bluuebunny/crossref_metadata_2025 huggingface dataset:
Parameters affecting the stress distribution around LTI carbon and aluminum oxide dental implants
Authors: Cook S. D. , Weinstein A. M. , Klawitter J. J.
Published: December 2004

Three‐dimensional finite element stress analysis was used to study the effects that implant neck geometry and the tissue properties at the implant‐bone interface have on the stress distribution around freestanding blade‐ and post‐type LTI carbon and aluminum oxide dental implants. Implants having neck flares of 13° and 26° were studied. In addition, to simulate fibrous encapsulation of the implant as opposed to a direct bone apposition retention mechanism, a soft tissue interposing layer between implant and bone was also modeled. The results of the study indicate that a reduction in neck flare from 26° to 13° was a positive design change for blade‐ and post‐type LTI carbon implants and blade‐type aluminum oxide implant but not for post‐type aluminum oxide implant. The results of the study indicate the presence of fibrous tissue surrounding the implants may be indicative of a failing system and may be the result of either hypophysiological stress (aluminum oxide implants) or hyperphysiological stress (LTI carbon implants).
A clinical comparison of LTI carbon, alumina, and carbon‐coated alumina blade‐type implants in baboons
Authors: Kent J. N. , Cook S. D. , Weinstein A. M. , Klawitter J. J.
Published: December 2004

The clinical performance of LTI carbon, carbon‐coated aluminum oxide, and uncoated aluminum oxide blade‐type dental implants was studied in baboons. The objective of the study was to determine the effect that implant material elastic modulus and surface composition have on implant performance. Clinical parameters of mobility, sulcus depth, soft tissue characteristics, and radiographic appearance were used in the evaluation. The implants were placed in healed extraction sites in adult female baboons and were used as a distal abutment for a three‐unit fixed gold prosthesis. The restorations were allowed to assume normal occlusal function and were left in situ for a period of two years. The radiographic and sulcus depth measurements appeared inferior for the LTI carbon implants and best for the carbon‐coated aluminum oxide implants. No differences in mobility or soft tissue characteristics were noted for the three implant systems. Two implants both in the same animal—one LTI carbon and one uncoated aluminum oxide—were definite clinical failures. The results of the study indicate that an elastic modulus mismatch between implant and bone is not an a priori cause of implant failure and that the implant surface composition had little apparent effect on the clinical and radiographic performance of these implant materials.
Microleakage of conventional and microfilled composite restorative resins
Authors: Retief D. H. , Rutland J. R. , Jamison H. C.
Published: December 2004

Microfilled composite resins have been introduced in clinical dentistry because of the difficulty in finishing conventional composite resins satisfactorily. Owing to the difference in coefficients of thermal expansion of the two resin systems, the objective of this in vitro study was to evaluate microleakage of a conventional and a microfilled composite resin. Class V cavities with butt cavosurface margins were prepared in the middle third of the facial surfaces of the crowns of 80 noncarious human premolar teeth; they were acid etched within the preparations only. Forty preparations were restored with Concise composite and forty with Silar microfilled resin. Ten teeth from each group were subjected to cyclic temperature changes between 5 and 55°C for 1000, 2500, or 5000 cycles, respectively, and ten teeth from each group were not cycled (controls). After suitable preparation, the teeth were immersed in 45Ca solution for 18 h and contact radiographs were prepared. Microleakage was scored 0–3 at both the cervical and occulusal margins of the restorations. Microleakage was significantly greater at the cervical margins than at the occlusal margins. Differences within occlusal and cervical microleakages among the two resins were not significant.
Physicochemical characterization and in vivo blood tolerability of cast and extruded biomer
Authors: Lelah Michael D. , Lambrecht Linda K. , Young Brian R. , Cooper Stuart L.
Published: December 2004

Solution grade and extruded grade Biomer (SB and EB, respectively) are polyurethanes that have been suggested for use in biomedical applications. The bulk materials were examined by elemental analysis, differential scanning calorimetry, thermomechanical testing, and stress‐strain testing. The extruded grade material has a lower soft segment molecular weight (650 g/mol) than the solution grade material (2000 g/mol). As a result of its higher molecular weight, the soft segment phase of SB is semicrystalline in the solid state. The hard segments of the extruded grade material are chain extended with water yielding a lower urea concentration than in the solution grade material in which the hard segments are chain extended with diamines. Chemical structures for the two materials consistent with elemental analysis, urea/urethane ratios and thermal and mechanical data, are proposed. X‐ray photoelectron spectroscopy (ESCA) was used to analyze the surfaces of extruded grade Biomer, solution grade Biomer cast on the inner surface of polyethylene tubing, and extruded grade Biomer dissolved in DMA and similarly cast on polyethylene (CB). Soft segment concentrations were highest on the EB surface and lowest on the SB surface. Soft segment concentrations on the EB surface were higher than on the CB surface, indicating that the method of fabrication affected the composition of the surface layer. The three materials were tested for blood tolerance in a canine femoral arteriovenous shunt configuration. Blood compatibility was correlated with increasing concentration of polyether soft segments on the surface.
Fatigue properties of implant materials in hip prosthesis form: A standardized test
Authors: Ducheyne P. , Wevers M. , De Meester P.
Published: December 2004

