Perforated Technique Research Articles

Influence of MPL Structure Modification on Fuel Cell Oxygen Transport Resistance

Proton exchange membrane fuel cell (PEMFC)) technology is the basis for a promising future automotive powertrain. However, PEMFC cost must be reduced and durability must be improved. The greatest opportunity to reduce cost is to run the fuel cell at high current density while not considerably lowering the cell voltage [1], which requires excellent mass (both oxygen and water) transport in the fuel cell electrode, as well as low ohmic loss. In this work we report the measurement of the resistances to oxygen transport in the fuel cell cathode electrode and the impact of microporous layer (MPL) structure modification on the oxygen transport. The oxygen transport resistance is measured by the limiting current density method [2-4] in a specially designed 5 cm2 cell using a variety of O2 concentrations. The total oxygen transport resistance in a fuel cell cathode sums the resistance from the diffusion media and that from the catalyst layer (CL). The CL resistance includes the Knudsen diffusion resistance and the ionomer permeation resistance: Rtot = RDM + RCL = RDM + RCL,Knud + RCL,ion, where RDM is quantified by varying the cathode gas pressure [2], and RCL,Knud and RCL,ion can be differentiated by varying the temperature [4]. The effect of MPL modification on the oxygen transport resistance has been studied. Straight holes of 20 mm diameter through the MPL, but not through the carbon fiber substrate, were made by a laser perforation technique. The oxygen transport resistances in the cell with the perforated MPL on the cathode were measured and compared to those in the cell with the baseline MPL. The total oxygen transport resistance depended on the water production rate, revealing a dry region and a dry-to-wet transition for both MPLs in response to the oxygen concentration increase. The MPL modification had little influence on the total transport resistance in the dry region, while the perforated MPL significantly reduced the transport resistance in the dry-to-wet transition region, indicating the perforated MPL improved the cathode water management. It is not clear at this moment whether the increased transport resistance under the wet condition occurs in the diffusion medium or in the catalyst layer. The transport resistance in the CL can only be obtained for the dry conditions and the MPL modification shows little influence on the CL resistance. A trend of decreasing CL resistance with increasing temperature was observed. This temperature effect is mainly attributable to the oxygen permeation in CL ionomer, while the Knudsen diffusion in CL secondary pores is only weakly dependent on temperature.

Ornaments from the Magdalenian burial area in El Mirón Cave (Cantabria, northern Spain). Were they grave goods?

El Mirón Cave, located in northern Atlantic Iberia, has produced important evidence of human occupation during the Lower Magdalenian (19–17.5 cal kya). Among the finds dating to this period is that of a disturbed primary burial of an adult woman. The excavation of the small area around the burial yielded a considerable number of ornamental items (mainly shell beads), but the actual association of any of them with the interment is problematic. The results of our study of the perforated marine shells and mammal teeth suggest that the ornamental objects were not grave goods, but rather were simply artifacts present in the occupation layers in this part of the cave. The materials used to make ornaments were gathered by collecting shells along the Late Glacial shore and by hunting ungulates. The perforation techniques used were similar to those found at contemporary sites in the Franco-Cantabrian region and the appearance of various elements from the manufacturing operatory chain indicates that some of the ornaments were made at the site. It was also possible to determine that some of the shells were used—probably suspended or attached to other objects. From a functional standpoint, the ornaments probably played not only an aesthetic role, but also a symbolic one, facilitating communication and exchanges among human groups.

Mo1519 The Efficacy of the Novel Tissue Grasper-Clips Technique for Large Sigmoid Colon Perforations in Experimental Simulation Model

Sigmoid colon perforations are difficult to handle because of excess mobility. Therefore, the aim of study was to evaluate the efficacy of the twin grasper-clips technique for large sigmoid colon perforations.

