Publications by authors named "Janet L Scott"

41 Publications

Keratin-Chitosan Microcapsules via Membrane Emulsification and Interfacial Complexation.

ACS Sustain Chem Eng 2021 Dec 1;9(49):16617-16626. Epub 2021 Dec 1.

Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.

The continuous fabrication via membrane emulsification of stable microcapsules using renewable, biodegradable biopolymer wall materials keratin and chitosan is reported here for the first time. Microcapsule formation was based on opposite charge interactions between keratin and chitosan, which formed polyelectrolyte complexes when solutions were mixed at pH 5.5. Interfacial complexation was induced by transfer of keratin-stabilized primary emulsion droplets to chitosan solution, where the deposition of chitosan around droplets formed a core-shell structure. Capsule formation was demonstrated both in batch and continuous systems, with the latter showing a productivity up to 4.5 million capsules per minute. Keratin-chitosan microcapsules (in the 30-120 μm range) released less encapsulated nile red than the keratin-only emulsion, whereas microcapsules cross-linked with glutaraldehyde were stable for at least 6 months, and a greater amount of cross-linker was associated with enhanced dye release under the application of force due to increased shell brittleness. In light of recent bans involving microplastics in cosmetics, applications may be found in skin-pH formulas for the protection of oils or oil-soluble compounds, with a possible mechanical rupture release mechanism (e.g., rubbing on skin).
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http://dx.doi.org/10.1021/acssuschemeng.1c05304DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8735752PMC
December 2021

Rheological modification of partially oxidised cellulose nanofibril gels with inorganic clays.

PLoS One 2021 7;16(7):e0252660. Epub 2021 Jul 7.

Department of Chemistry, University of Bath, Claverton Down, Bath, United Kingdom.

This study aimed to quantify the influence of clays and partially oxidised cellulose nanofibrils (OCNF) on gelation as well as characterise their physical and chemical interactions. Mixtures of Laponite and montmorillonite clays with OCNF form shear-thinning gels that are more viscous across the entire shear range than OCNF on its own. Viscosity and other rheological properties can be fine-tuned using different types of clay at different concentrations (0.5-2 wt%). Laponite particles are an order of magnitude smaller than those of montmorillonite (radii of 150 Å compared to 2000 Å) and are therefore able to facilitate networking of the cellulose fibrils, resulting in stronger effects on rheological properties including greater viscosity. This work presents a mechanism for modifying rheological properties using renewable and environmentally-friendly nanocellulose and clays which could be used in a variety of industrial products including home and personal care formulations.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0252660PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8263268PMC
October 2021

Influence of Calcium Silicate and Hydrophobic Agent Coatings on Thermal, Water Barrier, Mechanical and Biodegradation Properties of Cellulose.

Nanomaterials (Basel) 2021 Jun 4;11(6). Epub 2021 Jun 4.

Centre for Sustainable Chemical Technologies, Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.

Thin films of cellulose and cellulose-CaSiO composites were prepared using 1-ethyl-3-methylimidazolium acetate (EMIMAc) as the dissolution medium and the composites were regenerated from an anti-solvent. The surface hydrophilicity of the resultant cellulose composites was lowered by coating them with three different hydrophobizing agents, specifically, trichloro(octadecyl)silane (TOS), ethyl 2-cyanoacrylate (E2CA) and octadecylphosphonic acid (ODPA), using a simple dip-coating technique. The prepared materials were subjected to flame retardancy, water barrier, thermal, mechanical and biodegradation properties analyses. The addition of CaSiO into the cellulose increased the degradation temperature and flame retardant properties of the cellulose. The water barrier property of cellulose-CaSiO composites under long term water exposure completely depends on the nature of the hydrophobic agents used for the surface modification process. All of the cellulose composites behaved mechanically as a pure elastic material with a glassy state from room temperature to 250 °C, and from 20% to 70% relative humidity (RH). The presence of the CaSiO filler had no effect on the elastic modulus, but it seemed to increase after the TOS surface treatment. Biodegradability of the cellulose was evaluated by enzyme treatments and the influence of CaSiO and hydrophobic agents was also derived.
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http://dx.doi.org/10.3390/nano11061488DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8226986PMC
June 2021

Salt-Responsive Pickering Emulsions Stabilized by Functionalized Cellulose Nanofibrils.

Langmuir 2021 06 3;37(23):6864-6873. Epub 2021 Jun 3.

Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.

Oil-in-water emulsions have been stabilized by functionalized cellulose nanofibrils bearing either a negative (oxidized cellulose nanofibrils, OCNF) or a positive (cationic cellulose nanofibrils, CCNF) surface charge. The size of the droplets was measured by laser diffraction, while the structure of the shell of the Pickering emulsion droplets was probed using small-angle neutron scattering (SANS), confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), and rheology measurements. Both OCNF- and CCNF-stabilized emulsions present a very thick shell (>100 nm) comprised of densely packed CNF. OCNF-stabilized emulsions proved to be salt responsive, influencing the droplet aggregation and ultimately the gel properties of the emulsions, while CCNF emulsions, on the other hand, showed very little salt-dependent behavior.
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http://dx.doi.org/10.1021/acs.langmuir.0c03306DOI Listing
June 2021

Monovalent Salt and pH-Induced Gelation of Oxidised Cellulose Nanofibrils and Starch Networks: Combining Rheology and Small-Angle X-ray Scattering.

