bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of hyaluronan on collagen fibrillar matrix contraction by fibroblasts
Authors: Huang‐Lee Lynn L. H. , Wu Julia H. , Nimni Marcel E.
Published: May 2005

Hyaluronan, found in high concentrations in fetal tissues, appears to have a major role in preventing scar formation in fetal wounds. Nevertheless, its role in inhibiting wound contractures associated with scar formation has not been clearly demonstrated. Our current study evaluated the effects of hyaluronan using an in vitro floating collagen fibrillar matrix (CFM) contraction model. The results demonstrated that the contraction of CFM by fibroblasts was significantly reduced when high concentrations (>1 mg/mL) of hyaluronan were present in the media. This phenomenon is unique to hyaluronan, because chondroitin sulfate was ineffective in this connection. Fibroblast migration and proliferation studies indicated that high concentrations of hyaluronan stimulated cell migration and had no cytotoxic effects.

Some possible mechanisms by which high concentrations of hyaluronan reduced CFM contraction by fibroblasts were proposed. Because the viscosity of a hyaluronan solution is much greater than that of chondroitin sulfate, and this increases with concentration, we investigated whether this property in itself was an important factor in inhibiting CFM contraction. No direct correlation was found between the viscosity of glycosaminoglycans and their ability to reduce CFM contraction. © 1994 John Wiley & Sons, Inc.
Screening of matrices and fibers for reinforced thermoplastics intended for dental applications
Authors: Goldberg A. Jon , Burstone Charles J. , Hadjinikolaou Ioannis , Jancar Joseph
Published: May 2005

Plastic reinforced with continuous fibers (FRC) are being developed for dental applications, such as prosthodontic frameworks and orthodontic retainers. Flexure properties, stress relaxation and hydrolytic stability of FRC based on six thermoplastic matrices, three types of fibers, and three fiber volume fractions were evaluated. Samples with clinically relevant dimensions were tested. Polycarbonate was the preferred matrix material. Polycarbonate reinforced with 42 volume percent glass fibers exhibited the highest combination of flexure modulus (17.9 ± 2.6 GPa), flexure strength (426 ± 40 MPa), reinforcing efficiency (0.79), and resistance to stress relaxation.

No statistically significant difference was observed between E and S2 glass reinforced composites under the experimental conditions used. Kevlar reinforced materials exhibited a low flexure modulus and strength. The apparent flexure moduli of all composites decreased with span length in the range of clinical interest. Generally, the prevalent mode of failure for all FRC investigated was brittle failur under flexure loading. Relatively large sample‐to‐sample variation in both composition and properties indicated that improved fabrication methods will be needed in future studies.

The combination of good flexure properties, formability, and translucency suggests that novel appliance designs for dentistry are feasible with FRC, but further studies of its properties and particularly the effects of fiber/ matrix interfacial quality are needed. © 1994 John Wiley & Sons, Inc.
Fatigue crack propagation behavior of ultra high molecular weight polyethylene under mixed mode conditions
Authors: Elbert K. E. , Wright T. M. , Rimnac C. M. , Klein R. W. , Ingraffea A. R. , Gunsallus K. , Bartel D. L.
Published: May 2005

Analytical studies of the stresses on and within ultra high molecular weight polyethylene joint components suggest that damage modes associated with polyethylene fatigue failure are caused by a combination of surface and subsurface crack propagation. Fatigue crack propagation tests under mixed mode loading conditions were conducted on center‐cracked tension specimens machined from extruded blocks of sterilized polyethylene in an attempt to determine how fatigue cracks change direction in this material. Cyclic testing was performed using a sinusoidal wave form at a frequency of 5 Hz and an R‐ratio (minimum load/ maximum load) of 0.15. Specimens had the notch oriented perpendicular to the direction of applied load and at angles of 60° and 45° to the loading direction. Numerical analyses were used to interpret the experimental test and to predict the fatigue behavior of polyethylene under mixed mode conditions. It was found that all cracks eventually propagated horizontally, regardless of the initial angle of inclination of the notch to the direction of applied cyclic load. In fact, the extent of the curvilinear crack growth was quite limited. An effective range of cyclic stress intensity factor was calculated for correlation with the rate of crack growth. The results followed a Paris relation, with crack growth rate linearly related to a power of the range of stress intensity, for all three crack orientations. The numerical analyses adequately modeled the experimental fatigue crack growth results. © 1994 John Wiley & Sons, Inc.
Thermal shock resistance of core reinforced all‐ceramic crown systems
Authors: Mora Gary P. , O'Brien William J.
Published: May 2005