The determination of the fatigue properties on small specimens is not accurate. It does not take into account the considerable scatter in fatigue properties which may arise in the implants. Therefore, testing of the properties on the actual implant is needed. The working hypothesis of the present article is that four‐point bending fatigue tests allow determination of the fatigue limit of the femoral component material in total hip prostheses. It eliminates the disadvantages of the previously proposed load on head test because (1) the reproducibility of the stress pattern is easy; (2) the fatigue testing is over the whole critical part of the stem; and (3) the stresses do not change during the test. Testing of a series of hip prostheses shows that (1) the measured fatigue limit is typical for the material tested; (2) the location of the fatigue fractures is over the critical medial third of the stem; and (3) the fractographic aspects correspond to those of in vivo failed prostheses. The four‐point bending procedure is proposed as a standard method.
Fracture of porous polyethylene‐bone composite
Authors: Mayer R. D. , Moyle D. D. , Sauer B. W.
Published: December 2004

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.
Biomaterials for drug delivery systems
Authors: Buckles Richard G.
Published: December 2004

Drug delivery systems have unusual materials requirements which derive mainly from their therapeutic role: to administer drugs over prolonged periods of time at rates that are independent of patient‐to‐patient variables. The chemical nature of the surfaces of such devices may stimulate biorejection processes which can be enhanced or suppressed by the simultaneous presence of the drug that is being administered. Selection of materials for such systems is further complicated by the need for compatibility with the drug contained within the system. A review of selected drug delivery systems is presented. This leads to a definition of the technologies required to develop successfully such systems as well as to categorize the classes of drug delivery systems available to the therapist. A summary of the applications of drug delivery systems will also be presented. There are five major challenges to the biomaterials scientist: (1) how to minimize the influence on delivery rate of the transient biological response that accompanies implantation of any object; (2) how to select a composition, size, shape, and flexibility that optimizes biocompatibility; (3) how to make an intravascular delivery system that will retain long‐term functionality; (4) how to make a percutaneous lead for those delivery systems that cannot be implanted but which must retain functionality for extended periods; and (5) how to make biosensors of adequate compatibility and stability to use with the ultimate drug delivery system—a system that operates with feedback control.
In vivo biocompatibility studies. I. The cage implant system and a biodegradable hydrogel
Authors: Marchant Roger , Hiltner Anne , Hamlin Clive , Rabinovitch Albert , Slobodkin Rimma , Anderson James M.
Published: December 2004

A cage implant system has been utilized to examine the in vivo biocompatibility of a biodegradable hydrogel, poly(2‐hydroxy‐ethyl‐L‐glutamine) (PHEG). This system permits the quantitative determination of the components of the inflammatory exudate which surrounds the implanted polymer within the cage system. This system permits the serial examination of exudate components without sacrificing the animal. In addition, this system allows the subsequent removal of the polymer for surface and mechanical studies. Following implantation of the biodegradable hydrogel, quantitative and differential white cell counts of the exudates were determined over a 21‐day period. In addition, concomitant extracellular enzyme analyses for alkaline phosphatase, acid phosphatase, prostatic acid phosphatase, leucine aminopeptidase, and Cathepsin B1 were determined. Corresponding control samples from exudates of the cage implant without the polymer were also determined. The two‐tailed Student's t‐test for unpaired samples was used to statistically compare the control and implanted polymer values for these respective analyses at the various time periods. A comparison of the cellular response for the control system and the PHEG system did not show statistically significant differences during the first 7 days following implantation. The acute inflammatory response, polymorphonuclear leukocyte predominant, was followed by a mild chronic inflammatory response, macrophage and lymphocyte predominant, and during this time period, 8–14 days, macrophages were present in significantly larger numbers for the PHEG system when compared to the control values. Enzymic analysis of the exudates revealed statistically significant differences between control and PHEG values at time intervals where no differences were noted in cell density or population. These results are discussed in terms of cell‐polymer interactions leading to cellular activation and enhanced enzyme exocytosis by the inflammatory cells. Stress‐strain measurements on implanted PHEG samples showed that significant in vivo degradation had occurred during the acute inflammatory phase of the response, i.e., the first 7 days.
Preparation of etched tantalum semimicro capacitor stimulation electrodes
Authors: Robblee L. S. , Kelliher E. M. , Langmuir M. E. , Vartanian H. , McHardy J.
Published: December 2004

