Daniel A. Hammer, Ph.D.
Professor and Chair, Department of Bioengineering
Professor, Institute for Medicine and Engineering
University of Pennsylvania

“The Transition From Rolling to Firm Adhesion in Leukocytes: A Model Biological Control System”

Biological cells are equipped with a wide diversity of surface molecules, called receptors, which enable them to carry out complex tasks. In this talk, we use engineering principles to explore how one particular type of cells -- the neutrophil leukocyte -- uses two distinct receptor systems in parallel to achieve its goal: attachment to blood vessel walls at a site of inflammation. Using both computer simulation and experiments involving cell mimetics, in which adhesion receptors are attached to polymeric microspheres, we show that a weak adhesive receptor can aid a strong adhesive receptor, the net result of which is adhesion beyond that achievable by either system itself. The weak adhesion receptor makes binding of the strong adhesion more likely in an exquisitely tuned dynamic interaction. An interesting additional dimension is that the strong adhesive receptor is only fully operational when the cell is activated and the signal for activation may come from the weak receptor itself. Thus, the interplay between these two receptors is complex and operates at different levels. Evidence from our work and others suggests interplay between receptors is ubiquitous throughout biology, and we suggest that quantitative tools are essential at understanding the complexity of how such multiple receptor systems interact.

Daniel A. Hammer’s specialty is cellular bioengineering and cell contact phenomena, specifically cell-cell and cell-surface adhesion, virus-cell interaction, and the diffusion of proteins in membranes. He applies engineering principles to elucidate the functional responsibilities of adhesion molecules in various situations in the human circulation. His work involves innovative theoretical analyses and computer simulations, as well as novel experimental approaches. He is an active teacher and mentor, attracting very bright graduate students to his laboratory.

The body of work produced from Hammer’s laboratory has had significant impact within the field of biomedical engineering, and he has demonstrated the merits of the chemical engineering profession in new ways by extending his reach into important problems in membrane biophysics. He has published more than 50 papers in journals of the first rank, and has been an invited speaker in international conferences. Hammer’s research support includes grants from the National Science Foundation, the National Institutes of Health, NASA, and Unilever. He is a recipient of the NSF Presidential Young Investigator Award (1989).

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