3D Printing Strategy Research Articles

Bioinspired 3D-Printed MXene and Spidroin-Based Near-Infrared Light-Responsive Microneedle Scaffolds for Efficient Wound Management.

Biomedical dressings have been comprehensively explored for wound healing; however, the complicated manufacturing process and mono-function of the dressing remain critical challenges for further applications. Here, a versatile extrusion three-dimensional (3D) printing strategy to prepare MXene and spidroin-incorporated microneedle scaffolds with photothermal responsive and self-healing properties for promoting wound healing is proposed. Inspired by the cactus, the microneedle scaffold is composed of a top porous scaffold, and microneedles whose inverse opal (IO) photonic crystal (PC) structure and the ample space between the scaffold gaps endow the microneedle scaffold with high drug-carrying capacity. Furthermore, the excellent electrical and photothermal properties of MXene allow the microneedle scaffold to perform sensitive wound movement monitoring and controlled drug release under near-infrared irradiation. Moreover, the extensive hydrogen bonding and Schiff base between the spidroin, polyurethane (PU), and aloe vera gel (avGel) molecules conferred high self-healing and mechanical performance to the microneedle scaffold. In vivo experiments with rat models of wounds have shown that drug-laden microneedle scaffolds under near-infrared (NIR) light can promote the recovery of full-skin wounds. These unique characteristics suggest that 3D-printed multifunctional microneedle scaffolds show great potential for applications in facilitating wound healing and will find widespread applications in wound management.

Features of the Macro-, Micro-, and Fine Structure of the Nickel Superalloy Product Material Formed by the Method of Electron Beam Additive Manufacturing.

In the present work, the products in the form of vertical walls were made of heat-resistant nickel-based superalloy ZhS32 via the method of electron beam additive technology. Unidirectional printing strategy was applied. The effect of heat input and 3D printing strategy on the macrostructure, dimensions, and morphology of microstructure elements was established. It was shown that the additive product material has a directed macrostructure. The only exclusion was the final layer with a thickness of no more than 3.5 mm. The directed macrostructure consisted of dendrites oriented predominantly along the crystallographic direction {001} of the primary dendrite arms. The misorientation of the dendrite axes did not exceed 9 degrees. The angle between the predominant dendrite growth direction and the normal to the substrate was 23 degrees. The average primary dendrite arms' spacing increased monotonically from 16 µm at 5 mm from the substrate to 23 µm in the final layers of the product material (the overall height was 41 mm). It was found that the average size of γ' (Ni3Al)-phase precipitations in the form of nanoscale and submicrocrystalline cuboids varied in the range of 76 to 163 nm depending on the distance from the substrate. The size of γ'-phase precipitations reached a maximum at about 30 mm from the substrate, while in the final layers of the product material, the average cuboid size did not exceed 135 nm. Extreme dependence of the size of γ'-phase precipitations on the height of the product followed from a combination of a given monotonic decrease in heat input and heat accumulation in the product material as it formed, as did additional heat removal by means of radiation during formation of the final layer of the product without re-melting. Chemical elements of the austenitic steel substrate material were not detected in the product material more than 8 mm from the substrate. There were no macrodefects, such as voids, in the entire volume of the product material.

Microfluidic 3D Printing of Emulsion Ink for Engineering Porous Functionally Graded Materials

AbstractIn the last decade, 3D printing systems have greatly evolved both in terms of processable materials and printing resolutions, becoming a top seed technology for many academic and industrial applications. Nevertheless, manufacturing polymeric materials characterized by a trabecular porosity and functionally graded architecture—where both the local porosity and chemical composition of the matrix change in the 3D space—through additive platforms remains an open technical challenge. In this study, a 3D extrusion printing strategy to tackle this problem is presented. The proposed systems are based on a flow‐focusing microfluidic printing head—to continuously generate oil‐in‐water emulsion inks—and on an agarose fluid–gel used as a temporary support bath for the deposition of the photo‐curable emulsion inks. It is demonstrated that through this strategy one can design a priori and build with high accuracy both discontinuous and continuous functionally graded polymeric foams, where both the density and composition of the materials could be varied independently within arbitrarily complex 3D architectures. This study provides new means for the synthesis of microporous, polymeric FGMs which could find applications ranging from interface tissue engineering to automotive and construction industries.

