Isabel Delgadillo-Holtfort | Universidad de Guanajuato (original) (raw)

Papers by Isabel Delgadillo-Holtfort

Journal of Biomedical Materials Research Part A

European Polymer Journal, 2006

Grafting polymerisation of methyl methacrylate and ethyl acrylate onto linen and cotton was carri... more Grafting polymerisation of methyl methacrylate and ethyl acrylate onto linen and cotton was carried out in order to reinforce these materials, when they underwent degradation. Take into account this aim, an artificially ageing was performed onto cellulose based textiles by metaperiodate oxidation, in order to obtain degraded model samples. Carbonyl groups were introduced in the cellulose and used as photosensitive agents, allowing the formation of radical sites during the polymerisation reaction, that started by irradiating the substrate by ultraviolet light. In this paper the effectiveness of grafting polymerisation as a method for textile conservation is discussed, starting from the results obtained from several characterisations, as the grafting yields and the grafting efficacy evaluation, the DSC analysis, the FTIR spectroscopy and the SEM observations. Moreover the consolidating and the protective effects were investigated by evaluating the mechanical properties and the wetting behaviour of the grafted samples, and comparing them with the original and aged substrates. The mechanical strength of cellulose based textiles has been improved, as well as the wetting behaviour has been enhanced.

Photothermal methods based on IR radiometry, photopyroelectric detection and thermoreflectance ha... more Photothermal methods based on IR radiometry, photopyroelectric detection and thermoreflectance have been applied to NiTi shape memory alloys to characterize the thermal properties of the as-prepared samples and to determine the changes of the thermal properties induced by thermal and mechanical treatment and cycling. Using photopyroelectric detection, the integral diffusivity of the treated and non treated samples has been determined. Depth profiles of the thermal properties of the mechanically and thermally cycled ribbon samples were measured using photothermal radiometry. A photothermal microscope based on thermoreflectance was applied to monitor the thermal properties across the ribbon edge and to image the thermal and optical variations inside a grove which had been milled into a NiTi shape memory specimen.

Res. Comput. Sci., 2019

Chitosan is a biopolymer widely used for many applications, especially in the biomedical field, d... more Chitosan is a biopolymer widely used for many applications, especially in the biomedical field, due to its interesting properties like excellent sorption capability, biodegradability and biocompatibility. The presence of reactive groups in the structure of this biopolymer makes possible the attachment of different molecules. In this study a chitosan thread is synthesized, using a microfluidic technique with two merging channels of acidic chitosan and hydroxide, in order to use it as a controlled release device of drugs. Varying the flows of the fluids in the channels is possible to control the diameter of the thread, obtaining samples of medium and high molecular weight for each flow rate used in the synthesis. The obtained thread of chitosan was mechanically characterized performing tensile tests until failure and stress relaxation tests. An optical system of polarizers was set to visualize the alignment of the polymeric chains while the material is elongated during the tensile test. Young modulus is obtained for each type of sample to quantify the stiffness of the material, and relaxation times were calculated to observe the viscoelastic behavior. Alignment of the material was confirmed, since birefringence was shown.

Research on computing science, 2020

The Electrical Bioimpedance (EBI) has been used for gastric activity monitoring as an alternative... more The Electrical Bioimpedance (EBI) has been used for gastric activity monitoring as an alternative to electrogastrography (EGG). The signal obtained by this technique has interference from all other motility signals from the gastrointestinal region, mainly the colon. This is because the colon motility appears in a frequency range that overlaps with that for the gastric frequency range. In fact, EGG technique has the same problem, but this is usually considered negligible and many times is not considered in the discussion. The main objective of this investigation is to elucidate if it is possible to discriminate, with simultaneous measurements in the abdominal region, both mechanical activities by non-invasive electrical bioimpedance technique.

The resonant ultrasound spectroscopy (RUS) is a non-destructive characterization or assessment te... more The resonant ultrasound spectroscopy (RUS) is a non-destructive characterization or assessment technique based upon the measurement of the mechanical resonant spectra of the samples [1]. In this work, RUS measurements have been performed upon composite samples consisting of a hard material embedded in a softer medium, as well as upon their separate components. The hard components used have been galvanized steel rods of 1 mm diameter and lengths of 15 and 27 mm. The softer medium was a seedless green grape of 29 mm length and 18 mm width. The two composite samples considered have been obtained by insertion into the grape of one rod at a time. The measured spectra have been compared and the feasibility of recognition of the spectra of the separate components from the composite spectrum is discussed.

