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Oxidised nanocelluloses have previously shown promise for the production of extruded filaments with high tensile strength properties. However, they also exhibit poor wet strength due to swelling upon immersion in water. This has resulted in the use of chemical cross-linkers, or co-extrusion with multivalent cations, or cationic polymers, to inhibit this. Here, we report on the effect of incorporating sugar alcohols (glycerol, sorbitol and maltitol) in an oxidised nanocellulose gel before extrusion. Whilst their presence weakens the initial gel, they enable the continuous wet spinning of filaments that are stable in aqueous media without the need for post extrusion processing. We conclude that the relative hydrophilicity of the sugar alcohol and its ability to protonate surface carboxyl groups upon drying are key parameters regarding the physicochemical effects observed.

Severe peripheral nerve injuries represent a large clinical problem with relevant challenges such as the development of successful synthetic scaffolds as substitutes to autologous nerve grafting. Numerous studies have reported the use of polyesters and type I collagen-based nerve guidance conduits (NGCs) to promote nerve regeneration through critical nerve defects while providing protection from external factors. However, none of the commercially available hollow bioresorbable NGCs have demonstrated superior clinical outcomes to an autologous nerve graft. Hence, new materials and NGC geometries have been explored in the literature to mimic the native nerve properties and architecture. Here, we report a novel blend of a natural medium chain length polyhydroxyalkanoate (MCL-PHA) with a synthetic aliphatic polyester, poly(ε-caprolactone) (PCL), suitable for extrusion-based high-throughput manufacturing. The blend was designed to combine the excellent ability of PHAs to support the growth and proliferation of mammalian cells with the good processability of PCL. The material exhibited excellent neuroregenerative properties and a good bioresorption rate, while the extruded porous tubes exhibited similar mechanical properties to the rat sciatic nerve. The NGCs were implanted to treat a 10 mm long sciatic nerve defect in rats, where significant differences were found between thin and thick wall thickness implants, and both electrophysiological and histological data, as well as the number of recovered animals, provided superior outcomes than the well-referenced synthetic Neurolac NGC.

Linseed oil-in-water Pickering emulsions are stabilized by both sulfated CNCs (sCNCs) and octylamine-modified CNCs (oCNCs). oCNCs with hydrophobic moieties grafted on the surfaces of otherwise intact nanocrystals provided emulsions exhibiting stronger resistance to creaming of oil droplets, compared with unmodified sCNCs. sCNCs were not able to completely stabilize linseed oil in water at low CNC concentrations while oCNCs provided emulsions with no unemulsified oil residue at the same concentrations. Oil droplets in oCNC emulsions were smaller than those in samples stabilized by sCNCs, corresponding with an increased hydrophobicity of oCNCs. Cryo-SEM imaging of stabilized droplets demonstrated the formation of a CNC network at the oil–water interface, protecting the oil droplets from coalescence even after compaction under centrifugal force. These oil droplets, protected by a stabilized CNC network, were dispersed in a water-based commercial varnish, to generate a composite coating. Scratches made on these coatings self-healed as a result of the reaction of the linseed oil bled from the damaged droplets with oxygen. The leakage and drying of the linseed oil at the location of the scratches happened without intervention and was accelerated by the application of heat.

The design of new functional materials and devices substantially relies on self-assembly of hierarchical structures. Formation of 2D platelets is known in the enzymatic synthesis of cellulose-like polymers. Here we demonstrate the feasibility of postsynthesis assembly of novel fluorinated cellodextrins. Highly ordered 2D structures of large lateral dimensions, unattainable in the polymerization process, can be formed because of postsynthesis assembly of the cellodextrins. These cellodextrins were also involved in coassembly with cellulose nanocrystals (CNCs) leading to hybrid systems. The hybrid architectures obtained depend on the content of fluorine atoms in the fluorinated cellodextrins. Monofluorinated cellodextrins coassemble with CNCs into a nanoweb, while multifluorinated cellodextrins assemble around the CNCs.

Organ dysfunction is a major cause of morbidity and mortality. Transplantation is typically the only definitive cure, challenged by the lack of sufficient donor organs. Tissue engineering encompasses the development of biomaterial scaffolds to support cell attachment, proliferation, and differentiation, leading to tissue regeneration. For efficient clinical translation, the forming technology utilized must be suitable for mass production. Herein, uniaxial polyhydroxyalkanoate scaffolds manufactured by pressurized gyration, a hybrid scalable spinning technique, are successfully used in bone, nerve, and cardiovascular applications. Chorioallantoic membrane and in vivo studies provided evidence of vascularization, collagen deposition, and cellular invasion for bone tissue engineering. Highly efficient axonal outgrowth was observed in dorsal root ganglion-based 3D ex vivo models. Human induced pluripotent stem cell derived cardiomyocytes exhibited a mature cardiomyocyte phenotype with optimal calcium handling. This study confirms that engineered polyhydroxyalkanoate-based gyrospun fibers provide an exciting and unique toolbox for the development of scalable scaffolds for both hard and soft tissue regeneration.

