James Serginson, web writer – Journal of Materials Chemistry Blog

Author Archive

Endothelial cell thrombogenicity is reduced by ATRP-mediated grafting of gelatin onto PCL surfaces

01 May 2014

One of the most promising areas of materials chemistry research is the creation of synthetic analogues of biological tissue. The development of such materials would reduce the need for transplants and their associated problems. For example, polymer-based, artificial vascular grafts are a promising candidate for use in bypass operations. Unfortunately, they increase the risk of increasing thrombus (blood clot) formation. This in turn can lead to risk of serious medical problems such as stroke, heart attack and pulmonary embolism.

Researchers at Nanyang Technological University in Singapore have found that using functionalised polycaprolactone (PCL) can lead to reduced thrombogenicity. PCL itself is already widely used for in vivo applications although its hydrophobicity reduces its usefulness as an artificial blood vessel. Hydrophobic materials are also thought to be unsuitable because of their weak interactions with endothelial cells (ECs) – something commonly implicated in thrombus formation. To overcome these limitations, poly(glycidyl methacrylate) (PGMA) was grown from PCL surfaces via a graft-from living polymerisation. The side chains of the PGMA were then used to attach gelatine molecules. It was found that the gelatin coat decreased the hydrophobicity of the surface leading to improved EC adhesion and a corresponding reduction in thrombogenicity.

Endothelial cell thrombogenicity is reduced by ATRP-mediated grafting of gelatin onto PCL surfaces
Gordon Minru Xiong, Shaojun Yuan, Chek Kun Tan, Jun Kit Wang, Yang Liu, Timothy Thatt Yang Tan, Nguan Soon Tan and Cleo Choong
J. Mater. Chem. B, 2014, 2, 485-493. DOI:10.1039/C3TB20760a

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Article: Noncytotoxic artificial bacterial flagella fabricated from biocompatible ORMOCOMP and iron coating

24 Mar 2014

Targeted drug delivery has developed greatly over the past fifty years although it remains a largely uncontrolled exercise. In general, even the most effective vectors rely on passive targeting analogous to a driver travelling from Land’s End to John o’ Groats by making random turns until they see a sign saying “Welcome to John o’ Groats”.

Nano- and microrobots have the potential to offer a more guided method of drug delivery as well as facilitating new approaches to non-invasive surgery and diagnosis. A recent paper by Qiu et al. describes the preparation of a helical microrobot inspired by the flagella used to propel bacteria. To start with, polymer helices of around 10 µm in length were prepared using a two-photon polymerisation whereby a laser is used to “write” a 3D structure is photoresist. These helices were then covered in iron or iron/titanium thin films.

It was found that by using low-strength magnetic fields it was possible to control the movement of the helices through water. Pleasingly, the helices also showed no signs of cytotoxicity according to both direct cellular imaging and an MTT assay.

Noncytotoxic artificial bacterial flagella fabricated from biocompatible ORMOCOMP and iron coating
Famin Qiu, Li Zhang, Kathrin E. Peyer, Marco Casarosa, Alfredo Franco-Obregón, Hongsoo Choi and Bradley J. Nelson
J. Mater. Chem. B, 2014, 2, 357. DOI:10.1039/C3TB20840k

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Article: Incorporation of benzocarborane into conjugated polymer systems: synthesis, characterisation and optoelectronic properties

03 Jan 2014

In addition to making the study of chemistry more complicated than it needs to be, three-centre-two-electron bonds also provide carboranes with many useful properties. The inclusion of carborane clusters allows the thermal and chemical stability of polymers to be improved, glass transition temperatures to be increased and the propensity for unwanted aggregation to be reduced.

Recent work by Marshall et al. has focused on the incorporation of ortho-carborane into conjugated polymers for use in organic electronics. Carboranes are of particular interest in this area due to the possibility that their electron deficiency will allow them to fulfil the role of the electron acceptor in a donor-acceptor polymer. By preparing a novel monomer based on benzocarborane, it was possible to carry out a Stille polymerisation with an electron donating monomer and prepare polymers with molecular weights of the order of 10 kDa.

In comparison to analogous materials that contained no carborane, both novel polymers showed a decrease in band gap. One polymer was found to behave as a p-type semiconductor in a field effect transistor (FET) – the first time that a carborane-containing polymer has been used in such a device.

