Thoracic trauma is the principle causative factor in 30% of road traffic deaths. Researchers have developed force-deflection corridors of the thorax for various loading conditions in order to elucidate injury mechanisms and to validate the mechanical response of ATDs and numerical human models. A corridor, rather than a single response characteristic, results from the variability inherent in biological experimentation. This response variability is caused by both intrinsic and extrinsic factors. The intrinsic factors are associated with individual differences among human subjects, e.g. the differences in material properties and in body geometry. The extrinsic sources of variability include fluctuations in the loading and supporting conditions in experimental tests. Recent studies have considered the intrinsic factors, especially the material-level response of the rib, which can be modified over a limited range within, e.g. a finite element (FE) model in order to fit a gross overall thoracic response corridor. Studies typically do not, however, consider uncertainty due to extrinsic factors. The purpose of this work was to estimate the contribution of selected extrinsic factors to the uncertainty in a response corridor by using a thorax FE model. The sensitivity of twelve response corridors to the relative positioning of the thorax, the loader and the test fixture was analyzed. Reasonable ranges of experimental uncertainty were established for loader angle, loader location, and thorax orientation, and response variability was analyzed for three tissue states (intact, denuded, and eviscerated) with four different loaders (hub, distributed belt, single diagonal belt, and double diagonal belts). Of the variables considered here, the thorax orientation has the largest effect on the force-deflection response, which increases and decreases the effective stiffness up to 20%. The simulation work isolated the extrinsic contribution from the corridor and indicated model deficiencies and refinements, which have the potential to improve model accuracy, particularly modeling the soft tissues and the costal cartilage.

BACKGROUND: Although in-stent restenosis (ISR) after bare-metal stent (BMS) implantation is considered to be clinically benign, ISR is often associated with adverse complications, such as acute coronary syndrome (ACS). The frequency, type, and location of thrombi in ISR lesions and their clinical presentation have not yet been precisely validated. METHODS: Thirty angiographic ISR lesions occurring within 3 to 8months after stenting were evaluated by optical coherence tomography (OCT). A thrombus was defined as a mass protruding into the lumen with an irregular surface, and its type was divided into red or white. The maximum size of a thrombus and the longitudinal distance from the thrombus to the narrowest lumen were measured. RESULTS: A thrombus was identified in 2 patients by angiography and in 10 patients by OCT (7% vs. 33%; P=0.01). OCT showed that 9 patients had white thrombus and another patient had both types of thrombi. ACS relevant to ISR was seen in 6 patients, and the frequency of ACS was significantly higher in patients with thrombus than in those without thrombus [50%(5/10) vs. 5%(1/20); P=0.003]. The maximum size of the thrombus was 412+/-220microm in height, 424+/-251microm in width, and the longitudinal distance between the thrombus and the minimum lumen area was 0.3+/-0.7mm. CONCLUSIONS: One third of ISR lesions following BMS deployment dominantly contained a white thrombus, and half of them were associated with ACS. A small thrombus formation adjacent to the narrowest lumen in an ISR lesion may therefore contribute to the clinical presentation of ACS.

Previous research has suggested that the pediatric ATD spine, developed from scaling the adult ATD spine, may not adequately represent a child's spine and thus may lead to important differences in the ATD head trajectory relative to a human. To gain further insight into this issue, the objectives of this study were, through non-injurious frontal sled tests on human volunteers, to 1) quantify the kinematic responses of the restrained child's head and spine and 2) compare pediatric kinematic responses to those of the adult. Low-speed frontal sled tests were conducted using male human volunteers (20 subjects: 6-14 years old, 10 subjects: 18-40 years old), in which the safety envelope was defined from an amusement park bumper-car impact. Each subject was restrained by a custom-fit lap and shoulder belt system and photo-reflective targets were attached to a tight-fitting cap worn on the head or adhered to the skin overlying skeletal landmarks on the head, spine, shoulders, sternum, and legs. A 3-D near-infrared target tracking system quantified the position of the following markers: head top, external auditory meatus, nasion, opisthocranion, C4, T1, T4, and T8. Trajectory data were normalized by subject seated height and head and spine rotations were calculated. The Generalized Estimating Equations method was used to determine the effect of age and key anthropometric measures on marker excursion. For all markers, the normalized forward excursion significantly decreased with age and all spinal markers moved upward due to a combination of rigid body rotation and spinal flexion with lesser upward movement with age. The majority of the spine flexion occurred at the base of the neck not in the upper cervical spine and the magnitude of flexion was greatest for the youngest subjects. Additional flexion occurred in the thoracic spine as well. Our findings indicate that the primary factor governing the differences in normalized head and spinal trajectories between the various age groups was decreasing head-to-neck girth ratio with increasing age. Other factors, such as muscle response and cervical vertebral structural properties, may also contribute to the differences, but were not evaluated in this paper. These results can serve as a data set for validating the responses of restrained ATDs and computational human models to low severity frontal collisions.

