Natural hydrogels for cartilage regeneration: Modification, preparation and application

Platelet-rich plasma alleviates knee arthritis in rats by inhibiting p65

Knee osteoarthritis (KOA) is a chronic joint disease characterized by the degeneration of articular cartilage. In this study, we explored the potential therapeutic effects of platelet-rich plasma (PRP) and identified molecular targets for treating KOA. A rat model of KOA was established via the Hulth method and primary knee joint chondrocytes were isolated to evaluate the effects of PRP and shRNA targeting p65 (sh-p65). ELISA was used to detect inflammatory factors, including IL-6, IL-1β, and TNF-α. HE staining, Safranin O/Fast Green staining and Masson staining were performed to evaluate the morphology of articular cartilage, followed by detection of p65, COL2A1, ACAN, MMP13, and ADAMTS5 expression. The proliferation and apoptosis of primary knee chondrocytes were detected by the CCK-8 assay and TUNEL staining, respectively. Treatment with either PRP or sh-p65 decreased IL-6, IL-1β, and TNF-α levels in the peripheral blood of KOA rats and chondrocyte culture supernatants, increased COL2A1 and ACAN levels, and decreased MMP13 and ADAMTS5 expression. Furthermore, administration of PRP or sh-p65 exerted protective effects on articular cartilage, enhanced the vitality of knee joint chondrocytes, and inhibited apoptosis. Collectively, PRP inhibited inflammation, promoted chondrocyte proliferation and cartilage matrix secretion, and induced cartilage regeneration by suppressing p65 expression; these effects allow PRP to alleviate KOA progression. P65-based targeted therapy administered in combination with PRP might be a promising strategy for treating KOA.

Microenvironment-responsive bilayer hydrogel microspheres with gelatin-shell for osteoarthritis treatment

Osteoarthritis is a long-term degenerative condition of the joints that is characterized by the breakdown of cartilage and inflammation of the synovial membrane. The presence of an inflammatory microenvironment and the degradation of the extracellular matrix produced by chondrocytes leads to the aggravation of cartilage injury, hindering the treatment of osteoarthritis. A promising approach to address this issue is to apply a combined strategy that is sensitive to the specific conditions in osteoarthritic joints and possesses properties that can reduce inflammation and promote cartilage healing. Here, inspired by the structure of chocolate-covered peanuts, we developed an injectable, environment-responsive bilayer hydrogel microsphere using microfluidics technology. The microsphere applied chondroitin sulfate methacryloyl (ChsMA) as its core and was coated with a methacryloyl gelatin (GelMA) shell that was loaded with celecoxib (CLX) liposomes (ChsMA+CLX@Lipo@GelMA). CLX was released from the liposomes when the GelMA shell rapidly degraded in response to the osteoarthritic microenvironment and suppressed the generation of inflammatory agents, demonstrating a beneficial impact of the outer shell in reducing inflammation. While the inner methacryloyl microsphere core degraded, chondroitin sulfate was released to promote chondrocyte anabolism and facilitate cartilage repair. Thus, the synthesized bilayer hydrogel microspheres hold great potential for treating osteoarthritis.

Collagen-Based Hydrogels for Cartilage Regeneration

Cartilage regeneration remains difficult due to a lack of blood vessels. Degradation of the extracellular matrix (ECM) causes cartilage defects, and the ECM provides the natural environment and nutrition for cartilage regeneration. Until now, collagen hydrogels are considered to be excellent material for cartilage regeneration due to the similar structure to ECM and good biocompatibility. However, collagen hydrogels also have several drawbacks, such as low mechanical strength, limited ability to induce stem cell differentiation, and rapid degradation. Thus, there is a demanding need to optimize collagen hydrogels for cartilage regeneration. In this review, we will first briefly introduce the structure of articular cartilage and cartilage defect classification and collagen, then provide an overview of the progress made in research on collagen hydrogels with chondrocytes or stem cells, comprehensively expound the research progress and clinical applications of collagen-based hydrogels that integrate inorganic or organic materials, and finally present challenges for further clinical translation.

Development and characterization of a poloxamer hydrogel composed of human mesenchymal stromal cells (hMSCs) for reepithelization of skin injuries

Wound healing is a natural physiological reaction to tissue injury. Hydrogels show attractive advantages in wound healing not only due to their biodegradability, biocompatibility and permeability but also because provide an excellent environment for cell migration and proliferation. The main objective of the present study was the design and characterization of a hydrogel loaded with human mesenchymal stromal cells (hMSCs) for use in would healing of superficial skin injures. Poloxamer 407® was used as biocompatible biomaterial to embed hMSCs. The developed hydrogel containing 20 % (w/w) of polymer resulted in the best formulation with respect to physical, mechanical, morphological and biological properties. Its high swelling capacity confirmed the hydrogel's capacity to absorb wounds' exudate. LIVE/DEAD® assay confirm that hMSCs remained viable for at least 48 h when loaded into the hydrogels. Adding increasing concentrations of hMSCs-loaded hydrogel to the epithelium did not affect keratinocytes' viability and healing capacity and all wound area was closed in less than one day. Our study opens opportunities to exploit poloxamer hydrogels as cell carriers for the treatment of skin superficial wound.

Biosensing with Polymerase Chain Reaction-Stable DNA-Functionalized Magnetically Susceptible Carbon-Iron Microparticles

We demonstrate a rapid and sensitive method for DNA detection without the need for fluorescence. This is based on carbon-coated magnetic iron (Fe) microparticles with a covalent surface attachment of DNA. We show that these magnetic microparticles can capture complementary DNA. Significantly, the DNA covalent surface bonds are robust to high temperatures and can be included in a sample during polymerase chain reaction (PCR). This method is employed for the detection of targeted DNA sequences (40-50 bp). Hybridization probes on the surface of the magnetically susceptible Fe microparticle recognize the target DNA sequence-specifically. The double-stranded DNA (dsDNA) microparticles are then quickly captured with a magnet from the sample matrix. This foregoes postpurification processes, such as electrophoresis, which make our technique time- and cost-effective. Captured dsDNA can be detected with intercalating dyes such as ethidium bromide through a loss in the UV absorption signal with a limit of detection (LOD) of 24 nM within 15 min. Likewise, surface-bound DNA can act as a primer in PCR to decrease the LOD to 5 pM within 2 h. This is the first instance of a nucleotide-modified magnetically susceptible carbon substrate that is PCR-compatible. Besides DNA capture, this strategy can eventually be applied to sequence-specific nucleic acid purification and enrichment, PCR cleanup, and single-strand generation. The DNA-coated particles are stable under PCR conditions (unlike commonly used polystyrene or gold particles).

