Abstract
The scaffold chemical composition and pore architecture are critical for successful bone regeneration. Although the effects of chemical composition, micron-scale pores, and macropores (≥100 μm) are known, those of nanometer-scale pores (nanopores) are unknown. Here, honeycomb scaffolds (HCSs) composed of carbonate apatite and bone mineral, were fabricated with three distinct nanopore volumes, while other parameters were comparable between HCSs. Their compressive strengths and nanopore volumes linearly correlated. The HCSs were implanted into critical-sized bone defects (CSDs) in the rabbit femur distal epiphyses. The nanopore volume affected both osteoclastogenesis and osteogenesis. HCSs with nanopore volumes of ≥0.15 cm3 g-1 promoted osteoclastogenesis, contributing to bone maturation and bone formation within 4 weeks. However, HCSs with nanopore volumes of 0.07 cm3 g-1 promoted significantly less bone maturation and neoformation. Nevertheless, HCSs with nanopore volumes of ≥0.18 cm3 g-1 did not undergo continuous bone regeneration throughout the 12 week period due to excessive osteoclastogenesis, which favored HCS resorption over bone neoformation. When the nanopore volume was 0.15 cm3 g-1, osteoclastogenesis and osteogenesis progressed harmonically, resulting in HCS replacement with new bone. Our results demonstrate that the nanopore volume is critical for controlling osteoclastogenesis and osteogenesis. These insights may help establish a coherent strategy for developing scaffolds for different applications.
Highlights
A primary factor affecting the outcome of bone regeneration is the chemical composition of the scaffold.[1]
The samples that were fabricated using CaCO3 honeycomb scaffolds (HCSs) subjected to heat treatment at 420, 450, 480, and 510 1C were designated as 420, 450, 480, and 510-HCSs, respectively
The X-ray diffraction (XRD) patterns of 420, 450, and 480-HCSs were coincident with a single phase of apatite, whereas 510-HCSs were composed of a mixed phase of apatite and calcite (Fig. 1). These results demonstrated that the temperature should be set at r480 to completely convert the composition from calcite to apatite in dissolution–precipitation reactions
Summary
Lan Levengood et al.,[9] a few studies on the scaffold micropore effects have been reported.[22,23,24,25,26,27,28,29] in some of these studies, the percentage of micropores (i.e., the microporosity) was not controlled,[22,27] or the micropore sizes were not revealed.[24,25] previous studies focused only on micropores with a size of 41 mm,[22,23,24,25,26,27,28,29] and the influence of micropores with sizes less than a few hundred nanometers have not been evaluated at all. The honeycomb structure is suitable for investigating the effects of micropores because (1) it comprises uniformly sized cells that correspond to macropores We evaluated the effects of micropores with sizes of less than a few hundred nanometers (designated as nanopores) in HCSs on their mechanical strength, bioresorption, and osteogenesis using three types of CO3Ap HCSs with different nanopore volumes. Other parameters, such as the carbonate content, macropore architecture, and nanopore size, were nearly equal between three sample groups
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