A programmable soft chemo-mechanical actuator exploiting a catalyzed photochemical water-oxidation reaction.

We describe a composite hydrogel containing an embedding coupled chemistry for light-sensitized catalytic reactions that enables chemo-mechanical actuation of poly(acrylic acid)-based gels. In these materials, a photosensitizer and catalyst-ruthenium trisbipyridine and iridium dioxide nanoparticles, respectively-are incorporated into the hydrogel where together, with visible light irradiation, they undergo a catalytic water-oxidation reaction that lowers the pH and induces a dissipative/chemically-driven strain change in the gel. To demonstrate the capacity for 3D chemo-mechanical actuation, a layer of non-pH responsive poly(2-hydroxyethyl methacrylate) is added to the photo-active composite gel to create a model bimorph actuator. Triggering and terminating the water-oxidation reaction leads to a programmatic expansion and contraction of the active layer, which induces different modes of biomimetic curling motions in the bimorph actuator in light and dark environments. The efficiency of this system is fundamentally limited by the system-level design, which provides no capacity to sustain a local pH gradient against diffusive mixing. Even so, if the initial pH of the background solution is reestablished either actively or passively between each reaction cycle, it is possible to realize multiple cycles of reversible actuation. We describe a thermodynamic analysis of this system which identifies specific features mediating efficiency losses and conceptual requirements for mesoscopic design rules for optimization of this system and for advancing soft actuation systems in general.

Complex structural dynamics of nanocatalysts revealed in Operando conditions by correlated imaging and spectroscopy probes.

Understanding how heterogeneous catalysts change size, shape and structure during chemical reactions is limited by the paucity of methods for studying catalytic ensembles in working state, that is, in operando conditions. Here by a correlated use of synchrotron X-ray absorption spectroscopy and scanning transmission electron microscopy in operando conditions, we quantitatively describe the complex structural dynamics of supported Pt catalysts exhibited during an exemplary catalytic reaction-ethylene hydrogenation. This work exploits a microfabricated catalytic reactor compatible with both probes. The results demonstrate dynamic transformations of the ensemble of Pt clusters that spans a broad size range throughout changing reaction conditions. This method is generalizable to quantitative operando studies of complex systems using a wide variety of X-ray and electron-based experimental probes.

Synthesis, assembly and applications of semiconductor nanomembranes.

Research in electronic nanomaterials, historically dominated by studies of nanocrystals/fullerenes and nanowires/nanotubes, now incorporates a growing focus on sheets with nanoscale thicknesses, referred to as nanomembranes. Such materials have practical appeal because their two-dimensional geometries facilitate integration into devices, with realistic pathways to manufacturing. Recent advances in synthesis provide access to nanomembranes with extraordinary properties in a variety of configurations, some of which exploit quantum and other size-dependent effects. This progress, together with emerging methods for deterministic assembly, leads to compelling opportunities for research, from basic studies of two-dimensional physics to the development of applications of heterogeneous electronics.

Nanopost plasmonic crystals.

We describe a class of plasmonic crystal that consists of square arrays of nanoposts formed by soft nanoimprint lithography. As sensors, these structure show somewhat higher bulk refractive index sensitivity for aqueous solutions in the visible wavelength range as compared to plasmonic crystals consisting of square arrays of nanowells with similar dimensions, with opposite trends for the case of surface bound layers in air. Three-dimensional finite-difference time-domain simulations quantitatively capture the key features and assist in the interpretation of these and related results.

Coordination-dependent surface atomic contraction in nanocrystals revealed by coherent diffraction.

Surface atoms have fewer interatomic bonds than those in the bulk that they often relax and reconstruct on extended two-dimensional surfaces. Far less is known about the surface structures of nanocrystals. Here, we show that coherent diffraction patterns recorded from individual nanocrystals are very sensitive to the atomic structure of nanocrystal surfaces. Nanocrystals of Au of 3-5 nm in diameter were studied by examining diffraction intensity oscillations around the Bragg peaks. Both results obtained from modelling the experimental data and molecular dynamics simulations strongly suggest inhomogeneous relaxations, involving large out-of-plane bond length contractions for the edge atoms (approximately 0.2 A); a significant contraction (approximately 0.13 A) for {100} surface atoms; and a much smaller contraction (approximately 0.05 A) for atoms in the middle of the {111} facets. These results denote a coordination/facet dependence that markedly differentiates the structural dynamics of nanocrystals from bulk crystalline surfaces.

Effect of baseline or changes in adrenergic activity on clinical outcomes in the beta-blocker evaluation of survival trial.

