Stretchable light-emitting electrochemical cells using an elastomeric emissive material.

Dispersing an ionic transition metal complex into an elastomeric matrix enables the fabrication of intrinsically stretchable light-emitting devices that possess large emission areas (∼175 mm(2)) and tolerate linear strains up to 27% and repetitive cycles of 15% strain. This work demonstrates the suitability of this approach to new applications in conformable lighting that require uniform, diffuse light emission over large areas.

Templated self-assembly of glass microspheres into ordered two-dimensional arrays under dry conditions.

This paper describes a new approach to mesoscale self-assembly in which a stream of nitrogen is used to propel micrometer-scale components toward a template of patterned liquid adhesive drops. This approach combines the use of capillary forces to hold the components in place with dry processing conditions. Eliminating the use of a liquid medium to suspend components is an important goal for mesoscale self-assembly methods because it eliminates the need for special encapsulation to protect electrically functional components. We demonstrate the dry self-assembly approach by assembling 100 microm glass microspheres into a variety of 2D patterns. A study of defects in these arrays relates parameters associated with the template--density of binding sites and volume of liquid adhesive comprising the drops--to the frequency of defects arising from the incorporation of additional microspheres into the array. Optimized template parameters and self-assembly conditions yield 2D arrays with defect rates of approximately 4-5%. We also demonstrate the versatility of this self-assembly method by producing ordered binary arrays of clear and black glass microspheres.

Selectively metallized polymeric substrates by microcontact printing an aluminum(III) porphyrin complex.

We report a simple, low-cost method for the fabrication of copper wires and contacts on a wide range of flexible, rigid, and inert polymeric substrates. This method relies on procedures to oxidize the polymeric substrates to form surface-bound carboxylic acid groups. Patterning of an aluminum porphyrin ink using microcontact printing results in the formation of an aluminum porphyrin monolayer that is covalently anchored to the oxidized polymer surface via an aluminum-carboxylate bond. We characterize this monolayer using ultraviolet-visible absorption spectra, reflection-absorption infrared spectroscopy, and contact angle measurements. Patterned aluminum porphyrin monolayers bind a Pd/Sn colloidal catalyst from solution that subsequently initiates the selective deposition of copper in an electroless plating solution. We demonstrate the fabrication of patterned copper films on a variety of both flexible and rigid polymers with minimum feature sizes of 2 microm over 2 cm(2) substrates. Measurements of electrical resistivity of copper wires fabricated on flexible poly(ethylene naphthalate) (PEN) substrates as a function of the bending radius show no negative impact on electrical performance at bending radii as small as 500 microm. Permanently damaging the PEN substrate by creasing (corresponding to a bending radius of 100 microm) results in only a modest increase in resistivity.

Coordination polymers based on aluminum(III) porphyrins.

Aluminum(III) porphyrin carboxylate complexes have shown an affinity for a sixth nitrogenous ligand. The use of isonicotinic or nicotinic acid, which offers both a carboxylate and a nitrogen donor in the same molecule, resulted in the formation of one-dimensional (1-D) coordination polymers. The complexes and their linear oligomers have been characterized by (1)H NMR spectroscopy and nanoelectrospray ionization spectrometry. X-ray analyses confirmed the formation of the 1-D polymers in the solid state.

Controlling the ON/OFF threading of a terpyridine containing [2]pseudorotaxane ligand via changes in coordination geometry.

A 1,2-bis(pyridinium)ethane type axle containing a terpyridine chelate group, when combined with 24-membered crown ethers, forms [2]pseudorotaxanes, the stability of which can be controlled by coordination of metal ions with different geometries.

The shift in muscle's length-tension relation after exercise attributed to increased series compliance.

Eccentric exercise can produce damage to muscle fibres. Here damage indicators are measured in the medial gastrocnemius muscle of the anaesthetised cat after eccentric contractions on the descending limb of the muscle's length-tension relation, compared with eccentric contractions on the ascending limb and concentric contractions on the descending limb. One damage indicator is a shift of the optimum length for peak active tension, in the direction of longer muscle lengths. The shift has been attributed to an increase in muscle compliance. It is a corollary of a current theory for the mechanism of the damage. With the intention of seeking further support for the theory, in these experiments we test the idea that other damage indicators, specifically the fall in twitch:tetanus ratio and in muscle force are due, in part, to such an increase in compliance. This was tested in an undamaged muscle by insertion of a compliant spring (0.19 mm N(-1)) in series with the muscle. This led to a fall in tetanic tension by 17%, a shift in optimum length of 1.7 mm in the direction of longer muscle lengths and a fall in twitch tetanus ratio by 15%. The fall in tension is postulated to be due to development of non-uniform sarcomere lengths within muscle fibres. It is concluded that after a series of eccentric contractions of a muscle, the fall in force is the result of a number of interdependent factors, not all of which are a direct consequence of the damage process.