The ideal electrode for stimulation of the nervous system is one that will inject charge by purely capacitive processes. One approach is to exploit the type of metal‐oxide combination used in electrolytic capacitors, e.g., Ta/Ta2O5. For this purpose, fine tantalum wire (0.25 mm diam) was etched electrolytically at constant current in a methanol solution of NH4Br containing 1.5 wt % H2O. Electrolytic etching produced a conical tip with a length of ca. 0.5 mm and shaft diameters ranging from 0.10 to 0.16 mm. The etched electrodes were anodized to 10 V (vs. SCE) in 0.1 vol % H3PO4. The capacitance values normalized to geometric area of etched electrodes ranged from 0.13 to 0.33 μF mm−2. Comparison of these values to the capacitance of “smooth” tantalum anodized to 10 V (0.011 μF mm−2) indicated that the degree of surface enhancement, or etch ratio, was 12–30. The surface roughness was confirmed by scanning electron microscopy studies which revealed an intricate array of irregularly shaped surface projections about 1–2 μm wide. The etched electrodes were capable of delivering 0.06–0.1 μC of charge with 0.1 ms pulses at a pulse repetition rate of 400 Hz when operated at 50% of the anodization voltage. This quantity of charge corresponded to volumetric charge densities of 20–30 μC mm−3 and area charge densities of 0.55–0.88 μC mm−2. Charge storage was proportionately higher at higher fractional values of the formation voltage. Leakage currents at 5 V were ca. 2 nA. Neither long‐term passive storage (1500 h) nor extended pulsing time (18 h) had a deleterious effect on electrode performance. The trend in electrical stimulation work is toward smaller electrodes. The procedures developed in this study should be particularly well‐suited to the fabrication of even smaller electrodes because of the favorable electrical and geometric characteristics of the etched surface.
Endothelial cell labeling with indium‐111‐oxine as a marker of cell attachment to bioprosthetic surfaces
Authors: Sharefkin John B. , Lather Carole , Smith Michael , Rich Norman M.
Published: December 2004

Canine vascular endothelium labeled with indium‐111‐oxine was used as a marker of cell attachment to vascular prosthetic surfaces with complex textures. Primarily cultured and freshly harvested endothelial cells both took up the label rapidly. An average of 72% of a 32 μCi labeling dose was taken up by 1.5 × 106 cells in 10 min in serum‐free medium. Over 95% of freshly labeled cells were viable by trypan blue tests and only 5% of the label was released after 1 h incubations at 37°C. Labeled and unlabeled cells had similar rates of attachment to plastic dishes. Scanning electron microscopic studies showed that labeled cells retained their ability to spread on tissue culture dishes even at low (1%) serum levels. Labeled endothelial cells seeded onto Dacron or expanded polytetrafluoroethylene vascular prostheses by methods used in current surgical models could be identified by autoradiography of microscopic sections of the prostheses, and the efficiency of cell attachment to the prosthesis could be measured by gamma counting. Indium‐111 labeling affords a simple and rapid way to measure initial cell attachment to, and distribution on, vascular prosthetic materials. The method could also allow measurement of early cell loss from a flow surface in vivo by using external gamma imaging.
In vivo and in vitro studies of the stress‐corrosion cracking behavior of surgical implant alloys
Authors: Bundy K. J. , Marek M. , Hochman R. F.
Published: December 2004

Behavior of implant alloys exposed simultaneously to tensile stresses and corrosion environments has been examined. In the in vivo studies, a stainless steel and a titanium alloy exhibited cracklike freatures when loaded to the yield stress σy and implanted for 16 weeks. A cobalt‐chromium alloy stressed beyond σy exhibited them in plastically deformed areas. A cobalt‐chromium‐nickel‐molybdenum alloy appeared to be immune. In vitro samples loaded to various stress levels were immersed in Ringer's solution at 37°C. Half of them were subjected to applied anodic potentials; the remaining control group was not. The applied potentials were dc potentials of magnitude similar to those generated by bioelectric effects. No attempt was made to duplicate time dependence or wave forms. Cracklike features were observed in the stainless steel and in the titanium alloy loaded to or beyond σy and polarized for 38 weeks. None were observed below σy. For the controls, no cracklike features were observed at any stress level after 53 1/2 weeks. Polarization measurements and potential versus time measurements were performed to study possible mechanisms for crack propagation. These investigations suggest that the in vivo corrosion environment is more severe than a 37°C Ringer's solution because of the influence of both bioelectric effects and organic constituents. The implications of these studies for the performance of prosthetic devices is discussed.
Microscopic observations of the wear of a tooth restorative composite in vivo
Authors: Abell A. K. , Leinfelder K. F. , Turner D. T.
Published: December 2004

The wear of a composite restorative material in the oral cavity was followed by examining impressions by scanning electron microscopy. It was demonstrated that filler particles protrude from the polymeric matrix and, eventually, are lost leaving holes in the surface. A measure of the rate of wear was obtained by following the reacession of the matrix on the faces of a large prominent particle. For a restoration that had been in place for 7 years, the average rate of wear over a further period of several months was estimated to be about 0.1 μm/day. For comparison, the gross wear of 2 mm over the entire 7‐year period gives a greater average rate of wear of 0.8 μm/day.
Relationship between release rate and surface concentration for heparinized materials
Authors: Basmadjian D. , Sefton M. V.
Published: December 2004

