Alginate based hydrogel inks for 3D bioprinting of engineered orthopedic tissues

Fabrication and Biomedical Application of Alginate Composite Hydrogels in Bone Tissue Engineering: A Review

Nowadays, as a result of the frequent occurrence of accidental injuries and traumas such as bone damage, the number of people causing bone injuries or fractures is increasing around the world. The design and fabrication of ideal bone tissue engineering (BTE) materials have become a research hotspot in the scientific community, and thus provide a novel path for the treatment of bone diseases. Among the materials used to construct scaffolds in BTE, including metals, bioceramics, bioglasses, biomacromolecules, synthetic organic polymers, etc., natural biopolymers have more advantages against them because they can interact with cells well, causing natural polymers to be widely studied and applied in the field of BTE. In particular, alginate has the advantages of excellent biocompatibility, good biodegradability, non-immunogenicity, non-toxicity, wide sources, low price, and easy gelation, enabling itself to be widely used as a biomaterial. However, pure alginate hydrogel as a BTE scaffold material still has many shortcomings, such as insufficient mechanical properties, easy disintegration of materials in physiological environments, and lack of cell-specific recognition sites, which severely limits its clinical application in BTE. In order to overcome the defects of single alginate hydrogels, researchers prepared alginate composite hydrogels by adding one or more materials to the alginate matrix in a certain proportion to improve their bioapplicability. For this reason, this review will introduce in detail the methods for constructing alginate composite hydrogels, including alginate/polymer composite hydrogels, alginate/bioprotein or polypeptide composite hydrogels, alginate/bioceramic composite hydrogels, alginate/bioceramic composite hydrogels, and alginate/nanoclay composite hydrogels, as well as their biological application trends in BTE scaffold materials, and look forward to their future research direction. These alginate composite hydrogel scaffolds exhibit both unexceptionable mechanical and biochemical properties, which exhibit their high application value in bone tissue repair and regeneration, thus providing a theoretical basis for the development and sustainable application of alginate-based functional biomedical materials.

Current and Future Perspectives of Bioactive Glasses as Injectable Material

This review covers recent compositions of bioactive glass, with a specific emphasis on both inorganic and organic materials commonly utilized as matrices for injectable materials. The major objective is to highlight the predominant bioactive glass formulations and their clinical applications in the biomedical field. Previous studies have highlighted the growing interest among researchers in bioactive glasses, acknowledging their potential to yield promising outcomes in this field. As a result of this increased interest, investigations into bioactive glass have prompted the creation of composite materials and, notably, the development of injectable composites as a minimally invasive method for administering the material within the human body. Injectable materials have emerged as a promising avenue to mitigate various challenges. They offer several advantages, including minimizing invasive surgical procedures, reducing patient discomfort, lowering the risk of postoperative infection and decreasing treatment expenses. Additionally, injectable materials facilitate uniform distribution, allowing for the filling of defects of any shape.

Hydrogel-Based 3D Bioprinting Technology for Articular Cartilage Regenerative Engineering

Articular cartilage is an avascular tissue with very limited capacity of self-regeneration. Trauma or injury-related defects, inflammation, or aging in articular cartilage can induce progressive degenerative joint diseases such as osteoarthritis. There are significant clinical demands for the development of effective therapeutic approaches to promote articular cartilage repair or regeneration. The current treatment modalities used for the repair of cartilage lesions mainly include cell-based therapy, small molecules, surgical approaches, and tissue engineering. However, these approaches remain unsatisfactory. With the advent of three-dimensional (3D) bioprinting technology, tissue engineering provides an opportunity to repair articular cartilage defects or degeneration through the construction of organized, living structures composed of biomaterials, chondrogenic cells, and bioactive factors. The bioprinted cartilage-like structures can mimic native articular cartilage, as opposed to traditional approaches, by allowing excellent control of chondrogenic cell distribution and the modulation of biomechanical and biochemical properties with high precision. This review focuses on various hydrogels, including natural and synthetic hydrogels, and their current developments as bioinks in 3D bioprinting for cartilage tissue engineering. In addition, the challenges and prospects of these hydrogels in cartilage tissue engineering applications are also discussed.

