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With the development of science and technology, flexible sensors play an indispensable role in body monitoring. Rapid prototyping of high-performance flexible sensors has become an important method to develop flexible sensors. The purpose of this study was to develop a flexible resin with multi-walled carbon nanotubes (MWCNTs) for the rapid fabrication of flexible sensors using digital light processing additive manufacturing. In this study, MWCNTs were mixed in thermoplastic polyurethane (TPU) photosensitive resin to prepare polymer-matrix composites, and a flexible strain sensor was prepared using self-developed additive equipment. The results showed that the 1.2 wt% MWCNTs/TPU composite flexible sensor had high gauge factor of 9.988 with a linearity up to 45% strain and high mechanical durability (1000 cycles). Furthermore, the sensor could be used for gesture recognition and monitoring and has good performance. This method is expected to provide a new idea for the rapid personalized forming of flexible sensors.

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Patterning Metal-Organic Frameworks (MOFs) is essential for their use in sensing, electronics, photonics, and encryption technologies. However, current lithography methods are limited in their ability to pattern more than two MOFs, hindering the potential for creating advanced multifunctional surfaces. Additionally, balancing design flexibility, simplicity, and cost often results in compromises. This study addresses these challenges by combining Digital-Light Processing (DLP) with a capillary-assisted stop-flow system to enable multimaterial MOF patterning. It demonstrates the desktop fabrication of multiplexed arbitrary micropatterns across cm-scale areas while preserving the MOF's pore accessibility. The ink, consisting of a MOF crystal suspension in a low volatile solvent, a mixture of high molecular weight oligomers, and a photoinitiator, is confined by capillarity in the DLP projection area and quickly exchanged using syringe pumps. The versatility of this method is demonstrated by the direct printing of a ZIF-8-based luminescent oxygen sensor, a 5-component dynamic information concealment method, and a PCN-224-based colorimetric sensor for amines, covering disparate pore and analyte sizes. The multi-MOF capabilities, simplicity, and accessibility of this strategy pave the way for the facile exploration of MOF materials across a wide range of applications, with the potential to significantly accelerate the design-to-application cycle of MOF-based devices.

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The first report of star poly(L-proline) crosslinkers is disclosed for digital light processing 3D printing of thermoresponsive hydrogels. Through chain end functionalization of star poly(L-proline)s with methacryloyl groups, access to high-resolution defined 3D hydrogel structures via digital light processing is achieved through photoinitiated free radical polymerization. Changing the poly(L-proline) molecular weight has a direct influence on both thermoresponsiveness and printability, while shape-morphing behavior can be induced thermally.

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Purpose: The paper shows a preliminary study of the basic strength parameters of printed parts made of biocompatible polymers with ceramic layers applied to increase the strength of the tool cutting surface. Methods: The specimens were made from different materials and using different 3D printing technologies and the working surfaces that will eventually form the cutting element of the tool were coated with Al2O3. Gloss tests were conducted, properties of the coating, a scratch test of the coated surface, also evaluated surface to-pography. Results: Based on the conducted research, it was found that polymeric materials are characterized by sufficient strength and can be used for disposable tools, however, the use of thin layers of Al2O3 significantly increases the surface strength parameters, which may have a significant impact on the reliability and durability of the tools. The polymer surface covered with an Al2O3 layer is characterised by increased scratch resistance ranging from 24% to 75% depending on the core material and printing technology. The gloss of the surfaces is disproportionately low compared to currently used metal tools, which indicates that they can be used in endoscopic procedures. Conclusions: Based on the conducted research, it was found that the use of thin layers of Al2O3 covering polymer 3D prints is an excellent way to increase strength parameters such as scratch resistance, tribological parameters and light reflections arising on the surface as a result of endoscopic lighting are disproportionately small compared to metallic biomaterials. This gives great hope for using polymer 3D prints for personalised neurosurgical tools.

