this study are partly or totally miscible at least up to 50 wt % with poly(vinyl chloride) (PVC) and could be used to produce flexible PVC formulations. The miscibility between PVC and the poly(ester ether carbonate)s reported in this paper was investigated by means of DSC and DMA analysis. PVC blends were also analyzed by determining their swellability and the amount of extractables in aqueous media. By comparison purposes, the chain-extension product of PCL1250, that is, PCL polycarbonate, was also synthesized and characterized. The results obtained demonstrated that the copolymers with shortest PEG segment length, i.e. PEG150, 400, and 600, give the best results in terms of miscibility with PVC and lead to blends with maximum resistance to extraction by water. Therefore, they represent, in principle, good substitutes for low-molecular-weight, leachable PVC plasticizers, such as di(ethylhexyl) phthalate.

Biopolymers↗
PubMedDate not supplied

Engineering of Ralstonia eutropha for production of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) from fructose and solid-state properties of the copolymer.

Recombinant Ralstonia eutropha capable of producing poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) copolymer [P(3HB-co-3HHx)] from fructose was engineered by introduction of genes for crotonyl-CoA reductase (CCR) from Streptomyces cinnamonensis (ccrSc) and for PHA synthase and (R)-specific enoyl-CoA hydratase from Aeromonas caviae (phaC-JAc). In this recombinant strain, C6-acyl-CoA intermediates were provided via beta-ketothiolase-mediated elongation of butyryl-CoA, which was generated from crotonyl-CoA by the function of CCR. The recombinant strain could accumulate the copolyester up to 48 wt % of dry cell weight with 1.5 mol % of 3HHx fraction from fructose, when the expression of ccrSc under the control of the PBAD promoter was induced with 0.01% L-arabinose. The absence of L-arabinose or the deletion of ccrSc from the plasmid resulted in accumulation of poly(3-hydroxybutyrate) homopolymer, indicating the critical role of CCR in the formation of the 3-hydroxyhexanoate unit. Higher CCR activity obtained by the addition of a larger amount of L-arabinose did not affect the composition but reduced the intracellular content of the copolyester. The P(3HB-co-1.5 mol % 3HHx) copolyester produced from fructose by the recombinant R. eutropha showed relatively lower melting temperatures (150 degrees C and 161 degrees C) and lower crystallinity (48 +/- 5%) compared to those (175 degrees C and 60 +/- 5%) of P(3HB) homopolymer. It has been found that the incorporation of a small amount (1.5 mol %) of 3HHx units into P(3HB) sequences leads to a remarkable change in the solid-state properties of P(3HB) crystals. The present study demonstrates the potential of the engineered pathway for the production of copolyesters having favorable characteristics from inexpensive carbon resources.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Biosynthesis and properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) polymers.

In support of programs to identify polyhydroxyalkanoates with improved materials properties, we report on our efforts to characterize the mechanical and thermal properties of copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx). The copolyesters, having molar fraction of 3HHx ranging from 2.5 to 35 mol % and average molecular weights ranging from 1.15 x 10(5) to 6.65 x 10(5), were produced by fermentation using Aeromonas hydrophila and a recombinant strain of Pseudomonas putida GPp104. The polymers were chloroform extracted and characterized by solution-state and solid-state nuclear magnetic resonance (NMR) spectroscopy and a variety of mechanical and thermal tests. Solution-state (1)H NMR data were used to determine polymer composition-of-matter, while solution-state (13)C NMR data provided polymer-sequence information. Solvent fractionation and NMR spectroscopic characterization of these polymers showed that polymers containing up to 9.5 mol % 3HHx had a Bernoullian compositional distribution. By contrast, polymers containing more than 9.5 mol % 3HHx had a bimodal polymer composition. Solvent fractionation of these 3HHx-rich polyesters produced two polymer fractions, each of which was again consistent with Bernoullian polymerization statistics. Solid-state NMR relaxation experiments provided insight into aging in poly(3HB-co-3HHx) copolymers, demonstrating increased polymer-chain motion with increasing 3HHx content. The elongation-to-break ratio in the polyesters increased with increasing molar fraction of 3HHx monomers. Aging properties of the poly(3HB-co-3HHx) copolymers were very similar to copolymers of 3HB and 3-hydroxyvalerate (3HV). However, poly(3HB-co-3HHx) exhibited increased activation energy to thermal degradation with increasing 3HHx content.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Self-organization of amphiphilic polymer in vesicle bilayers composed of surfactant mixtures.

