An implanted porous palladium compact and platinum black with poly (tetrafluoroethylene) and poly (vinyl chloride) binders FIGURE 4. Surface area of platinum and palladium compacts FIGURE 5. Potential difference versus time across a platinum — iridium electrode and a porous palladium electrode. for various compacting pressures. The product of Vm, the cross-sectional area of the absorbate and Avogadro's number corrected to standard temperature and pressure gives the surface area, SBET 2.3. Scanning Electronmicrographs A scanning electron-microscope 2,3 was used to study the loose powders and compacts. The preparation of biological materials for the scanning electron microscope was as follows: Upon removal from the animal, the sample was washed in saline to remove mucous and fixed in glutaraldehyde. The sample was then using a succession of ethyl alcohol-water baths, i.e., 58, 90, 95, and 100 percent alcohol. The alcohol was dehydrated then replaced with amyl acetate. The samples were then freeze-dried in conventional manner, coated with gold, and examined in the scanning electron microscope. 2.4. Impedance Measurements a Electrode polarization, which greatly influences electrical impedance measurements, can be studied both from time and frequency domain measurements [19, 21, 33, 40]. Plastic cells of poly(tetrafluoroethylene) and poly(methyl methacrylate), consisting of thin-walled measuring chambers surrounded by circulating water for temperature control, were used for studying a variety of porous electrodes. For time domain measurements constant current pulse source is connected to the electrodes and the amplitude of the current pulse is increased in steps. The potential across the electrodes and current are measured at each level. The impedance measurements were made using a Wayne Kerr B221 Admittance Bridge which measures the parallel conductance and capacitance. The amplitude of the applied sinusoidal voltage is only 25 millivolts RMS which insures the electrical impedances are measured in the linear range, i.e., not in the range where impedance is a function of the amplitude of the applied signal. Measurements were made at 25 °C over the frequency range from 200 Hz to 20 kHz. While cell temperature was controlled and the pH and oxygen concentration was monitored with an oxygen meter. 3. Materials 3.1. Fabrication of Porous Electrodes Following powder metallurgy techniques, the loose powder is placed in a hardened metal die and is compressed und the particles becom magnitude of the influences the den compact. The re pends upon the which the powde pacts at 10,000powders at 30,00 tungsten at 80 Since no publi regarding comp strength, a nu powder electro compacting pre 30,000 and 50.0 with gradually strength of the sterilization in therefore left The stimula under a vari were fabricat powders wit then sintered poly(methyl blended wit under a hot Type JSM-2. Japan Electron Optics Laboratory Company, Ltd. 3 Certain commercial materials may be identified in this publication in order to adequately specify the experimental procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does it imply that the material are the best available for the purpose. [14] DeRosa, J. F., Beard, R. B., and Koerner, R. M., Improved Cathodes for Implantable Power Generating Electrodes, 23rd ACEMB, Washington, D.C., (1970). [15] Beard, R. B. DeRosa, J. F., Koerner, R. M., Dubin, S. E. and Lee, K. J., Porous cathodes for implantable hybrid cells, IEEE Trans. Biomed. Engr. BME-19, 233-238 (1972). [16] Koerner, R. M., Beard, R. B., DeRosa, J. F. and Miller, A. S., Porous Electrode-Tissue Interface Studies for Implantable Power Sources, Letters in Applied and Engineering Sciences 1, 163–177, (1973). [17] Greatback, W., Piersma, B., Shannon, F. D., and Calhoon, S. W., Jr., Polarization phenomena relating to physiological electrodes, in Part V of Advances in Cardiac Pacemakers, S. Furman, Editor, Annals of N.Y.A.S. 167, 722-744 (1969). [18] Jaron, D., A Study In-Vivo