Biomechanics of the Human Osteochondral Unit: A Systematic Review

The damping system ensured by the osteochondral (OC) unit is essential to deploy the forces generated within load-bearing joints during locomotion, allowing furthermore low-friction sliding motion between bone segments. The OC unit is a multi-layer structure including articular cartilage, as well as subchondral and trabecular bone. The interplay between the OC tissues is essential in maintaining the joint functionality; altered loading patterns can trigger biological processes that could lead to degenerative joint diseases like osteoarthritis. Currently, no effective treatments are available to avoid degeneration beyond tissues' recovery capabilities. A thorough comprehension on the mechanical behaviour of the OC unit is essential to (i) soundly elucidate its overall response to intra-articular loads for developing diagnostic tools capable of detecting non-physiological strain levels, (ii) properly evaluate the efficacy of innovative treatments in restoring physiological strain levels, and (iii) optimize regenerative medicine approaches as potential and less-invasive alternatives to arthroplasty when irreversible damage has occurred. Therefore, the leading aim of this review was to provide an overview of the state-of-the-art-up to 2022-about the mechanical behaviour of the OC unit. A systematic search is performed, according to PRISMA standards, by focusing on studies that experimentally assess the human lower-limb joints' OC tissues. A multi-criteria decision-making method is proposed to quantitatively evaluate eligible studies, in order to highlight only the insights retrieved through sound and robust approaches. This review revealed that studies on human lower limbs are focusing on the knee and articular cartilage, while hip and trabecular bone studies are declining, and the ankle and subchondral bone are poorly investigated. Compression and indentation are the most common experimental techniques studying the mechanical behaviour of the OC tissues, with indentation also being able to provide information at the micro- and nanoscales. While a certain comparability among studies was highlighted, none of the identified testing protocols are currently recognised as standard for any of the OC tissues. The fibril-network-reinforced poro-viscoelastic constitutive model has become common for describing the response of the articular cartilage, while the models describing the mechanical behaviour of mineralised tissues are usually simpler (i.e., linear elastic, elasto-plastic). Most advanced studies have tested and modelled multiple tissues of the same OC unit but have done so individually rather than through integrated approaches. Therefore, efforts should be made in simultaneously evaluating the comprehensive response of the OC unit to intra-articular loads and the interplay between the OC tissues. In this regard, a multidisciplinary approach combining complementary techniques, e.g., full-field imaging, mechanical testing, and computational approaches, should be implemented and validated. Furthermore, the next challenge entails transferring this assessment to a non-invasive approach, allowing its application in vivo, in order to increase its diagnostic and prognostic potential.

Prediction of the mechanical properties of TPMS structures based on Back propagation neural network

Triply Periodic Minimal Surface (TPMS) has the characteristics of high porosity, a highly interconnected network, and a smooth surface, making it an ideal candidate for bone tissue engineering applications. However, due to the complex relationship between multiple parameters of the TPMS structure and mechanical properties, it is a challenging task to optimize the properties of TPMS structures with different parameters. In this study, a Back-Propagation Neural Network (BPNN) was utilized to construct the relationship between TPMS parameters. Its mechanical performance and the TPMS structure were optimized using the BPNN. Results indicated that after training the correlation coefficient (R) between the BPNN prediction and the experimental results is 0.955475, it shows that our BPNN model has an adequate accuracy in describing the TPMS structures properties. Result of TPMS structure optimization shows that after optimization the yield strength of Hybridized Gyroid-Diamond Structure (HGDS) is 6.20 MPa, which is increased by 102.61% when compared with the original Hybridized Gyroid-Diamond Structure (3.06 MPa). Result of topological morphology indicates the effective bearing area of the optimized model was increased by 12.92% compared with the original model, which ascribe the increase in yield strength of the optimization model.

Physical and Mechanical Behavior of New Ternary and Hybrid Eco-Cements Made from Construction and Demolition Waste

Construction and demolition waste (CDW) currently constitutes a waste stream with growing potential use as a secondary raw material in the manufacture of eco-cements that offer smaller carbon footprints and less clinker content than conventional cements. This study analyzes the physical and mechanical properties of two different cement types, ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement, and the synergy between them. These cements are manufactured with different types of CDW (fine fractions of concrete, glass and gypsum) and are intended for new technological applications in the construction sector. This paper addresses the chemical, physical, and mineralogical characterization of the starting materials, as well as the physical (water demand, setting time, soundness, water absorption by capillary action, heat of hydration, and microporosity) and mechanical behavior of the 11 cements selected, including the two reference cements (OPC and commercial CSA). From the analyses obtained, it should be noted that the addition of CDW to the cement matrix does not modify the amount of water by capillarity with respect to OPC cement, except for Labo CSA cement which increases by 15.7%, the calorimetric behavior of the mortars is different depending on the type of ternary and hybrid cement, and the mechanical resistance of the analysed mortars decreases. The results obtained show the favorable behavior of the ternary and hybrid cements made with this CDW. Despite the variations observed in the different types of cement, they all comply with the current standards applicable to commercial cements and open up a new opportunity to improve sustainability in the construction sector.

