bluuebunny/crossref_metadata_2025 huggingface dataset:
The electrochemical properties of dental amalgam
Authors: Mueller H. J. , Greener E. H. , Crimmins D. S.
Published: May 2005

The effects of variations in composition and processing on the open‐circuit electrode potentials measured as a function of time of amalgams made from silver–tin, silver–tin–copper, silver–tin–zinc, and silver–tin–copper–zinc alloys have been determined at 37°C in distilled water, in saline solution, as well as in acetate and citrate solutions buffered to pH values of 3, 7, and 10. The electrochemical potentials of the alloys measured as a function of time in neutral acetate solutions show anodic polarization from an initial cathodic potential value of approximately 0.1 v with respect to the standard hydrogen electrode to a constant potential level depending upon alloy composition. In neutral acetate solution the potential–time curves of silver–tin amalgams with 7:5 mercury to alloy ratio show a rapid anodic polarization from an initial anodic potential value of 0.28 v to a minimum value of 0.05 v at approximately 1 hr followed by a potential reversal to a plateau value of 0.40 v. For 7:5 amalgams in neutral acetate solutions increases in both the trituration time and in the severity of processing deformation cause a small increase in initial potential, with a decrease in anodic polarization, while an increase in amalgam age lowers both the initial potential value and the longer‐time potential plateau. Increasing the mercury content of the amalgam to a 2:1 ratio decreases the rate of potential reversal from the minimum, whereas decreasing the ratio to 4:5 decreases the amount of depolarization from the minimum value. The effects of copper and zinc additions to silver–tin alloys are mixed. In neutral acetate solution the 7:5 ratio amalgams from silver–tin–copper alloys show anodic polarization from the same initial value as the silver–tin amalgams, followed by a region of decreased polarization. Both silver–tin–zinc and silver–tin–copper–zinc alloys exhibit a much higher initial anodic potential (0.78 v), and following the achievement of the potential plateau have a slow anodic polarization to the long‐time potential value shown by silver–tin amalgam. Three commercial alloy amalgams were studied in neutral acetate solution. The two amalgams containing zinc have a potential behavior similar to that of the experimental zinc‐containing amalgam; the non‐zinc amalgam shows a rapid anodic polarization from an initial anodic potential value of 0.24 v, a minimum at 1 hr, and a reversal to the long‐time potential values of 0.40 v shown by the zinc‐containing amalgam.
Cutaneous absorption of N‐alkyl α‐cyanoacrylate
Authors: Ousterhout Cpt. D. K. , Gladieux G. V. , Leonard F.
Published: May 2005

Three monomers, β‐14C‐tagged methyl, n butyl, and n‐heptyl α‐cyanoacrylate, have been applied to intact skin and split‐thickness skin‐graft donor sites on rats. The data indicate that the urinary 14C activity is in the order: methyl > n‐butyl or n heptyl. Also, the urinary activity, when the monomers are applied to the split thickness skin graft donor sites, is approximately threefold greater than when the monomers are applied to intact skin. The conclusion is that the application of cyanoacrylate monomer to the skin is not only topical in nature, but may involve the internal milieu as well.
Purchase specifications for biomedical materials. I. Sheet or film of polytetrafluoroethylene plastic
Authors: Homsy Charles A.
Published: May 2005

The critical need for purchase specifications for implantable biomedical materials is the focus of this contribution. The elements in development of such specifications are presented with specific reference to a widely used high polymer, polytetrafluoroethylene. A specification for sheet or film of this plastic, as instituted by a major urban hospital, is presented in detail.
Toxicity profiles of vinyl and polyolefinic plastics and their additives
Authors: Guess Wallace L. , Haberman Sol
Published: May 2005

This paper reports on three investigations into the toxic potential of plastics, resins and addivtives, with emphasis on those having medical, dental, or pharmaceutical application. The following points were noted: (1) two different lots of PVC resin contained toxic material which was leachable into a biological system and an extreme eosinophilic response was noted; (2) a large group of chemical agents currently being used or having potential for use in various plastics formulations were investigated for toxic potential. As a group, the stabilizers showed the greatest degree of toxicity and if these are used in conjunction with a plasticizer in a plastic formulation, the toxic potential is greatly increased due to an increased opportunity to migrate from the plastic. It may be concluded from this work that safe plastics for medical, dental, and pharmaceutical applications can technically be manufactured. In order to protect the patient who ultimately comes in contact with the plastic device in one way or another, it behooves the concerned manufacturer to be certain his product is not responsible for injury to the user. This certianty can only be gained by an adequate and diverse evaluation program.
The effect of materials on the later stages of the in vitro clotting of human plasma in relation to the development of vascular prostheses
Authors: Matthews Dennis B. , Reger Stephen I. , Catlin Avery
Published: May 2005

The photometric method of clot detection has been used to measure the effect of surface contact on the later, or polymerization, stage of in vitro blood coagulation. Preliminary evidence has been obtained for the existence of such an effect and the importance of protein adsorption and mass transfer to the interpretation of clotting rates has been underlined.
Synthetic aortas for systemic simulators
Authors: Krokosky E. M. , Krouskop T.
Published: May 2005

The in vitro viscoelastic properties of the human aorta were characterized by subjecting excised aortas of different ages to various mechanical testing procedures. A complete characterization of the properties of the human aorta was necessary in order to find a comparable synthetic material for use in a systemic simulator. Several synthetic materials were tested. One silicone rubber system had properties closely approximating those of the human aorta.
Über ionotrope proteinsymplexe
Authors: Schütt Hans‐Werner
Published: May 2005

