Alginate and its application to tissue engineering

Three-Dimensional Culture for In Vitro Folliculogenesis in the Aspect of Methods and Materials

In vitro ovarian follicle culture is a reproduction technique used to obtain fertilizable oocytes, for overcoming fertility issues due to premature ovarian failure. This requires the establishment of an in vitro culture model that is capable of better simulating the in vivo ovarian growth environment. Two-dimensional (2D) culture systems have been successfully set up in rodent models. However, they are not suitable for larger animal models as the follicles of larger animals cultured in 2D culture systems often lose their shape due to dysfunction in the gap junctions. Three-dimensional (3D) culture systems are more suitable for maintaining follicle architecture, and therefore are proposed for the successful in vitro culturing of follicles in various animal models. The role of different methods, scaffolds, and suspension cultures in supporting follicle development has been studied to provide direction for improving in vitro follicle culture technologies. The three major strategies for in vitro 3D follicle cultures are discussed in this article. First, the in vitro culture systems, such as microfluidics, hanging drop, hydrogels, and 3D-printing, are reviewed. We have focused on the 3D hydrogel system as it uses different materials for supporting follicular growth and oocyte maturation in several animal models and in humans. We have also discussed the criteria used for biomaterial evaluations such as solid concentration, elasticity, and rigidity. In addition, future research directions for advancing in vitro 3D follicle culture system are discussed. Impact statement A new frontier in assisted reproductive technology is in vitro tissue or follicle culture, particularly for fertility preservation. The in vitro three-dimensional (3D) culture technique enhances follicular development and provides mature oocytes, overcoming the limitations of traditional in vitro two-dimensional cultures. Polymer biomaterials have good compatibility and retain the physiological structure of follicles in the 3D culture system. Utilizing hybrid in vitro culture materials by merging matrix, hydrogel, and unique patterned materials may facilitate follicular growth in the future.

Design strategies for composite matrix and multifunctional polymeric scaffolds with enhanced bioactivity for bone tissue engineering

Over the past few decades, various bioactive material-based scaffolds were investigated and researchers across the globe are actively involved in establishing a potential state-of-the-art for bone tissue engineering applications, wherein several disciplines like clinical medicine, materials science, and biotechnology are involved. The present review article's main aim is to focus on repairing and restoring bone tissue defects by enhancing the bioactivity of fabricated bone tissue scaffolds and providing a suitable microenvironment for the bone cells to fasten the healing process. It deals with the various surface modification strategies and smart composite materials development that are involved in the treatment of bone tissue defects. Orthopaedic researchers and clinicians constantly focus on developing strategies that can naturally imitate not only the bone tissue architecture but also its functional properties to modulate cellular behaviour to facilitate bridging, callus formation and osteogenesis at critical bone defects. This review summarizes the currently available polymeric composite matrices and the methods to improve their bioactivity for bone tissue regeneration effectively.

Challenges with Cell-based Therapies for Type 1 Diabetes Mellitus

Type 1 diabetes (T1D) is a chronic, lifelong metabolic disease. It is characterised by the autoimmune-mediated loss of insulin-producing pancreatic β cells in the islets of Langerhans (β-islets), resulting in disrupted glucose homeostasis. Administration of exogenous insulin is the most common management method for T1D, but this requires lifelong reliance on insulin injections and invasive blood glucose monitoring. Replacement therapies with beta cells are being developed as an advanced curative treatment for T1D. Unfortunately, this approach is limited by the lack of donated pancreatic tissue, the difficulties in beta cell isolation and viability maintenance, the longevity of the transplanted cells in vivo, and consequently high costs. Emerging approaches to address these limitations are under intensive investigations, including the production of insulin-producing beta cells from various stem cells, and the development of bioengineered devices including nanotechnologies for improving islet transplantation efficacy without the need for recipients taking toxic anti-rejection drugs. These emerging approaches present promising prospects, while the challenges with the new techniques need to be tackled for ultimately clinical treatment of T1D. This review discussed the benefits and limitations of the cell-based therapies for beta cell replacement as potential curative treatment for T1D, and the applications of bioengineered devices including nanotechnology to overcome the challenges associated with beta cell transplantation.

Progressive Application of Marine Biomaterials in Targeted Cancer Nanotherapeutics

The marine microenvironment harbors many unique species of organisms that produce a plethora of compounds that help mankind cure a wide range of diseases. The diversity of products from the ocean bed serves as potentially healing materials and inert vehicles carrying the drug of interest to the target site. Several composites still lay undiscovered under the blue canopy, which can provide treatment for untreated diseases that keep haunting the earth periodically. Cancer is one such disease that has been of interest to several eminent scientists worldwide due to the heterogenic complexity involved in the disease's pathophysiology. Due to extensive globalization and environmental changes, cancer has become a lifestyle disease continuously increasing exponentially in the current decade. This ailment requires a definite remedy that treats by causing minimal damage to the body's normal cells. The application of nanotechnology in medicine has opened up new avenues of research in targeted therapeutics due to their highly malleable characteristics. Marine waters contain an immense ionic environment that succors the production of distinct nanomaterials with exceptional character, yielding highly flexible molecules to modify, thus facilitating the engineering of targeted biomolecules. This review provides a short insight into an array of marine biomolecules that can be probed into cancer nanotherapeutics sparing healthy cells.

Design of a New 3D Gelatin-Alginate Scaffold Loaded with Cannabis sativa Oil

There is an increasing medical need for the development of new materials that could replace damaged organs, improve healing of critical wounds or provide the environment required for the formation of a new healthy tissue. The three-dimensional (3D) printing approach has emerged to overcome several of the major deficiencies of tissue engineering. The use of Cannabis sativa as a therapy for some diseases has spread throughout the world thanks to its benefits for patients. In this work, we developed a bioink made with gelatin and alginate that was able to be printed using an extrusion 3D bioprinter. The scaffolds obtained were lyophilized, characterized and the swelling was assessed. In addition, the scaffolds were loaded with Cannabis sativa oil extract. The presence of the extract provided antimicrobial and antioxidant activity to the 3D scaffolds. Altogether, our results suggest that the new biocompatible material printed with 3D technology and with the addition of Cannabis sativa oil could become an attractive alternative to common treatments of soft-tissue infections and wound repair.

