Fabrication and mechanical characterization of 3D printed vertical uniform and gradient scaffolds for bone and osteochondral tissue engineering

• Published in: Acta biomaterialia 2019-05, Vol.90, p.37-48
• Main Authors: Bittner, Sean M., Smith, Brandon T., Diaz-Gomez, Luis, Hudgins, Carrigan D., Melchiorri, Anthony J., Scott, David W., Fisher, John P., Mikos, Antonios G.
• Format: Article
• Language: English
• Subjects: 3D printing; Animals; Biocompatibility; Biocompatible Materials - chemistry; Bone and Bones; Cancellous bone; Ceramics; Composition; Compression; Compression tests; Compressive properties; Computed tomography; Data compression; Durapatite - chemistry; Extrusion; Fabrication; Gradient; Humans; Hydroxyapatite; Materials Testing; Mechanical properties; Modulus of elasticity; Polyesters - chemistry; Pore size; Porosity; Porous scaffold; Printing, Three-Dimensional; Regeneration; Scaffolds; Scaling; Scaling laws; Surgical implants; Three dimensional printing; Tissue Engineering; Tissue Scaffolds - chemistry; Yield strength; Yield stress
• ISSN: 1742-7061; 1878-7568
• DOI: 10.1016/j.actbio.2019.03.041

[Display omitted] Recent developments in 3D printing (3DP) research have led to a variety of scaffold designs and techniques for osteochondral tissue engineering; however, the simultaneous incorporation of multiple types of gradients within the same construct remains a challenge. Herein, we describe the fabrication and mechanical characterization of porous poly(ε-caprolactone) (PCL) and PCL-hydroxyapatite (HA) scaffolds with incorporated vertical porosity and ceramic content gradients via a multimaterial extrusion 3DP system. Scaffolds of 0 wt% HA (PCL), 15 wt% HA (HA15), or 30 wt% HA (HA30) were fabricated with uniform composition and porosity (using 0.2 mm, 0.5 mm, or 0.9 mm on-center fiber spacing), uniform composition and gradient porosity, and gradient composition (PCL-HA15-HA30) and porosity. Micro-CT imaging and porosity analysis demonstrated the ability to incorporate both vertical porosity and pore size gradients and a ceramic gradient, which collectively recapitulate gradients found in native osteochondral tissues. Uniaxial compression testing demonstrated an inverse relationship between porosity, ϕ, and compressive modulus, E, and yield stress, σy, for uniform porosity scaffolds, however, no differences were observed as a result of ceramic incorporation. All scaffolds demonstrated compressive moduli within the appropriate range for trabecular bone, with average moduli between 86 ± 14–220 ± 26 MPa. Uniform porosity and pore size scaffolds for all ceramic levels had compressive moduli between 205 ± 37–220 ± 26 MPa, 112 ± 13–118 ± 23 MPa, and 86 ± 14–97 ± 8 MPa respectively for porosities ranging between 14 ± 4–20 ± 6%, 36 ± 3–43 ± 4%, and 54 ± 2–57 ± 2%, with the moduli and yield stresses of low porosity scaffolds being significantly greater (p  0.05) to those of the highest porosity uniform scaffolds (porosity gradient scaffolds 98 ± 23–107 ± 6 MPa, and 102 ± 7 MPa for dual composition/porosity gradient scaffolds), indicating that these properties are more heavily influenced by the weakest section of the gradient. The compression data for uniform scaffolds were also readily modeled, yielding scaling laws of the form E ∼ (1 − ϕ)1.27 and σy ∼ (1 − ϕ)1.37, which demonstrated that the compressive properties evaluated in this study were well-aligned with expectations from previous literat