Extrusion-based 3D Bioprinting Research Articles

Characterization and optimization of a biomaterial ink aided by machine learning-assisted parameter suggestion

Bio-inks and biomaterial inks are crucial to the success of 3D bioprinting, as they form the foundation of almost every 3D bio-printed structure. Despite the use of various biomaterial inks with potential biomedical applications in 3D printing, developing printable biomaterial inks for extrusion-based 3D bioprinting remains a major challenge in additive manufacturing. To be effective, the inks must possess suitable mechanical properties, high biocompatibility, and the ability to print precisely. In this study, machine learning (ML) was employed to develop a chitosan-gelatin-agarose biomaterial ink. The ink's printability, rheological properties, hydrophilicity, degradability, and biological response were evaluated after an optimization process. The optimized ink exhibited adequate viscosity for reliable printing, and 3D structures were created to assess printability and shape integrity. Bone marrow mesenchymal stem/stromal cells (BMSCs) were cultured on the ink's surface, and cell adhesion, growth, and morphology were assessed. Results showed favorable cell morphology, and cell viability within the optimized ink. The ink consisting of 27 % agarose, 53 % chitosan, and 20 % gelatin (ACG), may be a suitable biomaterial for fabricating 3D complex tissue constructs.

Characterization and optimization of a biomaterial ink aided by machine learning-assisted parameter suggestion

Bio-inks and biomaterial inks are crucial to the success of 3D bioprinting, as they form the foundation of almost every 3D bio-printed structure. Despite the use of various biomaterial inks with potential biomedical applications in 3D printing, developing printable biomaterial inks for extrusion-based 3D bioprinting remains a major challenge in additive manufacturing. To be effective, the inks must possess suitable mechanical properties, high biocompatibility, and the ability to print precisely. In this study, machine learning (ML) was employed to develop a chitosan-gelatin-agarose biomaterial ink. The ink's printability, rheological properties, hydrophilicity, degradability, and biological response were evaluated after an optimization process. The optimized ink exhibited adequate viscosity for reliable printing, and 3D structures were created to assess printability and shape integrity. Bone marrow mesenchymal stem/stromal cells (BMSCs) were cultured on the ink's surface, and cell adhesion, growth, and morphology were assessed. Results showed favorable cell morphology, and cell viability within the optimized ink. The ink consisting of 27% agarose, 53% chitosan, and 20% gelatin (ACG), may be a suitable biomaterial for fabricating 3D complex tissue constructs.

Advancing scaffold porosity through a machine learning framework in extrusion based 3D bioprinting

Three Dimensional (3D) bioprinting holds great promise for tissue and organ regeneration due to its inherent capability to deposit biocompatible materials containing live cells in precise locations. Extrusion-based 3D bioprinting (EBP) method stands out for its ability to achieve a higher cell release rate, ensuring both external and internal scaffold structures. The systematic adjustment of key process parameters of EBP, including nozzle diameter, printing speed, print distance, extrusion pressure, material fraction, and viscosity allows for precise control over filament dimensions, ultimately shaping the desired scaffold porosity as per user specifications. However, managing these factors with all possible interactions simultaneously to achieve the desired filament width can be intricate and resource intensive. This study presents a novel framework designed to construct a predictive model for the filament width of 3D bioprinted scaffolds for various process parameters. A total of 157 experiments have been conducted under various combinations of process parameters and biomaterial’s weight fraction for this study purpose. A regression-based machine learning approach is employed to develop the predictive model utilizing Adj. R2, Mallow’s Cp, and Bayesian Information Criterion (BIC). Following model development, rigorous experimental validations are conducted to assess the accuracy and reliability of the model. Based on the cross-validation of randomly split test data, Adj. R2 model emerges as the highest performing machine learning model (Mean Squared Error, MSE = 0.0816) compared to Mallow’s Cp and BIC (MSE = 0.0841 and 0.0877, respectively) models. The comparative analysis results between the experimental and model’s data demonstrate that our predictive model achieves an accuracy of approximately 85% in filament width prediction. This framework presents a significant advancement in the precise control and optimization of 3D bioprinted scaffold fabrication, offering valuable insights for the advancement of tissue engineering and regenerative medicine applications.

