Barrier Devices Research Articles

Histopathological Observations of a Polylactic Acid‐Based Device Intended for Guided Bone/Tissue Regeneration

Barrier devices have been shown to support alveolar bone and periodontal regeneration, a procedure also known as guided bone/tissue regeneration (GBR/GTR). Popular demand and clinical convenience have raised an interest in bioresorbable barrier devices. Tissue reactions to such bioresorbable devices are, however, generally not well explored. The objective of this study was to evaluate short- and long-term tissue reactions following implantation of a bioresorbable polylactic acid (PLA)-based barrier device using a rat model. Twenty-one young adult male Sprague-Dawley rats were used. The animals were divided into three groups including 15 animals receiving the PLA device and animals serving as sham surgery (five) or nonoperated (one) controls. Using aseptic techniques, the PLA device was surgically implanted in direct contact with the calvarial bone. Animals receiving the PLA device were sacrificed at 3, 5, 7, and 12 months postsurgery to provide longitudinal histopathological observations of tissue and biomaterials reactions. Control animals were sacrificed at 3 months. Animals were maintained without adverse events. Sham surgery and nonoperated control animals showed no signs of new bone formation or resorption, or signs of inflammatory reactions in adjoining soft tissues. In contrast, extensive amounts of residual biomaterial with evidence of foreign body reactions and bone resorption were observed in animals receiving the PLA device over 12 months. The results suggest that the PLA device may induce bone resorbing foreign body reactions. Importantly, the PLA device does not resorb within a 12-month healing interval. These biomaterials properties may influence new bone formation and maintenance when applying the device for GBR/GTR.

SPIN DEPENDENT WIGNER FUNCTION SIMULATIONS OF DILUTED MAGNETIC SEMICONDUCTOR SUPERLATTICES – B FIELD TUNING

Two terminal devices have traditionally provided band-structure based high frequency operation. Third terminal control often involves hybrid design approaches. The presence of diluted magnetic semiconductor layers in device fabrication should permit the magnetic field to function as a pseudothird terminal. This is discussed for single barrier, double barrier and superlattice structures, where control is demonstrated. The limits of high frequency operation are discussed in general terms with application to barrier devices and superlattices containing DMS layers.

Assessment of diffusion coefficient from mucoadhesive barrier devices using artificial neural networks

This study is aimed to elucidate the physicodynamic phenomena governing diffusion coefficient ( D) of the loaded drugs in a female controlled drug delivery system (FcDDS) and to find the most influencing variable on the diffusivity using artificial neural networks (ANN). The release profiles of sodium dodecyl sulphate (SDS), a topical microbicide used as a model drug, from FcDDS were obtained using in vitro apparatus, the Simulant Vaginal System (SVS), under various conditions. The effects of formulation and intrinsic/extrinsic variables on the diffusivity of SDS were assessed using artificial neural networks (ANN). The release profiles of SDS from FcDDS revealed a non-linear relationship between the diffusivity and formulation/physiological variables. Intrinsic variables (vaginal fluid pH, vaginal fluid secretion rate) have a more prominent role in defining the diffusion coefficient of SDS from FcDDS than formulation variables (formulation loading weight and loaded doses in the formulation) or extrinsic variables (inserting position). Among 5 variables, pH of vagina fluids is the most influencing factor in defining the diffusion coefficient (maximum value of 0.95 ± 0.04) of SDS from FcDDS. The external exposure conditions clearly outweighed the effects of the formulation variables on the diffusion coefficient of SDS. A model-based approach can be used to assess the diffusion coefficient of loaded drugs in FcDDS under the given conditions, leading to a parameter-specific prevention strategy against sexually transmitted diseases (STD) with a high degree of confidence.

Simple models for electron and spin transport in barrier–conductor–barrier devices

We use two simple models, a phase accumulation model for quantum well (QW) resonances and a two-current circuit model, to study electron and spin transport in nanoscale systems consisting of barrier–conductor–barrier structures. Such structures include double barrier tunnel junctions, and long chain molecules with weak contacts to two electrodes. The phase accumulation model is applied to QW states in ultrathin films and nanodots sandwiched between two barriers. This model is used to illustrate the difference in the QW confinement effect between thin films and nanodots, and justifies circuit model which describes sequential tunneling. The circuit model for spin transport leads to a generalization of the well-known Julliere’s formula and accounts for the conductivity mismatch. The circuit model is also applied to organic light-emitting diodes and yields a simple formula for the quantum efficiency. The results yield excellent agreement with experiment.

