Bioprinted Injectable Hierarchically Porous Gelatin Methacryloyl Hydrogel Constructs with Shape-Memory Properties

Hyperelastic, shape-memorable, and ultra-cell-adhesive degradable polycaprolactone-polyurethane copolymer for tissue regeneration

Novel polycaprolactone-based polyurethane (PCL-PU) copolymers with hyperelasticity, shape-memory, and ultra-cell-adhesion properties are reported as clinically applicable tissue-regenerative biomaterials. New isosorbide derivatives (propoxylated or ethoxylated ones) were developed to improve mechanical properties by enhanced reactivity in copolymer synthesis compared to the original isosorbide. Optimized PCL-PU with propoxylated isosorbide exhibited notable mechanical performance (50 MPa tensile strength and 1150% elongation with hyperelasticity under cyclic load). The shape-memory effect was also revealed in different forms (film, thread, and 3D scaffold) with 40%-80% recovery in tension or compression mode after plastic deformation. The ultra-cell-adhesive property was proven in various cell types which were reasoned to involve the heat shock protein-mediated integrin (α5 and αV) activation, as analyzed by RNA sequencing and inhibition tests. After the tissue regenerative potential (muscle and bone) was confirmed by the myogenic and osteogenic responses in vitro, biodegradability, compatible in vivo tissue response, and healing capacity were investigated with in vivo shape-memorable behavior. The currently exploited PCL-PU, with its multifunctional (hyperelastic, shape-memorable, ultra-cell-adhesive, and degradable) nature and biocompatibility, is considered a potential tissue-regenerative biomaterial, especially for minimally invasive surgery that requires small incisions to approach large defects with excellent regeneration capacity.

Photopolymerized 3D Printing Scaffolds with Pt(IV) Prodrug Initiator for Postsurgical Tumor Treatment

Biomedical scaffolds have shown great success in postsurgical tumor treatment; their current efforts are focusing on eradicating residual tumor cells and circulating tumor cells and simultaneously repairing postoperative tissue defects. Herein, we report a novel photopolymerized 3D scaffold with Pt(IV) prodrug initiator to achieve the desired features for tumor comprehensive therapy. The Pt-GelMA scaffold was fabricated from the microfluidic 3D printing of methacrylate gelatin (GelMA) bioinks through a Pt(IV)-induced photocrosslinked process without any other additional photoinitiator and chemotherapeutic drug. Thus, the resultant scaffold displayed efficient cell killing ability against breast cancer cells in vitro and significantly inhibited the local tumor growth and distant metastases on an orthotopic postoperative breast cancer model in vivo. Besides, benefiting from their ordered porous structures and favorable biocompatibility, the scaffolds supported the cell attachment, spreading, and proliferation of normal cells in vitro; could facilitate the nutrient transportation; and induced new tissue ingrowth for repairing tissue defects caused by surgery. These properties indicate that such 3D printing scaffold is a promising candidate for efficient postoperative tumor treatment in the practical application.

Human Endometrium-Derived Adventitial Cell Spheroid-Loaded Antimicrobial Microneedles for Uterine Regeneration

Asherman's syndrome (AS) occurs as a consequence of severe damage to the endometrial basalis, usually leading to menstrual abnormalities, infertility, and recurrent miscarriage in women. Currently, human endometrium-derived adventitial cells (En-ADVs) are considered ideal seed cells with high pluripotency for regenerative medicine. However, critical issues such as noninvasive repair of tissues, targeting of native stem cells, and continuous action in the injured sites are not well resolved. Herein, En-ADV spheroid-loaded hierarchical microneedles (MN/En-ADV) for in situ intrauterine repair are developed. The flexible microneedles are fabricated with gelatin methacryloyl and lactoferrin, imparting the characteristics of rapid degradation and antimicrobial activity. Benefiting from an array of microwells on microneedles, En-ADVs can rapidly form 3D cell spheroids, which display higher potential for cell proliferation, differentiation, and migration than dissociated cells. With the application of MN/En-ADV, the repaired uteri show well-defined myometrial regeneration, angiogenesis, and an increase of endometrial receptivity in a rat AS model. Notably, embryos are able to implant in the reconstructed sites and remain viable, indicating that this system promotes the restoration of both normal morphology and reproductive function in the injured uterus. It is anticipated that multifunctional MN/En-ADV can be an ideal candidate for versatile in situ tissue regeneration.

Photo-Crosslinkable Hydrogels for 3D Bioprinting in the Repair of Osteochondral Defects: A Review of Present Applications and Future Perspectives

An osteochondral defect is a common and frequent disease in orthopedics and treatment effects are not good, which can be harmful to patients. Hydrogels have been applied in the repair of cartilage defects. Many studies have reported that hydrogels can effectively repair osteochondral defects through loaded cells or non-loaded cells. As a new type of hydrogel, photo-crosslinked hydrogel has been widely applied in more and more fields. Meanwhile, 3D bioprinting serves as an attractive platform to fabricate customized tissue-engineered substitutes from biomaterials and cells for the repair or replacement of injured tissues and organs. Although photo-crosslinkable hydrogel-based 3D bioprinting has some advantages for repairing bone cartilage defects, it also has some disadvantages. Our aim of this paper is to review the current status and prospect of photo-crosslinkable hydrogel-based 3D bioprinting for repairing osteochondral defects.

Hydrogels for Treatment of Different Degrees of Osteoarthritis

Osteoarthritis (OA) is a common disease that severely restricts human activities and degrades the quality of life. Every year, millions of people worldwide are diagnosed with osteoarthritis, placing a heavy burden on society. Hydrogels, a polymeric material with good biocompatibility and biodegradability, are a novel approach for the treatment of osteoarthritis. In recent years, this approach has been widely studied with the development of materials science and tissue engineering technology. We reviewed the research progress of hydrogels in the treatment of osteoarthritis in the past 3 years. We summarized the required hydrogel properties and current applications according to the development and treatment of osteoarthritis. Furthermore, we listed the challenges of hydrogels for different types of osteoarthritis and presented prospects for future development.

