Microbial Poly Research Articles

Modification of Microbial Polymalic Acid With Hydrophobic Amino Acids for Drug‐Releasing Nanoparticles

Microbial poly(β, l-malic acid) was modified with either l-leucine ethyl ester (L) or l-phenylalanine methyl ester (F) to produce amphiphylic copolymers. The degradation of these copolymers in aqueous buffer took place under physiological conditions in a few weeks by hydrolysis of the side chain ester group followed by cleavage of the main chain. Spherical nanoparticles with diameters ranging between 70 and 230 nm were prepared from these copolymers by the dialysis-precipitation method. No alteration of the cell viability was observed after incubation of these nanoparticles in different cell lines. Anticancer drugs temozolomide and doxorubicin were encapsulated in the nanoparticles. Temozolomide was released within several hours whereas doxorubicin took several weeks to be completely liberated.

Biodegradation and Medical Application of Microbial Poly(3-Hydroxybutyrate)

This review is designed to be a comprehensive source for biodegradable polymer: poly(3-hydroxybutyrate)—PHB research, including fundamental structure/property relationships and biodegradation kinetics for samples of different geometry. In addition to presenting the scientific framework for the advances in PHB research, this review focuses on applications of PHB in biomedicine and environment with a discussion on commercial applications and health/safety concerns for biodegradable materials.

Extruded foams from microbial poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) and its blends with cellulose acetate butyrate

AbstractExtrusion foaming of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV) and two blends of PHBV with cellulose acetate butyrate (CAB) were studied using an azodicarbonamide (AZ) blowing agent and a single‐screw extruder. The concentration of the blowing agent was systematically varied from 0 to 4.0 phr to achieve maximum density reduction reaching 41%, as well as to obtain information on the dependence of cell growth on blowing agent concentration. Extruded foams were characterized in terms of their bulk densities and cellular morphologies. Stereological and statistical methods permitted full characterization of the three‐dimensional cell size distributions, assessing the average cell diameters (ranging from 58 to 290 μm) and cell densities (ranging from 650 to 180,000 cm−3). The variation in cellular morphology among foams consisting of different polymer matrix or blowing agent concentration was compared. The results were analyzed by considering the influence of viscoelastic properties of the polymer matrix on the bubble growth during foaming. Significantly higher melt viscosity and elasticity and reduced gas solubility of the PHBV/CAB blends are believed to retard cell coalescence and collapse during foam expansion, resulting in more uniform cell size distribution and better homogeneity of cellular morphology. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

SOLID STATE NMR STUDY ON MICROBIAL POLY(ε-L-LYSINE)/CARBOXYMETHYL CELLULOSE BLENDS

The miscibility of microbial poly(ε- L -lysine)/carboxymethyl cellulose sodium salt (ε-PL/CMC) blends was investigated by solid-state nuclear magnetic resonance methods. 1 H spin-lattice relaxation time in the laboratory frame T1, and in the rotating frame, T1ρ measurements indicate that the blends are miscible at all compositions on a scale of 2–5 nm. Formation of carbamates and its reversibility were examined. ε-PL/CMC hydrogel was formed by bubbling carbon dioxide gas into ε-PL and CMC aqueous solution mixture.

Structural analysis of microbial poly(ɛ-L-lysine)/poly(acrylic acid) complex by FT-IR, DSC, and solid-state 13C and 15N NMR

Interpolymer complexes of microbial poly(ɛ-L-lysine) (ɛ-PL) and poly(acrylic acid) (PAA) were studied by Fourier transform infrared spectroscopy, differential scanning calorimetry and solid-state 13C and 15N nuclear magnetic resonance (NMR) experiments. These measurements suggested the poly-ionic complex formation between ɛ-PL and PAA, ɛ-PL-H3N+···−OOC-PAA. By analyzing 13C NMR spectra of the complex, we concluded that there exist three forms of the carboxyl group of PAA, namely: (1) the ionized form, interpolymer ion-complex between ɛ-PL and PAA, (2) the dimeric form, intrapolymer hydrogen bonding among PAA molecules and (3) the free form, no particular form of hydrogen bonding.

