Measurement of the Viscoelastic Properties of the Vocal Folds

Objectives: Studies of the viscoelastic properties of the vocal folds are normally performed with rheometers that use parallel assigned a fixed value. In tissues subject to variation of thickness plates whose interplate space is usually at between samples, fixed gaps could result in different compressions, compromising the comparison among them. We performed,in experimental study to determine whether different compressions call lead to different results in measurements of dynamic viscosity (DV) of vocal fold samples. Methods: We Measured the DV of vocal fold samples of 10 larynges of cadavers under 3 different compression levels, corresponding to 0.2, 0.5, and 10 N on an 8-mm-diameter parallel-plate rheometer. Results: The DV directly varied with compression. We observed statistically significant differences between the results of 0.2 and 10 N (p = 0.0396) and 0.5 and 10 N (p = 0.0442). Conclusions: The study demonstrated that the level of compression influences the DV measure and Suggests that a defined compression level should be used in rheometric studies of biological tissues.

Thin films of xyloglucans for BSA adsorption

In this work. XG extracted from Tamarindus indica (XGT) and Copaifera langsdorffii (XGC) seeds were deposited onto Si wafers as thin films. The characteristics of XGT and XGC adsorbed layers were compared with a commercial XG sample (TKP, Tamarind kernel powder) by ellipsometry, and atomic force microscopy (AFM). Moreover, the adsorption of oxidized derivative of XGT (To60) onto amino-terminated Si wafers and the immobilization of bovine serum albumin (BSA) onto polysaccharides covered wafers, as a function of pH, were also investigated. The XG samples presented molar ratios Glc:Xyl:Gal of 2.4:2.1:1 (XGC) 2.8: 23: 1 (XGT) and 1.91.91 (TKP). The structure of XGT and XGC was determined by O-methy alditol acetate derivatization and showed similar features, but XGC confirmed the presence of more alpha-D-Xyl branches due to more beta-D-Gal ends. XGT deposited onto Si adsorbed as fibers and small entities uniformly distributed, as evidenced by AFM, while TPK and XGC formed larger aggregates. The thickness of To60 onto amino-terminated surface was similar to that determined for XGT onto Si wafers. A maximum in the adsorbed amount of BSA occurred close to its isoelectric point (5.5). These findings indicate that XGT and To60 are potential materials for the development of biomaterials and biotechnological devices. (C) 2008 Elsevier B.V. All rights reserved.

Microwave-Assisted Derivatization of Cellulose in an Ionic Liquid: An Efficient, Expedient Synthesis of Simple and Mixed Carboxylic Esters

Microwave (MW)-assisted cellulose dissolution in ionic liquids (ILs) has routinely led either to incomplete biopolymer solubilization, or its degradation. We show that these problems can be avoided by use of low-energy MW heating, coupled with efficient stirring. Dissolution of microcrystalline cellulose in the IL 1-allyl-3-methylimidazolium chloride has been achieved without changing its degree of polymerization; regenerated cellulose showed pronounced changes in its index of crystallinity, surface area, and morphology. MW-assisted functionalization of MCC by ethanoic, propanoic, butanoic, pentanoic, and hexanoic anhydrides has been studied. Compared with conventional heating, MW irradiation has resulted in considerable decrease in dissolution and reaction times. The value of the degree of substitution (DS) was found to be DS(ethanoate) > DS(propanoate) > DS(butanoate). The values of DS(pentanoate) and DS(hexanoate) were found to be slightly higher than DS(ethanoate). This surprising dependence on the chain length of the acylating agent has been reported before, but not rationalized. On the basis of the rate constants and activation parameters of the hydrolysis of ethanoic, butanoic, and hexanoic anhydrides in aqueous acetonitrile (a model acyl transfer reaction), we suggest that this result may be attributed to the balance between two opposing effects, namely, steric crowding and (cooperative) hydrophobic interactions between the anhydride and the cellulosic surface, whose lipophilicity has increased, due to its partial acylation. Four ethanoate-based mixed esters were synthesized by the reaction with a mixture of the two anhydrides; the ethanoate moiety predominated in all products. The DS is reproducible and the IL is easily recycled. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 134-143, 2010

Application of 1-Allyl-3-(1-butyl)imidazolium Chloride in the Synthesis of Cellulose Esters: Properties of the Ionic Liquid, and Comparison with Other Solvents

