bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of cold working on fatigue behavior of stainless steels used for prothesis: Application to the study of wires with small sections
Authors: Coquillet B. , Vincent L. , Guiraldenq P.
Published: December 2004

Orthodontists mainly use stainless austenitic wires with a wide range of ultimate tensile strength. To characterize the dynamical behavior of these wires, the authors have perfected machines to test materials with their original surface roughness without any prior machining of surfaces. Fatigue limits are discussed through mechanical and structural properties of the austenitic steels, with special attention given to cold working. Typical features of fracture, and particularly of the first cracks, are shown by means of scanning electron microscopy.
Platelet interaction with synthetic copolypeptide films
Authors: Solomon D. D. , Cowan D. H. , Anderson J. M. , Walton A. G.
Published: December 2004

Kinetic and equilibrium studies of blood platelet binding to copolypeptide films show that attachment and serotonin release are not dependent upon the composition of the copolypeptide. Data may be explained by postulating that platelets frequently collide elastically with the surface but leave behind material that modifies subsequent behavior. Similarly, material released from platelets adsorbs at the interface and the extent of attachment and serotonin release are modified and controlled by these adsorbed species. Basically, if the platelet is exposed to a clean surface, its collision with the surface leads to activation and release. In the presence of inert protein, the collision is cushioned by the protein and platelets do not attach or release to any extent. Finally, if protein (or other entities) released from the platelet provide attachment sites, than attachment occurs without release. It is postulated that the behavior of platelets at surfaces is controlled by these interrelated processes.
Trituration and creep
Authors: Rehberg H. J. , Gramberg U.
Published: December 2004

Greep values of amalgam have been thought to be typical and nearly equal to their order of magnitude, depending on composition and particle shape. Recently it has been shown that trituration time may cause changes in creep magnitudes. The type of mixer and its frequency have contributed additional variabilities. These variations could not be related consistently to changes in creep values. Increases in condensation pressure did contribute to more predictable and constant values found with different mixing times.
Performance analysis of total hip prostheses: Some particular metallurgical observations
Authors: Ducheyne Paul , De Meester Paul , Aernoudt Etienne
Published: December 2004

Metallurgical observations of phenomena which influence the clinically successful performance of permanent implants and implant materials are reported. The effect of casting voids in cast cobalt chromium femoral stems of total hip replacements is discussed first. Pitting corrosion occurred in a retrieved stainless‐steel implant type AISI 316 containing 2.7% Mo. The fractographic pattern of this device retrieved for fatigue failure shows typical characteristics of corrosion‐enhanced fatigue.
Synthesis of a fine neurological electrode by plasma polymerization processing
Authors: Cannon J. G. , Dillon R. O. , Bunshah R. F. , Crandall P. H. , Dymond A. M.
Published: December 2004

This research is part of a continuing program for the development of a coaxial depth electrode for research and diagnostic studies of neurological diseases. The requirements for this electrode include (1) strength and resistance to buckling sufficient to ensure self‐forced penetration of brain tissue to a depth of 6 cm; (2) biocompatibility of the materials employed; (3) resistance to brittle fracture; and (4) a total diameter of less than 200 μm to minimize tissue damage. Earlier synthesis efforts using chemical vapor deposition techniques have been successful, although the process yield was 40% and an outer insulating layer had yet to be deposited. Plasma polymerization processes have been employed to realize an increase in the yield and provide an outer insulating layer. The starting material is W‐26 at.% Re wire, nominally 125 μm in diameter. Hexamethyldisilazane (CH3)3SiNHSi(CH3)3 is used to deposit the insulating layers. The paper describes factors influencing the choice of materials, deposition techniques, and properties of electrodes.
The flow properties of dental cements
Authors: Wilson Alan D. , Lewis Brian G.
Published: December 2004

The flow properties of several major types of dental cements were investigated using slow compressive strength and creep techniques. Considerable differences were found in their behavior. Whereas the phosphate‐bonded and glass‐ionomer cements exhibited brittle fracture, the other cements tended to distort to a greater or lesser extent under load. All cements showed some creep under load but the extent of this varied considerably: the creep of phosphate‐bonded cements being very small and that of the eugenol and related cements considerable.
The interaction of plasma proteins with polymers. I. Relationship between polymer surface energy and protein adsorption/desorption
Authors: Baszkin Adam , Lyman Donald J.
Published: December 2004

Adsorption of bovine albumin, γ‐globulin and fibrinogen from phosphate buffer solution (pH = 7.5) onto several polymer films was studied using the radioiodinated proteins (125I). The kinetics of desorption of the proteinated polymer films in bovine plasma was determined. Contact angle measurements on these same polymers allowed the calculation of dispersive (W) and polar (Ip) components of the polymer‐protein solution system. Results from these measurements show that the nondispersive‐dispersive force balance at the polymer‐protein solution interface, expressed by the Ip/W ratio, is an important factor for binding of proteins on polymer surfaces. The purity of fibrinogen and the cleaning procedures for the polymer surfaces influence the absolute values of proteins adsorbed on polymer surfaces.
Prevention of platelet adhesion to porous surfaces
Authors: Predecki Paul , Life L. , Newman M. M.
Published: December 2004

