bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical and physical properties of collagen implants influence their fate in vivo as evaluated by light and confocal microscopy
Authors: Vardaxis N. J. , Ruijgrok J. M. , Rietveld D. C. , Marres E. M. , Boon M. E.
Published: May 2005

Porcine collagen membranes having a rough and a smooth side were used for subcutaneous implantation studies in rats. Two tanning protocols were used for the membranes, a new one involving microwaving and glutaraldehyde treatment (NEWGA), and the other, a conventional method using glutaraldehyde treatment at room temperature (OLDGA). Untreated membranes (NONGA) were also implanted. Sections of the implants were examined by light microscopy and with the confocal laser scanning microscope focusing on neovascularization and incorporation of the implant. At 64 days, the smooth sides of NEWGA and OLDGA implants were not well incorporated, with scarring subjacent to the surface and dystrophic calcification of that side of the membrane. At the same time, the rough sides of the NEWGA and OLDGA were not calcified with a giant cell reaction around the porcine collagen. The best incorporation was found in the NONGA membranes with no dystrophic calcification, excellent neovascularization of all layers, and complete remodeling at day 64. After 5 months, the completely remodeled NONGA membrane still could be identified, and the NEWGA and OLDGA membranes were calcified with a giant cell reaction having a dense fibrous capsule. It is concluded that if cross‐linking is deemed necessary, the microwave cross‐linking method is advisable because in the early stages there is less reactive inflammation around it, and the implant surfaces should be rough with an open structure, making calcification of crosslinked collagen unlikely. © 1994 John Wiley & Sons, Inc.
Bonding of low‐fusing dental porcelain to commercially pure titanium
Authors: Könönen M. , Kivilahti J.
Published: May 2005

The objective of the investigation was to study the basic problems related to the firing of dental porcelain to commercially pure titanium. The firing of a low‐fusing porcelain to sandblasted or electrolytically polished titanium was carried out in an ordinary dental furnace. The interfacial regions between the ceramic coatings and titanium were analyzed using scanning acoustic microscopy (C‐SAM) and scanning electron microscopy (SEM) techniques. Thermal stresses in the joints were evaluated by means of a finite element model based on multilayer elastic strain analysis. The chemical reactions and their formation sequence at 750°C was predicted thermodynamically and observed experimentally both at 750 and 800°C. The C‐SAM results gave evidence that the integrity of the porcelain‐titanium joints are better in the sandblasted samples than in the elecropolished ones, where defects were larger. SEM analyses of the same samples confirmed the C‐SAM findings. Because the reaction layers are more continuous in the electropolished samples, cracks propagated more readily in these samples during the cooling procedure. Both thermodynamic calculations and experimental chemical analyses strongly indicate that the cause for the cracking of the reaction zone is thin layer of Ti (oxo) silicide and/or a relatively thick solid solution layer of Ti and oxygen. © 1994 John Wiley & Sons, Inc.
Transmission electron and high‐voltage electron microscopy of osteocyte cellular processes extending to the dental implant surface
Authors: Steflik D. E. , Sisk A. L. , Parr G. R. , Lake F. T. , Hanes P. J. , Berkery D. J. , Brewer P.
Published: May 2005

Examination of the morphology of osteocytes within the bone supporting endosteal dental implants was performed using conventional transmission and high‐voltage transmission electron microscopy (HVEM). The in vivo dog model used 72 implants inserted into the premolar region of 18 experimental animals. Forty‐eight implants in 12 dogs were used as anterior abutments for fixed bridges for periods up to 12 months. The mineralized matrix of the supporting bone was either directly apposed to the implant surface or was separated from the implant by a narrow region of unmineralized matrix. Osteocytes were routinely observed to be closely associated with the bone‐implant interface, as well as at a distance from the implant. Osteocytes were found to extend cellular processes directly to the implant surface through canaliculi. The osteocyte processes contained microfilaments. The three‐dimensional capabilities of HVEM elucidated the nature of these cell processes at the point of exit from the osteocyte, as the processes extended through the mineralized matrix, and as the processes terminated at the implant interface. This report suggests that avenues of communication may exist between the implant and the osseous cells, providing intriguing hypotheses regarding biomechanical forces and osteogenesis at the implant interface. Furthermore, an electron‐dense deposit was observed upon the inner confines of the canalicular wall, upon the outer aspects of the osteocyte lacuna, and upon the outer aspect of the bone interfacing the implant. © 1994 John Wiley & Sons, Inc.
Healing of large segmental defects in rat femurs is aided by RhBMP‐2 in PLGA matrix
Authors: Lee S. C. , Shea M. , Battle M. A. , Kozitza K. , Ron E. , Turek T. , Schaub R. G. , Hayes W. C.
Published: May 2005