The ionic liquid (IL), 1-allyl-3-(1-butyl)imidazolium chloride (AlBuImCl), has been synthesized and its properties determined. Increase in the temperature increased its conductivity and decreased its density, polarity, and viscosity. Microcrystalline cellulose (MCC), dissolves in thisIL by heating at 80 degrees C; this did not affect its degree of polymerization, decreased its index of crystallinity (Ic), and changed in morphology after regeneration. Convenient acylation of MCC was achieved by using 50% excess anhydride at 80 degrees C, for 24 or 48 h for acetic and butyric anhydride, respectively. The composition of the mixed esters depended on the initial ratio of the anhydrides, and their order of addition.

Isosorbide Polyesters from Enzymatic Catalysis

The synthesis of isosorbide aliphatic polyesters is demonstrated by the use of Novozym 435, a catalyst consisting of Candida antarctica lipase B immobilized on a macroporous support Several experimental procedures were tested and azeotropic distillation was most effective in removing low mass byproduct Furthermore, the use of diethyl ester derivatives of diacid comonomers gave isosorbide copolyesters with highest Isolated yield and molecular weights The length of the diacid aliphatic chain was less restrictive, but with a clear preference for longer aliphatic chains The molecular mass values of the obtained products were equivalent or higher than those obtained by nonenzymatic polymerizations, a clear illustration of the potential of enzymatic over conventional catalysis The ability of Novozym 435 to catalyze the synthesis of isosorbide polyester with weight-average molecular weights in excess of 40000 Da was unexpected given that isosorbide has two chemically distinct secondary hydroxyl groups This is the first example in which isosorbide polyesters were synthesized by enzyme catalysis, opening a large array of possibilities for this important class of biomass-derived building blocks Because these polymers are potential biomaterials the total absence of conventional Lewis acid catalyst residues represents a major Improvement in the toxicity of the material

Effects of alloying elements on the cytotoxic response of titanium alloys

Titanium alloys, alloys, especially beta-type alloys containing beta-stabilizing elements, constitute a highly versatile category of metallic materials that have been under constant development for application in orthopedics and dentistry. This type of alloy generally presents a high mechanical strength-to-weight ratio, excellent corrosion resistance and low elastic modulus. The purpose of this study is to evaluate the cytotoxicity and adhesion of fibroblast cells on titanium alloy substrates containing Nb, Ta, Zr, Cu, Sn and Mo alloying elements. Cells cultured on polystyrene were used as controls. In vitro results with Vero cells demonstrated that the tested materials, except Cu-based alloy, presented high viability in short-term testing. Adhesion of cells cultured on disks showed no differences between the materials and reference except for the Ti-Cu alloy, which showed reduced adhesion attributed to poor metabolic activity. Titanium alloys with the addition of Nb, Ta, Zr, Sn and Mo elements show a promising potential for biomedical applications. (C) 2011 Elsevier B.V. All rights reserved.

On the interaction of bovine serum albumin with ionic surfactants: Temperature induced EPR changes of a maleimide nitroxide reflect local protein dynamics and probe solvent accessibility

The interaction of bovine serum albumin (BSA) with the ionic surfactants sodium dodecylsulfate (SDS, anionic), cetyltrimethylammonium chloride (CTAC, cationic) and N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS, zwitterionic) was studied by electron paramagnetic resonance (EPR) spectroscopy of spin label covalently bound to the single free thiol group of the protein. EPR spectra simulation allows to monitor the protein dynamics at the labeling site and to estimate the changes in standard Gibbs free energy, enthalpy and entropy for transferring the nitroxide side chain from the more motionally restricted to the less restricted component. Whereas SDS and CTAC showed similar increases in the dynamics of the protein backbone for all measured concentrations. HPS presented a smaller effect at concentrations above 1.5 mM. At 10 mM of surfactants and 0.15 mM BSA, the standard Gibbs free energy change was consistent with protein backbone conformations more expanded and exposed to the solvent as compared to the native protein, but with a less pronounced effect for HPS. In the presence of the surfactants, the enthalpy change, related to the energy required to dissociate the nitroxide side chain from the protein, was greater, suggesting a lower water activity. The nitroxide side chain also detected a higher viscosity environment in the vicinity of the paramagnetic probe induced by the addition of the surfactants. The results suggest that the surfactant-BSA interaction, at higher surfactant concentration, is affected by the affinities of the surfactant to its own micelles and micelle-like aggregates. Complementary DLS data suggests that the temperature induced changes monitored by the nitroxide probe reflects local changes in the vicinity of the single thiol group of Cys-34 BSA residue. (C) 2011 Elsevier B.V. All rights reserved.

