Kartogenin-Incorporated Thermogel Supports Stem Cells for Significant Cartilage Regeneration

Engineering biomimetic scaffolds for bone regeneration: Chitosan/alginate/polyvinyl alcohol-based double-network hydrogels with carbon nanomaterials

In this study, new types of hybrid double-network (DN) hydrogels composed of polyvinyl alcohol (PVA), chitosan (CH), and sodium alginate (SA) are introduced, with the hypothesis that this combination and incorporating multi-walled carbon nanotubes (MWCNTs) and graphene nanoplatelets (GNPs) will enhance osteogenetic differentiation and the structural and mechanical properties of scaffolds for bone tissue engineering applications. Initially, the impact of varying mass ratios of the PVA/CH/SA mixture on mechanical properties, swelling ratio, and degradability was examined. Based on this investigation, a mass ratio of 4:6:6 was determined to be optimal. At this ratio, the hydrogel demonstrated a Young's modulus of 47.5 ± 5 kPa, a swelling ratio of 680 ± 6 % after 3 h, and a degradation rate of 46.5 ± 5 % after 40 days. In the next phase, following the determination of the optimal mass ratio, CNTs and GNPs were incorporated into the 4:6:6 composite resulting in a significant enhancement in the electrical conductivity and stiffness of the scaffolds. The introduction of CNTs led to a notable increase of 36 % in the viability of MG63 osteoblast cells. Additionally, the inhibition zone test revealed that GNPs and CNTs increased the diameter of the inhibition zone by 49.6 % and 52.6 %, respectively.

Engineered Exosomes with ATF5-Modified mRNA Loaded in Injectable Thermogels Alleviate Osteoarthritis by Targeting the Mitochondrial Unfolded Protein Response

Osteoarthritis (OA) progression is highly associated with chondrocyte mitochondrial dysfunction and disorders of catabolism and anabolism of the extracellular matrix (ECM) in the articular cartilage. The mitochondrial unfolded protein response (UPRmt), which is an integral component of the mitochondrial quality control (MQC) system, is essential for maintaining chondrocyte homeostasis. We successfully validated the pivotal role of activating transcription factor 5 (ATF5) in upregulating the UPRmt, mitigating IL-1β-induced inflammation and mitochondrial dysfunction, and promoting balanced metabolism in articular cartilage ECM, proving its potential as a promising therapeutic target for OA. Modified mRNAs (modRNAs) have emerged as novel and efficient gene delivery vectors for nucleic acid therapeutic approaches. In this study, we combined Atf5-modRNA (modAtf5) with engineered exosomes derived from bone mesenchymal stem cells (ExmodAtf5) to exert cytoprotective effects on chondrocytes in articular cartilage via Atf5. However, the rapid localized metabolization of ExmodAtf5 limits its application. PLGA-PEG-PLGA (Gel), an injectable thermosensitive hydrogel, was used as a carrier of ExmodAtf5 (Gel@ExmodAtf5) to achieve a sustained release of ExmodAtf5. In vitro and in vivo, the use of Gel@ExmodAtf5 was shown to be a highly effective strategy for OA treatment. The in vivo therapeutic effect of Gel@ExmodAtf5 was evidenced by the preservation of the intact cartilage surface, low OARSI scores, fewer osteophytes, and mild subchondral bone sclerosis and cystic degeneration. Consequently, the combination of ExmodAtf5 and PLGA-PEG-PLGA could significantly enhance the therapeutic efficacy and prolong the exosome release. In addition, the mitochondrial protease ClpP enhanced chondrocyte autophagy by modulating the mTOR/Ulk1 pathway. As a result of our research, Gel@ExmodAtf5 can be considered to be effective at alleviating the progression of OA.

Catalpol promotes articular cartilage repair by enhancing the recruitment of endogenous mesenchymal stem cells

Articular cartilage defect is challenged by insufficient regenerative ability of cartilage. Catalpol (CA), the primary active component of Rehmanniae Radix, could exert protective effects against various diseases. However, the impact of CA on the treatment of articular cartilage injuries is still unclear. In this study, full-thickness articular cartilage defect was induced in a mouse model via surgery. The animals were intraperitoneally injected with CA for 4 or 8 weeks. According to the results of macroscopic observation, micro-computed tomography CT (μCT), histological and immunohistochemistry staining, CA treatment could promote mouse cartilage repair, resulting in cartilage regeneration, bone structure improvement and matrix anabolism. Specifically, an increase in the expression of CD90, the marker of mesenchymal stem cells (MSCs), in the cartilage was observed. In addition, we evaluated the migratory and chondrogenic effects of CA on MSCs. Different concentration of CA was added to C3H10 T1/2 cells. The results showed that CA enhanced cell migration and chondrogenesis without affecting proliferation. Collectively, our findings indicate that CA may be effective for the treatment of cartilage defects via stimulation of endogenous MSCs.

Kartogenin-loaded polyvinyl alcohol/nano-hydroxyapatite composite hydrogel promotes tendon-bone healing in rabbits after anterior cruciate ligament reconstruction

Accumulating evidence supports the role of cartilage tissue engineering in cartilage defect repair, but the biological function has yet to be fully explained. In this work, kartogenin (KGN), an emerging chondroinductive nonprotein small molecule, was incorporated into a composite hydrogel of polyvinyl alcohol/nano-hydroxyapatite (PVA/n-HA) to fabricate an appropriate microenvironment for tendon-bone healing after anterior cruciate ligament (ACL) reconstruction. KGN/PVA/n-HA composite hydrogel scaffolds were prepared by in situ synthesis and physical adsorption, followed by characterization under a scanning electron microscope. The scaffolds were transplanted into healthy New Zealand White (NZW) rabbits. It was confirmed that KGN/PVA/n-HA scaffolds were successfully prepared and exhibited good supporting properties and excellent biocompatibility. Unilateral ACL reconstruction was constructed with tendon autograft in NZW rabbits, and the morphology and diameter of collagen fiber were analyzed. The scaffolds were shown to promote ACL growth and collagen fiber formation. Furthermore, microcomputerized tomography analysis and bone formation histology were performed to detect new bone formation. KGN/PVA/n-HA scaffolds effectively alleviated cartilage damage and prevented the occurrence of osteoarthritis. Meanwhile, ligament-bone healing and bone formation were observed in the presence of KGN/PVA/n-HA scaffolds. In conclusion, these results suggest that the KGN/PVA/n-HA scaffolds can facilitate tendon-bone healing after ACL reconstruction and might be considered novel hydrogel biomaterials in cartilage tissue engineering.

Polysaccharide-Based Double-Network Hydrogels: Polysaccharide Effect, Strengthening Mechanisms, and Applications

Polysaccharides are carbohydrate polymers that are major components of plants, animals, and microorganisms, with unique properties. Biological hydrogels are polymeric networks that imbibe and retain large amounts of water and are the major components of living organisms. The mechanical properties of hydrogels are critical for their functionality and applications. Since synthetic polymeric double-network (DN) hydrogels possess unique network structures with high and tunable mechanical properties, many natural functional polysaccharides have attracted increased attention due to their rich and convenient sources, unique chemical structure and chain conformation, inherently desirable cytocompatibility, biodegradability and environmental friendliness, diverse bioactivities, and rheological properties, which rationally make them prominent constituents in designing various strong and tough polysaccharide-based DN hydrogels over the past ten years. This review focuses on the latest developments of polysaccharide-based DN hydrogels to comprehend the relationship among the polysaccharide properties, inner strengthening mechanisms, and applications. The aim of this review is to provide an insightful mechanical interpretation of the design strategy of novel polysaccharide-based DN hydrogels and their applications by introducing the correlation between performance and composition. The mechanical behavior of DN hydrogels and the roles of varieties of marine, microbial, plant, and animal polysaccharides are emphatically explained.

