Investigating the Interplay Between Matrix Compliance and Passaging History on Chondrogenic Differentiation of Mesenchymal Stem Cells Encapsulated Within Alginate-Gelatin Hybrid Hydrogels

Mesenchymal stem cells (MSCs) are used widely in tissue engineering and regenerative medicine because of their ease of isolation and their pluripotency. The low survival and retention rate of MSCs at the target site upon implantation can be addressed via encapsulation within hydrogels capable of directing their fate. In this study, the interplay between matrix mechanics and the passage number of MSCs on their chondrogenic differentiation was assessed. Human bone marrow-derived MSCs between passages 4 and 6 were encapsulated within alginate-gelatin hybrid gels. The stiffness of the gels was varied by varying alginate concentrations while maintaining the concentration of gelatin and consequently, the cell adhesion sites, constant. The study revealed that within 4.8 kPa gels, GAG deposition was higher by P4 MSCs compared to P6 MSCs. However, an opposite trend was observed with collagen type 2 deposition. Further, we observed enhanced chondrogenic differentiation upon encapsulation of MSCs within 6.7 kPa hydrogel irrespective of passaging history. However, the effect of matrix compliance was more prominent in the case of higher passaged MSCs suggesting that matrix stiffness can help rescue the reduced differentiation capability of these cells.

Effects of Steam Sterilization on the Properties of Stimuli-Responsive Polymer-Based Hydrogels

Hydrogels based on stimuli-responsive polymers can change their characteristics in response to small variations in environmental conditions, such as temperature, pH, and ionic strength, among others. In the case of some routes of administration, such as ophthalmic and parenteral, the formulations must meet specific requirements, namely sterility. Therefore, it is essential to study the effect of the sterilization method on the integrity of smart gel systems. Thus, this work aimed to study the effect of steam sterilization (121 °C, 15 min) on the properties of hydrogels based on the following stimuli-responsive polymers: Carbopol® 940, Pluronic® F-127, and sodium alginate. The properties of the prepared hydrogels-pH, texture, rheological behavior, and sol-gel phase transition-were evaluated to compare and identify the differences between sterilized and non-sterilized hydrogels. The influence of steam sterilization on physicochemical stability was also investigated by Fourier-transform infrared spectroscopy and differential scanning calorimetry. The results of this study showed that the Carbopol® 940 hydrogel was the one that suffered fewer changes in the studied properties after sterilization. By contrast, sterilization was found to cause slight changes in the Pluronic® F-127 hydrogel regarding gelation temperature/time, as well as a considerable decrease in the viscosity of the sodium alginate hydrogel. There were no considerable differences in the chemical and physical characteristics of the hydrogels after steam sterilization. It is possible to conclude that steam sterilization is suitable for Carbopol® 940 hydrogels. Contrarily, this technique does not seem adequate for the sterilization of alginate or Pluronic® F-127 hydrogels, as it could considerably alter their properties.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Marine Polysaccharides for Wound Dressings Application: An Overview

Wound dressings have become a crucial treatment for wound healing due to their convenience, low cost, and prolonged wound management. As cutting-edge biomaterials, marine polysaccharides are divided from most marine organisms. It possesses various bioactivities, which allowing them to be processed into various forms of wound dressings. Therefore, a comprehensive understanding of the application of marine polysaccharides in wound dressings is particularly important for the studies of wound therapy. In this review, we first introduce the wound healing process and describe the characteristics of modern commonly used dressings. Then, the properties of various marine polysaccharides and their application in wound dressing development are outlined. Finally, strategies for developing and enhancing marine polysaccharide wound dressings are described, and an outlook of these dressings is given. The diverse bioactivities of marine polysaccharides including antibacterial, anti-inflammatory, haemostatic properties, etc., providing excellent wound management and accelerate wound healing. Meanwhile, these biomaterials have higher biocompatibility and biodegradability compared to synthetic ones. On the other hand, marine polysaccharides can be combined with copolymers and active substances to prepare various forms of dressings. Among them, emerging types of dressings such as nanofibers, smart hydrogels and injectable hydrogels are at the research frontier of their development. Therefore, marine polysaccharides are essential materials in wound dressings fabrication and have a promising future.

