Thermal diffusion as a mechanism for biological transport.

Accumulated experimental information is used to assess the possible significance of thermal diffusion to mass transport in living matter. Possible thermal gradients across membranes, a single living cell, and an ensemble of such cells (e.g. an organ, tumor, etc.) are estimated. The corresponding model calculations, although not describing the biological process in detail, lead to conclusions about the possibilities for thermal diffusion as follows. Adequate thermal gradients to support substantial thermal diffusion could exist across biological membranes. Thermal diffusive flow would become significant when ordinary Fickian diffusion is sufficiently suppressed, e.g. in more concentrated systems near critical points of solution (i.e. near incipient phase separations). Conditions favorable to thermal diffusion functioning as a mechanism for active transport appear possible. Thermal diffusion appears much more important for transport into and out of an ensemble of cells than into or out of a single cell. Such mass transport by thermal diffusion could assume a sizable magnitude for an ensemble of cells with the dimensions of an organ or a tumor.