bluuebunny/crossref_metadata_2025 huggingface dataset:
Quantitative analysis of early in vivo tissue response to synthetic apatite implants
Authors: Ellies L. G. , Carter J. M. , Natiella J. R. , Featherstone J. D. B. , Nelson D. G. A.
Published: December 2004

Studies have shown synthetic calcium phosphates such as hydroxyapatite and beta tricalcium phosphate to be biocompatible in vivo. However, few studies have quantitated histological responses to the implants.

The aim of this study was to develop a method for the quantitative assessment of tissue biocompatibility to ceramic materials in vivo and to use this method to compare noncarbonated and carbonated apatite implants. Synthetic sintered apatites of 0, 3, and 6% carbonate by weight were prepared and cut into implants 4 × 4 × 1 mm. These were placed 2 mm into the medial aspect of rat fermurs. Following sacrifice at 4 weeks, the femurs were fixed in formalin, demineralized in formic acid, and embedded in glycol methacrylate. Sections were cut on an ultramicrotome set at 1.5 μm and stained with toluidine blue. A point counting technique using standard stereological grids and a low‐power microscope was used to measure areas of new bone formation. The width of the connective tissue zone adjacent to muscle was measured using an image analyzer. All implants were well accepted by the host tissues judging from criteria of minimal inflammation and degree of fixation. Results showed an increase in new bone formed in the marrow cavity with increasing carbonate content. This may improve stability of the implant in the host bone, particularly during the initial healing period. A technique which should enable quantitative histological evaluation of different ceramic materials has been developed. The use of this method indicates that further studies are warranted to investigate carbonated apatite as an implant material.
Locking mechanism strength of absorbable ligating devices
Authors: Hay D. L. , von Fraunhofer J. A. , Chegini N. , Masterson B. J.
Published: December 2004

The locking mechanism strenghts of the absorbable Absolok and Lactomer ligating clips and the absorbable Lactomer staple have been determined following implantation in an animal model. Three sizes of each type of clip and the single size of staple were enclosed in open mesh nylon pouches and implanted subcutaneously in rabbits for periods of 4, 7, 14, 21, and 28 days before tensile testing of the lock mechanisms. No change in the lock mechanism strength was detected for the Absolok clips before 21 days. The Lactomer clips and staples, however, showed significant decrease in lock mechanism strength within 7 days of implantation, this loss increasing with longer implantation times. A proportion of all the devices were found to have dissolved to an extent that precluded testing at 21 and 28 days. The findings indicate that the lock mechanisms of absorbable ligating clips differ significantly in their short‐term (30 days) durability.
Albumin adsorption on alkyl chain derivatized polyurethanes: I. The effect of C‐18 alkylation
Authors: Pitt W. G. , Cooper S. L.
Published: December 2004

The initial adsorption rate of delipidized Human Serum Albumin (HSA) is increased by addition of C‐18 alkyl chains to a poly‐urethane. The presence of alkyl chains does not appear to influence the total amount of HSA adsorbed after one hour exposure to a 5.0 mg/mL HSA solution. Neither does the desorption following one hour of adsorption appear to be influenced by the presence of alkyl chains. A study of the effects of solution concentration and temperature showed that the initial adsorption rates on both polymers are proportional to the protein concentration raised to the 0.36 power, and that alkylation of the polymer increases the activation energy of the initial adsorption rate above the 14 kJ/mol observed for the underivatized polyurethane. A new technique is presented to quantify the mass of adsorbed protein using Fourier transform infrared spectroscopy and attenuated total reflection optics. This technique uses the absorbance of bulk protein as an internal calibration reference, and appears to be as accurate and perhaps more precise than radiolabeling techniques.
Immobilization of enzymes on polypropylene bead surfaces by anhydrous ammonia gaseous plasma technique
Authors: Sipehia R. , Chawla A. S. , Daka J. , Chang T. M. S.
Published: December 2004

Anhydrous ammonia gaseous plasma technique was used for the surface modification of polypropylene beads. Amino groups were added onto the surfaces of beads by exposing them to ammonia plasma. Through these amino groups covalent immobilization of glucose oxidase and peroxidase were carried out. The total amounts of immobilized glucose oxidase and immobilized peroxdase were found to be 52 and 43 μg/cm2, respectively. To assess the stability of enzyme–polypropylene linkage, beads with covalently immobilized glucose oxidase and peroxidase were washed with phosphate buffer. It was found that after the removal of the adsorbed enzymes, the concentration of covalently immobilized enzymes tended to reach a steady state. After additional washing with buffer for 5 to 6 h, 40–55% of the immobilized enzymes were found to be in the active form.
Mineralization and calcium fixation within a porous apatitic ceramic material after implantation in the femur of rabbits
Authors: Krajewski A. , Ravaglioli A. , Mongiorgi R. , Moroni A.
Published: December 2004

