Evaluation of novel alginate dialdehyde cross-linked chitosan/calcium polyphosphate composite scaffolds for meniscus tissue engineering

Cleaner Leather Tanning and Post-Tanning Processes Using Oxidized Alginate as Biodegradable Tanning Agent and Nano-Hydroxyapatite as Potential Flame Retardant

In this study, sodium alginate (SA) was oxidized with potassium periodate to produce an alginate-based tanning agent. Using OSA as a biodegradable tanning agent and a nano-hydroxyapatite (nano-HAp) low concentration suspension to give flame retardancy to leather, eco-design concepts were applied to establish a chrome-, aldehyde-, and phenol-free tanning process. Micro-DSC, 1H unilateral nuclear magnetic resonance (NMR), attenuated total reflection mode Fourier transform infrared spectroscopy (FTIR-ATR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) were used to investigate the complex matrix collagen-OSA-nano-HAp. Micro-differential scanning calorimetry (micro-DSC) was used to assess OSA's ability to interact with collagen and stabilize the collagen-OSA matrix, while 1H unilateral (NMR) was used to investigate the aqueous environment and its limitations around collagen molecules caused by their association with OSA and nano-HAp. Industrial standard tests were used to assess the mechanical properties and fire resistance of the new leather prototype. The findings reported here indicate that both OSA and nano-HAp are suitable alternatives for cleaner tanning technologies and more sustainable leather.

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

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

Synthesis and characterization of electroconductive hydrogels based on oxidized alginate and polypyrrole-grafted gelatin as tissue scaffolds

Electroconductive biocompatible hydrogels with tunable properties have extensively been taken into account in tissue engineering applications due to their potential to provide suitable microenvironmental responses for the cells. In the present study, novel electroconductive hydrogels are designed and synthesized by reacting oxidized alginate with polypyrrole-grafted gelatin copolymer (PPy-g-gelatin) via formation of a Schiff-base linkage. The influence of the composition and the concentration of the components on the compressive modulus and functional performance of the hydrogels is investigated. The conductivity of the hydrogels measured by a two-probe method increased by increasing the level of polypyrrole-grafted gelatin, and a conductivity of 0.7753 S m^-1 was exhibited by the hydrogel composed of 8% w/v polypyrrole-grafted gelatin (oxidized alginate:gelatin:polypyrrole-grafted gelatin; 30 : 35 : 35% v/v). The hydrogel compressive modulus was shown to be enhanced by increasing the total concentration of hydrogel. The characteristic features of the prepared hydrogels, including swelling ratio, volume fraction, cross-link density, and mesh size, are also studied and analyzed. Besides, the conductive hydrogels have a smaller mesh size and higher cross-link density than the non-conductive hydrogels. However, the hydrogels with high cross-link density, small mesh size, and large pore size presented higher electroconductivity as a result of easier movement of the ions throughout the hydrogel. These conductive hydrogels exhibited electrical conductivity and biodegradability with cell viability, implying potential as scaffolds for tissue engineering.

Applications of oxidized alginate in regenerative medicine

Because of its ideal degradation rate and features, oxidized alginate (OA) is selected as an appropriate substitute and has been introduced into hydrogels, microspheres, 3D-printed/composite scaffolds, membranes, and electrospinning and coating materials. By taking advantage of OA, the OA-based materials can be easily functionalized and deliver drugs or growth factors to promote tissue regeneration. In 1928, it was first found that alginate could be oxidized using periodate, yielding OA. Since then, considerable progress has been made in the research on the modification and application of alginate after oxidation. In this article, we summarize the key properties and existing applications of OA and various OA-based materials and discuss their prospects in regenerative medicine.

pH-Responsive dopamine-based nanoparticles assembled via Schiff base bonds for synergistic anticancer therapy

Dopamine-based nanoparticles are constructed via Schiff base bonds to serve as pH-responsive drug nanocarriers for combined photodynamic therapy and chemotherapy.

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.

