Roles of support materials in 3D bioprinting - Present and future

Advances in Additive Manufacturing of Polymer-Fused Deposition Modeling on Textiles: From 3D Printing to Innovative 4D Printing-A Review

Technological advances and the development of new and advanced materials allow the transition from three-dimensional (3D) printing to the innovation of four-dimensional (4D) printing. 3D printing is the process of precisely creating objects with complex shapes by depositing superimposed layers of material. Current 3D printing technology allows two or more filaments of different polymeric materials to be placed, which, together with the development of intelligent materials that change shape over time or under the action of an external stimulus, allow us to innovate and move toward an emerging area of research, innovative 4D printing technology. 4D printing makes it possible to manufacture actuators and sensors for various technological applications. Its most significant development is currently in the manufacture of intelligent textiles. The potential of 4D printing lies in modular manufacturing, where fabric-printed material interaction enables the creation of bio-inspired and biomimetic devices. The central part of this review summarizes the effect of the primary external stimuli on 4D textile materials, followed by the leading applications. Shape memory polymers attract current and potential opportunities in the textile industry to develop smart clothing for protection against extreme environments, auxiliary prostheses, smart splints or orthoses to assist the muscles in their medical recovery, and comfort devices. In the future, intelligent textiles will perform much more demanding roles, thus envisioning the application fields of 4D printing in the next decade.

Embedded 3D bioprinting - An emerging strategy to fabricate biomimetic & large vascularized tissue constructs

Three-dimensional bioprinting is an advanced tissue fabrication technique that allows printing complex structures with precise positioning of multiple cell types layer-by-layer. Compared to other bioprinting methods, extrusion bioprinting has several advantages to print large-sized tissue constructs and complex organ models due to large build volume. Extrusion bioprinting using sacrificial, support and embedded strategies have been successfully employed to facilitate printing of complex and hollow structures. Embedded bioprinting is a gel-in-gel approach developed to overcome the gravitational and overhanging limits of bioprinting to print large-sized constructs with a micron-scale resolution. In embedded bioprinting, deposition of bioinks into the microgel or granular support bath will be facilitated by the sol-gel transition of the support bath through needle movement inside the granular medium. This review outlines various embedded bioprinting strategies and the polymers used in the embedded systems with advantages, limitations, and efficacy in the fabrication of complex vascularized tissues or organ models with micron-scale resolution. Further, the essential requirements of support bath systems like viscoelasticity, stability, transparency and easy extraction to print human scale organs are discussed. Additionally, the organs or complex geometries like vascular constructs, heart, bone, octopus and jellyfish models printed using support bath assisted printing methods with their anatomical features are elaborated. Finally, the challenges in clinical translation and the future scope of these embedded bioprinting models to replace the native organs are envisaged.

3D-bioprintable endothelial cell-laden sacrificial ink for fabrication of microvessel networks

Although various research efforts have been made to produce a vascular-like network structure as scaffolds for tissue engineering, there are still several limitations. Meanwhile, no articles have been published on the direct embedding of cells within a glucose sensitive sacrificial hydrogel followed by three-dimensional (3D) bioprinting to fabricate vascular structures. In this study, the hydrogel composed of reversibly crosslinked poly(ethylene glycol) diacrylate and dithiothreitol with borax and branched polyethylenimine was used as the sacrificial hydrogel to fabricate vascular-like network structure. The component proportion ratio of the sacrificial hydrogel was optimized to achieve proper self-healing, injectable, glucose-sensitive, and 3D printing properties through the balance of boronate ester bond, hydrogen bond, and steric hinderance effect. The endothelial cells (ECs) can be directly embedded into sacrificial hydrogel and then bioprinted through a 110μm nozzle into the neural stem cell (NSC)-laden non-sacrificial hydrogel, forming the customized EC-laden vascularized microchannel (one-step). The EC-laden sacrificial hydrogel was dissolved immediately in the medium while cells kept growing. The ECs proliferated well within the vascularized microchannel structure and were able to migrate to the non-sacrificial hydrogel in one day. ECs and NSCs interacted around the vascularized microchannel to form capillary-like structure and vascular-like structure expressing CD31 in 14 d. The sacrificial hydrogel conveniently prepared from commercially available chemicals through simple mixing can be used in 3D bioprinting to create customized and complex but easily removable vascularized structure for tissue engineering applications.

