This Thesis has characterized two different approaches for the fabrication of scaffolds for tissue engineering: the surface functionalization by means of ELRs and the fabrication of PLA- based scaffolds using the properties of the PLA/EtLac system. Many aspects have been deeply analysed, such as the effects of the different functionalization strategies, the advantages of engineered proteins against short peptides, the enhanced surface properties obtained with ELRs, the characteristics of the PLA/EtLac gelation process, the conditions for the fabrication of highly porous nano-fibrous PLA-based scaffolds, the properties of the resultant scaffolds, the adjustability of such properties and the capability to produce different 3D shapes. As a consequence of the obtained results, new possible research lines are opened for further investigation. This section is devoted to expose some suggestions to be further developed in the future.
In Chapter 3 and 4 it has been observed that ELRs without integrin-ligands sequences can prevent the unspecific adhesion of cells and proteins on polymeric surfaces. In order to better understand the implications of this, further studies could analyse and quantify in more detail if there is any type of promotion towards the adhesion of certain types of proteins or not, since this can have important effects on cell response. Moreover, in order to trigger specific cell adhesion and proliferation, it is necessary to move towards different systems, since RGD is not specific for any cell-type. Instead, the REDV amino acid sequence is known to promote endothelial cells attachment and proliferation over smooth muscles cells [1]. The inclusion of this peptidic sequence into an ELR construct or any other construct with similar properties could be a strategic tool on the functionalization of synthetic vessel grafts to promote the endothelization of the graft lumen while preventing the spreading of smooth muscles cells.
In Chapter 5, the use of the PLA/EtLac system properties for the fabrication of porous scaffolds has been deeply studied. It is suggested that further studies consider exploring the
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interaction of different PLA-based materials with EtLac. Indeed, results not shown on this Thesis has already proved that different biodegradable polymers can be dissolved in EtLac and gelate in a similar manner than PLA. In such a way, it is possible to incorporate new mechanical properties on the resultant scaffold (i.e., elastomeric properties), which may be useful for engineering vascular scaffolds. Furthermore, the different PLA-based gelating systems could be used in combination with other processing techniques, such as solid free-form or porogen leaching. It could be also possible to entrap different molecules inside the nano-fibrous matrix, like collagen or any other hydrogel, to include different capabilities and properties (i.e., drug delivery). The combination of different processing techniques and materials can be a powerful tool for the design of intelligent scaffolds. On a different perspective, it is also suggested to study the feasibility of obtaining nano-fibrous structures by lyophilizing the EtLac solvent, which would greatly simplify the process. Currently, there are no studies considering this approach. Thus, firstly it would be necessary to determine the feasibility of the process, and secondly determine if nanofibrous matrices can be similarly obtained.
In Chapter 6 the fabrication of off-the-shelf vessel grafts has been studied. Results suggest that used system must include elastomeric behaviour. For this approach it could be possible to work with PLA copolymers that include elastomeric polymers. In such a way, less rigid and more compliant scaffolds would be obtained. Also, dynamic cellular studies should be performed in order to assess cellular attachment, recruitment and proliferation under mechanical stress conditions.
7.3. References
1. Wei Y, Ji Y, Xiao L, Lin Q, Ji J. Different complex surfaces of polyethyleneglycol (PEG) and REDV ligand to enhance the endothelial cells selectivity over smooth muscle cells. Colloids Surf B Biointerfaces 2011;84(2):369-78.
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CKNOWLEDGEMENTS
When I was about to start this journey I had no clue of what was waiting for me. It has been an adventure that has put me into continuous contact with two things that I love the most in the world, people and knowledge. All things I have learned and experienced would have not been possible without the generosity and kindness of people I have met along the way. These words are addressed to them, to express my gratitude and love towards them.
First of all, I want to express my most honest gratitude to my thesis director, Dr. Miguel Ángel Mateos Timoneda. Miguel has been my guide during the entire journey. He has taken care of me, putting me on the wright way when I was lost, opening doors to me and being a helping hand every time I needed. The deep knowledge he has on the scientific field is something that I have always deeply admired and respected, and has been a reference for me. I owe him my outmost appreciation, for his guide, generosity and friendship along all these years.