Cylinders (0.8 cm long, 1.0 cm of diameter and with an axial hole), constituted, after firing, of a ceramic mixture of hydroxylapatite (HA) and β‐ricalciumphosphate (β‐TCP) in a 10:1 ratio, were implanted into mid‐diaphiseal defects of one femur of 20 rabbits and stabilized with intramedullary rods. The implantation sites were checked radiographically every month, and after 3 months (3 animals) and 6 months (17 animals) the rabbits were sacrificed and the implants with the surrounding tissue were embedded in methylmetacrylate, cut to thick sections and analyzed by scanning electron microscopy (SEM). Porosimetric and x‐rays diffraction analyses were carried out before and after implantation of the cylinders, and the state of mineralization at the bone–implant interface was determined by EDAX microprobe analysis. Bony callus formation started at 1 month at the osteotomy sites, as judged by radiography, but after 3 months a not‐mineralized zone had still been demonstrated between bone and the implants. At 6 months, 13 implants showed themselves firmly fixed in their implantations beds, while 4 implants were only incorporated at their proximal ends. In bone contact zones, an enrichment of Ca2+ was displayed by microanalytical techniques in the outer zone of the implanted samples which may be explained by an apparent additional phase transformation of HA into TCP, thanks to the change of the Ca/P ratio, that takes place in vivo.
Silicone rubber temporomandibular joint (TMJ) meniscal replacements: Postimplant histopathologic and material evaluation
Authors: Hartman Laurie C. , Bessette Russell W. , Baier Robert E. , Meyer Anne E. , Wirth John
Published: December 2004

Medical grade silicone rubber has long been considered a suitable meniscal replacement, but there has been increasing concern about migration of this material into adjacent tissues. The objectives of this study were to determine the definitive composition of tissue‐incorporated material which is presumed by light microscopy to be silicone and to identify long term histopathologic sequelae of meniscal replacements. Adult female patients underwent meniscectomy and replacement with silicone rubber (Silastic) implants. After 12 to 18 months, recurrence of symptoms in 8% of these cases led to implant removal with excision of peri‐implant fibrous pseudo‐capsules. Excised tissues, including one preauricular lymph node and implants were submitted for light microscopy, SEM, and energy dispersive x‐ray microanalysis (EDX) for the identification of elemental composition, critical surface tension measurement, and internal reflection infrared spectroscopy. EDX revealed prominent peaks for silicon in both pseudocapsular and nodal tissues. Morphologic findings surrounding the long‐term implants included foreign body reaction, synovitis, dystrophic calcification, fibrocartilaginous metaplasia, hyalinization, and scarring. Particulate silicone debris induced a pathologic response in the tissues and migrated to nodes. These findings suggest that periodic evaluation be performed over the life of such implants to rule out breakdown under function. These findings should intensify the search for improvements or replacements for silicone rubber as an interpositional material in the temporomandibular joint.
Analysis of in vitro enzymatic and oxidative degradation of polyurethanes
Authors: Ratner B. D. , Gladhill K. W. , Horbett T. A.
Published: December 2004

In vitro biodegradation studies were performed to assess the long‐term stability of poly(ether urethane) (PEU) implants. Three PEU's and one poly(ester urethane) were treated with enzymes characteristic of those released from inflammatory cells during the foreign body reaction. In addition, the effect of hydrogen peroxide was observed to examine oxidative degradation. Polymers were prepared as thin films on glass, gold, silver, and copper substrates to test the possibility of metal‐catalyzed degradation. Molecular weights and polydispersities of the polymers were measured by gel permeation chromatography (GPC) before and after treatment. Changes in peak shape and location were also monitored. The results demonstrate that varying degrees of both enzymatic and oxidative degradation occurred.
Crystallographic structure and surface morphology of sintered carbonated apatites
Authors: Ellies L. G. , Nelson D. G. A. , Featherstone J. D. B.
Published: December 2004

Densely sintered synthetic hydroxyapatite (HA) is used as an implant material because of its excellent tissue biocompatibility. In order to maximize the biological potential of this calcium phosphate, we have investigated the incorporation of carbonate into HA to make a material which more closely resembles the mineral found in bones and teeth. The aim of the present study was to determine the conditions under which sintered carbonated apatites of specific carbonate content could be produced. The apatites were prepared by heating compressed pellets of precipitated carbonated apatite under a carbon dioxide/steam or nitrogen/steam atmosphere between 825 and 1050°C. The products were analyzed chemically and the surfaces examined by x‐ray diffraction, infrared spectroscopy, reflected light microscopy, and scanning electron microscopy. The results showed that carbonate loss during sintering could be reliably predicted, making it possible to produce materials with specific carbonate content, and with specific physical and chemical composition.
Stability of performances of vascular prostheses retrospective study of 22 cases of human implanted prostheses
Authors: Vinard Elisabeth , Eloy Rosy , Descotes Jacques , Brudon Jean Robert , Guidicelli Henri , Magne Jean Luc , Patra Philippe , Berruet Régis , Huc Alain , Chauchard Jacques
Published: December 2004

Twenty‐two cases of vascular graft failures (thrombosis, pseudoaneurysm, dilation, infection) were investigated by means of physicochemical, histological, and ultrastructural studies. A general decrease of mechanical resistance to stress of the prostheses was observed. Its magnitude ranged from 2 to 75% of the values of identical virgin prostheses and there was no relation with the duration of implantation. In addition to the breakage of yarn filaments (SEM), migration of fiber debris (histology) was observed in 7 cases. The structure of the polyester molecule had evolved after implantation. A decrease of crystallinity (x‐ray diffraction and differential scanning calorimetry) was noted. These observations raise the question of the established stability of vascular prostheses and emphasize the need for further investigations in human graft retrieval programs.
Corrosion behavior of nickel‐containing alloys in artificial sweat
Authors: Randin Jean‐Paul
Published: December 2004