Injectable hydrogels based on oxidized alginate-gelatin reinforced by carbon nitride quantum dots for tissue engineering

Stem cell treatment is promising in the various disorders treatment, but its effect is confined by the adverse conditions in the damaged tissues. The utilization of hydrogels has been suggested as a procedure to defeat this issue by developing the engraftment and survival of injected stem cells. Specifically, injectable hydrogels have drawn much attention due to their shape adaptability, ease of use, and the capability to reach body parts that are hard to access. In this study, the thermosensitive injectable hydrogels based on oxidized alginate, gelatin, and carbon nitride quantum dots (CNQDs) have been fabricated for tissue engineering. The mechanical characteristics of the nanocomposite hydrogels were investigated by rheology analysis. The results show that increasing the amount of CNQDs improve the mechanical strength of the nanocomposite hydrogels. The Cross-section morphology of freeze dried hydrogels comprising 0.25, 1.5, and 3.0% CNQDs indicate porous structure with interrelated pores. Besides, the result of in vitro degradation reveals that the hydrogels comprising CNQDs are more durable than the one without CNQDs. A reduction in the biodegradation and swelling ratio is perceived with the addition of CNQDs. The cell viability and attachment show that the nanocomposite hydrogels are biocompatible (>88%) with great cell adhesion to osteosarcoma cell line MG63 depending on the presence of CNQDs.

Applications of Biocompatible Scaffold Materials in Stem Cell-Based Cartilage Tissue Engineering

Cartilage, especially articular cartilage, is a unique connective tissue consisting of chondrocytes and cartilage matrix that covers the surface of joints. It plays a critical role in maintaining joint durability and mobility by providing nearly frictionless articulation for mechanical load transmission between joints. Damage to the articular cartilage frequently results from sport-related injuries, systemic diseases, degeneration, trauma, or tumors. Failure to treat impaired cartilage may lead to osteoarthritis, affecting more than 25% of the adult population globally. Articular cartilage has a very low intrinsic self-repair capacity due to the limited proliferative ability of adult chondrocytes, lack of vascularization and innervation, slow matrix turnover, and low supply of progenitor cells. Furthermore, articular chondrocytes are encapsulated in low-nutrient, low-oxygen environment. While cartilage restoration techniques such as osteochondral transplantation, autologous chondrocyte implantation (ACI), and microfracture have been used to repair certain cartilage defects, the clinical outcomes are often mixed and undesirable. Cartilage tissue engineering (CTE) may hold promise to facilitate cartilage repair. Ideally, the prerequisites for successful CTE should include the use of effective chondrogenic factors, an ample supply of chondrogenic progenitors, and the employment of cell-friendly, biocompatible scaffold materials. Significant progress has been made on the above three fronts in past decade, which has been further facilitated by the advent of 3D bio-printing. In this review, we briefly discuss potential sources of chondrogenic progenitors. We then primarily focus on currently available chondrocyte-friendly scaffold materials, along with 3D bioprinting techniques, for their potential roles in effective CTE. It is hoped that this review will serve as a primer to bring cartilage biologists, synthetic chemists, biomechanical engineers, and 3D-bioprinting technologists together to expedite CTE process for eventual clinical applications.

Polysaccharide-Based In Situ Self-Healing Hydrogels for Tissue Engineering Applications

In situ hydrogels have attracted increasing interest in recent years due to the need to develop effective and practical implantable platforms. Traditional hydrogels require surgical interventions to be implanted and are far from providing personalized medicine applications. However, in situ hydrogels offer a wide variety of advantages, such as a non-invasive nature due to their localized action or the ability to perfectly adapt to the place to be replaced regardless the size, shape or irregularities. In recent years, research has particularly focused on in situ hydrogels based on natural polysaccharides due to their promising properties such as biocompatibility, biodegradability and their ability to self-repair. This last property inspired in nature gives them the possibility of maintaining their integrity even after damage, owing to specific physical interactions or dynamic covalent bonds that provide reversible linkages. In this review, the different self-healing mechanisms, as well as the latest research on in situ self-healing hydrogels, is presented, together with the potential applications of these materials in tissue regeneration.

