Free space nanoprinting beyond optical limitations can create 4D functional structures

Two photon polymerization is a potential method for nanofabrication of integrated nanomaterials based on femtosecond laser technology. The challenges faced in the field of 3D nanoprinting include slow layer by layer printing speed and limited material selection due to laser material interactions.

In a new report in Progress in Science, Chenqi Yi and a team of scientists in the fields of technical science, medicine, and industrial engineering at Wuhan University in China and Purdue University in the United States presented a new 3D nanoprinting method called free space nanoprinting, which uses optical force brushes.

This concept enables them to develop precise spatial writing paths beyond optical limitations to form 4D functional structures. This method promotes the rapid aggregation and solidification of free radicals, thereby promoting polymerization while increasing sensitivity to laser energy, providing high-precision, free space painting, just like Chinese ink painting on paper.

Using this method, they improved the printing speed and successfully printed various biomimetic muscle models derived from 4D nanostructures. These models have adjustable mechanical properties, can respond to electrical signals, and have excellent biocompatibility.

Device Engineering
Nanodevices and nanostructures can be designed with high resolution and speed to form the next generation of products. The semiconductor industry can use photolithography, deposition, and etching to create 3D structures from various materials, although high processing costs and limited material selection may affect the flexible manufacturing of functional material 3D structures.

Materials scientists use femtosecond laser direct writing technology based on two-photon polymerization to form photonic quasicrystals, metamaterials, and nanostructures using micro/nano polymers, thereby creating complex 3D nanostructures.

However, this method is still limited by slow printing speed, stepped surface texture, and limited photocurable materials. In this work, Yi et al. We studied free space laser writing to analyze how it generates photochemical forces to complete nano painting based on optical force brushes.

Using femtosecond lasers for free space painting
When the time scale reaches femtosecond, molecules can absorb photons and excite electrons to higher states on surfaces with repulsive potential energy, thereby generating free radicals.

Scientists can use the multiphoton absorption mechanism to absorb the energy of ultrashort pulse photons in molecules and activate the transition of electrons between the ground and excited states. Yi and colleagues irradiated active free radicals with femtosecond lasers, using optical force to quickly aggregate and combine them into large molecules. Curing can be quickly completed without post-processing, while minimizing the thermal movement of solvent molecules.

Researchers have developed a hydrogel based ink as an optical switch activated during femtosecond laser writing through two-photon absorption, in which the free radicals in the gel absorb the photon energy from the femtosecond laser. When free radicals form binding energy in molecules, the research team connects long chain molecules to different functional groups to achieve various applications.

Printable hydrogel inks provide highly biocompatible, flexible and flexible conditions for various applications of free space printable nanostructures in biomedicine.

Mechanism of action
The laser beam moves freely in solution, just like a pen in space, involving three steps: activation, aggregation, and solidification of free radicals. Scientists used a multi physical field model to cultivate the aggregation rates of two photons and a light brush, respectively.

This method greatly improves the efficiency of writing structures through layer by layer and line by line printing methods, where the number of layers is directly related to the thickness resolution. This method also greatly improves the writing efficiency and accuracy of 3D nanostructures. They improved the experimental results to demonstrate how the optical force applied to free radicals is directly related to the number of pulses, laser field intensity, and absorption coefficient.

When a femtosecond laser irradiates a material, the kinetic energy of photons exchanges with active free radicals, which move through the force of light, ultimately forming clear and high-resolution 3D nanoprinting. The team investigated the basic mechanisms behind these processes through numerical simulations of multiple physical fields to examine the movement and recombination processes of free radicals.

Designing Nested Muscle Systems
This method enables Yi and colleagues to print muscle, abdominal, and tendon tissues composed of multiple nested fibers and bundles, which are difficult to print using traditional 3D printing methods. The team printed the inner and outer shapes of the muscles, while using functional hydrogel inks to activate their movements through electrical stimulation. This led to the initial example of achieving both structural and functional biomimetic nanoprinting simultaneously.

Scientists demonstrated the structure of rat hamstring tendons and abdomen printed using a light brush and layer by layer printing method. These methods demonstrate the potential of printing multi-layer structures in 3D space, while muscle fiber thickness changes from thin to thick to endow various functions.

Researchers have demonstrated the possibility of fully implanting micro and nanostructures into organisms to achieve functional and structural biological structures of this scale. This free space printing method using optical force brush technology provides the possibility of applying multifunctional micrometers and nanostructures in biology.

appearance
In this way, Chenqi Yi and colleagues used optical force brushes as a method of integrating femtosecond laser brushes to print functional structures with true 3D degrees of freedom. The light brush has unique functions, and its bottom layer adopts the light nano painting process, which can achieve ultra-high curing rate, low curing threshold, and high sensitivity to laser, thereby accurately adjusting the printing process. Sensitivity enables them to accurately adjust and create complex structures with fine details.

This brings true 3D printing freedom, allowing for continuous printing and seamless transitions between different planes. This work further explores the optical mechanism of free space nanoprinting during the use of optical brushes. This includes the interaction between femtosecond laser and free radicals in the hydrogel ink optical switch; A mechanism was also explored through numerical simulation.

This study emphasizes the ability of optical force brushes to develop biomimetic functional structures and paves the way for further research in tissue engineering and regenerative medicine with breakthrough characteristics.

Source: Laser Network