bluuebunny/crossref_metadata_2025 huggingface dataset:
A histological and histomorphometrical investigation of fluorapatite, magnesiumwhitlockite, and hydroxylapatite plasma‐sprayed coatings in goats
Authors: Dhert W. J. A. , Klein C. P. A. T. , Jansen J. A. , van der Velde E. A. , Vriesde R. C. , Rozing P. M. , de Groot K.
Published: December 2004

Plasma‐sprayed ceramic coatings of fluorapatite (FA), magnesiumwhitlockite (MW), and hydroxylapatite (HA), and noncoated Ti‐6Al‐4V alloy (Ti) implants were evaluated histologically and histomorphometrically in a goat animal study. Cylindrical Ti‐6Al‐4V plugs were plasma‐spray‐coated with FA, MW, and HA. Noncoated, gritblasted Ti plugs served as controls. The plugs were implanted into the right femur and left humerus of 20 adults goats. The results were evaluated using descriptive histology and histomorphometry. The histomorphometry consisted of measurements of bone apposition and coating thickness. The results demonstrated that FA showed a high amount of bone apposition without signs of degradation or dissolution. MW showed considerable reduction in thickness and at 12 weeks an adverse tissue reaction. However, at 25 weeks the amount of bone apposition was significantly increased compared with the 12‐week implants. HA revealed considerable and progressive reduction in thickness and at 25 weeks a lower amount of bone apposition than FA and MW. At 12 weeks the Ti implants did reveal bone apposition, although frequently localized fibrous tissue was visible. At 25 weeks the Ti implants did not differ in bone apposition from the HA implants. Further studies are necessary on the effect of degradation or dissolution of HA on the compatibility with bone. © 1993 John Wiley & Sons, Inc.
Organoapatites: Materials for artificial bone. II. Hardening reactions and properties
Authors: Stupp Samuel I. , Mejicano George C. , Hanson Jacqueline A.
Published: December 2004

This article reports on chemical reactions and the properties they generated in artificial bone materials termed “organoapatites.” These materials are synthesized using methodology we reported in the previous article of this series1. Two different processes were studied here for the transition from organoapatite particles to implants suitable for the restoration of the skeletal system. One process involved the hardening of powder compacts by beams of blue light derived from a lamp or a laser and the other involved pressure‐induced interdiffusion of polymers. In both cases, the hardening reaction involved the formation of a polyion complex between two polyelectrolytes. In the photo‐induced reaction an anionic electrolyte polymerizes to from the coulombic network and in the pressure‐induced one, pressure forms the complex by interdiffusion of two polyions. Model reactions were studied using various polycations. Based on these results the organoapatite selected for the study was that containing dispersed poly(L‐lysine) and sodium acrylate as the anionic monomer. The organomineral particles can be pressed at room temperature into objects of great physical integrity and hydrolytic stability relative to anorganic controls. The remarkable fact about these objects is that intimate molecular dispersion of only 2–3% by weight organic material provides integrity to the mineral network in an aqueous medium and also doubles its tensile strength. This integrity is essentially nonexistent in “anorganic” samples prepared by the same methodology used in organoapatite synthesis. The improvement in properties was most effectively produced by molecular bridges formed by photopolymerization. The photopolymerization leads to the “hardening” of pellets prepared by pressing of organoapatite powders. The reaction was found to be more facile in the microstructure of the organomineral, and it is potentially useful in the surgical application of organoapatites as artificial bone. © 1993 John Wiley & Sons, Inc.
Variations between biomer lots. 2: The effect of differences between lots on in vitro enzymatic and oxidative degradation of a commercial polyurethane
Authors: Tyler Bonnie J. , Ratner Buddy D.
Published: December 2004

In vitro degradation of two lots of Biomer, a commercial poly(ether urethane urea), has been investigated in order to understand possible mechanisms for in vivo degradation. Two lots of Biomer, BSUA001 and BSP067, were used in the study. Lot BSUA001 contained a poly(diisopropylaminoethyl‐methacrylate), an ultraviolet‐stabilizing additive. This additive was absent in lot BSP067. Samples of each lot were exposed to two hydrolytic enzymes, papain and leucine aminopeptidase, and to hydrogen peroxide for 24 h. The extent of degradation was assessed using high‐pressure gel permeation chromatography and x‐ray photoelectron spectroscopy (XPS). Statistically significant changes in the molecular‐weight distribution occured in lot BSP067 for all three treatments. Only the hydrogen peroxide treatment resulted in statistically significant changes in the molecular weight of lot BSUA001. XPS data for samples of lot BSUA001 that had been treated with hydrogen peroxide revealed the formation of nitroso groups and protonated amines at the surface. The data suggest that surface chemistry is important for enzyme catalyzed degradation, while permeability is important for degradation by hydrogen peroxide. © 1993 John Wiley & Sons, Inc.
Platelet deposition onto polymeric surfaces during shunting
Authors: Fujimoto Keiji , Minato Masao , Tadokoro Hideki , Ikada Yoshito
Published: December 2004