The Influence of Surface Modification with Biopolymers on the Structure of Melt-Blown and Spun-Bonded Poly(lactic acid) Nonwovens

The article presents the continuation of the research on modification of fibrous carriers based on poly(lactic acid) using the electrophoretic deposition (EPD) method by the two types of biocompatible polymers-sodium hyaluronate and sodium alginate. Such modified nonwovens, differing in the structural parameters due to different manufacturing methods, could be potentially used in different biomedical applications. The results of the analysis indicate that the EPD process significantly changes the structural characteristics of the carrier in terms of thickness and porosity, which not always can be beneficial in terms of the final application. The varying structure of both carriers significantly influences the mode of deposition of the layer, the efficiency of the deposition process as well as the structural characteristics of the carrier after deposition. Microtomographic and SEM studies were employed to analyze the structure of deposits, and FTIR analysis allowed for confirmation of the occurrence of the polymer layers and its chemical structure.

Dual Dynamic Covalently Crosslinked Alginate Hydrogels with Tunable Properties and Multiple Stimuli-Responsiveness

Alginate is a biopolymer that can be crosslinked with calcium ions to fabricate cytocompatible hydrogels. However, using calcium ions to crosslink alginate provides limited properties and functions to alginate hydrogels, restricting their biomedical applications. Here, phenylboronic acid-functionalized polyethyleneimine (PBA-PEI) was developed to introduce two orthogonal dynamic covalent crosslinks in the alginate hydrogels, where PBA-PEI was used to crosslink alginate dialdehyde (ADA) through imine bonds and boronate ester bonds. The grafting degree of PBA in the PEI structure was applied to fine-tune the properties of PBA-PEI/ADA hydrogels, including the rheological property, mechanical strength, swelling behavior, and antibacterial activity. In particular, the highly sensitive boronate ester bonds in the network enabled PBA-PEI/ADA hydrogels to be responsive to several stimuli, such as glucose, fructose, and hydrogen peroxide. Taken together, PBA-PEI/ADA hydrogels with tunable properties and multiple stimuli-responsiveness have been demonstrated as smart biomaterials for advanced biomedical applications.

An Investigation of the Constructional Design Components Affecting the Mechanical Response and Cellular Activity of Electrospun Vascular Grafts

Cardiovascular disease is anticipated to remain the leading cause of death globally. Due to the current problems connected with using autologous arteries for bypass surgery, researchers are developing tissue-engineered vascular grafts (TEVGs). The major goal of vascular tissue engineering is to construct prostheses that closely resemble native blood vessels in terms of morphological, mechanical, and biological features so that these scaffolds can satisfy the functional requirements of the native tissue. In this setting, morphology and cellular investigation are usually prioritized, while mechanical qualities are generally addressed superficially. However, producing grafts with good mechanical properties similar to native vessels is crucial for enhancing the clinical performance of vascular grafts, exposing physiological forces, and preventing graft failure caused by intimal hyperplasia, thrombosis, aneurysm, blood leakage, and occlusion. The scaffold's design and composition play a significant role in determining its mechanical characteristics, including suturability, compliance, tensile strength, burst pressure, and blood permeability. Electrospun prostheses offer various models that can be customized to resemble the extracellular matrix. This review aims to provide a comprehensive and comparative review of recent studies on the mechanical properties of fibrous vascular grafts, emphasizing the influence of structural parameters on mechanical behavior. Additionally, this review provides an overview of permeability and cell growth in electrospun membranes for vascular grafts. This work intends to shed light on the design parameters required to maintain the mechanical stability of vascular grafts placed in the body to produce a temporary backbone and to be biodegraded when necessary, allowing an autologous vessel to take its place.

Bioactive scaffold (sodium alginate)-g-(nHAp@SiO2@GO) for bone tissue engineering

Globally, people suffering from bone disorders are steadily increasing and bone tissue engineering is an advanced approach to treating fractured and defected bone tissues. In this study, we have prepared polymeric nanocomposite by free-radical polymerization from sodium alginate, hydroxyapatite, and silica with different GO amounts. The porous scaffolds were fabricated using the freeze drying technique. The structural, morphological, mechanical, and wetting investigation was conducted by Fourier-transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, universal tensile machine, and water contact angle characterization techniques. The swelling, biodegradation, and water retention were also studied. The biological studies were performed (cell viability, cell adherence, proliferation, and mineralization) against osteoblast cell lines. Scaffolds have exhibited different pore morphology SAG-1 (pore size = 414.61 ± 56 μm and porosity = 81.45 ± 2.17 %) and SAG-4 (pore size = 195.97 ± 82 μm and porosity = 53.82 ± 2.45 %). They have different mechanical behavior as SAG-1 has the least compression strength and compression modulus 2.14 ± 2.35 and 16.51 ± 1.27 MPa. However, SAG-4 has maximum compression strength and compression modulus 13.67 ± 2.63 and 96.16 ± 1.97 MPa with wetting behavior 80.70° and 58.70°, respectively. Similarly, SAG-1 exhibited the least and SAG-4 presented maximum apatite mineral formation, cell adherence, cell viability, and cell proliferation against mouse pre-osteoblast cell lines. The increased GO amount provides different multifunctional materials with different characteristics. Hence, the fabricated scaffolds could be potential scaffold materials to treat and regenerate fracture bone tissues in bone tissue engineering.

