bluuebunny/crossref_metadata_2025_split huggingface dataset:
Macrophage phagocytosis of biodegradable microspheres composed of L‐lactic acid/glycolic acid homo‐ and copolymers
Authors: Tabata Yasuhiko , Ikada Yoshito 
Published: December 2004

AbstractA variety of biodegradable microspheres were prepared from L‐lactic acid, DL‐lactic acid, or glycolic acid homopolymers and copolymers of different molecular weights and monomer compositions. Phagocytosis of the microspheres by mouse peritoneal macrophages was studied in cell culture system using scanning electron microscopy as well as light microscopy. The diameter of microspheres prepared was less than 2 μm, regardless of the starting polymers. No dependence of the chemical nature of starting polymers was observed on the extent of phagocytosis of the microspheres by macrophages. Precoating the microspheres with water‐soluble macromolecules such as proteins had great influence on phagocytosis by macrophages. It was demonstrated that precoating with bovine serum albumin and non‐proteinaceous macromolecules reduced the phagocytosis of microspheres, while bovine γ‐globulin, human fibronectin, bovine tuftsin, and gelatin precoating enhanced the phagocytosis. This trend was not influenced by the presence of serum. Only in the case of gelatin precoating, the phagocytosis was greatly enhanced by the presence of serum as compared to precoating with other proteins. Microscopic observation clearly indicated that the phagocytosed microspheres were gradually degraded in the macrophage interior with the incubation time, leading to release of a fluorescent dye encapsulated in the microspheres. The rate of microsphere degradation in cells could be controlled by changing the molecular weight and the monomer composition of the copolymers comprising the microspheres.
Apatite–wollastonite containing glass ceramic–fibrin mixture as a bone defect filler
Authors: Ono Kozo , Yamamuro Takao , Nakamura Takashi , Kakutani Yoshiaki , Kitsugi Toshiaki , Hyakuna Katsubumi , Kokubo Tadashi , Oka Masanori , Kotoura Yoshihiko 
Published: December 2004

AbstractThe purpose of this study was to evaluate the usefulness of a mixture of apatitewollastonite containing glass ceramic (A–W · GC, 42–60 mesh in granule size) with fibrin as a bone defect filler. A bone defect was drilled in the proximal metaphysis of the rat tibia and was filled with (1) fibrin glue, (2) A–W · GC granules, or (3) A–W · GC–fibrin mixture. Nothing was placed in the defect of the controls. The animals were serially sacrificed until 8 weeks after the operation, and the defect site was histologically examined and histomorphometrically analyzed for quantitative evaluation of newly formed bone and blood vessels. The use of fibrin glue as the binder markedly increased the ease of handling the A–W · GC granules. In the controls, little trabecular regeneration was observed in the defect site. Early vascularization (confirmed by microangiography) increased and the repairing process was accelerated in the defects filled with fibrin. In these defects filled with A–W · GC granules, good bone formation was observed around the granules. Bone formation was accelerated in the defects filled with A–W · GC fibrin mixture. Thus, the mixture showed good osteoconductive potential as well as acceleration of the repair process. Therefore, A–W · GC–fibrin mixture is considered to be a useful bone defect filler.
Structure of a collagen‐GAG dermal skin substitute optimized for cultured human epidermal keratinocytes
Authors: Boyce Steven T. , Christianson Deborah J. , Hansbrough John F. 
Published: December 2004

AbstractCollagen and glycosaminoglycan (GAG) dermal skin substitutes (membranes) were studied as substrates for cultured human epidermal keratinocytes. Structure of dermal substitutes was optimized for pore size to promote ingrowth of fibrovascular tissue from the wound bed and for culture of human keratinocytes of the membrane's surface. Pore size of the freeze‐dried material was regulated by control of the temperature of freezing between −50°C and −20°C and by concentration of starting materials between 0.17% and 1.62% wt/vol. A nonporous surface of collagen‐GAG was laminated to the membranes to provide a planar substrate for cultured epidermal kerationocytes. Thickness of dermal substitutes was regulated by control of the volume and concentration of starting materials. Biotin was conjugated to solubilized collagen for binding with avidin of specific quantities of biologically active molecules. The optimized membranes are suitable substrates for the culture of human epidermal keratinocytes, and together with the cells yield a composite material that is histologically similar to skin.
Attachment and spreading of human gingival fibroblasts on potentially bioactive glasses in vitro
Authors: Häkkinen Lari , Yli‐Urpo Antti , Heino Jyrki , Larjava Hannu 
Published: December 2004

