QUANTIFYING CELL-SURFACE INTERACTIONS USING MODEL CELLS AND TOTAL INTERNAL-REFLECTION MICROSCOPY

Nonspecific colloidal forces play an important role in controlling the adhesion of cells and liposomes to surfaces, A better understanding o f cell-surface interactions is therefore needed for the development of improved drug delivery systems and biomemetic materials, The nonspeci fic interactions between model cells and a glass plate at low ionic st rengths were quantified using total internal reflection microscopy (TI RM). Model cells were developed using 4.32 and 9.98 mu m polystyrene s pheres coated with phospholipids. Varying ratios of zwitterionic dipal mitoyl phosphatidylcholine (DPPC) and negatively charged dimyristoyl p hosphatidylglycerol (DMPG) were used to coat the spheres to mimic the lipid charge composition of actual cell membranes, Measured potential energies of interaction between the model cells and a glass plate show excellent agreement with theoretical predictions based on an exponent ial model for the electrostatic energy. Debye lengths calculated from the experiments agree well with those predicted from solution conducti vity measurements, The data presented show that TIRM is very effective in measuring interaction forces in model biological systems and can b e used to screen potential stabilizing molecules for use in liposomes and biomimetic materials.