Mathematical models are used to predict surface concentrations that result from the release of heparin into flowing blood and stagnant or well‐mixed plasma. Two release rates—4 × 10−2 and 3 × 10−5 μg/cm2 min–are considered, which describe elution from an ionically heparinized material and from an immobilized heparin‐PVA hydrogel, respectively. When heparin is released at the higher rate into blood flowing in cylindrical tubes with dimensions characteristic of the vasculature, or annular tubes representative of catheter experiments, a minium surface concentration of 0.5 μg/mL is attained virtually at the tube inlet. Release at the lower rate requires tube lengths of several thousand meters to attain the same critical value. Similarly, heparin released from a suspension of beads at the higher rate leads to critical surface concentrations of 0.2 μg/mL within a fraction of a second in stagnant plasma, or ca. 5 s in a well‐mixed environment. At the lower release rate, 45 or 100 min must elapse before the same level is achieved. These results support the validity of 4 × 10−2 μg/cm2 min as a reasonable minimum release rate to produce a heparin microenvironment sufficient to prevent thrombosis. The lower rate is shown to be insufficient to generate a critical concentration, thus supporting the argument that heparin‐PVA does not owe its biological activity to a heparin microenvironment. The model equations can be applied to the release of any material to determine surface concentrations.
Report on the Consensus Development Conference on “Clinical Applications of Biomaterials,” 1–3 November 1983
Authors: Galletti Pierre M. , Boretos John W.
Published: December 2004

A report on the Consensus Development Conference on “Clinical Applications of Biomaterial” held at the NIH, 1–3 November 1983 is presented. Included is the complete text of the Conference Statement.
Biocompatibility test procedures for materials evaluation in vitro. I. Comparative test system sensitivity
Authors: Johnson H. J. , Northup S. J. , Seagraves P. A. , Garvin P. J. , Wallin R. F.
Published: December 2004

Relative sensitivity of in vitro biocompatibility test systems was explored. Cellular responses of 12 standardized cell lines to 20 materials representing a range of toxicity were measured. Each cell line and material combination was tested in duplicate using four different culture methods, and each culture plate was examined by two graders. Results of the tissue culture assays were compared to those obtained for the same materials in vivo using a 5‐day rabbit intramuscular implant assay. Methods involving measurement of cellular growth (colony counts or present of confluence) in serumfortified media extracts of test samples were generally more sensitive and discriminating than those in which test materials were placed directly in cell cultures (measurement of zone of growth inhibition). There was good agreement between graders for all test methods. Antibiotics were not used in the test program. Based upon sensitivity, reproducibility, ability to discriminate materials, and grader agreement, 4 of the 12 cell lines and 2 of the 4 test methods appeared most suitable for screening and evaluation of materials. Agreement of results using these four cell lines with intramuscular implantation tests for the 30 materials ranged from 60 to 90%.
Macromolecular, histological, ultrastructural and immunocytochemical characteristics of the neointima developed within PTFE vascular grafts. Experimental study in dogs
Authors: Chignier Elza , Guidollet Jeanine , Heynen Yves , Serres Mireille , Clendinnen Guy , Louisot Pierre , Eloy Rosy
Published: December 2004

The nature and characteristics of the tissue that develops on the inner surfaces of vascular arterial PTFE prostheses have been investigated by histological, morphometrical, ultrastructural, and immunocytochemical criteria. The ability of this tissue to synthetize glycoproteins and glycosamino‐glycuronoglycans (previously called mucopolysaccharides) has been compared to that of the normal arterial wall. PTFE prostheses were used for carotid replacement in the dog and studied until the 90th postoperative day. These prostheses were mainly characterized by (1) a limited or even absent neointimal tissue proliferation; (2) the absence of an endothelial‐like structure on the prosthesis using scanning electron microscopy and immunocytochemical staining with rabbit antidog factor VIII‐related antigen sera; (3) limited activities of both microsomial enzymes (sialyl transferase and N‐acetyl‐glucosaminyl‐transferase) but marked xylosyl transferase activity; and (4) inverse qualitative distribution of the glycosaminoglycans, i.e., decrease of heparan sulfate and chondroitin‐6‐sulfate and increase of hyaluronic acid and dermatan sulfate. The absence of morphological evidence of an endothelial structure at the blood‐prosthesis interface even 3 months after implantation and the marked functional impairment in the biosynthesis of macromolecular components responsible for the normal blood‐vessel interface suggest that this newly developed tissue cannot be considered a true vascular endothelium.
Biochemical features of pseudomembrane at the bone‐cement interface of loosened total hip prostheses
Authors: Shoji Hiromu , Karube Shunji , D'ambrosia Robert D. , Dabezies Eugene J. , Miller Douglas R.
Published: December 2004

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.
Strong composites of dimethylacrylates with 4‐methacryloxyethyl trimellitic anhydride
Authors: Atsuta M. , Nagata K. , Turner D. T.
Published: December 2004