Incorporation of benzocarborane into conjugated polymer systems: synthesis, characterisation and optoelectronic properties
Jonathan Marshall, Zhuping Fei, Chin Pang Yau, Nir Yaacobi-Gross, Stephan Rossbauer, Thomas D. Anthopoulos, Scott E. Watkins, Peter Beavis and Martin Heeney
J. Mater. Chem. C, 2014, 2, 232. DOI:10.1039/C3TC31663g

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Article: Biocatalysed mineralization in an aqueous two-phase system: effect of background polymers and enzyme partitioning

03 Jan 2014

Although the chemistry of life is usually considered to be organic, living organisms also need to carry out inorganic synthesis. The formation of bones, teeth and shells all depend on the ability of cellular machinery to efficiently prepare inorganic materials with the correct morphology. This machinery is complex and involves the concerted action of small molecules, enzymes and high concentrations of macromolecules.

It is the role of the macromolecules that is the focus of a recent paper by David N. Carace and Christine D. Keating. They aimed to mimic the formation of CaCO₃ by conducting a mineralization reaction in an aqueous two-phase system (ATPS). This system consisted of two immiscible polymer solutions: a poly(ethylene glycol) (PEG) solution floating on a solution of dextran. The mineralisation reaction involved the urease–mediated conversion of urea to carbonate ions and their subsequent reaction with calcium. It was found that biomineralization occurred predominantly in the dextran layer due to the localization of urease. It was also found that decreasing the relative volume of the dextran phase increased the rate of CaCO₃ formation.

This work has demonstrated a fascinating method of biological reaction compartmentalization that does not rely on membranes.

Biocatalysed mineralization in an aqueous two-phase system: effect of background polymers and enzyme partitioning
David N. Cacace and Christine D. Keating
J. Mater. Chem. B, 2013, 1, 1794. DOI:10.1039/C3TB00550j

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Article: Transparent, stretchable, carbon-nanotube-inlaid conductors enabled by standard replication technology for capacitive pressure, strain and touch sensors

30 Oct 2013

Although the constant miniaturisation of consumer electronics has made it perfectly normal for somebody to leave their home in the morning carrying more screens than they leave behind, modern devices are still limited to being as physically rigid as spinning wheels and seed drills. The usefulness of flexible displays, wearable electronics and tactile sensors would all be improved dramatically by the development of reliable non-rigid conductors.

Wang et al. have recently devised a methodology for the manufacture of a stretchable material composed of highly conductive single-walled carbon nanotubes (SWCNTs) and a polydimethylsiloxane (PDMS) elastomer. The procedure starts with the preparation of a “non-stick” substrate obtained by perfluorinating glass. A suspension of SWCNTs in chloroform is then airbrushed over the substrate followed by the application of uncured PDMS. Following curing, an elastomer film with embedded nanotubes is obtained. An experiment examining the change in resistance with respect to tensile strain revealed that although resistance increased with strain when first stretched (as is generally observed), when the strain was removed and for the next ninety-nine strain-release cycles the resistance consistently decreased with increasing strain. This suggests that the first strain serves to orient the nanotubes in a particular way leading to this unexpected behaviour. In addition, the researchers found that specific patterns could be obtained by using patterned substrates or by simply spraying the SWCNT suspension through a patterned mask. The latter allowed the fabrication of a proof-of-concept strain sensor, touch pad and pressure sensor. All three devices were effective and demonstrate the utility of the fabrication technique.

Transparent, stretchable, carbon-nanotube-inlaid conductors enabled by standard replication technology for capacitive pressure, strain and touch sensors
Xiaolong Wang, Tingjie Le, Jillian Adams and Jun Yang
J. Mater. Chem. A, 2013, 1, 3580. DOI:10.1039/C3TA00079f

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Article: Construction of high strength hollow fibers by self-assembly of a stiff polysaccharide with short branches in water

06 Sep 2013

Anybody who has spent time working in a chemistry laboratory would be forgiven for being jealous of nature’s ability to reliably prepare functional materials. One of its greatest tricks is the use of intermolecular forces to spontaneously create structures of incredible complexity out of many constituent parts. Recently, a great deal of research has focused on understanding these natural processes with a view to creating new materials unknown to nature.

