The compression of deformed microgels at an air/water interface.

The compression of deformed hydrogel microspheres (microgels) at air/water interfaces was investigated using a Langmuir-Blodgett trough with simultaneous in situ visualization of the process using a fluorescent microscope. The relationship between the structure of the microgel arrays and the compression behavior was clarified using microgels with different degrees of crosslinking.

Nanoparticle-Based Tough Polymers with Crack-Propagation Resistance.

Although thin elastomer films of polymer nanoparticles are regarded as environmentally friendly materials, the low mechanical strength of the films limits their use in various applications. In the present study, we investigated the fracture resistance of latex films composed of acrylic nanoparticles where a small quantity of a rotaxane crosslinker was introduced. In contrast to conventional nanoparticle-based elastomers, the latex films composed of the rotaxane-crosslinked nanoparticles exhibited unusual crack propagation behavior; the direction of crack propagation changed from a direction parallel to the crack to one perpendicular to the crack, resulting in an increase in tear resistance. These findings will help to broaden the scope of design of new types of tough polymers composed of environmentally friendly polymer nanoparticles.

Single microgel degradation governed by heterogeneous nanostructures.

Although the degradation of colloidal particles is one of the most attractive phenomena in the field of biological and environmental science, the degradation mechanism of single particles remains to be elucidated. In this study, in order to clarify the impact of the structure of a single particle on the oxidative degradation processes, thermoresponsive colloidal particles with chemical cleavage points were synthesized as a model, and their degradation behavior was evaluated using high-speed atomic force microscopy (HS-AFM) as well as conventional scattering techniques. The real-time observation of single-particle degradation revealed that the degradation behavior of microgels is governed by their inhomogeneous nanostructure, which originates from the polymerization method and their hydrophilicity. Our findings can be expected to advance the design of carriers for drug-delivery and the understanding of the formation processes of micro (nano)plastics.

Clarification of Surface Deswelling of Thermoresponsive Microgels by Electrophoresis.

Although many investigations of thermoresponsive microgels have been reported, their surface properties, which are crucial in colloid science, are still not fully understood. In this study, microgels with surface-localized charged groups were synthesized by precipitation polymerization, and their electrophoretic behaviors were analyzed using a modified version of Ohshima's equation to obtain two surface properties of the soft particles: the softness parameter and the surface charge density. This systematic evaluation allows us to discuss the thermoresponsiveness of the overall microgels and their surfaces separately. Furthermore, the validity of the surface properties obtained from electrophoresis was verified by comparing them with the results of seeded emulsion polymerization in the presence of the microgels and the force-indentation curves obtained via high-speed atomic force microscopy (HS-AFM).

Durable gelfoams stabilized by compressible nanocomposite microgels.

Although hydrogel microspheres (microgels) are useful as emulsion stabilizers, typical microgels cannot stabilize foams over a prolonged period of time. Here, we found that compressible nanocomposite microgels with solid nanoparticles can overcome undesired desorption of microgels from the air/water interface of bubbles, and form highly durable, microgel-surrounded foams (gelfoams).

The effects of vertical trunk supportability improvement on one-leg rebound jump efficiency.

The purpose of this study was to examine the effects of vertical trunk supportability improvement on activities. The study participants were 36 people. Trunk function and physical performance were evaluated using the following tests: trunk righting test (TRT), maximal isometric knee extensor strength test, side hop test, triple hop distance test, stabilometry of one-leg standing, and one-leg rebound jump. The measurement was performed three times: pre-trunk training (pre), post-trunk training for 1 month (post), and 2 months after the second measurement (detraining). Details of trunk training: Two sets of 30-s maximal lateral reach exercises on each side, following the four sets of 15-s maximal raising trunk exercises on each side. The results with TRT in post-training were significantly larger than those in pre-and detraining. Similarly, the results with one-leg rebound jump efficiency in post-training were significantly larger than those in pre-and detraining. Our findings indicate that jump efficiency changes in proportion to the change in vertical trunk supportability.