Polymers (Basel) 2021 Mar 19;13(6). Epub 2021 Mar 19.

Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.

Water quality parameters such as salt content and various pH environments can alter the stability of gels as well as their rheological properties. Here, we investigated the effect of various concentrations of NaCl and different pH environments on the rheological properties of TEMPO-oxidised cellulose nanofibril (OCNF) and starch-based hydrogels. Addition of NaCl caused an increased stiffness of the OCNF:starch (1:1 wt%) blend gels, where salt played an important role in reducing the repulsive OCNF fibrillar interactions. The rheological properties of these hydrogels were unchanged at pH 5.0 to 9.0. However, at lower pH (4.0), the stiffness and viscosity of the OCNF and OCNF:starch gels appeared to increase due to proton-induced fibrillar interactions. In contrast, at higher pH (11.5), syneresis was observed due to the formation of denser and aggregated gel networks. Interactions as well as aggregation behaviour of these hydrogels were explored via ζ-potential measurements. Furthermore, the nanostructure of the OCNF gels was probed using small-angle X-ray scattering (SAXS), where the SAXS patterns showed an increase of slope in the low-q region with increasing salt concentration arising from aggregation due to the screening of the surface charge of the fibrils.
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http://dx.doi.org/10.3390/polym13060951DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8003611PMC
March 2021

Enzyme-Functionalized Cellulose Beads as a Promising Antimicrobial Material.

Biomacromolecules 2021 02 6;22(2):754-762. Epub 2021 Jan 6.

Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.

The extensive use of antibiotics over the last decades is responsible for the emergence of multidrug-resistant (MDR) microorganisms that are challenging health care systems worldwide. The use of alternative antimicrobial materials could mitigate the selection of new MDR strains by reducing antibiotic overuse. This paper describes the design of enzyme-based antimicrobial cellulose beads containing a covalently coupled glucose oxidase from (GOx) able to release antimicrobial concentrations of hydrogen peroxide (HO) (≈ 1.8 mM). The material preparation was optimized to obtain the best performance in terms of mechanical resistance, shelf life, and HO production. As a proof of concept, agar inhibition halo assays (Kirby-Bauer test) against model pathogens were performed. The two most relevant factors affecting the bead functionalization process were the degree of oxidation and the pH used for the enzyme binding process. Slightly acidic conditions during the functionalization process (pH 6) showed the best results for the GOx/cellulose system. The functionalized beads inhibited the growth of all the microorganisms assayed, confirming the release of sufficient antimicrobial levels of HO. The maximum inhibition efficiency was exhibited toward () and (), although significant inhibitory effects toward methicillin-resistant (MRSA) and were also observed. These enzyme-functionalized cellulose beads represent an inexpensive, sustainable, and biocompatible antimicrobial material with potential use in many applications, including the manufacturing of biomedical products and additives for food preservation.
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http://dx.doi.org/10.1021/acs.biomac.0c01536DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7884000PMC
February 2021

Multienzyme Cellulose Films as Sustainable and Self-Degradable Hydrogen Peroxide-Producing Material.

Biomacromolecules 2020 12 17;21(12):5315-5322. Epub 2020 Nov 17.

Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.

The use of hydrogen peroxide-releasing enzymes as a component to produce alternative and sustainable antimicrobial materials has aroused interest in the scientific community. However, the preparation of such materials requires an effective enzyme binding method that often involves the use of expensive and toxic chemicals. Here, we describe the development of an enzyme-based hydrogen peroxide-producing regenerated cellulose film (RCF) in which a cellobiohydrolase (CBHI) and a cellobiose dehydrogenase (CDHA) were efficiently adsorbed, 90.38 ± 2.2 and 82.40 ± 5.7%, respectively, without making use of cross-linkers. The enzyme adsorption kinetics and binding isotherm experiments showed high affinity of the proteins possessing cellulose-binding modules for RCF, suggesting that binding on regenerated cellulose via specific interactions can be an alternative method for enzyme immobilization. Resistance to compression and porosity at a micrometer scale were found to be tunable by changing cellulose concentration prior to film regeneration. The self-degradation process, triggered by stacking CBHI and CDHA (previously immobilized onto separate RCF), produced 0.15 nmol/min·cm of HO. Moreover, the production of HO was sustained for at least 24 h reaching a concentration of ∼2 mM. The activity of CDHA immobilized on RCF was not affected by reuse for at least 3 days (1 cycle/day), suggesting that no significant enzyme leakage occurred in that timeframe. In the material herein designed, cellulose (regenerated from a 1-ethyl-3-methylimidazolium acetate/dimethyl sulfoxide (DMSO) solution) serves both as support and substrate for the immobilized enzymes. The sequential reaction led to the production of HO at a micromolar-millimolar level revealing the potential use of the material as a self-degradable antimicrobial agent.
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http://dx.doi.org/10.1021/acs.biomac.0c01393DOI Listing
December 2020

Impact of wormlike micelles on nano and macroscopic structure of TEMPO-oxidized cellulose nanofibril hydrogels.

