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Recent developments in DNA nanotechnology brought rich structural and functional diversity. However, for DNA nanostructures to perform in a biologically relevant context, obstacles such as nuclease activity and low divalent ion concentrations have to be addressed. For drug delivery or gene therapy applications, ultimately the lipid membrane barriers must be targeted and overcome. In this article, we highlight efforts and achievements in enhancing the stability of DNA nanostructures including chemical modifications, covalent crosslinking and coating with protective layers composed of polymers or lipids. We then review interactions between DNA nanostructures and lipid membranes, which are often mediated by ligands for membrane receptors or hydrophobic domains incorporated into the structure. Finally, we present applications of DNA nanostructures on and in lipid membranes, including higher order assembly, controlling membrane curvature, targeting and arranging membrane proteins in living cells and DNA-based synthetic lipid channels.

DNA-based nanoconstructs possess great potential for biomedical applications. However, the in vivo behavior of such constructs at the microscopic tissue/cell level as well as their inflammatory potential is largely unknown. Unmethylated CpG sequences of DNA are recognized by Toll-like receptor 9 (TLR9), and thus initiate an innate immune response. In this study, we investigated the use of DNA-based nanotubes as carrier systems for CpG delivery and their effect on immune cells in vivo and in real time. DNA nanotubes were microinjected into skeletal muscle of anesthetized mice. Using in vivo microscopy, we observed that the DNA tubes were internalized within minutes by tissue-resident macrophages and localized in their endosomes. Only microinjection of CpG-decorated DNA nanotubes but not of plain DNA nanotubes or CpG oligonucleotides induced a significant recruitment of leukocytes into the muscle tissue as well as activation of the NF-ĸB pathway in surrounding cells. These results suggest that DNA nanotubes are promising delivery vehicles to target tissue macrophages, whereupon the immunogenic potential depends on the decoration with CpG oligonucleotides.

Bone tissue regeneration is accomplished by concerted regulation of protein-based extracellular matrix components, glycosaminoglycans (GAGs) and inductive growth factors. GAGs constitute a significant portion of the extracellular matrix and have a significant impact on regulating cellular behavior, either directly or through encapsulation and presentation of growth factors to the cells. In this study we utilized a supramolecular peptide nanofiber system that can emulate both the nanofibrous architecture of collagenous extracellular matrix and the major chemical composition found on GAGs. GAGs and collagen mimetic peptide nanofibers were designed and synthesized with sulfonate and carboxylate groups on the peptide scaffold. The GAG mimetic peptide nanofibers interact with bone morphogenetic protein-2 (BMP-2), which is a critical growth factor for osteogenic activity. The GAG mimicking ability of the peptide nanofibers and their interaction with BMP-2 promoted osteogenic activity and mineralization by osteoblastic cells. Alkaline phosphatase activity, Alizarin red staining and energy dispersive X-ray analysis spectroscopy indicated the efficacy of the peptide nanofibers in inducing mineralization. The multifunctional and bioactive microenvironment presented here provides osteoblastic cells with osteogenic stimuli similar to those observed in native bone tissue. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.