Sustainable Development Approaches through Wooden Adhesive Joints Design

Over recent decades, the need to comply with environmental standards has become a concern in many industrial sectors. As a result, manufacturers have increased their use of eco-friendly, recycled, recyclable, and, overall, more sustainable materials and industrial techniques. One technique highly dependent on petroleum-based products, and at the edge of a paradigm change, is adhesive bonding. Adhesive bonding is often used to join composite materials and depends upon an adhesive to achieve the connection. However, the matrices of the composite materials and the adhesives used, as well as, in some cases, the composite fibres, are manufactured from petrochemical products. Efforts to use natural composites and adhesives are therefore ongoing. One composite that has proven to be promising is wood due to its high strength and stiffness (particularly when it is densified), formability, and durability. However, wood must be very carefully characterised since its properties can be variable, depending on the slope of the grains, irregularities (such as knots, shakes, or splits), and on the location and climate of each individual tree. Therefore, in addition to neat wood, wood composites may also be a promising option to increase sustainability, with more predictable properties. To bond wood or wooden composite substrates, bio-adhesives can be considered. These adhesives are now formulated with increasingly enhanced mechanical properties and are becoming promising alternatives at the structural application level. In this paper, wooden adhesive joints are surveyed considering bio-adhesives and wood-based substrates, taking into consideration the recent approaches to improve these base materials, accurately characterise them, and implement them in adhesive joints.

Effect of Processed Volcanic Ash as Active Mineral Addition for Cement Manufacture

In the last quarter of 2021, there was a very significant eruption of the Cumbre Vieja volcano on the island of La Palma, belonging to the Canary Islands, Spain. It generated a large amount of pyroclastic volcanic materials, which must be studied for their possible applicability. This work studies the properties and applicability of the lava and volcanic ash generated in this process. The need for reconstruction of the areas of the island that suffered from this environmental catastrophe is considered in this study from the point of view of the valuation of the waste generated. For this purpose, the possibility of using the fine fraction of ashes and lava as a supplementary cement material (SCM) in the manufacture of cement is investigated. The volcanic material showed a chemical composition and atomic structure suitable for replacing clinker in the manufacture of Portland cement. In this study, the cementing and pozzolanic reaction characteristics of unprocessed volcanic materials and those processed by crushing procedures are analysed. To evaluate the cementitious potential by analysing the mechanical behaviour, a comparison with other types of mineral additions (fly ash, silica fume, and limestone filler) commonly used in cement manufacture or previously studied was carried out. The results of this study show that volcanic materials are feasible to be used in the manufacture of cement, with up to a 22% increase in pozzolanicity from 28 to 90 days, showing the high potential as a long-term supplementary cementitious material in cement manufacturing, though it is necessary to carry out crushing processes that improve their pozzolanic behaviour.

On the mechanical aspect of additive manufactured polyether-ether-ketone scaffold for repair of large bone defects

Polyether-ether-ketone (PEEK) is widely used in producing prosthesis and have gained great attention for repair of large bone defect in recent years with the development of additive manufacturing. This is due to its excellent biocompatibility, good heat and chemical stability and similar mechanical properties which mimics natural bone. In this study, three replicates of rectilinear scaffolds were designed for compression, tension, three-point bending and torsion test with unit cell size of 0.8 mm, a pore size of 0.4 mm, strut thickness of 0.4 mm and nominal porosity of 50%. Stress-strain graphs were developed from experimental and finite element analysis models. Experimental Young's modulus and yield strength of the scaffolds were measured from the slop of the stress-strain graph to be 395 and 19.50 MPa respectively for compression, 427 and 6.96 MPa respectively for tension, 257 and 25.30 MPa respectively for three-point bending and 231 and 12.83 MPa respectively for torsion test. The finite element model was found to be in good agreement with the experimental results. Ductile fracture of the struct subjected to tensile strain was the main failure mode of the PEEK scaffold, which stems from the low crystallinity of additive manufacturing PEEK. The mechanical properties of porous PEEK are close to those of cancellous bone and thus are expected to be used in additive manufacturing PEEK bone implants in the future, but the lower yield strength poses a design challenge.

