ALBERT

Notes: The weight-loss method was employed to determine the diffusion coeffcients of mercury in Ag2Hg3 alloy at temperatures in the range of 64-120°C. Diffusion coeffcients for nonhomogeneous specimens obey the relationship: \documentclass{article}\pagestyle{empty}\begin{document}$$ D = 2.18 \times 10^{ - 2} \exp \left({\frac{{ - 9.58 \times 10^3 }}{{RT}}} \right)\left({{{{\rm cm}^2 } \mathord{\left/ {\vphantom {{{\rm cm}^2 } {\sec }}} \right. \kern-\nulldelimiterspace} {\sec }}} \right) $$\end{document} Diffusion coeffcients for nonhomogeneous samples were found to be an order of magnitude greater than values found for homogeneous samples.

Notes: Various methods of roughening type 316 stainless steel substrate surfaces for flame-spraying alumina (Al2O3) were investigated and tested for the best alumina-to-metal bond strength. Best strength values were obtained by means of roughening via anodic polarization pitting of the stainless steel. Subsequent in vitro testing indicated a severe loss in bond strength following exposure to aerated Ringer's solution. It is suggested that the utilization of flame-sprayed devices has potential in orthopedic prostheses, but precautions must be observed.

Notes: A biomechanical concept of interface maturation around cement-free implanted alumina-ceramic hip endoprostheses in sheep is explained. Provided there is rigid primary stability of the implant within the bone bed, hard tissue formation along the support areas of the implant is mainly dependent on implant shape and main local stress direction. Three subsequent phases of interface maturation can be distinguished, finally resulting in firm fixation of the implant by mechanical interlocking of supporting bone and ceramic.A new composite alumina-metal hip endoprosthesis for partial cement-free implantation (cup) is presented. The technique, postoperative care, and encouraging early results in 5 patients are demonstrated. A new ceramic femoral component for cement-free implantation is proposed.

Notes: An animal model system for the investigation of the influence of in vivo- produced metallic corrosion products upon tissues has been developed. Externally applied electrical stimulation produces the corrosion over a short period of time, and a poststimulation period is allowed for tissue stabilization.Tissue reaction adjacent to the metallic alloys shows fibrous tissue capsules and metallic corrosion product contamination.These preliminary studies show that this animal model and methodology may provide a technique for investigating long-term tissue biomaterial interactions and the influence of iron (316L), cobalt (Vitallium), and titanium (Tivanium) alloy corrosion products upon the susceptibility of tissues to various biocompatibility challenges.

Notes: Research to determine whether porous-coated Vitallium intramedullary rods could be used to bridge segmental defects in long bones was performed using rabbit tibias as a suitable model for human bone growth. One-centimeter segments of the midshaft of tibias of mature rabbits were removed surgically and replaced with equal-sized segments of Silastic tubing to maintain leg length. A coated rod was inserted through the proximal tibial segment, through the tubing, and into the distal bone segment. The legs were taken out of plaster at 3 weeks, and x-rays were taken periodically until sacrifice.At sacrifice, 30 weeks postoperatively, the mechanical properties of both tibias from each rabbit were measured destructively in a torsional testing machine. The load at failure of the tibia with the segmental defect averaged 90% of the contralateral control tibia. Rod pullout data and electron-probe x-ray microanalysis indicated that a substantial rod-endosteal bone bond existed due to ingrowth into the porous coating. The torsional data may have been somewhat obscured by the presence of a bony callus which grew over the Silastic tubing and bridged the segmental defect exosteally in every case.

Notes: Procedures for applying nonporous bioglass coatings to fully dense, high-purity alumina are described. By altering firing temperatures and number of coatings, the rate of surface reactivity of the coated alumina can be varied. Bonding of bioglass-coated alumina to rat bones is reported as early as three weeks.

Notes: Efforts to explain blood compatibility with synthetic and natural surfaces based on a single parameter or a single biological test procedure have either been unsuccessful or led to misleading generalizations. The problem reflects the complex interdependence between material's properties, the composition and properties of blood, and in vivo biorheological conditions. Among the initial events that occur when materials contact blood is the very rapid adsorption of plasma proteins; this process effectively influences the subsequent interactions with the formed blood elements, especially the platelets with the proteinated surfaces.In the case of natural surfaces, when the endothelium is damaged, collagen may become exposed that may cause the activation, adhesion, and aggregation of platelets leading to thrombosis. Current evidence indicates that the platelet-aggregating ability of collagen depends on its “multimeric” or fibrillar structure, rather than on the activation of the platelet-bound enzyme system. Under normal conditions, the flowing blood is probably not in direct contact with endothelial cells that line the blood vessel walls, but with an adsorbed layer of plasma proteins. Should a formation of a multilayer of plasma proteins occur following the initial adsorption of a monolayer, this process could be influenced by changes in the solubility of the proteins, especially fibrinogen, the solubility of which is quite low in plasma. The hypothesis is proposed that such changes may be intimately related to the electrical properties of proteins present in the vascular wall and in blood. It is possible that these properties play a much greater role in thrombogenesis and in the problem of blood compatibility than is currently appreciated.Considering synthetic polymers, a number of these have been prepared that exhibit little adverse effects on blood components and, at the same time, retain their physical properties for various periods of time in the physiological environment. These combined biological and physical properties make them useful for various prosthetic and other biomedical applications in surgery and therapy.

Notes: The enzymatic activity of α-chymotrypsin (CT), immobilized on hydrogelcoated polymer film supports, has been investigated. The support was prepared by radiation-graft copolymerization of 2-hydroxyethyl methacrylate (HEMA) and methacrylic acid (MAAc) on silicone rubber films. The enzyme was covalently coupled to the carboxylic group of MAAc via the N-hydroxysuccinimide (NHS) ester active intermediate.Increasing MAAc contents of the hydrogel resulted in increased attachment of CT. The integrity of the CT active site after attachment was assessed by an active site titration with diisopropyl fluorophosphate (DFP). As the MAAc content of the hydrogel was increased, an increasing fraction of the attached CT retained its activity to DFP. A greater fraction of CT was active towards DFP when adsorbed than when coupled.The rates of hydrolysis of some synthetic model substrates by the immobilized CT were also measured. The negative charge on the hydrogel had a large effect on the rates of these hydrolyses. The pH optimum for the hydrolysis of N-acetyl-L-tyrosine ethyl ester (ATEE) by immobilized CT was higher than that of free CT. Increasing MAAc content of the hydrogel resulted in larger shifts in the pH optimum. The maximum rates of ATEE hydroylsis per mg CT declined sharply with increasing MAAc content of the hydrogel. This is probably related to the increasing repulsive force between the ATEE (negatively charged above ⋍ pH 9.5) and the hydrogel with increasing MAAc content. The activity of immobilized CT to ATEE is small compared to that of free CT, partly due to this charge effect. Conversely, the rate of hydrolysis of BAEE, a positively charged substrate, by immobilized CT at pH 11, is almost fourfold greater than that by free CT at its pH optimum.

Notes: A single application of fluoride to the epiphysis of the femur induced accelerated bone formation. The additional bone gave rise to a stability effect on the implant inserted in the femur as expressed by an increased dislodgement force required.

Notes: An evaluation of 0.2% buffered glutaraldehyde fixed tendon as a potential tendon replacement prosthesis was evaluated in rabbit and chicken models. In vivo implantations were done to determine compatability, function, and strenght of grafts, Autogenous fresh grafts were used as controls in the strenght in tension compares favorably to a fresh autogenous control. These preliminary evaluations indicate a useful potential for this fixed biomaterial as a tendon prosthesis.

Notes: A new biomaterial containing covalently bound hyaluronidase was prepared. An application of this enzyme membrane is to improve the performance of an implantable fuel cell. Hyaluronic acid is a contributor to the viscosity of tissue fluids but can be a potential fuel source because of its sugar content. The incorporation of immobilized hyaluronidase would not only contribute to a more available fuel supply by splitting hyaluronic acid but, perhaps more importantly, enhance the rate of mass transport of fuel, O2, and reaction products by reducing the viscosity near the electrode membranes. Hyaluronidase was bound to Sepharose gel and its thermoplastic membrane after activation by cyanogen bromide. Fourteen and 22% of the activities were recovered from the gel and membrane, respectively. The activity of the bound enzyme was stable for six months at 0°C. The addition of hyaluronic acid, 1 mg/ml, to a typical implantable type bioautofuel cell in vitro increased external solution viscosity from 1.1 to 2.5-2.8 cP and reduced voltage output under 10 kΩ by 60% in 3 hr. When the hyaluronidase bound membrane was placed at the anode, viscosity of the glucose-hyaluronic acid solution was lowered to 1.8 cP and the cell output increased to the original level of a glucose-fueled cell in 3 hr. Glucosamine-equivalent released from hyaluronic acid at the electrode was 3.1 mg after 22.5 hr. This represents 90% of the theoretical consumption. Restoration of the cell output was probably a combination of the enhanced transport of fuel, O2 and products, and/or appearance of a new fuel, glucosamine-equivalent.

