bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimization of photopolymerized bioerodible hydrogel properties for adhesion prevention
Authors: Sawhney Amarpreet S. , Pathak Chandrashekhar P. , van Rensburg Jillian J. , Dunn Randall C. , Hubbell Jeffrey A.
Published: May 2005

The aim of this study was to optimize the properties of a lubricious bioerodible hydrogel barrier for the prevention of postoperative adhesions. Water‐soluble macromers based on block copolymers of poly(ethylene glycol) (PEG) and poly(lactic acid) or poly(glycolic acid) with terminal acrylate groups were used, and these macromers were gelled in vivo by exposure to long wavelength ultraviolet light. The precursor was photopolymerized from buffered saline solution while in contact with the tissues. This resulted in the conformal coating of the tissue with an adherent hydrogel film, while forming a nonadhesive barrier at the free surface, on the treated wound site. The hydrogels were evaluated in two animal models of postsurgical adhesions, first in a rat cecum abrasion model and then in a rabbit utreine hornischemia model. In the rat cecum model, six of seven animals treated with a hydrogel, with glycolide in the precursor as the comonomer, showed no adhesions; untreated animals and animals treated with precursor, but not gelled with light, showed consistent dense adhesions. In the rabbit uterine horn ischemia model, using hydrogels with lactide in the precursor as the comonomer, and PEG of molecular weight from 6,000 to 18,500 Da, adhesions were dramatically reduced, with occurrence in none of seven animals treated with a gel containing PEG 10,000. By contrast, the seven animals in the control group demonstrated a mean of 35% involvement of the horn length in dense, fibrous adhesions. These materials, photopolymerized in vivo in direct contact with the tissues, appear to form an adherent hydrogel barrier that is highly effective in reducing postoperative adhesions in the models used. An optimum exists in the molecular weight of the PEG and in the composition of the degradable link for most effective performance. © 1994 John Wiley & Sons, Inc.
The effects of ultrasound irradiation on a biodegradable 50–50% copolymer of polylactic and polyglycolic acids
Authors: Agrawal C. M. , Kennedy M. E. , Micallef D. M.
Published: May 2005

The aim of this study was to investigate the effects of ultrasound irradiation on a biodegradable drug delivery system. Microporous, disk‐shaped specimens of a 50‐50% copolymer of polylactic and polyglycolic acids were gel cast from an acetone solution. A protein was incorporated in these specimens, which were then immersed in phosphate buffered saline and subjected to ultrasound irradiation every second day. The investigation was performed in two phases: in the first, a study was performed for 58 days to determine if ultrasonic irradiation affected the kinetics of protein release from the specimens. In the second phase, effects of frequency and duration of the ultrasound signal on the degradation of the implant were studied for 40 days. The results indicate that ultrasound irradiation resulted in almost a threefold increase in protein elution from the specimens. Both the ultrasound frequency and signal duration affected the molecular weight loss and mass loss, and changed the overall degradation kinetics of the polymer. © 1994 John Wiley & Sons, Inc.
The effect of additive hyaluronic acid on animal joints with experimentally reduced lubricating ability
Authors: Mabuchi Kiyoshi , Tsukamoto Yukio , Obara Takeo , Yamaguchi Toshijiro
Published: May 2005

A series of in vitro experiments demonstrated a clear effect of additive hyaluronic acid (HA) on animal joints with experimentally reduced lubricating ability. Eleven canine hip joints were utilized and the experimental conditions tested were: (i) intact joints, (ii) after washing the joint surfaces, and (iii) after adding 1% HA to them. The frictional coefficient of every joint increased after washing and subsequently decreased after adding HA. The mean values were 0.007 (SD 0.004) on the intact joints, 0.020 (SD 0.009) after washing, and 0.013 (SD 0.005) after the addition of HA. The differences between the three values of frictional coefficients were shown to be statistically significant (p < 0.01). © 1994 John Wiley & Sons, Inc.
Evaluation of a series of tyrosine‐derived polycarbonates as degradable biomaterials
Authors: Ertel Sylvie I. , Kohn Joachim
Published: May 2005

A series of four polycarbonates derived from the ethyl, butyl, hexyl, and octyl esters of desaminotyrosyl‐tyrosine was prepared by condensation polymerization. The resulting polymers had weight average molecular weights ranging from 120,000–450,000, and their chemical structure was confirmed by elemental analysis, nuclear magnetic resonance, and Fourier transform infrared spectroscopy. The polycarbonates were evaluated as degradable biomaterials. Their surface properties were determined by electron spectroscopy for chemical analysis, attenuated total reflectance‐Fourier transformed infrared spectroscopy, and contact angle measurement. The degree of surface hydrophobicity was related to the length of the alkyl ester pendent chain. The tensile properties were dependent on the chemical structure of the polymers: For thin, solvent cast film specimens, the tensile modulus varied from 1.2–1.6 GPa, and the strength at break from 60–220 MPa. The degradation of polymeric films was followed in vitro by measuring changes in mechanical strength for up to 40 weeks, and the decrease in molecular weight and changes in surface chemistry for up to 80 weeks. The length of the pendent chain affected the degradation behavior and strength retention; the polymers with short pendent chains were more readily hydrolyzable. For sterilization, ethylene oxide treatment was less destructive, as judged by molecular weight retention, than γ‐irradiation. Spin‐cast films of all tested polycarbonates were not cytotoxic toward cultured rat lung fibroblasts. The cell response was influenced by the chemical structure of the polymer. The least hydrophobic polycarbonate (having a short ethyl ester pendent chain) was a more stimulating substrate for cell growth than the more hydrophobic polymers (carrying longer alkyl ester pendent chains).
Effect of molecular structure of poly(glycidyl ether) reagents on crosslinking and mechanical properties of bovine pericardial xenograft materials
Authors: Lee J. Michael , Pereira Christopher A. , Kan Lincoln W. K.
Published: May 2005