Microbicides and HIV prevention

Currently, there are an estimated 15,000 new infections that occur on a daily basis despite availability of ARVs since 1996. Between 2003 and 2005, for each new person who got treatment for HIV, about 10 people became infected. This underscores the need for effective preventive methods.Male condoms, despite being able to prevent more than 80% of HIV infections when used correctly and consistently, are not acceptable to most male clients.Women in many areas where HIV had reached epidemic proportions are unable to negotiate its use. The female condom has similar limitations, as it also requires the cooperation of the male partner, in addition to being poorly accessible and expensive. Hence, efforts need to be stepped up to find a method which will empower women to take charge of HIV prevention. A microbicide is a substance that can be used to prevent (or at least significantly reduce) the heterosexual transmission of HIV and other sexually transmitted infections, when applied vaginally or rectally.Microbicide agents come in different preparations and/or formulations. The first generation microbicides are gels and creams; whereas subsequent generations include vaginal rings, films, sponges, gels with barrier devices and suppositories, and work by altering the environment of the genital tract to make it unsuitable for the virus to act and survive. Antiretroviral agents, being specific in their mode of action by attacking the HIV, are part of the third generation microbicides. Another possibility is to combine different agents with different mechanisms of action e.g. combining an agent altering the genital tract pH and that inhibiting fusion or entry of the virus to the target cell. Obstetrics & Gynaecology Forum Vol. 17 (3) 2007: pp. 71-73

Evaluation of Nasendoscope Sheaths Used as Protective Barriers

BACKGROUND/OBJECTIVES: Flexible nasendoscopy is an important procedure that's use is ever increasing in ambulatory care settings. However, there are no ENT endoscope reprocessing guidelines other than those put forth by the manufacturers. In the 1990's a sterile barrier sheath protection system between the scope and the patient was developed for use; current technology includes a nasendoscope sheath. Recent guidelines suggest endoscopes employing disposable components (e.g., protective barrier devices or sheaths) can provide an alternative to conventional liquid chemical high-level disinfection/sterilization.

Basic Life Support Ventilation in Mountain Rescue

Cardiopulmonary resuscitation in the mountains usually has to be performed under difficult and hostile circumstances and sometimes for extended periods of time. Therefore, mountain rescuers should have the ability and the appropriate equipment to perform prolonged, efficient, and safe ventilation. Members of the International Commission for Mountain Emergency Medicine (ICAR MEDCOM) discussed the results of a literature review, focusing on the advantages and disadvantages of common ventilation techniques in basic life support and their training methods with specific respect to use in mountain rescue, and recommendations were proposed. Bystanders fear the potential risk of infection and lack the willingness to perform mouth-to-mouth ventilation, though the risk of infection is low. Mouth-to-mouth ventilation remains the standard technique for bystander ventilation and, in the absence of a barrier device, bystanders should not hesitate to ventilate a patient by this technique. For mountain rescue teams, we encourage the use of a barrier device for artificial ventilation. Mouth-to-mask ventilation devices are most likely to fulfill the requirements of being safe, simple, and efficient in the hands of a basic-trained rescuer. The use of a mouth-to-mask ventilation device is recommended for out-of-hospital ventilation in the mountains and should be part of the mountain rescuer's standard equipment. Bag-valve-mask ventilation is efficient, if performed by well-trained rescuers, but it leads to a low ventilation quality in the hands of a less experienced rescuer. It should be emphasized that regular training every 6 to 12 months is necessary to perform proper ventilation.

Prevention of peritoneal adhesions with an in situ cross-linkable hyaluronan hydrogel delivering budesonide

Peritoneal adhesions are tissue connections that form within the abdominopelvic cavity following surgery or other injuries. They can cause major medical complications. Barrier devices and pharmacological agents have been used to prevent adhesion formation, with mixed success. We hypothesize that an adhesion barrier which also delivers anti-adhesion drugs can address both physical and physiological causes for adhesion formation. Here, we describe an in situ cross-linking hyaluronan hydrogel (barrier device) containing the glucocorticoid receptor agonist budesonide. Budesonide was chosen because of the known role of inflammation in adhesion formation, hyaluronan because of its known biocompatibility in the peritoneum. The system, consisting of two cross-linkable precursor liquids, was applied using a double-barreled syringe, forming a flexible and durable hydrogel in less than 5 s. We applied this formulation or controls to the injured sites after the second injury in a severe repeat sidewall defect–cecum abrasion model of peritoneal adhesion formation in the rabbit. Large adhesions (median area 15.4 cm 2) developed in all saline-treated animals. Adhesion formation and area were slightly mitigated in animals treated with budesonide in saline (median area 5.0 cm 2) or the hydrogel without budesonide (median area 4.9 cm 2). The incidence and area of adhesions were dramatically reduced in animals treated with budesonide in the hydrogel (median area 0.0 cm 2). In subcutaneous injections in rats, budesonide in hydrogel reduced inflammation compared to hydrogel alone. In summary, budesonide in a hyaluronan hydrogel is easy to use and highly effective in preventing adhesions in our severe repeated injury model. It is a potentially promising system for post-surgical adhesion prevention, and suggests that the effectiveness of barrier devices can be greatly enhanced by concurrent drug delivery.

