Effect of liquid rubber coating on hydration, mechanical properties and strain measurement in biomechanical testing of bone.

OBJECTIVES: This study evaluates liquid-rubber-coating to prevent moisture loss in bone during long-term biomechanical testing and digital image correlation (DIC) measurements. Can liquid-rubber-coating preserve bone mechanical properties and enhance DIC measurements? METHODS: Two experimental series used porcine femora in a 4-point-bending setup (n=6). Series 1 compared dehydration with and without rubber-coating during a 21-h drying period, focusing on bending stiffness and weight loss. Series 2 compared liquid-rubber-coating to acrylic-paint for DIC measurements across 50-2,000 µε principal strain. RESULTS: After 21 h, weight loss of the uncoated samples was almost three times higher (7.9 ± 0.4 % vs. 2.9 ± 0.6 %, p<0.001). Bare samples increased bending stiffness by 16.3 ± 4.7 % (p=0.003) vs. 5.8 ± 4.0 % (p=0.155) with coating. DIC noise was 174 ± 121 µε with acrylic-coating and 158 ± 113 µε with liquid-rubber (p=0.700). Bland-Altman analysis showed no significant differences between the groups (p≥0.128). CONCLUSIONS: The liquid-rubber-coating substantially reduced moisture loss and maintained bone mechanical properties over 21 h, without significant alteration to mechanical properties. DIC performance showed no consistent coating-related differences, indicating the coating as a time-stable, water-impermeable alternative to acrylics. Notably, coated samples exhibited reduced odour. Future work should test liquid-rubber-coatings under physiological loading in human bone to improve DIC accuracy for finite element validation and digital twin precision.