Proper modeling of the human trunk requires a quantitative assessment of the stiffness of the costovertebral joints. Twelve samples (adjacent thoracic vertebrae and one rib segment) were harvested from three subjects. The ribs were loaded in the cranial-caudal direction, the ventral-dorsal direction and in torsion around the cervical rib axis. The force applied to and the displacement of the loading point on the rib were measured and used to determine the moment-angle responses. Characteristic average curves and boundary curves containing the dataset were developed. The torsion response presented a range of motion-defined as the change in the angle for an applied moment varying from -0.1 to 0.1Nm-of 16.9+/-6.8 degrees which is more than three times the range in cranial-caudal flexion and five times the range in ventral-dorsal flexion. Statistical tests showed a significant difference between these ranges of motion. Significant inter-subject variability was observed for the cranial-caudal flexion (p<0.05) while no intra-subject variability appeared. The characteristic moment-angle responses of the joints were well represented by third order polynomials (R(2)>0.9). This study expands and supplements the limited data available in the literature. Furthermore, it provides biomechanical data (closed-form moment-angle functions) that can be directly integrated into spine-ribcage models.

BACKGROUND: Although coronary angiograms after bare-metal stent (BMS) implantation show late luminal narrowing beyond 4 years, the detailed changes inside the BMS have not yet been fully elucidated. METHODS AND RESULTS: Serial angiographic and angioscopic examinations were performed immediately (baseline), 6 to 12 months (first follow-up), and >/=4 years (second follow-up) after stenting without target lesion revascularization in 26 segments of 26 patients who received BMS deployment for their native coronary arteries. Angioscopic observation showed atherosclerotic yellow plaque crushed out by stent struts in 22 patients (85%) and mural thrombus in 21 patients (81%) at baseline. At first follow-up, white neointimal hyperplasia was almost completely buried inside the struts, and both yellow plaque and thrombus had decreased in comparison with baseline (12% and 4%, respectively; P<0.001). The frequencies of yellow plaque and thrombus increased from the first to second follow-ups (58% and 31%, respectively; P<0.05). All of the yellow plaques in the second follow-up were located not exterior to the struts but protruding from the vessel wall into the lumen. Late luminal narrowing, defined as an increasing of percent diameter stenosis between the first and second follow-ups, was greater in segments with yellow plaque than in those without yellow plaque (18.4+/-17.3% versus 3.6+/-4.2%, respectively; P=0.011). CONCLUSIONS: This angiographic and angioscopic study suggests that white neointima of the BMS may often change into yellow plaque over an extended period of time, and atherosclerotic progression inside the BMS may contribute to late luminal narrowing.

