Hydrolytic and enzymatic incubation of polyhydroxyoctanoate (PHO): a short-term in vitro study of a degradable bacterial polyester

Electrochemical Decarboxylative Alkoxy-alkoxycarbonylation of Alkenes

A method is presented for decarboxylative alkoxy-alkoxycarbonylation of various alkenes with alcohols by electrochemical anodic oxidation of monopotassium ethyloxalate salts with good functional group compatibility. The reaction involves anodic oxidation to form an acyl radical, followed by addition to an olefin to yield a new alkyl radical, which is anodically oxidized to a carbon cation and captured by alcohols to afford β-alkoxyalkanoates. Adding catalytic amounts of ammonium iodide enhanced the efficiency of the reactions.

Investigation of the Impact of Poly(Ethylene Glycol)-Modulation of Poly(B-Hydroxybutyrate) Syntheses on Cell Interactions of the Resulting Polymers

Poly(-hydroxybutyrate), PHB is a bacterial polyester known for its excellent bone compatibility, however, the material lacks blood and tissue compatibility. Poly(ethylene glycol), PEG,-modulated fermentation of Alcaligenes latus and Azotobacter vinelandii UWD was employed to yield copolymers consisting of PHB and PEG that exhibit diminished cell-adhesion surface properties. PEGs with molecular weights of 3400, 2000, and 400 as well as diethylene glycol, DEG, and pentaerythritol ethoxylate, PEE, were used in a concentration of 2% (w/v) for amending the fermentation broths. This modulation of the fermentation conditions did not influence polymer yields. However, the resulting copolymers had drastically reduced molecular weights, 82% less for the DEG-amended fermentation of A. latus. The reduction in molecular weight was attributed to an end-capping reaction of the nascent PHB-chain with PEG and/or early chain termination by water facilitated by the presence of the highly hydrophilic PEG-molecules. The formation of a covalent linkage was proven unambiguously by H-NMR-spectroscopic methods only for the copolymers obtained in the DEG-modified fermentations of both strains. Cell growth experiments using SK-MEL 28 and MDA-MB 231 cells were used for the evaluation of polymer-cell interaction. Copolymer films obtained from PEG-modulated syntheses showed significantly less cell adhesion with reductions in cell adhesions; up to 74% less in the two-day experiments (MDA-MB 231 on the copolymer obtained in DEG-modified fermentation of A. latus) and 48% less in the seven-day experiments (SK-MEL 28 on the copolymer obtained in PEG 400-modified fermentation of A. vinelandii UWD). In the two-day experiments, no differences in the cellinteraction was observed between the polymers obtained from two different bacterial sources, the polymers differed in their long-term, seven-day, cell interaction with copolymers obtained from A. vinelandii UWD maintaining more effective cell repulsion.

Preparation and hydrolytic degradation of semi-interpenetrating networks of poly(3-hydroxyundecenoate) and poly(lactide-co-glycolide)

Semi-interpenetrating networks (semi-IPNs), where poly(lactide-co-glycolide) (PLGA) molecules were entrapped in the crosslinked matrices of poly(3-hydroxyundecenoate) (PHU), were prepared by irradiating homogeneous solutions of PHU and PLGA in chloroform with UV light. Attenuated total reflectance infrared spectroscopy showed that the PLGA chains were entrapped in PHU networks. The semi-IPNs showed enhanced mechanical strength as the PLGA content increased. The semi-IPNs were incubated at 37 degrees C in a 0.01N NaOH solution, and the extent of hydrolytic degradation was investigated by monitoring changes in various parameters such as water uptake, pH, mass, and morphology. Hydrolysis of semi-IPNs were significantly affected by the presence of PLGA. A semi-IPN prepared from a 9:1 (by weight) mixture of PHU and PLGA lost 25% of its original weight in 12 weeks while a PHU sample containing no PLGA lost only 5% of its weight during the same period under identical conditions. The hydrolysis was most likely accelerated when the pH of the medium was lowered by the hydrolyzed products of PLGA, 2-hydroxyalkanoic acids. These results showed that hydrolysis of PHA could be enhanced by incorporating a second component that lowered the pH of the hydrolysis system.

