Cellular Shellization: Surface Engineering For Single-Cell Functionalization

In all living organisms, whether very basic or highly complex, nature provides a multiplicity of materials, architectures, systems and functions. A number of unicellular organisms have an outer-surface proteinaceous membrane as a template for biomineralization. The resultant thin mineral layer is a functional covering. For example, the mineral shell can protect an egg from invasion from the exterior, and the diatom has an ornately patterned silicified shell that evolved as mechanical protection. But most cells in nature cannot make their own hard shells. Here we show a strategy to fashion an artificial shell for single cell so that it has extensive protection. The potential applications of shell engineering in the fields of biomedicine, protection of ecological environment and sustainable development are also illustrated in this article.Individual Saccharomyces cerevisiae (S. cerevisiae) cells are coated with a uniform calcium mineral layer by first self-assembly of functional polymers (layer-by-layer technique, LbL) and then in situ mineralization under physiological conditions. The viability of the cells is maintained after the encapsulation. The enclosed cells become inert (stationary phase) and their lifetime can be extended. Furthermore, the mineral shell protects the cell under harsh conditions. The encapsulated S. cerevisiae can even survive the attack of the lytic enzyme zymolyase. The shell can also be used as a scaffold for chemical and biological functionalization. For example, S. cerevisiae becomes magnetic by the incorporation of Fe3O34 nanoparticles in the mineral layer. The present work demonstrates that the artificial shell has a great potential in the storage, protection, delivery, and modification of living cells. Furthermore, insights from systems biology combined with an understanding of the molecular mechanisms of functional shells will facilitate the tailoring of "super cells" through biomimetic mineralization.Different from unicellular organisms and fertilized egg cells, cells inside human tissues are not separate but connected together by extracellular matrix (ECM). The ECM provides a physiological microenvironment for cells and regulates intercellular communication and a cell's dynamic behavior. Based on two over-expressed factors in the tumor microenvironment, matrix metalloproteinases (MMPs) and transferrin (TRF) receptors on the cell surfaces, we develop an enzyme-responsive locally injectable hydrogel system that target the tumor microenvironment. The cell-responsive hydrogel system is designed to release the encapsulated transferrin-drug conjugate in presence of MMPs secreted by cancer cells. The released conjugate is selectively targeted to tumor cells via receptor-mediated endocytosis by TRF receptors that are over-expressed in cancer cell, reducing nonspecific cytotoxicity to the normal cells. The injectable hydrogel drug-delivery system is minimally invasive, offering a highly tunable and programmable platform to modulate drug release through MMP crosslinker peptide sensitivity or tumor stage dependent MMP enzyme expression.