Co-reporter:Lewis D. Blackman, Spyridon Varlas, Maria C. Arno, Alice Fayter, Matthew I. Gibson, and Rachel K. O’Reilly
ACS Macro Letters November 21, 2017 Volume 6(Issue 11) pp:1263-1263
Publication Date(Web):October 31, 2017
DOI:10.1021/acsmacrolett.7b00725
Enzyme loading of polymersomes requires permeability to enable them to interact with the external environment, typically requiring addition of complex functionality to enable porosity. Herein, we describe a synthetic route toward intrinsically permeable polymersomes loaded with functional proteins using initiator-free visible light-mediated polymerization-induced self-assembly (photo-PISA) under mild, aqueous conditions using a commercial monomer. Compartmentalization and retention of protein functionality was demonstrated using green fluorescent protein as a macromolecular chromophore. Catalytic enzyme-loaded vesicles using horseradish peroxidase and glucose oxidase were also prepared and the permeability of the membrane toward their small molecule substrates was revealed for the first time. Finally, the interaction of the compartmentalized enzymes between separate vesicles was validated by means of an enzymatic cascade reaction. These findings have a broad scope as the methodology could be applied for the encapsulation of a large range of macromolecules for advancements in the fields of nanotechnology, biomimicry, and nanomedicine.
Co-reporter:Daniel E. Mitchell, Guy Clarkson, David J. Fox, Rebecca A. Vipond, Peter Scott, and Matthew I. Gibson
Journal of the American Chemical Society July 26, 2017 Volume 139(Issue 29) pp:9835-9835
Publication Date(Web):July 17, 2017
DOI:10.1021/jacs.7b05822
Antifreeze proteins are produced by extremophile species to control ice formation and growth, and they have potential applications in many fields. There are few examples of synthetic materials which can reproduce their potent ice recrystallization inhibition property. We report that self-assembled enantiomerically pure, amphipathic metallohelicies inhibited ice growth at just 20 μM. Structure–property relationships and calculations support the hypothesis that amphipathicity is the key motif for activity. This opens up a new field of metallo-organic antifreeze protein mimetics and provides insight into the origins of ice-growth inhibition.
Co-reporter:Guillaume Hedir, Christopher Stubbs, Phillip Aston, Andrew P. Dove, and Matthew I. Gibson
ACS Macro Letters December 19, 2017 Volume 6(Issue 12) pp:1404-1404
Publication Date(Web):December 1, 2017
DOI:10.1021/acsmacrolett.7b00905
Poly(vinyl alcohol) (PVA) is the most active synthetic mimic of antifreeze proteins and has extremely high ice recrystallization inhibition (IRI) activity. Addition of PVA to cellular cryopreservation solutions increases the number of recovered viable cells due to its potent IRI, but it is intrinsically nondegradable in vivo. Here we report the synthesis, characterization, and IRI activity of PVA containing degradable ester linkages. Vinyl chloroacetate (VClAc) was copolymerized with 2-methylene-1,3-dioxepane (MDO) which undergoes radical ring-opening polymerization to install main-chain ester units. The use of the chloroacetate monomer enabled selective deacetylation with retention of esters within the polymer backbone. Quantitative IRI assays revealed that the MDO content had to be finely tuned to retain IRI activity, with higher loadings (24 mol %) resulting in complete loss of IRI activity. These degradable materials will help translate PVA, which is nontoxic and biocompatible, into a range of biomedical applications.
Co-reporter:Christopher Stubbs, Julia Lipecki, and Matthew I. Gibson
Biomacromolecules 2017 Volume 18(Issue 1) pp:
Publication Date(Web):December 12, 2016
DOI:10.1021/acs.biomac.6b01691
Antifreeze proteins from polar fish species are potent ice recrystallization inhibitors (IRIs) effectively stopping all ice growth. Additives that have IRI activity have been shown to enhance cellular cryopreservation with potential to improve the distribution of donor cells and tissue. Polyampholytes, polymers with both anionic and cationic side chains, are a rapidly emerging class of polymer cryoprotectants, but their mode of action and the structural features essential for activity are not clear. Here regioregular polyampholytes are synthesized from maleic anhydride copolymers to enable stoichiometric installation of the charged groups, ensuring regioregularity, which is not possible using conventional random copolymerization. A modular synthetic strategy is employed to enable the backbone and side chain hydrophobicity to be varied, with side chain hydrophobicity found to have a profound effect on the IRI activity. The activity of the regioregular polymers was found to be superior to those derived from a standard random copolymerization with statistical incorporation of monomers, demonstrating that sequence composition is crucial to the activity of IRI active polyampholytes.
Co-reporter:Sangho Won;Sarah-Jane Richards;Marc Walker
Nanoscale Horizons (2016-Present) 2017 vol. 2(Issue 2) pp:106-109
Publication Date(Web):2017/02/27
DOI:10.1039/C6NH00202A
Nature dynamically controls carbohydrate expression on cells rather than static presentation. Here we report synthetic glycosylated nanoparticles that contain polymeric ‘gates’ to enable external control (via temperature changes) of glycan surface expression, as an alternative to enzymatic control in nature. This approach offers a new dynamic multivalent scaffold for glycan recognition.
Co-reporter:Caroline I. Biggs;Christopher Packer;Steven Hindmarsh;Marc Walker;Neil R. Wilson;Jonathan P. Rourke
Physical Chemistry Chemical Physics 2017 vol. 19(Issue 33) pp:21929-21932
Publication Date(Web):2017/08/23
DOI:10.1039/C7CP03219F
Base-washed graphene-oxide which has been sequentially-modified by thiol–epoxy chemistry, results in materials with ice-nucleation activity. The role of hydro-philic/phobic grafts and polymers was evaluated with the most potent functioning at just 0.25 wt%. These 2-D hybrid materials may find use in cryopreservation and fundamental studies on ice formation.
Co-reporter:L. D. Blackman;M. I. Gibson;R. K. O'Reilly
Polymer Chemistry (2010-Present) 2017 vol. 8(Issue 1) pp:233-244
Publication Date(Web):2016/12/20
DOI:10.1039/C6PY01191H
Self-assembled thermoresponsive polymers in aqueous solution have great potential as smart, switchable materials for use in biomedical applications. In recent years, attention has turned to the reversibility of these polymers’ thermal transitions, which has led to debate over what factors influence discrepancies in the transition temperature when heating the system compared to the temperature obtained when cooling the system, known as the thermal hysteresis. Herein, we synthesize micelles with tunable aggregation numbers (Nagg) whose cores contain poly(n-butyl acrylate-co-N,N-dimethylacrylamide) (p(nBA-co-DMA)) and four different thermoresponsive corona blocks, namely poly(N-isopropylacrylamide) (pNIPAM), poly(N,N-diethylacrylamide) (pDEAm), poly(diethylene glycol monomethyl ether methacrylate) (pDEGMA) and poly(oligo(ethylene glycol) monomethyl ether methacrylate) (pOEGMA). By studying their thermoresponsive behavior, we elucidate the effects of changing numerous important characteristics both in the thermoresponsive chain chemistry and architecture, and in the structure of their self-assemblies. Our findings demonstrate large deviations in the reversibility between the self-assemblies and the corresponding thermoresponsive homopolymers; specifically we find that micelles whose corona consist of polymers with a brush-like architecture (pDEGMA and pOEGMA) exhibit irreversible phase transitions at a critical chain density. These results lead to a deeper understanding of stimuli-responsive self-assemblies and demonstrate the potential of tunable Nagg micelles for uncovering structure–property relationships in responsive polymer systems.
Co-reporter:Lewis D. Blackman;Kay E. B. Doncom;Rachel K. O'Reilly
Polymer Chemistry (2010-Present) 2017 vol. 8(Issue 18) pp:2860-2871
Publication Date(Web):2017/05/09
DOI:10.1039/C7PY00407A
Polymerization-induced self-assembly (PISA) is an emerging industrially relevant technology, which allows the preparation of defined and predictable polymer self-assemblies with a wide range of morphologies. In recent years, interest has turned to photoinitiated PISA processes, which show markedly accelerated reaction kinetics and milder conditions, thereby making it an attractive alternative to thermally initiated PISA. Herein, we attempt to elucidate the differences between these two initiation methods using isothermally derived phase diagrams of a well-documented poly(ethylene glycol)-b-(2-hydroxypropyl methacrylate) (PEG-b-HPMA) PISA system. By studying the influence of the intensity of the light source used, as well as an investigation into the thermodynamically favorable morphologies, the factors dictating differences in the obtained morphologies when comparing photo- and thermally initiated PISA were explored. Our findings indicate that differences in a combination of both reaction kinetics and end group fidelity led to the observed discrepencies between the two techniques. We find that the loss of the end group in photoinitiated PISA drives the formation of higher order structures and that a morphological transition from worms to unilamellar vesicles could be induced by extended periods of light and heat irradiation. Our findings demonstrate that PISA of identical block copolymers by the two different initiation methods can lead to structures that are both chemically and morphologically distinct.
Co-reporter:Ben Graham;Trisha L. Bailey;Joseph R. J. Healey;Dr. Moreno Marcellini;Dr. Sylvain Deville; Matthew I. Gibson
Angewandte Chemie 2017 Volume 129(Issue 50) pp:16157-16160
Publication Date(Web):2017/12/11
DOI:10.1002/ange.201706703
AbstractTissue engineering, gene therapy, drug screening, and emerging regenerative medicine therapies are fundamentally reliant on high-quality adherent cell culture, but current methods to cryopreserve cells in this format can give low cell yields and require large volumes of solvent “antifreezes”. Herein, we report polyproline as a minimum (bio)synthetic mimic of antifreeze proteins that is accessible by solution, solid-phase, and recombinant methods. We demonstrate that polyproline has ice recrystallisation inhibition activity linked to its amphipathic helix and that it enhances the DMSO cryopreservation of adherent cell lines. Polyproline may be a versatile additive in the emerging field of macromolecular cryoprotectants.
