Fabrication and Characterization of Graphene-Mesoporous Carbon-Nickel-Poly(Vinyl Alcohol)-Coated Mandrel-Coiled TCPFLNR Artificial Muscle

This study investigates the performance enhancement of mandrel-coiled twisted and coiled polymer fibers with a nichrome heater (TCPFLNR) by coating with a solution of graphene-mesoporous carbon-nickel-polyvinyl alcohol. The coating process involved a one-pot synthesis utilizing graphene powder, Ni nanoparticles, mesoporous carbon, and PVA as a binding agent. The coating was performed by manually shaking the TCPFLNR and the subsequent annealing process, which results in improved thermal conductivity and actuation behavior of the TCPFLNR. Experimental results on a 60 mm long actuator demonstrated significant enhancements in actuation displacement and actuation strain (20% to 42%) under various loads with an input current of 0.27 A/power 2.16 W. The blocked stress is ~10 MPa under this 2.16 W power input and the maximum strain is 48% at optimum load of 1.4 MPa. The observed actuation strain correlated directly with the input power. The coated TCPFLNR exhibited better thermal contacts, facilitating enhanced heat transfer, and reducing power consumption by 6% to 9% compared to non-coated actuators. It was found that the nanomaterial coating helps the TCP actuator to be reliable for more than 75,000 actuation cycles at 0.1 Hz in air due to improved thermal conductivity. These findings highlight the potential for further research to optimize electrothermally operated TCP actuators and unlock advancements in this field.

Recent Advances in the Investigation of Poly(lactic acid) (PLA) Nanocomposites: Incorporation of Various Nanofillers and their Properties and Applications

Poly(lactic acid) (PLA) is considered the most promising biobased substitute for fossil-derived polymers due to its compostability, biocompatibility, renewability, and good thermomechanical properties. However, PLA suffers from several shortcomings, such as low heat distortion temperature, thermal resistance, and rate of crystallization, whereas some other specific properties, i.e., flame retardancy, anti-UV, antibacterial or barrier properties, antistatic to conductive electrical characteristics, etc., are required by different end-use sectors. The addition of different nanofillers represents an attractive way to develop and enhance the properties of neat PLA. Numerous nanofillers with different architectures and properties have been investigated, with satisfactory achievements, in the design of PLA nanocomposites. This review paper overviews the current advances in the synthetic routes of PLA nanocomposites, the imparted properties of each nano-additive, as well as the numerous applications of PLA nanocomposites in various industrial fields.

Exploring the coating of 3D-printed insulating substrates with conductive composites: a simple, cheap and versatile strategy to prepare customized high-performance electrochemical sensors

The development of 3D-printed electrochemical sensors by fused deposition modeling (FDM) has been increasing exponentially in the last five years. In this context, commercial conductive filaments composed of a blend of carbon particles (e.g., graphene or carbon black (CB)) and insulating thermoplastic polymers (e.g., polylactic acid (PLA) or acrylonitrile butadiene styrene (ABS)) have been widely used for electrode fabrication. However, such materials may be expensive and the electrodes when used "as-printed" exhibit poor electrochemical performance as a function of the low content of conductive particles in the composition (∼10 to 20 wt%), which requires one or more post-treatment steps (e.g. polishing, chemical, electrochemical, and photochemical) to reach good electrochemical performance. In this technical note a less used approach to produce "ready-to-use" electrochemical platforms based on 3D printing is explored, which consists of the coating of 3D-printed insulating substrates with homemade conductive composites. To demonstrate the potentiality of this alternative protocol, 3D-printed ABS insulating substrates at two geometries were coated in a highly loaded graphite (55 wt%) homemade composite (G-ABS) and evaluated for the detection of the ferri/ferrocyanide redox probe and model analytes in stationary and hydrodynamic 3D-printed systems (nitrite in micro-flow injection analysis/μFIA and paracetamol in batch injection analysis/BIA, respectively). The analytical parameters acquired with the coated electrodes were comparable to those obtained using conventional electrodes (glassy carbon, boron-doped diamond and carbon screen-printed) and 3D-printed sensors fabricated with commercial filaments. Moreover, the inclusion of carbon black in the fluid conductive composite was demonstrated as a perspective to obtain modified coated 3D-printed surfaces easily for the first time. This alternative "do it yourself" strategy is promising for the large-scale production of very cheap (US$ 0.08) and high-performance electrodes based on FDM 3D printing. Moreover, this approach dispenses the acquisition of commercial conductive filaments and the laborious development of homemade filaments.

