3D bioprinting of a cell-laden antibacterial polysaccharide hydrogel composite

Development of novel iron(III) crosslinked bioinks comprising carboxymethyl cellulose, xanthan gum, and hyaluronic acid for soft tissue engineering applications

The advent of three-dimensional (3D) bioprinting offers a feasible approach to construct complex structures for soft tissue regeneration. Carboxymethyl cellulose (CMC) has been emerging as a very promising biomaterial for 3D bioprinting. However, due to the inability to maintain the post-printed stability, CMC needs to be physically blended and/or chemically crosslinked with other polymers. In this context, this study presents the combination of CMC with xanthan gum (XG) and hyaluronic acid (HA) to formulate a multicomponent bioink, leveraging the printability of CMC and XG, as well as the cellular support properties of HA. The ionic crosslinking of printed constructs with iron(III) via the metal-ion coordination between ferric cations and carboxylate groups of the three polymers was introduced to induce improved mechanical strength and long-term stability. Moreover, immortalized human epidermal keratinocytes (HaCaT) and human foreskin fibroblasts (HFF) encapsulated within iron-crosslinked printed hydrogels exhibited excellent cell viability (more than 95%) and preserved morphology. Overall, the presented study highlights that the combination of these three biopolymers and the ionic crosslinking with ferric ions is a valuable strategy to be considered for the development of new and advanced hydrogel-based bioinks for soft tissue engineering applications.

Biofabrication of Cellulose-based Hydrogels for Advanced Wound Healing: A Special Emphasis on 3D Bioprinting

Even with the current advancements in wound management, addressing most skin injuries and wounds continues to pose a significant obstacle for the healthcare industry. As a result, researchers are now focusing on creating innovative materials utilizing cellulose and its derivatives. Cellulose, the most abundant biopolymer in nature, has unique properties that make it a promising material for wound healing, such as biocompatibility, tunable physiochemical characteristics, accessibility, and low cost. 3D bioprinting technology has enabled the production of cellulose-based wound dressings with complex structures that mimic the extracellular matrix. The inclusion of bioactive molecules such as growth factors offers the ability to aid in promoting wound healing, while cellulose creates an ideal environment for controlled release of these biomolecules and moisture retention. The use of 3D bioprinted cellulose-based wound dressings has potential benefits for managing chronic wounds, burns, and painful wounds by promoting wound healing and reducing the risk of infection. This review provides an up-to-date summary of cellulose-based dressings manufactured by 3D bioprinting techniques by looking into wound healing biology, biofabrication methods, cellulose derivatives, and the existing cellulose bioinks targeted toward wound healing.

A review of biomacromolecule-based 3D bioprinting strategies for structure-function integrated repair of skin tissues

When skin is damaged or affected by diseases, it often undergoes irreversible scar formation, leading to aesthetic concerns and psychological distress for patients. In cases of extensive skin defects, the patient's life can be severely compromised. In recent years, 3D printing technology has emerged as a groundbreaking approach to skin tissue engineering, offering promising solutions to various skin-related conditions. 3D bioprinting technology enables the precise fabrication of structures by programming the spatial arrangement of cells within the skin tissue and subsequently printing skin replacements either in a 3D bioprinter or directly at the site of the defect. This study provides a comprehensive overview of various biopolymer-based inks, with a particular emphasis on chitosan (CS), starch, alginate, agarose, cellulose, and fibronectin, all of which are natural polymers belonging to the category of biomacromolecules. Additionally, it summarizes artificially synthesized polymers capable of enhancing the performance of these biomacromolecule-based bioinks, thereby composing hybrid biopolymer inks aimed at better application in skin tissue engineering endeavors. This review paper examines the recent advancements, characteristics, benefits, and limitations of biological 3D bioprinting techniques for skin tissue engineering. By utilizing bioinks containing seed cells, hydrogels with bioactive factors, and biomaterials, complex structures resembling natural skin can be accurately fabricated in a layer-by-layer manner. The importance of biological scaffolds in promoting skin wound healing and the role of 3D bioprinting in skin tissue regeneration processes is discussed. Additionally, this paper addresses the challenges and constraints associated with current 3D bioprinting technologies for skin tissue and presents future perspectives. These include advancements in bioink formulations, full-thickness skin bioprinting, vascularization strategies, and skin appendages bioprinting.

