bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodifferential analysis of ceramic implants
Authors: Cini L. , Pizzofferrato A. , Trentani C. , Sandrolini S. , Paltrinieri M.
Published: December 2004

Ceramic pelletes (in Al2O3 92% and in calcium aluminate) implanted into the muscles of rabbits for varying periods of time, and samples of similar material, not implanted but mixed with organic substances, have been analyzed by means of thermal differential analysis (TDA).

Which hydrated calcium aluminates are formed from implants after contact with the tissure fluid, has been established.

It has also been ascertained that the ceramic implants absorb organic substances from the tissue fluid, which, from a first evaluation, seem to be composed of simple molecules.

The results of this initial inquiry have provided positive indications of the utility of TDA to assist in elucidating the phenomena that occur between implant and tissue.
Adhesive bonding of various materials to hard tooth tissues. IX. The concept of polyfunctional surface‐active comonomers
Authors: Bowen R. L.
Published: December 2004

The concept of surface‐active comonomers of higher functionality is propsed as a means of increasing reliability of the bonding between preventive and restorative dental materials and tooth structures.
Viscoelastic properties of human dentin
Authors: Korostoff Edward , Pollack Solomon R. , Duncanson Manville G.
Published: December 2004

Stress relaxation measurements were performed on thick‐walled cylinders of radicular human dentin. The experimentally measured relaxation moduli were used to obtain an approximation to the logarithmic distribution functions of relaxation times. This distribution function was used to predict the behavior of other viscoelastic properties. In particular, the prediction of the strain and strain rate dependence of the modulus was determined and compared with experimental results.
An ultrastructural study of the biocompatibility of poly(2‐hydroxyethyl methacrylate) in bone
Authors: Murray David G. , Dow Jo‐Anne Sessa
Published: December 2004

Because of the unique properties for swelling in a fluid medium and variable modulus of elasticity, hydrophilic methacrylates may be of potential usefulness for implanting prosthetic devices in bone. To investigate the biocompatibility, electron micrographic studies were done on specimens of poly(2‐hydroxyethyl methacrylate) imbedded in bone for varying periods of time. Ultrastructural examination revealed progressive ossification of surrounding connective tissue up to the tissue polymer junction over a 6 month period. There was no evidence of inflammatory response. Based upon this study, it would appear that bone adjusts to an implant of hydrophilic methacrylate by ossification to the implant junction. This supports continued studies into the usefulness of this material as an implant.
Surface hydroxylation of styrene–butadiene–styrene block copolymers for biomaterials
Authors: Sefton Michael V. , Merrill Edward W.
Published: December 2004

This work pertains to the development of high strength elastomers potentially useful as nonthrombogenic cardiovascular prostheses. Triblock copolymers of the styrene–butadiene–styrene type have been subjected to surface hydroxylation which provide reactive sites at the surface for the subsequent coupling of heparin while retaining the unique mechanical properties of the SBS copolymers. Curves of hydroxyl content versus the copolymer film thickness demonstrate the effect of swelling in the surface region on the product distribution and on the time dependence of the hydroxylation process. In addition, the effect of time, temperature, and the composition of the reaction bath on the diffusion/reaction process is shown. Finally, the general applicability of this surface modification scheme to the development of biomaterials is discussed.
Canine tendon studies. II. Biomechanical evaluation of normal and regrown canine tendons
Authors: Walker P. , Amstutz H. C. , Rubinfeld M.
Published: December 2004

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.
Influence of application technique on microstructure and strength of acrylic restorations
Authors: Kusy R. P. , Mahan J. R. , Turner D. T.
Published: December 2004

An investigation was made of the influence of application techniques on the microstructure and properties of an acrylic tooth restorative. Mixtures of acrylic powder and monomer (“Sevriton Simplified”) were applied by the brush technique of Nealon (J. Prosth. Dent., 2, 513, 1952) and by two bulk flow techniques. While similar porosities (about 4%) were observed, the brush technique resulted in a greater quantity of grains from the acrylic powder. Despite this, there was little difference in values of compression modulus, compressive yield stress, and diametral compressive strength.

