Evaluating the Piezoelectric Energy Harvesting Potential of 3D-Printed Graphene Prepared Using Direct Ink Writing and Fused Deposition Modelling.

This research aims to use energy harvested from conductive materials to power microelectronic components. The proposed method involves using vibration-based energy harvesting to increase the natural vibration frequency, reduce the need for battery replacement, and minimise chemical waste. Piezoelectric transduction, known for its high-power density and ease of application, has garnered significant attention. Additionally, graphene, a non-piezoelectric material, exhibits good piezoelectric properties. The research explores a novel method of printing graphene material using 3D printing, specifically Direct Ink Writing (DIW) and fused deposition modelling (FDM). Both simulation and experimental techniques were used to analyse energy harvesting. The experimental technique involved using the cantilever beam-based vibration energy harvesting method. The results showed that the DIW-derived 3D-printed prototype achieved a peak power output of 12.2 µW, surpassing the 6.4 µW output of the FDM-derived 3D-printed prototype. Furthermore, the simulation using COMSOL Multiphysics yielded a harvested output of 0.69 µV.

Development of hybrid polyvinylpyrrolidone/carboxymethyl cellulose/collagen incorporated oregano scaffolds via direct ink write printing for potential wound healing applications.

Additive manufacturing can develop regenerative scaffolds for wound healing. 3D printing offers meticulous porosity, mechanical integrity, cell adhesion and cost-effectiveness. Herein, we prepared ink composed of carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), collagen, and oregano extract for the fabrication of tissue constructs. The blend was optimized to form a homogeneous ink and rheological characterization demonstrated shear thinning behavior. The scaffolds were printed using Direct Ink Write (DIW) at a flow speed of 4 mm3/s and a layer height of 0.18 mm. The fabricated scaffolds demonstrated an ultimate tensile strength (UTS) and toughness of 730 KPa and 2.72 MJ/m3, respectively. Scanning Electron Microscopy (SEM) revealed an average pore size of 300 ± 30 µm. Fourier transform infrared spectroscopy (FTIR) analysis confirmed that all materials were present. The contact angle of the composite scaffold was 68° ± 1°. Moreover, the scaffolds presented 82 % mass loss (degradation) in phosphate buffer saline (PBS) over 14 days. The composite scaffold exhibited inhibition zones of 9 mm and 12 mm against Staphylococcus aureus and Escherichia coli, respectively. The PVP/CMC/collagen/oregano 3D printed scaffolds exhibited excellent biocompatibility with the mesenchymal stem cells and humman dermal fibroblast cells, confirmed by water-soluble tetrazolium - 8 (WST-8) assay (test conducted for 7 days). The enhanced angiogenic potential of said scaffold was assesed by release of vascular endothelial growth factor followed by further validation through in-vivo CAM assay. Thus, confirming suitability for the potential wound healing application.

Three-Dimensional Printing of Yttrium Oxide Transparent Ceramics via Direct Ink Writing.

The utilization of 3D printing technology for the fabrication of intricate transparent ceramics overcomes the limitations associated with conventional molding processes, thereby presenting a highly promising solution. In this study, we employed direct ink writing (DIW) to prepare yttrium oxide transparent ceramics using a ceramic slurry with excellent moldability, solid content of 45 vol%, and shear-thinning behavior. A successfully printed transparent yttrium oxide ring measuring 30 mm in diameter, 10 mm in inner diameter, and 0.9 mm in thickness was obtained from the aforementioned slurry. After de-binding and sintering procedures, the printed ceramic exhibited in-line transmittance of 71% at 850 nm. This work not only produced complex yttria transparent ceramics with intricate shapes, but also achieved in-line transmittance that was comparable to that of the CIP method (79%), which can meet certain optical applications.

Chitosan-based electroconductive inks without chemical reaction for cost-effective and versatile 3D printing for electromagnetic interference (EMI) shielding and strain-sensing applications.

