•Silk Fibroin (SF) and Cellulose Nanofibers (CNF) are mixed in different ratios to fabricate the soft composites.•Solution casting followed by a freeze-drying fabrication technique is ...adopted.•Chemical, morphological, viscoelastic and mechanical characterization is reported.•A particular mixing ratio shows a considerable strength as well as elongation-at-break point.•Effect of loading rate is studied alongside stress-relaxation and creep tests.
Soft hydrophilic composites are excellent candidate materials for biomedical applications such as scaffold engineering, tissue regeneration and cell culture. Their porous internal architecture and compliance help promote cell growth and proliferation. Silk fibroin (SF) and nanocellulose fibres (CNF) are two of the most widely-used materials for the development of soft biomimetic scaffolds. In this study, SF and CNF are mixed in different mass ratios to develop compliant composites with varying mechanical properties and morphology. After fabricating these soft biomimetic composites, we observe that a particular combination of the individual phases yield the optimum mechanical properties in terms of stiffness, strength as well as elongation-at-break point (EOB). Internal architecture, rate-dependent, viscoelastic characterization and FTIR spectra are reported.
Polyvinylidene fluoride (PVDF) composite films have witnessed widespread applications in biomedical and flexible electronic devices in recent years. These applications require a material that has ...enhanced electrical properties, mechanical flexibility along with sufficient strength. A lot of research has been carried out to enhance the piezoelectric and dielectric properties of the PVDF composite films. However, the improvements in the mechanical properties of nano filler reinforced PVDF composite films has not received due attention. In this regard, the present work focuses towards enhancing the mechanical strength and load-bearing capability of PVDF, by preparing composites of PVDF films impregnated with Cellulose Nanocrystals (CNC) and Barium Titanate (BTO) nanoparticles. Solution casting method was adapted to fabricate the PVDF/BTO/CNC films. X-ray diffractograms and FTIR (Fourier Transform infrared spectroscopy) corroborate the presence of ferroelectric γ phase in PVDF. Mechanical and viscoelastic measurements have been carried out to examine the influence of CNC and BTO nano fillers in the PVDF matrix. The addition of CNC and BTO in PVDF film has improved the mechanical strength significantly. The stress achieved for PVDF/5% BTO and PVDF/5% BTO with 0.9% of CNC at 5% strain was 17% and 130% higher than the pristine PVDF, respectively. This study can be helpful for the design engineers to meet custom/specific requirements for a myriad of end-user applications such as piezoelectric nanogenerators.
•Lead-Free PVDF nanocomposite thin films were fabricated using solvent casting method.•Surface modified BTO and CNC nanofillers were impregnated into PVDF.•Crystallo-chemo-morpho-mechanical studies have been performed to understand their chemical, structure and mechanical properties.
Saliva is vital for the maintenance of normal oral physiology and mucosal health. The loss of salivary function can have far-reaching consequences, as observed with dry mouth, which is associated ...with increased orodental disease, speech impairment, dysphagia, and a significant negative effect on quality of life. The timely diagnosis of oral dryness is vital for the management of orodental disease and any associated often-undiagnosed systemic disease (e.g., Sjögren syndrome). Our aim was to investigate differences in mucin glycoproteins and saliva rheological properties between sufferers and nonsufferers of dry mouth in order to understand the relationship between saliva composition, rheological properties, and dryness perception and provide additional potential diagnostic markers. All patients exhibited objective and subjective oral dryness, irrespective of etiology. Over half of the patients (n = 20, 58.8%) had a saliva secretion rate above the gland dysfunction cutoff of 0.1 mL/min. Mucin (MUC5B and MUC7) concentrations were generally similar or higher in patients. Despite the abundance of these moisture-retaining proteins, patients exhibited reduced mucosal hydration (wetness) and significantly lower saliva spinnbarkeit (stringiness), suggesting a loss of the lubricating and retention/adhesion properties of saliva, which, at least partially, are associated with mucin glycoproteins. Over 90% of patients with dry mouth (DMPs) consistently had unstimulated whole mouth saliva (UWMS) spinnbarkeit below the proposed normal cutoff (10 mm). Further analysis of mucins revealed the reduced glycosylation of mucins in DMPs compared to healthy controls. Our data indicate that UWMS mucin concentrations are not reduced in dry mouth but that the mucin structure (glycosylation) is altered. UWMS from DMPs had reduced spinnbarkeit, the assessment of which, in conjunction with sialometry, could improve sensitivity for the diagnosis of dry mouth. Additionally, it may be useful to take into consideration the altered mucin glycosylation and saliva rheological properties when designing synthetic or purified mucins for saliva substitutes and dry mouth therapy.
•Transversely isotropic PVA xerogels are synthesized using unidirectional freeze-drying technique.•Morphological and mechanical characterization is carried out for the developed ...xerogels.•Microbuckling is observed in the xerogel microstructure when loaded along the longitudinal direction.•Creasing and wrinkling occurs in xerogels due to loading along longitudinal and transverse directions, respectively.•Viscoelastic tests are carried out to understand the time-dependent response of the xerogels.
