Crystallization behavior and environmental biodegradability of the blend films of poly(3-hydroxybutyric acid) with chitin and chitosan

Crystallization behavior and environmental biodegradability were investigated for the films of bacterial poly(3-hydroxybutyric acid) (PHB) blends with chitin and chitosan. The blend films showed X-ray diffractive peaks that arose from the PHB crystalline component. It was suggested that the lamellar thickness of the PHB crystalline component in the blends was large enough to show detectable X-ray diffractive peaks, but this was too small to show observable melting endotherm in the DSC thermogram and the crystalline band absorption in the FT-IR spectrum. In the PHB/chitin and PHB/chitosan blends, thermal transition temperatures of PHB amorphous region observed by dynamic mechanical thermal analysis were almost the same as that of neat PHB. Both the PHB/chitin and the PHB/chitosan blend films biodegraded in an environmental medium. Several blend films showed faster biodegradation than the pure-state component polymers.     

Nanofibers from blends of polyvinyl alcohol and polyhydroxy butyrate as potential scaffold material for tissue engineering of skin

Nanofibers were prepared by electrospinning from pure polyvinyl alcohol (PVA), polyhydroxybutyrate (PHB), and their blends. Miscibility and morphology of both polymers in the nanofiber blends were studied by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC), revealing that PVA and PHB were miscible with good compatibility. DSC also revealed suppression of crystallinity of PHB in the blend nanofibers with increasing proportion of PVA. The hydrolytic degradation of PHB was accelerated with increasing PVA fraction. Cell culture experiments with a human keratinocyte cell line (HaCaT) and dermal fibroblast on the electrospun PHB and PVA/PHB blend nanofibers showed maximum adhesion and proliferation on pure PHB. However, the addition of 5 wt % PVA to PHB inhibited growth of HaCaT cells but not of fibroblasts. On the contrary, adhesion and proliferation of HaCaT cells were promoted on PVA/PHB (50/50) fibers, which inhibited growth of fibroblasts.     

Structure and properties of hydroxyapatite/cellulose nanocomposite films

The aim of this study was to develop a new inorganic-organic hybrid film. Nanohydroxyapaptite (nHAP) particles as the inorganic phase was mixed with cellulose in 7 wt.% NaOH/12 wt.% urea aqueous solution with cooling to prepare a blend solution, and then inorganic-organic hybrid films were fabricated by coagulating with Na₂SO₄ aqueous solution. The structure and properties of the hybrid films were characterized by high resolution transmitting electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), thermo-gravimetric analysis (TGA), Fourier transform infra-red (FT-IR) spectra, wide angle X-ray diffraction (WAXD) and tensile testing. The results revealed that the HAP nanoparticles with mean diameter of about 30 nm were uniformly dispersed and well immobilized in the hybrid film as a result of the role of the nano-and micropores in the cellulose substrate. A strong interaction existed between HAP and cellulose matrix, and their thermal stability and mechanical strength were improved as a result of good miscibility. Furthermore, the results of 293T cell viability assay indicated that the HAP/cellulose films had excellent biocompatibility and safety, showing potential applications in biomaterials.     

Microbial communities responsible for the degradation of poly(lactic acid)/poly(3-hydroxybutyrate) blend mulches in soil burial respirometric tests

