Physico-chemical properties of Artificial tear ducts from Fractionated Thai silk fibroin

Abstract

Artificial tear ducts (ATD) or Jones tubes, have been used in patients with tear ducts obstruction for draining tears into the nose. Commercial ATDs are generally made of glass but they have slippery surfaces causing the ducts pushed out and easily broken. Polymer-based ATDs, are more flexible and adhesive to tissues. However, the users could encounter material-related problems due to allergic reactions, low tissue adhesion and complications. We designed artificial tear ducts from Thai silk fibroin (SF) solution. The SF was fractionated using freeze-thaw cycles (-4°C and 25°C for 5 cycles) into SF-P (precipitants, 63.53±4.58% yields) and SF-S (soluble, 34.05±5.76% yields (w/v)). The concentrated solutions (20%W/W) of SF, SF-P and SF-S were dip-coated into tubes. The leaking test was performed using simulated natural tear flow rate of 0.0022 mL/min for 6 h. SF-S duct lost its shape and leaked. Absorption of the balanced salt solution (BSS) of the SF and SF-P were at 5.67±0.76% and 8.05±1.28 wt.% respectively, giving their wet inner and outer diameters at 2 and 2.5 mm. and the thickness 500 microns. Crystallinities of SF and SF-P analyzed using ATR-FTIR, were at 42.27 and 44.51% respectively. The thermal decomposition temperature of SF and SF-P analyzed using TGA, were at 277 and 280°C. Degradability in BSS containing lysozyme 1.69 U/mg to mimic tears at 37°C in vitro showing that both ATDs are stabilized for at least 4 weeks. BSS height obtained capillary test that compared with glass ducts, SF and SF-P at 7.0±0.0, 6.9±0.4 and 7.1±0.4 mm, respectively, while glass ducts were 34.81±0.0. The SF and SF-P have flexural stress were 55.24±7.68 MPa and 81.42±2.71 MPa, %flexural strain at max stress was 5.43±0.46% and 2.54±0.17% and flexural Modulus was 1.82±0.29 GPa and 6.13±0.51GPa respectively. The results of all experiments indicate that SF-P had the highest potential for further development into natural polymer-based ATDs.