Apparent Mechanical Properties Research Articles

Chitosan/pre-gelatinized waxy corn starch composite edible orally disintegrating film for taurine delivery

In this study, chitosan/per-gelatinized waxy corn starch composite edible orally disintegrating films (ODFs) incorporated with taurine were prepared and the morphology, release behavior and storage stability of the ODFs were investigated. The XRD, ATR-FTIR and microscopic investigation results revealed that taurine could be uniformly dispersed in the film matrix. The optimal level of taurine addition was 1.0% (w/w). The incorporation of taurine improved the apparent morphology, mechanical properties and water holding capacity while slightly increased the film thickness, disintegration time and contact angle of the composite films. In addition, taurine exhibited a rapid release behavior in the films. The fitted results of the Ritger-Peppas model indicated that the release mechanism of taurine in the composite films was mainly Fickian diffusion with minor skeleton erosion. As a delivery carrier, the composite film had a positive effect on the preservation of taurine, increasing the retention of taurine by 8.34% ± 1.48% during storage. The study confirmed the feasibility for the development of taurine ODF carriers and provided a basis for the development of functional packaging materials.

Mechanical impact of regional structural deterioration and tissue-level compensation on proximal femur trabecular bone.

Osteoporosis-induced changes in bone structure and composition significantly reduce bone strength, particularly in the human proximal femur. This study examines how these changes affect the mechanical performance of trabecular bone to enhance diagnosis, prevention, and treatment strategies. A proximal femur sample was scanned using micro-CT at 40μm resolution. Five regions of interest were selected within the femoral head, femoral neck, and greater trochanter. Structural models simulating various stages of osteoporosis were created using image processing software. Micro-finite element analysis evaluated the mechanical properties of trabecular bone under different conditions of structural deterioration and tissue-level elastic modulus variations. The combined effects of structural deterioration and tissue-level mechanical properties on trabecular bone mechanical performance were further analyzed. The mechanical performance of trabecular bone generally follows a power-law relationship with its microstructural characteristics. However, in any specific region, the apparent mechanical properties linearly decrease with structural deterioration. The femoral neck and greater trochanter are more sensitive to structural deterioration than the femoral head. A 5% bone mass loss in the femoral head led to a 7% reduction in mechanical performance, while the femoral neck experienced a 12% loss. Increasing tissue-level elastic modulus improved mechanical performance, partially offsetting bone mass reduction effects. Trabecular bone in low bone mass regions is more affected by bone mass loss. Structural deterioration primarily reduces bone strength, but improvements in tissue-level properties can mitigate this effect, especially in early osteoporosis. Targeted assessments and interventions are crucial for effective management. Future research should explore heterogeneous deterioration models to better understand osteoporosis progression.

Preparation and Keep-Refreshing Effect of Chitosan/Sea Buckthorn Polysaccharide Composite Film on the Preservation of Yellow Cherry Tomatoes.

In this study, sea buckthorn polysaccharides (SBP) were added as functional substances to chitosan (CS), and chitosan/sea buckthorn polysaccharide (SCS) composite films were prepared using the casting method. The effects of SBP addition on the optical properties, physical properties, mechanical properties, structure, antioxidant activity, and antibacterial activity of the SCS composite films were studied, and the prepared SCS composite films were used to preserve yellow cherry tomatoes. The results showed that SCS composite films exhibited good UV resistance, water solubility, and antioxidant activity, but its apparent structure, hydrophobicity, and mechanical properties needed further improvement. Meanwhile, SBP has inhibitory effects on all 8 experimental strains. In addition, the SCS composite film with the addition of 200 mg/L SBP could reduce the weight loss rate of yellow cherry tomatoes, maintain hardness, delay the decrease of total soluble solids, titratable acid, and Vitamin C content, and inhibit the accumulation of malondialdehyde. SCS composite films are beneficial for enhancing the quality of yellow cherry tomatoes during storage, and their application in fruit and vegetable preservation has development prospects.