The coefficient of thermal expansion of core and veneer porcelains for all ceramic crowns must be compatible to prevent formation of stresses during the firing cycles. The purpose of this study was to use a thermal shock test to evaluate the crazing resistance of six all‐ceramic crown systems. The systems tested were: Vita In‐Ceream®, Vita Hi‐Ceram®, Dicor™ veneered with Vitadur® N, magnesia core veneered with Ceramco® II, magnesia core veneered with Silhouette™, and magnesia core veneered with Vita VMK® 68. A maxillary central incisor was prepared with 1.0 mm axial and 1.5 mm incisal reduction. Refractory dies were prepared and crowns were fabricated using the manufactures recommendations. Six specimens of each system were placed inside a beaker in a furnace at 90°C. After 15 min heat soak, ice water was poured into the beaker through a funnel. The samples were dried in air, reheated, and inspected for crazing using light microscopy. If crazing was observed, this would constitute a failure at a temperature difference (ΔT) of 90°C. If no failure occurred, the test was repeated at increasing temperature increments of 10°C until failure. The crazing resistance of each system, expressed as the mean ΔT, was: > 200 (Hi‐Ceram®), 152 ± 19 (Dicor™ / Vitadur® N), 143 ± 5 (magnesia core/Vita VMK® 68), 122 ± 21 (magnesia core/Silhouette™), and 118 ± 10 (magnesia core/Ceramco® II) °C. All systems tested resisted crazing due to quenching in ice cold water from 100°C. Systems with lower coefficients of expansion showed significantly greater resistance to thermal shock using ANOVA. © 1994 John Wiley & Sons, Inc.
Microvascular endothelial cell sodding of ePTFE vascular grafts: Improved patency and stability of the cellular lining
Authors: Williams Stuart K. , Rose Deborah G. , Jarrell Bruce E.
Published: May 2005

Small diameter (<6 mm) synthetic vascular grafts fail at a clinically unacceptable rate due in large part to their inherent thrombogenicity. The development of a new cellular lining on synthetic vascular grafts would most likely improve the patency rates observed for these grafts in small diameter positions. We have evaluated the use of endothelial cell transplantation to accelerate the formation of a cell lining using microvascular endothelial cells derived from canine falciform ligament fat. This source of fat is histologically similar to human liposuction fat and was isolated using a collagenase digestion technique identical to methods used for human liposuction fat microvessel endothelial cell isolation. The isolated fat endothelial cells were sodded onto 4 mm ePTFE grafts using pressure to force the cells onto the luminal surface. This pressure sodding method permitted cell deposition in less then 3 min. Sodded and control (non—cell‐treated) grafts were implanted as interpositional paired grafts using end‐to‐end anastomoses in the carotid arteries of mixed breed dogs. Each dog therefore received a sodded graft on one side and a control graft on the contralateral side. After 12 weeks of implantation all control grafts were occluded while 86% of the cell‐sodded grafts remained patent. Statistical evaluation of the data revealed a significant improvement in patency of cell sodded grafts (McNemar's χ2 P =.02). Morphological evaluation of grafts explanted at 5, 12, 26, and 52 weeks following implantation revealed the presence of a cell lining on sodded grafts which remained stable for a period of at least one year. This new cell lining exhibited morphologic characteristics of a nonthrombogenic endothelial cell lining. The development of this new intima, evaluated 5 weeks–1 year after implantation, was not associated with a progressive intimal hyperplasia. From these data we conclude that microvessel endothelial cells derived from canine falciform ligament fat can be rapidly isolated using an operating room compatible method. Cell deposition on synthetic grafts is subsequently accelerated using a pressure sodding technique. A cellular lining forms on the inner surface and is associated with a statistically significant improvement in the function of sodded grafts in a canine carotid artery model. © 1994 John Wiley & Sons, Inc.
Confocal laser scanning microscopy (CLSM) for the study of collagen sponge microstructure
Authors: Hanthamrongwit M. , Grant M. H. , Wilkinson R.
Published: May 2005

This study uses confocal laser scanning microscopy (CLSM) to assess the microstructure of collagen sponges providing an accurate quantification of porosity under conditions similar to those experienced by cells growing on the sponges during culture. CLSM offers several advantages over scanning electron microscopy (SEM) and conventional optical microscopy for this kind of study, the most important of which is probably the absence of artifacts associated with the extensive preparation of samples required for the latter two methods. When the “pan‐side” surface of collagen sponges was studied, it was found that the pore sizes increased with increasing depth into the sponge. Collagen sponges frozen in a −70°C freezer had a more open structure than ones frozen on the stage of a tissue dryer. These different pore sizes are thought to reflect different freezing rates in the samples. © 1994 John Wiley & Sons, Inc.
Interfacial behavior of PEO/PBT copolymers (polyactive®) in a calvarial system: An in vitro study
Authors: Radder A. M. , Davies J. E. , Leenders H. , van Blitterswijk C. A.
Published: May 2005

Polyactive®, a polyethylene oxide/ polybutylene terephthalate (PEO/PBT) copolymer, has been reported to display bone‐bonding behavior. Although a detailed description of the in vivo bone/ Polyactive® interface is available, the underlying bone‐bonding mechanism is still largelyunknown. In this in vitro study, a calvarial envelope method has been adopted to reproduce the in vivo bone‐bonding phenomenon and subsequently to obtain information on the biological effect of varying PEO/PBT segment ratios. The following PEO/PBT ratios were examined: 70/30, 60/40, 55/45, 40/60, and 30/70. Light microscopy (LM) and scanning (SEM), transmission (TEM), and backscatter electron microscopy (BSE), as well as X‐ray microanalysis (XRMA), were employed. Within the period of analysis (3 weeks), an intimate contact between mineralized deposition and the 70/30, 60/40, and, to a lesser extent, the 55/45 surface was observed. Calcified areas developed within the surface of these PEO/BPT proportions during the culture period. Needle‐shaped crystals from the mineralized tissue compartment and from calcified areas within the materials surface were intermingled at the interface, providing a morphologic continuity. A cellular layer was interposed with the mineralization front and the noncalcified 40/60 and 30/70 substrates. Apparently, the percentage of PEO is important for calcification within the near surface of the polymer. This relation is such that the highter the PEO content in PEO/PBT ratios, the more rapid the calcification is considered. The occurrence of material calcification is considered to be largely responsible for the subsequent interfacial interactions. The calvarial envelope culture method allows not only reproduction of the in vivo bone/Polyactive® interface, but also a relatively rapid differentiation within the range of PEO/PBT ratios. It was therefore concluded that this in vitrosystem is suitable for further studies toward a better understanding of the bone/Polyactive® interfacial composition and the underlying mechanisms. © 1994 John Wiley & Sons, Inc.
Calcium phosphate formation on sol‐gel‐derived bioactive glasses in vitro
Authors: Pereira M. M. , Clark A. E. , Hench L. L.
Published: May 2005

