Patient-Specific Variations in Local Strain Patterns on the Surface of a Trussed Titanium Interbody Cage

Introduction: 3D printed trussed titanium interbody cages may deliver bone stimulating mechanobiological strains to cells attached at their surface. The exact size and distribution of these strains may depend on patient-specific factors, but the influence of these factors remains unknown. Therefore, this study aimed to determine patient-specific variations in local strain patterns on the surface of a trussed titanium interbody fusion cage.Materials and Methods: Four patients eligible for spinal fusion surgery with the same cage size were selected from a larger database. For these cases, patient-specific finite element models of the lumbar spine including the same trussed titanium cage were made. Functional dynamics of the non-operated lumbar spinal segments, as well as local cage strains and caudal endplate stresses at the operated segment, were evaluated under physiological extension/flexion movement of the lumbar spine.Results: All patient-specific models revealed physiologically realistic functional dynamics of the operated spine. In all patients, approximately 30% of the total cage surface experienced strain values relevant for preserving bone homeostasis and stimulating bone formation. Mean caudal endplate contact pressures varied up to 10 MPa. Both surface strains and endplate contact pressures varied more between loading conditions than between patients.Conclusions: This study demonstrates the applicability of patient-specific finite element models to quantify the impact of patient-specific factors such as bone density, degenerative state of the spine, and spinal curvature on interbody cage loading. In the future, the same framework might be further developed in order to establish a pipeline for interbody cage design optimizations.

Estimation of ergonomic indicators of special purpose clothing for patients with thermal injuries

This article discusses the determination of the optimal design allowances for a full factorial experiment in the development of special-purpose clothing for patients with thermal injuries in a hospital. To assess the ergonomic performance of special-purpose clothing, was used of pressure exerted by clothing on the human body. Based on the results of the study, a mathematical model was developed based on a full factorial experiment. In accordance with the presented mathematical models, the minimum values of contact pressures are obtained for the following values of construction parameters: for a cut with a sewn-in sleeve Warmhole = 15 cm, Ifa = 5,0 cm, Ic = 9 cm, Hse = 10 cm; for a cut with a raglan sleeve Warmhole = 15 cm, Ifa = 6 cm, Ic = 10 cm; for a cut with a one-piece sleeve Warmhole = 16 cm, Ifa = 6 cm, Ic = 11 cm.

A Novel Reciprocating Tribometer for Friction and Wear Measurements with High Contact Pressure and Large Area Contact Configurations

There are many moving machine assemblies with conformal tribological contacts at very high contact pressures, e.g., sliding bearings, propeller shaft bearings and machine guideways. Furthermore, applications such as trunnion and guide vane bearing in Kaplan turbines have very low sliding speeds and oscillatory types of motion. Although there is a vast selection of tribology test rigs available, there is still a lack of test equipment to perform friction and wear tests under high contact pressure, reciprocatory sliding and large area contact. The aim of this work is thus to develop a novel reciprocating tribometer and test method that enables friction and wear tests under low-speed reciprocatory sliding with contact pressures up to 90 MPa in a flat-on-flat contact configuration. First, a thorough description of the test rig design is given. Secondly, the influence of contact pressure and stroke length on the tribological properties of a stainless steel and polymer composite material combination is studied. The significance of considering creep, friction during the stroke and contact temperature is specifically highlighted. The novel tribometer can be used to screen different bearing and shaft material combinations and to evaluate the friction and wear performance of self-lubricating bearings for the specific operating conditions found in Kaplan turbines.