Challenges and future scope of exosomes in the treatment of cardiovascular diseases

Exosomes are nanosized vesicles that carry biologically diverse molecules for intercellular communication. Researchers have been trying to engineer exosomes for therapeutic purposes by using different approaches to deliver biologically active molecules to the various target cells efficiently. Recent technological advances may allow the biodistribution and pharmacokinetics of exosomes to be modified to meet scientific needs with respect to specific diseases. However, it is essential to determine an exosome's optimal dosage and potential side effects before its clinical use. Significant breakthroughs have been made in recent decades concerning exosome labelling and imaging techniques. These tools provide in situ monitoring of exosome biodistribution and pharmacokinetics and pinpoint targetability. However, because exosomes are nanometres in size and vary significantly in contents, a deeper understanding is required to ensure accurate monitoring before they can be applied in clinical settings. Different research groups have established different approaches to elucidate the roles of exosomes and visualize their spatial properties. This review covers current and emerging strategies for in vivo and in vitro exosome imaging and tracking for potential studies.

Injectable hydrogels: An emerging therapeutic strategy for cartilage regeneration

The impairment of articular cartilage due to traumatic incidents or osteoarthritis has posed significant challenges for healthcare practitioners, researchers, and individuals suffering from these conditions. Due to the absence of an approved treatment strategy for the complete restoration of cartilage defects to their native state, the tissue condition often deteriorates over time, leading to osteoarthritic (OA). However, recent advancements in the field of regenerative medicine have unveiled promising prospects through the utilization of injectable hydrogels. This versatile class of biomaterials, characterized by their ability to emulate the characteristics of native articular cartilage, offers the distinct advantage of minimally invasive administration directly to the site of damage. These hydrogels can also serve as ideal delivery vehicles for a diverse range of bioactive agents, including growth factors, anti-inflammatory drugs, steroids, and cells. The controlled release of such biologically active molecules from hydrogel scaffolds can accelerate cartilage healing, stimulate chondrogenesis, and modulate the inflammatory microenvironment to halt osteoarthritic progression. The present review aims to describe the methods used to design injectable hydrogels, expound upon their applications as delivery vehicles of biologically active molecules, and provide an update on recent advances in leveraging these delivery systems to foster articular cartilage regeneration.

Regeneration of Rabbit Auricular Cartilage After the Intravenous Stem Cell Injection

Background

The restoration of auricular cartilage is a major problem of otolaryngology. The low regenerative capacity of cartilage requires alternative approaches such as cell and tissue engineering. Stem cells are one of the ways to repair auricular cartilage damages. The aim of the investigation was the regeneration of an artificial defect of the auricular cartilage of rabbits after the intravenous injection of stem cells.

Materials and Methods

The study was carried out on rabbits. A narrow strip of auricular cartilage was surgically removed. A previously prepared suspension of homologous mesenchymal stem cells (5 million) in 0.5 ml physiological solution was injected into the vein of the opposite ear. Tissue samples from the site of the injury were collected after 1, 2, and 3 months. Histological examinations of the tissues were carried out after staining with fuchsin-eosin, azure II-eosin, and according to Weigert. In addition, the amount of interleukin-6 (IL-6) and the transforming growth factor β1 (TGF-β1) in the blood serum were determined.

Results

The main method of healing is the formation of a connective tissue scar. Yret, an increase of the number of fibroblasts and single islands of the newly formed auricular cartilage was found, which indicates the migration of the injected stem cells to the site of the damage and settling there. The intravenous injection of stem cells did not affect the secretion of pro-inflammatory IL-6, but significantly increased the amount of TGF-β1.

Conclusions

We assume that regenerative processes were stimulated. Nevertheless, they were aimed at quickly restoring the tissue integrity through the typical stages of scar formation. The restoration of cartilage integrity requires additional regulatory factors which will determine the chondrogenic differentiation of stem cells.

3D-bioimplants mimicking the structure and function of spine units for the treatment of spinal tuberculosis

Approximately 1-2% of the reported tuberculosis (TB) cases have skeletal system problems, particularly spinal TB. The complications of spinal TB involve the destruction of vertebral body (VB) and intervertebral disc (IVD) which consequently leads to kyphosis. This work aimed at utilizing different technologies to develop, for the first time, a functional spine unit (FSU) replacement to mimic the structure and function of the VB and IVD along with a good ability to treat spinal TB. 3D-printed scaffolds with different porous patterns (hexagonal or grid) were fabricated from biocompatible acrylonitrile butadiene styrene, and polylactic acid to replace damaged VB and IVD, respectively. The VB scaffold is filled with gelatine-based semi-IPN hydrogel containing mesoporous silica nanoparticles loaded with two antibiotics, rifampicin and levofloxacin, to act against TB. The IVD scaffold incorporates a gelatin hydrogel loaded with regenerative platelet-rich plasma and anti-inflammatory simvastatin-loaded mixed nanomicelles. The obtained results confirmed the superior mechanical strength of both 3D-printed scaffolds and loaded hydrogels as compared to normal bone and IVD with high in vitro (cell proliferation, anti-inflammation and anti-TB), and in vivo biocompatibility profiles. Moreover, the custom-designed replacements have achieved the expected prolonged release of antibiotics up to 60 days. Given the promising study findings, the utilization of the developed drug-eluting scaffold system can be extrapolated to treat not only spinal TB but also to resolve diverse backbone/spine problems that need a critical surgical process including degenerative IVD and its consequences like atherosclerosis, sliding or spondylolisthesis and severe traumatic bone fracture.

Marine Gelatin-Methacryloyl-Based Hydrogels as Cell Templates for Cartilage Tissue Engineering

Marine-origin gelatin has been increasingly used as a safe alternative to bovine and porcine ones due to their structural similarity, avoiding the health-related problems and sociocultural concerns associated with using mammalian-origin materials. Another benefit of marine-origin gelatin is that it can be produced from fish processing-products enabling high production at low cost. Recent studies have demonstrated the excellent capacity of gelatin-methacryloyl (GelMA)-based hydrogels in a wide range of biomedical applications due to their suitable biological properties and tunable physical characteristics, such as tissue engineering applications, including the engineering of cartilage. In this study, fish gelatin was obtained from Greenland halibut skins by an acidic extraction method and further functionalized by methacrylation using methacrylic anhydride, developing a photosensitive gelatin-methacryloyl (GelMA) with a degree of functionalization of 58%. The produced marine GelMA allowed the fabrication of photo-crosslinked hydrogels by incorporating a photoinitiator and UV light exposure. To improve the biological performance, GelMA was combined with two glycosaminoglycans (GAGs): hyaluronic acid (HA) and chondroitin sulfate (CS). GAGs methacrylation reaction was necessary, rendering methacrylated HA (HAMA) and methacrylated CS (CSMA). Three different concentrations of GelMA were combined with CSMA and HAMA at different ratios to produce biomechanically stable hydrogels with tunable physicochemical features. The 20% (w/v) GelMA-based hydrogels produced in this work were tested as a matrix for chondrocyte culture for cartilage tissue engineering with formulations containing both HAMA and CSMA showing improved cell viability. The obtained results suggest these hybrid hydrogels be used as promising biomaterials for cartilage tissue engineering applications.