Structural Investigation of a Self-Cross-Linked Chitosan/Alginate Dialdehyde Multilayered Film with in Situ QCM-D and Spectroscopic Ellipsometry

A chitosan/alginate dialdehyde multilayered film was fabricated using the layer-by-layer assembly method. Besides electrostatic interaction that promotes alternate adsorption of the oppositely charged polyelectrolytes, the Schiff base reaction between the amine groups on chitosan and the aldehyde groups on alginate dialdehyde provides a covalently cross-linked film, which after reduction by sodium cyanoborohydride is stable under both acidic and alkaline conditions. Moreover, the cross-linked film is responsive to changes in pH and addition of multivalent salts. The structural properties of the multilayered film such as thickness, refractive index, and water content were examined using simultaneous quartz crystal microbalance with dissipation monitoring and spectroscopic ellipsometry.

Human Knee Meniscus Regeneration Strategies: a Review on Recent Advances

PURPOSE OF REVIEW

Lack of vascularity in the human knee meniscus often leads to surgical removal (total or partial meniscectomy) in the case of severe meniscal damage. However, complete recovery is in question after such removal as the meniscus plays an important role in knee stability. Thus, meniscus tissue regeneration strategies are of intense research interest in recent years.

RECENT FINDINGS

The structural complexity and inhomogeneity of the meniscus have been addressed with processing technologies for precisely controlled three dimensional (3D) complex porous scaffold architectures, the use of biomolecules and nanomaterials. The regeneration and replacement of the total meniscus have been studied by the orthopedic and scientific communities via successful pre-clinical trials towards mimicking the biomechanical properties of the human knee meniscus. Researchers have attempted different regeneration strategies which contribute to in vitro regeneration and are capable of repairing meniscal tears to some extent. This review discusses the present state of the art of these meniscus tissue engineering aspects.

Modification of collagen with a natural derived cross-linker, alginate dialdehyde

The interaction between collagen and a natural derived cross-linker alginate dialdehyde (ADA) was investigated. Fourier transform infrared (FTIR) spectroscopy and the circular dichroism (CD) measurements indicate that the structure integrity of collagen is still maintained after the ADA treatment, while the differential scanning calorimetry (DSC) study suggests that ADA could promote collagen-ADA membrane's thermostability compared to pure collagen. And the atomic force microscopy (AFM) of cross-linked collagen reveals a denser network structure. Besides, the water contact angle test indicates that the hydrophilic property of collagen-ADA membrane is promoted, which is favorable for cell's attachment and proliferation. Meanwhile, the cytocompatibility results imply that not only no extra cytotoxicity is introduced into the collagen-ADA membrane after ADA treatment, but also collagen-ADA membrane facilitates cell's proliferation when the content of ADA is less than 20%. In conclusion, our study reveals that ADA stabilizes collagen as a cross-linker and preserves its triple helical structure.

Assembled microcapsules by doxorubicin and polysaccharide as high effective anticancer drug carriers

Doxorubicin, together with the modified polysaccharide (alginate dialdehyde), was used as a wall material to fabricate microcapsules through self-cross-linking by a template method. The microcapsules as-prepared are pH-responsive. Relevant scanning electronic microscopy, atom force microscopy and confocal laser scanning microscopy confirm the morphology of the uniform microcapsules. The spectroscopic results show that the microcapsules are assembled through electrostatic interaction and Schiff's base covalent bonding. Doxorubicin can be released sustainably from the capsules in buffer solution at a lower pH value. The cellular uptake of the microcapsules and drug release induced by acidic microenvironment are time-dependent processes. The cell cytotoxicity experiments in vitro demonstrate that the doxorubicin-based microcapsules have high efficiency to kill the cancer cells.

Optimization strategies on the structural modeling of gelatin/chitosan scaffolds to mimic human meniscus tissue

Meniscus lesions are frequently occurring injuries with poor ability to heal. Typical treatment procedure includes removal of damaged regions, which can lead to sub-optimal knee biomechanics and early onset of osteoarthritis. Some of the drawbacks of current treatment approach present an opportunity for a tissue engineering solution. In this study, gelatin (G)/chitosan (Cs) scaffolds were synthesized via gel casting method and cross-linked with naturally derived cross-linker, genipin, through scaffold cross-linking method. Based on the characteristics of native meniscus tissue microstructure and function, three different layers were chosen to design the macroporous multilayered scaffolds. The multi-layered scaffolds were investigated for their ability to support human-derived meniscus cells by evaluating their morphology and proliferation using MTT assay at various time points. Based on structural, mechanical and cell compatibility considerations, laminated scaffolds composed of G60/Cs40, G80/Cs20 and G40/Cs60 samples, for the first, second and third layers, respectively, could be an appropriate combination for meniscus tissue engineering applications.

