Young Persons' Lecture Competition - Abstracts from the London Local Heat

London Materials Society
14 Feb 2009

Multifunctional bioactive scaffolds for bone tissue engineering

Decheng Meng, Imperial College London

A novel multi-functional polyhydroxybutyrate (P(3HB))/45S5 Bioglass® composite scaffold was developed with the potential for drug delivery, in the context of bone tissue engineering. 45S5 Bioglass® scaffolds were produced using the foam-replication technique and were subsequently coated with P(3HB) microspheres (1.0 – 1.5 μm in diameter), which were produced using a solid-oil-in-water emulsion solvent extraction/evaporation technique. A simple slurry-dipping method was used to achieve a uniform coating throughout the scaffold. The bioactive glass 3D structure provides both structural support and bioreactivity while the microspheres are used as controlled drug delivery vehicles. The new composite scaffold was shown to have higher mechanical strength, and the microsphere coating did not inhibit the bioactivity of the scaffold. However, the roughness of the HA layer, which was form when scaffolds were immersed in simulated body fluid over a period of time, increased significantly in the composite, it is thought to facilitate cell attachment and proliferation. 

Surface Modification of Electrospun fibres by Photoembossing

Nanayaa F Hughes-Brittain, Queen Mary University of London

Rough or textured surfaces promote cell migration and adhesion which are vital for cell proliferation and extracellular matrix synthesis in biomedical scaffolds. A recent technique called photoembossing has the potential of forming relief structures on any type of substrates including fibres. Photoembossing creates relief structures by using a chemically reactive photopolymer system which is exposed to UV light through a contact photomask. In this study, it is shown that photopolymers consisting of 1:1 mixture of polymer to monomer ratio can be electrospun  on to a substrate while maintaining the fibre geometry. Also, it is shown that in-flight polymerisation by flood exposure is possible and that oriented fibres are obtained.  Photoembossing was performed using a mask exposure and it was shown that relief structures were obtained especially if residual amount of solvent was present. The formation of the relief structures is accompanied by beading and consequently fibres with geometric structures on multiple length scales are obtained. 

Modelling Textile Composites: unveiling a new scale.

Nelson Vieira de Carvalho, Imperial College London

I will discuss a synergetic approach which, combining knowledge from fields as diverse as medicine and crystallography, enables efficient Finite Element (FE) modelling of high-performance textile composites. These FE analyses, at reinforcement level (meso-scale), provide detailed stress-strain fields; these can be used to accurately predict homogenized proper­ties, determine damage initiation and propagation, and as part of multi­-scale analyses. Ultimately, meso-scale FE modelling provides a better understanding of woven composites' behaviour, offers a tool to optimize their manufacture and usage, and leads to their increased use in many industries such as Aerospace. However due to the complexity of the tex­tile reinforcement, their FE modelling and analysis can be prohibitively complex and time consuming. The approach I will present combines voxel meshing with automatic symmetries-recognition, enabling more accurate and time-efficient FE modelling and analysis of Orthogonal 2D-Woven Composites. The concept’s capabilities and applications, namely to 3D-Woven Composites, will he discussed in detail. 

Structure and Properties of β-Tricalcium Phosphate and Related Minerals

Eleanor E Jay, Imperial College London

Apatite based materials are of great importance in a diverse range of fields, primarily due to their structure and chemistry providing the possibility of many different species substituting into the structure. In particular they are attractive as long term stable nuclear waste forms; as they can incorporate a vast range of waste species including those that cannot be incorporated into more conventional waste forms, e.g. in glass. In this study the efficacy of fluroapatite (FAp), chlorapatite (ClAp), fluor-chlorapatite (F-ClAp) and a related structure, β-tricalcium phosphate (β-TCP), have been assessed.Atomic scale modelling brings analytical theory and experimental data together; it is a tool that can predict certain properties of complex crystallographic systems, which would not be possible by other means. To better understand the suitability of these structures as waste forms, the solubility of diferent metal cations has been established. Modified interatomic potential parameter sets were derived that are able to reproduce the apatite and β-TCP structures, but defect behaviour was predicted using a quantum mechanical QM) approach. Michie et al., have shown that for apatite and β- TCP, QM techniques, although more computationally demanding than pair potential techniques, provide results in better agreement with experimental data. However, this difference is not significant enough to rule out the use of pair potentials for structure simulations, especially for computationally demanding molecular dynamics MD) simulations. MD type modelling techniques allows the study of dynamic lattice response to radiation damage events; the future success of β-TCP as a waste form will depend upon how it is able to withstand radiation damage over the long term. 

Closing the loop: recycling a design approach for recycled CFRPs

Soraia Pimenta, Imperial College London

Carbon-fibre reinforced-polymers (CFRPs) have an outstanding structural response. However, their complex behaviour and lack of appropriate design tools initially restricted their use. Through an integrated triangular approach –with experimental, analytical and numerical components –the confidence in structural design with CFRPs has improved, so their application range is now broader.The increasing use of CFRPs nevertheless raises a problem: disposal. Land-filling and incineration are unsustainable, so recycling solutions were recently developed. However, the same lack of understanding of material behaviour –as once occurred with virgin CFRPs –hinders the application of recyclates.