Symplexes of proteins were taken for comparison with biological structures like the skin of mammals. Particles of these symplexes were set into regular order by diffusing and fixing polyvalent metal ions of protons, yielding anisotropic membranes with some properties of extracellular strucutres. Determination of the symplex optimum allowed a comparison of the properties with different acid partners. Four fifths of the amino groups of the scleroproteins that could be titrated by monomeric acids could be bounded by the polyacids. In a neutral medium, all symplexes behave like coherent polyamphiions with the behavior of long chain molecules. Swelling and dissolving of mammalian skin desintegrates the scleroproteins, partly down to the primary helix. These proteins with polyuronic acids such as alginic acid in form of a symplex did not give individual or specific reactions when implanted into the living organism but were slowly decomposed by unspecific proteases.
Application of the mocroprobe analyzer to biological materials investigations
Authors: Domagala Robert F. , Van Thyne Ray J. , Lenke John W.
Published: May 2005

The microprobe analyzer has proved to be a valuable tool in investigation of dental and medical materials problems, and the results of a number of studies are described. Interesting aspects of the amalgam–tooth interface have been examined and dental calculus compostion has been determined. Surgical implant studies have included evaluation of appliance alloys and failure analysis of surgical devices.
Correlation of microstructures and open‐circuit potentials of gold–iron alloys with their in‐vivo corrosion behavior
Authors: Acharya Abhijit , Sandrik J. L. , Wragg L. E. , Greener E. H.
Published: May 2005

The in vitro behavior of a number of Au–Fe precipitation‐hardenable alloys have been investigated in distilled water and in Ringer's solution (simulating the extracellular body fluids) by the open‐circuit potential versus time method. The in vivo behavior of these materials as muscle implants has been studied by conventional histopathological and histochemical techniques. Optical and electron microscopic techniques have been used to study the extent and morphology of massive discontinuous precipitation as well as the mode of corrosion attack. A clear correlation has been established between the microstructural features presented by a given alloy and the time‐dependent open‐circuit potential and in vivo corrosion behavior. It can be concluded for this alloy system that the microstructure and the open‐circuit potential pattern may be taken to be a reasonable indication of the expected in vivo corrosion behavior.
Adherence of prosthetic skin
Authors: Skornik William A. , Dressler Donal P. , Rhicard John K.
Published: May 2005

Recently, a new successful prosthetic skin was reported from this laboratory. Utilizing the burned rat model, this prosthesis, controlled burn wound sepsis, prevented insensible water vapor loss and remained indefinitely. A prime factor necessary for the success of this prosthesis is its ability to adhere early to the recipient site. Thus, in order to investigate the underlying mechanisms of adherence and to be able to evaluate more closely different types of prosthetic skin, materials, and designs, a quantitative technique was developed using a modified Keil tester. The force (dynes/cm2) necessary to tear the prosthesis free was recorded on a direct writing apparatus. Tensile strength measurements of the prosthetic skin revealed a gradully increasing adherence of the tissue to the prosthesis. Initial values, days 2 through 5 post‐application, were low as recorded in dynes/cm2. The graft when removed on these days showed little or no gross fascial adherence, however, edge adherence steadily increased. After a few days the successful prosthesis could not be peeled without removing some tissue. Histologic studies show that by day 9 the prosthesis is an integral part of the subcutaneous tissue with foreign body giant cell reaction, ingrowth of of fibroblasts and collagen, and few inflammatory cells or bacteria. The adhesion values reveal that as the day post‐application increased the mean value in dynes/cm2 increased from an initial 2.137 on day 2 to 8.019 on day 50.
A heat‐transfer device for the monitoring of thrombus formation on prosthetic surfaces
Authors: Klopp Edward H. , Jacobs Lloyd A. , Topaz Stephen R. , Gott Vincent L.
Published: May 2005

In order to monitor changes in thrombus size on prosthetic surfaces in dogs, a simple heat transfer measuring system was incorporated into a small right atrial sword which has been previously described.1 This system provided a reliable and continuous measure of the amount of thrombus present on the sword. Initial thrombus formation was found to be complete within 45–90 min. Subsequent lysis of the thrombus was seem to occur in many cases after 8–12 hr of implantation.
Direct chemical bond of bioactive glass‐ceramic materials to bone and muscle
Authors: Hench L. L. , Paschall H. A.
Published: May 2005

The objective of this research is to achieve direct chemical bonding of structurally strong implant materials with hard and soft tissues. This objective has been achieved through the development of a series of surface‐active bioglasses and bioglass‐ceramics. A controlled release of Ca, P, and Na ions from the surface of the materials produces an alkaline pH and nutrient constituents at a time when the body can incorporate the ions into newly formed tissues. Optical and electron microscopy of in‐vivo implants in rat femurs and muscles show the development of stable chemically bonded physiological interfaces after 6 weeks. Microstructure and crystallinity of the materials do not influence the bonding achieved. Mechanical measurements of the bond strength in bone show that the bone fractures before the interface does. In‐vitro studies of protein epitaxy, hydroxyapatite crystallization, and solubility kinetics correlate with the proposed interfacial bonding theory.
The clinical experience with silicone‐Dacron metacarpophalangeal and interphalangeal joint prostheses
Authors: Goldner J. Leonard , Urbaniak James R.
Published: May 2005

Our 4‐year clinical experience with reconstruction of worn metacarpo‐phalangeal and proximal interphalangeal joints with silicone‐Dacron prostheses in 121 patients is presented.

