DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers
October 25th, 2017
Semiflexible polymers display unique mechanical properties that are extensively applied by living systems. However, systematic studies on biopolymers are limited since properties such as polymer rigidity are inaccessible. This manuscript describes how this limitation is circumvented by programmable DNA nanotubes, enabling experimental studies on the impact of filament rigidity.
The overall goal of this new DNA-based model system is to understand the fundamental properties of a class of semiflexible polymers, which also describes the behavior of a vital class of biopolymers. This new method allows us to study key questions in the field of soft metaphysics, specifically, it allows to explore the behavior of semiflexible filaments and their arrangements into networks. The main advantage of this technique is that the mechanical properties of intravisive filaments are experimentally accessible and can be precisely tuned.
Semiflexible polymers are defined by the special properties of the filaments which were previously only treated in the theoretical framework due to the lack of a tunable experimental systems. Though this method provides insight into the defining quantity of semiflexible polymers, it can also be applied as a new hydrogel to study cell migration in matrices of different stiffness's without changing the under laying mesh size. The smallest repetitive unit in the nanotube can be thought of as a unit ring.
Several of these unit rings stack during hybridization. This leads to the formation of elongated nanotube's. To begin, re-suspend lyophilized oligonucleotides in purified water and follow the further re-suspension steps given in the corresponding manual from the company.
Adjust the amount of water to obtain a final concentration of 200 micromolar. Determine the concentration's of the single DNA strands to verify the values given by the distributor since the exact stoichiometry is crucial for the assembly process. Using a micropipette, mix the DNA strands each of the same concentration in a container suitable for the thermocycler to form the desired DNA and helix tubes.
Hybridize the DNA and helix tubes in a thermocycler using the parameters found in the text protocol. Store the hybridized DNA and helix tubes for up to 3 weeks at 4 degrees celsius without detectable degradation. Before performing rheology, carefully dilute the sample to the desired final concentration using the sample buffer if necessary.
Choose an appropriate geometry for the dynamic shear rheometer. Then, load the sample on the rheometer. To prevent potential evaporation effects, passivate the air water interface of the sample and environment through 1 of 3 techniques.
Either surround the sample with 2.5 milliliters of the sample buffer bath. Or, add a surfactant just below the micelle concentration to the sample. Alternatively, use the hamilton syringe to surround the sample with lipid to avoid direct contact of the sample with air.
Seal the sample chamber using a cap equipped with wet sponges. And, if possible use an additional water bath to further suppress evaporation. Start the measurement using the rheometer specific software at room temperature allowing the sample to equilibrate for 2 hours at room temperature.
The equilibration time is crucial to allow the thermoflect system to a complete isotropic randomized state since this is the only confirmation allowing comparison between the different measurements. Following measurement, process the data as described in the text protocol. Prepare 8 aliquots of 12 microliters for each sample using 1 to 4 micromolar DNA per strand, 12.5 millimolar magnesium chloride, and 1x nucleic acid gel stain.
Also, make a negative control with no DNA, but include the nucleic acid gel stain. Transfer the aliquots to a real time PCR plate and seal with adhesive film. Centrifuge the plate at 100 times G for 1 minute at room temperature to remove the gas bubbles.
It's critical to remove the gas bubbles because it can expand during measurements and the samples cannot be analyzed. Following centrifugation, load the sealed plate into a real time quantitative PCR system. Program an annealing program to denature the DNA at ninety degree celsius for 10 minutes and drop the temperature quickly to seventy two degrees celsius.
Then the temperature should decrease slowly by 0.5 degrees celsius every thirty minutes. After the signal has decayed, accelerate the temperature ramp. Make sure that the lid of the cycler heats to at least one hundred degrees celsius to prevent the condensation of evaporated sample on the adhesive film.
During the assembly, excite the samples with an argon ion laser at four hundred eighty eight nanometers and detect the fluorescence at five hundred fifty nanometers when using a CY3 dye. For other dyes, choose an appropriate excitation emission combination. Measure the fluorescence signal as often as possible to increase the overall signal quality using the built in camera.
Representative raw data of a rheological measurement are shown revealing the elasticity of the network. Shown here is the time sweep during equilibration time. This plot reveals the strain dependent behavior of the network.
In this plot, the frequency dependent behavior of the network is evident. At this point the values at a specific frequency are chosen. The values for the specific DNA helix tube population were plotted against the concentration.
This process was repeated for all the DNA and helix tubes. The slope was then extracted in a log logged plot yielding the power law exponent. Finally, the values were replotted against the persistent length for each measured concentration.
These graphs allow extraction of the scaling of the elastic plateau modulus with respect to the concentration and persistence length. After development, this technique paved the way for researchers in the field of soft matter and polymer physics to explore the effect of the filament stiffness for the class semiflexible polymers. Following this procedure, additional effects such as the recitation of the entangled networks, crossing networks in general, and structure formation process can be addressed.
