Polymer/layered silicate nanocomposites: a review from preparation to processing

SUMMARY Review date: 1969 to 2003, 34 years. Background and context: Simulations are now in widespread use in medical education and medical personnel evaluation. Outcomes research on the use and effectiveness of simulation technology in medical education is scattered, inconsistent and varies widely in methodological rigor and substantive focus. Objectives: Review and synthesize existing evidence in educational science that addresses the question, ‘What are the features and uses of high-fidelity medical simulations that lead to most effective learning?’. Search strategy: The search covered five literature databases (ERIC, MEDLINE, PsycINFO, Web of Science and Timelit) and employed 91 single search terms and concepts and their Boolean combinations. Hand searching, Internet searches and attention to the ‘grey literature’ were also used. The aim was to perform the most thorough literature search possible of peer-reviewed publications and reports in the unpublished literature that have been judged for academic quality. Inclusion and exclusion criteria: Four screening criteria were used to reduce the initial pool of 670 journal articles to a focused set of 109 studies: (a) elimination of review articles in favor of empirical studies; (b) use of a simulator as an educational assessment or intervention with learner outcomes measured quantitatively; (c) comparative research, either experimental or quasi-experimental; and (d) research that involves simulation as an educational intervention. Data extraction: Data were extracted systematically from the 109 eligible journal articles by independent coders. Each coder used a standardized data extraction protocol. Data synthesis: Qualitative data synthesis and tabular presentation of research methods and outcomes were used. Heterogeneity of research designs, educational interventions, outcome measures and timeframe precluded data synthesis using meta-analysis. Headline results: Coding accuracy for features of the journal articles is high. The extant quality of the published research is generally weak. The weight of the best available evidence suggests that high-fidelity medical simulations facilitate learning under the right conditions. These include the following:

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Features and uses of high-fidelity medical simulations that lead to effective learning: a BEME systematic review

The invention concerns medical diagnosis and monitoring equipment with wireless electrodes (2a...2f) designed to be secured to the skin of the patient (3). The electrodes (2a...2f) include, as well as microsensors, a digital transmitter (31) and receiver (30) unit and an antenna (36a). The electrodes (2a...2f) can be used, for instance, to detect EEG and ECG signals or to monitor body/berathing movements, temperature or perspiration. A preferred embodiment has an electrode which incorporates all functions in a semiconductor chip designed as an integrated circuit with the appropriate sensor, sensor-control, frequency-generation, transmitter and receiver units plus a switching control unit. The antenna (36a) can be mounted either in the flexible electrode covering or directly on the chip.

Wireless medical diagnosis and monitoring equipment

Measuring small normal pressures is essential to accurately evaluate external stimuli in curvilinear and dynamic surfaces such as natural tissues. Usually, sensitive and spatially accurate pressure sensors are achieved through conformal contact with the surface; however, this also makes them sensitive to mechanical deformation (bending). Indeed, when a soft object is pressed by another soft object, the normal pressure cannot be measured independently from the mechanical stress. Here, we show a pressure sensor that measures only the normal pressure, even under extreme bending conditions. To reduce the bending sensitivity, we use composite nanofibres of carbon nanotubes and graphene. Our simulations show that these fibres change their relative alignment to accommodate bending deformation, thus reducing the strain in individual fibres. Pressure sensitivity is maintained down to a bending radius of 80 μm. To test the suitability of our sensor for soft robotics and medical applications, we fabricated an integrated sensor matrix that is only 2 μm thick. We show real-time (response time of ∼20 ms), large-area, normal pressure monitoring under different, complex bending conditions. A composite fibrous material made of carbon nanotubes and graphene responds to small pressure but not to bending deformation.

A transparent bending-insensitive pressure sensor

Large-scale failure modes of dielectric elastomer actuators

The LionHeart LVD-2000: a completely implanted left ventricular assist device for chronic circulatory support.