Soft Matter 2020 May 19;16(20):4887-4896. Epub 2020 May 19.

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

In this work, we investigated the effect of adding surfactant mixtures on the rheological properties of TEMPO-oxidized cellulose nanofibril (OCNF) saline dispersions. Three surfactant mixtures were studied: cocamidopropyl betaine (CAPB)/sodium dodecyl sulfate (SDS), which forms wormlike micelles (WLMs); cocamidopropylamine oxide (CAPOx)/SDS, which forms long rods; and CAPB/sodium lauroyl sarcosinate (SLS), which forms spherical micelles. The presence of micelles in these surfactant mixtures, independent of their morphology, leads to an increase of tan δ, making the gels less solid-like, therefore acting as a plasticizer. WLMs were able to suppress strain stiffening normally observed in OCNF gels at large strains. OCNF/WLM gels have lower G' values than OCNF gels while the other micellar morphologies have a reduced impact on G'. The presence of unconnected micelles leads to increased dissipative deformation in OCNF gels without affecting the connectivity of the fibrils, while the presence of entangled micelles interferes with the OCNF network.
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http://dx.doi.org/10.1039/d0sm00135jDOI Listing
May 2020

Core-Shell Spheroidal Hydrogels Produced via Charge-Driven Interfacial Complexation.

ACS Appl Polym Mater 2020 Mar 12;2(3):1213-1221. Epub 2020 Feb 12.

Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom.

Through charge-driven interfacial complexation, we produced millimeter-sized spheroidal hydrogels (SH) with a core-shell structure allowing long-term stability in aqueous media. The SH were fabricated by extruding, dropwise, a cationic cellulose nanofibril (CCNF) dispersion into an oppositely charged poly(acrylic acid) (PAA) bath. The SH have a solid-like CCNF-PAA shell, acting as a semipermeable membrane, and a liquid-like CCNF suspension in the core. Swelling behavior of the SH was dependent on the osmotic pressure of the aging media. Swelling could be suppressed by increasing the ionic strength of the media as this enhanced interfibrillar interactions and thus strengthened the outer gel membrane. We further validated a potential application of SH as reusable matrixes for glucose oxidase (GOx) entrapment, where the SH work as microreactors from which substrate and product are freely able to migrate through the SH shell while avoiding enzyme leakage.
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http://dx.doi.org/10.1021/acsapm.9b01086DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7147256PMC
March 2020

Filler size effect in an attractive fibrillated network: a structural and rheological perspective.

Soft Matter 2020 Apr;16(13):3303-3310

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

The effect of the filler size on the structural and mechanical properties of an attractive fibrillated network composed of oxidised cellulose nanofibrils (OCNF) in water was investigated. Silica nanoparticles with a diameter of ca. 5 nm (SiNp5) and and ca. 158 nm (SiNp158) were chosen as non-interacting fillers of the OCNF network. These filler sizes were chosen, respectively, to have a particle size which was either similar to that of the network mesh size or much larger than it. Contrast matched small angle neutron scattering (SANS) experiments revealed that the presence of the fillers (SiNp5 and SiNp158) did not perturb the structural properties of the OCNF network at the nanometer scale. However, the filler size difference strongly affected the mechanical properties of the hydrogel upon large amplitude oscillatory shear. The presence of the smaller filler, SiNp5, preserved the mechanical properties of the hydrogels, while the larger filler, SiNp158, allowed a smoother breakage of the network and low network recoverability after breakage. This study showed that the filler-to-mesh size ratio, for non-interacting fillers, is pivotal for tailoring the non-linear mechanical properties of the gel, such as yielding and flow.
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http://dx.doi.org/10.1039/c9sm02175bDOI Listing
April 2020

Cationic surfactants as a non-covalent linker for oxidised cellulose nanofibrils and starch-based hydrogels.

Carbohydr Polym 2020 Apr 31;233:115816. Epub 2019 Dec 31.

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom; Centre for Sustainable Chemical Technologies, University of Bath, Claverton Down, Bath, BA2 7AY, United Kingdom. Electronic address:

Rheological properties of hydrogels composed of TEMPO-oxidised cellulose nanofibrils (OCNF)-starch in the presence of cationic surfactants were investigated. The cationic surfactants dodecyltrimethylammonium bromide (DTAB) and cetyltrimethylammonium bromide (CTAB) were used to trigger gelation of OCNF at around 5 mM surfactant. As OCNF and DTAB/CTAB are oppositely charged, an electrostatic attraction is suggested to explain the gelation mechanism. OCNF (1 wt%) and soluble starch (0.5 and 1 wt%) were blended to prepare hydrogels, where the addition of starch to the OCNF resulted in a higher storage modulus. Starch polymers were suggested to form networks with cellulose nanofibrils. The stiffness and viscosity of OCNF-Starch hydrogels were enhanced further by the addition of cationic surfactants (5 mM of DTAB/CTAB). ζ -potential and amylose-iodine complex analyses were also conducted to confirm surface charge and interaction of OCNF-starch-surfactant in order to provide an in-depth understanding of the surfactant-induced gel networks.
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http://dx.doi.org/10.1016/j.carbpol.2019.115816DOI Listing
April 2020

Hydrophobization of Cellulose Nanocrystals for Aqueous Colloidal Suspensions and Gels.

