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Dr. Easan Sivaniah

Telephone: +44 (0) 1223 337007
E-mail: es10009 [at] cam.ac.uk

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Sivaniah Research Group

Welcome!! Our signature work is based around materials development for sustainability , and our approach has been via synthetic and bio-based routes. This research includes the development of polymer membranes for separation (gas, water) and energy storage. It also includes the development of supported enzymes scaffolds for generation of non-fossil-fuel-based plastics and tissue-engineering technology.

Recent Research Highlights

A robust route to enzymatically functional, hierarchically self-assembled peptide frameworks (Advanced Materials, 2013)

The addition of enzyme biofunctionality to self-assembling peptide nanofibers is challenging since such additions can inhibit functionality or self-assembly. We introduce a method for peptide nanofiber enzyme functionalization, demonstrated by the attachment of a polymerization synthase to peptide nanofibers. The enzyme generates a biocompatible, biodegradable biopolyester coat on the fibers with applicablity in medical engineering. This approach provides a template for generation of functional bionanomaterials.

Complex stiffness gradient substrates for studying mechanotactic cell migration (Advanced Materials, 2012)

Cell migration is known to respond to a number of external stimuli (e.g. chemical, thermal and optical). Mechanotaxis is another stimulus whereby cells migrate in the direction of a change in the stiffness of its environment. However decoupling mechanotactic stimuli from chemical ones is often impossible since local chemistry is involved in enhancing local stiffness. An innovative platform is developed which aims to exclusively study mechanotaxis. Soft polyacrylamide-gel-based cell culture surfaces are used to fabricate flat surfaces containing elasticity gradients through changes in the depth of the soft gel to a patterned stiff support. Where the soft gel thicknesses are low enough (<10 microns), the cells are able to sense the presences of the stiffer substrates, leading to directed cell migration to those areas. This implementation of material physics makes it possible to construct complex mechanically patterned surfaces with lithographic precision. Using these scaffolds, we can show that durotactic migration can be mitigated by treating fibroblast cells with drugs that interfere with cell cytoskeletal organization or through the knock-out of key genes in migratory cancer cells.

Zeolitic imidazolate framework (ZIF-8) based polymer nanocomposite membranes for gas separation (Energy and Env. Science, 2012)

As synthesised ZIF-8 nanoparticles (size~60 nm and specific surface area ~1300-1600 m2/g) were directly incorporated into a model polymer membrane (Matrimid® 5218). This produces flexible transparent membranes with excellent dispersion of nanoparticles (up to loadings of 30 wt%) with good adhesion within the polymer matrix, as confirmed by scanning electron microscopy, dynamic mechanical thermal analysis and gas sorption studies. Pure gas (H2, CO2, O2, N2 and CH4) permeation tests showed enhanced permeability of the mixed matrix membrane with negligible losses in selectivity. Positron annihilation lifetime spectroscopy (PALS) indicated that an increase in polymer free volume with ZIF-8 loading together with the free diffusion of gas through the cages of ZIF-8 contributed to an increase in the composite membrane permeability. The gas transport properties of the composite membranes were well predicted by a Maxwell model whilst the processing strategy reported can be extended to fabricate other polymer nanocomposite membranes intended for a wide range of emerging energy applications.

Collective osmotic shock in ordered materials (Nature Materials, 2012)

Osmotic shock in a vesicle or cell is the stress build-up and subsequent rupture of the phospholipid membrane that occurs when a relatively high concentration of salt is unable to cross the membrane and instead an inflow of water alleviates the salt concentration gradient. This is a well-known failure mechanism for cells and vesicles (for example, hypotonic shock) and metal alloys (for example, hydrogen embrittlement). We propose the concept of collective osmotic shock, whereby a coordinated explosive fracture resulting from multiplexing the singular effects of osmotic shock at discrete sites within an ordered material results in regular bicontinuous structures. The concept is demonstrated here using self-assembled block copolymer micelles, yet it is applicable to organized heterogeneous materials where a minority component can be selectively degraded and solvated whilst ensconced in a matrix capable of plastic deformation. We discuss the application of these self-supported, perforated multilayer materials in photonics, nanofiltration and optoelectronics.

Imaging Internal Features of Whole, Unfixed Bacteria (Scanning, 2011)

Wet scanning-transmission electron microscopy (STEM) is a technique that allows high-resolution transmission imaging of biological samples in a hydrated state, with minimal sample preparation. However, it has barely been used for the study of bacterial cells. In this study, we present an analysis of the advantages and disadvantages of wet STEM compared with standard transmission electron microscopy (TEM). To investigate the potential applications of wet STEM, we studied the growth of polyhydroxyalkanoate and triacylglycerol carbon storage inclusions. These were easily visible inside cells, even in the early stages of accumulation. Although TEM produces higher resolution images, wet STEM is useful when preservation of the sample is important or when studying the relative sizes of different features, since samples do not need to be sectioned. Furthermore, under carefully selected conditions, it may be possible to maintain cell viability, enabling new types of experiments to be carried out. To our knowledge, internal features of bacterial cells have not been imaged previously by this technique. (Right image: Fluorescence microscopy highlights polyhydroxyalkanoate inclusions inside bacteria; optical image left, fluorescence image right)

The cavity-to-cavity migration of leukaemic cells through 3D honey-combed hydrogels with adjustable internal dimension and stiffness (Biomaterials, 2010)

Whilst rigid, planar surfaces are often used to study cell migration, a physiological scenario requires three-dimensional (3D) scaffolds with tissue-like stiffness. This paper presents a method for fabricating periodic hydrogel scaffolds with a 3D honeycomb-like structure from colloidal crystal templates. The scaffolds, made of hydrogel-walled cavities interconnected by pores, have separately tuneable internal dimensions and adjustable gel stiffness down to that of soft tissues. In conjunction with confocal microscopy, these scaffolds were used to study the importance of cell compliance on invasive potential. Acute promyelocytic leukaemia (APL) cells were differentiated with all-trans retinoic acid (ATRA) and treated with paclitaxel. Their migration ability into the scaffolds' size-restricted pores, enabled by cell softening during ATRA differentiation, was significantly reduced by paclitaxel treatment, which interferes with cell shape recovery. These findings demonstrate the usability of the scaffolds for investigating factors that affect cell migration, and potentially other cell functions, in a realistic 3D tissue model.

Magnetically induced pattern formation in phase separating polymer-solvent-nanoparticle mixtures (Phys. Rev. Lett., 2010)

Permanent magnetic structures with controlled dimension and architecture (labyrinthine, hexagonal, or dispersed columnar) are formed in a partially miscible ferrofluid-nonferrofluid mixture under the influence of a perpendicular magnetic field. The origin of the permanent structures, which have characteristic lateral dimensions ranging from 1 to 10mum, is the repartitioning of the ferrofluid carrier solvent into the nonferrofluid polymeric phase. This polymer-solvent phase separation under a magnetic field leads to departures from the expected final dimension of the magnetically stabilized ferrofluid droplet sizes.


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