15:30-16:15

Cell membrane mimetic polymers and their biomedical applications

The cell membrane establishes an ideal paradigm for the design of biomimetic, immuno-insulating barriers to enhance the performance of biomaterials and biomedical devices. Although phospholipid bilayers coated on a material surface can induce biocompatibility, such a physically adsorbed coating is not robust enough for in vivo applications. In order to control protein and cellular interactions with materials, cell membrane mimetic polymers were designed for surface modifications of a variety of materials and devices, such as nanoparticles, artificial organs, and biosensors. This lecture introduces the idea of cell membrane mimetic polymers, the development of various kinds of functionalized polymers and their applications in biomedical science. Several effective strategies to link such bioactive molecules to surfaces will be highlighted by presenting some exciting examples of biomimetically-engineered nanoparticles useful for multimodal diagnostics and for target-specific drug/gene delivery applications. Critical directions for future research and applications of the surface modification will also be discussed.

Speaker

Prof. Yong-Kuan Gong, College of Chemistry & Materials Science, Northwest University, China

Chair

Prof. Françoise Winnik, MANA Satellite Principal Investigator, NIMS

16:15-17:00

Stem Cell Culture on Surface having Nano-segments: (a) Xeno-free Preparation and Culture of iPS Cells and (b) Preservation of Hematopoietic Stem Cells

Millions of people suffer loss and damage of organ and tissue every year from accidents, birth defects and diseases. Stem cells are attractive source of cells for tissue engineering and cell therapy (i.e., regenerative medicine using stem cells) because of their unique biological properties. Embryonic stem cells (ESCs) derived from pre-implantation embryos have the potential to differentiate into any cell types derived from the three germ layers of ectoderm (epidermal tissues and nerves, etc.), mesoderm (muscle, bone, and blood, etc.), and endoderm (liver, pancreas, gastrointestinal tract, and lungs, etc.).

Although hESCs are promising donor sources in cell transplantation therapies, they face immune rejection after transplantation and there are ethical issues regarding the usage of human embryos. These concerns can be overcome if pluripotent stem cells can be directly derived from patients’ somatic cells. Recently, pluripotent stem cells similar to ESCs were derived from an adult somatic cell by inducing a "forced" expression of certain pluripotent (stem cell) genes such as Oct3/4, Sox2, (c-myc) and klf-4, miRNA, or their proteins (piPS), which is known as induced pluripotent stem cells (iPSCs)^[1]. The iPSCs are believed to be similar to ESCs in many respects, such as the expression of certain stem cell genes and proteins, chromatin methylation patterns, doubling time, embryoid body formation, teratoma formation, viable chimera formation, pluripotency, and differentiability.

iPSCs have significant potential to use the therapeutic applications for cure of many diseases, which hold their specific ability to differentiate into all kinds of somatic cells.

The pluripotent nature of iPSCs open avenues for potential stem cell-based regenerative therapiesand for development of drug discovery platforms. However, there are several barriers to use iPSCs for the clinical application such as viral vector usage, cultivation using xeno-derived materials (e.g., mouse embryonic fibroblasts [MEFs]), and extremely low probability to generate iPSCs. Here, I will report xeno-free preparation of iPSCs cultured on dishes having nano-segments (i.e., vitronectin binding domain) in the first section.

Once cells are attached to the surface of a material, intracellular signals regulating their proliferation and differentiation are generated via interaction between specific receptors and cell signaling molecules adsorbed or expressed on the materials. However, the surfaces of materials on which cells do not proliferate, differentiate or de-differentiate have not yet been studied extensively. These materials should be useful with or without a specific ligand interacting with specific cells (e.g., E-cadherin, N-cadherin, extracellular matrix and cell binding molecules) for the culture and or preservation of embryonic stem (ES) cells, induced pluripotent stem (iPS) cells, mesenchymal stem cells and hematopoietic stem cells. Therefore, we developed a tissue culture flask with immobilized amphiphilicnano-segments of Pluronic F68 and F127 (Pluronic-immobilized flask) in this study.

The triblock copolymer Pluronic was composed of polyethylene oxide (PEO)-polypropylene oxide (PPO)-PEO triblocks, exhibits amphiphilic properties. When fibroblasts (L929 cells) were cultured in a Pluronic F127-immobilized flask, their morphology was mainly spherical, and they showed less spreading behavior than in Pluronic F68-immobilized flasks or conventional tissue culture flasks.This indicated that the PluronicF127-immobilized flask provideda specificenvironment (i.e., bioinert) for the culture of these cells. Therefore, to evaluate the specificityof this flask, umbilical cord blood was preserved in a Pluronic-immobilized flask having several surface concentration of Pluronic and in conventional tissue culture flasks at 4°C.

We examined the effect of surface concentration of Pluronic on the number and survival of hematopoietic stem cells from umbilical cord blood stored in such flasks. The expression ratio of surface markers (CD34) on hematopoietic stem cells stored in Pluronic-immobilized flasks was significantly higher than that in polystyrene tissue culture flasks or commercially available bio-inert flasks (i.e., low cell-binding cultureware). This was due to the presence of flexible brush-like segments of Pluronic on the Pluronic-immobilized flask. A good correlation was found between the number of CD34+ cells and the ratio of viable CD34+ cells from cord blood in several flasks after five days of storage. Therefore, the high number of CD34+ cells was thought to have originated from the high viability of these cells stored in Pluronic-immobilized flasks. It was found that there was an optimal surface concentration of Pluronic on the Pluronic-immobilized flask surfaces for the preservation (high number and survival) of these stem and progenitor cells. The foregoing results were attributable to the high density of Pluronicnano-segments on the flask surface, limiting the movement of these flexible segments^[2].

[1] A. Higuchi et al., Chemical Reviews, 111 (2011) 3021-3034.

[2] A. Higuchi et al., Biomacromolecules, 9 (2008) 634-639.

Speaker

Prof. Akon Higuchi, Department of Chemical and Materials Engineering, National Central University, Jhongli, Taoyuan

Chair

Dr. Guoping Chen, MANA Principal Investigator, NIMS