Advancements and Frontiers in the High Performance of Natural Hydrogels for Cartilage Tissue Engineering

Cartilage injury originating from trauma or osteoarthritis is a common joint disease that can bring about an increasing social and economic burden in modern society. On account of its avascular, neural, and lymphatic characteristics, the poor migration ability of chondrocytes, and a low number of progenitor cells, the self-healing ability of cartilage defects has been significantly limited. Natural hydrogels, occurring abundantly with characteristics such as high water absorption, biodegradation, adjustable porosity, and biocompatibility like that of the natural extracellular matrix (ECM), have been developed into one of the most suitable scaffold biomaterials for the regeneration of cartilage in material science and tissue engineering. Notably, natural hydrogels derived from sources such as animal or human cadaver tissues possess the bionic mechanical behaviors of physiological cartilage that are required for usage as articular cartilage substitutes, by which the enhanced chondrogenic phenotype ability may be achieved by facilely embedding living cells, controlling degradation profiles, and releasing stimulatory growth factors. Hence, we summarize an overview of strategies and developments of the various kinds and functions of natural hydrogels for cartilage tissue engineering in this review. The main concepts and recent essential research found that great challenges like vascularity, clinically relevant size, and mechanical performances were still difficult to overcome because the current limitations of technologies need to be severely addressed in practical settings, particularly in unpredictable preclinical trials and during future forays into cartilage regeneration using natural hydrogel scaffolds with high mechanical properties. Therefore, the grand aim of this current review is to underpin the importance of preparation, modification, and application for the high performance of natural hydrogels for cartilage tissue engineering, which has been achieved by presenting a promising avenue in various fields and postulating real-world respective potentials.

In Situ Gelling Hydrogel with Anti-Bacterial Activity and Bone Healing Property for Treatment of Osteomyelitis

Background

Despite the development of progressive surgical techniques and antibiotics, osteomyelitis is a big challenge for orthopedic surgeons. The main aim of this study is to fabricate an in situ gelling hydrogel that permits sustained release of antibiotic (for control of infection) and growth factor (for induction of new bone formation) for effective treatment of osteomyelitis.

Methods

An in situ gelling alginate (ALG)/hyaluronic acid (HA) hydrogel containing vancomycin (antibiotic) and bone morphogenetic protein-2 (BMP-2; growth factor) was prepared by simple mixing of ALG/HA/Na₂HPO₄ solution and CaSO₄/vancomycin/BMP-2 solution. The release behaviors of vancomycin and BMP-2, anti-bacterial effect (in vitro); and therapeutic efficiency for osteomyelitis and bone regeneration (in vivo, osteomyelitis rat model) of the vancomycin and BMP-2-incorporated ALG/HA hydrogel were investigated.

Results

The gelation time of the ALG/HA hydrogel was controlled into approximately 4 min, which is sufficient time for handling and injection into osteomyelitis lesion. Both vancomycin and BMP-2 were continuously released from the hydrogel for 6 weeks. From the in vitro studies, the ALG/HA hydrogel showed an effective anti-bacterial activity without significant cytotoxicity for 6 weeks. From an in vivo animal study using Sprague-Dawley rats with osteomyelitis in femur as a model animal, it was demonstrated that the ALG/HA hydrogel was effective for suppressing bacteria (Staphylococcus aureus) proliferation at the osteomyelitis lesion and enhancing bone regeneration without additional bone grafts.

Conclusions

From the results, we suggest that the in situ gelling ALG/HA hydrogel containing vancomycin and BMP-2 can be a feasible therapeutic tool to treat osteomyelitis.

An Overview of Injectable Thermo-Responsive Hydrogels and Advances in their Biomedical Applications

BACKGROUND

Injectable hydrogels are a thermo-responsive system based on biomaterials. Injectable hydrogels have been broadly investigated mainly as vehicles or scaffolds of therapeutic agents that include drugs, proteins, cells, and bioactive molecules among others, utilized in the treatment of diseases such as cancers and the repair and regeneration of tissues.

