Viscoelastic Nature Research Articles

Castor‐oil derived polyurethane/barium titanate piezoelectric smart composite coatings for energy harvesting applications: Prediction and experimental characterization of electro‐elastic properties

AbstractSustainable and environment‐friendly polymer composite smart paints/coatings with polyurethane (PU) derived from castor‐oil (CO) as the matrix and barium titanate (BTO) microparticles as piezo‐active inclusions (2, 4, 6, 8, and 10 vol.%) have been prepared employing ultrasonication and solvent casting, followed by contact DC poling method. Relative dielectric constants varied from 5.26 ± 0.37 for pristine COPU to 8.9 ± 0.36 for COPU/10 vol.% BTO composite, at a frequency of 1 kHz. Piezoelectric strain constant d33 of the poled films varied from 0.0 pC/N for pristine castor‐oil based polyurethane (COPU) to 1.2 pC/N for COPU/10 vol.% BTO (CPBT‐5) composite. Tensile tests showed that the elastic modulus varied from 1.98 ± 0.003 MPa for pristine COPU to 5.13 ± 0.02 MPa for COPU/10 vol.% BTO composite. Dynamic mechanical analysis confirmed the viscoelastic nature of the smart paints. Measurement of current–voltage response under different compressive loads indicates that COPU/10 vol.% BTO composite can generate a current of ~28 nA and voltage of ~8 V under a dynamic compressive load of 40 N, applied at a frequency of 1 Hz. These experiments were complemented by Fourier transform infra‐red spectroscopy and scanning electron microscopy. In addition, finite element analyses based on periodic boundary conditions have been performed to predict the effective electro‐elastic properties of these piezoelectric smart composite coatings.Highlights Castor‐oil‐based PU piezoelectric composites with BTO inclusions were developed. Increase in BTO content up to 10 vol.% increases dielectric constant by ~1.7 times. COPU/BTO composites exhibit significantly increased piezoelectric response. Elastic and viscoelastic properties are also enhanced with increasing BTO content. Finite element models show a good match with experimental results.

I-Rheo-optical assay: Measuring the viscoelastic properties of multicellular spheroids

This study introduces a novel mechanobiology assay, named “i-Rheo-optical assay”, that integrates rheology with optical microscopy for analysing the viscoelastic properties of multicellular spheroids. These spheroids serve as three-dimensional models resembling tissue structures. The innovative technique enables real-time observation and quantification of morphological responses to applied stress using a cost-effective microscope coverslip for constant compression force application. By bridging a knowledge gap in biophysical research, which has predominantly focused on the elastic properties while only minimally exploring the viscoelastic nature in multicellular systems, the i-Rheo-optical assay emerges as an effective tool. It facilitates the measurement of broadband viscoelastic compressional moduli in spheroids, here derived from cancer (PANC-1) and non-tumoral (NIH/3T3) cell lines during compression tests.This approach plays a crucial role in elucidating the mechanical properties of spheroids and holds potential for identifying biomarkers to discriminate between healthy tissues and their pathological counterparts. Offering comprehensive insights into the biomechanical behaviour of biological systems, i-Rheo-optical assay marks a significant advancement in tissue engineering, cancer research, and therapeutic development.

Mechanics of blood flow through narrow artery using Prandtl viscoelastic model

BackgroundThe mechanics of blood flow via converging diverging conduits is an intriguing phenomenon that involves multiple fundamental principles of fluid dynamics. Blood arteries can diverge, which means they expand, or converge, which means they contract down. This specific structure is essential for controlling blood flow and preserving adequate circulation across the body. The theory of fluid mechanics is significant concept related to blood flow along converging/divergent channels. Elevated shear strains near the narrower artery throat can stimulate platelets, causing thrombosis that can completely or partially stop blood supply to the human brain or heart. This communication addresses the blood flow in convergent and diverging artery using fundamental concept of fluid mechanics. The Prandtl fluid model is considered as a blood, because of its viscoelastic nature. The influence of heat source, frictional dissipations and a chemical reaction are included. MethodsThe Jaffrey-Hamel flow in a converging and diverging conduits is generalized to Prandtl fluid model considering the purely radial flow through cylindrical pipe like artery with an arbitrary cross section. The governing equations are solved computationally using the Runge–Kutta-Fehlberg (RKF-4) method. Significant findingThe rheological parameters ε and δ of blood show opposite tendencies for blood circulation. The Brownian and thermophoresis parameters has a significant effect on heat and mass transport rate. The presence of slip (semi blockage) produces flow reversal and higher drag forces at the arterial wall. Significant flow dynamics and heat-mass transport was reveled for diverging (wider) artery β > 0. The non-uniform heat source show similar trends for thermal profile and heat transfer rate.