Nanostructured Biopolymer-Based Constructs for Cartilage Regeneration: Fabrication Techniques and Perspectives

The essential functions of cartilage, such as shock absorption and resilience, are hindered by its limited regenerative capacity. Although current therapies alleviate symptoms, novel strategies for cartilage regeneration are desperately needed. Recent developments in three-dimensional (3D) constructs aim to address this challenge by mimicking the intrinsic characteristics of native cartilage using biocompatible materials, with a significant emphasis on both functionality and stability. Through fabrication methods such as 3D printing and electrospinning, researchers are making progress in cartilage regeneration; nevertheless, it is still very difficult to translate these advances into clinical practice. The review emphasizes the importance of integrating various fabrication techniques to create stable 3D constructs. Meticulous design and material selection are required to achieve seamless cartilage integration and durability. The review outlines the need to address these challenges and focuses on the latest developments in the production of hybrid 3D constructs based on biodegradable and biocompatible polymers. Furthermore, the review acknowledges the limitations of current research and provides perspectives on potential avenues for effectively regenerating cartilage defects in the future.

Tailoring Network Topology in Mechanically Robust Hydrogels for 3D Printing and Injection

Tissue engineering and regenerative medicine are confronted with a persistent challenge: the urgent demand for robust, load-bearing, and biocompatible scaffolds that can effectively endure substantial deformation. Given that inadequate mechanical performance is typically rooted in structural deficiencies─specifically, the absence of energy dissipation mechanisms and network uniformity─a crucial step toward solving this problem is generating synthetic approaches that enable exquisite control over network architecture. This work systematically explores structure-property relationships in poly(ethylene glycol)-based hydrogels constructed utilizing thiol-yne chemistry. We systematically vary polymer concentration, constituent molar mass, and cross-linking protocols to understand the impact of architecture on hydrogel mechanical properties. The network architecture was resolved within the molecular model of Rubinstein-Panyukov to obtain the densities of chemical cross-links and entanglements. We employed both nucleophilic and radical pathways, uncovering notable differences in mechanical response, which highlight a remarkable degree of versatility achievable by tuning readily accessible parameters. Our approach yielded hydrogels with good cell viability and remarkably robust tensile and compression profiles. Finally, the hydrogels are shown to be amenable to advanced processing techniques by demonstrating injection- and extrusion-based 3D printing. Tuning the mechanism and network regularity during the cell-compatible formation of hydrogels is an emerging strategy to control the properties and processability of hydrogel biomaterials by making simple and rational design choices.

A Remarkable Impact of pH on the Thermo-Responsive Properties of Alginate-Based Composite Hydrogels Incorporating P2VP-PEO Micellar Nanoparticles

A heterograft copolymer with an alginate backbone, hetero-grafted by polymer pendant chains displaying different lower critical solution temperatures (LCSTs), combined with a pH-responsive poly(2-vinyl pyridine)-b-poly(ethylene oxide) (P2VP-b-PEO) diblock copolymer forming micellar nanoparticles, was investigated in aqueous media at various pHs. Due to its thermo-responsive side chains, the copolymer forms hydrogels with a thermo-induced sol-gel transition, above a critical temperature, Tgel (thermo-thickening). However, by lowering the pH of the medium in an acidic regime, a remarkable increase in the elasticity of the formulation was observed. This effect was more pronounced in low temperatures (below Tgel), suggesting secondary physical crosslinking, which induces significant changes in the hydrogel thermo-responsiveness, transforming the sol-gel transition to soft gel-strong gel. Moreover, the onset of thermo-thickening shifted to lower temperatures followed by the broadening of the transition zone, implying intermolecular interactions between the uncharged alginate backbone with the PNIPAM side chains, likely through H-bonding. The shear-thinning behavior of the soft gel in low temperatures provides injectability, which allows potential applications for 3D printing. Furthermore, the heterograft copolymer/nanoparticles composite hydrogel, encapsulating a model hydrophobic drug in the hydrophobic cores of the nanoparticles, was evaluated as a pH-responsive drug delivery system. The presented tunable drug delivery system might be useful for biomedical potential applications.