Micropore-Forming Gelatin Methacryloyl (GelMA) Bioink Toolbox 2.0: Designable Tunability and Adaptability for 3D Bioprinting Applications

It is well-known that tissue engineering scaffolds that feature highly interconnected and size-adjustable micropores are oftentimes desired to promote cellular viability, motility, and functions. Unfortunately, the ability of precise control over the microporous structures within bioinks in a cytocompatible manner for applications in 3D bioprinting is generally lacking, until a method of micropore-forming bioink based on gelatin methacryloyl (GelMA) was reported recently. This bioink took advantage of the unique aqueous two-phase emulsion (ATPE) system, where poly(ethylene oxide) (PEO) droplets are utilized as the porogen. Considering the limitations associated with this very initial demonstration, this article has furthered the understanding of the micropore-forming GelMA bioinks by conducting a systematic investigation into the additional GelMA types (porcine and fish, different methacryloyl-modification degrees) and porogen types (PEO, poly(vinyl alcohol), and dextran), as well as the effects of the porogen concentrations and molecular weights on the properties of the GelMA-based ATPE bioink system. This article exemplifies not only the significantly wider range of micropore sizes achievable and better emulsion stability, but also the improved suitability for both extrusion and digital light processing bioprinting with favorable cellular responses.

Engineered assistive materials for 3D bioprinting: support baths and sacrificial inks

Three-dimensional (3D) bioprinting is a promising technique for spatially patterning cells and materials into constructs that mimic native tissues and organs. However, a trade-off exists between printability and biological function, where weak materials are typically more suited for 3D cell culture but exhibit poor shape fidelity when printed in air. Recently, a new class of assistive materials has emerged to overcome this limitation and enable fabrication of more complex, biologically relevant geometries, even when using soft materials as bioinks. These materials include support baths, which bioinks are printed into, and sacrificial inks, which are printed themselves and then later removed. Support baths are commonly yield-stress materials that provide physical confinement during the printing process to improve resolution and shape fidelity. Sacrificial inks have primarily been used to create void spaces and pattern perfusable networks, but they can also be combined directly with the bioink to change its mechanical properties for improved printability or increased porosity. Here, we outline the advantages of using such assistive materials in 3D bioprinting, define their material property requirements, and offer case study examples of how these materials are used in practice. Finally, we discuss the remaining challenges and future opportunities in the development of assistive materials that will propel the bioprinting field forward toward creating full-scale, biomimetic tissues and organs.

Coordination with zirconium: A facile approach to improve the mechanical properties and thermostability of gelatin hydrogel

The poor mechanical property and thermostability restricted applications of gelatin hydrogel. Herein, a facile and inexpensive approach of immerging cooling induced gelatin hydrogels into Zr(SO₄)₂ dilute solution was applied to overcome these shortages. After this treatment, the micropores in hydrogel decreased to tens of microns while the water content slightly decreased. XPS results revealed that the coordination bonds formed between amino or carboxyl groups of gelatins and Zr⁴⁺. After immerging in 0.06 M Zr⁴⁺ solution, mechanical tests showed that the elastic modulus, compressive modulus and compressive strength of hydrogel were about 400, 1192 and 476 kPa, respectively, which were approximate 100, 11 and 5 times larger than those of pure gelatin. The DSC data indicated that the thermoreversible temperature of triple helix structure in gelatin was improved from about 30 °C to 55 °C. More importantly, the rheological temperature sweep test revealed that hydrogels with 0.06 M Zr⁴⁺ treatment can maintain the hydrogel state without melting even at 80 °C. CCK-8 tests and Calcein-AM/PI double-stain experiments demonstrated Zr⁴⁺ coordination was non-cytotoxic. These promising data indicated this nontoxic method was efficient and had potential to fabricate gelatin related materials for further application.

Tunable Microgel-Templated Porogel (MTP) Bioink for 3D Bioprinting Applications

Micropores are essential for tissue engineering to ensure adequate mass transportation for embedded cells. Despite the considerable progress made by advanced 3D bioprinting technologies, it remains challenging to engineer micropores of 100 µm or smaller in cell-laden constructs. Here, a microgel-templated porogel (MTP) bioink platform is reported to introduce controlled microporosity in 3D bioprinted hydrogels in the presence of living cells. Templated gelatin microgels are fabricated with varied sizes (≈10, ≈45, and ≈100 µm) and mixed with photo-crosslinkable formulations to make composite MTP bioinks. The addition of microgels significantly enhances the shear-thinning and self-healing viscoelastic properties and thus the printability of bioinks with cell densities up to 1 × 108 mL-1 in matrix. Consistent printability is achieved for a series of MTP bioinks based on different component ratios and matrix materials. After photo-crosslinking the matrix phase, the templated microgels dissociated and diffused under physiological conditions, resulting in corresponding micropores in situ. When embedding osteoblast-like cells in the matrix phase, the MTP bioinks support higher metabolic activity and more uniform mineral formation than bulk gel controls. The approach provides a facile strategy to engineer precise micropores in 3D printed structures to compensate for the limited resolution of current bioprinting approaches.

(Bio)manufactured Solutions for Treatment of Bone Defects with Emphasis on US-FDA Regulatory Science Perspective

Bone defects, with second highest demand for surgeries around the globe, may lead to serious health issues and negatively influence patient lives. The advances in biomedical engineering and sciences have led to the development of several creative solutions for bone defect treatment. This review provides a brief summary of bone graft materials, an organized overview of top-down and bottom-up (bio)manufacturing approaches, plus a critical comparison between advantages and limitations of each method. We specifically discuss additive manufacturing techniques and their operation mechanisms in detail. Next, we review the hybrid methods and promising future directions for bone grafting, while giving a comprehensive US-FDA regulatory science perspective, biocompatibility concepts and assessments, and clinical considerations to translate a technology from a research laboratory to the market. The topics covered in this review could potentially fuel future research efforts in bone tissue engineering, and perhaps could also provide novel insights for other tissue engineering applications.

A multifunctional micropore-forming bioink with enhanced anti-bacterial and anti-inflammatory properties

Three-dimensional (3D) bioprinting has emerged as an enabling tool for various biomedical applications, such as tissue regeneration and tissue model engineering. To this end, the development of bioinks with multiple functions plays a crucial role in the applications of 3D bioprinting technologies. In this study, we propose a new bioink based on two immiscible aqueous phases of gelatin methacryloyl (GelMA) and dextran, further endowed with anti-bacterial and anti-inflammatory properties. This micropore-forming GelMA-dextran (PGelDex) bioink exhibited excellent printability with vat-polymerization, extrusion, and handheld bioprinting methods. The porous structure was confirmed after bioprinting, which promoted the spreading of the encapsulated cells, exhibiting the exceptional cytocompatibility of this bioink formulation. To extend the applications of such a micropore-forming bioink, interleukin-4 (IL-4)-loaded silver-coated gold nanorods (AgGNRs) and human mesenchymal stem cells (MSCs) were simultaneously incorporated, to display synergistic anti-infection behavior and immunomodulatory function. The results revealed the anti-bacterial properties of the AgGNR-loaded PGelDex bioink for both Gram-negative and Gram-positive bacteria. The data also indicated that the presence of IL-4 and MSCs facilitated macrophage M2-phenotype differentiation, suggesting the potential anti-inflammatory feature of the bioink. Overall, this unique anti-bacterial and immunomodulatory micropore-forming bioink offers an effective strategy for the inhibition of bacterial-induced infections as well as the ability of immune-regulation, which is a promising candidate for broadened tissue bioprinting applications.

