Direct-write 3D Printing Research Articles

Enhanced mass transfer by 3D printing to promote the degradation of organic pollutants in electro-Fenton system

In this study, researchers constructed a monolithic 3D-FeO/C electrode with a macro-ordered pore structure using direct-write 3D printing technology. Experimental results showed that the 3D-FeO/C electrode possessed excellent degradation performance for ornidazole (ONZ) (complete degradation within 120 min) and pharmaceutical wastewater (51.13 % in TOC and 63.72 % in COD removal within 420 min). The detailed reaction mechanism of the EF system was revealed through characterization analysis, mass transfer simulation, and experimental results, in which the excellent EF performance is mainly due to the confinement effect of FeO active sites encapsulated in the carbon layer, as well as the enhancement of mass transfer induced by 3D printing macro-ordered structure network. In addition, the degradation pathway of ONZ, the toxicity of its degradation intermediates, and the degradation pathway of actual pharmaceutical wastewater were revealed in detail. This study proposes a new 3D printing method to enhance the mass transfer of electrode materials in EF systems, which has good potential for application to real wastewater.

Three-Dimensional-Printed Composite Structures: The Effect of LSCF Slurry Solid Loading, Binder, and Direct-Write Process Parameters.

In this research, a direct-write 3D-printing method was utilized for the fabrication of inter-digitized solid oxide fuel cells (SOFCs) using ceramic materials. The cathode electrode was fabricated using the LSCF (La0.6Sr0.2Fe0.8Co0.2O3-δ) slurry loading and the Polyvinyl butyral (PVB) binder. The rheological parameters of slurries with varying LSCF slurry loading and PVB binder concentration were evaluated to determine their effect on the cathode trace performance in terms of microstructure, size, and resistance. Additionally, the dimensional shrinkage of LSCF lines after sintering was investigated to realize their influence on cathode line width and height. Moreover, the effect of the direct-write process parameters such as pressure, distance between the nozzle and substrate, and speed on the cathode line dimensions and resistance was evaluated. LSCF slurry with 50% solid loading, 12% binder, and 0.2% dispersant concentration was determined to be the optimal value for the fabrication of SOFCs using the direct-write method. The direct-write process parameters, in addition to the binder and LSCF slurry concentration ratios, had a considerable impact on the microstructure of cathode lines. Based on ANOVA findings, pressure and distance had significant effects on the cathode electrode resistance. An increase in the distance between the nozzle and substrate, speed, or extrusion pressure of the direct writing process increased the resistance of the cathode lines. These findings add to the ongoing effort to refine SOFC fabrication techniques, opening the avenues for advanced performance and efficiency of SOFCs in energy applications.

Feasibility assessment of polyvinyl alcohol-based bioresorbable cardiovascular stents manufactured via solvent-cast direct writing extrusion

BackgroundBioresorbable stents represent a promising approach in cardiovascular interventions compared to drug-eluting stents. Additive manufacturing, particularly ink deposition, offers customization and versatility. This study delves into the potential of solvent cast direct-write 3D printing to fabricate cardiovascular stents using environmentally friendly solvents. MethodologyPolyvinyl alcohol, a biocompatible synthetic polymer that dissolves in water, was investigated as a suitable material for stent fabrication. The polymer was deposited on a rotating mandrel and subsequently crosslinked to establish a pseudostable state. Test specimens and stents were fabricated for characterization of both the material and stent dynamics. ResultsThis outcome is potentially suitable for deployment in the human body environment and adaptable to various biomedical applications, such as drug delivery patches or implants. The research optimized the fabrication of various stent geometries using polyvinyl alcohol and evaluated the kinetics of the working environment of these stents. Specifically, the 8-cell diamond stent showed remarkable characteristics, such as a high overexpansion of more than 0.5 mm, a compression force of 0.02 N and an elastic recovery of 88.85 %, with a strut thickness of 50.25 μm. Additionally, the study discusses the possibility of sterilizing polyvinyl alcohol with different methods, ethanol and autoclave were selected. ConclusionsThe results indicate that autoclaving leads to an increase in crystallinity. This yields a decrease in water absorption and an increase in mechanical properties. These results suggest that polyvinyl alcohol-based stents fabricated by solvent-cast direct writing are potential candidates for bioresorbable stent design.

