Figure 2 |. Nanobead properties.

a | Polymeric nanoparticles (schematic transections are shown) are sub-μm colloidal particles. They include: nanospheres, in which the cargo is dissolved, adsorbed or dispersed throughout the matrix, attached to the surface or attached to the polymer matrix; nanocapsules, in which the cargo is in solution and surrounded by a shell-like wall; and nanomicelles, in which amphiphilic co-polymers with hydrophobic and hydrophilic blocks self assemble to entrap the cargo. b | The different types of nanoparticles and microparticles that have been used for tuberculosis (TB) treatment (such as those encapsulating first-line and second-line anti-TB drugs alone or in combination) and for vaccination (such as those encapsulating or adsorbing Mycobacterium tuberculosis (Mtb) immunogenic proteins, peptides and DNA with or without adjuvants), as well as other, potentially useful particles that have not yet been used for TB applications (such as those encapsulating or adsorbing anti-M. tuberculosis peptides, other unconventional drugs and immunostimulants, or immunogenic M. tuberculosis lipids and carbohydrates). c | The main nanoparticle properties that can influence the uptake and efficacy of nanoparticle-based vaccines and therapies. The natural or synthetic polymer used for nanoparticle engineering profoundly affects the characteristics of the particle, such as its biocompatibility and biodegradability, its encapsulation or adsorption efficiency, its internalization or cellular uptake and its release of cargo, as well as affecting its adjuvant and immunological properties and its eventual clearance. The size of a nanoparticle affects its uptake route and its clearance¹⁶ and also influences the type of immune response that is induced^38,39. Positively charged particles are preferentially taken up by living cells owing to the negative charge of the cellular membrane. surface hydrophobicity also increases nanoparticle uptake, whereas hydrophilicity (resulting from, for example, surface modifications with polyethylene glycol and poloxamer polymers) decreases uptake and phagocytosis, increasing the systemic circulation of the particle. Targeting ligands can also be used to direct nanoparticles to cells of interest. Toll-like receptor ligands, adhesins and antibodies for specific cell surface receptors and molecules have been used to this end^10,27,60.