Mechanism of lens capsular rupture following blunt trauma: a finite element study

Blunt impact on the eye could results in lens capsular rupture that allows foreign substances to enter into the lens and leads to cataract formation. This paper aimed to investigate the mechanism of lens capsular rupture using finite element (FE) method. A FE model of the human eye was developed to simulate dynamic response of the lens capsule to a BB (a standard 4.5-mm-diameter pellet) impact. Sensitivity studies were conducted to evaluate the effect of the parameters on capsular rupture, including the impact velocity, the elastic modulus of the lens, the thickness and the elastic modulus of the lens capsule. The results indicated that the lens was subjected to anterior compression and posterior intension when the eye was stricken by a BB pellet. The strain on the posterior capsule (0.392) was almost twice as much as that on the anterior capsule (0.207) at an impact velocity of 20 m/s. The strain on the capsule was proportional to the impact velocity, while the capsular strain showed no significant change when the lens modulus elastic varied with age. The findings confirmed that blunt traumatic capsular rupture is the result of shockwave propagation throughout the eye. The posterior capsule is subjected to greater tension in blunt trauma, which is the main cause that ruptures are more commonly found on the posterior capsule than the anterior capsule. Also, thinner thickness and lower elastic modulus would contribute to the posterior capsular rupture.     

Comparison of nonlinear mechanical properties of bovine articular cartilage and meniscus

Nonlinear, linear and failure properties of articular cartilage and meniscus in opposing contact surfaces are poorly known in tension. Relationships between the tensile properties of articular cartilage and meniscus in contact with each other within knee joints are also not known. In the present study, rectangular samples were prepared from the superficial lateral femoral condyle cartilage and lateral meniscus of bovine knee joints. Tensile tests were carried out with a loading rate of 5 mm/min until the tissue rupture. Nonlinear properties of the toe region, linear properties in larger strains, and failure properties of both tissues were analysed. The strain-dependent tensile modulus of the toe region, Young's modulus of the linear region, ultimate tensile stress and toughness were on average 98.2, 8.3, 4.0 and 1.9 times greater (p<0.05) for meniscus than for articular cartilage. In contrast, the toe region strain, yield strain and failure strain were on average 9.4, 3.1 and 2.3 times greater (p<0.05) for cartilage than for meniscus. There was a significant negative correlation between the strain-dependent tensile moduli of meniscus and articular cartilage samples within the same joints (r=−0.690, p=0.014). In conclusion, the meniscus possesses higher nonlinear and linear elastic stiffness and energy absorption capability before rupture than contacting articular cartilage, while cartilage has longer nonlinear region and can withstand greater strains before failure. These findings point out different load carrying demands that both articular cartilage and meniscus have to fulfil during normal physiological loading activities of knee joints.     

Strain-rate dependent material properties of the porcine and human kidney capsule

This study was performed to characterize the mechanical properties of the kidney capsular membrane at strain-rates associated with blunt abdominal trauma. Uniaxial quasi-static and dynamic tensile experiments were performed on fresh, unfrozen porcine and human renal capsules at deformation rates ranging from 0.0001 to 7 m/s (strain-rates of 0.005-250 s(-1)). Single stroke, dynamic tests were performed on samples of porcine renal capsule at strain-rates of 0.005 s(-1) (n = 33), 0.05 s(-1) (n = 17), 0.5 s(-1) (n = 38), 2 s(-1) (n = 10), 4 s(-1) (n = 10), 50 s(-1) (n = 21), 100 s(-1) (n = 18), 150 s(-1) (n = 17), 200 s(-1) (n = 10), and 250 s(-1) (n = 17). Due to limited availability of human tissues, only quasi-static tests were performed (0.005 s(-1), n = 25). Porcine renal capsule properties were found to match the material properties of human capsular tissue sufficiently well such that porcine tissue material can be used as a human test surrogate. The apparent elastic modulus and breaking stress of the porcine renal capsule were observed to increase significantly with increasing strain-rate (p < 0.01). Breaking strain was inversely related to strain-rate (p < 0.01). The effect of increasing strain-rate on material properties diminished appreciably at rates exceeding 150 s(-1). Empirically derived mathematical models of constitutive behavior were developed using a hyperelastic/viscoelastic Ogden formulation, as well as a Cowper-Symonds law material curve multiplication.     

