Development of conductive nanomaterials for biomedical sensors and electric skin

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Darabi, Mohammad Ali
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The future success in healthcare is now strictly entangled with the advances in tissue engineering and bio sensing technologies. Solutions to overcome current limitations in this multidisciplinary field have been actively pursued which has resulted in new materials and properties. Stretchable electronics with tunable mechanical, chemical and electrical properties which are compatible with 3D printing process are highly demanded for biomedical, tissue engineering and health monitoring applications. However, current existing studies have been rather failed to be used in clinics and industries. Cost efficiency and facile preparation method are other dissuasive factors for further achievements. Introducing self-healing properties to the elastic electronics can ensure higher safety and be helpful for bio mimicking purposes. Hydrogels enable mimicking most tissues of human and animal bodies due to their tissue like properties. With tuning different mechanical, physical, chemical and electrical parameters of hydrogels, one can develop bio mimicking hydrogels for countless applications. Herein, three approaches are represented to synthesize conductive nanocomposites applicable in biomedical sensing for health monitoring systems, electric skin and artificial organs. Briefly, in chapter 2, an innovative strategy is presented to fabricate a CNT-based stretchable strain gauge which can detect high strains with high sensitivity. Contrary to some other sensors in which the conductive particles are required to be deposited on elastomer substrates, in this design, CNTs are distributed uniformly on the entire substrate material. Beside, a facile and very unique approach is presented to reach CNTs with aligned arrangement. Another feature of our sensor is the ability to recognize the humid changes with a high sensitivity and fast resistance response capable of monitoring the human breathing. The moldable and plastic material of gum sensors allow a very uniform dispersion of nanotube solution and the ability of being folded leads to a good alignment of nanotubes with good conductivity. In chapter 3, a mechanically and electrically self-healing hydrogel was synthesized with pressure and extension sensitive features, introducing a promising candidate for wearable sensors. The hydrogel was prepared with physically and chemically cross-linked networks through a two-step synthesis. Another feature of our hydrogel is the injectability which enables to print a CSH hydrogel for the first time. The non-covalent and reversible bonds can be disrupted and reformed by an introduction and removal of an external force, respectively. Furthermore, we revealed that the current CSH hydrogel has the ability to monitor human motions with fast resistance response. In chapter 4, a new class of tunable hydrogels was developed based on poly vinyl alcohol. A new method of gelation was introduced which enables both layer by layer and 3D printing fabrications. PVA hydrogels perform shape memory and artificial muscle behav-iour and can retrieve 90% of plastic deformation upon adding water. Strong mechanical and stable chemistry of this hydrogel led to new injectable electronics. This material can be an alternative for microfluidic chip and be introduced as new class of catheters. Appli-cations of this new approach are discussed. Biocompatibility, protein and bacterial anti-fouling and blood-compatibility of this material are confirmed with in vitro experiments which opens new gates for the field of biomaterials.
Electric skin,, Conductive self-healing hydrogels,, Strong hydrogels,, Catheters,, Injectable electronics,, Microfluidics, 3D printing