Polyhydroxyalkanoates - what are the uses? Current challenges and perspectives.

Over the past few decades, a considerable attention has been focused on the microbial polyhydroxyalkanoates (PHAs) owing to its multifaceted properties, i.e. biodegradability, biocompatibility, non-toxicity and thermo-plasticity. This article presents a critical review of the foregoing research, current trends and future perspectives on the value added applications of PHAs in the biomedical, environmental and industrial domains of life.

Effect of cation type, alkyl chain length, adsorbate size on adsorption kinetics and isotherms of bromide ionic liquids from aqueous solutions onto microporous fabric and granulated activated carbons.

The adsorption from aqueous solution of imidazolium, pyrrolidinium and pyridinium based bromide ionic liquids (ILs) having different alkyl chain lengths was investigated on two types of microporous activated carbons: a fabric and a granulated one, well characterized in terms of surface chemistry by "Boehm" titrations and pH of point of zero charge measurements and of porosity by N2 adsorption at 77 K and CO2 adsorption at 273 K. The influence of cation type, alkyl chain length and adsorbate size on the adsorption properties was analyzed by studying kinetics and isotherms of eight different ILs using conductivity measurements. Equilibrium studies were carried out at different temperatures in the range [25-55 °C]. The incorporation of ILs on the AC porosity was studied by N2 adsorption-desorption measurements at 77 K. The experimental adsorption isotherms data showed a good correlation with the Langmuir model. Thermodynamic studies indicated that the adsorption of ILs onto activated carbons was an exothermic process, and that the removal efficiency increased with increase in alkyl chain length, due to the increase in hydrophobicity of long chain ILs cations determined with the evolution of the calculated octanol-water constant (Kow). The negative values of free energies indicated that adsorption of ILs with long chain lengths having hydrophobic cations was more spontaneous at the investigated temperatures.

Preparation, characterization and evaluation of HPßCD-PTX/PHB nanoparticles for pH-responsive, cytotoxic and apoptotic properties.

Paclitaxel (PTX) is a potent anticancer drug. However, PTX exhibits extremely poor solubility in aqueous solution along with severe side effects. Therefore, in this study, an inclusion complex was prepared between PTX and hydroxypropyl-ß-cyclodextrin (HPßCD) by solvent evaporation to enhance the drug's solubility. The HPßCD-PTX inclusion complex was then encapsulated in poly-3-hydroxybutyrate (PHB) to fabricate drug-loaded nanoparticles (HPßCD-PTX/PHB NPs) by nanoprecipitation. The HPßCD-PTX/PHB NPs depicted a higher release of PTX at pH 5.5 thus demonstrating a pH-dependent release profile. The cytotoxic properties of HPßCD-PTX/PHB NPs were tested against MCF-7, MDA-MB-231 and SW-620 cell lines. The cytotoxic potential of HPßCD-PTX/PHB NPs was 2.59-fold improved in MCF-7 cells in comparison to free PTX. Additionally, the HPßCD-PTX/PHB NPs improved the antimitotic (1.68-fold) and apoptotic (8.45-fold) effects of PTX in MCF-7 cells in comparison to PTX alone. In summary, these pH-responsive nanoparticles could be prospective carriers for enhancing the cytotoxic properties of PTX for the treatment of breast cancer.

Synthesis of poly-(3-hydroxybutyrate-co-12 mol % 3-hydroxyvalerate) by Bacillus cereus FB11: its characterization and application as a drug carrier.

The synthesis of microbial polyhydroxyalkanoate is investigated in this work for it potential application as drug carrier for cancer therapy. The bacterial isolate Bacillus cereus FB11 has synthesized poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) copolymer under nutrient stress conditions using glucose as a sole carbon source. The FTIR spectrum of the purified copolymer showed the characteristic absorption bands at 1,719, 1,260 and 2,931 cm(-1) attributing to C=O, C-O stretching and C-H vibrations, respectively. The result of (1)H-NMR confirmed that it was composed of 88 mol % of 3-hydroxybutyrate and 12 mol % of 3-hydroxyvalerate monomeric subunits. The nanoparticles were fabricated from copolymer and used as a carrier for anticancer drug ellipticine. The in vitro drug release studies showed that % inhibition of A549 cancer cell line receiving ellipticine loaded poly-(3-hydroxybutyrate-co-3-hydroxyvalerate) nanoparticles was two-fold higher in comparison to ellipticine alone. This drug delivery system offers exciting possibilities for cancer therapy by increasing the bioavailability of anti-neoplastic drug to the tumor site.