Experimental Subarachnoid Hemorrhage in Rats: Comparison of Two Endovascular Perforation Techniques with Respect to Success Rate, Confounding Pathologies and Early Hippocampal Tissue Lesion Pattern

Recently aside from the “classic” endovascular monofilament perforation technique to induce experimental subarachnoid hemorrhage (SAH) a modification using a tungsten wire advanced through a guide tube has been described. We aim to assess both techniques for their success rate (induction of SAH without confounding pathologies) as primary endpoint. Further, the early tissue lesion pattern as evidence for early brain injury will be analyzed as secondary endpoint. Sprague Dawley rats (n=39) were randomly assigned to receive either Sham surgery (n=4), SAH using the “classic” technique (n=18) or using a modified technique (n=17). Course of intracranial pressure (ICP) and regional cerebral blood flow (rCBF) was analyzed; subsequent pathologies were documented either 6 or 24 h after SAH. Hippocampal tissue samples were analyzed via immunohistochemistry and western blotting. SAH-induction, regardless of confounding pathologies, was independent from type of technique (p=0.679). There was no significant difference concerning case fatality rate (classic: 40%; modified: 20%; p=0.213). Successful induction of SAH without collateral ICH or SDH was possible in 40% with the classic and in 86.7% with the modified technique (p=0.008). Peak ICP levels differed significantly between the two groups (classic: 94 +/- 23 mmHg; modified: 68 +/- 19 mmHg; p=0.003). Evidence of early cellular stress response and activation of apoptotic pathways 6 h after SAH was demonstrated. The extent of stress response is not dependent on type of technique. Both tested techniques successfully produce SAH including activation of an early stress response and apoptotic pathways in the hippocampal tissue. However, the induction of SAH with less confounding pathologies was more frequently achieved with the modified tungsten wire technique.

Technology Focus: Hydraulic Fracturing (March 2015)

Technology Focus Hydraulic fracturing is a necessary enabler to exploit oil and gas from moderate and tight reservoirs. Numerous novel technologies and state-of-the-art procedures have been applied recently. These include drilling technologies, completions assemblies, stimulation fluids, fracturing proppant, and pumping sequences. The goal of these approaches is to improve the efficiency of hydraulic fracturing, increase reservoir contact with the wellbore, expedite cleanup, and enhance well productivity. Among the tools and techniques being used to exploit hydrocarbons efficiently are real-time geomechanics to avoid wellbore instability, multistage openhole or plug-and-perforate (PAP) completions to induce multiple independent fractures, high-strength proppants to overcome fluid damage and sustain conductivity during the depletion stages as stresses rapidly increase, clean fluids to ensure permeability stays high and fractures clean up quickly during production while enabling proppant transport and fracture propagation, and pump-stage pulsing to induce open channels to enhance fracture conductivity further. The widely used resin-coated proppants that prevent proppant flowback during production but contribute to lower conductivity are being replaced by irregularly shaped proppants with grains that bond to one another, thereby preventing proppant movement while providing high conductivity. Initiating and propagating independent hydraulic fractures is challenging in an openhole completion because fractures tend to cross zonal-isolation boundaries, particularly during acid fracturing. Swellable-packer assemblies, which are much longer than conventional mechanical packers and can assume the shape of the hole, have addressed this challenge somewhat successfully. Swellable packers compress the rock at a much lower pressure than mechanical packers, thereby eliminating rock cracking and the creation of unintentional fractures. Completing and stimulating wells with PAP technology has gathered attention because zonal-isolation problems are readily solved and multiple independent fractures are generated easily. The challenge is to know and accurately perforate the sweet spots and drill out the plugs efficiently after the treatment. To stimulate long intervals with high heterogeneity and variations in reservoir properties, fluid additives such as chemical and fiber diverters are being improved continuously to achieve near-equal distribution of acid throughout the stimulated interval. The challenge of breaking down very tight and high-stress formations without reaching tubing pressure limitations and compromising integrity remains, and several processes—including higher completion grading, the use of chemicals and progressive propellant pretreatments, and enhanced perforation techniques—are being investigated. Improvement in well-stimulation and hydraulic-fracturing processes is dynamic. The USD-30-billion industry contributes to a giant share of the total world energy market. It is truly a great sign and encouragement to see that the industry has the talents needed to optimize the technology. JPT Recommended additional reading at OnePetro: www.onepetro.org. SPE 170743 Minimizing Overflush Volumes at the End of Fracture- Stimulation Stages—An Eagle Ford Case Study by Wadhah Al-Tailji, StrataGen, et al. OTC 24975 Numerical Analysis on the Interaction Between Two Zipper Frac Wells Using the Continuum Damage Method by Xinpu Shen, Halliburton SPE 163975 Evolving Khuff Formation Gas-Well Completions in Saudi Arabia: Technology as a Function of Reservoir Characteristics Improves Production by Zillur Rahim, Saudi Aramco, et al. IPTC 16580 Rock Mechanical Properties of Shale Gas Reservoirs and Their Influences on Hydraulic Fractures by Qinghui Li, China University of Petroleum, Beijing, et al.