Bubble-based microrobots enable digital assembly of heterogeneous microtissue modules

The specific spatial distribution of tissue generates a heterogeneous micromechanical environment that provides ideal conditions for diverse functions such as regeneration and angiogenesis. However, to manufacture microscale multicellular heterogeneous tissue modules in vitro and then assemble them into specific functional units is still a challenging task. In this study, a novel method for the digital assembly of heterogeneous microtissue modules is proposed. This technique utilizes the flexibility of digital micromirror device-based optical projection lithography and the manipulability of bubble-based microrobots in a liquid environment. The results indicate that multicellular microstructures can be fabricated by increasing the inlets of the microfluidic chip. Upon altering the exposure time, the Young's modulus of the entire module and different regions of each module can be fine-tuned to mimic normal tissue. The surface morphology, mechanical properties, and internal structure of the constructed bionic peritoneum were similar to those of the real peritoneum. Overall, this work demonstrates the potential of this system to produce and control the posture of modules and simulate peritoneal metastasis using reconfigurable manipulation.

Vertical Extrusion Cryo(bio)printing for Anisotropic Tissue Manufacturing

Due to the poor mechanical properties of many hydrogel bioinks, conventional 3D extrusion bioprinting is usually conducted based on the X-Y plane, where the deposited layers are stacked in the Z-direction with or without the support of prior layers. Herein, a technique is reported, taking advantage of a cryoprotective bioink to enable direct extrusion bioprinting in the vertical direction in the presence of cells, using a freezing plate with precise temperature control. Of interest, vertical 3D cryo-bioprinting concurrently allows the user to create freestanding filamentous constructs containing interconnected, anisotropic microchannels featuring gradient sizes aligned in the vertical direction, also associated with enhanced mechanical performances. Skeletal myoblasts within the 3D-cryo-bioprinted hydrogel constructs show enhanced cell viability, spreading, and alignment, compared to the same cells in the standard hydrogel constructs. This method is further extended to a multimaterial format, finding potential applications in interface tissue engineering, such as creation of the muscle-tendon unit and the muscle-microvascular unit. The unique vertical 3D cryo-bioprinting technique presented here suggests improvements in robustness and versatility to engineer certain tissue types especially those anisotropic in nature, and may extend broad utilities in tissue engineering, regenerative medicine, drug discovery, and personalized therapeutics.

Advances in hydrogel-based vascularized tissues for tissue repair and drug screening

The construction of biomimetic vasculatures within the artificial tissue models or organs is highly required for conveying nutrients, oxygen, and waste products, for improving the survival of engineered tissues in vitro. In recent times, the remarkable progress in utilizing hydrogels and understanding vascular biology have enabled the creation of three-dimensional (3D) tissues and organs composed of highly complex vascular systems. In this review, we give an emphasis on the utilization of hydrogels and their advantages in the vascularization of tissues. Initially, the significance of vascular elements and the regeneration mechanisms of vascularization, including angiogenesis and vasculogenesis, are briefly introduced. Further, we highlight the importance and advantages of hydrogels as artificial microenvironments in fabricating vascularized tissues or organs, in terms of tunable physical properties, high similarity in physiological environments, and alternative shaping mechanisms, among others. Furthermore, we discuss the utilization of such hydrogels-based vascularized tissues in various applications, including tissue regeneration, drug screening, and organ-on-chips. Finally, we put forward the key challenges, including multifunctionalities of hydrogels, selection of suitable cell phenotype, sophisticated engineering techniques, and clinical translation behind the development of the tissues with complex vasculatures towards their future development.

Recycling of Load-Bearing 3D Printable Double Network Granular Hydrogels

Sustainable materials, such as recyclable polymers, become increasingly important as they are often environmentally friendlier than their one-time-use counterparts. In parallel, the trend toward more customized products demands for fast prototyping methods which allow processing materials into 3D objects that are often only used for a limited amount of time yet, that must be mechanically sufficiently robust to bear significant loads. Soft materials that satisfy the two rather contradictory needs remain to be shown. Here, the authors introduce a material that simultaneously fulfills both requirements, a 3D printable, recyclable double network granular hydrogel (rDNGH). This hydrogel is composed of poly(2-acrylamido-2-methylpropane sulfonic acid) microparticles that are covalently crosslinked through a disulfide-based percolating network. The possibility to independently degrade the percolating network, with no harm to the primary network contained within the microgels, renders the recovery of the microgels efficient. As a result, the recycled material pertains a stiffness and toughness that are similar to those of the pristine material. Importantly, this process can be extended to the fabrication of recyclable hard plastics made of, for example, dried rDNGHs. The authors envision this approach to serve as foundation for a paradigm shift in the design of new sustainable soft materials and plastics.

Bioprinting and regeneration of auricular cartilage using a bioactive bioink based on microporous photocrosslinkable acellular cartilage matrix

Tissue engineering provides a promising strategy for auricular reconstruction. Although the first international clinical breakthrough of tissue-engineered auricular reconstruction has been realized based on polymer scaffolds, this approach has not been recognized as a clinically available treatment because of its unsatisfactory clinical efficacy. This is mainly since reconstruction constructs easily cause inflammation and deformation. In this study, we present a novel strategy for the development of biological auricle equivalents with precise shapes, low immunogenicity, and excellent mechanics using auricular chondrocytes and a bioactive bioink based on biomimetic microporous methacrylate-modified acellular cartilage matrix (ACMMA) with the assistance of gelatin methacrylate (GelMA), poly(ethylene oxide) (PEO), and polycaprolactone (PCL) by integrating multi-nozzle bioprinting technology. Photocrosslinkable ACMMA is used to emulate the intricacy of the cartilage-specific microenvironment for active cellular behavior, while GelMA, PEO, and PCL are used to balance printability and physical properties for precise structural stability, form the microporous structure for unhindered nutrient exchange, and provide mechanical support for higher shape fidelity, respectively. Finally, mature auricular cartilage-like tissues with high morphological fidelity, excellent elasticity, abundant cartilage lacunae, and cartilage-specific ECM deposition are successfully regenerated in vivo, which provides new opportunities and novel strategies for the fabrication and regeneration of patient-specific auricular cartilage.

