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Influencia de la piezoelectricidad del colágeno tipo I en la adhesión celular
Abstract and Figures
Bone healing and growth are controlled by the rate of deposition of hydroxyapatite (HA). This process have been so far accredited to the work of osteoblasts, which are attracted by the electrical dipoles produced either by piezo-electricity, due to deformation of the bone, specially the colla-gen in it, or due to outside electrical stimuli. The main purpose of this work was to study the influence of the cortical bone collagen piezoelectricity effect, on the osteoblastic cells orienta-tion. To evaluate the cellular adhesion on the cortical bone collagen subject to deformation, bone cells of newborn cal-varia's rats were extracted. The bone collagen was prepared and deformed following the specifications described in earlier studies. The results of this study shown that the piezoelectric phenomena of bone collagen promotes the cell's adhesion on the compression side more than tension side compared with undeformed surface. Further studies ascertaining the os-teoblastic activity due to the electric field are being advanced. Palabras claves— hidroxiapatita, colágeno, osteoblastos, piezoelectricidad, tejido oseo. I. INTRODUCCIÓN El incremento del número de personas que cada año sufren traumas o enfermedades óseas se traduce en un aumento de intervenciones quirúrgicas o tratamientos para la reparación de estas deficiencias óseas. Es por ello que día tras día la búsqueda de materiales sintéticos biocompatibles que puedan ser usados en dispositivos médicos destinados a interaccionar con sistemas biológicos que puedan cumplir las funciones del tejido se ha intensificado. En la actualidad el uso de ciertos materiales inertes tales como metales y cementos óseos han sido usados ampliamente. Sin embargo dado que el hueso es un tejido vivo que sufre constantemente modificaciones en ciertos casos, estos materiales no son compatibles con el tejido y por lo tanto son rechazados por el sistema inmune del cuerpo. Dadas estas limitaciones se busca mimetizar fenómenos que ocurren en el cuerpo humano, implementando nuevas estrategias para crear reemplazos de tejidos más completos para la reparación de los defectos y enfermedades óseas. La integración de un material apropiado que funcione como soporte de las células regeneradoras del hueso para que puedan proliferar y diferenciarse va a depender de las características de la superficie del material (estructura, composición y ciertas propiedades). Se ha demostrado, de acuerdo a la ley de Wolf, que si el hueso sufre una deformación progresiva esta produce una estructura anatómica la cual es capaz de resistir la fuerza aplicada, generándose un crecimiento en la zona cóncava (compresión) y degradación en la zona convexa (tensión). Partiendo de esta ley diversos trabajos se han realizado en este campo. Iwao Yasuda (1957) fue el primero en demostrar que el hueso seco es un piezoeléctrico, ya que al someter el hueso a cierta deformación mecánica este generaba impulsos eléctricos que estimulaban el crecimiento óseo en concordancia con la ley de Wolf [1]. El proceso de reconstrucción de los huesos se relaciona con un proceso bioquímico, sin embargo las características piezoeléctricas del hueso, sugieren que el crecimiento puede ser afectado y/o controlado por los potenciales producidos por compresión o tensión del hueso y/o colágeno. Ciertos materiales biológicos como el colágeno y biopolímeros exhiben una orientación polar uniaxial de los dipolos en su estructura molecular y pueden ser considerados como bioeléctricos. Dichos materiales pueden ser piroeléctricos y/o piezoeléctricos [2]. El colágeno comprende el 90% de la matriz ósea y junto con la hidroxiapatita (HA), gobierna las propiedades biomecánicas y la integridad funcional del este tejido [3]. La piezoelectricidad en colágeno óseo y su influencia en la fisiología y funcionalidad en el hueso ha sido altamente estudiada. Sin embargo el proceso de mineralización ha sido atribuido fundamentalmente a la actividad de los osteoblastos (células regeneradoras de los huesos) las cuales son atraídas eléctricamente por los dipolos generados por el efecto piezoeléctrico al deformar el hueso, especialmente el colágeno, por un estímulo eléctrico externo. [4]. En trabajos anteriores se ha demostrado que el efecto piezoeléctrico del colágeno generado al deformar el material favorece la deposición de la hidroxiapatita (HA) en la zona cargada negativamente, es decir sometida a compresión (Ver figura 1). [5] El objetivo del presente estudio es determinar la influencia del efecto piezoeléctrico del colágeno tipo I en la orientación celular, generado al aplicarse un esfuerzo mecánico.