Kartogenin delivery systems for biomedical therapeutics and regenerative medicine

Kartogenin, a small and heterocyclic molecule, has emerged as a promising therapeutic agent for incorporation into biomaterials, owing to its unique physicochemical and biological properties. It holds potential for the regeneration of cartilage-related tissues in various common conditions and injuries. Achieving sustained release of kartogenin through appropriate formulation and efficient delivery systems is crucial for modulating cell behavior and tissue function. This review provides an overview of cutting-edge kartogenin-functionalized biomaterials, with a primarily focus on their design, structure, functions, and applications in regenerative medicine. Initially, we discuss the physicochemical properties and biological functions of kartogenin, summarizing the underlying molecular mechanisms. Subsequently, we delve into recent advancements in nanoscale and macroscopic materials for the carriage and delivery of kartogenin. Lastly, we address the opportunities and challenges presented by current biomaterial developments and explore the prospects for their application in tissue regeneration. We aim to enhance the generation of insightful ideas for the development of kartogenin delivery materials in the field of biomedical therapeutics and regenerative medicine by providing a comprehensive understanding of common preparation methods.

Nanofiber Composite Microchannel-Containing Injectable Hydrogels for Cartilage Tissue Regeneration

Articular cartilage tissue is incapable of self-repair and therapies for cartilage defects are still lacking. Injectable hydrogels have drawn much attention in the field of cartilage regeneration. Herein, the novel design of nanofiber composite microchannel-containing hydrogels inspired by the tunnel-piled structure of subway tunnels is proposed. Based on the aldehydized polyethylene glycol/carboxymethyl chitosan (APA/CMCS) hydrogels, thermosensitive gelatin microrods (GMs) are used as a pore-forming agent, and coaxial electrospinning polylactic acid/gelatin fibers (PGFs) loaded with kartogenin (KGN) are used as a reinforcing agent and a drug delivery system to construct the nanofiber composite microchannel-containing injectable hydrogels (APA/CMCS/KGN@PGF/GM hydrogels). The in situ formation, micromorphology and porosity, swelling and degradation, mechanical properties, self-healing behavior, as well as drug release of the nanofiber composite microchannel-containing hydrogels are investigated. The hydrogel exhibits good self-healing ability, and the introduction of PGF nanofibers can significantly improve the mechanical properties. The drug delivery system can realize sustained release of KGN to match the process of cartilage repair. The microchannel structure effectively promotes bone marrow mesenchymal stem cell (BMSC) proliferation and ingrowth within the hydrogels. In vitro and animal experiments indicate that the APA/CMCS/KGN@PGF/GM hydrogels can enhance the chondrogenesis of BMSCs and promote neocartilage formation in the rabbit cartilage defect model.

Ultra-durable cell-free bioactive hydrogel with fast shape memory and on-demand drug release for cartilage regeneration

Osteoarthritis is a worldwide prevalent disease that imposes a significant socioeconomic burden on individuals and healthcare systems. Achieving cartilage regeneration in patients with osteoarthritis remains challenging clinically. In this work, we construct a multiple hydrogen-bond crosslinked hydrogel loaded with tannic acid and Kartogenin by polyaddition reaction as a cell-free scaffold for in vivo cartilage regeneration, which features ultra-durable mechanical properties and stage-dependent drug release behavior. We demonstrate that the hydrogel can withstand 28000 loading-unloading mechanical cycles and exhibits fast shape memory at body temperature (30 s) with the potential for minimally invasive surgery. We find that the hydrogel can also alleviate the inflammatory reaction and regulate oxidative stress in situ to establish a microenvironment conducive to healing. We show that the sequential release of tannic acid and Kartogenin can promote the migration of bone marrow mesenchymal stem cells into the hydrogel scaffold, followed by the induction of chondrocyte differentiation, thus leading to full-thickness cartilage regeneration in vivo. This work may provide a promising solution to address the problem of cartilage regeneration.

A Homochiral Diphenylalanine Analog Based Mechanoresponsive Hydrogel: An Insight Towards Its Wound Healing Efficacy

Deciphering the most promising strategy for the evolution of potential wound-healing therapeutics is one of the greatest challenging affairs to date. The development of peptide-based smart scaffolds with innate antimicrobial, anti-inflammatory, and antioxidant properties is an appealing way out. Aligned to the goal a set of Hydrogelators I-IV were developed utilizing the concept of chiral orchestration in diphenylalanine fragment, such that the most potent construct with all the bench marks namely mechanoresponsiveness, biocompatibility, consistent antimicrobial and antioxidant properties, could be fished out from the design. Interestingly, our in vitro Antifungal and Lipid peroxidation analysis identified the homochiral isomer Boc-δ-Ava-L-Phe-L-Phe-OH (Hydrogelator I), as an ideal candidate for the wound healing experiment, so we proceeded for the in vivo histopathological and antioxidant measurements in Wister rats. Indeed the wound images obtained from the different sets of animals on the 14th day of treatment demonstrated that with increased recovery time, hydrogelator I displayed a significant reduction in the lesion diameter compared to the marketed drug, and negative control. Even the histopathological measurements using H & E staining demonstrated diminished tissue destruction, neutrophil infiltration necrosis, and lymphatic proliferation in the hydrogelators, in comparison to others, backed by in vivo lipid peroxidation data. Overall our investigation certifies hydrogelator I as an effective therapeutic for managing the wound healing complication.

Injectable, In Situ Self-cross-linking, Self-healing Poly(l-glutamic acid)/Polyethylene Glycol Hydrogels for Cartilage Tissue Engineering

Injectable hydrogels have drawn much attention in the field of tissue engineering because of advantages such as simple operation, strong plasticity, and good biocompatibility and biodegradability. Herein, we propose the novel design of injectable hydrogels via a Schiff base cross-linking reaction between adipic dihydrazide (ADH)-modified poly(l-glutamic acid) (PLGA-ADH) and benzaldehyde-terminated poly(ethylene glycol) (PEG-CHO). The effects of the mass fraction and the molar ratio of -CHO/-NH₂ on the gelation time, mechanical properties, equilibrium swelling, and in vitro degradation of the hydrogels were examined. The PLGA/PEG hydrogels cross-linked by dynamic Schiff base linkages exhibited good self-healing ability. Additionally, the PLGA/PEG hydrogels had good biocompatibility with bone marrow-derived mesenchymal stem cells (BMSCs) and could effectively support BMSC proliferation and deposition of glycosaminoglycans and upregulate the expression of cartilage-specific genes. In a rat cartilage defect model, PLGA/PEG hydrogels significantly promoted new cartilage formation. The results suggest the prospect of the PLGA/PEG hydrogels in cartilage tissue engineering.

