The relationship between the pH value of a hydration solution and the biomechanical properties of Crosado-embalmed human iliotibial bands.

Determining the biomechanical properties of human tissues commonly involves the immersion or spraying of the tissues to maintain them in a hydrated state. However, the influence of the pH value of these solutions on the biomechanical properties of the tissues is not well understood. This study investigated the effects of the pH value on the biomechanical properties of the collagen-rich human iliotibial band (ITB). A total of 124 samples were allocated to polyethylene glycol (PEG) solutions of pH values between 3 and 13 for 24 h, which is a frequently used immersion time prior to biomechanical tests. After this, the samples were biomechanically tested in a uniaxial tensile testing setup using an established testing routine. Similarly, 69 samples were allocated to pH groups of 6, 7 and 8 and biomechanically tested after 1, 2 and 3 weeks. The cross-sectional area of all samples was determined after immersion into the PEG solutions for the specified time frames. In the 24-h experiment, the elastic modulus (pH 12: p ≤ 0.045; pH 13: p ≤ 0.020) and the ultimate tensile strength (pH 12: p ≤ 0.031; pH 13: p ≤ 0.026) of the pH groups 12 and 13 were significantly lower and their cross-sectional areas were higher (pH 12: p ≤ 0.005; pH 13: p ≤ 0.003) compared to several groups of acidic to alkaline pH values. There was no difference in the maximum forces between the different groups within a 24-h immersion time (p > 0.999). In the 3-week-test, a decrease of the ultimate tensile strength was noted between the 24-h and 3 week values for the pH groups 7 (p = 0.034) and 8 (p = 0.029). It is concluded that pH-dependent tissue swelling influences the cross-sectional area-dependent biomechanical properties of the human ITB. Therefore, the pH value of storage and hydration solutions for the preparation of biomechanical tests should be recorded. From a biomechanical perspective, the collagen stability of the human ITB is largely unaltered in PEG solutions with pH values between 3 and 13 over 24 h.

Biomechanics of vascular areas of the human cranial dura mater.

Accurate biomechanical properties of the human cranial dura mater are paramount for computational head models, artificial graft developments and biomechanical basic research. Yet, it is unclear whether areas of the dura containing meningeal vessels biomechanically differ from avascular areas. Here, 244 dura mater samples with or without vessels from 32 cadavers were tested in a quasi-static uniaxial tensile testing setup. The thicknesses of the meningeal and periosteal dura in vascular and avascular areas were histologically investigated in 36 samples using van Gieson staining. The elastic modulus of 112 MPa from dura samples containing vessels running transversely was significantly lower than samples with vessels running longitudinally (151 MPa; p < 0.001). The ultimate tensile strength of dura samples with transversely running vessels (11.1 MPa) was significantly lower in comparison to both avascular samples (14.9 MPa; p < 0.001) and samples with a longitudinally running vessel (15.0 MPa; p < 0.001). The maximum force of dura samples with longitudinally running vessels was 37 N (p < 0.001), this was significantly higher compared to the other groups which were 23 N (p < 0.001). The meningeal and periosteal dura layer thicknesses were not statistically different in avascular areas (p > 0.222). However, around the vessels, the meningeal dura layer was significantly thicker compared to the periosteal layer (p ≤ 0.019). The sum of the meningeal and periosteal layers was similar between vascular and avascular areas (p ≥ 0.071). Vascular areas of the human cranial dura mater withstand the same forces as avascular areas when being stretched. When stretched along the vessel, the dura-vessel composite can withstand even higher tensile forces compared to avascular areas. Vascular areas of the cranial dura mater seem to be similar when compared to avascular areas making their separate simulation in computational models non-essential.