Processing conditions and characterization of novel electrospun poly (3-hydroxybutyrate-co-hydroxyvalerate)/chitosan blend fibers

Novel hybrid fibrous membranes with potential application on the biomedical field were successfully developed via electrospinning of blend solutions of two biocompatible and biodegradable polymers, poly (3-hydroxybutyrate-co-hydroxyvalerate) [PHBV] and chitosan. The effect of solvent, using different proportions of trifluoracetic acid (TFA) and 1,1,1,3,3,3-hexafluoro-2-isopropanol (HFIP), PHBV/chitosan ratio, and chitosan molecular weight on solution spinnability, fiber morphology and size, and in vitro degradation were investigated. Continuous nanofiber structures were obtained from pristine PHBV to a PHBV/chitosan ratio of 2:3 (w/w), at 10% (w/v) total polymer concentration. In general, main fiber average diameters increased as chitosan content and molecular weight increased and decreased with the decrease of HFIP content in the solvent. In vitro dissolution tests revealed that the hybrid fibers show much higher degradation rates than the neat PHBV.     

Evaluation of PHBHHx and PHBV/PLA fibers used as medical sutures

Two types of fibers were prepared by using bio-based materials: a mono-filament made from poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and a multi-filament made from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polylactic acid (PLA) blend. The two fibers were evaluated for mechanical properties, biocompatibility and degradability for the potential application as medical sutures. The PHBHHx fiber showed remarkable biocompatibility by H.E. Stainning, with very little impact to the surrounding tissues. The degradation of the fiber was observed by SEM after implantation for 36 weeks, and the major degradation product was detected after 96 weeks. Consistently, the PHBHHx fiber maintained more than half of the mechanical properties after 96 weeks. The other fiber was prepared by twisting PHBV/PLA blend strands to a bunch, and showed high biocompatibility and relatively high degradability. The bunched structure loosed after 36 weeks of implantation. These low-cost and easily prepared fibers have great potential in medical applications, since they could avoid the formation of fibrous capsule, reduce the size of scar, and degrade into non-toxic and even beneficial products.     

Processing and characterization of solid and microcellular PHBV/PBAT blend and its RWF/nanoclay composites

Solid and microcellular components made of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/poly (butylene adipate-co-terephthalate) (PBAT) blend (weight ratio of PHBV:PBAT = 30:70), recycled wood fiber (RWF), and nanoclay (NC) were prepared via a conventional and microcellular-injection molding process, respectively. Morphology, thermal properties, and mechanical properties were investigated. The addition of 10% RWF (both untreated and silane-treated) reduced the cell size and increased the cell density of the microcellular components. Also, the addition of 10% RWF (both untreated and silane-treated) generally increased the specific Young’s modulus and tensile strength, but decreased the specific toughness and strain-at-break in both solid and microcellular components. Moreover, unlike the neat PHBV/PBAT blend, microcellular PHBV/PBAT/RWF (both untreated and silane-treated) composites showed higher specific toughness and strain-at-break compared to their solid counterparts. In addition, higher specific toughness and strain-at-break was observed in the PHBV/PBAT/untreated-RWF composite compared with the PHBV/PBAT/silane-treated RWF composite, particularly in the microcellular components. The degree of PHBV crystallinity increased significantly in both solid and microcellular PHBV/PBAT/RWF composites although the degree of PHBV crystallinity in the solid components was slightly higher than that of their microcellular counterparts. The effects of adding 2% nanoclay on the properties of the PHBV/PBAT/silane-treated-RWF composite were also investigated. The nanoclays exhibited an intercalated structure in the composites based on XRD analysis and did not induce significant changes in the cell morphology and mechanical properties of the PHBV/PBAT/silane-treated-RWF composite. However, it did improve its thermal stability.     