The mechanical strength of the materials studied was less than one‐half that of high molecular weight poly (methyl methacrylate) (PMMA). Crack propagation studies established that the interface between the grains and matrix was not a source of weakness. However, as the matrix was crosslinked this could not be checked by solution methods of polymer characterization.
Growth of cultured calf aortic smooth muscle cells on cardiovascular prosthetic materials
Authors: Eskin S. G. , Armeniades C. D. , Lie J. T. , Trevino L. , Kennedy John H.
Published: December 2004

The growth of cultured calf aortic smooth muscle cells on cardiovascular biomaterials was investigated, using native and oxidized polyacrylonitrile (orlon) fabrics, dacron velour, and Parylene‐C coated polypropylene microfabric as substrates. By light microscopic evaluation, surface cell coverage was most complete on microfabric, followed by native orlon, dacron velour, and oxidized orlon. Native orlon supported the greatest total cell growth, as determined by chemically extractable protein, followed by oxidized orlon, dacron velour, and the microfabric. The observed differences appear to be related to the pore size and fiber thickness of the different substrates.
A Dacron wool packed‐bed extracorporeal reactor: A kinetic study of immobilized Escherichia coli II L‐asparaginase
Authors: Ko R. Y. C. , Hersch L. S.
Published: December 2004

An extracorporeal reactor containing a packed bed of Dacron fibers has been developed. Escherichia coli II L‐asparaginase was coupled to the Dacron using γ‐aminopropyltriethoxysilane and glutaraldehyde. The preparation had an activity of 37 IU per gram of Dacron (37°C). The apparent Km was studied as a function of the flow rate. The data indicated that the apparent Km approached the Km of the native enzyme at floe rates of about 300 ml/min. In vivo use of L‐asparaginase immobolized on the Dacron indicated effective lowering of Plasmatic L‐asparagine levels.
Hyaluronidase‐bound membrane as a biomaterial for implantable fuel cells
Authors: Ahn B. K. , Wolfson S. K. , Yao S. J. , Liu C. C. , Todd R. C. , Weiner S. B.
Published: December 2004

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.
Some new studies of the wear behavior of ultrahigh molecular weight polyethylene
Authors: Rostoker W. , Galante J. O.
Published: December 2004

The wear rate of ultrahigh molecular weight (UHMW) polyethylene over a long campaign of sliding distance is not constant. Both unfilled and graphite filled polyethylene show a high rate early, which reduces to a low value. The graphite‐filled product shows a late stage increase in wear rate. Increased molding temperature reduces the molecular weight and increases the wear rate. Titanium articulating with UHMW polyethylene develops frequently an abnormally high wear rate with the generation of a black wear product.
Preliminary observations of bone ingrowth into porous materials
Authors: Robertson Diane M. , St. Pierre Leon , Chahal Ramlal
Published: December 2004

A preliminary investigation has been performed (a) to determine the kinetics of bone ingrowth into porous materials and to determine if this ingrowth could be catalyzed by the presence of a foreign substrate; and (b) to measure the bonding capability of bone with a porous‐surfaced metallic implant.

Tests on porous‐surfaced implants corroborate the work of other investigators in showing that bony tissue will grow into a porous substance that has pores large enough to support tissue nourishment. The shear strength of the bone–implant interface appears to increase with pore size and time of healing. Furthermore, it may be possible to catalyze this tissue ingrowth by the introduction into the fracture site of a foreign substance; in this experiment, glass beads 200–290 μ in diameter were used.
The effects of pylon shape on bone–pylon interface performance in direct skeletal attachment
Authors: Krouskop T. A. , Trono Ruben , Adamski A. J.
Published: December 2004

The attachment of a prosthesis directly to the part of the skeleton remaining after an amputation offers many improvements over coupling schemes used in conventional prostheses. However, the stresses induced in the bone by the macrostructure of the attached prosthetic device must first be understood because they are a significant consideration in the design of a successful direct skeletal attachment (DSA) system.

This investigation utilizes the finite element method of analysis to structurally model some possible DSA systems. Static stress‐response models for an above‐the‐knee human femoral amputation are formulated to investigate the effect of variations in pylon macrostructure on system performance. The models approximate the initial stages of support following the insertion of a pylon into the medullary cavity of the bone and are also used to assess the bond strengths that must be developed between the bone and pylon for a “no–slip” condition to hold at their interface.