Xerogels are attractive candidates for scaffolds in tissue engineering and drug delivery. Polyvinyl alcohol xerogels are extensively used for biomedical applications owing to their ease of synthesis, biocompatibility and biodegradability. However, these materials are challenged in terms of their weak mechanical properties and structural instabilities. This work is aimed to look into the morpho-mechanical response of transversely isotropic freeze-dried PVA xerogels under mechanical compressive loads. Microstructurally aligned PVA xerogels are synthesized using unidirectional freeze-drying technique. Uniaxial compressive tests are performed alongside viscoelastic characterization. The effect of mechanical compressive loads upon the xerogel microstructure is studied. Microbuckling of material fibers, creasing and wrinkling of the bulk xerogels are some of the microstructural and surface instabilities discussed.
Soft materials undergo large mechanical deformation prior to failure when subjected to external loads. They exhibit nonlinearity alongside coupled elastic, viscous, and plastic behavior due to their ...multi-phase material composition, hierarchical structure, and multiple length and time scale effects. It is thus, mandatory to understand the nonlinear behavior of soft materials from a fundamental perspective. In this work, we propose a theoretical framework for the development of a thermodynamically-consistent coupled hyperelastic viscoplastic damage model to study the rate-dependent large deformation mechanical behavior of soft materials, subjected to a wide range of strain rates. A time-integration return-mapping algorithm is used to fit the experimental data previously reported for the human patellar tendons, hydrogels, xerogels, polymers, and sponges. Further, parametric studies are carried out to understand the mechanics of nanocellulose-loaded polyvinyl alcohol xerogels, liver tissues, PVA hydrogels, and skin tissues. It is observed that the proposed model is able to fit and predict the experimental observation with an error of less than 4%.
•A thermodynamically-consistent hyperelastic viscoplastic damage model is proposed to study large deformation mechanics of soft materials.•The model accounts for tension–compression asymmetry, and can predict rate-dependent behavior.•The developed model fits the mechanical response for a wide range of soft materials such as hydrogels, biological tissues, elastomers, and sponges.•Parametric studies have been performed for xerogels, skin and liver tissues.
The paper presents a methodology in the SPH framework to analyze physical phenomena those occur in detonation process of an explosive. It mainly investigates the dynamic failure mechanism in ...surrounding brittle rock media under blast-induced stress wave and expansion of high pressure product gases. A program burn model is implemented along with JWL equation of state to simulate the reaction zone in between unreacted explosive and product gas. Numerical examples of detonation of one- and two-dimensional explosive slab have been carried out to investigate the effect of reaction zone in detonation process and outward dispersion of gaseous product. The results are compared with those obtained from existing solutions. A procedure is also developed in SPH framework to apply continuity conditions between gas and rock interface boundaries. The modified Grady–Kipp damage model for the onset of tensile yielding and Drucker–Prager model for shear failure are implemented for elasto-plastic analysis of rock medium. The results show that high compressive stress causes high crack density in the vicinity of blast hole. The major principal stress (tensile) is responsible for forming radial cracks from the blast hole. Spalling zones are also developed due to stress waves reflected from the free surfaces.
Magnetoelectric core-shell nanocomposites have tremendous applications in biomedical sectors such as targeted and controlled drug delivery for cancer treatment and non-invasive brain stimulation for ...treatment of Parkinson's disease. The neural activity deep in the brain is triggered with the help of these magnetoelectric nanocomposites by externally applied magnetic fields, since these materials exhibit substantial magneto-mechano-electrical coupling. Also, they posses better connectivity between the ferroelectric and ferromagnetic phases without interface effects. BaTiO3 (BTO) and CoFe2O4 (CFO) exhibits significant ferroelectric and ferromagnetic properties which are able to induce effective multiferroic properties. Core-shell nanocomposites of CoFe2O4 as core and BaTiO3 as shell, were synthesized by co-precipitation and sol-gel techniques, respectively. The optimum calcination temperature required to get pure BaTiO3 phase was observed to be 900∘C. The tetragonal phase of pure BaTiO3 and the spinal perovskite structure of pure CoFe2O4 was in accordance with the X-ray diffraction patterns. The core-shell type morphology of the synthesized nanocomposites were corroborated using Transmission Electron Microscopic images. The piezoelectric and magnetization response of these magnetoelectric nanocomposites were captured as functions of temperature and volume fractions of individual phases.
Soft materials are known for their plethora of biomedical applications, intricate structure–property correlation and nonlinear mechanical response. Multiple length–time scale phenomena and ...hierarchical structure results in their nonlinearity. Phenomenological and continuum mechanical models have been developed to predict their mechanics, which have mostly been very material-specific with inability to predict the mechanics of different types of soft materials simultaneously. This shortcoming has been addressed in the present work, wherein a generic nonlinear viscoelastic model has been proposed to predict the mechanical response of hydrogels, sponges, and xerogels. A fractal derivative viscoelastic model is proposed considering a fractal Maxwell model in parallel with a nonlinear spring. In particular, this model is chosen to qualitatively mimic the material nonlinearity inherent in soft materials. The fractal dashpot in combination with the nonlinear spring accounts for the power law time-dependent rheology of generic soft materials. These two different aspects in the form of nonlinear stiffness and non-Newtonian rheology account for mechanics of most soft materials. The present model is shown to fit well the existing literature results for mechanical response of a multitude of soft material classes with different test conditions and loading rates, which is one of the salient features of the model, apart from its simplistic mathematical framework. Further, a parametric study is reported on the mechanics of nanocellulose loaded poly(vinyl alcohol) xerogel. The model predictions are observed to be in conjunction with the experimental observations.
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