Study on interaction of Viscoelastic and Mechano-sorptive creep and effect of Fibre Reinforcement on creep of Timber beams

Timber is a sustainable material widely used in structural elements. Its viscoelastic nature, in which the stress-strain relation varies with time, poses significant challenge to the durability of timber structures. Creep of timber under constant loading depends on various factors like stress level, moisture content, load-to-grain angle, temperature, relative humidity etc. Among these, relative humidity and moisture content in timber are the most crucial. Drastically varying moisture content causes mechano-sorptive creep. However, the interaction and contribution of various factors causing creep is still a matter of research. Various codes provide generalized creep coefficient for long term deflection and load reduction factors. A detailed rheological model was proposed by Toratti which addresses mechano-sorptive creep explicitly, incorporating both recoverable and irrecoverable part in creep. This paper aims to review the study on interaction between viscoelastic creep and Mechano-sorptive creep in various environmental conditions. Effect of reinforcing timber beams, on the long term deflection due to creep is also made a subject of study to identify a possible solution to the accelerated deflection by Mechano-sorptive creep, which will be unavoidable in tropical areas with extreme climactic changes. A comparative study between the various standard codes with Indian Standard Codes for timber with respect to creep, is also made, to identify the gaps in IS codes.

Theory construction and computation for polymer film melt stretching by modified Leonov model

Polymer film melt stretching exhibits a unique stress–strain behavior, featuring a stress plateau followed by a sudden increase with increasing the strain. This phenomenon poses a challenge to conventional melt-extension theories and methods. To address this, we derive a simplified flow theory according to the symmetric characteristics of thin melt-stretching, and propose a modified multi-mode Leonov model (m-Leonov) that accounts for molecular orientation effects, a crucial factor in accurately simulating the process. In order to improve the computational efficiency, an iterative algorithm was developed to decouple the interdependence between governing and constitutive equations. The computational results reveal that the viscoelastic nature of the film contributes to a delay in the transformation of stretching forces, leading to the observed stress plateau. Significantly, our m-Leonov model successfully predicts both the plateau and the subsequent abrupt increase in stress, across various temperatures and stretching rates. These simulations closely agree with experimental data, underlining the robustness of our approach. Our findings would enhance the understanding of rheological complexities in film stretching, offering potential applications in various materials and polymer processing.

Comparative Analysis and Error Assessment of Nanoindentation Evaluation Techniques for NafionTM117

AbstractAdvances in the application of polymers for electrochemical cells require an understanding of their viscous deformation mechanisms and their interaction with moisture. Nanoindentation offers a localized, microscale testing alternative to traditional tensile testing. However, the viscoelastic nature of the polymers, combined with their increased compliance, presents challenges in the analysis of nanoindentation results. In addition, the dependence on moisture results in significant scatter and low repeatability. This study combines nanoindentation and tensile testing as a verification method and compares different correction protocols for static nanoindentation to investigate the mechanical behavior of polymer electrolyte membranes. Comparisons of different indentation devices, analysis methods, and indentation protocols show a significant overestimation of Young’s modulus using the classical Oliver–Pharr method compared to values determined from tensile tests. Nanoindentation at different humidity levels revealed different mechanisms leading to a decrease in Young’s modulus and hardness with increasing humidity.