Optimization of All-Desert Sand Concrete Aggregate Based on Dinger–Funk Equation

In recent years, with the development of the construction industry and the wide application of concrete materials, the demand for natural resources such as sand and gravel in China has continued to grow. The Xinjiang region is rich in natural desert sand resources due to its large desert area, which are inexpensive and easy to obtain, providing new possibilities for the production of concrete materials. The use of natural desert sand as concrete aggregate not only reduces the cost of construction but also contributes to the protection of the environment and the rational development and utilization of natural resources. However, poor particle gradation in natural desert sand leads to poor concrete properties. In this study, the Dinger–Funk equation was used to optimize the aggregate gradation of natural desert sand from Toksun, Xinjiang, and concrete specimens were prepared for mechanical properties and sulfate erosion resistance tests. The test results show that the four groups of aggregates optimized by the Dinger–Funk equation are better than the single gradation and natural gradation in terms of apparent density, bulk density, void ratio, mechanical properties, and durability of concrete. Where the distribution modulus n = 0.3 was the best, the compressive strength, splitting strength, and flexural strength were increased by 13.14%, 15.71%, and 11.08%, respectively, as compared to the natural gradation. After 90 sulfate erosion and dry–wet cycles, the mass change rate and relative dynamic elastic modulus of concrete specimens first increased and then decreased, and at the distribution modulus n = 0.3, the aggregate particles of 0.3–0.6 mm, 0.6–1.18 mm, and 1.18–2.36 mm accounted for 26.98%, 32.33%, and 40.69%, respectively, and the smallest of the mass change rates of durability was the best.

CNN-based prediction of microstructure-derived random property fields of composite materials

The simulation of random spatial variation in the mechanical properties of composite materials using random fields derived from their microstructure can be computationally demanding, since it often requires numerical homogenization of a large number of stochastic volume elements (SVEs). These SVEs are usually extracted from an initial image of the composite microstructure by using a moving window technique and their homogenized properties constitute the discrete data points of the random field at the centroid of each SVE. By replacing the expensive and highly repetitive homogenization procedure with a convolutional neural network (CNN), it is possible to perform nearly instant computations of random property fields. In this work, a CNN is proposed, that takes as input an SVE image and returns its apparent mechanical properties, and can therefore be applied along with the moving window technique. Training is performed on randomly generated SVEs with varying volume fractions and inclusion positions, which are representative of the SVEs obtained during processing of the initial large composite image. It is shown that the proposed CNN can accurately predict the mechanical properties of SVEs and it is subsequently applied for the prediction of random property fields derived from computer simulated and real microstructure images. Results show that, with the proposed methodology, it is possible to make accurate predictions of random fields within a few seconds, a procedure which could potentially require hours of computation time with the finite element based approach.

Development of High-Sensitivity Thermoplastic Polyurethane/Single-Walled Carbon Nanotube Strain Sensors through Solution Electrospinning Process Technique

In this study, nanofibers obtained through the electrospinning process are explored for strain-sensing applications. Thermoplastic polyurethane (TPU) flexible structures were fabricated using the solution electrospinning process (SEP) technique. Subsequently, these structures were nanomodified with single-walled carbon nanotubes (SWCNTs) through immersion into an ultrasonicated suspension containing 0.3 wt% SWCNTs. The nanomodification aimed to impart an electrically conductive network to the structures. Micro-tensile tests and electrical resistance measurements were conducted to characterize the apparent mechanical and electrical properties, respectively. The fabricated structures demonstrated potential as wearable strain sensors for monitoring changes in strain across various applications. The samples exhibited excellent performance, high sensitivity, outstanding mechanical properties, and a broad stretching range. Scanning electron microscopy (SEM) observations provided qualitative insights into the activated conductive pathways during operation.

Rigid polyurethane foams from commercial castor oil resins

Rigid polyurethane foams (RPUFs) are among the most used polymeric materials due to their tailorable properties. Greener and biobased polyol sources for synthesising RPUFs have been recently prototyped because of the ever-growing demand for more sustainable materials solutions. Castor Oil has also rapidly become one of the most successful alternatives to replace polyurethane fossil-based components. This study extensively investigates three types of RPUFs developed from commercially available Castor Oil-based resins, correlating their properties across different length scales. In particular, X-ray diffraction identified a characteristic peak whose intensity correlated with the apparent foam density, morphology (obtained from computed tomography scans) and mechanical properties. Furthermore, quasi-static compression and vibration transmissibility tests revealed distinctive anisotropic mechanical responses among the foams, with one type of RPUF consistently outperforming the others due to its lower porosity, reaching 13.3 MPa of compressive modulus. These findings demonstrate the possibility of tuning the mechanical properties of foams via compositional control.

