SciCombinator

Discover the most talked about and latest scientific content & concepts.

Journal: Journal of the mechanical behavior of biomedical materials

180

While the predominant function of all tendons is to transfer force from muscle to bone and position the limbs, some tendons additionally function as energy stores, reducing the cost of locomotion. Energy storing tendons experience extremely high strains and need to be able to recoil efficiently for maximum energy storage and return. In the equine forelimb, the energy storing superficial digital flexor tendon (SDFT) has much higher failure strains than the positional common digital extensor tendon (CDET). However, we have previously shown that this is not due to differences in the properties of the SDFT and CDET fascicles (the largest tendon subunits). Instead, there is a greater capacity for interfascicular sliding in the SDFT which facilitates the greater extensions in this particular tendon (Thorpe et al., 2012). In the current study, we exposed fascicles and interfascicular matrix (IFM) from the SDFT and CDET to cyclic loading followed by a test to failure. The results show that IFM mechanical behaviour is not a result of irreversible deformation, but the IFM is able to withstand cyclic loading, and is more elastic in the SDFT than in the CDET. We also assessed the effect of ageing on IFM properties, demonstrating that the IFM is less able to resist repetitive loading as it ages, becoming stiffer with increasing age in the SDFT. These results provide further indications that the IFM is important for efficient function in energy storing tendons, and age-related alterations to the IFM may compromise function and predispose older tendons to injury.

Concepts: Collagen, Muscle, Cartilage, Tendon

28

Orientated focal cross-linking can be used to generate surface anisotropy, improve material stiffness and layer integration for the production of a stable 3D construct. Riboflavin (0.25mM) diffusion into plastically compressed (PC) collagen gel was assessed by measuring the diffusion depth of riboflavin with time. The dynamic force analyser was used for peel force testing for interlayer cross-linking and material stiffness in perpendicular axis after orientated/topical cross-linking. One minute riboflavin diffusion time on either surface will saturate >12% of the collagen gel. Bonding strength doubled between PC collagen gel layers with a 5min increase in cross-linking time (between 4 and 9min) and break stress was increased significantly after cross-linking. Importantly, mechanical anisotropy was introduced in the break stress using orientated stripes of riboflavin in cross-linking, almost doubling the break stress parallel to the stripes. Limited riboflavin penetration in 1min means that surface photo-dynamic cross-linking will enhance deep cell survival within the gel. Riboflavin mediated focal/orientated cross-linking generated new predictable anisotropy at the construct. The increase in bonding strength between layers after cross-linking enhances layer integration and graded surface stiffness will impact on cellular/mechanical properties of compressed gels.

Concepts: Layer, Force, Materials science, Classical mechanics, Young's modulus, Gel, Gelatin

28

Ag core MP35N (Ag/MP35N) wire has been used in lead electric conductor wires in the medical device industry for many years. Recently it was noticed that the combination of silver and MP35N restricts its wire drawing process. The annealing temperature in Ag/MP35N has to be lower than the melting temperature of pure Ag (960°C), which cannot fully anneal MP35N. The lower annealing temperature results in a highly cold worked MP35N, which significantly reduces Ag/MP35N ductility. The embrittlement phenomenon of Ag/MP35N cable was observed in tension and bending deformation. The effect of the embrittlement on the wire flex fatigue life was evaluated using a newly developed flex fatigue testing method. The Ag/MP35N cable fatigue results was analyzed with a Coffin-Manson approach and compared to the MP35N cable fatigue results. The root causes of the Ag/Mp35N embrittlement phenomenon are discussed.

Concepts: Copper, Silver, Steel, Wire, Cable, Ductility, Wire drawing

28

The mechanism of crack initiation from a clinically relevant notch is not well-understood for crosslinked ultra high molecular weight polyethylene (UHMWPE) used in total joint replacement components. Static mode driving forces, rather than the cyclic mode conditions typically associated with fatigue processes, have been shown to drive crack propagation in this material. Thus, in this study, crack initiation in a notched specimen under a static load was investigated. A video microscope was used to monitor the notch surface of the specimen and crack initiation time was measured from the video by identifying the onset of crack initiation at the notch. Crack initiation was considered using a viscoelastic fracture theory. It was found that the mechanism of crack initiation involved both single layer and a distributed multi-layer phenomenon and that multi-layer crack initiation delayed the crack initiation time for all loading conditions examined. The findings of this study support that the viscoelastic fracture theory governs fracture mechanics in crosslinked UHMWPE. The findings also support that crack initiation from a notch in UHMWPE is a more complex phenomenon than treated by traditional fracture theories for polymers.

Concepts: Fracture, Physics, Shock, Fracture mechanics, Fractography, Fatigue, Polyethylene, Fracture toughness

28

The mathematical modelling of column buckling or beam bending under an axial or transverse load is well established. However, the existent models generally assume a high degree of symmetry in the structure of the column and minor longitudinal and transverse displacements. The situation when the column is made of several components with different mechanical properties asymmetrically distributed in the transverse section, semi-rigid, and subjected to multiple axial loads with significant longitudinal and transverse displacements through compression and bending has not been well characterised. A more comprehensive theoretical model allowing for these possibilities and assuming a circular arc contour for the bend is developed, and used to establish the bending axes, balance between compression and bending, and equivalent stiffness of the column. In certain situations, such as with pull cable catheters commonly used for minimally invasive surgical procedures, the compression loads are applied via cables running through channels inside a semi-rigid column. The model predicts the mathematical relationships between the radius of curvature of the bend and the tension in and normal force exerted by such cables. Conjugate extension with reciprocal compression-bending is a special structural arrangement for a semi-rigid column such that extension of one segment is linked to compression-bending of another by inextensible cables running between them. Leads are cords containing insulated electrical conductor coil and cables between the heart muscle and cardiac implantable electronic devices. Leads can behave like pull cable catheters through differential component pulling, providing a possible mechanism for inside-out abrasion and conductor cable externalisation. Certain design features may predispose to this mode of structural failure.

