Mechanical and Transport Properties of 3- Dimensional Alginate Hydrogels For Cell Encapsulation

Three-dimensional (3D) cell culture employing encapsulation technologies represents the most advantageous method both to engineer tissue outside the body and to serve as a platform for understanding and manipulating fundamental biological phenomena on the bench top. However, uncertainty and unpredictability regarding cell viability and functionality within these constructs has resulted in suboptimal devices and the inability to establish realistic in vitro systems. Research has demonstrated that a thorough understanding of cell-material interactions is needed for proper direction of cell function and that cells behave differently when seeded on biomaterial scaffolds as opposed to encapsulated within those same scaffolds. The creation of ideal 3D scaffolds that support cell growth and functionality requires fundamental understanding of the primary factors that influence performance: 1) gaseous transport, 2) protein and small molecule transport, and 3) mechanical properties. In this work, these three primary factors are explored for alginate and composite alginate hydrogels. Alginate is an ideal biomaterial for cell-based applications due to its overall biocompatibility and biofunctionality, stemming from its natural source as a component of sea kelp. Alginate can easily be combined with additives, such as perfluorocarbon emulsions for enhancing oxygen transport. Alginate is also unique in its gelation properties (i.e., ionic gelation due to cation diffusion), forming hydrogels, or composite materials, with mechanical properties similar to that of skin or soft tissue. Novel alginate hydrogel formulations were explored to promote cell function through increased oxygen transport, but were shown to reduce protein transport through the evaluation of effective diffusion coefficients for small molecules and proteins. This body of work demonstrates the complexity of transport processes within 3D constructs and the need for approaches that provide a better spatiotemporal picture of hydrogel properties. To address this challenge, a new technique, cavitation microrheology, was adapted and applied to quantify local mechanical properties within alginate hydrogels. This technique was used to determine how local microscale mechanical properties change over time based on varying bulk environments, providing important new information on alginate degradation. On-going and future work is directed towards understanding cellular remodeling within these 3D constructs as a function of local mechanical microenvironment. This research serves as an important step in the development of rational strategies to promote desired cell functionality within 3D constructs, which will further the translational potential of tissue-engineered devices