Biomacromolecules 2020 05 6;21(5):1812-1823. Epub 2020 Feb 6.

Department of Aerospace Engineering, Bristol Composites Institute (ACCIS), University of Bristol, Bristol BS8 1TR, United Kingdom.

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.
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http://dx.doi.org/10.1021/acs.biomac.9b01721DOI Listing
May 2020

Charge-driven interfacial gelation of cellulose nanofibrils across the water/oil interface.

Soft Matter 2020 Jan;16(2):357-365

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

Interfacial gels, obtained by the interaction of water-dispersible oxidised cellulose nanofibrils (OCNF) and oil-soluble oleylamine (OA), were produced across water/oil (W/O) interfaces. Surface rheology experiments showed that the complexation relies on the charge coupling between the negatively-charged OCNF and OA. Complexation across the W/O interface was found to be dependent on the ζ-potential of the OCNF (modulated by electrolyte addition), leading to different interfacial properties. Spontaneous OCNF adsorption at the W/O interface occurred for particles with ζ-potential more negative than -30 mV, resulting in the formation of interfacial gels; whilst for particles with ζ-potential of ca. -30 mV, spontaneous adsorption occurred, coupled with augmented interfibrillar interactions, yielding stronger and tougher interfacial gels. On the contrary, charge neutralisation of OCNF (ζ-potential values more positive than -30 mV) did not allow spontaneous adsorption of OCNF at the W/O interface. In the case of favourable OCNF adsorption, the interfacial gel was found to embed oil-rich droplets - a spontaneous emulsification process.
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http://dx.doi.org/10.1039/c9sm01551eDOI Listing
January 2020

Mechanically robust cationic cellulose nanofibril 3D scaffolds with tuneable biomimetic porosity for cell culture.

J Mater Chem B 2019 01 30;7(1):53-64. Epub 2018 Nov 30.

Centre for Sustainable Chemical Technologies, University of Bath, Bath, BA2 7AY, UK.

3D foam scaffolds were produced in a "bottom-up" approach from lyophilised cationic cellulose nanofibril (CCNF) dispersions and emulsions (CCNF degree of substitution 23.0 ± 0.9%), using a directional freezing/lyophilisation approach, producing internal architectures ranging from aligned smooth walled micro channels, mimicking vascularised tissue, to pumice-like wall textures, reminiscent of porous bone. The open, highly porous architecture of these biomimetic scaffolds included mesopores within the walls of the channels. A combination of SEM and NMR cryoporometry and relaxometry was used to determine the porosity at different length scales: CCNF foams with aligned channels had an average macropore (channel) size of 35 ± 9 μm and a mesopore (wall) diameter of 26 ± 2 nm, while CCNF foams produced from directional freezing and lyophilisation of Pickering emulsions had mesoporous walls (5 ± 3 μm) in addition to channels (54 ± 20 μm). Glyoxal crosslinking both enhanced robustness and stiffness, giving Young's moduli of 0.45 to 50.75 MPa for CCNF foams with degrees of crosslinking from 0 to 3.04 mol%. Porosity and channels are critical scaffold design elements for transport of nutrients and waste products, as well as O/CO exchange. The viability of MG-63 cells was enhanced on crosslinked, mechanically stiff scaffolds, indicating that these exquisitely structured, yet robust, foams could provide biomaterial scaffolds suitable for industrial applications requiring 3D cell culturing.
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http://dx.doi.org/10.1039/c8tb02482kDOI Listing
January 2019

Alcohol induced gelation of TEMPO-oxidized cellulose nanofibril dispersions.

Soft Matter 2018 Nov;14(45):9243-9249

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

Solvent-induced physical hydrogels of TEMPO-oxidized cellulose nanofibrils (OCNFs) were obtained from aqueous/alcoholic dispersions of fibrils in lower alcohols, namely, methanol, ethanol, 1-propanol and 2-propanol. The sol-gel transition occurs above a critical alcohol concentration of ca. 30 wt% for all alcohols tested. The rheological properties of the hydrogels depend on the nature of the alcohol: for ethanol, 1-propanol and 2-propanol the magnitude of the shear storage modulus follows the alcohol hydrophilicity, whilst methanol produces the weakest gels in the group. Above a second critical concentration, ca. 60 wt% alcohol, phase separation is observed as the gels undergo syneresis. Analysis of small-angle X-ray scattering data shows that the OCNFs may be modelled as rigid rods. In the presence of lower alcohols, attractive interactions between nanofibrils are present and, above the alcohol concentration leading to gelation, an increase of the OCNF cross-section is observed, suggesting alcohol induced aggregation of nanofibrils.
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http://dx.doi.org/10.1039/c8sm01815dDOI Listing
November 2018

Understanding heat driven gelation of anionic cellulose nanofibrils: Combining saturation transfer difference (STD) NMR, small angle X-ray scattering (SAXS) and rheology.

J Colloid Interface Sci 2019 Feb 25;535:205-213. Epub 2018 Sep 25.

Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK. Electronic address:

A novel mechanism of heat-triggered gelation for oxidised cellulose nanofibrils (OCNF) is reported. We demonstrate that a synergistic approach combining rheology, small-angle X-ray scattering (SAXS) and saturation transfer difference NMR (STD NMR) experiments enables a detailed characterisation of gelation at different length scales. OCNF dispersions experience an increase in solid-like behaviour upon heating as evidenced by rheological studies, associated with enhanced interfibrillar interactions measured using SAXS. Interactions result in an increased fibrillar overlap and increased population of confined water molecules monitored by STD NMR. In comparison, cationic cellulose nanofibrils (produced by reaction of cellulose with trimethylglycidylammonium chloride) were found to be heat-unresponsive.
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http://dx.doi.org/10.1016/j.jcis.2018.09.085DOI Listing
February 2019

Surfactant controlled zwitterionic cellulose nanofibril dispersions.

Soft Matter 2018 Oct;14(38):7793-7800

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

Zwitterionic cellulose nanofibrils (ZCNFs) with an isoelectric point of 3.4 were obtained by grafting glycidyltrimethylammonium chloride onto TEMPO/NaBr/NaOCl-oxidised cellulose nanofibrils. The ZCNF aqueous dispersions were characterized via transmission electron microscopy, rheology and small angle neutron scattering, revealing a fibril-bundle structure with pronounced aggregation at pH 7. Surfactants were successfully employed to tune the stability of the ZCNF dispersions. Upon addition of the anionic surfactant, sodium dodecyl sulfate, the ZCNF dispersion shows individualized fibrils due to electrostatic stabilization. In contrast, upon addition of the cationic species dodecyltrimethylammonium bromide, the dispersion undergoes charge neutralization, leading to more pronounced flocculation.
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http://dx.doi.org/10.1039/c8sm00752gDOI Listing
October 2018

Predicting Ligand-Free Cell Attachment on Next-Generation Cellulose-Chitosan Hydrogels.

ACS Omega 2018 Jan 25;3(1):937-945. Epub 2018 Jan 25.

Department of Chemical Engineering, Centre for Sustainable Chemical Technologies, and Department of Chemistry, University of Bath, Bath BA2 7AY, U.K.

There is a growing appreciation that engineered biointerfaces can regulate cell behaviors, or functions. Most systems aim to mimic the cell-friendly extracellular matrix environment and incorporate protein ligands; however, the understanding of how a ligand-free system can achieve this is limited. Cell scaffold materials comprised of interfused chitosan-cellulose hydrogels promote cell attachment in ligand-free systems, and we demonstrate the role of cellulose molecular weight, MW, and chitosan content and MW in controlling material properties and thus regulating cell attachment. Semi-interpenetrating network (SIPN) gels, generated from cellulose/ionic liquid/cosolvent solutions, using chitosan solutions as phase inversion solvents, were stable and obviated the need for chemical coupling. Interface properties, including surface zeta-potential, dielectric constant, surface roughness, and shear modulus, were modified by varying the chitosan degree of polymerization and solution concentration, as well as the source of cellulose, creating a family of cellulose-chitosan SIPN materials. These features, in turn, affect cell attachment onto the hydrogels and the utility of this ligand-free approach is extended by forecasting cell attachment using regression modeling to isolate the effects of individual parameters in an initially complex system. We demonstrate that increasing the charge density, and/or shear modulus, of the hydrogel results in increased cell attachment.
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http://dx.doi.org/10.1021/acsomega.7b01583DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6045362PMC
January 2018

TEMPO-oxidised cellulose nanofibrils; probing the mechanisms of gelation via small angle X-ray scattering.

Phys Chem Chem Phys 2018 Jun;20(23):16012-16020

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

The structure of dispersions of TEMPO-oxidised cellulose nanofibrils (OCNF), at various concentrations, in water and in NaCl aqueous solutions, was probed using small angle X-ray scattering (SAXS). OCNF are modelled as rod-like particles with an elliptical cross-section of 10 nm and a length greater than 100 nm. As OCNF concentration increases above 1.5 wt%, repulsive interactions between fibrils are evidenced, modelled by the interaction parameter νRPA > 0. This corresponds to gel-like behaviour, where G' > G'' and the storage modulus, G', shows weak frequency dependence. Hydrogels can also be formed at OCNF concentration of 1 wt% in 0.1 M NaCl(aq). SAXS patterns shows an increase of the intensity at low angle that is modelled by attractive interactions (νRPA < 0) between OCNF, arising from the screening of the surface charge of the fibrils. Results are supported by ζ potential and cryo-TEM measurements.
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http://dx.doi.org/10.1039/c8cp00355fDOI Listing
June 2018

Recent Advances in Modified Cellulose for Tissue Culture Applications.

Molecules 2018 Mar 14;23(3). Epub 2018 Mar 14.

Centre for Sustainable Chemical Technologies, University of Bath, Bath BA2 7AY, UK.

