3. Biocompatibility

Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is 1/! \_z+.z0+z)+.!z!),%.%(z(%\*%(z/1!//z+"zz3\$+(!z !2%!z%\*z3\$%\$z0\$!z)0!.%(z+.z)0!.%¥ als are featured. The ambiguity of the term reflects the ongoing development of insights into \$+3z%+)0!.%(/z%\*0!.0z3%0\$z 0\$!z\$1)\*z+ 5z\* z!2!\*01((5z\$+3z 0\$+/!z%\*0!.0%+\*/z !¥ termine the clinical success of a medical device (such as pacemaker, hip replacement or /0!\*0d^z
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Mostly, efforts to develop SiC for MEMS have focused on developing device technologies for harsh environment applications where Si, the dominant material in MEMS, is not well suited. Such environments include high temperature (>600 °C), high mechanical wear, high radiation, high oxidation, and harsh chemicals. Properties that make SiC particularly well suited for harsh environments include a wide electronic bandgap (ranging from 2.9 eV for

ing in acids and bases, slow oxidation rates, and very strong covalent Si–C bonds. SiC is of particular interest for use in MEMS-based microactuators, where its inert surface resists the deleterious effects of stiction and its high Young's modulus (~400 GPa) enables fabrication of mechanical resonators that can operate over a very wide frequency range, including the GHz range. Its chemical inertness, favorable mechanical properties, and biocompatibility make SiC particularly attractive for bioMEMS applications. Several comprehensive reviews of SiC MEMS technology, including material properties, processing techniques, and device

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Biocompatibility is related to the behavior of biomaterials in various contexts. The term may refer to specific properties of a material without specifying where or how the material is 1/! \_z+.z0+z)+.!z!),%.%(z(%\*%(z/1!//z+"zz3\$+(!z !2%!z%\*z3\$%\$z0\$!z)0!.%(z+.z)0!.%¥ als are featured. The ambiguity of the term reflects the ongoing development of insights into \$+3z%+)0!.%(/z%\*0!.0z3%0\$z 0\$!z\$1)\*z+ 5z\* z!2!\*01((5z\$+3z 0\$+/!z%\*0!.0%+\*/z !¥ termine the clinical success of a medical device (such as pacemaker, hip replacement or /0!\*0d^z
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3C-SiC to 3.2 eV for 4H-SiC), high hardness (2,480 kg/mm2

examples have recently been published [2, 3].

352 Physics and Technology of Silicon Carbide Devices

lus is typically reported to be around 400 GPa.

the tests performed) and sterilizable [2].

3. Biocompatibility

Several papers have discussed testing silicon SiC in vitro. In one study the researchers tested SiC deposited from radiofrequency sputtering using alveolar bone osteoblasts and gingival fibroblasts for 27 days. The investigators reported that ''Silicon carbide looks cytocompatible +0\$z +\*z /(z \* z /,!%"%z 50++),0%%(%05z(!2!(/^z+3!2!.\_z "%.+(/0z \* z +/0!+(/0z 0¥ 0\$)!\*0z%/z\*+0z\$%#\$(5z/0%/"0+.5\_z\* z 1.%\*#z0\$!z/!+\* z,\$/!z+"z+/0!+(/0z#.+30\$\_z+/0!+¥ blast proliferation is very significantly reduced by 30%''. According to another paper, in a 48 \$z/01 5z1/%\*#z\$1)\*z)+\*+50!/\_z%z\$ zz/0%)1(0+.5z!""!0z+),.(!z0+z,+(5)!0\$.5¥ late. Cytotoxicity and mutagenicity has been performed on SiC-coated tantalum stents. )+.,\$+1/z %z % z \*+0z /\$+3z \*5z 50+0+4%z .!0%+\*z 1/%\*#z)%!z "%.+(/0/z LELz !((z 1(¥ tures when incubated for 24 h or mutagenic potential when investigated using Salmonella typhimurium mutants TA98, TA100, TA1535, and TA1537. An earlier study by the same authors of a SiC-coated tantalum stent reported similar results [5].

Kotzar et al. [6] evaluated materials used in microelectromechanical devices for biocompatibility. These included single crystal silicon, polysilicon (coating, chemical vapor deposition, CVD), single crystal cubic SiC (3C SiC or β-SiC, CVD), and titanium (physical vapor deposition). They concluded that the tested Si, SiC and titanium were biocompatible. Even though crystalline SiC biocompatibility has not been investigated in the past, information exists concerning the biocompatibility of the amorphous phase of this material (a-SiC). Materials commonly used in the fabrication and packaging of standard MEMS devices were recently evaluated for cytotoxicity using the ISO 10993 biocompatibility testing standards [7]. The material set comprised of: silicon (Si, 500 um-thick), silicon dioxide (SiO2 0.5 µm-thick), silicon nitride (SigNy, 0.2 µm-thick), polycrystalline silicon (polysilicon, 0.5 µm-thick), silicon carbide (SiC, 0.5 um-thick), titanium (Ti, 0.5 um-thick), and SU-8 (50 um-thick) (Table 1).

The biocompatibility of the materials used in silicon-based devices, such as single crystalline silicon, polysilicon, silicon dioxide, silicone nitride and silicon carbide, were evaluated according to ISO 10993 standards by Kotzar et al. [6]. Using mouse fibroblasts in the tests, none of the materials were found to be cytotoxic. An in vivo tests based on implantation in rabbit muscle showed no sign of irritation. Only silicone nitride and SU-8 showed detectable nonvolatile residues. Furthermore, in vivo studies using Stainless Steel cages and Teflon cages reveal that silicon, silicon nitride, silicon dioxide, gold, and SU-8 are biocompatible. However, silicon and SU-8 have shown increased biofouling.


Table 1. In vitro cytotoxicity of MEMS materials [7]
