Study of molecular and water dynamics in hyaluronic acid (HA) and HA+CNTS and HA+SIO2

Abstract

Consulta en la Biblioteca ETSI Industriales (Riunet)

[EN] The present thesis focuses on the study of hyaluronic acid (HA) as a hydrogel. Hyaluronic acid presents potential applications in medicine as a biomaterial, since it can be found naturally in all living organisms, which means that HA has a high biocompatibility with the body. For this reason, it is used to regenerate tendons, develop cartilage or to ease the pain of osteoarthritis. However, hyaluronic acid has poor mechanical properties and also fast degradation. Therefore, this project aims to analyse hyaluronic acid, as well as to try to improve its properties by modifying its matrix with inclusions. Three different systems have been studied: one of pure hyaluronic acid, another one of hyaluronic acid with carbon nanotubes (CNTs) and a third one of hyaluronic acid reinforced with silica nanoparticles (SiO2). For both reinforced systems, two different concentrations of inclusions have been used. In the case of the CNTs, one sample contained 0.1%wt1 CNTs and the other one 3%wt CNTs, whereas in the case of SiO2 one sample was 0.5%wt SiO2 and the other 5%wt SiO2. Each of these systems was studied at dry conditions and at four different levels of relative humidity (33%, 65%, 85% and 98%). The samples at RH33%, 65%, 85% and 98% result in water fractions of 7%, 15%, 25% and 50%, respectively. Dielectric relaxation spectroscopy (DRS), in a broad frequency (10-1-106Hz) and temperature (-150°C-20°C) range, was used to study molecular and water dynamics in the systems. These measurements allowed us to identify the different relaxations in the samples studied and find the influence of water on them. In addition, Differential Scanning Calorimetry (DSC) technique was used to study thermal transitions (crystallization, melting) in the samples. For pure hyaluronic acid, three relaxations at low water fractions (dry, 7% and 15%) have been found. At low temperatures relaxation I is observed, which is plasticized when water fraction increases up to a limit of ~20%. This relaxation becomes more intense with increasing water fraction. Another relaxation of high intensity, shown as a clear peak (relaxation III), has been observed at high temperatures and low frequencies. This relaxation becomes faster as water fraction increases, which means that, like relaxation I, it is plasticized. Moreover, a third relaxation (relaxation II) with time scale in between of the other two is shown. However, it is difficult to observe this third relaxation as a clear peak due to the high magnitude of relaxation III. In systems of hyaluronic acid with carbon nanotubes, the three relaxations that appear for pure HA at low water fractions are also shown in this system. For low levels of relative humidity (dry, 33% and 65%) relaxations I and III are located at the same position in both samples (0.1 and 3%CNTs), although relaxation III is faster in CNTs systems, as compared to pure HA. In regard to HA with silica systems, relaxation I has exactly the same behaviour as those for pure HA and HA + CNTs systems. Regarding relaxation III at low relative humidity (dry, 33% and 65%), its behaviour is similar to the other systems, but the difference is that, in this case, relaxation II is more pronounced...