Notes: A technique of creating localized heating by implanting metallic materials in the brain and inserting the head into a radiofrequency electromagnetic field is described. The heating properties of various materials for implantation were studied, and the two best materials were carbon steel rods and Hysterloy (1000 and 655 cal/g-min, respectively). Heating of these materials was done primarily by eddy current since their heating rates were significantly affected by their shapes and orientation in the field, rods oriented parallel to the field producing the most heat. There is evidence that warmer cells have a greater uptake of chemotherapeutic agents. This suggests a combined therapeutic approach employing localized brain heating in conjunction with systemic or intrathecal chemotherapy. In this way, large doses of chemotherapeutic drugs might be concentrated in a warmed brain tumor while toxicity is prevented by keeping the rest of the brain and body hypothermic.

Notes: Extensive studies have been made of the biomechanical properties of tissues in vitro. The majority of experiments demonstrate a “preconditioning” effect. This effect is associated with the differences between in vivo and in vitro conditions. Failure to utilize initial or isochronal data may lead to erroneous conclusions. Objective criteria would permit comparison between experiments.

Notes: Adhesion of Platelets to several polymer- and protein-coated glass surfaces has been studied in vitro. The apparatus consists of a cylindrical probe rotating in a test tube containing the platelet medium and allows close control of fluid shear and mass transport. Suspensions of washed pig platelets constitute the basic platelet medium, and can be modified by adding back red cells and plasma proteins. Adhesion is measured via 51Cr-labeling of platelets. In the absence of red cells, identical low levels of adhesion were seen on all surfaces and saturation was reached within 2 min. In the presence of red cells, adhesion was greater. Saturation on all surfaces except fibrinogen and collagen again occurred within 2 min. The adhesion levels on polymer surfaces and glass were indistinguishable, while those on albumin were lower and those on fibrinogen were higher. Collagen was the most reactive surface. It did not equilibrate within 15 min, and kinetic data indicated a platelet diffusivity strongly dependent on hematocrit. These effects were attributed to rotational and translational motion of the red cells causing increased diffusion and surface-platelet collision energy.

Notes: A percutaneous implant for the attachment of an artificial limb has been designed and tested in 14 pigs. Firm fixation to beone was achieved with the porous-surface layered metal intramedullary stem design in some cases. Dacron velour was used at the soft tissue interface. Evidence of soft tissue ingrowth was seen. However, the velour was unable to maintain adequate epithelial adhesion to form an anatomical seal and a barrier to bacteria.

Notes: A bioglass-coated fully dense alumina total hip was evaluated in sheep without using polymer bone “cement.” After 3 months following surgery, both the acetabular cup and femoral stem component were firmly attached to bone. Histologic and radiographic analysis of the bone-implant interface showed regions of woven and even lamellar bone formation where high load transmission occurred. In regions of low loading or poor fit, a pseudosynovial fibrous lining was present.

Notes: Utilizing rats as a model, it was demonstrated that both iliac crest bone and porous carbon disks, when used as onlay grafts, become vascularized as early as 3 days. There is no significant difference between the two. The soft tissues, periosteum, and recipient bone are all capable of supplying vascularization to the graft or implant.

Notes: The purpose of this report is to present our 5-year experience in reconstructing large bony defects in the cranial vault of 16 patients. The method employs an alloplastic implant device made of elastomer-coated cloth mesh, used in conjunction with bone grafting [D. L. Leake and M. Habal, J. Biomed. Mater. Res., 10, 555 (1976)]. The cranial defects ranged in size from 6 × 6 cm to 15 × 17 cm. The defects were in the frontal, temporoparietal, and occipital regions. Particularly challenging was the frontal-orbital region involving the superciliary ridges. The alloplastic implant provides controlled contour of the bone graft material while providing strength and stability during healing. The implant has adequate but not complete rigidity, allowing adaptability in the operating room. The elastomer used is a polyetherurethane. Any biocompatible cloth mesh can be used, but Dacron [poly(ethylene terephthalate)] was chosen because of its extensive implant history.Contrasted with reconstruction using only bone, where as many as half of the cases had uneveness and were found to be aesthetically unsatisfactory, the technique described here has resulted in aesthetically excellent results and an intact neurocranium in the 16 patients studied thus far.

Notes: A new adhesive fissure sealant, which consists of a solution of 3% 2-hydroxy-3-β-naphthoxypropyl methacrylate in methyl methacrylate (MMA), poly-MMA powder and an oxidized tri-n-butyl borane, a polymerization initiator, was developed. Tensile bond strength between an acid-etched bovine enamel and a poly-MMA bar joined by this sealant was 60 kg/cm2, and the value did not decrease much after 30 days immersion in water at 37°C. Penetration of fuchsin into the sealant-enamel interface during a percolation test was not observed. SEM observation showed no voids between the enamel and the cured sealant.

Notes: The adsorption of fibrinogen from single solution and from mixed solution with albumin and γ-globulin has been followed at the air-buffer, isooctane-buffer, and methylene iodide-buffer interfaces by the pendant drop technique. Fibrinogen is shown to form substantial coherent films on isooctane and methylene iodide, suggesting considerable unfolding and lateral association. From this, a novel hypothesis has been proposed to account for the dominance of fibrinogen adsorption from mixed solutions on certain hydrophobic surfaces, in which the spreading pressure of rapidly unfolding fibrinogen molecules is sufficient to desorb other plasma proteins.

Notes: Five composite filling materials were finished using six finishing procedures currently in clinical use. The average roughness produced by each procedure was measured by means of a Surfanalyzer with four replications for each procedure on each of the five materials. Statistical analysis indicated that finishing with silicon carbide disks produced the smoothest surfaces. Acceptable surfaces were obtained with stones or with burs. Use of an alumina paste after a green stone-white Arkansas sequence did not produce a significant improvement.Two processes of filler particle abrasion were distinguished by means of electron microscopy: wear and shear. Fracture striations indicated particle shear.The roughest surfaces were produced by the use of a diamond instrument which is contraindicated. Acceptable finishing procedures for the composite materials tested include silicon carbide disks for accessible areas or 12 fluted finishing burs for more inaccessible areas.

Notes: The daily in vitro release of hydrocortisone from composite polymer capsules is reported here for over 120 days. Increase in vinyl acetate comonomer content of the ethylene-vinyl acetate copolymer matrix brought about an increase in the diffusion rate. Variation in the initial drug content of the capsules from 40 mg to 20 mg affects the daily drug release less significantly than the variation in copolymer ratio. The correlation between vinyl acetate comonomer content and the percent crystallinity of the copolymer matrix is suggested as one of the possible major factors in controlling diffusion rate from this drug-polymer system. The diffusion constant (D) calculated was 0.212 × 10-10 cm2/sec when the copolymer carrier has 30% vinyl acetate content and 0.430 × 10-11 cm2/sec when the copolymer carrier has 20% vinyl acetate content for capsules with 20 mg initial drug content, and 0.118 × 10-11 cm2/sec and 0.226 × 10-11 cm2/sec, respectively, for capsules with 40 mg initial drug content.

Notes: Four self-curing acrylic bone cements were surveyed by infrared, solubility, viscometry, quantitative metallography, microscopy, and physical testing techniques: CMW, Palacos R, Sulfix-6, and Surgical Simplex P. Results show that these bone cements were primarily composed of poly(methyl methacrylate) and that no cross-linking was evident. Solubility analysis confirmed this latter observation, as the bone cements dissolved completely except for a small insoluble fraction, which was identified as the radiopaque filler. For each bone cement, the viscosity-average molecular weights of both the powdered phase and the cured two-phase product remained unchanged, varying overall from 1 to 5 × 105. Using standard quantitative metallography, porosity ranged from 1 to 8% and the dispersed powder phase decreased 11-46%. Microscopy revealed the nature of the porosity, radiopaque fillers, the powder size and shape, and the fracture morphology. From tensile and fracture toughness tests, five physical properties were determined at ambient conditions and at 37°C after conditioning in distilled water at 37°C for 10 months: the modulus of elasticity, the ultimate tensile strength, the elongation at break, the fracture energy, and the mean inherent flaw size. At ambient conditions, the ultimate tensile strength decreased 33-55% when compared with commercial unmodified poly(methyl methacrylate), Plexiglas G. While the fracture energy remained rather invariant, the mean inherent flaw size increased fivefold over the commercial acrylic tested. This marked increase in the mean inherent flaw size could lower the fatigue resistance of a material, since more and/or larger fracture initiation sites are available. When tested at 37°C after protracted conditioning, the deleterious trends observed at ambient temperature continued. To some degree, porosity, particle-matrix interfaces, residual stresses, low molecular weight products, inorganic and/or other organic additions, and water contributed to the inherent flaw size at the expense of the working stress. Several modifications are suggested by which the importance of these factors might be minimized.