Direct-write 3D printing of plasmonic nanohelicoids by circularly polarized light

Chiral plasmonic surfaces with 3D "forests" from nanohelicoids should provide strong optical rotation due to alignment of helical axis with propagation vector of photons. However, such three-dimensional nanostructures also demand multi-step nanofabrication, which is incompatible with many substrates. Large-scale photonic patterns on polymeric and flexible substrates remain unattainable. Here, we demonstrate the substrate-tolerant direct-write printing and patterning of silver nanohelicoids with out-of-plane 3D orientation using circularly polarized light. Centimeter-scale chiral plasmonic surfaces can be produced within minutes using inexpensive medium-power lasers. The growth of nanohelicoids is driven by the symmetry-broken site-selective deposition and self-assembly of the silver nanoparticles (NPs). The ellipticity and wavelength of the incident photons control the local handedness and size of the printed nanohelicoids, which enables on-the-fly modulation of nanohelicoid chirality during direct writing and simple pathways to complex multifunctional metasurfaces. Processing simplicity, high polarization rotation, and fine spatial resolution of the light-driven printing of stand-up helicoids provide a rapid pathway to chiral plasmonic surfaces, accelerating the development of chiral photonics for health and information technologies.

Research on rice starch gel preparation and crosslink network structure-rheological property based on direct-writing 3D printing

Amylopectin and amylose components are natural polymers within rice starch granules, intertwined in specific conditions to form gel polymerized with pore crosslink network, has potential printing properties. In this study, a rice starch gel preparation scheme is proposed for stable properties, and starch granule phase transition mechanism is analyzed based on RVA test during preparation, it can be divided into four-stage, swelling, reacting, homogenizing and self-assembling stages. Gel surface tension and contact angle tested with starch concentration effect, a correlation is developed, reflecting a competition result to gel droplet macro-morphology between the intermolecular cohesion and crosslink network. SEM is used to reveal typical crosslink structures of different starch molecular component proportions, providing objective support for starch gel rheologic property change. Results indicate gel interior crosslink network formed under concentration 12 %, the gel with amylose 4.475 % presents better printing accuracy. Gel shear modulus positively correlated with amylose proportion. Japonica gel under 20 % is of higher viscosity and rapid reassembly ability after interior crosslink network is broken. Max dynamic viscosity is positively correlated with starch concentration. The study aims to provide theoretical and practical support for in-depth analysis of rice starch material application in direct-write 3D printing.

Facile preparation of patterned anode substrate for solid oxide fuel cells by direct-writing 3D printing technology

3D printing has revolutionized solid oxide fuel cell (SOFC) by introducing complicated structure and new functionalities that cannot be realized using traditional preparation process. This work provides guide and insights into the application of direct-writing 3D printing to fabricate the patterned electrolyte|electrode interface for the anode-supported SOFC using 3 mol % yttria-stabilized zirconia-nickel oxide (3YSZ-NiO) as the anode substrate material. The parameters that affected the shaping and performance of SOFC including the rheological properties of 3YSZ-NiO anode paste, the printing parameters, and the heat treatment process of the pre-sintered anode substrate were evaluated. The prepared 3YSZ-NiO paste exhibited a typical shear-thinning characteristic, “yielding” solid-like behavior, and time- and temperature-independent stability performance, which ensured the paste suitable for extrusion while allowing the shape of the printed body to be maintained after extrusion during the direct-writing printing process. The as-prepared anode paste, combined with the obtained values of 0.1 MPa, 100 mm s−1, 100 rpm, and 0.3 mm for printing parameters of the extrusion pressure, the printing speed, the screw speed, and the nozzle diameter, respectively, as well as the devised heat treatment program for the pre-sintered 3YSZ-NiO anode substrate, successfully produced defect-free corrugated anode substrates. The cell made from the as-mentioned anode substrate showed an open circuit voltage of 1.02 V and a maximum power density of 619.44 mW cm−2 at 850 °C, which was comparable to the other identical cells fabricated by traditional and other 3D printing processes. Using the 3D printing process shown here, the preparation time of patterned anode substrate can be reduced and simplified.

Synergistic Effect of Physical and Chemical Cross-Linkers Enhances Shape Fidelity and Mechanical Properties of 3D Printable Low-Modulus Polyesters.