Porcine spleen as a model organ for blunt injury impact tests: An experimental and histological study

The spleen is a large and highly vascularized secondary lymphatic organ. Spleen injuries are among the most frequent trauma-related injuries in the abdominal region. The aims of the study were to assess the volume fractions of the main splenic tissue components (red pulp, white pulp, trabeculae and reticular fibres) and to determine the severity of splenic injury due to the experimental impact test. Porcine spleens (n = 17) were compressed by 6.22 kg wooden plate using a drop tower technique from three impact heights (50, 100 and 150 mm corresponding to velocities 0.79, 1.24 and 1.58 m/s). The pressure was measured via catheters placed in the splenic vein. The impact velocity was measured using lasers. The severity of induced injuries was analysed on the macroscopic level. The volume fractions of splenic components were assessed microscopically using stereology. The volume fraction of the red pulp was 76.4%, white pulp 21.3% and trabeculae 2.7% respectively. All impact tests, even with the low impact velocities, led to injuries that occurred mostly in the dorsal extremity of the spleen, and were accompanied by bleeding, capsule rupture and parenchyma crushing. Higher impact height (impact velocity and impact energy) caused more severe injury. Porcine spleen had the same volume fraction of tissue components as human spleen, therefore we concluded that the porcine spleen was a suitable organ model for mechanical experiments. Based on our observations, regions around hilum and the diaphragmatic surface of the dorsal extremity, that contained fissures and notches, were the most prone to injury and required considerable attention during splenic examination after injury. The primary mechanical data are now available for the researchers focused on the splenic trauma modelling.

Effects of Temperature on the Evolution of Yield Surface and Stress Asymmetry in A356-T7 Cast Aluminium Alloy

As the electrification of vehicle powertrains takes prominence to meet stringent emission norms, parts of internal combustion engines like cylinder heads are subjected to an increased number of thermal load cycles. The cost-effective design of such structures subjected to cyclic thermo-mechanical loads relies on the development of accurate material models capable of describing the continuum deformation behaviour of the material. This study investigates the effect of temperature on the evolution of flow stress under cyclic loading in A356-T7 + 0.5% Cu cast aluminium alloy commonly used in modern internal combustion engine cylinder heads. The material exhibits peak stress and flow stress asymmetry with the stress response and flow stress of the material under compressive loading higher than under tension. This peak and flow stress asymmetry decrease with an increase in temperature. To compare this stress asymmetry against conventional steel, cyclic strain-controlled fatigue tests are run on fully pearlitic R260 railway steel material. To study the effect of mean strain on the cyclic mean stress evolution and fatigue behaviour of the alloy, tests with tensile and compressive mean strains of +0.2% and -0.2% are compared against fully reversed (R_ε = -1) strain-controlled tests. The material exhibits greater stress asymmetry between the peak tensile and peak compressive stresses for the strain-controlled tests with a compressive mean strain than the tests with an identical magnitude tensile mean strain. The material exhibits mean stress relaxation at all temperatures. Reduced durability of the material is observed for the tests with tensile mean strains at lower test temperatures of up to 150 °C. The tensile mean strains at elevated temperatures do not exhibit such a detrimental effect on the endurance limit of the material.

Modification of Surface and Subsurface Properties of AA1050 Alloy by Shot Peening

AA1050 Al alloy samples were shot-peened using stainless-steel shots at shot peening (SP) pressures of 0.1 and 0.5 MPa and surface cover rates of 100% and 1000% using a custom-designed SP system. The hardness of shot-peened samples was around twice that of unpeened samples. Hardness increased with peening pressure, whereas the higher cover rate did not lead to hardness improvement. Micro-crack formation and embedment of shots occurred by SP, while average surface roughness increased up to 9 µm at the higher peening pressure and cover rate, indicating surface deterioration. The areal coverage of the embedded shots ranged from 1% to 5% depending on the peening parameters, and the number and the mean size of the embedded shots increased at the higher SP pressure and cover rate. As evidenced and discussed through the surface and cross-sectional SEM images, the main deformation mechanisms during SP were schematically described as crater formation, folding, micro-crack formation, and material removal. Overall, shot-peened samples demonstrated improved mechanical properties, whereas sample surface integrity only deteriorated notably during SP at the higher pressure, suggesting that selecting optimal peening parameters is key to the safe use of SP. The implemented methodology can be used to modify similar soft alloys within confined compromises in surface features.

