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Drop-on-Demand additive manufacturing could offer a facile solution for scalable on-site manufacturing. With an increasing number of functional materials available for this technology, there are growing opportunities for applications, such as electronics. Here we report on a novel printing strategy, Off-the-Grid (OtG), which enables refined positioning of individual droplets and enhanced resolution compared to the traditional printing strategy. We demonstrate successful printing of structures with feature position control smaller than a single droplet size, and hence enhanced shape fidelity for intricate designs. This strategy is extended to filled patterns, enabling improved layer coverage and customisable inter-layer droplet positioning to control surface morphology. The OtG strategy is applied to produce functional designs, such as conformable circuitry and miniaturized antennae, and is transferable to different materials, from metal nanoparticle and polymeric inks on inkjet platforms, to molten metals on a MetalJet printer. These results could advance exploitation of AM in electronics, wearable electronics, medical devices, and metamaterials.

Alginate is among the most popular bioinks for 3D bioprinting because it is biocompatible, biodegradable, and is easily crosslinked using divalent cations. Here, we investigate the addition of cellulose nanocrystals (CNCs) to an alginate-based bioink to strengthen bioprinted structures. Using coaxial 3D bioprinting, alginate strands were constructed with a core-sheath structure reinforced by CNCs within the core. The addition of CNCs resulted in an increase in the storage modulus. Formulations containing CNCs resulted in more stable strands with uniformity factors and printability numbers close to 1. Based on the uniformity factor, the formulations containing 1.5 wt% CNCs deviated the least from a theoretically flawless strand. The alginate strands displayed microporous internal structures that were evident by scanning electron microscopy of the strand cross-sections. The addition of CNCs to the core compartment doubled both the modulus and the tensile strength, and the material was able to resist a strain above 50% before failure, thus demonstrating that the addition of the CNCs to the core of the strand leads to resilient printed structures.

The study presents the basic terms of three-dimensional bioprinting and physical, chemical, and biological properties affecting the printability of hydrogel biomaterials. It deals with the principle of evaluating the quality of threedimensional bioprinting. The goal was to design a procedural algorithm to analyze prints produced by extrusion 3D bioprinting critically. Forty-one cylindrical scaffolds were created experimentally from the same material and under varying printing parameters. The settings of the most plausible sample compared to the CAD design were used to 3D bioprint ten cylindrical samples. Analysis of measurement system (ASM) with three operators was used for evaluation. The results showed that the printability measurement system is conditionally suitable. At the same time, the methodology for evaluating the shape similarity of samples through macroscopic pore classification requires re-evaluation and further experiments. [ABSTRACT FROM AUTHOR]

Among various available 3D bioprinting techniques, extrusion-based three-dimensional (3D) bioprinting allows the deposition of cell-laden bioink, ensuring predefined scaffold architecture that may offer living tissue regeneration. With a combination of unique characteristics such as biocompatibility, less cell toxicity, and high water content, natural hydrogels are a great candidate for bioink formulation for the extrusion-based 3D bioprinting process. However, due to its low mechanical integrity, hydrogel faces a common challenge in maintaining structural integrity. To tackle this challenge, the rheological properties, specifically the shear thinning behavior (reduction of viscosity with increasing the applied load/shear rate on hydrogels) of a set of hybrid hydrogels composed of cellulose-derived nanofiber (TEMPO-mediated nano-fibrillated cellulose, TO-NFC), carboxymethyl cellulose (CMC), and commonly used alginate, were explored. A total of 46 compositions were prepared using higher (0.5% and 1.0%) and lower percentages (0.005% and 0.01%) of TO-NFC, 1–4% of CMC, and 1–4% of alginate to analyze the shear thinning factors such as the values of n and K, which were determined for each composition from the flow diagram and co-related with the 3D printability. The ability to tune shear thinning factors with various ratios of a nanofiber can help achieve a 3D bio-printed scaffold with defined scaffold architecture. [ABSTRACT FROM AUTHOR]

Abstract Additive manufacturing, or three‐dimensional printing (3DP) technology, has been recently explored in every field of science and technology for its unique features and ease of operation. 3DP technology has a wide range of applications in the food industry. The technology has enormous potential for the development of functional foods, for food and drug delivery, and for people with special needs, including dysphagia patients. This review envisages the recent interest in plant proteins and the development of food products using additive manufacturing (3DP), which is an exciting opportunity for the food industry and legume producers. The development of the formulation prior to printing requires a thorough rheological characterization for the smooth operation of the printer and fidelity. The steady flow properties and viscoelasticity of legume proteins, as well as their role in 3DP, are elucidated. Finally, this review provides insights into the current state of legume protein‐based 3DP and food product development.