Polypyrrole fabricated Laponite RD conductive nanocomposites: influence of grafting efficiency on structural and conductive properties.

In the present work novel conductive organic-inorganic nanocomposites were produced by grafting of pyrrole monomer onto silanized Laponite RD utilizing emulsion graft polymerization. Influence of some important factors like concentration of monomer, initiator and surfactant were investigated on grafting efficiency. Grafting of polypyrrole chains onto modified Laponite RD was verified by Fourier transform infrared spectroscopy (FT-IR). Scanning electron microscope (SEM) revealed the spherical particles of nanocomposite with average diameter of 271.5 nm. XRD pattern showed that molecular framework of pure polypyrrole almost remains same in nanocomposite. Surface area and pore volume of Laponite RD, measured by Brunauer-Emmett-Teller (BET) analysis, was also altered indicating effective grafting of polypyrrole chains onto modified substrate. Maximum grafting efficiency (%), determined gravimetrically, was 87.3% at monomer, initiator, and surfactant concentrations of 1.50, 1.00, and 0.50% respectively. Prepared nanocomposites with grafting efficiency of 87.3% have displayed maximum electrical conductivity of 0.23 × 10-2 Scm-1. These nanocomposites can be used for manifold applications like biomedical and energy storage devices.

Enhanced Photocatalytic H2 Generation by Light-Induced Carbon Modification of TiO2 Nanotubes.

Titanium dioxide (TiO2 ) is the material of choice for photocatalytic and electrochemical applications owing to its outstanding physicochemical properties. However, its wide bandgap and relatively low conductivity limit its practical application. Modifying TiO2 with carbon species is a promising route to overcome these intrinsic complexities. In this work, we propose a facile method to modify TiO2 nanotubes (NTs) based on the remnant organic electrolyte retained inside the nanotubes after the anodization process, that is, without removing it by immersion in ethanol. Carbon-modified TiO2 NTs (C-TiO2 NTs) showed enhanced H2 evolution in photocatalysis under UV illumination in aqueous solutions. When the C-TiO2 NTs were subjected to UV light illumination, the carbon underwent modification, resulting in higher measured photocurrents in the tube layers. After UV illumination, the IPCE of the C-TiO2 NTs was 4.4-fold higher than that of the carbon-free TiO2 NTs.

Synthesis, Characterization, and Adsorptive Characteristics of Radiation-Grafted Glycidyl Methacrylate Bamboo Fiber Composites.

In the present study, a biosorbent was prepared through the radiation-induced graft polymerization (RIGP) technique by using a glycidyl methacrylate (GMA) monomer. Functionalized bamboo materials were used for grafting. The grafting percentage (G %) of GMA on bamboo fibers was assessed based on the optimization of the absorbed dose and concentration of the monomer. The chemical modification of the polymerized product into the sulfonated form of the grafted biopolymer was carried out by using sodium sulfite solution. The modification of the biopolymer at various stages was analyzed by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) techniques. By performing scanning electron microscopy (SEM), the morphological changes of the prepared biopolymer were analyzed. The temperature stability of the synthesized material was assessed by the thermogravimetric analysis (TGA) technique. The prepared sulfonated biosorbent was used in the batch adsorption study for the uptake of copper. We examined a variety of variables, including pH, adsorbent dosage, and time. The adsorption kinetics were studied using pseudo-first-order (PFO) and pseudo-second-order (PSO) models. Adsorption isotherms and thermodynamic parameters were also applied to study the adsorption capacity of the biosorbent. The maximum copper adsorption capacity was found to be 198 mg g-1 from the Langmuir isotherm. Copper adsorption followed PSO kinetics (R2 = 0.999). This inexpensive and eco-friendly biosorbent removed 96% of copper ions from the solution.

