Naturally biocompatible melanin based iron-complex nanoparticles for pH-responsive magnetic resonance imaging.

The sensitivity and diagnostic accuracy of magnetic resonance imaging mainly depend on the relaxation capacity of contrast agents (CAs) and their accumulated amount at the pathological region. Due to the better biocompatibility and high-spin capacity, Fe-complexes have been studied widely as an alternative to replace popular Gd-based CAs associated with potential biotoxicity. Compared with a variety of Fe complex-based CAs, such as small molecular, macrocyclic, multinuclear complexes, the form of nanoparticle exhibits outstanding longitudinal relaxation, but the clinical transformation was still limited by the inconspicuous difference of contrast between tumor and normal tissue. The enhanced effect of contrast is a positive relation as relaxation of CAs and their concentration in desired region. To specifically improve the amount of CAs accumulated in the tumor, pH-responsive polymer poly(2-ethyl-2-oxazoline) (PEOz) was modified on melanin, a ubiquitous natural pigment providing much active sites for chelating with Fe(III). The Fe(III)-Mel-PEOz we prepared could raise the tumor cell endocytosis efficiency via switching surface charge from anion to cation with the stimuli of the decreasing pH of tumor microenvironment. The change of pH has negligible effect on ther1of Fe(III)-Mel-PEOz, which is always maintained at around 1.0 mM-1s-1at 0.5 T. Moreover, Fe(III)-Mel-PEOz exhibited low cytotoxicity, and satisfactory enhancement of positive contrast effectin vivo. The excellent biocompatibility and stable relaxation demonstrate the high potential of Fe(III)-Mel-PEOz in the diagnosis of tumor.

Tissue adhesive, ROS scavenging and injectable PRP-based 'plasticine' for promoting cartilage repair.

Platelet-rich plasma (PRP) that has various growth factors has been used clinically in cartilage repair. However, the short residence time and release time at the injury site limit its therapeutic effect. The present study fabricated a granular hydrogel that was assembled from gelatin microspheres and tannic acid through their abundant hydrogen bonding. Gelatin microspheres with the gelatin concentration of 10 wt% and the diameter distribution of 1-10 µm were used to assemble by tannic acid to form the granular hydrogel, which exhibited elasticity under low shear strain, but flowability under higher shear strain. The viscosity decreased with the increase in shear rate. Meanwhile, the granular hydrogel exhibited self-healing feature during rheology test. Thus, granular hydrogel carrying PRP not only exhibited well-performed injectability but also performed like a 'plasticine' that possessed good plasticity. The granular hydrogel showed tissue adhesion ability and reactive oxygen species scavenging ability. Granular hydrogel carrying PRP transplanted to full-thickness articular cartilage defects could integrate well with native cartilage, resulting in newly formed cartilage articular fully filled in defects and well-integrated with the native cartilage and subchondral bone. The unique features of the present granular hydrogel, including injectability, plasticity, porous structure, tissue adhesion and reactive oxygen species scavenging provided an ideal PRP carrier toward cartilage tissue engineering.

Oxygen-Generating Hydrogels as Oxygenation Therapy for Accelerated Chronic Wound Healing.

Hypoxia in chronic wounds impairs the activities of reparative cells, resulting in tissue necrosis, bacterial infections, decreased angiogenesis, and delayed wound healing. To achieve effective oxygenation therapy and restore oxygen homeostasis, oxygen-generating hydrogels based on different oxygen sources have been developed to release dissolved oxygen in the wound bed, which not only alleviate hypoxia, but also accelerate chronic wound healing. This review first discusses the vital role of oxygen and hypoxia in the wound healing process. The advancements in oxygen-generating hydrogels, which produce oxygen through the decomposition of hydrogen peroxide, metal peroxides, glucose-activated cascade reactions, and photosynthesis of algae microorganisms for chronic wound healing, are discussed and summarized. The therapeutic effects and challenges of using oxygen-generating hydrogels for the clinical treatment of chronic wounds are concluded and prospected.

Pluronic F127-Lipoic Acid Adhesive Nanohydrogel Combining with Ce3+/Tannic Acid/Ulinastatin Nanoparticles for Promoting Wound Healing.