Solvent selective gelation of cetyltrimethylammonium bromide: structure, phase evolution and thermal characteristics.

We report herein the gelation behaviour of cetyltrimethylammonium bromide (CTAB), a cationic surfactant, in a variety of solvent compositions. A turbid gel of CTAB in a binary solvent mixture at a critical composition was observed to be 1 : 3 v/v toluene : water. The molecular structure of the as-formed gel was investigated by X-ray diffraction and microscopic techniques, namely, optical and polarizing microscopy, scanning electron microscopy and small-angle X-ray scattering (SAXS). The phase evolution has been studied using UV-visible transmittance measurements and the thermal characteristics of the gel by differential scanning calorimetry measurements. SAXS studies, in conjunction with molecular modelling, revealed the gel to assemble as lamellae with high interdigitation of bilayer assembly of CTAB molecules with predominant non-covalent interactions, where the gel lamellae were inferred from the interplanar spacings. Rheological studies revealed the viscoelastic nature of the CTAB gels. The ability to form a gel has been evaluated in several polar solvents, such as methanol and chloroform, and non-polar solvents, such as toluene and carbon tetrachloride.

A Novel Viscoelastic Deformation Mechanism Uncovered during Vickers Hardness Study of Bone.

This study investigates the viscoelastic deformation mechanisms of bone as a response to Vickers hardness indentation. We utilized advanced high-resolution scanning electron microscopy (SEM) to investigate a distinct deformation pattern that originates from the indentation site within the bone matrix. The focus of our research was to analyze a unique deformation mechanism observed in bone tissue, which has been colloquially termed as "screw-like" due to its resemblance to a screw thread when viewed under an optical microscope. The primary goals of this research are to investigate the distinctive characteristics of the "screw-like" deformation pattern and to determine how the microstructure of bone influences the initiation and control of this mechanism. These patterns, emerging during the dwell period of indentation, underscore the viscoelastic nature of bone, indicating its propensity for energy dissipation and microstructural reconfiguration under load. This study uncovered a direct correlation between the length of the "screw-like" deformation and the duration of the indentation dwell time, providing quantifiable evidence of the bone's viscoelastic behavior. This finding is pivotal in understanding the mechanical properties of bone, including its fracture toughness, as it relates to the complex interplay of factors such as energy dissipation, microstructural reinforcement, and stress distribution. Furthermore, this study discusses the implications of viscoelastic properties on the bone's ability to resist mechanical challenges, underscoring the significance of viscoelasticity in bone research.

On the free vibration characteristics of multiscale hybrid conical panels utilizing Chebyshev–Ritz route

This study investigates the vibrational behavior of three-phase polymer-glass fiber (FG)-carbon nanotubes (CNT) nanocomposites conical panels. Effects of the wavy shape of CNTs and the viscoelastic nature of the polymer matrix are considered. First and foremost, the equivalent material properties are estimated in the context of a three-step hierarchical approach. Then, the governing equations are attained by combining the first-order shear deformation theory (FSDT) and Hamilton’s principle. Furthermore, the Ritz method is employed to extract the frequency responses with the help of Chebyshev polynomials for both simply supported and clamped ends panels. For the parametrical studies, the effect of different geometrical constraints, for instance, the effects of relaxation time and the effect of considering different waviness coefficients for the CNT, are reported. The findings of this paper reveal the significant effect of the viscoelastic properties of the polymer matrix on the estimation of the dimensionless frequency. For instance, under simply supported boundary conditions and a relaxation parameter of 60 s, the frequency of the structure reduces by approximately 23% after 100 s.