The analyses indicate that either a shaped, marrow cavity‐fit pylon or four 135 degree wedges with a complementary pylon are favorable geometries for a DSA system. The stress levels caused by these two geometries are on the order of 20% of the axial compressive strength of cortical bone. For each, local stress levels at the bone–biomaterial interface remain the critical parameters for investigation.
Dead or alive: The problem of in vitro tissue mechanics
Authors: Black Jonathan
Published: December 2004

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.
Tissue response to implanted polymers: The significance of sample shape
Authors: Matlaga Barbara F. , Yasenchak Lewis P. , Salthouse Thomas N.
Published: December 2004

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.
The interaction of macromolecular solutions with macromolecular monolayers adsorbed on a hydrophobic surface
Authors: Fromageot Henri P. M. , Groves James N. , Sears Alan R. , Brown John F.
Published: December 2004

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.
Bone ingrowth into dynamically loaded porous‐coated intramedullary nails
Authors: Collier J. P. , Colligan G. A. , Brown S. A.
Published: December 2004

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.
Animal studies on bone ingrowth kinetics of ceramic material under dynamic stress
Authors: Dörre E. , Geduldig D. , Happel M. , Lade R. , Prüssner P. , Willert H.‐G. , Zichner L.
Published: December 2004

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.
Chemical and mechanical behavior of bioglass‐coated alumina
Authors: Greenspan D. C. , Hench L. L.
Published: December 2004

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.
Biomechanically induced tissue reactions after Al2O3–ceramic hip joint replacement. Experimental and early clinical results
Authors: Griss P. , Silber R. , Merkle B. , Haehner K. , Heimke G. , Krempien B.
Published: December 2004

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.
Postyield behavior of subchondral trabecular bone
Authors: Hayes W. C. , Carter D. R.
Published: December 2004

Cylindrical specimens of bovine subchondral trabecular bone were tested to uniaxial compressive strain levels of 75% to study energy absorption during pore collapse. Stress–strain curves were characterized by macroscopic yield at about 8% strain followed by a significant horizontal pore collapse regime. Energy absorption occurred largely in this postyield regime. Yield strength and energy absorption capacity were found to increase linearly with specimen apparent density. Microstructural analysis of the deformed specimens verified that the mechanism for energy absorption was primarily fracture and buckling of trabeculae. The results suggest that during fracture, the collapse of trabecular bone (and the consequent absorption of energy) serves to attenuate stresses transmitted through the skeleton and thus protect vital structures such as the brain.
Biocompatibility studies on surgical‐grade titanium‐, cobalt‐, and iron‐base alloys
Authors: Lemons J. E. , Niemann K. M. W. , Weiss A. B.
Published: December 2004

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.
A simple in vitro screening test for blood compatibility of materials
Authors: Kambic Helen E. , Kiraly Raymond J. , Nosé Yukihiko
Published: December 2004

An in vitro closed‐cell kinetic blood‐coagulation test was developed and used to evaluate the blood compatibility of materials. The test compares the clot formation rate on a test surface to that of a control material, Silastic. This method avoids anticoagulants, blood flow variations, and the exposure to air and other foreign surfaces. Eight pairs of cells are sequentially evaluated as to the weight of thrombus formed, the amount of unclotted blood, and the reduction in platelet count of the blood exposed to both the test materials and the control. These data are used to calculate a relative index whereby materials can be rated quantitatively as to the rate of clot formation on their surface. The order of decreasing clot formation on one group of materials studied was as follows: biolized (Imai et al., Trans. Amer. Soc. Artif. Int. Organs, 17, 6, 1973) poly(ether urethane), segmented polyurethane, formaldehyde‐treated pericardium, Hydron, glutaraldehyde‐treated pericardium, biolized natural rubber, Hexsyn, heparinized natural rubber, Silastic, and natural rubber. Urethane and aldehyde‐treated natural tissue had a lower percentage of red thrombus formation. These results generally correlate with in vivo observations.
Design and biomechanical evaluation of a cementable endosteal blade implant
Authors: Pugh James , Weiss Charles , Weiss Fredric , Malkin David
Published: December 2004

A cementable endosteal blade implant has been developed and evaluated. Inherent in the design are the following factors: minimization of stress concentrators, ease of implantation, and high resistance to loosening. Other potential advantages of this design as compared with conventional endosteal blade implants include reduced hazards of postoperative infection and reduced likelihood of metallic corrosion.

