Three-Dimensional Printed Polyamide 12 (PA12) and Polylactic Acid (PLA) Alumina (Al2O3) Nanocomposites with Significantly Enhanced Tensile, Flexural, and Impact Properties

The effect of aluminum oxide (Al₂O₃) nanoparticles (NPs) as a reinforcing agent of Polyamide 12 (PA12) and Polylactic acid (PLA) in fused filament fabrication (FFF) three-dimensional printing (3DP) is reported herein for the first time. Alumina NPs are incorporated via a melt-mixing compounding process, at four different filler loadings. Neat as well as nanocomposite 3DP filaments are prepared as feedstock for the 3DP manufacturing of specimens which are thoroughly investigated for their mechanical properties. Thermogravimetric analyses (TGA) and Raman spectroscopy (RS) proved the nature of the materials. Their morphological characteristics were thoroughly investigated with scanning electron and atomic force microscopy. Al₂O₃ NPs exhibited a positive reinforcement mechanism at all filler loadings, while the mechanical percolation threshold with the maximum increase of performance was found between 1.0-2.0 wt.% filler loading (1.0 wt.% for PA12, 41.1%, and 56.4% increase in strength and modulus, respectively; 2.0 wt.% for PLA, 40.2%, and 27.1% increase in strength and modulus, respectively). The combination of 3DP and polymer engineering using nanocomposite PA12 and PLA filaments with low-cost filler additives, e.g., Al₂O₃ NPs, could open new avenues towards a series of potential applications using thermoplastic engineering polymers in FFF 3DP manufacturing.

Printed Single-Wall Carbon Nanotube-Based Joule Heating Devices Integrated as Functional Laminae in Advanced Composites

This work reports the design and fabrication of novel printed single-wall carbon nanotube (SWCNT) electrothermal Joule heating devices. The devices are directly deposited on unidirectional (UD) glass fiber (GF) fabrics. The GF-SWCNT Joule heaters were integrated during manufacturing as "system" plies in carbon fiber reinforced polymer (CFRP) composite laminates. Specific secondary functions were imparted on the composite laminate endowing thus a multifunctional character. The efficient out-of-oven curing (OOC) of a CFRP laminate was demonstrated using a sandwich configuration comprising top/bottom GF-SWCNT system plies. A total power consumption of ca. 10.5 kWh for the efficient polymerization of the thermoset matrix was required. Infrared thermography (IR-T) monitoring showed a uniform and stable temperature field before and after impregnation with epoxy resin. Quasi-static three-point bending and dynamic mechanical analysis (DMA) revealed a minor knock-down effect of the OOC-CFRP laminates properties compared to oven cured CFRPs, whereas the glass transition temperature (T_g) was almost identical. The OOC-CFRP laminates were efficient in providing additional functions such as deicing and self-sensing that are highly sought in the energy and transport sectors, i.e., wind turbine blades or aircraft wings. The novel modular design provides unique opportunities for large-area applications via multiple interconnected arrays of printed devices.

Advanced Glass Fiber Polymer Composite Laminate Operating as a Thermoelectric Generator: A Structural Device for Micropower Generation and Potential Large-Scale Thermal Energy Harvesting

This study demonstrates for the first time a structural glass fiber-reinforced polymer (GFRP) composite laminate with efficient thermal energy harvesting properties as a thermoelectric generator (TEG). This TEG laminate was fabricated by stacking unidirectional glass fiber (GF) laminae coated with p- and n-type single-wall carbon nanotube (SWCNT) inks via a blade coating technique. According to their thermoelectric (TE) response, the p- and n-type GF-SWCNT fabrics exhibited Seebeck coefficients of +23 and -29 μV/K with 60 and 118 μW/m·K² power factor values, respectively. The in-series p-n interconnection of the TE-enabled GF-SWCNT fabrics and their subsequent impregnation with epoxy resin effectively generated an electrical power output of 2.2 μW directly from a 16-ply GFRP TEG laminate exposed to a temperature difference (ΔT) of 100 K. Both experimental and modeling work validated the TE performance. The structural integrity of the multifunctional GFRP was tested by three-point bending coupled with online monitoring of the steady-state TE current (I_sc) at a ΔΤ of 80 K. I_sc was found to closely follow all transitions and discontinuities related to structural damage in the stress/strain curve, thus showing its potential to serve the functions of power generation and damage monitoring.