Investigation of the effect of silymarin on the liver in experimental sepsis

ABSTRACT The aim of the study is to investigate the possible protective effect of silymarin (extract of Silybum marianum) on the liver of septic rats was at early stage of sepsis. Polymicrobial sepsis was induced by the cecal ligation and perforation (CLP) technique. Sepsis and sepsis + silymarin treated groups received vehicle or silymarin (50 mg/kg, orally). The rats were decapitated 6 h after the CLP procedure. Protein, glutathione, lipid peroxidation levels, tissue factor activity and some enzyme activities were determined and polyacrylamid gel electrophoresis was carried on liver samples. TNF-a, IL-1b and IL-6 were determined in blood samples. Glutathione levels significantly increased and tissue factor activity significantly decreased in both sepsis and sepsis+silymarin treated groups when compared with control. Superoxide dismutase activity significantly decreased in sepsis+silymarin treated group when compared control and sepsis groups. No significant difference was found in electrophoresis protein bands. Blood proinflammatory cytokine levels were significantly decreased in silymarin treated sepsis group when compared with sepsis group. The effect of silymarin was not apparent since oxidative damage was not obvious in liver consequently it can be suggested that some protective mechanisms related with glutathione in liver may be involved in early stage sepsis. Key Words: Sepsis, Silymarin, Liver, Tissue factor, Oxidative stress

Oil well perforation technology: Status and prospects

Abstract Perforation is a key link in well completion. To meet the development requirements of different types of oil and gas fields, after over ten years of research and development, a series of perforation methods and matching processes have been established, such as deep penetration shaped perforation, composite perforation, directional perforation etc, which on the one hand improve the result and efficiency of perforation completion and stimulation, on the other hand prolong the service life of reservoir by protecting the reservoir. Meanwhile, the optimization of perforation design and the improvement of perforation check method further enhance the safety and success rate of perforation, and make the perforation test process and field application more standardized. For unconventional tight oil and gas reservoirs, deep−ultra-deep reservoirs, thin and poor reservoirs, reservoirs with edge or bottom water, staged fracturing of horizontal wells, and re-perforating of old wells, perforation techniques such as 3D perforation, ultra-deep penetration perforation, and high temperature high pressure perforation, and supplement perforation etc should be studied according to the features of the specific oil and gas reservoir and well.

Blood-brain barrier permeability change and regulation mechanism after subarachnoid hemorrhage.

