Polymeric biocomposites surface-modified

Polymeric biocomposites that have utilized techniques to modify the surface of the solid phase before combination with the polymer binder narrow the field. The filler material and polymer binder combinations that fit this criterion and are highlighted in this chapter are paired in Table 3.1. In addition to the surface-modification techniques, what differentiates these biocomposites from one another are the fabrication processes used to combine the polymer and bioactive components and the polymerization of the polymer itself. A general schematic of how surface-modified polymeric... 

Figure 3.3 Surface-modified polymeric biocomposites, (a) Schematic of general fabrication of polymeric biocomposites. Cross-section SEM images of biocomposites made with silane modified fillers (b) Ti02/HDPE (c) phosphate glass fibers/PCL (d) modified HA/BisGMA, and silane-i-PCL modified fillers (e) BG/PUR.

Monomer transfer molding is similar to compression molding in that a predetermined shape is filled to create a pre-fabricated composite, but instead of utilizing force, monomers are polymerized within a heated mold cavity. The monomer mixture remains enclosed in a mold until it has polymerized and fully cured. Using this method, surface-modified bioglass fiber/PCL biocomposites have been made (Jiang et al., 2(X)5a Khan et al., 2010), proving there is more than one way to produce a biocomposite with the same basic components. 

Effects of surface-modified fillers on the properties of resultant polymeric biocomposites... 

Modifying the surface of sohd fillers used in polymeric biocomposites controls the surface properties (both primary and secondary), which affects both the mechanical and physical properties of the resultant polymeric biocomposite as well as its ability to remodel in vivo. An overview of the surface-modification techniques and how they alter the resultant biocomposite properties is outlined in Table 3.3. The fundamental theory of composite design is to obtain physical properties that lie between those of the individual components. As previously outlined, a primary motivator to modify the surface of a solid filler is to inaease adhesion between the solid filler and polymer components, and thus the overall mechanical properties of the biocomposite. This observation has been supported by numerous studies citing an increase in tensile properties. Other overall biocomposite properties that are affected by surface modification of filler components include binding to polymer phase, solid-filler incorporation into polymer binder, water uptake, and degradation. 

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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