Enhanced Mechanical, Thermal and Antimicrobial Properties of Additively Manufactured Polylactic Acid with Optimized Nano Silica Content

The scope of this work was to create, with melt mixing compounding process, novel nanocomposite filaments with enhanced properties that industry can benefit from, using commercially available materials, to enhance the performance of three-dimensional (3D) printed structures fabricated via fused filament fabrication (FFF) process. Silicon Dioxide (SiO₂) nanoparticles (NPs) were selected as fillers for a polylactic acid (PLA) thermoplastic matrix at various weight % (wt.%) concentrations, namely, 0.5, 1.0, 2.0 and 4.0 wt.%. Tensile, flexural and impact test specimens were 3D printed and tested according to international standards and their Vickers microhardness was also examined. It was proven that SiO₂ filler enhanced the overall strength at concentrations up to 1 wt.%, compared to pure PLA. Atomic force microscopy (AFM) was employed to investigate the produced nanocomposite extruded filaments roughness. Raman spectroscopy was performed for the 3D printed nanocomposites to verify the polymer nanocomposite structure, while thermogravimetric analysis (TGA) revealed the 3D printed samples' thermal stability. Scanning electron microscopy (SEM) was carried out for the interlayer fusion and fractography morphological characterization of the specimens. Finally, the antibacterial properties of the produced nanocomposites were investigated with a screening process, to evaluate their performance against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).

High-Power All-Carbon Fully Printed and Wearable SWCNT-Based Organic Thermoelectric Generator

In this study, we introduce the fabrication process of a highly efficient fully printed all-carbon organic thermoelectric generator (OTEG) free of metallic junctions with outstanding flexibility and exceptional power output, which can be conveniently and rapidly prepared through ink dispensing/printing processes of aqueous and low-cost CNT inks with a mask-assisted specified circuit architecture. The optimal p-type and n-type films produced exhibit ultrahigh power factors (PFs) of 308 and 258 μW/mK², respectively, at ΔΤ = 150 K (T_HOT = 175 °C) and outstanding stability in air without encapsulation, providing the OTEG device the ability to operate at high temperatures up to 200 °C at ambient conditions (1 atm, relative humidity: 50 ± 5% RH). We have successfully designed and fabricated the flexible thermoelectric (TE) modules with superior TE properties of p-type and n-type SWCNT films resulting in exceptionally high performance. The novel design OTEG exhibits outstanding flexibility and stability with attained TE values among the highest ever reported in the field of organic thermoelectrics, that is, open-circuit voltage V_OC = 1.05 V and short-circuit current I_SC = 1.30 mA at ΔT = 150 K (T_HOT = 175 °C) with an internal resistance of R_TEG = 806 Ω, generating a 342 μW power output. It is also worth noting the remarkable PFs of 145 and 127 μW/mK² for the p-type and n-type films, respectively, at room temperature. The fabricated device is highly scalable, providing opportunities for printable large-scale manufacturing/industrial production of highly efficient flexible OTEGs.

Sustainable Additive Manufacturing: Mechanical Response of Polyethylene Terephthalate Glycol over Multiple Recycling Processes

The continuous demand for thermoplastic polymers in a great variety of applications, combined with an urgent need to minimize the quantity of waste for a balanced energy-from-waste strategy, has led to increasing scientific interest in developing new recycling processes for plastic products. Glycol-modified polyethylene terephthalate (PETG) is known to have some enhanced properties as compared to polyethylene terephthalate (PET) homopolymer; this has recently attracted the interest from the fused filament fabrication (FFF) three-dimensional (3D) printing community. PET has shown a reduced ability for repeated recycling through traditional processes. Herein, we demonstrate the potential for using recycled PETG in consecutive 3D printing manufacturing processes. Distributed recycling additive manufacturing (DRAM)-oriented equipment was chosen in order to test the mechanical and thermal response of PETG material in continuous recycling processes. Tensile, flexure, impact strength, and Vickers micro-hardness tests were carried out for six (6) cycles of recycling. Finally, Raman spectroscopy as well as thermal and morphological analyses via scanning electron microscopy (SEM) fractography were carried out. In general, the results revealed a minor knockdown effect on the mechanical properties as well as the thermal properties of PETG following the process proposed herein, even after six rounds of recycling.