We aimed to investigate the blood brain barrier (BBB) change caused by subarachnoid hemorrhage (SAH) and to explore the molecular mechanisms of acute brain injury after SAH. The SD rat model of SAH was firstly established by endovascular filament perforation technique. The changes of regional cerebral blood flow (rCBF), BBB permeability and ultrastructure of brain tissue at different time points after SAH were respectively observed by Doppler flowmetry, evans blue extravasation and transmission electron microscopy. Meanwhile, the expression changes of Claudin-5, Occludin, Zo-1 and Caveolin-1 were detected by immunohistochemistry and Western blot. Furthermore, the expressions of Akt, P-Akt and Foxo1A were also measured by Western blot. The change of BBB permeability showed two peaks at 3 and 72 h after SAH, corresponding to the change of rCBF. The BBB tight junction opening can be observed after SAH, and the largest opening was occurred at 3 h and 72 h. There was no significant change in Caveolin-1, Claudin-5 and Akt expressions after SAH (P > 0.05), while Zo-1 and Occludin were significantly down-regulated (P < 0.05). The expression of P-Akt was obviously reduced at 30 min and then increased at 1 and 24 h, while Foxo1A was up-regulated at 1 and 24 h after SAH (P < 0.05). Down-regulated Zo-1 and Occludin, as well as Akt/FOXO signaling pathway may be involved in the regulation of tight junction opening and the BBB permeability in the early stage after SAH.

Myringoplasty using rotation flap of canal skin for total tympanic membrane perforation

To evaluate the efficacy of a novel technique of using rotation flap of canal skin in patients with total or subtotal tympanic membrane (TM) perforation with no anterior residual tympanic membrane. A retrospective study of 50 patients with total or subtotal perforation repaired with rotation flap of canal skin. Clinical and audiometric data were recorded. The overall perforation closure rate was 96%. A statistically significant shortened healing time was observed. The rotation flap of canal skin could be an effective and safe technique for perforations with no anterior residual TM.

Hydraulic Fracture Initiation and Propagation from Wellbore with Oriented Perforation

Considering the influence of casing, analytical solutions for stress distribution around a cased wellbore are derived, based on which a prediction model for hydraulic fracture initiation with the oriented perforation technique (OPT) is established. Taking well J2 of Z5 oilfield for an example, the predicted initiation pressure with the OPT of our model is about 4.2 MPa higher than the existing model, which neglects the influence of casing. In comparison with the results of laboratory fracturing experiments with OPT on a 400 × 400 × 400 mm3 rock sample for a cased well with the deviation of 45°, the fracture initiation pressure of our model has an error of 3.2 %, while the error of the existing model is 6.6 %; when the well azimuth angle is 0° and the perforation angle is 45°, the prediction error of the fracture initiation pressure of the existing model and our model are 3.4 and 7.7 %, respectively. The study verifies that our model is more applicable for hydraulic fracturing prediction of wells with OPT completion; while the existing model is more suitable for hydraulic fracturing with conventional perforation completion.

A comparison of hearing results following stapedotomy under local versus general anesthesia

Advances in operative technique, instrumentation, and prosthesis design in otosclerosis surgery continue since Shea performed the first successful surgery. This is the first analysis to specifically compare post-operative hearing outcomes following stapedotomy surgery performed under local versus general anesthesia. Hearing outcomes were further stratified by comparing conventional perforator and Er:YAG laser ablation perforation techniques. Pre- and post-operative audiograms were retrospectively analyzed together with the method of anesthesia and the perforation technique for all patients with otosclerosis who underwent stapedotomy between 1998 and 2007. Pre-operative individual standard audiometry frequency thresholds (IFTs), air (AC) and bone conduction pure tone averages (PTA), and air bone gaps (ABG) were compared against post-operative results. Differences between pre- and post-operative PTAs and ABGs were compared between patients who received stapedotomy under local versus general anesthesia, as well as for patients who underwent conventional versus Er:YAG laser ablation perforations. Eighty-six patients were identified of which 24 % (n = 21) received local and 76 % (n = 65) received general anesthesia. Post-operative audiograms were available for 84 and 48 patients, respectively. Significant improvements were seen across all groups for standard 4-frequency AC-PTA and ABG and for IFTs up to 3 kHz. No significant difference was seen for IFTs between 4 and 6 kHz. A significant decline in post-operative hearing thresholds was seen at 8 kHz. Significant improvements in PTA and ABG were seen for all groups. There was a trend toward general compared to local anesthesia post-operative hearing results furthermore in combination with conventional perforation technique then with laser technique.

