Predetermined Shape Research Articles

Shape memory alloys in minimally invasive therapy

SummaryShape memory alloys are ideally suited to minimally invasive therapy, as their shape memory and superelastic properties facilitate entry through a narrow aperture before ‘expansion’ into predetermined shapes. An increasing number of shape memory alloy devices are being designed and patented although as yet they have made little impact on minimal invasive therapeutic procedures due to the complexities of effective thermal processing and accurate transformation. Within the next few years shape memory alloy technology is likely to make a big impact on laparoscopic, endovascular and endo-scopic surgical practice.

Cartilage Engineered in Predetermined Shapes Employing Cell Transplantation on Synthetic Biodegradable Polymers

Cartilage is often used as structural support tissue for cosmetic repair in plastic and reconstructive surgery. We describe the efficacy of a new approach for the generation of cartilage in predetermined shapes using specially configured biodegradable synthetic polymer devices as delivery vehicles for transplanted cells. Synthetic biodegradable polymer scaffolds were configured in one of four specific shapes, i.e., a triangle, a rectangle, a cross, and a cylinder. The polymer matrices were seeded with freshly isolated bovine articular chondrocytes and then implanted subcutaneously into nude mice. Gross examination of excised specimens 12 weeks after implantation revealed the presence of new hyaline cartilage of approximately the same dimensions as the original construct. This cartilage showed no signs of resorption or overgrowth over the 12-week time course of the experiment. Histologic evaluation using hematoxylin and eosin stains confirmed the presence of normal mature hyaline cartilage in 46 of 48 specimens. These results suggest that cartilage can be created in predetermined shapes and dimensions using cell transplantation on appropriate polymer templates. This technology would be useful in cosmetic and reconstructive surgery.

Development and applications of a synthetic material to simulate soft sedimentary rocks

Due to the fact that a model material can be made homogeneous, the influence of different variables on behavioural mechanisms can be investigated independently. Consequently, large experimental scatter attributed to inherent variables (generally unknown) of a natural material can be avoided. This Paper presents the development of an artificial material which can effectively simulate the behaviour of an array of weak, sedimentary rocks. This synthetic soft rock was constituted with gypsum cement, fine sand and water, and characterized with homogeneous and isotropic properties with insignificant variability from one batch to another. It can be easily manufactured in the laboratory and can be cast either in large or small volumes to occupy any predetermined shape of given physical dimensions. An experimental application to study the behaviour of reinforced composites (simulated bolted rock) is also described in this Paper. Puis qu'une matière-modèle peut être rendue homogène, il est possible d'étudier de façon indépendante l'influence exercée par de diverses variables sur les mécanismes de comportement. On peut par conséquent éviter la dispersion considérable expérimentale attribuée aux variabilités inhérentes, généralement inconnues, à une matière naturelle. L'article décrit le développement d'une matière artificielle qui peut simuler effectivement le comportement d'un groupe de roches tendres Sédimentaires. Cette rocbe tendre synthétique comprenait du ciment de gypse, du sable fin et de l'eau et possédait des propriétés homogènes et isotropes qui ne variaient que très peu d'un lot à l'autre. Cette matière peut se produire très facilement dans le laboratoire et être coulée dans de petits ou grands volumes pour prendre n'importe quelle forme prédeterminée de dimensions données. L'article présente aussi une application expérimentale pour étudier le comportement des matières composites renforcées (simulation de rocbes boulonnées).

Changing perceptions of the requirements of cavity preparations

Perceptions of the requirements of cavity preparations have changed over the years. These have had a significant effect on undergraduate teaching at the University of Bristol Dental School, an explanation of which may help general dental practitioners in their quest for information on this important aspect of dental practice. A method is described for teaching undergraduate dental students cavity preparation in caries-free teeth, based upon the position, shape and extent of imaginary carious lesions. Scale diagrams of teeth are used, on which imaginary caries at the amelodentinal junction has been marked. The students are instructed to apply the principles of cavity preparation to equivalent, but caries-free, teeth in the laboratory. 'Outline forms' and other predetermined cavity shapes are not taught. Dental practitioners may find it appropriate to apply similar thinking to cavities they prepare in everyday practice, in an endeavour to avoid the unnecessary removal of tooth tissue that would be better retained.