Recombinant human bone morphogenetic protein‐ (rhBMP‐) can be used to enhance the repair of congenital or acquired bone pathologies when formulated in the appropriate carrier. Poly [D, L‐(lactide‐co‐glycolide)] (PLGA) has been shown to be an effective carrier of rhBMP‐. We investigated several particle sizes PLGA and several doses of rhBMP‐ in a rat orthotopic model. We also investigated the effects of a fibrinolytic inhibitory agent, epsilon aminocaproic acid (EACA), on the healing response. Our data indicate that higher doses of rhBMP‐ resulted in increased failure torque (408 ± 70 N‐mm or 60% of the intact value) and higher incidence of union (100%). The induced bone in femurs treated with the smaller particle size PLGA achieved the greatest torsional stiffness and strength. The presence of rhBMP‐ was necessary for new bone to form, but the presence of EACA did not change these results; the use of the PLGA carrier appeared to increase bone strength and stiffness. In fact, with higher doses of rhBMP‐ in PLGA, the stiffness of the new bone was equal to that of intact controls (64 ± 20 N‐mm/deg [intact femurs] versus 45 ± 10 N‐mm/degree [medium dose in small PLGA], 61 ± 17 N‐mm/degree [high dose in small PLGA], and 36 ± 11 N‐mm/degree [medium dose in large PLGA]; P > .05). In conclusion, PLGA implanted with rhBMP‐ effectively aided in healing large segmental defects in rat femurs. © 1994 John Wiley & Sons, Inc.
Adherent platelet morphology on adsorbed fibrinogen: Effects of protein incubation time and albumin addition
Authors: Sheppard J. I. , McClung W. G. , Feuerstein I. A.
Published: May 2005

The composition of the protein layer adsorbed to a polymer has been thought to be important for the adhesion of platelets. The state of activation of adherent platelets is an additional factor that may be a predictor of biocompatibility. Activation refers to the degree of change from discoid shape to any of several spread shapes. The conformation and orientation of adsorbed adhesive proteins, which interact with receptors on the membrane of platelets, such as fibrinogen, fibronectin, and von Willebrand factor, may also be important for platelet adhesion and activation. This work deals with the behaviour of fibrinogen adsorbed to PMMA alone, where the experimental variable was incubation time with the substrate, and with adsorbed fibrinogen mixed with albumin, where the experimental variable was the molar percent of fibrinogen in the adsorption solution. Shorter protein incubation times and increased albumin levels in the initial fibrinogen adsorption solution enhanced the percentages of activated platelet morphologies and increased adsorbed fibrinogen redistribution by the platelet. Lower concentrations of albumin in the initial adsorption solution enhanced platelet adhesion numbers; fibrinogen incubation time had no effect. Together, these factors can contribute to the biocompatibility of a biomaterial through their effect on platelet adhesion and activation. © 1994 John Wiley & Sons, Inc.
Long‐term durability of the interface in FRP composites after exposure to simulated physiologic saline environments
Authors: Meyer Matthew R. , Friedman Richard J. , Del Schutte H. , Latour Robert A.
Published: May 2005

Fiber/matrix interfacial bond strength significantly influences the mechanical behavior of fiber‐reinforced polymer (FRP) composites. Interfacial bond strength durability is therefore particularly important in the development of FRP composites for implant applications where diffused moisture may potentially weaken the material over time. In this study, the long‐term durability of interfacial bonding in carbon fiber/380 grade polyetheretherketone (C/PEEK) and carbon fiber/polysulfone (C/PSF) composites was investigated after exposure to hygrothermal environments. A single fiber pull‐out test was used to quantitatively determine the ultimate bond strength (UBS) of the samples following exposure. Samples were tested at three temperatures (37, 65, and 95°C) for six time periods (0–5000 h) and in two environments (dry and physiologic saline‐immersed). A mathematical model based on nth order chemical reaction kinetics was applied to describe the long‐term durability of the interface. The results of this study indicate that interfacial bond strengths in C/PSF and C/PEEK (380 grade) composites are significantly decreased by exposure to physiologic saline and are functions of both time and temperature. For each material, the kinetics of degradation analysis predicts further bond strength losses following initial saturation, which then stabilizes at temperature‐dependent equilibrium bond strength levels. © 1994 John Wiley & Sons, Inc.
Studies on two new radiopaque polymeric biomaterials
Authors: Kruft M. A. B. , Benzina A. , Bär F. , van Der Veen F. H. , Bastiaansen C. W. M. , Blezer R. , Lindhout T. , Koole L. H.
Published: May 2005

Two new polymeric materials (polymers A and B) containing covalently bound iodine were prepared. These polymers were evaluated with respect to their possible use as radiopaque implant biomaterials—that is, materials that are visible in a noninvasive manner using routine X‐ray absorption imaging techniques. Polymer A is a copolymer of methyl methacrylate (MMA) and 1 (80 and 20 mol%, respectively). Polymer B was prepared from MMA, 1, and 2‐hydroxyethyl methacrylate (HEMA) (mol ratio 65:20:15, respectively). Compound 1 was synthesized from 4‐io‐dophenol and methacryloyl chloride. The resulting polymers were characterized with GPC, DSC, NMR, and by measuring both the advancing and receding contact angles. Thrombogenicity of the polymers was determined by an in vitro thrombin generation test procedure. The maximum concentration of free thrombin was 76 ± 1 nM for polymer A, and 64 ± 3 nM for polymer B. The lag times (i.e., time onset of thrombin generation) were 392 seconds for polymer A and 553 seconds for polymer B. For PVC‐T, which is known as a passive material, a lag time of 583 seconds was found. This indicates that polymer B is comparable to PVCT, and more passive than polymer A. Polymer A exhibited minor activation of platelets. Polymer B did not induce platelet activation at all. The polymers exhibited, even as fibers with a diameter of ca. 0.3 mm, good radiopacity with routine imaging X‐ray techniques in the clinic. It is argued that polymers A and B—which actually represent a whole family of radiopaque polymeric biomaterials—exhibit promising properties with respect to applications as construction materials for a new generation of endovascular stents. © 1994 John Wiley & Sons, Inc.
Effect of Ca/P coating resorption and surgical fit on the bone/implant interface
Authors: Maxian Suzanne H. , Zawadsky Joseph P. , Dunn Michael G.
Published: May 2005