Porous samples of cellulose diacetate/nitrate CAN (millipore filter), polycarbonate PC (nuclepore filter), cellulose diacetate CA, and polydimethyl siloxane SR of various pore sizes were immersed in stirred heparinzied human blood while being perfused with lactated Ringer's solution at variours rates. Control samples were exposed to the blood in the absence of perfusion. The control tests showed that CAN and PC adhered platelets rapidly to plateau levels of 1–5 × 106/cm2 in ∼ 4 min, while CA and SR remained platelet‐free. The critical perfusion rate, v to prevent adhesion of platelets (and all formed elements) to the CAN and PC was ∼0.1 cc/min cm2 at a shear rate of ∼620 sec−1 independent of pore size tested. v increased slightly with stirring rate. A simplified diffusion‐convection model was used to qualitatively account for the effects observed.
Corrosion currents of dental amalgams
Authors: Grajower Rafael , Greener Evan H.
Published: December 2004

The polarization resistance and anodic polarization curves of three amalgam types were determined in saline solution. Corrosion currents were determined by extrapolation of anodic Tafel slopes. A good correlation was found between corrosion currents and reciprocal polarization resistances, according to Ic = 0.02/PR.
An in vivo model for evaluating the response of pulp to various biomaterials
Authors: McClugage Sam G. , Holmstedt Jan O. V. , Malloy Randy B.
Published: December 2004

An in vivo model has been designed to study the acute response of exposed or unexposed dental pulp to the topical application of various biomaterials. This model permits sequential microscopic observations of the microvascular system of dental pulp before and after application of pulp capping agents, cementing agents, or cavity liners. The use of this experimental model provides useful information related to the tolerability of dental pulp to various biomaterials used in dentistry. Furthermore, this model serves as a useful supplement to more traditional long term methods for evaluating the biocompatability of dental materials.
Dynamic mechanical properties of amalgams
Authors: Kusy R. P. , Greenberg A. R.
Published: December 2004

A recently developed dynamic mechanical analysis technique was utilized to determine the setting rates of dental amalgams. Via a compound parallel beam apparatus the dynamic mechanical properties of five amalgam materials were continuously measured at 37°C within ca. 7 min after the start of trituration. Over a 15 hr period results showed that the modulus of elasticity (Ea) increased from 1.2 × 1010 Pa to 6.5 × 1010 Pa—the latter generally approaching those values reported via ultrasonic techniques. Moduli results via compression tests on microspecimens (3 × 2 × 1 mm) paralleled previous reliable literature data, nominally yielding values for Ea of 2–3 × 1010 Pa. The extent of Ea scatter from both inter‐ and intrapreparer experiments appeared similar, although superior technique generally could be recognized by a systematic shift of the mean results to higher Ea's. In addition to modulus studies both compressive strengths (σmax) and their corresponding strains (ϵ) were measured on microspecimens at a strain rate (ϵ) of 0.031 min−1, with a significant increase being noted in σmax for the one material tested at over an order of magnitude increase in ϵ.
Thrombogenesis: An epitaxial phenomena. I
Authors: Barenberg S. A. , Anderson J. M. , Mauritz K. A.
Published: December 2004

A semiempirical epitaxial model has been derived which correlates and interrelates the surface free energy, ultrastructural morphology, surface charge, surface chemistry, and surface molecular motions of a model triblock copolymer to thrombogenesis. This paper addresses the aspect of: (1) ultrastructure order versus disorder, (2) primary and secondary molecular motions, (3) surface and side chain chemistry, (4) thrombogenesis, and (5) the derived epitaxial model based on the above observations. This model can be extrapolated to include and predict the relative thrombogenic responses of various crystalline and semicrystalline polymeric substrates, i.e., aliphatic polyolefins, polyurethanes, and polypeptides.
A clinical experience with the NCGT graft
Authors: Reddy K. , Haque S. N. , Cohen L. , Sophie Z. , Feller J. , Stillman R. M. , Fitzgerald J. , Stanczewski B. , Sawyer P. N.
Published: December 2004

A comparison of 130 grafts done in 101 patients included 47 veins, 25 Johnson & Johnson dialdehyde‐starch‐tanned collagen prostheses, and 58 NCGT grafts that had been followed for a 40‐month period. This study had documented the fact that in spite of frequent poor runoff, a useful result is provided by the NCGT graft apparently due in part to its built‐in nonthrombogenic structure providing a cumulative patency of 73%. The patency rate was even superior with venous bypasses. Therefore, we still feel that the autogenous vein provides the most useful bypass conduit available in vascular reconstruction. In situations where a vein could not be used or was not available the NCGT graft offers an equally useful nonthrombogenic surface to maintain prolonged patency. Thus, collagen appropriately modified can provide a useful prosthesis in vascular reconstruction.
Adsorption characteristics of plasma fibronectin in relationship to biological activity
Authors: Grinnell Frederick , Feld Marian K.
Published: December 2004