NEW BEARING STEEL FOR HIGH-SPEED APPLICATIONS

The requirements for speed suitability and fatigue strength of motor spindle bearings are constantly increasing. These challenges can be met by further developing the spindle bearings, e.g. by using higher-performance bearing steels. In the following, the experimental investigation results of a spindle bearing made of a new raceway steel tested on a high-speed rolling bearing test rig are presented. Spindle bearings of the type 7008 (hybrid execution) were tested in an endurance run at a rotational speed of 46 krpm and 3 kN axial load. The operating behaviour was validated based on the bearing outer ring temperature and the vibration behaviour. Microscope analysis of the raceways after the test shows that the new steel has good resistance to micropitting and surface fatigue. The calculated contact pressures, wear parameter and lifetime for the bearings in the tests show that the performance limits of spindle bearings are significantly higher than initially assumed.

The contribution of plastic sink-in to the static friction of single asperity microscopic contacts

We report microscale friction experiments for diamond/metal and diamond/silica contacts under gigapascal contact pressures. Using a new nanoprobe technique that has a sufficient dynamic range of force and stiffness, we demonstrate the processes involved in the transition from purely interface sliding at the nanoscale to the situation where at least one of the sliding bodies undergoes some plastic deformation. For sliding of micrometre-sized tips on metallic substrates, additional local plastic yielding of the substrate resulting from tangential tractions causes the tip to sink into the surface, increasing the contact area in the direction of loading and resulting in a static friction coefficient higher than the kinetic during ploughing. This sink-in is largely absent in fused silica, and no friction drop is observed, along with lower friction in general. The transition from sink-in within the static friction regime to ploughing in the sliding friction regime is mediated by failure of the contact interface, indicated by a sharp increase in energy dissipation. At lower contact pressures, the elastic interfacial sliding behaviour characteristic of scanning probe or surface force apparatus experiments is recovered, bridging the gap between the exotic realm of nanotribology and plasticity-dominated macroscale friction.

Clinical Replacement Strategies for Meniscus Tissue Deficiency

Meniscus tissue deficiency resulting from primary meniscectomy or meniscectomy after failed repair is a clinical challenge because the meniscus has little to no capacity for regeneration. Loss of meniscus tissue has been associated with early-onset knee osteoarthritis due to an increase in joint contact pressures in meniscectomized knees. Clinically available replacement strategies range from allograft transplantation to synthetic implants, including the collagen meniscus implant, ACTIfit, and NUSurface. Although short-term efficacy has been demonstrated with some of these treatments, factors such as long-term durability, chondroprotective efficacy, and return to sport activities in young patients remain unpredictable. Investigations of cell-based and tissue-engineered strategies to treat meniscus tissue deficiency are ongoing.

Modelling of contact and tribotechnical parameters of metal–polymer gears taking into account wear and correction of teeth

The estimation and the analysis of the arising contact pressures and tribotechnical parameters, that is, wear and durability, of metal-polymer spur gears using the author's computational method are presented in this study. Gears with a steel gear and pinion made of polyamide PA6 modified with dispersed carbon fibers (CF) or glass fibers (GF) whose content was 30%, PA6 + 30CF and PA6 + 30GF correspondingly, are studied. This took into account the parity of engagement, the effect of composite pinion teeth wear and gear correction. Quantitative and qualitative regularities of change of the specified parameters depending on composite type and gear correction type are established. It is found that the teeth wear of composite toothed wheels has a significant effect on reducing the values of the initial maximum contact pressures in the engagement. The distribution of linear wear along the teeth working profile and the localization of its maximum values, depending on the correction of engagement, are determined. The minimum durability of metal–polymer gears is calculated by simplified and improved methods. The optimal values of the correction coefficients at which the minimum durability is highest for both combination types of metal–polymer gears with height and angular teeth correction are established. The durability of metal–polymer gears with a driving pinion made of PA6 + 30CF composite calculated with the improved method is about seven times higher than the pinion made of PA6 + 30GF composite. In contrast to the methods of calculation of metal gears known from publications, the method presented in this study takes into account such practically significant factors as change of radii of tooth profile curvature owing to wear, their correction and number of teeth pairs at the engagement. In metal–polymer gears, there are no analytical calculation methods for modelling wear and tribological durability compared with that of the author's method.