Preliminary results have shown that bioelectrical impedance measurements performed on different p... more Preliminary results have shown that bioelectrical impedance measurements performed on different parts of the human body strongly depend upon the subcutaneous fat of the considered region. In this work, a method for the determination of subcutaneous fat thickness is explored. Within this method the measurement of the bioelectrical impedance response of the fat-muscle system, both along the direction defined by the muscle fibers and along the corresponding perpendicular direction, are performed. Measurements have been carried out on human female and male subjects of ages around 25 years old at the region of the biceps. Correlation has been performed with skinfold caliper measurements.

Macromolecular Bioscience

Macromolecular bioscience, Jan 25, 2018

The polarization of macrophages M0 to M1 or M2 using molecules embedded in matrices and hydrogels... more The polarization of macrophages M0 to M1 or M2 using molecules embedded in matrices and hydrogels is an active field of study. The design of biomaterials capable of promoting polarization has become a paramount need nowadays, since in the healing process macrophages M1 and M2 modulate the inflammatory response. In this work, several immunocytochemistry and ELISA tests strongly suggest the achievement of polarization using collagen-based membranes crosslinked with tri-functionalized oligourethanes and coated with silica. Measuring the amount of TGF-β1 secreted to culture media by macrophages growth on these materials, and quantifying the macrophage morphology, it is proved that it is possible to stimulate the anti-inflammatory pathway toward M2, having measurements with p ≤ 0.05 of statistical significance between the control and the collagen-based membranes. Furthermore, some physicochemical characteristics of the hybrid materials are tested envisaging future applications: collagena...

In this work we employ the resonant ultrasound spectroscopy technique in time-domain to perform a... more In this work we employ the resonant ultrasound spectroscopy technique in time-domain to perform an explorative geometrical study of bone phantoms. We measured a set of acrylic tubes of equal length but with different internal diameters in order to make a first step study related to the decrease in wall thickness due to osteoporosis process in human bones. We considered the spectra obtained with the sample subjected to pressure and their development to the free body resonance frequency spectra.

Materials Science Forum, 2002

World Journal of Gastrointestinal Pathophysiology, 2013

The aim of this review is to provide a general overview of the relationship between occupational ... more The aim of this review is to provide a general overview of the relationship between occupational stress and gastrointestinal alterations. The International Labour Organization suggests occupational health includes psychological aspects to achieve mental well-being. However, the definition of health risks for an occupation includes biological, chemical, physical and ergonomic factors but does not address psychological stress or other affective disorders. Nevertheless, multiple investigations have studied occupational stress and its physiological consequences, focusing on specific risk groups and occupations considered stressful. Among the physiological effects of stress, gastrointestinal tract (GIT) alterations are highly prevalent. The relationship between occupational stress and GIT diseases is evident in everyday clinical practice; however, the usual strategy is to attack the effects but not the root of the problem. That is, in clinics, occupational stress is recognized as a source of GIT problems, but employers do not ascribe it enough importance as a risk factor, in general, and for gastrointestinal health, in particular. The identification, stratification, measurement and evaluation of stress and its associated corrective strategies, particularly for occupational stress, are important topics to address in the near future to establish the basis for considering stress as an important risk factor in occupational health.

Materialwissenschaft und Werkstofftechnik, 2000

Protective layers, such as CVD and PVD coatings on steel substrates, surface modifications relate... more Protective layers, such as CVD and PVD coatings on steel substrates, surface modifications related to friction wear, and the effects of mechanical and thermal cycling of SMA samples have been analysed with respect to the depth profile of the thermal properties by using IR detection of thermal waves. The advantage of IR detection of thermal waves is that this method is most appropriate for remote sensing under industrial conditions, working absolutely contactless with remote detection and without any sample preparation. Hartstoffschichten und Oberfla Èchenmodifikationen, die durch Reibungsverschleiû oder thermisches und mechanisches Zyklieren von FGL-Proben erzeugt wurden, werden hier mittels IR-Radiometrie thermischer Wellen in Bezug auf die Tiefenprofilierung ihrer thermischen Eigenschaften untersucht. Diese Messungen geben direkte Information u Èber das Tiefenprofil der thermischen Parameter und u Èber damit verbundene andere Gro Èûen, z.B. die Dicke von Schichten unterschiedlicher thermischer Eigenschaften. Die IR-Radiometrie thermischer Wellen ist besonders gut fu Èr den Einsatz im industriellen Umfeld geeignet, da die Methode absolut kontaktlos arbeitet, u Èber gro Èûere Entfernungen hinweg zwischen Probe und Messsystem, und ohne eine besondere Probenvorbereitung eingesetzt werden kann.