Plant polysaccharides as novel biomaterials for microcapsule construction and therapeutics delivery

Natural polysaccharides derived from medicinal plants, that are Dendrobium (DPS), Lycium barbarum (LBP), Ginseng (GPS), and Poria Cocos (PCP) were firstly combined with sodium alginate (SA) to construct microcapsules and improved the morphology, encapsulation efficiency, Biocompatibility and protective capability in drug loading. Diverse typical therapeutics, including VO₂@ZIF67 nanoparticles, small molecule drugs salvianolic acid B (SaB)/ginsenoside (Rg1), probiotic Bacillus bifidus, and biomacromolecules SDF-1 were wrapped into 1.5 % GPS-0.5 % SA model microcapsules, respectively. Better mobility and formability were significantly observed, and showed 75 % survival rate of probiotics in simulated gastric juice and around 99 % encapsulation efficiency which is higher than single 2 % SA microcapsules. The microcapsules also obtained a delayed release and a higher cell index for SDF-1, which indicated better stability, biocompatibility and protective effect than single 2 % SA microcapsules. This study provides a strategy in developing plant derived polysaccharides as novel materials for the construction and improvement of traditional microcapsules.

Centrifugally spun alginate-poly(lactic acid) microbeads: A promising carrier for drug delivery and tissue engineering

A facile and high yield centrifugal spinning technique known as Forcespinning® (FS) was used to develop unique microstructures consisting of PLA microbeads along alginate fibers. Morphological variation and structural features appeared in the field-emission scanning electron micrographs for the PLA-alginate composites and dried PLA-alginate films from precursor emulsions at constant PLA and varied alginate contents. Shrunk and deflated microbeads were observed for composites whilst spherical beads were evident for the PLA control. Furthermore, PLA was found surrounding the alginate when the alginate was present at 0.24 wt% or lower, while alginate (mushroom-like structures), were seen protruding through the PLA layer at ≥0.34 wt% alginate. Rheological characterization of the composite emulsions revealed that the filler (alginate) provided shear thinning properties including pseudoplasticity, desirable for printing and other related applications in contrast to the Newtonian flow shown by the PLA control. Along with infra-red spectroscopy, the nanocomposites were further characterized using thermal gravimetry and differential scanning calorimetry featuring reversible events influenced by heat capacity and irreversible kinetic/thermodynamic counterparts. The work provides a comprehensive investigation of biocompatible networks of PLA-alginate microbeads embedded in nano-sized fibers and the prospective application of these microbeads as a drug delivery system.

Recent Developments and Current Applications of Organic Nanomaterials in Cartilage Repair

Regeneration of cartilage is difficult due to the unique microstructure, unique multizone organization, and avascular nature of cartilage tissue. The development of nanomaterials and nanofabrication technologies holds great promise for the repair and regeneration of injured or degenerated cartilage tissue. Nanomaterials have structural components smaller than 100 nm in at least one dimension and exhibit unique properties due to their nanoscale structure and high specific surface area. The unique properties of nanomaterials include, but are not limited to, increased chemical reactivity, mechanical strength, degradability, and biocompatibility. As an emerging nanomaterial, organic nanocomposites can mimic natural cartilage in terms of microstructure, physicochemical, mechanical, and biological properties. The integration of organic nanomaterials is expected to develop scaffolds that better mimic the extracellular matrix (ECM) environment of cartilage to enhance scaffold-cell interactions and improve the functionality of engineered tissue constructs. Next-generation hydrogel technology and bioprinting can be used not only for healing cartilage injury areas but also for extensive osteoarthritic degenerative changes within the joint. Although more challenges need to be solved before they can be translated into full-fledged commercial products, nano-organic composites remain very promising candidates for the future development of cartilage tissue engineering.

Effect of Chitosan on Alginate-Based Macroporous Hydrogels for the Capture of Glioblastoma Cancer Cells

Glioblastoma multiforme is a type of brain cancer associated with a very low survival rate since a large number of cancer cells remain infiltrated in the brain despite the treatments currently available. This work presents a macroporous hydrogel trap, destined to be implanted in the surgical cavity following tumor resection and designed to attract and retain cancer cells, in order to eliminate them afterward with a lethal dose of stereotactic radiotherapy. The biocompatible hydrogel formulation comprises sodium alginate (SA) and chitosan (CHI) bearing complementary electrostatic charges and stabilizing the gels in saline and cell culture media, as compared to pristine SA gels. The highly controlled and interconnected porosity, characterized by X-ray microCT, yields mechanical properties comparable to those of brain tissues and allows F98 glioblastoma cells to penetrate the gels within the entire volume, as confirmed by fluorescence microscopy. The addition of a grafted -RGD peptide on SA, combined with CHI, significantly enhances the adhesion and retention of F98 cells within the gels. Overall, the best compromise between low proliferation and a high level of accumulation and retention of F98 cells was obtained with the hydrogel formulated with 1% SA and 0.2% CHI, without the -RGD adhesion peptide.

3D Printed Gene-Activated Sodium Alginate Hydrogel Scaffolds

Gene therapy is one of the most promising approaches in regenerative medicine to restore damaged tissues of various types. However, the ability to control the dose of bioactive molecules in the injection site can be challenging. The combination of genetic constructs, bioresorbable material, and the 3D printing technique can help to overcome these difficulties and not only serve as a microenvironment for cell infiltration but also provide localized gene release in a more sustainable way to induce effective cell differentiation. Herein, the cell transfection with plasmid DNA directly incorporated into sodium alginate prior to 3D printing was investigated both in vitro and in vivo. The 3D cryoprinting ensures pDNA structure integrity and safety. 3D printed gene-activated scaffolds (GAS) mediated HEK293 transfection in vitro and effective synthesis of model EGFP protein in vivo, thereby allowing the implementation of the developed GAS in future tissue engineering applications.

