Types of silicone rubber for human medical use

There are 4 types of silicone rubber.

Solid type: There are two kinds of soft and hard, the color is milky white, opaque, hard like bone, soft is medium hardness, elastic, easy to process and plastic.

Foam type (sponge type): It is sponge-like with fine pores, soft, white or light yellow in color, with great elasticity and stretchability.

Film type: It is a transparent or translucent film, light yellow or milky white in color, with high elasticity.

Liquid type: Also known as silicone oil, it is a viscous liquid, yellowish in color or white latex.

Surface modification

Surface modification is an effective way to improve the biocompatibility and anticoagulant properties of the material without changing the excellent properties of the polymer itself. The surface-modified silicone rubber elastomer needs to meet the following requirements:

1. Good biocompatibility;
2. Good anticoagulant properties;
3. Appropriate surface hydrophilic-hydrophobic balance;
4. Strong ability to eliminate non-specific recognition.

The plasma surface modification method mainly adopts plasma polymerization. Plasma polymerization is to expose the polymer material to a polymerizable gas and deposits a thin polymer film on the surface of the polymer material. This method can introduce functional groups such as the phosphoric acid group and hydroxyl group on the surface of the material to improve the interaction between the material and the biological environment.

There have been numerous reports on the use of plasma technology to modify the surface of silicone rubber. The related data reported that the stability of plasma-treated silicone rubber and the effect of plasma treatment on interfacial hemocompatibility were studied in four different gaseous media. It was found that in 4 different gaseous media, the treated silicone rubber surface was etched to different degrees, resulting in a corresponding increase in water absorption, and the blood compatibility of the silicone rubber surface treated with O2 and Ar decreased, while the anticoagulant properties of the silicone rubber surface treated with N2 and NH3 were improved.

Surface grafting

Surface grafting mainly includes radiation (ultraviolet radiation, laser radiation, X-ray and γ-ray radiation) induced grafting, plasma-induced grafting and ozone-induced grafting.

Radiation grafting is the use of high-energy radiation to generate active sites (free radicals or ions) on the polymer surface, and then the active sites initiate the graft polymerization of monomers. The monomers used in radiation grafting are mainly hydrophilic compounds, such as N-vinylpyrrolidone, β-methacrylate, hydroxy ester (HEMA), acrylic acid (Acc), acrylamide (AAm), and so on.

With the development of tissue engineering, the requirements for the surface of materials are getting higher and higher. In order to inhibit non-specific interactions and enable cells to perform their functions in an extracellular matrix similar to in vivo, people try to graft natural polymers on the surface of polymers. Material. It has been reported that o-butyryl chitosan (OBCS) was grafted onto the surface of silicone rubber by radiation grafting, and it was found that the amount of platelet adhesion on the surface of the grafted silicone rubber was significantly reduced.

The hydrophilicity of the silicone rubber surface treated with simple plasma will deteriorate after a period of time, and this phenomenon can be avoided by plasma-induced grafting. There have been many reports on the use of plasma-induced grafting. The monomers used in the graft polymer include hydrophilic substances, such as HEMA, AAm, Acc, etc., as well as natural macromolecular substances. Phosphocholine (MPC) is the main component of biological cell membranes, and fixing it to the polymer surface can effectively improve the biocompatibility of materials.

Ozone-initiated grafting is a new surface modification technology, which is easy to operate, can handle complex-shaped silicone rubber surfaces, and has low cost. It is to place the polymer in ozone gas to form peroxy groups on the surface of the polymer. These peroxy groups have the ability to initiate the polymerization of vinyl monomers. After grafting with ozone, the hydrophilicity of the surface of the medical silicone rubber material And blood compatibility has been greatly improved.

Surface coating

Surface coating methods mainly include spray coating, dip coating, surface gold plating, plasma deposition and biomimetic synthesis. According to the substance that forms the coating, it can be divided into hydrophilic polymer coating, natural polymer coating, metal coating, and coating with special functions (such as drugs, etc.). According to the function of the coating, it can be divided into the antibacterial coating, coating with physiological function and drug release coating.

The antibacterial coating can inhibit the adhesion of bacteria and reduce the infection rate of the implant; while the coating with physiological function acts as a transition layer that can adapt to the bioactive body, providing a better growth environment for the cells on the surface of the material. Domestic researchers used the dip coating method to form a chitosan coating on the surface of silicone rubber, which improved the biocompatibility and antibacterial properties of silicone rubber.

The unique properties of mucin coatings can be used to reduce microbial infections. MPC has been recognized as a biomimetic coating for biomaterials for more than 10 years. This type of coating film contains the natural properties of MPC cell membranes, such as antithrombotic, anti-inflammatory and low somatic and bacterial adhesion.

Biomimetic synthesis technology is a new synthesis method that has appeared since the 1990s to simulate the formation of inorganic substances under the modulation of organic substances in biomineralization. Hydroxyapatite (HA) microcrystalline coating was prepared on the surface of silicone rubber by biomimetic synthesis.

Ontology modification

The purpose of bulk modification of silicone rubber is to give it new surface composition or specific properties by designing its bulk structure. Researchers from Jinan University prepared a hyaluronic acid/silicone rubber composite biomaterial by a blending method, which has improved tear strength and tensile strength compared with unmodified silicone rubber and has good biocompatibility.

IPNs are a way of bringing together two or more polymers, at least one of which is synthesized or cross-linked in the presence of other polymers. The main types of IPNs are co-forming, gradient, thermoplastic, emulsion, and semi-interpenetrating polymer networks.

Silicon oligomers with polar end groups (such as silicon hydroxyl groups, hydroxyl groups, acid chloride groups, etc.) have surface activation effects, especially in practice, they have the effect of promoting skin penetration, which provides the modification of silicone rubber elastomers. A new method has been developed, namely end group functionalization.

For more information on medical silicone manufacturing, please contact Newtop’s engineers, we provide free consulting services and first-class silicone custom manufacturing services.