Cationic Poly([R]‐3‐hydroxybutyrate) Copolymers as Antimicrobial Agents

Poly([R]‐3‐hydroxybutyrate) (PHB), a natural biodegradable polyester, has attracted much attention as a new biomaterial because of its sustainability and good biocompatibility. In this study, it is discovered that PHB can be conveniently functionalized to obtain a number of platform chain architectures that may provide a wide range of functional copolymers. In a transesterification reaction, linear (di‐hydroxylated) and star shaped (tri‐ and tetra‐hydroxylated) PHB oligomers are synthesized, followed by copolymerization with 2‐(dimethylamino)ethyl methacrylate and quaternization with benzyl bromide to afford antimicrobial properties. The antimicrobial activities of the quaternary salts against clinically relevant pathogens on the interactions with outer and cytoplasmic membranes, lethal mechanisms, multipassage resistance, and synergy effect with antibiotics are investigated. Cationic PHB copolymers show effectiveness as antimicrobial agents, with minimum inhibitory concentration values 0.24–0.65 µm (or µmol dm^?3) (or 32–128 µg mL^?1) against Gram‐positive and Gram‐negative bacteria. Modifying the copolymer architectures into star shapes results in enhanced effectiveness to disrupt the membrane integrity. Synergistic effects are attained for all the quaternized PHB derivatives when they are used together with tobramycin. Multipassage resistance does not occur in both the linear and star derivatives against Gram‐negative bacteria after 20 passages.     

Uracil as Nucleating Agent for Bacterial Poly[(3‐Hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] Copolymers

In this study, uracil has been introduced as the nucleating agent (NA) for bacterially synthesized poly[(3‐hydroxybutyrate)‐co‐(3‐hydroxyhexanoate)] (PHBHHx) copolymers with HHx content of 5, 10, 18 mol‐%, and poly(3‐hydroxybutyrate) (PHB) homopolymer for the first time. Its effect was compared with the conventional NA of PHB, that is, boron nitride (BN), and two other naturally occurring pyrimidine derivatives, i.e., thymine and cytosine. The effects of uracil on the crystallization kinetics, melting behavior, spherulite morphology, and crystalline structure of PHBHHx and PHB were investigated by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and wide‐angle X‐ray diffraction (WAXD). Uracil and BN exhibit the comparable nucleation efficiency on the crystallization of PHB, whereas uracil shows much more effective nucleation ability than BN for PHBHHx copolymers. With incorporation of 1 wt.‐% uracil, PHBHHx with 0–10 mol‐% HHx units can finish crystallization upon cooling at 10 °C · min^?1. The crystallization half‐times (t_1/2) of all the PHB and PHBHHx samples decrease significantly with presence of uracil. The crystallization rate of polymers further enhances with increase in uracil concentration. With addition of 1 wt.‐% uracil, the t_1/2 value of PHBHHx with 10 mol‐% HHx units melt‐crystallizing at 80 °C decreases to ≈4.0% of the neat polymer, and the nucleation density increases by 3–4 orders of magnitude. The incorporation of uracil has no discernable effect on the crystalline structure of PHBHHx, as evidenced by WAXD results. It was proposed that the nucleation mechanism of the uracil/PHBHHx (or PHB) system might be the epitaxial nucleation.

     

A New Antimicrobial Agent: Poly (3‐hydroxybutyric acid) Oligomer

In this work, it is first reported that the poly (3‐hydroxybutyric acid) (PHB) oligomer with a few degrees of polymerization possesses effective antibacterial and antifungal properties. Two preparation methods for the PHB oligomer are described, namely, one‐step ring‐opening polymerization of β‐butyrolactone and extraction from the fermented PHB polymer. An appropriate amount of the synthesized PHB oligomer shows no physiological toxicity to the skin and major organs of mice. Topological application of the synthesized PHB oligomer imparts antimicrobial ability to non‐antibacterial fabrics with washing resistance. The synthesized PHB oligomer offers effective sterilization and promotes wound healing in infected nude mice. Most importantly, the PHB oligomer is also reactive to drug‐resistant bacteria. These results suggest that the PHB oligomer is not only a great candidate for antimicrobial modification but also a promising one for biomedical applications. Finally, the antimicrobial mechanisms of the PHB oligomer are revealed, and these include disruption of biofilm and the bacterial wall/membrane, leakage of the intracellular content, inhibition of protein activity, and change in the transmembrane potential.     