Development of an extrusion-based 3D-printing strategy for clustering of human neural progenitor cells

3D bioprinting offers a simplified solution for the engineering of complex tissue parts for in-vitro drug discovery or, in-vivo implantation. However, significant amount of challenges exist in 3D bioprinting of neural tissues, as these are sensitive cell types to handle via extrusion bioprinting techniques. We assessed the feasibility of bioprinting human neural progenitor cells (NPCs) in 3D hydrogel lattices using a fibrinogen-alginate-chitosan bioink, previously optimized for neural-cell growth, and subsequently modified for structural support during extrusion printing, in this study. The original bioink used in this study was made by adding optimized amounts of high- and medium-viscosity alginate to the fibrinogen-chitosan-based bioink and making it extrudable under shear pressure. The mechanically robust 3D constructs promoted NPC cluster formation and maintained their morphology and viability during the entire culture period. This strategy may be useful for co-culturing of NPCs along with other cell types such as cardiac, vascular, and other cells during 3D bioprinting.

Continuous resin refilling and hydrogen bond synergistically assisted 3D structural color printing

3D photonic crystals (PCs) have attracted extensive attention due to their unique optical properties. However, fabricating 3D PCs structure by 3D printing colloidal particles is limited by control of assembly under a fast-printing speed. Here, we employ continuous digital light processing (DLP) 3D printing strategy with hydrogen bonds assisted colloidal inks for fabricating well-assembled 3D PCs structures. Stable dispersion of colloidal particles inside UV-curable system induced by hydrogen bonding and suction force induced by continuous curing manner cooperatively realize the simultaneous macroscopic printing and microscopic particle assembly, which endows volumetric color property. Structural color can be well regulated by controlling the particle diameter and printing speed, through which various complex 3D structures with desired structural color distribution and optical light-guide properties are acquired. This 3D color construction approach shows great potential in customized jewelry accessories, decoration and optical device preparation, and will innovate the development of structural color.

Effect of annealing and carbon nanotube infill on the mechanical and electrical properties of additively manufactured polyether-ether-ketone nanocomposites via fused filament fabrication

The light-weight, high-strength poly-ether-ether-ketone (PEEK) and its composite materials are the ideal candidate for a plethora of engineering applications. However, the inherent high viscosity and melting temperature of PEEK pose great challenges for the extrusion-based 3D printing process, leaving a wide knowledge gap on the properties and functionalities of novel PEEK-based composites. In this work, the PEEK/CNT composite filaments with different CNT content ranging from 1 to 7 wt% are prepared by single-screw extruder and subsequently printed with a custom-made high temperature 3D printer. The effects of CNT content and annealing on the mechanical strength and electrical conductivity of the 3D printed parts are investigated in detail. The tensile test result shows that the presence of CNT significantly enhances the mechanical strength of the composite. With 7 wt% CNT content, the maximum tensile strength and elastic modulus reaches 107.7 MPa and 1908.0 MPa, respectively, which amounts to a rise of 27.4% and 17.0% compared with the neat PEEK sample. The annealing treatment is similarly effective in strengthening the printed composites. The addition of CNT is also found to greatly improve the electrical conductivity to the PEEK, reaching 101 S/m for 7 wt% CNT. With such superior electrical conductivity, the printed PEEK/CNT composite sample exhibits outstanding electromagnetic interference (EMI) shielding performance, reaching 32.4 dB. However, additional annealing treatment decreases the electrical conductivity as wells as EMI shielding performance. Such decrease is mainly attributed to the growth of the crystals during annealing, which expels the CNTs to the grain boundaries and leads to remarkable agglomeration, which disconnects the pervasive conductive networks. The finding in this work can provide insights on the new designs of PEEK composite feedstock materials and cultivate new 3D printing strategies targeted specifically for highly-functional, high-strength novel composites.

