190 research outputs found
Chiral design of tough spring-shaped hydrogels for smart umbrellas
Get PDFDeveloping hydrogel artificial muscles to mimic the motion of natural muscles has long attracted scientists from the perspective of materials science for potential applications in soft robotics. However, rational design of hydrogel artificial muscles with large stroke, rapid actuation speed, and high work capacity remains a major challenge. Herein, we reported two kinds of chiral spring-shaped hydrogels that were prepared via consecutive shaping process (e.g., stretching, twisting, folding, coiling, and fixing). By switching the chirality of coil, homochiral muscle and heterochiral muscle were obtained, respectively. Homochiral muscle could rapidly expand to 560% with an average speed of 6.7 % sâ1 in response to NIR irradiation, whose maximum work capacity reached 45 J kgâ1. On contrary, heterochiral muscle contracted 69% within 1 min under NIR irradiation with a maximum work capacity of 33 J kgâ1. Interestingly, the parasol containing homochiral muscles opened autonomously during dehydration process, while the umbrellas containing heterochiral muscle could opened rapidly when water was applied. This work provided an innovative strategy for developing tough hydrogel muscles with opposite chiralities
Additive manufacturing of sustainable biomaterials for biomedical applications
Get PDFBiopolymers are promising environmentally benign materials applicable in multifarious applications. They are especially favorable in implantable biomedical devices thanks to their excellent unique properties, including bioactivity, renewability, bioresorbability, biocompatibility, biodegradability, and hydrophilicity. Additive manufacturing (AM) is a flexible and intricate manufacturing technology, which is widely used to fabricate biopolymer-based customized products and structures for advanced healthcare systems. Three-dimensional (3D) printing of these sustainable materials is applied in functional clinical settings including wound dressing, drug delivery systems, medical implants, and tissue engineering. The present review highlights recent advancements in different types of biopolymers, such as proteins and polysaccharides, which are employed to develop different biomedical products by using extrusion, vat polymerization, laser, and inkjet 3D printing techniques in addition to normal bioprinting and four-dimensional (4D) bioprinting techniques. This review also incorporates the influence of nanoparticles on the biological and mechanical performances of 3D-printed tissue scaffolds. This work also addresses current challenges as well as future developments of environmentally friendly polymeric materials manufactured through the AM techniques. Ideally, there is a need for more focused research on the adequate blending of these biodegradable biopolymers for achieving useful results in targeted biomedical areas. We envision that biopolymer-based 3D-printed composites have the potential to revolutionize the biomedical sector in the near future
3D/4D printing of cellulose nanocrystals-based biomaterials: Additives for sustainable applications
Get PDFCellulose nanocrystals (CNCs) have gained significant attraction from both industrial and academic sectors, thanks to their biodegradability, non-toxicity, and renewability with remarkable mechanical characteristics. Desirable mechanical characteristics of CNCs include high stiffness, high strength, excellent flexibility, and large surface-to-volume ratio. Additionally, the mechanical properties of CNCs can be tailored through chemical modifications for high-end applications including tissue engineering, actuating, and biomedical. Modern manufacturing methods including 3D/4D printing are highly advantageous for developing sophisticated and intricate geometries. This review highlights the major developments of additive manufactured CNCs, which promote sustainable solutions across a wide range of applications. Additionally, this contribution also presents current challenges and future research directions of CNC-based composites developed through 3D/4D printing techniques for myriad engineering sectors including tissue engineering, wound healing, wearable electronics, robotics, and anti-counterfeiting applications. Overall, this review will greatly help research scientists from chemistry, materials, biomedicine, and other disciplines to comprehend the underlying principles, mechanical properties, and applications of additively manufactured CNC-based structures
An additively manufactured silicone polymer: Thermo-viscoelastic experimental study and computational modelling
Get PDFThe additive manufacturing (AM) is a new paradigm across various disciplines of engineering sciences. Despite significant advances in the areas of hard material printings, the options for 3D printed soft materials are still limited. Most of the existing 3D printed polymers are in the areas of acrylics and polyurethanes or their composites. Recently emerged Digital Light Synthesis (DLS) technology hugely accelerates the additive manufacturing of soft polymers. A DLS-inspired 3D printer uses a continuous building technique instead of a layer-by-layer approach, where the curing process is activated by an ultra-violet (UV) light. In this contribution, a DLS-based digitally printed silicone (SIL30) is experimentally characterized. To understand polymer's temperature-dependent mechanical responses, an extensive thermo-viscoelastic experimental characterisation at various strain rates under tensile deformation and temperature fields from -20° C to 60° C is performed. The study reveals significant effects of time-and temperature-dependency on the mechanical responses of the 3D printed silicone. Motivated by the thermo-mechanical results of the polymer, a thermodynamically consistent constitutive model at large strain is devised. Afterwards, the model is calibrated to the data that results in the identification of relevant parameters. The model predicts the experimental results with a good accuracy. 