Recent Developments in 3D-(Bio)printed Hydrogels as Wound Dressings

Wound healing is a physiological process occurring after the onset of a skin lesion aiming to reconstruct the dermal barrier between the external environment and the body. Depending on the nature and duration of the healing process, wounds are classified as acute (e.g., trauma, surgical wounds) and chronic (e.g., diabetic ulcers) wounds. The latter take several months to heal or do not heal (non-healing chronic wounds), are usually prone to microbial infection and represent an important source of morbidity since they affect millions of people worldwide. Typical wound treatments comprise surgical (e.g., debridement, skin grafts/flaps) and non-surgical (e.g., topical formulations, wound dressings) methods. Modern experimental approaches include among others three dimensional (3D)-(bio)printed wound dressings. The present paper reviews recently developed 3D (bio)printed hydrogels for wound healing applications, especially focusing on the results of their in vitro and in vivo assessment. The advanced hydrogel constructs were printed using different types of bioinks (e.g., natural and/or synthetic polymers and their mixtures with biological materials) and printing methods (e.g., extrusion, digital light processing, coaxial microfluidic bioprinting, etc.) and incorporated various bioactive agents (e.g., growth factors, antibiotics, antibacterial agents, nanoparticles, etc.) and/or cells (e.g., dermal fibroblasts, keratinocytes, mesenchymal stem cells, endothelial cells, etc.).

Recent advances in 3D printed cellulose-based wound dressings: A review on in vitro and in vivo achievements

Chronic wounds, especially diabetic ulcers, pose a significant challenge in regenerative medicine. Cellulose derivatives offer remarkable wound management properties, such as effective absorption and retention of wound exudates, maintaining an optimal moisture environment crucial for successful chronic wound regeneration. However, conventional dressings have limited efficacy in managing and healing these types of skin lesions, driving scientists to explore innovative approaches. The emergence of 3D printing has enabled personalized dressings that meet individual patient needs, improving the healing process and patient comfort. Cellulose derivatives meet the demanding requirements for biocompatibility, printability, and biofabrication necessary for 3D printing of biologically active scaffolds. However, the potential applications of nanocellulose and cellulose derivative-based inks for wound regeneration remain largely unexplored. Thus, this review provides a comprehensive overview of recent advancements in cellulose-based inks for 3D printing of personalized wound dressings. The composition and biofabrication approaches of cellulose-based wound dressings are thoroughly discussed, including the functionalization with bioactive molecules and antibiotics for improved wound regeneration. Similarly, the in vitro and in vivo performance of these dressings is extensively examined. In summary, this review aims to highlight the exceptional advantages and diverse applications of 3D printed cellulose-based dressings in personalized wound care.

Bio-based polymers containing traditional medicinal fillers for wound healing applications - An evaluation of neoteric development and future perspectives

In recent years, health-care providers have seen more patients with difficult-to-treat wounds and burns. The biopolymer-based wound dressing protects the wounded area while assisting in the recovery of dermal and epithelial tissues throughout the healing process. The overall number of patients with chronic lesions has been expanding due to developing society, over weight, and cardiovascular illness. For the treatment of chronic wounds, there is an increasing demand for the development of ideal wound dressing materials with excellent properties such as antibacterial activity, biocompatibility, free radical scavenging capacity, non-adherent property, hydrophilicity, and so on. Nevertheless, owing to the above mention properties, natural polymers are being used for several key functions of biomedicine like narcotic distribution systems, tissue manufacturing, bandages, and so on. Accordingly, the significance of these bio-based polymers interfered with healing functions that lead to informing and inspiring youth and scientist researchers worldwide to grab with these far-reaching areas of medicine and biology. The review highlights the physiochemical properties of natural polymers, the biological evaluation of various materials as wound dressings, their synthesis and mechanical properties, clinical status, challenges, and future perspectives.