Six conventional endosteal implants and six cementable implants were installed in steer mandibles using standard dental surgical techniques and Simplexbrand methyl methacrylate bone cement. They were loaded in uniaxial compression at a loading rate of 0.0122 in./min. The stiffness (S), deformation at 900‐lb load (D900), proportional limit (PL), and load at 0.04 in. deformation (L0.04) were calculated for each test.

The cementable design showed a twofold increase in stiffness, only 17% of the deformation at 900 lb, more than twice the proportional limit, and at least twice the load at 0.04 in. deformation when compared with similar values for the conventional endosteal implants.

This study reveals that, in addition to being unstable in bone, conventional endosteal implants are also unstable when used with acrylic bone cement. The new design should eliminate most of the problems associated with endosteal blade implantation.
Bone growth into porous high‐density polyethylene
Authors: Spector M. , Flemming W. R. , Kreutner A. , Sauer B. W.
Published: December 2004

The purpose of this study was to delineate the process by which bone comes to fill the pores of porous high‐density polyethylene (PHDPE) implants. PHDPE (450μ pore size) pellets 4 mm in diameter and 1 cm long were implanted into the femurs of dogs. A bone biopsy procedure was utilized to obtain PHDPE pellets implanted for periods of 3 days through 8 weeks. A one‐year biopsy specimen taken from the PHDPE coating on the stem of a canine total‐hip prosthesis was also studied. The results demonstrated that significant amounts of bone formed within the PHDPE pellets as early as 14 days after implantation. Bone was identified throughout the specimens after 4 weeks. After 6 weeks, the tissue in the implants consisted of well‐developed lamellar bone spicules and healthy hematopoietic marrow. Scanning electron microscopy was utilized in conjunction with light microscopy and microradiography to study the ultrastructural features of the bone ingrowth process.
Structure and function of the human patella: The role of cancellous bone
Authors: Townsend P. R. , Miegel R. E. , Rose R. M. , Raux P. , Radin E. L.
Published: December 2004

Total joint and other prostheses often require the removal and replacement of considerable quantities of cancellous bone, and often are anchored in place by grouting into cancellous bone. Thus, a possible source of failure or loosening of many types of prostheses may be rooted in the lack of understanding of the structure, properties, and function of this material. In addition, as we have pointed out before, cancellous bone may play an important biomechanical role in the etiology of joint degeneration. With these considerations in mind, the architecture of the cancellous bone in the human patella was studied by serial sectioning and microradiography, using an improved technique developed in our laboratory. Volumes of cancellous bone with apparently different functional roles were identified. Stereological techniques were used to quantify the structural characteristics and geometrical relationships throughout the patella. These results led to a structural model for the cancellous bone of the patella, and a comprehensive picture of the internal architecture.

The distribution of mechanical compliance and yield stress was also measured, as a function of location and orientation, by a specially constructed micro‐compression testing machine. The measurements reflected the distribution of trabecular architecture, and both the properties and architecture reflected the gross biomechanical function of the patella. Furthermore, a true structure–function relationship was derived. Patellar contact area studies were performed on fresh cadavers and mapped for various angles of flexion. The variation in contact areas and the spatial variations in stiffness are discussed relative to the biomechanics and clinical aspects of the patella.
The fracture mechanics of fatigue crack propagation in compact bone
Authors: Wright T. M. , Hayes W. C.
Published: December 2004

The purpose of this investigation was to apply the techniques of fracture mechanics to a study of fatigue crack propagation in compact bone. Small cracks parallel to the long axis of the bone were initiated in standardized specimens of bovine bone. Crack growth was achieved by cyclically loading these specimens. The rate of crack growth was determined from measurements of crack length versus cycles of loading. The stress intensity factor at the tip of the crack was calculated from knowledge of the applied load, the crack length, and the specimen geometry. A strong correlation was found between the exprimentally determined crack growth rate and the applied stress intensity. The relationship takes the form of a power law similar to that for other materials. Visual observation and scanning electron microscopy revealed that crack propagation occurred by initiation of subcritical cracks ahead of the main crack.
Preparation and characterization of wear debris of orthopedic materials for biocompatibility studies
Authors: Wagner C. N. J. , Shabaik A. H. , Schurman D. J. , Amstutz H. C.
Published: December 2004

