Dual Function of Glucosamine in Gelatin/Hyaluronic Acid Cryogel to Modulate Scaffold Mechanical Properties and to Maintain Chondrogenic Phenotype for Cartilage Tissue Engineering

In-Bath 3D Printing of Anisotropic Shape-Memory Cryogels Functionalized with Bone-Bioactive Nanoparticles

Cryogels exhibit unique shape memory with full recovery and structural stability features after multiple injections. These constructs also possess enhanced cell permeability and nutrient diffusion when compared to typical bulk hydrogels. Volumetric processing of cryogels functionalized with nanosized units has potential to widen their biomedical applications, however this has remained challenging and relatively underexplored. In this study, we report a novel methodology that combines suspension 3D printing with directional freezing for the fabrication of nanocomposite cryogels with configurable anisotropy. When compared to conventional bulk or freeze-dried hydrogels, nanocomposite cryogel formulations exhibit excellent shape recovery (>95%) and higher pore connectivity. Suspension printing, assisted with a prechilled metal grid, was optimized to induce anisotropy. The addition of calcium- and phosphate-doped mesoporous silica nanoparticles into the cryogel matrix enhanced bioactivity toward orthopedic applications without hindering the printing process. Notably, the nanocomposite 3D printed cryogels exhibit injectable shape memory while also featuring a lamellar topography. The fabrication of these constructs was highly reproducible and exhibited potential for a cell-delivery injectable cryogel with no cytotoxicity to human-derived adipose stem cells. Hence, in this work, it was possible to combine a gravity defying 3D printed methodology with injectable and controlled anisotropic macroporous structures containing bioactive nanoparticles. This methodology ameliorates highly tunable injectable 3D printed anisotropic nanocomposite cryogels with a user-programmable degree of structural complexity.

Recent progress and treatment strategy of pectin polysaccharide based tissue engineering scaffolds in cancer therapy, wound healing and cartilage regeneration

Natural polymers and its mixtures in the form of films, sponges and hydrogels are playing a major role in tissue engineering and regenerative medicine. Hydrogels have been extensively investigated as standalone materials for drug delivery purposes as they enable effective encapsulation and sustained release of drugs. Biopolymers are widely utilised in the fabrication of hydrogels due to their safety, biocompatibility, low toxicity, and regulated breakdown by human enzymes. Among all the biopolymers, polysaccharide-based polymer is well suited to overcome the limitations of traditional wound dressing materials. Pectin is a polysaccharide which can be extracted from different plant sources and is used in various pharmaceutical and biomedical applications including cartilage regeneration. Pectin itself cannot be employed as scaffolds for tissue engineering since it decomposes quickly. This article discusses recent research and developments on pectin polysaccharide, including its types, origins, applications, and potential demands for use in AI-mediated scaffolds. It also covers the materials-design process, strategy for implementation to material selection and fabrication methods for evaluation. Finally, we discuss unmet requirements and current obstacles in the development of optimal materials for wound healing and bone-tissue regeneration, as well as emerging strategies in the field.

Biomimetic Injectable Hydrogel Based on Methacrylate-Modified Silk Fibroin Embedded with Kartogenin for Superficial Cartilage Regeneration

The weak regeneration ability of chondrocytes is one of the main reasons that limit the therapeutic effect of clinical cartilage injury. Injectable hydrogels are potential scaffolds for cartilage tissue engineering with advantages such as minimally invasive surgery, porous structure, and drug sustained-release ability. At present, many biomaterials have been developed for the repair of deep cartilage defects. However, cartilage injury often begins on the surface, which requires us to propose a treatment strategy suitable for superficial cartilage injury repair. In this study, we fabricated a biomimetic injectable hydrogel based on methacrylate-modified silk fibroin (SilMA) embedded with kartogenin (KGN). The SilMA/KGN hydrogels have good biohistocompatibility and the ability to promote cartilage differentiation. In addition, SEM results show that it has a porous structure conducive to cell adhesion and proliferation. Most importantly, it has demonstrated remarkable superficial cartilage repair ability in vivo, showing potential in cartilage tissue engineering.

Superporous soy protein isolate matrices as superabsorbent dressings for successful management of highly exuding wounds: In vitro and in vivo characterization

Soy protein isolate (SPI) has received widespread attention of the biomedical research community primarily due to its good biocompatibility, biodegradability, high availability and low cost. Herein, glutaraldehyde cross-linked microporous sponge-like SPI scaffolds were prepared using the cryogelation technique for tissue engineering applications. The prepared SPI scaffolds possess an interconnected porous structure with approximately 90% porosity and an average pore size in the range of 45-92 μm. The morphology, porosity, swelling capacity and degradation rate of the cryogels were found to be dependent on the concentration of polymer to crosslinking agent. All cryogels were found to be elastic and able to maintain physical integrity even after being compressed to one-fifth of their original length during cyclic compression analysis. These cryogels showed excellent mechanical properties, immediate water-triggered shape restoration and absorption speed. Furthermore, cryogels outperformed cotton and gauze in terms of blood clotting and blood cell adherence. The in vitro and in vivo studies demonstrated the potency of SPI scaffolds for skin tissue engineering applications. Our findings showed that crosslinking with glutaraldehyde had no detrimental effects on cell viability. In addition, an in vivo wound healing study in rats validated them as good potential wound dressing materials.

Injectable gelatin/glucosamine cryogel microbeads as scaffolds for chondrocyte delivery in cartilage tissue engineering

In this study, we fabricate squeezable cryogel microbeads as injectable scaffolds for minimum invasive delivery of chondrocytes for cartilage tissue engineering applications. The microbeads with different glucosamine concentrations were prepared by combining the water-in-oil emulsion and cryogelation through crosslinking of gelatin with glutaraldehyde in the presence of glucosamine. The physicochemical characterization results show the successful preparation of cryogel microbeads with uniform shape and size, high porosity, large pore size, high water uptake capacity, and good injectability. In vitro analysis indicates proliferation, migration, and differentiated phenotype of rabbit chondrocytes in the cryogel scaffolds. The seeded chondrocytes in the cryogel scaffold can be delivered by injecting through an 18G needle to fully retain the cell viability. Furthermore, the incorporation of glucosamine in the cryogel promoted the differentiated phenotype of chondrocytes in a dose-dependent manner, from cartilage-specific gene expression and protein production. The in vivo study by injecting the cryogel microbeads into the subcutaneous pockets of nude mice indicates good retention ability as well as good biocompatibility and suitable biodegradability of the cryogel scaffold. Furthermore, the injected chondrocyte/cryogel microbead constructs can form ectopic functional neocartilage tissues following subcutaneous implantation in 21 days, as evidenced by histological and immunohistochemical analysis.