Thermal and spectrophotometric studies of new crosslinking method for collagen matrix with glutaraldehyde acetals

Despite the many existing crosslinking procedures, glutaraldehyde (GA) is still the method of choice used in the manufacture of bioprosthesis. The major problems with GA are: (a) uncontrolled reactivity due to the chemical complexity or GA solutions; (b) toxicity due to the release of GA from polymeric crosslinks; and (c) tissue impermeabilization due to polymeric and heterogeneous crosslinks formation, partially responsible for the undesirable calcification of the bioprosthesis. A new method of crosslinking glutaraldehyde acetals has been developed with GA in acid ethanolic solution, and after the distribution inside de matrix, GA is released to crosslinking. Concentrations of hydrochloride acid in ethanolic solutions between 0.1 and 0.001 mol/L with GA concentration between 0.1 and 1.0% were measured in an ultraviolet spectrophotometer to verify the presence of free aldehyde groups and polymeric compounds of GA. After these measurements, the solutions were used to crosslink bovine pericardium. The spectrophotometric results showed that GA was better protected in acetal forms for acid ethanolic solution with HCl at 0.003 mol/L and GA 1.0%(v/v). The shrinkage temperature results of bovine pericardium crosslinked with acetal solutions showed values near 85 C after the exposure to triethylamine vapors.

Implants of polyanionic collagen matrix in bone defects of ovariectomized rats

In recent years, there has been a great interest in the development of biomaterials that could be used in the repair of bone defects. Collagen matrix (CM) has the advantage that it can be modified chemically to improve its mechanical properties. The aim of the present study was to evaluate the effect of three-dimensional membranes of native or anionic (submitted to alkaline treatment for 48 or 96 h) collagen matrix on the consolidation of osteoporosis bone fractures resulting from the gonadal hormone alterations caused by ovariectomy in rats subjected to hormone replacement therapy. The animals received the implants 4 months after ovariectomy and were sacrificed 8 weeks after implantation of the membranes into 4-mm wide bone defects created in the distal third of the femur with a surgical bur. Macroscopic analysis revealed the absence of pathological alterations in the implanted areas, suggesting that the material was biocompatible. Microscopic analysis showed a lower amount of bone ingrowth in the areas receiving the native membrane compared to the bone defects filled with the anionic membranes. In ovariectomized animals receiving anionic membranes, a delay in bone regeneration was observed mainly in animals not subjected to hormone replacement therapy. We conclude that anionic membranes treated with alkaline solution for 48 and 96 h presented better results in terms of bone ingrowth.

Interaction of giant extracellular Glossoscolex paulistus hemoglobin (HbGp) with zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS): Effects of oligomeric dissociation

The present work focuses on the interaction between the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp). Electronic optical absorption, fluorescence emission and circular dichroism spectroscopy techniques, together with Gel-filtration chromatography, were used in order to evaluate the oligomeric dissociation as well as the autoxidation of HbGp as a function of the interaction with HPS. A peculiar behavior was observed for the HPS-HbGp interaction: a complex ferric species formation equilibrium was promoted, as a consequence of the autoxidation and oligomeric dissociation processes. At pH 7.0, HPS is more effective up to 1 mM while at pH 9.0 the surfactant effect is more intense above 1 mM. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to two factors: (i) the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants, and (ii) the low cmc of HPS, which probably reduces the interaction of the surfactant in the monomeric form with the protein. The present work emphasizes the importance of the electrostatic contribution in the interaction between ionic surfactants and HbGp. Furthermore, in the whole HPS concentration range used in this study, no folding and autoxidation decrease induced by this surfactant were observed. This is quite different from the literature data on the interaction between surfactants and tetrameric hemoglobins, that supports the occurrence of this behavior for the intracellular hemoglobins at low surfactant concentration range. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin-surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on their structure-activity relationship. (c) 2007 Elsevier B.V. All rights reserved.

