Artificial Organs Vol. 3, No. 3

5.4

5.5

5.6

5.7

5.8

6. Test 6.1

6.2

determined by the formula: Fraction of unclotted blood=K, X O.D./ (gHb/cc blood)X(Volume in cell) K, is the predetermined proportionality constant of gHb/100 cc water to mea- sured optical density O.D. of the solution. The second is the direct measurement of the amount of clot formed. This is done by determining the dry weight of the clot, normalized by the amount of blood in the cell and hematocrit of the donor. The fraction of clotted blood is determined by the formula: Fraction of clotted blood= g dried blood/Hct% X K2 X Volume in cell K2 is the predetermined proportionality constant of dried whole blood (g) to the hematocrit of dogs blood. Normalized clot weight is plotted versus time. The difference between the clot weights obtained with the test material and the control is also plotted as a function of time; the area difference between the two curves provides a quantitative direct index for comparing different materials. The differences between the amounts of unclotted hemoglobin obtained with the test material and a control are also plotted, and the area difference between the two curves provides a n indirect index. Another set of test cells lined with test and control materials are filled as de- scribed and platelet counts are done on the unclotted blood after ten minutes of blood exposure to the material surface The reduction of the number of platelets as compared to that of the donors blood is termed platelet consumption. This rep- resents a n indication of the degree of nonadhesion of platelets to the materials studied. A minimum of ten tests are performed for each test material. The statistical signi- ficance for each curve is determined.

The test materials and control sheets were cut 2V2” in diameter and soaked in saline overnight prior to use. All test ma- terials were prepared at one time and stored in covered glass jars. The control sample used for this test is Silastic@ 372, MDX4-4156 (Dow Corn- ing, Midland, Michigan, U.S.A.) vul- canized at 150°C, coated with NaHC03,

Specimens

and washed in saline several days be- fore use. Healthy 20-25 kg dogs were fasted over- night and anesthetized intravenously with 300 mg of sodium thiamylal. Hema- tological parameters are checked fre- quently.

For the direct index, the more negative the number obtained with one particular material, the less clot formation on the surface of a material and, hence, the better its blood compatibility. For indirect index, the more positive number predicts better blood compatibil- ity than for the control material. The amount of unclotted blood (indirect index) is a n indication of the amount of red cell entrapment on a material’s surface. Platelet consumption rate in the ten- minute test cell will give information as to the natures of clot formed (Tables I and 11) whether it be a red thrombus or white thrombus type.

6.3

7. Interpreting the Results 7.1

7.2

7.3

5th Annual Meeting of the Biornaterials Society -

1st Meeting of the Canadian Society for Biornaterials

The 1979 annual meeting was held on May 16th, 1979, following a Workshop on Biomaterials in the Medical Devices Workshop Series sponsored by the Health Protection Branch (Health and Welfare Canada), the Canadian Association of Manufac- turers of Medical Devices and the Canadian Bio- materials Society at the Constellation Hotel in Toronto, Ontario, Canada. Orthopedic Session

The session on Orthopedics was chaired by G. M. McNeice and included the following papers: “The Troubled Hip - A Materials Problem”, H. U. Cameron, Toronto General Hospital, Toronto, Ontario, Canada. The failure rate of hip replace- ment is 1% per year mostly due to biomaterials problems. The long stem which is inserted into the femur has to be metallic as only metals are suffi- ciently tough. The metals currently being used are too stiff resulting in unphysiological load transfer and in relative movement between metal, bone and

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grouting agent. “The Effect of Time after Death and Preserua-

tion by Freezing on Properties of Canine Cruciate Ligament”, J. M. Dorlot, M. Ait Ba Sidi, G. M. Tremblay and G. Drouin, Ecole Polytechnique, Mo n tr ea 1 and Hot el Die u Ho sp it a I, Mo n t re a I, Quebec, Canada. The mechanical properties of the ligament were tested at regular time intervals up to thirty hours after dissection, and after being frozen at -18°C for 5 to 60 days. The results were as follows:

Average Results on Ten Ligaments in the Fresh State and after Conservation by Freezing

% variation % elongation

Stiffness at 100 N, N per unit strain 1790 ? 120 2100 ? 220 +17% Fracture not load, M 545 ? 180 590 f 200 significant “A Mechanical Fuse for Artificial Tendons and

Ligaments - A Preliminary Report”, G. J. Gouw and H. W. Wevers, Department o f Mechanical En- gineering, Queens University, Kingston, Ontario, Canada. Failure may occur either at one of the attachments of the prosthesis to the tissue, or in the prosthesis itself. A mechanical fuse, built into the prosthesis, allows control at the overload where the weakest link of the prosthesis will fail. The mechani- cal fuse should be chosen so that in case of failure, the least damage is done to the surrounding tissue, and that the best opportunities exist for salvage and repair or replacement. In the case of substitute medial collateral ligament, the mechanical fuse was incorporated between the layer of polyurethane and the polyester cords. The bonding strength between polyurethane and the polyester determines the load at which the fuse acts.