AbstractThe attachment and spreading of cultured fibroblasts on potentially bioactive glasses (bioglasses) of ten different compositions were studied. Human gingival fibroblasts were allowed to attach and spread on bioglasses for 1–72 h. Unreactive silica glass and cell culture polystyrene served as controls. The attachment and spreading of cells were examined by 3H‐thymidine labeling of cells, planimetric analysis, cytological staining, immunocytochemistry, and scanning electron microscopy. The cell attachment to bioglasses and silica glass and the cell spreading on bioglasses were slower and cell morphology more elongated compared to control plastic. In spite of great differences in bioglass compositions no great differences in cell behavior on these surfaces were detected. Thus the initial events in the tissue–implant interface might be independent on the bioglass composition, and furthermore the differences in the organization of the tissue–implant interface in vivo might depend on the nature of the surrounding tissues and subsequent changes of the implant surface and the extracellular environement.
In vitro characterization and biomechanical optimization of a biodegradable particulate composite bone cement
Authors: Gerhart Tobin N. , Miller Richard L. , Kleshinski Stephen J. , Hayes Wilson C. 
Published: December 2004

AbstractWe have developed a biodegradable particulate composite bone cement and used in vitro and in vivo methods for studying its suitability for orthopaedic applications. The composite matrix consists of gelatin, water, and sodium salicylate. The particulate phase is made up of powdered and particulate (355–600 μm diameter) tricalcium phosphate. Paraformaldehyde (0.1% to 0.5% by weight) is used as a matrix cross‐linking agent. The effects of incubation time, particulate volume fraction, density of the individual particles, water content, concentration of crosslinking agent, and freeze‐drying on the unconfined compressive strength and modulus of the particulate composite were measured. Compressive strengths of 7 MPa and moduli of 65 MPa could be achieved. Mechanical properties depended critically upon the water content of the particulate composite, with values of strength and modulus decreasing rapidly outside a range of 10–14% of specimen dry weight. High‐density tri‐calcium phosphate particulate produced cement with twice the strength found with porous particulate. In a companion study we document in vivo performance of this particulate composite in an animal model system.
Decreased neutrophil respiratory burst on exposure to cobalt‐chrome alloy and polystyrene in vitro
Authors: Shanbhag Arun , Yang Jun , Lilien Jack , Black Jonathan 
Published: December 2004

AbstractThe effect of biomaterials on the super‐oxide‐producing ability of neutrophils was studied. Human peripheral blood neutrophils were incubated with cobalt‐base alloy (F‐75) or polystyrene beads of nonphagocytosable size. Respiratory burst activity was studied by measuring super‐ oxide dismutase inhibitable reduction of cytochrome C. Neutrophils were found to release no more superoxide anion on incubation for up to 3 h with either material in a protein‐free medium than controls without foreign material. However, the ability of neutrophils incubated with either biomaterial to subsequently respond to phorbol myristate acetate challenge was decreased (p < 0.05). Chemical analysis of supernatants for the F‐75 samples showed a high concentration of cobalt in the medium within 1 h of incubation. Minimal chromium and nickel was detected. No correlation could be demonstrated between metal in solution and the respiratory burst defect in neutrophils. Instead it appears that interaction of cells with either surface was the critical event in altering the response to phorbol myristate acetate. This observed functional defect may play an important role in rendering tissue around implanted biomaterials susceptible to infections.
Influence of the substrate binding characteristics of fibronectin on corneal epithelial cell outgrowth
Authors: Pettit Dean K. , Horbett Thomas A. , Hoffman Allan S. 
Published: December 2004