Particles of a lithium aluminum silicate, which had been treated with a silane coupling agent, were centrifuged either in an adduct of bisphenol‐A/glycidyl methacrylate (Bis‐GMA) or in a mixture of Bis‐GMA and methyl methacrylate. Polymerization was effected by heating with 2,5‐dimethyl‐hexane‐2,5‐dihydroperoxide. Flexural strength passed through an optimum value with increasing loading of the silicate. Inclusion of 4‐methacryloxyethyl trimellitic anhydride, 4‐META (5 wt % on monomer), increased the optimum flexural strength by about 20% (to 240 MPa). Evidence that 4‐META increased the adhesion of filler particles to the polymeric matrix was obtained by examination of fracture surfaces.
Gel route preparation of low fusing dental porcelain frit
Authors: Mabie C. P. , Menis D. L. , Whitenton E. P. , Trout R. L. , Metherate R. S. , Ferry C. H.
Published: December 2004

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.
Separation of macrophages from mouse peritoneal exudate cells with substrata coated with chemically modified collagens
Authors: Kasai Shunji , Akaike Toshihiro , Miyata Teruo , Kunimoto Takehiko , Nitta Kazuo
Published: December 2004

A cell‐separation technique was designed on the basis of specific interaction between macrophages and chemically modified collagens in the presence of serum. When unseparated mouse peritoneal exudate cells containing approximately 50% macrophages and 50% lymphocytes were incubated in dishes coated with unmodified and chemically modified collagens, only macrophages adhered more rapidly and in greater numbers to succinylated and methylated collagen than to unmodified collagen. The adherent macrophages could be easily detached from the substrata by divalent cation chelating agents. The purity and recovery of macrophages separated by this method were approximately 92–94% and 41–48%, respectively.
Water sorption in a bis(GMA)/TEGDMA resin
Authors: Söderholm Karl‐Johan
Published: December 2004

Some water sorption–desorption properties of a heat‐cured copolymer of bisphenol‐A‐glycidyl methacrylate/triethylene‐glycol‐dimethacrylate [bis(GMA)/TEGDMA] were investigated during three sequential water sorption–desorption cycles at 60, 37, and 60°C. The results showed that the investigated polymer absorbed almost one molecule of water for each bis(GMA)/TEGDMA molecule, causing a volumetric expansion slightly smaller than the volume of the absorbed water. The determined mean value of the sorption and desorption diffusion coefficients for a specific cycle, here named the “true” diffusion coefficient, was about 1.5 × 10−8cm2s−1 at 60°C, decreasing to one‐third of that value at 37°C. Although there were differences in leaching between the two sorption–desorption cycles at 60°C, no differences in true diffusion coefficients were found during the two cycles at that temperature. However, the sorption process proceeded slower than the desorption process during the first cycle, while the opposite occurred during the second cycle. These variations could be an effect of leaching occuring during the first cycle at 60°C and also the effects of induced swelling stresses on the diffusion process.
Healing pattern of small caliber Dacron grafts in the baboon: An animal model for the study of vascular prostheses
Authors: Keough E. M. , Callow A. D. , Connolly R. J. , Weinberg K. S. , Aalberg J. J. , O'Donnell T. F.
Published: December 2004

Although dogs have been used widely to study the healing of large caliber synthetic grafts, hypercoagulability probably makes the dog a poor model for studies of small caliber vascular prostheses. The baboon's coagulation system is similar to man's, but large caliber baboon grafts were reported to endothelialize rapidly. In this study the healing pattern of 4mm internal diameter Dacron carotid interpositon grafts in baboons was determined using specimens harvested at time points between 2 weeks and 18 months post‐implantation and examined with light and scanning electron microscopy. The luminal surface of baboon grafts in the acute healing phase (<1 month) was comparable to that reported in the literature for dogs. Baboon grafts did not completely endothelialize until 10–12 weeks post‐implantation. For work with small caliber vascular protheses, the dog appears to have no advantage over the baboon as an animal model on the basis of graft healing.
Applications and failure modes of percutaneous devices: A review
Authors: von Recum Andreas F.
Published: December 2004

Percutaneous devices (PD) are designed to serve a variety of clinical and biomedical research purposes. Characteristically they are objects that permanently penetrate through a defect in the skin. The histological aspects of the implant skin interfacial reactions are reviewed in this article. A short description is presented of common applications of PDs. The five presently identified interfacial failure modes are described histologically with the aid of schematic drawings. These failure modes are marsupialization, permigration, avulsion, infection, alone or in combination. Single or multiple etiological factors may be responsible for these failure modes. These factors can be surgically created skin defects around the penetrating foreign implant, epidermal healing characteristics that prevent the formation of a suitable seal at the implant‐skin interface and mechanical forces that may disrupt dermal attempts to seal the interface. Eventually the interface becomes infected necessitating removal of the device. Terminology recommended for use in percutaneous device research is indexed and defined.
Design criteria for percutaneous devices
Authors: Grosse‐Siestrup Christian , Affeld Klaus
Published: December 2004

