Nonlinear optical collagen cross-linking and mechanical stiffening: a possible photodynamic therapeutic approach to treating corneal ectasia

Abstract

Abstract. In this study we test the hypothesis that nonlinear optical (NLO) multiphoton photoactivation of riboflavin using a focused femtosecond (FS) laser light can be used to induce cross-linking (CXL) and mechanically stiffen collagen as a potential clinical therapy for the treatment of keratoconus and corneal ectasia. Riboflavin-soaked, compressed collagen hydrogels are cross-linked using a FS laser tuned to 760 nm and set to either 100 mW (NLO CXL I) or 150 mW (NLO CXL II) of laser power. FS pulses are focused into the hydrogel using a 0.75 NA objective lens, and the hydrogel is three-dimensionally scanned. Measurement of hydrogel stiffness by indentation testing show that the calculated elastic modulus (E) values are significantly increased over twofold following NLO CXL I and II compared with baseline values (P < 0.05). Additionally, no significant differences are detected between NLO CXL and single photon, UVA CXL (P > 0.05). This data suggests that NLO CXL has a comparable effect to conventional UVA CXL in mechanically stiffening collagen and may provide a safe and effective approach to localize CXL at different regions and depths within the cornea. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Custom built nonlinear optical crosslinking (NLO CXL) device capable of producing mechanical stiffening in ex vivo rabbit corneas

“…Chai et al has shown that it is possible to mechanically stiffen collagen hydrogels using twophoton, nonlinear excitation of riboflavin comparable to that achieved using UVA CXL [16]. However, in this earlier study a high NA lens (0.8) was used that crosslinked only a very small volume.…”

“…Previous studies have shown that it is possible to mechanically stiffen compressed type I collagen hydrogels to a degree similar to that achieved by standard UVA CXL using NLO CXL [16]. It has also been shown that a similar degree of enhanced CAF, used as a measure of collagen CXL, can be detected in ex vivo rabbit eyes treated with both NLO CXL and UVA CXL, depending on the scanning parameters [17].…”

“…After treatment, eyes were prepared for mechanical stiffness testing using the indentation approach described by Chai et al and Levental et al [16,19] An indentation approach was used because of the need to measure local tissue stiffness in the region of NLO CXL. Specifically, indentation allows for mechanical stiffness testing in a 1 mm diameter region whereas more standard tensiometry or stretch testing would require using a strip of cornea, for which much of the tissue would have been un-crosslinked.…”

Biomechanical Differences Between Femtosecond Lenticule Extraction (FLEx) and Small Incision Lenticule Extraction (SmILE) Tested by 2D-Extensometry in Ex Vivo Porcine Eyes

“…This amount of strain still allowed full recovery of the induced deformation in pure collagen hydrogels 30 and therefore did not involve plastic strain.…”

Corticosteroids and Anti-Complement Therapy in Retinal Diseases

“…In one study, riboflavin was activated by a femtosecond laser tuned to 760 nm, and this was able to provide localized treatments to stiffen collagen in hydrogels (Chai et al 2013). …”