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Comprehensive proteomic characteristics of the acellular cartilage matrix.

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Bioactive bioink based on ACMMA, GelMA, and PEO promoted cell behavior.

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Bioactive bioink contained biomimetic ECM components and microporous structure.

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Higher biomechanics was provided by alternately bioactive bioink and PCL strands.

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Mature auricle cartilage with high shape fidelity and good mechanics was regenerated.

Nanoparticle-Stabilized Emulsion Bioink for Digital Light Processing Based 3D Bioprinting of Porous Tissue Constructs

A challenge for bioprinting tissue constructs is enabling the viability and functionality of encapsulated cells. Rationally designed bioink that can create appropriate biophysical cues shows great promise for overcoming such challenges. Here, a nanoparticle-stabilized emulsion bioink for direct fabrication of porous tissue constructs by digital light processing based 3D bioprinting technology is introduced. The emulsion bioink is integrated by the mixture of aqueous dextran microdroplets and gelatin methacryloyl solution and is further rendered stable by β-lactoglobulin nanoparticles. After bioprinting, the printed tissue constructs create the macroporous structure via removal of dextran, thereby providing favorable biophysical cues to promote the viability, proliferation, and spreading of the encapsulated cells. Moreover, a trachea-shaped construct containing chondrocytes is bioprinted and implanted in vivo. The results demonstrate that the generated macroporous construct is of benefit to cartilage tissue rebuilding. This work offers an advanced bioink for the fabrication of living tissue constructs by activating the cell behaviors and functions in situ and can lead to the development of 3D bioprinting.

Conductive Nerve Guidance Conduits Based on Morpho Butterfly Wings for Peripheral Nerve Repair

Peripheral nerve injury (PNI), causing loss of sensory and motor function, is a complex and challenging disease in the clinic due to the restricted regeneration capacity. Nerve guidance conduits (NGCs) have become a promising substitute for peripheral nerve regeneration, but their efficacy is often limited. Here, inspired by the physiological structures of peripheral nerves, we present a conductive topological scaffold for nerve repair by modifying Morpho butterfly wing with reduced graphene oxide (rGO) nanosheets and methacrylated gelatin (GelMA) hydrogel encapsulated brain-derived neurotrophic factor (BDNF). Benefiting from the biocompatibility of GelMA hydrogel, the conductivity of rGO and parallel nanoridge structures of wing scales, PC12 cells, and neural stem cells grown on the modified wing have an increased neurite length with guided cellular orientation. In addition, the NGCs are successfully obtained by manually rolling up the scaffolds and exhibited great performance in repairing 10 mm sciatic nerve defects in rats, and we believe that the NGCs can be applied in reparing longer nerve defects in the future by further optimization. We also demonstrate the feasibility of electrically conductive NGCs based on the rGO/BDNF/GelMA-integrated Morpho butterfly wing as functional nerve regeneration conduits, which may have potential value for application in repairing peripheral nerve injuries.

“Invisible” orthodontics by polymeric “clear” aligners molded on 3D-printed personalized dental models

The malalignment of teeth is treated classically by metal braces with alloy wires, which has an unfavorable influence on the patients appearance during the treatment. With the development of digitization, computer simulation and three-dimensional (3D) printing technology, herein, a modern treatment was tried using clear polymeric aligners, which were fabricated by molding polyurethane films via thermoforming on the 3D-printed personalized dental models. The key parameters of photocurable 3D printing of dental models and the mechanical properties of the clear aligner film material were examined. The precision of a 3D-printed dental model mainly relied on characteristics of photocurable resin, the resolution of light source and the exposure condition, which determined the eventual shape of the molded clear aligner and thus the orthodontic treatment efficacy. The biocompatibility of the polyurethane film material was confirmed through cytotoxicity and hemolysis tests in vitro. Following a series of 3D-printed personalized dental models and finite element analysis to predict and plan the fabrication and orthodontic processes, corresponding clear aligners were fabricated and applied in animal experiments, which proved the efficacy and biocompatibility in vivo. Clinical treatments of 120 orthodontic cases were finally carried out with success, which highlights the advantage of the clear aligners as an esthetic, compatible and efficient appliance.

Freeform Cell-Laden Cryobioprinting for Shelf-Ready Tissue Fabrication and Storage

One significant drawback of existing bioprinted tissues is their lack of shelf-availability caused by complications in both fabrication and storage. Here, we report a cryobioprinting strategy for simultaneously fabricating and storing cell-laden volumetric tissue constructs through seamlessly combining extrusion bioprinting and cryopreservation. The cryobioprinting performance was investigated by designing, fabricating, and storing cell-laden constructs made of our optimized cryoprotective gelatin-based bioinks using a freezing plate with precisely controllable temperature. The in situ freezing process further promoted the printability of cell-laden hydrogel bioinks to achieve freeform structures otherwise inconvenient with direct extrusion bioprinting. The effects of bioink composition on printability and cell viability were evaluated. The functionality of the method was finally investigated using cell differentiation and chick ex ovo assays. The results confirmed the feasibility and efficacy of cryobioprinting as a single-step method for concurrent tissue biofabrication and storage.

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.

Digital Light Processing Based Bioprinting with Composable Gradients

Recapitulation of complex tissues signifies a remarkable challenge and, to date, only a few approaches have emerged that can efficiently reconstruct necessary gradients in 3D constructs. This is true even though mimicry of these gradients is of great importance to establish the functionality of engineered tissues and devices. Here, a composable-gradient Digital Light Processing (DLP)-based (bio)printing system is developed, utilizing the unprecedented integration of a microfluidic mixer for the generation of either continual or discrete gradients of desired (bio)inks in real time. Notably, the precisely controlled gradients are composable on-the-fly by facilely by adjusting the (bio)ink flow ratios. In addition, this setup is designed in such a way that (bio)ink waste is minimized when exchanging the gradient (bio)inks, further enhancing this time- and (bio)ink-saving strategy. Various planar and 3D structures exhibiting continual gradients of materials, of cell densities, of growth factor concentrations, of hydrogel stiffness, and of porosities in horizontal and/or vertical direction, are exemplified. The composable fabrication of multifunctional gradients strongly supports the potential of the unique bioprinting system in numerous biomedical applications.