BACKGROUND: It recently has been hypothesized that a larger late loss may have a protective role against stent thrombosis. The relationship between angiographic late loss and the presence of thrombus based on angioscopic findings within paclitaxel-eluting stents (PES) and sirolimus-eluting stents (SES) was investigated in this study. METHODS AND RESULTS: Prospective 6-month follow-up angiographic and angioscopic examinations were performed on 18 patients for PES and on 20 patients for SES. Late loss was measured by quantitative coronary angiography. Angioscopic neointimal stent coverage (NSC) grade was classified as follows: 0=uncovered struts without neointima, 1=visible struts through thin neointima, and 2=no visible struts. In each patient, maximum NSC, minimum NSC, and the existence of thrombus were evaluated. Late loss and maximum NSC were greater in PES than in SES (0.38+/-0.43 versus 0.10+/-0.23 mm; P=0.02 and P=0.0004, respectively). Late loss was correlated with maximum NSC (grade 0, 0.06+/-0.01 mm; grade 1, 0.10+/-0.05 mm; and grade 2, 0.48+/-0.46 mm), whereas there was no correlation between late loss and minimum NSC. The prevalence of patients with uncovered struts did not differ (44% of PES, 40% of SES; P=0.78). In-stent thrombus was found more frequently in PES than in SES (72% versus 40%, P=0.046) despite no occurrence of stent thrombosis. Only within PES were thrombi found in the segments of NSC grade 2 associated with large late loss. CONCLUSIONS: The present study suggests that angiographic large late loss was not associated with a low risk of in-stent thrombus.

The purpose of this study was to investigate whether using a finite-element (FE) mesh composed entirely of hexahedral elements to model cortical and trabecular bone (all-hex model) would provide more accurate simulations than those with variable thickness shell elements for cortical bone and hexahedral elements for trabecular bone (hex-shell model) in the modeling human ribs. First, quasi-static non-injurious and dynamic injurious experiments were performed using the second, fourth, and tenth human thoracic ribs to record the structural behavior and fracture tolerance of individual ribs under anterior-posterior bending loads. Then, all-hex and hex-shell FE models for the three ribs were developed using an octree-based and multi-block hex meshing approach, respectively. Material properties of cortical bone were optimized using dynamic experimental data and the hex-shell model of the fourth rib and trabecular bone properties were taken from the literature. Overall, the reaction force-displacement relationship predicted by both all-hex and hex-shell models with nodes in the offset middle-cortical surfaces compared well with those measured experimentally for all the three ribs. With the exception of fracture locations, the predictions from all-hex and offset hex-shell models of the second and fourth ribs agreed better with experimental data than those from the tenth rib models in terms of reaction force at fracture (difference <15.4%), ultimate failure displacement and time (difference <7.3%), and cortical bone strains. The hex-shell models with shell nodes in outer cortical surfaces increased static reaction forces up to 16.6%, compared to offset hex-shell models. These results indicated that both all-hex and hex-shell modeling strategies were applicable for simulating rib responses and bone fractures for the loading conditions considered, but coarse hex-shell models with constant or variable shell thickness were more computationally efficient and therefore preferred.

The objective of this study was to document the motion and potential injury mechanisms of obese occupants in frontal car crashes compared to a control group of nonobese occupants in controlled laboratory impacts. Eight cadavers were divided into obese (n = 3) and a nonobese (n = 5) groups and exposed to a 48 km/h impact. High speed digital video documented the motion of the belted subjects. Compared to the nonobese cohort, the obese exhibited a characteristically different set of motions. As expected, the obese (heavier) subjects experienced greater maximum forward displacement (excursion) before their motion was arrested by the restraint. In addition, the obese exhibited a different distribution of excursions among body segments. The primary difference between the cohorts was substantially larger hip excursion in the obese (452 +/- 83 mm vs. 203 +/- 42 mm, P < 0.01), which was the proximate cause of a tendency of the obese cadavers' torsos to pitch forward less during impact. Some of the published epidemiology can be elucidated by the results reported here. The increased hip excursion and concomitant decreased torso pitch may reduce the risk of the head striking some component of the vehicle interior. Furthermore, the reclined torso during belt loading may increase the risk of rib and pulmonary trauma because the load is concentrated on the compliant and vulnerable lower thorax and less on the stiff upper ribs and clavicle. The lower extremities also experience increased excursion as a result of this hip excursion, and thus an increased risk of a hard contact and resulting injury.