The corrosion resistance of various nickel‐containing alloys was measured in artificial sweat (perspiration) using the Tafel extrapolation method. It was found that Ni, CuNi 25 (coin alloy), NiAl (colored intermetallic compounds), WC + Ni (hard metal), white gold (jewelry alloy), FN42 and Nilo Alby K (controlled expansion alloys), and NiP (electroless nickel coating) are in an active state and dissolve readily in oxygenated artificial sweat. By contrast, austenitic stainless steels, TiC + Mo2C + Ni (hard metal), NiTi (shape‐memory alloy), Hastelloy χ (superalloy), Phydur (precipitation hardening alloy), PdNi and SnNi (nickel‐containing coatings) are in a passive state but may pit under certain conditions. Cobalt, Cr, Ti, and some of their alloys were also investigated for the purpose of comparison. Cobalt and its alloys have poor corrosion resistance except for Stellite 20. Chromium and high‐chromium ferritic stainless steels have a high pitting potential but the latter are susceptible to crevice corrosion. Ti has a pitting potential >3 V. Comparison between the in vitro measurements of the corrosion rate of nickel‐based alloys and the clincial observation of the occurrence of contact dermatitis is discussed.
Permeability of a heparin–polyvinyl alcohol hydrogel to thrombin and antithrombin III
Authors: Smith Barbara A. H. , Sefton Michael V.
Published: December 2004

The diffusivities of thrombin and antithrombin III in a heparin–polyvinyl alcohol hydrogel were estimated and used to demonstrate that diffusion limits the effectiveness of the immobilized heparin in the interior of such hydrogels. Diffusivities were calculated from permeabilities and partition coefficients measured with films in a diffusion chamber apparatus. The diffusion coefficients were estimated to be 6 ± 4 × 10−8 cm2/s for thrombin and 4 ± 2 × 10−8 cm2/s for antithormbin III in 10% gel membranes with or without immobilized heparin. Using the diffusivity of thrombin and a Thiele‐type modulus, the effectiveness factor of a spherical heparin–PVA bead used to accelerate the inactivation of thrombin by antithrombin III was found to be 4–9% (diameter range 250–105 μm). While indicating that diffusion of thrombin limited the full utilization of the immobilized heparin, these values for the effectiveness factor could not completely account for the low apparent heparin activity (0.2%) in a thrombin time test of heparin–PVA “beads” (J. Biomed. Mater. Res., 17, 359 (1983)). Other factors such as the immobilization chemistry or the diffusion of thrombin–antithrombin III complex must be considered for a full explanation of the thrombin time results.
Multilayered bead ceramic composite coating for hip prostheses: Experimental studies and preliminary clinical results
Authors: Pizzoferrato A. , Toni A. , Sudanese A. , Ciapetti G. , Tinti A. , Venturini A.
Published: December 2004

The clinical use of a new ceramic composite material made up of multilayered alumina beads and adhered to a ceramic surface with a high‐temperature‐melting bioglass is proposed. The result is a structure characterised by a 27% porosity and an average pore diameter of 400 μm. The actual structure of the parts as well as their interface interaction were determined by Raman laser. The mechanical resistance of the adherence of this coating for the ceramic substratum was good enough to resist the stress to which it was submitted when used for a new model of prosthetic acetabulum. Experiments with rabbits revealed the good biocomatibility of the composite. The osteoproductive activity of the tissue surrounding the implant led to the gradual filling of the porosity with trabecular structures. The preliminary results of the clinical experience which began in November 1985, confirm the good compatibility of the ceramic composite.
Ceramic systems for long‐term delivery of chemicals and biologicals
Authors: Bajpai P. K. , Benghuzzi H. A.
Published: December 2004

Evaluation of devices, drugs, and drug delivery systems have been investigated by both in vitro and in vivo procedures. Ceramic drug delivery systems can be used to evaluate chemicals and biologicals by both in vitro and in vivo procedures. The system can also reduce handling of the animals and facilitate long‐term evaluations before conducting clinical trials. To date, ceramic systems have been used to deliver aldosterone, androstanedione, beta‐lactoglobulin, bovine serum albumin, chymotrypsin, danazol, difluoromeythylornithine, dihydrotestosterone, estradiol, gamma globulin, gonadotrophic releasing hormone, gossypol, growth hormone, insulin, methylene blue, pepsin, progesterone, and testosterone. The data obtained suggest that ceramic delivery systems can be used in the near future to treat diseases requiring long‐term chronic drug therapy as well as disorders caused by deficiency of certain hormones.
Mechanical properties and short‐term in vivo evaluation of yttrium‐oxide‐partially‐stabilized zirconia
Authors: Christel P. , Meunier A. , Heller M. , Torre J. P. , Peille C. N.
Published: December 2004

Yttrium‐oxide‐partially‐stabilized zirconia (YPSZ) belongs to a new class of ceramics exhibiting an improved toughness when compared to alumina. The toughening mechanism is related to a martensitic‐like transformation of tetragonal metastable grains into a monoclinic state occurring at the crack tip. Specific tests showed that YPSZ exhibited a high bending strength (900–1200 MPa), a low Young's modulus (200 GPa), and a high toughness (KIC = 9–10 MN/m3/2). Its average grain size of 0.5 m̈m allows a surface roughness as low as 0.008 m̈m. Sterilization or aging in saline solution at room temperature for 100 days did not affect the toughness of this material. Cylindrical YPSZ samples, manufactured by cold isostatic pressing and sintering, were implanted in the paraspinal muscles in the rat up to 12 weeks. The tissue reaction was evaluated with reference to alumina (ISO requirements) by means of quantitative histomorphometry. No significant differences were found between YPSZ and alumina for both the membrane thickness and cell distributions surrounding the implants.
Elastic and ultimate properties of acrylic bone cement reinforced with ultra‐high‐molecular‐weight polyethylene fibers
Authors: Pourdeyhimi B. , Wagner H. D.
Published: December 2004