and In-Vitro of Electrical Correlates of Artificial Cardiac, Ph.D. Thesis, University of Penn., (1967). [19] Jaron, D., Schwan, H. P. and Geselowitz, D., A mathematical model for the polarization impedance of cardiac pacemaker electrodes, Med. and Biol. Engr. 6, 579–594 (1968). [20] Myers, G. H., and Parsonnet, V., Engineering in the Heart and Blood Vessels (Wiley-Interscience, New York, N.Y., 1969). [21] Jaron, D., Briller, S., Schwan, H. P., and Geselowitz, D., Non-linearity of cardiac pacemaker electrodes, IEEE Trans. in Biomed. Engr. 16, No. 2, 132 (1969). [22] Parsonnet, V., Zucker, R., Gilbert, L., Gerhard, L., Myers, G. and Avery, R., Clinical use of a new transvenous electrode, Part V, N.Y.A.S. 167, 756-760 (1969). [23] Thalen, T. H. J., van den Berg, J. W., van der Heide, J. N. H., and Nieveen, J., The Artificial Cardiac Pacemaker, C. C. Thomas, Springfield, Ill., (1969). [24] Hirschhorn, J. A., and Reynolds, J. T., Powder Metallurgy Fabrication of Cobalt Alloy and Surgical Implant Materials in research in Dental and Medical Materials, E. Korostoff, Editor (Plenum Press, New York, N.Y., 1969). [25] Hulbert, S. F., Morrison, S. J., and Klawitter, J. J., Tissue reaction to three ceramics of porous and nonporous structures, J. Biomed. Materials Res. 6, 347-374 (1972). [26] Smith, W. K., Frankl, W. S. and Boland, J. P., Transvenous pacemakers in clinical practice, Medical Clinics of North America 57, No. 4, (1973). [27] Schwan, H. P., Determination of Biological Impedances in Physical Techniques in Biological Research, Vol. VI, Part B, W. L. Nastuk, Ed. (Academic Press, New York, N.Y., 1963). [28] Schwan, H. P. and Ferris, C. D., Four electrode null technique for impedance measurement with high resolution, Rev. Sci. Inst. 39, No. 1, (April, 1968). [29] Schwan, H. P., Electrode polarization impedance and measurements in biological materials, Ann. N.Y.A.S. 148, (1968). [30] DeRosa, J. F., and Beard, R. B., Electrode Polarization Studies on Solid and Porous Platinum and Palladium, Proc. of 26th ACEMB, Minneapolis, Minn., Sept. 30Oct. 4, 1973. [31] Ferris, C. D., Further Studies of Signal Distortion by A-C Electrode Polarization and Other Factors In Neurological Recording, Proc. of 26th ACEMB, Minneapolis, Minn., Sept. 30-Oct. 4, 1973. [32] Pollak, V., An Equivalent Diagram for the Interface Impedance of Metal Electrodes, Proc. of 26th ACEMB, Minneapolis, Minn., Sept. 30-Oct. 4, 1973. [33] Damaskin, B. D., The Principles of Current Methods for the Study of Electrochemical Reactions (McGraw-Hill, New York, N.Y., 1967). [34] Bockris, J. O'M. and Reddy, A. K. N., Modern Electrochemistry, Vol. 2 (Plenum Press, New York, N.Y., 1970). [35] Brunauer, S., Emmett, P. H. and Teller, E. Adsorption of gases and multimolecular layers, Chem. Soc. 60, 309 (1938). [36] Emmett, P. H., Measurement of the Surface Area of Solid Catalysts, Chapter 2 of Catalysis, Vol. I, Edited by P. H. Emmett (Reinhold Pub. Corp., New York 1954). [37] Broekhoff, J. C. P. and Linsen, B. G., Studies on Pore Systems in Adsorbents and Catalysts in Physical and Chemical Aspects of Adsorbents and Catalysts, Edited by B. G. Linsen (Academic Press, London, 1970). [38] Krieger, K. A., Apparatus for surface area measurement, Ind. Chem. Engr. Annl. Ed., 398–399 (1944). [39] Adamson, A. W., Physical Chemistry of Surfaces (J. Wiley and Sons, New York, N.Y., 1967). [40] DeRosa, J., Linear Electrode Polarization Studies on Solid and Porous Platinum and Palladium, Dissertation, Drexel University, 1974. [41] Sturm, L. J., Fabrication and Evaluation of Cardiac Pacemaker Stimulating Electrodes, M.S. Thesis, Drexel University, 1974. [42] Klafter, R. D., An optimally energized cardiac pacemaker, IEEE Trans. on Bio-Med. Engr. BME-20, No. 5 (Sept. 1973). [43] Beard, R. B., Carim, H. M., Dubin, S. E., DeRosa, J. F., and Miller, A. S., Corrosion and Histopathological Studies on Anode Materials for Implantable Power Sources, J. Electro. Chem. Soc. 121, No. 8, 277C (1974). [44] Carim, H. M., Beard, R. B., DeRosa, J. F., and Dubin, S. E., Corrosion Studies on Anode Materials for Implantable Power Sources, ACS Div. of Organic Coatings and Plastic Chem., Symposium on Biomed. Application of Polymers, Chicago, Aug. 26, 1973. [45] Hoare, J. P., The Electrochemistry of Oxygen (Interscience, New York, 1968). [46] Ahrland, S., Chatt, J., and Davies, N. R., The relative affinities of ligand atoms for acceptor molecules and ions, Quart. Rev. (Chemical Society London) 12, 265 (1958). NATIONAL BUREAU OF STANDARDS SPECIAL PUBLICATION 415, Biomaterials, Proceedings of a Symposium held in conjunction with the Ninth Annual Meeting of the Association for the (Issued May 1975). Properties of Fibrous Biomaterials With Statistically Dispersed Orientation* E. Y. Robinson Prototype Development Associates, Santa Ana, Calif. 92705 Many factors influence the interaction between bone or soft tissue and implanted synthetic biomaterials, e.g., biocompatibility, implant configuration, functional requirements, bone and tissue structure, and relative mechanical properties. Of the many active factors, one aspect is considered here: the theoretical consequences of the fibrous-lamellar structure of bone, and of the degree of fibrous orientation present in the individual lamellae. This orientation is known to be statistically dispersed about certain preferred directions in each layer, with possible large orientation changes from layer to layer. Analysis of this type of structure is presented with graphical illustration of the effects of orientation and of statistical dispersion of orientation on conventional engineering material parameters. New biomaterials are being evolved which combine fiber reinforcement with polymer resin matrices (e.g., graphite fibers/polyethylene matrix). Such materials may be tailored to yield certain specific properties by controlling fiber orientation and quantity. Materials of this type are of interest in implants which may be required to behave in a similar fashion to adjacent bone tissue (as in bone splints, hip prostheses, etc.). The analysis presented here provides a rapid and convenient basis for calculating the effect of controlled and dispersed fibrous orientation on material properties. The methods described lay a base for first approximations and show certain directions which should be followed in further investigation. Graphical results include examples for both fibrous bone tissue models and synthetic types of fiber-reinforced biomaterials. Key words: Biomaterial properties; biomechanics; composites; fiber orientation; fibrous biomaterials. € (i) Strains Principal Young's modulus Secondary Young's modulus = E2/E1; anisotropy parameter Shear modulus in 1-2 plane direction; Coefficients of the multiple-angle formu- Angle of orientation of the natural longi- Stress-strain (stiffness) matrix of the *This paper presents the results of one phase of research carried out at the Jet Propulsion Laboratory. California Institute of Technology, under Contract No. NAS 7-100, sponsored by the National Aeronautics and Space Administration. 1. Bone and Soft Tissue as Layered Fibrous Materials The structure of bone tissue is highly fibrous and the fiber networks are often found in aggregated layers or lamellae. The nature of the lamellar bone structure varies within the musculoskeletal system and also within localized regions. Enlow in Evans [1] gave a concise description of several characteristic bone structures, two of which are reproduced here in figure 1. Various mechanisms of bone development described by Enlow result in generally striated or at least localized layering of bone. In some cases this oriented lamellar structure develops by successive layering around a nucleus, such as an osteon. In other cases the process seems to be a progressive densification, as in cancellous compaction. In still other cases the bone exhibits regular strata with 'Figures in brackets indicate the literature references at the end of this paper. |