Extrusion-based 3D bioprinting is a promising technique for fabricating multi-layered, complex biostructures, as it enables multi-material dispersion of bioinks with a straightforward procedure (particularly for users with limited additive manufacturing skills). Nonetheless, this method faces challenges in retaining the shape fidelity of the 3D-bioprinted structure, i.e., the collapse of filament (bioink) due to gravity and/or spreading of the bioink owing to the low viscosity, ultimately complicating the fabrication of multi-layered designs that can maintain the desired pore structure. While low viscosity is required to ensure a continuous flow of material (without clogging), a bioink should be viscous enough to retain its shape post-printing, highlighting the importance of bioink properties optimization. Here, two quantitative analyses are performed to evaluate shape fidelity. First, the filament collapse deformation is evaluated by printing different concentrations of alginate and its crosslinker (calcium chloride) by a co-axial nozzle over a platform to observe the overhanging deformation over time at two different ambient temperatures. In addition, a mathematical model is developed to estimate Young's modulus and filament collapse over time. Second, the printability of alginate is improved by optimizing gelatin concentrations and analyzing the pore size area. In addition, the biocompatibility of proposed bioinks is evaluated with a cell viability test. The proposed bioink (3% w/v gelatin in 4% alginate) yielded a 98% normalized pore number (high shape fidelity) while maintaining >90% cell viability five days after being bioprinted. Integration of quantitative analysis/simulations and 3D printing facilitate the determination of the optimum composition and concentration of different elements of a bioink to prevent filament collapse or bioink spreading (post-printing), ultimately resulting in high shape fidelity (i.e., retaining the shape) and printing quality. [ABSTRACT FROM AUTHOR]

[Display omitted] A range of 3D printing methods have been investigated intensively in the literature for manufacturing personalised solid dosage forms, with infill density commonly used to control release rates. However, there is limited mechanistic understanding of the impacts of infill adjustments on in vitro performance when printing tablets of constant dose. In this study, the effects and interplay of infill pattern and tablet geometry scaling on dose and drug release performance were investigated. Paracetamol (PAC) was used as a model drug. An immediate release erodible system (Eudragit E PO) and an erodible swellable system (Soluplus) were prepared via wet granulation into granules and printed using Arburg Plastic Freeforming (APF). Both binary formulations, despite not FDM printable, were successfully APF printed and exhibited good reproducibility compared to pharmacopoeia specification. The physical form of the drug and its integrity following granulation and printing was assessed using DSC, PXRD and ATR-FTIR. Two infill patterns (SM1 and SM2) were employed to print tablets with equal porosity, but different pore size, structure and surface area to volume ratio (SA/V). Geometry scaling (tablet height and diameter) of Eudragit-PAC tablets was not found to significantly influence the release rate of the tablets with 30 to 70% infill density. When increased to 90% infill density, geometric scaling was found to have a significant effect on release rate with the constant diameter tablet releasing faster than the constant height tablet. Soluplus-PAC tablets printed using different infill patterns demonstrated similar release profiles, due to swelling. Geometric parameters were found to significantly influence release profiles for tablets printed at certain infill densities giving new insight into how software parameters can be used to tune drug release. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) bio-printing has recently emerged as a crucial technology in tissue engineering, yet there are still challenges in selecting materials to obtain good print quality. Therefore, it is essential to study the influence of the chosen material (i.e., bio-ink) and the printing parameters on the final result. The “printability” of a bio-ink indicates its suitability for bio-printing. Hydrogels are a great choice because of their biocompatibility, but their printability is crucial for exploiting their properties and ensuring high printing accuracy. However, the printing settings are seldom addressed when printing hydrogels. In this context, this study explored the printability of double network (DN) hydrogels, from printing lines (1D structures) to lattices (2D structures) and 3D tubular structures, with a focus on printing accuracy. The DN hydrogel has two entangled cross-linked networks and a balanced mechanical performance combining high strength, toughness, and biocompatibility. The combination of poly (ethylene glycol)-diacrylate (PEDGA) and sodium alginate (SA) enables the qualities mentioned earlier to be met, as well as the use of UV to prevent filament collapse under gravity. Critical correlations between the printability and settings, such as velocity and viscosity of the ink, were identified. PEGDA/alginate-based double network hydrogels were explored and prepared, and printing conditions were improved to achieve 3D complex architectures, such as tubular structures. The DN solution ink was found to be unsuitable for extrudability; hence, glycerol was added to enhance the process. Different glycerol concentrations and flow rates were investigated. The solution containing 25% glycerol and a flow rate of 2 mm/s yielded the best printing accuracy. Thanks to these parameters, a line width of 1 mm and an angle printing inaccuracy of less than 1° were achieved, indicating good shape accuracy. Once the optimal parameters were identified, a tubular structure was achieved with a high printing accuracy. This study demonstrated a 3D printing hydrogel structure using a commercial 3D bio-printer (REGEMAT 3D BIO V1) by synchronizing all parameters, serving as a reference for future more complex 3D structures.