A triphasic biomimetic BMSC-loaded scaffold for osteochondral integrated regeneration in rabbits and pigs

Osteochondral tissue involves cartilage, calcified cartilage and subchondral bone. These tissues differ significantly in chemical compositions, structures, mechanical properties and cellular compositions. Therefore, the repairing materials face different osteochondral tissue regeneration needs and rates. In this study, we fabricated an osteochondral tissue-inspired triphasic material, which was composed of a poly(lactide-co-glycolide) (PLGA) scaffold loaded with fibrin hydrogel, bone marrow stromal cells (BMSCs) and transforming growth factor-β1 (TGF-β1) for cartilage tissue, a bilayer poly(L-lactide-co-caprolactone) (PLCL)-fibrous membrane loaded with chondroitin sulfate and bioactive glass, respectively, for calcified cartilage, and a 3D-printed calcium silicate ceramic scaffold for subchondral bone. The triphasic scaffold was press-fitted into the osteochondral defects in rabbit (cylindrical defects with a diameter of 4 mm and a depth of 4 mm) and minipig knee joints (cylindrical defects with a diameter of 10 mm and a depth of 6 mm). The μ-CT and histological analysis showed that the triphasic scaffold was partly degraded, and significantly promoted the regeneration of hyaline cartilage after they were implanted in vivo. The superficial cartilage showed good recovery and uniformity. The calcified cartilage layer (CCL) fibrous membrane was in favor of a better cartilage regeneration morphology, a continuous cartilage structure and less fibrocartilage tissue formation. The bone tissue grew into the material, while the CCL membrane limited bone overgrowth. The newly generated osteochondral tissues were well integrated with the surrounding tissues too.

Recent progress in the manipulation of biochemical and biophysical cues for engineering functional tissues

Tissue engineering (TE) is currently considered a cutting-edge discipline that offers the potential for developing treatments for health conditions that negatively affect the quality of life. This interdisciplinary field typically involves the combination of cells, scaffolds, and appropriate induction factors for the regeneration and repair of damaged tissue. Cell fate decisions, such as survival, proliferation, or differentiation, critically depend on various biochemical and biophysical factors provided by the extracellular environment during developmental, physiological, and pathological processes. Therefore, understanding the mechanisms of action of these factors is critical to accurately mimic the complex architecture of the extracellular environment of living tissues and improve the efficiency of TE approaches. In this review, we recapitulate the effects that biochemical and biophysical induction factors have on various aspects of cell fate. While the role of biochemical factors, such as growth factors, small molecules, extracellular matrix (ECM) components, and cytokines, has been extensively studied in the context of TE applications, it is only recently that we have begun to understand the effects of biophysical signals such as surface topography, mechanical, and electrical signals. These biophysical cues could provide a more robust set of stimuli to manipulate cell signaling pathways during the formation of the engineered tissue. Furthermore, the simultaneous application of different types of signals appears to elicit synergistic responses that are likely to improve functional outcomes, which could help translate results into successful clinical therapies in the future.

A hybrid cartilage extracellular matrix-based hydrogel/poly (ε-caprolactone) scaffold incorporated with Kartogenin for cartilage tissue engineering

Despite extensive studies, hydrogels are unable to meet the mechanical and biological requirements for successful outcomes in cartilage tissue engineering. In the present study, beta cyclodextrin (β-CD)-modified alginate/cartilage extracellular matrix (ECM)-based interpenetrating polymer network (IPN) hydrogel was developed for sustained release of Kartogenin (KGN). Furthermore, the hydrogel was incorporated within a 3D-printed poly (ε-caprolactone) (PCL)/starch microfiber network in order to reinforce the construct for cartilage tissue engineering. All the synthesized compounds were characterized by H¹-NMR spectroscopy. The hydrogel/microfiber composite with a microfiber strand size and strand spacing of 300 μm and 2 mm, respectively showed a compressive modulus of 17.2 MPa, resembling the properties of the native cartilage tissue. Considering water uptake capacity, degradation rate, mechanical property, cell cytotoxicity and glycosaminoglycan secretions, β-CD-modified hydrogel reinforced with printed PCL/starch microfibers with controlled release of KGN may be considered as a promising candidate for using in articular cartilage defects.

Drug delivery systems based on polyethylene glycol hydrogels for enhanced bone regeneration

Drug delivery systems composed of osteogenic substances and biological materials are of great significance in enhancing bone regeneration, and appropriate biological carriers are the cornerstone for their construction. Polyethylene glycol (PEG) is favored in bone tissue engineering due to its good biocompatibility and hydrophilicity. When combined with other substances, the physicochemical properties of PEG-based hydrogels fully meet the requirements of drug delivery carriers. Therefore, this paper reviews the application of PEG-based hydrogels in the treatment of bone defects. The advantages and disadvantages of PEG as a carrier are analyzed, and various modification methods of PEG hydrogels are summarized. On this basis, the application of PEG-based hydrogel drug delivery systems in promoting bone regeneration in recent years is summarized. Finally, the shortcomings and future developments of PEG-based hydrogel drug delivery systems are discussed. This review provides a theoretical basis and fabrication strategy for the application of PEG-based composite drug delivery systems in local bone defects.

Adhesive hydrogels in osteoarthritis: from design to application

Osteoarthritis (OA) is the most common type of degenerative joint disease which affects 7% of the global population and more than 500 million people worldwide. One research frontier is the development of hydrogels for OA treatment, which operate either as functional scaffolds of tissue engineering or as delivery vehicles of functional additives. Both approaches address the big challenge: establishing stable integration of such delivery systems or implants. Adhesive hydrogels provide possible solutions to this challenge. However, few studies have described the current advances in using adhesive hydrogel for OA treatment. This review summarizes the commonly used hydrogels with their adhesion mechanisms and components. Additionally, recognizing that OA is a complex disease involving different biological mechanisms, the bioactive therapeutic strategies are also presented. By presenting the adhesive hydrogels in an interdisciplinary way, including both the fields of chemistry and biology, this review will attempt to provide a comprehensive insight for designing novel bioadhesive systems for OA therapy.

An antioxidant and antibacterial polydopamine-modified thermo-sensitive hydrogel dressing for Staphylococcus aureus-infected wound healing

Bacteria-infected wound healing is a complex and chronic process that poses a great threat to human health. A thermo-sensitive hydrogel that undergoes a sol-gel transition at body temperature is an attractive wound dressing for healing acceleration and infection prevention. In this paper, we present a thermo-sensitive and reactive oxygen species (ROS)-scavenging hydrogel based on polydopamine modified poly(ε-caprolactone-co-glycolide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-glycolide) (PDA/P2) triblock copolymer. The PDA/P2 solution at a concentration of 30 wt% could form a gel at 34-38 °C. The ROS-scavenging ability of PDA/P2 was demonstrated by DPPH and ABTS assays and intracellular ROS downregulation in RAW264.7 cells. Furthermore, silver nanoparticles were encapsulated in the hydrogel (PDA/P2-4@Ag gel) to provide antibacterial activity against E. coli and S. aureus. An in vivo S. aureus-infected rat model demonstrated that the PDA/P2-4@Ag hydrogel dressing could promote wound healing via inhibiting bacterial growth, alleviating the inflammatory response, and inducing angiogenesis and collagen deposition. This study provides a new strategy to prepare temperature-sensitive hydrogel-based multifunctional wound dressings.