Understanding the fine details of the self‐assembly of building blocks into complex hierarchical structures represents a major challenge en route to the design and preparation of soft‐matter materials with specific properties. Enzymatically synthesised cellodextrins are known to have limited water solubility beyond DP9, a point at which they self‐assemble into particles resembling the antiparallel cellulose II crystalline packing. We have prepared and characterised a series of site‐selectively fluorinated cellodextrins with different degrees of fluorination and substitution patterns by chemoenzymatic synthesis. Bearing in mind the potential disruption of the hydrogen‐bond network of cellulose II, we have prepared and characterised a multiply 6‐fluorinated cellodextrin. In addition, a series of single site‐selectively fluorinated cellodextrins was synthesised to assess the structural impact upon the addition of one fluorine atom per chain. The structural characterisation of these materials at different length scales, combining advanced NMR spectroscopy and microscopy methods, showed that a 6‐fluorinated donor substrate yielded multiply 6‐fluorinated cellodextrin chains that assembled into particles presenting morphological and crystallinity features, and intermolecular interactions, that are unprecedented for cellulose‐like materials., Generating glycomaterials: Enzymatic incorporation of singly and multiply fluorinated glucose residues into cellodextrin chains produces selectively fluorinated cellodextrins that self‐assemble into crystalline materials. Multiply 6‐fluorinated cellodextrin gave rise to an allomorph not previously reported for celluloses or cellulose‐like materials. Our findings highlight the potential of chemoenzymatic synthesis for generating novel glycomaterials of controlled molecular structure and morphology.

Locust bean/xanthan gum (LBG/XG) synergistic networks have previously been well studied, with evidence that junction zones between the two polymers result in hydrophobic domains. Here we report on the effect of both hydrophilic and hydrophobic cellulose nanocrystals (CNCs) on the rheological properties of the individual gums, the gum networks, and emulsion gels consisting of the gum network and corn oil. We also take advantage of differences in the autofluorescent spectra for each of the components to map their distribution within the gel and emulsion gel systems. Whilst both types of CNC confer thermal stability to the systems, hydrophilic CNCs induce minor changes in rheological properties of synergistic gels and prove to be detrimental to the stability of the emulsion gels. In contrast, hydrophobic CNCs associate with the LBG/XG network, affecting the rheological response. Their inclusion in the emulsion gel system results in smaller, more homogeneously distributed oil droplets with a resultant increase in the storage modulus by an order of magnitude compared to the CNC-free and hydrophilic CNC systems. We conclude that hydrophobic CNCs play a critical role in stabilising LBG/XG network gels and emulsions.

Nerve guidance conduits (NGCs) are used as an alternative to the “gold standard” nerve autografting, preventing the need for surgical intervention required to harvest autologous nerves. However, the regeneration outcomes achieved with the current NGCs are only comparable with autografting when the gap is short (less than 10 mm). In the present study, we have developed NGCs made from a blend of polyhydroxyalkanoates, a family of natural resorbable polymers. Hollow NGCs made from a 75:25 poly(3‐hydroxyoctanoate)/poly(3‐hydroxybutyrate) blend (PHA‐NGCs) were manufactured using dip‐molding. These PHA‐NGCs showed appropriate flexibility for peripheral nerve regeneration. In vitro cell studies performed using RT4‐D6P2T rat Schwann cell line confirmed that the material is capable of sustaining cell proliferation and adhesion. PHA‐NGCs were then implanted in vivo to repair 10 mm gaps of the median nerve of female Wistar rats for 12 weeks. Functional evaluation of the regenerated nerve using the grasping test showed that PHA‐NGCs displayed similar motor recovery as the autograft, starting from week 7. Additionally, nerve cross‐sectional area, density and number of myelinated cells, as well as axon diameter, fiber diameter, myelin thickness and g‐ratio obtained using the PHA‐NGCs were found comparable to an autograft. This preclinical data confirmed that the PHA‐NGCs are indeed highly promising candidates for peripheral nerve regeneration.

The biocompatibility and neuron regenerating properties of various bioactive glass (BG)/polyhydroxyalkanoate (PHA) blend composites were assessed in order to study their suitability for peripheral nerve tissue applications, specifically as lumen structures for nerve guidance conduits. BG/PHA blend composites were fabricated using Bioactive glass® 45 S5 (BG1) and BG 1393 (BG2) with the 25:75 poly(3-hydroxyoctanoate/poly3-hydroxybutyrate), 25:75 P(3HO)/P(3HB) blend (PHA blend). Various concentrations of each BG (0.5 wt%, 1.0 wt% and 2.5 wt%) were used to determine the effect of BG on neuronal growth and differentiation, in single culture using NG108-15 neuronal cells and in a co-culture along with RN22 Schwann cells. NG108-15 cells exhibited good growth and differentiation on all the PHA blend composites showing that both BGs have good biocompatibility at 0.5 wt%, 1.0 wt% and 2.5 wt% within the PHA blend. The Young’s modulus values displayed by all the PHA blend/BG composites ranged from 385.6 MPa to 1792.6 MPa, which are able to provide the required support and protective effect for the regeneration of peripheral nerves. More specifically, the tensile strength obtained in the PHA blend/BG1 (1.0 wt%) (10.0 ± 0.6 MPa) was found to be similar to that of the rabbit peroneal nerve. This composite also exhibited the best biological performance in supporting growth and neuronal differentiation among all the substrates. The neurite extension on this composite was found to be remarkable with the neurites forming a complex connection network.

