The Effects Of Additional Weight Bearing In Combination With Low-Magnitude High-Frequency Vibration On Bone Mechanical Properties Of Rats

Bone has its functional shape and architecture,which indicates that bone architecture and shape match its function.Mechanical environment plays an important role in influencing bone architecture and its mechanical properties.In addition to mechanical environment,drugs could also affect bone architecture and its mechanical properties;however,using drugs chronically may induce side effects.Therefore,it is necessary to investigate the effets of a non-invasive and non-pharmacological therapy on bone.Lots of previous studies have been performed concerning low-magnitude high-frequency vibration(LMHFV)and additional weight bearing exercise,respectively.These LMHFV studies varied in terms of treatment duration,outcomes measured,and applied conditions,thus achieving inconsistent conclusions.Additional weight bearing activities,defined as force-generating exercises placing higher mechanical stress on human skeleton than daily living,also affect the mechanical properties of bone,and contribute to bone mineral accrual and bone mass gains.However,little is known on the effects of additional weight bearing in combination with LMHFV on bone.Investigation on the effects of additional weight bearing in combination with LMHFV on bone quality serves to give an insight into the mechanism of the combined mechanical stimuli.This study aimed to explore the effects of additional weight bearing in combination with low-magnitude high-frequency vibration(LMHFV;45 Hz,0.3 g)on bone at macroscale,microscale and nanoscale.A total of 120 rats were randomly divided into 10 groups on average,namely,sedentary(SED),additional weight bearing in which the rat wears a backpack whose weight is x% of the body weight(WBx;x=5,12,19,26),basic vibration(V),and additional weight bearing in combination with LMHFV in which the rat wears a backpack whose weight is x% of the body weight(Vx;x=5,12,19,26).The experiment was conducted for 12 weeks,7 days per week,and 15 min per day.The body weight of each rat was measured one day before the experiment to determine the weights of backpacks.On every weekend,the weight of each rat was measured,and the weights of backpacks used in the next week were determined during the experiment.After twelve weeks,the rats were sacrificed.Serum samples and left femurs were harvested.TRAP5 b,ALP,Ca and P from serum were quantitatively analyzed.As for the left femurs,three-point bending mechanical test was used to evaluate the mechanical properties at macroscale.Micro-computed tomography(micro-CT)was adopted to quantitatively assess the microarchitecture in femur head and diaphysis.And nanoindentation test was employed to examine the nanomechanical properties of bone material.It showed that SED had better macromechanical properties,microarchitecture,and nanomechanical properties.Failure load in V19 was significantly lower than that in SED(P<0.05).Vx(x=5,12,19,26)showed poor microarchitectures.The content of TRAP5 b was significantly higher in Vx(x=5,12,19,26)than that in SED(P<0.05).V26 demonstrated comparatively better nanomechanical properties of materials than WB26.Body weight in SED,which showed the highest body weight,was significantly higher than that in V5,V19 and V26(P<0.05).This study achieved the following conclusions:(1)Additional weight bearing in combination with LMHFV did not positively affect the macromechanical properties and microarchitecture of bone.And with the increase of additional weight bearing,the microarchitecture was negatively influenced.Microarchitecture was not significantly influenced by additional weight bearing.With the increase of additional weight bearing,the microarchitecture was negatively influenced to some extent,but it did not result in significant changes in macromechanical properties.(2)Additional weight bearing in combination with LMHFV was shown to improve the nanomechanical properties of bone material.But heavy additional weight bearing,such as 26% of body weight,in combination with LMHFV was able to improve the nanomechanical properties of growing bone material compared with LMHFV.(3)Proper Additional weight bearing in combination with LMHFV was indicated to induce weight loss.Weight loss not only affected BMD,but also had an influence on microarchitecture parameters,such as BV/TV,Tb.Th and Tb.Sp.