With the identification of the exacerbating effect of glutaraldehyde on calcification of heart valve materials, there exists a renewed interest in both alternative reagents and the effects of crosslinking on connective tissues. One potentially useful class of reagents are poly(glycidyl ether) compounds. We have examined 5 of these reagents with different molecular sizes and functionalities for their effects on mechanical properties and collagen denaturation (shrinkage) temperature. Samples of bovine pericardium were tested fresh or after 48 h fixation in one of the five compounds for denaturation temperature, stress‐strain response, stress relaxation, plastic deformation, and fracture properties. Of the compounds tested, those with intermediate length backbones and 4 or 5 epoxide groups were most effective in producing intrahelical crosslinking and increased denaturation temperature over 48 h. However, in samples examined after 17 months of fixation, all reagents had equivalently increased the denaturation temperature. Examination of mechanical results revealed two distinct mechanisms for mechanical change. Observed shifting of the stress‐strain curve to the right (due to shrinkage), increased plastic deformation, and some reduction of stress relaxation are all unrelated to denaturation temperature (and hence to changes in intrahelical crosslinking). An alternate mechanism, perhaps formation of intermolecular crosslinks may be responsible. Intrahelical crosslinking produces only lesser reductions in stress relaxation. Cross‐comparison of reagents of differing molecular structure provides a useful tool toward increased understanding of the mechanical consequences of tissue crosslinking. © 1994 John Wiley & Sons, Inc.
In vivo reactions of Ca,P particle containing surface reactive glasses
Authors: Kangasniemi I. M. O. , Vähätalo K. , Happonen R.‐P. , Yli‐Urpo A. , De Groot K.
Published: May 2005

Four Ca,P particle containing surface reactive glass composites and two glasses(in the SiO2‐aO‐P2O5‐Na2O‐Al2O3 system) were implanted in the diaphyseal area of goat femora up to 24 weeks. Scanning electron microscopic, energy dispersive x‐ray, and histological analysis were performed to evaluate the material‐tissue interactions. A new type of integration mechanism was observed. Instead of the bone growing to the material surface, a gel‐like silica formation appeared between the cortex bone and the material surface. In time the gel‐like formation was replaced by a Ca,P layer. The results provided indirect evidence that pure silica gel formed in the tissues could also achieve an apatite layer formation and bone bonding on its surface. © 1994 John Wiley & Sons, Inc.
Feasibility of agarose microbeads with xenogeneic islets as a bioartificial pancreas
Authors: Iwata Hiroo , Kobayashi Kazuo , Takagi Tatsuya , Oka Takayuki , Yang Hua , Amemiya Hiroshi , Tsuji Takayuki , Ito Fumiaki
Published: May 2005

A bioartificial pancreas, that is, transplantation of islets of Langerhans (islets) which are enclosed in a semipermeable membrane, has been proposed as a treatment for type I diabetes. The islets are immuno‐isolated from the host by the semipermeable membrane preventing rejection while maintaining control of glucose metabolism for an extended period. The purpose of the current research is to evaluate the feasibility of preparing agarose microbeads with xenogeneic hamster islets as a bioartificial pancreas in streptozotocin induced diabetic mice. In the recipients with a low level of anti‐hamster antibodies, the combination of encapsulation of hamster islets in 5% agarose microbeads and in vitro culture of them prolonged xenograft survivals. Four of 6 recipients were still normoglycemic at 100 days after implantation. However, the same procedure was not effective in the recipients which were sensitized in advance by transplantation of free hamster islets and thus had high levels of anti‐hamster antibodies. The average normoglycemic period was 32 days. Antibodies permeated through the microbeads and activated complement on the cell surfaces. The network of agarose microbeads was rendered dense by increasing the concentration of agarose to restrict the diffusion of antibodies. Graft survivals were prolonged with increasing concentrations of agarose. As an analysis using diffusion equations predicted, the survivals were inversely proportional to the diffusion coefficient of IgG in each agarose gel. Islet xenotransplantation was enabled by the combination of the microbeads with a concentration of agarose higher than 7.5% and in vitro culture even in recipients having a high level of preformed antibodies. © 1994 John Wiley & Sons, Inc.
Biocompatibility of a new semisolid bioerodible poly(ortho ester) intended for the ocular delivery of 5‐flurouracil
Authors: Bernatchez Stéphanie F. , Merkli Alain , Minh Tri Le , Tabatabay Cyrus , Anderson James M. , Gurny Robert
Published: May 2005