Modification, 3D printing process and application of sodium alginate based hydrogels in soft tissue engineering: A review

Sodium alginate (SA) is an inexpensive and biocompatible biomaterial with fast and gentle crosslinking that has been widely used in biological soft tissue repair/regeneration. Especially with the advent of 3D bioprinting technology, SA hydrogels have been applied more deeply in tissue engineering due to their excellent printability. Currently, the research on material modification, molding process and application of SA-based composite hydrogels has become a hot topic in tissue engineering, and a lot of fruitful results have been achieved. To better help readers have a comprehensive understanding of the development status of SA based hydrogels and their molding process in tissue engineering, in this review, we summarized SA modification methods, and provided a comparative analysis of the characteristics of various SA based hydrogels. Secondly, various molding methods of SA based hydrogels were introduced, the processing characteristics and the applications of different molding methods were analyzed and compared. Finally, the applications of SA based hydrogels in tissue engineering were reviewed, the challenges in their applications were also analyzed, and the future research directions were prospected. We believe this review is of great helpful for the researchers working in biomedical and tissue engineering.

Classification, processing, and applications of bioink and 3D bioprinting: A detailed review

With the advancement in 3D bioprinting technology, cell culture methods can design 3D environments which are both, complex and physiologically relevant. The main component in 3D bioprinting, bioink, can be split into various categories depending on the criterion of categorization. Although the choice of bioink and bioprinting process will vary greatly depending on the application, general features such as material properties, biological interaction, gelation, and viscosity are always important to consider. The foundation of 3D bioprinting is the exact layer-by-layer implantation of biological elements, biochemicals, and living cells with the spatial control of the implantation of functional elements onto the biofabricated 3D structure. Three basic strategies underlie the 3D bioprinting process: autonomous self-assembly, micro tissue building blocks, and biomimicry or biomimetics. Tissue engineering can benefit from 3D bioprinting in many ways, but there are still numerous obstacles to overcome before functional tissues can be produced and used in clinical settings. A better comprehension of the physiological characteristics of bioink materials and a higher level of ability to reproduce the intricate biologically mimicked and physiologically relevant 3D structures would be a significant improvement for 3D bioprinting to overcome the limitations.

Nanofibrillated cellulose/gellan gum hydrogel-based bioinks for 3D bioprinting of skin cells

The development of suitable bioinks is an important research topic in the field of three-dimensional (3D) bioprinting. Herein, novel hydrogel-based bioinks composed of nanofibrillated cellulose (NFC) and gellan gum (GG) in different NFC/GG mass proportions (90:10, 80:20, 70:30, and 60:40) were developed and characterized. The increase in the content of GG, as well as its combination with NFC, enhanced their rheological properties, increasing both storage (G') and loss (G") moduli and the G' recovery capacity of the hydrogels (from 70.05 ± 3.06 % (90:10) to 82.63 ± 1.21 % (60:40)), as well as their mechanical properties, increasing the compressive stiffness and stress from 114.02 ± 10.93 Pa (90:10) to 337.16 ± 34.03 Pa (60:40) and from 18.27 ± 1.32 kPa (90:10) to 47.17 ± 3.59 kPa (60:40), respectively. The hydrogels were non-cytotoxic against human keratinocyte cells (HaCaT), with cell viabilities above 70 % for up to 72 h. The hydrogel 60:40 was loaded with HaCaT cells (3 × 10⁶ cells mL^-1) and bioprinted. The cell viability was maintained elevated until day 7 (90 ± 3 %) after bioprinting. These results highlight that the combination of these two biopolymers was a good strategy for the development of novel hydrogel-based bioinks for extrusion 3D bioprinting applications.

3D Printing as a Technological Strategy for the Personalized Treatment of Wound Healing

Wound healing is a dynamic process which involves stages of hemostasis, inflammation, proliferation and remodeling. Any error in this process results in abnormal wound healing, generating financial burdens for health systems and even affecting the physical and mental health of the patient. Traditional dressings do not meet the complexities of ideal treatment in all types of wounds. For this reason, in the last decades, different materials for drug delivery and for the treatment of wounds have been proposed reaching novel level of standards, such as 3D printing techniques. The use of natural or synthetic polymers, and the correct design of these printed products loaded with cells and/or combined with active compounds, can generate an effective system for the treatment of wounds, improving the healing process and generating customized dressings according to the patient needs. This manuscript provides a comprehensive review of different types of 3D printing techniques, as well as its use in wound healing and its different stages, including the advantages and limitations of additive manufacturing and future perspectives.