Tissue engineering is a rapidly advancing field in regenerative medicine, with much research directed towards the production of new biomaterial scaffolds with tailored properties to generate functional tissue for specific applications. Recently, principles of sustainability, eco-efficiency and green chemistry have begun to guide the development of a new generation of materials, such as cellulose, as an alternative to conventional polymers based on conversion of fossil carbon (e.g., oil) and finding technologies to reduce the use of animal and human derived biomolecules (e.g., foetal bovine serum). Much of this focus on cellulose is due to it possessing the necessary properties for tissue engineering scaffolds, including biocompatibility, and the relative ease with which its characteristics can be tuned through chemical modification to adjust mechanical properties and to introduce various surface modifications. In addition, the sustainability of producing and manufacturing materials from cellulose, as well as its modest cost, makes cellulose an economically viable feedstock. This review focusses specifically on the use of modified cellulose materials for tissue culturing applications. We will investigate recent techniques used to promote scaffold function through physical, biochemical and chemical scaffold modifications, and describe how these have been utilised to reduce reliance on the addition of matrix ligands such as foetal bovine serum.
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http://dx.doi.org/10.3390/molecules23030654DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6017284PMC
March 2018

Modulating cell response on cellulose surfaces; tunable attachment and scaffold mechanics.

Cellulose (Lond) 2018 19;25(2):925-940. Epub 2017 Dec 19.

1Centre for Sustainable Chemical Technologies, University of Bath, Bath, BA2 7AY UK.

Combining surface chemical modification of cellulose to introduce positively charged trimethylammonium groups by reaction with glycidyltrimethylammonium chloride (GTMAC) allowed for direct attachment of mammalian MG-63 cells, without addition of protein modifiers, or ligands. Very small increases in the surface charge resulted in significant increases in cell attachment: at a degree of substitution (DS) of only 1.4%, MG-63 cell attachment was > 90% compared to tissue culture plastic, whereas minimal attachment occurred on unmodified cellulose. Cell attachment plateaued above DS of ca. 1.85% reflecting a similar trend in surface charge, as determined from ζ-potential measurements and capacitance coupling (electric force microscopy). Cellulose film stiffness was modulated by cross linking with glyoxal (0.3-2.6% degree of crosslinking) to produce a range of materials with surface shear moduli from 76 to 448 kPa (measured using atomic force microscopy). Cell morphology on these materials could be regulated by tuning the stiffness of the scaffolds. Thus, we report tailored functionalised biomaterials based on cationic cellulose that can be tuned through surface reaction and glyoxal crosslinkin+g, to influence the attachment and morphology of cells. These scaffolds are the first steps towards materials designed to support cells and to regulate cell morphology on implanted biomaterials using only scaffold and cells, i.e. without added adhesion promoters.
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http://dx.doi.org/10.1007/s10570-017-1612-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6954015PMC
December 2017

Unravelling cationic cellulose nanofibril hydrogel structure: NMR spectroscopy and small angle neutron scattering analyses.

Soft Matter 2018 01;14(2):255-263

Centre for Sustainable Chemical Technologies, University of Bath, Bath BA2 7AY, UK.

Stiff, elastic, viscous shear thinning aqueous gels are formed upon dispersion of low weight percent concentrations of cationically modified cellulose nanofibrils (CCNF) in water. CCNF hydrogels produced from cellulose modified with glycidyltrimethylammonium chloride, with degree of substitution (DS) in the range 10.6(3)-23.0(9)%, were characterised using NMR spectroscopy, rheology and small angle neutron scattering (SANS) to probe the fundamental form and dimensions of the CCNF and to reveal interfibrillar interactions leading to gelation. As DS increased CCNF became more rigid as evidenced by longer Kuhn lengths, 18-30 nm, derived from fitting of SANS data to an elliptical cross-section, cylinder model. Furthermore, apparent changes in CCNF cross-section dimensions suggested an "unravelling" of initially twisted fibrils into more flattened ribbon-like forms. Increases in elastic modulus (7.9-62.5 Pa) were detected with increased DS and H solution-state NMR T relaxation times of the introduced surface -N(CH) groups were found to be longer in hydrogels with lower DS, reflecting the greater flexibility of the low DS CCNF. This is the first time that such correlation between DS and fibrillar form and stiffness has been reported for these potentially useful rheology modifiers derived from renewable cellulose.
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http://dx.doi.org/10.1039/c7sm02113eDOI Listing
January 2018

A screen-printed paper microbial fuel cell biosensor for detection of toxic compounds in water.

Biosens Bioelectron 2018 Apr 6;102:49-56. Epub 2017 Nov 6.

Department of Chemical Engineering, University of Bath, Bath BA2 7AY, United Kingdom. Electronic address:

Access to safe drinking water is a human right, crucial to combat inequalities, reduce poverty and allow sustainable development. In many areas of the world, however, this right is not guaranteed, in part because of the lack of easily deployable diagnostic tools. Low-cost and simple methods to test water supplies onsite can protect vulnerable communities from the impact of contaminants in drinking water. Ideally such devices would also be easy to dispose of so as to leave no trace, or have a detrimental effect on the environment. To this aim, we here report the first paper microbial fuel cell (pMFC) fabricated by screen-printing biodegradable carbon-based electrodes onto a single sheet of paper, and demonstrate its use as a shock sensor for bioactive compounds (e.g. formaldehyde) in water. We also show a simple route to enhance the sensor performance by folding back-to-back two pMFCs electrically connected in parallel. This promising proof of concept work can lead to a revolutionizing way of testing water at point of use, which is not only green, easy-to-operate and rapid, but is also affordable to all.
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http://dx.doi.org/10.1016/j.bios.2017.11.018DOI Listing
April 2018

Cellulose ionics: switching ionic diode responses by surface charge in reconstituted cellulose films.