Materials Science and Engineering: A, 2004

Dislocations are induced in polycrystalline NiTi shape memory alloy by thermal and mechanical cyc... more Dislocations are induced in polycrystalline NiTi shape memory alloy by thermal and mechanical cycling. The variation of the ultrasonic velocity and the attenuation with frequency in the range 2-60 MHz was measured at room temperature. The frequency dependent experimental data are well described in the frame of a vibrating string-model. The fits yield length and density of the dislocations in cycled and non-cycled samples. Depositing the sample at 300 K for a couple of days leads to a reduction of the dislocation density accompanied with an increase of the transition temperature.

Materials Science and Engineering: A, 2004

Local variations of the phase transition temperatures are important for the functionality of actu... more Local variations of the phase transition temperatures are important for the functionality of actuators based on NiTi shape memory alloys. Mechanical distortions induced by process treatment can suppress the phase transition from the austenitic to the martensitic structure. In this work, local changes of the phase transition have been investigated by time-dependent IR thermography. For the quantitative interpretation of the thermographical measurements, information about the IR emissivity is important. In this work a new thermal wave method based on two detection techniques is presented, which can be used to measure both the IR emissivity and the thermal transport properties.

Materials Science and Engineering A, 2004

ABSTRACT In this work we study the influence of thermal treatment and thermal cycling on the temp... more ABSTRACT In this work we study the influence of thermal treatment and thermal cycling on the temperature dependence of the elastic constants of polycrystalline Ni-rich Ni–Ti showing “unusual” multistage martensitic transformations. With this aim, the ultrasonic pulse echo technique has been applied and the temperature dependence of the longitudinal and shear elastic constant has been measured as a function of temperature after successive heat treatments of the sample. The ultrasonic measurements were complemented by differential scanning calorimetry (DSC). The multistage martensitic transformations could be observed for both DSC and ultrasonic pulse echo experiments.

Journal of Biomedical Materials Research Part A

European Polymer Journal, 2006

Grafting polymerisation of methyl methacrylate and ethyl acrylate onto linen and cotton was carri... more Grafting polymerisation of methyl methacrylate and ethyl acrylate onto linen and cotton was carried out in order to reinforce these materials, when they underwent degradation. Take into account this aim, an artificially ageing was performed onto cellulose based textiles by metaperiodate oxidation, in order to obtain degraded model samples. Carbonyl groups were introduced in the cellulose and used as photosensitive agents, allowing the formation of radical sites during the polymerisation reaction, that started by irradiating the substrate by ultraviolet light. In this paper the effectiveness of grafting polymerisation as a method for textile conservation is discussed, starting from the results obtained from several characterisations, as the grafting yields and the grafting efficacy evaluation, the DSC analysis, the FTIR spectroscopy and the SEM observations. Moreover the consolidating and the protective effects were investigated by evaluating the mechanical properties and the wetting behaviour of the grafted samples, and comparing them with the original and aged substrates. The mechanical strength of cellulose based textiles has been improved, as well as the wetting behaviour has been enhanced.

Photothermal methods based on IR radiometry, photopyroelectric detection and thermoreflectance ha... more Photothermal methods based on IR radiometry, photopyroelectric detection and thermoreflectance have been applied to NiTi shape memory alloys to characterize the thermal properties of the as-prepared samples and to determine the changes of the thermal properties induced by thermal and mechanical treatment and cycling. Using photopyroelectric detection, the integral diffusivity of the treated and non treated samples has been determined. Depth profiles of the thermal properties of the mechanically and thermally cycled ribbon samples were measured using photothermal radiometry. A photothermal microscope based on thermoreflectance was applied to monitor the thermal properties across the ribbon edge and to image the thermal and optical variations inside a grove which had been milled into a NiTi shape memory specimen.