When soluble salts are used in the sol‐gel processing of bioactive glasses, the resulting materials are not homogeneous. To produce homogeneous gel‐glasses, a sol‐gel method using all alkoxide precursors was developed. In this work the in vitro bioactivity of the new all‐alkoxide gel‐glasses is investigated. Three compositions in the system, CaOP2O5SiO2, were studied. Solid samples were soaked in Tris buffer and simulated body fluid (SBF), and the rate of formation of hydroxy carbonate apatite (HCA) on the surface of the glasses was measured by Fourier transform infrared spectroscopy. The solutions were analyzed before and after reaction by inductively coupled plasma. All compositions studied formed a hydroxy carbonate apatite (HCA) layer within 8 h in both test solutions. The HCA layer grew rapidly when SBF was used. © 1994 John Wiley & Sons, Inc.
In vitro chondrocyte collagen deposition within porous HDPE: Substrate microstructure and wettability effects
Authors: Livecchi A. B. , Tombes R. M. , LaBerge M.
Published: May 2005

The effects of microstructure and wettability of porous high density polyethylene (HDPE) substrates on chondrocyte collagen synthesis in vitro were assayed. Three size grades of hydrophilic and hydrophobic HDPE substrates with ranges of pore volumes of 40–60%, pore sizes of 115–335 μm, and surface areas per unit volumes of 7–20 mm2/mm3 were seeded with fetal bovine chondrocytes. After 7 days of incubation, the cells within all substrates remained spherical, and contained mainly type II collagen (as verified by type I and II collagen I‐ELISAs). After 21 days, the majority of cells had spread; however, the matrices still contained mainly type II collagen. The hydrophilic matrices contained significantly more type II collagen than the hydrophobic matrices at both 7 and 21 days, whereas the amount of type II collagen was not influenced by the pore attributes. A significantly higher percentage of type II collagen was also observed in all seeded porous substrates as compared with seeded polystyrene culture dishes, perhaps indicating that the three‐dimensional particular nature of the HDPE matrices enhanced the maintenance of phenotypically differentiated chondrocytes and entrapment of their extracellular matrix products. © 1994 John Wiley & Sons, Inc.
Resistance of hyaluronate coatings to hyaluronidase
Authors: Lowry Karen M. , Beavers Ellington M.
Published: May 2005

Mucopolysaccharides such as hyaluronic acid and its salts are essential components of new hydrophilic bilaminar coatings being developed in these laboratories. The polysaccharide top‐coat is covalently bonded by periodic urethane links to a substrate copolymer which in this study has been coated on polymethyl methacrylate slabs. Such coated slabs were exposed for up to 28 months to three levels of hyaluronidase in phosphate buffered saline at 37°C, the enzyme concentration ranging from that normally present in human serum to 60 times that level. The coating survived without damage. The rationale proposed is that the enzyme is unable to position its active site with the immobilized hyaluronate molecule and is therefore unable to catalyze the hydrolysis. © 1994 John Wiley & Sons, Inc.
Calcium phosphate plasma‐sprayed coatings and their stability: An in vivo study
Authors: Klein C. P. A. T. , Wolke J. G. C. , De Blieck‐Hogervorst J. M. A. , de Groot K.
Published: May 2005

Several factors playing a possible role in determining coating stability and bone tissue response were studied in in vivo experiments. These factors involving the plasmaspray coating procedure were as follows: (1) plasmaspray powder port 2 or 6; (2) particle size distribution; (3) hydroxylapatite versus fluorapatite coatings; and (4) the effect of post‐heat treatment. Coating stability and bone tissue response were examined by measuring coating thickness, coating thickness, coating length, and bone apposition against the coatings. The result was that heat treatment influenced coating stability significantly. Also, bone formation was more intense. Fluorapatite proved to be more stable than hydroxylapatite, which was in agreement with our previous reports. © 1994 John Wiley & Sons, Inc.
Characterizations of titanium implant surfaces. III
Authors: Keller John C. , Stanford Clark M. , Wightman James P. , Draughn Robert A. , Zaharias Rebecca
Published: May 2005