Analyst 2017 Sep;142(19):3707-3714

Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.

Cellulose films as well as chitosan-modified cellulose films of approximately 5 μm thickness, reconstituted from ionic liquid media onto a poly(ethylene-terephthalate) (PET, 6 μm thickness) film with a 5, 10, 20, or 40 μm diameter laser-drilled microhole, show significant current rectification in aqueous NaCl. Reconstituted α-cellulose films provide "cationic diodes" (due to predominant cation conductivity) whereas chitosan-doped cellulose shows "anionic diode" effects (due to predominant anion conductivity). The current rectification, or "ionic diode" behaviour, is investigated as a function of NaCl concentration, pH, microhole diameter, and molecular weight of the chitosan dopant. Future applications are envisaged exploiting the surface charge induced switching of diode currents for signal amplification in sensing.
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http://dx.doi.org/10.1039/c7an00918fDOI Listing
September 2017

Combining random walk and regression models to understand solvation in multi-component solvent systems.

Phys Chem Chem Phys 2017 Jul 28;19(27):17805-17815. Epub 2017 Jun 28.

Department of Chemistry, University of Bath, Claverton Down, Bath, BA2 7AY, UK.

Polysaccharides, such as cellulose, are often processed by dissolution in solvent mixtures, e.g. an ionic liquid (IL) combined with a dipolar aprotic co-solvent (CS) that the polymer does not dissolve in. A multi-walker, discrete-time, discrete-space 1-dimensional random walk can be applied to model solvation of a polymer in a multi-component solvent mixture. The number of IL pairs in a solvent mixture and the number of solvent shells formable, x, is associated with n, the model time-step, and N, the number of random walkers. The mean number of distinct sites visited is proportional to the amount of polymer soluble in a solution. By also fitting a polynomial regression model to the data, we can associate the random walk terms with chemical interactions between components and probe where the system deviates from a 1-D random walk. The 'frustration' between solvents shells is given as ln x in the random walk model and as a negative IL:IL interaction term in the regression model. This frustration appears in regime II of the random walk model (high volume fractions of IL) where walkers interfere with each other, and the system tends to its limiting behaviour. In the low concentration regime, (regime I) the solvent shells do not interact, and the system depends only on IL and CS terms. In both models (and both regimes), the system is almost entirely controlled by the volume available to solvation shells, and thus is a counting/space-filling problem, where the molar volume of the CS is important. Small deviations are observed when there is an IL-CS interaction. The use of two models, built on separate approaches, confirm these findings, demonstrating that this is a real effect and offering a route to identifying such systems. Specifically, the majority of CSs - such as dimethylformide - follow the random walk model, whilst 1-methylimidazole, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone and tetramethylurea offer a CS-mediated improvement and propylene carbonate results in a CS-mediated hindrance. It is shown here that systems, which are very complex at a molecular level, may, nonetheless, be effectively modelled as a simple random walk in phase-space. The 1-D random walk model allows prediction of the ability of solvent mixtures to dissolve cellulose based on only two dissolution measurements (one in neat IL) and molar volume.
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http://dx.doi.org/10.1039/c7cp02873cDOI Listing
July 2017

Surface modified cellulose scaffolds for tissue engineering.

Cellulose (Lond) 2017 9;24(1):253-267. Epub 2016 Nov 9.

1Centre for Sustainable Chemical Technologies, University of Bath, Claverton Down, Bath, BA2 7AY UK.

We report the ability of cellulose to support cells without the use of matrix ligands on the surface of the material, thus creating a two-component system for tissue engineering of cells and materials. Sheets of bacterial cellulose, grown from a culture medium containing organism were chemically modified with glycidyltrimethylammonium chloride or by oxidation with sodium hypochlorite in the presence of sodium bromide and 2,2,6,6-tetramethylpipiridine 1-oxyl radical to introduce a positive, or negative, charge, respectively. This modification process did not degrade the mechanical properties of the bulk material, but grafting of a positively charged moiety to the cellulose surface (cationic cellulose) increased cell attachment by 70% compared to unmodified cellulose, while negatively charged, oxidised cellulose films (anionic cellulose), showed low levels of cell attachment comparable to those seen for unmodified cellulose. Only a minimal level of cationic surface derivitisation (ca 3% degree of substitution) was required for increased cell attachment and mediating proteins were required. Cell adhesion studies exhibited the same trends as the attachment studies, while the mean cell area and aspect ratio was highest on the cationic surfaces. Overall, we demonstrated the utility of positively charged bacterial cellulose in tissue engineering in the absence of proteins for cell attachment.
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http://dx.doi.org/10.1007/s10570-016-1111-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7175690PMC
November 2016

Ibuprofen delivery into and through the skin from novel oxidized cellulose-based gels and conventional topical formulations.

Int J Pharm 2016 Nov;514(1):238-243

Centre for Sustainable Chemical Technologies, and Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.