Cryogel Scaffolds for Tissue-Engineering: Advances and Challenges for Effective Bone and Cartilage Regeneration

Critical-sized bone defects and articular cartilage injuries resulting from trauma, osteonecrosis, or age-related degeneration can be often non-healed by physiological repairing mechanisms, thus representing a relevant clinical issue due to a high epidemiological incidence rate. Novel tissue-engineering approaches have been proposed as an alternative to common clinical practices. This cutting-edge technology is based on the combination of three fundamental components, generally referred to as the tissue-engineering triad: autologous or allogenic cells, growth-stimulating factors, and a scaffold. Three-dimensional polymer networks are frequently used as scaffolds to allow cell proliferation and tissue regeneration. In particular, cryogels give promising results for this purpose, thanks to their peculiar properties. Cryogels are indeed characterized by an interconnected porous structure and a typical sponge-like behavior, which facilitate cellular infiltration and ingrowth. Their composition and the fabrication procedure can be appropriately tuned to obtain scaffolds that match the requirements of a specific tissue or organ to be regenerated. These features make cryogels interesting and promising scaffolds for the regeneration of different tissues, including those characterized by very complex mechanical and physical properties, such as bones and joints. In this review, state-of-the-art fabrication and employment of cryogels for supporting effective osteogenic or chondrogenic differentiation to allow for the regeneration of functional tissues is reported. Current progress and challenges for the implementation of this technology in clinical practice are also highlighted.

Bioconjugation of Carbohydrates to Gelatin Sponges Promoting 3D Cell Cultures

Gelatin sponges are widely employed as hemostatic agents, and are gaining increasing interest as 3D scaffolds for tissue engineering. To broaden their possible application in the field of tissue engineering, a straightforward synthetic protocol able to anchor the disaccharides, maltose and lactose, for specific cell interactions was developed. A high conjugation yield was confirmed by ¹H-NMR and FT-IR spectroscopy, and the morphology of the resulting decorated sponges was characterized by SEM. After the crosslinking reaction, the sponges preserve their porous structure as ascertained by SEM. Finally, HepG2 cells cultured on the decorated gelatin sponges show high viability and significant differences in the cellular morphology as a function of the conjugated disaccharide. More spherical morphologies are observed when cultured on maltose-conjugated gelatin sponges, while a more flattened aspect is discerned when cultured onto lactose-conjugated gelatin sponges. Considering the increasing interest in small-sized carbohydrates as signaling cues on biomaterial surfaces, systematic studies on how small carbohydrates might influence cell adhesion and differentiation processes could take advantage of the described protocol.

Preparation of gum tragacanth/poly (vinyl alcohol)/halloysite hydrogel using electron beam irradiation with potential for bone tissue engineering

Nanocomposite hydrogels based on tyramine conjugated gum tragacanth, poly (vinyl alcohol) (PVA), and halloysite nanotubes (HNTs) were prepared by electron beam irradiation and characterized. The FTIR, ¹H NMR, and TGA results confirmed the chemical incorporation of HNTs into gum tragacanth. Gel content and swelling of hydrogels decreased with HNTs loading up to 20 % wt. The mechanical strength of hydrogels increased by increasing HNTs content up to 10 % with 371 kPa fracture stress at 0.95 fracture strain, compared to 312 kPa stress at 0.79 strain for gum tragacanth/PVA hydrogel. Hydrogel's biocompatibility and osteogenic activity were tested by seeding rabbit bone marrow mesenchymal stem cells. The cell viability was >85 % after 7 days of culture. In vitro secretion of ALP and calcium deposition on hydrogels in alizarin red assay after 21 days of culture indicated hydrogel potential for bone tissue engineering.

Nanoparticle-Reinforced Tough Hydrogel as a Versatile Platform for Pharmaceutical Drug Delivery: Preparation and in Vitro Characterization

Natural polymer-based hydrogels are excellent for encapsulating hydrophilic drugs, but they are mechanically weak and degrade easily. In this communication, we exploit the electrostatic interaction between nanosilicates (nSi) and gelatin methacrylate (GelMA) to form a mechanically tough nanocomposite hydrogel for pharmaceutical drug delivery. These hydrogels, prepared at subzero temperatures to form cryogels, displayed macroporous structures, which favors cell infiltration. The designed tough cryogel also showed a slower rate of degradation. Furthermore, we encapsulated the small molecule metformin and sustained the drug release under physiological conditions. Cryogel-loaded metformin reduced the effect of endothelial cell injury caused by nutrient deprivation in vitro. Finally, we hypothesize that this versatile nanocomposite material will find use in diverse biomedical applications.

Recent Advances in "Functional Engineering of Articular Cartilage Zones by Polymeric Biomaterials Mediated with Physical, Mechanical, and Biological/Chemical Cues"

Articular cartilage (AC) plays an unquestionable role in joint movements but unfortunately the healing capacity is restricted due to its avascular and acellular nature. While cartilage tissue engineering has been lifesaving, it is very challenging to remodel the complex cartilage composition and architecture with gradient physio-mechanical properties vital to proper tissue functions. To address these issues, a better understanding of the intrinsic AC properties and how cells respond to stimuli from the external microenvironment must be better understood. This is essential in order to take one step closer to producing functional cartilaginous constructs for clinical use. Recently, biopolymers have aroused much attention due to their versatility, processability, and flexibility because the properties can be tailored to match the requirements of AC. This review highlights polymeric scaffolds developed in the past decade for reconstruction of zonal AC layers including the superficial zone, middle zone, and deep zone by means of exogenous stimuli such as physical, mechanical, and biological/chemical signals. The mimicked properties are reviewed in terms of the biochemical composition and organization, cell fate (morphology, orientation, and differentiation), as well as mechanical properties and finally, the challenges and potential ways to tackle them are discussed.

Effects of low-intensity pulsed ultrasound stimulation on cell seeded 3D hybrid scaffold as a novel strategy for meniscus regeneration: An in vitro study

Menisci are fibrocartilaginous structures in the knee joint with an inadequate regenerative capacity, which causes low healing potential and further leads to osteoarthritis. Recently, three-dimensional (3D) printing techniques and ultrasound treatment have gained plenty of attention for meniscus tissue engineering. The present study investigates the effectiveness of low-intensity pulsed ultrasound stimulations (LIPUS) on the proliferation, viability, morphology, and gene expression of the chondrocytes seeded on 3D printed polyurethane scaffolds dip-coated with gellan gum, hyaluronic acid, and glucosamine. LIPUS stimulation was performed at 100, 200, and 300 mW/cm² intensities for 20 min/day. A faster gap closure (78.08 ± 2.56%) in the migration scratch assay was observed in the 200 mW/cm² group after 24 h. Also, inverted microscopic and scanning electron microscopic images showed no cell morphology changes during LIPUS exposure at different intensities. The 3D cultured chondrocytes under LIPUS treatment revealed a promotion in cell proliferation rate and viability as the intensity doses increased. Additionally, LIPUS could stimulate chondrocytes to overexpress the aggrecan and collagen II genes and improve their chondrogenic phenotype. This study recommends that the combination of LIPUS treatment and 3D hybrid scaffolds can be considered as a valuable treatment for meniscus regeneration based on our in vitro data.