Systematic error in mechanical measures of damage during four-point bending fatigue of cortical bone

Accumulation of fatigue microdamage in cortical bone specimens is commonly measured by a modulus or stiffness degradation after normalizing tissue heterogeneity by the initial modulus or stiffness of each specimen measured during a preloading step. In the first experiment, the initial specimen modulus defined using linear elastic beam theory (LEBT) was shown to be nonlinearly dependent on the preload level, which subsequently caused systematic error in the amount and rate of damage accumulation measured by the LEBT modulus degradation. Therefore, the secant modulus is recommended for measurements of the initial specimen modulus during preloading. In the second experiment, different measures of mechanical degradation were directly compared and shown to result in widely varying estimates of damage accumulation during fatigue. After loading to 400,000 cycles, the normalized LEBT modulus decreased by 26% and the creep strain ratio decreased by 58%, but the normalized secant modulus experienced no degradation and histology revealed no significant differences in microcrack density. The LEBT modulus was shown to include the combined effect of both elastic (recovered) and creep (accumulated) strain. Therefore, at minimum, both the secant modulus and creep should be measured throughout a test to most accurately indicate damage accumulation and account for different damage mechanisms. Histology revealed indentation of tissue adjacent to roller supports, with significant sub-surface damage beneath large indentations, accounting for 22% of the creep strain on average. The indentation of roller supports resulted in inflated measures of the LEBT modulus degradation and creep. The results of this study suggest that investigations of fatigue microdamage in cortical bone should avoid the use of four-point bending unless no other option is possible.     

Sensitivity of multiple damage parameters to compressive overload in cortical bone

Damage accumulation plays a key role in weakening bones prior to complete fracture and in stimulating bone remodeling. The goal of this study was to characterize the degradation in the mechanical properties of cortical bone following a compressive overload. Longitudinally oriented, low-aspect ratio specimens (n=24) of bovine cortical bone were mechanically tested using an overload-hold-reload protocol. No modulus reductions greater than 5% were observed following overload magnitudes less than 0.73% strain. For each specimen, changes in strength and Poisson's ratio were greater (p=0.02) than that in modulus by 10.8- and 26.6-fold, respectively, indicating that, for the specimen configuration used in this study, longitudinal elastic modulus is one of the least sensitive properties to a compressive overload. Residual strains were also proportionately greater by 6.4-fold (p=0.01) in the transverse than axial direction. These results suggest that efforts to relate microcrack density and morphology to changes in compressive mechanical properties of cortical bone may benefit from considering alternative parameters to modulus reductions.     

Zonal and directional variations in tensile properties of bovine articular cartilage with special reference to strain rate variation

