Progress and prospects for stem cell engineering

Abstract

Stem cells offer tremendous biomedical potential owing to their abilities to self-renew and differentiate into cell types of multiple adult tissues. Researchers and engineers have increasingly developed novel discovery technologies, theoretical approaches, and cell culture systems to investigate microenvironmental cues and cellular signaling events that control stem cell fate. Many of these technologies facilitate high-throughput investigation of microenvironmental signals and the intracellular signaling networks and machinery processing those signals into cell fate decisions. As our aggregate empirical knowledge of stem cell regulation grows, theoretical modeling with systems and computational biology methods has and will continue to be important for developing our ability to analyze and extract important conceptual features of stem cell regulation from complex data. Based on this body of knowledge, stem cell engineers will continue to develop technologies that predictably control stem cell fate with the ultimate goal of being able to accurately and economically scale up these systems for clinical-grade production of stem cell therapeutics.

Figure 1

Engineering approaches for stem cell biology and therapeutics. Stem cells (a) process both biochemical and biophysical signals from adjacent cells, the extracellular matrix, and the soluble medium in their niche. The complex signal transduction and genetic networks (black and gray arrows inside cell, respectively) that process these microenvironmental signals to regulate self-renewal, death, or differentiation behaviors can be mathematically modeled to facilitate our understanding of stem cell biology. High-throughput screening technologies, such as seeding stem cells on arrays of micropatterned extracellular matrix proteins or synthetic polymers (b), promote the discovery of regulatory factors that can be applied in engineering synthetic microenvironments (c) to study and control stem cell behavior ex vivo. Knowledge gained about stem cell biology and microenvironmental factors from modeling and the use of engineered microenvironments will facilitate the design of bioreactors (d) for large-scale and clinical-grade stem cell therapeutics.

Figure 2

Soft lithography in stem cell research. Investigation of the myriad factors that influence stem cell fate can be enhanced through the use of soft lithography techniques. For example, microfabricated polydimethylsiloxane (PDMS) molds/stamps with micrometer-scale patterns can be used in soft lithographic techniques as pattern transfer agents to modify biosurfaces (microcontact printing) and regulate fluid flow (microfluidics). In brief, PDMS molds are fabricated by an initial lithography step that patterns photoresist onto a silicon wafer (a). Next, PDMS is cured on top of the patterned silicon wafer to create a soft, or elastomeric, micropatterned mold. The mold can then be used either directly as a microwell platform (i) or to form other PDMS stamps by replica molding, which can further transfer the patterns to culture surfaces by microcontact printing (ii). Finally, PDMS molds can be used to synthesize microfluidic devices, which could be used to generate microscale gradients of soluble factors (b) (18).