Surface hydrophobization of cellulose nanomaterials has been used in the development of nanofiller-reinforced polymer composites and formulations based on Pickering emulsions. Despite the well-known effect of hydrophobic domains on self-assembly or association of water-soluble polymer amphiphiles, very few studies have addressed the behavior of hydrophobized cellulose nanomaterials in aqueous media. In this study, we investigate the properties of hydrophobized cellulose nanocrystals (CNCs) and their self-assembly and amphiphilic properties in suspensions and gels. CNCs of different hydrophobicity were synthesized from sulfated CNCs by coupling primary alkylamines of different alkyl chain lengths (6, 8, and 12 carbon atoms). The synthetic route permitted the retention of surface charge, ensuring good colloidal stability of hydrophobized CNCs in aqueous suspensions. We compare surface properties (surface charge, ζ potential), hydrophobicity (water contact angle, microenvironment probing using pyrene fluorescence emission), and surface activity (tensiometry) of different hydrophobized CNCs and hydrophilic CNCs. Association of hydrophobized CNCs driven by hydrophobic effects is confirmed by X-ray scattering (SAXS) and autofluorescent spectroscopy experiments. As a result of CNC association, CNC suspensions/gels can be produced with a wide range of rheological properties depending on the hydrophobic/hydrophilic balance. In particular, sol–gel transitions for hydrophobized CNCs occur at lower concentrations than hydrophilic CNCs, and more robust gels are formed by hydrophobized CNCs. Our work illustrates that amphiphilic CNCs can complement associative polymers as modifiers of rheological properties of water-based systems.

Understanding the fine details of self-assembly of building blocks into complex hierarchical structures represents a major challenge en route to the design and preparation of soft matter materials with specific properties. Enzymatically-synthesised cellodextrins are known to have limited water solubility beyond DP9, a point at which they self-assemble into particles resembling the anti-parallel cellulose II crystalline packing. We have prepared and characterized a series of site-selectively fluorinated cellodextrins of different degrees of fluorination and substitution patterns by chemoenzymatic synthesis. The structural characterization of these materials at different length scales, combining advanced NMR and microscopy methods, showed that multiply 6-fluorinated cellodextrin chains assembled into particles presenting morphological and crystallinity features that are unprecedented for cellulose-like materials. In contrast, the introduction of a single fluorine atom per cellodextrin chain had a minor impact on materials structure. Our work emphasizes the strength of combining chemoenzymatic synthesis, fluorinated building blocks and advanced NMR and microscopy methods for the thorough characterization of hierarchical structures, leading to the controlled design of new biomaterials with specific properties.

Utilization of reversible non-covalent interactions is a versatile design strategy for the development of stimuli responsive soft materials. In this study, hydrophobic interactions were harnessed to assemble water-soluble macromolecules and nanoparticles into a transient hybrid network forming thermosensitive hydrogels with tunable rheological properties. Hybrid hydrogels were built of biopolymer derived components: cellulose nanocrystals (CNCs), nanoparticles of high aspect ratio, and hydroxypropyl methylcellulose (HPMC). To enable polymer/CNC assembly via hydrophobic interactions, the surface of highly hydrophilic CNCs was modified by binding octyl moieties (octyl-CNCs). The amphiphilicity of octyl-CNCs was confirmed by surface tension measurements. The molecular and particulate amphiphiles assemble into hybrid networks, which result in stiffer and stronger hydrogels compared to HPMC hydrogels and hydrogels reinforced with hydrophilic CNCs. Hybrid hydrogels retain the ability of HPMC hydrogels to flow under applied shear stress. However, significantly higher viscosity was achieved for HPMC/octyl-CNCs compared with HPMC/CNCs hydrogels. The inherent thermal response of rheological properties of HPMC hydrogels was further amplified in combination with octyl-CNCs due to temperature-induced polymer/nanoparticle association via hydrophobic interactions. Saturation transfer difference NMR spectroscopy demonstrated the growth of network-bound water with an increase in temperature, which correlates with the increase of stiffness and viscosity of hydrogels upon heating. Rheological properties of these hybrid hydrogels are defined by the content of the soluble polymer and the CNCs, and it is shown that they can be finely adjusted for a required application.

