Development and Validation of an Artificial Mechanical Skin Model for the Study of Interactions between Skin and Microneedles

Abstract

Microneedles are small needle-like structures that are almost invisible to the naked eye. They have an immense potential to serve as a valuable tool in many medical applications, such as painless vaccination. Microneedles work by breaking through the stratum corneum, the outermost barrier layer of the skin, and providing a direct path for drug delivery into the skin. A lot of research has been presented over the past two decades on the applications of microneedles, yet the fundamental mechanism of how they interact, pressure, and penetrate the skin in its native state is worth examining further. As such, a major diffi culty with understanding the mechanism of microneedle-skin interaction is the lack of an artifi cial mechanical human skin model to use as a standardized substrate. In this research news, the development of an artifi cial mechanical skin model based on a thorough mechanical study of fresh human and porcine skin samples is presented. The artifi cial mechanical skin model can be used to study the mechanical interactions between microneedles and skin, but not diffusion of molecules across skin. This model can assist in improving the performance of microneedles by enhancing the reproducibility of microneedle depth insertions for optimal drug delivery and biosensing.

A micromechanical comparison of human and porcine skin before and after preservation by freezing for medical device development

“…The E SC of fresh human skin decreased from 139 MPa (35% RH) to 111 MPa (100% RH), but the E SC of fresh porcine skin increased from 56 MPa (35% RH) to 67 MPa (100% RH). This opposite effect of decrease/increase in E SC of human and porcine skin for increasing RH indicated potential structural, compositional and/or functional differences between human and porcine skin that influence moisture retention of the skin (especially at low RH) and its consequential mechanical properties (see Table S2, Supplement Material; P  = 0.007), as previously suggested by Ranamukhaarachchi et al 3. According to Silva et al 16, moisture is predominantly retained by the corneocytes of the SC at low RH, yielding a higher E SC ; whereas, both corneocytes and SC lipids swell substantially at high RH yielding a lower E SC due to softening of the SC.…”

“…2c) and was correlated with the UTS of fresh human and porcine skin3. The influence of RH on in-plane mechanical properties of skin differed from out-of-plane properties3. Since microneedle insertions applied in-plane stress (tension) on the skin, and corneocytes in the viable epidermis and the SC are naturally stacked on top of each other in an out-of-plane orientation (similar to a brick-mortar structure; Fig.…”

“…Many studies thus used porcine skin as a substitution for human skin151617 without confirming the mechanical similarities of both skin types in controlled experiments. The first controlled mechanical comparison of human and porcine abdominal skin specimens was performed by Ranamukhaarachchi et al 3,. where porcine and human skin samples were treated and evaluated using identical test protocols.…”

A Comparison of Drug Delivery into Skin Using Topical Solutions, Needle Injections and Jet Injections

“…In theory, a needle-free injection might penetrate less deep into human than porcine skin due to the different and larger Young's moduli of the stratum corneum. 21,33,34 It is assumed that the penetration depth of the solid needle injection is not affected due to its high penetration strength S, which is defined by the ratio between injection pressure and Young's modulus.…”

Novel dry metal electrode with tilted microstructure fabricated with laser micromilling process

“…Two dry metal electrodes were placed on the forearm to measure the electrode-skin impedance, with a distance between the electrodes of 5 cm [22][23]. The dry metal electrodes did not require any treatment of the skin before the measurement [24][25][26]. Based on the two-electrode measurement principle, the same pair of electrodes could be used for the driving and measurement electrodes.…”