AbstractThe outgrowth of corneal epithelial cells onto a polymeric substrate is expected to be the primary event in the epithelialization of a synthetic corneal graft. Circular corneal buttons (5 mm) were punched from excised rabbit corneas and placed onto bare substrates or substrates preadsorbed with fibronectin (fn), albumin, or binary mixtures of both fn and albumin. Cell outgrowth areas were measured after culturing the buttons for 4 days in serumfree medium. Fibronectin adsorption to the materials was measured from pure and binary solutions with 125‐radiolabeled fibronectin. A parameter thought to be related to the binding strength of fn to polymeric substrates was measured in parallel experiments by partial elution of the adsorbed fn by 3% sodium dodecyl sulfate (SDS). Following pure solution fibronectin adsorption a range of out growth areas was measured (from 0.86 ± 0.03 cm2 for glass to 1.49 2 0.03 cm2 for TCPS). On all of the materials tested cell outgrowth areas increased following fn preadsorption and decreased following albumin preadsorption relative to bare surfaces (p < 0.05). Following preadsorption with binary protein mixtures cell out growth areas increased with fibronectin adsorption, however, the outgrowth areas were not determined solely by the concentration of fn adsorbed onto the surfaces. This result suggested that the biological efficiency of the adsorbed fibronectin was substrate‐dependent. When the cell outgrowth data were cross‐plotted against fn retention following SDS elution, the outgrowth areas were found to increase along with increases in fn retention. Based on these data we suggest that epithelial cell outgrowth may be partially governed by the tightness of binding between the fn molecules and the underlying substrate. © 1992 John Wiley & Sons, Inc.
A comparative study of ultrastructures of the interfaces between four kinds of surface‐active ceramic and bone
Authors: Neo M. , Kotani S. , Nakamura T. , Yamamuro T. , Ohtsuki C. , Kokubo T. , Bando Y. 
Published: December 2004

AbstractThe interfaces between four kinds of surfaceactive ceramic and bone were studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) using undecalcified specimens. The materials were Bioglass®‐type glass (Bioglass®), Ceravital‐type glass‐ceramic (KGS), apatite and wollastonitecontaining glass‐ceramic (A‐W · GC) and hydroxyapatite (HA)· Particles of these materials, ranging between about 100 and 300 μm in diameter, were implanted into rat tibiae, and specimens were prepared for observation at 8 weeks after implantation. All materials were observed to bond to bone through a collagen‐free layer consisting of fine apatite crytals distinct from those in bone. The crystals of this apatite layer and those of bone were intermingled at their interface, suggesting chemical bonding. In Bioglass®, which had only a glassy phase, several tens of microns of the material surface had changed to such an apatite layer. In KGS and A‐W · GC, which had macrocrystals in the glassy phase, an intervening apatite layer about 0.5 μm thick was observed between the materials and bone. Furthermore, fine apatite crystals were also observed among the macrocrystals near the surface of the materials. In HA, which had no glassy phase, an intervening apatite layer was much less distinct and sometimes absent. These differences were considered to be attributable to the differences in chemical composition, crystallization, and solubility of the materials. © 1992 John Wiley & Sons, Inc.
Influence of fibril length upon ePTFE graft healing and host modification of the implant
Authors: Hirabayashi K. , Saitoh E. , Ijima H. , Takenawa T. , Kodama M. , Hori M. 
Published: December 2004

AbstractInfluence of fibril length (porosity) upon synthetic vascular graft healing has not been investigated in detail. The purpose of this study was to determine the dependence of neoendothelial healing, cellular response, and biocompatibility on the fibril length of expanded polytetrafluoroethylene (ePTFE) grafts with an internal diameter of 1.5 mm. ePTFE grafts of different fibril length, 20, 40, 60, and 90 μm, were implanted into the abdominal aorta of rats (n = 5 for each group). After 5 weeks, the implants were harvested and examined for neointimal and pseudointimal coverage by light microscopy and SEM. The hydroxyproline content of the implants was measured, and the distribution of collagen types was examined. The neointimal and pseudointimal coverage was related to the fibril length, and the neoendothelial healing was better on 60‐μm and 90‐μm grafts than on 20‐μm and 40‐μm grafts, The amount of hydroxyproline was also related to the fibril length, however, no significant difference could be observed between 60‐μm and 90‐μm grafts. Collagen types I and III were almost identically located in the middle portion of the implants. Our results demonstrate that the fibril length of ePTFE grafts affected neoendothelial healing and its affinity to collagen. © 1992 John Wiley & Sons, Inc.
Spatial and temporal changes in compliance following implantation of bioresorbable vascular grafts
Authors: Greisler Howard P. , Joyce Kathleen A. , Kim Dae Un , Pham Si M. , Berceli Scott A. , Borovetz Harvey S. 
Published: December 2004