The effect of coating resorption on bone apposition and attachment strength to resorbable hydroxyapatite (HA), nonresorbable HA‐coated, and uncoated rough titanium implants was evaluated in interference‐ and noninterferencefit (gap of 2–3 mm) surgical models 2, 4, and 12 weeks postoperatively. Interference and noninterference fits showed differences in bone bridging. Bone apposition was circumferential around the implants in noninterference fit. Significantly greater bone apposition was seen to nonresorbable HA‐coated implants than uncoated and resorbable HA‐coated implants at 4 and 12 weeks. Only resorbable HA coatings showed significantly lower bone apposition for noninterference versus interference fit and from 4–12 weeks. At 2 weeks, strengths of bone attachment to resorbable HA‐coated implants were greater than the other implants, and decreased to lower values (not significant) than the nonresorbable HA‐coated implants at 4 and 12 weeks. Differences in push‐out shear strengths between interference‐ and noninterference‐fit surgical models were significant for uncoated implants at 4 weeks, but not for HA‐coated implants at any time period. Significant differences were seen between the three implant types only for the noninterference‐fit model, where the HA‐coated implants showed greater strengths than the uncoated implants (significant at 2 and 4 weeks). This study showed that presence of resorbable or nonresorbable HA coatings is beneficial when a gap of 2–3 mm is present between the implant and the bone. The resorbable HA‐coated implants showed greatest strengths at the early time period. At later time periods, resorbable HA‐coated implants showed lower bone apposition and attachment strengths than nonresorbable HA coatings. However, resorbable HA‐coated implants showed equivalent bone apposition and attachment to uncoated implants, suggesting that HA coating resorption and remodeling at the bone/implant interface can provide good osteoconduction and fixation. © 1994 John Wiley & Sons, Inc.
Dissolution/reprecipitation and protein adsorption studies of calcium phosphate coatings by FT‐IR/ATR techniques
Authors: Ong J. L. , Chittur K. K. , Lucas L. C.
Published: May 2005

The surfaces of bioactive Ca‐P ceramics immediately change when exposed to proteinaceous solutions. The dissolution behavior and protein interactions of these bioactive materials at the bone/implant interface need to be investigated to understand their material‐cellular interactions fully. In this study, FT‐IR/ATR techniques were used to study the in situ phosphate release kinetics of Ca‐P coatings. The net loss of phosphate molecules from coatings was slower in saline solutions compared with α‐MEM solutions. Coatings exposed to α‐MEM solutions containing fibronectin released phosphate molecules slower than coatings exposed to α‐MEM solutions containing albumin. Conformational changes in fibronectin and albumin adsorbed onto Ca‐P and uncoated germanium surfaces were also investigated using FT‐IR/ATR spectroscopy. Analysis of changes in the amide I bands indicated that there was a greater loss of β‐sheet structure in adsorbed fibronectin on Ca‐P coatings when compared with bare germanium surfaces. Although albumin did change its structure upon adsorption on both Ca‐P and germanium, unlike fibronectin, adsorbed albumin structure was similar on Ca‐P coatings and germanium. Furthermore, with time the conformation of adsorbed fibronectin and albumin appeared to be very stable on Ca‐P coatings, whereas albumin adsorbed to germanium exhibited an increase in ratio of α‐helix to βturn. © 1994 John Wiley & Sons, Inc.
Selective adhesion of platelets on a polyion complex composed of phospholipid polymers containing sulfonate groups and quarternary ammonium groups
Authors: Ishihara Kazuhiko , Inoue Hikaru , Kurita Kimio , Nakabayashi Nobuo
Published: May 2005

We investigated the effects of electrical charges on cellpolymer interactions of poly[2‐methacryloyloxyethyl phosphorylcholine(MPC)‐co‐n‐butyl methacrylate (BMA)] (PMB) having excellent blood compatibility, by copolymerizing anionic or cationic methacrylates with MPC and BMA. A polyion complex (PIC) composed of anionic and cationic MPC copolymers was also prepared. When the cell adhesion on these polymer surfaces from rabbit whole blood was evaluated, we observed a considerable reduction in cell adhesion on the MPC copolymers compared with that on poly(BMA), even when the MPC copolymer was electrically charged. On the other hand, many platelets selectively adhered to the PIC surface from whole blood, but the adherent platelets maintained a discoid shape. The amount of adenosine triphosphate (ATP) in platelets adherent on the PMB or the PIC from a platelet‐rich plasma (PRP) was more than 75% of that in the original PRP, which indicated that the activity of these platelets remained high. However, in the platelets adherent to poly(BMA), only a small amount of ATP remained. Protein adsorption on the polymer surface from human plasma was investigated using a goldcolloid‐labeled immunoassay against albumin γ‐globulin, and fibrinogen. Many of these proteins adsorbed on poly(BMA), whereas a small amount of protein was observed on the MPC copolymers that had an electrical charge. Albumin adsorption and suppression of γ‐globulin and fibrinogen adsorption were found on the PIC. Therefore, the introduction of electrical charges in the PMB did not have an adverse effect on cell adhesion and protein adsorption. The PIC composed of anionic and cationic MPC copolymers induced considerable adsorption of albumin and selective adhesion of platelets. Furthermore, the adherent platelets suppressed changes in their shapes and activity. © 1994 John Wiley & Sons, Inc.
In vitro hydroxyapatite deposition onto a film surface‐grafted with organophosphate polymer
Authors: Tretinnikov O. N. , Kato K. , Ikada Y.
Published: May 2005