Application of Hydrogels as Three-Dimensional Bioprinting Ink for Tissue Engineering

The use of three-dimensional bioprinting technology combined with the principle of tissue engineering is important for the construction of tissue or organ regeneration microenvironments. As a three-dimensional bioprinting ink, hydrogels need to be highly printable and provide a stiff and cell-friendly microenvironment. At present, hydrogels are used as bioprinting inks in tissue engineering. However, there is still a lack of summary of the latest 3D printing technology and the properties of hydrogel materials. In this paper, the materials commonly used as hydrogel bioinks; the advanced technologies including inkjet bioprinting, extrusion bioprinting, laser-assisted bioprinting, stereolithography bioprinting, suspension bioprinting, and digital 3D bioprinting technologies; printing characterization including printability and fidelity; biological properties, and the application fields of bioprinting hydrogels in bone tissue engineering, skin tissue engineering, cardiovascular tissue engineering are reviewed, and the current problems and future directions are prospected.

Fabrication of Biodegradable and Biocompatible Functional Polymers for Anti-Infection and Augmenting Wound Repair

The problem of bacteria-induced infections threatens the lives of many patients. Meanwhile, the misuse of antibiotics has led to a significant increase in bacterial resistance. There are two main ways to alleviate the issue: one is to introduce antimicrobial agents to medical devices to get local drug releasing and alleviating systemic toxicity and resistance, and the other is to develop new antimicrobial methods to kill bacteria. New antimicrobial methods include cationic polymers, metal ions, hydrophobic structures to prevent bacterial adhesion, photothermal sterilization, new biocides, etc. Biodegradable biocompatible synthetic polymers have been widely used in the medical field. They are often used in tissue engineering scaffolds as well as wound dressings, where bacterial infections in these medical devices can be serious or even fatal. However, such materials usually do not have inherent antimicrobial properties. They can be used as carriers for drug delivery or compounded with other antimicrobial materials to achieve antimicrobial effects. This review focuses on the antimicrobial behavior, preparation methods, and biocompatibility testing of biodegradable biocompatible synthetic polymers. Degradable biocompatible natural polymers with antimicrobial properties are also briefly described. Finally, the medical applications of these polymeric materials are presented.

Advances and Innovations of 3D Bioprinting Skin

Three-dimensional (3D) bioprinted skin equivalents are highlighted as the new gold standard for alternative models to animal testing, as well as full-thickness wound healing. In this review, we focus on the advances and innovations of 3D bioprinting skin for skin regeneration, within the last five years. After a brief introduction to skin anatomy, 3D bioprinting methods and the remarkable features of recent studies are classified as advances in materials, structures, and functions. We will discuss several ways to improve the clinical potential of 3D bioprinted skin, with state-of-the-art printing technology and novel biomaterials. After the breakthrough in the bottleneck of the current studies, highly developed skin can be fabricated, comprising stratified epidermis, dermis, and hypodermis with blood vessels, nerves, muscles, and skin appendages. We hope that this review will be priming water for future research and clinical applications, that will guide us to break new ground for the next generation of skin regeneration.

3D printing of bone and cartilage with polymer materials

Damage and degeneration to bone and articular cartilage are the leading causes of musculoskeletal disability. Commonly used clinical and surgical methods include autologous/allogeneic bone and cartilage transplantation, vascularized bone transplantation, autologous chondrocyte implantation, mosaicplasty, and joint replacement. 3D bio printing technology to construct implants by layer-by-layer printing of biological materials, living cells, and other biologically active substances in vitro, which is expected to replace the repair mentioned above methods. Researchers use cells and biomedical materials as discrete materials. 3D bio printing has largely solved the problem of insufficient organ donors with the ability to prepare different organs and tissue structures. This paper mainly discusses the application of polymer materials, bio printing cell selection, and its application in bone and cartilage repair.

Modulation of bioactive calcium phosphate micro/nanoparticle size and shape during in situ synthesis of photo-crosslinkable gelatin methacryloyl based nanocomposite hydrogels for 3D bioprinting and tissue engineering

Background

The gelatin-methacryloyl (GelMA) polymer suffers shape fidelity and structural stability issues during 3D bioprinting for bone tissue engineering while homogeneous mixing of reinforcing nanoparticles is always under debate.

