December 23, 2013.
In recent years, there is a growing interest in developing silicon oxide films for use in biomedical applications such as bioelectronics, and biomaterials [1-5]. Plasma enhanced chemical vapor deposition (PECVD) is widely used to deposit silicon oxide films on polymeric biomaterials because it can adjust the mechanical properties with the deposition parameters . Post-deposition oxygen (O2) plasma was used to adapt wettability of SiOx films because O2 plasma enhanced higher O2-containing functionalities and more drastic morphology change. These would be beneficial to certain biomedicine application potentials such as polymeric cell-culture dishes and biosensors whose cell attachment and proliferation properties could be modified by depositing SiOx thin films.
We deposited SiOx films on PLA substrate using the PECVD technique and further treated with O2-plasma to investigate protein adsorption and cell attachment and proliferation. The O2-plasma significantly enhanced the surface wettability of the SiOx films without changing the thickness of the films but smoothing the surface morphology. Increase in the OH bond was responsible for the enhancement of the wettability due to hydrogen replacement and incorporation into the oxide films to contribute to the polar surface. BSA protein was more adsorbed on the hydrophilic SiOx films treated by O2-plasma with the low energy band gap. The results provide some hints for designing certain applications of SiOx films on polymers in biomedicine .
Figure 1. The concentration of the nitrogen bonds on protein adsorbed on films SiOx only and SiOx treated with O2-plasma measured by XPS. (a) An example of the original x-ray photoelectron spectroscopy (XPS) spectrum with deconvoluted components. (b) The calculated N-signal intensity indicating the N concentration in the films.
Figure 1 shows the concentration of the nitrogen bonds on bovine serum albumin (BSA) adsorbed on the SiOx films and O-plasma treated SiOx films measured by XPS. It is seen that the O-plasma-treated SiOx films had more nitrogen than the untreated films, indicating the former absorbing more protein than the latter due to a lower energy band gap. The energy band gap has been rarely taken into account for a material surface factor of protein adsorption. Gandhiraman  studied the fibrinogen adsorption on SiOxCyHz, TiOx and SiO-TiO films with the surface factors of wettability, roughness and energy band gap. They found that fibrinogen adsorption was the highest on the low energy band gap.
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Assoc. Prof. Dr. Dheerawan Boonyawan
Plasma-Bio and Clean Energy Research Laboratory
Plasma and Beam Physics Research Facility
Department of Physics and Materials Science
Faculty of Science, Chiangmai University
Chiangmai, 50200, THAILAND
Tel : 053-943379 Email : email@example.com