The burgeoning interest in biopolymer 3D printing arises from its capacity to meticulously engineer tailored, intricate structures, driven by the intrinsic benefits of biopolymers-renewability, chemical functionality, and biosafety. Nevertheless, the accessibility of economical and versatile 3D-printable biopolymer-based inks remains highly constrained. This study introduces an electroconductive ink for direct-ink-writing (DIW) 3D printing, distinguished by its straightforward preparation and commendable printability and material properties. The ink relies on chitosan as a binder, carbon fibers (CF) a low-cost electroactive filler, and silk fibroin (SF) a structural stabilizer. Freeform 3D printing manifests designated patterns of electroconductive strips embedded in an elastomer, actualizing effective strain sensors. The ink's high printability is demonstrated by printing complex geometries with porous, hollow, and overhanging structures without chemical or photoinitiated reactions or support baths. The composite is lightweight (density 0.29 ± 0.01 g/cm3), electroconductive (2.64 ± 0.06 S/cm), and inexpensive (20 USD/kg), with tensile strength of 20.77 ± 0.60 MPa and Young's modulus of 3.92 ± 0.06 GPa. 3D-printed structures exhibited outstanding electromagnetic interference (EMI) shielding effectiveness of 30-31 dB, with shielding of >99.9 % incident electromagnetic waves, showcasing significant electronic application potential. Thus, this study presents a novel, easily prepared, and highly effective biopolymer-based ink poised to advance the landscape of 3D printing technologies.

3D-printed polyether-ether ketone/carboxymethyl cellulose scaffolds coated with Zn-Mn doped mesoporous bioactive glass nanoparticles.

Patient-specific fabrication of scaffold/implant requires an engineering approach to manufacture the ideal scaffold. Herein, we design and 3D print scaffolds comprised of polyether-ether-ketone (PEEK) and sodium-carboxymethyl cellulose (Na-CMC). The fabricated scaffold was dip coated with Zn and Mn doped bioactive glass nanoparticles (Zn-Mn MBGNs). The synthesized ink exhibit suitable shear-thinning behavior for direct ink write (DIW) 3D printing. The scaffolds were crafted with precision, featuring 85% porosity, 0.3 mm layer height, and 1.5 mm/s printing speed at room temperature. Scanning electron microscopy images reveal a well-defined scaffold with an average pore size of 600 ± 30 µm. The energy dispersive X-ray spectroscopy analysis confirmed a well dispersed/uniform coating of Zn-Mn MBGNs on the PEEK/Na-CMC scaffold. Fourier transform infrared spectroscopy approved the presence of PEEK, CMC, and Zn-Mn MBGNs. The tensile test revealed a Young's modulus of 2.05 GPa. Antibacterial assays demonstrate inhibition zone against Staphylococcus aureus and Escherichia Coli strains. Chick Chorioallantoic Membrane assays also present significant angiogenesis potential, owing to the antigenic nature of Zn-Mn MBGNs. WST-8 cell viability assays depicted cell proliferation, with a 103% viability after 7 days of culture. This study suggests that the PEEK/Na-CMC scaffolds coated with Zn-Mn MBGNs are an excellent candidate for osteoporotic fracture treatment. Thus, the fabricated scaffold can offer multifaceted properties for enhanced patient outcomes in the bone tissue regeneration.

Enhancing Electrical Conductivity of Stretchable Liquid Metal-Silver Composites through Direct Ink Writing.

Structure-property-process relationships are a controlling factor in the performance of materials. This offers opportunities in emerging areas, such as stretchable conductors, to control process conditions during printing to enhance performance. Herein, by systematically tuning direct ink write (DIW) process parameters, the electrical conductivity of multiphase liquid metal (LM)-silver stretchable conductors is increased by a maximum of 400% to over 1.06 × 106 S·m-1. This is achieved by modulating the DIW print velocity, which enables the in situ elongation, coalescence, and percolation of these multiphase inclusions during printing. These DIW printed filaments are conductive as fabricated and are soft (modulus as low as 1.1 MPa), stretchable (strain limit >800%), and show strain invariant conductivity up to 80% strain. These capabilities are demonstrated through a set of electromagnetic induction coils that can transfer power wirelessly through air and water, even under deformation. This work provides a methodology to program properties in stretchable conductors, where the combination of material composition and process parameters leads to greatly enhanced performance. This approach can find use in applications such as soft robots, soft electronics, and printed materials for deformable, yet highly functional devices.

Embedded Sensors with 3D Printing Technology: Review.