In an attempt to develop blood‐contacting tubes that can be applied for short‐term uses with a reduced heparin concentration or, ideally, without heparinization, we evaluated the blood compatibility of polymeric materials with a rabbit ex vivo shunt model. The shunt tubes employed were made of silicone, plasticized poly(vinyl chloride) (PVC), and segmented poly(ether urethane) (PU). In addition, two kinds of surface‐modified tube were used: poly(vinyl alcohol) (PVA)‐coated PVC and poly(dimethylacrylamide) (PDMAA)‐grafted PU. The ex vivo shunt results correlated well with protein adsorption and platelet adhesion in vitro. The following order for the extent of platelet deposition was given, irrespective of the blood‐contacting duration: PDMAA‐grafted PU < PVA‐coated PVC < PU < silicone, PVC. It is likely that many platelet aggregates detached from the PVA‐coated PVC surface. For PDMAA‐grafted PU, no trace of detachment of aggregates could be detected on any of the SEM photographs. The number and morphology of blood cells adhered onto the tube surfaces during ex vivo shunting were dependent on the kind of polymer surfaces, the blood exposure time, and the flow rate of blood. © 1993 John Wiley & Sons, Inc.
Dissolution and scanning electron microscopic studies of Ca,P particle‐containing bioactive glasses
Authors: Kangasniemi I. M. O. , Vedel E. , de Blick‐Hogerworst J. , Yli‐Urpo A. U. , de Groot K.
Published: December 2004

Calcium phosphate (Ca, P) precipitation behavior on the surface of two bioactive glasses and four bioactive glass composites—two with hydroxylapatite (Ca10(PO4)6(OH)2) and two with rhenanite (CaNaPO4)—were studied in simulated body fluid (SBF) and in Tris‐Buffer at 5, 8, 16, 24, 48, 72, and 144 h. The Weight loss of the materials was measured and the amount of precipitation was estimated using scanning electron microscopy with electrochemical detection (SEM‐EDX) analysis. The test was repeated for one glass and its respective rhenanite composite every 3 h until 60 h and thereafter every 10 h until 150 h in SBF. Atomic absorption spectroscopy, spectrophotometry, SEM‐EDX analysis, and pH measurements were performed on these samples. It is shown that in vitro the composite materials have a higher capacity for Ca, P precipitation than the glasses. Weight losses of the materials correlate well with their composition. Both the glass and Ca, P phases influence the precipitation mechanism and rate. Precipitation begins preferably from the glass phase. Ca, P particles clearly influence the time of onset and rate of precipitation. Cross‐sectional EDX analysis of the samples revealed an absence of a clear Sirich layer in glass AOBO (SiO2 53.9 mol %, Na2O 27.5, CaO 12.4, P2O5 6.2, Al2O3 0.0 and B2O3 0.0) composites. This was attributed to the presence of extra calcium and phosphate ions on the surface of the material. The ion‐concentration and pH change curves offered insight into the mechanism of precipitation. A connection was established between SEM‐EDX results and the release curves. Formation of an Si, Ca, Na film was observed that seemed to initiate the Ca, P precipitation. It is speculated that it is a characteristic of this particular glass composition. Two possible models for the mechanism of Ca, P precipitation are discussed. Phosphate polycondensation with silicate network or Ca binding to silicate network can both explain the results and it is assumed that in general both mechanisms play a role in the precipitation process. © 1993 John Wiley & Sons, Inc.
Compliance effects on small diameter polyurethane graft patency
Authors: Uchida Naoki , Kambic Helen , Emoto Hideto , Chen Ji‐Feng , Hsu Shan‐Hui , Murabayshi Shun , Harasaki Hiroaki , Nosé Yukihiko
Published: December 2004

Microporous compliance matched and noncompliant grafts were compared in a dog carotid artery interposition model. We fabricated 4 mm diameter sponge type polyurethane (Biomer) tubes 5 cm in length with a 0.5 mm wall thickness. The luminal surface was covered with a 50 μm coating of cross‐linked gelatin. Compliance was measured in vitro and in vivo by volume and vessel diameter changes. Over a mean arterial pressure range of 55–155 mm Hg, the diameter changes of grafts and stump arteries were measured in situ using an ultrasonic Hokanson device. Compliance matched grafts were found to have the same in vitro compliance values as the natural canine carotid at a mean arterial pressure of 100 mm Hg. Compliance matched and noncompliant grafts had values of 10.3 ± 1.3 and 0.9 ± 0.1 × 10−2 mm Hg, respectively. End to end arterial anastomoses were constructed between the graft and the host arteries.

The use of synthetic grafts with matched compliance to the adjacent natural vessels has been advocated as the ideal solution to circumvent the problems of graft failure. These studies indicate that compliance values for compliance matched grafts decreased immediately after implantation (from 10.3 to 6.5 × 10−2 %/mm Hg) and within 6 weeks decreased to 3.6 × 10−2 %/mm Hg. The compliance values for noncompliant grafts remained constant throughout the test period.

At autopsy all grafts showed a tightly adhered tissue capsule. The thickness of the anastomotic hyperplasia at the distal sites of compliance matched grafts was significantly different (P < .05) than that of the adjacent artery. The patency for compliant and noncompliant grafts was 64% and 50%, respectively. Evidence for polyurethane graft degradation was obtained by Fourier transform infrared spectroscopy and gel permeation chromatography analysis of patent explants. Compliance mismatch alone does not contribute to graft failure, however, material degradation, suture technique and/or capsule formation can play a contributory role although these were not tested directly. © 1993 John Wiley & Sons, Inc.
Development of FRP composite structural biomaterials: Fatigue strength of the fiber/matrix interfacial bond in simulatedin vivoenvironments
Authors: Latour R. A. , Black J.
Published: December 2004