Nanostructures, Thermoresponsiveness, and Assembly Mechanism of Hydrogel Microspheres during Aqueous Free-Radical Precipitation Polymerization.

Although techniques to produce uniformly sized hydrogel microspheres (microgels) by aqueous free-radical precipitation polymerization are well established, the details of the polymerization process remain mysterious. In the present study, the structural evolution and thermoresponsiveness of the developing microgels during the polymerization were evaluated by temperature-controlled high-speed atomic force microscopy. This analysis clarified that the swelling properties of the precursor microgels formed in the early stages of the polymerization are quite low due to the high incorporation of cross-linkers and that non-thermoresponsive deca-nanosized spherical domains are already present in the precursor microgels. Furthermore, we succeeded in tracking the formation of nuclei and their growth process, which has never been fully understood, in aqueous solution by real-time observations. These findings will help us to design functional microgels with the desired nanostructures via precipitation polymerization.

Nanostructure and thermoresponsiveness of poly(N-isopropyl methacrylamide)-based hydrogel microspheres prepared via aqueous free radical precipitation polymerization.

Thermoresponsive hydrogel microspheres (microgels) are smart materials that quickly respond to external stimuli, and their thermoresponsiveness can be tuned by varying the constituent chemical species. Although uniformly sized microgels can be prepared via aqueous free radical precipitation polymerization, the nanostructure of the obtained microgels is complex and remains unclear so far. In the present study, the nanostructure and thermoresponsiveness of poly(N-isopropyl methacrylamide) (pNIPMAm)-based microgels, which have a volume-transition temperature of ∼43 °C, were evaluated mainly using temperature-controllable high-speed atomic force microscopy. These observations, which are characterized by high spatio-temporal resolution, revealed that the pNIPMAm microgels have a peculiar heterogeneous structure, for example a core-shell and non-thermoresponsive nanostructure in the core region, that originates from the precipitation polymerization process. Furthermore, it was found that the adsorption concentration of the microgels on the substrate is one of the keys for controlling their thermoresponsiveness. These findings can be expected to advance the design of new materials such as thermoresponsive nanosheets and stimuli-responsive coatings.

Non-close-packed arrangement of soft elastomer microspheres on solid substrates.

Unlike rigid microparticles, soft and deformable elastomer (rubber) microspheres were found to exhibit a non-close-packed arrangement on solid substrates after the evaporation of water from their dispersions. The microscopic observation revealed that individual microspheres are ordered in regular intervals at the air/water interface of a sessile droplet and remain fixed on the substrate without being affected by the capillary forces during evaporation due to their deformability. Moreover, using the Langmuir-Blodgett method, thin films of non-close-packed structures could be successfully generated over large areas. Our findings may potentially help to control the arranged structures of elastomer microspheres, which can be expected to improve the nano-science and technology for the precise control for e.g. surface patterning.

RNA interference-independent reprogramming of DNA methylation in Arabidopsis.

DNA methylation is important for silencing transposable elements (TEs) in diverse eukaryotes, including plants. In plant genomes, TEs are silenced by methylation of histone H3 lysine 9 (H3K9) and cytosines in both CG and non-CG contexts. The role of RNA interference (RNAi) in establishing TE-specific silent marks has been extensively studied, but the importance of RNAi-independent pathways remains largely unexplored. Here, we directly investigated transgenerational de novo DNA methylation of TEs after the loss of silent marks. Our analyses uncovered potent and precise RNAi-independent pathways for recovering non-CG methylation and H3K9 methylation in most TE genes (that is, coding regions within TEs). Characterization of a subset of TE genes without the recovery revealed the effects of H3K9 demethylation, replacement of histone H2A variants and their interaction with CG methylation, together with feedback from transcription. These chromatin components are conserved among eukaryotes and may contribute to chromatin reprogramming in a conserved manner.

Hydrophobic Monomers Recognize Microenvironments in Hydrogel Microspheres during Free-Radical-Seeded Emulsion Polymerization.