A theoretical model of a percutaneous device is described. The model is split into several components, each with its own function. Special structures such as horns, hair, feathers, fingernails, hoofs, teeth, and antlers are taken as examples where nature has solved the problems of “percutaneous devices.” These structures have been regarded in relation to dimensional and structural differences of epidermis, dermis, and subcutis. Theoretical guidelines are described for the design of a prosthetic percutaneous device.
The mechanical strength of maxillary complete dentures
Authors: Vlissidis D. , Paipetis S. A.
Published: December 2004

A complete study of the static and dynamic strength of complete maxillary dentures was undertaken. First, the denture base material was investigated in its various forms from the point of view of tension, creep, relaxation, fatigue, and the effect of a corrosive environment. Complete dentures were tested under static compression, and the distribution of stresses along the midline of the upper dentures was determined by means of strain rosettes and by reciprocating compression, the determination of their fatigue strength. The results were found to conform with experience as far as lifetime of complete dentures is concerned.
Mechanical properties of bone cement: A review
Authors: Saha S. , Pal S.
Published: December 2004

Many authors have examined the mechanical properties of bone cement and the various factors that affect its mechanical behavior. This article presents a comprehensive survey on the reported mechanical properties of bone cement. Variables that influence the mechanical properties, such as handling characteristics, strain rate, loading modes, additives, porosity, blood inclusion, in vivo environment, temperature, etc. have also been reviewed. The importance of specifying these variables in reporting test results on the mechanical properties of bone cement is pointed out. Previous attempts to improve the mechanical properties of bone cement are also summarized. Future research areas important for fully characterizing the physical properties of PMMA are also suggested.
A canine ex vivo series shunt for evaluating thrombus deposition on polymer surfaces
Authors: Lelah Michael D. , Lambrecht Linda K. , Cooper Stuart L.
Published: December 2004

A new acute canine ex vivo femoral A‐V series shunt experiment is described. Platelet and fibrinogen deposition on a series of up to ten different polymers may be tested in the same nonanticoagulated animal. The method reduces the time and expense associated with animal testing, and also allows for the simultaneous monitoring of platelet and fibrinogen deposition on a number of polymer surfaces. The series shunt technique was used to examine platelet and fibrinogen deposition on polyethylene, Silastic, polyvinylchloride, and oxidized polyethylene surfaces. Following an initial period of minimal deposition, platelet deposition increased dramatically to a peak by about 15–20 min of blood contact on all surfaces studied. The amount of adsorbed fibrinogen fell from initial levels to a minimum at about 5–10 min of blood contact and then increased to a peak at about the same time as observed for the platelet response. Oxidized polyethylene was the most thrombogenic surface studied, followed by polyethylene, polyvinylchloride, and Silastic. Peak platelet and fibrinogen levels were found to be inversely related to flow rate over the range studied. In this experiment it appears that the interaction of blood components with a foreign surface in vivo or ex vivo is localized to the interface with the flowing blood. Within experimental errors, no effect of segment position or any downstream effects were observed. These results suggest that a series shunt may be used to investigate the short‐term interactions of blood with a number of test surfaces.
Fatigue properties of carbon‐ and porous‐coated Ti6Al4V alloy
Authors: Cook Stephen D. , Georgette Frederick S. , Skinner Harry B. , Haddad Ray J.
Published: December 2004

A porous metal coating applied to a solid substrate implant has been shown,in vivo, to offer advantages over current polymethylmethacrylate cement fixation in orthopedic devices. These advantages may be lost, however, in devices requiring a sintering heat treatment to apply the coating since these treatments may have a detrimental effect on the substrate material mechanical properties. In addition, more biocompatible interface coating materials have come of interest with recent literature reports of metal ion release. These coatings may be of particular use in porous‐coated systems since the surface area of implant in contact with the surrounding tissues is greatly increased. This study investigated the effects that both a porous Ti6Al4V alloy coating and a ULTI carbon coating have on the fatigue properties of a Ti6Al4V alloy substrate system. The fatigue properties of uncoated as‐received, uncoated sinter heat treated and notched Ti6Al4V material were also investigated. The results of this study revealed endurance limits for Ti6Al4V alloy tested with a rotating beam system of 617 MN/m2(uncoated as‐received), 624 MN/m2(ULTI carbon‐coated), 377 MN/m2(sinter heat treated), 220 MN/m2(notched) and 138 MN/m2(porous‐coated). No effects on fatigue properties were observed when testing the material in saline compared with air. The slight increase in fatigue strength for the carbon‐coated material is thought to be due to the increase in surface hardness resulting from the formation of titanium carbides on the surface. The low‐endurance limit of the porous‐coated material is due to both the transition from the as‐received equiaxed microstructure to a lamellar microstructure upon sintering and to the notch effect created by the porous coating.
Release of corrosion products by F‐75 cobalt base alloy in the rat. I: Acute serum elevations
Authors: Koegel A. , Black J.
Published: December 2004