THE AIMS of this study were: (i) to investigate the variation in the tensile properties of articular cartilage with depth through cartilage thickness and fibre orientation; (ii) to determine the effect of strain rate on tensile properties of articular cartilage. MATERIALS AND METHOD: All experimental work was performed on cartilage specimens taken from two bovine knee joints. Osteochondral plugs 12 mm in diameter were harvested with a special reamer from the femur and the tibial plateaux of each knee. Slices (0.2 mm thick), of articular cartilage were cut from the plug with a microtome. The predominant orientation of the collagen fibres on the cartilage surface was determined using the pinpricking technique. Each specimen used for the tensile test was cut, so as to produce a dumbbell shape, with a gauge length of 6 mm. Uniaxial tensile tests were performed on each specimen in order to determine the tensile Young's modulus, and ultimate tensile strength (UTS). In this investigation, these tensile tests were carried out at different strain rate: 1, 20, 50 and 70%/sec. RESULTS: As regards the zonal properties, it was found that tensile stiffness was greater in the superficial layer than in deep layer. However, a few specimens from the deep layer displayed similar or greater stiffness compared to the superficial layer. With respect to the directional properties, the specimens oriented parallel to the predominant alignment of collagen, were stiffer than those, which were perpendicular to it in each layer. However, only the results regarding the deep layer can be considered statistically significant. In regard to the variation of modulus with the strain-rate, the results showed that there is no significant increase of the modulus with increasing strain rate from 20 to 50% per second. However, at 70% per second, articular cartilage stiffness considerably increased by up to one order of magnitude greater than that determined at lower strain rates in both the superficial and deep layer. Moreover, the UTS of cartilage specimens tested at 70% per second showed a significant rise, reaching values of four to five times that of those measured at 1, 20 or 50% per second. CONCLUSION: The steep increases in both the stiffness and ultimate tensile strength of cartilage at high strain rates point to the existence in cartilage of a mechanism for its protection from damage by stresses arising in trauma, which are usually applied at high rates. This mechanism needs to be elucidated. The reduced anisotropy found in the present study pointed out that collagen is likely to be less organized in bovine cartilage than in the human and therefore, a study of its ultra-structure would be appropriate.     

The Elastic Properties of the Cryptococcus neoformans Capsule

Microbial capsules are important for virulence, but their architecture and physical properties are poorly understood. The human pathogenic fungus Cryptococcus neoformans has a large polysaccharide capsule that is necessary for virulence and is the target of protective antibody responses. To study the C. neoformans capsule we developed what we believe is a new approach whereby we probed the capsular elastic properties by applying forces using polystyrene beads manipulated with optical tweezers. This method allowed us to determine the Young's modulus for the capsule in various conditions that affect capsule growth. The results indicate that the Young's modulus of the capsule decreases with its size and increases with the Ca²⁺ concentration in solution. Also, capsular polysaccharide manifests an unexpected affinity for polystyrene beads, a property that may function in attachment to host cells and environmental structures. Bead probing with optical tweezers provides a new, nondestructive method that may have wide applicability for studying the effects of growth conditions, immune components, and drugs on capsular properties.     

Elastic moduli, yield stress, and ultimate stress of cancellous bone in the canine proximal femur

Elastic moduli, yield stress and ultimate compressive stress were determined for cancellous bone from the femoral head and neck regions of the canine femur. Unconfined compression tests were performed on 5 mm cubic samples which were cut from two femurs. Elastic moduli were measured in three orthogonal directions, and the yield stress and ultimate stress were measured along the proximal-distal axis. The results from this investigation support previous assumptions that the mechanical behavior of canine cancellous bone is qualitatively similar to human cancellous bone. The canine cancellous bone was observed to be anisotropic in elastic modulus. For two thirds of the cubic specimens tested, the elastic modulus was largest in the load-bearing, proximal-distal direction. A linear relationship between yield stress and elastic modulus was observed for canine bone, as is typical of human bone. A similar linear relationship between ultimate stress and elastic modulus was observed. Thus, for canine bone as well as for human bone, failure appears to be governed by a strain level which is position independent. The yield strain of 0.0259 and ultimate strain of 0.0288 for canine bone were both less than the yield strain of 0.0395 reported for human bone.     