The biocompatibility of a new semisolid, hydrophobic poly‐(ortho ester) (POE) intended for controlled drug delivery to the eye was evaluated. The polymer was injected subconjunctivally in rabbits, and clinical and histologic examinations were performed 3, 10, 15, and 21 days after injection. Polymers injected as controls were an aqueous gel of sodium hyaluronate (SH), 1% in phosphate buffer, and medical grade silicone oil. After injection, the POE emulsified into small droplets and a focal eosinophilic reaction was noted at 3 days' implantation. At 10 days' implantation, the inflammatory reaction had resolved, with fibroblasts being the predominant cell type. At 15 and 21 days, no POE was identified and normal appearing tissue was present in the injection site. Sodium hyaluronate was not inflammatory over the period of the implantations. Silicone oil induced a slight inflammation at 3 days, with the presence of eosinophils and limited necrosis with cellular debris. Silicone oil was present in the implantation site at 3, 10, 15, and 21 days. The inflammatory response to the respective polymers was evaluated in the subconjunctival tissue. The inflammatory reaction was quantified at the implant site, adjacent subconjunctival tissues, and scleral and corneal stroma. The inflammatory cell densities in these respective tissue zones were determined, and the ratio of eosinophils over total inflammatory cells was calculated. POE did not become encapsulated with fibrous tissue, but biodegraded in a short time, indicating its potential for use after glaucoma filtration surgery. © 1994 John Wiley & Sons, Inc.
Tissue reaction to soft‐tissue anchored percutaneous implants in rabbits
Authors: Jansen J. A. , Paquay Y. G. C. J. , van Der Waerden J. P. C. M.
Published: May 2005

This study reports on the soft‐tissue response to titanium fiber mesh percutaneous implants. The implants were inserted in the backs of 15 rabbits. The surgical procedure was performed in two steps: implantation of the subcutaneous part of the implants and, after 3 months, fixation of the percutaneous part into the subcutaneous part. Two and 6 months after insertion the animals were sacrificed and the implants, with their surrounding tissues, were processed histologically. Light microscopic analysis demonstrated that only one implant showed considerable skin retraction in the percutaneous area. Around the rest of the implants no downgrowth or only a very limited epidermal downgrowth was observed. Furthermore, the fiber mesh material showed good biocompatible behavior. These results confirm the previous finding that sintered titanium fiberweb structures are effective for the stabilization of percutaneous devices located in soft tissues and can improve their performance. © 1994 John Wiley & Sons, Inc.
Fate and biocompatibility of three types of microspheres implanted into the brain
Authors: Menei P. , Croué A. , Daniel V. , Pouplard‐Barthelaix A. , Benoit J. P.
Published: May 2005

The implantation of polymer devices in the brain that release neuroactive drugs locally and in a controlled manner is gaining increasing interest. The fates and tissue reactions of poly(∈‐caprolactone), ethylcellulose, and polystyrene microspheres, prepared by the solvent evaporation method, radiosterilized by γ‐irradiation, and stereotactically implanted in rat brain have been studied by routine staining and immunohistochemistry. During the first few days after implantation, a nonspecific astrocytic brain tissue reaction was observed along with a macrophagous‐microglial cell reaction typically found following any damage in the central nervous system, except in the presence of certain foreign body giant cells. Nine months into the experiment, microspheres appeared to be engulfed by histiocytic cells. The microsphere cluster was surrounded by a sheath composed of collagen and astrocytic cells. No necrosis was observed, suggesting the absence of toxicity. In some animals, however, an hydrocephalus developed as a result of obstruction of the medial ventricle by some microspheres. © 1994 John Wiley & Sons, Inc.
Production of spherical ZrO2‐Y2O3 and ZnO particles
Authors: Yaparpalvi R. , Loyalka S. K. , Tompson R. V.
Published: May 2005

In recent years substantial effort has been focused on the use of engineered ceramics for biomedical applications. To produce ceramic components with reliable and reproducible properties for such speciality applications, it is necessary to use high‐purity raw material powders with specific properties. Fine ceramic particles having specific shapes and sizes are also required for conducting biocompatibility experiments. This article reports on the laboratory scale production, in an aerosol reactor, of spherical, submicron zirconia (partially stabilized by yttria; ZrO2‐Y2O3) and zinc oxide (ZnO) particles by the thermal decomposition of mists generated from aqueous solutions of inorganic metal salt precursors. The particles produced were characterized by scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy. © 1994 John Wiley & Sons, Inc.
Photochemical conjugation of mammalian cells to polymeric supports and membranes: A kinetic study
Authors: Bellobono I. R. , D'Ambrosio A. , Raimondi M. L. , Marangoni F. , Sirchia G.
Published: May 2005

A commercial polyester acrylate prepolymer, to which a 2:3 wt/wt ratio of tripropyleneglycol diacrylate was added to increase photopolymerization rate, was employed as photochemical conjugating agent, through photografting. 1,2‐Diphenyl,2,2‐dimethoxyethanone was added as standard photoinitiator (7.0 wt/wt%), together with varying amounts (0.003–4.0 wt/wt%) of some proprietary photocatalytic systems, based on the following photocataiysts: m̈‐peroxobis [N,N′‐ethylene‐bis(salicylideneiminato)cobalt](III) (I), vanadium (V) triethoxide (II), and a synergic mixture of vanadium (V) tri‐t‐butoxide and tri‐i‐propoxide (III). A homogeneous suspension containing (10 ± 2) × 105 human thyroid follicular cells per milliliter of photochemically reacting medium was photografted, at a surface density of 6.5 ± 0.7 mg · cm −2 of diacrylate prepolymer mixture, onto polystyrene plates or onto commercial microfiltration and ultrafiltration membranes consisting of nonwoven cellulose tissues with known porosities varying between 5 and 30 m̈m and in photografted polyester acrylate‐based membranes with a cutoff of 50 ± 5 KD. Bioconjugation yields, as a function of photografting time, were measured gravimetrically and by multiple internal reflection IR spectroscopy. Three series of experiments were performed: (1) measurements of graft yields of the prepolymer, and of the parallel disappearance of double bonds, in the absence of mammalian cells; (2) the same as (1), in the presence of thyroid follicular cells; (3) the same as (2), but with the photoinitiating system formed by the standard photoinitiator alone, with no photocatalyst. Results show that if a suitable photocatalyst is not added, no practical conjugation is possible. An appropriate choice of the photocatalytic system and of its concentration allows reduction of irradiation times (e. g., by a factor of about 2 × 104 calculated as the mean lifetime ratio, between the uncatalyzed system and that with 0.1 wt% of [III]), thus minimizing cell inactivation and/or improving responsiveness to the bioassay. From this point of view, photoactivity of (III) is outstanding. The very small, but clearly perceptible, influence of polymeric support on bioconjugation is also commented upon. © 1994 John Wiley & Sons, Inc.
Strategy for developing microbeads applicable to islet xenotransplantation into a spotaneous diabetic NOD mouse
Authors: Iwata Hiroo , Takagi Tatsuya , Kobayashi Kazuo , Oka Takayuki , Tsuji Takayuki , Ito Fumiaki
Published: May 2005

