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Record 4421 to 4438

Western blotting as a method for studying cell-biomaterial interactions: the role of protein collection
van Kooten, T. G., C. L. Klein, et al. (2001), J Biomed Mater Res 54(3): 385-9.
Abstract: Research of cell-biomaterial interactions is building on knowledge and methods available in cell and molecular biology. Western blotting is one of the options to characterize protein expression in cell populations. Method transfer to biomaterial model systems is not trivial because of the structure that exists in many biomaterials, preventing the collection of cell lysate by mechanical means. In this technical report, we describe the influence of different protein collection methods in a model system for cell-biomaterial interactions, consisting of endothelial cells exposed to different stimuli. In particular, the influence of trypsinization before lysis, and handling complexity were determined. The results of this study indicate that many changes in proteins occur because of the intermediate enzymatic treatment, despite the use of ice-cold solutions and protease and tyrosine phosphatase inhibitors throughout the procedure. Protein degradation and slight depressions in molecular weight were observed. The enzymatic treatment induced a changed cell status associated with detachment from the substratum. Western blotting of lysates of cells obtained through enzymatic harvest therefore can only be used with internal controls for the assessment of artifacts introduced by trypsinization, or alternative methods should be sought.

Wettability of cross-linked collagenous biomaterials: in vitro study
Cote, M. F. and C. J. Doillon (1992), Biomaterials 13(9): 612-6.
Abstract: Collagenous biomaterials can be treated by chemical and physical agents to decrease biodegradation rate. Treatments to collagen may modify surface properties and subsequently cell and platelet behaviour. Collagenous films were either uncross-linked and cross-linked by glutaraldehyde, formaldehyde or cyanamide and/or treated by a severe dehydration. Contact angles, platelet contacting assay and fibroblast morphology were investigated. After severe dehydration, wettability was diminished except for formaldehyde-cross-linked and severely dehydrated films. Glutaraldehyde-cross-linked collagen results in an increase in wettability. Platelets were similarly distributed, except on formaldehyde-cross-linked films that exhibited no platelet aggregation. Fibroblasts were in a spreading phase on most collagenous films. However, cytotoxicity was noticed on some aldehyde-cross-linked films. No direct relationship was found between contact angles and platelet-cell attachment.

What future for zirconia as a biomaterial?
Chevalier, J. (2006), Biomaterials 27(4): 535-43.
Abstract: The failure events of Prozyr femoral heads in 2001-2002 have opened a strong, controversial issue on the future of zirconia as a biomaterial. The aim of this paper is to review and analyze the current knowledge on ageing process and on its effect on the long term performance of implants in order to distinguish between scientific facts and speculation. Current state of the art shows the strong variability of zirconia to in vivo degradation, as a consequence of the strong influence of processing on ageing process. As different zirconia from different vendors have different process related microstructure, there is a need to assess their ageing sensitivity with advanced and accurate techniques, and ISO standards should be modified, especially to gain confidence from clinicians. There is a trend today to develop alumina-zirconia composites as an alternative to monolithic alumina and zirconia: the issue of ageing is also discussed for these composites.