Fiber/matrix interfacial bonding in fiber reinforced polymer (FRP) composite materials is potentially sensitive to degradation in aqueous environments. Ultimate bond strength (UBS) in carbon fiber/polysulfone (CF/PSF) and polyaramid/polysulfone (K49/PSF) was previously reported to be significantly decreased in two simulatedin vivoenvironments. While UBS is a useful parameter, for orthopedic implant applications the fatigue behavior of the interface is probably a more relevant indicator of long‐term composite material performance. In this article, the effects of simulatedin vivoenvironments (saline, exudate) upon the fatigue behavior of the interface of CF/PSF and K49/PSF are reported. The fatigue behavior of both material combinations was linearly dependent on the logarithm of fatigue life in the dry (control), saline, and exudate environments. Testing either material in saline and exudate resulted in significantly lower fatigue strength than in the dry environment; however, results in the two wet environments were indistinguishable. The CF/PSF interface experienced fatigue failure at approximately 105load cycles at a maximum applied load level of only 15% of its ultimate dry bond strength without indication of a endurance limit being reached. These results raise some important questions regarding the durability of CF/PSF composite in load bearing orthopedic applications. © 1993 John Wiley & Sons, Inc.
Quantification of the edge effect in calcified bioprosthetic tissues
Authors: Wika Kent E. , Utoh Junichi , Brown Joy , Harasaki Hiroaki
Published: December 2004

In bioprosthetic tissue samples that had been implanted in the subcutaneous space of rats, and recurring pattern of calcification was observed. In this pattern, which we call the edge effect, the interior of the tissue is calcified and is surrounded and separated from the subcutaneous fluid by a zone that is free from calcification. The edge effect has been qualitatively described in the literature for subcutaneous implants and for valve leaflets, and it may be related to the mechanism of calcification for these materials. The thickness of the calcification free outer layer was quantified for glutaraldehyde treated bovine pericardium, glycerol treated bovine pericardium, glutaraldehyde treated human dura mater, and glycerol treated human dura mater. The edge effect values were found to be unique and consistent for each material type, and they were inversely related to the shrinkage temperatures and the calcium contents of the materials. It was determined that the chemical treatment was more important than the tissue type in determining the edge effect value. © 1993 John Wiley & Sons, Inc.
Chemical durability of Y2O3‐Al2O3‐SiO2 glasses for the in vivo delivery of beta radiation
Authors: Erbe Erik M. , Day Delbert E.
Published: December 2004

Microspheres made from Y2O3‐Al2O3‐SiO2 (YAS) glasses, which contain radioactive Y‐90, are currently being used to treat liver cancer in humans, where their chemical durability is of prime importance. In deionized water or saline at 37°C, the weight percent Yttrium (Y) dissolved from eight different YAS glasses ranged from only 0.02–0.13% of the total Y present and their dissolution rate was barely measurable, ≤ 1.0 × 10−9 g/cm2‐min. The most chemically durable YAS glass was 17Y2O3‐19Al2O3‐64SiO2, mol %. The small amount of Y released from microspheres, 25–35 μm diameter, of this glass after corrosion in saline or deionized water at 37°C was essentially the same as for bulk glass samples. Based on their excellent chemical durability, it is concluded that YAS glass microspheres are suitable for in vivo use. © 1993 John Wiley & Sons, Inc.
The shear strength and the failure mode of plasma‐sprayed hydroxyapatite coating to bone: The effect of coating thickness
Authors: Wang B. C. , Lee T. M. , Chang E. , Yang C. Y.
Published: December 2004

Plasma‐sprayed hydroxyapatite coated (HAC) 50 and 200 μm thick on Ti‐6Al‐4v cylinders was transcortically implanted in the femora of canines to to evaluate in detail the effect of coating thickness on the pushout shear strength and failure mode examined under scanning electron microscope after the periods of 4, 6, 8, and 12 weeks. The HAC coating exhibited higher shear strength at 50 μm than at 200 μm. Its failure mode was conclusively at or near the HAC–bone interface, and the slight attack of body fluid had not degraded the implant to the extent that failure occurred at the HAC‐Ti alloy interface after 12 weeks of observation. For 200 μm‐HAC, failure was found at the HAC–bone interface, inside the HAC lamellar splat layer and at the HAC‐Ti alloy substrate interface, depending on the period of implantation. It was also deduced that the variation of failure mode of 200 μm‐HAC with time could not be accounted for by the attack of body fluid alone; the degradation must be a synergetic adverse result of residual stress in the HAC and the attack of body fluid. © 1993 John Wiley & Sons, Inc.
Bicomponent vascular grafts consisting of synthetic absorbable fibers. I. In vitro study
Authors: Yu Tarng‐Jenn , Chu C. C.
Published: December 2004

The objective of this study is to determine the effects of the location and concentration of synthetic absorbable yarn components in bicomponent vascular graft fabrics on their structure and properties in a controlled in vitro hydrolytic environment. Bicomponent vascular fabrics were made from Dacron and polyglycolic acid (PGA) yarns with a range of composition ratios of PGA to Dacron and a range of locations of PGA. Both woven and single jersey knit fabrics were made. These fabrics were characterized by standard textile methods and subject to in vitro hydrolytic degradation study. In vitro hydrolytic degradation study showed that the most dramatic changes in the bicomponent fabric characteristics and properties occurred 30 and 60 days of hydrolysis. This schedule coincided with the hydrolytic degradation rate of PGA absorbable sutures. In the woven (W) group, the incorporation of absorbable yarns in the weft direction (W3) of the bicomponent fabrics resulted in the velour‐like, loose, and porous surface morphology of the fabric for potential subsequent tissue ingrowth, while those woven fabrics with absorbable yarns in the warp direction (W1) did not have this unique velour‐like surface. In the knitted (K) group, the concentration of absorbable yarns appeared to be closely related to the observed changes in fabric properties and structure. The incorporation of absorbable yarns into knitted fabrics did not result in the same level change in fabric structure and property as woven fabrics. In both W and K groups, a minimal level of mechanical strength of the fabrics was maintained due to the remaining Dacron yarns. Structural integrity of these fabrics was retained at the end of hydrolytic degradation study. The data obtained could be used to correlate with the subsequent in vivo performance of these bicomponent vascular grafts. If correlations exist, they could be used to improve the design of future bicomponent vascular grafts for improved performance. © 1993 John Wiley & Sons, Inc.
Degradation of polyurethane foams used in the mêcme breast implant
Authors: Benoit Frank M.
Published: December 2004

