X-ray diffraction (XRD) is a non-destructive laboratory technique that assesses the lattice spacing of crystalline solids [1]. Lattice spacings and distortions can be used to identify elastic properties, residual stresses, and the identities of unknown materials in a sample [1]. XRD can help characterize critical material properties for information on how a material might interact with biological tissue upon implantation. XRD collects lattice spacing by shooting an X-ray into a crystalline solid at a known wavelength, λ, and a known angle, θ, and then gathering the intensity of the collected refracted X-ray [2]. When shooting the X-ray at the crystal, part of the beam will pass through the atomic plane, and part will hit a lattice and refract back into the diffractometer, which measures the intensity of the refracted beam [2]. The angle that the X-rays are fired into the sample, with a range of angles from 0 – 90° [3]. The X-ray beam is rotated so that different atomic planes can be activated; firing at 20° may not hit an atomic plane and the entire beam might pass through, whereas firing at 65° may hit the lattices on the atomic plane and refract the beam towards the diffractometer [2]. XRD has many advantages when being used for the characterization of a biomaterial, as XRD is typically non-destructive and does not require a vacuum to function.
The powdered technique of XRD involves the irradiation of a powdered crystalline material to identify different (hkl) miller indices from different lattice spacings throughout the sample [2]. The intensity readings correspond uniquely to a specific element; the powdered technique allows the identification of elements present in the sample by identifying the miller indices and atomic spacings of the element present, which are unique to that element [2]. If a sample contains more than one material, there will be multiple intensity readings that can be used to identify the present elements [2]. This technique can prove especially useful with material intended for medical use, as biomaterials are typically some sort of composite involving a mixture of elemental compositions which can all be identified with XRD. XRD is not only time-effective, but it is often cost-effective as well when considering the costs of electron microscopy, which can provide similar information. XRD is a convenient and effective solution for characterizing materials for use in medical devices, biomaterials, drug delivery solutions, and more.
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[1] – Wang, A.N., Chuang, C.P., Yu, G.P., & Huang, J.H. (2014). Determination of average X-ray strain (AXS) on TiN hard coatings using cos2αsin2ψ X-ray diffraction method. Surface & Coatings Technology 262, 2015 (40-47). http://dx.doi.org/10.1016/j.surfcoat.2014.12.009
[2] – Kasap, S.O. (2006). Principles of Electronic Materials and Devices 3rd ed. p.(848-852). ISBN 0-07-295791-3
