Abstract
Biodegradable composite materials represent one of the major areas of investigation for bone tissue engineering due to their tuneable compositional and mechanical properties, which can potentially mimic those of bone and potentially avoid the removal of implants, mitigating the risks for the patient and reducing the overall clinical costs. In addition, the introduction of additive manufacturing technologies enables a strict control over the final morphological features of the scaffolds. In this scenario, the optimisation of 3D printable resorbable composites, made of biocompatible polymers and osteoinductive inorganic phases, offers the potential to produce a chemically and structurally biomimetic implant, which will resorb over time. The present work focuses on the development and process optimisation of two hybrid composite filaments, to be used as feedstock for the fused filament fabrication 3D printing process. A Poly L-lactic acid matrix was blended with either rod-like nano-hydroxyapatite (nano-HA) or nanoparticles of mesoporous bioactive glasses, both partially substituted with strontium (Sr2+), due to the well-known pro-osteogenic effect of this ion. Both inorganic phases were incorporated into Poly L-lactic acid using an innovative combination of processes, obtaining a homogeneous distribution throughout the polymer whilst preserving their ability to release Sr2+. The filament mechanical properties were not hindered after the incorporation of the inorganic phases, resulting in tensile strengths and moduli within the range of cancellous bone, 50 ± 10 MPa and 3 ± 1 GPa. Finally, the rheological characterization of the hybrid composites indicated a shear thinning behaviour, ideal for the processing with fused filament fabrication, proving the potential of these materials to be processed into 3D structures aiming bone regeneration.
Highlights
Bone is a dynamic tissue with the ability to self-renewal and heal, to maintain its stability and integrity (Lehmann et al, 2012; Kalani et al, 2019)
The X-ray diffraction (XRD) patterns confirmed that the degree of crystallinity was similar to bone apatite, despite the Sr2+ inclusion (Ofudje et al, 2019), with a slight shift in the peaks position towards higher two theta and change in intensity compared to non-substituted HA, due to slight modification of the unit cell parameters upon Sr2+ incorporation (Ofudje et al, 2019)
The need for improved devices targeting pathologies such as osteoporosis has created an increasing interest for additive manufactured scaffolds, which are capable of mimicking bone composition and mechanical properties
Summary
Bone is a dynamic tissue with the ability to self-renewal and heal, to maintain its stability and integrity (Lehmann et al, 2012; Kalani et al, 2019). PLLA is attractive for its mechanical properties such as high tensile strength, low elongation, and elastic modulus comparable to bone (Middleton and Tipton, 2000; Narayanan et al, 2016). This FDA approved polymer is biodegradable, biocompatible, and processed
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