3D printed soft polymers are major candidates in designing complex and intricate architectured metamaterials for biomedical applications. Hence, a comprehensive thermo-mechanical experimental study and subsequent constitutive modelling will facilitate in designing and simulating more complex cellular metamaterials using 3D printed silicones
Mathematical formulations for elastic magneto-electrically coupled soft materials at finite strains: Time-independent processes
Get PDFRecently, among other smart and multifunctional materials, magneto-electric soft materials are expected to open a new horizon with myriad of potential applications such as wireless energy harvesting, spintronics and nonvolatile memories, magneto-electric random access memory, to mention a few. Magneto-electric coupling can be defined as the ability of a material to electrically polarize upon the application of a magnetic field and conversely, to magnetize under the application of an electric field. In contrast to traditional multi-ferroic hard materials, magneto-electric soft materials are of largely deformable where electric and magnetic fields and mechanical deformations are intricately coupled at finite strians. In this contribution, we will emphasis to formulate generalised mathematical frameworks of finitely deformed magneto-electric soft materials. After elaborating fundamental and governing equations, some homogeneous and non-homogeneous classical boundary value problems are studied under magneto-electrically coupled loads
Hard magnetics in ultra-soft magnetorheological elastomers enhance fracture toughness and delay crack propagation
Get PDFPre-existing flaws in highly stretchable elastomers trigger fracture under large deformations. For multifunctional materials, fracture mechanics may be influenced by additional physical phenomena. This work studies the implications of hard magnetics on the fracture behaviour of ultra-soft magnetorheological elastomers (MREs). We experimentally demonstrate that MREs with remanent magnetisation have up to a 50 % higher fracture toughness than non pre-magnetised samples. Moreover, we report crack closure due to the magnetic field as a mechanism that delays the opening of cracks in pre-magnetised MREs. To overcome experimental limitations and provide further understanding, a phase-field model for the fracture of MREs is conceptualised. The numerical model incorporates magneto-mechanical coupling to demonstrate that the stress concentration at the crack tip is smaller when the MRE is pre-magnetised. Overall, this work unveils intriguing applications for functional actuators, with better fracture behaviour and potential better performance under cyclic loading
Cobalt iron oxide (CoFe2O4) reinforced polyvinyl alcohol (PVA) based magnetoactive polymer nanocomposites for remote actuation
Get PDFMagnetoactive polymer composites (MAPCs) are materials composed of a polymer matrix embedded with magnetic particles that mechanically respond to external magnetic fields. MAPCs can be programmed to be adjusted remotely without physical interventions using a magnetic field to generate the desired response; therefore, MAPCs are being actively explored for their applications in remote sensing, soft robotics, electronics, and biomedical areas. In this work, novel MAPCs were synthesised comprising polyvinyl alcohol (PVA) as the matrix and cobalt iron oxide (CoFeâOâ) nanoparticles as the magnetic component with varying concentrations (i.e., 1.25%, 2.5%, and 5%). MAPCs were synthesised using the solution casting technique, and field emission scanning electron microscopy (FE-SEM) and x-ray diffraction (XRD) results revealed the successful integration of CoFeâOâ nanoparticles within the polymer matrix. The synthesised MAPC films were also characterised for their chemical, thermal, magnetic, and biological properties. The incorporation of CoFeâOâ nanoparticles resulted in an improved magnetic and biological response, with improvements in these properties with increasing CoFeâOâ content. However, PVA/5% CoFeâOâ revealed toxicity and requires further investigation of using these materials with higher CoFeâOâ concentrations. The magnetic response and biological properties of the PVA/CoFeâOâ MAPCs revealed their potential uses for remote actuation and sensing in the biomedical sector
Nonlocal plasticity-based damage modeling in quasi-brittle materials using an isogeometric approach