Developing strong anti-inflammatory wound dressings is of great significance for protecting inflammatory cutaneous wounds and promoting wound healing. The present study develops a nanocomposite Pluronic F127 (F127)-based hydrogel dressing with injectable, tissue adhesive, and anti-inflammatory performance. Briefly, Ce3+/tannic acid/ulinastatin nanoparticles (Ce3+/TA/UTI NPs) are fabricated. Meanwhile, α-lipoic acid is bonded to the ends of F127 to prepare F127-lipoic acid (F127LA) and its nanomicelles. Due to the gradual viscosity change instead of mutation during phase transition, the mixed Ce3+/TA/UTI NPs and F127LA nanomicelles show well-performed injectability at 37 °C and can form a semisolid composite nanohydrogel that can tightly attach to the skin at 37 °C. Furthermore, ultraviolet (UV) irradiation without a photoinitiator transforms the semisolid hydrogel into a solid hydrogel with well-performed elasticity and toughness. The UV-cured composite nanohydrogel acts as a bioadhesive that can firmly adhere to tissues. Due to the limited swelling property, the hydrogel can firmly adhere to tissues in a wet environment, which can seal wounds and provide a reliable physical barrier for the wounds. Ce3+/TA/UTI NPs in the hydrogel exhibit lipopolysaccharide (LPS)-scavenging ability and reactive oxygen species (ROS)-scavenging ability and significantly reduce the expression of inflammatory factors in wounds at the early stage, accelerating LPS-induced wound healing.

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.

Injectable, self-healing poly(amino acid)-hydrogel based on phenylboronate ester bond for osteochondral tissue engineering.

A new generation of osteochondral integrated scaffolds is needed for articular osteochondral regeneration, which can not only facilitate the accurate construction of osteochondral scaffolds in a minimally invasive manner but also firmly combine the subchondral bone layer and cartilage layer. Herein, an osteochondral integrated hydrogel scaffold was constructed by the poly(L-glutamic acid) (PLGA) based self-healing hydrogels with phenylboronate ester (PBE) as the dynamic cross-linking. The bone layer self-healing hydrogel (hydrogel O-S) was prepared by physically blending nanohydroxyapatite into the self-healing hydrogel PLGA-PBE-S, which was fabricated by 3-aminophenylboronic acid/glycidyl methacrylate-modified PLGA (PLGA-GMA-PBA) and 3-amino-1,2-propanediol/N-(2-aminoethyl) acrylamide-modified PLGA (PLGA-ADE-AP). The cartilage layer self-healing hydrogel (hydrogel C-S) was prepared by PLGA-GMA-APBA and glucosamine- modified PLGA-ADE-AP (PLGA-ADE-AP-G). Excellent injectability and self-healing profiles of hydrogel O-S and C-S were observed, the self-healing efficiencies were 97.02% ± 1.06% and 99.06% ± 0.57%, respectively. Based on the injectability and spontaneous healing on the interfaces of hydrogel O-S and C-S, the osteochondral hydrogel (hydrogel OC) was conveniently constructed in a minimally invasive manner. In addition,in situphotocrosslinking was used to enhance the mechanical strength and stability of the osteochondral hydrogel. The osteochondral hydrogels exhibited good biodegradability and biocompatibility. The osteogenic differentiation genes BMP-2, ALPL, BGLAP and COL I of adipose-derived stem cells (ASCs) in the bone layer of the osteochondral hydrogel were significantly expressed, and the chondrogenic differentiation genes SOX9, aggrecan and COL II of ASCs in the cartilage layer of the osteochondral hydrogel were obviously upregulated after 14 d of induction. The osteochondral hydrogels could effectively promote repair of osteochondral defects after 3 months post-surgery.

Cardiac organoid: multiple construction approaches and potential applications.

The human cardiac organoid (hCO) is three-dimensional tissue model that is similar to an in vivo organ and has great potential on heart development biology, disease modeling, drug screening and regenerative medicine. However, the construction of hCO presents a unique challenge compared with other organoids such as the lung, small intestine, pancreas, liver. Since heart disease is the dominant cause of death and the treatment of such disease is one of the most unmet medical needs worldwide, developing technologies for the construction and application of hCO is a critical task for the scientific community. In this review, we discuss the current classification and construction methods of hCO. In addition, we describe its applications in drug screening, disease modeling, and regenerative medicine. Finally, we propose the limitations of the cardiac organoid and future research directions. A detailed understanding of hCO will provide ways to improve its construction and expand its applications.