In recent years, three-dimensional (3D) printing of environmentally friendly structures with a high concentration of nanocellulose (NC) has gained much attention because of health and environmental issues. However, there remain challenges due to poor adhesion between printed layers, resulting in low mechanical properties and shape fidelity. This research demonstrates an economical approach to printing environmentally friendly 3D structures by directly extruding high-concentration NC (∼25.5 wt %) paste to deal with the challenges. Different low concentrations (2.5, 5, and 10 wt %) of polyvinyl alcohol (PVA) were mixed with NC as a crosslinker to facilitate the adhesion between the printed layers. A twin-screw extrusion machine was used to eject the high-concentration NC paste for 3D printing. After the printing process, the final structures were dried at a controlled relative humidity of 45% and a temperature of 25 °C. An optimum 5 wt % PVA-crosslinked high-concentration NC paste showed the highest flexural strength of 121 ± 2 MPa (233% improvement) and a flexural modulus of 15.0 ± 0.1 GPa (263% improvement), which are much higher than the previously reported results until now. It suggests that the extremely low content of PVA effectively improved the bilayer adhesion, resulting in high shape fidelity and mechanical strength of the 3D printed structures for environmentally friendly structural applications. [ABSTRACT FROM AUTHOR]

This study aims to update the existing SG PW laser system and improve the temporal contrast and shape fidelity of a compressed pulse with a 150 fs level for multi-PW (5–10 PW). The design of third-order dispersion (TOD) compensation via a birefringent crystal was studied through numerical simulations and experiments. The dispersions introduced by the birefringent crystal were calculated using the Jones matrix element by changing the in-plane rotation angle ϕ, thickness d, incident angle θ, and temperature T, while also considering the transmission spectral bandwidth. The group-velocity dispersion (GVD), TOD, and fourth-order dispersion (FOD) of the existing SG PW laser system and its influence on the compressed pulse with different pulse durations were analyzed. The results suggest that a TOD of 1.3 × 10 6 fs3 needs to compensate for the multi-PW design. The compensation scheme is designed using a quartz crystal of d = 6.5 mm, θ = 90 ° , ϕ = 17 ° , and T = 21 °C, corresponding to the thickness, inclination angle, in-plane rotation angle, and temperature, respectively. Furthermore, we show a principle-proof experiment offline and measure the GVD and TOD by the Wizzler, which is based on theoretical simulations. These results can be applied to independently and continuously control the TOD of short-pulse laser systems. [ABSTRACT FROM AUTHOR]