3D printed hierarchically porous zero-valent copper for efficient pollutant degradation through peroxymonosulfate activation

Three-dimensional (3D) printing has demonstrated great potential in wastewater purification. Herein, a facile 3D printing strategy is utilized to prepare zero-valent copper (3D-ZVC). The obtained 3D-ZVC framework displays a hierarchically porous structure and a rough surface, which correspond to excellent mechanical robustness and catalytic performance in degrading multiple organic pollutants through peroxymonosulfate (PMS) activation. The 3D-ZVC/PMS/Vis system is capable of achieving a tetracycline (TC) degradation efficiency of over 96.5 % within 20 min, which greatly exceeds that of homogeneous Cu2+/PMS/Vis and contemporary powder/PMS/Vis systems as a result of the unique hierarchical porous structure and cycling of Cu(I)/Cu(II) in 3D-ZVC. Furthermore, the 3D-ZVC/PMS/Vis system exhibits a broad pH resistance range (3.21–10.18), spectacular adaptability, unparalleled stability, and excellent reusability after 23 successive cycles. Electrons and various reactive oxygen species, including SO4−, OH, O2−, and 1O2, are all involved in the decomposition of TC, with 1O2 playing a dominant role. The influence parameters and possible intermediates of the 3D-ZVC/PMS/Vis system are investigated. Toxicity estimation analysis indicates that the toxicity of TC degradation products has been significantly reduced, which is further confirmed through growth control experiments of bean sprouts. This study highlights a prospective and feasible application of 3D printing in environmental remediation through PMS activation.

3D printing of carbon tile-modulated well-interconnected hierarchically porous pseudocapacitive electrode

Pseudocapacitive electrode architecture with well-interconnected open pores is essential and critical to the high-performance energy storage. However, challenges remain pertaining to consistent and scalable manufacturing, as well as fast ion/electron transport, especially at a high mass loading of active materials. Herein, with kapok-derived proper-curved quasi-2D carbon tile (CT) featuring thin wall and high microporosity as unique skeleton support, a novel pseudocapacitive CT-single-wall carbon nanotube (SWNT)-NiCo2O4 electrode was constructed via a scalable and controllable extrusion-based 3D printing strategy. The resulting 3D-printed electrode demonstrated abundant well-interconnected hierarchical pores and continuous conductive network built by coupling CTs and SWNTs, thereby enabling uniform and high mass loading of active NiCo2O4 (31 mg cm−2), and meanwhile guaranteeing unimpeded channels and adequate pathways acting as “superhighways” for ultrafast ion diffusion and electron transport throughout the entire device. Benefiting from these prominent features, an asymmetric supercapacitor assembled with 3D-printed CT-modulated electrode delivered high specific capacitance (588 mF cm−2) and energy density (138 µWh cm−2), exceptional long-term cycling stability (82% after 50000 cycles), and superior capacity even at large electrode thickness. This work has shed light on new strategies for fabricating rational pseudocapacitive electrode architectures toward high-capacity, rapidly cycling devices.

Bio-based vitrimeric elastomers enable completely sustainable triboelectric nanogenerator

Completely sustainable triboelectric nanogenerators (TENGs) with bio-based raw materials, green synthesis, resource-saving processing, durable mechanical and electrical performance, facile recycling, and degradation properties are highly desired for green energy harvesting and wearable electronics, but their preparation remains a challenge. This study develops bio-based vitrimers combining green synthesis, excellent elasticity, biodegradability, and recyclability to address this challenge. A salt-assisted three-dimensional (3D) printing strategy is developed to fabricate mechanically robust TENGs with hierarchical porous structures. The triboelectric contact between the surfaces and external triboelectric materials as well as that of the internal hierarchical pore’s wall contributes to the excellent electrical output performance. The resultant TENGs could be easily recycled into different forms by light-assisted fabrication to extend their lifetime. The main part of discarded TENGs shows facile degradation under benign conditions without negative influence on the environment, while the high-value conductive fillers can be readily recycled. Overall, this work presents a new paradigm for completely sustainable TENGs, which will inspire the development of sustainable electronic devices.