Notes: The evaluation of the efficiency of polymer additives with special emphasis on uv absorbers and antioxidants in polyurethane elastomers has been completed. Aliphatic polyurethanes were chosen for this study because their properties closely relate to the requirements of maxillofacial prosthesis. The polyurethane elastomers were either synthesized by ourselves or formulated according to the manufacturer's recommendation. Eleven different types of uv absorbers, coupled with one antioxidant, were incorporated into the polyurethane systems. The Atlas twin-lamp carbon arc Weatherometer was used as the source of uv. The samples were periodically withdrawn for examination of yellowing and tackiness. It was found that, although the incorporation of uv stabilizers enhanced the uv resistance of polyurethanes, the problem of tackiness resulting from uv aging was not solved satiafactorily. The phenomenon of yellowing, however, was significantly improved, mainly due to the aliphatic structure of polyurethanes. The most promising uv absorbers are Tinuvin 770 and the combination of Tinuvin 328, ZnO, and an antioxidant. Their effectiveness in other polyurethane systems is not known and further research is underway to explore this field. Hopefully, these findings will greatly assist the successful application of polyurethane elastomers in maxillofacial prosthesis.

Notes: Heparinized dog blood was exposed to shear and foreign surfaces in conicylindrical test cells. The cells were injection molded from polycarbonate and were filled using a technique that avoided contact of the blood with air. Particulate-matter formation was measured and was found to be dominated by the surface-to-blood-volume ratio and to be independent of shear rate. Hemolysis was also measured and was found to vary linearly with shear rate and to increase with increasing surface-to-blood volume ratio. Thus, at low shear rates and high specific surface conditions, the degree of hemolysis was found to be minimal while particulate-matter formation was high. The results suggest that the safety of extracorporeal perfusion procedures cannot be inferred from hemolysis measurements alone. In one series of tests, a gas-blood interface was generated at a rate equivalent to the rate of surface renewal in conventional disc oxygenators. The gas-blood interface failed to contribute significantly to the damage indices, which suggests that the apparent superiority of membrane oxygenators may be a result of factors other than the absence of a blood-gas interface.

Notes: A microporous filler giving greatly improved finishability, systemic nontoxic X-ray opacification, low thermal expansion (27.2 × 10-6/°C), and satisfactory translucencies has been developed for dental composite resin restorations. These fillers are prepared from frits obtained by the low-temperature calcination of gelled inorganic sols followed by a pulsed high-temperature treatment. Composites prepared from these fillers are within the range of commercial products with regard to strength and setting contraction.

Notes: Reconstituted bovine collagen has been used extensively in our laboratory as a carrier for immobilized E. coli L-asparaginase. The activity and catalytic stability of these collagen-asparaginase membranes can be altered substantially by conditions used in membrane crosslinking with glutaraldehyde. As the concentration of glutaraldehyde used in tanning is increased, the initial specific activity of collagen-asparaginase membranes decreased asymptotically to a limiting value. Similar results occurred when membranes were subjected to increasing time periods of tanning at a constant glutaraldehyde concentration. These observations point to a time-concentration relationship for glutaraldehyde tanning and its effect on the specific activity of collagen-asparaginase membranes. Specific activities of membranes tanned at glutaraldehyde concentrations of 5% or higher appear to be very stable over long periods of alternate storage and assay. This result, however, is not observed with membranes tanned at glutaraldehyde concentrations lower than 5% for short periods of time (approximately 30 sec to 1 min). It is not clear whether the instability of membranes tanned at lower concentrations of glutaraldehyde or shorter intervals of tanning is due to enzyme elution from the membrane or denaturation of the bound enzyme.

Notes: The corrosion of carved, burnished, polished, and burnished-polished samples of a conventional spherical amalgam was studied by anodic polarization in Ringer's solution. The effect of the variation of the mercury content from 40 to 60 wt% on the corrosion of burnished or polished samples was also investigated. It was found that burnished and burnished-polished samples corrode the least and carved samples the most. The current-density peak associated with γ2 was of greater magnitude in polished specimens than in burnished specimens throughout the range of mercury concentrations investigated. It is hypothesized that lower porosity and more ready passivation of the surface due to a high amount of γ2 are the reasons that burnished samples corroded less than polished samples in this anodic polarization test.

Notes: A method is shown by which to identify wear particles of implanted plastic materials in tissue. A Mettler FP2 hot stage was used to determine the melting point of different elastomer particles in normal histological sections between the crossed nicols. By using a microcolorimeter Type MPE (Leitz, Wetzlar, Germany), additional information about the molecular degradation of wear particles was obtained.

Notes: We describe the preparation and some of the properties of heparin-bound α-chymotrypsin that were obtained via activation of heparin with water-soluble carbodiimide. Immobilized enzyme has unchanged kinetic characteristics toward low-molecular-weight and macromolecular substrates. The heparin-bound enzymes could have a wide range of medical applications.

Notes: Surface configurations are vessels fabricated from tubing and plate, films deposited on the surface of vessels, and beads confined in vessels. The average association constant between thrombin and sites on commercial poly(methyl methacrylate) surface (Lucite) is near 4 × 108 liters/mole at 22°C, pH 7.0, and ionic strength 0.15. Depending on Lucite composition, average adsorption U, in molecules/cm2 of apparent solution-surface interface, ranges from 0.7 to 8.8 × 1011. Analysis based on the assumptions that solution dimensions are preserved, adsorption is random, and surface rearrangement is negligible indicates a paucity of surface sites. Plasma albumin competes with thrombin for surface sites. Attempts to detect, by thrombin adsorption, the presence of free sites at 4.5 × 10-9 M albumin or the displacement of bound albumin indicate an albumin-site association contrast greater than 1.6 × 109. Cross-linked poly(methyl acrylate) bead surface has U less than 5 × 1010. In contrast to acrylic resins are silicone gum, polypropylene, and polyisobutylene, for which U ranges from 15 to 20 × 1011. Analysis as above indicates that sites are of frequent occurrence. Material composition suggests that thrombin can interact with nonpolar groups. Further characteristics of low-energy surfaces are that progressive surface denaturation is small and there is a large variance between nominally equivalent configurations.

Notes: A high-modulus polymer, polysulfone, was evaluated as a porous bone implant material. The bone ingrowth into canine cortical pellets of sintered polysulfone particles was assessed by microradiography and histology. The shear strength of the porous polysulfone-bone interface was determined by push-out and pull-out tests of cortical and trochanteric implants, respectively. Results indicated that the bone in-growth into porous polysulfone specimens proceeded in such a fashion as to mimic the normal repair at the site. Mechanical testing of cortical and cancellous implants revealed that the interfacial shear strength of the porous polysulfone-bone composite was similar to that achieved using porous metals.

Notes: A method is shown for deducing the surface area of a pendant drop from the same profile photograph as is normally used to determine interfacial tension. Manipulation of such drops by a micrometer syringe then enables the pendant drop to be used as a surface balance for studying adsorption from bulk solutions. Results are given for the compression of films from solutions of albumin, γ-globulin, fibrinogen, albumin-γ-globulin mixture and albumin-γ-globulin-fibrinogen mixture, and from serum, plasma, and blood at the isooctane-buffer interface. It is suggested that γ-globulin and fibrinogen films are unfolded at the interface but that albumin films are different in that they consist of an inner, unfolded layer and an outer, globular layer. A film from serum resembles that from γ-globulin alone, and not that from albumin-γ-globulin mixture, whereas a film from plasma resembles that of fibrinogen at low compression and that of albumin-γ-globulin-fibrinogen mixture at high compression. A film from blood is shown to resemble that from plasma.

Notes: The rates of adhesion of melanoma cells (carcinogenic) onto nonionic polymer surfaces were studied by using radioactively labeled cells and measuring the fraction of cells which adhered to the surface in a given time. Glow discharge (plasma) polymerization of 1,1,3,3-tetramethyldisiloxane and of nitrogen-acetylene-water (mole ratio 0.4:1.0:0.2) was used to modify the surface energy of the substrate. The cell adhesion rate was found to be given by Y = 1 - exp [-k0(γs - γ0)t], where Y is the fraction of cells adhered, - k0 is a characteristic rate constant, γs is the total surface energy of the substrate, γ0 is the threshold surface energy of cell adhesion, and t is time.

Notes: An ideal combination of mechanical and corrosion properties of long-term implants such as joint endoprostheses has yet to be found. Besides being resistant to pitting and crevice attack, which can lead to corrosion fatigue and stress corrosion cracking failures, the implant material must be highly resistant to wear and abrasion. Two cobalt-based alloys, wrought CoNiMoTi and air-cast CoCrMo, were subjected to a number of selected in vitro electrochemically and chemically accelerated corrosion tests in chloride-containing solutions with wrought AISI-316L used as a reference alloy. A limited number of immersion tests in FeCl3 and acidified FeCl3 solutions were also conducted. It is found that the mechanical properties of wrought CoNiCrMoTi alloy qualify it as a substitute for cast CoCrMo alloy and wrought AISI-316L in anchorage shaft production for all types of joint endoprostheses. Wrought CoNiCrMoTi has a higher resistance to fatigue cracking compared with cast CoCrMo and is as resistant to selective corrosion phenomena such as stress corrosion cracking.

