3D printing (additive manufacturing) is currently an emerging technology that could revolutionize the traditional manufacturing process. The application of 3D printing technology has been examined in many different fields including manufacturing, science, medicine, and electronics. Another application of 3D printing technology which holds promising potential is fabrication of electrochemical sensors and transducers. Electroanalytical devices hold advantages such as low cost, portability, ease of use, and rapid analysis. Here we examined the feasibility of utilizing 3D‐printed metal electrodes for the electrochemical detection of the pain reliever acetaminophen (AC) also known as paracetamol and the neurotransmitter dopamine (DA) in aqueous solutions. 3D‐printed stainless steel helical‐shaped electrodes were tested before and after surface modification by electro‐plating with a thin gold film (3D gold).

With inherent biocompatibility, biodegradability, and unique programmability, hydrogels with a DNA framework show great potential in three-dimensional (3D) cell culture. Here, a DNA hydrogel was assembled by a dendritic DNA with four branches. The hydrogel showed tunable mechanical strength and reversible thixotropy even under a nanomolar DNA concentration. The cell culture medium can be converted into the hydrogel isothermally at physiological temperature. This DNA hydrogel allows both cancer and somatic cells to be seeded in situ and to achieve high proliferation and viability. The bis-entity of dendritic branches enabled the specific loading of bioactive clues to regulate cell behaviors. Thus, the dendritic DNA-assembled hydrogel could serve as a highly biocompatible, readily functionalizing, and easy-casting gel platform for 3D cell culture.

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DNA is gaining favorable attention as the versatile building block material for hydrogel formation due to its unique properties such as sequence programmability, multifunctional tunability, precise recognition, structural rigidity, and biocompatibility. The DNA hydrogel self-assembly is formed purely by the supramolecular interaction between the complementary DNA base pairs which results in the dynamic interaction in the hydrogel and confers to the thixotropic properties and designable responsiveness of the hydrogel. Thus, allowing the DNA building block as the competitive alternative for the formation of hydrogel with tailored function and precise molecular structure design. By taking advantage of these features, DNA hydrogels have been developed for application in tissue engineering such as 3D cell culture and bioprinting. However, some challenges still remain, such as the complex design of the DNA building block to load functionalities into the hydrogel and the low mechanical strength of the pure DNA hydrogel.In this thesis, we focus on the development of the self-assembled dendritic DNA hydrogel design to offer tailored bio-functionality and enhanced mechanical property to suit the different needs of in vitro 3D cell culture platform. Most DNA hydrogel building blocks require complex design for functionalization and high gelation concentration to form the hydrogel. Hence, in chapter 2 we design a dendritic DNA structure to have a defined composition and offer simultaneous multifunction of bio-cue loading and gelation by independently programming the DNA branches. Tunable mechanical property and cell reharvesting and regeneration into a new DNA hydrogel can be achieved due to the dynamic nature of the DNA hydrogel.