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Materials that exhibit highly nonlinear behaviour are intricate to study. This is due to their physical properties, as they possess a very large deformation. Silicone rubber is among the materials that can be classified as possessing such characteristics, despite their being soft and frequently applied in medical applications. Due to their low mechanical properties, however, it is believed that a filler addition could enhance them. This study, therefore, aims to investigate the effect of the addition of bamboo cellulosic filler to silicone rubber in terms of its compressive properties in order to quantify its material constants using the hyperelastic theory, specifically the Neo-Hookean and Mooney-Rivlin models. The specimens' compressive properties were also compared between specimens immersed in seawater and those not immersed in seawater. The findings showed that the compressive properties, stiffness, and compressive strength of the bamboo cellulosic fibre reinforced the silicone rubber biocomposites, improved with higher bamboo filler addition. Specimens immersed in seawater showed that they can withstand a compressive load of up to 83.16 kPa in comparison to specimens not immersed in seawater (up to 79.8 kPa). Using the hyperelastic constitutive models, the Mooney-Rivlin model displayed the most accurate performance curve fit with the experimental compression data with an R2 of up to 0.9999. The material constant values also revealed that the specimens immersed in seawater improved in stiffness property, as the C1 material constant values are higher than for the specimens not immersed in seawater. From these findings, this study has shown that bamboo cellulosic filler added into silicone rubber enhances the material's compressive properties and that the rubber further improves with immersion in seawater. Thus, these findings contribute significantly towards knowledge of bamboo cellulosic fibre-reinforced silicone rubber biocomposite materials.

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The development of environmentally benign silicone composites from sugar palm fibre and silicone rubber was carried out in this study. The mechanical, physical, and morphological properties of the composites with sugar palm (SP) filler contents ranging from 0% to 16% by weight (wt%) were investigated. Based on the uniaxial tensile tests, it was found that the increment in filler content led to higher stiffness. Via dynamic mechanical analysis (DMA), the viscoelastic properties of the silicone biocomposite showed that the storage modulus and loss modulus increased with the increment in filler content. The physical properties also revealed that the density and moisture absorption rate increased as the filler content increased. Inversely, the swelling effect of the highest filler content (16 wt%) revealed that its swelling ratio possessed the lowest rate as compared to the lower filler addition and pure silicone rubber. The morphological analysis via scanning electron microscopy (SEM) showed that the sugar palm filler was evenly dispersed and no agglomeration could be seen. Thus, it can be concluded that the addition of sugar palm filler enhanced the stiffness property of silicone rubber. These new findings could contribute positively to the employment of natural fibres as reinforcements for greener biocomposite materials.

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PURPOSE: To investigate two different methods of suture fixation and tendon behaviour when using an Endobutton and a tripled tendon. METHODS: Thirty bovine tendons and foam blocks were randomly allocated to three groups: group 1: The tendon was doubled through 40-mm Endobutton; group 2: Tripled tendon--whip-stitched with No. 2 Ultrabraid, passed through an Endobutton and third limb secured to the loop via seven knots; and group 3: Tripled tendon--whip-stitched with No. 2 Fibreloop and fixed as group 2. A tunnel matching the graft diameter was drilled through the block. The graft was passed through the tunnel and fixed with an interference screw. The constructs were cycled at 1 Hz from 10 to 50 N for 10 cycles followed by 50-250 N at 1 Hz for 500 cycles. Load-to-failure test was then carried out at a rate of 20 mm/min. A custom digital image capture technique was used to measure and calculate displacement, strain and stress. Statistical analysis was carried out using Kruskal-Wallis test and paired t test. RESULTS: There was no statistical significant difference between ultimate tensile strength (UTS) (P = 0.35) and yield load (0.41) between the 3 groups. The mean displacement of the third tendon limb in group 2 was 4.8 mm and in group 3, 1.5 mm. Displacement was not statistically significant (P = 0.07). The mean stress in the third limb versus the doubled portion of tendon in group 2 was 0.4 ± 0.02 versus 4.8 ± 0.52 MPa and in group 3, 0.5 ± 0.03 versus 5.2 ± 0.52 MPa. CONCLUSIONS: In this biomechanical study, there was no mechanical difference in the overall properties between a doubled and tripled tendon graft. Significant cyclic elongation occurred in the third limb of the tripled tendon in comparison with the doubled portioned. Further work is needed to determine whether these mechanical findings translate to clinical practice. Caution should be used when tripling hamstring grafts. In particular, tripling small grafts provides no biomechanical advantage immediately and possibly long term, thus potentially increasing the risk of failure.

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This study highlights a new experimental method developed to measure full-field deformation of human skin in vivo. The technique uses a small-scale Qualisys (Sweden) 3D motion capture system and an array of reflective markers placed on the forearm of five healthy volunteers. A load of up to 1.5N was applied to induce skin deformation by pulling a fine wire attached to the centre of the marker configuration. Loading and marker displacements were recorded simultaneously. 3D marker trajectory data was generated for three different load directions. Tests were repeated to investigate accuracy and repeatability. Calibration results indicate the accuracy of the motion capture system with an average residual of 0.05 mm. The procedure was found to be repeatable and accurate for five repeated tests of measured displacements with a maximum variance of 5%. Experimental data are presented to demonstrate robustness and the ability to produce significant outputs. For all five subjects, at 1N load, the mean and standard deviations of skin axial and lateral displacements were found to be 11.7+/-1.6mm and 12.3+/-3.3mm, respectively. The axial displacements ratio (u(90)/u(0)) ranges from 0.63 to 1.45 with mean+/-standard deviation of 0.982+/-0.34 and 0.982+/-0.32 for left and right arms, respectively. The experiments generated useful and accurate data that can be used to study the viscoelastic, hyperelastic or anisotropic behaviour of human skin. The measured displacements will be analysed further to determine the mechanical properties of skin using inverse Finite Element Analysis and Ogden model.

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