bluuebunny/crossref_metadata_2025 huggingface dataset:
Maxillofacial prostheses of chlorinated polyethylene
Authors: May P. D. , Guerra L. R.
Published: December 2004

There is clearly a need for maxillofacial prosthetic materials with improved properties. The chlorinated polyethylenes are thermoplastic elastomers which have particularly promising properties, and were used by us to prepare improved maxillofacial prostheses. Suitable CPE resins were compounded with other polymers and with pigments on a heated rubber mill to form thin sheets in a variety of shades. These were heated at 190°C for 10 min and placed between heated linotype mold halves. The prosthesis was formed in a hand press. Sometimes heating and pressing were repeated. After cooling in water, the prosthesis was removed and hand‐shaded with oil‐soluble dyes. Physical properties were evaluated using standard techniques; skin irritation studies were conducted by 14‐day insult patch tests on rabbits. Clinical evaluations were conducted on human volunteers. Parallel evaluations were conducted on commercially available materials for comparison. The CPE was superior to all of the three commercial materials in most properties, and comparable to the better of the three in the remaining properties. On balance, CPE was significantly superior. Early results indicate that the materials and techniques required are easily handled in the dental lab and that the final prosthesis has excellent aesthetic and patient acceptability.
A high‐modulus polymer for porous orthopedic implants: Biomechanical compatibility of porous implants
Authors: Spector M. , Michno M. J. , Smarook W. H. , Kwiatkowski G. T.
Published: December 2004

A high‐modulus polymer, polysulfone, was evaluated as a porous bone implant material. The bone ingrowth into canine cortical pellets of sintered polysulfone particles was assessed by microradiography and histology. The shear strength of the porous polysulfone–bone interface was determined by push‐out and pull‐out tests of cortical and trochanteric implants, respectively. Results indicated that the bone in‐growth into porous polysulfone specimens proceeded in such a fashion as to mimic the normal repair at the site. Mechanical testing of cortical and cancellous implants revealed that the interfacial shear strength of the porous polysulfone‐bone composite was similar to that achieved using porous metals.
The rate of adhesion of melanoma cells onto nonionic polymer surfaces
Authors: Yasuda H. , Yamanashi B. S. , Devito D. P.
Published: December 2004

The rates of adhesion of melanoma cells (carcinogenic) onto nonionic polymer surfaces were studied by using radioactively labeled cells and measuring the fraction of cells which adhered to the surface in a given time. Glow discharge (plasma) polymerization of 1,1,3,3‐tetramethyldisiloxane and of nitrogen‐acetylene‐water (mole ratio 0.4:1.0:0.2) was used to modify the surface energy of the substrate. The cell adhesion rate was found to be given by Y = 1 − exp [−k0(γs − γ0)t], where Y is the fraction of cells adhered, − k0 is a characteristic rate constant, γs is the total surface energy of the substrate, γ0 is the threshold surface energy of cell adhesion, and t is time.
Corrosion behavior of cast and forged cobalt‐based alloys for double‐alloy joint endoprostheses
Authors: Süry P. , Semlitsch M.
Published: December 2004

An ideal combination of mechanical and corrosion properties of long‐term implants such as joint endoprostheses has yet to be found. Besides being resistant to pitting and crevice attack, which can lead to corrosion fatigue and stress corrosion cracking failures, the implant material must be highly resistant to wear and abrasion. Two cobalt‐based alloys, wrought CoNiMoTi and air‐cast CoCrMo, were subjected to a number of selected in vitro electrochemically and chemically accelerated corrosion tests in chloride‐containing solutions with wrought AISI‐316L used as a reference alloy. A limited number of immersion tests in FeCl3 and acidified FeCl3 solutions were also conducted. It is found that the mechanical properties of wrought CoNiCrMoTi alloy qualify it as a substitute for cast CoCrMo alloy and wrought AISI‐316L in anchorage shaft production for all types of joint endoprostheses. Wrought CoNiCrMoTi has a higher resistance to fatigue cracking compared with cast CoCrMo and is as resistant to selective corrosion phenomena such as stress corrosion cracking.
Measurement of the rate of wear of dental composite resins by a 90Sr beta particle transmission gauge
Authors: Moores G. E. , Glentworth P. , Harrison A.
Published: December 2004

The wear rate of restorative dental composite resins is an important parameter in the assessment of their in vivo performance. The two more widely used methods of quantifying wear are measuring the dimensional change and measuring the change in the mass of the specimen. The former method is complicated by uneven wear of specimens and presents difficulties with samples of irregular shape, and the latter method involves measurements of changes in mass as small as tens of micrograms with specimens of sizes similar to those encountered clinically. A 90Sr beta particle transmission gauge has been designed and constructed to enable the wear rate of small specimens of dental composite resins to be measured. The 90Sr beta particle transmission gauge enables indirect measurements of changes in mass to be made and overcomes some of the difficulties inherent in the direct measurement of mass and length. Applications of the 90Sr beta particle transmission gauge to the measurement of wear rates are given for restorative dental resins having a range of inorganic filler contents and types. The results show that the 90Sr beta particle transmission gauge is capable of measuring the rate of wear to a degree of precision similar to that of micrometer‐derived measurements.
Macroporous hydrogel membranes for a hybrid artificial pancreas. I. Synthesis and chamber fabrication
Authors: Ronel Samuel H. , D'Andrea Mark J. , Hashiguchi Hiroshi , Klomp Gregory F. , Dobelle William H.
Published: December 2004

