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If you missed out, or just want a refresher then some of the presentations from our Industrial Group sessions at the 2011 spring meeting can be found below.
IG Plenary Combinational Studies of Biomaterials Nora H. de Leeuw, Department of Chemistry, University College, London Nora began by saying mammalian bone and tooth enamel are organic/inorganic composites, comprising of inorganic hydroapatite as the mineral phase and the collagen I protein as the organic phase. Due to its importance in natural bone tissue, hydroxyapatite is also used as a synthetic biomaterial, for example in hydroxyapatite/glass and hydroxyapatite/polymer composites. The talk presented an overview of the computational research carried out at UCL, to understand the structures and properties of a number of biomaterials.
D.F. Williams in 1987 defined a biomaterial as a material used in medical devices, intended to react with biological systems. For biocompatibility the chemistry of the implant and its leach-ability need to be understood. Nora said that U.S.A. data for 2002 says that the overall medical device market is $77, 000 million and that of this the biomaterials market is $9,000 million.
Natural bone contains a relatively simple protein phase (collagen). Nora showed high magnification images of the bone structure in which sheets of collagen fibres were clearly evident. Bone research presents many scientific challenges: 1) biomineralisation of organic/inorganic deposits. 2) design and integration of bioactive glass/ceramic implants 3) the gap between experiment and computation 4) the need for high accuracy but also large systems need to be studied. Hydroxyapatite, bioglasses and collagen for soft tissue replacement are some of the materials being studied.
Nora described in some detail her work with hydroxyapatite, Ca10(PO4)6(OH)2. Its natural crystal structure is hexagonal and its laboratory, synthetic, structure is monoclinic. The hydroxyl groups occupy different positions within the structure. OH ordering is evident. Type A defects are when carbonate, CO3, groups are in the OH channel. Type B defects are due to charge compensation arising from calcium vacancies and charge compensation by hydroxyl and cation (e.g. sodium) groups. Carbonates occur in natural apatite. Apatites in synthetic and high temperature apatites contain Type A or Type A and B defects whereas apatites in bone and enamel contain Type B defects.
Investigations of silica-hydroxyapatite interfaces have taken place. For hydroxylated surfaces the adhesion energy converges to a single value which is independent of the substrate surface or film rotation. It was found that the strongest apatite adhesion is to a de-protonated silica surface.
Nora went on to discuss Phosphate Based Bioactive Glasses (PBG’s). These are the third generation of biomaterial whereby they promote tissue regeneration yet degrade after tissue repair. Calcium increases the rigidity of PBG structures by slowing down the dissolution.
The collagen phase of natural bone has also been investigated. Initial work concentrated on hydroxyapatite nucleation in an aqueous environment and on collagen bulk behaviour. Better mathematical models had to be developed to produce a 3-D representation of the collagen matrix. This reproduces the experimental structure and water content.
Nora Leeuw with I.G. Chair Judith Shackleton Mark Farnworth. Pilkington-NSG, Lancashire
IG1 and IG2 were joint sessions between the BACG (British Association of Crystal Growth) and two BCA groups: the Industrial Group and the Chemical Crystallography Group. The organisers were Sven Schroder, representing the BACG, Louise Male from the CCG and Anne Kavanagh from the IG.
IG1 was chaired by Dr. Sven Schroder of Manchester University and was comprised of three talks covering crystallization in the nuclear and photographic industries, and new tools to assess crystal structures from the CCDC.
Dr. Karen Harvey (Harman Technology) spoke about the controlled crystallization of silver halides for use in photographic materials. She explained how the product performance of film and paper are determined by the crystal, size, size distribution and chemical composition of the silver halide particles. For photographic papers, sub-micron, monosized cubes of silver chlorobromide are required. For films, the particles are larger, tabular and consist of silveriodobromide, with a core-shell structure in which the core of the particle has a higher iodide content than the shell. The design and manufacture of these particles involves double-jetting of silver nitrate and sodium or potassium halide solutions into a gelatin solution, with precise control of the composition of the growth solution.
