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On the yield stress of complex materials
F. Calderas,E. E. Herrera-Valencia,A. Sanchez-Solis,O. Manero,L. Medina-Torres,A. Renteria,G. Sanchez-Olivares 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.4
In the present work, the yield stress of complex materials is analyzed and modeled using the Bautista-Manero-Puig (BMP) constitutive equation, consisting of the upper-convected Maxwell equation coupled to a kinetic equation to account for the breakdown and reformation of the fluid structure. BMP model predictions for a complex fluid in different flow situations are analyzed and compared with yield stress predictions of other rheological models, and with experiments on fluids that exhibit yield stresses. It is shown that one of the main features of the BMP model is that it predicts a real yield stress (elastic solid or Hookean behavior) as one of the material parameters, the zero shear-rate fluidity, is zero. In addition, the transition to fluid-like behavior is continuous, as opposed to predictions of more empirical models.
Rheology and gel point of the enzymatic hydrolysis of urea in the presence of urease
R. Serrato-Millán,L. Medina-Torres,F. Calderas,B.L. España-Sánchez,M. Estevez,A.R. Hernandez-Martínez,M. Cruz-Soto,I.C. Sánchez,R. Gómez-García,I. Sánchez-Betancourt,M.C. Velasquillo-Martínez,G. Luna- 한국유변학회 2017 Korea-Australia rheology journal Vol.29 No.1
This study reports on the rheology of the gelation kinetics of raw chitosan (CTS) solutions (2% w/v) produced by enzymatic hydrolysis of urea at different urea concentrations (40, 50, 60, 80, and 100 mM) in the presence of urease at 1 U/mL. Viscoelastic parameters and pH values were evaluated during gelation process and the rheological properties of CTS hydrogels produced were monitored after 24 h at 37°C to simulate human body temperatures. pH measurements suggest that above some critical urea concentration (50 mM) the time required (tgel) to reach the critical pH gelation shows no dependence on urea concentration (tgel was ca. 70 minutes). Above 50 mM of urea concentration, CTS hydrogels exhibit an elastic modulus G' higher than the viscous modulus G'' with no frequency dependence characteristic of a gel behavior. Gelation kinetics analyzed by rheology suggest that the G' (i.e., structure) development depends on urea concentration during solution neutralization.
Simultaneous pulsatile flow and oscillating wall of a non-Newtonian liquid
E.E. Herrera-Valencia,M.L. Sánchez-Villavicencio,F. Calderas,M. Pérez-Camacho,L. Medina-Torres 한국유변학회 2016 Korea-Australia rheology journal Vol.28 No.4
In this work, analytical predictions of the rectilinear flow of a non-Newtonian liquid are given. The fluid is subjected to a combined flow: A pulsatile time-dependent pressure gradient and a random longitudinal vibration at the wall acting simultaneously. The fluctuating component of the combined pressure gradient and oscillating flow is assumed to be of small amplitude and can be adequately represented by a weakly stochastic process, for which a quasi-static perturbation solution scheme is suggested, in terms of a small parameter. This flow is analyzed with the Tanner constitutive equation model with the viscosity function represented by the Ellis model. According to the coupled Tanner-Ellis model, the flow enhancement can be separated in two contributions (pulsatile and oscillating mechanisms) and the power requirement is always positive and can be interpreted as the sum of a pulsatile, oscillating, and the coupled systems respectively. Both expressions depend on the amplitude of the oscillations, the perturbation parameter, the exponent of the Ellis model (associated to the shear thinning or thickening mechanisms), and the Reynolds and Deborah numbers. At small wall stress values, the flow enhancement is dominated by the axial wall oscillations whereas at high wall stress values, the system is governed by the pulsating noise perturbation. The flow transition is obtained for a critical shear stress which is a function of the Reynolds number, dimensionless frequency and the ratio of the two amplitudes associated with the pulsating and oscillating perturbations. In addition, the flow enhancement is compared with analytical and numerical predictions of the Reiner-Phillipoff and Carreau models. Finally, the flow enhancement and power requirement are predicted using biological rheometric data of blood with low cholesterol content.
Edith E. Lopéz-Martínez,Jesús A. Claudio-Rizo,Martín Caldera-Villalobos,Juan J. Becerra-Rodríguez,Denis A. Cabrera-Munguía,Lucía F. Cano-Salazar,Rebeca Betancourt-Galindo 한국고분자학회 2022 Macromolecular Research Vol.30 No.6
Determining the controlled release capacity of drugs with therapeutic interest as well as the biocompatibility of hydrogels based on natural and synthetic polymers is of the utmost importance to evaluate their potential performance in regenerative medicine strategies. Novel hydrogels were synthesized by semi-interpenetration of guar gum (GG) in a matrix of crosslinked collagen with hydrophilic polyurethane. GG concentrations of 10, 20, 30 and 40 wt% on the semi-IPN matrices were tested. These hydrogels have excellent in vitro biocompatibility, not demonstrating cytotoxic character for cells important in the healing process such as monocytes and fibroblasts, stimulating their proliferation, as well as evidencing hemocompatibility and antibacterial capacity. Also these matrices can encapsulate and release methylene blue in a controlled manner. The results of the evaluation of human monocyte signaling indicate that the semi-IPN matrix containing 30 wt% of GG allows higher segregation of beta-1 transforming growth factor (β1-TGF), a determinant cytokine in the construction of new tissue, showing that these hydrogels have potential application in biomedicine as dressings for chronic wound healing.
Edith E. Lopéz-Martínez,Jesús A. Claudio-Rizo,Martín Caldera-Villalobos,Juan J. Becerra-Rodríguez,Denis A. Cabrera-Munguía,Lucía F. Cano-Salazar,Rebeca Betancourt-Galindo 한국고분자학회 2022 Macromolecular Research Vol.30 No.6
Novel synthetic strategies to produce biopolymer based hydrogels for biomedical applications are required currently. Collagen hydrogels for wound healing can improve their structural and physicochemical properties by incorporating polysaccharides within the fibrillar matrix. Novel hydrogels were synthesized by semi-interpenetration of guar gum (GG) in a matrix of crosslinked collagen with hydrophilic polyurethane. GG concentrations of 10, 20, 30, and 40 wt% on the semi- IPN matrices were tested. The addition of the polysaccharide accelerates the gelling time of the hydrogels; 30 wt% of GG allows a 68 ± 5% of physicochemical crosslinking, exhibiting a maximum swelling of 3496 ± 89% and both improved mechanical and thermal resistance. The short-range interactions established in these matrices, mainly of the hydrogen bond type, make it possible to delay their hydrolytic and proteolytic degradation. The structure and properties of these hydrogels could have potential application in biomedicine as dressings for chronic wound healing, tailoring the controlled release of drugs with therapeutic interest, cell viability and proliferation, cell signaling, hemocompatibility and antibacterial character.