We report development of special macroporous semipermeable membranes and diffusion chambers made of polymerized 2‐hydroxyethyl methacrylate (pHEMA), synthesized specifically to enclose living insulin‐producing pancreatic islet cells for the treatment of diabetes. This material was selected to minimize the fibrotic encapsulation which has limited hybrid artificial pancreas efforts with other membranes, including Millipore and Nuclepore filters. The pore density and pore size distribution were dependent on the ratio of water to HEMA monomer and also on the crosslinker (EGDMA) concentration. A macroporous membrane resulted only when the ratio of water/HEMA monomer was greater than 50%. 125I‐insulin permeability was studied in vitro. A technique is also described to fuse the membranes to form diffusion chambers used for implantation into diabetic rats.
The retention mechanics of LTI carbon, carbon‐coated aluminum oxide, and uncoated aluminum oxide dental implants
Authors: Cook S. D. , Weinstein A. M. , Klawitter J. J.
Published: December 2004

The in vitro mechanical behavior of identical geometry LTI carbon, carbon‐coated aluminum oxide, and uncoated aluminum oxide blade‐type dental implants has been evaluated using rosette type strain gauges and a LVDT system. The implants served as a distal abutment for a three‐unit fixed prosthesis and functioned for a period of 2 years in female baboons. The comparison of the LTI carbon implants to the carbon‐coated aluminum oxide implants allowed for a study of the effect of implant elastic modulus on the mechanical behavior, while the comparison of the carbon‐coated and uncoated aluminum oxide implants allowed for a study of the effect of chemical composition at the tissue–implant interface. The results of the mechanical testing indicate that the implant displacement response of the LTI carbon implants was greater than that of the carbon‐coated and uncoated aluminum oxide implants. Little difference in displacement response was observed for the carbon‐coated and uncoated aluminum oxide implants. No clear trend in the strain response of the buccal mandibular bone was observed for the three implant systems. The greatest differences in strain response, however, was observed between the uncoated aluminum oxide implants and the LTI carbon and carbon‐coated aluminum oxide implants.
Supermolecular organization of some polyurethanes containing sugar derivatives in the main chain
Authors: Lipatova T. E. , Pkhakadze G. A. , Snegirev A. I. , Vorona V. V. , Shilov V. V.
Published: December 2004

X‐ray studies on polyurethanes containing sugar derivatives in the main chain were performed. It was demonstrated that the microphase separation of rigid and flexible fragments was dependent on the nature of sugar derivatives. The supermolecular organization in disaccharide‐based polymers is the most ordered one. In xylose‐ and arabinose‐based polyurethanes the phase separation is defined least of all. Glucose‐ and dulcitol‐based polymers are intermediates as to their supermolecular organization. Supermolecular organization models for block copolyurethanes under investigation were proposed.
Macrophage phagocytosis of biodegradable microspheres composed of L‐lactic acid/glycolic acid homo‐ and copolymers
Authors: Tabata Yasuhiko , Ikada Yoshito
Published: December 2004

A variety of biodegradable microspheres were prepared from L‐lactic acid, DL‐lactic acid, or glycolic acid homopolymers and copolymers of different molecular weights and monomer compositions. Phagocytosis of the microspheres by mouse peritoneal macrophages was studied in cell culture system using scanning electron microscopy as well as light microscopy. The diameter of microspheres prepared was less than 2 μm, regardless of the starting polymers. No dependence of the chemical nature of starting polymers was observed on the extent of phagocytosis of the microspheres by macrophages. Precoating the microspheres with water‐soluble macromolecules such as proteins had great influence on phagocytosis by macrophages. It was demonstrated that precoating with bovine serum albumin and non‐proteinaceous macromolecules reduced the phagocytosis of microspheres, while bovine γ‐globulin, human fibronectin, bovine tuftsin, and gelatin precoating enhanced the phagocytosis. This trend was not influenced by the presence of serum. Only in the case of gelatin precoating, the phagocytosis was greatly enhanced by the presence of serum as compared to precoating with other proteins. Microscopic observation clearly indicated that the phagocytosed microspheres were gradually degraded in the macrophage interior with the incubation time, leading to release of a fluorescent dye encapsulated in the microspheres. The rate of microsphere degradation in cells could be controlled by changing the molecular weight and the monomer composition of the copolymers comprising the microspheres.
Apatite–wollastonite containing glass ceramic–fibrin mixture as a bone defect filler
Authors: Ono Kozo , Yamamuro Takao , Nakamura Takashi , Kakutani Yoshiaki , Kitsugi Toshiaki , Hyakuna Katsubumi , Kokubo Tadashi , Oka Masanori , Kotoura Yoshihiko
Published: December 2004

The purpose of this study was to evaluate the usefulness of a mixture of apatitewollastonite containing glass ceramic (A–W · GC, 42–60 mesh in granule size) with fibrin as a bone defect filler. A bone defect was drilled in the proximal metaphysis of the rat tibia and was filled with (1) fibrin glue, (2) A–W · GC granules, or (3) A–W · GC–fibrin mixture. Nothing was placed in the defect of the controls. The animals were serially sacrificed until 8 weeks after the operation, and the defect site was histologically examined and histomorphometrically analyzed for quantitative evaluation of newly formed bone and blood vessels. The use of fibrin glue as the binder markedly increased the ease of handling the A–W · GC granules. In the controls, little trabecular regeneration was observed in the defect site. Early vascularization (confirmed by microangiography) increased and the repairing process was accelerated in the defects filled with fibrin. In these defects filled with A–W · GC granules, good bone formation was observed around the granules. Bone formation was accelerated in the defects filled with A–W · GC fibrin mixture. Thus, the mixture showed good osteoconductive potential as well as acceleration of the repair process. Therefore, A–W · GC–fibrin mixture is considered to be a useful bone defect filler.
Structure of a collagen‐GAG dermal skin substitute optimized for cultured human epidermal keratinocytes
Authors: Boyce Steven T. , Christianson Deborah J. , Hansbrough John F.
Published: December 2004