To produce a bone‐bonding polymer surface that is capable of inducing deposition of a hydroxyapatite (HA) layer in the body fluid, an organophosphate polymer was covalently immobilized onto a high‐density polyethylene film by surface graft polymerization of a phosphate‐containing monomer. The grafted film was immersed in simulated physiologic solution (SPS). The chemical composition and structure of the formed apatite layer as well as its bonding strength to the polymer surface were investigated. To distinguish the effect of phosphate groups on the deposition of apatite layer from the simple calcium absorption by the anion, a comparative study was done using a polyethylene film with surface immobilized carboxylic groups. Calcium phosphate deposition was observed on all the materials investigated, but the kinetics, composition, deposit amount, and bonding strength of the new phase were found to be significantly different among the modified materials, depending on the density and chemical nature of the surface immobilized ionic groups. It was found that the polymeric materials modified by surface graft polymerization of a phosphate‐containing monomer produce a carbonated HA layer firmly bonded with the material upon immersion in SPS. Carboxyl groups in the grafted layer was not enough to activate bonding with the HA layer. © 1994 John Wiley & Sons, Inc.
Endothelial injury during extracorporeal circulation: Neutrophil–endothelium interaction induced by complement activation
Authors: Matsuda Takehisa , Itoh Satoshi , Anderson James
Published: May 2005

This study was designed to understand the physiologic intravascular and intradevice events at the cellular level following complement system activation during extracorporeal circulation. The addition of anaphylatoxin C5a or complement‐activated serum into neutrophil‐ or endothelial cell‐suspensions resulted in a dose‐dependent transmembrane stimulation that was assessed by an intracellular free calcium ion mobilization technique using a calcium‐sensitive photoprotein, aequorin. The adhesion and ruffle formation of neutrophils on endothelial cell monolayers were markedly enhanced when both cell types were treated with C5a or activated serum. The significance of complement activation on intravascular events during extracorporeal circulation is emphasized and discussed from the viewpoint of surface‐expressed adhesion molecules. © 1994 John Wiley & Sons, Inc.
Splenic response to silicon drain material following intraperitoneal implantation
Authors: Guo Weidun , Willén Roger , Liu Xiaoying , Odelius Rolf , Carlén Brigitta
Published: May 2005

To study the splenic response to intraperitoneal biomaterials, 100% silicon rubber drain fragments were intraperitoneally implanted in the rat. Four days after implantation, specimens of the spleen and implanted rubber fragment were retrieved and subjected to scanning electron microscopy (SEM) and energy dispersive X‐ray microanalysis (EDX). In SEM, macrophages with membrane fusion and cytoplasmic spreading were noted on the surfaces of implanted rubber fragments. Specimens of the spleen from animals with implants showed light 3–10‐μm structures that were not observed in those without implants. EDX revealed the presence of silicon both in the rubber fragment and in the spleen of the implanted animals. Both light microscopy and transmission electron microscopy showed a large number of particles inside giant cells of the spleen. The present study demonstrated an active transport of rubber fragments containing silicon from the peritoneal cavity to the spleen by adherent macrophages, reflecting a splenic response to intraperitoneal implantation of biomaterials. The modes of silicon rubber degradation and transportation remain to be elucidated. © 1994 John Wiley & Sons, Inc.
Drug release from a novel self‐setting bioactive glass bone cement containing cephalexin and its physicochemical properties
Authors: Otsuka Makoto , Matsuda Yoshihisa , Kokubo Tadashi , Yoshihara Satoru , Nakamura Takashi , Yamamuro Takao
Published: May 2005

A novel device containing cephalexin as a model drug using a self‐setting bioactive cement based on CaOSiO2P2O5 glass was investigated. The device consisted of 95 wt/wt% glass powders and 5 wt/wt% cephalexin powder hardened within 5 min after mixing with a phosphate buffer. After setting, in vitro drug release from homogeneous orheterogeneous drug‐loaded cement pellets in a simulated body fluid (SBF) at pH 7.25 and 37°C continued for over 4 weeks. The hardened cement gradually formed low‐crystallinity hydroxyapatite with high bioactivity in hard bone tissue and reduced in volume by about 5% during dissolution testing in SBF. Consequently, 30% of the loaded drug was squeezed from the cement system at the initial stage of the drug release, and the remainder released more slowly. Because the heterogeneous system consisting of the cement and drug‐loaded pellet avoided the drug‐squeezing effect, it showed a longer drug release term than the homogeneous drug‐loaded cement. The heterogeneous system using the hardened cement after soaking in SBF at 37°C for 10 days showed very slow drug release at the initial stage because it completely avoided the drug‐squeezing effect, and the release was a zero‐order pattern. © 1995 John Wiley & Sons, Inc.
Surface field of forces and protein adsorption behavior of poly(hydroxyethylmethacrylate) films deposited from plasma
Authors: Morra M. , Cassinelli C.
Published: May 2005

