| Summary: | Printing technology is mainly used for graphic arts and packaging applications, but also is a potential technology for the micro manufacture of electronic devices, biosensors and tissue engineering scaffolds. The main goal of this research is to print fine lines of biopolymer by means of volume printing processes. To assess the feasibility of printing fine features for bioscaffolds using conventional printing technology, an experimental investigation into the rheological behaviour of biopolymer inks was conducted. This is because the rheological characteristics of the biopolymers have a significant influence on the performance of different printing processes. The biopolymers undergo significant phase transition which affects the printed products. The rheological tests focus on ink viscosity, viscoelastic and gelation properties. Gelatine appeared to be more favourable than collagen for scaffolds fabrication by printing technologies. Thus this study was mainly focused on aqueous gelatine solution as printing ink. All inks display shear-thinning and thixotropic behaviours which are important for good printing. The temperature ramp and multi-frequency sweep tests yield information on gelation temperature and gel point. The rate of ordering and gel formation of biopolymer inks was found to be strongly concentration-, temperature- and time-dependent. An increase in gelatine concentrations caused a reduction in the dynamic surface tension of the inks. Printing conditions that are compatible with printing biopolymer inks were being optimised in terms of operation temperature interval to accommodate phase transition. Three printing processes inkjet printing, flexography and screen printing were evaluated for printing fine features of biopolymers. Surfactants were used to lower the ink surface tension to below 30 mN/m, so that the ink could be jetted onto substrate. These printing methods are aimed to produce cost effective bioscaffolds in mass production. The quality of printed lines was examined in terms of width and film thickness to establish the best printing method for gelatine printing. Fine lines printed by inkjet and flexographic printing processes were mostly broken. Screen printing process looks more promising because the printed gelatine fine lines showed the best quality. The line width and line film thickness measured were more consistent and closer to the desired dimensions. A laboratory screen printing trial was conducted using Lie orthogonal array technique to investigate the effect of process parameters on the reproduction of the screen printed fine gelatine lines in terms of line width and film thickness. Six parameters studied were ink type, mesh type, squeegee hardness, snap-off gap, squeegee speed and squeegee pressure. The most significant parameter was the ink type, followed by snap-off gap and mesh type. The effect of squeegee parameters (squeegee type, speed and pressure) was considered insignificant. The orientation has an effect on line width but insignificant effect on line film thickness. Most process parameters had interactions with one another which complicated the optimisation of the process parameters.
|
|---|