Injectable, Pore-Forming, Perfusable Double-Network Hydrogels Resilient to Extreme Biomechanical Stimulations

Biological tissues hinge on blood perfusion and mechanical toughness to function. Injectable hydrogels that possess both high permeability and toughness have profound impacts on regenerative medicine but remain a long-standing challenge. To address this issue, injectable, pore-forming double-network hydrogels are fabricated by orchestrating stepwise gelation and phase separation processes. The interconnected pores of the resulting hydrogels enable direct medium perfusion through organ-sized matrices. The hydrogels are amenable to cell encapsulation and delivery while promoting cell proliferation and spreading. They are also pore insensitive, tough, and fatigue resistant. When tested in biomimetic perfusion bioreactors, the hydrogels maintain physical integrity under prolonged, high-frequency biomechanical stimulations (>6000 000 cycles at 120 Hz). The excellent biomechanical performance suggests the great potential of the new injectable hydrogel technology for repairing mechanically dynamic tissues, such as vocal folds, and other applications, such as tissue engineering, biofabrication, organs-on-chips, drug delivery, and disease modeling.

Suction-Cup-Inspired Adhesive Micromotors for Drug Delivery

Micromotors have opened novel avenues for drug delivery due to their capacity for self-propelling. Attempts in this field trend towards ameliorating their functions to promote their clinical applications. In this paper, an ingenious suction-cup-inspired micromotor is presented with adhesive properties for drug delivery in the stomach. The micromotors are fabricated by using hydrogel replicating the structure of suction-cup-like microparticles, which derive from self-assembly of colloidal crystals under rapid solvent extraction, followed by loading magnesium (Mg) in the bottom spherical surface. The Mg-loaded micromotors can realize spontaneous movement due to the continual generation of hydrogen bubbles in gastric juice. The combination of unique suction-cup-like structure with excellent motion performance makes the micromotor an ideal carrier for drug delivery as they can efficiently adhere to the tissue. Moreover, benefiting from the porous structure, the hydrogel micromotors exhibit a high volume-surface ratio, which enables efficient drug loading. It is demonstrated that the suction-cup-inspired micromotors can adhere efficiently to the ulcer-region in the stomach and release drugs due to their distinctive architecture and spontaneous motion, exhibiting desirable curative effect of gastric ulcer. Thus, the suction-cup-inspired micromotors with adhesive properties are expected to advance the development of micromotor in clinical applications.

Porous MOF Microneedle Array Patch with Photothermal Responsive Nitric Oxide Delivery for Wound Healing

Patches with the capacity of controllable delivering active molecules toward the wound bed to promote wound healing are expectant all along. Herein, a novel porous metal-organic framework (MOF) microneedle (MN) patch enabling photothermal-responsive nitric oxide (NO) delivery for promoting diabetic wound healing is presented. As the NO-loadable copper-benzene-1,3,5-tricarboxylate (HKUST-1) MOF is encapsulated with graphene oxide (GO), the resultant NO@HKUST-1@GO microparticles (NHGs) are imparted with the feature of near-infrared ray (NIR) photothermal response, which facilitate the controlled release of NO molecules. When these NHGs are embedded in a porous PEGDA-MN, the porous structure, larger specific surface area, and sufficient mechanical strength of the integrated MN could promote a more accurate and deeper delivery of NO molecules into the wound site. By applying the resultant NHG-MN to the wound of a type I diabetic rat model, the authors demonstrate that it is capable of accelerating vascularization, tissue regeneration, and collagen deposition, indicating its bright prospect applied in wound healing and other therapeutic scenarios.

Hierarchical Hydrogels with Ordered Micro-Nano Structures for Cancer-on-a-Chip Construction

In the drug therapy of tumor, efficient and stable drug screening platforms are required since the drug efficacy varies individually. Here, inspired by the microstructures of hepatic lobules, in which hepatocytes obtain nutrients from both capillary vessel and the central vein, we present a novel hierarchical hydrogel system with ordered micro-nano structure for liver cancer-on-a-chip construction and drug screening. The hierarchical hydrogel system was fabricated by using pregel to fill and replicate self-assembled colloidal crystal arrays and microcolumn array template. Due to the synergistic effect of its interconnected micro-nano structures, the resultant system could not only precisely control the size of cell spheroids but also realize adequate nutrient supply of cell spheroids. We have demonstrated that by integrating the hierarchical hydrogel system into a multichannel concentration gradients microfluidic chip, a functional liver cancer-on-a-chip could be constructed for high-throughput drug screening with good repeatability and high accuracy. These results indicated that the hierarchical hydrogel system and its derived liver cancer-on-a-chip are ideal platforms for drug screening and have great application potential in the field of personalized medicine.

Colloidal multiscale porous adhesive (bio)inks facilitate scaffold integration

Poor cellular spreading, proliferation, and infiltration, due to the dense biomaterial networks, have limited the success of most thick hydrogel-based scaffolds for tissue regeneration. Here, inspired by whipped cream production widely used in pastries, hydrogel-based foam bioinks are developed for bioprinting of scaffolds. Upon cross-linking, a multiscale and interconnected porous structure, with pores ranging from few to several hundreds of micrometers, is formed within the printed constructs. The effect of the process parameters on the pore size distribution and mechanical and rheological properties of the bioinks is determined. The developed foam bioinks can be easily printed using both conventional and custom-built handheld bioprinters. In addition, the foam inks are adhesive upon in situ cross-linking and are biocompatible. The subcutaneous implantation of scaffolds formed from the engineered foam bioinks showed their rapid integration and vascularization in comparison with their non-porous hydrogel counterparts. In addition, in vivo application of the foam bioink into the non-healing muscle defect of a murine model of volumetric muscle loss resulted in a significant functional recovery and higher muscle forces at 8 weeks post injury compared with non-treated controls.

