Time Dependent Behaviour of Trabecular Bone at Multiple Load Levels

The deformation of bone when subjected to loads is not instantaneous but varies with time. To investigate this time-dependent behaviour sixteen bovine trabecular bone specimens were subjected to compressive loading, creep, unloading and recovery at multiple load levels corresponding to apparent strains of 2000-25,000 με. We found that: the time-dependent response of trabecular bone comprises of both recoverable and irrecoverable strains; the strain response is nonlinearly related to applied load levels; and the response is linked to bone volume fraction. Although majority of strain is recovered after the load-creep-unload-recovery cycle some residual strain always exists. The analysis of results indicates that trabecular bone becomes stiffer initially and then experiences stiffness degradation with the increasing load levels. Steady state creep rate was found to be dependent on applied stress level and bone volume fraction with a power law relationship.

Rheological properties and critical concentrations of a hyperbranched polysaccharide from Lignosus rhinocerotis sclerotia

The application of polysaccharides in the food industry mainly depends on their rheological properties and the polysaccharides in different concentration regions exhibit different rheological properties due to the interactions between polymer chains. Hence, this work investigated the concentration-dependent rheological behavior of Lignosus rhinocerotis polysaccharide (LRP) in water and determined the critical concentrations. The intrinsic viscosity of LRP was 378 ± 32 mL/g and the LRP exhibited more apparent shear-thinning behavior with increasing concentration. The LRP critical overlap and aggregation concentration in water was ~2.5 mg/mL, implicating the formation of hydrophobic regions may result from the aggregation and overlap between hyperbranched LRP molecules. The LRP/water system showed higher storage modulus than loss modulus with slight frequency dependence at the concentration of 15 mg/mL, exhibiting the structured liquid behavior. When the concentration increased from 10 mg/mL to 30 mg/mL, the compliance recovery percentage value increased from 58.51% to 92.30%, indicating the formation of a strong gel network in the LRP/water system. Furthermore, the micro-rheological test revealed that the LRP/water system exhibited a concentration-dependent increase in elasticity and viscosity and deterioration in fluidity.

Full biomechanical mapping of the ovine knee joint to determine creep-recovery, stiffness and thickness variation

BACKGROUND

Clinical cartilage repair strategies can be tested using the sheep model as suggest by the European Medicines Agency. To characterize variation within the joint a full biomechanical mapping is necessary. The aim of this study is to establish a loading model, to map regional differences within the knee and determine reference areas for area specific replacement techniques.

METHODS

A porous indenter was selected to evaluate 22 defined test locations (femoral condyles, tibia plateau, patella, femoral groove) on ovine knees (n = 7). A high-dynamic force-controlled micro creep and creep-recovery indentation test system applied five loading (0.11 MPa) and unloading (5.6 kPa) cycles for 60 s each and recorded creep-recovery. Needle indentation was used to measure cartilage thickness and calculate total strain.

FINDINGS

Steady state behaviour was observed from the third cycle and further evaluated. Little variation of stiffness in N/mm was found within the patella (4.3SD0.5) and femoral groove (8.1SD0.7) compared to larger variations in the femur (7.9SD2.0) and tibia (7.5SD3.2). Creep indentation showed values of 14.5%(SD2.7%) for the patella and 17.4%(SD3%) for the femoral grove opposed to 13.4%(SD4.3%) for the femoral condyles and 21.8%(SD6.6%) for the tibia plateau. Similar trends were observed analysing creep-recovery. Values were normalized to cartilage thickness which ranged between 0.36 mm and 1.14 mm.

INTERPRETATION

Our setup allows a reliable evaluation of zonal differences. Homogenous biomechanical behaviour is found within the patella and femoral groove whereas significant biomechanical variation within the femoral condyles and tibia plateau indicates the need for site-specific cartilage repair products.

Extrusion of wheat gluten-peanut oil complexes and their rheological characteristics

In order to clarify the effects of extrusion treatment on the processing properties of extrudates, providing a theoretical basis for the production of gluten-based extrudates with favorable sensory quality. This study examined the effects of various extrusion temperatures on the rheological properties of wheat gluten-peanut oil complexes (WPE) and wheat gluten (WG). At the extrusion temperature conditions of this study, the dynamic moduli of gluten in WG and WPE reached the maximum, and the creep strain reached a minimum at 160 °C. Extrusion treatment resulted in the decrease in β-sheet and α-helix content and an increase in the amount of β-turns and random coils. The secondary structural changes and increase in the number of disulfide bonds led to gluten aggregation, thus affecting their rheological properties. These results enhance our understanding of the variations in the rheological properties of extrudates and promote the potential application of gluten-based complexes in extrusion.

Effect of retrograded starch with different amylose content on the rheological properties of stored yogurt

Resistant starch (RS) promotes health benefits; however, when added to foods, it could change the rheological properties. The effect of adding different concentrations (2.5, 5, 7.5, and 10%) of retrograded corn starch with 27% (RNS) or 70% (RHS) amylose content on the properties of yogurt was evaluated through measurements of flow behavior and gel structure. Syneresis and resistant starch content were also assessed. Results were analyzed using multiple regression to describe the effect of starch concentration and storage time on the properties of yogurt added with RNS or RHS. Syneresis was reduced, RNS reinforced the structure increasing the water absorption capacity and the consistency index; meanwhile, RHS provided a yogurt containing up to 10 g of RS in 100 g of sample, allowing obtaining a functional dairy product. Creep-recovery test showed that adding RNS or RHS favored the matrix conformation, and the yogurt samples were able to recover. The final product behaved like a solid material with a firmer and more stable gel structure, resulting in a strengthened gel without weakening the yogurt structure, showing a characteristic like Greek-style or stirred yogurt depending on the type and concentration of retrograded starch.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05735-x.

Effects of creep and creep-recovery on ratcheting strain of articular cartilage under cyclic compression

Since the accumulations of ratcheting strain combined with creep deformation, which are produced in normal activities, can accelerate the fatigue damage of cartilage in joint, the creep-ratcheting and creep-recovery-ratcheting behaviors of articular cartilage are experimentally investigated under creep-fatigue loads. The effect of pre-creep on ratcheting behavior of cartilage was probed firstly and it is found that the initial ratcheting strain of cartilage presents the larger value (30% and 35%) due to its pre-creep deformation in spite of the short pre-creep time applied. With the increasing pre-creep time the ratcheting strain of sample increases while the ratcheting strain rate decreases. The effects of pre-creep and recovery on ratcheting behavior of cartilage were also investigated and it is noted that the strain of cartilage increases fast at first, decreases partly and then changes periodically with cyclic stress. The ratcheting strain evolutions of different layers are not coincident for cartilage sample after the pre-creep or pre-creep-recovery and the ratcheting strains of different layers with pre-creep are larger than them with pre-creep-recovery. Finally the creep-ratcheting strain of cartilage with different peak-holding time during cyclic compression was studied and it is found that the creep-ratcheting strain with peak-holding time is significantly greater than that without peak-holding time. The creep-ratcheting strain increases with increase of peak-holding time or stress amplitude, while it reduces with rising of stress rate. The creep-ratcheting behavior of cartilage is dependent on its depth. These findings point out that the accumulated deformations, including creep deformation and ratcheting deformation, can accelerate the cartilage's damage.