Recent Progress in Development of Dressings Used for Diabetic Wounds with Special Emphasis on Scaffolds

Diabetic wound (DW) is a secondary application of uncontrolled diabetes and affects about 42.2% of diabetics. If the disease is left untreated/uncontrolled, then it may further lead to amputation of organs. In recent years, huge research has been done in the area of wound dressing to have a better maintenance of DW. These include gauze, films, foams or, hydrocolloid-based dressings as well as polysaccharide- and polymer-based dressings. In recent years, scaffolds have played major role as biomaterial for wound dressing due to its tissue regeneration properties as well as fluid absorption capacity. These are three-dimensional polymeric structures formed from polymers that help in tissue rejuvenation. These offer a large surface area to volume ratio to allow cell adhesion and exudate absorbing capacity and antibacterial properties. They also offer a better retention as well as sustained release of drugs that are directly impregnated to the scaffolds or the ones that are loaded in nanocarriers that are impregnated onto scaffolds. The present review comprehensively describes the pathogenesis of DW, various dressings that are used so far for DW, the limitation of currently used wound dressings, role of scaffolds in topical delivery of drugs, materials used for scaffold fabrication, and application of various polymer-based scaffolds for treating DW.

Microfluidic Tissue Engineering and Bio-Actuation

Bio-hybrid technologies aim to replicate the unique capabilities of biological systems that could surpass advanced artificial technologies. Soft bio-hybrid robots consist of synthetic and living materials and have the potential to self-assemble, regenerate, work autonomously, and interact safely with other species and the environment. Cells require a sufficient exchange of nutrients and gases, which is guaranteed by convection and diffusive transport through liquid media. The functional development and long-term survival of biological tissues in vitro can be improved by dynamic flow culture, but only microfluidic flow control can develop tissue with fine structuring and regulation at the microscale. Full control of tissue growth at the microscale will eventually lead to functional macroscale constructs, which are needed as the biological component of soft bio-hybrid technologies. This review summarizes recent progress in microfluidic techniques to engineer biological tissues, focusing on the use of muscle cells for robotic bio-actuation. Moreover, the instances in which bio-actuation technologies greatly benefit from fusion with microfluidics are highlighted, which include: the microfabrication of matrices, biomimicry of cell microenvironments, tissue maturation, perfusion, and vascularization.

Electroactive calcium-alginate/polycaprolactone/reduced graphene oxide nanohybrid hydrogels for skeletal muscle tissue engineering

Graphene derivatives such as reduced graphene oxide (rGO) are used as components of novel biomaterials for their unique electrical properties. Electrical conductivity is a crucial factor for muscle cells, which are electrically active. This study reports the development of a new type of semi-interpenetrated polymer network based on two biodegradable FDA-approved biomaterials, sodium alginate (SA) and polycaprolactone (PCL), with Ca²⁺ ions as SA crosslinker. Several drawbacks such as the low cell adhesion of SA and weak structural stability can be improved with the incorporation of PCL. Furthermore, this study demonstrates how this semi-IPN can be engineered with rGO nanosheets (0.5% and 2% wt/wt rGO nanosheets) to produce electroactive nanohybrid composite biomaterials. The study focuses on the microstructure and the enhancement of physical and biological properties of these advanced materials, including water sorption, surface wettability, thermal behavior and thermal degradation, mechanical properties, electrical conductivity, cell adhesion and myogenic differentiation. The results suggest the formation of a complex nano-network with different interactions between the components: bonds between SA chains induced by Ca²⁺ ions (egg-box model), links between rGO nanosheets and SA chains as well as between rGO nanosheets themselves through Ca²⁺ ions, and strong hydrogen bonding between rGO nanosheets and SA chains. The incorporation of rGO significantly increases the electrical conductivity of the nanohybrid hydrogels, with values in the range of muscle tissue. In vitro cultures with C2C12 murine myoblasts revealed that the conductive nanohybrid hydrogels are not cytotoxic and can greatly enhance myoblast adhesion and myogenic differentiation. These results indicate that these novel electroactive nanohybrid hydrogels have great potential for biomedical applications related to the regeneration of electroactive tissues, particularly in skeletal muscle tissue engineering.

Polysaccharides, as biological macromolecule-based scaffolding biomaterials in cornea tissue engineering: A review

Corneal-related diseases and injuries are the leading causes of vision loss, estimated to affect over 10 million people worldwide. Currently, cadaveric corneal grafts are considered the gold standard of treatment to restore cornea-related vision. However, this treatment modality faces different challenges such as donor shortage and graft failure. Therefore, the need for alternative solutions continues to grow. Tissue engineering has dramatically progressed to produce artificial cornea implants in order to repair, regenerate, or replace the damaged cornea. In this regard, a variety of polysaccharides such as cellulose, chitosan, alginate, agarose, and hyaluronic acid have been widely explored as scaffolding biomaterials for the production of tissue-engineered cornea. These polymers are known for their excellent biocompatibility, versatile properties, and processability. Recent progress and future perspectives of polysaccharide-based biomaterials in cornea tissue engineering is reviewed here.

Alginate-based Composites Microspheres: Preparations and Applications for Bone Tissue Engineering

Alginate-based biomaterials have been extensively studied for bone tissue engineering. Scaffolds, microspheres, and hydrogels can be developed using alginate, which is biocompatible, biodegradable, and able to deliver growth factors and drugs. Alginate microspheres can be produced using crosslinking, microfluidic, three-dimensional printing, extrusion, and emulsion methods. The sizes of the alginate microspheres range from 10 µm to 4 mm. This review describes the chemical characterization and mechanical assessment of alginate-based microspheres. Combinations of alginate with hydroxyapatite, chitosan, collagen, polylactic acid, polycaprolactone, and bioglass were discussed for bone tissue repair and regeneration. In addition, alginate combinations with bone morphogenetic proteins, vascular endothelial growth factor, transforming growth factor beta-3, other growth factors, cells, proteins, drugs, and osteoinductive drugs were analyzed for tissue engineering applications. Furthermore, the biocompatibility of developed alginate microspheres was discussed for different cell lines. Finally, alginate microsphere-based composites with stem cell interaction for bone tissue regeneration were presented. In the present review, we have assessed the preclinical research on in vivo models of alginate-based microspheres for bone tissue repair and regeneration. Overall, alginate-based microspheres are potential candidates for graft substitutes and the treatment of various bone-related diseases.

