科研之友
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摘要
The subcutaneous injection of porcine adipose tissue by a hypodermic needle involves two stages: tissue penetration followed by the delivery of liquid into the tissue. The force required to penetrate adipose tissue by a series of conically tipped and flat-bottomed circular punches has been measured. Scanning electron microscopy and light microscopy are used to observe the mechanism of crack formation during penetration. The experiments reveal that penetration by either a flat bottomed or 45 degrees conically tipped punch involves the formation of a mode II ring crack. The predicted penetration pressure according to the Shergold-Fleck model (Proc. R. Soc. Lond. A 460 (2004), 3037-3058) is in good agreement with the measured pressure on the punch. The subsequent delivery of liquid into adipose tissue by the hypodermic needle has also been examined: the injection pressure for phosphate buffered saline has been measured for a range of flow rates. X-ray images of the injected liquid suggest that micro-cracks are formed by the fluid pressure within the tissue and this leads to an increase in permeability. A seepage model is developed, based on the Darcy flow law, to relate the volumetric flow rate to the injection delivery pressure. Finally, a model of hydraulic fracture is used to assess the toughness associated with the formation of the micro-cracks during injection.
- 出版日期2011-6