Post-creep residual tensile properties of multi-walled carbon nanotube/epoxy nanocomposites

Epoxy resin as a thermoset polymer is vulnerable to creep loading even at room temperature due to its viscoelastic nature. This study investigated the effect of reinforcing epoxy resin with different functionalized multi-walled carbon nanotubes (MWCNT) contents on the creep response and post-creep residual tensile properties of nanocomposites. The creep tests were performed on the nanocomposite specimens containing different filler contents and the neat epoxy specimen at 40°C under a constant load level of 200 N. It was found that the nanocomposites containing 0.3 wt% MWCNTs experienced 29.6%, 69.1%, and 74.1% decreases in the elastic strain, creep strain, and steady-state creep strain rate, respectively, compared to the neat epoxy. Furthermore, the tensile strength and stiffness of the neat epoxy and nanocomposite specimens were evaluated before and after a partial creep test (at a load level of 200 N for 150 min) by conducting tensile tests. The nanocomposites containing 0.3 wt% MWCNTs demonstrated considerable improvements of 35.9%, 41.2%, 27.9%, and 28.1% in strength, residual strength, stiffness, and residual stiffness, respectively, compared to the neat epoxy. Furthermore, scanning electron microscopy assessment was utilized to investigate the fracture surfaces of the nanocomposite specimens.

A Metabolomics Approach to Establish the Relationship between the Techno-Functional Properties and Metabolome of Indian Goat Yoghurt.

Goat milk has poorer fermentation characteristics due to the absence or only traces of αs1-casein, due to which goat yoghurt contains a less dense gel structure. Moreover, the fermentation characteristics of the milk vary between the breeds of the same species. Therefore, it becomes imperative to explore a few metabolites which could regulate the techno-functional properties of goat yoghurt. This study was aimed at relating the metabolite profile of yoghurt prepared from milk of Barbari, an indigenous goat breed of India, and its techno-functional properties (firmness, whey syneresis, and flow behaviour) using multivariate data analysis and regression models. Goat yoghurt was prepared with two different total solids (TS) levels (12 and 16%) and cultures, namely, commercial culture comprising a thermophilic yoghurt culture (A) and NCDC-263 comprising a mixed yoghurt culture (B). Results demonstrated a significant difference (p < 0.05) in whey syneresis with the increase in the TS level. Flow behaviour of all yoghurt samples showed a decrease in viscosity with an increase in shear rate, which confirmed its non-Newtonian behaviour and shear thinning nature, whereas frequency sweep confirmed its viscoelastic nature. Firmness was the most affected under the influence of different TS and culture levels. It was higher (p < 0.05) for 16-A, followed by 16-3B, and minimum for 12-2B. GC-MS-based metabolomics of the yoghurt revealed a total of 102 metabolites, out of which 15 metabolites were differentially expressed (p < 0.05), including 2-hydroxyethyl palmitate, alpha-mannobiose, and myo-inositol. Multivariate data analysis revealed clear separation among groups using principal component analysis and several correlations using a correlation heat map. Further, regression analysis exhibited methylamine (0.669) and myo-inositol (0.947) with higher regression coefficients (R2 values) exceeding 0.6, thus demonstrating their significant influence on the techno-functional properties, mainly firmness, of the yogurt. In conclusion, A gas chromatography-based metabolomics approach could successfully establish a relationship between the metabolome and the techno-functional properties of the yoghurt.

Effect of Ghee Residue Powder and Pearl Millet Flour Substitution on Rheological, Textural, and Sensorial Characteristics of Eggless Muffin

Bakery products are becoming an essential part of the human diet. Millets are the staple grains in Asia and African countries, and they are the super future food because of their nutritive and disease-preventive nature. Pearl millet is one of the most nutritious cereal grains, and its protein lacks gluten, which makes it a suitable base material for the preparation of gluten-free products. However, gluten is necessary because of its unique viscoelastic nature, which makes the most innovative bakery items. In this study, 50% refined wheat flour (RWF) has been replaced with pearl millet flour (PMF) to prepare a muffin, and a ghee residue is utilized to make a ghee residue powder (GRP) as a functional ingredient to replace whey protein concentrate (WPC) in the eggless muffin. Substitution of fat with GRP reduced the specific gravity of batter from 1.05 to 0.99; lightness value was considerably decreased, whereas the redness and yellowness values increased from 1.06 to 8.32 and 23.62 to 26.20, respectively. Replacement of RWF with PMF affected the lightness and specific gravity of the batter. Substitution with PMF and GRP reduced the viscosity from 13.83 Pa·s to7.08 Pa·s. Gelatinization temperature of batters varied with substitution of flour and fat with PMF and GRP. Muffin volume dramatically decreased from 56.19 to 36.84 cm3 with substitution of GRP and PMF. Weight loss was increased from 12.14 to 13.68% by substitution. The hardness and springiness were reduced with substitution. The GRP can replace fat up to 25%; thereafter, muffin’s quality characteristic reduces; hence, 50% PMF and 25% GRP combination give satisfiable muffin product.

