Supermacroprous chitosan-agarose-gelatin cryogels: in vitro characterization and in vivo assessment for cartilage tissue engineering

Biocomposite Scaffolds Based on Chitosan Extraction from Shrimp Shell Waste for Cartilage Tissue Engineering Application

Chitosan-based scaffolding possesses unique properties that make it highly suitable for tissue engineering applications. Chitosan is derived from deacetylating chitin, which is particularly abundant in the shells of crustaceans. This study aimed to extract chitosan from shrimp shell waste (Macrobrachium rosenbergii) and produce biocomposite scaffolds using the extracted chitosan for cartilage tissue engineering applications. Chitinous material from shrimp shell waste was deproteinized and deacetylated. The extracted chitosan was characterized and compared to commercial chitosan through various physicochemical analyses. The findings revealed that the extracted chitosan shares similar trends in the Fourier transform infrared spectroscopy spectrum, energy dispersive X-ray mapping, and X-ray diffraction pattern to commercial chitosan. Despite differences in the degree of deacetylation, these results underscore its comparable quality. The extracted chitosan was mixed with agarose, collagen, and gelatin to produce the blending biocomposite AG-CH-COL-GEL scaffold by freeze-drying method. Results showed AG-CH-COL-GEL scaffolds have a 3D interconnected porous structure with pore size 88-278 μm, high water uptake capacity (>90%), and degradation percentages in 21 days between 5.08% and 30.29%. Mechanical compression testing revealed that the elastic modulus of AG-CH-COL-GEL scaffolds ranged from 44.91 to 201.77 KPa. Moreover, AG-CH-COL-GEL scaffolds have shown significant potential in effectively inducing human chondrocyte proliferation and enhancing aggrecan gene expression. In conclusion, AG-CH-COL-GEL scaffolds emerge as promising candidates for cartilage tissue engineering with their optimal physical properties and excellent biocompatibility. This study highlights the potential of using waste-derived chitosan and opens new avenues for sustainable and effective tissue engineering solutions.

Tuning Mechanical Properties, Swelling, and Enzymatic Degradation of Chitosan Cryogels Using Diglycidyl Ethers of Glycols with Different Chain Length as Cross-Linkers

Cross-linking chitosan at room and subzero temperature using a series of diglycidyl ethers of glycols (DEs)-ethylene glycol (EGDE), 1,4-butanediol (BDDE), and poly(ethylene glycol) (PEGDE) has been investigated to demonstrate that DEs can be a more powerful alternative to glutaraldehyde (GA) for fabrication of biocompatible chitosan cryogels with tunable properties. Gelation of chitosan with DEs was significantly slower than with GA, allowing formation of cryogels with larger pores and higher permeability, more suitable for flow-through applications and cell culturing. Increased hydration of the cross-links with increased DE chain length weakened intermolecular hydrogen bonding in chitosan and improved cryogel elasticity. At high cross-linking ratios (DE:chitosan 1:4), the toughness and compressive strength of the cryogels decreased in the order EGDE > BDDE > PEGDE. By varying the DE chain length and concentration, permeable chitosan cryogels with elasticity moduli from 10.4 ± 0.8 to 41 ± 3 kPa, toughness from 2.68 ± 0.5 to 8.3 ± 0.1 kJ/m3, and compressive strength at 75% strain from 11 ± 2 to 33 ± 4 kPa were fabricated. Susceptibility of cryogels to enzymatic hydrolysis was identified as the parameter most sensitive to cross-linking conditions. Weight loss of cryogels increased with increased DE chain length, and degradation rate of PEGDE-cross-linked chitosan decreased 612-fold, when the cross-linker concentration increased 20-fold.

Transforming growth factor-β1-loaded RADA-16 hydrogel scaffold for effective cartilage regeneration

Cartilage repair remains a major challenge in clinical trials. These current cartilage repair materials can not effectively promote chondrocyte generation, limiting their practical application in cartilage repair. In this work, we develop an implantable scaffold of RADA-16 peptide hydrogel incorporated with TGF-β1 to provide a microenvironment for stem cell-directed differentiation and chondrocyte adhesion growth. The longest release of growth factor TGF-β1 release can reach up to 600 h under physiological conditions. TGF-β1/RADA-16 hydrogel was demonstrated to be a lamellar porous structure. Based on the cell culture with hBMSCs, TGF-β1/RADA-16 hydrogel showed excellent ability to promote cell proliferation, directed differentiation into chondrocytes, and functional protein secretion. Within 14 days, 80% of hBMSCs were observed to be directed to differentiate into vigorous chondrocytes in the co-culture of TGF-β1/RADA-16 hydrogels with hBMSCs. Specifically, these newly generated chondrocytes can secrete and accumulate large amounts of collagen II within 28 days, which can effectively promote the formation of cartilage tissue. Finally, the exploration of RADA-16 hydrogel-based scaffolds incorporated with TGF-β1 bioactive species would further greatly promote the practical clinical trials of cartilage remediation, which might have excellent potential to promote cartilage regeneration in areas of cartilage damage.

Role of crosstalk between synovial cells and chondrocytes in osteoarthritis (Review)

Osteoarthritis (OA) is a low-grade, nonspecific inflammatory disease that affects the entire joint. This condition is characterized by synovitis, cartilage erosion, subchondral bone defects, and subpatellar fat pad damage. There is mounting evidence demonstrating the significance of crosstalk between synovitis and cartilage destruction in the development of OA. To comprehensively explore the phenotypic alterations of synovitis and cartilage destruction, it is important to elucidate the crosstalk mechanisms between chondrocytes and synovial cells. Furthermore, the updated iteration of single-cell sequencing technology reveals the interaction between chondrocyte and synovial cells. In the present review, the histological and pathological alterations between cartilage and synovium during OA progression are described, and the mode of interaction and molecular mechanisms between synovial cells and chondrocytes in OA, both of which affect the OA process mainly by altering the inflammatory environment and cellular state, are elucidated. Finally, the current OA therapeutic approaches are summarized and emerging therapeutic targets are reviewed in an attempt to provide potential insights into OA treatment.

Hydrogel-based immunoregulation of macrophages for tissue repair and regeneration

The rational design of hydrogel materials to modulate the immune microenvironment has emerged as a pivotal approach in expediting tissue repair and regeneration. Within the immune microenvironment, an array of immune cells exists, with macrophages gaining prominence in the field of tissue repair and regeneration due to their roles in cytokine regulation to promote regeneration, maintain tissue homeostasis, and facilitate repair. Macrophages can be categorized into two types: classically activated M1 (pro-inflammatory) and alternatively activated M2 (anti-inflammatory and pro-repair). By regulating the physical and chemical properties of hydrogels, the phenotypic transformation and cell behavior of macrophages can be effectively controlled, thereby promoting tissue regeneration and repair. A full understanding of the interaction between hydrogels and macrophages can provide new ideas and methods for future tissue engineering and clinical treatment. Therefore, this paper reviews the effects of hydrogel components, hardness, pore size, and surface morphology on cell behaviors such as macrophage proliferation, migration, and phenotypic polarization, and explores the application of hydrogels based on macrophage immune regulation in skin, bone, cartilage, and nerve tissue repair. Finally, the challenges and future prospects of macrophage-based immunomodulatory hydrogels are discussed.