The release of toluene diisocyanate derivatives from polyurethane foam covers that were removed from the Měme breast implant was studied. The polyurethane foam covers as retrieved from the implants were contaminated on average with 2,4‐ and 2,6‐toluene diamine (TDA), 2,4‐ and 2,6‐toluene diisocyanate (TDI), and toluene isocyanate amine (TIA) at the 1086 ppm level (combined TDA, TDI, and TIA). When cleaned foam was incubated in Ringer's solution at 37°C for periods ranging from 6–35 days, 4.6 ppm/day of TDA, TDI, and TIA (combined) was formed; the projected annual degradation rate of the foam under these conditions was estimated to be about 0.8%. When cleaned foam was incubated dry at 37°C, 1.5 ppm/day of TDA, TDI, and TIA (combined) was produced. Hence, the polyurethane foam covers used in the Měme breast implants are susceptible to both thermal and hydrolytic degradation under simulated physiological conditions. © 1993 John Wiley & Sons, Inc.
Endothelial cell compatibility testing of three different Pellethanes
Authors: Bordenave L. , Baquey Ch. , Bareille R. , Lefebvre F. , Lauroua C. , Guerin V. , Rouais F. , More N. , Vergnes Ch. , Anderson J. M.
Published: December 2004

There is a need for viable small diameter vascular grafts, the luminal surface of which could be seeded by endothelial cells (ECs) to prevent thrombosis. In order to select candidates for EC seeding before implantation, the in vitro cytocompatibility of three different Pellethanes® (polyetherurethanes) using human ECs was investigated. The methodology included two stages depending on either direct contact between cells and materials or contact between cells and material extracts, obtained under standardized conditions. By the latter method, we observed a cytotoxic effect on cell growth with 2363‐55 D Pellethane extract at a 50% (v/v) concentration in the nutrient medium, likely provoked by leachables and correlated with the lowest levels of tPA, PAI1, and vWF antigens in the supernatants. By the former method, we studied EC attachment and growth. Morphology was studied by classical means and completed by scintigraphy and microautoradiography after 111Indium‐labeling of the EC monolayer. Differentiation was determined by the release of vWF antigen and measurement of vWF activity (multimeric organization) after human thrombin stimulation. Despite an inhibition of proliferation for both 55 D and 75 D types (compared to the control), a functional monolayer of ECs was obtained on 75 D. Pellethane 75 D could be the best support for in vitro endothelialization. © 1993 John Wiley & Sons, Inc.
Osteogenic differentiation of marrow stromal stem cells in porous hydroxyapatite ceramics
Authors: Ohgushi Hajime , Dohi Yoshiko , Tamai Susumu , Tabata Shiro
Published: December 2004

Bioactive materials such as hydroxyapatite ceramics (HA) are known to show a stable interfacial bond with tissues (the bone bonding property has been especially well documented). However, the biological phenomenon on the material surface that evoke bone bonding is not well documented. To address this issue, composites of porous HA and rat marrow cells were implanted into ectopic (subcutaneous) sites. At 3 weeks after implantation, active osteoblasts lining the HA surface initiated bone formation, primarily as mature bone (lamellar type). Gene expression study using Northern blot analysis of the composites showed that alkaline phosphatase (ALP) and bone Gla protein (BGP) mRNAs began to appear at 2 weeks and the level of BGP mRNA at 4 weeks was comparable to that of cancerous bone. However, HA implantation without marrow cells did not show bone formation and neither BGP nor ALP mRNA were detected. These results indicate that the HA surface is able to support cell differentiation (osteoblastic phenotype expression of marrow stromal stem cells), as well as cell coordination resulting in mature bone formation that bonds to the HA. © 1993 John Wiley & Sons, Inc.
Difference in bone ingrowth after one versus two daily episodes of micromotion: Experiments with titanium chambers in rabbits
Authors: Goodman Stuart , Wang Jian‐Sheng , Doshi Amol , Aspenberg Per
Published: December 2004

Mechanical stimulation has been shown to affect the differentiation and development of mesenchymal tissue. In the present study, we compared the histological and histomorphometric results of tissue ingrowth into micromotion chambers that were moved at 0 cycles per day, 20 cycles once per day, and 20 cycles twice per day over 20–30 sec, for 3 weeks. In each case, a chamber having a 1 × 1 × 5 mm square‐holed groove for tissue ingrowth was used. The total amplitude of motion was 0.75 mm. Histological sections from nonmoved chambers contained extensive trabecular bone, embedded in a fibrovascular stroma. Histomorphometric analysis disclosed that bone comprised a mean of 31 ± 2% (mean ± SEM) of the ingrown tissue. Twenty movements per day appeared to further stimulate bone ingrowth (46 ± 5%). Extensive ingrowth of more immature woven and trabecular bone was noted in a more cellular stroma. In general, increasing the degree of micromotion to 20 movements twice per day resulted in a decreased amount of bone formation (19 ± 7%). In several of these specimens, little or no bone could be found. These experiments have demonstrated that, for the parameters chosen in this study, a short daily period of low frequency, micromotion may facilitate bone ingrowth; however, when the same motion is delivered twice daily, bone ingrowth is depressed. Thus a “window” of externally applied strain appears to exist, which may facilitate or discourage tissue differentiation to bone. © 1993 John Wiley & Sons, Inc.
Inhibition of calcification of glutaraldehyde pretreated porcine aortic valve cusps with sodium dodecyl sulfate: Preincubation and controlled release studies
Authors: Hirsch Danielle , Drader Joelle , Thomas Theresa J. , Schoen Frederick J. , Levy Judith T. , Levy Robert J.
Published: December 2004

