ABSTRACT
Measuring Principles 99 Hardware 102
Instrument Hardware and ControL 102 Calibration of the LSR 104
Software 105 Taking and Interpreting LSR Measurements 105
Reproducibility and Measurement Site 105 LSR Measurement Case Study 106
Study Protocols 106 Results and Interpretation 107
Discussion 108 Acknowledgments 109 References 109
The Gas-Bearing Electrodynamometer (GBEI-5) has been used for the last 20 years to obtain sensitive measurements of the stratum corneum. The Linear Skin Rheometer (LSR6) is a new instrument for measuring the mechanical properties of the stratum corneum that incorporates all of the measurement principles of the GBE but none of its components. A force-controlled miniature DC servo, gearing, and lead screw replace the magnet/solenoid arrangement of the GBE. Error resulting from conversion of an electrical signal to a mechanical force is automatically compensated for. Consequently,
100 Bioengineering of the Skin: Skin Biomechanics
this control renders the need for a friction-free bearing redundant. The original Linear Variable Differential Transformer (LVDT) has been replaced with a unit with a sensitivity of 0.01 % and force is now measured by a calibrated 100 g load beam. The function generator, signal conditioner, and storage oscilloscope have been replaced by user-friendly software run by a small portable computer. The new design offers greater inherent accuracy than the GBE and requires minimal servicing. The new LSR instrument has been shown to provide sensitive measurements of stratum corneum mechanics. A simple case study is presented in which the LSR was used to measure the mechanical responses of the stratum corneum to two topical moisturizing treatments of differing relative hydration performance (as determined by impedance measurements using the Nova® DPM9003). The relative performance of the two products as measured by the LSR compared favorably with corresponding impedance data, indicating the ability of the LSR to differentiate varying degrees of stratum corneum plasticization in response to hydration.