Fabrication of Sodium Trimetaphosphate-Based PEDOT:PSS Conductive Hydrogels.

Conductive hydrogels are highly attractive for biomedical applications due to their ability to mimic the electrophysiological environment of biological tissues. Although conducting polymer polythiophene-poly-(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS) alone exhibit high conductivity, the addition of other chemical compositions could further improve the electrical and mechanical properties of PEDOT:PSS, providing a more promising interface with biological tissues. Here we study the effects of incorporating crosslinking additives, such as glycerol and sodium trimetaphosphate (STMP), in developing interpenetrating PEDOT:PSS-based conductive hydrogels. The addition of glycerol at a low concentration maintained the PEDOT:PSS conductivity with enhanced wettability but decreased the mechanical stiffness. Increasing the concentration of STMP allowed sufficient physical crosslinking with PEDOT:PSS, resulting in improved hydrogel conductivity, wettability, and rheological properties without glycerol. The STMP-based PEDOT:PSS conductive hydrogels also exhibited shear-thinning behaviors, which are potentially favorable for extrusion-based 3D bioprinting applications. We demonstrate an interpenetrating conducting polymer hydrogel with tunable electrical and mechanical properties for cellular interactions and future tissue engineering applications.

Persuasive factors on the bioink printability and cell viability in the extrusion-based 3D bioprinting for tissue regeneration applications

Persuasive factors on the bioink printability and cell viability in the extrusion-based 3D bioprinting for tissue regeneration applications

Preparation and characterization of 3D bioprinted gelatin methacrylate hydrogel incorporated with curcumin loaded chitosan nanoparticles for in vivo wound healing application

This study developed a biomimetic composite bioink consisting of gelatin methacrylate (GelMA) /chitosan nanoparticles (CSNPs) for extrusion-based 3D bioprinting. Additionally, curcumin(Cur)-loaded nanoparticles were incorporated which increased the proliferation and antibacterial activity of biomimetic skin constructs. The hydrogel, curcumin-loaded NPs, and the biocomposite was characterized chemically and physically. The results indicated proper modified gelatin with tunable physical characteristics, e.g., swelling ratio and biodegradability up to 1200 % and 25 days, respectively. In addition, the characterized CSNPs showed good distribution with a size of 370 nm and a zeta potential of 41.1 mV. We investigated the mechanical and cytocompatibility properties of chitosan nanoparticles encapsulated in hydrogel for emulating an extracellular matrix suitable for skin tissue engineering. CSNPs entrapped in GelMA (15 % w/v) exhibited controlled drug release during 5 days, which was fitted into various kinetic models to study the mass transfer mechanism behavior. Also, the composite hydrogels were effective as a barrier against both gram-positive and gram-negative bacteria at a concentration of 50 μg/ml nanoparticles in GelMA 15 %. Furthermore, the biocomposite was applied on Wistar rats for wound healing. As a result, this study provides a GelMA-NP50-Cur3 scaffold that promotes cell proliferation and decreases microbial infections in wounds.

Customization of an Ultrafast Thiol-Norbornene Photo-Cross-Linkable Hyaluronic Acid-Gelatin Bioink for Extrusion-Based 3D Bioprinting.

Light-based three-dimensional (3D) bioprinting has been widely studied in tissue engineering. Despite the fact that free-radical chain polymerization-based bioinks like hyaluronic acid methacrylate (HAMA) and gelatin methacryloyl (GelMA) have been extensively explored in 3D bioprinting, the thiol-ene hydrogel system has attracted increasing attention for its ability in building hydrogel scaffolds in an oxygen-tolerant and cell-friendly way. Herein, we report a superfast curing thiol-ene bioink composed of norbornene-modified hyaluronic acid (NorHA) and thiolated gelatin (GelSH) for 3D bioprinting. A new facile approach was first introduced in the synthesis of NorHA, which circumvented the cumbersome steps involved in previous works. Additionally, after mixing NorHA with macro-cross-linker GelSH, the customized NorHA/GelSH bioinks exhibited fascinating superiorities over the gold standard GelMA bioinks, such as an ultrafast curing rate (1-5 s), much lowered photoinitiator concentration (0.03% w/v), and flexible physical performances. Moreover, the NorHA/GelSH hydrogel greatly avoided excess ROS generation, which is important for the survival of the encapsulated cells. Last, compared with the GelMA scaffold, the 3D-printed NorHA/GelSH scaffold not only exhibited excellent cell viability but also guaranteed cell proliferation, revealing its superior bioactivity. In conclusion, the NorHA/GelSH system is a promising candidate for 3D bioprinting and tissue engineering applications.

