Writing with Fluid: Structuring Hydrogels with Micrometer Precision by AFM in Combination with Nanofluidics

Area of Science:

• Biomaterials Science
• Nanotechnology
• Surface Chemistry

Background:

• Hydrogels are crucial for biomedical applications like surface modification and tissue engineering.
• Structuring soft hydrogels post-formation remains a significant challenge.
• Existing additive patterning techniques have limitations in resolution and material compatibility.

Purpose of the Study:

• To develop a novel subtractive method for precise hydrogel patterning.
• To demonstrate the applicability of atomic force microscopy (AFM) combined with nanofluidics (FluidFM) for hydrogel structuring.
• To investigate the parameters influencing the resolution and effectiveness of this chemical writing process.

Main Methods:

• Utilizing a hollow AFM-cantilever connected to a nanofluidic controller for precise liquid ejection.
• Applying controlled alkaline solution ejection to selectively dissolve supramolecular hydrogel films (e.g., 1,3,5-benzene tricarboxamides - BTAs).
• Employing AFM force control to prevent mechanical damage to the delicate hydrogel structures.

Main Results:

• Achieved precise structuring of hydrogel films through a subtractive "chemical writing" process.
• Demonstrated that achievable precision is mainly limited by diffusion rates and aperture dimensions.
• Validated the influence of applied pressure and ejection time on the patterning process.
• Showcased the potential for selective loading of patterned hydrogels with active substances or nanoparticles.

Conclusions:

• The presented AFM-nanofluidic approach provides a high-resolution subtractive method for patterning various reversible hydrogels.
• This technique overcomes limitations of existing additive methods and enables precise control over hydrogel structures.
• The developed chemical writing process opens new avenues for advanced hydrogel-based devices and functional materials.