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The piezoelectric effect of bone has been observed similarly to the case of wood or ramie. The specimens were cut out from the femur of man and ox, and dried completely by heating. The piezoelectric constants were measured by three different experiments, that is, measurements of the static direct effect, the dynamic direct effect and the dynamic converse effect. The piezoelectric effect appears only when the shearing force is applied to the collagen fibres to make them slip past erch other. The magnitude of piezoelectric constant depends on the angle between the applied pressure and the axis of the bone. The maximum value of piezoelectric constant amounts to 6x 10-9c.g.s.e.s.u., which is about one-tenth of a piezoelectric constant du of quarts crystal. The specimens which were boiled in hot water and afterwards dried completely showed little change in the piezoelectric effect, the fact ascertaining that the effect is not of biological origin. The origin to piezoelectricity in bone may be ascribed to the piezoelectric effect of the crystalline micelle of collagen molecules. The consideration of the symmetry of the configulation of collagen fibres in the bone texture shows the existence of effects which are represented by only two piezoelectric constants d14 and d25, which are the same in magnitude but opposite in sign.
One of the most revolutionary trends of the past four decades should be named the innovative use of specials ceramics designed to reproduce different function of living organisms. Ceramics used for these purposes are defined as bioceramics. In this category we find bioactive glasses of SiO2.Na2O.CaO.K2O.MgO.P2O5 system that show the capacity of chemical bonding between bone and this material. AI2O3 and B2O3 have been used in bioactive glasses to modify its surface dissolution and durability. However, Al2O3 in contrast to B2O3 can inhibit bone bonding, being the acceptable amount of alumina a function of glass composition. In the present work were evaluated glasses of SiO2.Na2O.CaO.K2O.MgO.P2O5 system, modified by a variable amount of Al2O3and B2O3. Our results showed alkalinization of culture medium. Therefore, the pH and glass composition could affect the cellular viability of the osteoblast; especially when the bioactive glass contained 1% alumina with 0% B2O3 in the composition. Whereas the glass contained 1.5% alumina combined with 1% B2O3 looks to enhances the adhesion and proliferation of the bone cells. Those results suggest that the assayed bioactive glasses could be used as coating materials for orthopedic and dental implant.
Bone healing and growth are controlled by the rate of deposition of hidroxiapatite (HA). This process have been so far accredited to the work of osteoblasts, which are attracted by the electrical dipoles produced either by piezoelectricity, due to deformation of the bone, specially the collagen in it, or due to outside electrical stimuli. The present work shows that even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen, can produce the precipitation of HA by electrochemical means, without catalyzer as in biomimetic deposition. These findings could clarify the contribution of osteoblasts in bone growth as compared to the electrochemical action by itself. Further studies ascertaining the osteoblastic activity due to the electric field are being advanced.
In the present work, we have studied the effect of the piezoelectricity of elastically deformed cortical bone collagen on surface using a biomimetic approach. The mineralization process induced as a consequence of the piezoelectricity effect was evaluated using scanning electron microscopy (SEM), thermally stimulated depolarization current (TSDC), and differential scanning calorimetry (DSC). SEM micrographs showed that mineralization occurred predominantly over the compressed side of bone collagen, due to the effect of piezoelectricity, when the sample was immersed in the simulated body fluid (SBF) in a cell-free system. The TSDC method was used to examine the complex collagen dielectric response. The dielectric spectra of deformed and undeformed collagen samples with different hydration levels were compared and correlated with the mineralization process followed by SEM. The dielectric measurements showed that the mineralization induced significant changes in the dielectric spectra of the deformed sample. DSC and TSDC results demonstrated a reduction of the collagen glass transition as the mineralization process advanced. The combined use of SEM, TSDC, and DSC showed that, even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen can produce the precipitation of hydroxyapatite by electrochemical means, without a catalytic converter as occurs in classical biomimetic deposition.