Emphasis is on preoperative assessment and proper selection of patients.

Three hundred sixty‐nine metacarpophalangeal joint prostheses and 27 proximal interphalangeal joint prostheses have been inserted. Most of the patients had rheumatoid arthritis; several had degenerative arthroses, and a few had traumatic arthrosis.

Particular attention is directed to minor modification of surgical techniques and emphasis is on postoperative management. Suggestions for implant redesigning and modification are made.

The silicone‐Dacron arthroplasties have been successful in decreasing pain, improving stability, increasing hand function, and in providing an adequate range of motion.

Complications have included five infections, two recognized fractured prostheses, and two instances of early dislocation of a prosthesis. The patients have consistently been relieved of pain: on the basis of this short‐term experience, we believe that the implant principle in the hand is successful, but improvements in design and material are needed.
The role of stress‐enhanced reactivity in failure of orthopaedic implants
Authors: Rose R. M. , Paul I. L. , Weightman B. , Simon S. R. , Radin E. L.
Published: May 2005

Scanning electron micrographs were made of the surfaces of silicone rubber finger joint prostheses which had been subjected to 107bending cycles at 37°C in bovine serum. Preferential attack at the regions of highest stress and the formation of microcracks of length 10μ and less were observed. By way of analogy with the corrosion fatigue phenomenon in metallic alloys, it is suggested that these may be initiation sites for the mechanical failures which have been observed, and that the acceleration of lipid absorption by tensile stress provides potential mechanisms for both initiation and accelerated propagation of fatigue cracks. It is demonstrated as a consequence of mechanochemical thermodynamics that any constituent of the body fluids (e.g. lipids) which can swell the elastomer will in fact be preferentially absorbed at the point of highest tensile stress, i.e., the crack tip, and that swelling will be accelerated by the applications of tensile stress.
In vivo and in vitro changes in strength of orthopedic calcium aluminates
Authors: Schnittgrund G. D. , Kenner G. H. , Brown S. D.
Published: May 2005

Calcium aluminate bars were formulated to study the effect of real and simulated biological environments on strength. Static fatigue tests revealed that the strength of these potential internal bone prostheses decreased to ca. 60% of their initial strength after less than 100 min while being held at constant stress in solution. Calcium aluminate bars aged for 12 weeks in water or Ringer solution were also found to exhibit large losses in strength, while bars implanted in vivo for the same period of time weakened somewhat less. Semi‐quantitative analysis of the solutions in which the calcium aluminate bars were aged revealed that Al3+ and Ca2+ were being leached from the bars in both the saline and water baths, while the concentration of Mg2+ was decreasing in the Ringer solution.

Scanning electron microscope (SEM) studies revealed extensive microstructural changes in specimens aged in water or saline solution for 1 and 12 weeks. Similar but far less extensive changes were seen in bars aged in vivo in rabbits for 12 weeks.
Corrosion of the η′(Cu‐Sn) phase in dental amalgam
Authors: Marek M. , Okabe T. , Butts M. B. , Fairhurst C. W.
Published: May 2005

Previous studies have shown preferential corrosion of the η′(Cu‐Sn) phase in highcopper dental amalgam both in vitro and in vivo, while samples of pure η′ have shown high corrosion resistance. To clarify this contradiction, samples of pure η′ crystals mixed with other phases were prepared and tested. Evaluation of the corrosion resistance was based on the results of coulometry at constant potential and potentiodynamic polarization. The corrosion susceptibility of η′ in the matrix of γ(Ag‐Hg) was considerably higher than the susceptibility of isolated η′. The susceptibility of pure η′ also could be increased by plating it will small amounts of Hg. It was concluded that in dental amalgam, the presence of mercury in the phases surrounding η′ reduces its resistance to corrosion. Although η′ is more resistant to corrosion than γ2(Sn‐Hg) which appears in low‐copper amalgams, it is the least corrosion resistant major phase in high‐copper amalgams and can suffer deterioration.
The electro‐osmotic actuation of implantable insulin micropumps
Authors: Uhlig E. L. P. , Graydon W. F. , Zingg W.
Published: May 2005

A study using an electro‐osmotic cell suitable for actuating an implantable insulin micropump showed that controlled variable flow rates in the order of 0.2 mL/day are possible. The cell functioned continuously with low energy and power requirements and long service life. The principle of operation is compatible with achieving the very low flow rates necessary if highly concentrated insulin is to be used to avoid frequent insulin reservoir refilling. An electro‐osmotic cell, Ag/ AgCl/NaCl(aq)/ cation exchange membrane/NaCl(aq)/ AgCl/ Ag, was connected to a constant current power supply which reversed the direction of the current every 10 mins causing a to‐and‐fro transport of fluid through the membrane. Flow rates of 0.15–0.60 μL/min were achieved with currents of 2.5–10 mA. At the low flow rate, energy consumption was 6.4 × 10−2 J/μL and peak power requirement was <2.0 × 10−4 W. Fluid was transported against a pressure gradient of 52 cm Hg. The cell contained a total electrolyte volume of <0.25 mL. The membrane showed no change in properties after 10,000 current reversals (69 days). To function as an actuator for an implantable insulin micropump, the electro‐osmotic cell requires a switching and valving assembly; a suitable design for this is briefly considered.
Grafted synthetic sorbents for enhanced removal of toxic chemical agents from plasma
Authors: McPhillips D. M. , Armer T. A. , Owen D. R.
Published: May 2005