Hydraulic fracturing experiments of highly deviated well with oriented perforation technique

Abstract. In order to investigate the effect of different perforation angles (the angle between the perforation direction and the maximum horizontal principal stress) on the fracture initiation and propagation during hydraulic fracturing of highly deviated well in oil & gas saturated formation, laboratory experiments of the hydraulic fracturing had been carried out on the basis of non-dimensional similar criteria by using 400^3 mm 3 cement cubes. A plane fracture can be produced when the perforations are placed in the direction of the maximum horizontal principal stress. When the perforation angle is 45°, the fractures firstly initiate from the perforations at the upper side of the wellbore, and then turn to the maximum horizontal principal stress direction. When the well deviation angle and perforation angle are both between 45° and 90°, the fractures hardly initiate from the perforations at the lower side of the wellbore. Well azimuth (the angle between the wellbore axis and the maximum horizontal principal stress) has a little influence on the fracture geometries; however it mainly increases the fracture roughness, fracture continuity and the number of secondary fractures, and also increases the fracture initiation and propagation pressure. Oriented perforating technology should be applied in highly deviated well to obtain a single plane fracture. If the well deviation angle is smaller, the fractures may link up.

Novel strategies for effective transdermal drug delivery: a review.

Skin is the largest and easily accessible organ of the body and therefore can be extensively used as a prominent route of delivery for local and systemic effects. Though it presents a multifunctional barrier between body and surrounding particles, there are chances to deliver therapeutic nanocarrier, particularly in diseased skin. Both for dermal and transdermal drug delivery, the horny layer, i.e., the uppermost layer of the skin serve as the most resistant layer to be crossed and for this purpose, different perforation techniques are used that relatively widen the skin opening and allow the passage of drug (≤ 10 mg) and micromolecules, but this amateur disruption of the skin can be avoided in order to preserve this barrier against cutaneous microbiota by using deformable nanocarriers. In this review, we discuss the nanosized aggregates and microneedle technology for the advanced delivery of vaccines, protein, peptides, nucleic acid, and hormone across the skin.

Are bovine pericardium underlay xenograft and butterfly inlay autograft efficient for transcanal tympanoplasty?

To evaluate the success rate and the surgical procedure of two different transcanal myringoplasty techniques using the Tutopatch(®) (Tutogen Medical, Inc., Alachua, FL, USA), a xenograft produced from bovine pericardium or the butterfly, an inlay tragal cartilage autograft. This is a retrospective study. We studied all cases of transcanal myringoplasty with Tutopatch and butterfly, performed by the same surgeon between April 2005 and May 2013. Perforations were secondary to chronic otitis media without cholesteatoma, perforation post ventilation tube or trauma. They were not exceeding one-third of the tympanic membrane surface for the Tutopatch and one quarter for the butterfly. We evaluated the anatomical success rate, complications and postoperative hearing results in both techniques. A total of 106 myringoplasties were performed: 66 with Tutopatch and 40 with butterfly with a mean follow-up of 16.5 and 5.2 months, respectively. Successful closure rates of Tutopatch and butterfly were 75.8% (P < 0.0001) and 85.0% (P < 0.0001), respectively. Myringitis controlled with topical antibiotics treatment occurred in 8 (12.1%) and 5 (12.5%) cases. Eighty percent of patients with Tutopatch had a mean residual air-bone gap within 10 dB, compared to 85.0% in patients with butterfly. When anatomically feasible, a transcanal approach myringoplasty with a Tutopatch(®) graft or butterfly appears to provide good anatomical and functional results. We show that both techniques provide good anatomical and functional results. The butterfly has the advantage to use an autograft, which is surgically easier because it does not require tympanomeatal flap elevation. We recommend the butterfly technique for non-marginal perforation not exceeding one quarter of the tympanic membrane after excision of the perforation edge and Tutopatch for bigger perforation or when standard autografts are not available. Myringitis is the only described complication without specific incidence.

