Dr Athina E Markaki
Fellow of Robinson College
Subject groups/Research projects
Highly Porous Fibre Network Materials
Bonded fibre networks constitute an interesting class of material, offering high levels of porosity, fluid permeability and specific surface area, in combination with considerable scope for controlling and tailoring of structure. While much of the emphasis is on metallic systems with fibre diameters of ~20-200 µm, such materials can also readily be produced from ceramic and polymeric fibres, and over a wide range of scale. They offer potential for use in applications with demanding requirements in thermal management, heat exchange, catalysis support, fluid filtration, specific stiffness, capacity for impact energy absorption etc. They can be used in various configurations, such as sandwich panels and surface layers. A central feature of the research is study of the various inter-relationships between processing conditions, network architecture (void content, distributions of fibre segment orientation and length, anisotropy, homogeneity etc.), microstructural factors (grain size, texture, second phase, fibre-fibre joints etc.) and thermo-mechanical properties (elastic constants, yield strength, fracture energy, conductivities etc.). Network architecture is often most effectively captured by computed X-ray microtomography and these data can be used in analytical and numerical models for property prediction. Nanoindentation and other fine scale mechanical interrogation techniques are used to study local property variations.
Magneto-Mechanical Actuation and Exploitation in Medical Devices
Fibre network materials are attractive for usage in various types of actuator application, since they can exhibit controlled reversible shape changes, while potentially offering good combinations of strength, toughness and rate of thermal response. Two particular types of actuation are being explored, one based on temperature changes, using shape memory effect (SME) fibres, and the other on magnetic actuation, using ferromagnetic fibres. The latter effect is being explored for certain biomedical applications, including magnetically active layers on the surface of prosthetic implants, which deform elastically on application of a magnetic field, stimulating in-growth of bone tissue via the creation of mechanical strain on the cell network, and hence improving the bonding between prosthesis and bone.