We studied the adsorption properties of plasma fibronectin (pFN) on wettable tissue culture (TC) dishes and nonwettable bacteriological (BAC‐T) dishes in relationship to its biological activity of promoting fibroblast spreading. The binding of pFN to the dish surfaces was found to be very tight and partially resistant to treatments with 1M NaOH, 2% SDS, 8M urea, or 6M guanidine HCl. Only the combination of trypsin (1 mg/ml) followed by 1M NaOH resulted in complete recovery of surface bound material. The amount of surface bound pFN did not directly correlate with its activity when comparing TC and BAC‐T dishes. At low concentrations, more pFN adsorbed onto the surfaces of BAC‐T dishes than TC dishes, but the adsorbed material was biologically less active on BAC‐T dishes. At high concentrations, pFN adsorbed similarly on both dish surfaces reaching a maximum level of 320 ng/cm2 or 4.4 X 1011 molecules/cm2. The possibility was considered that pFN unfolded into an inactive conformation when adsorbed on BAC‐T dishes at a low concentration but that at high concentrations, molecular packing requirements prevented unfolding. Evidence in favor of this hypothesis was the observation that addition of 50 μg/ml of serum albumin simultaneously with low pFN concentrations resulted in adsorption of pFN on BAC‐T dishes in an active conformation even though the amount of adsorbed pFN decreased. Competition experiments between pFN and other proteins were carried out, and it was found that pFN has a much higher affinity for BAC‐T or TC dish surfaces than albumin or fibrinogen. It was also found that mild heat denaturation of albumin increased its affinity for the surface by an order of magnitude.
Biodegradation of a poly‐(α‐amino acid) hydrogel. II. In vitro
Authors: Dickinson Helen R. , Hiltner Anne
Published: December 2004

Proteolytic enzymes have been employed in an in vitro model to simulate the in vivo degradation of a synthetic poly(amino acid) hydrogel. Trypsin and collagenase had no effect on crosslinked poly(2‐hydroxyethyl‐L‐glutamine) but pronase and papain dissolved the hydrogel. The initial effect of papain was to decrease the effective cross‐link density without producing soluble material. This effect was similar to that observed previously in vivo. Analysis of the papain digestion products showed that oligomers of degree of polymerization 4–9 were the chief products. The rate at which oligomers were formed increased with increasing crosslink density. This phenomenon was attributed to hydrophobic effects.
An evaluation of ion‐textured aluminum oxide dental implants
Authors: Weinstein A. M. , Cook S. D. , Klawitter J. J. , Weinberg L. A. , Zide M.
Published: December 2004

A study was undertaken to evaluate the ion‐beam texturing of aluminum oxide as a means of providing a surface which will produce a biological prosthetic attachment. A wafflelike pattern of surface contours 150 × 75 × 35 μm deep was produced on cylindrical dental implants. The textured surfaces were compared to the as received surfaces in adult mongrel dogs. Implants were inserted into surgically modified healed extraction sites and were left in place for six months. Post‐sacrifice mechanical testing was used to quantify the displacement response of the implants.

The clinical, radiographic and mechanical testing evaluations did not reveal any statistically significant differences in the performance of the dental implants. However, it was observed that anatomical site and mandibular geometry with respect to implant size play a significant role in affecting implant retention.
The tensile creep characteristics of dental amalgam. I. Stress dependence
Authors: Cruickshanks‐Boyd D. W. , Roswati N.
Published: December 2004

Equipment is described which enables the determination of the creep behavior of small specimens of dental amalgam under tensile stresses. The apparatus has been used to measure the creep strain of both low and high copper dental amalgams at 34°C, in the stress range 9.4 to 38.8 MNm−2, for time periods of up to 24 h. Significant differences were found in the controlling creep mechanisms for the various amalgam types. Conventional amalgam displayed classical steady‐state creep. The high copper amalgams, however, were best represented by transient creep equations implying interference to the motion of dislocations by the presence of hardening precipitates.
Cu2O and CuCl2·3Cu(OH)2 corrosion products on copper rich dental amalgams
Authors: Marshall Sally J. , Lin Jiin‐Huey C. , Marshall Grayson W.
Published: December 2004

In addition to Sn‐rich corrosion products found in conventional amalgams, Cu‐rich amalgams also form Cu‐containing corrosion products. The nature of these Cu‐rich products was investigated by immersion of samples of 13 Cu‐rich amalgam systems in Ringer's solution for prolonged periods. SEM/EDS and x‐ray diffraction studies were used to identify the compounds formed and their morphology. Two products were identified: Cu2O, a red product, and CuCl2·3Cu(OH)2, a green product.
A fabric pouch for maintaining transducer and catheter terminations
Authors: McCutcheon Ernest P. , Evans Joyce M. , Wibel Franklin H.
Published: December 2004

Management of the chronically instrumented animal is improved by enclosing the terminations of catheters and transducer wires in a subcutaneous nylon velour pouch. Six or more days after implantation, an opening is made into the pouch by removing a portion of the overlying skin; subsequent healing processes provide a satisfactory bond. Thereafter the leads can be extracted and replaced without need for anesthesia or dissection. Results in 35 animals (26 dogs and 9 monkeys) for intervals up to four months showed fibrous encapsulation was complete in 28 and partial in 7, with no mortality or significant morbidity attributable solely to the presence of the pouch. Gross and microscopic tissue examination indicated a localized foreign body reaction in response to the nylon fibers. The technique is especially useful in experimental protocols for which continuous restraint is undesirable, such as the chronically instrumented primate periodically exposed to environmental stress.
Toxicity evaluation of a novel filler free silicone rubber biomaterial by cell culture techniques
Authors: Chawla Attar S.
Published: December 2004