Notes: Measurements of the permeability coefficients of various compounds up to a molecular weight of about 70,000 have shown clearly that membranes prepared from hydrolyzed polyacrylonitrile are about 10 times more permeable than those made of poly(2-hydroxyethyl) methacrylate. The higher permeability is probably due more to the higher water content (about 75%) than to the type of network. The high mechanical strength of the membranes and their good permeability to compounds possessing a comparatively high molecular weight seem to designate the material for some new applications in medicine.

Notes: A study has been made of the fractures and associated material from 34 prostheses broken in service. All the fractures appear to be of the fatigue type. Search by me-tallographic analysis for cracklike generating defects in material near the fracture reveals such conditions as abnormally coarse crystals, large nonmetallic inclusions, large inclusion population, undissolved master alloy particles, abnormal carbide segregation, interdendritic segregation, shrinkage, and gas porosity. Recommendations are made for the choice of metallic alloys for femoral stem application.

Notes: The effect of combining gentamicin and cephalothin with Surgical Simplex bone cement was tested in vitro. Experiments were designed to determine (1) quantitative elution rates and period of time the antibiotics were eluted and (2) effective bactericidal qualities. Both antibiotics were eluted from polymerized acrylic cement in large quantities within 24-48 hr after coming in contact with fluid and continued to be released in smaller amounts for 21 days to more than 175 days. This varied with the antibiotic, concentration of antibiotic in the cement, surface area of cement, and volume of elution fluid. Quantitative determinations of numbers of bacteria in broth cultures demonstrated that sufficient quantities of antibiotics were released to be bactericidal to microorganisms within 45 min to 20 hr. This was dependent on the type of antibiotic, type of bacteria, concentration of antibiotic in the cement, and time of contact.

Notes: The present study was conducted in order to understand the microstructural characteristics in dental amalgam which consists of both spherical and irregular Ag3Sn alloy particles with gold substituted in varying amounts for silver (0, 9, and 15%). Spherical alloy particles were used as obtained from Western Gold and Platinum and irregular alloy particles were prepared in the laboratory and then employed in the present study. The amalgam was prepared from the alloy particles by the trituration and condensation method. The polished and etched samples were studied using the techniques of X-ray diffraction, optical metallography, scanning electron microscopy, and X-ray energy dispersive spectroscopy. The microstructure in both types amalgam studied after two weeks of preparation contains γ (unreacted Ag3Sn particles), γ1 (Ag2Hg3), and γ2 (Sn7-8Hg) phases in pure Ag3Sn-amalgam and γ, γ1, and (Au-Sn) phases in gold-containing amalgam. The (Au-Sn) phase existed in the form of rings surrounding the γ grains and acted as a barrier for mercury diffusion in Ag3Sn particles.

Notes: Some of the mechanical properties of regrown canine tendons are compared to those of normal tendons of young and mature animals. Patellar and Achilles tendons from 12 beagle dogs were removed and studied with their bone origin and insertions. Mechanical tests were performed within 24 hr and test conditions simulated the physiological function of the tendon in vivo at room temperature. Specimens were soaked in Ringers solution and mounted in an Instron testing machine with load deflection curves plotted automatically. The parameters used for analysis were load extension, stress relaxation, elastic limit, and strain rate dependence.The regrown tendons in young animals appeared to quickly adjust in dimension and structure so that their properties were not significantly different from those of normal tendons on a load extension basis.The normal tendons were stiffer than regrown ones but the modulus of elasticity increased with age. The Achilles were stiffer than patellar tendons. Cyclic loading with 25 kg did not affect reconstructed tendon models, although some increase in stiffness was noted. The elastic modulus decreased with an increase in ambient temperature and increasing strain rate.

Notes: A biostability test program was designed after evaluation of the relevant literature on in vivo aging phenomena in plastics and elastomers. The program comprised macroscopic, microscopic, mechanical, and physicochemical investigations. Five silicone rubbers, one polyester, and one polyamid were tested as to their aging behavior and their suitability for long-term implantation in the human body was assessed. In order to be able to state the applicability of materials used for endotheses, the various aging phenomena had to be divided into three groups, viz. unspecific, relative, and absolute indications of aging or unserviceability.Changes due to aging were found in all types of implanted plastics and elastomers. Thus, the formation of layers on inlay surfaces occurred regularly and the same would apply to changes in mechanical characteristics during the tensile test. Aging processes resulting in total unserviceability were fragmentation and crazing in the polyester and polyamide sheetings. Other aging phenomena which will easily fit into the classification given above are changes in electrical test values, protein, and lipid depositions without stronger absorptive adhesion, crystallizations on the surface of silicone vulcanizates, and chemical changes in the polyester and polyamide sheetings.Following the assessment of the materials used for endotheses, the test methods used have been evaluated with regard to their suitability for the testing of biostability.

Notes: Studies were designed to demonstrate the need for standardization of shape of samples used as implants to evaluate histotoxicity of polymer materials. Six medical-grade polymers (polypropylene, polyethylene, polyurethane, silicone rubber, poly(vinyl chloride), and Teflon) were extruded as rods with circular-, triangular-, and pentagonal-shaped crosss ections, and were implanted in rat gluteal muscles for 14 days. Evaluation of the tissue response was assessed by quantitating cellular lysosomal acid phosphatase enzyme activity by using microspectrophotometry. All triangular-shaped implants showed the highest enzyme activity and cellular response; pentagon shapes showed less, and circular rods showed the lowest activity. The results demonstrate the need for standard sample shape for valid comparative studies of tissue response to implanted polymers.

Notes: In recent years, significant advances have been made in treating surfaces to enhance their biocompatibility. This has generally involved the chemical attachment of very thin molecular coatings to a substrate. Because failure of coated surfaces occurs often, an investigation of the stability of one such molecular coating was undertaken.The specific system being studied is a polytetrafluoroethylene polymer (Teflon) with organic macromolecules of heparin ionically bonded to the polymer through use of an intermediate bonding agent. Polymers properly treated in this fashion have been shown to have excellent antithrombogenic properties. To investigate the molecular stability of the heparin coating, the surface heparin concentration of a properly coated sample was reduced by using three different methods: exposure of bonding agent to a suitable solvent; mechanical flexing; and ultrasonic vibration in saline solution. Changes in heparin distribution, average concentration, and biocompatibility were measured.Observation of the heparin distribution was accomplished by decorating the surface with vapor-deposited gold nuclei, stripping, and then examining the replica in a transmission electron microscope. Comparisons of the nucleation replicas show definite differences in the gold nuclei patterns for heparin, untreated Teflon, and the intermediate bonding agent-covered areas. Average heparin concentrations were measured separately by radioisotope labeling. Biocompatibility was determined by exposing the samples to platelet-rich plasma in closed flow chambers and subsequent examination for microthrombi on the scanning electron microscope.These experiments have shown that the original molecular coat does not completely cover the surface even though radioisotope labeling indicates enough molecules present to form a 5000-10,000 Å covering. The heparin does cover more than 95% of the surface; however, uncoated areas less than 2 μ in diameter are dispersed throughout.In all three methods of surface heparin removal, the heparin was removed in association with its intermediate bonding agent. Rather than the molecular layers gradually decreasing in thickness, certain areas become void of heparin while adjacent areas are unaffected. This results in the formation of heparin islands as the concentration is further reduced.The treated surfaces can lose their biocompatibility whenever heparin-denuded areas greater than 20 μ in diameter are present. Usually, this will occur when the heparin-coated surface area drops below 30%. Such a surface theoretically has sufficient heparin for a 500 Å thick continuous molecular coat.Definite differences exist in the heparin distribution pattern resulting from the different techniques used for degrading the surface. Mechanical flexing results in highly selective areas of heparin loss, ultrasonic vibration results in more continuous hepain loss, and solution exposure results in random areas of heparin loss.A molecular coated surface may fail prematurely, even when enough molecules are present to form a multilayer continuous coat, due to the presence or creation of microscopic molecular denuded areas. The creation of these denuded areas on a surface is dependent upon the type of degradation the surface undergoes.