Collagen and glycosaminoglycan (GAG) dermal skin substitutes (membranes) were studied as substrates for cultured human epidermal keratinocytes. Structure of dermal substitutes was optimized for pore size to promote ingrowth of fibrovascular tissue from the wound bed and for culture of human keratinocytes of the membrane's surface. Pore size of the freeze‐dried material was regulated by control of the temperature of freezing between −50°C and −20°C and by concentration of starting materials between 0.17% and 1.62% wt/vol. A nonporous surface of collagen‐GAG was laminated to the membranes to provide a planar substrate for cultured epidermal kerationocytes. Thickness of dermal substitutes was regulated by control of the volume and concentration of starting materials. Biotin was conjugated to solubilized collagen for binding with avidin of specific quantities of biologically active molecules. The optimized membranes are suitable substrates for the culture of human epidermal keratinocytes, and together with the cells yield a composite material that is histologically similar to skin.
Attachment and spreading of human gingival fibroblasts on potentially bioactive glasses in vitro
Authors: Häkkinen Lari , Yli‐Urpo Antti , Heino Jyrki , Larjava Hannu
Published: December 2004

The attachment and spreading of cultured fibroblasts on potentially bioactive glasses (bioglasses) of ten different compositions were studied. Human gingival fibroblasts were allowed to attach and spread on bioglasses for 1–72 h. Unreactive silica glass and cell culture polystyrene served as controls. The attachment and spreading of cells were examined by 3H‐thymidine labeling of cells, planimetric analysis, cytological staining, immunocytochemistry, and scanning electron microscopy. The cell attachment to bioglasses and silica glass and the cell spreading on bioglasses were slower and cell morphology more elongated compared to control plastic. In spite of great differences in bioglass compositions no great differences in cell behavior on these surfaces were detected. Thus the initial events in the tissue–implant interface might be independent on the bioglass composition, and furthermore the differences in the organization of the tissue–implant interface in vivo might depend on the nature of the surrounding tissues and subsequent changes of the implant surface and the extracellular environement.
In vitro characterization and biomechanical optimization of a biodegradable particulate composite bone cement
Authors: Gerhart Tobin N. , Miller Richard L. , Kleshinski Stephen J. , Hayes Wilson C.
Published: December 2004

We have developed a biodegradable particulate composite bone cement and used in vitro and in vivo methods for studying its suitability for orthopaedic applications. The composite matrix consists of gelatin, water, and sodium salicylate. The particulate phase is made up of powdered and particulate (355–600 μm diameter) tricalcium phosphate. Paraformaldehyde (0.1% to 0.5% by weight) is used as a matrix cross‐linking agent. The effects of incubation time, particulate volume fraction, density of the individual particles, water content, concentration of crosslinking agent, and freeze‐drying on the unconfined compressive strength and modulus of the particulate composite were measured. Compressive strengths of 7 MPa and moduli of 65 MPa could be achieved. Mechanical properties depended critically upon the water content of the particulate composite, with values of strength and modulus decreasing rapidly outside a range of 10–14% of specimen dry weight. High‐density tri‐calcium phosphate particulate produced cement with twice the strength found with porous particulate. In a companion study we document in vivo performance of this particulate composite in an animal model system.
Decreased neutrophil respiratory burst on exposure to cobalt‐chrome alloy and polystyrene in vitro
Authors: Shanbhag Arun , Yang Jun , Lilien Jack , Black Jonathan
Published: December 2004

The effect of biomaterials on the super‐oxide‐producing ability of neutrophils was studied. Human peripheral blood neutrophils were incubated with cobalt‐base alloy (F‐75) or polystyrene beads of nonphagocytosable size. Respiratory burst activity was studied by measuring super‐ oxide dismutase inhibitable reduction of cytochrome C. Neutrophils were found to release no more superoxide anion on incubation for up to 3 h with either material in a protein‐free medium than controls without foreign material. However, the ability of neutrophils incubated with either biomaterial to subsequently respond to phorbol myristate acetate challenge was decreased (p < 0.05). Chemical analysis of supernatants for the F‐75 samples showed a high concentration of cobalt in the medium within 1 h of incubation. Minimal chromium and nickel was detected. No correlation could be demonstrated between metal in solution and the respiratory burst defect in neutrophils. Instead it appears that interaction of cells with either surface was the critical event in altering the response to phorbol myristate acetate. This observed functional defect may play an important role in rendering tissue around implanted biomaterials susceptible to infections.
Influence of the substrate binding characteristics of fibronectin on corneal epithelial cell outgrowth
Authors: Pettit Dean K. , Horbett Thomas A. , Hoffman Allan S.
Published: December 2004

