Showing papers in "Journal of Biomedical Materials Research in 1977"

Reactions of the articular capsule to wear products of artificial joint prostheses.

Abstract: 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.

Degradation rates of oral resorbable implants (polylactates and polyglycolates): Rate modification with changes in PLA/PGA copolymer ratios

Abstract: 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.

Collagen sponge: Theory and practice of medical applications

Abstract: Theoretical as well as practical-clinical applications of one form of collagen (collagen sponge) as a biodegradable material is reviewed. The role of porosity of the sponge and surface characteristics of the meshwork in relation to cell ingrowth are considered essential features of collagen sponge. Rate of resorption and antigenicity could be controlled by graded crosslinking of collagenous framework. Four basic examples of clinical use of collagen sponge are presented: as wound (burn) dressing material, as a matrix, for bone and cartilage repair, as an intravaginal contraceptive diaphragm, and as surgical tampons.

Evaluation of biodegradable ceramic

Abstract: 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.

Development of semicrystalline poly(vinyl alcohol) hydrogels for biomedical applications.

Abstract: Swollen crosslinked poly(vinyl alcohol) (PVA) networks were developed and tested as potential biomaterials. They were prepared by electron-beam irradiation of aqueous PVA solutions at various temperatures and doses of irradiation. These materials were characterized by low mechanical properties and especially by low elongation at break and ultimate tensile strength. Reinforcement was achieved by a two-stage dehydration-annealing process, introducing crystallites in the polymeric network. Improved mechanical properties were achieved due to the presence of this crystalline PVA phase. Due to their structure, these hydrogels are proposed to be used as biomembranes for selective transport of macromolecules and as biomaterials for synthetic articular cartilage applications. Surface heparinization was accomplished by reacting heparin to the hydroxyl groups of the PVA surface, through covalent acetal bridges.

New prospects for a prolonged functional life‐span of artificial hip joints by using the material combination polyethylene/aluminium oxide ceramic/metal

Abstract: Investigations over the years have shown that the mirror-finished Al2O3 ceramic is a much more suitable frictional counterpart to ultrahigh molecular weight (UHMW) polyethylene than metal. Despite the extremely gread hardness difference between polyethylene and Al2O3 ceramic, a considerable lower wear rate is obtained for the polyethylene socked with this new low-friction material combination. The unexpectedly favorable tribological behavior of this ceramic material in contact with polyethylene may be attributed to the following factors: better values for corrosion resistance characteristics, wettability with liquids, surfact gloss, hardness, and scratch resistance of the ceramic material in comparison with those of the hitherto used metallic implant materials (AISI-316L steel or cast Co-Cr-Mo alloy). It appears that, by using this new combination of materials for the socket and the ball, it will be possible to prolong the service life of artificial hip joints considerably without having effecy any fundamental changes in the present design and implantation principle retaining the hitherto used anchorage shaft made of wrought Co-Ni-Cr-Mo-Ti alloy Protasul-10 of extremely high corrosion fatigue strength.

Influence of a functional dynamic loading on bone ingrowth into surface pores of orthopedic implants.

Abstract: 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.

Mechanochemical studies of enzymatic degradation of insoluble collagen fibers.

Abstract: A mechanochemical method was developed for studying the enzymatic degradation of insoluble collagen fibers. The method involves stretching the collagen fiber to a fixed extension in the presence of a solution of collagenase and measuring the rate of relaxation of the force induced in the fiber. In this work, bacterial collagenase was used for reasons of availability. We observed invariably an exponential decrease in force with respect to ttime. The slope of the linear plot of logarithm of the force versus time was taken as a measure of the rate of enzymatic degradation. This rate was found a) to vary linearly with collagenase concentration; b) to be maximal at pH 7-8; c) to vary with temperature according to the Arrhenius relationship in the range 10-56 degrees C; d) to be reduced to varying extent by addition of EDTA omicron-phenanthroline, 2,3-dimercaptopropanolol, and D,L-cysteine; e) to be minimal when the strain on the fiber was ca. 4%; f) to be increased dramatically by denaturation of the collagen fiber; and g) to be reduced by an increase in the crosslink density of the collagen fiber. Except for the effect of strain, which can not be conveniently studied by existing methods these results are consistent with those observed by other methods for the study of the enzymatic degradation of collagen. The mechanochemical method is, however, uniquely suited to monitor continuously the enzymatically induced decay in the stress-bearing ability of collagen fibers. It has also been found useful in the design of collagenous implants with specified resistance to enzymatic degradation in vivo.

