Mechanical properties and osteointegration of the mesh structure of a lumbar fusion cage made by 3D printing.

The currently popular 3D printing makes it possible to produce spatial scaffolds, the main purpose of which is to obtain implants that have favourable mechanical properties to promote cell adhesion. This study aims to prove the influence of changes in selected geometrical parameters of scaffolds, used in intervertebral cages, on the mechanical properties obtained and thus on the osteointegration of the studied constructs with osteoblasts and fibroblasts. The stiffness values and maximum failure force of four modifications to geometric dimensions of the meshes were determined from the intendation test. Adhesion assays were conducted (including gentle pendulum motion) for Balb/3T3 fibroblasts and NHOst osteoblasts. The study revealed that an important geometrical parameter affecting the strength of the mesh is the height (h) of the connection point between arms of successive mesh cells. There was no significant effect of the mesh geometry on the abundance and survival of Balb/3T3 and NHOst cells. At the same time, fibroblasts were more likely to form colonies in the area where there is fusion of mesh cells, as opposed to osteoblasts that were more numerous at vertices of the mesh.

The influence of facet joint orientation in the lumbar spine segment on the intervertebral disc bulge.

PURPOSE: Due to the growing percentage of degenerative spinal diseases among the population, it is extremely important to assess how the orientation of the articular facets affects the changes in the intervertebral disc. Therefore, the aim of this study was to assess the effect of the orientation of the articular facets on the changes occurring in individual layers of the annulus fibrosus of the intervertebral disc under the influence of the load causing extension. METHODS: Numerical simulations were performed for five configurations of the functional spinal units: physiological, with moderate tropism, severe tropism, and segments in which non-physiological orientation was modelled of both processes with different ranges. RESULTS: It can be concluded that severe tropism causes more significant changes in intervertebral disc bulging on the physiological side of the orientation of the articular facets. Furthermore, the value of stress on articular processes increases tenfold on the side of severe tropism compared to the physiological facet joint orientation. CONCLUSION: Facet joint orientation plays an important role in the transfer of loads by the spine and the posterior column provides important support for the spine during extension.

Effect of overload on changes in mechanical and structural properties of the annulus fibrosus of the intervertebral disc.

The research focussed on analysing structural and mechanical properties in the intervertebral disc (IVD), caused by long-term cyclic loading. Spinal motion segments were divided into two groups: the control (C), and the group in which it was analysed the impact of posterior column in the load-bearing system of the spine-specimens with intact posterior column (IPC) and without posterior column (WPC). To evaluate the structural and mechanical changes, the specimens were tested with simulation of 100,000 compression-flexion load cycles after which it was performed macroscopic analysis. Mechanical properties of the annulus fibrosis (AF) from the anterior and posterior regions of the IVD were tested at the uniaxial tension test. The stiffness coefficient values were statistically 32% higher in the WPC group (110 N/mm) than in the IPC (79 N/mm). The dynamics of increase in this parameter does not correspond with the course of decrease in height loss. WPC segments revealed clear structural changes that mainly involve the posterior regions of the IVD (bulging and delamination with the effect of separation of collagen fibre bundles). Pathological changes also caused decreases in the value of stress in the AF. The greatest changes in the stress value about group C (7.43 ± 4.49 MPa) were observed in the front part of the fibrous ring, where this value was for IPC 4.49 ± 4.78 MPa and WPC 2.56 ± 1.01 MPa. The research indicates that the applied load model allows simulating damage that occurs in pathological IVD. And the posterior column's presence affects this change's dynamics, structural and mechanical properties of AF.

Wall stress correlates with intimal entry tear localization in Type A aortic dissection.

