The effect of morphology on poly(vinylidene fluoride-trifluoroethylene- chlorotrifluoroethylene)-based soft actuators: Films and electrospun aligned nanofiber mats

This paper analyzes soft actuators realized as unimorph cantilever beams, in which the active layer can have two different morphologies, i.e., either an extruded film or an aligned electrospun nanofiber mat of the poly (vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene). Six different soft actuators are fabricated, with active layers of varying thicknesses and morphologies, to study the electrostrictive effect of the polymer and to evaluate the stiffening properties, the mechanical work, and the blocking forces of the actuators when stimulated by different direct current electric fields. The comparison between the different actuators is performed by introducing weight specific properties, i.e., specific stiffness and specific work, showing improved specific properties for the nanofibers-based actuators. Moreover, the blocking forces, the tip deflections, and the leakage currents of the actuators are evaluated when stimulated by alternating current electric fields. The experiments show faster viscoelastic relaxation and lower electrical power consumption for the nanofibers-based actuators. This study concludes that, thank to its electro-mechanical properties, the poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) in the form of aligned electrospun nanofiber mat has high potential to be used as the active layer of electrostrictive unimorph beam soft actuators

Influence of electrospun nanofibers on the interlaminar properties of unidirectional epoxy resin/glass fiber composite laminates

Nylon 6,6 nanofibers were interleaved in the mid-plane of glass fiber/epoxy matrix composite laminates for Mode I and II fracture mechanic tests. The present study investigates the effect of the nanofibers on the laminates' mechanical response. Results showed that Nylon 6,6 nanofibers improved specimen's fracture mechanic behavior: the initial energy release rates GIC and GIIC increased 62% and 109%, respectively, when nanofibrous interlayer was used. Scanning electron microscope micrographs showed that nanofiber bridging mechanism enhances performances of the nanomodified specimens, still able to link the layers when the matrix is broken

Using Acoustic Emission to Evaluate Fracture Toughness Energy Release Rate (GI) at Mode I Delamination of Composite Materials

Delamination is a critical damage mode in composite structures, not necessarily because it will cause the structure split into two or more pieces at the end of the damaging process, but because it can degrade the laminate strength to such a degree that it becomes useless in service. The design of composite structures to account for delamination and other forms of damage involves two fundamental considerations, namely damage resistance and damage tolerance. Knowledge of a laminated composite material’s resistance to interlaminar fracture is useful for product development and material selection

Morphology, thermal, mechanical properties and ageing of nylon 6,6/graphene nanofibers as Nano2 materials

Nylon 6,6 nanofibers loaded with different Graphene (G) amounts were successfully produced with stable process and good fiber quality, using an optimized solvent system suitable both for electrospinning and for G-suspension. G addition is found to significantly affect diameter but not thermal behaviour. A new phenomenological model is proposed for the interpretation of mechanical behaviour of nanofibrous mat, trying to take into account the nanofibrous morphology. The model highlights a G contribution to mechanical properties that mainly affects the initial steps of deformation where fibers stretch, slide, twist and re-orient. Finally, the nanofibers were analysed after 20 months ageing, showing no significant alteration with respect to the pristine ones, thus the lack of detrimental ageing-effects due to G addition

Effects of short‐loop material recycling on mechanical properties of parts by Arburg Plastic Freeforming

Arburg Plastic Freeforming allows for transforming granulated thermoplastics with variable shapes and sizes. This opens marvellous opportunities for in-place recycling of process waste and auxiliary structures. The present study investigates for the first time the effects of recycled material on the mechanical properties of manufactured parts. To this end, the mechanical, thermomechanical and rheological properties of parts produced with different contents of recycled material are investigated. Findings demonstrate that a balanced mixture of primary and secondary material determines a drop in mechanical performances due to a less accurate deposition. A higher percentage of recycled material determines a sharp decrease in viscosity, leading to a more homogeneous layer and tensile properties similar to those of the virgin polymer. The drop in viscosity also affects the accuracy of deposition, determining a worse definition of sharp edges

Editorial: Electrospinning of Bioinspired Materials and Structures for Bioengineering and Advanced Biomedical Applications