Fabrication and assessment of a novel hybrid scaffold consisted of polyurethane-gellan gum-hyaluronic acid-glucosamine for meniscus tissue engineering

The meniscus has inadequate intrinsic regenerative capacity and its damage can lead to degeneration of articular cartilage. Meniscus tissue engineering aims to restore an injured meniscus followed by returning its normal function through bioengineered scaffolds. In the present study, the structural and biological properties of 3D-printed polyurethane (PU) scaffolds dip-coated with gellan gum (GG), hyaluronic acid (HA), and glucosamine (GA) were investigated. The optimum concentration of GG was 3% (w/v) with maintaining porosity at 88.1%. The surface coating of GG-HA-GA onto the PU scaffolds increased the compression modulus from 30.30 kPa to 59.10 kPa, the water uptake ratio from 27.33% to 60.80%, degradation rate from 5.18% to 8.84%, whereas the contact angle was reduced from 104.8° to 59.3°. MTT assay, acridine orange/ethidium bromide (AO/EB) fluorescent staining, and SEM were adopted to assess the behavior of the seeded chondrocytes on scaffolds, and it was found that the ternary surface coating stimulated the cell proliferation, viability, and adhesion. Moreover, the coated scaffolds showed higher expression levels of collagen II and aggrecan genes at day 7 compared to the control groups. Therefore, the fabricated PU-3% (w/v) GG-HA-GA scaffold can be considered as a promising scaffold for meniscus tissue engineering.

Recent Developments in Hyaluronic Acid-Based Hydrogels for Cartilage Tissue Engineering Applications

Articular cartilage lesions resulting from injurious impact, recurring loading, joint malalignment, etc., are very common and encompass the risk of evolving to serious cartilage diseases such as osteoarthritis. To date, cartilage injuries are typically treated via operative procedures such as autologous chondrocyte implantation (ACI), matrix-associated autologous chondrocyte implantation (MACI) and microfracture, which are characterized by low patient compliance. Accordingly, cartilage tissue engineering (CTE) has received a lot of interest. Cell-laden hydrogels are favorable candidates for cartilage repair since they resemble the native tissue environment and promote the formation of extracellular matrix. Various types of hydrogels have been developed so far for CTE applications based on both natural and synthetic biomaterials. Among these materials, hyaluronic acid (HA), a principal component of the cartilage tissue which can be easily modified and biofunctionalized, has been favored for the development of hydrogels since it interacts with cell surface receptors, supports the growth of chondrocytes and promotes the differentiation of mesenchymal stem cells to chondrocytes. The present work reviews the various types of HA-based hydrogels (e.g., in situ forming hydrogels, cryogels, microgels and three-dimensional (3D)-bioprinted hydrogel constructs) that have been used for cartilage repair, specially focusing on the results of their preclinical and clinical assessment.

Allogeneic Bone-Marrow Mesenchymal Stem Cell with Moldable Cryogel for Craniofacial Bone Regeneration

Allogeneic bone-marrow mesenchymal stem cells (BMSCs) can promote bone regeneration and substitute for autologous BMSCs if autologous sources are unavailable, but the efficacy of bone regeneration by allogeneic BMSCs is still inconsistent. A Lewis rat cranium defect model was used to investigate the efficacy of bone regeneration between autologous and allogeneic BMSCs in gelatin-nanohydroxyapatite cryogel scaffolds. BMSCs from Wistar rats served as the allogeneic cell lineage. The full-thickness cranium defects were treated by either blank control, cryogel only, allogeneic BMSC-seeded cryogel, or autologous BMSC-seeded cryogel (n = 5). Bone regeneration was monitored by micro-computed tomography and examined histologically at week 12. In addition, we assessed the immune responses in vitro by mixed lymphocyte reaction (MLR) assay and CD₄⁺ immunochemistry staining ex vivo. The MLR showed that allogeneic BSMCs elicited a weak immune response on day 14 that progressively attenuated by day 28. In vivo, the bone regeneration in allogeneic BMSCs was inferior at week 4, but progressively matched the autologous BMSCs by week 12. Our results suggest that allogeneic BMSCs can serve as an alternative source for bone regeneration.

Glycosaminoglycan-Based Cryogels as Scaffolds for Cell Cultivation and Tissue Regeneration

Cryogels are a class of macroporous, interconnective hydrogels polymerized at sub-zero temperatures forming mechanically robust, elastic networks. In this review, latest advances of cryogels containing mainly glycosaminoglycans (GAGs) or composites of GAGs and other natural or synthetic polymers are presented. Cryogels produced in this way correspond to the native extracellular matrix (ECM) in terms of both composition and molecular structure. Due to their specific structural feature and in addition to an excellent biocompatibility, GAG-based cryogels have several advantages over traditional GAG-hydrogels. This includes macroporous, interconnective pore structure, robust, elastic, and shape-memory-like mechanical behavior, as well as injectability for many GAG-based cryogels. After addressing the cryogelation process, the fabrication of GAG-based cryogels and known principles of GAG monomer crosslinking are discussed. Finally, an overview of specific GAG-based cryogels in biomedicine, mainly as polymeric scaffold material in tissue regeneration and tissue engineering-related controlled release of bioactive molecules and cells, is provided.

Preparation and evaluation of gellan gum hydrogel reinforced with silk fibers with enhanced mechanical and biological properties for cartilage tissue engineering

Various research about cartilage regeneration using biomaterials has been done recently. Particularly, gellan gum hydrogel (GG) is reported to be suitable as a biomaterial for cartilage tissue engineering (TE) for its water uptaking ability, producibility, and environmental resemblance of native cartilage. Despite these advantages, mechanical and cell adhesion properties are still difficult to modulate. Reinforcement is essential to overcome these problems. Herein, GG was modified by physically blending with different lengths of silk fiber (SF). As SF is expected to improve such disadvantages of GG, mechanical and biological properties were characterized to confirm its reinforcement ability. Mechanical properties such as degradation rate, swelling rate, compression strength, and viscosity were studied and it was confirmed that SF significantly reinforces the mechanical properties of GG. Furthermore, in vitro study was carried out to confirm morphology, biocompatibility, proliferation, and chondrogenesis of chondrocytes encapsulated in the hydrogels. Overall, chondrocytes in the GG blended with SF (SF/GG) showed enhanced cell viability and growth. According to this study, SF/GG can be a promising biomaterial for cartilage TE biomaterial.