After watching this video you should have a good understanding on how to hybridize DNA nanotubes and how to measure the rheological properties of their networks.
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Overview
This study introduces a DNA-based model system to investigate semiflexible polymers, which are crucial for understanding biopolymer behavior. The method allows for experimental access to the mechanical properties of these polymers, enabling insights into their rigidity and network arrangements.
Key Study Components
Area of Science
- Biopolymers
- Soft matter physics
- Mechanical properties of polymers
Background
- Semiflexible polymers have unique mechanical properties.
- Previous studies on these polymers were largely theoretical.
- Understanding their rigidity is essential for various biological applications.
- Programmable DNA nanotubes provide a new experimental approach.
Purpose of Study
- To explore the behavior of semiflexible filaments.
- To investigate their arrangements into networks.
- To provide a tunable experimental system for studying mechanical properties.
Methods Used
- Development of programmable DNA nanotubes.
- Experimental tuning of filament rigidity.
- Application of the system to study cell migration in hydrogels.
- Analysis of mechanical properties in relation to network formation.
Main Results
- The DNA nanotubes allow precise control over filament rigidity.
- Insights into the mechanical properties of semiflexible polymers were gained.
- The method can be applied to study cell behavior in varying stiffness matrices.
- Experimental results support theoretical predictions about polymer behavior.
Conclusions
- This study provides a new framework for understanding semiflexible polymers.
- Programmable DNA nanotubes are a valuable tool for experimental biology.
- Future research can leverage this method for broader applications in biophysics.
Frequently Asked Questions
Executive Industry Relevance
Programmable DNA nanotubes provide a tunable experimental system to study semiflexible polymers, addressing a key limitation in modeling biopolymer mechanics. This enables mechanistic de-risking in target validation by linking filament stiffness to network behavior relevant to cellular environments. The approach supports predictive confidence in preclinical models of extracellular matrix interactions and hydrogel-based drug delivery systems.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Scientific Value: Enables interrogation of how persistence length influences filament mechanics and network formation.
- Operational Value: Provides a stable, tunable system over weeks, reducing variability in early-stage hypothesis testing.
- Scientific Value: Supports functional target validation by modeling semiflexible biopolymers like actin in a controllable format.
Screening & Assay Development
- Scientific Value: Generates quantifiable rheological outputs (elastic plateau modulus) correlated with persistence length and concentration.
- Operational Value: Enables standardized preparation of micron-length filaments with reproducible polymerization kinetics.
- Scientific Value: Facilitates assay development for screening compounds that alter semiflexible polymer network mechanics.
Translational & Preclinical Research
- Scientific Value: Models extracellular matrix mechanics to study cell migration in stiffness-tunable hydrogels without altering mesh size.
- Operational Value: Allows long-term storage (up to 3 weeks at 4°C) without degradation, supporting multi-day preclinical assays.
- Scientific Value: Bridges single-molecule persistence length measurements to bulk network mechanics for translational continuity.
Pipeline & Workflow Integration
The method fits within the discovery continuum from target validation through preclinical evaluation by providing a tunable platform to assess how filament stiffness influences biological outcomes in matrix-dependent assays.
- Discovery Biology: Supports hypothesis testing on semiflexible polymer behavior through precise experimental tuning of rigidity.
- Screening: Delivers quantitative, reproducible rheological readouts enabling reliable compound screening in hydrogel matrices.
- Analytics: Yields power law exponents and scaling relationships between elastic modulus, concentration, and persistence length for data-driven comparisons.
- Translational Research: Connects molecular-scale stiffness to network-level mechanics relevant to tissue engineering and cell migration studies.
- Enterprise Reuse: Establishes a reusable platform for studying semiflexible polymer mechanics across multiple projects in biophysics and biomaterials.
Operational & Enterprise Impact
- Scientific Value: Reduces mechanistic ambiguity in semiflexible polymer studies by providing a tunable, stable model system.
- Operational Value: Ensures reproducibility through standardized hybridization, dilution, and rheometry protocols.
- Strategic Value: Improves go/no-go decisions in biomaterial design by predicting network mechanics from molecular design parameters.
- Portfolio Impact: Enables risk-adjusted advancement of hydrogel formulations based on validated structure-property relationships.
Implementation Considerations
- Requires expertise in DNA hybridization, rheometry, and fluorescence-based quantification.
- Needs access to thermocycler, dynamic shear rheometer, and real-time PCR system for assembly and validation.
- Demands standardization of oligonucleotide concentrations and magnesium chloride conditions across teams.
- Involves adaptation considerations when translating nanotube mechanics to natural biopolymer or hydrogel systems.
- Includes practical limitations such as the need to prevent evaporation during rheometry and remove gas bubbles prior to qPCR analysis.