Self-crosslinked polyvinyl alcohol/cellulose nanofibril cryogels loaded with synthesized aminophosphonates as antimicrobial wound dressings

Microbial infection is the most common obstacle in the wound healing process, leading to wound healing impairment and complications and ultimately increasing morbidity and mortality. Due to the rising number of pathogens evolving resistance to the existing antibiotics used for wound care, alternative approaches are urgently required. In this study, α-aminophosphonate derivatives as antimicrobial agents were synthesized and incorporated into self-crosslinked tri-component cryogels composed of fully hydrolyzed polyvinyl alcohol (PVA-F), partially hydrolyzed polyvinyl alcohol (PVA-P), and cellulose nanofibrils (CNFs). Initially, the antimicrobial activity of four α-aminophosphonate derivatives against selected skin bacterial species was tested and their minimum inhibitory concentration was determined based on which the most effective compound was loaded into the cryogels. Next, the physical and mechanical properties of cryogels with various blending ratios of PVA-P/PVA-F and fixed amounts of CNFs were assessed, and drug release profiles and biological activities of drug-loaded cryogels were analyzed. Assessment of α-aminophosphonate derivatives showed the highest efficacy of a cinnamaldehyde-based derivative (Cinnam) against both Gram-negative and Gram-positive bacteria compared to other derivatives. The physical and mechanical properties of cryogels showed that PVA-P/PVA-F with a 50/50 blending ratio had the highest swelling ratio (1600%), surface area (523 m² g^-1), and compression recoverability (72%) compared to that with other blending ratios. Finally, antimicrobial and biofilm development studies showed that the cryogel loaded with a Cinnam amount of 2 mg (relative to polymer weight) showed the most sustained drug release profile over 75 h and had the highest efficacy against Gram-negative and Gram-positive bacteria. In conclusion, self-crosslinked tri-component cryogels loaded with the synthesized α-aminophosphonate derivative, having both antimicrobial and anti-biofilm formation properties, can have a significant impact on the management of uprising wound infection.

Role of macrophage polarization in osteoarthritis (Review)

Osteoarthritis (OA) is a disease involving the whole joint that seriously reduces the living standards of individuals. Traditional treatments include physical therapy, administration of anti-inflammatory and analgesic drugs and injection of glucocorticoids or hyaluronic acid into the joints. However, these methods have limited efficacy and it is difficult to reverse the progression of OA, therefore it is urgent to find new effective treatment methods. Immune microenvironment is significant in the occurrence and development of OA. Recent studies have shown that macrophages are important targets for the treatment of OA. Macrophages are polarized into M1 pro-inflammatory phenotype and M2 anti-inflammatory phenotype under stimulation of different factors, which release and regulate inflammatory response and cartilage growth. Accumulating studies have tried to alleviate OA by regulating macrophage homeostasis. The present study summarized the related studies, discuss the mechanism of various therapeutic reagents on OA, expound the molecular mechanism of drug effect on OA and attempted to provide clues for the treatment of OA.

Multifunctional chitosan/gelatin@tannic acid cryogels decorated with in situ reduced silver nanoparticles for wound healing

Background

Most traditional wound dressings only partially meet the needs of wound healing because of their single function. Patients usually suffer from the increasing cost of treatment and pain resulting from the frequent changing of wound dressings. Herein, we have developed a mutifunctional cryogel to promote bacterial infected wound healing based on a biocompatible polysaccharide.

Methods

The multifunctional cryogel is made up of a compositive scaffold of chitosan (CS), gelatin (Gel) and tannic acid (TA) and in situ formed silver nanoparticles (Ag NPs). A liver bleeding rat model was used to evaluate the dynamic hemostasis performance of the various cryogels. In order to evaluate the antibacterial properties of the prepared cryogels, gram-positive bacterium Staphylococcus aureus (S. aureus) and gram-negative bacterium Escherichia coli (E. coli) were cultured with the cryogels for 12 h. Meanwhile, S. aureus was introduced to cause bacterial infection in vivo. After treatment for 2 days, the exudates from wound sites were dipped for bacterial colony culture. Subsequently, the anti-inflammatory effect of the various cryogels was evaluated by western blotting and enzyme-linked immunosorbent assay. Finally, full-thickness skin defect models on the back of SD rats were established to assess the wound healing performances of the cryogels.

Results

Due to its porous structure, the multifunctional cryogel showed fast liver hemostasis. The introduced Ag NPs endowed the cryogel with an antibacterial efficiency of >99.9% against both S. aureus and E. coli. Benefited from the polyphenol groups of TA, the cryogel could inhibit nuclear factor-κB nuclear translocation and down-regulate inflammatory cytokines for an anti-inflammatory effect. Meanwhile, excessive reactive oxygen species could also be scavenged effectively. Despite the presence of Ag NPs, the cryogel did not show cytotoxicity and hemolysis. Moreover, in vivo experiments demonstrated that the biocompatible cryogel displayed effective bacterial disinfection and accelerated wound healing.

Conclusions

The multifunctional cryogel, with fast hemostasis, antibacterial and anti-inflammation properties and the ability to promote cell proliferation could be widely applied as a wound dressing for bacterial infected wound healing.

Shape memory injectable cryogel based on carboxymethyl chitosan/gelatin for minimally invasive tissue engineering: In vitro and in vivo assays

Shape-memory cryogels have drawn attention as an injectable system to minimize the risks associated with surgical implantation in tissue engineering. To achieve shape memory behavior with hydration as an external stimulus, it is necessary to have a porous elastic network. To achieve this, it is crucial to control the crosslinking process at the time of pore formation, especially for natural-based polymers. In this study, a versatile method using a cryogelation method in the presence of chemical and physical crosslinkers is investigated to obtain an injectable super macroporous elastic structure based on a poly(ampholyte) (carboxymethyl chitosan) and a protein (gelatin). Mechanical, swelling, shape memorizing behavior, injectability, and in vitro and in vivo behavior of cryogels were studied. Cryogelation in a subzero temperature led to the formation of scaffolds with interconnected pores of the size of 350 μm which swelled completely after 3 min. Cryogels had crosslink density up to 22% and elastic modulus in the hydrated state up to 0.054 and 1.733 MPa at low and high strains, respectively, and low hysteresis (<30 kPa). Injectability studies confirmed the ability of the cryogels to be injected through a 16G needle. In vitro studies demonstrated good cellular penetration, cell adhesion, and high cell viability (>100%). In vivo studies using mice showed that the body's response was befitting without inflammation and any side effect for the liver and kidneys.