The microbial communities responsible for the degradation of poly(lactic acid)/poly(3-hydroxybutyrate) (PLA/PHB) blend foils were investigated in 1 year long laboratory soil burial experiments. Different PLA/PHB foils were tested: (a) PLA/PHB original transparent foil, (b) PLA/PHB carbon black filled foil and (c) PLA/PHB black foil previously exposed for 90 days to sun light. The microbiome diversity of these three types of foil was compared with that identified from soil/perlite sample at the beginning of experiment and that developed on a cellulose mat. Culture-dependent and culture-independent (DGGE-cloning) approaches together with PLA, PHB and PLA/PHB degradation plate assays were employed. The cultivation strategy combined with degradation tests permitted the isolation and evaluation of several PLA/PHB blend degrading microorganisms such as members of the genera Bacillus, Paenibacillus, Streptomyces, Rhodococcus, Saccharothrix, Arthrobacter, Aureobasidium, Mortierella, Absidia, Actinomucor, Bjerkandera, Fusarium, Trichoderma and Penicillium. The DGGE-cloning investigation increased the information about the microbial communities occurring during bioplastic degradation detecting several bacterial and fungal taxa and some of them (members of the orders Anaerolineales, Selenomonadales, Thelephorales and of the genera Pseudogymnoascus and Pseudeurotium) were revealed here for the first time. This survey showed the microbiome colonizing PLA/PHB blend foils and permitted the isolation of several microorganisms able to degrade the tested polymeric blends.     

Condensed state structure and biocompatibility of the konjac glucomannan/chitosan blend films

Specialised blend films have been prepared by blending 1% w/v konjac glucomannan aqueous with 1% w/v chitosan solution in acetate solution and drying at room temperature for 24 h. The condensed state structure and miscibility of the blend films were studied by Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and wide-angle X-ray diffraction. The results indicated that the blend film obtained from an 80/20 mixing ratio of konjac glucomannan and chitosan derivate showed the highest miscibility and blend homogeneity, and that strong intermolecular hydrogen bonds took place between the amino groups of chitosan and the hydroxyl groups of konjac glucomannan; thus the tensile strength also achieved its maximum in this ratio. The cell morphologies on the pure and blend films were examined by light microscopy and cell viability was studied by using MTT assay. The results showed that the particular blend film was more suitable for the cell culture than the pure konjac glucomannan film, and that the cells cultured on this blend film had greater spreading coefficients than that of the pure konjac glucomannan film. As a result of the good mechanical properties, miscibility and biocompatibility, the blend film is a promising biomaterial matrix.     

Biodegradability studies of polyhydroxyalkanoate (PHA) film produced by a marine bacteria using Jatropha biodiesel byproduct as a substrate

Polyhydroxyalkanoates are water-insoluble, hydrophobic polymers and can be degraded by microorganisms that produce extracellular PHA depolymerase. The present work was aimed to evaluate the degradability of Polyhydroxyalkanoate film produced by Halomonas hydrothermalis using Jatropha biodiesel byproduct as a substrate. PHB films were subjected to degradation in soil and compared with the synthetic polymer (acrylate) and blend prepared using the synthetic polymer (acrylate) and PHB. After 50 days, 60% of weight loss in PHB film and after 180 days 10% of blended film was degraded while no degradation was found in the synthetic film. Scanning electron microscopy and confocal microscopy revealed that after 50 days the PHB film and the blended film became more porous after degradation while synthetic film was not porous. The degradative process was biologically mediated which was evident by the control in which the PHB films were kept in sterile soil and the films showed inherent integrity over time. The TGA and DSC analysis shows that the melting temperatures were changed after degradation indicating physical changes in the polymer during degradation.     

Preparation and characterization of biodegradable poly-3-hydroxybutyrate-starch blend films

Bacterial polyesters have attracted much attention as biodegradable biocompatible polymers. Poly-3-hydroxybutyrate, a microbially produced thermoplastic, has similar material properties to polypropylene. Its potential application as biodegradable and biocompatible plastics is well documented. However, due to high cost it is used mainly in biomaterials for medical applications. Materials with useful properties may result from blending bacterial polyhydroxybutyrate (PHB) with other polymers. In this paper, the compatibility of PHB with starch for improved properties and cost reduction is discussed. The thermal and mechanical properties of the blended films were studied by means of thermogravimetry, differential scanning calorimetry and an automated material testing system. The results revealed that blend films had a single glass transition temperature for all the proportions of PHB:starch tested. The nature of all combinations was found to be crystalline. The tensile strength was optimum for the PHB:starch ratio of 0.7:0.3 (wt/wt). The variation in tensile strength, Young's modulus, extension needed to break, thermal stability, glass transition temperature, melting temperature, for the different proportions of PHB:starch are discussed.     