Peritoneal adhesion prevention with an in situ cross-linkable hyaluronan gel containing tissue-type plasminogen activator in a rabbit repeated-injury model

Postoperative peritoneal adhesions can have serious, potentially lethal consequences. Pharmacotherapy and barrier devices can reduce adhesion formation to varying degrees, but their efficacy is limited by rapid clearance from the peritoneum and lack of biological activity, respectively. To overcome these limitations, we have delivered tissue-type plasminogen activator (tPA), which is deficient in the first 2–3 postoperative days, using a highly cross-linked in situ forming hyaluronan gel (HAX hx). We demonstrated this formulation's anti-adhesion activity in a rigorous animal model that involved recurrent adhesions. While non-treated or saline-treated animals developed widespread adhesions (frequency, both 100%; median adhesion area, 12.7 and 15.4 cm 2, respectively), tPA delivered by HAX hx (tPA-HAX hx) was highly effective in preventing recurrent adhesions (frequency, 44%; median adhesion area, 0.1 cm 2). HAX hx itself, tPA solution, and inactivated tPA in HAX hx did not provide comparable anti-adhesion activity. tPA-HAX hx is a system that is easy to use and potentially promising for adhesion prevention.

Scattering and space-charge effects in Wigner Monte Carlo simulations of single and double barrier devices

Transport in single and double barrier devices is studied using a Monte Carlo solver for the Wigner transport equation. This approach allows the effects of tunneling and scattering to be included. Several numerical methods have been improved to render the Wigner Monte Carlo technique more robust, including a newly developed particle annihilation algorithm. A self-consistent iteration scheme with the Poisson equation was introduced. The role of scattering and space charge effects on the electrical characteristics of n-i-n nanostructures, ultra-scaled double gate MOSFETs, and GaAs resonant tunneling diodes is demonstrated.

Bone reconstruction following implantation of rhBMP‐2 and guided bone regeneration in canine alveolar ridge defects

Alveolar ridge aberrations commonly require bone augmentation procedures for optimal placement of endosseous dental implants. The objective of this study was to evaluate local bone formation following implantation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in an absorbable collagen sponge (ACS) carrier with or without provisions for guided bone regeneration (GBR) as potential treatment modalities for alveolar augmentation. Surgically induced, large, mandibular alveolar ridge saddle-type defects (2 defects/jaw quadrant) in seven young adult Hound dogs were assigned to receive rhBMP-2/ACS, rhBMP-2/ACS combined with GBR (rhBMP-2/GBR), GBR, and surgery controls. The animals were euthanized at 12 weeks post-surgery when block sections of the defect sites were collected for histologic analysis. Clinical complications included swelling for sites receiving rhBMP-2 and wound failure with exposure of the barrier device for sites receiving GBR (4/6) or rhBMP-2/GBR (3/7). The radiographic evaluation showed substantial bone fill for sites receiving rhBMP-2/ACS, rhBMP-2/GBR, and GBR. In particular, sites receiving rhBMP-2/GBR presented with seroma-like radiolucencies. The surgery control exhibited moderate bone fill. To evaluate the biologic potential of the specific protocols, sites exhibiting wound failure were excluded from the histometric analysis. Sites receiving rhBMP-2/ACS or rhBMP-2/GBR exhibited bone fill averaging 101%. Bone fill averaged 92% and 60%, respectively, for sites receiving GBR and surgery controls. Bone density ranged from 50% to 57% for sites receiving rhBMP-2/ACS, GBR, or surgery controls. Bone density for sites receiving rhBMP-2/GBR averaged 34% largely due to seroma formation encompassing 13% to 97% of the sites. rhBMP-2/ACS appears to be an effective alternative to GBR in the reconstruction of advanced alveolar ridge defects. Combining rhBMP-2/ACS with GBR appears to be of limited value due to the potential for wound failure or persistent seromas.