The immune microenvironment in cartilage injury and repair

The ability of articular cartilage to repair itself is limited because it lacks blood vessels, nerves, and lymph tissue. Once damaged, it can lead to joint swelling and pain, accelerating the progression of osteoarthritis. To date, complete regeneration of hyaline cartilage exhibiting mechanical properties remains an elusive goal, despite the many available technologies. The inflammatory milieu created by cartilage damage is critical for chondrocyte death and hypertrophy, extracellular matrix breakdown, ectopic bone formation, and progression of cartilage injury to osteoarthritis. In the inflammatory microenvironment, mesenchymal stem cells (MSCs) undergo aberrant differentiation, and chondrocytes begin to convert or dedifferentiate into cells with a fibroblast phenotype, thereby resulting in fibrocartilage with poor mechanical qualities. All these factors suggest that inflammatory problems may be a major stumbling block to cartilage repair. To produce a milieu conducive to cartilage repair, multi-dimensional management of the joint inflammatory microenvironment in place and time is required. Therefore, this calls for elucidation of the immune microenvironment of cartilage repair after injury. This review provides a brief overview of: (1) the pathogenesis of cartilage injury; (2) immune cells in cartilage injury and repair; (3) effects of inflammatory cytokines on cartilage repair; (4) clinical strategies for treating cartilage defects; and (5) strategies for targeted immunoregulation in cartilage repair. STATEMENT OF SIGNIFICANCE: Immune response is increasingly considered the key factor affecting cartilage repair. It has both negative and positive regulatory effects on the process of regeneration and repair. Proinflammatory factors are secreted in large numbers, and necrotic cartilage is removed. During the repair period, immune cells can secrete anti-inflammatory factors and chondrogenic cytokines, which can inhibit inflammation and promote cartilage repair. However, inflammatory factors persist, which accelerate the degradation of the cartilage matrix. Furthermore, in an inflammatory microenvironment, MSCs undergo abnormal differentiation, and chondrocytes begin to transform or dedifferentiate into fibroblast-like cells, forming fibrocartilage with poor mechanical properties. Consequently, cartilage regeneration requires multi-dimensional regulation of the joint inflammatory microenvironment in space and time to make it conducive to cartilage regeneration.

Evaluating potential of tissue-engineered cryogels and chondrocyte derived exosomes in articular cartilage repair

Treatment of articular cartilage injuries especially osteochondral tissue requires intervention of bioengineered scaffold. In this study, we investigated the potential of the tissue-engineered cryogel scaffold fabricated using cryogelation technology. Two types of cryogels viz. chitosan-gelatin-chondroitin sulfate (CGC) for articular cartilage and nano-hydroxyapatite-gelatin (HG) for subchondral bone were fabricated. Further, novel bilayer cryogel designed using single process fabrication of two layers (CGC as top layer and HG as the lower layer) was designed to mimic osteochondral unit. CGC cryogel was tested for their biocompatibility using the enzymatically isolated chondrcoytes from goat articular cartilage while HG cryogel was tested using pre-osteoblast cell line. Extracellular vesicles, specifically exosomes were isolated from the spent media of chondrocytes to validate their effect over cell proliferation and migration which are required for defect healing and infiltration respectively. These isolated exosomes were characterized and analyzed for confirming their size distribution profile and visualized morphologically using advanced microscopy techniques. For cartilage part, CGC cryogels were examined as delivery system for delivering exosomes at defect site, where 80% of release was observed in 72 h. Release of 18.7 µg chondroitin sulfate/mg cryogel was obtained in a period of one week from CGC cryogel (termed cryogel extract) which has chondroprotective effect. Further, effect of exosome concentration (10 and 20 µg/ml), CGC extract and combination of exosome and CGC extract (Exo-Ex) were assessed over the chondrocytes. In addition, in vitro scratch wound assay was performed to analyse the migration capacity over the micro-injury when treated with exosomes, cryogel extract and Exo-Ex. The overall results thus answer key questions of therapeutic potential of chondrocyte exosomes, cryogel extract in addition to potential of CGC and HG cryogel for osteochondral repair.

Photo-Crosslinked Gelatin-Based Hydrogel Films to Support Wound Healing

Gelatin is used widely in the biomedical field, among other for wound healing. Given its upper critical solution temperature, crosslinking is required. To this end, gelatin is chemically modified with different photo-crosslinkable moieties with low (32-34%) and high (63-65%) degree of substitution (DS): gelatin-methacrylamide (gel-MA) and gelatin-acrylamide (gel-AA) and gelatin-pentenamide (gel-PE). Next to the more researched gel-MA, it is especially interesting and novel to compare with other gelatin-derived compounds for the application of wound healing. An additional comparison is made with commercial dressings. The DS is directly proportional to the mechanical characteristics and inversely proportional to the swelling capacity. Gel-PE shows weaker mechanical properties (G' < 15 kPa) than gel-AA and gel-MA (G' < 39 and 45 kPa, respectively). All derivatives are predominantly elastic (recovery indices of 89-94%). Gel-AA and gel-MA show excellent biocompatibility, whereas gel-PE shows a significantly lower initial biocompatibility, evolving positively toward day 7. Overall, gel-MA shows to have the most potential to be applied as wound dressing. Future blending with gel-AA to improve the curing kinetics can lead to dressings able to compete with current commercial dressings.

An Overview on Collagen and Gelatin-Based Cryogels: Fabrication, Classification, Properties and Biomedical Applications

Decades of research into cryogels have resulted in the development of many types of cryogels for various applications. Collagen and gelatin possess nontoxicity, intrinsic gel-forming ability and physicochemical properties, and excellent biocompatibility and biodegradability, making them very desirable candidates for the fabrication of cryogels. Collagen-based cryogels (CBCs) and gelatin-based cryogels (GBCs) have been successfully applied as three-dimensional substrates for cell culture and have shown promise for biomedical use. A key point in the development of CBCs and GBCs is the quantitative and precise characterization of their properties and their correlation with preparation process and parameters, enabling these cryogels to be tuned to match engineering requirements. Great efforts have been devoted to fabricating these types of cryogels and exploring their potential biomedical application. However, to the best of our knowledge, no comprehensive overviews focused on CBCs and GBCs have been reported currently. In this review, we attempt to provide insight into the recent advances on such kinds of cryogels, including their fabrication methods and structural properties, as well as potential biomedical applications.