There are several reports in the literature concerning the similarities and the differences between the oxide on cpTi and Ti‐6Al‐4V alloy; however, their biological sequelae are not entirely known. In this work, a series of surface characterization techniques were used in conjunction with short termin vitrobiological assays to assess the effects of materials selection (cpTi and Ti alloy) on osteoblast‐like cell responses. Surface analysis indicated that with the exception of oxide thickness, there were no significant differences in surface characteristics between the two implant materials. These results were reflected in the biological studies, where the levels of cell attachment and adaptation of the attached cells to the titanium surfaces were similar. These results are in general agreement with previousin vivostudies and continue to indicate that cpTi and Ti alloy are suitable, biologically compatible materials for fabrication of dental implants. © 1994 John Wiley & Sons, Inc.
Features of calcium phosphate plasma‐sprayed coatings: An in vitro study
Authors: Klein C. P. A. T. , Wolke J. G. C. , de Blieck‐Hogervorst J. M. A. , De Groot K.
Published: May 2005

Factors involved with the plasma‐spray coating procedure, such as starting powder compound (fluorapatite, hydroxylapatite, magnesium‐whitlockite, or tetra‐calcium phosphate), powder particle distribution 1–45 or 1–125 (μm), powder port gun (port 2 or 6), and post–heat treatment of 1 h at 600°C, were examined for their effects on crystallinity and solubility/stability of the coating. From solubility tests, X‐ray diffractometry, and scanning microscopy studies, the solubility and crystallinity were found to be dependent on Ca/P ratio, particle distribution, and post‐heat treatment. The post‐heat treatment influenced the degree of both crystallinity and solubility. The plasma‐spray powder port factor for the hydroxylapatite coatings was not significant. Incubation in buffer of the coatings introduced precipitation at the surfaces of all non–heat‐treated coatings except fluorapatite. No precipitation could be observed in any of the heat‐treated coatings. © 1994 John Wiley & Sons, Inc.
Mutagenicity of dentin bonding agents
Authors: Schweikl H. , Schmalz G. , Bey B.
Published: May 2005

Aside from the considerable number of reports on the physical and chemical properties of dental bonding agents, information concerning their biologic effects is sparse. Three dentin bonding agents (Prisma Universal Bond, Pertac Universal Bond, and Syntac) and the ingredients methylmethacrylate, 2‐hydroxyethyl‐methacrylate, and glutaraldehyde were investigated in the Salmonella typhimurium mutagenicity test system using five different bacterial strains (TA97a, TA98, TA100, TA102, and TA104). The materials as well as the ingredients were eluted in both dimethyl sulfoxide and physiologic saline, and serially diluted eluates were used in the plate incorporation test. Pertac Universal Bond and Prisma Universal Bond did not elicit any mutagenic effects in any of the bacterial strains. In contrast, Syntac adhesive showed clear mutagenicity in S. typhimurium strain TA102. Dimethyl sulfoxide eluates, as well as physiologic saline eluates of the Syntac bonding agent, caused numbers of revertants that were about 6 times higher than control values. Reversion rates with other strains were moderately enhanced. Glutaraldehyde, an ingredient of Syntac adhesives, caused mutagenicity in a manner similar to Syntac adhesive eluates. Neither 2‐hydroxyethyl‐methacrylate nor methylmethacrylate monomer was found to be mutagenic over a broad concentration range. © 1994 John Wiley & Sons, Inc.
Evaluation of three new hydrocolloid dressings: Retention of dressing integrity and biodegradability of absorbent components attenuate inflammation
Authors: Chakravarthy Debashish , Rodway Nancy , Schmidt Steven , Smith Daniel , Evancho Michelle , Sims Rick
Published: May 2005

Residues from hydrocolloid dressings (HCDs) that originate from matrix disintegration and nonbiodegradability of the absorbent components, may cause deep‐seated, unresolved inflammation in tissue that appears otherwise healed. The purpose of this study was to evaluate three new HCDs that were formulated with the goal of attenuating the inflammatory responses that may arise from HCD therapy. Two of the HCDs (A‐06 and A‐07) consisted of conventional absorbents dispersed in a new maceration resistant adhesive matrix. The same matrix, mixed with potentially biodegradable dextran microspheres, formed the third dressing (Dextran Bead Dressing [DBD]). In this pilot scale study these novel dressings were evaluated on full‐thickness dermal wounds on swine. Restore (Hollister) and DuoDERM CGF® (Convatec) dressings were used as controls. Wound healing was evaluated histomorphometrically. Pertinent histologic parameters were ranked from wound tissue that was harvested 18 days after wounding. Grossly visible dressing disintegration ranged from minimal (DBD) to servere (Restore). Disintegration of other dressings was moderate. The percentage of tissue sections exhibiting giant cells reflected, in parallel, the observed extent of dressing disintegration. Thirty‐eight percent of wounds dressed with DBD contained giant cells; 74 and 100% of wounds treated with Duo DERM CGF® and Restore, respectively, contained giant cells. DBD‐dressed wounds had relatively fewer chronic inflammatory cells than other dressings. These wounds were also characterized by a well‐organized collagen matrix and complete reepithelialization. The extent of wound closures was similar for all dressing types except Restore. Closure of Restore‐dressed wounds was delayed compared with closure with DBD and DuoDERM CGF® on all days of evaluation except one. A‐06 and A‐07 were comparable to DuoDERM CGF® in retention of dressing integrity and the elicited inflammatory tissue response. The DBD dressing appears to possess equivalent properties of typical HCDs while causing minimal tissue reactions. © 1994 John Wiley & Sons, Inc.
Biodegradation evaluation of polyether and polyester‐urethanes with oxidative and hydrolytic enzymes
Authors: Santerre J. P. , Labow R. S. , Duguay D. G. , Erfle D. , Adams G. A.
Published: May 2005

