Catálogo de publicaciones - libros

The stress-strain curve of an industrial composite such as a fiber-reinforced plastic falls between those of fibers and plastic matrix. On the other hand, despite the fact that the biological soft tissue is composed of collagen fascicles in a matrix whose Young’s modulus is almost negligible, the Young’s modulus of the tissue is higher than the fascicles. To insight into the mechanism of such inverse characteristics, we developed a mathematical model of a ligament, by taking into account a fascicle’s kinematic non-uniformity along its longitudinal direction and mechanical interaction between fascicles or a fascicle and matrix. Simulations results demonstrated the inverse characteristics and also helped to understand the mechanism of ligament’s failure.

Trying to make a SAW microfluidic micro-mixer we studied the compatibility between the piezoelectric ceramic substrate and a biological cell suspension. Two aspects were studied: (i) the influence of this kind of substrate on the cell population and (ii) the influence of the cell suspension on the piezoelectric ceramic substrate. A niobium substituted PZT wafer with 40 mm diameter and 0.5 mm thickness was used in our experiments. First, the wafer surface was analyzed by optical microscopy and the surface roughness was estimated by AFM measurements. Then the wafer was put in a Petri dish containing a cell suspension. A second Petri dish containing the same biological medium but without ceramic wafer was kept as reference. Both Petri dishes were observed for 4 days in order to see the cell population development. Both the cell cultures developed in the same manner, the experimental cell culture having some initial time delay (in the first day). Finally, the ceramic wafer was treated with HBSS in order to remove the cells. The ceramic surface was not affected excepting that the remains of dead cells on the wafer surface were rather difficult to clean out.

Replacement of the first metatarsophalangeal (MTP) joint is a relatively uncommon procedure. A cobalt chrome-on-cobalt chrome MTP prosthesis, which had a diamond like carbon (DLC) coating applied to its articulating faces, was implanted. However, due to poor clinical results the cohort of implants were removed and one was obtained for ex vivo analysis. In addition, calculation of predicted lubrication regimes applicable to this implant design was undertaken. Modeling the ball and socket implant as an equivalent ball-on-plane model and employing elastohydrodynamic theory allowed the minimum film thickness to be calculated and in turn the lambda value to indicate the lubrication regime. Boundary lubrication is indicated for lambda less than 1, mixed lubrication for lambda between 1 and 3, and fluid film lubrication for lambda greater than 3. The calculations were undertaken for a 10 to 800N range of loading values, and a 0 to 30mm/s range of entraining velocities, for both worn and unworn situations. Calculations showed that, for the range of loads and entraining velocities considered, the implant would almost always operate in the boundary lubrication regime, both when new and when worn. Therefore surface to surface contact would most frequently take place, with little separation due to lubrication between the articulating surfaces. The presence of scratches on the articulating faces of the ex vivo sample further implied boundary lubrication. The DLC coating had been removed from the entire face of the phalangeal component and from most of the face of the metatarsal component. From the latter it appeared as if the coating had been scratched and then flaked away parallel to the scratches. In turn this suggested a corrosion based failure of the interface between the DLC coating and the cobalt chrome subsurface.

There is a demand in the field of regenerative medicine for measurement technology that enables functions of engineered tissue to be determined. Articular cartilage, which has already been applied in clinical regenerative medicine, has specific mechanical functions. For meeting this demand, we previously proposed a noninvasive method for determination of the viscoelastic property based on photoacoustic measurements. However, characterization of the extracellular matrix of articular cartilage as well as determination of the viscoelastic property should be carried out for evaluation of regenerative medicine because the extracellular matrix plays an important role in the function of articular cartilage. The purpose of this study was to develop noninvasive measurement method for simultaneous evaluation of the viscoelastic properties by the photoacoustic method and characterization of the extracellular matrix of tissue engineered cartilage by the time-resolved autofluorescence spectroscopy. Third harmonic Q-switched Nd:YAG laser pulses were used as an excitation light source. Photoacoustic waves induced by the light pulses were detected using a piezoelectric transducer. The time-resolved fluorescence spectroscopy was obtained by using a photonic multichannel analyzer. The ratio of viscosity to elasticity measured by the photoacoustic method agreed well with the intrinsic viscoelastic parameters with a correlation coefficient of 0.98 when tissue-engineered cartilage tissues cultured for various periods (up to 12 weeks) were used as samples. There were significant differences in the measured fluorescent parameters among the culture conditions of cartilage because chondrocytes produce a specific extracellular matrix depending on its culture condition. The specific extracellular matrix contained a specific type of collagen such as collagen type I or type II, which each have specific fluorescent features. The combination of time-resolved autofluorescence spectroscopy and the photoacoustic measurement is expected to become a useful evaluation method in regenerative medicine of articular cartilage.