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OBJECTIVES: To determine the impact of build orientation, increased layer thickness, and dental crowding on the trueness of three-dimensional (3D)-printed models, and to evaluate how these parameters affect the fit of thermoformed appliances. MATERIALS AND METHODS: Ninety-six dental models were printed horizontally and vertically on the building platform using different 3D-printing technologies: (1) a stereolithography (SLA) printer with layer thicknesses of 160 µm and 300 µm and (2) a digital light processing (DLP) printer with layer thicknesses of 100 µm and 200 µm. Each printed model was digitalized and superimposed on the corresponding source file using 3D rendering software, and deviations were quantified by the root mean square values. Subsequently, a total of 32 thermoformed appliances were fabricated on top of the most accurate 3D-printed models, and their fit was evaluated by digital superimposition and inspection by three blinded orthodontists. Paired t-tests were used to analyze the data. RESULTS: Significant differences (P < .05) between printing technologies used were identified for models printed horizontally, with the SLA system achieving better trueness, especially in crowded dentitions. No significant differences between technology were found when models were printed vertically. The highest values of deviation were recorded in appliances fabricated on top of DLP-printed models. The results of the qualitative evaluation indicated that appliances fabricated on top of SLA models outperformed the DLP-modeled appliances. CONCLUSIONS: Three-dimensional printing with increased layer height seems to produce accurate working models for orthodontic applications.

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PURPOSE: This in vitro study investigated the effect of build orientation on the wear resistance and hardness of denture teeth fabricated using digital light processing (DLP) compared to other denture tooth materials. METHODS: Disc-shaped specimens were prepared using denture tooth monomers and DLP devices in three build orientations: 0°, 45°, and 90°. Specimens of the same shape were fabricated using denture tooth materials for subtractive manufacturing, commercially available polymethylmethacrylate (PMMA) resin, and composite resin. The wear resistance was evaluated as the wear volume loss after 50,000 wear cycles using a ball-on-disc wear device in water for two-body wear and poppy seed slurry for three-body wear. The Vickers hardness values of the materials were measured. Two-way and one-way analyses of variance were performed for wear resistance and hardness, respectively, followed by Tukey's honest significance test. RESULTS: The interaction between the denture tooth resins and maximum wear volume was significant (P < 0.01). The 0° build orientation exhibited the lowest wear volume in the three-body wear test and the highest hardness among the three build orientations. The 0° DLP-fabricated specimens demonstrated significantly less wear volume than that of the PMMA specimens and a wear volume comparable to that of the milled specimens. However, the 0° DLP-fabricated specimens showed significantly lower hardness than that of the milled and PMMA specimens. The composite resin specimens exhibited the highest wear resistance and hardness. CONCLUSIONS: A 0° build orientation is recommended for DLP-fabricated denture teeth compared to 45° and 90° orientations to achieve greater wear resistance and hardness.

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Shaping hard and brittle materials, e.g. cermets, at micrometer resolution has long been known challenging for both mechanical machining and high energy beam based additive manufacturing. Digital light processing (DLP), which features great printing quality and decent precision, unfortunately lacks capability to deal with the popular slurry-typed cermet precursor due to the tremendous optical absorption by its particles. Here, an innovative protocol based on a versatile collapsable matrix is devised to allow high-precision printing of WC-Co cermets on DLP platform. By tuning the external environment, this matrix attenuates composite powders to facilitate photopolymerization at the printing stage, and shrinks to condense green parts prior to thermal sintering. The as-obtained samples by collapsable matrix assisted DLP can reach a relative density of ≈90%, a record-breaking resolution of ≈10 µm, and a microhardness of up to 14.5 GPa. Complex delicate structures, including school emblem, honeycomb, and micro-drill can be directly fabricated, which has never been achieved before. Impressively, the as-obtained micro-drill is able to be directly used in drilling tasks. The above strategy represents a great progress in DLP by enabling shaping strong light attenuating materials at high resolution. Such advantages are ideal for the next generation ceramic-metal composite additive manufacturing.

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Current additive manufacturing (AM) techniques for tungsten, such as powder bed fusion and directed energy deposition, often generate parts with rough surfaces. Vat photopolymerization presents a promising alternative for fabricating tungsten structures with high shape fidelity and low surface roughness. However, existing vat photopolymerization approaches suffer from surface defects and low final density, leading to compromised mechanical properties. Therefore, achieving high-density tungsten structures using vat photopolymerization remains a crucial challenge. This work presents a straightforward and reliable method for fabricating complex, micro-architected tungsten structures with superior density and hardness. The approach utilizes a water-based photoresin with exceptional tungsten ion loading capacity. The photoresin is then patterned using digital light processing (DLP) to create tungsten-laden precursors. A three-step debinding and sintering process subsequently achieves 3D tungsten structures with dense surface morphology and minimal internal defects. The microstructures achieve a minimum feature size of 35 µm, a low surface roughness of 2.86 µm, and demonstrate exceptional mechanical properties. This new method for structuring tungsten opens doors to a broad range of applications, including micromachining, collimators, detectors, and metamaterials.