Enzyme‐induced liberation of components from seven different radiolabeled polyurethanes was monitored by radiolabel counting of the incubation solutions and product isolation by high performance liquid chromatography (HPLC). The polyurethanes were selected to reflect variations in the hard‐segment chemistry, soft‐segment chemistry, soft‐segment chemistry, and polyurethane hydrophilicity resulting from combinations of hydrophobic/hydrophilic soft segments. All materials were characterized using electron spectroscopy for chemical analysis, differential scanning calorimetry, size exclusion chromatography, and Fourier transform infrared spectroscopy. The material surfaces were examined both before and after incubation with enzyme and control solutions using scanning electron microscopy. Biodegradation assays were carried out at 37°C using cholesterol esterase (CE) and horseradish peroxidase (HRP) under optimal pH conditions for each enzyme. The hydrolytic enzyme (CE) was effective in releasing degradation products that contained hard‐segment components from some of the polyurethanes. HPLC analysis of products for a polyesterurethane synthesized with toluene diisocyanate (TDI) suggested that the bulk of the incorporated radiolabeled TDI was still covalently bonded within the cleaved chain segments of the original polymer and was not released as pure toluene diamine (TDA). The data suggest that urethane linkages in the soft‐segment domains of phase separated polyetherurea‐urethanes may be more prone to cleavage by CE than are the urea/urethane groups in the hard‐segment domains. This could be related to the nature of the hard‐segment domain structures. The oxidative enzyme (HRP) was not able to induce liberation of radiolabeled segments from either the polyether or polyester‐based polyurethanes. © 1994 John Wiley & Sons, Inc.
Materials testing protocol for small joint prostheses
Authors: Savory Kevin M. , Hutchinson Douglas T. , Bloebaum Roy
Published: May 2005

In this article, a protocol for the evaluation of new materials for small joint prostheses is introduced. The testing methods employed in the protocol were developed by reviewing reported clinical failure modes and conditions found in vivo. The methods developed quantitatively evaluates the fatigue, fatigue crack propagation, and wear resistance properties of materials. For this study, a silicone elastomer similar to Dow Corning Silastic HP100, a radiation stable polypropylene, and a copolymer of polypropylene and ethylene propylene‐diene monomer (EPDM) are evaluated. None of the materials tested demonstrated the ideal properties that are sought in a self‐hinging joint prostheses. The silicone elastomer had excellent wear properties; however, cracks quickly propagated, causing catastrophic failure when fatigued. Conversely, the copolymer showed excellent fatigue crack propagation resistance and less than favorable wear properties. The polypropylene did not perform well in any evaluation. © 1994 John Wiley & Sons, Inc.
Detection of antibodies against corrosion products in patients after CoCr total joint replacements
Authors: Yang Jun , Merritt Katharine
Published: May 2005

Sensitivity to nickel, cobalt, and chromium is common among the general population. The identification of these sensitivities is generally by the detection of cell‐mediated immunity. Detection of humoral immunity to these metals has rarely been undertaken because suitable assays are not available. To further our knowledge about the systemic humoral immune system response to weak hapten‐systemic or allogeneic protein conjugates (corrosion and wear products of metallic orthopedic devices), a sensitive enzymelinked immunosorbent assay (ELISA) method for testing for antibody (humoral immunity) to metals was developed. Microtiter plates were coated with human serum albumin (HSA) or glutathione (GSH) and then conjugated with metal ions. Plates coated with HSA or GSH and without metal ions served as background controls. An indirect ELISA method was used to detect antibody binding. Patients bearing cobalt‐chromium alloy devices were considered to be the most likely candidates as sources of antibody to metal and were used to document the usefulness of the test. Specificity of the test was documented by inhibition studies with these metal ions in the ELISA assay. The serum samples of 10 patients were screened for the presence of Cr‐, Co‐, or Ni‐specific antibody at various periods up to 5.5 years after implantation of F‐75 cobalt alloy total joint replacements. All patients had implants that were functioning well. The pre‐ and postimplantation humoral immune profiles of patients were determined and compared with each preimplantation control and with a pooled normal serum sample. This study presents evidence that metalprotein complex‐specific antibodies can be detected. The clinical implications remain to be determined. © 1994 John Wiley & Sons, Inc.
Mineralization of alkaline phosphatase‐complexed collagenous implants in the rat: Relation with age, sex, and site of implantation
Authors: van den Bos T. , Beertsen W.
Published: May 2005

This study was designed to determine the effects of age, sex, and site of implantation on the extent of alkaline phosphatase‐complexed collagen sheets mineralization in the animal body. Collagen sheets were prepared from bovine dentin and cortical bone and complexed with varying amounts of intestinal alkaline phosphatase (ALP).1 Controls were without enzyme or with heat‐inactivated enzyme. Sheets were implanted subcutaneously over the skull and in the dorsolateral abdominal wall in 5‐ or 20‐ week‐old male and female Wistar rats. After 2–3 weeks the implants were removed and analyzed for phosphate and calcium content. Our findings have shown that alkaline phosphatase‐induced mineralization of collagenous implants is influenced to a considerable extent by age, sex, and site of implantation. Highest mineral influx was seen in the younger males. Implants in younger females and older males contained less mineral, whereas those installed in the older females were almost free of calcium phosphate deposits. Dentinal implants in the skull region contained more mineral than those in the abdominal wall. © 1994 John Wiley & Sons, Inc.
Correlations between orthogonal mechanical properties and density of trabecular bone: Use of different densitometric measures
Authors: Keyak J. H. , Lee I. Y. , Skinner H. B.
Published: May 2005