A bioartificial pancreas (BAP) created through the encapsulation of islets of Langerhans (islets) in a semipermeable membrane has been proposed as a promising approach to treating insulin‐dependent diabetes patients. A nonobese diabetic (NOD) mouse, which shares many features of human insulin‐dependent diabetes mellitus, is an ideal model for evaluating the function of BAP. However, the functions of BAPs that have been developed have been limited in NOD mice. We propose novel microbeads that can realize long‐term BAP function in NOD mice. The novel microbeads were composed of agarose and poly(styrene sulfonic acid) (PSSa) mixed gel. A polyion complex layer between PSSa and polycationic polybrene was formed on and just inside the microbead, and the microbead surfaces were further covered by polyanions to produce anionic surface charges. The islets in the novel microbeads were intraperitoneally implanted. Graft‐functioning periods were dependent on both PSSa concentration and the kinds of polyanion. Islets in the microbeads composed of 5% agarose and 5% PSSa, which had an outermost surface covered by carboxymethyl cellulose, produced normoglycemic periods of more than 60 days in all five recipients. Control mice receiving either transplants of unenclosed islets or islets in agarose microbeads showed normoglycemic periods of less than 12 days. We believe that agarose/PSSa microbeads are promising for producing semipermeable membranes that enable xenotransplantation of islets in spontaneous diabetes mellitus. © 1994 John Wiley & Sons, Inc.
Comparison of tissue factor and prostacyclin production by human umbilical vein endothelial cells on Dacron vascular prostheses and Dacron smooth films
Authors: Tunstall Ann , Eberhart Robert C. , Prager Morton D.
Published: May 2005

The functional capacity of human umbilical vein endothelial cells (HUVEC) grown on Dacron (polyethylene terephthalate; PET) vascular prosthetic material was compared with the function of cells on smooth surfaced PET, tissue culture polystyrene (TCPS), and Natrix‐coated TCPS. Prosthetic materials include two knitted fabrics (Bionit I and II) and two woven preparations (DeBakey Soft Woven and Extra Low Porosity). Two entities produced by HUVEC that influence blood coagulation were assessed: the procoagulant tissue factor (TF) and the anticoagulant prostacyclin (PGI2). Although TF activity was stimulated on all substrates by endotoxin (LPS), there was no difference among prostheses and no difference among smooth surface materials, but TF was reduced in cells on the prosthetic materials relative to those on smooth surface substrates. The reduced TF production by HUVEC on prosthetic material could be reversed by returning them to TCPS. In contrast, PGI2 production on prostheses was comparable to that on smooth surfaces for both stimulated and unstimulated cells. Stimulation with histamine (1 µM) gave a 2.4‐fold increase in PGI2 whereas mellitin (10 µg/ml) increased production 12.5‐fold. The differential response of HUVEC with regard to these two coagulation factors, one of which is secreted and the other membrane bound, may reflect the distorted shape of cells on fibers of the prosthesis. © 1994 John Wiley & Sons, Inc.
Inhibition of Staphylococcus adherence to biomaterials by extracellular slime of S. epidermidis RP12
Authors: Giridhar G. , Kreger A. S. , Myrvik Q. N. , Gristina A. G.
Published: May 2005

Adherence of selected strains of coagulase‐negative staphylococci to various biomaterials, and the inhibition of their adherence by extracellular slime obtained from the RP12 strain of Staphylococcus epidermidis were studied in vitro. S. epidermidis RP12 adhered considerably more to polymethylmethacrylate (PMMA) discs than did the SP2 strain of S. hominis and the SE‐360 strain of S. hyicus. Strain RP12 was less adherent to titanium alloy, ultrahigh molecular weight polyethylene (UHMWPE), and Teflon discs than to PMMA discs. Exposure of PMMA discs to extracellular slime extracted from strain RP12 greatly reduced adherence of strain RP12, SP2, SE‐360, adn S. epidermidis RP‐62A. The active component(s) was present in the <10 kD mol wt fraction obtained by Amicon YM10 ultrafiltration of crude slime; heat treatment of the fraction did not affect its inhibitory activity. When the bacteria and RP12 slime fractions were added simultaneously to the PMMA discs, the >10 kD mol wt fraction of slime competitively inhibited adherence of strain RP12 to PMMA discs; in contrast, the <10 kD mol wt fraction enhanced adherence of strain RP12 to PMMA discs. © 1994 John Wiley & Sons, Inc.
Effect of bioactive ceramic composition and structure on in vitro behavior. III. Porous versus dense ceramics
Authors: Radin S. R. , Ducheyne P.
Published: May 2005