A study of the fracture behavior of poly‐(methyl methacrylate) (PMMA) bone cement reinforced with short ultra‐high‐molecular‐weight polyethylene (Spectra 900) fibers is presented. Linear elastic and nonlinear elastic fracture mechanics results indicate that a significant reinforcing effect is obtained at fiber contents as low as 1% by weight, but beyond that concentration a plateau value is reached and the fracture toughness becomes insensitive to fiber content. The flexural strength and modulus are apparently not improved by the incorporation of polyethylene fibers in the acrylic cement, probably because of the presence of voids, the poor mixing practice and the weakness of the fiber/ matrix interfacial bond. The present polyethylene/PMMA composite presents several advantages as compared to other composite cements, but overall the mechanical performance of this system resembles that of Kevlar 29/PMMA cement, with a few differences. Scanning electron microscopy reveals characteristic micromechanisms of energy absorption in Spectra 900/PMMA bone cement. A scheme for the strength of random fiber‐reinforced composites, which is a simple extension of the Kelly and Tyson model for the strength of unidirectional composites, is presented and discussed. Young's modulus and the fracture toughness results are discussed in the framework of existing theories. More fundamental modeling treatments are needed in terms of fracture micromechanisms to understand and optimize the various mechanical properties with respect to structural parameters and cement preparation technique.
Tissue biocompatibility of cellulose and its derivatives
Authors: Miyamoto Takeaki , Takahashi Shin‐ichi , Ito Hiraku , Inagaki Hiroshi , Noishiki Yasuhara
Published: December 2004

Tissue biocompatibility of cellulose and its derivatives was examined in two in vivo tests, one for absorbance by living tissue and one for foreign body reaction. The samples examined were regenerated celluloses and cellulose derivatives: methylcellulose, ethyl cellulose, aminoethyl cellulose, hydroxyethyl cellulose, and cellulosic polyion complexes. The in vivo absorbance by living tissue was found to depend on the degree of crystallinity and the chemical structure of the sample. The foreign body reaction was relatively mild for all the samples examined, showing that cellulose can be converted to biocompatible materials by physical and/or chemical transformation.
Enhancement of the kinetics of the aeration of ethylene oxide sterilized polymers using microwave radiation
Authors: Matthews I. P. , Gibson C. , Samuel A. H.
Published: December 2004

Ethylene oxide (EO) is used extensively to sterilize medical supplies that are heat sensitive. EO residues in materials post sterilization can present a hazard to patients at the point of use. Protracted aeration (i. e. degassing) times are necessary post sterilization to reduce EO residues to an accepted level. The sorption of EO into polyvinylchloride was found to be an active process given that at sorption equilibrium (i. e. when the net flow of diffusant into the host material has reduced to zero) the number of molecules of EO per unit volume was greater in PVC than in its external environment. The diffusion coefficient (D) was concentration (C) dependent and the relationship which best describes this dependence was D(c) ∝︁ In C. The diffusion of EO was dramatically accelerated (as evidenced by a time saving in degassing of up to 400%) if microwave heating (2.45 GHz) was used instead of conventional heating for the same macroscopic temperature. The values of activation energy for diffusion were obtained from the respective Arrhenius plots of diffusion coefficient versus inverse temperature for each process. In general, even small reductions in activation energy can greatly increase the specific rate of reaction. The relative efficacy of microwaves in eliminating EO residues as evidenced by this data occurs as a result of microwaves reducing the activation energy for diffusion by almost a factor of two. The relative efficiency of microwave desorption compared to conventional aeration offers considerable gains in the cost‐effectiveness of gas sterilization since it will permit a much greater throughput of material, thereby obviating the need for excessively large inventories of equipment.
Oligomers with pendant isocyanate groups as tissue adhesives. I. Synthesis and characterization
Authors: Brauer G. M. , Lee C. H.
Published: December 2004

A series of methacrylate oligomers containing pendant isocyanate groups were synthesized by reacting 2‐isocyanatoethyl methacrylate (IEM) and/or m‐isopropenyl‐ α, α‐dimethylbenzyl isocyanate (TMI) in ethoxyethyl acetate with methacrylates ranging from methyl to stearyl methacrylate or allyl‐, cyclohexyl‐, glycidyl‐, i‐bornyl‐, or dicyclopentenyloxyethyl methacrylate. The oligomers which are stable at room temperature were characterized by IR for NCO, ester, and C  C groups and by their refractive indices. They have a small number of residual double bonds and a molecular weight low enough so that the compounds are liquids at room temperature and dissolve readily in esters and chlorinated hydrocarbons. HPLC showed no residual monomer. GPC and intrinsic viscosity of selected oligomers indicated a molecular weight range from 1400 to 2600. Isocyanate groups were determined titrimetrically and ranged from 15.9% to 5.1%. Concurrent studies have demonstrated that these oligomers bond strongly to hard and soft tissues. Thus, subject to their biocompatibility they could find many applications as tissue adhesives.
Properties and biological inteactions of polyurethane anionomers: Effect of sulfonate incorporation
Authors: Grasel Timothy G. , Cooper Stuart L.
Published: December 2004