Potentiation of Antimicrobial Photodynamic Therapy by Curcumin-loaded Graphene Quantum Dots.

Increasing resistance to existing antibiotics by microbes is currently the biggest dilemma. Antimicrobial photodynamic therapy is a promising alternative for the treatment of multidrug-resistant infections. The aim of the current study was to fabricate graphene quantum dots loaded with curcumin as photosensitizer for improved antimicrobial photodynamic therapy. The study involved fabrication of blank and curcumin-loaded graphene quantum dots, their characterizations (TEM, UV-visible and fluorescence emission spectra), cytotoxicity assay, ROS assay and investigation of enhanced antimicrobial photodynamic effect against resistant microbes. The fabrication of blank and loaded graphene quantum dots was confirmed by the observation of peak shift and changes in peak intensity of blank graphene quantum dots, curcumin alone compared with curcumin-loaded graphene quantum dots in UV-visible and fluoresce emission spectra. Cytotoxicity assay showed that 100 µm concentration was not toxic to NIH/3t3 fibroblasts. In ROS assay, the curcumin-loaded formulation showed three-fold increase in ROS production. Blue-light (405 nm) irradiance of 30 J cm-2 and photosensitizer concentration of 100 µm showed ~3.5 log10 enhanced CUF reduction against Pseudomonas aeruginosa, MRSA, Escherichia coli and Candida albicans. In conclusion, curcumin-loaded graphene quantum dots shoed enhanced antimicrobial photodynamic effects and can be used as an alternative effective treatment for resistant infections.

Removal of copper using chitosan beads embedded with amidoxime grafted graphene oxide nanohybids.

This study explores a biopolymer-based composite system for metal decontamination of water using copper {Cu (II)} as a model pollutant. Novel composite beads of chitosan and amidoxime grafted graphene oxide (AOGO) were successfully prepared and used for the Cu (II) removal from aqueous solutions. For this purpose, acrylonitrile was first polymerized onto a gamma-irradiated and silanized graphene oxide substrate. The nitrile groups of polyacrylonitrile grafted graphene oxide (GO-g-PAN) were then chemically modified into amidoxime groups to form AOGO nanohybrids. These nanohybrids were mixed with a blend of chitosan (CS) and polyvinyl alcohol (PVA) and crosslinked using tetraethylorthosilicate (TEOS) to form composite CP/AOGO beads. Fourier transform infrared spectroscopy (FTIR) was used to study the structural changes at each step during the formation of composite beads. Scanning electron microscopic (SEM) analysis demonstrated that the beads had a well-developed spherical structure. The adsorption of Cu (II) onto CP/AOGO composite beads was studied under different conditions (initial concentration, pH, and contact time). The results revealed the potential of composite beads in copper removal from aqueous solutions.

Fabrication and characterization of amidoxime-functionalized silica decorated with copper: a catalytic assembly for rapid reduction of dyes.

In this study, amidoxime-functionalized silica decorated with copper (AFS-Cu) was fabricated and tested for its catalytic application. Fourier transform infrared spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction were employed to characterize its structure and morphology. The application of AFS-Cu as a catalyst for the catalytic reduction of methylene blue (MB) in aqueous media using NaBH4 as reductant was evaluated. The ability to reuse as well as the effect of catalyst dose and pH of solution on the catalytic activity was investigated. The reduction of MB followed pseudo-first-order kinetics and the rate constant (k) was 0.6224 min-1. AFS-Cu was found to be a highly effective catalyst for MB reduction reaction and can be easily recovered and reused several times with no appreciable loss of catalytic activity.

A comparative review of 1,004 orthopaedic trauma patients before and during the COVID-19 pandemic.