Comparison of diaphragm and combined oral contraceptive pill users in the Australian family planning setting

Objectives To determine the number of women fitted with a diaphragm or cervical cap at family planning clinics across the Australian State of New South Wales (NSW) from 2000 to 2005. To compare the demographic characteristics of women fitted with this form of contraceptive with women prescribed the combined oral contraceptive pill (COCP).Method An audit of women presenting for contraceptive services between 2000 and 2005 was undertaken. The demographic characteristics of women fitted with a barrier method or prescribed the COCP between 1st April, 2002, and 31st October, 2004, were obtained from the Family Planning NSW Activity Data Set (FADS).Results The proportion of women fitted with a diaphragm or cap remained constant between 2001 and 2005 at approximately 5%. During the 31 months that the study period lasted, 793 women were fitted with a diaphragm or cervical cap compared with 8047 women prescribed the COCP during the same time frame (including 76 women who received both a diaphragm and COCP prescription during this period). Women fitted with the barrier contraceptive were significantly more likely to be older, to have received a tertiary level education and to have private health insurance than their counterparts prescribed the COCP. They were less likely to come from a non-English speaking background.Discussion The diaphragm and cervical cap are viable contraceptive methods for a specific group of older, well-educated women. The possible benefits of female-controlled barrier devices in the prevention of sexually transmissible infections may result in a wider demographic use in the future.

Two-dimensional simulation of ac-driven microplasmas confined to 100–300μm diameter cylindrical microcavities in dielectric barrier devices

Cylindrical microcavity plasma devices with diameters (D) in the 100–300μm range and a dielectric barrier structure similar to that described by Park et al. [J. Appl. Phys. 99, 026107 (2006)] for Al∕Al2O3 devices have been investigated numerically. A two-dimensional fluid simulation of microplasmas in Ne/7% Xe gas mixtures with pD values (where p is the total gas pressure) in the 3–9Torrcm interval yields the temporal history of the spatially resolved electron and ion number densities in response to a 250kHz bipolar excitation wave form. Calculations show two distinct regions of plasma development, along the microcavity axis and near the wall, each of which dominates the plasma characteristics in separate pD regions. For low pD values (<4Torrcm), the negative glow produced at the cavity wall extends to the microcavity axis which, in combination with the strong axial electric field, produces an intense glow discharge on axis. For 4≲pD≲6Torrcm, a weakened axial discharge is observed early in the life of the plasma but the radial variation of the electron density flattens. Further increases in the gas pressure (to the largest pD values investigated, 6–9Torrcm) result in the retreat of the negative glow to the vicinity of the microcavity wall, thereby producing a diffuse but annular discharge. Even at the higher pD values, the axial discharge appears to facilitate ignition of the negative glow. The predictions of the simulations are consistent with the behavior of Al∕Al2O3 microplasma devices for which D=100–300μm.

Endolumenal therapies for gastroesophageal reflux disease: are they dead?

Since first approved for clinical use in 2000 endolumenal therapies for gastroesophageal reflux have filled a desirable niche. Patients and endoscopists alike were allured by the prospect of an outpatient procedure without skin incisions that would alleviate reflux symptoms. However, the introduction of endolumenal therapies for GERD preceded sound clinical data supporting their use. Some of the devices were either ineffective or caused an inordinate number of complications. Because of the early shortcomings of certain endolumenal therapies for GERD this type of therapy is now being scrutinized closely. Overwhelmingly positive data have been called for to support their use. In fact, endolumenal therapies are at risk of being held to a higher standard than either medical or surgical management of GERD. We must recall that our current gold standard, the laparoscopic Nissen fundoplication, provides symptom relief in 85% of patients, but about 1 in 20 experience prolonged dysphagia. There has been a series of specific criticisms of endolumenal therapies for GERD. Some commentators note the lack of sham controls in published randomized controlled trials [1], which might be critical in a disease such as reflux where a 25% to 50% placebo response is routinely reported. Additionally, the efficacy and safety of some therapies has been questioned, with the recent withdrawal of one of the prosthetic barrier devices. In order for endolumenal therapies to gain a foothold, realistic endpoints should be met. Requiring greater than 90% efficacy is unnecessary, but a durable barrier to reflux and symptom relief in 75% of patients is realistic and achievable. Herein, we review the extant literature concerning endolumenal therapies for GERD and look toward the future in this burgeoning field. Suturing devices Akin to laparoscopic Nissen fundoplication, endolumenal suturing devices serve to alter the hiatal anatomy in order to prevent reflux. Systems for both mucosal apposition and full thickness sutures have been introduced, with more durable results achieved by full thickness gastric plication.

