Despite the tremendous potential of bioprinting techniques toward the fabrication of highly complex biological structures and the flourishing progress in 3D bioprinting, the most critical challenge ...of the current approaches is the printing of hollow tubular structures. In this work, an advanced 4D biofabrication approach, based on printing of shape‐morphing biopolymer hydrogels, is developed for the fabrication of hollow self‐folding tubes with unprecedented control over their diameters and architectures at high resolution. The versatility of the approach is demonstrated by employing two different biopolymers (alginate and hyaluronic acid) and mouse bone marrow stromal cells. Harnessing the printing and postprinting parameters allows attaining average internal tube diameters as low as 20 µm, which is not yet achievable by other existing bioprinting/biofabrication approaches and is comparable to the diameters of the smallest blood vessels. The proposed 4D biofabrication process does not pose any negative effect on the viability of the printed cells, and the self‐folded hydrogel‐based tubes support cell survival for at least 7 d without any decrease in cell viability. Consequently, the presented 4D biofabrication strategy allows the production of dynamically reconfigurable architectures with tunable functionality and responsiveness, governed by the selection of suitable materials and cells.
An advanced 4D biofabrication approach, based on shape‐morphing biopolymer hydrogels, is presented for the fabrication of hollow self‐folding tubes with unprecedented control over their diameters and architectures at high resolution. The approach paves new avenues for the creation of tailored cell‐laden shape‐morphing architectures for tissue engineering and regenerative medicine applications.
Self‐folding microscale origami patterns are demonstrated in polymer films with control over mountain/valley assignments and fold angles using trilayers of photo‐crosslinkable copolymers with a ...temperature‐sensitive hydrogel as the middle layer. The characteristic size scale of the folds W = 30 μm and figure of merit A/
W
2 ≈ 5000, demonstrated here represent substantial advances in the fabrication of self‐folding origami.
4D bioprinting has emerged as a powerful technique where the fourth dimension “time” is incorporated with 3D bioprinting. In this technique, the printed bioconstructs are able to change their shapes ...or functionalities when triggered by either internal or external stimuli. In 4D bioprinting, the materials with/without cells enable the spatial–temporal control of the shape and/or functionality of the constructs. Using this method, researchers have printed bioconstructs that can transform into rather complex structures which are difficult to obtain directly by 3D bioprinting or other methods. Although the history of 4D bioprinting is short, rapid progress in this field is witnessed recently, with focus mainly on developing novel 4D printable materials, exploring novel methods to precisely control the process, and pursuing biomedical applications. To better understand this technique, the recent advances of 4D bioprinting, including the mechanism, structure design principles, applications in biomedical engineering, and also the facing challenges are reviewed.
In four dimensional bioprinting, the printed objects are able to change their shapes or functionalities when triggered by stimuli. Using this method, researchers have fabricated bioconstructs that can transform into rather complex shapes. To better understand this technique, the recent advances of 4D bioprinting are reviewed, including the mechanism, design principles, biomedical applications, and also the facing challenges.
Self‐folding origami is of great interest in current research on functional materials and structures, but there is still a challenge to develop a simple method to create freestanding, reversible, and ...complex origami structures. This communication provides a feasible solution to this challenge by developing a method based on the digit light processing technique and desolvation‐induced self‐folding. In this new method, flat polymer sheets can be cured by a light field from a commercial projector with varying intensity, and the self‐folding process is triggered by desolvation in water. Folded origami structures can be recovered once immersed in the swelling medium. The self‐folding process is investigated both experimentally and theoretically. Diverse 3D origami shapes are demonstrated. This method can be used for responsive actuators and the fabrication of 3D electronic devices.
Reversible and freestanding self‐folding origami structures are created by digit light processing and desolvation‐induced volume contraction. Complex origami shapes are achieved through the variation of light intensity in three dimensions. Applications of the method to stimulus responsive actuators and the fabrication of 3D electronics are presented.
The integration of swellable metal–organic frameworks (MOFs) into polymeric composite films is a straightforward strategy to develop soft materials that undergo reversible shape transformations ...derived from the intrinsic flexibility of MOF crystals. However, a crucial step toward their practical application relies on the ability to attain specific and programmable actuation, which enables the design of self‐shaping objects on demand. Herein, a chemical etching method is demonstrated for the fabrication of patterned composite films showing tunable self‐folding response, predictable and reversible 2D‐to‐3D shape transformations triggered by water adsorption/desorption. These films are fabricated by selective removal of swellable MOF crystals allowing control over their spatial distribution within the polymeric film. Upon exposure to moisture, various programmable 3D architectures, which include a mechanical gripper, a lift, and a unidirectional walking device, are generated. Remarkably, these 2D‐to‐3D shape transformations can be reversed by light‐induced desorption. The reported strategy offers a platform for fabricating flexible MOF‐based autonomous soft mechanical devices with functionalities for micromanipulation, automation, and robotics.