RESULTS

There are several studies that have described the multiple features of hydrogels. However, the main aspect that breaks the paradigm in the application of hydrogels is the thermoresponsiveness that some of them have, which is an abrupt modification in their properties in response to small variations in temperature. For that reason, the thermo-responsive hydrogels with the unique property of sol-gel transition have received special attention over the past decades. These hydrogels show phase transition near physiological human body temperature. This feature is key for being applied in promising areas of human health-related research.

CONCLUSION

The purpose of this study is the overview of injectable hydrogels and their latest advances in medical applications including bioactive compound delivery, tissue engineering, and regenerative medicine.

Natural hydrogels for cartilage regeneration: Modification, preparation and application

Hydrogels, consisting of hydrophilic polymers, can be used as films, scaffolds, nanoparticles and drug carriers. They are one of the hot research topics in material science and tissue engineering and are widely used in the field of biomedical and biological sciences. Researchers are seeking for a type of material that is similar to human tissues and can partially replace human tissues or organs. The hydrogel has brought possibility to solve this problem. It has good biocompatibility and biodegradability. After entering the body, it does not cause immune and toxic reactions. The degradation time can be controlled, and the degradation products are nontoxic and nonimmunogenic; the final metabolites can be excreted outside the body. Owing to the lack of blood vessels and poor migration ability of chondrocytes, the self-healing ability of damaged cartilage is limited. Tissue engineering has brought a new direction for the regeneration of cartilage. Drug carriers and scaffolds made of hydrogels are widely used in cartilage tissue engineering. The present review introduces the natural hydrogels, which are often used for cartilage tissue engineering with respect to synthesis, modification and application methods.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

This review introduces the natural hydrogels that are often used in cartilage tissue engineering with respect to synthesis, modification and application methods. Furthermore, the essential concepts and recent discoveries were demonstrated to illustrate the achievable goals and the current limitations. In addition, we propose the putative challenges and directions for the use of natural hydrogels in cartilage regeneration.

In Situ Gelling Scaffolds Loaded with Platelet Growth Factors to Improve Cardiomyocyte Survival after Ischemia

Myocardial infarction is caused by prolonged ischemia and it is one of the main cause that leads to heart failures. The aim of the present work was the development of in situ gelling systems, based on poloxamer 407 (P407) or sodium alginate (Alg), loaded with platelet lysate (PL) to enhance cardiomyocyte survival after ischemia. Chondroitin sulfate (CS), a negatively charged glycosaminoglycan able to interact with different positively charged bioactive molecules, such as growth factors, was also investigated with both the systems. The gelation properties of both systems (viscosity, viscoelasticity, consistency by means of penetrometry, and injectability) were characterized in a physiological environment. In vitro evaluation of biocompatibility using fetal cardiac cells (cardiomyocytes and cardiac fibroblasts) demonstrated that the PL loaded alginate/chondroitin sulfate system retained the highest number of viable cells with equal distribution of the populations of cardiomyocytes and fibroblasts. Furthermore, the ability of the systems to improve cardiomyocyte survival after ischemia was also assessed. PL allowed for the highest degree of survival of cardiomyocytes after oxidative damage (simulating ischemic conditions due to MI) and both the Alg + CS PL and, to a greater extent, the PL alone demonstrated a considerable increase in survival of cardiomyocytes. In conclusion, an in situ gelling alginate-chondroitin sulfate system, loaded with platelet lysate, was able to improve the survival of cardiomyocytes after oxidative damage resulting in a promising system to improve cardiac cell viability after ischemia.