Tailored alginate/PCL-gelatin-β-TCP membrane for guided bone regeneration

Membranes prepared for guided bone regeneration (GBR) signify valued resources, inhibiting fibrosis and assisting bone regenration. However, existing membranes lack bone regenerative capacity or adequate degradation profile. An alginate-casted polycaprolactone (PCL)-gelatin-β-tricalcium phosphate (β-TCP) dual membrane was fabricated by electrospinning and casting processes to enhance new bone formation under a guided bone regeneration (GBR) process. Porous membranes were synthesized with suitable hydrophilicity, swelling, and degradation behavior to confirm the compatibility of the product in the body. Furthermore, osteoblast-type cell toxicity and cell adhesion results showed that the electrospun membrane offered compatible environment to cells while the alginate sheet was found capable enough to supress the cellular attachment, but was a non-toxic material. Post-implantation, the in-vivo outcomes of the dual-layered membrane, showed appreciable bone formation. Significantly, osteoid islands had fused in the membrane group by 8 weeks. The infiltration of fibrous tissues was blocked by the alginate membrane, and the ingrowth of new bone was enhanced. Immunocytochemical analysis indicated that the dual membrane could direct more proteins which control mineralization and convene osteoconductive properties of tissue-engineered bone grafts.

Polysaccharide Layer-by-Layer Coating for Polyimide-Based Neural Interfaces

Implantable flexible neural interfaces (IfNIs) are capable of directly modulating signals of the central and peripheral nervous system by stimulating or recording the action potential. Despite outstanding results in acute experiments on animals and humans, their long-term biocompatibility is hampered by the effects of foreign body reactions that worsen electrical performance and cause tissue damage. We report on the fabrication of a polysaccharide nanostructured thin film as a coating of polyimide (PI)-based IfNIs. The layer-by-layer technique was used to coat the PI surface due to its versatility and ease of manufacturing. Two different LbL deposition techniques were tested and compared: dip coating and spin coating. Morphological and physiochemical characterization showed the presence of a very smooth and nanostructured thin film coating on the PI surface that remarkably enhanced surface hydrophilicity with respect to the bare PI surface for both the deposition techniques. However, spin coating offered more control over the fabrication properties, with the possibility to tune the coating's physiochemical and morphological properties. Overall, the proposed coating strategies allowed the deposition of a biocompatible nanostructured film onto the PI surface and could represent a valid tool to enhance long-term IfNI biocompatibility by improving tissue/electrode integration.

Improved 3D Printing and Cell Biology Characterization of Inorganic-Filler Containing Alginate-Based Composites for Bone Regeneration: Particle Shape and Effective Surface Area Are the Dominant Factors for Printing Performance

The use of organic-inorganic 3D printed composites with enhanced properties in biomedical applications continues to increase. The present study focuses on the development of 3D printed alginate-based composites incorporating inorganic fillers with different shapes (angular and round), for bone regeneration. Reactive fillers (bioactive glass 13-93 and hydroxyapatite) and non-reactive fillers (inert soda-lime glass) were investigated. Rheological studies and the characterization of various extrusion-based parameters, including material throughput, printability, shape fidelity and filament fusion, were carried out to identify the parameters dominating the printing process. It was shown that the effective surface area of the filler particle has the highest impact on the printing behavior, while the filler reactivity presents a side aspect. Composites with angular particle morphologies showed the same high resolution during the printing process, almost independent from their reactivity, while composites with comparable amounts of round filler particles lacked stackability after printing. Further, it could be shown that a higher effective surface area of the particles can circumvent the need for a higher filler content for obtaining convincing printing results. In addition, it was proven that, by changing the particle shape, the critical filler content for the obtained adequate printability can be altered. Preliminary in vitro biocompatibility investigations were carried out with the bioactive glass containing ink. The 3D printed ink, forming an interconnected porous scaffold, was analyzed regarding its biocompatibility in direct or indirect contact with the pre-osteoblast cell line MC3T3-E1. Both kinds of cell tests showed increased viability and a high rate of proliferation, with complete coverage of the 3D scaffolds' surface already after 7 d post cell-seeding.

Graphene Oxide-Protein-Based Scaffolds for Tissue Engineering: Recent Advances and Applications

The field of tissue engineering is constantly evolving as it aims to develop bioengineered and functional tissues and organs for repair or replacement. Due to their large surface area and ability to interact with proteins and peptides, graphene oxides offer valuable physiochemical and biological features for biomedical applications and have been successfully employed for optimizing scaffold architectures for a wide range of organs, from the skin to cardiac tissue. This review critically focuses on opportunities to employ protein-graphene oxide structures either as nanocomposites or as biocomplexes and highlights the effects of carbonaceous nanostructures on protein conformation and structural stability for applications in tissue engineering and regenerative medicine. Herein, recent applications and the biological activity of nanocomposite bioconjugates are analyzed with respect to cell viability and proliferation, along with the ability of these constructs to sustain the formation of new and functional tissue. Novel strategies and approaches based on stem cell therapy, as well as the involvement of the extracellular matrix in the design of smart nanoplatforms, are discussed.

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.

