Abstract
The influence of polymer infiltration on the flexural strength and toughness of β-tricalcium phosphate (β-TCP) scaffolds fabricated by robocasting (direct-write assembly) is analyzed. Porous structures consisting of a tetragonal three-dimensional lattice of interpenetrating rods were impregnated with biodegradable polymers (poly(lactic acid) (PLA) and poly(ε-caprolactone) (PCL)) by immersion of the structure in a polymer melt. Infiltration increased the flexural strength of these model scaffolds by a factor of 5 (PCL) or 22 (PLA), an enhancement considerably greater than that reported for compression strength of analogue materials. The greater strength improvement in bending was attributed to a more effective transfer of stress to the polymer under this solicitation since the degree of strengthening associated to the sealing of precursor flaws in the ceramic rod surfaces should remain unaltered. Impregnation with either polymer also improved further than in compression the fracture energy of the scaffolds (by more than two orders of magnitude). This increase is associated to the extraordinary strengthening provided by impregnation and to a crack bridging toughening mechanism produced by polymer fibrils.
Highlights
Biodegradable scaffolds are called to be the long-term future materials for bone tissue engineering applications
Robocasting fabrication has been shown to provide a significant improvement in the compressive strength of β-tricalcium phosphate (β-tricalcium phosphates (TCPs)) scaffolds [11,12]
Density measurements determined a total porosity of ~68% in the bare β-TCP scaffolds of which
Summary
Biodegradable scaffolds are called to be the long-term future materials for bone tissue engineering applications. To allow vascularization and diffusion of nutrients in order to promote cell ingrowth This requirement implies a large total porosity for those scaffolds that are fabricated by conventional fabrication techniques [8,9,10]. Such bioceramic structures are extremely brittle, which prevents a more widespread usage of these materials. This hurdle is partially overcome by additive manufacturing ( known as rapid prototyping or solid freeform fabrication) techniques as they allow a precise control over scaffold external—which enable the fabrication of patient-specific scaffolds from medical scans—and internal geometry, making it possible to optimize the pore architecture, by maximizing pore interconnectivity while keeping the total porosity to a minimum. The strength of these TCP robocast scaffolds, not to mention their toughness, remains far short of bone properties with the same level of porosity
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