Study on the heat treatment of multispectral ZnS for residual stress reduction

Multispectral ZnS (M − ZnS) will inevitably introduce stresses during the chemical vapor deposition (CVD) polycrystalline growth and hot isostatic pressing (HIPping) stages. In this paper, the generation mechanism and elimination method of residual stresses in M − ZnS are analyzed by means of SEM, transmittance, XRD analysis and mechanical property characterization, and the effects of heat treatment temperature, time and material annealing structure on the apparent morphology, optical and mechanical properties of M − ZnS materials are investigated. The results show that the internal stresses of M − ZnS mainly originate from the CVD ZnS growth and HIPping stages, and the most effective method to reduce the stresses is heat treatment. The key factors affecting the effect of heat treatment include temperature, time, and annealing structure. Selecting a GZ(G) annealing structure combined with a suitable cooling rate for heat treatment of M − ZnS materials will significantly improve the heat treatment effect. More annealing time has a significant effect on the transmittance in the 0.38–3 μm band, and insignificant effect on the transmittance in the 3–5 μm and 8–10 μm bands. Heat treatment will bring some degree of structural changes to the material, often manifested including a trace of hexagonal phase structure, which will affect the optical imaging quality of the window material. Heat treatment contributes to secondary grain growth, with an increase in grain size and a decrease in grain boundaries. Excessive heat treatment accelerates the loss of hardness and bending strength, and also leads to the generation of micro-cracks and macro-cracks in the material, reducing the mechanical properties of the material. Heat treatment holding 200 h and 100 h compared to the unannealed, Vickers hardness decreased by 13.518 and 7.96, respectively, bending strength decreased by 4.77 MPa and 1.73 MPa, respectively. Therefore, in actual production, should not be selected excessive heat treatment time.

Mandrel diameter effect on ring-pull testing of nuclear fuel cladding

Inconsistencies in ring-pull testing methods for thin-walled tubes make it difficult to compare a material's mechanical properties in the hoop direction presented in past publications. The effect of test setup, specifically mandrel diameter, was investigated for nuclear fuel cladding tubes of the iron-chromium-aluminium (FeCrAl) alloy, C26M (Fe-12Cr-6Al-2Mo). Mandrel diameter for ring-pull testing can change how the ring deforms and friction effects, further convoluting the results from testing. To address the impact of mandrel size in relation to ring diameter, gaugeless ring-pull samples were tested across a range of mandrel diameters and compared to uniaxial tensile tests from the same tube of material. Two groups of samples were tested: an as-received, low ductility sample set and an annealed, high ductility sample set, both cut from the same extruded tube. By pairing systematic variation of mandrel geometry with analysis of local strain gradients using digital image correlation, this study investigates the effect of test fixture geometry on apparent mechanical properties and effective strain fields and provides guidance for comparing previously published data. Certain features in uniaxial stress-strain curves (namely the yield strength, ultimate tensile strength, and uniform elongation) appeared to have analogies in the effective stress-strain curves from ring-pull testing. These corresponding features are compared to expose biases in the analysis of material properties using gaugeless ring-pull and to provide novel guidance on test setup during experimental design.

The loading direction dramatically affects the mechanical properties of the mouse tibia.

