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At least 1,027 records · Page 57Linked to original sources
PubMed2004

Acoustomechanical properties of open TTP titanium middle ear prostheses.

OBJECTIVE: The purpose of the study was to identify acoustcomechanical properties of various biostable and biocompatible materials to create a middle ear prosthesis with the following properties: (i) improved handling including a good view of the head of the stapes or footplate and adjustable length, (ii) improved acoustical characteristics that are adequate for ossiculoplastic. The identified material should serve to build CE and FDA approved prostheses for clinical use in patients. METHODS: Test models made of Teflon, polyetheretherketone, polyethylenterephtalate, polysulfone, gold, Al2O3 ceramics, carbon and titanium were investigated for their potential to fulfill the requirements. Acoustical properties were investigated by laser Doppler velocimetry (LDV) in mechanical middle ear models (MMM). Measured data were fed in to a recently created computer model of the middle ear (multibody systems approach, MBS). Using computer-aided design (CAD) measured and computed data allowed creation and fine precision of titanium prostheses (Tübingen Titanium Protheses, TTP). Their handling was tested in temporal bones. Acoustomechanical properties were investigated using the MBS and mechanical middle ear models. MAIN OUTCOME MEASURES: Input impedance, mass, stiffness, and geometry of test models and prostheses were determined. Furthermore, their influence on the intraprosthetic transfer functions and on coupling to either tympanic membrane or stapes was investigated. RESULTS: Final results were FDA- and CE-approved filigreed titanium prostheses with an open head that fulfilled the four requirements detailed above. The prostheses (TTP) were developed in defined lengths of between 1.75 and 3.5 mm (partial) and 3.0 and 6.5 mm (total) as well as in adjustable lengths (TTP-Vario). CONCLUSIONS: The results suggest acoustomechanical advantages of TTPs because they combine a significantly low mass with high stiffness. In contrast to closed prostheses, the open head and filigreed design allow an excellent view of the prosthesis foot during coupling to the head or footplate of stapes, contributing to an improved intraoperative reliability of prosthesis coupling.

Acoustics↗
PubMed2003

A three terminal ring interferometer logic gate.

We propose a carbon-based logic gate where and, or, and xor logic operations are available. It consists of a carbon nanotube (CNT) ring coupled to three external CNT-leads, two of them used as input channels, and the third as the output channel. The total transmission for two inputs displays characteristic interference effects. The constructive interference leads to total transmission significantly larger than that for a single input and validates and gates, whereas the destructive interference corresponds to xor gates. For or gates a negligible interference between the transmittance of each single inputs is needed.

Computer Simulation↗
PubMedDate not supplied

A CAD-CAM ceramic inlay technique.

This article details the technique of a Cerec computer-aided designed (CAD) and computer-aided manufactured (CAM) inlay. Using a ceramic material the unit can mill an inlay from an optical "impression" that is then bonded to place using a dual-cure composite resin cement.

Dental Porcelain↗
PubMed1986

Computer-aided simulation, analysis, and design in orthopedic surgery.

Three-dimensional computer reconstructions of bony anatomy based on computed tomographic images and radiographs may be used to analyze, simulate, and design certain orthopedic procedures. In osteotomy surgery, the computer-reconstructed models may be used to measure critical angles, surface area, and congruity of the joint surfaces. Computer reconstructions may be used in total joint replacement surgery to simulate the effect of surgical reamers and rasps, to select the geometrically optimum standard implant, or to design a custom implant. In allograft reconstructive surgery, computer reconstructions may be used to measure bony defects and to identify the appropriate allografts for the reconstruction. Plastic models may be sterilized and used as templates to sculpt the allografts immediately preoperatively. In all three applications in orthopedic surgery, three-dimensional, computer-aided reconstructions have the potential to improve results and reduce morbidity.

Bone Transplantation↗
PubMed1991

CEREC(R) CAD-CAM ceramic restorations. A case report after 5 years in place.

At least three different techniques have been described for preparing computer-aided designed (CAD) and computer-aided manufactured (CAM) inlays and veneers. This paper details a clinical case in which 13 Cerec CAD-CAM inlays have been in function for five years. The Cerec--System produces ceramic inlays which are designed, fabricated and placed during one appointment. Advantages and system-related limitations are discussed.

Adult↗
PubMed1998

A computer-based expert system designs and analyzes a 2(k - p) fractional factorial design for the formulation optimization of novel multicomponent liposomes.

