# 3D DNA Nanostructures: The Nanoscale Architect
## 5 Applications
### Challenges & Future Perspectives  
The economics of DNA nanostructures is unfavorable as long as it is a strategy that depends on the custom synthesis of hundreds of distinct oligonucleotides. It is unlikely that structural DNA nanotechnology will ever be decoupled from the cost of oligonucleotide synthesis. There are enzymatic and bacteriophage toolkits [179; 180] that may lower costs, but this trend is counteracted by the ambition of continuing to pursue larger and more complex DNA nanostructures. However, as argued by [PERSON] and [PERSON] [181], this may not be prohibitive at all. Instead, the challenges facing widespread adoption of DNA nanomachines are technical, regulatory, and ethical. No other biomaterial thus far discovered has such ubiquitous functionality as DNA, and as such, it is doubtful that it would not have some role in designing future therapeutics to be safe, smart, and multifunctional. DNA is unlikely to provoke concerning immunological effects, or there will be sufficient techniques to ensure that [35; 83], but for the time being, there is insufficient evidence to guarantee that inclination beyond all doubt, and DNA nanostructures are likely still far away from even entering any clinical trials. Positive progress is still ongoing in regards to the size, complexity, synthesis, and design strategies for 3D DNA nanostructures. There is wide support, interest, and efforts in addressing their stability across a broad range of environments and increasing their list of compatibilities with chemical or biomolecule targets. However, more practical usage may beckon that the responsivity of operating DNA nanomachines is improved. DNA nanodevices lack reliable and rapid methods of signal transduction and real-time communication into and out of nanomechanical DNA systems, even the fastest still on the timescale of minutes or hours; this in part due to the intrinsic limits of reaction speeds or challenges with measuring DNA nanodevices with high resolution via fluorescence due to the scale of DNA nanodevices falling under diffraction limits. Further examples of the application of physical forces by DNA nanomachines are a pressing and interesting new research direction. While there are demonstrations of the enforcement of rigid shape [92; 129], measurements of physical forces [175; 178], transport of molecules by DNA nanodevices [182], examples of dynamic nanomechanical DNA devices applying physical forces have only recently appeared [177]. There are still yet many possible architectures for applying piconewton forces to explore [61; 183]. On the scale of microrobots, the capability to self-propel and autonomously navigate fluidic environments has been a phenomenal development, but there does not seem to be a path of development there for DNA nanomachines, which may always require a nanotrack. There are recent demonstrations of DNA walkers operating in vivo which indicates a hopeful trend [184]. Design of DNA nanostructures and their functions have also proceeded in a vacuum, where scientists have attempted to accomplish almost everything with only DNA. It will be interesting to see the progress of future devices that are interdependently integrated with natural mechanisms, such as the diffusion of membrane proteins upon a cell membrane [185], borrowing the function of natural motors like kinesin and driving nanomechanical motion with ATP rather than DNA springs [186], or relying on or reinforcing other structures, such as viral capsids or liposomes, while providing functionality that DNA is advantaged in like computing or actuation. Some of these directions are naturally limited by DNA as a material, that while they can be accomplished may not surpass competing technologies, as properties such as bond strength and reaction rate are built into the material such that to change them would mean to change the chemical makeup of the material itself.