Nanofiber self-consistent additive manufacturing process for 3D microfluidics

3D microfluidic devices have emerged as powerful platforms for analytical chemistry, biomedical sensors, and microscale fluid manipulation. 3D printing technology, owing to its structural fabrication flexibility, has drawn extensive attention in the field of 3D microfluidics fabrication. However, the collapse of suspended structures and residues of sacrificial materials greatly restrict the application of this technology, especially for extremely narrow channel fabrication. In this paper, a 3D printing strategy named nanofiber self-consistent additive manufacturing (NSCAM) is proposed for integrated 3D microfluidic chip fabrication with porous nanofibers as supporting structures, which avoids the sacrificial layer release process. In the NSCAM process, electrospinning and electrohydrodynamic jet (E-jet) writing are alternately employed. The porous polyimide nanofiber mats formed by electrospinning are ingeniously applied as both supporting structures for the suspended layer and percolating media for liquid flow, while the polydimethylsiloxane E-jet writing ink printed on the nanofiber mats (named construction fluid in this paper) controllably permeates through the porous mats. After curing, the resultant construction fluid–nanofiber composites are formed as 3D channel walls. As a proof of concept, a microfluidic pressure-gain valve, which contains typical features of narrow channels and movable membranes, was fabricated, and the printed valve was totally closed under a control pressure of 45 kPa with a fast dynamic response of 52.6 ms, indicating the feasibility of NSCAM. Therefore, we believe NSCAM is a promising technique for manufacturing microdevices that include movable membrane cavities, pillar cavities, and porous scaffolds, showing broad applications in 3D microfluidics, soft robot drivers or sensors, and organ-on-a-chip systems.

Influence of Light-Intensity-Dependent Droplet Directionality on Dimensions of Structures Constructed Using an In Situ Light-Guided 3D Printing Method.

As an alternative to conventional 3D printing methods that require supports, a new 3D printing strategy that utilizes guided light in situ has been developed for fabricating freestanding overhanging structures without supports. Light intensity has been found to be a crucial factor in modifying the dimensions of structures printed using this method; however, the underlying mechanism has not been clearly identified. Therefore, the light-intensity-dependent changes in the structure dimensions were analyzed in this study to elucidate the associated mechanism. Essentially, the entire process of deposition was monitored by assessing the behavior of photocurable droplets prior to their collision with the structure using imaging analysis tools such as a high-speed camera and MATLAB®. With increasing light intensity, the instability of the ejected falling droplets increased, and the droplet directionality deteriorated. This increased the dispersion of the droplet midpoints, which caused the average midpoints of the deposited single layers to shift further away from the center of the structure. Consequently, the diameter of the structure formed by successive stacking of single layers increased, and the layer thickness per droplet decreased. These led to light-intensity-dependent differences in the diameter and height of structures that were created from the same number of droplets.

Three-Dimensional Printing and Fracture Mapping in Pelvic and Acetabular Fractures: A Systematic Review and Meta-Analysis.