Effects of insulin on norepinephrine- and acetylcholine-induced membrane currents of pinealocytes from healthy Wistar and type 2 diabetic GK rats

The neurohormone melatonin is synthesized by the pineal gland under the stimulation of norepinephrine (NE). Its synthesis is inhibited by acetylcholine (ACh) and by insulin. Type 2 diabetic Goto Kakizaki (GK) rats have higher insulin and lower melatonin plasma levels than healthy Wistar rats. We investigate membrane potentials and currents of isolated pinealocytes in both rat strains and the influence of NE, ACh and insulin by using the perforated patch whole cell clamp technique. Pinealocyte membranes displayed a high resting Na(+) conductance. Stimulation with NE further increased this Na(+) conductance, which led to a slight depolarization in unclamped cells. The amplitude of the NE-evoked current was similar in both rat strains but the current fraction carried by Na(+) was stronger in GK rats. Stimulation with ACh induced a transient inward current and depolarization. These effects were much more pronounced in the pinealocytes of GK rats. The NE-induced current, the ACh-induced current and the membrane depolarization were reduced by pre-administration of insulin in Wistar pinealocytes. Our results provide the first electrophysiological evidence for the modulation, by insulin, of the effects of NE and ACh in pinealocytes of normal rats. The pinealocytes of type 2 diabetic rats were not responsive to insulin. This might explain the reported correlation between the decreased insulin receptor mRNA transcript levels in GK rat pinealocytes and the lack of effect of insulin on ion channels in their cell membranes.

The perforation technique: A modification to the frontal sinus osteoplastic flap

Methods: Seven consecutive patients who underwent an osteoplastic flap approach to the frontal sinus by two surgeons using the following surgical variation were analyzed. Rather than using a sagittal saw for cuts through the frontal sinus anterior wall, a 1.1 mm wire-passing drill bit was used to methodically perforate the bone and create a form-fitting beveled cut. The overlying periosteum was preserved. The inferior hinge was created by drilling approximately 4-6 holes across the desired hinge point. An osteotome was used to out-fracture the flap. At the conclusion of the frontal sinus work, the flap was replaced back into its form-fitted window without need for fixation. Patients were evaluated for postoperative ecchymosis, pain, numbness, and cosmetic deformity.

Perforation optimization of hydraulic fracturing of oil and gas well

Considering the influences of fluid penetration, casing, excavation processes of wellbore and perforation tunnels, the seepage-deformation finite element model of oil and gas well coupled with perforating technique is established using the tensile strength failure criterion, in which the user-defined subroutine is developed to investigate the dynamic evolvement of the reservoir porosity and permeability. The results show that the increases of perforation angle and decreases of perforation density lead to a higher fracture initiation pressure, while the changes of the perforation diameter and length have no evident influences on the fracture initiation pressure. As for initiation location for the fracture in wellbore, it is on the wellbore face while considering the presence of the casing. By contrast, the fractures firstly initiate on the root of the tunnels without considering casing. Besides, the initial fracture position is also related with the perforation angle. The fracture initiation position is located in the point far away from the wellbore face, when the perforation angle is around <TEX>$30^{\circ}$</TEX>; however, when the perforation angle is increased to <TEX>$45^{\circ}$</TEX>, a plane fracture is initiated from the wellbore face in the maximum horizontal stress direction; no fractures was found around perforation tunnels, when the angel is close to <TEX>$90^{\circ}$</TEX>. The results have been successfully applied in an oilfield, with the error of only 1.1% comparing the fracture initiation pressure simulated with the one from on-site experiment.