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.

Mammalian and Fish Gelatin Methacryloyl-Alginate Interpenetrating Polymer Network Hydrogels for Tissue Engineering

Gelatin methacryloyl (GelMA) has been widely studied as a biomaterial for tissue engineering. Most studies focus on mammalian gelatin, but certain factors, such as mammalian diseases and diet restrictions, limit the use of mammalian gelatin. Thus, fish gelatin has received much attention as a substitute material in recent years. To develop a broadly applicable hydrogel with excellent properties, an interpenetrating polymer network (IPN) hydrogel was synthesized, since IPN hydrogels consist of at least two different hydrogel components to combine their advantages. In this study, we prepared GelMA using type A and fish gelatin and then synthesized IPN hydrogels using GelMA with alginate. GelMA single-network hydrogels were used as a control group. The favorable mechanical properties of type A and fish hydrogels improved after the synthesis of the IPN hydrogels. Type A and fish IPN hydrogels showed different mechanical properties (mechanical strength, swelling ratio, and degradation rate) and different cross-sectional morphologies, since the degree of mechanical enhancement in fish IPN hydrogels was less than that in type A; however, the cell biocompatibilities were not significantly different. Therefore, these findings could serve as a reference for future studies when selecting GelMA as a biological material for tissue engineering.

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.

A Biodegradable Chitosan-Polyurethane Cryogel with Switchable Shape Memory

Cryogels are matrices that are formed in moderately frozen solutions of monomeric or polymeric precursors. They have the advantages of interconnected macropores, structural stability, and compressibility. Meanwhile, thermally induced shape memory is an attractive feature of certain functional materials. Although there have been several studies concerning shape-memory cryogels, little work has been conducted on shape-memory cryogels with biodegradability. In this study, a water-based biodegradable difunctional polyurethane with a shape-memory property was synthesized and used as the nanoparticulate crosslinker to react with chitosan to form a shape-memory cryogel. The thermally induced shape-memory mechanism was clarified using in situ wide-angle X-ray scattering (WAXS) and small-angle X-ray scattering (SAXS) during the shape-memory process. The in situ WAXS showed the changes of crystallinity in the crosslinker and the cryogel during the shape fixation and recovery processes. The in situ SAXS revealed the orientation of crystallinity of the crosslinker and the cryogel as the mechanism for shape memory. The strip-shape cryogel was deformed at 50 °C to U-shape and fixed at - 20 °C, which was squeezable at 25 °C and returned to the strip-shape at 50 °C in air. The shape recovery was further tested in water at two different temperatures. The injected cryogel recovered the U-shape in 4 °C water, representing elastic recovery, and transformed to a long strip in 37 °C water, representing the switchable shape memory. Moreover, the shape-memory cryogel sheet with a large dimension (10 mm × 10 mm × 1.1 mm cryogel sheet) or with complex structures (N, T, and U shapes) could be fixed as a rod, injected through a 16 G needle, and return to its original shape in 37 °C water, all of which could not be achieved by the conventional cryogel. Human mesenchymal stem cells grown in the shape-memory cryogel scaffolds displayed long-term proliferation and chondrogenic potential. Their unique injectability and cytocompatibility suggested potential applications of shape-memory cryogels as injectable and expandable templates for tissue engineering and minimally invasive surgery.

Influence of the Mechanical Environment on the Regeneration of Osteochondral Defects

Articular cartilage is a highly specialised connective tissue of diarthrodial joints which provides a smooth, lubricated surface for joint articulation and plays a crucial role in the transmission of loads. In vivo cartilage is subjected to mechanical stimuli that are essential for cartilage development and the maintenance of a chondrocytic phenotype. Cartilage damage caused by traumatic injuries, ageing, or degradative diseases leads to impaired loading resistance and progressive degeneration of both the articular cartilage and the underlying subchondral bone. Since the tissue has limited self-repairing capacity due its avascular nature, restoration of its mechanical properties is still a major challenge. Tissue engineering techniques have the potential to heal osteochondral defects using a combination of stem cells, growth factors, and biomaterials that could produce a biomechanically functional tissue, representative of native hyaline cartilage. However, current clinical approaches fail to repair full-thickness defects that include the underlying subchondral bone. Moreover, when tested in vivo, current tissue-engineered grafts show limited capacity to regenerate the damaged tissue due to poor integration with host cartilage and the failure to retain structural integrity after insertion, resulting in reduced mechanical function. The aim of this review is to examine the optimal characteristics of osteochondral scaffolds. Additionally, an overview on the latest biomaterials potentially able to replicate the natural mechanical environment of articular cartilage and their role in maintaining mechanical cues to drive chondrogenesis will be detailed, as well as the overall mechanical performance of grafts engineered using different technologies.

Hyaluronan-Loaded Liposomal Dexamethasone-Diclofenac Nanoparticles for Local Osteoarthritis Treatment

Osteoarthritis (OA) remains one of the common degenerative joint diseases and a major cause of pain and disability in older adult individuals. Oral administration of non-steroidal anti-inflammatory drugs (NSAIDs) (such as diclofenac, DIC) or intra-articular injected gluco-corticosteroids (such as dexamethasone, DEX) were the conventional treatment strategies for OA to reduce joint pain. Current limitations for both drugs including severe adverse effects with risks of toxicity were noted. The aim of the present study was to generate a novel OA treatment formulation hyaluronic acid (HA)-Liposomal (Lipo)-DIC/DEX to combat joint pain. The formulation was prepared by constructing DIC with DEX-loaded nanostructured lipid carriers Lipo-DIC/DEX mixed with hyaluronic acid (HA) for prolonged OA application. The prepared Lipo-DIC/DEX nanoparticles revealed the size as 103.6 ± 0.3 nm on average, zeta potential as −22.3 ± 4.6 mV, the entrapment efficiency of 90.5 ± 5.6%, and the DIC and DEX content was 22.5 ± 4.1 and 2.5 ± 0.6%, respectively. Evidence indicated that HA-Lipo-DIC/DEX could reach the effective working concentration in 4 h and sustained the drug-releasing time for at least 168 h. No significant toxicities but increased cell numbers were observed when HA-Lipo-DIC/DEX co-cultured with articular chondrocytes cells. Using live-animal In vivo imaging system (IVIS), intra-articular injection of each HA-Lipo-DIC/DEX sufficed to reduce knee joint inflammation in OA mice over a time span of four weeks. Single-dose injection could reduce the inflammation volume down to 77.5 ± 5.1% from initial over that time span. Our results provided the novel drug-releasing formulation with safety and efficiency which could be a promising system for osteoarthritis pain control.

