Biomaterials, hemocompatibility requirements

The in vitro study of the hemocompatibility of biomaterials requires the consideration of many parameters, static or dynamic contact, flow rate, wall shear rate, form of biomaterial to be tested, pathway to consider (platelet adhesion, platelet activation, complement activation, contact phase activation etc..) and duration of contact(39). It has previously been demonstrated t t hemodynamic circumstances play a significant role in determining localization, growth and fiagmentation of thrombi and platelet adhesion in vivo, and that flow rate controls platelet transport to a surface and their adhesion (40). This evidence is siqtpoited by observed differences in platelet activity predominance in venous and arterial flow (41). Qearly, defining the blood compatibility of a material is a conqrromise between a number of these factors. 

Crystallized silicon is very nonreactive and requires extremely high temperatures to become reactive. It is also known to be a nonbiocompatible material with very poor hemocompatibility [9]. However, in 1995, Canham [10] demonstrated the bioactivity of pSi layers in simulated body fluids (SBFs). Here, the term bioactive refers to silicon as a biomaterial, which is deflned as a nonviable material intended to interact with biological systems when used in a medical device. As noted by Canham, the transition of silicon to a bioactive state via the introduction of pores is consistent with the fact that aU other natural biological materials are porous [77]. In Canham s study, 1 gm-thick pSi layers were incubated in various SBFs for periods ranging from 6h to 6 weeks. While the highly porous Si (porosity >70%) dissolved in aU SBFs tested, the silicon with medium porosity (<70%) was slowly biodegradable. Similar to solid silicon, very low-porosity silicon was shown to be bioinert Thus, porosity is directly related to bioactivity. 

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