Res. Comput. Sci., 2019

Chitosan is a biopolymer widely used for many applications, especially in the biomedical field, d... more Chitosan is a biopolymer widely used for many applications, especially in the biomedical field, due to its interesting properties like excellent sorption capability, biodegradability and biocompatibility. The presence of reactive groups in the structure of this biopolymer makes possible the attachment of different molecules. In this study a chitosan thread is synthesized, using a microfluidic technique with two merging channels of acidic chitosan and hydroxide, in order to use it as a controlled release device of drugs. Varying the flows of the fluids in the channels is possible to control the diameter of the thread, obtaining samples of medium and high molecular weight for each flow rate used in the synthesis. The obtained thread of chitosan was mechanically characterized performing tensile tests until failure and stress relaxation tests. An optical system of polarizers was set to visualize the alignment of the polymeric chains while the material is elongated during the tensile test. Young modulus is obtained for each type of sample to quantify the stiffness of the material, and relaxation times were calculated to observe the viscoelastic behavior. Alignment of the material was confirmed, since birefringence was shown.

Research on computing science, 2020

The Electrical Bioimpedance (EBI) has been used for gastric activity monitoring as an alternative... more The Electrical Bioimpedance (EBI) has been used for gastric activity monitoring as an alternative to electrogastrography (EGG). The signal obtained by this technique has interference from all other motility signals from the gastrointestinal region, mainly the colon. This is because the colon motility appears in a frequency range that overlaps with that for the gastric frequency range. In fact, EGG technique has the same problem, but this is usually considered negligible and many times is not considered in the discussion. The main objective of this investigation is to elucidate if it is possible to discriminate, with simultaneous measurements in the abdominal region, both mechanical activities by non-invasive electrical bioimpedance technique.

The resonant ultrasound spectroscopy (RUS) is a non-destructive characterization or assessment te... more The resonant ultrasound spectroscopy (RUS) is a non-destructive characterization or assessment technique based upon the measurement of the mechanical resonant spectra of the samples [1]. In this work, RUS measurements have been performed upon composite samples consisting of a hard material embedded in a softer medium, as well as upon their separate components. The hard components used have been galvanized steel rods of 1 mm diameter and lengths of 15 and 27 mm. The softer medium was a seedless green grape of 29 mm length and 18 mm width. The two composite samples considered have been obtained by insertion into the grape of one rod at a time. The measured spectra have been compared and the feasibility of recognition of the spectra of the separate components from the composite spectrum is discussed.

Preliminary results have shown that bioelectrical impedance measurements performed on different p... more Preliminary results have shown that bioelectrical impedance measurements performed on different parts of the human body strongly depend upon the subcutaneous fat of the considered region. In this work, a method for the determination of subcutaneous fat thickness is explored. Within this method the measurement of the bioelectrical impedance response of the fat-muscle system, both along the direction defined by the muscle fibers and along the corresponding perpendicular direction, are performed. Measurements have been carried out on human female and male subjects of ages around 25 years old at the region of the biceps. Correlation has been performed with skinfold caliper measurements.

Macromolecular Bioscience

Macromolecular bioscience, Jan 25, 2018

The polarization of macrophages M0 to M1 or M2 using molecules embedded in matrices and hydrogels... more The polarization of macrophages M0 to M1 or M2 using molecules embedded in matrices and hydrogels is an active field of study. The design of biomaterials capable of promoting polarization has become a paramount need nowadays, since in the healing process macrophages M1 and M2 modulate the inflammatory response. In this work, several immunocytochemistry and ELISA tests strongly suggest the achievement of polarization using collagen-based membranes crosslinked with tri-functionalized oligourethanes and coated with silica. Measuring the amount of TGF-β1 secreted to culture media by macrophages growth on these materials, and quantifying the macrophage morphology, it is proved that it is possible to stimulate the anti-inflammatory pathway toward M2, having measurements with p ≤ 0.05 of statistical significance between the control and the collagen-based membranes. Furthermore, some physicochemical characteristics of the hybrid materials are tested envisaging future applications: collagena...

In this work we employ the resonant ultrasound spectroscopy technique in time-domain to perform a... more In this work we employ the resonant ultrasound spectroscopy technique in time-domain to perform an explorative geometrical study of bone phantoms. We measured a set of acrylic tubes of equal length but with different internal diameters in order to make a first step study related to the decrease in wall thickness due to osteoporosis process in human bones. We considered the spectra obtained with the sample subjected to pressure and their development to the free body resonance frequency spectra.