Transferring the integrated triangular approach to recycled CFRPs is the proposed solution. The concept behind this approach is illustrated through the most challenging failure mode in composites: kink-band formation. It is shown how experimental observation has guided analytical modelling of kink-band formation, validated through numerical simulations. By applying this methodology to recycled CFRPs, the last open loop will be closed.

Ceramic – Carbon Nanotube Nanocomposites

Fawad Inam, Queen Mary, University of London

The increasing availability of nanopowders and nanotubes combined with modern processing techniques is enabling the development of new multi-functional materials. This will be illustrated by ceramic - Carbon Nanotube (CNT) nanocomposites. The addition of relatively small amounts (<1 vol%) of CNTs can convert an insulating ceramic into a good electrical conductor. Alumina - CNT nanocomposites, having electrical conductivities upto 550 S/m were sintered using Spark Plasma Sintering (SPS). These materials provide a new envelope of mechanical properties. They offer the advantages of ceramics combined with good electrical and thermal conductivities. There are two critical steps in their processing: dispersion of the CNTs; and densification by sintering. To minimise any degradation of the CNT, the nanocomposites are sintered by rapid (300 ºC/min), pulsed electrical heating in a vacuum environment. Using this approach it is possible to densify nanocomposites at processing temperatures of >1800 ºC without significant degradation of the CNTs.  

Detecting failure in composite materials using acoustic emission:

from laboratory testing to structural health monitoring

Renaud Gutkin, Imperial College London

During their service life, composites structures are damaged by fatigue-loading, impacts, and environmental conditions. In aircraft structures, damage development is monitored during routine visual inspections, eventually assisted by non-destructive equipment. This technique leaves the structure exposed to catastrophic damage growth in between inspections or in non-accessible parts. Employment of acoustic emissions (of growing damage) can provide an efficient and real time health-monitoring of such structures. My lecture will discuss how acoustic emissions can be recorded and analysed to detect, locate and classify different types of damage. The application of different signal processing methods to coupon testing, using Fourier and Wavelets transforms, as well as pattern recognition techniques, will be detailed. The potential of the method in assisting in-service structural health-monitoring will be discussed with relevant examples from the aeronautics and wind turbine industry. 

How tough is tough? Accurate translaminar fracture toughness measurement in composites

Matthew Laffan, Imperial College London

When fracture initiates and propagates through any structure, the consequences canbe disastrous. Thus accurate measurements of fracture toughness are key in both materials selection and design processes. To characterise these properties, reliable experimental procedures are needed; results need to be reproducible and the test method itself should not introduce scatter.A composite structure’s damage tolerance and response during damage propagationcan be dictated by the fracture toughness associated with mode I fibre tensile failure,G 0 Ic, though there have been relatively few attempts to measure this property.This presentation will discuss factors affecting the accurate measurement of G 0 Ic fora unidirectional carbon/epoxy composite. Using the compact tension configuration, adapted from an ASTM standard for metals, G 0 Ic has been measured for a range of specimen sizes and lay-ups. By combining results with fractographic analyses, it will be demonstrated that G 0 Ic is not simply a material property, but dependent on specimen lay-up. 

Hypoxia-mimicking Bioactive Materials for Regenerative Medicine

Maria Manuel Azevedo, Imperial College London

A major challenge in designing materials for tissue engineering is to provide a suitable environment to promote tissue regeneration. Here, we report the development of novel “smart” materials which activate a natural “self-healing” mechanism, namely the cellular response to low oxygen pressure (hypoxia).All cells in the body respond to changes in the oxygen pressure (caused by damaged vasculature or increased energy demands of growing tissue) through a hypoxia-sensing pathway. This pathway then activates numerous cellular processes involved in tissue regeneration by stimulating new blood vessel growth, recruiting stem cells, directing cell differentiation and promoting proliferation. These fundamental processes, essential for natural healing response, could be critical for many tissue engineering strategies. Several approaches to regulating the hypoxia pathway may be used, including recombinant proteins or gene target technology. The possibility of using novel resorbable bioactive glasses as delivery system for hypoxia-stimulating ions (Co2+) will be discussed in this lecture.

Thermal Analysis of Zirconium Carbide by Laser Melting

Heather F. Jackson, Imperial College London

Zirconium carbide (ZrC) is a candidate coating material for advanced nuclear fuels, promising for its high temperature mechanical strength and inertness, thermal conductivity, and neutron transparency. The more demanding temperature and irradiation conditions of next-generation nuclear power plants, acting on multi-component fuels and wasteforms containing ZrC, will affect stability and durability in ways current technology is at a loss to predict. The goals of safe, reliable, efficient, and sustainable energy production drive the need for an improved understanding of the fundamental chemical and physical processes limiting fuel performance.As part of a study of thermodynamic stability in the Zr-C system, melting of ZrC ceramics has been investigated via a novel laser heating thermal analysis technique. Laser melting is promising for probing extremely high temperature (>3000°C) phase transitions in refractory materials for which traditional techniques are problematic. Ultimately, this study aims to assess the feasibility and validity of this new technique for ZrC and to contribute new thermodynamic data to the Zr-C system.