Multi-material Printing Research Articles

Melt-Extrusion-Based Additive Manufacturing of Transparent Fused Silica Glass.

In recent years, additive manufacturing (AM) of glass has attracted great interest in academia and industry, yet it is still mostly limited to liquid nanocomposite‐based approaches for stereolithography, two‐photon polymerization, or direct ink writing. Melt‐extrusion‐based processes, such as fused deposition modeling (FDM), which will allow facile manufacturing of large thin‐walled components or simple multimaterial printing processes, are so far inaccessible for AM of transparent fused silica glass. Here, melt‐extrusion‐based AM of transparent fused silica is introduced by FDM and fused feedstock deposition (FFD) using thermoplastic silica nanocomposites that are converted to transparent glass using debinding and sintering. This will enable printing of previously inaccessible glass structures like high‐aspect‐ratio (>480) vessels with wall thicknesses down to 250 µm, delicate parts including overhanging features using polymer support structures, as well as dual extrusion for multicolored glasses.

Lithium-Ion Battery 3D Printing: From Thermoplastic Material Extrusion to Vat Photopolymerization Process

Transitioning from conventional 2D to complex 3D lithium-ion battery (LIB) architectures will increase electrochemically active surface area and lithium-ion diffusion paths, leading to improved specific capacity and power performance [1]. Our recent in-depth modeling studies and preliminary experiments [2] involving the simulation of a classical Ragone plot that exhibits the energy-power relationship illustrated that a gyroid 3D battery architecture has +158% performance at a high current density of 6C, in comparison to planar geometry. The fabrication of complex electrodes has been widely investigated through an electrochemically-assisted templated growth of current collector arrays, followed by electrophoretic deposition of the electroactive material [3]. However, such an approach is limited in geometries, and the interpenetration of both electrode networks often results in short circuits due to surface defects. The latter can be addressed with the geometric freedom of additive manufacturing, colloquially known as 3D printing, which paves the way toward fabricating complex shape-conformable battery components [4]. Here, a summary of our recent works on lithium-ion battery 3D printing via thermoplastic material extrusion will be presented [5-9]. In particular, the development of printable composite filaments (Graphite-, LiFePO4-, Li2TP-, PEO/LiTFSI-, SiO2-, Ag/Cu-based) corresponding to each part of a classical LIB (electrodes, electrolyte, separator, current collectors), as well as the importance of introducing an adequate plasticizer (such as poly(ethylene glycol) dimethyl ether average Mn 500 for polylactic acid) as an additive to enhance both printability and further electrochemical performances, will be addressed. Printing of the complete LIB in a single step using multi-material printing options, and the implementation of a solvent-free protocol [7] will also be discussed. Finally, the capability of vat photopolymerization processes, including stereolithography, digital light processing and two-photon polymerization (offering a greater resolution down to 0.1µm), to print high resolution LIB components will be presented.[1] J.W. Long, B. Dunn, D.R. Rolison, H.S. White, Three-dimensional battery architectures, Chemical Reviews 104(10) (2004) 4463-4492.[2] A. Maurel, M. Haukka, E. MacDonald, L. Kivijärvi, E. Lahtinen, H. Kim, M. Armand, A. Cayla, A. Jamali, S. Grugeon, L. Dupont, S. Panier, Considering lithium-ion battery 3D-printing via thermoplastic material extrusion and polymer powder bed fusion, Additive Manufacturing (2020) 101651.[3] L. Taberna, S. Mitra, P. Poizot, P. Simon, J.M. Tarascon, High rate capabilities Fe3O4-based Cu nano-architectured electrodes for lithium-ion battery applications, Nature Materials 5(7) (2006) 567-573.[4] H. Ragones, S. Menkin, Y. Kamir, A. Gladkikh, T. Mukra, G. Kosa, D. Golodnitsky, Towards smart free form-factor 3D printable batteries, Sustainable Energy & Fuels 2(7) (2018) 1542-1549.[5] A. Maurel, M. Courty, B. Fleutot, H. Tortajada, K. Prashantha, M. Armand, S. Grugeon, S. Panier, L. Dupont, Highly Loaded Graphite-Polylactic Acid Composite-Based Filaments for Lithium-Ion Battery Three-Dimensional Printing, Chemistry of Materials 30(21) (2018) 7484-7493.[6] A. Maurel, S. Grugeon, B. Fleutot, M. Courty, K. Prashantha, H. Tortajada, M. Armand, S. Panier, L. Dupont, Three-Dimensional Printing of a LiFePO4/Graphite Battery Cell via Fused Deposition Modeling, Scientific Reports 9(1) (2019) 18031.[7] A. Maurel, R. Russo, S. Grugeon, S. Panier, L. Dupont, Environmentally Friendly Lithium-Terephthalate/Polylactic Acid Composite Filament Formulation for Lithium-Ion Battery 3D-Printing via Fused Deposition Modeling, ECS Journal of Solid State Science and Technology 10(3) (2021) 037004.[8] A. Maurel, M. Armand, S. Grugeon, B. Fleutot, C. Davoisne, H. Tortajada, M. Courty, S. Panier, L. Dupont, Poly(Ethylene Oxide)-LiTFSI Solid Polymer Electrolyte Filaments for Fused Deposition Modeling Three-Dimensional Printing, Journal of the Electrochemical Society 167(7) (2020).[9] A. Maurel, H. Kim, R. Russo, S. Grugeon, M. Armand, S. Panier, L. Dupont, Ag-Coated Cu/Polylactic Acid Composite Filament for Lithium and Sodium-Ion Battery Current Collector Three-Dimensional Printing via Thermoplastic Material Extrusion, Frontiers in Energy Research 9(70) (2021).

