A study on the development of a fully injectable calcium phosphate cement for orthopedic and dental applications is presented. The paper describes its characteristic properties including results of biocompatibility studies. A conventional two-component calcium phosphate cement formulation (having a powder part containing dry mixture of acidic and basic calcium phosphate particles and a liquid part containing phosphate solution) is modified with a biocompatible gelling agent, to induce flow properties and cohesion. The quantity of the gelling agent is optimized to get a viscous paste, which is smoothly injectable through an 18-gauge needle, with clinically relevant setting parameters. The new formulation has a setting time of 20 min and a compressive strength of 11 MPa. The X-ray diffraction, Fourier transform infrared spectrometry, and energy dispersive electron microprobe analyses showed the phase to be hydroxyapatite, the basic bone mineral. Scanning electron microscopy revealed a porous structure with particle sizes of a few micrometers. The cement did not show any appreciable dimensional or thermal change during setting. The injectability is estimated by extruding through needle and the cohesive property is assessed by water contact method. The cement passed the in vitro biocompatibility screening (cytotoxicity and haemolysis) tests.
The problem of predicting flow patterns during condensation inside horizontal tubes is discussed. Using the condensation flow pattern data of several investigators, a new flow regimes map with dimensionless gas velocity jg* as ordinate and (1-α)/α as abscissa, where α is the void fraction, is generated. Based on these data, a set of new criteria for the transition between different flow regimes is suggested. The proposed flow regimes map gives excellent agreement for annular, semiannular, and wavy flows which exist over a major part of the condensing length during condensation inside horizontal tubes.
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