Sustainable Additive Manufacturing: Mechanical Response of Polyamide 12 over Multiple Recycling Processes

Plastic waste reduction and recycling through circular use has been critical nowadays, since there is an increasing demand for the production of plastic components based on different polymeric matrices in various applications. The most commonly used recycling procedure, especially for thermoplastic materials, is based on thermomechanical process protocols that could significantly alter the polymers’ macromolecular structure and physicochemical properties. The study at hand focuses on recycling of polyamide 12 (PA12) filament, through extrusion melting over multiple recycling courses, giving insight for its effect on the mechanical and thermal properties of Fused Filament Fabrication (FFF) manufactured specimens throughout the recycling courses. Three-dimensional (3D) FFF printed specimens were produced from virgin as well as recycled PA12 filament, while they have been experimentally tested further for their tensile, flexural, impact and micro-hardness mechanical properties. A thorough thermal and morphological analysis was also performed on all the 3D printed samples. The results of this study demonstrate that PA12 can be successfully recycled for a certain number of courses and could be utilized in 3D printing, while exhibiting improved mechanical properties when compared to virgin material for a certain number of recycling repetitions. From this work, it can be deduced that PA12 can be a viable option for circular use and 3D printing, offering an overall positive impact on recycling, while realizing 3D printed components using recycled filaments with enhanced mechanical and thermal stability.

Decoration of SiO2 and Fe3O4 Nanoparticles onto the Surface of MWCNT-Grafted Glass Fibers: A Simple Approach for the Creation of Binary Nanoparticle Hierarchical and Multifunctional Composite Interphases

We report on a versatile method for chemically grafting multiwalled carbon nanotubes (MWCNTs) onto the surface of conventional glass fibers (GFs), as well as depositing further silica (SiO2) or superparamagnetic (SPM) magnetite (Fe3O4) nanoparticles (NPs) creating novel hierarchical reinforcements. The CNT-grafted GFs (GF-CNT) were utilized further as the support to decorate nano-sized SiO2 or Fe3O4 via electrostatic interactions, resulting finally into double hierarchy reinforcements. SiO2 NPs were first used as model nano-particulate objects to investigate the interfacial adhesion properties of binary coated GFs (denoted as GF-CNT/SiO2) in epoxy matrix via single fiber pull-out (SFPO) tests. The results indicated that the apparent interfacial shear strength (IFSS or τapp) was significantly increased compared to the GF-CNT. Fe3O4 NPs were assembled also onto CNT-grafted GFs resulting into GF-CNT/Fe3O4. The fibers exhibited a magnetic response upon being exposed to an external magnet. Scanning electron microscopy (SEM) revealed the surface morphologies of the different hierarchical fibers fabricated in this work. The interphase microstructure of GF-CNT and GF-CNT/SiO2 embedded in epoxy was investigated by transmission electron microscopy (TEM). The hybrid and hierarchical GFs are promising multifunctional reinforcements with appr. 85% increase of the IFSS as compared to typical amino-silane modified GFs. It could be envisaged that, among other purposes, GF-CNT/Fe3O4 could be potentially recyclable reinforcements, especially when embedded in thermoplastic polymer matrices.