“Properties of CO-CR-MO Alloy Processed by Hot Isostatic Pressing of Powder”, W. Starkebaum, Zimmer USA, Warsaw, Indiana, U.S.A., and L. J. Barnard, Kelsey-Hayes Company, Brighton, Michi- gan, U.S.A. This alloy was originally developed in the 1930’s as a dental casting material and has served well in a wide variety of orthopedic implants, but there have been a n increasing number of reports of fatigue fractures of the femoral components of total hip prostheses. By using the process of hot isostatic pressing, the ASTM F75 alloy can more than double its fatigue strength, without changes in the chemical composition or the physical properties of the alloy.

‘% n v I ro n me n t a 1 I n f 1 ue nc es o n Mechanic a 1 Strength and Fracture of Metallic Implants”’, W. E. White, Department o f Mechanical Engineering,

at 100 N 9.4 * 0.4 7.3 k 0.9 -22%

Calgary, Alberta, Canada. Fracture in orthopedic implants is often initiated by stress-electrochemi- cal effects. The present study was designed to assess the specific roles played by various dissolved mineral ions (e.g., C1-, Na+, Ca2’. . .) and other en- vironmental influences (e.g., stress, temperature, pH . . .) on fracture initiation and subsequent crack propagation.

“Fatigue Testing of Harrington Spinal Distrac- t ion Rods - A N e w Design f o r Non-Fusion Surgery”, G. McNeice, E. Wong, J. Leidner and R. Gillespie, University of Waterloo, Ontario Research Foundation and The Hospital for Sick Children, Toronto, Ontario, Canada. In a number of pediatric patients, spinal distraction without spinal fusion is indicated. The Harrington rods are inadequate for this purpose because of fractures due to metal fatigue. New improved rod designs include 316L stainless steel and continuous carbon fiber rein- forced epoxy.

“Electrical Stimulation o f the Hard Tissue (State of the Art)”, K. Piekarski, Department of Mechanical Engineering, University of Waterloo, Toronto, Ontario, Canada. At a recent workshop on this subject, two clinically successful methods were presented: electromagnetic field stimulation and partially invasive D.C. stimulation. Research is in progress on electrostatic stimulation and on non- invasive methods of D.C. coupling through the skin.

‘%re Size Effect on Rate of Implant Fixation by Bone Ingrowth’, J. D. Bobyn, R. M. Pilliar, G. C. Weatherly and H. U. Cameron, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada. The purpose of this study was to determine the effect of pore size variation on 1) the rate of bone growth into porous surfaced metallic implants, and 2) the strength of fixation resulting from this ingrowth. Implants with porous surfaces of four distinct pore size ranges were implanted into canine femurs for 4, 8 and 12 weeks. The shear strength of fixation of the implants to cortical bone was determined. Pores in the range of 50 to 400 micrometers resulted in the greatest fixation strength (17 MN/m2) in 8 weeks. Invited Speakers

The following papers were presented by the invited speakers: “Tissue Tolerance o f Implant Materials I n Vivo”, V. Geret and S. Perren, Labora- tory o f Experimental Surgery, Davos, Switzerland. Implants with a specific form and shape are used for tissue tolerance studies in rodents. The shape is such that the tissue surrounding the implant fixes the material, thus precluding motion. The implant is placed some distance away from the incision, thus avoiding any effects of the surgical procedure or of

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the presence of suture materials. “The Use of Organ Culture for Testing o f Tissue

Compatibility o f Soluble Corrosion Products”, S. Perren, Laboratory fo r Experimental Surgery, Davos, Switzerland. Rat embryo femurs are dis- sected under the microscope and cultured using conventional methods of organ cultures. The growth rate is influenced by soluble corrosion pro- ducts providing a convenient quantitative assess- ment of the biological effects. Cardiovascular Materials and Artificial Organs

Robert Guidoin chaired the session on cardio- vascular materials and artificial organs: “Clarifica- tion of Flow Regimes in Platelet Adhesion Studies”, B. Thompson, A. Strong and W. Zingg, Department of Mechanical Engineering, University of Waterloo and The Hospital for Sick Children, Toronto, On- tario, Canada. The hydrodynamic characteristics of a new flow cell were analyzed using hot film ane- mometer techniques. Using controlled pulsatile flow, it was demonstrated that for the range of flow rate to be encountered experimentally, the flow is laminar. For purposes of transport or assessing flow damage, it is important to distinguish between unsteady laminar flow and turbulent flow.