In order to test the biocompatibility of wear debris of orthopedic materials, a method has been developed to produce artificial debris of stainless steel, cobalt–chromium alloy, and high‐density polyethylene. In this process, called the accelerated rubbing process, two cylindrical blocks of the same alloy were held under normal pressure in triply distilled water. One block remained stationary while the other rotated at ∼4000 rpm. The water with the metal debris was recirculated between the rubbing surfaces. To prepare debris from polyethylene, a stainless steel block was rubbed over a polyethylene block submersed in liquid nitrogen.

The shape of the metal debris was granular, whereas the polyethylene debris had a shted‐like shape. The size distributions were determined from scanning electron micrographs, and it was found that the particles of the metal debris (stainless steel or cobalt–chrome alloy) ranged in sizes from 0.1–10 μ with 75% of all particles <2 μ in diameter. The size of polyethylene debris, expressed as the volume of an ellipsoid, ranged from 10–20,000 μ3 with 45% of all particles in the range of 400–2500 μ3.

The x‐ray diffraction pattern revealed that the debris of stainless steel consisted primarily of the face‐centered cubic (fcc) alloy with small amounts of body‐centered cubic (bcc) alloy and Fe3O4, whereas the cobalt–chrome debris consisted of the fcc alloy with a small amount of Cr2O3.

The structure of the polyethylene debris was quite similar to that of the solid sample used in its preparation. The percent crystallinity Pc and the size of the crystalline regions D were slightly smaller in the debris than in the solid sample, i.e., Pc = 52 and 55%, D = 90 and 130 Å, in the debris and the solid, respectively.

To test the suitability of the artificial debris for biocompatibility studies, stainless steel debris was implanted into knees of adult female New Zealand rabbits. Bacterial challenge studies indicated prolongation, but not increased susceptibility to infection.
Polymer–ceramic composite for tooth‐root implant
Authors: Greenberg A. R. , Kamel Ihab
Published: December 2004

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.
In vitro corrosion of dental amalgam phases
Authors: Marek M. , Hochman R. F. , Okabe T.
Published: December 2004

The effects of corrosion on the major phases of dental amalgam microstructure have been studied in vitro on samples prepared by electroplating mercury on Ag3Sn. Tests were made in synthetic saliva, and samples were examined in a scanning electron microscope before and after the exposure.

Simple immersion had little effect on the phases. Contact of amalgam with gold increased the probability of deterioration of the γ2 phase. By anodic polarization beyond the breakdown potential, the γ2 phase was selectively dissolved. Under conditions simulating a crevice, the γ2 phase was dissolved and the γ1 phase suffered morphological changes.
In vivo tissue reactivity of radiation‐cured silicone rubber implants
Authors: Gifford George H. , Merrill Edward W. , Morgan Michael S.
Published: December 2004

Silicone rubber implants are clinically used in large numbers and elicit a mild tissue reaction. An occasional patient develops an accentuated reaction, an observation which has stimulated clinicians to try to understand this process more fully. The chemistry of medical silicone implants, including quantitative composition, is reviewed. This in vitro laboratory study show less tissue reaction from radiation‐cured pure silicone polymer, as compared with radiation‐cured silicone with SiO2 filler. A proposed system for fabrication and curing of a silicone implant, with the qualities of strength and diminished tissue reactivity, is discussed.
Poly(glycolic acid) sutures in canine vascular anastomoses
Authors: Watts David R. , Carr Stephen H. , Hohf Robert P.
Published: December 2004

Poly(glycolic acid) (Dexon; Davis and Geck Company) canine vascular anastomoses between aorta and synthetic grafts and between severed femoral vessels were compared with comparable anastomoses made with Teflon‐coated Dacron (Tevdek; The Deknatel Company) with respect to clinical performance, morphologic characteristics, and tensile strength. While the Dexon anastomoses performed well and were morphologically superior to Tevdek, their tensile strength was significantly lower. Implications of these findings for vascular wound healing are discussed.
Using the shape recovery of nitinol in the Harrington rod treatment of scoliosis
Authors: Schmerling M. A. , Wilkov M. A. , Sanders A. E. , Woosley J. E.
Published: December 2004

