Self-assembly refers to a technology in which basic structural units (such as molecules, nanomaterials, micrometers, etc.) or larger-scale substances spontaneously form ordered structures. Contact printing is a printing technology that uses pressure as the basis and uses the printing plate or other methods to transfer the graphic information on the original to the substrate. It uses printing ink or coloring pigments to reproduce images and text on the surface of paper or other materials with the help of printing machinery and equipment. There is a very close relationship between self-assembly and contact printing. The ordered structure formed by self-assembly technology can be widely used in contact printing. Self-assembled monomolecular membranes are long-chain organic molecules that spontaneously react to form oriented, tightly arranged two-dimensional ordered monomolecular membranes connected by chemical bonds on the substrate surface. Self-assembled monolayers are an important part of contact printing. Through contact printing technology (CP) to form a self-assembled monomolecular film (SAM) pattern, the chemical properties of the substrate at the pattern can be changed. The pattern can also be used as a mask in etching and many other uses.

Figure 1. Gold nanoparticles (GNPs) modified with amphiphilic block copolymers (BCPs) assembly to form spherical vesicles

Applications:

The initial research on self-assembled monomolecular membranes (SAM) focused on the self-assembly system of organosilane adsorbed on the surface of silicon and silicon dioxide. With further exploration, many other self-assembling systems have been established. Among them, the best properties are the SAMs formed by alkyl mercaptans on gold substrates. The development and research of various self-assembly systems make contact printing play an important application value in more and more fields.

• Liquid crystal alignment film: The liquid crystal alignment film is bonded to the surface of the substrate, and directly contacts the liquid crystal during contact printing. The thin film generates van der Waals force, attraction between dipoles, hydrogen bond and other physical and chemical interaction forces with the liquid crystal molecules, so that the liquid crystal molecules can be regularly aligned in a certain direction. Using polydimethylsiloxane (PDMS) as the raw material, the micro-contact printing method with a relatively simple process is used to first prepare a micrometer-scale groove-shaped film on a glass substrate, and then assemble Cu²⁺ on the film to prepare a liquid crystal alignment film. The liquid crystal alignment film can prepare a liquid crystal type chemical sensor. This sensor utilizes changes in the orientation of the liquid crystal molecules on the surface of the sensitive film before and after detecting the target compound, thereby changing the ability of the liquid crystal to refract light, resulting in changes in the color and brightness of the sensor, and finally to detect biological molecules and harmful chemicals.
• Self-assembling peptide nanoparticles: Taking peptide as the basic structural unit, nano-tissue engineering framework materials obtained by self-assembly of nanopeptide molecules have become a new research hotspot in the field of tissue engineering. This type of nano-multi-skin biomaterial has good biocompatibility and degradability, whose most prominent advantage is its biological activity. With the rise and rapid development of 3D printing technology, 3D printing has been widely used in the medical fields to for precise and personalized medicine. Ad-MSCs loaded with self-assembled multi-nano solutions are used as "biological ink", and 3D bioprinting technology can be used to print out three-dimensional structures, such as bones, blood vessels, and artificial livers.

Figure 2. Self-assembled peptide nanoparticles form organs through 3D printing

References:

1. Draw horn R A. (1995). "Anchoring of nematic liquid crystals o n self-assembled monolay ers fo rmed from alkanethiols on semitransparent films of gold." J Phy s Chem 99(45), 16511 -16515.
2. Chen Y. (2000). "Microcontact printing and pattem transfer with a tri-layer processing." Microelectron Eng 53, 253-256.
3. PARK C S. (2001), "Thiol-Based Self -Assembled Monolayers: Formation Or ganization." Encyclopedia of Materials: Science and Technology 12, 9332-9344.