Synergistic treatment strategies to combat resistant bacterial infections using Schiff base modified nanoparticulate - hydrogel system

Antibiotic resistance is of much prevalence and is one of the alarming realities for the rise in morbidity and mortality. Antibiotics; once regarded as wonder drugs have lost its credit of combating bacteria due to the rapid rise in variety of nosocomial pathogens. The underlying cause for the resistance spread is due to sudden drift in genetic mutation and the recalcitrant behavior of bacterial species. On the other hand, illegal and overconsumption of drugs fuels up the issue, wherein resistance development is directly proportional to the rate of drug consumption. Our pursuit was in reviving antibiotic, and further repurposing them into more potent formulation with reduced side effects to completely deplete resistant bacteria. In this work we present gentamicin encapsulated zein nanoparticle modified with Schiff base incorporated in immobilized chitosan-polyvinyl alcohol gel matrix([GM-ZNP]PG CsPVA) resulting in synergistic antibacterial activity. Schiff base modified zein nanoparticle exhibited an average diameter of 240 ± 8 nm and stability of -29.85 ± 2 mV. The nanocomposite system exhibited enhanced penetration rate when applied to dermis eliciting combinatorial antibacterial activity. Gentamicin in combination with Schiff base was found to lyse bacteria by ruining its cell integrity as depicted by SEM analysis. The formulation upon application stays intact to the impaired dermal tissues and releases drug in a sustained manner without the need of recurrent administration. The gel system was extremely biocompatible towards L929 cells without any toxicity. Overall, the work reports use of [GM-ZNP]PG CsPVA for resistant bacterial infections.

Multivalent ion-based in situ gelling polysaccharide hydrogel as an injectable bone graft

We prepared in situ gelling alginate (ALG)/hyaluronic acid (HA) hydrogels with a controllable gelation rate using CaSO₄ as a crosslinking agent and Na₂HPO₄ as a crosslinking retardation agent. The ALG/HA hydrogels provided sustained release of bone morphogenetic protein-2 (BMP-2) immobilized in the hydrogels over 5 weeks. The BMP-2-immobilized ALG/HA hydrogels with different ALG/HA ratios were investigated for their in vitro osteogenic differentiation behavior of human bone marrow stem cells (hBMSCs) and in vivo bone regeneration behavior using an animal model (mandibular defect model of miniature pigs). Our findings from cell culture and animal study demonstrated that the osteogenic differentiation of hBMSCs was improved with increasing HA composition in the hydrogel. The hBMSCs/BMP-2-immobilized ALG/HA hydrogel allowed greatly enhanced osteogenic differentiation of hBMSCs (in vitro) and bone regeneration (in vivo) compared with the ALG/HA hydrogel itself and single hBMSCs- or BMP-2-immobilized hydrogel groups.

Smart Carriers and Nanohealers: A Nanomedical Insight on Natural Polymers

Biodegradable polymers are popularly being used in an increasing number of fields in the past few decades. The popularity and favorability of these materials are due to their remarkable properties, enabling a wide range of applications and market requirements to be met. Polymer biodegradable systems are a promising arena of research for targeted and site-specific controlled drug delivery, for developing artificial limbs, 3D porous scaffolds for cellular regeneration or tissue engineering and biosensing applications. Several natural polymers have been identified, blended, functionalized and applied for designing nanoscaffolds and drug carriers as a prerequisite for enumerable bionano technological applications. Apart from these, natural polymers have been well studied and are widely used in material science and industrial fields. The present review explains the prominent features of commonly used natural polymers (polysaccharides and proteins) in various nanomedical applications and reveals the current status of the polymer research in bionanotechnology and science sectors.

Marine macromolecules cross-linked hydrogel scaffolds as physiochemically and biologically favorable entities for tissue engineering applications

Marine biopolymer composite materials provide a technological platform for launching biomedical applications. Biomaterials demand good biocompatibility without the possibility of inflammation or foreign body reactions. In this study, we prepared two biocomposite hydrogels namely; HAC (hydroxyapatite, alginate & chitosan) and HACF (hydroxyapatite, alginate, chitosan & fucoidan) followed by calcium chloride cross linking. The prepared scaffolds were characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. Porosity measurement, swelling, biodegradation, hemolysis, RBC aggregation, plasma protein adsorption and cytotoxicity studies were also done. The hydrogel scaffold HACF possessed a well-defined porous architecture, sufficient water holding capacity, better hemocompatibility and biodegradability. The biocompatibility was confirmed through in vitro cytotoxicity studies such as MTT assay, Neutral red uptake, DAPI staining, Trypan blue dye exclusion test and direct contact assay in L929 mouse fibroblast cells. In addition, immunomodulatory and anti-inflammatory properties of both of these scaffolds were revealed by the mRNA expressions of major inflammatory marker genes in cytotoxic condition such as TNF-α, IL-6 and NF-κB. The physiochemical characterization and biological responses of HACF hydrogel signifies its suitability for various tissue engineering applications.