The seaweed holobiont: from microecology to biotechnological applications

In the ocean, seaweed and microorganisms have coexisted since the earliest stages of evolution and formed an inextricable relationship. Recently, seaweed has attracted extensive attention worldwide for ecological and industrial purposes, but the function of its closely related microbes is often ignored. Microbes play an indispensable role in different stages of seaweed growth, development and maturity. A very diverse group of seaweed‐associated microbes have important functions and are dynamically reconstructed as the marine environment fluctuates, forming an inseparable ‘holobiont’ with their host. To further understand the function and significance of holobionts, this review first reports on recent advances in revealing seaweed‐associated microbe spatial and temporal distribution. Then, this review discusses the microbe and seaweed interactions and their ecological significance, and summarizes the current applications of the seaweed–microbe relationship in various environmental and biological technologies. Sustainable industries based on seaweed holobionts could become an integral part of the future bioeconomy because they can provide more resource‐efficient food, high‐value chemicals and medical materials. Moreover, holobionts may provide a new approach to marine environment restoration.

Poly (vinyl alcohol)-alginate as potential matrix for various applications: A focused review

Advances in polymers have made significant contribution in diverse application oriented fields. Multidisciplinary applicability of polymers generates a range of strategies, which is pertinent in a wide range of fields. Blends of natural and synthetic polymers have spawned a different class of materials with synergistic effects. Specifically, poly (vinyl alcohol) (PVA) and alginate (AG) blends (PVAG) have demonstrated some promising results in almost every segment, ranging from biomedical to industrial sector. Combination of PVAG with other materials, immobilization with specific moieties and physical and chemical crosslinking could result in amendments in the structure and properties of the PVAG matrices. Here, we provide an overview of the recent developments in designing PVAG based matrix and complexes with their structural and functional properties. The article also provides a comprehensive outline on the applicability of PVAG matrix in wastewater treatment, biomedical, photocatalysis, food packaging, and fuel cells and sheds light on the challenges that need to be addressed. Finally, the review elaborates the future prospective of PVAG matrices in other unexplored fields like aircraft industry, nuclear science and space exploration.

Biomaterial-based strategies for in vitro neural models

In vitro models have been used as a complementary tool to animal studies in understanding the nervous system's physiological mechanisms and pathological disorders, while also serving as platforms to evaluate the safety and efficiency of therapeutic candidates. Following recent advances in materials science, micro- and nanofabrication techniques and cell culture systems, in vitro technologies have been rapidly gaining the potential to bridge the gap between animal and clinical studies by providing more sophisticated models that recapitulate key aspects of the structure, biochemistry, biomechanics, and functions of human tissues. This was made possible, in large part, by the development of biomaterials that provide cells with physicochemical features that closely mimic the cellular microenvironment of native tissues. Due to the well-known material-driven cellular response and the importance of mimicking the environment of the target tissue, the selection of optimal biomaterials represents an important early step in the design of biomimetic systems to investigate brain structures and functions. This review provides a comprehensive compendium of commonly used biomaterials as well as the different fabrication techniques employed for the design of neural tissue models. Furthermore, the authors discuss the main parameters that need to be considered to develop functional platforms not only for the study of brain physiological functions and pathological processes but also for drug discovery/development and the optimization of biomaterials for neural tissue engineering.

Fabrication and Characterization of Nanocomposite Hydrogel Based on Alginate/Nano-Hydroxyapatite Loaded with Linum usitatissimum Extract as a Bone Tissue Engineering Scaffold

In the current paper, we fabricated, characterized, and applied nanocomposite hydrogel based on alginate (Alg) and nano-hydroxyapatite (nHA) loaded with phenolic purified extracts from the aerial part of Linum usitatissimum (LOH) as the bone tissue engineering scaffold. nHA was synthesized based on the wet chemical technique/precipitation reaction and incorporated into Alg hydrogel as the filler via physical cross-linking. The characterizations (SEM, DLS, and Zeta potential) revealed that the synthesized nHA possess a plate-like shape with nanometric dimensions. The fabricated nanocomposite has a porous architecture with interconnected pores. The average pore size was in the range of 100–200 µm and the porosity range of 80–90%. The LOH release measurement showed that about 90% of the loaded drug was released within 12 h followed by a sustained release over 48 h. The in vitro assessments showed that the nanocomposite possesses significant antioxidant activity promoting bone regeneration. The hemolysis induction measurement showed that the nanocomposites were hemocompatible with negligible hemolysis induction. The cell viability/proliferation confirmed the biocompatibility of the nanocomposites, which induced proliferative effects in a dose-dependent manner. This study revealed the fabricated nanocomposites are bioactive and osteoactive applicable for bone tissue engineering applications.

Modification of Alginates to Modulate Their Physic-Chemical Properties and Obtain Biomaterials with Different Functional Properties

Modified alginates have a wide range of applications, including in the manufacture of dressings and scaffolds used for regenerative medicine, in systems for selective drug delivery, and as hydrogel materials. This literature review discusses the methods used to modify alginates and obtain materials with new or improved functional properties. It discusses the diverse biological and functional activity of alginates. It presents methods of modification that utilize both natural and synthetic peptides, and describes their influence on the biological properties of the alginates. The success of functionalization depends on the reaction conditions being sufficient to guarantee the desired transformations and provide modified alginates with new desirable properties, but mild enough to prevent degradation of the alginates. This review is a literature description of efficient methods of alginate functionalization using biologically active ligands. Particular attention was paid to methods of alginate functionalization with peptides, because the combination of the properties of alginates and peptides leads to the obtaining of conjugates with properties resulting from both components as well as a completely new, different functionality.