The outgrowth of corneal epithelial cells onto a polymeric substrate is expected to be the primary event in the epithelialization of a synthetic corneal graft. Circular corneal buttons (5 mm) were punched from excised rabbit corneas and placed onto bare substrates or substrates preadsorbed with fibronectin (fn), albumin, or binary mixtures of both fn and albumin. Cell outgrowth areas were measured after culturing the buttons for 4 days in serumfree medium. Fibronectin adsorption to the materials was measured from pure and binary solutions with 125‐radiolabeled fibronectin. A parameter thought to be related to the binding strength of fn to polymeric substrates was measured in parallel experiments by partial elution of the adsorbed fn by 3% sodium dodecyl sulfate (SDS). Following pure solution fibronectin adsorption a range of out growth areas was measured (from 0.86 ± 0.03 cm2 for glass to 1.49 2 0.03 cm2 for TCPS). On all of the materials tested cell outgrowth areas increased following fn preadsorption and decreased following albumin preadsorption relative to bare surfaces (p < 0.05). Following preadsorption with binary protein mixtures cell out growth areas increased with fibronectin adsorption, however, the outgrowth areas were not determined solely by the concentration of fn adsorbed onto the surfaces. This result suggested that the biological efficiency of the adsorbed fibronectin was substrate‐dependent. When the cell outgrowth data were cross‐plotted against fn retention following SDS elution, the outgrowth areas were found to increase along with increases in fn retention. Based on these data we suggest that epithelial cell outgrowth may be partially governed by the tightness of binding between the fn molecules and the underlying substrate. © 1992 John Wiley & Sons, Inc.
A comparative study of ultrastructures of the interfaces between four kinds of surface‐active ceramic and bone
Authors: Neo M. , Kotani S. , Nakamura T. , Yamamuro T. , Ohtsuki C. , Kokubo T. , Bando Y.
Published: December 2004

The interfaces between four kinds of surfaceactive ceramic and bone were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using undecalcified specimens. The materials were Bioglass®‐type glass (Bioglass®), Ceravital‐type glass‐ceramic (KGS), apatite and wollastonitecontaining glass‐ceramic (A‐W · GC) and hydroxyapatite (HA)· Particles of these materials, ranging between about 100 and 300 μm in diameter, were implanted into rat tibiae, and specimens were prepared for observation at 8 weeks after implantation. All materials were observed to bond to bone through a collagen‐free layer consisting of fine apatite crytals distinct from those in bone. The crystals of this apatite layer and those of bone were intermingled at their interface, suggesting chemical bonding. In Bioglass®, which had only a glassy phase, several tens of microns of the material surface had changed to such an apatite layer. In KGS and A‐W · GC, which had macrocrystals in the glassy phase, an intervening apatite layer about 0.5 μm thick was observed between the materials and bone. Furthermore, fine apatite crystals were also observed among the macrocrystals near the surface of the materials. In HA, which had no glassy phase, an intervening apatite layer was much less distinct and sometimes absent. These differences were considered to be attributable to the differences in chemical composition, crystallization, and solubility of the materials. © 1992 John Wiley & Sons, Inc.
Influence of fibril length upon ePTFE graft healing and host modification of the implant
Authors: Hirabayashi K. , Saitoh E. , Ijima H. , Takenawa T. , Kodama M. , Hori M.
Published: December 2004

Influence of fibril length (porosity) upon synthetic vascular graft healing has not been investigated in detail. The purpose of this study was to determine the dependence of neoendothelial healing, cellular response, and biocompatibility on the fibril length of expanded polytetrafluoroethylene (ePTFE) grafts with an internal diameter of 1.5 mm. ePTFE grafts of different fibril length, 20, 40, 60, and 90 μm, were implanted into the abdominal aorta of rats (n = 5 for each group). After 5 weeks, the implants were harvested and examined for neointimal and pseudointimal coverage by light microscopy and SEM. The hydroxyproline content of the implants was measured, and the distribution of collagen types was examined. The neointimal and pseudointimal coverage was related to the fibril length, and the neoendothelial healing was better on 60‐μm and 90‐μm grafts than on 20‐μm and 40‐μm grafts, The amount of hydroxyproline was also related to the fibril length, however, no significant difference could be observed between 60‐μm and 90‐μm grafts. Collagen types I and III were almost identically located in the middle portion of the implants. Our results demonstrate that the fibril length of ePTFE grafts affected neoendothelial healing and its affinity to collagen. © 1992 John Wiley & Sons, Inc.
Spatial and temporal changes in compliance following implantation of bioresorbable vascular grafts
Authors: Greisler Howard P. , Joyce Kathleen A. , Kim Dae Un , Pham Si M. , Berceli Scott A. , Borovetz Harvey S.
Published: December 2004