Electrospun PHBV/PEO co-solution blends: Microstructure,thermal and mechanical properties

Blending allows to tailor and modulate the properties of selected polymers. Blends of poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and polyethylene oxide (PEO) were fabricated by electrospinning in different weight ratios i.e. 100:0, 80:20, 70:30, 50:50, 0:100.In order to evaluate the influence of PEO addition on the final properties of PHBV, a complete microstructural, thermal and mechanical characterization of PHBV/PEO blends has been performed. The two neat polymeric membranes were also considered for the sake of comparison. The following characterization techniques were employed: scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy, simultaneous thermogravimetric and differential analyses (TG-DTA), differential scanning calorimetry (DSC), and uniaxial tensile tests.All electrospun mats consisted of randomly oriented and uniform fibers. It has been observed that the microstructure of PHBV/PEO was remarkably affected by blend composition. The average fiber size ranged between 0.5 μm and 2.6 μm. It resulted that the electrospun polymeric blends consisted of separate crystalline domains associated to an amorphous interdisperse phase. PHBV/PEO blends presented intermediate mechanical properties, in terms of tensile modulus and ultimate tensile stress, with respect to the two neat components.     

可全生物降解PLA/PBAT/PHBV共混材料的结构与性能

为了得到刚性与韧性平衡的聚乳酸（PLA）基可生物降解共混材料,通过熔融共混挤出法制备了不同质量比的PLA/己二酸-对苯二甲酸-丁二酯共聚物（PBAT）/聚（3-羟基丁酸-co-羟基戊酸共聚酯（PHBV）可全生物降解共混材料,采用SEM、TG、DSC、毛细管流变仪和万能材料试验机对PLA/PBAT/PHBV共混材料的形态结构、热性能、流变性能和力学性能进行了研究。结果表明:PLA/PBAT/PHBV共混材料的热失重起始分解温度相对纯PHBV提高了45 ℃,热稳定性提高;共混体系中各组分的玻璃化转变温度与单一体系相比几乎无变化,PLA/PBAT/PHBV共混体系为完全不相容体系,同时PBAT和PHBV的加入阻碍了PLA的冷结晶;PLA/PBAT/PHBV 共混体系的共混形态呈“海-岛”分布,PBAT和PHBV均匀地分散于PLA基体中,相界面分明;随着PBAT含量增加,PLA/PBAT/PHBV共混材料熔体的流动性增加,温度变化对黏度的影响变大;PLA/PBAT/PHBV质量比为70/20/10的共混材料可在保留纯PLA 60%拉伸应力的同时,拉伸应变提高到纯PLA的2.6倍,韧性得到改善。所得结论表明PLA/PBAT/PHBV质量比为70/20/10的共混材料的综合力学性能较纯PLA好。      

Synthesis of gelatin-containing PHBV nanofiber mats for biomedical application

Electrospinning is one of the fabrication method to form ultra-fine fiber in a nano-scale made of synthetic and natural extracellular matrix components for tissue-engineering applications. In this study, a nanofibrous scaffold was obtained by co-electrospinning poly (3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and gelatin in 2,2,2-trifluoroethanol (TFE) at a ratio of 50/50. The resulting fiber diameters were in the range of 400-1,000 nm without any beads. The nanofiber surfaces were characterized by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), electron spectroscopy for chemical analysis (ESCA), and atomic force microscopy. It was found, from cell culture experiments, that NIH 3T3 cells on the PHBV/gelatin nanofibrous scaffold more proliferated than on the PHBV nanofibrous scaffold.     

Photo-induced liquid crystal alignment of poly(vinyl cinnamate) and fluorinated polyimide blends

Liquid crystal(LC) alignment properties were mainly affected by surface properties of alignment layers. In our previous work, we prepared poly(vinyl cinnamate) (PVCi) and polyimide blend alignment layer for thermally stable LC alignment. In this work, we utilized fluorinated polyimide for blend alignment layers in order to modify surface properties of alignment layers. For this purpose, polyimides containing fluorine unit were synthesized and used for the blend alignment layers. Fluorine containing diamine, 4,4′-bis[2-(4-aminophenyl)hexafluoropropyl]-diphenyl ether(BDAF), is used for the polyimide synthesis. We prepared the fluorinated polyimide and PVCi blend alignment layers and investigated the effect of fluorine on the LC alignment properties and pretilt angle of LC.     