Dynamics of Nanocomposite Hydrogel Alignment during 3D Printing to Develop Tissue Engineering Technology.

Taking inspiration from spider silk protein spinning, we developed a method to produce tough filaments using extrusion-based 3D bioprinting and salting-out of the protein. To enhance both stiffness and ductility, we have designed a blend of partially crystalline, thermally sensitive natural polymer gelatin and viscoelastic G-polymer networks, mimicking the components of spider silk. Additionally, we have incorporated inorganic nanoparticles as a rheological modifier to fine-tune the 3D printing properties. This self-healing nanocomposite hydrogel exhibits exceptional mechanical properties, biocompatibility, shear thinning behavior, and a well-controlled gelation mechanism for 3D printing.

3D-printed triaxial nozzles fabricated by stereolithography to prevent backflow in soft matter biofabrication

Three-dimensional (3D) bioprinting has a significant influence on tissue engineering by virtue of its capacity to produce complicated structures with complex geometries that are challenging to recreate using conventional manufacturing methods. However, the nozzle design and fabrication remain a limitation within extrusion-based 3D bioprinting, restricting and compromising the overall potential of this technology. The proposed nozzle design combines three Luer-Lok compatible inlets and an outlet within the printed body, eliminating manual assembly and enhancing fabrication consistency and quality. Furthermore, a finite element analysis of the fluid flow in the nozzle demonstrated the effectiveness of the nozzle to minimize backflow, in comparison with a traditional nozzle design. The tetrameric IIZK (Ac-Ile-IIe-Cha-Lys-NH2) and IIFK (Ac-Ile-IIe-Phe-Lys-NH2) peptide bioinks were used to 3D-print a variety of 3D scaffolds of varying complexity, with good resolution and gel continuity. Our work successfully demonstrated the fabrication of a novel design and its potential, and by means of 3D bioprinting, we assessed the biocompatibility and cell viability of the cell-laden constructs. This study highlights the capability of the novel design, which aids the field of tissue engineering, allowing 3D extrusion-based bioprinting to be utilized in the production of cell-incorporated constructions or scaffolds.

Formulation and Characterization of a Novel Oxidized Alginate-Gelatin-Silk Fibroin Bioink with the Aim of Skin Regeneration.

In the present study, a novel bioink was suggested based on the OAlg, GL, and SF hydrogels. The composition of the bioink was optimized by the rheological and printability measurements, and the extrusion-based 3D bioprinting process was performed by applying the optimum OAlg-based bioink. The results demonstrated that the viscosity of bioink was continuously decreased by increasing the SF/GL ratio, and the bioink displayed a maximum achievable printability (92 ± 2%) at 2% (w/v) of SF and 4% (w/v) of GL. Moreover, the cellular behavior of the scaffolds investigated by MTT assay and live/dead staining confirmed the biocompatibility of the prepared bioink. The bioprinted OAlg-GL-SF scaffold could have the potential for using in skin tissue engineering applications, which needs further exploration.

Application of 3D Bioprinting in Liver Diseases.

Liver diseases are the primary reason for morbidity and mortality in the world. Owing to a shortage of organ donors and postoperative immune rejection, patients routinely suffer from liver failure. Unlike 2D cell models, animal models, and organoids, 3D bioprinting can be successfully employed to print living tissues and organs that contain blood vessels, bone, and kidney, heart, and liver tissues and so on. 3D bioprinting is mainly classified into four types: inkjet 3D bioprinting, extrusion-based 3D bioprinting, laser-assisted bioprinting (LAB), and vat photopolymerization. Bioinks for 3D bioprinting are composed of hydrogels and cells. For liver 3D bioprinting, hepatic parenchymal cells (hepatocytes) and liver nonparenchymal cells (hepatic stellate cells, hepatic sinusoidal endothelial cells, and Kupffer cells) are commonly used. Compared to conventional scaffold-based approaches, marked by limited functionality and complexity, 3D bioprinting can achieve accurate cell settlement, a high resolution, and more efficient usage of biomaterials, better mimicking the complex microstructures of native tissues. This method will make contributions to disease modeling, drug discovery, and even regenerative medicine. However, the limitations and challenges of this method cannot be ignored. Limitation include the requirement of diverse fabrication technologies, observation of drug dynamic response under perfusion culture, the resolution to reproduce complex hepatic microenvironment, and so on. Despite this, 3D bioprinting is still a promising and innovative biofabrication strategy for the creation of artificial multi-cellular tissues/organs.

