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Living tissues, such as muscle, autonomously grow and remodel themselves to adapt to their surrounding mechanical environment through metabolic processes. By contrast, typical synthetic materials cannot grow and reconstruct their structures once formed. We propose a strategy for developing “self-growing” polymeric materials that respond to repetitive mechanical stress through an effective mechanochemical transduction. Robust double-network hydrogels provided with a sustained monomer supply undergo self-growth, and the materials are substantially strengthened under repetitive loading through a structural destruction-reconstruction process. This strategy also endows the hydrogels with tailored functions at desired positions by mechanical stamping. This work may pave the way for the development of self-growing gel materials for applications such as soft robots and intelligent devices.

Recent progresses in developing tough hydrogels promise the great potential of this class of soft and wet materials as biomaterials, soft robotics, smart actuators and sensors. [1][2][3][4][5][6][7][8][9][10] Any practical application of these hydrogels as smart materials, however, requires a combination of mechanical properties including stiffness, strength, toughness, and self-healing. For instance, along with the high strength and toughness, a cartilage substitute material requires a high stiffness to bear the load, while a blood vessel substitute material requires flexibility.Self-healing not only merits the long term durability of the load-bearing materials, but also gives possibility to reconstruct the material with desired shape from its microgels. While many hydrogels possess some of these requirements, it is a challenge to develop hydrogels satisfying all of these criteria. [2,[11][12][13] In this work, we report a new class of physical hydrogels that possess these multiple functions. These hydrogels are obtained from concentrated solution of oppositely charged polyelectrolytes. After dialysis of their small counter ions, the oppositely charged polyelectrolytes form polyion complexes of a wide strength distribution, which give dynamic crosslinking of an extremely wide life time scale. The strong, long life time bonds serve as permanent cross-linking, imparting elasticity, whereas the weak, short life

A series of physical double-network hydrogels is synthesized based on an amphiphilic triblock copolymer. The gel, which contains strong hydrophobic domains and sacrificial dynamic bonds of hydrogen bonds, is stiff and tough, and even stiffens in concentrated saline solution. Furthermore, due to its supramolecular structure, the gel features improved self-healing and self-recovery abilities

Two well-characterized cannabinoid receptors (CBrs), CB1 and CB2, mediate the effects of cannabinoids and marijuana use, with functional evidence for other CBrs. CB1 receptors are expressed primarily in brain and peripheral tissues. For over a decade several laboratories were unable to detect CB2 receptors in brain and were known to be intensely expressed in peripheral and immune tissues and have traditionally been referred to as peripheral CB2 CBrs. We have reported the discovery and functional presence of CB2 cannabinoid receptors in mammalian brain that may be involved in depression and drug abuse and this was supported by reports of identification of neuronal CB2 receptors that are involved in emesis. We used RT-PCR, immunoblotting, hippocampal cultures, immunohistochemistry, transmission electron microscopy, and stereotaxic techniques with behavioral assays to determine the functional expression of CB2 CBrs in rat brain and mice brain exposed to chronic mild stress (CMS) or those treated with abused drugs. RT-PCR analyses supported the expression of brain CB2 receptor transcripts at levels much lower than those of CB1 receptors. In situ hybridization revealed CB2 mRNA in cerebellar neurons of wild-type but not of CB2 knockout mice. Abundant CB2 receptor immunoreactivity (iCB2) in neuronal and glial processes was detected in brain and CB2 expression was detected in neuron-specific enolase (NSE) positive hippocampal cell cultures. The effect of direct CB2 antisense oligonucleotide injection into the brain and treatment with JWH015 in motor function and plus-maze tests also demonstrated the functional presence of CB2 cannabinoid receptors in the central nervous system (CNS). Thus, contrary to the prevailing view that CB2 CBrs are restricted to peripheral tissues and predominantly in immune cells, we demonstrated that CB2 CBrs and their gene transcripts are widely distributed in the brain. This multifocal expression of CB2 immunoreactivity in brain suggests that CB2 receptors may play broader roles in the brain than previously anticipated and may be exploited as new targets in the treatment of depression and substance abuse.

Natural structural materials (such as tendons and ligaments) are comprised of multiscale hierarchical architectures, with dimensions ranging from nano- to macroscale, which are difficult to mimic synthetically. Here a bioinspired, facile method to fabricate anisotropic hydrogels with perfectly aligned multiscale hierarchical fibrous structures similar to those of tendons and ligaments is reported. The method includes drying a diluted physical hydrogel in air by confining its length direction. During this process, sufficiently high tensile stress is built along the length direction to align the polymer chains and multiscale fibrous structures (from nano- to submicro- to microscale) are spontaneously formed in the bulk material, which are well-retained in the reswollen gel. The method is useful for relatively rigid polymers (such as alginate and cellulose), which are susceptible to mechanical signal. By controlling the drying with or without prestretching, the degree of alignment, size of superstructures, and the strength of supramolecular interactions can be tuned, which sensitively influence the strength and toughness of the hydrogels. The mechanical properties are comparable with those of natural ligaments. This study provides a general strategy for designing hydrogels with highly ordered hierarchical structures, which opens routes for the development of many functional biomimetic materials for biomedical applications.

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