Print Fidelity Research Articles

Direct Ink Writing of Carbon-Doped Polymeric Composite Ink: A Review on Its Requirements and Applications.

Direct Ink Writing (DIW) opens new possibilities in three-dimensional (3D) printing of carbon-based polymeric ink. This is due to its ability in design flexibility, structural complexity, and environmental sustainability. This area requires exhaustive study because of its wide application in different manufacturing sectors. The present article is related to the variant emerging 3D printing techniques and DIW of carbonaceous materials. Carbon-based materials, extensively used for various applications in 3D printing, possess impressive chemical stability, strength, and flexible nanostructure. Fine printable inks consist predominantly of uniform solutions of carbon materials, such as graphene, graphene oxide (GO), carbon fibers (CFs), carbon nanotubes (CNTs), and solvents. It also contains compatible polymers and suitable additives. This review article elaborately discusses the fundamental requirements of DIW in structuring carbon-doped polymeric inks viz. ink formulation, required ink rheology, extrusion parameters, print fidelity prediction, layer bonding examination, substrate selection, and curing method to achieve fine functional composites. A detailed description of its application in the fields of electronics, medical, and mechanical segments have also been focused in this study.

BC enhanced photocurable hydrogel based on 3D bioprinting for nasal cartilage repair

The repair of nasal cartilage lesions and defects is still a difficult problem in nasal surgery, and nasal cartilage tissue engineering will be an effective way to solve this problem. Hydrogel has excellent application potential in tissue engineering. In order to produce a 3D printable scaffold for cartilage regeneration, we prepared gelatin methacryloyl (GelMA)/hyaluronic acid methacryloyl (HAMA)/bacterial cellulose (BC) composite hydrogel. The composite hydrogel was characterized by swelling, mechanical properties, and printing performance test. Compared with GelMA/HAMA hydrogel, the addition of BC not only significantly enhanced the mechanical properties of the hydrogels, but also improved the printing fidelity. At the same time, the mouse chondrocyte cell line (ATDC5) was used to evaluate the biocompatibility of the composite hydrogel. After 7 d of culture, the cells encapsulated within the composite hydrogels proliferated significantly and maintain the expression of specific proteins. In addition, the cell viability of the encapsulated ATDC5 cells in the 3D bioprinted hybrid constructs was evaluated. In summary, these results indicate that BC-enhanced GelMA/HAMA hydrogel is a promising candidate material for nasal cartilage repair.

Effect of Calcium Sulphate Pre-crosslinking on Rheological Parameters of Alginate Based Bio-Inks and on Human Corneal Stromal Fibroblast Survival in 3D Bio-Printed Constructs

The principle of three-dimensional (3D) bio-printing involves integration of biomaterials, live cells and controlled motor systems for creating complex biomimetic constructs. Bio-ink is one of the most important components in the process of 3D bio-printing and needs to be sufficiently viscous to be dispensed as a free-standing filament but be biocompatible to maintain cell viability and function. Alginate has been used widely for 3D bio-printing due to its biocompatibility, tunable properties, rapid gelation, low cost, and ability to be functionalized to direct cell behavior. By tuning the physiochemical parameters of alginate-based bio-inks, such as viscosity, improvements in print resolution, fidelity and growth characteristics of encapsulated cells can be achieved. This study aimed to improve the printability of low concentration alginate bio-inks by utilizing calcium sulphate (CaSO4) pre-crosslinking. A variety of alginates, differing in their viscosity, molecular weight and b-D-mannuronate and α-L-guluronate residues were investigated by wet spinning and bio-printing. Rheological and structural properties of pre-crosslinked alginates were characterized with the aim of mitigating the resolution problems associated with the use of low percentage alginate bio-inks, more favorable for maintaining cell viability. Pre-crosslinking produced a significant effect on viscosity of biomaterials improving their suitability for the bio-printing process and influencing the final resolution of the printed structure. Medium viscosity high b-D-mannuronate containing alginate (MVM) showed the highest degree of viscosity change compared to the control (p < 0.0001; n = 6), assessed by single value viscometry analysis and shear rheology, after pre-crosslinking and was subsequently used in experiments with cells. The survival of human corneal stromal fibroblasts (CSFs) was assessed using CellTiterGlo metabolic assay and confirmed with Calcein acetoxymethyl and Ethidium homodimer -1 live/dead staining in pre-crosslinked alginate fibers and bio-printed lattices. Encapsulation of CSFs in pre-crosslinked alginate-based bio-inks did not have a detrimental effect on CSF viability compared to the non-pre-crosslinked control over 7 days under standard cell culture conditions (p > 0.05, n = 3). Overall, printability of low percentage alginate bio-inks was improved by pre-crosslinking without affecting the biocompatibility of the bio-inks.

