bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractTo 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

AbstractLiposome 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

AbstractWe 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

AbstractDensely 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

AbstractExperiments 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

AbstractThis 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

AbstractThe 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

AbstractThe 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.
Blood–biomaterial interactions in a flow system in the presence of bacteria: Effect of protein adsorption
Authors: Sapatnekar Suneeti , Kieswetter Kristine M. , Merritt Katharine , Anderson James M. , Cahalan Linda , Verhoeven Michel , Hendriks Marc , Fouache Benedicte , Cahalan Patrick 
Published: December 2004

AbstractAn in vitro continuous flow system with whole human blood was used to study blood–biomaterial interactions on a base polyurethane and three modified surfaces in the presence and absence of circulating Staphyloccus epidermidis. We hypothesized that the composition of the protein layer adsorbed on the surface of the biomaterial would influence the response of blood components and bacteria. We examined the test surfaces for adsorption of nine plasma proteins and adsorption profiles differed on the four surfaces. The positively charged surface, UC, adsorbed significantly higher amounts of fibronectin (P < .01), von Willbrand factor (P < .01), and fibrinogen (P < .05) than the other materials. As a consequence of increased adsorption of these adhesive proteins, the adhesion of platelets and bacteria was greater on UC than on any other surface. On the base polyurethane, BC, and the negatively charged surface, UA, protein adsorption was low, and these materials were largely free of adherent blood cells and bacteria. The heparinized surface, UH, adsorbed higher quantities (P < .01) of Hageman factor and high molecular weight kininogen relative to the other surfaces. Platelet adhesion, and surface coagulation were prominent on UC, and may have contributed to increased bacterial adhesion on this surface. In the presence of circulating bacteria, adsorption was generally lower than in the absence of bacteria. The pattern of protein adsorption was largely unaffected by the strain of circulating bacteria, but platelet responses (adhesion and activation) were greater in the presence of slime‐producing S. epidermidis as compared to the non‐slime‐producing strain, suggesting that slime may have a direct activating effect on platelets. © 1995 John Wiley & Sons, Inc.
Influence of discharge power level on the properties of hydroxyapatite films deposited on Ti6A14V with RF magnetron sputtering
Authors: van Dijk K. , Schaeken H. G. , Wolke J. C. G. , Marée C. H. M. , Habraken F. H. P. M. , Verhoeven J. , Jansen J. A. 
Published: December 2004

AbstractThe effects of discharge radiofrequency (RF) power and film thickness were studied on the characteristics of Ca5(PO4)3OH (hydroxyapatite) thin films fabricated by RF magnetron sputtering. The structure and chemical composition were investigated with α‐step (thickness), scanning electron microscopy (SEM), X‐ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), and infrared absorption spectrometry (FTIR). The films were analyzed assputtered and after annealing at 550°C under argon flow. SEM showed that the film surfaces had no cracks or other defects. X‐ray diffraction showed that the deposited films were amorphous with low‐discharge RF power, and crystalline with high‐discharge RF power. After annealing, all the films had the same crystalline structure as apatite. However, the RBS measurements revealed that all films had a higher calcium–phosphate ratio than standard synthetic hydroxyapatite. Furthermore, statistical testing of the RBS data revealed the existence of only a weak correlation between the Ca/P ratio and the discharge power level. Although all sputtered films showed phosphate bonds in the infrared spectrum, only after annealing did the OH bonds of hydroxyapatite become visible. © 1995 John Wiley & Sons, Inc.
The incorporation and sustained release of bioactive insulin from a bead‐formed macroporous hydrogel matrix
Authors: Atkins Terence W. , McCallion Roisin L. , Tighe Brian J. 
Published: December 2004