Cryogel/hydrogel biomaterials and acupuncture combined to promote diabetic skin wound healing through immunomodulation

Unhealed chronic wounds often deteriorate into multiple infection with several kinds of bacteria and excessive proteolytic wound exudate and remains one of the common healthcare issues. Here, the functional and antimicrobial hydrogel and cryogel biomaterials were prepared from glycol chitosan and a novel biodegradable Schiff base crosslinker difunctional polyurethane (DF-PU). The cryogel exhibited ~2730 ± 400% of water absorption with abundant macropores and 86.5 ± 1.6% of porosity formed by ice crystal as well as ~240% cell proliferation effect; while the hydrogel demonstrated considerable antimicrobial activity and biodegradability. As an optimized procedure to treat the diabetic skin wound in a rat model, the combined application of adipose stem cell-seeded cryogel/hydrogel biomaterials on the wound and acupuncture surrounding the wound may attain 90.34 ± 2.3% of wound closure and secure the formation of granulation tissue with sufficient microvessels and complete re-epithelialization in 8 days. The average increases in the superficial temperature of wounded animals after acupuncture were about 1-2 °C. Through the activation of C3a and C5a, the increased secretion of cytokines SDF-1 and TGFβ-1, as well as the down-regulation of proinflammatory cytokines TNF-α and IL-1β, the combined treatment of stem cell-seeded cryogel/hydrogel biomaterials and acupuncture on wounds produced synergistic immunomodulatory effects. The strategy using the combined treatment of biomaterials, stem cells, and acupuncture reveals a perspective new approach to accelerate the tissue regeneration.

Synthesis and characterization of PLGA/HAP scaffolds with DNA-functionalised calcium phosphate nanoparticles for bone tissue engineering

Porous scaffolds of poly(lactide-co-glycolide) (PLGA; 85:15) and nano-hydroxyapatite (nHAP) were prepared by an emulsion-precipitation procedure from uniform PLGA-nHAP spheres (150-250 µm diameter). These spheres were then thermally sintered at 83 °C to porous scaffolds that can serve for bone tissue engineering or for bone substitution. The base materials PLGA and nHAP and the PLGA-nHAP scaffolds were extensively characterized by X-ray powder diffraction, infrared spectroscopy, thermogravimetry, differential scanning calorimetry, and scanning electron microscopy. The scaffold porosity was about 50 vol% as determined by relating mass and volume of the scaffolds, together with the computed density of the solid phase (PLGA-nHAP). The cultivation of HeLa cells demonstrated their high cytocompatibility. In combination with DNA-loaded calcium phosphate nanoparticles, they showed a good activity of gene transfection with enhanced green fluorescent protein (EGFP) as model protein. This is expected enhance bone growth around an implanted scaffold or inside a scaffold for tissue engineering.

Cartilage tissue engineering using injectable functionalized Demineralized Bone Matrix scaffold with glucosamine in PVA carrier, cultured in microbioreactor prior to study in rabbit model

Using 3D model of injectable scaffolds for cartilage tissue engineering is one of the challenges that should be addressed to avoid invasive surgery for treatment. For this purpose, chondrocytes on Demineralized Bone Matrix (DBM) scaffolds functionalized with glucosamine in 20% polyvinyl alcohol (PVA) as a carrier was applied to the micro-bioreactor in-vitro, then the study was continued on in-vivo stage. Scaffold biocompatibility tests were performed and the mechanical and physicochemical properties were studied showing the fact that DBM was functionalized by Glucosamine, scaffold degradation rate was 53% after 720 h and swelling ratio was 2.5 times after 16 h, injectable scaffold demonstrated better mechanical characteristics (P < 0.05) than other concentrations of PVA. Consequently, in-vitro tests, including live-dead imaging resulting in 99% viability after 14 days (P < 0.001), DAPI staining and scanning electron microscope imaging were performed to determine the number and viability of the cells on the scaffold, showing a cells proliferation property of this group compared with the control after 14 days (P < 0.0001), then relative gene expression was evaluated and protein expression was assessed. The overall chondrogenic gene expression improved (P < 0.05) compared to the control (2D culture). Subsequently, the scaffold were loaded with chondrocytes and injected into the cartilage lesion part After 24 weeks of surgery, MRI and immunocytochemistry were performed. Then all outputs proved that the scaffold plus cell group had a significantly higher topological score (P < 0.0001) than other groups compared to normal cartilage. Finally, studies have shown that transplantation of chondrocytes in DBM, polyvinyl alcohol and glucosamine scaffold through one surgical stage improves cartilage lesion and it can be considered as a breakthrough in tissue engineering.

Physicomechanical, rheological and in vitro cytocompatibility properties of the electron beam irradiated blend hydrogels of tyramine conjugated gum tragacanth and poly (vinyl alcohol)

In the present study, preparation of blend hydrogels of tyramine conjugated gum tragacanth and poly (vinyl alcohol) was carried out by electron beam irradiation, and modification of hydrogel properties with poly (vinyl alcohol) was demonstrated. Gel content, swelling behavior, pore size and mechanical and rheological properties of hydrogels prepared at 14, 28 and 56 kilogray (kGy) with different ratios of polymers were investigated. Gel content increased from 67 ± 2% for pure tyramine conjugated gum tragacanth hydrogel to >92% for blend hydrogels. However, the corresponding equilibrium swelling degree decreased from 35.21 ± 1.51 to 9.14 ± 1.66 due to the higher crosslink density of blend hydrogel. The mechanical strength of the hydrogels with interconnected pores increased significantly in the presence of poly (vinyl alcohol) and increasing irradiation dose up to 28 kGy with a twenty-fold enhancement of stress fracture and excellent elastic recovery in cyclic compression analysis. The equilibrium swelling degree of blend hydrogel containing 3% w/v tyramine conjugated gum tragacanth and 2% w/v poly (vinyl alcohol) prepared at 28 kGy was 16.59 ± 0.81. The biocompatibility of hydrogels was tested in the presence of rabbit bone marrow mesenchymal stem cells. The viability of cells exposed to hydrogel extract was >92% after 7 days of culture and indicated hydrogel biocompatibility with potential biomedical applications.

