Multiscale Approach to Characterize Mechanical Properties of Tissue Engineered Skin.

Tissue engineered skin usually consist of a multi-layered visco-elastic material composed of a fibrillar matrix and cells. The complete mechanical characterization of these tissues has not yet been accomplished. The purpose of this study was to develop a multiscale approach to perform this characterization in order to link the development process of a cultured skin to the mechanical properties. As a proof-of-concept, tissue engineered skin samples were characterized at different stages of manufacturing (acellular matrix, reconstructed dermis and reconstructed skin) for two different aging models (using cells from an 18- and a 61-year-old man). To assess structural variations, bi-photonic confocal microscopy was used. To characterize mechanical properties at a macroscopic scale, a light-load micro-mechanical device that performs indentation and relaxation tests was designed. Finally, images of the internal network of the samples under stretching were acquired by combining confocal microscopy with a tensile device. Mechanical properties at microscopic scale were assessed. Results revealed that adding cells during manufacturing induced structural changes, which provided higher elastic modulus and viscosity. Moreover, senescence models exhibited lower elastic modulus and viscosity. This multiscale approach was efficient to characterize and compare skin equivalent samples and permitted the first experimental assessment of the Poisson's ratio for such tissues.

Rheological behaviour of reconstructed skin.

Reconstructed skins have been developed to replace skin when the integrity of tissue has been compromised following severe injury, and to provide alternative methods validating the innocuousness and effectiveness of dermatological and cosmetic products. However the functional properties of tissue substitutes have not been well characterised, mainly since mechanical measurement devices have not been designed to test cell culture materials in vitro. From the mechanical standpoint, reconstructed skin is a heterogeneous multi-layer viscoelastic material. To characterise the time-dependent behaviour of reconstructed skin, spherical indentation load-relaxation tests were performed with a specific original device adapted to measure small soft tissue samples. Load-relaxation indentation tests were performed on a standard reconstructed skin model and on sub-components of the reconstructed skin (3D-scaffold alone and dermal equivalent). Generalised Maxwell and Kelvin-Voigt rheological models are proposed for analysing the mechanical behaviour of each biological tissue. The results indicated a modification of the rheological behaviour of the samples tested as a function of their biological structure. The 3D-scaffold was modelled using the one-branch Maxwell model, while the dermis equivalent and the reconstructed skin were modeled using a one-branch and a two-branch Kelvin-Voigt model, respectively. Finally, we demonstrated that skin cells contribute to global mechanical behaviour through an increase of the instantaneous relaxation function, while the 3D-scaffold alone influences the mechanical response of long relaxation times.

Mucoadhesion evaluation of polysaccharide gels for vaginal application by using rheological and indentation measurements.

The influence of hyaluronic acid (HA) and fructooligosaccharides (FOS) addition on low methyl pectin (LMP) gelation has been investigated in order to produce adhesive gel-based microparticles suitable for the development of a vaginal delivery system of pro- and prebiotics. First, dynamic rheological measurements were performed on LMP/Ca(2+) gels with or without FOS and HA in presence or not of porcine stomach mucins. This rheological method is known to translate the interactions between polymer and mucins and then simulate the polymer bioadhesion potential. Nevertheless, as this method is disputed, in vitro and ex vivo indentation test measurements were also achieved in order to correlate the results obtained. Despite some different results, the overall tendency indicates that addition of HA and FOS enhanced the mucoadhesive properties of LMP gels. Moreover, gel-based microparticles obtained according to an emulsification/gelation method and composed by LMP 3% (w/v), FOS 5% (w/v) and HA 0.5% (w/v) displayed a mucoadhesive potential adapted to vaginal delivery system.