This study validated the utilization of triacylglycerides (TAGs) by Pseudomonas mendocina CH50, a wild type strain, resulting in the production of novel mcl-PHAs with unique physical properties. A PHA yield of 58% dcw was obtained using 20 g/L of coconut oil. Chemical and structural characterisation confirmed that the mcl-PHA produced was a terpolymer comprising of three different repeating monomer units, 3-hydroxyoctanoate, 3-hydroxydecanoate and 3-hydroxydodecanoate or P(3HO-3HD-3HDD). Bearing in mind the potential of P(3HO-3HD-3HDD) in biomedical research, especially in neural tissue engineering, in vitro biocompatibility studies were carried out using NG108-15 (neuronal) cells. Cell viability data confirmed that P(3HO-3HD-3HDD) supported the attachment and proliferation of NG108-15 and was therefore confirmed to be biocompatible in nature and suitable for neural regeneration.

Cellulose nanocrystals (CNCs) that bind to each other through associative hydrophobic interactions have been synthesized by modifying sulfated CNCs (sCNCs) with hydrophobic moieties. These octyl-CNCs form gels at significantly lower concentrations than parent sCNCs, producing extremely strong hydrogels. Unlike sCNCs, these octyl-CNCs do not form ordered liquid crystalline phases indicating a random association into a robust network driven by hydrophobic interactions. Furthermore, involvement of the octyl-CNCs into multicomponent supramolecular assembly was demonstrated in combination with starch. AFM studies confirm favorable interactions between starch and octyl-CNCs, which is thought to be the source of the dramatic increase in gel strength.

The only types of polyhydroxyalkanoates (PHAs) that have been explored for use in nerve regeneration are poly(3-hydroxybutyrate), P(3HB), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(3HB-co-3HHx)). However, nerve regeneration induced by these PHAs is inferior to that of autologous nerve grafting. The aim of this work was to study novel PHA blends as resorbable biomaterials for the manufacture of nerve guidance conduits. PHA blend films with varying ratios of poly(3-hydroxyoctanoate)/P(3HB) (P(3HO)/P(3HB)) were produced using the solvent-casting method. Neat films of P(3HO) and P(3HB), along with 25:75, 50:50, and 75:25 blend films of P(3HO)/P(3HB), were characterized with respect to chemical, material, and biological properties. On surface analysis, the blends exhibited higher values of roughness compared with the neat films. The differential scanning calorimetry characterization of the blends confirmed that P(3HO) and P(3HB) formed immiscible blends. FTIR and XRD analysis of the blends showed a decrease in crystallinity along with an increase of the proportion of P(3HO) . However, an increase in the stiffness of the blends was observed when the proportion of P(3HB) increased. Although all of the blends were biocompatible with NG108-15 neuronal cells, the 25:75 P(3HO)/P(3HB) blend showed significantly better support for growth and differentiation of these cells. The mechanical properties of PHA blends correspond to the reported properties of peripheral nerves. Therefore, they could serve as base material for the manufacture of nerve guidance conduits.

Polyhydroxyalkanoates (PHAs) are natural biopolymers produced by various microorganisms as a reserve of carbon and energy. PHA synthesis generally occurs during fermentation under nutrient limiting conditions with excess carbon. There are two main types of PHAs, short chain length PHAs (scl-PHAs) and medium chain length PHAs (mcl-PHAs). The mechanical and thermal properties of PHAs depend mainly on the number of carbons in the monomer unit and its molecular weight. PHAs are promising materials for biomedical applications because they are biodegradable, non-toxic and biocompatible. The large range of PHAs, along with their varying physical properties and high biocompatibility, make them highly attractive biomaterials for use in drug delivery. They can be used to produce tablets, micro- and nanoparticles as well as drug eluting scaffolds. A large range of different PHAs have been explored and the results obtained suggest that PHAs are excellent candidates for controlled and targeted drug delivery systems. © 2015 Society of Chemical Industry

Progress in tissue engineering is dependent on the availability of suitable biomaterials. In an effort to overcome the brittleness of poly(3-hydroxybutyrate), P(3HB), a natural biodegradable polyester, and widen its biomedical applications, plasticising of P(3HB) with oligomeric substances of related structure has been studied. A biosynthesised medium-chain-length polyhydroxyalkanoate (mcl-PHA) copolymer, the plasticiser precursor, was obtained using vegetable waste frying oil as a sole carbon source. The mcl-PHA was transformed into an oligomeric derivative by acid hydrolysis. The plasticising effect of the oligomeric mcl-PHA on P(3HB) was studied via characterisation of thermal and mechanical properties of the blends in the course of ageing at ambient conditions. Addition of oligomeric mcl-PHA to P(3HB) resulted in softer and more flexible materials based entirely on PHAs. It was shown that the oligomeric mcl-PHA transformed highly crystalline P(3HB) into materials with a dominant amorphous phase when the content of oligomeric mcl-PHA exceeded 10 wt%. In vitro biocompatibility studies of the new binary PHA materials showed high viability and proliferation of C2C12 myoblast cells. Thus, the proposed approach for P(3HB) plasticisation has the potential for the generation of more pliable biomaterials based on P(3HB) which can find application in unique soft tissue engineering applications where a balance between stiffness, tensile strength and ductility is required.Polyhydroxyalkanoates, a broad family of natural biodegradable and biocompatible polymers, have emerged as highly promising biomaterials both for bulk and biomedical applications. Here we describe an approach to tune the mechanical properties of stiff and brittle poly(3-hydroxybutyrate) and thereby to expand its potential biomedical applications. Plasticisation, a common practice in the plastic industry to modify polymer mechanical properties, has been used very cautiously for biomedical applications due to plasticiser toxicity and migration. We have developed a plasticiser for poly(3-hydroxybutyrate) based on a structurally related but softer and pliable medium chain length polyhydroxyalkanoate. Additives of oligomeric derivatives of this polymer improved ductility of poly(3-hydroxybutyrate), greatly widening the future applicability of this well-established biomaterial. In parallel, the binary polyhydroxyalkanoate materials also exhibited improved cell attachment and proliferation, a highly desirable outcome.

