Hydrogels are common materials, like soft contact lenses and gelatin desserts, that absorb large amounts of water to form a gel. Scientists have developed a specialized type that uses deoxyribonucleic acid (DNA) as its primary structural component. In these materials, DNA is not used for its genetic code. Instead, DNA hydrogels are three-dimensional networks of cross-linked DNA strands that swell in water, combining a hydrogel’s framework with DNA’s unique properties.
The Building Blocks and Assembly
The construction of a DNA hydrogel is guided by Watson-Crick base pairing, where adenine (A) binds with thymine (T), and guanine (G) pairs with cytosine (C). This predictable pairing acts as a molecular glue, allowing scientists to direct how DNA strands connect with high precision.
To create these structures, researchers synthesize short, single strands of DNA with specific, complementary sequences. When mixed in a solution, these engineered strands spontaneously connect at their complementary sites. This self-assembly process results in a complex, three-dimensional mesh.
This DNA network forms the hydrogel’s backbone, trapping water molecules to form the gel. The structure is held together by the hydrogen bonds between the paired bases, creating a stable material from precisely designed components.
Programmable and Responsive Properties
Using DNA as a foundation makes these hydrogels highly programmable. By designing the DNA sequences, scientists can dictate the gel’s physical properties, including its stiffness, density, and pore size. This customization is possible due to the predictable nature of DNA base pairing.
These materials are also responsive to their environment. DNA hydrogels can be engineered to change in response to external triggers, such as temperature or pH. For instance, a hydrogel can be designed to transition from a solid gel to a liquid when the temperature is altered.
This responsiveness can be tailored for specific triggers by incorporating DNA sequences that act as sensors. When a target molecule like viral DNA or a protein binds to these sensor sequences, it can trigger a structural change. The hydrogel might swell, shrink, or dissolve, providing a clear signal that the target is present.
Applications in Biomedicine
DNA hydrogels have several biomedical uses, including targeted drug delivery. The hydrogel can act as a microscopic container, encapsulating drugs within its porous network. These hydrogels can be designed to release their cargo only when they encounter specific biological cues, like the proteins on a cancer cell, delivering medication directly to the intended site.
In tissue engineering, DNA hydrogels function as scaffolds that support cell growth. Their structure can be customized to mimic the natural matrix that surrounds cells, providing an environment for cellular attachment. For example, hydrogels have been developed to promote bone regeneration. The scaffold biodegrades over time, leaving behind new tissue.
These materials also show promise in wound care. A DNA hydrogel can be applied as a protective dressing that maintains a moist environment for healing. The hydrogel can also be loaded with growth factors or other therapeutic agents, which can be released in a sustained manner to accelerate natural repair processes.
Use as Diagnostic Biosensors
Separate from their therapeutic roles, DNA hydrogels are developed as diagnostic tools to detect and signal the presence of specific molecules. A hydrogel can be engineered with DNA sequences complementary to the genetic material of a pathogen, like a virus or bacterium.
When a sample containing the pathogen is introduced, its DNA binds to the complementary strands in the hydrogel. This binding event can trigger an easily observable change, such as the hydrogel dissolving, changing color, or fluorescing. This provides a clear indication that the target molecule has been detected.
This approach allows for simple and portable diagnostic tests, such as a small patch that changes color when it contacts a disease biomarker in saliva or blood. This “detect and report” mechanism leverages the specificity of DNA interactions to create fast and accurate sensors for many purposes.