The three-dimensional structure of nanocomposite microgels was precisely determined by cryo-electron micrography. Several nanocomposite microgels that differ with respect to their nanocomposite structure, which were obtained from seeded emulsion polymerization in the presence of microgels, were used as model nanocomposite materials for cryo-electron micrography. The obtained three-dimensional segmentation images of these nanocomposite microgels provide important insights into the interactions between the hydrophobic monomers and the microgels, that is, hydrophobic styrene monomers recognize molecular-scale differences in polarity within the microgels during the emulsion polymerization. This result led to the formation of unprecedented multi-layered nanocomposite microgels, which promise substantial potential in colloidal applications.

Non-Thermoresponsive Decanano-sized Domains in Thermoresponsive Hydrogel Microspheres Revealed by Temperature-Controlled High-Speed Atomic Force Microscopy.

Despite the tremendous efforts devoted to the structural analysis of hydrogel microspheres (microgels), many details of their structures remain unclear. Reported in this study is that thermoresponsive poly(N-isopropyl acrylamide) (pNIPAm)-based microgels exhibit not only the widely accepted core-shell structures, but also inhomogeneous decanano-sized non-thermoresponsive spherical domains within their dense cores, which was revealed by temperature-controlled high-speed atomic force microscopy (TC-HS-AFM). Based on a series of experiments, it is concluded that the non-thermoresponsive domains are characteristic for pNIPAm microgels synthesized by precipitation polymerization, and plausible structures for microgels prepared by other polymerization techniques are proposed.

The concomitant lateral meniscus injury increased the pivot shift in the anterior cruciate ligament-injured knee.

PURPOSE: Concomitant meniscus injuries in the anterior cruciate ligament (ACL) have been suggested to exacerbate rotational laxity. However, the effect is supposed to be so small, if any, that some quantitative pivot-shift measurement is needed. The purpose of this prospective study was to determine the effect of meniscus tear on rotational laxity in ACL-deficient knees by an quantitative measurement. It was hypothesized that a concomitant meniscus tear, especially a lateral one, would induce greater pivot shift. METHODS: Fifty-seven unilateral ACL-injured patients (26 men and 31 women, mean age: 24 ± 10 years) were included. The pivot-shift test was performed prior to ACL reconstruction, while a quantitative evaluation using an electromagnetic system to determine tibial acceleration and a clinical grading according to the IKDC were performed. Meniscus injuries were diagnosed arthroscopically, and concomitant meniscus tear was confirmed in 32 knees. RESULTS: The clinical grade was not different between the ACL-injured knees of patients with and without meniscus tear (n.s.). Tibial acceleration did not show a statistical significant difference (meniscus-injured knees: 1.6 ± 1.1 m/s2 versus meniscus-intact knees: 1.2 ± 0.7 m/s2, n.s.). However, the subgroup analysis demonstrated that there was increased tibial acceleration in ACL-deficient knees with lateral meniscus tear (2.1 ± 1.1 m/s2, n = 13) compared with meniscus-intact knees (p < 0.05), whereas rotational laxity did not increase in the medial meniscus-injured and bilateral-injured knees (1.2 ± 0.9 m/s2, n = 12, n.s. and 1.4 ± 1.1 m/s2, n = 7, n.s., respectively). CONCLUSION: A concomitant meniscus tear, especially a lateral meniscus tear, has a significant impact on rotational laxity in ACL-injured knees. When a large pivot shift is observed in the ACL-injured knee, a concomitant meniscus tear should be suspected and an aggressive treatment would be considered. Meniscus injuries should be inspected carefully when substantial pivot shift is encountered in ACL-injured knees. LEVEL OF EVIDENCE: Diagnostic study, Level III.

Post-cam clunk syndrome after posterior stabilized total knee arthroplasty as a sign of early femoral component loosening.

