CONICET | Buscador de Institutos y Recursos Humanos

Fused deposition modeling (FDM) uses polymer/composite-based filaments to build three-dimensional structures by successively depositing layer-by-layer extruded filaments potentially useful to treat bone defects. CAD models, obtained directly from computed tomography, allow the generation of tailored structures for each patient [1]. While FDM developments have been remarkable thus far, they are still significantly limited by the availability of printable, functional material systems that meet the requirements of a broad range of industries (i.e., healthcare, manufacturing, packaging, aerospace, automotive, and biomedical industries). Despite the dominance of commodity plastics (i.e., PET, PP, PS, ABS, etc.), biopolymers and synthetic biodegradable polymers have recently emerged for the development of innovative printable polymer-based systems [2]. Over the last years, bioresorbable polymeric / bioactive ceramic composites have been proposed as attractive materials for bone tissue engineering applications. In this regard, bioactive glasses and apatite-wollastonite glass-ceramics (GC) have been widely explored for these applications [3] since they confer osteoconductive and osteoinductive properties to the composite.In this work, 3D printed composite scaffolds based on bioresorbable polyesterurethanes (SPEU) were developed for bone tissue engineering applications. Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a natural-based polyester synthesized using microbial fermentation of carbon-based feedstock, Bioglass 45S5(BG) and GC were incorporated in the filament formulation [4,5].SPEU were synthesized from 1,6-hexamethylenediisocyanate, poly(ε-caprolactone) diol and 1,4-butanediol by two-step polymerization. Formulations with 50% and 60% w/w hard segment content (HS), named SPEU50 and SPEU60 respectively, were obtained. SPEU50 and SPEU60 were mixed with 5% and 10% (w/w) of GC (20-45 μm). Furthermore, SPEU50 was mixed with 30% (w/w) PHBV and 5% (w/w) BG. All the mixtures were milled and extruded using a Thermo Fisher ScientificTM Process 11 twin screw mini-extruder. The effect of different FDM printing parameters, such as printing speed, layer thickness, printing orientation patterns, nozzle and platform temperature on the scaffold fabrication was evaluated.All the filaments and scaffolds with rectilinear patterns were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), infrared spectroscopy (ATR-FTIR), dynamic mechanical analysis (DMA), compression test (EMIC 23?50, Instron), contact angle, and scanning electron microscopy (SEM). Bioactivity tests were performed upon immersion of scaffolds in simulated body fluid (SBF) for different periods within 28 days. In addition, biological assays were performed with human osteoblast-like cells (MG-63) and osteoblastic precursor cell line (MC3T3-E1). Cell viability, adhesion, proliferation, and morphology were evaluated by fluorescence microscopy, SEM and WST-8 cell counting Kit-8.SPEU composite filaments with uniform diameter were obtained without needing additives. The incorporated inorganic particles were found mainly inside the filament.FTIR spectra were normalized in order to perform a semiquantitative analysis. As expected, a decrease in the absorbance of carbonyl-ester band together with an increase in carbonyl-urethane bands was observed with the increase in HS content. Moreover, the increase in H-bonded carbonyl-urethane bands could be associated to a rise in phase separation. TGA and DSC thermograms displayed no changes in thermal stability nor crystallinity of the filaments with the processing technique. As expected, the incorporation of PHBV and inorganic particles led to an increase in the elastic modulus of filaments. The increase in hard segment content (SPEU60 respect to SPEU50) led also to a stiffer material, as observed by tensile tests of the filaments and compression assays of the 3D structures.It was reported that scaffolds with a mean pore size in the range of 300-350 μm are optimal for bone tissue engineering. Therefore, FDM parameters were explored to control pore size for the different materials. Printed scaffolds with an adequate pore size were obtained, except for the SPEU50/PHBV/BG system. Contact angle measurements of SPEU matrices were close to 90°, while the systems containing PHBV (hydrophobic and crystalline polymer) displayed a value of 105-110°. SPEU60, SPEU60-GC, SPEU50/PHBV and SPEU50/PHBV/BG scaffolds displayed good viability and proliferation cell response, being the latter the more promising. Bioactivity tests evidenced the deposition of crystals on the surface of the matrices. However, their morphology was not typical of carbonated hydroxyapatite (HCA) (acicular and cauliflower type), and as the characteristic infrared bands of HCA overlap with those of SPEU the formation of HCA could not be confirmed by these techniques. Despite this, SEM-EDS analysis corroborated the presence of HCA with a ratio of Ca/P ≈ 1.68 for SPEU50/PHBV/BG scaffolds.Matrices based on SPEU composite filaments were successfully obtained by FDM. The desired geometry, pore size and porosity could be achieved by properly setting FDM parameters. The printed scaffolds showed dimensional stability and high reproducibility. We believe these findings may benefit the design and fabrication of advanced implants, where a lack of 3D printable biomaterials exists for use in tissue engineering applications. To improve the in vitro performance of the scaffolds, a surface modification to increase their hydrophilicity and promote cell adhesion and proliferation is being carried out.

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