AbstractFreeze‐thaw photopolymerization of a mixed solution of monomers and bovine insulin around frozen ice crystals has been used to generate a bead‐formed macroporous hydrophilic matrix of p‐HEMA. The largest proportion of beads was 500–1000 μm in size (distribution <106–1700 μm) with a mean EBC of 71.7 ± 0.92%. Insulin release was monitored using RIA and insulin bioactivity determined using the rate of insulin stimulated D‐[U14C] glucose oxidation to 14CO2. The cumulative insulin release profile was characterized by an initial lag phase followed by an almost linear increase in insulin release for up to 30 days. Insulin release at 4°C was significantly greater than release at 37°C both in the presence and absence of 2.5% thiomersalate as preservative. The latter served to extend the time period over which significant insulin release could be detected. Increasing the monomer concentration decreased the mean equilibrium buffer content (EBC), the total mean cumulative release of insulin, and the proportion of the incorporated insulin load subsequently released at both 4°C and 37°C in the presence of preservative. Insulin determination using RIA and bioassay confirmed that insulin released from beads was bioactive and that immunoreactivity was a reasonably reliable indicator of bioactivity. © 1995 John Wiley & Sons, Inc.
The effects of centrifugation and titanium fiber reinforcement on fatigue failure mechanisms in poly(methyl methacrylate) bone cement
Authors: Topoleski L. D. Timmie , Ducheyne Paul , Cuckler John M. 
Published: December 2004

AbstractThe contributions to fatigue resistance in poly(methyl methacrylate) bone cement (PMMA) by centrifugation and titanium fiber addition were studied. Three modified bone cements were tested: porosity reduced cement (C‐PMMA); titanium (Ti) fiber‐reinforced cement (R‐PMMA), using a novel method to incorporate fibers; and porosity reduced and Ti fiber‐reinforced cement (C‐R‐PMMA). Specimens of untreated bone cement (PMMA) were included as controls. Non‐notched and notched specimens were cyclically loaded in fully reversed bending. For the non‐notched specimens, at all stress levels, C‐R‐PMMA had significantly greater fatigue life than either C‐PMMA or R‐PMMA (except C‐PMMA at 30 MPa). R‐PMMA had lower fatigue life than the control at 30 MPa (nominal maximum stress), but higher fatigue life at 20 and 15 MPa. At both 20 and 15 MPa, there was no statistical difference between the fatigue lives of C‐PMMA and R‐PMMA. Fractography revealed that, at 30 MPa, characteristics of rapid fracture predominated. At 20 and 15 MPa, in contrast, almost the entire fracture surface showed the characteristic fatigue morphology, indicating that subcritical crack growth was predominant. For the notched specimens, C‐PMMA showed greater life than PMMA at the highest stress intensity, but the lifetimes converged with decreasing stress intensity. In contrast, the lifetimes for PMMA and R‐PMMA diverged with decreasing stress intensity. The effect of centrifugation appeared to be strongest at higher stress intensities, and diminished with decreasing stress intensity. The reinforcing effect of Ti fiber addition increased the notched fatigue life at high initial stress intensities, and the reinforcing effect increased with decreased stress intensity. In both the non‐notched and notched fatigue experiments, the combination of porosity reduction and Ti fiber reinforcement (C‐R‐PMMA) led to substantial improvements in fatigue life at each stress and stress intensity level, suggesting that Ti fiber reinforcement and porosity reduction effects are additive. Fiber reinforcement affects the fatigue crack propagation phase of failure in bone cement, enhancing the fatigue crack propagation resistance. Pore reduction may affect fatigue crack initiation as well as fatigue crack propagation resistance. © 1995 John Wiley & Sons, Inc.
In vivo calcium phosphate formation induced by sol—gel‐prepared silica
Authors: Li Panjian , Ye X. , Kangasniemi I. , de Blieck‐Hogervorst J. M. A. , Klein C. P. A. T. , de Groot K. 
Published: December 2004

AbstractImplantation with plugs made of a porous sol‐gel‐prepared silica into the femurs of goats demonstrated that a calcium phosphate was formed both on the silica plugs and within the pores inside the silica plugs 12 weeks postoperatively. This observation indicates that a highly hydrated silica surface is effectively catalytic for calcium phosphate nucleation. Calcification can be triggered in physiologic solution under stimulation of the silica gel. A high level of silicon in the uncalcified osteoid region of young bone is thus thought to provide a number of SiOH groups for initiating calcium phosphate formation. Our results provide some information about the mechanism of calcium phosphate mineralization in higher animals. We believe that heterogeneous nucleation of apatite can be induced from metastable calcium phosphate solutions including physiologic fluids on those specific surfaces of materials, where there are abundant acidic OH groups. © 1995 John Wiley & Sons, Inc.