What is the risk of stent thrombosis associated with the use of paclitaxel-eluting stents for percutaneous coronary intervention? a meta-analysis
Bavry, A. A., D. J. Kumbhani, et al. (2005), J Am Coll Cardiol 45(6): 941-6.
Abstract: OBJECTIVES: This study investigated the risk of stent thrombosis associated with the use of paclitaxel-eluting stents (PES) compared to bare-metal stents (BMS). BACKGROUND: Clinical experience with coronary drug-eluting stents (DES) is relatively limited. There is concern that DES used for percutaneous coronary intervention may result in subsequent thrombosis. METHODS: We conducted a meta-analysis on eight trials (total of 13 study arms) in 3,817 patients with coronary artery disease who were randomized to either PES or BMS. RESULTS: As compared with BMS, PES do not increase the hazard for thrombosis up to 12 months (risk ratio [RR] = 1.06, 95% confidence interval [CI] 0.55 to 2.04, p = 0.86]). There was no evidence of heterogeneity among the studies (chi-square value for Q-statistic = 5.90 [10 degrees of freedom], p = 0.82). Similar results were obtained when the analysis was restricted to trials with a polymeric stent platform (Treatment of de novo coronary disease using a single pAclitaXel elUting Stent [TAXUS]-I, -II, -IV, and -VI) (RR = 1.01, 95% CI 0.40 to 2.53, p = 0.99), trials with longer lesions (TAXUS-IV and -VI) (RR = 0.62, 95% CI 0.2 to 1.91, p = 0.41), and trials that used a higher dose of paclitaxel (ASian Paclitaxel-Eluting Stent Clinical trial [ASPECT], European evaLUaTion of paclitaxel Eluting Stents [ELUTES], and DELIVER-I) (RR = 1.87, 95% CI 0.52 to 6.81, p = 0.34). CONCLUSIONS: Current evidence suggests that standard dose PES do not increase the hazard of stent thrombosis compared to BMS.

What physical and/or biochemical characteristics of roughened endosseous implant surfaces particularly enhance their bone-implant contact capability?
Cooper, L. F., D. Deporter, et al. (2005), Int J Oral Maxillofac Implants 20(2): 307-12.

What's new in hip arthroplasty
Huo, M. H. and N. F. Gilbert (2005), J Bone Joint Surg Am 87(9): 2133-46.

Which glycosaminoglycans are suitable for antithrombogenic or athrombogenic coatings of biomaterials? Part I: Basic concepts of immobilized GAGs on partially cationized cellulose membrane
Baumann, H., U. Mueller, et al. (1997), Semin Thromb Hemost 23(2): 203-13.
Abstract: Six different GAGs of different natural origin such as unfractionated heparin (HE), chondroitin sulfate (CS), dermatan sulfate (DS), keratan sulfate (KS), endothelial cell surface heparan sulfate (ESHS), and hyaluronan (HA) have been ionically immobilized onto partially cationized cellulose membranes with a substitution degree of 0.06. The GAGs have been characterized in terms of total sulfate content and relative molecular weight. The amount of immobilized GAGs was 10(3) times higher than the theoretical amount for monomolecular side-to-side coordination on polymer surfaces. In a standardized perfusion system with shear rates of 1050 sec-1, 37 degrees C, and 5 minutes with citrated blood, the level of platelet adhesion was 100% for partially cationized membrane, 90% for HA, 75% for each HE, CS, DS, KS, 5% for unmodified cellulose membrane, and 5% for confluent bovine aorta endothelial cells, referred to subendothelial matrix as standard for 100% platelet adhesion. ESHS-coated membranes were completely inert to platelets. The amount of ionically released GAGs during perfusion was also estimated. The partial cationic membrane is a suitable polymer surface in combination with the perfusion system to estimate the hemocompatibility of ionically immobilized water-soluble polyanions in terms of platelet adhesion at defined shear rates. The results of platelet adhesion are discussed in terms of structure and analytical parameter of the immobilized GAGs.

Which glycosaminoglycans are suitable for antithrombogenic or athrombogenic coatings of biomaterials? Part II: Covalently immobilized endothelial cell surface heparan sulfate (ESHS) and heparin (HE) on synthetic polymers and results of animal experiments
Baumann, H. and R. Keller (1997), Semin Thromb Hemost 23(2): 215-23.
Abstract: A systematic study was performed on immobilizing unfractionated heparin and endothelial cell surface heparan sulfate covalently with the spacer concept onto two polymer surfaces, followed by characterization of the surface concentration and in vitro and in vivo platelet adhesion properties under comparable high shear rates for microvascular vessels. Oligoamide spacer with a 16-atom chain length on cellulose surface and an 11-atom chain length on silicon surface, respectively, was used for immobilizing HE and ESHS via amino groups of glucosamine to the spacer which was anchored to the polymer surface. The surface concentration was in the range of 7 to 10 pmol/cm2 for HE and 1 to 1.5 pmol/cm2 for ESHS. This is in agreement with a calculated monolayer covering of ESHS and HE. In vitro and preliminary in vivo measurements (beagle, sheep) showed no platelet adhesion on the ESHS coatings, whereas HE showed high platelet adhesion and thrombus formation in vitro as well as in vivo. ESHS coating may be a potential candidate for preparing smooth artificial microvascular blood vessels.