BACKGROUND: Adrenergic activation is thought to be an important determinant of outcome in subjects with chronic heart failure (CHF), but baseline or serial changes in adrenergic activity have not been previously investigated in a large patient sample treated with a powerful antiadrenergic agent. METHODS AND RESULTS: Systemic venous norepinephrine was measured at baseline, 3 months, and 12 months in the beta-Blocker Evaluation of Survival Trial (BEST), which compared placebo treatment with the beta-blocker/sympatholytic agent bucindolol. Baseline norepinephrine level was associated with a progressive increase in rates of death or death plus CHF hospitalization that was independent of treatment group. On multivariate analysis, baseline norepinephrine was also a highly significant (P<0.001) independent predictor of death. In contrast, the relation of the change in norepinephrine at 3 months to subsequent clinical outcomes was complex and treatment group-dependent. In the placebo-treated group but not in the bucindolol-treated group, marked norepinephrine increase at 3 months was associated with increased subsequent risks of death or death plus CHF hospitalization. In the bucindolol-treated group but not in the placebo-treated group, the 1st quartile of marked norepinephrine reduction was associated with an increased mortality risk. A likelihood-based method indicated that 18% of the bucindolol group but only 1% of the placebo group were at an increased risk for death related to marked reduction in norepinephrine at 3 months. CONCLUSIONS: In BEST, a subset of patients treated with bucindolol had an increased risk of death as the result of sympatholysis, which compromised the efficacy of this third-generation beta-blocker.

Catalytic amplification of the soft lithographic patterning of Si. Nonelectrochemical orthogonal fabrication of photoluminescent porous Si pixel arrays.

Photoluminescent, porous silicon pixel arrays were fabricated via a Pt-promoted wet etching of p-type Si(100) using a 1:1:1 EtOH/HF/H2O2 solution. The pixels were fabricated with micrometer-scale design rules on a silicon substrate that had been modified with an octadecyltrichlorosilane (OTS) monolayer patterned using microcontact printing. The printed OTS layer serves as an orthogonal resist template for the deposition of a Pt(0) complex, which preferentially deposits metal species in areas not covered with OTS. The Pt centers generate a localized oxidative dissolution process that pits the Si in the Pt-coated regions, resulting in the formation of a porous silicon microstructure that luminesces around 580 nm upon illumination with a UV source. Scanning electron microscopy and fluorescence microscopy images of the fabricated porous silicon structures showed that features in the size range of approximately 10-150 microm, and possibly smaller, can be generated by this catalytically amplified soft lithographic patterning method. Importantly, the OTS acts as an etch mask, so that, even with significant hole transport, etching is confined to areas coated with the Pt(0) complex.

A method for filling complex polymeric microfluidic devices and arrays.

This paper describes an improved method for filling microfluidic structures with aqueous solutions. The method, channel outgas technique (COT), is based on a filling procedure carried out at reduced pressures. This procedure is compared with previously reported methods in which microfluidic channels are filled either by using capillary forces or by applying a pressure gradient at one or more empty reservoirs. The technique has proven to be > 90% effective in eliminating the formation of bubbles within microfluidic networks. It can be applied to many devices, including those containing PDMS-terminated channel features, a single channel inlet, and three-dimensional arrays.

Additive fabrication and the mechanisms of nucleation and growth in chemical vapor deposition processes.

In this Account, we present several representative studies of thin-film growth by chemical vapor deposition, with particular emphasis given to elucidating the mechanistic, energetic, and structural aspects of nucleation and growth. These understandings have allowed us to develop new methods to deposit patterned, as opposed to blanket, thin films. We show how such procedures can be exploited to effect the directed assembly (i.e., the additive fabrication) of a device architecture.

Intracellular reduction of selenite into glutathione peroxidase. Evidence for involvement of NADPH and not glutathione as the reductant.

Selenium (Se) in selenite is present in an oxidized state, and must be reduced for it to be incorporated as selenocysteine into selenoenzymes such as glutathione peroxidase (GPx). In vitro, Se, as in selenite, can be reduced utilizing glutathione (GSH) and glutathione reductase (GRed). We determined the effects of decreasing GSH levels, inhibiting GRed activity, and decreasing cellular NADPH on the selenite-dependent rate of GPx synthesis in cultured cells: PC3, CHO, and the E89 glucose-6-phosphate dehydrogenase (G-6-PD)-deficient cell line. A novel statistical analysis method was developed (using Box Cox transformed regression and a bootstrap method) in order to assess the effects of these manipulations singly and in combinations. Buthionine sulfoximine (BSO) was used to decrease GSH levels, 1,3 bis-(2 chloroethyl)-1 -nitrosourea (BCNU) was used to inhibit GRed activity and methylene blue (MB) was used to decrease cellular NADPH levels. This statistical method evaluates the effects of BSO, BCNU, MB and selenite alone and in combinations on GPx activity. Decreasing the GSH level (< 5% of control) did not have an effect on the selenite-dependent rate of GPx synthesis in PC3 or CHO cells, but did have a small inhibitory effect on the rate of GPx synthesis in E89 cells. Inhibiting GRed activity was also associated with either no effect (CHO, E89) or a small effect (PC3) on GPx activity. In contrast, decreasing NADPH levels in cells treated with MB was associated with a large decrease in the selenite-dependent rate of GPx synthesis to 36, 34 and 25% of control in PC3, CHO, and E89 cells, respectively. The effects of BSO plus BCNU were not synergistic in any of the cell lines. The effects of BSO plus MB were synergistic in G-6-PD-deficient E89 cells, but not in PC3 or CHO cells. We therefore conclude that under normal culture conditions, NADPH, and not glutathione, is the primary reductant of Se in selenite to forms that are eventually incorporated into GPx. For cells with abnormal ability to generate NADPH, lowering the GSH levels had a small effect on selenite-dependent GPx synthesis. GRed activity is not required for the selenite-dependent synthesis of GPx.