Thermal degradation kinetics of biodegradable poly(3‐hydroxybutyrate)/layered double hydroxide nanocomposites

The thermal degradation behaviors of biodegradable poly(3‐hydroxybutyrate) (PHB) and PHB/poly(ethylene glycol) phosphonates (PEOPAs)‐modified layered double hydroxide (PMLDH) nanocomposites have been investigated using thermogravimetric analysis. Effects of PMLDH contents on the isothermal degradation kinetics of PHB were explored. These experimental results show that the degradation kinetics of PHB/PMLDH nanocomposites is the chain‐scission process of cyclic β‐elimination reaction with the following autocatalytic reactions, which is very similar to that of pure PHB matrix. Further calculated data based on the autocatalytic model can fit very well with the experimental data. The E_a value of PHB/PMLDH nanocomposites is increased as the content of PMLDH increases. This can be attributed to the incorporation of more PMLDH loading to PHB induced a decrease in the degradation rate and an increase in the residual weight for PHB/PMLDH nanocomposites. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1207–1213, 2008     

Poly[(R)‐3‐hydroxybutyrate)]/poly(styrene) blends compatibilized with the relevant block copolymer

A novel triblock copolymer PS–PHB–PS based on the microbial polyester Poly[(R)‐3‐hydroxybutyrate)] (PHB) and poly(styrene) (PS) was prepared to be used as compatibilizer for the corresponding PHB/PS blends. It was prepared in a three‐step procedure consisting of (i) transesterification reaction between ethylene glycol and a high‐molecular‐weight PHB, (ii) synthesis of bromo‐terminated PHB macroinitiator, and (iii) atom transfer radical polymerization polymerization of styrene initiated by the PHB‐based macroinitiator. Fourier transform infrared, gel permeation chromatography, ¹H‐, and ¹³C‐NMR spectroscopies were used to determine the molecular structure and/or end‐group functionalities at each step of the procedure. Although thermogravimetric analysis showed that the block copolymer underwent a stepwise thermal degradation and had better thermal stability than their respective homopolymers, differential scanning calorimetry displayed that the PHB block in the copolymer could not crystallize, and thus generating a total amorphous structure. Atomic force microscopy images indicated that the block copolymer was phase segregated in a well‐defined morphological structure with nanodomain size of ～40 nm. Contact angle measurements proved that the wettability properties of the block copolymer were in between those of the PHB and PS homopolymers. Blends analyzed for their morphology and thermal properties showed good miscibility and had well‐defined morphological features. Polymer blends exhibited lower crystallinity and decreased stiffness which was proportional to the amount of compatibilizer content in the blends. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Production,ultrasonic extraction,and characterization of poly (3‐hydroxybutyrate) (PHB) using Bacillus megaterium and Cupriavidus necator

Biodegradable polymer polyhydroxyalkanoates are one of the promising alternatives for conventional plastics. The present article focuses on a modified and novel method for the synthesis of poly (3‐hydroxybutyrate) (PHB) by two microorganisms, viz. Bacillus megaterium and Cupriavidus necator. These microbial cells were grown over fructose as a carbon source, and the produced PHB was recovered using ultrasound as well as solvent assisted extraction. The extracted PHB was characterized using FTIR, ¹H, and ¹³C NMR to observe the functional groups in the PHB molecule. The XRD characterization confirmed the partial crystalline nature of PHB, and the results of TGA, DTG, and DSC analysis attributed to the thermal stability of PHB. The major step of weight loss of PHB derived by B. megaterium and C. necator in TGA analysis was found to be 415°C and 289°C, respectively. These values were comparatively higher than standard PHB, for which it is 260°C. Similarly, the maximum degradation temperature for standard PHB is 236°C, whereas the maximum degradation temperature of PHB synthesized by B. megaterium and C. necator are 248°C and 277°C, respectively. This ascertains that the produced PHB has greater resistance to thermal degradation as compared with PHB standard. The melting point of synthesized PHBs were found to be 175°C to 176°C, which is similar to standard PHB. The glass transition temperature of the synthesized PHBs varies from –8°C to 6°C. The plausible reason behind the variances could be due to difference in crystallinity and molecular weight of polymer matrix. Nevertheless, thermal properties of PHB produced by B. megaterium and C. necator are found to be similar or much better than commercial PHB. The degree of crystallinity of synthesized PHBs are lower than previously reported literatures, which extends its range of applications.     