Cytotoxicity of a novel filler free silicone rubber (FFSR) was evaluated by studying its effect on mouse L929 cells. Silastic and a laboratory rubber tubing (RT) were used as control materials. Three different experimental methods were used. In method A, after six days of cell culturing in the sample extracts, there were 95, 80, and 50% of control viable cells for FFSR, Silastic, and RT, respectively. Similarly, in method B, after six days of direct contact between samples and the cells, there were 80, 40, and 20% of control viable cells for FFSR, Silastic, and RT, respectively. For the Agar Overlay Test, method C, the cells under the FFSR samples were normal and healthy compared to those under Silastic and RT. From these studies it was concluded that FFSR had the least cytotoxicity of the three materials studied.
Long‐term in vivo studies of poly(2‐hydroxyethyl methacrylate)
Authors: Imai Yohji , Masuhara Eiichi
Published: December 2004

Poly(hydroxyethyl methacrylate) (PHEMA) was implanted subcutaneously in rats, hamsters, and guinea pigs for up to 24, 23, and 13 months, respectively. The tissue response and tumorigenesis caused by PHEMA were compared among the three species of the animals. Thick fibrous capsule formation and tumor production were noted only in rats, while no tumorigenesis and thin fibrous capsule formation were observed in hamsters and guinea pigs.

These results support our previous hypothesis that animals producing a thick and avascular capsule tend to develop tumors at the implant site. PHEMA retrieved was characterized by scanning electron microscopy and x‐ray energy dispersive analysis. Calcium and phosphorus were the main elements detected on the surface of PHEMA implants. PHEMA is suggested to be not suitable for long‐term implant material.
Enzymatic removal of formalin‐fixed tissues from polyester arteries, and its effect on physical properties of fibers
Authors: Needham D. K. , Buchanan D. R. , Gupta B. S. , Horton H. R.
Published: December 2004

A method is presented that can be utilized for the removal of formalin‐fixed tissues from arterial grafts without. Affecting fiber material properties. Such a method could prove highly useful for studying the changes in the structure and properties of graft fiber as functions of important clinical variables. Information on what actually happens to the arterial graft material in situ with passage of time is greatly lacking in the current graft literature. The method proposed involves treatment of the formalin fixed fiber–tissue complex with an enzymatic preparation containing enzymes derived from the porcine pancreas (pancreatin) in solution with tris(hydroxymethyl) aminomethane buffer at pH 7.6. Studies with two different grafts—a Microknit Dacron Bifurcation from a clinical patient 10¼ years after implantation and stored in formalin for 11 months, and a Sauvage Filamentous Velour of Dacron from an animal 24 h after implantation and stored in formalin for nine months—showed that the treatment was highly effective in completely removing the tissues at concentrations of pancreatin as low as 2.5%. The same treatment given to the virgin yarns of grafts revealed no significant effects on tensile, dimensional, and morphological properties.
Polymer analogs of 3‐chloro‐4‐benzyloxyphenylacetic acid and their pharmacological activity
Authors: Hrabák F. , Grimová J. , Maturová E. , Kuchař M.
Published: December 2004

Polymer analogs of 3‐chloro‐4‐benzyloxyphenylacetic acid (BPh) were prepared, representing esters of BPh with three polymer alcohols: poly(vinyl alcohol) (P‐I), poly(2‐hydroxyethyl methacrylate) (P‐II), and poly(2,3‐dihydroxypropyl methacrylate) (P‐III). Their anti‐inflammatory activity was determined by testing their inhibitory effect on the growth of edema in the hind legs of rats. The relative activities of the esters P‐I‐BPh and P‐II‐BPh with respect to that of BPh are 0.06 and 0.10, respectively. In the case of P‐III‐BPh the activity is stronger (0.37), probably owing to the easier release of BPh from P‐III‐BPh due to hydrolysis. No prolonged effect of BPh polymeric esters could be achieved.
In vivo and in vitro aging of orthopedic aluminas
Authors: Fahr A. , Brown R. F. , Day D. E.
Published: December 2004

The flexural strength, microstructure and relative Ca and Si concentration at the surface of two commercial orthopedic aluminas were studied before and after aging up to 52 weeks in simulated body fluids or in subcutaneous implantation in rodents. There was no significant reduction in flexural strength after aging, but there was evidence of Ca and Si dissolution from the external grain boundary surfaces, particularly for specimens aged in demineralized water. No change occurred in the Ca and Si concentrations within the specimen's bulk during either in vivo or in vitro aging.
A method for the prediction of protein adsorption on implant surfaces
Authors: Bagnall Robert David , Arundel Philip Anthony
Published: December 2004

A simple method is described for predicting aspects of the adsorptive behavior of selected plasma proteins on a wide range of implant surfaces from a limited number of interfacial free energy measurements. Although the theoretical basis of the predictive treatment is open to debate, it is suggested that the method may be of value in the further understanding of implant biocompatibility.
In vitro electrochemical corrosion study of coupled surgical implant materials
Authors: Griffin Charles D. , Buchanan R. A. , Lemons J. E.
Published: December 2004

The objective of this study was to produce corrosion behavior data for each of the commonly used metallic alloys in surgical implants. In addition, by applying the known electrochemical corrosion theory, the study aims to predict the behavior of galvanic couples made of any two of the materials. From this predicted behavior, potentially useful couples that are not expected to show significantly increased corrosion rates were identified.
Influence of the suture diameter on the tensile strength of polypropylene monofilaments and its relationship to the USP specification
Authors: Kusy R. P. , Whitley J. Q.
Published: December 2004