Computer-Aided Reengineering towards Plastic Part Failure Minimization

The work reported here intends to identify and mitigate the causes for failure in a plastic faucet holder, a part of an integral float faucet with a well-documented history of fracture occurrence. A methodology for the identification of hidden internal defects in plastic parts and the elaboration of the required corrective actions towards quality improvement is, therefore, presented. Firstly, part defects were identified via injection moulding process numerical simulation. The latter has enabled the prediction of an excessive volumetric shrinkage at the core of the faucet holder, highlighting the presence of internal voids and, hence, the possible deterioration of the load-bearing capacity. The supposition was later confirmed by X-ray topography scans. Part reengineering, consisting of localized thickness reduction, was the option chosen for decreasing the high shrinkage at the core. For validation purposes, structural analyses were carried out, with and without accounting for the injection moulding processing history. The results obtained during part structural analysis have enabled us to conclude that, when taking into account the residual stresses generated during injection moulding, the analysis more closely reflects the experimental data and allows us to implicitly envisage the propensity to fracture. Moreover, the part modifications, undertaken during the faucet holder reengineering, led to the reduction of the cumulative (processing and imposed by load) stresses by 50%, when compared to the original design analysed.

Self-Compacting Recycled Concrete Using Biomass Bottom Ash

In recent years, the use of self-compacting concrete has been a great advantage and garnered undoubted interest in construction. Due to the environmental impact caused by the consumption of natural aggregates in the manufacture of concrete, a more sustainable approach is needed. An approach for more sustainable construction is to use industrial waste such as bottom ash from the combustion of biomass as a replacement for natural aggregates. This research aims to use biomass bottom ash as a replacement for natural sand (10%, 20% and 30% replacement); in addition, by utilizing a crushing process of the bottom ash, the ash has been used as a filler replacement (replacement 20%, 40% and 60%). The fresh and hardened properties have been evaluated according to the standard. The results show the feasibility of using biomass bottom ash in self-compacting concrete, providing a sustainable alternative in order to minimise environmental impacts related to the extraction and depletion of natural resources.

Biodegradable magnesium alloys for orthopaedic applications

There is increasing interest in the development of bone repair materials for biomedical applications. Magnesium (Mg)-based alloys have a natural ability to biodegrade because they corrode in aqueous media; they are thus promising materials for orthopaedic device applications in that the need for a secondary surgical operation to remove the implant can be eliminated. Notably, Mg has superior biocompatibility because Mg is found in the human body in abundance. Moreover, Mg alloys have a low elastic modulus, close to that of natural bone, which limits stress shielding. However, there are still some challenges for Mg-based fracture fixation. The degradation of Mg alloys in biological fluids can be too rapid, resulting in a loss of mechanical integrity before complete healing of the bone fracture. In order to achieve an appropriate combination of bio-corrosion and mechanical performance, the microstructure needs to be tailored properly by appropriate alloy design, as well as the use of strengthening processes and manufacturing techniques. This review covers the evolution, current strategies and future perspectives of Mg-based orthopaedic implants.

Alkali-Activated Stainless Steel Slag as a Cementitious Material in the Manufacture of Self-Compacting Concrete

This work develops the manufacture of self-compacting concrete (SCC) with 50% cement reduction. As an alternative binder to cement, the viability of using an alkali-activated combination of stainless steel slag (SSS) and fly ash (FA) has been demonstrated. SSS was processed applying three different treatments. Binders were manufactured mixing 35% SSS with 65% FA, as precursors, and a hydroxide activating solution. This binder was replaced by the 50% cement for the manufacture of SCC. The results obtained show good mechanical properties and durability. The study shows a reduction in the use of cement in the manufacture of SCC reusing two wastes.

Influence of HRGO Nanoplatelets on Behaviour and Processing of PMMA Bone Cement for Surgery

Bone cement, frequently based on poly (methyl methacrylate), is commonly used in different arthroplasty surgical procedures and its use is essential for prosthesis fixation. However, its manufacturing process reaches high temperatures (up to 120 °C), producing necrosis in the patients’ surrounding tissues. To help avoid this problem, the addition of graphene could delay the polymerisation of the methyl methacrylate as it could, simultaneously, favour the optimisation of the composite material’s properties. In this work, we address the effect of different percentages of highly reduced graphene oxide with different wt.% (0.10, 0.50, and 1.00) and surface densities (150, 300, 500, and 750 m²/g) on the physical, mechanical, and thermal properties of commercial poly (methyl methacrylate)-based bone cement and its processing. It was noted that a lower sintering temperature was achieved with this addition, making it less harmful to use in surgery and reducing its adverse effects. In contrast, the variation of the density of the materials did not introduce significant changes, which indicates that the addition of highly reduced graphene oxide would not significantly increase bone porosity. Lastly, the mechanical properties (strength, elastic modulus, and fracture toughness) were reduced by almost 20%. Nevertheless, their typical values are high enough that these new materials could still fulfil their structural function. In conclusion, this paper presents a way to control the sintering temperature, without significant degradation of the mechanical performance, by adding highly reduced graphene oxide so that local necrosis of bone cement based on poly (methyl methacrylate) used in surgery is avoided.

