Explosives under pressurethe crystal structure of γ-RDX as determined by high-pressure X-ray and neutron di raction COMMUNICATION Swift et al. Structure of a lead urate complex and its e ect on the nucleation of monosodium urate monohydrate CrystEngComm www.rsc.org/crystengcomm

The crystal structure of the highly metastable beta-form of RDX shows that the molecules adopt different conformations compared to the alpha-form and that, contrary to previous reports, the beta-form obtained at ambient pressure is not the same form as that obtained at elevated temperatures and pressures.

By means of a straightforward modi®cation to the Paris±Edinburgh cell gasket con®guration, it is now possible to utilize¯uid pressure-transmitting media up to at least 9 GPa. Test data on various representative samples are presented, discussed and contrasted with typical results obtained using the earlier gasket arrangement and Fluorinert pressure-transmitting medium. For the case of deuterated urea, the signi®cant improvement in compression conditions revealed the existence of two new structural phases (IV and V) which are ®rst observed at 3.0 GPa and 7.5 GPa. Future development possibilities for the technique of sample encapsulation are presented and discussed.

The cementite phase of Fe 3 C has been studied by high-resolution neutron powder diffraction at 4.2 K and at 20 K intervals between 20 and 600 K. The crystal structure remains orthorhombic (Pnma) throughout, with the fractional coordinates of all atoms varying only slightly (the magnetic structure of the ferromagnetic phase could not be determined). The ferromagnetic phase transition, with T c 9 480 K, greatly affects the thermal expansion coef®cient of the material. The average volumetric coef®cient of thermal expansion above T c was found to be 4.1 (1) Â 10 À5 K À1; below T c it is considerably lower (< 1.8 Â 10 À5 K À1) and varies greatly with temperature. The behaviour of the volume over the full temperature range of the experiment may be modelled by a thirdorder Gru È neisen approximation to the zero-pressure equation of state, combined with a magnetostrictive correction based on mean-®eld theory.

While new biomaterials for regenerative therapies are being reported in the literature, clinical translation is slow. Some existing regenerative approaches rely on high doses of growth factors, such as bone morphogenetic protein‐2 (BMP‐2) in bone regeneration, which can cause serious side effects. An ultralow‐dose growth factor technology is described yielding high bioactivity based on a simple polymer, poly(ethyl acrylate) (PEA), and mechanisms to drive stem cell differentiation and bone regeneration in a critical‐sized murine defect model with translation to a clinical veterinary setting are reported. This material‐based technology triggers spontaneous fibronectin organization and stimulates growth factor signalling, enabling synergistic integrin and BMP‐2 receptor activation in mesenchymal stem cells. To translate this technology, plasma‐polymerized PEA is used on 2D and 3D substrates to enhance cell signalling in vitro, showing the complete healing of a critical‐sized bone injury in mice in vivo. Efficacy is demonstrated in a Münsterländer dog with a nonhealing humerus fracture, establishing the clinical translation of advanced ultralow‐dose growth factor treatment.