One-step hydrothermal synthesis with in situ milling of biologically relevant hydroxyapatite.

Biologically relevant synthetic hydroxyapatite (HA) has become a much-desired material for use within the medical field with an emphasis on orthopedic applications. However, there are very few sources of sub-micron scale HA powders that are economical. Many current procedures to generate synthetic HA, that is both biological and chemically analogous to naturally occurring HA, tend to involve complicated synthesis procedures that are difficult to simultaneously produce desired stoichiometric ratios and particle diameter. This paper reports the development of a one-step hydrothermal method with in situ ball milling of synthetic HA. That has the potential to be a biological substitute with similar calcium to phosphate stoichiometric ratio and particle diameter of HA found in many natural biologically occulting sources. Parameters affecting particle diameter investigated included varying ball milling media, in situ and ex situ ball milling, and simultaneous agitation. The stoichiometric ratios of the resulting powders indicated that 4-hour hydrothermal reaction time produced materials that are analogous to natural HA, confirmed from spectra acquired via Fourier Transform Infrared spectroscopy (FT-IR). X-ray diffraction and Scanning Electron Microscopy both indicate that the predominant size of primary crystallites is around ~25 nm. Particle size distributions of dried in situ ball-milled HA suggest that primary crystallites exist as aggregates, with aggregate diameters ranging between 1 and 100 µm.

Intrinsic property measurement of surfactant-templated mesoporous silica films using time-resolved single-molecule imaging.

Mesoporous silica membranes fabricated by the surfactant-templated sol-gel process have received attention because of the potential to prepare membranes with a narrow pore size distribution and ordering of the interconnected pores. Potential applications include ultrafiltration, biological separations and drug delivery, and separators in lithium-ion batteries. Despite advancements in synthesis and characterization of these membranes, a quantitative description of the membrane microstructure remains a challenge. Currently the membrane microstructure is characterized by the combination of results from several techniques, i.e., gas permeance testing, x-ray diffraction scanning electron microscopy, transmission electron microscopy, and permporometry. The results from these ensemble methods are then compiled and the data fitted to a particular flow model. Although these methods are very effective in determining membrane performance, general pore size distribution, and defect concentration, they are unable to monitor molecular paths through the membrane and quantitatively measure molecular interactions between the molecular specie and pore network. Single-molecule imaging techniques enable optical measurements that probe materials on nanometer length scales through observation of individual molecules without the influence of averaging. Using single-molecule imaging spectroscopy, we can quantitatively characterize the interaction between the probe molecule and the interior of the pore within mesoporous silica membranes. This approach is radically different from typical membrane characterization methods in that it has the potential to spatially sample the underlying pore structure distribution, the surface energy, and the transport properties. Our hope is that this new fundamental knowledge can be quantitatively linked to both the preparation and the performance of membranes, leading to the advancement of membrane science and technology. Fluorescent molecules, 1,1-dioctadecyl-3,3,3,3-tetramethylindo-carbocyanine perchlorate, used to interrogate the available free volume in their vicinity, were loaded into the mesoporous silica membranes at subnanomolar concentrations. The mesoporous silica films were prepared using a nonionic ethylene oxide-propylene oxide-ethylene oxide triblock copolymer surfactant, Pluronic P123, on single crystal silicon substrates using dip coating of a silica sol. Membranes were prepared resulting in an average pore diameter of approximately 5 nm as measured by helium, nitrogen permeance, and porosimetry. Fluorescent images and time transient experiments were recorded using a custom built single-molecule scanning confocal microscope at differing temperatures (10, 20, 30, 40, and 50 degrees C). Time-dependent polarization anisotropy was used to obtain the enthalpy of adsorption and Henry's law constant of the probe molecule.