Enhancing accuracy of predictive fatigue life model in rejuvenated RAP binders through LAS test and complex modulus test at multiple temperatures

The linear amplitude sweep (LAS) test is widely accepted as a valuable tool for assessing binder fatigue. However, due to the binder's viscoelastic nature, the fatigue life varies with temperature, leading to a challenge in determining the LAS testing temperature. This research primarily addressed inaccurate assumptions of a linear relationship between the logarithms of the storage modulus (logG′(ω)) and angular frequency (log (ω)), as well as intermediate testing temperature. Then, by performing the LAS test at four different temperatures on rejuvenated RAP binders, a method for determining the rejuvenated RAP binder's fatigue behavior was introduced. The results demonstrated that LAS parameters, including A and B, correlated linearly at various temperatures with the rejuvenated RAP binder's complex modulus (|G*|) calculated at corresponding temperatures. Therefore, a fatigue life model, considering strain level and temperature effects, was developed using a power function of |G*|. It was found that the residual analysis exhibited a lack of fit, indicating that the linear model was inadequate throughout the whole range of experimental frequencies at multiple temperatures. Moreover, the newly introduced model predicted fatigue life more accurately at various temperatures utilizing the maximum stress failure criterion and the 35% damage level. This model will allow the LAS procedure to be used in a wider range of temperatures and strain levels for which rejuvenated RAP binders are used in the flexible pavement.

Mapping deformation and dissipation during fracture of soft viscoelastic solid

Energy dissipation around a propagating crack is the primary mechanism for the enhanced fracture toughness in viscoelastic solids. Such dissipation is spatially non-uniform and is highly coupled to the crack propagation process due to the history-dependent nature of viscoelasticity. We present an experimental approach to map the dissipation field during crack propagation in soft viscoelastic solid. Specifically, we track randomly distributed tracer particles to measure the evolving deformation field. The measured deformation field is then put into a nonlinear constitutive model to determine the dissipation field. Our methodology was used to investigate the deformation and dissipation fields around a propagating crack in a Polyampholyte (PA) hydrogel. The deformation field measurements allowed us to assess whether the commonly assumed translational invariance in viscoelastic fracture theories holds true in practical experiments. Furthermore, by combining the obtained deformation fields with a nonlinear viscoelastic model, we captured the complete history of the dissipation field during crack propagation. We found that dissipation occurred even at material points that are a few millimeters away from the crack tip. The mapped dissipation field also enabled the separate determination of the intrinsic and dissipative components of fracture toughness for the viscoelastic hydrogel.

Towards a high-performance asphalt concrete for extreme climatic conditions using asphaltenes and polyethylene terephthalate fibres

Asphalt pavement experiences various deteriorations in different weather conditions due to the viscoelastic nature of asphalt binder. This study aims to develop a high-performance asphalt concrete (HPAC) for extreme temperature conditions by incorporating waste polyethylene terephthalate (PET) fibres and asphaltenes, a by-product from Alberta oil sands. First, performance of asphalt binder modified with asphaltenes is evaluated according to the Superpave performance grading (PG) system. Next, to improve low-temperature properties, HPAC mixtures modified with PET fibre at percentages of 0.05–0.30% are tested for compactibility to reflect field construction considerations. Then, performance tests including dynamic modulus; indirect tensile strength test at low temperatures; and Hamburg wheel-track at high temperature are conducted for an effective evaluation of the unmodified and modified mixtures that are prepared using a combination of the dry and wet mix methods. Results of binder PG tests reveal that with 12% asphaltenes, the modified binder is suitable for HPAC applications. The mixes with and without PET fibres exhibit similar compactibility and meet air void requirements of a maximum 6%, and incorporating PET fibres increases stiffness by up to 3.3%. Compared with the unmodified mixes, an optimum dosage of 0.15% PET fibre increases fracture energy by up to 27% at −10 °C and enhances tensile strength by up to 18% at 0 °C. The mixture with the optimum dosage also exhibits excellent rut resistance at 60 °C showing no signs of moisture damage sensitivity. As a result, it boasts a remarkable rutting resistance index that is five times higher than that of the control unmodified mix.

