Additive Manufacturing Approaches for Hydroxyapatite‐Reinforced Composites

Abstract

Additive manufacturing (AM) techniques have gained interest in the tissue engineering field, thanks to their versatility and unique possibilities of producing constructs with complex macroscopic geometries and defined patterns. Recently, composite materials-namely, heterogeneous biomaterials identified as continuous phase (matrix) and reinforcement (filler)-have been proposed as inks that can be processed by AM to obtain scaffolds with improved biomimetic and bioactive properties. Significant efforts have been dedicated to hydroxyapatite (HA)-reinforced composites, especially targeting bone tissue engineering, thanks to the chemical similarities of HA with respect to mineral components of native mineralized tissues. Herein, applications of AM techniques to process HA-reinforced composites and biocomposites for the production of scaffolds with biological matrices, including cellular tissues, are reviewed. The primary outcomes of recent investigations in terms of morphological, structural, and in vitro and in vivo biological properties of the materials are discussed. The approaches based on the nature of the matrices employed to embed the HA reinforcements and produce the tissue substitutes are classified, and a critical discussion is provided on the presented state of the art as well as the future perspectives, to offer a comprehensive picture of the strategies investigated as well as challenges in this emerging field of materiomics.

Tympanic Membrane Collagen Expression by Dynamically Cultured Human Mesenchymal Stromal Cell/Star-Branched Poly(ε-Caprolactone) Nonwoven Constructs

“…Alteration of polymer solution parameters has a direct effect on fiber size, which has been found to result in a different porosity, thus affecting the nonwoven density [48,49]. The decreased Young's modulus is suggestive that, in our experimental setting, due to insufficient interfacial properties, HA acted as a defect for the *PCL fibers, and not as a reinforcement, as reported in other nano-HA/PCL studies [22,50], thus reducing the stiffness of the nanocomposite [51]. It has to be considered that, for the same molecular weight, a star-branched polymer, like *PCL, accounts for many shorter polymer chains than its linear counterpart [23,24].…”

Tympanic Membrane Collagen Expression by Dynamically Cultured Human Mesenchymal Stromal Cell/Star-Branched Poly(ε-Caprolactone) Nonwoven Constructs

“…Alteration of polymer solution parameters has a direct effect on fiber size, which has been found to result in a different porosity, thus affecting the nonwoven density [48,49]. The decreased Young's modulus is suggestive that, in our experimental setting, due to insufficient interfacial properties, HA acted as a defect for the *PCL fibers, and not as a reinforcement, as reported in other nano-HA/PCL studies [22,50], thus reducing the stiffness of the nanocomposite [51]. It has to be considered that, for the same molecular weight, a star-branched polymer, like *PCL, accounts for many shorter polymer chains than its linear counterpart [23,24].…”

Computer simulation of stress-strain states in zygomatic bones after complex installation of implants

“…The maximum  eq values did not exceed 1.1% in bone tissue (Fig. 5, b), surpassing the reported critical elongation level [32]. As in all the above-described cases, the maximum  eq value of 183 MPa was observed at the "implant-zygomatic bone" interface, which was lower by ~20 MPa than that for the right position according to Fig.…”

A 3D multifunctional bi-layer scaffold to regulate stem cell behaviors and promote osteochondral regeneration

“…It has been reported that PCL is biodegradable but more stable compared to other polymers (e.g., PLA) due to its less frequent ester bonds per monomer. 32 Therefore, as observed in this degradation test in vitro, the stable 3D-printed PCL or PCL/HA scaffold could provide the structural and mechanical support for cell growth and tissue regeneration. The macroscopic views and SEM images of PCL and PCL/HA scaffolds are shown in Fig.…”

Tympanic Membrane Collagen Expression by Dynamically Cultured Human Mesenchymal Stromal Cell/Star-Branched Poly(ε-Caprolactone) Nonwoven Constructs

“…Alteration of polymer solution parameters has a direct effect on fiber size, which has been found to result in a different porosity, thus affecting the nonwoven density [48,49]. The decreased Young's modulus is suggestive that, in our experimental setting, due to insufficient interfacial properties, HA acted as a defect for the *PCL fibers, and not as a reinforcement, as reported in other nano-HA/PCL studies [22,50], thus reducing the stiffness of the nanocomposite [51]. It has to be considered that, for the same molecular weight, a star-branched polymer, like *PCL, accounts for many shorter polymer chains than its linear counterpart [23,24].…”

Computer simulation of stress-strain states in zygomatic bones after complex installation of implants

“…The maximum  eq values did not exceed 1.1% in bone tissue (Fig. 5, b), surpassing the reported critical elongation level [32]. As in all the above-described cases, the maximum  eq value of 183 MPa was observed at the "implant-zygomatic bone" interface, which was lower by ~20 MPa than that for the right position according to Fig.…”

A 3D multifunctional bi-layer scaffold to regulate stem cell behaviors and promote osteochondral regeneration

“…It has been reported that PCL is biodegradable but more stable compared to other polymers (e.g., PLA) due to its less frequent ester bonds per monomer. 32 Therefore, as observed in this degradation test in vitro, the stable 3D-printed PCL or PCL/HA scaffold could provide the structural and mechanical support for cell growth and tissue regeneration. The macroscopic views and SEM images of PCL and PCL/HA scaffolds are shown in Fig.…”

Tympanic Membrane Collagen Expression by Dynamically Cultured Human Mesenchymal Stromal Cell/Star-Branched Poly(ε-Caprolactone) Nonwoven Constructs

“…Alteration of polymer solution parameters has a direct effect on fiber size, which has been found to result in a different porosity, thus affecting the nonwoven density [48,49]. The decreased Young's modulus is suggestive that, in our experimental setting, due to insufficient interfacial properties, HA acted as a defect for the *PCL fibers, and not as a reinforcement, as reported in other nano-HA/PCL studies [22,50], thus reducing the stiffness of the nanocomposite [51]. It has to be considered that, for the same molecular weight, a star-branched polymer, like *PCL, accounts for many shorter polymer chains than its linear counterpart [23,24].…”

Computer simulation of stress-strain states in zygomatic bones after complex installation of implants

“…The maximum  eq values did not exceed 1.1% in bone tissue (Fig. 5, b), surpassing the reported critical elongation level [32]. As in all the above-described cases, the maximum  eq value of 183 MPa was observed at the "implant-zygomatic bone" interface, which was lower by ~20 MPa than that for the right position according to Fig.…”

A 3D multifunctional bi-layer scaffold to regulate stem cell behaviors and promote osteochondral regeneration

“…It has been reported that PCL is biodegradable but more stable compared to other polymers (e.g., PLA) due to its less frequent ester bonds per monomer. 32 Therefore, as observed in this degradation test in vitro, the stable 3D-printed PCL or PCL/HA scaffold could provide the structural and mechanical support for cell growth and tissue regeneration. The macroscopic views and SEM images of PCL and PCL/HA scaffolds are shown in Fig.…”