Erratum: Bio-based biodegradable hydrogels prepared by crosslinking of microbial poly(γ-glutamic acid) with L-lysine in aqueous solution

Correction to: Polymer Journal (2011) 43, 414–420; published online 19 January 2011; doi:10.1038/pj.2010.142 In the above article, unit given for x axis variables for Figure 8 line graph was wrong. It should have been cultivation time in number of days, as shown below.

Formation of carbamates and cross-linking of microbial poly(ε-l-lysine) studied by 13C and 15N solid-state NMR

Formation of carbamates by amino groups of poly(e-l-lysine) (e-PL) and cross-linking of e-PL were studied by using 13C and 15N solid-state NMR. It is a characteristic found in e-PL cast from basic aqueous solution exposed to the air or gaseous CO2. It is not observed in e-PL cast from acidic aqueous solution and e-PL cast from degassed aqueous solution under CO2 free environment. The carboxyl carbon and amide nitrogen appear at 164 ppm in 13C spectrum and 92 ppm in 15N spectrum, respectively, which arise when some amino groups of e-PL react with gaseous CO2 to make carbamates. In addition to these peaks a peak at 171 ppm appears. We assigned it to amide C=O carbons which can not make intermolecular hydrogen bondings since there exist bulky carbamates groups close to these C=O groups. Self-assembly of ionic pairs of ammonium groups and carbamate anions leads to cross-linking of e-PL.

Bio-based biodegradable hydrogels prepared by crosslinking of microbial poly(γ-glutamic acid) with L-lysine in aqueous solution

Bio-based biodegradable hydrogels were prepared by crosslinking microbial homo poly(amino acid), poly(γ-glutamic acid) (PGA), with L-lysine in a one-pot synthesis in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) at 25 °C. The crosslinking was carried out in aqueous solution and the yields of the gels prepared with DMT-MM were higher than those prepared with water-soluble carbodiimide. The water absorption of the PGA gels crosslinked with L-lysine ranged from 300 to 2100 g/g. The water absorption of the PGA gel was affected by the amount of crosslinker and DMT-MM, which had an effect on the crosslinking density of the PGA gel. It was confirmed in a hydrolysis test in a buffer of pH 9 at 37 °C that the obtained gel that was crosslinked with L-lysine by amide bonds was more resistant to hydrolysis than the gel crosslinked by ester bonds. biochemical oxygen demand-biodegradability of the PGA gel crosslinked with L-lysine reached 60% in activated sludge at 25 °C. Bio-based biodegradable hydrogels were prepared by crosslinking microbial poly(γ-glutamic acid) (PGA) with L-lysine in aqueous solution in the presence of 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMT-MM) in a one-pot synthesis. The crosslinking was carried out in aqueous solution in a high yield. The gels obtained in this study were readily biodegraded in the biochemical oxygen demand test. The PGA gel and the crosslinking method by DMT-MM in aqueous solution will be applicable to the development of functional bio-based materials. WSC, water-soluble carbodiimide.

The use of poly(3-hydroxybutyrate- co-3-hydroxyhexanoate) scaffolds for tarsal repair in eyelid reconstruction in the rat

Tarsal repair is an important part for eyelid reconstruction. Presently traditional clinic treatments do not produce satisfactory repair effects. The key is to find a proper tarsal repair material. Microbial poly(3-hydroxybutyrate- co-3-hydroxyhexanoate) (PHBHHx) was studied for application as tarsal substitute in this study. PHBHHx scaffolds were implanted into tarsal defects of Sprague-Dawley rats. Eyelid samples of implanted materials and blank defect controls were collected for histological examination at weekly intervals post surgery. Results were compared among PHBHHx scaffolds, commercial acellular dermal matrices (ADM) and blank defect controls. Both PHBHHx scaffolds and ADM provided satisfactory repair results compared with the blank controls even though the implanted PHBHHx scaffolds showed a 2 weeks inflammation. Fibrous encapsulation and scaffold degradation were observed for the PHBHHx implants. Combined with its strong, elastic mechanical properties, the tissue compatible and biodegradable PHBHHx was proven to be a suitable candidate for tarsal repair.