“Heparinized SBS: Preparation, Evaluation, and Mechanism of Heparin Action”, M. F. A. Goosen and M. V. Sefton, Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, Ontario, Canada. The surface of the elastomer was hydroxylated and then coated with a n adhesive coating mixture containing heparin, polyvinyl alcohol (PVA), glutaraldehyde and magnesium chloride resulting in a permanent binding of heparin to the surface. In vitro and ex vivo testing indicated that the surface-bound hepa- rin is biologically active. Further studies suggest that a surface-bound heparidthrombin interaction brings about a conformational change i n t h e enzyme which accelerates complex formation with ATIII.

“Biomaterial Characterization by Interfacial Concentrations of Secretions from Adherent Plate- lets”, G. A. Adams and I. A. Feuerstein, Depart- ments o f Pathology and Chemical Engineering, McMaster University, Hamilton, Ontario, Canada. When platelets adhere to a surface they may release the contents of their granules into the blood. To as- certain which materials are available in sufficient quantites to exert an effect on thrombogenesis, the local concentration of released agents, which is flow dependent, must be compared with the minimum concentration known to stimulate platelets. The local concentration of released material is presented as a new parameter for predicting thrombogenicity

of biomaterials. ‘%xperimental Evaluation of Blood Compatible

Surfaces”, J. Pollock, W. G. Williams, E. W. Wong, B. J. Bellhouse, M. M. Silver and W. S. Howarth, The Hospital for Sick Children, Ontario Research Foundation, Toronto, Ontario, Canada, and The Department of Engineering Science, Oxford Uni- versity, Oxford, England. Test surfaces were sus- pended in the left and right atria of goats. The thrombogenicity of polyurethanes is influenced by the technique of sterilization and washing. Smooth surfaces elicit a different tissue response than porous surfaces.

“A Single Leaflet Mitral Valve: I t s Initial Design and Evaluation”, W. G. Williams, B. J. Bell- house, F. H. Bellhouse, W. s. Howarth, G. Kent and R. W. H. Lewis, The Hospital for Sick Children, Toronto, Ontario, Canada, and The Department of Engineering Science, University o f Oxford, Oxford, England. The newly designed mitral valve is D- shaped to conform to the normal mitral annulus. The central rigid occluder is hinged along the straight edge by a thin layer of polyurethane. In vitro tests have demonstrated superior fluid dy- namics; fatigue tests demonstrated normal function up to 650 million cycles. I n vivo performance has been studied in eight animals between 6 weeks and 1% years.

‘%lyethylene Terephthalate (Dacron@) Pros- theses as Arterial Substitutes - Evaluation of Com- mercial Grafts as Substitutes for the Canine Abdom- inal Aorta”’, R. Guidoin, P. A. Levaillant, M. Marois, C. Gosselin, L. Martin, C. Rouleau, P. Blais, P. Garneau, D. Gagnon and S. Bourassa, Laboratoire de Chirurgie Experimentale, Centre de Biomedecine et Departement de Chirurgie, Faculte de Medecine, Universite Laval, Quebec, Canada. Seventeen types of prostheses were investigated with scanning elec- tron microscopy and conventional light microscopy after implantation periods of one to six months. Velours exhibit superior tissue ingrowth but the in- ternal tissue lining does not generally submerge all of the fibers. Complete neoendothelialization is not achieved. More meaningful performance criteria should be described to allow a closer matching be- tween the products and clinical needs.

“Silicone Coated Biomaterials: Their Prep- aration and Preliminary Ex Vivo Evaluations”, A. S. Chawla, Artificial Organs Research Unit, McGitl University, Montreal, Quebec, Canada. Polymeric materials were modified by depositing thin layers of silicone polymer on their surfaces using plasma polymerization of hexamethylcyclotrisiloxane. There was a linear increase in the weight of the sub- strate material with time, reaching about 100

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pg/cm2 after 30 minutes of reaction. Blood com- patibility was established by circulating the blood from mongrel dogs over the test materials placed in a n ex uivo circuit.

