James C. Weaver

A three-dimensional actuated origami-inspired transformable metamaterial with multiple degrees of freedom

Reconfigurable devices, whose shape can be drastically altered, are central to expandable shelters, deployable space structures, reversible encapsulation systems and medical tools and robots. All these applications require structures whose shape can be actively controlled, both for deployment and to conform to the surrounding environment. While most current reconfigurable designs are application specific, here we present a mechanical metamaterial with tunable shape, volume and stiffness. Our approach exploits a simple modular origami-like design consisting of rigid faces and hinges, which are connected to form a periodic structure consisting of extruded cubes. We show both analytically and experimentally that the transformable metamaterial has three degrees of freedom, which can be actively deformed into numerous specific shapes through embedded actuation. The proposed metamaterial can be used to realize transformable structures with arbitrary architectures, highlighting a robust strategy for the design of reconfigurable devices over a wide range of length scales.

Rational design of reconfigurable prismatic architected materials

Advances in fabrication technologies are enabling the production of architected materials with unprecedented properties. Most such materials are characterized by a fixed geometry, but in the design of some materials it is possible to incorporate internal mechanisms capable of reconfiguring their spatial architecture, and in this way to enable tunable functionality. Inspired by the structural diversity and foldability of the prismatic geometries that can be constructed using the snapology origami technique, here we introduce a robust design strategy based on space-filling tessellations of polyhedra to create three-dimensional reconfigurable materials comprising a periodic assembly of rigid plates and elastic hinges. Guided by numerical analysis and physical prototypes, we systematically explore the mobility of the designed structures and identify a wide range of qualitatively different deformations and internal rearrangements. Given that the underlying principles are scale-independent, our strategy can be applied to the design of the next generation of reconfigurable structures and materials, ranging from metre-scale transformable architectures to nanometre-scale tunable photonic systems.

Grade 3 ischemia on the admission electrocardiogram is associated with severe microvascular injury on cardiac magnetic resonance imaging after ST elevation myocardial infarction

BACKGROUND Grade 3 ischemia during ST elevation myocardial infarction (STEMI) is defined as ST elevation with distortion of the terminal portion of the QRS on electrocardiogram (ECG). The aim of this study was to evaluate the effect of ischemic grade on cardiac magnetic resonance (CMR) imaging infarct characteristics such as infarct size, microvascular obstruction (MVO), intramyocardial hemorrhage (IMH), and myocardial salvage. METHODS Patients with STEMI treated with primary percutaneous coronary intervention had a 12-lead ECG on presentation for analysis of ischemic grade. Gadolinium-enhanced CMR imaging was performed within 7 days to assess infarct size, MVO, IMH, and myocardial salvage. RESULTS Of the 37 patients enrolled in the study, grade 3 ischemia was present in 32%. Those with grade 3 ischemia had higher peak troponin I levels (P = .013), more MVO (P < .001), more IMH (P < .001), larger infarct size (P = .025), and less myocardial salvage (P = .012). Regression analysis found that grade 3 ischemia, infarct size, and peak troponin I level were significantly associated with MVO and IMH. CONCLUSION Grade 3 ischemia on the admission ECG during STEMI is closely associated with the development of severe microvascular damage on CMR imaging.

Dynamic Changes in ST Segment Resolution After Myocardial Infarction and the Association with Microvascular Injury on Cardiac Magnetic Resonance Imaging

BACKGROUND persistent ST elevation after reperfused ST elevation myocardial infarction (STEMI) is believed to be related to poor microvascular perfusion. Cardiac magnetic resonance imaging (CMR) can evaluate microvascular obstruction (MVO) and intramyocardial haemorrhage (IMH) both of which represent severe microvascular damage, have independent prognostic value and are dynamic and evolving over the first 48hours after reperfusion. The aim of this study was to assess whether the development of MVO or IMH has an impact upon ST segment resolution. METHODS patients undergoing primary percutaneous coronary intervention (PCI) for STEMI had serial 12 lead electrocardiograms (ECG) from one hour after PCI until discharge. Persistent single lead maximal residual ST elevation (maxSTE) at each time point was calculated. ST segment deterioration (re-elevation) was calculated on each ECG until discharge compared with one hour post PCI ECG. CMR was performed within seven days post infarct utilising T2 weighted imaging to evaluate culprit artery area at risk (AAR) and IMH. Gadolinium delayed enhancement CMR quantified infarct size and MVO. RESULTS in the 41 patients studied 58% had MVO and 41% had IMH. ST segment deterioration was more common in those with MVO or IMH (p=0.03 and p=0.008 respectively). MaxSTE was higher at each time point after PCI in those with MVO but only became statistically significant after 24hours. The measurement of maxSTE at 48 or 72hours after revascularisation provided the best correlation with the combination of infarct size, AAR, MVO and intramyocardial haemorrhage. CONCLUSION microvascular injury as defined on CMR is associated with dynamic changes and persistence of ST segment elevation in the first 72hours after reperfusion.