In vitro reaction kinetics of surface transformations of porous and dense bioactive ceramics were studied after immersion in simulated physiologic solution (SPS). Porous ceramics with identical macroporosity were commercially obtained: calcium carbonate marine coral (I‐CC), coralline HA (I‐HA), and a product, labeled as β‐tricalcium phosphate, which was partially transformed into β‐calcium pyrophosphate (I‐β‐CP). Previously studied dense ceramics were used for comparison: Ca‐deficient HA (CDHA), stoichiometric HA, both well and not well crystallized (wc and nwc s‐HA), β‐and α‐tricalcium phosphate (β‐ and α‐TCP). The induction time to precipitation increased as follows: CDHA, nec HA < wc HA, I‐HA < β‐TCP, I‐CC < I‐β‐CP. The reaction kinetics of ceramics with identical macroporosity varied substantially depending on composition, crystal structure, and ultrastructure. One of the porous ceramics, I‐β‐CP, showed an inhibiting effect on precipitation reactions. © 1994 John Wiley & Sons, Inc.
Interaction of chlorhexidine digluconate with and adsorption of chlorhexidine on hydroxyapatite
Authors: Misra D. N.
Published: May 2005

It is well known that chlorhexidine digluconate provides an effective microbicidal activity during oral rinsing, and therefore, it was considered worthwhile to investigate its interaction with hydroxyapatite on a fundamental level. The kinetics of uptake (or reaction) of the compound from aqueous solutions by synthetic hydroxyapatite was studied at 23°C for four time periods by monitoring its concentration. There was no uptake at low concentrations for any time period. The uptake curves for higher concentrations shifted towards the lower concentrations as the period increased and became more and more vertically oriented to the concentration axis. The concentrations of calcium ions increased, phosphate ions decreased and hydrogen ions decreased a little for a given period as the concentration of the compound was increased. All of these experimental facts can be qualitatively explained on the basis of the solubility considerations of hydroxyapatite and of chlorhexidine phosphate, the reaction product that slowly precipitates out of the solution. The needle‐shaped birefringent crystals of the phosphate salt are clearly visible in the apatite matrix under a microscope, and its refractive index and differential Fourier transform infrared spectra match almost exactly with those of a well‐characterized, synthesized phosphate salt. To explore the nature of interaction, the uptake of chlorhexidine base was studied from p‐dioxane and it is irreversible. The uptake is total below a threshold equilibrium concentration and constant above it. © 1994 John Wiley & Sons, Inc.
Study of the surface characteristics of magnetron‐sputter calcium phosphate coatings
Authors: Wolke J. G. C. , van Dijk K. , Schaeken H. G. , de Groot K. , Jansen J. A.
Published: May 2005

Plasma‐sprayed hydroxylapatite coatings on metals such as titanium have been investigated for many years and have shown a good biocompatibility when implanted in bony tissues. Radiofrequency magnetron sputtering was used as an alternative method to deposit thin films of hydroxylapatite on titanium substrates. X‐ray diffraction demonstrated that the sputtered layer was crystalline with a preferred (001) crystallographic orientation with the C‐axis perpendicular to the substrate surface. Scanning electron microscopy showed that the deposited films had a uniform and dense structure. The calcium phosphate ratio varied between 1.5 and 2.0, as determined by energy‐dispersive X‐ray analysis. The in vitro dissolution appeared to be determined by the degree of the coating's crystallinity. © 1994 John Wiley & Sons, Inc.
Distinguishing wear and creep in clinically retrieved polyethylene inserts
Authors: McDonald Michael D. , Bloebaum Roy D.
Published: May 2005

There is an increasing awareness of the clinical problems associated with ultra‐high‐molecular‐weight polyethylene (UHMWPE) wear and failure in orthopedics. To better understand the reasons for wear and failure, methods were developed using polarized light microscopic analysis and backscattered electron (BSE) imaging with correlated elemental analysis to distinguish the contributions of wear, creep, and third‐body particulate. This study determined that microscopic metal particles (<10 μm) previously not observed with the stereomicroscope could be easily observed with the BSE technique. BSE imaging identified embedded metal in 5/5 of the tibial and 2/4 of the acetabular inserts, which were thought to be free of metal debris after stereoscopic examination. Correlated elemental analysis showed that the microscopic particles could be traced to the elements known to be present in the porous coatings of the retrieved uncemented implants. Creep was distinguished from wear in the total hip and total knee inserts by using polarized light microscopic techniques. Continued development of polarized light microscopic techniques applied in this investigation should assist biomaterials experts in the future to better distinguish wear and creep in retrieved clinical inserts. The correlated BSE and elemental analysis will assist in determining the roll of microscopic third‐body particular in wear and osteolysis in total joint replacement. © 1995 John Wiley & Sons, Inc.
Mixed‐metal fretting corrosion of Ti6Al4V and wrought cobalt alloy
Authors: Kawalec Jill S. , Brown Stanley A. , Payer Joe H. , Merritt Katharine
Published: May 2005