The effect of electrospun cellulose nanocrystals (CNCs)-polyetherimide (PEI) hybrid nanofibrous mats on Mode I and Mode II interlaminar fracture toughness of unidirectional carbon/epoxy composite laminates is demonstrated. It is shown that the CNCs reinforced PEI nanofibrillar interleaves result in a ~28% increase in Mode I initial fracture toughness values compared to neat PEI nanofibrous interleaves. Specifically, the interrelated micro- and nano-scale toughening mechanisms including carbon fibre bridging, fibre necking, fibre rupture with CNCs aggregates, and nanofibre rupture contributed to the fracture toughness improvements under Mode-I loading. Nano-scale mechanisms of shear hackles, and crack pinning by CNCs aggregates increased the Mode II fracture toughness up to ~3 kJ/m2 as a result of a 6 wt% CNCs reinforced PEI nanofibrillar mat interleave. Interleaving laminated composites with electrospun CNCs-PEI hybrid nanofibrillar mats has been demonstrated as a novel and prospective strategy to strengthen and toughen interlaminar zones of carbon/epoxy composite laminates.

Biocides are widely explored in the design of materials and surfaces in order to address a variety of problems, such as biodeterioration, biofouling or infections. Materials with migrating biocides are under scrutiny due to potential health and environmental risks, as well as instability of the antimicrobial activity in time. This paper focuses on the onium-functionalised polymers in the design of bioactive materials and surfaces, which are capable to kill micro-organism or efficiently inhibit their growth on contact. The review highlights synthetic and processing routes towards the integration of onium functionalities into solid materials. The influence of materials structure on the antimicrobial activity and possible applications are discussed.

There is a need to develop high-performance cellulose fibers as sustainable replacements for glass fibers, and as alternative precursors for carbon filaments. Traditional fiber spinning uses toxic solvents, but in this study, by using dimethyl sulfoxide (DMSO) as a co-solvent with an ionic liquid, a novel high-performance fiber with exceptional mechanical properties is produced. This involves a one-step dissolution, and cost-effective route to convert high concentrations of low molecular weight microcrystalline cellulose into high stiffness cellulose fibers. As the cellulose concentration increases from 20.8 to 23.6 wt%, strong optically anisotropic patterns appear for cellulose solutions, and the clearing temperature (T c) increases from ≈100 °C to above 105 °C. Highly aligned, stiff cellulose fibers are dry-jet wet spun from 20.8 and 23.6 wt% cellulose/1-ethyl-3-methylimidazolium diethyl phosphate/DMSO solutions, with a Young's modulus of up to ≈41 GPa. The significant alignment of cellulose chains along the fiber axis is confirmed by scanning electron microscopy, wide-angle X-ray diffraction, and powder X-ray diffraction. This process presents a new route to convert high concentrations of low molecular weight cellulose into high stiffness fibers, while significantly reducing the processing time and cost.

The intercalation of cationic copolymer into a smectic clay, montmorillonite, has been used to produce polymerically modified organoclays. The organoclays of different lamellar morphology and content of quaternary ammonium groups have been prepared by altering the clay/polymer ratio. The organoclays prepared have been explored in the design of antimicrobial materials based on clay/polymer nanotechnology. Polyamide nanocomposites containing organoclays with incorporated cationic polymer showed an antimicrobial activity and improved mechanical properties. The antimicrobial efficiency and the mechanical properties of the nanocomposites were controlled by the variation of the content of the cationic polymer incorporated into the organoclay and organoclay loading.

To render the surface of ultrafiltration membranes biocidal, cellulose membranes were modified with chitosan, a naturally occurring polycationic biocide. Through the use of chitosans of different molecular weights and membranes with different pore sizes, the alteration of the morphological structure of tethered chitosan layers was achieved. The importance of such structural differences in the antimicrobial activity of the prepared membranes against gram-positive Staphylococcus aureus and gram-negative Escherichia coli was studied. The antimicrobial efficiency improved with the use of chitosans with higher molecular weights and membranes with smaller pore sizes. This suggested that the surface location of the grafted chitosan chains was more preferential for a higher antimicrobial activity of the surface. Membranes modified with chitosan showed higher antimicrobial efficiency against gram-positive S. aureus than against gram-negative E. coli. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

A robust processing of polymers into antimicrobial materials is introduced using polymer/clay nanotechnology. Antimicrobial activity of commercially available organoclays modified with cationic surfactants has been screened in tests against gram-negative Escherichia coli and gram-positive Staphylococcus aureus bacteria. Despite the leaching biocidal surfactants, cell interactions with organoclay surface have been identified to be responsible for antimicrobial activity of organoclays. Distribution of clay platelets within polymer matrix by melt extrusion process resulted in polymer/clay nanocomposites active against both gram-positive and gram-negative bacteria by contact. The study discloses a much overlooked function of organoclays modified with cationic surfactants for nanocomposite application, i.e., the ability of organoclays to render polymer nanocomposites biocidal.