Serum Thromboxane B2 Compared to Five Other Platelet Function Tests for the Evaluation of Aspirin Effect in Stable Cardiovascular Disease

BACKGROUND To assess the role of serum thromboxane B(2) (TXB(2)) measurements and the correlation between platelet function studies, in patients with stable cardiovascular disease on aspirin or clopidogrel. METHODS 76 patients (47 on aspirin, 16 clopidogrel, 13 both) underwent assessment of TXB(2), whole blood aggregometry (WBA) after stimulation with (i) arachidonic acid (0.5mM), (ii) ADP (5 microM), (iii) collagen (1 and 5 microg/ml), PFA-100, and Cone and Plate Analyzer. Clopidogrel patients were additionally assessed by the VerifyNow System. RESULTS TXB(2) values ranged between 0.2 and 56.2 ng/ml, with significant separation between those taking aspirin, clopidogrel and controls (0.45 ng/ml vs 6.85 ng/ml vs 12.97 ng/ml, p<0.001). There was moderate correlation between WBA-AA and TXB(2) (r=0.487, p<0.001), PFA-100((R)) (r=0.599, p<0.001), WBA-Col1 (r=0.424, p<0.001), WBA-Col1:5 (r=0.417, p<0.001), and between TXB(2) and PFA-100((R)) (r=0.509, p<0.001). The prevalence of aspirin non-responders for WBA-AA, TXB(2), PFA-100((R)), CPA and Coll1:5 was 13.1%, 8.2%, 14.8%, 9.7% and 16.4% respectively. Individual patients were not consistently classified as aspirin non-responders in all tests. Those with inadequate aspirin response on > or =3 tests had higher TXB(2) levels (mean 1.57+/-1.66, range 0.553-4.45 vs mean 0.45+/-0.18, range 0.23-1.50) (p=0.001). Clopidogrel suppressed TXB(2) (p=0.02), WBA-AA (p<0.001), WBA-Col1 (p=0.012) and WBA-ADP (p<0.001) compared to controls. TXB(2) in patients ingesting fish oil tablets was lower compared to those without (0.4 ng/ml vs 0.52 ng/ml, p=0.004). Obesity was associated with higher TXB(2) values (0.61 vs 0.41, p=0.01). CONCLUSION Serum TXB(2) measurements are a direct measure of the pharmacological effect of aspirin, are easily performed and correlate with other measures of platelet function. Serum TXB(2) measurements could be a useful sole measure of aspirin non-response, and may be even more predictive when performed in tandem with a global measure of platelet function. Aspirin and clopidogrel both suppressed several platelet pathways.

Dimpled elastic sheets: a new class of non-porous negative Poisson’s ratio materials

In this study, we report a novel periodic material with negative Poisson’s ratio (also called auxetic materials) fabricated by denting spherical dimples in an elastic flat sheet. While previously reported auxetic materials are either porous or comprise at least two phases, the material proposed here is non-porous and made of a homogeneous elastic sheet. Importantly, the auxetic behavior is induced by a novel mechanism which exploits the out-of-plane deformation of the spherical dimples. Through a combination of experiments and numerical analyses, we demonstrate the robustness of the proposed concept, paving the way for developing a new class of auxetic materials that significantly expand their design space and possible applications.