Introduction: The in vivo tibial loading mouse model has been extensively used to evaluate bone adaptation in the tibia after mechanical loading treatment. However, there is a prevailing assumption that the load is applied axially to the tibia. The aim of this in silico study was to evaluate how much the apparent mechanical properties of the mouse tibia are affected by the loading direction, by using a validated micro-finite element (micro-FE) model of mice which have been ovariectomized and exposed to external mechanical loading over a two-week period. Methods: Longitudinal micro-computed tomography (micro-CT) images were taken of the tibiae of eleven ovariectomized mice at ages 18 and 20weeks. Six of the mice underwent a mechanical loading treatment at age 19weeks. Micro-FE models were generated, based on the segmented micro-CT images. Three models using unitary loads were linearly combined to simulate a range of loading directions, generated as a function of the angle from the inferior-superior axis (θ, 0°-30° range, 5° steps) and the angle from the anterior-posterior axis (ϕ, 0°: anterior axis, positive anticlockwise, 0°-355° range, 5° steps). The minimum principal strain was calculated and used to estimate the failure load, by linearly scaling the strain until 10% of the nodes reached the critical strain level of -14,420με. The apparent bone stiffness was calculated as the ratio between the axial applied force and the average displacement along the longitudinal direction, for the loaded nodes. Results: The results demonstrated a high sensitivity of the mouse tibia to the loading direction across all groups and time points. Higher failure loads were found for several loading directions (θ = 10°, ϕ 205°-210°) than for the nominal axial case (θ = 0°, ϕ = 0°), highlighting adaptation of the bone for loading directions far from the nominal axial one. Conclusion: These results suggest that in studies which use mouse tibia, the loading direction can significantly impact the failure load. Thus, the magnitude and direction of the applied load should be well controlled during the experiments.

Influence of a triaxial stress state on the load-deformation behaviour of axisymmetrically corroded reinforcing bars

Local corrosion damage reduces the load-bearing capacity of reinforcing bars and, even more severely, their deformation capacity. These effects are mainly attributed to the reduced cross-sectional area and the accompanying strain localisation. However, several experimental studies found an altered load-deformation behaviour of naturally corroded as well as artificially damaged reinforcing bars, including an apparently increased tensile strength, which cannot be explained solely by strain localisation. Accordingly, in an experimental campaign carried out by the authors on locally axisymmetrically damaged reinforcing bars, the observed peak load increased with decreasing damage length, and the deformation capacity was much less impaired than predicted by established strain localisation models. A series of nonlinear FE analyses was carried out to investigate a potential effect of the local stress state in the vicinity of the local corrosion damage. The results indeed revealed a triaxial stress state in this region, caused by the local deviation of the stress trajectories, explaining the experimental observations on a mechanical basis, and indicating a pronounced influence of the triaxial stresses on the uniaxial stress–strain behaviour of the bar in the vicinity of the corrosion pit. A parametric study was conducted to investigate a broader range of corrosion damage geometries and the corresponding triaxial stresses. The results indicate that the transverse stresses strongly affect the apparent uniaxial mechanical steel properties (yield stress, tensile strength, deformation capacity, loss of yield plateau) for short damage lengths typically found for pitting corrosion. A simplified modelling approach is proposed to capture the governing effects on the apparent uniaxial stress–strain curve of locally corroded reinforcing bars.

Optimization of Spark Plasma Sintering Technology by Taguchi Method in the Production of a Wide Range of Materials: Review.

This paper reviews the production of sinters using the spark plasma sintering method. SPS (spark plasma sintering) technology has been used for several decades, mainly in laboratories, to consolidate a huge number of both new and traditional materials. However, it is now more often introduced into practical industrial use, with equipment as early as the fifth generation capable of producing larger-size components at competitive costs. Although the mechanism of sintering with the use of this method is not yet understood, the effectiveness of the SPS process for the rapid and efficient consolidation of a wide range of materials with novel micro-structures remains indisputable. With a relatively wide variation in chemical composition, the structure allows the selection of appropriate consolidation parameters for these materials. The influence on the values of apparent density and mechanical properties depends on the parameters of the spark plasma sintering process. In order to achieve a density close to the theoretical density of sinters, optimization of the sintering parameters, i.e., sintering temperature, heating rate, sintering time, pressing pressure and protective atmosphere, should be carried out. In this paper, the optimization of spark plasma sintering of Si3N4-Al2O3-ZrO2 composite was carried out using the Taguchi method. The effects of four sintering factors, namely heating rate, sintering time, sintering temperature and sintering pressure, on the final density were investigated. Optimal sintering conditions were proposed and a confirmation experiment was conducted. The optimal combination of sintering conditions for spark plasma sintering (SPS) of Si3N4-Al2O3-ZrO2 composite for high apparent density was determined as A3-B3-C3-D2. Based on ANOVA analysis, it was found that the apparent density of sintering was significantly influenced by sintering temperature, followed by pressing pressure, sintering time and heating rate. Validation of the developed mathematical model predicting the apparent density of sinters showed close agreement between the predicted response results and experimental results.

