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Abstract Simultaneous achievement of lightweight, ultrahigh strength, large fracture strain, and high damping capability is challenging because some of these mechanical properties are mutually exclusive. Here, we utilize self-assembled polymeric carbon precursor materials in combination with scalable nano-imprinting lithography to produce nanoporous carbon nanopillars. Remarkably, nanoporosity induced via sacrificial template significantly reduces the mass density of amorphous carbon to 0.66 ~ 0.82 g cm−3 while the yield and fracture strengths of nanoporous carbon nanopillars are higher than those of most engineering materials with the similar mass density. Moreover, these nanopillars display both elastic and plastic behavior with large fracture strain. A reversible part of the sp2-to-sp3 transition produces large elastic strain and a high loss factor (up to 0.033) comparable to Ni-Ti shape memory alloys. The irreversible part of the sp2-to-sp3 transition enables plastic deformation, leading to a large fracture strain of up to 35%. These findings are substantiated using simulation studies. None of the existing structural materials exhibit a comparable combination of mass density, strength, deformability, and damping capability. Hence, the results of this study illustrate the potential of both dense and nanoporous amorphous carbon materials as superior structural nanomaterials.

Abstract Osteoarthritis affects millions of people worldwide but current treatments using analgesics or anti-inflammatory drugs only alleviate symptoms of this disease. Here, we present an injectable, biodegradable piezoelectric hydrogel, made of short electrospun poly-L-lactic acid nanofibers embedded inside a collagen matrix, which can be injected into the joints and self-produce localized electrical cues under ultrasound activation to drive cartilage healing. In vitro, data shows that the piezoelectric hydrogel with ultrasound can enhance cell migration and induce stem cells to secrete TGF-β1, which promotes chondrogenesis. In vivo, the rabbits with osteochondral critical-size defects receiving the ultrasound-activated piezoelectric hydrogel show increased subchondral bone formation, improved hyaline-cartilage structure, and good mechanical properties, close to healthy native cartilage. This piezoelectric hydrogel is not only useful for cartilage healing but also potentially applicable to other tissue regeneration, offering a significant impact on the field of regenerative tissue engineering.

Modulus of resilience, the maximum strain energy density that can be stored in an elastically deformed solid, is an important mechanical property for developing artificial muscles in robotics, soft electronics panels, and micro-/nano-electromechanical actuators. In this study, core–shell SU-8 nanocomposites were fabricated via vapor-phase infiltration of nanoscale amorphous aluminum oxides into SU-8 nanopillars and performed transmission electron microscopy, nanomechanical testing, analytical modeling, and atomistic simulations to gain a fundamental insight into the ultrahigh modulus of resilience much higher than that of most high-strength materials. This study shows that the ultrahigh modulus of resilience results from: the low aspect ratio of amorphous aluminum oxide nano-particulates; the particulate size thicker than the free volume size; and the thin aluminum oxide interconnecting links within nano-particulates. These unique microstructural features produce the unusual combination of low specific Young’s modulus (E), 4 MPa/(kg/m3), and high specific yield strength (σy), 0.2 MPa/(kg/m3), leading to the specific modulus of resilience, 5.21 ± 0.39 kJ/kg (σy2/(2E)) about ten times higher than materials with the similar yield strength. This study demonstrates that vapor-phase infiltration is an excellent fabrication method to produce a polymer nanocomposite that can absorb and release a large amount of elastic strain energy.