Saliva Influence on the Mechanical Properties of Advanced CAD/CAM Composites for Indirect Dental Restorations

This study aims to evaluate the microstructural and mechanical properties of three commercial resin-based materials available for computer-aid design and manufacturing (CAD/CAM)-processed indirect dental restoration: Lava^TM Ultimate Restorative (LU), 3M ESPE; Brilliant Crios (BC), COLTENE and Cerasmart^TM (CS), GC Dental Product. The three types of resin-based composite CAD/CAM materials were physically and mechanically tested under two conditions: directly as received by the manufacturer (AR) and after storage under immersion in artificial saliva (AS) for 30 days. A global approximation to microstructure and mechanical behaviour was evaluated: density, hardness and nanohardness, nanoelastic modulus, flexural strength, fracture toughness, fracture surfaces, and microstructures and fractography. Moreover, their structural and chemical composition using X-ray fluorescence analysis (XRF) and field emission scanning electron microscopy (FESEM) were investigated. As a result, LU exhibited slightly higher mechanical properties, while the decrease of its mechanical performance after immersion in AS was doubled compared to BC and CS. Tests of pristine material showed 13 GPa elastic modulus, 150 MPa flexural strength, 1.0 MPa·m^1/2 fracture toughness, and 1.0 GPa hardness for LU, 11.4 GPa elastic modulus; 140 MPa flexural strength, 1.1 MPa·m^1/2 fracture toughness, and 0.8 GPa hardness for BC; and 8.3 GPa elastic modulus, 140 MPa flexural strength, 0.9 MPa·m^1/2 fracture toughness, and 0.7 GPa hardness for CS. These values were significantly reduced after one month of immersion in saliva. The interpretation of the mechanical results could suggest, in general, a better behaviour of LU compared with the other two despite it having the coarsest microstructure of the three studied materials. The saliva effect in the three materials was critically relevant for clinical use and must be considered when choosing the best solution for the restoration to be used.

Mechanical testing of glutaraldehyde cross-linked mitral valves. Part one: In vitro mechanical behaviour

The aim of this study was to perform an initial assessment, in vitro, of the feasibility of using a glutaraldehyde cross-linked porcine mitral valve to retain acute functionality, focusing on assessing mitral regurgitation. Six porcine hearts were tested using an in vitro simulator. Testing was repeated following cross-linking of mitral valves; where cross-linking was achieved by placing them in a glutaraldehyde solution. The simulator enabled systolic pressure on the ventricular side of the valve to be mimicked. Following testing, mitral valve leaflets underwent Scanning Electron Microscopy of the ventricular surface of both the anterior and posterior leaflets (1 cm² samples). The peak pressure withstood by cross-linked valves was significantly lower than for untreated valves (108 mmHg cf. 128 mmHg for untreated valves; p  < 0.05). The peak pressure was typically reached 0.5 s later than for the untreated valve. While both cross-linked and untreated valves exhibited endothelium denudation, the unfixed valve had less endothelial loss. Glutaraldehyde cross-linking of porcine mitral valves may be of potential value in assessing improved bioprosthetic mitral valve replacements. However, a more immobile valve exhibiting endothelial denudation (i.e. sclerosis) was a possible concerns identified following in vitro acute assessment.

Mechanical Characterisation of Single-Walled Carbon Nanotube Heterojunctions: Numerical Simulation Study

The elastic properties of single-walled carbon nanotube heterojunctions were investigated using conventional tensile, bending and torsion tests. A three-dimensional finite element model was built in order to describe the elastic behaviour of cone heterojunctions (armchair-armchair and zigzag-zigzag). This comprehensive systematic study, to evaluate the tensile, bending and torsional rigidities of heterojunctions, enabled the formulation analytical methods for easy assessment of the elastic properties of heterojunctions using a wide range of their geometrical parameters.

The Impact Behaviour of Crab Carapaces in Relation to Morphology

Brachyuran crab carapaces are protective, impact-resistant exoskeletons with elaborate material microstructures. Though several research efforts have been made to characterise the physical, material and mechanical properties of the crab carapace, there are no studies detailing how crab morphologies might influence impact resistance. The purpose of this paper is to characterise and compare Brachyuran crab carapace morphologies in relation to their impact properties, using opto-digital, experimental and numerical methods. We find that crab carapaces with both extended carapace arc-lengths and deep carapace grooves lose stiffness rapidly under cyclic impact loading, and fail in a brittle manner. Contrarily, carapaces with smaller arc lengths and shallower, more broadly distributed carapace grooves are more effective in dissipating stresses caused by impact throughout the carapace structure. This allows them to retain stiffness for longer, and influences their failure mode, which is ductile (denting), rather than brittle fracture. The findings in this paper provide new bioinspired approaches for the geometrical designs by which means material failure under cyclic impact can be controlled and manipulated.

