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BIOMECHANICS

March 2022 ESRFnews

deform samples while being tilted and rotated. Key to his proposal was his goal to make the computer code access- ible to other users, so that it can have benefits beyond his own work. After all, hierarchical structures and intricate crystallographic texture are found in a huge proportion of materials, from aerogels to carbon-fibre composites. Understanding these materials requires an understanding of their crystallographic textures. The computer code can t be a ship that only I can steer,

says Grünewald. It will need care, and thought, and I want to host workshops to help the community to be able to work with my software. There s already a bit of a community among those who use small-angle X-ray scattering tensor tomography this will be in a similar spirit. Texture tomography should image an entire enthe-

sis structure with 100 nm spatial resolution; the EBS high-energy X-rays will allow this at micron resolution during in situ tensile deformation at several load steps. That, in turn, will allow Grünewald to build a micro- mechanical enthesis model that reveals the load trans- fer between tendon and bone; he will collaborate with Martine Pithioux s team at the Institut des Sciences du Mouvement. Tendon is soft, bone is hard there needs to be an interface, he says. Orthopaedic injuries often involve damage to this interface in one form or another. As soon as you reattach tendon you are attempting to recreate this interface. Besides helping with the rehabilitation of those with orthopaedic injuries, he adds, a better under- standing of the load transfer could help avoid injuries in the first place, and even, in the long term, help scientists to develop replacement tissue scaffolds. Understanding the crystallographic texture is a prob-

lem that has been with me since my PhD, he says. You re always trying to push what is possible, one step at a time. 

Jon Cartwright

summer he completed his PhD he became a postdoctoral researcher at the ESRF at the ID13 microfocus beamline, working with scientist-in-charge Manfred Burghammer. After three years, while remaining an ESRF user,

Grünewald moved to the Institut Fresnel to learn about coherent X-ray diffraction imaging, as applied to the study of the nanostructural development of biominerals such as mollusc shells. But this was the time when the ESRF was shutting down to commission the EBS, and his mind was abuzz with the potential benefits of high flux, highly coherent synchrotron X-rays for biomineralisation stud- ies. If you had told me five years ago that you could get an X-ray beam as small as a few hundred nanometres at 100 keV, I would have laughed at you, he says. Extra flux and increased brilliance at higher energies this is what ultimately enables you to work swiftly, to catch the defor- mation of biomineralised samples in situ.

New source, new possibilities One problem in particular was distracting Grünewald: the inability of any instrumental technique to resolve, at once, the individual 3D orientations of the components of a crystalline material over a large volume in other words, the crystallographic texture. At last, the EBS gave him confidence that this could be done, and he set to work on a solution. The technique would require a sample to be tilted and rotated in an X-ray beam to satisfy the Bragg dif- fraction condition in multiple orientations; meanwhile, computer processing would be required to reconstruct the preferred crystal orientations in every voxel. Grünewald s proposal was accepted by the ERC at the

beginning of this year with a view to start work at the ESRF (while being based at Marseille) in the summer at the ID13 and ID15A beamlines the former as a place to reach ultimate spatial resolution down to 100 nm, and the latter as a site for a bespoke tensile rig, able to

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Tilman Grünewald began in academia studying wood, but swiftly moved on to biomineralisation and X-ray techniques.

The EBS provides extra flux and increased brilliance at high energies, so you can work swiftly, to catch the deformation of biomineralised samples in situ

The ID15A beamline will host a bespoke tensile rig to deform enthesis samples while texture tomography is taking place.