“Molecular Basis of Immunological Response to Polymers”, N. Samji, L. Sun and P. Y. Wang, Insti- tute o f Biomedical Engineering, University o f Toronto, Toronto, Ontario, Canada. The essential requirement for immunogenicity is a reasonably high molecular weight (>500 daltons), while the nature and the sequence of the composing units do not appear to be important. According to this crite- rion, the possibility of immunological response to a number of synthetic polymers currently used as bio- materials cannot be excluded. Totally synthetic polymers with a hydrocarbon backbone may be im- munogenic in rabbits. Dental Mater ia ls

The session on dental materials was chaired by Derek W. Jones and included: “Dental Ceramic Materials”, D. W. Jones, Division of Dental Ma- terials, Faculty of Dentistry, Dalhousie University, Halifax, Nova Scotia, Canada. The so-called dental porcelains are closer to a glass in structure than a true ceramic or porcelain material. The majority of porcelain dental restorations use ceramic bonded to metal systems. Porcelain is an almost ideal den- tal restorative material; however, like all glassy materials it suffers from brittle fracture.

“Bonding of Model Bis GMA Resins Containing Various Dichlorotriazine Derivatives to Dentine”, G. Vougiouklakis, D. C. Smi th and B. Maric, Facul ty of Dentis try , Uniuersi ty of Toronto, Toronto, Ontario, Canada. Although bonding to enamel h a s been successfully achieved both through the acid etch technique-resin systems and materials based on the polyacrylic acid, bonding to dentine has proved more difficult. Current research involves the development of materials which chemi- cally interact with dentine through complexation with the calcium of the inorganic phase or through interaction with the organic phase (collagen). A new polymerizable system used as a thin interlayer be- tween a treated dentine surface and a commercial composite resin material is described.

“Dimensional Change o f Amalgam During the Setting Reaction’, L. N . Johnson, The Faculty of Dentistry, University of Western Ontario, London, Ontario, Canada. A new method for the study of di- mensional change of setting amalgam is described. A photonic sensor was employed which operates on the principle of reflected light. As the specimen expands or contracts, the distance between the tip of the sensor probe and specimen surface decreases or increases with corresponding change in output

signal. Twenty different amalgams commonly used in dental practice show great differences in dimen- sional profiles.

“Bonding to Calcified Tissues Through Crystal Growth”, D. C. Smith, R. Maijer, G. Keyes, G. Ben- nett and R. Peltoniemi, The Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada. A new method of bonding is based on the observation that enamel treated with polyacrylic acid contain- ing sulphate ions rapidly develops a copious growth of gypsum crystals on the surface. When a fluid polymerizable composition or a cement is flowed over the treated tooth surface, the crystalline de- posits provide strong anchor points for the material and a strong bond may result. Bond strength is similar to that obtained with the acid edge tech- nique. It was shown that similar crystals can be grown on dentine and bone surfaces. Business Meeting

Judges for the student paper competition were F. W. Rhinelander, P. Blais and G. Drouin. First prize was awarded to N. Samji. Second prize was given to J. D. Bobyn and third prize went to G. Vougiouklakis.

At the annual business meeting, the Canadian Society for Biomaterials (tentative name) was formally established. At the 1978 meeting, the Executive Committee of the Biomaterials Society was asked to obtain the opinions of scientists active in biomaterials research across Canada regarding the formation of a national society. As the opinions expressed were generally favorable, a motion was introduced to establish the Canadian Society for Biomaterials; the motion carried unanimously.

The following officers were elected - W. Zingg, President; R. M. Pilliar, Secretary-Treasurer; three regional representatives - D. Jones (Maritimes), G. Drouin (Quebec), R. H. Roydhouse (Western Canada). At the next annual meeting, a constitution will be introduced. The officers will explore the relationship of the new society with other organizations with similar interests on a national and international level, for instance with the Society for Biomaterials (The President, L. Katz, attended the 1978 meeting) and the European Society for Biomaterials (The Vice-president, J. L. Leray, attended the 1979 meet- ing). The Canadian Society for Biomaterials will participate in the World Congress in Vienna in 1980. The next annual meeting will be held in Mon- treal in August, 1980, under the chairmanship of G. Drouin.

Walter Zingg, M.D. The Hospital for Sick Children

Toronto, Ontario Canada

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