Mechanical behaviour of agro-residue reinforced poly(3-hydroxybutyrate-co-3-hydroxyvalerate), (PHBV) green composites: A comparison with traditional polypropylene composites

Novel green composites were successfully fabricated by incorporating agro-residues as corn straw (CS), soy stalk (SS) and wheat straw (WS) into the bacterial polyester, poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, by melt mixing technique. Effects of these biomass fibers on mechanical, thermal, and dynamic mechanical properties of PHBV were investigated. A comparative study of biomass fiber-reinforced polypropylene composite systems was performed. The tensile and storage modulus of PHBV was improved by maximum 256% and 308% with the reinforcement of 30 wt.% agricultural byproducts to it. For equal amounts of (30%) biomass fibers, tensile and flexural modulii of PHBV composites showed much higher values than corresponding PP composites. Alkali treatment of wheat straw fibers enhanced strain @ break and impact strength of PHBV composites by ∼35%, hardly increasing strength and modulus compared to their untreated counterparts. DMA studies indicated better interfacial interaction of PHBV with the biomass fibers than PP. Scanning electron microscopy (SEM), used to study the morphology of composites, also revealed similar outcomes.     

Formation and morphological stability of polybutadiene rubber fibers prepared through combination of electrospinning and in-situ photo-crosslinking

Herein we report that fibers of polybutadiene rubber (BR) with high morphological stability were made through combination of electrospinning and in-situ photo-crosslinking. This study revealed that (1) the formation of electrospun BR fibers was correlated with the overlap/entanglement of BR macromolecules in the spinning solutions; for the formation of uniform fibers without beads and/or beaded fibers, the concentration of spinning solution had to be higher than the “critical chain entanglement concentration (Ce)”; and (2) the in-situ photo-crosslinking was an effective method to considerably improve the morphological stability of electrospun BR fibers; upon prolonged storage under ambient condition or even upon immersion in tetrahydrofuran (a good solvent for BR), the crosslinked BR fibers well retained their morphology. It is envisioned that electrospun rubber fibers could be utilized for the development of innovative composites with substantially improved toughness and/or impact strength.     

Electrospinning of aligned biodegradable polymer fibers and composite fibers for tissue engineering applications

Fibrous membranes of aligned poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) fibers have been made through electrospinning. A high-speed rotating drum was used as the fiber collector while the electric field was manipulated by using five knife-edged auxiliary electrodes. It was found that a high drum rotating speed of 3000 rpm could lead to a nearly perfect alignment of PHBV fibers during electrospinning. Multilayered fibrous structures with each layer having a different direction of fiber alignment could also be constructed through electrospinning. The electrospun PHBV fibers were further modified by incorporating carbonated hydroxyapatite (HA) nanospheres (up to 20% of HA) in the fibers. The fibrous membranes made of aligned PHBV fibers and made of HA/PHBV composite fibers should be very useful for the tissue engineering of different human body tissues.     

Temperature-sensitivity and cell biocompatibility of freeze-dried nanocomposite hydrogels incorporated with biodegradable PHBV

The structure, morphology, thermal behaviors and cytotoxicity of novel hydrogels, composed of poly(N-isopropylacrylamide)(PNIPAM) and biodegradable polyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) under nanoclay hectorite “Laponite XLG” severed as physical cross-linker, were characterized by X-ray diffraction, scanning electron microscopy, gravimetric method, differential scanning calorimetry, and cell culture experiments. It was found that, due to the introduction of hydrophobic PHBV, the homogeneity of interior pore in the pure PNIPAM nanocomposite hydrogel was disrupted, the transparency and swelling degree gradually decreased. Although the weight ratio between PHBV and NIPAM increased from 5 to 40 wt.%, the volume phase transition temperature (VPTTs) of hydrogel were not altered compared with the pure PNIPAM nanocomposite hydrogel. No matter what PHBV content, the PHBV/PNIPAM/Hectorite hydrogels always exhibit good stimuli-responsibility. In addition, human hepatoma cells(HepG2) adhesion and spreading on the surface of PHBV-based hydrogels was greatly improved than that of pure PNIPAM nanocomposite hydrogel at 37 °C due to the introduction of PHBV.     

