Demand for wearable electronics is expected to at least triple by 2020, embracing all sorts of Internet of Everything (IoE) applications, such as activity tracking, environmental mapping, and advanced healthcare monitoring, in the purpose of enhancing the quality of life. This entails the wide availability of free-form multifunctional sensory systems (i.e “skin” platforms) that can conform to the variety of uneven surfaces, providing intimate contact and adhesion with the skin, necessary for localized and enhanced sensing capabilities. However, current wearable devices appear to be bulky, rigid and not convenient for continuous wear in everyday life, hindering their implementation into advanced and unexplored applications beyond fitness tracking. Besides, they retail at high price tags which limits their availability to at least half of the World’s population. Hence, form factor (physical flexibility and/or stretchability), cost, and accessibility become the key drivers for further developments. To support this need in affordable and adaptive wearables and drive academic developments in “skin” platforms into practical and functional consumer devices, compatibility and integration into a high performance yet low power system is crucial to sustain the high data rates and large data management driven by IoE. Likewise, scalability becomes essential for batch fabrication and precision. Therefore, I propose to develop three distinct but necessary “skin” platforms using scalable and cost effective manufacturing techniques. My first approach is the fabrication of a CMOS-compatible “silicon skin”, crucial for any truly autonomous and conformal wearable device, where monolithic integration between heterogeneous material-based sensory platform and system components is a challenge yet to be addressed. My second approach displays an even more affordable and accessible “paper skin”, using recyclable and off-the-shelf materials, targeting environmental mapping through 3D stacked arrays, or advanced personalized healthcare through the developed “paper watch” prototype. My last approach targets a harsh environment waterproof “marine skin” tagging system, using marine animals as allies to study the marine ecosystem. The “skin” platforms offer real-time and simultaneous monitoring while preserving high performance and robust behaviors under various bending conditions, maintaining system compatibility using cost-effective and scalable approaches for a tangible realization of a truly flexible wearable device.

Next-generation soft robots, wearable health monitoring devices, and human-machine interfaces require electronic systems that can maintain their performance under deformations. Thus, researchers have been developing materials and methods to enable high-performance soft electronic systems in diverse applications. While a variety of solutions have been presented, development of stretchable materials with a combination of high stretchability, electrical conductivity, cyclic stability, and manufacturability is still an open challenge. Throughout this dissertation, gallium-based<br>liquid metal alloy is used as the conductive material, leveraging its high conductivity and intrinsic stretchability for maintained performance under deformations. This dissertation presents both new liquid metal-based conductive materials and scalable manufacturing methods for the development of a diverse range of flexible and stretchable electronic circuits. First, a laser sintering method was developed to coalesce liquid metal micro/nanoparticles into soft, conductive structures enabled by oxide rupturing. The fast, non-contact, and maskless laser sintering technique, in combination with large-area spray-printing deposition, and high-throughput emulsion processing, provided a methodology to create different physical manifestations of liquid metal-based soft, stretchable, and reconfigurable electronics. Second, a liquid metal-based biphasic material was created using a thermal processing technique, yielding a printable, mechanically stable, and extremely stretchable conductor. This material’s compatibility with existing scalable manufacturing methods, robust interfaces with off-the-shelf electronic components, and electrical/mechanical cyclic stability enabled direct conversion of established circuit board assemblies to stretchable forms. The work presented in this dissertation paves the way for future mass-manufacturing of<br>soft, stretchable circuits for direct integration into smart garments or soft robots. <br>

<p>Microbes play key roles in processes that shape the world around us having direct impact in crop  production,  food  safety,  digestion,  and  overall  health.  Developing  tools  to  monitor  their activity in-situ is the key towards better understanding the true impact of microbial activity in these processes and, eventually, harnessing their potential. Many conventional techniques for microbial activity assessment require sample collection, expensive benchtop equipment, skilled technicians, and   destructive   sample   processing   which   makes   their   adaptation   for   in-situ   monitoring cumbersome. The need for technologies for in-situ monitoring has led to the development of many sensordesigns,  capable  of  detecting  single  strains  of  bacteria  to  low  limits  of  detection  (LOD). These designs, however, are limited to their complex manufacturing procedures, cost, and delicacy which makes them difficult to implement outside of a laboratory setting into harsh environments.</p> <p>In  the  last  25  years,  impedimetric  sensing  methods  have  been used  as  powerful  analytical tools  to  characterize  the  degradation  and  dissolution  of  polymers.  Known  for  their  robustness, these techniqueswere mainly used for characterizing polymer’s properties as corrosion-protective layers on metals. At the time, someresearchers pondered onthe potential use of this technique for biosensing  applications.In  this  thesis,  the  ability  of  monitoring  microbial  activity  in-situ  was explored by  integratingdifferent  bioresponsive  polymers  with  low-cost electronic  impedimetricplatformsand assessing their degradation kinetics in response to microbes</p> <p>This  novel  use  of  impedimetric  sensing  methods  and  approach  towards  microbial  activity sensing was systematically studied in different  areas including  agriculture, food packaging, and healthcare.  Microbes,  the  good,  the  bad,  and  the  ugly,  were  studied  within  their  ecosystems  to demonstrate  the  ability  of  using  the  described  systems  in  in-situ  monitoring.  In  agriculture, polymer  degradation  was  successfully  correlated  to  the  concentration  of  decomposing  bacteria directly in soil. In food packaging, spoilage of chicken samples was successfully detected within their package through a non-reversible system. In healthcare, a wireless and electronic-free wound monitoring  system  capable of  detecting  early  onset  of  infection  while  delivering  therapeutics without the need of external actuation was achieved. Further developments of this technology will present the key towards monitoring microbial activity in-situ in a large scale, providing solutions to  humanity’s  toughest  upcoming  challenges  including  food  production,  food  safety,  and healthcare.</p>