Compliance matching between the host vessel and vascular grafts used for smalldiameter arterial replacements is thought to be important for longterm patency. However, currently available grafts elicit fibroplastic reactions, resulting in decreasing compliance with time after implantation. Bioresorbable prostheses elicit ingrowth of myofibroblasts containing abundant contractile elements. This led us to investigate whether compliance of implanted bioresorbable prostheses decreased as a function of time and if the kinetics of change correlated with the progession of tissue ingrowth. Woven polyglactin 910 prostheses (10 mm × 4 mm i.d.) were implanted into adult NZW rabbit infrarenal aortas and replicates were harvested serially through 8 months. Control grafts were implanted, and immediately resected. Dynamic compliance was measured a t 1‐mm axial increments along each explant using a pulse duplicator apparatus which exposed the harvested samples to realistic pulsatile hemodynamics. Compliance was calculated for proximal, mid, and distal segments of each graft and averaged at each time point by grouping into control (zero time, n =3), early (1‐4 weeks, n = 13), and late (6‐36 weeks, n = 9) explant periods. At late explant periods both proximal and distal compliance were significantly greater than mid graft compliance (p ≤ .02 and p ≤ .03, respectively). There was a significant increase in proximal compliance between early and late explant times (p ≤ .01). Measured increases in mid and distal segment compliance over time did not reach statistical significance. Myofibroblast laden tissue ingrowth into the inner capsule followed macrophage phagocytosis and was nearly complete prior to the time that an increase in compliance was demonstrated. Thus since the major histologic episodes precede the change in compliance, these are not likely initiated by this biomechanical change. We hypothesize the graft resorption coupled with the ingrowth of more compliant tissue likely leads to the increased compliance of the graft material. © 1992 John Wiley & Sons, Inc.
Toxicity test of biodegradable polymers by implantation in rabbit cornea
Authors: Kobayashi Hisatoshi , Shiraki Kaneto , Ikada Yoshito
Published: December 2004

To evaluate whether or not the corneal micropocket implantation is effective for determining the toxicity of polymeric materials, currently used biodegradable polymers such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), LA‐GA copolymers, and three kinds of poly(2‐cyanoacrylate)s (PCA) were implanted in a rabbit corneal pouch and the tissue responses were observed macroscopically and microscopically. It was found that PLA induced no vascularization, whereas a residual solvent and ethylene oxide gas remaining in the PLA matrix invoked vascularization. Vascularization clearly took place when PGA was implanted in the cornea, which became opaque, probably because of cellular infiltration. In the case of PCA implantation, severe inflammation as well as vascular invasion occurred in the initial stage. It is likely that these tissue reactions were caused by the leachables from the implanted materials, the extent being dependent on the leaching rate and the toxicity. It was concluded that the corneal micropocket assay is a good means to detect trace amounts of leachables from implanted materials without sacrificing the animals with the implanted materials. © 1992 John Wiley & Sons, Inc.
Effect of surface plasma treatment on the chemical, physical, morphological, and mechanical properties of totally absorbable bone internal fixation devices
Authors: Ibnabddjalil M'hamed , Loh Ih‐houng , Chu C. C. , Blumenthal Norman , Alexander Harold , Turner David
Published: December 2004

The purpose of this work was threefold: to enhance the adhesion between the reinforced absorbable calcium phosphate (CaP) fibers and the absorbable polyglycolide acid (PGA) matrix, to improve the hydrolytic degradation of the CaP fibers, and preliminarily to evaluate the cytotoxicity of the plasma treated surface of CaP fibers. CH4plasma treatment was used to achieve these goals. The microbond method was used to evaluate the effects of the plasma treatment on the interfacial shear strength between the PGA matrix and CaP fibers. The treatment increased the mean interfacial shear strength of the CaP/PGA composite system by 30%. AFM data showed that CH4‐treated CaP fibers had considerable microscopic surface roughness, which facilitated mechanical interlocking between the reinforced CaP fibers and PGA matrix. The untreated and plasma‐treated fibers were also subjected toin vitrohydrolytic degradation in a phosphate buffer solution of pH 7.44 at 37°C for up to 15 h. CH4plasma treatment resulted in a considerable lower polar term of the surface energy and a significantly higher disperse term in water media. This change in the proportion of surface energy terms may reduce the capillary wicking phenomena of water through the CaP fiber/PGA matrix interface. The CaP fiber dissolution studies revealed that both CH4and Parylene plasma polymer coatings appeared to reduce the solubility of CaP fibers, and that the magnitude of reduction was higher in an acidic than a physiologic pH environment. A preliminary cytotoxicity test revealed that both CH4and Parylene plasma‐treated CaP fibers were noncytotoxic. Additional research should be done to determine the optimum plasma conditions and the possible use of other plasma gases to improve the interfacial shear stress of the composite and the dissolution properties of CaP fibers. © 1994 John Wiley & Sons, Inc.
Ultrastructural study of the A‐W GC‐bone interface after long‐term implantation in rat and human bone
Authors: Neo M. , Nakamura T. , Ohtsuki C. , Kasai R. , Kokubo T. , Yamamuro T.
Published: December 2004

The interface between apatite‐ and wollastonite‐containing glass‐ceramic (A‐W GC) and bone after long‐term implantation was studied by scanning and transmission electron microscopy (SEM and TEM) using rat and human specimens. First, particles of A‐W GC (100–200 μm in diameter) were implanted into rat tibiae, and specimens were prepared for observation at 24, 48, 72, and 96 weeks after the operation. These long‐term specimens showed an A‐W GC—bone interface different from that at an earlier stage, which was investigated in our previous studies. SEM showed that the Ca‐P ‐rich layer was wider, suggesting that leaching of ions from the A‐W GC had continued even after bonding with bone. In some regions, the material particles were evidently replaced by the bone. TEM showed that the intervening apatite layer had become indistinct, and that A‐W GC had intermingled with bone at the interface. In some regions, the surface of the A‐W GC was degraded. These findings suggest that the surface region of A‐W GC is slowly replaced by bone. Second, a human bone specimen, which included A‐W GC particles (300–700 μm in diameter) implanted as a bone filler for about 75 weeks was harvested and investigated. Excellent A‐W GC—bone bonding was observed, and the ultrastructure of the interface was similar to that in rats after long‐term implantation. This finding demonstrated that A‐W GC possibly worked in human bone in the same way as in rat bone, showing excellent bioactivity. © 1994 John Wiley & Sons, Inc.
Experimental evaluation of a new composite mesh with the selective property of incorporation to the abdominal wall without adhering to the intestines
Authors: Amid Parviz K. , Shulman Alex. G. , Lichtenstein Irving L. , Sostrin Stuart , Young John , Hakakha Michael
Published: December 2004