Dr Sophie Janbon (AstraZeneca) presented a joint contribution with the CCDC (Cambridge Crystallographic data Centre). A collaboration between the CCDC and thirteen companies interested in the structure of small organic molecules has resulted in a new tool to study the frequency of Hydrogen bonding motifs. This is relevant to the pharmaceutical industry because typical drug molecules contain several hydrogen bond donors or acceptors. The basis of the propensity tool is that the most energetically-favourable hydrogen bond interactions will be formed. The tool will help understand polymorphism in drug molecules by indicating when a particular hydrogen bond motif is common or unusual, and hence suggest whether a polymorph is metastable. Sophie illustrated her talk with pharmaceutical examples of Ritonavir, a treatment for HIV infection, and Bicalutamide, an anti-cancer drug.
Dr Scott Owens (National Nuclear Lab) gave intriguing insights into the challenges faced by crystallization studies in the nuclear industry, and the key part these studies play in, for instance, manufacture of fuel rods, scale formation and the recycling of fuel. Manufacture of fuel rods involves the formation of uranium oxide powders from the gas phase, and these powders must have the correct morphology (tabular) and particle size to ensure high quality fuel is produced. Formation of ‘crud’ in the reactor cooling circuit can cause blockages, Understanding crystallisation is also important in dealing with spent fuel rods, whether for reprocessing or for sending to waste. Reprocessing starts with dissolution of the spent fuel rods followed by mixing and concentrating several waste streams, without allowing crystallisation to occur, before calcining to form precursors to new fuel rods. Dr Owens alsoshowed some amazing footage taken by a remotely operated camera from pipes in and around the reactor.
IG1. L to R: Sophie Janbon, Louise Male, Sven Schroder, Karen Harvey, Scott Owens.
Dr. Louise Male of Birmingham University chaired IG2, which consisted of two presentations on protein crystal growth, and the YC Prize Lecture.
Dr. Patrick Shaw Stewart of Douglas Instruments described the benefits of seeded crystallization of protein crystals and offered many practical hints and tips for success, based on twenty years of experience. He explained that use of seeds increases the success rate because crystals could be obtained from within the metastable zone, without the need to go to the higher supersaturations required for spontaneous nucleation. Recommendations included using ground seed particles, suspending crushed seeds in reservoir solution, freezing seed stocks and avoiding the waste of seed by contact dispensing. The use of cross-seeding (with other proteins, ground glass or zeolites) can also be effective. The difficulties caused by salt formation and the possible polymorphism of the proteins was also discussed.
Dr. Fabrice Gorrec of the Laboratory of Molecular Biology, Cambridge, described an automated and extensive screening process for obtaining protein single crystals using a variety of ‘LMB screens’. The screens aim to cover a wide range of conditions to maximize the chances of success, but are sufficiently straightforward that the non-expert can perform them. Recent developments include the use of statistical design of the screens to cover a wide range of conditions in as few wells as possible. Dr Gorrec finished his talk with some examples of the structures solved at the LMB in recent years.
The winner of the IG Prize for the best talk given at the YC meeting was Oliver Zeldin, of Oxford University for his talk ‘High-throughput metallo-protein analysis by microPIXE’. Oliver explained the basis of micro-PIXE (a high energy proton beam excites characteristic X-Ray emission form the sample) and how it can be used to determine the identity and stoichiometry of the bound metals. Currently the application of the technique is limited by the number of samples that can be run in a day and Oliver is developing methods to overcome this constraint using high throughput sample preparation via a technique of ink-jet printing the samples onto polypropylene. He has printed samples in arrays of 12x12 and demonstrated that no cross-talk between the drops is occurring during preparation or analysis, and is now working to finesse the technique.
Anne Kavanagh and Louise Male, Astra Zeneca
WEDNESDAY 13 April, Stress-strain microstructure Chair J Shackleton, Materials Science Centre, University of Manchester.
IG Award Lecture "Raising the Standard" Dr Steve Norval, Consultant, Guisborough, North Yorkshire.
Steve’s talk was a fascinating journey through a 30 year career in XRD Steve described his interests The materials studied ranged from catalysts to polymer composites to biomedical devices to foodstuffs, it was quite a list! A common theme throughout Steve’s career was the use of lanthanum hexaboride (SRM660), the diffraction standard for line shape and line positions. Steve described the importance of this standard to enable confidence in the data, techniques and methods. Perhaps most importantly it provided the reference point for line profile analysis. The microstructure of nano-materials is particularly relevant to many of today’s industrial processes. Steve also discussed techniques developed for non-ambient and reactive environment studies.