The Research Topic “Electrospinning of Bioinspired Materials and Structures for Bioengineering and Advanced Biomedical Applications” includes submissions that relate to the “Biomaterials” and “Bionics and Biomimetics” sections of Frontiers in Bioengineering and Biotechnology. The collection aims to provide an overview of how electrospinning, inspired by nature, can reproduce the hierarchical structure and biomechanical properties of biological tissues, ranging from the nanoscale to the macroscale. The development of such innovative nanofibrous structures requires the improvement of both functionalization and biofabrication strategies, to enhance the scaffold bioactivity and to drive cells in the regeneration of the extracellular matrix (ECM) of the target tissues of interest. Recent technological advances have given rise to the availability of intelligent and smart biomaterials for the regeneration of innovative procedures for manufacturing nanometric structures, and methods for assembling multiscale hierarchical structures. Furthermore, imaging has improved considerably in the last few years, allowing multimodal imaging with nanometric resolution

Hierarchical fibrous structures for muscle-inspired soft-actuators:A review

Inspired by Nature, one of the most ambitious challenge in soft robotics is to design actuators capable of reaching performances comparable to the skeletal muscles. Considering the perfectly balanced features of natural muscular tissue in terms of linear contraction, force‐to‐weight ratio, scalability and morphology, scientists have been working for many years on mimicking this structure. Focusing on the biomimicry, this review investigates the state‐of‐the‐art of synthetic fibrous, muscle‐inspired actuators that, aiming to enhance their mechanical performances, are hierarchically designed from the nanoscale up to the macroscale. In particular, this review focuses on those hierarchical fibrous actuators that enhance their biomimicry employing a linear contraction strategy, closely resembling the skeletal muscles actuation system. The literature analysis shows that bioinspired artificial muscles, developed up to now, only in part comply with skeletal ones. The manipulation and control of the matter at the nanoscale allows to realize ordered structures, such as nanofibers, used as elemental actuators characterized by high strains but moderate force levels. Moreover, it can be foreseen that scaling up the nanostructured materials into micro‐ and macroscale hierarchical structures, it is possible to realize linear actuators characterized by suitable levels of force and displacement

Soft composite actuators of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene)-based nanofibers and polydimethylsiloxane:Fabrication, electromechanical characterization, and dynamic modeling

Nanofibrous unimorph cantilever beam soft actuators offer remarkable advantages, such as rapid viscoelastic relaxation, low power consumption, and high weight-specific properties. However, the presence of high porosity in the nanofibrous active layer poses a challenge due to its low breakdown voltage, limiting the practical applications of this class of soft actuators. This study proposes an innovative solution to enhance the relative permittivity of the nanofibrous layer by redesigning it as a composite layer. By integrating electrospun aligned nanofibers of poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethylene) into a polydimethylsiloxane elastomeric matrix, the composite active layer achieves a notable increase in relative permittivity (10.5 at 100 Hz), surpassing the individual materials' values (2.5 and 2.7 at 100 Hz for the nanofibers and polydimethylsiloxane, respectively). To realize novel soft actuators, the composite active layer is placed between carbon black electrodes, with Kapton® serving as the passive layer. Remarkably, aligning the nanofibers in the transversal direction of the actuator enhances its actuation capabilities significantly. When subjected to a 25 MVm−1 electric field, the tip deflection and blocking force exhibit a ∼400% improvement compared to polydimethylsiloxane-based actuators. To support these findings, a physics-based dynamic model is derived and validated through experimental tests in both static and transient time simulations

Environmental drawbacks of lightweight design algorithms in material extrusion additive manufacturing: a case study

Lightweight design is often assumed to be the leading strategy to improve the sustainability of parts produced by additive manufacturing. The present study confutes such an assumption by a cradle-to-gate life cycle assessment of different lightweight strategies applied to a specific case study in the medical field. In particular, a patient-specific finger splint made of polyamide is redesigned by means of generative design, topology optimization and lattice structures. The analysis investigates two markedly different deposition processes, namely Arburg plastic freeforming and fused filament fabrication. The former is carried out on an industrial-grade machine, while a desktop printer is used for the latter. This allows for observing the impact of the redesign in two quite distinct scenarios. Findings demonstrate that, since environmental impacts are mainly driven by building time, the adoption of automated design algorithms can be detrimental to the sustainability of the process. On the other hand, relevant benefits on environmental impacts were achieved by reducing the infill percentage of parts. The results of this work highlight the most relevant aspects which must be considered to limit environmental impacts when designing parts for deposition-based additive manufacturing. This information can be used by designers to drive weight reduction towards sustainability