Method

In this study, amorphous calcium phosphates micro/nanoparticles (CNP) incorporated GelMA is synthesized by developing specific sites for gelatin structure-based nucleation and stabilization in a one-pot processing. The process ensures homogenous distribution of CNPs while different concentrations of gelatin control their growth and morphologies. After micro/nanoparticles synthesis in the gelatin matrix, methacrylation is carried out to prepare homogeneously distributed CNP-reinforced gelatin methacryloyl (CNP GelMA) polymer. After synthesis of CNP and CNP GelMA gel, the properties of photo-crosslinked 3D bioprinting scaffolds were compared with those of the conventionally fabricated ones.

Results

The shape (spindle to spherical) and size (1.753 μm to 296 nm) of the micro/nanoparticles in the GelMA matrix are modulated by adjusting the gelatin concentrations during the synthesis. UV cross-linked CNP GelMA (using Irgacure 2955) has significantly improved mechanical (three times compressive strength), 3D printability (160 layers, 2 cm self-standing 3D printed height) and biological properties (cell supportiveness with osteogenic differentiation). The photo-crosslinking becomes faster due to better methacrylation, facilitating continuous 3D bioprinting or printing.

Conclusion

For 3D bioprinting using GelMA like photo cross-linkable polymers, where structural stability and homogeneous control of nanoparticles are major concerns, CNP GelMA is beneficial for even bone tissue regeneration within short period.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40824-022-00301-6.

A Review on Antibacterial Biomaterials in Biomedical Applications: From Materials Perspective to Bioinks Design

In tissue engineering, three-dimensional (3D) printing is an emerging approach to producing functioning tissue constructs to repair wounds and repair or replace sick tissue/organs. It allows for precise control of materials and other components in the tissue constructs in an automated way, potentially permitting great throughput production. An ink made using one or multiple biomaterials can be 3D printed into tissue constructs by the printing process; though promising in tissue engineering, the printed constructs have also been reported to have the ability to lead to the emergence of unforeseen illnesses and failure due to biomaterial-related infections. Numerous approaches and/or strategies have been developed to combat biomaterial-related infections, and among them, natural biomaterials, surface treatment of biomaterials, and incorporating inorganic agents have been widely employed for the construct fabrication by 3D printing. Despite various attempts to synthesize and/or optimize the inks for 3D printing, the incidence of infection in the implanted tissue constructs remains one of the most significant issues. For the first time, here we present an overview of inks with antibacterial properties for 3D printing, focusing on the principles and strategies to accomplish biomaterials with anti-infective properties, and the synthesis of metallic ion-containing ink, chitosan-containing inks, and other antibacterial inks. Related discussions regarding the mechanics of biofilm formation and antibacterial performance are also presented, along with future perspectives of the importance of developing printable inks.

Robust Silk Protein Hydrogels Made by a Facile One-Step Method and Their Multiple Applications

Silk fibroin is a natural polymer that has various material forms and wide applications. Hydrogel is one of the most attractive silk materials because of its hydrophilicity, biocompatibility, and flexibility. However, its applications are still quite limited because they have a complicated preparation process and/or low mechanical strength. Herein, a simple way to prepare tough silk fibroin hydrogels via a solvent-exchange method is introduced. The degummed silk fiber was directly dissolved in a calcium chloride/formic acid solution and then water was used to replace the solvent. The silk fibroin hydrogel that was obtained using this facile method exhibited even better mechanical properties than most silk fibroin hydrogels that have been reported in the literature. Also, the silk fibroin hydrogel maintained biocompatibility that was as good as that prepared via other methods. Finally, the possibility of using this regenerated silk fibroin hydrogel as a multi-functional platform (such as a catalyst carrier, photothermal agent, and underwater adhesive) has been discussed. Therefore, such a natural, sustainable, robust, and good biocompatible silk fibroin hydrogel that is prepared by an improved method may have great potential for further applications.