Investigation of the 3D Printability of Covalently Cross-Linked Polypeptide-Based Hydrogels.

The 3D printability of poly(l-lysine-ran-l-alanine) and four-arm poly(ethylene glycol) (P(KA)/4-PEG) hydrogels as 3D biomaterial inks was investigated using two approaches to develop P(KA)/4-PEG into 3D biomaterial inks. Only the “composite microgel” inks were 3D printable. In this approach, P(KA)/4-PEG hydrogels were processed into microparticles and incorporated into a polymer solution to produce a composite microgel paste. Polymer solutions composed of either 4-arm PEG-acrylate (4-PEG-Ac), chitosan (CS), or poly(vinyl alcohol) (PVA) were used as the matrix material for the composite paste. The three respective composite microgel inks displayed good 3D printability in terms of extrudability, layer-stacking ability, solidification mechanism, and 3D print fidelity. The biocompatibility of P(KA)/4-PEG hydrogels was retained in the 3D printed scaffolds, and the biofunctionality of bioinert 4-PEG and PVA hydrogels was enhanced. CS-P(KA)/4-PEG inks demonstrated excellent 3D printability and proved highly successful in printing scaffolds with a narrow strand diameter (∼200 μm) and narrow strand spacing (∼500 μm) while the integrity of the vertical and horizontal pores was maintained. Using different needle IDs and strand spacing, certain physical properties of the hydrogels could be tuned, while the 3D printed porosity was kept constant. This included the surface area to volume ratio, the macropore sizes, and the mechanical properties. The scaffolds demonstrated adequate adhesion and spreading of NIH 3T3 fibroblasts seeded on the scaffold surfaces for 4 days. Consequently, the scaffolds were considered suitable for potential applications in wound healing, as well as other soft tissue engineering applications. Apart from the contribution to new 3D biomaterial inks, this work also presented a new and facile method of processing covalently cross-linked hydrogels into 3D printed scaffolds. This could potentially “unlock” the 3D printability of biofunctional hydrogels, which are generally excluded from 3D printing applications.

Fabrication of Microstructured Calcium Phosphate Ceramics Scaffolds by Material Extrusion-Based 3D Printing Approach

Natural materials such as bone and enamel have intricate microstructures with inorganic minerals oriented to perform multiple mechanical and biological functions. Current additive manufacturing methods for biominerals from the calcium phosphate (CaP) family enable fabrication of custom-shaped bioactive scaffolds with controlled pore structures for patient-specific bone repair. Yet, these scaffolds do not feature intricate microstructures similar to those found in natural materials. In this work, we used direct material extrusion to 3D print water-based inks containing CaP microplatelets, and obtained microstructured scaffolds with various designs. To be shear-thinning and printable, the ink incorporated a concentration of 21 – 24 vol% CaP microplatelets of high aspect ratio. Good shape retention, print fidelity and overhanging layers were achieved by simultaneous printing and drying. Combined with the 3D design, versatile CaP microstructured objects can be built, from porous scaffolds to bulk parts. Extruded filaments featured a core-shell microstructure with graded microplatelet orientations, which was not affected by the printing parameters and the print design. A simple model is proposed to predict the core-shell microstructure according to the ink rheology. Given the remaining open porosity after calcination, microstructured scaffolds could be infiltrated with an organic phase in future to yield CaP biocomposites for hard tissue engineering.