Programmable self‐shaping composite films are successfully fabricated via controlled chemical etching of swellable metal–organic framework (MOF) crystals embedded in a polymer matrix. This method allows the preparation of multiple types of patterned structures, which exhibit enhanced self‐folding response and predictable 2D‐to‐3D shape transformations driven by water adsorption, and which can be reversed by light‐induced desorption.
Flexible thermoresponsive polymeric microjets are formed by the self‐folding of polymeric layers containing a thin Pt film used as catalyst for self‐propulsion in solutions containing hydrogen ...peroxide. The flexible microjets can reversibly fold and unfold in an accurate manner by applying changes in temperature to the solution in which they are immersed. This effect allows microjets to rapidly start and stop multiple times by controlling the radius of curvature of the microjet. This work opens many possibilities in the field of artificial nanodevices, for fundamental studies on self‐propulsion at the microscale, and also for biorelated applications.
Micro jet boating: Flexible thermoresponsive polymer microjets can be fabricated. These self‐propelled microjets can reversibly fold and unfold in an accurate manner by applying changes in temperature to the solution in which they are immersed. This effect allows them to start and stop multiple times by controlling the radius of curvature of the microtube.
The presented microrobotic platform combines together the advantages of self‐folding NIR light sensitive polymer bilayers, magnetic alginate microbeads, and a 3D manipulation system, to propose a ...solution for targeted, on‐demand drug and cell delivery. First feasibility studies are presented together with the potential of the full design.
Peripheral nerve interfacing (PNI) has a high clinical potential for treating various diseases, such as obesity or diabetes. However, currently existing electrodes present challenges to the ...interfacing procedure, which limit their clinical application, in particular, when targeting small peripheral nerves (<200 µm). To improve the electrode handling and implantation, a nerve interface that can fold itself to a cuff around a small nerve, triggered by the body moisture during insertion, is fabricated. This folding is achieved by printing a bilayer of a flexible polyurethane printing resin and a highly swelling sodium acrylate hydrogel using photopolymerization. When immersed in an aqueous liquid, the hydrogel swells and folds the electrode softly around the nerve. Furthermore, the electrodes are robust, can be stretched (>20%), and bent to facilitate the implantation due to the use of soft and stretchable printing resins as substrates and a microcracked gold film as conductive layer. The straightforward implantation and extraction of the electrode as well as stimulation and recording capabilities on a small peripheral nerve in vivo are demonstrated. It is believed that such simple and robust to use self‐folding electrodes will pave the way for bringing PNI to a broader clinical application.
An electric peripheral nerve interface that can fold itself to a cuff around small nerves during the implantation is presented. This actuation property, combined with the use of stretchable materials, makes the device robust and straightforward to use. The stimulation and recording capabilities are shown on small nerves in vivo.
2D metal nanosheets are attractive for various applications stemming from the intriguing characteristics related with their dimensionality; however, their effective and scalable preparation remains a ...great challenge. Herein, a scalable preparation process of relatively active metal nanosheets (e.g., Zn, Al, and Cu) with the thickness down to several nanometers at low cost is demonstrated, which involves an initial self‐folding‐rolling step followed by the subsequent ultrasonication to exfoliate them without any etching step. The native oxide on the surface of the metals, which acts as a barrier between the adjacent metal layers, plays a special role in enabling the successful preparation of 2D metal nanosheets. As a demonstration for their practicability, a hierarchical Zn anode, which is constructed by the Zn microsheets coated with carbon (Zn MS@C) via in situ carbonization of carboxymethylcellulose (CMC) binder, is successfully implemented as anode for rechargeable aqueous Zn‐ion batteries. When applied in symmetrical battery, the Zn MS@C delivers a long lifespan of over 800 h at 0.2 mA cm−2 with a capacity of 0.1 mA h cm−2. Importantly, the full battery of MnO2 || Zn MS@C also performs a high discharge capacity of 217.4 mA h g−1 after 140 cycles at 300 mA g−1.
A scalable preparation process of relatively active metal nanosheets, which involves a self‐folding‐rolling step and the subsequent ultrasonication without any etching step, is demonstrated. A hierarchical carbon‐coated Zn microsheets anode (Zn MS@C) is successfully implemented for Zn‐ion batteries, which performs well whether in the symmetrical battery or the Zn‐MnO2 full battery.
Thermally activated, untethered microgrippers can reach narrow conduits in the body and be used to excise tissue for diagnostic analyses. As depicted in the figure, the feasibility of an in vivo ...biopsy of the porcine bile duct using untethered microgrippers is demonstrated.
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