Magneto-Responsive Microneedle Robots for Intestinal Macromolecule Delivery

Oral administration is the most convenient and commonly used approach for drug delivery, while it is still a challenge to overcome the complicated gastrointestinal barriers and realize efficient macromolecular drug absorption. Here, novel magneto-responsive microneedle robots are presented for efficient oral delivery of versatile macromolecules. These microneedle robots with three components of the magnetic substrate, the separable connection, and tips are generated by a Lego-brick-stacking-inspired multistage 3D fabrication strategy. With the assistance of commercial enteric capsule encapsulation, they can be taken orally and be released when entering the small intestine. Benefitting from their polarized magnetic substrate, the tips of the microneedle robots can orient to the small intestinal wall, overcome the barriers, insert into the tissue, and deliver encapsulated actives under specific magnetic fields. Besides, after the separable connection degrades, the tips can be left inside the tissue for continuous actives release, and the magnetic substrate can be excreted safely. Based on these features, the practical values of the microneedle robots are demonstrated by using them to orally deliver insulin and efficiently regulate the blood glucose of pigs. It is believed that the proposed microneedle robots can orally deliver diverse macromolecules and thus open a new chapter for oral administration.

Elastic MXene Hydrogel Microfiber-Derived Electronic Skin for Joint Monitoring

Effective and timely joint monitoring has been a significantly vital research direction in human healthcare. As an emerging technology, flexible electronics provides more possibilities and applicabilities for practical sensing and signal transmission. Here, we provide novel elastic MXene microfibers of controllable morphologies at a microscale through microfluidic technology for actual joint motion monitoring. Double-network hydrogels including covalently cross-linking polyacrylamide and ionically cross-linking alginate were chosen for superelasticity. For the improvement of the electrical conductivity of superelastic hydrogel microfibers, MXene was selected to mix with them. By introducing the cross-linker to the outer channel, microfibers with controllable diameters along with high electrical conductivities and tensile properties could be fabricated successfully. The practical value of the synthesized microfibers in joint movement sensing has been demonstrated by acting as the element of new motion sensors. Based on these features, it is believed that these elastic MXene hydrogel microfibers have high potential for rapid sensing and diagnosis of joint diseases.

Magnetic materials: a journey from finding north to an exciting printed future

The potential implications/applications of printing technologies are being recognized worldwide across different disciplines and industries. Printed magnetoactive smart materials, whose physical properties can be changed by the application of external magnetic fields, are an exclusive class of smart materials that are highly valuable due to their magnetically activated smart and/or multifunctional response. Such smart behavior allows, among others, high speed and low-cost wireless activation, fast response, and high controllability with no relevant limitations in design, shape, or dimensions. Nevertheless, the printing of magnetoactive materials is still in its infancy, and the design apparatus, the material set, and the fabrication procedures are far from their optimum features. Thus, this review presents the main concepts that allow interconnecting printing technologies with magnetoactive materials by discussing the advantages and disadvantages of this joint field, trying to highlight the scientific obstacles that still limit a wider application of these materials nowadays. Additionally, it discusses how these limitations could be overcome, together with an outlook of the remaining challenges in the emerging digitalization, Internet of Things, and Industry 4.0 paradigms. Finally, as magnetoactive materials will play a leading role in energy generation and management, the magnetic-based Green Deal is also addressed.

The Food-Materials Nexus: Next Generation Bioplastics and Advanced Materials from Agri-Food Residues

The most recent strategies available for upcycling agri-food losses and waste (FLW) into functional bioplastics and advanced materials are reviewed and the valorization of food residuals are put in perspective, adding to the water-food-energy nexus. Low value or underutilized biomass, biocolloids, water-soluble biopolymers, polymerizable monomers, and nutrients are introduced as feasible building blocks for biotechnological conversion into bioplastics. The latter are demonstrated for their incorporation in multifunctional packaging, biomedical devices, sensors, actuators, and energy conversion and storage devices, contributing to the valorization efforts within the future circular bioeconomy. Strategies are introduced to effectively synthesize, deconstruct and reassemble or engineer FLW-derived monomeric, polymeric, and colloidal building blocks. Multifunctional bioplastics are introduced considering the structural, chemical, physical as well as the accessibility of FLW precursors. Processing techniques are analyzed within the fields of polymer chemistry and physics. The prospects of FLW streams and biomass surplus, considering their availability, interactions with water and thermal stability, are critically discussed in a near-future scenario that is expected to lead to next-generation bioplastics and advanced materials.

Composite Inks for Extrusion Printing of Biological and Biomedical Constructs

Extrusion-based three-dimensional (3D) printing is an emerging technology for the fabrication of complex structures with various biological and biomedical applications. The method is based on the layer-by-layer construction of the product using a printable ink. The material used as the ink should possess proper rheological properties and desirable performances. Composite materials, which are extensively used in 3D printing applications, can improve the printability and offer superior performances for the printed constructs. Herein, we review composite inks with a focus on composite hydrogels. The properties of different additives including fibers and nanoparticles are discussed. The performances of various composite inks in biological and biomedical systems are delineated through analyzing the synergistic effects between the composite ink components. Different applications, including tissue engineering, tissue model engineering, soft robotics, and four-dimensional printing, are selected to demonstrate how 3D-printable composite inks are exploited to achieve various desired functionality. This review finally presents an outlook of future perspectives on the design of composite inks.

High-resolution lithographic biofabrication of hydrogels with complex microchannels from low-temperature-soluble gelatin bioresins

Biofabrication via light-based 3D printing offers superior resolution and ability to generate free-form architectures, compared to conventional extrusion technologies. While extensive efforts in the design of new hydrogel bioinks lead to major advances in extrusion methods, the accessibility of lithographic bioprinting is still hampered by a limited choice of cell-friendly resins. Herein, we report the development of a novel set of photoresponsive bioresins derived from ichthyic-origin gelatin, designed to print high-resolution hydrogel constructs with embedded convoluted networks of vessel-mimetic channels. Unlike mammalian gelatins, these materials display thermal stability as pre-hydrogel solutions at room temperature, ideal for bioprinting on any easily-accessible lithographic printer. Norbornene- and methacryloyl-modification of the gelatin backbone, combined with a ruthenium-based visible light photoinitiator and new coccine as a cytocompatible photoabsorber, allowed to print structures resolving single-pixel features (∼50 ​μm) with high shape fidelity, even when using low stiffness gels, ideal for cell encapsulation (1-2 ​kPa). Moreover, aqueous two-phase emulsion bioresins allowed to modulate the permeability of the printed hydrogel bulk. Bioprinted mesenchymal stromal cells displayed high functionality over a month of culture, and underwent multi-lineage differentiation while colonizing the bioresin bulk with tissue-specific neo-deposited extracellular matrix. Importantly, printed hydrogels embedding complex channels with perfusable lumen (diameter <200 ​μm) were obtained, replicating anatomical 3D networks with out-of-plane branches (i.e. brain vessels) that cannot otherwise be reproduced by extrusion bioprinting. This versatile bioresin platform opens new avenues for the widespread adoption of lithographic biofabrication, and for bioprinting complex channel-laden constructs with envisioned applications in regenerative medicine and hydrogel-based organ-on-a-chip devices.

