Medical application of silicone rubber and its future development (2)
◆ surface modification
Surface modification is both an effective way to improve the biocompatibility and anticoagulant properties of the material without changing the excellent properties of the polymer itself. Surface-modified silicone rubber bio-elastomer needs to meet the following requirements: 1, good biocompatibility; 2, good anticoagulant; 3, the appropriate surface hydrophilic - hydrophobic balance; 4, Heterosexual recognition ability.
Plasma surface modification methods mainly use plasma polymerization. Plasma polymerization exposes the polymer material to a polymerizable gas, and deposits a thin polymer film on the surface of the polymer material. The method can introduce functional groups such as phosphate groups and hydroxyl groups on the surface of the material to improve the interaction between the material and the biological environment. Plasma technology for the modified silicone rubber surface has a large number of reports at home and abroad. Foreign data reported that the stability of plasma-treated silicone rubber and the effect of plasma treatment on the interface blood compatibility were investigated in four different gas media. The results showed that in the four different gas medium, the surface of the treated silicone rubber have different degrees of etching, resulting in a corresponding increase in water absorption, and O2 and Ar treated silicone rubber surface blood compatibility decreased, and with The anticoagulant properties of N2 and NH3-treated silicone rubber surfaces increased.
◆ Surface grafting
Surface grafting mainly radiation (UV radiation, laser radiation, X-ray and γ-ray radiation) initiated grafting, plasma-initiated grafting and ozone-initiated grafting
Radiation grafting is the use of high-energy radiation in the polymer surface active points (free radicals or ions), and then by the active site initiated monomer graft polymerization. Radical grafting monomers are mainly hydrophilic compounds, such as N-vinyl pyrrolidone, methacrylic acid β, hydroxy ester (HEMA), acrylic acid (Acc), acrylamide (AAm) and so on. With the development of tissue engineering, the surface requirements of materials are also getting higher and higher. In order to suppress nonspecific interactions and make cells play their functions in similar extracellular matrix, people try to graft natural polymers onto the surface of polymers material. Foreign materials reported by grafting o-butyryl chitosan (OBCS) to the surface of silicone rubber, the results showed that the graft silicone rubber surface platelet adhesion was significantly reduced.
Silicone rubber surfaces treated with simple plasma can exhibit hydrophilic deterioration after being left in place for a period of time, and grafting with plasma can eliminate this phenomenon. There have been many reports on the use of plasma-initiated grafting. Monomers used in graft polymers are hydrophilic, such as HEMA, AAm, Acc, etc., as well as natural polymeric materials. Phosphocholine (MPC) is the main component of the biological cell membrane, which is fixed to the polymer surface, which can effectively improve the biocompatibility of the material.
Ozone-initiated grafting is a new surface modification technique that is easy to handle, handles complex shaped silicone rubber surfaces and costs less. It is the polymer is placed in the ozone gas, the surface of the polymer to form peroxy groups, these peroxyl groups have the ability to trigger the polymerization of vinyl monomers, through the ozone graft, the surface of the hydrophilic silicone rubber material And blood compatibility have greatly increased.
◆ surface coating
Surface coating methods are spray coating, dip coating, surface gold plating, plasma deposition and biomimetic synthesis. According to the formation of coating material can be divided into hydrophilic polymer coating, natural polymer coating, metal coating and special function coating (such as drugs, etc.). According to the function of the coating can be divided into antibacterial coating, with physiological functions of the coating and drug release coating. Antibacterial coating can inhibit the adhesion of bacteria and reduce the infection rate of the implant; while the physiologically functional coating acts as a transition layer that can adapt to the bioactive body to provide a better growth environment for the cells on the surface of the material . Domestic researchers use dip coating to form chitosan coating on the surface of silicone rubber to improve the biocompatibility and antibacterial property of silicone rubber. The unique properties of mucin coatings can be used to reduce microbial infections. MPC has been recognized as a biomimetic coating of biomaterials for more than 10 years. Such coatings contain the natural properties of MPC membranes with antithrombotic, anti-inflammatory and low somatic and bacterial adherence.
Biomimetic synthesis technology is a new synthetic method that imitates the formation of inorganic matter under the modulation of biological mineralization in the 1990s since the 1990s. Domestic researchers made the hydroxyapatite (HA) microcrystalline coating on the surface of silicone rubber through the method of bionic synthesis.
◆ body modification
The purpose of silicone rubber body modification is to give it a new surface composition or specific properties by designing its body structure. Researchers at Jinan University prepared hyaluronic acid / silicone rubber composite biomaterials by blending method, and the tear strength and tensile strength of the hyaluronic acid / silicone rubber composite biomaterials were improved compared with the unmodified silicone rubber, and the biocompatibility was good.
IPNs are one way of bringing two or more polymers together tightly, where at least one of the polymers is synthesized or crosslinked in the presence of the other polymers. The main types of IPNs are simultaneously formed, gradient, thermoplastic, emulsion and semi-interpenetrating polymer networks.
Foreign materials reported that silicon oligomers with polar end groups (such as silanols, hydroxyls, acid chlorides and the like) have surface activation, especially in practice to promote skin penetration, which is the role of silicone rubber bioelastomer Modification provides a new way to end-group functionalization.
GE's latest Tufel brand of silicone rubber is a two-component platinum vulcanizate that provides excellent resilience and low compression set for peristaltic pump tubing with significantly improved flow accuracy. Medical applications such as quantitative infusion pumps , Intestinal pumps and portable pumps, etc., to accurately transfusion and infusion for patients.
Long-acting subcutaneous implants with silicone rubber as the carrier must be removed after the expiration of the placing period, which increases the user's pain and expense. Therefore, researches on biodegradable subdermal contraceptive implants have been initiated. At present, And steroid drug permeability polymer research as a carrier of releasing progesterone to become a hot research, both at home and abroad have been developed biodegradable implants, such as the Chinese Academy of Medical Sciences Institute of Biomedical Engineering has a Biodegradable subcutaneous contraceptive implants CaproF, preliminary studies and experiments have ended, ready to enter the clinical stage.
With the development of biomedical engineering and tissue engineering, the technical and performance requirements for materials are increasing. For silicone rubber, how to make it fully used in bioengineering and tissue engineering is the main direction of future research work. Such as biosensors is a biotechnology introduced today, miniaturization of biosensors, and biological adaptability, will become an important research topic associated with artificial organs, as the main material of artificial viscera silicone rubber, the future Great potential for development.
At present, the backward development of medical silicone rubber in our country will accelerate the pace of development in the future. First, we should establish an industrialized production base for medical silicone materials. We should focus on breakthrough in medical silicone materials implanted in the human body and device performance and quality evaluation techniques. ; To promote the formation of a series of medical silicone rubber material, high-grade, large-scale, standardized management.