Abstract Background Previous research has suggested that poor oral health is positively associated with frailty. The objective of this study was to explore associations of key oral diseases (periodontal disease, tooth loss), and oral hygiene and management behaviors with the level of frailty in community-dwelling older Korean adults using national representative survey data. Methods This study used cross-sectional, 6th and 7th Korea National Health and Nutrition Examination Survey (KNHANES VI, VII) data. Adults aged 50+ years were included. Frailty was measured using frailty phenotype (FP) and frailty index (FI). FP was determined using five frailty criteria, i.e., weight loss, weakness, exhaustion, slowness, or low physical activity, and the level of frailty was classified with the number of criteria present (robust, none; pre-frail, 1–2; frail, 3+). FI was determined using a 44-item FI constructed according to a standard protocol, and the level of frailty was classified as robust (FI: ≤ 0.08), pre-frail (FI: 0.08–0.25), and frail (FI: ≥ 0.25). Multiple ordinal regression analyses were conducted with each type of frailty as the outcome variable. Independent variables of interest were the periodontal status, number of teeth, and practices on oral hygiene and management. Analyses were additionally adjusted for participants’ socioeconomic, diet, and behavioral characteristics. Results The prevalence of frailty was 4.38% according to the FP classification (n = 4156), 10.74% according to the FI classification (n = 15,073). In the final adjusted model, having more teeth and brushing after all three meals were significantly associated with lower odds of being more frail (in both frailty models); no significant association was observed between periodontal disease and frailty. Conclusions Findings from this study show having more teeth and practicing adequate brushing are significantly associated with frailty. Due to limitations of the study design, well-designed longitudinal studies are needed to confirm these findings.

Magnesium is widely regarded as an excellent structural material, primarily because it forms the basis for a range of light-weight high-strength alloys. Recently, high-strain rate deformation of magnesium has received a great deal of attention due to the complicated deformation modes that involve combinations of dislocation slip and deformation twinning. In this study, single crystal magnesium samples were shock-compressed along the c- and a-axis, then released back to ambient conditions. Post-mortem transmission electron microscopy revealed that extension twins developed for both c- and a-axis shock loading. Also, the nanoindentation hardness values for these shocked samples were compared to those for samples compressed under quasi-static conditions; it was found that the hardness decreased with increasing strain rate for both c- and a-axis loading. Molecular dynamics simulations were performed to elucidate the detailed mechanisms of deformation twinning in terms of inertial confinement of sample geometry and different stress relaxation speed between impact and lateral directions. The conversion from work-done to heat was discussed to explain the influence of shock-induced heating on the residual hardness. These results give new insights into the residual mechanical response in shock-compressed materials and may help to develop a more fundamental understanding of shock phenomena in metallic materials.

Amorphous boron can be synthesized by chemical vapor deposition (CVD) onto a tungsten wire substrate, and this core-shell fiber has been widely used in high-performance composites due to its superior mechanical properties. Although the amorphous boron coating makes a significant contribution to the high fracture strength, its mechanical properties have not been studied rigorously due to its thin thickness and strong adhesion to the substrate. Furthermore, the medium-range atomic ordering of CVD amorphous boron has not been clearly understood, and the determination of the closest crystalline structure has been a challenge. In this study, high-resolution transmission electron microscopy (HRTEM), nanoindentation, and in-situ micropillar compression were performed to investigate the atomic arrangement and mechanical properties. Electron diffraction and autocorrelation function analysis revealed α-rhombohedral boron ordering as the closest crystalline structure. Micropillar compression displayed near-ideal yield strength (~13 GPa), but nanoindentation a relatively moderate Young's modulus (~320 GPa), leading to a modulus of resilience (2.64 × 108 J/m3) unprecedentedly higher than most advanced engineering materials. Our structural and mechanical data will be discussed in terms of lattice point spacing and the influence of surface defects on fracture strength, respectively. Our results will be potentially useful to improve mechanical properties of amorphous boron core-shell fibers and related composites.

In this study, our goal is to design solid solution strengthened aluminum alloys for manufacturing technologies that involve high cooling rates. This investigation starts with an analysis of solid solution strengthening using first principles calculations to determine elastic property changes and local lattice distortions from the introduction of different elements into a host aluminum lattice. These results, coupled with both equilibrium and non-equilibrium solubility data, leads to the selection of cerium and cobalt as the primary candidate alloying elements. Alloys of AlCe and AlCo at concentrations of 0.5, 1.0, and 3.0 at. % are then synthesized and subjected to laser glazing to produce non-equilibrium microstructures. The microstructure and solid solution characteristics are determined using a combination of scanning electron microscopy and transmission electron microscopy. Furthermore, nanoindentation is used to measure the hardness showing that both candidate systems harden significantly after glazing. In addition, Al-1.0Co at. % achieves a hardness comparable to Al6061-T6. These results conclusively show that cerium and cobalt are promising elements in the next generation aluminum alloys which make use of non-equilibrium processing conditions such as additive manufacturing.