A total internal-reflection technique for the examination of protein adsorption.

Abstract: A total internal-reflection fluorescence (TIRF) technique for examining protein adsorption at solid-liquid interfaces is described. For the representative case of adsorption of bovine gamma-globulin onto silicone rubber, the applicability of the technique to serveral important aspects of protein adsorption phenomena is demonstrated. Specifically, in addition to the tightly adsorbed protein layer observed herein and previously by maany others, the presence of a loosely adsorbed protein layer was also noted under conditions of either static or flowing protein solutions. Taking advantage of the continuous real-time measurements possible with TIRF, a rate constant for the protein adsorption step during laminar flow was estimated at both 25 and 37 degrees C. These results serve to demonstrate that the TIRF technique represents a significant and versatile new tool for the study of protein adsorption phenomena.

Histological reaction to various conductive and dielectric films chronically implanted in the subdural space.

Abstract: Thirty different test patches of various thin film materials were chronically implanted in the subdural space of cats to determine their suitability as components for proposed neuroprosthetic devices. In particular, materials employed by the microelectronics industry were screened, and reactions were found to be quite dependent on specific formulations or surface preparations of otherwise similar materials. A nonspecific but severe complication of pressure necrosis under thin films that spontaneously roll and curl in vivo was noted.

Analysis of bioglass fixation of hip prostheses.

Abstract: The analysis of the bonding interface between hip prostheses and bone after functional use in animals was carried out. Scanning electron microscopy (SEM) with energy dispersive analysis (EDX), and Auger electron spectroscopy were used to evaluate the bonding interface. Various methods of postsacrifice sample preparation were used to evaluate the effect of such different methods on the analysis of the bonding interface. Comparison of the results with several rat tibia implant experiments is also presented.

Fracture characteristics of acrylic bone cements. II. Fatigue

Abstract: The vital first phase of the overall materials study to protract the life of total joint replacements is the identification of the fracture toughness and fatigue properties of bone cements. Information gained from fatigue testing, performed in a manner which simulates in vivo conditions, and fracture toughness, which is a measure of the propensity of a crack to propagate, is the first step towards the prediction of the life of the total joint replacement. Part I of this study identified the fracture toughness characteristics of two acrylic bone cements, while the present work has been concerned with determining the fatigue behavior by means of tests conducted in a rotating bending fatigue apparatus. Fatigue specimens were fabricated under conditions which approximated clinical procedures and then tested while immersed in bovine serum at 37°C in order to simulate in vivo conditions. In addition, a similar study was completed on specimens tested in air at ambient temperature for purposes of comparison. Testing was conducted in both of these environments on specimens containing zero and 10.0 wt % BaSO4. Cyclic loading frequency was maintained between 1200 and 1400 cycles/min in order to insure that crack propagation was the sole mechanism of failure, i.e., failure via cyclic thermal softening was obviated. Results of this phase of the study, when analyzed by a Student t-test at the 90% confidence level with four degrees of freedom, indicate that the fatigue life of specimens tested in bovine serum at 37°C is superior to that of specimens tested in air at ambient temperature. The addition of BaSO4 to Simplex-P cement, while not significant at the 90% confidence level, was significant in increasing the fatigue life in air at the 80% confidence level; however, this effect was not noticeable when testing in bovine serum at 37°C. Examination of the fracture surfaces enabled calculation of the critical stress intensity factor which when compared with values from an earlier work showed good agreement.

Immobilization of enzymes on slowly soluble carriers.