Progressive use of nanocomposite hydrogels materials for regeneration of damaged cartilage and their tribological mechanical properties

Osteoarthritis (OA) is a non-inflammatory deteriorating debilitating state that bring about remarkable health and economic issues globally. Break down/deterioration of the articular cartilage (AC) is one of the pathologic characteristics of osteoarthritis (OA). Nanocomposite hydrogels (NCH) materials are evolving as a potential class of scaffolds for organ regeneration and tissue engineering. In recent years, innovative hydrogels specifically loaded with nanoparticles have been developed and synthesized with the goal of changing conventional cartilage treatments. The detailed development of a tailored nanocomposite hydrogels (NCH) material utilized for tissue engineering is presented in this review study. Also, the mechanical characteristics, particularly the tribological behavior, of these produced NCH have been highlighted. Large amounts of research and data on the hydrogel substance utilized in cartilage healing are summarized in the current review study. When determining future research gaps in the area of hydrogels for cartilage regeneration, such information will provide researchers an advantage to further develop NCH.

A static magnetic field enhances the repair of osteoarthritic cartilage by promoting the migration of stem cells and chondrogenesis

Objective

To investigate the therapeutic effects of static magnetic field (SMF) and its regulatory mechanism in the repair of osteoarthritic cartilage.

Methods

Fourteen-week-old female C57BL/6 mice were randomly divided into the sham operation group and the osteoarthritis (OA) groups with and without SMF application. SMF was applied at 200 ​mT for two consecutive weeks. Changes in knee cartilage were examined by histomorphometry, and the chondrogenesis and migration of endogenous stem cells were assessed. The expression of SRY-related protein 9 (SOX9), Collagen type II (COL2), matrix metallopeptidase 13 (MMP13), stromal cell-derived factor 1/C-X-C chemokine receptor type 4 (SDF-1/CXCR4), Piezo1 and other genes was evaluated, and the mechanism of SMF's action was tested using the CXCR4 inhibitor, AMD3100, and Piezo1 siRNA.

Results

SMF significantly decreased the OARSI scores after induction of OA. SMF was beneficial to chondrogenesis by elevating SOX9. In the OA mouse model, an increase in MMP13 with a decrease in COL2 led to the destruction of the cartilage extracellular matrix, which was suppressed by SMF. SMF promoted the migration of cartilage-derived stem/progenitor cells and bone marrow-derived mesenchymal stem cells (MSCs). It increased SDF-1 and CXCR4, while the CXCR4 inhibitor significantly suppressed the beneficial effects of SMF. The application of Piezo1 siRNA inhibited the SMF-induced increase of CXCR4.

Conclusion

SMF enhanced chondrogenesis and improved cartilage extracellular matrices. It activated the Piezo1-mediated SDF-1/CXCR4 regulatory axis and promoted the migration of endogenous stem cells. Collectively, it attenuated the pathological progression of cartilage destruction in OA mice.

The Translational potential of this article

The findings in this study provided convincing evidence that SMF could enhance cartilage repair and improve OA symptoms, suggesting that SMF could have clinical value in the treatment of OA.

3D Bioprinting of Smart Oxygen-Releasing Cartilage Scaffolds

Three-dimensional bioprinting is a powerful technique for manufacturing improved engineered tissues. Three-dimensional bioprinted hydrogels have significantly advanced the medical field to repair cartilage tissue, allowing for such constructs to be loaded with different components, such as cells, nanoparticles, and/or drugs. Cartilage, as an avascular tissue, presents extreme difficulty in self-repair when it has been damaged. In this way, hydrogels with optimal chemical and physical properties have been researched to respond to external stimuli and release various bioactive agents to further promote a desired tissue response. For instance, methacryloyl gelatin (GelMA) is a type of modified hydrogel that allows for the encapsulation of cells, as well as oxygen-releasing nanoparticles that, in the presence of an aqueous medium and through controlled porosity and swelling, allow for internal and external environmental exchanges. This review explores the 3D bioprinting of hydrogels, with a particular focus on GelMA hydrogels, to repair cartilage tissue. Recent advances and future perspectives are described.

Practical Use of Quartz Crystal Microbalance Monitoring in Cartilage Tissue Engineering

Quartz crystal microbalance (QCM) is a real-time, nanogram-accurate technique for analyzing various processes on biomaterial surfaces. QCM has proven to be an excellent tool in tissue engineering as it can monitor key parameters in developing cellular scaffolds. This review focuses on the use of QCM in the tissue engineering of cartilage. It begins with a brief discussion of biomaterials and the current state of the art in scaffold development for cartilage tissue engineering, followed by a summary of the potential uses of QCM in cartilage tissue engineering. This includes monitoring interactions with extracellular matrix components, adsorption of proteins onto biomaterials, and biomaterial–cell interactions. In the last part of the review, the material selection problem in tissue engineering is highlighted, emphasizing the importance of surface nanotopography, the role of nanofilms, and utilization of QCM as a “screening” tool to improve the material selection process. A step-by-step process for scaffold design is proposed, as well as the fabrication of thin nanofilms in a layer-by-layer manner using QCM. Finally, future trends of QCM application as a “screening” method for 3D printing of cellular scaffolds are envisioned.

Ancient fibrous biomaterials from silkworm protein fibroin and spider silk blends: Biomechanical patterns

Silkworm silk protein fibroin and spider silk spidroin are known biocompatible and natural biodegradable polymers in biomedical applications. The presence of β-sheets in silk fibroin and spider spidroin conformation improves their mechanical properties. The strength and toughness of pure recombinant silkworm fibroin and spidroin are relatively low due to reduced molecular weight. Hence, blending is the foremost approach of recent studies to optimize silk fibroin and spidroin's mechanical properties. As summarised in the present review, numerous research investigations evaluate the blending of natural and synthetic polymers. The effects of blending silk fibroin and spidroin with natural and synthetic polymers on the mechanical properties are discussed in this review article. Indeed, combining natural and synthetic polymers with silk fibroin and spidroin changes their conformation and structure, fine-tuning the blends' mechanical properties. STATEMENT OF SIGNIFICANCE: Silkworm and spider silk proteins (silk fibroin and spidroin) are biocompatible and biodegradable natural polymers having different types of biomedical applications. Their mechanical and biological properties may be tuned through various strategies such as blending, conjugating and cross-linking. Blending is the most common method to modify fibroin and spidroin properties on demand, this review article aims to categorize and evaluate the effects of blending fibroin and spidroin with different natural and synthetic polymers. Increased polarity and hydrophilicity end to hydrogen bonding triggered conformational change in fibroin and spidroin blends. The effect of polarity and hydrophilicity of the blending compound is discussed and categorized to a combinatorial, synergistic and indirect impacts. This outlook guides us to choose the blending compounds mindfully as this mixing affects the biochemical and biophysical characteristics of the biomaterials.

Current Advances of Three-Dimensional Bioprinting Application in Dentistry: A Scoping Review

Three-dimensional (3D) bioprinting technology has emerged as an ideal approach to address the challenges in regenerative dentistry by fabricating 3D tissue constructs with customized complex architecture. The dilemma with current dental treatments has led to the exploration of this technology in restoring and maintaining the function of teeth. This scoping review aims to explore 3D bioprinting technology together with the type of biomaterials and cells used for dental applications. Based on PRISMA-ScR guidelines, this systematic search was conducted by using the following databases: Ovid, PubMed, EBSCOhost and Web of Science. The inclusion criteria were (i) cell-laden 3D-bioprinted construct; (ii) intervention to regenerate dental tissue using bioink, which incorporates living cells or in combination with biomaterial; and (iii) 3D bioprinting for dental applications. A total of 31 studies were included in this review. The main 3D bioprinting technique was extrusion-based approach. Novel bioinks in use consist of different types of natural and synthetic polymers, decellularized extracellular matrix and spheroids with encapsulated mesenchymal stem cells, and have shown promising results for periodontal ligament, dentin, dental pulp and bone regeneration application. However, 3D bioprinting in dental applications, regrettably, is not yet close to being a clinical reality. Therefore, further research in fabricating ideal bioinks with implantation into larger animal models in the oral environment is very much needed for clinical translation.