Scattering and space-charge effects in Wigner Monte Carlo simulations of single and double barrier devices

Transport in single and double barrier devices is studied using a Monte Carlo solver for the Wigner transport equation. This approach allows the effects of tunneling and scattering to be included. Several numerical methods have been improved to render the Wigner Monte Carlo technique more robust, including a newly developed particle annihilation algorithm. A self-consistent iteration scheme with the Poisson equation was introduced. The role of scattering and space charge effects on the electrical characteristics of n-i-n nanostructures, ultra-scaled double gate MOSFETs, and GaAs resonant tunneling diodes is demonstrated.

Critical Current Oscillations in Strong FerromagneticπJunctions

We report magnetic and electrical measurements of Nb Josephson junctions with strongly ferromagnetic barriers of Co, Ni, and Ni80Fe20 (Py). All these materials show multiple oscillations of critical current with a barrier thickness implying repeated 0-pi phase transitions in the superconducting order parameter. We show, in particular, that the Co barrier devices can be accurately modeled using existing clean limit theories and that, despite the high exchange energy (309 meV), the large IcR(N) value in the pi state means Co barriers are ideally suited to the practical development of superconducting pi-shift devices.

Peritoneal application of chitosan and UV‐cross‐linkable chitosan

The suitability of chitosan and UV-cross-linkable chitosan for intraperitoneal use, for example as a barrier device for preventing peritoneal adhesions or for drug delivery, was examined. In vitro experiments using two major cell types present in the peritoneal cavity (mesothelial cells and peritoneal macrophages) revealed neither attractive interactions between cross-linked chitosan gels and the cells nor a proliferative effect. However, the same UV-cross-linked chitosan applied in the peritoneal cavity of rabbits caused a granulomatous reaction with adhesion formation within two weeks in all animals, which persisted up to 4 weeks after exposure. Unmodified chitosan also caused adhesions, while UV irradiation did not. UV-cross-linkable chitosan induced significant elevations in MIP-2 and TNF-alpha from peritoneal macrophages, suggesting that soluble mediators could play a role in inducing adhesion formation. These results reinforce the view that the predictive value of in vitro cytotoxicity assays in matters of biocompatibility may not be sufficient, and suggest that other assays such as cytokine levels may be of value in predicting outcomes in situations involving multiple cell types (i.e. in vivo).

EMS provider reluctance to perform mouth-to-mouth resuscitation

Objectives. To assess the willingness of EMS providers to perform mouth-to-mouth resuscitation (MMR) both with and without a barrier device (e.g., face shield), while not on duty; and to determine the providers' perceived risk from performing MMR and the frequency with which they carry a barrier device. Methods. A survey was mailed to 543 EMS providers presenting four scenarios describing a patient in respiratory arrest. The respondents were asked whether they would perform MMR in each scenario both with and without a barrier device. Results. Of those surveyed, 342 (64%) responded. Strikingly few (≤5%) of the respondents would perform MMR without a barrier on each of the cases, except for the case of a pediatric drowning (52%). The respondents were least likely to perform MMR on a patient with AIDS (< 1%). The respondents were much more likely to perform MMR in each case if a barrier device was available. The respondents were very concerned about the risk of contagion from MMR, yet 44% of the respondents rarely or never carried a barrier device with them. Conclusion. Emergency medical services providers are quite reluctant to perform MMR, and this is likely related to their perception of a high risk of contagion. The availability of barrier devices greatly decreases this reluctance, but EMS personnel carry such devices infrequently. PREHOSPITAL EMERGENCY CARE 2000;4:48-52

The Role of Metal−Nanotube Contact in the Performance of Carbon Nanotube Field-Effect Transistors

Single-wall carbon nanotube field-effect transistors (CNFETs) have been shown to behave as Schottky barrier (SB) devices. It is not clear, however, what factors control the SB size. Here we present the first statistical analysis of this issue. We show that a large data set of more than 100 devices can be consistently accounted by a model that relates the on-current of a CNFET to a tunneling barrier whose height is determined by the nanotube diameter and the nature of the source/drain metal contacts. Our study permits identification of the desired combination of tube diameter and type of metal that provides the optimum performance of a CNFET.

Negative charged excitons in double barrier diodes

We have studied the effects of excitonic complexes formation, such as excitons and trions, on the optical and on transport properties of GaAs–GaAlAs n–i–n double barrier diodes, by measuring the current–voltage characteristics and the photoluminescence emission, as function of bias. The observation of a pre-resonance shoulder in the I(V) curves, under high laser intensities, and a negative charged excitons in the photoluminescence spectra, under the same bias conditions, were associated to the dissociation of these complexes either by thermal excitation or by scattering with ‘free’ carriers in the quantum well layer. A simple rate equation model allows us to explain the kinetics of the excitonic complexes in double barrier devices.