Functional tissues from intelligent materials, 3D printing and stem cells

Regenerative medicine has evolved into the stage of “smart regenerative medicine” where biomaterials can actively influence cell fate and behavior to form and regulate tissue function. Tissue engineering is a prominent tool of regenerative medicine that can utilise stem cells for regenerative therapy because of their capacity to proliferate and differentiate into lineage specific cell types. The status of stem cells is dependent on the extracellular conditions, which include chemical signals such as growth factors, and the properties of extracellular materials in a three-dimensional (3D) environment. With the development of materials science and 3D bioprinting, it is possible to build complicated functional tissues in vitro for regrowth of lost and damaged tissues or organs. Therefore, through “additive manufacturing”, advanced tissue constructs can be fabricated using bioactive and biodegradable materials with integrated tissue-specific cells, whereby the mechanical structure and cell-cell interactions closely emulate in vivo tissue and function. The work described herein relates to the development of simple and reproducible approaches to constructing neural tissue by bioprinting human neural or induced pluripotent stem cells that are differentiated in situ to functional neurons and neuroglia. The supporting biomaterials (comprising alginate, carboxymethyl-chitosan and agarose) form a novel clinically relevant 3D porous gel by stable crosslinking after printing, which encapsulates stem cells for subsequent expansion and differentiation. Differentiated neurons are spontaneously active, show a bicuculline-induced increased calcium response, and are predominantly gamma-aminobutyric acid expressing. In addition to neural tissue, human induced pluripotent stem cells could be induced to generate the embryoids within printed constructs comprising cells of three germ lineages endoderm, ectoderm, and mesoderm. A second component to this thesis related to the investigation of electrical stimulation via conductive biomaterials for future potential application with 3D bioprinting for tissue engineering. Electric field is one important parameter involved in the cell growth and embryo development. In support of further controlling/regulating stem cell state, obtained results provisionally indicate that electrical stimulation via a conducting biopolymer augments human iPSCs to differentiate into neuronal cells. While further research will be necessary, the present findings provide support for the development of 3D configured conductive materials to enhance stem cell differentiation to neural and other tissues. Furthermore, conductive constructs may be produced by adapting the presently described 3D bioprinting platform. In conclusion, the methods described herein provide a foundation to build upon for advanced manufacturing of 3D human neural and other tissues for near-term research of tissue development, function and disease, and longer-term regenerative medicine including transplantation therapy