Suction Cups-Inspired Adhesive Patch with Tailorable Patterns for Versatile Wound Healing

Medical patches play an important role in wound healing because of their tissue conformality, drug release capacity, and convenient operation. Great efforts have been devoted to developing new-generation patches with distinctive features promoting wound healing. Here, inspired by the structure of octopus suction cups and the component of natural tissue, a biocompatible wound patch with selective adhesiveness and individualized design using a combined strategy of template-replication and mask-guided lithography is presented. Such patches are based on Ecoflex film with suction-cup-mimicking microstructures to adhere to normal skin and with biocompatible gelatin methacryloyl (GelMA) hydrogel to contact wounded areas. An ultraviolet mask with a tailorable pattern is employed to shape the GelMA hydrogel into customized geometry replicating individual wound areas, and thus both adhesion and antiadhesion properties are integrated into the same patch. In addition, vascular endothelial growth factor is loaded to accelerate the healing process. Based on these advantages, the authors demonstrate that the present patches not only adhere to different skin surfaces, but also promote the treatment of a rat cutaneous wound model. Thus, it is believed that this versatile patch can break through the limitation of traditional patches and be ideal candidates for wound healing and related biomedical applications.

Handheld bioprinting strategies for in situ wound dressing

Handheld bioprinting has recently attracted considerable attention as a technology to deliver biomaterials and/or cells to injury sites by using freeform, user-instructed deposition approaches, specifically targeted towards in situ wound dressing and healing. In this review, we present a concise introduction of handheld bioprinting, and a thorough discussion on design and manufacture of handheld bioprinters and choice over bioinks. Finally, the advantages, challenges, and prospective of the said technologies are elaborated. It is believed that handheld bioprinting will play an essential role in the field of in situ wound healing mainly due to its excellent portability, user-friendliness, cost-effectiveness, and amenability to various wound needs.

3D hollow-structured hydrogels with editable macrostructure, function, and mechanical properties induced by segmented adjustments

Currently, it is challenging to prepare uniform hollow-structured hydrogels with tailorable comprehensive properties. Herein, making full use of the different gelation routes of polyvinyl alcohol (PVA), we propose a distinctive two-stage method for preparing hollow-structured hydrogels, which is to arrange the microstructure of the hydrogel through segmented adjustment. The mechanical properties, macrostructure, and functions of the obtained hollow hydrogel can be easily designed and edited. Specifically, the mechanical properties of the hollow hydrogel can be improved from "soft" to "hard" by changing the preparation conditions. In addition, hollow hydrogels with diverse macrostructures can also be developed through different templates, such as tubes, gloves, and rings. More importantly, the hollow hydrogels can be endowed with conductive, anti-drying, anti-freezing, and photothermal-converting functions due to the great system compatibility of the gel precursor. Benefiting from the advantages of the hollow hydrogel, the conductive gel ring-based bioelectrodes and sensors were developed. Interestingly, the adaptive gel ring-based electronics can stably record the electrophysiological and strain signals of the human body without the help of adhesive tape. This study opens more opportunities for development and applications of other hydrogel-based hollow materials.

An Innovative Solvent-Responsive Coiling-Expanding Stent

Coronary artery disease is the "first killer" in the world, while the classical treatment for this disease is to implant stent. An ideal vascular stent should be nontoxic with self-expanding characteristics, quick expanding speed, and appropriate mechanical supporting property. However, no existing vascular stent covers all properties. Herein, a two-way shape-memory cellulose vascular stent, which can realize shape adjustments by mild solutions such as water and alcohol, is constructed. The shape-memory characteristics, mechanical properties, cell toxicity, and biocompatibility, are systemically investigated by ex vivo experiment as well as molecule simulation and theoretical modeling, revealing that the achieved bilayer two-way shape-memory films (BSMFs) can be used as an artificial vascular stent. In particular, this vascular stent made from BSMFs shows superb biocompatibility according to live/dead cell viability assays. Ex vivo experiments reveal that the novel vascular stent can support arteria coronaria sinistra, or the left main coronary artery, at the opening state while the cross-section of the vessel becomes two times larger than that of the initial state after implantation. Thus, it is believed that effective and scalable BSMFs can make meritorious fundamental contributions to biomaterials science and practical applications such as vascular stents.

Pre-shear bioprinting of highly oriented porous hydrogel microfibers to construct anisotropic tissues

Anisotropic tissues in vivo have special structural characteristics and biological functions. Nowadays, bioprinting is widely used in tissue engineering and an effective way to process cell-laden hydrogels. However, the direct bioprinting of oriented cell-laden hydrogel structures to engineer anisotropic tissues is still difficult. Meanwhile, the inherent dense micropore network after the gelation of hydrogel-based bioinks usually limits the normal growth of encapsulated cells due to the inadequate supply of nutrient/oxygen. Herein, we proposed a pre-shear bioprinting strategy of highly oriented porous hydrogel microfibers to construct anisotropic tissues. Firstly, based on the phase separation of viscous high-molecular compound mixtures, we utilized a general viscous porous bioink paradigm, e.g., mixing a polymer thickener (PEO) with a hydrogel precursor (GelMA) with excellent biological properties. Secondly, based on the shear-oriented property of the viscous porous bioink, we designed the pre-shear in situ coaxial bioprinting of highly oriented porous hydrogel microfibers. The viscous porous bioink (GelMA/PEO) was shear-oriented through an injection tube and pumped into the inner needle of a coaxial nozzle. When GelMA/PEO passed through a transparent glass tube connected to the coaxial nozzle, GelMA can be in situ photo-crosslinked to form highly oriented porous microfibers. In addition, we showed the manufacturing of heterogeneous oriented microfibers and the manual assembly of microfibers, and within oriented microfibers, different cells or co-cultured cells exhibited highly oriented growth behaviors similar to that in vivo. As far as we know, the direct bioprinting of anisotropic tissues through high orientation induced by pre-shearing is firstly reported in our study. We believe that the pre-shear bioprinting strategy of anisotropic tissues will open more avenues for further biomedical research.