The release of corrosion products by implants has become a matter of concern. Using a microsphere model, the release of chromium, cobalt, and nickel, secondary to implantation of various surface area exposures of F‐75, a cast cobalt‐chromium alloy, was studied over a 30 day period in the rat. Dose related elevations were observed in the serum concentration of chromium and cobalt but not of nickel, with the maxima being achieved at 3 days after metal implantation followed by declines in concentration. The chromium elevation, approximately twelvefold for a surface area to body weight (SA/BW) ratio of 300 x is similar to that previously reported in patients receiving total hip replacement arthoplasties. However, the cobalt elevation, twentyfold for a SA/BW ratio of 300 x, has not been previously observed. These serum concentration changes are as yet unexplained, but are probably not due to fibrous capsule maturation or alloy repassivation.
Characterization of plasma polymerized silicone coatings useful as biomaterials
Authors: Chawla Attar S. , Sipehia R.
Published: December 2004

Plasma polymerization techniques were used to deposit a layer of filler‐free silicone rubber on a variety of substrate materials. The thickness of the deposited film was 0.5–0.8 m̈m. As it is the surface of the biomaterial that comes in direct contact with the body fluids, the surface of the biomaterial is of paramount importance. In this study, the plasma polymerized biomaterials were characterized. Thus, the scanning electron microscope (SEM) showed the surfaces to be smooth. To study the surface layer of the deposited polymer, Fourier‐transform infrared spectrometry in the attenuated total reflection (ATR) mode was used. The deposited material was indeed silicone polymer with adsorption bands at 1262, 1020, and 802 cm−1 for the SiCH3 bending, SiOSi stretching, and SiCH3 bending, respectively. To find the bonding nature of the polymer, electron spectrometry for chemical analysis (ESCA) was used. The silicone polymer was shown to be highly cross‐linked. To find the molecular weight between cross‐links, swelling studies were done. Thus the results of the study show that the plasma polymerization could produce a filler‐free silicone layer on a variety of substrate materials.
In situ immunoradiometric assay of fibrinogen adsorbed to artificial surfaces
Authors: Chuang Hanson Y. K.
Published: December 2004

An in situ immunoradiometric assay was devised to quantitate human fibrinogen deposited on hemodialysis membrane, Cuprophane, from in vitro exposure to fibrinogen solution and from ex vivo extracorporally clinical use. The method requires a monospecific 125I‐labeled antifibrinogen‐IgG purified by DEAE chromatography and immunoadsorption. The labeled antifibrinogen IgG was shown to react specifically with fibrinogen adsorbed and immobilized (by glutaraldehyde) on Cuprophane. Other plasma proteins such as human albumin, IgG, or α‐thrombin, adsorbed singly or coadsorbed with fibrinogen on the surface did not seem to affect the fibrinogen‐antifibrinogen reaction. The presence of blood cells such as platelets and granulocytes with fibrinogen on Cuprophane reduced only slightly the uptake of 125I‐antifibrinogen‐IgG. The examination of fibrinogen‐fibrin deposition on clinically used Cuprophane by this technique and by autoradiography of the same material following 125I‐antifibrinogen‐IgG conjugation indicated that the deposition of fibrinogen was heavy and heterogeneous. We concluded that this in situ method may be useful to monitor fibrinogen‐fibrin deposition and adsorption of other plasma proteins that occur under in vitro, ex vivo, and in vivo conditions.
The quantitation of cultured cellular surface coverage: Applications for transparent and opaque surfaces
Authors: Herring Malcom , Evans David , Baughman Sally , Glover John
Published: December 2004

A planimetric technique is described for the analysis of cellular linings cultured on vascular prostheses and tissue culture plates. The method is not destructive of the cells and uses a calibrated eyepiece grid and an inverted microscope. The technique allows a rapid assessment of the percent of the prosthetic surface covered by cells, the average size of the cellular islands, and their distribution. In addition, the cells may be counted, their average surface area computed, and growth curves constructed for cells grown on tissue culture plates without the need for multiple concurrent cultures. Different cell types may be counted on the same surface. The method is more accurate than methods that require the resuspension of cells for counting, and it saves time and cells.
Detection of cyanoacrylate tissue adhesives in histological sections
Authors: Galil K. A. , Schofield I. D. , Wright G. Z.
Published: December 2004