Among various available 3D bioprinting techniques, extrusion-based three-dimensional (3D) bioprinting allows the deposition of cell-laden bioink, ensuring predefined scaffold architecture that may offer living tissue regeneration. With a combination of unique characteristics such as biocompatibility, less cell toxicity, and high water content, natural hydrogels are a great candidate for bioink formulation for the extrusion-based 3D bioprinting process. However, due to its low mechanical integrity, hydrogel faces a common challenge in maintaining structural integrity. To tackle this challenge, the rheological properties, specifically the shear thinning behavior (reduction of viscosity with increasing the applied load/shear rate on hydrogels) of a set of hybrid hydrogels composed of cellulose-derived nanofiber (TEMPO-mediated nano-fibrillated cellulose, TO-NFC), carboxymethyl cellulose (CMC), and commonly used alginate, were explored. A total of 46 compositions were prepared using higher (0.5% and 1.0%) and lower percentages (0.005% and 0.01%) of TO-NFC, 1–4% of CMC, and 1–4% of alginate to analyze the shear thinning factors such as the values of n and K, which were determined for each composition from the flow diagram and co-related with the 3D printability. The ability to tune shear thinning factors with various ratios of a nanofiber can help achieve a 3D bio-printed scaffold with defined scaffold architecture.

Extrusion-based 3D bioprinting is a promising technique for fabricating multi-layered, complex biostructures, as it enables multi-material dispersion of bioinks with a straightforward procedure (particularly for users with limited additive manufacturing skills). Nonetheless, this method faces challenges in retaining the shape fidelity of the 3D-bioprinted structure, i.e., the collapse of filament (bioink) due to gravity and/or spreading of the bioink owing to the low viscosity, ultimately complicating the fabrication of multi-layered designs that can maintain the desired pore structure. While low viscosity is required to ensure a continuous flow of material (without clogging), a bioink should be viscous enough to retain its shape post-printing, highlighting the importance of bioink properties optimization. Here, two quantitative analyses are performed to evaluate shape fidelity. First, the filament collapse deformation is evaluated by printing different concentrations of alginate and its crosslinker (calcium chloride) by a co-axial nozzle over a platform to observe the overhanging deformation over time at two different ambient temperatures. In addition, a mathematical model is developed to estimate Young’s modulus and filament collapse over time. Second, the printability of alginate is improved by optimizing gelatin concentrations and analyzing the pore size area. In addition, the biocompatibility of proposed bioinks is evaluated with a cell viability test. The proposed bioink (3% w/v gelatin in 4% alginate) yielded a 98% normalized pore number (high shape fidelity) while maintaining >90% cell viability five days after being bioprinted. Integration of quantitative analysis/simulations and 3D printing facilitate the determination of the optimum composition and concentration of different elements of a bioink to prevent filament collapse or bioink spreading (post-printing), ultimately resulting in high shape fidelity (i.e., retaining the shape) and printing quality.

Polycaprolactone (PCL) and hydroxyapatite (HA) composite are widely used in tissue engineering (TE). They are fit to being processed with three-dimensional (3D) printing technique to create scaffolds with verifiable porosity. The current challenge is to guarantee the reliability and reproducibility of 3D printed scaffolds and to create sterile scaffolds which can be used for in vitro cell cultures. In this context it is important for successful cell culture, to have a protocol in order to evaluate the sterility of the printed scaffolds. We proposed a systematic approach to sterilise 90%PCL-10%HA pellets using a 3D bioprinter before starting the printing process. We evaluated the printability of PCL-HA composite and the shape fidelity of scaffolds printed with and without sterilised pellets varying infill pattern, and the sterility of 3D printed scaffolds following the method established by the United States Pharmacopoeia. Finally, the thermal analyses supported by the Fourier Transform Infrared Spectroscopy were useful to verify the stability of the sterilisation process in the PCL solid state with and without HA. The results show that the use of the 3D printer, according to the proposed protocol, allows to obtain sterile 3D PCL-HA scaffolds suitable for TE applications such as bone or cartilage repair. [ABSTRACT FROM AUTHOR]