Ethylene gas sterilized polypropylene monofilaments were tested in a straight pull as well as in a conventional knot pull tensile test. In either case an analysis of the results indicates that the occurrence of “surface steps” may explain the relationship between strength and suture diameter. The present investigation not only shows that the polypropylene specification could be established on a more fundamental basis (using 60% of the ultimate tensile strength as the generalized criterion) but also suggests that other sutures should be evaluated similarly.
Inhibition of surface induced coagulation by preadsorption of albumin‐heparin conjugates
Authors: Hennink W. E. , Kim S. W. , Feijen J.
Published: December 2004

Surface coatings of the albumin‐heparin conjugates were developed to improve the blood compatibility of polymeric materials. Glass, PVC, Biomer and cellulose acetate were coated with albumin‐heparin conjugate and its adsorption and desorption behavior on glass in particular was studied using 3H and 51Cr radiolabeled conjugates. Precoated materials showed a significant prolongation of the Lee‐White clotting time as compared with noncoated ones. It was demonstrated that the prolonged clotting time for pretreated glass was due to surface bound conjugate. Prolonged recalcification times of plasma exposed to glass, Biomer, and PVC were obtained using albumin‐heparin conjugate precoated surfaces. Albumin‐heparin conjugates with high affinity for antithrombin III gave more prolonged clotting times as low affinity conjugates when used as coatings for glass. This indicates that the behaviour of heparin in preadsorbed conjugates resembles that of heparin in solution.
The electrical stimulation of bone using a filamentous carbon cathode
Authors: Zimmerman M. , Parsons J. R. , Alexander H. , Weiss A. B.
Published: December 2004

Filamentous carbon fiber is an extremely compatible biomaterial. It does not corrode and elicits almost no foreign body response. In addition, this material is an efficient electrical conductor in vivo. These desirable characteristics suggest that carbon fiber may be of use as an electrode material for the stimulation of bone and/or soft tissue growth. This possibility has been investigated in a well established laboratory animal model. When used as a cathode material in conjunction with an implantable constant direct current device, carbon fiber was shown to be an effective electrode material for the stimulation of bone and fibrous tissue within the medullary canal of the tibia of the rabbit. Further, adjustment of current levels appear to allow some selectivity in terms of the amount and type of tissue produced. Currents in the 1 m̈A range produced a maximum amount of bone, whereas a 20 μA current produced a maximum amount of fibrous tissue. Intermediate current levels produced a proportional mix of bone and soft tissue.
Blood distribution of nickel, cobalt, and chromium following intramuscular injection into hamsters
Authors: Merritt K. , Brown S. A. , Sharkey N. A.
Published: December 2004

In vivo experiments were undertaken to study the transport of metal ions away from the intramuscular (IM) injection site and to study the binding of the metals to blood cells. Hamsters were injected intramuscularly with metal salts or with corrosion products generated by fretting corrosion of 316 LVM stainless steel or MP‐35N plates and screws. The animals were bled at 0 time, and 2, 4, 6, 24, 48, and 96 h after injection. The concentration of nickel, cobalt, and chromium in the serum, attached to red cells, and attached to white cells was determined. This study showed that metals are rapidly transported from the intramuscular site with high levels in the blood by 2 h. The level of metal in the blood varied considerably with nickel being transported in high concentration to the blood, chromium with a valence of 6+ being transported to the blood, and cobalt and chromium with a valence of 3+ being transported less to the blood. The highest amount of cell binding was observed with chromium 6+. Cobalt showed negligible binding to blood cells. When all the metal salts injected together were compared with the individual salts injected alone, there was no difference. This indicated that the each metal behaves independently of the presence of the others.
Assessment of tissue reactions to biomaterials: A model system using the foreign body response in the mouse lung to intravenously injected divinyl copolymer beads
Authors: Hood C. Ian , Schoen Frederick J. , Coleman Sylvia E. , Mickley Linda D.
Published: December 2004

We have developed a reproducible model of granuloma formation in the mouse lung using a narrow size range (45–53 μm) of divinyl benzene copolymer beads as a standard test material. Approximately 10,000 beads are given by intravenous injection into the tail veins of mice whence they embolize to the lung and incite granuloma formation. This delivery system eliminates the superimposed inflammatory reaction due to trauma that occurs when materials are directly implanted at the test site by surgical incision. Granuloma size was quantitated at intervals from 3 h to 6 weeks by tracing mid‐bead granuloma areas on the ground glass screen of a light microscope at a known magnification and measuring the areas with a digitizer interfaced with a microcomputer programmed to prepare histograms and to merge data from replicate experiments. At 3 h only a few polymorphonuclear leukocytes could be observed adhering to the beads. At 48 h, the time of maximum granuloma size (mean area = 750l μm2), the granulomas consisted of both polymorphonuclear and mononuclear leukocytes. After 6 weeks, the granulomas were smaller, composed predominantly of mononuclear leukocytes and had a mean area of 2893 m̈m2. This model system allows the analysis of a large number of measurements, is reproducible, and provides a useful method for comparing the hosts' inflammatory response to a variety of potential biomaterials, as well as for determining the effectiveness of anti‐inflammatory drugs.
Polyester prostheses as substitutes in the thoracic aorta of dogs. II. Evaluation of albuminated polyester grafts stored in ethanol
Authors: Guidoin R. , Martin L. , Marois M. , Gosselin C. , King M. , Gunasekera K. , Domurado D. , Sigot‐Luizard M. F. , Sigot M. , Blais P.
Published: December 2004