Print fidelity evaluation of PVA hydrogel using computational fluid dynamics for extrusion dependent 3D printing

This study presents a practical method of print fidelity evaluation for an extrusion-dependent technique of 3D printing. Simulation through computational fluid dynamics (CFD) tool has been used for evaluating the fidelity of printing. The polyvinyl alcohol (PVA) based hydrogel was prepared with deionized (DI) water and PVA powder using a magnetic stirrer at 90 °C for 3D printing. Rheological tests were carried out for checking the viscosity at various shear rates. CFD simulation was done by employing the Bird-Carreau modelusing rheological values. Velocity, pressure, shearing rate, and viscosity distributions through nozzle were obtained. From the shear rate and viscosity results, the increase in shear rate and decrease in gel’s viscosity for both the nozzles prove that the material can be extruded. It was seen that the nozzle with a diameter of 0.51mm shows better results than the 0.41mm diameter, which was concluded from the values of maximum shear rate at the edges of the nozzles. The maximum shear rate value has reached a maximum of up to 326.5102s –1 whereas for a 0.41 mm diameter nozzle, it is 623.8037s –1 increasing the chances of developing wavy edges in a 0.41mm diameter nozzle than a 0.51mm diameter nozzle concluding that the nozzle with 0.51mm diameter gives far better results than the 0.41mm diameter nozzle.

Mineralized collagen as a bioactive ink to support encapsulation of human adipose stem cells: A step towards the future of bone regeneration

Bioprinting – printing with incorporated living cells – has earned special attention on tissue engineering approaches, aiming to closer reproduce the 3D microenvironment of the target tissue. However, it raises extra complexity related to the need to use cell-friendly printing conditions that still comply with material printing fidelity. Inspired by the composite nano structural organization of mineralized tissues, this work reports the efficiency of the chemical approach followed to in situ mineralize blue shark skin collagen, at a nano scale level, to ultimately produce stable inks. The influence of initial cellular density was evaluated by assessing three different concentrations (2.5, 5 and 7.5 × 106 cells·ml−1) of human adipose stem cells (hASC), with the higher density of encapsulated cells presenting improved viability in a long culture term. Immunodetection of osteogenic-related markers, like RUNX2 and osteopontin, 21 days after cell culture in basal conditions confirmed the potential of the ink to be applied for osteogenic purposes, which may be associated with the success of the cell-to-ink interaction and the Ca2+ ions released from the co-precipitated hydroxyapatite. A combination of mineralized shark collagen, alginate and hASC is thus proposed as a bioactive bioink with potential properties for regeneration of bone tissue.

Nanoengineered biomimetic hydrogels: A major advancement to fabricate 3D-printed constructs for regenerative medicine.

Nanostructured compounds already validated as performant reinforcements for biomedical applications together with different fabrication strategies have been often used to channel the biophysical and biochemical features of hydrogel networks. Ergo, a wide array of nanostructured compounds has been employed as additive materials integrated with hydrophilic networks based on naturally-derived polymers to produce promising scaffolding materials for specific fields of regenerative medicine. To date, nanoengineered hydrogels are extensively explored in (bio)printing formulations, representing the most advanced designs of hydrogel (bio)inks able to fabricate structures with improved mechanical properties and high print fidelity along with a cell-interactive environment. The development of printing inks comprising organic-inorganic hybrid nanocomposites is in full ascent as the impact of a small amount of nanoscale additive does not translate only in improved physicochemical and biomechanical properties of bioink. The biopolymeric nanocomposites may even exhibit additional particular properties engendered by nano-scale reinforcement such as electrical conductivity, magnetic responsiveness, antibacterial or antioxidation properties. The present review focus on hydrogels nanoengineered for 3D printing of biomimetic constructs, with particular emphasis on the impact of the spatial distribution of reinforcing agents (0D, 1D, 2D). Here, a systematic analysis of the naturally-derived nanostructured inks is presented highlighting the relationship between relevant length scales and size effects that influence the final properties of the hydrogels designed for regenerative medicine.