Counterparalysis for treatment of paralytic scoliosis with botulinum toxin type A.

In this study, botulinum toxin was used to treat paralytic scoliosis. Twelve children with paralytic scoliosis and severe, complicating additional diseases required surgical delay. Although this use of botulinum toxin is experimental, alternative treatments posed greater risks. An institutional review board protocol for nonestablished dosage and indication for treatment was initiated to monitor safety and effect. Treatment was intended to supplement, not replace, other desirable treatment modalities. The effect was to be measured by the return of efficacy of conservative treatment in halting curve progression. Short-term results show that none of the children had worsened scoliosis; all had some reduction in curve measurement (up to >50 degrees).

Contralateral compensation with knee impairment.

Knee motion of four healthy teenagers was unilaterally impaired by means of cast braces. Computerized analysis from video recording of walking was used to study the compensatory effects and to compare them with six patients. Restricted knee flexion caused little change in stance-phase knee motion on the restricted side. The unimpaired knee displayed exaggerated stance phase flexion and phase shifts, which in turn produced pelvic vaulting. The forces on the braces were high. Impairments to extension produced bilateral crouch without loss of flexion extension patterns within the limits of the impairment. Fatigue was more prominent than with blocks to flexion. Circumduction was found to be overrated as a compensation for stiff-leggedness. Lateral shift to the well side, combined with freezing of the well-side stance adduction, was a frequently used effective clearance mechanism. Phasic changes in motion of many body parts may combine to produce low-level pelvic displacement, especially when clinical weakness is present. Shortened stride length is the most sensitive indicator of this phenomenon. Graphs of individual joint motion do not easily convey the important phasic relationships that are fundamental to that motion and to the interpretation of its effects. Stick figures were better for analysis of this aspect of motion analysis, even though they are more subjective.

A simple treatment of genu recurvatum in ataxic and athetoid cerebral palsy.

An inexpensive, simple treatment for ataxic- or athetoid-related genu recurvatum is presented with analysis of the relevant gait mechanics. An exaggerated posterior heel flair is used in combination with a functionally dorsiflexed, below-knee orthosis to overcome terminal swing phase recurvatum at heel strike, and to provide an effective forward knee thrust through the solid ankle link. This combination is very effective in some patients, even when more extensive treatments have failed. It is easily reversible. Computerized gait analysis, used in this report for illustration, is not essential for implementation, nor for patient selection. However, video examinations are useful for adjustment of the treatment geometry.

A computer model of slipped capital femoral epiphysis. Causes of fixation error and chondrolysis.

Penetration of the joint by metal pins can occur when treating slipped capital femoral epiphysis. Predisposing factors are present in the usual surgical methods. These include x-ray detail loss secondary to the pelvic projection and failure to obtain specific x-ray orientation to the axis of the capital epiphysis. One operative strategy to reduce these predispositions is presented. A probable mechanism of how chondrolysis can occur without joint penetration following extra capsular osteotomy is described with a theoretical remedy. Computer disease modeling and treatment simulation are the basis of this study. The computer model, which closely simulates all degrees of the disease, suggests that SCFE deformation is caused by hip extension against anterior hip capsule contracture. The latter is also the proposed cause of chondrolysis following realignment procedures.

High-Performance Activity With Below-Knee Cast Treatment, Part II: Clinical Application and The Weak Link Hypothesis.

High-performance casting methods offer a different approach to treating a variety of ailments. Because this approach has excellent patient acceptance, it can be used when more aggressive treatments are undesirable or refused. Observations made during six years of experience with high-performance casting and orthotic management are divided into clinically related groups. These clinical groupings cross conventional diagnostic boundaries. Success depends upon careful patient selection, which, in turn, requires both a detailed history and the seeking of subtle physical signs. The practical details of high-performance cast application are described for each group. Although specific cases so treated have had spectacular results, many of the clinical groupings remain hypothetical, in recognition of the need for a wider experience over a longer span of time. If a casting technique that leaves the patient fully functional is available, treatment methods for a variety of ailments can be reconsidered. In so treating patients with orthotics and casts over the last six years, the author has made a series of observations that have evolved into a rather simple and unifying theory that may prove useful to the clinician.