The delivery of ibuprofen into and through the skin from novel formulations containing TEMPO-oxidized cellulose nanofibril-based (TOCN) gels was compared to that from two conventional and commercially available products. The gels were evaluated in-vitro (using both silicone membranes, and pig skin) and in-vivo in human volunteers. All gels showed consistent behaviour in a standard in vitro release test. The stratum corneum (SC) uptake and skin penetration of ibuprofen in vitro from the novel gels and the marketed formulations were generally comparable even though the drug loading in the TOCN-based vehicles was only 20% of that in the 'reference' products. In vivo, the new gels appeared to enhance drug uptake into the SC following a relatively short application time, again matching the performance of the commercial formulations. Taken together, the results of this research provide proof-of-concept for the idea that the sustainable, oxidized cellulose gels may provide more efficient drug delivery into and through the skin, thereby improving drug utilisation and reducing potential adverse effects when such formulations are applied chronically over large skin areas.
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http://dx.doi.org/10.1016/j.ijpharm.2016.09.028DOI Listing
November 2016

A "by-productless" cellulose foaming agent for use in imidazolium ionic liquids.

Chem Commun (Camb) 2011 Mar 18;47(10):2970-2. Epub 2011 Jan 18.

Unilever Home and Personal Care R&D Port Sunlight, Quarry Road East, Port Sunlight, CH63 3JW, UK.

Cellulose foams, or sponges, are produced from solutions in ionic liquids by the aqueous acid mediated decomposition of 1-alkyl-3-methylimidazolium-2-carboxylates, where the alkyl group and acid may be selected such that the by-product is the ionic liquid solvent: a by-productless foaming.
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http://dx.doi.org/10.1039/c0cc05057aDOI Listing
March 2011

Synthesis and biological activity of Delta-5,6-norcantharimides: importance of the 5,6-bridge.

Eur J Med Chem 2010 May 14;45(5):1717-23. Epub 2010 Jan 14.

Centre for Green Chemistry, Monash University, Wellington Road, Clayton, Victoria 3800, Australia.

Cantharidin (1) and norcantharidin (2) are potent protein phosphatase 1 and 2A inhibitors that also display high levels of anticancer activity against a broad range of tumor cells lines. Surprisingly, Delta-5,6-ethyl norcantharidin (3, cis-tetrahydrofurano[3,4-c]furan-1,3-dione) displays neither phosphatase inhibition nor anticancer activity. This suggests that the 5,6-ethyl bridge is pivotal to both anti-cancer and protein phosphatase activity. Additionally bioisosteric replacement of the ethereal oxygen has no effect on biological activity nor does modification of the anhydride moiety. Unlike the parent norcantharidin, anhydride ring opening has no effect on either protein phosphatase inhibition or anti-cancer activity. Additionally, this work highlights the discovery of the octyl substituted, cis-5-benzyl-2-hexyltetrahydro-2H,3aH-pyrrolo[3,4-c]pyrrole-1,3-dione, 9p, and the octyl substituted, cis-octyltetrahydro-5H-furo[3,4-c]pyrrole-4,6-dione, 8p, as two new cytotoxic agents which are equipotent (9p) with, and more potent (8p) than norcantharidin.
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http://dx.doi.org/10.1016/j.ejmech.2010.01.004DOI Listing
May 2010

Partial exchange of Fe(III) montmorillonite with hexadecyltrimethylammonium cation increases catalytic activity for hydrophobic substrates.

Langmuir 2010 Mar;26(6):4258-65

Centre for Green Chemistry, Monash University, Clayton, Victoria 3800, Australia.

Fe(III) montmorillonite clay that was partially exchanged with hexadecyltrimethylammonium (HDTMA(+)) cations achieved increased catalytic activity for the oxidative coupling of hydrophobic organic substrates. A series of mixed-cation organoclays were produced, where the organic cation content ranged from 6 to 50% relative to the cation-exchange capacity (CEC) of the clay, and were tested for catalytic activity using different Fe(III)-mediated oxidative coupling reactions. Enhanced catalytic activity by Fe(3+)/HDTMA(+) montmorillonite for coupling hydrophobic substrates was observed, with maximum catalytic activity in the oxidative coupling of 2-naphthol observed at 6% HDTMA(+) coverage. However, maximum catalytic activity with a more hydrophobic substrate, anthrone, was achieved with 50% HDTMA(+) coverage, indicating that matching levels of organic modification to substrate hydrophobicity improves catalytic activity. The organization of the organic cations at the clay surfaces proved to be heterogeneous, as determined by scanning transmission X-ray microscopy (STXM) and powder X-ray diffraction. Results from molecular dynamics simulations supported the heterogeneous nature of the catalysts but also pointed toward large regions within the interlayers that may be filled with nonreactive hydrated Fe oxides resulting from the organic cation treatment. The exchangeable Fe content of the organic treated clays, as determined by AAS and ICP measurements, was observed to be higher than expected relative to that of Fe-saturated clay, substantiating this hypothesis. These findings have implications for the development of substrate-specific clay catalysts, where the composition and configuration of exchangeable cations can be matched to a particular substrate or reaction.
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http://dx.doi.org/10.1021/la9033047DOI Listing
March 2010
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