Nicotinamide mononucleotide based hyaluronic acid methacryloyl hybrid hydrogel regulating stem cells fate for bone regeneration via SIRT1/RUNX2 signaling

Efficient bone reconstruction, especially of the critical size after bone damage, remains a challenge in the clinic. Bone marrow mesenchymal stem cell (BMSC) osteogenic differentiation is considered as a promising strategy for bone repair. Nicotinamide adenine dinucleotide (NAD+) regulating BMSC fate and cellular function enhance osteogenesis, but is hardly delivered and lack of targeting. Herein, a novel and biocompatible scaffold was fabricated to locally deliver a precursor of NAD+, nicotinamide mononucleotide (NMN) to the bone defect site, and its bone repair capability and healing mechanism were clarified. NMN-based hyaluronic acid methacryloyl hybrid hydrogel scaffold (denoted as NMN/HAMA) was prepared via photopolymerization. In vitro RT-qPCR analysis, western blotting, Elisa and alizarin red S staining assays demonstrated that the NMN/HAMA hybrid hydrogel regulated BMSCs cellular function in favour of osteogenic differentiation and mineralization by upregulating the mRNA and proteins expression of the osteogenic genes type I pro-collagen (Col-1), bone morphogenic protein 4 (BMP4), and runt-related transcription factor 2 (RUNX2) via the SIRT1 pathway. Implantation of such hybrid hydrogels significantly enhanced bone regeneration in rodent critical calvarial defect models. Furthermore, restoration of the bone defect with NMN administration was inhibited in Prx1 Cre+; SIRT1flox/flox mice, confirming that the NMN/HAMA hybrid hydrogel scaffold promoted bone regeneration via the SIRT1-RUNX2 pathway. These results imply that NMN-based scaffold may be a promising and economic strategy for the treatment of bone defects.

Three-Dimensional Extrusion Printed Urinary Specific Grafts: Mechanistic Insights into Buildability and Biophysical Properties

The compositional formulations and the optimization of process parameters to fabricate hydrogel scaffolds with urological tissue-mimicking biophysical properties are not yet extensively explored, including a comprehensive assessment of a spectrum of properties, such as mechanical strength, viscoelasticity, antimicrobial property, and cytocompatibility. While addressing this aspect, the present work provides mechanistic insights into process science, to produce shape-fidelity compliant alginate-based biomaterial ink blended with gelatin and synthetic nanocellulose. The composition-dependent pseudoplasticity, viscoelasticity, thixotropy, and gel stability over a longer duration in physiological context have been rationalized in terms of intermolecular hydrogen bonding interactions among the biomaterial ink constituents. By varying the hybrid hydrogel ink composition within a narrow compositional window, the resulting hydrogel closely mimics the natural urological tissue-like properties, including tensile stretchability, compressive strength, and biophysical properties. Based on the printability assessment using a critical analysis of gel strength, we have established the buildability of the acellular hydrogel ink and have been successful in fabricating shape-fidelity compliant urological patches or hollow cylindrical grafts using 3D extrusion printing. Importantly, the new hydrogel formulations with good hydrophilicity, support fibroblast cell proliferation and inhibit the growth of Gram-negative E. coli bacteria. These attributes were rationalized in terms of nanocellulose-induced physicochemical changes on the scaffold surface. Taken together, the present study uncovers the process-science-based understanding of the 3D extrudability of the newly formulated alginate-gelatin-nanocellulose-based hydrogels with urological tissue-specific biophysical, cytocompatibility, and antibacterial properties.

Enhancing the Properties of Self-Healing Gelatin Alginate Hydrogels by Hofmeister Mediated Electrostatic Effect

The cross-linker-free hydrogels have gained attention due to their lack of need for chemically modified polymers, resulting in better biocompatibility. The hydrogel properties can be enhanced by altering physical forces such as electrostatics and H-bonds. Tuning the physical interactions between polymers, salts, and plasticisers can unlock new horizons in material properties. This article examines four different salts and mixtures to determine their impact on gelatin-alginate biomaterial design. Drug release, swelling, and rheological properties are represented using a 3-D plot, and optimum samples are identified. It is concluded that kosmotropes yield better release and swelling results than chaotropes. The physical interactions of these salts with polymers are explained using DLS and FTIR/ATR studies, and these findings are corroborated with release, swelling, and rheological analyses. Another aspect of the biomaterial, self-healing property, is also considered. A 3-D plot is prepared using release kinetics, gel strength, and recovery percentage (three important factors for self-healing hydrogels). Chaotropes are identified as better candidates for self-healing behaviour. However, when considering gel strength, release, and self-healing, kosmotropes are favourable. Hence, different salts can be selected based on the desired application for hydrogels. It is also concluded that electrostatic forces hinder the formation of H-bonds between polymer chains.