Three-dimensional (3D) printing is becoming increasingly prevalent in tissue engineering, driving the demand for low-modulus, high-performance, biodegradable, and biocompatible polymers. Extrusion-based direct-write (EDW) 3D printing enables printing and customization of low-modulus materials, ranging from cell-free printing to cell-laden bioinks that closely resemble natural tissue. While EDW holds promise, the requirement for soft materials with excellent printability and shape fidelity postprinting remains unmet. The development of new synthetic materials for 3D printing applications has been relatively slow, and only a small polymer library is available for tissue engineering applications. Furthermore, most of these polymers require high temperature (FDM) or additives and solvents (DLP/SLA) to enable printability. In this study, we present low-modulus 3D printable polyester inks that enable low-temperature printing without the need for solvents or additives. To maintain shape fidelity, we incorporate physical and chemical cross-linkers. These 3D printable polyester inks contain pendant amide groups as the physical cross-linker and coumarin pendant groups as the photochemical cross-linker. Molecular dynamics simulations further confirm the presence of physical interactions between different pendants, including hydrogen bonding and hydrophobic interactions. The combination of the two types of cross-linkers enhances the zero-shear viscosity and hence provides good printability and shape fidelity.

Direct-writing of three-dimensional porous Fe3N/FeS electrode for efficient degradation of organic pollutants in water through Electro-Fenton process

The Electro-Fenton process is getting a rapid development recently as a novel advanced electro-oxidation technology for the removal of organic pollutants from water. In this work, a three-dimensional (3D) porous Fe3N/FeS composite electrode was created from a Fe2(SO4)3-based composite ink by the direct-writing 3D printing technology combined with a high temperature heat treatment under ammonia atmosphere. Fe3N served as the conductive skeleton of the electrode, while FeS could provide Fe2+ to react with in-situ generated H2O2 in the Electro-Fenton process to generate ·OH radicals. Thus, it could eliminate the need of external ferrous ion addition. The 3D porous Fe3N/FeS composite electrode had desired 3D interconnected macro-channels for efficient mass transport and rough rod surfaces to provide more active sites, which resulted in its superior degradation performance on organics than its traditional two-dimensional (2D) plate counterpart. A two-step H2O2 production path was found on the 3D Fe3N/FeS composite electrode, which had been found to possess a faster reaction kinetics. It effectively degraded rhodamine B (RhB) within a wide pH range from ∼3 to ∼ 10, demonstrated stable performances in repeated uses, and had low iron ion leaching, all of which were beneficial for its potential applications. Furthermore, it also demonstrated effective degradation performances on antibiotics of amoxicillin (AMX) and tetracycline hydrochloride (TC-HCl) in both deionized (DI) water and tap water matrixes, indicating its potential to solve the emerging contaminant problem in real water treatment practices.

Depletion attraction driven formation of Spirulina emulsion gels for 3D printing

3D printing has been applied to create nutritious foods with tailored textures for the elderly. However, the edible materials that possess the elastoplastic properties and shear-thinning behavior required for direct-write 3D printing are limited. In this study, we developed a simple approach to fabricate Spirulina emulsion gels as edible 3D printable material by exploiting depletion attraction between emulsion droplets. By controlling the volume ratio of continuous and oil phases, mixing highly viscous Spirulina slurry and vegetable oil could form self-standing oil-in-water emulsion gels with elastoplastic rheological properties. Also, adding food polysaccharides into the continuous phase could act as depletants to drive the formation of emulsion gels. Auto-fluorescence spectroscopy and microscopy were employed to characterize the interfacial protein compositions of the emulsion, showing that phycobilisome (PBS) particles might play a dominant role in the formation of Spirulina emulsions. The depletion attraction could drive the adsorption of PBS particles onto the droplet interface, and the particle-armored droplets in the dispersed phase connected into a percolating droplet cluster, resulting in arrested dynamics and gelation. Overall, this novel approach can be applied by exploiting depletion attraction and opens up possibilities for using high-solids viscous food slurries to produce personalized 3D-printed foods.

Direct-write 3D printing of UV-curable composites with continuous carbon fiber

Continuous fiber-reinforced polymer composites, with their superior combinations of high stiffness, high strength, lightweight, and corrosion resistance, have been leading contenders in various applications ranging from aerospace to ground transportation. The integration with 3D printing allows the composite products to be customized quickly and fabricated inexpensively to meet unique specifications. However, the material-process-property relationships of 3D printed thermoset composites with continuous fiber are insufficiently explored in the field. In this work, a cost-effective 3D printing method is developed based on the direct ink writing method to print UV-curable composites reinforced with continuous carbon fiber. During the printing, the fiber tow is impregnated with an acrylate ink inside the printer head and then extruded onto the printer bed, where it is cured upon UV irradiation. The influences of different material and processing variables, such as the resin viscosity, nozzle size, printing speed, and substrate temperature, on the quality and mechanical properties of composites, are investigated. The porosity, stiffness, and strength of printed symmetric laminate are also examined. Finally, the 3D printing of composite structures and the conformal coating of curved surfaces along a defined printing path are demonstrated. The findings reported in this work could contribute to the rapid design and manufacturing of composite components with unprecedented mechanical properties and emerging functionalities for the automotive, defense, and aerospace industries.