Development and testing of a modular strain measurement clip

A novel, multi-use, low-stiffness and low-cost transducer for measuring in vitro strains has been developed and tested. Currently available strain measurement methods are either too expensive, too complicated or too inflexible for multi-use strain measurement. The stainless-steel modular strain measurement clip introduced here was instrumented with four 350 Omega axial strain gauges in a full Wheatstone bridge configuration to take advantage of commonly available strain gauge amplifier equipment. Adjustable extension arms were designed to allow greater application versatility. The clip was calibrated and produced a linear response (R(2)>0.99) over a minimum of 1.04 mm at high amplifier gain. With reduced amplifier settings, testing showed a linear response over a range of 30.5 mm (R(2)>0.99). Clip stiffness was 0.6N/mm of extension arm tip displacement for minimal instrumentation artifact. A validation test was conducted through a comparison of strain clips, surface-mounted strain gauges and theoretical strain in an aluminium rod subjected to axial tensile loading. The two measurement techniques were used to determine the modulus of elasticity of the aluminium rod. Results were within 6% of the known modulus of elasticity for aluminium. A comparative biomechanical test was also performed on an equine third metacarpal specimen. The traditional bonded strain gauging method produced similar results as the new strain clip, but failed to measure ultimate strains since all strain gauges failed prior to specimen failure. Further investigations into the multiple uses of the clip are underway and recommendations for future versions of the clip are given.     

Bi-directional mechanical properties of the posterior region of the glenohumeral capsule

The objective of this study was to determine the mechanical properties of the posterior region of the glenohumeral capsule in the directions perpendicular (transverse) and parallel (longitudinal) to the longitudinal axis of the posterior band of the inferior glenohumeral ligament. A punch was used to excise one transverse and one longitudinal tissue sample from the posterior capsule of 11 cadaveric shoulders. All tissue samples exhibited the typical nonlinear behavior reported for ligaments and tendons. Significant differences (p < 0.05) were detected between the transverse and longitudinal tissue samples for ultimate stress (1.5+/-1.4 and 4.9+/-2.9 MPa, respectively) and tangent modulus (10.3+/-6.6 and 31.5+/-12.7 MPa, respectively). No significant differences (p > 0.05) were observed between the ultimate strain (transverse: 22.3+/-12.5%, longitudinal: 22.8+/-11.1%) and strain energy density (transverse: 27.2+/-52.8 MPa, longitudinal: 67.5+/-88.2 MPa) of the transverse and longitudinal tissue samples. The ratio of the longitudinal to transverse moduli (4.8+/-4.2) was similar to that found for the axillary pouch (3.3+/-2.8) in a previous study. Thus, both the axillary pouch and the posterior capsule function to stabilize the joint multi-axially. Future analytical models of the glenohumeral joint should consider the properties of the posterior capsule in its transverse and longitudinal directions to fully describe the behavior of the glenohumeral capsule. These models will be clinically important by providing a more accurate representation of the intact capsule as well as simulated capsular injuries and surgical repair procedures.     

Phospholipids trigger Cryptococcus neoformans capsular enlargement during interactions with amoebae and macrophages

A remarkable aspect of the interaction of Cryptococcus neoformans with mammalian hosts is a consistent increase in capsule volume. Given that many aspects of the interaction of C. neoformans with macrophages are also observed with amoebae, we hypothesized that the capsule enlargement phenomenon also had a protozoan parallel. Incubation of C. neoformans with Acanthamoeba castellanii resulted in C. neoformans capsular enlargement. The phenomenon required contact between fungal and protozoan cells but did not require amoeba viability. Analysis of amoebae extracts showed that the likely stimuli for capsule enlargement were protozoan polar lipids. Extracts from macrophages and mammalian serum also triggered cryptococcal capsular enlargement. C. neoformans capsule enlargement required expression of fungal phospholipase B, but not phospholipase C. Purified phospholipids, in particular, phosphatidylcholine, and derived molecules triggered capsular enlargement with the subsequent formation of giant cells. These results implicate phospholipids as a trigger for both C. neoformans capsule enlargement in vivo and exopolysaccharide production. The observation that the incubation of C. neoformans with phospholipids led to the formation of giant cells provides the means to generate these enigmatic cells in vitro. Protozoan- or mammalian-derived polar lipids could represent a danger signal for C. neoformans that triggers capsular enlargement as a non-specific defense mechanism against potential predatory cells. Hence, phospholipids are the first host-derived molecules identified to trigger capsular enlargement. The parallels apparent in the capsular response of C. neoformans to both amoebae and macrophages provide additional support for the notion that certain aspects of cryptococcal virulence emerged as a consequence of environmental interactions with other microorganisms such as protists.     