Polymeric films were deposited from hydroxyethylmethacrylate (HEMA) plasma on non‐woven poly(butyleneterephtalate) (PBT) filter materials. To test the effect of deposition conditions on surface properties, film were deposited using a constant monomer flow rate and a discharge power ranging from 40–100 W. Surface composition and surface energetics were evaluated by Electron Spectroscopy for Chemical Analysis (ESCA) and contact angle measurement, respectively. Albumin (Alb) and fibrinogen (Fg) adsorption from single protein solution to the plasmacoated filters was measured. Results illustrate the marked effects of the deposition conditions on the surface composition, the surface field of forces, and the protein adsorption behavior. The latter is modeled by the application of the Good‐van Oss‐Chaudhury theory of Lewis acid‐base contribution to interfacial energetics. Materials endowed with widely different properties are obtained from the same monomer and different deposition conditions, a result that must be taken into account both in the production step, to assure constant quality, and in the development of specifically tailored materials. © 1995 John Wiley & Sons, Inc.
Zeta potential of bone from particle electrophoresis: Solution composition and kinetic effects
Authors: Kowalchuk Roman M. , Pollack Solomon R. , Corcoran Thomas A.
Published: May 2005

The morphology of bone may be influenced by many factors, including electromechanical ones such as electric potentials, electric fields, or zeta potentials. Stress‐generated potential studies in bone and particle electrophoresis studies using calcium‐deficient hydroxyapatite have shown that the zeta potential depends on the composition of the steeping fluid and steeping time. To better quantify and understand these in situ potential changes in bovine cortical bone, the effects of alterations in calcium, phosphate, and fluoride concentrations in Neuman's Fluid (NF), which simulates in vivo bone extracellular fluid, were investigated using particle electrophoresis. The zeta potential increased in magnitude with increased calcium concentration in NF in as little as 17 min. Increasing phosphate concentration in NF also increased the zeta potential magnitude. These results provide support for a structural model of the bone matrix surface‐bone fluid interface, which incorporates the bone surface proper (composed of collagen, mineral, and boundary regions), stationary layer (in which ions, ionic complexes, and proteins may be adsorbed), and bone extracellular fluid. These results, coupled with those of previous studies, indicate that the protein phase probably has an important role in the determination of the physiologic zeta potential; the role of the mineral phase may also be important. © 1995 John Wiley & Sons, Inc.
Studies on the tumor‐promoting activity of biomaterials: Inhibition of metabolic cooperation by polyetherurethane and silicone
Authors: Tsuchiya Toshie , Hata Hideyo , Nakamura Akitada
Published: May 2005

When V79 metabolic cooperation (MC) assay was performed to detect tumor‐promoting activities, inhibitory activities on the gap‐junctional intercellular communication were first detected in both extracts prepared from polyetherurethane (PEU) and silicone. The former inhibited more strongly than the latter. Furthermore, the lowest effective concentrations in MC assay correlated well with the values of the total active incidences obtained by histologic evaluation of the 2‐year implantation test in rats. Poly(tetramethylene oxide) (PTMO) showed the highest inhibitory activities among the constituents of PU. Thus, the shorter the chain length of PTMO, the stronger the inhibitory activities of PTMO in MC assay. PTMO moiety may play an important role in the tumor‐promotion stage during tumorigenesis induced by PU. © 1995 John Wiley & Sons, Inc.
Formation and properties of a synthetic bone composite: Hydroxyapatite–collagen
Authors: TenHuisen Kevor S. , Martin Roger I. , Klimkiewicz Maria , Brown Paul W.
Published: May 2005

Composites composed of microcrystalline calcium‐deficient hydroxyapatite (HAp) and collagen were formed at 38°C via an acid‐base reaction between calcium phosphate precursors in the presence of a collagen matrix. Formation of composites having HAp:collagen weight ratios of 4.5:1, 11:1, and 22:1, along with that of pure mineral were investigated. Isothermal calorimetry and X‐ray diffraction indicated complete reaction within 5 h resulting in hardened monoliths. The rate of HAp formation increased with an increase in the proportion of collagen present. Electron microscopy indicated that the acceleratory effect of collagen was associated with the provision of nucleation sites for HAp crystallization. Analysis of the solution chemistry also showed that collagen affected the calcium and phosphate concentrations and the pH. While collagen was shown to effect the kinetics of HAp formation, the rate limiting step, as shown by X‐ray diffraction and solution chemistry, was the dissolution of the acidic calcium phosphate precursor, CaHPO4. Preliminary mechanical data indicated that the Young's modulus, yield strength, and work to fracture were at the lower end of the range of those values reported for bone. The porosities observed in these composites suggest that they might be osteoinductive while their compositions should allow their eventual resorption. Thus, microstructure, kinetics, and mechanical data suggest that these composites might be suitable as bone substitutes which form in vivo. © 1995 John Wiley & Sons, Inc.
Heparin release from thermosensitive polymer coatings: in vivo studies
Authors: Gutowska Anna , Bae You Han , Jacobs Harvey , Mohammad Fazal , Mix Donald , Feijen Jan , Kim Sung Wan
Published: May 2005