To compare the numerous modulus‐density and strengthdensity relations that have been found for human trabecular bone from the proximal tibia, correlations between various measures of density were sought. Hydrated and dry apparent density, ash density, and density from quantitative computed tomography (QCT) were determined for cubic trabecular specimens taken from the proximal portion of human tibiae, and correlations between these measures were found(r > 0.99, P <.001). Orthogonal moduli and strengths of the specimens were measured mechanically, and were significantly correlated with ash density according to power relations (r ≥ 0.85, P <.001). The strong correlation between density from QCT and ash density indicates that these measures can be used with nearly equal precision in estimating modulus and strength of tibial trabecular bone. Equations between mechanical properties and density reported in previous studies were converted to use a common density measure and, after considering the effects of specimen size, were in general agreement with results of the present study. © 1994 John Wiley & Sons, Inc.
Osteoclastic resorption of apatite formed on apatite‐ and wollastonite‐containing glass‐ceramic by a simulated body fluid
Authors: Yamada S. , Nakamura T. , Kokubo T. , Oka M. , Yamamuro T.
Published: May 2005

We immersed mirror‐polished apatite‐ and wollastonite‐containing glass‐ceramic (A‐W GC) disks in a simulated body fluid (SBF) for 5 days to form bonelike apatite on their surface. Neonatal rabbit bone cells were cultured on these on plain A‐W GC disks for 10, 24, and 48 h. We observed the substrates by scanning electron microscopy after treating them with pronase E plus EDTA to remove all cells except osteoclasts. Osteoclasts with a non‐motile appearance formed no lacunae on the plain A‐W GC, whereas on the bonelike apatite formed on A‐W GC by the SBF, actively moving osteoclasts made many tracklike resorption lacunae. These were evident even after 10 h of culture and became more extensive after longer culture periods. The bonelike apatite was therefore a more suitable medium than plain A‐W GC for maintaining osteoclast activity. This study demonstrated in vitro osteoclastic resorption of bonelike apatite formed on A‐W GC by an SBF. It suggests that the apatite layer, through which a surface‐active ceramic bonds to bone in vivo, can be resorbed by osteoclasts and subjected to bone remodeling. © 1994 John Wiley & Sons, Inc.
In vitro flexural fatigue limits of dental composites
Authors: Braem M. J. A. , Davidson C. L. , Lambrechts P. , Vanherle G.
Published: May 2005

The flexural fatigue test equipment developed was used to study the fatigue behavior of dental restorative composites, using a “staircase” approach. Three commercial composites were tested after dry and wet storage conditions. The findings indicate that the method is accurate and reliable, and that changes due to water sorption are clearly reflected: The flexural fatigue limit decreases after water sorption. From the present results it seems that under environmentally controlled conditions, the fatigue stress level above which the composites tested fail rapidly, and below which they survive. © 1994 John Wiley & Sons, Inc.
Mineralization and pH relationships in healing skeletal defects grafted with demineralized bone matrix
Authors: Chakkalakal D. A. , Mashoof A. A. , Novak J. , Strates B. S. , McGuire M. H.
Published: May 2005

Early studies had indicated that tissue repair is intially associated with a lower than normal serum pH that later becomes more alkaline. To determine how tissue pH may affect skeletal healing and mineralization, we used a rat skeletal repair model consisting of a long bone segmental defect grafted with acid‐demineralized bone matrix (DBM), a biomaterial possessing both osteoinductive and osteoconductive repair properties. In this study, femoral and tibial diaphyses from young adult Sprague Dawley rats were cut into cylinders approximately 0.5 cm in length, demineralized in acid, perforated to accommodate a needle‐type combination pH microelectrode, and grafted around a 0.3‐cm‐long diaphyseal fibula defect. The pH of repair tissues was recorded at various time intervals up to 28 days postgrafting. Healing and mineralization were monitored histologically and by the ash and calcium content of repair tissues. During the early healing phase, tissue pH was lower than normal serum pH, presumably because of an accumulation of acidic metabolites in tissue fluids. Subsequent pH increases to more alkaline values were accompanied by a rapid mineral deposition phase and a later phase characterized by a slow, gradual increase in tissue calcium content. The results of this study support previous observations suggesting that the pH of repair tissue fluids may play a regulatory role in the healing and mineralization of bone. © 1994 John Wiley & Sons, Inc.
Erosion of a new family of biodegradable polyanhydrides
Authors: Shieh L. , Tamada J. , Chen I. , Pang J. , Domb A. , Langer R.
Published: May 2005

