Ultra-High Sensitivity Anisotropic Piezoelectric Sensors for Structural Health Monitoring and Robotic Perception.

Monitoring minuscule mechanical signals, both in magnitude and direction, is imperative in many application scenarios, e.g., structural health monitoring and robotic sensing systems. However, the piezoelectric sensor struggles to satisfy the requirements for directional recognition due to the limited piezoelectric coefficient matrix, and achieving sensitivity for detecting micrometer-scale deformations is also challenging. Herein, we develop a vector sensor composed of lead zirconate titanate-electronic grade glass fiber composite filaments with oriented arrangement, capable of detecting minute anisotropic deformations. The as-prepared vector sensor can identify the deformation directions even when subjected to an unprecedented nominal strain of 0.06%, thereby enabling its utility in accurately discerning the 5 µm-height wrinkles in thin films and in monitoring human pulse waves. The ultra-high sensitivity is attributed to the formation of porous ferroelectret and the efficient load transfer efficiency of continuous lead zirconate titanate phase. Additionally, when integrated with machine learning techniques, the sensor's capability to recognize multi-signals enables it to differentiate between 10 types of fine textures with 100% accuracy. The structural design in piezoelectric devices enables a more comprehensive perception of mechanical stimuli, offering a novel perspective for enhancing recognition accuracy.

Recycling of Acrylonitrile Butadiene Styrene from Electronic Waste for the Production of Eco-Friendly Filaments for 3D Printing.

In this work, acrylonitrile butadiene styrene (ABS) copolymer from electronic waste (e-waste) was used to produce filaments for application in 3D printing. Recycled ABS (rABS) from e-waste was blended with virgin ABS (vABS) in different concentrations. By differential scanning calorimetry, it was observed that the values of the glass transition temperatures for vABS/rABS blends ranged between the values of vABS and rABS. Torque rheometry analysis showed that the processability of vABS was not compromised with the addition of rABS. Rheological measurements showed that the viscosity of vABS was higher than that of rABS at low frequencies and indicated that vABS and rABS are immiscible. Impact strength (IS) tests of the 3D printed samples showed an increase in the IS with an increase in the rABS content up to 50 wt%. Blending vABS with rABS from e-waste is promising and proved to be feasible, making it possible to recycle a considerable amount of plastics from e-waste and, thus, contributing to the preservation of the environment.

COL8A2 Activation Enhances Function of Corneal Endothelial Cells through HIPPO Signaling/Mitochondria Pathway.

Corneal endothelial cells (CECs) are essential for maintaining corneal transparency and hydration through their barrier and pump functions. The COL8A2 gene encodes a component of the extracellular matrix of the cornea, which is crucial for the normal functioning of these cells. Mutations in COL8A2 are linked to corneal dystrophies, emphasizing the gene's importance in corneal health. The purpose of this research is to explore the effects of COL8A2 activation within CECs, to understand its contribution to cellular behavior and health. COL8A2 CRISPR/dCas9 activation system (aCOL8A2) was used to activate the COL8A2. In rats, wound healing and mitochondrial function were assessed after COL8A2 activation. As a result, aCOL8A2 promoted wound healing of rat corneal endothelium by increasing mitochondrial membrane potential. In cultured human CECs, proteomic analysis was performed to screen and identify the differential protein profiles between control and aCOL8A2 cells. Western blot was used to validate the differential proteins from both cells. Mitochondrial function and intracellular distribution were assessed by measuring ATP production and mitochondrial membrane potential. In cultured human CECs, aCOL8A2 increased COL8A2 and phospho-YAP levels. Transendothelial electrical resistance (TEER) was increased and actin cytoskeleton was attenuated by aCOL8A2. Gene ontology analysis revealed that the proteins were mainly involved in the regulation of folate biosynthesis, ECM-receptor interaction, cell differentiation, NADP activity and cytoskeleton. ATP production was increased, mitochondrial membrane potential was polarized and mitochondrial distribution was widespread in the aCOL8A2 group. In conclusion, aCOL8A2 induces a regulatory cascade affecting mitochondrial positioning and efficiency, mediated by alterations in the cytoskeletal architecture and the YAP signaling pathway. This sequence of events serves to bolster the functional capacities of corneal endothelial cells, including their pump and barrier functions, essential for corneal health and transparency.