Crystallization kinetics of poly(hydroxybutyrate- co -hydroxyvalerate) and poly(dicyclohexylitaconate) PHBV/PDCHI blends: thermal properties and hydrolytic degradation

The influence of poly(dicyclohexylitaconate) (PDCHI) content, on the crystallization kinetics, thermal properties, and hydrolytic degradation of poly(hydroxybutyrate-co-hydroxyvalerate), PHBV, was studied. Irrespective of the blend composition, the calorimetric and FTIR spectroscopy analyses indicate that the blend components are immiscible. The kinetics of non-isothermal crystallization and melting behavior of PHBV were studied by differential scanning calorimetry (DSC) and examined using non-isothermal Avrami and Mo’s analyses. Based on Mo’s model, the PDCHI content has significant effect on the crystallization kinetics of PHBV matrix. Despite the immiscibility of these polymers, the amorphous polyvinyl ester could extensively control the rate of hydrolytic degradation.     

Processing and characterization of solid and microcellular poly(lactic acid)/polyhydroxybutyrate-valerate (PLA/PHBV) blends and PLA/PHBV/Clay nanocomposites

The morphology, microstructure, tensile properties, and dynamic mechanical properties of solid and microcellular poly(lactic acid) (PLA)/polyhydroxybutyrate-valerate (PHBV) blends, as well as PLA/PHBV/clay nanocomposites, together with the thermal and rheological properties of solid PLA/PHBV blends and PLA/PHBV/clay nanocomposites, were investigated. Conventional and microcellular injection-molding processes were used to produce solid and microcellular specimens in the form of ASTM tensile test bars. Nitrogen in the supercritical state was used as the physical blowing agent in the microcellular injection molding experiments. In terms of rheology, the PLA/PHBV blends exhibited a Newtonian fluid behavior, and their nanocomposite counterparts showed a strong shear-thinning behavior, over the full frequency range. An obvious pseudo-solid-like behavior over a wide range of frequencies in the PLA/PHBV/clay nanocomposites suggested a strong interaction between the PLA/PHBV blend and the nanoclay that restricted the relaxation of the polymer chains. PLA/PHBV/clay nanocomposites possess a higher modulus and greater melt strength than PLA/PHBV blends. The addition of nanoclay also decreased the average cell size and increased the cell density of microcellular PLA/PHBV specimens. As a crystalline nucleating agent, nanoclay significantly improved the crystallinity of PHBV in the blend, thus leading to a relatively high modulus for both solid and microcellular specimens. However, the addition of nanoclay had less of an effect on the tensile strength and strain-at-break.     

Self-aligned and bundled electrospun fibers prepared from blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with a hairy-rod polyphenylene copolymer

Bundled and self-aligned fibers were obtained by electrospinning blends of polystyrene (PS) and poly(methyl methacrylate) (PMMA) with a hairy-rod polyphenylene-g-polystyrene/poly(a-caprolactone) (PP-g-PS/PCL) copolymer. The self-alignment and bundling characteristics of these electrospun fibers were ascribed to the unique molecular architecture of the conjugated polymer, PP-g-PS/PCL, and its interactions with the solvent and the polymer matrixes used for the electrospinning. The self-alignment and bundling was found to be much more pronounced for PP-g-PS/PCL-PS blend when compared to PP-g-PS/PCL-PMMA blend. Furthermore we found that the degree of self-alignment of the fiber bundles was enhanced by increasing the amount of PP-g-PS/PCL in the blends but the alignment completely disappeared when the solvent dimethylformamide was changed to chloroform.     