Corrosion has been reported at the modular interfaces of total joint replacement implants, but with conflicting theories as to the cause of such damage. The modular design itself leaves the interface susceptible to galvanic, crevice, or fretting corrosion, or a combination of the three. The purpose of this study was to quantify the effect of material combination on fretting corrosion of orthopedic alloys. Each test specimen consisted of a two‐hole plate with spherical countersinks of a two cortical bone screws. The plates and screws were made of either Ti6Al4V or wrought cobalt–chromium–molybdenum (CCM), and were tested in all mixed‐metal and similar‐alloy combinations. Fretting corrosion experiments were conducted for 14 days in 10% calf serum, according to ASTM F897. Corrosion damage was evaluated by weight‐loss measurements, atomic absorption spectrophotometry and scanning electron microscopy analyses. The results indicated that Ti6Al4V suffered relatively severe damage when fretted against itself, as a result of adhesive galling. The extent of titanium damage was reduced considerably, however, when Ti6Al4V was fretted against wrought CCM. In contrast, there was essentially no difference in wrought CCM damage when the alloy was fretted against itself compared to fretting against Ti6Al4V. Finally, in similar‐alloy combinations, Ti6Al4V suffered more severe damage than wrought CCM. © 1995 John Wiley & Sons, Inc.
Effects of some technological aspects on the fatigue strength of a cementless hip stem
Authors: Viceconti Marco , Toni Aldo , Giunti Armando
Published: May 2005

Four prototype cementless hip stems were tested following the ISO 7206 protocol for the assessment of the endurance properties and compared with a cast CrCoMo (ASTM F75) commercially available stem which was used as reference design. All the tested stems were similar in shape and size, but with some substantial differences. The first was made of forged Ti6Al4V alloy (ASTM F136). The second, made of the same material, featured a central hole intended to reduce the bending stiffness of the stem itself. The third was identical to the second but for a small tooling notch in one of the fillets of the hole. The fourth was similar to the first but had a coating of sintered titanium beads in the proximal part. All of these modifications were made to evaluate the effect of fatigue strength of intentional or unintentional features commonly found in commercial stems. The forged Ti6Al4V alloy was found to be substantially stronger than the cast ASTM F75 CrCoMo alloy. However, tooling notches or sintered coatings were found to dramatically reduce this strength. Thus, the Ti6Al4V alloy calls for an accurate design process, especially when complex shapes or sintered structures are required. © 1995 John Wiley & Sons, Inc.
Mechanical properties of xenogeneic small‐intestinal submucosa when used as an aortic graft in the dog
Authors: Hiles M. C. , Badylak S. F. , Lantz G. C. , Kokini K. , Geddes L. A. , Morff R. J.
Published: May 2005

Small‐intestinal submucosa (SIS) has been shown to induce tissue remodeling in vivo when used as a vascular graft. The present study investigated the physical and mechanical properties of remodeled aortic grafts derived from xenogeneic SIS material. Eight infrarenal aortic grafts were implanted in mongrel dogs. The grafts were explanted at 1 or 2 months and tested for compliance and hoop mechanical properties. The morphologic changes within the grafts were also characterized. The remodeling process produced graft structures which were significantly stronger than both the normal artery (P = .012) and the original SIS graft (P = .0001), and the compliance of these structures was one third that of normal artery and similar to the original SIS grafts. The remodeled grafts were > 10 times the thickness of the implanted SIS. Immunohistochemical analysis of remodeled tissues suggest that the SIS material was degraded and resorbed over time. The remodeling process transformed a material which was physically and mechanically quite different from normal aorta into a blood conduit which had the physical and mechanical properties needed to function in this mammalian arterial system. © 1995 John Wiley & Sons, Inc.
In vitro biocompatibility, mechanical properties, and corrosion resistance of TiZrNbTaPd and TiSnNbTaPd alloys
Authors: Ito Atsuo , Okazaki Yoshimitsu , Tateishi Tetsuya , Ito Yoshimasa
Published: May 2005

There is much discussion about the toxic effect of vanadium and aluminum contained in Ti6Al4V alloy for prosthetic implants. The goal of the present investigation was to develop new titanium alloys with sufficient mechanical properties using more biocompatible alloying elements: zirconium, tin, niobium, tantalum, and palladium. The relative growth rates of L929 and MC3T3‐E1 cells were significantly higher when cultured with the extraction of Ti10Zr8Nb2Ta0.2Pd or Ti15Zr4Nb2Ta0.2Pd alloys than when cultured with the extraction of Ti6Al4V ELI alloy. The tensile strength, elongation, and reduction of area for Ti15Sn4Nb2Ta0.2Pd alloy were 989 MPa, 14.4%, and 49.3%, respectively, surpassing Ti6Al4V ELI alloy (ASTM F13884); those for Ti15Zr4Nb2Ta0.2Pd alloy were 725 MPa, 23.6% and 54.9%, respectively. More than 15% addition of tin as well as zirconium deteriorated the tensile properties. Titanium release into a 5% hydrochloric acid solution from the new titanium alloys was 20–50 μg/cm2 per day, though that from Ti6Al4V ELI alloy was 1300 μg/cm2 per day. The optimum alloy compositions are Ti15Zr4Nb2Ta0.2Pd and Ti15Sn4Nb2Ta0.2Pd, judging from cytocompatibility, corrosion resistance, and mechanical properties. The former is characterized by its high level cytocompatibility and corrosion resistance, while the latter is characterized by mechanical properties. © 1995 John Wiley & Sons, Inc.
Anchorage of TiO2‐blasted, HA‐coated, and machined implants: An experimental study with rabbits
Authors: Gotfredson Klaus , Wennerberg Ann , Johansson Carina , Skovgaard Lene Teil , Hjørting‐Hansen Erik
Published: May 2005