Hydroxyapatite Reinforced Polyvinyl Alcohol/Polyvinyl Pyrrolidone Based Hydrogel for Cartilage Replacement

Polyvinyl alcohol (PVA) and Polyvinyl Pyrrolidone (PVP) hydrogels are desirable biomaterials for soft tissue repair and replacement. However, the bio-inertness and poor cell adhesive potency of the PVA and PVP hinder the wide range of biomedical applications. In the present work, PVA and PVP were blended with a one-dimensional hydroxyapatite nanorod (HNr), and PVA/PVP/HNr composite hydrogel was synthesized by the freeze-thaw process. The developed hydrogels were characterized by Scanning Electron Microscope (SEM). The bio-ceramic nanohydroxyapatite content was optimized, and it was found that reinforcement improves mechanical strength as well as bioactivity. The compression strength values are 2.47 ± 0.73 MPa for the composite having 2 wt% of nanohydroxyapatite. The storage modulus was much higher than the loss modulus, which signifies the elastic dominancy similar to cartilage. Besides, the antimicrobial activity of nanohydroxyapatite reinforced PVA hydrogel towards bacterial species, Escherichia coli (E. Coli), Staphylococcus aureus (S. aureus) was satisfactory, and the in vitro biocompatibility response towards Human Mesenchymal stem cells(hMSC) after 72 h of culture confirms nanohydroxyapatite reinforced PVA/PVP hydrogels are the promising alternatives for next-generation cartilage substitutes.

Tribological Evaluation of Silica Nanoparticle Enhanced Bilayer Hydrogels as A Candidate for Cartilage Replacement

Polymeric hydrogels can be used as artificial replacement for lesioned cartilage. However, modulating the hydrogel formulation that mimics articular cartilage tissue with respect to mechanical and tribological properties has remained a challenge. This study encompasses the tribological evaluation of a silica nanoparticle (SNP) loaded bilayer nanocomposite hydrogel (NCH), synthesized using acrylamide, acrylic acid, and alginate via modulated free-radical polymerization. Multi-factor pin-on-plate sliding wear experiments were carried out with a steel ball counterface using a linear reciprocating tribometer. Tribological properties of NCHs with 0.6 wt% SNPs showed a significant improvement in the wear resistance of the lubricious layer and a low coefficient of friction (CoF). CoF of both non-reinforced hydrogel (NRH) and NCH at maximum contact pressure ranged from 0.006 to 0.008, which is in the order of the CoF of healthy articular cartilage. Interfacial surface energy was analysed according to Johnson, Kendall, and Robert’s theory, and NCHs showed superior mechanical properties and surface energy compared to NRHs. Lubrication regimes’ models were drawn based on the Stribeck chart parameters, and CoF results were highlighted in the elastoviscous transition regime.

Additive Manufacturing of Biomaterials-Design Principles and Their Implementation

Additive manufacturing (AM, also known as 3D printing) is an advanced manufacturing technique that has enabled progress in the design and fabrication of customised or patient-specific (meta-)biomaterials and biomedical devices (e.g., implants, prosthetics, and orthotics) with complex internal microstructures and tuneable properties. In the past few decades, several design guidelines have been proposed for creating porous lattice structures, particularly for biomedical applications. Meanwhile, the capabilities of AM to fabricate a wide range of biomaterials, including metals and their alloys, polymers, and ceramics, have been exploited, offering unprecedented benefits to medical professionals and patients alike. In this review article, we provide an overview of the design principles that have been developed and used for the AM of biomaterials as well as those dealing with three major categories of biomaterials, i.e., metals (and their alloys), polymers, and ceramics. The design strategies can be categorised as: library-based design, topology optimisation, bio-inspired design, and meta-biomaterials. Recent developments related to the biomedical applications and fabrication methods of AM aimed at enhancing the quality of final 3D-printed biomaterials and improving their physical, mechanical, and biological characteristics are also highlighted. Finally, examples of 3D-printed biomaterials with tuned properties and functionalities are presented.

The Emerging Use of ASC/Scaffold Composites for the Regeneration of Osteochondral Defects

Articular cartilage is composed of chondrocytes surrounded by a porous permeable extracellular matrix. It has a limited spontaneous healing capability post-injury which, if left untreated, can result in severe osteochondral disease. Currently, osteochondral (OC) defects are treated by bone marrow stimulation, artificial joint replacement, or transplantation of bone, cartilage, and periosteum, while autologous osteochondral transplantation is also an option; it carries the risk of donor site damage and is limited only to the treatment of small defects. Allografts may be used for larger defects; however, they have the potential to elicit an immune response. A possible alternative solution to treat osteochondral diseases involves the use of stromal/stem cells. Human adipose-derived stromal/stem cells (ASCs) can differentiate into cartilage and bone cells. The ASC can be combined with both natural and synthetic scaffolds to support cell delivery, growth, proliferation, migration, and differentiation. Combinations of both types of scaffolds along with ASCs and/or growth factors have shown promising results for the treatment of OC defects based on in vitro and in vivo experiments. Indeed, these findings have translated to several active clinical trials testing the use of ASC-scaffold composites on human subjects. The current review critically examines the literature describing ASC-scaffold composites as a potential alternative to conventional therapies for OC tissue regeneration.

Elastomer–Hydrogel Systems: From Bio-Inspired Interfaces to Medical Applications

Novel advanced biomaterials have recently gained great attention, especially in minimally invasive surgical techniques. By applying sophisticated design and engineering methods, various elastomer–hydrogel systems (EHS) with outstanding performance have been developed in the last decades. These systems composed of elastomers and hydrogels are very attractive due to their high biocompatibility, injectability, controlled porosity and often antimicrobial properties. Moreover, their elastomeric properties and bioadhesiveness are making them suitable for soft tissue engineering. Herein, we present the advances in the current state-of-the-art design principles and strategies for strong interface formation inspired by nature (bio-inspiration), the diverse properties and applications of elastomer–hydrogel systems in different medical fields, in particular, in tissue engineering. The functionalities of these systems, including adhesive properties, injectability, antimicrobial properties and degradability, applicable to tissue engineering will be discussed in a context of future efforts towards the development of advanced biomaterials.