In this paper we report a study of the physicochemical, dielectric and piezoelectric properties of anionic collagen and collagen–hydroxyapatite (HA) composites, considering the development of new biomaterials which have potential applications in support for cellular growth and in systems for bone regeneration. The piezoelectric strain tensor element d14, the elastic constant s55, and the dielectric permittivity ε11 were measured for the anionic collagen and collagen–HA films. The thermal analysis shows that the denaturation endotherm is at 59.47 °C for the collagen sample. The collagen–HA composite film shows two transitions, at 48.9 and 80.65 °C. The X-ray diffraction pattern of the collagen film shows a broad band characteristic of an amorphous material. The main peaks associated to the crystalline HA is present in the sample of collagen–HA. In the collagen–HA composite, one can also notice the presence of other peaks with low intensities which is an indication of the formation of other crystalline phases of apatite. The scanning electron photomicrograph of anionic collagen membranes shows very thin bundles of collagen. The scanning electron photomicrography of collagen–HA film also show deposits of hydroxyapatite on the collagen fibers forming larger bundles and suggesting that a collagenous structure of reconstituted collagen fibers could act as nucleators for the formation of apatite crystal similar to those of bone. The piezoelectric strain tensor element d14 was measured for the anionic collagen, with a value of 0.062 pC N−1, which is in good agreement compared with values reported in the literature obtained with other techniques. For the collagen–HA composite membranes, a slight decrease of the value of the piezoelectricity (0.041 pC N−1) was observed. The anionic collagen membranes present the highest density, dielectric permittivity and lowest frequency constant f.L.
Bone collagen cross-links are now widely used to assess bone resorption levels in many metabolic bone diseases. The post-translational modifications of bone and other mineralizing collagens are significantly different from those of other type I collagen matrices, a fact that has been exploited during recent advances in the development of biochemical markers of bone resorption. The enzymatic collagen cross-linking mechanism is based upon aldehyde formation from specific telopeptide lysine or hydroxylysine residues. The immature ketoimine cross-links in bone form via the condensation of a telopeptide aldehyde with a helical lysine or hydroxylysine. Subsequent maturation to the pyridinoline and pyrrole cross-links occur by further reaction of the ketoimines with telopeptide aldehydes. In mineralizing tissues, a relatively low level of lysyl hydroxylation results in low levels of hydroxylysyl pyridinoline, and the occurrence of the largely bone specific lysyl pyridinoline and pyrrolic cross-links. The collagen post-translational modifications appear to play an integral role in matrix mineralization. The matrix of the turkey tendon only mineralizes after a remodeling of the collagen and the subsequent formation of a modified matrix more typical of bone than tendon. Further, disturbances in the post-translational modification of collagen can also affect the mineralization density and crystal structure of the tissue. In addition to their use as a convenient measure of matrix degradation, collagen cross-links are of significant importance for the biomechanical integrity of bone. Recent studies of osteoporotic bone, for example, have demonstrated that subtle perturbations in the pattern of lysine hydroxylation result in changes in the cross-link profile. These alterations, specifically changes in the level of the pyrrolic cross-link, also correlate with the strength of the bone. Further research into the biochemistry of bone collagen cross-links may expand current understanding and their clinical application in metabolic bone disease. This review also demonstrates the potential for further study into this area to provide more subtle information into the mechanisms and etiology of disease and aging of mineralizing tissues.
Calle: Carretera Nacional de Baruta Ciudad: Caracas País: Venezuela E-mail: knoris@usb.ve Fig. 6 Modelo propuesto de regulación de la funcionalidad celular según la adhesión preferencial de las células óseas
- Autor
Autor: Karem Noris Suárez
Instituto: Universidad Simon Bolivar
Calle:
Carretera Nacional de Baruta
Ciudad: Caracas
País:
Venezuela
E-mail: knoris@usb.ve
Fig. 6 Modelo propuesto de regulación de la funcionalidad celular
según la adhesión preferencial de las células óseas.