OBJECTIVES: The risk of aortic dissection should be assessed based not only on the aortic diameter, but also on other biomechanical parameters that have an impact on the stress in the aortic wall. This study evaluates very rare clinical scenarios of patients with both pre- and post-dissection computed tomography (CT) images and evaluates whether an increased wall stress correlates with the localization of an intimal entry tear in Type A aortic dissection. METHODS: CT-angiography images of 4 patients performed shortly prior to and after developing Type A aortic dissection were evaluated. The stress distribution in the pre-dissection aortas was evaluated using the finite elements method. Then, the areas of high stress in the pre-dissection aortas were compared to the localization of the intimal entry tears in the dissected vessels. RESULTS: In all the patients, the pre-dissection areas of high wall stress correlated with the location of the intimal tears. The highest stress was not observed in the most dilated segments of the aorta but was predominantly found in the areas of an abrupt change in the geometry of the aorta. CONCLUSIONS: Wall stress can indicate the areas susceptible to the formation of an intimal tear and subsequent aortic dissection. Stress analysis may be a valuable tool to predict the risk of aortic dissection in patients with aortic dilatation.

Finite element analysis of the influence of three-joint spinal complex on the change of the intervertebral disc bulge and height.

This study evaluated the changes of height and bulging occurring in individual layers of the annulus fibrosus of the intervertebral disc for 3 load scenarios (axial compression, flexion, and extension). The numerical model of a single motion segment of the thoracic spine was analysed for 2 different configurations, ie, for the model of a physiological segment and a segment with the posterior column removed. In the physiological segment, all annulus fibrosus layers decrease in height regardless of the applied load, bulging outside the intervertebral disc. Removal of the posterior column increases mobility and disrupts the load transfer system, with the lamellae bulging into the intervertebral disc.

The combined impact of mechanical factors on the wall stress of the human ascending aorta - a finite elements study.

BACKGROUND: Biomechanical factors influence stress in the aortic wall. The aim of this study was to assess how the diameter and shape of the vessel, blood pressure and longitudinal systolic aortic stretching (SAS) caused by the contraction of the myocardium influence stress in the aortic wall. METHODS: Three computational models of the non-dilated aorta and aneurysms of the ascending aorta and aortic root were created. Then, finite elements analyses were carried out. The models were subjected to blood pressure (120 mmHg and 160 mmHg) and longitudinal systolic aortic stretching (0 mm, 5 mm, 10 mm and 15 mm). The influence of wall elasticity was examined too. RESULTS: Blood pressure had a smaller impact on the stress than the SAS. An increase in blood pressure from120 mmHg to 160 mmHg increased the peak wall stress (PWS) on average by 0.1 MPa in all models. A 5 mm SAS caused a 0.1­0. 2 MPa increase in PWS in all the models. The increase in PWS caused by a 10mm and 15mmSAS was 0.2 MPa and 0. 4 MPa in the non-dilated aorta, 0.2­0.3 MPa and 0.3­0.5 MPa in the aneurysm of the ascending aorta, and 0.1­0.2 MPa and 0.2­0.3 MPa in the aortic root aneurysm model, respectively. The loss of elasticity of the aneurysmal wall resulted in an increase of PWS by 0.1­0.2 MPa. CONCLUSIONS: Aortic geometry, wall stiffness, blood pressure and SAS have an impact on PWS. However, SAS had the biggest impact on wall stress. The results of this study may be useful in future patient-specific computational models used to assess the risk of aortic complications.

Analysis of the impact of the course of hydration on the mechanical properties of the annulus fibrosus of the intervertebral disc.

PURPOSE: The aim of this study was to determine the impact of free hydration on the mechanical parameters of the annulus fibrosus (AF) of the intervertebral disc (IVD), determined in a standard manner. Attention was also given to the hydration occurring in real time and geometric changes resulting from swelling of the AF. METHODS: Uniaxial tensile tests of multilayer samples of the AF with bone attachment were performed for two groups: samples subjected to 30 min of hydration prior to the mechanical test, and control samples, which were not subjected to additional hydration. RESULTS: As a result of hydration, the values of both the failure stress (σ UTS) and the tensile modulus (E) were lower than in the control group. A decrease in these values was observed for the AF from both the anterior and posterior parts of the IVD. CONCLUSIONS: The tests showed a significant dependence of the determined mechanical parameters on the cross-sectional area. The larger the cross-sectional area, the lower the obtained value of stress. By contrast, the value of the stiffness coefficient is independent of the cross-sectional area. The differences in mechanical parameters are related mainly to water absorption into structures of the AF during hydration. This is confirmed by microscopic analysis of geometric dimensions of the AF during hydration conducted in real time. The greatest changes occurred in the radial direction, where the thickness increased by 2.05 mm, while in the axial direction the main change concerned an increase in height by 0.69 mm. There were negligible changes in the circumferential direction.