Studies of chitosan: II. Preparation and characterization of chitosan/poly(vinyl alcohol)/gelatin ternary blend films

Chitosan/poly(vinyl alcohol)/gelatin (CS/PVA/GA) ternary blend films were prepared by solution blending method in this study. The thermal properties of the CS/PVA/GA ternary blend films were examined by differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The melting point of the CS/PVA/GA ternary blend film was increased when the amount of GA in the blend film was increased based upon the DSC thermal analysis. Results of X-ray diffraction (XRD) analyses indicated that the intensity of diffraction peak at 19 degrees of PVA became lower and broader with increasing the amount of GA in the CS/PVA/GA ternary blend film. Although CS, PVA, and GA are hydrophilic biodegradable polymers, the results of water contact angle measurements are still as high as 83 degrees, 68 degrees, and 66 degrees, respectively. A minimum water contact angle (56 degrees) was observed when the ternary blend film contains 50 wt.% GA (i.e. GA5). This behavior is primarily due to the reorientation of polar functional groups toward to the top surface of CS/PVA/GA ternary blend films.     

Fabrication,Characterization and Cellular Compatibility of Poly(Hydroxy Alkanoate) Composite Nanofibrous Scaffolds for Nerve Tissue Engineering

Tissue engineering techniques using a combination of polymeric scaffolds and cells represent a promising approach for nerve regeneration. We fabricated electrospun scaffolds by blending of Poly (3-hydroxybutyrate) (PHB) and Poly (3-hydroxy butyrate-co-3- hydroxyvalerate) (PHBV) in different compositions in order to investigate their potential for the regeneration of the myelinic membrane. The thermal properties of the nanofibrous blends was analyzed by differential scanning calorimetry (DSC), which indicated that the melting and glass temperatures, and crystallization degree of the blends decreased as the PHBV weight ratio increased. Raman spectroscopy also revealed that the full width at half height of the band centered at 1725 cm⁻¹ can be used to estimate the crystalline degree of the electrospun meshes. Random and aligned nanofibrous scaffolds were also fabricated by electrospinning of PHB and PHBV with or without type I collagen. The influence of blend composition, fiber alignment and collagen incorporation on Schwann cell (SCs) organization and function was investigated. SCs attached and proliferated over all scaffolds formulations up to 14 days. SCs grown on aligned PHB/PHBV/collagen fibers exhibited a bipolar morphology that oriented along the fiber direction, while SCs grown on the randomly oriented fibers had a multipolar morphology. Incorporation of collagen within nanofibers increased SCs proliferation on day 14, GDNF gene expression on day 7 and NGF secretion on day 6. The results of this study demonstrate that aligned PHB/PHBV electrospun nanofibers could find potential use as scaffolds for nerve tissue engineering applications and that the presence of type I collagen in the nanofibers improves cell differentiation.     

Environmental degradation of polyester blends containing atactic poly(3-hydroxybutyrate). Biodegradation in soil and ecotoxicological impact

The degradation of poly[(R,S)-3-hydroxybutyrate], a-PHB, binary blends with natural PHB (n-PHB) and poly(L-lactic acid), PLLA, respectively, has been investigated in soil. In such a natural environment, a-PHB blend component was found to biodegrade. The degradation of a-PHB-containing blends proceeded faster than that of respective plain n-PHB and PLLA. The molecular weight decrease of the n-PHB component was higher, while the same rate of bioerosion of both components was observed for the a-PHB/n-PHB binary blend. For the a-PHB blend with PLLA, the weight loss was accompanied by blend composition changes and the decrease of a-PHB content. However, the PLLA molecular weight decrease was lower in the blend in comparison with the plain PLLA sample. The increase of the number of microorganisms particularly observed for the soil where binary blends were incubated indicates that microbial degradation of a-PHB takes place. The terrestrial plant growth test (cress and barley) demonstrates no environmental toxicity of the materials studied.     