Multilayer 3D bioprinting and complex mechanical properties of alginate-gelatin mesostructures

In the biomedical field, extrusion-based 3D bioprinting has emerged as a promising technique to fabricate tissue replacements. However, a main challenge is to find suitable bioinks and reproducible procedures that ensure good printability and generate final printed constructs with high shape fidelity, similarity to the designed model, and controllable mechanical properties. In this study, our main goal is to 3D print multilayered structures from alginate-gelatin (AG) hydrogels and to quantify their complex mechanical properties with particular focus on the effects of the extrusion process and geometrical parameters, i.e. different mesostructures and macroporosities. We first introduce a procedure including a pre-cooling step and optimized printing parameters to control and improve the printability of AG hydrogels based on rheological tests and printability studies. Through this procedure, we significantly improve the printability and flow stability of AG hydrogels and successfully fabricate well-defined constructs similar to our design models. Our subsequent complex mechanical analyses highlight that the extrusion process and the mesostructure, characterized by pore size, layer height and filament diameter, significantly change the complex mechanical response of printed constructs. The presented approach and the corresponding results have important implications for future 3D bioprinting applications when aiming to produce replacements with good structural integrity and defined mechanical properties similar to the native tissue, especially in soft tissue engineering. The approach is also applicable to the printing of gelatin-based hydrogels with different accompanying materials, concentrations, or cells.

3D bio-printed living nerve-like fibers refine the ecological niche for long-distance spinal cord injury regeneration.

3D bioprinting holds great promise toward fabricating biomimetic living constructs in a bottom-up assembly manner. To date, various emergences of living constructs have been bioprinted for in vitro applications, while the conspicuous potential serving for in vivo implantable therapies in spinal cord injury (SCI) has been relatively overlooked. Herein, living nerve-like fibers are prepared via extrusion-based 3D bioprinting for SCI therapy. The living nerve-like fibers are comprised of neural stem cells (NSCs) embedded within a designed hydrogel that mimics the extracellular matrix (ECM), assembled into a highly spatial ordered architecture, similar to densely arranged bundles of the nerve fibers. The pro-neurogenesis ability of these living nerve-like fibers is tested in a 4mm-long complete transected SCI rat model. Evidence shows that living nerve-like fibers refine the ecological niche of the defect site by immune modulation, angiogenesis, neurogenesis, neural relay formations, and neural circuit remodeling, leading to outstanding functional reconstruction, revealing an evolution process of this living construct after implantation. This effective strategy, based on biomimetic living constructs, opens a new perspective on SCI therapies.

Dual-Crosslinking of Gelatin-Based Hydrogels: Promising Compositions for a 3D Printed Organotypic Bone Model.

Gelatin-based hydrogels have emerged as a popular scaffold material for tissue engineering applications. The introduction of variable crosslinking methods has shown promise for fabricating stable cell-laden scaffolds. In this work, we examine promising composite biopolymer-based inks for extrusion-based 3D bioprinting, using a dual crosslinking approach. A combination of carefully selected printable hydrogel ink compositions and the use of photoinduced covalent and ionic crosslinking mechanisms allows for the fabrication of scaffolds of high accuracy and low cytotoxicity, resulting in unimpeded cell proliferation, extracellular matrix deposition, and mineralization. Three selected bioink compositions were characterized and the respective cell-laden scaffolds were bioprinted. Temporal stability, morphology, swelling, and mechanical properties of the scaffolds were thoroughly studied and the biocompatibility of the constructs was assessed using rat mesenchymal stem cells while focusing on osteogenesis. Experimental results showed that the composition of 1% alginate, 4% gelatin, and 5% (w/v) gelatine methacrylate, was found to be optimal among the examined, with shape fidelity of 88%, large cell spreading area and cell viability at around 100% after 14 days. The large pore diameters that exceed 100 µm, and highly interconnected scaffold morphology, make these hydrogels extremely potent in bone tissue engineering and bone organoid fabrication.