Embedded sensors (ESs) are used in smart materials to enable continuous and permanent measurements of their structural integrity, while sensing technology involves developing sensors, sensory systems, or smart materials that monitor a wide range of properties of materials. Incorporating 3D-printed sensors into hosting structures has grown in popularity because of improved assembly processes, reduced system complexity, and lower fabrication costs. 3D-printed sensors can be embedded into structures and attached to surfaces through two methods: attaching to surfaces or embedding in 3D-printed sensors. We discussed various additive manufacturing techniques for fabricating sensors in this review. We also discussed the many strategies for manufacturing sensors using additive manufacturing, as well as how sensors are integrated into the manufacturing process. The review also explained the fundamental mechanisms used in sensors and their applications. The study demonstrated that embedded 3D printing sensors facilitate the development of additive sensor materials for smart goods and the Internet of Things.

Thermoelectric Properties of One-Pot Hydrothermally Synthesized Solution-Processable PEDOT:PSS/MWCNT Composite Materials.

The combination of organic and inorganic materials has been considered an effective solution for achieving ambient thermoelectric energy harvesting and has been developing rapidly. Here, PEDOT:PSS/MWCNT (PPM) composite hydrogels were synthesized using the self-assembled gelation process of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) and the interaction between PEDOT:PSS and multi-walled carbon nanotubes (MWCNTs) without the addition of any surfactant. After immersion in dimethyl sulfoxide and freeze-drying, the hydrogel is easily dispersed in water and used as a direct ink writing (DIW) 3D printing ink. At room temperature, the PPM-20 printed film with 20 wt% MWCNT solids achieved a maximum power factor of 7.37 µW m-1 K-2 and maintained stable thermoelectric properties during repeated bending cycles. On this basis, a thermoelectric generator (TEG) consisting of five legs was printed, which could be produced to generate an open circuit voltage of 6.4 mV and a maximum output power of 40.48 nW at a temperature gradient of 50 K, confirming its great potential for application in high-performance flexible organic/inorganic thermoelectric materials.

3D Printing of Ionogels with Complementary Functionalities Enabled by Self-Regulating Ink.

Shaping soft and conductive materials into sophisticated architectures through 3D printing is driving innovation in myriad applications, such as robotic counterparts that emulate the synergic functions of biological systems. Although recently developed multi-material 3D printing has enabled on-demand creation of intricate artificial counterparts from a wide range of functional viscoelastic materials. However, directly achieving complementary functionalities in one ink design remains largely unexplored, given the issues of printability and synergy among ink components. In this study, an easily accessible and self-regulating tricomponent ionogel-based ink design to address these challenges is reported. The resultant 3D printed objects, based on the same component but with varying ratios of ink formulations, exhibit distinct yet complementary properties. For example, their Young's modulus can differ by three orders of magnitude, and some structures are rigid while others are ductile and viscous. A theoretical model is also employed for predicting and controlling the printing resolution. By integrating complementary functionalities, one further demonstrates a representative bioinspired prototype of spiderweb, which mimics the sophisticated structure and multiple functions of a natural spiderweb, even working and camouflaging underwater. This ink design strategy greatly extends the material choice and can provide valuable guidance in constructing diverse artificial systems by 3D printing.

High throughput disassembly of cellulose nanoribbons and colloidal stabilization of gel-like Pickering emulsions.

We introduce a strategy to disintegrate cellulose microfibrils present in the cell walls of plant fibers. The process includes impregnation and mild oxidation followed by ultrasonication, which loosens the hydrophilic planes of crystalline cellulose while preserving the hydrophobic ones. The resultant molecularly-sized cellulose structures (cellulose ribbons, CR) retain a length of the order of a micron (1.47 ± 0.48 µm, AFM). A very high axial aspect ratio is determined (at least 190), considering the CR height (0.62 ± 0.38 nm, AFM), corresponding to 1-2 cellulose chains, and width (7.64 ± 1.82 nm, TEM). The new molecularly-thin cellulose proposes excellent hydrophilicity and flexibility, enabling a remarkable viscosifying effect when dispersed in aqueous media (shear-thinning, zero shear viscosity of 6.3 × 105 mPa·s). As such, CR suspensions readily develop into gel-like Pickering emulsions in the absence of crosslinking, suitable for direct ink writing at ultra-low solids content.