Magnetic Hydrogel for Cartilage Tissue Regeneration as well as a Review on Advantages and Disadvantages of Different Cartilage Repair Strategies

There is a clear clinical need for efficient cartilage healing strategies for treating cartilage defects which burdens millions of patients physically and financially. Different strategies including microfracture technique, osteochondral transfer, and scaffold-based treatments have been suggested for curing cartilage injuries. Although some improvements have been achieved in several facets, current treatments are still less than satisfactory. Recently, different hydrogel-based biomaterials have been suggested as a therapeutic candidate for cartilage tissue regeneration due to their biocompatibility, high water content, and tunability. Specifically, magnetic hydrogels are becoming more attractive due to their smart response to magnetic fields remotely. We seek to outline the context-specific regenerative potential of magnetic hydrogels for cartilage tissue repair. In this review, first, we explained conventional techniques for cartilage repair and then compared them with new scaffold-based approaches. We illustrated various hydrogels used for cartilage regeneration by highlighting the magnetic hydrogels. Also, we gathered in vitro and in vivo studies of how magnetic hydrogels promote chondrogenesis as well as studied the biological mechanism which is responsible for cartilage repair due to the application of magnetic hydrogel.

Fabrication and Characterization of Bioactive Gelatin-Alginate-Bioactive Glass Composite Coatings on Porous Titanium Substrates

In this research work, the fabrication of biphasic composite implants has been investigated. Porous, commercially available pure Ti (50 vol % porosity and pore distributions of 100-200, 250-355, and 355-500 μm) has been used as a cortical bone replacement, while different composites based on a polymer blend (gelatin and alginate) and bioactive glass (BG) 45S5 have been applied as a soft layer for cartilage tissues. The microstructure, degradation rates, biofunctionality, and wear behavior of the different composites were analyzed to find the best possible coating. Experiments demonstrated the best micromechanical balance for the substrate containing 200-355 μm size range distribution. In addition, although the coating prepared from alginate presented a lower mass loss, the composite containing 50% alginate and 50% gelatin showed a higher elastic recovery, which entails that this type of coating could replicate the functions of the soft tissue in areas of the joints. Therefore, results revealed that the combinations of porous commercially pure Ti and composites prepared from alginate/gelatin/45S5 BG are candidates for the fabrication of biphasic implants not only for the treatment of osteochondral defects but also potentially for any other diseases affecting simultaneously hard and soft tissues.

Mussel-inspired extracellular matrix-mimicking hydrogel scaffold with high cell affinity and immunomodulation ability for growth factor-free cartilage regeneration

Background

Injury to articular cartilage cause certain degree of disability due to poor self-repair ability of cartilage tissue. To promote cartilage regeneration, it is essential to develop a scaffold that properly mimics the native cartilage extracellular matrix (ECM) in the aspect of compositions and functions.

Methods

A mussel-inspired strategy was developed to construct an ECM-mimicking hydrogel scaffold by incorporating polydopamine-modified hyaluronic acid (PDA/HA) complex into a dual-crosslinked collagen (Col) matrix for growth factor-free cartilage regeneration. The adhesion, proliferation, and chondrogenic differentiation of cells on the scaffold were examined. A well-established full-thickness cartilage defect model of the knee in rabbits was used to evaluated the efficacy and functionality of the engineered Col/PDA/HA hydrogel scaffold.

Results

The PDA/HA complex incorporated-hydrogel scaffold with catechol moieties exhibited better cell affinity than bare negatively-charged HA incorporated hydrogel scaffold. In addition, the PDA/HA complex endowed the scaffold with immunomodulation ability, which suppressed the expression of inflammatory cytokines and effectively activated the polarization of macrophages toward M2 phenotypes. The in vivo results revealed that the mussel-inspired Col/PDA/HA hydrogel scaffold showed strong cartilage inducing ability to promote cartilage regeneration.

Conclusions

The PDA/HA complex-incorporated hydrogel scaffold overcame the cell repellency of negatively-charged polysaccharide-based scaffolds, which facilitated the adhesion and clustering of cells on the scaffold, and therefore enhanced cell-HA interactions for efficient chondrogenic differentiation. Moreover, the hydrogel scaffold modulated immune microenvironment, and created a regenerative microenvironment to enhance cartilage regeneration.

The translational potential of this article

This study gives insight into the mussel-inspired approach to construct the tissue-inducing hydrogel scaffold in a growth-factor-free manner, which show great advantage in the clinical treatment. The hydrogel scaffold composed of collagen and hyaluronic acid as the major component, providing cartilage ECM-mimicking environment, is promising for cartilage defect repair.

New Insights of Scaffolds Based on Hydrogels in Tissue Engineering

In recent years, biomaterials development and characterization for new applications in regenerative medicine or controlled release represent one of the biggest challenges. Tissue engineering is one of the most intensively studied domain where hydrogels are considered optimum applications in the biomedical field. The delicate nature of hydrogels and their low mechanical strength limit their exploitation in tissue engineering. Hence, developing new, stronger, and more stable hydrogels with increased biocompatibility, is essential. However, both natural and synthetic polymers possess many limitations. Hydrogels based on natural polymers offer particularly high biocompatibility and biodegradability, low immunogenicity, excellent cytocompatibility, variable, and controllable solubility. At the same time, they have poor mechanical properties, high production costs, and low reproducibility. Synthetic polymers come to their aid through superior mechanical strength, high reproducibility, reduced costs, and the ability to regulate their composition to improve processes such as hydrolysis or biodegradation over variable periods. The development of hydrogels based on mixtures of synthetic and natural polymers can lead to the optimization of their properties to obtain ideal scaffolds. Also, incorporating different nanoparticles can improve the hydrogel’s stability and obtain several biological effects. In this regard, essential oils and drug molecules facilitate the desired biological effect or even produce a synergistic effect. This study’s main purpose is to establish the main properties needed to develop sustainable polymeric scaffolds. These scaffolds can be applied in tissue engineering to improve the tissue regeneration process without producing other side effects to the environment.

Polysaccharide hydrogels: Functionalization, construction and served as scaffold for tissue engineering

Polysaccharide hydrogels have been widely utilized in tissue engineering. They interact with the organismal environments, modulating the cargos release and realizing of long-term survival and activations of living cells. In this review, the potential strategies for modification of polysaccharides were introduced firstly. It is not only used to functionalize the polysaccharides for the consequent formation of hydrogels, but also used to introduce versatile side groups for the regulation of cell behavior. Then, techniques and underlying mechanisms in inducing the formation of hydrogels by polysaccharides or their derivatives are briefly summarized. Finally, the applications of polysaccharide hydrogels in vivo, mainly focus on the performance for alleviation of foreign-body response (FBR) and as cell scaffolds for tissue regeneration, are exemplified. In addition, the perspectives and challenges for further research are addressed. It aims to provide a comprehensive framework about the potentials and challenges that the polysaccharide hydrogels confronting in tissue engineering.

Does vehicle-based delivery of mesenchymal stromal cells give superior results in knee osteoarthritis? Meta-analysis of randomized controlled trials

STUDY DESIGN

Meta-analysis.

OBJECTIVES

We aim to analyze and compare the efficacy and safety of vehicle-based delivery of Mesenchymal Stromal Cells (MSCs) in the management of osteoarthritis of the knee from Randomized Controlled Trials (RCTs) available in the literature.