Abstract: 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.

Analysis of biomaterials deposited on soft contact lenses

Abstract: 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 microgram/lens), carbohydrate (1.0-1.2 microgram/lens), and phospholipids (0.01-0.05 micronmole/lens). Cholesterol and glucose were not present at detectable levels. Fluorescent antibody tests with appropriate controls gave positive tests for albumin, lysozyme, gamma-G-globulin, and alpha1-lipoprotein in the deposits, all proteins present 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.

A new antithrombogenic heparinized polymer.

Abstract: 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.

Crevice corrosion in orthopedic implant metals.

Abstract: Studies of orthopedic implant alloys in crevice configuration suggest that cobalt-chromium alloys such as Haynes-Stellite 25 are the best choice for multicomponent implants. It is also shown that severe crevice attack may result from use of mixed metals.

Effects of polymer surface molecular structure and force-field characteristics on blood interfacial phenomena. I

Abstract: To quantify the effects of major surface structural factors influencing interfacial reactions induced by polymers in native blood, model surfaces of solvent-cast films of two analogous poly(ether urethanes) and three homologous polyamides (nylon 4, 6/6, and 12) were exposed ex vivo to canine blood under the well-defined hemodynamic conditions of the Stagnation Point Flow Experiment. The selected surfaces allow for incremental changes in properties and were characterized by their "Composite Surface Free ENergy Function," gamma'S, which describes the surface force field as the sum of the mean dispersion (gammaSd) and polar (gammaSp) contributions and is computed from wettability spectra obtained with ultrapure diagnostic liquids. Blood interfacial effects were measured by the shear-limited diameter of the white cell circle formed around the stagnation point, the flow parameter at which symmetric aggregation occurred, and the surface-number density of platelets, [P s], remaining adherent under fixed conditions. At identical flows, within each group of polymers, both the WBC-circle diameter and [P s] scale with gamma Sp/gamma'S, implying that 1) only the magnitude but not the interaction mechanism varies as a function of incremental structural and surface changes, 2) the primary determinant of surface-induced effects is the polar force contribution, and 3) the magnitude of gamma'S is secondary if gammaSd/gamma'S is sufficiently great.

An in vitro and in vivo analysis of anodized tantalum capacitive electrodes: corrosion response, physiology, and histology.

Abstract: Oxidation-reduction reactions which can destroy high current-density metal-stimulating electrodes are avoided when using capacitive electrodes. The results of in vitro and in vivo testing of anodized, high surface area, sintered tantalum electrodes are presented. The corrosion response of the electrodes is excellent; there is no evidence of dissolution of the electrode. A deposit forms on the surface of the electrodes, but has little effect on the voltage response to constant current stimulation. The physiological and histopathological results indicate the capacitive tantalum electrode to be the safest yet tested.

Development of blood compatible elastomers. V. surface structure and blood compatibility of Avcothane elastomers

Abstract: 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.

Effect of collagen crosslinking on the rate of resorption of implanted collagen tubing in rabbits

Abstract: Collagen tubes were tanned with glutaraldehyde for different periods of time. Some were oxidized with periodate and sterilized with either 60Co (1.5 Mrad) or propylene oxide. The tubes were coated with polyfilamentous polyester fabric, filled with x-ray contrast material, and implanted subcutaneously in rats and rabbits. Rate of resorption was ascertained by x-ray procedure of progressive leakage of contrast material. A close relation between tanning time of the collagen fabric-combined prostheses and rate of their resorption in subcutis was found in both rats and rabbits. In rabbits, however, the implants were resorbed at a significantly faster rate than in rats. No effect of oxidation of collagen on the resorption was observed. Collagen tubes tanned for shorter time periods and sterilized with propylene oxide were more resistant to degradation than those sterilized with irradiation. This difference was absent, however, with material tanned for longer times. The mechanism of resorption of implanted collagen tubes was studied by morphological methods. The role of inflammatory cells in resorption is documented. The paper indicates the advantages as well as limits of the x-ray method of studying the resorption rate of biodegradable materials.

