The Biomechanics of eyelid tarsus tissue

Reconstruction of the eyelid remains challenging due to the unique properties of the tarsal plate, which is a fibrocartilagenous structure within the eyelid providing structural support and physical form. There are no previous studies investigating the biomechanical properties of tarsus tissue, which is vital to the success of bioengineered tarsal substitutes. We therefore aimed to determine the biomechanical properties of human tarsus tissue, and used a CellScale BioTester 5000 (CellScale, Waterloo, Canada) to perform uniaxial tensile tests on ten samples of healthy eyelid tarsus. All samples were tested 'fresh' within two hours of harvest. A tensile preload of 50 mN was applied for 10 min before the sample was subjected to uniaxial tension under linear ramp displacement control. Maximum strain was 30% of the original tissue length and thirty dynamic cycles were performed at a strain rate of 1%/s using a triangular waveform. Of the samples tested, the mean (SD) width was 5.51 mm (1.45 mm) whilst mean thickness was 1.6 mm (0.51 mm). The mean toe modulus was 0.14 (0.10) MPa, elastic modulus was 1.73 (0.61) MPa, with an extensibility of 15.8 (2.1)%, and phase angle of 6.4° (2.4)°. After adjusting for the initial tissue slack, the maximum strain ranged from 23.8% to 30.0%. At maximum strain, it was observed that the linear region of the stress-strain curve was reached without the sample slipping out of the clamps. Our results establish a benchmark for native tarsus tissue, which can be used when evaluating tissue engineered tarsal substitutes in the future.