Cryogenic transmission electron microscopy (cryo-TEM) and small angle neutron scattering (SANS) are used to investigate the association of amphiphilic polymers consisting of a double-chain hydrophobic tail attached onto poly(ethylene glycol) (PEG) polymer chains into two different systems of equilibrium vesicles. For cetyltrimethylammonium bromide (CTAB)/sodium perfluorohexanoate (FC(5)) vesicle bilayers, the size distribution of the vesicles slightly becomes narrow in the presence of the polymers, suggesting that the wedge-shaped polymers increase the spontaneous curvature of the vesicles. In contrast, the confinement of polymer molecules inside the CTAB/sodium perfluorooctanoate (FC(7)) vesicles that are stabilized by spontaneous curvature causes an abrupt decrease in the bilayer rigidity. By an analysis of vesicle size distribution, it is found that the membrane elasticity of CTAB/FC(7) vesicles is varied considerably from 6k(B)T to 0.3k(B)T, implying the transition of stabilization mechanism from spontaneous curvature to thermal fluctuation in the presence of polymer. The polymer incorporation mechanism into the bilayers is understood, in the comparison of the vesicle radius and size distribution before and after adding polymer, as that the polymer is anchored into the vesicle bilayer owing to hydrophobic property after the adsorption on the surface of the bilayer.

Caproates↗
PubMedDate not supplied

Structural characterization of a lipase-catalyzed copolymerization of epsilon-caprolactone and D,L-lactide.

The copolymerization of epsilon-caprolactone (epsilon-CL) and d,l-lactide catalyzed by Candida antarctica lipase B was studied. Copolymerizations with different epsilon-CL-to-lactide ratios were carried out, and the product was monitored and characterized by MALDI-TOF MS, GPC, and (1)H NMR. The polymerization of epsilon-CL, which is normally promoted by C. antarctica lipase B, is initially slowed by the presence of lactide. During this stage, lactide is consumed more rapidly than epsilon-CL, and the incorporation occurs dimer-wise with regard to the lactic acid (LA) units. As the reaction proceeds, the relative amount of CL units in the copolymer increases. The nonrandom copolymer structure disappears with time, probably due to a lipase-catalyzed transesterification reaction. In the copolymerizations with a low content of lactide, macrocycles of poly(epsilon-caprolactone) and copolymers having up to two LA units in the ring were detected.

Biocompatible Materials↗
PubMedDate not supplied

Modeling of lipase catalyzed ring-opening polymerization of epsilon-caprolactone.

Enzymatic ring-opening polymerization of epsilon-caprolactone by various lipases was investigated in toluene at various temperatures. The determination of molecular weight and structural identification was carried out with gel permeation chromatography and proton NMR, respectively. Among the various lipases employed, an immobilized lipase from Candida antartica B (Novozym 435) showed the highest catalytic activity. The polymerization of epsilon-caprolactone by Novozym 435 showed an optimal temperature of 65 degrees C and an optimum toluene content of 50/50 v/v of toluene and epsilon-caprolactone. As lipases can degrade polyesters, a maximum in the molecular weight with time was obtained due to the competition of ring opening polymerization and degradation by specific chain end scission. The optimum temperature, toluene content, and the variation of molecular weight with time are consistent with earlier observations. A comprehensive model based on continuous distribution kinetics was developed to model these phenomena. The model accounts for simultaneous polymerization, degradation and enzyme deactivation and provides a technique to determine the rate coefficients for these processes. The dependence of these rate coefficients with temperature and monomer concentration is also discussed.

Caproates↗
PubMedDate not supplied

Development of biodegradable injectable thermoplastic oligomers.

