A colloidal supra-structure of responsive microgels as a potential cell scaffold

Abstract

A colloidal supra-structure that regulates essential cellular functions such as cell proliferation rate can better mimic the extracellular matrix for engineering complex tissues. Such a colloidal supra-structure can be built from the thermo-driven gelation of the colloidal dispersion of poly(N-isopropylacrylamide-co-acrylamide) (poly(NIPAM-co-AAm)) microgels, which exhibit a reversible and continuous volume phase transition in water at a temperature of ≈35 °C and remain partially swollen and soft at 37 °C. In our experimental size range (hydrodynamic radius ∼100 to 250 nm at 37 °C), the microgels of a larger particle size displayed a larger critical effective concentration ϕ_effective, above which the microgel dispersions undergo a sol-to-gel transition to form a solid-like colloidal supra-structure under the physiological conditions. While the syneresis kinetics of all colloidal supra-structures fitted well to the Tanaka–Fillmore model, indicating a polymer-like nature, the colloidal supra-structures built from the larger microgel particles exhibited a smaller degree of syneresis. The colloidal supra-structures can serve as scaffolds for cell culture. The larger the microgel particles used to build the colloidal supra-structures for scaffolds, the greater the enhancement in the relative cell viability. The relative small difference in size (2.5-fold) of the building microgel particles could lead to a large difference in the cell proliferation rate (as high as 4.5-fold). These results indicate that the size of microgel building blocks takes an important role in controlling the sol-to-gel transitions, degree of syneresis, and permeability of the constructed colloidal supra-structures, thus providing a simple way to construct desirable cell scaffolds to regulate the cellular functions.