Medical applications, polysiloxanes

Polysiloxanes are used in the form of elastomers, liquids, and foams for medical applications. Polysiloxanes are hemocompatible, exhibit high long-term resistance to hydrolytic and enzymatic degradation, and are autoclaveable [1008]. 

Processing requirements for thermoset composites, with specific examples of silicones, were recently reported.514 Composites based on the low molecular weight polysiloxanes for medical applications have been reviewed (in Russian).515 Silicone rubber/hydrogel composites have been evaluated for medical applications.516... 

Research of biologically active silicone materials continues. The synthesis and characterization of polysiloxanes having bioactive pendant groups,556 557 and the preparation of bioactive porous organic-inorganic hybrids for medical applications,558 have been reported. 

The same authors developed a process of encapsulation of polymers swelled by halogenated solvents in which ozone is greatly soluble but not monomers to be grafted. After ozonization of polymers swelled in solvents, mixtures of mono unsaturated or di unsaturated monomers are added to the activated polymers. Then, grafting is operated by UV irradiation. Grafting is mainly located at the surface of the starting polymer what prevents the modification of its intrinsic properties. This process permits to produce hydrophilic polysiloxanes used in medical applications (contact lenses, tubes, catheters, etc.). 

Applications. Medical Applications. The medical applications of si-loxane polymers are numerous (7, 8, 36). For example, prostheses, artificial organs, facial reconstruction, and catheters take advantage of the inertness, stability, and pliability of the polysiloxanes. Artificial skin, contact lenses, and drug delivery systems take advantage of the high permeability of these polymers, as well. 

The polysiloxane sequence can be shorter or longer, the compounds with about 20% carborane being typicaly used. Polycarborane siloxanes have high resistance to heating and are used for various purposes, including stationary phases for gas chromatography [2] and in medical applications. 

Substitute for Conventional Vulcanized Rubbers, For this application, the products are processed by techniques and equipment developed for conventional thermoplastics, ie, injection molding, extrusion, etc. The S—B—S and S—EB—S polymers are preferred (small amounts of S—EP—S are also used). To obtain a satisfactory balance of properties, they must be compounded with oils, fillers, or other polymers compounding reduces costs. Compounding ingredients and their effects on properties are given in Table 8. Oils with high aromatic content should be avoided because they plasticize the polystyrene domains. Polystyrene is often used as an ingredient in S—B—S-based compounds it makes the products harder and improves their processibility. In S—EB—S-based compounds, crystalline polyolefins such as polypropylene and polyethylene are preferred. Some work has been reported on blends of liquid polysiloxanes with S—EB—S block copolymers. The products are primarily intended for medical and pharmaceutical-type applications and hardnesses as low as 5 on the Shore A scale have been reported (53). 

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