Mobilizing Endogenous Repair Through Understanding Immune Reaction With Biomaterials

With few exceptions, humans are incapable of fully recovering from severe physical trauma. Due to these limitations, the field of regenerative medicine seeks to find clinically viable ways to repair permanently damaged tissue. There are two main approaches to regenerative medicine: promoting endogenous repair of the wound, or transplanting a material to replace the injured tissue. In recent years, these two methods have fused with the development of biomaterials that act as a scaffold and mobilize the body's natural healing capabilities. This process involves not only promoting stem cell behavior, but by also inducing activity of the immune system. Through understanding the immune interactions with biomaterials, we can understand how the immune system participates in regeneration and wound healing. In this review, we will focus on biomaterials that promote endogenous tissue repair, with discussion on their interactions with the immune system.

Alginate-Based Smart Materials and Their Application: Recent Advances and Perspectives

Nature produces materials using available molecular building blocks following a bottom-up approach. These materials are formed with great precision and flexibility in a controlled manner. This approach offers the inspiration for manufacturing new artificial materials and devices. Synthetic artificial materials can find many important applications ranging from personalized therapeutics to solutions for environmental problems. Among these materials, responsive synthetic materials are capable of changing their structure and/or properties in response to external stimuli, and hence are termed "smart" materials. Herein, this review focuses on alginate-based smart materials and their stimuli-responsive preparation, fragmentation, and applications in diverse fields from drug delivery and tissue engineering to water purification and environmental remediation. In the first part of this report, we review stimuli-induced preparation of alginate-based materials. Stimuli-triggered decomposition of alginate materials in a controlled fashion is documented in the second part, followed by the application of smart alginate materials in diverse fields. Because of their biocompatibility, easy accessibility, and simple techniques of material formation, alginates can provide solutions for several present and future problems of humankind. However, new research is needed for novel alginate-based materials with new functionalities and well-defined properties for targeted applications.

The Emerging Role of Decellularized Plant-Based Scaffolds as a New Biomaterial

The decellularization of plant-based biomaterials to generate tissue-engineered substitutes or in vitro cellular models has significantly increased in recent years. These vegetal tissues can be sourced from plant leaves and stems or fruits and vegetables, making them a low-cost, accessible, and sustainable resource from which to generate three-dimensional scaffolds. Each construct is distinct, representing a wide range of architectural and mechanical properties as well as innate vasculature networks. Based on the rapid rise in interest, this review aims to detail the current state of the art and presents the future challenges and perspectives of these unique biomaterials. First, we consider the different existing decellularization techniques, including chemical, detergent-free, enzymatic, and supercritical fluid approaches that are used to generate such scaffolds and examine how these protocols can be selected based on plant cellularity. We next examine strategies for cell seeding onto the plant-derived constructs and the importance of the different functionalization methods used to assist in cell adhesion and promote cell viability. Finally, we discuss how their structural features, such as inherent vasculature, porosity, morphology, and mechanical properties (i.e., stiffness, elasticity, etc.) position plant-based scaffolds as a unique biomaterial and drive their use for specific downstream applications. The main challenges in the field are presented throughout the discussion, and future directions are proposed to help improve the development and use of vegetal constructs in biomedical research.

Poly(lactic acid)/Zinc/Alginate Complex Material: Preparation and Antimicrobial Properties

The aim of this study was to investigate an antimicrobial and degradable composite material consisting of melt-blown poly(lactic acid) nonwoven fabrics, alginate, and zinc. This paper describes the method of preparation and the characterization of the physicochemical and antimicrobial properties of the new fibrous composite material. The procedure consists of fabrication of nonwoven fabric and two steps of dip-coating modification: (1) impregnation of nonwoven samples in the solution of alginic sodium salt and (2) immersion in a solution of zinc (II) chloride. The characterization and analysis of new material included scanning electron microscopy (SEM), specific surface area (SSA), and total/average pore volume (BET). The polylactide/alginate/Zn fibrous composite were subjected to microbial activity tests against colonies of Gram-positive (Staphylococcus aureus), Gram-negative (Escherichia coli) bacterial strains, and the following fungal strains: Aspergillus niger van Tieghem and Chaetomium globosum. These results lay a technical foundation for the development and potential application of new composite as an antibacterial/antifungal material in biomedical areas.

Recent developments in mussel-inspired materials for biomedical applications

Over the decades, researchers have strived to synthesize and modify nature-inspired biomaterials, with the primary aim to address the challenges of designing functional biomaterials for regenerative medicine and tissue engineering. Among these challenges, biocompatibility and cellular interactions have been extensively investigated. Some of the most desirable characteristics for biomaterials in these applications are the loading of bioactive molecules, strong adhesion to moist areas, improvement of cellular adhesion, and self-healing properties. Mussel-inspired biomaterials have received growing interest mainly due to the changes in mechanical and biological functions of the scaffold due to catechol modification. Here, we summarize the chemical and biological principles and the latest advancements in production, as well as the use of mussel-inspired biomaterials. Our main focus is the polydopamine coating, the conjugation of catechol with other polymers, and the biomedical applications that polydopamine moieties are used for, such as matrices for drug delivery, tissue regeneration, and hemostatic control. We also present a critical conclusion and an inspired view on the prospects for the development and application of mussel-inspired materials.

Natural Polymers for the Maintenance of Oral Health: Review of Recent Advances and Perspectives

The success of modern dental treatment is strongly dependent on the materials used both temporarily and permanently. Among all dental materials, polymers are a very important class with a wide spectrum of applications. This review aims to provide a state-of-the-art overview of the recent advances in the field of natural polymers used to maintain or restore oral health. It focuses on the properties of the most common proteins and polysaccharides of natural origin in terms of meeting the specific biological requirements in the increasingly demanding field of modern dentistry. The use of naturally derived polymers in different dental specialties for preventive and therapeutic purposes has been discussed. The major fields of application cover caries and the management of periodontal diseases, the fabrication of membranes and scaffolds for the regeneration of dental structures, the manufacturing of oral appliances and dentures as well as providing systems for oral drug delivery. This paper also includes a comparative characteristic of natural and synthetic dental polymers. Finally, the current review highlights new perspectives, possible future advancements, as well as challenges that may be encountered by researchers in the field of dental applications of polymers of natural origin.