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In this research, a foam three-dimensional (3D) printing method using digital light processing (DLP) technology was developed to fabricate 3D-printed porous structures. To address the challenges in preparing DLP precursor foam fluid, we designed a specialized foaming device. This device enables the precursor solution to be blended with air, resulting in a stable foam precursor with an adjustable air/liquid fraction and suitable fluidity, crucially enhancing the gas-liquid contact time for the printing process. By manipulation of fluid flow rates, cycle counts, and gas/liquid ratios, one can easily prepare uniform foams with precise control over the pore size and porosity. To avoid significant volume reduction during ultraviolet (UV) curing, nanoparticle fillers were introduced into the network to prevent collapse of the foam structure. Furthermore, the inclusion of an UV absorber enhanced the quality of the printing process by addressing the limitations associated with particle scattering and reflection. The DLP process can readily fabricate intricate structures, featuring a planar resolution below 30 µm and a printing accuracy of less than 1%. Several examples were also demonstrated to highlight the advantages of this technology and its ability to directly print custom foam structures, thereby saving time and material resources.

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Hydrogels are extensively explored as biomaterials for tissue scaffolds, and their controlled fabrication has been the subject of wide investigation. However, the tedious mechanical property adjusting process through formula control hindered their application for diverse tissue scaffolds. To overcome this limitation, we proposed a two-step process to realize simple adjustment of mechanical modulus over a broad range, by combining digital light processing (DLP) and post-processing steps. UV-curable hydrogels (polyacrylamide-alginate) are 3D printed via DLP, with the ability to create complex 3D patterns. Subsequent post-processing with Fe3+ ions bath induces secondary crosslinking of hydrogel scaffolds, tuning the modulus as required through soaking in solutions with different Fe3+ concentrations. This innovative two-step process offers high-precision (10 µm) and broad modulus adjusting capability (15.8-345 kPa), covering a broad range of tissues in the human body. As a practical demonstration, hydrogel scaffolds with tissue-mimicking patterns were printed for cultivating cardiac tissue and vascular scaffolds, which can effectively support tissue growth and induce tissue morphologies.

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OBJECTIVES: To evaluate the fabrication trueness of additively manufactured maxillary definitive casts with various tooth preparations fabricated with different 3-dimensional (3D) printers and print orientations. METHODS: A maxillary typodont with tooth preparations for a posterior 3-unit fixed partial denture, lateral incisor crown, central incisor and canine veneers, first premolar and second molar inlays, and a first molar crown was digitized with an industrial scanner. This scan file was used to fabricate definitive casts with a digital light processing (DLP) or stereolithography (SLA) 3D printer in different orientations (0-degree, 30-degree, 45-degree, and 90-degree) (n = 7). All casts were digitized with the same scanner, and the deviations within each preparation site were evaluated. Generalized linear model analysis was used for statistical analysis (α = 0.05). RESULTS: The interaction between the 3D printer and the print orientation affected measured deviations within all preparations (P ≤ 0.001) except for the lateral incisor crown and canine veneer (P ≥ 0.094), which were affected only by the main factors (P < 0.001). DLP-90 mostly led to the highest and DLP-0 mostly resulted in the lowest deviations within posterior tooth preparations (P ≤ 0.014). DLP-30 led to the lowest deviations within the first premolar inlay and DLP-45 led to the lowest deviations within the central incisor veneer preparation (P ≤ 0.045). CONCLUSIONS: Posterior preparations of tested casts had the highest trueness with DLP-0 or DLP-30, while central incisor veneer preparations had the highest trueness with DLP-45. DLP-90 led to the lowest trueness for most of the tooth preparations. CLINICAL SIGNIFICANCE: Definitive casts with tooth preparations fabricated with the tested DLP 3D printer and the print orientation adjusted on tooth preparation may enable well-fitting restorations. However, 90-degree print orientation should be avoided with this 3D printer, as it led to the lowest fabrication trueness.