In an attempt to find an alternative procedure to the preclotting of porous textile vascular prostheses, the feasibility of an albumin coating and ethanol preservation technique has been evaluated by implanting albuminated polyester prostheses as substitutes in the thoracic aorta of dogs. Nine different grafts representing woven, knitted, and velour constructions were implanted for periods ranging from 4 h to 6 months. At the sacrifice, the grafts were excized for measurement of the thrombogenicity of the flow surface, for pathological examination by light microscopy and SEM, and for quantifying the changes in the textile structure during implantation. Also the kidneys were removed and examined for infarcts caused by trapped circulating emboli. The healing characteristics of the nine different grafts proved similar and followed the same sequence of events as preclotted control grafts. The albumin coating and ethanol preservation resulted in a somewhat slower rate of healing. Yet, given sufficient time, a more completely healed graft was achieved as evidenced by the presence of endothelial‐like cells throughout the length of the graft. In addition, the albumin is believed to reinforce the textile structure by reducing the tendency to stretch and dilate in vivo.
Regulation of drug release from polymer matrices by oscillating magnetic fields
Authors: Edelman E. R. , Kost J. , Bobeck H. , Langer R.
Published: December 2004

The reproducible regulation of release of a macromolecule (bovine serum albumin) from biocompatible polymer systems has been demonstrated. Small magnetic spheres or cylindrical magnets were embedded within the polymer matrix which was then subjected to an oscillating magnetic field. In this fashion baseline release rates could be increased 5‐ to 10‐fold with 5–10% standard error. Parameters critical to the regulation of this release included the position, orientation, and magnetic strength of the embedded objects and the amplitude and frequency of the applied magnetic field. Scanning electronmicrographs of the polymer matrix surface reveal that a gap, approximately 100/μm wide, is formed between the embedded object and adjacent polymer material after repeated exposure to an oscillating magnetic field.
Creep of posterior dental composites
Authors: Papadogianis Yannis , Boyer Daniel B. , Lakes Roderic S.
Published: December 2004

The creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50°C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age.
Heparinized polyurethanes: In vitro and in vivo studies
Authors: Heyman P. W. , Cho C. S. , McRea J. C. , Olsen D. B. , Kim S. W.
Published: December 2004

Heparin immobilization chemistry using alkyl spacer arms was adapted to optimize yield on polyurethane (PU) surfaces. The resultant biological activity of immobilized heparin (HI) was examined in vitro and in vivo, and compared with a heparin releasing (HR) system. Immobilized heparin retained its ability to bind and inactivate thrombin and Factor Xa; nonspecific coagulation factor binding was insignificant. Such activity cannot be attributed to the leakage of improperly bound heparin. Immobilized heparin–polurethane catheters implanted in canine femoral and jugular veins for 1 h periods exhibited significant reduction in thrombus formation compared with untreated PU contralateral controls. Polyurethane catheters coated with a 9% heparin dispersion in PU (HR) system provided even greater improvement in antithrombogenicity.
Biocompatibility of Delrin 150: A creep‐resistant polymer for total joint prostheses
Authors: Fister James S. , Memoli Vincent A. , Galante Jorge O. , Rostoker William , Urban Robert M.
Published: December 2004

A thermoplastic polymer, Delrin 150 (polyoxymethylene homopolymer), with creep resistance ten times that of ultrahigh‐molecular‐weight polyethylene, is used as a material for total joint protheses. A study was made of the local and systemic host response to this polymer when implanted in three different mammalian species. 316 LC stainless steel was used as a control. The materials were implanted into muscle and bone as solid cylinders. A total of 446 samples were implanted into 74 animals. The duration of implantation ranged from 2 weeks to 2 years. A semiquantitative evaluation of local tissue reaction was performed. For each implant, 16 histological criteria were graded for severity of host tissue reaction. The liver, spleen, kidneys, pancreas, and lungs from each animal were also studied for evidence of systemic toxicity. The polymer implants exhibited a mild tissue reaction with the same characteristics as the control. Local tumor formation, bone osteolysis, and surrounding muscle necrosis were not seen. No pathological changes compatible with systemic toxicity by Delrin 150 were observed in the study of the organs. Delrin 150 in solid form did not exhibit local or systemic toxicity and is therefore biocompatible by this study. Powder implantation studies should be performed to simulate tissue response to wear particles.
The interaction of blood components with PDMS(polydimethylsiloxane) and LDPE (low‐density polyethylene) in a baboon ex vivo arteriovenous shunt model
Authors: Keough E. M. , Mackey W. C. , Connolly R. , Foxall T. , Ramberg‐Laskaris K. , McCullough J. L. , O'Donnell T. F. , Callow A. D.
Published: December 2004