Wound healing: bone and biomaterials
Kent, J. N. and M. F. Zide (1984), Otolaryngol Clin North Am 17(2): 273-319.

Xeroradiography for imaging biomaterials--A comparison with conventional radiography
Gratt, B. M., E. A. Sickles, et al. (1980), J Prosthet Dent 44(5): 567-72.
Abstract: Our visual comparison of dental xeroradiographs versus conventional film radiographs demonstrated the superiority of the dental xeroradiographic technique for the imaging of all radiolucent and mild-to-moderately radiopaque materials. Both systems were equally valuable for the imaging of very dense radiographic materials such as gold and amalgam alloys.

X-ray absorption fine structure analysis of the local environment of zinc in dentine treated with zinc compounds
Takatsuka, T., J. Hirano, et al. (2005), Eur J Oral Sci 113(2): 180-3.
Abstract: It has been reported that zinc oxide (ZnO) inhibits dentine demineralization. By using the X-ray absorption fine structure (XAFS) technique, our aims in this study were to provide information about the local environment of zinc atoms in dentine that had been treated with zinc compounds. We measured the Zn K-edge X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) of dentine specimens treated with zinc chloride or ZnO. In XAFS analyses, the spectra of dentine specimens treated with ZnO (D-ZO) or with zinc chloride (D-ZC) were similar and obviously different from the reference ZnO spectrum. This suggests that most of the zinc atoms detected in D-ZO are not derived from particles of ZnO. The spectra of D-ZO and D-ZC were similar to the spectrum of the synthetic, zinc-containing hydroxyapatite, but were not similar to that of zinc in ZnCl2-treated collagen. The results of this study suggest that most of the zinc atoms detected were attached to hydroxyapatite and not to collagen.

X-ray beam/biomaterial thermal interactions in third-generation synchrotron sources
Kuzay, T. M., M. Kazmierczak, et al. (2001), Acta Crystallogr D Biol Crystallogr 57(Pt 1): 69-81.
Abstract: Third-generation synchrotron sources generate strong X-ray beams. The beam's interaction with biomaterials gives rise to concerns related to thermal damage and radiation damage. Of the two issues, the thermal interaction is conducive to rigorous analysis from first principles, although this has not been performed to date in a comprehensive manner. In this study, the interaction of the X-ray beam emanating from a third-generation synchrotron with a typical frozen biocrystal is theoretically studied, focusing specifically on the resulting unsteady (time-dependent) and steady heat-transfer phenomena. A unique regime map is developed to explain and to identify, on the basis of Fourier and Biot numbers as governing parameters, the applicable mathematical models that predict the subsequent thermal behavior. Depending on the values of these parameters, some simplified but realistic 'generic' solutions are generated that are suitable for that particular domain of applicability. Classical heat-transfer theory was used to describe the third-generation X-ray beam and biomaterial thermal interaction. Besides the generalized approach presented, numerous illustrative cases were solved and the resulting temperature levels are explicitly presented. Overall, the resulting thermal behavior of the system, i.e. peak and local temperature distribution, during both early transient development and for sustained long-time steady-state conditions, depends on a number of factors including the amount of energy absorbed, convective heat-transfer film coefficient and gas temperature, the sample size and shape, and the thermophysical properties of the sample and cooling gas. Results of the analysis revealed the strong influence that convection has on the transient and final steady-state temperature of the sample and the impact of internal heat conduction. The characteristic timescales of the important and dominant thermal processes with respect to the two types of thermal models are clearly identified.