Building a Poly(amino acid)/Chitosan-Based Self-Healing Hydrogel via Host-Guest Interaction for Cartilage Regeneration.

Cartilage injury is a very common joint disease, and cartilage repair is a great challenge in clinical treatment due to the specific structure of cartilage tissue and its microenvironment in vivo. The injectable self-healing hydrogel is a very promising candidate as a cartilage repair material because of its special network structure, high water retention and self-healing properties. In this work, a self-healing hydrogel cross-linked by host-guest interaction between cyclodextrin and cholic acid was developed. The host material was composed of ß-cyclodextrin and 2-hydroxyethyl methacrylate-modified poly(l-glutamic acid) (P(LGA-co-GM-co-GC)), while the guest material was chitosan modified by cholic acid, glycidyl methacrylate, and (2,3-epoxypropyl)trimethylammonium chloride (EPTAC) (QCSG-CA). The host-guest interaction self-healing hydrogels, named as HG hydrogels (HG gel), exhibited excellent injectability and self-healable property, and the self-healing efficiency was greater than 90%. Furthermore, in order to enhance the mechanical properties and slow down the degradation of the HG gel in vivo, the second network was constructed by photo-cross-linking in situ. Biocompatibility tests showed that the enhanced multi-interaction hydrogel (MI gel) was extremely suitable for cartilage tissue engineering both in vitro and in vivo. In addition, the adipose derived stem cells (ASCs) in MI gel were able to differentiate cartilage effectively in vitro in the presence of inducing agents. Subsequently, the MI gel without ASCs was transplanted into rat cartilage defects in vivo for the regeneration of cartilage. After 3 months postimplantation, new cartilage tissue was successfully regenerated in a rat cartilage defect. All results indicated that the injectable self-healing host-guest hydrogels have important potential applications in cartilage injury repair.

Highly tough and elastic microspheric gel for transarterial catheter embolization in treatment of liver metastasis tumor.

Transarterial embolization is a widely recognized clinical treatment method for liver tumors. Given that the soft and easily damaged features of embolic particles may limit tumor embolization efficiency, the present study carries out an attempt of fabricating tough and elastic microspheric gel for promoting embolization efficiency. To promote the toughness of hydrogel, poly(ethylene glycol)-co-poly(ε-caprolactone)-co-poly(ethylene glycol) (PPP) and PPP with two terminal double bonds (PPPDA) are co-assembled into nano-micelles, which are connected with methacrylated chitosan (CSMA) to fabricate microspheric gels via microfluidic technology. Lowering double bond density of micelles promotes the freedom degree of micelles, significantly enhancing hydrogel toughness. To compensate for the strength loss caused by the decrease of double bond density of micelles, phytic acid (PA) are employed to interact with CS to form a physical network, further improving hydrogel strength and toughness. The CS-PPPDA&PPP-PA microspheric gels exhibit higher blocking effect in vitro. A rabbit VX2 liver metastasis tumor model is prepared to verify the embolization efficacy of CS-PPPDA&PPP-PA microspheric gels. Compared with clinical used microspheres, fewer CS-PPPDA&PPP-PA microspheric gels can achieve enough embolization efficiency. After embolization for 14 days, CS-PPPDA&PPP-PA microspheric gels exhibit improved tumor necrosis rate and promoted tumor cells apoptosis with reduced inflammation in surrounding tissues, confirming advanced embolic efficiency of tough microgels.

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 tumor-targeting and ROS-responsive iron-based T1 magnetic resonance imaging contrast agent for highly specific tumor imaging.