Novel glucosamine-loaded thermosensitive hydrogels based on poloxamers for osteoarthritis therapy by intra-articular injection

Glucosamine (GlcN) is a common drug used to treat osteoarthritis (OA). To prolong the action time of glucosamine on OA and improve its therapeutic effect, this research explored the potential application of GlcN-loaded thermosensitive hydrogels based on poloxamer 407 and poloxamer 188 for OA therapy by intra-articular injection. The thermosensitive hydrogels were prepared by cold method, and the effects of P407, P188, and GlcN on sol-gel transition temperature (T_sol-gel) were compared. After screening was performed, the optimized formulation showed good temperature sensitivity, and T_sol-gel was approximately 35 °C. In vitro release tests showed that GlcN was slowly released from the thermosensitive hydrogels. After the gels were intra-articularly administered to treat OA in rabbits, the degree of swelling and inflammatory factors were significantly decreased in the hydrogel group compared with those in the OA model group (P < 0.05). Histological results showed that the GlcN-administered group had a good repair effect on damaged cartilage. At the same dose, the effect of the thermosensitive hydrogels was better than that of the aqueous solution. Therefore, GlcN-loaded thermosensitive hydrogels based on poloxamers are promising sustainable delivery systems for OA therapy by intra-articular injection.

Preparation, Characterization, and Biological Testing of Novel Magnetic Nanocomposite Hydrogels

To provide a novel approach for the clinical treatment of cartilage tissue defects, we prepared a new type of magnetic nanocomposite hydrogel with an optimal raw material ratio using Fe3O4, polyvinyl alcohol (PVA), and type-II collagen (COLII). Briefly, five groups of PVA and collagen hydrogel matrices with different mass ratios were prepared by a combination of repeated thawing cycles and foam-frozen ice crystal separation methods. Microscopic characterization was conducted using electron microscopy, and the biomechanical properties of each group of hydrogels were then tested. The highest performing component hydrogel matrix was selected after which Fe3O4 with different mass ratios was introduced to construct a new Fe3O4/PVA/COLII hydrogel. The prepared composite hydrogels were also microscopically characterized using electron microscopy along with scanning, measurements for porosity and moisture content, and biomechanical, infrared spectrum and degradation performance testing. CCK-8 detection and staining to determine the amount of living and dead cells were also performed. Collectively, these results showed that PVA/COLII,95:5 was the optimal hydrogel matrix. Using this hydrogel matrix, five groups of composite hydrogels with different Fe3O4 mass ratios were then prepared. There was no significant difference in the microscopic characteristics between these different hydrogels. Fe3O4/PVA/COLII,5:95:5 had better physical properties as well as swelling performance and cell compatibility. The PVA/COLII,95:5 hydrogel matrix was determined to be the best, while the new magnetic nanocomposite hydrogel Fe3O4/PVA/COLII,5:95:5 had good, comprehensive properties.

Incorporating chitin derived glucosamine sulfate into nanofibers via coaxial electrospinning for cartilage regeneration

Chitin is the second abundant natural polysaccharide, and the development of chitin and its derivatives have received more and more attention. Glucosamine sulfate (GAS) obtained by the hydrolysis of chitin can promote the growth of chondrocytes. The coaxial electrospinning technology had been utilized to encapsulated GAS into the core of polycaprolactone (PCL) nanofibers. It could protect the GAS from the environment and allow it to release sustainably over time. From the results of scanning electron microscopy (SEM), PCL/GAS nanofibers performed a typical fiber scaffold surface. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDX) results confirmed the feasibility to use coaxial electrospinning to load GAS. Tensile tests exhibited that PCL/GAS mats could be stretched more than twice its own length. Besides, the cell experiments illustrated that PCL/GAS had a significant effect on the proliferation and growth of rat articular chondrocytes, attesting its prospect for cartilage regeneration.

Osteogenic potential of induced pluripotent stem cells from human adipose-derived stem cells

BACKGROUND

Bone regeneration is a crucial and challenging issue in clinical practice. Bone tissue engineering (BTE) with an optimal cell source may provide an ideal strategy for the reconstruction of bone defects. This study examined whether induced pluripotent stem cells (iPSCs) derived from adipose-derived stem cells (ASCs) could act as an osteogenic substitute and whether these ASC-iPSCs yield more new bone formation than ASCs in hydrogel scaffolds.

METHODS

ASC-iPSCs were reprogrammed from ASCs through a retroviral system. ASCs were harvested and isolated from adipose tissue of humans. An aliquot of cell suspension (1 × 106 cells/mL) was seeded directly onto the nHAP-gelatin cryogel scaffolds. Nude mice back implantation of cell-seeded scaffolds was designed for in vivo comparison of osteogenic potentials between ASCs and ASC-iPSCs. Samples were harvested 4 and 8 weeks after implantation for further analysis based on histology and RT-PCR.

RESULTS

ASC-iPSCs were successfully obtained from human adipose-derived stem cells. PCR results also showed that specific genes of iPSCs with the ability to cause the differentiation of cells into the three germ layers were expressed. In our in vivo experiments, iPSCs were subcutaneously injected into nude mice to induce teratoma formation. The morphology of the three germ layers was confirmed by histological staining. ASC is an essential cell source for BTE with benefits of high volume and less-invasive acquisition. With additional transforming Yamanaka factors, ASC-iPSCs showed higher osteogenic differentiation and elevated expression of collagen type I (Col I), osteocalcin (OCN), alkaline phosphate (ALP), and runt-related transcription factor 2 (RunX-2).

CONCLUSIONS

This report suggests that ASC-iPSCs could be a superior cell source in BTE with better osteogenic differentiation efficacy for future clinical applications.

Enhanced chondrogenic differentiation of human mesenchymal stem cells in silk fibroin/chitosan/glycosaminoglycan scaffolds under dynamic culture condition

Cartilage tissue damage and diseases are the most common clinical situation that occurs because of aging and injury, thereby causing pain and loss of mobility. The inability of cartilage tissue to self-repair is instrumental in developing tissue engineered substitutes. To this effect, the present study aims to engineer cartilage construct by culturing umbilical cord blood-derived human mesenchymal stem cells (hMSCs) on novel 3D porous scaffolds developed from natural biopolymers, silk fibroin (SF) and chitosan (CS), with addition of cartilage matrix components, glucosamine (Gl) and chondroitin sulfate (Ch). The presence of Gl and Ch is expected to enhance cartilage regeneration. The developed SF/CS-Gl-Ch scaffolds possess desired pore size in the range 56.55-168.15 μm, 88-92% porosity, 44.7-46.8̊ contact angle, controlled swelling and biodegradability. Upon culturing under dynamic condition in a spinner flask bioreactor, the scaffold supported hMSCs attachment, proliferation, and further promoted chondrogenic differentiation. Cartilage-specific matrix and gene (Collagen II, Sox9 and aggrecan) expression analyses by histology, immunophenotype, immunofluorescence and quantitative PCR studies showed superiority of cell-scaffold construct generated in dynamic culture towards cartilage tissue generation as compared to cell aggregates formed by pellet culture. This study demonstrates the potentiality of SF/CS-Gl-Ch porous scaffold for the development of tissue construct for cartilage regeneration under dynamic culture condition.