A Self-Adaptive Biomimetic Periosteum Employing Nitric Oxide Release for Augmenting Angiogenesis in Bone Defect Regeneration

The periosteum plays a vital role in the regeneration of critical-size bone defects and highly comminuted fractures, promoting the differentiation of osteoblasts, accelerating the reconstruction of the vascular network, and guiding bone tissue regeneration. However, the materials loaded with exogenous growth factors are limited by the release and activity of the elements. Therefore, the material structure must be carefully designed for the periosteal function. Here, a self-adaptive biomimetic periosteum strategy is proposed, which is a novel interpenetrating double network hydrogel consisting of diselenide-containing gelatin and calcium alginate (modified natural collagen and polysaccharide) to enhance the stability, anti-swelling, and delayed degradation of the hydrogel. The diselenide bond continuously releases nitric oxide (NO) by metabolizing endogenous nitrosated thiols (RSNO), activates the nitric oxide-cycle guanosine monophosphate (NO-cGMP) signal pathway, coordinates the coupling effect of angiogenesis and osteogenesis, and accelerates the repair of bone defects. This self-adaptive biomimetic periosteum with the interpenetrating double network structure formed by the diselenide-containing gelatin and calcium alginate has been proven to be safe and effective in repairing critical-size bone defects and is expected to provide a promising strategy for solving clinical problems.

Recent advances in biopolymer-based hydrogels and their potential biomedical applications

Hydrogels are three-dimensional networks of polymer chains containing large amounts of water in their structure. Hydrogels have received significant attention in biomedical applications owing to their attractive physicochemical properties, including flexibility, softness, biodegradability, and biocompatibility. Different natural and synthetic polymers have been intensely explored in developing hydrogels for the desired applications. Biopolymers-based hydrogels have advantages over synthetic polymers regarding improved cellular activity and weak immune response. These properties can be further improved by grafting with other polymers or adding nanomaterials, and they structurally mimic the living tissue environments, which opens their broad applicability. The hydrogels can be physically or chemically cross-linked depending on the structure. The use of different biopolymers-based hydrogels in biomedical applications has been reviewed and discussed earlier. However, no report is still available to comprehensively introduce the synthesis, advantages, disadvantages, and biomedical applications of biopolymers-based hydrogels from the material point of view. Herein, we systematically overview different synthesis methods of hydrogels and provide a holistic approach to biopolymers-based hydrogels for biomedical applications, especially in bone regeneration, wound healing, drug delivery, bioimaging, and therapy. The current challenges and prospects of biopolymers-based hydrogels are highlighted rationally, giving an insight into the progress of these hydrogels and their practical applications.

Harnessing the Interplay of Triple Cross-Linked Hydrogels toward Multiresponsive Alginate-Based Injectable Gels for 3D Printing Bioapplications

We report on a single chain polymer gelator comprising an alginate backbone double grafted with thermoresponsive P(NIPAM86-co-NtBAM14)-NH2 polymer grafts and 3-aminophenylboronic acid moieties. The resulting polymer forms robust polymer networks resulting from three cooperative cross-linking mechanisms: (i) the hydrophobic association of the T-responsive polymer grafts above 24 °C, (ii) the formation of boronate esters between the boronic acid and the diols of the alginate backbone at physiological pH, and (iii) the ionic interactions of the residual carboxylate moieties with Ca2+ ions. The resulting material showed excellent tunability of the mechanical properties driven by stimuli combinations such as temperature, pH, or the addition of glucose as a network disruptor covering a storage modulus range from ∼260 Pa up to ∼1390 Pa by selective stimuli combinations. Also, the material was found to be nontoxic and could form arbitrary structures via 3D printing that can undergo multi-stimuli-responsive erosion profiles.

Rheology in Product Development: An Insight into 3D Printing of Hydrogels and Aerogels

Rheological characterisation plays a crucial role in developing and optimising advanced materials in the form of hydrogels and aerogels, especially if 3D printing technologies are involved. Applications ranging from tissue engineering to environmental remediation require the fine-tuning of such properties. Nonetheless, their complex rheological behaviour presents unique challenges in additive manufacturing. This review outlines the vital rheological parameters that influence the printability of hydrogel and aerogel inks, emphasising the importance of viscosity, yield stress, and viscoelasticity. Furthermore, the article discusses the latest developments in rheological modifiers and printing techniques that enable precise control over material deposition and resolution in 3D printing. By understanding and manipulating the rheological properties of these materials, researchers can explore new possibilities for applications such as biomedicine or nanotechnology. An optimal 3D printing ink requires strong shear-thinning behaviour for smooth extrusion, forming continuous filaments. Favourable thixotropic properties aid viscosity recovery post-printing, and adequate yield stress and G' are crucial for structural integrity, preventing deformation or collapse in printed objects, and ensuring high-fidelity preservation of shapes. This insight into rheology provides tools for the future of material design and manufacturing in the rapidly evolving field of 3D printing of hydrogels and aerogels.