This study aims to update the existing SG PW laser system and improve the temporal contrast and shape fidelity of a compressed pulse with a 150 fs level for multi-PW (5–10 PW). The design of third-order dispersion (TOD) compensation via a birefringent crystal was studied through numerical simulations and experiments. The dispersions introduced by the birefringent crystal were calculated using the Jones matrix element by changing the in-plane rotation angle ϕ, thickness d, incident angle θ, and temperature T, while also considering the transmission spectral bandwidth. The group-velocity dispersion (GVD), TOD, and fourth-order dispersion (FOD) of the existing SG PW laser system and its influence on the compressed pulse with different pulse durations were analyzed. The results suggest that a TOD of 1.3×106 fs3 needs to compensate for the multi-PW design. The compensation scheme is designed using a quartz crystal of d = 6.5 mm, θ = 90°, ϕ = 17°, and T = 21 °C, corresponding to the thickness, inclination angle, in-plane rotation angle, and temperature, respectively. Furthermore, we show a principle-proof experiment offline and measure the GVD and TOD by the Wizzler, which is based on theoretical simulations. These results can be applied to independently and continuously control the TOD of short-pulse laser systems.

Maintaining shape fidelity of 3D bio-printed scaffolds with soft biomaterials is an ongoing challenge. Here, a rheological investigation focusing on identifying useful physical and mechanical properties directly related to the geometric fidelity of 3D bio-printed scaffolds is presented. To ensure during- and post-printing shape fidelity of the scaffolds, various percentages of Carboxymethyl Cellulose (CMC) (viscosity enhancer) and different calcium salts (CaCl2 and CaSO4, physical cross-linkers) were mixed into alginate before extrusion to realize shape fidelity. The overall solid content of Alginate-Carboxymethyl Cellulose (CMC) was limited to 6%. A set of rheological tests, e.g., flow curves, amplitude tests, and three interval thixotropic tests, were performed to identify and compare the shear-thinning capacity, gelation points, and recovery rate of various compositions. The geometrical fidelity of the fabricated scaffolds was defined by printability and collapse tests. The effect of using multiple cross-linkers simultaneously was assessed. Various large-scale scaffolds were fabricated (up to 5.0 cm) using a pre-crosslinked hybrid. Scaffolds were assessed for the ability to support the growth of Escherichia coli using the Most Probable Number technique to quantify bacteria immediately after inoculation and 24 h later. This pre-crosslinking-based rheological property controlling technique can open a new avenue for 3D bio-fabrication of scaffolds, ensuring proper geometry.

This paper presents a breakthrough in the shape fidelity and mechanical strength of 3D-printed high-concentration nanocellulose structures, demonstrating a record flexural strength of 149 ± 2 MPa and a flexural modulus of 15 ± 0.8 GPa. These findings replace the previous method of 3D printing on conventional substrates with wood substrates for highly concentrated nanocellulose (HCNC) structures. The HCNC structures are 3D-printed using extrusion and processed under controlled drying conditions (Relative humidity: 60 % and 45 %, Temperature: 25 °C) to achieve outstanding mechanical properties without sacrificing structure shape fidelity/retention. It was noticed that the drying phenomenon of HCNC structures on the conventional substrates is responsible for the adhesion issues between the printed layers resulting in low shape fidelity/retention. In contrast with conventional substrates, the wood substrates offer an increased drying rate from the bottom side of printed HCNC structures due to its hydrophilicity and wicked nature, which helps maintain the shape fidelity without using additional crosslinkers, resulting in improved shape fidelity/retention and mechanical properties. The 3D-printed nanocellulose structure bears twice the load compared to a commercial poly lactic acid 3D-printed one. These features open a new horizon for fabricating 3D-printed nanocellulose structures for advanced environmentally friendly structural applications. [Display omitted] [ABSTRACT FROM AUTHOR]

