We report the ability of cellulose to support cells without the use of matrix ligands on the surface of the material, thus creating a two-component system for tissue engineering of cells and materials. Sheets of bacterial cellulose, grown from a culture medium containing Acetobacter organism were chemically modified with glycidyltrimethylammonium chloride or by oxidation with sodium hypochlorite in the presence of sodium bromide and 2,2,6,6-tetramethylpipiridine 1-oxyl radical to introduce a positive, or negative, charge, respectively. This modification process did not degrade the mechanical properties of the bulk material, but grafting of a positively charged moiety to the cellulose surface (cationic cellulose) increased cell attachment by 70% compared to unmodified cellulose, while negatively charged, oxidised cellulose films (anionic cellulose), showed low levels of cell attachment comparable to those seen for unmodified cellulose. Only a minimal level of cationic surface derivitisation (ca 3% degree of substitution) was required for increased cell attachment and no mediating proteins were required. Cell adhesion studies exhibited the same trends as the attachment studies, while the mean cell area and aspect ratio was highest on the cationic surfaces. Overall, we demonstrated the utility of positively charged bacterial cellulose in tissue engineering in the absence of proteins for cell attachment.

Five different samples of Stöber silica monodisperse particles show large variations in their swelling ability as well as on their chemical compositions. Nanosized particle diameters were determined under four different conditions, using suitable techniques:  photon correlation spectroscopy (PCS) in water and ethanol, AFM at 25 °C under 55% relative humidity, high-resolution scanning electron microscopy and transmission electron microscopy, under 10-6 mbar. The comparison of these results shows that the smaller particles are highly swollen in ethanol, to a greater extent than in water. The swelling coefficients are lower for the larger particles, with a preference for water. Evidence for changes in the chemical composition were obtained by electron energy-loss and infrared absorption spectra:  the smaller particles contain detectable amounts of C−H groups, which are not detected by IR in the larger ones, and O energy-loss spectra fine structure changes continuously with particle sizes. The location of carbon constituents in the particles was determined by electron spectroscopy imaging in the transmission electron microscope (ESI-TEM):  they are dispersed throughout the finer particles, but they are excluded from the core of the larger particles. The results are interpreted considering the kinetics and extent of TEOS hydrolysis dependence on base concentration and the limiting effect of ethoxy residual groups on the densification of the silica network.

This work verifies a model for the creation and dissipation of reproducible electric potential patterns on silica surfaces, based on water adsorption, ionization, and ion migration under applied electric potential. Samples were thin silica films grown on silicon wafers and partially covered with sets of parallel gold stripe interdigitated electrodes that are normally used for Kelvin force microscope calibration. Noncontact electric potential measurements with a 20 nm spatial resolution were done using the Kelvin method under controlled atmosphere, in an atomic force microscope (AFM) with a Kelvin force attachment (KFM) mounted within an environmental chamber. Patterns were observed in micrographs acquired while one electrode set was biased and the other was grounded and when both were short-circuited and grounded. Electrostatic charging and discharging are much faster at high relative humidity, showing that the charged or discharged silica states are both changed faster under high humidity, while pattern preservation is effective under low humidity. The results are explained considering surface conductance and the partitioning of water cluster ions both in the solid−gas interfaces and the atmosphere, under the biased electrode potential.

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