In order to investigate the factors affecting the interaction of polyurethanes and blood, a series of poly (tetramethylene oxide)‐based polyurethane block copolymers was synthesized with systematically varying levels of ion incorporation in the hard segment block. A bimolecular nucleophilic substitution reaction was used to replace up to 20% of the urethane hydrogens with propyl sulfonate groups. Bulk and surface characterization was performed, and a canine ex vivo arteriovenous shunt was used to monitor initial platelet and fibrinogen deposition on these surfaces. The microphase separation and bulk physical properties were found to vary with ionic content. Surface analysis using both in vacuo (ESCA) and water‐equilibrated (contact angle) methods indicated that these polymers, and especially the highly sulfonated materials, could rearrange to minimize their interfacial tension, depending on the contacting environment. Platelet deposition onto these materials decreased as the level of sulfonation increased, with the highly sulfonated polymer showing substantially less platelet spreading and activation than previously seen in the same experiment with other polymers.
Protein‐resistant surfaces prepared by PEO‐containing block copolymer surfactants
Authors: Lee Jin Ho , Kopecek Jindrich , Andrade Joseph D.
Published: December 2004

Polyethylene oxide(PEO)‐containing non‐ionic polymeric surfactants were studied as a possible means to produce PEO‐rich surfaces by a simple coating treatment of a common hydrophobic medical material—polyethylene. Surface tension and adsorption properties of PEO/polypropylene oxide(PPO) and PEO/polybutylene oxide(PBO) block copolymer surfactants on a hydrophobic surface (low density polyethylene, LDPE) were investigated, using the Wilhelmy plate surface tension technique and x‐ray photoelectron spectroscopy(XPS). The protein resistance of the surfactant‐treated surfaces was evaluated by XPS and 125I‐labeled proteins. The data presented indicate that adsorption of the surfactants on LDPE is dependent on the molecular geometry of the surfactants. Adsorption of human albumin was significantly decreased on the surfactant‐treated LDPE surfaces, as compared with the untreated surface. Surfactants suitable for the preparation of PEO‐rich surfaces and possible mechanisms for their protein resistance are discussed.
The role of physical and chemical characteristics in assessing the performance of a new biological vascular graft
Authors: Roberts G. , McCormack H. , Ketharanathan V. , Macleish D. G. , Field P. L. , Milne P. Y.
Published: December 2004

Information obtained from physical and chemical characterization of vascular grafts can prove valuable in obtaining a preliminary assessment of potential in vivo performance. The data presented illustrate the concept and show that the new biological graft made from bovine ureters has adequate performance characteristics for use as a potentially successful vascular graft.
The bovine pericardial xenograft: II. Effect of tethering or pressurization during fixation on the tensile viscoelastic properties of bovine pericardium
Authors: Lee J. Michael , Corrente Ralph , Haberer Sean A.
Published: December 2004

Our previous article suggested that control of the extensibility of aldehyde‐fixed pericardium could be achieved by controlling shrinkage during fixation. Therefore, to prevent shrinkage, we have used sandpaper‐lined plexiglass plates to clamp circular samples of bovine pericardium during fixation in glutaraldehyde, tethering them at their original dimensions. As well, we have applied transmural pressures of 50 or 100 mm Hg during fixation using a hydraulic column of glutaraldehyde solution. Strips cut at 0°, 30°, 60° and 90° to the base‐to‐apex cardiac direction have been examined for cyclic stress–strain response, stress relaxation, plastic deformation, and fracture behavior. Under physiological stresses, tethered and pressure‐fixed materials were both nearly isotropic. Tethering during fixation produced a material with extensibility nearly identical to that of fresh tissue. Plastic deformation during cyclic loading was reduced below that seen in simple fixation while stress relaxation was unchanged. Pressure‐fixation produced reduced extensibility similar to that produced in porcine aortic valve leaflets. Plastic deformation and stress relaxation were both markedly reduced. Pressure‐fixation reduced the strain at fracture, but fracture behavior was otherwise unaffected. Tethering and pressure‐fixation offer attractive means to control the mechanical behavior of bovine xenograft materials.
Antithrombogenic surfaces: Characterization and bioactivity of surface immobilized PGE1‐heparin conjugate
Authors: Jacobs Harvey A. , Okano Teruo , Kim Sung Wan
Published: December 2004

A covalently bonded conjugate of commercial grade heparin and prostaglandin E1 (PGE1) was synthesized to prevent both fibrin formation and platelet aggregation during thrombus formation. The PGE1‐heparin conjugate was immobilized on an imidazole carbamate derivatized sepharose bead surface through hydrophilic spacer groups (diamino‐terminated polyethylene oxides). One end of the spacer group was coupled to the derivatized surface through a urethane bond between the amine group of the spacer and the derivatized surface. The free amine group of the immobilized spacers was coupled to a carboxylic group of the PGE1‐heparin conjugate through an amide bond. Bioactivity of the immobilized conjugate (heparin activity) was measured in terms of increased clotting times (thrombin time assay) and for the inactivation of Factor Xa. Bioactivity of the immobilized compound (PGE1 activity) was analyzed by platelet adhesion and platelet release reactions using C14‐5‐hydroxytryptamine (5‐HT). The conjugate immobilized via the C2 spacer showed the highest incidence of platelet adhesion, 5‐HT released and the lowest activity for coagulation factors. In contrast, the 1000 and 4000 immobilized systems showed a significant reduction in platelet activation, while having the greatest effect on coagulation factors. The results of these experiments imply that the immobilized conjugate is active in preventing both pathways of thrombus formation, and the efficacy is improved thorugh the use of long‐chain hydrophilic spacer groups.
Bone bonding behavior of MgOCaOSiO2P2O5CaF2 glass (mother glass of A · W‐glass‐ceramics)
Authors: Kitsugi Toshiaki , Yamamuro Takao , Nakamura Takashi , Kokubo Tadashi
Published: December 2004

