Silicone Elastomer Bioactive Reinforcement

Sihcone elastomers have relatively weak mechanical properties and require fillers to provide reinforcement. Surface-treated sihca fillers with small particle size and, therefore, with high surface area, are commonly used. Facial prosthe-ses are normally cleaned in water and, therefore, the incorporation of hydrophobic sihca filler into the base polymer is a good choice for medical-grade materials. 

Tsuru et al. [87] reported that in PDMS-CaO-SiOj hybrids prepared by the sol-gel method, apatite appeared on their surfaces upon immersion into a simulated body fluid (SBF), which suggests that these hybrids can be bioactive. Similarly, Chen et al. [88] synthesized PDMS-CaO-SiO -TiOj hybrids and found that these systems show an apatite-forming ability, while being deformable. It was shown that PDMS-CaO-SiOj hybrids present apatite-forming ability when immersed in SBF and, moreover, these materials exhibit mechanical properties analogous to those of human cancellous bones. 

Some other attempts include the work of Kamitakahara et al. [89] who studied CaO-ffee PDMS-modified hybrids, which are able to form apatite on their surfaces. The above authors prepared a highly deformable PDMS-TiO hybrid with apatite forming abiUty by hydrolysis and polycondensation of PDMS and titanium ethoxide, followed by hot-water treatment in order to precipitate anatase nanoparticles. 

Salinas et al. [90] prepared CaO-SiOj-PDMS hybrid materials and their in vitro bioactivity was assessed by immersion into simulated body fluid (SBF). Due to their bioactivity and good mechanical properties, these materials could be used for soft tissue substitution or for coating metallic implants to damp the differences in rigidity of metal and bone. 

P-Tricalcium phosphate (P-TCP), is a calcium-phosphate bioactive ceramic with excellent degradation properties[91]. Incorporation of [)-TCP in siUcone rubber led to a material that fulfills the mechanical and biological requirements 

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Initially, a literature survey focusing on the maxillofacial and other prosthetic applications of silicone elastomers is presented in this chapter. Next, the biocompatihUity aspects, aging and failure mechanisms, and modifications for improved properties in biomedical applications wfil be discussed. The state of the art regarding bioactive reinforcement of silicones is also included, due to the promising effects of bio ceramics that can encourage prosthetic materials adherence to tissues. 

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