Synthesis of scale-like nano-hydroxyapatite and preparation of biodegradable woven scaffolds for bone tissue engineering

Bone tissue engineering scaffolds should have bone compatibility, biological activity, porosity, and degradability. In this study, flake-like hydroxyapatite was synthesized by hydrothermal method and mixed with sodium alginate to make a gel, which was injected into a hollow braid. Porous and degradable SA/n-Hap woven scaffolds were prepared by freeze-drying technology. The morphology of hydroxyapatite was characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), and x-ray diffraction. The scaffolds were characterized by an improved liquid replacement method, compression test, and degradation test. The results showed that the hydroxyapatite synthesized at 160 °C had a scaly morphology. The prepared scaffold had a pore size of 5-100 μm, a porosity of 60%-70%, and a swelling rate of more than 300%. After 21 d the degradation rate reached 5.54%, and a cell survival rate of 214.98%. In summary, it is feasible to prepare porous bone scaffolds for potential bone tissue engineering. This study shows the feasibility of applying textile structures to the field of tissue scaffolds and provides a new idea for the application structure of tissue engineering scaffolds.

Biomimetic Hydrogel Applications and Challenges in Bone, Cartilage, and Nerve Repair

Tissue engineering and regenerative medicine is a highly sought-after field for researchers aiming to compensate and repair defective tissues. However, the design and development of suitable scaffold materials with bioactivity for application in tissue repair and regeneration has been a great challenge. In recent years, biomimetic hydrogels have shown great possibilities for use in tissue engineering, where they can tune mechanical properties and biological properties through functional chemical modifications. Also, biomimetic hydrogels provide three-dimensional (3D) network spatial structures that can imitate normal tissue microenvironments and integrate cells, scaffolds, and bioactive substances for tissue repair and regeneration. Despite the growing interest in various hydrogels for biomedical use in previous decades, there are still many aspects of biomimetic hydrogels that need to be understood for biomedical and clinical trial applications. This review systematically describes the preparation of biomimetic hydrogels and their characteristics, and it details the use of biomimetic hydrogels in bone, cartilage, and nerve tissue repair. In addition, this review outlines the application of biomimetic hydrogels in bone, cartilage, and neural tissues regarding drug delivery. In particular, the advantages and shortcomings of biomimetic hydrogels in biomaterial tissue engineering are highlighted, and future research directions are proposed.

Recent Advances in Stem Cell Differentiation Control Using Drug Delivery Systems Based on Porous Functional Materials

The unique characteristics of stem cells, which include self-renewal and differentiation into specific cell types, have paved the way for the development of various biomedical applications such as stem cell therapy, disease modelling, and drug screening. The establishment of effective stem cell differentiation techniques is essential for the effective application of stem cells for various purposes. Ongoing research has sought to induce stem cell differentiation using diverse differentiation factors, including chemicals, proteins, and integrin expression. These differentiation factors play a pivotal role in a variety of applications. However, it is equally essential to acknowledge the potential hazards of uncontrolled differentiation. For example, uncontrolled differentiation can give rise to undesirable consequences, including cancerous mutations and stem cell death. Therefore, the development of innovative methods to control stem cell differentiation is crucial. In this review, we discuss recent research cases that have effectively utilised porous functional material-based drug delivery systems to regulate stem cell differentiation. Due to their unique substrate properties, drug delivery systems based on porous functional materials effectively induce stem cell differentiation through the steady release of differentiation factors. These ground-breaking techniques hold considerable promise for guiding and controlling the fate of stem cells for a wide range of biomedical applications, including stem cell therapy, disease modelling, and drug screening.