This preliminary study examined the possibility of preventing intestinal adhesions to biomaterials while preserving their incorporation with the abdominal wall. White New Zealand rabbits received intraperitoneal implants of different biomaterials for repair of defects created on the abdominal wall. The following biomaterials were used: polypropylene, polyester, expanded polytetraflueroethylene, polypropylene mesh/polypropylene sheeting (polypropylene mesh covered with polypropylene sheeting on the peritoneal side), polypropylene/silastic, polypropylene/polyglactin, polypropylene/polyglycolic acid, and polypropylene/fibrin. All biomaterials evaluated caused adhesions to the intestines except for polypropylene mesh/polypropylene sheeting and polypropylene mesh/silastic composites. Because adhesion of the intestine to the biomaterial is the first stage of biomaterial‐related intestinal fistula, its prevention is logical for the elimination of this complication. Composites with the selective property of adhering to the abdominal wall, yet sparing the viscera, would facilitate thoracic and abdominal wall surgeries, as well as intraperitoneal laparoscopic hernioplasties. © 1994 John Wiley & Sons, Inc.
Effect of a change in interfacial geometry on the fatigue strength of porous‐coated Ti‐6Al‐4V
Authors: Wolfarth D. , Ducheyne P.
Published: December 2004

Porous‐coated Ti‐6Al‐4V has a fatigue strength approximately one‐third that of the uncoated alloy. The interfacial geometry between the porous coating and the implant substrate is notchlike, leading to stress concentrations that have been shown to be the main cause for the reduction in fatigue strength. In this study, the effect of interfacial geometry on fatigue strength of porouscoated Ti‐6Al‐4V is quantified. The interface between porous coating and implant is modeled using linear elastic, plane strain finite element analysis. Integrated with the numerical analysis is an experimental verification of enhanced fatigue behavior. Changes in interfacial geometry are conceived, and their effectiveness in reducing stress concentrations are determined. A doubling of fatigue strength can be achieved for newly conceived geometries over conventional porous coating geometries. © 1994 John Wiley & Sons, Inc.
In Vitro effect of metal ions on cellular metabolism and the correlation between these effects and the uptake of the ions
Authors: Wataha J. C. , Hanks C. T. , Craig R. G.
Published: December 2004

The effects of Ag+1, Au+3, Cd+2, Cu+2, Ga+3, In+3, Ni+2, Pd+2, and Zn+2 on DNA synthesis, protein synthesis, succinic dehydrogenase activity, and total cellular protein of mammalian fibroblasts were measured for exposures less than 12 h. The rates at which these cellular functions responded to metal ion exposure were compared and related to the uptake rate of the ions into the cells. These rates of response were significantly different: DNA synthesis decreased the fastest, followed by protein synthesis, succinic dehydrogenase activity, and total protein. This order of response was similar for most metal ions. At 4 h, the rate of uptake of the metal ions correlated most closely with depression of succinic dehydrogenase activity, whereas at 8 h, the uptake correlated most closely with depression of protein synthesis. The similar response of cells to all metal ions may imply that these ions act on cells by similar mechanisms. The rates of uptake of Ag+1, Cu+2, and Zn+2 were sufficiently fast that in vivo exposures of tissues to these metals for periods less than 12 h would be capable of disrupting cellular metabolism. © 1994 John Wiley & Sons, Inc.
Granule secretion markers on fluid‐phase platelets in whole blood perfused through capillary tubing
Authors: Rhodes N. P. , Zuzel M. , Williams D. F. , Derrick M. R.
Published: December 2004

The effect of material composition and shear rate on fluid‐phase platelet activation was investigated using a capillary perfusion model. Citrated whole blood was perfused along the lumens of tubes constructed from silicone, PVC, Pellethane, W124 (an experimental polyetherurethane), and glass. Platelet activation was determined by measuring the increase in α‐granule membrane protein P‐selectin (GMP‐140, CD62) and the lysosomal granule membrane protein GP‐53 (CD63) on fluid‐phase platelets by flow cytometry. All tubes caused an increase over the negative control in the number of P‐selectin and GP‐53 molecules detectable on the surface of these platelets. The activation response of platelets to changes in shear rate was also investigated. It was found that lysosomal release paralleled α‐granule release in glass, but not in Pellethane, over a range of wall shear rates (100–1,000 s−1). © 1994 John Wiley & Sons, Inc.
Creep of a poly(etherurethane urea) in an oxidative environment
Authors: Wu Y. K. , Lodoen G. A. , Anderson J. M. , Baer E. , Hiltner A.
Published: December 2004

