Effect of Electron Beam Sterilization on Three-Dimensional-Printed Polycaprolactone/Beta-Tricalcium Phosphate Scaffolds for Bone Tissue Engineering

Abstract

Three-dimensional printing of composite materials such as polycaprolactone/beta-tricalcium phosphate (PCL/b-TCP) enables the design and manufacturing of scaffolds with advanced geometries, along with improved physical and biological properties for large bone defect repair. Terminal sterilization of the scaffolds is inevitable for clinical applications. Electron beam (E-beam) is nontoxic, and can be used for sterilizing heatsensitive scaffolds by the use of high radiation dose in a short period of time. In this article, we assessed the influence of E-beam sterilization on the properties of 3D-printed PCL/b-TCP scaffolds, focusing on the key physical and biological properties for bone tissue engineering. More specifically, we characterized the effect of a single-dose E-beam sterilization (25 kGy, ISO 11137) on surface morphology, hydrophilicity, degradation, and mechanical properties of the scaffolds as well as in vitro biological responses. The results showed that Ebeam irradiation did not alter the surface properties of scaffolds. A 14% increase in initial mechanical stiffness and strength of the scaffolds was observed after E-beam treatment. In addition, the E-beam-treated scaffolds had 25% faster degradation. The PCL chains within the scaffolds had larger polydispersity after the E-beam irradiation that was indicative of a concurrent cross-linking and chain scission. Moreover, in vitro cell studies showed no influence of E-beam sterilization on viability, attachment, proliferation, and osteogenic differentiation of cells seeded on the PCL/b-TCP scaffolds.

The Influence of Electron Beam Sterilization on In Vivo Degradation of β-TCP/PCL of Different Composite Ratios for Bone Tissue Engineering

“…In our previous study, we found a 14% increase in the initial Young's modulus and a 25% faster in vitro degradation profile for scaffolds that received E-beam compared to those that did not [23]. The increased Young's modulus values after E-beam were likely due to crosslinking, which strengthens the β-TCP/PCL composite structure, while the increase in degradation rate after E-beam in vitro was likely due to chain scissioning, which is thought to weaken the composite structure [23].…”

“…In our previous study, we found a 14% increase in the initial Young's modulus and a 25% faster in vitro degradation profile for scaffolds that received E-beam compared to those that did not [23]. The increased Young's modulus values after E-beam were likely due to crosslinking, which strengthens the β-TCP/PCL composite structure, while the increase in degradation rate after E-beam in vitro was likely due to chain scissioning, which is thought to weaken the composite structure [23]. Furthermore, since β-TCP particles are merely suspended in the polymer matrix, degradation of β-TCP/PCL scaffolds in any given solution is mainly driven by polymer degradation via the hydrolytic cleavage or scissioning of ester-ester linkages [19,20,23,25].…”

“…Additionally, E-beam has higher dosage rates than both ultraviolet and gamma irradiation methods, resulting in less exposure time [22]. This is particularly important for polymers like PCL, because irradiation methods like E-beam and gamma have been shown to increase the polydispersity of PCL chains and affect mechanical properties and degradation rates [22][23][24]. This is a result of PCL ester-ester chain scissioning, in addition to crosslinking, or the formation of chemical bonds to connect polymer chains [23,24].…”

“…The increased Young's modulus values after E-beam were likely due to crosslinking, which strengthens the β-TCP/PCL composite structure, while the increase in degradation rate after E-beam in vitro was likely due to chain scissioning, which is thought to weaken the composite structure [23]. Furthermore, since β-TCP particles are merely suspended in the polymer matrix, degradation of β-TCP/PCL scaffolds in any given solution is mainly driven by polymer degradation via the hydrolytic cleavage or scissioning of ester-ester linkages [19,20,23,25]. Previous studies, including ours, have focused solely on 20% TCP/80% PCL [19,20,23,26,27], so this study extends the work by examining the in vivo degradation profiles of various β-TCP/PCL composite ratios by mass (0:100, 20:80, 40:60, and 60:40) in a rat model, particularly studying the effect of E-beam sterilization among these different ratios on in vivo degradation.…”

“…Furthermore, since β-TCP particles are merely suspended in the polymer matrix, degradation of β-TCP/PCL scaffolds in any given solution is mainly driven by polymer degradation via the hydrolytic cleavage or scissioning of ester-ester linkages [19,20,23,25]. Previous studies, including ours, have focused solely on 20% TCP/80% PCL [19,20,23,26,27], so this study extends the work by examining the in vivo degradation profiles of various β-TCP/PCL composite ratios by mass (0:100, 20:80, 40:60, and 60:40) in a rat model, particularly studying the effect of E-beam sterilization among these different ratios on in vivo degradation. We have chosen to use extruded filament samples over scaffold samples for this in vivo study for simplification and as a screening test for chemical compositions.…”