Resumen de Innovadors materials de cel·lulosa bacteriana: estructuració, nanocompostos funcionals i hidrogels fotocurables
Worldwide production of plastics has increased significantly during the past decade and its environmental impact requires efforts to improve and establish new waste management routes, reuse products and create alternative biodegradable materials. Cellulose arises as a good candidate to substitute some of the petroleum-based products since it is the most abundant natural biopolymer in the biosphere and, more specifically, nanocelluloses, as they combine the cellulose characteristics with the properties of nanomaterials. Nanocelluloses are mainly obtained from wood digestion; however, the increasing demand for cellulose has generated the research of source alternatives. Among the possible options, several microorganisms’ producers of this biopolymer can be found in nature. This is the case of some bacteria strains, which excrete cellulose nanofibers creating a three-dimensional porous hydrogel pellicle with a reticulated network known as bacterial cellulose. The properties of the bacterial cellulose together with its versatility to be physically and chemically tuned, open a wide range of opportunities for this material and its composites.
Due to the outstanding properties and limitless design opportunities of bacterial cellulose, new applications for the material and its industrialization are currently being explored. This dissertation aims to provide new structures and functionalities to bacterial cellulose taking advantage of its easy tunability and pave the way towards new advanced bioresource-based materials. For that, several strategies were employed. Firstly, bacterial cellulose films, nanofibers and 3D structures, such as spheres, were produced and analyzed under static and agitation conditions. Interestingly, film mechanical properties were improved by a simple self-adhesion approach, creating multilaminates and hybrid materials. The adhesion mechanism was molecular and macroscopically studied, appreciating the prominent influence of the hydrogen bonds formation. In addition, by adapting the static culture procedure over hydrophobic surfaces, the size and morphology of spheres of bacterial cellulose were easily controlled and modulated, creating hollow structures that are not achieved with agitation culture. Secondly, the structuration of films was examined through two approaches using polydimethylsiloxane stamps and the fidelity of the feature replication when applying different drying conditions was studied. On one hand, bio-lithography, which is produced in-situ during bacterial cellulose biosynthesis, enables replication on large surface areas with self-standing pillars from 200 to 10 µm and with an arranged nanofiber order. On the other hand, soft-imprint lithography, which occurred ex-situ (i.e., after the biosynthesis), allows the transference of sub-micron motifs and selectively patterned functionalization, not affordable with bio-lithography, although at the expense of a large depth loss of the motifs. The third research line explored the functionalization of the previously produced structures with inorganic nanoparticles (gold, silver, titania and iron oxide) through different strategies (in-situ nanoparticle addition during the biosynthesis or ex-situ nanoparticle formation by microwave-assisted reaction) creating on-demand multilayered arrangements or Janus-like spheres with multiple and localized functionalities, negligible leaching and controlled nanoparticle loading. Finally, the applicability of bacterial cellulose nanofibers as reinforcement of a synthetic polymer, such as polyacrylic acid, for tissue engineering is presented. The synthesized hydrogel showed enhanced mechanical properties and greater dimensional stability upon pH changes.