Bonding and Strengthening the PLA Biopolymer in Multi-Material Additive Manufacturing

3D printing is a revolutionary additive manufacturing method that enables rapid prototyping and design flexibility. A variety of thermoplastic polymers can be used in printing. As it is necessary to reduce the consumption of petrochemical resources, alternative solutions are being researched, and the interest in using bioplastics and biocomposites is constantly growing. Often, however, the properties of biopolymers are insufficient and need to be improved to compete with petroleum-based plastics. The paper aims to analyze the available information on elements produced from more than one material, with additive manufacturing resulting from 3D printing using biopolymer Polylactic Acid (PLA). The study notes the possibility of modifying and improving the properties of PLA using layered printing or by modifying PLA filaments. Several modifications improving and changing the properties of PLA were also noted, including printing parameters when combined with other materials: process temperatures, filling, and surface development for various sample geometries.

A Novel Manufacturing Concept of LCP Fiber-Reinforced GPET-Based Sandwich Structures with an FDM 3D-Printed Core

The presented research was focused on the development of a new method of sandwich structure manufacturing involving FDM-printing (fused deposition modeling) techniques and compression molding. The presented concept allows for the preparation of thermoplastic-based composites with enhanced mechanical properties. The sample preparation process consists of 3D printing the sandwich's core structure using the FDM method. For comparison purposes, we used two types of GPET (copolymer of polyethylene terephthalate)-based filaments, pure resin, and carbon fiber (CF)-reinforced filaments. The outer reinforcing layer "skins" of the sandwich structure were prepared from the compression molded prepregs made from the LCP (liquid-crystal polymer)-fiber fabric with the GPET-based matrix. The final product consisting of an FDM-printed core and LCP-based prepreg was prepared using the compression molding method. The prepared samples were subjected to detailed materials analyses, including thermal analyses (thermogravimetry-TGA, differencial scanning calorimetry-DSC, and dynamic thermal-mechanical analysis-DMTA) and mechanical tests (tensile, flexural, and impact). As indicated by the static test results, the modulus and strength of the prepared composites were slightly improved; however, the stiffness of the prepared materials was more related to the presence of the CF-reinforced filament than the presence of the composite prepreg. The main advantage of using the developed method is revealed during impact tests. Due to the presence of long LCP fibers, the prepared sandwich samples are characterized by very high impact resistance. The impact strength increased from 1.7 kJ/m² for pure GPET samples to 50.4 kJ/m² for sandwich composites. For GPET/CF samples, the increase is even greater. The advantages of the developed solution were illustrated during puncture tests in which none of the sandwich samples were pierced.

Specific Heat Capacity and Thermal Conductivity Measurements of PLA-Based 3D-Printed Parts with Milled Carbon Fiber Reinforcement

This research focuses on the thermal characterization of 3D-printed parts obtained via fused filament fabrication (FFF) technology, which uses a poly(lactic acid) (PLA)-based filament filled with milled carbon fibers (MCF) from pyrolysis at different percentages by weight (10, 20, 30 wt%). Differential scanning calorimetry (DSC) and thermal conductivity measurements were used to evaluate the thermal characteristics, morphological features, and heat transport behavior of the printed specimens. The experimental results showed that the addition of MCF to the PLA matrix improved the conductive properties. Scanning electron microscopy (SEM) micrographs were used to obtain further information about the porosity of the systems.