Concepts: Force, Structural engineering, Beam, Column, Bending, Buckling, Skin effect, Truss

28

This paper reports on property-process correlations in simulated clinical abrasive adjusting of a wide range of dental restorative ceramics using a dental handpiece and diamond burs. The seven materials studied included four mica-containing glass ceramics, a feldspathic porcelain, a glass-infiltrated alumina, and a yttria-stabilized tetragonal zirconia. The abrasive adjusting process was conducted under simulated clinical conditions using diamond burs and a clinical dental handpiece. An attempt was made to establish correlations between process characteristics in terms of removal rate, chipping damage, and surface finish and material mechanical properties of hardness, fracture toughness and Young’s modulus. The results show that the removal rate is mainly a function of hardness, which decreases nonlinearly with hardness. No correlations were noted between the removal rates and the complex relations of hardness, Young’s modulus and fracture toughness. Surface roughness was primarily a linear function of diamond grit size and was relatively independent of materials. Chipping damage in terms of the average chipping width decreased with fracture toughness except for glass-infiltrated alumina. It also had higher linear correlations with critical strain energy release rates (R(2)=0.66) and brittleness (R(2)=0.62) and a lower linear correlation with indices of brittleness (R(2)=0.32). Implications of these results can provide guidance for the microstructural design of dental ceramics, optimize performance, and guide the proper selection of technical parameters in clinical abrasive adjusting conducted by dental practitioners.

Concepts: Correlation and dependence, Materials science, Young's modulus, Roughness, Fracture toughness, Hardness, Toughness, Strain energy release rate

27

We developed an innovative non-fusion correction system (XS LATOR) consisting of two individual implants that are extendable and extremely flexible. One implant, the XS LAT, generates a lateral, bending moment and one implant, the XS TOR, generates a torsion moment. Two ‘inverse’ implants were developed for generating torsion and lateral bending in a porcine model was tested for force delivery. An in vitro experiment was set up to describe the mechanical behavior of both implants.

Concepts: Torque, Force, In vitro, Group, Second moment of area, Polar moment of inertia

27

Fourier Transform Raman Spectroscopy was used to investigate the molecular changes of structural proteins in human skin subjected to strain. In the Raman spectrum of unstrained skin, bands assigned mainly to collagen and elastin were observed at 1658cm(-1) (amide I), 1271 and 1255cm(-1) (amide III), and 935 and 817cm(-1) (CC stretching modes of the protein backbone). Moreover, bands characteristic for amino acids were observed at 1336cm(-1) (desmosine), 1004cm(-1) (phenylalanine), 919 and 856cm(-1) (proline), and 877cm(-1) (hydroxyproline). Positions and intensities of the listed Raman bands were analysed as a function of applied strain. A clear correlation between Raman wavenumbers and the level of mechanical stress was established. Wavenumbers of the analysed bands changed gradually with increasing strain. Distinct responses, depending on the sample cutting direction, i.e. longitudinal or perpendicular to the Langer’s lines, were noticed. It was concluded that elastin and non-helical domains of collagen are initially involved in the load transfer and triple helices of collagen are gradually joining this process. It was proved that Raman spectroscopy give insight into skin deformation micromechanics.

Concepts: Protein, Spectroscopy, Amino acid, Collagen, Raman spectroscopy, Raman scattering, Infrared spectroscopy, Proline

26

We evaluated the effects of repeated heat-pressing on the mechanical properties and microstructure of IPS e.max Press.

Concepts: Thermodynamics

26

This study evaluated the mechanical, thermal, and morphological characteristics of different classifications of dental composites as a function of the material condition (new, aged and expired). Specimens were obtained according to these factors: Composites: Filtek P60, Filtek Z250, Filtek Z350XT, and Filtek Silorane; and Material conditions: new, aged, and expired. The syringe composites underwent an accelerated aging protocol (Arrhenius model). The flexural strength (FS) and flexural modulus (E) were obtained. The thermogravimetric analysis (TGA) and differential thermal analysis (DTA) were also performed and the glass transition temperature (Tg) and the weight loss calculated. Topographic analysis of the composites was performed under SEM. The material conditions influenced the mechanical properties of the composites. The silorane composite exhibited a characteristic thermal behavior different from that of the methacrylates. In general, the Tg increased after the accelerated aging protocol and decreased for expired ones, compared to the new composites. A significant increase in FS of Filtek Z350XT after aging was accompanied by an increase in the Tg. The filler packings were in accordance with the manufacture׳s information. The topographic aspects of the composites were modified as a function of the material condition. The mechanical properties of the composites following a simplified protocol of accelerated aging varied as a function of the expiration date. The silorane composite presented a characteristic thermal behavior. Although the dental manufacturers may not be able to control variables as storage temperature and transportation conditions, these effects on the composite clinical performance can be minimized if properly considered.

Concepts: Thermodynamics, Materials science, Composite material, Differential scanning calorimetry, Glass, Glass transition, Dental composite, Thermal analysis