Suppressing the Step Effect of 3D Printing for Constructing Contact Lenses (Adv. Mater. 4/2022)

3D Printing In article number 2107249, Lei Wu, Yanlin Song, and co-workers propose a continuous liquid film confined 3D printing strategy to fabricate high-precision 3D structures. Reutilization and good control of the liquid residual can improve the printing fidelity and avoid a post-washing process. A centimeter-scale contact-lens structure with nanoscale roughness, high-definition imaging and homogeneous mechanical characteristic is printed, indicating its great potential in scalable 3D printing of optical structures.

Synergistic effects of nanoattapulgite and hydroxyapatite on vascularization and bone formation in a rabbit tibia bone defect model.

Hydroxyapatite (HA) is a promising scaffold material for the treatment of bone defects. However, the lack of angiogenic properties and undesirable mechanical properties (such as fragility) limits the application of HA. Nanoattapulgite (ATP) is a nature-derived clay mineral and has been proven to be a promising bioactive material for bone regeneration due to its ability to induce osteogenesis. In this study, polyvinyl alcohol/collagen/ATP/HA (PVA/COL/ATP/HA) scaffolds were printed. Mouse bone marrow mesenchymal stem/stromal cells (BMSCs) and human umbilical vein endothelial cells (HUVECs) were used in vitro to assess the biocompatibility and the osteogenesis and vascularization induction potentials of the scaffolds. Subsequently, in vivo micro-CT and histological staining were carried out to evaluate new bone formation in a rabbit tibial defect model. The in vitro results showed that the incorporation of ATP increased the printing fidelity and mechanical properties, with values of compressive strengths up to 200% over raw PC-H scaffolds. Simultaneously, the expression levels of osteogenic-related genes and vascularization-related genes were significantly increased after the incorporation of ATP. The in vivo results showed that the PVA/COL/ATP/HA scaffolds exhibited synergistic effects on promoting vascularization and bone formation. The combination of ATP and HA provides a promising strategy for vascularized bone tissue engineering.

Structural characterization and fluidness analysis of lactose/whey protein isolate composite hydrocolloids as printing materials for 3D printing

In this study, the lactose/Whey Protein Isolate (WPI) composite hydrocolloids were prepared as an printing material for subsequent 3D printing. The results showed that the rheological, viscoelastic, thermal and mechanical properties of the studied hydrocolloids were composition dependent, which was directly linked to the printing fidelity of printed objects. The morphology of all printed objects showed a porous microstructure, and their porosity was changed by lactose addition. This outcome resulted from lactose-derived co-solvation discouraging WPI aggregation during the printing process, which was necessary for improving printing performance. Moreover, an innovative Fluidness concept (F), using material-specific WLF analysis of relaxation times, was introduced to quantify the fluidness of lactose/WPI composite hydrocolloids at a certain decay of timescales (from 102 to 10-3 s). This F concept was superior for the description and control of printing fidelity, dimensional deviation, and textural properties of 3D-printed objects. Therefore, the F concept is a “printable indicator” for dairy by-products that may possess proper printability and provides an alternative approach to make attractive designs for 3D printing foods.

Graphene oxide modulates inter-particle interactions in 3D printable soft nanocomposite hydrogels restoring magnetic hyperthermia responses

Hydrogels loaded with magnetic iron oxide nanoparticles that can be patterned and which controllably induce hyperthermic responses on AC-field stimulation are of interest as functional components of next-generation biomaterials. Formation of nanocomposite hydrogels is known to eliminate any Brownian contribution to hyperthermic response (reducing stimulated heating) while the Néel contribution can also be suppressed by inter-particle dipolar interactions arising from aggregation induced before or during gelation. We describe the ability of graphene oxide (GO) flakes to restore the hyperthermic efficiency of soft printable hydrogels formed using Pluronics F127 and PEGylated magnetic nanoflowers. Here, by varying the amount of GO in mixed nanocomposite suspensions and gels, we demonstrate GO-content dependent recovery of hyperthemic response in gels. This is due to progressively reduced inter-nanoflower interactions mediated by GO, which largely restore the dispersed-state Néel contribution to heating. We suggest that preferential association of GO with the hydrophobic F127 blocks increases the preponderance of cohesive interactions between the hydrophilic blocks and the PEGylated nanoflowers, promoting dispersion of the latter. Finally we demonstrate extrusion-based 3D printing with excellent print fidelity of the magnetically-responsive nanocomposites, for which the inclusion of GO provides significant improvement in the spatially-localized open-coil heating response, rendering the prints viable components for future cell stimulation and delivery applications.