PLA based biodegradable bionanocomposite filaments reinforced with nanocellulose: development and analysis of properties.

The 3D printing technique has recently become more prevalent among researchers for the fabrication of nanocomposites. The low crystallinity of polylactic acid (PLA) leads to the poor mechanical and thermal properties of its 3D-printed products, which restrict their applications in many fields. To overcome the limitations of PLA, the present work aims to develop PLA-based bionanocomposite filaments with varying percentages (1, 3, and 5 wt%) of crystalline nanocellulose (CNC) through a single screw extruder. The filaments will be further utilized for the development of bionanocomposite samples to evaluate their properties. The effect of CNC reinforcement on the chemical structure of the filaments was analyzed by FTIR analysis. XRD analysis revealed that the crystallinity of the filaments was significantly improved due to the nucleating effect of CNC. The maximum crystallinity was observed in the filament containing 1 wt% CNC, which was 26% higher than the pure PLA filament. The thermal and mechanical performance of the filaments was also considerably improved after CNC reinforcement, which was confirmed by DSC-TGA and tensile test analysis. The maximum tensile strength and tensile modulus were observed to be 48.9 MPa and 1700 MPa, respectively, in the filament reinforced with 1 wt% CNC, which was 35.5% and 21.89%, respectively, higher than those of the pure PLA filament. Rheological analysis showed that the complex viscosity, storage modulus, and loss modulus of the filaments were significantly affected by the reinforcement of CNC.

Assessment of the carcinogenic potential of particulate matter generated from 3D printing devices in Balb/c 3T3-1-1 cells.

Recently, there have been reports of sarcoma occurring in a Korean science teachers who used a 3D printer with acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA) filaments for educational purposes. However, limited toxicological research data on 3D printing make it challenging to confirm a causal relationship between 3D printing and cancer. Therefore, occupational accidents involving teachers who have developed sarcoma have not been officially recognized. To address this gap, we aimed to evaluate the carcinogenic potential of particulate matter produced from ABS and PLA filaments commonly used in 3D printing. We created a generator mimicking 3D printing to generate particulate matter, which was used as an experimental material. The collected particulate matter was exposed to an in vitro system to investigate genetic damage, effects on cell transformation, and changes in carcinogenesis-related genes. Various assays, such as the comet assay, cell transformation assays, microarray analysis, and glucose consumption measurement, were employed. Cytotoxicity tests performed to determine the exposure concentration for the comet assay showed that cell viability was 83.6, 62.6, 42.0, and 10.2% for ABS at exposure concentrations of 50, 100, 200, and 400 µg/mL, respectively. PLA showed 91.7, 80.3, 65.1, and 60.8% viability at exposure concentrations of 50, 100, 200, and 400 µg/mL, respectively. Therefore, 50 µg/mL was set as the highest concentration for both ABS and PLA, and 25 and 12.5 µg/mL were set as the medium and low concentrations, respectively. The comet assay showed no changes in genetic damage caused by the particulate matter. Cytotoxicity results performed to establish exposure concentrations in the transformation assay showed that ABS showed cell viability of 88.0, 77.4, 84.7, and 85.5% at concentrations of 1.25, 2.5, 5, and 10 µg/mL, respectively, but few cells survived at concentrations above 20 µg/mL. PLA showed minimal cytotoxicity up to a concentration of 20 µg/ml. Therefore, in the cell transformation assay, a concentration of 10 µg/mL for ABS and 20 µg/mL for PLA was set as the highest exposure concentration, followed by medium and low exposure concentrations with a common ratio of 2. In cell transformation assays, only one transformed focus each was observed for both ABS and PLA particulate matter-exposed cells. The microarray assay revealed changes in gene expression, with a 41.7% change at 10 µg/mL for ABS and an 18.6% change at 20 µg/mL for PLA compared to the positive control group. Analysis of carcinogenesis-related gene expression changes on days 1, 7, and 25 of the promotion phase revealed that in cells exposed to 5 µg/mL of ABS, RBM3 gene expression increased by 3.66, 3.26, and 3.74 times, respectively, while MPP6 gene expression decreased by 0.33, 0.28, and 0.38 times, respectively, compared to the negative control group. Additionally, the measurement of glucose consumption showed that it increased in cells exposed to ABS and PLA particulate matter. Our findings suggest that the carcinogenic potential of ABS- and PLA-derived particulate matter in 3D printing cannot be completely ruled out. Therefore, further research in other test systems and analysis of additional parameters related to carcinogenesis, are deemed necessary to evaluate the carcinogenic risk of 3D printers using these materials.

