A thermomechanical framework for reconciling the effects of ultraviolet radiation exposure time and wavelength on connective tissue elasticity

摘要

Augmentation of the mechanical properties of connective tissue using ultraviolet (UV) radiation-by targeting collagen cross-linking in the tissue at predetermined UV exposure time (t) and wavelength (λ)-has been proposed as a therapeutic method for supporting the treatment for structural-related injuries and pathologies. However, the effects of λ and t on the tissue elasticity, namely elastic modulus (E) and modulus of resilience (u_Y), are not entirely clear. We present a thermomechanical framework to reconcile the t- and λ-related effects on E and u_Y. The framework addresses (1) an energy transfermodel to describe the dependence of the absorbed UV photon energy, ξ, per unit mass of the tissue on t and λ, (2) an intervening thermodynamic shear-related parameter, G, to quantify the extent of UVinduced cross-linking in the tissue, (3) a threshold model for the G versus ξ relationship, characterized by ~tC-the critical t underpinning the association of ξ with G-and (4) the role of G in the tissue elasticity.We hypothesized that G regulates E (UV-stiffening hypothesis) and u_Y (UV-resilience hypothesis). The framework was evaluated with the support from data derived from tensile testing on isolated ligament fascicles, treated with two levels of λ (365 and 254nm) and three levels of t (15, 30 and 60 min). Predictions from the energy transfer model corroborated the findings from a two- factor analysis of variance of the effects of t and λ treatments. Student's t test revealed positive change in E and u_Y with increases in G-the findings lend support to the hypotheses, implicating the implicit dependence of UV-induced crosslinks on t and λ for directing tissue stiffness and resilience. From a practical perspective, the study is a step in the direction to establish a UV irradiation treatment protocol for effective control of exogenous cross-linking in connective tissues.