Plasma was first proposed by Langmuir in 1928 to describe the physical form of gases with multi-component interactions in a discharge tube. Plasma is a high-energy, high-energy ionized gas group that uses the high kinetic energy of an electric or magnetic field to eject electrons from the outer layer, converting atoms into charged ions. Plasma is often referred to as the fourth form of matter, mainly composed of electrons, positively or negatively charged ions, free radicals, electromagnetic radiation, molecules, and molecular fragments. Therefore, plasma is a mixture of energy and reactive substances coexisting, and its important characteristic is that it is in a state of charged equilibrium, that is, the total charge of the plasma is neutral. Therefore, in order to obtain the plasma state of the gas, it is necessary to transfer energy during the ionization process to obtain sufficient kinetic energy to excite ionization. The generation of plasma requires three elements, namely ionization energy, a vacuum system to maintain the plasma state, and a plasma reaction chamber. Gas source plasma generation is the process of placing gas in a vacuum plasma reactor and exciting ionized atomic and molecular cascades through low current and high voltage discharge, thereby generating non thermal plasma such as radio frequency glow discharge, corona discharge, and atmospheric arc. Due to its mature technology, significant effects, and easy operation, it has been widely applied in fields such as biology, physics, and chemistry, and has become a research hotspot in the field of medical engineering in recent years.

Application of plasma treatment technology for surface modification and modification

The poor hydrophilicity of polymer surfaces and the lack of natural recognition sites limit their application in the field of bone tissue engineering. Surface modification technology can effectively change the surface properties of materials such as roughness, morphology, charge, chemical composition, surface energy, and wettability, thereby effectively promoting the interaction between polymer and tissue. The active substances in plasma, such as free radicals, ions, excited atoms, molecules, and electromagnetic radiation, can inactivate microorganisms and viruses without damaging the material itself, and can activate the material surface without using chemical solvents or generating toxic waste, thereby increasing its biocompatibility. In addition, the modified material surface undergoes chain breakage reaction when subjected to higher energy, forming new chemical configurations and functions through covalent bonds, further promoting the interaction between the material and the host, enhancing cell adhesion and proliferation, and improving the biological activity of the material.

According to the types of plasma surface reactions, they are mainly divided into the following four categories: 1) sputtering etching effect; 2) Introduction of functional active sites; 3) Grafting and polymerization reactions of free radicals; 4) Deposition coating. The sputtering etching effect etches the material surface through physical bombardment of atoms, molecules, and excited substances. The degree of erosion mainly depends on the input power of the plasma source, reaction time, and applied voltage. The surface morphology of materials is usually changed at the nanoscale, which increases the surface area of the material, thereby affecting the biological interface reaction and enhancing biocompatibility. The introduction of functional active sites can be divided into two forms: one is to introduce active sites through free radicals using inert gases, and the other is to introduce chemical functional sites through functional groups using strong oxidizing gases and highly reactive gases. Functionalized active sites can not only change the surface hydrophilicity of materials, but also be further modified based on this. When free radicals and functional groups come into contact with monomers in liquid or gas phase, polymerization reactions are initiated, and the newly formed grafting surface provides reaction sites for chemical covalent modifications, such as chemical crosslinking, electrostatic interactions between macromolecules and biomolecules, etc. Deposition coatings are usually formed on the surface of materials using chemical vapor deposition to form a layer of nanoscale thickness coating, whose properties, thickness, strength, smoothness, and hydrophilicity all improve the biocompatibility of polymer materials.

Plasma modification treatment enhances the biocompatibility of polymer materials

There are two main ways to improve the biocompatibility of polymers through plasma treatment modification: one is to enhance the hydrophilicity of the material surface, introduce active groups, increase the surface roughness of the material, and change the surface charge through plasma modification technology; The second is to fix bioactive molecules on the basis of plasma modification, enhancing the ability of biological recognition. The interfacial free energy of materials determines their hydrophilicity/hydrophobicity, and materials with low surface energy have poor adhesion and relatively fewer cells. Research has found that biomaterials have no adhesion properties when their surface energy is between 20 and 30mJ/m2, but exhibit good adhesion characteristics when it is between 40 and 70mJ/m2. Plasma introduces carboxyl (- COOH), peroxide (- O-O -), hydroxyl (- OH), amino (- NH3) groups and polar substances on the surface of polymers, causing polar groups to rearrange and non-polar groups to migrate on the surface, increasing material surface energy, promoting contact reactions between body fluids and blood, and cell adhesion and fixation. Polymer materials are etched by plasma to form rough surfaces resembling grooves at the micrometer to nanometer level. After cell contact, they diffuse, arrange, and migrate along the rough surface. This phenomenon is called "contact guidance effect", which means that cell integrin receptors transfer changes in tension or pressure to the cytoskeleton based on the different surface morphologies they come into contact with. After the cell tension receptors undergo changes in force, they activate and restructure the cytoskeleton, causing a series of biological effects. At the same time, the structural damage to the surface area of the material leads to changes in surface free energy, which synergistically affects cell adhesion and migration. The impact of different rough surfaces on cells also depends on the cell type, material composition, and the interaction between the two. Research has confirmed that surface grooves (depth 0.5-1 μ m, width 1-10 μ m) can effectively enhance alkaline phosphatase activity in rat bone marrow cells and accelerate extracellular matrix mineralization. In addition, plasma treatment can generate widely distributed anions, cations, functional groups, free radicals, etc. on the surface of the material. Cations promote protein adhesion through electrostatic interactions, while anions bind with calcium ions to promote extracellular matrix mineralization.