Physical Modification of Hybrid Hydrogels to Fabricate Full-Scale Construct Using Three-Dimensional Bio-Printing Process

Bioprinting for regenerative medicine has been gaining a lot of popularity in today's world. Despite being one of the rigorously studied fields, there are still several challenges yet to be solved. Geometric fidelity and mechanical complexities stand as roadblocks when it comes to the printability of the customized constructs. Exploring the rheological properties of the compositions helps us understand the physical and mechanical properties of the biomaterials which are closely tied to the printability of the filament and eventually, geometric fidelity of the constructs. To ensure the structural integrity of the constructs, viscosity enhancers such as carboxymethyl cellulose (CMC) and crosslinkers like CaCl₂ and CaSO₄ were used. These crosslinkers can be used before (precrosslinking) and after (postcrosslinking) the extrusion of considered compositions to investigate and compare the outcome. To do this, mixtures of CMC (viscosity enhancer), Alginate, and CaCl₂ and CaSO₄ (crosslinkers) were prepared at various concentrations maintaining minimum solid content (≤8%). Each composition was subjected to a set of rheological tests like flow curve for shear thinning behavior, three points thixotropic for recovery rate, and amplitude test for gelation point. Various geometric fidelity identification tests were conducted and correlated with their physical properties. Some compositions were used to fabricate large-scale constructs (in cm-scale) to demonstrate their capability. This research is a thorough investigation of compositions when they are introduced to crosslinkers and viscosity enhancers which can be crucial for the 3D printing world.

The 3D Bioprinted Scaffolds for Wound Healing

Skin tissue engineering and regeneration aim at repairing defective skin injuries and progress in wound healing. Until now, even though several developments are made in this field, it is still challenging to face the complexity of the tissue with current methods of fabrication. In this review, short, state-of-the-art on developments made in skin tissue engineering using 3D bioprinting as a new tool are described. The current bioprinting methods and a summary of bioink formulations, parameters, and properties are discussed. Finally, a representative number of examples and advances made in the field together with limitations and future needs are provided.

Advancement of Gallium and Gallium-Based Compounds as Antimicrobial Agents

With the abuse and misuse of antibiotics, antimicrobial resistance has become a challenging issue in the medical system. Iatrogenic and non-iatrogenic infections caused by multidrug-resistant (MDR) pathogens pose serious threats to global human life and health because the efficacy of traditional antibiotics has been greatly reduced and the resulting socio-economic burden has increased. It is important to find and develop non-antibiotic-dependent antibacterial strategies because the development of new antibiotics can hardly keep pace with the emergence of resistant bacteria. Gallium (III) is a multi-target antibacterial agent that has an excellent antibacterial activity, especially against MDR pathogens; thus, a gallium (III)-based treatment is expected to become a new antibacterial strategy. However, some limitations of gallium ions as antimicrobials still exist, including low bioavailability and explosive release. In recent years, with the development of nanomaterials and clathrates, the progress of manufacturing technology, and the emergence of synergistic antibacterial strategies, the antibacterial activities of gallium have greatly improved, and the scope of application in medical systems has expanded. This review summarizes the advancement of current optimization for these key factors. This review will enrich the knowledge about the efficiency and mechanism of various gallium-based antibacterial agents and provide strategies for the improvement of the antibacterial activity of gallium-based compounds.

Bacterial Succinoglycans: Structure, Physical Properties, and Applications

Succinoglycan is a type of bacterial anionic exopolysaccharide produced from Rhizobium, Agrobacterium, and other soil bacteria. The exact structure of succinoglycan depends in part on the type of bacterial strain, and the final production yield also depends on the medium composition, culture conditions, and genotype of each strain. Various bacterial polysaccharides, such as cellulose, xanthan, gellan, and pullulan, that can be mass-produced for biotechnology are being actively studied. However, in the case of succinoglycan, a bacterial polysaccharide, relatively few reports on production strains or chemical and structural characteristics have been published. Physical properties of succinoglycan, a non-Newtonian and shear thinning fluid, have been reported according to the ratio of substituents (pyruvyl, succinyl, acetyl group), molecular weight (M_w), and measurement conditions (concentration, temperature, pH, metal ion, etc.). Due to its unique rheological properties, succinoglycan has been mainly used as a thickener and emulsifier in the cosmetic and food industries. However, in recent reports, succinoglycan and its derivatives have been used as functional biomaterials, e.g., in stimuli-responsive drug delivery systems, therapeutics, and cell culture scaffolds. This suggests a new and expanded application of succinoglycan as promising biomaterials in biomedical fields, such as tissue engineering, regenerative medicine, and pharmaceuticals using drug delivery.

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.