Nitinol, a metal alloy which is able to remember (and return to with slight heating) the shape it had before it was deformed, is demonstrated to be useful in the Harrington rod treatment of scoliosis. A bent nitinol rod can return to its original straight length, applying both axial and lateral forces to the spine during the operation or postoperatively by means of external heating. A research program using simulated spinal forces in a test fixture and implantation in a cadaver was undertaken to show the feasibility of modifying the existing procedure.
An in vitro model for evaluating neural stimulating electrodes
Authors: Johnson P. F. , Hench L. L.
Published: December 2004

A model for in vitro evaluation of materials for use as neural stimulation electrodes is developed. Critical areas of concern in developing an in vitro test model discussed include: selection of environment, choice of material, design of stimulating equipment, and analytical procedures used to evaluate materials response. A method of providing quantitative analysis of materials response to stimulation conditions is presented. Evaluation techniques involve the use of scanning electron microscopy, x‐ray spectroscopy, atomic absorption spectrometry, and potentiographic and dielectric analysis of the test electrodes. A diagnostics matrix is presented which assigns a scale factor to quantify the relative corrosion response of the candidate materials. The corrosion response of Pt electrodes is evaluated in terms of scale factors assigned through use of the diagnostics matrix.
Mechanical properties of bone cements containing large doses of antibiotic powders
Authors: Lautenschlager E. P. , Jacobs J. J. , Marshall G. W. , Meyer P. R.
Published: December 2004

The addition of up to 10 g gentamicin sulfate antibiotic powder to 60 g units of Simplex‐P acrylic bone cement caused gradual, proportional decreases in the bulk mechanical properties of compressive and diametral tensile stengths. Water leaching of the antibiotic from the cement did not significantly decrease these strengths.

Scanning electron microscopy (SEM) and energy‐dispersive x‐ray spectroscopy (EDS) showed the antibiotic to reside in the acrylic matrix as discrete particles not usually associated with internal porosity. The surface‐sensitive flexural strength of a proprietary bone cement was lowered immediately by small quantities of antibiotic powder, and continued to decrease as doses of up to 10 g/unit were admixed. Water leaching caused channeling as the antibiotic was removed from the surface, but it did not create further changes in flexural strength.
Subcutaneous implants of polypropylene filaments
Authors: Liebert Timothy C. , Chartoff Richard P. , Cosgrove Stanley L. , McCuskey Robert S.
Published: December 2004

Exturded filaments of unmodified polypropylene (PP) with and without antioxidant were implanted subcutaneously in hamsters in order to determine their rate of degradation. Specimens were removed periodically during a 5 month test period and analyzed by infrared spectroscopy and dynamic mechanical testing. The analyses show that degradation begins to occur after only a few days. Although the reaction sequence is not known, several factors suggest that the in vivo degradation process is similar to autoxidation which occurs in air or oxygen.

The infrared data indicate that the hydroxyl content of the implants increases at a rate of 0.061 mg/g polypropylene per day during the initiation phase of the reaction. An induction time of 108 days was established. Carbonyl bonds appear after an implantation time of 50–90 days and increase thereafter. Mechanical tests indicate a decrease in the dynamic loss tangent, tan δ, during the first month of implantation for unmodified polypropylene. No change in the infrared spectra or tan δ was observed, however, for implants containing an antioxidant.

Thus, it is apparent that polypropylene filaments implanted subcutaneously in hamsters degrade by an oxidation process which is retarded effectively by using an antioxidant. While the findings reported are specific to subcutaneous polypropylene implants, they suggest that degradation of other systems may involve similar processes. This notion suggests directions for further research on increasing the in vivo stability of synthetic polymers.