Calcification of bioprosthetic heart valves fabricated from glutaraldehyde pretreated bovine pericardium or porcine aortic valves (PAV) is a frequent cause of the failure of these devices. Of all strategies considered thus far, only detergent preincubations using compounds such as sodium dodecyl sulfate (SDS) ingibited PAV bioprosthetic mineralization in circulatory sheep bioprosthetic valve replacements. The present study sought to characterize the mechanism of action of SDS preincubation. Results of transport and material characterization studies showed that SDS had a relatively high affinity for PAV, with a maximum uptake of 167.1 ± 6.8 μg SDS/mg tissue over 24 h at 37°C with a partition coefficient of 19.3. The PAV diffusion of SDS was 1.95 ± 0.35 10−6 cm2/sec. The principal effect of SDS on PAV was phospholipid extraction. The residual organic phospholipid extraction. The residual organic phosphate in the SDS pretreated tissue was 2.22 ± 0.72 nmol/mg tissue compared to the control untreated group with 18.52 ± 2.1 nmol/mg tissue. Incubations of PAV specimens in a 1% SDS solution for 24 h significantly inhibited calcification after 21 days in subdermal implants in 3‐week‐old male rats (PAV Ca2+ = 18.0 ± 11.8 μg/mg) compared to control (177.8 ± 6.0 μg/mg). In contrast, coimplants of 30% SDS silicone rubber polymers, for regional sustained SDS administration, did not impede PAV calcification in 21 day implants Ca2+ = 166.0 ± 14.0 μg/mg compared to the nondrug silicone matrix controls, (Ca2+ = 173.0 ± 6.6 μg/mg). Thus, we conclude that the mechanisms of SDS inhibition of PAV calcification is due to material effects which occur during preincubation, and is not facilitated by sustained SDS administration. © 1993 John Wiley & Sons, Inc.
Calcium phosphate formation within sol‐gel prepared titania in vitro and in vivo
Authors: Li Panjian , de Groot K.
Published: December 2004

Calcium phosphate formation is induced within sol‐gel prepared titania and grows toward a calcium phosphate solution in which the titania is immersed. The implantation of this sol‐gel prepared titania film coating on TiA16V4 core into the femurs of goats shows an accumulation of calcium phosphate within the titania film 12 weeks postoperatively, which leads to the connection of the titania film coating to the bone. Therefore, sol‐gel prepared titania is probably bioactive. The results indicate that hydrated titania gel is able to generate calcium phosphate by intake of calcium and phosphate from the surrounding solution. Sufficient TiOH concentration at the titania surface is needed to start this process. Titanium could be bioactive, if its hydrolysis can be accelerated. © 1993 John Wiley & Sons, Inc.
Prevention of changes in platelet cytoplasmic free calcium levels by interaction with 2‐hydroxyethyl methacrylate/styrene block copolymer surfaces
Authors: Okano Teruo , Suzuki Ken , Yui Nobuhiko , Sakurai Yasuhisa , Nakahama Seiichi
Published: December 2004

Changes in platelet cytoplasmic free calcium levels were investigated in contact with cast film surfaces of a block copolymer containing 2‐hydroxyethyl methacrylate (HEMA) and styrene (St) (0.5 mole fraction HEMA). These copolymer surfaces demonstrate microdomain alternating lamellae structures composed of hydrophilic HEMA domains (5 nm width) and hydrophobic St domains (20 nm width). The results were compared with those obtained from platelets contacting a random copolymer of HEMA‐St (0.5 mole fraction HEMA) and from homopolymers of polystyrene (PSt) and poly(2‐hydroxyethyl methacrylate) (HEMA). Cytoplasmic free calcium levels in platelets contacting the microdomain structured surfaces of the HEMA‐St block copolymer remained relatively constant in contrast to the significant increases observed for the radically prepared HEMA‐St copolymer, PSt, and PHEMA surfaces. Adhering platelets were stimulated by exogenously introduced thrombin and calcium ionophore A23187 20 min after platelet adherence to the polymer surfaces. Only platelets on the block copolymer surfaces showed active metabolic responses. These results suggest that adhering platelets on the microdomain structured surfaces maintain high sensitivities to external stimulation due to an intrinsic strong inhibition of platelet functional changes induced by surface contact. © 1993 John Wiley & Sons, Inc.
Hydroxylapatite supported Dacron plugs for repair of isolated full‐thickness osteochondral defects of the rabbit femoral condyle: Mechanical and histological evaluations from 6–48 weeks
Authors: Messner Karola
Published: December 2004