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.

A supramolecular injectable hydrogel based on β-cyclodextrin-grafted alginate and pluronic-amine loaded with kartogenin for chondrogenic differentiation of mesenchymal stem cells

Owing to the similarity of hydrogels to cartilage ECM, they have been extensively utilized in the chondral lesions. Moreover, their tunable administration properties are desirable for reducing injuries in lesion sites. Generally, injectable hydrogels are mechanically weak, requiring some modifications for being used as a cell carrier in place of articular cartilage. In this study, a combination of β-cyclodextrin-grafted alginate (Alg-β-CD) and pluronic-amine (PA) with multiple physical crosslinking was used for the first time. Supramolecular interactions, including electrostatic forces, host-guest interaction, and hydrophobic interaction with increasing temperature maintain injectability of hydrogels while these interactions boost mechanical properties to the extent that shear modulus surpassed 40 kPa. Vacant β-CD cavities in conjunction with gel network was exploited for kartogenin (KGN) loading. All groups had gel time of less than one minute and gel temperature was 28 ℃. No toxic effect of hydrogels on encapsulated cells was observed. While the optimum combination of polymers provided a sustainable release for KGN, it also extended the in vitro degradation time of hydrogels from 6 days to 2 weeks. KGN facilitated encapsulated mesenchymal stem cells (MSCs) differentiation towards chondrocytes. Taken together, the synthesized hydrogel proved to be a promising candidate for being utilized in cartilage regeneration.

Kartogenin (KGN)/synthetic melanin nanoparticles (SMNP) loaded theranostic hydrogel scaffold system for multiparametric magnetic resonance imaging guided cartilage regeneration

Cartilage regeneration after injury is still a great challenge in clinics, which suffers from its avascularity and poor proliferative ability. Herein we designed a novel biocompatible cellulose nanocrystal/GelMA (gelatin-methacrylate anhydride)/HAMA (hyaluronic acid-methacrylate anhydride)-blended hydrogel scaffold system, loaded with synthetic melanin nanoparticles (SMNP) and a bioactive drug kartogenin (KGN) for theranostic purpose. We found that the SMNP-KGN/Gel showed favorable mechanical property, thermal stability, and distinct magnetic resonance imaging (MRI) contrast enhancement. Meanwhile, the sustained release of KGN could recruit bone-derived mesenchymal stem cells to proliferate and differentiate into chondrocytes, which promoted cartilage regeneration in vitro and in vivo. The hydrogel degradation and cartilage restoration were simultaneously monitored by multiparametric MRI for 12 weeks, and further confirmed by histological analysis. Together, these results validated the multifunctional hydrogel as a promising tissue engineering platform for noninvasive imaging-guided precision therapy in cartilage regenerative medicine.

Construction of Biocompatible Hydrogel Scaffolds With a Long-Term Drug Release for Facilitating Cartilage Repair

In tissue engineering, hydrogel scaffolds allow various cells to be cultured and grown in vitro and then implanted to repair or replace the damaged areas. Here in this work, kartogenin (KGN), an effectively chondro-inductive non-protein bioactive drug molecule, was incorporated into a composite hydrogel comprising the positively charged chitosan (CS) and methacrylated gelatin (GelMA) polymers to fabricate appropriate microenvironments of bone marrow mesenchymal stem cells (BMSCs) for cartilage regeneration. Based on the combination of physical chain entanglements and chemical crosslinking effects, the resultant GelMA-CS@KGN composite hydrogels possessed favorable network pores and mechanical strength. In vitro cytotoxicity showed the excellent biocompatibility for facilitating the cell growth, adhesion, proliferation, and differentiation. The long-term sustainable KGN release from the hydrogel scaffolds in situ promoted the chondrogenic differentiation that can be employed as an alternative candidate for cartilage tissue regeneration.

Evaluation of Electrospun PCL-PLGA for Sustained Delivery of Kartogenin

In this study, kartogenin was incorporated into an electrospun blend of polycaprolactone and poly(lactic-co-glycolic acid) (1:1) to determine the feasibility of this system for sustained drug delivery. Kartogenin is a small-molecule drug that could enhance the outcome of microfracture, a cartilage restoration procedure, by selectively stimulating chondrogenic differentiation of endogenous bone marrow mesenchymal stem cells. Experimental results showed that kartogenin did not affect the electrospinnability of the polymer blend, and it had negligible effects on fiber morphology and scaffold mechanical properties. The loading efficiency of kartogenin into electrospun membranes was nearly 100%, and no evidence of chemical reaction between kartogenin and the polymers was detected by Fourier transform infrared spectroscopy. Analysis of the released drug using high-performance liquid chromatography-photodiode array detection indicated an abundance of kartogenin and only a small amount of its major hydrolysis product. Kartogenin displayed a typical biphasic release profile, with approximately 30% being released within 24 h followed by a much slower, constant rate of release up to 28 days. Although additional development is needed to tune the release kinetics and address issues common to electrospun scaffolds (e.g., high fiber density), the results of this study demonstrated that a scaffold electrospun from biodegradable synthetic polymers is a suitable kartogenin delivery vehicle.

Instructive cartilage regeneration modalities with advanced therapeutic implantations under abnormal conditions

The development of interdisciplinary biomedical engineering brings significant breakthroughs to the field of cartilage regeneration. However, cartilage defects are considerably more complicated in clinical conditions, especially when injuries occur at specific sites (e.g., osteochondral tissue, growth plate, and weight-bearing area) or under inflammatory microenvironments (e.g., osteoarthritis and rheumatoid arthritis). Therapeutic implantations, including advanced scaffolds, developed growth factors, and various cells alone or in combination currently used to treat cartilage lesions, address cartilage regeneration under abnormal conditions. This review summarizes the strategies for cartilage regeneration at particular sites and pathological microenvironment regulation and discusses the challenges and opportunities for clinical transformation.

Harnessing Bifunctional Ferritin with Kartogenin Loading for Mesenchymal Stem Cell Capture and Enhancing Chondrogenesis in Cartilage Regeneration

Methods that leverage bone marrow mesenchymal stem cells (BMSCs) and stimulating factor kartogenin (KGN) for chondrocyte differentiation have paved the way for cartilage repair. However, the scarce carriers for efficiently bridging the two components significantly impede their further application. Therefore, one kind of bifunctional ferritin has designed and synthesized: RC-Fn, a genetically engineered ferritin nanocage with RGD peptide and WYRGRL peptide on the surface. The RGD can target the integrin αvβ3 of BMSCs and promote proliferation, and the WYRGRL peptide has an inherent affinity for the cartilage matrix component of collagen II protein. RC-Fn nanocages have an ideal size for penetrating the proteoglycan network of cartilage. Thus, intra-articularly injected RC-Fn with KGN loading can convert the articular cavity from a barrier into a reservoir to prevent rapid release and clearance of KGN and exogenous BMSCs, which results in efficient and persistent chondrogenesis in cartilage regeneration.