Customisable Tablet Printing: The Development of Multimaterial Hot Melt Inkjet 3D Printing to Produce Complex and Personalised Dosage Forms.

One of the most striking characteristics of 3D printing is its capability to produce multi-material objects with complex geometry. In pharmaceutics this translates to the possibility of dosage forms with multi-drug loading, tailored dosing and release. We have developed a novel dual material hot-melt inkjet 3D printing system which allows for precisely controlled multi-material solvent free inkjet printing. This reduces the need for time-consuming exchanges of printable inks and expensive post processing steps. With this printer, we show the potential for design of printed dosage forms for tailored drug release, including single and multi-material complex 3D patterns with defined localised drug loading where a drug-free ink is used as a release-retarding barrier. For this, we used Compritol HD5 ATO (matrix material) and Fenofibrate (model drug) to prepare both drug-free and drug-loaded inks with drug concentrations varying between 5% and 30% (w/w). The printed constructs demonstrated the required physical properties and displayed immediate, extended, delayed and pulsatile drug release depending on drug localisation inside of the printed formulations. For the first time, this paper demonstrates that a commonly used pharmaceutical lipid, Compritol HD5 ATO, can be printed via hot-melt inkjet printing as single ink material, or in combination with a drug, without the need for additional solvents. Concurrently, this paper demonstrates the capabilities of dual material hot-melt inkjet 3D printing system to produce multi-material personalised solid dosage forms.

4D Multimaterial Printing of Programmable and Selective Light‐Activated Shape‐Memory Structures with Embedded Gold Nanoparticles

Abstract4D printing is based on 3D printing of objects that can change their shape upon a proper triggering. Here, a novel approach is reported for fabricating programmable 3D printed objects composed of shape‐memory polymers (SMPs) that are activated by light. The light activation of the movement and shape morphing are based on combining gold nanoparticles (AuNPs) as photothermal converters with acrylate‐based printing compositions that form an SMP with tunable transition temperatures. The shape change of the printed objects is triggered by remote irradiation with a low‐cost LED light at a wavelength specific to the surface plasmon resonance of the embedded AuNPs. The light is converted to heat which enables the shape transition when the temperature reaches the Tg of the polymer. Excellent SMP properties are achieved with shape fixity and recovery ratios over 95%. This material composition and triggering approach enable fabricating programmable light‐activated 3D printed structures with a dual transition while tuning the concentration. Furthermore, numerical simulations performed by finite‐element analysis result in the excellent prediction of the shape‐memory recovery. The presented approach can be applied in remotely controlling morphing, mainly for applications in the fields of actuators and soft robotics.