MATERIALS AND METHODS

We conducted independent and duplicate electronic database searches including PubMed, Embase, Web of Science, and Cochrane Library till August 2021 for RCTs analyzing the efficacy and safety of vehicle-based delivery of MSCs in the management of knee osteoarthritis. Visual Analog Score (VAS) for Pain, Western Ontario McMaster Universities Osteoarthritis Index (WOMAC), Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score, and adverse events were the outcomes analyzed. Analysis was performed in R-platform using OpenMeta [Analyst] software.

RESULTS

21 studies involving 936 patients were included for analysis. None of the studies made a direct comparison of the direct and vehicle-based delivery of MSCs, hence we pooled the results of all the included studies of both groups and made a comparative analysis of their outcomes. Although at 6 months, both direct and vehicle-based delivery of MSCs showed significantly better VAS improvement (p = 0.002, p = 0.010), it was not consistent at 1 year for the vehicle delivery (p = 0.973). During 6 months and 12 months, direct delivery of MSCs (p < 0.001, p < 0.001) outperformed vehicle delivery (p = 0.969, p = 0.922) compared to their control based on WOMAC scores respectively. Both direct (p = 0.713) and vehicle-based delivery (p = 0.123) of MSCs did not produce significant adverse events compared to their controls.

CONCLUSION

Our analysis of literature showed that current clinically employed methods of vehicle-based delivery of MSCs such as platelet-rich plasma, hyaluronic acid did not demonstrate superior results compared to direct delivery, concerning the efficacy of treatment measured by improvement in pain, functional outcomes, and safety. Hence, we urge future clinical trials to be conducted to validate the effectiveness of advanced delivery vehicles such as composite bioscaffolds to establish their practical utility in cartilage regeneration with respect to its encouraging in-vitro evidence.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

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

Effect of Chitosan Deacetylation on Its Affinity to Type III Collagen: A Molecular Dynamics Study

The ability to form strong intermolecular interactions by linear glucosamine polysaccharides with collagen is strictly related to their nonlinear dynamic behavior and hence bio-lubricating features. Type III collagen plays a crucial role in tissue regeneration, and its presence in the articular cartilage affects its bio-technical features. In this study, the molecular dynamics methodology was applied to evaluate the effect of deacetylation degree on the chitosan affinity to type III collagen. The computational procedure employed docking and geometry optimizations of different chitosan structures characterized by randomly distributed deacetylated groups. The eight different degrees of deacetylation from 12.5% to 100% were taken into account. We found an increasing linear trend (R2 = 0.97) between deacetylation degree and the collagen-chitosan interaction energy. This can be explained by replacing weak hydrophobic contacts with more stable hydrogen bonds involving amino groups in N-deacetylated chitosan moieties. In this study, the properties of chitosan were compared with hyaluronic acid, which is a natural component of synovial fluid and cartilage. As we found, when the degree of deacetylation of chitosan was greater than 0.4, it exhibited a higher affinity for collagen than in the case of hyaluronic acid.

Fabrication and biomedical applications of Arabinoxylan, Pectin, Chitosan, Soy protein, and Silk fibroin hydrogels via laccase - ferulic acid redox chemistry

The unique physiochemical properties and the porous network architecture of hydrogel seek the attention to be explored in broad range of fields. In the last decade, numerous studies on the development of enzymatically cross-linked hydrogels have been elucidated. Implementing enzyme based cross-linking for fabrication of biomaterials over other crosslinking methods harbor various advantages, especially hydrogels designed using laccase exhibits mild reaction environment, high cross-linking efficiency and less toxicity. To our knowledge this is the first report reviewing the formulation of laccase mediated cross-linking for hydrogel preparation. Here, laccase catalyzed synthesis of hydrogel using polysaccharide viz. arabinoxylan, sugar beet pectin, galactomannan, chitosan etc. and proteins namely soy protein, gelatin, silk fibroin were discussed on highlighting their mechanical properties and its possible field of application. We have summarized the role of phenolic acids in laccase mediated crosslinking particularly ferulic acid which is a component of lignocellulose, serving cell rigidity via crosslinkage. The review also discusses on various biomedical applications such as controlled protein release, tissue engineering, and wound healing. It is anticipated that this review will give a detailed information on different laccase mediated reaction strategies that can be applied for the synthesis of various new biomaterials with tailor made properties.

Physicochemical Characteristics of Chitosan-Based Hydrogels Modified with Equisetum arvense L. (Horsetail) Extract in View of Their Usefulness as Innovative Dressing Materials

This work focused on obtaining and characterizing hydrogels with their potential application as dressing materials for chronic wounds. The research included synthesizing chitosan-based hydrogels modified with Equisetum arvense L. (horsetail) extract via photopolymerization, and their characteristics determined with regard to the impact of both the modifier and the amount of crosslinker on their properties. The investigations included determining their sorption properties and tensile strength, evaluating their behavior in simulated physiological liquids, and characterizing their wettability and surface morphology. The release profile of horsetail extract from polymer matrices in acidic and alkaline environments was also verified. It was proved that hydrogels showed swelling ability while the modified hydrogels swelled slightly more. Hydrogels showed hydrophilic nature (all contact angles were <77°). Materials containing horsetail extract exhibited bigger elasticity than unmodified polymers (even by 30%). It was proved that the extract release was twice as effective in an acidic medium. Due to the possibility of preparation of hydrogels with specific mechanical properties (depending on both the modifier and the amount of crosslinker used), wound exudate sorption ability, and possibility of the release of active substance, hydrogels show a great application potential as dressing materials.

Squarate Cross-Linked Gelatin Hydrogels as Three-Dimensional Scaffolds for Biomedical Applications

Hydrogels are useful platforms as three-dimensional (3D) scaffolds for cell culture, drug-release systems, and regenerative medicine applications. Here, we propose a novel chemical cross-linking approach by the use of 3,4-diethoxy-3-cyclobutene-1,2-dione or diethyl squarate for the preparation of 5 and 10% w/v gelatin-based hydrogels. Hydrogels showed good swelling properties, and the 5% gelatin-based hydrogel proved suitable as a 3D cell culture scaffold for the chondrocyte cell line C28/I2. In addition, diffusion properties of different sized molecules inside the hydrogel were determined.

Advanced Hydrogels for Cartilage Tissue Engineering: Recent Progress and Future Directions

Cartilage is a tension- and load-bearing tissue and has a limited capacity for intrinsic self-healing. While microfracture and arthroplasty are the conventional methods for cartilage repair, these methods are unable to completely heal the damaged tissue. The need to overcome the restrictions of these therapies for cartilage regeneration has expanded the field of cartilage tissue engineering (CTE), in which novel engineering and biological approaches are introduced to accelerate the development of new biomimetic cartilage to replace the injured tissue. Until now, a wide range of hydrogels and cell sources have been employed for CTE to either recapitulate microenvironmental cues during a new tissue growth or to compel the recovery of cartilaginous structures via manipulating biochemical and biomechanical properties of the original tissue. Towards modifying current cartilage treatments, advanced hydrogels have been designed and synthesized in recent years to improve network crosslinking and self-recovery of implanted scaffolds after damage in vivo. This review focused on the recent advances in CTE, especially self-healing hydrogels. The article firstly presents the cartilage tissue, its defects, and treatments. Subsequently, introduces CTE and summarizes the polymeric hydrogels and their advances. Furthermore, characterizations, the advantages, and disadvantages of advanced hydrogels such as multi-materials, IPNs, nanomaterials, and supramolecular are discussed. Afterward, the self-healing hydrogels in CTE, mechanisms, and the physical and chemical methods for the synthesis of such hydrogels for improving the reformation of CTE are introduced. The article then briefly describes the fabrication methods in CTE. Finally, this review presents a conclusion of prevalent challenges and future outlooks for self-healing hydrogels in CTE applications.