Injectable thermoplastic oligomers represent a promising biomaterial for drug delivery provided they possess a melting point at or very near physiologic temperature, as well as a low melt viscosity. One approach would be to prepare an oligolactone. In this paper, we examine the role of different alcohol initiators used in the ring-opening polymerization of epsilon-caprolactone oligomers on the melting point and melt viscosity of the resultant thermoplastics. We found that the initiator used plays a significant role in the final properties of the final oligomer. For primary alcohols, the longer the chain length of the oligomer the lower its melt viscosity, until a chain length of 8 carbons, after which there was no noticeable effect. There was no significant effect observed of primary initiators on the melting point. The use of secondary alcohols produced oligomers with higher viscosities but with reduced overall crystallinity. The use of an unsaturated alcohol, oleyl alcohol, not only reduced the melting point and overall crystallinity but also reduced the melt viscosity of the oligomer. The oleyl alcohol initiated oligomer appears to be a promising vehicle for localized, sustained drug delivery applications.

Biocompatible Materials↗
PubMedDate not supplied

Bio-based polymeric composites comprising wood flour as filler.

The increasing effort on development of bio-based polymeric materials in recent years is motivated by the basic concept of meeting the sustainability criteria for industrial development in the third millennium. Within this framework, our research group is currently involved in assessing the potentiality of some agro-industrial overproduction and byproducts in the formulation of eco-compatible bio-based polymeric materials displaying, among others, the propensity to biodegrade under controlled environment conditions. In the present work, beech wood flour (Bwf) composites were prepared from plasticized poly(3-hydroxybutyrate) (PHB). The type of plasticizer [tri(ethylene glycol) bis(2-ethylhexanoate) (TEGB) and poly(ethylene glycol) (PEG200)] and the amount [5 and 20 wt %] were selected as independent variables in a factorial design. Thermal and mechanical properties of 90 wt % PHB composites were investigated. Incorporation of PEG200 was found to compromise thermal stability of PHB as demonstrated by the higher decrease on the onset decomposition temperature (T(d)) and the drop in its average molecular weight (M(w)). The present study underlines the fact that TEGB/PHB/beech wood flour composites can be optimized to obtain new materials for disposable items.

Biodegradation, Environmental↗
PubMedDate not supplied

Copolymerizations of epsilon-caprolactone and glycolide-a comparison of tin(II)octanoate and bismuth(III)subsalicylate as initiators.

Copolymerizations of epsilon-caprolactone (epsilonCL) and glycolide (GL) were conducted in bulk at 120 degrees C with variation of the reaction time. Either Sn(II) 2-ethylhexanoate (SnOct(2)) or bismuth(III)subsalicylate (BiSS) were used as initiators combined with tetra(ethylene glycol) as co-initiator. The resulting copolyesters were analyzed by (1)H and (13)C NMR spectroscopy with regard to the total molar composition and to the sequence of the comonomers. Furthermore, two series of copolymerizations (either Sn- or Bi-initiated) were performed at constant time with variation of the temperature. It was found that BiSS favors alternating sequences more than SnOct(2). Time-conversion curves and MALDI-TOF mass spectrometry of homopolymerization suggest that SnOct(2) is the more efficient transesterification catalyst. A hypothetical reaction mechanism is discussed.

Bismuth↗
PubMedDate not supplied

Gelatin blending improves the performance of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) films for biomedical application.

To improve the performance of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx), gelatin was blended with PHBHHx at different ratios. With increasing gelatin content, the weight loss of gelatin/PHBHHx blend in simulated body fluid at 37 degrees C was accelerated. After 2 months, there was about 15% weight loss in PHBHHx blending with 30% gelatin. Scanning electron microscopy and X-ray diffraction results showed that gelatin blending increased the surface porosity and decreased the crystallinity, which may be responsible for the acceleration of the weight loss. Second harmonic generation results indicated that 10% gelatin blending had less disruption to PHBHHx spatial structure, resulting in better tensile mechanical properties. At the same time, increased surface porosity and decreased crystallinity caused by gelatin incorporation may be beneficial for cell growth compared with pure PHBHHx. All these indicated that gelatin incorporation may improve the performances of PHBHHx to meet the need of different situations during medical implantation.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Caprolactonic poloxamer analog: PEG-PCL-PEG.

