Toward Directing Cell Fate: Carbon Nanotubes As Modulators of Extracellular and Transporters of Intracellular Cues

The unique properties of CNTs lead CNTs attractive in biological engineering applications. It is expected to use CNT based biomaterials for clinic use in the near future. CNTs can be used to tune cellular fate through bother extracellular pathway and intracellular pathway. CNT based biomaterials has been applied into bone, nerves, and cardiovascular system. There has also been progress in the use of CNTs in controlling cellular alignment, to enhance tissue regeneration, growth factor delivery and gene delivery. Pluripotent stem cells (hPSCs) offer a promising tool in tissue engineering strategies, as their differentiated derivatives can be used to reconstruct most biological tissues. These approaches rely on controlling the extracellular and intracellular cues that tune the ultimate fate of hPSCs. In this context, significant effort has gone to parse out the role of conflicting matrix-elicited signals (eg. topography and elasticity) in regulation of macroscopic characteristics of cells (eg. shape and polarity). A critical hurdle lies in our inability to recapitulate the nanoscale spatiotemporal pattern of these signals. We used CNTs as a tool to tune nanoscaled architecture in cellular microenvironment in Chapter 2 and Chapter 3. After recapitulating the basic understanding of how CNT pattern controlling cellular polarization and human embryonic stem cell attachment in 2D substrate in Chapter 2, we took a step forward by developing a porous scaffold with appropriate mechanical strength and controllable surface roughness for bone repair in chapter 3. We found that the incorporation of CNTs led to an enhanced surface roughness and mechanical strength of CNT-PLGA composites. Most interestingly, the in vitro osteogenesis studies demonstrated a significantly higher rate of osteogenic differentiation of osteoblasts on CNT/PLGA scaffolds compared to the control PLGA composite groups. All these basic understanding lead us to enhance the utility and efficacy of using CNTs for directing stem cell fate by both 2D and 3D substrate. On the other hand, cancer has arisen to be of the most prominent health care issues across the world in recent years. Doctors have used physiological intervention as well as chemical and radioactive therapeutics to treat cancer thus far. As an alternative to current methods, gene delivery systems with high efficiency, specificity, and safety that can reduce side effects such as necrosis of tissue are under development. Although viral vectors are highly efficient, concerns have arisen from the fact that viral vectors are sourced from lethal diseases. With all this in mind, rod shaped nano-materials such as CNTs have become an attractive option for drug delivery due to the enhanced permeability and retention effect in tumors as well as the ability to penetrate the cell membrane. In Chapter 4, we successfully engineered PLGA functionalized CNTs to reduce toxicity concerns, provide attachment sites for a pro-apoptotic protein, caspase-3 (CP3), and tune the temporal release profile of CP3 within bone cancer cells. Our results showed that CP3 was able to attach to functionalized CNTs, forming CNT-PLGA-CP3 conjugates. We show this conjugate can efficiently transduce cells at dosages as low as 0.05 g/ml and suppress cell proliferation up to a week with no further treatments. In all, these results are essential to showing the capabilities of CNTs as both extracellular cues and intracellular cues to tune cell fate