Bioactive Porous Silicon

Ji et al. have adapted soft lithographic microcontact printing [69, 70] with specific etching procedures to produce patterned porous silicon substrates for the spatially-controlled deposition of calcium phosphate [71]. Calcification, confirmed 

SBF for 30 min. (Reprinted with permission from [71]. Copyright 2002 Wiley-VCH. J. L. Coffer is thanked for permission to reprint this figure.) 

The bioactivity of porous silicon toward living cellular systems is also under investigation. Efforts have been made by Bayliss, Buckberry, and their collabo- 

Micro Enzyme Reactors (yilMERS) and Total Analysis Systems (/ TAS) 

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The term biocompatibility is defined as the ability of a material to perform with an appropriate host response in a specific situation" (Williams 2008). A biocompatible material can be inert, where it would not induce a host immune response and have little or no toxic properties. A biocompatible material can also be bioactive, initiating a controlled physiological response. For porous silicon, bioactive properties were initially suggested based on the observation that hydroxyapatite (HA) crystals grow on microporous silicon films. HA has implications for bone tissue implants and bone tissue engineering (Canham 1995). An extension of this work showed that an applied cathodic current was able to further promote calcification on the surface (Canham et al. 1996). More recently, Moxon et al. showed another example of bioactive porous silicon where the material promoted neuron viability when inserted into rat brains as a potential neuronal biosensor, whereas planar silicon showed significantly fewer viable neurons surrounding the implant site (Moxon et al. 2007). 

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 biocompatibility of porous silicon is critical to its potential biomedical uses, both in vivo within the human body for therapy and diagnostics, and in vitro for biosensing and biofiltration. Published data from cell culture and in vivo studies are reviewed, and a number of emerging applications for bioactive or biodegradable silicon are discussed. 

Henstock JR, Ruktanonchai UR, Canham LT, Anderson SI (2014) Porous silicon confers bioactivity to polycaprolactone composites in vitro. J Mater Sci 25(4) 1087-1097 Hon NK, Shaposhnik Z, Diebold ED, Tamanoi F, Jalali B (2012) Tailoring the biodegradability of porous silicon nanoparticles. J Biomed Mater Res 100(12) 3416-3421... 

Canham LT, Newey JP, Reeves CL, Houlton MR, Loni A, Simmons AJ, Cox T1 (1996) The effects of DC electric currents on the in-vitro caleifieation of bioactive Si wafers. Adv Mater 8 847-849 Canham LT, Reeves CL, Loni A, Houlton MR, Newey JP, Simons AJ, Cox T1 (1997) Calcium phosphate nucleation on porous silicon factors influencing kinetics in acellular simulated body fluids. Thin Solid Films 297 304-307... 

Administration route 1 Bioactive 1 Biocompatibility 1 Biodegradable porous silicon 1 Bioresorbable property 1 Composite structures 5 Degradation products 5 Drug delivery 1 In vitro drug 2 In vivo drug 2 Intravenous delivery 4 Intravitreal delivery 4 Microparticles 1 Nanoparticles 1 Oral delivery 2 Peptide 3... 

Mery E, Malhaire C, Remaki B, Barbier D (2007) Electrical study of microfluidic channels isolated with chemically modified porous silicon. Physica Status Solidi C 4(6) 2098-2102 Moxon KA, Hallman S, Aslani A, KaUdioran NM, Lelkes PI (2007) Bioactive properties of nanostructured porous silicon for enhancing electrode to neuron interfaces. J Biomater Sci PolymEd 18(10) 1263-1281... 

Ronci M, Rudd D, Guinan T, Benkendorff K, Voelcker NH (2012) Mass spectrometry imaging on porous silicon investigating the distribution of bioactives in marine mollusc tissues. Anal Chem 84 8996-9001... 

Another advantage of the silicon oxide network is that it can be modified in various ways as shown in Fig. 18.2. One way is co-condensation of the most nsed tetramethylol silanes with other kinds of metal oxides. Another way is cohydrolysis and co-polycondensation with snbstitnted trimethoxy silanes where this substituent is, for example, a long alkyl chain for hydrophobation, an organic portion with polar structures for antistatic effects, a fluorocarbon for the release of water, oil and soil or a bioactive group. The easiest method of modification is the physical one, the simple addition of the desired chemicals. They are then incorporated in the porous network of the metal oxides and are released in a more or less controlled way. 

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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