Fabrication of a time-temperature indicator by inkjet printing of a spore-based bio-ink

Abstract

Bio-indicators are nowadays being increasingly used by the food and drug industry to detect the changes in environmental conditions. In this study, a time-temperature indicator (TTI) is fabricated by using an office thermal inkjet printer to print a new custom-made bio-ink for detecting changes in color that occur with time and temperature variation. In lieu of the regular inks, the TTI uses solutions containing Geobacillus stearothermophilus (G. stearothermophilus) and Bacillus atrophaeus (B. atrophaeus) spores, tryptic soy broth, pH indicators, and a combination of polyvinyl alcohol and borax as the gelling agent, to be dispensed from the printer cartridge. Following the printing process, the samples thus obtained are coated with a protective film to avoid moisture loss. The effects of bio-ink gelatinization, pH, color intensity, and print resolution on bacterial printing are determined by varying the level of each parameter. The presence of the protective film on printed bacteria is found not only to lead to the growth and proliferation of bacteria but also to reveal color with sharper contrast. The indicator’s initial and final colors are modified by varying the pH levels of the solutions. Increasing color intensity (20%, 40%, 60%, 80%, and 100%) in the software settings is used to induce significant enhancements in the printed bacterial populations, thereby controlling the rate of color change. It is, moreover, observed that changes in print resolution do not have any significant effects on the populations of printed bacterial spores. In general, the TTI’s endpoint may be modified so as to suit various pharmaceutical and food applications.