Electrospun fiber mats of poly(3‐hydroxybutyrate), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate), and their blends

Electrospinning of poly(3‐hydroxybutyrate) (PHB), poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV), and their blends was first carried out in chloroform at 50 °C on a stationary collector. The average diameter of the as‐spun fiber from PHB and PHBV solutions decreased with increasing collection distance and increased with increasing solution concentration and applied electrical potential. In all of the spinning conditions investigated, the average diameter of the as‐spun pure fibers ranged between 1.6 and 8.8 μm. Electrospinning of PHB, PHBV, and their blends was carried out further at a fixed solution concentration of 14% w/v on a homemade rotating cylindrical collector. Well‐aligned, cross‐sectionally round fibers without beads were obtained. The average diameter of the as‐spun pure and blend fibers ranged between 2.3 and 4.0 μm. The as‐spun fiber mats appeared to be more hydrophobic than the corresponding films and much improvement in the tensile strength and the elongation at break was observed for the blend fiber mats over those of the pure fiber ones. Lastly, indirect cytotoxicity evaluation of the as‐spun pure and blend fiber mats with mouse fibroblasts (L929) indicated that these mats posed no threat to the cells. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2923–2933, 2006     

New biodegradable polymers from renewable sources: Polyester‐carbonates based on 1,3‐propylene‐co‐1,4‐cyclohexanedimethylene succinate

α,ω‐Dihydroxy‐terminated copolymeric oligomers of a 1,3‐propylene/1,4‐cyclohexanedimethylene succinate structure were obtained by the thermal polycondensation of 1,3‐propanediol/1,4‐cyclohexanedimethanol/succinic acid mixtures. They were subsequently chain‐extended via phosgene synthesis to high molecular weight aliphatic/alicyclic copolyester‐carbonates. These new polymers, besides having a biodegradable backbone, originate from two monomers, namely, 1,3‐propanediol and succinic acid, which can be obtained by renewable sources. Therefore, they have a potential as environmentally friendly materials. All synthesized materials were characterized in reference to their molecular structure by ¹H NMR and ¹³C NMR. Their molecular weights and molecular weight distributions were determined by size exclusion chromatography, and their main thermal properties were measured by DSC. Spectroscopic characterizations were in full agreement with the proposed structures. 1,4‐Cyclohexanedimethanol was used as a diol comonomer to improve the overall thermal properties of poly(1,3‐propylene succinate). The results of the characterization performed show that the initial expectations were only partially satisfied. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2508–2519, 2001     

New Linear and Star‐Shaped Thermogelling Poly([R]‐3‐hydroxybutyrate) Copolymers

The synthesis of multi‐arm poly([R]‐3‐hydroxybutyrate) (PHB)‐based triblock copolymers (poly([R]‐3‐hydroxybutyrate)‐b‐poly(N‐isopropylacrylamide)‐b‐[[poly(methyl ether methacrylate)‐g‐poly(ethylene glycol)]‐co‐[poly(methacrylate)‐g‐poly(propylene glycol)]], PHB‐b‐PNIPAAM‐b‐(PPEGMEMA‐co‐PPPGMA), and their subsequent self‐assembly into thermo‐responsive hydrogels is described. Atom transfer radical polymerization (ATRP) of N‐isopropylacrylamide (NIPAAM) followed by poly(ethylene glycol) methyl ether methacrylate (PEGMEMA) and poly(propylene glycol) methacrylate (PPGMA) was achieved from bromoesterified multi‐arm PHB macroinitiators. The composition of the resulting copolymers was investigated by ¹H and ¹³C J‐MOD NMR spectroscopy as well as size‐exclusion chromatography (SEC), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The copolymers featuring different architectures and distinct hydrophilic/hydrophobic contents were found to self‐assemble into thermo‐responsive gels in aqueous solution. Rheological studies indicated that the linear one‐arm PHB‐based copolymer tend to form a micellar solution, whereas the two‐ and four‐arm PHB‐based copolymers afforded gels with enhanced mechanical properties and solid‐like behavior. These investigations are the first to correlate the gelation properties to the arm number of a PHB‐based copolymer. All copolymers revealed a double thermo‐responsive behavior due to the NIPAAM and PPGMA blocks, thus allowing first the copolymer self‐assembly at room temperature, and then the delivery of a drug at body temperature (37 °C). The non‐significant toxic response of the gels, as assessed by the cell viability of the CCD‐112CoN human fibroblast cell line with different concentrations of the triblock copolymers ranging from 0.03 to 1 mg mL^?1, suggest that these PHB‐based thermo‐responsive gels are promising candidate biomaterials for drug‐delivery applications.     