Sub-resolution assist feature placement with generative adversarial network

Background: As the design layout of integrated circuits (ICs) is continually scaling down, sub-resolution assist features (SRAF) have been extensively used in resolution enhancement technique applications to enhance lithography printing fidelity and widen the manufacturing process window (PW). With conventional SRAF insertion techniques, rule-based SRAF (RB-SRAF) and model-based SRAF (MB-SRAF) methods have since been widely adopted. Aim: The typical RB-SRAF is an efficient method to generate SRAFs consistently for simple designs but cannot be optimized for multiple critical patterns or complex layout schemes. Although MB-SRAF is able to achieve better PW as well as reducing conflicts between placement rules and clean-up rules, many iterations for convergence and extremely high computational costs are required. The explosion of machine learning techniques could facilitate the complex processes of mask optimization, such as SRAF insertion. Approach: Generative adversarial network was studied on a Via layer of advanced 3D NAND flash memory, by training target images and Inverse Lithography Technology (ILT) images of target patterns. GAN models, pix2pix, and CycleGAN, were first trained and then utilized to synthesize realistic ILT images. Results: These ILT images were eventually translated to polygons of SRAF with simplification process and mask manufacturing rules check constraints. The simulation results demonstrate that CycleGAN approach can place SRAF with comparable performance to mask optimization (MO) result which was optimized by the Tachyon source-mask optimizer (SMO). Conclusions: Methodologies of SRAF placement based on GANs were demonstrated in this paper. While traditional MO approach showed the best lithography performance, CycleGAN in particular was close behind and had much better performance than conventional RB-SRAF approach, whilst achieving good stability for different layout environments. Most importantly, the efficiency of SRAF insertion can be enhanced significantly through GANs.

Solvent‐Cast 3D Printing of Biodegradable Polymer Scaffolds

Abstract3D printing is a popular fabrication technique because of its ability to produce complex architectures. Melt‐based 3D printing is widely used for thermoplastic polymers like poly(caprolactone) (PCL), poly(lactic acid) (PLA), and poly(lactic‐co‐glycolic acid) (PLGA) because of their low processing temperatures. However, traditional melt‐based techniques require processing temperatures and pressures high enough to achieve continuous flow, limiting the type of polymer that can be printed. Solvent‐cast printing (SCP) offers an alternative approach to print a wider range of polymers. Polymers are dissolved in a volatile solvent that evaporates during deposition to produce a solid polymer filament. SCP, therefore, requires optimizing polymer concentration in the ink, print pressure, and print speed to achieve desired print fidelity. Here, capillary flow analysis shows how print pressure affects the process‐apparent viscosity of PCL, PLA, and PLGA inks. Ink viscosity is also measured using rheology, which is used to link a specific ink viscosity to a predicted set of print pressure and print speed for all three polymers. These results demonstrate how this approach can be used to accelerate optimization by significantly reducing the number of parameter combinations. This strategy can be applied to other polymers to expand the library of polymers printable with SCP.

3D Printing of Thermal Insulating Polyimide/Cellulose Nanocrystal Composite Aerogels with Low Dimensional Shrinkage.