The early degeneration of neocartilage commonly observed after experimental cartilage repair is attributed in part to the impaired cartilage‐bone mechanics caused by an insufficient regrowth of the subchondral bone plate. In order to enhance bone regrowth after cartilage repair Dacron plugs supported by hydroxylapatite were implanted into 3 mm diameter full‐thickness defects of both medial femoral condyles in 21 rabbits. In addition, the plug in one knee of each animal was wrapped with autologeous periosteum from the proximal tibia. The repair sites were evaluated at 6, 12, 24, and 48 weeks. Except for the mechanics of the repair site at 24 weeks additional periosteum did not improve the overall results. In specimens with additional periosteum the compression compliance of the repair sites improved gradually from abnormal high to almost normal values at 24 weeks, but were found softened again at 48 weeks. All other repairs were softer than normal cartilage at all time intervals. In all specimens a well‐defined byt irregularly shaped, subchondral bone plate had developed by 12 weeks. The neocartilage was initially thicker than normal cartilage, but the thickness decreased gradually and reached normal values by 48 months. Neocartilage formation with moderate morphological scores appeared already at 6 weeks, but the scores did not improve with time. High variations in quality of the regenerated tissue, from insufficient regeneration to hyaline‐like cartilage, were found at all time intervals, but none of the specimens had developed normal cartilage. Most knees had a low‐grade synovitis and some had particle debris. © 1993 John Wiley & Sons, Inc.
Fibroblast anchorage to microtextured surfaces
Authors: Meyle J. , Gültig K. , Wolburg H. , von Recum A. F.
Published: December 2004

The contact between tissue and the implanted biomaterial is influenced by the micromorphology of the implant surface as well as biomechanical reactions. This effect is mediated by subcellular morphological structures and can affect the anchorage of the material inside the body of the host. The aim of the present study was to ascertain by transmission electron microscopy how human gingival fibroblasts interact with surface events. A special replica technique was used to produce a line pattern of 1 μm pitch with a depth of 1 μm. It was demonstrated, by transmission electron microscopy, that cells seeded on this surface extended cellular processes into the grooves, leading to an intensive contact and probably to mechanical interlocking. The typical morphological structures at several points indicated the presence of focal adhesion sites. © 1993 John Wiley & Sons, Inc.
Protein adsorption and platelet adhesion onto polyurethane grafted with methoxy‐poly(ethylene glycol) methacrylate by plasma technique
Authors: Fujimoto Keiji , Inoue Hiroyuki , Ikada Yoshito
Published: December 2004

Graft polymerization of methoxy‐poly(ethylene glycol) methacrylate, an ester of methacrylic acid and monomethoxy‐poly(ethylene glycol) (PEO), was performed onto a polyetherurethane (PU) film and tube under different polymerization conditions by a plasma treatment technique. The surface of grafted PU film was characterized by staining with dye, x‐ray photoelectron spectroscopy, contact angle, and zeta potential. All these measurements indicated that water‐soluble chains were immobilized on the PU surface, their location being restricted to the film surface region. The PU surface showed reduced protein adsorption in vitro and reduced platelet adhesion in vitro and ex vivo. The optimum graft density suppressing the protein adsorption was as low as 5 μg cm−2. When a small amount of dimethacrylate was added to the monomer solution for graft polymerization to introduce crosslinking in the grafted layer, protein adsorption was further slightly reduced. The extent of reduction in serum albumin adsorption was always less than that of γ‐globulin. Although platelet adhesion was largely reduced by the surface graft polymerization, a definite amount of protein was always adsorbed to the grafted surface. © 1993 John Wiley & Sons, Inc.
Development of a glass reinforced hydroxyapatite with enhanced mechanical properties. The effect of glass composition on mechanical properties and its relationship to phase changes
Authors: Knowles J. C. , Bonfield W.
Published: December 2004

Utilizing glasses of the types xNa2O‐(1−x)P2O5 and xCaO‐(1−x)P2O5 (where x = 0.2, 0.3, and 0.5), a systematic study of the effect of increasing network modifying oxides in glasses was made on the mechanical properties of a glass reinforced hydroxyapatite, at glass additions of 2.5 and 5 wt%. For the soda type glass, phase changes were promoted much more readily compared to the lime type glass. This was true for both 2.5 and 5 wt% additions of glass. For the lime type glass, considerable differences between the effects of 2.5 and 5 wt% additions were seen. At 5 wt%, the increased amount of liquid phase present promotes an increased level of phase inversion to alpha and beta tricalcium phosphate. At 2.5 wt%, a larger percentage of the HA remains stable at higher temperatures. Furthermore, the effect of the composition may be seen. As the mol% of network forming oxide increases, (i.e., the Ca/P ratio moves towards 1.67, the ratio for HA) the HA remains more stable. This is seen in the maintenance of both the HA phase and also the enhanced mechanical properties. © 1993 John Wiley & Sons, Inc.
Changes in the mechanical properties of dermal sheep collagen during in vitro degradation
Authors: Damink L. H. H. Olde , Dijkstra P. J. , Van Luyn M. J. A. , Van Wachem P. B. , Nieuwenhuis P. , Feijen J.
Published: December 2004

The changes in tensile strength, elongation at break, and high strain modulus of dermal sheep collagen (DSC) during in vitro degradation using bacterial collagenase were studied. The changes in mechanical properties were compared with the change in weight of the samples as a function of degradation time. DSC was crosslinked with either glutaraldehyde (GA) or hexamethylene diisocyanate (HMDIC). During degradation, the changes in mechanical properties of the N‐DSC, H‐DSC or G‐DSC samples were more pronounced than the changes in the weight of the samples. Of the mechanical properties studied, the tensile strength was most susceptible to degradation of the DSC samples. After 2.5 h, N‐DSC samples had lost only 55% of their initial weight, but the samples had no tensile strength left. Similar results were obtained for H‐DSC, which retained no tensile strength after 24 h degradation, whereas only 45% of the initial weight was lost. G‐DSC lost 3.5% of its weight after 24 h degradation, but only 25% of the initial tensile strength remained. © 1995 John Wiley & Sons, Inc.
Biocompatibility study of as‐polymerized poly(L‐lactide) in rats using a cage implant system
Authors: Bergsma J. E. , Rozema F. R. , Bos R. R. M. , Boering G. , de Bruijn W. C. , Pennings A. J.
Published: December 2004