The restoration of articular surfaces overlying replamineform porous biomaterials

Abstract: Replamineform porous implants (4 mm X 4 mm diameter) were placed into full-thickness cartilage and bone defects of the weight-bearing surface of the lateral femoral condyles of adult male white rabbits. These were analyzed at 1 day, 1 week, 6 weeks, 3 months, and 6 months for 1) ingrowth of tissue within the implants and 2) restoration of the articular surface overlying them. Appropriate unfilled, but similar, control defects were also studied. Mineralized bone was seen within the substance of both the TiO2 and hydroxyapatite implants at 1 week; this extremely rapid response was present in every specimen studied and was not seen with alphaAl2O3 or control animals. With the passage of time, maturation of this bone ingrowth occurred so that by 3 months, they were all incorporated into the surrounding bone. Only the hydroxyapatite implants showed consistent regenerative healing of hyaline articular cartilage from the margins of the defects with the passage of time; this occurred whenever the subchondral bone adjacent to the defect proliferated in a "creeping" fashion over the articular aspect of the implant, and the undamaged cartilage then followed it. Fibrocartilage, and not hyaline cartilage, formed the articular surface over the TiO2 and alphaAl2O3 implants and in the controls.

Tolerance of mouse macrophages in vitro to barium sulfate used in orthopedic bone cement.

Abstract: Barium sulfate, used as a radio-opaque marker in some orthopedic bone cements, has been shown to escape into the surrounding tissues. This may present a potential hazard. In particular, phagocytic cells may be exposed to relatively high internal levels of barium once the particles have been phagocytosed. Mouse peritoneal macrophages exposed to barium sulfate for periods up to 144 hr showed a marked cytoplasmic vacuolization from which they recovered only partially. Barium sulfate did not appear to damage the cell membrane as judged by lactic dehydrogenase release. In the relatively low doses and with the periods of exposure described here, barium sulfate does not appear to present a serious toxic hazard in the short term. It is possible, however, that longer exposures and larger doses may result in the death of phagocytic cells which have ingested barium sulfate.

Analysis of the ingredients and determination of the residual components of acrylic bone cements.

Abstract: 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 coventional 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 degrees 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 degrees C. A semiquantitative colorimetric test indicated that the hydroquinone content of specimens analyzed within 24 hr after curing amounted to 9 ppm.

Interactions of synthetic and natural surfaces with blood in the physiological environment

Abstract: 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 lead to misleading generalizations. The problem reflects the complex interdependence between the material 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, which process effectively influences the subsequent interactions with the formed blood elements, especially the platelets with the proteinated surfaces.

Evaluation of wound-covering materials.

Abstract: Physical and in vivo (burned rat model) evaluations as wound coverings were performed for 1) a freeze-dried collagen/poly (epsilon-caprolactone) (PCL) film laminate, 2) a freeze-dried PCL "foam"/PCL film laminate, and 3) a heat-dried collagen/PCL film laminate. Porcine skin and cadaver skin were also evaluated in vivo for the purpose of comparison. Water-vapor transmission rates and Young's moduli were measured. The degree of adherence of the coverings to the wound were measured. Grafts which became significantly adherent (greater than 150 dyne/cm2) to the wound within 1 day were most successful in promoting the formation of a viable tissue bed which appeared ready to accept further grafting. The force required to remove the PCL foam laminate from a full-thickness excision wound was found to increase from 170 dyne/cm2 on the first day postgraft to 1500 dyne/cm2 by the tenth day. The force required to remove freeze-dried collagen laminate remained constant at 200 dyne/cm2 over the 10 day test period. For the heat-dried collagen laminate, a force of only 50 dyne/cm2 was required on day 1, increasing to 200 dyne/cm2 on day 6. Insensible water-loss rates of animals grafted with the laminates were found to be similar to those from animals with human cadaver skin grafts and less than that from animals with porcine skin grafts. When moistened, the laminates prepared using the freeze-dried materials were flexible and somewhat transparent permitting observation of the wound.