In this study, it was found that a CaP layer and a Si layer were formed on the interface of the mother glass of apatite–wollastonite containing glass‐ceramics (designated AW) and bone tissue. The dissolution of Si, Ca, and P from glass (MgOCaOSiO2P2O5CaF2) is necessary to form a chemical film (a Si layer and a CaP layer). The three kinds of glasses used were (1) a mirror surface of the mother glass (MgO 4.6, CaO 44.9, SiO2 34.2, P2O5 16.3, CaF 0.5 weight ratio) of AW (designated GAW (mirror)), (2) an abraded surface of GAW (designated GAW (#2000)), (3) a mirror surface SiO2 glass (designated GSi, 100%SiO2). The glass plates (15 mm × 10 mm × 2 mm) were implanted into the metaphysis of tibia of mature male rabbits for 10 and 25 weeks. The failure load, when an implant detached from the bone or when the bone itself broke, was measured by a detaching test and the interface of glass/bone was observed by SEM‐EPMA. Failure loads in GSi, GAW (mirror), and GAW (#2000) 10 weeks after implantation were 0.18 ± 0.24, 3.06 ± 1.29, and 2.94 ± 1.77 kg, respectively. Those in GSi, GAW (mirror), and GAW (#2000) 25 weeks after implantation were 1.30 ± 1.18, 3.88 ± 1.06, and 3.55 ± 1.51, respectively. The failure loads in GSi vs. GAW (mirror) and those in GSi vs. GAW (#2000) differed significantly (P < 0.01). There were no significant differences in the failure load according to the surface roughness of GAW. As shown by SEM‐EPMA observation, a Si layer next to G was adjacent to a CaP layer next to the bone. The chemical film showed no increase in thickness as time passed. A CaP layer did not form on the interface of SiG and bone.
Collagen organization in mandrel‐grown vascular grafts
Authors: Ramshaw John A. M. , Peters David E. , Werkmeister Jerome A. , Ketharanathan V.
Published: December 2004

The organization of collagen in custombuilt biosynthetic vascular prostheses (Omniflow Vascular Graft), which are suitable for periphareral revascularization, has been examined. The grafts were a glutaraldehyde‐tanned ovine‐collagen composite with a polymer mesh reinforcement. Comparisons were made between grafts using different mesh fiber polymers and knit patterns. There was a basic similarity in the arrangement of the tissue structure in all graft types. Scanning electron microscopy and light microscopy showed that the collagen formed a layered structure which fully encased the polymer mesh and held it firmly in position. Rather than polymer mesh, the inner surface of the graft was found to be collagen, and lined with a layer of flattened cells. Collagen formed a continuous layer surrounding the mesh, with no distinct boundary membrane or structurally weak point being apparent. Immunohistology, using a monoclonal antibody specific for type III collagen, and chemical analysis, indicated that there was a high proportion of type III collagen in the grafts, particularly in the region surrounding the mesh fibers.
Creep studies of multiphase acrylic systems
Authors: Øysæd Harry , Ruyter Ivar Eystein
Published: December 2004

The influence of type and quantity of five different crosslinking agents on tensile creep properties of multiphase acrylic systems has been studied. The polymeric materials, commonly applied in bioengineering, were processed by polymerization of a mixture of liquid methacrylate monomers and poly(methyl methacrylate) powder. The specimens were made with various ratios of methyl methacrylate and crosslinking agents in the monomer liquid. Two different processing conditions were used, i.e., heat‐polymerization at 100°C and autopolymerization at 45°C. Creep behavior was determined at 37 ± 0.2°C and 50 ± 0.5°C. The investigation showed higher creep values for autopolymerized than for heat‐polymerized materials. In heat‐polymerized materials the creep curves showed little variation with type and quantity of crosslinking agents at low stress levels. However, at high stress levels the creep values decreased with increasing quantity of crosslinking agents. The autopolymerized materials showed a more inhomogeneous structure, and great variation in creep. Both among the heat‐polymerized and autopolymerized materials, the systems with diethyleneglycol dimethacrylate clearly deviated from the others by showing higher creep values.
Interfacial analysis of fiber‐reinforced bioactive glass dental root implants
Authors: Schepers E. , Ducheyne P. , De Clercq M.
Published: December 2004