Development of a novel alginate-polyvinyl alcohol-hydroxyapatite hydrogel for 3D bioprinting bone tissue engineered scaffolds

Three-dimensional printed biomaterials used as personalized tissue substitutes have the ability to promote and enhance regeneration in areas of defected tissue. The challenge with 3D printing for bone tissue engineering remains the selection of a material with optimal rheological properties for printing in addition to biocompatibility and capacity for uniform cell incorporation. Hydrogel biomaterials may provide sufficient printability to allow cell encapsulation and bioprinting of scaffolds with uniform cell distribution. In this study, a novel alginate-polyvinyl alcohol (PVA)-hydroxyapatite (HA) hydrogel formulation with optimal rheological properties for 3D bioprinting of mouse calvaria 3T3-E1 (MC3T3) cells into scaffolds of high shape fidelity has been developed. A systematic investigation was conducted to determine the effect of varying concentrations of alginate, phosphate, calcium, and the PVA-HA suspension in the formulation on the resulting viscosity and thus printability of the hydrogel. HA, the main mineral component in natural bone, was incorporated into the hydrogel formulation to create a favorable bone-forming environment due to its excellent osteoconductivity. Degradation studies in α-MEM cell culture media showed that the 3D printed alginate-PVA-HA scaffolds remained in-tact for 14 days. MC3T3 cells were well distributed and encapsulated throughout the optimal hydrogel formulation and expressed high viability through the completion of the 3D printing process. Thus, the development of this novel, osteoconductive, biodegradable, alginate-PVA-HA formulation and its ability to 3D bioprint tissue engineered scaffolds make it a promising candidate for treating personalized bone defects. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 1457-1468, 2017.

Injectable hydrogel-based scaffolds for tissue engineering applications

Hydrogels are highly hydrated materials that may absorb from 10% to 20% up to hundreds of times their dry weight in water and are composed of three-dimensional hydrophilic polymeric networks that are similar to those in natural tissue. The structural integrity of hydrogels depends on cross-links formed between the polymer chains. Hydrogels have been extensively explored as injectable cell delivery systems, owing to their high tissue-like water content, ability to mimic extracellular matrix, homogeneously encapsulated cells, efficient mass transfer, amenability to chemical and physical modifications, and minimally invasive delivery. A variety of naturally and synthetically derived materials have been used to form injectable hydrogels for tissue engineering applications. The current review article focuses on these biomaterials, on the design parameters of injectable scaffolds, and on the

Calcium triggered self-assembly of alginate-graft-POEGMA via RAFT for the encapsulation of lipophillic actives

Self-assembly of alginate into nanoparticles was realized by grafting hydrophilic brushes via RAFT.

Injectable and 3D Bioprinted Polysaccharide Hydrogels: From Cartilage to Osteochondral Tissue Engineering

Biomechanical performance of functional cartilage is executed by the exclusive anisotropic composition and spatially varying intricate architecture in articulating ends of diarthrodial joint. Osteochondral tissue constituting the articulating ends comprise superfical soft cartilage over hard subchondral bone sandwiching interfacial soft-hard tissue. The shock-absorbent, lubricating property of cartilage and mechanical stability of subchondral bone regions are rendered by extended chemical structure of glycosaminoglycans and mineral deposition, respectively. Extracellular matrix glycosaminoglycans analogous polysaccharides are major class of hydrogels investigated for restoration of functional cartilage. Recently, injectable hydrogels have gained momentum as it offers patient compliance, tunable mechanical properties, cell deliverability, and facile administration at physiological condition with long-term functionality and hyaline cartilage construction. Interestingly, facile modifiable functional groups in carbohydrate polymers impart tailorability of desired physicochemical properties and versatile injectable chemistry for the development of highly potent biomimetic in situ forming scaffold. The scaffold design strategies have also evolved from single component to bi- or multilayered and graded constructs with osteogenic properties for deep subchondral regeneration. This review highlights the significance of polysaccharide structure-based functions in engineering cartilage tissue, injectable chemistries, strategies for combining analogous matrices with cells/stem cells and biomolecules and multicomponent approaches for osteochondral mimetic constructs. Further, the rheology and precise spatiotemporal positioning of cells in hydrogel bioink for rapid prototyping of complex three-dimensional anisotropic cartilage have also been discussed.

