Siaw Meng Chou

Development of a finger biomechanical model and its considerations

The development of a biomechanical model for a human finger is faced with many challenges, such as extensor mechanism complexity, statistical indeterminacy and suitability of computational processes. Motivation for this work was to develop a computer model that is able to predict the internal loading patterns of tendons and joint surfaces experienced by the human finger, while mitigating these challenges. Proposed methodology was based on a non-linear optimising mathematical technique with a criterion of boundary conditions and equality equations, maximised against unknown parameters to reduce statistical indeterminacy. Initial validation was performed via the simulation of one dynamic and two static postures case studies. Past models and experiments were used, based on published literature, to verify the proposed models methodology and results. The feasibility of the proposed methodology was deemed satisfactory as the simulated results were concordant with in-vivo results for the extrinsic flexors.

The changes in the tensile properties of tendons after freeze storage in saline solution.

Abstract The objective of this study is to evaluate the influence of saline solution (0.9 per cent NaCl) on the tensile properties of freeze-stored tendons. Firstly, 170 pieces of chicken flexor digitorum profundus tendons were retrieved and wrapped in saline-soaked gauze before they were stored at -40 °. Then specimens were tensile tested at various time points over 360 days, scanning electron microscopy (SEM) was performed on fresh specimens, and specimens were freeze-stored for 233 days to investigate microstructure change after freeze storage. The mean values of strain ultimate tensile strength (UTS) did not deviate significantly (analysis of variance; p = 0.249) following freeze storage while the UTS and elastic modulus increased gradually with the duration of freeze storage and the growth became significant (p < 0.01) for durations longer than 70 and 40 days respectively. The SEM study showed that the collagen fibre density of specimens stored for 233 days decreased because of porosity growth. These findings suggested that the saline increased the tensile strength and modulus of the collagen.

Cartilage Tissue Engineering with Silk Fibroin Scaffolds Fabricated by Indirect Additive Manufacturing Technology

Advanced tissue engineering (TE) technology based on additive manufacturing (AM) can fabricate scaffolds with a three-dimensional (3D) environment suitable for cartilage regeneration. Specifically, AM technology may allow the incorporation of complex architectural features. The present study involves the fabrication of 3D TE scaffolds by an indirect AM approach using silk fibroin (SF). From scanning electron microscopic observations, the presence of micro-pores and interconnected channels within the scaffold could be verified, resulting in a TE scaffold with both micro- and macro-structural features. The intrinsic properties, such as the chemical structure and thermal characteristics of SF, were preserved after the indirect AM manufacturing process. In vitro cell culture within the SF scaffold using porcine articular chondrocytes showed a steady increase in cell numbers up to Day 14. The specific production (per cell basis) of the cartilage-specific extracellular matrix component (collagen Type II) was enhanced with culture time up to 12 weeks, indicating the re-differentiation of chondrocytes within the scaffold. Subcutaneous implantation of the scaffold-chondrocyte constructs in nude mice also confirmed the formation of ectopic cartilage by histological examination and immunostaining.

Effects of frozen storage temperature on the elasticity of tendons from a small murine model.

The basic mechanism of reinforcement in tendons addresses the transfer of stress, generated by the deforming proteoglycan (PG)-rich matrix, to the collagen fibrils. Regulating this mechanism involves the interactions of PGs on the fibril with those in the surrounding matrix and between PGs on adjacent fibrils. This understanding is key to establishing new insights on the biomechanics of tendon in various research domains. However, the experimental designs in many studies often involved long sample preparation time. To minimise biological degradation the tendons are usually stored by freezing. Here, we have investigated the effects of commonly used frozen storage temperatures on the mechanical properties of tendons from the tail of a murine model (C57BL6 mouse). Fresh (unfrozen) and thawed samples, frozen at temperatures of -20°C and -80°C, respectively, were stretched to rupture. Freezing at -20°C revealed no effect on the maximum stress (σ), stiffness (E), the corresponding strain (ε) at σ and strain energy densities up to ε (u) and from ε until complete rupture (up). On the other hand, freezing at -80°C led to higher σ, E and u; ε and up were unaffected. The results implicate changes in the long-range order of radially packed collagen molecules in fibrils, resulting in fibril rupture at higher stresses, and changes to the composition of extrafibrillar matrix, resulting in an increase in the interaction energy between fibrils via collagen-bound PGs.

