Andrew P. Carlson

Transfer Printing Techniques for Materials Assembly and Micro/Nanodevice Fabrication

Transfer printing represents a set of techniques for deterministic assembly of micro-and nanomaterials into spatially organized, functional arrangements with two and three-dimensional layouts. Such processes provide versatile routes not only to test structures and vehicles for scientific studies but also to high-performance, heterogeneously integrated functional systems, including those in flexible electronics, three-dimensional and/or curvilinear optoelectronics, and bio-integrated sensing and therapeutic devices. This article summarizes recent advances in a variety of transfer printing techniques, ranging from the mechanics and materials aspects that govern their operation to engineering features of their use in systems with varying levels of complexity. A concluding section presents perspectives on opportunities for basic and applied research, and on emerging use of these methods in high throughput, industrial-scale manufacturing.

Microstructured elastomeric surfaces with reversible adhesion and examples of their use in deterministic assembly by transfer printing

Reversible control of adhesion is an important feature of many desired, existing, and potential systems, including climbing robots, medical tapes, and stamps for transfer printing. We present experimental and theoretical studies of pressure modulated adhesion between flat, stiff objects and elastomeric surfaces with sharp features of surface relief in optimized geometries. Here, the strength of nonspecific adhesion can be switched by more than three orders of magnitude, from strong to weak, in a reversible fashion. Implementing these concepts in advanced stamps for transfer printing enables versatile modes for deterministic assembly of solid materials in micro/nanostructured forms. Demonstrations in printed two- and three-dimensional collections of silicon platelets and membranes illustrate some capabilities. An unusual type of transistor that incorporates a printed gate electrode, an air gap dielectric, and an aligned array of single walled carbon nanotubes provides a device example.

Treatment of dural arteriovenous fistula using ethylene vinyl alcohol (onyx) arterial embolization as the primary modality: short-term results.

OBJECT A dural arteriovenous fistula (DAVF) typically involves meningeal feeding arteries and can cause clinical symptoms ranging from tinnitus to rupture of draining cortical or parenchymal veins. Surgical treatment may be technically demanding. Ethylene vinyl alcohol (Onyx, ev3 Neurovascular) has several properties that make it potentially useful as a primary treatment agent for DAVF. Onyx is expected to be a permanent embolic agent. It should have a decreased risk of catheter retention when compared with other permanent embolic materials. METHODS The authors report a series of six patients with symptomatic DAVF who were treated initially with transarterial Onyx embolization and other endovascular techniques. RESULTS Five patients had complete occlusion of their DAVF noted on the follow-up angiogram obtained between 2 and 4 months. One patient had residual filling via a small arterial branch that was stable on follow-up angiography. None of the patients had worsening of neurological function. One case was complicated by a retained catheter fragment. CONCLUSIONS Transarterial Onyx embolization and other endovascular methods can angiographically obliterate DAVF. In some cases, embolization allowed occlusion of multiple arterial feeding arteries from a single arterial injection. Technically, the embolization was optimized when a microcatheter position immediately adjacent to the point(s) of fistulization was achieved.

The continuum of spreading depolarizations in acute cortical lesion development: Examining Leão's legacy.

A modern understanding of how cerebral cortical lesions develop after acute brain injury is based on Aristides Leão’s historic discoveries of spreading depression and asphyxial/anoxic depolarization. Treated as separate entities for decades, we now appreciate that these events define a continuum of spreading mass depolarizations, a concept that is central to understanding their pathologic effects. Within minutes of acute severe ischemia, the onset of persistent depolarization triggers the breakdown of ion homeostasis and development of cytotoxic edema. These persistent changes are diagnosed as diffusion restriction in magnetic resonance imaging and define the ischemic core. In delayed lesion growth, transient spreading depolarizations arise spontaneously in the ischemic penumbra and induce further persistent depolarization and excitotoxic damage, progressively expanding the ischemic core. The causal role of these waves in lesion development has been proven by real-time monitoring of electrophysiology, blood flow, and cytotoxic edema. The spreading depolarization continuum further applies to other models of acute cortical lesions, suggesting that it is a universal principle of cortical lesion development. These pathophysiologic concepts establish a working hypothesis for translation to human disease, where complex patterns of depolarizations are observed in acute brain injury and appear to mediate and signal ongoing secondary damage.

Shear-enhanced adhesiveless transfer printing for use in deterministic materials assembly

This letter describes the physics and application of an approach to transfer printing that utilizes targeted shear loading to modulate stamp adhesion in a controlled and repeatable fashion. Experimental measurements of pull-off forces as functions of shear and stamp dimension reveal key scaling properties and provide a means for comparison to theory and modeling. Examples of printed structures in suspended and multilayer configurations demonstrate some capabilities in micro/nanoscale materials assembly.

