SUMMARY / RELATED TOPICS

Organic electronics

Organic electronics is a field of materials science concerning the design, synthesis and application of organic small molecules or polymers that show desirable electronic properties such as conductivity. Unlike conventional inorganic conductors and semiconductors, organic electronic materials are constructed from organic small molecules or polymers using synthetic strategies developed in the context of organic and polymer chemistry. One of the promised benefits of organic electronics is their potential low cost compared to traditional inorganic electronics. Attractive properties of polymeric conductors include their electrical conductivity that can be varied by the concentrations of dopants. Relative to metals, they have mechanical flexibility; some have high thermal stability. One class of materials of interest in organic electronics are electrical conductive, i.e. substances that can transmit electrical charges with low resistivity. Traditionally, conductive materials are inorganic. Classical conductive materials are metals such as aluminum as well as many alloys.

The earliest reported organic conductive material, was described by Henry Letheby in 1862. Work on other polymeric organic materials began in earnest in the 1960s, A high conductivity of 1 S/cm was reported in 1963 for a derivative of tetraiodopyrrole. In 1977, it was discovered that polyacetylene can be oxidized with halogens to produce conducting materials from either insulating or semiconducting materials; the 2000 Nobel Prize in Chemistry was awarded to Alan J. Heeger, Alan G. MacDiarmid, Hideki Shirakawa jointly for their work on conductive polymers; these and many other workers identified large families of electrically conducting polymers including polythiophene, polyphenylene sulfide, others. In the 1950s, a second class of electric conductors were discovered based on charge-transfer salts. Early examples were derivatives of polycyclic aromatic compounds. For example, pyrene was shown to form semiconducting charge-transfer complex salts with halogens. In 1972, researchers found metallic conductivity in the charge-transfer complex TTF-TCNQ.

Conductive plastics have undergone development for applications in industry. In 1987, the first organic diode was produced at Eastman Kodak by Ching W. Tang and Steven Van Slyke; the initial characterization of the basic properties of polymer light emitting diodes, demonstrating that the light emission phenomenon was injection electroluminescence and that the frequency response was sufficiently fast to permit video display applications, was reported by Bradley, Friend, et al. in a 1990 Nature paper. Moving from molecular to macromolecular materials solved the problems encountered with the long-term stability of the organic films and enabled high-quality films to be made. Subsequent research developed multilayer polymers and the new field of plastic electronics and organic light-emitting diodes research and device production grew rapidly. Organic conductive materials can be grouped into two main classes: conductive polymers and conductive molecular solids and salts. Semiconducting small molecules include polycyclic aromatic compounds such as rubrene.

Conductive polymers are typically intrinsically conductive or at least semiconductors. They sometimes show mechanical properties comparable to those of conventional organic polymers. Both organic synthesis and advanced dispersion techniques can be used to tune the electrical properties of conductive polymers, unlike typical inorganic conductors; the most well-studied class of conductive polymers include polyacetylene, polypyrrole and their copolymers. Poly and its derivatives are used for electroluminescent semiconducting polymers. Poly are a typical material for use in solar cells and transistors. An OLED consists of a thin film of organic material that emits light under stimulation by an electric current. A typical OLED consists of a cathode, OLED organic material and a conductive layer. André Bernanose was the first person to observe electroluminescence in organic materials, Ching W. Tang, reported fabrication of an OLED device in 1987; the OLED device incorporated a double-layer structure motif consisting of separate hole transporting and electron-transporting layers, with light emission taking place in between the two layers.

Their discovery opened a new era of current OLED device design. OLED organic materials can be divided into two major families: small-molecule-based and polymer-based. Small molecule OLEDs include organometallic chelates and phosphorescent dyes, conjugated dendrimers. Fluorescent dyes can be selected according to the desired range of emission wavelengths. Dr. Kim J. et al. at University of Michigan reported a pure organic light emitting crystal, Br6A, by modifying its halogen bonding, they succeeded in tuning the phosphorescence to different wavelengths including green and red. By modifying the structure of Br6A, scientists are attempting to achieve a next generation organic light emitting diode. Devices based on small molecules are fabricated by thermal evaporation under vacuum. While this method enables the formation of well-controlled homogeneous film. Polymer light-emitting diodes, similar to SM-OLED, emit light under an applied electric current. Polymer-based OLEDs are more efficient than SM-OLEDs requiring a comparatively lower amount of energy to produce the same luminescence.

Common polymers used in PLED

Sagebrush steppe

Sagebrush steppe is a type of shrub-steppe, a plant community characterized by the presence of shrubs, dominated by sagebrush, any of several species in the genus Artemisia. This ecosystem is found in the Intermountain West in the United States; the most common sagebrush species in the sagebrush steppe in most areas is big sagebrush. Others include three-tip low sagebrush. Sagebrush is found alongside many species of grasses. Sagebrush steppe is a diverse habitat, with more than 350 recorded vertebrate species, it is open rangeland for livestock, a recreation area, a source of water in otherwise arid regions. It is key habitat for declining flora and fauna species, such as greater sage-grouse and pygmy rabbit. Sagebrush steppe is a threatened ecosystem in many regions, it was once widespread in the regions that form the Intermountain West, such as the Great Basin and Colorado Plateau. It has become degraded by a number of forces. Steppe has been overgrown with introduced species and has changed to an ecosystem resembling pine and juniper woodland.