Bioactive glass can form an effective bond with bone. Essential for this connection are the interfacial reactions which lead to the development of a Si‐rich film covered by a CaP‐rich film. The presence of these layers can be demonstrated clearly by EDX analysis of fiber‐reinforced bioactive glass and bulk bioactive glass implants installed for 4 and 16 months in the partial edentulous jaws of beagle dogs. EDX analysis reveals three types of microchemical interface. The first type develops when the implant is bonded to bone. Here, a smooth transition of the CaP profile can be observed between bioactive glass and the bone, thus providing for a compositional gradient between the implant and the surrounding tissues. The second type is seen when the implant surface is surrounded by fibrous tissue. This causes a discontinuity in the CaP profile. The third type is characterized by a gradual decrease in the Ca and P concentrations across the interface, caused by the presence of Ca and P in the fibrous tissue near the implant surface. This suggests that the interface is dynamic in time and transforms to a functionally better optimized interface. EDX analysis does not reveal any metal fiber ion contamination of the outer glass rim of the implant. When stainless‐steel or wrought Co‐Cr alloy is exposed to the surrounding fluids, the interfacial osteogenesis is disturbed, possibly by a synergistic effect of glass ions and metal ions. Exposure of titanium does not interfere with this osteogenesis. The bone bonding can also be influenced by surgical trauma. However, with precise implantation techniques, an enhancement of bone growth by osteoconductivity can be measured.
Comparison of coral resorption and bone apposition with two natural corals of different porosities
Authors: Guillemin G. , Meunier A. , Dallant P. , Christel P. , Pouliquen J‐C. , Sedel L.
Published: December 2004

Previous studies showed that natural coral implanted into bone tissue was gradually resorbed and progressively replaced by newly formed bone. The objectives of this study were to compare the fate of two Madreporian corals, Porites and Acropora, after implantation during 1 and 2 months into sheep and pig long bones. These materials are identical in composition (CaCo3) but differ in volume (49 ± 2%, 12 ± 4%, respectively) and mean size (250 vs. 500 μm) of porosities. The non‐decalcified histological slices were observed under light microscopy. Implant resorption and new bone formation were quantified through an automatic image analysis system. Quantitative results showed that the larger the porosity volume, the greater was the coral resorption as well as the new bone apposition. Large differences were found between the two animal species. Histological findings were identical to those previously reported: implants were resorbed and progressively replaced by newly formed bone. Coral was found to be an osteoconductive biomaterial which acted as a scaffold for a direct osteoblastic apposition and consequently could be an interesting alternative to bone auto‐, allo‐, or xenografts.
The effect of gamma irradiation on injectable human amnion collagen
Authors: Liu Bingci , Harrell Randall , Davis Robert H. , Dresden Marc H. , Spira Melvin
Published: December 2004

The effect of gamma irradiation on the physicochemical properties of injectable human amninon collagen was investigated. Pepsin‐extracted human amnion collagen was purified, reconstituted, and irradiated with varying doses of gamma irradiation (0.25 Mrads to 2.5 Mrads). Gamma irradiation had a significant impact on the physical characteristics of the collagen. The neutral solubility of collagen in PBS at 45°C was decreased from 100% for the nonirradiated control sample to 16% for the 2.5 Mrads irradiated sample. SDS polyacrylamide gel electrophoresis also demonstrated the dose‐dependent effect of gamma irradiation on collagen crosslinks. Electron microscopic observation revealed that even at low irradiation dose (0.25 Mrads), collagen fibril diameter increased. The average diameter was 50 nm for nonirradiated control fibrils, while 4.4% percent of the irradiated collagen fibrils had a diameter greater than 100 nm. Irradiated collagen showed little evidence of damage. Well‐preserved cross‐strations were found in collagen fibrils at all doses of irradiation. Native amnion collagen irradiated with gamma rays demonstrated a slight increase in resistance to collagenase degradation compared with nonirradiated native collagen samples. Increased resistance to collagenase did not correlate with increasing irradiation dose. After 30 min of incubation at 37°C, both irradiated and non‐irradiated collagen was completely digested by collagenase. However, gamma‐irradiated collagen did become more sensitive to hydrolysis by trypsin. The higher the irradiation doses used, the greater sensitivity to trypsin was observed. At 0.25 Mrads irrdiation only a slight increase was found. No marked differences in amino acid composition were noted among the high dose irradiated, low dose irradiated and control amnion collagen.
Heparinizable segmented polyurethanes containing poly‐amidoamine blocks
Authors: Tanzi M. C. , Levi M.
Published: December 2004

A poly‐ether‐urea‐urethane was synthesized by copolymerization of 4,4′‐diphenylmethanediisocyanate (MDI), propanediamine, and poly‐oxytetra‐methylene glycol (M.W. 1000). Two other corresponding copolymers were also synthesized by adding amino terminated poly‐amidoamine macromonomers, purposely synthesized, so as to insert relatively small amounts (6 and 15 weight %) of two types of poly‐amidoamine segments in the final product. Of the three copolymers several physicochemical and mechanical properties have been determined, and their heparin adsorption ability, blood compatibility, and cytotoxicity evaluated.
Transformation of biphasic calcium phosphate ceramicsin vivo: Ultrastructural and physicochemical characterization
Authors: Daculsi G. , Legeros R. Z. , Nery E. , Lynch K. , Kerebel B.
Published: December 2004

Specially prepared biphasic calcium phosphate (BCP) macroporous ceramics consisting of an intimate association of beta tricalcium phosphate (b̃‐TCP) and hydroxyapatite (HA) with b̃‐TCP/HA weight ratios of 15/85, 35/65, and 85/15 were implanted in surgically created periodontal osseous defects in dogs and recovered after 6 months. A decrease in average size of crystals in BCP ceramics and an increase in the size of microporosities in the surface and at the core of the ceramic after implantation were observed, indicating thatin vivodissolution has taken place. The resorbability (reflectingin vivodissolution) of BCP ceramics depended on their b̃‐TCP/HA ratios, the higher the ratio, the greater the resorbability. The formation of microcrystals with crystallographic properties and Ca/P ratio similar to those of bone apatite crystals were also observed. The abundance of these crystals were directly related to the b̃‐TCP/HA ratio of the BCP ceramic before implantation. The formation of the bone apatite‐like crystals may be due to the precipitation of calcium and phosphate ions released from the dissolving ceramic crystals (the b̃‐TCP component dissolving preferentially to the HA component). Results from this study suggested that one of the means of controlling resorbability (in vivodissolution) of BCP ceramic is by varying its b̃‐TCP/HA ratio.
Foreign body reaction against cellophane in the athymic nude mice
Authors: Smetana K. , Holub M. , Slavčev A.
Published: December 2004