Stretchable and compressible thin films of stiff materials on compliant wavy substrates

This letter presents experimental, numerical, and analytical studies of Au thin films on elastomeric substrates of poly(dimethylsiloxane) that are designed with sinusoidal, “wavy” features of surface relief. Such systems can be useful as stretchable conductors in electronic or sensory devices. The maximum film strain is obtained in terms of film and substrate elastic moduli, film thickness, amplitude and wavelength of the wavy profile, and the applied strain. These analytical solutions agree well with both finite element analysis and experimentally measured changes in the sinusoidal profile under small, uniaxial strains. A simple expression for the system stretchability and compressibility is established.

Elastomer Surfaces with Directionally Dependent Adhesion Strength and Their Use in Transfer Printing with Continuous Roll‐to‐Roll Applications

In this paper we present mechanics and materials aspects of elastomeric stamps that have angled features of relief on their surfaces, designed to enable control of adhesion strength by peeling direction, in a way that can be exploited in schemes for deterministic assembly by transfer printing. Detailed mechanics models capture the essential physics of interface adhesion in this system. Experiments with cylindrical stamps that have this design demonstrate their potential for use in a continuous, roller mode of operation.

Recording, analysis, and interpretation of spreading depolarizations in neurointensive care: Review and recommendations of the COSBID research group

Spreading depolarizations (SD) are waves of abrupt, near-complete breakdown of neuronal transmembrane ion gradients, are the largest possible pathophysiologic disruption of viable cerebral gray matter, and are a crucial mechanism of lesion development. Spreading depolarizations are increasingly recorded during multimodal neuromonitoring in neurocritical care as a causal biomarker providing a diagnostic summary measure of metabolic failure and excitotoxic injury. Focal ischemia causes spreading depolarization within minutes. Further spreading depolarizations arise for hours to days due to energy supply-demand mismatch in viable tissue. Spreading depolarizations exacerbate neuronal injury through prolonged ionic breakdown and spreading depolarization-related hypoperfusion (spreading ischemia). Local duration of the depolarization indicates local tissue energy status and risk of injury. Regional electrocorticographic monitoring affords even remote detection of injury because spreading depolarizations propagate widely from ischemic or metabolically stressed zones; characteristic patterns, including temporal clusters of spreading depolarizations and persistent depression of spontaneous cortical activity, can be recognized and quantified. Here, we describe the experimental basis for interpreting these patterns and illustrate their translation to human disease. We further provide consensus recommendations for electrocorticographic methods to record, classify, and score spreading depolarizations and associated spreading depressions. These methods offer distinct advantages over other neuromonitoring modalities and allow for future refinement through less invasive and more automated approaches.

Utility of routine follow-up head CT scanning after mild traumatic brain injury: a systematic review of the literature

Objective To evaluate the efficacy of routine follow-up CT scans of the head after complicated mild traumatic brain injury (TBI). Methods 74 English language studies published from 1999 to February 2011 were reviewed. The papers were found by searching the PubMed database using a combination of keywords according to Cochrane guidelines. Excluding studies with missing or inappropriate data, 1630 patients in 19 studies met the inclusion criteria: complicated mild TBI, defined as a GCS score 13–15 with abnormal initial CT findings and the presence of follow-up CT scans. For these studies, the progression and type of intracranial haemorrhage, time from trauma to first scan, time between first and second scans, whether second scans were obtained routinely or for neurological decline and the number of patients who had a neurosurgical intervention were recorded. Results Routine follow-up CT scans showed hemorrhagic progression in 324 patients (19.9%). Routine follow-up head CT scans did not predict the need for neurosurgical intervention (p=0.10) but a CT scan of the head performed for decline in status did (p=0.00046). For the 56 patients (3.4%) who declined neurologically, findings on the second CT scan were worse in 38 subjects (67%) and unchanged in the rest. Overall, 39 patients (2.4%) underwent neurosurgical intervention. Conclusion Routine follow-up CT scans rarely alter treatment for patients with complicated mild TBI. Follow-up CT scans based on neurological decline alter treatment five times more often than routine follow-up CT scans.

Failure of Cerebral Hemodynamic Selection in General or of Specific Positron Emission Tomography Methodology?: Carotid Occlusion Surgery Study (COSS)

Background and Purpose— The Carotid Occlusion Surgery Study (COSS) was an improvement over the Extracranial–Intracranial Bypass Study, which did not utilize physiological selection. To assess possible reasons for early closure of the COSS trial, we reviewed COSS methods used to identify high-risk patients and compared results with separate quantitative data. Methods— Increased oxygen extraction fraction (OEF) by positron emission tomography is a gold standard for ischemia, but the specific thresholds and equivalency of the semiquantitative OEF ratio utilized in COSS and quantitative OEF are at issue. Results— The semiquantitative hemispheric OEF ratio used in COSS did not identify the same group of patients as did quantitative OEF using a threshold of 50%. Conclusions— The failure of COSS is likely caused by a failure of the semiquantitative, hemispheric OEF ratio method rather than by the selection for bypass based on hemodynamic compromise.Background and Purpose The Carotid Occlusion Surgery Study (COSS) was an improvement over the extracranial-Intracranial (EC-IC) bypass study, which did not utilize physiological selection. To assess possible reasons for the early closure of COSS trial, we reviewed COSS methods used to identify high-risk patients and compared results with separate quantitative data.