that red blood cells (RBCs) circulate over 100 days although they are larger than the smallest capillaries. Nature not only employs the surface chemistry of the cells, but also their geometry and mechanical properties, i.e., the biconcave shape of the RBCs, give them the deformability to pass capillaries. Therefore, efforts to mimic RBCs are being reported from fabricating geometrically matching entities to matching their chemical composition. [2] However, making an artificial copy of a cell is challenging. Hence, the compromise between relying on a single interaction point (typically receptor-antibody interactions) of nanoformulations with cells and tissue, and the great complexity of an entire cell is currently a more realistic approach. An interesting example in this context is the use of purified cell membrane to camouflage (nano)particles. This concept offers opportunity to mimic cell−cell interactions employing multiple types of contact points while avoiding the need to obtain/purify specific proteins. This nature-inspired approach was first shown in 2011 with RBC membranes to enhance particle blood circulation times and developed in the next 4-5 years to include white blood cells, platelets, and cancerous cell sources. [3] The field gained increasing attention over the past years, expanding on types of cell sources, coated particles, and envisioned applications. This progress report will highlight selected efforts in the field from the past 2-3 years focusing on mammalian cell sources and coating of colloidal systems (Scheme 1). Efforts pre-dating 2017/2018 were already discussed in detail in several reviews. [4] First, a short overview over the general cell membrane purification procedure and subsequent characterization will be provided. Then, we will outline advances made when non-nuclei or nuclei containing cells sources were used. Finally, coatings consisting of two types of cell membrane (hybrid coatings) will be discussed 2. Formation and Characterization of Cell Membrane Coated Particles Despite of the variation in cell sources, the general purification methods of cell membranes and sequential coating of particles are rather similar and therefore described only briefly. Furthermore, important characterization techniques for size, protein content, and surface charge are discussed. We would like to note that there are a variety of other techniques not mentioned here specifically that can provide valuable specific information such as Fourier transform infrared spectroscopy for analysis of Nanoformulations are widely considered in the biomedical field for drug delivery, imaging, or detoxification purposes. Cell membrane coatings are a growing concept that aims to camouflage nanomaterials. The cell membranes are the first point of contact for cells to other biological or synthetic materials and nature has established signaling pathways in this context. In contrast to using purified membrane associated proteins, the use of purified cell membranes contains the protein of interest in a very native environme...
Bottom-up synthetic biology aims to integrate artificial moieties with living cells and tissues. Here, two types of structural scaffolds for artificial organelles were compared in terms of their ability to interact with macrophage-like murine RAW 264.7 cells. The amphiphilic block copolymer poly(cholesteryl methacrylate)- block -poly(2-carboxyethyl acrylate) was used to assemble micelles and polymer–lipid hybrid vesicles together with 1,2-dioleoyl- sn -glycero-3-phosphocholine or 1,2-dioleoyl- sn -glycero-3-phosphoethanolamine (DOPE) lipids in the latter case. In addition, the pH-sensitive fusogenic peptide GALA was conjugated to the carriers to improve their lysosomal escape ability. All assemblies had low short-term toxicity toward macrophage-like murine RAW 264.7 cells, and the cells internalized both the micelles and hybrid vesicles within 24 h. Assemblies containing DOPE lipids or GALA in their building blocks could escape the lysosomes. However, the intracellular retention of the building blocks was only a few hours in all the cases. Taken together, the provided comparison between two types of potential scaffolds for artificial organelles lays out the fundamental understanding required to advance soft material-based assemblies as intracellular nanoreactors.
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