A new nanofiber fabrication technique based on coaxial electrospinning

In tissue engineering, nanofibrous scaffolds can achieve better biological responses than microfibrous scaffolds and electrospinning is a common method for producing fibrous scaffolds. However, not all biopolymers can be made into nanofibers through conventional electrospinning. The current investigation developed an innovative nanofiber fabrication technique based on coaxial electrospinning and used poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) as an example for achieving nanofibers. For obtaining PHBV nanofibers, core-shell structured fibers were fabricated first via coaxial electrospinning, with PHBV being the core and chitosan being the shell. The chitosan shell was then removed by washing electrospun scaffolds with water, leading to the formation of nanofibrous PHBV scaffolds. The PHBV nanofiber diameter was affected by the inner polymer (i.e., PHBV) solution concentration during coaxial electrospinning, which can be explained in terms of the coaxial electrospinning process and polymer solution viscosity. Compared to the approach of using a conductivity-enhancing salt in polymer solution to produce polymer nanofibers, the new technique not only eliminates the biocompatibility concerns but also provides a more effective way of reducing fiber diameters to the nano-size range.     

Improving the interfacial adhesion in a new renewable resource-based biocomposites from biofuel coproduct and biodegradable plastic

Biocomposites of a biopolymer and the coproduct of corn bioethanol industry, dried distillers’ grains with solubles (DDGS), were produced by reactive melt extrusion and injection molding. The biopolymer matrix was a blend of polyhydroxy(butyrate-co-valrerate), PHBV, and poly(butylene adipate-co-terphthalate), PBAT. The effect of compatibilizer, polymeric methylene diphenyl diisocyanate (PMDI), and corn oil lubricant was studied. The change in melt processing force suggested the occurrence of chemical reactions during the processing. This hypothesis was further investigated by infrared spectroscopy by which the formation of urethane and urea bonds between DDGS and polymeric matrix was approved. Dynamic mechanical analysis confirmed the occurrence of crosslinks at PBAT–PHBV interface showing that the tan δ curves for PBAT and PHBV of the matrix shifted slightly towards each other. Moreover, the calculated parameter of interaction, A, from tan δ curves admitted the stronger bond at the DDGS–matrix interface as a result of addition of PMDI compatibilizer. Also, scanning electron microscopy images revealed improved interfacial adhesion at the DDGS–matrix interface as well as PBAT–PHBV interface within the matrix itself. The obtained crosslinked interfaces resulted in improvement in the strength, modulus, and elongation-at-break of biocomposites. Moreover, a synergism of PMDI and corn oil effects led to a dramatic improvement in impact strength of this biocomposite system so that the respective value for the prepared DDGS biocomposite increased from 75 to 212 J/m with addition of 1 % of PMDI and 3 % of corn oil.     

Processing and characterization of solid and microcellular PHBV/coir fiber composites

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/coir fiber composites were prepared via both conventional and microcellular injection-molding processes. The surface of the hydrophilic coir fiber was modified by alkali- and silane-treatment to improve its adhesion with PHBV. The morphology, thermal, and mechanical properties were investigated. The addition of coir fiber (treated and untreated) reduced cell size and increased cell density. Further decrease in cell size and increase in cell density was observed for treated fibers compared with PHBV/untreated-fiber composites. Mechanical properties such as specific toughness and strain-at-break improved for both solid and microcellular specimens with the addition of coir fibers (both treated and untreated); however, the specific modulus remained essentially the same statistically while the specific strength decreased slightly. The silane-treated coir fiber composites showed the greatest improvement in specific toughness and strain-at-break among the treated-fiber composites. In addition, adding coir fibers (treated and untreated) also increased the degree of crystallinity of the PHBV composites. PHBV with treated coir fibers showed a higher degree of crystallinity compared with untreated coir fibers.     

