Bioactive surfaces with atomic layer deposition

Abstract

The overall goal of this work has been to make bioactive surfaces with atomic layer deposition (ALD). To do this, a new ALD system with titanium tetraisopropoxide (TTIP) and lysine as precursors was developed with emphasis on studying the effects of pulsing times and deposition temperatures. TTIP was chosen as titanium is regarded to be biocompatible and lysine was chosen as poly-L-lysine is a part of the extra-cellular matrix (ECM) and hence affects cell adhesion. The effect of a water pulse in the system has also been investigated. An imagined application for bioactive ALD coatings is on 3D cell growth scaffolds such as electrospun membranes, and coating of cellulose membranes was therefore also attempted. As the last part of this work, cell growth experiments were performed on various TTIP/lysine films and the proliferation of the cells was studied. Quartz crystal microbalance (QCM) experiments at 225 oC proved that self-limiting growth was taking place for both the TTIP/lysine and TTIP/lysine/water systems. QCM experiments also found that 1s/1s/2s/1s/2s/3s were adequate pulsing and purging parameters for TTIP, lysine and water respectively. Using these parameters at 225 oC, a growth rate of 0.09 Å/cycle was obtained for the TTIP/lysine system and a growth rate of 0.53 Å/cycle was obtained for the TTIP/lysine/water system. These films were further characterized with fourier transform infrared spectroscopy (FTIR) which showed that both systems indeed gave films with various organic functional groups, meaning that the films had an inorganic-organic hybrid character. Gracing incidence x-ray diffraction (GIXRD) revealed that both systems gave amorphous films, and atomic force microscopy (AFM) showed that they were smooth with a roughness, Rq, of about 0.3 nm. Spectroscopic ellipsometry showed that the films were stable over time, apart from a slight decrease in refractive index over time for the TTIP/lysine system. Moreover, the films did not dissolve in either water or cell culture medium. Retinal pigment epithelium (RPE) cells were seeded on the substrates. They proliferated equally well on the TTIP/lysine and TTIP/lysine/water coated substrates as on the reference glass plate. However, the cells seeded on titanium oxide films did not proliferate.