Polyimide (PI)-based aerogels have been widely applied to aviation, automobiles, and thermal insulation because of their high porosity, low density, and excellent thermal insulating ability. However, the fabrication of PI aerogels is still restricted to the traditional molding process, and it is often challenging to prepare high-performance PI aerogels with complex 3D structures. Interestingly, renewable nanomaterials such as cellulose nanocrystals (CNCs) may provide a unique approach for 3D printing, mechanical reinforcement, and shape fidelity of the PI aerogels. Herein, we proposed a facile water-based 3D printable ink with sustainable nanofillers, cellulose nanocrystals (CNCs). Polyamic acid was first mixed with triethylamine to form an aqueous solution of polyamic acid ammonium salts (PAAS). CNCs were then dispersed in the aqueous PAAS solution to form a reversible physical network for direct ink writing (DIW). Further freeze-drying and thermal imidization produced porous PI/CNC composite aerogels with increased mechanical strength. The concentration of CNCs needed for DIW was reduced in the presence of PAAS, potentially because of the depletion effect of the polymer solution. Further analysis suggested that the physical network of CNCs lowered the shrinkage of aerogels during preparation and improved the shape-fidelity of the PI/CNC composite aerogels. In addition, the composite aerogels retained low thermal conductivity and may be used as heat management materials. Overall, our approach successfully utilized CNCs as rheological modifiers and reinforcement to 3D print strong PI/CNC composite aerogels for advanced thermal regulation.

Facile Bioprinting Process for Fabricating Size‐Controllable Functional Microtissues Using Light‐Activated Decellularized Extracellular Matrix‐Based Bioinks

AbstractThe concept of microtissues has evolved to adapt to the generation of human tissue analogs that mimic physiologically relevant morphological and functional features. These microtissues can provide an in vitro testing platform for the development of advanced therapeutic options. Optimizing the manufacturing process of biomaterials brings several great benefits to achieve the desired mechanical, chemical, and biological properties for tissue modeling. Hence, 3D bioprinting technology has been utilized to fabricate functional microtissues. However, current microtissue bioprinting systems still require a cumbersome and time‐consuming task, such as washing, which renders it difficult to maintain the shape of intact constructs, thereby resulting in inappropriate tissue morphogenesis. To overcome this limitation, a single‐step bioprinting method is developed easier and more versatile for microtissue production based on a dual‐crosslinkable decellularized extracellular matrix with ruthenium/sodium persulfate (dERS). The developed method enables the fabrication of spheroidal and tubular microstructures into a medium chamber, followed by the immediate culturing of printed structures without multiple postprocesses. The structural characteristics can be controlled by adjusting the printing parameters. Each dERS‐based microtissue promotes tissue maturation and exhibits biofunctional attributes. These results suggest that the developed method may enable the simultaneous achievement of adequate print fidelity and tissue functionality.

Compositional effects on cure kinetics, mechanical properties and printability of dual-cure epoxy/acrylate resins for DIW additive manufacturing

Interest in 3D printing of thermoset resins has increased significantly in recent years. One approach to additive manufacturing of thermoset resins is printing dual-cure resins with direct ink write (DIW). Dual-cure resins are multi-component resins which employ an in situ curable constituent to enable net-shape fabrication while a second constituent and cure mechanism contribute to the final mechanical properties of the printed materials. In this work, the cure kinetics, green strength, printability, and print fidelity of dual-cure epoxy/acrylate thermoset resins are investigated. Resin properties are evaluated as a function of acrylate concentration and in situ UV exposure conditions. The acrylate cure kinetics are probed using photo-differential scanning calorimetry and the impacts of resin composition and UV cure profile on the acrylate extent of conversion are presented. Continuous and pulsed UV cure profiles are shown to affect total conversion due to variances in radical efficiency at different UV intensities and acrylate concentrations. The effects of acrylate concentration on the kinetics of the epoxy thermal cure and the final mechanical properties are also investigated using dynamic mechanical analysis and three-point bend measurements. The glass transition temperature is dependent on formulation, with increasing acrylate content decreasing the Tg. However, the room temperature shear moduli, flexural moduli, strength, strain-to-failure, and toughness values are relatively independent of resin composition. The similarity of the final properties allows for greater flexibility in resin formulation and in situ cure parameters, which can enable the printing of complex parts that require high green strength. We found that the in situ UV print intensities and exposure profiles that are necessary to achieve the best print quality are not, in most cases, the conditions that maximize conversion of the acrylate network. This highlights the importance of developing optimized resin compositions which enable complete cure of the acrylate network by promoting acrylate dark cure or thermal cure.