Long‐term effects of polymer implantation upon tissue were not studied in this work.
Radiotracer techniques for protein adsorption measurements
Authors: Grant Warren H. , Smith Leslie E. , Stromberg Robert R.
Published: December 2004

Factors which contribute to measurement errors associated with the use of radiotracers to measure protein adsorption are considered. Techniques for removal of excess adsorbent solution and for estimation of surface area are described. Artifacts induced by the incorporation of a radio‐label both by specific adsorption of the labeling atom and by changes in the protein are discussed.
Surface characteristics of cardiac prostheses in vivo
Authors: Nosé Yukihiko , Kiraly Raymond J. , Picha George
Published: December 2004

The pseudoneointima (PNI) deposited onto a cardiac prosthesis surface reflects many factors of biocompatibility, surface morphology, flow distribution, design, animal's physiological condition, and duration. In the evaluation of any prosthesis, the PNI is one of the prime considerations from both material and functional standpoints.

Historically, Dacron fabric has been used as an internal lining for cardiac prostheses. However, we have observed cracks on the Dacron fibers, fiber fracture, fiber protrusion, and poor attachment to the diaphragm, which can cause potentially disastrous complications. In addition, there are basic differences in the PNI formation on aldehyde‐treated pericardium and natural aortic valves as compared to the Dacron fabric.

Minimal degeneration takes place on the chemically treated natural tissue compared with the fabric surface. Intact cells on the tissue suggest a greater compatibility. In later specimens (13 and 24 days), there is active cell infiltration into the pericardium structure with capillary formation.

The deposits on natural tissue are mostly fibrin, with minimum cellular involvement and a trend toward reduction in thickness.

Fibroblast cells are found on the natural tissue as early as 7 days but were not observed on the Dacron fabrics.

Based on these findings, the Dacron fabric‐covered diaphragm studied was not favorable for use in long‐term implantation of cardiac prostheses.
The reactivity of α‐chymotrypsin immobilized on radiation‐grafted hydrogel surfaces
Authors: Venkataraman S. , Horbett Thomas A. , Hoffman Allan S.
Published: December 2004

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.
Perfusion trails with a collagen‐immobilized enzyme in an extracorporeal reactor: Activity, stability, and biocompatibility
Authors: Olanoff L. S. , Venkatasubramanian K. , Bernath F. R. , Joyeuse R.
Published: December 2004

This paper is concerned with the evaluation of the in vivo performance characteristics of reconstituted bovine collagen as an insoluble carrier matrix for therapeutic enzymes. The enzyme that was chosen as a model for this evaluation was E. coli L‐asparaginase, which has been widely investigated as a soluble chemotherapeutic agent for the treatment of acute lymphocytic leukemia in humans (Oettgen et al., Cancer Res., 27, 2619, 1967; Beard et al., Brit. Med. J., 1, 191, 1970; Ohnuma et al., Cancer Res., 30, 2297, 1970). The results presented here were obtained from perfusion trials with a collagen–asparaginase reactor incorporated into an extracorporeal circuit attached to the vascular systems of healthy mongrel dogs. A series of 1–2 hr perfusions were conducted with a single collagen‐asparaginase membrane over a period of 4 months. Serum asparagine levels were reduced by more than 98% after 15–30 min perfusion time. Red blood cell (RBC), hemoglobin, hematocrit, and fibrinogen values remained constant during each perfusion. An average decrease of 48% in white blood cell (WBC) and 24% in platelet levels was observed, but these values began to rise slowly even before cessation of the perfusion. No serious toxic or antigenic reactions or mechanical or clotting difficulties were observed. In vitro activity, when assayed between perfusions, remained constant over a period of 4 months of intermittent use and storage. The potential advantages of collagen–enzyme complexes for the administration of therapeutic enzymes is discussed.
The restoration of articular surfaces overlying replamineform porous biomaterials
Authors: Chiroff Richard T. , White Rodney A. , White E. W. , Weber J. N. , Roy D.
Published: December 2004

Replamineform porous implants (4 mm × 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 αAl2O3 or control animals. With the passage of time, maturation of this bone ingrowth occurred so that by 3 months, they were all incorportated 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 αAl2O3 implants and in the controls.
Evaluation of a biodegradable ceramic
Authors: Cameron H. U. , Macnab I. , Pilliar R. M.
Published: December 2004

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.
Effect of fluoride on the stabilization of metal implants in the femur of rabbits
Authors: Laor Mark , Gedalia Itzhak , Simkin Ariel , Yosipovitch Zvi , Arcan Mircea
Published: December 2004

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.