Preparation of Gelatin and Gelatin/Hyaluronic Acid Cryogel Scaffolds for the 3D Culture of Mesothelial Cells and Mesothelium Tissue Regeneration

Mesothelial cells are specific epithelial cells that are lined in the serosal cavity and internal organs. Nonetheless, few studies have explored the possibility to culture mesothelial cells in a three-dimensional (3D) scaffold for tissue engineering applications. Towards this end, we fabricated macroporous scaffolds from gelatin and gelatin/hyaluronic acid (HA) by cryogelation, and elucidated the influence of HA on cryogel properties and the cellular phenotype of mesothelial cells cultured within the 3D scaffolds. The incorporation of HA was found not to significantly change the pore size, porosity, water uptake kinetics, and swelling ratios of the cryogel scaffolds, but led to a faster scaffold degradation in the collagenase solution. Adding 5% HA in the composite cryogels also decreased the ultimate compressive stress (strain) and toughness of the scaffold, but enhanced the elastic modulus. From the in vitro cell culture, rat mesothelial cells showed quantitative cell viability in gelatin (G) and gelatin/HA (GH) cryogels. Nonetheless, mesothelial cells cultured in GH cryogels showed a change in the cell morphology and cytoskeleton arrangement, reduced cell proliferation rate, and downregulation of the mesothelium specific maker gene expression. The production of key mesothelium proteins E-cadherin and calretinin were also reduced in the GH cryogels. Choosing the best G cryogels for in vivo studies, the cell/cryogel construct was used for the transplantation of allograft mesothelial cells for mesothelium reconstruction in rats. A mesothelium layer similar to the native mesothelium tissue could be obtained 21 days post-implantation, based on hematoxylin and eosin (H&E) and immunohistochemical staining.

Rational design of gelatin/nanohydroxyapatite cryogel scaffolds for bone regeneration by introducing chemical and physical cues to enhance osteogenesis of bone marrow mesenchymal stem cells

Identification of key components in the chemical and physical milieu for directing osteogenesis is a requirement in the investigation of tissue engineering scaffolds for advancement of bone regeneration. In this study, we engineered different gelatin-based cryogels and studied the effect of nanohydroxyapatite (nHAP) and crosslinking agents on scaffold properties and its osteogenic response towards bone marrow stem cells (BMSCs). The cryogels examined are 5% gelatin and 5% gelatin/2.5% nHAP, crosslinked either with 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) or glutaraldehyde (GA). We confirmed that nHAP or the crosslinking agent has no effects on scaffold pore size and porosity. Nonetheless, incorporation of nHAP increased mechanical strength, swelling ratio and degree of crosslinking, but decreased degradation rate. Cryogels crosslinked with EDC showed faster degradation and promoted osteogenic differentiation of BMSCs while those prepared from GA crosslinking promoted proliferation of BMSCs. Furthermore, osteogenic differentiation was always enhanced in the presence of nHAP irrespective of the culture medium (normal or osteogenic) used but osteogenic medium always provide a higher extent of osteogenic differentiation. Employing gelatin/nHAP cryogel crosslinked by EDC in a bioreactor for dynamic culture of BMSCs, cyclic compressive mechanical simulation was found to be beneficial for both cell proliferation and osteogenic differentiation. However, the optimum conditions for osteogenic differentiation and cell proliferation were found at 30% and 60% strain, respectively. We thus demonstrated that osteogenic differentiation of BMSCs could be tuned by taking advantages of chemical cues generated from scaffold chemistry or physical cues generated from dynamic cell culture in vitro. Furthermore, by combining the best cryogel preparation and in vitro cell culture condition for osteogenesis, we successfully employed in vitro cultured cryogel/BMSCs constructs for repair of rabbit critical-sized cranial bone defects.

Chitosan-Based Nanofibrous Membrane Unit with Gradient Compositional and Structural Features for Mimicking Calcified Layer in Osteochondral Matrix

Chitosan (CH), silk fibroin (SF), and hydroxyapatite (HA) were used to prepare CH/SF/HA composites and the resulting composites were electrospun into nanofibrous membrane units with gradient compositional and structural features. The optimal membrane unit was used together with CH/HA and CH/SF composites to fabricate a type of three-layer scaffold that is intended for osteochondral repair. The bottom layer of the scaffold was built with CH/HA composites and it served as a subchondral layer, the integrated nanofibrous membrane unit functioned as the middle layer for mimicking the calcified layer and the top layer was constructed using CH/SF composites for acting as a chondral layer. The nanofibrous membrane unit was found to be permeable to some molecules with limited molecular weight and was able to prevent the seeded cells from migrating cross the unit, functioning approximately like the calcified layer in the osteochondral matrix. Layered scaffolds showed abilities to promote the growth of both chondrocytes and osteoblasts that were seeded in their chondral layer and bony layer, respectively, and they were also able to support the phenotype preservation of seeded chondrocytes and the mineralization of neotissue in the bony layer. Results suggest that this type of layered scaffolds can function as an analogue of the osteochondral matrix and it has potential in osteochondral repair.

Injectable Hyaluronic Acid-co-Gelatin Cryogels for Tissue-Engineering Applications

Polymeric scaffolds such as hydrogels can be engineered to restore, maintain, or improve impaired tissues and organs. However, most hydrogels require surgical implantation that can cause several complications such as infection and damage to adjacent tissues. Therefore, developing minimally invasive strategies is of critical importance for these purposes. Herein, we developed several injectable cryogels made out of hyaluronic acid and gelatin for tissue-engineering applications. The physicochemical properties of hyaluronic acid combined with the intrinsic cell-adhesion properties of gelatin can provide suitable physical support for the attachment, survival, and spreading of cells. The physical characteristics of pure gelatin cryogels, such as mechanics and injectability, were enhanced once copolymerized with hyaluronic acid. Reciprocally, the adhesion of 3T3 cells cultured in hyaluronic acid cryogels was enhanced when formulated with gelatin. Furthermore, cryogels had a minimal effect on bone marrow dendritic cell activation, suggesting their cytocompatibility. Finally, in vitro studies revealed that copolymerizing gelatin with hyaluronic acid did not significantly alter their respective intrinsic biological properties. These findings suggest that hyaluronic acid-co-gelatin cryogels combined the favorable inherent properties of each biopolymer, providing a mechanically robust, cell-responsive, macroporous, and injectable platform for tissue-engineering applications.

