Scaffolding Applications of Nanofibers

The main characteristics of scaffolding materials or synthetic ECM can be readily anticipated  

The material in contact with the host body tissue should not elicit any undesirable immune or tissue responses. The polymers selected and their products of biodegradation should not interfere with the physiology of the body tissue about it. 

The material used should ideally biodegrade once initial tissue growth has taken hold in the implant (avoiding the need for a second invasive surgery to remove it). Cell growth, proliferation, and differentiation in vivo should ideally occur over the timescale of biodegradation of the scaffold. 

Scaffolding topology should be conducive to attachment or proliferation of cells and its pore-size distribution must match the requirement of the cells being cultured on it. A biomaterial such as trabecular bone, for instance, is 50-90% porous. In vascular grafts the effective pore diameter for cell ingrowth was reported to be in the range of 20-60 p.m (von Recum et al. 1996). 

The mechanical characteristics of the scaffolding material must match those of the tissue with which it will interface. The choice of material therefore varies with the type of tissue in question thus, scaffolds based on a single material but seeded with appropriate cellular components still cannot always be expected to be generic replacements for all tissue types. In small-diameter vascular grafts, for instance, compliance mismatch between the implanted graft and host artery has been reported to be a major factor in graft failure (Kinley and Marble 1980). 

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Nanosized objects perform various functions in the biomedical field. In the human body, nanosized particulate substances behave very differently from larger particles. In 1986, Maeda et al. found that the stained albumin, having a size of several nanometers, naturally accumulates in the region of cancerous tissues, which is now well known as the enhanced permeability and retention (EPR) effect. Many studies in the field of nanoparticles are based on this finding. Another application of nanoparticles is the delivery system using various polyplexes that are composed of carrier molecules and plasmid DNA or nucleic acid drugs such as antisenses and siRNA. In addition, nanofibers are mainly used for biodegradable scaffolds in tissue... 

In another case, PAs were designed to function as magnetic resonance imaging (MRI) contrast agents (Bull et al. 2005) by covalently linking the peptide portion to a derivative of l,4,7,10-tetraazacyclododecane-l,4,7,10-tetraacetic acid followed by chelation of Gd ions by this moiety. The PAs were modified such that self-assembly produce either nanofibers or spherical micelles. The application of this self-assembling system could be extended to noninvasive MRI of PA scaffolds in vivo. 

Potential applications of scaffolds made from chitosan and chitin nanofibers have been explored in tissue engineering. Chitin and chitosan can be electrospun into nanoscaffolds that could resemble the native extracellular matrix and have improved cytocompatibility for tissue engineering... 

Like small amphiphile nanotubes [14], block copolymer nanotubes should have potential applications in controlled deUvery and release [97,98], in encapsulation [99], and in nanoelectronics [100] etc. Although there have been reports on laboratory use of block copolymer nanofibers as vehicles for drug delivery [101], as scaffolds for cell growth [88,102], as precursors for ceramic magnetic nanowires [103,104], and as precursors for carbon nanofibers [105,106[, practical applications of block copolymer nanotubes have not been reported. This is probably due to the difficulty in making such structures. Their preparation from the self-assembly of block copolymers and interests from industry will likely change the scenery of nanotube appUca-tions in the futme. 

It was reported that as the amount of PANI increased, nanofibers diameters were increased, and higher decomposition temperatures, lower crystallinities, and lower elastic modulus were obtained. PANI was blended with a natural protein, gelatin, and coelectrospun into nanofibers to investigate the potential application of such a blend as conductive scaffolds for tissue engineering purposes. An increasing trend in diameters was reported at increasing PANI concentration. 

There is currently a renewed interest in the use of electrospinning techniques for the fabrication of membranes. Chapter 8 reviews the use of this versatile technique for the production of nanofiber webs or membranes. The chemical and physical properties of nanofiber manbrane surfaces play an important role in their application to filtration, biomedical materials, tissue engineering scaffolds, drug delivery... 

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