Evaluation and Preparation of a Designed Kartogenin Drug Delivery System (DDS) of Hydrazone-Linkage-Based pH Responsive mPEG-Hz-b-PCL Nanomicelles for Treatment of Osteoarthritis

Osteoarthritis (OA) is a chronic disease caused by the damage of articular cartilage. Kartogenin (KGN) is a well-recognized small molecule which could induce MSCs chondrogenesis and promote cartilage repair treatments. Nano-level micells could be a suitable drug carrier technology for the treatments. In this study, the acid-responsive methoxy poly(ethylene oxide)-hydrazone-poly(ε-caprolactone) copolymers, mPEG-Hz-b-PCL, were synthesized. The structure was characterized by ¹H NMR. The evaluation of a designed kartogenin drug delivery system (DDS) of hydrazone-linkage-based pH responsive mPEG-Hz-b-PCL nanomicelles for treatment of osteoarthritis could be carried out.

Pralatrexate Sustainably Released from Polypeptide Thermogel Is Effective for Chondrogenic Differentiation of Mesenchymal Stem Cells

Folic acid was reported to significantly improve chondrogenic differentiation of mesenchymal stem cells. In a similar mechanism of action, we investigated clinically approved antifolates by the U.S. Food and Drug Administration as chondrogenic-promoting compounds for tonsil-derived mesenchymal stem cells. A poly(ethylene glycol)-poly(l-alanine) thermogelling system was used as a three-dimensional cell culture matrix, where stem cells and antifolates could be incorporated simultaneously during a heat-induced in situ sol-to-gel transition. The antifolates could be supplied over several days by the sustained release of the drug from the thermogel. Initially, seven antifolates were prescreened based on cell viability and expression of a typical chondrogenic biomarker of type II collagen (COL II) at the mRNA level. Then, dapsone, pralatrexate, and trimethoprim were selected as candidate compounds in the second round screening, and detailed studies were carried out on the mRNA and protein expression of various chondrogenic biomarkers including COL II, SRY box transcription factor 9, and aggrecan. Three-dimensional cultures of stem cells in the thermogel in the absence of a chondrogenic promoter compound and in the presence of kartogenin (KGN) were performed as a negative control and positive control, respectively. The chondrogenic biomarkers were significantly increased in the selected antifolate-incorporating systems compared to the negative control system, without an increase in type I collagen (an osteogenic biomarker) expression. Pralatrexate was the best compound for inducing chondrogenic differentiation of the stem cells, even better than the positive control (KGN). Nuclear translocation of the core-binding factor β subunit (CBFβ) and enhanced nuclear runt-related transcription factor 1 (RUNX1) by antifolate treatment suggested that the chondrogenesis-enhancing mechanism is mediated by CBFβ and RUNX1. An in silico modeling study confirmed the mechanism by proving the high binding affinity of pralatrexate to a target protein of filamin A compared with other antifolate candidates. To conclude, pralatrexate was rediscovered as a lead compound, and the polypeptide thermogel incorporating pralatrexate and mesenchymal stem cells can be a very effective system in promoting chondrogenic differentiation of stem cells and might be used in injectable tissue engineering for cartilage repair.

Folic acid pretreatment and its sustained delivery for chondrogenic differentiation of MSCs

Dietary uptake of folic acid (FA) improves cartilage regeneration. In this work, we discovered that three days of FA treatment is highly effective for promoting chondrogenic differentiation of tonsil-derived mesenchymal stem cells (TMSCs). In a three-dimensional pellet culture, the levels of typical chondrogenic biomarkers, sulfated glycosaminoglycan, proteoglycan, type II collagen (COL II), SRY box transcription factor 9 (SOX 9), cartilage oligomeric matrix protein (COMP), and aggrecan (ACAN) increased significantly in proportion to FA concentration up to 30 μM. At the mRNA expression level, COL II, SOX 9, COMP, and ACAN increased 3.6-6.0-fold with FA treatment at 30 μM compared with the control system that did not receive FA treatment, and the levels with FA treatment were 1.6-2.5 times greater than those in the kartogenin-treated positive control system. FA treatment did not increase type I collagen α1 (COL I α1), an osteogenic biomarker which is a concern with most chondrogenic promoters. At the high FA concentration of 100 μM, significant decreases in chondrogenic biomarkers were observed, which might be related to DNA methylation. A thermogel system incorporating TMSCs and FA provided sustained release of FA over several days, similar to the FA treatment. The thermogel system confirmed the efficacy of FA in promoting chondrogenic promotion of TMSCs. The increased nuclear translocation of core-binding factor β subunit (CBFβ) and the runt-related transcription factor 1 (RUNX1) expression after FA treatment, together with molecular docking studies, suggest that the chondrogenic enhancement mechanism of FA is mediated by CBFβ and RUNX1.

Bionic Biphasic Composite Scaffold with Osteochondrogenic Factors for Regeneration of Full-Thickness Osteochondral Defect

Full-thickness osteochondral defects lack the capability to self-repair owing to their complicated hierarchical structure. At present, clinical treatments including microfracture etc. have shown some efficacy; however, the newborn tissue exhibits...

Synergic adhesive chemistry-based fabrication of BMP-2 immobilized silk fibroin hydrogel functionalized with hybrid nanomaterial to augment osteogenic differentiation of rBMSCs for bone defect repair

Bone defect repair and tissue engineering is specifically challenging process because of the distinctive morphological and structural behaviours of natural bone with complex healing and biochemical mechanisms. In the present investigation, we designed dopamine adhesive chemistry-based fabrication of silk fibroin hydrogel (SFD) with incorporation of nano-hydroxyapatite (nHA)-graphene oxide (GO) hybrid nanofillers with well-arranged porous morphology immobilized with bone morphogenic protein-2 (BMP-2) for the effective in vitro rabbit bone marrow derived mesenchymal stem cells loading compatibility and in vivo new bone regrowth and collagen deposition ability. We have achieved bone-specific hydrogel scaffolds with upgraded structural features, mechanical properties and particularly promoted in vitro osteogenic differentiation and compatibility of rabbit bone marrow mesenchymal stem cells (rBMSCs). Structural and microscopic analyses established greater distributions of components and well-ordered and aligned porous structure of the hydrogel network. In vivo result of new bone regrowth was promisingly higher in the Bm@nHG-SFD hydrogel (85%) group as compared to the other treatment groups of nHG-SFD (77%) and nH-SFD (64%) hydrogel. Overall, we summarized that morphologically improved hydrogel material with immobilization of BMP-2 could be have more attentions for new generation bone regeneration therapies.

Articular cartilage and osteochondral tissue engineering techniques: Recent advances and challenges

In spite of the considerable achievements in the field of regenerative medicine in the past several decades, osteochondral defect regeneration remains a challenging issue among diseases in the musculoskeletal system because of the spatial complexity of osteochondral units in composition, structure and functions. In order to repair the hierarchical tissue involving different layers of articular cartilage, cartilage-bone interface and subchondral bone, traditional clinical treatments including palliative and reparative methods have showed certain improvement in pain relief and defect filling. It is the development of tissue engineering that has provided more promising results in regenerating neo-tissues with comparable compositional, structural and functional characteristics to the native osteochondral tissues. Here in this review, some basic knowledge of the osteochondral units including the anatomical structure and composition, the defect classification and clinical treatments will be first introduced. Then we will highlight the recent progress in osteochondral tissue engineering from perspectives of scaffold design, cell encapsulation and signaling factor incorporation including bioreactor application. Clinical products for osteochondral defect repair will be analyzed and summarized later. Moreover, we will discuss the current obstacles and future directions to regenerate the damaged osteochondral tissues.