Combinations of Hydrogels and Mesenchymal Stromal Cells (MSCs) for Cartilage Tissue Engineering-A Review of the Literature

Cartilage offers limited regenerative capacity. Cell-based approaches have emerged as a promising alternative in the treatment of cartilage defects and osteoarthritis. Due to their easy accessibility, abundancy, and chondrogenic potential mesenchymal stromal cells (MSCs) offer an attractive cell source. MSCs are often combined with natural or synthetic hydrogels providing tunable biocompatibility, biodegradability, and enhanced cell functionality. In this review, we focused on the different advantages and disadvantages of various natural, synthetic, and modified hydrogels. We examined the different combinations of MSC-subpopulations and hydrogels used for cartilage engineering in preclinical and clinical studies and reviewed the effects of added growth factors or gene transfer on chondrogenesis in MSC-laden hydrogels. The aim of this review is to add to the understanding of the disadvantages and advantages of various combinations of MSC-subpopulations, growth factors, gene transfers, and hydrogels in cartilage engineering.

Mechanotransducive Biomimetic Systems for Chondrogenic Differentiation In Vitro

Osteoarthritis (OA) is a long-term chronic joint disease characterized by the deterioration of bones and cartilage, which results in rubbing of bones which causes joint stiffness, pain, and restriction of movement. Tissue engineering strategies for repairing damaged and diseased cartilage tissue have been widely studied with various types of stem cells, chondrocytes, and extracellular matrices being on the lead of new discoveries. The application of natural or synthetic compound-based scaffolds for the improvement of chondrogenic differentiation efficiency and cartilage tissue engineering is of great interest in regenerative medicine. However, the properties of such constructs under conditions of mechanical load, which is one of the most important factors for the successful cartilage regeneration and functioning in vivo is poorly understood. In this review, we have primarily focused on natural compounds, particularly extracellular matrix macromolecule-based scaffolds and their combinations for the chondrogenic differentiation of stem cells and chondrocytes. We also discuss different mechanical forces and compression models that are used for In Vitro studies to improve chondrogenic differentiation. Summary of provided mechanical stimulation models In Vitro reviews the current state of the cartilage tissue regeneration technologies and to the potential for more efficient application of cell- and scaffold-based technologies for osteoarthritis or other cartilage disorders.

Injectable Nanocomposite Hydrogels for Cancer Therapy

Hydrogel is a kind of 3D polymer network with strong swelling ability in water and appropriate mechanical and biological properties, which make it feasible to maintain bioactive substances and has promising applications in the fields of biomaterials, soft machines, and artificial tissues. Unfortunately, traditional hydrogels prepared by chemical crosslinking have poor mechanical properties and limited functions, which limit their further application. In recent years, with the continuous development of nanoparticle research, more and more studies have combined nanoparticles with hydrogels to make up for the shortcomings of traditional hydrogels. In this article, the types and functions of hydrogels and nanomaterials are introduced first, as well as the functions and applications of injectable nanocomposite hydrogels (INHs), then the latest progress of INHs for cancer treatment is reviewed, some existing problems are summarized, and the application prospect of NHs is prospected.

Designed protein- and peptide-based hydrogels for biomedical sciences

Proteins are fundamentally the most important macromolecules for biochemical, mechanical, and structural functions in living organisms. Therefore, they provide us with diverse structural building blocks for constructing various types of biomaterials, including an important class of such materials, hydrogels. Since natural peptides and proteins are biocompatible and biodegradable, they have features advantageous for their use as the building blocks of hydrogels for biomedical applications. They display constitutional and mechanical similarities with the native extracellular matrix (ECM), and can be easily bio-functionalized via genetic and chemical engineering with features such as bio-recognition, specific stimulus-reactivity, and controlled degradation. This review aims to give an overview of hydrogels made up of recombinant proteins or synthetic peptides as the structural elements building the polymer network. A wide variety of hydrogels composed of protein or peptide building blocks with different origins and compositions - including β-hairpin peptides, α-helical coiled coil peptides, elastin-like peptides, silk fibroin, and resilin - have been designed to date. In this review, the structures and characteristics of these natural proteins and peptides, with each of their gelation mechanisms, and the physical, chemical, and mechanical properties as well as biocompatibility of the resulting hydrogels are described. In addition, this review discusses the potential of using protein- or peptide-based hydrogels in the field of biomedical sciences, especially tissue engineering.

Synthesis and Physicochemical Evaluation of Bees' Chitosan-Based Hydrogels Modified with Yellow Tea Extract

The novelty of the research involves designing the measurement methodology aimed at determining the structure-property relationships in the chitosan-based hydrogels containing yellow tea extract. Performed investigations allowed us to determine the swelling properties of hydrogels in selected time intervals, evaluate the mutual interactions between the hydrogels and simulated physiological liquids via pH measurements and directly assess the impact of such interactions on the chemical structure of hydrogels using Fourier transform infrared (FT-IR) spectroscopy and their wettability by the measurements of the flatness of the drop on the surface of the tested samples via the static drop method. Next, the surface morphology of hydrogels was characterized by the Scanning Electron Miscorcopy (SEM) and their elasticity under the tension applied was also verified. It was proved that incubation in simulated physiological liquids resulted in a decrease in contact angles of hydrogels, even by 60%. This also caused their certain degradation which was reflected in lower intensities of bands on FT-IR spectra. Further, 23% v/v yellow tea extract in hydrogel matrices caused the decrease of their tensile strength. An increase in the amount of the crosslinker resulted in a decrease in the sorption capacity of hydrogels wherein their modification caused greater swelling ability. In general, the investigations performed provided much information on the tested materials which may be meaningful considering their application, e.g., as dressing materials.

Articular and Artificial Cartilage, Characteristics, Properties and Testing Approaches-A Review

The design and manufacture of artificial tissue for knee joints have been highlighted recently among researchers which necessitates an apt approach for its assessment. Even though most re-searches have focused on specific mechanical or tribological tests, other aspects have remained underexplored. In this review, elemental keys for design and testing artificial cartilage are dis-cussed and advanced methods addressed. Articular cartilage structure, its compositions in load-bearing and tribological properties of hydrogels, mechanical properties, test approaches and wear mechanisms are discussed. Bilayer hydrogels as a niche in tissue artificialization are presented, and recent gaps are assessed.