A biofabrication method to align cells within bioprinted photocrosslinkable and cell-degradable hydrogel constructs via embedded fibers

The extracellular matrix (ECM) is composed of biochemical and biophysical cues that control cell behaviors and bulk mechanical properties. For example, anisotropy of the ECM and cell alignment are essential in the directional properties of tissues such as myocardium, tendon, and the knee meniscus. Technologies are needed to introduce anisotropic behavior into biomaterial constructs that can be used for the engineering of tissues as models and towards translational therapies. To address this, we developed an approach to align hydrogel fibers within cell-degradable bioink filaments with extrusion printing, where shear stresses during printing align fibers and photocrosslinking stabilizes the fiber orientation. Suspensions of hydrogel fibers were produced through the mechanical fragmentation of electrospun scaffolds of norbornene-modified hyaluronic acid, which were then encapsulated with meniscal fibrochondrocytes, mesenchymal stromal cells, or cardiac fibroblasts within gelatin-methacrylamide bioinks during extrusion printing into agarose suspension baths. Bioprinting parameters such as the needle diameter and the bioink flow rate influenced shear profiles, whereas the suspension bath properties and needle translation speed influenced filament diameters and uniformity. When optimized, filaments were formed with high levels of fiber alignment, which resulted in directional cell spreading during culture over one week. Controls that included bioprinted filaments without fibers or non-printed hydrogels of the same compositions either with or without fibers resulted in random cell spreading during culture. Further, constructs were printed with variable fiber and resulting cell alignment by varying print direction or using multi-material printing with and without fibers. This biofabrication technology advances our ability to fabricate constructs containing aligned cells towards tissue repair and the development of physiological tissue models.

Prediction of elastic material properties in additively fabricated multimaterials

The use of multimaterial 3d printers allow not to only shape the geometry but also the material properties of the part being designed. The difficulty for the designer is now to anticipate, what the resulting material properties of the mixture might be. Here a continuum mechanical approach is presented, and how this can be applied to currently used multimaterial printers using photopolymers and its use in a digital design process.

Fluid support

Additive Manufacturing Three-dimensional printing is a powerful tool for rapidly creating customized shapes, particularly out of soft materials such as polymers. However, it still can be challenging to print very soft materials such as hydrogels, which are of interest for medical devices and cell delivery, because of their low mechanical stiffness. Beh et al. overcame this by patterning a fluid-supported hydrogel precursor that provides structural support for the growing object while rinsing excess precursor from the printed regions. The authors were able to print materials spanning three orders of magnitude in stiffness and combined the printer with an extruder to perform multimaterial printing. Biomaterials 276 , 121034 (2021).

Direct Writing Corrugated PVC Gel Artificial Muscle via Multi-Material Printing Processes.

Electroactive PVC gel is a new artificial muscle material with good performance that can mimic the movement of biological muscle in an electric field. However, traditional manufacturing methods, such as casting, prevent the broad application of this promising material because they cannot achieve the integration of the PVC gel electrode and core layer, and at the same time, it is difficult to create complex and diverse structures. In this study, a multi-material, integrated direct writing method is proposed to fabricate corrugated PVC gel artificial muscle. Inks with suitable rheological properties were developed for printing four functional layers, including core layers, electrode layers, sacrificial layers, and insulating layers, with different characteristics. The curing conditions of the printed CNT/SMP inks under different applied conditions were also discussed. The structural parameters were optimized to improve the actuating performance of the PVC gel artificial muscle. The corrugated PVC gel with a span of 1.6 mm had the best actuating performance. Finally, we printed three layers of corrugated PVC gel artificial muscle with good actuating performance. The proposed method can help to solve the inherent shortcomings of traditional manufacturing methods of PVC gel actuators. The printed structures have potential applications in many fields, such as soft robotics and flexible electronic devices.