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The hypothesis of the study was that (1) 3D printed drug delivery systems (DDS) could be characterized in situ during drug release using NMR/MRI techniques in terms of mass transport phenomena description (interfacial phenomena), particularly for systems dealing with two mobile phases (e.g., water and low molecular weight liquid polymer); (2) consequently, it could be possible to deduce how these interfacial mass transport phenomena influence functional properties of 3D printed DDS. Matrix drug delivery systems, prepared using masked stereolithography (MSLA), containing poly(ethylene glycol) diacrylate (PEGDA) and low molecular weight polyethylene glycol (PEG) with ropinirole hydrochloride (RH) were studied as example formulations. The PEGDA to PEG (mobile phase) concentration ratio influenced drug release. It was reflected in spatiotemporal changes in parametric T2 relaxation time (T2) and amplitude (A) images obtained using magnetic resonance imaging (MRI) and T1-T2 relaxation time correlations obtained using low-field time-domain nuclear magnetic resonance (LF TD NMR) relaxometry during incubation in water. For most of the tested formulations, two signal components related to PEG and water were assessed in the hydrated matrices by MRI relaxometry (parametric T2/A images). The PEG component faded out due to outward PEG diffusion and was gradually replaced by the water component. Both components spatially and temporally changed their parameters, reflecting evolving water-polymer interactions. The study shows that dynamic phenomena related to bidirectional mass transport can be quantified in situ using NMR and MRI techniques to gain insight into drug release mechanisms from 3D printed DDS systems.

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New gelatin methacryloyl (GelMA)-strontium-doped nanosize hydroxyapatite (SrHA) composite hydrogel scaffolds were developed using UV photo-crosslinking and 3D printing for bone tissue regeneration, with the controlled delivery capacity of strontium (Sr). While Sr is an effective anti-osteoporotic agent with both anti-resorptive and anabolic properties, it has several important side effects when systemic administration is applied. Multi-layer composite scaffolds for bone tissue regeneration were developed based on the digital light processing (DLP) 3D printing technique through the photopolymerization of GelMA. The chemical, morphological, and biocompatibility properties of these scaffolds were investigated. The composite gels were shown to be suitable for 3D printing. In vitro cell culture showed that osteoblasts can adhere and proliferate on the surface of the hydrogel, indicating that the GelMA-SrHA hydrogel has good cell viability and biocompatibility. The GelMA-SrHA composites are promising 3D-printed scaffolds for bone repair.

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Gelatin-based photo-crosslinkable hydrogels are promising scaffold materials to serve regenerative medicine. They are widely applicable in additive manufacturing, which allows for the production of various scaffold microarchitectures in line with the anatomical requirements of the organ to be replaced or tissue defect to be treated. Upon their in vivo utilization, the main bottleneck is to monitor cell colonization along with their degradation (rate). In order to enable non-invasive visualization, labeling with MRI-active components like N-(2,2-difluoroethyl)acrylamide (DFEA) provides a promising approach. Herein, we report on the development of a gelatin-methacryloyl-aminoethyl-methacrylate-based biomaterial ink in combination with DFEA, applicable in digital light processing-based additive manufacturing towards bone tissue regeneration. The fabricated hydrogel constructs show excellent shape fidelity in line with the printing resolution, as DFEA acts as a small molecular crosslinker in the system. The constructs exhibit high stiffness (E = 36.9 ± 4.1 kPa, evaluated via oscillatory rheology), suitable to serve bone regeneration and excellent MRI visualization capacity. Moreover, in combination with adipose tissue-derived stem cells (ASCs), the 3D-printed constructs show biocompatibility, and upon 4 weeks of culture, the ASCs express the osteogenic differentiation marker Ca2+.