Bioprinted tissues are currently being utilized for drug and cosmetic screening mostly, but the long-term goal is to achieve human scale functional tissues and organs for transplantation. Hence, recapitulating the multiscale architecture, 3D structures, and complexity of native tissues is the key to produce bioengineered tissues/organs. Decellularized extracellular matrix (dECM)-based biomaterials are widely being used as bioinks for 3D bioprinting for tissue engineering applications. Their potential to provide excellent biocompatibility for the cells drove researchers to use them extensively. However, the decellularization process involves many detergents and enzymes which may contribute to their loss of mechanical properties. Moreover, thermal gelation of dECM-based hydrogels is typically slow which affects the shape fidelity, printability, and physical properties while printing complex structures with 3D printing. But, thermally gelled dECM hydrogels provide excellent cell viability and functionality. To overcome this, a novel dual crosslinking of unmodified dECM has been proposed in this study to render shape fidelity and enhance cell viability and functionality. The dECM-based bioink can be initially polymerized superficially on exposure to light to achieve immediate stability and can attain further stability upon thermal gelation. This dual crosslinking mechanism can maintain the microenvironment of the structure, hence allowing the printing of stable flexible structures. Optimized concentrations of novel photo crosslinkers have been determined and printing of a few complex-shaped anatomical structures has been demonstrated. This approach of fabricating complex scaffolds employing dual crosslinking can be used for the bioprinting of different complex tissue structures with tissue-specific dECM based bioinks., Competing Interests: Declaration of competing interest The authors declare no conflict of interest., (Copyright © 2023 Elsevier B.V. All rights reserved.)

[Display omitted] • Combined 3D food printing and freeze-drying technology to manufacture crisp pumpkin snacks. • Reducing the filling rate improved the shape fidelity and crispness of the sample. • The varying filling patterns had significant effects on the shape fidelity and crispness of the sample. • Regardless of the filling patterns, the crispness of the cast samples was less than that of the 100% filled printed samples. This study aimed to use the internal design of 3D food printing (3DFP) technology to obtain freeze-dried pumpkin with controllable crispness and higher shape fidelity. Two internal structural variables, namely filling pattern (honeycomb, rectilinear, grid, and triangular) and filling rate (25, 50, 75, and 100%), were studied to assess the impact on the shape fidelity and crispness characteristic of the product. As the filling rate decreased, the printing accuracy of the samples increased. Regardless of the filling patterns, the 75% filled samples exhibited the greatest deformation. The crispness of the samples was closely related to the filling pattern and filling rate. In the case of the high filling rate, the internal structure of the samples was dense. It was less likely to be broken under the action of force and the crispness was reduced. In addition, the internal structure of the sample influenced its physical properties, and the crispness customization of the product can be achieved by designing the porosity. Morphological differences between printed and cast samples suggested that 3DFP was beneficial for the processing and preparation of highly viscoelastic materials. The crispness of cast sample was obviously less than that of the 100% filled printed samples. The results opened an interesting perspective to create crisp foods with high shape fidelity that meet specific texture requirements and provide new sensory perceptions. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) bio-printing has recently emerged as a crucial technology in tissue engineering, yet there are still challenges in selecting materials to obtain good print quality. Therefore, it is essential to study the influence of the chosen material (i.e., bio-ink) and the printing parameters on the final result. The "printability" of a bio-ink indicates its suitability for bio-printing. Hydrogels are a great choice because of their biocompatibility, but their printability is crucial for exploiting their properties and ensuring high printing accuracy. However, the printing settings are seldom addressed when printing hydrogels. In this context, this study explored the printability of double network (DN) hydrogels, from printing lines (1D structures) to lattices (2D structures) and 3D tubular structures, with a focus on printing accuracy. The DN hydrogel has two entangled cross-linked networks and a balanced mechanical performance combining high strength, toughness, and biocompatibility. The combination of poly (ethylene glycol)-diacrylate (PEDGA) and sodium alginate (SA) enables the qualities mentioned earlier to be met, as well as the use of UV to prevent filament collapse under gravity. Critical correlations between the printability and settings, such as velocity and viscosity of the ink, were identified. PEGDA/alginate-based double network hydrogels were explored and prepared, and printing conditions were improved to achieve 3D complex architectures, such as tubular structures. The DN solution ink was found to be unsuitable for extrudability; hence, glycerol was added to enhance the process. Different glycerol concentrations and flow rates were investigated. The solution containing 25% glycerol and a flow rate of 2 mm/s yielded the best printing accuracy. Thanks to these parameters, a line width of 1 mm and an angle printing inaccuracy of less than 1° were achieved, indicating good shape accuracy. Once the optimal parameters were identified, a tubular structure was achieved with a high printing accuracy. This study demonstrated a 3D printing hydrogel structure using a commercial 3D bio-printer (REGEMAT 3D BIO V1) by synchronizing all parameters, serving as a reference for future more complex 3D structures., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Greco, Miskovic, Varon, Marraffa and Iorio.)