Electrochemical (Bio)Sensors Enabled by Fused Deposition Modeling-Based 3D Printing: A Guide to Selecting Designs, Printing Parameters, and Post-Treatment Protocols

The 3D printing (or additive manufacturing, AM) technology is capable to provide a quick and easy production of objects with freedom of design, reducing waste generation. Among the AM techniques, fused deposition modeling (FDM) has been highlighted due to its affordability, scalability, and possibility of processing an extensive range of materials (thermoplastics, composites, biobased materials, etc.). The possibility of obtaining electrochemical cells, arrays, pieces, and more recently, electrodes, exactly according to the demand, in varied shapes and sizes, and employing the desired materials has made from 3D printing technology an indispensable tool in electroanalysis. In this regard, the obtention of an FDM 3D printer has great advantages for electroanalytical laboratories, and its use is relatively simple. Some care has to be taken to aid the user to take advantage of the great potential of this technology, avoiding problems such as solution leakages, very common in 3D printed cells, providing well-sealed objects, with high quality. In this sense, herein, we present a complete protocol regarding the use of FDM 3D printers for the fabrication of complete electrochemical systems, including (bio)sensors, and how to improve the quality of the obtained systems. A guide from the initial printing stages, regarding the design and structure obtention, to the final application, including the improvement of obtained 3D printed electrodes for different purposes, is provided here. Thus, this protocol can provide great perspectives and alternatives for 3D printing in electroanalysis and aid the user to understand and solve several problems with the use of this technology in this field.

Development and Characterization of 3D Printed Multifunctional Bioscaffolds Based on PLA/PCL/HAp/BaTiO3 Composites

Bone substitute materials are placed in bone defects and play an important role in bone regeneration and fracture healing. The main objective of the present research is fabrication through the technique of 3D printing and the characterization of innovative composite bone scaffolds composed of polylactic acid (PLA), poly (ε-caprolactone) (PCL) while hydroxyapatite (HAp), and/or barium titanate (BaTiO3—BT) used as fillers. Composite filaments were prepared using a single screw melt extruder, and finally, 3D composite scaffolds were fabricated using the fused deposition modeling (FDM) technique. Scanning electron microscopy (SEM) images showed a satisfactory distribution of the fillers into the filaments and the printed objects. Furthermore, differential scanning calorimetry (DSC) measurements revealed that PLA/PCL filaments exhibit lower glass transition and melting point temperatures than the pure PLA filaments. Finally, piezoelectric and dielectric measurements of the 3D objects showed that composite PLA/PCL scaffolds containing HAp and BT exhibited piezoelectric coefficient (d33) values close to the human bone and high dielectric permittivity values.

Extrusion-Based 3D Printing Applications of PLA Composites: A Review

Polylactic acid (PLA) is the most widely used raw material in extrusion-based three-dimensional (3D) printing (fused deposition modeling, FDM approach) in many areas since it is biodegradable and environmentally friendly, however its utilization is limited due to some of its disadvantages such as mechanical weakness, water solubility rate, etc. FDM is a simple and more cost-effective fabrication process compared to other 3D printing techniques. Unfortunately, there are deficiencies of the FDM approach, such as mechanical weakness of the FDM parts compared to the parts produced by the conventional injection and compression molding methods. Preparation of PLA composites with suitable additives is the most useful technique to improve the properties of the 3D-printed PLA parts obtained by the FDM method. In the last decade, newly developed PLA composites find large usage areas both in academic and industrial circles. This review focuses on the chemistry and properties of pure PLA and also the preparation methods of the PLA composites which will be used as a raw material in 3D printers. The main drawbacks of the pure PLA filaments and the necessity for the preparation of PLA composites which will be employed in the FDM-based 3D printing applications is also discussed in the first part. The current methods to obtain PLA composites as raw materials to be used as filaments in the extrusion-based 3D printing are given in the second part. The applications of the novel PLA composites by utilizing the FDM-based 3D printing technology in the fields of biomedical, tissue engineering, human bone repair, antibacterial, bioprinting, electrical conductivity, electromagnetic, sensor, battery, automotive, aviation, four-dimensional (4D) printing, smart textile, environmental, and luminescence applications are presented and critically discussed in the third part of this review.