The nanocapsule's size changes with temperature. The group determined that the permeability to trehalose of the crossed-linked Pluronic-PEI nanocapsule wall is high at room temperature and very low at 37 °C.

To encapsulate the trehalose, the researchers soak the nanocapsules in an aqueous trehalose solution at room temperature and then freeze dry the particles to remove the water. After being heated and dissolved in a cell culture medium to incubate with cells at 37 °C, the small, positively charged, trehalose (blue dots) encapsulated nanocapsules (1) absorb onto the negatively charged cell plasma membrane and gradually become enwrapped in a membrane pit (2) that pinches off to form the early endosome (3), as shown schematically in the figure.

When the solution is cooled from 37 °C to room temperature, the nanocapsule expands (from ~150 nm in diameter to ~250 nm). The increase in volume breaks the endosome (4) and allows the nanocapsule to escape. Trehalose (dissolved in water sucked into the nanocapsule during volume expansion) is expelled from the nanocapsule into the cytosol when the temperature is returned to 37 °C (5).

Uptake and cell survival

A significant amount of trehalose (up to 0.3 M) was taken up by NIH 3T3 fibroblasts during a short incubation (40 min). The cells loaded with trehalose were found to survive well, proliferate normally, and function (collagen production) as usual.

The researchers are developing protocols to preserve important mammalian cells loaded with trehalose using the nanocapsule mediated approach at both cryogenic and ambient temperatures for future use as a therapeutic tool. They are also performing studies to deliver small but membrane-impermeable therapeutic molecules into cancer cells using the nanocapsule to enhance cancer treatment.