The purpose of this study was to evaluate the histometrical and biomechanical anchorage of TiO2‐blasted implants and TiO2‐blasted implants coated with hydroxyapatite. The control implants were machined. Twenty‐six rabbits had a total of 156 implants placed in the proximal part of the tibia. Each rabbit had a machined, a TiO2‐blasted, and a TiO2‐blasted, HA‐coated implant placed in each tibia. After a healing period of 3 and 12 weeks, respectively, the implants placed in the right tibia were used for removal torque test, and the implants placed in the left tibia were used for histomorphometrical measurements. Preoperatively, implants from the same batches were examined topographically with a TopScan 3D system. The TiO2‐blasted implants demonstrated significantly higher removal torque values than the machined implants, and they also had a significantly more irregular surface. Furthermore, significantly higher bone‐to‐implant contact length fractions were measured adjacent to the TiO2‐blasted implants in contrast to the machined implants. The advantages of a TiO2‐blasted surface were more pronounced after 3 weeks than after 12 weeks. The results demonstrated that it was possible to influence the anchorage of implants by altering the surface structure morphology. The new method with TiO2 blasting on the titanium surface improves the anchorage o fimplants but is not yet practicable for HA coating. © 1995 John Wiley & Sons, Inc.
Interaction of antithrombin III with surface‐immobilized albumin—heparin conjugates
Authors: van Delden C. J. , Engbers G. H. M. , Feijen Jan
Published: May 2005

The interaction between antithrombin III (ATIII) and albumin–heparin conjugates covalently coupled onto carboxylated polystyrene beads either in buffer containing albumin or in plasma was studied using 14C‐labeled ATIII. Binding isotherms of ATIII were modeled using a summation of two Langmuir equations. These equations describe the binding of ATIII to two different sets of binding sites, one with a high, the other with a low affinity for ATIII. The average binding constants for the binding of ATIII to these sites are 9 × 106 L/mol and 0.3 × 106 L/mol, respectively. The binding of ATIII to surface binding sites with a high affinity for ATIII was correlated with the presence of specific ATIII binding sites in the immobilized heparin. Binding of ATIII from albumin solutions to binding sites with a low affinity for ATIII was dominated by nonspecific binding of ATIII to the immobilized heparin. A third small fraction of the surface bound ATIII is probably adsorbed to sites on the surface not covered with heparin. In the case of the binding of ATIII to the heparinized surface from plasma solutions, a fraction of initially adsorbed ATIII was desorbed by other plasma proteins. This desorption in combination with direct competition between ATIII and other plasma proteins resulted in lower ATIII surface concentrations using plasma as compared to the ATIII surface concentrations obtained using albumin solutions. The binding of ATIII to nonspecific binding sites was almost completely inhibited in the presence of plasma proteins. The amount of ATIII bound to immobilized heparin via specific ATIII binding sites was 30% lower in plasma solutions as compared to the specific binding of ATIII using albumin solutions. It is concluded that the accessibility of immobilized heparin for ATIII in plasma decreases by binding of heparin–binding proteins onto the immobilized heparin and/or by adsorption of other plasma proteins on the heparinized surface. © 1995 John Wiley & Sons, Inc.
The rat epididymal fat pad as an implantation site for the study of microcapsule biocompatibility: Validation of the method
Authors: Pariseau Jean‐François , Leblond François A. , Harel François , Lepage Yves , Hallé Jean‐Pierre
Published: May 2005

The study of microcapsule biocompatibility is hindered by their uneven distribution and low recovery when implanted into the peritoneum. We evaluated the use of the rat epididymal fat pad as a microcapsule implantation site for biocompatibility studies. The recovery rate of microcapsules containing 85Sr‐labeled microspheres was 99.6 ± 0.75%. Microcapsules, made from the same batch of nonpurified alginate, were injected into both fat pads of male Lewis rats (n = 18) and retrieved 14 days later. A semiquantitative fibrosis score scaled from 0 to 3.0 showed that the pericapsular reaction was uniform throughout a fat pad, and that the results of the two fat pads were equivalent because the null hypothesis of inequivalence was rejected (P < .001). Thus, this method can be used to compare the biocompatibility of microcapsule of differing compositions. © 1995 John Wiley & Sons, Inc.
Evaluation of poly(DTH carbonate), a tyrosine‐derived degradable polymer, for orthopedic applications
Authors: Ertel Sylvie I. , Kohn Joachim , Zimmerman Mark C. , Parsons J. Russell
Published: May 2005

The polymerization of desaminotyrosinetyrosylhexyl ester (DTH) with phosgene gives rise to poly(DTH carbonate), a new pseudopoly(amino acid). To evaluate the performance of this bioabsorbable material in orthopedic applications, the tissue responses elicited by compression‐molded pins of poly(DTH carbonate) and clinically used polydioxanone pins (PDS; Orthosorb®) were compared. The two types of pins were implanted in the paravertebral muscle and in the metaphyseal proximal tibia and distal femur of 10 White New Zealand Rabbits for 1, 2, 4, and 26 weeks. The tissue response was evaluated using histologic staining of softand hard‐tissue sections, fluorescent bone marker incorporation, and backscattered electron imaging. In soft tissue, both poly(DTH carbonate) and PDS elicited a mild inflammatory response resulting in encapsulation. During the disintegration phase, the PDS implants triggered a foreign body response involving the phagocytosis of polymeric debris by histiocytes and giant cells. No such response was observed for poly(DTH carbonate). In hard tissue, close bone apposition was observed throughout the 26‐week test period for poly(DTH carbonate) implants. At the 26‐week time point, the poly(DTH carbonate) implants exhibited surface erosion and were penetrated by new bone. In contrast, an intervening fibrous tissue layer was always present between the PDS pins and the bone. At 26 weeks, the PDS implants had partially resorbed and a foreign body response characterized by infiltration of inflammatory cells, and bone resorption was observed in several of the implantation sites. This study indicates that poly(DTH carbonate) and PDS exhibit fundamentally different interactions with hard tissue, and that poly(DTH carbonate) is a promising orthopedic implant material. © 1995 John Wiley & Sons, Inc.
Effects of γ‐alumina and hydroxyapatite coatings on the growth and metabolism of human osteoblasts
Authors: Labat Béatrice , Chamson Annette , Frey Jacques
Published: May 2005