This has changed the fire regime of the landscape, increasing fuel loads and increasing the chance of unnaturally severe wildfires. Cheatgrass is an important introduced plant species that increases fire risk in this ecosystem. Other forces leading to these habitat changes include fire overgrazing of livestock. Besides severe fire, consequences of the breakdown of sagebrush steppe include increased erosion of the land and sedimentation in local waterways, decreased water quality, decreased quality of forage available for livestock, degradation of habitat for wildlife and game crabs

Renal sympathetic denervation

Renal sympathetic denervation, is a minimally invasive, endovascular catheter based procedure using radiofrequency ablation or ultrasound ablation aimed at treating resistant hypertension. Nerves in the wall of the renal artery are ablated by applying radiofrequency pulses or ultrasound to the renal arteries; this causes reduction of sympathetic afferent and efferent activity to the kidney and blood pressure can be decreased. Early data from international clinical trials without sham controls was promising - demonstrating large blood pressure reductions in patients with treatment-resistant hypertension. However, in 2014 a prospective, single-blind, sham-controlled clinical trial failed to confirm a beneficial effect on blood pressure. A 2014 consensus statement from The Joint UK Societies did not recommend the use of renal denervation for treatment of resistant hypertension on current evidence. Prior to pharmacological management of hypertension, surgical sympathectomy was a recognized treatment for hypertension.

This was successful in reducing blood pressure but due to its non-selective nature the side effects of the procedure were poorly tolerated. Side effects included orthostatic hypotension, anhydrosis, intestinal disturbances, loss of ejaculation, thoracic duct injuries and atelectasis. Modern antihypertensive pharmacological interventions have improved the control of hypertension, but only 34-66% of people with hypertension in England, USA and Canada have blood pressure at or below target levels. Resistant hypertension is defined as blood pressure above target despite concomitant use of 3 or more anti-hypertensives – one of which should be a diuretic, it has been estimated. Several commercial devices exist; these include Medtronic's Symplicity Renal Denervation System, St. Jude Medical’s EnligHTN™ System, Boston Scientific's Vessix V2™ Renal Denervation System, Covidien’s OneShot™ System, Recor’s Paradise™ System, Terumo's Iberis™ System and Cordis Corporation's RENLANE™ Renal Denervation System.

No renal denervation device has FDA approval. The procedure involves endovascular access via the femoral artery with advancement of a catheter-mounted device into the renal artery; the device uses ultrasound to ablate the renal nerves. Numerous ablations are applied at a different longitudinal and rotational positions to ensure maximal denervation; the procedure does not involve a permanent implant. The most widely-discussed studies to date are the Symplicity HTN-1, HTN-2 and HTN-3 trials, conducted with Medtronic's Symplicity RDN System. Symplicity HTN-1 looked at outcomes in 153 patients. Three-year follow-up data have demonstrated an average blood pressure reduction of -33/-19mm Hg. Symplicity HTN-2 was a randomized, controlled trial that compared 54 control patients with 52 patients who underwent catheter-based renal denervation. Six month follow-up data demonstrated a blood pressure reduction of -32/12mm Hg in the treated group compared with a change of 1/0 mm Hg in the control group. Meta-analyses of renal denervation have yielded conflicting results.

Whilst office systolic blood pressure reductions average around 30 mmHg, reductions observed on ambulatory blood pressure monitoring are much smaller, around 10 mmHg. Explanations offered for this mismatch include renal denervation obliterating the white coat response, thereby disproportionately reducing clinic pressures, or inadvertent bias arising from the unblinded design and lack of sham control procedure in all renal denervation trial designs to date; the most recent study, Symplicity HTN-3, was a prospective, single-blind, sham-controlled trial in which 535 patients with severe resistant hypertension were randomized to undergo renal denervation or a sham procedure. The results showed no statistically significant difference between renal denervation and the sham procedure. Following the publication of Symplicity HTN-3 the Joint UK Societies produced a consensus statement that did not recommend the use of renal denervation for treatment of resistant hypertension in routine clinical practice.

However they advocated further research with better designed randomised studies. The Symplicity HTN-1, HTN-2 and HTN-3 trials have demonstrated acceptable safety profiles for catheter based renal denervation. Patients may experience pain during application of radiofrequency pulses and intraprocedural bradycardia requiring atropine has been reported. Other documented procedure related complications include femoral artery pseudoaneurysm and renal artery dissection. Of particular concern is the theoretical risk of damage to renal arteries during delivery of radiofrequency energy. An animal study using swine showed no damage to the renal arteries at 6 month follow up; this finding is further supported in human studies in the HTN-1 and HTN-2 trial where follow up imaging has not demonstrated renal vascular damage. Other diseases may be associated with an overactive sympathetic drive and therefore, in theory, renal denervation could be of benefit. Congestive heart failure, left ventricular hypertrophy, atrial fibrillation, obstructive sleep apnea, insulin resistance/type 2 diabetes mellitus all have been associated with increased activity of the sympathetic nervous system.

Current clinical trials are examining the effect of renal denervation in these conditions