Normal and malaligned talonavicular fusion alters cadaveric foot pressure and kinematics.

Talonavicular (TN) fusion is a common treatment for TN arthritis or deformity correction. There is incongruous evidence regarding remaining motion at the talocalcaneal and calcaneocuboid joints after TN fusion. Additionally, the effects of a malaligned TN fusion are not well understood and alignment of the fusion may be important for overall foot integrity. This project assessed the kinematic and kinetic effects of neutral and malaligned TN fusions. Ten cadaveric feet were tested on a gait simulator in four conditions: unfused, fused in neutral, fused in varus, and fused in valgus. The fusions were simulated with external fixation hardware. An eight-camera motion analysis system and a 10-segment foot model generated kinematic data, and a pressure mat captured pressure data. Simulated TN fusion was achieved in eight feet. From unfused to fused-neutral, range of motion (ROM) was not eliminated in the adjacent joints, but the positions of the joints changed significantly throughout stance phase. Furthermore, the ROM increased at the tibiotalar joint. Plantar pressure and center of pressure shifted laterally with neutral fusion. The malalignments marginally affected the ROM but changed joint positions throughout stance phase. Pressure patterns were shifted laterally in varus malalignment and medially in valgus malalignment. The residual motion and the altered kinematics at the joints in the triple joint complex after TN fusion may subsequently increase the incidence of arthritis. Clinical significance: This study quantifies the effects of talonavicular fusion and malalignment on the other joints of the triple joint complex.

Ankle fusion and replacement gait similar post-surgery, but still exhibit differences versus controls regardless of footwear.

Persons with ankle osteoarthritis (AOA) often seek surgical intervention to alleviate pain and restore function; however, recent research has yielded no superior choice between the two primary options: fusion and replacement. One factor yet to be considered is the effect of footwear on biomechanical outcomes. Comparisons of AOA biomechanics to a normative population are also sparse. The objectives of this study were to (1) determine how footwear uniquely affected gait in persons with ankle fusion and replacement and (2) provide context for AOA biomechanics via comparisons to a healthy adult sample. Thirty-four persons with AOA performed overground walking trials barefoot and shod before surgical intervention and then received either an ankle fusion (n = 14) or replacement (n = 20). Two and/or three years post-surgery, patients returned for gait analysis. Nineteen controls performed the same gait procedures during a single study visit. Spatiotemporal variables and peak angles, internal moments, powers, and forces were calculated to quantify gait behavior. Overall, the two surgical groups performed similarly to each other but demonstrated marked differences from controls both pre- and post-surgery. No significant differences were detected when examining the effect of footwear. The motion of the midfoot with respect to the hindfoot and forefoot may be instrumental in gait biomechanics following an ankle fusion or replacement and should be considered in future investigations.

Surface structure, optoelectronic properties and charge transport in ZnO nanocrystal/MDMO-PPV multilayer films.

Blends of semiconducting nanocrystals and conjugated polymers continue to attract major research interest because of their potential applications in optoelectronic devices, such as solar cells, photodetectors and light-emitting diodes. In this study we investigate the surface structure, morphological and optoelectronic properties of multilayer films constructed from ZnO nanocrystals (NCs) and poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV). The effects of layer number and ZnO concentration (CZnO) used on the multilayer film properties are investigated. An optimised solvent blend enabled well-controlled layers to be sequentially spin coated and the construction of multilayer films containing six ZnO NC (Z) and MDMO-PPV (M) layers (denoted as (ZM)6). Contact angle data showed a strong dependence on CZnO and indicated distinct differences in the coverage of MDMO-PPV by the ZnO NCs. UV-visible spectroscopy showed that the MDMO-PPV absorption increased linearly with the number of layers in the films and demonstrates highly tuneable light absorption. Photoluminescence spectra showed reversible quenching as well as a surprising red-shift of the MDMO-PPV emission peak. Solar cells were constructed to probe vertical photo-generated charge transport. The measurements showed that (ZM)6 devices prepared using CZnO = 14.0 mg mL-1 had a remarkably high open circuit voltage of ∼800 mV. The device power conversion efficiency was similar to that of a control bilayer device prepared using a much thicker MDMO-PPV layer. The results of this study provide insight into the structure-optoelectronic property relationships of new semiconducting multilayer films which should also apply to other semiconducting NC/polymer combinations.