Cell unit-inspired natural nano-based biomaterials as versatile building blocks for bone/cartilage regeneration

The regeneration of weight-bearing bone defects and critical-sized cartilage defects remains a significant challenge. A wide range of nano-biomaterials are available for the treatment of bone/cartilage defects. However, their poor compatibility and biodegradability pose challenges to the practical applications of these nano-based biomaterials. Natural biomaterials inspired by the cell units (e.g., nucleic acids and proteins), have gained increasing attention in recent decades due to their versatile functionality, compatibility, biodegradability, and great potential for modification, combination, and hybridization. In the field of bone/cartilage regeneration, natural nano-based biomaterials have presented an unparalleled role in providing optimal cues and microenvironments for cell growth and differentiation. In this review, we systematically summarize the versatile building blocks inspired by the cell unit used as natural nano-based biomaterials in bone/cartilage regeneration, including nucleic acids, proteins, carbohydrates, lipids, and membranes. In addition, the opportunities and challenges of natural nano-based biomaterials for the future use of bone/cartilage regeneration are discussed.

Biodegradable redox sensitive chitosan based microgels for potential agriculture application

In this work, we report redox sensitive, 2,3-dihydroxybenzoic acid (DH) functionalized chitosan/stearic acid microgels (DH-ChSt MGs) for controlled delivery of insecticide and capturing of heavy metal ions. DH-ChSt MGs (≈146 nm) are prepared by disulfide crosslinking of SH functionalized chitosan and stearic acid rendering them biodegradable. DH-ChSt MGs exhibit high loading (≈8 %) and encapsulation (≈85 %) efficiency for imidacloprid insecticide, and offer its prolonged release (≈75 % after 133 h) under reducing conditions. Functionalization with DH provides enhanced foliar adhesion on pea leaves. DH-ChSt MGs also bind Fe³⁺ very efficiently due to the strong chelation of Fe³⁺ by DH, offering the opportunity of supplying Fe³⁺ nutrient for plant care. MTT assay results using different cells confirm that DH-ChSt MGs are nontoxic up to the experimental concentration of 120 μg/mL. Additionally, reduced DH-ChSt MGs having free thiol groups are also capable of binding heavy metal ions, thus presenting the reported formulation as a promising platform for agriculture application.

3D Printing of Extracellular Matrix-Based Multicomponent, All-Natural, Highly Elastic, and Functional Materials toward Vascular Tissue Engineering

3D printing offers an exciting opportunity to fabricate biological constructs with specific geometries, clinically relevant sizes, and functions for biomedical applications. However, successful application of 3D printing is limited by the narrow range of printable and bio-instructive materials. Multicomponent hydrogel bioinks present unique opportunities to create bio-instructive materials able to display high structural fidelity and fulfill the mechanical and functional requirements for in situ tissue engineering. Herein, 3D printable and perfusable multicomponent hydrogel constructs with high elasticity, self-recovery properties, excellent hydrodynamic performance, and improved bioactivity are reported. The materials' design strategy integrates fast gelation kinetics of sodium alginate (Alg), in situ crosslinking of tyramine-modified hyaluronic acid (HAT), and temperature-dependent self-assembly and biological functions of decellularized aorta (dAECM). Using extrusion-based printing approach, the capability to print the multicomponent hydrogel bioinks with high precision into a well-defined vascular constructs able to withstand flow and repetitive cyclic compressive loading, is demonstrated. Both in vitro and pre-clinical models are used to show the pro-angiogenic and anti-inflammatory properties of the multicomponent vascular constructs. This study presents a strategy to create new bioink whose functional properties are greater than the sum of their components and with potential applications in vascular tissue engineering and regenerative medicine.

A bioactive microparticle-loaded osteogenically enhanced bioprinted scaffold that permits sustained release of BMP-2

Extrusion-based bioprinting technology is widely used for tissue regeneration and reconstruction. However, the method that uses only hydrogel as the bioink base material exhibits limited biofunctional properties and needs improvement to achieve the desired tissue regeneration. In this study, we present a three-dimensionally printed bioactive microparticle-loaded scaffold for use in bone regeneration applications. The unique structure of the microparticles provided sustained release of growth factor for > 4 weeks without the use of toxic or harmful substances. Before and after printing, the optimal particle ratio in the bioink for cell viability demonstrated a survival rate of ≥ 85% over 7 days. Notably, osteogenic differentiation and mineralization-mediated by human periosteum-derived cells in scaffolds with bioactive microparticles-increased over a 2-week interval. Here, we present an alternative bioprinting strategy that uses the sustained release of bioactive microparticles to improve biofunctional properties in a manner that is acceptable for clinical bone regeneration applications.