A series of porous polymeric sorbents and activated carbon were used to remove di‐isopropyl methylphosphonate (DIMP) from human plasma and normal saline. The sorptive capacities of the commercially available sorbents Amberlite XAD‐4, XAD‐2, XN1010, and XE348, and Calgon 400 were determined. Butyl‐ and palmityl‐grafted XAD‐4 were prepared with graft efficiencies of 32 and 6%, respectively, and tested for sorptive capacities. DIMP removal efficiencies were compared to dialysis with a 1.8 m2 Cordis‐Dow hollow fiber artificial kidney (HFAK). Butyl‐grafted XAD‐4 and active carbon outperformed the other sorbents in removing DIMP from both saline and plasma. An order of magnitude reduction in removal ability was noted for all the adsorbents when the mobile media was plasma. Pronounced plasma precipitation was elicited by activated carbon, an effect not observed with any of the polymeric resins tested. The removal efficiencies on a 18.0 g basis of XAD‐4, butyl‐grafted XAD‐4, and active carbon were comparable to that of the HFAK used in this study. These sorbents, however, possess a macroscopic surface area of approximately 0.1 m2, an order of magnitude lower than that of the HFAK. This reduction in contact area is believed to reduce substantially the possibility of undesirable molecular and cellular effects.
Histological investigation of bone induction by demineralized allogeneic bone matrix: A natural biomaterial for osseous reconstruction
Authors: Vandersteenhoven J. J. , Spector M.
Published: May 2005

The objective of the study was to delineate the histological sequence of events associated with bone formation induced in extraosseous sites by implants of demineralized allogeneic bone matrix (DABM) in order to provide a more complete basis for the clinical use of the natural biomaterial for osseous reconstruction. The rat was the experimental animal model. Implants were prepared by demineralization of diaphyseal cortical rat bone in 0.6N HCl for 18–24 h. A total of 104 specimens, 4 mm square, were implanted both subcutaneously and intramuscularly in 26 rats for periods of 3 days to 22 weeks. Histological evaluation revealed a sequence of events that at 3 days displayed an inflammatory response to surgical trauma and after 6 weeks exhibited the formation of a mature lamellar ossicle with central marrow which was maintained through 22 weeks. Resorption of the DABM, first evident at 1 week, was accompanied by the appearance of chondroblasts in vascular canals and in crevices in the implant. Osteoblastic activity, initially seen at 2 weeks, appeared to be associated with capillary and blood vessel formation around the implant and within enlarged resorptive cavities within the specimens. Calcification occurred in the cartilaginous matrix and osteoid and within the implanted matrix.

The osteoinductive process comprises (1) the inflammation / granulation / scar formation processes elicited by implantation of a material, (2) the resorptive response elicited by DABM, and (3) the process of induction of nonosseous mesenchymal cells to differentiate to chondroblasts and osteoblasts. The results of the present study support previous investigations demonstrating the bone‐inducing property of DABM and provide further evidence for the potential value of this natural biomaterial for use in osseous reconstruction.
The effect of gamma irradiation on the enzymatic degradation of polyglycolic acid absorbable sutures
Authors: Chu C. C. , Williams David F.
Published: May 2005

The purpose of the study was to examine the effect of γ irradiation on the enzymatic as well as the in vivo degradation of polyglycolic acid sutures. The sutures of size 2–0 were irradiated at dosage levels of 0–20 mrad. The three enzymes chosen for this study, were esterase, α‐chymotrypsin, and trypsin. The irradiated sutures were both immersed in the enzyme solutions, their corresponding buffer controls, and implanted in inbred black‐and‐white hooded hister rats (Liverpool strain). The degradation of PGA sutures was determined mechanically. Among the three enzymes studied, esterase showed the highest enzymatic effect on the degradation of the unirradiated and irradiated PGA sutures. Trypsin's effect on PGA sutures was not observed until 20 mrad. The findings of trypsin demonstrated the hypothesis that synthetic high molecular weight polymers, which are initially resistant to enzymatic degradation, could become prone to enzymatic attack after altering their physical and chemical structures. Implanted PGA sutures maintained a similar or slightly higher mean tensile breaking strength in in vivo degradation compared to in vitro degradation (0.1M tris buffer of pH = 7.5); these degradation profiles suggest that PGA does not display similar behavior in in vivo and in vitro degradations. The magnitude of dissimilarity depends on the radiation dosage and on the duration of degradation, and is speculated to be attributable to the specific action of enzymes with respect to the con‐figuration and chemical structure of the PGA sutures.
Strain‐rate dependence of the compressive properties of normal and carbon‐fiber‐reinforced bone cement
Authors: Saha Subrata , Pal Subrata
Published: May 2005

Normal and carbon‐fiber‐reinforced (1 wt. %) bone cement samples were tested in compression at various strain rates. Both the compressive strength and proportional limit increased in general with increasing strain rate. Similar strain‐rate sensitivity was also shown by the carbon‐fiber‐reinforced bone cement. The mechanical properties, namely the modulus of elasticity, the proportional limit, and the compressive strength of the carbon‐fiber‐reinforced bone cement showed highly significant positive correlations with the strain rate.
Variations between Biomer™ lots. I. Significant differences in the surface chemistry of two lots of a commercial poly(ether urethane)
Authors: Tyler B. J. , Ratner B. D. , Castner D. G. , Briggs D.
Published: May 2005