AIMS: COVID-19 necessitated abrupt changes in trauma service delivery. We compare the demographics and outcomes of patients treated during lockdown to a matched period from 2019. Findings have important implications for service development. METHODS: A split-site service was introduced, with a COVID-19 free site treating the majority of trauma patients. Polytrauma, spinal, and paediatric trauma patients, plus COVID-19 confirmed or suspicious cases, were managed at another site. Prospective data on all trauma patients undergoing surgery at either site between 16 March 2020 and 31 May 2020 was collated and compared with retrospective review of the same period in 2019. Patient demographics, injury, surgical details, length of stay (LOS), COVID-19 status, and outcome were compared. RESULTS: There were 1,004 urgent orthopaedic trauma patients (604 in 2019; 400 in 2020). Significant reductions in time to theatre and LOS stay were observed. COVID-19 positive status was confirmed in 4.5% (n = 18). The COVID-19 mortality rate was 1.8% (n = 7). Day-case surgery comprised 47.8% (n = 191), none testing positive for COVID-19 or developing clinically significant COVID-19 symptoms requiring readmission, at a minimum of 17 days follow-up. CONCLUSION: The novel split-site service, segregating suspected or confirmed COVID-19 cases, minimized onward transmission and demonstrated improved outcomes regarding time to surgery and LOS, despite altered working patterns and additional constraints. Day-surgery pathways appear safe regarding COVID-19 transmission. Lessons learned require dissemination and should be sustained in preparation for a potential second wave or, the return of a "normal" non-COVID workload.Cite this article: Bone Joint Open 2020;1-9:568-575.

A comparative study looking at trauma and orthopaedic operating efficiency in the COVID-19 era.

BACKGROUD: COVID-19 has led to a reduction in operating efficiency. We aim to identify these inefficiencies and possible solutions as we begin to pursue a move to planned surgical care. METHODS: All trauma and orthopaedic emergency surgery were analysed for May 2019 and May 2020. Timing data was collated to look at the following: anaesthetic preparation time, anaesthetic time, surgical preparation time, surgical time, transfer to recovery time and turnaround time. Data for 2019 was collected retrospectively and data for 2020 was collected prospectively. RESULTS: A total of 222 patients underwent emergency orthopaedic surgery in May 2019 and 161 in May 2020. A statistically significant increase in all timings was demonstrated in 2020 apart from anaesthetic time which demonstrated a significant decrease. A subgroup analysis for hip fractures demonstrated a similar result. No increase in surgical time was observed in hand and wrist surgery or for debridement and washouts.Although the decrease in anaesthetic time is difficult to explain, this could be attributed to a reduction in combined anaesthetic techniques and possibly the effect of fear. The other increases in time demonstrated can largely be attributed to the PPE required for aerosol generating procedures and other measures taken to reduce spread of the virus. These procedures currently form a large amount of the orthopaedic case load. CONCLUSION: COVID-19 has led to significant reductions in operating room efficiency. This will have significant impact on waiting times. Increasing frequency of regional anaesthesia concurrently with non-aerosol generating surgeries may improve efficiency.

Preparation, characterization and evaluation of glycerol plasticized chitosan/PVA blends for burn wounds.

Chitosan like natural polymers have been widely used in burn wound management. Novel low molecular weight chitosan-PVA soft membranes have been studied for antibacterial and wound healing properties. The effectiveness of antibacterial activity was carried against bacterial pathogens while wound healing nature of chitosan was conducted in second degree burns on rabbits as model animal. Rabbits were divided into three groups; control untreated, treated with commercial Fusidic acid (Fu-A) cream and chitosan-PVA membranes. Low molecular weight chitosan showed significant antibacterial property towards bacterial pathogens. Wound healing experiments on second degree burn exhibited chitosan as significant wound healing agent for wound dressings. In morphological studies, normal growth of epidermis was observed and chitosan exhibited more effective for wound healing. Morphological studies also showed that chitosan wound dressings accelerated the granule and fibrous connective tissues formation. Physical characteristics of chitosan-PVA membranes were evaluated by water uptake capacity, SEM analysis, mechanical and water barrier studies.

Comparison of the effects of gamma or sonochemical irradiation of carbon nanotubes and the influence on the mechanical and dielectric properties of chitosan nanocomposites.