Three-Dimensional Printed Antimicrobial Objects of Polylactic Acid (PLA)-Silver Nanoparticle Nanocomposite Filaments Produced by an In-Situ Reduction Reactive Melt Mixing Process

In this study, an industrially scalable method is reported for the fabrication of polylactic acid (PLA)/silver nanoparticle (AgNP) nanocomposite filaments by an in-situ reduction reactive melt mixing method. The PLA/AgNP nanocomposite filaments have been produced initially reducing silver ions (Ag⁺) arising from silver nitrate (AgNO₃) precursor mixed in the polymer melt to elemental silver (Ag⁰) nanoparticles, utilizing polyethylene glycol (PEG) or polyvinyl pyrrolidone (PVP), respectively, as macromolecular blend compound reducing agents. PEG and PVP were added at various concentrations, to the PLA matrix. The PLA/AgNP filaments have been used to manufacture 3D printed antimicrobial (AM) parts by Fused Filament Fabrication (FFF). The 3D printed PLA/AgNP parts exhibited significant AM properties examined by the reduction in Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria viability (%) experiments at 30, 60, and 120 min duration of contact (p < 0.05; p-value (p): probability). It could be envisaged that the 3D printed parts manufactured and tested herein mimic nature’s mechanism against bacteria and in terms of antimicrobial properties, contact angle for their anti-adhesive behavior and mechanical properties could create new avenues for the next generation of low-cost and on-demand additive manufacturing produced personal protective equipment (PPE) as well as healthcare and nosocomial antimicrobial equipment.

Mechanical Properties of 3D-Printed Acrylonitrile-Butadiene-Styrene TiO2 and ATO Nanocomposites

In order to enhance the mechanical performance of three-dimensional (3D) printed structures fabricated via commercially available fused filament fabrication (FFF) 3D printers, novel nanocomposite filaments were produced herein following a melt mixing process, and further 3D printed and characterized. Titanium Dioxide (TiO₂) and Antimony (Sb) doped Tin Oxide (SnO₂) nanoparticles (NPs), hereafter denoted as ATO, were selected as fillers for a polymeric acrylonitrile butadiene styrene (ABS) thermoplastic matrix at various weight % (wt%) concentrations. Tensile and flexural test specimens were 3D printed, according to international standards. It was proven that TiO₂ filler enhanced the overall tensile strength by 7%, the flexure strength by 12%, and the micro-hardness by 6%, while for the ATO filler, the corresponding values were 9%, 13%, and 6% respectively, compared to unfilled ABS. Atomic force microscopy (AFM) revealed the size of TiO₂ (40 ± 10 nm) and ATO (52 ± 11 nm) NPs. Raman spectroscopy was performed for the TiO₂ and ATO NPs as well as for the 3D printed nanocomposites to verify the polymer structure and the incorporated TiO₂ and ATO nanocrystallites in the polymer matrix. The scope of this work was to fabricate novel nanocomposite filaments using commercially available materials with enhanced overall mechanical properties that industry can benefit from.

Three-Dimensional (3D) Conductive Network of CNT-Modified Short Jute Fiber-Reinforced Natural Rubber: Hierarchical CNT-Enabled Thermoelectric and Electrically Conductive Composite Interfaces

Jute fibers (JFs) coated with multiwall carbon nanotubes (MWCNTs) have been introduced in a natural rubber (NR) matrix creating a three-dimensional (3D) electrically conductive percolated network. The JF-CNT endowed electrical conductivity and thermoelectric properties to the final composites. CNT networks fully covered the fiber surfaces as shown by the corresponding scanning electron microscopy (SEM) analysis. NR/JF-CNT composites, at 10, 20 and 30 phr (parts per hundred gram of rubber) have been manufactured using a two-roll mixing process. The highest value of electrical conductivity (σ) was 81 S/m for the 30 phr composite. Thermoelectric measurements revealed slight differences in the Seebeck coefficient (S), while the highest power factor (PF) was 1.80 × 10⁻² μW/m K⁻² for the 30 phr loading. The micromechanical properties and electrical response of the composite’s conductive interface have been studied in peak force tapping quantitative nanomechanical (PFT QNM) and conductive atomic force microscopy (c-AFM) mode. The JF-CNT create an electrically percolated network at all fiber loadings endowing electrical and thermoelectric properties to the NR matrix, considered thus as promising thermoelectric stretchable materials.

