Why Mechanical Properties of Collagen Scaffolds Should Be Tested in a Pseudo-Physiological Environment?

Abstract

Collagen gels constitute an adequate scaffold for supporting the adhesion, proliferation and tissue regeneration of vascular cells inside a bioreactor. However, their mechanical properties should be enhanced not only for their manipulation but also to resist the mechanical constraints applied in the bioreactor. Actually, assessing the mechanical properties of a hydrogel requires many precautions since they are very sensitive to the environmental conditions (temperature, ionic strength, aqueous environment, etc). Whereas mechanical properties are usually measured directly in the air, the aim of this work was to evaluate the effects of a pseudo-physiological environment (PPE) on the mechanical properties of collagen gels. Furthermore, reinforcement was also tested using UV treatments (λ = 254 nm, 20 J/cm2), known to induce crosslinking. Irradiated samples were more resistant to enzymatic degradation and swelling tests showed that the crosslink density was increased by a factor of 30. This increase was thereafter correlated to the mechanical properties. Results showed that the UV-treated samples were stiffer and more brittle than the non-treated ones when tested in air. However, a 20% decrease and 40% increase were respectively measured on the linear modulus and strain at rupture when the gels were tested in the PPE. In the perspective of vascular tissue regeneration, these results show that the mechanical properties of a hydrogel should be performed in PPE in order to take into account the plasticization phenomenon that will occur in a bioreactor.