Alginate: Microbial production, functionalization, and biomedical applications

Alginates are natural polysaccharides widely participating in food, pharmaceutical, and environmental applications due to their excellent gelling capacity. Their excellent biocompatibility and biodegradability further extend their application to biomedical fields. The low consistency in molecular weight and composition of algae-based alginates may limit their performance in advanced biomedical applications. It makes microbial alginate production more attractive due to its potential for customizing alginate molecules with stable characteristics. Production costs remain the primary factor limiting the commercialization of microbial alginates. However, carbon-rich wastes from sugar, dairy, and biodiesel industries may serve as potential substitutes for pure sugars for microbial alginate production to reduce substrate costs. Fermentation parameter control and genetic engineering strategies may further improve the production efficiency and customize the molecular composition of microbial alginates. To meet the specific needs of biomedical applications, alginates may need functionalization, such as functional group modifications and crosslinking treatments, to achieve enhanced mechanical properties and biochemical activities. The development of alginate-based composites incorporated with other polysaccharides, gelatin, and bioactive factors can integrate the advantages of each component to meet multiple requirements in wound healing, drug delivery, and tissue engineering applications. This review provided a comprehensive insight into the sustainable production of high-value microbial alginates. It also discussed recent advances in alginate modification strategies and alginate-based composites for representative biomedical applications.

Abundant tannic acid modified gelatin/sodium alginate biocomposite hydrogels with high toughness, antifreezing, antioxidant and antibacterial properties

The acidity of high tannic acid (TA) content solution can destroy the structure of protein, such as gelatin (G). This causes a big challenge to introduce abundant TA into the G-based hydrogels. Here, the G-based hydrogel system with abundant TA as hydrogen bonds provider was constructed by a "protective film" strategy. The protective film around the composite hydrogel was first formed by the chelation of sodium alginate (SA) and Ca2+. Subsequently, abundant TA and Ca2+ were successively introduced into the hydrogel system by immersing method. This strategy effectively protected the structure of the designed hydrogel. After treatment with 0.3 w/v TA and 0.06 w/v Ca2+ solutions, the tensile modulus, elongation at break and toughness of G/SA hydrogel increased about 4-, 2-, and 6-fold, respectively. Besides, G/SA-TA/Ca2+ hydrogels exhibited good water retention, anti-freezing, antioxidant, antibacterial properties and low hemolysis ratio. Cell experiments showed that G/SA-TA/Ca2+ hydrogels possessed good biocompatibility and could promote cell migration. Therefore, G/SA-TA/Ca2+ hydrogels are expected to be used in the field of biomedical engineering. The strategy proposed in this work also provides a new idea for improving the properties of other protein-based hydrogels.

Global hotspots and emerging trends in 3D bioprinting research

Three-dimensional (3D) bioprinting is an advanced tissue engineering technique that has received a lot of interest in the past years. We aimed to highlight the characteristics of articles on 3D bioprinting, especially in terms of research hotspots and focus. Publications related to 3D bioprinting from 2007 to 2022 were acquired from the Web of Science Core Collection database. We have used VOSviewer, CiteSpace, and R-bibliometrix to perform various analyses on 3,327 published articles. The number of annual publications is increasing globally, a trend expected to continue. The United States and China were the most productive countries with the closest cooperation and the most research and development investment funds in this field. Harvard Medical School and Tsinghua University are the top-ranked institutions in the United States and China, respectively. Dr. Anthony Atala and Dr. Ali Khademhosseini, the most productive researchers in 3D bioprinting, may provide cooperation opportunities for interested researchers. Tissue Engineering Part A contributed the largest publication number, while Frontiers in Bioengineering and Biotechnology was the most attractive journal with the most potential. As for the keywords in 3D bioprinting, Bio-ink, Hydrogels (especially GelMA and Gelatin), Scaffold (especially decellularized extracellular matrix), extrusion-based bioprinting, tissue engineering, and in vitro models (organoids particularly) are research hotspots analyzed in the current study. Specifically, the research topics "new bio-ink investigation," "modification of extrusion-based bioprinting for cell viability and vascularization," "application of 3D bioprinting in organoids and in vitro model" and "research in personalized and regenerative medicine" were predicted to be hotspots for future research.