Biodegradation kinetics of poly(3-hydroxybutyrate)-based biopolymer systems

The aim of this study was to evaluate and to compare the long-term kinetics curves of biodegradation of poly(3-hydroxybutyrate) (PHB), its copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate), and a PHB/polylactic acid composite. The total weight loss and the change of average viscosity molecular weight were used as the parameters reflecting the biodegradation degree. The rate of biodegradation was analyzed in vitro in the presence of lipase and in vivo after film implantation in animal tissues. The morphology of the PHB film surface was studied by the atomic force microscopy technique. It was shown that PHB biodegradation involves both polymer hydrolysis and its enzymatic biodegradation. The results obtained in this study can be used for the development of various PHB-based medical devices.     

Floating Elementary Osmotic Pump Tablet (FEOPT) for Controlled Delivery of Diethylcarbamazine Citrate: a Water-Soluble Drug

The present work investigates the feasibility of the design of a novel floating elementary osmotic pump tablet (FEOPT) to prolong the gastric residence of a highly water-soluble drug. Diethylcarbamazine citrate (DEC) was chosen as a model drug. The FEOPT consisted of an osmotic core (DEC, mannitol, and hydrophilic polymers) coated with a semipermeable layer (cellulose acetate) and a gas-generating gelling layer (sodium bicarbonate, hydrophilic polymers) followed by a polymeric film (Eudragit RL 30D). The effect of formulation variables such as concentration of polymers, types of diluent, and coat thickness of semipermeable membrane was evaluated in terms of physical parameters, floating lag time, duration of floatation, and in vitro drug release. The Fourier transform infrared and X-ray diffraction analysis were carried out to study the physicochemical changes in the drug excipients powder blend. The integrity of the orifice and polymeric film layer was confirmed from scanning electron microscopy image. All the developed FEOPT showed floating lag time of less than 8 min and floating duration of 24 h. A zero-order drug release could be attained for DEC. The formulations were found to be stable up to 3 months of stability testing at 40°C/75% relative humidity.     

Diffusion of a freely water-soluble drug in aqueous enteric-coated pellets

The effects of filler used in the pellet cores (ie, waxy cornstarch or lactose) and the enteric film coat thickness on the diffusion and dissolution of a freely soluble drug were studied. Two kinds of pellet cores containing riboflavin sodium phosphate as a model drug, microcrystalline cellulose (MCC) as a basic filler, and waxy cornstarch or lactose as a cofiller were film coated (theoretically weight increase 20% or 30%) with an aqueous dispersion of cellulose acetate phthalate (CAP). The diffusion of riboflavin sodium phosphate in aqueous enteric-coated pellets was investigated using noninvasive confocal laser scanning microscopy (CLSM). The in vitro release tests were performed using a USP apparatus I (basket method). Diffusion of drug from the core to the film coat was found to be greater with lactose-containing pellets than with waxy cornstarch-containing pellets. The dissolution test showed that 30% enteric-coated waxy cornstarch pellets had a good acidic resistance in 0.1 N HCl solution for at least 1 hour, while the other enteric pellet formulations failed the test. The waxy cornstarch-containing enteric pellets dissolved at SIF in less than 10 minutes. Confocal images of film-coated pellets showed that waxy cornstarch-containing pellets had less drug dissolved than respective lactose-containing pellets. The observations were further confirmed by measurement of fluorescence intensity of riboflavin sodium phosphate in the film coat. The dissolution test was consistent with the confocal microscopy results. In conclusion, waxy cornstarch as a cofiller in the pellet cores minimizes premature drug diffusion from the core into the film coat layer.     