Biomer/poly(N‐isopropylacrylamide)/[poly(NiPAAm)] thermosensitive polymer blends were prepared and their application as heparin‐releasing polymer coatings for the prevention of surface‐induced thrombosis was examined. The advantage of using poly(NiPAAm)‐based coatings as heparin‐releasing polymers is based of the unique temperature‐dependent swelling of these materials. At room temperature, i.e., below the lower critical solution temperature (LCST) of poly(NiPAAm), the Biomer/(poly(NiPAAm)) coatings are highly swollen. The high swelling enables fast loading of hydrophilic macromolecules (e.g., heparin) into the coating by a solutions sorption technique. At a body temperature, i.e., above the LCST of poly(NiPAAm) the coatings are in a deswollen state and the absorbed macromolecules may be slowly released from a dense coating via a diffusion controlled mechanism. Biomer/poly(NiPAAm)) coatings were obtained by blending and coprecipitation of the two linear polymers, Biomer and (poly(NiPAAm). The structure and water‐swelling properties of the coatings were examined. Significant differences in water swelling at room temperature (RT) and 37°C were observed as a result of the thermosensitivity of poly(NiPAAm). The surface structure of the coatings in dry and swollen states at RT and 37°C was examined by scanning electron microscopy. Heparin was loaded into the coatings via a solution sorption at room temperature. Kinetic studies of heparin loading demonstrated that maximum loading was obtained within 1 h. The in vitro (37°C) release profiles were characterized by a rapid initial release due to the squeezing effect of the collapsing polymer network, followed by a slower release phase controlled by heparin diffusion through the dense coating. The short‐term antithrombogenicity of intravenous polyurethane catheters coated with heparin‐releasing Biomer/poly(NiPAAm) thermosensitive coating was evaluated in a canine animal model. The results show that the heparin release from Biomer/poly(NiPAAm)‐coated surfaces resulted in a significant reduction of thrombus formation on test surfaces in contact with venous blood as compared to control surfaces. © 1995 John Wiley & Sons, Inc.
Interspecies variation of compressive biomechanical properties of the meniscus
Authors: Joshi Meena D. , Suh Jun‐Kyo , Marui Takashi , Woo Savio L.‐Y.
Published: May 2005

Various animal models have been used to investigate the normal and reparative properties of the knee meniscus. Yet, only limited data on meniscal biomechanical properties of various animals are available. It was therefore the objective of this study to compare measurements of meniscal biomechanical properties between six species: human, bovine, monkey, canine, sheep, and porcine. Uniaxial confined compression tests were conducted on 1‐mm‐thick, 4‐mm‐diameter meniscal discs, and the viscoelastic creep deformation was obtained. Two biomechanical parameters, the aggregate modulus (HA) and permeability (κ), were found by implementing the linear biphasic theory and a newly developed nonlinear regression scheme. A one‐way analysis of variance was conducted along with Student‐Newman‐Keuls comparison tests to assess the differences in these parameters among the species. Sheep menisci exhibited HA and κ values most similar to human menisci. The water content of each specimen was also measured and correlated significantly with κ. The interspecies variations found in material properties of the knee meniscus indicate the need for caution in extrapolating data on the biomechanical behavior of the human meniscus from animal models. © 1995 John Wiley & Sons, Inc.
Viscoelastic and adherence properties of dental relining materials
Authors: Buch D. , Wehbi D. , Roques‐Carmes C.
Published: May 2005

The viscoelastic properties of three classes of soft relining materials (acrylic resins, silicones, and EVA copolymers) were studied comparatively. Their behaviors were investigated by in vitro tests at a frequency ω = 1 Hz, which simulates the masticatory cycle. The experimental parameter was the temperature (T). Black graphs giving the variations of the stiffness K—proportional to the complex viscoelastic modulus E*(T)ω—according to the phase angle δ, were used for a predictive approach to increase the comfort of removable dentures. Cole–Cole diagrams, describing the variation of the loss modulus E″(T)ω in relation to the storage modulus E′(T)ω additionally provide quantitative data. The values obtained were related to the noninteger parameter h used for modelization of the viscoelastic behavior of the materials by means of nonlinear Zener models. An attempt was made to correlate the experimental data to the viscoelastic energy loss observed when instability of the prosthetic structure occurs. This attempt takes into account the formation of “cracks” (areas of inadaptation) between the prosthetic intrados and the mucosa. © 1995 John Wiley & Sons, Inc.
Water transport in dehydrating hydrogel contact lenses: Implications for corneal desiccation
Authors: Martin Donald K.
Published: May 2005

This article provides direct evidence that the rate of evaporation from the anterior surface of a hydrogel contact lens is related to the bulk water transport within the contact lens, analogous to diffusion‐controlled evaporation. The evaporative flux of water from the anterior surface of a contact lens, with free access to water at its posterior surface, was greater for contact lenses of greater overall water content. Blockage of the water entry to the posterior surface of the contact lens reduced the evaporative loss from the anterior surface by 44%. These results suggested that a decrease in the rate of lens bulk water transport during wear would lead to a reduced evaporation rate from the anterior lens surface, for example, if the contact lens water content was reduced due to lipid and mucus adsorption. In addition, a rise in the external temperature of 1.3° was required to produce a significant increase (2 SD) in the evaporative flux from the contact lenses. This suggests that the steadystate water content in vivo may not be significantly influenced by temperature cycling during blinking. © 1995 John Wiley & Sons, Inc.
Surface microarchitectural design in biomedical applications: Preparation of microporous polymer surfaces by an excimer laser ablation technique
Authors: Nakayama Yasuhide , Matsuda Takehisa
Published: May 2005