Processing parameters effects on the morphology, especially fiber diameter was investigated. Various parameters such as concentration, applied voltage, distance from needle to collector etc. effect the morphology of fiber matrix. The concentration of polymer solution was the key parameter to control the fiber diameert. Fiber matrix obtained by electrospinning immersed FITC labeled protein solution. And then, we conformed adsorption of proteins using LSCM. The possibility of quantitative analysis of adsorbed proteins by UV spectroscopy was invesgated.

We are interested in developing novel multifunctional biomaterials applied for dental surgery and the fabrication of artificial bone scaffolds with a controlled pore structure. Hydroxyapatite (noted HAp) is a useful biomaterial due to its good biocompatibility. Small amount of iron has been known to influence the crystallinity and solubility of HAp. In this study, various kinds of trace iron containing HAp (noted FeHAp) were synthesized by adding an aqueous solution of iron nitrate into a modified pseudo-body solution with an excess of phosphate ion concentration. The crystal structures of FeHAp were refined by the Rietveld analysis. The optical properties of FeHAp were measured by UV-vis spectroscopy. The results indicate that the cell parameters become longer and the photo-absorption become stronger with increasing iron within the studied composition range. This implies that FeHAp is possible to have additional functions comparing with plain HAp when is used as a biomaterial. In this paper, syntheses and characterization of the novel FeHAp are reported.

An X-ray diffraction study of crystal structure of bone apatite of Mongols and its changes and dependence on human ages has been carried out. The FullProt program based on the Rietveld method was used. In apart from separating proteins molecule off each sample was heated at 800°C during 30 minutes. Not depending on this heat treatment of all the samples consist only the fluoric apatite (Ca(PO)F) phase. As a result of refinement of the diffractograms it was established variation of parameters of bone apatite crystal structures (the unite cell constants, the coordinates of atoms, Debye-Waller heat factors of atoms, the atom contents and the unite cell volume) on different ways. It is also evident that the Ca1 atomic content increases with aging.

This study has adjusted with research result that bone cell decreases and osteoseptum adjacent when people to get on in years. The bone main elements content changing is a very important factor to determine defect relating formation and function and aging process. Crystal structure of the bone apatite and osteostereometric analysis leads to a hypothesis Mongolian human aging process and specially bone structure changing is over-due.

Dielectric measurements as a function of temperature and frequency are reported for unmodified and ethylene glycol (MPEG)-modified collagen. Measurements were performed over the frequency range of 10Hz – 100kHz and temperatures from 22 to 200°C. The effect of γ-irradiation on the dielectric properties of these materials is observed in the whole temperature range. This fact is supported by lower values of ɛ′ and ɛ″ for irradiated unmodified and modified collagen than for non-irradiated collagen. Results of this paper suggest that the irradiation of these materials with dose 30kGy initiates the process of side and main chains degradation of the unmodified and modified collagen. The data obtained also indicate that the cross-linking of collagen with MPEG is an effective way to increase the thermal stability of collagen macromolecules.

The advances reported herein form part of a larger project that has as its objective the development of a full flow-structure-interaction model of the human upper airway. Here we first briefly report on a two-dimensional (saggital section) model built using published CT-scan geometric data. For the development of our three-dimensional capability, we use the unique data captured in vivo by an endoscopic optical technique that we have developed. This measurement system, described as anatomical optical coherence tomography ( a OCT), allows quantitative real-time imaging of the internal anatomy of the human upper airway with minimal invasiveness. Moreover, the system permits motions of the internal geometry at a fixed location to be recorded. The a OCT data set is insufficient by itself to construct a complete geometry because only the polar coordinates are obtained in a local reference frame. Accordingly, the locus described by the endoscope, in which the a OCT is housed, is obtained by orthogonal CT scans. The combination of CT scans and a OCT measurements then provides the required geometric information for the construction of the computational model. Results of a two-dimensional model show how the soft palate responds to the mean-flow variations of the breathing cycle. For the three-dimensional work, the key results of this paper rest in the reconstruction of the time-dependent geometry of the upper airway, the first time that this has been accomplished using direct internally-based measurement.

In order to dissolve a blood clot and restore the patency of a blood vessel, various treatments have been used. Direct or intravenous injection of thrombolytic agents, such as tissue plasminogen activator (tPA), urokinase(uPA), streptokinase (SK), has been used for the treatment of thrombosis. Direct injection of thrombolytic agents to the clot may increase the effectiveness of thrombolysis by enhancing the permeation of a thrombolytic agent into the blood clot. Injection velocity and methodology, such as continuous infuson and pulsed injection, would affect the thrombolytic efficiecy. In order to explore the effectivenesss of injection methods, we modeled clot dissolution numerically. Species transport equation was solved along with three dimensional momentum equations. The blood clots were modeled as prorous media. Pressure, velocity and species concentration fields were calculated by computational fluid mechanics methods. Two different thrombus models - arterial and venous thrombus - were simulated. The results showed that thrombolytic speed increased as the injection velocity increased, and intermittent injection was more efficient in dissolving clots comparing to comtinuous perfusion.