AbstractCompliance matching between the host vessel and vascular grafts used for smalldiameter arterial replacements is thought to be important for longterm patency. However, currently available grafts elicit fibroplastic reactions, resulting in decreasing compliance with time after implantation. Bioresorbable prostheses elicit ingrowth of myofibroblasts containing abundant contractile elements. This led us to investigate whether compliance of implanted bioresorbable prostheses decreased as a function of time and if the kinetics of change correlated with the progession of tissue ingrowth. Woven polyglactin 910 prostheses (10 mm × 4 mm i.d.) were implanted into adult NZW rabbit infrarenal aortas and replicates were harvested serially through 8 months. Control grafts were implanted, and immediately resected. Dynamic compliance was measured a t 1‐mm axial increments along each explant using a pulse duplicator apparatus which exposed the harvested samples to realistic pulsatile hemodynamics. Compliance was calculated for proximal, mid, and distal segments of each graft and averaged at each time point by grouping into control (zero time, n =3), early (1‐4 weeks, n = 13), and late (6‐36 weeks, n = 9) explant periods. At late explant periods both proximal and distal compliance were significantly greater than mid graft compliance (p ≤ .02 and p ≤ .03, respectively). There was a significant increase in proximal compliance between early and late explant times (p ≤ .01). Measured increases in mid and distal segment compliance over time did not reach statistical significance. Myofibroblast laden tissue ingrowth into the inner capsule followed macrophage phagocytosis and was nearly complete prior to the time that an increase in compliance was demonstrated. Thus since the major histologic episodes precede the change in compliance, these are not likely initiated by this biomechanical change. We hypothesize the graft resorption coupled with the ingrowth of more compliant tissue likely leads to the increased compliance of the graft material. © 1992 John Wiley & Sons, Inc.
Toxicity test of biodegradable polymers by implantation in rabbit cornea
Authors: Kobayashi Hisatoshi , Shiraki Kaneto , Ikada Yoshito 
Published: December 2004

AbstractTo evaluate whether or not the corneal micropocket implantation is effective for determining the toxicity of polymeric materials, currently used biodegradable polymers such as poly(lactic acid) (PLA), poly(glycolic acid) (PGA), LA‐GA copolymers, and three kinds of poly(2‐cyanoacrylate)s (PCA) were implanted in a rabbit corneal pouch and the tissue responses were observed macroscopically and microscopically. It was found that PLA induced no vascularization, whereas a residual solvent and ethylene oxide gas remaining in the PLA matrix invoked vascularization. Vascularization clearly took place when PGA was implanted in the cornea, which became opaque, probably because of cellular infiltration. In the case of PCA implantation, severe inflammation as well as vascular invasion occurred in the initial stage. It is likely that these tissue reactions were caused by the leachables from the implanted materials, the extent being dependent on the leaching rate and the toxicity. It was concluded that the corneal micropocket assay is a good means to detect trace amounts of leachables from implanted materials without sacrificing the animals with the implanted materials. © 1992 John Wiley & Sons, Inc.
Effect of surface plasma treatment on the chemical, physical, morphological, and mechanical properties of totally absorbable bone internal fixation devices
Authors: Ibnabddjalil M'hamed , Loh Ih‐houng , Chu C. C. , Blumenthal Norman , Alexander Harold , Turner David 
Published: December 2004

AbstractThe purpose of this work was threefold: to enhance the adhesion between the reinforced absorbable calcium phosphate (CaP) fibers and the absorbable polyglycolide acid (PGA) matrix, to improve the hydrolytic degradation of the CaP fibers, and preliminarily to evaluate the cytotoxicity of the plasma treated surface of CaP fibers. CH4plasma treatment was used to achieve these goals. The microbond method was used to evaluate the effects of the plasma treatment on the interfacial shear strength between the PGA matrix and CaP fibers. The treatment increased the mean interfacial shear strength of the CaP/PGA composite system by 30%. AFM data showed that CH4‐treated CaP fibers had considerable microscopic surface roughness, which facilitated mechanical interlocking between the reinforced CaP fibers and PGA matrix. The untreated and plasma‐treated fibers were also subjected toin vitrohydrolytic degradation in a phosphate buffer solution of pH 7.44 at 37°C for up to 15 h. CH4plasma treatment resulted in a considerable lower polar term of the surface energy and a significantly higher disperse term in water media. This change in the proportion of surface energy terms may reduce the capillary wicking phenomena of water through the CaP fiber/PGA matrix interface. The CaP fiber dissolution studies revealed that both CH4and Parylene plasma polymer coatings appeared to reduce the solubility of CaP fibers, and that the magnitude of reduction was higher in an acidic than a physiologic pH environment. A preliminary cytotoxicity test revealed that both CH4and Parylene plasma‐treated CaP fibers were noncytotoxic. Additional research should be done to determine the optimum plasma conditions and the possible use of other plasma gases to improve the interfacial shear stress of the composite and the dissolution properties of CaP fibers. © 1994 John Wiley & Sons, Inc.
Ultrastructural study of the A‐W GC‐bone interface after long‐term implantation in rat and human bone
Authors: Neo M. , Nakamura T. , Ohtsuki C. , Kasai R. , Kokubo T. , Yamamuro T. 
Published: December 2004