Impact of internal structural design on quality and nutritional properties of 3D printed food products during post-printing: a critical review

3D food printing (3DFP) provides an excellent opportunity to deposit layers of multiple food materials to create unique complex structures of products with more engaging visuals, specific textures, and customized nutritional properties. Many printed products require post-printing processing which can result in sensory variance, texture changes, and even nutritional modification. Hence it is necessary to implement the design of the complex internal structure to ensure the desired quality of the printed products following post-printing. 3-D printing of various types of food products, for example, chocolate, cheese, meat, vegetables, fruits, fish, eggs, cereal-based products, and so on, has been examined with regard to post-printing requirements. This review aims to summarize the current work on the latest developments in 3DFP technology concerning the internal structure design of 3D printed products and its effect on quality during post-printing. The quality parameters include: textural, physical, morphological, and dimensional characteristics as well as nutritional properties. Furthermore, post-printing modifications such as 4D are also analyzed.

A Guide to Polysaccharide-Based Hydrogel Bioinks for 3D Bioprinting Applications

Three-dimensional (3D) bioprinting is an innovative technology in the biomedical field, allowing the fabrication of living constructs through an approach of layer-by-layer deposition of cell-laden inks, the so-called bioinks. An ideal bioink should possess proper mechanical, rheological, chemical, and biological characteristics to ensure high cell viability and the production of tissue constructs with dimensional stability and shape fidelity. Among the several types of bioinks, hydrogels are extremely appealing as they have many similarities with the extracellular matrix, providing a highly hydrated environment for cell proliferation and tunability in terms of mechanical and rheological properties. Hydrogels derived from natural polymers, and polysaccharides, in particular, are an excellent platform to mimic the extracellular matrix, given their low cytotoxicity, high hydrophilicity, and diversity of structures. In fact, polysaccharide-based hydrogels are trendy materials for 3D bioprinting since they are abundant and combine adequate physicochemical and biomimetic features for the development of novel bioinks. Thus, this review portrays the most relevant advances in polysaccharide-based hydrogel bioinks for 3D bioprinting, focusing on the last five years, with emphasis on their properties, advantages, and limitations, considering polysaccharide families classified according to their source, namely from seaweed, higher plants, microbial, and animal (particularly crustaceans) origin.

3D bioprinting of a gelatin-alginate hydrogel for tissue-engineered hair follicle regeneration

Hair follicle (HF) regeneration remains challenging, principally due to the absence of a platform that can successfully generate the microenvironmental cues of hair neogenesis. Here, we demonstrate a 3D bioprinting technique based on a gelatin/alginate hydrogel (GAH) to construct a multilayer composite scaffold simulating the HF microenvironment in vivo. Fibroblasts (FBs), human umbilical vein endothelial cells (HUVECs), dermal papilla cells (DPCs), and epidermal cells (EPCs) were encapsulated in GAH (prepared from a mixture of gelatin and alginate) and respectively 3D-bioprinted into the different layers of a composite scaffold. The bioprinted scaffold with epidermis- and dermis-like structure was subsequently transplanted into full-thickness wounds in nude mice. The multilayer scaffold demonstrated suitable cytocompatibility and increased the proliferation ability of DPCs (1.2-fold; P < 0.05). It also facilitated the formation of self-aggregating DPC spheroids and restored DPC genes associated with hair induction (ALP, β-catenin, and α-SMA). The dermal and epidermal cells self-assembled successfully into immature HFs in vitro. HFs were regenerated in the appropriate orientation in vivo, which can mainly be attributed to the hierarchical grid structure of the scaffold and the dot bioprinting of DPCs. Our 3D printed scaffolds provide a suitable microenvironment for DPCs to regenerate entire HFs and could make a significant contribution in the medical management of hair loss. This method may also have broader applications in skin tissue (and appendage) engineering. STATEMENT OF SIGNIFICANCE: Hair loss remains a challenging clinical problem that influences quality of life. Three-dimensional (3D) bioprinting has become a useful tool for the fabrication of tissue constructs for transplantation and other biomedical applications. In this study, we used a 3D bioprinting technique based on a gelatin/alginate hydrogel to construct a multi-layer composite scaffold with cuticular and corium layers to simulate the microenvironment of dermal papilla cells (DPCs) in the human body. This new approach permits the controllable formation of self-aggregating spheroids of DPCs in a physiologically relevant extracellular matrix and the initiation of epidermal-mesenchymal interactions, which results in HF formation in vivo. The ability to regenerate entire HFs should have a significant impact on the medical management of hair loss.