Soft tissue impingements are well-known complications of total knee arthroplasty. The impingements usually occur between the medial or lateral femoral component and tibial insert, and between the patella and femoral components. We report a rare case of impingement of the soft tissue between the femoral intercondylar fossa and post of the polyethylene insert, which caused pain and walking disability. After the surgery for the arthroscopic removal of the soft tissue, the symptoms disappeared. However, prosthetic loosening of the femur occurred several months after the arthroscopic surgery, requiring revision surgery. We would propose to call this symptom as post-cam clunk syndrome.

Monitoring Thermoresponsive Morphological Changes in Individual Hydrogel Microspheres.

Real-time morphology/structure changes in individual hydrogel microspheres (microgels) were directly visualized at high spatiotemporal resolution using high-speed atomic force microscopy (HS-AFM) under temperature control ranging from room temperature to ∼40 °C. The recorded HS-AFM movies demonstrate that the size and morphology of thermoresponsive poly(N-isopropyl acrylamide)-based microgels change with increasing temperature at the individual microgel level. Specifically, the height of the microgels gradually decreases and domain structures appeared even below the volume phase transition temperature. Moreover, the domain structure is retained, even after the microgels have fully collapsed. The present study thus demonstrates that temperature-controlled HS-AFM is a useful tool for monitoring stimulus-responsiveness of microgels. In the near future, it should furthermore be possible to extend this temperature-controlled HS-AFM to other stimulus-responsive materials, including autonomously oscillating microgels.

The diagnostic reliability of the quantitative pivot-shift evaluation using an electromagnetic measurement system for anterior cruciate ligament deficiency was superior to those of the accelerometer and iPad image analysis.

PURPOSE: Several non-invasive devices have been developed to obtain quantitative assessment of the pivot-shift test in clinical setting using similar but diverse measurement parameters. However, the clinical usability of those measurements has yet to be closely investigated and compared. The purpose of this study was to compare the diagnostic accuracy of three non-invasive measurement devices for the pivot-shift test. METHODS: Thirty patients with unilateral anterior cruciate ligament (ACL) injury were enrolled. The pivot-shift test was performed under general anaesthesia. Three devices, an accelerometer system (KiRA), an image analysis iPad application (iPad), and electromagnetic measurement system (EMS), were used simultaneously to provide two parameters, namely tibial acceleration monitored using KiRA and EMS, and tibial translation recorded using iPad and EMS. Side-to-side differences in each parameter and correlation between the measurements were tested, and a receiver-operating characteristic (ROC) curve analysis was conducted to compare their measurement accuracy. RESULTS: Significant side-to-side differences were successfully detected using any of the measurements (all p < 0.01). KiRA demonstrated moderate correlation with the EMS for tibial acceleration (r = 0.54; p < 0.01), while poor correlation was observed between iPad and the EMS for the translation (r = 0.28; p < 0.01). The ROC curve analysis demonstrated better accuracy for the detection of ACL insufficiency in the EMS than KiRA and iPad for tibial acceleration and translation, respectively. CONCLUSIONS: Although all three measurements were similarly capable of detecting ACL deficiency, the EMS has the advantage of comprehensive evaluation of the pivot-shift test by evaluating both tibial acceleration and translation with higher accuracy than those of KiRA and iPad. It could be suggested that any of those measurement tools might improve the clinical diagnosis of ACL insufficiency. LEVEL OF EVIDENCE: Diagnostic study of consecutive patients with a universally applied gold standard, Level Ib.

Stress distribution is deviated around the aperture of the femoral tunnel in the anatomic anterior cruciate ligament reconstruction.

