Synthesis of silicone magnetic fluid for use in eye surgery

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Abstract

Retinal detachment is repaired by external and internal tamponade. There is as yet no direct internal tamponade which provides 360° coverage to the retina. With a magnetized encircling scleral buckle, magnetic fluids would provide 360° encircling internal tamponade. Our magnetic fluid is a dispersion of ultrafine (4–10 nm) magnetic particles in silicone secured with triblock copolymer steric stabilizers. Triblock copolymers are good steric stabilizers for suspensions of γ-Fe2O3 powder in octamethylcyclotetrasiloxane (D4).

Section snippets

Background

The anterior segment of the eye is bounded by cornea and lens–iris diaphragm, and contains the aqueous humor. The posterior segment begins behind the lens–iris diaphragm and includes, from inside outwards: the vitreous (gel/fluid), retina (neurosensory tissue), and choroid (heavily vascular). The retinal photoreceptors are supported by the choroid. The retina and choroid stay attached to each other with a suction pump which keeps the subretinal space dry.

Retinal detachment is a major cause of

Preparation of magnetic fluids

Critical to the success of these magnetic fluids is the development of the steric stabilizers, which must prevent the coagulation of the metal particles. Block copolymers are now recognized to be more efficient than homopolymers as dispersion stabilizers. The “anchor” block is designed to strongly adsorb onto the particle surface, and the “tail” block extends outward into the polydimethylsiloxane (PDMS) fluid preventing aggregation of the particles (Fig. 6). Cyano groups have an established

Reagents

Dichloromethane (Baxter) was washed twice with concentrated sulfuric acid, then with water until neutral. Subsequently, it was pre-dried with anhydrous magnesium sulfate and distilled from phosphorus pentoxide. Hexamethylcyclotrisiloxane (General Electric Co.) was stirred over calcium hydride powder at 80°C for 12 h, then distilled into a dry flask where it was diluted with anhydrous dichloromethane. Tetrahydrofuran (E.M. 99.5%), Triethylene glycol dimethyl ether (TEGDME, Aldrich, 99%) were

Results

Initials samples of triblock copolymers with block lengths of 2.5 k–2.5 k–2.5 k, 4 k–4 k–4 k, and 8 k–8 k–8 k g/mol have been prepared and characterized. Equilibration of DxCN(x=3–5) with dilithium diphenylsilanediolate as both catalyst and chain stopper was followed by 29Si NMR and GPC by sampling the reaction mixture at different reaction times. The macroinitiators were generally heated at 100°C for 48 h to allow the mixture to reach equilibrium. PCPMS macroinitiators are soluble in THF,

Conclusion

Nitrile containing triblock copolymers have been developed as stabilizers for silicone magnetic fluids (PDMS-b-PCPMS-b-PDMS)s has been successfully prepared by living polymerization of D3 using lithium silanolate ended poly (3-cyanopropyl) methylsiloxane macroinitiators. The macroinitiators were prepared by equilibration of mixtures of (3-cyanopropyl)methylcyclosiloxanes and dilithium diphenylsilanediolate, and the molecular weight of the macroinitators was controlled by the ratio of monomer to

Acknowledgements

The authors wish to thank Dr. S. Charles for evaluation of silicone magnetic particle fluids, Drs. R. Stratton, T. Rice and K. Olsen for editorial advice, Dr. S. Davis for DSC, Dr. Q. Ji for GPC, MR. T. Glass for quantitative NMR, Mr. M. Price for graphics, and Dow Corning for materials.

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