We have studied the surface chemistry of two lots of Biomer™ (BSP067 and BSUAOOl), and widely used commercial poly(ether urethane) (PEU). Although transmission infrared adsorption studies revealed no differences in the bulk chemistry of the two lots, the surface chemistry, as seen by x‐ray photoelectron spectroscopy (XPS) and static secondary ion mass spectrometry (SIMS), was different. Lot BSP067 showed softsegment enrichment at the surface, which is typical of PEU. Lot BSUAOOl showed no evidence of either hard‐ or soft‐segment PEU components at the surface. The surface of this lot was completely covered with a nonextractable additive identified as poly(diisopropy1 amino ethyl methacrylate). Small amounts of a low‐molecular‐weight antioxidant were observed at the surface of both samples. Because the biological response to polymers is dependent on surface structure, these results are of considerable importance to biomaterials research.
Formation of focal contacts by osteoblasts cultured on orthopedic biomaterials
Authors: Puleo D. A. , Bizios R.
Published: May 2005

The nature of the contact sites formed during the adhesion of osteoblasts to orthopedic implant materials was investigated by fluorescence microscopy. More specifically, the cytoskeletal organization of and the focal contact formation by neonatal rat calvarial osteoblasts attaching to and spreading on 316L stainless steel, Ti‐6A1– 4V, Co–Cr–Mo, Synamel (hydroxyapatite), alumina, and borosilicate glass were examined. Focal contacts are regions where the plasma membrane approaches the substrate to within 10–15 nm and where bundles of cytoskeletal microfilaments terminate. Fluorescent‐labeling of F–actin– containing microfilaments demonstrated a typical sequence of events as rounded, suspended osteoblasts spread onto the substrates. Immunofluorescent‐labeling of the protein vinculin, which is found at the cytoplasmic face of focal contacts, initially showed the formation of streak‐like focal patches. On the biomaterials, the vinculin staining subsequently extended up and along, but ventral to, the microfilament bundles. The fibrillar patterns observed at later times may evidence the formation of extracellular matrix contacts.
Synthesis of photoreactive poly(ethylene glycol) and its application to the prevention of surface‐induced platelet activation
Authors: Tseng Y.‐C. , Park K.
Published: May 2005

Photoreactive poly(ethy1ene glycol) (PEG) was synthesized by reacting 4‐fluoro‐ 3‐nitrophenyl azide (FNPA) with sodium salt of PEG. The synthesized 4‐azido‐2‐ nitrophenyl PEG (ANP‐PEG) was charac‐ terized by 1H‐NMR, IR, and UV spectro‐ scopy. ANP‐PEG was grafted to dimethyldichlorosilane‐coated glass (DDS‐glass) by photolysis without any premodification of the surface. The effects of various grafting factors, such as the polymer adsorption time, concentration of ANP‐PEG, and UV irradiation time, on the PEG grafting efficiency were examined. The PEG‐grafted DDS‐glass was characterized by measuring surface free energies, surface‐induced platelet activation, and the relative amount of PEG grafted on the surface using electron spectroscopy for chemical analysis (ESCA). Platelet adhesion and activation was analyzed by measuring the number and spread area of adherent platelets. The results showed that ANP‐PEG had to be adsorbed onto DDS‐glass for at least 12 h before photolysis for the maximum grafting efficiency. No platelets could adhere to the PEG‐grafted DDS‐glass, if the bulk concentration of ANP‐PEG in the adsorption solution was between 1 mg/mL and 10 mg/mL. Above 10 mg/mL, platelet activation gradually increased and reached the maximum at 30 mg/mL. Our data indicate that the grafting of ANP‐PEG requires careful control of the grafting conditions and that the grafted PEG can prevent surface‐induced platelet activation.
Cell adhesion and growth on synthetic elastomeric matrices containing ARG‐GLY–ASP–SER–3
Authors: Nicol Alastair , Channe Gowda D. , Urry Dan W.
Published: May 2005

Synthetic elastomeric polypeptide matrices based on the repeating amino acid sequences of elastin have biophysical and biological properties which are favorable for prosthetic materials. An important requirement envisaged for some applications is the ability to support cell adhesion and growth. The X20–poly– (GVGVP), the γ–irradiation cross‐linked elastomeric matrix based on the repeatin poly[n(GVGVP), (GRGDSP)] containing the covalently incorporated cell adhesion sequence Arg–Gly–Asp–Ser (RGDS) were synthesized. These matrices were tested for their ability to support the adhesion and growth of bovine aortic endothelial cells and of bovine ligamentum nuchae fibroblasts. Adhesion experiments carried pentamer Val–Pro–Gly–Val–Gly, and X2 B – out in albumin‐containing media showed that matrices containing 60:1, 40:1, and 20:l ratios of (GVGVP):(GRGDSP) supported maximal cell attachment, that matrices containing 100:l exhibited an intermediate level of attachment and that matrices composed of 500:l and (GVGVP) alone were very poor supports for cell attachment. Serum in the media promoted submaximal cell attachment to X20–poly– (GVGVP) but did not permit substantial cell growth. Cell growth was supported by matrices having high ratios of (GRGDSP). Ratios of 60:1, 40:1, and 2O:l supported three population doublings of endothelial cells over 3 days resulting in confluent matrix‐adherent monolayers. Ratios of 40:l and 20:l similarly supported the growth of fibroblasts.
Albumin‐binding surfaces for implantable devices
Authors: Keogh James R. , Velander Fredrik F. , Eaton John W.
Published: May 2005