To evaluate the biocompatibility of in vitro predegraded as polymerized poly(L‐lactide) (PLLA), a cage implant system was used to investigate white cell and enzyme concentrations with time. The use of a cage permits in a serial fashion a quantitative and qualitative measurement of exudate components formed around an implant. Subcutaneously in rats, caped cages manufactured from stainless‐steel mesh were implanted with in vitro predegraded, as‐polymerized PLLA, as‐polymerized PLLA cylinders, and empty cages serving as controls. In vitro predegradation was used to simulate the degradation products of long‐term in vitro degradation. Predegraded PLLA particles were obtained by in vitro hydrolysis at elevated temperatures. The first 7 days of implantation were characterized by an acute inflammatory reaction; the exudate extracted from the cages showed predominantly neutrophils for all types of implants. After day 7, there was a more chronic inflammatory reaction with predominantly macrophages and lymphocytes. There were no significant differences in the total leukocyte concentration or macrophage concentration for any of the cages in the period from 10–21 days. Extracellular enzyme activity also did not show any significant differences among the three types of cages. A possible explanation for the absence of any significant differences could be that the in vitro predegraded particles were sieved before implantation, thus eliminating all small particles (≤ 70 μm) that are probably mandatory to provoke an increased cellular reaction. © 1995 John Wiley & Sons, Inc.
Histopathologic study following administration of liposome‐encapsulated hemoglobin in the normovolemic rat
Authors: Rudolph Alan S. , Spielberg Helmut , Spargo Barry J. , Kossovsky Nir
Published: December 2004

Liposome encapsulated hemoglobin is being developed as an artificial resuscitative fluid for in vivo oxygen delivery. In the present report, we examine the effect of accumulation of liposome encapsulated hemoglobin on the structure of reticuloendothelial organs following administration of liposome encapsulated bovine hemoglobin in the normovolmic rat. We have also examined the administration of the liposome vehicle, tetrameric bovine hemoglobin, and liposome encapsulated bovine hemoglobin that has been lyophilized with 300 mM trehalose and rehydrated just before injection. Following injection into the tail vein, rats were sacrificed and liver, spleen, kidney, and lung harvested at 2 h, 24 h, 1 week, and 2 weeks for analysis. Gross pathologic findings of animals injected with liposome encapsulated hemoglobin showed statistically significant splenomegaly with a waxy parenchymal pallor at early time points. Microscopic findings indicate that the liver and spleen are principally involved with liposome encapsulated hemoglobin removal over the course of 24 h with transient cytoplasmic vacuolization in tissue resident phagocytes as evidenced by both light and electron microscopic examination. Presence of liposome encapsulated hemoglobin in these vacuoles was confirmed by oil red O and prussian blue stains. Splenic weight was observed to decline after 24 h but still remained significant above sham‐treated controls at 2 weeks and could be correlated with increased hematopoietic activity. Other findings only in animals injected with lyophilized liposome encapsulated hemoglobin included transient loss of laminae rara in the basal lamina, poducyte fusion in the kidney, and small pulmonary infarcts in the lung over the course of 24 h. This latter finding may be associated with trapping of large particles or agglutinated liposome encapsulated hemoglobin. These data indicate that the administration of liposome encapsulated hemoglobin causes transient changes in the organs of the reticuloendothelial system. © 1995 John Wiley & Sons, Inc.
Sustained release of basic fibroblast growth factor from the synthetic vascular prosthesis using hydroxypropylchitosan acetate
Authors: Yamamura Keiko , Sakurai Tsunehisa , Yano Kohji , Nabeshima Toshitaka , Yotsuyanagi Toshihisa
Published: December 2004

We designed a model vascular prosthesis consisting of expanded polytetrafluoroethylene (Gore Tex®) loaded with basic fibroblast growth factor (bFGF), and studied its in vivo bFGF release behavior. To control the release rate of bFGF, biodegradable hydroxypropylchitosan acetate (HPCHA) was also incorporated into the Gore Tex® disks with bFGF. HPCHA was dissolved in bFGF solution (180 μg/ml) at a concentration of 4% (wt/vol). A Gore Tex® tube was cut into a length of about 5 cm and one end was sealed with a vascular clamp. The tube was then filled with resulting solution under appropriate pressure until the solvents seeped through the pores. The tube loaded with BFGF solution was freeze‐dried and was cut into disks (0.75 cm in diameter). bFGF content in a HPCHA‐free Gore disk was 2.05 ± 0.32 μg (SE, n = 5). BFGF content in a HPCHA Gore disk was 2.71 ± 0.41 μg (SE, n = 5). In an in vivo study in which the bFGF loaded Gore Tex® disk was implanted in rabbit skin pockets, almost 100% of bFGF from HPCHA‐free disks was released within 24 h, whereas some 60% remained after 24 h in the HPCHA‐loaded disks. HPCHA is a useful biodegradable carrier for controlling the release rate of the drug from the synthetic vascular prosthesis. © 1995 John Wiley & Sons, Inc.
Densely crosslinked polymer networks of poly(ethylene glycol) in trimethylolpropane triacrylate for cell‐adhesion‐resistant surfaces
Authors: Drumheller Paul D. , Hubbell Jeffrey A.
Published: December 2004