A three-year prospective comparative gait study between patients with ankle arthrodesis and arthroplasty.

BACKGROUND: End-stage ankle arthritis is a debilitating condition that often requires surgical intervention after failed conservative treatments. Ankle arthrodesis is a common surgical option, especially for younger and highly active patients; however, ankle arthroplasty has become increasingly popular as advancements in implant design improve device longevity. The longitudinal differences in biomechanical outcomes between these surgical treatments remain indistinct, likely due to the challenges associated with objective study of a heterogeneous population. METHODS: Patients scheduled for arthroplasty (n = 27) and arthrodesis (n = 20) were recruited to participate in this three-year prospective study. Postoperative functional outcomes were compared at distinct annual time increments using measures of gait analysis, average daily step count and survey score. FINDINGS: Both surgical groups presented reduced pain, improved survey scores, and increased walking speed at the first-year postoperative session, which were generally consistent across the three-year follow-up. Arthrodesis patients walked with decreased sagittal ankle RoM, increased sagittal hip RoM, increased step length, and increased transient force at heel strike, postoperatively. Arthroplasty patients increased ankle RoM and cadence, with no changes in hip RoM, step length or heel strike transient force. INTERPRETATION: Most postoperative changes were detected at the first-year follow-up session and maintained across the three-year time period. Despite generally favorable outcomes associated with both surgeries, several underlying postoperative biomechanical differences were detected, which may have long-term functional consequences. Furthermore, neither technique was able to completely restore gait biomechanics to the levels of the contralateral unaffected limb, leaving potential for the development of improved surgical and rehabilitative treatments.

Towards substrate engineering of graphene-silicon Schottky diode photodetectors.

Graphene-silicon Schottky diode photodetectors possess beneficial properties such as high responsivities and detectivities, broad spectral wavelength operation and high operating speeds. Various routes and architectures have been employed in the past to fabricate devices. Devices are commonly based on the removal of the silicon-oxide layer on the surface of silicon by wet-etching before deposition of graphene on top of silicon to form the graphene-silicon Schottky junction. In this work, we systematically investigate the influence of the interfacial oxide layer, the fabrication technique employed and the silicon substrate on the light detection capabilities of graphene-silicon Schottky diode photodetectors. The properties of devices are investigated over a broad wavelength range from near-UV to short-/mid-infrared radiation, radiation intensities covering over five orders of magnitude as well as the suitability of devices for high speed operation. Results show that the interfacial layer, depending on the required application, is in fact beneficial to enhance the photodetection properties of such devices. Further, we demonstrate the influence of the silicon substrate on the spectral response and operating speed. Fabricated devices operate over a broad spectral wavelength range from the near-UV to the short-/mid-infrared (thermal) wavelength regime, exhibit high photovoltage responses approaching 106 V W-1 and short rise- and fall-times of tens of nanoseconds.

Coherent diffractive imaging of graphite nanoparticles using a tabletop EUV source.

Structural information of nanostructures plays a key role in synthesis of novel nano-sized materials for promising applications such as high-performance nanoelectronics and nanophotonics. In this study, we apply for the first time the state-of-the-art coherent diffractive imaging method to characterize the structure of graphite nanoparticles. A sample with nanographites on a Si3N4 support was exposed to 30 nm radiation from a tabletop laser-driven high-order harmonic generation extreme ultraviolet (EUV) source. From the measured far-field diffraction pattern, we were able to reconstruct the distribution of the graphite nanoparticles with a spatial resolution of ∼330 nm using the standard iterative phase retrieval algorithms. A closer look at the reconstructed images reveals possible absorption effects of graphite nanoparticles. This experiment demonstrates the first step towards wide-field and high-resolution imaging of nuclear materials using the newly established lab-scale EUV source. Having such a source opens the door to performing investigations of nuclear graphite and other radioactive material in the lab, thus avoiding the need to transport samples to external facilities.