Various filament-extrusion models have been assessed for their accuracy in predicting the width of filament deposited during extrusion-based 3D printing of food materials. Slicer software uses such models in algorithms to determine appropriate nozzle toolpaths and material extrusion flow rates for printing 3D structures. Prediction and experiment were compared for various printer operating conditions encompassing slow-to moderate-speed and coarse-to fine-resolution 3D food printing. The model that assumes filaments of oblong cross-section predicts filament width well. Fractionated animal fat and 20% rice-starch gel generally form smooth, continuous and stable filaments over a broad range of printer operating conditions, making them ideal materials for 3D food printing. Practical issues in 3D food printing were highlighted, including the non-uniformity of filament width that results from even the slightest build-platform slope or nozzle skew, and the relevance of the extrusion multiplier in slicer software for fine-tuning 3D printing to account for differences in rheology between food materials. • Slicers use filament models to compute toolpaths and extrusion rates in 3D-printing. • Various filament models were assessed in the context of 3D food printing. • Model that assumes filaments of oblong cross-section predicts filament width well. • Even slight build-platform slope or nozzle skew affect filament-width uniformity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Print quality depends on printability, extrudability, shape fidelity, accuracy and precision; • Rheology is valuable to predict extrudability, printing accuracy and shape fidelity; • Nozzle geometry can influence print speed and pressure setting; • A series of print runs should be used to evaluate the ink deposition in x, y, z; • Comprehensive and dynamic characterization protocols should be adopted. One of the exciting future directions in the 3D printing field is the development of innovative personalized smart constructions for bio-applications, including drug delivery, namely high-throughput drug screening and customized topical/oral administration of pharmaceuticals, as well as tissue engineering. In this context, hydrogels have emerged as a promising material that, when combined with extrusion 3D printing, allow the creation of soft-material structures with defined spatial locations, that can be printed at room temperature and customized by tuning the geometric design and/or the formulation components. Thus, the efficacy and quality of such vehicles is dependent on formulation, design, and printing process parameters. However, hydrogel inks are often designed and characterized using different methods and this lack of uniformity impairs. Characterization techniques are usually arbitrary and differ among research groups, challenging the inference of possible conclusions on hydrogel behaviour and potential applications. Therefore, to properly analyse the potential of a particular hydrogel ink formulation, we review, for the first time, the most frequently employed characterization procedures, from rheological approaches to printing parameters and settings, and discuss their relevance, limitations and drawbacks, and highlight future perspectives. Overall, to accelerate the development of high-quality 3D constructs, comprehensive characterization protocols for both pre-printing and printing assays should be adopted. Furthermore, their transversal adoption could serve as a boost in terms of quality requirements and regulatory aspects. [ABSTRACT FROM AUTHOR]

Maintaining shape fidelity of 3D bio-printed scaffolds with soft biomaterials is an ongoing challenge. Here, a rheological investigation focusing on identifying useful physical and mechanical properties directly related to the geometric fidelity of 3D bio-printed scaffolds is presented. To ensure during- and post-printing shape fidelity of the scaffolds, various percentages of Carboxymethyl Cellulose (CMC) (viscosity enhancer) and different calcium salts (CaCl2 and CaSO4, physical cross-linkers) were mixed into alginate before extrusion to realize shape fidelity. The overall solid content of Alginate-Carboxymethyl Cellulose (CMC) was limited to 6%. A set of rheological tests, e.g., flow curves, amplitude tests, and three interval thixotropic tests, were performed to identify and compare the shear-thinning capacity, gelation points, and recovery rate of various compositions. The geometrical fidelity of the fabricated scaffolds was defined by printability and collapse tests. The effect of using multiple cross-linkers simultaneously was assessed. Various large-scale scaffolds were fabricated (up to 5.0 cm) using a pre-crosslinked hybrid. Scaffolds were assessed for the ability to support the growth of Escherichia coli using the Most Probable Number technique to quantify bacteria immediately after inoculation and 24 h later. This pre-crosslinking-based rheological property controlling technique can open a new avenue for 3D bio-fabrication of scaffolds, ensuring proper geometry. [ABSTRACT FROM AUTHOR]