Background: There is a hypothesis that advanced neointimal stent coverage may protect against stent thrombosis. In the present study, differences in neointimal growth and prevalence of in-stent thrombus between paclitaxel- and sirolimus-eluting stent (PES and SES) were evaluated by optical coherence tomography (OCT). Methods and Results: Follow-up angiographic and OCT examinations at approximately 6 months were performed for 40 patients (20 PES, 20 SES). Late loss was measured by quantitative coronary angiography. Neointimal hyperplasia (NIH) thickness on stent struts was measured by cross-sectional OCT images at 1 mm intervals. After measuring the NIH area in each cross-section, NIH volume was calculated as integral of NIH area within the stent. Late loss, NIH thickness, and NIH volume were greater for PES than for SES (0.42 +/-0.44 vs 0.13 +/-0.12 mm, 118 +/-141 vs 31 +/-39 mum, 53.2 +/-30.5 vs 24.3 +/-14.0 mm(3); P<0.05, respectively). In-stent thrombus was found more frequently in PES than in SES (50 vs 15%; P=0.02). Conclusions: Although the degree of neointimal growth in PES was generally greater, in-stent thrombus was more common compared with SES. Presence of thrombus in first-generation drug-eluting stents was not related to advanced neointimal growth.

An important aim of regenerative medicine is to restore tissue function with implantable, laboratory-grown constructs that contain tissue-specific cells that replicate the function of their counterparts in the healthy native tissue. It remains unclear, however, whether cells used in bone regeneration applications produce a material that mimics the structural and compositional complexity of native bone. By applying multivariate analysis techniques to micro-Raman spectra of mineralized nodules formed in vitro, we reveal cell-source-dependent differences in interactions between multiple bone-like mineral environments. Although osteoblasts and adult stem cells exhibited bone-specific biological activities and created a material with many of the hallmarks of native bone, the 'bone nodules' formed from embryonic stem cells were an order of magnitude less stiff, and lacked the distinctive nanolevel architecture and complex biomolecular and mineral composition noted in the native tissue. Understanding the biological mechanisms of bone formation in vitro that contribute to cell-source-specific materials differences may facilitate the development of clinically successful engineered bone.

In this study, the disk type of a thermal barrier coating (TBC) system for a gas turbine blade was isothermally aged at 1100 degrees C for various times up to 400 hours. For each aging condition, the thickness of the thermally grown oxide (TGO) was measured by optical microscope and mechanical properties such as the elastic modulus and hardness were measured by micro-indentation and nano-indentation on the cross-section of a coating specimen. In the case of micro-indentation, the mechanical properties of a Ni-base superalloy substrate and MCrAlY bond coat material did not significantly change with an increase in exposure time. In the case of nano-indentation, the gamma-Ni phase and beta-NiAl phase in the bond coat and top coat material show no significant change in their properties. However, the elastic modulus and the hardness of TGO show a remarkable decrease from 100 h to 200 h then remain nearly constant after 200 h due to the internal delamination of TBC. It has been confirmed that the nano-indentation technique is a very effective way to evaluate the degradation of a thermal barrier coating system.

The popularity of biomimetic membranes has recently increased due to their biomedical applications such as tissue engineering/regenerative medicine and biosensors. Characterization of the viscoelastic properties of these membranes is important in developing functional membranes. A new micro-shaft poking technique has been developed, which is free from the complication of substrate backing, and which is normally an intractable problem in conventional indentation testing of membrane materials. A tailored indentation apparatus with a spherical indenter and a force resolution and displacement of 1muN and 1mum was constructed. Alginate and agarose were used to fabricate biomimetic membranes. Chicken epidermis was examined to represent a real biological tissue. The results show that the elastic modulus increased with concentration in hydrogels. Epidermis moduli appeared to increase with increased strain. Stress relaxation tests have also been conducted to examine the time-dependent behaviours of various hydrogels and a viscoelastic model has been correspondingly developed and applied to describe the experimental results. Potential applications of this new instrument to other membranes, both artificial and biological, have also been addressed.