Fabrication of Metastable Crystalline Nanocomposites by Flash Annealing of Cu47.5Zr47.5Al5 Metallic Glass Using Joule Heating

Flash Joule-heating was applied to the Cu_47.5Zr_47.5Al₅ metallic glass for designing fully crystalline metastable nanocomposites consisting of the metastable B2 CuZr and low-temperature equilibrium Cu₁₀Zr₇ phases. The onset of crystallization was in situ controlled by monitoring resistivity changes in the samples. The effect of heating rate and annealing time on the volume fraction of the crystalline phases and mechanical properties of the nanocomposites was studied in detail. Particularly, an increase of the heating rate and a decrease of the annealing time lead to a lower number of equilibrium Cu₁₀Zr₇ precipitates and an increase of tensile ductility. Tailoring of these non-equilibrium microstructures and mechanical properties may not be possible unless one starts with a fully glassy material that opens new perspectives for designing metastable nanomaterials with unique physical properties.

Long-term leaching and mechanical behaviour at recycled aggregate with different gypsum contents

Construction and demolition recycling is regarded as an essential subject in the EU, as the target established by its policies to 2020 ratio is far from being achieved. The use of materials recycled from such waste has been widely deemed a contribution to the sustainability of the construction sector. Gypsum is one the limiting components of recycled aggregates used as a base layer in road construction. The aim of this research was to analyse the effect on mechanical properties, leaching behaviour and dimensional changes at long term in recycled aggregates with different gypsum contents. Load bearing capacity was conducted by California bearing ratio on prepared samples. Moreover, the compressive strength was conducted on samples prepared with a 3% cement addition. Both tests were studied long term. Dimensional changes were studied through swelling in California bearing ratio test mould under the modified Proctor conditions for 1 year and using an oedometer device for 5 months. Furthermore, environmental risk assessment was performed, classifying the material with gypsum addition as non-hazardous, given that sulphate anion was above the inert limit. Good mechanical behaviour in the long term and no significant dimensional changes were found regardless of gypsum content.

A Non-linear Viscoelastic Model of the Incudostapedial Joint

The ossicular joints of the middle ear can significantly affect middle-ear function, particularly under conditions such as high-intensity sound pressures or high quasi-static pressures. Experimental investigations of the mechanical behaviour of the human incudostapedial joint have shown strong non-linearity and asymmetry in tension and compression tests, but some previous finite-element models of the joint have had difficulty replicating such behaviour. In this paper, we present a finite-element model of the joint that can match the asymmetry and non-linearity well without using different model structures or parameters in tension and compression. The model includes some of the detailed structures of the joint seen in histological sections. The material properties are found from the literature when available, but some parameters are calculated by fitting the model to experimental data from tension, compression and relaxation tests. The model can predict the hysteresis loops of loading and unloading curves. A sensitivity analysis for various parameters shows that the geometrical parameters have substantial effects on the joint mechanical behaviour. While the joint capsule affects the tension curve more, the cartilage layers affect the compression curve more.

Investigation about the Effect of Manufacturing Parameters on the Mechanical Behaviour of Natural Fibre Nonwovens Reinforced Thermoplastic Composites

To date, nonwoven fabrics made with natural fibres and thermoplastic commingled fibres have been extensively used in the composite industry for a wide variety of applications. This paper presents an innovative study about the effect of the manufacturing parameters on the mechanical behaviour of flax/PP nonwoven reinforced composites. The mechanical properties of nonwoven fabric reinforced composites are related directly to the ones of dry nonwoven reinforcements, which depend strongly on the nonwoven manufacturing parameters, such as the needle-punching and areal densities. Consequently, the influence of these manufacturing parameters will be analysed through the tensile and flexural properties. The results demonstrated that the more areal density the nonwoven fabric has, the more the mechanical behaviour can be tested for composites. By contrast, it has a complex influence on needle-punching density on the load-strain and bending behaviours at the composite scale.

A critical review on the three-dimensional finite element modelling of the compression therapy for chronic venous insufficiency

Compression therapy is an adjuvant physical intervention providing the benefits of calibrated compression and controlled stretch and consequently is increasingly applied for the treatment of chronic venous insufficiency. However, the mechanism of the compression therapy for chronic venous insufficiency is still unclear. To elaborate the mechanism of compression therapy, in recent years, the computational modelling technique, especially the finite element modelling method, has been widely used. However, there are still many unclear issues regarding the finite element modelling of compression therapy, for example, the selection of appropriate material models, the validation of the finite element predictions, the post-processing of the results. To shed light on these unclear issues, this study provides a state-of-the-art review on the application of finite element modelling technique in the compression therapy for chronic venous insufficiency. The aims of the present study are as follows: (1) to provide guidance on the application of the finite element technique in healthcare and relevant fields, (2) to enhance the understanding of the mechanism of compression therapy and (3) to foster the collaborations among different disciplines. To achieve these aims, the following parts are reviewed: (1) the background on chronic venous insufficiency and the computational modelling approach, (2) the acquisition of medical images and the procedure for generating the finite element model, (3) the definition of material models in the finite element model, (4) the methods for validating the finite element predictions, (5) the post-processing of the finite element results and (6) future challenges in the finite element modelling of compression therapy.

