Cellulose Nanofibers and their Assembly for Biomedical and Materials Sciences: Focus on Charged Cellulose Nanofibers

Cellulose nanomaterials have novel and improved properties compared to traditional cellulose materials. This combined to the demand for high value-added products and applications made from renewable and sustainable resources makes nanocellulose an appealing material candidate in many fields. In their native state, plant-based cellulose nanofibers (CNFs) are hierarchically aligned. This alignment is lost when individual CNFs are disintegrated from the plant cellulose, and the CNF molecules end up in a gel with entangled shape. Many applications would benefit from materials with aligned structures. Therefore, the alignment of CNF has also been investigated for various purposes, including for advanced biomedical materials and applications. The alignment of CNF is challenging as such, and even more challenging in the presence of other materials.

The main aim of this dissertation was to investigate self-assembly methods for creating aligned and functional CNF and composite film surfaces. The aim was to develop surfaces with aligned CNF and study cell growth and orientation. From skin tissue engineering point of view, the aim was to improve cytocompatibility of a low- cost cellulose mesh using charged CNF coatings and compare cell behavior on anionic (a-) and cationic (c-) CNF coatings. The dissertation also aimed for developing a method to align c-CNF in the presence of multiwall carbon nanotube (MWCNT) component to obtain electrically anisotropic nanocomposite films.

In this thesis, evaporation induced self-assembly was used to align c-CNF along an evaporating boundary line, resulting in surfaces with aligned anisotropic c-CNF. Mouse embryonal fibroblasts were shown to orient and elongate along these aligned CNFs. CNF-driven evaporation-induced assembly was also investigated in the presence of MWCNTs, and this was used to produce nanocomposite films with anisotropic electric conductivity. It was possible to obtain nanocomposite films either with isotropic or anisotropic electrical properties. This was done by careful selection and pretreatment of the nanocomponents for the preparation of the nanocomposite films. Isotropic, evenly conductive films were obtained when high energy sonicated c-CNF/MWCNT dispersion was evaporated. Anisotropic films were formed when additional c-CNF was added to the dispersion inducing c-CNF alignment along the evaporating boundary line.

In this dissertation, cells were cultivated on different CNF surfaces and CNF- coated low-cost cellulose meshes. Mouse embryonal fibroblast proliferation and viability was the highest on a-CNF surfaces. Also, c-CNF surfaces promoted cell proliferation. Human adipose derived stem cell (ADSC) growth was highest on a- CNF coated cellulose meshes. c-CNF coated cellulose meshes induced fast adhesion of ADSCs. However, the viability of ADSCs on c-CNF coated meshes after the 1st day was significantly reduced compared to that of ADSCs on a-CNF and c+a-CNF. Human dermal fibroblast grew well on a-CNF coated and c+a-CNF coated meshes. Their viability on c-CNF coated meshes were poor, although better than on uncoated cellulose meshes.

In conclusion, this thesis showed for the first time that evaporation-induced self- assembly can be used for producing surfaces with aligned CNF, which also promoted cell orientation along the CNF alignment direction. The same CNF driven self-assembly method was used – for the first time – to manufacture anisotropic electrically conductive c-CNF/MWCNT nanocomposite films.