Interaction of bovine serum albumin (BSA) with ionic surfactants evaluated by electron paramagnetic resonance (EPR) spectroscopy

EPR spectra of 5- and 16-doxyl stearic acid nitroxide probes (5-DSA and 16-DSA, respectively) bound to bovine serum albumin (BSA) revealed that in the presence of ionic surfactants, at least, two label populations coexist in equilibrium. The rotational correlation times (tau) indicated that component I displays a more restricted mobility state, associated to the spin labels bound to the protein; the less immobilized component 2 is due to label localization in the surfactant aggregates. For both probes, the increase of surfactant concentration leads to higher motional levels of component 1 followed by a simultaneous decrease of this fraction of nitroxides and its conversion into component 2. For 10 mM cethyltrimethylammonium chloride (CTAC), the nitroxides are 100% bound to the protein, whereas at 10mM N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and sodium dodecyl sulfate (SDS) the fractions of bound nitroxides are reduced to 18% and 86%, respectively. No significant polarity changes were observed in the whole surfactant concentration range for component 1. Moreover, at higher surfactant concentration, component 2 exhibited a similar polarity as in the pure surfactant micelles. For 16-DSA the surfactant effect is different: at 10mM of HPS and CTAC the fractions of bound nitroxides are 76% and 49%, respectively, while at 10 mM SDS they are present exclusively in a micellar environment, consistent with 100% of component 2. Overall, both SDS and HPS are able to effectively displace the nitroxide probes from the protein binding sites. while CTAC seems to affect the nitroxide binding to a significantly smaller extent. (C) 2008 Elsevier B.V. All rights reserved.

Fabrication of novel metal alloy foams for biomedical applications

Degeneration of the weight bearing bones of the ageing population often requires the inception of metallic biomaterials. Research in this area is receiving increased attention globally. However, most of today's artificial bone materials are dense and suffer from problems of adverse reaction, biomechanical mismatch and lack of appropriate space for the regeneration of new bone tissues. In the present study, novel ZrTi alloy foams with a porous structure and mechanical properties that are very close to those of bone were fabricated. These ZrTi alloy foams are biocompatible, and display a porous structure permitting the ingrowth of new bone tissues.

Fabrication of novel TiZr alloy foams for biomedical applications

Bone injuries and failures often require the inception of implant biomaterial. Research in this area has received increasing attention recently. In particular, porous metals are attractive due to its unique physical, mechanical, and new bone tissue ingrowth properties. In the present study, TiZr alloy powders were prepared using mechanical alloying. Novel TiZr alloy foams with relative densities of approximately 0.3 were fabricated by a powder metallurgical process. The TiZr alloy foams displayed an interconnected porous structure resembling bone and the pore size ranged from 200 to 500 μm. The compressive plateau stress and the Young’s modulus of the TiZr foam were 78.4 MPa and 15.3 GPa, respectively. Both the porous structure and the mechanical properties of the TiZr foam were very close to those of natural bone.

Processing of biocompatible porous Ti and Mg

A new powder manufacturing process for Ti and Mg metallic foams designs porosity, pore size and morphology. These open-cellular foams (pores: 200–500 μm) have exceptional characteristics (e.g., Ti foam porosity 78%, compressive strength 35 MPa, Young's modulus 5.3 GPa). Anticipated applications include biocompatible implant materials.

Preparation and characterisation of new titanium based alloys for orthopaedic and dental applications

Various types of titanium alloys with high strength and low elastic modulus and, at the same time, vanadium and aluminium free have been developed as surgical biomaterials in recent years. Moreover, porous metals are promising hard tissue implants in orthopaedic and dentistry, where they mimic the porous structure and the low elastic modulus of natural bone. In the present study, new biocompatible Ti-based alloy foams with approximate relative densities of 0.4, in which Sn and Nb were added as alloying metals, were synthesised through powder metallurgy method.
The new alloys were prepared by mechanical alloying and subsequently sintered at high temperature using a vacuum furnace. The characteristics and the processability of the ball milled powders and the new porous titanium-based alloys were characterised by X-ray diffraction, optical
microscopy and scanning electron microscopy .The mechanical properties of the new titanium alloys were examined by Vickers microhardness measurements and compression testing.