An oxygen-enriched thermosensitive hydrogel for the relief of a hypoxic tumor microenvironment and enhancement of radiotherapy

The rapid proliferation of tumor cells and tortuous vasculature in solid tumors often bring about a hypoxic tumor microenvironment, which renders tumor cells more resistant to many cancer treatments, including radiotherapy. In this study, an injectable and thermosensitive composite hydrogel composed of perfluorooctanoic acid (PFOA) modified monomethoxy poly(ethylene glycol)-poly(D,L-lactide-co-glycolide) (mPEG-PLGA-PFOA) and perfluorooctyl bromide (PFOB) that presented a thermoreversible sol-gel transition upon heating was developed to deliver exogenous oxygen for the relief of tumor hypoxia and enhancement of radiotherapy. The fluorinated modification of copolymers significantly increased the stability of PFOB in the mPEG-PLGA-PFOA aqueous solution owing to the fluorophilic interaction between PFOB and PFOA-modified copolymers. The introduction of PFOB not only efficiently heightened the oxygen loading capacity of the composite hydrogel, but also endowed it with excellent X-ray opacity, allowing the visual observation of the hydrogel via micro-CT imaging. After peritumoral injection of the oxygen-enriched composite hydrogel, the continuous supply of oxygen effectively relieved tumor hypoxia and down-regulated the expression of hypoxia-inducible factor-1α. Profiting from this, the hyposensitivity of tumor cells to radiation was successfully reversed, and the tumor growth in mice was significantly suppressed and the survival of mice was prolonged when combined with multiple X-ray exposure. As a result, the oxygen-enriched composite hydrogel shows a great potential for radiosensitization to improve the radiotherapeutic efficacy.

Antibacterial Hydrogel with Self-Healing Property for Wound-Healing Applications

Hydrogels with inherent antibacterial ability are a focus in soft tissue repair. Herein, a series of antibacterial hydrogels were fabricated by quaternized N-[3-(dimethylamino)propyl] methacrylamide (quaternized P(DMAPMA-DMA-DAA)) bearing copolymers with dithiodipropionic acid dihydrazide (DTDPH) as cross-linker. The hydrogels presented efficient self-healing capability as well as a pH and redox-triggered gel-sol-gel transition property that is based on the dynamic acylhydrazone bond and disulfide linkage. Furthermore, the hydrogels showed good antibacterial activity, biocompatibility, degradability, and sustained release ability. More importantly, the in vivo experiments demonstrated that the hydrogels loaded with mouse epidermal growth factor (mEGF) significantly accelerated wound closure by preventing bacterial infection and promoting cutaneous regeneration in the wound model. The antibacterial hydrogels with self-healing behavior hold great potential in wound treatment.

3D-bioprinted BMSC-laden biomimetic multiphasic scaffolds for efficient repair of osteochondral defects in an osteoarthritic rat model

Osteochondral defect repair in osteoarthritis (OA) remains an unsolved clinical problem due to the lack of enough seed cells in the defect and chronic inflammation in the joint. To address this clinical need, we designed a bone marrow-derived mesenchymal stem cell (BMSC)-laden 3D-bioprinted multilayer scaffold with methacrylated hyaluronic acid (MeHA)/polycaprolactone incorporating kartogenin and β-TCP for osteochondral defect repair within each region. BMSC-laden MeHA was designed to actively introduce BMSCs in situ, and diclofenac sodium (DC)-incorporated matrix metalloproteinase-sensitive peptide-modified MeHA was induced on the BMSC-laden scaffold as an anti-inflammatory strategy. BMSCs in the scaffolds survived, proliferated, and produced large amounts of cartilage-specific extracellular matrix in vitro. The effect of BMSC-laden scaffolds on osteochondral defect repair was investigated in an animal model of medial meniscectomy-induced OA. BMSC-laden scaffolds facilitated chondrogenesis by promoting collagen II and suppressed interleukin 1β in osteochondral defects of the femoral trochlea. Congruently, BMSC-laden scaffolds significantly improved joint function of the injured leg with respect to the ground support force, paw grip force, and walk gait parameters. Therefore, this research demonstrates the potential of 3D-bioprinted BMSC-laden scaffolds to simultaneously inhibit joint inflammation and promote cartilage defect repair in OA joints.

In situ subcutaneously injectable thermosensitive PEG-PLGA diblock and PLGA-PEG-PLGA triblock copolymer composite as sustained delivery of bispecific anti-CD3 scFv T-cell/anti-EGFR Fab Engager (BiTEE)

In this study, PEGylated poly (lactide-co-glycolide) (PLGA) thermosensitive composite hydrogels (DTgels) loaded with bispecific anti-cluster of differentiation 3 (CD3) scFv T-cell/anti-epidermal growth factor receptor (EGFR) Fab engager (BiTEE) were subcutaneously (s.c.) injected for the in situ formation of a drug deposit to resolve limitations of the clinical application of the BiTEE of a short half-life and potential side effects. Three kinds of DTgels prepared with different ratios of methoxy poly (ethylene glycol) (mPEG)-PLGA (diblock copolymer, DP) and PLGA-PEG-PLGA (triblock copolymer, TP) were designated DTgel-1, DTgel-2, and DTgel-2S. All three DTgel formulations showed thermosensitive properties with a sol-gel transition temperature at 28-34 °C, which is suitable for an injection. An in vitro release study showed that all DTgel formulations loaded with stabilized BiTEE extended the release of the BiTEE for up to 7 days. In an animal pharmacokinetics study, an s.c. injection of BiTEE/DTgel-1, BiTEE/DTgel-2, or BiTEE/DTgel-2S respectively prolonged the half-life of the BiTEE by 3.5-, 2.0-, and 2.2-fold compared to an intravenous injection of the BiTEE solution. Simultaneously, BiTEE/DTgel formulations showed almost no proinflammatory cytokine release in mice injected with T cells after s.c. administration. Results of an animal antitumor (MDA-MB-231) study indicated that an s.c. injection of the BiTEE/DTgel formulations significantly improved the antitumor efficacy compared to an intravenous (i.v.) or s.c. injection of the BiTEE solution. Moreover, BiTEE/DTgel formulations led to enhanced T-cell recruitment to solid-tumor sites. In conclusion, the in situ formation of injectable PEGylated PLGA thermosensitive hydrogels loaded with the BiTEE was successfully carried out to increase its half-life, maintain a constant blood level within therapeutic windows, and enhance T-cell recruitment to solid-tumor sites resulting in exceptional treatment efficacy.

