Medical applications silicones

Examples of nanomaterials can be classified in different ways. Some of the common classes are based on application and consist of the following carbon nanotubes (fuUerenes), nanoparticles, nanorods, and nanoelectronic devices. Other more specific are, for example, medical applications, silicon solar cells, semiconductors, nanoelectromechanical systems (NEMS) or microelectromechanical systems (MEMS), and nanolithography. Another major potential application is in the medical field as nanorobotics. 

Silicone mbbers have been widely used for medical applications, particularly for body implants in structural cosmetic surgery. One high-profile application has been that of breast implants, but the award in early 1994 of enormous damages by a US court in respect of faulty implants may discourage development of this application. 

As a preeminent biomaterial, silicones have been the most thoroughly studied polymer over the last half century. From lubrication for syringes to replacements for soft tissue, silicones have set the standard for excellent blood compatibility, low toxicity durability, and bioinertness. Many medical applications would not have been possible without this unique polymer. 

Hron P. Hydrophilisation of silicone rubber for medical applications. Polym Int, 2003, 52, 1531-1539. Tcholakian RK and Raad. Durability of anti-infective effect of long term silicone sheath catheters impregnated with antimicrobial agents. Antimicrob Agents Chemother, 2001, 45(7), 1990-1993. 

Ikada Y. Surface modification of polymers for medical application. Biomaterials, 1994, 15, 725-736. James SJ, Pogribna M, Miller BJ, Bolon B, and Muskhelishvili L. Characterization of cellular response to silicone implants in rats Implications for foreign-body carcinogenesis. Biomaterials, 1997, 18, 667-675. 

Two further interesting points of note are that on burning silicones form silica which is an insulator, and thus cables insulated with silicone can function after short term exposure in a fire situation silicones are also physiologically inert and this has led to their use in a wide variety of medical applications, including medical implants. 

Particle size of the silica and tight control of its size distribution decides the ability of the compounded silicone rubber to be optically clear, even at quite high levels of addition. This feature can be used to advantage in a number of medical applications such as intraocular and contact lenses, medical tubing, flexible lights and a number of other industrial applications where sustained clarity of transparency is important. 

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... 

In dentistry, silicones are primarily used as dental-impression materials where chemical- and bioinertness are critical, and, thus, thoroughly evaluated.546 The development of a method for the detection of antibodies to silicones has been reviewed,547 as the search for novel silicone biomaterials continues. Thus, aromatic polyamide-silicone resins have been reviewed as a new class of biomaterials.548 In a short review, the comparison of silicones with their major competitor in biomaterials, polyurethanes, has been conducted.549 But silicones are also used in the modification of polyurethanes and other polymers via co-polymerization, formation of IPNs, blending, or functionalization by grafting, affecting both bulk and surface characteristics of the materials, as discussed in the recent reviews.550-552 A number of papers deal specifically with surface modification of silicones for medical applications, as described in a recent reference.555 The role of silicones in biodegradable polyurethane co-polymers,554 and in other hydrolytically degradable co-polymers,555 was recently studied. 

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 protection of microelectronics from the effects of humidity and corrosive environments presents especially demanding requirements on protective coatings and encapsulants. Silicone polymers, epoxies, and imide resins are among the materials that have been used for the encapsulation of microelectronics. The physiological environment to which implanted medical electronic devices are exposed poses an especially challenging protection problem. In this volume, Troyk et al. outline the demands placed on such systems in medical applications, and discuss the properties of a variety of silicone-based encapsulants. 

Prior to their current phase-out, chlorofluorocarbons (CFCs) were widely used as processing solvents for various materials. CFCs were well suited for many medical applications owing to their high solvency, nonflammability, good materials compatibility, and low toxicity. The uses for CFCs include a silicone deposition solvent, a fluoropolymer dispersion liquid, and processing solvents. However, the Montreal Protocol phase-out of ozone-depleting substances has required that alternative dispersants and solvents be found. Limitations of most available alternatives include flammability, low volatility, poor solvency, and poor materials compatibility. 