An alternative filament fabrication method as the basis for 3D-printing personalized implants from elastic ethylene vinyl acetate copolymer.

In this work, a novel tool for small-scale filament production is presented. Unlike traditional methods such as hot melt extrusion (HME), the device (i) allows filament manufacturing from small material amounts as low as three grams, (ii) ensures high diameter stability almost independent of the viscoelastic behavior of the polymer melt, and (iii) enables processing of materials with rheological profiles specifically tailored toward fused filament fabrication (FFF). Hence, novel materials, previously difficult to process due to HME limitations, become easily accessible for FFF for the first time. Here, we showcase the production of highly flexible drug-free, and drug-loaded filaments based on ethylene-vinyl acetate polymers with a vinyl acetate content of 28 w% (EVA28) and unprecedented high melt flow rates of up to 400 g/10 min. Owing to their low viscosity, FFF with low print nozzle sizes of 250 µm was achieved for the first time for EVA28. These small nozzle diameters facilitate 3D-printing of high-resolution structures in small-dimensional dosage forms such as subcutaneous implantable drug delivery systems, which can later be used for personalization. Consequently, the material portfolio for FFF is tremendously broadened, allowing material and formulation optimization toward FFF, independent of a preliminary extrusion process.

Desmoplakin CSM models unravel mechanisms regulating the binding to intermediate filaments and putative therapeutics for cardiocutaneous diseases.

Arrhythmogenic cardiomyopathy (AC) is a common cause of sudden cardiac arrest and death in young adults. It can be induced by different types of mutations throughout the desmoplakin gene including the R2834H mutation in the extreme carboxyterminus tail of desmoplakin (DP CT) which remains structurally uncharacterized and poorly understood. Here, we have created 3D models of DP CT which show the structural effects of AC-inducing mutations as well as the implications of post-translational modifications (PTMs). Our results suggest that, in absence of PTMs, positively charged wildtype DP CT likely folds back onto negatively-charged plectin repeat 14 of nearby plakin repeat domain C (PRD C) contributing to the recruitment of intermediate filaments (IFs). When phosphorylated and methylated, negatively-charged wildtype DP CT would then fold back onto positively-charged plectin repeat 17 of PRD C, promoting the repulsion of intermediate filaments. However, by preventing PTMs, the R2834H mutation would lead to the formation of a cytoplasmic mutant desmoplakin with a constitutively positive DP CT tail that would be aberrantly recruited by cytoplasmic IFs instead of desmosomes, potentially weakening cell-cell contacts and promoting AC. Virtual screening of FDA-approved drug libraries identified several promising drug candidates for the treatment of cardiocutaneous diseases through drug repurposing.

Continuous Material Deposition on Filaments in Fused Deposition Modeling.