Three-dimensional printing and fracture mapping technology is gaining popularity for preoperative planning of fractures. The aim of this meta-analysis is to further understand for the effects of 3D printing and fracture mapping on intraoperative parameters, postoperative complications, and functional recovery on pelvic and acetabular fractures. The PubMed, Embase, Cochrane and Web of Science databases were systematically searched for articles according to established criteria. A total of 17 studies were included in this study, of which 3 were RCTs, with a total of 889 patients, including 458 patients treated by traditional open reduction and internal fixation methods and 431 patients treated using 3D printing strategies. It was revealed that three-dimensional printing and fracture mapping reduced intraoperative surgical duration (RoM 0.74; 95% CI; 0.66–0.83; I2 = 93%), and blood loss (RoM 0.71; 95% CI; 0.63–0.81; I2 = 71%). as compared to traditional surgical approaches. In addition, there was significantly lower exposure to intraoperative imaging (RoM 0.36; 95% CI; 0.17–0.76; I2 = 99%), significantly lower postoperative complications (OR 0.42; 95% CI; 0.22–0.78; I2 = 9%) and significantly higher excellent/good reduction (OR 1.53; 95% CI; 1.08–2.17; I2 = 0%) in the three-dimensional printing and fracture mapping group. Further stratification results with only prospective studies showed similar trends. Three-dimensional printing and fracture mapping technology has potential in enhancing treatment of complex fractures by improving surgical related factors and functional outcomes and therefore could be considered as a viable tool for future clinical applications.

Generative shaping and material-forming (GSM) enables structure engineering of complex-shaped Li4SiO4 ceramics based on 3D printing of ceramic/polymer precursors

Vat photopolymerization (VPP) 3D printing of ceramics normally uses ceramic slurries directly made of the target ceramic powder. It may become challenging when the ceramic powders are difficult-to-make and thus are expensive or rarely accessible. We have previously proposed a generative shaping and material-forming (GSM) 3D printing strategy, which involves the use of low-cost multi-component inorganic ceramic precursors as powder sources. The shaping of complex structures was realized through VPP, followed by reaction sintering to form the target ceramic material. In the current study, as a step further, ceramic (Li 2 CO 3 ) and polymer (methyl polysiloxane) combined precursors were employed as an alternative material source for the first time to go through the 3D printing and reaction sintering processes, complementing the application range of the proposed GSM strategy. The slurry formulation and printability, the sinterability of the printed parts and the microstructures and mechanical performance of the sintered parts were characterized and optimized in accordance with the ingredient contents, particularly the stoichiometric ratios of Si:Li in the precursors. As a result, complex-structured Li 4 SiO 4 ceramics with high purity were fabricated based on the use of Li 2 CO 3 ceramic and Si-rich polymer as precursors. Through the advanced characterization and analysis of material phase and microstructural evolution, it was found that the fabricated complex-structured Li 4 SiO 4 ceramics based on a precursor slurry with a solid content of 40 vol%, a Si:Li ratio of 1:2.5, and a sintering temperature of 850 ℃ showed a high phase purity of 97.23% and a compressive strength of 15.24 ± 0.33 MPa, with a skeleton’s relative density of 65.31% is achieved. The results showed greatly enhanced strength at much higher porosities, which might be advantageous and beneficial to structure engineering for mechanical enhancement and the improvement of tritium release effectiveness. Compared with the previous study using multi-component ceramic powder precursors, the ceramics prepared in this study exhibited enhanced microstructural stability and higher phase purity with an advantageously lower sintering temperature. Further analysis revealed that compared with the high temperature solid-state reaction of multi-component ceramic powder precursors, the involvement of the Si-rich polymer precursor enabled the more efficient and complete synthesis of Li 4 SiO 4 as a result of the accelerated covering and cleavage of Si–O–Si bonds on the Li 2 CO 3 particles at a much lower temperature. The present work suggests that the GSM strategy using combined ceramic and polymer precursors as proposed in this study is a promising alternative method to produce high quality Li 4 SiO 4 components with complex structures. • Our GSM strategy is extended to 3D printing using ceramic/polymer precursors. • Slurry formulation and printability, sinterability of parts and microstructures of sintered parts were characterized. • High material phase purity and strength for the skeleton were achieved with lower sintering temperature. • Improved strength by GSM enabled structure engineering with complete synthesis/rearrangement of material/microstructures.