Co-reporter:
Journal of Polymer Science Part A: Polymer Chemistry 2017 Volume 55(Issue 7) pp:1200-1208
Publication Date(Web):2017/04/01
DOI:10.1002/pola.28481
ABSTRACTCarbohydrates dictate many biological processes including infection by pathogens. Glycosylated polymers and nanomaterials which have increased affinity due to the cluster glycoside effect, are therefore useful tools to probe function, but also as prophylactic therapies or diagnostic tools. Here, the effect of polymer structure on the coating of gold nanoparticles is studied in the context of grafting density, buffer stability, and in a lectin binding assay. RAFT polymerization is used to generate poly(oligoethyleneglycol methacrylates) and poly(N-vinylpyrrolidones) with a thiol end-group for subsequent immobilization onto the gold. It is observed that poly(oligoethylene glycol methacrylates), despite being widely used particle coatings, lead to low grafting densities which in turn resulted in lower stability in biological buffers. A depression of the cloud point upon nanoparticle immobilization is also seen, which might compromise performance. In comparison poly(vinylpyrrolidones) resulted in stable particles with higher grafting densities due to the compact size of each monomer unit. The higher grafting density also enabled an increase in the number of carbohydrates which can be installed per nanoparticle at the chain ends, and gave increased binding in a lectin recognition assay. These results will guide the development of new nanoparticle biosensors with enhanced specificity, affinity, and stability. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 55, 1200–1208
Co-reporter:Sarah-Jane Richards, Lucienne Otten and Matthew I. Gibson
Journal of Materials Chemistry A 2016 vol. 4(Issue 18) pp:3046-3053
Publication Date(Web):27 Oct 2015
DOI:10.1039/C5TB01994J
Glycan/lectin interactions drive a wide range of recognition and signal transduction processes within nature. However, their measurement is complicated or limited by the analytical tools available. Most technologies require fluorescently labelled proteins (e.g. microarrays) or expensive infrastructure (such as surface plasmon resonance). This also limits their application in biosensing, especially for low-resource settings, where detection of pathogens based on glycan binding could speed up diagnosis. Here we employ a library-oriented approach to immobilise a range of monosaccharides onto polymer-stabilised gold nanoparticles to enable rapid and high-throughput evaluation of their binding specificities with a panel of lectins. The red to blue colour shift upon gold nanoparticle aggregation is used as the output, removing the need for labelled protein, enabling compatibility with 96-well microplates. Furthermore, we demonstrate the use of a flatbed scanner (or digital camera) to extract biophysical data, ensuring that only minimal resources are required. Finally, linear discriminant analysis is employed to demonstrate how the glyconanoparticles can be applied as a multiplexed biosensor capable of identifying pathogenic lectins without the need for any infrastructure and overcoming some of the issues of lectin promiscuity.
Co-reporter:Daniel J. Phillips, Thomas R. Congdon and Matthew I. Gibson
Polymer Chemistry 2016 vol. 7(Issue 9) pp:1701-1704
Publication Date(Web):29 Jan 2016
DOI:10.1039/C5PY01948F
Antifreeze (glyco)proteins (AF(G)Ps) have potent ice recrystallisation inhibition (IRI) activity – a desirable phenomenon in applications such as cryopreservation, frozen food and more. In Nature AF(G)P activity is regulated by protein expression levels in response to an environmental stimulus; temperature. However, this level of regulation is not possible in synthetic systems. Here, a synthetic macromolecular mimic is introduced, using supramolecular assembly to regulate activity. Catechol-terminated poly(vinyl alcohol) was synthesised by RAFT polymerization. Upon addition of Fe3+, larger supramolecular star polymers form by assembly with two or three catechols. This increase in molecular weight effectively ‘switches on’ the IRI activity and is the first example of external control over the function of AFP mimetics. This provides a simple but elegant solution to the challenge of external control of AFP-mimetic function.
Co-reporter:Lucienne Otten, Elizabeth Fullam and Matthew I. Gibson
Molecular BioSystems 2016 vol. 12(Issue 2) pp:341-344
Publication Date(Web):01 Dec 2015
DOI:10.1039/C5MB00720H
Antibiotic resistance is a global health concern meaning there is an urgent need for new treatments and diagnostics. Here glycosylated surfaces are used to profile the binding patterns of a range of Gram-negative, Gram-positive and mycobacteria. This enables the creation of ‘barcodes’ to enable identification and discrimination between the strains, which could not be achieved by single-point glycan binding and offers a new concept in bacteria detection.
Co-reporter:Caroline I. Biggs, Marc Walker, and Matthew I. Gibson
Biomacromolecules 2016 Volume 17(Issue 8) pp:
Publication Date(Web):July 13, 2016
DOI:10.1021/acs.biomac.6b00662
Surface-grafted polymers have been widely applied to modulate biological interfaces and introduce additional functionality. Polymers derived from reversible addition–fragmentation transfer (RAFT) polymerization have a masked thiol at the ω-chain end providing an anchor point for conjugation and in particular displays high affinity for gold surfaces (both flat and particulate). In this work, we report the direct grafting of RAFTed polymers by a “thiol–ene click” (Michael addition) onto glass substrates rather than gold, which provides a more versatile surface for subsequent array-based applications but retains the simplicity. The immobilization of two thermoresponsive polymers are studied here, poly[oligo(ethylene glycol) methyl ether methacrylate] (pOEGMA) and poly(N-isopropylacrylamide) (pNIPAM). Using a range of surface analysis techniques the grafting efficiency was compared to thiol–gold and was quantitatively compared to the gold alternative using quartz crystal microbalance. It is shown that this method gives easy access to grafted polymer surfaces with pNIPAM resulting in significantly increased surface coverage compared to pOEGMA. The nonfouling (protein resistance) character of these surfaces is also demonstrated.
Co-reporter:Thomas R. Congdon, Rebecca Notman, and Matthew I. Gibson
Biomacromolecules 2016 Volume 17(Issue 9) pp:3033
Publication Date(Web):July 31, 2016
DOI:10.1021/acs.biomac.6b00915
Antifreeze (glyco) proteins are produced by many cold-acclimatized species to enable them to survive subzero temperatures. These proteins have multiple macroscopic effects on ice crystal growth which makes them appealing for low-temperature applications—from cellular cryopreservation to food storage. Poly(vinyl alcohol) has remarkable ice recrystallization inhibition activity, but its mode of action is uncertain as is the extent at which it can be incorporated into other high-order structures. Here the synthesis and characterization of well-defined block copolymers containing poly(vinyl alcohol) and poly(vinylpyrrolidone) by RAFT/MADIX polymerization is reported, as new antifreeze protein mimetics. The effect of adding a large second hydrophilic block is studied across a range of compositions, and it is found to be a passive component in ice recrystallization inhibition assays, enabling retention of all activity. In the extreme case, a block copolymer with only 10% poly(vinyl alcohol) was found to retain all activity, where statistical copolymers of PVA lose all activity with very minor changes to composition. These findings present a new method to increase the complexity of antifreeze protein mimetic materials, while retaining activity, and also to help understand the underlying mechanisms of action.
Co-reporter:Daniel E. Mitchell;Joseph R. Lovett;Dr. Steven P. Armes;Dr. Matthew I. Gibson
Angewandte Chemie 2016 Volume 128( Issue 8) pp:2851-2854
Publication Date(Web):
DOI:10.1002/ange.201511454
Abstract
The first fully synthetic polymer-based approach for red-blood-cell cryopreservation without the need for any (toxic) organic solvents is reported. Highly hydroxylated block copolymer worms are shown to be a suitable replacement for hydroxyethyl starch as a extracellular matrix for red blood cells. When used alone, the worms are not a particularly effective preservative. However, when combined with poly(vinyl alcohol), a known ice-recrystallization inhibitor, a remarkable additive cryopreservative effect is observed that matches the performance of hydroxyethyl starch. Moreover, these block copolymer worms enable post-thaw gelation by simply warming to 20 °C. This approach offers a new solution for both the storage and transport of red blood cells and also a convenient matrix for subsequent 3D cell cultures.
Co-reporter:Daniel E. Mitchell;Joseph R. Lovett;Dr. Steven P. Armes;Dr. Matthew I. Gibson
Angewandte Chemie International Edition 2016 Volume 55( Issue 8) pp:2801-2804
Publication Date(Web):
DOI:10.1002/anie.201511454
Abstract
The first fully synthetic polymer-based approach for red-blood-cell cryopreservation without the need for any (toxic) organic solvents is reported. Highly hydroxylated block copolymer worms are shown to be a suitable replacement for hydroxyethyl starch as a extracellular matrix for red blood cells. When used alone, the worms are not a particularly effective preservative. However, when combined with poly(vinyl alcohol), a known ice-recrystallization inhibitor, a remarkable additive cryopreservative effect is observed that matches the performance of hydroxyethyl starch. Moreover, these block copolymer worms enable post-thaw gelation by simply warming to 20 °C. This approach offers a new solution for both the storage and transport of red blood cells and also a convenient matrix for subsequent 3D cell cultures.