Boron nitride-based nanocomposite hydrogels: preparation, properties and applications

Hexagonal boron nitride (h-BN) nanostructures are well-known for their good chemical stability, thermal conductivity and high elastic modulus. BN can be used as a filler in hydrogels to significantly improve their mechanical and thermal properties, to reinforce their biocompatibility and to provide self-healing capacity. Moreover, in contrast with their carbon equivalents, BN nanocomposites are transparent and electrically insulating. Herein, we present an overview of BN-based nanocomposite hydrogels. First, the properties of h-BN are described, as well as common exfoliation and functionalization techniques employed to obtain BN nanosheets. Then, methods for preparing BN-nanocomposite hydrogels are explained, followed by a specific overview of the relationship between the composition and structure of the nanocomposites and the functional properties. Finally, the main properties of these materials are discussed in view of the thermal, mechanical, and self-healing properties, along with the potential applications in tissue engineering, thermal management, drug delivery and water treatment.

Unsaturated and thiolated derivatives of polysaccharides as functional matrixes for tissue engineering and pharmacology: A review

This review examines investigations into the functionalization of polysaccharides by substituents containing multiple (CC) bonds and thiol (SH) groups that are prone to (co)polymerization in the presence of thermal, redox and photoinitiators or Michael addition reactions. A comparative analysis of the approaches to grafting the mentioned substituents onto the polysaccharide macromolecules was conducted. The use of the modified polysaccharides for the design of the 3D structures, including for the development of the pore bearing matrixes of cells or scaffolds utilized in regenerative medicine was examined. These modified polymers were also examined toward the design of excipient matrixes in pharmacological compositions, including with controllable release of active pharmaceuticals, as wel as of antibacterial and antifungal agents and others. In addition, a few examples of the use of modified derivatives in other areas are given.

Alginate sulfate-based hydrogel/nanofiber composite scaffold with controlled Kartogenin delivery for tissue engineering

In this study, we fabricated two different arrangements of laminated composite scaffolds based on Alginate:Alginate sulfate hydrogel, PCL:Gelatin electrospun mat, and Kartogenin-PLGA nanoparticles (KGN-NPs). The optimized composite scaffold revealed a range of advantages such as improved mechanical features as well as less potential of damage (less dissipated energy), interconnected pores of hydrogel and fiber with adequate pore size, excellent swelling ratio, and controlled biodegradability. Furthermore, the synthesized KGN-NPs with spherical morphology were incorporated into the composite scaffold and exhibited a linear and sustained release of KGN within 30 days with desirable initial burst reduction (12% vs. 20%). Additionally, the cytotoxicity impact of the composite was evaluated. Resazurin assay and Live/Dead staining revealed that the optimized composite scaffold has no cytotoxic effect and could improve cell growth. Overall, according to the enhanced mechanical features, suitable environment for cellular growth, and sustained drug release, the optimized scaffold would be a good candidate for tissue regeneration.

Self-Assembly and Mechanical Properties of Engineered Protein Based Multifunctional Nanofiber for Accelerated Wound Healing

The present work reports a new route for preparing tunable multifunctional biomaterials through the combination of synthetic biology and material chemistry. Genetically encoded catechol moiety is evolved in a nanofiber mat with defined surface and secondary reactive functional chemistry, which promotes self-assembly and wet adhesion property of the protein. The catechol moiety is further exploited for the controlled release of boric acid that provides a congenial cellular microenvironment for accelerated wound healing. The presence of 3,4-dihydroxyphenylalanine in the nanofiber mat act as a stimulus to trigger cell proliferation, migration, and vascularization to accelerate wound healing. Electron paramagnetic resonance, NMR, FTIR, and circular dichroism spectroscopy confirm the structural integrity, antioxidant property, and controlled release of boric acid. Fluorescent and scanning electron microscopy reveals the 3D architecture of nanofiber mat, which favors fibroblast growth, endothelial cell attachment, and tube formation, which are the desirable properties of a wound-healing material. Animal studies in the murine wound healing model assert that the multifunctional biomaterial significantly improve re-epithelialization and accelerate wound closure.

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

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

Poly(chitosan-ester-ether-urethane) Hydrogels as Highly Controlled Genistein Release Systems

Polymeric hydrogels play an increasingly important role in medicine, pharmacy and cosmetology. They appear to be one of the most promising groups of biomaterials due to their favorable physicochemical properties and biocompatibility. The objective of the presented study was to synthesize new poly(chitosan-ester-ether-urethane) hydrogels and to study the kinetic release of genistein (GEN) from these biomaterials. In view of the above, six non-toxic hydrogels were synthesized via the Ring-Opening Polymerization (ROP) and polyaddition processes. The poly(ester-ether) components of the hydrogels have been produced in the presence of the enzyme as a biocatalyst. In some cases, the in vitro release rate of GEN from the obtained hydrogels was characterized by near-zero-order kinetics, without “burst release” and with non-Fickian transport. It is important to note that developed hydrogels have been shown to possess the desired safety profile due to lack of cytotoxicity to skin cells (keratinocytes and fibroblasts). Taking into account the non-toxicity of hydrogels and the relatively highly controlled release profile of GEN, these results may provide fresh insight into polymeric hydrogels as an effective dermatological and/or cosmetological tool.

Structural and biological investigation of chitosan/hyaluronic acid with silanized-hydroxypropyl methylcellulose as an injectable reinforced interpenetrating network hydrogel for cartilage tissue engineering

Cartilage damage continues to pose a threat to humans, but no treatment is currently available to fully restore cartilage function. In this study, a new class of composite hydrogels derived from water-soluble chitosan (CS)/hyaluronic acid (HA) and silanized-hydroxypropyl methylcellulose (Si-HPMC) (CS/HA/Si-HPMC) has been synthesized and tested as injectable hydrogels for cartilage tissue engineering when combined without the addition of a chemical crosslinking agent. Mechanical studies of CS/HA and CS/HA/Si-HPMC hydrogels showed that as Si-HPMC content increased, swelling rate and rheological properties were higher, compressive strength decreased and degradation was faster. Our results demonstrate that the CS and HA-based hydrogel scaffolds, especially the ones with 3.0% (w/v) Si-HPMC and 2.5/4.0% (w/v) CS/HA, have suitable physical performance and bioactive properties, thus provide a potential opportunity to be used for cartilage tissue engineering. In vitro studies of CS/HA and CS/HA/Si-HPMC hydrogels encapsulated in chondrocytes have shown that the proper amount of Si-HPMC increases the proliferation and deposition of the cartilage extracellular matrix. The regeneration rate of the CS/HA/Si-HPMC (3%) hydrogel reached about 79.5% at 21 days for long retention periods, indicating relatively good in vivo bone regeneration. These CS/HA/Si-HPMC hydrogels are promising candidates for tissue compatibility injectable scaffolds. The data provide proof of the principle that the resulting hydrogel has an excellent ability to repair joint cartilage using a tissue-engineered approach.

RESEARCH HIGHLIGHTS

An injectable hydrogel based on CS/HA/Si-HPMC composites was developed.

The CS/HA/Si-HPMC hydrogel displays the tunable rheological with mechanical properties.

The CS/HA/Si-HPMC hydrogel is highly porous with high swelling and degradation ratio.

Increasing concentration of Si-HPMC promote an organized network in CS/HA/Si-HPMC hydrogels.

Injectable CS/HA/Si-HPMC hydrogels have a high potential for cartilage tissue engineering.