Surface Stress Effects on the Bending Direction and Twisting Chirality of Lamellar Crystals of Chiral Polymer

Expression of chirality in the highly ordered assembly structures of various types of natural and synthetic materials is still a mystery. Although surface stresses have been known to widely exist in polymer lamellae, how they affect the twisting chirality is yet an unsolved issue. Here we report inversion of the lamellar twisting chirality of microbial poly(R-3-hydroxybutyrate) copolymers from left-handed to right-handed via copolymerization or blending, with the molecular chirality and the structures in the crystalline core unchanged. We interpret the observed inversion of twisting chirality and the complicated lamellar curvature with a continuum model based on surface elasticity theory. Quantitative simulations reveal that the distribution of the anisotropic surface stresses and the surface elasticity property of the lamellae significantly affect the morphological chirality of lamellar twisting. For different chiral polymers, the same bending direction may correlate to the opposite twisting chirality.

Biodegradation and Medical Application of Microbial Poly(3-hydroxybutyrate)

This review is designed to be a comprehensive source for biodegradable polymer: poly(3-hydroxybutyrate) research, including fundamental structure/property relationships and biodegradation kinetics for samples of different geometry. In addition to presenting the scientific framework for the advances in PHB research, this review focuses on applications of PHB in biomedicine and environment with a discussion on commercial applications and health/safety concerns for biodegradable materials.

Effect of hydrophilic and hydrophobic monomers grafting on microbial poly(3-hydroxybutyrate)

The radiation-induced graft polymerization of hydrophilic [sodium p-styrene sulfonate (SSS), acrylic acid (AAc)] and hydrophobic [styrene (St), methyl acrylate (MAAc)] monomers onto microbial poly(3-hydroxybutyrate) (PHB) powder was performed and the characteristics of the both grafting films obtained after remolding were compared. The grafting of various monomers onto the PHB powder increased with reaction time. The degree of grafting ( X g) onto the PHB by these various monomers followed the order St, SSS, MAAc and AAc. The PHB films onto which were grafted St, SSS, MAAc and AAc were characterized by measuring the contact angle, the adsorption of enzyme PHB depolymerase, and the biodegradability, as well as by differential scanning calorimetry. Both hydrophobic and hydrophilic monomers affected the contact angle of grafted PHB film with St, SSS, MAAc and AAc monomers. However, the adsorption of enzyme on the grafted PHB film increased with the amount of hydrophilic monomer and degree of grafting. Consequently, the enzyme PHB depolymerase easily approached the PHB film when the hydrophilic groups were grafted onto its surface. The enzymatic degradation of grafted PHB films with hydrophilic monomer proceeded more quickly than that of hydrophobic monomers.

Synthesis, Characterization and Cell Compatibility of Novel Poly(ester urethane)s Based on Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) and Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) Prepared by Melting Polymerization