A novel approach, i.e., Continuous Material Deposition on Filaments (CMDF), for the incorporation of active materials within 3D-printed structures is presented. It is based on passing a filament through a solution in which the active material is dissolved together with the polymer from which the filament is made. This enables the fabrication of a variety of functional 3D-printed objects by fused deposition modeling (FDM) using commercial filaments without post-treatment processes. This generic approach has been demonstrated in objects using three different types of materials, Rhodamine B, ZnO nanoparticles (NPs), and Ciprofloxacin (Cip). The functionality of these objects is demonstrated through strong antibacterial activity in ZnO NPs and the controlled release of the antibiotic Cip. CMDF does not alter the mechanical properties of FDM-printed structures, can be applied with any type of FDM printer, and is, therefore, expected to have applications in a wide variety of fields.

Tailoring 3D-printed sensor properties with reduced-graphene oxide: improved conductive filaments.

The development of a tailored filament is reported composed of reduced graphene oxide (rGO) and carbon black (CB) in a polylactic acid (PLA) matrix and its use in the production of electrochemical sensors. The electrodes containing rGO showed superior performance when compared with  those prepared in the absence of this material. Physicochemical and electrochemical characterizations of the electrodes showed the successful incorporation of both rGO and CB and an improved conductivity in the presence of rGO (lower resistance to charge transfer). As a proof-of-concept, the developed electrodes were applied to the detection of the forensic analytes TNT and cocaine. The electrodes containing rGO presented a superior analytical performance for both TNT and cocaine detection, showing the lower limit of detection values (0.22 and 2.1 µmol L-1, respectively) in comparison with pure CB-PLA electrodes (0.93 and 11.3 µmol L-1, respectively). Besides, better-defined redox peaks were observed, especially for TNT, as well as increased sensitivity for both molecules.

Nano-pregabalin effectively mitigates Glut, CGRP and NE neurotransmitters abnormalities in the brain of gamma irradiated rats with reserpine-induced fibromyalgia model: Behavioral and neurochemical studies.

AIMS: Fibromyalgia (FM) is an idiopathic syndrome with painful burdensome symptoms. Radiotherapy is one of the main therapeutic modalities for treating various malignancies and there is a probable association between FM exacerbation and exposure to ionizing radiation. Based on that nanomedicines progressively being explored for their promising applications in medicine, the aim of the current study is to assess the possible therapeutic benefits of nanoform of pregabalin (N-PG) in managing FM symptoms during being exposed to ionizing radiation. MAIN METHODS: Rats were allocated into four groups. First group served as control, the other three groups received gamma radiation (2 Gy/day) after 1 h of reserpine administration (1 ml/kg per day, s.c.) to induce FM for three successive days. On the next day, third and fourth groups received (30 mg/kg, p.o.) of PG and N-PG, respectively once daily for ten consecutive days. Tail flick test was performed and von Frey filaments were used to assess mechanical allodynia/hyperalgesia, and then rats were sacrificed to obtain brains. KEY FINDINGS: N-PG effectively replenished reserpine effects and treated both allodynia and hyperalgesia, improved thermal allodynia, effectively recovered all neurotransmitters near to normal baseline, inhibited oxidative stress status via decreasing malondialdehyde (MDA), increasing glutathione (GSH) and superoxide dismutase (SOD), it had strong anti-inflammatory effect as verified by reducing both cyclooxygenase-2 (COX-2) and nuclear factor kappa B (NF-kB) in addition to inhibition of intrinsic apoptosis through caspase-3 (casp-3) decrease and B-cell lymphoma-2 (Bcl-2) increase. Histopathological and immunohistochemical results confirmed the biochemical findings. SIGNIFICANCE: N-PG could be a promising drug for treating FM especially when there is urgent need to expose patient to ionizing radiation.

Keratin 8/18a.1 Expression Influences Embryonic Neural Crest Cell Dynamics and Contributes to Postnatal Corneal Regeneration in Zebrafish.

