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Although itch sensation is an important protective mechanism for animals, chronic itch remains a challenging clinical problem. Itch processing has been studied extensively at the spinal level. However, how itch information is transmitted to the brain and what central circuits underlie the itch-induced scratching behavior remain largely unknown. We found that the spinoparabrachial pathway was activated during itch processing and that optogenetic suppression of this pathway impaired itch-induced scratching behaviors. Itch-mediating spinal neurons, which express the gastrin-releasing peptide receptor, are disynaptically connected to the parabrachial nucleus via glutamatergic spinal projection neurons. Blockade of synaptic output of glutamatergic neurons in the parabrachial nucleus suppressed pruritogen-induced scratching behavior. Thus, our studies reveal a central neural circuit that is critical for itch signal processing.

Itch is an annoying sensation consisting of both sensory and emotional components. It is known to involve the parabrachial nucleus (PBN), but the following transmission nodes remain elusive. The present study identified that the PBN-central medial thalamic nucleus (CM)-medial prefrontal cortex (mPFC) pathway is essential for itch signal transmission at the supraspinal level in male mice. Chemogenetic inhibition of the CM-mPFC pathway attenuates scratching behavior or chronic itch-related affective responses. CM input to mPFC pyramidal neurons is enhanced in acute and chronic itch models. Specifically chronic itch stimuli also alter mPFC interneuron involvement, resulting in enhanced feedforward inhibition and a distorted excitatory/inhibitory balance in mPFC pyramidal neurons. The present work underscores CM as a transmit node of the itch signal in the thalamus, which is dynamically engaged in both the sensory and affective dimensions of itch with different stimulus salience. Itch is known to involve the parabrachial nucleus, but the following transmission nodes remain elusive. Here, the authors show in male mice that the central medial thalamic nucleus—medial prefrontal cortex (mPFC) pathway transmits itch signals and is involved in both acute scratching and chronic itch-related affective behavior, with an altered excitatory/inhibitory balance in mPFC in chronic itch models.

Socially contagious itch is ubiquitous in human society, but whether it exists in rodents is unclear. Using a behavioral paradigm that does not entail prior training or reward, we found that mice scratched after observing a conspecific scratching. Molecular mapping showed increased neuronal activity in the suprachiasmatic nucleus (SCN) of the hypothalamus of mice that displayed contagious scratching. Ablation of gastrin-releasing peptide receptor (GRPR) or GRPR neurons in the SCN abolished contagious scratching behavior, which was recapitulated by chemogenetic inhibition of SCN GRP neurons. Activation of SCN GRP/GRPR neurons evoked scratching behavior. These data demonstrate that GRP-GRPR signaling is necessary and sufficient for transmitting contagious itch information in the SCN. The findings may have implications for our understanding of neural circuits that control socially contagious behaviors.

Itch in response to light touch of the skin is an aging-associated problem. This phenomenon is called alloknesis and can become a major medical condition associated with dry skin. Feng et al. discovered that loss or dysfunction of Merkel cells causes scratching in mice (see the Perspective by Lewis and Grandl). Reduction of Merkel cell numbers results in reduced firing patterns and frequencies and changes the activation thresholds of slowly adapting afferent nerve fibers. Like hair cells, Merkel cells are lost with age. A painful scratch will temporarily alleviate itch because it induces enough activity through the remaining Merkel cells. Science , this issue p. 530 ; see also p. 492 Chronic itch caused by aging and dry skin is associated with the loss of skin Merkel cells involved in light touch sensation. The somatosensory system relays many signals ranging from light touch to pain and itch. Touch is critical to spatial awareness and communication. However, in disease states, innocuous mechanical stimuli can provoke pathologic sensations such as mechanical itch (alloknesis). The molecular and cellular mechanisms that govern this conversion remain unknown. We found that in mice, alloknesis in aging and dry skin is associated with a loss of Merkel cells, the touch receptors in the skin. Targeted genetic deletion of Merkel cells and associated mechanosensitive Piezo2 channels in the skin was sufficient to produce alloknesis. Chemogenetic activation of Merkel cells protected against alloknesis in dry skin. This study reveals a previously unknown function of the cutaneous touch receptors and may provide insight into the development of alloknesis.

SiC f /SiC composites are important advanced materials in aerospace and energy fields, but their hard and brittle properties lead to severe machining damage during conventional machining, which limits their application performance. In this study, ultrasonic vibration rotary scratching experiments using single crystal diamond particles were conducted to characterize the scratching force and post-machining surface morphology, and to investigate the effect of ultrasonic vibration on the material removal mechanism. The results show that the axial force shows significant fluctuations with the fiber orientation angle, following the pattern of ASF 0° (transverse) ≫ ASF 0° (longitudinal), ASF 30°> ASF 45°. At scratch depths of 30 μm and 40 μm, the average axial force of ultrasonic vibratory scrubbing decreased by 21.61% and 8.80%, and the average tangential force decreased by 25.27% and 15.91%, respectively, compared with the normal planar scrubbing force. In the conventional rotational rubbing, the material surface showed characteristic skewing phenomenon and debonding phenomenon, and the width of the fiber fracture zone after rubbing was large and irregular. All of them were effectively suppressed after the introduction of ultrasonic vibration. This indicates that ultrasonic vibration significantly reduces the processing force and surface damage by changing the material removal mechanism, providing technical support for the precision manufacturing of advanced equipment.