Co-reporter:Daniel J. Phillips, Gemma-Louise Davies and Matthew I. Gibson
Journal of Materials Chemistry A 2015 vol. 3(Issue 2) pp:270-275
Publication Date(Web):07 Nov 2014
DOI:10.1039/C4TB01501K
Inspired by nature's exploitation of the 1,2-dihydroxybenzene unit (or catechol) in mammalian and bacterial siderophores, we report the first example of a nanoparticle sensing system that utilises the strong catechol–Fe3+ binding motif to trigger nanoparticle aggregation, promoting a powerful optical response. Gold nanoparticles are functionalised with RAFT polymerisation-prepared water-soluble poly(N-hydroxyethyl acrylamide) containing a catechol moiety at the α-chain-end. A strong red-to-purple colorimetric response occurs in the presence of Fe3+ at serum concentrations (8–25 μM) in saline solution. Sodium chloride is critical in generating a strong optical output, as is the length of polymer used to coat the AuNPs. This behaviour is also demonstrated to be selective for Fe3+ over a host of other biologically relevant ions.
Co-reporter:Daniel E. Mitchell, Neil R. Cameron and Matthew I. Gibson
Chemical Communications 2015 vol. 51(Issue 65) pp:12977-12980
Publication Date(Web):08 Jul 2015
DOI:10.1039/C5CC04647E
Antifreeze (glyco) proteins AF(G)Ps are potent ice recrystallization inhibitors, which is a desirable property to enhance cryopreservation of donor tissue/cells. Here we present the rational synthesis of a new, biomimetic, ice-recrystallization inhibiting polymer derived from a cheap commodity polymer, based on an ampholyte structure. The polymer is used to enhance the cryopreservation of red blood cells, demonstrating a macromolecular solution to tissue storage.
Co-reporter:Daniel J. Phillips and Matthew I. Gibson
Polymer Chemistry 2015 vol. 6(Issue 7) pp:1033-1043
Publication Date(Web):05 Dec 2014
DOI:10.1039/C4PY01539H
Responsive polymers have found diverse application across polymer, biomaterials, medical, sensing and engineering fields. Despite many years of study, this has focussed mainly on those polymers which undergo thermally-induced changes – either a lower or upper critical solution temperature. To rival the adaptability of Nature's macromolecules, polymers must respond in a ‘smarter’ way to other triggers such as enzymes, biochemical gradients, ion concentration or metabolites, to name a few. Here we review the concept of ‘isothermal’ responses where core thermoresponsive polymers are chemically engineered such that they undergo their useful response (such as coil-globule transition, cell uptake or cargo release) but at constant temperature. This is achieved by consideration of their phase diagram where solubility can be changed by small structural changes to the end-group, side-chain/substituents or through main chain modification/binding. The current state-of-the-art is summarised here.
Co-reporter:Helen R. Thomas, Daniel J. Phillips, Neil R. Wilson, Matthew I. Gibson and Jonathan P. Rourke
Polymer Chemistry 2015 vol. 6(Issue 48) pp:8270-8274
Publication Date(Web):06 Oct 2015
DOI:10.1039/C5PY01358E
The direct grafting of poly(N-isopropylacrylamide) to the basal plane of graphene oxide has been achieved in a single step: cleavage of the terminal thiocarbonylthio group on RAFT grown poly(N-isopropylacrylamide) reveals a reactive thiol that attacks the epoxides present across the surface of graphene oxide. The new composite material was characterised by a combination of SSNMR, FTIR, Raman, EDX, XPS, TGA and contact angle measurement; it shows enhanced thermal stability and solubility in water.
Co-reporter:Thomas Congdon, Peter Shaw and Matthew I. Gibson
Polymer Chemistry 2015 vol. 6(Issue 26) pp:4749-4757
Publication Date(Web):01 Jun 2015
DOI:10.1039/C5PY00775E
Thermoresponsive polymers have attracted huge interest as adaptable biomaterials based on their reversible solubility behaviour which can be exploited for controlled drug delivery or cellular uptake. The most famous and successful of these is poly(ethylene glycol) (PEG), but the thermal transition temperatures that are practically accessible are not physiologically useful. There are some notable examples of synthetic, responsive, polymers that are highly tunable over a physiologically relevant range, but there is still a need for these to be clinically validated in terms of toxicology and immunogenity for in vivo usage, in addition to their widely used in vitro applications. Poly(vinyl alcohol), PVA, is an appealing biocompatible polymer which is already used for a huge range of biomedical applications. Here, PVA is shown to be a highly tunable, thermoresponsive polymer scaffold. RAFT/MADIX polymerization is used to obtain a library of well-defined polymers between 8 and 50 kDa. Selective alkanoylation of the obtained PVA enabled the effect of side-chains, end-groups and molecular weight on the observable transition temperatures to be studied by turbidimetry. It was found that increasingly hydrophobic side chains (acetyl, propanoyl, butanoyl), or increasing their density led to corresponding decreases in cloud point. PVA with just 10 mol% butanoylation was shown to have a thermal transition temperature close to physiological temperatures (37 °C), compared to 70 mol% for acetylation, with temperatures in between accessible by controlling both the relative degree of functionalization, or by altering the chain length. Finally, a secondary response to esterase enzymes was demonstrated as a route to ‘turn off’ the responsive behaviour on demand. This study suggests that PVA-derived polymers may be a useful platform for responsive biomaterials.
Co-reporter:Lewis D. Blackman, Daniel B. Wright, Mathew P. Robin, Matthew I. Gibson, and Rachel K. O’Reilly
ACS Macro Letters 2015 Volume 4(Issue 11) pp:1210
Publication Date(Web):October 19, 2015
DOI:10.1021/acsmacrolett.5b00551
The chain density of polymer micelles, dictated by their aggregation number (Nagg), is an often overlooked parameter that governs the macroscopic behavior of responsive assemblies. Using a combination of variable-temperature light scattering, turbidimetry, and microcalorimetry experiments, the cloud point and thermal collapse of micellar poly(N-isopropylacrylamide) (pNIPAM) corona chains at lower temperatures than the cloud point were found to be largely independent of the micelle’s Nagg. By controlling the core composition, the degree of hysteresis associated with the thermal transition was found to increase as a function of core hydrophobicity. We performed this study on well-characterized micelles with tunable Nagg values, composed of a thermoresponsive corona (pNIPAM) and a nonresponsive core block poly(n-butyl acrylate-co-N,N-dimethylacrylamide) (p(nBA-co-DMA)), which were synthesized using reversible addition–fragmentation chain transfer (RAFT) polymerization. This allowed for a distinction to be made between thermoresponsive behavior at both the molecular and macroscopic level. The study of the subtle differences between these behaviors was made possible using a combination of complementary techniques. These results highlight the critical need for consideration of the effect that self-assembly plays on the responsive behavior of polymer chains when compared with free unimers in solution.
Co-reporter:Caroline I. Biggs, Steve Edmondson and Matthew I. Gibson
Biomaterials Science 2015 vol. 3(Issue 1) pp:175-181
Publication Date(Web):18 Sep 2014
DOI:10.1039/C4BM00176A
Carbohydrate arrays are a vital tool in studying infection, probing the mechanisms of bacterial, viral and toxin adhesion and the development of new treatments, by mimicking the structure of the glycocalyx. Current methods rely on the formation of monolayers of carbohydrates that have been chemically modified with a linker to enable interaction with a functionalised surface. This includes amines, biotin, lipids or thiols. Thiol-addition to gold to form self-assembled monolayers is perhaps the simplest method for immobilisation as thiolated glycans are readily accessible from reducing carbohydrates in a single step, but are limited to gold surfaces. Here we have developed a quick and versatile methodology which enables the use of thiolated carbohydrates to be immobilised as monolayers directly onto acrylate-functional glass slides via a ‘thiol–ene’/Michael-type reaction. By combining the ease of thiol chemistry with glass slides, which are compatible with microarray scanners this offers a cost effective, but also useful method to assemble arrays.
Co-reporter:L. Otten and M. I. Gibson
RSC Advances 2015 vol. 5(Issue 66) pp:53911-53914
Publication Date(Web):12 Jun 2015
DOI:10.1039/C5RA08857G
Carbohydrate–lectin interactions dictate a range of signalling and recognition processes in biological systems. The exploitation of these, particularly for diagnostic applications, is complicated by the inherent promiscuity of lectins along with their low affinity for individual glycans which themselves are challenging to access (bio)synthetically. Inspired by how a ‘tongue’ can discriminate between hundreds of flavours using a minimal set of multiplexed sensors and a training algorithm, here individual lectins are ‘profiled’ based on their unique binding profile (barcode) to a range of monosaccharides. By comparing the relative binding of a panel of 5 lectins to 3 monosaccharide-coated surfaces, it was possible to generate a training algorithm that enables correct identification of lectins, even those with similar glycan preferences. This is demonstrated to be useful for discrimination between the cholera and ricin toxin lectins showing the potential of this minimalist approach for exploiting glycan complexity.