AbstractThe interface between apatite‐ and wollastonite‐containing glass‐ceramic (A‐W GC) and bone after long‐term implantation was studied by scanning and transmission electron microscopy (SEM and TEM) using rat and human specimens. First, particles of A‐W GC (100–200 μm in diameter) were implanted into rat tibiae, and specimens were prepared for observation at 24, 48, 72, and 96 weeks after the operation. These long‐term specimens showed an A‐W GC—bone interface different from that at an earlier stage, which was investigated in our previous studies. SEM showed that the Ca‐P ‐rich layer was wider, suggesting that leaching of ions from the A‐W GC had continued even after bonding with bone. In some regions, the material particles were evidently replaced by the bone. TEM showed that the intervening apatite layer had become indistinct, and that A‐W GC had intermingled with bone at the interface. In some regions, the surface of the A‐W GC was degraded. These findings suggest that the surface region of A‐W GC is slowly replaced by bone. Second, a human bone specimen, which included A‐W GC particles (300–700 μm in diameter) implanted as a bone filler for about 75 weeks was harvested and investigated. Excellent A‐W GC—bone bonding was observed, and the ultrastructure of the interface was similar to that in rats after long‐term implantation. This finding demonstrated that A‐W GC possibly worked in human bone in the same way as in rat bone, showing excellent bioactivity. © 1994 John Wiley & Sons, Inc.
Experimental evaluation of a new composite mesh with the selective property of incorporation to the abdominal wall without adhering to the intestines
Authors: Amid Parviz K. , Shulman Alex. G. , Lichtenstein Irving L. , Sostrin Stuart , Young John , Hakakha Michael 
Published: December 2004

AbstractThis preliminary study examined the possibility of preventing intestinal adhesions to biomaterials while preserving their incorporation with the abdominal wall. White New Zealand rabbits received intraperitoneal implants of different biomaterials for repair of defects created on the abdominal wall. The following biomaterials were used: polypropylene, polyester, expanded polytetraflueroethylene, polypropylene mesh/polypropylene sheeting (polypropylene mesh covered with polypropylene sheeting on the peritoneal side), polypropylene/silastic, polypropylene/polyglactin, polypropylene/polyglycolic acid, and polypropylene/fibrin. All biomaterials evaluated caused adhesions to the intestines except for polypropylene mesh/polypropylene sheeting and polypropylene mesh/silastic composites. Because adhesion of the intestine to the biomaterial is the first stage of biomaterial‐related intestinal fistula, its prevention is logical for the elimination of this complication. Composites with the selective property of adhering to the abdominal wall, yet sparing the viscera, would facilitate thoracic and abdominal wall surgeries, as well as intraperitoneal laparoscopic hernioplasties. © 1994 John Wiley & Sons, Inc.
Effect of a change in interfacial geometry on the fatigue strength of porous‐coated Ti‐6Al‐4V
Authors: Wolfarth D. , Ducheyne P. 
Published: December 2004

AbstractPorous‐coated Ti‐6Al‐4V has a fatigue strength approximately one‐third that of the uncoated alloy. The interfacial geometry between the porous coating and the implant substrate is notchlike, leading to stress concentrations that have been shown to be the main cause for the reduction in fatigue strength. In this study, the effect of interfacial geometry on fatigue strength of porouscoated Ti‐6Al‐4V is quantified. The interface between porous coating and implant is modeled using linear elastic, plane strain finite element analysis. Integrated with the numerical analysis is an experimental verification of enhanced fatigue behavior. Changes in interfacial geometry are conceived, and their effectiveness in reducing stress concentrations are determined. A doubling of fatigue strength can be achieved for newly conceived geometries over conventional porous coating geometries. © 1994 John Wiley & Sons, Inc.