A. Cuneyt Tas

The use of physiological solutions or media in calcium phosphate synthesis and processing.

This review examined the literature to spot uses, if any, of physiological solutions/media for the in situ synthesis of calcium phosphates (CaP) under processing conditions (i.e. temperature, pH, concentration of inorganic ions present in media) mimicking those prevalent in the human hard tissue environments. There happens to be a variety of aqueous solutions or media developed for different purposes; sometimes they have been named as physiological saline, isotonic solution, cell culture solution, metastable CaP solution, supersaturated calcification solution, simulated body fluid or even dialysate solution (for dialysis patients). Most of the time such solutions were not used as the aqueous medium to perform the biomimetic synthesis of calcium phosphates, and their use was usually limited to the in vitro testing of synthetic biomaterials. This review illustrates that only a limited number of research studies used physiological solutions or media such as Earles balanced salt solution, Bachra et al. solutions or Tris-buffered simulated body fluid solution containing 27mM HCO3(-) for synthesizing CaP, and these studies have consistently reported the formation of X-ray-amorphous CaP nanopowders instead of Ap-CaP or stoichiometric hydroxyapatite (HA, Ca10(PO4)6(OH)2) at 37°C and pH 7.4. By relying on the published articles, this review highlights the significance of the use of aqueous solutions containing 0.8-1.5 mMMg(2+), 22-27mM HCO3(-), 142-145mM Na(+), 5-5.8mM K(+), 103-133mM Cl(-), 1.8-3.75mM Ca(2+), and 0.8-1.67mM HPO4(2-), which essentially mimic the composition and the overall ionic strength of the human extracellular fluid (ECF), in forming the nanospheres of X-ray-amorphous CaP.

X-ray-amorphous calcium phosphate (ACP) synthesis in a simple biomineralization medium

An inorganic solution similar to the inorganic electrolyte compartment of the DMEM (Dulbeccos modified Eagles medium) cell culture medium is developed. This biomineralization medium contains 44.05 mM HCO3 -, 126.86 mM Na+, 93.37 mM Cl-, 5.33 mM K+, 2.26 mM Ca2+, 0.905 mM H2PO4 -, and 0.81 mM Mg2+. Its Ca/P molar ratio is set to be identical to that of human blood plasma, i.e., 2.50. The medium is free of any Tris or Hepes but maintains a pH of 7.45 both at 37 and 65 °C. The first novelty of this solution is that it has the unique ability to homogeneously coat X-ray-amorphous calcium phosphate (ACP) on glass slides vertically immersed in it and kept at 37 °C for less than 48 h. The second innovative aspect of this solution is that it has the unprecedented ability to produce monodisperse ACP nanospheres with diameters less than 180 nm when simply heated at 65 °C for 1 h while being stirred. The third novelty of this solution is that it only forms ACP and it does not form apatite in stark contrast to many other synthetic calcification or biomineralization media known. Samples were characterized by X-ray diffraction, energy-dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, BET surface area, contact angle goniometry, field emission-scanning and transmission electron microscopy analyses.

Development of a gas-fed plasma source for pulsed high-density plasma/material interaction studies

A gas-fed capillary plasma source has been developed to study plasma-surface interactions under pulsed high pressure arc conditions, without the use of an exploding fuse wire or ablative liner. A nonintrusive preionization source has been developed to break down relatively large interelectrode gaps at low charge voltages of 2-6 kV. The preionization source comprises a nonequilibrium surface streamer discharge that forms a conducting channel through which the main thermal arc discharge is initiated. The arc electron temperature and number density are estimated to be Te ~ 1-2 eV and ne ~ 1023 m-3. Silicon and sapphire samples were exposed to the arc plasma and revealed deposition of electrode and wall materials. Substitution of Elkonite 50W3 for brass electrodes reduced plasma contamination to acceptable levels. The plasma-material interactions were examined and quantified using scanning electron microscopy and energy dispersive X-ray spectroscopy.

Grade-1 titanium soaked in a DMEM solution at 37 °C

DMEM (Dulbeccos modified Eagle medium) solutions are used in performing in vitro cell culture experiments to assess the cell biocompatibility of synthetic biomaterials. In this study, Hepes-buffered, phenol red- and sodium pyruvate-free DMEM solutions were used, for the first time as immersion media at 37°C, to test alkali-treated (5M NaOH, 60°C, 24h) grade-1 titanium substrates. Such DMEM solutions were found to deposit X-ray-amorphous calcium phosphate (ACP), in one or two weeks, on the soaked grade-1 Ti substrates. A limited number of previous studies focusing on the biomimetic coating of alkali-treated Ti6Al4V coupons in DMEM have actually used different DMEM solutions, which were not Hepes-buffered and containing phenol red and sodium pyruvate. The previous studies with such DMEM solutions reported the deposition of cryptocrystalline apatitic calcium phosphate (Ap-CaP) on Ti6Al4V substrates, but not ACP. An inorganic solution (free of amino acids, vitamins, glucose, sodium pyruvate and phenol red), simulating the ion concentrations of the DMEM solutions, was also used for the first time in depositing ACP on grade-1 Ti substrates upon soaking at 37°C for only 24h. The solutions and deposits of this study were analyzed by AAS, ICP-AES, FTIR, XRD, XPS, and surface profilometry.