Notes: In order to elucidate the general patterns of intermacromolecular surface interactions that may be involved in hemocompatibility phenomena, monolayers of representative macromolecules on an octadecylsilylated glass surface were exposed to solutions of other macromolecules, and the changes in interfacial composition were characterized by zeta potential-pH titration curves, as measured by alternating flow streaming current analysis and, in some cases, by radiotracer labeling. Experiments with poly(vinylpyrrolidone) (PVP), a blood-compatible linear polymer; bovine serum albumin (BSA), a representative serum protein; whole human serum (HS), a complex mixture of proteins; and erythrocyte surface glycoprotein (GP), an extended-chain macromolecular amphiphile, showed the following: (1) Penetration of the original monolayer occured within 24 hr in 9 of the 12 possible cases; it did not occur for BSA or HS monolayers exposed to PVP, and probably not for PVP exposed to GP. (2) In all cases, penetration was accompanied by no more than partial displacement of the original monolayer, thereby generating a mixed monolayer. Each of the six possible binary mixed monolayers could be obtained by at least one of the two possible mixing sequences. (3) In the three binary systems containing BSA, the formation of the mixed monolayer could be related to increased adsorption in the two-component system. (4) The two components of the mixed monolayers were not equally distributed across their thicknesses: thus, the outer surfaces of the PVP-BSA and (at neutral pH) the PVP-HS mixed monolayers contained only PVP; that of the BSA-HS mixtures only HS. In the PVP-HS, and probably the GP-BSA and GP-HS mixed monolayers, the composition of the outer surface appeared pH-dependent. The resultant zeta potential versus pH profiles in the latter two cases resembled those of intact blood cells.The results suggest that neither the compact monolayers of globular proteins nor the diffuse monolayers of randomly coiled water-soluble polymers can, by their prior adsorption on a synthetic surface, prevent the subsequent adsorption of other globular macromolecules. It is possible that the randomly coiled polymers may impede the adhesion of platelets to the substrate since the results indicate that the adsorption of such polymers causes a displacement of the shear plane.

Notes: Two of the primary problems of implants in use today result from the materials used in their construction (metal and polyethylene) and from the necessary additional fixation with bone cement. In order to alleviate these well known difficulties, we studied ceramic material (99.7% Al2O3 with 0.25% MgO) which exhibits several advantages in these areas, but has a diminished bending stregth.To take advantage of the ceramic material, we tested a cement-free implantation which should allow unhindered growth of bone tissue to or into the material. In particular, the interface relationship under load bearing was investigated.The course of the tissue differentiation and ingrowth on the surface of the ceramic implants under dynamic stress, was studied by a specifically designed distance-spacer. These were tested on the femur of foxhounds and sheep, as well as by use of temporary immobilization. Histological investigations in intervals of 4 weeks showed the course of the development of the interface tissue. After removal of the binding materials, the behavior of the implant support is studied in 4-week intervals with free load bearing. Radiological and histological development studies are shown.The results we obtained implicate the use of ceramic implants. But the application in humans still seems to be problematic, as there is a need for designs which are loaded by pressure only.

Notes: Success in the use of custom-fabricated Silastic implants in patients with facial contour defects led us to utilize this method in reconstructing mandibular defects. However, mandibular reconstruction with alloplastic material is quite difficult because of the presence of continuous stress and motion in that region. The evolution in the use of the mandibular implant from the commercially available one to the K-wire reinforced, prefabricated, silicone implant was largely dependent on the availability of silicone and the ultimate result obtained.In the past few years, about 30 subdermal implants were inserted. Some of those implants were placed immediately into patients undergoing resection for tumor. The implant was prefabricated prior to surgery from x-ray measurements of the anticipated segment to be resected; it was then used to reconstruct the defect prior to the final closure of the operative wound. Other implants were manufactured 6-18 months after resection for tumor or for deformity as a result of trauma. The implants were used to reconstruct the facial defects and to correct the functional abnormality, such as drooling or deviation of the affected side by the unstable mandibular segment. Patients with severe congenital malformation have soft tissue deficiency in association with their bony malformation. Therefore, implants in such conditions were doomed to failure.Patient selection is the key to successful implantation.

Notes: Following the initial successes of Goldberg and Gershkoff (Dental Digest, 5, 11, 1947) with the placement of subperiosteal implants, interest in all types of implants emerged. As an aid to the evaluation of various designs and materials without resorting to clinical testing, finite element analyses are being conducted by a number of researchers to determine the stress system induced in bone. The present study investigates the effects of variation in the thicknesses of the periodontal membrane and cortical bone and of the model boundary on the stresses developed around a natural tooth or a tooth-shaped implant. The results show that strong effects due to the variation in these parameters can be expected. As a consequence, the problem of the analysis of any single implant must consider additional factors. These can influence overall implant design and may eventually help to explain what could appear as anomalies in clinical test results.

Notes: Determinations were made of how the corrosion-resistant properties of the passive film on 316-L stainless steel are influenced by the material's mechanical and surface states, and the variable pH and PO2 conditions of the interstitial fluid.Cold-rolled and annealed specimens were surface-prepared, commercially and in the laboratory, respectively, as if for orthopedic implantation. Passive film behavior was studied by the anodic polarization and pulse- potentiostatic capacitance methods. The pH and PO2 of the Ringer's test solution were varied to include interstitial fluid values occurring postoperatively and onto recovery.The anodic polarization behavior of all specimens was found to be pH- and PO2-independent. Breakdown potentials of annealed specimens were 800-950 mV (SCE), in contrast to previously reported values of approximately 350 mV. This substantial increase is related to the influence of surface preparation and, in particular, to the optimization of electropolishing time which acts to produce a microscopically smooth surface, free of debris and disarrayed material. Capacitance behavior of annealed material for potentials 〉 400 mV was consistent with a model involving the entry of chloride and metal ions (mostly Fe) into the passive film. This entry is related to the onset of pitting.

Notes: The derivation and experimental verification of a unified mathematical model for the estimation of drug release rate from drug-polymer composite tablets are presented. Cylindrical coordinates are utilized in the solution of the diffusion equation for a three-dimensional system. The model is applicable to tablets that range from the shape of a flat disk (radius 〉 thickness) to that of a cylindrical rod (radius 〈 thickness). The general solution for the fraction of drug released at a time t is \documentclass{article}\pagestyle{empty}\begin{document}$$ \frac{{M\left(t \right)}}{{M\left(\infty \right)}} = 1 - \frac{8}{{l^2 a^2 }}\sum\limits_{m = 1}^{10} {\exp \left({ - D\alpha _m ^2 t} \right)\left({\alpha _m ^{ - 2} } \right)\sum\limits_{n = 1}^{10} {\exp \left({ - D\beta ^2 _n t} \right)} \left({\beta _n ^{ - 2} } \right)} $$\end{document} This approach to a three-dimensiona system, utilizing cylindrical coordinates, presents a comprehensive method for the estimation of drug release rates from sustained release tablets with drug distributed homogeneously throughout a polymer matrix. The calculated and experimental drug diffusion rate of pyrimethamine from pyrimethamine-silicone rubber composite tablets that range in shape from that of a disk to a cylinder, and of hydrocortisone from EVA, poly-caprolactone, and PVA terpolymer, are compared.

Notes: A new polymer-ceramic composite suitable for tooth-root implants has been developed in this study. This material exhibited the desirable combination of good mechanical properties, controlled porosity, and ease of processing. A thermal processing technique was utilized to polymerize acrylic acid (AA) in the presence of either 0.3 or 0.05 μ alumina particles. Porosity and pore size distribution were influenced by the alumina particle size and the processing technique. For a 50 vol % AA solution, the composite had an average compressive strength of 18,000 psi and 38% porosity when 0.3 μ filler particles were used. In comparison, the 0.05 μ alumina-filled composite had an average compressive strength of 28,000 psi with a 15% porosity.Data on the physical and structural characteristics of the composite are presented in this study. Based on these results, the composite material shows good potential for use in tooth-root implants as well as other orthopedic implant applications.

Notes: A tougher, more fatigue-resistant bone cement consisting of short, highmodulus carbon fibers dispersed randomly in normal poly(methyl methacrylate) bone cement has been developed. Fatigue and impact tests are reported that demonstrate the superior fracture resistance and prolonged load-carrying ability of this system.The use of this carbon fiber-reinforced bone cement in the treatment of a pathological fracture of the femur associated with neoplastic disease of the bone is reported. The tougher cement has provided long-term stability of the fracture.

Notes: The elimination and retention of a new, fully synthetic plasma prosthesis of Czechoslovak origin under the working name of Duxon (poly[N-(2-hydroxypropyl)methacrylamide]) was investigated in experiments on rabbits by using a 14C-labeled polymer. Results published earlier on elimination have been confirmed and extended. Retention was examined after repeated application. The effect of molecular weight prevailed both in elimination and in retention. Polymers of lower molecular weights, which possess a good therapeutical effect, are not permanently deposited in the organism.

Notes: We have studied the contact interaction of platelets with hydrogels. In the form of microspheres, 0.6-1.0 μ, poly (glycol methacrylate) (poly HEMA) and poly (methyl methacrylate) beads cause platelets to aggregate at concentrations of about 108 beads/ml. Polyacrylamide and (20/80) poly (acrylamide-HEMA) copolymer were ineffective in aggregating platelets. The admixture of 20% methacrylate to polyHEMA rendered the beads inactive. Blood plasma components other than fibrinogen were found essential to the interaction of the beads with platelets. Near-infrared spectra of the hydrogels polyacrylamide and polyHEMA showed the water hydrogen bonds to be the same for both and different from those in pure water. The monomer HEMA is an inhibitor of platelet aggregation and the release reaction at levels of 0.1%. It is concluded that the two hydrogels have different blood compatibilities, which depend more on the network structures than the water structures in the respective gels.