Studies investigating the erosion mechanism of the newly developed poly (fatty acid dimer: sebacic acid) polyanhydride (p:[FAD:SA]) are described. The overall erosion of different monomer compositions of p(FAD:SA) copolymers was examined to determine whether and to what extent copolymer properties affected polymer erosion. Increasing the hydrophobic monomer (FAD) content up to 50 wt% in the copolymer resulted in longer erosion, whereas further increases up to 70 wt% decreased the erosion period. Polymer crystallinity depended on copolymer FAD content. Copolymer degradation was studied by examining anhydride bond hydrolysis using infrared spectroscopy. Much faster hydrolysis was found in p(FAD:SA) 70:30 compared with more crystalline copolymers of higher SA content. Light microscopy indicates the presence of an erosion zone, a distinct area where mass loss occurs. This erosion zone moves from the outside toward the interior of the polymer matrix. It plays an important role in erosion because any water or monomer must diffuse through this eroded layer. © 1994 John Wiley & Sons, Inc.
Nanoapatite and organoapatite implants in bone: Histology and ultrastructure of the interface
Authors: Müller‐Mai C. M. , Stupp S. I. , Voigt C. , Gross U.
Published: May 2005

This article reports on the reaction of bone to a new family of nanocrystalline hydroxyapatite biomaterials with crystal sizes similar to those of human bone. Pure nanoapatite cylinders and organoapatite cylinders containing a synthetic nanopeptide were analyzed 28 days after implantation into the spongy bone of Chinchilla rabbits. The experimental techniques used for analysis were light microscopy, scanning electron microscopy, and transmission electron microscopy. Both implant types were well incorporated, and interface events were found to be similar to those observed on human bone surfaces with regard to resorption by osteoclast‐like cells and bone formation by osteoblasts. Different types of giant cells were observed resorbing the outermost surfaces of implants. There seemed to be both dissolution of the implant and particulate biodegradation leading to less dense implant regions near the interface, whereas the bulk of the implants remained denser. Transmission electron micrographs revealed that bone bonding occurred with and without an afibrillar intervening layer. Given the biologic reaction observed, these implant materials should be suitable for bone replacement and the organoapatite form could be useful for additional functions such as the release of drugs and optimized release of antibiotics, growth factors, or other substances. The organic component can also be used to control physical properties in a bony implantation bed. © 1995 John Wiley & Sons, Inc.
Comparison of bone‐implant interface shear strength of hydroxyapatite‐coated and alumina‐coated metal implants
Authors: Inadome T. , Hayashi K. , Nakashima Y. , Tsumura H. , Sugioka Y.
Published: May 2005

We performed a transcortical push‐out test to determine the effect of surface roughness of hydroxyapatite (HA)‐coated implants on bone‐implant shear strength in a canine model. Hydroxyapatite‐ and alumina‐coated SUS316L with the same surface roughness (roughness average: Ra = 5 μm) and HA‐coated Ti‐6Al‐4V (Ra = 8.4 μm), sintered HA (Ra = 0.9 μm), and dense alumina (Ra = 1.3 μm) were inserted into the dog's femur. The interface shear strength of the dense alumina was significantly lower than that of other implants at both 4 and 12 weeks after implantation. At 4 weeks after implantation, the interface shear strength of the alumina‐coated SUS316L was significantly lower than that of other implants (P < .05) except the dense alumina, but at 12 weeks, there was no significant difference between the implant types except the dense alumina. This indicates that the surface roughness of the HA coating affects the enhancement of the bone‐implant interface shear strength at the early period after implantation, and that a surface roughness of several micrometers does not influence the bond strength between bone and HA. A scanning electron microscopic study indicated that in almost all cases at 12 weeks, the failure site after push‐out testing was the coating‐substrate interface, not the coating‐bone interface. Therefore, protection of the coating‐substrate interface from direct shear loading is needed. © 1995 John Wiley & Sons, Inc.
Effect of particle size of metastable calcium phosphates on mechanical strength of a novel self‐setting bioactive calcium phosphate cement
Authors: Otsuka Makoto , Matsuda Yoshihisa , Suwa Yoshiko , Fox Jeffrey L. , Higuchi William I.
Published: May 2005

Resistance to compressive strength after setting of the calcium phosphate cement consisting of tetracalcium phosphate (TECP), dicalcium phosphate dihydrate (DCPD), and 40 wt/wt% of a synthetic hydroxyapatite (HAP) was tested. An equimolar mixture of the calcium phosphate powder containing DCPD (particle diameter [D] 0.52–3.33 μm) and TECP (D, 1.1–13.1 μm) transformed into HAP at 37°C, 100% RH after being mixed with 25 mM phosphoric acid. X‐ray diffraction suggested that the cement containing fine particles of DCPD and TECP completely transformed to HAP, but that mixtures containing larger particles did not. Because particle size of both DCPD and TECP affected the compressive strength of the cement, the crystal growth of HAP during cement formation depended on the specific surface area (Sw) of the raw materials. The crystallite size of transformed HAP was estimated based on X‐ray diffraction peaks at 25.8 and 32.8° attributable to the 002 and 300 planes. The crystallite size attributable to the 300 plane decreased with increasing Sw, but that attributable to the 002 plane showed no significant relationship. The compressive strength of the cement after hardening increased with an increase of its Sw. This suggested that the harder calcium phosphate cement was (derived) from the smaller particle size of the raw materials. © 1995 John Wiley & Sons, Inc.
Kinetic study of release of silicon compounds from polysiloxane tissue expanders
Authors: Raimondi M. L. , Sassara C. , Bellobono Ignazio Renato , Matturri L.
Published: May 2005

