[The establishment of a new mechanobiology model of bone and functional adaptation studies in vivo]

Abstract

Objectives: to study the functional adaptation in response to artificial loading in vivo.

Methods: A single element strain gauge of < 2 mm x 3 mm in size was attached in longitudinal alignment to the medial surface of the ulnar midshaft, in vivo recordings of ulnar strains during locomotion were obtained. The ulnae of natural female rats were subjected to dynamic axial loading in vivo simulate strains during locomotion using INSTRON materials-testing machine. The left ulna of adult female rats were subjected to applied loading at frequencies of 5 Hz, 10 Hz, 15 Hz for 10 min/d with a haversian, low-magnitude (1mm peak to peak) waveform for a two weeks period, the peak strains at the Left ulnar midshaft is 2000 microepsilon and 3000 microepsilon, the right ulna of each rat served as a paired internal control. Dual Energy X-ray Absorptiometry (DXA) was used to measure bone mineral density (BMD) at the ulnar; 3-point bending was used to test mechanical characteristics; the ulna's response to loading was traced by subcutaneously injecting each rat twice with 7.5 mg/kg calcein and 30 mg/kg Tetracycline Hcl on days 3 and 12 of the loading period, and analyzed by histomorphometry; immunohistochemistry as an effect of elevated strain in the bone matrix.

Results: at frequencies of 10 Hz, 15 Hz groups, loading promoted obviously secreted of alkaline phosphatase (ALP), osteocalcin (OCN) and collagen I; a relative benefit in BMD was found compare to the control (P < 0.05) followed the decline of material mechanical properties (modulus of elasticity, ultimate stress) (P < 0.01).

Conclusion: These data show that a new bionics mechanobiology model of the axial ulna loading technique had be established successfully in rat. A short daily period of low-magnitude, high-frequency mechanical stimuli results in an osteogenic response related to peak strain magnitude.