Microbial degradation of poly(d-3-hydroxybutyrate) by a new thermophilic Streptomyces isolate

A new thermophilic microorganism capable of degrading poly(D-3-hydroxybutyrate) (PHB) was isolated from soil. A phylogenetic analysis based on 16S rDNA sequences indicated that the new isolate belongs to genus Streptomyces. PHB film and powder were completely degraded after 6 and 3 d cultivation, respectively at 50 degrees C. Scanning micrographs showed adherence of the microbial cells to the entire film surface, indicating that biodegradation occurs by colonization of the PHB surface. The film was degraded both by microbial attack and by the action of an extracellular enzyme secreted by the microorganism. The strain can also degrade poly(ethylene succinate), poly(ester carbonate), polycaprolactone and poly(butylene succinate), but to a lesser extent.     

Biomimetic nanofibrous scaffolds: preparation and characterization of PGA/chitin blend nanofibers

Electrospinning of poly(glycolic acid) (PGA)/chitin blend solutions in 1,1,1,3,3,3-hexafluoro-2-propanol was investigated to fabricate biodegradable and biomimetic nanostructured scaffolds for tissue engineering. The morphology of the electrospun PGA/chitin blend nanofibers was investigated with a field emission scanning electron microscope. The PGA/chitin blend fibers have average diameters of around 140 nm, and their diameters have a distribution in the range 50-350 nm. The miscibility of PGA/chitin blend fibers was examined by differential scanning calorimetry. The PGA and chitin were immiscible in the as-spun nanofibrous structure. An in vitro degradation study of PGA/chitin blend nanofibers was conducted in phosphate-buffered saline, pH 7.2. It was found that the hydrolytic cleavage of PGA in the blend nanofibers was accelerated by the coexistence of hydrophilic chitin. To assay the cytocompatability and cell behavior on the PGA/chitin blend nanofibrous scaffolds, cell attachment and spreading of normal human epidermal fibroblasts seeded on the scaffolds were studied. Our results indicate that the PGA/chitin blend nanofibrous matrix, particularly the one that contained 25% PGA and 75% chitin with bovine serum albumin coating, could be a good candidate for tissue engineering scaffolds, because it has an excellent cell attachment and spreading for normal human fibroblasts.     

Preparation and performance evaluation of glucomannan–chitosan–nisin ternary antimicrobial blend film

The material behaviour and antimicrobial effect of konjac glucomannan edible film incorporating chitosan and nisin at various ratio or concentrations is discussed. This activity was tested against food pathogenic bacteria namely Escherichia coli, Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus. Mechanical and physical properties were determined and the results indicated that the blend film KC2 (mixing ratio konjac glucomannan 80/chitosan 20) showed the maximum tensile strength (102.8 ± 3.8 MPa) and a good transparency, water solubility, water vapor transmission ratio. The differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), etc. were used to characterize the structural change of the blend films. The results showed that the strong intermolecular hydrogen bonds took place between chitosan and konjac glucomannan. Incorporation of nisin at 42,000 IU/g of film for the selected blend film KC2 was found to have antimicrobial activity against S. aureus, L. monocytogenes, and B. cereus. The antimicrobial effect of chitosan or KC2 incorporating nisin was much better than that of konjac glucomannan incorporating nisin at each corresponding concentration and existed significant difference (p < 0.05), however, there was no significant difference on the antimicrobial effect between chitosan and KC2 both incorporating nisin. At all these levels, the ternary blend film KC2-nisin had a satisfactory mechanical, physical properties and antimicrobial activity, and could be applied as a potential ‘active’ packaging material.     

Supermolecular structure of cellulose/amylose blends prepared from aqueous NaOH solutions and effects of amylose on structural formation of cellulose from its solution

We previously proposed a mechanism for the structural formation of cellulose from its solution using a molecular dynamics (MD) simulation and suggested that the initial structure from its solution plays a critical role in determining its final structure. Structural changes in the van der Waals-associated cellulose molecular sheet as the initial structure were examined by MD simulation; the molecular sheet was found to be disordered due to maltohexaoses as an amylose model in terms of the hydrogen bonding system of cellulose. The structure and properties of cellulose/amylose blends prepared from an aqueous NaOH solution were examined experimentally by wide-angle X-ray diffraction and dynamic viscoelasticity measurements. The crystallinity of cellulose in the cellulose/amylose blend films was lower than that of cellulose film. The diffraction peaks of the cellulose/amylose blends were slightly shifted; specifically, () was shifted to a higher angle, and (1 1 0) and (0 2 0) were shifted to lower angles. These experimental results probably resulted from the disordered molecular sheet, as revealed by MD simulations.     