Laser Line Heating

Many shipyards now employ line-heating processes to form metal by controlled heating and cooling. The benefits of line-heat forming include improved accuracy and productivity. The current line-heating method utilizes an oxyacetylene torch as the heat input. A new forming technique that uses a high-power laser as the heat source is being researched. The feasibility of forming mild-and high-strength steels with a laser heat input is reviewed. The primary incentives for using a laser are the capability to accurately control the forming process; the capability to minimize the material degradation; the capability to form high-strength steels; and the increased compatibility with other advanced manufacturing systems. In summary, by manipulating the laser power, laser beam diameter, and plate travel speed, one may form metal plates to a predetermined shape in a repeatable manner.

On the propagation of streamers through a large population of neutral droplets

Streamers were injected into a large population of small droplets, of radii about 20 μm, confined to a given region of pre-determined shape on a photographic film, and situated in a gap between which a variable electric field can be applied. Results showed that the droplet region behaves like a dipole discharging from both ends if its inclination to the electric field is less than 45° and the field is not less than −230 kV/m at atmospheric pressure.

Crystal growth and electron microprobe analysis of bismuth-antimony alloys ( Bi100− xSbx)

Bismuth-antimony alloys are suitable for the investigation of processes during crystal growth from the melt because they have a special interest for their semimetallic or semiconducting properties, their electronic properties have been well studied, homogeneous crystals of any composition can be made, the necessary temperature level is relatively low, the segregation effects are remarkable and the determination of composition can be made very exactly. For growing homogeneous bismuth-antimony crystals several methods are described. Large single crystals with long homogeneous portions were prepared by the zone-levelling technique. By mould growing, a modified version of the Bridgman technique, crystals can be given a predetermined shape and orientation of the crystallographic axes. For many investigation methods a further preparation of crystals is not necessary. The quantitative electron microprobe analysis is shown to be a very precise method for investigation of bismuth-antimony alloys, for determination of composition sensitive to concentration differences. It was pointed out and it has now been verified that BiSb alloys are suitable for performance of crystal growth experiments from the melt in a microgravity environment.

Dilation of Arterial Stenoses

To the Editor:— The recent CLINICAL NOTE Renovascular Hypertension Secondary to Arterial Fibrodysplasia: Treatment by Dilation Using a Fogarty Balloon (242:1396, 1979) invites reply. The article reports the operative dilation of an angiographically demonstrated fibromuscular stenosis of a main renal artery. There is currently a surge in the treatment of occlusive vascular disease by the interventional angiographic technique of percutaneous transluminal angioplasty (PTA). This interest has been kindled by the development of maneuverable, percutaneous catheters incorporating polyvinyl balloons for dilation. 1 Unlike the latex of Fogarty balloons, polyvinyl has a low compliance and a nonlinear, pressure-volume relationship. This balloon can be inflated to a predetermined cylindrical shape and diameter, with minimal risk of overdistension and undesirable vascular injury. Furthermore, in contrast to previous rigid dilating catheters, these newer systems allow selective percutaneous catheterization, and, because of the affixed balloon, greater degrees of dilation are possible with catheters of small diameter.

(ErEu)3 (FeGa)5O12 garnet films for magnetic writing and magneto-optic displays

Thin films of (ErEu)3 (FeGa)5O12 garnet have been grown by liquid-phase epitaxy onto (111) -oriented GGG substrates, by increasing in steps the Ga2O3 concentration in the melt. For the molar ratio Fe2O3/Ga2O3 ranging from 8.3 to 7.6, the films show large ’’rag’’ domains rather than the usual strip-domain pattern. These ’’rag’’ domains can be given any predetermined shape under the drive of external magnetic fields, the obtained figures being stable without need of any bias field. These features make rag-domain films suitable for magnetic writing and magneto-optic displays. Measurements of the relevant parameters of a number of such films show that reasonable material performances are obtainable.

Optimum Design of Ribbon and Wire Wound Cylinders for Metal Forming Dies

The ribbon winding process enables the manufacture of metal forming dies with higher allowable internal working pressure than is possible by conventional shrink-fit constructions. Varying the tensile stress in the ribbon in the winding process, the stress distribution in the die can be given a predetermined shape. Based on the assumption that all ribbon layers carry the same shear stress when the internal working pressure is acting, a new winding theory is derived. This method permits the internal working pressure to be increased about 30 percent compared to that of the previously known winding theories and about 60 percent compared to that of shrink-fit constructions.

A computer program for the analysis of time-of-flight spectra

A computer program has been developed for the automatic analysis of time-of-flight spectra by least square methods. The program will correct multichannel data for background and fit single or overlapping peaks with distributions of an arbitrary predetermined shape. No information on the position or number of lines is necessary.