Synthesis and characterization of a novel injectable alginate–collagen–hydroxyapatite hydrogel for bone tissue regeneration

This novel fabrication process allowed for the development of an injectable hydrogel system with a gelation time suitable for a surgical setting and components necessary for promoting enhanced bone regeneration.

Blends and Nanocomposite Biomaterials for Articular Cartilage Tissue Engineering

This review provides a comprehensive assessment on polymer blends and nanocomposite systems for articular cartilage tissue engineering applications. Classification of various types of blends including natural/natural, synthetic/synthetic systems, their combination and nanocomposite biomaterials are studied. Additionally, an inclusive study on their characteristics, cell responses ability to mimic tissue and regenerate damaged articular cartilage with respect to have functionality and composition needed for native tissue, are also provided.

Manufacture of β-TCP/alginate scaffolds through a Fab@home model for application in bone tissue engineering

The growing need to treat bone-related diseases in an elderly population compels the development of novel bone substitutes to improve patient quality of life. In this context, the advent of affordable and effective rapid prototyping equipment, such as the Fab@home plotter, has contributed to the development of novel scaffolds for bone tissue engineering. In this study, we report for the first time the use of a Fab@home plotter for the production of 3D scaffolds composed by beta-tricalcium phosphate (β-TCP)/alginate hybrid materials. β-TCP/alginate mixtures were used in a proportion of 50/50% (w/w), 30/70% (w/w) and 20/80% (w/w). The printing parameters were optimized to a nozzle diameter of 20 Gauge for the production of rigid scaffolds with pre-defined architectures. We observed that, despite using similar printing parameters, both the precision and resolution of the scaffolds were significantly affected by the blend's viscosity. In particular, we demonstrate that the higher viscosity of 50/50 scaffolds (150.0 ± 3.91 mPa s) provides a higher precision in the extrusion process. The physicochemical and biological characterization of the samples demonstrated that the 50/50 scaffolds possessed a resistance to compression comparable to that of native trabecular bone. Moreover, this particular formulation also exhibited a Young's modulus that was higher than that of trabecular bone. Scanning electron microscopy and fluorescence microscopy analysis revealed that osteoblasts were able to adhere, proliferate and also penetrate into the scaffold's architecture. Altogether, our findings suggest that the Fab@home printer can be employed in the manufacture of reproducible scaffolds, using a formulation 50/50 alginate-β-TCP that has suitable properties to be applied as bone substitutes in the future.

Hydrogel based injectable scaffolds for cardiac tissue regeneration

Tissue engineering promises to be an effective strategy that can overcome the lacuna existing in the current pharmacological and interventional therapies and heart transplantation. Heart failure continues to be a major contributor to the morbidity and mortality across the globe. This may be attributed to the limited regeneration capacity after the adult cardiomyocytes are terminally differentiated or injured. Various strategies involving acellular scaffolds, stem cells, and combinations of stem cells, scaffolds and growth factors have been investigated for effective cardiac tissue regeneration. Recently, injectable hydrogels have emerged as a potential candidate among various categories of biomaterials for cardiac tissue regeneration due to improved patient compliance and facile administration via minimal invasive mode that treats complex infarction. This review discusses in detail on the advances made in the field of injectable materials for cardiac tissue engineering highlighting their merits over their preformed counterparts.