Co-reporter:Thomas Congdon, Charline Wilmet, Rebecca Williams, Julia Polt, Mary Lilliman, Matthew I. Gibson
European Polymer Journal 2015 Volume 62() pp:352-362
Publication Date(Web):January 2015
DOI:10.1016/j.eurpolymj.2014.06.001
•A series of reactive oligomers/polymers based on methacrylated carbohydrates have been synthesis.•Thiol-ene ‘click’ modification was employed to introduce thermoresponsive and carbohydrate functionality.•The properties of these polymers were investigated.Nature is capable of synthesizing perfectly defined, sequence-controlled oligomers and polymers, whereas synthetic polymerization methods inherently give rise to dispersity and limited reproducibility. This inherent dispersity provides a barrier to translation into biomedical applications and for probing material-biology interactions. Templating of polymers based upon biosynthesized cores offers a route to reproducible oligo/polymers if the template itself is readily available and highly tunable. Here oligosaccharides are employed as monodisperse scaffolds for the synthesis of highly functional biomaterials. The pendant hydroxyl units are converted to reactive methacrylates, which are themselves amenable for thiol-ene (‘click’) functionalization. Using this strategy, extremely well defined (MW/MN < 1.05) polymers are prepared bearing thermoresponsive or lectin-binding moieties. The templatation strategy ensures identical polymers are obtained from each synthesis. Their thermoresponsive behavior and multivalent interactions with a bacterial lectin are studied as a function of the discrete number of functional groups. Due to the ester linkage, these polymers are also shown to be inherently degradable.
Co-reporter:Laura E. Wilkins, Daniel J. Phillips, Robert C. Deller, Gemma-Louise Davies, Matthew I. Gibson
Carbohydrate Research 2015 Volume 405() pp:47-54
Publication Date(Web):20 March 2015
DOI:10.1016/j.carres.2014.09.009
•This research studies how glucose-rich nanostructures interact with erythrocytes.•Glycopolymers were obtained by RAFT polymerisation of a glucose-methacrylamide.•Gold nanoparticles were decorated with glucose on their corona.•Several assays revealed no evidence of polymer binding to the cells.•The results suggest glucose rich polymers are compatible with erythrocytes.Carbohydrate–protein interactions can assist with the targeting of polymer- and nano-delivery systems. However, some potential protein targets are not specific to a single cell type, resulting in reductions in their efficacy due to undesirable non-specific cellular interactions. The glucose transporter 1 (GLUT-1) is expressed to different extents on most cells in the vasculature, including human red blood cells and on cancerous tissue. Glycosylated nanomaterials bearing glucose (or related) carbohydrates, therefore, could potentially undergo unwanted interactions with these transporters, which may compromise the nanomaterial function or lead to cell agglutination, for example. Here, RAFT polymerisation is employed to obtain well-defined glucose-functional glycopolymers as well as glycosylated gold nanoparticles. Agglutination and binding assays did not reveal any significant binding to ovine red blood cells, nor any haemolysis. These data suggest that gluco-functional nanomaterials are compatible with blood, and their lack of undesirable interactions highlights their potential for delivery and imaging applications.
Co-reporter:Robert C. Deller, Manu Vatish, Daniel A. Mitchell, and Matthew I. Gibson
ACS Biomaterials Science & Engineering 2015 Volume 1(Issue 9) pp:789
Publication Date(Web):July 29, 2015
DOI:10.1021/acsbiomaterials.5b00162
Cryopreservation is fundamental in prolonging the viabilities of cells and tissues of clinical and biotechnological relevance ex vivo. Furthermore, there is an increasing need to address storage at more easily accessible temperatures in the developing world because of limited resources. Here, the cryopreservation of erythrocytes (red blood cells) with storage at −20 °C using hydroxyethyl starch (HES) and the ice recrystallization inhibitor poly(vinyl alcohol) (PVA), which is a biomimetic of naturally occurring antifreeze (glyco)proteins (AF(G)Ps), is described. This strategy eliminates the need for high concentrations of membrane penetrating solvents such as glycerol or dimethyl sulfoxide (DMSO). The addition of only 0.1–0.5 wt % PVA to the polymeric cryoprotectant, HES, significantly enhances cell recovery under conditions that promote damage due to ice recrystallization. The comparative ease with which the addition and removal of both HES and PVA can be attained is an additional attractive quality. Coupled with the benefits attained by the ice recrystallization inhibition activity of PVA, this methodology therefore offers a strategy that could aid the storage and distribution of biological materials.Keywords: AF(G)P; blood; cryopreservation; erythrocytes; poly(vinyl alcohol)
Co-reporter:Thomas Congdon, Bethany T. Dean, James Kasperczak-Wright, Caroline I. Biggs, Rebecca Notman, and Matthew I. Gibson
Biomacromolecules 2015 Volume 16(Issue 9) pp:
Publication Date(Web):August 10, 2015
DOI:10.1021/acs.biomac.5b00774
Nature has evolved many elegant solutions to enable life to flourish at low temperatures by either allowing (tolerance) or preventing (avoidance) ice formation. These processes are typically controlled by ice nucleating proteins or antifreeze proteins, which act to either promote nucleation, prevent nucleation or inhibit ice growth depending on the specific need, respectively. These proteins can be expensive and their mechanisms of action are not understood, limiting their translation, especially into biomedical cryopreservation applications. Here well-defined poly(vinyl alcohol), synthesized by RAFT/MADIX polymerization, is investigated for its ice nucleation inhibition (INI) activity, in contrast to its established ice growth inhibitory properties and compared to other synthetic polymers. It is shown that ice nucleation inhibition activity of PVA has a strong molecular weight dependence; polymers with a degree of polymerization below 200 being an effective inhibitor at just 1 mg.mL–1. Other synthetic and natural polymers, both with and without hydroxyl-functional side chains, showed negligible activity, highlighting the unique ice/water interacting properties of PVA. These findings both aid our understanding of ice nucleation but demonstrate the potential of engineering synthetic polymers as new biomimetics to control ice formation/growth processes
Co-reporter:Daniel E. Mitchell and Matthew I. Gibson
Biomacromolecules 2015 Volume 16(Issue 10) pp:
Publication Date(Web):September 25, 2015
DOI:10.1021/acs.biomac.5b01118
Organisms living in polar regions have evolved a series of antifreeze (glyco) proteins (AFGPs) to enable them to survive by modulating the structure of ice. These proteins have huge potential for use in cellular cryopreservation, ice-resistant surfaces, frozen food, and cryosurgery, but they are limited by their relatively low availability and questions regarding their mode of action. This has triggered the search for biomimetic materials capable of reproducing this function. The identification of new structures and sequences capable of inhibiting ice growth is crucial to aid our understanding of these proteins. Here, we show that plant c-type lectins, which have similar biological function to human c-type lectins (glycan recognition) but no sequence homology to AFPs, display calcium-dependent ice recrystallization inhibition (IRI) activity. This IRI activity can be switched on/off by changing the Ca2+ concentration. To show that more (nonantifreeze) proteins may exist with the potential to display IRI, a second motif was considered, amphipathicity. All known AFPs have defined hydrophobic/hydrophilic domains, rationalizing this choice. The cheap, and widely used, antimicrobial Nisin was found to have cation-dependent IRI activity, controlled by either acid or addition of histidine-binding ions such as zinc or nickel, which promote its amphipathic structure. These results demonstrate a new approach in the identification of antifreeze protein mimetic macromolecules and may help in the development of synthetic mimics of AFPs.
Co-reporter:Daniel J. Phillips, Marleen Wilde, Francesca Greco, and Matthew I. Gibson
Biomacromolecules 2015 Volume 16(Issue 10) pp:
Publication Date(Web):August 28, 2015
DOI:10.1021/acs.biomac.5b00929
Polymers which can respond to externally applied stimuli have found much application in the biomedical field due to their (reversible) coil–globule transitions. Polymers displaying a lower critical solution temperature are the most commonly used, but for blood-borne (i.e., soluble) biomedical applications the application of heat is not always possible, nor practical. Here we report the design and synthesis of poly(oligoethylene glycol methacrylate)-based polymers whose cloud points are easily varied by alkaline phosphatase-mediated dephosphorylation. By fine-tuning the density of phosphate groups on the backbone, it was possible to induce an isothermal transition: A change in solubility triggered by removal of a small number of phosphate esters from the side chains activating the LCST-type response. As there was no temperature change involved, this serves as a model of a cell-instructed polymer response. Finally, it was found that both polymers were non cytotoxic against MCF-7 cells (at 1 mg·mL–1), which confirms promise for biomedical applications.
Co-reporter:M. W. Jones, L. Otten, S.-J. Richards, R. Lowery, D. J. Phillips, D. M. Haddleton and M. I. Gibson
Chemical Science 2014 vol. 5(Issue 4) pp:1611-1616
Publication Date(Web):06 Feb 2014
DOI:10.1039/C3SC52982G
The application of synthetic glycopolymers to anti-adhesive therapies has so far been limited by their lack of lectin specificity. Here we employ a macromolecular engineering approach to mimic glycan architecture. A new, 3-step tandem post-polymerisation methodology was developed which afforded precise control over both chain length and carbohydrate (galactose)-polymer backbone linker distance. This route also allowed a secondary binding (branched) motif to be introduced onto the linker, increasing specificity and affinity towards bacterial toxins without the need for extensive carbohydrate or organic chemistry. Sequential variation of this motif was found to dramatically alter both the affinity and the specificity of the glycopolymers towards two lectins, CTx and PNA, by up to 20-fold either via direct binding, or increased steric constraints. Using this method, a glycopolymer that showed increased specificity towards CTx was identified.