Densely crosslinked semi‐interpenetrating polymer networks (semi‐IPNs) of poly(ethylene glycol) (PEG) were synthesized by photopolymerizing a melt of PEG of various molecular weights and end‐group functionalities in neat trimethylolpropane triacrylate (TMPTA). Increasing the molecular weight of PEG in the matrix from 1000 to 100,000 g/mol reduced the advancing and receding contact angles, contact angle hysteresis, and adsorption of human fibrinogen and bovine serum albumin. Crosslinked TMPTA homonetworks supported human fibroblast adhesion in vitro, whereas the resistance to cell adhesion of the semi‐IPNs depended upon PEG molecular weight: Lower molecular weight PEG reduced the number of adherent cells; higher molecular weight PEG further reduced and eliminated cell adhesion, as did networks containing acrylate‐functionalized PEG. A polymer system incorporated with PEG throughout a hydrophobic, densely crosslinked matrix, rather than as a blend or surface treatment, may be particularly useful for limiting biologic interactions when bulk material properties must be independent of the solvent environment and where surface abrasion may occur. © 1995 John Wiley & Sons, Inc.
Calcification of valved aortic allografts in rats: Effects of age, crosslinking, and inhibitors
Authors: Levy Robert J. , Qu Xuan , Underwood Thomas , Trachy Joseph , Schoen Frederick J.
Published: December 2004

Experiments were carried out to investigate rat aortic allograft calcification using valved abdominal aortic allografts. Results indicated that this was a potentially useful model for investigating fresh allograft calcification, as well as mineralization of glutaraldehyde‐crosslinked valved allografts. Valve cusp results, however, were not comparable to those noted in large animal or human studies, while aortic wall calcification was more comparable. Calcification inhibitor investigations demonstrated that nearly complete inhibition of the calcification of the aortic wall of glutaraldehyde‐crosslinked allografts was achieved using a number of individual inhibitors, including controlled release diphosphonates, and pretreatment with either ferric chloride or aluminum chloride. However, aminopropanehydroxydiphosphonate pretreatment was not efficacious, and sodium dodecyl sulfate pretreatment was only partially effective for inhibiting the aortic wall calcification in the glutaraldehyde‐crosslinked allografts. It is concluded that valved aortic allografts in rats provide a useful model for investigating aortic wall (but not valve cusp) calcification and its inhibition. © 1995 John Wiley & Sons, Inc.
Cementum‐impregnated gelatine membrane: Its effect on periodontal tissue regeneration
Authors: Nishimura K. , Kitamura H. , Naito M. , Yamaoka A. , Yoshikawa E. , Makita T.
Published: December 2004

This study was designed to evaluate the ability of cementum‐impregnated gelatine membrances (CGM) to stimulate regeneration of periodontal ligament following surgery. Three monkeys with no periodontal disease were used. Following flap elevation, recession type defects were created on the buccal side of maxillary lateral incisors and second premolars, and roots were subsequently planed. Experimental sites received CGM at approximately 2–3 mm below the cementoenamel junction while control sites received gelatine membrane (GM) free of cementum. Wounds were allowed to heal for 3 weeks, during which time daily plaque control measures were maintained. Tissues prepared from sacrificed animals revealed that experimental specimens exhibited formation of new cementum, new bone, and periodontal ligament. Control specimens exhibited connective tissue adhesion without either new cementum or significant new bone formation. Histometric analysis showed that the average vertical growth of cementum (NC) and bone (NB) at experimental sites were 3.48 ± 0.29 and 0.64 ± 0.43 mm, respectively. At the control sites the corresponding results were NC = 0.09 ± 0.03 and NB = 0.06 ± 0.28. It was concluded that placement of CGM resulted in significantly greater postsurgical cementum and bone formation than that of GM alone. © 1995 John Wiley & Sons, Inc.
Micromechanisms of fatigue crack initiation and propagation in bone cements
Authors: Bhambri Sushil K. , Gilbertson Leslie N.
Published: December 2004

The micromechanisms of fatigue fracture in bone cements were explored and characterized in this investigation. Fatigue crack initiation sites were identified and the microscopic features responsible for crack initiation are illustrated. Differences in the fracture morphology of PMMA beads, in early crack growth and rapid crack growth stages, are brought out. Based on the fractographic features, a micromechanism of PMMA bead fracture is proposed. © 1995 John Wiley & Sons, Inc.
In vivo mechanical and histological characteristics of HA‐coated implants vary with coating vendor
Authors: Dalton Jeanette E. , Cook Stephen D.
Published: December 2004

The purpose of this study was to evaluate the interface attachment strength and histology of hydroxylapatite (HA) coated and uncoated titanium and cobalt–chromium alloy implants. The canine transcortical plug model was utilized. Four different hydroxylapatite coatings were evaluated. In vitro analysis confirmed that all coatings met FDA guidelines for HA coatings. An unspecified FDA parameter, porosity was found to range from 5–15%. Mechanical testing of the bone–implant interface demonstrated large variation in the performance of the coatings. However, further evaluation of two of the coatings did not demonstrate variations in mechanical characteristics. The histologic findings confirmed the mechanical testing results. The coatings which demonstrated the best mechanical characteristics had excellent bone apposition and uniformity and maintenance of the HA coating at all time periods upon histologic evaluation. Conversely, the coatings which demonstrated inferior mechanical characteristics demonstrated variable amounts of bone apposition and moderate to severe coating degradation and breakup. Cell‐mediated osteolysis was observed in regions of severe coating degradation, and particle migration was noted in regions far from the interface. It was hoped that the four coatings would behave similarly as they all met current FDA guidelines. The only parameter which differed significantly among the coatings was coating porosity. Our results indicate that coatings with large porosities were associated with increased coating degradation and poor mechanical performance and osteolysis at the bone–coating interface. © 1995 John Wiley & Sons, Inc.