Design and Assessment of Biodegradable Macroporous Cryogels as Advanced Tissue Engineering and Drug Carrying Materials

Cryogels obtained by the cryotropic gelation process are macroporous hydrogels with a well-developed system of interconnected pores and shape memory. There have been significant recent advancements in our understanding of the cryotropic gelation process, and in the relationship between components, their structure and the application of the cryogels obtained. As cryogels are one of the most promising hydrogel-based biomaterials, and this field has been advancing rapidly, this review focuses on the design of biodegradable cryogels as advanced biomaterials for drug delivery and tissue engineering. The selection of a biodegradable polymer is key to the development of modern biomaterials that mimic the biological environment and the properties of artificial tissue, and are at the same time capable of being safely degraded/metabolized without any side effects. The range of biodegradable polymers utilized for cryogel formation is overviewed, including biopolymers, synthetic polymers, polymer blends, and composites. The paper discusses a cryotropic gelation method as a tool for synthesis of hydrogel materials with large, interconnected pores and mechanical, physical, chemical and biological properties, adapted for targeted biomedical applications. The effect of the composition, cross-linker, freezing conditions, and the nature of the polymer on the morphology, mechanical properties and biodegradation of cryogels is discussed. The biodegradation of cryogels and its dependence on their production and composition is overviewed. Selected representative biomedical applications demonstrate how cryogel-based materials have been used in drug delivery, tissue engineering, regenerative medicine, cancer research, and sensing.

Biofunctionalized Nanofibrous Bilayer Scaffolds for Enhancing Cell Adhesion, Proliferation and Osteogenesis

A simple and efficient method for fabricating functionalized multilayered nanofibrous scaffolds has been developed by combining electrospinning and thermally induced phase separation (TIPS) techniques. In this investigation, functionalized bilayer scaffolds were constructed using this method for bone tissue engineering, which consisted of a nanofibrous poly(lactic acid-co-glycolic acid) (PLGA) membrane as the base and a nanofibrous chitosan (CS) or gelatin (Gel) mesh as the surface layer, with the PLGA nanofibers having a biomimetic polydopamine (PDA) coating. It was shown that the PDA coating strongly bonded TIPS-formed CS or Gel networks onto PDA-coated electrospun PLGA membranes. The nanofibrous PLGA membrane provided adequate mechanical support for the whole structure, and the nanofibrous CS or Gel networks enhanced cell growth and maturation. The bioinspired surface modification of PLGA scaffolds through PDA coating could not only provide strong adhesion between the two scaffold layers but also improve biological properties of scaffolds. It was demonstrated that functionalized bilayer scaffolds could promote cell adhesion, spreading and proliferation of mouse preosteoblastic MC3T3-E1 cells and rat bone-marrow-derived stromal cells (rBMSCs). Furthermore, immunofluorescence staining and calcium deposition studies revealed that functionalized bilayer scaffolds could enhance osteogenic differentiation of MC3T3-E1 cells and rBMSCs in comparison with simple electrospun PLGA scaffolds. The functionalized bilayer scaffolds are promising structures for bone tissue engineering.

Potential of a novel scaffold composed of human platelet lysate and fibrin for human corneal endothelial cells

Cell-based therapies have been emerged to find innovative solutions for corneal endothelial dysfunction. The aim of this study is to investigate the suitability of a blended scaffold containing human platelet lysate (HPL) and fibrin not only for cultivating human corneal endothelial cells (HCECs) but also for serving as a scaffold for the respected cells. We isolated HCECs from human donors and encapsulated the cells with three concentrations of HPL/Fibrin scaffold, namely HPL/Fibrin 1, HPL/Fibrin 2 and HPL/Fibrin 3, by adding 28.9, 57.8 and 86.7 mg/dl of fibrinogen to HPL to obtain a final percentage of 10, 20 and 30 % of fibrinogen, respectively. SEM imaging and swelling test were done to characterize the scaffolds. Cell viability assay and cell counting were performed on the cells. HCECs were characterized by morphology and immunocytochemistry. SEM imaging on freeze-dried scaffolds showed higher porosity of HPL/Fibrin 1 and HPL/Fibrin 2 than HPL/Fibrin 3, but larger pores were observed only in HPL/Fibrin 1. Cellular attachment and morphology on HPL/Fibrin 1 were appropriate by SEM imaging. A higher swelling rate was observed in HPL/Fibrin 1. After 3 and 5 days, higher numbers of cells were observed specifically in HPL/Fibrin 1. A higher expression of Na+/K+-ATPase, ZO-1 and vimentin proteins was detected in the HPL/Fibrin 1-cultured HCECs as compared with control (no scaffold). HPL/Fibrin can be used as a suitable scaffold for HCECs while preserving the cells viability. Further investigations are necessitated to approve the beneficial effects of the suggested scaffold for delivering and transplantation of cultivated HCECs into the anterior chamber of the eye.

Optimized hydrophobically modified chitosan cryogels for strength and drug delivery systems

This research reports the success of the fabrication of hydrophobically modified chitosan cryogel. Chitosan was modified with alkyl groups through reductive animation. By varying the alkyl chain length and the substitution degree, the resulting cryogel could be optimized for strength, and the adsorption and release of hydrophobic dye, a model for hydrophobic medicines. By optimizing these attributes, the hydrogel was found to have the potential as a biomedical material.

Sulfonated cryogel scaffolds for focal delivery in ex-vivo brain tissue cultures

The human brain has unique features that are difficult to study in animal models, including the mechanisms underlying neurodevelopmental and psychiatric disorders. Despite recent advances in human primary brain tissue culture systems, the use of these models to elucidate cellular disease mechanisms remains limited. A major reason for this is the lack of tools available to precisely manipulate a specific area of the tissue in a reproducible manner. Here we report an easy-to-use tool for site-specific manipulation of human brain tissue in culture. We show that line-shaped cryogel scaffolds synthesized with precise microscale dimensions allow the targeted delivery of a reagent to a specific region of human brain tissue in culture. 3-sulfopropyl acrylate (SPA) was incorporated into the cryogel network to yield a negative surface charge for the reversible binding of molecular cargo. The fluorescent dyes BODIPY and DiI were used as model cargos to show that placement of dye loaded scaffolds onto brain tissue in culture resulted in controlled delivery without a burst release, and labelling of specific regions without tissue damage. We further show that cryogels can deliver tetrodotoxin to tissue, inhibiting neuronal function in a reversible manner. The robust nature and precise dimensions of the cryogel resulted in a user-friendly and reproducible tool to manipulate primary human tissue cultures. These easy-to-use cryogels offer an innovate approach for more complex manipulations of ex-vivo tissue.

In Vivo Cartilage Regeneration with Cell-Seeded Natural Biomaterial Scaffold Implants: 15-Year Study

Articular cartilage can be easily damaged from human's daily activities, leading to inflammation and to osteoarthritis, a situation that can diminish the patients' quality of life. For larger cartilage defects, scaffolds are employed to provide cells the appropriate three-dimensional environment to proliferate and differentiate into healthy cartilage tissue. Natural biomaterials used as scaffolds, attract researchers' interest because of their relative nontoxic nature, their abundance as natural products, their easy combination with other materials, and the relative easiness to establish Marketing Authorization. The last 15 years were chosen to review, document, and elucidate the developments on cell-seeded natural biomaterials for articular cartilage treatment in vivo. The parameters of the experimental designs and their results were all documented and presented. Considerations about the newly formed cartilage and the treatment of cartilage defects were discussed, along with difficulties arising when applying natural materials, research limitations, and tissue engineering approaches for hyaline cartilage regeneration.