Mechanical Behaviour of Stamped Aluminium Alloy Components by Means of Response Surfaces

In the automotive industry, the use of stamped aluminium alloy components has become a very common occurrence. For the appropriate design of these components, it is necessary to know how the manufacturing process affects the material properties. In the first place, high plastic strains (εp) can be generated during the stamping process, which can result in a change in the residual stress and mechanical properties in the plastically deformed areas. Furthermore, if a last coat of paint that is usually subjected to a thermal cycle, characterized by temperature (T) and exposure time (t), is applied, it can also influence mechanical behaviour. Consequently, this paper studies how both processes affect the mechanical behaviour of an aluminium alloy of the 5000 series, commonly used in these types of components. In particular, the mechanical properties such as the yield stress at 0.2% (σ0.2), the ultimate tensile strength (sut) and the engineering strain at break (ef) have been analysed. To achieve this, a response surface technique, based on the design of experiments, has been used. The response surfaces obtained allow for the prediction of mechanical properties σ0.2, sut and ef for any combination of values of t, T and εp.

The Effect of Dynamic Recrystallization on Monotonic and Cyclic Behaviour of Al-Cu-Mg Alloy

The paper presents an investigation that was conducted to determine the possibility of the occurrence of the process of dynamic recrystallization in 2024 alloy during monotonic tensile and creep tests at the elevated temperatures of 100 °C, 200 °C, and 300 °C. As-extruded material was subjected to creep process with constant force at elevated temperatures, until two varying degrees of deformation were reached. After cooling at ambient temperature, the pre-deformed material was subjected to monotonic and fatigue tests as well as metallographic analysis. The process of dynamic recrystallization was determined in monotonic tests to occur at low strain rate (0.0015/s) only at the temperature of 300 °C. However, in the creep tests, this process occurred with varying efficiency, both during creep at 200 °C and 300 °C. Dynamic recrystallization was indicated to have a significant influence on the monotonic and cyclic properties of the material.

Stiffness distribution in insect cuticle: a continuous or a discontinuous profile?

Insect cuticle is a biological composite with a high degree of complexity in terms of both architecture and material composition. Given the complex morphology of many insect body parts, finite-element (FE) models play an important role in the analysis and interpretation of biomechanical measurements, taken by either macroscopic or nanoscopic techniques. Many previous studies show that the interpretation of nanoindentation measurements of this layered composite material is very challenging. To develop accurate FE models, it is of particular interest to understand more about the variations in the stiffness through the thickness of the cuticle. Considering the difficulties of making direct measurements, in this study, we use the FE method to analyse previously published data and address this issue numerically. For this purpose, sets of continuous or discontinuous stiffness profiles through the thickness of the cuticle were mathematically described. The obtained profiles were assigned to models developed based on the cuticle of three insect species with different geometries and layer configurations. The models were then used to simulate the mechanical behaviour of insect cuticles subjected to nanoindentation experiments. Our results show that FE models with discontinuous exponential stiffness gradients along their thickness were able to predict the stress and deformation states in insect cuticle very well. Our results further suggest that, for more accurate measurements and interpretation of nanoindentation test data, the ratio of the indentation depth to cuticle thickness should be limited to 7% rather than the traditional '10% rule'. The results of this study thus might be useful to provide a deeper insight into the biomechanical consequences of the distinct material distribution in insect cuticle and also to form a basis for more realistic modelling of this complex natural composite.

A numerical investigation and experimental verification of size effects in loaded bovine cortical bone

In this paper, we present 2- and 3-dimensional finite element-based numerical models of loaded bovine cortical bone that explicitly incorporate the dominant microstructural feature: the vascular channel or Haversian canal system. The finite element models along with the representation of the microstructure within them are relatively simple: 2-dimensional models, consisting of a structured mesh of linear elastic planar elements punctuated by a periodic distribution of circular voids, are used to represent beam samples of cortical bone in which the channels are orientated perpendicular to the sample major axis, while 3-dimensional models, using a corresponding mesh of equivalent solid elements, represent those samples in which the canals are aligned with the axis. However, these models are exploited in an entirely novel approach involving the representation of material samples of different sizes and surface morphology. The numerical results obtained for the virtual material samples when loaded in bending indicate that they exhibit size effects not forecast by either classical (Cauchy) or more generalized elasticity theories. However, these effects are qualitatively consistent with those that we observed in a series of carefully conducted experiments involving the flexural testing of bone samples of different sizes. Encouraged by this qualitative agreement, we have identified appropriate model parameters, primarily void volume fraction but also void separation and matrix modulus by matching the computed size effects to those we observed experimentally. Interestingly, the parameter choices that provide the most suitable match of these effects broadly concur with those we actually observed in cortical bone.