Robust, Conductive, and High Loading Fiber-Shaped Electrodes Fabricated by 3D Active Coating for Flexible Energy Storage Devices.

Flexible power sources are critical to achieve the wide adoption of portable and wearable electronics. Herein, a facile and general strategy of fabricating a fibrous electrode was developed by 3D active coating technology, in which a stepping syringe with electrode paste was synchronously injected onto a rotating conductive wire, distinguished from the conventional direct-write 3D printing without a current collector. A series of such electrodes with different coating weight can be fabricated accurately and efficiently by adjusting critical process parameters following a set of derived equations. The demonstrated fibrous Zn-MnO2 battery with a high commercial ε-MnO2 loading of 14.9 mg cm-2 onto a stainless steel wire shows a reasonable energy density of 108 mWh cm-3, while the fiber-shaped supercapacitor with commercial porous graphene exhibits a high capacitance of 142.9 F g-1 and good durability for bending 10,000 cycles. This work constructs a bridge between materials and fiber-shaped electrodes for flexible energy storage devices.

Integrating helicoid channels for passive control of fiber alignment in direct-write 3D printing

3D printing of fiber-reinforced composites has been receiving increasing attention as an efficient additive approach enabling lightweight, functional, and high-performance components required for industrial applications. The properties of fiber composites significantly depend on internal microstructures, including fiber orientation, distribution, and degree of alignment. Although multiple strategies have been introduced for controlling the fiber composites microstructures, these strategies are mostly active approaches relying on additional control of mechatronics parts, external forces, or intentionally introduced unstable flows inside narrow nozzles. These methods suffer from higher risk of nozzle clogging and requiring extra parts in 3D printing. Here, we introduce helicoid channels into extrusion system as a passive approach to control the fiber alignment without any additional moving parts in direct-write 3D printing. The helicoid channels automatically guide the composite inks and align fibers before flowing into narrow nozzle space, avoiding clogging and improving printability. The analyses indicate that both helicoid surface to volume ratio and helix angle affect the pre-alignment of fibers, leading to tunable mechanical properties of printed fiber-reinforced composites with increased stiffness and strength up to 77.6% and 47.8%, respectively.

Synthesis, Rheology, and Assessment of 3D Printability of Multifunctional Polyesters for Extrusion-Based Direct-Write 3D Printing

Three-dimensional (3D) printing offers the unprecedented ability to create medical devices with complex architectures matched to the patient’s anatomy. However, the development of 3D printable synthetic polymers for biomedical applications has been relatively slow. Here, we present the synthesis and characterization of a library of single-component, undiluted, modular multifunctional polyesters for extrusion-based direct-write 3D printing (EDP). The polyesters were synthesized using carbodiimide-mediated polyesterification of pendant functionalized diols and succinic acid and characterized using 1H NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and rheology. The rheology was characterized by using small amplitude oscillatory shear rheology and at steady-state shear flow conditions. The viscoelasticity of the polyesters was characterized by plotting master curves using the time–temperature superposition (TTS) principle, which were then validated by Van Gurp-Palmen and Cole–Cole plots. The 3D printability of the polyesters was assessed on the basis of several key parameters including the ability to extrude as continuous filaments, retain the printed shape, form multilayer constructs, and form bridge-spanning filaments without significant sagging or collapse. The rheological characterization suggests that the polyesters are unentangled melts that facilitate printing at ambient temperatures without the use of external additives or solvents. The presence of supramolecular interactions inducing pendant functional groups forms a temporary, physical cross-link-like network that enables 3D shape retention. The insights from this study will further assist in the design and characterization of 3D printable polymer melts for biomedical applications and standardizing the assessment of polymer 3D printability.

