still susceptible to fatigue fracture during multiple-cycle mechanical loads, exhibiting fatigue threshold (i.e., the minimal fracture energy required for crack propagation under cyclic loads) below 100 J m −2 . [5][6][7] Therefore, the long-term reliability has substantially hampered the in practical utility of hydrogels and hydrogel-based devices, and remains a key challenge in these fields.On the contrary, biological tissues, such as skeletal muscles, tendon and cartilage, are well known for not only their superior strength, modulus, toughness, but also long-term robustness. [8][9][10] For example, skeletal muscles can sustain a high stress (i.e., 1 MPa) over millions cycles per year without fracture, exhibiting fatigue thresholds (i.e., the minimal fracture energy required for crack propagation under cyclic loads) over 1000 J m −2 , despite their high water content (≈80%). [8,11] Such unrivalled fatigue-resistance originates from their hierarchically-arranged collagen fibrillar micro/nanostructures. [10] Despite bioinspired construction of structural materials has been promising for the design of fatigue-resistant hydrogels, [12][13][14][15][16][17] how to produce hydrogel materials with unprecedented fatigue-resistance in a universal and viable manner still remains an open issue. More recently, fatigue-resistant hydrogels have been fabricated by engineering the crystalline domains, [12][13][14] fibril structures, [15,16] or mesoscale phase separation. [17] Ice-templated freeze-casting strategy has been utilized as a powerful technology to impart Nature builds biological materials from limited ingredients, however, with unparalleled mechanical performances compared to artificial materials, by harnessing inherent structures across multi-length-scales. In contrast, synthetic material design overwhelmingly focuses on developing new compounds, and fails to reproduce the mechanical properties of natural counterparts, such as fatigue resistance. Here, a simple yet general strategy to engineer conventional hydrogels with a more than 100-fold increase in fatigue thresholds is reported. This strategy is proven to be universally applicable to various species of hydrogel materials, including polysaccharides (i.e., alginate, cellulose), proteins (i.e., gelatin), synthetic polymers (i.e., poly(vinyl alcohol)s), as well as corresponding polymer composites. These fatigueresistant hydrogels exhibit a record-high fatigue threshold over most synthetic soft materials, making them low-cost, high-performance, and durable alternatives to soft materials used in those circumstances including robotics, artificial muscles, etc.

Congenital vertebral malformations (CVMs) are associated with human TBX6 compound inheritance that combines a rare null allele and a common hypomorphic allele at the TBX6 locus. Our previous in vitro evidence suggested that this compound inheritance resulted in a TBX6 gene dosage of less than haploinsufficiency (i.e. <50%) as a potential mechanism of TBX6-associated CVMs. To further investigate this pathogenetic model, we ascertained and collected 108 Chinese CVM cases and found that 10 (9.3%) of them carried TBX6 null mutations in combination with common hypomorphic variants at the second TBX6 allele. For in vivo functional verification and genetic analysis of TBX6 compound inheritance, we generated both null and hypomorphic mutations in mouse Tbx6 using the CRISPR-Cas9 method. These Tbx6 mutants are not identical to the patient variants at the DNA sequence level, but instead functionally mimic disease-associated TBX6 variants. Intriguingly, as anticipated by the compound inheritance model, a high penetrance of CVM phenotype was only observed in the mice with combined null and hypomorphic alleles of Tbx6. These findings are consistent with our experimental observations in humans and supported the dosage effect of TBX6 in CVM etiology. In conclusion, our findings in the newly collected human CVM subjects and Tbx6 mouse models consistently support the contention that TBX6 compound inheritance causes CVMs, potentially via a gene dosage-dependent mechanism. Furthermore, mouse Tbx6 mutants mimicking human CVM-associated variants will be useful models for further mechanistic investigations of CVM pathogenesis in the cases associated with TBX6.

This study is aimed at investigation of the osteochondral regeneration potential of bilayered PLGA/PLGA-HAp composite scaffolds with one layer made of biodegradable polymer poly(D,L-lactide-co-glycolide) (PLGA) and another layer made of PLGA polymeric matrix coated by bioactive ceramics hydroxyapatite (HAp). The composite scaffolds were fabricated by compression molding/particle leaching and plasma-treated surface deposition. The pore morphology, mechanical properties, and surface deposition of the scaffold were characterized, and the growth of bone marrow derived mesenchymal stem cells or medicinal signaling cells (MSCs) in the scaffold was verified. Thereafter, rabbit models with an artificial osteochondral defect in joint were randomized into three treatment groups: virgin bilayered scaffold, bilayered scaffold preseeded in vitro with MSCs, and untreated blank control. At 16-week postoperation, both the virgin scaffolds and cell-seeded bilayered scaffolds exhibited osteochondral repair, as verified by biomechanics analysis, histological evaluations, and Western blot. The results highlighted the potentiality of the bilayered PLGA/PLGA-HAp composite scaffold for osteochondral tissue engineering, and in particular tissue regeneration or in situ tissue induction, probably by recruiting the local cells toward chondrogenic and osteogenic differentiation in the porous biomaterials.

Hydrogel bioadhesion technology has offered unprecedented opportunities in minimally-invasive surgeries, which are routinely performed to reduce postoperative complication, recovery time, and patient discomfort. Existing hydrogelbased adhesives are challenged either by their inherent weak adhesion under wet and dynamic conditions, or potential immunological side-effects, especially for synthetic hydrogel bioadhesives. Here, a kind of synthetic hydrogel bioadhesives from a variety of polymer precursors are reported, featuring instant formation of tough biointerface, allowing for wet and robust adhesion with highly dynamic biological tissues. Moreover, by getting rid of monomers during the hydrogel fabrication, these hydrogel adhesives do not cause any inflammatory response during the in vivo wound sealing, promising for immediate vascular defects repairing and surgical hemostasis. Additionally, they could also serve as human-electronics interfacing materials, enabling bioelectronics implantation for real-time physiological and clinical monitoring.

