Eugene W. White

Replamineform: A New Process for Preparing Porous Ceramic, Metal, and Polymer Prosthetic Materials

The replamineform process (meaning replicated life forms) is a technique for duplicating the microstructure of carbonate skeletal components in ceramic, metal, or polymer materials. The special pore structures of marine invertebrate skeletal materials such as echinoid spines and corals, which are difficult or impossible to create artificially, can thus be copied in useful materials. Of immediate interest is the possibility of using these replicated microstructures in the fabrication of orthopedic prosthetic devices. By means of this technique, prosthetic materials having a controlled pore microstructure for optimum strength and tissue ingrowth may be obtained.

Correlation of density banding in reef coral skeletons with environmental parameters; the basis for interpretation of chronological records preserved in the coralla of corals

Many species of scleractinian reef corals deposit aragonite skeletons with cyclic bands of higher and lower density whose periodicity is annual. As these growth bands are frequently preserved in fossil corals, attention has been focused on their possible use as en- vironmental indicators in as much as density variations may reflect changes in water tem- perature and/or light intensity. Relationships between skeletal growth banding and environ- mental parameters have been investigated by X-radiographic examination of 1488 specimens of modern reef corals representing 31 reef localities widely distributed over the Indo-Pacific and Caribbean regions. Average monthly seawater temperature and solar radiation data are available for each locality, and the date of collection is known for each sample. Of the 47 genera and subgenera included in the study, density variations were most pronounced in skeletons of Astreopora, Coscinarea, Cyphdstrea, Favia (especially species with small corallites such as F. stelligera), Goniastrea, Hydnophora (massive forms only, e.g. M. microconos), Leptoria, Montastrea (especially M. annularis, with small corallites), Pavona, Polyastra, and Plesiastrea. Less useful are Diploastrea, Diploria, and Favites (which tend to have large corallite diameters), and Goniopora, Alveopora, Porites, Siderastrea, and Stephanaria (which frequently exhibit numerous secondary density variations within the annual cycle). Despite considerable variability among different individual corals from the same population, the average thickness of the skeletal growth bands is positively correlated with mean annual wa- ter temperature. By comparing characteristics of the outermost growth increment and the date of collection with monthly records of water temperature and solar radiation, it appears that maximum skeletal density is associated with those periods of the year when seawater

Unusual strength properties of echinoderm calcite related to structure.

Echinoderm skeletons are composed of high-magnesium calcite having a fenestrate structure. Each skeletal ossicle appears to be a single crystal of calcium carbonate rather than a polycrystalline aggregate as, for example, are mollusc shells. Measurements of crushing strength for spines of three species of sea urchin demonstrate that the strength to weight ratio of these spines is equivalent to or greater than that of mollusc skeletons and most calcareous rocks. Echinoderms utilize calcium carbonate with unusually high efficiency, fulfilling the strength and volumetric requirements of a suitable skeleton with a minimum amount of material. Comparative dimensional analysis of structural and mechanical properties of these skeletal materials may provide further insight into the evolution of echinoderms.

Carbon-metal graded composites for permanent osseous attachment of non-porous metals

Abstract The recently devised REPLAMINEFORM process for imparting controlled pore microstructures to metals, ceramics, and plastics now makes it possible to join materials which differ greatly in chemical, physical, mechanical, or biological properties, by means of composite bonding at the interface. A solution to the long-standing problem of attaching metal to bone is proposed as one application. The join would be accomplished with a porous carbon intermediary permitting a transition from solid, non-porous metal to metal-carbon composite to carbon-bone composite to bone. As a result, advantage can be taken of the superior biocompatibility qualities of carbon which is otherwise of limited value for implant purposes because of its poor strength characteristics. Additional advantages include reduction or elimination of problems arising from metal corrosion or toxicity, and the formation of a much more desirable stress distribution pattern. A carbon-composite intermediate will minimize the poor match of mechanical properties at a bone-metal interface, thus preventing the development of large stress concentrations which cause tissue necrosis, bone resorption, deterioration of implant attachment, and other adverse effects.