T1 contrast agents (CAs) exhibit outstanding capacity in enhancing the magnetic resonance imaging (MRI) contrast between tumor tissues and normal tissues for generating bright images. However, the clinical application of representative gadolinium(III) chelate-based T1 CAs is limited due to their potential toxicity and low specificity for pathological tissues. To obtain MRI CAs with a combination of low toxicity and high tumor specificity, herein, we report a reactive oxygen species (ROS)-responsive T1 CA (GA-Fe(II)-PEG-FA), which was constructed by chelating Fe(II) with gallic acid (GA), and modified with tumor-targeted folic acid (FA). The resultant CA could accumulate in tumor tissues via the affinity between FA and their receptors on the tumor cell membrane. It realized the switch from Fe(II) to Fe(III), and further enhancing the longitudinal relaxation rate (r1) under the stimuli of ROS in the tumor microenvironment. The r1 of GA-Fe(II)-PEG-FA on a 0.5 T nuclear magnetic resonance analyzer increased to 2.20 mM-1 s-1 under ROS stimuli and was 5 times greater than the r1 (0.42 mM-1 s-1) before oxidation. The cell and in vivo experiments demonstrated that GA-Fe(II)-PEG-FA exhibited good biocompatibility and significant targeting specificity to tumor cells and tumor tissues. Furthermore, in vivo MRI studies demonstrated that the enhanced T1 contrast effect against tumors could be achieved after injecting the CA for 3 h, indicating that GA-Fe(II)-PEG-FA has the potential as an ideal tumor MRI CA to increase the contrast and improve the diagnostic precision.

Hyaluronic acid-g-lipoic acid granular gel for promoting diabetic wound healing.

Diabetic patients are prone to developing chronic inflammation after trauma and have persistent nonhealing wounds. Reactive oxygen species (ROS) and recurrent bacterial infections at the site of long-term wounds also further delay skin wound healing and tissue regeneration. In this study, a granular gel (which exhibits ROS scavenging and antibacterial properties) is fabricated based on hyaluronic acid-g-lipoic acid (HA-LA). Briefly, HA-LA is synthesized to fabricate HA-LA microgels, which are further assembled by Ag+ via its coordination effect with disulfide in dithiolane to form a granular gel. The extrudable bulk granular gel possesses a shear-thinning feature and is immediately restored to a solid state after extrusion, and this can be easily applied to the whole wound area. Therefore, the grafted LA not only allows for the construction of the granular gel but also removes excess ROS from the microenvironment. Additionally, the presence of Ag+ realizes the assembly of microgels and has antibacterial effects. In vivo experiments show that the HA-LA granular gel eliminates excessive ROS at the wound site and up-regulates the secretion of reparative growth factors, thus, accelerating common and diabetic wound healing significantly. Therefore, the ROS-scavenging granular gel that can be applied to the wound surface with chronic inflammation demonstrates strong clinical utility.

Injectable macro-porous chitosan/polyethylene glycol-silicotungstic acid double-network hydrogels based on "smashed gels recombination" strategy for cartilage tissue engineering.

The lack of interconnected macro-porous structure of most injectable hydrogels lead to poor cell and tissue infiltration. Herein, we present the fabrication of injectable macro-porous hydrogels based on "smashed gels recombination" strategy. Chitosan/polyethylene glycol-silicotungstic acid (CS/PEG-SiW) double-network hydrogels were prepared via dual dynamic interactions. The bulk CS/PEG-SiW hydrogels were then smashed into micro-hydrogels with average sizes ranging from 47.6 to 63.8 µm by mechanical fragmentation. The CS/PEG-SiW micro-hydrogels could be continuously injected and rapidly recombined into a stable porous hydrogel based on the dual dynamic interactions between micro-hydrogels. The average pore size of the recombined porous CS/PEG-SiW hydrogels ranged from 52 to 184 µm. The storage modulus, compress modulus and maximum compressive strain of the recombined porous CS/PEG-SiW1.0 hydrogels reached about 47.2 %, 28.2 % and 127.6 % of the values for their corresponding bulk hydrogels, respectively. The recombined porous hydrogels were cytocompatible and could effectively support proliferation and chondrogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). In a rat cartilage defect model, recombined porous CS/PEG-SiW hydrogels could promote cartilage regeneration. Hematoxylin and eosin (H&E), Safranin-O/Fast green and immunohistochemical staining confirmed the accumulation of glycosaminoglycans (GAG) and type II collagen (Col II) in regenerated cartilage.

Thermal-Assisted Laser Fabrication of Broadband Ultralow Reflectance Surface by Combining Marangoni Flow with In Situ Deposition.