Bioluminescent microcapsules: applications in activating a photosensitizer

Bioluminescent microcapsules uploading D-luciferin have been fabricated by using the covalent assembly of firefly luciferase and alginate dialdehyde through a layer-by-layer technique. Such assembled microcapsules can produce visible light in the region of 520-680 nm, which can activate the photosensitizers rose bengal (RB) and hypocrellin B (HB) after adding ATP. The microcapsules uploading photosensitizers (RB or HB) have an obvious property to prevent the proliferation of tumor cells in the dark. The assembled bioluminescent microcapsules can be potentially used as photon donors for bioimaging, ATP detection, and photodynamic therapy.

Self-assembly of conjugated polymer on hybrid nanospheres for cellular imaging applications

A new kind of hybrid core-shell nanosphere was fabricated by combining the in situ formation of Au nanoparticles and covalent cross-linking of biocompatible carboxymethyl starch dialdehyde (CMSD) and chitosan (CTS). When the fluorescent dye poly[9,9'-bis(6″-(N,N,N-trimethylammonium)-hexyl)fluorene-2,7-ylenevinylene-co-alt-1,4-phenylene dibromide] (PFV) was assembled on the surface of the hybrid nanospheres through electrostatic attraction, these biocompatible hybrid nanospheres exhibited metal-enhanced fluorescence effects. The fluorescence intensity of (CTS-Au)@CMSD/PFV hybrid nanosphere is 1.43 times that of CTS-CMSD/PFV hybrid nanospheres lacking Au nanoparticle. In addition, the (CTS-Au)@CMSD/PFV hybrid nanospheres exhibit excellent biodegradability upon exposure to enzymatic aqueous solution and good biocompatibility when cocultured with HeLa cervical carcinoma cells; these advantages make them attractive for cellular imaging and biological analysis and detection.

pH- and redox-responsive polysaccharide-based microcapsules with autofluorescence for biomedical applications

Autofluorescent microcapsules were assembled by covalent cross-linking of polysaccharide alginate dialdehyde (ADA) derivative and cystamine dihydrochloride (CM) through a layer-by-layer (LBL) technique. The formulated Schiff base and disulfide bonds render capsules with pH- and redox-responsive properties for pinpointed intracellular delivery based on the physiological difference between intracellular and extracellular environments. This simple and versatile method could be extended to other polysaccharide derivatives for the fabrication of autofluorescent nano- and micromaterials with dual stimuli response for biomedical applications.

Bioactive surface modification on amide-photografted poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Collagen was chemically immobilized on poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) films via hydrophilic polyacrylamide spacers, aiming to establish the bioactive surface and the inner surface models. The inner surface modified films presented higher wettability than the surface modified films. Wide-angle x-ray diffraction results showed that the d-spacing values of the inner surface model increased compared with those of the surface model, but there was no significant difference between the amide- and collagen-modified PHBV films. The peak melting temperatures of PHBV and the special endotherm around 70 °C were following the order: PHBV > amide-modified PHBV > collagen-modified PHBV. The weight loss of the collagen-modified PHBV (inner surface model) might involve hydrolyzation and mineralization during 360 days of incubation, with a maximum value of 18.24%, while PHBV films did not show significant weight loss. The pH value of the degradation fluids fluctuated in the range of 6.86-7.22, as the initial pH was recorded at 7.20. Based on the surface model, collagen-modified PHBV scaffolds were prepared, which enhanced chondrocyte adhesion and spread on the biomimetic surface. Two surface modification models might develop a protocol with a view to generating a biocompatible and biomechanical scaffold for use in meniscus regeneration.