The development of silk fibroin scaffolds using an indirect rapid prototyping approach: Morphological analysis and cell growth monitoring by spectral-domain optical coherence tomography

To date, naturally derived biomaterials are rarely used in advanced tissue engineering (TE) methods despite their superior biocompatibility. This is because these native materials, which consist mainly of proteins and polysaccharides, do not possess the ability to withstand harsh processing conditions. Unlike synthetic polymers, natural materials degrade and decompose rapidly in the presence of chemical solvents and high temperature, respectively. Thus, the fabrication of tissue scaffolds using natural biomaterials is often carried out using conventional techniques, where the efficiency in mass transport of nutrients and removal of waste products within the construct is compromised. The present study identified silk fibroin (SF) protein as a suitable material for the application of rapid prototyping (RP) or additive manufacturing (AM) technology. Using the indirect RP method, via the use of a mould, SF tissue scaffolds with both macro- and micro-morphological features can be produced and qualitatively examined by spectral-domain optical coherence tomography (SD-OCT). The advanced imaging technique showed the ability to differentiate the cells and SF material by producing high contrasting images, therefore suggesting the method as a feasible alternative to the histological analysis of cell growth within tissue scaffolds.

Biomechanical Properties of Extensor Tendon Repair Using the Six-Strand Single-Loop Suture Technique: A Comparative Analysis With Three Other Techniques in Cadaveric Models

A six-strand single-loop technique has been implemented for repairing extensor tendons. This paper describes an investigation to compare the biomechanical properties of extensor tendons repaired using this technique with three other commonly used techniques, namely the Kessler-Tajima (two-stand) technique, the Tsuge (two-strand) technique, and the modified (four-strand and double-loop) Tsuge technique. Epitendinous stitches were implemented on all techniques. From human cadaveric hands, extensor tendons were harvested, transected, and repaired using these techniques. Tensile test was performed on the repaired tendons to determine the force at the first gap opening, 1-mm and 2-mm gap distances and at the maximum load. We have observed that at the first gap opening, the forces generated in the tendons repaired using the six-strand, Kessler-Tajima, and modified Tsuge techniques are significantly larger than the Tsuge technique. Thereafter, the force generated at gap distances of 1 mm, 2 mm, and the maximum force depend on the number of strands and the epitendinous stitches. In this case, the maximum force (31.80 N ± 4.73 N) from the six-strand technique is significantly higher than that from the Kessler-Tajima technique. In particular, all samples from the six-strand technique failed by suture pull-out. In contrast, suture pull-out is less common for the other techniques; these samples also exhibited suture rupture. This study is important because it reveals that cadaveric tendons repaired using the Kessler-Tajima, modified Tsuge, and six-strand techniques can accommodate higher initial forces (compared to the Tsuge technique) and, thus, are more effective for resisting gap formation. Among these techniques, it is shown that the six-strand configuration is reliable because the strands, rather than breaking, results in pull-out at sufficiently high loads. Thus, the six-strand approach for anchoring the ruptured tissue results in the transfer of large forces to the suture. It is suggested that the six-strand technique may be a viable technique since it requires only a single-loop suture and this may simplify the repair procedure and tendon handling without increasing the bulk of the repaired tendon appreciably.

CROSS-SECTIONAL AREA MEASUREMENT OF SOFT TISSUES IN VITRO: A NON-CONTACT LASER SCAN METHOD

Measurements of cross-sectional areas (CSAs) of soft tissues such as tendons and ligaments allow for the evaluation of the biomechanical properties of the tissue. Underlying in vitro techniques are data reduction approaches for determining the average thickness of the tissue and the assumption of the geometry of the cross-section, i.e. circular or elliptical. However, tissue distortions, sagging, and concavities could affect the reliability of these techniques, since these features may not be accounted for adequately. To address some of the concerns faced by these techniques, a non-contact (non-destructive) laser scan technique has been developed. In this technique, a laser scans along the axis of the tissue, a coordinate measuring machine simultaneously locates the corresponding point on the tissue based on the detection of reflected (attenuated) intensity, and, finally, computerized image analysis reconstructs the morphology of the tissue. This technique was applied to patellar tendons (PTs) from New Zealand rabbits. The scanning time for each PT was less than 2 minutes. Reconstructed three-dimensional surface plots revealed microconcavities consistent with images seen under optical microscopy. CSAs of these PTs were determined for repeatability and precision; results from a conventional approach which estimated the corresponding CSAs based on the average thickness and the assumption of ellipsoidal cross-sectional geometry were also determined for the purpose of comparison. Based on the standard cuboid model, the error between the laser technique and the conventional approach was within 0.4%; the reproducibility of the laser technique was within 2%.