Hyaluronic Acid-Based Shape-Memory Cryogel Scaffolds for Focal Cartilage Defect Repair

Traumatic joint injuries can result in significant cartilage defects, which can greatly increase the risk of osteoarthritis development. Due to the limited self-healing capacity of avascular cartilage, tissue engineering approaches are required for filling defects and promoting cartilage regeneration. Current approaches utilize invasive surgical procedures for extraction and implantation of autologous chondrocytes; therefore, injectable biomaterials have gained interest to minimize the risk of infection as well as patient pain and discomfort. In this study, we engineered biomimetic, hyaluronic acid (HA)-based cryogel scaffolds that possess shape-memory properties as they contract and regain their shape after syringe injection to noninvasively fill cartilage defects. The cryogels, fabricated with HA and glycidyl methacrylate at -20°C, resulted in an elastic, macroporous, and highly interconnected network that provided a conducive microenvironment for chondrocytes to remain viable and metabolically active after injection through a syringe needle. Chondrocytes seeded within cryogels and cultured for 15 days exhibited enhanced cell proliferation, metabolism, and production of cartilage extracellular matrix glycosaminoglycans compared with HA-based hydrogels. Furthermore, immunohistochemical staining revealed production of collagen type II from chondrocyte-seeded cryogels, indicating the maintenance of cell phenotype. These results demonstrate the potential of chondrocyte-seeded, HA-based, injectable cryogel scaffolds to promote regeneration of cartilage tissue for nonsurgically invasive defect repair. Impact statement Hyaluronic acid-based shape-memory cryogels provide a conducive microenvironment for chondrocyte adhesion, proliferation, and matrix biosynthesis for use in repair of cartilage defects. Due to their sponge-like elastic properties, cryogels can fully recover their original shape back after injection while not impacting metabolism or viability of encapsulated cells. Clinically, they provide an opportunity for filling focal cartilage defects by using a single, minimally invasive injection of a cell encapsulating biocompatible three-dimensional scaffold that can return to its original structure to fit the defect geometry and enable matrix regeneration.

Dextran-polyethylene glycol cryogels as spongy scaffolds for drug delivery

Cryogels are a particular type of hydrogels that possess great potential in both fields of drug delivery and tissue engineering. Based on these premises, the goal of this work was to develop a cytocompatible polymeric cryogel, which could be used as a spongy scaffold to promote the delivery of biomolecules. Precisely, the novel formulation was fabricated by combining dextran methacrylate (DEX-MA) and polyethylene glycol dimethacrylate (PEG-DMA) through radical polymerization at a temperature of -15 °C. The swelling, porosity, mechanical properties, and the drug release profile of vitamin B12 from the optimized cryogel were evaluated and compared to hydrogels fabricated at room temperature. The use of the cryo-gelation technique enabled the formation of scaffolds with improved swelling, increased interconnected porosity, and higher mechanical resistance than conventional hydrogels. The cryogels proved to be non-toxic and suitable carriers for the delivery of water-soluble biomolecules. Overall, the novel cytocompatible cryogel formulation could be used for biomedical applications that require the need of a macroporous scaffold for localized delivery of bioactive molecules.

Needle-injectable microcomposite cryogel scaffolds with antimicrobial properties

Porous three-dimensional hydrogel scaffolds have an exquisite ability to promote tissue repair. However, because of their high water content and invasive nature during surgical implantation, hydrogels are at an increased risk of bacterial infection. Recently, we have developed elastic biomimetic cryogels, an advanced type of polymeric hydrogel, that are syringe-deliverable through hypodermic needles. These needle-injectable cryogels have unique properties, including large and interconnected pores, mechanical robustness, and shape-memory. Like hydrogels, cryogels are also susceptible to colonization by microbial pathogens. To that end, our minimally invasive cryogels have been engineered to address this challenge. Specifically, we hybridized the cryogels with calcium peroxide microparticles to controllably produce bactericidal hydrogen peroxide. Our novel microcomposite cryogels exhibit antimicrobial properties and inhibit antibiotic-resistant bacteria (MRSA and Pseudomonas aeruginosa), the most common cause of biomaterial implant failure in modern medicine. Moreover, the cryogels showed negligible cytotoxicity toward murine fibroblasts and prevented activation of primary bone marrow-derived dendritic cells ex vivo. Finally, in vivo data suggested tissue integration, biodegradation, and minimal host inflammatory responses when the antimicrobial cryogels, even when purposely contaminated with bacteria, were subcutaneously injected in mice. Collectively, these needle-injectable microcomposite cryogels show great promise for biomedical applications, especially in tissue engineering and regenerative medicine.

Bone marrow-derived mesenchymal stem cells and extracellular vesicles enriched collagen chitosan scaffold in skin wound healing (a rat model)

BACKGROUND

Over the past ten years, regenerative medicine has focused on the regeneration and the reconstruction of damaged, diseased, or lost tissues and organs. Skin, being the largest organ in the human body, had attained a good attraction in this field. Delayed wound healing is one of the most challenging clinical medicine complications. This study aimed to evaluate the collagen chitosan scaffold's effect alone, or enriched with either bone marrow-derived mesenchymal stem cells (BM-MSCs) or their secreted extracellular vesicles (EVs) on the duration and quality of skin wound healing.

METHODS

A full-thickness skin wound was induced on the back of 32 adult male Sprague-Dawley rats. The wounds were either covered with collagen chitosan scaffolds alone, scaffolds enriched with stem cells, or extracellular vesicles. Unprotected wounds were used as control. Healing duration, collagen deposition and alignment, CD 68+ macrophage count, and functional tensile strength of healed skin were assessed (α = 0.05, n = 8).

RESULTS

The rate of skin healing was significantly accelerated in all treated groups compared to the control. Immuno-histochemical assessment of CD68+ macrophages showed enhanced macrophages count, in addition to higher collagen deposition and better collagen alignment in EVs and BM-MSCs treated groups compared to the control group. Higher tensile strength values reflected the better collagen deposition and alignment for these groups. EVs showed higher amounts of collagen deposition and better alignment compared to MSCs treated group.

CONCLUSION

The collagen chitosan scaffolds enriched with MSCs or their EVs improved wound healing and improved the quantity and remodeling of collagen with a better assignment to EVs.

