Control of Cell-Material Interactions in 2D and 3D System

Animals exploit the deformability of soft structures to move efficiently in complex natural environments. These soft structures are inherently compliant and enable large strains in components not typically found in robotics. Such capabilities have inspired robotic engineers to incorporate soft technologies into their designs. One goal in soft robotics is to endow robots with new, bioinspired features that permit morphologically adaptive interactions with unpredictable environments. There are three key elements of bioinspired soft robots from a mechanics vantage point, namely, materials selection, actuation, and design. Soft materials are necessary for safe interaction and overall actuation of bio-inspired soft robots. The intrinsic properties of materials in soft robots allow for an “embodied intelligence” that can potentially reduce the mechanical and algorithmic complexity in ways not possible with rigid-bodied robots. Finally, soft robotics can be combined with tissue engineering and synthetic biology to create biohybrid systems with unique sensing, dynamic response, and mobility. Bioinspired soft robots have the ability to also expedite the evolution of co-robots that can safely interact with humans. This thesis revolves around understanding of the structure-property relations in 2D and 3D soft components that aid in the design objectives of biohybrid systems. 

The propensity of cells to align in particular directions is relevant to a number of areas, including tissue engineering and biohybrid soft robotics. Cell alignment is modulated through various extracellular conditions including surface topographies, mechanical cues from cell-matrix interactions, and cell-cell interactions. Understanding of these conditions provides guidance for desirable cellular structure constructions. In chapter 2, we examine the roles of surface topographies and cell-cell interactions in inducing cell alignment. We employed wavy surface topographies at the nanometer scale as a model extracellular environment for cell culture. The results show that, within a certain range of wavelengths and amplitudes of the surface topographies, cell alignment is dependent on cell confluency. This dependence on both topology and confluency suggests interplay between cell-cell and cell-matrix interactions in inducing cell alignment. Images of sparsely distributed and confluent cells also demonstrated clear differences in the structures of their focal adhesion complexes. To understand this effect, we introduced anti-N-cadherin to cell culture to inhibit cell-cell interactions. The results show that, when anti-N-cadherin was applied, cells on wavy surfaces required greater confluency to achieve the same alignment compared to that in the absence of anti-N-cadherin. The understanding of the cell alignment mechanisms will be important in numerous potential applications such as scaffold design, tissue repair, and development of biohybrid robotic systems.

Muscle cell-based biohybrid actuators have generated much interest for the future of soft robotics for their mimicry of living muscle performances. Unfortunately, current biohybrid actuators move without having much control over their actuation behavior. Integration of microelectrodes into the backbone of these systems may enable modulated control over these actuators with specific activation patterns. In chapter 3, we address biocompatibility challenges in incorporating eutectic gallium-indium (EGaIn) microelectrodes into biocompatible constructs for cell stimulation. Although EGaIn has advantageous conductive and rheological properties as a microelectrode, studies show that the material is cytotoxic when in direct contact with cells and currently there are few methods for the material to viably interface with the cell culture. The goal of this chapter is to improve EGaIn biocompatibility by embedding the liquid metal into biocompatible elastomers. Such advancements in EGaIn biocompatibility will allow for applications that improve the controllability of bio-hybrid robots and expedite the evolution of soft robots that can safely interact with humans and natural complex environments. 

One of the most critical challenges in the fabrication of thick, 3D tissue is vascularization. Without vascularization, engineered tissue lacks oxygen and access to nutrients, which prompts cells to undergo cell death through apoptosis. In vivo, vasculogenesis and healthy maintenance of the structure and morphology of each blood vessel is mediated via competing mechanical, chemical, and physiological factors. In chapter 4, we propose a novel vascular wall model of endothelial cells cultured onto smooth muscle cells utilizing cell sheet stacking techniques for modular control of tissue thickness, cell orientation, and mechanical stimuli. Modular control of these variables is a convenient method to isolate how each stimulus promotes self-organization of the endothelial-vascular smooth muscle cell co-culture. Such advancements in understanding endothelial-vascular smooth muscle cell co-culture will inform the mechanics that stimulate well organized vascularization in engineered tissue.