3D-Printed HA-Based Scaffolds for Bone Regeneration: Microporosity, Osteoconduction and Osteoclastic Resorption

Abstract

Additive manufacturing enables the realization of the macro- and microarchitecture of bone substitutes. The macroarchitecture is determined by the bone defect and its shape makes the implant patient specific. The preset distribution of the 3D-printed material in the macroarchitecture defines the microarchitecture. At the lower scale, the nanoarchitecture of 3D-printed scaffolds is dependent on the post-processing methodology such as the sintering temperature. However, the role of microarchitecture and nanoarchitecture of scaffolds for osteoconduction is still elusive. To address these aspects in more detail, we produced lithography-based osteoconductive scaffolds from hydroxyapatite (HA) of identical macro- and microarchitecture and varied their nanoarchitecture, such as microporosity, by increasing the maximum sintering temperatures from 1100 to 1400 °C. The different scaffold types were characterized for microporosity, compression strength, and nanoarchitecture. The in vivo results, based on a rabbit calvarial defect model showed that bony ingrowth, as a measure of osteoconduction, was independent from scaffold’s microporosity. The same applies to in vitro osteoclastic resorbability, since on all tested scaffold types, osteoclasts formed on their surfaces and resorption pits upon exposure to mature osteoclasts were visible. Thus, for wide-open porous HA-based scaffolds, a low degree of microporosity and high mechanical strength yield optimal osteoconduction and creeping substitution. Based on our study, non-unions, the major complication during demanding bone regeneration procedures, could be prevented.

Osteoconductivity of bone substitutes with filament-based microarchitectures: Influence of directionality, filament dimension, and distance

“…Osteoconduction in wide-open porous scaffolds, however, is guiding bone tissue growth and represents no surface phenomenon since bone formation does not occur predominantly on the surface of the scaffold but between the rods of lattice microarchitectures as shown for two different materials: TCP and titanium [ 1 , 32 ] . Therefore, for osteoconduction, the microarchitecture and to a lesser extent the nanoarchitecture represented by the surface morphology or the microporosity is the dominant determinant as was shown for hydroxyapatite-based 3D-printed scaffolds [ 34 ] . For TCP-based scaffolds, surface morphology, and/or microporosity tuned by the sintering temperature affect osteoconductivity [ 30 ] .…”

Reconstruction of Load-Bearing Segmental Bone Defects Using Carbonate Apatite Honeycomb Blocks

“…The sintering temperature used in the fabrication process of ceramic blocks strongly affects the resulting pore parameters. ,− An increase in the sintering temperature reduces the pore volumes and sizes, which leads to enhanced mechanical strength and decreased osteoconductivity and bioresorbability. ,,,, Based on this principle, we controlled the debinding temperatures of HC green bodies. The HC green bodies were sintered up to 600, 650, and 700 °C at a heating rate of 0.03 °C/min and maintained at each temperature for 24 h under a CO 2 flow.…”

“…Generally, synthetic bone blocks are used to clinically treat the defect in osteotomy surgeries of loading limbs. − Therefore, the effects of the pore characteristics in blocks on mechanical strength, osteoconductivity, and bioresorbability should be evaluated by implanting blocks in load-bearing segmental defects. However, previous studies have investigated the effect of the pore characteristics in synthetic bone blocks on bone reconstruction using nonload-bearing bone defects. − Furthermore, while these studies did not evaluate the mechanical strength of the blocks, they did investigate osteoconductivity and bioresorbability. Therefore, the optimal pore characteristics for the reconstruction of load-bearing segmental defects remain unclear.…”

The Effect of Low-Temperature Thermal Processing on Bovine Hydroxyapatite Bone Substitutes, toward Bone Cell Interaction and Differentiation

“…15240062; Life Technologies Ltd., Carlsbad, CA, USA). RAW 264.7 cells are routinely used in osteoclast studies and are an important tool for in vitro studies of osteoclast formation and activation [ 28 , 29 ].…”