Design of an innovative new extrusion system for a printing machine for ceramics

The introduction of ceramic materials in the medical field is becoming a vital necessity because of its stable physicochemical characteristics, high biocompatibility, and good osteoconductivity. On the contrary, machining ceramic components is difficult, owing to their extreme hardness and brittleness. Additive manufacturing (AM) technologies are an appropriate alternative to obtain the complex shapes of implants, which can have porous structures. Thus, since the development of 3D printing, direct ink writing (DIW) is one of the most promising and inexpensive techniques for shaping free-form ceramic medical components such as prostheses or dental implants from liquids or pastes. However, the assurance of performance criteria of the extrusion system for simultaneous usage becomes the major challenge for most direct ink writing (DIW) platforms, for instance for printing large parts, for multi-material printing, to decrease printing time, and to increase efficiency in terms of motor usage and weight of the extruders. To address the current deficiencies, a new extrusion system is designed for a 3D printing machine for ceramics that is compatible with different low-cost, open-source 3D printers. The proposed extrusion model enables printing with a loader with different syringes simultaneously, without stopping the operational process while switching the syringe. It adopts three subsystems. The automatic syringe loading system, which is operational to manually receive several syringes of the same or different volumes, allows the syringe feeding system to be loaded and unloaded once the syringe is empty. The syringes are automatically transferred to the holding system using an arm. The holding system allows the fixing of the syringe in order to perform printing with ceramic material. Pugh concept analysis was used to select the optimum design shape. After that, the 3D CAD environment was used to combine the strength of Pugh’s method and the design space. This brings a new concept into the mechanical design field for 3D printers, which is in line with the technological trends prevalent in the industry.

A fluid-supported 3D hydrogel bioprinting method

Hydrogels are used in many biomedical applications, including regenerative medicine and surgical training phantoms. However, the ability to shape these materials into complex anatomical structures using additive manufacturing is limited in part by their low mechanical stiffness. We developed a hydrogel 3D printer, that projects patterns directly onto a thin layer of fluid-supported hydrogel precursor, which serves as a floating, liquid projection screen. This approach avoids inadvertent adhesion that affects typical resin-based 3D printers, and enables fast, continuous printing. As a consequence, we can print smooth objects free of layering artifacts, at rates of 200 mm/h along the Z-axis. We demonstrate the versatility of our approach by printing various complex structures, including free-standing channel networks with 500 μm-thick walls, using hydrogels with a wide range of stiffness from 7 kPa to more than 4 MPa. Lastly, because the printer features a free surface, we combined it with an extruder to perform multi-material printing. We use this strategy to create centimeter-scale, cell-laden hydrogels containing channels, that help address the key nutrient supply problem in bioprinting.

3D Printing of Multilayered and Multimaterial Electronics: A Review

Abstract3D printing, also known as additive manufacturing, is a manufacturing process in which the materials are deposited layer by layer in an additive manner. With the advancement in materials and manufacturing technology, 3D printing has found its applications in the field of electronics manufacturing. Initially, 3D printing is used for the fabrication of electronic components with single material designs such as resistors, inductors, circuits, antennas, strain gauges, etc. Recently, there are many works involving the use of 3D printing fabrication techniques for advanced electronic components and devices such as parallel plate capacitors, inductors, organic light‐emitting diodes, photovoltaics, transistors, displays, etc. which involve multilayer multimaterial printing. Despite these many works, there has been no review on the design and fabrication consideration for the 3D printing of multilayered and multimaterial (MLMM) electronics. As such, this review aims to summarize the current landscape of 3D printing of MLMM electronics and provide some insights on the design consideration, fabrication strategies, and challenges of 3D printing of MLMM electronics. In particular, the focus will be placed on discussing the interface conditions between different materials such as surface wettability, surface roughness, material compatibility, and the considerations for postprocessing treatments.