A computer-based technique based on a 2(k - p) fractional factorial design was applied for the optimization of recently described multicomponent protective liposomal formulations. These formulations contain sodium ascorbate (vitamin C) as a model drug sensitive to photochemical oxidation, as well as oil red O and/or oxybenzone as oil soluble light absorbers, incorporated into the lipid bilayers and sulisobenzone as a water soluble light absorber incorporated into the aqueous phase of liposomes. The three light absorbers (present or absent) incorporated in multilamellar liposomes and the drug in free or in complexed with alpha-cyclodextrin form comprised the four factors of the system. The stabilization ratio and the percentage entrapment in the liposomes of the vitamin were the two response variables of the system to be optimized. The entrapment values were calculated for all the materials either spectrophotometrically or by using second order derivative spectrophotometry. The response variables were predicted by multiple regression equations comprising combinations of the four formulation factors. Both the higher entrapment and the higher protection for the drug should characterize the optimum formulation.

Chemistry, Pharmaceutical↗
PubMed2002

Design considerations for a computer controlled multileaf collimator for the Harper Hospital fast neutron therapy facility.

The d(48.5) + Be neutron beam from the Harper Hospital superconducting cyclotron is collimated using a unique multirod collimator (MRC). A computer controlled multileaf collimator (MLC) is being designed to improve efficiency and allow for the future development of intensity modulated radiation therapy with neutrons. For the current study the use of focused or unfocused collimator leaves has been studied. Since the engineering effort associated with the leaf design and materials choice impacts significantly on cost, it was desirable to determine the clinical impact of using unfocused leaves in the MLC design. The MRC is a useful tool for studying the effects of using focused versus unfocused beams on beam penumbra. The effects of the penumbra for the different leaf designs on tumor and normal tissue DVHs in two selected sites (prostate and head and neck) was investigated. The increase in the penumbra resulting from using unfocused beams was small (approximately 1.5 mm for a 5 x 5 cm2 field and approximately 7.6 mm for a 25 x 25 cm2 field at 10 cm depth) compared to the contribution of phantom scatter to the penumbra width (5.4 and 20 mm for the small and large fields at 10 cm depth, respectively). Comparison of DVHs for tumor and critical normal tissue in a prostate and head and neck case showed that the dosimetric disadvantages of using an unfocused rather than focused beam were minimal and only significant at shallow depths. For the rare cases, where optimum penumbra conditions are required, a MLC incorporating tapered leaves and, thus, providing focused collimation in one plane is necessary.

Adenocarcinoma↗
PubMed2005

Carbon nanotube interaction with DNA.

We investigate a system consisting of B-DNA and an array of (10,0) carbon nanotubes periodically arranged to fit into the major groove of the DNA. We obtain an accurate electronic structure of the combined system, which reveals that it is semiconducting and that the bands on either end of the gap are derived exclusively from one of the two components. We discuss in detail how this system can be used as either an electronic switch involving transport through both components, or as a device for ultrafast DNA sequencing.

Computer Simulation↗
PubMed2003

TranSIESTA: a spice for molecular electronics.

Our recently developed method, TranSIESTA, enables modelling of molecular electronic devices under operation conditions. The method is based on density functional theory, and calculates the self-consistent electronic structure of a nanostructure coupled to three-dimensional electrodes with different electrochemical potentials. It uses a full atomistic ab initio description of both the electrodes and the nanoscale device. The calculations reveal information about the scattering states, transmission coefficients, electron current, and non-equilibrium forces in the systems. In this paper we use the method to investigate the electrical properties of three ring phenyl-ethynylene oligomers (OPE). We present results for the electrical effect of side groups and molecular conformations of the molecules. The calculations indicate that molecular switching and negative differential conductance (NDC) are related to rotations of the middle phenyl ring.

Algorithms↗
PubMed1990

CAD-CAM ceramic inlays and onlays: a case report after 3 years in place.

At least three different techniques are available for preparing computer-aided designed (CAD) and computer-aided manufactured (CAM) inlays and veneers. This paper details a clinical case in which 13 Cerec CAD-CAM inlays have been functioning for 3 years. Advantages and limitations of this system are discussed.

Adult↗
PubMed1989

Microcomputer-aided removable partial denture design.

A microcomputer-based program for the design of removable partial dentures is described that has an interactive user interface to conduct a heuristic search of removable partial denture design data and produces computer-generated design graphics. The program is useful educationally and clinically.

Computers↗
PubMed2003

Strategy to assess the efficiency of U1 RNA-hammerhead ribozyme constructs using GFP-tagged targets.

The application of ribozymes for gene therapy of autosomal dominant diseases has become popularized in recent years. Further this technology has widespread utility in the treatment of any disease, acquired or inherited, by inhibition of gene expression. The design of ribozymes is usually accomplished using computer assisted design programs, however they are not very useful in predicting the behavior of the ribozyme in the in vivo setting. To overcome this technical challenge, we developed a simple in vivo strategy to accurately assess the efficiency of ribozyme cleavage that significantly enhances the computer based design programs.

Animals↗
PubMed2005

Computational tradeoffs in multiplex PCR assay design for SNP genotyping.

