Directional foaming of scaffolds by integration of 3D printing and supercritical CO2 foaming

摘要

Introduction: Cartilage repair is a challenging clinical problem because once damaged in adults, it never regenerates and resulting defects may further lead to osteoarthritisl1'. Tissue Engineering has emerged as a possible solution to the problem. One of the challenges is to produce an optimum scaffold, able to reproduce the natural ECM and to carry tissue functions in the early stage of the implant process, while inducing the regeneration. While many techniques as applied to process biomaterials, physical methods as supercritical foaming and Additive Manufacturing represent a clean way to control the exact composition of the final construct. This work represents a first attempt to combine the advantages of the two techniques while overcoming some of the main drawbacks, producing 3D anisotropic size-controlled structures. Methods: An Ultimaker Original+ was used to produce the raw scaffold by fusion deposition modelling. Fibers were first created from PLA Natureworks 4043D and 2003D acquired respectively from FiloAlfa and TreeDFilament. Fibers. Three 2D structures were printed for each PLA isomer, with a dimension of 10mm × 10mm × 1mm and with inner windows of 3.5mm × 3.5mm. Then, three 3D scaffolds were produced from each PLA, (4.4mm × 4.4mm × 4.4 mm, 0.4mm fibers and 0.6mm fibers spacing). Each 2D and 3D structure was then foamed with supercritical CO2 in a GMP medical autoclave from SITEC SIEBER Engineering AGPI. Porosity, pore size distribution, interconnectivity and scaffold expansion post foaming were determined by uCT (Microcomputed Technologies Inc. Skyscan 1076, Belgium) and Scanning Electron Microscopy (Microscopy XLF30 microscope) (SEM). Compression behaviour was investigated with an Ultimate Tensile Strength machine (Test Machine Systeme, Germany). Results: The minimum architecture deformation and the maximum interconnected porosity were obtained by tuning the foaming parameters, offering the desired cellular architectures, with fibre directional porosity in the micro meter range (Figure 1). Fig. 1: Scaffold before (left) and after (right) supercritical foaming. A range of mechanical properties were obtained, from solid to foamed cellular material, reducing the stiffness of scaffolds with solid walls and introducing anisotropic properties related to the orientation of the fibres. A model of expansion from 3D printed structure to 3D foamed structure is finally proposed. Discussion and Conclusions: The results shows a possibility to overcome the porosity limit of 3D printed scaffold and anisotropy control of foams. A controlled anisotropy, a homogeneous macro- and an oriented micro-porosity in 3D structures are obtained by combining 3D additive manufacturing and supercritical foaming, two solvent-free processes which could integrate living cells. We are currently investigating the possibility to apply it to medical grade PLA and biomaterials as Polyglycolic acid (PGA) and Polycaprolactone (PCL).