Levofloxacin HCl-Loaded Eudragit L-Based Solvent Exchange-Induced In Situ Forming Gel Using Monopropylene Glycol as a Solvent for Periodontitis Treatment.

Solvent exchange-induced in situ forming gel (ISG) is currently an appealing dosage form for periodontitis treatment via localized injection into the periodontal pocket. This study aims to apply Eudragit L and Eudragit S as matrix components of ISG by using monopropylene glycol as a solvent for loading levofloxacin HCl for periodontitis treatment. The influence of Eudragit concentration was investigated in terms of apparent viscosity, rheological behavior, injectability, gel-forming behavior, and mechanical properties. Eudragit L-based formulation presented less viscosity, was easier to inject, and could form more gel than Eudragit S-based ISG. Levofloxacin HCl-loading diminished the viscosity of Eudragit L-based formulation but did not significantly change the gel formation ability. Higher polymer loading increased viscosity, force-work of injectability, and hardness. SEM photographs and µCT images revealed their scaffold formation, which had a denser topographic structure and less porosity attained owing to higher polymer loading and less in vitro degradation. By tracking with fluorescence dyes, the interface interaction study revealed crucial information such as solvent movement ability and matrix formation of ISG. They prolonged the drug release for 14 days with fickian drug diffusion kinetics and increased the release amount above the MIC against test microbes. The 1% levofloxacin HCl and 15% Eudragit L dissolved in monopropylene glycol (LLM15) was a promising ISG because of its appropriate viscosity (3674.54 ± 188.03 cP) with Newtonian flow, acceptable gel formation and injectability (21.08 ± 1.38 N), hardness (33.81 ± 2.3 N) and prolonged drug release with efficient antimicrobial activities against S. aureus (ATCC 6538, 6532, and 25923), methicillin-resistant S. aureus (MRSA) (S. aureus ATCC 4430), E. coli ATCC 8739, C. albicans ATCC 10231, P. gingivalis ATCC 33277, and A. actinomycetemcomitans ATCC 29522; thus, it is the potential ISG formulation for periodontitis treatment by localized periodontal pocket injection.

Effect of damage on Rayleigh wave propagation in second gradient lattice materials

The frequencies of the Rayleigh waves propagating in periodic lattice materials prone to internal damage is analysed, using a second gradient displacement effective model as an enriched substitution continuum to capture the dispersive wave features. In this work, we model the damage by randomly eliminating beams from the full networks constructed from periodic unit cells. The apparent mechanical properties of progressively damaged structures are evaluated using dedicated homogenization techniques in the context of second gradient continuum mechanics. The wave frequency is computed, for different relative densities, versus the amount of damage for the square and hexagonal networks. Results reveal that the hexagonal lattice has higher values of frequency compared to the square lattice. Charts of the wave frequencies versus wavenumber for different amounts of global lattice damage can serve as a non-destructive technique to infer the amount of damage that exists in beam-lattice materials.

Evaluating Residual Stress in Carbon Fiber-Reinforced Polymer (CFRP) at Microscale Using Fiber Push-Out Experiment and Finite Element Modeling.

Microscale residual stress may develop during the manufacturing of Carbon Fiber-Reinforced Polymer (CFRP) composites and negatively affect apparent macroscale mechanical properties. Accordingly, accurately capturing residual stress may be essential in computational methods used for composite material design. This work presents a new data-driven methodology for the evaluation of microscale residual stress in CFRPs using fiber push-out experiments with in situ scanning electron microscopy (SEM) imaging. SEM images reveal significant through-thickness matrix sink-in deformation in resin-rich areas after nearby fibers are pushed out, which is attributed to the release of microscale process-induced residual stress. The sink-in deformation is measured experimentally, and a Finite Element Model Updating (FEMU) method is used to retrieve the associated residual stress. The finite element (FE) analysis includes simulation of the curing process, test sample machining, and fiber push-out experiment. Significant out-of-plane matrix deformation larger than 1% of the specimen thickness is reported and associated with a high level of residual stress in resin-rich areas. This work emphasizes the importance of in situ data-driven characterization for integrated computational materials engineering (ICME) and material design.