Electron Microprobe and Optical Absorption Study of Colored Kyanites

The characteristic blue color of the mineral kyanite is shown to be caused by traces of Ti+++ in the range of a few parts per million. Evidence from the intensity and position of optical absorption bands indicates that the unusually intense color probably arises from electron delocalization into narrow d-bands.

Computer analysis of multi-channel SEM and X-ray images from fine particles

Abstract : Techniques involving the computer processing of scanning electron microscope (SEM) images using a binary coded map approach have been developed. For each picture from one to six different SEM signals are converted from analog to digital form and recorded on magnetic tape for subsequent computer analysis. The analysis of fine grained A1203 particles and multiphase particulate mixtures are carried through from the sample preparation, the actual examination under the SEM, the digital recording of the image and finally the computer processing of the images. The computer program and the results are viewed step by step - with an explanation of the possibilities. A listing of the entire computer program is given in the Appendix. (Author)

Computer processing of SEM images by contour analyses

Abstract Techniques involving the computer processing of scanning electron microscope (SEM) images using a contour approach have been developed. For each picture from one to six different SEM signals are converted from analog to digital form and recorded on magnetic tape for subsequent computer analysis. A program finds and analyzes coordinate arrays representing the reconstructed computer picture. Least squares fitting of the contour arrays to ellipses provides measurements of the aspect ratios and orientations of the picture fields. Line integration techniques produce areas and perimeters. Computer plotting enables both the visual comparison of the reconstructed picture with a photograph of the image on the cathode ray tube of the SEM and an estimate of the accuracy of the ellipse fits.

Use of x-ray emission spectroscopy in the characterization of thin films of aluminum oxides and hydroxides

Abstract X-ray emission bands (AlK β ) of several aluminum oxides and hydroxides have been compared. The bands from the oxyhydroxides and γ-Al 2 O 3 are single peaks with some variations in peak position from material to material. However, the band from α-Al 2 O 3 is much broader and forms a distinct doublet. The bands from the oxyhydroxides occur at shorter wavelengths than the peaks from α-Al 2 O 3 . These results may be used to aid in the characterization of thin films (crystalline as well as non-crystalline) on aluminum and aluminum alloys.

Use of the electron microprobe in the characterization of bone, cartilage, and tendon

Specimens of human, dog, and rabbit articular cartilage, annulus fibrosis, meniscus, tendon, and subchondral bone were analyzed using the electron microprobe to weight percentage content sulfur, calcium, and phosphorus. Sulfur concentrations were highest in articular cartilage and progressively decreased for annulus fibrosis, meniscus, tendon, and subchondral bone. Calcium and phosphorus content determinations were significant only in bone and confirmed values previously determined. Sulfur determinations have delineated a new technique for characterizing these musculo-skeletal tissues and, in some cases, appear to enable identification of a particular tissue by means of determining its sulfur concentration alone.

A POROUS SURFACED DIAPHYSEAL PROSTHESIS FOR LONG BONES

Publisher Summary This chapter describes a project that is currently underway in which segmental femoral prostheses made of cast solid core zimalloy with a replamineform porous coating replicated from the microstructure of astreopora are being tested. This gives a surface with average pore diameters of 300–500 urn. For production of these prostheses in the cobalt, chrome, molybdenum alloy, the machined coral aragonite is sintered to form CaO by dissociation of C0 2 without destruction or degradation of the original coral microstructure. Based on the measurements of the length and outer and inner diameters of the femora of more than twenty 15 kg adult dogs, a cylindrical stemmed prosthesis designed to replace the majority of the femoral diaphysis was manufactured. In all but three animals, there was evidence of radiolucency around one of the stems. This study represents one of the longer clinical trials in which segmental porous coated prosthetic replacements for long bones under true physiologic weight bearing stresses have been carried out. The results recommend that replacement for long bones can be made that will become fixed via bony ingrowth and produce a satisfactory clinical result.