Formation of aerobic granules and their PHB production at various substrate and ammonium concentrations

Aerobic granular sludge rich in polyhydroxybutyrate (PHB) was cultivated in a sequencing batch reactor (SBR) by seeding anaerobic granular sludge. The PHB content in aerobic granules was investigated and the experimental results reveal that both influent chemical oxygen demand (COD) and ammonium concentrations had a significant effect on the morphological characteristics and the PHB production of the aerobic granular sludge. At a COD and ammonium concentration of 750 mg/L and 8.5mg/L, respectively, the PHB content of the granules reached 44%, but their poor settling ability, as evidenced by a high sludge volume index, was observed. This was attributed to the outgrowth of filamentous bacteria on the granule surface. However, an increase in the ammonium concentration resulted in an elevated sludge concentration and a decrease in the PHB content in the granules. In this case, the aerobic granular sludge with a regular and compact structure was formed. The results suggest that, through controlling the COD and ammonium concentrations in the influent, the PHB-rich aerobic granular sludge with good settling ability could be cultivated.     

Phase structure and enzymatic degradation of poly(L-lactide)/atactic poly(3-hydroxybutyrate) blends: an atomic force microscopy study

Phase structures and enzymatic degradation of poly(l-lactide) (PLLA)/atactic poly(3-hydroxybutyrate) (ata-PHB) blends with different compositions were characterized by using atomic force microscopy (AFM). Differential scanning calorimetry (DSC) thermograms of PLLA/ata-PHB blends with different compositions showed two glass transition temperatures, indicating that the PLLA/ata-PHB blends are immiscible in the melt. Surface morphologies of the thin films for PLLA/ata-PHB blends were determined by AFM. Phase separated morphology was recognized from the AFM topography and phase images. The domain size of the components was dependent on the blend ratio. Enzymatic degradation of the PLLA/ata-PHB blends was performed by using both PHB depolymerase and proteinase K. Either PLLA or ata-PHB domains were eroded depending on the kinds of enzyme. Surface morphologies after enzymatic degradation have revealed the phase structure along the depth direction. Enzymatic adsorption of PHB depolymerase was examined on the surface of PLLA/ata-PHB blends. The enzyme molecules were found on both domains of the binary blends. The larger number of enzyme molecules was found on the PLLA domains relative to those on the ata-PHB domains, suggesting the higher affinity of the enzyme against PLLA domain.     

Preparation and characterization on mechanical and antibacterial properties of chitsoan/cellulose blends

Polysaccharides-based membranes of chitosan and cellulose blends were prepared using trifluoroacetic acid as a co-solvent. Morphology and mechanical property of prepared membranes were studied by Instron and dynamic mechanical thermal analysis. The mechanical and dynamic mechanical thermal properties of the cellulose/chitosan blends appear to be dominated by cellulose, suggests that cellulose/chitosan blends were not well miscible. It is believed that the intermolecular hydrogen bonding of cellulose is supposed to be break down to form cellulose–chitosan hydrogen bonding; however, the intra-molecular and intra-strand hydrogen bonds hold the network flat. The reduced water vapor transpiration rate through the chitosan/cellulose membranes indicates that the membranes used as a wound dressing may prevent wound from excessive dehydration. The chitosan/cellulose blend membranes demonstrate effective antimicrobial capability against Escherichia coli and Staphylococcus aureus, as examined by the antimicrobial test. These results indicate that the chitosan/cellulose blend membranes may be suitable to be used as a wound dressing with antibacterial properties.