Hydrogels: "Poly(ethylene)glycol Hydrogel Platform"
We have developed a novel approach to maintaining stem cell properties in culture by deconstructing the stem cell niche, or in vivo microenvironment. To this end, we have bioengineered a hydrogel platform that allows us to decouple the effects of biochemical and biophysical ‘niche’ cues on stem cell behavior and fate in culture.
Hydrogels are an advantageous class of biomaterials for cell culture, as they are inert to protein adsorption and mimic natural tissue in that they are soft and highly hydrated (up to 98% water), thus allowing diffusion of nutrients and presentation of proteins in a more physiological manner than conventional plastic dishes.
Our hydrogel formulation is poly(ethylene)glycol-based (PEG) and is comprised of two components; a 10kDa 8-arm PEG functionalized at each arm with vinyl sulfone and a 10kDa 4-arm PEG functionalized at each arm with thiols. Via a ‘Michael-type’ addition reaction, precursor solutions consisting of these two polymers will spontaneously polymerize resulting in a non-swelling hydrogel lattice. Using a micro-contact printing approach it is possible to covalently cross-link proteins into the gel network. Further, these PEG hydrogels are amenable to standard photolithography approaches, which allow for patterning of the hydrogel surface.
Using this innovative platform we can control protein identity, concentration, and presentation, as well as niche size, and hydrogel matrix mechanical properties. Single stem cells are isolated and exposed to bioengineered microenvironments (“niches”) in which selected protein components known to be present in the niche in vivo can be systematically tested for effects on cell division behavior (asymmetric or symmetric cell divisions), quiescence or activation, in vitro.
Because the hydrogel substrates are completely transparent, the optics are excellent for microscopy. Microwell arrays make it possible to track cell fate changes via time-lapse microscopy for clonal populations of single stem cells and perform quantitative statistical analyses of outcomes.