Chitosan-carbon nanotube (Chi-CNT) composite materials have been prepared with CNTs that were surface treated using either dilute acid combined with 20 kHz ultrasound or gamma-irradiation in air. The mechanical and dielectric properties have been measured and compared. Both modification methods gave nanocomposites with much improved tensile properties over native chitosan. The sonochemically treated samples were stronger with higher tensile strength but at the expense of lower elasticity and extensibility than found when γ-irradiation was used. Impedance spectra showed differences in the polymer chain transitions and in the conduction mechanisms within the nanocomposites. The results correlated well with previous work suggesting that the two modification techniques result in CNT surfaces with higher polarity. This enhances interfacial interactions with the chitosan matrix although the extent of functionalisation was greater in the sonochemical case. This work demonstrates that sonochemical modification under mild conditions is a useful method for modifying CNTs for inclusion in nanocomposite materials. However, the resulting material properties depend on the level of treatment so that the sonochemical conditions need to be carefully evaluated and controlled if the effects are to be optimised.

Sonochemical modification of carbon nanotubes for enhanced nanocomposite performance.

Multi-walled carbon nanotubes (CNTs) have been treated using 20kHz ultrasound in combination with dilute nitric and sulfuric acids at much lower concentrations than previously reported. The measurements revealed an optimum set of sonication conditions (in this case 30min at 12Wcm-2) exists to overcome aggregation of the nanotubes and to allow efficient dispersion in ethanol or in chitosan. Transmission electron microscopy and Raman spectroscopy suggested the removal of amorphous material and reduction of the CNT diameter as well as modifications to their defect structures. The surface oxidation was determined by FTIR spectroscopy. At longer times or higher ultrasound intensities, degradation such as nanotube shortening and additional defect generation in the graphitic network occurred and the benefits of using ultrasound decreased. The modified CNTs were used as fillers for chitosan films and gave a tenfold increase in tensile strength and integrity of the films. The methodology was combined with sonochemical generation of gold or iron oxide nanoparticles to produce a range of functional membranes for catalytic reductive hydrogenation or dye degradation under conditions that are more environmentally benign than those previously used. Our results further add to the usefulness of sonochemistry as a valuable tool in preparative materials chemistry but also illustrate the crucial importance of careful control over the experimental conditions if optimum results are to be obtained.

Characterization of physical and biodegradation properties of poly-3-hydroxybutyrate-co-3-hydroxyvalerate/sepiolite nanocomposites.

The pristine sepiolite was treated with the 3-aminopropyl triethoxy silane (APTES). The APTES grafted sepiolite (APTES-G-SP) was used to develop the poly-3-hydroxybutyrate-co-3-hydroxyvalerate (PHBV)/sepiolite nanocomposite films by the solution-casting method. Scanning electron micrographs showed that the APTES-G-SP fibers were well embedded in the polymer matrix. Fourier transform Infrared spectroscopy attributed the formation of covalent bonds between the APTES-G-SP and PHBV in the nanocomposite film. Thermal and water-barrier properties of the nanocomposite films were significantly improved. Biodegradation studies indicated the conversion of the crystalline structure of the nanocomposite films into the amorphous one as a result of the synergistic effect of the abiotic and biotic degradation processes. The results of this study provide sound evidence about the use of the biodegradable nanocomposite films with the better thermal and water barrier properties for the food packaging industry.

Effect of glucose and olive oil as potential carbon sources on production of PHAs copolymer and tercopolymer by Bacillus cereus FA11.

In this study, the influence of different physicochemical parameters on the yield of polyhydroxyalkanoates (PHAs) produced by Bacillus cereus FA11 is investigated. The physicochemical factors include pH, temperature, time, inoculum size and its age, agitation speed and composition of the glucose rich peptone deficient (GRPD) medium. During two-stage fermentation, B. cereus FA11 produced a significantly high (p < 0.05) yield (80.59% w/w) of PHAs copolymer using GRPD medium containing glucose (15 g/L) and peptone (2 g/L) at pH 7, 30 °C and 150 rpm after 48 h of incubation. On the other hand, the presence of olive oil (1% v/v) and peptone (2 g/L) in the GRPD medium resulted in biosynthesis of tercopolymer during two-stage fermentation and the yield of tercopolymer was 60.31% (w/w). The purified PHAs was characterized by Fourier transform infrared spectroscopy and proton resonance magnetic analysis. Proton resonance magnetic analysis confirmed that the tercopolymer was comprised of three different monomeric subunits, i.e., 3-hydroxybutyrate, 3-hydroxyvalerate and 6-hydroxyhexanoate.

