A Novel Approach for Optimization of Soft Material Constitutive Model Parameters Based on a Genetic Algorithm and Drucker's Stability Criterion.

The growing interest in soft materials to develop flexible devices involves the need to create accurate methodologies to determine parameter values of constitutive models to improve their modeling. In this work, a novel approach for the optimization of constitutive model parameters is presented, which consists of using a genetic algorithm (GA) to obtain a set of solutions from data of uniaxial tensile tests, which are later used to simulate the mechanical test using finite element analysis (FEA) software to find an optimal solution considering Drucker's stability criterion. This approach was applied to the elastomer Ecoflex 00-30 considering the Warner and Yeoh models and Rivlin's phenomenological theory. The correlation between the experimental and the predicted data by the models was determined using the root mean squared error (RMSE), where the found parameter sets provided a close fit to the experimental data with RMSE values of 0.022 (ANSYS) and 0.024 (ABAQUS) for Warner's model, while for Yeoh's model were 0.014 (ANSYS) and 0.012 (ABAQUS). It was found that the best parameter values accurately follow the experimental material behavior using FEA. The proposed GA not only optimizes the material parameters but also has a high reproducibility level with average RMSE values of 0.024 for Warner's model and 0.009 for Yeoh's model, fulfilling Drucker's stability criterion.

Modelling Volume Change and Deformation in Food Products/Processes: An Overview.

Volume change and large deformation occur in different solid and semi-solid foods during processing, e.g., shrinkage of fruits and vegetables during drying and of meat during cooking, swelling of grains during hydration, and expansion of dough during baking and of snacks during extrusion and puffing. In addition, food is broken down during oral processing. Such phenomena are the result of complex and dynamic relationships between composition and structure of foods, and driving forces established by processes and operating conditions. In particular, water plays a key role as plasticizer, strongly influencing the state of amorphous materials via the glass transition and, thus, their mechanical properties. Therefore, it is important to improve the understanding about these complex phenomena and to develop useful prediction tools. For this aim, different modelling approaches have been applied in the food engineering field. The objective of this article is to provide a general (non-systematic) review of recent (2005-2021) and relevant works regarding the modelling and simulation of volume change and large deformation in various food products/processes. Empirical- and physics-based models are considered, as well as different driving forces for deformation, in order to identify common bottlenecks and challenges in food engineering applications.

Cutaneous asthenia in a domestic cat (Felis silvestris catus)

Background: Cutaneous asthenia or Ehlers-Danlos syndrome is an inherited and rare disease. This infirmity is from an autosomal mutation that influences the collagen synthesis of the carrier. Thus, its skeleton, formed of fibers, is structurally defective. The disease is characterized by hyperelasticity and skin fragility, leading to lesions throughout the skin. The lesions may manifest in specific places or in a generalized way, being more frequent in the limbs, neck, and back. This disease does not have a specific treatment, only management care to avoid new traumas. Case: A 3-year-old male castrated, no defined race cat, was attended at one veterinary clinic with a history of intense itching. The rapid tests for feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) were negative. On physical examination, infestation by fleas, lesions all over the body, and skin hyperelasticity were observed. Topical treatment for ectoparasites as well as for body wounds was established. After the treatment, he returned without itching, but with the complaints of new lesions that did not heal. The patient underwent a total shearing to facilitate the treatment of the skin, and then he underwent blood tests, biochemistry, hormonal tests, and ultrasound, which showed no suggestive changes for hyperadrenocorticism and diabetes mellitus. His clinical signs, besides not matching with these diseases, also did not indicate skin fragility due to his history of age and balanced diet. The confirmation of the cutaneous asthenia syndrome was acquired through biopsy of skin fragment, in which it was observed disarray of collagen fibers, hypertrophy, and fibroblast hyperplasia, together with the rate of extensibility of the skin where the value reached the mark of 27.5%. Throughout the hospitalization, it was noted the progression of the disease with the appearance of new lesions, where there was no bleeding and they appeared even with the patient wearing padded clothes. Its progression lasted one year until the patient's euthanasia. Discussion: For the disposal of diabetes mellitus and hyperadrenocorticism as causes of the appearance of lesions by the body in the patient, he was submitted to the suppression tests with dexamethasone, in which he presented normality, in the biochemical examination it was dosed with fructosamine and glucose. The fructosamine was in the reference value, but the glucose was slightly altered, this increase may have been a result of stress at the time of blood collection. In addition to the patient not showing specific clinical signs such as polyphagia, polyuria, polydipsia, and weight loss, these are characteristic clinical signs of the disease. For the diagnosis of Ehlers-Danlos syndrome, histological examination, and calculation of the skin extensibility index were used, where the results obtained confirmed the suspicion. This genetic anomaly has no treatment, being progressive, so only environmental management is done to mitigate the appearance of the lesions and provide animal welfare. This case report contributes to aggregating the scientific literature in the area of veterinary medicine since skin asthenia is a rare disease and when its extent is total it becomes even more atypical. The availability of this article will provide a vision of palliative treatment for other cases, demonstrating the progressive nature of the lesions and the methods of diagnosis.