Biocompatibility evaluation of antioxidant cocktail loaded gelatin methacrylamide as bioink for extrusion-based 3D bioprinting

Three-dimensional (3D) liver bioprinting is a promising technique for creating 3D liver models that can be used for in vitro drug testing, hepatotoxicity studies, and transplantation. The functional performance of 3D bioprinted liver constructs are limited by the lack of cell–cell interactions, which calls for the creation of bioprinted tissue constructs with high cell densities. This study reports the fabrication of 3D bioprinted liver constructs using a novel photocrosslinkable gelatin methacrylamide (GelMA)-based bioink formulation. However, the formation of excess free radicals during photoinitiation poses a challenge, particularly during photocrosslinking of large constructs with high cell densities. Hence, we designed a bioink formulation comprising the base polymer GelMA loaded with an antioxidant cocktail containing vitamin C (L-ascorbic acid (AA)) and vitamin E (α-tocopherol (α-Toc)). We confirmed that the combination of antioxidants loaded in GelMA enhanced the ability to scavenge intracellular reactive oxygen species formed during photocrosslinking. The GelMA formulation was evaluated for biocompatibility in vitro and in vivo. These results demonstrated that the bioink had adequate rheological characteristics and was biocompatible. Furthermore, when compared to bioprinted constructs with lower cell density, high-density primary rat hepatocyte constructs demonstrated improved cell-cell interactions and liver-specific functions like albumin and urea secretion, which increased 5-fold and 2.5-fold, respectively.

Visible light photocrosslinking of sugar beet pectin for 3D bioprinting applications

Herein, we report the hydrogelation of sugar beet pectin (SBP) via visible light-mediated photocrosslinking and its applications in extrusion-based 3D bioprinting. Rapid hydrogelation (<15 s) was achieved by applying 405 nm visible light to an SBP solution in the presence of tris(bipyridine)ruthenium(II) chloride hexahydrate ([Ru(bpy)3]2+) and sodium persulfate (SPS). The mechanical properties of the hydrogel could be tuned by controlling the visible light irradiation time and concentrations of SBP, [Ru(bpy)3]2+, and SPS. High-fidelity 3D hydrogel constructs were fabricated by extruding inks containing 3.0 wt% SBP, 1.0 mM [Ru(bpy)3]2+, and 1.0 mM SPS. Human hepatoblastoma (HepG2) cells encapsulated in SBP hydrogels remained viable and metabolically active after 14 d of culture. Overall, this study demonstrates the feasibility of applying SBP and a visible light-mediated photocrosslinking system to the 3D bioprinting of cell-laden constructs for tissue engineering applications.

Extrusion-Based 3D Bioprinting of Adhesive Tissue Engineering Scaffolds Using Hybrid Functionalized Hydrogel Bioinks.

Adhesive tissue engineering scaffolds (ATESs) have emerged as an innovative alternative means, replacing sutures and bioglues, to secure the implants onto target tissues. Relying on their intrinsic tissue adhesion characteristics, ATES systems enable minimally invasive delivery of various scaffolds. This study investigates development of the first class of 3D bioprinted ATES constructs using functionalized hydrogel bioinks. Two ATES delivery strategies, in situ printing onto the adherend versusprinting and then transferring to the target surface, aretested using two bioprinting methods, embedded versus air printing. Dopamine-modified methacrylated hyaluronic acid (HAMA-Dopa) and gelatin methacrylate (GelMA) are used as the main bioink components, enabling fabrication of scaffolds with enhanced adhesion and crosslinking properties. Results demonstrate that dopamine modification improved adhesive properties of the HAMA-Dopa/GelMA constructs under various loading conditions, while maintaining their structural fidelity, stability, mechanical properties, and biocompatibility. While directly printing onto the adherend yields superior adhesive strength, embedded printing followed by transfer to the target tissue demonstrates greater potential for translational applications. Together, these results demonstrate the potential of bioprinted ATESs as off-the-shelf medical devices for diverse biomedical applications.