Printability of Poly(lactic acid) Ink by Embedded 3D Printing via Immersion Precipitation.

Immersion precipitation three-dimensional printing (ip3DP) and freeform polymer precipitation (FPP) are unique and versatile methods of 3D printing to fabricate 3D structures based on nonsolvent-induced phase separation via direct ink writing (DIW). Immersion precipitation involves complex dynamics among solvents, nonsolvents, and dissolved polymers, and the printability of 3D models in these methods requires further understanding. To this end, we characterized these two methods of 3D printing using polylactide (PLA) dissolved in dichloromethane (7.5-30% w/w) as model inks. We analyzed the rheological properties of the solutions and the effect of printing parameters on solvent-nonsolvent diffusion to achieve printability. The PLA inks exhibited shear-thinning properties, and their viscosities varied over three orders of magnitude (10-1∼102 Pa·s). A processing map was presented to understand the ideal ranges of the concentration of PLA in inks and the nozzle diameter to ensure printability, and the fabrication of complex 3D structures was fabricated with adequate applied pressure and nozzle speed. The processing map also highlighted the advantages of embedded 3D printing over solvent-cast 3D printing based on solvent evaporation. Lastly, we demonstrated that the porosity of the interface and inner structure of the printed objects was readily tailored by the concentration of the PLA and the porogen added to the ink. The methods presented here offer new perspectives to fabricate micro-to-centimeter objects of thermoplastics with nanometer-scale inner pores and provide guidelines for successful embedded 3D printing based on immersion precipitation.

A Printable Magnetic-Responsive Iron Oxide Nanoparticle (ION)-Gelatin Methacryloyl (GelMA) Ink for Soft Bioactuator/Robot Applications.

The features or actuation behaviors of nature's creatures provide concepts for the development of biomimetic soft bioactuators/robots with stimuli-responsive capabilities, design convenience, and environmental adaptivity in various fields. Mimosa pudica is a mechanically responsive plant that can convert pressure to the motion of leaves. When the leaves receive pressure, the occurrence of asymmetric turgor in the extensor and flexor sides of the pulvinus from redistributing the water in the pulvinus causes the bending of the pulvinus. Inspired by the actuation of Mimosa pudica, designing soft bioactuators can convert external stimulations to driving forces for the actuation of constructs which has been receiving increased attention and has potential applications in many fields. 4D printing technology has emerged as a new strategy for creating versatile soft bioactuators/robots by integrating printing technologies with stimuli-responsive materials. In this study, we developed a hybrid ink by combining gelatin methacryloyl (GelMA) polymers with iron oxide nanoparticles (IONs). This hybrid ION-GelMA ink exhibits tunable rheology, controllable mechanical properties, magnetic-responsive behaviors, and printability by integrating the internal metal ion-polymeric chain interactions and photo-crosslinking chemistries. This design offers the inks a dual crosslink mechanism combining the advantages of photocrosslinking and ionic crosslinking to rapidly form the construct within 60 s of UV exposure time. In addition, the magnetic-responsive actuation of ION-GelMA constructs can be regulated by different ION concentrations (0-10%). Furthermore, we used the ION-GelMA inks to fabricate a Mimosa pudica-like soft bioactuator through a mold casting method and a direct-ink-writing (DIW) printing technology. Obviously, the pinnule leaf structure of printed constructs presents a continuous reversible shape transformation in an air phase without any liquid as a medium, which can mimic the motion characteristics of natural creatures. At the same time, compared to the model casting process, the DIW printed bioactuators show a more refined and biomimetic transformation shape that closely resembles the movement of the pinnule leaf of Mimosa pudica in response to stimulation. Overall, this study indicates the proof of concept and the potential prospect of magnetic-responsive ION-GelMA inks for the rapid prototyping of biomimetic soft bioactuators/robots with untethered non-contact magneto-actuations.

3D Printing in Regenerative Medicine: Technologies and Resources Utilized.