Three-Dimensional Printed Polylactic Acid (PLA) Surgical Retractors with Sonochemically Immobilized Silver Nanoparticles: The Next Generation of Low-Cost Antimicrobial Surgery Equipment

A versatile method is reported for the manufacturing of antimicrobial (AM) surgery equipment utilising fused deposition modelling (FDM), three-dimensional (3D) printing and sonochemistry thin-film deposition technology. A surgical retractor was replicated from a commercial polylactic acid (PLA) thermoplastic filament, while a thin layer of silver (Ag) nanoparticles (NPs) was developed via a simple and scalable sonochemical deposition method. The PLA retractor covered with Ag NPs (PLA@Ag) exhibited vigorous AM properties examined by a reduction in Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa) and Escherichia coli (E. coli) bacteria viability (%) experiments at 30, 60 and 120 min duration of contact (p < 0.05). Scanning electron microscopy (SEM) showed the surface morphology of bare PLA and PLA@Ag retractor, revealing a homogeneous and full surface coverage of Ag NPs. X-Ray diffraction (XRD) analysis indicated the crystallinity of Ag nanocoating. Ultraviolent-visible (UV-vis) spectroscopy and transmission electron microscopy (TEM) highlighted the AgNP plasmonic optical responses and average particle size of 31.08 ± 6.68 nm. TEM images of the PLA@Ag crossection demonstrated the thickness of the deposited Ag nanolayer, as well as an observed tendency of AgNPs to penetrate though the outer surface of PLA. The combination of 3D printing and sonochemistry technology could open new avenues in the manufacturing of low-cost and on-demand antimicrobial surgery equipment.

Temperature-Controlled Catalysis by Core-Shell-Satellite AuAg@pNIPAM@Ag Hybrid Microgels: A Highly Efficient Catalytic Thermoresponsive Nanoreactor

A novel wet-chemical protocol is reported for the synthesis of "temperature-programmable" catalytic colloids consisting of bimetallic core@shell AuAg nanoparticles encapsulated into poly(N-isopropylacrylamide) (pNIPAM) microgels with silver satellites (AgSTs) incorporated within the microgel structure. Spherical AuNPs of 50 nm in diameter are initially synthesized and used for growing a pNIPAM microgel shell with temperature stimulus response. A silver shell is subsequently grown on the Au core by diffusing Ag salt through the hydrophilic pNIPAM microgel (AuAg@pNIPAM microgel). The use of allylamine as a co-monomer during pNIPAM polymerization facilitates the coordination of Ag⁺ with the NH₂ nitrogen lone pair of electrons, which are reduced to Ag seeds (∼14 nm) using a strong reducing agent, obtaining thus AuAg@pNIPAM@Ag hybrid microgels. The two systems are tested as catalysts toward the reduction of 4-nitrophenol (4-Nip) to 4-aminophenol (4-Amp) by NaBH₄. Both exhibit extremely sensitive temperature-dependent reaction rate constants, with the highest K₁ value of the order of 0.6 L/m² s, which is one of the highest values ever reported. The presence of plasmonic entities is confirmed by UV-vis spectroscopy. Dynamic light scattering proves the temperature responsiveness in all cases. Transmission electron microscopy and energy-dispersive X-ray (EDX) elemental mapping highlight the monodispersity of the synthesized hybrid nanostructured microgels, as well as their size and metallic composition. The amount of gold and silver in both systems is obtained by thermogravimetric analysis and the EDX spectrum. The reduction reaction kinetics is monitored by UV-vis spectroscopy at different temperatures for both catalytic systems, with the AuAg@pNIPAM@Ag microgels showing superior catalytic performance at all temperatures because of the synergistic effect of the AuAg core and the AgSTs. The principal novelty of this study lies in the "hierarchical" design of the metal-polymer-metal core@shell@satellite nanostructured colloids exhibiting synergistic capabilities of the plasmonic NPs for, among others, temperature-controlled catalytic applications.