Surfaces of implantable and blood contact‐devices accumulate adsorbed and denatured proteins. This anomalous layer of proteins may help trigger unwanted events such as activation of coagulation systems and, perhaps, chronic inflammation. Because, in many experimental systems, the purposeful coating of surfaces with albumin will biologically “passivate” materials, we have attempted to develop polymers which, when exposed to blood or body fluids, will spontaneously, selectively, and reversibly adsorb host albumin. We report here a novel derivatization technique for increasing the albumin affinity of implantable polyetherurethane (PU). The technique is based on the incorporation of high‐molecular‐weight dextran to which the albumin‐binding dye Cibacron Blue is covalently attached. Somewhat surprisingly, the amounts of human albumin adsorbed by Blue Dextran‐modified and unmodified PU are quite similar. There are, however, important differences. First, the binding of albumin to derivatized PU is specific and not readily blocked by proteins in albumin‐depleted human serum. Second, the majority of albumin associated with derivatized PU appears to be reversibly bound. Third, the binding of albumin to derivatized PU evidently is mediated primarily through ligandspecific binding of the protein to the albumin‐binding dextran‐dye conjugate. We conclude that it is possible to produce implantable polymers having surfaces which display albumin‐binding dyes that selectively and reversibly bind albumin. Materials with this property, when implanted or exposed to blood, should form an infinitely renewable coating of albumin derived from physiologic fluids. This surface modification strategy may spawn a new generation of implantable materials with improved biologic compatibility.
High‐voltage electron microscopy and conventional transmission electron microscopy of the interface zone between bone and endosteal dental implants
Authors: Steflik D. E. , Sisk A. L. , Parr G. R. , Hanes P. J. , Lake F. , Song M. J. , Brewer P. , McKinney R. V.
Published: May 2005

The interface between mandibular bone and endosteal dental implants was examined with an in vivo dog model. Undecalcified mandibular implant samples were observed with both conventional transmission electron microscopy and highvoltage transmission electron microscopy (HVEM). Results demonstrated the variable nature of the interfacial support tissues. Mineralized bone was often found within 50 nm of the implant surface, separated from that surface only by an electron dense deposit. Osteocytes were observed close to the interface encased within lacunae extending numerous cellular processes through canaliculi. An osteoblast was also observed directly at the interface within a developing lacuna. Other interfacial areas exhibited a finely fibrillar and more electron lucent morphology. Furthermore, other areas were shown to be composed of wider zones of extracellular products containing collagen fibrils, ground substance, and calcified inclusions. Because bone is a n actively growing and remodeling tissue, these different morphological zones around the entire area of the implants would appear to confirm the dynamic tissue response to endosteal dental implants. Further, HVEM stereology was shown to be an exciting research tool to investigate this tissue response.
Bone apposition to plasma‐sprayed cobalt‐chromium alloy
Authors: Luckey Hugh A. , Lamprecht Elden G. , Walt Michael J.
Published: May 2005

The use of porous metallic coatings for fixation of total joint prostheses by bone ingrowth has become a widespread alternative to fixation with PMMA bone cement. However, concerns about such coatings include long‐term effects of metal ion release, potential coating loss, and decreased substrate fatigue strength. The biological fixation capability of a nonporous, high‐integrity plasmasprayed CoCr coating with low surface area was compared to a conventional sintered bead coating in goat cortical and cancellous bone sites after 8 and 16 weeks of implantation. Histological evaluation showed substantial variations in fixation quality between individual animals and between surgical sites with no consistent difference between implant types. Shear testing of bonelimplant interfaces showed that although conventional porous coating exhibited higher overall average shear strengths in cortical bone sites at both time periods, the differences were not statistically significant. In cancellous sites, the average shear strengths achieved with conventional porous and plasmasprayed coatings were essentially equal. Analysis using average paired differences, however, revealed that when porous and plasma‐coated implants are placed in identical sites of contralateral limbs, the plasma coatings consistently yielded higher shear strengths in cancellous bone sites at the later time period. Since current design theory for biological fixation favors metaphysical fixation, this surface may offer potential advantages over conventional porous coatings.
Preparation of dense hydroxylapatite or rhenanite containing bioactive glass composites
Authors: Kangasniemi I. M. O. , de Groot K. , Becht J. G. M. , Yli‐Urpo A.
Published: May 2005

The effect of time at 600°C and of small additions of Al2O3 and B2O3 on the sintering of two composite materials of (1) hydroxylapatite (C ∼I O (P O ∼)∼(O H )∼) and bioactive glass (SiO2‐CaO‐P2O5‐Na2O) or (2) rhenanite (CaNaPO,) and bioactive glass were studied. Scanning microscopy, quantitative EDX, x‐ray diffraction, helium gas density measurements, and diametral measurements were performed on the resulting composites. No reactions were observed with the SEM or XRD between the hydroxylapatite particles and the glass matrix within sufficient sintering times to achieve maximum density. (∼) The rhenanitecontaining composites were observed to form Na2O2CaO3SiO2 crystals by x‐ray diffraction, probably as a result of dissolution of the rhenanite particle surfaces into the glass phase, the crystals formed in the glass or at the interface of the glass, and the ceramic particles. However, within the short sintering times needed to achieve maximum density the rhenanite particles remained mostly intact. The rhenanitecontaining materials gave better results than the hydroxylapatite‐containing materials. The glass composition had a great effect on the densification process.
The effect of lipase on the release of naltrexone from triglyceride‐coated cellulose acetate phthalate microspheres
Authors: Tefft J. A. , Roskos K. V. , Heller J.
Published: May 2005