Abstract A critical challenge in the predictive capability of materials deformation behavior under extreme environments is the availability of computational methods to model the microstructural evolution at the mesoscale. The capability of the recently-developed quasi-coarse-grained dynamics (QCGD) method to model mesoscale behavior is demonstrated for the phenomenon of supersonic impact of 20 µm sized Al particles on to an Al substrate at various impact velocities and over time and length scales relevant to cold spray deposition. The QCGD simulations are able to model the kinetics related to heat generation and dissipation, and the pressure evolution and propagation, during single particle impact over the time and length scales that are important experimentally. These simulations are able to unravel the roles of particle and substrate deformation behavior that lead to an outward/upward flow of both the particle and the substrate, which is a likely precursor for the experimentally observed jetting and bonding of the particles during cold spray impact.

Shape memory materials are capable of returning to their original form post-deformation, but those with high actuation performances remain scarce. Here the authors reveal that CaFe2As2 exhibits cryogenic linear shape memory behaviour with high recoverable strain and yield strength, owing to a reversible uni-axial phase transformation.

Intermetallic compounds possess unique atomic arrangements that often lead to exceptional material properties, but their extreme brittleness usually causes fracture at a limited strain of less than 1% and prevents their practical use. Therefore, it is critical for them to exhibit either plasticity or some form of structural transition to absorb and release a sufficient amount of mechanical energy before failure occurs. This study reports that the ThCr2Si2-structured intermetallic compound (CaFe2As2) and a hybrid of its structure (CaKFe4As4) with 2 µm in diameter and 6 µm in height can exhibit superelasticity with strain up to 17% through a reversible, deformation-induced lattice collapse, leading to a modulus of resilience orders of magnitude higher than that of most engineering materials. Such superelasticity also can enable strain engineering, which refers to the modification of material properties through elastic strain. Density functional theory calculations and cryogenic nanomechanical tests predict that superconductivity in CaKFe4As4 could be turned on/off through the superelasticity process, before fracture occurs, even under uniaxial compression, which is the favorable switching loading mode in most engineering applications. Our results suggest that other members with the same crystal structure (more than 2500 intermetallic compounds) and substitution series based on them should be examined for the possibility of manifesting similar superelastic and strain-engineerable functional properties.

We report on an abnormal output characteristics in p-type low temperature polycrystalline silicon thin-film transistors fabricated on polyimide (PI); negative differential conductance behavior is often observed in saturation region of drain current from large width devices. To understand such abnormal output characteristics, device dimension dependence was studied in a systematic way. As a result, we found that enhanced self-heating is mainly responsible originating from the poor thermal conductivity of PI substrate. A related degradation model is also proposed.

Background and Objectives: Recent evidence suggests that oral health is associated with various systemic diseases including psychiatric illnesses. This study examined the association between depression and access to dental care in Korean adults. Materials and Methods: A cross-sectional evaluation was performed using data from the Sixth Korea National Health and Nutrition Examination Survey 2014. The general characteristics of the participants, the current depression status, and issues with access to dental care were collected to evaluate the factors for not being able to make dental visits according to care needs. Results: The study population comprised a total of 5976 participants who were 19 years of age and older and represented 40.7 million Koreans. A multivariable logistic regression analysis with weighted observations revealed that participants with current depressive illness were about two times more likely to express that they could not make dental visits in spite of their perceived care needs (adjusted odds ratio (OR) = 2.097; 95% confidence interval (CI) 1.046–4.203). The reasons for not making dental visits included financial problems, perceived importance of the dental problem, and fear of visiting dental professionals. Conclusions: Korean adults with current depressive illness were less likely to make dental visits when they had dental care needs. To improve dental health accessibility for patients with depressive illness, coordinated efforts can be considered involving multidisciplinary health care professionals.

[This corrects the article DOI: 10.1371/journal.pone.0188755.].