Aluminium(III) porphyrins as supramolecular building blocks.

Aluminium(III) porphyrin-carboxylate complexes, including a porphyrin pentamer, have been characterised by NMR spectroscopy, MALDI spectrometry and single crystal X-ray diffraction; these complexes can also be coordinated by a sixth, nitrogenous, ligand to the aluminium(III) centre.

Wire-type ruthenium(II) complexes with terpyridine-containing [2]rotaxanes as ligands: Synthesis, characterization, and photophysical properties.

[2]Rotaxanes based on the 1,2-bis(pyridinium)ethane subset[24]crown-8 ether motif were prepared that contain a terminal terpyridine group for coordination to a transition-metal ion. These rotaxane ligands were utilized in the preparation of a series of heteroleptic [Ru(terpy)(terpy-rotaxane)]2+ complexes. The compounds were characterized by 1D and 2D 1H NMR spectroscopy, X-ray crystallography, and high-resolution electrospray ionization mass spectrometry. The effect of using a rotaxane as a ligand was probed by UV/Vis/NIR absorption and emission spectroscopy of the Ru(II) complexes. In contrast with the parent [Ru(terpy)(2)]2+ complex, at room temperature the examined complexes exhibit a luminescence band in the near infrared region and a relatively long lived triplet metal-to-ligand charge-transfer (3MLCT) excited state, owing to the presence of strong-electron-acceptor pyridinium substituents on one of the two terpy ligands. Visible-light excitation of the Ru-based chromophore in acetonitrile at room temperature causes an electron transfer to the covalently linked 4,4'-bipyridinium unit and the quenching of the MLCT luminescence. The 3MLCT excited state, however, is not quenched at all in rigid matrix at 77 K. The rotaxane structure was found to affect the absorption and luminescence properties of the complexes. In particular, when a crown ether surrounds the cationic axle, the photoinduced electron-transfer process is slowed down by a factor from 2 to 3. Such features, together with the synthetic and structural advantages offered by [Ru(terpy)2]2+-type complexes compared to, for example, [Ru(bpy)3]2+-type compounds, render these rotaxane-metal complexes promising candidates for the construction of photochemical molecular devices with a wire-type structure.

Force matching errors following eccentric exercise.

During eccentric exercise contracting muscles are forcibly lengthened, to act as a brake to control motion of the body. A consequence of eccentric exercise is damage to muscle fibres. It has been reported that following the damage there is disturbance to proprioception, in particular, the senses of force and limb position. Force sense was tested in an isometric force-matching task using the elbow flexor muscles of both arms before and after the muscles in one arm had performed 50 eccentric contractions at a strength of 30% of a maximum voluntary contraction (MVC). The exercise led to an immediate reduction of about 40%, in the force generated during an MVC followed by a slow recovery over the next four days, and to the development of delayed onset muscle soreness (DOMS) lasting about the same time. After the exercise, even though participants believed they were making an accurate match, they made large matching errors, in a direction where the exercised arm developed less force than the unexercised arm. This was true whichever arm was used to generate the reference forces, which were in a range of 5-30% of the reference arm's MVC, with visual feedback of the reference arm's force levels provided to the participant. The errors were correlated with the fall in MVC following the exercise, suggesting that participants were not matching force, but the subjective effort needed to generate the force: the same effort producing less force in a muscle weakened by eccentric exercise. The errors were, however, larger than predicted from the measured reduction in MVC, suggesting that factors other than effort might also be contributing. One factor may be DOMS. To test this idea, force matches were done in the presence of pain, induced in unexercised muscles by injection of hypertonic (5%) saline or by the application of noxious heat to the skin over the muscle. Both procedures led to errors in the same direction as those seen after eccentric exercise.

The influence of fatigue on damage from eccentric contractions in the gastrocnemius muscle of the cat.

Eccentric exercise is unique in that it can lead to muscle damage and soreness. Concentric exercise is not accompanied by evidence of damage. There are reports in the literature that muscle fatigue is a factor determining the amount of damage from eccentric exercise. Our theory for the damage process predicts that susceptibility for damage is independent of fatigue. Experiments were carried out to test this prediction as well as to seek other evidence in support of our theory. Comparisons were made between the effects of eccentric and concentric contractions. The nerve supply to the medial gastrocnemius muscle of the anaesthetized cat was divided into three equal portions in terms of the tension they generated. In the first experiment a muscle portion was fatigued by giving it 200 shortening contractions over 12 mm at a shortening speed of 50 mm s(-1). This led to a mean fall in isometric tension (37 +/- 4%) without a significant shift in the optimum length for peak active tension. Giving the fatigued muscle 10 eccentric contractions, active stretches over 6 mm at 50 mm s(-1), beginning from the muscle's optimum length led to a further fall in tension (11% +/- 7%) and a significant shift in optimum length (3.7 mm +/- 0.6 mm) in the direction of longer muscle lengths. The shift in optimum was taken as an indicator of muscle damage. This shift was not significantly different from that seen after eccentric contractions carried out on an unfatigued muscle. After a series of eccentric or concentric contractions, tension at the end of a ramp shortening of 6 mm at 10 mm s(-1) fell more than isometric tension, and by near equal amounts for the two kinds of contractions. In an unfatigued muscle, if tension was altered by changing the rate of stimulation, the fall in shortening tension was greater than after either concentric or eccentric contractions. These observations were seen to be consistent with predictions of the proposed mechanism for the damage process.