An antibacterial ε-poly-L-lysine-derived bioink for 3D bioprinting applications

Limited bioinks have hindered applying 3D bioprinting to tissue engineering, and bacterial infection is a serious threat to these applications. Aiming to solve this problem, a novel ε-poly-L-lysine (EPL) derived...

3D Bio-Printability of Hybrid Pre-Crosslinked Hydrogels

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

An Overview of Cellulose Derivatives-Based Dressings for Wound-Healing Management

Presently, notwithstanding the progress regarding wound-healing management, the treatment of the majority of skin lesions still represents a serious challenge for biomedical and pharmaceutical industries. Thus, the attention of the researchers has turned to the development of novel materials based on cellulose derivatives. Cellulose derivatives are semi-synthetic biopolymers, which exhibit high solubility in water and represent an advantageous alternative to water-insoluble cellulose. These biopolymers possess excellent properties, such as biocompatibility, biodegradability, sustainability, non-toxicity, non-immunogenicity, thermo-gelling behavior, mechanical strength, abundance, low costs, antibacterial effect, and high hydrophilicity. They have an efficient ability to absorb and retain a large quantity of wound exudates in the interstitial sites of their networks and can maintain optimal local moisture. Cellulose derivatives also represent a proper scaffold to incorporate various bioactive agents with beneficial therapeutic effects on skin tissue restoration. Due to these suitable and versatile characteristics, cellulose derivatives are attractive and captivating materials for wound-healing applications. This review presents an extensive overview of recent research regarding promising cellulose derivatives-based materials for the development of multiple biomedical and pharmaceutical applications, such as wound dressings, drug delivery devices, and tissue engineering.

Fabricating scalable, personalized wound dressings with customizable drug loadings via 3D printing

In recent times, 3D printing has been gaining traction as a fabrication platform for customizable drug dosages as a form of personalized medicine. While this has been recently demonstrated as oral dosages, there is potential to provide the same customizability and personalization as topical applications for wound healing. In this paper, the application of 3D printing to fabricate hydrogel wound dressings with customizable architectures and drug dosages was investigated. Chitosan methacrylate was synthesized and mixed with Lidocaine Hydrochloride and Levofloxacin respectively along with a photoinitiator before being used to print wound dressings of various designs. These designs were then investigated for their effect on drug release rates and profiles. Our results show the ability of 3D printing to customize drug dosages and drug release rates through co-loading different drugs at various positions and varying the thickness of drug-free layers over drug-loaded layers in the wound dressing respectively. Two scale-up approaches were also investigated for their effects on drug release rates from the wound dressing. The influence that each wound dressing design has on the release profile of drugs was also shown by fitting them with drug release kinetic models. This study thus shows the feasibility of utilizing 3D printing to fabricate wound dressings with customizable shapes, drug dosage and drug release rates that can be tuned according to the patient's requirements.

Converging 2D Nanomaterials and 3D Bioprinting Technology: State-of-the-Art, Challenges, and Potential Outlook in Biomedical Applications

The development of next-generation of bioinks aims to fabricate anatomical size 3D scaffold with high printability and biocompatibility. Along with the progress in 3D bioprinting, 2D nanomaterials (2D NMs) prove to be emerging frontiers in the development of advanced materials owing to their extraordinary properties. Harnessing the properties of 2D NMs in 3D bioprinting technologies can revolutionize the development of bioinks by endowing new functionalities to the current bioinks. First the main contributions of 2D NMS in 3D bioprinting technologies are categorized here into six main classes: 1) reinforcement effect, 2) delivery of bioactive molecules, 3) improved electrical conductivity, 4) enhanced tissue formation, 5) photothermal effect, 6) and stronger antibacterial properties. Next, the recent advances in the use of each certain 2D NMs (1) graphene, 2) nanosilicate, 3) black phosphorus, 4) MXene, 5) transition metal dichalcogenides, 6) hexagonal boron nitride, and 7) metal-organic frameworks) in 3D bioprinting technology are critically summarized and evaluated thoroughly. Third, the role of physicochemical properties of 2D NMSs on their cytotoxicity is uncovered, with several representative examples of each studied 2D NMs. Finally, current challenges, opportunities, and outlook for the development of nanocomposite bioinks are discussed thoroughly.