Acquisition of full-field strain distributions on ovine fracture callus cross-sections with electronic speckle pattern interferometry

This study evaluated the feasibility of assessing continuous strain distributions on fracture callus cross-sections with an electronic speckle pattern interferometry (ESPI) system. Mid-sagittal callus cross-sections were harvested from ovine tibiae. One low stiffness (LS) specimen and one high stiffness (HS) specimen were selected to evaluate the feasibility for strain acquisition over a range of callus properties. The HS specimen was 147 times stiffer in compression than the LS specimen. ESPI captured continuous strain distributions on both specimens. Peak strain was located adjacent to cortical boundaries in the osteotomy gap. In response to 5N compression, peak compressive strain of 5.8% in the LS specimen was over two orders of magnitude higher than peak compressive strain of 0.013% in the HS specimen. In conclusion, ESPI-based strain acquisition enables reproducible quantification of strain distributions on callus cross-sections. Such measurements may support validation of computational models and evaluation of experimental results in fracture healing research.     

Finite element models predict cancellous apparent modulus when tissue modulus is scaled from specimen CT-attenuation

High-resolution architecture-based finite element models are commonly used for characterizing the mechanical behavior of cancellous bone. The vast majority of studies use homogeneous material properties to model trabecular tissue. The objectives of this study were to demonstrate that inhomogeneous finite element models that account for microcomputed tomography-measured tissue modulus variability more accurately predict the apparent stiffness of cancellous bone than homogeneous models, and to examine the sensitivity of an inhomogeneous model to the degree of tissue property variability. We tested five different material cases in finite element models of ten cancellous cubes in simulated uniaxial compression. Three of these cases were inhomogeneous and two were homogeneous. Four of these cases were unique to each specimen, and the remaining case had the same tissue modulus for all specimens. Results from all simulations were compared with measured elastic moduli from previous experiments. Tissue modulus variability for the most accurate of the three inhomogeneous models was then artificially increased to simulate the effects of non-linear CT-attenuation-modulus relationships. Uniqueness of individual models was more critical for model accuracy than level of inhomogeneity. Both homogeneous and inhomogeneous models that were unique to each specimen had at least 8% greater explanatory power for apparent modulus than models that applied the same material properties to all specimens. The explanatory power for apparent modulus of models with a tissue modulus coefficient of variation (COV) range of 21-31% was 13% greater than homogeneous models (COV=0). The results of this study indicate that inhomogenous finite element models that have tissue moduli unique to each specimen more accurately predict the elastic behavior of cancellous cubic specimens than models that have common tissue moduli between all specimens.     

Assembly of type I collagen: fusion of fibril subunits and the influence of fibril diameter on mechanical properties.

Structural stability of the extracellular matrix is primarily a consequence of fibrillar collagen and the extent of cross-linking. The relationship between collagen self-assembly, consequent fibrillar shape and mechanical properties remains unclear. Our laboratory developed a model system for the preparation of self-assembled type I collagen fibers with fibrillar substructure mimicking the hierarchical structures of tendon. The present study evaluates the effects of pH and temperature during self-assembly on fibrillar structure, and relates the structural effects of these treatments on the uniaxial tensile mechanical properties of self-assembled collagen fibers. Results of the analysis of fibril diameter distributions and mechanical properties of the fibers formed under the different incubation conditions indicate that fibril diameters grow via the lateral fusion of discrete approximately 4 nm subunits, and that fibril diameter correlates positively with the low strain modulus. Fibril diameter did not correlate with either the ultimate tensile strength or the high strain elastic modulus, which suggests that lateral aggregation and consequently fibril diameter influences mechanical properties during small strain mechanical deformation. We hypothesize that self-assembly is mediated by the formation of fibrillar subunits that laterally and linearly fuse resulting in fibrillar growth. Lateral fusion appears important in generating resistance to deformation at low strain, while linear fusion leading to longer fibrils appears important in the ultimate mechanical properties at high strain.     

