Micro-, nano-integrated composites based on cellulose microfibers.

摘要

Three different cellulose microfiber based composites have been fabricated through micro-, nano-integrated methods. The morphology, properties and application of these composites were demonstrated.Biocomposites of cellulose microfibers and enzymes (laccase and urease) were obtained through layer-by-layer assembly by alternate adsorption with oppositely charged polycations and enzymes. The formation of organized polyelectrolyte and enzyme multilayer films of 15-20 nm thickness was demonstrated by quartz crystal microbalance, zeta-potential analysis and confocal laser scanning microscope. These biocomposites retained enzymatic catalytic activity, which was proportional to the number of coated enzyme layers. For laccase-fiber composites, around 70% of its initial activity was retained after 45 days storage at 4°C. The synthesis of calcium carbonate microparticles on urease-fiber composites confirmed urease functionality and demonstrated its possible applications. This strategy could be employed to fabricate fiber-based composites with novel biological functions.Nanocoating of poly(3,4-ethylenedioxythiophene) - poly(styrenesulfonate) (PEDOT-PSS) and aqueous dispersion of carbon nanotubes (CNT-PSS) on cellulose microfibers has been developed to make a conductive cellulose microfibers based composite. To construct the multilayers on cellulose microfibers, cationic poly(ethyleneimine) (PEI) has been used in alternate deposition with anionic conductive PEDOT-PSS and solubilized CNT-PSS. Using a Keithley microprobe measurement system, current--voltage measurements have been carried out on single composite microfibers after deposition of each layer to optimize the electrical properties of the coated microfibers. The conductivity of the resultant wood microfibers was in the range of 10-2 to 2 S.cm -1, depending on the architecture of the coated layer. Further, the conductivity of the coated wood microfibers increased up to 20 S.cm -1 by sandwiching a multilayer of conductive co-polymer PEDOT-PSS with CNT-PSS through a polycation (PEI) interlayer. Moreover, paper hand sheets were manufactured from these coated wood microfibers with conductivity ranging from 1 to 10 S.cm-1. A paper composite structure consisting of conductive/dielectric/conductive layers that acts as a capacitor, has also been fabricated and is reported.Cellulose microfibers were combined with cross-linked gelatin to make biocompatible porous microscaffolds for the sustained growth of brain cell and human Mesenchymal Stem Cells (hMSCs) in a three dimensional (3-D) structure. Live imaging, using confocal microscopy, indicated that 3-D microscaffolds, composed of gelatin or cellulose fiber/gelatin, both supported brain cell adhesion and growth for 16 days in vitro. Cellulose microfiber/gelatin composites containing up to 75% cellulose fibers can withstand higher mechanical load than gelatin alone, and composites also provided linear pathways along which brain cells could grow compared to more clumped cell growth in gelatin alone. Therefore, the bulk cellulose microfiber provides a novel skeleton in this new scaffold material. The cellulose fiber/gelatin scaffold supported hMSCs growth and extra cellular matrix formation. hMSCs osteogenic and adipogenic assays indicated that hMSCs cultured in cellulose fiber/gelatin composite preserved the multi-lineage differentiation potential. As natural, biocompatible components, the combination of gelatin and cellulose microfibers, fabricated into 3-D matrices, may therefore provide optimal porosity and tensile strength for long-term maintenance and observation of cells.