In this report we demonstrate a microprocessing method to prepare microporous polymer films by an excimer laser ablation technique, which may enable the fabrication of functional biomedical devices such as advanced artificial organs. The irradiation of a KrF excimer laser pulses (wavelength 248 nm; fluence 1 J/cm2 pulse) onto several polymer films was achieved by passing a laser pulse through an optical microscope, resulting in the formation of an etched pit on the irradiated surface due to ablative photodecomposition. The number of pulses and the micropositioning of the irradiation were precisely controlled by a computeraided control unit. Minimal ablation was observed for polyethylene with very small absorption coefficient (α) at 248 nm. For polymers which absorbed the laser photons, the etch depth increased linearly with number of pulses. The etch depth per pulse decreased with an increase in α values. An excellent structural quality, with micron‐order precision of an etched pit, was found for those polymers with larger α a values, such as polyimide, segmented polyurethane, and polycarbonate. © 1995 John Wiley & Sons, Inc.
Contact activation during incubation of five different polyurethanes or glass in plasma
Authors: van der Kamp K. W. H. J. , Hauch K. D. , Feijen J. , Horbett T. A.
Published: May 2005

During blood‐material interaction, the enzymes factor XII fragment (factor XIIf) and kallikrein are generated (contact activation). In this study, the enzymatic activities of factor XIIf and kallikrein were examined with an assay based on the conversion of tripeptide‐p‐nitroanilide substrate. With the use of aprotinin to inhibit kallikrein, the proteolytic activities of factor XIIf and kallikrein could be separately determined. In this in vitro study, two commercially available polyurethanes, Pellethane and Biomer®; three custom synthesized polyurethanes; a biomerlike 2000 Mw polytetramethyleneoxide containing polyurethane (PU‐2000); an octadecyl extended (ODCE) biomer‐like 2000 Mw Polytetramethyleneoxide containing polyurethane (PU‐2000‐ODCE); a hard‐segment polyurethane (HS‐PU); and glass (reference material) were incubated in 25% diluted plasma. In both series of experiments, glass caused the highest amidolytic activities by factor XIIf and kallikrein compared with any of the polyurethanes. In contrast, within the polyurethane group of materials, lower amidolytic activities by factor XIIf and kallikrein were measured on the custom‐made polyurethanes than on the commercially available polyurethanes, although the differences among the polyurethanes were small. In addition, the influence of different ratios of material surface to the plasma incubation volume was studied. An increased ratio of surface area over plasma volume resulted in reduced contact activation, suggesting that plasma components are the limiting factor. © 1995 John Wiley & Sons, Inc.
Effect of annealing temperature on the degradation of reinforcing fibers for absorbable implants
Authors: Choueka Jack , Charvet Jose Luis , Alexander Harold , Oh Young H. , Joseph Gary , Blumenthal Norman C. , LaCourse William C.
Published: May 2005

Calcium phosphate fibers designed for reinforcement of bioabsorbable fracture fixation devices were evaluated for their properties upon annealing. The composition of these fibers were 54% PO4, 27% Ca, 12% ZnO, 2.5% NaPO3, and 4.5% Fe2O3, and they were either not annealed, annealed at 250°C, or annealed at 420°C. Chemical degradation, mass loss, and morphology upon degradation were studied. Chemical degradation was performed in Tris‐buffered HCl, while mass loss and morphologic studies were performed in both physiologic and nonphysiologic solutions. The results showed that degradation rates for fibers were inversely proportional to the annealing temperature. Mass loss analysis of fibers immersed in the two physiologic solutions (calf serum and simulated body fluid) revealed little change in fiber diameter up to 60 days. Morphologic examination revealed little change in fibers immersed in the two physiologic solutions until 60 days, after which thin shells were found to be peeling off the outer coating of the fiber. Samples in tris‐buffered HCl revealed a dramatic difference in mode of degradation among the three fibers. Fibers not annealed and those annealed at lower temperatures underwent a delaminating type of degradation that appeared to destroy the overall integrity of the fiber, whereas fibers annealed at 420°C underwent crater‐like deterioration in which the overall alignment of the fiber remained intact. It is therefore concluded that annealing fibers at higher temperatures slows degradation. The fibers annealed at the highest temperatures also undergo a mode of degradation that allows them to maintain their structural integrity. Although annealing of fibers close to glass transition temperature may produce an initially weaker fiber, chemical and physical degradation occur much slower, making these fibers most suitable for reinforcement of biodegradable implants. © 1995 John Wiley & Sons, Inc.
Preparation of a macroporous biodegradable polylactide implant for neuronal transplantation
Authors: Schugens Ch. , Grandfils Ch. , Jerome R. , Teyssie Ph. , Delree P. , Martin D. , Malgrange B. , Moonen G.
Published: May 2005

This article reports the production of a surgical implant meeting several specific requirements such as biocompatibility, biodegradability, macroporosity, and flexibility. Porosity was controlled by an original method consisting of the aggregation of calibrated poly‐D,L‐lactide microparticles. The size of the interstices between the aggregated microspheres was in a direct relationship to the microsphere diameter. A first approach was based on coating the microspheres with poly(vinyl alcohol) followed by chemically crosslinking the coating layers that were in mutual contact. This method was disregarded because of the acute cytotoxicity of glutaraldehyde used as the crosslinking agent, the absence of macroporosity, and the complete lack of flexibility. A physical technique of aggregation was then tested, which relied on the plasticization of poly‐D,L‐lactide microspheres with triethylcitrate to the point where microspheres strongly adhered to each other when they were in contact. This method has proved to be straightforward and definitely superior to the chemical approach, particularly with respect to cytotoxicity, control of macroporosity, and flexibility. A polymer support was thus successfully produced which was biodegradable, macroporous (interconnected pores of 10–100 μm in diameter), and flexible. This potential medical device is presently being used for neuronal transplantation in the central nervous system. © 1995 John Wiley & Sons, Inc.
Development of fibroblast‐seeded ligament analogs for ACL reconstruction
Authors: Dunn Michael G. , Liesch Janice B. , Tiku Moti L. , Zawadsky Joseph P.
Published: May 2005

