# 3D DNA Nanostructures: The Nanoscale Architect
## 5 Applications
### Surface Templating
#### 5.2.1 Hybrid DNA-Lipid Nanostructures  
Lipid vesicles are lipid bilayer membranes typically encapsulating some fluid. Generally, cells and organelles all have such an encapsulating lipid bilayer membrane. Lipid vesicles that are artificially created are _liposomes_, which are self-assembled from amphiphilic lipid molecules. Liposomes preferably self-assemble into spherical shapes, but in natural systems, there also exist membrane proteins that can regulate the deformation of cellular membranes to consequently dictate cellular function. The function of these membrane-deforming mechanisms still warrants study, and DNA nanostructures could help both probe and mimic their effects.  
DNA nanostructures have been shown to template both the size and shape of lipid membranes. A DNA nanostructure template can be decorated with hydrophobic functional groups, usually lipid membrane components like cholesterol, but also hydrocarbon chains [116], that can embed into a lipid membrane. A lipid membrane self-assembles around the DNA nanostructure spanning the anchored hydrophobic groups [118], and this has been shown to manipulate continuous lipid membranes into unnatural configurations such as cuboids [119] or winding tubular configurations that have been also shown to mimic the structure of the golgi apparatus [120] (Figure 7B). The study of lipid vesicles is also made more challenging by inconsistencies of size and shape in leading synthesis techniques which still necessitate strict filtration of undesired specimens [121]. Round DNA barrels have been shown to act as a physical template for synthesizing lipid vesicles where it becomes energetically favorable for the lipid vesicle to conform to the size of DNA nanostructure template [122]. In biomimicry of nanodiscs [123], circular DNA templates can also consolidate a lipid bilayer for biophysical studies [116; 124]. Another circular template, a DNA barrel extruded using hierarchical assembly, was also shown to be able to template the formation of a lipid membrane along the outer profile of the structure, forming a long, tubular lipid membrane [125].  
Biophysical studies of lipid membranes is also possible by using DNA nanostructures as an architectural framework. For example, joint work by the [PERSON] and [PERSON] groups used a DNA column as a ruler for spacing liposomes, which were themselves suspended in circular DNA origami templates at each end of the ruler. This provided insight into the transfer of lipids between lipid membranes [128]. Shaped DNA nanostructures can also be used to mechanically impose shape upon an existing membrane [129; 130; 131]. This is similar to the BAR-family of proteins, which have a role in forming tubular substructures in cells. For example, they may form filopodia, which are protrusions of the cell membrane that allow the cell to probe its environment. Composition and the organization of lipid membranes and their membrane proteins can also be studied by tracking DNA barges that have targeted specific behavior or interactions upon the membrane surface [132; 133]. These studies help to show how DNA origami can elucidate the mechanical properties of cellular function. For further reading, interactions of DNA nanostructures with membrane surfaces has also recently been thoroughly reviewed [134].