3D-Printed disposable nozzles for cost-efficient extrusion-based 3D bioprinting

3D bioprinting has significantly impacted tissue engineering with its capability to create intricate structures with complex geometries that were difficult to replicate through traditional manufacturing techniques. Extrusion-based 3D bioprinting methods tend to be limited when creating complex structures using bioinks of low viscosity. However, the capacity for creating multi-material structures that have distinct properties could be unlocked through the mixture of two solutions before extrusion. This could be used to generate architectures with varying levels of stiffness and hydrophobicity, which could be utilized for regenerative medicine applications. Moreover, it allows for combining proteins and other biological materials in a single 3D-bioprinted structure. This paper presents a standardized fabrication method of disposable nozzle connectors (DNC) for 3D bioprinting with hydrogel-based materials. This method entails 3D printing connectors with dual inlets and a single outlet to mix the material internally. The connectors are compatible with conventional Luer lock needles, offering an efficient solution for nozzle replacement. IVZK (Ac-Ile-Val-Cha-Lys-NH2) peptide-based hydrogel materials were used as a bioink with the 3D-printed DNCs. Extrusion-based 3D bioprinting was employed to print shapes of varying complexities, demonstrating potential in achieving high print resolution, shape fidelity, and biocompatibility. Post-printing of human neonatal dermal fibroblasts, cell viability, proliferation, and metabolic activity were observed, which demonstrated the effectiveness of the proposed design and process for 3D bioprinting using low-viscosity bioinks.

Biomimetic three-dimensional glioma model printed in vitro for the studies of glioma cells and neurons interactions.

1The interactions between glioma cells and neurons are important for glioma progression but are rarely mimicked and recapitulated in in vitro three-dimensional (3D) models, which may affect the success rate of relevant drug research and development. In this study, an in vitro bioprinted 3D glioma model consisting of an outer hemispherical shell with neurons and an inner hemisphere with glioma cells is proposed to simulate the natural glioma. This model was produced by extrusion-based 3D bioprinting technology. The cells survival rate, morphology, and intercellular Ca2+ concentration studies were carried out up to 5 days of culturing. It was found that neurons could promote the proliferation of glioma cells around them, associate the morphological changes of glioma cells to be neuron-like, and increase the expression of intracellular Ca2+ of glioma cells. Conversely, the presence of glioma cells could maintain the neuronal survival rate and promote the neurite outgrowth. The results indicated that glioma cells and neurons facilitated each other implying a symbiotic pattern established between two types of cells during the early stage of glioma development, which were seldom found in the present artificial glioma models. The proposed bioprinted glioma model can mimic the natural microenvironment of glioma tissue, provide an in-depth understanding of cell-cell interactions, and enable pathological and pharmacological studies of glioma.

Versatile and non-cytotoxic GelMA-xanthan gum biomaterial ink for extrusion-based 3D bioprinting

Extrusion-based 3D bioprinting allows the 3D printing of bioinks, composed of cells and biomaterials, to mimic the complex 3D hierarchical structure of native tissues. Successful 3D bioprinting requires bioinks with specific properties, such as biocompatibility, printability, and biodegradability according to the desired application. In the present work, we aimed at developing a new versatile blend of gelatin methacryloyl-xanthan gum (GelMA-XG) suitable for extrusion-based 3D bioprinting with a straightforward process. To this end, we first optimized the process of gelatin methacryloyl (GelMA) synthesis by investigating the impact of different buffer solutions on the degree of functionalization, swelling degree, and degradation rate. The addition of xanthan gum (XG) enabled further tuning of biodegradability and an improvement of GelMA printability. Specifically, an optimal concentration of XG was found through rheological characterization and printability tests. The optimized blend showed enhanced printability and improved shape fidelity as well as its degradation products turned out to be non-cytotoxic, thus laying the foundation for cell-based applications. In conclusion, our newly developed biomaterial ink is a promising candidate for extrusion-based 3D bioprinting.