A Critical Review on Classified Excipient Sodium-Alginate-Based Hydrogels: Modification, Characterization, and Application in Soft Tissue Engineering

Alginates are polysaccharides that are produced naturally and can be isolated from brown sea algae and bacteria. Sodium alginate (SA) is utilized extensively in the field of biological soft tissue repair and regeneration owing to its low cost, high biological compatibility, and quick and moderate crosslinking. In addition to their high printability, SA hydrogels have found growing popularity in tissue engineering, particularly due to the advent of 3D bioprinting. There is a developing curiosity in tissue engineering with SA-based composite hydrogels and their potential for further improvement in terms of material modification, the molding process, and their application. This has resulted in numerous productive outcomes. The use of 3D scaffolds for growing cells and tissues in tissue engineering and 3D cell culture is an innovative technique for developing in vitro culture models that mimic the in vivo environment. Especially compared to in vivo models, in vitro models were more ethical and cost-effective, and they stimulate tissue growth. This article discusses the use of sodium alginate (SA) in tissue engineering, focusing on SA modification techniques and providing a comparative examination of the properties of several SA-based hydrogels. This review also covers hydrogel preparation techniques, and a catalogue of patents covering different hydrogel formulations is also discussed. Finally, SA-based hydrogel applications and future research areas concerning SA-based hydrogels in tissue engineering were examined.

Alginate-Based Biomaterials in Tissue Engineering and Regenerative Medicine

Today, with the salient advancements of modern and smart technologies related to tissue engineering and regenerative medicine (TE-RM), the use of sustainable and biodegradable materials with biocompatibility and cost-effective advantages have been investigated more than before. Alginate as a naturally occurring anionic polymer can be obtained from brown seaweed to develop a wide variety of composites for TE, drug delivery, wound healing, and cancer therapy. This sustainable and renewable biomaterial displays several fascinating properties such as high biocompatibility, low toxicity, cost-effectiveness, and mild gelation by inserting divalent cations (e.g., Ca2+). In this context, challenges still exist in relation to the low solubility and high viscosity of high-molecular weight alginate, high density of intra- and inter-molecular hydrogen bonding, polyelectrolyte nature of the aqueous solution, and a lack of suitable organic solvents. Herein, TE-RM applications of alginate-based materials are deliberated, focusing on current trends, important challenges, and future prospects.

Biodegradable dual stimuli responsive alginate based microgels for controlled agrochemicals release and soil remediation

To meet the growing food demand of increasing world population while reducing the harmful environmental effects of agrochemicals, development of smart nanoformulation is of prime importance. Herein, dual stimuli responsive alginate based microgels (OAlgDP MGs) (≈160 nm) are developed for controlled release of agrochemicals and soil remediation. These microgels are prepared using octyl amine functionalized alginate which is crosslinked by 3, 3'-dithiopropionohydrazide crosslinker providing both hydrazone and disulfide bonds in microgels network. OAlgDP MGs are further loaded with hydrophobic diuron herbicide displaying ≈85 % encapsulation efficiency. Sustained release of diuron is obtained in 2 mM GSH (≈100 % after 380 h) and at pH 5 (≈72 % after 240 h). Furthermore, OAlgDP MGs are nontoxic up to 150 μg/mL against HEK293T cells while their reduced form is capable of capturing the heavy metal ions (Cu²⁺ and Hg²⁺) showing the potential of the developed system for moving toward sustainable agriculture.

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.

Redox responsive poly(allylamine)/eudragit S-100 nanoparticles for dual drug delivery in colorectal cancer

Herein, we report redox responsive, colon cancer targeting poly(allylamine) (PA)/eudragit S-100 (EU) nanoparticles (PAEU NPs) (≈59 nm). These disulfide crosslinked PAEU NPs are developed via air oxidation of thiolated PA and thiolated EU, eliminating the need of any external crosslinking agent for dual drug delivery. PAEU NPs can effectively encapsulate both hydrophilic doxorubicin (DOX) and hydrophobic curcumin (Cur) drug with ≈85 % and ≈97 % encapsulation efficiency respectively. Here, the combination of drugs having different anticancer mechanism offers the possibility of developing nanosystem with enhanced anticancer efficacy. The developed PAEU NPs show good colloidal stability and low drug release under physiological conditions, while high DOX (≈98 %) and Cur (≈93 %) release is observed in reducing environment (10 mM GSH). Further, DOX and Cur loaded PAEU NPs exhibit higher cancer cell killing efficiency as compared to individual free drugs. In vivo biodistribution studies with Balb/C mice display the retention of PAEU NPs in the colon region up to 24 h presenting the developed approach as an efficient way for colorectal cancer therapy.