The interaction of 111Indium‐labeled platelets, and other blood components with the luminal surface of polydimethylsiloxane (PDMS) and low‐density polyethylene (LDPE) was determined using an ex vivo arteriovenous shunt in the baboon. Both PDMS and LDPE showed little platelet accumulation at either high (200 cc/min) or low (25 cc/min) flow rates. PDMS accumulated more platelets at low than at high flow. When the surfaces of PDMS and LDPE were examined under scanning electron microscopy after 2.5 h of flow in the shunt circuit, red and white blood cells were attached. Platelets appeared to be confined to patchy areas covered by a fibrinlike network. The low platelet reactivity of LDPE and PDMS suggests their potential use as coatings for conventional, more platelet reactive, vascular graft materials.
Influence of 4‐methacryloxyethyl trimellitic anhydride on composites subjected to hygrothermal cycling
Authors: Nagata K. , Turner D. T.
Published: December 2004

Pastes were made by spatulating a hydroxyapatite powder into triethylene glycol dimethacrylate (TEGDMA) that contained benzoyl peroxide. For comparison, similar pastes included 5 wt‐% 4‐methacryloxyethyl trimellitic anhydride (4‐META) in the TEGDMA. Composites were made by heating at 120°C under pressure. Inclusion of 4‐META reduced the rate of diffusion of water by about one‐third, at 27°C. Also after thermal cycling in water, inclusion of 4‐META decreased the fractional drop in compressive strength by about one‐half. Examination of fracture surfaces indicated that inclusion of 4‐META improved the wetting of filler particles and gave more coherent composites. All these findings are consistent with the view that 4‐META acts as a coupling agent.
Wire‐induced osteogenesis in marrow
Authors: Schaberg S. J. , Liboff A. R. , Falk M. C.
Published: December 2004

Although it has been reported, in observations connected to electrically stimulated bone repair, that intramedullary electrodes not attached to any electrical source can also induce osteogenesis, there has been only one systematic attempt to study this effect per se. We have extended these studies, implanting selected metal and plastic wires longitudinally into the medullary diaphyses of rat femora. Atomic absorption analysis was used for the first time in analyzing for medullary calcium. This technique and the histologic evaluation clearly indicate that osteogenesis occurs within 2 weeks after this wire implantation. Osteogenesis was not observed when the wire was immediately removed after the original trauma of wire insertion.
Change in creep rate and microstructure in an aged, low‐copper amalgam
Authors: Okabe Toru , Mitchell Richard J. , Butts Michael B. , Galloway Sidney S. , Twiggs Warren S.
Published: December 2004

Low‐copper amalgams aged at 37°C, 50°C, 60°C, 70°C, and 80°C for periods of 7 and 30 days were examined using a scanning electron microscope and an x‐ray diffractometer. Gamma‐one Ag‐Hg grain size and γ2 Sn‐Hg volume fraction, and surface area were determined by quantitative metallography. At 60°C and below, γ1 was the predominant matrix phase. Little β1 Ag‐Hg was found. In this temperature range, both γ1 grain size and ADA creep were found to obey an Arrhenius law. A linear relationship was found between the log of the mean ADA creep and the mean γ1 grain size. Above 60°C, the γ1 phases and the majority of the γ Ag‐Sn particles disappeared. In their place, β1 appeared. Gamma‐two volume fraction increased during aging at temperatures over 60°C, but a coarsening of γ2, reflected in a decrease in γ2 surface area per unit volume, also took place. Aging for 30 days or less resulted in decreases in ADA creep. At 60°C and below, the decrease was caused by increases in γ1 grain size. Above 60°C, the decrease in ADA creep was caused by several factors, one of which was the appearance of large β1 grains.
Human platelet spreading on substrata of known surface chemistry
Authors: Baier R. E. , Depalma V. A. , Goupil D. W. , Cohen E.
Published: December 2004

Using platelet‐rich plasma freshly obtained by plasmapheresis, the spread areas of human platelets settled onto substrata of different surface energies were measured to evaluate the hypothesis that initial platelet spreading response is surface dependent. At 37°C, minimal platelet spread areas were found on substrata with critical surface tension between 20 and 30 mN/m (dynes/cm), and increased spreading and morphologic changes occurred on substrata of both higher and lower critical surface tension. This differential response was absent at 25°C. Therefore, measurement of spread platelet area at physiologic temperature rather than number of attached cells is proposed as a superior method of estimating apparent blood compatibility of new biomaterials.
An examination of the biologic response to injectable, glutaraldehyde cross‐linked collagen implants
Authors: McPherson J. M. , Sawamura S. , Armstrong R.
Published: December 2004