Click Chemistry Hydrogels for Extrusion Bioprinting: Progress, Challenges, and Opportunities

The emergence of 3D bioprinting has allowed a variety of hydrogel-based "bioinks" to be printed in the presence of cells to create precisely defined cell-loaded 3D scaffolds in a single step for advancing tissue engineering and/or regenerative medicine. While existing bioinks based primarily on ionic cross-linking, photo-cross-linking, or thermogelation have significantly advanced the field, they offer technical limitations in terms of the mechanics, degradation rates, and the cell viabilities achievable with the printed scaffolds, particularly in terms of aiming to match the wide range of mechanics and cellular microenvironments. Click chemistry offers an appealing solution to this challenge given that proper selection of the chemistry can enable precise tuning of both the gelation rate and the degradation rate, both key to successful tissue regeneration; simultaneously, the often bio-orthogonal nature of click chemistry is beneficial to maintain high cell viabilities within the scaffolds. However, to date, relatively few examples of 3D-printed click chemistry hydrogels have been reported, mostly due to the technical challenges of controlling mixing during the printing process to generate high-fidelity prints without clogging the printer. This review aims to showcase existing cross-linking modalities, characterize the advantages and disadvantages of different click chemistries reported, highlight current examples of click chemistry hydrogel bioinks, and discuss the design of mixing strategies to enable effective 3D extrusion bioprinting of click hydrogels.

A three-dimensional bioprinting technique, based on a gelatin/alginate hydrogel, for the tissue engineering of hair follicle reconstruction

Hair loss remains a challenging clinical problem that influences the quality of life. Three-dimensional (3D) bioprinting has become a valuable tool for fabricating tissue constructs for transplantation and other biomedical applications. Although some simple organs, such as skin and cartilage, have been successfully simulated, it remains challenging to make hair follicles (HFs), which are highly complex organs. The tissue engineering of human HFs has been a long-standing challenge, and progress with this has lagged behind that with other lab-grown tissues. This is principally due to a lack of availability of a platform that can successfully recapitulate the microenvironmental cues required to maintain the requisite cellular interactions for hair neogenesis. In this study, we used a 3D bioprinting technique based on a gelatin/alginate hydrogel to construct a multilayer composite scaffold with cuticular and corium layers to simulate the microenvironment of dermal papilla cells (DPCs) in the human body. This new approach permits the controllable formation of self-aggregating spheroids of DPCs in a physiologically relevant extracellular matrix and the initiation of epidermal-mesenchymal interactions, which results in HF formation in vivo. In conclusion, our 3D-bioprinted multilayer composite scaffold prepared using a gelatin/alginate hydrogel provides a suitable 3D microenvironment for DPCs to induce HF formation. The ability to regenerate entire HFs should have a significant impact on the medical management of hair loss. This method may also have critical applications for skin tissue engineering, with its appendages, for other purposes.

Establishing a point-of-care additive manufacturing workflow for clinical use

Additive manufacturing, or 3-Dimensional (3-D) Printing, is built with technology that utilizes layering techniques to build 3-D structures. Today, its use in medicine includes tissue and organ engineering, creation of prosthetics, the manufacturing of anatomical models for preoperative planning, education with high-fidelity simulations, and the production of surgical guides. Traditionally, these 3-D prints have been manufactured by commercial vendors. However, there are various limitations in the adaptability of these vendors to program-specific needs. Therefore, the implementation of a point-of-care in-house 3-D modeling and printing workflow that allows for customization of 3-D model production is desired. In this manuscript, we detail the process of additive manufacturing within the scope of medicine, focusing on the individual components to create a centralized in-house point-of-care manufacturing workflow. Finally, we highlight a myriad of clinical examples to demonstrate the impact that additive manufacturing brings to the field of medicine.

Controllable four axis extrusion-based additive manufacturing system for the fabrication of tubular scaffolds with tailorable mechanical properties

Many tubular tissues such as blood vessels and trachea can suffer long-segmental defects through trauma and disease. With current limitations in the use of autologous grafts, the need for a synthetic substitute is of continuous interest as possible alternatives. Fabrication of these tubular organs is commonly done with techniques such as electrospinning and melt electrowriting using a rotational collector. Current additive manufacturing (AM) systems do not commonly implement the use of a rotational axis, which limits their application for the fabrication of tubular scaffolds. In this study, a four axis extrusion-based AM system similar to fused deposition modeling (FDM) has been developed to create tubular hollow scaffolds. A rectangular and a diamond pore design were further investigated for mechanical characterization, as a standard and a biomimicry pore geometry respectively. We demonstrated that in the radial compression mode the diamond pore design had a higher Young's modulus (19,8 ± 0,7 MPa compared to 2,8 ± 0,5 MPa), while in the longitudinal tensile mode the rectangular pore design had a higher Young's modulus (5,8 ± 0,2 MPa compared to 0,1 ± 0,01 MPa). Three-point bending analyses revealed that the diamond pore design is more resistant to luminal collapse compared to the rectangular design. This data showed that by changing the scaffold pore design, a wide range of mechanical properties could be obtained. Furthermore, a full control over scaffold design and geometry can be achieved with the developed 4-axis extrusion-based system, which has not been reported with other techniques. This flexibility allow the manufacturing of scaffolds for diverse tubular tissue regeneration applications by designing suitable deposition patterns to match their mechanical pre-requisites.

