Micro-injection Molded Polymeric Surfaces for the Maintenance of Human Mesenchymal Stem Cells (hMSCs)
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Micro-injection Molded Polymeric Surfaces for the Maintenance of Human Mesenchymal Stem Cells (hMSCs) Meghan E. Casey1, John W. Rodgers2, Courtney E. LeBlon2, John P. Coulter2, Sabrina S. Jedlicka1,3,4 1
Bioengineering, 2Mechanical Engineering and Mechanics, 3Materials Science and Engineering, 4 Center for Advanced Materials and Nanotechnology Lehigh University, Bethlehem, PA 18015, USA
ABSTRACT In this work, we take advantage of injection molding as a high volume and repeatable method to create surface areas for the growth of human mesenchymal stem cells (hMSCs). Ultraviolet lithography, combined with deep reactive ion etching, was used to generate microfeatures over a relatively large surface area of a silicon wafer. The micro-featured silicon wafer was used as a mold insert for the micro-injection molding process to create polystyrene and low density polyethylene surfaces. Micro-geometry was used to alter the effective surface stiffness of the polymer substrate. Created samples were characterized via scanning electron microscopy and tensile testing. hMSCs were seeded onto samples for initial studies. Actin and vinculin were visualized through ICC to compare cytoskeletal elements. Changes in cell morphology were examined using ICC. Results indicate that injection molding of microfeatured substrates is a viable technique to produce surfaces amenable to stem cell growth.
INTRODUCTION Bone marrow-derived human mesenchymal stem cells (hMSCs) have been used extensively as a cellular differentiation model in the fields of tissue engineering and cellular therapeutics. hMSCs are isolated from human bone marrow in small quantities and must therefore be expanded in vitro [1]. After numerous passages in vitro, hMSCs lose their proliferative state, slowing cell division and in many cases, eliminating the cellular differentiation potential [2,3]. Recent work links the inability of stem cells to grow and proliferate to the shortening of telomeres and stiffening of the cell [2,4]. The onset of cell stiffening may be correlated to the surfaces upon which the stem cells are cultured [5]. Therefore, one possibility of limiting surface-induced stem cell aging involves engineering cell culture surfaces that limit the cell stiffening phenomenon. Cells interact with the extracellular domain at the micro- and nanoscale, features not represented on traditional cell culture substrates such as tissue-culture treated polystyrene (TCPS) [6,7]. Additionally, TCPS possesses mechanical properties that may be unsuitable for maintaining stem cells in vitro, as the bulk elastic moduli of in vivo tissues are orders of magnitude lower [7]. However, if stem cells are presented with the same polymer substrates fabricated with an array of microscale pillars, the ability of the pillars to bend in response to the applied cellular forces creates a locally compliant mechanical environment greater than that of the bulk material. The stiffness of a polymer is measured through applying force to a specific crosssectional area and measuring the resultant def
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