Biomimetic hydrogels for in situ bone tissue engineering: nature-inspired crosslinking methods as a tool to tune scaffold physical properties
- Autores: Aitor Sánchez Ferrero
- Directores de la Tesis: Elisabet Engel López (dir. tes.)
- Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2015
- Idioma: inglés
- Tribunal Calificador de la Tesis: Manuel Monleón Pradas (presid.), Carlos Alemán Llausó (secret.), Jerónimo Blanco Fernández (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The global incidence of bone fractures, and subsequently that of non-healing ones, is expected to rise in the coming decades, mostly due to an increased risk of age-related conditions. Currently, the biomaterials field is moving towards the design of scaffolds mimicking the cell microenvironment to guide stem cells differentiation and recapitulate the development of target tissues. Biomimicry is a wide concept and several approaches have been adopted to produce cellinstructive scaffolds. Herein, we have explored the use of citric acid and lysyl oxidase, both of them related to bone nanostructure and mechanical performance, to develop scaffolds resembling the extracellular matrix of developing bone. First, elastin-like recombinamers (ELRs) hydrogels were achieved through a one-step chemical crosslinking reaction with citric acid, a molecule currently considered to be essential for the proper performance of bone tissue. By systematically studying the crosslinking reaction and its contribution to hydrogel properties, we were able to control the architecture and stiffness of citric acid-crosslinked hydrogels while preserving the integrity of adhesion sequences in ELRs. Interestingly, the use of citric acid conferred so-produced hydrogels the ability to nucleate calcium phosphate. Mechanically-tailored citric acid-crosslinked hydrogels were shown to be able to support the growth of human mesenchymal stem cells and to lead to seemingly biocompatible degradation products. Despite in vitro differentiation studies weren¿t conclusive as to their osteogenic potential, both mechanically-tailored and non-tailored citric acid-crosslinked hydrogels were shown to integrate into bone and to be partially degraded upon implantation in critical size defects in mouse calvaria. Despite cell invasion in mechanically-tailored scaffolds was seemingly lower than in non-tailored counterparts, both types of matrices allowed the formation of bone tissue, by intramembranous ossification, to a similar extent by the end of the study. At the time points selected for the in vivo study, both tailored and non-tailored hydrogels were found to be osteoconductive; osteoinduction was not observed in any of the cases. Mechanically-tailored hydrogels not being seemingly superior to control matrices at selected time points could to be due to (i) a high surface polymer density hindering cell invasion and thus delaying osteoinduction, or to (ii) a non-osteoinductive combination of properties (chemical + physical) despite hydrogels possessing theoretically osteoinductive stiffness. These results point out that scaffolds must be seen as a whole given the high complexity of the in vivo cell niche, whose signals act synergistically to define cell behavior. Thus, more complex designs are required if recapitulation of bone development is to be targeted. Additionally, recombinant lysyl oxidase (LOX) from human aorta was successfully produced in Escherichia coli to high purity. Despite achieving LOX with copper cofactor amounts and activity higher than those found in the literature, overall activity was low and the insolubilization of ELRs was not achieved, suggesting that novel expression and purification systems not compromising enzymatic activity are required if LOX is to be used to produce scaffolds.