Co-reporter:Sarah-Jane Richards, Elizabeth Fullam, Gurdyal S. Besra and Matthew I. Gibson
Journal of Materials Chemistry A 2014 vol. 2(Issue 11) pp:1490-1498
Publication Date(Web):24 Jan 2014
DOI:10.1039/C3TB21821J
The identification and treatment of bacterial infections remains a major healthcare challenge, especially to ensure appropriate application of a limited spectrum of antibiotics. Here we describe a system capable of discriminating between different strains of Escherichia coli using multivalent, carbohydrate-functionalised, gold nanoparticles based on their different expression levels of the FimH adhesin. Upon binding of the glycosylated nanoparticles to FimH positive bacteria, the nanoparticles' optical properties change enabling the identification of bacteria strain. Comparison between direct conjugation, or via a linker, of the carbohydrate to the nanoparticle revealed significant effects on the performance of the detection system. Using a poly(ethylene glycol) spacer increased the stability, and specificity, of the glycosylated nanoparticles but also reduced aggregation upon bacterial binding. This prevented the well-known red-blue gold colour change, meaning spectrophometric, rather than optical, assessment methods were required. Using this method, FimH positive bacteria could be detected at approximately 1.5 × 107 colony forming units per mL.
Co-reporter:Daniel J. Phillips, Ivan Prokes, Gemma-Louise Davies, and Matthew I. Gibson
ACS Macro Letters 2014 Volume 3(Issue 12) pp:1225
Publication Date(Web):November 13, 2014
DOI:10.1021/mz500686w
Thermoresponsive polymers have attracted huge interest as a way of developing smart/adaptable materials for biomedicine, particularly due to changes in their solubility above the LCST. However, temperature is not always an appropriate or desirable stimulus given the variety of other cellular microenvironments that exist, including pH, redox potentials, ionic strength, and metal ion concentration. Here, we achieve a highly specific, isothermal solubility switch for poly(N-isopropylacrylamide) by application of ferric iron (Fe3+), a species implicated in a range of neurodegenerative conditions. This is achieved by the site-specific incorporation of (Fe3+-binding) catechol units onto the polymer chain-end, inspired by the mechanism by which bacterial siderophores sequester iron from mammalian hosts. The ability to manipulate the hydrophilicity of responsive systems without the need for a temperature gradient offers an exciting approach toward preparing increasingly selective, targeted polymeric materials.
Co-reporter:Daniel J. Phillips, Joseph P. Patterson, Rachel K. O'Reilly and Matthew I. Gibson
Polymer Chemistry 2014 vol. 5(Issue 1) pp:126-131
Publication Date(Web):15 Aug 2013
DOI:10.1039/C3PY00991B
The encapsulation and selective delivery of therapeutic compounds within polymeric nanoparticles offers hope for the treatment of a variety of diseases. Traditional approaches to trigger selective cargo release typically rely on polymer degradation which is not always sensitive to the biological location of a material. In this report, we prepare nanoparticles from thermoresponsive polymers with a ‘solubility release catch’ at the chain-end. This release catch is exclusively activated in the presence of intracellular glutathione, triggering an ‘isothermal’ response and promoting a change in polymer solubility. This solubility switch leads to specific and rapid nanoparticle disassembly, release of encapsulated cargo and produces completely soluble polymeric side-products.
Co-reporter:Sarah-Jane Richards and Matthew I. Gibson
ACS Macro Letters 2014 Volume 3(Issue 10) pp:1004
Publication Date(Web):September 16, 2014
DOI:10.1021/mz5004882
The development of new analytical tools to probe pathogenic infection processes and as point-of-care biosensors is crucial to combat the spread of infectious diseases or to detect biological warfare agents. Glycosylated gold nanoparticles that change color due to lectin (carbohydrate-binding protein) mediated aggregation may find use as biosensors but require a polymer coating between the particle surface and sugar to ensure stability in complex media. Here, RAFT polymerization is employed to generate glycosylated polymers to coat gold nanoparticles. Rather than being a passive component, it is shown here that the polymer coating has to be precisely tuned to achieve a balance between saline (steric) stability and speed of the readout. If the polymer is too long it can prevent or slow aggregation and hence lead to a poor readout in sensing assays. The optimized glyco-nanoparticles are also demonstrated to be useful for rapid detection of a ricin surrogate.
Co-reporter:Daniel E. Mitchell, Mary Lilliman, Sebastian G. Spain and Matthew I. Gibson
Biomaterials Science 2014 vol. 2(Issue 12) pp:1787-1795
Publication Date(Web):15 Sep 2014
DOI:10.1039/C4BM00153B
Antifreeze (glyco) proteins (AF(G)Ps) from the blood of polar fish species are extremely potent ice recrystallization inhibitors (IRI), but are difficult to synthesise or extract from natural sources. Despite this challenge, materials which display IRI are appealing due to their ability to enhance cellular cryopreservation, for applications including regenerative and transplantation medicine. Here, poly(ampholytes), which contain a mixture of cationic and anionic side chains are quantitatively evaluated for their IRI activity. Poly(aminoethyl methacrylate), obtained by RAFT polymerization, is functionalised with succinic anhydride to generate the poly(ampholytes). The charge balance of the side chains is shown to be crucial, with only 50:50 mixtures having strong IRI activity, which also scales with molecular weight. This is the first example of a non-hydroxylated synthetic polymer with quantifiable IRI activity and raises questions about the mechanism of IRI, as the polymers have no obvious ice-binding motif. The ampholytic structure is shown to be transferable to carbohydrate-centred polymers with activity retained, but poly(betaines) are shown to be inactive.
Co-reporter:Matthew I. Gibson and Rachel K. O'Reilly
Chemical Society Reviews 2013 vol. 42(Issue 17) pp:7204-7213
Publication Date(Web):09 Apr 2013
DOI:10.1039/C3CS60035A
The aim of this review is to highlight some of the challenges in designing thermally responsive nanoparticles, where the responsivity is endowed by a responsive polymeric corona. A review of the literature reveals many contradictory observations upon heating these particles through their transition temperature. Indeed, both an increase in size due to aggregation and particle shrinkage have been reported for apparently similar materials. Furthermore, careful review of the literature shows that responsive nanoparticles do not have the same transition temperature or properties as their constituent polymers. These observations raise serious questions as to how to achieve the rational design of a responsive particle with a predictable and reproducible response. Here we highlight specific cases where conflicting results have been observed for spherical particles and put these results into the context of flat-surface grafted polymer brushes to explain the behaviour in terms of grafting density, curvature, chain end effects and the role of the underlying substrate. A better understanding of these observations should lead to the improved design of nanoparticles with real function and applications.
Co-reporter:Lucienne Otten, Sarah-Jane Richards, Elizabeth Fullam, Gurdyal S. Besra and Matthew I. Gibson
Journal of Materials Chemistry A 2013 vol. 1(Issue 20) pp:2665-2672
Publication Date(Web):10 Apr 2013
DOI:10.1039/C3TB20259C
Traditional methods of measuring the affinity of lectins (or other carbohydrate-binding proteins) to their target carbohydrate ligand rely on the use of chemically/recombinantly modified proteins in sorbent assays, microarrays or the use of expensive label-free methods such as surface plasmon resonance spectrometry. In this work we exploit the extremely high extinction coefficient (i.e. colour) of gold nanoparticles as resolving agents in sorbent assays. The anionic nanoparticles adhere strongly to immobilized proteins, but not to the carbohydrate-surfaces allowing investigation of protein binding and screening of novel multivalent inhibitors. Furthermore, the use of a simple digital camera (or mobile phone) to obtain the data is shown, providing a simple ultra-low cost route to the detection of unmodified, carbohydrate-binding proteins.
Co-reporter:Matthew J. Summers, Daniel J. Phillips and Matthew I. Gibson
Chemical Communications 2013 vol. 49(Issue 39) pp:4223-4225
Publication Date(Web):06 Jul 2012
DOI:10.1039/C2CC34236G
The α-termini of RAFT-derived thermoresponsive polymers were functionalised via thiol exchange with pyridyl disulfide. Addition of hydrophilic end-groups dramatically increased the observed cloud point of the polymers, without changing the composition of the main chain. Selective cleavage of the disulfide-linked end-groups was observed under conditions intended to mimic intracellular glutathione concentration. This allowed the thermoresponsive behaviour to be ‘switched on’ without the need for a temperature stimulus – an ‘isothermal’ switch.
Co-reporter:Mathew W. Jones, Sarah-Jane Richards, David M. Haddleton and Matthew I. Gibson
Polymer Chemistry 2013 vol. 4(Issue 3) pp:717-723
Publication Date(Web):08 Oct 2012
DOI:10.1039/C2PY20757E
The synthesis of polymers with latent reactivity suitable for ‘click’ type modifications in a tandem post-polymerisation modification process starting with poly(azlactone) precursors is investigated. Poly(azlactones), obtained by copper(I) mediated radical polymerisation, were functionalised in a one-pot process with amines bearing functional groups which are incompatible with controlled radical polymerisation: alkynes, alkenes, furfuryl and phenol. The reaction is quantitative and 100% atom efficient presenting an efficient route to clickable scaffolds without the need for protecting group chemistry. Additionally, the poly(azlactones) were exploited to obtain synthetic glycopolymers. The ring opening procedure introduces a 5-atom spacer between glycan and backbone, which provides improved access to carbohydrate-binding proteins with deep binding pockets, such as the cholera toxin, for anti-adhesion applications.