Over the past ten years, the use of additive manufacturing techniques, also known as "3D printing", has steadily increased in a variety of scientific fields. There are a number of inherent advantages to these fabrication methods over conventional manufacturing due to the way that they work, which is based on the layer-by-layer material-deposition principle. These benefits include the accurate attribution of complex, pre-designed shapes, as well as the use of a variety of innovative raw materials. Its main advantage is the ability to fabricate custom shapes with an interior lattice network connecting them and a porous surface that traditional manufacturing techniques cannot adequately attribute. Such structures are being used for direct implantation into the human body in the biomedical field in areas such as bio-printing, where this potential is being heavily utilized. The fabricated items must be made of biomaterials with the proper mechanical properties, as well as biomaterials that exhibit characteristics such as biocompatibility, bioresorbability, and biodegradability, in order to meet the strict requirements that such procedures impose. The most significant biomaterials used in these techniques are listed in this work, but their advantages and disadvantages are also discussed in relation to the aforementioned properties that are crucial to their use.

Embedded Core-Shell 3D Printing (eCS3DP) with Low-Viscosity Polysiloxanes.

Flexible core-shell 3D structures are essential for the development of soft sensors and actuators. Despite recent advancements in 3D printing, the fabrication of flexible 3D objects with internal architectures (such as channels and void spaces) remains challenging with liquid precursors due to the difficulty to maintain the printed structures. The difficulty of such fabrication is prominent especially when low-viscosity polysiloxane resins are used. This study presents a unique approach to applying direct ink writing (DIW) 3D printing in a three-phase system to overcome this limitation. We performed core-shell 3D printing using a low-viscosity commercial polysiloxane resin (Ecoflex 10) as shell inks combined with a coaxially extruded core liquid (Pluronic F127) in Bingham plastic microparticulate gels (ethanol gel). In the process termed embedded core-shell 3D printing (eCS3DP), we highlighted the dependence of the rheological characteristics of the three fluids on the stability of the printed core-shell filament. With the core liquid with a sufficiently high concentration of Pluronic F127 (30 w/w%; σy = 158.5 Pa), the interfacial instability between the shell liquid and core liquid was suppressed; the removal of the core liquid permitted the fabrication of perfusable channels. We identified the printing conditions to ensure lateral attachments of printed core-shell filaments. Interestingly, judicious selection of the rheological properties and flow rates of three phases allowed the formation of droplets consisting of core liquids distributed along the printed filaments. eCS3DP offers a simple route to fabricate 3D structures of a soft elastomeric matrix with embedded channels and should serve as a useful tool for DIW-based fabrication of flexible wearable devices and soft robotic components.

Tunable Size of Hierarchically Porous Alumina Ceramics Based on DIW 3D Printing Supramolecular Gel.

A new three-dimensional (3D) printing gel is developed to construct hierarchically porous ceramics with adjustable millimeter-, micrometer-, and nanometer-scale size for application in thermal management. Not only does the gel based on supramolecular micelles exhibit excellent DIW 3D printability but also the supramolecular micelles act as templates that can precisely control the structure of micrometer-scale pores. The effect of millimeter- and µmicrometer-scale size on properties of porous ceramics is investigated in detail. The 3D-printed ceramic foam with millimeter-scale pores and smaller micrometer-scale pores shows better thermal insulation and lower compressive strength. For the thermal insulation, the local temperature of a chip exposed to contact heat is only 34.2 °C in the presence of a printed foam cap with a pore size of 41.5 µm, while the local temperature is 54.8 °C in the absence of the printed foam cap. The study provides a new method to construct hierarchically porous alumina ceramics with precisely tunable size, avoiding the issues of subtractive manufacturing and opening up new applications in portable devices or consumer electronics.

Programmable Anisotropic Hydrogel Composites for Soft Bioelectronics.

Fabrication of hydrogel composites embedded with aligned 1D nanoparticles has shown substantial growth over the past 5 years. Direct ink printing technology (DIW) has been used in this work to create the alignment of the 1D nanoparticles due to the shear gradient of the pseudoplastic precursor (2-hydroxyethyl methacrylate (HEMA) with thickening agents). Orderly distributed 1D particles constructing anisotropic nanostructures endow the hydrogel composite with unique mechanical, electric, or electromechanical coupling properties. Quasi-static uniaxial tensile test, electric resistivity, and piezoresistivity measurements have been conducted for investigating the mechanical, electric, and electromechanical coupling properties of the hydrogel composites, respectively. Based on the experimental results, it can be speculated that the developed printing process is able to fabricate hydrogel composites with programmable anisotropic mechanical, electric, and electromechanical properties. The products pumped out from this work have the potential of being substrates for soft devices and may have a great impact on the fields of flexible bioelectronics.