Fabricating Tough Interpenetrating Network Cryogels with DNA as the Primary Network for Biomedical Applications

This work investigates a sequential strategy to develop DNA-based hydrogel scaffolds with interpenetrating polymeric network. The scaffolds were formed via a two-step procedure. First, a covalently cross-linked DNA-based cryogel was formed by the chemical reaction between DNA strands and a bifunctional cross-linker, polyethylene glycol diepoxide at subzero temperatures. In the second step, alginate chains were absorbed into the preformed macroporous DNA cryogel network, followed by ionic cross-linking with divalent calcium ions. The individual and synergistic effects of covalent and ionic cross-linkings on mechanical and physical properties of the IPN cryogel were tested. The IPN cryogels were able to sustain large deformations higher than 95% of strain under compressive forces without exhibiting any failure. Addition of a physically cross-linked alginate network to the covalently linked DNA cryogel significantly enhanced its toughness and energy dissipation compared to the covalent network alone. The formulated hydrogels also exhibited excellent biocompatibility with human stem cells. Overall, this DNA-based IPN cryogel has the potential to be used as a biomaterial scaffold for a diverse range of tissue engineering applications.

In vivo cartilage regeneration in a multi-layered articular cartilage architecture mimicking scaffold

AIMS

Extracellular matrix (ECM) and its architecture have a vital role in articular cartilage (AC) structure and function. We hypothesized that a multi-layered chitosan-gelatin (CG) scaffold that resembles ECM, as well as native collagen architecture of AC, will achieve superior chondrogenesis and AC regeneration. We also compared its in vitro and in vivo outcomes with randomly aligned CG scaffold.

METHODS

Rabbit bone marrow mesenchymal stem cells (MSCs) were differentiated into the chondrogenic lineage on scaffolds. Quality of in vitro regenerated cartilage was assessed by cell viability, growth, matrix synthesis, and differentiation. Bilateral osteochondral defects were created in 15 four-month-old male New Zealand white rabbits and segregated into three treatment groups with five in each. The groups were: 1) untreated and allogeneic chondrocytes; 2) multi-layered scaffold with and without cells; and 3) randomly aligned scaffold with and without cells. After four months of follow-up, the outcome was assessed using histology and immunostaining.

RESULTS

In vitro testing showed that the secreted ECM oriented itself along the fibre in multi-layered scaffolds. Both types of CG scaffolds supported cell viability, growth, and matrix synthesis. In vitro chondrogenesis on scaffold showed an around 400-fold increase in collagen type 2 (COL2A1) expression in both CG scaffolds, but the total glycosaminoglycan (GAG)/DNA deposition was 1.39-fold higher in the multi-layered scaffold than the randomly aligned scaffold. In vivo cartilage formation occurred in both multi-layered and randomly aligned scaffolds treated with and without cells, and was shown to be of hyaline phenotype on immunostaining. The defects treated with multi-layered + cells, however, showed significantly thicker cartilage formation than the randomly aligned scaffold.

CONCLUSION

We demonstrated that MSCs loaded CG scaffold with multi-layered zonal architecture promoted superior hyaline AC regeneration.Cite this article: Bone Joint Res 2020;9(9):601-612.

Monitoring matrix remodeling in the cellular microenvironment using microrheology for complex cellular systems

Multiple particle tracking (MPT) microrheology was employed for monitoring the development of extracellular matrix (ECM) mechanical properties in the direct microenvironment of living cells. A customized setup enabled us to overcome current limitations: (i) Continuous measurements were enabled using a cell culture chamber, with this, matrix remodeling by fibroblasts in the heterogeneous environment of macroporous scaffolds was monitored continuously. (ii) Employing tracer laden porous scaffolds for seeding human mesenchymal stem cells (hMSCs), we followed conventional differentiation protocols. Thus, we were, for the first time able to study the massive alterations in ECM elasticity during hMSC differentiation. (iii) MPT measurements in 2D cell cultures were enabled using a long distance objective. Exemplarily, local mechanical properties of the ECM in human umbilical vein endothelial cell (HUVEC) cultures, that naturally form 2D layers, were investigated scaffold-free. Using our advanced setup, we measured local, apparent elastic moduli G_0,app in a range between 0.08 and 60 Pa. For fibroblasts grown in collagen-based scaffolds, a continuous decrease of local matrix elasticity resulted during the first 10 hours after seeding. The osteogenic differentiation of hMSC cells cultivated in similar scaffolds, led to an increase of G_0,app by 100 %, whereas after adipogenic differentiation it was reduced by 80 %. The local elasticity of ECM that was newly secreted by HUVECs increased significantly upon addition of protease inhibitor and in high glucose conditions even a twofold increase in G_0,app was observed. The combination of these advanced methods opens up new avenues for a broad range of investigations regarding cell-matrix interactions and the propagation of ECM mechanical properties in complex biological systems. STATEMENT OF SIGNIFICANCE: Cells sense the elasticity of their environment on a micrometer length scale. For studying the local elasticity of extracellular matrix (ECM) in the direct environment of living cells, we employed an advanced multipleparticle tracking microrheology setup. MPT is based on monitoring the Brownian motion oftracer particles, which is restricted by the surrounding network. Network elasticity can thusbe quantified. Overcoming current limitations, we realized continuous investigations of ECM elasticityduring fibroblast growth. Furthermore, MPT measurements of stem cell ECM showed ECMstiffening during osteogenic differentiation and softening during adipogenic differentiation.Finally, we characterized small amounts of delicate ECM newly secreted in scaffold-freecultures of endothelial cells, that naturally form 2D layers.

A Collagen Based Cryogel Bioscaffold that Generates Oxygen for Islet Transplantation

The aim of this work was to develop, characterize and test a novel 3D bioscaffold matrix which can accommodate pancreatic islets and provide them with a continuous, controlled and steady source of oxygen to prevent hypoxia-induced damage following transplantation. Hence, we made a collagen based cryogel bioscaffold which incorporated calcium peroxide (CPO) into its matrix. The optimal concentration of CPO integrated into bioscaffolds was 0.25wt.% and this generated oxygen at 0.21±0.02mM/day (day 1), 0.19±0.01mM/day (day 6), 0.13±0.03mM/day (day 14), and 0.14±0.02mM/day (day 21). Accordingly, islets seeded into cryogel-CPO bioscaffolds had a significantly higher viability and function compared to islets seeded into cryogel alone bioscaffolds or islets cultured alone on traditional cell culture plates; these findings were supported by data from quantitative computational modelling. When syngeneic islets were transplanted into the epididymal fat pad (EFP) of diabetic mice, our cryogel-0.25wt.%CPO bioscaffold improved islet function with diabetic animals re-establishing glycemic control. Mice transplanted with cryogel-0.25wt.%CPO bioscaffolds showed faster responses to intraperitoneal glucose injections and had a higher level of insulin content in their EFP compared to those transplanted with islets alone (P<0.05). Biodegradability studies predicted that our cryogel-CPO bioscaffolds will have long-lasting biostability for approximately 5 years (biodegradation rate: 16.00±0.65%/year). Long term implantation studies (i.e. 6 months) showed that our cryogel-CPO bioscaffold is biocompatible and integrated into the surrounding fat tissue with minimal adverse tissue reaction; this was further supported by no change in blood parameters (i.e. electrolyte, metabolic, chemistry and liver panels). Our novel oxygen-generating bioscaffold (i.e. cryogel-0.25wt.%CPO) therefore provides a biostable and biocompatible 3D microenvironment for islets which can facilitate islet survival and function at extra-hepatic sites of transplantation.