Textured ZnO films from evaporation-triggered aggregation of nanocrystal dispersions and their use in solar cells.

Due to its high electron mobility, good stability and potential for low-temperature synthesis ZnO has received considerable attention for use in solar cells, photodetectors and sensors. Whilst there have been reports involving the formation ZnO films with porous morphologies the majority of those have involved elaborate or time-consuming preparation methods. In this study we investigate a simple new method for preparing textured porous ZnO (tp-ZnO) films. We used colloidal instability triggered by the evaporation of a volatile stabilising ligand during spin-coating of a ZnO nanocrystal (NC) dispersion to deposit crack-free tp-ZnO films. The porosity of the tp-ZnO films was 56% and they could be prepared using amine-based ligands with boiling points less than or equal to 78 °C. To demonstrate the ability to use the tp-ZnO films as electron acceptors they were infiltrated with poly(3-hexylthiophene) (P3HT) and solar cells prepared. The power conversion efficiencies of the tp-ZnO/P3HT devices reached values that were three times higher than a control bilayer ZnO/P3HT device prepared using a sol-gel derived ZnO film. Because our method used a low temperature treatment and ZnO films are used in a wide variety of third-generation solar cells, the new tp-ZnO films introduced here may offer a low cost method for improving the efficiency of other solar cells.

Reducing hole transporter use and increasing perovskite solar cell stability with dual-role polystyrene microgel particles.

Perovskite solar cells (PSCs) are a disruptive technology that continues to attract considerable attention due to their remarkable and sustained power conversion efficiency increase. Improving PSC stability and reducing expensive hole transport material (HTM) usage are two aspects that are gaining increased attention. In a new approach, we investigate the ability of insulating polystyrene microgel particles (MGs) to increase PSC stability and replace the majority of the HTM phase. MGs are sub-micrometre crosslinked polymer particles that swell in a good solvent. The MGs were prepared using a scalable emulsion polymerisation method. Mixed HTM/MG dispersions were subsequently spin-coated onto PSCs and formed composite HTM-MG layers. The HTMs employed were poly(triaryl amine) (PTAA), poly(3-hexylthiophene) (P3HT) and Spiro-MeOTAD (Spiro). The MGs formed mechanically robust composite HTMs with PTAA and P3HT. In contrast, Spiro-MG composites contained micro-cracks due the inability of the relatively small Spiro molecules to interdigitate. The efficiencies for the PSCs containing PTAA-MG and P3HT-MG decreased by only ∼20% compared to control PSCs despite PTAA and P3HT being the minority phases. They occupied only ∼35 vol% of the composite HTMs. An unexpected finding from the study was that the MGs dispersed well within the PTAA matrix. This morphology aided strong quenching of the CH3NH3PbI3-xClx fluorescence. In addition, the open circuit voltages for the PSCs prepared using P3HT-MG increased by ∼170 mV compared to control PSCs. To demonstrate their versatility the MGs were also used to encapsulate P3HT-based PSCs. Solar cell stability data for the latter as well as those for PSCs containing composite HTM-MG were both far superior compared to data measured for a control PSC. Since MGs can reduce conjugated polymer use and increase stability they have good potential as dual-role PSC additives.

CH3NH3PbI3 films prepared by combining 1- and 2-step deposition: how crystal growth conditions affect properties.

