The biodegradability of scaffolds reinforced by fibers or tubes for tissue repair

The present chapter gives an overview of the fabrication, biocompatibility and biodegradability of flexible scaffold materials reinforced with stiffer nanofiber or nanotube inclusions. The need for such filler nanomaterials results from the necessity to increase the elastic modulus and fracture toughness of biopolymer materials, such as gelatin, chitosan, as well as synthetic biodegradable polymers, such as polylactic acid and polycaprolactone, that are to be used in large bone defect regeneration. For such biomedical applications it must be possible for the material to support the forces exerted by the skeletal network, until the new bone tissue is regenerated. Hence, the scaffold mechanical properties must not be altered much during the initial and intermediate degradation stages at which bone formation occurs. Furthermore, degradation of the scaffold must occur slowly not only so that sufficient tissue is formed, but so the degraded scaffold products can be at levels that can be tolerated by the cells without inducing cytotoxicity. The most widely examined fillers for reinforcing the scaffold strength are hydroxyapatite (HA) nanotubes, as HA is a natural mineral found in bone, while other promising candidates include silk, boron nitride, and magnesium alloy nanowires. Another common combination is the use of stiffer polymer fiber reinforcements, within a soft polymer matrix, or polymer fiber meshes embedded in hydrogels, to form laminates that are then stacked. The particular systems to be covered in this chapter are: (i) gelatin reinforced with hydroxyapatite nanofibers, (ii) chitosan reinforced with boron nitride nanotubes, (iii) polylactide-polycaprolactone reinforced with boron nitride nanotubes, (iv) nano-hydroxyapatite/collagen/PLLA reinforced by chitin fibers, (v) poly-lactic acid reinforced with magnesium alloy nanowires, (vi) polycaprolactone reinforced with poly-L-lactic acid fibers, (vii) polyactic acid reinforced with silk fibers, (viii) poly(lactide-co-ethylene oxide fumarate) gel reinforced with a mesh of poly-L-lactic acid fibers, and (ix) protein hydrogels reinforced with a nano-HAp/ PHB fiber network. Standard mechanical testing (such tension and bending) has.