Effect of interfacial serum proteins on melanoma cell adhesion to biodegradable poly(l-lactic acid) microspheres coated with hydroxyapatite

We have measured the interaction forces between a murine melanoma cell and a poly(l-lactic acid) (PLLA) microsphere coated with/without hydroxyapatite (HAp) nanoparticles (i.e., an HAp/PLLA or a bare PLLA microsphere) in a serum-free culture medium, using atomic force microscopy (AFM) with colloid probe technique, in order to investigate how the HAp-nanoparticle coating as well as interfacial serum proteins influence the cell–microsphere adhesion. The cell adhesion force of the HAp/PLLA microspheres was 1.4-fold stronger than that of the bare PLLA microspheres. When the microspheres were pretreated with a culture medium supplemented with 10% fetal bovine serum, the cell adhesion force of the HAp/PLLA microspheres was increased by a factor of 2.1; in contrast, no change was observed in the cell adhesion force of the bare PLLA microspheres before/after the pretreatment. Indeed, the cell adhesion force of the HAp/PLLA was 2.8-fold larger than that of the bare PLLA after the pretreatment. Additionally, we have investigated the effect of interfacial serum proteins on the zeta potentials of these microspheres. On the basis of the obtained results, possible mechanism of cell adhesion to the HAp/PLLA and bare PLLA microspheres in the presence/absence of the interfacial serum proteins is discussed.