PURPOSE: Final tunnel location in the anterior cruciate ligament (ACL) reconstruction is unpredictable due to tunnel widening and/or transposition. The mechanical stress around the tunnel aperture seems to be a major factor but is not fully investigated. The purpose of this study was to measure the stress from the ACL graft around the tunnel aperture when the ACL graft tension reaches its peak. METHODS: Six cadaveric knees were used. Single-bundle ACL reconstruction was performed using a hamstrings graft. Both femoral and tibial tunnels were created at the centre of the original ACL footprint. A 7-mm-internal-diameter aluminium cylinder with pressure sensors was placed in the femoral tunnel. Hamstrings graft with a microtension sensor was inserted. After fixation, passive extension-flexion was performed while monitoring the tunnel aperture pressure and the graft tension simultaneously. The pressure on the femoral tunnel aperture when the ACL graft tension reach its peak was compared between four directions. RESULTS: The ACL graft tension peaked (67 ± 49 N) at full extension (-5.8 ± 4.1°). Pressure at the femoral tunnel aperture was different between different directions (p < 0.01). Distal part had significantly larger pressure (1.7 ± 1.3 MPa) than the other directions (p < 0.01). Second largest pressure was carried in the anterior part (0.6 ± 0.5 MPa), followed by proximal and posterior parts (0.4 ± 0.3, 0.2 ± 0.2 MPa respectively). CONCLUSION: The stress distribution at the femoral tunnel aperture is not equal in different directions, while the distal part dominantly bears the stress from the ACL graft. Surgeons should pay close attention to the distal edge of the femoral tunnel which should be inside the anatomic ACL footprint eventually.

Comparison Between Intra- and Extra-articular Tension of the Graft During Fixation in Anterior Cruciate Ligament Reconstruction.

PURPOSE: To evaluate the tension deprivation through the tunnels with and without preconditioning at the time of fixation, and the influences of cyclic loading and pretensioning on graft tension in anatomic single bundle anterior cruciate ligament (ACL) reconstruction using a hamstring tendon. METHODS: Nine fresh-frozen cadaveric knees underwent anatomic ACL reconstruction using hamstring grafts. Each specimen was examined to ensure that there was no severe osteoarthritic change, ligament insufficiency, or torn menisci by manual and arthroscopic evaluation. Applied graft tension was measured at the tibial tunnel outlet using a graft tensor with a load cell. Intra-articular graft tension was evaluated by using an originally developed microforce sensor, which was sutured into the graft. Both tensions were simultaneously measured just after initial tensioning under 3 different conditions: condition 1, just after initial tensioning of 20 N at 20° of knee flexion without preconditioning; condition 2, after the same initial tensioning following 5 rounds of passive cyclic flexion-extension movement; and condition 3, after the same initial tensioning following 5 minutes of static pretensioning of 20 N. RESULTS: The intra-articular tension was 12.7 ± 5.3 N in condition 1, 12.0 ± 4.8 N in condition 2, and 13.5 ± 4.8 N in condition 3. In these 3 conditions, intra-articular graft tension was significantly lower than the applied tension of around 20 N (no pretension: P = .009, cyclic pretension: P = .004, static pretension: P = .008), with no difference among the 3 conditions (P = .82). CONCLUSIONS: The intra-articular graft tension was significantly lower than the applied tension from the outside of the joint, even after cyclic loading and pretensioning. CLINICAL RELEVANCE: It is difficult to evaluate the intra-articular graft tension precisely on the basis of the extra-articular tension at time zero in ACL reconstruction.

Controlled Separation and Release of Organoiodine Compounds Using Poly(2-methoxyethyl acrylate)-Analogue Microspheres.

A selective adsorption/desorption of organoiodine compounds was achieved on poly(2-methoxyethyl acrylate)-analogue microspheres, wherein the side chains in the polymers act as halogen-bonding sites. These results demonstrate that the halogen-bonding sites in the side chains exhibit adequate specific affinity for organoiodine compounds. In addition, the water-swollen pMEA-analogue microspheres (microgels) showed a thermoresponsive swelling/deswelling behavior that permitted a controlled release of the organoiodine compounds upon changing the temperature. Thus, it seems plausible that a variety of problems associated with, e.g., the recovery of rare iodine-containing compounds, such as the marine-derived iodine compounds, the delivery of iodine-containing drugs, or the removal of halogen compounds from wastewater, could be resolved by polymer microspheres that exhibit controlled halogen bonding.