Perovskite solar cells continue to attract strong attention because of their unprecedented rate of power conversion efficiency increase. CH3NH3PbI3 (MAPbI3) is the most widely studied perovskite. Typically one-step (1-s) or two-step (2-s) deposition methods are used to prepare MAPbI3 films. Here, we investigate a new MAPbI3 film formation method that combines 1-s and 2-s deposition (termed 1 & 2-s) and uses systematic variation of the stoichiometric mole ratio (x) for the PbI2 + xMAI solutions employed. The PbI2 + xMAI solutions were used to deposit precursor films that were subsequently dipped in MAI solution as a second step to produce the final MAPbI3 films. The morphologies of the 1 & 2-s MAPbI3 films consisted of three crystal types: tree-like microcrystals (≫1 µm), cuboid meso-crystals (∼0.1-1 µm) and nanocrystals (∼50-80 nm). Each crystal type and their proportions were controlled by the value for x. The new 1 & 2-s deposition method produced MAPbI3 films with tuneable optoelectronic properties that were related to those for the conventional 1-s and 2-s films. However, the 1 & 2-s film properties were not simply a combination of those for the 1-s and 2-s films. The 1 & 2-s films showed enhanced light scattering and the photoluminescence spectra displayed a morphologically-dependent red-shift. The unique morphologies for the 1 & 2-s films also strongly influenced PbI2 conversion, power conversion efficiency, hysteresis and recombination. The trends for the performance parameters and hysteresis were compared for devices constructed using spiro-MeOTAD and P3HT and were similar. The 1 & 2-s method should apply to other perovskite formulations and the new insights concerning MAPbI3 crystal growth conditions, morphology and material properties established in this study should also be transferable.

The sensitivity of standard radiographic foot measures to misalignment.

BACKGROUND: The purpose of this study was to identify the effects that X-ray source misalignment has on common measurements made from anterior-poster (AP) and medial-lateral (ML) view foot radiographs. METHODS: A cadaveric foot model was used to obtain ML radiographs with ±25 degree transverse plane misalignment. From these images the calcaneal pitch angle (CPA) and lateral talometatarsal angle (LTMA) were measured. AP images were captured with up to 30 degree sagittal plane misalignment as well as ±15 degree misalignment in the transverse plane at each sagittal angle. From these images the talonavicular coverage angle (TNCA) and talometatarsal angle (TMA) were measured. RESULTS: On the ML images, the CPA was sensitive to transverse plane misalignment from -10 to -25 degrees and from 15 to 25 degrees (P < .005). The LTMA was a more reliable measurement than the CPA and did not demonstrate sensitivity to transverse plane misalignment. On the AP images, the TNCA and TMA were not sensitive to sagittal plane misalignment alone. However, at 0, 10, and 15 degrees sagittal misalignment the TNCA showed sensitivity to transverse plane misalignment (P < .0083). CONCLUSION: Misalignment of an X-ray source can lead to errors in the measurement of foot radiographic parameters, especially the CPA when there is transverse plane misalignment and the TNCA when there is both sagittal and transverse plane misalignment. The LTMA and TMA can be measured reliably, even with significant misalignment present. CLINICAL RELEVANCE: If a researcher or clinician is interested in measuring the CPA or TNCA, the current best practices guidelines for obtaining ML and AP images should be closely followed.

Determination of the quasi-TE mode (in-plane) graphene linear absorption coefficient via integration with silicon-on-insulator racetrack cavity resonators.

We examine the near-IR light-matter interaction for graphene integrated cavity ring resonators based on silicon-on-insulator (SOI) race-track waveguides. Fitting of the cavity resonances from quasi-TE mode transmission spectra reveal the real part of the effective refractive index for graphene, n(eff) = 2.23 ± 0.02 and linear absorption coefficient, α(gTE) = 0.11 ± 0.01dBµm(-1). The evanescent nature of the guided mode coupling to graphene at resonance depends strongly on the height of the graphene above the cavity, which places limits on the cavity length for optical sensing applications.

Second metatarsal osteotomies for metatarsalgia: a robotic cadaveric study of the effect of osteotomy plane and metatarsal shortening on plantar pressure.