X-ray diffraction method for the investigation of contacts between solid surfaces
Keymeulen, H. R., T. Lackner, et al. (2005), J Synchrotron Radiat 12(Pt 4): 484-7.
Abstract: A coherent X-ray scattering method for investigating the formation of the contact region between two solid surfaces is presented. Diffraction of X-rays from two crossed cylindrical quartz surfaces, coated with Cr and TiO(2), revealed a total contact area of 90 +/- 10 microm. In the so-called Hertz model for two surfaces in non-adhesive contact, this value is directly related to the displacement of the surfaces and the applied external force. Values of 40 +/- 3 nm for the displacement and 24 +/- 3 mN for the force are found. The method is also useful for studying liquids in confinement.

X-ray photoelectron spectroscopy studies, surface tension measurements, immobilization of human serum albumin, human fibrinogen and human fibronectin onto ammonia plasma treated surfaces of biomaterials useful for cardiovascular implants and artificial cornea implants
Sipehia, R. (1993), Biomater Artif Cells Immobilization Biotechnol 21(5): 647-58.
Abstract: XPS studies of untreated and ammonia plasma treated surfaces of PTFE, ePTFE, Dacron, P(HEMA), PMMA, Silastic and PS were carried out. Ammonia plasma treatment caused significant changes in the surface composition. The curve-fitting results confirmed the incorporation of nitrogen and oxygen in the form of functional groups such as C-N, C=O, C-O, Si-N, Si-OH etc. Increases in the values of surface tension occurred. The surface tension of plasma treated surfaces varied between 44-48 erg/cm2 with the exception of Dacron which became wettable. Enhanced immobilization of human albumin on plasma treated surfaces was achieved. When washed with 0.2% Tween in buffer, these albuminated surfaces were found to be stable compared to control samples. Increased immobilization of human fibrinogen was also observed. The ammonia plasma treated surfaces showed high binding properties and retention for human fibronectin. Ionic interaction between proteins solution and plasma treated surfaces may be cause of the increase attachment of these biological molecules.

X-ray-diffraction characterization of Pt(111) surface nanopatterning induced by C60 adsorption
Felici, R., M. Pedio, et al. (2005), Nat Mater 4(9): 688-92.
Abstract: Understanding the adsorption mechanisms of large molecules on metal surfaces is a demanding task. Theoretical predictions are difficult because of the large number of atoms that have to be considered in the calculations, and experiments aiming to solve the molecule-substrate interaction geometry are almost impossible with standard laboratory techniques. Here, we show that the adsorption of complex organic molecules can induce perfectly ordered nanostructuring of metal surfaces. We use surface X-ray diffraction to investigate in detail the bonding geometry of C(60) with the Pt(111) surface, and to elucidate the interaction mechanism leading to the restructuring of the Pt(111) surface. The chemical interaction between one monolayer of C(60) molecules and the clean Pt(111) surface results in the formation of an ordered sqrt[13] x sqrt[13]R13.9 degrees reconstruction based on the creation of a surface vacancy lattice. The C(60) molecules are located on top of the vacancies, and 12 covalent bonds are formed between the carbon atoms and the 6 platinum surface atoms around the vacancies. In-plane displacements induced on the platinum substrate are of the order of a few picometres in the top layer, and are undetectable in the deeper layers.

Yeast extract and methyl jasmonate-induced silymarin production in cell cultures of Silybum marianum (L.) Gaertn
Sanchez-Sampedro, M. A., J. Fernandez-Tarrago, et al. (2005), J Biotechnol 119(1): 60-9.
Abstract: The biosynthesis of the flavonolignan silymarin, a constitutive compound of the fruits of Silybum marianum with strong antihepatotoxic and hepatoprotective activities, is severely reduced in cell cultures of this species. It is well known that elicitation is one of the strategies employed to increase accumulation of secondary metabolites. Our study here reports on the effect of several compounds on the production of silymarin in S. marianum cultures. Yeast extract (YE), chitin and chitosan were compared with respect to their effects on silymarin accumulation in S. marianum suspensions and only yeast extract stimulated production. Jasmonic acid (JA) potentiated the yeast extract effect. One of the jasmonic acid derivatives, methyl jasmonate (MeJA), strongly promoted the accumulation of silymarin. Methyl jasmonate acted in a number of steps of the metabolic pathway of flavonolignans and its stimulating effect was totally dependent of "de novo" protein synthesis. Chalcone synthase (CHS) activity was enhanced by methyl jasmonate; however there did not appear to be a temporal relationship between silymarin accumulation and increase in enzyme activity. Also, this increase was not blocked by the protein synthesis inhibitor cycloheximide (CH). This study indicates that elicitor treatment promotes secondary metabolite production in S. marianum cultures and that jasmonic acid and its functional analogue plays a critical role in elicitation.