The release behavior of typical commercial tissue expanders has been examined by carrying out two kinds of experiments: (1) Determination of chemical nature and its modification after in vivo use by X‐ray photoelectron spectroscopy for chemical analysis. This study has been parallelled by scanning electron microscopy with associated energy dispersive X‐ray analysis of surface, as well as by silicon compounds analysis of tissues around implants. (2) Kinetic examination of silicon compounds released by the biomaterial in physiologic solution at 36 ± 0.3°C. Results of these investigations have shown independently that the starting material was not a filler‐free, pure polymer, but a composite, reinforced elastomer, with the reinforcing agent most seemingly represented by silicon dioxide. Release of latter, with a relatively fast kinetics, is compatible with data of the simulating laboratory runs in the physiologic solution. All these facts seem to rule out any hypothesis of a prevailing siloxane oligomer migration. The correlation of kinetic and physicochemical tests with the in vivo behavior is discussed. © 1995 John Wiley & Sons, Inc.
Crystal structure of the surface oxide layer on titanium and its changes arising from immersion
Authors: Effah E. A. B. , Bianco P. D. , Ducheyne P.
Published: May 2005

The passivating surface oxide on titanium is one of the elements considered in the explanation of the favorable biolgic response of this metal in implant applications. In the present study, transmission electron microscopy was used to identify the crystal structure and morphology of the oxide film on commercially pure titanium specimens befor and after immersion in simulated physiologic fluids. The results show that the oxide layer is composed mainly of anatase and rutile, both of which are tetragonal in structure. Although the simulated physiologic fluids did not induce an observable change in the crystal structure for the immersion times investigated, the results indicate an immersion‐induced change in microstructure from a finegrained to a coarser‐grained structure. The grain growth observed could be attributed to the growth of the native oxide crystals; however, it most likely results from the formation of a new oxide layer. The results also support oxide thickening as one of the processes associated with passive dissolution of titanium. © 1995 John Wiley & Sons, Inc.
Variation in contact guidance by human cells on a microstructured surface
Authors: Meyle J. , Gültig K. , Nisch W.
Published: May 2005

Contact guidance induced by the surface topography of the underlying substratum influences the interaction of tissue cells with implanted material. It was the aim of this study to compare the reaction of different human cells on the same surface microtexture. After staining with fluoresceinediacetate, the orientation of human fibroblasts, gingival keratinocytes, neutrophils, monocytes, and macrophages on a regular surface microstructure of 1 μm pitch and 1 μm depth was analyzed by fluorescence microscopy. Contact guidance could not be observed in the experiments with keratinocytes and neutrophils, but 100% of the fibroblasts and approximately 20% of the monocytes and macrophages reacted with alignment. After 2 h some of the macrophages extended long dendritic cellular processes parallel to the long axis of the microstructures. © 1995 John Wiley & Sons, Inc.
Simple technique for the preparation of silicone gel particles: The effect of silicone gel particles on oxidative responses of macrophages
Authors: Azizsoltani E. , Myrvik Q. N. , Foster L. A. , Giridhar G. , Gristina A. G.
Published: May 2005

A simple technique was developed to prepare phagocytosable‐size particles from the silicone gel used in breast implants. Sonication of silicone gel (1 g) in 5 ml of 20 mM sodium phosphate buffer (pH 7.2) containing 1% (wt/vol) polyoxypropylene‐polyethylene block surfactant (F‐68 or F‐108) produced silicone gel particles ranging from 1–50 μm in diameter. Passage of the suspension through a series of filters yielded phagocytosable particles (1–5 μm in diameter) at a concentration of ca. 2 × 109 particles/ml. The particles remained as individual particles, did not coalesce to form large clumps, and were not pelleted by centrifugation (2000 × g, 20 min). They were not toxic for rabbit alveolar macrophages (AM) during 24 h of incubation at 37°C, did not elicit an oxidative burst from AM in vitro in a luminolenhanced chemiluminescent assay, and did not significantly increase the phorbol myristate acetate (PMA)‐elicited oxidative burst by AM. AM isolated from rabbits 2 days after the intravenous injection of silicone particles were not primed or activated (i.e., the AM did not show an enhanced oxidative burst when elicited with PMA in vitro). However, AM isolated from rabbits 2 days after intratracheal injection of the particles were primed but only exhibited a 4–6‐fold increase in the oxidative burst elicited with PMA. © 1995 John Wiley & Sons, Inc.
Effects of a structural change in collagen upon binding to conditioned dentin studied by 13C NMR
Authors: Nishiyama Norihiro , Asakura Tetsuo , Suzuki Kazuomi , Horie Kozo , Nemoto Kimiya
Published: May 2005

To develop a better adhesive functional monomer, it is imperative to understand the adhesion mechanisms of the resin to the dentin surface. Bond strength to the decalcified dentin surface pretreated with dentin primer, an aqueous ethanol solution of N‐methacryloyl glycine, increases by increasing the water content in the primer. The aqueous primer could increase the thickness of the hybrid layer. The structural change of dentinal collagen with NMαA was studied by using a model compound for collagen,—(1Pro‐2Pro‐3Gly)10—, by 13C nuclear magnetic resonance (NMR). The model compound was aggregated in ethanol but dissociated in water. It was found that NMαA effectively dissociated the aggregated model compound in water. The dissociation of decalcified dentin was essential to create a thick hybrid layer that could afford a higher bond strength to dentin. © 1995 John Wiley & Sons, Inc.