The creep behavior of a PEUU without added stabilizers was examined in H2O2/CoCl2, an environment that simulates the biodegradation of this polymer. Creep in the control environments, air, water, and H2O2, was logarithmic with time as is characteristic of primary or viscoelastic creep. At short times, creep in H2O2/CoCl2 followed the same time dependency as creep in H2O2; however, at longer times an acceleration in the creep rate was observed. Creep in H2O2/CoCl2 was satisfactorily described by addition of a linear time term to the creep equation with an induction time, ti. The induction time was extended by stress‐induced crystallization of the soft segments, but was reduced by an increase in H2O2 concentration. Oxidative degradation of the PEUU soft segments was detected by infrared and GPC analysis at times less than ti. This led to the speculation that an initial “precursor” layer was created at the surface by chain cleavage. Microcracking in a subsequent stage was postulated to be responsible for the observed effect on the creep behavior. © 1994 John Wiley & Sons, Inc.
A light and laser scanning microscopy study of bone/hydroxyapatite‐coated titanium implants interface: Histochemical evidence of unmineralized material in humans
Authors: Piattelli Adriano , Trisi Paolo
Published: December 2004

The authors describe a light and laser scanning microscopy study of hydroxyapatite‐coated titanium implants retrieved from humans. A histochemical technique, using von Kossa and basic fuchsin, allowed clear differentiation between mineralized bone and unmineralized bone matrix. The bone‐hydroxyapatite (HA) interface presented variable features: in some areas the mineralized bone was directly apposed to the HA surface, while in others an unmineralized red‐stained material, probably osteoid, was interposed. Laser scanning microscopy confirmed these findings showing a thin layer of fluorescent material at the interface. © 1994 John Wiley & Sons, Inc.
Evaluation of carcinogenicity and chronic toxicity associated with orthopedic implants in mice
Authors: Takamura Kazuyuki , Hayashi Kazuo , Ishinishi Noburu , Yamada Teruki , Sugioka Yoichi
Published: December 2004

The carcinogenicity and chronic toxicity of 316L stainless steel, nickel, Ti‐6Al‐4V, hydroxyapatite (HA)‐coated Ti‐6Al‐4V, aluminum oxide containing yttrium oxide were evaluated by implanting solid rods of each material in the thigh muscle of C57BL/6N mice for 24 months. Nickel alloy showed high carcinogenic and toxic potencies, whereas other materials showed no evidence of them. Tumors retaining nickel alloys were malignant fibrous histiocytoma or fibrosarcoma. In some cases, lymphomata that seemed to develop spontaneously were found around the implants because lymphocytes were known to accumulate in chronic inflammatory lesions, and this phenomenon also might be applied to lymphoma. © 1994 John Wiley & Sons, Inc.
The origins of barriers to orbital symmetry/topology‐allowed pericyclic reactions: Conjugate addition of methylene to s‐cis‐1,3‐butadiene
Authors: Bauld Nathan L. , Wirth David
Published: December 2004

The barriers on the MINDO/3 reaction paths for π and σ approaches to concerted cycloaddition of methylene to s‐cis‐1,3‐butadiene are analyzed by a new energy decomposition scheme and compared to the results of published extended Hückel calculations. The relatively small (6 kcal) preference for the σ approach is essentially based on next‐nearest‐neighbor (1,3) resonance interactions, which are stabilizing in the σ but destabilizing in the π approach. Both routes are characterized by large distortion energies (mainly disrotation at the diene termini in the case of the π approach) and nonbonded repulsions. The excessive magnitude of both of these effects ultimately derives from the weak pericyclic binding which prevails at initial diene geometries, especially the pericyclic topology involving the methylene LUMO. Although previous work has emphasized the contribution of closed‐shell repulsions to the barrier, no such effect is explicitly included in MINDO. The closed‐shell repulsions to which the extended Hückel barrier has been solely attributed are shown to involve next‐nearest‐neighbor (antiaromatic) resonance interactions.
Ab initio calculation of spin–orbit interaction in polyatomic molecules using Gaussian‐type wavefunctions
Authors: Breulet Jacques
Published: December 2004

A set of programs has been developed to calculate molecular spin–orbit interaction with Gaussian‐type wavefunctions in connection with the popular GAUSSIAN 76 program. The spin–orbit contributions to the fine structure of O2 (X3∑g−), NH (X3∑−), and CH2 (X3B1) are evaluated with the standard STO‐3G and 6‐31G basis sets; for NH the influence of bond functions added to the latter basis set is also investigated. The results are compared to values previously obtained with other types of basis sets.
Molecular orbital theory of the hydrogen bond. 27. Substituent effects in water: 4‐R‐pyrimidine complexes
Authors: Bene Janet E. Del
Published: December 2004

Ab initio SCF calculations with the STO‐3G basis set have been performed to investigate substituent effects on the structures and stabilization energies of water:4‐R‐pyrimidine complexes, with R including CH3, NH2, OH, F, C2H3, CHO, and CN. Except for the cyclic water:4‐aminopyrimidine complex hydrogen bonded at N3, these complexes have open structures stabilized by a nearly linear hydrogen bond formed through a nitrogen lone pair of electrons. When hydrogen bonding occurs at N3, the complexes may have planar or perpendicular conformations depending on the substituent, but when hydrogen bonding occurs at N1, the perpendicular is generally slightly preferred, and there is essentially free rotation of the 4‐R‐pyrimidine. Primary substituent effects alter the electronic environment at the nitrogens, and tend to make N3 a poorer site for hydrogen bonding than N1, primarily because of a stronger π electron‐withdrawing effect at N3. However, the relative stabilities of complexes hydrogen bonded at N1 and N3 are also influenced by secondary substituent effects, which may be significant in stabilizing complexes bonded at N3. Substitutent effects on the structures and stabilization energies of the water:4‐R‐pyrimidine complexes are similar to substitutent effects in water:2‐R‐pyridine and water:4‐R‐pyrimidine complexes are similar to substitutent effects in water:2‐R‐pyridine and water:4‐R‐pyridine complexes. Configuration interaction calculations indicate that although absorption of energy by the pyrimidine ring destabilizes the water:4‐R‐pyrimidine complexes, these may still remain bound in the excited n → π* state. This is in contrast to the fate of open water:2‐R‐pyridine and water:4‐R‐pyridine complexes, which dissociate in this state.
Conformational energy calculation on the neurotensin c‐terminal pentapeptide Arg–Pro–Tyr–Ile–Leu OH
Authors: Cotrait Michel , Ptak Marius
Published: December 2004