Synchronous semi-solid extrusion and photopolymerization of antimicrobial dressing hydrogel for wound healing

Bacterial infections at wound sites require more time for a fast and efficient wound-healing process. Antibacterial methyl cellulose-based hydrogel wound dressing can be an excellent option because it can show antibacterial action, absorb wound exudates, and have a cooling and soothing effect on the wound bed. The ultraviolet (UV) ray-assisted semi-solid extrusion 3D printing technique was used to prepare 3D printed construct into a high surface area mesh-like structure utilizing UV radiation for photocrosslinking of hydrogel matrix in the presence of Poly (ethylene glycol) Diacrylate. The prepared hydrogel was characterized for contact angle, and rheological analysis before semi-solid extrusion-based 3D printing. After optimization of printing parameters, the 3D printed mesh was subjected to physicochemical characterizations like dimensional analysis, swelling study, drug content, in vitro drug release, and in vitro antimicrobial activity study. A rheological analysis confirmed the viscosity, thixotropy, and viscoelastic nature of prepared hydrogel. Drug release study showed approximately 50 % release in 4 h, and >80 % drug release in 24 h. After optimization of one batch, hydrogel polymerization was done by functional group analysis followed by validation of thread thickness by electron microscopy images and mechanical property assessment. The 3D-printed mesh was further evaluated for its in-vitro antibacterial performance against Escherichia coli and Staphylococcus aureus. The area of inhibition was one-fold more in Staphylococcus aureus and two-fold in E. coli, ensuring diffusion of the drug from 3D printed mesh and killing of bacteria. The work reported herein represents a universal platform to generate multifunctional and customized hydrogels with various functional substances for wound dressing applications.

Instability analysis of swirling cylindrical Rivlin–Ericksen viscoelastic fluid–viscous fluid interface with heat and mass transfer

The applications of swirling interfaces with heat and mass transfer are diverse and impactful, spanning industries from energy and manufacturing to healthcare and environmental protection. This study focuses on the stability of such interfaces where a viscous fluid interacts with a Rivlin–Ericksen (RE) viscoelastic fluid, undergoing heat and mass transfer. In this paper, the fluids are enclosed between two cylinders, one stationary and the other rotating. Mathematical equations are solved using potential flow theory. The interface stability is assessed using a normal mode procedure, leading to a second-order polynomial equation. The study finds that swirling flow reduces perturbation amplification, especially when heat and mass transfer occur simultaneously. However, the viscoelastic nature of the Rivlin–Ericksen fluid destabilizes the interface. Overall, this research provides valuable insights into complex fluid behavior with applications across industries.

Experimental synthesis and characterization of PVA‐fumaric acid cross‐linked biodegradable films: Implications as a sustainable matrix for composites