In vitro degradation and drug-release properties of water-soluble chitosan cross-linked oxidized sodium alginate core-shell microgels

Hydrogels based on sodium alginate (SA) have already been widely used in biomedical applications using Ca(2+) as a cross-linker; however, these hydrogels tend to disintegrate in electrolyte solutions. To solve this problem, we present a kind of oxidized sodium alginate (OSA) microgel using water-soluble chitosan (WSC) as a cross-linker. This microgel was successfully prepared via an emulsion cross-linking technique at room temperature. The microgel was cross-linked by the formation of both Schiff base bonds and inter-polyelectrolyte complexes, which can efficiently eliminate the disintegration of the microgel in electrolyte solutions. Morphological properties of the resulting microgels were determined by transmission electron microscopy (TEM), hydrodynamic diameters of the microgels were characterized by dynamic light scattering (DLS). The objective of this work was to achieve the colon-specific delivery of an anti-ulcerative colitis drug. 5-Aminosalicylic acid (5-ASA) was chosen as a model drug and the in vitro drug-release profile was established in buffer solutions with 0.1 M HCl/NaCl (pH 1.2) and 0.1 M phosphate-buffered saline (PBS, pH 7.4) at 37°C. The microgel was incubated in 0.1 M PBS (pH 7.4) at 37°C to determine its degradation behavior. Cell cytotoxicity (tested by MTT assay) showed that this microgel had no significant cytotoxicity. These results indicated that this microgel prepared by introducing WSC into OSA may have potential applications in oral controlled drug-delivery systems. Therefore, the OSA/WSC microgel may be a useful carrier for the colon-specific delivery of anti-inflammatory drugs including 5-ASA and the enhanced therapeutic effect of ulcerative colitis.

A novel hydrogel-collagen composite improves functionality of an injectable extracellular matrix

Cellular transplantation is now closer to becoming a practical clinical strategy to repair, regenerate or restore the function of skin, muscle, nerves and pancreatic islets. In this study we sought to develop a simple injectable collagen matrix that would preserve the normal cellular organization of skin cells. Three different scaffolds were created and compared: collagen-glycosaminoglycan (GAG) scaffolds, crosslinked collagen-GAG scaffolds without polyvinyl alcohol (PVA) and crosslinked collagen-GAG scaffolds containing PVA hydrogel. Importantly, all scaffolds were found to be non-cytotoxic. PVA-containing gels exhibited a higher tensile strength (P<0.05), faster fibril formation (P<0.001) and reduced collagenase digestion (P<0.01) compared with other gels. Free floating fibroblast-populated, PVA-borate scaffolds resisted contraction over a 10 day period (P<0.001). The fibroblast-populated scaffolds containing PVA demonstrated a 3-fold reduction in cellularity over 10 days compared with the control gels (P<0.001). Multicellular skin substitutes containing PVA-borate networks display a linear cellular organization, reduced cellularity and the formation of a keratinized epidermis that resembles normal skin. In conclusion, these data underscore the multifunctionality of a simple PVA-borate-collagen matrix as an injectable composite for tissue engineering or cell transplantation.

Dual growth factor-releasing nanoparticle/hydrogel system for cartilage tissue engineering

In order to induce the chondrogenesis of mesenchymal stem cells (MSCs) in tissue engineering, a variety of growth factors have been adapted and encouraging results have been demonstrated. In this study, we developed a delivery system for dual growth factors using a gelation rate controllable alginate solution (containing BMP-7) and polyion complex nanoparticles (containing TGF-beta(2)) to be applied for the chondrogenesis of MSCs. The dual growth factors (BMP-7/TGF-beta(2))-loaded nanoparticle/hydrogel system showed a controlled release of both growth factors: a faster release of BMP-7 and a slower release of TGF-beta(2), ca., approximately 80 and 30% release at the end of an incubation period (21 days), respectively, which may be highly desirable for chondrogenic differentiation of MSCs. On the contrary, the release of each growth factor from the dual growth factors-loaded hydrogel (without the nanoparticles) was much slower than that of the nanoparticle/hydrogel system, approximately 36% (BMP-7) and 16% (TGF-beta(2)) for 21 days, and this is more than likely attributed to the aggregation between growth factors during the hydrogel fabrication step. The nanoparticle/hydrogel system with separate growth factor loading may provide desirable growth factor delivery kinetics for cartilage regeneration, as well as the chondrogenesis of MSCs.