The Preparation and Performance of Silicone Rubber/hydroxyapatite Composite Materials

Abstract: Hydroxyapatite and silicone rubber are commonly and widely used in clinical filled Materials. Hydroxyapatite is an important apatite-type material among organic non-metallic ones. It has long been associated with excellent biocompatibility, non-toxic, non-irritating rejection and combines with bone tissue, which make it popular in many fields. Medicinal silicone rubber is dimethylsiloxane, which has the resistance to aging, both high temperature and low temperature. Medicinal applied silicone rubber has non-toxic, tasteless, non-carcinogenic, stable physical and chemical properties. There are characteristics of high transparency, physiological inertia, and non-adhesion to human tissues and blood, good biological adaptation, and easy-molded shape, so it is a good implantation which is convenient to shaping, disinfection and preservation. Hydroxyapatite and silicone rubber also have some shortcomings. First, hydroxyapatite is prone to brittle fracture and fatigue damage even though hydroxyapatite has a high intensity of pressure. Hydroxyapatite particles are too loose to shape, and it is very inconvenient to operate. Moreover, the characteristic of hydroxyapatite particles cause the loss of implanted materials. These shortcomings limit its applications in bone repair or bone substitute under load. Second, silicone rubber is hydrophobic and has low osteogenic activity, and patients have the feeling of foreign body after implantation. Silicone rubber is an inert material, and it is poorly combined with organization. Silicone rubber is prone to form a integumentum, and the contracture will occur under certain condition, and there is inflammatory cell infiltration in the integumentum.Silicone rubber was mixed with the hydroxyapatite in order to obtain the composite materials with excellent mechanical properties and biological properties. The properties of the composite materials, which were made in different proportion, were evaluated in this paper. The composite materials were new organizational fillers which held the advantages of silicone rubber and hydroxyapatite. The composite materials were supposed to be used as the framework and prosthetic material of the organization with good biocompatibility.In this paper, hydroxyapatite was prepared by precipitation method using calcium nitrate tetrahydrate and diammonium hydrogen phosphate, and it was treated with the octamethylcyclotetrasiloxane. The effects of different methods of octamethylcyclotetrasiloxane treatment on the morphology of hydroxyapatite particles and the physical and mechanical properties of the silicone rubber-hydroxyapatite composite materials were studied. The results showed that the treatment temperature is about 200°C, the reaction time is about 16 hours and the amount of octamethylcyclotetrasiloxane is about 25wt% of hydroxyapatite.In this paper, the composite materials were prepared with hydroxyapatite treated with octamethylcyclotetrasiloxane and addition-cured high-temperature vulcanized silicone rubber or organic peroxides-type high-temperature vulcanized silicone rubber. The results showed that with the increasing of the hydroxyapatite, the hardness of composite materials was improved. However, other mechanical properties such as tensile strength, tear strength were reduced.The effects of different amount of hydroxyapatite on the fatigue strength of the composite materials of the silicone rubber and hydroxyapatite were studied. The results showed that with the increasing of hydroxyapatite, the endurance bending strength of the composite materials had fallen rapidly. When the hydroxyapatite amount was 30wt% of the composite materials, its frequency of six crack had been less than 1000.The effects of different amount of hydroxyapatite on the surface wettability of the composite materials were studied. The results showed that with the increasing of hydroxyapatite, the composite materials' surface wettability was increased. When the hydroxyapatite amount was 40wt% of the composite materials, the wetting angle was close to 90°. At the same time, swelling degree of the composite materials was increased with the increasing of hydroxyapatite, but the increase extent is on the small side.Furthermore, connected samples of pure silicone rubber and the composite materials were prepared and the connectivity between the interfaces of them were tested. The results showed that with the increasing of hydroxyapatite, the connectivity between them was well. When the amount of hydroxyapatite was under 30wt% of addition-cured high-temperature vulcanized silicone rubber-hydroxyapatite composite materials, they could connect well, and its interface force was close to single composite materials mechanical properties. When the amount of hydroxyapatite was under 40wt% of organic peroxides-type high-temperature vulcanized silicone rubber-hydroxyapatite composite materials, they could connect well, and its interface force was close to single composite materials mechanical properties…
Key words: silicone rubber; hydroxyapatite; preparation; performance

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