Silicone functionalized PIB is particularly suitable as a pressure sensitive adhesive composition in medical applications including transdermal drug delivery applications (83). 

In addition to dense monolithic ceramics, porous silicon nitrides are gaining more importance in technological applications [24], Some porous silicon nitrides with high specific surface area have already been applied as catalysis supports, hot gas filters and biomaterials [25], There is an emerging tendency to facilitate silicon nitride as biomaterial, because of specific mechanical properties that are important for medical applications [25], Moreover, in a recent study it was shown that silicon nitride is a non-toxic, biocompatible ceramic which has the ability to propagate human bone cells in vitro [25], Bioglass and silicon nitride composites have already been realized to combine... 

The Raman microprobe has been used to detect foreign bodies in various tissues (38). Figure 3-9 shows spectra of lymph node tissue of 5 pm size, which was obtained by biopsy from a patient. The foreign body was identified as a particle of silicon rubber (dimethyl siloxane). For more biological and medical applications, see Section 6.2.4. 

The new generation of silicon technology imaging transducers combined with ongoing electronic miniaturization and the availability of extremely fast and powerful portable laptop computers will lead to the development of portable or even wearable high-resolution scanners affording wireless data transfer. This technology will help to make communication with remote locations and advanced medical applications more affordable. 

In consumer markets, keypads, baby bottle nipples, and pacifiers are said to be the applications for molded silicone products with greatest growth potential. Silicone elastomers are particularly well suited for food contact and medical applications. 

An inherent advantage of silicon microfabrication techniques is that numerous devices can be rapidly and cheaply produced. This presents the opportunity to develop disposable systems which would be valuable for many chemical analysis and medical applications or to operate many devices in parallel to scale-up production from microreaction systems. The large knowledge base for these processes due to their long history of use in the microelectronics industry also presents a major advantage. A major drawback to silicon microfabrication is the high cost of much of the associated equipment. 

The device was manufactured as two parts the first part is a disposable silicon chip - with the electrochemical cells arrays. The sihcon chip was wire bonded to a special printed circuit board (PCB) platform, which was directly connected to the data processing units. The second part of the device is reusable, which includes a multiplexer, potentiostat, temperature control and a pocket PC for sensing and data analysis (for more details see [5]). This design enables performance of multi experiments simultaneously and each electrochemical cell can be measured independently. The total weight of the entire system is -900 g, making it ideal for medical applications. 

J. Bagdahn, D. Katzer, M. Petzold, Strength and reliability of silicon based MEMS for automotive and medical applications, Materialsweek 2000, Proceedings (2000). 

Rimplast (Petrarch Systems) Blend PA Silicone rubber Medical applications... 

Elastomeric silicone IPN with TPU and S-EB-S thermoplastic elastomer matrices have found some medical applications [Carew and Deisher, 1989]. The silicone contributes to the excellent release characteristics and to the bio-compatibility. Typical applications include medical tubing, catheters, implants, diaphragms, seals, gaskets, etc. 

Among the many classes of polymeric materials now available for use as biomaterials, non-degradable, hydrophobic polymers are the most widely used. Silicone, polyethylene, polyurethanes, PMMA, and EVAc account for the majority of polymeric materials currently used in clinical applications. Consider, for example, the medical applications listed in Table A.l most of these applications require a polymer that does not change substantially during the period of use. This chapter describes some of the most commonly used non-degradable polymers that are used as biomaterials, with an emphasis on their use in drug delivery systems. 

Many of the silicone elastomers that are used in biomedical applications are produced by Dow Chemical Corp., under the trade name SILASTIC . For example, a typical medical-grade silicone (like SILASTIC MDX4-4210 Medical grade elastomer) contains, after curing, cross-linked drmethylsiloxane polymer and silica for reinforcement. Silcones are also reinforced with PET (Dacron) fiber meshes for certain biomedical applications. For implantable medical devices, it is important to realize that the cured polymer contains residual catalysts and silicone cross-linkers, which are necessary for the polymerization. 

---