Notes: The Avcothane 51 elastomer, a member of a series of proprietary materials best characterized as polyurethane/poly(dialkylsiloxane) block copolymers, displays considerable hemocompatibility without any incorporated anticoagulants. In the form of intra-aortic balloons, the elastomer was implanted in several thousands of cardiac patients without intolerable hematologic effects. Hemocompatibility has been assumed to result from a predominantly dispersion-type surface force field whose intensity fluctuates within small domains, maintaining adsorbed blood proteins in an unstable state. The relative hemocompatibility of films, which were obtained from a prepolymer solution cast on substrates impenetrable to the solvent, is a function of the effective surface molecular structure. This can vary as a function of preparative conditions (temperature and rate of evaporation), and has been correlated with an anisotropic distribution of the silicone component in cured films. The concentration of this component in surface layers was quantified independently by IRATR spectroscopy and electronmicroprobe analysis, giving consistent results. An IRATR index, which is computed from the ratio of absorptivities measured at 13.00 and 12.62 μ and is inversely proportional to the relative silicone content of surface layers, was found to correlate with the apparent hemocompatibility determined by different in vitro methods. Optimized reproducible hemocompatibility is attained by strict process controls.

Notes: Examination of a great number of tissue samples taken from the newly formed capsules surrounding artificial joints reveals small particles of prosthetic material. Abraded from the joint by wear and tear, these particles of plastic, metal, and acrylic cement initiate a foreign-body reaction and result in the formation of granulation tissue, including macrophages and foreign-body giant cells. Typical features of tissue reactions exist for each of the materials from which prostheses are made. The consequent formation of scar tissue produces a thickening of the capsule, which, in turn, may cause a reduction in the mobility of the joint.In small amounts, the foreign-body particles are eliminated via the perivascular lymph spaces. Where this transport system is insufficient to handle the volume, however, the foreign-body response may extend to the whole environment surrounding the joint. In such cases, there may be loosening of the cemented prosthetic parts because of deterioration of contiguous bone anchors by the tissue membrane lining the bone cement.

Notes: An evaluation of a porous biodegradable ceramic, tricalcium phosphate, has been carried out. When implanted in cancellous bone, it is rapidly infiltrated with bone and slowly resorbed. When held rigidly against raw, bleeding, cortical bone, again rapid bone ingrowth occurs.The material does not give rise to any untoward tissue reaction, nor does it cause any systemic reaction. It can therefore be concluded that the material is safe for use in clinical practice, and can be used in specific instances either to replace or to supplement bone grafting.

Notes: The preparation and some properties of microspheres composed of oxidized polysaccharides and some vinyl polymers are described. The microspheres contain immobilized enzyme and can be slowly solubilized in water solutions, thereby releasing active a enzyme into the surrounding medium. The kinetic characteristics of the immobilized enzyme bound with a fragment of matrix after complete solubilization are unchanged, but the enzyme exhibits high thermostability. These preparations could have a wide range of medical applications, e.g., to form a drug “depot” directly in an affected organ.

Notes: A new antithrombogenic polymer was synthesized by photoinduced graft copolymerization of both a hydrophilic polymer and a cationic polymer to hydrophobic poly (vinyl chloride) copolymer, and by quarternizing and heparinizing the obtained graft copolymer.For polymers of various compositions obtained by the method described above, chemical composition, water absorption, membrane potential, and quantity of adsorbed heparin were determined and antithrombogenicity evaluated in vivo. Thus, it has been found that the polymer of excellent antithrombogenicity has a negative membrane potential, a moderate elution rate of heparin, adsorbs heparin in a quantity of approximately 15 wt-%, and has a degree of water adsorption of about 30 wt-%. Also, measurement of membrane potential was very useful for the estimation of the quantity of the adsorbed heparin and its change with time.

Notes: The influence of heat treatment of dental alloys at several temperatures on the phases present in the alloy and the creep of the resulting amalgam as well as the correlation between phase changes and the creep was investigated. A dependence of the creep on the temperature of the heat treatment of the alloy was established. Substantial phase changes were observed after the different heat treatments. No correlation was detected between the creep rate and the changes in phases present in the dental alloys. A thermodynamically oriented explanation of the relation between the creep of the amalgam and the state of (non-) equilibrium of the corresponding amalgam alloy was proposed and discussed.

Notes: Techniques are described for fabrication of electrode arrays for stimulation and/or recording from a human cerebral cortex. These arrays may be neurosurgically inserted (with or without a Penrose drain) in the course of a conventional craniotomy or craniectomy, and are easily removed without reopening the ineision. Termination of the connecting wires in a special percutaneous pedestal has also permitted chronic implantation. The contacts and connecting wires are made of pure platinum embedded in a Teflon ribbon-cable matrix. The choice of materials combines biological acceptability, electrochemical stability, and integrity of the insulation, but imposes special fabrication procedures.

Notes: A series of copoly(α-amino acids) with varying percentages of hydrophilic (l-aspartic acid) and hydrophobic monomers (l-leucine, β-methyl-l-aspartate, and β-benzyl-l-aspartate) were implanted subcutaneously in rats and the macroscopic degradation behavior was studied. Three groups of materials (A, B, C) with different ranges of hydrophilicity were distinguished: A) hydrophobic materials showed no degradation after 12 weeks; B) more hydrophilic materials revealed a gradual reduction in size of the samples, but were still present after 12 weeks; and C) hydrophilic copolymers disappeared within 24 hr.The tissue reactions caused by the materials of group A resembled that of silicone rubber, whereas those of group B showed a more cellular reaction.

Notes: In vitro mechanical tests have been performed on a variety of LTI pyrolytic carbon blade-type dental implants, and the test results have been analyzed using an analytical model. Tensile stresses at fracture were calculated to be about 5 × 104 psi and 8 × 103 psi in the LTI carbon coating and the graphite substrate, respectively. These values are close to their respective fracture strengths. The fracture loads predicted by the model are in good agreement with data obtained from the mechanical tests and are higher than forces expected in mastication.

Notes: Spiral-coiled membrane lungs of 0.6 m2 surface area were fabricated from silicone rubber membranes coated with four types of commercially available pure-gum polysiloxane rubber: 1) polytrifluoropropylmethylvinylsiloxane, 2) polymethylphenylsioxane, 3) polymethylvinylsiloxane, and 4) polydimethylsiloxane.Membrane lungs were tested in an arteriovenous shunt without added heparin after bypass was begun. All groups except group 4 had major rise in resistance to blood flow or clotting in over 33% of the membrane lungs studied, after 6 hr of bypass. Membrane lungs with polydimethylsiloxane (group 4) had no rise in resistance to blood flow during 24 hr of bypass and had the least amount of changes in blood platelet count.

Notes: Formation of opaque deposits on the anterior (air) surface of hydrophilic soft contact lenses is a problem worthy of investigation by all concerned. These deposits have been analyzed for biomaterials by chemical, biochemical, electrophoretic, and immunological techniques. Qualitative and quantitative chemical colorimetric tests revealed the presence of variable amounts of protein (5-10 μg/lens), carbohydrate (1.0-1.2 μg/lens), and phospholipids (0.01-0.05 μmole/lens). Cholesterol and glucose were not present at detectable levels. Fluorescent antibody tests with appropriate controls gave positive tests for albumin, lysozyme, γ-G-globulin, and α1-lipoprotein in the deposits, all proteins presents in tear fluid. Deposits were most effectively removed from the lenses by the combination of heat, sodium dodecyl sulfate (SDS) detergent, and the thiol reagent dithiothreitol (DTT). SDS-denatured protein migrated on polyacrylamide gels with electrophoretic patterns corresponding to molecular weights for those proteins detected by the above antibody tests. The nature of the bonding interactions of biomaterials to the lenses was probed by chemical reagents used to remove them, employed singly and in all possible combinations. Urea, guanidine hydrochloride, potassium thiocyanate, potassium perchlorate, hydroxylamine, and EDTA were much less effective than SDS and DTT. These data suggest that apolar interactions plus disulfide bonds may be important in stabilizing the deposit structure, and point to improved cleaning procedures.