The ultimate objective of this work is to develop a device that can be triggered by morphine to release naltrexone. In this device, naltrexone is dispersed in cellulose acetate phthalate microspheres which are then spray‐coated with a trilaurin protective coating. The microspheres are contained within a macroporous cylinder which also contains a reversibly inactivated lipase. This enzyme in its inactive state is unable to remove the protective coating but in its active state is able to do so. Inactivation is achieved by the covalent attachment of morphine followed by complexation with a morphine antibody. Triggering is accomplished by the displacement of the lipase‐morphine conjugate from the antibody. In this phase we have investigated the effect of lipase on the release of naltrexone from trilaurincoated microspheres and found that the coated microspheres are stable in a pH 7.4 phosphate buffer at 37°C for at least 1 month, but release 80% of the incorporated naltrexone in one hour when 100 nig of capsules in 5 mL buffer are exposed to 25 μg of lipase.
Effect of soft segment chemistry on the biostability of segmented polyurethanes. II. In vitro hydrolytic degradation and lipod sorption
Authors: Takahara Atsushi , Hergenrother Robert W. , Coury Arthur J. , Cooper Stuart L.
Published: May 2005

A series of segmented polyurethanes (SPUs) with various polyol soft segments was prepared and their hydrolytic degradation and degradation due to lipid sorption was investigated. The hydrolytic degradation of the SPUs was investigated in a papain solution, where it was shown that the SPU based on poly(ethy1eneoxide) (PEO) soft segment was susceptible to hydrolytic degradation. X‐ray photoelectron spectroscopic (XPS) data suggest dissociation of the urethane linkage by enzymatic degradation. Degradation by lipid sorption was observed for the SPU based on a poly(dimethylsi1oxane) (PDMS) soft segment. This is ascribed to the high solubility of lipid in the PDMS segment of the SPU.
Bone formation processin porous calcium carbonate and hydroxyapatite
Authors: Ohgushi Hajime , Okumura Motoaki , Yoshikawa Takafumi , Inboue Keisuke , Senpuku Norio , Tamai Susumu , Shors Edwin C.
Published: May 2005

This study determined the bone formation in porous calcium carbonate (CC) and porous hydroxyapatite (HA) in ectopic sites. The bone formation stimulus was derived from bone marrow cells. CC and HA in the shape of disks were implanted with or without rat marrow cells into subcutaneous sites of syngeneic rats. The CC and HA had identical microstructure: pore size was 190–;230 μm, porosity was 50–60% and they were fully interconnected. Bone did not form in any implants without marrow cells (disks themselves), whereas bone consistently formed in the pores of all implants with marrow cells after 4 weeks. The bone formation of both CC and HA occurred initially on surface of the pore regions and progressed toward the center of the pore. Scanning electron microscopy and electronprobe microanalysis revealed a continuum of calcium at the interfaces of both bone/CC and bone/HA implants. These results indicate that the bone formation in calcium carbonate derived from marine corals is comparable to the bioactive hydroxyapatite.
Agarose for a bioartificial pancreas
Authors: Iwata Hiroo , Takagi Tatsuya , Amemiya Hiroshi , Shimizu Hiroshi , Yamashita Kazuya , Kobayashi Kazuo , Akutsu Tessuzo
Published: May 2005

Islets were encapsulated into 5% concentration agarose microbeads. The effect of microencapsulation on islet allograft survivals was determined using a streptozotocininduced diabetic (STZ) mouse and a nonobese diabetic (NOD) mouse as recipients. All five STZ BALB/c mice receiving microencapsulated islets (C57BL/6) maintained normoglycemia indefinitely. When NOD mice were used as recipients of the bioartificial pancreas, four of five grafts (islets from C3H/He) functioned for more than 80 d. Two of five NOD mice maintained normoglycemia until animals were sacrificed at 102 and 192 postoperative d. Microbeads made of commercially available agarose can effectively prolong alloislets functioning in the STZ‐diabetic mouse and even in the NOD mouse (animal model of human type I diabetes) without the use of any immunosuppressive drug.
Theoretical analysis on cell size distribution and kinetics of foreign‐body giant cell formation in vivo on polyurethane elastomers
Authors: Zhao Q. H. , Anderson J. M. , Hiltner A. , Lodoen G. A. , Payet C. R.
Published: May 2005

The nature of in vivo leukocyte adhesion and foreign‐body giant cell (FBGC) formation on polyurethanes was studied through theoretical and statistical analyses in terms of cell size distribution, density changes, and kinetics of FBGC formation. The results showed that the size distribution of FBGCs followed a “most probable” distribution. During FBGC formation, the densities of FBGCs changed with time. At an early stage, the number of FBGCs increased with time to a maximum at the expense of macrophages. As more FGBCs were formed and less macrophages were present, the fu‐ sion of FBGCs among themselves became significant. This, in turn, caused a gradual decrease of FBGC density with time. The rate of FBGC formation was characterized by a rate constant that represented certain characteristics of cell fusion and FBGC formation and the density of initial FBGC‐forming macrophages that were a small fraction of leukocytes adhering to the surface. The direct correlations of surface cracking and pitting and adherent FBGCs demonstrated the influence of phagocytic actions of FBGCs on the biostability of implanted polyurethanes. While the cracking was thought to be caused by oxidative degradation facilitated by oxygen ion/radical release of FBGCs, the pitting appeared to result from the Methacrol 2138F aggregates diffusing out of the polymer in an acidic microenvironment under FBGCs, which in turn could be enhanced by the surface degradation and cell phagocytosis. The added Santowhite powder in polyurethane had a significant influence on FBGC formation: It reduced FBGC den‐ sity and rate of FBGC formation by reducing leukocyte adhesion and the number of macrophages participating in FBGC formation.
Biomaterial‐induced alterations of neutrophil superoxide production
Authors: Kaplan S. S. , Basford R. E. , Mora E. , Jeong M. H. , Simmons R. L.
Published: May 2005