In this article we describe our continuing research on a novel nanocomposite approach for reducing gas permeability through biomedical polyurethane membranes. Nanocomposites were prepared using commercially available poly(urethane urea)s (PUU) and two organically modified layered silicates (OLS). Wide-angle X-ray diffraction experiments showed that the silicate layer spacing in the nanocomposites increased significantly compared with the neat OLS, signifying the formation of intercalated PUU/OLS structures. The nanocomposite materials exhibit increased modulus with increasing OLS content, while maintaining polymer strength and ductility. Water vapor permeability was reduced by about fivefold at the highest OLS contents, as a result of PUU/inorganic composite formation.

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Low permeability biomedical polyurethane nanocomposites.

The electromechanical behavior of dielectric elastomers is to be exploited for medical application in artificial blood pumps. It is required that the pump diaphragm achieves a swept volume increase of 70 cc into a systolic pressure of 120 mmHg with the main design objective being volumetric efficiency. As such, a model that accommodates large deformation behavior is used. In order to design prosthetic blood pumps that closely mimic the natural pumping chambers of the heart, a dielectric elastomer diaphragm design is proposed. The elastomer's change in shape in response to the applied electric field will permit it to be the active element of the pump just as the ventricular walls are in the natural heart. A comprehensive analytical model that accounts for the combined elastic and dielectric behavior of the membrane is used to compute the stresses and deformations of the inflated membrane. Dielectric elastomers are often pre-strained in order to obtain optimal electromechanical performance. The resulting model incorporates pre-strain and shows how system parameters such as pre-strain, pressure, electric field, and edge constraints affect membrane deformation. The model predicts more than adequate volume displacement for moderate pre-strain of the elastomer.

Modeling of a dielectric elastomer diaphragm for a prosthetic blood pump

Platelet adhesion is a key event in thrombus development on blood-contacting medical devices. It has been demonstrated that changes to the chemistry of a material surface can reduce platelet adhesion. In this work, it is hypothesized that sub-micron surface textures may also reduce adhesion via a decrease in the surface area of material with which platelets can make contact, and hence a decreased probability of interaction with adhesive ligands. A polyether(urethane urea) was textured with two different sizes of sub-micron pillars using a replication molding technique that did not alter the material surface chemistry. Adhesion of platelets was assessed in a physiologically relevant shear stress range of 0–67 dyn/cm2 using a rotating disk system. Platelets were immunofluorescently labeled and adhesion was compared on smooth and textured samples. Platelet adhesion was greatest at low shear stress ranging from 0 to 5 dyn/cm2, and sub-micron textures were observed to reduce platelet adhesion in this range. Additionally, non-adherent platelets did not demonstrate large-scale activation after exposure to textured samples. We conclude that surface textures with sub-platelet dimensions may reduce platelet adhesion from plasma to polyether(urethane urea) at low shear stress. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006

Sub-micron texturing for reducing platelet adhesion to polyurethane biomaterials.

Background: In the area of instrument evaluation, one aspect that still requires objective assessment is the dynamics of instrument maneuver and exchange. If we could gain a better understanding of these phenomena, we could improve the design of the instruments themselves. Methods: A total of 29 laparoscopic procedures were videotaped and reviewed using time motion analysis. Instrument multifunctionality was determined using a standardized list of laparoscopic maneuvers. State transition diagrams were utilized to document the sequence of instrument exchanges. Results: The curved dissector, atraumatic grasper, and cautery scissors were identified as the most multifunctional instruments; each was able to perform five distinct maneuvers. Instrument sequences were found to consist of a three-part dissect ? clip ? cut cycle and a two-part dissect ? suction cycle of instrument exchange. Conclusion: This study demonstrated that laparoscopic instruments are often used to perform a variety of maneuvers in addition to their primary function. Furthermore, there are common patterns in instrument exchange that provide a potential source of design parameters for improved surgical efficiency.

Alan J. Snyder

Papers

The LionHeart LVD-2000: a completely implanted left ventricular assist device for chronic circulatory support.

Low permeability biomedical polyurethane nanocomposites.

Modeling of a dielectric elastomer diaphragm for a prosthetic blood pump

Sub-micron texturing for reducing platelet adhesion to polyurethane biomaterials.

Sequence and task analysis of instrument use in common laparoscopic procedures.