Crystallization behavior of poly(hydroxybytyrate-<Emphasis Type="Italic">co</Emphasis>-valerate) in model and bulk PHBV/kenaf fiber composites

The kinetics of non-isothermal crystallization and melting behavior of poly(hydrohybutyrate-co-valerate) (PHBV) in model, bulk and compatibilized (PHBV)/kenaf fiber composites were investigated using differential scanning calorimetry (DSC). Analysis of the non-isothermal crystallization data was carried out based on the Avrami and Mo’s models. Activation energies of the crystallization process were determined by the Kissinger approach, and were in the range between 41 and 48 kJ/mol for all investigated samples. It was shown that the kenaf fibers, as well as their content, do not affect significantly the crystallization kinetics of PHBV matrix. The results indicate that crystallization behavior of polymer resin in bulk composites is not affected by the melt processing, thus suggesting absence of degradation processes.     

Design of a 3D aligned myocardial tissue construct from biodegradable polyesters

The heart does not regenerate new functional tissue when myocardium dies following coronary artery occlusion, or if it is defective. Ventricular restoration involves excising the infarct and replacing it with a cardiac patch to restore the heart to a more healthy condition. The goal of this study was to design and develop a clinically applicable myocardial patch to replace myocardial infarcts and improve long-term heart function. A basic design composed of 3D microfibrous mats that house mesenchymal stem cells (MSCs) was developed from human umbilical cord matrix (Wharton’s Jelly) cells aligned in parallel to each other mimicking the native myocardium. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), poly(L-D,L-lactic acid) (P(L-D,L)LA) and poly(glycerol sebacate) (PGS) were blended and electrospun into aligned fiber mats with fiber diameter ranging between 1.10 and 1.25 μm. The micron-sized parallel fibers of the polymer blend were effective in cell alignment and cells have penetrated deep within the mat through the fiber interstices, occupying the whole structure; 8–9 cell layers were obtained. Biodegradable macroporous tubings were introduced to serve as nutrient delivery route. It was possible to create a thick myocardial patch with structure similar to the native tissue and with a capability to grow.     

Fabrication and characterization of biodegradable PHBV/SiO2 nanocomposite for thermo‐mechanical and antibacterial applications in food packaging

In the present study, biogenic silica nanoparticles (bSNPs) were synthesized from groundnut shells, and thoroughly characterized to understand its phase, and microstructure properties. The biopolymer was synthesized from yeast Wickerhamomyces anomalus and identified as Poly (3‐hydroxybutyrate‐co ‐3‐hydroxyvalerate) (PHBV) by GC‐MS and NMR analysis. The bSNPs were reinforced to fabricate PHBV/SiO₂ nanocomposites via solution casting technique. The fabricated PHBV/SiO₂ nanocomposites revealed intercalated hybrid interaction between the bSNPs and PHBV matrix through XRD analysis. PHBV/SiO₂ nanocomposites showed significant improvement in physical, chemical, thermo‐mechanical and biodegradation properties as compared to the bare PHBV. The cell viability study revealed excellent biocompatibility against L929 mouse fibroblast cells. The antibacterial activity of PHBV/SiO₂ nanocomposites was found to be progressively improved upon increasing bSNPs concentration against E. coli and S. aureus.Inspec keywords: X‐ray diffraction, microorganisms, antibacterial activity, nanoparticles, cellular biophysics, nanofabrication, silicon compounds, nanocomposites, filled polymers, nanomedicine, biomedical materials, casting, biodegradable materials, food packaging, food safety, biological NMROther keywords: antibacterial applications, poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), PHBV matrix, biodegradable PHBV‐SiO₂ nanocomposite, thermomechanical biodegradation properties, biogenic silica nanoparticles, groundnut shells, microstructure properties, biopolymer, yeast Wickerhamomyces anomalus, GC‐MS, NMR analysis, food packaging, intercalated hybrid interaction, XRD analysis, cell viability study, solution casting, SiO₂