3D Printing of Next‐generation Electrochemical Energy Storage Devices: from Multiscale to Multimaterial

The increasing energy requirements to power the modern world has driven active research into more advanced electrochemical energy storage devices (EESD) with both high energy densities and power densities. Wide range of newly discovered materials with promising electrochemical properties has shown great potential for next‐generation devices, but their performance is normally associated with contradicting demands of thin electrodes and high mass loading that can be hardly achieved for practical applications. Design of three‐dimensional (3D) porous electrodes can increase the mass loading while maintaining the effective charge transport even with thick electrodes, which has proven to be efficient to overcome the limitations. 3D structures have also been demonstrated excellent structural stability to withstand strong strains and stresses generated during charge/discharge cycle. 3D printing, which can fabricate various delicate and complex structural designs, thus offering brand‐new opportunities for the rational design and facile construction of next‐generation EESDs. The recent developments in 3D printing of next‐generation EESDs with high performance are reviewed. Advanced/multiscale electrode structures, such as hierarchically porous structure that can be constructed via high‐resolution 3D printing or with post‐treatment, are further emphasized. The ability of current 3D printing techniques to fulfill multimaterial printing to fulfill simple packaging will be covered.

Additive Manufacturing of a W-Band System-on-Package

In this article, we demonstrate the design, fabrication, and characterization of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band system-on-package (SoP). This package is fully additively manufactured using a chip-first process and aerosol jet printing. With this method, we implement a transceiver consisting of two bare die amplifiers for transmitted and received signals, a bare die switch, printed bypass capacitors, surface-mount resistors for biasing networks, and a printed patch antenna, operating between 77.1 and 79.0 GHz. The second patch antenna of the same design, fabricated simultaneously, is used to characterize the antenna performance alone and the packaged components. Package substrates (dielectrics), conductors, and interconnects are printed around bare die attached to a carrier. Thin-film bypass capacitor dielectrics were printed using multimaterial aerosol jet printing (MMAJP), where aerosols of barium titanate and polyimide inks are mixed in place to form a high <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\epsilon _{r}$ </tex-math></inline-formula> polymer matrix nanocomposite film. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band interconnect performance is achieved using conformal-shaped ramp interconnects, allowing for frequency agnostic performance of the interconnect with no impedance discontinuity, within the physical limits of the printer. The antenna alone achieves a maximum gain of 6.7 dBi at 78.3 GHz, and the SoP achieves a gain of 16.4 dBi for the package. We estimate the package loss to be 2.8 dB or 0.6 dB/mm, including interconnects.

Emerging 3D printing technologies for drug delivery devices: Current status and future perspective.

The 'one-size-fits-all' approach followed by conventional drug delivery platforms often restricts its application in pharmaceutical industry, due to the incapability of adapting to individual pharmacokinetic traits. Driven by the development of additive manufacturing (AM) technology, three-dimensional (3D) printed drug delivery medical devices have gained increasing popularity, which offers key advantages over traditional drug delivery systems. The major benefits include the ability to fabricate 3D structures with customizable design and intricate architecture, and most importantly, ease of personalized medication. Furthermore, the emergence of multi-material printing and four-dimensional (4D) printing integrates the benefits of multiple functional materials, and thus provide widespread opportunities for the advancement of personalized drug delivery devices. Despite the remarkable progress made by AM techniques, concerns related to regulatory issues, scalability and cost-effectiveness remain major hurdles. Herein, we provide an overview on the latest accomplishments in 3D printed drug delivery devices as well as major challenges and future perspectives for AM enabled dosage forms and drug delivery systems.