As well as being inspired by naturally occurring self-assembly processes, Shuqin Xu et al. go one step further and also make use of a naturally occurring molecule – extracted from the commercially available fungus Auricularia auricula-judae. The molecule is a polysaccharide with a relatively hydrophobic backbone and hydrophilic side-chains. This combination of features means that – much like the self-assembly of lipids into bilayers – the chains self-assemble into hollow nanofibres with a hydrophilic surface and hydrophobic core. Fluorescence microscopy revealed these fibres to be several microns long with diameters of less than 100 nm. Furthermore, increasing the concentration of the nanofibres led to self-assembly into high aspect ratio thin films followed by rolling of the films into tubes. This fascinating hierarchical structure is believed to contribute to improved mechanical properties over comparable materials such as glucose.

Construction of high strength hollow fibers by self-assembly of a stiff polysaccharide with short branches in water

J. Mater. Chem. A, 2013, 1, 4198. DOI:10.1039/C3TA00050H

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Article: Transition metal oxide alloys as potential solar energy conversion materials

06 Aug 2013

Transition metal oxide alloys as potential solar energy conversion materials

Although calculating the likelihood that the Sun will rise tomorrow is far from trivial, solar power remains an extremely promising source of sustainable energy. Widespread adoption of current-generation photovoltaics (PV) is held back by low efficiency and the high cost of manufacturing the necessary single-crystal silicon. Inexpensive, naturally occurring transition metal oxides (TMOs) such as iron(II) oxide, manganese(II) oxide and nickel(II) oxide would be cost-effective but they currently suffer from extremely low efficiency.

Toroker and Carter recently attempted to tackle this problem using a computational approach. They simulated the effect that combining different TMOs would have on their usefulness in PV applications. They considered four key properties: band gap, the type of states at band edges, the band edge positions and the band gap centre (BGC) offset – a new metric proposed by the authors. Through the simulations, they found it was possible to prepare more useful materials when using combinations of TMOs. For example, the band gaps of MgO, MnO, NiO and ZnO – which are normally too high to absorb solar energy – could be reduced in an alloy formed with FeO.

Their calculations suggest that an alloy of 3:1 NiO:FeO would satisfy all their criteria for a useful PV. They suggest that the next step in the process is to devise a strategy for doping to improve conductivity.

Transition metal oxide alloys as potential solar energy conversion materials

J. Mater. Chem. A, 2013, 1, 2474. DOI:10.1039/C2TA00816E

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Article: Electrochemically assisted bacteria encapsulation in thin hybrid sol–gel films

12 Jul 2013

Electrochemically assisted bacteria encapsulation in thin hybrid sol–gel films

Bacteria are typically cast in one of two roles: either vile, disease-causing microkillers evolving faster than science can keep up or as benevolent, yoghurt-borne wardens of the digestive system. An increasingly important third job is that of efficient, microscopic machines capable of producing complex biomolecules such as DNA or insulin, working as biosensors or acting as highly-specific catalysts.

A recent paper by Ghach et al. focuses on encapsulating bacteria in thin silica films in order to make them more practical for use in bioelectronic sensors. They developed two methods of preparing films. Firstly, a two-step process where bacteria were immobilised on an indium tin oxide (ITO) electrode before a silica-based sol was deposited over them. The second method was a one-step where the sol and the bacteria were deposited at the same time (shown above). Trehalose, poly(ethylene glycol) (PEG) and chitosan were also present in the sol to improve cell viability.

Using the two-step process, the researchers found that by varying deposition times it was possible to prepare films with a thickness between 82 nm and 2 μm. With optimum conditions, 95% cell viability was observed after one month. For the one-step process, which resulted in a composite film containing homogeneously dispersed bacteria, it was shown that encapsulated luminescent E. coli still exhibited 50% luminescence after storage for four weeks.

Electrochemically assisted bacteria encapsulation in thin hybrid sol–gel films

J. Mater. Chem. B, 2013, 1, 1052. DOI:10.1039/C2TB00421F

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot Paper: Bioreducible polypeptide micelles for chemotherapy

15 Apr 2013

The use of antitumour drugs has always been problematic due to the risk of severe side-effects consistent with such cytotoxic compounds. A logical method of reducing side effects is to exercise more control over the deployment of drugs, ensuring that they are only delivered to cancer cells and not across the entire body. The first stage in the development of such a system is the design of biocompatible drug carriers.