Characterization of a novel herbicide and antibiotic-resistant Chlorella sp. with an extensive extracellular matrix

A herbicide and antibiotic-resistant microalgal strain, isolated from a eutrophic site at Giofyros river (Heraklion, Crete, Greece) was extensively characterized. In the presence of relatively high concentrations of common photosynthesis inhibitors (DCMU and atrazine), as well as various antibiotics (spectinomycin, kanamycin, and chloramphenicol), the green microalga was able to increase its biomass in approximately equal levels compared to the control. Despite the high concentrations of the inhibitors, photosynthetic efficiency and chlorophyll a amount per dry cell biomass were comparable to those of control cultures in almost all cases. 18S rDNA analysis showed that this microalga belongs to the Chlorella genus. Optical and electron microscopy studies revealed the presence of an extensive extracellular matrix (EM) that surrounds the cells and plays an important role in colony formation and cell-cell interactions. Fourier transform infrared spectroscopy provided evidence that the EM consists of a polysaccharide. This matrix could be separated from the cells with a simple centrifugation. Depending on growth conditions, the dry cell biomass of this Chlorella strain was found to contain 35-39% proteins and 27-42% carbohydrates. The results of this study have demonstrated that the EM plays a protective role for cell homeostasis maintenance against the various chemical agents. This green microalga is a suitable candidate for further studies regarding sustainable biomass production in waste waters for a series of applications.

A Smart Drug Delivery System Based on Biodegradable Chitosan/Poly(allylamine hydrochloride) Blend Films

The amalgamation of natural polysaccharides with synthetic polymers often produces fruitful results in the area of drug delivery due to their biodegradable and biocompatible nature. In this study, a series of blend films composed of chitosan (CS)/poly(allylamine hydrochloride) (PAH) in different compositions were prepared as smart drug delivery matrices. The properties of these polymeric films were then explored. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) analysis confirmed an intermolecular hydrogen bonding between CS and PAH. Atomic force microscopy (AFM) revealed improvements in surface morphology as the percentage of PAH in the blend films increased up to 60% (w/w). Water contact angle (WCA) ranged between 97° to 115°, exhibiting the hydrophobic nature of the films. Two films were selected, CTH-1 (90% CS and 10% PAH) and CTH-2 (80% CS and 20% PAH), to test for in vitro cumulative drug release (%) at 37 ± 0.5 °C as a function of time. It was revealed that for simulated gastric fluid (SGF) with pH 1.2, the cumulative drug release (CDR) for CTH-1 and CTH-2 was around 88% and 85% in 50 min, respectively. Both films converted into gel-like material after 30 min. On the other hand, in pH 7.4 phosphate buffer saline (PBS) solution, the maximum CDR for CTH-1 and CTH-2 was 93% in 90 min and 98% in 120 min, respectively. After 120 min, these films became fragments. Sustained drug release was observed in PBS, as compared to SGF, because of the poor stability of the films in the latter. These results demonstrate the excellent potential of blend films in sustained-release drug delivery systems for hydrophilic or unstable drugs.

Xanthan Gum-Konjac Glucomannan Blend Hydrogel for Wound Healing

Hydrogels are considered to be the most ideal materials for the production of wound dressings since they display a three-dimensional structure that mimics the native extracellular matrix of skin as well as a high-water content, which confers a moist environment at the wound site. Until now, different polymers have been used, alone or blended, for the production of hydrogels aimed for this biomedical application. From the best of our knowledge, the application of a xanthan gum-konjac glucomannan blend has not been used for the production of wound dressings. Herein, a thermo-reversible hydrogel composed of xanthan gum-konjac glucomannan (at different concentrations (1% and 2% w/v) and ratios (50/50 and 60/40)) was produced and characterized. The obtained data emphasize the excellent physicochemical and biological properties of the produced hydrogels, which are suitable for their future application as wound dressings.

Hybrid and Composite Scaffolds Based on Extracellular Matrices for Cartilage Tissue Engineering

IMPACT STATEMENT

Scaffolds fabricated from extracellular matrix (ECM) derivatives are composed of conducive structures for cell attachment, proliferation, and differentiation, but generally do not have proper mechanical properties and load-bearing capacity. In contrast, scaffolds based on synthetic biomaterials demonstrate appropriate mechanical strength, but the absence of desirable biological properties is one of their main disadvantages. To integrate mechanical strength and biological cues, these ECM derivatives can be conjugated with synthetic biomaterials. Hence, hybrid scaffolds comprising both advantages of synthetic polymers and ECM derivatives can be considered a robust vehicle for tissue engineering applications.

Fabrication of chitosan/agarose scaffolds containing extracellular matrix for tissue engineering applications

One of the most effective approaches for treatment of cartilage involves the use of porous three-dimensional scaffolds, which are useful for improving not only cellular adhesion but also mechanical properties of the treated tissues. In this study, we manufactured a composite scaffold with optimum properties to imitate nasal cartilage attributes. Cartilage extracellular matrix (ECM) was used in order to improve the cellular properties of the scaffolds; while, chitosan and agarose were main materials that are used to boost the mechanical and rheological properties of the scaffolds. Furthermore, we explored the effect of the various weight ratios of chitosan, agarose, and ECM on the mechanical and biomedical properties of the composite scaffolds using the Taguchi method. The resulting composites display a range of advantages, including good mechanical strength, porous morphology, partial crystallinity, high swelling ratio, controlled biodegradability rate, and rheological characteristics. Additionally, we performed the cytotoxicity tests to confirm the improvement of the structure and better cell attachments on the scaffolds. Our findings illustrate that the presence of the ECM in chitosan/agarose structure improves the biomedical characteristics of the final scaffold. In addition, we were able to control the mechanical properties and microstructure of the scaffolds by optimizing the polymers' concentration and their resulting interactions. These results present a novel scaffold with simultaneously enhanced mechanical and cellular attributes comparing to the scaffolds without ECM for nasal cartilage tissue engineering applications.

Progress in the Development of Chitosan-Based Biomaterials for Tissue Engineering and Regenerative Medicine

Over the last few decades, chitosan has become a good candidate for tissue engineering applications. Derived from chitin, chitosan is a unique natural polysaccharide with outstanding properties in line with excellent biodegradability, biocompatibility, and antimicrobial activity. Due to the presence of free amine groups in its backbone chain, chitosan could be further chemically modified to possess additional functional properties useful for the development of different biomaterials in regenerative medicine. In the current review, we will highlight the progress made in the development of chitosan-containing bioscaffolds, such as gels, sponges, films, and fibers, and their possible applications in tissue repair and regeneration, as well as the use of chitosan as a component for drug delivery applications.