The biologic response to injectable, glutaraldehyde cross‐linked, fibrillar collagen implants in the rat subcutaneous model was shown to be a function of the concentration of glutaraldehyde used for cross‐linking. The collagen was prepared from bovine hide by pepsin solubilization and reconstituted as a fibrillar suspension of 35 mg collagen/mL. Fibrillar collagen implants cross‐linked with glutaraldehyde concentrations equal to or less than 0.01% exhibited a response characterized by fibroblast invasion, neovascularization and little, if any, evidence of inflammation. Implants cross‐linked with 0.1 and 1.0% glutaraldehyde elicited a foreign body/giant cell reaction and varying degrees of implant erosion. The interaction of human skin fibroblasts with 0.01% glutaraldehyde cross‐linked collagen in vitro was found to be dependent on the culture conditions utilized to evaluate the interaction. When the ratio of cell culture media to collagen was 20:1, cell invasion of the cross‐linked preparations was observed, whereas, when this ratio was reduced to 1:1, such interactions could not be detected. Noncross‐linked preparations were colonized by cells regardless of the experimental conditions used. Studies of implants in both the rat and guinea pig subcutaneous models indicated that glutaraldehyde cross‐linking concentrations as low as 0.0075% provided enhanced wet weight recovery (wet weight persistence) and resistence to biologic degradation (collagen persistence) as compared to noncross‐linked fibrillar collagen preparations. These cross‐linked implants also exhibited a greater degree of fibroblast infiltration and vascularization. Between 30 and 60 days, some degree of calcification developed in both collagen formulations implanted in rats and guinea pigs; however, the reaction occurred with greater frequency and intensity in cross‐linked preparations in guinea pigs. Calcification in the guinea pig was followed by the appearance of focal areas of ossification.
SEM analysis of surface‐treated dialdehydestarch
Authors: Shimizu Toshimi , Tanaka Yoshio , Yamazaki Yoshihiko , Ueda Masayoshi , Isa Isao
Published: December 2004

Surface characteristics of protein‐treated dialdehydestarch (DAS), which is utilizable as a gastrointestinal sorbent for the treatment of uremia, are examined by scanning electron microscopy (SEM). Unique wrinkles or continuous depressions were observed on the surface of some albumin‐treated DAS particles. An increase in concentration and composition of albumin to DAS produces more particles with this kind of rugged surface. On the other hand, gelatin treatment provided a DAS with somewhat rough surface. As the stoichiometric ratio of gelatin to DAS increases, some fibrous or thin‐leaves‐like projections became outstanding on the surface. Urea‐binding properties of protein‐treated DAS are just about the same regardless of the protein concentration or composition. In addition, wrinkles or depressions partly observed on the surface of albumin‐treated DAS are of little benefit in terms of effective urea binding. These results mean that inherent physical properties of DAS such as dialdehyde content would be a critical factor in urea‐sorption ability, rather than surface characteristic or the presence of protein.
Immobilization of factor XIII on collagen membranes
Authors: Blanchy B. G. , Coulet P. R. , Gautheron D. C.
Published: December 2004

Factor XIII from placenta was successfully grafted onto collagen membranes by the acyl‐azide procedure. The transamidase activity retained on collagen membranes was determined by measuring the increase of fluorescence resulting from dansylcadaverine incorporation into casein. We studied the effect of different factors on the grafting: concentration and composition of the factor XIII preparation in the coupling solution and influence of the preactivation of factor XIII by thrombin. Stability studies have shown that the activity of factor XIII grafted on collagen membranes was almost constant over a period of 8 months. Sterilization by γ‐irradiation of factor XIII revealed a drastic loss of activity while the use of high‐energized electron bombardment caused a reduced loss of activity. The potential of such a material for biomedical use is presently under investigation.
Acute surface‐induced thrombosis in the canine ex vivo model: Importance of protein composition of the initial monolayer and platelet activation
Authors: Park Kinam , Mosher Deane F. , Cooper Stuart L.
Published: December 2004

The initial events occuring at the blood‐polymer interface were examined using a canine ex vivo arteriovenous shunt model. Thrombogenic (fibrinogen) and nonthrombogenic (albumin) proteins were preadsorbed on poly(vinyl chloride), polyethylene, and silicone rubber shunt surfaces, and the blood responses were analyzed using the platelet deposition profile as an indicator of surface thrombogenicity. The distributions of preadsorbed protein molecules on the various polymer surfaces were studied using an immunogold bead (colloidal gold particles coated with antibodies) staining technique and shown to be homogeneous. A sequential protein adsorption technique was developed to probe the nature of competitive protein adsorption and to observe the effect of surface protein concentration on thrombogenicity. The thrombogenicity of a surface was determined by the composition of the initial protein layer rather than the total concentration of protein on the polymer surfaces. The composition of this layer determines the extent of platelet activation and the adhesive strength between platelets and the polymer surface.
Collagen‐based wound dressings: Control of the pore structure and morphology
Authors: Doillon C. J. , Whyne C. F. , Brandwein S. , Silver F. H.
Published: December 2004

Collagen‐based sponges have been used as both temporary and permanent coverings for dermal defects in animals and humans. Cellular ingrowth within such a sponge has been shown to depend on the porosity and the presence of fibrous structure. Collagen sponges were made by freezing and freezedrying dispersions under acidic conditions. These studies involved the effects of dispersion pH and viscosity as well as freezing temperature on the surface and bulk morphology of collagen‐based sponges. Using scanning electron and light microscopy, the results of these studies indicated that large surface pores that form connections (channels) with the interior of the sponge were formed using low‐viscosity collagen dispersions. At high dispersion pH (3.2) and at a moderate freezing temperature (−30°C), fibrous structure and a large number of channels were present. When a lower dispersion pH (2.0) and freezing temperature (−80°C) were used, pores sizes were smaller with channels and fibrous structure, whereas a higher freezing temperature (−20°C) resulted in a sheet‐like structure and increased pore sizes. Differences in pore size and surface morphology were explained on the basis of ice crystal growth. In the case of abundant free water (high pH) and high freezing temperature, the pore size was greatest because of enhanced ice crystal growth.