Objectives Molecular mechanism of the pathogenicity of Enterococcus faecalis (E. faecalis), a suspected endodontic pathogen, has not yet been adequately elucidated due to limited information on its virulence factors. Here we report the identification of in vivo expressed antigens of E. faecalis by using a novel immunoscreening technique called change-mediated antigen technology (CMAT) and an experimental animal model of endodontic infection. Materials and Methods Among 4,500 E. coli recombinant clones screened, 19 positive clones reacted reproducibly with hyperimmune sera obtained from rabbits immunized with E. faecalis cells isolated from an experimental endodontic infection. DNA sequences from 16 of these in vivo-induced (IVI) genes were determined. Results Identified protein antigens of E. faecalis included enzymes involved in housekeeping functions, copper resistance protein, putative outer membrane proteins, and proteins of unknown function. Conclusions In vivo expressed antigens of E. faecalis could be identified by using a novel immune-screening technique CMAT and an experimental animal model of endodontic infection. Detailed analysis of these IVI genes will lead to a better understanding of the molecular mechanisms involved in the endodontic infection of E. faecalis.

Periodontal disease is caused by dental plaque biofilms. Fusobacterium nucleatum is an important periodontal pathogen involved in the development of bacterial complexity in dental plaque biofilms. Human gingival fibroblasts (GFs) act as the first line of defense against oral microorganisms and locally orchestrate immune responses by triggering the production of reactive oxygen species and pro-inflammatory cytokines (IL-6 and IL-8). The frequency and severity of periodontal diseases is known to increase in elderly subjects. However, despite several studies exploring the effects of aging in periodontal disease, the underlying mechanisms through which aging affects the interaction between F. nucleatum and human GFs remain unclear. To identify genes affected by infection, aging, or both, we performed an RNA-Seq analysis using GFs isolated from a single healthy donor that were passaged for a short period of time (P4) 'young GFs' or for longer period of time (P22) 'old GFs', and infected or not with F. nucleatum. Comparing F. nucleatum-infected and uninfected GF(P4) cells the differentially expressed genes (DEGs) were involved in host defense mechanisms (i.e., immune responses and defense responses), whereas comparing F. nucleatum-infected and uninfected GF(P22) cells the DEGs were involved in cell maintenance (i.e., TGF-β signaling, skeletal development). Most DEGs in F. nucleatum-infected GF(P22) cells were downregulated (85%) and were significantly associated with host defense responses such as inflammatory responses, when compared to the DEGs in F. nucleatum-infected GF(P4) cells. Five genes (GADD45b, KLF10, CSRNP1, ID1, and TM4SF1) were upregulated in response to F. nucleatum infection; however, this effect was only seen in GF(P22) cells. The genes identified here appear to interact with each other in a network associated with free radical scavenging, cell cycle, and cancer; therefore, they could be potential candidates involved in the aged GF's response to F. nucleatum infection. Further studies are needed to confirm these observations.

Background and Objectives: The current study was performed to evaluate the prevalence of periodontitis and to examine the association between reduced pulmonary function and periodontitis using Sixth Korea National Health and Nutrition Examination Survey (KNHANES) in 2014. Materials and Methods: A cross-sectional evaluation was conducted to estimate the prevalence of periodontitis and to examine the association between periodontitis and reduced pulmonary function while adjusting for sociodemographic characteristics and current smoking status in survey participants between 40 and 79 years old. The presence of periodontitis was evaluated by community periodontal index defined by the World Health Organization, and the assessments of reduced pulmonary function data were made as “normal,” “restrictive impairment,” or “obstructive impairment.” Results: A total of 4004 survey participants representing 25.4 million Koreans were included in the study. Overall, 41.1% of the study population were determined to have periodontitis, and 22.1% had reduced pulmonary function; 7.9% and 14.2% had restrictive- and obstructive- pulmonary impairments, respectively. Age, male gender, and current smoking status were positive predictors for periodontitis. Insurance coverage by workplace and higher education were protective factors against periodontitis. The association between periodontitis and restrictive impairment (adjusted odds ratio (OR) = 1.059, 95% CI 0.729−1.540) or obstructive impairment (adjusted OR = 1.140, 95% CI 0.849−1.530) was not significant. Conclusions: For Koreans, 40−79 years old, age, smoking status, gender, education, and insurance coverage were significant predictors of periodontitis. The prevalence of periodontitis was not significantly associated with reduced pulmonary function. To better understand the relationship between periodontitis and reduced pulmonary function, well-designed and larger scale epidemiologic studies are needed.

