Bone regrowth

Conducting polymers have been explored as biomaterials to replace metals or modify metal surfaces in tissue engineering. Localized electrical stimulation has been shown to promote tissue repair, cell growth, bone regrowth, and wound healing [52, 58]. 

Polymers generally have a low absorption coefficient for x-rays. Thus for a pure polymer sample, contrast is more likely to be a limiting factor than the instrument resolution in normal absorption mode x-ray tomography. Most published x-ray tomography on polymer samples has involved higher contrast systems. These include determination of the distribution of catalyst residue in as-polymerized particles [286], fiber composites [287] and damage in these composites [288,289], bone regrowth into biomaterial [290], and many porous structures such as foams [291] and biopolymer scaffolds [292]. The laboratory and tabletop instruments... 

Beyond the described advancements, a growing interest in development of novel materials and processes for medical applications is noticed. Up to now, freeform fabrication of patient-spedfic osteoconductive implants for bone regrowth represents the most investigated of such applications. However, it appears likely that research RP developments will address further tasks in tissue engineering and organ printing in the near future. 

The ester protection technique has also been used in the preparation of amino acid derivatives of polyphosphazenes (70, 71). For example, eAyl glycinate reacts with poly(dichlorophosphazene) to link the amino function to e phosphorus atoms of the backbone. Subs uent exposure of the protected polymer to water in a biological environment leads to hydrolysis of the ester function and breakdown of the polymer to ethanol, glycine, phosphate, and ammonia. This has been used both for the controlled delivery of drugs and for stimulating the regrowth of bone in tissue engineering experiments (72). 

Glass ionomer cements have been used for some years in dentistry for bonding restorations to teeth. It has been found in certain circumstances that these can also be used for bonding bone, though as the current formulations contain acrylic polymers, these are not resorbable and can only be used in situations where the bond is intended to be permanent and not replaced by regrowth of the tissue. One such commercial application is for repair of the tiny bones in the ear (Tysome and Harcourt 2005). 

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