Co-reporter:Robert C. Deller, Thomas Congdon, Mohammed A. Sahid, Michael Morgan, Manu Vatish, Daniel A. Mitchell, Rebecca Notman and Matthew I. Gibson
Biomaterials Science 2013 vol. 1(Issue 5) pp:478-485
Publication Date(Web):22 Jan 2013
DOI:10.1039/C3BM00194F
The ability of polyols to act as ice recrystallisation inhibitors (IRI), inspired by antifreeze (glyco)proteins are studied. Poly(vinyl alcohol), PVA, a known IRI active polymer was compared to a panel of mono and polysaccharides, with the aim of elucidating why some polyols are active and others show no activity. When corrected for total hydroxyl concentration all the carbohydrate-based polyols displayed near identical activity with no significant influence of molecular weight. Conversely, PVA was several orders of magnitude more active and its activity displays significant dependence on molecular-weight implying that its mechanism of action is not identical to that of carbohydrates. In a second step, the role of hydrophobicity was studied and it is observed that monosaccharide IRI activity is enhanced by alkylation. Dye-quenching assays demonstrated that PVA is able to present a hydrophobic surface without self-aggregation. Therefore, the ability to present a hydrophobic domain is hypothesised to be essential to obtain high IRI activity, which has many biotechnological applications.
Co-reporter:Thomas Congdon, Rebecca Notman, and Matthew I. Gibson
Biomacromolecules 2013 Volume 14(Issue 5) pp:
Publication Date(Web):March 28, 2013
DOI:10.1021/bm400217j
This manuscript reports a detailed study on the ability of poly(vinyl alcohol) to act as a biomimetic surrogate for antifreeze(glyco)proteins, with a focus on the specific property of ice-recrystallization inhibition (IRI). Despite over 40 years of study, the underlying mechanisms that govern the action of biological antifreezes are still poorly understood, which is in part due to their limited availability and challenging synthesis. Poly(vinyl alcohol) (PVA) has been shown to display remarkable ice recrystallization inhibition activity despite its major structural differences to native antifreeze proteins. Here, controlled radical polymerization is used to synthesize well-defined PVA, which has enabled us to obtain the first quantitative structure–activity relationships, to probe the role of molecular weight and comonomers on IRI activity. Crucially, it was found that IRI activity is “switched on” when the polymer chain length increases from 10 and 20 repeat units. Substitution of the polymer side chains with hydrophilic or hydrophobic units was found to diminish activity. Hydrophobic modifications to the backbone were slightly more tolerated than side chain modifications, which implies an unbroken sequence of hydroxyl units is necessary for activity. These results highlight that, although hydrophobic domains are key components of IRI activity, the random inclusion of addition hydrophobic units does not guarantee an increase in activity and that the actual polymer conformation is important.
Co-reporter:Daniel J. Phillips and Matthew I. Gibson
Chemical Communications 2012 vol. 48(Issue 7) pp:1054-1056
Publication Date(Web):08 Dec 2011
DOI:10.1039/C1CC16323J
Disulfide linkages were introduced into poly (N-isopropylacrylamide) by the polycondensation of a RAFT-derived, telechelic macromonomer to give degradable yet vinyl-based polymers. These polymers displayed a redox-sensitive lower critical solution temperature (LCST) with the shorter, degraded product displaying a higher LCST than its non-degraded counterpart.
Co-reporter:Yanzi Gou, Sarah-Jane Richards, David M. Haddleton and Matthew I. Gibson
Polymer Chemistry 2012 vol. 3(Issue 6) pp:1634-1640
Publication Date(Web):27 Apr 2012
DOI:10.1039/C2PY20140B
Glycopolymers offer many opportunities for interfacing synthetic materials with biological systems. However, the nature of the interactions between glycopolymers and their biological targets, lectins, and the structural features necessary to obtain high-affinity materials are not fully understood. Here, the enhancement in binding affinity of multivalent glycopolymers to their corresponding lectins is investigated by quartz-crystal microbalance with dissipation monitoring (QCM-d). This technique allows the conformation of the adsorbed polymers to be probed and the direct observation of spanning of multiple binding sites on lectin-functional surfaces. The measured affinity was compared to the anti-adhesion activity of the polymers in solution, and it is shown that increased association constants did not directly correlate with inhibitory activity.
Co-reporter:Nga Sze Ieong, Muhammad Hasan, Daniel J. Phillips, Yussif Saaka, Rachel K. O'Reilly and Matthew I. Gibson
Polymer Chemistry 2012 vol. 3(Issue 3) pp:794-799
Publication Date(Web):23 Jan 2012
DOI:10.1039/C2PY00604A
The potential to fine-tune the transition temperatures of polymers displaying lower-critical solution temperatures (LCST) by a simple mixing strategy is investigated. Using a panel of four distinct polymer classes (poly[oligo(ethyleneglycol)methacrylate], poly(N-vinylpiperidone), poly(N-vinylcaprolactam) poly(N-isopropylacrylamide)) it was shown that only those with strong molecular weight dependent LCSTs produced a single, cooperative, transition when blended together. Furthermore, the actual transition temperature was linked to the weight average not the number average molecular weight. The only polymer which did not show strong molecular-weight-LCST correlation was poly(oligo(ethyleneglycol)methacrylate), which showed two independent transitions, one for each polymer.
Co-reporter:Yussif Saaka;Robert C. Deller;Alison Rodger
Macromolecular Rapid Communications 2012 Volume 33( Issue 9) pp:779-784
Publication Date(Web):
DOI:10.1002/marc.201100873
Abstract
Upon heating above their lower critical solution temperature (LCST) poly[oligo(ethyleneglycol)methacrylate]s (POEGMA) were shown to undergo a shift in their partition coefficient triggering aqueous to organic phase transfer, which indicated their potential to partition into cell membranes upon application of an external stimulus. Fluorescence-based assays indicated that the LCST transition did not induce lysis of model phospholipid vesicles but did promote fusion, as confirmed by dynamic light scattering. Membrane perturbation assays and linear dichroism spectroscopy investigations suggest that POEGMAs above their transition temperatures can interact with, or insert into, membranes. These findings will help develop the application of responsive polymers in drug delivery.
Co-reporter:Sarah-Jane Richards;Dr. Mathew W. Jones;Mark Hunaban; David M. Haddleton ;Dr. Matthew I. Gibson
Angewandte Chemie 2012 Volume 124( Issue 31) pp:7932-7936
Publication Date(Web):
DOI:10.1002/ange.201202945
Co-reporter:Daniel J. Phillips and Matthew I. Gibson
Biomacromolecules 2012 Volume 13(Issue 10) pp:
Publication Date(Web):September 10, 2012
DOI:10.1021/bm300989s
Telechelic, RAFT (reversible addition–fragmentation chain transfer)-derived macromonomers with a pyridyl disulfide end-group were converted into high molecular weight, disulfide-linked polymers using a polycondensation, step-growth procedure. The applicability of the method to polycondense a library of macromonomers with different functionalities including (meth)acrylates and acrylamides was investigated. Side-chain sterics were found to be important as nonlinear poly(ethylene glycol) analogues, which proved incompatible with this synthetic methodology, as were methacrylates due to their pendant methyl group. This method was used to incorporate disulfide bonds into poly(N-isopropylacrylamide), pNIPAM, precursors to give dual-responsive (thermo- and redox) materials. These polymers were shown to selectively degrade in the presence of intracellular concentrations of glutathione but be stable at low concentrations. Due to the molecular weight-dependent cloud point of pNIPAM, the lower critical solution temperature behavior could be switched off by a glutathione gradient without a temperature change: an isothermal transition.
Co-reporter:Sarah-Jane Richards;Dr. Mathew W. Jones;Mark Hunaban; David M. Haddleton ;Dr. Matthew I. Gibson
Angewandte Chemie International Edition 2012 Volume 51( Issue 31) pp:7812-7816
Publication Date(Web):
DOI:10.1002/anie.201202945
Co-reporter:Nga Sze Ieong, Konstantinos Brebis, Laura E. Daniel, Rachel K. O'Reilly and Matthew I. Gibson
Chemical Communications 2011 vol. 47(Issue 42) pp:11627-11629
Publication Date(Web):29 Sep 2011
DOI:10.1039/C1CC15171A
The synthesis and application of thermally-responsive macromolecules and nanoparticles relies on the underpinning control of their transition temperatures. The present study shows that two structurally diverse classes of nanoparticle have very strong diameter-dependent responses to temperature-stimuli, demonstrating that the exact size of the nanostructure can significantly impact its performance.
Co-reporter:Konstantinos Bebis, Mathew W. Jones, David M. Haddleton and Matthew I. Gibson
Polymer Chemistry 2011 vol. 2(Issue 4) pp:975-982
Publication Date(Web):07 Feb 2011
DOI:10.1039/C0PY00408A
Thermoresponsive poly[oligo(ethyleneglycol) methacrylate]s with a variety of different oligo(ethyleneglycol) graft lengths were synthesised by reversible-addition fragmentation chain transfer (RAFT) polymerisation. The lower critical solution temperature (LCST) behaviour of these polymers was evaluated as a function of the polymer concentration and the concentration of dissolved solutes, in order to understand their applicability for in vitro and in vivo applications. It was observed that in the relevant dilute (<1 mg mL−1) concentration range the observed LCSTs increased by approximately 6 °C compared to higher concentrations. This was confirmed by complimentary dynamic light scattering and differential scanning calorimetry measurements. The impact of biological solutions on the LCST was determined using bovine blood plasma, which resulted in observed LCSTs lower than what is found in traditional buffer or pure aqueous solutions. Finally, a well-defined polymer–protein conjugate was synthesised by ‘grafting from’ using single-electron transfer (SET) polymerisation. This model polymer–protein therapeutic also displayed similar concentration dependant behaviour, highlighting the importance of testing novel ‘smart’ materials and conjugates at both relevant concentration ranges and in appropriate solvent systems in order to use them in biotechnological applications.