Pinus densiflora (Korean red pine) is widely distributed in East Asia and considered one of the most important species in Korea. In this study, the complete chloroplast genome of P. densiflora was sequenced by combining the advantages of Oxford Nanopore MinION and Illumina MiSeq. The sequenced genome was then compared with that of a previously published conifer plastome. The chloroplast genome was found to be circular and comprised of a quadripartite structure, including 113 genes encoding 73 proteins, 36 tRNAs and 4 rRNAs. It had short inverted repeat regions and lacked ndh gene family genes, which is consistent with other Pinaceae species. The gene content of P. densiflora was found to be most similar to that of P. sylvestris. The newly attempted sequencing method could be considered an alternative method for obtaining accurate genetic information, and the chloroplast genome sequence of P. densiflora revealed in this study can be used in the phylogenetic analysis of Pinus species.

Osteoclasts are large multinucleated cells which are induced by the regulation of the receptor activator of nuclear factor kappa-Β ligand (RANKL), which is important in bone resorption. Excessive osteoclast differentiation can cause pathologic bone loss and destruction. Numerous studies have targeted molecules inhibiting RANKL signaling or bone resorption activity. In this study, 11 compounds from commercial libraries were examined for their effect on RANKL-induced osteoclast differentiation. Of these compounds, only 2-(3-(2-fluoro-4-methoxyphenyl)-6-oxo-1(6H)-pyridazinyl)-N-1H-indol-5-ylacetamide (2N1HIA) caused a significant decrease in multinucleated tartrate-resistant acid phosphatase (TRAP)-positive cell formation in a dose-dependent manner, without inducing cytotoxicity. The 2N1HIA compound neither affected the expression of osteoclast-specific gene markers such as TRAF6, NFATc1, RANK, OC-STAMP, and DC-STAMP, nor the RANKL signaling pathways, including p38, ERK, JNK, and NF-κB. However, 2N1HIA exhibited a significant impact on the expression levels of CD47 and cathepsin K, the early fusion marker and critical protease for bone resorption, respectively. The activity of matrix metalloprotease-9 (MMP-9) decreased due to 2N1HIA treatment. Accordingly, bone resorption activity and actin ring formation decreased in the presence of 2N1HIA. Taken together, 2N1HIA acts as an inhibitor of osteoclast differentiation by attenuating bone resorption activity and may serve as a potential candidate in preventing and/or treating osteoporosis, or other bone diseases associated with excessive bone resorption.

This paper presents a miniaturized magnetic induction sensor (MMIS), wheregeomagnetism and high rpm rotation of ammunition are used to detect the turn number ofthe ammunition for applications to small-caliber turn-counting fuzes. The MMIS, composedof cores and a coil, has a robust structure without moving parts to increase the shocksurvivability in a gunfire environment of ~30,000 g’s. The MMIS is designed and fabricatedon the basis of the simulation results of an electromagnetic analysis tool, Maxwell® 3D. Inthe experimental study, static MMIS test using a solenoid-coil apparatus and dynamicMMIS test (firing test) have been made. The present MMIS has shown that an inductionvoltage of 6.5 mVp-p is generated at a magnetic flux density of 0.05 mT and a rotationalvelocity of 30,000 rpm. From the measured signal, MMIS has shown a signal-to-noise ratioof 44.0 dB, a nonlinearity of 0.59%, a frequency-normalized sensitivity of 0.256±0.010V/T·Hz and a drift of 0.27% in the temperature range of -30~ 43°C. Firing test has shownthat the MMIS can be used as a turn-counting sensor for small-caliber ammunition,verifying the shock survivability of the MMIS in a high-g environment.