title: A thermomechanical framework for reconciling the effects of ultraviolet radiation exposure time and wavelength on connective tissue elasticity.
abstract: 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 [Formula: see text] and wavelength [Formula: see text]-has been proposed as a therapeutic method for supporting the treatment for structural-related injuries and pathologies. However, the effects of [Formula: see text] and [Formula: see text] on the tissue elasticity, namely elastic modulus [Formula: see text] and modulus of resilience [Formula: see text], are not entirely clear. We present a thermomechanical framework to reconcile the [Formula: see text]- and [Formula: see text]-related effects on [Formula: see text] and [Formula: see text]. The framework addresses (1) an energy transfer model to describe the dependence of the absorbed UV photon energy, [Formula: see text], per unit mass of the tissue on [Formula: see text] and [Formula: see text], (2) an intervening thermodynamic shear-related parameter, [Formula: see text], to quantify the extent of UV-induced cross-linking in the tissue, (3) a threshold model for the [Formula: see text] versus [Formula: see text] relationship, characterized by   [Formula: see text]-the critical [Formula: see text] underpinning the association of [Formula: see text] with [Formula: see text]-and (4) the role of [Formula: see text] in the tissue elasticity. We hypothesized that [Formula: see text] regulates [Formula: see text] (UV-stiffening hypothesis) and [Formula: see text] (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 [Formula: see text] (365 and 254 nm) and three levels of [Formula: see text] (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 [Formula: see text] and [Formula: see text] treatments. Student's t test revealed positive change in [Formula: see text] and [Formula: see text] with increases in [Formula: see text]-the findings lend support to the hypotheses, implicating the implicit dependence of UV-induced cross-links on [Formula: see text] and [Formula: see text] 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.
authors.affiliation: School of Mechanical and Systems Engineering, Newcastle University, Newcastle upon Tyne, UK, kheng-lim.goh@ncl.ac.uk.
authors.forename: K L
authors.initials: KL
authors.lastname: Goh
authors.forename: S Y
authors.initials: SY
authors.lastname: Chen
authors.forename: K
authors.initials: K
authors.lastname: Liao
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D003094:Collagen / Q000378:metabolism; D003238:Connective Tissue / Q000502:physiology* / Q000528:radiation effects*; D055119:Elastic Modulus / Q000528:radiation effects*; D005109:Extracellular Matrix / Q000378:metabolism / Q000528:radiation effects; D008022:Ligaments / Q000528:radiation effects / Q000648:ultrastructure; D008954:Models, Biological; D015203:Reproducibility of Results; D012756:Sheep; D013696:Temperature; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D003094:Collagen