This study attempts to define a universal description of the constitutive formulation of mechanical properties of synthetic hydrogels that can be manufactured as load-bearing structures to replace diseased or damaged soft tissues. While the strain energy density function (SEF) describing the elastic properties of a soft tissue generally depends on two invariants, we propose a SEF that depends on only the first strain invariant. This allows quantifying the SEF from data of a uniaxial extension test. The single invariant SEF was used to predict the mechanical response of a thick-walled tube inflated by an internal pressure. The results show excellent concordance with recorded experimental data, indicating that the mechanical properties of elastic hydrogels can be accurately represented by a SEF that is an exponential function of the first strain invariant with two material constants.

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PURPOSE: Flap necrosis caused by inadequate blood supply and infl ammation is a common postoperative complication in reconstructive surgery. 1 Lu et al. claimed adipose-derived stem cells increase the viability of random pattern skin fl aps via subcutaneous injection. 2 The purpose of this study is to examine if administration of human adipose-derived stem cells via local intra-arterial injection could improve survival of the random component of axial skin fl ap by animal study. MATERIALS AND METHODS:Human adipose-derived stem cells were isolated from a healthy 48 year-old woman by liposuction with patient consent and expanded ex vivo as standard protocol. After the elevation of axial epigastric fl ap in nude mice, human adipose-derived stem cells were then injected via right femoral artery (Figure 1) in different concentration (group A=1x10 3 , group B=1x10 4 , group C=1x10 5 ). The control group received 0.2 ml phosphate-buffered saline solution. After local injection, right superfi cial epigastric vessels were ligated to create unipedicle skin fl ap with random extension. The percentage of necrotic area was measured at postoperative day 7 for evaluation of fl ap viability. Specimens were also harvested for histologic analysis and ELISA assay. Figure 1. Human adipose-derived stem cells were then injected via right femoral artery.