Additive Manufactured Scaffolds for Bone Tissue Engineering: Physical Characterization of Thermoplastic Composites with Functional Fillers

Abstract

Thermoplastic polymer–filler composites are excellent materials for bone tissue engineering (TE) scaffolds, combining the functionality of fillers with suitable load-bearing ability, biodegradability, and additive manufacturing (AM) compatibility of the polymer. Two key determinants of their utility are their rheological behavior in the molten state, determining AM processability and their mechanical load-bearing properties. We report here the characterization of both these physical properties for four bone TE relevant composite formulations with poly(ethylene oxide terephthalate)/poly(butylene terephthalate (PEOT/PBT) as a base polymer, which is often used to fabricate TE scaffolds. The fillers used were reduced graphene oxide (rGO), hydroxyapatite (HA), gentamicin intercalated in zirconium phosphate (ZrP-GTM) and ciprofloxacin intercalated in MgAl layered double hydroxide (MgAl-CFX). The rheological assessment showed that generally the viscous behavior dominated the elastic behavior ( G ″ > G ′) for the studied composites, at empirically determined extrusion temperatures. Coupled rheological–thermal characterization of ZrP-GTM and HA composites showed that the fillers increased the solidification temperatures of the polymer melts during cooling. Both these findings have implications for the required extrusion temperatures and bonding between layers. Mechanical tests showed that the fillers generally not only made the polymer stiffer but more brittle in proportion to the filler fractions. Furthermore, the elastic moduli of scaffolds did not directly correlate with the corresponding bulk material properties, implying composite-specific AM processing effects on the mechanical properties. Finally, we show computational models to predict multimaterial scaffold elastic moduli using measured single material scaffold and bulk moduli. The reported characterizations are essential for assessing the AM processability and ultimately the suitability of the manufactured scaffolds for the envisioned bone regeneration application.

Biomaterials Based on Organic Polymers and Layered Double Hydroxides Nanocomposites: Drug Delivery and Tissue Engineering

“…These limitations can be minimized, and even novel properties on polymer-based materials can be achieved, by the presence of a wide variety of inorganic structures. Especially for bone-related applications, hybrid materials based on the combination of LDH and polymers are promising to owe to: (i) the enhancement of the mechanical properties of the resulting composite [ 271 , 277 ]; (ii) the improvement of osteogenic differentiation associated with the release of Mg 2+ ions from the LDH structure and the alkaline microenvironment [ 272 , 278 ]; (iii) good biocompatibility, low toxicity and structural homogeneity [ 169 ]; (iv) thermal stability and drug release of bioactive compounds from the intercalated LDH structure [ 279 ]; (v) thermal insulation from the exothermic polymerization process, and (vi) creation of surface irregularities that could benefit osteointegration [ 272 ].…”

Extrusion 3D printing of a multiphase collagen‐based material: An optimized strategy to obtain biomimetic scaffolds with high shape fidelity

“…Considering the current trialand-error approach in 3D printing, 9 CFD simulations allow to screen feasible printing conditions and to estimate the printing parameters in advance, therefore enabling the reduction of potential material waste and the optimization of the overall workflow. 10 After assessing the actual processability of the material with the selected technique, the final print set-up requires further optimization according to its specific physico-chemical properties. Despite extrusion printing techniques proving their high potential in the realization of more complex structures compared to traditional manufacturing, the choice of cytocompatible inks is still limited, particularly in the case of naturally derived materials and biopolymers such as type I collagen.…”

“…In this context, computational fluid dynamics (CFD) models can support the identification of the most promising printing set‐up by combining the rheological properties of the developed biomaterial with the features of the selected printing systems. Considering the current trial‐and‐error approach in 3D printing, 9 CFD simulations allow to screen feasible printing conditions and to estimate the printing parameters in advance, therefore enabling the reduction of potential material waste and the optimization of the overall workflow 10 …”

Fabrication of hydrophobic PLA filaments for additive manufacturing

“…There is the possibility for PPE to be manufactured from thermoplastics without compromising any of its integrity or functionality. Although AM can be used to produce PPE by combining thermoplastics, such as polylactic acid (PLA), polyvinyl ether (PVE), and polythene (PE), there are practical challenges associated with handling this kind of material [ 42 ].…”