Drug release from and hydrolytic degradation of a poly(ethylene glycol) grafted poly(3-hydroxyoctanoate)

Monoacrylate-poly(ethylene glycol)-grafted poly(3-hydroxyoctanoate) (PEGMA-g-PHO) copolymers were synthesized to develop a swelling-controlled release delivery system for ibuprofen as a model drug. The in vitro hydrolytic degradation of and the drug release from a film made of the PEGMA-g-PHO copolymer were carried out in a phosphate buffer saline (pH 7.4) medium. The hydrolytic degradation of the copolymer was strongly dependent on the degree of grafting (DG) of the PEGMA group. The degradation rate of the copolymer films in vitro increased with increasing DG of the PEGMA group on the PHO chain. The copolymer films showed a controlled delivery of ibuprofen to the medium in periods of time that depend on the composition, hydrophilic/hydrophobic characteristics, initial drug loading amount and film thickness of the graft copolymer support. The drug release rate from the grafted copolymer films was faster than the rate of weight loss of the films themselves. In particular, a combination of the low DG of the PEGMA group in the PHO chains with the low ibuprofen solubility in water led to long-term constant release from these matrices in vitro.

Preparation and cell compatibility of acrylamide-grafted poly(3-hydroxyoctanoate)

Poly(3-hydroxyoctanoate) (PHO) films were treated with plasma of different discharge powers (10-50 W) and then treated with acryl amide solutions in order to prepare films with surfaces that contained different amounts of amide groups. The surfaces were characterized by contact angle measurement, attenuated total reflectance infrared spectroscopy, electron spectroscopy for chemical analysis, and scanning electron microscopy. Results from all these measurements indicated that amide groups were present on the surfaces. The amount of amide groups increased in proportion to the discharge power of the plasma. The interaction of Chinese hamster ovary cells with these grafted surfaces was investigated. The number of cells that adhered to and grew on the surfaces was highest for films grafted at 30 W of plasma discharge power, indicating that the moderate hydrophilicity was optimal for cells to adhere and grow. The present results support the suggestion that acryl amide-grafted PHO could be used as cell-compatible biomedical applications.

Mechanism and rate of degradation of polyhydroxyoctanoate films in aqueous media: A long-term in vitro study

The present study investigated the in vitro mechanism and degradation rate of polyhydroxyoctanoate (PHO). Solution-cast PHO films were incubated in either water or isoosmotic phosphate-buffered saline (PBS) for periods ranging from 1 to 24 months. Physical characterization included weight loss, water absorption, pH change, tensile strength, and scanning electron microscopy (SEM) studies. Analytical investigations including electron spectroscopy for chemical analysis, Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), wide-angle X-ray diffraction, and size exclusion chromatography were also performed to assess chemical and morphological changes to the structure of the PHO. The results show that the PHO-cast films incubated in either water or isoosmotic PBS underwent a simple hydrolytic degradation process characterized by water absorption, gradual molecular weight decrease, and negligible mass loss after 24 months of incubation. DSC results suggest that degradation occurred in the amorphous zone, followed by an attack in the crystalline domain. An increase in the vibration stretching of OH after 24 months of incubation, as revealed by FTIR, may indicate that the degradation process began internally, moving outwardly toward the surface of the PHO films. This process was more rapid in the films incubated in PBS than in those incubated in water. However, no significant changes in the morphology of the films were detected by SEM. This study demonstrated that the in vitro degradation of PHO in water or in PBS is a very slow hydrolytic process, exceeding 2 years. Our findings also suggest that the internal degradation mechanism is faster in PBS because of the ionic strength of the medium and that this internal process surface moves gradually toward the surface.