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In this work, various methods were used to improve the printability of a photocurable polyvinylsilazane resin filled with silicon nitride particles for digital light processing. The developed resin was used as a preceramic polymer for polymer-to-ceramic conversion. The pyrolysis-induced structural changes of the additively manufactured objects were evaluated by comparing samples with different thicknesses, filler amounts and heating profiles. The printed green body retained its original geometry better and showed fewer cracks due to the addition of silicon nitride particles to the resin. Based on the thermally induced changes in a polyvinylsilazane resin system, a customized heating profile for the pyrolysis process was developed, which contributed to the reduction of pores and cracks while the average pyrolysis heating rate remained relatively high. This work provides insight into the pyrolysis of additively manufactured preceramic polymer green bodies and highlights various strategies for additive manufacturing of polymer-derived ceramics.

The presented work systematically demonstrates the microstructural optimization of additively manufactured polymer-derived ceramics through combination of high refractive index filler inclusion and pyrolysis procedure customization.

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Bioengineering seeks to replicate biological tissues exploiting scaffolds often based on polymeric biomaterials. Digital light processing (DLP) has emerged as a potent technique to fabricate tissue engineering (TE) scaffolds. However, the scarcity of suitable biomaterials with desired physico-chemical properties along with processing capabilities limits DLP's potential. Herein, we introduce acrylate-endcapped urethane-based polymers (AUPs) for precise physico-chemical tuning while ensuring optimal computer-aided design/computer-aided manufacturing (CAD/CAM) mimicry. Varying the polymer backbone (i.e. poly(ethylene glycol) (PEG) versus poly(propylene glycol) (PPG)) and photo-crosslinkable endcap (i.e. di-acrylate versus hexa-acrylate), we synthesized a series of photo-crosslinkable materials labeled as UPEG2, UPEG6, UPPG2 and UPPG6. Comprehensive material characterization including physico-chemical and biological evaluations, was followed by a DLP processing parametric study for each material. The impact of the number of acrylate groups per polymer (2 to 6) on the physico-chemical properties was pronounced, as reflected by a reduced swelling, lower water contact angles, accelerated crosslinking kinetics, and increased Young's moduli upon increasing the acrylate content. Furthermore, the different polymer backbones also exerted a substantial effect on the properties, including the absence of crystallinity, remarkably reduced swelling behaviors, a slight reduction in Young's modulus, and slower crosslinking kinetics for UPPG vs UPEG. The mechanical characteristics of DLP-printed samples showcased the ability to tailor the materials' stiffness (ranging from 0.4 to 5.3 MPa) by varying endcap chemistry and/or backbone. The in vitro cell assays confirmed biocompatibility of the material as such and the DLP-printed discs. Furthermore, the structural integrity of 3D scaffolds was preserved both in dry and swollen state. By adjusting the backbone chemistry or acrylate content, the post-swelling dimensions could be customized towards the targeted application. This study showcases the potential of these materials offering tailorable properties to serve many biomedical applications such as cartilage TE.

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BACKGROUND/AIM: 3D printing processes can be used to manufacture custom-made mouthguards for sports activities. Few studies have compared the impact performance of industrial-created mouthguards with that of custom-made mouthguards manufactured by thermoforming or 3D printing. The objective of this in vitro study was to compare the shock absorption capacities of custom-made mouthguards manufactured by 3D printing with industrial mouthguards and thermoformed ethylene vinyl acetate (EVA) mouthguards. MATERIALS AND METHODS: For each type of mouthguard, eight samples were produced. 3D-printed mouthguards were manufactured using digital light processing technology. Each mouthguard was subjected to an impact performance test defined by the standard AFNOR XP S72-427, which evaluate maximum deceleration and force transmitted during impact. The thickness of each mouthguard before and after a series of five impacts was measured at the impacted inter-incisal area. RESULTS: The mean maximum decelerations during impact ranged from 129 to 189 g for industrial mouthguards, 287 to 425 g for thermoformed EVA mouthguards, and 277 to 302 g for 3D-printed mouthguards. The mean reduction in mouthguard thickness at the impact zone after five tests was 1.2 mm for industrial mouthguards, 0.6 mm for 3D-printed mouthguards, and 2.2 mm for thermoformed EVA mouthguards. CONCLUSIONS: Custom-made 3D printed mouthguards showed slightly better shock absorption ability than thermoformed mouthguards with respect to the indicator proposed in XP S72-427. They seemed to combine the practical advantages of thermoformed mouthguards in sports with better shock absorption capacity and lower cost. Furthermore, they had the least thickness variation during the test, and their shock absorption capacity was the least affected by repeated mechanical tests. Other types of 3D-printing resin materials that will become available must continue to be tested for shock absorption to provide the best protection to users at low cost.