Polymeric Hydrogel Scaffolds: Skin Tissue Engineering and Regeneration

Tissue engineering is a novel regenerative approach in the medicinal field that promises the regeneration of damaged tissues. Moreover, tissue engineering involves synthetic and natural biomaterials that facilitate tissue or organ growth outside the body. Not surprisingly, the demand for polymer-based therapeutical approaches in skin tissue defects has increased at an effective rate, despite the pressing clinical need. Among the 3D scaffolds for tissue engineering and regeneration approaches, hydrogel scaffolds have shown significant importance for their use as 3D cross-linked scaffolds in skin tissue regeneration due to their ideal moisture retention property and porosity biocompatibility, biodegradable, and biomimetic characteristics. In this review, we demonstrated the choice of ideal biomaterials to fabricate the novel hydrogel scaffolds for skin tissue engineering. After a short introduction to the bioactive and drug-loaded polymeric hydrogels, the discussion turns to fabrication and characterisation techniques of the polymeric hydrogel scaffolds. In conclusion, we discuss the excellent wound healing potential of stem cell-loaded hydrogels and Nano-based approaches to designing hydrogel scaffolds for skin tissue engineering.

Maintaining Inducibility of Dermal Follicle Cells on Silk Fibroin/Sodium Alginate Scaffold for Enhanced Hair Follicle Regeneration

The extracellular matrix (ECM) is important for maintaining cell phenotype and promoting cell proliferation and differentiation. In order to better solve the problem of skin appendage regeneration, a combination of mechanical/enzymatic digestion methods was used to self-extract dermal papilla cells (DPCs), which were seeded on silk fibroin/sodium alginate scaffolds as seed cells to evaluate the possibility of skin regeneration/regeneration of accessory organs. Scanning electron microscopy (SEM) graphs showed that the interconnected pores inside the scaffold had a pore diameter in the range of 153-311 μm and a porosity of 41-82%. Immunofluorescence (IF) staining and cell morphological staining proved that the extracted cells were DPCs. The results of a Cell Counting Kit-8 (CCK-8) and Calcein-AM/PI live-dead cell staining showed that the DPCs grew well in the composite scaffold extract. Normal cell morphology and characteristics of aggregation growth were maintained during the 3-day culture, which showed that the silk fibroin/sodium alginate (SF/SA) composite scaffold had good cell-compatibility. Hematoxylin-eosin (H&E) staining of tissue sections further proved that the cells adhered closely and aggregated to the pore wall of the scaffold, and retained the ability to induce differentiation of hair follicles. All these results indicate that, compared with a pure scaffold, the composite scaffold promotes the adhesion and growth of DPCs. We transplanted the SF/SA scaffolds into the back wounds of SD rats, and evaluated the damage model constructed in vivo. The results showed that the scaffold inoculated with DPCs could accelerate the repair of the skin and promote the regeneration of the hair follicle structure.

Current Insight of Printability Quality Improvement Strategies in Natural-Based Bioinks for Skin Regeneration and Wound Healing

Skin tissue engineering aimed to replace chronic tissue injury commonly occurred due to severe burn and chronic wound in diabetic ulcer patients. The normal skin is unable to be regenerated until the seriously injured tissue is disrupted and losing its function. 3D-bioprinting has been one of the effective methods for scaffold fabrication and is proven to replace the conventional method, which reported several drawbacks. In light of this, researchers have developed a new fabrication approach via 3D-bioprinting by combining biomaterials (bioinks) with cells and biomolecules followed by a suitable crosslinking approach. This advanced technology has been subcategorised into three different printing techniques including inject-based, laser-based, and extrusion-based printing. However, the printable quality of the currently available bioinks demonstrated shortcomings in the physicochemical and mechanical properties. This review aims to identify the limitations raised by using natural-based bioinks and the optimum temperature for various applied printing techniques. It is essential to ensure maintaining the acceptable printed scaffold property such as the optimum pore sizes and porosity that allow cell migration activity. In addition, the properties required for an ideal bioinks design for better scaffold printability were also summarised.

Coaxial Alginate Hydrogels: From Self-Assembled 3D Cellular Constructs to Long-Term Storage

Alginate as a versatile naturally occurring biomaterial has found widespread use in the biomedical field due to its unique features such as biocompatibility and biodegradability. The ability of its semipermeable hydrogels to provide a favourable microenvironment for clinically relevant cells made alginate encapsulation a leading technology for immunoisolation, 3D culture, cryopreservation as well as cell and drug delivery. The aim of this work is the evaluation of structural properties and swelling behaviour of the core-shell capsules for the encapsulation of multipotent stromal cells (MSCs), their 3D culture and cryopreservation using slow freezing. The cells were encapsulated in core-shell capsules using coaxial electrospraying, cultured for 35 days and cryopreserved. Cell viability, metabolic activity and cell-cell interactions were analysed. Cryopreservation of MSCs-laden core-shell capsules was performed according to parameters pre-selected on cell-free capsules. The results suggest that core-shell capsules produced from the low viscosity high-G alginate are superior to high-M ones in terms of stability during in vitro culture, as well as to solid beads in terms of promoting formation of viable self-assembled cellular structures and maintenance of MSCs functionality on a long-term basis. The application of 0.3 M sucrose demonstrated a beneficial effect on the integrity of capsules and viability of formed 3D cell assemblies, as compared to 10% dimethyl sulfoxide (DMSO) alone. The proposed workflow from the preparation of core-shell capsules with self-assembled cellular structures to the cryopreservation appears to be a promising strategy for their off-the-shelf availability.