In situ biomimetic lyotropic liquid crystal gel for full-thickness cartilage defect regeneration

There is a great challenge in regenerating cartilage defects, which usually involve absent bearing capacity and poor adaptation to joint movement, further exacerbating subchondral bone damage. Therefore, ideal tissue-engineering cartilage scaffolds should be endowed with biomimetic and sustained-release function for promoting long-term chondrogenesis while protecting subchondral bone. Herein, in situ self-assembling gel based on glyceryl monooleate (GMO)-hyaluronic acid (HA) composite lyotropic liquid crystal (HLC) was developed as the biomimetic scaffold to deliver kartogenin for long-term cartilage regeneration. Compared to the GMO based (LLC) gel, HLC gel with modified lattice structure exhibited improved rheological properties for better joint protection by increasing mechanical strength, elasticity and lubrication. Besides, HLC gel successfully prolonged drug release and retention in the joint cavity over 4 weeks to provide combined effect of kartogenin and HA for cartilage repair. Pharmacodynamic studies demonstrated that HLC gel was the most effective to promote chondrogenesis and protect subchondral bone, making the damaged bone tissue restored to normal in divergent features as evidenced by the MRI, Micro-CT and histological results. Therefore, the HLC gel with joint protection and controlled drug release can serve as a firm scaffold for providing long-term cartilage repair.

Thermosensitive polymer hydrogel as a physical shield on colonic mucosa for colitis treatment

Inflammatory bowel disease (IBD), including Crohn's disease and ulcerative colitis (UC), is a chronic disease characterized by diffuse mucosal inflammation limited to the colon. Topical drug delivery systems that could be facilely performed and efficiently retained at colon sites are attractive for clinical IBD treatment. Herein, we report the exploration of an injectable thermosensitive copolymer hydrogel as a topical formulation for IBD treatment and demonstrate its feasibility in UC treatment by shielding ulcer sites from the external environment and being a drug reservoir for sustained release. Poly(aliphatic ester)-based triblock copolymer, poly(dl-lactic acid)-poly(ethylene glycol)-poly(dl-lactic acid) (PDLLA-PEG-PDLLA), adopts the solution state at room temperature yet a gel state at body temperature when the polymer concentration is more than 11%. The gel acts not only as a physical mucosal barrier for protecting ulcer sites from microorganisms like bacteria but also as a mesalazine depot for enhanced drug retention in the colon for localized, sustained drug release. In vivo UC treatment reveals that blank gel as a mucosal protector shows nearly the same treatment effect to mesalazine SR granules. Mesalazine-loaded gel significantly suppresses inflammation and has the best outcomes of indices such as colonic length, mucosal injury index, pathological tissue, and inflammatory factor. The injectable thermosensitive polymer hydrogel represents a novel, robust platform for the efficient treatment of IBD by acting as a physical shield to block out the pro-inflammatory factors as well as a drug depot for enhanced drug retention and controlled delivery.

Intra-articular Injection of Kartogenin-Enhanced Bone Marrow-Derived Mesenchymal Stem Cells in the Treatment of Knee Osteoarthritis in a Rat Model

BACKGROUND

In this study, we investigated the in vitro and in vivo chondrogenic capacity of kartogenin (KGN)-enhanced bone marrow-derived mesenchymal stem cells (BMSCs) for cartilage regeneration.

PURPOSE

To determine (1) whether functionalized nanographene oxide (NGO) can effectively deliver KGN into BMSCs and (2) whether KGN would enhance BMSCs during chondrogenesis in vitro and in vivo in an animal model.

STUDY DESIGN

Controlled laboratory study.

METHODS

Functionalized NGO with line chain amine-terminated polyethylene glycol (PEG) and branched polyethylenimine (BPEI) were used to synthesize biocompatible NGO-PEG-BPEI (PPG) and for loading hydrophobic KGN molecules noncovalently via π-π stacking and hydrophobic interactions (PPG-KGN). Then, PPG-KGN was used for the intracellular delivery of hydrophobic KGN by simple mixing and co-incubation with BMSCs to acquire KGN-enhanced BMSCs. The chondrogenic efficacy of KGN-enhanced BMSCs was evaluated in vitro. In vivo, osteoarthritis (OA) was induced by anterior cruciate ligament transection in rats. A total of 5 groups were established: normal (OA treated with nothing), phosphate-buffered saline (PBS; intra-articular injection of PBS), PPG-KGN (intra-articular injection of PPG-KGN), BMSCs (intra-articular injection of BMSCs), and BMSCs + PPG-KGN (intra-articular injection of PPG-KGN-preconditioned BMSCs). At 6 and 9 weeks after the surgical induction of OA, the rats received intra-articular injections of PPG-KGN, BMSCs, or KGN-enhanced BMSCs. At 14 weeks after the surgical induction of OA, radiographic and behavioral evaluations as well as histological analysis of the knee joints were performed.

RESULTS

The in vitro study showed that PPG could be rapidly uptaken in the first 4 hours after incubation, reaching saturation at 12 hours and accumulating in the lysosome and cytoplasm of BMSCs. Thus, PPG-KGN could enhance the efficiency of the intracellular delivery of KGN, which showed a remarkably high chondrogenic differentiation capacity of BMSCs. When applied to an OA model of cartilage injuries in rats, PPG-KGN-preconditioned BMSCs contributed to protection from joint space narrowing, pathological mineralization, OA development, and OA-induced pain, as well as improved tissue regeneration, as evidenced by radiographic, weightbearing, and histological findings.

CONCLUSION

Our results demonstrate that KGN-enhanced BMSCs showed markedly improved capacities for chondrogenesis and articular cartilage repair. We believe that this work demonstrates that a multifunctional nanoparticle-based drug delivery system could be beneficial for stem cell therapy. Our results present an opportunity to reverse the symptoms and pathophysiology of OA.

CLINICAL RELEVANCE

The intracellular delivery of KGN to produce BMSCs with enhanced chondrogenic potential may offer a new approach for the treatment of OA.

PEG-based thermosensitive and biodegradable hydrogels

Injectable thermosensitive hydrogels are free-flowing polymer solutions at low or room temperature, making them easy to encapsulate the therapeutic payload or cells via simply mixing. Upon injection into the body, in situ forming hydrogels triggered by body temperature can act as drug-releasing reservoirs or cell-growing scaffolds. Finally, the hydrogels are eliminated from the administration sites after they accomplish their missions as depots or scaffolds. This review outlines the recent progress of poly(ethylene glycol) (PEG)-based biodegradable thermosensitive hydrogels, especially those composed of PEG-polyester copolymers, PEG-polypeptide copolymers and poly(organophosphazene)s. The material design, performance regulation, thermogelation and degradation mechanisms, and corresponding applications in the biomedical field are summarized and discussed. A perspective on the future thermosensitive hydrogels is also highlighted. STATEMENT OF SIGNIFICANCE: Thermosensitive hydrogels undergoing reversible sol-to-gel phase transitions in response to temperature variations are a class of promising biomaterials that can serve as minimally invasive injectable systems for various biomedical applications. Hydrophilic PEG is a main component in the design and fabrication of thermoresponsive hydrogels due to its excellent biocompatibility. By incorporating hydrophobic segments, such as polyesters and polypeptides, into PEG-based systems, biodegradable and thermosensitive hydrogels with adjustable properties in vitro and in vivo have been developed and have recently become a research hotspot of biomaterials. The summary and discussion on molecular design, performance regulation, thermogelation and degradation mechanisms, and biomedical applications of PEG-based thermosensitive hydrogels may offer a demonstration of blueprint for designing new thermogelling systems and expanding their application scope.

