title: Multi-Level Assessment of Fracture Calluses in Rats Subjected to Low-Magnitude High-Frequency Vibration with Different Rest Periods.
abstract: The aim of this study was to investigate the influences of low-magnitude high-frequency vibration (LMHFV) with different rest period regimes (vibrational loading per day [with or without the loading divided into bouts]; or vibrational loading for 7 day followed by 7 day rest [with or without the loading divided into bouts]) on bone healing at multi-levels. Transverse fractures of rat bilateral tibias were established using a Kirschner wire inserted for fixation. The animals were randomly assigned to five groups (n = 7 for each group): four for vibrational groups by LMHFV with different rest period regimes and one for fractured model without mechanical loading. The macromechanical properties of the fractured tibias and the nanomechanical properties of the calluses were investigated through three-point bending and nanoindentation tests, respectively. Atomic force microscopy (AFM) was performed to analyze the nanostructure of the calluses. Micro-computed tomography (micro-CT) scanning was conducted to evaluate the microarchitecture of the calluses. The serum concentration of osteocalcin (OG) and tartrate-resistant acid phosphatase 5b (TRAP5b) were measured to assess the bone formation and resorption rates, respectively. Significantly higher values of failure load and elastic modulus were observed in DL (vibrational loading for 15 min per day) and DLR (vibrational loading per day in which three bouts of 5 min of vibration were separated by 4 h) than FBC (fractured model without mechanical loading) at macro-level (P < 0.05). The results of nanoindentation test showed the highest values of indentation modulus and hardness in DLR (significantly higher than FBC; P < 0.05); besides, higher value of hardness was also observed in DL (significantly higher than FBC; P < 0.05). Though AFM imaging showed no significant differences in grain sizes between the vibrational groups and FBC, roughness of DLR showed the highest value, i.e. it was significantly higher than that in FBC (P < 0.05). For microarchitectural parameters obtained from micro-CT imaging, tissue mineral density (TMD) of DLR and VL7 (vibrational loading for 7 day followed by a 7-day rest, 15 min per day during vibrational periods) were significantly higher than that in FBC (P < 0.05), but no significant differences in other parameters were observed between vibrational groups and FBC. There were no significant differences of OG between vibrational groups and FBC; however, FBC showed significantly higher TRAP5b concentration than all vibrational groups (P < 0.05). The results show that LMHFV with different rest period regimes not only altered the macro- and nano-level bone mechanical properties but also influenced the TMD of calluses and nano-level spatial arrangement (roughness) significantly. The most significant effect of LMHFV with different rest period regimes was observed in DLR, which indicated that both osteogenic accumulation and cellular resensitization can be satisfied under this regimen. Hence, the DLR group demonstrated a great potential in clinical applications.
authors.affiliation: State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun, People's Republic of China.|Department of Engineering Mechanics, Nanling Campus, Jilin University, Changchun, 130025, People's Republic of China.
authors.forename: Jiazi
authors.initials: J
authors.lastname: Gao
authors.affiliation: State Key Laboratory of Automotive Simulation and Control, Jilin University, Changchun, People's Republic of China. gonghe1976@yahoo.com.|Department of Engineering Mechanics, Nanling Campus, Jilin University, Changchun, 130025, People's Republic of China. gonghe1976@yahoo.com.
authors.forename: He
authors.initials: H
authors.lastname: Gong
authors.affiliation: Department of Radiology, The First Hospital of Jilin University, Changchun, People's Republic of China.
authors.forename: Xu
authors.initials: X
authors.lastname: Huang
authors.affiliation: Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Biological Science and Medical Engineering, Beihang University, Beijing, People's Republic of China.
authors.forename: Rui
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Department of Emergency, The First Hospital of Jilin University, Changchun, People's Republic of China.
authors.forename: Renshi
authors.initials: R
authors.lastname: Ma
authors.affiliation: Department of Traumatic Orthopedics, The First Hospital of Jilin University, Changchun, People's Republic of China.
authors.forename: Dong
authors.initials: D
authors.lastname: Zhu
mesh_terms: D000818:Animals; D002146:Bony Callus / Q000000981:diagnostic imaging / Q000503:physiopathology; D005260:Female; D017102:Fracture Healing; D018625:Microscopy, Atomic Force; D051381:Rats; D013978:Tibial Fractures / Q000000981:diagnostic imaging / Q000503:physiopathology; D014732:Vibration; D055114:X-Ray Microtomography
keywords: Fracture healing; Loading-rest days; Low-magnitude high-frequency vibration; Rest pauses inserted