Co-reporter:Nicola Vinson, Yanzi Gou, C. Remzi Becer, David M. Haddleton and Matthew I. Gibson
Polymer Chemistry 2011 vol. 2(Issue 1) pp:107-113
Publication Date(Web):04 Oct 2010
DOI:10.1039/C0PY00260G
In this paper we investigate the optimum procedure for the post-polymerisation modification of alkyne-bearing polymer scaffolds with glycosyl azides. We first elaborate the one-pot synthesis of glycosyl azides, in aqueous solution, without the need for protecting groups and in multigram scale. Using these azides, the ligand tris[(1-benzyl-1H-1,2,3-triazol-4-yl)methyl]amine (TBTA) was shown to give the fastest kinetics for the ‘click’ reaction at ambient temperature, and was used to prepare homogenous oligosaccharide-modified glycopolymers. The terminal sugars of these oligosaccharides were used to introduce α-linked glucose which is typically synthetically challenging.
Co-reporter:Matthew I. Gibson
Polymer Chemistry 2010 vol. 1(Issue 8) pp:1141-1152
Publication Date(Web):26 May 2010
DOI:10.1039/C0PY00089B
Biological antifreezes are a relatively large and diverse class of proteins (and very recently expanded to include lipopolysaccharides) which are capable of interacting with ice crystals in such a manner as to influence and, under the correct conditions, to prevent their growth. These properties allow for the survival of organisms which are either continuously or sporadically exposed to subzero temperatures which would otherwise lead to cryo-injury/death. These proteins have been found in a range of organisms, including plants, bacteria, insects and fish, and the proteins themselves have a diverse range of chemical structures ranging from the highly conserved antifreeze glycoproteins (AFGPs) to the more diverse antifreeze proteins AFPs. Their unique abilities to non-colligatively decrease the freezing point of aqueous solutions, inhibit ice recrystallisation and induce dynamic ice shaping suggest they will find many applications from cell/tissue/organ cryostorage, frozen food preservatives, texture enhancers or even as cryosurgery adjuvants. However, these applications have been limited by a lack of available material and also underlying questions regarding their mode of activity. The aim of this review article is to highlight the potential of polymeric materials to act as synthetic mimics of antifreeze(glyco) proteins, as well as to summarise the current general challenges in designing compounds capable of mimicking AF(G)Ps. This will cover the basic properties and modes of action of AF(G)Ps along with the methods commonly used to evaluate their activity. This section is essential to specifically define the ‘antifreeze’ terminology in terms of these proteins' unique function and to distinguish them from conventional antifreezes. A detailed evaluation of the processes involved in AF(G)P activity is beyond the scope of this review, but the reader will be pointed towards relevant literature. This will then be placed in the context of modern polymer science, with a focus on the ability of synthetic polymers to display some type of specific antifreeze activity, which will be summarised. Finally, the potential applications of these materials will be highlighted and future avenues for their research and the challenges faced in achieving these goals suggested.
Co-reporter:Thomas R. Congdon, Rebecca Notman, Matthew I. Gibson
European Polymer Journal (March 2017) Volume 88() pp:
Publication Date(Web):March 2017
DOI:10.1016/j.eurpolymj.2017.01.039
•The design and synthesis of a simple and efficient trifunctional MADIX agent is reported.•Excellent VAc control was achieved and well defined 3-arm PVA stars with no crosslinking were prepared.•Star polymers were evaluated for their Ice Recrystallization Inhibition Activity.Antifreeze proteins are potent inhibitors of ice crystal growth (recrystallization), which is a highly desirable property for cryopreservation and other low temperature applications. It has emerged that relatively simple polymers based on poly(vinyl alcohol) can mimic this activity, but the link between architecture and activity is not known. Here, a trifunctional xanthate was designed and synthesized to prepare star-branched poly(vinyl alcohols) by RAFT/Xanthate mediated polymerization, and their ice growth inhibition activity probed for the first time. The trifunctional agent design affords the formation of well-defined star polymers, with no evidence of star-star linking, even at high conversions, and narrow molecular weight dispersity. It is observed that three-arm stars have identical activity to two-armed (i.e. linear) equivalents, suggesting that the total hydrodynamic size of the polymer (diameter three-arm ∼ two-arm) rather than total valence of the functional groups is the key descriptor of activity.
Co-reporter:Sangho Won, Daniel J. Phillips, Marc Walker and Matthew I. Gibson
Journal of Materials Chemistry A 2016 - vol. 4(Issue 34) pp:NaN5682-5682
Publication Date(Web):2016/08/02
DOI:10.1039/C6TB01336H
Responsive polymers and polymer-coated nanoparticles have many potential bio-applications with the crucial parameter being the exact temperature where the transition occurs. Chemical modification of hydrophobic/hydrophilic or ligand binding sites has been widely explored as a tool for controlling this transition, but requires the synthesis of many different components to achieve precise control. This study reports an extensive investigation into the use of blending (i.e. mixing) as a powerful tool to modulate the transition temperature of poly(N-isopropylacrylamide) (PNIPAM) coated gold nanoparticles. By simply mixing two nanoparticles of different compositions, precise control over the transition temperature can be imposed. This was shown to be flexible to all possible mixing parameters (different polymers on different particles, different polymers on same particles and different sized particles with identical/different polymers). Evidence of the co-operative aggregation of differently sized nanoparticles (with different cloud points) is shown using transmission electron microscopy; particles with higher cloud points aggregate with those with lower cloud points with homo-aggregates not seen, demonstrating the co-operative behaviour. These interactions, and the opportunities for transition tuning will have implications in the rational design of responsive biomaterials.
Co-reporter:Daniel E. Mitchell, Mary Lilliman, Sebastian G. Spain and Matthew I. Gibson
Biomaterials Science (2013-Present) 2014 - vol. 2(Issue 12) pp:NaN1795-1795
Publication Date(Web):2014/09/15
DOI:10.1039/C4BM00153B
Antifreeze (glyco) proteins (AF(G)Ps) from the blood of polar fish species are extremely potent ice recrystallization inhibitors (IRI), but are difficult to synthesise or extract from natural sources. Despite this challenge, materials which display IRI are appealing due to their ability to enhance cellular cryopreservation, for applications including regenerative and transplantation medicine. Here, poly(ampholytes), which contain a mixture of cationic and anionic side chains are quantitatively evaluated for their IRI activity. Poly(aminoethyl methacrylate), obtained by RAFT polymerization, is functionalised with succinic anhydride to generate the poly(ampholytes). The charge balance of the side chains is shown to be crucial, with only 50:50 mixtures having strong IRI activity, which also scales with molecular weight. This is the first example of a non-hydroxylated synthetic polymer with quantifiable IRI activity and raises questions about the mechanism of IRI, as the polymers have no obvious ice-binding motif. The ampholytic structure is shown to be transferable to carbohydrate-centred polymers with activity retained, but poly(betaines) are shown to be inactive.
Co-reporter:Sarah-Jane Richards, Lucienne Otten and Matthew I. Gibson
Journal of Materials Chemistry A 2016 - vol. 4(Issue 18) pp:NaN3053-3053
Publication Date(Web):2015/10/27
DOI:10.1039/C5TB01994J
Glycan/lectin interactions drive a wide range of recognition and signal transduction processes within nature. However, their measurement is complicated or limited by the analytical tools available. Most technologies require fluorescently labelled proteins (e.g. microarrays) or expensive infrastructure (such as surface plasmon resonance). This also limits their application in biosensing, especially for low-resource settings, where detection of pathogens based on glycan binding could speed up diagnosis. Here we employ a library-oriented approach to immobilise a range of monosaccharides onto polymer-stabilised gold nanoparticles to enable rapid and high-throughput evaluation of their binding specificities with a panel of lectins. The red to blue colour shift upon gold nanoparticle aggregation is used as the output, removing the need for labelled protein, enabling compatibility with 96-well microplates. Furthermore, we demonstrate the use of a flatbed scanner (or digital camera) to extract biophysical data, ensuring that only minimal resources are required. Finally, linear discriminant analysis is employed to demonstrate how the glyconanoparticles can be applied as a multiplexed biosensor capable of identifying pathogenic lectins without the need for any infrastructure and overcoming some of the issues of lectin promiscuity.
Co-reporter:Matthew I. Gibson and Rachel K. O'Reilly
Chemical Society Reviews 2013 - vol. 42(Issue 17) pp:NaN7213-7213
Publication Date(Web):2013/04/09
DOI:10.1039/C3CS60035A
The aim of this review is to highlight some of the challenges in designing thermally responsive nanoparticles, where the responsivity is endowed by a responsive polymeric corona. A review of the literature reveals many contradictory observations upon heating these particles through their transition temperature. Indeed, both an increase in size due to aggregation and particle shrinkage have been reported for apparently similar materials. Furthermore, careful review of the literature shows that responsive nanoparticles do not have the same transition temperature or properties as their constituent polymers. These observations raise serious questions as to how to achieve the rational design of a responsive particle with a predictable and reproducible response. Here we highlight specific cases where conflicting results have been observed for spherical particles and put these results into the context of flat-surface grafted polymer brushes to explain the behaviour in terms of grafting density, curvature, chain end effects and the role of the underlying substrate. A better understanding of these observations should lead to the improved design of nanoparticles with real function and applications.