Integrated rapid-prototyping and strength-increasing all-in-one 3D printing of chitosan hydrogels

Chitosan (CS), as the only alkaline polysaccharide with inherent biocompatibility and biodegradability in nature, is one of the most studied biopolymers for hydrogel preparation. However, the inherent low mechanical strength and uncontrollable swelling of CS hydrogels limit their use as printing inks. Herein, we present an integrated rapid-prototyping and strength-increasing CS hydrogels 3D printing strategy using only saturated NaCl containing trace initiator as the ink-receiving solution. Moreover, the hydrogel also exhibits excellent anti-swelling and cytocompatibility, providing a customized, high-strength scaffold for tissue engineering applications.

Ordered porous and uniform electric-field-strength micro-supercapacitors by 3D printing based on liquid-crystal V2O5 nanowires compositing carbon nanomaterials

The design of electrode internal structure plays an important role in improving the performance of micro-supercapacitors (MSCs). However, the complexity of the program hinders the development and application of Three-dimensional(3D)-printed MSCs. Herein, printable inks were prepared by using vanadium pentoxide nanowires as active materials, carbon nanotubes as collector and conductive agent, graphene oxide as adhesive, scaffold and water retaining agent. Benefiting from the liquid–crystal properties of materials and 3D printing technology as well as the adjustment of the materials proportion, onion-like structures with ordered porous layered structure and uniform electric-field-strength MSCs were constructed. The 3D-printed MSC has fine area capacitance (34.68 mF cm−2) and area energy density (1.73 µWh cm−2 at a current density of 0.24 mA cm−2). Therefore, using the unique characteristics of materials to build an efficient 3D printing strategy is expected to provide a feasible solution for the construction of various MSCs and other high-energy storage systems.

Jammed Microgel-Based Inks for 3D Printing of Complex Structures Transformable via pH/Temperature Variations.

Structure changes mediated by anisotropic volume changes of stimuli-responsive hydrogels are useful for many research fields, yet relatively simple structured objects are mostly used due to limitation in fabrication methods. To fabricate complex 3 dimensional (3D) structures that undergo structure changes in response to external stimuli, jammed microgel-based inks containing precursors of stimuli-responsive hydrogels are developed for extrusion-based 3D printing. Specifically, the jammed microgel-based inks are prepared by absorbing precursors of poly(acrylic acid) or poly(N-isopropylacrylamide) in poly(acrylamide) (PAAm) microgels, and jamming them. The inks exhibit shear-thinning and self-healing properties that allow extrusion of the inks through a nozzle and rapid stabilization after printing. Stimuli-mediated volume changes are observed for the extruded structures when they are post-crosslinked by UV light to form interpenetrating networks of PAAm microgels and stimuli-responsive hydrogels. Using this method, a dumbbell-shaped object that can transform to a biconvex shape, and a gripper that can grasp and lift an object in response to stimuli are 3D-printed. The jammed microgel-based 3D printing strategy is a versatile method useful for variety of applications as diverse types of monomers absorbable in the microgels can be used to fabricate complex 3D objects transformable by external stimuli.

3D-printing of polymer‐derived SiCN ceramic matrix composites by digital light processing

In this study, we present a DLP 3D-printing strategy for the fabrication of SiCN ceramic matrix composites (CMCs). The polysilazane-based preceramic polymer containing inert fillers was UV-cured into a green body and then converted to SiCN CMCs after pyrolysis. The introduced fillers (Si3N4 particles and Si3N4 whiskers) as reinforcements are well dispersed in the matrix, which can not only effectively reduce the linear shrinkage and weight loss, but also greatly improve the mechanical properties of the SiCN CMCs. The bending strength of the SiCN CMCs reinforced with 10 wt% Si3N4 whiskers (without surface polished) reached 180.7 ± 15.6 MPa. Furthermore, the effect of fillers content on microstructure and porosity of the SiCN CMCs are discussed, and it was found that the excessive fillers led to increased pore defects and decreased continuity of the matrix, thereby reducing the mechanical properties of the SiCN CMCs. This strategy provides a promising ceramic manufacturing technique to fabricate polymer‐derived CMCs with complex-shaped and high-performance for potential demanding applications.