Recent advances in PLGA-based biomaterials for bone tissue regeneration

Bone regeneration is an interdisciplinary complex lesson, including but not limited to materials science, biomechanics, immunology, and biology. Having witnessed impressive progress in the past decades in the development of bone substitutes; however, it must be said that the most suitable biomaterial for bone regeneration remains an area of intense debate. Since its discovery, poly (lactic-co-glycolic acid) (PLGA) has been widely used in bone tissue engineering due to its good biocompatibility and adjustable biodegradability. This review systematically covers the past and the most recent advances in developing PLGA-based bone regeneration materials. Taking the different application forms of PLGA-based materials as the starting point, we describe each form's specific application and its corresponding advantages and disadvantages with many examples. We focus on the progress of electrospun nanofibrous scaffolds, three-dimensional (3D) printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds, and stents prepared by other traditional and emerging methods. Finally, we briefly discuss the current limitations and future directions of PLGA-based bone repair materials. STATEMENT OF SIGNIFICANCE: As a key synthetic biopolymer in bone tissue engineering application, the progress of PLGA-based bone substitute is impressive. In this review, we summarized the past and the most recent advances in the development of PLGA-based bone regeneration materials. According to the typical application forms and corresponding crafts of PLGA-based substitutes, we described the development of electrospinning nanofibrous scaffolds, 3D printed scaffolds, microspheres/nanoparticles, hydrogels, multiphasic scaffolds and scaffolds fabricated by other manufacturing process. Finally, we briefly discussed the current limitations and proposed the newly strategy for the design and fabrication of PLGA-based bone materials or devices.

Injectable and thermosensitive hydrogels mediating a universal macromolecular contrast agent with radiopacity for noninvasive imaging of deep tissues

It is very challenging to visualize implantable medical devices made of biodegradable polymers in deep tissues. Herein, we designed a novel macromolecular contrast agent with ultrahigh radiopacity (iodinate content > 50%) via polymerizing an iodinated trimethylene carbonate monomer into the two ends of poly(ethylene glycol) (PEG). A set of thermosensitive and biodegradable polyester-PEG-polyester triblock copolymers with varied polyester compositions synthesized by us, which were soluble in water at room temperature and could spontaneously form hydrogels at body temperature, were selected as the demonstration materials. The addition of macromolecular contrast agent did not obviously compromise the injectability and thermogelation properties of polymeric hydrogels, but conferred them with excellent X-ray opacity, enabling visualization of the hydrogels at clinically relevant depths through X-ray fluoroscopy or Micro-CT. In a mouse model, the 3D morphology of the radiopaque hydrogels after injection into different target sites was visible using Micro-CT imaging, and their injection volume could be accurately obtained. Furthermore, the subcutaneous degradation process of a radiopaque hydrogel could be non-invasively monitored in a real-time and quantitative manner. In particular, the corrected degradation curve based on Micro-CT imaging well matched with the degradation profile of virgin polymer hydrogel determined by the gravimetric method. These findings indicate that the macromolecular contrast agent has good universality for the construction of various radiopaque polymer hydrogels, and can nondestructively trace and quantify their degradation in vivo. Meanwhile, the present methodology developed by us affords a platform technology for deep tissue imaging of polymeric materials.

Bioresorbable Depot for Sustained Release of Immunostimulatory Resiquimod in Suppressing Both Primary Triple-Negative Breast Tumors and Metastatic Occurrence

In light of immune facilities trafficking toward the pathological sites along upward gradient of immunostimulatory cytokines, a localized resiquimod (Toll-like receptor 7/8 agonist) release depot was manufactured for pursuit of precision immunostimulation toward intractable triple-negative breast carcinoma. In principle, resiquimod/poly(lactic-co-glycolic acid) microspheres were fabricated and embedded into injectable and biodegradable poly(ethylene glycol) (PEG)-based hydrogel. The subsequent investigations approved persistent retention of immunostimulatory resiquimod in tumors upon peritumoral administration, which consequently led to localized and consistent secretion of immunostimulatory cytokines. Initially, not only innate tumor phagocytosis but also adaptive antitumor immunities were successfully cultivated for in situ suppression of the growth of primary solid tumors, more importantly, capable of inhibiting distant pulmonary metastasis, as evidenced by observation of enormous lymphocytes selectively gathering in the pulmonary artery. Hence, our presented study provided an important clinical indication of using immunostimulatory drugs to activate potent innate and adaptive antitumor immunities for precision antitumor therapy. Further immunomodulatory strategies, such as checkpoint blockage and tumor immunogenicity, could also be complementary for development of advanced antitumor immunotherapeutics in treatment of a number of intractable tumors.

Injectable Thermogel Generated by the "Block Blend" Strategy as a Biomaterial for Endoscopic Submucosal Dissection

Endoscopic submucosal dissection is an established method for the removal of early cancers and large lesions from the gastrointestinal tract but is faced with the risk of perforation. To decrease this risk, a submucosal fluid cushion (SFC) is needed clinically by submucosal injection of saline and so on to lift and separate the lesion from the muscular layer. Some materials have been tried as the SFC so far with disadvantages. Here, we proposed a thermogel generated by the "block blend" strategy as an SFC. This system was composed of two amphiphilic block copolymers in water, so it was called a "block blend". We synthesized two non-thermogellable copolymers poly(d,l-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(d,l-lactide-co-glycolide) and blended them in water to achieve a sol-gel transition upon heating in both pure water and physiological saline. We explored the internal structure of the resultant thermogel with transmission electron microscopy, three-dimensional light scattering, ¹³C NMR, fluorescence resonance energy transfer, and rheological measurements, which indicated a percolated micelle network. The biosafety of the synthesized copolymer was preliminarily confirmed in vitro. The main necessary functions as an SFC, namely, injectability of a sol and the maintained mucosal elevation as a gel after injection, were verified ex vivo. This study has revealed the internal structure of the block blend thermogel and illustrated its potential application as a biomaterial. This work might be stimulating for investigations and applications of intelligent materials with both injectability and thermogellability of tunable phase-transition temperatures.

A chondrogenesis induction system based on a functionalized hyaluronic acid hydrogel sequentially promoting hMSC proliferation, condensation, differentiation, and matrix deposition

Hydrogel scaffolds are widely used in cartilage tissue engineering as a natural stem cell niche. In particular, hydrogels based on multiple biological signals can guide behaviors of mesenchymal stem cells (MSCs) during neo-chondrogenesis. In the first phase of this study, we showed that functionalized hydrogels with grafted arginine-glycine-aspartate (RGD) peptides and lower degree of crosslinking can promote the proliferation of human mesenchymal stem cells (hMSCs) and upregulate the expression of cell receptor proteins. Moreover, grafted RGD and histidine-alanine-valine (HAV) peptides in hydrogel scaffolds can regulate the adhesion of the intercellular at an early stage. In the second phase, we confirmed that simultaneous use of HAV and RGD peptides led to greater chondrogenic differentiation compared to the blank control and single-peptide groups. Furthermore, the controlled release of kartogenin (KGN) can better facilitate cell chondrogenesis compared to other groups. Interestingly, with longer culture time, cell condensation was clearly observed in the groups with RGD and HAV peptide. In all groups with RGD peptide, significant matrix deposition was observed, accompanied by glycosaminoglycan (GAG) and collagen (Coll) production. Through in vitro and in vivo experiments, this study confirmed that our hydrogel system can sequentially promote the proliferation, adhesion, condensation, chondrogenic differentiation of hMSCs, by mimicking the cell microenvironment during neo-chondrogenesis.