Evaluation of soft-tissue properties under controlled expansion for reconstructive surgical use.

The field of tissue surgery using silicone inflatable expanders presently relies on a surgeon's qualitative prediction of the tissue yield during the expansion regime. This work examines the viscoelastic behaviour of pig tissue whilst undergoing expansion and compares the results with classical tensile test methods. Close correlation between the stress relaxation constants for each method is found. The time relaxation of the tissue conforms to a quasi-linear viscoelastic model which enables the time to achieve the maximum viscous tissue yield to be determined. The elastic fraction of tissue has been shown to increase progressively with increasing applied strain whilst the viscous fraction decreases. The greatest tissue yield is generated at low strains and is largely due to the reorientating of the collagen matrix in the direction of the applied stress. This analysis suggests that it may be possible to develop a set of protocols to control and quantify the generation of new tissue during an expansion regime.

Determination of relative contributions of 'mechanical' and 'biological' creep in tissue expansion using in vivo pressure monitoring: a preliminary report.

This work outlines the theory underlying tissue deformation in response to an applied force and presents a model to evaluate relative contributions to tissue generation from mechanical and biological creep. Using in vivo pressure measurement, this model has been tested with clinical data generated from a heterogeneous series of 10 patients undergoing tissue expansion. Preliminary results indicate that the model proposed is able to fit accurately both in vitro and in vivo data. Extrapolation of the model, in time, may lead to a prediction of the relative contributions of 'biological' and 'mechanical' creep.

Developmental toxicity of desbromoleptophos in chicks: enzyme inhibition, malformations and functional deficits.

The relationship among inhibition of acetylcholinesterase (AChE), inhibition of neuropathy target enzyme (NTE), and developmental toxicity of the organophosphorus ester desbromoleptophos (DBL) was evaluated in chicks exposed on day 3 or day 15 of incubation or 10 days posthatching. DBL induced prolonged inhibition of AChE and NTE when administered either early or late in incubation, structural malformations if administered before organogenesis, posthatching paresis if administered after organogenesis, and delayed deficits of gait if administered after hatching. The posthatching paresis and abnormal gait are not determined solely by either AChE inhibition of NTE inhibition, since they occur in the absence of the latter and are not invariably seen in the presence of the former (Toxicology 49: 253-261; 1988).