Biodegradable and biocompatible graphene-based scaffolds for functional neural tissue engineering: A strategy approach using dental pulp stem cells and biomaterials

Neural tissue engineering aims to restore the function of nervous system tissues using biocompatible cell-seeded scaffolds. Graphene-based scaffolds combined with stem cells deserve special attention to enhance tissue regeneration in a controlled manner. However, it is believed that minor changes in scaffold biomaterial composition, internal porous structure, and physicochemical properties can impact cellular growth and adhesion. The current work aims to investigate in vitro biological effects of three-dimensional (3D) graphene oxide (GO)/sodium alginate (GOSA) and reduced GOSA (RGOSA) scaffolds on dental pulp stem cells (DPSCs) in terms of cell viability and cytotoxicity. Herein, the effects of the 3D scaffolds, coating conditions, and serum supplementation on DPSCs functions are explored extensively. Biodegradation analysis revealed that the addition of GO enhanced the degradation rate of composite scaffolds. Compared to the 2D surface, the cell viability of 3D scaffolds was higher (p < 0.0001), highlighting the optimal initial cell adhesion to the scaffold surface and cell migration through pores. Moreover, the cytotoxicity study indicated that the incorporation of graphene supported higher DPSCs viability. It is also shown that when the mean pore size of the scaffold increases, DPSCs activity decreases. In terms of coating conditions, poly- l-lysine was the most robust coating reagent that improved cell-scaffold adherence and DPSCs metabolism activity. The cytotoxicity of GO-based scaffolds showed that DPSCs can be seeded in serum-free media without cytotoxic effects. This is critical for human translation as cellular transplants are typically serum-free. These findings suggest that proposed 3D GO-based scaffolds have favorable effects on the biological responses of DPSCs.

Simple and Fast One-Pot Cellulose Gel Preparation in Aqueous Pyrrolidinium Hydroxide Solution-Cellulose Solvent and Antibacterial Agent

Cellulose is the main component of biomass and is the most abundant biopolymer on earth; it is a non-toxic, low-cost material that is biocompatible and biodegradable. Cellulose gels are receiving increasing attention as medical products, e.g., as wound dressings. However, the preparation of cellulose hydrogels employing unmodified cellulose is scarcely reported because of the cumbersome dissolution of cellulose. In previous studies, we developed the new promising cellulose solvent N-butyl-N-methylpyrrolidinium hydroxide in an aqueous solution, which can dissolve up to 20 wt% cellulose within a short time at room temperature. In this study, we employed this solvent system and investigated the gelation behavior of cellulose after crosslinker addition. The swelling behavior in water (swelling ratio, water uptake), the mechanical properties under compression, and the antibacterial activity against Escherichia coli and Bacillus subtilis were investigated. We have developed a simple and fast one-pot method for the preparation of cellulose gels, in which aqueous pyrrolidinium hydroxide solution was acting as the solvent and as an antibacterial reagent. The pyrrolidinium hydroxide content of the gels was controlled by adjustment of the water volume employed for swelling. Simple recovery of the solvent system was also possible, which makes this preparation method environmentally benign.

Collagen-Alginate Composite Hydrogel: Application in Tissue Engineering and Biomedical Sciences

Alginate (ALG), a polysaccharide derived from brown seaweed, has been extensively investigated as a biomaterial not only in tissue engineering but also for numerous biomedical sciences owing to its wide availability, good compatibility, weak cytotoxicity, low cost, and ease of gelation. Nevertheless, alginate lacks cell-binding sites, limiting long-term cell survival and viability in 3D culture. Collagen (Col), a major component protein found in the extracellular matrix (ECM), exhibits excellent biocompatibility and weak immunogenicity. Furthermore, collagen contains cell-binding motifs, which facilitate cell attachment, interaction, and spreading, consequently maintaining cell viability and promoting cell proliferation. Recently, there has been a growing body of investigations into collagen-based hydrogel trying to overcome the poor mechanical properties of collagen. In particular, collagen-alginate composite (CAC) hydrogel has attracted much attention due to its excellent biocompatibility, gelling under mild conditions, low cytotoxicity, controllable mechanic properties, wider availability as well as ease of incorporation of other biomaterials and bioactive agents. This review aims to provide an overview of the properties of alginate and collagen. Moreover, the application of CAC hydrogel in tissue engineering and biomedical sciences is also discussed.