Low-frequency depression of tension in the cat gastrocnemius muscle after eccentric exercise.

Subjecting a muscle to a series of eccentric contractions in which the contracting muscle is lengthened results in a number of changes in its mechanical properties. These include a fall in isometric tension that is particularly pronounced during low-frequency stimulation, a phenomenon known as low-frequency depression (LFD). Reports of LFD have not taken into account the shift in optimum length for active tension generation to longer muscle lengths that takes place after eccentric contractions. Given the length dependence of the stimulation frequency-tension curve, we tested the hypothesis that the change in this relationship after eccentric exercise is due to the shift in optimum length. We measured LFD by recording tension in response to a linearly increasing rate of stimulation of the nerve to medial gastrocnemius of anesthetized cats, over the range 0-100 pulses per second. Tension responses were measured before and after 50 eccentric contractions consisting of 6-mm stretches starting at 3 mm below optimum length and finishing at 3 mm above it. An index of LFD was derived from the tension responses to ramp stimulation. It was found that LFD after the eccentric contractions was partly, but not entirely, due to changes in the muscle's optimum length. An additional factor was the effect of fatigue. These observations led to the conclusion that the muscle length dependence of LFD was reduced by eccentric contractions. All of this means that after eccentric exercise the tension deficit at low rates of muscle activation is likely to be less severe than first thought.

Responses of muscle spindles following a series of eccentric contractions.

To investigate the effects of eccentric exercise on the signalling properties of muscle spindles, experiments were done using the medial gastrocnemius muscle of cats anaesthetised with 40 mg/kg sodium pentobarbitone, i.p. Responses were recorded from single afferent nerve fibres in filaments of dorsal root during slow stretch of the passive muscle and during intrafusal contractions at a range of lengths, before and after a series of eccentric contractions. The sensitivity to slow stretch was measured as the average firing rate between muscle lengths 10.5 and 9.5 mm shorter than the physiological maximum (Lm), during stretch at 1 mm/s over the whole physiological range. The mean sensitivity of both primary and secondary spindle endings increased slightly, but not significantly, after a series of 20-150 eccentric contractions consisting of a 6 mm stretch, at 50 mm/s, to a final length of between Lm -7 mm and Lm, during stimulation of the whole muscle or sometimes of single fusimotor fibres. Discharges were recorded from primary endings during fusimotor stimulation at 100-150 pulses/s, and from secondary endings during static bag intrafusal contractures produced by i.v. injection of 0.2 mg/kg succinyl choline. Spindle responses were recorded, over a range of muscle lengths, in steps covering the whole physiological range. About half of the responses showed a peak in the relation between length and net increase in firing rate, while the remainder either progressively increased or progressively decreased over the physiological range. No large or consistent changes were seen after the eccentric contractions. It is concluded that the intrafusal fibres of muscle spindles are not prone to damage of the kind seen in extrafusal fibres after a series of eccentric contractions.

Host-guest interactions template: the synthesis of a [3]catenane.

Formation of a [3]catenane containing dibenzo-24-crown ether wheels and a large dipyridiniumethane ring is templated by formation of a host-guest adduct between the [3]catenane and the external crown ether.

Force-matching errors after eccentric exercise attributed to muscle soreness.

1. Experiments were performed to test the ability of human subjects to match forces in their elbow flexor muscles following eccentric exercise of one arm and, in a second series, after biceps brachii of one arm had been made sore by injection of hypertonic saline. 2. In the force-matching task, the elbow flexors of one arm, the reference arm, generated 30% of maximum voluntary contraction (MVC) under visual control. Subjects matched that level with their other arm, the indicator arm, without visual feedback. 3. After eccentric exercise of elbow flexors of the indicator arm, subjects felt they had achieved a satisfactory match while indicating forces that were significantly lower, by approximately 5%, than the reference level. Errors were in the opposite direction (i.e. forces were overestimated) when the reference arm was exercised. 4. Errors were reduced when matching forces were expressed as fractions of the sessional MVC rather than the pre-exercise MVC. Residual errors from 24 h postexercise onwards were attributed to muscle soreness from the exercise. 5. In support of this view, a similar pattern of matching errors was observed when an unexercised arm was made sore by injection of hypertonic saline into the biceps. 6. It is concluded that muscle soreness can interfere with a subject's ability to match forces, perhaps as a result of a reduced excitability of motor cortex. It implies that muscle soreness may contribute to the weakness experienced after a period of unaccustomed eccentric exercise.