High-performance activity with below-knee cast treatment, part I: mechanics and demonstration.

Much of the disability associated with wearing a below-knee cast is a result of the treatment rather than the disease. A simple practice of placing thecasted limb in a shoe with a cushioned heel to tilt the cast so that the knee is ahead of the ankle at mid-stance reduces this disability. High-performance activity, including participation in sports, is possible in most (including bilateral) cases. Despite increased activity, this method reduces the incidence of cast failure. Healing does not appear to suffer and in some instances may be superior. Mechanics are discussed in Part I, including illustrative cases and comparative evaluation. Part Il will deal with methods of cast application as well as treatment groups that include fracture, Achilles rupture, idiopathic and spastic equinus (not excluding th ose with rocker deformity of the foot) , muscular dystrophy, and a newly proposed disease category made up of ailments that the author suspects share a common cause or aggravating aspect. This latter group includes Sever's disease, adolescent (and occasionally adult) Achilles tendinitis, shin splints, painful kneecaps, and flat feet. Methods of cast application differ for each group. Gait mechanics is reviewed to illustrate similarities when comparing function levels achieved by cast treatment with those achieved by orthotic or prosthetic management.

Dry ice freezing as a prelude to surgical amputation.

Emergency amputation in the critically ill is associated with 17 to 25% mortality, and a high rate of postoperative infection. Mortality arid morbidity can be reduced by freezing the diseased tissues with dry ice, and deferring surgery until the patient is rendered stable, and metabolically able to heal. Methods of freezing previously reported are cumbersome to maintain, and prone to complications. This paper presents a safe and simple method of physiologic amputation, with emphasis on those details useful to the institution or practitioner who will only occasionally use it. Three illustrative cases demonstrate the utility of this form of treatment in the presence of anticoagulation, gas gangrene, and extreme debility, rendering the patient unable to heal central and peripheral injury simultaneously. Concomitant K-wire fixation and hip disarticulation preceded by above knee freezing, not previously reported, were used successfully.

Dynamic bracing: elastics for patients with cerebral palsy, muscular dystrophy and myelodysplasia.

Conventional bracing places constraints on the determinants of gait, which in the borderline patient, may derange gait as much or more than the postural deformity being treated. A small number of children with cerebral palsy, spina bifida, and muscular dystrophy were treated with below-knee orthoses (BKO) along with elastic bracing of the remainder of the limb. The elastics were used to augment muscle power in weakness, oppose spastic muscles, supply antagonism to unopposed muscle, and improve function. The key elements in this system include proximal attachment of elastics to the below-knee orthosis resultin in effective knee action independent of foot control; variable 2-joint function of elastics; and emphasis on a BKO-shoe combination, which positions the knee in front of the ankle at midstance. Because a small number of components are employed to produce a variety of actions, an understanding of the mechanics fo gait is needed for the rational application of this method of treatment as well as for the selection of suitable patients.

Genu recurvatum in spastic cerebral palsy. Report on findings by gait analysis.

Using high-speed motion pictures, electromyography, a dynamic piezoelectric force plate, and computer analysis of the data, the gait patterns of fifteen children, four to sixteen years old, with spastic cerebral palsy and genu recurvatum were analyzed to determine the mechanisms producing genu recurvatum and the effect of fixed-ankle below-the-knee orthoses. In all children the recurvatum during stance phase began when the tibia stopped moving forward and disappeared when tibial movement resumed. In six patients (Group I), excessive activity of the calf muscles in response to the increasing dorsiflexion moment about the ankle produced by the foot-floor reaction force arrested the forward motion of the tibia. In six others (Group II), the contraction of the calf muscles was not sufficiently strong to resist the dorsiflexion moment and the tibia moved forward until maximum dorsiflexion had occurred and then stopped. In both instances recurvatum was produced when the femur continued to move forward over the stationary tibia and an extension moment was produced at the knee. In no patient did activity of the knee flexors prevent recurvatum, which was eliminated only by resumption of forward movement of the tibia. This movement of the tibia was produced either by heel-off (Group I) or by sudden unweighting of the limb due to opposite heel-strike (Group II). In Group I, when tibial motion stopped in the first half of stance phase the position of the hip rapidly changed from flexion to extension and there was forward leaning of the trunk, while in Group II the change from hip flexion to extension occurred with backward leaning of the trunk. The fixed-ankle below-the-knee orthosis, by preventing excessive dorsiflexion and plantar flexion, produced more normal moments about all joints, especially the knee. In the three children (Group III) whose recurvatum was permanently corrected by the brace, no explanation for the improvement was evident in these studies.