3D-printed flexible, multilayered ceramic-polymer composite grid with integrated structural-self-sensing function

Piezo-polymer is widely used for pressure sensors or electromechanical transducers; and normally, it is simply designed and prepared into thin film as a force-sensing element integrated in smart structures or robots. In this paper, we report a flexible, three-dimensional multilayer composite grid complex structure containing inside electrode layers prepared totally based on direct-writing 3D printing method. The composite material is composed of a polydimethylsiloxane (PDMS) elastomer matrix and 0.55Pb (Ni1/3Nb2/3) O3-0.135PbZrO3- 0.315PbTiO3 (PNN-PZT) piezoelectric ceramic particles coated with Ag and multi-walled carbon nanotubes (1 wt% of the Ag@PNN-PZT ceramic powders). The 3D-printed composite grid exhibits both large piezoelectric effect (with an effect piezoelectric coefficient (d33) of 21 pC/N) and qualified mechanical performances, such as a large failure tensile strain of 150% and tensile stress of 2.2 MPa. Under a dynamic compression stress of 0.125 MPa at 3.5 Hz, a 3D-printed 7-layer composite grid (550 μm in thickness) with internal electrode layers inside could produce output voltage peak of 3 V accompanying with a peak current of 0.7 μA. In comparison with a single layer composite grid, its peak output current shows a 7-time increase, although its peak output voltage keeps unchanged under the same compression stress. This work shows that the 3D-printed multilayer composite grid exhibits the integrated structural-self-sensing function, which will bring great benefits to future artificial muscle in robots and other flexible intelligent structures.

Additive manufacturing of conductive and high-strength epoxy-nanoclay-carbon nanotube composites

Additive Manufacturing has increased our ability to fabricate complex shapes and multi-material structures. Epoxy is excellent as the base for structural composite materials. Furthermore, carbon nanotube (CNT) is an outstanding filler due to its unique properties and functionalities. Here, conductive epoxy-nanoclay-CNT nanocomposite structures were fabricated by direct-write 3D printing. In this process, 3D-printable composite inks were synthesized by incorporation of nanoclay and different concentrations of CNTs – 0.25, 0.5, and 1 vol%, 0.43, 0.86, and 1.7 wt% – in epoxy. CNTs were found to significantly improve the electrical and mechanical properties. Rheological characterization of the inks revealed a shear-thinning behavior for all the nanocomposite inks and an increase in the complex viscosity, storage, and loss moduli with the incorporation of CNTs. The CNT concentration of 0.5 vol% was found to be the optimum condition for enhancement of mechanical properties; an average increase of 61%, 59%, and 31% was measured for flexural strength, flexural modulus, and tensile strength, respectively, compared to the 3D printed epoxy-nanoclay nanocomposite structures. The electrical conductivity of 2.4 × 10 −8 and 2.2 × 10 −6 S/cm was measured for the nanocomposites containing 0.5 and 1 vol% CNTs, respectively. Multi-scale characterization of the morphology revealed partial alignment of CNTs in the direction of printing, CNT pull-out and breakage at the fracture surfaces, and nano-scale interactions of the constituents, all of which contribute to the superiority of the nanocomposite with CNTs. The findings show the promise of this ink material and printing method for various applications such as aerospace structures and electronics.

Thermal oxidation–electroreduction modified 3D NiCu for efficient alkaline hydrogen evolution reaction

The preparation of high-efficiency and low-cost electrocatalysts is vital to the development of green hydrogen energy. In this study, 3D NiCu electrodes with hierarchical micro-nano structure was constructed by a simple direct-write 3D printing technology and followed by the treatment of thermal oxidation - electroreduction steps. The composite structure of Cu NWs/Cu2O and Ni/NiO in the prepared 3D NiCu promotes the dissociation of water and the conversion of hydrogen, and the special micro-nano structure displays a large active surface area. Therefore, the 3D NiCu exhibits a low overpotential of 70 mV to deliver a current density of 10 mA cm−2. It demonstrates outstanding stability in the hydrogen evolution reaction experiment for 100 h in 1 M KOH. Overall, this research provides a pioneer of modified 3D printing to hydrogen production by water electrolysis.

Impact of cell density on the bioprinting of gelatin methacrylate (GelMA) bioinks

