Fig. 4. Particle optimization.

a | Materials can be designed to be biodegradable, anti-inflammatory, biomimetic or stimuli-responsive. b | Microparticles are phagocytosed and target the vascular wall, whereas nanoparticles permeate the vasculature. c | Polymeric materials can be formulated into a variety of shapes to target specific cell populations. d | Functional groups on polymeric materials can be conjugated with targeting ligands or stealth polymeric chains. In addition, the polymer can be positively or negatively charged. e | Particle rigidity can be modified to selectively target specific cell populations and endothelium in the blood. Soft particles are ideal for marginating along the endothelium in blood flow compared to rigid particles. RBC, red blood cell; PEG, polyethylene glycol; MMP, matrix metalloproteinase.