A novel ultra-light suction device for mechanical characterization of skin

Abstract

Suction experiments have been extensively applied for skin characterization. In these tests the deformation behavior of superficial tissue layers determines the elevation of the skin surface observed when a predefined negative (suction) pressure history is applied. The ability of such measurements to differentiate between skin conditions is limited by the variability of the elevation response observed in repeated experiments. The scatter was shown to be associated with the force exerted by the observer when holding the instrument against the skin. We have developed a novel suction device and a measurement procedure aiming at a tighter control of mechanical boundary conditions during the experiments. The new device weighs only 3.5 g and thus allows to minimize the force applied on the skin during the test. In this way, it is possible to reliably characterize the mechanical response of skin, also in case of low values of suction pressure and deformation. The influence of the contact force is analyzed through experiments on skin and synthetic materials, and rationalized based on corresponding finite element calculations. A comparative study, involving measurements on four body locations in two subjects by three observers, showed the good performance of the new procedure, specific advantages, and limitations with respect to the Cutometer®, i.e. the suction device most widely applied for skin characterization. As a byproduct of the present investigation, a correction procedure is proposed for the Cutometer measurements, which allows to partially compensate for the influence of the contact force. The characteristics of the new suction method are discussed in view of future applications for diagnostic purposes.

On the Reliability of Suction Measurements for Skin Characterization

“…These parameters were assessed in two ways: by directly using the tissue elevation readings (R0 or h ¼ 0.5 mm) or by applying the correction scheme proposed in Ref. [21] to reduce the influence of the contact force between device and tissue. The elevation value reported in the Cutometer measurement considers the initial position of the tissue apex as the "zero-point" and quantifies the additional elevation from that position.…”

“…The Cutometer parameter called Offset is measured as the elevation prior to start of the measurement, i.e., at p 5 0 mbar. (c) Tissue stiffness calculation applying the correction procedure [21]. Here, the Offset is considered as part of the total elevation.…”

“…As demonstrated in Ref. [21], using the total elevation for tissue characterization partially compensates for the stiffening effect associated with the predeformation caused by the contact force.…”

“…The second suction protocol used the Nimble [21], a novel suction device specifically developed to drastically reduce the contact force in skin suction measurements. As illustrated in Fig.…”

“…The suction method is pain-free, noninvasive, and thus highly promising for clinical applications. Existing devices however have not been widely adopted for medical use, mainly due to the measurement uncertainty associated with the variability of the contact force between the aspiration probe and the tissue surface during the procedure [20,21]. We have recently proposed a new suction device addressing this issue by a light-weight design [21], which reduces the influence of contact force and relative movements between observer and patient.…”