Bioactivity of Variant Molecular Weight Chitosan Against Drug-Resistant Bacteria Isolated from Human Wounds.

Chitosan available from crab shells is usually of high molecular weight which may result in reduced efficiency for its antibacterial activity. One of the techniques for improving chitosan antibacterial efficiency is reducing its molecular weight. The irradiation of chitosan by gamma radiations is considered to be one of the most effective and widely used methods for improving its antibacterial activity. Chitosan obtained from crab shells was irradiated with gamma radiations at different doses, and effects on chitosan were analyzed by molecular weight determination and Fourier Transform Infrared spectroscopy. Unirradiated and irradiated chitosans were studied for their antibacterial properties against bacterial pathogens, that is, Pseudomonas aeruginosa (SS29), Escherichia coli (SS2, SS9), Proteus mirabilis (SS77), and Staphylococcus aureus (LM15). Studies have shown that irradiation has significantly developed and improved the antibacterial activity of crab shell chitosan. A correlation was found between bacterial metabolites and antibacterial activity by the analysis for 4-hydroxy-2-alkylquinolines and related metabolites of P. aeruginosa (SS29) in the absence and presence of chitosan by liquid chromatography mass spectrometer, exhibiting the suppression of these virulence factors due to chitosan. Antibacterial efficiency of chitosan was found to be molecular weight dependent and applied concentration of the chitosan. The findings suggest on the use of low-molecular weight chitosan as antibacterial agent in pharmaceutical preparations.

Chitosan: A potential biopolymer for wound management.

It has been seen that slow healing and non-healing wounds conditions are treatable but still challenging to humans. Wound dressing usually seeks for biocompatible and biodegradable recipe. Natural polysaccharides like chitosan have been examined for its antimicrobial and healing properties on the basis of its variation in molecular weight and degree of deacetylation. Chitosan adopts some vital characteristics for treatment of various kinds of wounds which include its bonding nature, antifungal, bactericidal and permeability to oxygen. Chitosan therefore has been modified into various forms for the treatment of wounds and burns. The purpose of this review article is to understand the exploitation of chitosan and its derivatives as wound dressings. This article will also provide a concise insight on the properties of chitosan necessary for skin healing and regeneration, particularly highlighting the emerging role of chitosan films as next generation skin substitutes for the treatment of full thickness wounds.

Characterization and application of roxithromycin loaded cyclodextrin based nanoparticles for treatment of multidrug resistant bacteria.

An outbreak of infections with a high mortality rate caused by multidrug resistant (MDR) bacteria is one of the biggest health challenges globally. A class IV drug, roxithromycin (ROX), has poor solubility. In this study, ROX was first encapsulated in the cavity of each of the ß-cyclodextrin (ßCD) and hydroxypropyl-ß-cyclodextrin (HPßCD). Then, each of the resulting ßCD-ROX inclusion complex and HPßCD-ROX inclusion complex were separately loaded into poly-(lactic-co-glycolic acid) (PLGA) to synthesize ßCD-ROX/PLGA and HPßCD-ROX/PLGA nanoparticles (NPs). Blank and ROX loaded PLGA (ROX-PLGA) NPs were also prepared. The loading efficiency of ROX is comparatively high for HPßCD-ROX/PLGA NPs in comparison to the ßCD-ROX/PLGA NPs and ROX-PLGA NPs. All designed formulations showed significant (P<0.0001) antibacterial activity against the selected MDR bacterial strains. In a nutshell, this study demonstrated a great therapeutic potential of the above-mentioned delivery systems for treatment of MDR bacteria.