A complete understanding of neural crest cell mechanodynamics during ocular development will provide insight into postnatal neural crest cell contributions to ophthalmic abnormalities in adult tissues and inform regenerative strategies toward injury repair. Herein, single-cell RNA sequencing in zebrafish during early eye development revealed keratin intermediate filament genes krt8 and krt18a.1 as additional factors expressed during anterior segment development. In situ hybridization and immunofluorescence microscopy confirmed krt8 and krt18a.1 expression in the early neural plate border and migrating cranial neural crest cells. Morpholino oligonucleotide (MO)-mediated knockdown of K8 and K18a.1 markedly disrupted the migration of neural crest cell subpopulations and decreased neural crest cell marker gene expression in the craniofacial region and eye at 48 h postfertilization (hpf), resulting in severe phenotypic defects reminiscent of neurocristopathies. Interestingly, the expression of K18a.1, but not K8, is regulated by retinoic acid (RA) during early-stage development. Further, both keratin proteins were detected during postnatal corneal regeneration in adult zebrafish. Altogether, we demonstrated that both K8 and K18a.1 contribute to the early development and postnatal repair of neural crest cell-derived ocular tissues.

Persistent Luminescent Nanoparticle-Loaded Filaments for Identification of Fabrics in the Visible and Infrared.

Persistent luminescent materials are those which can store an amount of energy locally and release it slowly in the form of light. In this work, persistent luminescent nanoparticles (PLNPs) were synthesized and incorporated into polypropylene (PP) filaments at various loading percentages. We investigated the optical properties of both the as-prepared PLNPs and the PLNP-loaded filaments, focusing on any changes resulting from the integration into the filaments. Specifically, visible and near-infrared spectroscopy were used to analyze the emission, excitation, and persistent luminescence of the PLNPs and PLNP-loaded filaments. The tensile properties of the extruded filaments were also investigated through breaking tenacity, elongation at break, Young's modulus, and secant modulus. All PLNP-loaded filaments were shown to exhibit persistent luminescence when exposed to ultraviolet light. While there were no significant changes in the elongation at break or Young's modulus for the loading percentages tested, there was a slight increase in breaking tenacity and a decrease in the secant modulus. Finally, the filaments were shown to maintain their optical properties and persistent luminescence even after abrasion testing used to simulate the normal wear and tear that fabric experiences during use. These results show that PLNPs can be successfully incorporated into filaments which can be used in fabrics and will maintain the persistent luminescent properties.

Localization-delocalization transition for light particles in turbulence.

Small bubbles in fluids rise to the surface due to Archimede's force. Remarkably, in turbulent flows this process is severely hindered by the presence of vortex filaments, which act as moving potential wells, dynamically trapping light particles and bubbles. Quantifying the statistical weights and roles of vortex filaments in turbulence is, however, still an outstanding experimental and computational challenge due to their small scale, fast chaotic motion, and transient nature. Here we show that, under the influence of a modulated oscillatory forcing, the collective bubble behavior switches from a dynamically localized to a delocalized state. Additionally, we find that by varying the forcing frequency and amplitude, a remarkable resonant phenomenon between light particles and small-scale vortex filaments emerges, likening particle behavior to a forced damped oscillator. We discuss how these externally actuated bubbles can be used as a type of microscopic probe to investigate the space-time statistical properties of the smallest turbulence scales, allowing to quantitatively measure physical characteristics of vortex filaments. We develop a superposition model that is in excellent agreement with the simulation data of the particle dynamics which reveals the fraction of localized/delocalized particles as well as characteristics of the potential landscape induced by vortices in turbulence. Our approach paves the way for innovative ways to accurately measure turbulent properties and to the possibility to control light particles and bubble motions in turbulence with potential applications to oceanography, medical imaging, drug/gene delivery, chemical reactions, wastewater treatment, and industrial mixing.

Composite suture material based on polylactide accelerates the healing of surgical wounds in in vivo experiment.