Because periprosthetic infection remains a vexing problem for patients receiving implanted devices, we evaluated the effect of several materials on neutrophil free radical production. Human peripheral blood neutrophils were incubated with several sterile, lipopolysaccharide (LPS)‐ free biomaterials used in surgically implantable prosthetic devices: polyurethane, woven dacron, and Velcro. Free radical formation as the superoxide (O2−) anion was evaluated by cytochrome c reduction in neutrophils that were exposed to the materials and then removed and in neutrophils allowed to remain in association with the materials. Neutrophils exposed to polyurethane or woven dacron for 30 or 60 min and then removed consistently exhibited an enhanced release of O2− after simulation via receptor engagement with formyl methionyl‐leucyl‐ phenylalanine. Enhanced reactivity to stimulation via protein kinase C with phorbol myristate acetate, however, was not consistently observed. The cells evalu‐ ated for O2− release during continuous association with the biomaterials showed enhanced metabolic activity during short periods of association (especially with polyurethane and woven dacron). Although O2− release by neutrophils in association with these materials decreased with longer periods of incubation, it was not obliterated. These studies, therefore, show that several commonly used biomaterials activate neutrophils soon after exposure and that this activated state diminishes with prolonged exposure but nevertheless remains measurable. The diminishing level of activity with prolonged exposure, however, suggests that ultimately a depletion of reactivity may occur and may result in increased susceptibility to periprosthetic infection.
Synthesis and nonthrombogenicity of polymer membrane with surface‐graft polymers carrying thrombin inhibitor
Authors: Ito Yoshihiro , Liu Lin‐Shu , Matsuo Ryuichi , Imanishi Yukio
Published: May 2005

An acrylamide derivative of a thrombin inhibitor was synthesized and graft polymerized to the surfaces of polymer mem‐ branes. The thrombin‐inhibitor activity was unaffected by the introduction of an acryloyl group. The surface‐graft membrane deactivated thrombin markedly and suppressed adhesion of platelets, resulting in a high nonthrombogenicity. Immersion of polymer membranes blended with the thrombin inhibitor in phosphate‐buffered saline for 10 d resulted in the loss of nonthrombogenicity, while the polymer membranes grafted with the thrombin inhibitor derivative maintained the non‐thrombogenicity over a long period.
Tissue reactions induced by modified poly(vinyl alcohol) hydrogels in rabbit cornea
Authors: Kobayashi Hisatoshi , Ikada Yoshito , Moritera Takeshi , Ogura Yuichiro , Honda Yoshihito
Published: May 2005

The purpose of this study was to compare the tissue reactions induced by modified poly(vinyl alcohol) (PVA) hydrogels with other materials implanted in the rabbit cornea. PVA hydrogels with and without covalently bonded collagen were compared to ethylene‐vinyl alcohol copolymer, and polysulfone discs. These materials were implanted in the rabbit corneal stroma. The resultant tissue reactions were histologically and clinically studied. The PVA hydrogels had high flux rates of glucose and L‐lactic acid in vitro. Covalent immobilization of collagen onto their surface was found to render them more biocompatible. However, excessive ulceration and vascularization of the cornea still ocurred in vivo, possibly because of extremely little blinking of the rabbits, which might cause desiccation of the cornea. © 1992 John Wiley & Sons, Inc.
Experimental determination of friction characteristics at the trabecular bone/porous‐coated metal interface in cementless implants
Authors: Shirazi‐Adl A. , Dammak M. , Paiement G.
Published: May 2005

An apparatus was developed to measure loaddisplacement friction properties at the cancellous bone/porous‐coated metal plate interface. Bone cubes were obtained from different proximal regions of four resurfaced cadaveric tibiae. Three different poroussurfaced metal plates (one fiber mesh and two bead) and a smooth‐surfaced metal plate were used. In the presence of a constant normal contact pressure (0.10, 0.15, or 0.25 MPa), a variable tangential load up to the maximum resistance of the interface was applied and both relative normal and tangential displacements were recorded. Repetitive and fatigue loadings were also considered. Measured results show that the interface friction curve is highly nonlinear, exhibiting large relative tangential displacements in the range of 50–400 μm before the maximum load is reached. Relative displacements in the normal direction remain below 10 μm. The maximum resistance in friction is independent of the bone excision site, type of porous‐surfaced metal plate, magnitude of normal load, placement of bone cubes on metal plates or vice versa, repetition of applied load, and conservation period of bone cubes in saline solution. The smoothsurfaced metal plate has significantly smaller friction resistance than porous‐coated ones. The fatigue loading of up to 4000 cycles at 1 Hz, in the presence of 0.25 MPa contact pressure, slightly decrease the interface friction coefficient. Finally, the initial secant stiffness of the interface at 75% of the maximum resistance load is found to be larger for the bone cubes from the lateral and medial regions and for the metal plate with smooth surface. © 1993 John Wiley & Sons, Inc.