Three-dimensional cryogels for biomedical applications

Cryogels are a subset of hydrogels synthesized under sub-zero temperatures: initially solvents undergo active freezing, which causes crystal formation, which is then followed by active melting to create interconnected supermacropores. Cryogels possess several attributes suited for their use as bioscaffolds, including physical resilience, bio-adaptability, and a macroporous architecture. Furthermore, their structure facilitates cellular migration, tissue-ingrowth, and diffusion of solutes, including nano- and micro-particle trafficking, into its supermacropores. Currently, subsets of cryogels made from both natural biopolymers such as gelatin, collagen, laminin, chitosan, silk fibroin, and agarose and/or synthetic biopolymers such as hydroxyethyl methacrylate, poly-vinyl alcohol, and poly(ethylene glycol) have been employed as 3D bioscaffolds. These cryogels have been used for different applications such as cartilage, bone, muscle, nerve, cardiovascular, and lung regeneration. Cryogels have also been used in wound healing, stem cell therapy, and diabetes cellular therapy. In this review, we summarize the synthesis protocol and properties of cryogels, evaluation techniques as well as current in vitro and in vivo cryogel applications. A discussion of the potential benefit of cryogels for future research and their application are also presented.

Investigating Manuka Honey Antibacterial Properties When Incorporated into Cryogel, Hydrogel, and Electrospun Tissue Engineering Scaffolds

Honey is well-known for its wound healing capability and Manuka honey (MH) contains a unique Manuka factor, providing an additional antibacterial agent. Previously, there has not been a practical way to apply MH to a wound site, which renders treatment for an extended period extremely difficult. Tissue-engineered scaffolds offer an alternative treatment method to standard dressings by providing varying geometries to best treat the specific tissue. MH was incorporated into cryogels, hydrogels, and electrospun scaffolds to assess the effect of scaffold geometry on bacterial clearance and adhesion, as well as cellular adhesion. Electrospun scaffolds exhibited a faster release due to the nanoporous fibrous geometry which led to a larger partial bacterial clearance as compared to the more three-dimensional cryogels (CG) and hydrogels (HG). Similarly, the fast release of MH from the electrospun scaffolds resulted in reduced bacterial adhesion. Overall, the fast MH release of the electrospun scaffolds versus the extended release of the HG and CG scaffolds provides differences in cellular/bacterial adhesion and advantages for both short and long-term applications, respectively. This manuscript provides a comparison of the scaffold pore structures as well as bacterial and cellular properties, providing information regarding the relationship between varying scaffold geometry and MH efficacy.

Chitin/Chitosan: Versatile Ecological, Industrial, and Biomedical Applications

Chitin is a linear polysaccharide of N-acetylglucosamine, which is highly abundant in nature and mainly produced by marine crustaceans. Chitosan is obtained by hydrolytic deacetylation. Both polysaccharides are renewable resources, simply and cost-effectively extracted from waste material of fish industry, mainly crab and shrimp shells. Research over the past five decades has revealed that chitosan, in particular, possesses unique and useful characteristics such as chemical versatility, polyelectrolyte properties, gel- and film-forming ability, high adsorption capacity, antimicrobial and antioxidative properties, low toxicity, and biocompatibility and biodegradability features. A plethora of chemical chitosan derivatives have been synthesized yielding improved materials with suggested or effective applications in water treatment, biosensor engineering, agriculture, food processing and storage, textile additives, cosmetics fabrication, and in veterinary and human medicine. The number of studies in this research field has exploded particularly during the last two decades. Here, we review recent advances in utilizing chitosan and chitosan derivatives in different technical, agricultural, and biomedical fields.

Microstructure, local viscoelasticity and cell culture suitability of 3D hybrid HA/collagen scaffolds

As mechanical properties of cell culture substrates matter, methods for mechanical characterization of scaffolds on a relevant length scale are required. We used multiple particle tracking microrheology to close the gap between elasticity determined from bulk measurements and elastic properties sensed by cells. Structure and elasticity of macroporous, three-dimensional cryogel scaffolds from mixtures of hyaluronic acid (HA) and collagen (Coll) were characterized. Both one-component gels formed homogeneous networks, whereas hybrid gels were heterogeneous in terms of elasticity. Most strikingly, local elastic moduli were significantly lower than bulk moduli presumably due to non-equilibrium chain conformations between crosslinks. This was more pronounced in Coll and hybrid gels than in pure HA gels. Local elastic moduli were similar for all gels, irrespective of their different swelling ratio and bulk moduli. Fibroblast cell culture proved the biocompatibility of all investigated compositions. Coll containing gels enabled cell migration, adhesion and proliferation inside the gels.

Nanoparticle-modified chitosan-agarose-gelatin scaffold for sustained release of SDF-1 and BMP-2

Background

Stromal cell-derived factor 1 (SDF-1) is an important chemokine for stem cell mobilization, and plays a critical role in mobilization of mesenchymal stem cells (MSCs). Bone morphogenetic protein 2 (BMP-2) plays a critical role in osteogenesis of MSCs. However, the use of SDF-1 and BMP-2 in bone tissue engineering is limited by their short half-lives and rapid degradation in vitro and in vivo.

Methods

The chitosan oligosaccharide/heparin nanoparticles (CSO/H NPs) were first prepared via self-assembly. Chitosan-agarose-gelatin (CAG) Scaffolds were then synthesized via gelation technology using cross-linked chitosan, agarose, and gelatin, and were modified by CSO/H NPs. The encapsulation efficiency and release kinetics of SDF-1 and BMP-2 were quantified using an enzyme-linked immunosorbent assay. A CCK-8 assays were used to evaluate biocompatibility of NP-modified scaffolds. The biological activity of the loaded SDF-1 and BMP-2 was evaluated using the transwell migration assay and osteogenic induction assay. An animal MSC recruitment model was used to study the ability of SDF-1 released from NP-modified scaffolds to induce migration of MSCs.

Results

In this study, we developed a novel nanoparticle-modified CAG scaffold for the delivery of SDF-1 and BMP-2. CCK-8 assays demonstrated excellent biocompatibility of NP-modified scaffolds. In addition, we investigated the release of SDF-1 and BMP-2 from NP-modified scaffolds, and evaluated the effect of released SDF-1 on MSC migration. The effect of released BMP-2 on MSC osteogenesis was also examined. In vitro cell migration assays showed that SDF-1 released from NP-modified scaffolds retained its migration activity; osteogenesis studies demonstrated that released BMP-2 exhibited a strong ability to induce differentiation towards osteoblasts. Our in vivo recruitment assays showed continuous chemotactic response of MSCs to SDF-1 released from the NP-modified scaffold.

Conclusion

The simplicity of synthesizing CSO/H NP-modified CAG scaffolds, combined with its high cytokine loading capacity and sustained release effect, renders NP-modified CAG scaffold an attractive candidate for sustained release of SDF-1 and BMP-2 to promote bone repair and regeneration.