Previous histological studies of cyanoacrylate in wound healing have all used Oil‐Red‐O staining of paraffin sections prepared by routine method. In the course of our studies we began to suspect that artifact was being introduced because of dissolution of cyanoacrylate during processing. Accordingly, biopsis of wounds sealed with cyanoacrylate and pieces of cyanoacrylate of a standard known dimension with no associated tissue were observed after every stage of histological preparation. It was observed that approximately 80% of the cyanoacrylate was lost at the deparaffinization in xylene stage. Accordingly, a number of solvents were tested, and it was found that petroleum ether could be used to remove paraffin completely without the loss of any of the cyanoacrylate from the specimen. This technique has been used to view the location and ultimate fate of cyanoacrylate applied to wounds and examined at different stages in healing process. It is concluded that previous histological studies of cyanoacrylate in wound healing have been inaccurate due to leaching out of most of the tissue adhesive during deparaffinization of the specimen.
Extracorporeal removal of mercury by hemoperfusion through agarose—polymercaptal microsphere beads
Authors: Margel Shlomo , Marcus Leon , Mashiah Aharon , Savin Hillel , Dalit Michael
Published: December 2004

Uniform agarose—polymercaptal microsphere beads (APMMB) of 1.0‐mm diameter were prepared by encapsulating thousands of polymercaptal microspheres of 0.8‐μm average diameter within an agarose matrix. Those beads show a high avidity and affinity for mercury and readily remove mercury compounds bound to serum proteins. In vivo detoxification trials in dosed rabbits and dogs showed the effectiveness of the APMMB for removal of mercury compounds by hemoperfusion. The rate for mercury removal is enhanced by addition of cysteine. The biocompatibility of the APMMB, measured by the depletion of the formed elements and various soluble components of the blood, is also demonstrated.
The interaction of urea with the generic class of poly(2‐hydroxyethyl methacrylate) hydrogels
Authors: Pinchuk L. , Eckstein E. C. , Van De Mark M. R.
Published: December 2004

Work reported here shows that, contrary to reports in the literature, hydrogels made from pure poly(2‐hydroxyethyl methacrylate), pHEMA, at crosslinker content greater than 0.15 mol % do not swell above the usual equilibrium values of 39–42% water content in aqueous urea solution. However, hydrogels containing small (impurity) amounts of methacrylic acid (MAA) do swell dramatically (approximately 90%) in dilute urea solution, but not directly due to the urea. The urea decomposes to produce ammonium ions, thus raising the pH of the solution. Ionization of MAA occurs above pH 6, causing electrostatic interactions within the gel. The grossly swollen state of these gels represents an internal equilibrium among forces due to rubber elasticity, polymer—polymer/solvent affinity, and electrostatic interactions.
Adsorption and reactivity of human prothrombin to artificial surfaces
Authors: Chuang Hanson Y. K. , Mitra Sankar P.
Published: December 2004

Human prothrombin in Tyrode's solution, in mock plasma (albumin, fibrinogen, and IgG mixture), and in citrated plasma adsorbs to Cuprophane, polyvinylchloride, and polyacrylonitrile surfaces. The adsorption of prothrombin is maximal in Tyrode's solution and minimal in plasma. The surface concentrations of prothrombin are highest on polyacrylonitrile, second on polyvinylchloride, and lowest on Cuprophane at all prothrombin concentrations tested in the bulk solution. Qualitative tests show that prothrombin adsorbed to polyvinylchloride can be activated by Taipan snake venom to generate thrombin that clots fibrinogen. However, more quantitative tests indicate that only part of the adsorbed prothrombin on all three materials can be activated to form thrombin exhibiting amidolytic activity. The partial reactivity of adsorbed prothrombin is further confirmed by release of 125I‐peptide from surface bound 125I‐prothrombin after treatment with Australian Taipan snake venom. Prothrombin bound to Cuprophane seems to promote granulocyte adhesion, but has no effect on platelet adhesion.
Direct electron microscopy studies of the bone—hydroxylapatite interface
Authors: Tracy B. M. , Doremus R. H.
Published: December 2004

The bone‐hydroxylapatite interface has been examined directly in the transmission electron microscope (TEM). The bone—hydroxylapatite interface was characterized by using several electron microscopy techniques, including bright and dark field imaging, electron diffraction, high‐resolution imaging, and energy dispersive analysis in the scanning‐transmission electron microscope (STEM EDS). Mechanical grinding followed by argon‐ion milling produced interface regions of unstained and undecalcified rat bone and hydroxylapatite that were transparent to electrons. Thus the exact location of the interface could be established and the bone at the interface studied. Conventional and high‐resolution imaging in the TEM demonstrated direct chemical bonding between bone and hydroxylapatite. The bone at the ceramic surface was the same as normal bone away from the interface.
Difference of bond bonding behavior among surface active glasses and sintered apatite
Authors: Fujiu T. , Ogino M.
Published: December 2004

Three types of surface active glasses and sintered apatite were implanted in femurs of rabbits for 8 and 16 weeks and subjected to the push‐out test to measure the bone bonding strength. The apatite surface layers of these materials, which were formed under in vitro treatment, were studied using IR, NMR, and AES. The difference in the bonding strength among these materials was shown statistically. The results of in vitro experiments explained the differences. It was concluded that the crystal chemistry and formation rate of the surface apatite layer significantly influenced the bonding strength. Materials that formed a surface apatite layer having a bone‐like crystal chemistry and fast formation rate showed high bone bonding strength.