Tendon organs as monitors of muscle damage from eccentric contractions.

Eccentric contractions, where the active muscle is stretched, can lead to muscle damage. One of the signs of damage is a rise in the whole-muscle passive tension. Here we have asked, how many eccentric contractions are necessary to produce a measurable rise in passive tension and can this be detected by the muscle's tension sensors, the tendon organs? Responses of tendon organs of the medial gastrocnemius muscle of the anaesthetised cat were recorded during and after a series of eccentric contractions. The contractions were arranged so that the length change to which the muscle was subjected lay symmetrically about the optimum length for active tension. Tendon organ responses were measured as a mean rate, calculated over a 1-mm length change during a slow stretch of the muscle. Progressive increases in passive tension and tendon organ response were measured after each of a series of 1-100 eccentric contractions of the whole muscle, bundles of motor units and single motor units. One to two eccentric contractions of a single motor unit were sufficient to produce measurable rises in passive tension and tendon organ response. After a series of eccentric contractions had been completed, passive tension and tendon organ response were seen to continue rising with similar time-courses over the next 50 min. Both tension and afferent response could be reduced by large passive stretches. There was also a large increase in the responses of tendon organs to combined stretch and vibration at 100 Hz after the eccentric contractions. All of this indicates that tendon organs are able to monitor the passive tension changes in the muscle, thought to result from muscle damage produced by the eccentric contractions. The findings are relevant to known changes in proprioception and motor control after eccentric exercise.

Rises in whole muscle passive tension of mammalian muscle after eccentric contractions at different lengths.

This is a report of experiments carried out on the medial gastrocnemius muscle of the anesthetized cat, investigating the effects of eccentric contractions carried out at different muscle lengths on the passive and active length-tension relationships. In one series of experiments, the motor supply to the muscle was divided into three approximately equal parts; in the other, whole muscles were used. Fifty eccentric contractions were carried out over different regions of the active length-tension curve for each partial or whole muscle. Active and passive length-tension curves were measured before and after the eccentric contractions. When eccentric contractions were carried out at longer lengths, there was a larger shift of the optimum length for active tension in the direction of longer muscle lengths and a larger fall in peak isometric tension. Passive tension was higher immediately after the eccentric contractions, and if the muscle was left undisturbed for 40 min, it increased further to higher values, particularly after contractions at longer lengths. A series of 20 passive stretches of the same speed and amplitude and covering the same length range as the active stretches, reduced the passive tension which redeveloped over a subsequent 40-min period. It is hypothesized that there are two factors influencing the level of passive tension in a muscle after a series of eccentric contractions. One is injury contractures in damaged muscle fibers tending to raise passive tension; the other is the presence of disrupted sarcomeres in series with still-functioning sarcomeres tending to reduce it.

Matching different levels of isometric torque in elbow flexor muscles after eccentric exercise.

Human subjects generated a specified level of isometric torque with elbow flexor muscles of one arm, the reference arm, under visual feedback. They were then asked to generate what they perceived to be the same level, with the other arm, the indicator, but with no visual feedback. A number of torque levels, between 2% and 30% of maximum were used in the matching trials. Elbow flexors of one arm were then exercised eccentrically on a dynamometer. Immediately after the exercise, there was a large (40%) drop in maximum voluntary torque, as well as some soreness and swelling 24 h later, indicative of muscle damage. When the torque-matching experiment was repeated after the indicator arm had been exercised, the indicator signalled torque levels significantly below the reference level (P<0.05). When the reference arm was exercised, errors were in the opposite direction. Over the 4 days of testing post-exercise, errors became less as torque levels returned to normal. When errors were expressed in terms of maximum torque post-exercise, they were significantly reduced. This suggested that subjects were using as a matching cue the perceived effort required to generate a given level of torque rather than the level of torque itself. Persisting matching errors, from 24 h onwards after the eccentric contractions, were proposed to include a component attributable to the muscle soreness. Changes in electromyogram recorded after eccentric exercise were consistent with the effort-matching hypothesis. The muscle's torque-angle relationship was used to estimate matching ability in the absence of fatigue. One forearm was placed at various angles and its reference torque was matched by the other, the indicator, always at 90 degrees. Again, matching errors were consistent with an interpretation based on a match of effort rather than torque.