Johannes M. Nitsche

PhD

Johannes M. Nitsche

PhD

Johannes M. Nitsche

PhD

SUNY Distinguished Professor
Director of Undergraduate Studies

Research Topics

Transport phenomena; bioactive surfaces; biological pores; transdermal transport

Contact Information

507 Furnas Hall

Buffalo NY, 14260

Phone: (716) 645-1182

Fax: (716) 645-3822

nitsche@buffalo.edu

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Research

Transport phenomena, bioactive surfaces, biological pores, transdermal transport

Geometry for a diffusion model of fluorescent dye molecule transfer between Xenopus frog eggs.

Research addresses fundamental problems in the transport of molecules and particles in pores, near surfaces and in other types of heterogeneous environments, and the application of such basic theory to mechanistic understanding and technological development in biology and biomedical engineering.

Configurational transport processes

Basic research focuses on the dynamics (“kinetic theory”) of configurational diffusion (rotation, stretching, bending) for nonspherical and flexible molecules. These types of Brownian motion have a particularly rich structure, both geometrically and physicochemically, when they occur in pores or near surfaces, and when they involve intermolecular forces, binding interactions or chemically reactive species. Specific problems studied are: (i) what is the macroscopically observable rate of diffusion and binding of a solute through a medium with a microscopically heterogeneous distribution of binding sites; (ii) how is the rate of a site-specific reaction affected when one of the reacting molecules is immobilized on a surface; and (iii) how do attractive and repulsive interactions with the wall affect the equilibrium distribution and diffusion of nonspherical and flexible molecules within fine pores?

Intercellular transport

The first biological application is a collaboration with Prof. Bruce J. Nicholson (Department of Biochemistry, University of Texas Health Sciences Center at San Antonio) aimed at understanding the permeability and selectivity properties of key intercellular pores called gap junctions, which are the primary means by which cells in the body exchange metabolites and signals. Although these pores were once thought to be simple aqueous conduits, it is now clear that they can, in fact, be highly selective in allowing different molecules to pass through them at different rates. Macroscopic modeling of intercellular diffusion is making it possible to convert macroscopic measurements of fluorescent dye transfer between cells into absolute values of permeability of individual channels. Microscopic theory of ion flow and molecular diffusion through these pores is being developed to explain the derived data on pore permeability.

Transdermal transport

The second application is related to theory for a collaborative investigation being pursued with Prof. Gerald B. Kasting (College of Pharmacy, University of Cincinnati) on drug and chemical transport through skin. The goal is to understand how fast applied agents pass through the skin, especially the outermost stratum corneum (barrier) layer, how and where they distribute themselves within tissue layers below the surface, and how fast they are absorbed into the blood stream through skin capillaries. Improved theoretical knowledge of these processes is key to the engineering of topical and transdermal drug delivery, as well as risk assessment of chemical exposure. Detailed diffusion models incorporating realistic representations of tissue microstructure, ultrastructure and physiochemical parameters are being developed to describe and predict: (i) permeability of the stratum corneum barrier; (ii) drug/chemical distribution in the epidermis, dermis and subcutaneous fat layers; (iii) systemic uptake by dermal capillaries; and (iv) drug distribution around hair follicles, and dermal permeability associated with follicles and other skin appendages.