387420 Fabrication of Layer By Layer Core and Hollow Particles to Study Phagocytosis
Fabrication of Layer by Layer Core and Hollow Particles to Study Phagocytosis
Anusha Garapaty1, Xingjie Zan1 and Julie A.Champion1, (1) School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA
Macrophages actively remove foreign materials introduced into the body through a process known as phagocytosis. Phagocytosis is mediated by actin-dependent processes involving adhesion, tyrosine phosphorylation, pseudopodial extension, and force generation. This cascade of events shares resemblance with cell migration, where physical and chemical parameters of the substrate play an important role. This suggests that biophysical properties of a material can also govern the process of phagocytosis. The material parameters size, shape and mechanical stiffness have been previously studied, by us and others, to establish their effect on interaction with macrophages. The two steps of phagocytosis, attachment and internalization, were shown to be affected by these parameters [1-3]. However, the combinatorial effects of these material biophysical parameters on phagocytosis have not been studied. This is in large part because current particulate materials are not able to be tuned according to all the parameters without affecting the others. To meet this challenge, we have fabricated novel particulate materials whose parameters size, shape and mechanical stiffness can be independently controlled. These materials have been fabricated by the development of a template based layer-by-layer (LbL) assembly process.
Polystyrene particles of a desired size are chosen as the template. Shape is imparted to the polystyrene particles by heat liquefaction while stretching. The polystyrene template particles are coated with polyelectrolytes poly (vinyl pyrrolidone) (PVP), poly (ethyleneimine) (PEI), and poly (acrylic acid) (PAA) by LbL self assembly. Mechanical stiffness can be varied by functionalization of PAA with thiol groups prior to LbL on particles, to achieve crosslinking between the layers. Finally, treatment with tetrahydrofuran removes the template to attain the hollow form of the particle. The hollow form combined with varying degrees of polyelectrolyte crosslinking helps achieve a range of mechanical stiffness. Size, shape and mechanical stiffness can be controlled independently by the choice of the template polystyrene size, the method of stretching, and the degree of functionalization of thiols on PAA respectively. This highlights the versatility of our system to generate a gamut of polymer carriers of controlled shape, size, and stiffness while retaining the same surface chemistry. These particles are being used to elucidate the interplay between the biophysical properties size, shape and stiffness in governing phagocytosis. This novel polymer particle platform can be functionalized with active ligands for modulation of macrophage activity and phenotype in immunological therapeutic applications.
1. Beningo, K.A. and Y.-l. Wang, Fc-receptor-mediated phagocytosis is regulated by mechanical properties of the target. Journal of cell science, 2002. 115(4): p. 849-856.
2. Champion, J.A. and S. Mitragotri, Role of target geometry in phagocytosis. Proceedings of the National Academy of Sciences of the United States of America, 2006. 103(13): p. 4930-4934.
3. Champion, J.A., A. Walker, and S. Mitragotri, Role of particle size in phagocytosis of polymeric microspheres. Pharmaceutical research, 2008. 25(8): p. 1815-1821.