Engineering Synthetic Erythrocytes as Next-Generation Blood Substitutes.

Blood scarcity is one of the main causes of healthcare disruptions worldwide, with blood shortages occurring at an alarming rate. Over the last decades, blood substitutes has aimed at reinforcing the supply of blood, with several products (e.g., hemoglobin-based oxygen carriers, perfluorocarbons) achieving a limited degree of success. Regardless, there is still no widespread solution to this problem due to persistent challenges in product safety and scalability. In this Review, we describe different advances in the field of blood substitution, particularly in the development of artificial red blood cells, otherwise known as engineered erythrocytes. We categorize the different strategies into natural, synthetic, or hybrid approaches, and discuss their potential in terms of safety and scalability. We identify synthetic engineered erythrocytes as the most powerful approach, and describe erythrocytes from a materials engineering perspective. We review their biological structure and function, as well as explore different methods of assembling a material-based cell. Specifically, we discuss how to recreate size, shape, and deformability through particle fabrication, and how to recreate the functional machinery through synthetic biology and nanotechnology. We conclude by describing the versatile nature of synthetic erythrocytes in medicine and pharmaceuticals and propose specific directions for the field of erythrocyte engineering.