In laboratory conditions, composite sutures based on polylactide (PLA) containing chitin nanofibrils modified with polyethylene glycol (CN-PEG) and poviargol (silver nanoparticles stabilized with poly(N-vinylpyrrolidone)) were obtained, studied, and used as a prototype. Surgical sutures threads with the addition of CN-PEG have stable mechanical properties both in air and in a buffer simulating the environment of a living organism. The yield strength of oriented threads decreased by an average of 15%, whereas for non-oriented threads the decrease was 3-4 times. The strength values in simple units of unfilled PLA, PLA containing 5 wt % CN-PEG, and PLA with 1 wt % Poviargol were on average 50% higher than the national standard 31620-2012. The results of in vivo experiments on albino rats (cross-linking skin and muscle tissue in the linea alba area) showed that composite sutures are best for suturing muscle tissue, whereas unfilled PLA sutures are more suitable for suturing skin. When suturing muscle tissue, suturing with composite sutures increased the number of collagen fibers of different diameters.

Development of Flexible and Partly Water-Soluble Binder Systems for Metal Fused Filament Fabrication (MF3) of Ti-6Al-4V Parts.

Metal Fused Filament Fabrication provides a simple and cost-efficient way to produce dense metal parts with a homogenous microstructure. However, current limitations include the use of hazardous and expensive organic solvents during debinding for flexible filaments the stiffness of filaments made from partly water-soluble binder systems. In this study, the influence of various additives on different partly water-soluble binder systems, with regard to the flexibility and properties of the final parts, was investigated. Furthermore, a method using dynamic mechanical analysis to quantify the flexibility of filaments was introduced and successfully applied. For the first time, it was possible to produce flexible, partly water-soluble filaments with 60 vol.% solid content, which allowed the 3D printing of complex small and large parts with a high level of detail. After sintering, density values of up to 98.9% of theoretical density were achieved, which is significantly higher than those obtained with existing binder systems.

Skeletal muscle adaptations following eccentric contractions are not mediated by keratin 18.

The molecular mechanisms that drive muscle adaptations after eccentric exercise training are multifaceted and likely impacted by age. Previous studies have reported that many genes and proteins respond differently in young and older muscles following training. Keratin 18 (Krt18), a cytoskeletal protein involved in force transduction and organization, was found to be upregulated after muscles performed repeated bouts of eccentric contractions, with higher levels observed in young muscle compared with older muscle. Therefore, the purpose of this study was to determine if Krt18 mediates skeletal muscle adaptations following eccentric exercise training. The anterior crural muscles of Krt18 knockout (KO) and wild-type (WT) mice were subjected to either a single bout or repeated bouts of eccentric contractions, with isometric torque assessed across the initial and final bouts. Functionally, Krt18 KO and WT mice did not differ prior to performing any eccentric contractions (P ≥ 0.100). Muscle strength (tetanic isometric torques) and the ability to adapt to eccentric exercise training were also consistent across strains at all time points (P ≥ 0.169). Stated differently, immediate strength deficits and the recovery of strength following a single bout or multiple bouts of eccentric contractions were similar between Krt18 KO and WT mice. In summary, the absence of Krt18 does not impede the muscle's ability to adapt to repeated eccentric contractions, suggesting it is not essential for exercise-induced remodeling.NEW & NOTEWORTHY The molecular processes that underlie the changes in skeletal muscle following eccentric exercise training are complex and involve multiple factors. Our findings indicate that Krt18 may not play a significant role in muscle adaptations following eccentric exercise training, likely due to its low expression in skeletal muscle. These results underscore the complexity of the molecular mechanisms that contribute to muscle plasticity and highlight the need for further research in this area.

The desmosome-intermediate filament system facilitates mechanotransduction at adherens junctions for epithelial homeostasis.