The behavior of human osteoblasts cultivated on hydroxyapatite or alumina‐coated disks of Ti6AL4V was studied in vitro. Cell anchorage and spreading were observed by scanning electron microscopy. Cell growth was monitored by counting cells and measuring DNA at 5 h and 2, 5, and 10 days after cell seeding. Cells grown for 10 days were labeled with 14C‐proline and total protein and collagen synthesis were measured; the type of collagen was also determined. Both ceramics showed excellent biocompatibility. At 10 days of culture the cells showed a higher rate of proliferation on alumina than on hydroxyapatite. Neither ceramic altered the collagen biosynthesis or the osteoblastlike properties of the cells, as indicated by the high percentage of type I collagen. © 1995 John Wiley & Sons, Inc.
Regeneration of full‐thickness wounds using collagen split grafts
Authors: van Luyn M. J. A. , Verheul J. , van Wachem P. B.
Published: May 2005

Collagen‐based skin substitutes are among the most promising materials to improve regeneration of full‐thickness wounds. However, additional meshed grafts or cultured epidermal grafts are still required to create epidermal regeneration. To avoid this, we substituted collagen‐based split grafts, i.e., grafts with a separated top and bottom layer, in a rat full‐thickness wound model and compared regeneration with nontreated, open control wounds. We hypothesized that epidermal regeneration would occur in the split in between the two layers, with the top layer functioning as a clot/scab and the bottom layer as a dermal substitute. Two types of dermal sheep collagen (DSC) split grafts were tested: one with a top layer of noncrosslinked DSC (NDSC) and bottom layer of hexamethylenediisocyanate crosslinked DSC (HDSC), further called N/HDSC; and the second with both a top and bottom layer of HDSC (H/HDSC). With the N/HDSC split graft NDSC did not function as a sponge for formed exudate and as a consequence the split was no longer available to facilitate epidermal regeneration. In contrast, with the H/HDSC graft the split facilitated proliferation and differentiation of the epidermal cells in the proper way. With this graft, clot formation was restricted to the top layer, which was rejected after 8 weeks, while the bottom layer functioned during gradual degradation as a temporary matrix for the formation of autologous dermal tissue. H/HDSC strongly inhibited infiltration of myofibroblasts, resulting in a 30% wound contraction, while a 100% contraction was found with the open control wound. The results show that H/HDSC split‐grafts function conforms to the hypothesis in regeneration of large, full‐thickness wounds without further addition of seeded cells or use of meshed autografts. © 1995 John Wiley & Sons, Inc.
Pyrolysis–gas chromatography of carbonate apatites used for sintering
Authors: Doi Y. , Koda T. , Adachi M. , Wakamatsu N. , Goto T. , Kamemizu H. , Moriwaki Y. , Suwa Y.
Published: May 2005

Gas chromatography was employed to quasi‐continuously determine the amount of carbon dioxide that evolved from carbonate apatite specimens during sintering. Assuming that the carbonate in the specimens decomposed to carbon dioxide on a mole‐for‐mole basis, the determination of the carbon dioxide evolved allowed for the determination of the amount of carbonate that remained in the specimens during different stages of sintering. Previously, this measurement could be carried out only after sintering was completed. Comparison of data obtained from specimens compacted isostatically at 600 MPa for sintering with powder specimens indicated that the amount of carbonate remaining in the sintered apatite mass strongly depended on heating rates, heating temperatures, and holding‐time intervals. © 1995 John Wiley & Sons, Inc.
Degradation potential of plasma‐sprayed hydroxyapatite‐coated titanium implants
Authors: Paschalis E. P. , Zhao Q. , Tucker B. E. , Mukhopadhayay S. , Bearcroft J. A. , Beals N. B. , Spector M. , Nancollas G. H.
Published: May 2005

The purpose of this study was to develop an analytical method for evaluating the dissolution behavior of plasmasprayed hydroxyapatite (HAP) coatings. Six commercially available and clinically used coatings applied to nonporous titanium coupons according to their respective specifications for orthopedic devices were used in this study. Dissolution behavior was monitored by first preconditioning the implant in 0.15 mol L−1 sodium chloride solution at 37°C until either equilibrium or the desired change in solution hydrogen and calcium ion concentrations had been reached. In the second step, the implants were subjected to dual constant composition (DCC) dissolution under conditions of controlled undersaturation. Results indicate that the dissolution rates of the HAP coatings may differ by as much as a factor of 5 despite the fact that analytical techniques, including X‐ray diffraction and FTIR, indicate no change in crystallinity or composition of the coatings before and after the solution treatment. These results indicate that HAP coatings from different sources react very differently when placed in the same local aqueous environment. However, more work will be necessary before these in vitro results can be used to predict in vivo behavior. © 1995 John Wiley & Sons, Inc.