Chronic total occlusions — Current techniques and future directions

Chronic total occlusions (CTOs) of coronary arteries represent a common and significant challenge to interventional cardiology. Medical therapy is often regarded as an adequate long term strategy in the management of these lesions with surgical intervention for refractory symptoms. Extensive collateralisation is used as a marker of distal coronary perfusion, further reinforcing non-invasive strategies. This together with relatively low percutaneous success rates outside of specialised centres has meant that rates of percutaneous intervention have remained low. Increasing evidence suggests that CTOs are not a benign entity. Further, symptom control and quality of life improve significantly with successful percutaneous revascularisation. Both factors have reignited interest in percutaneous modalities. The Japanese have been pioneers in the field of CTO intervention although their success rates have been difficult to replicate. New techniques and equipment developed in North America offer an alternative to the Japanese approach. These techniques focus on time, radiation and contrast minimisation. This review will assess the histopathology of CTO and shifting paradigms in CTO treatment strategies.

Responsive materials: A novel design for enhanced machine-augmented composites

The concept of novel responsive materials with a displacement conversion capability was further developed through the design of new machine-augmented composites (MACs). Embedded converter machines and MACs with improved geometry were designed and fabricated by multi-material 3D printing. This technique proved to be very effective in fabricating these novel composites with tuneable elastic moduli of the matrix and the embedded machines and excellent bonding between them. Substantial improvement in the displacement conversion efficiency of the new MACs over the existing ones was demonstrated. Also, the new design trebled the energy absorption of the MACs. Applications in energy absorbers as well as mechanical sensors and actuators are thus envisaged. A further type of MACs with conversion ability, viz. conversion of compressive displacements to torsional ones, was also proposed.

Do Beta 2-Glycoprotein I Disulfide Bonds Protect the Human Retina in the Setting of Age-Related Macular Degeneration?

Age-related macular degeneration (AMD) affects the region of the retina that is responsible for high-resolution vision. It is a major cause of blindness in the aging population. This is the first study that examines the association of redox-modified, cysteine-based, post-translational forms of beta 2-glycoprotein I (β2GPI) in the plasma of individuals with early and late stages of patients with AMD compared with controls. Exploration is also undertaken to assess whether the free thiol form of β2GPI versus the oxidized disulfide form have distinct functional properties in the setting of hydrogen peroxide (H(2)O(2))-mediated cell death of an immortalized human retinal pigment epithelium (RPE) cell line. We demonstrate β2GPI in the retina and choroid of patients with AMD. Free thiol β2GPI is shown to protect the immortalized human RPE cell line against H(2)O(2)-induced cell death, whereas the oxidized form of β2GPI and free thiol bovine serum albumin were not protective. Free thiol β2GPI levels were significantly decreased in patients with late AMD compared with early AMD and healthy controls. Our observations lead to the hypothesis that free thiol β2GPI may protect against oxidative stress injury to RPE cells in the early stages of AMD.

Contrast-enhanced cardiac MRI in myocardial infarction.

I the setting of acute myocardial infarction initial treatment strategies are primarily focused on the re-establishment of coronary epicardial patency. Upon completion of this, non-invasive imaging modalities facilitate assessment of prognosis and tailoring of further therapy. Cardiac magnetic resonance (CMR) has now developed a role in this setting. versus chronic pathology. Uniquely, T2-weighted imaging performed early post-infarction is capable of defining regions of increased interstitial oedema (increased water content) which appear as zones of high signal (bright white) alongside the darker, non-injured (less oedematous) myocardium beyond the area subtended by the infarct vessel (Fig. 1). This allows the detection of acute versus chronic injury. The time course of this hyperintense signal on T2 imagInfarct characteristics such asmicrovascular obstruction (MVO) and the transmural extent of infarction (TME) have been related to prognosis, adverse left ventricular remodelling and functional recovery of themyocardium.Cardiac magnetic resonance is well positioned to provide insight into both the pathophysiology and clinical impact of these processes. The intrinsic tissue contrast and spatial resolution achievedwith CMR, provides a clear definition ofmyocardial tissue structure (fat, myocardium, water content, calcium, iron and surrounding tissue borders). The presence of contrast-enhanced techniques has allowed additional information regarding the presence, extent and time course of myocardial injury to be acquired. The role of CMR in definingmyocardial injury is, andwill continue to be, an area of intense research. ing and its significance in terms of final infarct size require furtherevaluationandare thesubjectof continuedstudyat several centres. The remainder of this review will explore the current knowledge regarding infarct detection using Gd contrast enhancement which has been the subject of numerous studies in acute and chronic infarction over the last decade.