Multi-material 3D printed PLA/PA6-TiO2 composite matrix: rheological, thermal, tensile, morphological and 4D capabilities

ABSTRACT The flexibility provided by fused deposition modelling (FDM) in processing of thermoplastic composite matrix (polylactic acid (PLA), polyamide6 (PA6) etc.) has made this process acceptable in different fields of research varying from structural, non-structural engineering, medicinal and space applications. But hitherto little has been reported on multi-material printing of PLA/PA6-TiO2 (70–30 wt %) matrix composite on FDM for biomedical scaffolding applications. In this work, the biocompatible grade of PLA, PA6-TiO2 (70–30 wt %) has been selected. An effort has been made for multi-material printing of PLA/PA6-TiO2 polymeric matrix and optimised printing conditions for FDM processing of selected layer combinations were ascertained. The results of mechanical testing suggest that, Infill speed: 90mm/s, Infill pattern: rectilinear and layer combination: PLA 5 layers/PA6-TiO2 5 layers are the optimised conditions for the FDM processing. From thermal analysis, it has been observed that both PLA and PA6-TiO2 are thermally stable. Finally, PLA/PA6-TiO2 based prototypes have shown controlled two-way 4D capabilities under the hot (70°C) and cold (10°C) water (selected as stimulus in present case). The results of mechanical testing have been supported by morphological analysis (surface porosity) on fractured surface.

Visual and haptic perceptibility of 3D printed skeletal models in orthognathic surgery

ObjectiveTo assess the anatomical and tactile quality of 3D printed models derived from medical printers for application in orthognathic surgery. MethodsA CBCT-scan of an 18 years old female patient was acquired with NewTom VGi evo (NewTom, Verona, Italy). Thereafter, mandibular bone was segmented and isolated from the scan using Mimics inPrint 2.0 software (Materialise NV, Leuven, Belgium). Six printers with different technologies were utilized for printing skeletal models, which included stereolithography (ProX800, 3D Systems, Rock Hill, SC, USA), digital light processing (Perfactory 4 mini XL, Envisiontec, Dearborn, MI, USA), fused deposition modeling (uPrint SE, Stratasys, Eden Prairie, MI, US), colorjet (ProJet CJP 660Pro, 3D Systems, Rock Hill, SC, USA), multijet (Objet Connex 350, Stratasys, Eden Prairie, MN, USA) and selective laser sintering (EOSINT P700, EOS GmbH, Munich, Germany). A questionnaire was designed, where 22 maxillofacial residents scored whether the printed models were able to mimic bone color, texture and anatomy. Five maxillofacial surgeons performed bone cutting with screw insertion/removal to assess the tactile perceptibility. ResultsIn relation to texture and cortical and medullary anatomy replication, Perfactory 4 mini XL printer showed the highest mean score, whereas, Objet Connex 350 scored highest for color replication. The haptic feedback for cutting and screw insertion/removal varied for each printer, however, overall it was found to be highest for ProX800, whereas, EOSINT P700 was found to be least favorable. ConclusionsThe digital light processing based Perfactory 4 mini XL printer offered the most acceptable anatomical model, whereas, deficiencies existed for the replication of haptic feedback to that of real bone with each printer. Clinical significanceThe study outcomes provide pearls and pitfalls of 3D printed models utilizing various printers and technologies. There is a need for research on multi-material printing as such to improve the haptic feedback of skeletal models and render the models more human bone-like to improve surgical planning and clinical training.

Multimaterial Aerosol Jet Printed Magnetic Nanocomposites for Microwave Circuits

This article demonstrates the process and characterization of additively manufactured polymer-matrix magnetic nanocomposites. These nanocomposites are composed of nickel-zinc ferrite (Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) nanoparticles in a polyimide matrix. These materials are printed using multimaterial aerosol jet printing where aerosols of nickel-zinc ferrite and polyimide inks are mixed in place to fabricate structures with nonunity relative permeability. To characterize these materials, we use energy-dispersive X-ray spectroscopy to estimate the content of ferrite in the composite, fitted simulation models, and ring resonator measurements to estimate the permeability. In fully aerosol jet printed 1-mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> inductors, we demonstrate an increase in inductance density of 40% in a 4.5-turn microstrip spiral inductor using this printed composite. These fully printed inductors demonstrate an inductance density of 4.2-nH/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . EDS analysis shows films with 18 wt.% Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Zn <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> . Finally, we show microstrip transmission lines on printed composite compared to the same on polyimide subjected to a dc magnetic bias, displaying a magnetic resonance behavior.

