Purpose This review paper aims to introduce the inkjet printing as a tool for fabrication of flexible/wearable sensors. It summarizes inkjet printing techniques including various modes of operation, commonly used substrates and inks, commercially available inkjet printers and variables affecting the printing process. More focus is on the drop-on-demand printing mode, a strongly considered printing technique for patterning conductive lines on flexible and stretchable substrates. As inkjet-printed patterns are influenced by various variables related to its conductivity, resistivity, durability and dimensions of printed patterns, the main printing parameters (e.g. printing multilayers, inks sintering, surface treatment, cartridge specifications and printing process parameters) are reported. The embedded approaches of adding electronic components (e.g. surface-mounted and optoelectronic devices) to the stretchable circuit are also included. Design/methodology/approach In this paper, inkjet printing techniques for fabrication of flexible/stretchable circuits will be reviewed. Specifically, the various modes of operation, commonly used substrates and inks and variables affecting the printing process will be presented. Next, examples of inkjet-printed electronic devices will be demonstrated. These devices will be compared to their rigid counterpart in terms of ease of implementation and electrical behavior for wearable sensor applications. Finally, a summary of key findings and future research opportunities will be presented. Findings In conclusion, it is evident that the technology of inkjet printing is becoming a competitor to traditional lithography fabrication techniques, as it has the advantage of being low cost and less complex. In particular, this technique has demonstrated great capabilities in the area of flexible/stretchable electronics and sensors. Various inkjet printing methods have been presented with emphasis on their principle of operation and their commercial availability. In addition, the components of a general inkjet printing process have been discussed in details. Several factors affect the resulting printed patterns in terms of conductivity, resistivity, durability and geometry. Originality/value The paper focuses on flexible/stretchable optoelectronic devices which could be implemented in stretchable circuits. Furthermore, the importance and challenges related to printing highly conductive and highly stretchable lines, as well as reliable electronic devices, and interfacing them with external circuitry for power transmission, data acquisition and signal conditioning have been highlighted and discussed. Although several fabrication techniques have been recently developed to allow patterning conductive lines on a rubber substrate, the fabrication of fully stretchable wearable sensors remains limited which needs future research in this area for the advancement of wearable sensors.

This paper presents the employment of LEGO Mindstorms NXT robotics as core component of low cost multidisciplinary platform for assisting elderly and visually impaired people. LEGO Mindstorms system offers a plug-and-play programmable robotics toolkit, incorporating construction guides, microcontrollers and sensors, all connected via a comprehensive programming language. It facilitates, without special training and at low cost, the use of such device for interpersonal communication and for handling multiple tasks required for elderly and visually impaired people in-need. The research project provides a model for larger-scale implementation, tackling the issues of creating additional functions in order to assist people in-need. The new functions were built and programmed using MATLAB through a user friendly Graphical User Interface (GUI). Power consumption problem, besides the integration of WiFi connection has been resolved, incorporating GPS application on smart phones enhanced the guiding and tracking functions. We believe that developing and expanding the system to encompass a range of applications beyond the initial design schematics to ease conducting a limited number of pre-described protocols. However, the beneficiaries for the proposed research would be limited to elderly people who require assistance within their household as assistive-robot to facilitate a low-cost solution for a highly demanding health circumstance.