Three-Dimensional Plant-Derived Biomaterials - Scaffolds for Tissue Engineering and Biophysical Manipulation

Cells are complex active materials that display fascinating phenomena in response to changes in their physical environments. It is well established that the physical environment dictates cell fate and function; nevertheless, the standard method of culturing and studying cells is on stiff 2- dimensional Petri dishes and glass cover slips. The difference in the magnitude of the stiffness of the substrate in addition to the 2-dimensional character, leads to an incomplete and perhaps misleading picture of the cellular process under scrutiny. As such, an entire field has been dedicated to developing materials that more closely match the characteristics of the natural cellular milieu: biomaterials. Despite significant progress in the field, we are still far from fully recapturing the native environment. Importantly, many of the current strategies for engineering 3-dimensional biomaterials have specific applications yet lack flexibility to be adapted to a wide variety of functions. Our approach is to repurpose existing complex, readily available materials to create a platform for biomaterial production; our biomaterials are derived from plant tissue. Plants have evolved over millions of years to attain structures with intricate geometries for specialized functions. Due to the wide variety of plant structures, one can easily select a plant-based material with analogous features to the tissue of interest. A series of investigations are presented on these novel biomaterials to demonstrate this approach, quantify the mechanical properties, and study the cellular responses. First, we developed a method of processing plant materials to yield decellularized, cellulose-based, biocompatible scaffolds that can be repopulated with mammalian cells. We then created composite materials by casting hydrogels around the cellulose-based scaffolds, which allowed us to incorporate distinct temporal and spatial cues to the local cell populations. Spatial organization of tissues and tissue interfaces remains a primary challenge in biomedical engineering, as tissue interfaces mark complex transitional zones between distinct cell populations. Replicating and repairing this intricate delineation of cell types and mechanical profiles has proven to be a major concern in regenerative medicine. As such, we sought to develop a platform for engineered tissue interfaces, wherein components are combined in a modular fashion into a functional unit. The mechanical cues of the microenvironment affect a plethora of cellular processes, namely cell migration, proliferation, and differentiation. Consequently, the rheological properties of our decellularized, plant-based scaffolds were thoroughly investigated. An in-depth knowledge of the mechanics of the underlying substrate is required to guide future applications and refinements of this technology. The potential applications of these 3-dimensional constructs, as demonstrated through our findings, include designing in vitro models of tissue interactions, new biomaterials for in vivo applications, and studies on fundamental cellular processes. We highlight the significance of our results in a collection of scientific articles, which are presented in the body of this thesis (Chapters 2-5). This work is focused on the use of plant- derived cellulose materials, which forms a subsection of the cellulose biomaterial field. A review article centered on the use of cellulose materials for tissue engineering serves as an introductory chapter.

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