Karreman was an exceptionally devoted educator, who was always supportive of his research associates, family, and friends; he was a generous man, obviously having not forgotten Rashevsky's help in his early life at the University of Chicago.
[5] Karreman was then selected as a consultant to Albert Szent-Györgyi at the Institute for Muscle Research, Marine Biological Laboratory, Woods Hole.
[4] He was appointed associate professor of physiology at the School of Medicine in the University of Pennsylvania, where he also worked at the Bockus Research Institute at the Graduate Hospital.
[7] His main research interests were many, but all were in related fields that included: mathematical biology and mathematical biophysics, membrane biophysics, photosynthetic mechanisms, quantum biochemistry and quantum biophysics,[8] biological energy transfer, quantum biology,[9] physiological irritability, mathematical and systems analysis of cardiovascular and other biosystems, cooperativity, threshold phenomena in biomembranes, adsorption mechanisms at membrane surfaces and ion binding to biomembranes.
After Rashevsky's passing away in 1972, Karreman was a co-founder of the Society for Mathematical Biology (SMB) in 1974—together with H. Landahl and A. Bartholomay, and in 1975 he became its first president.