Mechanical Assessment and Hyperelastic Modeling of Polyurethanes for the Early Stages of Vascular Graft Design.

The material design of vascular grafts is required for their application in the health sector. The use of polyurethanes (PUs) in vascular grafts intended for application in the body appears to be adequate due to the fact that native tissues have similar properties as PUs. However, the influence of chemical structure on the biomechanics of PUs remains poorly described. The use of constitutive models, together with numerical studies, is a powerful tool for evaluating the mechanical behavior of materials under specific physiological conditions. Therefore, the aim of this study was to assess the mechanical properties of different PU mixtures formed by polycaprolactone diol, polyethylene glycol, and pentaerythritol using uniaxial tensile, strain sweep, and multistep creep-recovery tests. Evaluations of the properties were also recorded after samples had been soaked in phosphate-buffer saline (PBS) to simulate physiological conditions. A hyperelastic model based on the Mooney-Rivlin strain density function was employed to model the performance of PUs under physiological pressure and geometry conditions. The results show that the inclusion of polyethylene glycol enhanced viscous flow, while polycaprolactone diol increased the elastic behavior. Furthermore, tensile tests revealed that hydration had an important effect on the softening phenomenon. Additionally, after the hydration of PUs, the ultimate strength was similar to those reported for other vascular conduits. Lastly, hyperelastic models revealed that the compliance of the PUs showed a cyclic behavior within the tested time and pressure conditions and is affected by the material composition. However, the compliance was not affected by the geometry of the materials. These tests demonstrate that the materials whose compositions are 5-90-5 and 46.3-46.3-7.5 could be employed in the designs of vascular grafts for medical applications since they present the largest value of compliance, ultimate strength, and elongation at break in the range of reported blood vessels, thus indicating their suitability. Moreover, the polyurethanes were revealed to undergo softening after hydration, which could reduce the risk of vascular trauma.

Frequency response curves for a Mooney-Rivlin hyperelastic microbubble oscillating as a contrast agent in an acoustic pressure field.

In this work, we have developed numerical simulations and weakly nonlinear analysis based on the multiple-scales perturbation technique for a coated microbubble that performs radial pulsations subject to an acoustic pressure disturbance in the far-field and whose encapsulated hyperelastic material obeys the Mooney-Rivlin equation. Departing from an elastic coating as a hyperelastic shell of finite thickness, we assume eventually that the shell is of very small thickness in comparison with the microbubble radius. Under this condition, we then perform weakly nonlinear analysis, to identify resonance conditions for small pressure disturbances of the acoustic field. In parallel and also for the limit of small thickness, we have carried out numerical simulations of the radial motion of the microbubble, identifying the onset of limit cycles via the construction of Poincare maps. Under both schemes, we have recognized the importance of two dimensionless hyperelastic parameters that dictate the main behavior of the oscillations: α∗ and ß∗. Decreasing the values of these parameters, the resonance conditions are drastically amplified, which is an expected result because of the weak rigidity of the hyperelastic solid, prevails. In this manner, we suggest that moderate values for these previous parameters can be widely advisable when, in medical diagnostic applications, we are applying microbubbles as contrast agents. Therefore, we recommend widely the use of shell softens, because in this case the amplitude of radial pulsation is always amplified.