Evaluation of composition and mineral structure of callus tissue in rat femoral fracture.

Callus formation is a critical step for successful fracture healing. Little is known about the molecular composition and mineral structure of the newly formed tissue in the callus. The aim was to evaluate the feasibility of small angle x-ray scattering (SAXS) to assess mineral structure of callus and cortical bone and if it could provide complementary information with the compositional analyses from Fourier transform infrared (FTIR) microspectroscopy. Femurs of 12 male Sprague-Dawley rats at 9 weeks of age were fractured and fixed with an intramedullary 1.1 mm K-wire. Fractures were treated with the combinations of bone morphogenetic protein-7 and/or zoledronate. Rats were sacrificed after 6 weeks and both femurs were prepared for FTIR and SAXS analysis. Significant differences were found in the molecular composition and mineral structure between the fracture callus, fracture cortex, and control cortex. The degree of mineralization, collagen maturity, and degree of orientation of the mineral plates were lower in the callus tissue than in the cortices. The results indicate the feasibility of SAXS in the investigation of mineral structure of bone fracture callus and provide complementary information with the composition analyzed with FTIR. Moreover, this study contributes to the limited FTIR and SAXS data in the field.

DNA with double-chained amphiphilic counterions and its interaction with lecithin.

Complex salts of double-stranded DNA with amphiphilic counterions offer novel opportunities for studies of DNA-lipid interactions. Here the effect of the hydrophobicity of the amphiphilic counterion is in focus. For this purpose, double stranded DNA with didodecyldimethylammonium ions as counterions, DDADNA, is prepared and investigated with respect to microstructure. In particular, in order to monitor the interactions with phospholipids, the phase diagram of the DDADNA/lecithin/water system is determined and compared with the previously determined phase diagram with single alkyl chain counterions, dodecyltrimethylammonium, DTA. In both systems, there is a formation of lamellar and reverse hexagonal phases, where hydrated DNA is sandwiched between bilayers or forms the core of reverse cylindrical micelles, respectively. However, whereas the lecithin lamellar phase can incorporate large amounts of DDADNA, there is in the case of the single chain surfactant, DTADNA, a transition to a bicontinuous cubic phase at higher DTADNA concentrations. The general appearance of the phase diagrams, and in particular the role of counterion hydrophobicity, can be rationalized in a simple geometric model.