Fabrication, mechanical and in vivo performance of polycaprolactone/tricalcium phosphate composite scaffolds

Abstract

In this paper, the use of the Selective Laser Sintering (SLS) process for the generation of bone tissue engineering scaffolds from PCL and PCL/TCP is explored. Different scaffold designs are generated and are assessed from the point of view of manufacturability, porosity and mechanical performance. Large scaffold specimens are generated, with a preferred design, and are assessed through an in vivo study in a critical size bone defect in the sheep tibia with subsequent microscopic, histological and mechanical evaluation. Further explorations are performed to generate scaffolds with increasing TCP contents.Scaffold fabrication from PCL and PCL/TCP mixtures with up to 50 mass-% TCP is shown to be possible. With increasing macroporosity the stiffness of the scaffolds is seen to drop, however, the stiffness can be increased by minor geometrical changes, such as the addition of a cage around the scaffold. In the animal study the selected scaffold for implantation did not perform as well as the TCP control in terms of new bone formation and the resulting mechanical performance of the defect area. A possible cause for this is presented.

Computational modelling of ovine critical-sized tibial defects with implanted scaffolds and prediction of the safety of fixator removal

“…This study is based around an in vivo study of two types of scaffolds implanted in criticalsized ovine tibial defects as part of the STEPS EU-FP6 project [6] (Figure 2(A)): 90/10wt% PCL/β-TCP scaffolds fabricated using selective laser sintering and commercially available β-TCP scaffolds (Biovision, Illmenau, Germany). Defects were stabilised using a titanium plate and fixation screws and defect imaging was carried out at 14 weeks post-operative using a μ-CT scanner (Fan Beam μ-Scope, Stratec, Pforzheim, Germany) and X-ray.…”

“…Four-point bend testing was carried out on both left and right tibiae (at 14 weeks), as per Figure 3(A), to a maximum load of 40 N. In each case, the right tibiae were operated on and the left tibia was left intact. Each tibia was rotated in 30° increments about the longitudinal axis to determine the bending stiffness in 360° [6]. Four defect cases/specimens were selected for study here; two with implanted PCL/β-TCP scaffolds and two with β-TCP scaffolds.…”

“…It is widely understood that while often effective, donor site morbidity is an issue with the use of autografts in treating this type of defect due to the volume of tissue required. Bone tissue engineering scaffolds have been developed from a wide range of materials to address this challenge [1][2][3][4][5][6]. External fixation of the bone is generally required for stabilisation of critical-sized defects during the early stages of healing until sufficient mechanical integrity has been achieved.…”

“…Similar methods were employed by Roshan-Ghias et al [13] to generate FE models of a scaffold-callus construct for uniaxial loading simulations. The use of four-point bending tests gives a more complete picture of the mechanical integrity of the scaffold-callus construct [6,11] under the complex loading conditions in-vivo [14] in comparison to the use of uniaxial loading alone.…”

“…Specifically, the first objective of the study is to generate detailed FE models of real defect geometries using µ-CT scans, and to verify the accuracy of the models against experimental data [6]. The second objective is to use the developed FE models to explain the experimentally observed mechanical performance of these defects, and to evaluate the safety of removing the fracture fixation device in each case.…”