Fracture modes under uniaxial compression in hydroxyapatite scaffolds fabricated by robocasting

Abstract

The fracture modes of hydroxyapatite (HA) scaffolds fabricated by direct-write assembly (robocasting) are analyzed in this work. Concentrated HA inks with suitable viscoelastic properties were developed to enable the fabrication of prototype structures consisting of a 3-D square mesh of interpenetrating rods. The fracture behavior of these model scaffolds under compressive stresses is determined from in situ uniaxial tests performed in two different directions: perpendicular to the rods and along one of the rod directions. The results are analyzed in terms of the stress field calculated by finite element modeling (FEM). This analysis provides valuable insight into the mechanical behavior of scaffolds for bone tissue engineering applications fabricated by robocasting.

Improving the compressive strength of bioceramic robocast scaffolds by polymer infiltration

“…In all cases the stress decline after the maximum was progressive, indicating that the structure retained some significant mechanical resistance after multiple cracking events, even in the case of the unimpregnated scaffolds. However, it should be noted that in this latter case the residual load-bearing capacity was provided by disjointed rods that would collapse if the load was removed [10], while in the infiltrated scaffolds it was a real effect, since the polymer provided the necessary link between the disconnected pillars. Qualitatively, the toughness (in terms of dissipated mechanical energy) of the structure was greatly increased after polymer infiltration, with the asymptotic nominal stress at high deformation increasing by more than one order of magnitude over the bare scaffolds.…”

“…3a and 3b, in which elements in the vicinity of the external surfaces of the ceramic rods had a minimum dimension of $5 lm. The stresses on the external surfaces of the rods were the most relevant, since it is there where failure will initiate during testing [10]. The selected refined element mesh thus allowed us to evaluate those surface stresses with greater precision.…”

“…Thus, a 3-D structure is printed directly as a network of ink rods extruded through the deposition nozzle. With the recent development of robocasting inks made from b-tricalcium phosphate [8] (b-TCP) and hydroxyapatite [9][10][11] (HA) powders, this technique has allowed customized calcium phosphate scaffolds to be built for bone regeneration.…”

Robocasting of biomimetic hydroxyapatite scaffolds using self-setting inks

“…7b and c), 34,36 which are known to break by the splitting of the pillar arrays constituted by the piled crisscrossing of the successive deposited layers. The pillars are solicited in compression until a rst pillar fails because of the propagation of cracks perpendicularly to both strand directions.…”

“…The pillars are solicited in compression until a rst pillar fails because of the propagation of cracks perpendicularly to both strand directions. 36 Subsequently, the bridges between pillars are solicited in exural mode, and a combined failure of the bridges linking the pillars occurs, splitting one or more pillars at a time. The rst pillars to fail were found on the outer part of the scaffold, due to the lower number of linkages linking them to other pillars.…”