On the possibility of stabilization of a contracted state after riboflavin/UV cross-linking of collagenous tissue in a partially dehydrated state

Background and Objectives: The method of riboflavin/UV collagen cross-linking is widely used to strengthen the corneal stroma in the treatment of keratoconus and is of considerable interest as a possible method to improve the biomechanical property of the sclera in the treatment of myopia. Regarding the application of this method to the sclera, one of the important problems is the rapid decrease in the intensity of UV radiation due to scattering as it propagates into the tissue. The depth of penetration of optical radiation into the sclera can be significantly increased using immersion optical clearing of the tissue. Under the action of immersion liquids used for optical clearing, partial dehydration of the tissue occurs. It is known that chemical cross-linking of tissue in a dehydrated state can lead to a significant decrease in the volume of tissue after its rehydration to a saturated state compared to the initial state, that is, it can lead to stabilization of a contracted state. In this case, the cross-linked tissue in the saturated rehydrated state contains less water than in the initial state. In this paper, we investigate the possibility of stabilizing a contracted state of the tissue after its riboflavin/UV cross-linking in a partially dehydrated state. Materials and Methods: Experiments were performed in vitro on samples of rat tail tendon fascicles. Before riboflavin/UV cross-linking, the sample was incubated in a 0.1% solution of riboflavin in normal saline solution for 20 minutes. Then the sample was dehydrated in a riboflavin-doped immersion liquid (37%, 58.5%, or 87% aqueous solution of polyethylene glycol PEG-300 containing 0.1% riboflavin) for 10 minutes (58.5% and 87% PEG solutions) or 15 minutes (37% PEG solution). After, a 4.5 mm-long section of the sample was exposed to UV radiation with a wavelength of 365 nm for 10 minutes. Finally, the sample was rehydrated in normal saline solution for 2 hours. At each stage of the treatment, the average group refractive index and geometry of the sample in UV-irradiated and non-irradiated sections of the sample were monitored using optical coherence tomography (OCT). The water content in the tissue was calculated from the measured values of its average group refractive index. Results: It was experimentally established that the retention of the contracted state of the tissue can occur, provided that the cross-linking is carried out at a volume hydration of the tissue less than 0.8. When the volume hydration of samples was less than 0.5 during UV exposure, the resulting contraction of the fascicle was found to be 8-15%. Conclusion: In this work, it was experimentally shown that riboflavin/UV cross-linking of collagenous tissue in a dehydrated state can lead to a decrease in tissue volume after its rehydration compared to the native one. The top level of hydration of the tissue during UV exposure at which the contracted state can be stabilized was found and the degree of resulting tissue contraction as a function of the degree of tissue hydration during UV exposure was estimated.