This paper reports a computational study of the indentation of a flat punch into a compressible elastic layer (with Poisson's ratio varying from 0 to 0.49) bonded to a rigid substrate. Based on the computational results and using Sneddon's solution [Sneddon IN. The relation between load and penetration in the axisymmetric Boussinesq problem for a punch of arbitrary profile. Int J Eng Sci 1965;3:47] and the asymptotic solution [Jaffar MJ. A general solution to the axisymmetric frictional contact problem of a thin bonded elastic layer. Proc Inst Mech Eng C 1997;211:549; Yang FQ. Asymptotic solution to axisymmetric indentation of a compressible elastic thin film. Thin Solid Films 2006;515:2274] as the two limits, a simple expression of the load-depth curve valid for an arbitrary ratio of the indenter radius to the thickness of the layer is obtained. Further, a correlation between indentation load and depth for a rigid flat punch indenting into linearly viscoelastic layers bonded to a rigid substrate is proposed by using the correspondence principle. Several procedures are suggested based on the results reported in this study to determine the viscoelastic properties of the layer in the time or frequency domains. The findings are verified by numerical examples. The results may facilitate the use of depth-sensing indentation tests to characterize the mechanical properties of polymeric films or functional coatings on hard substrates, and some biological materials, e.g. articular cartilage.

OBJECTIVE: To investigate the age-related change in biomechanical properties of the costal cartilage and its relevance to the timing of ear reconstruction with costal cartilage framework. METHODS: The patients of 5 to 25 years old were divided into three groups according to their age. The biomechanical properties of costal cartilage harvested from these patients during ear reconstruction were tested, including stree-strain relationship, stress relaxation and creep, tensile strength. All the results were analyzed statistically. RESULTS: The costal cartilage from children group had the best biomechanical properties, while the costal cartilage from the adolescent group had the worst. The difference had a statistically significance (P < 0.05). CONCLUSIONS: The biomechanical properties of costal cartilage are age-related. So it is recommended that ear reconstruction with costal cartilage framework should be performed in childhood when the costal cartilage has the best biomechanical properties.

The human skin, the interface between the body and the outside environment, has a very complex mechanical behaviour. Knowledge of its in vivo mechanical characteristics is essential to characterize the effects of medical or cosmetic products. The aim of this work is to present a non-invasive device using dynamic indentation to quantify the viscoelatic properties of human skin in vivo. The frequency and strain amplitude are in the range of 10 to 60 Hz and 1 to 10 ¿m. The results on 4 subjects show that a Kelvin Voigt model describes the mechanical behaviour of in vivo human skin with dynamic indentation well. The frequency average values of stiffness and damping have also been used to compare skin properties. We found a stiffness value of 47.3 to 128.3 N/m, and damping of 0.08 to 0.121 N.s/m, corresponding to a complex modulus of 13.2 to 33.4 kPa. These results show the ability of this device to characterize viscoelastic properties of human skin.

OBJECTIVE: Various bone and cartilage changes after the Ravitch thoracoplasty have recently been reported. In this study, quantitative measurements of long-term changes in the bone, cartilage, and contour of the chest wall through the use of multislice computed tomography with 3-dimensional reconstruction are presented. METHODS: Between 1985 and 2002, 114 patients with pectus excavatum received the Ravitch thoracoplasty in our hospital. Multislice computed tomography with 3-dimensional reconstruction was undertaken in 36 patients 4 to 18 years after the initial operation. Twenty-four patients with pectus excavatum without a surgical intervention were enrolled as a control group. The voxel size of calcification/ossification in regenerated cartilage, costal cartilage shortening ratio, and clubbing index were calculated to quantify the long-term bone and cartilage changes. RESULTS: The calcification/ossification volume was measured as 5.29 +/- 6.94 cm(3), which was significantly correlated with the patient's age at the time of the operation (P =.001). The costal cartilage shortening ratio showed significant shortening of the regenerated cartilage in the third to sixth ribs bilaterally (P < 0.05), and the clubbing index confirmed significant clubbing in the bony ends of the third to fifth ribs (P < 0.05). These changes were not demonstrated in the control group. CONCLUSIONS: After undergoing the Ravitch thoracoplasty, patients sustained significant bone and cartilage changes. The use of multislice computed tomography with 3-dimensional reconstruction may offer both images and quantitative measurements of these changes, but further investigation is necessary to elucidate the clinical impact of these phenomena.