Three-dimensional printing of click functionalized, peptide patterned scaffolds for osteochondral tissue engineering

Osteochondral repair remains a significant clinical challenge due to the multiple tissue phenotypes and complex biochemical milieu in the osteochondral unit. To repair osteochondral defects, it is necessary to mimic the gradation between bone and cartilage, which requires spatial patterning of multiple tissue-specific cues. To address this need, we have developed a facile system for the conjugation and patterning of tissue-specific peptides by melt extrusion of peptide-functionalized poly(ε-caprolactone) (PCL). In this study, alkyne-terminated PCL was conjugated to tissue-specific peptides via a mild, aqueous, and Ru(II)-catalyzed click reaction. The PCL-peptide composites were then 3D printed by multimaterial segmented printing to generate user-defined patterning of tissue-specific peptides. To confirm the bioactivity of 3D printed PCL-peptide composites, bone- and cartilage-specific scaffolds were seeded with mesenchymal stem cells and assessed for deposition of tissue-specific extracellular matrix in vitro. PCL-peptide scaffolds successfully promoted osteogenic and chondrogenic matrix deposition, with effects dependent on the identity of conjugated peptide.

A 4D printing strategy and integrated design for programmable electroactive shape-color double-responsive bionic functions

The extraordinary potential of 4D printing regarding shape-changing, property-changing and functionality-changing could be widely utilized in the biomedical, aerospace, and robotics fields. Shape-color double-responsive 4D printing further expands the connotation of 4D printing by integrating both shape-changing and visual-changing, thereby providing new ideas and methods for actualizing active functions. However, current shape-color double-responsive 4D printing utilizes an external heat source, which is a sizeable limitation for actualizing the programmable shape-color dual-response function. Here, to overcome this issue, an electroactive shape-changing material, and thermal shape-color dual-response material are prepared, integrated, and printed with a double-nozzle multi-material printer. After preparing the materials, programmable electrothermal effects in different regions are actualized by controlling their resistances. Furthermore, multi-material printing allows for electroactive shape-changing materials to be embedded into thermal shape-color dual-response materials, thus actualizing programmable electroactive shape-color double-responsive 4D printing. This ingenious design concept and high-performance materials involved are demonstrated by mimicking biological functions such as mimosa leaves closing in turn, colorful starfish, and shape-color dual-changing wings. This study paves the way for development of programmable multi-functionality actuators with simultaneous fast responses and easy-fabrication for utilization in promising applications on biomedical devices and bioinspired robotics.

3D Printed Multi-material Medical Phantoms for Needle-tissue Interaction Modelling of Heterogeneous Structures

The fabrication of multi-material medical phantoms with both patient-specificity and realistic mechanical properties is of great importance for the development of surgical planning and medical training. In this work, a 3D multi-material printing system for medical phantom manufacturing was developed. Rigid and elastomeric materials are firstly combined in such application for an accurate tactile feedback. The phantom is designed with multiple layers, where silicone ink, Thermoplastic Polyurethane (TPU), and Acrylonitrile Butadiene Styrene (ABS) were chosen as printing materials for skin, soft tissue, and bone, respectively. Then, the printed phantoms were utilized for the investigation of needle-phantom interaction by needle insertion experiments. The mechanical needle-phantom interaction was characterized by skin-soft tissue interfacial puncture force, puncture depth, and number of insertion force peaks. The experiments demonstrated that the manufacturing conditions, i.e. the silicone grease ratio, interfacial thickness and the infill rate, played effective roles in regulating mechanical needle-phantom interaction. Moreover, the influences of material properties, including interfacial thickness and ultimate stress, on needle-phantom interaction were studied by finite element simulation. Also, a patient-specific forearm phantom was printed, where the anatomical features were acquired from Computed Tomography (CT) data. This study provided a potential manufacturing method for multi-material medical phantoms with tunable mechanical properties and offered guidelines for better phantom design.