BACKGROUND: Multiplex PCR is a key technology for detecting infectious microorganisms, whole-genome sequencing, forensic analysis, and for enabling flexible yet low-cost genotyping. However, the design of a multiplex PCR assays requires the consideration of multiple competing objectives and physical constraints, and extensive computational analysis must be performed in order to identify the possible formation of primer-dimers that can negatively impact product yield. RESULTS: This paper examines the computational design limits of multiplex PCR in the context of SNP genotyping and examines tradeoffs associated with several key design factors including multiplexing level (the number of primer pairs per tube), coverage (the % of SNP whose associated primers are actually assigned to one of several available tube), and tube-size uniformity. We also examine how design performance depends on the total number of available SNPs from which to choose, and primer stringency criterial. We show that finding high-multiplexing/high-coverage designs is subject to a computational phase transition, becoming dramatically more difficult when the probability of primer pair interaction exceeds a critical threshold. The precise location of this critical transition point depends on the number of available SNPs and the level of multiplexing required. We also demonstrate how coverage performance is impacted by the number of available snps, primer selection criteria, and target multiplexing levels. CONCLUSION: The presence of a phase transition suggests limits to scaling Multiplex PCR performance for high-throughput genomics applications. Achieving broad SNP coverage rapidly transitions from being very easy to very hard as the target multiplexing level (# of primer pairs per tube) increases. The onset of a phase transition can be "delayed" by having a larger pool of SNPs, or loosening primer selection constraints so as to increase the number of candidate primer pairs per SNP, though the latter may produce other adverse effects. The resulting design performance tradeoffs define a benchmark that can serve as the basis for comparing competing multiplex PCR design optimization algorithms and can also provide general rules-of-thumb to experimentalists seeking to understand the performance limits of standard multiplex PCR.

Algorithms↗
PubMed1998

Applications of computer modelling for the design of orthopaedic, dental and cardiovascular biomaterials.

Biomaterials do not escape from the general trend present in all contemporary science and technology towards increasing use of computers and information technology. In this paper the use of computer modelling for the design of biomaterials is discussed. The word 'biomaterials' is interpreted in its broadest sense, i.e. referring to any foreign object brought into the body for temporary or permanent use. Computer modelling will first be discussed as a tool to model biological structures (bones, arteries) or to investigate and simulate biological interactions at implant-host interfaces. It will then be illustrated how computer modelling, using insights gained from the modelling of the biological structures themselves, is used in the design process of dental, orthopaedic and cardiovascular prostheses. The area of computer modelling for biomaterials applications has become so vast that an exhaustive overview is impossible in the framework of one paper. Rather, some illustrative case studies will be discussed which are, in the opinion of the authors, representative of general trends in this challenging domain of science on the boundary between engineering and medicine.

Cardiovascular Diseases↗
PubMed2005

Design optimization of blood shearing instrument by computational fluid dynamics.

Rational design of blood-wetted devices requires a careful consideration of shear-induced trauma and activation of blood elements. Critical levels of shear exposure may be established in vitro through the use of devices specifically designed to prescribe both the magnitude and duration of shear exposure. However, it is exceptionally difficult to create a homogeneous shear-exposure history by conventional means. This study was undertaken to develop a Blood Shearing Instrument (BSI) with an optimized flow path which localized shear exposure within a rotating outer ring and a stationary conical spindle. By adjustment of the rotational speed and the gap dimension, the BSI is designed to generate shear stress magnitudes up to 1500 Pa for exposure time between 0.0015 and 0.20 s with a pressure drop of 100 mm Hg. Computational fluid dynamics (CFD) revealed that a flow path designed by first-order analysis and intuition exhibited unfavorable pressure gradient, vortices, and undesirable regions of reverse flow. An optimized design was evolved utilizing a parameterized geometric model and automatic mesh generation to eliminate vortices and reversal flow and to avoid unfavorable pressure gradients. Analysis of the flow and shear fields for the extreme limits of the shear gap demonstrated an improvement in homogeneity due to shape optimization and the limitations of an annular shear device for achieving completely uniform shear exposure.

Algorithms↗
PubMed1992

An intelligent computer-assisted instruction system designed for rural health workers in developing countries.

This paper describes an intelligent computer-assisted instruction system that was designed for rural health workers in developing countries. This system, called Consult-EAO, includes an expert module and a coaching module. The expert module, which is derived from the knowledge-based decision support system Tropicaid, covers most of medical practice in developing countries. It allows for the creation of outpatient simulations without the help of a teacher. The student may practice his knowledge by solving problems with these simulations. The system gives some initial facts and controls the simulation during the session by guiding the student toward the most efficient decisions. All student answers are analyzed and, if necessary, criticized. The messages are adapted to the situation due to the pedagogical rules of the coaching module. This system runs on PC-compatible computer.

Computer Simulation↗