Notes: Rapid and reliable methods for the characterization and quantitative determination of ingredients usually present in self-curing methacrylate bone cements were developed using spectrophotometric, gas chromatographic (GC), and conventional gravimetric procedures. These procedures are applicable to non-crosslinked methacrylate resins. In the presence of some copolymers, polymer blends or crosslinking agents, or other ingredients which will result in the formation of insoluble methacrylate resins, some modification of the identification procedures and quantitative estimation of the resin components will be required. Molecular weight and molecular weight distribution of the powder and cured cement were obtained from viscosity and gel-permeation measurements. Residual low molecular weight materials in the cured cement were determined for various storage times. Residual and water-leachable monomer and residual dimethyl-p-toluidine (DMPT) were measured by GC. In air, the monomer content of the cured resin decreased from 3.3% after 1 hr to 2.4% after 215 days. When stored in water at 37°C, over 65% of the extractable monomer is leached out within 10 min. After 6 hr, the rate of diffusion of monomer into the aqueous phase is low. The cured cement contains as much as 0.6% DMPT, which does not leach out. Residual peroxide, estimated spectrophotometrically, amounts to 0.8%, but decreases to 0.14% after 15 months in water at 37°C. A semiquantitative colorimetric test indicated that the hydroquinone content of specimens analyzed within 24 hr after curing amounted to 9 ppm.

Notes: The effect of collagen modification on the magnitude of stress-generated potentials has been studied. A whole bone model has been developed for determining the effects of collagen crosslinking on the electrical signals. Increased crosslinking results in larger electrical signals, and such increases result whether in vivo or in vitro changes in the collagen are made.

Notes: The peak temperature reached during the polymerization of a bone cement was reduced by addition of solid N-vinylcarbazole to the powder component. It was also necessary to saturate the liquid component with N-vinylcarbazole to prevent dissolution from the modified powder component on mixing. It is believed that this technique is generally applicable and opens up the possibility of achieving temperature control of bone cements with choice from a range of crystalline monomers.

Notes: This study determined the difference in rate of degradation between pure polymers of lactic acid (PLA), glycolic acid (PGA), and various ratios of copolymers of these two substances. Fast-cured and slow-cured polyglycolide was compared with copolymers of glycolide/lactide intermixed in ratios of 75:25, 50:50, and 25:75, as well as pure polylactide. A total of 420 rats were implanted with carbon-14 and tritium-labeled polymers in bone and soft tissue. At intervals of 1, 2, 3, 5, 7, 9, and 11 months, groups of five animals with the implants in bone and five with the implants in the abdominal wall were sacrificed. The implant area as well as tissue from the liver, spleen, kidney, lung and some muscle tissue was analyzed for radioactivity along with the urine and feces collected throughout the experiment. Half-lives of the different polymers and copolymers were calculated from the radioactivity present in the implant area for each time interval. Half-life of the polymers and copolymers decreased from 5 months for 100% PGA to 1 week with 50:50 PGA:PLA copolymer and rapidly increased to 6.1 months for 100% PLA. Fast-cured PGA had a half-life in tissue of 0.85 months. No difference in rate of degradation was seen in soft tissue or bone. No significant radioactivity was detected in urine, feces, or tissue samples. From this study, it is concluded that control of degradation rate of the implant could best be attained by varying the composition of PLA and PGA between 75% and 100% PLA along with a corresponding 25% to 0% PGA. This would provide a half-life range of the implant of from 2 weeks to 6 months.

Notes: The feasibility of preventing platelet adhesion to porous foreign surfaces in contact with blood by passing (perfusing) a physiologic fluid through the pores into the blood was tested. Porous-walled tubes of Teflon (Gore-tex) and aluminosilicate ceramic were perfused with lactated Ringer's solution at rates between 3.13 and 0.3 cc/min per cm2 of perfused surface and exposed to heparinized and unheparinized flowing human whole blood for periods of 3-6 min. Under these conditions, with 0.159 cm I.D. tubes and a mean blood flow rate of 8.3 cm/sec, the adhesion of all blood cells was prevented, compared with the adhesion of 1 to 8 × 106 platelets/cm2 on the nonperfused controls. The adhesion of plasma proteins was also markedly reduced as determined by bromophenol blue staining.The critical perfusion rate to prevent platelet adhesion to Gore-tex (0.5 μ pore size, 60% pore volume) was found to be between 0.04 and 0.3 cc/ (min · cm2). The boundary layer produced by a perfused segment of porous tubing prevented platelet adhesion for several centimeters downstream from the perfusing segment under experimental conditions used.

Notes: The present status of skeletal fixation of permanent orthopedic implants by poly(methyl methacrylate) (PMMA) is discussed. It is proposed that alternatives to the acrylic cement can improve the skeletal fixation. The present paper is concerned with the fixation method by bone ingrowth into pores of the implant surface.Two different implantation models have been designed to investigate the influence of load bearing upon ingrowth in surface pores of the implant: intramedullary nails as a means of fixation of a femoral pseudarthrosis and hinged knee prostheses. In each animal, implants with identical material characteristics (pore size, density, and thickness of the porous layer) but different loading conditions were used: one implant was “statically” loaded, the other “dynamically.” This procedure allows the evaluation of ingrowth with regard to load bearing only.Two different mean pore sizes, viz., 87 and 110 μm, have been used with the two models. After an 8 week implantation period, bone ingrowth was evident for the statically loaded implants. Calcified tissue ingrowth was, however, not observed in the dynamically loaded implants. The discrepancy in bone ingrowth behavior between the statically and the dynamically loaded implants has been attributed to 1) the gross movement or the micromovement existing at the bone prosthesis interface and 2) the fact that the critical mean pore size for ingrowth with static loading is smaller than the one with dynamic loading.The experimental implantations allow still another conclusion: the results suggest that designs of present clinical prostheses fixed by bone cement cannot be used with the alternative fixation by bone ingrowth unless the deisgn has been changed in a fundamental way. Mechanical factors as well as the phenomenology of bone ingrowth fixation account for this conclusion.

Notes: A study has been carried out on the structure and surface texture of a new dental implant material composed of silica microspheres (3 or 5 wt %) and poly(methyl methacrylate). A recently developed composite material composed of vitreous carbon microballoons and poly(methyl methacrylate) has proven highly successful in clinical use, but the black color presents aesthetic problems at the gingival margin. The new material was developed in order to reproduce the many desirable qualities of the vitreous carbon-polymethacrylate composite, while omitting the black color. Square wafers (10 mm × 10 mm × 1 mm) were studied, with the surface sandblasted in half of the specimens. Light microscopy revealed an even spacing of spherical configurations throughout the material. Scanning electron microscope studies revealed a finely porous surface with many large craters in the sandblasted specimens.

Notes: An in vitro method has been developed for screening of candidate biomaterials in an early phase of their development. The test is based on L-929 mouse fibroblast cultures and their response to powdered polymer samples. It applies microscopic observation for the detection of morphological changes, uses dye exclusion testing for cell viability determination, and utilizes estimation of population doublings as an end point. The test is shown to be reliable and reproducible and is compared to in vivo implantation studies in rats, previously reported.

Notes: Surgically produced fractures of rabbit tibiae were internally stabilized with in tramedullary rods of stainless steel (316LVM), titanium (6A1,4V), polyacetal (Delrin), and polyamide (Nylon 101). Periodic radiographs were taken until sacrifice at 16 weeks after fracture. Structural properties of the tibiae were determined in torsion with the rods in situ, and then the tissue was prepared for histology or microradiography.The results demonstrated that fracture remodeling was adversely affected by the metal rods. New bone was seen to have formed over the ends of the metal rods, and cortical bone resorption was observed in the fracture region, suggestive of transfer of mechanical stress to the rods, resulting in stress shielding of the diaphysis. Negligible osseous response to the polymeric rods was observed; fracture callus remodeling was extensive. The torsional test results demonstrated that fractures with polymeric rods were significantly stronger and tougher than those with metallic rods. With the exception of titanium, the strength of healed fractures was inversely related to the elastic moduli of the implant materials.

Notes: The degree of microleakage between a restoration and the cavity wall is difficult to quantify objectively. A silver-staining method is used and compared to the radioisotope method with results that indicate a superior definition and more accurate evaluation of microleakage. In addition to the accuracy, two advantages are presented: (1) scoring of the leakage can be refined and divided into more precise numbers, and (2) teeth can be observed directly in a microscope without resorting to the indirect interpretation of film or photograph.

Notes: Porous high-density polyethylene specimens were implanted in the femurs of mongrel canines. At the end of the residency period (3 or 6 months), the animals were sacrificed and the implants were retrieved. The work-of-fracture of the implant specimens was then determined using the technique of Tattersall and Tappin. The work required to fracture a specimen in three-point bending by controlled crack propagation through a triangular cross section was obtained directly from the load-deflection curve. The area of the resulting fracture surface was measured by macro-photographic techniques, and the work-of-fracture was calculated as work per unit area. The implants were subsequently sectioned and examined microradiographically to determine the extent of bone ingrowth. Bone specimens adjacent to the implants and porous high-density polyethylene controls (no ingrowth) were also tested to determine their work-of-fracture. The results showed that bone adjacent to the implant specimens had a higher work-of-fracture than normal medial, canine femoral bone and was not appreciably different from the composite. The work-of-fracture of porous high-density polyethylene was not significantly increased by an increase in bone infiltration, and this anomalous behavior was attributed to a degradation of the polyethylene during implant residence. Control studies supported this hypothesis.