Epithelial homeostasis can be critically influenced by how cells respond to mechanical forces, both local changes in force balance between cells and altered tissue-level forces.1 Coupling of specialized cell-cell adhesions to their cytoskeletons provides epithelia with diverse strategies to respond to mechanical stresses.2,3,4 Desmosomes confer tissue resilience when their associated intermediate filaments (IFs)2,3 stiffen in response to strain,5,6,7,8,9,10,11 while mechanotransduction associated with the E-cadherin apparatus12,13 at adherens junctions (AJs) actively modulates actomyosin by RhoA signaling. Although desmosomes and AJs make complementary contributions to mechanical homeostasis in epithelia,6,8 there is increasing evidence to suggest that these cytoskeletal-adhesion systems can interact functionally and biochemically.8,14,15,16,17,18,19,20 We now report that the desmosome-IF system integrated by desmoplakin (DP) facilitates active tension sensing at AJs for epithelial homeostasis. DP function is necessary for mechanosensitive RhoA signaling at AJs to be activated when tension was applied to epithelial monolayers. This effect required DP to anchor IFs to desmosomes and recruit the dystonin (DST) cytolinker to apical junctions. DP RNAi reduced the mechanical load that was applied to the cadherin complex by increased monolayer tension. Consistent with reduced mechanical signal strength, DP RNAi compromised assembly of the Myosin VI-E-cadherin mechanosensor that activates RhoA. The integrated DP-IF system therefore supports AJ mechanotransduction by enhancing the mechanical load of tissue tension that is transmitted to E-cadherin. This crosstalk was necessary for efficient elimination of apoptotic epithelial cells by apical extrusion, demonstrating its contribution to epithelial homeostasis.

Intermediate filaments at a glance.

Intermediate filaments (IFs) comprise a large family of versatile cytoskeletal proteins, divided into six subtypes with tissue-specific expression patterns. IFs have a wide repertoire of cellular functions, including providing structural support to cells, as well as active roles in mechanical support and signaling pathways. Consequently, defects in IFs are associated with more than 100 diseases. In this Cell Science at a Glance article, we discuss the established classes of IFs and their general features, their functions beyond structural support, and recent advances in the field. We also highlight their involvement in disease and potential use as clinical markers of pathological conditions. Finally, we provide our view on current knowledge gaps and the future directions of the IF field.

Dynamics of Actin Filaments Play an Important Role in Root Hair Growth under Low Potassium Stress in Arabidopsis thaliana.

Potassium (K) is an essential nutrient for the growth and development of plants. Root hairs are the main parts of plants that absorb K+. The regulation of plant root hair growth in response to a wide range of environmental stresses is crucially associated with the dynamics of actin filaments, and the thick actin bundles at the apical and sub-apical regions are essential for terminating the rapid elongation of root hair cells. However, the dynamics and roles of actin filaments in root hair growth in plants' response to low K+ stress are not fully understood. Here, we revealed that root hairs grow faster and longer under low K+ stress than the control conditions. Compared to control conditions, the actin filaments in the sub-apex of fast-growing wild-type root hairs were longer and more parallel under low K+ stress, which correlates with an increased root hair growth rate under low K+ stress; the finer actin filaments in the sub-apex of the early fully grown Col-0 root hairs under low K+ stress, which is associated with low K+ stress-induced root hair growth time. Further, Arabidopsis thaliana actin bundling protein Villin1 (VLN1) and Villin4 (VLN4) was inhibited and induced under low K+ stress, respectively. Low K+ stress-inhibited VLN1 led to decreased bundling rate and thick bundle formation in the early fully grown phase. Low K+ stress-induced VLN4 functioned in keeping long filaments in the fast-growing phase. Furthermore, the analysis of genetics pointed out the involvement of VLN1 and VLN4 in the growth of root hairs under the stress of low potassium levels in plants. Our results provide a basis for the dynamics of actin filaments and their molecular regulation mechanisms in root hair growth in response to low K+ stress.