Abstract P403: Three-dimensional Bioprinting Of Adhesive Cardiac Patch Systems

Rapid advancements in 3D bioprinting have enabled the design of functionalized bioinks to create scaffolds with robust adhesive properties. These constructs are of great interest in cardiac tissue engineering, where the integration of grafted patch with the host myocardium, through sutures, staples, or adhesives, faces risks such as bleeding, cytotoxicity, and infection. We introduce the first generation of functional adhesive bioinks that can be bioprinted through various modalities to fabricate patch structures with intrinsic adhesive properties. A dopamine-modified hyaluronic acid methacrylate (HAMA-Dopa) and gelatin methacrylate (gelMA) composite bioink is used to create the patch via air and embedded bioprinting. Constructs are crosslinked onto a collagen sheet substrate simulating the host cardiac tissue ( Figure 1A-C ). We developed novel in vitro methods to assess adhesion properties of printed patch under shear, tension, or dynamic loading ( Figure 1C ). Our approach allowed for steady and precise application of stress to the adhesion interface. Embedded-printed HAMA-Dopa/gelMA scaffold showed significantly enhanced adhesion strength (1025 Pa) compared to gelMA (495 Pa) and HAMA (477 Pa) control groups under tension, and under shear (548 Pa vs. 234 and 239 Pa). The adhesion strength of air-printed HAMA-Dopa/gelMA constructs was markedly higher (10,128 Pa) than the embedded ones, possibly due to the more effective, in-situ crosslinking. We also investigated the dynamic adhesive properties in aqueous environment using an ex vivo beating heart model. Air-printed HAMA-Dopa/gelMA showed the greatest adhesion under wet conditions, tolerating 345,600 cycles. We further characterized printing fidelity, mechanical properties, swelling, and biocompatibility of HAMA-Dopa/gelMA constructs, demonstrating adequate functionality of this bioprinted adhesive scaffold for cardiac tissue engineering applications. Figure 1 . Summary of workflow to develop bioprinted adhesive scaffolds. A: Embedded (top) or air (bottom) bioprinting was used to create 3D patch geometries. B: Printing fidelity assessment and optimization. C: Different adhesion mechanisms were assessed using novel customized tools and approaches to apply tensile ( C-i ), shear ( C-ii ), and dynamic ( C-iii ) loading.

3D printed nanocellulose-based label for fruit freshness keeping and visual monitoring

Food packaging systems with a single function of freshness keeping or monitoring may not be able to meet all practical needs. Herein, cellulose nanofibers (CNF)-based labels with dual functions of fruit freshness keeping and visual monitoring were prepared by coaxial 3D printing. CNF-based ink with blueberry anthocyanin was used to create the shell of fibers, exhibiting high formability and print fidelity as well as sensitive visual pH-responsiveness for freshness monitoring. Chitosan containing 1-methylcyclopropene (1-MCP) was loaded into the hollow microchannels of fibers, in which 1-MCP was trapped by the electrostatic effect of chitosan and CNF and exhibited a sustained release behavior. The 3D printed labels prolonged the shelf life of litchis for 6 days, meanwhile, they sensitively indicated the changes in freshness and the accuracy was confirmed by Headspace-Gas Chromatography-Ion Mobility Spectrometry. The CNF-based integrated labels developed in this work provided a new idea for the development of food intelligent packaging.

Nanomaterials for bioprinting: functionalization of tissue-specific bioinks.

Three-dimensional (3D) bioprinting is rapidly evolving, offering great potential for manufacturing functional tissue analogs for use in diverse biomedical applications, including regenerative medicine, drug delivery, and disease modeling. Biomaterials used as bioinks in printing processes must meet strict physiochemical and biomechanical requirements to ensure adequate printing fidelity, while closely mimicking the characteristics of the native tissue. To achieve this goal, nanomaterials are increasingly being investigated as a robust tool to functionalize bioink materials. In this review, we discuss the growing role of different nano-biomaterials in engineering functional bioinks for a variety of tissue engineering applications. The development and commercialization of these nanomaterial solutions for 3D bioprinting would be a significant step towards clinical translation of biofabrication.