Tissue bioactive fillers

Synthetic Biomedical Composites and Their Bioactivity 443 Table 22.2 Bioactive fillers used in tissue engineering applications. 

In order to improve the properties of the tissue engineering biomaterials nanostructured bioactive fillers have been investigated. Nanoparticles can disperse more uniformly in the polymer matrix, thus enhancing the coating characteristics of the apatite layer formed and also result in a better cell attachment and proliferation. 

Fibrous fillers for biomedical PLA-based FRPs include carbon and inorganic fibres [406], PLLA (i.e. self-reinforcement) [407,408], poly(p-dioxane) fibre [409], chitin [410], biodegradable fibre (e.g. bioactive glass, chitosan fibre, polyester amides) [411], hydroxyapatite fibre [412], hydroxyapatite whiskers [413], halloysite (Al2Si205(0H)4) nanotubes [414] and the fibre from different tissue types of Picea sitchensis [415],... 

Composites of chitosan and P-TCP with improved compressive modulus and strength have been prepared by a soUd-Uquid phase separation of the polymer solution and evaporation of the solvent [8]. The composites exhibited bioactivity when immersed in SBF. Variation of polymer/filler ratio and development of different macroporous structures resulted in products with potential applications in tissue engineering. 

P-Tiicalcium phosphate (P-TCP) fillers were also used in PCL electrospun fibers [65,67] to obtain bioactive nanocomposite fibers for applications in the bone tissue engineering field, as weU as calcium carbonate (CaCOs), which was incorporated in PCL membranes for guided bone regeneration [68]. 

Thus, the introduction of bioactive glass nanoparticles as fillers in biodegradable polymers adds many interesting features, and represents a promising step towards the development of improved biomaterials for bone regeneration, as well as engineered scaffolds for tissue engineering appUcations. 

As an extension to this surface-modification method, researchers have utilized plasma polymerization of acrylic acid to immobilize biologically active molecules, such as recombinant human bone formation protein-2 (rhBMP-2). rhBMP-2 is a signaling molecule that promotes bone formation by osteoinduction that has been utilized for various orthopedic tissue-engineering applications (Kim et al., 2013). One research group modified a PCL scaffold surface with plasma-polymerized acrylic acid (PPAA) and rhBMP-2 via electrostatic interactions (Kim et al., 2013) (which is outside of the scope of this chapter). This interesting approach may be apphed to the surface modification of solid fillers and provide additional benefits compared to the surface-modification techniques currently utihzed in orthopedic polymeric biocomposite development. The acrylic acid and rhBMP-2-modifled surface showed improved cell attachment and adhesion compared to the surface with acrylic acid alone. The ability to modify the surface of a solid-filler particle in a polymeric biocomposite with a bioactive molecule, such as rhBMP-2, provides a delivery vehicle for the bioactive molecule to the polymeric biocomposite and the eventual implantation site of this biomaterial. Such surface-modification and immobihzation approaches may provide a method to control the release kinetics of attached molecules to the localized bone-defect site. 

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