Spinal sections and regional variations in the mechanical properties of the annulus fibrosus subjected to tensile loading.

The annulus fibrosus is the primary load-bearing component of the intervertebral disc responsible for proper transfer of loads in the spine. The aim of this study was to determine selected mechanical parameters of multilayer specimens of the annulus fibrosus of the intervertebral disc during uniaxial tensile loading. The anatomical location (anterior/posterior) of the test specimens of the annulus fibrosus and its location along the length of the spine were analysed to determine their impact on the maximum failure force, stiffness, the value of Young's modulus and dissipated energy. The results indicated high energy losses over the five consecutive precondition loops while the value of the force remained at a constant level. The thoracic and lumbar specimens showed the highest values of the parameters analysed. There were also significant changes depending on the anatomical region of the intervertebral disc, where anterior specimens demonstrated higher mechanical values compared to posterior specimens.

Determination of the mechanical properties of the skin of pig foetuses with respect to its structure.

Skin is an important barrier protecting the organism against external environmental factors. Determination of its mechanical characteristics as regards its structure has significant scientific and application value. In this work, uniaxial tensile tests were conducted to determine the basic mechanical parameters of skin with respect to its structure. The subject of the study were skin samples taken from domestic pig foetuses. They were excised from different parts of body, in the direction parallel to the long axis of the body. Regardless of the sampling site, the tests revealed no significant differences in the values of the maximum tensile strength (2.08 ± 0.25 MPa) and the conventional Young's modulus (5.87 ± 1.52 MPa). The mechanical and structural tests confirmed that regardless of the sampling region the skin of domestic pig foetuses may constitute a human skin substitute model.

Locating multiple interacting quantitative trait Loci using rank-based model selection.

In previous work, a modified version of the Bayesian information criterion (mBIC) was proposed to locate multiple interacting quantitative trait loci (QTL). Simulation studies and real data analysis demonstrate good properties of the mBIC in situations where the error distribution is approximately normal. However, as with other standard techniques of QTL mapping, the performance of the mBIC strongly deteriorates when the trait distribution is heavy tailed or when the data contain a significant proportion of outliers. In the present article, we propose a suitable robust version of the mBIC that is based on ranks. We investigate the properties of the resulting method on the basis of theoretical calculations, computer simulations, and a real data analysis. Our simulation results show that for the sample sizes typically used in QTL mapping, the methods based on ranks are almost as efficient as standard techniques when the data are normal and are much better when the data come from some heavy-tailed distribution or include a proportion of outliers.

Lower percentage of CD8(high+)CD152(+) but not CD8(high+)CD28(+) T lymphocytes in the elderly may be reverted by interleukin 2 in vitro.

An expression of the surface co-stimulatory molecules-the CD152 and the CD28 has been compared between young and old individuals on the CD8(high+) lymphocytes. Sixty five elderly healthy (65-96 years old) and 31 young (19-40 years old) volunteers were examined. An expression of CD152 and CD28 surface antigens was analyzed by flow cytometry ex vivo and on whole blood cell cultures lymphocytes stimulated with interleukin 2 (IL2). The elderly population was characterized by a lower percentage of the CD8(high+) lymphocytes than the young population. The percentages of CD28(+) lymphocytes as well as those of CD8(high+)CD28(+) subpopulation were lower in the old group compared to the young group. The surface expression of CD152 antigen was similar to that of CD28 with a lower percentage of the CD152(+) lymphocytes and CD8(high+)CD152(+) cells in the old group. Stimulation of lymphocytes in vitro with IL2 resulted in an increase of the CD8(high+)CD152(+) cells in the elderly, while it had no effect on lymphocytes of the young group. Our results indicate that lymphocytes of the elderly population are characterized by a lower expression of the surface CD28 and CD152 molecules. An age-related decrease of an expression of the co-stimulatory molecules CD28 and CD152 on the surface of lymphocytes, found in our study, may be compatible with a hypothesis of a 'remodelling' of immune response in the healthy elderly.