The effects of tumor necrosis factor-alpha on systolic and diastolic function in rat ventricular myocytes

The proinflammatory cytokine tumor necrosis factor-alpha (TNF-α) is associated with myocardial dysfunction observed in sepsis and septic shock. There are two fundamental components to this dysfunction. (1) systolic dysfunction; and (2) diastolic dysfunction. The aim of these experiments was to determine if any aspect of whole-heart dysfunction could be explained by alterations to global intracellular calcium ([Ca2+]i), contractility, and [Ca2+]i handling, by TNF-α, at the level of the individual rat myocyte. We took an integrative approach to simultaneously measure [Ca2+]i, contractility and sarcolemmal Ca fluxes using the Ca indicator fluo-3, video edge detection, and the perforated patch technique, respectively. All experiments were performed at 37°C. The effects of 50 ng/mL TNF-α were immediate and sustained. The amplitude of systolic [Ca2+]i was reduced by 31% and systolic shortening by 19%. Diastolic [Ca2+]i, myocyte length and relaxation rate were not affected, nor were the activity of the [Ca2+]i removal mechanisms. The reduction in systolic [Ca2+]i was associated with a 14% reduction in sarcoplasmic reticulum (SR) content and a 11% decrease in peak L-type Ca current (ICa-L). Ca influx was decreased by 7% associated with a more rapid ICa-L inactivation. These data show that at the level of the myocyte, TNF-α reduces SR Ca which underlies a reduction in systolic [Ca2+]i and thence shortening. Although these findings correlate well with aspects of systolic myocardial dysfunction seen in sepsis, in this model, acutely, TNF-α does not appear to provide a cellular mechanism for sepsis-related diastolic myocardial dysfunction.

Investigation of Water Transport in Perforated Gas Diffusion Layer by Neutron Radiography

The influence of gas diffusion layer (GDL) modifications by laser perforation technique on fuel cell water management is investigated in this study. The liquid water distribution in membrane-electrode-assembly (MEA) and water breakthrough in GDL are visualized using high resolution neutron radiography. The perforated GDL reduces water transport resistance, enhances water breakthrough in GDL, and promotes uniform water distribution in MEA. The observed effects account for the improved fuel cell performance caused by the perforated GDL.

The button graft technique for perforations affecting less than 25% of the tympanic membrane: a non‐randomised comparison of a new modification to cartilage tympanoplasty with underlay and overlay grafts

To evaluate a new composite cartilage-perichondrium graft (button graft) for repair of small-sized tympanic membrane perforations and to compare its success rate with that of the underlay and overlay techniques with temporal fascia or tragal perichondrium. Prospective, sequential allocation of surgical technique study. Tertiary care university hospital. One hundred 95 patients aged 14-42 years with central, uncomplicated tympanic membrane perforations with completely visualised margins affecting less than 25% of the tympanic membrane, distributed in three groups: 1 (underlay), 2 (overlay) and 3 (button graft). Patients were allocated in sequence to: 1 underlay graft, 2 overlay graft and 3 cartilage tympanoplasty with button graft technique. Patients were operated on under local anaesthesia. Postoperative status of the tympanic membrane, hearing improvement, duration of surgery and incidence of complications at 12 months postoperative. Group 1 (underlay) had 66 patients; group 2 (overlay), 65; and group 3 (cartilage), 66. Success was defined as the complete closure of the tympanic membrane one year after the operation. The success rates were 98.5% (65 of 66), 97% (63 of 65) and 98.5% (65 of 66) cases, and the mean air-bone gap gains were 10.18 (±5.4) dB, 8.5 (+6.5) dB and 9.1 (+5.1) dB for groups 1, 2 and 3, respectively. No bone conduction threshold or speech discrimination score worsening was noted. The mean durations of the operative procedure were 35 ± 8.4 (range 22,63), 42 ± 6.8 (range 33,75) and 23 ± 6.3 (range 15,41) min for groups 1, 2 and 3, respectively (P = 0.02). Tympanic membrane retraction occurred in three cases in underlay group 1, and tympanic membrane cholesteatoma pearls occurred in two cases in overlay group 2. The button graft technique is an effective and fast alternative for the repair of small tympanic membrane perforations if complete visualisation of the margin is possible. The shorter time taken with the button grafts is mainly due to the non-requirement for a skin incision. The results are comparable to those of the underlay and overlay techniques.