Vol. 6, No. 1-4, 2011

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ISSN: 1559-3959
Deep penetration and liquid injection into adipose tissue

Kerstyn Comley and Norman Fleck

Vol. 6 (2011), No. 1-4, 127–140
Abstract

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 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.

Keywords
adipose tissue, soft solids, deep penetration, injection, fracture mechanics, toughness
Milestones
Received: 18 August 2010
Revised: 20 October 2010
Accepted: 23 October 2010
Published: 28 June 2011
Authors
Kerstyn Comley
Cambridge University
Department of Engineering
Trumpington Road
Cambridge  CB2 1PZ
United Kingdom
Norman Fleck
Cambridge University
Department of Engineering
Trumpington Road
Cambridge  CB2 1PZ
United Kingdom