At the end of his talk Steve received a model of lanthanum hexaboride as a gesture of appreciation for his many contributions to Industrial Crystallography. I’m sure that we all would like to thank Steve for his expert advice and support and wish him all the very best for the future.
The Influence Of the a/b Phase Fraction on the Lattice Strain Evolution in Thermo-mechanically-Processed Ti-6246 Dr. Moataz Attallah, School of Metallurgy & Materials, University of Birmingham
Dr Moataz Attallah described in-situ, tensile loading experiments using synchrotron diffraction. Plates of b-forged Ti-6246 were thermo-mechanically processed using a combination of cross rolling and aging to give different fractions of the a and b phases. Although, the effects of lattice strain evolution during in-situ loading of a/b containing Ti-alloys had been studied previously using neutron and synchrotron x-ray diffraction, and successfully modelled; the influence of the relative fractions of the a and b had not been systematically investigated. Moataz described how the variation in the phase fractions affected the load-bearing orientations.
Day 3 THURSDAY 14 April, Materials Science - White Beam Methods Chair Prof Bob Cernik, Materials Science Centre, University of Manchester
Characterisation of Polycrystal Deformation at Different Scales by White Beam X-Ray Diffraction Dr Xu Song University of Oxford
Dr Xu Song described the widely accepted belief in Industry that residual stresses and prior deformation (e.g. forging during fabrication) in structural components can have a strong influence on their fatigue performance and life in service. He described how the white beam diffraction method is increasingly used as a major tool for residual stress and deformation evaluation. Xu presented an overview of recent work on white beam diffraction, with examples of the measurement of the residual stresses in a Rolls-Royce Trent 500 aero-engine turbine blade, around an Electron Beam) weld of a soleplate in an aero-engine combustion casing, and Friction Stir Welded aluminium alloy plates used in aircraft fuselage panels.
Xu described the use of the new, high flux, high energy station on beam-line I12 called JEEP at Diamond The instrument has a 23-element Germanium EDXD detector which permits the simultaneous collection of multiple diffraction patterns. This enables “single shot” complete analysis of the two-dimensional strain state within the sample. Xu illustrated this with some examples of the measurement of stresses in linear friction welds AA2024 aluminium alloy bars. Diffraction Tomography Using Synchrotron Sources and its Application to the Imaging of Materials in Static and Dynamic Systems Dr Simon Jaques, Materials Science Centre, University of Manchester
Dr Simon Jaques described the continued advancement of X-ray generation and data collection meaning that it is now possible to obtain high quality scattering data from materials , very quickly, with second/sub-second time resolution. This has facilitated the practical application of diffraction based imaging as a tool to map materials within samples. Such methods have the obvious advantage over contrast imaging techniques such as traditional computed tomography scanning, in that the diffraction signal (and other scattering signals) can be used to uniquely identify and quantify the materials within the sample/object under investigation. Simon’s presentation gave an overview of diffraction based imaging methods, showing what information can be obtained as well as the current limitations.
White-Beam X-Ray Topography and Microscopy Prof Morton Moore Royal Holloway College
Prof Morton Moore’s talk described white beam X-ray topography as the simplest X-ray imaging technique for crystals. He described how an X-ray topograph is formed by a Bragg reflection and is in effect a high-resolution Laue ‘spot’. Synchrotron radiation has advanced X-ray topography given the sources’ broad continuous spectrum, small beam divergence, high intensity, strong polarization and regular pulsed time structure. Morton described how the configuration of the experiment must be chosen carefully to minimize geometrical image distortions. The detector may be an image plate or a charge-coupled device; but for the best resolution (1 or 2 micrometers), photographic plates are used to image individual dislocations.
Whole specimens can be illuminated with synchrotron X rays, or regions could be selected using slits. The former case, is useful for checking crystals (in this case diamonds) looking for for distortions or for twinning. In the latter, an image can be made of a slice precisely parallel to a chosen crystallographic plane. Crystalline defects and strains associated with crystal growth, plastic deformation, phase transitions, polytypes and magnetic domains can be studied non-destructively by X-ray topography.
Afterwards Prof Bob Cernik led a lively discussion of the papers which ran well into the tea break as there was so much interest in the papers, which the audience thoroughly enjoyed.
Judith Shackleton, Manchester Materials Science Centre
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2011 BCA Spring Meeting at Keele |