The aqueous solution of poly(ethylene glycol)-poly(caprolactone)-poly(ethylene glycol) (PEG-PCL-PEG) triblock copolymers (> 15. wt. %) undergoing "clear sol-gel-turbid sol" transition as the temperature increases from 20 to 60 degrees C has been developed. Light scattering and 13C NMR study suggested that the transition mechanisms are the micellar aggregation for the clear sol to gel transition (lower transition), whereas the increase in PCL molecular motion for gel to turbid sol transition (upper transition). In contrast to the previous thermogelling biodegradable polymers with a sticky paste morphology, the powder form of the PEG-PCL-PEG triblock copolymers makes it easy to handle and allows fast dissolution in water. Therefore, the lyophilization into a powder form followed by facile reconstitution was possible. This system is believed to be promising for drug delivery, cell therapy, and tissue engineering.

Biocompatible Materials↗
PubMedDate not supplied

Structure-property relationships of copolymers obtained by ring-opening polymerization of glycolide and epsilon-caprolactone. Part 2. Influence of composition and chain microstructure on the hydrolytic degradation.

A series of glycolide/epsilon-caprolactone copolymers were compression molded and allowed to degrade in a pH 7.4 phosphate buffer at 37 degrees C. Degradation was monitored by various analytical techniques such as (1)H NMR, X-ray diffraction, DSC, CZE, ESI-MS, and inherent viscosity measurements. The results show that the degradation rate depends not only on the copolymer composition but also on its chain microstructure. Generally, copolymers with a higher C-G bond content or a higher degree of randomness exhibit higher degradation rates. Sequences with odd numbers of glycolyl units such as -CGC- and -CGGGC-, which result from the second mode transesterification, appear more resistant to hydrolysis. As a consequence, degradation residues obtained at the later stages of degradation are mainly composed of long glycolyl and caproyl sequences linked by -CGC- and -CGGGC- ones. The degradation rate of the copolymers depends also on the degree of crystallinity of each component which is related to the block length. The caproyl component can be preferentially degraded if it is in the amorphous state and the glycolyl component is semicrystalline.

Caproates↗
PubMedDate not supplied

Structure-property relationships of copolymers obtained by ring-opening polymerization of glycolide and epsilon-caprolactone. Part 1. Synthesis and characterization.

A series of copolymers with various compositions were synthesized by bulk ring-opening polymerization of glycolide and epsilon-caprolactone, using stannous (II) octoate or zirconium (IV) acetylacetonate as initiator. Reaction time and temperature were varied so as to induce different chain microstructures. The resulting copolymers were characterized by (1)H NMR, SEC, DSC, and X-ray diffraction. The average lengths of glycolyl (L(G)) and caproyl sequences (L(C)) and the degree of randomness (R) were calculated and compared to the values of completely random chains. The concentration of CGC sequences was also obtained which resulted from transesterification reactions. Data showed that stannous (II) octoate leads to less transesterification than zirconium (IV) acetylacetonate, and lower temperatures lead to less transesterification than higher ones. The copolymers exhibited a more or less blocky chain structure because of the reactivity difference between glycolide and epsilon-caprolactone. The crystalline structure and thermal properties depend on both the composition and the chain microstructure. PGA- and PCL-type crystallites were obtained for copolymers with intermediate compositions.

Caproates↗
PubMedDate not supplied

Influence of DL-beta-hydroxybutyric acid on cell proliferation and calcium influx.

Poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx), a member of the polyhydroxyalkanoate family of biopolyesters, has superior mechanical properties and biocompatibilities that enable it to meet diverse biomedical requirements. The main component of PHBHHx is DL-beta-hydroxybutyric acid (HB), a ketone body that is also produced in vivo. The effects of HB treatment on murine fibroblast L929 cells, human umbilical vein endothelial cells, and rabbit articular cartilages were investigated. HB (0.005-0.10 g/L) promoted cell proliferation for each cell line. Cell cycle analysis indicated that HB had a stimulatory effect on DNA synthesis. Flow cytometric analysis of L929 cells revealed changes in the [Ca2+]i for different stages of the cell cycle. In L929 cells, HB (0.02 g/L) stimulated a rapid increase in the concentration of cytosolic calcium that was blocked by verapamil and diltiazem, inhibitors of L-type Ca2+ channels. Finally, verapamil inhibited HB-induced L929 cell proliferation. Collectively, these results indicated that HB had a stimulatory effect on cell cycle progression that is mediated by a signaling pathway dependent upon increases in [Ca2+]i. This trophic effect may underlie the good biocompatibility observed for PHBHHx.

