Elena Llorens Domenjó
Electrospinning is a manufacturing process that uses an electric field to produce fibers from a polymer solution. The accumulation of these fibers conform a three-dimensional fiber matrix or scaffold. Fibers can be prepared in a wide diameter range, namely from a micrometer to nanometer size. Furthermore, the fiber matrix or scaffold has a large surface per mass unit, a porous structure and mechanical properties influenced by the orientation of the fibers. The electrospinning technique is highly versatile and therefore a large number of polymers with different properties can be processed. However, a large number of variables can influence the characteristics of the resulting fibers, either because they are related to the polymer properties (e.g., solubility, molecular weight, etc.) or with the specific processing parameters (voltage, flow rate or distance tip-collector). Electrospun fiber matrices are attractive for biomedical applications as for example tissue engineering and drug delivery systems. In the last case, it is important the possibility to load the fibers with different drugs for their direct and localized administration into the human body. The goal of this Thesis is the study of different matrices constituted by electrospun micro- nanofibers and specifically four points have been considered. In the first one, polylactide electrospun scaffolds have been loaded with different molecules with antioxidant activity (i.e., vitamin B6 in pyridoxine and pyridoxal forms, p-coumaric acid and caffeic acid). The influence of these molecules on physical properties, morphology, in vitro release profiles and biocompatibility was determined. Furthermore, the application of these new materials for the inhibition of oxidative DNA damage caused by free radical initiators was demonstrated, and consequently, they appear appropriate candidates for purification of plasmidic or genomic DNA. In the second point, PLLA matrices loaded with two or three drugs were prepared in order to get a multifunctional activity. Thus, antioxidant, anti-inflammatory and antimicrobial molecules were considered in order to prevent chain oxidation processes in different biomolecules (proteins, DNA, etc.), avoid the subsequent local inflammation, and reduce the potential risk of microbial infection of wounds, respectively. These matrices are especially interesting due to the synergies and antagonisms that may occur during their simultaneous release. In the third point, the possibility of preparing biodegradable scaffolds from non electrospinable polymers has been considered. These polymers may have advantages like conductivity/electroactivity or bactericide activity. Hybrid scaffolds constituted by different ratios of polylactide as a biodegradable polymer and (poly(3-thiophene methyl acetate)) as electroactive polymer were evaluated. PLA nanofibers were also successfully loaded with polyhexamethylenebiguanide hydrochloride giving rise to 3D biodegradable scaffolds with a well proven antibacterial activity and a release that was highly dependent on the hydrophilicity of the medium. Finally electrospun scaffolds were obtained using a sacrificial polymer (e.g. poly(ethylene glycol) (PEG)) that could easily be subsequently removed by solubilization in aqueous media. Three approaches were evaluated: a) Preparation of scaffolds constituted by different ratios of PLA and PEG electrospun fibers, b) Preparation of scaffolds constituted by electrospun fibers with different PLA and PEG content; c) Preparation of scaffolds constituted by coaxial electrospun fibers with different core-shell polymer distributions. Cell colonization was in all cases favoured. The three procedures allowed preparing scaffolds with a differentiated drug release behavior.
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