Development of Bioinspired Functional Chitosan/Cellulose Nanofiber 3D Hydrogel Constructs by 3D Printing for Application in the Engineering of Mechanically Demanding Tissues

Soft tissues are commonly fiber-reinforced hydrogel composite structures, distinguishable from hard tissues by their low mineral and high water content. In this work, we proposed the development of 3D printed hydrogel constructs of the biopolymers chitosan (CHI) and cellulose nanofibers (CNFs), both without any chemical modification, which processing did not incorporate any chemical crosslinking. The unique mechanical properties of native cellulose nanofibers offer new strategies for the design of environmentally friendly high mechanical performance composites. In the here proposed 3D printed bioinspired CNF-filled CHI hydrogel biomaterials, the chitosan serves as a biocompatible matrix promoting cell growth with balanced hydrophilic properties, while the CNFs provide mechanical reinforcement to the CHI-based hydrogel. By means of extrusion-based printing (EBB), the design and development of 3D functional hydrogel scaffolds was achieved by using low concentrations of chitosan (2.0-3.0% (w/v)) and cellulose nanofibers (0.2-0.4% (w/v)). CHI/CNF printed hydrogels with good mechanical performance (Young's modulus 3.0 MPa, stress at break 1.5 MPa, and strain at break 75%), anisotropic microstructure and suitable biological response, were achieved. The CHI/CNF composition and processing parameters were optimized in terms of 3D printability, resolution, and quality of the constructs (microstructure and mechanical properties), resulting in good cell viability. This work allows expanding the library of the so far used biopolymer compositions for 3D printing of mechanically performant hydrogel constructs, purely based in the natural polymers chitosan and cellulose, offering new perspectives in the engineering of mechanically demanding hydrogel tissues like intervertebral disc (IVD), cartilage, meniscus, among others.

Minimalist Tissue Engineering Approaches Using Low Material-Based Bioengineered Systems

From an "over-engineering" era in which biomaterials played a central role, now it is observed to the emergence of "developmental" tissue engineering (TE) strategies which rely on an integrative cell-material perspective that paves the way for cell self-organization. The current challenge is to engineer the microenvironment without hampering the spontaneous collective arrangement ability of cells, while simultaneously providing biochemical, geometrical, and biophysical cues that positively influence tissue healing. These efforts have resulted in the development of low-material based TE strategies focused on minimizing the amount of biomaterial provided to the living key players of the regenerative process. Through a "minimalist-engineering" approach, the main idea is to fine-tune the spatial balance occupied by the inanimate region of the regenerative niche toward maximum actuation of the key living components during the healing process.

Review on the Vascularization of Organoids and Organoids-on-a-hip

The use of human cells for the construction of 3D organ models in vitro based on cell self-assembly and engineering design has recently increased in popularity in the field of biological science. Although the organoids are able to simulate the structures and functions of organs in vitro, the 3D models have difficulty in forming a complex vascular network that can recreate the interaction between tissue and vascular systems. Therefore, organoids are unable to survive, due to the lack of oxygen and nutrients, as well as the accumulation of metabolic waste. Organoids-on-a-chip provides a more controllable and favorable design platform for co-culture of different cells and tissue types in organoid systems, overcoming some of the limitations present in organoid culture. However, the majority of them has vascular networks that are not adequately elaborate to simulate signal communications between bionic microenvironment (e.g., fluid shear force) and multiple organs. Here, we will review the technological progress of the vascularization in organoids and organoids-on-a-chip and the development of intravital 3D and 4D bioprinting as a new way for vascularization, which can aid in further study on tissue or organ development, disease research and regenerative medicine.

Injectable GelMA Cryogel Microspheres for Modularized Cell Delivery and Potential Vascularized Bone Regeneration

Cell therapeutics hold tremendous regenerative potential and the therapeutic effect depends on the effective delivery of cells. However, current cell delivery carriers with unsuitable cytocompatibility and topological structure demonstrate poor cell viability during injection. Therefore, porous shape-memory cryogel microspheres (CMS) are prepared from methacrylated gelatin (GelMA) by combining an emulsion technique with gradient-cooling cryogelation. Pore sizes of the CMS are adjusted via the gradient-cooling procedure, with the optimized pore size (15.5 ± 6.0 µm) being achieved on the 30-min gradient-cooled variant (CMS-30). Unlike hydrogel microspheres (HMS), CMS promotes human bone marrow stromal cell (hBMSC) and human umbilical vein endothelial cell (HUVEC) adhesion, proliferated with high levels of stemness for 7 d, and protects cells during the injection process using a 26G syringe needle. Moreover, CMS-30 enhances the osteogenic differentiation of hBMSCs in osteoinductive media. CMS can serve as building blocks for delivering multiple cell types. Here, hBMSC-loaded and HUVEC-loaded CMS-30, mixed at a 1:1 ratio, are injected subcutaneously into nude mice for 2 months. Results show the development of vascularized bone-like tissue with high levels of OCN and CD31. These findings indicate that GelMA CMS of a certain pore size can effectively deliver multiple cells to achieve functional tissue regeneration.

Preparation and biomedical application of injectable hydrogels

The preparation of multifunctional injectable hydrogels, as well as the classification of injectable hydrogels according to different functions, most summarize the applications of injectable hydrogels in different biomedical fields.

A Versatile Open-Source Printhead for Low-Cost 3D Microextrusion-Based Bioprinting

Three-dimensional (3D) bioprinting promises to be essential in tissue engineering for solving the rising demand for organs and tissues. Some bioprinters are commercially available, but their impact on the field of Tissue engineering (TE) is still limited due to their cost or difficulty to tune. Herein, we present a low-cost easy-to-build printhead for microextrusion-based bioprinting (MEBB) that can be installed in many desktop 3D printers to transform them into 3D bioprinters. We can extrude bioinks with precise control of print temperature between 2-60 °C. We validated the versatility of the printhead, by assembling it in three low-cost open-source desktop 3D printers. Multiple units of the printhead can also be easily put together in a single printer carriage for building a multi-material 3D bioprinter. Print resolution was evaluated by creating representative calibration models at different temperatures using natural hydrogels such as gelatin and alginate, and synthetic ones like poloxamer. Using one of the three modified low-cost 3D printers, we successfully printed cell-laden lattice constructs with cell viabilities higher than 90% after 24-h post printing. Controlling temperature and pressure according to the rheological properties of the bioinks was essential in achieving optimal printability and great cell viability. The cost per unit of our device, which can be used with syringes of different volume, is less expensive than any other commercially available product. These data demonstrate an affordable open-source printhead with the potential to become a reliable alternative to commercial bioprinters for any laboratory.