Co-reporter:M. W. Jones, L. Otten, S.-J. Richards, R. Lowery, D. J. Phillips, D. M. Haddleton and M. I. Gibson
Chemical Science (2010-Present) 2014 - vol. 5(Issue 4) pp:NaN1616-1616
Publication Date(Web):2014/02/06
DOI:10.1039/C3SC52982G
The application of synthetic glycopolymers to anti-adhesive therapies has so far been limited by their lack of lectin specificity. Here we employ a macromolecular engineering approach to mimic glycan architecture. A new, 3-step tandem post-polymerisation methodology was developed which afforded precise control over both chain length and carbohydrate (galactose)-polymer backbone linker distance. This route also allowed a secondary binding (branched) motif to be introduced onto the linker, increasing specificity and affinity towards bacterial toxins without the need for extensive carbohydrate or organic chemistry. Sequential variation of this motif was found to dramatically alter both the affinity and the specificity of the glycopolymers towards two lectins, CTx and PNA, by up to 20-fold either via direct binding, or increased steric constraints. Using this method, a glycopolymer that showed increased specificity towards CTx was identified.
Co-reporter:Caroline I. Biggs, Steve Edmondson and Matthew I. Gibson
Biomaterials Science (2013-Present) 2015 - vol. 3(Issue 1) pp:NaN181-181
Publication Date(Web):2014/09/18
DOI:10.1039/C4BM00176A
Carbohydrate arrays are a vital tool in studying infection, probing the mechanisms of bacterial, viral and toxin adhesion and the development of new treatments, by mimicking the structure of the glycocalyx. Current methods rely on the formation of monolayers of carbohydrates that have been chemically modified with a linker to enable interaction with a functionalised surface. This includes amines, biotin, lipids or thiols. Thiol-addition to gold to form self-assembled monolayers is perhaps the simplest method for immobilisation as thiolated glycans are readily accessible from reducing carbohydrates in a single step, but are limited to gold surfaces. Here we have developed a quick and versatile methodology which enables the use of thiolated carbohydrates to be immobilised as monolayers directly onto acrylate-functional glass slides via a ‘thiol–ene’/Michael-type reaction. By combining the ease of thiol chemistry with glass slides, which are compatible with microarray scanners this offers a cost effective, but also useful method to assemble arrays.
Co-reporter:Robert C. Deller, Thomas Congdon, Mohammed A. Sahid, Michael Morgan, Manu Vatish, Daniel A. Mitchell, Rebecca Notman and Matthew I. Gibson
Biomaterials Science (2013-Present) 2013 - vol. 1(Issue 5) pp:NaN485-485
Publication Date(Web):2013/01/22
DOI:10.1039/C3BM00194F
The ability of polyols to act as ice recrystallisation inhibitors (IRI), inspired by antifreeze (glyco)proteins are studied. Poly(vinyl alcohol), PVA, a known IRI active polymer was compared to a panel of mono and polysaccharides, with the aim of elucidating why some polyols are active and others show no activity. When corrected for total hydroxyl concentration all the carbohydrate-based polyols displayed near identical activity with no significant influence of molecular weight. Conversely, PVA was several orders of magnitude more active and its activity displays significant dependence on molecular-weight implying that its mechanism of action is not identical to that of carbohydrates. In a second step, the role of hydrophobicity was studied and it is observed that monosaccharide IRI activity is enhanced by alkylation. Dye-quenching assays demonstrated that PVA is able to present a hydrophobic surface without self-aggregation. Therefore, the ability to present a hydrophobic domain is hypothesised to be essential to obtain high IRI activity, which has many biotechnological applications.
Co-reporter:Sarah-Jane Richards, Elizabeth Fullam, Gurdyal S. Besra and Matthew I. Gibson
Journal of Materials Chemistry A 2014 - vol. 2(Issue 11) pp:NaN1498-1498
Publication Date(Web):2014/01/24
DOI:10.1039/C3TB21821J
The identification and treatment of bacterial infections remains a major healthcare challenge, especially to ensure appropriate application of a limited spectrum of antibiotics. Here we describe a system capable of discriminating between different strains of Escherichia coli using multivalent, carbohydrate-functionalised, gold nanoparticles based on their different expression levels of the FimH adhesin. Upon binding of the glycosylated nanoparticles to FimH positive bacteria, the nanoparticles' optical properties change enabling the identification of bacteria strain. Comparison between direct conjugation, or via a linker, of the carbohydrate to the nanoparticle revealed significant effects on the performance of the detection system. Using a poly(ethylene glycol) spacer increased the stability, and specificity, of the glycosylated nanoparticles but also reduced aggregation upon bacterial binding. This prevented the well-known red-blue gold colour change, meaning spectrophometric, rather than optical, assessment methods were required. Using this method, FimH positive bacteria could be detected at approximately 1.5 × 107 colony forming units per mL.
Co-reporter:Lucienne Otten, Sarah-Jane Richards, Elizabeth Fullam, Gurdyal S. Besra and Matthew I. Gibson
Journal of Materials Chemistry A 2013 - vol. 1(Issue 20) pp:NaN2672-2672
Publication Date(Web):2013/04/10
DOI:10.1039/C3TB20259C
Traditional methods of measuring the affinity of lectins (or other carbohydrate-binding proteins) to their target carbohydrate ligand rely on the use of chemically/recombinantly modified proteins in sorbent assays, microarrays or the use of expensive label-free methods such as surface plasmon resonance spectrometry. In this work we exploit the extremely high extinction coefficient (i.e. colour) of gold nanoparticles as resolving agents in sorbent assays. The anionic nanoparticles adhere strongly to immobilized proteins, but not to the carbohydrate-surfaces allowing investigation of protein binding and screening of novel multivalent inhibitors. Furthermore, the use of a simple digital camera (or mobile phone) to obtain the data is shown, providing a simple ultra-low cost route to the detection of unmodified, carbohydrate-binding proteins.
Co-reporter:Nga Sze Ieong, Konstantinos Brebis, Laura E. Daniel, Rachel K. O'Reilly and Matthew I. Gibson
Chemical Communications 2011 - vol. 47(Issue 42) pp:NaN11629-11629
Publication Date(Web):2011/09/29
DOI:10.1039/C1CC15171A
The synthesis and application of thermally-responsive macromolecules and nanoparticles relies on the underpinning control of their transition temperatures. The present study shows that two structurally diverse classes of nanoparticle have very strong diameter-dependent responses to temperature-stimuli, demonstrating that the exact size of the nanostructure can significantly impact its performance.
Co-reporter:Daniel E. Mitchell, Neil R. Cameron and Matthew I. Gibson
Chemical Communications 2015 - vol. 51(Issue 65) pp:NaN12980-12980
Publication Date(Web):2015/07/08
DOI:10.1039/C5CC04647E
Antifreeze (glyco) proteins AF(G)Ps are potent ice recrystallization inhibitors, which is a desirable property to enhance cryopreservation of donor tissue/cells. Here we present the rational synthesis of a new, biomimetic, ice-recrystallization inhibiting polymer derived from a cheap commodity polymer, based on an ampholyte structure. The polymer is used to enhance the cryopreservation of red blood cells, demonstrating a macromolecular solution to tissue storage.
Co-reporter:Matthew J. Summers, Daniel J. Phillips and Matthew I. Gibson
Chemical Communications 2013 - vol. 49(Issue 39) pp:NaN4225-4225
Publication Date(Web):2012/07/06
DOI:10.1039/C2CC34236G
The α-termini of RAFT-derived thermoresponsive polymers were functionalised via thiol exchange with pyridyl disulfide. Addition of hydrophilic end-groups dramatically increased the observed cloud point of the polymers, without changing the composition of the main chain. Selective cleavage of the disulfide-linked end-groups was observed under conditions intended to mimic intracellular glutathione concentration. This allowed the thermoresponsive behaviour to be ‘switched on’ without the need for a temperature stimulus – an ‘isothermal’ switch.
Co-reporter:Daniel J. Phillips, Gemma-Louise Davies and Matthew I. Gibson
Journal of Materials Chemistry A 2015 - vol. 3(Issue 2) pp:NaN275-275
Publication Date(Web):2014/11/07
DOI:10.1039/C4TB01501K
Inspired by nature's exploitation of the 1,2-dihydroxybenzene unit (or catechol) in mammalian and bacterial siderophores, we report the first example of a nanoparticle sensing system that utilises the strong catechol–Fe3+ binding motif to trigger nanoparticle aggregation, promoting a powerful optical response. Gold nanoparticles are functionalised with RAFT polymerisation-prepared water-soluble poly(N-hydroxyethyl acrylamide) containing a catechol moiety at the α-chain-end. A strong red-to-purple colorimetric response occurs in the presence of Fe3+ at serum concentrations (8–25 μM) in saline solution. Sodium chloride is critical in generating a strong optical output, as is the length of polymer used to coat the AuNPs. This behaviour is also demonstrated to be selective for Fe3+ over a host of other biologically relevant ions.
Co-reporter:Daniel J. Phillips and Matthew I. Gibson
Chemical Communications 2012 - vol. 48(Issue 7) pp:NaN1056-1056
Publication Date(Web):2011/12/08
DOI:10.1039/C1CC16323J
Disulfide linkages were introduced into poly (N-isopropylacrylamide) by the polycondensation of a RAFT-derived, telechelic macromonomer to give degradable yet vinyl-based polymers. These polymers displayed a redox-sensitive lower critical solution temperature (LCST) with the shorter, degraded product displaying a higher LCST than its non-degraded counterpart.
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