Drug carriers must be designed in such a way that they do not interfere with the therapeutic action of the drug yet also be sufficiently resilient that their payload is not released before their cellular destination. A solution to this is to use a chemical trigger that exploits differences in the extracellular and intracellular environments. One such difference is redox potential. Inside the cell, the concentration of the thiol-containing tripeptide glutathione (GSH) is around one order of magnitude higher than it is outside the cell. Disulfides (-S-S-) can be rapidly degraded by GSH meaning that structures that contain them are extremly unstable inside the cell yet remain completely stable in the mildly oxidising conditions found in the extracellular milieu.

Ding et al. prepared micelles consisting of poly(ethylene glycol) (PEG) and poly(ε-benzyloxycarbonyl-L-lysine) (PZLL) linked by a disulfide group. Upon entering the cell, it was envisaged that the fission of the disulfide would greatly undermine the structural integrity of the micelle. The carriers formed were of the order of 100 nm in size and were loaded with the drug Doxorubicon (DOX). In a non-reducing environment more than 50% of the drug was held after sixty hours; in the presence of GSH less than 10% was held demonstrating the effectiveness of the trigger. In vitro efficacy of the micelles was demonstrated using cellular imaging and the biocompatibility of the micelles was found to be extremely high.

Biocompatible reduction-responsive polypeptide micelles as nanocarriers for enhanced chemotherapy efficacy in vitro

J. Mater. Chem. B, 2013, 1, 69. DOI: 10.1039/c2tb00063f

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Hot paper: Dendritic Carbon Nanotube Networks

21 Feb 2013

Dendritic Carbon Nanotube Networks

Dendrimers (or apparently “arborols” for those who prefer nomenclature with a Latin flavour) offer some of the most fascinating molecular architectures in chemistry. Molecules such as PAMAM are robust, well defined spherical structures with several possible applications in the fields of sensors and drug delivery. They also provide the opportunity for chemists to produce some first-rate molecular models.

Fans of photogenic chemistry will now be pleased to hear that dendritic architectures have recently been observed in samples of another journal cover mainstay: the carbon nanotube.

The usefulness of composite materials prepared by introducing carbon nanotubes (CNTs) into a bulk polymer is well known; mechanical properties, conductivity and thermal properties can all be improved greatly. There is unfortunately a problem with getting the tubes sufficiently well dispersed throughout the polymer. Kobashi et al. have recently published work showing the formation and dispersion of a dendritic network of CNTs that is strikingly reminiscent of the structure of a tree or a circulatory system. The tubes form large, central “trunks” and then branch off again and again until, at the extremities of the network, only single tubes are visible.

The structures are not only aesthetically pleasing; they are also extremely useful. Use of the network allows a ten-fold increase in the conductivity of a rubber composite compared to individually dispersed tubes. When combined with epoxy resins the network was also able to improve the Young’s Modulus of the material (by 200% to 5.6 GPa) and the tensile strength (by 170% to 85 MPa). To prepare the networks the researchers use long (0.1 – 1 mm) tubes which are flexible and entangled. The nanotube forests (“carpets” of vertical tubes grown off a flat surface) are also imperfectly aligned which is believed to cause the required “meshes” instead of bundles. It is also envisaged that this novel method of CNT dispersion is scalable offering the potential for use in industry.

A dispersion strategy: dendritic carbon nanotube network dispersion for advanced composites

Chem. Sci., 2013, 4, 727. DOI: 10.1039/c2sc21266h

James Serginson is a guest web writer for the Journal of Materials Chemistry blog. He currently works at Imperial College London carrying out research into nanocomposites.

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Journal of Materials Chemistry Blog

Author Archive

Endothelial cell thrombogenicity is reduced by ATRP-mediated grafting of gelatin onto PCL surfaces

Hot Article: Noncytotoxic artificial bacterial flagella fabricated from biocompatible ORMOCOMP and iron coating

Hot Article: Incorporation of benzocarborane into conjugated polymer systems: synthesis, characterisation and optoelectronic properties

Hot Article: Biocatalysed mineralization in an aqueous two-phase system: effect of background polymers and enzyme partitioning

Hot Article: Transparent, stretchable, carbon-nanotube-inlaid conductors enabled by standard replication technology for capacitive pressure, strain and touch sensors

Hot Article: Construction of high strength hollow fibers by self-assembly of a stiff polysaccharide with short branches in water

Hot Article: Transition metal oxide alloys as potential solar energy conversion materials

Hot Article: Electrochemically assisted bacteria encapsulation in thin hybrid sol–gel films

Hot Paper: Bioreducible polypeptide micelles for chemotherapy

Hot paper: Dendritic Carbon Nanotube Networks

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