Get PDFPurposeThis paper aims to present a nonlocal gradient plasticity damage model to demonstrate the crack pattern of a body, in an elastic and plastic state, in terms of damage law. The main objective of this paper is to reconsider the nonlocal theory by including the material in-homogeneity caused by damage and plasticity. The nonlocal nature of the strain field provides a regularization to overcome the analytical and computational problems induced by softening constitutive laws. Such an approach requires C1 continuous approximation. This is achieved by using an isogeometric approximation (IGA). Numerical examples in one and two dimensions are presented.Design/methodology/approachIn this work, the authors propose a nonlocal elastic plastic damage model. The nonlocal nature of the strain field provides a regularization to overcome the analytical and computational problems induced by softening constitutive laws. An additive decomposition of strains in to elastic and inelastic or plastic part is considered. To obtain stable damage, a higher gradient order is considered for an integral equation, which is obtained by the Taylor series expansion of the local inelastic strain around the point under consideration. The higher-order continuity of nonuniform rational B-splines (NURBS) functions used in isogeometric analysis are adopted here to implement in a numerical scheme. To demonstrate the validity of the proposed model, numerical examples in one and two dimensions are presented.FindingsThe proposed nonlocal elastic plastic damage model is able to predict the damage in an accurate manner. The numerical results are mesh independent. The nonlocal terms add a regularization to the model especially for strain softening type of materials. The consideration of nonlocality in inelastic strains is more meaningful to the physics of damage. The use of IGA framework and NURBS basis functions add to the nonlocal nature in approximations of the field variables.Research limitations/implicationsThe method can be extended to 3D. The model does not consider the effect of temperature and the dissipation of energy due to temperature. The method needs to be implemented for more real practical problems and compare with experimental work. This is an ongoing work.Practical implicationsThe nonlocal models are suitable for predicting damage in quasi brittle materials. The use of elastic plastic theories allows to capture the inelastic deformations more accurately.Social implicationsThe nonlocal models are suitable for predicting damage in quasi brittle materials. The use of elastic plastic theories allows to capture the inelastic deformations more accurately.Originality/valueThe present work includes the formulation and implementation of a nonlocal damage plasticity model using an isogeometric discretization, which is the novel contribution of this paper. An implicit gradient enhancement is considered to the inelastic strain. During inelastic deformations, the proposed strain tensor partitioning allows the use of a distinct potential surface and distinct failure criterion for both damage and plasticity models. The use of NURBS basis functions adds to more nonlocality in the approximation
Ecoflex polymer of different Shore hardnesses: Experimental investigations and constitutive modelling
Get PDFEcoflex, a commercially available silicone polymer, has attracted considerable attention due to its wide range of applications. The polymer has various Shore hardnesses that represent its wide range of stiffnesses. In this contribution, we have conducted a plethora of experiments under the uniaxial mode of tensile deformation. These experiments consist of loading-unloading cyclic tests, stretchability tests, single-step relaxation tests, Mullins effect tests, stress recovery tests, and temperature-dependence tests at different strain levels. All tests are revisited with Ecoflex of five Shore hardnesses ranging from Shore 00-10 to Shore 00-50. Extensive experimental findings illustrate that the material consists of an equilibrium stress part and an overstress part. Constitutive frameworks with an amplified strain invariant are proposed to predict the mechanical responses of Ecoflex over a wide range of Shore hardnesses. Afterwards, the frameworks are extended to capture the stress softening behaviour significantly observed in the material. Relevant examples illustrate that proposed constitutive models accurately predict stress-strain responses and the stress softening behaviour of Ecoflex. The current experimental study will work as a guide in selecting Ecoflex with an appropriate Shore hardness for applications in stretch sensors, soft robotics, and energy harvesters. Moreover, the novel concept of Shore-dependent modelling proposed herein can be applied to predict the stress-strain behaviour of other soft polymers appearing with various Shore hardnesses where there exist difficulties in obtaining experimental data of a particular Shore hardness
Renormalized FloryâHuggins lattice model of physicochemical kinetics and dynamic complexity in selfâhealing doubleânetwork hydrogel
Get PDFSelfâhealing capability offers great designability on mechanical properties of doubleânetwork (DN) hydrogel. However, the thermodynamics understanding behind such physicochemical transitions and selfâhealing behaviors are yet to be explored properly. This study describes a renormalized FloryâHuggins lattice model for DN hydrogels, of which the physicochemical kinetics and dynamic complexity are resulted from stressâinduced bond scission and macromolecule rearrangement. Based on the FloryâHuggins lattice model and Gaussian distribution theory, an extended freeâenergy model was formulated by the steric repulsive freeâenergy function. Afterwards, the function was used to identify the working mechanisms and thermodynamics in selfâhealing DN hydrogels with ultraâhigh mechanical strength. Finally, the effectiveness of model was demonstrated by applying it to predict the mechanical behaviors of DN hydrogels, where the analytical results showed good agreements with experiment data
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