Antibacterial poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) fibrous membranes containing quaternary ammonium salts

In this study, antimicrobial membranes based on biodegradable material poly(3‐hydroxybutyrate‐co‐4‐hydroxybutyrate) [P(3HB‐4HB)] and quaternary ammonium salts (QASs) by two methods have been performed. Three QASs with varied alkyl chain lengths have been synthesized successfully and characterized by ¹H nuclear magnetic resonance and Fourier transform infrared. The synthesized QASs were blended with P(3HB‐4HB) and electrospun into composite fibrous membranes or casted into conventional membranes. Electrospun fibrous membranes with large surface areas are a superior type of antimicrobial biomaterials, and they exhibit preferable properties than solution casting membranes. Specifically, electrospun fibrous membranes are tougher and can inactivate both Gram‐positive Staphylococcus aureus and Gram‐negative Escherichia coli O157:H7 in a contact time of 30 min, whereas the solution casting membranes cannot. The length of alkyl chain in the quaternary ammonium groups on the modified P(3HB‐4HB) membranes is able to influence the antimicrobial activity. This type of antimicrobial material may have potential applications in biomaterial field. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis and Thermal Properties of Biodegradable Poly(ester‐urethane)s Based on Chemo‐Synthetic Poly[(R,S)‐3‐hydroxybutyrate]

A series of telechelic oligo[(R,S)‐3‐hydroxybutyrate]‐diols (PHB‐diols) was synthesized from ethyl (R,S)‐3‐hydroxybutyrate (ethyl (HB)) and four different aliphatic diols, namely, 1,4‐butanediol, 1,6‐hexanediol, 1,8‐octanediol and 1,10‐decanediol by transesterification and condensation in bulk. The structures of the synthesized oligomers were confirmed by ¹H NMR spectroscopy and MALDI‐TOF mass spectroscopy. The use of 1,4‐butanediol results in an oligoester with hydroxyl functionality of approximately 2. In the case of the higher aliphatic diols, the number average functionalities were found to be lower than 2. These differences were ascribed to side reactions which occur during polymerization, yielding unreactive end groups. Other novel families of biodegradable poly(ester‐urethane)s were synthesized either from PHB‐diol alone, or PHB‐diol mixed with poly(ε‐caprolactone)‐diol (PCL‐diol), poly(butylene adipate)‐diol (PBA‐diol) or poly(diethylene glycol adipate)‐diol (PDEGA‐diol). In each case, 1,6‐hexamethylene diisocyanate was used as a nontoxic connecting agent. The homopolymers prepared from PCL‐diol, PBA‐diol and PDEGA‐diol were also synthesized for the sake of comparison. All the prepared copolymers possess high molecular weight with glass transition temperature (T_g) values varying from –54 to –23°C. Some of the prepared copoly(ester‐urethane)s are partially crystalline with melting temperatures (T_m's) varying from 37 to 56°C.     

Comparison of different nucleating agents on crystallization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerates)

In this study, thymine and melamine were introduced as nucleating agents for poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerates) (PHBVs) and poly(3‐hydroxybutyrate) (PHB), and their effects were compared with that of boron nitride (BN). Because the overall crystallization rate of PHBVs decreases significantly with the increase in the 3‐hydroxyvalerate comonomer content, the study focused on the crystallization of PHBVs. Isothermal crystallization kinetics of the neat PHBVs and the nucleated PHBVs were studied by differential scanning calorimetry (DSC). The Avrami equation was derived and the parameters were assessed for the nucleation and crystal growth mechanism. The nucleation and crystal growth were examined using polarized optical microscopy. All nucleating agents had similar particle sizes and showed good dispersion in the polymer matrix, as revealed by scanning electron microscopy. The results indicated that BN and thymine significantly increased the overall crystallization rate for all PHBVs studied and demonstrated very similar nucleating effects. Melamine reacted with PHBVs and accelerated the thermal degradation, and hence was less effective in nucleating PHBVs. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1564–1577, 2007     

TH‐11, a Streptomyces sp. Strain that Degrades Poly(3‐Hydroxybutyrate) and Poly(Ethylene Succinate)

TH‐11, a bacterial strain with strong depolymerase activity that breaks down aliphatic esters such as poly(3‐hydroxybutyrate) (PHB) and poly(ethylene succinate) (PES) was isolated from a soil sample collected from the sediment of Tou‐Chain River, Taiwan, R.O.C. It was phenotypically and genetically characterized to be a Streptomyces strain. The degradation of PHB and PES were tested both using emulsified polymers in solid agar and thin polymer films in liquid culture media. The degradations were measured by clear‐zone formation on solid agar plates, or direct weight measurements and electromicroscope inspection of the incubated polymer films in the liquid culture. The depolymerase activities can be detected in the cell‐free preparation of the culture medium, and can be enhanced by gelatin.     

Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester‐urethane)s Based on Bacterial Poly[(R)‐3‐hydroxybutyrate]

Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using ¹H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the T_g of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as α_S and α_H, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains.     

S‐Nitrosoglutathione‐Based Nitric Oxide‐Releasing Nanofibers Exhibit Dual Antimicrobial and Antithrombotic Activity for Biomedical Applications

The novel use of nanofibers as a physical barrier between blood and medical devices has allowed for modifiable, innovative surface coatings on devices ordinarily plagued by thrombosis, delayed healing, and chronic infection. In this study, the nitric oxide (NO) donor S‐nitrosoglutathione (GSNO) is blended with the biodegradable polymers polyhydroxybutyrate (PHB) and polylactic acid (PLA) for the fabrication of hemocompatible, antibacterial nanofibers tailored for blood‐contacting applications. Stress/strain behavior of different concentrations of PHB and PLA is recorded to optimize the mechanical properties of the nanofibers. Nanofibers incorporated with different concentrations of GSNO (10, 15, 20 wt%) are evaluated based on their NO‐releasing kinetics. PLA/PHB + 20 wt% GSNO nanofibers display the greatest NO release over 72 h (0.4–1.5 × 10^?10 mol mg^?1 min^?1). NO‐releasing fibers successfully reduce viable adhered bacterial counts by ≈80% after 24 h of exposure to Staphylococcus aureus. NO‐releasing nanofibers exposed to porcine plasma reduce platelet adhesion by 64.6% compared to control nanofibers. The nanofibers are found noncytotoxic (>95% viability) toward NIH/3T3 mouse fibroblasts, and 4′,6‐diamidino‐2‐phenylindole and phalloidin staining shows that fibroblasts cultured on NO‐releasing fibers have improved cellular adhesion and functionality. Therefore, these novel NO‐releasing nanofibers provide a safe antimicrobial and hemocompatible coating for blood‐contacting medical devices.     

Mechanistic Investigations of the Stereoselective Rare Earth Metal‐Mediated Ring‐Opening Polymerization of β‐Butyrolactone

Poly(3‐hydroxybutyrate) (PHB) is produced by numerous bacteria as carbon and energy reserve storage material. Whereas nature only produces PHB in its strictly isotactic (R) form, homogeneous catalysis, when starting from racemic (rac) β‐butyrolactone (BL) as monomer, can in fact produce a wide variety of tacticities. The variation of the metal center and the surrounding ligand structure enable activity as well as tacticity tuning. However, no homogeneous catalyst exists to date that is easy to modify, highly active, and able to produce PHB with high isotacticities from rac‐β‐BL. Therefore, in this work, the reaction kinetics of various 2‐methoxyethylamino‐bis(phenolate) lanthanide (Ln=Sm, Tb, Y, Lu) catalysts are examined in detail. The order in monomer and catalyst are determined to elucidate the reaction mechanism and the results are correlated with DFT calculations of the catalytic cycle. Furthermore, the enthalpies and entropies of the rate‐determining steps are determined through temperature‐dependent in situ IR measurements. Experimental and computational results converge in one specific mechanism for the ring‐opening polymerization of BL and even allow us to rationalize the preference for syndiotactic PHB.     