The conformational behavior of the C‐terminal neurotensin pentapeptide, Arg–Pro–Tyr–Ile–Leu OH [NT(9–13)], was investigated using empirical energy calculations. A special aim was to display the specific contribution of each residue to induce conformations able to interact with biological receptors. Restrictions were then introduced in intramolecular interactions involving the Arg side chain and the terminal COOH group. The stablest conformations include in the order of decreasing stability: a distorted helical form for the C‐terminal tetrapeptide, a (Pro2–Tyr3) β turn I, an α helix, an extended form, and a (Tyr2–Ile3) β turn III, which are energetically rather close (ΔE < 3 kcal/mol). The NT(9–13) peptide appears then as a rather flexible molcule with a noteworthy ability of adaptation to a substrate. Extended forms would be in agreement with a zipper model of interactions with receptors, whereas folded forms involving helices and β, γ turns would support a lock and key model. The specific contribution of side chains, specially those of Tyr and Arg residues as well as the key position of the Pro residue emerge clearly from this study.
Studies in hydrogen bonding: Association within mixed dimers of water, methanol, ammonia, and methylamine using the empirical potential EPEN
Authors: Brink George , Glasser Leslie
Published: December 2004

An empirical potential EPEN has been used to find the stable geometries and approximate hydrogenbond energies of the mixed dimers formed between molecules of water, methanol, ammonia, and methylamine. These results are compared with results in the literature obtained using ab initio methods.
Thermochemical data from ab initio calculations. I. Estimation of SCF energies for augmented basis sets and Hartree–Fock limit energies
Authors: Cremer Dieter
Published: December 2004

A procedure is outlined which allows an estimation of molecular energies both for a finite basis set including polarization functions and for the Hartree–Fock limit. It is shown that the orbital error of a given minimal basis is covered to a certain relatively constant percentage by an augmented basis set calculation. Thus an improvement factor Qav can be determined by analyzing the corresponding results of small molecules where reasonable estimates of HF limit energies can be taken from the literature. For a combination of Pople's STO‐3G and 6‐31G* basis sets Qav turns out to be 0.955.
Fast semiempirical calculations
Authors: Stewart J. J. P. , Császár P. , Pulay P.
Published: December 2004

Most quantum chemists regard semiempirical methods as ephemeral and computationally cost efficient. For this reason, an article dealing with computational efficiency of semiempirical methods is probably very unfashionable. However, experience at a big computer installation, shared by ab‐initio and semiempirical quantum chemists shows that the second group actually consumes more computer time than the first. Obviously, the greater size of the molecules in semiempirical calculations outweighs the inherent efficiency of these methods. The present article describes a simple method for accelerating SCF‐type semiempirical methods.
Stabilization of methyl anions by first‐row substituents. The superiority of diffuse function‐augmented basis sets for anion calculations
Authors: Spitznagel Günther W. , Clark Timothy , Chandrasekhar Jayaraman , Schleyer Paul Von Ragué
Published: December 2004

The entire set of methyl anions, XCH2−, substituted by first‐row substituents, Li, BeH, BH2, CH3, NH2, OH, and F, was examined at various ab initio levels. Diffuse orbital‐augmented basis sets, such as 4−31+G and 6−31+G*, are needed to describe the energies of these anions adequately. Estimates of proton affinities are further improved by second‐order Møller–Plesset (MP2) electron correlation corrections, but relative energies are less affected. The methyl group in the ethyl anion is destabilizing, the amino substituent is borderline, but all other groups are stabilizing. Very large π effects are exhibited by BH2 and BeH groups; inductive stabilization by the electronegative F and OH groups is less effective. Lithium also is stabilizing, but the best singlet geometry of CH2Li− is not planar. A planar CH2Li− triplet with a π1 configuration may be lower in energy.
The conformation of pithomycolide
Authors: Hall David , Pavitt Nicola , Wood Murray K.
Published: December 2004

The conformation of the depsipeptide pithomycolide has been deduced by systematically generating possible models for the molecule, and minimizing their conformation energy. Only one of low‐energy solutions is consistent with the reported NMR data.
Principles for a direct SCF approach to LICAO–MOab‐initio calculations
Authors: Almlöf J. , Faegri K. , Korsell K.
Published: December 2004

The principles and structure of an LCAO‐MO ab‐initio computer program which recalculates all two‐electron integrals needed in each SCF iteration are formulated and discussed. This approach—termed “direct SCF”—is found to be particularly efficient for calculations on very large systems, and also for calcuations on small and medium‐sized molecules with modern minicomputers. The time requirements for a number of sample calculations are listed, and the distribution of two‐electron integrals according to magnitude is investigated for model systems.