Splitting fracture in bovine bone using a porosity-based spring network model

We examine the specific role of the structure of the network of pores in plexiform bone in its fracture behaviour under compression. Computed tomography scan images of the sample pre- and post-compressive failure show the existence of weak planes formed by aligned thin long pores extending through the length. We show that the physics of the fracture process is captured by a two-dimensional random spring network model that reproduces well the macroscopic response and qualitative features of fracture paths obtained experimentally, as well as avalanche statistics seen in recent experiments on porcine bone.

Translational challenges for the development of a novel nucleus pulposus substitute: Experimental results from biomechanical and in vivo studies

Nucleus pulposus replacement therapy could offer a less invasive alternative to restore the function of moderately degenerated intervertebral discs than current potentially destructive surgical procedures. Numerous nucleus pulposus substitutes have already been investigated, to assess their applicability for intradiscal use. Still, the current choice of testing methods often does not lead to efficient translation into clinical application. In this paper, we present the evaluation of a novel nucleus pulposus substitute, consisting of a hydromed core and an electrospun envelope. We performed three mechanical evaluations and an in vivo pilot experiment. Initially, the swelling pressure of the implant was assessed in confined compression. Next, we incorporated the implant into mechanically damaged caprine lumbar intervertebral discs to determine biomechanical segment behaviour in bending and torsion. Subsequently, segments were serially tested in native, damaged and repaired conditions under dynamic axial compressive loading regimes in a loaded disc culture system. Finally, nucleus pulposus substitutes were implanted in a live goat spine using a transpedicular approach. In confined compression, nucleus pulposus samples as well as implants showed some load-bearing capacity, but the implant exhibited a much lower absolute pressure. In bending and torsion, we found that the nucleus pulposus substitute could partly restore the mechanical response of the disc. During dynamic axial compression in the loaded disc culture system, on the other hand, the implant was not able to recover axial compressive behaviour towards the healthy situation. Moreover, the nucleus pulposus substitutes did not remain in place in the in vivo situation but migrated out of the disc area. From these results, we conclude that implants may mimic native disc behaviour in simple mechanical tests, yet fail in other, more realistic set-ups. Therefore, we recommend that biomaterials for nucleus pulposus replacement be tested in testing modalities of increasing complexity and in their relevant anatomical surroundings, for a more reliable prediction of clinical potential.

Nanostructured Ti-Zr-Pd-Si-(Nb) bulk metallic composites: Novel biocompatible materials with superior mechanical strength and elastic recovery

The microstructure, mechanical behaviour, and biocompatibility (cell culture, morphology, and cell adhesion) of nanostructured Ti45 Zr15 Pd35- x Si5 Nbx with x = 0, 5 (at. %) alloys, synthesized by arc melting and subsequent Cu mould suction casting, in the form of rods with 3 mm in diameter, are investigated. Both Ti-Zr-Pd-Si-(Nb) materials show a multi-phase (composite-like) microstructure. The main phase is cubic β-Ti phase (Im3m) but hexagonal α-Ti (P63/mmc), cubic TiPd (Pm3m), cubic PdZr (Fm3m), and hexagonal (Ti, Zr)5 Si3 (P63/mmc) phases are also present. Nanoindentation experiments show that the Ti45 Zr15 Pd30 Si5 Nb5 sample exhibits lower Young's modulus than Ti45 Zr15 Pd35 Si5 . Conversely, Ti45 Zr15 Pd35 Si5 is mechanically harder. Actually, both alloys exhibit larger values of hardness when compared with commercial Ti-40Nb, (HTi-Zr-Pd-Si ≈ 14 GPa, HTi-Zr-Pd-Si-Nb ≈ 10 GPa and HTi-40Nb ≈ 2.7 GPa). Concerning the biological behaviour, preliminary results of cell viability performed on several Ti-Zr-Pd-Si-(Nb) discs indicate that the number of live cells is superior to 94% in both cases. The studied Ti-Zr-Pd-Si-(Nb) bulk metallic system is thus interesting for biomedical applications because of the outstanding mechanical properties (relatively low Young's modulus combined with large hardness), together with the excellent biocompatibility.