Engineering conventional hydrogels with muscle‐like anisotropic structures can efficiently increase the fatigue threshold over 1000 J m−2 along the alignment direction; however, the fatigue threshold perpendicular to the alignment is still as low as ≈100–300 J m−2, making them nonsuitable for those scenarios where isotropic properties are desired. Here, inspired by the distinct structure–properties relationship of heart valves, a simple yet general strategy to engineer conventional hydrogels with unprecedented yet isotropic fatigue resistance, with a record‐high fatigue threshold over 1,500 J m−2 along two arbitrary in‐plane directions is reported. The two‐step process involves the formation of preferentially aligned lamellar micro/nanostructures through a bidirectional freeze‐casting process, followed by compression annealing, synergistically contributing to extraordinary resistance to fatigue crack propagation. The study provides a viable means of fabricating soft materials with isotropically extreme properties, thereby unlocking paths to apply these advanced soft materials toward applications including soft robotics, flexible electronics, e‐skins, and tissue patches.

Hydrogel bioadhesives have emerged as one of the most promising alternatives to sutures and staples for wound sealing and repairing, owing to their unique advantages in biocompatibility, mechanical compliance, and minimally invasive manipulation. However, only a few hydrogel bioadhesives have been successfully used for gastric perforation repair, due to their undesirable swelling when in direct contact with extremely acidic gastric fluids, and are thereby accompanied by a gradually deteriorating adhesion performance. Herein, an acid-tolerant hydrogel (ATGel) bioadhesive is developed, which integrates two distinct components, an acid-tolerant hydrogel substrate and an adhesive polymer brush layer. The ATGel bioadhesive can form instant, atraumatic, fluid-tight, and sutureless sealing of gastric perforation, and enable robust biointerfaces in direct contact with gastric fluids, addressing the key limitations with sutures and commercially-available tissue adhesives. Moreover, in vivo investigation on gastric perforation of rat model validates the proposed acid-tolerant bioadhesion, and identifies the mechanisms for accelerated gastric perforation repair through alleviated inflammation, which suppresses fibrosis and enhances angiogenesis.

BackgroundWith the ageing of the population and the increase of sports injuries, the number of joint injuries has increased greatly. Tissue engineering or tissue regeneration is an important method to repair articular cartilage defects. While it has recently been paid much attention to use bilayered porous scaffolds to repair both cartilage and subchondral bone, it is interesting to examine to what extent a bilayer scaffold composed of the same kind of the biodegradable polymer poly(lactide-co-glycolide) (PLGA) can restore an osteochondral defect. Herein, we fabricated bilayered PLGA scaffolds and used a rabbit model to examine the efficacy of implanting the porous scaffolds with or without bone marrow mesenchymal stem cells (BMSCs). The present manuscript reports the regenerative potential up to 24 weeks.MethodsThe osteochondral defect, 4 mm in diameter and 5 mm in depth, was created in the medial condyle of each knee in 23 rabbits. The bilayered PLGA scaffolds with a pore size of 100–200 μm in the chondral layer and a pore size of 300–450 μm in the osseous layer, seeded with or without BMSCs in the chondral layer, were then transplanted into the osteochondral defect of each knee. The osteochondral defect created in the same manner was untreated to act as the control. At 12 and 24 weeks postoperatively, condyles were harvested and analyzed using histology, immunohistochemistry, real-time polymerase chain reaction, and biomechanical testing to evaluate the efficacy of osteochondral repair.ResultsNo joint erosion, inflammation, swelling, or deformity was observed, and all animals maintained a full range of motion. Compared with the untreated blank group, the groups implanting the bilayered scaffolds with or without cells exhibited much better resurfacing, similar to the surrounding normal tissue. The histological scores of neotissues repaired by the scaffold with cells were closer to that of normal tissue. Although the biomechanical properties of neotissues were not as good as the normal tissue, no significant difference was found between the gene levels of neotissues repaired by the scaffold with or without cells and that of the normal tissue. The repair of the osteochondral defect tends to be stable 12 weeks after implantation.ConclusionsOur bilayered PLGA porous scaffold supports long-term osteochondral repair via in vivo tissue engineering or regeneration, and its effect can be further facilitated under the scaffold seeded with allogenic BMSCs.The translational potential of this articleThe bilayered PLGA porous scaffold can facilitate the repair of osteochondral defects and has potential for application in osteochondral tissue engineering.

Nature builds structurally ordered and environmentally adaptive composite materials by harnessing biologically catalyzed mineralization under mild conditions. Despite recent advancements in engineering conventional materials with microorganisms through biomimetic mineralization, it remains difficult to produce mineralized composites that integrate the hierarchical structure and living attributes of their natural counterparts. Here, a kind of functional material is developed by integrating 3D printed hydrogel architectures with enzyme-induced biomineralization. It is shown that the enzyme-induced mineralization intensely transforms flexible and soft hydrogels (modulus of 125 kPa) to rigid (150 MPa) and highly mineralized hydrogel composites. Coupling with embedded 3D printing, sophisticated and mineralized freeform architectures are fabricated in the absence of sacrificial inks, which were previously unattainable through conventional manufacturing strategies. Moreover, by exploiting multi-material 3D printing to tailor the construct composition, exquisite control over the mineral distribution within the hydrogel constructs can be achieved, thus composite materials with tessellated architectures and unconventional mechanics could be obtained. The study provides a viable means to fabricate composite materials with highfidelity architectures and tailored mechanical properties, unlocking paths to the next generation of functional materials and structures by integrating 3D printing with biomineralization.