Functional surfaces with broadband ultralow optical reflectance have many potential applications in the fields of enhancing solar energy utilization, stray light shielding, infrared stealth, and so on. To fabricate broadband anti-reflection surfaces with low cost, high quality, and more controllability, a strategy of preparing multi-scale structures by thermal-assisted nanosecond laser was proposed. This strategy combines laser ablation with Marangoni flow of molten materials and in situ deposition of nanoparticles. The thermal-assisted strategy increases the depth to width ratio of the anti-reflection structures. The average reflectance of laser-textured TC4 (Ti-6Al-4V) surface is as low as 1.71% in the wavelength range of 200-2250 nm and 7.8% in the 2500-25,000 nm. The ultra-low reflectance surface has a significantly enhanced photothermal conversion performance. Meanwhile, the anti-reflection effect can be extended to the mid-infrared band, which has potential stealth application prospect. This synergetic manufacturing strategy has wide adaptability of materials, which provides new paths for the preparation of broadband ultralow reflectance surface. Moreover, this thermal-assisted laser fabrication strategy is prospective in the preparation of other functional micro-nano structures.

An anti-bacterial porous shape memory self-adaptive stiffened polymer for alveolar bone regeneration after tooth extraction.

The regeneration of alveolar bone after tooth extraction is critical for the placement of dental implants. Developing a rigid porous scaffold with defect shape adaptability is of great importance but challenging for alveolar bone regeneration. Herein, we design and synthesize a biocompatible poly(l-glutamic acid)-g-poly(ε-caprolactone) (PLGA-g-PCL) porous shape memory (SM) polymer. The PLGA-g-PCL is then copolymerized with acryloyl chloride grafted poly(ω-pentadecalactone) (PPDLDA) having a higher phase transition temperature than shape recovery temperature to maintain stiffness after shape recovery to resist chewing force. The hybrid polydopamine/silver/hydroxyapatite (PDA/Ag/HA) is coated to the surface of (PLGA-g-PCL)-PPDL scaffold to afford the anti-bacterial activity. The porous SM scaffold can be deformed into a compact size and administered into the socket cavity in a minimally invasive mode, and recover its original shape with a high stiffness at body temperature, fitting well in the socket defect. The SM scaffold exhibits robust antibacterial activity against Staphylococcus aureus (S. aureus). The porous microstructure and cytocompatibility of PLGA allow for the ingrowth and proliferation of stem cells, thus facilitating osteogenic differentiation. The micro-CT and histological analyses demonstrate that the scaffold boosts efficient new bone regeneration in the socket of rabbit mandibular first premolar. This porous shape memory self-adaptive stiffened polymer opens up a new avenue for alveolar bone regeneration.

General Strategy toward Laser Single-Step Generation of Multiscale Anti-Reflection Structures by Marangoni Effect.

The anti-reflection of transparent material surfaces has attracted great attention due to its potential applications. In this paper, a single-step controllable method based on an infrared femtosecond laser is proposed for self-generation multiscale anti-reflection structures on glass. The multiscale composite structure with ridge structures and laser-induced nano-textures is generated by the Marangoni effect. By optimizing the laser parameters, multiscale structure with broadband anti-reflection enhancement is achieved. Meanwhile, the sample exhibits good anti-glare performance under strong light. The results show that the average reflectance of the laser-textured glass in the 300-800 nm band is reduced by 45.5% compared with the unprocessed glass. This work provides a simple and general strategy for fabricating anti-reflection structures and expands the potential applications of laser-textured glass in various optical components, display devices, and anti-glare glasses.

A Simple and Efficient Strategy for Preparing a Cell-Spheroid-Based Bioink.

Cell spheroids are a promising bioprinting building block that can mimic several physiological conditions in embryonic development. However, it remains challenging to efficiently prepare cell-spheroid-based bioink (Sph-bioink) with favorable printability and spheroid fusion ability. In this work, a poly(N-isopropylacrylamide) (PNIPAAm)-based porous hydrogel is developed as an "all-in-one" platform for Sph-bioink preparation. On the one hand, the nonadhesive porous structure in hydrogels is an effective tool for fabricating adipose-derived stem cell (ASC) spheroids in high yield, and the hydrogel itself also serves as a "carrier" for conveniently transferring cell spheroids to the bioprinter. On the other hand, the integration of redox/thermo-responsiveness allows the hydrogel to shift from a solid spheroid-making tool to an extrudable bioprinting medium that is sensitive to temperature. These features enabled a simple procedure for preparing Sph-bioink, in which the cell spheroids were densely packed to retain fusion capability. The present study also demonstrates that ASC spheroids formed in hydrogels have good biological preservation and superior chondrogenic differentiation, and verified the feasibility of using Sph-bioink to build custom-shaped mature cartilage. In conclusion, this strategy provides a simple, efficient, and standardized approach for Sph-bioink preparation, making it possible to produce tissue-engineered constructs with accelerated maturation and functionalization.