3D Printing of parts using metal extrusion: an overview of shaping debinding and sintering technology

Additive Manufacturing (AM) is the fabrication of real three-dimensional objects from plastics and metals by adding material, layer by layer. One of the most common AM processes is the Material Extrusion (ME) based on different approaches: plunger, filament and screw. Material Extrusion technologies of metal-polymer composites is expanding and it mainly uses the filament or plunger-based approaches. The feedstock used is a mixture of metal powder (from 55 vol% to about 80 vol%) dispersed in a thermoplastic matrix, as the Metal Injection Molding (MIM) materials. The process consists of three steps: shaping, debinding and sintering. The first step provides the extrusion of filament to realize a primary piece called “green part”; subsequent steps, debinding and sintering, allow to obtain a full metal part by dissolving the polymeric binder. The latter can be carried out using solvents, heat and the combination of them. The interest toward this technology is driven by the possibility to replace other Metal AM technologies, such as Selective Laser Melting or Direct Energy Deposition, in sectors like rapid-tooling or mass production, with several benefits: simplicity, safety to use and saving material and energy. The aim of this keynote is to provide a general overview of the main metal ME technologies considering the more technical aspects such as process methodologies, 3D printing strategy, process parameters, materials and possible applications for the manufacturing of samples on a 3D consumer printer.

Low‐Cost Volumetric 3D Printing of High‐Precision Miniature Lenses in Seconds

Abstract3D printing is a promising method for the generation of complex‐shaped optical components. However, the printing efficiency, form accuracy, and surface smoothness are still challenging, especially for the printing of optical components. In this study, by synergizing the volumetric projection stereolithography, meniscus equilibrium effect, and iterative learning scheme, a low‐cost volumetric 3D printing method is developed for the ultra‐fast and high‐precision fabrication of miniature lenses with sub‐nanometric roughness. By including the covered liquid film as a part of the printed lens in the iterative learning, a low form error at the micrometer scale is achieved for the printed lens without any prior knowledge of the 3D printing process. As a demonstration, a sphere lens at the millimeter scale is directly printed in 2 s, achieving a peak‐to‐valley profile error of less than 5 µm, a sub‐nanometric roughness of rms = 0.614 nm, and an imaging resolution of 203.2 lp mm−1. It suggests that besides fast prototyping, the developed 3D printing strategy is suitable for the massive production of precise lenses.

Dynamically Responsive Scaffolds from Microfluidic 3D Printing for Skin Flap Regeneration.

Biological scaffolds hold promising perspectives for random skin flap regeneration, while the practical application is greatly limited by their insufficient vascularization ability and the lack of responsiveness during the dynamical healing process. Herein, a novel MXene‐incorporated hollow fibrous (MX‐HF) scaffold with dynamically responsive channels is presented for promoting vascularization and skin flap regeneration by using a microfluidic‐assisted 3D printing strategy. Benefiting from the photothermal conversion capacity of the MXene nanosheets and temperature‐responsive ability of poly(NIPAM) hydrogels in the MX‐HF scaffolds, they display a near‐infrared (NIR)‐responsive shrinkage/swelling behavior, which facilitates the cell penetration into the scaffold channels from the surrounding environment. Moreover, by incorporating vascular endothelial growth factor (VEGF) into the hydrogel matrix for controllable delivery, the MX‐HF scaffolds can achieve promoted proliferation, migration, and proangiogenic effects of endothelial cells under NIR irradiation. It is further demonstrated in vivo that the NIR‐responsive VEGF@MX‐HF scaffolds can effectively improve skin flap survival by promoting angiogenesis, decreasing inflammation, and attenuating apoptosis in skin flaps. Thus, it is believed that such responsive MX‐HF scaffolds are promising candidates for clinical random skin flap regeneration as well as other diverse tissue engineering applications.