An investigation of potential vascular connections between the kidney and the adrenal gland

This study was conducted on two species of monkeys, Macaca fascicularis and Macaca mulatta, to determine if there were vascular connections between the kidney and other abdominal structures such as the adrenal glands. Microfil vascular perfusions, followed by microscopic observations and dissections, were utilized to investigate the existence of these potential connections. Highly anastomotic renal capsular vessels were always observed on the outer surface of the renal capsule. However, these capsular vessels did not make connections with the subcapsular capillary plexus in the majority of monkeys studied. Vascular connections between the adrenal gland and kidney were not observed. It was concluded that, although the region between the adrenal gland and kidney was rich in vasculature, it did not appear to play an anatomical role in anastomosing the extrarenal and intrarenal circulations.     

Exposure of cell surface structures inEscherichia coli as studied with ultrastructural immunohistochemistry

The surfaces of two smoothEscherichia coli O6 strains, one with K13 capsular antigen and one without demonstrable capsule, and one roughE. coli strain were analyzed by using a sandwich technique with ultrastructural immunohistochemistry. Peroxidase-conjugated anti-rabbit serum and antisera corresponding to the distal lipopolysaccharide ofE. coli (O antigen), to the capsule (K antigen), or to the lipid part of the lipopolysaccharide, lipid A, were used. Using the anti-capsule serum on the smooth-capsule-producing strain, we observed the capsule as loosely connected clusters covering less of the surface than the O antigen. No reactions were observed with the capsule-negative strain having the same O antigen. The O antigen was identified all over the outer membrane in a patchy pattern with knobs covering the whole surface on the capsule-negative strain. Fewer knobs, but more variable in size than on the capsule-negative strain, were observed on the capsule-producing strain. The rough strain showed no reactions with either the O or K antiserum. Lipid A was not available for anti-lipid A serum on the rough or smooth strains.     

The role of fabric in the large strain compressive behavior of human trabecular bone

Osteoporosis-related vertebral body fractures involve large compressive strains of trabecular bone. The small strain mechanical properties of the trabecular bone such as the elastic modulus or ultimate strength can be estimated using the volume fraction and a second order fabric tensor, but it remains unclear if similar estimations may be extended to large strain properties. Accordingly, the aim of this work is to identify the role of volume fraction and especially fabric in the large strain compressive behavior of human trabecular bone from various anatomical locations. Trabecular bone biopsies were extracted from human T12 vertebrae (n=31), distal radii (n=43), femoral head (n=44), and calcanei (n=30), scanned using microcomputed tomography to quantify bone volume fraction (BV/TV) and the fabric tensor (M), and tested either in unconfined or confined compression up to very large strains (～70%). The mechanical parameters of the resulting stress-strain curves were analyzed using regression models to examine the respective influence of BV/TV and fabric eigenvalues. The compressive stress-strain curves demonstrated linear elasticity, yielding with hardening up to an ultimate stress, softening toward a minimum stress, and a steady rehardening followed by a rapid densification. For the pooled experiments, the average minimum stress was 1.89 ± 1.77 MPa, while the corresponding mean strain was 7.15 ± 1.84%. The minimum stress showed a weaker dependence with fabric as the elastic modulus or ultimate strength. For the confined experiments, the stress at a logarithmic strain of 1.2 was 8.08 ± 7.91 MPa, and the dissipated energy density was 5.67 ± 4.42 MPa. The latter variable was strongly related to the volume fraction (R(2)=0.83) but the correlation improved only marginally with the inclusion of fabric (R(2)=0.84). The influence of fabric on the mechanical properties of human trabecular bone decreases with increasing strain, while the role of volume fraction remains important. In particular, the ratio of the minimum versus the maximum stress, i.e., the relative amount of softening, decreases strongly with fabric, while the dissipated energy density is dominated by the volume fraction. The collected results will prove to be useful for modeling the softening and densification of the trabecular bone using the finite element method.     