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In this study, digital light processing (DLP) was utilized to generate 3D-printed blends composed of photosensitive acrylate-modified polylactic acid (PLA) resin mixed with varying weight ratios of lignin extracted from softwood, typically ranging from 5 wt% to 30 wt%. The microstructure of these 3D-printed blends was examined through X-ray microtomography. Additionally, the tensile mechanical properties of all blends were assessed in relation to the weight ratio and post-curing treatment. The results suggest that post-curing significantly influences the tensile properties of the 3D-printed composites, especially in modulating the brittleness of the prints. Furthermore, an optimal weight ratio was identified to be around 5 wt%, beyond which UV light photopolymerization experiences compromises. These findings regarding acrylate-modified PLA/lignin blends offer a cost-effective alternative for producing 3D-printed bio-sourced components, maintaining technical performance in reasonable-cost, low-temperature 3D printing, and with a low environmental footprint.

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Photopolymerization-based additive manufacturing requires selectively exposing a feedstock resin to ultraviolet (UV) light, which in digital light processing is achieved either using a digital micromirror device or a digital mask. The minimum tolerances and resolution for a multilayer process are separate for resolution through the Z-axis, looking through the thickness of a printed part, and resolution in the XY-axes, in the plane of the printed layer. The former depends wholly on the rate of attenuation of the incident UV light through the material relative to the mechanical motion of the build layer, while the latter is determined by a two-dimensional pattern of irradiance on the resin formed by the digital micromirror device or the digital mask. The size or the spacing of elements or pixels of this digital mask is frequently given by manufacturers as the "resolution" of the device, however, in practice the achievable resolution is first determined by the beam distribution from each pixel. The beam distribution is, as standard, modeled as a two-parameter Gaussian distribution but the key parameters of peak intensity and standard deviation of the beam are hidden to the user and difficult to measure directly. The ability of models based on the Gaussian distribution to correctly predict the polymerization of printed features in the microscale is also typically poor. In this study, we demonstrate an alternative model of beam distribution based on a heavy-tailed Lorentzian model, which is able to more accurately predict small build areas for both positive and negative features. We show a simple calibration method to derive the key space parameters of the beam distribution from measurements of a single-layer printed model. We propose that the standard Gaussian model is insufficient to accurately predict a print outcome as it neglects higher-order terms, such as beam skew and kurtosis, and in particular failing to account for the relatively heavy tails of the beam distribution. Our results demonstrate how the amendments to the beam distribution can avoid errors in microchannel formation, and better estimates of the true XY-axes resolution of the printer. The results can be used as the basis for voxel-based models of print solidification that allow software prediction of the photopolymerization process.

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Repairing and regenerating damaged tissues or organs, and restoring their functioning has been the ultimate aim of medical innovations. 'Reviving healthcare' blends tissue engineering with alternative techniques such as hydrogels, which have emerged as vital tools in modern medicine. Additive manufacturing (AM) is a practical manufacturing revolution that uses building strategies like molding as a viable solution for precise hydrogel manufacturing. Recent advances in this technology have led to the successful manufacturing of hydrogels with enhanced reproducibility, accuracy, precision, and ease of fabrication. Hydrogels continue to metamorphose as the vital compatible bio-ink matrix for AM. AM hydrogels have paved the way for complex 3D/4D hydrogels that can be loaded with drugs or cells. Bio-mimicking 3D cell cultures designed via hydrogel-based AM is a groundbreaking in-vivo assessment tool in biomedical trials. This brief review focuses on preparations and applications of additively manufactured hydrogels in the biomedical spectrum, such as targeted drug delivery, 3D-cell culture, numerous regenerative strategies, biosensing, bioprinting, and cancer therapies. Prevalent AM techniques like extrusion, inkjet, digital light processing, and stereo-lithography have been explored with their setup and methodology to yield functional hydrogels. The perspectives, limitations, and the possible prospects of AM hydrogels have been critically examined in this study.

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