I also want to express my thankfulness to Dr. Elisabeth Engel, the group leader of the Biomaterials for Regenerative Therapies group. She was the person that gave me the opportunity to join this excellent team, and has always put a lot of trust on me. I am extremely grateful to her for sharing her excellence with me. She has been a person always open to listen and understand. The difficult questions have been always easy to talk and discuss with her. Her trust towards me, her perseverance and positive actitude has motivated me to pursue my goals. I will be always grateful for her generosity and warm personality.
I also want to thank Prof. Josep A. Planell, the former director of the group and institute, for his effort and passion. He has provided to us a culture based on the effort and positive attitude that is still present in our group. I want to show as well my gratitude to Dr. Oscar Castaño and Dr. Soledad Pérez. They have been a really good company either professionally and personally, being always helpful and always kind.
It is impossible to imagine the greatness of all these years without my lab mates. First of all, I want to say, to all of them, how much I admire their professional dedication and effort. It has been easy to keep fighting against struggles at their side. They have been a source of strength, inspiration and happiness. Tiziano, Aitor, Nadege, Arlyng, Zaida, Marta, Irene, Claudia, Joan, Cris, Laura, Jenifer, Doug and, specially, Riccardo; they have made this travel
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easier, better and funnier. I also want to give a special mention to Rodolphe, my first student. With him, I had one of my best times, and I am very happy to have seen his success in his life. I also want to thank Pablo and Maria for everything we shared, and for making me laugh during the hard and the good moments. I want also to express my thoughts to the members of BIBITE group, led by Prof. Maria Pau Ginebra, for all the help and support through all these years.
I also want to express my gratitude to Prof. Gustavo V. Guinea, from the Universidad Politécnica de Madrid, for giving me the opportunity to work in his lab. His friendly attitude made me feel welcome from the very beginning, and his scientific advice had a great impact over my experience. It was a pleasure to enjoy his passion towards science. I am also thankful to Dr. Didier Letourneur, from the UMR 1148 in Paris. During my stay in his lab, he was a very close person, always helpful and attentive. He helped me to overcome unexpected problems, and his scientific skills were of great value. I am also very thankful to Prof. Maria Lluisa Maspoch and Dr. Orlando Onofre, from Centre Català del Plàstic, for their priceless help and support on the development of my work.
Els meus més profunds agraïments al suport i la companyia dels meus amics. He crescut i m’he format com a persona al vostre costat. Amb vosaltres he après a estimar i he forjat els valors que em guien avui dia. Sense la vostra companyia, el vostre amor, la vostra amistat, i les nostres aventures, no es podria entendre perquè em llevo cada dia amb alegria. Víctor, Carol, Ivan, Rubén, Sergio, Helena, Marta, Riccardo, Edu, Moni, Patri, David, Alejandro; gràcies per ser com sou, us estimo enormement. Em doneu l’energia que he necessitat dia a dia per arribar fins aquí.
Toni, la teva arribada a la meva vida ha sigut tan inesperada com màgica. Compartir els moments amb tu és una de les millors alegries que he tingut mai. Fas que perseguir els somnis resulti senzill i divertit. La teva tendresa, alegria i capacitat de volar han sigut una inspiració. Gràcies per ajudar-me i acompanyar-me en aquesta etapa. T’estimo moltíssim.
Finalment volia dedicar els meus darrers pensaments a la meva família. Ells m’ho han donat tot. M’he sentit increïblement estimat i feliç. Ells m’han donat totes les eines i totes les forces necessàries per viatjar a través de la vida. Dels meus pares, Xavi i Montse; del meu germà Joan; de la meva tieta Agnès; i del meu avi Miquel; he après a estimar i a estimar-me, a ser crític, a ser persona, a ser humà, a ser independent, a ser valent, a disfrutar, a ser somiador, a ser lluitador, a respectar i a ser generós. Per ells, i gràcies a ells, m’esforço a ser millor persona. Em feu sentir orgullós de la família que tinc. Us estimo i admiro moltíssim.