Biofabrication of Hepatic Constructs by 3D Bioprinting of a Cell-Laden Thermogel: An Effective Tool to Assess Drug-Induced Hepatotoxic Response

A thermoresponsive Pluronic/alginate semisynthetic hydrogel is used to bioprint 3D hepatic constructs, with the aim to investigate liver-specific metabolic activity of the 3D constructs compared to traditional 2D adherent cultures. The bioprinting method relies on a bioinert hydrogel and is characterized by high-shape fidelity, mild depositing conditions and easily controllable gelation mechanism. Furthermore, the dissolution of the sacrificial Pluronic templating agent significantly ameliorates the diffusive properties of the printed hydrogel. The present findings demonstrate high viability and liver-specific metabolic activity, as assessed by synthesis of urea, albumin, and expression levels of the detoxifying CYP1A2 enzyme of cells embedded in the 3D hydrogel system. A markedly increased sensitivity to a well-known hepatotoxic drug (acetaminophen) is observed for cells in 3D constructs compared to 2D cultures. Therefore, the 3D model developed herein may represent an in vitro alternative to animal models for investigating drug-induced hepatotoxicity.

An insight into cell-laden 3D-printed constructs for bone tissue engineering

In this review, we have spotlighted various combinations of bioinks to optimize the biofabrication of 3D bone constructs.

Extrusion-Based Bioprinting: Current Standards and Relevancy for Human-Sized Tissue Fabrication

The field of bioengineering has long pursued the goal of fabricating large-scale tissue constructs for use both in vitro and in vivo. Recent technological advances have indicated that bioprinting will be a key technique in manufacturing these specimens. This chapter aims to provide an overview of what has been achieved to date through the use of microextrusion bioprinters and what major challenges still impede progress. Microextrusion printer configurations will be addressed along with critical design characteristics including nozzle specifications and bioink modifications. Significant challenges within the field with regard to achieving long-term cell viability and vascularization, and current research that shows promise in mitigating these challenges in the near future are discussed. While microextrusion is a broad field with many applications, this chapter aims to provide an overview of the field with a focus on its applications toward human-sized tissue constructs.

3D Printing in Personalized Drug Delivery

Background:

Personalized medicines are becoming more popular as they enable the use of patient’s genomics and hence help in better drug design with fewer side effects. In fact, several doses can be combined into one dosage form which suits the patient’s demography. 3 Dimensional (3D) printing technology for personalized medicine is a modern day treatment method based on genomics of patient.

Methods:

3D printing technology uses digitally controlled devices for formulating API and excipients in a layer by layer pattern for developing a suitable personalized drug delivery system as per the need of patient. It includes various techniques like inkjet printing, fused deposition modelling which can further be classified into continuous inkjet system and drop on demand. In order to formulate such dosage forms, scientists have used various polymers to enhance their acceptance as well as therapeutic efficacy. Polymers like polyvinyl alcohol, poly (lactic acid) (PLA), poly (caprolactone) (PCL) etc can be used during manufacturing.

Results:

Varying number of dosage forms can be produced using 3D printing technology including immediate release tablets, pulsatile release tablets, and transdermal dosage forms etc. The 3D printing technology can be explored successfully to develop personalized medicines which could play a vital role in the treatment of lifethreatening diseases. Particularly, for patients taking multiple medicines, 3D printing method could be explored to design a single dosage in which various drugs can be incorporated. Further 3D printing based personalized drug delivery system could also be investigated in chemotherapy of cancer patients with the added advantage of the reduction in adverse effects.

Conclusion:

In this article, we have reviewed 3D printing technology and its uses in personalized medicine. Further, we also discussed the different techniques and materials used in drug delivery based on 3D printing along with various applications of the technology.