Novel tailor-made poly(ester urethane)s (PUs) based on microbial polyesters poly(3-hydroxybutyrate-co-4hydroxybutyrate) (P3HB4HB) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) were synthesized by melting polymerization (MP) using 1,6-hexamethylene diisocyanate (HDI) as a coupling agent. A comprehensive characterization using 1H-NMR, Fourier transform infrared spectroscopy (FT-IR), gel-permeation chromatography (GPC), differential scanning calorimetry (DSC), mechanical properties, static water contact angles, cell proliferation using smooth muscle cells from rabbit aorta (RaSMCs) and immortalized human keratinocytes (HaCat), and blood coagulation behavior were conducted on the synthesized PUs films. DSC showed that PU samples had a low degree of crystallinity at room temperature and became fully amorphous after a melt-quenched process. The series of tailor-made PUs based on different mass ratios of P3HB4HB and PHBHHx revealed a ductile and flexile mechanical property especially for PHBHHx-rich PU, or a hydrophobic property for 4HB-rich PU. A 4 days incubation experiment showed that all PU films had a better cell proliferation than poly(lactic acid) (PLA), polyhydroxybutyrate (PHB), P3HB4HB and PHBHHx. RaSMCs cultured on PU films had a quiescent contractile phenotype, indicating that they were fully functional. HaCat incubated on tailor-made PU films showed a proliferation approximately equal to tissue-culture plates (TCPs). Blood coagulation behavior tests revealed a strong platelet adhesion and a short coagulation time on PU films. This study demonstrated potential medical applications for P3HB4HB and PHBHHx based polyurethane as a hydrophobic wound-healing and hemostatic materials.

Nanoparticles Made of Microbial Poly(γ-glutamate)s for Encapsulation and Delivery of Drugs and Proteins

This study focused on the preparation and evaluation of nanoparticles made of alkyl esters of microbial poly(γ-glutamic acid) (PGGA) to be used as drugs and proteins carrier and delivery systems. Racemic PGGA of bacterial origin was fully methylated or partially esterified to render non-water-soluble polymers. A set of co-polymers containing poly(glutamic acid) and ethyl, hexyl, dodecyl and octadecyl glutamate units with alkyl contents of 50 and 75% was prepared. Spherical nanoparticles with a diameter of 200–250 nm and a narrow distribution were generated from the alkylated polymers by the precipitation-dialysis method. These nanoparticles readily degraded hydrolytically upon incubation in simulated physiological medium at a rate dependent on the alkylation degree and the length of the alkyl group. All these nanoparticles were able to encapsulate efficiently erythromycin. Those made of carboxyl containing polyglutamates were also effective to load α-chymotrypsin. The release of such compounds from nanoparticles upon incubation proceeded essentially following the same profile that is followed in the hydrolysis of the corresponding substrate polymers. The loss of enzyme activity of the incubated protein diminished significantly upon encapsulation in these systems.

Synthesis, Degradability, and Drug Releasing Properties of Methyl Esters of Fungal Poly(β,L‐malic acid)

Methyl esters of microbial poly(beta,L-malic acid) for conversion degrees of 25, 50, 75, and 100% were prepared by treatment of the polyacid with diazomethane. Esterification proceeded with retention of the molecular weight of the parent polyacid and the copolymers displayed a blocky microstructure consisting of short segments of malic and methyl malate sequences. The thermal stability of the copolyesters was lower than those of the parent homopolymers and all of them were fairly crystalline with melting temperatures within the range of 170-175 degrees C. They were degraded rapidly by water, the hydrolysis rate being highly dependent on the methylation degree. Microspheres with mean-average diameters in the range of 1-20 microm were prepared from the 100% methylated product by the emulsion-evaporation solvent method. Encapsulation of erythromycin was efficiently performed in these microparticles and its releasing upon incubation in simulated physiological medium was evaluated for different drug loads. Drug delivery was observed to occur by a releasing mechanism largely determined by the hydrodegradation of the host polymer and independent of the amount of loaded drug.

Phonon Dispersion and Heat Capacity in Microbial Poly(ε-L-lysine)(M-ε-PL)

Microbial poly(ε-L-lysine)(M-ε-PL) is a naturally occurring biomaterial, which is water soluble, biodegradable, edible and non-toxic towards humans and environment. Normal mode analysis including phonon dispersion has been performed to understand completely the vibrational spectra of this polymer. Various characteristic features of the dispersion curves have been reported. The heat capacity is calculated as a function of temperature via density-of-states in the range 1–450 K.

