Processing of Sr2+ Containing Poly L-Lactic Acid-Based Hybrid Composites for Additive Manufacturing of Bone Scaffolds

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.

Biomimetic Scaffolds Obtained by Electrospinning of Collagen-Based Materials: Strategies to Hinder the Protein Denaturation

“…After the optimization of collagen concentration and solvent, nanoparticles of mesoporous bioactive glasses (MBG_SG), prepared following a sol-gel route previously optimized by the authors ( Supplementary Material ) [ 36 , 37 ], were used to obtain bioactive hybrid formulations. After complete dissolution of collagen powders in 40% AA at 4 °C, MBG_SG nanoparticles were sonicated in the same solvent using a horn sonicator (Sonoplus Ultraschall-Homogenisation HD 2200, 20 kHz ± 500 Hz frequency, 50% amplitude) for 6 min and subsequently incorporated into the collagen solution to obtain final concentrations of 5 wt%.…”

Poly-l-Lactic Acid (PLLA)-Based Biomaterials for Regenerative Medicine: A Review on Processing and Applications

“…Due to its polyorthoester trait, PLLA presents a hydrophobic nature allowing it to degrade while remaining structurally intact [ 61 ]. Thermal degradation strongly reduces the length of PLLA chains, leading to a decrease in the molecular weight and structural stability under thermal and mechanical stresses [ 11 ]. The α-crystalline form of PLLA is the most thermodynamically stable owing to the C=O dipoles that are randomly oriented along the main chain, resulting in a non-polar form [ 62 ].…”

“…Among the biodegradable polymers used for tissue engineering, poly- l -lactic acid (PLLA) has been widely studied because of its interesting mechanical properties and tailorable biodegradability [ 9 ]. As a result, it can maintain mechanical and structural integrity during in vitro and in vivo applications while supporting tissue formation [ 10 , 11 , 12 ]. PLLA belongs to the PLA family, and, compared to PDLA (created through the polymerization of D-lactide), it exhibits higher crystallinity, chemical stability, and degradation resistance to enzymes and, as a consequence, a much longer resorption time [ 1 , 13 , 14 , 15 ].…”

Promotion of In Vitro Osteogenic Activity by Melt Extrusion-Based PLLA/PCL/PHBV Scaffolds Enriched with Nano-Hydroxyapatite and Strontium Substituted Nano-Hydroxyapatite

“…These are all key factors to consider nano-HA for applications in BTE [ 31 , 32 , 33 ]. Common combinations of materials include poly(vinyl alcohol) (PVA)/beta-tricalcium phosphate [ 34 ], PCL/HA [ 35 ] and PLA/HA [ 36 ]. In a recent study, Zavrel et al explored the use of HME to obtain a composite filament from PCL and HA [ 37 ].…”