There are no differences in the multinucleate cell formation in normal and athymic mice after the subcutaneous implantation of a cellophane strip. The number of Ia+ epitheloid cells and multinucleate foreign body giant cells was lower and the number of epitheloid cells sharing the marker of activated macrophages (M 57) was higher in athymic compared to normal mice. The epitheloid cells of athymic and euthymic animals exhibited no difference in the expression of Mac‐2 molecule. The difference of the expression of surface markers between athymic and euthymic animals does not influence the foreign body giant cell formation.
Bioabsorption of polylactides with different molecular properties
Authors: Nakamura T. , Hitomi S. , Watanabe S. , Shimizu Y. , Jamshidi K. , Hyon S.‐H. , Ikada Y.
Published: December 2004

In order to study the effects of factors governing the bioabsorption rate of polylactides, implantation tests were carried out in rabbits using various samples (20 × 10 × 2 mm3) differing in their chemical composition, residual monomer content, and molecular orientation. Copolymer samples with a higher lactic acid content showed a lower rate of absorption, whereas those with a higher unreacted monomer content were absorbed faster and showed a more drastic decrease in molecular weight. In contrast, degradation of the purified polymers was slow; the purified poly‐L‐lactide showed no weight change and a 50% reduction in molecular weight after 6 months of implantation. Scanning electron microscopy of the samples containing monomers showed a microporous structure extending from the surface to the inner region a few days after implantation, whereas the purified poly‐L‐lactide did not exhibit a microporous structural change even after 10 months of implantation.
Mechanical properties of BIS‐GMA resin short glass fiber composites
Authors: Krause William R. , Park Sang‐Hyun , Straup Robert A.
Published: December 2004

The use of short glass fibers as a filler for dental restorations or cement resins have not been examined extensively. The mechanical properties and untreated glass fibers (5 μm dia × 25 μm) in Bis‐phenol A glycidyl methacrylate (BIS‐GMA) diluted with triethylene‐glycol dimethacrylate (TEGDMA) resin were investigated for possible use as a restorative dental composite or bone cement. Compression, uniaxial tension and fracture toughness tests were conducted for each filler composite mixtures of 40, 50, 60 and 70%. Set time and maximum temperature of polymerization were determined. The results show that the elastic modulus, tensile strength and compressive strength are dependent on the percent of filler content. Elastic modulus and compressive yield (0.2%) strength of silane treated glass fibers filled composite increased from 2.26 to 4.59 GPa and 43.3 to 66.6 MPa, respectively, with increasing the filler content while the tensile strength decreased from 26.7 to 18.6 MPa. The elastic modulus of the untreated composite was less than that of the silane treated fiber composite. The tensile strength and compressive strengths were 20 to 50% lower than those of silane treated composites. The fracture toughness of the silane treated glass fiber additions were not significantly different from the untreated additions. The highest fracture toughness was obtained at 50% filler content with 1.65 MPa m.5. Set time increased from 3.5 to 7.7 minutes with increased filler content and peak temperature dropped from 68.3 to 34°C. The results of this study indicate that the addition of silane coated glass fiber to BIS‐GMA resin increased the elastic modulus, tensile and compressive strengths compared with non‐treated fibers. The addition of either treated or non‐treated fibers increased the set time of the material and decreased the maximum temperature.
In vivo and in vitro degradation of glycine/DL‐lactic acid copolymers
Authors: Schakenraad J. M. , Nieuwenhuis P. , Molenaar I. , Helder J. , Dijkstra P. J. , Feijen J.
Published: December 2004

A series of copolymers of glycine and DL‐lactic acid with various compositions was synthesized and their in vivo and in vitro degradation behavior was studied. For the in vivo examination, discs of the copolymer films were subcutaneously implanted in rats. The in vitro studies were carried out in phosphate buffer at pH = 7.4 and 37°C. The decrease in molecular weight, the loss of weight, and the tissue reactions of the different copolymers were determined after 2, 5, and 10 weeks. Poly(DL‐lactic acid) was used as reference material. The in vivo and in vitro degradation behavior of the polymers was comparable. The decrease of molecular weight of the copolymers and poly(DL‐lactic acid) in time was similar. The weight loss for copolymers with a higher mole fraction of glycine units started earlier. The copolymer with the highest content of glycine units disappeared completely within 10 weeks both in vivo and in vitro. The poly(DL‐lactic acid) implant lost only 25% weight over the same period. Tissue reactions against all materials started with an acute inflammatory reaction caused by the trauma of implantation, followed by wound‐healing processes, ending in a very mild foreign body reaction for the poly(DL‐lactic acid) and a more excessive macrophage mediated foreign body reaction for the glycine/DL‐lactic acid copolymers. The tissue reaction was more severe for polymers having a higher rate of degradation.