Novel Biomaterials Used in Medical 3D Printing Techniques

The success of an implant depends on the type of biomaterial used for its fabrication. An ideal implant material should be biocompatible, inert, mechanically durable, and easily moldable. The ability to build patient specific implants incorporated with bioactive drugs, cells, and proteins has made 3D printing technology revolutionary in medical and pharmaceutical fields. A vast variety of biomaterials are currently being used in medical 3D printing, including metals, ceramics, polymers, and composites. With continuous research and progress in biomaterials used in 3D printing, there has been a rapid growth in applications of 3D printing in manufacturing customized implants, prostheses, drug delivery devices, and 3D scaffolds for tissue engineering and regenerative medicine. The current review focuses on the novel biomaterials used in variety of 3D printing technologies for clinical applications. Most common types of medical 3D printing technologies, including fused deposition modeling, extrusion based bioprinting, inkjet, and polyjet printing techniques, their clinical applications, different types of biomaterials currently used by researchers, and key limitations are discussed in detail.

A highly printable and biocompatible hydrogel composite for direct printing of soft and perfusable vasculature-like structures

Vascularization is one major obstacle in bioprinting and tissue engineering. In order to create thick tissues or organs that can function like original body parts, the presence of a perfusable vascular system is essential. However, it is challenging to bioprint a hydrogel-based three-dimensional vasculature-like structure in a single step. In this paper, we report a new hydrogel-based composite that offers impressive printability, shape integrity, and biocompatibility for 3D bioprinting of a perfusable complex vasculature-like structure. The hydrogel composite can be used on a non-liquid platform and is printable at human body temperature. Moreover, the hydrogel composite supports both cell proliferation and cell differentiation. Our results represent a potentially new vascularization strategy for 3D bioprinting and tissue engineering.

The bio in the ink: cartilage regeneration with bioprintable hydrogels and articular cartilage-derived progenitor cells

Cell-laden hydrogels are the primary building blocks for bioprinting, and, also termed bioinks, are the foundations for creating structures that can potentially recapitulate the architecture of articular cartilage. To be functional, hydrogel constructs need to unlock the regenerative capacity of encapsulated cells. The recent identification of multipotent articular cartilage-resident chondroprogenitor cells (ACPCs), which share important traits with adult stem cells, represents a new opportunity for cartilage regeneration. However, little is known about the suitability of ACPCs for tissue engineering, especially in combination with biomaterials. This study aimed to investigate the potential of ACPCs in hydrogels for cartilage regeneration and biofabrication, and to evaluate their ability for zone-specific matrix production. Gelatin methacryloyl (gelMA)-based hydrogels were used to culture ACPCs, bone marrow mesenchymal stromal cells (MSCs) and chondrocytes, and as bioinks for printing. Our data shows ACPCs outperformed chondrocytes in terms of neo-cartilage production and unlike MSCs, ACPCs had the lowest gene expression levels of hypertrophy marker collagen type X, and the highest expression of PRG4, a key factor in joint lubrication. Co-cultures of the cell types in multi-compartment hydrogels allowed generating constructs with a layered distribution of collagens and glycosaminoglycans. By combining ACPC- and MSC-laden bioinks, a bioprinted model of articular cartilage was generated, consisting of defined superficial and deep regions, each with distinct cellular and extracellular matrix composition. Taken together, these results provide important information for the use of ACPC-laden hydrogels in regenerative medicine, and pave the way to the biofabrication of 3D constructs with multiple cell types for cartilage regeneration or in vitro tissue models.

STATEMENT OF SIGNIFICANCE

Despite its limited ability to repair, articular cartilage harbors an endogenous population of progenitor cells (ACPCs), that to date, received limited attention in biomaterials and tissue engineering applications. Harnessing the potential of these cells in 3D hydrogels can open new avenues for biomaterial-based regenerative therapies, especially with advanced biofabrication technologies (e.g. bioprinting). This study highlights the potential of ACPCs to generate neo-cartilage in a gelatin-based hydrogel and bioink. The ACPC-laden hydrogel is a suitable substrate for chondrogenesis and data shows it has a bias in directing cells towards a superficial zone phenotype. For the first time, ACPC-hydrogels are evaluated both as alternative for and in combination with chondrocytes and MSCs, using co-cultures and bioprinting for cartilage regeneration in vitro. This study provides important cues on ACPCs, indicating they represent a promising cell source for the next generation of cartilage constructs with increased biomimicry.

Cell powered biobots and more perspectives for IJB

At the end of 2016, International Journal of Bioprinting (IJB) is able to estimate its first mock impact factor. Based on one issue published in 2015, the 2016 mock impact factor for IJB is calculated to be 6, excluding self-citations! This result is surprising, impressive and encouraging. However, this is just a beginning and more and more quality articles and reviews are needed in order to maintain it.