Chondrogenic differentiation of mesenchymal stem cells on silk fibroin:chitosan–glucosamine scaffold in dynamic culture

Aim: Cartilage damage is a common age-related problem that leads to progressive proteoglycan loss. Glucosamine stimulates proteoglycan synthesis and, therefore, its effect on the cartilage extracellular matrix synthesis over silk fibroin:chitosan (SF:CS) tissue-engineered scaffold was investigated for cartilage construct generation. Materials & methods: Human mesenchymal stem cells (hMSCs) were cultured and differentiated over SF:CS–glucosamine porous scaffold, under dynamic culture condition in spinner flask bioreactor. Results: hMSCs-seeded scaffold in dynamic culture exhibited homogenous cell distribution, proliferation and higher cell density at the core than static culture. Glucosamine in scaffold promoted proteoglycan and collagenous matrix synthesis as revealed by histological and immunofluorescence studies. Quantitative-PCR analysis showed upregulation of cartilage-specific genes, thereby confirming the chondrogenic differentiation. Conclusion: The chondrogenic differentiation of hMSCs was enhanced by the synergistic effect of glucosamine incorporated in SF:CS scaffold and influence of 3D dynamic culture environment, thereby resulting in chondrogenic phenotype of the cells that promoted cartilage regeneration.

Synthesis and in vitro evaluation of thermosensitive hydrogel scaffolds based on (PNIPAAm-PCL-PEG-PCL-PNIPAAm)/Gelatin and (PCL-PEG-PCL)/Gelatin for use in cartilage tissue engineering

BACKGROUND

Biodegradable thermosensitive hydrogel scaffolds based on novel three-block PCL-PEG-PCL and penta block PNIPAAm-PCL-PEG-PCL-PNIPAAm copolymers blended with gelatin were prepared and examined on functional behavior of chondrocytes.

METHODS

In this work, we compared two different thermosensitive hydrogel scaffolds (PNIPAAm-PCL-PEG-PCL-PNIPAAm)/Gelatin and (PCL-PEG-PCL)/Gelatin prepared by TIPS (thermally induced phase separation) method. The feature of copolymers was characterized by FT-IR, ¹H NMR. The lower critical solution temperatures (LCSTs) of aqueous solutions of copolymers were measured by cloud point (turbidity) measurements. We also examined water absorption capacity and swelling ratio. Mechanical features of the prepared hydrogels were evaluated by stress-strain measurements. Thereafter, isolated chondrocytes were cultured on each scaffold for a period of 10 days and cell arrangement and morphology studied pre-and post-plating. Cell survival assay was done by using MTT assay. The transcription level of genes Sox-9, Collagen-II, COMP, MMP-13 and oligomeric matrix protein was monitored by real-time PCR assay. The samples were also stained by Toluidine blue method to monitor the synthesis of proteoglycan.

RESULTS

Data demonstrated an increased survival rate in cells coated seeded on scaffolds, especially (PNIPAAm-PCL-PEG-PCL-PNIPAAm)/Gelatin as compared to control cells on the plastic surface. (PNIPAAm-PCL-PEG-PCL-PNIPAAm)/Gelatin had potential to increase the expression of genes Sox-6, Collagen-II, COMP and after 10 days in vitro.

CONCLUSION

Thermosensitive PCEC/Gel and (PNIPAAm-PCEC-PNIPAAm)/Gel hydrogel scaffolds that fabricated by TIPS method possesses useful hydrophilic properties for growth and cell embedding and secretion of extracellular matrix. It can serve as an ideal strategy to promote the formation of cartilage tissue.

Effect of Cyclic Dynamic Compressive Loading on Chondrocytes and Adipose-Derived Stem Cells Co-Cultured in Highly Elastic Cryogel Scaffolds

In this study, we first used gelatin/chondroitin-6-sulfate/hyaluronan/chitosan highly elastic cryogels, which showed total recovery from large strains during repeated compression cycles, as 3D scaffolds to study the effects of cyclic dynamic compressive loading on chondrocyte gene expression and extracellular matrix (ECM) production. Dynamic culture of porcine chondrocytes was studied at 1 Hz, 10% to 40% strain and 1 to 9 h/day stimulation duration, in a mechanical-driven multi-chamber bioreactor for 14 days. From the experimental results, we could identify the optimum dynamic culture condition (20% and 3 h/day) to enhance the chondrocytic phenotype of chondrocytes from the expression of marker (Col I, Col II, Col X, TNF-α, TGF-β1 and IGF-1) genes by quantitative real-time polymerase chain reactions (qRT-PCR) and production of ECM (GAGs and Col II) by biochemical analysis and immunofluorescence staining. With up-regulated growth factor (TGF-β1 and IGF-1) genes, co-culture of chondrocytes with porcine adipose-derived stem cells (ASCs) was employed to facilitate chondrogenic differentiation of ASCs during dynamic culture in cryogel scaffolds. By replacing half of the chondrocytes with ASCs during co-culture, we could obtain similar production of ECM (GAGs and Col II) and expression of Col II, but reduced expression of Col I, Col X and TNF-α. Subcutaneous implantation of cells/scaffold constructs in nude mice after mono-culture (chondrocytes or ASCs) or co-culture (chondrocytes + ASCs) and subject to static or dynamic culture condition in vitro for 14 days was tested for tissue-engineering applications. The constructs were retrieved 8 weeks post-implantation for histological analysis by Alcian blue, Safranin O and Col II immunohistochemical staining. The most abundant ectopic cartilage tissue was found for the chondrocytes and chondrocytes + ASCs groups using dynamic culture, which showed similar neo-cartilage formation capability with half of the chondrocytes replaced by ASCs for co-culture. This combined co-culture/dynamic culture strategy is expected to cut down the amount of donor chondrocytes needed for cartilage-tissue engineering.

Glycosaminoglycan-based resorbable polymer composites in tissue refurbishment

Regeneration of tissue structure with the aid of bioactive polymer matrices/composites and scaffolds for respective applications is one of the emerging areas of biomedical engineering. Recent advances in conjugated glycosaminoglycan (GAG) hybrids using natural and synthetic polymers have opened new avenues for producing a wide variety of resorbable polymer matrices. These hybrid scaffolds are low-immunogenic, highly biocompatible and biodegradable with incredible mechanical and tensile properties. GAG-based resorbable polymeric matrices are being exploited in migration of stem cells, cartilage and bone replacement/regeneration and production of scaffolds for various tissue engineering applications. In the current review, we will discuss the role of GAG-based resorbable polymer matrices in the field of regenerative medicine.