Thermal behavior and intermolecular interactions in blends of poly(3‐hydroxybutyrate) and maleated poly(3‐hydroxybutyrate) with chitosan

The thermal behavior and intermolecular interactions of blends of poly(3‐hydroxybutyrate) (PHB) and maleated PHB with chitosan were studied with differential scanning calorimetry, Fourier transform infrared (FTIR), wide‐angle X‐ray diffraction (WAXD), and X‐ray photoelectron spectroscopy (XPS). The differences in the two blend systems with respect to their thermal behavior and intermolecular interactions were investigated. The melting temperatures, melting enthalpies, and crystallinities of the two blend systems gradually decreased as the chitosan content in the blends increased. Compared with that of the PHB component with the same composition, the crystallization of the maleated PHB component was more intensively suppressed by the chitosan component in the blends because of the rigid chitosan molecular chains and the intermolecular hydrogen bonds between the components. FTIR, WAXD, and XPS showed that the intermolecular hydrogen bonds in the blends were caused by the carbonyls of PHB or maleated PHB and chitosan aminos, and their existence depended on the compositions of the blends. The introduction of maleic anhydride groups onto PHB chains promoted intermolecular interactions between the maleated PHB and chitosan components. In addition, the intermolecular interactions disturbed the original crystal structures of the PHB, maleated PHB, and chitosan components; this was further proven by WAXD results. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 35–47, 2005     

Poly(lactic acid)‐based nanocomposites

Classic plastics accumulate in nature causing environmental pollution, yet as a counterbalance they benefit society in many ways. They are versatile, cost‐effective, and can be tailored to have desired properties. The global environment has led to the fabrication of commodity plastics from environmentally degradable polymers. Poly(lactic acid) (PLA) is the most promising among the environmentally friendly polymers available. PLA‐based plastics have mechanical, thermal, and transparency similar to traditional plastics, and they can be molded and fabricated using the same equipment and procedures. Their material properties are enhanced through nanocomposites, compatibilizers, plasticizers, and other fillers (flame retardant, ultraviolet filter, etc.). This review summarizes mass production techniques and property reinforcements (focusing on nanocomposites and plasticizers) for PLA‐based plastics for commodity use. Copyright © 2016 John Wiley & Sons, Ltd.     

Model-Based Nutrient Feeding Strategies for the Increased Production of Polyhydroxybutyrate (PHB) by <Emphasis Type="Italic">Alcaligenes latus</Emphasis>

Polyhydroxyalkanoates (PHAs) are biodegradable polymers which are considered as an effective alternative for conventional plastics due to their mechanical properties similar to the latter. However, the widespread use of these polymers is still hampered due to their higher cost of production as compared to plastics. The production cost could be overcome by obtaining high yields and productivity. The goal of the present research was to enhance the yield of polyhydroxybutyrate (PHB) with the help of two simple fed-batch cultivation strategies. In the present study, average batch kinetic and substrate limitation/inhibition study data of Alcaligenes latus was used for the development of PHB model which was then adopted for designing various off-line nutrient feeding strategies to enhance PHB accumulation. The predictive ability of the model was validated by experimental implementation of two fed-batch strategies. One such dynamic strategy of fed-batch cultivation under pseudo-steady state with respect to nitrogen and simultaneous carbon feeding strategy resulted in significantly high biomass and PHB concentration of 39.17 g/L and 29.64 g/L, respectively. This feeding strategy demonstrated a high PHB productivity and PHB content of 0.6 g/L h and 75%, respectively, which were remarkably high in comparison to batch cultivation. The mathematical model can also be employed for designing various other nutrient feeding strategies.     

Enzyme Degradable Polymersomes from Chitosan‐g‐[poly‐l‐lysine‐block‐ε‐caprolactone] Copolymer

The scope of this study includes the synthesis of chitosan‐g‐[peptide‐poly‐ε‐caprolactone] and its self‐assembly into polymeric vesicles employing the solvent shift method. In this way, well‐defined core–shell structures suitable for encapsulation of drugs are generated. The hydrophobic polycaprolactone side‐chain and the hydrophilic chitosan backbone are linked via an enzyme‐cleavable peptide. The synthetic route involves the functionalization of chitosan with maleimide groups and the preparation of polycaprolactone with alkyne end‐groups. A peptide functionalized with a thiol group on one side and an azide group on the other side is prepared. Thiol‐ene click‐chemistry and azide–alkyne Huisgen cycloaddition are then used to link the chitosan and poly‐ε‐caprolactone chains, respectively, with this peptide. For a preliminary study, poly‐l ‐lysin is a readily available and cleavable peptide that is introduced to investigate the feasibility of the system. The size and shape of the polymersomes are studied by dynamic light scattering and cryo‐scanning electron microscopy. Furthermore, degradability is studied by incubating the polymersomes with two enzymes, trypsin and chitosanase. A dispersion of polymersomes is used to coat titanium plates and to further test the stability against enzymatic degradation.