The oxidative degradation of organic pollutants present in cork-processing water at natural pH (6.45) was studied in a bubble column ozonation reactor. A steady reduction in both chemical oxygen demand (COD) and total organic carbon (TOC) was observed under the action of ozone alone and the feasibility of deep mineralisation (organic matter removal more than 90% in 120 min under the following experimental conditions: liquid volume 9L; superficial gas velocity 6.8x10(-3) m s(-1); ozone partial pressure 1.31 kPa; initial COD 328 mg L(-1); initial TOC 127 mg L(-1)) was demonstrated. The monitoring of pH, redox potential (ORP) and the mean oxidation number of carbon (MOC) was correlated with the oxidation and mineralisation of the organic species in the water. The ozonation of cork-processing water in the bubble column was analysed in terms of a mole balance coupled with ozonation kinetics modelled by the two-film theory of mass transfer and chemical reaction. Under the experimental conditions used, and in contrast with the literature, it was determined that the reaction follows a fast kinetic regime at the beginning of the oxidation process, shifting to the moderate and the slow kinetic regimes at later stages of the oxidation reaction. The dynamic change of the rate coefficient estimated by the model was correlated to changes in the water composition.

Sequential reduction of chromate and nitrate, two competitive electron acceptors, has been demonstrated for strains of Pseudomonas genus for both planktonic cells and cells immobilised in agar layers on the surface of synthetic membrane. Denitrification occurs practically after chromate depletion. This order of reduction process is consistent with redox potentials of the respective reactions. In a membrane bioreactor, competitive inhibition results in nitrate transfer through the membrane without transformation. Thus the receiving phase is contaminated with nitrate. To address this problem, a membrane has been used for spatial sequencing of chromate and nitrate reduction. Bacterial cells were immobilised in two layers with each layer placed on opposing sides of the membrane. By this means, chromate reduction is localised into the layer contacting the feed phase while nitrate reduction occurs in the layer facing the receiving phase. As a result, only traces of the pollutants are detected in the receiving phase.

In this paper, lipase-immobilized membranes were prepared by both non-covalent and covalent immobilization methods using (i) lipase adsorption on membranes, (ii) inclusion of enzyme in membrane structure by filtration and (iii) covalent attachment of lipase to membrane. The catalytic properties of these membranes have been studied in reaction of butyloleate synthesis through esterification of oleic acid with n-butanol in isooctane. Ultrafiltration membranes made of regenerated cellulose (C030F) and polyethersulphone (PM30) were used for lipase immobilization. It was found that the lipase inclusion in the wide porous supporting layer of membrane was the most efficient method in preparing highly effective biocatalytic membranes. The degree of oleic acid conversion using these membranes was about 70–72% with a reaction time of 8 h. It was shown that the distribution profile of the lipase in the membrane was important for the effective enzyme utilization. The profile imaging atomic force microscopy (AFM) technique was used to visualize surfaces of lipase-immobilized biocatalytic membranes. AFM has also been used to directly quantify interactions between lipase-coated tip and membrane surfaces. It was concluded that the direct measurements of the interaction force between the enzyme-coated tip and the membrane surface would be a useful and practical approach for the choice of membranes as porous polymeric support for lipase immobilization through adsorption.

Two microfiltration membranes made of polyvinilidene fluoride (PVDF) and polyethersulfone (PES) of the same nominal pore size have been modified by photo-initiated graft copolymerisation of quaternary salt of dimethylamino ethyl methacrylate (qDMAEM). Atomic force microscopy (AFM) has been used to characterise changes in surface morphology with variation of the degree of polymer grafting and therefore the process of modification. Comparative analysis of pore size distribution (PSD) of the initial and modified membranes has revealed differences in the modification process. Although polymer grafting resulted in PSD shifting towards smaller pore sizes, modification of PES membrane narrowed PSD, whereas modified PVDF showed wider PSD. This was attributed to different free-radical density for photo-reactive PES and more inert PVDF with possible contribution of the surface roughness.

Membrane‐based processes are very susceptible to flux decline due to concentration polarization and fouling problems and the concept of fouling control via process optimization, membrane surface modification, and cleaning have been the focus of research in wastewater and water treatment. MF and UF membranes are utilized in many areas of industry. The main sector of application includes water and wastewater. There has been emphasis on the various methods used to reduce and, where possible, eliminate fouling. This review is a comprehensive insight into the wide range of techniques used in the control of fouling in both MF and UF membranes. It also addresses the amount of research that has gone into the various techniques used and the results achieved after experimental work.