Notes: Removal of bilirubin by hemoperfusion with ion exchange resin particles is suggested to replace exchange transfusion of blood of jaundiced infants in some cases of unconjugated hyperbilirubinemia. The hemoperfusion system developed here consists of a packed bed of a macroreticular resin which is made biocompatible by a coating of a monomolecular layer of albumin. The choice of the appropriate ionic form of the resin and the proper albumin coating and crosslinking procedure assures a high bilirubin adsorption capacity and excellent blood compatibility of the resin. The albumin coated resin removes in vitro 80-90% of the bilirubin initially present in the plasma. The results encourage in vivo clinical studies.

Notes: Double catheter systems consisting of a stiff outer catheter and a flexible, buoyant, flow-directed, inner catheter which is often balloon-tipped have been employed with increasing frequency recently in both therapeutic and diagnostic procedures. Their use, however, has been restricted because of the excessive friction generated between the two catheters. In an attempt to decrease friction between polymers commonly used as catheter materials, oxidation of polyethylene, fluorinated ethylene-propylene copolymer, poly(vinyl chloride), silicone rubber, and polystyrene surfaces was induced by exposing the polymers to radio frequency glow discharge (RFGD) in a helium environment. All polymers were surface characterized utilizing x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and contact angle measurements before and after oxidation. This article describes the materials and methods used to fabricate and characterize the polymer surfaces and the results of the characterization. The results indicate that increases in oxygen concentration at the surface of the polymers and decreases in air-water contact angles occur with increased RFGD exposure time. Plateau values were usually obtained after 5-30 s exposure time, yet no apparent changes in surface topography were noted by scanning electron microscopy. The hydrophilic surfaces produced were stable for up to three months storage time in air.

Notes: The new composite concept of microfilled composites has certain advantages, such as polishability, permanent smoothness, and high abrasion resistance. In the mouth, however, these new materials are not perfect and they often fail in stress-bearing restorations. In the present study, the weak links and imperfections of these materials are determined by means of direct and indirect SEM techniques. The chemical adhesion between polymer blocks and polymer matrix is questionable; fractures occur most often at the filler-matrix interface. In vivo, there is still a certain preferential wear of the resin matrix. In Estic Microfill, rear weak zones with starlike condensations are observed, which could be related to a certain incompatibility of its composing resins and/or to incomplete and inhomogeneous polymerization. In a fractured Isopast restoration, the polymer blocks are clearly revealed, scattered in a three-dimensional polymerized matrix network.

Notes: Ion beam etching has provided a system which can produce a controllable surface morphology in the micron range without altering surface chemistry or surface energy. PTFE (polytetrafluoroethylene) develops a surface texture having conical projections with average dimensions: height = 12 μm, base width = 4 μm, tip radius = 0.1 μm. Smooth and textured PTFE disks (1 cm diam. × 250 μm thick) were implanted subcutaneously into the dorsum of Sprague-Dawley rats for time periods of 1 and 3 days and 1,2,3,4, and 8 weeks. Smooth control samples consisted of untreated surfaces and surfaces that were exposed to an ion beam environment producing a smooth surface. All smooth surfaces behaved identically by both histochemical and histological methods. Consequently, the ion beam environment had no effect on the soft tissue response. Textured surfaces, however, demonstrated increased cell adhesion and increased succinic dehydrogenase and acid phosphatase staining in the interfacial cells. Interfacial cells consisted of foreign body giant cells and macrophages. These macrophages possessed increases in the cytoplasmic-to-nuclear ratio, number and interdigitation of filopodia, and vacuolization as demonstrated by TEM. The textured surfaces also influence the kinetics of fibrous capsule formation. At 8 weeks, capsules associated with textured interfaces were reduced in thickness by 30% when compared to smooth surfaces. The results of this investigation demonstrate that the surface texture of an implant is a critical variable in determining the soft tissue response to a material.

Notes: Some physical, chemical, and biological characteristics of a heparin-PVA hydrogel potentially useful as a thromboresistant coating for the preparation of small-diameter vascular prostheses and blood-sampling catheters have been determined. The molecular weight between crosslinks in the acetal crosslinked gel was approximately 8000, permitting proteins the size of albumin to enter the interior of the gel. The release rate of heparin from a gel containing 7 mg/g gel was 10-2 μg/g min which was significantly lower than the reported minimum required for thromboresistance of ionically heparinized materials. Nevertheless, in vitro biological activity was observed in both thrombin time and plasma recalcification time assays, which could not be attributed to the release of heparin into the incubated plasma. Correlation of final heparin contents with the amount of terminal amino acid residues in three samples of heparin suggests that the heparin is bound to the PVA in the gel through the amino acid terminus; this provides a plausible explanation for the retention of biological activity by the immobilized heparin.

Notes: The flexural strength, microstructure and relative Ca and Si concentration at the surface of two commercial orthopedic aluminas were studied before and after aging up to 52 weeks in simulated body fluids or in subcutaneous implantation in rodents. There was no significant reduction in flexural strength after aging, but there was evidence of Ca and Si dissolution from the external grain boundary surfaces, particularly for specimens aged in demineralized water. No change occurred in the Ca and Si concentrations within the specimen's bulk during either in vivo or in vitro aging.

Notes: Biochemical features of pseudomembrane formed at the bone-cement interface of 13 failed total hip replacements were studied and histological examination of the pseudomembrane was conducted. The results of biochemical analyses revealed on average hydroxyproline, 86 μg/mg; water content, 57%; hexosamine, 12 μg/mg; glucosamine/galactosamine, 1.4%; and calcium, 2.1%. Approximately 78% of collagen was extracted with pepsin, whereas only 8 and 0.3% collagen were extracted with acetic acid and neutral salt, respectively. On further differential salting out of the extracted collagen, about 77% was type I collagen, 19% type III, and 2.6% type V. Unlike pseudoarthrosis of fracture, no type II collagen was identified. Overall biochemical features in the light of the histological appearance suggested that pseudomembrane resembles granulation tissue. Bone healing mechanisms at the bone-cement interface appear to differ from that of fracture healing.

Notes: Dental porcelain frits have been prepared by the gel route, a procedure involving solubilization of alkalies, boron, rare earth, and other compounds in an alumina-silica sol. Using this procedure, porcelain frits suitable for metal-ceramic application have been prepared that fire to maturity at temperatures lower than current commercial porcelains. Solubilities, translucencies, thermal expansion coefficients, dilatometric softening temperatures, and flexure strengths are within the ranges of current commercial porcelains. The high degree of dispersion of pigments and phosphors made possible by gel route technology and the technology's ability to disperse crystalline phases to strengthen porcelain offers many processing advantages. Gel route technology also offers a great degree of freedom in modifying porcelain properties.

Notes: Cell spreading and cell division rates of a transformed line of mouse lung fibroblasts were studied on various polymer surfaces in the presence of serum proteins. The bare polymer surfaces, as well as the protein-coated surfaces, were characterized by their polar (γsp) and dispersion (γsd) surface free energies. Cell spreading appeared to be dependent on the polar surface free energy. Cell spreading is low when the γsp of the bare surface is lower than 5 erg cm-2; marked spreading occurs when γsp is higher than 15 erg cm-2. A similar relationship was found between cell spreading and polarity of the protein-coated surfaces, although less pronounced than for the bare surfaces. Cell spreading appeared independent of the dispersion surface free energy. Cell division rate was the same on all surfaces tested.

Notes: Strain measurement within the cement surrounding stemmed total hip femoral components was accomplished using PMMA encapsulated and embedded strain gauges. Cement strain measurement associated with a well-bonded stem-cement interface and an unbonded stem-cement interface (i.e., loose prosthesis) was performed. The presence of a stem-cement bond was found to reduce proximal cement strain magnitudes while having little effect on distal cement strain magnitudes. The assurance of a stem-cement bond on only the proximal third of the interface was found to have an effect similar to that of a complete stem-cement bond. The results of this experimental investigation confirm the theoretical prediction that the stem-cement bond is important in maintaining the integrity of the cement mantle surrounding a stemmed femoral component.

Notes: We report development of special macroporous semipermeable membranes and diffusion chambers made of polymerized 2-hydroxyethyl methacrylate (pHEMA), synthesized specifically to enclose living insulin-producing pancreatic islet cells for the treatment of diabetes. This material was selected to minimize the fibrotic encapsulation which has limited hybrid artificial pancreas efforts with other membranes, including Millipore and Nuclepore filters. The pore density and pore size distribution were dependent on the ratio of water to HEMA monomer and also on the crosslinker (EGDMA) concentration. A macroporous membrane resulted only when the ratio of water/HEMA monomer was greater than 50%. 125I-insulin permeability was studied in vitro. A technique is also described to fuse the membranes to form diffusion chambers used for implantation into diabetic rats.