3D printing of cell laden bioinks has the potential to recapitulate the hierarchical and spatial complexity of native tissues. However, the addition of cells can alter physical properties of printable resins, which in turn may impede or induce cellular sedimentation or affect the printability and shape fidelity of the final construct. In this study we investigated these considerations by bioprinting gelatin methacrylate (GelMA) bioinks, loaded with various concentrations of mouse fibroblast cells (L929), using extrusion-based direct-write 3D printing (EDP). The impact of various cellular concentrations on viscosity, and temperature-driven gelation of GelMA was examined with a rheometer. The effect of cell concentration on quality of 3D printed GelMA hydrogels was investigated by analyzing the geometric compliance of the 3D printed scaffolds to the theoretical model, and by studying compressive properties of the 3D printed scaffolds. The addition of cells did not significantly affect GelMA zero-shear viscosity or viscosity at shear rates associated with EDP (>102 s−1). While quality and resolution of cell-laden 3D scaffolds of GelMA hydrogel were slightly better than that of GelMA hydrogels without cells, there were no significant differences due to various cell concentrations. The cellular sedimentation in GelMA bio-inks within the printer cartridge was evaluated using DNA quantification. Sedimentation was not statistically significant at the studied cell concentrations of up to 10 ​× ​106 ​cells/ml. Immunofluorescent imaging indicated improved cell spreading and more uniform scaffold coverage over time for higher cell densities. This study provides insights into the effect of cell density on the rheology, and 3D printability of GelMA bioinks which will assist in the designing and standardizing bioprinting of high-quality 3D bioengineered structures.

3D-printed thermoset syntactic foams with tailorable mechanical performance

3D-printed syntactic foams have advantages over traditionally fabricated foams such as design flexibility, in-field fabrication and low investment cost. Current 3D printing methods developed for thermoplastic syntactic foams suffer from unavoidable porosity and low mechanical performance. In this study, we overcame these limitations by fabricating thermoset-based syntactic foams using direct-write 3D printing which allowed us to fabricate buoyant syntactic foams with unprecedented strength (> 100 MPa) and modulus (1.2 GPa). This study also showed that the mechanical performance of these materials can be tailored by reinforcing the thermoset foams via milled carbon fibers. 3D-printed thermoset-based syntactic foams with high scalability and tailored mechanical performance have great potential to find immediate applications where weight reduction, mechanical performance and component complexity are desired.

Direct-write 3D printing and characterization of a GelMA-based biomaterial for intracorporeal tissue engineering

We develop and characterize a biomaterial formulation and robotic methods tailored for intracorporeal tissue engineering (TE) via direct-write (DW) 3D printing. Intracorporeal TE is defined as the biofabrication of 3D TE scaffolds inside of a living patient, in a minimally invasive manner. A biomaterial for intracorporeal TE requires to be 3D printable and crosslinkable via mechanisms that are safe to native tissues and feasible at physiological temperature (37 °C). The cell-laden biomaterial (bioink) preparation and bioprinting methods must support cell viability. Additionally, the biomaterial and bioprinting method must enable the spatially accurate intracorporeal 3D delivery of the biomaterial, and the biomaterial must adhere to or integrate into the native tissue. Current biomaterial formulations do not meet all the presumed intracorporeal DW TE requirements. We demonstrate that a specific formulation of gelatin methacryloyl (GelMA)/Laponite®/methylcellulose (GLM) biomaterial system can be 3D printed at physiological temperature and crosslinked using visible light to construct 3D TE scaffolds with clinically relevant dimensions and consistent structures. Cell viability of 71%–77% and consistent mechanical properties over 21 d are reported. Rheological modifiers, Laponite® and methylcellulose, extend the degradation time of the scaffolds. The DW modality enables the piercing of the soft tissue and over-extrusion of the biomaterial into the tissue, creating a novel interlocking mechanism with soft, hydrated native tissue mimics and animal muscle with a 3.5–4 fold increase in the biomaterial/tissue adhesion strength compared to printing on top of the tissue. The developed GLM biomaterial and robotic interlocking mechanism pave the way towards intracorporeal TE.

Tunable structural color of bottlebrush block copolymers through direct-write 3D printing from solution.

Additive manufacturing of functional materials is limited by control of microstructure and assembly at the nanoscale. In this work, we integrate nonequilibrium self-assembly with direct-write three-dimensional (3D) printing to prepare bottlebrush block copolymer (BBCP) photonic crystals (PCs) with tunable structure color. After varying deposition conditions during printing of a single ink solution, peak reflected wavelength for BBCP PCs span a range of 403 to 626 nm (blue to red), corresponding to an estimated change in d-spacing of >70 nm (Bragg- Snell equation). Physical characterization confirms that these vivid optical effects are underpinned by tuning of lamellar domain spacing, which we attribute to modulation of polymer conformation. Using in situ optical microscopy and solvent-vapor annealing, we identify kinetic trapping of metastable microstructures during printing as the mechanism for domain size control. More generally, we present a robust processing scheme with potential for on-the-fly property tuning of a variety of functional materials.