Experimental Study on the Influence of Snow-Melting Agents on Fiber-Reinforced Cemented Soil under Freezing-Thawing Cycles

To explore the effect of snow-melting agents on the glass fiber-reinforced cemented soil under freezing-thawing cycles, three widely used snow-melting agents, including potassium acetate, magnesium chloride, and sodium sulfate, were used in this article. The effects of snow-melting agent types on the apparent damage, mass loss, and mechanical properties of fiber-reinforced cemented soil under freezing-thawing cycles were analyzed through salt freezing and unconfined compressive strength tests. The results show that the snow-melting effect of potassium acetate is the best, the snow-melting effect of magnesium chloride is the second, and the snow-melting effect of sodium sulfate is the worst. Notably, as the number of freezing-thawing cycles increases, the strength of the test block decreases to varying degrees. After the fifth freezing-thawing cycle, the strength of the block without fiber decreased by 61.30%, 70.22%, and 81.58% in clear water, potassium acetate, and magnesium chloride solution, respectively, while the test block in sodium sulfate solution lost its bearing capacity. A series of studies proved that the snow-melting agent with sodium sulfate as the main component has the most apparent erosion effect on the cemented soil, followed by magnesium chloride, and the erosion effect of potassium acetate is the weakest. The incorporation of glass fiber can effectively improve the resistance of the cemented soil under the action of various salt solution erosion and freezing-thawing coupling and has a significant effect on slowing the development of surface cracks, improving peak strength, and reducing the mass loss rate. This research will provide theoretical support for the design of subgrade and the selection of snow-melting agents in cold areas.

Experimental investigation of effects of indentation depth and probe tip radius on apparent young's modulus of Xenopus laevis oocytes

Throughout their lifespan cells are constantly subjected to mechanical forces. Numerous studies have been conducted to measure mechanical properties of animal cells and understand their effects of the cells’ biological processes. However, the range of the apparent Young's moduli reported in the literature spans three orders of magnitude from 0.1 kPa to 100 kPa, and no clear explanation is given for the source of variation. One of the commonly used experimental techniques to measure material properties at nano- and microscale is nanoindentation. Nanoindentation works by applying a force on a sample via a small probe and recording a force-displacement curve. Probes with different tip shapes and sizes are available. However, there is little guidance on the appropriate choice of probe geometry and size for measurement of properties of animal cells. Eukaryotic cells have a complex structure including a membrane, an actin cortex, a cytoplasm, a nucleus and a cytoskeleton which consists of microfilaments, intermediate filaments and microtubules. These components have different mechanical properties contributing to the overall properties of cells. This work focuses on the effect of tip size and indentation depth on the apparent Young's modulus of Xenopus laevis oocytes measuring approximately 1 mm in diameter. Live cell fluorescent labeling using Lifeact-EGFP and confocal microscopy was used to measure the thickness of the oocyte actin cortex which is expected to have a significant contribution to the cell's stiffness. Apparent mechanical properties were measured using the JPK NanoWizard 4 BioAFM system. Indentations 5, 100 and 400 nm deep using probes with spherical tips of 0.1, 1, and 10 μm radii were performed. Contributions of the membrane and the actin cortex on the overall mechanical properties of the oocytes are analyzed.

Biodegradable dual-layer Polyhydroxyalkanoate (pha)/Polycaprolactone (pcl) mulch film for agriculture: Preparation and characterization