The efficiency of heavy metal removal from water containing humic substances (HS) has been investigated by means of ultrafiltration. The rejection coefficient of Pb (II), Cu (II), Ni (II) and Co (II) in the presence of humic (HA) and fulvic acids (FA) was studied for different composition of feed solution (pH, concentration of metal ions and background electrolytes) and cellulose acetate ultrafiltration membranes of different molecular weight cut-off. HS rejection increases with pH due to conformational transformation of ionizable molecules. The interactions of HS with multi-charged metals do not practically affect the HS retention. Involvement of heavy metals ions into complexation with HS provides effective removal of trace metals from solutions as a result of complex retention. The metal rejection increases with pH growth and in neutral/alkaline solutions it exceeds 80%. Thus, ultrafiltration is an effective method for simultaneous removal of HS and heavy metals harnessing the principle of reagent-reinforced ultrafiltration. In conformity with this principle degree of heavy metal rejection improves with an increase in HS–Me ratio due to increase in completeness of metal binding. HS–Me ratio also is responsible for phase-dispersion state of the solution initiating a transition of intra-molecular complexes to inter-molecular ones at higher concentrations of metal ions with respect to higher molecular weight HA. This leads to an aggregation of HA–Me complexes and decrease in the trans-membrane flux. FA do not tend to form inter-molecular aggregates.

A new approach is proposed to immobilize lipase into microporous polymeric membrane via embedding cross-linked enzyme aggregates (CLEA) within membrane pores. Preparation of biocatalytic membranes was implemented with hydrophilic cellulose and hydrophobic PTFE membranes. Formation of lipase CLEAs is initiated by solvent exchange between aqueous solution of the enzyme filling membrane pores and organic media containing cross-linking agent. The influence of organic media composition and matrix hydrophilicity/hydrophobicity on membrane biocatalytic properties has been studied. Highly effective biocatalytic membranes with embedded lipase CLEA have been obtained on the base of both hydrophilic and hydrophobic membranes by varying the content of glutaric dialdehyde used as a cross-linking agent. Bio-imprinting has been tested as a mean to improve efficiency of the biocatalytic membranes. Biocatalytic esterification of oleic acid with n-butanol has been studied in cross-flow membrane bioreactor with membrane-supported lipase CLEA using hexane and iso-octane as reaction solvents of different hydrophobicity.

Chromate reduction was studied in a membrane bioreactor under action of Pseudomonas bacteria immobilized in agar–agar films on the surface of synthetic membrane. Immobilized cells are protected from the excessive toxic action at high chromate concentration that improves cell activity compared with free cells. Almost complete chromate reduction was observed at stepwise introducing of chromate in feed solution allowing maintenance of optimal chromate concentration. Reduction is suppressed by high metabolite concentrations, which reached on the sixth step of chromate adding in studied system. Cell ability to reduce chromate is restored after changing of feed and receiving solutions allowing remediation of Cr(VI)-contaminated water in semi-batch operation of membrane bioreactor.

The potential for membrane distillation (MD) flux enhancement in apple juice concentration by removal of biopolymers has been investigated. Introduction of additional enzymatic deproteinization to conventional treatment with pectinase/amylase complexes and application UF as a clarification method provide an obtaining of clarified apple juice with minimal content of biopolymers. Such a pre-treatment enhances trans-membrane flux during concentration of clarified juice by MD. This has been attributed to a reduction in juice viscosity resulting in decrease of concentration and temperature polarisation. Lower initial viscosity is especially favourable for the treatment of highly viscous streams of concentrated juices.

The chiral separation of ibuprofen has been performed by ultrafiltration in solutions containing the protein bovine serum albumin (BSA) as a chiral selector. The effectiveness of optical resolution was characterized in terms of enantiomeric enrichment and solute recovery in the permeate. Working conditions, including parameters of feed solution and hydrodynamic conditions, which can influence thermodynamic equilibrium and nonselective solute binding, have been investigated with regard to the separation effectiveness. Enantioselectivity is strongly pH-dependent and reaches a maximal value at pH 9.0–9.2. It was established that nonspecific interactions also played a significant role in total ibuprofen binding, decreasing both enantioselectivity and solute recovery in permeates. Nonspecific interactions are suppressed in the presence of organic solvents (acetonitrile, methanol) in the feed solution thereby increasing the solute recovery in the permeate. Increase in BSA content in the feed solution results in...

The application of polyvinylchloride materials in sensor systems has been studied previously. A new method of protein immobilisation has been developed, in which the topochemistry of the antigen–antibody reaction is located in the porous structure of a PVC membrane This allows an improvement in the sensitivity of the proposed sensor system. The device is based on a bioaffinity polymeric membrane (with immobilised antibody [Ab]) which is able to change its ion permeability during an immunochemical reaction. The electrical conductivity of the system with the Ab-bound membrane increases in the presence of the antigen (Ag) allowing the determination of its concentration. Comparable sensitivity (5 ng ml−1) and reduced response time (5–6 min) with regard to the established ELISA method were achieved. The transmembrane potential of the membranes studied was measured and a possible mechanism for the sensor response formation is proposed.