Itch triggers scratching, a behavioural defence mechanism that aids in the removal of harmful irritants and parasites 1 . Chemical itch is triggered by many endogenous and exogenous cues, such as pro-inflammatory histamine, which is released during an allergic reaction 1 . Mechanical itch can be triggered by light sensations such as wool fibres or a crawling insect 2 . In contrast to chemical itch pathways, which have been extensively studied, the mechanisms that underlie the transduction of mechanical itch are largely unknown. Here we show that the mechanically activated ion channel PIEZO1 (ref. 3 ) is selectively expressed by itch-specific sensory neurons and is required for their mechanically activated currents. Loss of PIEZO1 function in peripheral neurons greatly reduces mechanically evoked scratching behaviours and both acute and chronic itch-evoked sensitization. Finally, mice expressing a gain-of-function Piezo1 allele 4 exhibit enhanced mechanical itch behaviours. Our studies reveal the polymodal nature of itch sensory neurons and identify a role for PIEZO1 in the sensation of itch. Experiments in mice show that the mechanically activated ion channel PIEZO1 is expressed in itch-specific sensory neurons and has a role in transducing mechanical itch.

Durable hydrophobic materials have attracted considerable interest in the last century. Currently, the most popular strategy to achieve hydrophobic coating durability is through the combination of a perfluoro-compound with a mechanically robust matrix to form a composite for coating protection. The matrix structure is typically large (thicker than 10 μm), difficult to scale to arbitrary materials, and incompatible with applications requiring nanoscale thickness such as heat transfer, water harvesting, and desalination. Here, we demonstrate durable hydrophobicity and superhydrophobicity with nanoscale-thick, perfluorinated compound-free polydimethylsiloxane vitrimers that are self-healing due to the exchange of network strands. The polydimethylsiloxane vitrimer thin film maintains excellent hydrophobicity and optical transparency after scratching, cutting, and indenting. We show that the polydimethylsiloxane vitrimer thin film can be deposited through scalable dip-coating on a variety of substrates. In contrast to previous work achieving thick durable hydrophobic coatings by passively stacking protective structures, this work presents a pathway to achieving ultra-thin (thinner than 100 nm) durable hydrophobic films. By now a plethora of ultrathin hydrophobic coatings are available but their durability are not well developed. Here, the authors present a thin, durable and fluorine-free PDMS-based vitrimer coating that implements many desirable aspects like energy efficiency, durability and sustainability.

Aiming at the difficulties of manual assembly and inconsistent assembly accuracy in the assembly of large components of servo motors, a self-aligning automatic assembly system was studied and designed. By studying high-precision pose measurement, automatic pose adjustment, and intelligent fixtures, the system can achieve precise alignment assembly. The system adopts a robotic arm measurement head scheme to measure the key coordinates of the mating surfaces of the parts to be assembled and determines the posture and position relationship of the parts to be assembled through normal vectors and center coordinates. A multi-axis adjustment mechanism was designed to achieve precise alignment assembly by adjusting the position and posture. Physical assembly experiments show that the system can achieve precise assembly of the large components of servo motors, effectively reducing the chance of cutting or scratching the sealing ring or inner wall of the housing during the assembly process, and can also record real-time assembly process data. The study results of this assembly system are of great significance for improving assembly efficiency and quality.

Micro/nano hierarchical structures could endow materials with various surface functions. However, the multilayer and multiscale characteristics of micro/nano hierarchical structures bring difficulties for their one step and controllable fabrication. Accordingly, based on tip-based fabrication techniques, this study proposed a micro-amplitude vibration-assisted scratching method by introducing a periodic backward displacement into the conventional scratching process, which enabled the synchronous creation of the microscale V-groove and nanoscale ripples, i.e. a typical micro/nano hierarchical structure. The experiments and finite element modeling were employed to explore the formation process and mechanism of the micro/nano hierarchical structures. Being different from conventional cutting, this method was mainly based on the plow mechanism, and it could accurately replicate the shape of the indenter on the material surface. The microscale V-groove was formed due to the scratching action, and the nanoscale ripple was formed due to the extrusion action of the indenter on the microscale V-groove’s surface. Furthermore, the relationships between the processing parameters and the dimensions of the micro/nano hierarchical structures were established through experiments, and optimized processing parameters were determined to achieve regular micro/nano hierarchical structures. By this method, complex patterns constructed by various micro/nano hierarchical structures were fabricated on both flat and curved surfaces, achieving diverse surface structural colors. A micro-amplitude vibration-assisted scratching method was proposed. One step and controllable fabrication of microscale V-groove and nanoscale ripples was achieved. The effects of processing parameters on the resultant structures were explored. Relationships between processing parameters and dimensions of the resultant structures were established. Complex patterns were fabricated on flat and curved surfaces, achieving various structural colors.