AbstractPolyvinyl alcohol (PVA) is a widely used polymer that is biocompatible, nontoxic, and water‐soluble due to the presence of hydroxyl groups in its domain. This study aims to investigate the effects of fumaric acid (FA) cross‐linking and thermal cross‐linking (TC) on the PVA's mechanical and thermal properties. When the FA is mixed with PVA, it was found in the chemical reaction that the OH groups of PVA are condensing with the carboxylic acid units of FA to yield new ester linkages and water as a by‐product, which further results in the reduction of the water absorption capacity. Quantitatively, the addition of 8 (wt. /wt. %) FA resulted in a minimum of 65% water absorption rate, as compared with 117% for pure PVA. The mechanical and thermal properties of PVA also enhanced with the addition of 2% to 8% FA by weight. For the TC case, the % increase in ultimate tensile strength was 30.9% and 42.5% with and without TC, respectively. As the wt. % of FA increased from 2 to 10%, the % elongation value decreased for both with and without TC films relative to pure PVA. The thermogravimetric analysis revealed the change in degradation temperature of FA‐PVA blended film in comparison with pure PVA. Dynamic mechanical analysis was utilized to analyze the viscoelastic nature and temperature variation at the glass transition temperature. The current fabricated film is a potential candidate for the food packaging films application; moreover, the results reported in this investigation will accelerate the industrial applications of biodegradable PVA.Highlights Increasing the weight percentage of fumaric acid leads to an enhancement in mechanical and thermal properties of the film. Esterification is the usual reaction between fumaric acid and polyvinyl alcohol (PVA), in which ester linkages are formed when the carboxyl groups (‐COOH) of fumaric acid and the hydroxyl groups (‐OH) of PVA combine. Water absorption characteristics of the film reduces as the wt. % of fumaric acid increases. Thermal cross‐linking of the film leads to further improvements in mechanical and thermal properties. The overall effect of increasing the wt. % of fumaric acid is negative on the glass transition temperature of the film. The developed film is a potential candidate for the food packaging films application.

Precise healing of oral and maxillofacial wounds: tissue engineering strategies and their associated mechanisms.

Precise healing of wounds in the oral and maxillofacial regions is usually achieved by targeting the entire healing process. The rich blood circulation in the oral and maxillofacial regions promotes the rapid healing of wounds through the action of various growth factors. Correspondingly, their tissue engineering can aid in preventing wound infections, accelerate angiogenesis, and enhance the proliferation and migration of tissue cells during wound healing. Recent years, have witnessed an increase in the number of researchers focusing on tissue engineering, particularly for precise wound healing. In this context, hydrogels, which possess a soft viscoelastic nature and demonstrate exceptional biocompatibility and biodegradability, have emerged as the current research hotspot. Additionally, nanofibers, films, and foam sponges have been explored as some of the most viable materials for wound healing, with noted advantages and drawbacks. Accordingly, future research is highly likely to explore the application of these materials harboring enhanced mechanical properties, reduced susceptibility to external mechanical disturbances, and commendable water absorption and non-expansion attributes, for superior wound healing.

Pressure drop non-linearities in material extrusion additive manufacturing: A novel approach for pressure monitoring and numerical modeling

Fused Filament Fabrication is an additive manufacturing technique in which molten thermoplastic polymers are extruded through a nozzle. Therefore, the interplay between the viscoelastic nature of the polymer melt, temperature, printing conditions and nozzle shape may lead to inconsistent extrusion. To improve the extrusion control and optimize the print-head performance, a better understanding of the flow process of the polymer melt both in the nozzle and the liquefier is needed. However, several challenges need to be overcome due to the complexity of gathering experimental data on the melt pressure in the nozzle and the lack of numerical models able to capture the full rheology of the molten polymer. This research introduces an innovative approach for monitoring the pressure within a material extrusion 3D printer’s nozzle. This method involves utilizing a pin in direct contact with the molten material, which then transmits the applied force from the material to an externally mounted load cell. The setup provides reliable, repeatable pressure data in steady-state conditions for two nozzle geometries and at different extrusion flows and temperatures. Moreover, the Giesekus model enabled capturing the viscoelastic rheometric features of the melt, and the numerical predictions have been compared with the experimental data. Results show that the numerical model accurately describes the flow conditions in the nozzle and allows the estimation of the behavior of the melt in the liquefier zone, the area of the print-head where the filament is molten. It could be concluded that the backflow, which is the backward flow of the molten polymer in the gap between the filament and the liquefier towards the cold end, caused significant non-linearities in the total pressure drop measured in the feeders, which were related to normal forces induced by shear in that region.