We fabricated “ligament analogs” in vitro, by seeding highstrength resorbable collagen fiber scaffolds with intraarticular (anterior cruciate ligament, ACL) or extraarticular (patellar tendon, PT) rabbit fibroblasts. Fibroblasts attached, proliferated, and secreted new collagen on the ligament analogs in vitro. Fibroblast function depended on the tissue culture substrate (ligament analog vs. tissue culture plate) and the origin of the fibroblasts (ACL vs. PT). PT fibroblasts proliferated more rapidly than ACL fibroblasts when cultured on ligament analogs. Collagen synthesis by ACL and PT fibroblasts was approximately tenfold greater on ligament analogs than on tissue culture plates. The composition, structure, and geometry of the collagen fiber scaffolds may promote collagen synthesis within ligament analogs in vitro., Ligament analogs roughly approximate the structure and strength of native ligament tissue. Ongoing in vivo studies suggest that autogenous fibroblast‐seeded ligament analogs remain viable after implantation into the knee joint. With further development, ligament analogs may be useful as implants for ACL reconstruction surgery. © 1995 John Wiley & Sons, Inc.
Physical crosslinking of collagen fibers: Comparison of ultraviolet irradiation and dehydrothermal treatment
Authors: Weadock Kevin S. , Miller Edward J. , Bellincampi Lisa D. , Zawadsky Joseph P. , Dunn Michael G.
Published: May 2005

The strength, resorption rate, and biocompatibility of collagenous biomaterials are profoundly influenced by the method and extent of crosslinking. We compared the effects of two physical crosslinking methods, ultraviolet irradiation (UV) (254 nm) and dehydrothermal (DHT) treatment, on the mechanical properties and molecular integrity of collagen fibers extruded from an acidic dispersion of type I bovine dermal collagen. Collagen fibers exposed to UV irradiation for 15 min had ultimate tensile strength (54 MPa) and modulus (184 MPa) values greater than or equivalent to values for fibers crosslinked with DHT treatment for 3 or 5 days. UV irradiation is a rapid and easily controlled means of increasing the mechanical strength of collagen fibers. Characterization of collagen extracted from the crosslinked samples by dilute acetic acid and limited pepsin digestion indicate that both UV and DHT treatments cause fragmentation of at least a portion of the collagen molecules. Partial loss of the native collagen structure may influence attachment, migration, and proliferation of cells on collagen fiberbased ligament analogs. These issues are currently being addressed in our laboratory. © 1995 John Wiley & Sons, Inc.
Delayed in vitro immune response to long‐term intraperitoneal polymer implant in mice
Authors: Maurin N. , Guernier C. , Daty N.
Published: May 2005

This paper presents an original experimental procedure designed to evaluate, by a two step in vivo/in vitro combination, the long‐term biocompatibility of synthetic materials developed for clinical applications. The efficacy of the test is illustrated by the experimental results obtained with various materials currently used in medicine (Dacron®, RCH®) and also with three recently synthesized compounds. In the first step of the procedure, the sample was grafted for at least 5 months in the peritoneal cavity of mice, allowing the possible development of delayed sensitization. In the second step, this sensitization was detected by an in vitro test, the Lymphoblastic Transformation Test (LTT), adapted for this new purpose. On the basis of this experiment, the 5 polymers tested were classified into 2 groups: one group did not significantly differ from the control, and the other had a significantly higher incidence of sensitization. As these results were in agreement with the known biocompatibility of these polymers, they demonstrate the validity of the test to classify new polymers. © 1995 John Wiley & Sons, Inc.
Biomechanical and ultrastructural comparison of cryopreservation and a novel cellular extraction of porcine aortic valve leaflets
Authors: Courtman David W. , Pereira Christopher A. , Omar Sue , Langdon Shari E. , Lee J. Michael , Wilson Gregory J.
Published: May 2005

Heart valve substitutes of biological origin often fail by degenerative mechanisms. Many authors have hypothesized that mechanical fatigue and structural degradation are instrumental to in vivo failure. Since the properties of the structural matrix at implantation may predetermine failure, we have examined the ultrastructure, fracture, mechanics, and uniaxial high‐strain‐rate viscoelastic properties of: (1) fresh, (2) cryopreserved, and (3) cellular extracted porcine aortic valve leaflets. The cellular extraction process is being developed in order to reduce immunological attack and calcification. Cryopreservation causes cellular disruption and necrotic changes throughout the tissue, whereas extraction removes all cells and lipid membranes. Both processes leave an intact collagen and elastin structural matrix and preserve the high‐strain‐rate viscoelastic characteristics of the fresh leaflets. Extraction does cause a 20% reduction in the fracture tension and increases tissue extensibility, with the percent strain at fracture rising to 45.3 ± 4 (mean ± SEM) from 31.5 ± 3 for fresh leaflets. However, extraction does preserve matrix structure and mechanics over the physiological loading range. Glutaraldehyde fixation produces increased extensibility, increased elastic behavior, and, when applied to extracted leaflets, it causes a marked drop in fracture tension, to 50% of that for fresh leaflets. The combination of extraction and fixation may lead to early degenerative failure. The cellular extraction technique alone may be a useful alternative to glutaraldehyde fixation in preparing bioprosthetic heart valves. © 1995 John Wiley & Sons, Inc.