3D Printable Conducting and Biocompatible PEDOT-graft-PLA Copolymers by Direct Ink Writing.

Tailor-made polymers are needed to fully exploit the possibilities of additive manufacturing, constructing complex, and functional devices in areas such as bioelectronics. In this paper, the synthesis of a conducting and biocompatible graft copolymer which can be 3D printed using direct melting extrusion methods is shown. For this purpose, graft copolymers composed by conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and a biocompatible polymer polylactide (PLA) are designed. The PEDOT-g-PLA copolymers are synthesized by chemical oxidative polymerization between 3,4-ethylenedioxythiophene and PLA macromonomers. PEDOT-g-PLA copolymers with different compositions are obtained and fully characterized. The rheological characterization indicates that copolymers containing below 20 wt% of PEDOT show the right complex viscosity values suitable for direct ink writing (DIW). The 3D printing tests using the DIW methodology allows printing different parts with different shapes with high resolution (200 µm). The conductive and biocompatible printed patterns of PEDOT-g-PLA show excellent cell growth and maturation of neonatal cardiac myocytes cocultured with fibroblasts.

3D printing of glass by additive manufacturing techniques: a review.

Additive manufacturing (AM), which is also known as three-dimensional (3D) printing, uses computer-aided design to build objects layer by layer. Here, we focus on the recent progress in the development of techniques for 3D printing of glass, an important optoelectronic material, including fused deposition modeling, selective laser sintering/melting, stereolithography (SLA) and direct ink writing. We compare these 3D printing methods and analyze their benefits and problems for the manufacturing of functional glass objects. In addition, we discuss the technological principles of 3D glass printing and applications of 3D printed glass objects. This review is finalized by a summary of the current achievements and perspectives for the future development of the 3D glass printing technique.

Embedded Ink Writing (EIW) of Polysiloxane Inks.

Polysiloxane is a desirable material for the fabrication of devices in microfluidics, lab-on-a-chip, and microelectromechanical systems, but direct patterning of microstructures using liquid polysiloxane resins would require adequate rheological and chemical properties of the resins. In this work, we developed a simple method to fabricate planar microstructures consisting of polysiloxane using commercially available liquid polysiloxane resins without changing their properties. We used a direct ink writing (DIW) printer to dispense curable liquid polysiloxane (with the viscosity in the range of 1-100 Pa·s) in a liquid immiscible with the resins (such as methanol, ethanol, and isopropanol). The contact angle (θ) of the dispensed polysiloxane on the Petri dish increased from 20° in air to 100° in methanol, ethanol, and isopropanol. The increase in the contact angles allowed maintaining the structures of patterned polysiloxane until curing, and the embedding liquid was readily removed by evaporation. We termed this method as embedded ink writing (EIW). The effects of curing time (τ) and nozzle speed (v) on the width of the printed filament (w) were evaluated. EIW achieved the minimum width of the printed filament of 65 µm. EIW enabled direct writing of polysiloxane resins and should find applications in fabricating microfluidic devices, flexible wearables, and soft actuators.

Highly Porous Polymer-Derived Bioceramics Based on a Complex Hardystonite Solid Solution.

Highly porous bioceramics, based on a complex hardystonite solid solution, were developed from silicone resins and micro-sized oxide fillers fired in air at 950 °C. Besides CaO, SrO, MgO, and ZnO precursors, and the commercial embedded silicone resins, calcium borate was essential in providing the liquid phase upon firing and favouring the formation of an unprecedented hardystonite solid solution, corresponding to the formula (Ca0.70Sr0.30)2(Zn0.72Mg0.15Si0.13) (Si0.85B0.15)2O7. Silicone-filler mixtures could be used in the form of thick pastes for direct ink writing of reticulated scaffolds or for direct foaming. The latter shaping option benefited from the use of hydrated calcium borate, which underwent dehydration, with water vapour release, at a low temperature (420 °C). Both scaffolds and foams confirmed the already-obtained phase assemblage, after firing, and exhibited remarkable strength-to-density ratios. Finally, preliminary cell tests excluded any cytotoxicity that could be derived from the formation of a boro-silicate glassy phase.