Drug delivery carriers on the fringes: natural red blood cells versus synthetic multilayered capsules

Red blood cells (RBC) and synthetic multilayered nanocarriers may appear as distant 'extremes' of the continuum of diverse drug delivery systems. The former are natural, old and simple, whereas the latter are artificial, novel and sophisticated. However, juxtaposition of features of these types of carriers, offered in a review article published in this issue, is instructive. Such an analysis helps to define both their distinctions and similarities (structural, functional, technological, specific areas of utility), and illustrates perspectives of their translation into the practice. Thus, synthetic multilayered carriers (which, in some embodiments, use elements of design inspired by RBC) represent an attractive research object offering high degree of control of their features. These carriers may find utility for intracellular delivery, controlled release of multiple cargoes and imaging. On the other hand, RBC provide arguably the most attractive carriers for sustained intravascular delivery of variety of drugs including biotherapeutics, either encapsulated into the inner RBC volume or coupled to RBC surface. The discussion of specific medical utility of these carriers and comparative analysis of the factors that may affect their translation (including complexity, costs, market value and therapeutic benefit/risk ratio) is timely and likely to intensify in the near future.