Development of Hot‐Melt Extrusion Method to Produce Hydroxyapatite/Polycaprolactone Composite Filaments

Abstract

The aim of this work is to develop a single‐step process to produce hydroxyapatite/polycaprolactone (HAp/PCL) composite filaments for 3D printing of bone scaffolds by fused deposition modeling (FDM). The HAp/PCL composite filaments are produced by hot‐melt extrusion, with direct in situ blending. For practical purposes, the effect of PCL particle size on filament homogeneity and printability is assessed between PCL in powder and pellet form. The effect of HAp content on processing parameters and filament properties is also evaluated. Filament extrudability, homogeneity, and shape consistency improve with increasing HAp content up to a threshold of 40 wt%. Furthermore, an optimal range of the composite melt viscosity for the extrusion process is defined. The produced filaments are successfully 3D printed by FDM and the resulting prototypes show improved compressive modulus and degradation rate with increasing HAp content. A cytocompatibility assay is conducted, which suggests an optimal HAp content to be less than 40 wt% in terms of cell viability, adhesion, and proliferation. The developed method offers several advantages, as it completely avoids the use of toxic solvents and enables the incorporation of very high HAp concentrations, further improving the chances of implementation of FDM for bone tissue regeneration medicine.

Fabrication and Characterization of PCL/HA Filament as a 3D Printing Material Using Thermal Extrusion Technology for Bone Tissue Engineering

“…Surprisingly, the material extrusion method has rarely been used for scaffold fabrication, probably due to the lack of suitable materials and control methods [21]. Historically, solvent casting has been the main method, with only a few studies focusing on hot-melt extrusion, although using higher HA contents which, in return, influences printability parameters, involves the use of more expensive printers, and increases the presence of cell byproducts [26][27][28][29]33].…”

“…Excluded scaffolds and parameters were tested and those which failed were either not extruded (temperature too low), too much extruded (temperature too high, low speed, or high flow factor), or the pores were interrupted (high speed or low temperature) (Supplementary Figure S2). Until now, the precise parameters for PCL/HA concentration had only partially been reported and limited to successful scaffold fabrication to expensive 3D printers [33]. We have precisely described the temperatures and speed required for each composition, reporting the causes of failure in the fabricated scaffolds.…”

“…Nonetheless, after obtaining a successful filament, the optimum build orientation, layer thickness, nozzle diameter, infill pattern, and bed temperature are necessary to fulfill this need [32]. Hot-melt PCL/HA filament fabrication and the scaffolds fabricated from this process are understudied; to date, only scant information is available on the fabrication settings for machines in research environments [33]. Additionally, further studies should be conducted to assess the optimal HA percentage for osteoconductive applications.…”

Viscoelastic, Thermal, and Mechanical Properties of Melt-Processed Poly (ε-Caprolactone) (PCL)/Hydroxyapatite (HAP) Composites

“…However, the 3D printed scaffolds can be alternative to solvent-processed scaffolds. Gerdes et al [ 24 ] and Zavřel et al [ 25 ] prepared 3D printed PCL/HAP scaffolds for bone tissue engineering. 3D scaffolds can easily be prepared at large scale since the process is free of solvents, and the scaffolds with different architectures can be prepared.…”

Use of Polyesters in Fused Deposition Modeling for Biomedical Applications

“…Indeed, it has been observed that particles can be isolated from the filament surface because of the presence of a plastic skin around them, thus preventing their bioactivity. [258] A possible solution to this problem is alkaline erosion of the final scaffold surface to better expose the bioactive agent; [259,260] still, this process adds a further step in the device production that increases the degree of complexity of the entire fabrication pipeline and also damages the structural stability if not correctly controlled. As also noted elsewhere, [42] when moving from traditional techniques to additive manufacturing, it is important to take into account the specific requirements of the printing process in the early stage of material development.…”