Synchrotron X-ray scattering studies on the structural evolution of microbial poly(3-hydroxybutyrate)

The crystallization behavior of microbially synthesized poly(3-hydroxybutyrate) was studied in detail using time-resolved small-angle X-ray scattering. This polyester was found to undergo primary crystallization as well as secondary crystallization. In the primary crystallization, the thicknesses of the lamellar crystals were sensitive to the crystallization temperature, but no thickening was observed throughout the entire crystallization at a given temperature. The thickness of the lamellar crystals in the polyester was always larger than that of the amorphous layers. Secondary crystallization favorably occurred during the later stage of isothermal crystallization in competition with the continuous primary crystallization, forming secondary crystals in amorphous regions, in particular in the amorphous layers between the primarily formed lamellar crystal stacks. Compared to the primarily formed lamellar crystals, the secondary crystals had short-range-ordered structures of smaller size, a broader size distribution, and a lower electron density.

Thermal and spectroscopic characterization of microbial poly(3‐hydroxybutyrate) submicrometer fibers prepared by electrospinning

AbstractSubmicrometer fibers based on the microbially synthesized ultra‐high‐molecular‐weight poly(3‐hydroxybutyrate) (PHB) were generated by an electrospinning (ES) process with chloroform as the solvent. To characterize the resulting electrospun fibers in comparison with the pure PHB before ES, differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy were performed. The diameters of the electrospun fibers characterized by SEM were in the range 400–1000 nm. Thermal analysis showed that the electrospun fibers contained both helical (α form) and trans‐zigzag (β form) crystals, whereas the solution‐cast PHB films mostly possessed the common helical structure. In addition, the crystallinity of the electrospun PHB fibers increased compared to that of the solution‐cast PHB films. Conformational changes occurred with the high extensional flow in the ES jets. Furthermore, the results from polarized FTIR measurements demonstrate that PHB molecules were oriented parallel to the fiber axis. As a result, the electrospun fibers exhibited strong birefringence under the polarized light. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1860–1867, 2007

Blending and characterizations of microbial poly(3‐hydroxybutyrate) with dendrimers

AbstractBlending of microbial polyester poly(3‐hydroxybutyrate) (PHB) with various dendritic polyester oligomers or dendrimers was achieved by solution casting to improve the film forming ability of PHB. Films of the blends were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), scanning electron micrograph (SEM), and Fourier transform infrared spectroscopy (FTIR). It was revealed that there were mainly two types of interactions in the blending system: the plasticizing or lubricating effect of the low melting spherical dendrimers molecules improved the polymer chain mobility through the suppression of PHB crystallization in the blends; The dendrimers also functioned as crosslinking agents or antiplasticizing agents via weak hydrogen bonding to enhance the overall intermolecular interactions which decrease the chain mobility and thus cause the increase of glass transition temperature (Tg) of PHB. TGA results concluded that incorporating the dendrimers could retard the thermal decomposition of PHB and enhanced its thermal stability accordingly. With the above blend processes, the so‐obtained PHB possessed better film forming ability and even patterned surface structures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3782–3790, 2006

High molecular weight methyl ester of microbial poly(β, l-malic acid): Synthesis and crystallization

High molecular weight poly(α-methyl β, l-malate) ( M n ∼ 25,000, PD ∼ 1.7) was prepared from microbial poly(β, l-malic acid) ( M n ∼ 29,000, PD ∼ 1.3) by methylation with diazomethane in dry acetone without substantial cleavage of the polyester main chain. The thermal properties of this poly(malate) were assessed and its crystal structure was preliminary examined. Two crystal forms were identified by X-ray diffraction, their occurrence being dependent on crystallization conditions. The kinetics of nonisothermal and isothermal crystallizations from the melt were studied and modelled using the Avrami approach. Results were compared to those recently reported by us for low molecular weight poly(α-methyl β, l-malate) ( M n ∼ 3000, PD ∼ 1.3).