Three-dimensional printing as an educational tool in colorectal surgery

3D printing is a rapidly advancing technology which represents a significant technological achievement that could be useful in a variety of biomedical applications. In the field of surgery, 3D printing is envisioned as a significant step in the areas of surgical planning, education and training. The 3D printed models are considered as high quality and efficient educational tools. In this paper A randomized controlled trial was performed to compare the educational role of 3D printed models with that of the conventional MRI films in the training of surgical residents. Statistical analysis revealed that Resident surgeons who studied only the anal fistula printed models, (Group B) achieved a higher overall score in the fistula assessment test (87,2 (82,6-91,6)) compared to resident surgeons (Group A) who studied only MRI images (74,85 (66,8-73,5)).  3D printing technology can lead to improvement in preoperative planning accuracy, followed by efficient optimization of the treatment strategy. It is believed that 3D printing technology could be used in the case of various other surgical applications, thus representing a novel tool for surgical education.

Transistor in a tube: A route to three-dimensional bioelectronics

Advances in three-dimensional (3D) cell culture materials and techniques, which more accurately mimic in vivo systems to study biological phenomena, have fostered the development of organ and tissue models. While sophisticated 3D tissues can be generated, technology that can accurately assess the functionality of these complex models in a high-throughput and dynamic manner is not well adapted. Here, we present an organic bioelectronic device based on a conducting polymer scaffold integrated into an electrochemical transistor configuration. This platform supports the dual purpose of enabling 3D cell culture growth and real-time monitoring of the adhesion and growth of cells. We have adapted our system to a 3D tubular geometry facilitating free flow of nutrients, given its relevance in a variety of biological tissues (e.g., vascular, gastrointestinal, and kidney) and processes (e.g., blood flow). This biomimetic transistor in a tube does not require photolithography methods for preparation, allowing facile adaptation to the purpose. We demonstrate that epithelial and fibroblast cells grow readily and form tissue-like architectures within the conducting polymer scaffold that constitutes the channel of the transistor. The process of tissue formation inside the conducting polymer channel gradually modulates the transistor characteristics. Correlating the real-time changes in the steady-state characteristics of the transistor with the growth of the cultured tissue, we extract valuable insights regarding the transients of tissue formation. Our biomimetic platform enabling label-free, dynamic, and in situ measurements illustrates the potential for real-time monitoring of 3D cell culture and compatibility for use in long-term organ-on-chip platforms.

CNT-grafted glass fibers as a smart tool for epoxy cure monitoring, UV-sensing and thermal energy harvesting in model composites

A ‘hierarchical’ reinforcement of glass fibers (GFs) chemically grafted with multiwall carbon nanotubes (MWCNTs) has been utilized for epoxy cure monitoring, UV-sensing, and thermal energy harvesting in model composites.

Oxygen-plasma-modified biomimetic nanofibrous scaffolds for enhanced compatibility of cardiovascular implants

Electrospun nanofibrous scaffolds have been extensively used in several biomedical applications for tissue engineering due to their morphological resemblance to the extracellular matrix (ECM). Especially, there is a need for the cardiovascular implants to exhibit a nanostructured surface that mimics the native endothelium in order to promote endothelialization and to reduce the complications of thrombosis and implant failure. Thus, we herein fabricated poly-ε-caprolactone (PCL) electrospun nanofibrous scaffolds, to serve as coatings for cardiovascular implants and guide tissue regeneration. Oxygen plasma treatment was applied in order to modify the surface chemistry of the scaffold and its effect on cell attachment and growth was evaluated. The conditions of the surface modification were properly adjusted in order to define those conditions of the treatment that result in surfaces favorable for cell growth, while maintaining morphological integrity and mechanical behavior. Goniometry (contact angle measurements), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) measurements were used to evaluate the morphological and chemical changes induced by the plasma treatment. Moreover, depth-sensing nanoindentation was performed to study the resistance of the plasma-treated scaffolds to plastic deformation. Lastly, the cell studies indicated that all scaffolds were cytocompatible, with the plasma-treated ones expressing a more pronounced cell viability and adhesion. All the above findings demonstrate the great potential of these biomimetic tissue-engineering constructs as efficient coatings for enhanced compatibility of cardiovascular implants.

Controlled growth of Ag nanoparticles decorated onto the surface of SiO2 spheres: a nanohybrid system with combined SERS and catalytic properties

A versatile water-method for the controlled growth of Ag nanoparticles deposited onto the surface of SiO₂ spheres is developed. The nanohybrid systems exhibited exceptional SERS and catalytic properties.