• Skogberg, Anne

Abstract

Cellulose nanomaterials have novel and improved properties compared totraditional cellulose materials. This combined to the demand for highvalue-added products and applications made from renewable andsustainable resources makes nanocellulose an appealing materialcandidate in many fields. In their native state, plant-based cellulosenanofibers (CNFs) are hierarchically aligned. This alignment is lostwhen individual CNFs are disintegrated from the plant cellulose, and theCNF molecules end up in a gel with entangled shape. Many applicationswould benefit from materials with aligned structures. Therefore, thealignment of CNF has also been investigated for various purposes,including for advanced biomedical materials and applications. Thealignment of CNF is challenging as such, and even more challenging inthe presence of other materials. <br/> <br/>The main aim of this dissertation was to investigate self-assemblymethods for creating aligned and functional CNF and composite filmsurfaces. The aim was to develop surfaces with aligned CNF and studycell growth and orientation. From skin tissue engineering point of view,the aim was to improve cytocompatibility of a low- cost cellulose meshusing charged CNF coatings and compare cell behavior on anionic (a-) andcationic (c-) CNF coatings. The dissertation also aimed for developing amethod to align c-CNF in the presence of multiwall carbon nanotube(MWCNT) component to obtain electrically anisotropic nanocompositefilms. <br/> <br/>In this thesis, evaporation induced self-assembly was used to alignc-CNF along an evaporating boundary line, resulting in surfaces withaligned anisotropic c-CNF. Mouse embryonal fibroblasts were shown toorient and elongate along these aligned CNFs. CNF-drivenevaporation-induced assembly was also investigated in the presence ofMWCNTs, and this was used to produce nanocomposite films withanisotropic electric conductivity. It was possible to obtainnanocomposite films either with isotropic or anisotropic electricalproperties. This was done by careful selection and pretreatment of thenanocomponents for the preparation of the nanocomposite films.Isotropic, evenly conductive films were obtained when high energysonicated c-CNF/MWCNT dispersion was evaporated. Anisotropic films wereformed when additional c-CNF was added to the dispersion inducing c-CNFalignment along the evaporating boundary line. <br/> <br/>In this dissertation, cells were cultivated on different CNFsurfaces and CNF- coated low-cost cellulose meshes. Mouse embryonalfibroblast proliferation and viability was the highest on a-CNFsurfaces. Also, c-CNF surfaces promoted cell proliferation. Humanadipose derived stem cell (ADSC) growth was highest on a- CNF coatedcellulose meshes. c-CNF coated cellulose meshes induced fast adhesion ofADSCs. However, the viability of ADSCs on c-CNF coated meshes after the1st day was significantly reduced compared to that of ADSCs on a-CNFand c+a-CNF. Human dermal fibroblast grew well on a-CNF coated andc+a-CNF coated meshes. Their viability on c-CNF coated meshes were poor,although better than on uncoated cellulose meshes. <br/> <br/>In conclusion, this thesis showed for the first time thatevaporation-induced self- assembly can be used for producing surfaceswith aligned CNF, which also promoted cell orientation along the CNFalignment direction. The same CNF driven self-assembly method was used –for the first time – to manufacture anisotropic electrically conductivec-CNF/MWCNT nanocomposite films.

Topics

• nanocomposite
• impedance spectroscopy
• dispersion
• surface
• Carbon
• nanotube
• anisotropic
• isotropic
• cellulose
• evaporation
• self-assembly
• aligned