Progress in Hydrogels for Skin Wound Repair.

As the first defensive line between the human body and the outside world, the skin is vulnerable to damage from the external environment. Skin wounds can be divided into acute wounds (mechanical injuries, chemical injuries, and surgical wounds, etc.) and chronic wounds (burns, infections, diabetes, etc.). In order to manage skin wound, a variety of wound dressings have been developed, including gauze, films, foams, nanofibers, hydrocolloids, and hydrogels. Recently, hydrogels have received much attention because of their natural extracellular matrix (ECM)-mimik structure, tunable mechanical properties, and facile bioactive substance delivery capability. They show great potential application in skin wound repair. This paper first introduces the anatomy and function of the skin, the process of wound healing and conventional wound dressings, and then introduces the composition and construction methods of hydrogels. Next, this paper introduces the necessary properties of hydrogels in skin wound repair and the latest research progress of hydrogel dressings for skin wound repair. Finally, the future development goals of hydrogel materials in the field of wound healing are proposed.

Solid multifunctional granular bioink for constructing chondroid basing on stem cell spheroids and chondrocytes.

Stem cell spheroids are advanced building blocks to produce chondroid. However, the multi-step operations including spheroids preparation, collection and transfer, the following 3D printing and shaping limit their application in 3D printing. The present study fabricates an 'ALL-IN-ONE' bioink based on granular hydrogel to not only produce adipose derived stem cell (ASC) spheroids, but also realize the further combination of chondrocytes and the subsequent 3D printing. Microgels (6-10µm) grafted with ß-cyclodextrin (ß-CD) (MGß-CD) were assembled and crosslinked byin-situpolymerized poly (N-isopropylacrylamide) (PNIPAm) to form bulk granular hydrogel. The host-guest action between ß-CD of microgels and PNIPAm endows the hydrogel with stable, shear-thinning and self-healing properties. After creating caves, ASCs aggregate spontaneously to form numerous spheroids with diameter of 100-200µm inside the hydrogel. The thermosensitive porous granular hydrogel exhibits volume change under different temperature, realizing further adsorbing chondrocytes. Then, the granular hydrogel carrying ASC spheroids and chondrocytes is extruded by 3D printer at room temperature to form a tube, which can shrink at cell culture temperature to enhance the resolution. The subsequent ASC spheroids/chondrocytes co-culture forms cartilage-like tissue at 21 din vitro, which further matures subcutaneouslyin vivo, indicating the application potential of the fully synthetic granular hydrogel ink toward organoid culture.

Preparation of Assemblable Chondral and Subchondral Bone Microtissues for Osteochondral Tissue Engineering.

Microtissues exhibit great advantages in injecting with minimum invasiveness, mimicking natural tissues, and promoting tissue regeneration. However, very few studies have focused on the construction of osteochondral microtissues that could simultaneously support hyaline-like cartilage and bone tissue regeneration. In this study, chondral microtissues that could favor the formation of hyaline-like cartilages and subchondral bone microtissues that could repair subchondral defects to support the neo-generated cartilages were successfully constructed for osteochondral tissue engineering. For chondral repair, the developed chondral microgels with high porosity and hydrophilicity could make cells spherical, favor the formation of cell aggregates, and show an excellent differentiation effect toward hyaline-like cartilage, thus contributing to the production of chondral microtissues. For subchondral bone repair, the fabricated subchondral microgels realize cell adhesion and proliferation and support the osteogenic differentiation of stem cells, thus favoring the formation of subchondral bone microtissues. The injectable chondral and subchondral bone microtissues could be stably assembled by Michael addition reaction between sulfhydryl groups of microtissues and double bonds of hydrophilic macromolecular cross-linker. At 12 weeks postimplantation, osteochondral microtissues could support the reconstruction of osteochondral-like tissues. The present study provides new insight into the microtissues for repair of osteochondral tissues.