Spatial patterning of bone stiffness in the anterior mandibular corpus of Macaca fascicularis: Implications for models of bone adaptation

Elastic modulus of bone from the anterior mandibular corpus was determined via microindentation in a mixed-sex ontogenetic sample (N = 14) of Macaca fascicularis. This investigation focused on the hypothesis that material heterogeneity in the macaque mandibular symphysis—provided an accounting of age and sex variation—is explicable as a means to homogenize strains in this region. Experimental data and theoretical models of masticatory loading indicate that in the absence of material compensation, large strain gradients exist in the anterior mandibular corpus of macaques, particularly between lingual and labial cortical plates owing to the effects of lateral transverse bending. Microindentation data indicate that juvenile macaques possess less stiff bone than their subadult and adult counterparts; however, sex differences in elastic modulus are not apparent. Anisotropy variation is idiosyncratic; that is, there is not a common pattern of variation in stiffness sampled among orthogonal planes across individuals. Similarly, differences in stiffness between lingual and labial cortical plates, as well as differences among alveolar, midcorpus, and basal regions are inconsistently observed. Consequently, we find little evidence in support of the hypothesis that spatial variation in bone stiffness functions to homogenize strains in the anterior corpus; in fact, in some individuals, this spatial variation serves to exacerbate, rather than to minimize, strain gradients. The mechanical benefit of elastic modulus variation in the macaque mandibular symphysis is unclear; this variation may not confer adaptive benefit in terms of structural integrity despite the fact that such variation has discernible functional consequences. Am J Phys Anthropol 156:649–660, 2015. © 2014 Wiley Periodicals, Inc.     

Design of a Biomimetic Skin for an Octopus-Inspired Robot – Part II: Development of the Skin Artefact

Octopus skin samples were tested under quasi-static and scissor cutting conditions to measure the in-plane material properties and fracture toughness. Samples from all eight arms of one octopus were tested statically to investigate how properties vary from arm to arm. Another nine octopus skins were measured to study the influence of body mass on skin properties. Influence of specimen location on skin mechanical properties was also studied. Material properties of skin, i.e. the Young's modulus, ultimate stress, failure strain and fracture toughness have been plotted against the position of skin along the length of arm or body. Statistical studies were carried out to help analyzing experimental data obtained. Results of this work will be used as guidelines for the design and development of artificial skins for an octopus-inspired robot.     

Noninvasive assessment of implant capsules

The assessment of implant capsular contracture has been imprecise and vulnerable to observer bias. Attempts to measure capsules with instruments that measure implant deformability are influenced by surrounding breast tissue, subcutaneous fat, and skin. Xeromammography, B-mode ultrasound, and CT were employed in an effort to provide a noninvasive and accurate method of capsule assessment. Through two study phases, implants were placed bilaterally in a total of 21 rabbits. At 4 months, animals underwent radiologic assessment and were then sacrificed for direct implant capsule measurements. Mammographic measurements, more than ultrasound-derived measurements, strongly correlated with laboratory measures of capsular dimensions and deformability. Cross-table lateral mammographic views were more informative than traditional views, providing measures of diameter and height that both strongly correlated with laboratory measurements. CT is theoretically the most accurate method to assess contracture, but it is impractical because of expense and time requirements. The results indicate that radiologic assessment, in particular by xeromammography, of implant capsules is accurate, practical, and noninvasive. Mammography strongly correlates with laboratory measures of implant capsular contracture and therefore could be used in the clinical setting to assess capsular contracture.