3-Hydroxybutyric Acid↗
PubMedDate not supplied

Degradation behavior of poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly(epsilon-caprolactone) micelles in aqueous solution.

Poly(epsilon-caprolactone)-b-poly(ethylene glycol)-b-poly(epsilon-caprolactone) triblock copolymers were synthesized by the ring-opening polymerization of epsilon-caprolactone in the presence of hydroxyl-terminated poly(ethylene glycol) with different molecular weights, using stannous octoate catalyst. Micelles prepared by the precipitation method with these triblock copolymers exhibit a core-shell structure. The degradation behaviors of these core-shell micelles in aqueous solution were investigated by FT-IR, 1H NMR, GPC, DLS, TEM, and AFM. It was found that the degradation behavior of micelles in aqueous solution was quite different from that of bulk materials. The size of the micelles increased in the initial degradation stages and decreased gradually when the degradation period was extended. The caprolactone/ethylene oxide (CL/EO) ratio in micelles measured by NMR also shows an increase at the initial degradation stage and a decrease at later stages. The morphology of these micelles became more and more irregular during the degradation period. We explain the observed behavior by a two-stage degradation mechanism with interfacial erosion between the cores and the shells followed by core erosion.

Caproates↗
PubMedDate not supplied

Morphology of elastic poly(L-lactide-co-epsilon-caprolactone) copolymers and in vitro and in vivo degradation behavior of their scaffolds.

Very elastic PLCL [poly(L-lactide-co-epsilon-caprolactone), 50:50] copolymers were synthesized and extruded into porous tubular scaffolds (pore size 150 +/- 50 microm, porosity 90%) for the application to tissue engineering. The copolymers were basically random and amorphous. However, two T(g)'s (glass transition temperatures) were observed in dynamic mechanical thermal analysis and also in differential scanning calorimetry thermograms. Furthermore, microdomains (about 17 nm in size) were indicated on the small-angle X-ray scattering profile and finally confirmed by transmission electron microscopy. Therefore, the PLCL copolymer was probably composed of a soft matrix of mainly epsilon-caprolactone moieties and hard domains containing more L-lactide units to exhibit a rubberlike elasticity in virtue of the physically cross-linked structure. The smooth muscle cells seeded scaffolds were implanted into nude mice subcutaneously for up to 15 weeks to monitor the in vivo degradation. In addition, they were degraded in vitro in phosphate buffer solution (pH 7.4) for up to 1 year to compare the results each other. All the scaffolds degraded slowly in vivo and in vitro even in the form of a highly porous thin membrane. However, the degradation rate was somewhat faster for in vivo than for in vitro. This should be explained by enzymes that might have played a certain role in the degradation in the body. In addition, the epsilon-caprolactone moieties degraded faster than the L-lactide units did in these PLCL scaffolds, although their hydrophilicities are in the opposite order. This behavior appeared more prominently in the in vivo case. This should result from that the amorphous regions composed of mainly epsilon-caprolactone units might have been first attacked by water because water can penetrate into the amorphous regions easier than the hard domains containing more L-lactides.

Animals↗
PubMedDate not supplied

Encapsulation of osteoblast seeded microcarriers into injectable, photopolymerizable three-dimensional scaffolds based on d,l-lactide and epsilon-caprolactone.

UMR-106 seeded microcarriers were encapsulated into in situ, photopolymerizable three-dimensional scaffolds based on d,l-lactide and epsilon-caprolactone. UMR-106 and rat bone marrow cells proliferated and differentiated well on the microcarriers. The microcarriers were completely colonized after 14 days in culture. The viscous polymer paste allowed to mix the UMR-106 seeded microcarriers and gelatin (porosigen) properly. After the photopolymerization process, microcarriers and gelatin were evenly distributed throughout the scaffold. Gelatin was leached out within 7 h, and a porous scaffold was obtained. The microcarriers remained in the scaffold even after 7 days which demonstrates that they were well entrapped in the polymer. Increasing the amount of entrapped microcarriers (20-50%) leads to scaffolds with a reduced cross-linking. Hence, the microcarriers leached out. The encapsulated UMR-106 cells did not show pyknotic nuclei which demonstrates that the photopolymerization and handling the viscous polymer/gelatin/microcarrier paste is not detrimental for the cells.

Animals↗