• Biodegradable dual-layer mulch film based on polyhydroxyalkanoate (PHA) and polycaprolactone (PCL) • Produce mulch film with higher biodegradability without generating microplastics • Use of radiation crosslinking technique to improve the adherence between PHA and PCL • Soil burial test with high degradability percentage for dual-layer mulch film. This study focused on preparing biodegradable dual-layered mulch film based on polyhydroxyalkanoate (PHA) and polycaprolactone (PCL). The main aim of this study is to prepare mulch film with higher biodegradability for rice seed germination. Common plastic mulch films are mostly non-readily biodegradable and stay as residual in soil for a very long duration leading to an increase in salt content and reduction in water and nutrient movement in the soil. This makes the farmland unusable for agricultural purposes. The PHA and PCL were the ideal options as both have their merits and demerits which compensates each other while being cast into double layers and are highly biodegradable. The novelty of this study emphasizes the attachment of PHA and PCL as a dual layer at different ratios that offers a higher bio-degradability percentage. The dual-layer mulch film is made of PHA as the first layer and a mixture of PHA and PCL at different ratios as the second layer. The ratio of PHA/PCL used was 90:10, 70:30, and 50:50. The dual-layered mulch film was prepared using the hot-press technique and later cross-linked by using electron beam irradiation in order to ensure the strong adherence between the two layers. The gel content analysis was performed to measure the crosslinking percentage. The radiation dose of 30 kGy was chosen as the minimum amount of crosslinking and approximately 3.00% was attained for the course. The mixture of PHA/PCL films with different ratios, PHA and PCL virgin film were subjected to a soil burial bio-degradability test. The PHA and PCL virgin film had shown the highest degradation percentage, almost 48.34% just in five weeks. Further characterization was performed on virgin dual-layered PHA/PCL (100%) based on their higher degradability tendency. The apparent properties, morphology, thermal stability, chemical composition, and mechanical properties of dual-layer PHA/PCL (100%) were tested thoroughly. The thickness and transparency attained for dual-layer PHA/PCL (100%) were around 175.25μm and 110.45%. The thermal properties of both single layer PHA and PCL showed good stability, Meanwhile, the virgin dual-layered PHA/PCL mulch film had shown a poor thermal stability. The peak positioning in FTIR for single layer PHA and PCL at 3042.37cm −1 , 2942.37cm −1 , 1719.54cm −1 ,1453.33cm −1 ,1378.95cm −1 and 1181.48cm −1 remained unchanged in virgin double-layered PHA/PCL film as well. The outcome of the analyses clearly indicates the possibilities of the dual-layer PHA/PCL (100%) with greater bio-degradability. The soil burial biodegradability test needs to be prolonged up to its full potential. The other characteristics such as water permeability, photo permeability, crystallinity, and heat preservation need to be investigated as well.

Effects of biofilm heterogeneity on the apparent mechanical properties obtained by shear rheometry.

Rheometry is an experimental technique widely used to determine the mechanical properties of biofilms. However, it characterizes the bulk mechanical behavior of the whole biofilm. The effects of biofilm mechanical heterogeneity on rheometry measurements are not known. We used laboratory experiments and computer modeling to explore the effects of biofilm mechanical heterogeneity on the results obtained by rheometry. A synthetic biofilm with layered mechanical properties was studied, and a viscoelastic biofilm theory was employed using the Kelvin-Voigt model. Agar gels with different concentrations were used to prepare the layered, heterogeneous biofilm, which was characterized for mechanical properties in shear mode with a rheometer. Both experiments and simulations indicated that the biofilm properties from rheometry were strongly biased by the weakest portion of the biofilm. The simulation results using linearly stratified mechanical properties from a previous study also showed that the weaker portions of the biofilm dominated the mechanical properties in creep tests. We note that the model can be used as a predictive tool to explore the mechanical behavior of complex biofilm structures beyond those accessible to experiments. Since most biofilms display some degree of mechanical heterogeneity, our results suggest caution should be used in the interpretation of rheometry data. It does not necessarily provide the "average" mechanical properties of the entire biofilm if the mechanical properties are stratified.

Revealing the apparent and local mechanical properties of heterogeneous lattice: a multi-scale study of functionally graded scaffold

ABSTRACT Functionally graded scaffold (FGS) can flexibly regulate the mechanical properties of bone scaffold and holds great promise for offering multifunctional responses of orthopaedic implants. Heterogeneous FGSs constructed by skeletal and sheet triply periodic minimal surfaces (TPMSs) have been proposed in this study. The diversified deformation mechanisms of TPMS-FGSs showed superior mechanical stability, and energy absorption efficiency was enhanced by 3.0–79.0% and 2.6–16.8% compared to uniform skeletal and sheet TPMS, respectively. The graded structure of TPMS-FGSs altered the large-scale 45° shear failure to layer-wise or zigzag failure mode. Moreover, the comprehensive reformation of strain distribution and crack propagation in transition region under small compressive strain was experimentally and numerically studied. The results shed light on the global and local mechanical regulation mechanism of TPMS-FGS.