Materials Science Forum, 2002

World Journal of Gastrointestinal Pathophysiology, 2013

The aim of this review is to provide a general overview of the relationship between occupational ... more The aim of this review is to provide a general overview of the relationship between occupational stress and gastrointestinal alterations. The International Labour Organization suggests occupational health includes psychological aspects to achieve mental well-being. However, the definition of health risks for an occupation includes biological, chemical, physical and ergonomic factors but does not address psychological stress or other affective disorders. Nevertheless, multiple investigations have studied occupational stress and its physiological consequences, focusing on specific risk groups and occupations considered stressful. Among the physiological effects of stress, gastrointestinal tract (GIT) alterations are highly prevalent. The relationship between occupational stress and GIT diseases is evident in everyday clinical practice; however, the usual strategy is to attack the effects but not the root of the problem. That is, in clinics, occupational stress is recognized as a source of GIT problems, but employers do not ascribe it enough importance as a risk factor, in general, and for gastrointestinal health, in particular. The identification, stratification, measurement and evaluation of stress and its associated corrective strategies, particularly for occupational stress, are important topics to address in the near future to establish the basis for considering stress as an important risk factor in occupational health.

Materialwissenschaft und Werkstofftechnik, 2000

Protective layers, such as CVD and PVD coatings on steel substrates, surface modifications relate... more Protective layers, such as CVD and PVD coatings on steel substrates, surface modifications related to friction wear, and the effects of mechanical and thermal cycling of SMA samples have been analysed with respect to the depth profile of the thermal properties by using IR detection of thermal waves. The advantage of IR detection of thermal waves is that this method is most appropriate for remote sensing under industrial conditions, working absolutely contactless with remote detection and without any sample preparation. Hartstoffschichten und Oberfla Èchenmodifikationen, die durch Reibungsverschleiû oder thermisches und mechanisches Zyklieren von FGL-Proben erzeugt wurden, werden hier mittels IR-Radiometrie thermischer Wellen in Bezug auf die Tiefenprofilierung ihrer thermischen Eigenschaften untersucht. Diese Messungen geben direkte Information u Èber das Tiefenprofil der thermischen Parameter und u Èber damit verbundene andere Gro Èûen, z.B. die Dicke von Schichten unterschiedlicher thermischer Eigenschaften. Die IR-Radiometrie thermischer Wellen ist besonders gut fu Èr den Einsatz im industriellen Umfeld geeignet, da die Methode absolut kontaktlos arbeitet, u Èber gro Èûere Entfernungen hinweg zwischen Probe und Messsystem, und ohne eine besondere Probenvorbereitung eingesetzt werden kann.

Materials Science and Engineering: A, 2004

Dislocations are induced in polycrystalline NiTi shape memory alloy by thermal and mechanical cyc... more Dislocations are induced in polycrystalline NiTi shape memory alloy by thermal and mechanical cycling. The variation of the ultrasonic velocity and the attenuation with frequency in the range 2-60 MHz was measured at room temperature. The frequency dependent experimental data are well described in the frame of a vibrating string-model. The fits yield length and density of the dislocations in cycled and non-cycled samples. Depositing the sample at 300 K for a couple of days leads to a reduction of the dislocation density accompanied with an increase of the transition temperature.

Materials Science and Engineering: A, 2004

Local variations of the phase transition temperatures are important for the functionality of actu... more Local variations of the phase transition temperatures are important for the functionality of actuators based on NiTi shape memory alloys. Mechanical distortions induced by process treatment can suppress the phase transition from the austenitic to the martensitic structure. In this work, local changes of the phase transition have been investigated by time-dependent IR thermography. For the quantitative interpretation of the thermographical measurements, information about the IR emissivity is important. In this work a new thermal wave method based on two detection techniques is presented, which can be used to measure both the IR emissivity and the thermal transport properties.

Materials Science and Engineering A, 2004

ABSTRACT In this work we study the influence of thermal treatment and thermal cycling on the temp... more ABSTRACT In this work we study the influence of thermal treatment and thermal cycling on the temperature dependence of the elastic constants of polycrystalline Ni-rich Ni–Ti showing “unusual” multistage martensitic transformations. With this aim, the ultrasonic pulse echo technique has been applied and the temperature dependence of the longitudinal and shear elastic constant has been measured as a function of temperature after successive heat treatments of the sample. The ultrasonic measurements were complemented by differential scanning calorimetry (DSC). The multistage martensitic transformations could be observed for both DSC and ultrasonic pulse echo experiments.