PD Dr. Herbert Tempfer (Salzburg / AT), Bettina Schwemberger (Salzburg / AT), Andreas Traweger (Salzburg / AT)
Abstract-Text (inkl. Referenzen und Bildunterschriften)
Background: Biomechanical testing of tendons is commonly performed by uniaxial tensile stretching along collagen fibre orientation. So far, only little is known about tendon biomechanical response to compression on a nanoscale, which may provide information on tissue quality not achievable by tensile testing.
Aims: It is the aim of this study provide first insight to the behaviour of healthy and injured tendon under compressive forces.
Material and methods: Cryosections of unfixed healthy rat patella tendons derived from male SD rats and from tendons 2, 4 and 6 weeks after creating a 2 mm punch defect were examined with a Chiaro Nanoindenter (Optics11 B.V.). Measurements were performed at several time points after immersion, either in Phosphate Buffered Saline (PBS) or 8% polyethylene glycole (PEG) in PBS. For indentation, a cantilever with a stiffness of 0.5 N/m and a sphere tip with a radius of 52 µm was used. Stiffness was calculated using the Hertzian model.
Results: In healthy tendons, E(eff) declined from 23.4±3.6 kPa after 5 minutes to 11.3±2.9 kPa after 60 minutes, stiffness of the tendon defect area only declined from 4.9 ± 1.4 kPa after 5 Minutes to 3.6± 1.1 kPa after 60 minutes (Figure 1). Interestingly, reprobing samples after rinsing in water and drying resulted in higher elastic modulus (35.8±4.7 kPa at 5 minutes after PBS immersion). Immersion in 8% PEG after 5 minutes hydration in PBS lead to an average stiffness of 135± 34.1 kPa after 10 minutes.
Discussion: The observed decline in elasiticity modulus due to PBS immersion needs to be considered for longer lasting measurements like surface mapping studies. Moreover, the use of PEG to avoid tissue swelling as it has been shown for tensile testing of tendons is not suitable for tendon nanoindentation. As nanoindentation measurements can only be performed in aqueous solutions, the "in vivo degree of hydration" remains an unknown variable, favouring semiquantitative, whithin- experiment analyses.