Zinc ion release from novel hard tissue biomaterials
Towler, M. R., S. Kenny, et al. (2004), Biomed Mater Eng 14(4): 565-72.
Abstract: Zinc polyalkenoate cements (ZPCs) and glass polyalkenoate cements (GPCs) are used routinely in dentistry, but have potential for orthopaedic applications as they set at body temperature without shrinkage or significant heat evolution. However, the materials have drawbacks; ZPCs are biocompatible in implant studies, but a fibrous collagen capsular layer forms adjacent to the cement. GPCs are bioactive in the bone environment as a result of the release of calcium, phosphate and fluoride ions, as well as the formation of a silicious gel phase, but research has shown that aluminum ions released result in defective bone mineralisation and as a consequence the ability of these cements to chemically bond to bone is lost. Two approaches have been developed to overcome these problems. The ZPC route considers a ZnO: hydroxyapatite (HA): poly(acrylic acid) (PAA) mixture, the HA incorporated to improve bioactivity. The GPC route employs a calcium zinc silicate glass; the zinc taking the role that aluminum plays in conventional GPCs. This study has shown that cements can be formulated by an acid base reaction between PAA and both calcium zinc silicate glasses (GPCs) and a mixture of hydroxyapatite and zinc oxide (ZPCs). The moduli of these cements are comparable to both bone and conventional acrylic cements, highlighting their potential for biomedical applications. Unfortunately, both materials have previously been shown to be toxic by cell culture methods, as a result of high zinc ion release, and so it is necessary to study ion release profiles of the cements in order to determine the magnitude of this release. Considering the ZPCs, the modulus of the cement has an inversely proportional relationship to the zinc ion release. From the data presented it is clear that increases in polymer concentration results in lower amounts of zinc ions being released, whilst molar mass of the PAA has no influence. Therefore it would appear that polymer concentration has a significant influence over ion release. Generally, the amount of Zn(2+) released decreases with increasing HA content and/or decreasing ZnO content. Considering the GPCs, the materials are all seen to release large amounts of the active ion, when compared to the commercial versions. The extent of this release increases with temperature and agitation. The release could be minimised by an increased P: L mixing ratio, and an increased PAA concentration, which would produce a more cross-linked cement matrix. Minimising the release of the active ion should improve the in vitro bioactivity of both materials. However, for a full understanding of the clinical benefits of such materials, an in vivo study would be required.

Zirconia as a ceramic biomaterial
Piconi, C. and G. Maccauro (1999), Biomaterials 20(1): 1-25.
Abstract: Zirconia ceramics have several advantages over other ceramic materials, due to the transformation toughening mechanisms operating in their microstructure that can give to components made out of them, very interesting mechanical properties. The research on the use of zirconia ceramics as biomaterials started about twenty years ago, and now zirconia (Y-YZP) is in clinical use in THR, but developments are in progress for application in other medical devices. Recent developments have concentrated on the chemistry of precursors, in forming and sintering processes, and on surface finish of components. Today's main applications of zirconia ceramics is in THR ball heads. This review takes into account the main results achieved up to now, and is focused on the role that microstructural characteristics play on the TZP ceramics behaviour in ball heads, namely mechanical properties and their stability, wear of the UHMWPE paired to TZP, and their influence on biocompatibility.

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