This work is concerned with hybrid nanocomposite materials that contain both clay and graphite oxide incorporated in an epoxy matrix. In order to assess the challenge of improving the thermal conductivity while not changing or even improving the electrical properties, a new composite system was designed by applying an additional thermal conductive phase represented by the graphite oxide. In this paper, extremely low quantities of graphite oxide were used (going from 0.0012 to 0.0025 wt%) in order to avoid the forming of an electrical conduction percolation network. The impact of the additional filler on the thermal and electrical properties of the clay/graphite oxide/epoxy nanocomposites were investigated. Using thermal conductivity measurements, it was found that even for low quantities of GO filler added to the clay/epoxy nanocomposite material, the thermal conductivity is improved significantly. Moreover, using dielectric characterization techniques (Dielectric Spectroscopy, Space Charge or Dielectric Breakdown measurements), it was found that the electrical properties of the material remain unchanged or are slightly improved by the extra graphite oxide filler.

Insufficient crosslinking and water uptake during fabrication or manipulation are known to affect the dielectric response of epoxies. Post thermal treatment may result in the completion of cross-linking, partial removal of water, and aging. In order to study the effect of manufacturing imprecision on dielectric response, several under-cured epoxybased nanocomposite samples with modified nanoclay fillers were investigated. In addition, the influence of silane coupling agents and the use of ultrasonic waves on the nanoclay intercalation were also studied. The structure of the samples and the extent of cross linking were characterized using X-ray Diffraction (XRD) and Differential Scanning Calorimetry (DSC) respectively. It was found that surface silanization lead to improved clay intercalation and higher extent of intercalation/exfoliation. The influence of post thermal treatment on the dielectric response of the materials was investigated using Broadband Dielectric Spectroscopy (BDS). Once the samples were in a stable dielectric state, relaxation maps were performed. It was found that the samples with silanized nanoclay have the lowest activation energy and they also proved to be the “strongest” vitreous materials.

Thermoset polymers are frequently used as matrices for nanocomposite materials because nanofillers, such as clay, can be easily incorporated into liquid polymer precursors. Since in the crystal structure of clay such as Montmorillonite the layers are physically linked by cations, replacing these cations with larger organophilic molecules changes the clay surface into hydrophobic and increases the interlayer space. This improves the compatability between montmorillonite and most of engineering polymers, making it suitable for nanocomposite application. This paper investigates the influence of surface treatment on calorimetric and dielectric properties of a commercially available organoclay with different extent of free surfactant and moisture level, using filled epoxy nanocomposites. The moisture content of the nanocomposites was measured using Thermogravimetric Analysis (TGA). Thermal stability was investigated using Differential Scanning Calorimetry (DSC) with the glass transition temperature chosen as an indicator. Finally, dielectric response of the materials was investigated at room temperature using Broadband Dielectric Spectroscopy (BDS).

The treatment of industrial cork-processing water at natural pH (6.45) by ozonation alone and ozone based advanced oxidation processes (O

The porous structure of ultrafiltration cellulose acetate membranes and the effect of alkaline saponification on their structure are studied by small-angle X-ray analysis and by sorption of the vapours of an inert sorbate. It is shown that these membranes have a two-level porous structure. Saponification is accompanied by a decrease in the membrane pore size, which is a result of an increase in the number of physical “cross-links” of the three-dimensional gel network.

The kinetics of the saponification of cellulose acetate ultrafiltration membranes and its effect on their transport characteristics and certain physicochemical properties are studied. It is established that the rate and effective activation energy of the saponification process are inversely related to the pore size, and that on passing from large pore to fine pore membranes the saponification process passes from the diffusional into the kinetic region. It is shown that on asymmetric hydrolysis of the membranes the process takes place in the presence of a moving boundary of reacted layer with a markedly diffuse front. Specification of the membranes is accompanied by a change in their transport characteristics and the state of the water in the membrane pores.

Colloidal probe microscopy has been used to study the interaction between model cellulose surfaces and the role of cellulose binding domain (CBD), peptides specifically binding to cellulose, in interfacial interaction of cellulose surfaces modified with CBDs. The interaction between pure cellulose surfaces in aqueous electrolyte solution is dominated by double layer repulsive forces with the range and magnitude of the net force dependent on electrolyte concentration. AFM imaging reveals agglomeration of CBD adsorbed on cellulose surface. Despite an increase in surface charge owing to CBD binding to cellulose surface, force profiles are less repulsive for interactions involving, at least, one modified surface. Such changes are attributed to irregularity of the topography of protein surface and non-uniform distribution of surface charges on the surface of modified cellulose. Binding double CBD hybrid protein to cellulose surfaces causes adhesive forces at retraction, whereas separation curves obtained with cellulose modified with single CBD show small adhesion only at high ionic strength. This is possibly caused by the formation of the cross-links between cellulose surfaces in the case of double CBD., European Commission (EC) - Fifth Framework Programme.