Bonding mechanism evidence in a ceramic–nonprecious alloy system

Abstract: Bonding between porcelain and dental ceramic alloys is thought to be dependent upon the establishment of a continous electron structure across the ceramicmetal interface (Pask, Proc. Procelain Enamel Inst., 33, 1, 1971). Such a structure most likely results from the compatibility of metal ions at the metal surface saturated in an oxide form with the complex oxide structure of the ceramic matrix. Reaction zone compounds are expected to play a prominent role in the strength of the ceramic–metal bonds but thus far none have been detected or identified. The present study was centered on the determination of possible adherence zone compounds in four composite ceramic–metal couples examined by x-ray energy analysis. Elemental analysis of four couples revealed the presence of a predominant AlCr interaction resulting from the formation of an AlCrO compound or mixed oxide complex. The Cr ions were supplied by the Cr2O3 oxide layer at the metal surface and the Al was provided by the initial bonding-agent coating.

Role of protein and fatty acid adsorption on platelet adhesion and aggregation at the blood polymer interface

Abstract: Thrombus formation on a foreign surface is a complicated process, involving many factors. However, there is little doubt that a foreign surface adsorbs plasma proteins upon blood contact and that the nature of this adsorbed layer may determine the mechanism of platelet adhesion and aggregation. The adhesion and aggregation of platelets play an important role in the initial events of thrombus formation on a foreign surface. In this work, adsorption studies using human blood plasma were done on several polymer surfaces. Some drugs which prevent platelet adhesion were utilized to verify the proposed mechanism for platelet adhesion which includes glycosyl transferase reaction. Also, adsorption and release of fatty acid salts, including fatty acid-bonded albumin, were investigated at different polymer interfaces. It is postulated that adsorbed fatty acid salts are released from the surface upon contact with plasma to form a high local concentration of fatty acid, and that this fatty acid suspension would cause platelet aggregation at the interface.

Properties of heparin--poly(methyl methacrylate) copolymers. II.

Abstract: A heparin–poly (methyl methacrylate) copolymer in which heparin has been covalently bound was studied. This copolymer showed no release of heparin but presented heparin-like anticoagulant activity when suspended in plasma. After contact with plasma, the copolymer lost part of its antithrombin activity which could be restored by a high ionic-strength medium. Because of its solid form, this copolymer offers new possibilities for producing interesting anticoagulant surfaces.

Porous acrylic cement.

Abstract: The use of acrylic bone cement has a number of shortcomings, viz., high curing temperatures that can cause thermal necrosis, release of toxic monomer, and a less than perfect cement-to-bone bond. However, by modifying the cement composition through the addition of a soluble, nontoxic filler such as sucrose or tricalcium phosphate which does not impair the workability of the material during surgery, a significant improvement in the performance of the cement can be achieved. Because the filler replaces part of the acrylic components, less heat is generated during curing while the filler itself acts as a heat sink. Also, less monomer, proportional to the amount replaced by the filler, diffuses from the implant site. Upon elution of the filler, a porous cement will be obtained provided that a critical minimum percentage loading is exceeded so that the filler crystals will make physical contact with each other. The value of this percentage depends on both crystal modification and size. In the 125–175 μm sucrose crystal size range, the critical minimum percentage lies in the range of 20–28 wt % loading. Above 30%, the interconnecting pore size increases sharply to a value which allows good tissue ingrowth into the pores. The introduction of filler and pores causes a drop in strength, but the diametral tensile strength of modified cement containing up to 40% pores and sucrose lies between .7 and 1.5 kg/mm2, respectively, which is still in the same range as that of bone.

Biodegradability and tissue reaction of random copolymers of L-leucine, L-aspartic acid, and L-aspartic acid esters

Abstract: A series of copoly(α-amino acids) with varying percentages of hydrophilic (l-aspartic acid) and hydrophobic monomers (l-leucine, s-methyl-l-aspartate, and s-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.