Symptom relief of recalcitrant metatarsalgia can be achieved through surgical shortening of the affected metatarsal, thus decreasing plantar pressure. Theoretically an oblique metatarsal osteotomy can be oriented distal to proximal (DP) or proximal to distal (PD). We characterized the relationship between the amount of second metatarsal shortening, osteotomy plane, and plantar pressure. We hypothesized that the PD osteotomy is more effective in reducing metatarsal peak pressure and pressure time integral. We performed eight DP and eight PD second metatarsal osteotomies on eight pairs of cadaveric feet. A custom designed robotic gait simulator (RGS) generated dynamic in vitro simulations of gait. Second metatarsals were incrementally shortened, with three trials for each length. We calculated regression lines for peak pressure and pressure time integral vs. metatarsal shortening. Shortening the second metatarsal using either osteotomy significantly affected the metatarsal peak pressure and pressure time integral (first and third metatarsal increased, p < 0.01 and <0.05; second metatarsal decreased, p < 0.01). Changes in peak pressure (p = 0.0019) and pressure time integral (p = 0.0046) were more sensitive to second metatarsal shortening with the PD osteotomy than the DP osteotomy. The PD osteotomy plane reduces plantar pressure more effectively than the DP osteotomy plane.

Comparison of transfer sites for flexor digitorum longus in a cadaveric adult acquired flatfoot model.

Posterior tibialis tendon (PTT) dysfunction (PTTD) is associated with adult acquired flatfoot deformity. PTTD is commonly treated with a flexor digitorum longus (FDL) tendon transfer (FDLTT) to the navicular (NAV), medial cuneiform (CUN), or distal residuum of the degraded PTT (rPTT). We assessed the kinetic and kinematic outcomes of these three attachment sites using cadaveric gait simulation. Three transfer locations (NAV, CUN, rPTT) were tested on seven prepared flatfoot models using a robotic gait simulator (RGS). The FDLTT procedures were simulated by pulling on the PTT with biomechanically realistic FDL forces (rPTT) or by pulling on the transected FDL tendon after fixation to the navicular or medial cuneiform (NAV and CUN, respectively). Plantar pressure and foot bone motion were quantified. Peak plantar pressure significantly decreased from the flatfoot condition at the first metatarsal (NAV) and hallux (CUN). No difference was found in the medial-lateral center of pressure. Kinematic findings showed minimal differences between flatfoot and FDLTT specimens. The three locations demonstrated only minimal differences from the flatfoot condition, with the NAV and CUN procedures resulting in decreased medial pressures. Functionally, all three surgical procedures performed similarly.

Foot bone kinematics as measured in a cadaveric robotic gait simulator.

The bony motion of the foot during the stance phase of gait is useful to further our understanding of joint function, disease etiology, injury prevention and surgical intervention. In this study, we used a 10-segment in vitro foot model with anatomical coordinate systems and a robotic gait simulator (RGS) to measure the kinematics of the tibia, talus, calcaneus, cuboid, navicular, medial cuneiform, first metatarsal, hallux, third metatarsal, and fifth metatarsal from six cadaveric feet. The RGS accurately reproduced in vivo vertical ground reaction force (5.9% body weight RMS error) and tibia to ground kinematics. The kinematic data from the foot model generally agree with invasive in vivo descriptions of bony motion and provides the most realistic description of bony motion currently available for an in vitro model. These data help to clarify the function of several joints that are difficult to study in vivo; for example, the combined range of motion of the talonavicular, naviculocuneiform, metatarsocuneiform joints provided more sagittal plane mobility (27.4°) than the talotibial joint alone (23.2°). Additionally, the anatomical coordinate systems made it easier to meaningfully determine bone-to-bone motion, describing uniplanar motion as rotation about a single axis rather than about three. The data provided in this study allow for many kinematic interpretations to be made about dynamic foot bone motion, and the methodology presents a means to explore many invasive foot biomechanics questions under near-physiologic conditions.