Age Effects on the Tensile and Stress Relaxation Properties Of Mouse Tail Tendons

Tendons are known to exhibit complex mechanical behavior when transferring forces from muscles to bone. This nonlinear mechanical response varies with age due to the presence of degenerative effects which is attributed to the structural changes and interactions observed in each hierarchical level of the dense connective tissue.

Plastic behaviour of two-dimensional regular hexagonal structures with bilinear and uniaxial strength asymmetry in cellular materials

An elasto-plastic micromechanical model of the two-dimensional regular hexagonal structure was developed. General analytical expressions for the incremental constitutive relations were derived in terms of parameters defining the architecture and material of an internal beam. Non-linearity of the structure was introduced by considering the elastic—linear strain hardening behaviour of each internal beam, in which uniaxial strength asymmetry of the cellular material was accounted for. The plastic stress—strain relationship of the structure under any loading conditions can therefore be analysed by localized beam deformation. The results show that the bending deformation of the internal beam dominates under uniaxial stress loading conditions, however, the axial displacement dominates under the uniaxial strain conditions. The structure will present different behaviours under different loading conditions. The corresponding stresses under the uniaxial strain condition are greater than those under the uniaxial stress condition. The analyses also show that the volume fraction is highly correlated with the elastic constants and yield stresses of the structure. The denser the structure, the higher the moduli and yield stresses.

Comparison of a simplified skin pointer device compared with a skeletal marker for knee rotation laxity: A cadaveric study using a rotation-meter

AIM To compare the measurements of knee rotation laxity by non-invasive skin pointer with a knee rotation jig in cadaveric knees against a skeletally mounted marker. METHODS Six pairs of cadaveric legs were mounted on a knee rotation jig. One Kirscher wire was driven into the tibial tubercle as a bone marker and a skin pointer was attached. Rotational forces of 3, 6 and 9 nm applied at 0°, 30°, 45°, 60° and 90° of knee flexion were analysed using the Pearson correlation coefficient and paired t-test. RESULTS Total rotation recorded with the skin pointer significantly correlated with the bone marker at 3 nm at 0° (skin pointer 23.9 ± 26.0° vs bone marker 16.3 ± 17.3°, r = 0.92; P = 0.0), 30° (41.7 ± 15.5° vs 33.1 ± 14.7°, r = 0.63; P = 0.037), 45° (49.0 ± 17.0° vs 40.3 ± 11.2°, r = 0.81; P = 0.002), 60° (45.7 ± 17.5° vs 34.7 ± 9.5°, r = 0.86; P = 0.001) and 90° (29.2 ± 10.9° vs 21.2 ± 6.8°, r = 0.69; P = 0.019) of knee flexion and 6 nm at 0° (51.1 ± 37.7° vs 38.6 ± 30.1°, r = 0.90; P = 0.0), 30° (64.6 ± 21.6° vs 54.3 ± 15.1°, r = 0.73; P = 0.011), 45° (67.7 ± 20.6° vs 55.5 ± 9.5°, r = 0.65; P = 0.029), 60° (62.9 ± 22.4° vs 45.8 ± 13.1°, r = 0.65; P = 0.031) and 90° (43.6 ± 17.6° vs 31.0 ± 6.3°, r = 0.62; P = 0.043) of knee flexion and at 9 nm at 0° (69.7 ± 40.0° vs 55.6 ± 30.6°, r = 0.86; P = 0.001) and 60° (74.5 ± 27.6° vs 57.1 ± 11.5°, r = 0.77; P = 0.006). No statistically significant correlation with 9 nm at 30° (79.2 ± 25.1° vs 66.9 ± 15.4°, r = 0.59; P = 0.055), 45° (80.7 ± 24.7° vs 65.5 ± 11.2°, r = 0.51; P = 0.11) and 90° (54.7 ± 21.1° vs 39.4 ± 8.2°, r = 0.55; P = 0.079). We recognize that 9 nm of torque may be not tolerated in vivo due to pain. Knee rotation was at its maximum at 45° of knee flexion and increased with increasing torque. CONCLUSION The skin pointer and knee rotation jig can be a reliable and simple means of quantifying knee rotational laxity with future clinical application.