Enhanced mechanical properties and cell separation with thermal control of PIPAAm-brushed polymer-blend microfibers.

We have developed thermoresponsive microfibers with improved mechanical properties and enhanced temperature modulated-cell separation. Microfiber substrates were electrospun using poly(4-vinylbenzyl chloride) (PVBC)-poly(n-butyl methacrylate) (PBMA) blend materials in different ratios. Although their diameters were similar to those of the PVBC homofibers, polymer-blend microfibers exhibited excellent mechanical properties including non-brittle softness, owing to PBMA with a low Tg. These polymer-blend microfibers enabled the preparation of thin, dense mats that were superior in the experimental handling of cell separation. Poly(N-isopropylacrylamide) (PIPAAm) brushes were grafted via surface-initiated atom transfer radical polymerization from the initiation sites of PVBC in the polymer-blend microfiber substrates. The microfiber in a 25 : 75 ratio of PVBC : PBMA had a reasonable amount of the initiation sites and superior mechanical properties. The PIPAAm-brushed microfibers of the 25 : 75 blend substrate were capable of temperature-modulation, both in terms of wettability and cell separation. Among the normal human dermal fibroblasts (NHDFs), human umbilical vein endothelial cells (HUVECs), and human skeletal muscle myoblasts (HSMMs), HUVEC cells showed significantly poor adhesion on fibers at 37 °C; they were separated from adhered NHDF and HSMM cells in the initial step. Reducing the temperature to 20 °C remarkably detached NHDF cells, allowing their separation from HSMM cells. Compared with the PIPAAm-brushed PVBC homopolymer microfibers, these cell-separating functions were enhanced in the thermoresponsive PBMA-rich polymer-blend microfibers, probably ascribed to the properties of PBMA and the moderate density of the PIPAAm-brush. Thus, the developed microfibers could be useful for temperature-modulated cell separation systems.

Micro/nano-imprinted substrates grafted with a thermoresponsive polymer for thermally modulated cell separation.

There is a great demand for effective cell separation techniques that do not require the labeling of cell surfaces for applications in cell transplantation therapy and cell analysis. In the present study, we prepared thermoresponsive convex or concave substrates with circular hole, cylindrical pillar, and line patterns of various sizes as thermally modulated cell separation materials through the combination of thermal nano-imprinted lithography and subsequent surface-initiated atom transfer radical polymerization of poly(N-isopropylacrylamide). Three types of human cells, human umbilical vein endothelial cells, normal human dermal fibroblasts, and human skeletal muscle myoblast cells, which are commonly used in cardiovascular tissue engineering, were employed in this study. All three cell types could adhere to the prepared thermoresponsive micro- or nano-imprinted substrates at 37 °C and detached at 20 °C. The specific cell adhesion and detachment properties were different for each cell type, and they could be altered simply by changing the pattern shapes and sizes of the surface. In particular, large differences between the three cell types were obtained on the 2 µm hole pattern. Using this difference in cell adhesion properties, thermally modulated cell separation application was achieved by successively incubating at 37 °C and 20 °C. Thus, our thermoresponsive micro/nano-imprinted substrates can be utilized as cooperative cell separating materials by combining appropriate convex or concave patterns and mild temperature changes.